Working on SFTP

.gitignore

@@ -1,2 +1,5 @@
 bagage
 .env
+*.swp
+id_rsa
+id_rsa.pub

auth_ldap.go

@@ -18,41 +18,17 @@ type LdapPreAuth struct {
 
 func (l LdapPreAuth) WithCreds(username, password string) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var e *LdapWrongPasswordError
 
-		// 1. Connect to the server
+		access_key, secret_key, err := LdapGetS3(l.WithConfig, username, password)
-		conn, err := ldapConnect(l.WithConfig)
-		if err != nil {
-			l.OnFailure.WithError(err).ServeHTTP(w, r)
-			return
-		}
-		defer conn.Close()
 		
-		// 2. Authenticate with provided credentials
+		if err == nil {
-		// @FIXME we should better check the error, it could also be due to an LDAP error
+			l.OnCreds.WithCreds(access_key, secret_key).ServeHTTP(w, r)
-		err = conn.auth(username, password)
+		} else if errors.As(err, &e) {
-		if err != nil {
 			l.OnWrongPassword.WithError(err).ServeHTTP(w, r)
-			return
+		} else {
+			l.OnFailure.WithError(e).ServeHTTP(w, r)
 		}
-
-		// 3. Fetch user's profile
-		profile, err := conn.profile()
-		if err != nil {
-			l.OnFailure.WithError(err).ServeHTTP(w, r)
-			return
-		}
-
-		// 4. Basic checks upon users' attributes
-		access_key := profile.GetAttributeValue("garage_s3_access_key")
-		secret_key := profile.GetAttributeValue("garage_s3_secret_key")
-		if access_key == "" || secret_key == "" {
-			err = errors.New(fmt.Sprintf("Either access key or secret key is missing in LDAP for %s", conn.userDn))
-			l.OnFailure.WithError(err).ServeHTTP(w, r)
-			return
-		}
-
-		// 5. Send fetched credentials to the next middleware
-		l.OnCreds.WithCreds(access_key, secret_key).ServeHTTP(w, r)
 	})
 }
 
@@ -66,6 +42,50 @@ type ldapConnector struct {
 	userDn string
 }
 
+type LdapError struct {
+	Username string
+	Err error
+}
+func (e *LdapError) Error() string { return "ldap error for "+e.Username+": "+e.Err.Error() }
+type LdapWrongPasswordError struct { LdapError }
+
+func LdapGetS3(c *Config, username, password string) (access_key, secret_key string, werr error) {
+	// 1. Connect to the server
+	conn, err := ldapConnect(c)
+	if err != nil {
+		werr = &LdapError { username, err }
+		return
+	}
+	defer conn.Close()
+
+	// 2. Authenticate with provided credentials
+	// @FIXME we should better check the error, it could also be due to an LDAP error
+	err = conn.auth(username, password)
+	if err != nil {
+		werr = &LdapWrongPasswordError { LdapError { username, err } }
+		return
+	}
+
+	// 3. Fetch user's profile
+	profile, err := conn.profile()
+	if err != nil {
+		werr = &LdapError { username, err }
+		return
+	}
+
+	// 4. Basic checks upon users' attributes
+	access_key = profile.GetAttributeValue("garage_s3_access_key")
+	secret_key = profile.GetAttributeValue("garage_s3_secret_key")
+	if access_key == "" || secret_key == "" {
+		err = errors.New(fmt.Sprintf("Either access key or secret key is missing in LDAP for %s", conn.userDn))
+		werr = &LdapError { username, err }
+		return
+	}
+
+	// 5. Send fetched credentials to the next middleware
+	return
+}
+
 func ldapConnect(c *Config) (ldapConnector, error) {
 	ldapSock, err := ldap.Dial("tcp", c.LdapServer)
 	if err != nil {

config.go

@@ -14,6 +14,7 @@ type Config struct {
 	UserNameAttr string `env:"BAGAGE_LDAP_USERNAME_ATTR" default:"cn"`
 	Endpoint     string `env:"BAGAGE_S3_ENDPOINT" default:"garage.deuxfleurs.fr"`
 	UseSSL       bool   `env:"BAGAGE_S3_SSL" default:"true"`
+	SSHKey       string `env:"BAGAGE_SSH_KEY" default:"id_rsa"`
 }
 
 func (c *Config) LoadWithDefault() *Config {

go.mod

@@ -4,6 +4,9 @@ go 1.16
 
 require (
 	github.com/go-ldap/ldap/v3 v3.4.1
+	github.com/kr/fs v0.1.0
 	github.com/minio/minio-go/v7 v7.0.12
+	github.com/pkg/sftp v1.13.4
+	golang.org/x/crypto v0.0.0-20210421170649-83a5a9bb288b
 	golang.org/x/net v0.0.0-20210813160813-60bc85c4be6d
 )

go.sum

@@ -21,6 +21,8 @@ github.com/jtolds/gls v4.20.0+incompatible/go.mod h1:QJZ7F/aHp+rZTRtaJ1ow/lLfFfV
 github.com/klauspost/cpuid v1.2.3/go.mod h1:Pj4uuM528wm8OyEC2QMXAi2YiTZ96dNQPGgoMS4s3ek=
 github.com/klauspost/cpuid v1.3.1 h1:5JNjFYYQrZeKRJ0734q51WCEEn2huer72Dc7K+R/b6s=
 github.com/klauspost/cpuid v1.3.1/go.mod h1:bYW4mA6ZgKPob1/Dlai2LviZJO7KGI3uoWLd42rAQw4=
+github.com/kr/fs v0.1.0 h1:Jskdu9ieNAYnjxsi0LbQp1ulIKZV1LAFgK1tWhpZgl8=
+github.com/kr/fs v0.1.0/go.mod h1:FFnZGqtBN9Gxj7eW1uZ42v5BccTP0vu6NEaFoC2HwRg=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
@@ -38,6 +40,8 @@ github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd/go.mod h1:6dJ
 github.com/modern-go/reflect2 v0.0.0-20180701023420-4b7aa43c6742/go.mod h1:bx2lNnkwVCuqBIxFjflWJWanXIb3RllmbCylyMrvgv0=
 github.com/modern-go/reflect2 v1.0.1 h1:9f412s+6RmYXLWZSEzVVgPGK7C2PphHj5RJrvfx9AWI=
 github.com/modern-go/reflect2 v1.0.1/go.mod h1:bx2lNnkwVCuqBIxFjflWJWanXIb3RllmbCylyMrvgv0=
+github.com/pkg/sftp v1.13.4 h1:Lb0RYJCmgUcBgZosfoi9Y9sbl6+LJgOIgk/2Y4YjMFg=
+github.com/pkg/sftp v1.13.4/go.mod h1:LzqnAvaD5TWeNBsZpfKxSYn1MbjWwOsCIAFFJbpIsK8=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rs/xid v1.2.1 h1:mhH9Nq+C1fY2l1XIpgxIiUOfNpRBYH1kKcr+qfKgjRc=
@@ -51,16 +55,19 @@ github.com/smartystreets/goconvey v1.6.4/go.mod h1:syvi0/a8iFYH4r/RixwvyeAJjdLS9
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
-github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.0.0-20201216223049-8b5274cf687f h1:aZp0e2vLN4MToVqnjNEYEtrEA8RH8U8FN1CU7JgqsPU=
 golang.org/x/crypto v0.0.0-20201216223049-8b5274cf687f/go.mod h1:jdWPYTVW3xRLrWPugEBEK3UY2ZEsg3UU495nc5E+M+I=
+golang.org/x/crypto v0.0.0-20210421170649-83a5a9bb288b h1:7mWr3k41Qtv8XlltBkDkl8LoP3mpSgBW8BUoxtEdbXg=
+golang.org/x/crypto v0.0.0-20210421170649-83a5a9bb288b/go.mod h1:T9bdIzuCu7OtxOm1hfPfRQxPLYneinmdGuTeoZ9dtd4=
 golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20200707034311-ab3426394381/go.mod h1:/O7V0waA8r7cgGh81Ro3o1hOxt32SMVPicZroKQ2sZA=
+golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20210813160813-60bc85c4be6d h1:LO7XpTYMwTqxjLcGWPijK3vRXg1aWdlNOVOHRq45d7c=
 golang.org/x/net v0.0.0-20210813160813-60bc85c4be6d/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
@@ -69,9 +76,11 @@ golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200625212154-ddb9806d33ae/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210423082822-04245dca01da h1:b3NXsE2LusjYGGjL5bxEVZZORm/YEFFrWFjR8eFrw/c=
 golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7 h1:iGu644GcxtEcrInvDsQRCwJjtCIOlT2V7IRt6ah2Whw=
+golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1 h1:v+OssWQX+hTHEmOBgwxdZxK4zHq3yOs8F9J7mk0PY8E=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
@@ -84,5 +93,6 @@ gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8
 gopkg.in/ini.v1 v1.57.0 h1:9unxIsFcTt4I55uWluz+UmL95q4kdJ0buvQ1ZIqVQww=
 gopkg.in/ini.v1 v1.57.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-gopkg.in/yaml.v2 v2.2.8 h1:obN1ZagJSUGI0Ek/LBmuj4SNLPfIny3KsKFopxRdj10=
 gopkg.in/yaml.v2 v2.2.8/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

internal/encoding/ssh/filexfer/attrs.go

@@ -0,0 +1,326 @@
+package filexfer
+
+// Attributes related flags.
+const (
+	AttrSize        = 1 << iota // SSH_FILEXFER_ATTR_SIZE
+	AttrUIDGID                  // SSH_FILEXFER_ATTR_UIDGID
+	AttrPermissions             // SSH_FILEXFER_ATTR_PERMISSIONS
+	AttrACModTime               // SSH_FILEXFER_ACMODTIME
+
+	AttrExtended = 1 << 31 // SSH_FILEXFER_ATTR_EXTENDED
+)
+
+// Attributes defines the file attributes type defined in draft-ietf-secsh-filexfer-02
+//
+// Defined in: https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-5
+type Attributes struct {
+	Flags uint32
+
+	// AttrSize
+	Size uint64
+
+	// AttrUIDGID
+	UID uint32
+	GID uint32
+
+	// AttrPermissions
+	Permissions FileMode
+
+	// AttrACmodTime
+	ATime uint32
+	MTime uint32
+
+	// AttrExtended
+	ExtendedAttributes []ExtendedAttribute
+}
+
+// GetSize returns the Size field and a bool that is true if and only if the value is valid/defined.
+func (a *Attributes) GetSize() (size uint64, ok bool) {
+	return a.Size, a.Flags&AttrSize != 0
+}
+
+// SetSize is a convenience function that sets the Size field,
+// and marks the field as valid/defined in Flags.
+func (a *Attributes) SetSize(size uint64) {
+	a.Flags |= AttrSize
+	a.Size = size
+}
+
+// GetUIDGID returns the UID and GID fields and a bool that is true if and only if the values are valid/defined.
+func (a *Attributes) GetUIDGID() (uid, gid uint32, ok bool) {
+	return a.UID, a.GID, a.Flags&AttrUIDGID != 0
+}
+
+// SetUIDGID is a convenience function that sets the UID and GID fields,
+// and marks the fields as valid/defined in Flags.
+func (a *Attributes) SetUIDGID(uid, gid uint32) {
+	a.Flags |= AttrUIDGID
+	a.UID = uid
+	a.GID = gid
+}
+
+// GetPermissions returns the Permissions field and a bool that is true if and only if the value is valid/defined.
+func (a *Attributes) GetPermissions() (perms FileMode, ok bool) {
+	return a.Permissions, a.Flags&AttrPermissions != 0
+}
+
+// SetPermissions is a convenience function that sets the Permissions field,
+// and marks the field as valid/defined in Flags.
+func (a *Attributes) SetPermissions(perms FileMode) {
+	a.Flags |= AttrPermissions
+	a.Permissions = perms
+}
+
+// GetACModTime returns the ATime and MTime fields and a bool that is true if and only if the values are valid/defined.
+func (a *Attributes) GetACModTime() (atime, mtime uint32, ok bool) {
+	return a.ATime, a.MTime, a.Flags&AttrACModTime != 0
+	return a.ATime, a.MTime, a.Flags&AttrACModTime != 0
+}
+
+// SetACModTime is a convenience function that sets the ATime and MTime fields,
+// and marks the fields as valid/defined in Flags.
+func (a *Attributes) SetACModTime(atime, mtime uint32) {
+	a.Flags |= AttrACModTime
+	a.ATime = atime
+	a.MTime = mtime
+}
+
+// Len returns the number of bytes a would marshal into.
+func (a *Attributes) Len() int {
+	length := 4
+
+	if a.Flags&AttrSize != 0 {
+		length += 8
+	}
+
+	if a.Flags&AttrUIDGID != 0 {
+		length += 4 + 4
+	}
+
+	if a.Flags&AttrPermissions != 0 {
+		length += 4
+	}
+
+	if a.Flags&AttrACModTime != 0 {
+		length += 4 + 4
+	}
+
+	if a.Flags&AttrExtended != 0 {
+		length += 4
+
+		for _, ext := range a.ExtendedAttributes {
+			length += ext.Len()
+		}
+	}
+
+	return length
+}
+
+// MarshalInto marshals e onto the end of the given Buffer.
+func (a *Attributes) MarshalInto(b *Buffer) {
+	b.AppendUint32(a.Flags)
+
+	if a.Flags&AttrSize != 0 {
+		b.AppendUint64(a.Size)
+	}
+
+	if a.Flags&AttrUIDGID != 0 {
+		b.AppendUint32(a.UID)
+		b.AppendUint32(a.GID)
+	}
+
+	if a.Flags&AttrPermissions != 0 {
+		b.AppendUint32(uint32(a.Permissions))
+	}
+
+	if a.Flags&AttrACModTime != 0 {
+		b.AppendUint32(a.ATime)
+		b.AppendUint32(a.MTime)
+	}
+
+	if a.Flags&AttrExtended != 0 {
+		b.AppendUint32(uint32(len(a.ExtendedAttributes)))
+
+		for _, ext := range a.ExtendedAttributes {
+			ext.MarshalInto(b)
+		}
+	}
+}
+
+// MarshalBinary returns a as the binary encoding of a.
+func (a *Attributes) MarshalBinary() ([]byte, error) {
+	buf := NewBuffer(make([]byte, 0, a.Len()))
+	a.MarshalInto(buf)
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom unmarshals an Attributes from the given Buffer into e.
+//
+// NOTE: The values of fields not covered in the a.Flags are explicitly undefined.
+func (a *Attributes) UnmarshalFrom(b *Buffer) (err error) {
+	flags, err := b.ConsumeUint32()
+	if err != nil {
+		return err
+	}
+
+	return a.XXX_UnmarshalByFlags(flags, b)
+}
+
+// XXX_UnmarshalByFlags uses the pre-existing a.Flags field to determine which fields to decode.
+// DO NOT USE THIS: it is an anti-corruption function to implement existing internal usage in pkg/sftp.
+// This function is not a part of any compatibility promise.
+func (a *Attributes) XXX_UnmarshalByFlags(flags uint32, b *Buffer) (err error) {
+	a.Flags = flags
+
+	// Short-circuit dummy attributes.
+	if a.Flags == 0 {
+		return nil
+	}
+
+	if a.Flags&AttrSize != 0 {
+		if a.Size, err = b.ConsumeUint64(); err != nil {
+			return err
+		}
+	}
+
+	if a.Flags&AttrUIDGID != 0 {
+		if a.UID, err = b.ConsumeUint32(); err != nil {
+			return err
+		}
+
+		if a.GID, err = b.ConsumeUint32(); err != nil {
+			return err
+		}
+	}
+
+	if a.Flags&AttrPermissions != 0 {
+		m, err := b.ConsumeUint32()
+		if err != nil {
+			return err
+		}
+
+		a.Permissions = FileMode(m)
+	}
+
+	if a.Flags&AttrACModTime != 0 {
+		if a.ATime, err = b.ConsumeUint32(); err != nil {
+			return err
+		}
+
+		if a.MTime, err = b.ConsumeUint32(); err != nil {
+			return err
+		}
+	}
+
+	if a.Flags&AttrExtended != 0 {
+		count, err := b.ConsumeUint32()
+		if err != nil {
+			return err
+		}
+
+		a.ExtendedAttributes = make([]ExtendedAttribute, count)
+		for i := range a.ExtendedAttributes {
+			a.ExtendedAttributes[i].UnmarshalFrom(b)
+		}
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the binary encoding of Attributes into e.
+func (a *Attributes) UnmarshalBinary(data []byte) error {
+	return a.UnmarshalFrom(NewBuffer(data))
+}
+
+// ExtendedAttribute defines the extended file attribute type defined in draft-ietf-secsh-filexfer-02
+//
+// Defined in: https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-5
+type ExtendedAttribute struct {
+	Type string
+	Data string
+}
+
+// Len returns the number of bytes e would marshal into.
+func (e *ExtendedAttribute) Len() int {
+	return 4 + len(e.Type) + 4 + len(e.Data)
+}
+
+// MarshalInto marshals e onto the end of the given Buffer.
+func (e *ExtendedAttribute) MarshalInto(b *Buffer) {
+	b.AppendString(e.Type)
+	b.AppendString(e.Data)
+}
+
+// MarshalBinary returns e as the binary encoding of e.
+func (e *ExtendedAttribute) MarshalBinary() ([]byte, error) {
+	buf := NewBuffer(make([]byte, 0, e.Len()))
+	e.MarshalInto(buf)
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom unmarshals an ExtendedAattribute from the given Buffer into e.
+func (e *ExtendedAttribute) UnmarshalFrom(b *Buffer) (err error) {
+	if e.Type, err = b.ConsumeString(); err != nil {
+		return err
+	}
+
+	if e.Data, err = b.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the binary encoding of ExtendedAttribute into e.
+func (e *ExtendedAttribute) UnmarshalBinary(data []byte) error {
+	return e.UnmarshalFrom(NewBuffer(data))
+}
+
+// NameEntry implements the SSH_FXP_NAME repeated data type from draft-ietf-secsh-filexfer-02
+//
+// This type is incompatible with versions 4 or higher.
+type NameEntry struct {
+	Filename string
+	Longname string
+	Attrs    Attributes
+}
+
+// Len returns the number of bytes e would marshal into.
+func (e *NameEntry) Len() int {
+	return 4 + len(e.Filename) + 4 + len(e.Longname) + e.Attrs.Len()
+}
+
+// MarshalInto marshals e onto the end of the given Buffer.
+func (e *NameEntry) MarshalInto(b *Buffer) {
+	b.AppendString(e.Filename)
+	b.AppendString(e.Longname)
+
+	e.Attrs.MarshalInto(b)
+}
+
+// MarshalBinary returns e as the binary encoding of e.
+func (e *NameEntry) MarshalBinary() ([]byte, error) {
+	buf := NewBuffer(make([]byte, 0, e.Len()))
+	e.MarshalInto(buf)
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom unmarshals an NameEntry from the given Buffer into e.
+//
+// NOTE: The values of fields not covered in the a.Flags are explicitly undefined.
+func (e *NameEntry) UnmarshalFrom(b *Buffer) (err error) {
+	if e.Filename, err = b.ConsumeString(); err != nil {
+		return err
+	}
+
+	if e.Longname, err = b.ConsumeString(); err != nil {
+		return err
+	}
+
+	return e.Attrs.UnmarshalFrom(b)
+}
+
+// UnmarshalBinary decodes the binary encoding of NameEntry into e.
+func (e *NameEntry) UnmarshalBinary(data []byte) error {
+	return e.UnmarshalFrom(NewBuffer(data))
+}

internal/encoding/ssh/filexfer/attrs_test.go

@@ -0,0 +1,231 @@
+package filexfer
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestAttributes(t *testing.T) {
+	const (
+		size  = 0x123456789ABCDEF0
+		uid   = 1000
+		gid   = 100
+		perms = 0x87654321
+		atime = 0x2A2B2C2D
+		mtime = 0x42434445
+	)
+
+	extAttr := ExtendedAttribute{
+		Type: "foo",
+		Data: "bar",
+	}
+
+	attr := &Attributes{
+		Size:        size,
+		UID:         uid,
+		GID:         gid,
+		Permissions: perms,
+		ATime:       atime,
+		MTime:       mtime,
+		ExtendedAttributes: []ExtendedAttribute{
+			extAttr,
+		},
+	}
+
+	type test struct {
+		name    string
+		flags   uint32
+		encoded []byte
+	}
+
+	tests := []test{
+		{
+			name: "empty",
+			encoded: []byte{
+				0x00, 0x00, 0x00, 0x00,
+			},
+		},
+		{
+			name:  "size",
+			flags: AttrSize,
+			encoded: []byte{
+				0x00, 0x00, 0x00, 0x01,
+				0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0,
+			},
+		},
+		{
+			name:  "uidgid",
+			flags: AttrUIDGID,
+			encoded: []byte{
+				0x00, 0x00, 0x00, 0x02,
+				0x00, 0x00, 0x03, 0xE8,
+				0x00, 0x00, 0x00, 100,
+			},
+		},
+		{
+			name:  "permissions",
+			flags: AttrPermissions,
+			encoded: []byte{
+				0x00, 0x00, 0x00, 0x04,
+				0x87, 0x65, 0x43, 0x21,
+			},
+		},
+		{
+			name:  "acmodtime",
+			flags: AttrACModTime,
+			encoded: []byte{
+				0x00, 0x00, 0x00, 0x08,
+				0x2A, 0x2B, 0x2C, 0x2D,
+				0x42, 0x43, 0x44, 0x45,
+			},
+		},
+		{
+			name:  "extended",
+			flags: AttrExtended,
+			encoded: []byte{
+				0x80, 0x00, 0x00, 0x00,
+				0x00, 0x00, 0x00, 0x01,
+				0x00, 0x00, 0x00, 0x03, 'f', 'o', 'o',
+				0x00, 0x00, 0x00, 0x03, 'b', 'a', 'r',
+			},
+		},
+		{
+			name:  "size uidgid permisssions acmodtime extended",
+			flags: AttrSize | AttrUIDGID | AttrPermissions | AttrACModTime | AttrExtended,
+			encoded: []byte{
+				0x80, 0x00, 0x00, 0x0F,
+				0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0,
+				0x00, 0x00, 0x03, 0xE8,
+				0x00, 0x00, 0x00, 100,
+				0x87, 0x65, 0x43, 0x21,
+				0x2A, 0x2B, 0x2C, 0x2D,
+				0x42, 0x43, 0x44, 0x45,
+				0x00, 0x00, 0x00, 0x01,
+				0x00, 0x00, 0x00, 0x03, 'f', 'o', 'o',
+				0x00, 0x00, 0x00, 0x03, 'b', 'a', 'r',
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		attr := *attr
+
+		t.Run(tt.name, func(t *testing.T) {
+			attr.Flags = tt.flags
+
+			buf, err := attr.MarshalBinary()
+			if err != nil {
+				t.Fatal("unexpected error:", err)
+			}
+
+			if !bytes.Equal(buf, tt.encoded) {
+				t.Fatalf("MarshalBinary() = %X, but wanted %X", buf, tt.encoded)
+			}
+
+			attr = Attributes{}
+
+			if err := attr.UnmarshalBinary(buf); err != nil {
+				t.Fatal("unexpected error:", err)
+			}
+
+			if attr.Flags != tt.flags {
+				t.Errorf("UnmarshalBinary(): Flags was %x, but wanted %x", attr.Flags, tt.flags)
+			}
+
+			if attr.Flags&AttrSize != 0 && attr.Size != size {
+				t.Errorf("UnmarshalBinary(): Size was %x, but wanted %x", attr.Size, size)
+			}
+
+			if attr.Flags&AttrUIDGID != 0 {
+				if attr.UID != uid {
+					t.Errorf("UnmarshalBinary(): UID was %x, but wanted %x", attr.UID, uid)
+				}
+
+				if attr.GID != gid {
+					t.Errorf("UnmarshalBinary(): GID was %x, but wanted %x", attr.GID, gid)
+				}
+			}
+
+			if attr.Flags&AttrPermissions != 0 && attr.Permissions != perms {
+				t.Errorf("UnmarshalBinary(): Permissions was %#v, but wanted %#v", attr.Permissions, perms)
+			}
+
+			if attr.Flags&AttrACModTime != 0 {
+				if attr.ATime != atime {
+					t.Errorf("UnmarshalBinary(): ATime was %x, but wanted %x", attr.ATime, atime)
+				}
+
+				if attr.MTime != mtime {
+					t.Errorf("UnmarshalBinary(): MTime was %x, but wanted %x", attr.MTime, mtime)
+				}
+			}
+
+			if attr.Flags&AttrExtended != 0 {
+				extAttrs := attr.ExtendedAttributes
+
+				if count := len(extAttrs); count != 1 {
+					t.Fatalf("UnmarshalBinary(): len(ExtendedAttributes) was %d, but wanted %d", count, 1)
+				}
+
+				if got := extAttrs[0]; got != extAttr {
+					t.Errorf("UnmarshalBinary(): ExtendedAttributes[0] was %#v, but wanted %#v", got, extAttr)
+				}
+			}
+		})
+	}
+}
+
+func TestNameEntry(t *testing.T) {
+	const (
+		filename = "foo"
+		longname = "bar"
+		perms    = 0x87654321
+	)
+
+	e := &NameEntry{
+		Filename: filename,
+		Longname: longname,
+		Attrs: Attributes{
+			Flags:       AttrPermissions,
+			Permissions: perms,
+		},
+	}
+
+	buf, err := e.MarshalBinary()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 0x03, 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 0x03, 'b', 'a', 'r',
+		0x00, 0x00, 0x00, 0x04,
+		0x87, 0x65, 0x43, 0x21,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalBinary() = %X, but wanted %X", buf, want)
+	}
+
+	*e = NameEntry{}
+
+	if err := e.UnmarshalBinary(buf); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if e.Filename != filename {
+		t.Errorf("UnmarhsalFrom(): Filename was %q, but expected %q", e.Filename, filename)
+	}
+
+	if e.Longname != longname {
+		t.Errorf("UnmarhsalFrom(): Longname was %q, but expected %q", e.Longname, longname)
+	}
+
+	if e.Attrs.Flags != AttrPermissions {
+		t.Errorf("UnmarshalBinary(): Attrs.Flag was %#x, but expected %#x", e.Attrs.Flags, AttrPermissions)
+	}
+
+	if e.Attrs.Permissions != perms {
+		t.Errorf("UnmarshalBinary(): Attrs.Permissions was %#v, but expected %#v", e.Attrs.Permissions, perms)
+	}
+}

internal/encoding/ssh/filexfer/buffer.go

@@ -0,0 +1,293 @@
+package filexfer
+
+import (
+	"encoding/binary"
+	"errors"
+)
+
+// Various encoding errors.
+var (
+	ErrShortPacket = errors.New("packet too short")
+	ErrLongPacket  = errors.New("packet too long")
+)
+
+// Buffer wraps up the various encoding details of the SSH format.
+//
+// Data types are encoded as per section 4 from https://tools.ietf.org/html/draft-ietf-secsh-architecture-09#page-8
+type Buffer struct {
+	b   []byte
+	off int
+}
+
+// NewBuffer creates and initializes a new buffer using buf as its initial contents.
+// The new buffer takes ownership of buf, and the caller should not use buf after this call.
+//
+// In most cases, new(Buffer) (or just declaring a Buffer variable) is sufficient to initialize a Buffer.
+func NewBuffer(buf []byte) *Buffer {
+	return &Buffer{
+		b: buf,
+	}
+}
+
+// NewMarshalBuffer creates a new Buffer ready to start marshaling a Packet into.
+// It preallocates enough space for uint32(length), uint8(type), uint32(request-id) and size more bytes.
+func NewMarshalBuffer(size int) *Buffer {
+	return NewBuffer(make([]byte, 4+1+4+size))
+}
+
+// Bytes returns a slice of length b.Len() holding the unconsumed bytes in the Buffer.
+// The slice is valid for use only until the next buffer modification
+// (that is, only until the next call to an Append or Consume method).
+func (b *Buffer) Bytes() []byte {
+	return b.b[b.off:]
+}
+
+// Len returns the number of unconsumed bytes in the buffer.
+func (b *Buffer) Len() int { return len(b.b) - b.off }
+
+// Cap returns the capacity of the buffer’s underlying byte slice,
+// that is, the total space allocated for the buffer’s data.
+func (b *Buffer) Cap() int { return cap(b.b) }
+
+// Reset resets the buffer to be empty, but it retains the underlying storage for use by future Appends.
+func (b *Buffer) Reset() {
+	b.b = b.b[:0]
+	b.off = 0
+}
+
+// StartPacket resets and initializes the buffer to be ready to start marshaling a packet into.
+// It truncates the buffer, reserves space for uint32(length), then appends the given packetType and requestID.
+func (b *Buffer) StartPacket(packetType PacketType, requestID uint32) {
+	b.b, b.off = append(b.b[:0], make([]byte, 4)...), 0
+
+	b.AppendUint8(uint8(packetType))
+	b.AppendUint32(requestID)
+}
+
+// Packet finalizes the packet started from StartPacket.
+// It is expected that this will end the ownership of the underlying byte-slice,
+// and so the returned byte-slices may be reused the same as any other byte-slice,
+// the caller should not use this buffer after this call.
+//
+// It writes the packet body length into the first four bytes of the buffer in network byte order (big endian).
+// The packet body length is the length of this buffer less the 4-byte length itself, plus the length of payload.
+//
+// It is assumed that no Consume methods have been called on this buffer,
+// and so it returns the whole underlying slice.
+func (b *Buffer) Packet(payload []byte) (header, payloadPassThru []byte, err error) {
+	b.PutLength(len(b.b) - 4 + len(payload))
+
+	return b.b, payload, nil
+}
+
+// ConsumeUint8 consumes a single byte from the buffer.
+// If the buffer does not have enough data, it will return ErrShortPacket.
+func (b *Buffer) ConsumeUint8() (uint8, error) {
+	if b.Len() < 1 {
+		return 0, ErrShortPacket
+	}
+
+	var v uint8
+	v, b.off = b.b[b.off], b.off+1
+	return v, nil
+}
+
+// AppendUint8 appends a single byte into the buffer.
+func (b *Buffer) AppendUint8(v uint8) {
+	b.b = append(b.b, v)
+}
+
+// ConsumeBool consumes a single byte from the buffer, and returns true if that byte is non-zero.
+// If the buffer does not have enough data, it will return ErrShortPacket.
+func (b *Buffer) ConsumeBool() (bool, error) {
+	v, err := b.ConsumeUint8()
+	if err != nil {
+		return false, err
+	}
+
+	return v != 0, nil
+}
+
+// AppendBool appends a single bool into the buffer.
+// It encodes it as a single byte, with false as 0, and true as 1.
+func (b *Buffer) AppendBool(v bool) {
+	if v {
+		b.AppendUint8(1)
+	} else {
+		b.AppendUint8(0)
+	}
+}
+
+// ConsumeUint16 consumes a single uint16 from the buffer, in network byte order (big-endian).
+// If the buffer does not have enough data, it will return ErrShortPacket.
+func (b *Buffer) ConsumeUint16() (uint16, error) {
+	if b.Len() < 2 {
+		return 0, ErrShortPacket
+	}
+
+	v := binary.BigEndian.Uint16(b.b[b.off:])
+	b.off += 2
+	return v, nil
+}
+
+// AppendUint16 appends single uint16 into the buffer, in network byte order (big-endian).
+func (b *Buffer) AppendUint16(v uint16) {
+	b.b = append(b.b,
+		byte(v>>8),
+		byte(v>>0),
+	)
+}
+
+// unmarshalUint32 is used internally to read the packet length.
+// It is unsafe, and so not exported.
+// Even within this package, its use should be avoided.
+func unmarshalUint32(b []byte) uint32 {
+	return binary.BigEndian.Uint32(b[:4])
+}
+
+// ConsumeUint32 consumes a single uint32 from the buffer, in network byte order (big-endian).
+// If the buffer does not have enough data, it will return ErrShortPacket.
+func (b *Buffer) ConsumeUint32() (uint32, error) {
+	if b.Len() < 4 {
+		return 0, ErrShortPacket
+	}
+
+	v := binary.BigEndian.Uint32(b.b[b.off:])
+	b.off += 4
+	return v, nil
+}
+
+// AppendUint32 appends a single uint32 into the buffer, in network byte order (big-endian).
+func (b *Buffer) AppendUint32(v uint32) {
+	b.b = append(b.b,
+		byte(v>>24),
+		byte(v>>16),
+		byte(v>>8),
+		byte(v>>0),
+	)
+}
+
+// ConsumeUint64 consumes a single uint64 from the buffer, in network byte order (big-endian).
+// If the buffer does not have enough data, it will return ErrShortPacket.
+func (b *Buffer) ConsumeUint64() (uint64, error) {
+	if b.Len() < 8 {
+		return 0, ErrShortPacket
+	}
+
+	v := binary.BigEndian.Uint64(b.b[b.off:])
+	b.off += 8
+	return v, nil
+}
+
+// AppendUint64 appends a single uint64 into the buffer, in network byte order (big-endian).
+func (b *Buffer) AppendUint64(v uint64) {
+	b.b = append(b.b,
+		byte(v>>56),
+		byte(v>>48),
+		byte(v>>40),
+		byte(v>>32),
+		byte(v>>24),
+		byte(v>>16),
+		byte(v>>8),
+		byte(v>>0),
+	)
+}
+
+// ConsumeInt64 consumes a single int64 from the buffer, in network byte order (big-endian) with two’s complement.
+// If the buffer does not have enough data, it will return ErrShortPacket.
+func (b *Buffer) ConsumeInt64() (int64, error) {
+	u, err := b.ConsumeUint64()
+	if err != nil {
+		return 0, err
+	}
+
+	return int64(u), err
+}
+
+// AppendInt64 appends a single int64 into the buffer, in network byte order (big-endian) with two’s complement.
+func (b *Buffer) AppendInt64(v int64) {
+	b.AppendUint64(uint64(v))
+}
+
+// ConsumeByteSlice consumes a single string of raw binary data from the buffer.
+// A string is a uint32 length, followed by that number of raw bytes.
+// If the buffer does not have enough data, or defines a length larger than available, it will return ErrShortPacket.
+//
+// The returned slice aliases the buffer contents, and is valid only as long as the buffer is not reused
+// (that is, only until the next call to Reset, PutLength, StartPacket, or UnmarshalBinary).
+//
+// In no case will any Consume calls return overlapping slice aliases,
+// and Append calls are guaranteed to not disturb this slice alias.
+func (b *Buffer) ConsumeByteSlice() ([]byte, error) {
+	length, err := b.ConsumeUint32()
+	if err != nil {
+		return nil, err
+	}
+
+	if b.Len() < int(length) {
+		return nil, ErrShortPacket
+	}
+
+	v := b.b[b.off:]
+	if len(v) > int(length) {
+		v = v[:length:length]
+	}
+	b.off += int(length)
+	return v, nil
+}
+
+// AppendByteSlice appends a single string of raw binary data into the buffer.
+// A string is a uint32 length, followed by that number of raw bytes.
+func (b *Buffer) AppendByteSlice(v []byte) {
+	b.AppendUint32(uint32(len(v)))
+	b.b = append(b.b, v...)
+}
+
+// ConsumeString consumes a single string of binary data from the buffer.
+// A string is a uint32 length, followed by that number of raw bytes.
+// If the buffer does not have enough data, or defines a length larger than available, it will return ErrShortPacket.
+//
+// NOTE: Go implicitly assumes that strings contain UTF-8 encoded data.
+// All caveats on using arbitrary binary data in Go strings applies.
+func (b *Buffer) ConsumeString() (string, error) {
+	v, err := b.ConsumeByteSlice()
+	if err != nil {
+		return "", err
+	}
+
+	return string(v), nil
+}
+
+// AppendString appends a single string of binary data into the buffer.
+// A string is a uint32 length, followed by that number of raw bytes.
+func (b *Buffer) AppendString(v string) {
+	b.AppendByteSlice([]byte(v))
+}
+
+// PutLength writes the given size into the first four bytes of the buffer in network byte order (big endian).
+func (b *Buffer) PutLength(size int) {
+	if len(b.b) < 4 {
+		b.b = append(b.b, make([]byte, 4-len(b.b))...)
+	}
+
+	binary.BigEndian.PutUint32(b.b, uint32(size))
+}
+
+// MarshalBinary returns a clone of the full internal buffer.
+func (b *Buffer) MarshalBinary() ([]byte, error) {
+	clone := make([]byte, len(b.b))
+	n := copy(clone, b.b)
+	return clone[:n], nil
+}
+
+// UnmarshalBinary sets the internal buffer of b to be a clone of data, and zeros the internal offset.
+func (b *Buffer) UnmarshalBinary(data []byte) error {
+	if grow := len(data) - len(b.b); grow > 0 {
+		b.b = append(b.b, make([]byte, grow)...)
+	}
+
+	n := copy(b.b, data)
+	b.b = b.b[:n]
+	b.off = 0
+	return nil
+}

internal/encoding/ssh/filexfer/extended_packets.go

@@ -0,0 +1,142 @@
+package filexfer
+
+import (
+	"encoding"
+	"sync"
+)
+
+// ExtendedData aliases the untyped interface composition of encoding.BinaryMarshaler and encoding.BinaryUnmarshaler.
+type ExtendedData = interface {
+	encoding.BinaryMarshaler
+	encoding.BinaryUnmarshaler
+}
+
+// ExtendedDataConstructor defines a function that returns a new(ArbitraryExtendedPacket).
+type ExtendedDataConstructor func() ExtendedData
+
+var extendedPacketTypes = struct {
+	mu           sync.RWMutex
+	constructors map[string]ExtendedDataConstructor
+}{
+	constructors: make(map[string]ExtendedDataConstructor),
+}
+
+// RegisterExtendedPacketType defines a specific ExtendedDataConstructor for the given extension string.
+func RegisterExtendedPacketType(extension string, constructor ExtendedDataConstructor) {
+	extendedPacketTypes.mu.Lock()
+	defer extendedPacketTypes.mu.Unlock()
+
+	if _, exist := extendedPacketTypes.constructors[extension]; exist {
+		panic("encoding/ssh/filexfer: multiple registration of extended packet type " + extension)
+	}
+
+	extendedPacketTypes.constructors[extension] = constructor
+}
+
+func newExtendedPacket(extension string) ExtendedData {
+	extendedPacketTypes.mu.RLock()
+	defer extendedPacketTypes.mu.RUnlock()
+
+	if f := extendedPacketTypes.constructors[extension]; f != nil {
+		return f()
+	}
+
+	return new(Buffer)
+}
+
+// ExtendedPacket defines the SSH_FXP_CLOSE packet.
+type ExtendedPacket struct {
+	ExtendedRequest string
+
+	Data ExtendedData
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *ExtendedPacket) Type() PacketType {
+	return PacketTypeExtended
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+//
+// The Data is marshaled into binary, and returned as the payload.
+func (p *ExtendedPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.ExtendedRequest) // string(extended-request)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeExtended, reqid)
+	buf.AppendString(p.ExtendedRequest)
+
+	if p.Data != nil {
+		payload, err = p.Data.MarshalBinary()
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+//
+// If p.Data is nil, and the extension has been registered, a new type will be made from the registration.
+// If the extension has not been registered, then a new Buffer will be allocated.
+// Then the request-specific-data will be unmarshaled from the rest of the buffer.
+func (p *ExtendedPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.ExtendedRequest, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if p.Data == nil {
+		p.Data = newExtendedPacket(p.ExtendedRequest)
+	}
+
+	return p.Data.UnmarshalBinary(buf.Bytes())
+}
+
+// ExtendedReplyPacket defines the SSH_FXP_CLOSE packet.
+type ExtendedReplyPacket struct {
+	Data ExtendedData
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *ExtendedReplyPacket) Type() PacketType {
+	return PacketTypeExtendedReply
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+//
+// The Data is marshaled into binary, and returned as the payload.
+func (p *ExtendedReplyPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		buf = NewMarshalBuffer(0)
+	}
+
+	buf.StartPacket(PacketTypeExtendedReply, reqid)
+
+	if p.Data != nil {
+		payload, err = p.Data.MarshalBinary()
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+//
+// If p.Data is nil, and there is request-specific-data,
+// then the request-specific-data will be wrapped in a Buffer and assigned to p.Data.
+func (p *ExtendedReplyPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Data == nil {
+		p.Data = new(Buffer)
+	}
+
+	return p.Data.UnmarshalBinary(buf.Bytes())
+}

internal/encoding/ssh/filexfer/extended_packets_test.go

@@ -0,0 +1,240 @@
+package filexfer
+
+import (
+	"bytes"
+	"testing"
+)
+
+type testExtendedData struct {
+	value uint8
+}
+
+func (d *testExtendedData) MarshalBinary() ([]byte, error) {
+	buf := NewBuffer(make([]byte, 0, 4))
+
+	buf.AppendUint8(d.value ^ 0x2a)
+
+	return buf.Bytes(), nil
+}
+
+func (d *testExtendedData) UnmarshalBinary(data []byte) error {
+	buf := NewBuffer(data)
+
+	v, err := buf.ConsumeUint8()
+	if err != nil {
+		return err
+	}
+
+	d.value = v ^ 0x2a
+
+	return nil
+}
+
+var _ Packet = &ExtendedPacket{}
+
+func TestExtendedPacketNoData(t *testing.T) {
+	const (
+		id              = 42
+		extendedRequest = "foo@example"
+	)
+
+	p := &ExtendedPacket{
+		ExtendedRequest: extendedRequest,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 20,
+		200,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 11, 'f', 'o', 'o', '@', 'e', 'x', 'a', 'm', 'p', 'l', 'e',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = ExtendedPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.ExtendedRequest != extendedRequest {
+		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extendedRequest)
+	}
+}
+
+func TestExtendedPacketTestData(t *testing.T) {
+	const (
+		id              = 42
+		extendedRequest = "foo@example"
+		textValue       = 13
+	)
+
+	const value = 13
+
+	p := &ExtendedPacket{
+		ExtendedRequest: extendedRequest,
+		Data: &testExtendedData{
+			value: textValue,
+		},
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 21,
+		200,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 11, 'f', 'o', 'o', '@', 'e', 'x', 'a', 'm', 'p', 'l', 'e',
+		0x27,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = ExtendedPacket{
+		Data: new(testExtendedData),
+	}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.ExtendedRequest != extendedRequest {
+		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extendedRequest)
+	}
+
+	if buf, ok := p.Data.(*testExtendedData); !ok {
+		t.Errorf("UnmarshalPacketBody(): Data was type %T, but expected %T", p.Data, buf)
+
+	} else if buf.value != value {
+		t.Errorf("UnmarshalPacketBody(): Data.value was %#x, but expected %#x", buf.value, value)
+	}
+
+	*p = ExtendedPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.ExtendedRequest != extendedRequest {
+		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extendedRequest)
+	}
+
+	wantBuffer := []byte{0x27}
+
+	if buf, ok := p.Data.(*Buffer); !ok {
+		t.Errorf("UnmarshalPacketBody(): Data was type %T, but expected %T", p.Data, buf)
+
+	} else if !bytes.Equal(buf.b, wantBuffer) {
+		t.Errorf("UnmarshalPacketBody(): Data was %X, but expected %X", buf.b, wantBuffer)
+	}
+}
+
+var _ Packet = &ExtendedReplyPacket{}
+
+func TestExtendedReplyNoData(t *testing.T) {
+	const (
+		id = 42
+	)
+
+	p := &ExtendedReplyPacket{}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 5,
+		201,
+		0x00, 0x00, 0x00, 42,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = ExtendedReplyPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+}
+
+func TestExtendedReplyPacketTestData(t *testing.T) {
+	const (
+		id        = 42
+		textValue = 13
+	)
+
+	const value = 13
+
+	p := &ExtendedReplyPacket{
+		Data: &testExtendedData{
+			value: textValue,
+		},
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 6,
+		201,
+		0x00, 0x00, 0x00, 42,
+		0x27,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = ExtendedReplyPacket{
+		Data: new(testExtendedData),
+	}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if buf, ok := p.Data.(*testExtendedData); !ok {
+		t.Errorf("UnmarshalPacketBody(): Data was type %T, but expected %T", p.Data, buf)
+
+	} else if buf.value != value {
+		t.Errorf("UnmarshalPacketBody(): Data.value was %#x, but expected %#x", buf.value, value)
+	}
+
+	*p = ExtendedReplyPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	wantBuffer := []byte{0x27}
+
+	if buf, ok := p.Data.(*Buffer); !ok {
+		t.Errorf("UnmarshalPacketBody(): Data was type %T, but expected %T", p.Data, buf)
+
+	} else if !bytes.Equal(buf.b, wantBuffer) {
+		t.Errorf("UnmarshalPacketBody(): Data was %X, but expected %X", buf.b, wantBuffer)
+	}
+}

internal/encoding/ssh/filexfer/extensions.go

@@ -0,0 +1,46 @@
+package filexfer
+
+// ExtensionPair defines the extension-pair type defined in draft-ietf-secsh-filexfer-13.
+// This type is backwards-compatible with how draft-ietf-secsh-filexfer-02 defines extensions.
+//
+// Defined in: https://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#section-4.2
+type ExtensionPair struct {
+	Name string
+	Data string
+}
+
+// Len returns the number of bytes e would marshal into.
+func (e *ExtensionPair) Len() int {
+	return 4 + len(e.Name) + 4 + len(e.Data)
+}
+
+// MarshalInto marshals e onto the end of the given Buffer.
+func (e *ExtensionPair) MarshalInto(buf *Buffer) {
+	buf.AppendString(e.Name)
+	buf.AppendString(e.Data)
+}
+
+// MarshalBinary returns e as the binary encoding of e.
+func (e *ExtensionPair) MarshalBinary() ([]byte, error) {
+	buf := NewBuffer(make([]byte, 0, e.Len()))
+	e.MarshalInto(buf)
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom unmarshals an ExtensionPair from the given Buffer into e.
+func (e *ExtensionPair) UnmarshalFrom(buf *Buffer) (err error) {
+	if e.Name, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if e.Data, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the binary encoding of ExtensionPair into e.
+func (e *ExtensionPair) UnmarshalBinary(data []byte) error {
+	return e.UnmarshalFrom(NewBuffer(data))
+}

internal/encoding/ssh/filexfer/extensions_test.go

@@ -0,0 +1,49 @@
+package filexfer
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestExtensionPair(t *testing.T) {
+	const (
+		name = "foo"
+		data = "1"
+	)
+
+	pair := &ExtensionPair{
+		Name: name,
+		Data: data,
+	}
+
+	buf, err := pair.MarshalBinary()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 3,
+		'f', 'o', 'o',
+		0x00, 0x00, 0x00, 1,
+		'1',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Errorf("ExtensionPair.MarshalBinary() = %X, but wanted %X", buf, want)
+	}
+
+	*pair = ExtensionPair{}
+
+	if err := pair.UnmarshalBinary(buf); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if pair.Name != name {
+		t.Errorf("ExtensionPair.UnmarshalBinary(): Name was %q, but expected %q", pair.Name, name)
+	}
+
+	if pair.Data != data {
+		t.Errorf("RawPacket.UnmarshalBinary(): Data was %q, but expected %q", pair.Data, data)
+	}
+
+}

internal/encoding/ssh/filexfer/filexfer.go

@@ -0,0 +1,54 @@
+// Package filexfer implements the wire encoding for secsh-filexfer as described in https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02
+package filexfer
+
+// PacketMarshaller narrowly defines packets that will only be transmitted.
+//
+// ExtendedPacket types will often only implement this interface,
+// since decoding the whole packet body of an ExtendedPacket can only be done dependent on the ExtendedRequest field.
+type PacketMarshaller interface {
+	// MarshalPacket is the primary intended way to encode a packet.
+	// The request-id for the packet is set from reqid.
+	//
+	// An optional buffer may be given in b.
+	// If the buffer has a minimum capacity, it shall be truncated and used to marshal the header into.
+	// The minimum capacity for the packet must be a constant expression, and should be at least 9.
+	//
+	// It shall return the main body of the encoded packet in header,
+	// and may optionally return an additional payload to be written immediately after the header.
+	//
+	// It shall encode in the first 4-bytes of the header the proper length of the rest of the header+payload.
+	MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error)
+}
+
+// Packet defines the behavior of a full generic SFTP packet.
+//
+// InitPacket, and VersionPacket are not generic SFTP packets, and instead implement (Un)MarshalBinary.
+//
+// ExtendedPacket types should not iplement this interface,
+// since decoding the whole packet body of an ExtendedPacket can only be done dependent on the ExtendedRequest field.
+type Packet interface {
+	PacketMarshaller
+
+	// Type returns the SSH_FXP_xy value associated with the specific packet.
+	Type() PacketType
+
+	// UnmarshalPacketBody decodes a packet body from the given Buffer.
+	// It is assumed that the common header values of the length, type and request-id have already been consumed.
+	//
+	// Implementations should not alias the given Buffer,
+	// instead they can consider prepopulating an internal buffer as a hint,
+	// and copying into that buffer if it has sufficient length.
+	UnmarshalPacketBody(buf *Buffer) error
+}
+
+// ComposePacket converts returns from MarshalPacket into an equivalent call to MarshalBinary.
+func ComposePacket(header, payload []byte, err error) ([]byte, error) {
+	return append(header, payload...), err
+}
+
+// Default length values,
+// Defined in draft-ietf-secsh-filexfer-02 section 3.
+const (
+	DefaultMaxPacketLength = 34000
+	DefaultMaxDataLength   = 32768
+)

internal/encoding/ssh/filexfer/fx.go

@@ -0,0 +1,147 @@
+package filexfer
+
+import (
+	"fmt"
+)
+
+// Status defines the SFTP error codes used in SSH_FXP_STATUS response packets.
+type Status uint32
+
+// Defines the various SSH_FX_* values.
+const (
+	// see draft-ietf-secsh-filexfer-02
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-7
+	StatusOK = Status(iota)
+	StatusEOF
+	StatusNoSuchFile
+	StatusPermissionDenied
+	StatusFailure
+	StatusBadMessage
+	StatusNoConnection
+	StatusConnectionLost
+	StatusOPUnsupported
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-03#section-7
+	StatusV4InvalidHandle
+	StatusV4NoSuchPath
+	StatusV4FileAlreadyExists
+	StatusV4WriteProtect
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-04#section-7
+	StatusV4NoMedia
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-05#section-7
+	StatusV5NoSpaceOnFilesystem
+	StatusV5QuotaExceeded
+	StatusV5UnknownPrincipal
+	StatusV5LockConflict
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-06#section-8
+	StatusV6DirNotEmpty
+	StatusV6NotADirectory
+	StatusV6InvalidFilename
+	StatusV6LinkLoop
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-07#section-8
+	StatusV6CannotDelete
+	StatusV6InvalidParameter
+	StatusV6FileIsADirectory
+	StatusV6ByteRangeLockConflict
+	StatusV6ByteRangeLockRefused
+	StatusV6DeletePending
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-08#section-8.1
+	StatusV6FileCorrupt
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-10#section-9.1
+	StatusV6OwnerInvalid
+	StatusV6GroupInvalid
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#section-9.1
+	StatusV6NoMatchingByteRangeLock
+)
+
+func (s Status) Error() string {
+	return s.String()
+}
+
+// Is returns true if the target is the same Status code,
+// or target is a StatusPacket with the same Status code.
+func (s Status) Is(target error) bool {
+	if target, ok := target.(*StatusPacket); ok {
+		return target.StatusCode == s
+	}
+
+	return s == target
+}
+
+func (s Status) String() string {
+	switch s {
+	case StatusOK:
+		return "SSH_FX_OK"
+	case StatusEOF:
+		return "SSH_FX_EOF"
+	case StatusNoSuchFile:
+		return "SSH_FX_NO_SUCH_FILE"
+	case StatusPermissionDenied:
+		return "SSH_FX_PERMISSION_DENIED"
+	case StatusFailure:
+		return "SSH_FX_FAILURE"
+	case StatusBadMessage:
+		return "SSH_FX_BAD_MESSAGE"
+	case StatusNoConnection:
+		return "SSH_FX_NO_CONNECTION"
+	case StatusConnectionLost:
+		return "SSH_FX_CONNECTION_LOST"
+	case StatusOPUnsupported:
+		return "SSH_FX_OP_UNSUPPORTED"
+	case StatusV4InvalidHandle:
+		return "SSH_FX_INVALID_HANDLE"
+	case StatusV4NoSuchPath:
+		return "SSH_FX_NO_SUCH_PATH"
+	case StatusV4FileAlreadyExists:
+		return "SSH_FX_FILE_ALREADY_EXISTS"
+	case StatusV4WriteProtect:
+		return "SSH_FX_WRITE_PROTECT"
+	case StatusV4NoMedia:
+		return "SSH_FX_NO_MEDIA"
+	case StatusV5NoSpaceOnFilesystem:
+		return "SSH_FX_NO_SPACE_ON_FILESYSTEM"
+	case StatusV5QuotaExceeded:
+		return "SSH_FX_QUOTA_EXCEEDED"
+	case StatusV5UnknownPrincipal:
+		return "SSH_FX_UNKNOWN_PRINCIPAL"
+	case StatusV5LockConflict:
+		return "SSH_FX_LOCK_CONFLICT"
+	case StatusV6DirNotEmpty:
+		return "SSH_FX_DIR_NOT_EMPTY"
+	case StatusV6NotADirectory:
+		return "SSH_FX_NOT_A_DIRECTORY"
+	case StatusV6InvalidFilename:
+		return "SSH_FX_INVALID_FILENAME"
+	case StatusV6LinkLoop:
+		return "SSH_FX_LINK_LOOP"
+	case StatusV6CannotDelete:
+		return "SSH_FX_CANNOT_DELETE"
+	case StatusV6InvalidParameter:
+		return "SSH_FX_INVALID_PARAMETER"
+	case StatusV6FileIsADirectory:
+		return "SSH_FX_FILE_IS_A_DIRECTORY"
+	case StatusV6ByteRangeLockConflict:
+		return "SSH_FX_BYTE_RANGE_LOCK_CONFLICT"
+	case StatusV6ByteRangeLockRefused:
+		return "SSH_FX_BYTE_RANGE_LOCK_REFUSED"
+	case StatusV6DeletePending:
+		return "SSH_FX_DELETE_PENDING"
+	case StatusV6FileCorrupt:
+		return "SSH_FX_FILE_CORRUPT"
+	case StatusV6OwnerInvalid:
+		return "SSH_FX_OWNER_INVALID"
+	case StatusV6GroupInvalid:
+		return "SSH_FX_GROUP_INVALID"
+	case StatusV6NoMatchingByteRangeLock:
+		return "SSH_FX_NO_MATCHING_BYTE_RANGE_LOCK"
+	default:
+		return fmt.Sprintf("SSH_FX_UNKNOWN(%d)", s)
+	}
+}

internal/encoding/ssh/filexfer/fx_test.go

@@ -0,0 +1,102 @@
+package filexfer
+
+import (
+	"bufio"
+	"errors"
+	"regexp"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+// This string data is copied verbatim from https://tools.ietf.org/html/draft-ietf-secsh-filexfer-13
+var fxStandardsText = `
+SSH_FX_OK                            0
+SSH_FX_EOF                           1
+SSH_FX_NO_SUCH_FILE                  2
+SSH_FX_PERMISSION_DENIED             3
+SSH_FX_FAILURE                       4
+SSH_FX_BAD_MESSAGE                   5
+SSH_FX_NO_CONNECTION                 6
+SSH_FX_CONNECTION_LOST               7
+SSH_FX_OP_UNSUPPORTED                8
+SSH_FX_INVALID_HANDLE                9
+SSH_FX_NO_SUCH_PATH                  10
+SSH_FX_FILE_ALREADY_EXISTS           11
+SSH_FX_WRITE_PROTECT                 12
+SSH_FX_NO_MEDIA                      13
+SSH_FX_NO_SPACE_ON_FILESYSTEM        14
+SSH_FX_QUOTA_EXCEEDED                15
+SSH_FX_UNKNOWN_PRINCIPAL             16
+SSH_FX_LOCK_CONFLICT                 17
+SSH_FX_DIR_NOT_EMPTY                 18
+SSH_FX_NOT_A_DIRECTORY               19
+SSH_FX_INVALID_FILENAME              20
+SSH_FX_LINK_LOOP                     21
+SSH_FX_CANNOT_DELETE                 22
+SSH_FX_INVALID_PARAMETER             23
+SSH_FX_FILE_IS_A_DIRECTORY           24
+SSH_FX_BYTE_RANGE_LOCK_CONFLICT      25
+SSH_FX_BYTE_RANGE_LOCK_REFUSED       26
+SSH_FX_DELETE_PENDING                27
+SSH_FX_FILE_CORRUPT                  28
+SSH_FX_OWNER_INVALID                 29
+SSH_FX_GROUP_INVALID                 30
+SSH_FX_NO_MATCHING_BYTE_RANGE_LOCK   31
+`
+
+func TestFxNames(t *testing.T) {
+	whitespace := regexp.MustCompile(`[[:space:]]+`)
+
+	scan := bufio.NewScanner(strings.NewReader(fxStandardsText))
+
+	for scan.Scan() {
+		line := scan.Text()
+		if i := strings.Index(line, "//"); i >= 0 {
+			line = line[:i]
+		}
+
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+
+		fields := whitespace.Split(line, 2)
+		if len(fields) < 2 {
+			t.Fatalf("unexpected standards text line: %q", line)
+		}
+
+		name, value := fields[0], fields[1]
+		n, err := strconv.Atoi(value)
+		if err != nil {
+			t.Fatal("unexpected error:", err)
+		}
+
+		fx := Status(n)
+
+		if got := fx.String(); got != name {
+			t.Errorf("fx name mismatch for %d: got %q, but want %q", n, got, name)
+		}
+	}
+
+	if err := scan.Err(); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+}
+
+func TestStatusIs(t *testing.T) {
+	status := StatusFailure
+
+	if !errors.Is(status, StatusFailure) {
+		t.Error("errors.Is(StatusFailure, StatusFailure) != true")
+	}
+	if !errors.Is(status, &StatusPacket{StatusCode: StatusFailure}) {
+		t.Error("errors.Is(StatusFailure, StatusPacket{StatusFailure}) != true")
+	}
+	if errors.Is(status, StatusOK) {
+		t.Error("errors.Is(StatusFailure, StatusFailure) == true")
+	}
+	if errors.Is(status, &StatusPacket{StatusCode: StatusOK}) {
+		t.Error("errors.Is(StatusFailure, StatusPacket{StatusFailure}) == true")
+	}
+}

internal/encoding/ssh/filexfer/fxp.go

@@ -0,0 +1,124 @@
+package filexfer
+
+import (
+	"fmt"
+)
+
+// PacketType defines the various SFTP packet types.
+type PacketType uint8
+
+// Request packet types.
+const (
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-3
+	PacketTypeInit = PacketType(iota + 1)
+	PacketTypeVersion
+	PacketTypeOpen
+	PacketTypeClose
+	PacketTypeRead
+	PacketTypeWrite
+	PacketTypeLStat
+	PacketTypeFStat
+	PacketTypeSetstat
+	PacketTypeFSetstat
+	PacketTypeOpenDir
+	PacketTypeReadDir
+	PacketTypeRemove
+	PacketTypeMkdir
+	PacketTypeRmdir
+	PacketTypeRealPath
+	PacketTypeStat
+	PacketTypeRename
+	PacketTypeReadLink
+	PacketTypeSymlink
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-07#section-3.3
+	PacketTypeV6Link
+
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-08#section-3.3
+	PacketTypeV6Block
+	PacketTypeV6Unblock
+)
+
+// Response packet types.
+const (
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-3
+	PacketTypeStatus = PacketType(iota + 101)
+	PacketTypeHandle
+	PacketTypeData
+	PacketTypeName
+	PacketTypeAttrs
+)
+
+// Extended packet types.
+const (
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-3
+	PacketTypeExtended = PacketType(iota + 200)
+	PacketTypeExtendedReply
+)
+
+func (f PacketType) String() string {
+	switch f {
+	case PacketTypeInit:
+		return "SSH_FXP_INIT"
+	case PacketTypeVersion:
+		return "SSH_FXP_VERSION"
+	case PacketTypeOpen:
+		return "SSH_FXP_OPEN"
+	case PacketTypeClose:
+		return "SSH_FXP_CLOSE"
+	case PacketTypeRead:
+		return "SSH_FXP_READ"
+	case PacketTypeWrite:
+		return "SSH_FXP_WRITE"
+	case PacketTypeLStat:
+		return "SSH_FXP_LSTAT"
+	case PacketTypeFStat:
+		return "SSH_FXP_FSTAT"
+	case PacketTypeSetstat:
+		return "SSH_FXP_SETSTAT"
+	case PacketTypeFSetstat:
+		return "SSH_FXP_FSETSTAT"
+	case PacketTypeOpenDir:
+		return "SSH_FXP_OPENDIR"
+	case PacketTypeReadDir:
+		return "SSH_FXP_READDIR"
+	case PacketTypeRemove:
+		return "SSH_FXP_REMOVE"
+	case PacketTypeMkdir:
+		return "SSH_FXP_MKDIR"
+	case PacketTypeRmdir:
+		return "SSH_FXP_RMDIR"
+	case PacketTypeRealPath:
+		return "SSH_FXP_REALPATH"
+	case PacketTypeStat:
+		return "SSH_FXP_STAT"
+	case PacketTypeRename:
+		return "SSH_FXP_RENAME"
+	case PacketTypeReadLink:
+		return "SSH_FXP_READLINK"
+	case PacketTypeSymlink:
+		return "SSH_FXP_SYMLINK"
+	case PacketTypeV6Link:
+		return "SSH_FXP_LINK"
+	case PacketTypeV6Block:
+		return "SSH_FXP_BLOCK"
+	case PacketTypeV6Unblock:
+		return "SSH_FXP_UNBLOCK"
+	case PacketTypeStatus:
+		return "SSH_FXP_STATUS"
+	case PacketTypeHandle:
+		return "SSH_FXP_HANDLE"
+	case PacketTypeData:
+		return "SSH_FXP_DATA"
+	case PacketTypeName:
+		return "SSH_FXP_NAME"
+	case PacketTypeAttrs:
+		return "SSH_FXP_ATTRS"
+	case PacketTypeExtended:
+		return "SSH_FXP_EXTENDED"
+	case PacketTypeExtendedReply:
+		return "SSH_FXP_EXTENDED_REPLY"
+	default:
+		return fmt.Sprintf("SSH_FXP_UNKNOWN(%d)", f)
+	}
+}

internal/encoding/ssh/filexfer/fxp_test.go

@@ -0,0 +1,84 @@
+package filexfer
+
+import (
+	"bufio"
+	"regexp"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+// This string data is copied verbatim from https://tools.ietf.org/html/draft-ietf-secsh-filexfer-13
+var fxpStandardsText = `
+SSH_FXP_INIT                1
+SSH_FXP_VERSION             2
+SSH_FXP_OPEN                3
+SSH_FXP_CLOSE               4
+SSH_FXP_READ                5
+SSH_FXP_WRITE               6
+SSH_FXP_LSTAT               7
+SSH_FXP_FSTAT               8
+SSH_FXP_SETSTAT             9
+SSH_FXP_FSETSTAT           10
+SSH_FXP_OPENDIR            11
+SSH_FXP_READDIR            12
+SSH_FXP_REMOVE             13
+SSH_FXP_MKDIR              14
+SSH_FXP_RMDIR              15
+SSH_FXP_REALPATH           16
+SSH_FXP_STAT               17
+SSH_FXP_RENAME             18
+SSH_FXP_READLINK           19
+SSH_FXP_SYMLINK            20 // Deprecated in filexfer-13 added from filexfer-02
+SSH_FXP_LINK               21
+SSH_FXP_BLOCK              22
+SSH_FXP_UNBLOCK            23
+
+SSH_FXP_STATUS            101
+SSH_FXP_HANDLE            102
+SSH_FXP_DATA              103
+SSH_FXP_NAME              104
+SSH_FXP_ATTRS             105
+
+SSH_FXP_EXTENDED          200
+SSH_FXP_EXTENDED_REPLY    201
+`
+
+func TestFxpNames(t *testing.T) {
+	whitespace := regexp.MustCompile(`[[:space:]]+`)
+
+	scan := bufio.NewScanner(strings.NewReader(fxpStandardsText))
+
+	for scan.Scan() {
+		line := scan.Text()
+		if i := strings.Index(line, "//"); i >= 0 {
+			line = line[:i]
+		}
+
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+
+		fields := whitespace.Split(line, 2)
+		if len(fields) < 2 {
+			t.Fatalf("unexpected standards text line: %q", line)
+		}
+
+		name, value := fields[0], fields[1]
+		n, err := strconv.Atoi(value)
+		if err != nil {
+			t.Fatal("unexpected error:", err)
+		}
+
+		fxp := PacketType(n)
+
+		if got := fxp.String(); got != name {
+			t.Errorf("fxp name mismatch for %d: got %q, but want %q", n, got, name)
+		}
+	}
+
+	if err := scan.Err(); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+}

internal/encoding/ssh/filexfer/handle_packets.go

@@ -0,0 +1,249 @@
+package filexfer
+
+// ClosePacket defines the SSH_FXP_CLOSE packet.
+type ClosePacket struct {
+	Handle string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *ClosePacket) Type() PacketType {
+	return PacketTypeClose
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *ClosePacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Handle) // string(handle)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeClose, reqid)
+	buf.AppendString(p.Handle)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *ClosePacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Handle, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// ReadPacket defines the SSH_FXP_READ packet.
+type ReadPacket struct {
+	Handle string
+	Offset uint64
+	Len    uint32
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *ReadPacket) Type() PacketType {
+	return PacketTypeRead
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *ReadPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		// string(handle) + uint64(offset) + uint32(len)
+		size := 4 + len(p.Handle) + 8 + 4
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeRead, reqid)
+	buf.AppendString(p.Handle)
+	buf.AppendUint64(p.Offset)
+	buf.AppendUint32(p.Len)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *ReadPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Handle, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if p.Offset, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+
+	if p.Len, err = buf.ConsumeUint32(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// WritePacket defines the SSH_FXP_WRITE packet.
+type WritePacket struct {
+	Handle string
+	Offset uint64
+	Data   []byte
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *WritePacket) Type() PacketType {
+	return PacketTypeWrite
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *WritePacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		// string(handle) + uint64(offset) + uint32(len(data)); data content in payload
+		size := 4 + len(p.Handle) + 8 + 4
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeWrite, reqid)
+	buf.AppendString(p.Handle)
+	buf.AppendUint64(p.Offset)
+	buf.AppendUint32(uint32(len(p.Data)))
+
+	return buf.Packet(p.Data)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+//
+// If p.Data is already populated, and of sufficient length to hold the data,
+// then this will copy the data into that byte slice.
+//
+// If p.Data has a length insufficient to hold the data,
+// then this will make a new slice of sufficient length, and copy the data into that.
+//
+// This means this _does not_ alias any of the data buffer that is passed in.
+func (p *WritePacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Handle, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if p.Offset, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+
+	data, err := buf.ConsumeByteSlice()
+	if err != nil {
+		return err
+	}
+
+	if len(p.Data) < len(data) {
+		p.Data = make([]byte, len(data))
+	}
+
+	n := copy(p.Data, data)
+	p.Data = p.Data[:n]
+	return nil
+}
+
+// FStatPacket defines the SSH_FXP_FSTAT packet.
+type FStatPacket struct {
+	Handle string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *FStatPacket) Type() PacketType {
+	return PacketTypeFStat
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *FStatPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Handle) // string(handle)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeFStat, reqid)
+	buf.AppendString(p.Handle)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *FStatPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Handle, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// FSetstatPacket defines the SSH_FXP_FSETSTAT packet.
+type FSetstatPacket struct {
+	Handle string
+	Attrs  Attributes
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *FSetstatPacket) Type() PacketType {
+	return PacketTypeFSetstat
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *FSetstatPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Handle) + p.Attrs.Len() // string(handle) + ATTRS(attrs)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeFSetstat, reqid)
+	buf.AppendString(p.Handle)
+
+	p.Attrs.MarshalInto(buf)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *FSetstatPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Handle, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return p.Attrs.UnmarshalFrom(buf)
+}
+
+// ReadDirPacket defines the SSH_FXP_READDIR packet.
+type ReadDirPacket struct {
+	Handle string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *ReadDirPacket) Type() PacketType {
+	return PacketTypeReadDir
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *ReadDirPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Handle) // string(handle)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeReadDir, reqid)
+	buf.AppendString(p.Handle)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *ReadDirPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Handle, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}

internal/encoding/ssh/filexfer/handle_packets_test.go

@@ -0,0 +1,282 @@
+package filexfer
+
+import (
+	"bytes"
+	"testing"
+)
+
+var _ Packet = &ClosePacket{}
+
+func TestClosePacket(t *testing.T) {
+	const (
+		id     = 42
+		handle = "somehandle"
+	)
+
+	p := &ClosePacket{
+		Handle: "somehandle",
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 19,
+		4,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 10, 's', 'o', 'm', 'e', 'h', 'a', 'n', 'd', 'l', 'e',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = ClosePacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Handle != handle {
+		t.Errorf("UnmarshalPacketBody(): Handle was %q, but expected %q", p.Handle, handle)
+	}
+}
+
+var _ Packet = &ReadPacket{}
+
+func TestReadPacket(t *testing.T) {
+	const (
+		id     = 42
+		handle = "somehandle"
+		offset = 0x123456789ABCDEF0
+		length = 0xFEDCBA98
+	)
+
+	p := &ReadPacket{
+		Handle: "somehandle",
+		Offset: offset,
+		Len:    length,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 31,
+		5,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 10, 's', 'o', 'm', 'e', 'h', 'a', 'n', 'd', 'l', 'e',
+		0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0,
+		0xFE, 0xDC, 0xBA, 0x98,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = ReadPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Handle != handle {
+		t.Errorf("UnmarshalPacketBody(): Handle was %q, but expected %q", p.Handle, handle)
+	}
+
+	if p.Offset != offset {
+		t.Errorf("UnmarshalPacketBody(): Offset was %x, but expected %x", p.Offset, offset)
+	}
+
+	if p.Len != length {
+		t.Errorf("UnmarshalPacketBody(): Len was %x, but expected %x", p.Len, length)
+	}
+}
+
+var _ Packet = &WritePacket{}
+
+func TestWritePacket(t *testing.T) {
+	const (
+		id     = 42
+		handle = "somehandle"
+		offset = 0x123456789ABCDEF0
+	)
+
+	var payload = []byte(`foobar`)
+
+	p := &WritePacket{
+		Handle: "somehandle",
+		Offset: offset,
+		Data:   payload,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 37,
+		6,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 10, 's', 'o', 'm', 'e', 'h', 'a', 'n', 'd', 'l', 'e',
+		0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0,
+		0x00, 0x00, 0x00, 0x06, 'f', 'o', 'o', 'b', 'a', 'r',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = WritePacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Handle != handle {
+		t.Errorf("UnmarshalPacketBody(): Handle was %q, but expected %q", p.Handle, handle)
+	}
+
+	if p.Offset != offset {
+		t.Errorf("UnmarshalPacketBody(): Offset was %x, but expected %x", p.Offset, offset)
+	}
+
+	if !bytes.Equal(p.Data, payload) {
+		t.Errorf("UnmarshalPacketBody(): Data was %X, but expected %X", p.Data, payload)
+	}
+}
+
+var _ Packet = &FStatPacket{}
+
+func TestFStatPacket(t *testing.T) {
+	const (
+		id     = 42
+		handle = "somehandle"
+	)
+
+	p := &FStatPacket{
+		Handle: "somehandle",
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 19,
+		8,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 10, 's', 'o', 'm', 'e', 'h', 'a', 'n', 'd', 'l', 'e',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = FStatPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Handle != handle {
+		t.Errorf("UnmarshalPacketBody(): Handle was %q, but expected %q", p.Handle, handle)
+	}
+}
+
+var _ Packet = &FSetstatPacket{}
+
+func TestFSetstatPacket(t *testing.T) {
+	const (
+		id     = 42
+		handle = "somehandle"
+		perms  = 0x87654321
+	)
+
+	p := &FSetstatPacket{
+		Handle: "somehandle",
+		Attrs: Attributes{
+			Flags:       AttrPermissions,
+			Permissions: perms,
+		},
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 27,
+		10,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 10, 's', 'o', 'm', 'e', 'h', 'a', 'n', 'd', 'l', 'e',
+		0x00, 0x00, 0x00, 0x04,
+		0x87, 0x65, 0x43, 0x21,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = FSetstatPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Handle != handle {
+		t.Errorf("UnmarshalPacketBody(): Handle was %q, but expected %q", p.Handle, handle)
+	}
+}
+
+var _ Packet = &ReadDirPacket{}
+
+func TestReadDirPacket(t *testing.T) {
+	const (
+		id     = 42
+		handle = "somehandle"
+	)
+
+	p := &ReadDirPacket{
+		Handle: "somehandle",
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 19,
+		12,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 10, 's', 'o', 'm', 'e', 'h', 'a', 'n', 'd', 'l', 'e',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = ReadDirPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Handle != handle {
+		t.Errorf("UnmarshalPacketBody(): Handle was %q, but expected %q", p.Handle, handle)
+	}
+}

internal/encoding/ssh/filexfer/init_packets.go

@@ -0,0 +1,99 @@
+package filexfer
+
+// InitPacket defines the SSH_FXP_INIT packet.
+type InitPacket struct {
+	Version    uint32
+	Extensions []*ExtensionPair
+}
+
+// MarshalBinary returns p as the binary encoding of p.
+func (p *InitPacket) MarshalBinary() ([]byte, error) {
+	size := 1 + 4 // byte(type) + uint32(version)
+
+	for _, ext := range p.Extensions {
+		size += ext.Len()
+	}
+
+	b := NewBuffer(make([]byte, 4, 4+size))
+	b.AppendUint8(uint8(PacketTypeInit))
+	b.AppendUint32(p.Version)
+
+	for _, ext := range p.Extensions {
+		ext.MarshalInto(b)
+	}
+
+	b.PutLength(size)
+
+	return b.Bytes(), nil
+}
+
+// UnmarshalBinary unmarshals a full raw packet out of the given data.
+// It is assumed that the uint32(length) has already been consumed to receive the data.
+// It is also assumed that the uint8(type) has already been consumed to which packet to unmarshal into.
+func (p *InitPacket) UnmarshalBinary(data []byte) (err error) {
+	buf := NewBuffer(data)
+
+	if p.Version, err = buf.ConsumeUint32(); err != nil {
+		return err
+	}
+
+	for buf.Len() > 0 {
+		var ext ExtensionPair
+		if err := ext.UnmarshalFrom(buf); err != nil {
+			return err
+		}
+
+		p.Extensions = append(p.Extensions, &ext)
+	}
+
+	return nil
+}
+
+// VersionPacket defines the SSH_FXP_VERSION packet.
+type VersionPacket struct {
+	Version    uint32
+	Extensions []*ExtensionPair
+}
+
+// MarshalBinary returns p as the binary encoding of p.
+func (p *VersionPacket) MarshalBinary() ([]byte, error) {
+	size := 1 + 4 // byte(type) + uint32(version)
+
+	for _, ext := range p.Extensions {
+		size += ext.Len()
+	}
+
+	b := NewBuffer(make([]byte, 4, 4+size))
+	b.AppendUint8(uint8(PacketTypeVersion))
+	b.AppendUint32(p.Version)
+
+	for _, ext := range p.Extensions {
+		ext.MarshalInto(b)
+	}
+
+	b.PutLength(size)
+
+	return b.Bytes(), nil
+}
+
+// UnmarshalBinary unmarshals a full raw packet out of the given data.
+// It is assumed that the uint32(length) has already been consumed to receive the data.
+// It is also assumed that the uint8(type) has already been consumed to which packet to unmarshal into.
+func (p *VersionPacket) UnmarshalBinary(data []byte) (err error) {
+	buf := NewBuffer(data)
+
+	if p.Version, err = buf.ConsumeUint32(); err != nil {
+		return err
+	}
+
+	for buf.Len() > 0 {
+		var ext ExtensionPair
+		if err := ext.UnmarshalFrom(buf); err != nil {
+			return err
+		}
+
+		p.Extensions = append(p.Extensions, &ext)
+	}
+
+	return nil
+}

internal/encoding/ssh/filexfer/init_packets_test.go

@@ -0,0 +1,114 @@
+package filexfer
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestInitPacket(t *testing.T) {
+	var version uint8 = 3
+
+	p := &InitPacket{
+		Version: uint32(version),
+		Extensions: []*ExtensionPair{
+			{
+				Name: "foo",
+				Data: "1",
+			},
+		},
+	}
+
+	buf, err := p.MarshalBinary()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 17,
+		1,
+		0x00, 0x00, 0x00, version,
+		0x00, 0x00, 0x00, 3, 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 1, '1',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalBinary() = %X, but wanted %X", buf, want)
+	}
+
+	*p = InitPacket{}
+
+	// UnmarshalBinary assumes the uint32(length) + uint8(type) have already been consumed.
+	if err := p.UnmarshalBinary(buf[5:]); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Version != uint32(version) {
+		t.Errorf("UnmarshalBinary(): Version was %d, but expected %d", p.Version, version)
+	}
+
+	if len(p.Extensions) != 1 {
+		t.Fatalf("UnmarshalBinary(): len(p.Extensions) was %d, but expected %d", len(p.Extensions), 1)
+	}
+
+	if got, want := p.Extensions[0].Name, "foo"; got != want {
+		t.Errorf("UnmarshalBinary(): p.Extensions[0].Name was %q, but expected %q", got, want)
+	}
+
+	if got, want := p.Extensions[0].Data, "1"; got != want {
+		t.Errorf("UnmarshalBinary(): p.Extensions[0].Data was %q, but expected %q", got, want)
+	}
+}
+
+func TestVersionPacket(t *testing.T) {
+	var version uint8 = 3
+
+	p := &VersionPacket{
+		Version: uint32(version),
+		Extensions: []*ExtensionPair{
+			{
+				Name: "foo",
+				Data: "1",
+			},
+		},
+	}
+
+	buf, err := p.MarshalBinary()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 17,
+		2,
+		0x00, 0x00, 0x00, version,
+		0x00, 0x00, 0x00, 3, 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 1, '1',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalBinary() = %X, but wanted %X", buf, want)
+	}
+
+	*p = VersionPacket{}
+
+	// UnmarshalBinary assumes the uint32(length) + uint8(type) have already been consumed.
+	if err := p.UnmarshalBinary(buf[5:]); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Version != uint32(version) {
+		t.Errorf("UnmarshalBinary(): Version was %d, but expected %d", p.Version, version)
+	}
+
+	if len(p.Extensions) != 1 {
+		t.Fatalf("UnmarshalBinary(): len(p.Extensions) was %d, but expected %d", len(p.Extensions), 1)
+	}
+
+	if got, want := p.Extensions[0].Name, "foo"; got != want {
+		t.Errorf("UnmarshalBinary(): p.Extensions[0].Name was %q, but expected %q", got, want)
+	}
+
+	if got, want := p.Extensions[0].Data, "1"; got != want {
+		t.Errorf("UnmarshalBinary(): p.Extensions[0].Data was %q, but expected %q", got, want)
+	}
+}

internal/encoding/ssh/filexfer/open_packets.go

@@ -0,0 +1,89 @@
+package filexfer
+
+// SSH_FXF_* flags.
+const (
+	FlagRead      = 1 << iota // SSH_FXF_READ
+	FlagWrite                 // SSH_FXF_WRITE
+	FlagAppend                // SSH_FXF_APPEND
+	FlagCreate                // SSH_FXF_CREAT
+	FlagTruncate              // SSH_FXF_TRUNC
+	FlagExclusive             // SSH_FXF_EXCL
+)
+
+// OpenPacket defines the SSH_FXP_OPEN packet.
+type OpenPacket struct {
+	Filename string
+	PFlags   uint32
+	Attrs    Attributes
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *OpenPacket) Type() PacketType {
+	return PacketTypeOpen
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *OpenPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		// string(filename) + uint32(pflags) + ATTRS(attrs)
+		size := 4 + len(p.Filename) + 4 + p.Attrs.Len()
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeOpen, reqid)
+	buf.AppendString(p.Filename)
+	buf.AppendUint32(p.PFlags)
+
+	p.Attrs.MarshalInto(buf)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *OpenPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Filename, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if p.PFlags, err = buf.ConsumeUint32(); err != nil {
+		return err
+	}
+
+	return p.Attrs.UnmarshalFrom(buf)
+}
+
+// OpenDirPacket defines the SSH_FXP_OPENDIR packet.
+type OpenDirPacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *OpenDirPacket) Type() PacketType {
+	return PacketTypeOpenDir
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *OpenDirPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) // string(path)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeOpenDir, reqid)
+	buf.AppendString(p.Path)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *OpenDirPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}

internal/encoding/ssh/filexfer/open_packets_test.go

@@ -0,0 +1,107 @@
+package filexfer
+
+import (
+	"bytes"
+	"testing"
+)
+
+var _ Packet = &OpenPacket{}
+
+func TestOpenPacket(t *testing.T) {
+	const (
+		id       = 42
+		filename = "/foo"
+		perms    = 0x87654321
+	)
+
+	p := &OpenPacket{
+		Filename: "/foo",
+		PFlags:   FlagRead,
+		Attrs: Attributes{
+			Flags:       AttrPermissions,
+			Permissions: perms,
+		},
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 25,
+		3,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 1,
+		0x00, 0x00, 0x00, 0x04,
+		0x87, 0x65, 0x43, 0x21,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = OpenPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Filename != filename {
+		t.Errorf("UnmarshalPacketBody(): Filename was %q, but expected %q", p.Filename, filename)
+	}
+
+	if p.PFlags != FlagRead {
+		t.Errorf("UnmarshalPacketBody(): PFlags was %#x, but expected %#x", p.PFlags, FlagRead)
+	}
+
+	if p.Attrs.Flags != AttrPermissions {
+		t.Errorf("UnmarshalPacketBody(): Attrs.Flags was %#x, but expected %#x", p.Attrs.Flags, AttrPermissions)
+	}
+
+	if p.Attrs.Permissions != perms {
+		t.Errorf("UnmarshalPacketBody(): Attrs.Permissions was %#v, but expected %#v", p.Attrs.Permissions, perms)
+	}
+}
+
+var _ Packet = &OpenDirPacket{}
+
+func TestOpenDirPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	p := &OpenDirPacket{
+		Path: path,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 13,
+		11,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = OpenDirPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+}

internal/encoding/ssh/filexfer/openssh/fsync.go

@@ -0,0 +1,73 @@
+package openssh
+
+import (
+	sshfx "github.com/pkg/sftp/internal/encoding/ssh/filexfer"
+)
+
+const extensionFSync = "fsync@openssh.com"
+
+// RegisterExtensionFSync registers the "fsync@openssh.com" extended packet with the encoding/ssh/filexfer package.
+func RegisterExtensionFSync() {
+	sshfx.RegisterExtendedPacketType(extensionFSync, func() sshfx.ExtendedData {
+		return new(FSyncExtendedPacket)
+	})
+}
+
+// ExtensionFSync returns an ExtensionPair suitable to append into an sshfx.InitPacket or sshfx.VersionPacket.
+func ExtensionFSync() *sshfx.ExtensionPair {
+	return &sshfx.ExtensionPair{
+		Name: extensionFSync,
+		Data: "1",
+	}
+}
+
+// FSyncExtendedPacket defines the fsync@openssh.com extend packet.
+type FSyncExtendedPacket struct {
+	Handle string
+}
+
+// Type returns the SSH_FXP_EXTENDED packet type.
+func (ep *FSyncExtendedPacket) Type() sshfx.PacketType {
+	return sshfx.PacketTypeExtended
+}
+
+// MarshalPacket returns ep as a two-part binary encoding of the full extended packet.
+func (ep *FSyncExtendedPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	p := &sshfx.ExtendedPacket{
+		ExtendedRequest: extensionFSync,
+
+		Data: ep,
+	}
+	return p.MarshalPacket(reqid, b)
+}
+
+// MarshalInto encodes ep into the binary encoding of the fsync@openssh.com extended packet-specific data.
+func (ep *FSyncExtendedPacket) MarshalInto(buf *sshfx.Buffer) {
+	buf.AppendString(ep.Handle)
+}
+
+// MarshalBinary encodes ep into the binary encoding of the fsync@openssh.com extended packet-specific data.
+//
+// NOTE: This _only_ encodes the packet-specific data, it does not encode the full extended packet.
+func (ep *FSyncExtendedPacket) MarshalBinary() ([]byte, error) {
+	// string(handle)
+	size := 4 + len(ep.Handle)
+
+	buf := sshfx.NewBuffer(make([]byte, 0, size))
+	ep.MarshalInto(buf)
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom decodes the fsync@openssh.com extended packet-specific data from buf.
+func (ep *FSyncExtendedPacket) UnmarshalFrom(buf *sshfx.Buffer) (err error) {
+	if ep.Handle, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the fsync@openssh.com extended packet-specific data into ep.
+func (ep *FSyncExtendedPacket) UnmarshalBinary(data []byte) (err error) {
+	return ep.UnmarshalFrom(sshfx.NewBuffer(data))
+}

internal/encoding/ssh/filexfer/openssh/fsync_test.go

@@ -0,0 +1,62 @@
+package openssh
+
+import (
+	"bytes"
+	"testing"
+
+	sshfx "github.com/pkg/sftp/internal/encoding/ssh/filexfer"
+)
+
+var _ sshfx.PacketMarshaller = &FSyncExtendedPacket{}
+
+func init() {
+	RegisterExtensionFSync()
+}
+
+func TestFSyncExtendedPacket(t *testing.T) {
+	const (
+		id     = 42
+		handle = "somehandle"
+	)
+
+	ep := &FSyncExtendedPacket{
+		Handle: handle,
+	}
+
+	data, err := sshfx.ComposePacket(ep.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 40,
+		200,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 17, 'f', 's', 'y', 'n', 'c', '@', 'o', 'p', 'e', 'n', 's', 's', 'h', '.', 'c', 'o', 'm',
+		0x00, 0x00, 0x00, 10, 's', 'o', 'm', 'e', 'h', 'a', 'n', 'd', 'l', 'e',
+	}
+
+	if !bytes.Equal(data, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", data, want)
+	}
+
+	var p sshfx.ExtendedPacket
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(sshfx.NewBuffer(data[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.ExtendedRequest != extensionFSync {
+		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extensionFSync)
+	}
+
+	ep, ok := p.Data.(*FSyncExtendedPacket)
+	if !ok {
+		t.Fatalf("UnmarshaledPacketBody(): Data was type %T, but expected *FSyncExtendedPacket", p.Data)
+	}
+
+	if ep.Handle != handle {
+		t.Errorf("UnmarshalPacketBody(): Handle was %q, but expected %q", ep.Handle, handle)
+	}
+}

internal/encoding/ssh/filexfer/openssh/hardlink.go

@@ -0,0 +1,79 @@
+package openssh
+
+import (
+	sshfx "github.com/pkg/sftp/internal/encoding/ssh/filexfer"
+)
+
+const extensionHardlink = "hardlink@openssh.com"
+
+// RegisterExtensionHardlink registers the "hardlink@openssh.com" extended packet with the encoding/ssh/filexfer package.
+func RegisterExtensionHardlink() {
+	sshfx.RegisterExtendedPacketType(extensionHardlink, func() sshfx.ExtendedData {
+		return new(HardlinkExtendedPacket)
+	})
+}
+
+// ExtensionHardlink returns an ExtensionPair suitable to append into an sshfx.InitPacket or sshfx.VersionPacket.
+func ExtensionHardlink() *sshfx.ExtensionPair {
+	return &sshfx.ExtensionPair{
+		Name: extensionHardlink,
+		Data: "1",
+	}
+}
+
+// HardlinkExtendedPacket defines the hardlink@openssh.com extend packet.
+type HardlinkExtendedPacket struct {
+	OldPath string
+	NewPath string
+}
+
+// Type returns the SSH_FXP_EXTENDED packet type.
+func (ep *HardlinkExtendedPacket) Type() sshfx.PacketType {
+	return sshfx.PacketTypeExtended
+}
+
+// MarshalPacket returns ep as a two-part binary encoding of the full extended packet.
+func (ep *HardlinkExtendedPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	p := &sshfx.ExtendedPacket{
+		ExtendedRequest: extensionHardlink,
+
+		Data: ep,
+	}
+	return p.MarshalPacket(reqid, b)
+}
+
+// MarshalInto encodes ep into the binary encoding of the hardlink@openssh.com extended packet-specific data.
+func (ep *HardlinkExtendedPacket) MarshalInto(buf *sshfx.Buffer) {
+	buf.AppendString(ep.OldPath)
+	buf.AppendString(ep.NewPath)
+}
+
+// MarshalBinary encodes ep into the binary encoding of the hardlink@openssh.com extended packet-specific data.
+//
+// NOTE: This _only_ encodes the packet-specific data, it does not encode the full extended packet.
+func (ep *HardlinkExtendedPacket) MarshalBinary() ([]byte, error) {
+	// string(oldpath) + string(newpath)
+	size := 4 + len(ep.OldPath) + 4 + len(ep.NewPath)
+
+	buf := sshfx.NewBuffer(make([]byte, 0, size))
+	ep.MarshalInto(buf)
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom decodes the hardlink@openssh.com extended packet-specific data from buf.
+func (ep *HardlinkExtendedPacket) UnmarshalFrom(buf *sshfx.Buffer) (err error) {
+	if ep.OldPath, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if ep.NewPath, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the hardlink@openssh.com extended packet-specific data into ep.
+func (ep *HardlinkExtendedPacket) UnmarshalBinary(data []byte) (err error) {
+	return ep.UnmarshalFrom(sshfx.NewBuffer(data))
+}

internal/encoding/ssh/filexfer/openssh/hardlink_test.go

@@ -0,0 +1,69 @@
+package openssh
+
+import (
+	"bytes"
+	"testing"
+
+	sshfx "github.com/pkg/sftp/internal/encoding/ssh/filexfer"
+)
+
+var _ sshfx.PacketMarshaller = &HardlinkExtendedPacket{}
+
+func init() {
+	RegisterExtensionHardlink()
+}
+
+func TestHardlinkExtendedPacket(t *testing.T) {
+	const (
+		id      = 42
+		oldpath = "/foo"
+		newpath = "/bar"
+	)
+
+	ep := &HardlinkExtendedPacket{
+		OldPath: oldpath,
+		NewPath: newpath,
+	}
+
+	data, err := sshfx.ComposePacket(ep.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 45,
+		200,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 20, 'h', 'a', 'r', 'd', 'l', 'i', 'n', 'k', '@', 'o', 'p', 'e', 'n', 's', 's', 'h', '.', 'c', 'o', 'm',
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 4, '/', 'b', 'a', 'r',
+	}
+
+	if !bytes.Equal(data, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", data, want)
+	}
+
+	var p sshfx.ExtendedPacket
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(sshfx.NewBuffer(data[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.ExtendedRequest != extensionHardlink {
+		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extensionHardlink)
+	}
+
+	ep, ok := p.Data.(*HardlinkExtendedPacket)
+	if !ok {
+		t.Fatalf("UnmarshaledPacketBody(): Data was type %T, but expected *HardlinkExtendedPacket", p.Data)
+	}
+
+	if ep.OldPath != oldpath {
+		t.Errorf("UnmarshalPacketBody(): OldPath was %q, but expected %q", ep.OldPath, oldpath)
+	}
+
+	if ep.NewPath != newpath {
+		t.Errorf("UnmarshalPacketBody(): NewPath was %q, but expected %q", ep.NewPath, newpath)
+	}
+}

internal/encoding/ssh/filexfer/openssh/openssh.go

@@ -0,0 +1,2 @@
+// Package openssh implements the openssh secsh-filexfer extensions as described in https://github.com/openssh/openssh-portable/blob/master/PROTOCOL
+package openssh

internal/encoding/ssh/filexfer/openssh/posix-rename.go

@@ -0,0 +1,79 @@
+package openssh
+
+import (
+	sshfx "github.com/pkg/sftp/internal/encoding/ssh/filexfer"
+)
+
+const extensionPosixRename = "posix-rename@openssh.com"
+
+// RegisterExtensionPosixRename registers the "posix-rename@openssh.com" extended packet with the encoding/ssh/filexfer package.
+func RegisterExtensionPosixRename() {
+	sshfx.RegisterExtendedPacketType(extensionPosixRename, func() sshfx.ExtendedData {
+		return new(PosixRenameExtendedPacket)
+	})
+}
+
+// ExtensionPosixRename returns an ExtensionPair suitable to append into an sshfx.InitPacket or sshfx.VersionPacket.
+func ExtensionPosixRename() *sshfx.ExtensionPair {
+	return &sshfx.ExtensionPair{
+		Name: extensionPosixRename,
+		Data: "1",
+	}
+}
+
+// PosixRenameExtendedPacket defines the posix-rename@openssh.com extend packet.
+type PosixRenameExtendedPacket struct {
+	OldPath string
+	NewPath string
+}
+
+// Type returns the SSH_FXP_EXTENDED packet type.
+func (ep *PosixRenameExtendedPacket) Type() sshfx.PacketType {
+	return sshfx.PacketTypeExtended
+}
+
+// MarshalPacket returns ep as a two-part binary encoding of the full extended packet.
+func (ep *PosixRenameExtendedPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	p := &sshfx.ExtendedPacket{
+		ExtendedRequest: extensionPosixRename,
+
+		Data: ep,
+	}
+	return p.MarshalPacket(reqid, b)
+}
+
+// MarshalInto encodes ep into the binary encoding of the hardlink@openssh.com extended packet-specific data.
+func (ep *PosixRenameExtendedPacket) MarshalInto(buf *sshfx.Buffer) {
+	buf.AppendString(ep.OldPath)
+	buf.AppendString(ep.NewPath)
+}
+
+// MarshalBinary encodes ep into the binary encoding of the hardlink@openssh.com extended packet-specific data.
+//
+// NOTE: This _only_ encodes the packet-specific data, it does not encode the full extended packet.
+func (ep *PosixRenameExtendedPacket) MarshalBinary() ([]byte, error) {
+	// string(oldpath) + string(newpath)
+	size := 4 + len(ep.OldPath) + 4 + len(ep.NewPath)
+
+	buf := sshfx.NewBuffer(make([]byte, 0, size))
+	ep.MarshalInto(buf)
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom decodes the hardlink@openssh.com extended packet-specific data from buf.
+func (ep *PosixRenameExtendedPacket) UnmarshalFrom(buf *sshfx.Buffer) (err error) {
+	if ep.OldPath, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if ep.NewPath, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the hardlink@openssh.com extended packet-specific data into ep.
+func (ep *PosixRenameExtendedPacket) UnmarshalBinary(data []byte) (err error) {
+	return ep.UnmarshalFrom(sshfx.NewBuffer(data))
+}

internal/encoding/ssh/filexfer/openssh/posix-rename_test.go

@@ -0,0 +1,69 @@
+package openssh
+
+import (
+	"bytes"
+	"testing"
+
+	sshfx "github.com/pkg/sftp/internal/encoding/ssh/filexfer"
+)
+
+var _ sshfx.PacketMarshaller = &PosixRenameExtendedPacket{}
+
+func init() {
+	RegisterExtensionPosixRename()
+}
+
+func TestPosixRenameExtendedPacket(t *testing.T) {
+	const (
+		id      = 42
+		oldpath = "/foo"
+		newpath = "/bar"
+	)
+
+	ep := &PosixRenameExtendedPacket{
+		OldPath: oldpath,
+		NewPath: newpath,
+	}
+
+	data, err := sshfx.ComposePacket(ep.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 49,
+		200,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 24, 'p', 'o', 's', 'i', 'x', '-', 'r', 'e', 'n', 'a', 'm', 'e', '@', 'o', 'p', 'e', 'n', 's', 's', 'h', '.', 'c', 'o', 'm',
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 4, '/', 'b', 'a', 'r',
+	}
+
+	if !bytes.Equal(data, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", data, want)
+	}
+
+	var p sshfx.ExtendedPacket
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(sshfx.NewBuffer(data[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.ExtendedRequest != extensionPosixRename {
+		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extensionPosixRename)
+	}
+
+	ep, ok := p.Data.(*PosixRenameExtendedPacket)
+	if !ok {
+		t.Fatalf("UnmarshaledPacketBody(): Data was type %T, but expected *PosixRenameExtendedPacket", p.Data)
+	}
+
+	if ep.OldPath != oldpath {
+		t.Errorf("UnmarshalPacketBody(): OldPath was %q, but expected %q", ep.OldPath, oldpath)
+	}
+
+	if ep.NewPath != newpath {
+		t.Errorf("UnmarshalPacketBody(): NewPath was %q, but expected %q", ep.NewPath, newpath)
+	}
+}

internal/encoding/ssh/filexfer/openssh/statvfs.go

@@ -0,0 +1,256 @@
+package openssh
+
+import (
+	sshfx "github.com/pkg/sftp/internal/encoding/ssh/filexfer"
+)
+
+const extensionStatVFS = "statvfs@openssh.com"
+
+// RegisterExtensionStatVFS registers the "statvfs@openssh.com" extended packet with the encoding/ssh/filexfer package.
+func RegisterExtensionStatVFS() {
+	sshfx.RegisterExtendedPacketType(extensionStatVFS, func() sshfx.ExtendedData {
+		return new(StatVFSExtendedPacket)
+	})
+}
+
+// ExtensionStatVFS returns an ExtensionPair suitable to append into an sshfx.InitPacket or sshfx.VersionPacket.
+func ExtensionStatVFS() *sshfx.ExtensionPair {
+	return &sshfx.ExtensionPair{
+		Name: extensionStatVFS,
+		Data: "2",
+	}
+}
+
+// StatVFSExtendedPacket defines the statvfs@openssh.com extend packet.
+type StatVFSExtendedPacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_EXTENDED packet type.
+func (ep *StatVFSExtendedPacket) Type() sshfx.PacketType {
+	return sshfx.PacketTypeExtended
+}
+
+// MarshalPacket returns ep as a two-part binary encoding of the full extended packet.
+func (ep *StatVFSExtendedPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	p := &sshfx.ExtendedPacket{
+		ExtendedRequest: extensionStatVFS,
+
+		Data: ep,
+	}
+	return p.MarshalPacket(reqid, b)
+}
+
+// MarshalInto encodes ep into the binary encoding of the statvfs@openssh.com extended packet-specific data.
+func (ep *StatVFSExtendedPacket) MarshalInto(buf *sshfx.Buffer) {
+	buf.AppendString(ep.Path)
+}
+
+// MarshalBinary encodes ep into the binary encoding of the statvfs@openssh.com extended packet-specific data.
+//
+// NOTE: This _only_ encodes the packet-specific data, it does not encode the full extended packet.
+func (ep *StatVFSExtendedPacket) MarshalBinary() ([]byte, error) {
+	size := 4 + len(ep.Path) // string(path)
+
+	buf := sshfx.NewBuffer(make([]byte, 0, size))
+
+	ep.MarshalInto(buf)
+
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom decodes the statvfs@openssh.com extended packet-specific data into ep.
+func (ep *StatVFSExtendedPacket) UnmarshalFrom(buf *sshfx.Buffer) (err error) {
+	if ep.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the statvfs@openssh.com extended packet-specific data into ep.
+func (ep *StatVFSExtendedPacket) UnmarshalBinary(data []byte) (err error) {
+	return ep.UnmarshalFrom(sshfx.NewBuffer(data))
+}
+
+const extensionFStatVFS = "fstatvfs@openssh.com"
+
+// RegisterExtensionFStatVFS registers the "fstatvfs@openssh.com" extended packet with the encoding/ssh/filexfer package.
+func RegisterExtensionFStatVFS() {
+	sshfx.RegisterExtendedPacketType(extensionFStatVFS, func() sshfx.ExtendedData {
+		return new(FStatVFSExtendedPacket)
+	})
+}
+
+// ExtensionFStatVFS returns an ExtensionPair suitable to append into an sshfx.InitPacket or sshfx.VersionPacket.
+func ExtensionFStatVFS() *sshfx.ExtensionPair {
+	return &sshfx.ExtensionPair{
+		Name: extensionFStatVFS,
+		Data: "2",
+	}
+}
+
+// FStatVFSExtendedPacket defines the fstatvfs@openssh.com extend packet.
+type FStatVFSExtendedPacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_EXTENDED packet type.
+func (ep *FStatVFSExtendedPacket) Type() sshfx.PacketType {
+	return sshfx.PacketTypeExtended
+}
+
+// MarshalPacket returns ep as a two-part binary encoding of the full extended packet.
+func (ep *FStatVFSExtendedPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	p := &sshfx.ExtendedPacket{
+		ExtendedRequest: extensionFStatVFS,
+
+		Data: ep,
+	}
+	return p.MarshalPacket(reqid, b)
+}
+
+// MarshalInto encodes ep into the binary encoding of the statvfs@openssh.com extended packet-specific data.
+func (ep *FStatVFSExtendedPacket) MarshalInto(buf *sshfx.Buffer) {
+	buf.AppendString(ep.Path)
+}
+
+// MarshalBinary encodes ep into the binary encoding of the statvfs@openssh.com extended packet-specific data.
+//
+// NOTE: This _only_ encodes the packet-specific data, it does not encode the full extended packet.
+func (ep *FStatVFSExtendedPacket) MarshalBinary() ([]byte, error) {
+	size := 4 + len(ep.Path) // string(path)
+
+	buf := sshfx.NewBuffer(make([]byte, 0, size))
+
+	ep.MarshalInto(buf)
+
+	return buf.Bytes(), nil
+}
+
+// UnmarshalFrom decodes the statvfs@openssh.com extended packet-specific data into ep.
+func (ep *FStatVFSExtendedPacket) UnmarshalFrom(buf *sshfx.Buffer) (err error) {
+	if ep.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the statvfs@openssh.com extended packet-specific data into ep.
+func (ep *FStatVFSExtendedPacket) UnmarshalBinary(data []byte) (err error) {
+	return ep.UnmarshalFrom(sshfx.NewBuffer(data))
+}
+
+// The values for the MountFlags field.
+// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL
+const (
+	MountFlagsReadOnly = 0x1 // SSH_FXE_STATVFS_ST_RDONLY
+	MountFlagsNoSUID   = 0x2 // SSH_FXE_STATVFS_ST_NOSUID
+)
+
+// StatVFSExtendedReplyPacket defines the extended reply packet for statvfs@openssh.com and fstatvfs@openssh.com requests.
+type StatVFSExtendedReplyPacket struct {
+	BlockSize     uint64 /* f_bsize:   file system block size */
+	FragmentSize  uint64 /* f_frsize:  fundamental fs block size / fagment size */
+	Blocks        uint64 /* f_blocks:  number of blocks (unit f_frsize) */
+	BlocksFree    uint64 /* f_bfree:   free blocks in filesystem */
+	BlocksAvail   uint64 /* f_bavail:  free blocks for non-root */
+	Files         uint64 /* f_files:   total file inodes */
+	FilesFree     uint64 /* f_ffree:   free file inodes */
+	FilesAvail    uint64 /* f_favail:  free file inodes for to non-root */
+	FilesystemID  uint64 /* f_fsid:    file system id */
+	MountFlags    uint64 /* f_flag:    bit mask of mount flag values */
+	MaxNameLength uint64 /* f_namemax: maximum filename length */
+}
+
+// Type returns the SSH_FXP_EXTENDED_REPLY packet type.
+func (ep *StatVFSExtendedReplyPacket) Type() sshfx.PacketType {
+	return sshfx.PacketTypeExtendedReply
+}
+
+// MarshalPacket returns ep as a two-part binary encoding of the full extended reply packet.
+func (ep *StatVFSExtendedReplyPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	p := &sshfx.ExtendedReplyPacket{
+		Data: ep,
+	}
+	return p.MarshalPacket(reqid, b)
+}
+
+// UnmarshalPacketBody returns ep as a two-part binary encoding of the full extended reply packet.
+func (ep *StatVFSExtendedReplyPacket) UnmarshalPacketBody(buf *sshfx.Buffer) (err error) {
+	p := &sshfx.ExtendedReplyPacket{
+		Data: ep,
+	}
+	return p.UnmarshalPacketBody(buf)
+}
+
+// MarshalInto encodes ep into the binary encoding of the (f)statvfs@openssh.com extended reply packet-specific data.
+func (ep *StatVFSExtendedReplyPacket) MarshalInto(buf *sshfx.Buffer) {
+	buf.AppendUint64(ep.BlockSize)
+	buf.AppendUint64(ep.FragmentSize)
+	buf.AppendUint64(ep.Blocks)
+	buf.AppendUint64(ep.BlocksFree)
+	buf.AppendUint64(ep.BlocksAvail)
+	buf.AppendUint64(ep.Files)
+	buf.AppendUint64(ep.FilesFree)
+	buf.AppendUint64(ep.FilesAvail)
+	buf.AppendUint64(ep.FilesystemID)
+	buf.AppendUint64(ep.MountFlags)
+	buf.AppendUint64(ep.MaxNameLength)
+}
+
+// MarshalBinary encodes ep into the binary encoding of the (f)statvfs@openssh.com extended reply packet-specific data.
+//
+// NOTE: This _only_ encodes the packet-specific data, it does not encode the full extended reply packet.
+func (ep *StatVFSExtendedReplyPacket) MarshalBinary() ([]byte, error) {
+	size := 11 * 8 // 11 × uint64(various)
+
+	b := sshfx.NewBuffer(make([]byte, 0, size))
+	ep.MarshalInto(b)
+	return b.Bytes(), nil
+}
+
+// UnmarshalFrom decodes the fstatvfs@openssh.com extended reply packet-specific data into ep.
+func (ep *StatVFSExtendedReplyPacket) UnmarshalFrom(buf *sshfx.Buffer) (err error) {
+	if ep.BlockSize, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.FragmentSize, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.Blocks, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.BlocksFree, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.BlocksAvail, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.Files, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.FilesFree, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.FilesAvail, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.FilesystemID, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.MountFlags, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+	if ep.MaxNameLength, err = buf.ConsumeUint64(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// UnmarshalBinary decodes the fstatvfs@openssh.com extended reply packet-specific data into ep.
+func (ep *StatVFSExtendedReplyPacket) UnmarshalBinary(data []byte) (err error) {
+	return ep.UnmarshalFrom(sshfx.NewBuffer(data))
+}

internal/encoding/ssh/filexfer/openssh/statvfs_test.go

@@ -0,0 +1,239 @@
+package openssh
+
+import (
+	"bytes"
+	"testing"
+
+	sshfx "github.com/pkg/sftp/internal/encoding/ssh/filexfer"
+)
+
+var _ sshfx.PacketMarshaller = &StatVFSExtendedPacket{}
+
+func init() {
+	RegisterExtensionStatVFS()
+}
+
+func TestStatVFSExtendedPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	ep := &StatVFSExtendedPacket{
+		Path: path,
+	}
+
+	data, err := sshfx.ComposePacket(ep.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 36,
+		200,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 19, 's', 't', 'a', 't', 'v', 'f', 's', '@', 'o', 'p', 'e', 'n', 's', 's', 'h', '.', 'c', 'o', 'm',
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(data, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", data, want)
+	}
+
+	var p sshfx.ExtendedPacket
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(sshfx.NewBuffer(data[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.ExtendedRequest != extensionStatVFS {
+		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extensionStatVFS)
+	}
+
+	ep, ok := p.Data.(*StatVFSExtendedPacket)
+	if !ok {
+		t.Fatalf("UnmarshaledPacketBody(): Data was type %T, but expected *StatVFSExtendedPacket", p.Data)
+	}
+
+	if ep.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", ep.Path, path)
+	}
+}
+
+var _ sshfx.PacketMarshaller = &FStatVFSExtendedPacket{}
+
+func init() {
+	RegisterExtensionFStatVFS()
+}
+
+func TestFStatVFSExtendedPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	ep := &FStatVFSExtendedPacket{
+		Path: path,
+	}
+
+	data, err := sshfx.ComposePacket(ep.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 37,
+		200,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 20, 'f', 's', 't', 'a', 't', 'v', 'f', 's', '@', 'o', 'p', 'e', 'n', 's', 's', 'h', '.', 'c', 'o', 'm',
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(data, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", data, want)
+	}
+
+	var p sshfx.ExtendedPacket
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(sshfx.NewBuffer(data[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.ExtendedRequest != extensionFStatVFS {
+		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extensionFStatVFS)
+	}
+
+	ep, ok := p.Data.(*FStatVFSExtendedPacket)
+	if !ok {
+		t.Fatalf("UnmarshaledPacketBody(): Data was type %T, but expected *FStatVFSExtendedPacket", p.Data)
+	}
+
+	if ep.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", ep.Path, path)
+	}
+}
+
+var _ sshfx.Packet = &StatVFSExtendedReplyPacket{}
+
+func TestStatVFSExtendedReplyPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	const (
+		BlockSize = uint64(iota + 13)
+		FragmentSize
+		Blocks
+		BlocksFree
+		BlocksAvail
+		Files
+		FilesFree
+		FilesAvail
+		FilesystemID
+		MountFlags
+		MaxNameLength
+	)
+
+	ep := &StatVFSExtendedReplyPacket{
+		BlockSize:     BlockSize,
+		FragmentSize:  FragmentSize,
+		Blocks:        Blocks,
+		BlocksFree:    BlocksFree,
+		BlocksAvail:   BlocksAvail,
+		Files:         Files,
+		FilesFree:     FilesFree,
+		FilesAvail:    FilesAvail,
+		FilesystemID:  FilesystemID,
+		MountFlags:    MountFlags,
+		MaxNameLength: MaxNameLength,
+	}
+
+	data, err := sshfx.ComposePacket(ep.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 93,
+		201,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 13,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 14,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 15,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 16,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 17,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 18,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 19,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 20,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 21,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 22,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 23,
+	}
+
+	if !bytes.Equal(data, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", data, want)
+	}
+
+	*ep = StatVFSExtendedReplyPacket{}
+
+	p := sshfx.ExtendedReplyPacket{
+		Data: ep,
+	}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(sshfx.NewBuffer(data[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	ep, ok := p.Data.(*StatVFSExtendedReplyPacket)
+	if !ok {
+		t.Fatalf("UnmarshaledPacketBody(): Data was type %T, but expected *StatVFSExtendedReplyPacket", p.Data)
+	}
+
+	if ep.BlockSize != BlockSize {
+		t.Errorf("UnmarshalPacketBody(): BlockSize was %d, but expected %d", ep.BlockSize, BlockSize)
+	}
+
+	if ep.FragmentSize != FragmentSize {
+		t.Errorf("UnmarshalPacketBody(): FragmentSize was %d, but expected %d", ep.FragmentSize, FragmentSize)
+	}
+
+	if ep.Blocks != Blocks {
+		t.Errorf("UnmarshalPacketBody(): Blocks was %d, but expected %d", ep.Blocks, Blocks)
+	}
+
+	if ep.BlocksFree != BlocksFree {
+		t.Errorf("UnmarshalPacketBody(): BlocksFree was %d, but expected %d", ep.BlocksFree, BlocksFree)
+	}
+
+	if ep.BlocksAvail != BlocksAvail {
+		t.Errorf("UnmarshalPacketBody(): BlocksAvail was %d, but expected %d", ep.BlocksAvail, BlocksAvail)
+	}
+
+	if ep.Files != Files {
+		t.Errorf("UnmarshalPacketBody(): Files was %d, but expected %d", ep.Files, Files)
+	}
+
+	if ep.FilesFree != FilesFree {
+		t.Errorf("UnmarshalPacketBody(): FilesFree was %d, but expected %d", ep.FilesFree, FilesFree)
+	}
+
+	if ep.FilesAvail != FilesAvail {
+		t.Errorf("UnmarshalPacketBody(): FilesAvail was %d, but expected %d", ep.FilesAvail, FilesAvail)
+	}
+
+	if ep.FilesystemID != FilesystemID {
+		t.Errorf("UnmarshalPacketBody(): FilesystemID was %d, but expected %d", ep.FilesystemID, FilesystemID)
+	}
+
+	if ep.MountFlags != MountFlags {
+		t.Errorf("UnmarshalPacketBody(): MountFlags was %d, but expected %d", ep.MountFlags, MountFlags)
+	}
+
+	if ep.MaxNameLength != MaxNameLength {
+		t.Errorf("UnmarshalPacketBody(): MaxNameLength was %d, but expected %d", ep.MaxNameLength, MaxNameLength)
+	}
+}

internal/encoding/ssh/filexfer/packets.go

@@ -0,0 +1,323 @@
+package filexfer
+
+import (
+	"errors"
+	"fmt"
+	"io"
+)
+
+// smallBufferSize is an initial allocation minimal capacity.
+const smallBufferSize = 64
+
+func newPacketFromType(typ PacketType) (Packet, error) {
+	switch typ {
+	case PacketTypeOpen:
+		return new(OpenPacket), nil
+	case PacketTypeClose:
+		return new(ClosePacket), nil
+	case PacketTypeRead:
+		return new(ReadPacket), nil
+	case PacketTypeWrite:
+		return new(WritePacket), nil
+	case PacketTypeLStat:
+		return new(LStatPacket), nil
+	case PacketTypeFStat:
+		return new(FStatPacket), nil
+	case PacketTypeSetstat:
+		return new(SetstatPacket), nil
+	case PacketTypeFSetstat:
+		return new(FSetstatPacket), nil
+	case PacketTypeOpenDir:
+		return new(OpenDirPacket), nil
+	case PacketTypeReadDir:
+		return new(ReadDirPacket), nil
+	case PacketTypeRemove:
+		return new(RemovePacket), nil
+	case PacketTypeMkdir:
+		return new(MkdirPacket), nil
+	case PacketTypeRmdir:
+		return new(RmdirPacket), nil
+	case PacketTypeRealPath:
+		return new(RealPathPacket), nil
+	case PacketTypeStat:
+		return new(StatPacket), nil
+	case PacketTypeRename:
+		return new(RenamePacket), nil
+	case PacketTypeReadLink:
+		return new(ReadLinkPacket), nil
+	case PacketTypeSymlink:
+		return new(SymlinkPacket), nil
+	case PacketTypeExtended:
+		return new(ExtendedPacket), nil
+	default:
+		return nil, fmt.Errorf("unexpected request packet type: %v", typ)
+	}
+}
+
+// RawPacket implements the general packet format from draft-ietf-secsh-filexfer-02
+//
+// RawPacket is intended for use in clients receiving responses,
+// where a response will be expected to be of a limited number of types,
+// and unmarshaling unknown/unexpected response packets is unnecessary.
+//
+// For servers expecting to receive arbitrary request packet types,
+// use RequestPacket.
+//
+// Defined in https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-3
+type RawPacket struct {
+	PacketType PacketType
+	RequestID  uint32
+
+	Data Buffer
+}
+
+// Type returns the Type field defining the SSH_FXP_xy type for this packet.
+func (p *RawPacket) Type() PacketType {
+	return p.PacketType
+}
+
+// Reset clears the pointers and reference-semantic variables of RawPacket,
+// releasing underlying resources, and making them and the RawPacket suitable to be reused,
+// so long as no other references have been kept.
+func (p *RawPacket) Reset() {
+	p.Data = Buffer{}
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+//
+// The internal p.RequestID is overridden by the reqid argument.
+func (p *RawPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		buf = NewMarshalBuffer(0)
+	}
+
+	buf.StartPacket(p.PacketType, reqid)
+
+	return buf.Packet(p.Data.Bytes())
+}
+
+// MarshalBinary returns p as the binary encoding of p.
+//
+// This is a convenience implementation primarily intended for tests,
+// because it is inefficient with allocations.
+func (p *RawPacket) MarshalBinary() ([]byte, error) {
+	return ComposePacket(p.MarshalPacket(p.RequestID, nil))
+}
+
+// UnmarshalFrom decodes a RawPacket from the given Buffer into p.
+//
+// The Data field will alias the passed in Buffer,
+// so the buffer passed in should not be reused before RawPacket.Reset().
+func (p *RawPacket) UnmarshalFrom(buf *Buffer) error {
+	typ, err := buf.ConsumeUint8()
+	if err != nil {
+		return err
+	}
+
+	p.PacketType = PacketType(typ)
+
+	if p.RequestID, err = buf.ConsumeUint32(); err != nil {
+		return err
+	}
+
+	p.Data = *buf
+	return nil
+}
+
+// UnmarshalBinary decodes a full raw packet out of the given data.
+// It is assumed that the uint32(length) has already been consumed to receive the data.
+//
+// This is a convenience implementation primarily intended for tests,
+// because this must clone the given data byte slice,
+// as Data is not allowed to alias any part of the data byte slice.
+func (p *RawPacket) UnmarshalBinary(data []byte) error {
+	clone := make([]byte, len(data))
+	n := copy(clone, data)
+	return p.UnmarshalFrom(NewBuffer(clone[:n]))
+}
+
+// readPacket reads a uint32 length-prefixed binary data packet from r.
+// using the given byte slice as a backing array.
+//
+// If the packet length read from r is bigger than maxPacketLength,
+// or greater than math.MaxInt32 on a 32-bit implementation,
+// then a `ErrLongPacket` error will be returned.
+//
+// If the given byte slice is insufficient to hold the packet,
+// then it will be extended to fill the packet size.
+func readPacket(r io.Reader, b []byte, maxPacketLength uint32) ([]byte, error) {
+	if cap(b) < 4 {
+		// We will need allocate our own buffer just for reading the packet length.
+
+		// However, we don’t really want to allocate an extremely narrow buffer (4-bytes),
+		// and cause unnecessary allocation churn from both length reads and small packet reads,
+		// so we use smallBufferSize from the bytes package as a reasonable guess.
+
+		// But if callers really do want to force narrow throw-away allocation of every packet body,
+		// they can do so with a buffer of capacity 4.
+		b = make([]byte, smallBufferSize)
+	}
+
+	if _, err := io.ReadFull(r, b[:4]); err != nil {
+		return nil, err
+	}
+
+	length := unmarshalUint32(b)
+	if int(length) < 5 {
+		// Must have at least uint8(type) and uint32(request-id)
+
+		if int(length) < 0 {
+			// Only possible when strconv.IntSize == 32,
+			// the packet length is longer than math.MaxInt32,
+			// and thus longer than any possible slice.
+			return nil, ErrLongPacket
+		}
+
+		return nil, ErrShortPacket
+	}
+	if length > maxPacketLength {
+		return nil, ErrLongPacket
+	}
+
+	if int(length) > cap(b) {
+		// We know int(length) must be positive, because of tests above.
+		b = make([]byte, length)
+	}
+
+	n, err := io.ReadFull(r, b[:length])
+	return b[:n], err
+}
+
+// ReadFrom provides a simple functional packet reader,
+// using the given byte slice as a backing array.
+//
+// To protect against potential denial of service attacks,
+// if the read packet length is longer than maxPacketLength,
+// then no packet data will be read, and ErrLongPacket will be returned.
+// (On 32-bit int architectures, all packets >= 2^31 in length
+// will return ErrLongPacket regardless of maxPacketLength.)
+//
+// If the read packet length is longer than cap(b),
+// then a throw-away slice will allocated to meet the exact packet length.
+// This can be used to limit the length of reused buffers,
+// while still allowing reception of occasional large packets.
+//
+// The Data field may alias the passed in byte slice,
+// so the byte slice passed in should not be reused before RawPacket.Reset().
+func (p *RawPacket) ReadFrom(r io.Reader, b []byte, maxPacketLength uint32) error {
+	b, err := readPacket(r, b, maxPacketLength)
+	if err != nil {
+		return err
+	}
+
+	return p.UnmarshalFrom(NewBuffer(b))
+}
+
+// RequestPacket implements the general packet format from draft-ietf-secsh-filexfer-02
+// but also automatically decode/encodes valid request packets (2 < type < 100 || type == 200).
+//
+// RequestPacket is intended for use in servers receiving requests,
+// where any arbitrary request may be received, and so decoding them automatically
+// is useful.
+//
+// For clients expecting to receive specific response packet types,
+// where automatic unmarshaling of the packet body does not make sense,
+// use RawPacket.
+//
+// Defined in https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-3
+type RequestPacket struct {
+	RequestID uint32
+
+	Request Packet
+}
+
+// Type returns the SSH_FXP_xy value associated with the underlying packet.
+func (p *RequestPacket) Type() PacketType {
+	return p.Request.Type()
+}
+
+// Reset clears the pointers and reference-semantic variables in RequestPacket,
+// releasing underlying resources, and making them and the RequestPacket suitable to be reused,
+// so long as no other references have been kept.
+func (p *RequestPacket) Reset() {
+	p.Request = nil
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+//
+// The internal p.RequestID is overridden by the reqid argument.
+func (p *RequestPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	if p.Request == nil {
+		return nil, nil, errors.New("empty request packet")
+	}
+
+	return p.Request.MarshalPacket(reqid, b)
+}
+
+// MarshalBinary returns p as the binary encoding of p.
+//
+// This is a convenience implementation primarily intended for tests,
+// because it is inefficient with allocations.
+func (p *RequestPacket) MarshalBinary() ([]byte, error) {
+	return ComposePacket(p.MarshalPacket(p.RequestID, nil))
+}
+
+// UnmarshalFrom decodes a RequestPacket from the given Buffer into p.
+//
+// The Request field may alias the passed in Buffer, (e.g. SSH_FXP_WRITE),
+// so the buffer passed in should not be reused before RequestPacket.Reset().
+func (p *RequestPacket) UnmarshalFrom(buf *Buffer) error {
+	typ, err := buf.ConsumeUint8()
+	if err != nil {
+		return err
+	}
+
+	p.Request, err = newPacketFromType(PacketType(typ))
+	if err != nil {
+		return err
+	}
+
+	if p.RequestID, err = buf.ConsumeUint32(); err != nil {
+		return err
+	}
+
+	return p.Request.UnmarshalPacketBody(buf)
+}
+
+// UnmarshalBinary decodes a full request packet out of the given data.
+// It is assumed that the uint32(length) has already been consumed to receive the data.
+//
+// This is a convenience implementation primarily intended for tests,
+// because this must clone the given data byte slice,
+// as Request is not allowed to alias any part of the data byte slice.
+func (p *RequestPacket) UnmarshalBinary(data []byte) error {
+	clone := make([]byte, len(data))
+	n := copy(clone, data)
+	return p.UnmarshalFrom(NewBuffer(clone[:n]))
+}
+
+// ReadFrom provides a simple functional packet reader,
+// using the given byte slice as a backing array.
+//
+// To protect against potential denial of service attacks,
+// if the read packet length is longer than maxPacketLength,
+// then no packet data will be read, and ErrLongPacket will be returned.
+// (On 32-bit int architectures, all packets >= 2^31 in length
+// will return ErrLongPacket regardless of maxPacketLength.)
+//
+// If the read packet length is longer than cap(b),
+// then a throw-away slice will allocated to meet the exact packet length.
+// This can be used to limit the length of reused buffers,
+// while still allowing reception of occasional large packets.
+//
+// The Request field may alias the passed in byte slice,
+// so the byte slice passed in should not be reused before RawPacket.Reset().
+func (p *RequestPacket) ReadFrom(r io.Reader, b []byte, maxPacketLength uint32) error {
+	b, err := readPacket(r, b, maxPacketLength)
+	if err != nil {
+		return err
+	}
+
+	return p.UnmarshalFrom(NewBuffer(b))
+}

internal/encoding/ssh/filexfer/packets_test.go

@@ -0,0 +1,132 @@
+package filexfer
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestRawPacket(t *testing.T) {
+	const (
+		id      = 42
+		errMsg  = "eof"
+		langTag = "en"
+	)
+
+	p := &RawPacket{
+		PacketType: PacketTypeStatus,
+		RequestID:  id,
+		Data: Buffer{
+			b: []byte{
+				0x00, 0x00, 0x00, 0x01,
+				0x00, 0x00, 0x00, 0x03, 'e', 'o', 'f',
+				0x00, 0x00, 0x00, 0x02, 'e', 'n',
+			},
+		},
+	}
+
+	buf, err := p.MarshalBinary()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 22,
+		101,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 0x01,
+		0x00, 0x00, 0x00, 3, 'e', 'o', 'f',
+		0x00, 0x00, 0x00, 2, 'e', 'n',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Errorf("RawPacket.MarshalBinary() = %X, but wanted %X", buf, want)
+	}
+
+	*p = RawPacket{}
+
+	if err := p.ReadFrom(bytes.NewReader(buf), nil, DefaultMaxPacketLength); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.PacketType != PacketTypeStatus {
+		t.Errorf("RawPacket.UnmarshalBinary(): Type was %v, but expected %v", p.PacketType, PacketTypeStat)
+	}
+
+	if p.RequestID != uint32(id) {
+		t.Errorf("RawPacket.UnmarshalBinary(): RequestID was %d, but expected %d", p.RequestID, id)
+	}
+
+	want = []byte{
+		0x00, 0x00, 0x00, 0x01,
+		0x00, 0x00, 0x00, 3, 'e', 'o', 'f',
+		0x00, 0x00, 0x00, 2, 'e', 'n',
+	}
+
+	if !bytes.Equal(p.Data.Bytes(), want) {
+		t.Fatalf("RawPacket.UnmarshalBinary(): Data was %X, but expected %X", p.Data, want)
+	}
+
+	var resp StatusPacket
+	resp.UnmarshalPacketBody(&p.Data)
+
+	if resp.StatusCode != StatusEOF {
+		t.Errorf("UnmarshalPacketBody(): StatusCode was %v, but expected %v", resp.StatusCode, StatusEOF)
+	}
+
+	if resp.ErrorMessage != errMsg {
+		t.Errorf("UnmarshalPacketBody(): ErrorMessage was %q, but expected %q", resp.ErrorMessage, errMsg)
+	}
+
+	if resp.LanguageTag != langTag {
+		t.Errorf("UnmarshalPacketBody(): LanguageTag was %q, but expected %q", resp.LanguageTag, langTag)
+	}
+}
+
+func TestRequestPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "foo"
+	)
+
+	p := &RequestPacket{
+		RequestID: id,
+		Request: &StatPacket{
+			Path: path,
+		},
+	}
+
+	buf, err := p.MarshalBinary()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 12,
+		17,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 3, 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Errorf("RequestPacket.MarshalBinary() = %X, but wanted %X", buf, want)
+	}
+
+	*p = RequestPacket{}
+
+	if err := p.ReadFrom(bytes.NewReader(buf), nil, DefaultMaxPacketLength); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.RequestID != uint32(id) {
+		t.Errorf("RequestPacket.UnmarshalBinary(): RequestID was %d, but expected %d", p.RequestID, id)
+	}
+
+	req, ok := p.Request.(*StatPacket)
+	if !ok {
+		t.Fatalf("unexpected Request type was %T, but expected %T", p.Request, req)
+	}
+
+	if req.Path != path {
+		t.Errorf("RequestPacket.UnmarshalBinary(): Request.Path was %q, but expected %q", req.Path, path)
+	}
+}

internal/encoding/ssh/filexfer/path_packets.go

@@ -0,0 +1,368 @@
+package filexfer
+
+// LStatPacket defines the SSH_FXP_LSTAT packet.
+type LStatPacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *LStatPacket) Type() PacketType {
+	return PacketTypeLStat
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *LStatPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) // string(path)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeLStat, reqid)
+	buf.AppendString(p.Path)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *LStatPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// SetstatPacket defines the SSH_FXP_SETSTAT packet.
+type SetstatPacket struct {
+	Path  string
+	Attrs Attributes
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *SetstatPacket) Type() PacketType {
+	return PacketTypeSetstat
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *SetstatPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) + p.Attrs.Len() // string(path) + ATTRS(attrs)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeSetstat, reqid)
+	buf.AppendString(p.Path)
+
+	p.Attrs.MarshalInto(buf)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *SetstatPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return p.Attrs.UnmarshalFrom(buf)
+}
+
+// RemovePacket defines the SSH_FXP_REMOVE packet.
+type RemovePacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *RemovePacket) Type() PacketType {
+	return PacketTypeRemove
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *RemovePacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) // string(path)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeRemove, reqid)
+	buf.AppendString(p.Path)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *RemovePacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// MkdirPacket defines the SSH_FXP_MKDIR packet.
+type MkdirPacket struct {
+	Path  string
+	Attrs Attributes
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *MkdirPacket) Type() PacketType {
+	return PacketTypeMkdir
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *MkdirPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) + p.Attrs.Len() // string(path) + ATTRS(attrs)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeMkdir, reqid)
+	buf.AppendString(p.Path)
+
+	p.Attrs.MarshalInto(buf)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *MkdirPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return p.Attrs.UnmarshalFrom(buf)
+}
+
+// RmdirPacket defines the SSH_FXP_RMDIR packet.
+type RmdirPacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *RmdirPacket) Type() PacketType {
+	return PacketTypeRmdir
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *RmdirPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) // string(path)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeRmdir, reqid)
+	buf.AppendString(p.Path)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *RmdirPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// RealPathPacket defines the SSH_FXP_REALPATH packet.
+type RealPathPacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *RealPathPacket) Type() PacketType {
+	return PacketTypeRealPath
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *RealPathPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) // string(path)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeRealPath, reqid)
+	buf.AppendString(p.Path)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *RealPathPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// StatPacket defines the SSH_FXP_STAT packet.
+type StatPacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *StatPacket) Type() PacketType {
+	return PacketTypeStat
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *StatPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) // string(path)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeStat, reqid)
+	buf.AppendString(p.Path)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *StatPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// RenamePacket defines the SSH_FXP_RENAME packet.
+type RenamePacket struct {
+	OldPath string
+	NewPath string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *RenamePacket) Type() PacketType {
+	return PacketTypeRename
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *RenamePacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		// string(oldpath) + string(newpath)
+		size := 4 + len(p.OldPath) + 4 + len(p.NewPath)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeRename, reqid)
+	buf.AppendString(p.OldPath)
+	buf.AppendString(p.NewPath)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *RenamePacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.OldPath, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if p.NewPath, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// ReadLinkPacket defines the SSH_FXP_READLINK packet.
+type ReadLinkPacket struct {
+	Path string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *ReadLinkPacket) Type() PacketType {
+	return PacketTypeReadLink
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *ReadLinkPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Path) // string(path)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeReadLink, reqid)
+	buf.AppendString(p.Path)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *ReadLinkPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Path, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// SymlinkPacket defines the SSH_FXP_SYMLINK packet.
+//
+// The order of the arguments to the SSH_FXP_SYMLINK method was inadvertently reversed.
+// Unfortunately, the reversal was not noticed until the server was widely deployed.
+// Covered in Section 3.1 of https://github.com/openssh/openssh-portable/blob/master/PROTOCOL
+type SymlinkPacket struct {
+	LinkPath   string
+	TargetPath string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *SymlinkPacket) Type() PacketType {
+	return PacketTypeSymlink
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *SymlinkPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		// string(targetpath) + string(linkpath)
+		size := 4 + len(p.TargetPath) + 4 + len(p.LinkPath)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeSymlink, reqid)
+
+	// Arguments were inadvertently reversed.
+	buf.AppendString(p.TargetPath)
+	buf.AppendString(p.LinkPath)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *SymlinkPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	// Arguments were inadvertently reversed.
+	if p.TargetPath, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if p.LinkPath, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}

internal/encoding/ssh/filexfer/path_packets_test.go

@@ -0,0 +1,450 @@
+package filexfer
+
+import (
+	"bytes"
+	"testing"
+)
+
+var _ Packet = &LStatPacket{}
+
+func TestLStatPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	p := &LStatPacket{
+		Path: path,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 13,
+		7,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = LStatPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+}
+
+var _ Packet = &SetstatPacket{}
+
+func TestSetstatPacket(t *testing.T) {
+	const (
+		id    = 42
+		path  = "/foo"
+		perms = 0x87654321
+	)
+
+	p := &SetstatPacket{
+		Path: "/foo",
+		Attrs: Attributes{
+			Flags:       AttrPermissions,
+			Permissions: perms,
+		},
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 21,
+		9,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 0x04,
+		0x87, 0x65, 0x43, 0x21,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = SetstatPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+
+	if p.Attrs.Flags != AttrPermissions {
+		t.Errorf("UnmarshalPacketBody(): Attrs.Flags was %#x, but expected %#x", p.Attrs.Flags, AttrPermissions)
+	}
+
+	if p.Attrs.Permissions != perms {
+		t.Errorf("UnmarshalPacketBody(): Attrs.Permissions was %#v, but expected %#v", p.Attrs.Permissions, perms)
+	}
+}
+
+var _ Packet = &RemovePacket{}
+
+func TestRemovePacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	p := &RemovePacket{
+		Path: path,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 13,
+		13,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = RemovePacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+}
+
+var _ Packet = &MkdirPacket{}
+
+func TestMkdirPacket(t *testing.T) {
+	const (
+		id    = 42
+		path  = "/foo"
+		perms = 0x87654321
+	)
+
+	p := &MkdirPacket{
+		Path: "/foo",
+		Attrs: Attributes{
+			Flags:       AttrPermissions,
+			Permissions: perms,
+		},
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 21,
+		14,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 0x04,
+		0x87, 0x65, 0x43, 0x21,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = MkdirPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+
+	if p.Attrs.Flags != AttrPermissions {
+		t.Errorf("UnmarshalPacketBody(): Attrs.Flags was %#x, but expected %#x", p.Attrs.Flags, AttrPermissions)
+	}
+
+	if p.Attrs.Permissions != perms {
+		t.Errorf("UnmarshalPacketBody(): Attrs.Permissions was %#v, but expected %#v", p.Attrs.Permissions, perms)
+	}
+}
+
+var _ Packet = &RmdirPacket{}
+
+func TestRmdirPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	p := &RmdirPacket{
+		Path: path,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 13,
+		15,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = RmdirPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+}
+
+var _ Packet = &RealPathPacket{}
+
+func TestRealPathPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	p := &RealPathPacket{
+		Path: path,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 13,
+		16,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = RealPathPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+}
+
+var _ Packet = &StatPacket{}
+
+func TestStatPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	p := &StatPacket{
+		Path: path,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 13,
+		17,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = StatPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+}
+
+var _ Packet = &RenamePacket{}
+
+func TestRenamePacket(t *testing.T) {
+	const (
+		id      = 42
+		oldpath = "/foo"
+		newpath = "/bar"
+	)
+
+	p := &RenamePacket{
+		OldPath: oldpath,
+		NewPath: newpath,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 21,
+		18,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 4, '/', 'b', 'a', 'r',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = RenamePacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.OldPath != oldpath {
+		t.Errorf("UnmarshalPacketBody(): OldPath was %q, but expected %q", p.OldPath, oldpath)
+	}
+
+	if p.NewPath != newpath {
+		t.Errorf("UnmarshalPacketBody(): NewPath was %q, but expected %q", p.NewPath, newpath)
+	}
+}
+
+var _ Packet = &ReadLinkPacket{}
+
+func TestReadLinkPacket(t *testing.T) {
+	const (
+		id   = 42
+		path = "/foo"
+	)
+
+	p := &ReadLinkPacket{
+		Path: path,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 13,
+		19,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = ReadLinkPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Path != path {
+		t.Errorf("UnmarshalPacketBody(): Path was %q, but expected %q", p.Path, path)
+	}
+}
+
+var _ Packet = &SymlinkPacket{}
+
+func TestSymlinkPacket(t *testing.T) {
+	const (
+		id         = 42
+		linkpath   = "/foo"
+		targetpath = "/bar"
+	)
+
+	p := &SymlinkPacket{
+		LinkPath:   linkpath,
+		TargetPath: targetpath,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 21,
+		20,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 4, '/', 'b', 'a', 'r', // Arguments were inadvertently reversed.
+		0x00, 0x00, 0x00, 4, '/', 'f', 'o', 'o',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = SymlinkPacket{}
+
+	// UnmarshalPacketBody assumes the (length, type, request-id) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.LinkPath != linkpath {
+		t.Errorf("UnmarshalPacketBody(): LinkPath was %q, but expected %q", p.LinkPath, linkpath)
+	}
+
+	if p.TargetPath != targetpath {
+		t.Errorf("UnmarshalPacketBody(): TargetPath was %q, but expected %q", p.TargetPath, targetpath)
+	}
+}

internal/encoding/ssh/filexfer/permissions.go

@@ -0,0 +1,114 @@
+package filexfer
+
+// FileMode represents a file’s mode and permission bits.
+// The bits are defined according to POSIX standards,
+// and may not apply to the OS being built for.
+type FileMode uint32
+
+// Permission flags, defined here to avoid potential inconsistencies in individual OS implementations.
+const (
+	ModePerm       FileMode = 0o0777 // S_IRWXU | S_IRWXG | S_IRWXO
+	ModeUserRead   FileMode = 0o0400 // S_IRUSR
+	ModeUserWrite  FileMode = 0o0200 // S_IWUSR
+	ModeUserExec   FileMode = 0o0100 // S_IXUSR
+	ModeGroupRead  FileMode = 0o0040 // S_IRGRP
+	ModeGroupWrite FileMode = 0o0020 // S_IWGRP
+	ModeGroupExec  FileMode = 0o0010 // S_IXGRP
+	ModeOtherRead  FileMode = 0o0004 // S_IROTH
+	ModeOtherWrite FileMode = 0o0002 // S_IWOTH
+	ModeOtherExec  FileMode = 0o0001 // S_IXOTH
+
+	ModeSetUID FileMode = 0o4000 // S_ISUID
+	ModeSetGID FileMode = 0o2000 // S_ISGID
+	ModeSticky FileMode = 0o1000 // S_ISVTX
+
+	ModeType       FileMode = 0xF000 // S_IFMT
+	ModeNamedPipe  FileMode = 0x1000 // S_IFIFO
+	ModeCharDevice FileMode = 0x2000 // S_IFCHR
+	ModeDir        FileMode = 0x4000 // S_IFDIR
+	ModeDevice     FileMode = 0x6000 // S_IFBLK
+	ModeRegular    FileMode = 0x8000 // S_IFREG
+	ModeSymlink    FileMode = 0xA000 // S_IFLNK
+	ModeSocket     FileMode = 0xC000 // S_IFSOCK
+)
+
+// IsDir reports whether m describes a directory.
+// That is, it tests for m.Type() == ModeDir.
+func (m FileMode) IsDir() bool {
+	return (m & ModeType) == ModeDir
+}
+
+// IsRegular reports whether m describes a regular file.
+// That is, it tests for m.Type() == ModeRegular
+func (m FileMode) IsRegular() bool {
+	return (m & ModeType) == ModeRegular
+}
+
+// Perm returns the POSIX permission bits in m (m & ModePerm).
+func (m FileMode) Perm() FileMode {
+	return (m & ModePerm)
+}
+
+// Type returns the type bits in m (m & ModeType).
+func (m FileMode) Type() FileMode {
+	return (m & ModeType)
+}
+
+// String returns a `-rwxrwxrwx` style string representing the `ls -l` POSIX permissions string.
+func (m FileMode) String() string {
+	var buf [10]byte
+
+	switch m.Type() {
+	case ModeRegular:
+		buf[0] = '-'
+	case ModeDir:
+		buf[0] = 'd'
+	case ModeSymlink:
+		buf[0] = 'l'
+	case ModeDevice:
+		buf[0] = 'b'
+	case ModeCharDevice:
+		buf[0] = 'c'
+	case ModeNamedPipe:
+		buf[0] = 'p'
+	case ModeSocket:
+		buf[0] = 's'
+	default:
+		buf[0] = '?'
+	}
+
+	const rwx = "rwxrwxrwx"
+	for i, c := range rwx {
+		if m&(1<<uint(9-1-i)) != 0 {
+			buf[i+1] = byte(c)
+		} else {
+			buf[i+1] = '-'
+		}
+	}
+
+	if m&ModeSetUID != 0 {
+		if buf[3] == 'x' {
+			buf[3] = 's'
+		} else {
+			buf[3] = 'S'
+		}
+	}
+
+	if m&ModeSetGID != 0 {
+		if buf[6] == 'x' {
+			buf[6] = 's'
+		} else {
+			buf[6] = 'S'
+		}
+	}
+
+	if m&ModeSticky != 0 {
+		if buf[9] == 'x' {
+			buf[9] = 't'
+		} else {
+			buf[9] = 'T'
+		}
+	}
+
+	return string(buf[:])
+}

internal/encoding/ssh/filexfer/response_packets.go

@@ -0,0 +1,243 @@
+package filexfer
+
+import (
+	"fmt"
+)
+
+// StatusPacket defines the SSH_FXP_STATUS packet.
+//
+// Specified in https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-7
+type StatusPacket struct {
+	StatusCode   Status
+	ErrorMessage string
+	LanguageTag  string
+}
+
+// Error makes StatusPacket an error type.
+func (p *StatusPacket) Error() string {
+	if p.ErrorMessage == "" {
+		return "sftp: " + p.StatusCode.String()
+	}
+
+	return fmt.Sprintf("sftp: %q (%s)", p.ErrorMessage, p.StatusCode)
+}
+
+// Is returns true if target is a StatusPacket with the same StatusCode,
+// or target is a Status code which is the same as SatusCode.
+func (p *StatusPacket) Is(target error) bool {
+	if target, ok := target.(*StatusPacket); ok {
+		return p.StatusCode == target.StatusCode
+	}
+
+	return p.StatusCode == target
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *StatusPacket) Type() PacketType {
+	return PacketTypeStatus
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *StatusPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		// uint32(error/status code) + string(error message) + string(language tag)
+		size := 4 + 4 + len(p.ErrorMessage) + 4 + len(p.LanguageTag)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeStatus, reqid)
+	buf.AppendUint32(uint32(p.StatusCode))
+	buf.AppendString(p.ErrorMessage)
+	buf.AppendString(p.LanguageTag)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *StatusPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	statusCode, err := buf.ConsumeUint32()
+	if err != nil {
+		return err
+	}
+	p.StatusCode = Status(statusCode)
+
+	if p.ErrorMessage, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	if p.LanguageTag, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// HandlePacket defines the SSH_FXP_HANDLE packet.
+type HandlePacket struct {
+	Handle string
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *HandlePacket) Type() PacketType {
+	return PacketTypeHandle
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *HandlePacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 + len(p.Handle) // string(handle)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeHandle, reqid)
+	buf.AppendString(p.Handle)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *HandlePacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	if p.Handle, err = buf.ConsumeString(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// DataPacket defines the SSH_FXP_DATA packet.
+type DataPacket struct {
+	Data []byte
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *DataPacket) Type() PacketType {
+	return PacketTypeData
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *DataPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 // uint32(len(data)); data content in payload
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeData, reqid)
+	buf.AppendUint32(uint32(len(p.Data)))
+
+	return buf.Packet(p.Data)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+//
+// If p.Data is already populated, and of sufficient length to hold the data,
+// then this will copy the data into that byte slice.
+//
+// If p.Data has a length insufficient to hold the data,
+// then this will make a new slice of sufficient length, and copy the data into that.
+//
+// This means this _does not_ alias any of the data buffer that is passed in.
+func (p *DataPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	data, err := buf.ConsumeByteSlice()
+	if err != nil {
+		return err
+	}
+
+	if len(p.Data) < len(data) {
+		p.Data = make([]byte, len(data))
+	}
+
+	n := copy(p.Data, data)
+	p.Data = p.Data[:n]
+	return nil
+}
+
+// NamePacket defines the SSH_FXP_NAME packet.
+type NamePacket struct {
+	Entries []*NameEntry
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *NamePacket) Type() PacketType {
+	return PacketTypeName
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *NamePacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := 4 // uint32(len(entries))
+
+		for _, e := range p.Entries {
+			size += e.Len()
+		}
+
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeName, reqid)
+	buf.AppendUint32(uint32(len(p.Entries)))
+
+	for _, e := range p.Entries {
+		e.MarshalInto(buf)
+	}
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *NamePacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	count, err := buf.ConsumeUint32()
+	if err != nil {
+		return err
+	}
+
+	p.Entries = make([]*NameEntry, 0, count)
+
+	for i := uint32(0); i < count; i++ {
+		var e NameEntry
+		if err := e.UnmarshalFrom(buf); err != nil {
+			return err
+		}
+
+		p.Entries = append(p.Entries, &e)
+	}
+
+	return nil
+}
+
+// AttrsPacket defines the SSH_FXP_ATTRS packet.
+type AttrsPacket struct {
+	Attrs Attributes
+}
+
+// Type returns the SSH_FXP_xy value associated with this packet type.
+func (p *AttrsPacket) Type() PacketType {
+	return PacketTypeAttrs
+}
+
+// MarshalPacket returns p as a two-part binary encoding of p.
+func (p *AttrsPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	buf := NewBuffer(b)
+	if buf.Cap() < 9 {
+		size := p.Attrs.Len() // ATTRS(attrs)
+		buf = NewMarshalBuffer(size)
+	}
+
+	buf.StartPacket(PacketTypeAttrs, reqid)
+	p.Attrs.MarshalInto(buf)
+
+	return buf.Packet(payload)
+}
+
+// UnmarshalPacketBody unmarshals the packet body from the given Buffer.
+// It is assumed that the uint32(request-id) has already been consumed.
+func (p *AttrsPacket) UnmarshalPacketBody(buf *Buffer) (err error) {
+	return p.Attrs.UnmarshalFrom(buf)
+}

internal/encoding/ssh/filexfer/response_packets_test.go

@@ -0,0 +1,296 @@
+package filexfer
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+)
+
+func TestStatusPacketIs(t *testing.T) {
+	status := &StatusPacket{
+		StatusCode:   StatusFailure,
+		ErrorMessage: "error message",
+		LanguageTag:  "language tag",
+	}
+
+	if !errors.Is(status, StatusFailure) {
+		t.Error("errors.Is(StatusFailure, StatusFailure) != true")
+	}
+	if !errors.Is(status, &StatusPacket{StatusCode: StatusFailure}) {
+		t.Error("errors.Is(StatusFailure, StatusPacket{StatusFailure}) != true")
+	}
+	if errors.Is(status, StatusOK) {
+		t.Error("errors.Is(StatusFailure, StatusFailure) == true")
+	}
+	if errors.Is(status, &StatusPacket{StatusCode: StatusOK}) {
+		t.Error("errors.Is(StatusFailure, StatusPacket{StatusFailure}) == true")
+	}
+}
+
+var _ Packet = &StatusPacket{}
+
+func TestStatusPacket(t *testing.T) {
+	const (
+		id           = 42
+		statusCode   = StatusBadMessage
+		errorMessage = "foo"
+		languageTag  = "x-example"
+	)
+
+	p := &StatusPacket{
+		StatusCode:   statusCode,
+		ErrorMessage: errorMessage,
+		LanguageTag:  languageTag,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 29,
+		101,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 5,
+		0x00, 0x00, 0x00, 3, 'f', 'o', 'o',
+		0x00, 0x00, 0x00, 9, 'x', '-', 'e', 'x', 'a', 'm', 'p', 'l', 'e',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = StatusPacket{}
+
+	// UnmarshalBinary assumes the uint32(length) + uint8(type) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.StatusCode != statusCode {
+		t.Errorf("UnmarshalBinary(): StatusCode was %v, but expected %v", p.StatusCode, statusCode)
+	}
+
+	if p.ErrorMessage != errorMessage {
+		t.Errorf("UnmarshalBinary(): ErrorMessage was %q, but expected %q", p.ErrorMessage, errorMessage)
+	}
+
+	if p.LanguageTag != languageTag {
+		t.Errorf("UnmarshalBinary(): LanguageTag was %q, but expected %q", p.LanguageTag, languageTag)
+	}
+}
+
+var _ Packet = &HandlePacket{}
+
+func TestHandlePacket(t *testing.T) {
+	const (
+		id     = 42
+		handle = "somehandle"
+	)
+
+	p := &HandlePacket{
+		Handle: "somehandle",
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 19,
+		102,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 10, 's', 'o', 'm', 'e', 'h', 'a', 'n', 'd', 'l', 'e',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = HandlePacket{}
+
+	// UnmarshalBinary assumes the uint32(length) + uint8(type) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Handle != handle {
+		t.Errorf("UnmarshalBinary(): Handle was %q, but expected %q", p.Handle, handle)
+	}
+}
+
+var _ Packet = &DataPacket{}
+
+func TestDataPacket(t *testing.T) {
+	const (
+		id = 42
+	)
+
+	var payload = []byte(`foobar`)
+
+	p := &DataPacket{
+		Data: payload,
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 15,
+		103,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 6, 'f', 'o', 'o', 'b', 'a', 'r',
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = DataPacket{}
+
+	// UnmarshalBinary assumes the uint32(length) + uint8(type) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if !bytes.Equal(p.Data, payload) {
+		t.Errorf("UnmarshalBinary(): Data was %X, but expected %X", p.Data, payload)
+	}
+}
+
+var _ Packet = &NamePacket{}
+
+func TestNamePacket(t *testing.T) {
+	const (
+		id       = 42
+		filename = "foo"
+		longname = "bar"
+		perms    = 0x87654300
+	)
+
+	p := &NamePacket{
+		Entries: []*NameEntry{
+			&NameEntry{
+				Filename: filename + "1",
+				Longname: longname + "1",
+				Attrs: Attributes{
+					Flags:       AttrPermissions | (1 << 8),
+					Permissions: perms | 1,
+				},
+			},
+			&NameEntry{
+				Filename: filename + "2",
+				Longname: longname + "2",
+				Attrs: Attributes{
+					Flags:       AttrPermissions | (2 << 8),
+					Permissions: perms | 2,
+				},
+			},
+		},
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 57,
+		104,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 0x02,
+		0x00, 0x00, 0x00, 4, 'f', 'o', 'o', '1',
+		0x00, 0x00, 0x00, 4, 'b', 'a', 'r', '1',
+		0x00, 0x00, 0x01, 0x04,
+		0x87, 0x65, 0x43, 0x01,
+		0x00, 0x00, 0x00, 4, 'f', 'o', 'o', '2',
+		0x00, 0x00, 0x00, 4, 'b', 'a', 'r', '2',
+		0x00, 0x00, 0x02, 0x04,
+		0x87, 0x65, 0x43, 0x02,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = NamePacket{}
+
+	// UnmarshalBinary assumes the uint32(length) + uint8(type) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if count := len(p.Entries); count != 2 {
+		t.Fatalf("UnmarshalBinary(): len(NameEntries) was %d, but expected %d", count, 2)
+	}
+
+	for i, e := range p.Entries {
+		if got, want := e.Filename, filename+string('1'+rune(i)); got != want {
+			t.Errorf("UnmarshalBinary(): Entries[%d].Filename was %q, but expected %q", i, got, want)
+		}
+
+		if got, want := e.Longname, longname+string('1'+rune(i)); got != want {
+			t.Errorf("UnmarshalBinary(): Entries[%d].Longname was %q, but expected %q", i, got, want)
+		}
+
+		if got, want := e.Attrs.Flags, AttrPermissions|((i+1)<<8); got != uint32(want) {
+			t.Errorf("UnmarshalBinary(): Entries[%d].Attrs.Flags was %#x, but expected %#x", i, got, want)
+		}
+
+		if got, want := e.Attrs.Permissions, FileMode(perms|(i+1)); got != want {
+			t.Errorf("UnmarshalBinary(): Entries[%d].Attrs.Permissions was %#v, but expected %#v", i, got, want)
+		}
+	}
+}
+
+var _ Packet = &AttrsPacket{}
+
+func TestAttrsPacket(t *testing.T) {
+	const (
+		id    = 42
+		perms = 0x87654321
+	)
+
+	p := &AttrsPacket{
+		Attrs: Attributes{
+			Flags:       AttrPermissions,
+			Permissions: perms,
+		},
+	}
+
+	buf, err := ComposePacket(p.MarshalPacket(id, nil))
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	want := []byte{
+		0x00, 0x00, 0x00, 13,
+		105,
+		0x00, 0x00, 0x00, 42,
+		0x00, 0x00, 0x00, 0x04,
+		0x87, 0x65, 0x43, 0x21,
+	}
+
+	if !bytes.Equal(buf, want) {
+		t.Fatalf("MarshalPacket() = %X, but wanted %X", buf, want)
+	}
+
+	*p = AttrsPacket{}
+
+	// UnmarshalBinary assumes the uint32(length) + uint8(type) have already been consumed.
+	if err := p.UnmarshalPacketBody(NewBuffer(buf[9:])); err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	if p.Attrs.Flags != AttrPermissions {
+		t.Errorf("UnmarshalBinary(): Attrs.Flags was %#x, but expected %#x", p.Attrs.Flags, AttrPermissions)
+	}
+
+	if p.Attrs.Permissions != perms {
+		t.Errorf("UnmarshalBinary(): Attrs.Permissions was %#v, but expected %#v", p.Attrs.Permissions, perms)
+	}
+}

main.go

@@ -1,6 +1,16 @@
 package main
 
 import (
+	"context"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net"
+	"git.deuxfleurs.fr/Deuxfleurs/bagage/sftp"
+	"git.deuxfleurs.fr/Deuxfleurs/bagage/s3"
+	"github.com/minio/minio-go/v7/pkg/credentials"
+	"github.com/minio/minio-go/v7"
+	"golang.org/x/crypto/ssh"
 	"log"
 	"net/http"
 )
@@ -11,6 +21,149 @@ func main() {
 
 	log.Println(config)
 
+	done := make(chan error)
+
+	go httpServer(config, done)
+	go sshServer(config, done)
+
+	err := <- done
+	if err != nil {
+		log.Fatalf("A component failed: %v", err)
+	}
+}
+
+type s3creds struct {
+	accessKey string
+	secretKey string
+}
+var keychain map[string]s3creds
+
+func sshServer(dconfig* Config, done chan error) {
+	keychain = make(map[string]s3creds)
+
+	config := &ssh.ServerConfig{
+		PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
+			log.Printf("Login: %s\n", c.User())
+			access_key, secret_key, err := LdapGetS3(dconfig, c.User(), string(pass))
+			if err == nil {
+				keychain[c.User()] = s3creds{ access_key, secret_key }
+			}
+			return nil, err
+		},
+	}
+
+	privateBytes, err := ioutil.ReadFile(dconfig.SSHKey)
+	if err != nil {
+		log.Fatal("Failed to load private key", err)
+	}
+
+	private, err := ssh.ParsePrivateKey(privateBytes)
+	if err != nil {
+		log.Fatal("Failed to parse private key", err)
+	}
+
+	config.AddHostKey(private)
+
+	// Once a ServerConfig has been configured, connections can be
+	// accepted.
+	listener, err := net.Listen("tcp", "0.0.0.0:2222")
+	if err != nil {
+		log.Fatal("failed to listen for connection", err)
+	}
+	log.Printf("Listening on %v\n", listener.Addr())
+
+	for {
+		nConn, err := listener.Accept()
+		if err != nil {
+			log.Printf("failed to accept incoming connection: ", err)
+			continue
+		}
+		go handleSSHConn(nConn, dconfig, config)
+	}
+}
+
+func handleSSHConn(nConn net.Conn, dconfig* Config, config *ssh.ServerConfig) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	defer nConn.Close()
+
+	// Before use, a handshake must be performed on the incoming
+	// net.Conn.
+	serverConn, chans, reqs, err := ssh.NewServerConn(nConn, config)
+	if err != nil {
+		log.Printf("failed to handshake: ", err)
+	}
+	defer serverConn.Conn.Close()
+	user := serverConn.Conn.User()
+	log.Printf("SSH connection established for %v\n", user)
+
+	// The incoming Request channel must be serviced.
+	go ssh.DiscardRequests(reqs)
+
+	// Service the incoming Channel channel.
+	for newChannel := range chans {
+		// Channels have a type, depending on the application level
+		// protocol intended. In the case of an SFTP session, this is "subsystem"
+		// with a payload string of "<length=4>sftp"
+		log.Printf("Incoming channel: %s\n", newChannel.ChannelType())
+		if newChannel.ChannelType() != "session" {
+			newChannel.Reject(ssh.UnknownChannelType, "unknown channel type")
+			log.Printf("Unknown channel type: %s\n", newChannel.ChannelType())
+			continue
+		}
+
+		channel, requests, err := newChannel.Accept()
+		if err != nil {
+			log.Print("could not accept channel.", err)
+		}
+		log.Printf("Channel accepted\n")
+
+		// Sessions have out-of-band requests such as "shell",
+		// "pty-req" and "env".  Here we handle only the
+		// "subsystem" request.
+		go func(in <-chan *ssh.Request) {
+			for req := range in {
+				log.Printf("Request: %v\n", req.Type)
+				ok := false
+				switch req.Type {
+				case "subsystem":
+					log.Printf("Subsystem: %s\n", req.Payload[4:])
+					if string(req.Payload[4:]) == "sftp" {
+						ok = true
+					}
+				}
+				log.Printf(" - accepted: %v\n", ok)
+				req.Reply(ok, nil)
+			}
+		}(requests)
+
+		creds := keychain[user] 
+		mc, err := minio.New(dconfig.Endpoint, &minio.Options{
+			Creds:  credentials.NewStaticV4(creds.accessKey, creds.secretKey, ""),
+			Secure: dconfig.UseSSL,
+		})
+		if err != nil {
+			return
+		}
+
+		fs := s3.NewS3FS(mc)
+		server, err := sftp.NewServer(ctx, channel, &fs)
+
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		if err := server.Serve(); err == io.EOF {
+			server.Close()
+			log.Print("sftp client exited session.")
+		} else if err != nil {
+			log.Print("sftp server completed with error:", err)
+		}
+	}
+}
+
+func httpServer(config* Config, done chan error) {
 	// Assemble components to handle WebDAV requests
 	http.Handle(config.DavPath+"/",
 		BasicAuthExtract{
@@ -30,6 +183,8 @@ func main() {
 		})
 
 	if err := http.ListenAndServe(config.HttpListen, nil); err != nil {
-		log.Fatalf("Error with WebDAV server: %v", err)
+		done <- fmt.Errorf("Error with WebDAV server: %v", err)
+	} else {
+		done <- nil
 	}
 }

s3/file.go

@@ -1,4 +1,4 @@
-package main
+package s3
 
 import (
 	"context"
@@ -11,7 +11,6 @@ import (
 	"path"
 
 	"github.com/minio/minio-go/v7"
-	"golang.org/x/net/webdav"
 )
 
 type S3File struct {
@@ -20,14 +19,16 @@ type S3File struct {
 	objw  *io.PipeWriter
 	donew chan error
 	pos   int64
-	path  S3Path
+	entries []fs.FileInfo
+	Path  S3Path
 }
 
-func NewS3File(s *S3FS, path string) (webdav.File, error) {
+func NewS3File(s *S3FS, path string) (*S3File, error) {
 	f := new(S3File)
 	f.fs = s
 	f.pos = 0
-	f.path = NewS3Path(path)
+	f.entries = nil
+	f.Path = NewS3Path(path)
 	return f, nil
 }
 
@@ -62,7 +63,7 @@ func (f *S3File) Close() error {
 
 func (f *S3File) loadObject() error {
 	if f.obj == nil {
-		obj, err := f.fs.mc.GetObject(f.fs.ctx, f.path.bucket, f.path.key, minio.GetObjectOptions{})
+		obj, err := f.fs.mc.GetObject(f.fs.ctx, f.Path.Bucket, f.Path.Key, minio.GetObjectOptions{})
 		if err != nil {
 			return err
 		}
@@ -82,6 +83,19 @@ func (f *S3File) Read(p []byte) (n int, err error) {
 	return f.obj.Read(p)
 }
 
+func (f *S3File) ReadAt(p []byte, off int64) (n int, err error) {
+	if err := f.loadObject(); err != nil {
+		return 0, err
+	}
+
+	return f.obj.ReadAt(p, off)
+}
+
+func (f *S3File) WriteAt(p []byte, off int64) (n int, err error) {
+	return 0, errors.New("not implemented")
+
+}
+
 func (f *S3File) Write(p []byte) (n int, err error) {
 	/*if f.path.class != OBJECT {
 		return 0, os.ErrInvalid
@@ -96,7 +110,7 @@ func (f *S3File) Write(p []byte) (n int, err error) {
 		f.donew = make(chan error, 1)
 		f.objw = w
 
-		contentType := mime.TypeByExtension(path.Ext(f.path.key))
+		contentType := mime.TypeByExtension(path.Ext(f.Path.Key))
 		go func() {
 			/* @FIXME
 			PutObject has a strange behaviour when used with unknown size, it supposes the final size will be 5TiB.
@@ -107,7 +121,7 @@ func (f *S3File) Write(p []byte) (n int, err error) {
 			Because Multipart uploads seems to be limited to 10 000 parts, it might be possible that we are limited to 50 GiB files, which is still good enough.
 			Ref: https://github.com/minio/minio-go/blob/62beca8cd87e9960d88793320220ad2c159bb5e5/api-put-object-common.go#L110-L112
 			*/
-			_, err := f.fs.mc.PutObject(context.Background(), f.path.bucket, f.path.key, r, -1, minio.PutObjectOptions{ContentType: contentType, PartSize: 5*1024*1024})
+			_, err := f.fs.mc.PutObject(context.Background(), f.Path.Bucket, f.Path.Key, r, -1, minio.PutObjectOptions{ContentType: contentType, PartSize: 5*1024*1024})
 			f.donew <- err
 		}()
 	}
@@ -133,43 +147,59 @@ If n > 0, ReadDir returns at most n DirEntry records. In this case, if ReadDir r
 If n <= 0, ReadDir returns all the DirEntry records remaining in the directory. When it succeeds, it returns a nil error (not io.EOF).
 */
 func (f *S3File) Readdir(count int) ([]fs.FileInfo, error) {
-	if count > 0 {
+	if f.Path.Class == ROOT {
-		return nil, errors.New("returning a limited number of directory entry is not supported in readdir")
-	}
-
-	if f.path.class == ROOT {
 		return f.readDirRoot(count)
 	} else {
 		return f.readDirChild(count)
 	}
 }
 
-func (f *S3File) readDirRoot(count int) ([]fs.FileInfo, error) {
+func min(a, b int64) int64 {
-	buckets, err := f.fs.mc.ListBuckets(f.fs.ctx)
+    if a < b {
-	if err != nil {
+        return a
-		return nil, err
+    }
-	}
+    return b
+}
 
-	entries := make([]fs.FileInfo, 0, len(buckets))
+func (f *S3File) readDirRoot(count int) ([]fs.FileInfo, error) {
-	for _, bucket := range buckets {
+	var err error
-		//log.Println("Stat from GarageFile.readDirRoot()", "/"+bucket.Name)
+	if f.entries == nil {
-		nf, err := NewS3Stat(f.fs, "/"+bucket.Name)
+		buckets, err := f.fs.mc.ListBuckets(f.fs.ctx)
 		if err != nil {
 			return nil, err
 		}
-		entries = append(entries, nf)
+
+		f.entries = make([]fs.FileInfo, 0, len(buckets))
+		for _, bucket := range buckets {
+			//log.Println("Stat from GarageFile.readDirRoot()", "/"+bucket.Name)
+			nf, err := NewS3Stat(f.fs, "/"+bucket.Name)
+			if err != nil {
+				return nil, err
+			}
+			f.entries = append(f.entries, nf)
+		}
+	}
+	beg := f.pos
+	end := int64(len(f.entries))
+	if count > 0 {
+		end = min(beg + int64(count), end)
+	}
+	f.pos = end
+
+	if end - beg == 0 {
+		err = io.EOF
 	}
 
-	return entries, nil
+	return f.entries[beg:end], err
 }
 
 func (f *S3File) readDirChild(count int) ([]fs.FileInfo, error) {
-	prefix := f.path.key
+	prefix := f.Path.Key
 	if len(prefix) > 0 && prefix[len(prefix)-1:] != "/" {
 		prefix = prefix + "/"
 	}
 
-	objs_info := f.fs.mc.ListObjects(f.fs.ctx, f.path.bucket, minio.ListObjectsOptions{
+	objs_info := f.fs.mc.ListObjects(f.fs.ctx, f.Path.Bucket, minio.ListObjectsOptions{
 		Prefix:    prefix,
 		Recursive: false,
 	})
@@ -180,7 +210,7 @@ func (f *S3File) readDirChild(count int) ([]fs.FileInfo, error) {
 			return nil, object.Err
 		}
 		//log.Println("Stat from GarageFile.readDirChild()", path.Join("/", f.path.bucket, object.Key))
-		nf, err := NewS3StatFromObjectInfo(f.fs, f.path.bucket, object)
+		nf, err := NewS3StatFromObjectInfo(f.fs, f.Path.Bucket, object)
 		if err != nil {
 			return nil, err
 		}
@@ -191,5 +221,5 @@ func (f *S3File) readDirChild(count int) ([]fs.FileInfo, error) {
 }
 
 func (f *S3File) Stat() (fs.FileInfo, error) {
-	return NewS3Stat(f.fs, f.path.path)
+	return NewS3Stat(f.fs, f.Path.Path)
 }

s3/fs.go

@@ -1,4 +1,4 @@
-package main
+package s3
 
 import (
 	"context"
@@ -37,9 +37,9 @@ func (s S3FS) Mkdir(ctx context.Context, name string, perm os.FileMode) error {
 
 	p := NewS3Path(name)
 
-	if p.class == ROOT {
+	if p.Class == ROOT {
 		return errors.New("Unable to create another root folder")
-	} else if p.class == BUCKET {
+	} else if p.Class == BUCKET {
 		log.Println("Creating bucket is not implemented yet")
 		return nil
 	}
@@ -54,7 +54,7 @@ func (s S3FS) Mkdir(ctx context.Context, name string, perm os.FileMode) error {
 	return nil
 }
 
-func (s S3FS) OpenFile(ctx context.Context, name string, flag int, perm os.FileMode) (webdav.File, error) {
+func (s S3FS) OpenFile2(ctx context.Context, name string, flag int, perm os.FileMode) (*S3File, error) {
 	s.ctx = ctx
 
 	// If the file does not exist when opening it, we create a stub
@@ -62,8 +62,8 @@ func (s S3FS) OpenFile(ctx context.Context, name string, flag int, perm os.FileM
 		st := new(S3Stat)
 		st.fs = &s
 		st.path = NewS3Path(name)
-		st.path.class = OBJECT
+		st.path.Class = OBJECT
-		st.obj.Key = st.path.key
+		st.obj.Key = st.path.Key
 		st.obj.LastModified = time.Now()
 		s.cache[name] = st
 	}
@@ -71,20 +71,24 @@ func (s S3FS) OpenFile(ctx context.Context, name string, flag int, perm os.FileM
 	return NewS3File(&s, name)
 }
 
+func (s S3FS) OpenFile(ctx context.Context, name string, flag int, perm os.FileMode) (webdav.File, error) {
+	return s.OpenFile2(ctx, name, flag, perm)
+}
+
 func (s S3FS) RemoveAll(ctx context.Context, name string) error {
 	//@FIXME nautilus deletes files one by one, at the end, it does not find its folder as it is "already deleted"
 	s.ctx = ctx
 
 	p := NewS3Path(name)
-	if p.class == ROOT {
+	if p.Class == ROOT {
 		return errors.New("Unable to create another root folder")
-	} else if p.class == BUCKET {
+	} else if p.Class == BUCKET {
 		log.Println("Deleting bucket is not implemented yet")
 		return nil
 	}
 
-	objCh := s.mc.ListObjects(s.ctx, p.bucket, minio.ListObjectsOptions{Prefix: p.key, Recursive: true})
+	objCh := s.mc.ListObjects(s.ctx, p.Bucket, minio.ListObjectsOptions{Prefix: p.Key, Recursive: true})
-	rmCh := s.mc.RemoveObjects(s.ctx, p.bucket, objCh, minio.RemoveObjectsOptions{})
+	rmCh := s.mc.RemoveObjects(s.ctx, p.Bucket, objCh, minio.RemoveObjectsOptions{})
 
 	for rErr := range rmCh {
 		return rErr.Err
@@ -98,9 +102,9 @@ func (s S3FS) Rename(ctx context.Context, oldName, newName string) error {
 
 	po := NewS3Path(oldName)
 	pn := NewS3Path(newName)
-	if po.class == ROOT || pn.class == ROOT {
+	if po.Class == ROOT || pn.Class == ROOT {
 		return errors.New("Unable to rename root folder")
-	} else if po.class == BUCKET || pn.class == BUCKET {
+	} else if po.Class == BUCKET || pn.Class == BUCKET {
 		log.Println("Moving a bucket is not implemented yet")
 		return nil
 	}
@@ -111,16 +115,16 @@ func (s S3FS) Rename(ctx context.Context, oldName, newName string) error {
 	}
 
 	//Gather all keys, copy the object, delete the original
-	objCh := s.mc.ListObjects(s.ctx, po.bucket, minio.ListObjectsOptions{Prefix: po.key, Recursive: true})
+	objCh := s.mc.ListObjects(s.ctx, po.Bucket, minio.ListObjectsOptions{Prefix: po.Key, Recursive: true})
 	for obj := range objCh {
 		src := minio.CopySrcOptions{
-			Bucket: po.bucket,
+			Bucket: po.Bucket,
 			Object: obj.Key,
 		}
 
 		dst := minio.CopyDestOptions{
-			Bucket: pn.bucket,
+			Bucket: pn.Bucket,
-			Object: path.Join(pn.key, obj.Key[len(po.key):]),
+			Object: path.Join(pn.Key, obj.Key[len(po.Key):]),
 		}
 
 		_, err := s.mc.CopyObject(s.ctx, dst, src)
@@ -128,7 +132,7 @@ func (s S3FS) Rename(ctx context.Context, oldName, newName string) error {
 			return err
 		}
 
-		err = s.mc.RemoveObject(s.ctx, po.bucket, obj.Key, minio.RemoveObjectOptions{})
+		err = s.mc.RemoveObject(s.ctx, po.Bucket, obj.Key, minio.RemoveObjectOptions{})
 		var e minio.ErrorResponse
 		log.Println(errors.As(err, &e))
 		log.Println(e)

s3/path.go

@@ -0,0 +1,68 @@
+package s3
+
+import (
+	"path"
+	"strings"
+
+	"github.com/minio/minio-go/v7"
+)
+
+type S3Class int
+
+const (
+	ROOT S3Class = 1 << iota
+	BUCKET
+	COMMON_PREFIX
+	OBJECT
+	OPAQUE_KEY
+
+	KEY = COMMON_PREFIX | OBJECT | OPAQUE_KEY
+)
+
+type S3Path struct {
+	Path   string
+	Class  S3Class
+	Bucket string
+	Key    string
+}
+
+func NewS3Path(p string) S3Path {
+	// Remove first dot, eq. relative directory == "/"
+	if len(p) > 0 && p[0] == '.' {
+		p = p[1:]
+	}
+
+	// Add the first slash if missing
+	p = "/" + p
+
+	// Clean path using golang tools
+	p = path.Clean(p)
+
+	exploded_path := strings.SplitN(p, "/", 3)
+
+	// If there is no bucket name (eg. "/")
+	if len(exploded_path) < 2 || exploded_path[1] == "" {
+		return S3Path{p, ROOT, "", ""}
+	}
+
+	// If there is no key
+	if len(exploded_path) < 3 || exploded_path[2] == "" {
+		return S3Path{p, BUCKET, exploded_path[1], ""}
+	}
+
+	return S3Path{p, OPAQUE_KEY, exploded_path[1], exploded_path[2]}
+}
+
+func NewTrustedS3Path(bucket string, obj minio.ObjectInfo) S3Path {
+	cl := OBJECT
+	if obj.Key[len(obj.Key)-1:] == "/" {
+		cl = COMMON_PREFIX
+	}
+
+	return S3Path{
+		Path:   path.Join("/", bucket, obj.Key),
+		Bucket: bucket,
+		Key:    obj.Key,
+		Class:  cl,
+	}
+}

s3/stat.go

@@ -1,4 +1,4 @@
-package main
+package s3
 
 import (
 	"errors"
@@ -24,7 +24,7 @@ func NewS3StatFromObjectInfo(fs *S3FS, bucket string, obj minio.ObjectInfo) (*S3
 	s.obj = obj
 	s.fs = fs
 
-	fs.cache[s.path.path] = s
+	fs.cache[s.path.Path] = s
 	return s, nil
 }
 
@@ -44,30 +44,30 @@ func NewS3Stat(fs *S3FS, path string) (*S3Stat, error) {
 		return nil, err
 	}
 
-	if s.path.class&OPAQUE_KEY != 0 {
+	if s.path.Class&OPAQUE_KEY != 0 {
 		return nil, errors.New("Failed to precisely determine the key type, this a logic error.")
 	}
 
 	cache[path] = s
-	cache[s.path.path] = s
+	cache[s.path.Path] = s
 	return s, nil
 }
 
 func (s *S3Stat) Refresh() error {
-	if s.path.class == ROOT || s.path.class == BUCKET {
+	if s.path.Class == ROOT || s.path.Class == BUCKET {
 		return nil
 	}
 
 	mc := s.fs.mc
 
 	// Compute the prefix to have the desired behaviour for our stat logic
-	prefix := s.path.key
+	prefix := s.path.Key
 	if prefix[len(prefix)-1:] == "/" {
 		prefix = prefix[:len(prefix)-1]
 	}
 
 	// Get info and check if the key exists
-	objs_info := mc.ListObjects(s.fs.ctx, s.path.bucket, minio.ListObjectsOptions{
+	objs_info := mc.ListObjects(s.fs.ctx, s.path.Bucket, minio.ListObjectsOptions{
 		Prefix:    prefix,
 		Recursive: false,
 	})
@@ -80,7 +80,7 @@ func (s *S3Stat) Refresh() error {
 
 		if object.Key == prefix || object.Key == prefix+"/" {
 			s.obj = object
-			s.path = NewTrustedS3Path(s.path.bucket, object)
+			s.path = NewTrustedS3Path(s.path.Bucket, object)
 			found = true
 			break
 		}
@@ -94,12 +94,12 @@ func (s *S3Stat) Refresh() error {
 }
 
 func (s *S3Stat) Name() string {
-	if s.path.class == ROOT {
+	if s.path.Class == ROOT {
 		return "/"
-	} else if s.path.class == BUCKET {
+	} else if s.path.Class == BUCKET {
-		return s.path.bucket
+		return s.path.Bucket
 	} else {
-		return path.Base(s.path.key)
+		return path.Base(s.path.Key)
 	}
 }
 
@@ -108,7 +108,7 @@ func (s *S3Stat) Size() int64 {
 }
 
 func (s *S3Stat) Mode() fs.FileMode {
-	if s.path.class == OBJECT {
+	if s.path.Class == OBJECT {
 		return fs.ModePerm
 	} else {
 		return fs.ModeDir | fs.ModePerm
@@ -120,7 +120,7 @@ func (s *S3Stat) ModTime() time.Time {
 }
 
 func (s *S3Stat) IsDir() bool {
-	return s.path.class != OBJECT
+	return s.path.Class != OBJECT
 }
 
 func (s *S3Stat) Sys() interface{} {

s3_path.go

@@ -1,57 +0,0 @@
-package main
-
-import (
-	"path"
-	"strings"
-
-	"github.com/minio/minio-go/v7"
-)
-
-type S3Class int
-
-const (
-	ROOT S3Class = 1 << iota
-	BUCKET
-	COMMON_PREFIX
-	OBJECT
-	OPAQUE_KEY
-
-	KEY = COMMON_PREFIX | OBJECT | OPAQUE_KEY
-)
-
-type S3Path struct {
-	path   string
-	class  S3Class
-	bucket string
-	key    string
-}
-
-func NewS3Path(path string) S3Path {
-	exploded_path := strings.SplitN(path, "/", 3)
-
-	// If there is no bucket name (eg. "/")
-	if len(exploded_path) < 2 || exploded_path[1] == "" {
-		return S3Path{path, ROOT, "", ""}
-	}
-
-	// If there is no key
-	if len(exploded_path) < 3 || exploded_path[2] == "" {
-		return S3Path{path, BUCKET, exploded_path[1], ""}
-	}
-
-	return S3Path{path, OPAQUE_KEY, exploded_path[1], exploded_path[2]}
-}
-
-func NewTrustedS3Path(bucket string, obj minio.ObjectInfo) S3Path {
-	cl := OBJECT
-	if obj.Key[len(obj.Key)-1:] == "/" {
-		cl = COMMON_PREFIX
-	}
-
-	return S3Path{
-		path:   path.Join("/", bucket, obj.Key),
-		bucket: bucket,
-		key:    obj.Key,
-		class:  cl,
-	}
-}

sftp/allocator.go

@@ -0,0 +1,101 @@
+package sftp
+
+/*
+  Imported from: https://github.com/pkg/sftp
+ */
+
+import (
+	"sync"
+)
+
+type allocator struct {
+	sync.Mutex
+	available [][]byte
+	// map key is the request order
+	used map[uint32][][]byte
+}
+
+func newAllocator() *allocator {
+	return &allocator{
+		// micro optimization: initialize available pages with an initial capacity
+		available: make([][]byte, 0, SftpServerWorkerCount*2),
+		used:      make(map[uint32][][]byte),
+	}
+}
+
+// GetPage returns a previously allocated and unused []byte or create a new one.
+// The slice have a fixed size = maxMsgLength, this value is suitable for both
+// receiving new packets and reading the files to serve
+func (a *allocator) GetPage(requestOrderID uint32) []byte {
+	a.Lock()
+	defer a.Unlock()
+
+	var result []byte
+
+	// get an available page and remove it from the available ones.
+	if len(a.available) > 0 {
+		truncLength := len(a.available) - 1
+		result = a.available[truncLength]
+
+		a.available[truncLength] = nil          // clear out the internal pointer
+		a.available = a.available[:truncLength] // truncate the slice
+	}
+
+	// no preallocated slice found, just allocate a new one
+	if result == nil {
+		result = make([]byte, maxMsgLength)
+	}
+
+	// put result in used pages
+	a.used[requestOrderID] = append(a.used[requestOrderID], result)
+
+	return result
+}
+
+// ReleasePages marks unused all pages in use for the given requestID
+func (a *allocator) ReleasePages(requestOrderID uint32) {
+	a.Lock()
+	defer a.Unlock()
+
+	if used := a.used[requestOrderID]; len(used) > 0 {
+		a.available = append(a.available, used...)
+	}
+	delete(a.used, requestOrderID)
+}
+
+// Free removes all the used and available pages.
+// Call this method when the allocator is not needed anymore
+func (a *allocator) Free() {
+	a.Lock()
+	defer a.Unlock()
+
+	a.available = nil
+	a.used = make(map[uint32][][]byte)
+}
+
+func (a *allocator) countUsedPages() int {
+	a.Lock()
+	defer a.Unlock()
+
+	num := 0
+	for _, p := range a.used {
+		num += len(p)
+	}
+	return num
+}
+
+func (a *allocator) countAvailablePages() int {
+	a.Lock()
+	defer a.Unlock()
+
+	return len(a.available)
+}
+
+func (a *allocator) isRequestOrderIDUsed(requestOrderID uint32) bool {
+	a.Lock()
+	defer a.Unlock()
+
+	_, ok := a.used[requestOrderID]
+	return ok
+}
+

sftp/attrs.go

@@ -0,0 +1,90 @@
+package sftp
+
+// ssh_FXP_ATTRS support
+// see http://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-5
+
+import (
+	"os"
+	"time"
+)
+
+const (
+	sshFileXferAttrSize        = 0x00000001
+	sshFileXferAttrUIDGID      = 0x00000002
+	sshFileXferAttrPermissions = 0x00000004
+	sshFileXferAttrACmodTime   = 0x00000008
+	sshFileXferAttrExtended    = 0x80000000
+
+	sshFileXferAttrAll = sshFileXferAttrSize | sshFileXferAttrUIDGID | sshFileXferAttrPermissions |
+		sshFileXferAttrACmodTime | sshFileXferAttrExtended
+)
+
+// fileInfo is an artificial type designed to satisfy os.FileInfo.
+type fileInfo struct {
+	name string
+	stat *FileStat
+}
+
+// Name returns the base name of the file.
+func (fi *fileInfo) Name() string { return fi.name }
+
+// Size returns the length in bytes for regular files; system-dependent for others.
+func (fi *fileInfo) Size() int64 { return int64(fi.stat.Size) }
+
+// Mode returns file mode bits.
+func (fi *fileInfo) Mode() os.FileMode { return toFileMode(fi.stat.Mode) }
+
+// ModTime returns the last modification time of the file.
+func (fi *fileInfo) ModTime() time.Time { return time.Unix(int64(fi.stat.Mtime), 0) }
+
+// IsDir returns true if the file is a directory.
+func (fi *fileInfo) IsDir() bool { return fi.Mode().IsDir() }
+
+func (fi *fileInfo) Sys() interface{} { return fi.stat }
+
+// FileStat holds the original unmarshalled values from a call to READDIR or
+// *STAT. It is exported for the purposes of accessing the raw values via
+// os.FileInfo.Sys(). It is also used server side to store the unmarshalled
+// values for SetStat.
+type FileStat struct {
+	Size     uint64
+	Mode     uint32
+	Mtime    uint32
+	Atime    uint32
+	UID      uint32
+	GID      uint32
+	Extended []StatExtended
+}
+
+// StatExtended contains additional, extended information for a FileStat.
+type StatExtended struct {
+	ExtType string
+	ExtData string
+}
+
+func fileInfoFromStat(stat *FileStat, name string) os.FileInfo {
+	return &fileInfo{
+		name: name,
+		stat: stat,
+	}
+}
+
+func fileStatFromInfo(fi os.FileInfo) (uint32, *FileStat) {
+	mtime := fi.ModTime().Unix()
+	atime := mtime
+	var flags uint32 = sshFileXferAttrSize |
+		sshFileXferAttrPermissions |
+		sshFileXferAttrACmodTime
+
+	fileStat := &FileStat{
+		Size:  uint64(fi.Size()),
+		Mode:  fromFileMode(fi.Mode()),
+		Mtime: uint32(mtime),
+		Atime: uint32(atime),
+	}
+
+	// os specific file stat decoding
+	fileStatFromInfoOs(fi, &flags, fileStat)
+
+	return flags, fileStat
+}

sftp/attrs_stubs.go

@@ -0,0 +1,11 @@
+// +build plan9 windows android
+
+package sftp
+
+import (
+	"os"
+)
+
+func fileStatFromInfoOs(fi os.FileInfo, flags *uint32, fileStat *FileStat) {
+	// todo
+}

sftp/attrs_unix.go

@@ -0,0 +1,16 @@
+// +build darwin dragonfly freebsd !android,linux netbsd openbsd solaris aix js
+
+package sftp
+
+import (
+	"os"
+	"syscall"
+)
+
+func fileStatFromInfoOs(fi os.FileInfo, flags *uint32, fileStat *FileStat) {
+	if statt, ok := fi.Sys().(*syscall.Stat_t); ok {
+		*flags |= sshFileXferAttrUIDGID
+		fileStat.UID = statt.Uid
+		fileStat.GID = statt.Gid
+	}
+}

sftp/conn.go

@@ -0,0 +1,189 @@
+package sftp
+
+import (
+	"encoding"
+	"fmt"
+	"io"
+	"sync"
+)
+
+// conn implements a bidirectional channel on which client and server
+// connections are multiplexed.
+type conn struct {
+	io.Reader
+	io.WriteCloser
+	// this is the same allocator used in packet manager
+	alloc      *allocator
+	sync.Mutex // used to serialise writes to sendPacket
+}
+
+// the orderID is used in server mode if the allocator is enabled.
+// For the client mode just pass 0
+func (c *conn) recvPacket(orderID uint32) (uint8, []byte, error) {
+	return recvPacket(c, c.alloc, orderID)
+}
+
+func (c *conn) sendPacket(m encoding.BinaryMarshaler) error {
+	c.Lock()
+	defer c.Unlock()
+
+	return sendPacket(c, m)
+}
+
+func (c *conn) Close() error {
+	c.Lock()
+	defer c.Unlock()
+	return c.WriteCloser.Close()
+}
+
+type clientConn struct {
+	conn
+	wg sync.WaitGroup
+
+	sync.Mutex                          // protects inflight
+	inflight   map[uint32]chan<- result // outstanding requests
+
+	closed chan struct{}
+	err    error
+}
+
+// Wait blocks until the conn has shut down, and return the error
+// causing the shutdown. It can be called concurrently from multiple
+// goroutines.
+func (c *clientConn) Wait() error {
+	<-c.closed
+	return c.err
+}
+
+// Close closes the SFTP session.
+func (c *clientConn) Close() error {
+	defer c.wg.Wait()
+	return c.conn.Close()
+}
+
+func (c *clientConn) loop() {
+	defer c.wg.Done()
+	err := c.recv()
+	if err != nil {
+		c.broadcastErr(err)
+	}
+}
+
+// recv continuously reads from the server and forwards responses to the
+// appropriate channel.
+func (c *clientConn) recv() error {
+	defer c.conn.Close()
+
+	for {
+		typ, data, err := c.recvPacket(0)
+		if err != nil {
+			return err
+		}
+		sid, _, err := unmarshalUint32Safe(data)
+		if err != nil {
+			return err
+		}
+
+		ch, ok := c.getChannel(sid)
+		if !ok {
+			// This is an unexpected occurrence. Send the error
+			// back to all listeners so that they terminate
+			// gracefully.
+			return fmt.Errorf("sid not found: %d", sid)
+		}
+
+		ch <- result{typ: typ, data: data}
+	}
+}
+
+func (c *clientConn) putChannel(ch chan<- result, sid uint32) bool {
+	c.Lock()
+	defer c.Unlock()
+
+	select {
+	case <-c.closed:
+		// already closed with broadcastErr, return error on chan.
+		ch <- result{err: ErrSSHFxConnectionLost}
+		return false
+	default:
+	}
+
+	c.inflight[sid] = ch
+	return true
+}
+
+func (c *clientConn) getChannel(sid uint32) (chan<- result, bool) {
+	c.Lock()
+	defer c.Unlock()
+
+	ch, ok := c.inflight[sid]
+	delete(c.inflight, sid)
+
+	return ch, ok
+}
+
+// result captures the result of receiving the a packet from the server
+type result struct {
+	typ  byte
+	data []byte
+	err  error
+}
+
+type idmarshaler interface {
+	id() uint32
+	encoding.BinaryMarshaler
+}
+
+func (c *clientConn) sendPacket(ch chan result, p idmarshaler) (byte, []byte, error) {
+	if cap(ch) < 1 {
+		ch = make(chan result, 1)
+	}
+
+	c.dispatchRequest(ch, p)
+	s := <-ch
+	return s.typ, s.data, s.err
+}
+
+// dispatchRequest should ideally only be called by race-detection tests outside of this file,
+// where you have to ensure two packets are in flight sequentially after each other.
+func (c *clientConn) dispatchRequest(ch chan<- result, p idmarshaler) {
+	sid := p.id()
+
+	if !c.putChannel(ch, sid) {
+		// already closed.
+		return
+	}
+
+	if err := c.conn.sendPacket(p); err != nil {
+		if ch, ok := c.getChannel(sid); ok {
+			ch <- result{err: err}
+		}
+	}
+}
+
+// broadcastErr sends an error to all goroutines waiting for a response.
+func (c *clientConn) broadcastErr(err error) {
+	c.Lock()
+	defer c.Unlock()
+
+	bcastRes := result{err: ErrSSHFxConnectionLost}
+	for sid, ch := range c.inflight {
+		ch <- bcastRes
+
+		// Replace the chan in inflight,
+		// we have hijacked this chan,
+		// and this guarantees always-only-once sending.
+		c.inflight[sid] = make(chan<- result, 1)
+	}
+
+	c.err = err
+	close(c.closed)
+}
+
+type serverConn struct {
+	conn
+}
+
+func (s *serverConn) sendError(id uint32, err error) error {
+	return s.sendPacket(statusFromError(id, err))
+}

sftp/debug.go

@@ -0,0 +1,9 @@
+// +build debug
+
+package sftp
+
+import "log"
+
+func debug(fmt string, args ...interface{}) {
+	log.Printf(fmt, args...)
+}

sftp/ls_formatting.go

@@ -0,0 +1,81 @@
+package sftp
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"os/user"
+	"strconv"
+	"time"
+
+	sshfx "git.deuxfleurs.fr/Deuxfleurs/bagage/internal/encoding/ssh/filexfer"
+)
+
+func lsFormatID(id uint32) string {
+	return strconv.FormatUint(uint64(id), 10)
+}
+
+type osIDLookup struct{}
+
+func (osIDLookup) Filelist(*Request) (ListerAt, error) {
+	return nil, errors.New("unimplemented stub")
+}
+
+func (osIDLookup) LookupUserName(uid string) string {
+	u, err := user.LookupId(uid)
+	if err != nil {
+		return uid
+	}
+
+	return u.Username
+}
+
+func (osIDLookup) LookupGroupName(gid string) string {
+	g, err := user.LookupGroupId(gid)
+	if err != nil {
+		return gid
+	}
+
+	return g.Name
+}
+
+// runLs formats the FileInfo as per `ls -l` style, which is in the 'longname' field of a SSH_FXP_NAME entry.
+// This is a fairly simple implementation, just enough to look close to openssh in simple cases.
+func runLs(idLookup NameLookupFileLister, dirent os.FileInfo) string {
+	// example from openssh sftp server:
+	// crw-rw-rw-    1 root     wheel           0 Jul 31 20:52 ttyvd
+	// format:
+	// {directory / char device / etc}{rwxrwxrwx}  {number of links} owner group size month day [time (this year) | year (otherwise)] name
+
+	symPerms := sshfx.FileMode(fromFileMode(dirent.Mode())).String()
+
+	var numLinks uint64 = 1
+	uid, gid := "0", "0"
+
+	switch sys := dirent.Sys().(type) {
+	case *sshfx.Attributes:
+		uid = lsFormatID(sys.UID)
+		gid = lsFormatID(sys.GID)
+	case *FileStat:
+		uid = lsFormatID(sys.UID)
+		gid = lsFormatID(sys.GID)
+	default:
+		numLinks, uid, gid = lsLinksUIDGID(dirent)
+	}
+
+	if idLookup != nil {
+		uid, gid = idLookup.LookupUserName(uid), idLookup.LookupGroupName(gid)
+	}
+
+	mtime := dirent.ModTime()
+	date := mtime.Format("Jan 2")
+
+	var yearOrTime string
+	if mtime.Before(time.Now().AddDate(0, -6, 0)) {
+		yearOrTime = mtime.Format("2006")
+	} else {
+		yearOrTime = mtime.Format("15:04")
+	}
+
+	return fmt.Sprintf("%s %4d %-8s %-8s %8d %s %5s %s", symPerms, numLinks, uid, gid, dirent.Size(), date, yearOrTime, dirent.Name())
+}

sftp/ls_plan9.go

@@ -0,0 +1,21 @@
+// +build plan9
+
+package sftp
+
+import (
+	"os"
+	"syscall"
+)
+
+func lsLinksUIDGID(fi os.FileInfo) (numLinks uint64, uid, gid string) {
+	numLinks = 1
+	uid, gid = "0", "0"
+
+	switch sys := fi.Sys().(type) {
+	case *syscall.Dir:
+		uid = sys.Uid
+		gid = sys.Gid
+	}
+
+	return numLinks, uid, gid
+}

sftp/ls_stub.go

@@ -0,0 +1,11 @@
+// +build windows android
+
+package sftp
+
+import (
+	"os"
+)
+
+func lsLinksUIDGID(fi os.FileInfo) (numLinks uint64, uid, gid string) {
+	return 1, "0", "0"
+}

sftp/ls_unix.go

@@ -0,0 +1,23 @@
+// +build aix darwin dragonfly freebsd !android,linux netbsd openbsd solaris js
+
+package sftp
+
+import (
+	"os"
+	"syscall"
+)
+
+func lsLinksUIDGID(fi os.FileInfo) (numLinks uint64, uid, gid string) {
+	numLinks = 1
+	uid, gid = "0", "0"
+
+	switch sys := fi.Sys().(type) {
+	case *syscall.Stat_t:
+		numLinks = uint64(sys.Nlink)
+		uid = lsFormatID(sys.Uid)
+		gid = lsFormatID(sys.Gid)
+	default:
+	}
+
+	return numLinks, uid, gid
+}

sftp/packet_manager.go

@@ -0,0 +1,221 @@
+package sftp
+
+/*
+  Imported from: https://github.com/pkg/sftp
+ */
+
+import (
+	"encoding"
+	"sort"
+	"sync"
+)
+
+// The goal of the packetManager is to keep the outgoing packets in the same
+// order as the incoming as is requires by section 7 of the RFC.
+
+type packetManager struct {
+	requests    chan orderedPacket
+	responses   chan orderedPacket
+	fini        chan struct{}
+	incoming    orderedPackets
+	outgoing    orderedPackets
+	sender      packetSender // connection object
+	working     *sync.WaitGroup
+	packetCount uint32
+	// it is not nil if the allocator is enabled
+	alloc *allocator
+}
+
+type packetSender interface {
+	sendPacket(encoding.BinaryMarshaler) error
+}
+
+func newPktMgr(sender packetSender) *packetManager {
+	s := &packetManager{
+		requests:  make(chan orderedPacket, SftpServerWorkerCount),
+		responses: make(chan orderedPacket, SftpServerWorkerCount),
+		fini:      make(chan struct{}),
+		incoming:  make([]orderedPacket, 0, SftpServerWorkerCount),
+		outgoing:  make([]orderedPacket, 0, SftpServerWorkerCount),
+		sender:    sender,
+		working:   &sync.WaitGroup{},
+	}
+	go s.controller()
+	return s
+}
+
+//// packet ordering
+func (s *packetManager) newOrderID() uint32 {
+	s.packetCount++
+	return s.packetCount
+}
+
+// returns the next orderID without incrementing it.
+// This is used before receiving a new packet, with the allocator enabled, to associate
+// the slice allocated for the received packet with the orderID that will be used to mark
+// the allocated slices for reuse once the request is served
+func (s *packetManager) getNextOrderID() uint32 {
+	return s.packetCount + 1
+}
+
+type orderedRequest struct {
+	requestPacket
+	orderid uint32
+}
+
+func (s *packetManager) newOrderedRequest(p requestPacket) orderedRequest {
+	return orderedRequest{requestPacket: p, orderid: s.newOrderID()}
+}
+func (p orderedRequest) orderID() uint32       { return p.orderid }
+func (p orderedRequest) setOrderID(oid uint32) { p.orderid = oid }
+
+type orderedResponse struct {
+	responsePacket
+	orderid uint32
+}
+
+func (s *packetManager) newOrderedResponse(p responsePacket, id uint32,
+) orderedResponse {
+	return orderedResponse{responsePacket: p, orderid: id}
+}
+func (p orderedResponse) orderID() uint32       { return p.orderid }
+func (p orderedResponse) setOrderID(oid uint32) { p.orderid = oid }
+
+type orderedPacket interface {
+	id() uint32
+	orderID() uint32
+}
+type orderedPackets []orderedPacket
+
+func (o orderedPackets) Sort() {
+	sort.Slice(o, func(i, j int) bool {
+		return o[i].orderID() < o[j].orderID()
+	})
+}
+
+//// packet registry
+// register incoming packets to be handled
+func (s *packetManager) incomingPacket(pkt orderedRequest) {
+	s.working.Add(1)
+	s.requests <- pkt
+}
+
+// register outgoing packets as being ready
+func (s *packetManager) readyPacket(pkt orderedResponse) {
+	s.responses <- pkt
+	s.working.Done()
+}
+
+// shut down packetManager controller
+func (s *packetManager) close() {
+	// pause until current packets are processed
+	s.working.Wait()
+	close(s.fini)
+}
+
+// Passed a worker function, returns a channel for incoming packets.
+// Keep process packet responses in the order they are received while
+// maximizing throughput of file transfers.
+func (s *packetManager) workerChan(runWorker func(chan orderedRequest),
+) chan orderedRequest {
+	// multiple workers for faster read/writes
+	rwChan := make(chan orderedRequest, SftpServerWorkerCount)
+	for i := 0; i < SftpServerWorkerCount; i++ {
+		runWorker(rwChan)
+	}
+
+	// single worker to enforce sequential processing of everything else
+	cmdChan := make(chan orderedRequest)
+	runWorker(cmdChan)
+
+	pktChan := make(chan orderedRequest, SftpServerWorkerCount)
+	go func() {
+		for pkt := range pktChan {
+			switch pkt.requestPacket.(type) {
+			case *sshFxpReadPacket, *sshFxpWritePacket:
+				s.incomingPacket(pkt)
+				rwChan <- pkt
+				continue
+			case *sshFxpClosePacket:
+				// wait for reads/writes to finish when file is closed
+				// incomingPacket() call must occur after this
+				s.working.Wait()
+			}
+			s.incomingPacket(pkt)
+			// all non-RW use sequential cmdChan
+			cmdChan <- pkt
+		}
+		close(rwChan)
+		close(cmdChan)
+		s.close()
+	}()
+
+	return pktChan
+}
+
+// process packets
+func (s *packetManager) controller() {
+	for {
+		select {
+		case pkt := <-s.requests:
+			debug("incoming id (oid): %v (%v)", pkt.id(), pkt.orderID())
+			s.incoming = append(s.incoming, pkt)
+			s.incoming.Sort()
+		case pkt := <-s.responses:
+			debug("outgoing id (oid): %v (%v)", pkt.id(), pkt.orderID())
+			s.outgoing = append(s.outgoing, pkt)
+			s.outgoing.Sort()
+		case <-s.fini:
+			return
+		}
+		s.maybeSendPackets()
+	}
+}
+
+// send as many packets as are ready
+func (s *packetManager) maybeSendPackets() {
+	for {
+		if len(s.outgoing) == 0 || len(s.incoming) == 0 {
+			debug("break! -- outgoing: %v; incoming: %v",
+				len(s.outgoing), len(s.incoming))
+			break
+		}
+		out := s.outgoing[0]
+		in := s.incoming[0]
+		// debug("incoming: %v", ids(s.incoming))
+		// debug("outgoing: %v", ids(s.outgoing))
+		if in.orderID() == out.orderID() {
+			debug("Sending packet: %v", out.id())
+			s.sender.sendPacket(out.(encoding.BinaryMarshaler))
+			if s.alloc != nil {
+				// mark for reuse the slices allocated for this request
+				s.alloc.ReleasePages(in.orderID())
+			}
+			// pop off heads
+			copy(s.incoming, s.incoming[1:])            // shift left
+			s.incoming[len(s.incoming)-1] = nil         // clear last
+			s.incoming = s.incoming[:len(s.incoming)-1] // remove last
+			copy(s.outgoing, s.outgoing[1:])            // shift left
+			s.outgoing[len(s.outgoing)-1] = nil         // clear last
+			s.outgoing = s.outgoing[:len(s.outgoing)-1] // remove last
+		} else {
+			break
+		}
+	}
+}
+
+// func oids(o []orderedPacket) []uint32 {
+// 	res := make([]uint32, 0, len(o))
+// 	for _, v := range o {
+// 		res = append(res, v.orderId())
+// 	}
+// 	return res
+// }
+// func ids(o []orderedPacket) []uint32 {
+// 	res := make([]uint32, 0, len(o))
+// 	for _, v := range o {
+// 		res = append(res, v.id())
+// 	}
+// 	return res
+// }
+

sftp/packet_typing.go

@@ -0,0 +1,135 @@
+package sftp
+
+import (
+	"encoding"
+	"fmt"
+)
+
+// all incoming packets
+type requestPacket interface {
+	encoding.BinaryUnmarshaler
+	id() uint32
+}
+
+type responsePacket interface {
+	encoding.BinaryMarshaler
+	id() uint32
+}
+
+// interfaces to group types
+type hasPath interface {
+	requestPacket
+	getPath() string
+}
+
+type hasHandle interface {
+	requestPacket
+	getHandle() string
+}
+
+type notReadOnly interface {
+	notReadOnly()
+}
+
+//// define types by adding methods
+// hasPath
+func (p *sshFxpLstatPacket) getPath() string    { return p.Path }
+func (p *sshFxpStatPacket) getPath() string     { return p.Path }
+func (p *sshFxpRmdirPacket) getPath() string    { return p.Path }
+func (p *sshFxpReadlinkPacket) getPath() string { return p.Path }
+func (p *sshFxpRealpathPacket) getPath() string { return p.Path }
+func (p *sshFxpMkdirPacket) getPath() string    { return p.Path }
+func (p *sshFxpSetstatPacket) getPath() string  { return p.Path }
+func (p *sshFxpStatvfsPacket) getPath() string  { return p.Path }
+func (p *sshFxpRemovePacket) getPath() string   { return p.Filename }
+func (p *sshFxpRenamePacket) getPath() string   { return p.Oldpath }
+func (p *sshFxpSymlinkPacket) getPath() string  { return p.Targetpath }
+func (p *sshFxpOpendirPacket) getPath() string  { return p.Path }
+func (p *sshFxpOpenPacket) getPath() string     { return p.Path }
+
+func (p *sshFxpExtendedPacketPosixRename) getPath() string { return p.Oldpath }
+func (p *sshFxpExtendedPacketHardlink) getPath() string    { return p.Oldpath }
+
+// getHandle
+func (p *sshFxpFstatPacket) getHandle() string    { return p.Handle }
+func (p *sshFxpFsetstatPacket) getHandle() string { return p.Handle }
+func (p *sshFxpReadPacket) getHandle() string     { return p.Handle }
+func (p *sshFxpWritePacket) getHandle() string    { return p.Handle }
+func (p *sshFxpReaddirPacket) getHandle() string  { return p.Handle }
+func (p *sshFxpClosePacket) getHandle() string    { return p.Handle }
+
+// notReadOnly
+func (p *sshFxpWritePacket) notReadOnly()               {}
+func (p *sshFxpSetstatPacket) notReadOnly()             {}
+func (p *sshFxpFsetstatPacket) notReadOnly()            {}
+func (p *sshFxpRemovePacket) notReadOnly()              {}
+func (p *sshFxpMkdirPacket) notReadOnly()               {}
+func (p *sshFxpRmdirPacket) notReadOnly()               {}
+func (p *sshFxpRenamePacket) notReadOnly()              {}
+func (p *sshFxpSymlinkPacket) notReadOnly()             {}
+func (p *sshFxpExtendedPacketPosixRename) notReadOnly() {}
+func (p *sshFxpExtendedPacketHardlink) notReadOnly()    {}
+
+// some packets with ID are missing id()
+func (p *sshFxpDataPacket) id() uint32   { return p.ID }
+func (p *sshFxpStatusPacket) id() uint32 { return p.ID }
+func (p *sshFxpStatResponse) id() uint32 { return p.ID }
+func (p *sshFxpNamePacket) id() uint32   { return p.ID }
+func (p *sshFxpHandlePacket) id() uint32 { return p.ID }
+func (p *StatVFS) id() uint32            { return p.ID }
+func (p *sshFxVersionPacket) id() uint32 { return 0 }
+
+// take raw incoming packet data and build packet objects
+func makePacket(p rxPacket) (requestPacket, error) {
+	var pkt requestPacket
+	switch p.pktType {
+	case sshFxpInit:
+		pkt = &sshFxInitPacket{}
+	case sshFxpLstat:
+		pkt = &sshFxpLstatPacket{}
+	case sshFxpOpen:
+		pkt = &sshFxpOpenPacket{}
+	case sshFxpClose:
+		pkt = &sshFxpClosePacket{}
+	case sshFxpRead:
+		pkt = &sshFxpReadPacket{}
+	case sshFxpWrite:
+		pkt = &sshFxpWritePacket{}
+	case sshFxpFstat:
+		pkt = &sshFxpFstatPacket{}
+	case sshFxpSetstat:
+		pkt = &sshFxpSetstatPacket{}
+	case sshFxpFsetstat:
+		pkt = &sshFxpFsetstatPacket{}
+	case sshFxpOpendir:
+		pkt = &sshFxpOpendirPacket{}
+	case sshFxpReaddir:
+		pkt = &sshFxpReaddirPacket{}
+	case sshFxpRemove:
+		pkt = &sshFxpRemovePacket{}
+	case sshFxpMkdir:
+		pkt = &sshFxpMkdirPacket{}
+	case sshFxpRmdir:
+		pkt = &sshFxpRmdirPacket{}
+	case sshFxpRealpath:
+		pkt = &sshFxpRealpathPacket{}
+	case sshFxpStat:
+		pkt = &sshFxpStatPacket{}
+	case sshFxpRename:
+		pkt = &sshFxpRenamePacket{}
+	case sshFxpReadlink:
+		pkt = &sshFxpReadlinkPacket{}
+	case sshFxpSymlink:
+		pkt = &sshFxpSymlinkPacket{}
+	case sshFxpExtended:
+		pkt = &sshFxpExtendedPacket{}
+	default:
+		return nil, fmt.Errorf("unhandled packet type: %s", p.pktType)
+	}
+	if err := pkt.UnmarshalBinary(p.pktBytes); err != nil {
+		// Return partially unpacked packet to allow callers to return
+		// error messages appropriately with necessary id() method.
+		return pkt, err
+	}
+	return pkt, nil
+}

sftp/pool.go

@@ -0,0 +1,79 @@
+package sftp
+
+// bufPool provides a pool of byte-slices to be reused in various parts of the package.
+// It is safe to use concurrently through a pointer.
+type bufPool struct {
+	ch   chan []byte
+	blen int
+}
+
+func newBufPool(depth, bufLen int) *bufPool {
+	return &bufPool{
+		ch:   make(chan []byte, depth),
+		blen: bufLen,
+	}
+}
+
+func (p *bufPool) Get() []byte {
+	if p.blen <= 0 {
+		panic("bufPool: new buffer creation length must be greater than zero")
+	}
+
+	for {
+		select {
+		case b := <-p.ch:
+			if cap(b) < p.blen {
+				// just in case: throw away any buffer with insufficient capacity.
+				continue
+			}
+
+			return b[:p.blen]
+
+		default:
+			return make([]byte, p.blen)
+		}
+	}
+}
+
+func (p *bufPool) Put(b []byte) {
+	if p == nil {
+		// functional default: no reuse.
+		return
+	}
+
+	if cap(b) < p.blen || cap(b) > p.blen*2 {
+		// DO NOT reuse buffers with insufficient capacity.
+		// This could cause panics when resizing to p.blen.
+
+		// DO NOT reuse buffers with excessive capacity.
+		// This could cause memory leaks.
+		return
+	}
+
+	select {
+	case p.ch <- b:
+	default:
+	}
+}
+
+type resChanPool chan chan result
+
+func newResChanPool(depth int) resChanPool {
+	return make(chan chan result, depth)
+}
+
+func (p resChanPool) Get() chan result {
+	select {
+	case ch := <-p:
+		return ch
+	default:
+		return make(chan result, 1)
+	}
+}
+
+func (p resChanPool) Put(ch chan result) {
+	select {
+	case p <- ch:
+	default:
+	}
+}

sftp/release.go

@@ -0,0 +1,5 @@
+// +build !debug
+
+package sftp
+
+func debug(fmt string, args ...interface{}) {}

sftp/request-attrs.go

@@ -0,0 +1,63 @@
+package sftp
+
+// Methods on the Request object to make working with the Flags bitmasks and
+// Attr(ibutes) byte blob easier. Use Pflags() when working with an Open/Write
+// request and AttrFlags() and Attributes() when working with SetStat requests.
+import "os"
+
+// FileOpenFlags defines Open and Write Flags. Correlate directly with with os.OpenFile flags
+// (https://golang.org/pkg/os/#pkg-constants).
+type FileOpenFlags struct {
+	Read, Write, Append, Creat, Trunc, Excl bool
+}
+
+func newFileOpenFlags(flags uint32) FileOpenFlags {
+	return FileOpenFlags{
+		Read:   flags&sshFxfRead != 0,
+		Write:  flags&sshFxfWrite != 0,
+		Append: flags&sshFxfAppend != 0,
+		Creat:  flags&sshFxfCreat != 0,
+		Trunc:  flags&sshFxfTrunc != 0,
+		Excl:   flags&sshFxfExcl != 0,
+	}
+}
+
+// Pflags converts the bitmap/uint32 from SFTP Open packet pflag values,
+// into a FileOpenFlags struct with booleans set for flags set in bitmap.
+func (r *Request) Pflags() FileOpenFlags {
+	return newFileOpenFlags(r.Flags)
+}
+
+// FileAttrFlags that indicate whether SFTP file attributes were passed. When a flag is
+// true the corresponding attribute should be available from the FileStat
+// object returned by Attributes method. Used with SetStat.
+type FileAttrFlags struct {
+	Size, UidGid, Permissions, Acmodtime bool
+}
+
+func newFileAttrFlags(flags uint32) FileAttrFlags {
+	return FileAttrFlags{
+		Size:        (flags & sshFileXferAttrSize) != 0,
+		UidGid:      (flags & sshFileXferAttrUIDGID) != 0,
+		Permissions: (flags & sshFileXferAttrPermissions) != 0,
+		Acmodtime:   (flags & sshFileXferAttrACmodTime) != 0,
+	}
+}
+
+// AttrFlags returns a FileAttrFlags boolean struct based on the
+// bitmap/uint32 file attribute flags from the SFTP packaet.
+func (r *Request) AttrFlags() FileAttrFlags {
+	return newFileAttrFlags(r.Flags)
+}
+
+// FileMode returns the Mode SFTP file attributes wrapped as os.FileMode
+func (a FileStat) FileMode() os.FileMode {
+	return os.FileMode(a.Mode)
+}
+
+// Attributes parses file attributes byte blob and return them in a
+// FileStat object.
+func (r *Request) Attributes() *FileStat {
+	fs, _ := unmarshalFileStat(r.Flags, r.Attrs)
+	return fs
+}

sftp/request-errors.go

@@ -0,0 +1,54 @@
+package sftp
+
+type fxerr uint32
+
+// Error types that match the SFTP's SSH_FXP_STATUS codes. Gives you more
+// direct control of the errors being sent vs. letting the library work them
+// out from the standard os/io errors.
+const (
+	ErrSSHFxOk               = fxerr(sshFxOk)
+	ErrSSHFxEOF              = fxerr(sshFxEOF)
+	ErrSSHFxNoSuchFile       = fxerr(sshFxNoSuchFile)
+	ErrSSHFxPermissionDenied = fxerr(sshFxPermissionDenied)
+	ErrSSHFxFailure          = fxerr(sshFxFailure)
+	ErrSSHFxBadMessage       = fxerr(sshFxBadMessage)
+	ErrSSHFxNoConnection     = fxerr(sshFxNoConnection)
+	ErrSSHFxConnectionLost   = fxerr(sshFxConnectionLost)
+	ErrSSHFxOpUnsupported    = fxerr(sshFxOPUnsupported)
+)
+
+// Deprecated error types, these are aliases for the new ones, please use the new ones directly
+const (
+	ErrSshFxOk               = ErrSSHFxOk
+	ErrSshFxEof              = ErrSSHFxEOF
+	ErrSshFxNoSuchFile       = ErrSSHFxNoSuchFile
+	ErrSshFxPermissionDenied = ErrSSHFxPermissionDenied
+	ErrSshFxFailure          = ErrSSHFxFailure
+	ErrSshFxBadMessage       = ErrSSHFxBadMessage
+	ErrSshFxNoConnection     = ErrSSHFxNoConnection
+	ErrSshFxConnectionLost   = ErrSSHFxConnectionLost
+	ErrSshFxOpUnsupported    = ErrSSHFxOpUnsupported
+)
+
+func (e fxerr) Error() string {
+	switch e {
+	case ErrSSHFxOk:
+		return "OK"
+	case ErrSSHFxEOF:
+		return "EOF"
+	case ErrSSHFxNoSuchFile:
+		return "no such file"
+	case ErrSSHFxPermissionDenied:
+		return "permission denied"
+	case ErrSSHFxBadMessage:
+		return "bad message"
+	case ErrSSHFxNoConnection:
+		return "no connection"
+	case ErrSSHFxConnectionLost:
+		return "connection lost"
+	case ErrSSHFxOpUnsupported:
+		return "operation unsupported"
+	default:
+		return "failure"
+	}
+}

sftp/request-interfaces.go

@@ -0,0 +1,121 @@
+package sftp
+
+import (
+	"io"
+	"os"
+)
+
+// WriterAtReaderAt defines the interface to return when a file is to
+// be opened for reading and writing
+type WriterAtReaderAt interface {
+	io.WriterAt
+	io.ReaderAt
+}
+
+// Interfaces are differentiated based on required returned values.
+// All input arguments are to be pulled from Request (the only arg).
+
+// The Handler interfaces all take the Request object as its only argument.
+// All the data you should need to handle the call are in the Request object.
+// The request.Method attribute is initially the most important one as it
+// determines which Handler gets called.
+
+// FileReader should return an io.ReaderAt for the filepath
+// Note in cases of an error, the error text will be sent to the client.
+// Called for Methods: Get
+type FileReader interface {
+	Fileread(*Request) (io.ReaderAt, error)
+}
+
+// FileWriter should return an io.WriterAt for the filepath.
+//
+// The request server code will call Close() on the returned io.WriterAt
+// ojbect if an io.Closer type assertion succeeds.
+// Note in cases of an error, the error text will be sent to the client.
+// Note when receiving an Append flag it is important to not open files using
+// O_APPEND if you plan to use WriteAt, as they conflict.
+// Called for Methods: Put, Open
+type FileWriter interface {
+	Filewrite(*Request) (io.WriterAt, error)
+}
+
+// OpenFileWriter is a FileWriter that implements the generic OpenFile method.
+// You need to implement this optional interface if you want to be able
+// to read and write from/to the same handle.
+// Called for Methods: Open
+type OpenFileWriter interface {
+	FileWriter
+	OpenFile(*Request) (WriterAtReaderAt, error)
+}
+
+// FileCmder should return an error
+// Note in cases of an error, the error text will be sent to the client.
+// Called for Methods: Setstat, Rename, Rmdir, Mkdir, Link, Symlink, Remove
+type FileCmder interface {
+	Filecmd(*Request) error
+}
+
+// PosixRenameFileCmder is a FileCmder that implements the PosixRename method.
+// If this interface is implemented PosixRename requests will call it
+// otherwise they will be handled in the same way as Rename
+type PosixRenameFileCmder interface {
+	FileCmder
+	PosixRename(*Request) error
+}
+
+// StatVFSFileCmder is a FileCmder that implements the StatVFS method.
+// You need to implement this interface if you want to handle statvfs requests.
+// Please also be sure that the statvfs@openssh.com extension is enabled
+type StatVFSFileCmder interface {
+	FileCmder
+	StatVFS(*Request) (*StatVFS, error)
+}
+
+// FileLister should return an object that fulfils the ListerAt interface
+// Note in cases of an error, the error text will be sent to the client.
+// Called for Methods: List, Stat, Readlink
+type FileLister interface {
+	Filelist(*Request) (ListerAt, error)
+}
+
+// LstatFileLister is a FileLister that implements the Lstat method.
+// If this interface is implemented Lstat requests will call it
+// otherwise they will be handled in the same way as Stat
+type LstatFileLister interface {
+	FileLister
+	Lstat(*Request) (ListerAt, error)
+}
+
+// RealPathFileLister is a FileLister that implements the Realpath method.
+// We use "/" as start directory for relative paths, implementing this
+// interface you can customize the start directory.
+// You have to return an absolute POSIX path.
+type RealPathFileLister interface {
+	FileLister
+	RealPath(string) string
+}
+
+// NameLookupFileLister is a FileLister that implmeents the LookupUsername and LookupGroupName methods.
+// If this interface is implemented, then longname ls formatting will use these to convert usernames and groupnames.
+type NameLookupFileLister interface {
+	FileLister
+	LookupUserName(string) string
+	LookupGroupName(string) string
+}
+
+// ListerAt does for file lists what io.ReaderAt does for files.
+// ListAt should return the number of entries copied and an io.EOF
+// error if at end of list. This is testable by comparing how many you
+// copied to how many could be copied (eg. n < len(ls) below).
+// The copy() builtin is best for the copying.
+// Note in cases of an error, the error text will be sent to the client.
+type ListerAt interface {
+	ListAt([]os.FileInfo, int64) (int, error)
+}
+
+// TransferError is an optional interface that readerAt and writerAt
+// can implement to be notified about the error causing Serve() to exit
+// with the request still open
+type TransferError interface {
+	TransferError(err error)
+}

sftp/request-plan9.go

@@ -0,0 +1,34 @@
+// +build plan9
+
+package sftp
+
+import (
+	"path"
+	"path/filepath"
+	"syscall"
+)
+
+func fakeFileInfoSys() interface{} {
+	return &syscall.Dir{}
+}
+
+func testOsSys(sys interface{}) error {
+	return nil
+}
+
+func toLocalPath(p string) string {
+	lp := filepath.FromSlash(p)
+
+	if path.IsAbs(p) {
+		tmp := lp[1:]
+
+		if filepath.IsAbs(tmp) {
+			// If the FromSlash without any starting slashes is absolute,
+			// then we have a filepath encoded with a prefix '/'.
+			// e.g. "/#s/boot" to "#s/boot"
+			return tmp
+		}
+	}
+
+	return lp
+}

sftp/request-server.go

@@ -0,0 +1,304 @@
+package sftp
+
+import (
+	"context"
+	"errors"
+	"io"
+	"path"
+	"path/filepath"
+	"strconv"
+	"sync"
+)
+
+var maxTxPacket uint32 = 1 << 15
+
+// Handlers contains the 4 SFTP server request handlers.
+type Handlers struct {
+	FileGet  FileReader
+	FilePut  FileWriter
+	FileCmd  FileCmder
+	FileList FileLister
+}
+
+// RequestServer abstracts the sftp protocol with an http request-like protocol
+type RequestServer struct {
+	Handlers Handlers
+
+	*serverConn
+	pktMgr *packetManager
+
+	mu           sync.RWMutex
+	handleCount  int
+	openRequests map[string]*Request
+}
+
+// A RequestServerOption is a function which applies configuration to a RequestServer.
+type RequestServerOption func(*RequestServer)
+
+// WithRSAllocator enable the allocator.
+// After processing a packet we keep in memory the allocated slices
+// and we reuse them for new packets.
+// The allocator is experimental
+func WithRSAllocator() RequestServerOption {
+	return func(rs *RequestServer) {
+		alloc := newAllocator()
+		rs.pktMgr.alloc = alloc
+		rs.conn.alloc = alloc
+	}
+}
+
+// NewRequestServer creates/allocates/returns new RequestServer.
+// Normally there will be one server per user-session.
+func NewRequestServer(rwc io.ReadWriteCloser, h Handlers, options ...RequestServerOption) *RequestServer {
+	svrConn := &serverConn{
+		conn: conn{
+			Reader:      rwc,
+			WriteCloser: rwc,
+		},
+	}
+	rs := &RequestServer{
+		Handlers: h,
+
+		serverConn: svrConn,
+		pktMgr:     newPktMgr(svrConn),
+
+		openRequests: make(map[string]*Request),
+	}
+
+	for _, o := range options {
+		o(rs)
+	}
+	return rs
+}
+
+// New Open packet/Request
+func (rs *RequestServer) nextRequest(r *Request) string {
+	rs.mu.Lock()
+	defer rs.mu.Unlock()
+
+	rs.handleCount++
+
+	r.handle = strconv.Itoa(rs.handleCount)
+	rs.openRequests[r.handle] = r
+
+	return r.handle
+}
+
+// Returns Request from openRequests, bool is false if it is missing.
+//
+// The Requests in openRequests work essentially as open file descriptors that
+// you can do different things with. What you are doing with it are denoted by
+// the first packet of that type (read/write/etc).
+func (rs *RequestServer) getRequest(handle string) (*Request, bool) {
+	rs.mu.RLock()
+	defer rs.mu.RUnlock()
+
+	r, ok := rs.openRequests[handle]
+	return r, ok
+}
+
+// Close the Request and clear from openRequests map
+func (rs *RequestServer) closeRequest(handle string) error {
+	rs.mu.Lock()
+	defer rs.mu.Unlock()
+
+	if r, ok := rs.openRequests[handle]; ok {
+		delete(rs.openRequests, handle)
+		return r.close()
+	}
+
+	return EBADF
+}
+
+// Close the read/write/closer to trigger exiting the main server loop
+func (rs *RequestServer) Close() error { return rs.conn.Close() }
+
+func (rs *RequestServer) serveLoop(pktChan chan<- orderedRequest) error {
+	defer close(pktChan) // shuts down sftpServerWorkers
+
+	var err error
+	var pkt requestPacket
+	var pktType uint8
+	var pktBytes []byte
+
+	for {
+		pktType, pktBytes, err = rs.serverConn.recvPacket(rs.pktMgr.getNextOrderID())
+		if err != nil {
+			// we don't care about releasing allocated pages here, the server will quit and the allocator freed
+			return err
+		}
+
+		pkt, err = makePacket(rxPacket{fxp(pktType), pktBytes})
+		if err != nil {
+			switch {
+			case errors.Is(err, errUnknownExtendedPacket):
+				// do nothing
+			default:
+				debug("makePacket err: %v", err)
+				rs.conn.Close() // shuts down recvPacket
+				return err
+			}
+		}
+
+		pktChan <- rs.pktMgr.newOrderedRequest(pkt)
+	}
+}
+
+// Serve requests for user session
+func (rs *RequestServer) Serve() error {
+	defer func() {
+		if rs.pktMgr.alloc != nil {
+			rs.pktMgr.alloc.Free()
+		}
+	}()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var wg sync.WaitGroup
+	runWorker := func(ch chan orderedRequest) {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			if err := rs.packetWorker(ctx, ch); err != nil {
+				rs.conn.Close() // shuts down recvPacket
+			}
+		}()
+	}
+	pktChan := rs.pktMgr.workerChan(runWorker)
+
+	err := rs.serveLoop(pktChan)
+
+	wg.Wait() // wait for all workers to exit
+
+	rs.mu.Lock()
+	defer rs.mu.Unlock()
+
+	// make sure all open requests are properly closed
+	// (eg. possible on dropped connections, client crashes, etc.)
+	for handle, req := range rs.openRequests {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		req.transferError(err)
+
+		delete(rs.openRequests, handle)
+		req.close()
+	}
+
+	return err
+}
+
+func (rs *RequestServer) packetWorker(ctx context.Context, pktChan chan orderedRequest) error {
+	for pkt := range pktChan {
+		orderID := pkt.orderID()
+		if epkt, ok := pkt.requestPacket.(*sshFxpExtendedPacket); ok {
+			if epkt.SpecificPacket != nil {
+				pkt.requestPacket = epkt.SpecificPacket
+			}
+		}
+
+		var rpkt responsePacket
+		switch pkt := pkt.requestPacket.(type) {
+		case *sshFxInitPacket:
+			rpkt = &sshFxVersionPacket{Version: sftpProtocolVersion, Extensions: sftpExtensions}
+		case *sshFxpClosePacket:
+			handle := pkt.getHandle()
+			rpkt = statusFromError(pkt.ID, rs.closeRequest(handle))
+		case *sshFxpRealpathPacket:
+			var realPath string
+			if realPather, ok := rs.Handlers.FileList.(RealPathFileLister); ok {
+				realPath = realPather.RealPath(pkt.getPath())
+			} else {
+				realPath = cleanPath(pkt.getPath())
+			}
+			rpkt = cleanPacketPath(pkt, realPath)
+		case *sshFxpOpendirPacket:
+			request := requestFromPacket(ctx, pkt)
+			handle := rs.nextRequest(request)
+			rpkt = request.opendir(rs.Handlers, pkt)
+			if _, ok := rpkt.(*sshFxpHandlePacket); !ok {
+				// if we return an error we have to remove the handle from the active ones
+				rs.closeRequest(handle)
+			}
+		case *sshFxpOpenPacket:
+			request := requestFromPacket(ctx, pkt)
+			handle := rs.nextRequest(request)
+			rpkt = request.open(rs.Handlers, pkt)
+			if _, ok := rpkt.(*sshFxpHandlePacket); !ok {
+				// if we return an error we have to remove the handle from the active ones
+				rs.closeRequest(handle)
+			}
+		case *sshFxpFstatPacket:
+			handle := pkt.getHandle()
+			request, ok := rs.getRequest(handle)
+			if !ok {
+				rpkt = statusFromError(pkt.ID, EBADF)
+			} else {
+				request = NewRequest("Stat", request.Filepath)
+				rpkt = request.call(rs.Handlers, pkt, rs.pktMgr.alloc, orderID)
+			}
+		case *sshFxpFsetstatPacket:
+			handle := pkt.getHandle()
+			request, ok := rs.getRequest(handle)
+			if !ok {
+				rpkt = statusFromError(pkt.ID, EBADF)
+			} else {
+				request = NewRequest("Setstat", request.Filepath)
+				rpkt = request.call(rs.Handlers, pkt, rs.pktMgr.alloc, orderID)
+			}
+		case *sshFxpExtendedPacketPosixRename:
+			request := NewRequest("PosixRename", pkt.Oldpath)
+			request.Target = pkt.Newpath
+			rpkt = request.call(rs.Handlers, pkt, rs.pktMgr.alloc, orderID)
+		case *sshFxpExtendedPacketStatVFS:
+			request := NewRequest("StatVFS", pkt.Path)
+			rpkt = request.call(rs.Handlers, pkt, rs.pktMgr.alloc, orderID)
+		case hasHandle:
+			handle := pkt.getHandle()
+			request, ok := rs.getRequest(handle)
+			if !ok {
+				rpkt = statusFromError(pkt.id(), EBADF)
+			} else {
+				rpkt = request.call(rs.Handlers, pkt, rs.pktMgr.alloc, orderID)
+			}
+		case hasPath:
+			request := requestFromPacket(ctx, pkt)
+			rpkt = request.call(rs.Handlers, pkt, rs.pktMgr.alloc, orderID)
+			request.close()
+		default:
+			rpkt = statusFromError(pkt.id(), ErrSSHFxOpUnsupported)
+		}
+
+		rs.pktMgr.readyPacket(
+			rs.pktMgr.newOrderedResponse(rpkt, orderID))
+	}
+	return nil
+}
+
+// clean and return name packet for file
+func cleanPacketPath(pkt *sshFxpRealpathPacket, realPath string) responsePacket {
+	return &sshFxpNamePacket{
+		ID: pkt.id(),
+		NameAttrs: []*sshFxpNameAttr{
+			{
+				Name:     realPath,
+				LongName: realPath,
+				Attrs:    emptyFileStat,
+			},
+		},
+	}
+}
+
+// Makes sure we have a clean POSIX (/) absolute path to work with
+func cleanPath(p string) string {
+	return cleanPathWithBase("/", p)
+}
+
+func cleanPathWithBase(base, p string) string {
+	p = filepath.ToSlash(filepath.Clean(p))
+	if !path.IsAbs(p) {
+		return path.Join(base, p)
+	}
+	return p
+}

sftp/request-unix.go

@@ -0,0 +1,27 @@
+// +build !windows,!plan9
+
+package sftp
+
+import (
+	"errors"
+	"syscall"
+)
+
+func fakeFileInfoSys() interface{} {
+	return &syscall.Stat_t{Uid: 65534, Gid: 65534}
+}
+
+func testOsSys(sys interface{}) error {
+	fstat := sys.(*FileStat)
+	if fstat.UID != uint32(65534) {
+		return errors.New("Uid failed to match")
+	}
+	if fstat.GID != uint32(65534) {
+		return errors.New("Gid failed to match")
+	}
+	return nil
+}
+
+func toLocalPath(p string) string {
+	return p
+}

sftp/request.go

@@ -0,0 +1,628 @@
+package sftp
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"sync"
+	"syscall"
+)
+
+// MaxFilelist is the max number of files to return in a readdir batch.
+var MaxFilelist int64 = 100
+
+// state encapsulates the reader/writer/readdir from handlers.
+type state struct {
+	mu sync.RWMutex
+
+	writerAt         io.WriterAt
+	readerAt         io.ReaderAt
+	writerAtReaderAt WriterAtReaderAt
+	listerAt         ListerAt
+	lsoffset         int64
+}
+
+// copy returns a shallow copy the state.
+// This is broken out to specific fields,
+// because we have to copy around the mutex in state.
+func (s *state) copy() state {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return state{
+		writerAt:         s.writerAt,
+		readerAt:         s.readerAt,
+		writerAtReaderAt: s.writerAtReaderAt,
+		listerAt:         s.listerAt,
+		lsoffset:         s.lsoffset,
+	}
+}
+
+func (s *state) setReaderAt(rd io.ReaderAt) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.readerAt = rd
+}
+
+func (s *state) getReaderAt() io.ReaderAt {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return s.readerAt
+}
+
+func (s *state) setWriterAt(rd io.WriterAt) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.writerAt = rd
+}
+
+func (s *state) getWriterAt() io.WriterAt {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return s.writerAt
+}
+
+func (s *state) setWriterAtReaderAt(rw WriterAtReaderAt) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.writerAtReaderAt = rw
+}
+
+func (s *state) getWriterAtReaderAt() WriterAtReaderAt {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return s.writerAtReaderAt
+}
+
+func (s *state) getAllReaderWriters() (io.ReaderAt, io.WriterAt, WriterAtReaderAt) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return s.readerAt, s.writerAt, s.writerAtReaderAt
+}
+
+// Returns current offset for file list
+func (s *state) lsNext() int64 {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return s.lsoffset
+}
+
+// Increases next offset
+func (s *state) lsInc(offset int64) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.lsoffset += offset
+}
+
+// manage file read/write state
+func (s *state) setListerAt(la ListerAt) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.listerAt = la
+}
+
+func (s *state) getListerAt() ListerAt {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return s.listerAt
+}
+
+// Request contains the data and state for the incoming service request.
+type Request struct {
+	// Get, Put, Setstat, Stat, Rename, Remove
+	// Rmdir, Mkdir, List, Readlink, Link, Symlink
+	Method   string
+	Filepath string
+	Flags    uint32
+	Attrs    []byte // convert to sub-struct
+	Target   string // for renames and sym-links
+	handle   string
+
+	// reader/writer/readdir from handlers
+	state
+
+	// context lasts duration of request
+	ctx       context.Context
+	cancelCtx context.CancelFunc
+}
+
+// NewRequest creates a new Request object.
+func NewRequest(method, path string) *Request {
+	return &Request{
+		Method:   method,
+		Filepath: cleanPath(path),
+	}
+}
+
+// copy returns a shallow copy of existing request.
+// This is broken out to specific fields,
+// because we have to copy around the mutex in state.
+func (r *Request) copy() *Request {
+	return &Request{
+		Method:   r.Method,
+		Filepath: r.Filepath,
+		Flags:    r.Flags,
+		Attrs:    r.Attrs,
+		Target:   r.Target,
+		handle:   r.handle,
+
+		state: r.state.copy(),
+
+		ctx:       r.ctx,
+		cancelCtx: r.cancelCtx,
+	}
+}
+
+// New Request initialized based on packet data
+func requestFromPacket(ctx context.Context, pkt hasPath) *Request {
+	method := requestMethod(pkt)
+	request := NewRequest(method, pkt.getPath())
+	request.ctx, request.cancelCtx = context.WithCancel(ctx)
+
+	switch p := pkt.(type) {
+	case *sshFxpOpenPacket:
+		request.Flags = p.Pflags
+	case *sshFxpSetstatPacket:
+		request.Flags = p.Flags
+		request.Attrs = p.Attrs.([]byte)
+	case *sshFxpRenamePacket:
+		request.Target = cleanPath(p.Newpath)
+	case *sshFxpSymlinkPacket:
+		// NOTE: given a POSIX compliant signature: symlink(target, linkpath string)
+		// this makes Request.Target the linkpath, and Request.Filepath the target.
+		request.Target = cleanPath(p.Linkpath)
+	case *sshFxpExtendedPacketHardlink:
+		request.Target = cleanPath(p.Newpath)
+	}
+	return request
+}
+
+// Context returns the request's context. To change the context,
+// use WithContext.
+//
+// The returned context is always non-nil; it defaults to the
+// background context.
+//
+// For incoming server requests, the context is canceled when the
+// request is complete or the client's connection closes.
+func (r *Request) Context() context.Context {
+	if r.ctx != nil {
+		return r.ctx
+	}
+	return context.Background()
+}
+
+// WithContext returns a copy of r with its context changed to ctx.
+// The provided ctx must be non-nil.
+func (r *Request) WithContext(ctx context.Context) *Request {
+	if ctx == nil {
+		panic("nil context")
+	}
+	r2 := r.copy()
+	r2.ctx = ctx
+	r2.cancelCtx = nil
+	return r2
+}
+
+// Close reader/writer if possible
+func (r *Request) close() error {
+	defer func() {
+		if r.cancelCtx != nil {
+			r.cancelCtx()
+		}
+	}()
+
+	rd, wr, rw := r.getAllReaderWriters()
+
+	var err error
+
+	// Close errors on a Writer are far more likely to be the important one.
+	// As they can be information that there was a loss of data.
+	if c, ok := wr.(io.Closer); ok {
+		if err2 := c.Close(); err == nil {
+			// update error if it is still nil
+			err = err2
+		}
+	}
+
+	if c, ok := rw.(io.Closer); ok {
+		if err2 := c.Close(); err == nil {
+			// update error if it is still nil
+			err = err2
+
+			r.setWriterAtReaderAt(nil)
+		}
+	}
+
+	if c, ok := rd.(io.Closer); ok {
+		if err2 := c.Close(); err == nil {
+			// update error if it is still nil
+			err = err2
+		}
+	}
+
+	return err
+}
+
+// Notify transfer error if any
+func (r *Request) transferError(err error) {
+	if err == nil {
+		return
+	}
+
+	rd, wr, rw := r.getAllReaderWriters()
+
+	if t, ok := wr.(TransferError); ok {
+		t.TransferError(err)
+	}
+
+	if t, ok := rw.(TransferError); ok {
+		t.TransferError(err)
+	}
+
+	if t, ok := rd.(TransferError); ok {
+		t.TransferError(err)
+	}
+}
+
+// called from worker to handle packet/request
+func (r *Request) call(handlers Handlers, pkt requestPacket, alloc *allocator, orderID uint32) responsePacket {
+	switch r.Method {
+	case "Get":
+		return fileget(handlers.FileGet, r, pkt, alloc, orderID)
+	case "Put":
+		return fileput(handlers.FilePut, r, pkt, alloc, orderID)
+	case "Open":
+		return fileputget(handlers.FilePut, r, pkt, alloc, orderID)
+	case "Setstat", "Rename", "Rmdir", "Mkdir", "Link", "Symlink", "Remove", "PosixRename", "StatVFS":
+		return filecmd(handlers.FileCmd, r, pkt)
+	case "List":
+		return filelist(handlers.FileList, r, pkt)
+	case "Stat", "Lstat", "Readlink":
+		return filestat(handlers.FileList, r, pkt)
+	default:
+		return statusFromError(pkt.id(), fmt.Errorf("unexpected method: %s", r.Method))
+	}
+}
+
+// Additional initialization for Open packets
+func (r *Request) open(h Handlers, pkt requestPacket) responsePacket {
+	flags := r.Pflags()
+
+	id := pkt.id()
+
+	switch {
+	case flags.Write, flags.Append, flags.Creat, flags.Trunc:
+		if flags.Read {
+			if openFileWriter, ok := h.FilePut.(OpenFileWriter); ok {
+				r.Method = "Open"
+				rw, err := openFileWriter.OpenFile(r)
+				if err != nil {
+					return statusFromError(id, err)
+				}
+
+				r.setWriterAtReaderAt(rw)
+
+				return &sshFxpHandlePacket{
+					ID:     id,
+					Handle: r.handle,
+				}
+			}
+		}
+
+		r.Method = "Put"
+		wr, err := h.FilePut.Filewrite(r)
+		if err != nil {
+			return statusFromError(id, err)
+		}
+
+		r.setWriterAt(wr)
+
+	case flags.Read:
+		r.Method = "Get"
+		rd, err := h.FileGet.Fileread(r)
+		if err != nil {
+			return statusFromError(id, err)
+		}
+
+		r.setReaderAt(rd)
+
+	default:
+		return statusFromError(id, errors.New("bad file flags"))
+	}
+
+	return &sshFxpHandlePacket{
+		ID:     id,
+		Handle: r.handle,
+	}
+}
+
+func (r *Request) opendir(h Handlers, pkt requestPacket) responsePacket {
+	r.Method = "List"
+	la, err := h.FileList.Filelist(r)
+	if err != nil {
+		return statusFromError(pkt.id(), wrapPathError(r.Filepath, err))
+	}
+
+	r.setListerAt(la)
+
+	return &sshFxpHandlePacket{
+		ID:     pkt.id(),
+		Handle: r.handle,
+	}
+}
+
+// wrap FileReader handler
+func fileget(h FileReader, r *Request, pkt requestPacket, alloc *allocator, orderID uint32) responsePacket {
+	rd := r.getReaderAt()
+	if rd == nil {
+		return statusFromError(pkt.id(), errors.New("unexpected read packet"))
+	}
+
+	data, offset, _ := packetData(pkt, alloc, orderID)
+
+	n, err := rd.ReadAt(data, offset)
+	// only return EOF error if no data left to read
+	if err != nil && (err != io.EOF || n == 0) {
+		return statusFromError(pkt.id(), err)
+	}
+
+	return &sshFxpDataPacket{
+		ID:     pkt.id(),
+		Length: uint32(n),
+		Data:   data[:n],
+	}
+}
+
+// wrap FileWriter handler
+func fileput(h FileWriter, r *Request, pkt requestPacket, alloc *allocator, orderID uint32) responsePacket {
+	wr := r.getWriterAt()
+	if wr == nil {
+		return statusFromError(pkt.id(), errors.New("unexpected write packet"))
+	}
+
+	data, offset, _ := packetData(pkt, alloc, orderID)
+
+	_, err := wr.WriteAt(data, offset)
+	return statusFromError(pkt.id(), err)
+}
+
+// wrap OpenFileWriter handler
+func fileputget(h FileWriter, r *Request, pkt requestPacket, alloc *allocator, orderID uint32) responsePacket {
+	rw := r.getWriterAtReaderAt()
+	if rw == nil {
+		return statusFromError(pkt.id(), errors.New("unexpected write and read packet"))
+	}
+
+	switch p := pkt.(type) {
+	case *sshFxpReadPacket:
+		data, offset := p.getDataSlice(alloc, orderID), int64(p.Offset)
+
+		n, err := rw.ReadAt(data, offset)
+		// only return EOF error if no data left to read
+		if err != nil && (err != io.EOF || n == 0) {
+			return statusFromError(pkt.id(), err)
+		}
+
+		return &sshFxpDataPacket{
+			ID:     pkt.id(),
+			Length: uint32(n),
+			Data:   data[:n],
+		}
+
+	case *sshFxpWritePacket:
+		data, offset := p.Data, int64(p.Offset)
+
+		_, err := rw.WriteAt(data, offset)
+		return statusFromError(pkt.id(), err)
+
+	default:
+		return statusFromError(pkt.id(), errors.New("unexpected packet type for read or write"))
+	}
+}
+
+// file data for additional read/write packets
+func packetData(p requestPacket, alloc *allocator, orderID uint32) (data []byte, offset int64, length uint32) {
+	switch p := p.(type) {
+	case *sshFxpReadPacket:
+		return p.getDataSlice(alloc, orderID), int64(p.Offset), p.Len
+	case *sshFxpWritePacket:
+		return p.Data, int64(p.Offset), p.Length
+	}
+	return
+}
+
+// wrap FileCmder handler
+func filecmd(h FileCmder, r *Request, pkt requestPacket) responsePacket {
+	switch p := pkt.(type) {
+	case *sshFxpFsetstatPacket:
+		r.Flags = p.Flags
+		r.Attrs = p.Attrs.([]byte)
+	}
+
+	switch r.Method {
+	case "PosixRename":
+		if posixRenamer, ok := h.(PosixRenameFileCmder); ok {
+			err := posixRenamer.PosixRename(r)
+			return statusFromError(pkt.id(), err)
+		}
+
+		// PosixRenameFileCmder not implemented handle this request as a Rename
+		r.Method = "Rename"
+		err := h.Filecmd(r)
+		return statusFromError(pkt.id(), err)
+
+	case "StatVFS":
+		if statVFSCmdr, ok := h.(StatVFSFileCmder); ok {
+			stat, err := statVFSCmdr.StatVFS(r)
+			if err != nil {
+				return statusFromError(pkt.id(), err)
+			}
+			stat.ID = pkt.id()
+			return stat
+		}
+
+		return statusFromError(pkt.id(), ErrSSHFxOpUnsupported)
+	}
+
+	err := h.Filecmd(r)
+	return statusFromError(pkt.id(), err)
+}
+
+// wrap FileLister handler
+func filelist(h FileLister, r *Request, pkt requestPacket) responsePacket {
+	lister := r.getListerAt()
+	if lister == nil {
+		return statusFromError(pkt.id(), errors.New("unexpected dir packet"))
+	}
+
+	offset := r.lsNext()
+	finfo := make([]os.FileInfo, MaxFilelist)
+	n, err := lister.ListAt(finfo, offset)
+	r.lsInc(int64(n))
+	// ignore EOF as we only return it when there are no results
+	finfo = finfo[:n] // avoid need for nil tests below
+
+	switch r.Method {
+	case "List":
+		if err != nil && (err != io.EOF || n == 0) {
+			return statusFromError(pkt.id(), err)
+		}
+
+		nameAttrs := make([]*sshFxpNameAttr, 0, len(finfo))
+
+		// If the type conversion fails, we get untyped `nil`,
+		// which is handled by not looking up any names.
+		idLookup, _ := h.(NameLookupFileLister)
+
+		for _, fi := range finfo {
+			nameAttrs = append(nameAttrs, &sshFxpNameAttr{
+				Name:     fi.Name(),
+				LongName: runLs(idLookup, fi),
+				Attrs:    []interface{}{fi},
+			})
+		}
+
+		return &sshFxpNamePacket{
+			ID:        pkt.id(),
+			NameAttrs: nameAttrs,
+		}
+
+	default:
+		err = fmt.Errorf("unexpected method: %s", r.Method)
+		return statusFromError(pkt.id(), err)
+	}
+}
+
+func filestat(h FileLister, r *Request, pkt requestPacket) responsePacket {
+	var lister ListerAt
+	var err error
+
+	if r.Method == "Lstat" {
+		if lstatFileLister, ok := h.(LstatFileLister); ok {
+			lister, err = lstatFileLister.Lstat(r)
+		} else {
+			// LstatFileLister not implemented handle this request as a Stat
+			r.Method = "Stat"
+			lister, err = h.Filelist(r)
+		}
+	} else {
+		lister, err = h.Filelist(r)
+	}
+	if err != nil {
+		return statusFromError(pkt.id(), err)
+	}
+	finfo := make([]os.FileInfo, 1)
+	n, err := lister.ListAt(finfo, 0)
+	finfo = finfo[:n] // avoid need for nil tests below
+
+	switch r.Method {
+	case "Stat", "Lstat":
+		if err != nil && err != io.EOF {
+			return statusFromError(pkt.id(), err)
+		}
+		if n == 0 {
+			err = &os.PathError{
+				Op:   strings.ToLower(r.Method),
+				Path: r.Filepath,
+				Err:  syscall.ENOENT,
+			}
+			return statusFromError(pkt.id(), err)
+		}
+		return &sshFxpStatResponse{
+			ID:   pkt.id(),
+			info: finfo[0],
+		}
+	case "Readlink":
+		if err != nil && err != io.EOF {
+			return statusFromError(pkt.id(), err)
+		}
+		if n == 0 {
+			err = &os.PathError{
+				Op:   "readlink",
+				Path: r.Filepath,
+				Err:  syscall.ENOENT,
+			}
+			return statusFromError(pkt.id(), err)
+		}
+		filename := finfo[0].Name()
+		return &sshFxpNamePacket{
+			ID: pkt.id(),
+			NameAttrs: []*sshFxpNameAttr{
+				{
+					Name:     filename,
+					LongName: filename,
+					Attrs:    emptyFileStat,
+				},
+			},
+		}
+	default:
+		err = fmt.Errorf("unexpected method: %s", r.Method)
+		return statusFromError(pkt.id(), err)
+	}
+}
+
+// init attributes of request object from packet data
+func requestMethod(p requestPacket) (method string) {
+	switch p.(type) {
+	case *sshFxpReadPacket, *sshFxpWritePacket, *sshFxpOpenPacket:
+		// set in open() above
+	case *sshFxpOpendirPacket, *sshFxpReaddirPacket:
+		// set in opendir() above
+	case *sshFxpSetstatPacket, *sshFxpFsetstatPacket:
+		method = "Setstat"
+	case *sshFxpRenamePacket:
+		method = "Rename"
+	case *sshFxpSymlinkPacket:
+		method = "Symlink"
+	case *sshFxpRemovePacket:
+		method = "Remove"
+	case *sshFxpStatPacket, *sshFxpFstatPacket:
+		method = "Stat"
+	case *sshFxpLstatPacket:
+		method = "Lstat"
+	case *sshFxpRmdirPacket:
+		method = "Rmdir"
+	case *sshFxpReadlinkPacket:
+		method = "Readlink"
+	case *sshFxpMkdirPacket:
+		method = "Mkdir"
+	case *sshFxpExtendedPacketHardlink:
+		method = "Link"
+	}
+	return method
+}

sftp/request_windows.go

@@ -0,0 +1,44 @@
+package sftp
+
+import (
+	"path"
+	"path/filepath"
+	"syscall"
+)
+
+func fakeFileInfoSys() interface{} {
+	return syscall.Win32FileAttributeData{}
+}
+
+func testOsSys(sys interface{}) error {
+	return nil
+}
+
+func toLocalPath(p string) string {
+	lp := filepath.FromSlash(p)
+
+	if path.IsAbs(p) {
+		tmp := lp
+		for len(tmp) > 0 && tmp[0] == '\\' {
+			tmp = tmp[1:]
+		}
+
+		if filepath.IsAbs(tmp) {
+			// If the FromSlash without any starting slashes is absolute,
+			// then we have a filepath encoded with a prefix '/'.
+			// e.g. "/C:/Windows" to "C:\\Windows"
+			return tmp
+		}
+
+		tmp += "\\"
+
+		if filepath.IsAbs(tmp) {
+			// If the FromSlash without any starting slashes but with extra end slash is absolute,
+			// then we have a filepath encoded with a prefix '/' and a dropped '/' at the end.
+			// e.g. "/C:" to "C:\\"
+			return tmp
+		}
+	}
+
+	return lp
+}

sftp/server.go

@@ -0,0 +1,643 @@
+package sftp
+
+// sftp server counterpart
+
+import (
+	"context"
+	"log"
+	"encoding"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"strconv"
+	"sync"
+	"syscall"
+	"time"
+
+	"git.deuxfleurs.fr/Deuxfleurs/bagage/s3"
+)
+
+const (
+	// SftpServerWorkerCount defines the number of workers for the SFTP server
+	SftpServerWorkerCount = 8
+)
+
+// Server is an SSH File Transfer Protocol (sftp) server.
+// This is intended to provide the sftp subsystem to an ssh server daemon.
+// This implementation currently supports most of sftp server protocol version 3,
+// as specified at http://tools.ietf.org/html/draft-ietf-secsh-filexfer-02
+type Server struct {
+	*serverConn
+	debugStream   io.Writer
+	readOnly      bool
+	pktMgr        *packetManager
+	openFiles     map[string]*s3.S3File
+	openFilesLock sync.RWMutex
+	handleCount   int
+	fs            *s3.S3FS
+	ctx           context.Context
+}
+
+func (svr *Server) nextHandle(f *s3.S3File) string {
+	svr.openFilesLock.Lock()
+	defer svr.openFilesLock.Unlock()
+	svr.handleCount++
+	handle := strconv.Itoa(svr.handleCount)
+	svr.openFiles[handle] = f
+	return handle
+}
+
+func (svr *Server) closeHandle(handle string) error {
+	svr.openFilesLock.Lock()
+	defer svr.openFilesLock.Unlock()
+	if f, ok := svr.openFiles[handle]; ok {
+		delete(svr.openFiles, handle)
+		return f.Close()
+	}
+
+	return EBADF
+}
+
+func (svr *Server) getHandle(handle string) (*s3.S3File, bool) {
+	svr.openFilesLock.RLock()
+	defer svr.openFilesLock.RUnlock()
+	f, ok := svr.openFiles[handle]
+	return f, ok
+}
+
+type serverRespondablePacket interface {
+	encoding.BinaryUnmarshaler
+	id() uint32
+	respond(svr *Server) responsePacket
+}
+
+// NewServer creates a new Server instance around the provided streams, serving
+// content from the root of the filesystem.  Optionally, ServerOption
+// functions may be specified to further configure the Server.
+//
+// A subsequent call to Serve() is required to begin serving files over SFTP.
+func NewServer(ctx context.Context, rwc io.ReadWriteCloser, fs *s3.S3FS, options ...ServerOption) (*Server, error) {
+	svrConn := &serverConn{
+		conn: conn{
+			Reader:      rwc,
+			WriteCloser: rwc,
+		},
+	}
+	s := &Server{
+		serverConn:  svrConn,
+		debugStream: ioutil.Discard,
+		pktMgr:      newPktMgr(svrConn),
+		openFiles:   make(map[string]*s3.S3File),
+		fs:          fs,
+		ctx:         ctx,
+	}
+
+	for _, o := range options {
+		if err := o(s); err != nil {
+			return nil, err
+		}
+	}
+
+	return s, nil
+}
+
+// A ServerOption is a function which applies configuration to a Server.
+type ServerOption func(*Server) error
+
+// WithDebug enables Server debugging output to the supplied io.Writer.
+func WithDebug(w io.Writer) ServerOption {
+	return func(s *Server) error {
+		s.debugStream = w
+		return nil
+	}
+}
+
+// ReadOnly configures a Server to serve files in read-only mode.
+func ReadOnly() ServerOption {
+	return func(s *Server) error {
+		s.readOnly = true
+		return nil
+	}
+}
+
+// WithAllocator enable the allocator.
+// After processing a packet we keep in memory the allocated slices
+// and we reuse them for new packets.
+// The allocator is experimental
+func WithAllocator() ServerOption {
+	return func(s *Server) error {
+		alloc := newAllocator()
+		s.pktMgr.alloc = alloc
+		s.conn.alloc = alloc
+		return nil
+	}
+}
+
+type rxPacket struct {
+	pktType  fxp
+	pktBytes []byte
+}
+
+// Up to N parallel servers
+func (svr *Server) sftpServerWorker(pktChan chan orderedRequest) error {
+	for pkt := range pktChan {
+		// readonly checks
+		readonly := true
+		switch pkt := pkt.requestPacket.(type) {
+		case notReadOnly:
+			readonly = false
+		case *sshFxpOpenPacket:
+			readonly = pkt.readonly()
+		case *sshFxpExtendedPacket:
+			readonly = pkt.readonly()
+		}
+
+		// If server is operating read-only and a write operation is requested,
+		// return permission denied
+		if !readonly && svr.readOnly {
+			svr.pktMgr.readyPacket(
+				svr.pktMgr.newOrderedResponse(statusFromError(pkt.id(), syscall.EPERM), pkt.orderID()),
+			)
+			continue
+		}
+
+		if err := handlePacket(svr, pkt); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func handlePacket(s *Server, p orderedRequest) error {
+	var rpkt responsePacket
+	orderID := p.orderID()
+	switch p := p.requestPacket.(type) {
+	case *sshFxInitPacket:
+		log.Println("pkt: init")
+		rpkt = &sshFxVersionPacket{
+			Version:    sftpProtocolVersion,
+			Extensions: sftpExtensions,
+		}
+	case *sshFxpStatPacket:
+		log.Println("pkt: stat: ", p.Path)
+		// stat the requested file
+		info, err := os.Stat(toLocalPath(p.Path))
+		rpkt = &sshFxpStatResponse{
+			ID:   p.ID,
+			info: info,
+		}
+		if err != nil {
+			rpkt = statusFromError(p.ID, err)
+		}
+	case *sshFxpLstatPacket:
+		log.Println("pkt: lstat: ", p.Path)
+		// stat the requested file
+		info, err := os.Lstat(toLocalPath(p.Path))
+		rpkt = &sshFxpStatResponse{
+			ID:   p.ID,
+			info: info,
+		}
+		if err != nil {
+			rpkt = statusFromError(p.ID, err)
+		}
+	case *sshFxpFstatPacket:
+		log.Println("pkt: fstat: ", p.Handle)
+		f, ok := s.getHandle(p.Handle)
+		var err error = EBADF
+		var info os.FileInfo
+		if ok {
+			info, err = f.Stat()
+			rpkt = &sshFxpStatResponse{
+				ID:   p.ID,
+				info: info,
+			}
+		}
+		if err != nil {
+			rpkt = statusFromError(p.ID, err)
+		}
+	case *sshFxpMkdirPacket:
+		log.Println("pkt: mkdir: ", p.Path)
+		err := os.Mkdir(toLocalPath(p.Path), 0755)
+		rpkt = statusFromError(p.ID, err)
+	case *sshFxpRmdirPacket:
+		log.Println("pkt: rmdir: ", p.Path)
+		err := os.Remove(toLocalPath(p.Path))
+		rpkt = statusFromError(p.ID, err)
+	case *sshFxpRemovePacket:
+		log.Println("pkt: rm: ", p.Filename)
+		err := os.Remove(toLocalPath(p.Filename))
+		rpkt = statusFromError(p.ID, err)
+	case *sshFxpRenamePacket:
+		log.Println("pkt: rename: ", p.Oldpath, ", ", p.Newpath)
+		err := os.Rename(toLocalPath(p.Oldpath), toLocalPath(p.Newpath))
+		rpkt = statusFromError(p.ID, err)
+	case *sshFxpSymlinkPacket:
+		log.Println("pkt: ln -s: ", p.Targetpath, ", ", p.Linkpath)
+		err := os.Symlink(toLocalPath(p.Targetpath), toLocalPath(p.Linkpath))
+		rpkt = statusFromError(p.ID, err)
+	case *sshFxpClosePacket:
+		log.Println("pkt: close handle: ", p.Handle)
+		rpkt = statusFromError(p.ID, s.closeHandle(p.Handle))
+	case *sshFxpReadlinkPacket:
+		log.Println("pkt: read: ", p.Path)
+		f, err := os.Readlink(toLocalPath(p.Path))
+		rpkt = &sshFxpNamePacket{
+			ID: p.ID,
+			NameAttrs: []*sshFxpNameAttr{
+				{
+					Name:     f,
+					LongName: f,
+					Attrs:    emptyFileStat,
+				},
+			},
+		}
+		if err != nil {
+			rpkt = statusFromError(p.ID, err)
+		}
+	case *sshFxpRealpathPacket:
+		log.Println("pkt: absolute path: ", p.Path)
+		f := s3.NewS3Path(p.Path).Path
+		rpkt = &sshFxpNamePacket{
+			ID: p.ID,
+			NameAttrs: []*sshFxpNameAttr{
+				{
+					Name:     f,
+					LongName: f,
+					Attrs:    emptyFileStat,
+				},
+			},
+		}
+	case *sshFxpOpendirPacket:
+		log.Println("pkt: open dir: ", p.Path)
+		p.Path = s3.NewS3Path(p.Path).Path
+
+		if stat, err := s.fs.Stat(s.ctx, p.Path); err != nil {
+			rpkt = statusFromError(p.ID, err)
+		} else if !stat.IsDir() {
+			rpkt = statusFromError(p.ID, &os.PathError{
+				Path: p.Path, Err: syscall.ENOTDIR})
+		} else {
+			rpkt = (&sshFxpOpenPacket{
+				ID:     p.ID,
+				Path:   p.Path,
+				Pflags: sshFxfRead,
+			}).respond(s)
+		}
+	case *sshFxpReadPacket:
+		log.Println("pkt: read handle: ", p.Handle)
+		var err error = EBADF
+		f, ok := s.getHandle(p.Handle)
+		if ok {
+			err = nil
+			data := p.getDataSlice(s.pktMgr.alloc, orderID)
+			n, _err := f.ReadAt(data, int64(p.Offset))
+			if _err != nil && (_err != io.EOF || n == 0) {
+				err = _err
+			}
+			rpkt = &sshFxpDataPacket{
+				ID:     p.ID,
+				Length: uint32(n),
+				Data:   data[:n],
+				// do not use data[:n:n] here to clamp the capacity, we allocated extra capacity above to avoid reallocations
+			}
+		}
+		if err != nil {
+			rpkt = statusFromError(p.ID, err)
+		}
+
+	case *sshFxpWritePacket:
+		log.Println("pkt: write handle: ", p.Handle, ", Offset: ", p.Offset)
+		f, ok := s.getHandle(p.Handle)
+		var err error = EBADF
+		if ok {
+			_, err = f.WriteAt(p.Data, int64(p.Offset))
+		}
+		rpkt = statusFromError(p.ID, err)
+	case *sshFxpExtendedPacket:
+		log.Println("pkt: extended packet")
+		if p.SpecificPacket == nil {
+			rpkt = statusFromError(p.ID, ErrSSHFxOpUnsupported)
+		} else {
+			rpkt = p.respond(s)
+		}
+	case serverRespondablePacket:
+		log.Println("pkt: respondable")
+		rpkt = p.respond(s)
+	default:
+		return fmt.Errorf("unexpected packet type %T", p)
+	}
+
+	s.pktMgr.readyPacket(s.pktMgr.newOrderedResponse(rpkt, orderID))
+	return nil
+}
+
+// Serve serves SFTP connections until the streams stop or the SFTP subsystem
+// is stopped.
+func (svr *Server) Serve() error {
+	defer func() {
+		if svr.pktMgr.alloc != nil {
+			svr.pktMgr.alloc.Free()
+		}
+	}()
+	var wg sync.WaitGroup
+	runWorker := func(ch chan orderedRequest) {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			if err := svr.sftpServerWorker(ch); err != nil {
+				svr.conn.Close() // shuts down recvPacket
+			}
+		}()
+	}
+	pktChan := svr.pktMgr.workerChan(runWorker)
+
+	var err error
+	var pkt requestPacket
+	var pktType uint8
+	var pktBytes []byte
+	for {
+		pktType, pktBytes, err = svr.serverConn.recvPacket(svr.pktMgr.getNextOrderID())
+		if err != nil {
+			// we don't care about releasing allocated pages here, the server will quit and the allocator freed
+			break
+		}
+
+		pkt, err = makePacket(rxPacket{fxp(pktType), pktBytes})
+		if err != nil {
+			switch {
+			case errors.Is(err, errUnknownExtendedPacket):
+				//if err := svr.serverConn.sendError(pkt, ErrSshFxOpUnsupported); err != nil {
+				//	debug("failed to send err packet: %v", err)
+				//	svr.conn.Close() // shuts down recvPacket
+				//	break
+				//}
+			default:
+				debug("makePacket err: %v", err)
+				svr.conn.Close() // shuts down recvPacket
+				break
+			}
+		}
+
+		pktChan <- svr.pktMgr.newOrderedRequest(pkt)
+	}
+
+	close(pktChan) // shuts down sftpServerWorkers
+	wg.Wait()      // wait for all workers to exit
+
+	// close any still-open files
+	for handle, file := range svr.openFiles {
+		fmt.Fprintf(svr.debugStream, "sftp server file with handle %q left open: %v\n", handle, file.Path.Path)
+		file.Close()
+	}
+	return err // error from recvPacket
+}
+
+type ider interface {
+	id() uint32
+}
+
+// The init packet has no ID, so we just return a zero-value ID
+func (p *sshFxInitPacket) id() uint32 { return 0 }
+
+type sshFxpStatResponse struct {
+	ID   uint32
+	info os.FileInfo
+}
+
+func (p *sshFxpStatResponse) marshalPacket() ([]byte, []byte, error) {
+	l := 4 + 1 + 4 // uint32(length) + byte(type) + uint32(id)
+
+	b := make([]byte, 4, l)
+	b = append(b, sshFxpAttrs)
+	b = marshalUint32(b, p.ID)
+
+	var payload []byte
+	payload = marshalFileInfo(payload, p.info)
+
+	return b, payload, nil
+}
+
+func (p *sshFxpStatResponse) MarshalBinary() ([]byte, error) {
+	header, payload, err := p.marshalPacket()
+	return append(header, payload...), err
+}
+
+var emptyFileStat = []interface{}{uint32(0)}
+
+func (p *sshFxpOpenPacket) readonly() bool {
+	return !p.hasPflags(sshFxfWrite)
+}
+
+func (p *sshFxpOpenPacket) hasPflags(flags ...uint32) bool {
+	for _, f := range flags {
+		if p.Pflags&f == 0 {
+			return false
+		}
+	}
+	return true
+}
+
+func (p *sshFxpOpenPacket) respond(svr *Server) responsePacket {
+	log.Println("pkt: open: ", p.Path)
+	var osFlags int
+	if p.hasPflags(sshFxfRead, sshFxfWrite) {
+		osFlags |= os.O_RDWR
+	} else if p.hasPflags(sshFxfWrite) {
+		osFlags |= os.O_WRONLY
+	} else if p.hasPflags(sshFxfRead) {
+		osFlags |= os.O_RDONLY
+	} else {
+		// how are they opening?
+		return statusFromError(p.ID, syscall.EINVAL)
+	}
+
+	// Don't use O_APPEND flag as it conflicts with WriteAt.
+	// The sshFxfAppend flag is a no-op here as the client sends the offsets.
+	// @FIXME these flags are currently ignored
+	if p.hasPflags(sshFxfCreat) {
+		osFlags |= os.O_CREATE
+	}
+	if p.hasPflags(sshFxfTrunc) {
+		osFlags |= os.O_TRUNC
+	}
+	if p.hasPflags(sshFxfExcl) {
+		osFlags |= os.O_EXCL
+	}
+
+	f, err := svr.fs.OpenFile2(svr.ctx, p.Path, osFlags, 0644)
+	if err != nil {
+		return statusFromError(p.ID, err)
+	}
+
+	handle := svr.nextHandle(f)
+	return &sshFxpHandlePacket{ID: p.ID, Handle: handle}
+}
+
+func (p *sshFxpReaddirPacket) respond(svr *Server) responsePacket {
+	log.Println("pkt: readdir: ", p.Handle)
+	f, ok := svr.getHandle(p.Handle)
+	if !ok {
+		return statusFromError(p.ID, EBADF)
+	}
+
+	dirents, err := f.Readdir(128)
+	if err != nil {
+		return statusFromError(p.ID, err)
+	}
+
+	idLookup := osIDLookup{}
+
+	ret := &sshFxpNamePacket{ID: p.ID}
+	for _, dirent := range dirents {
+		ret.NameAttrs = append(ret.NameAttrs, &sshFxpNameAttr{
+			Name:     dirent.Name(),
+			LongName: runLs(idLookup, dirent),
+			Attrs:    []interface{}{dirent},
+		})
+	}
+	return ret
+}
+
+func (p *sshFxpSetstatPacket) respond(svr *Server) responsePacket {
+	log.Println("pkt: setstat: ", p.Path)
+	// additional unmarshalling is required for each possibility here
+	b := p.Attrs.([]byte)
+	var err error
+
+	p.Path = toLocalPath(p.Path)
+
+	debug("setstat name \"%s\"", p.Path)
+	if (p.Flags & sshFileXferAttrSize) != 0 {
+		var size uint64
+		if size, b, err = unmarshalUint64Safe(b); err == nil {
+			err = os.Truncate(p.Path, int64(size))
+		}
+	}
+	if (p.Flags & sshFileXferAttrPermissions) != 0 {
+		var mode uint32
+		if mode, b, err = unmarshalUint32Safe(b); err == nil {
+			err = os.Chmod(p.Path, os.FileMode(mode))
+		}
+	}
+	if (p.Flags & sshFileXferAttrACmodTime) != 0 {
+		var atime uint32
+		var mtime uint32
+		if atime, b, err = unmarshalUint32Safe(b); err != nil {
+		} else if mtime, b, err = unmarshalUint32Safe(b); err != nil {
+		} else {
+			atimeT := time.Unix(int64(atime), 0)
+			mtimeT := time.Unix(int64(mtime), 0)
+			err = os.Chtimes(p.Path, atimeT, mtimeT)
+		}
+	}
+	if (p.Flags & sshFileXferAttrUIDGID) != 0 {
+		var uid uint32
+		var gid uint32
+		if uid, b, err = unmarshalUint32Safe(b); err != nil {
+		} else if gid, _, err = unmarshalUint32Safe(b); err != nil {
+		} else {
+			err = os.Chown(p.Path, int(uid), int(gid))
+		}
+	}
+
+	return statusFromError(p.ID, err)
+}
+
+func (p *sshFxpFsetstatPacket) respond(svr *Server) responsePacket {
+	log.Println("pkt: fsetstat: ", p.Handle)
+	f, ok := svr.getHandle(p.Handle)
+	if !ok {
+		return statusFromError(p.ID, EBADF)
+	}
+
+	// additional unmarshalling is required for each possibility here
+	//b := p.Attrs.([]byte)
+	var err error
+
+	debug("fsetstat name \"%s\"", f.Path.Path)
+	if (p.Flags & sshFileXferAttrSize) != 0 {
+		/*var size uint64
+		if size, b, err = unmarshalUint64Safe(b); err == nil {
+			err = f.Truncate(int64(size))
+		}*/
+		log.Println("WARN: changing size of the file is not supported")
+	}
+	if (p.Flags & sshFileXferAttrPermissions) != 0 {
+		/*var mode uint32
+		if mode, b, err = unmarshalUint32Safe(b); err == nil {
+			err = f.Chmod(os.FileMode(mode))
+		}*/
+		log.Println("WARN: chmod not supported")
+	}
+	if (p.Flags & sshFileXferAttrACmodTime) != 0 {
+		/*var atime uint32
+		var mtime uint32
+		if atime, b, err = unmarshalUint32Safe(b); err != nil {
+		} else if mtime, b, err = unmarshalUint32Safe(b); err != nil {
+		} else {
+			atimeT := time.Unix(int64(atime), 0)
+			mtimeT := time.Unix(int64(mtime), 0)
+			err = os.Chtimes(f.Name(), atimeT, mtimeT)
+		}*/
+		log.Println("WARN: chtimes not supported")
+	}
+	if (p.Flags & sshFileXferAttrUIDGID) != 0 {
+		/*var uid uint32
+		var gid uint32
+		if uid, b, err = unmarshalUint32Safe(b); err != nil {
+		} else if gid, _, err = unmarshalUint32Safe(b); err != nil {
+		} else {
+			err = f.Chown(int(uid), int(gid))
+		}*/
+		log.Println("WARN: chown not supported")
+	}
+
+	return statusFromError(p.ID, err)
+}
+
+func statusFromError(id uint32, err error) *sshFxpStatusPacket {
+	ret := &sshFxpStatusPacket{
+		ID: id,
+		StatusError: StatusError{
+			// sshFXOk               = 0
+			// sshFXEOF              = 1
+			// sshFXNoSuchFile       = 2 ENOENT
+			// sshFXPermissionDenied = 3
+			// sshFXFailure          = 4
+			// sshFXBadMessage       = 5
+			// sshFXNoConnection     = 6
+			// sshFXConnectionLost   = 7
+			// sshFXOPUnsupported    = 8
+			Code: sshFxOk,
+		},
+	}
+	if err == nil {
+		return ret
+	}
+
+	debug("statusFromError: error is %T %#v", err, err)
+	ret.StatusError.Code = sshFxFailure
+	ret.StatusError.msg = err.Error()
+
+	if os.IsNotExist(err) {
+		ret.StatusError.Code = sshFxNoSuchFile
+		return ret
+	}
+	if code, ok := translateSyscallError(err); ok {
+		ret.StatusError.Code = code
+		return ret
+	}
+
+	switch e := err.(type) {
+	case fxerr:
+		ret.StatusError.Code = uint32(e)
+	default:
+		if e == io.EOF {
+			ret.StatusError.Code = sshFxEOF
+		}
+	}
+
+	return ret
+}

sftp/server_statvfs_darwin.go

@@ -0,0 +1,21 @@
+package sftp
+
+import (
+	"syscall"
+)
+
+func statvfsFromStatfst(stat *syscall.Statfs_t) (*StatVFS, error) {
+	return &StatVFS{
+		Bsize:   uint64(stat.Bsize),
+		Frsize:  uint64(stat.Bsize), // fragment size is a linux thing; use block size here
+		Blocks:  stat.Blocks,
+		Bfree:   stat.Bfree,
+		Bavail:  stat.Bavail,
+		Files:   stat.Files,
+		Ffree:   stat.Ffree,
+		Favail:  stat.Ffree,                                                      // not sure how to calculate Favail
+		Fsid:    uint64(uint64(stat.Fsid.Val[1])<<32 | uint64(stat.Fsid.Val[0])), // endianness?
+		Flag:    uint64(stat.Flags),                                              // assuming POSIX?
+		Namemax: 1024,                                                            // man 2 statfs shows: #define MAXPATHLEN      1024
+	}, nil
+}

sftp/server_statvfs_impl.go

@@ -0,0 +1,29 @@
+// +build darwin linux
+
+// fill in statvfs structure with OS specific values
+// Statfs_t is different per-kernel, and only exists on some unixes (not Solaris for instance)
+
+package sftp
+
+import (
+	"syscall"
+)
+
+func (p *sshFxpExtendedPacketStatVFS) respond(svr *Server) responsePacket {
+	retPkt, err := getStatVFSForPath(p.Path)
+	if err != nil {
+		return statusFromError(p.ID, err)
+	}
+	retPkt.ID = p.ID
+
+	return retPkt
+}
+
+func getStatVFSForPath(name string) (*StatVFS, error) {
+	var stat syscall.Statfs_t
+	if err := syscall.Statfs(name, &stat); err != nil {
+		return nil, err
+	}
+
+	return statvfsFromStatfst(&stat)
+}

sftp/server_statvfs_linux.go

@@ -0,0 +1,22 @@
+// +build linux
+
+package sftp
+
+import (
+	"syscall"
+)
+
+func statvfsFromStatfst(stat *syscall.Statfs_t) (*StatVFS, error) {
+	return &StatVFS{
+		Bsize:   uint64(stat.Bsize),
+		Frsize:  uint64(stat.Frsize),
+		Blocks:  stat.Blocks,
+		Bfree:   stat.Bfree,
+		Bavail:  stat.Bavail,
+		Files:   stat.Files,
+		Ffree:   stat.Ffree,
+		Favail:  stat.Ffree,         // not sure how to calculate Favail
+		Flag:    uint64(stat.Flags), // assuming POSIX?
+		Namemax: uint64(stat.Namelen),
+	}, nil
+}

sftp/server_statvfs_plan9.go

@@ -0,0 +1,13 @@
+package sftp
+
+import (
+	"syscall"
+)
+
+func (p *sshFxpExtendedPacketStatVFS) respond(svr *Server) responsePacket {
+	return statusFromError(p.ID, syscall.EPLAN9)
+}
+
+func getStatVFSForPath(name string) (*StatVFS, error) {
+	return nil, syscall.EPLAN9
+}

sftp/server_statvfs_stubs.go

@@ -0,0 +1,15 @@
+// +build !darwin,!linux,!plan9
+
+package sftp
+
+import (
+	"syscall"
+)
+
+func (p *sshFxpExtendedPacketStatVFS) respond(svr *Server) responsePacket {
+	return statusFromError(p.ID, syscall.ENOTSUP)
+}
+
+func getStatVFSForPath(name string) (*StatVFS, error) {
+	return nil, syscall.ENOTSUP
+}

sftp/sftp.go

@@ -0,0 +1,258 @@
+// Package sftp implements the SSH File Transfer Protocol as described in
+// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02
+package sftp
+
+import (
+	"fmt"
+)
+
+const (
+	sshFxpInit          = 1
+	sshFxpVersion       = 2
+	sshFxpOpen          = 3
+	sshFxpClose         = 4
+	sshFxpRead          = 5
+	sshFxpWrite         = 6
+	sshFxpLstat         = 7
+	sshFxpFstat         = 8
+	sshFxpSetstat       = 9
+	sshFxpFsetstat      = 10
+	sshFxpOpendir       = 11
+	sshFxpReaddir       = 12
+	sshFxpRemove        = 13
+	sshFxpMkdir         = 14
+	sshFxpRmdir         = 15
+	sshFxpRealpath      = 16
+	sshFxpStat          = 17
+	sshFxpRename        = 18
+	sshFxpReadlink      = 19
+	sshFxpSymlink       = 20
+	sshFxpStatus        = 101
+	sshFxpHandle        = 102
+	sshFxpData          = 103
+	sshFxpName          = 104
+	sshFxpAttrs         = 105
+	sshFxpExtended      = 200
+	sshFxpExtendedReply = 201
+)
+
+const (
+	sshFxOk               = 0
+	sshFxEOF              = 1
+	sshFxNoSuchFile       = 2
+	sshFxPermissionDenied = 3
+	sshFxFailure          = 4
+	sshFxBadMessage       = 5
+	sshFxNoConnection     = 6
+	sshFxConnectionLost   = 7
+	sshFxOPUnsupported    = 8
+
+	// see draft-ietf-secsh-filexfer-13
+	// https://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#section-9.1
+	sshFxInvalidHandle           = 9
+	sshFxNoSuchPath              = 10
+	sshFxFileAlreadyExists       = 11
+	sshFxWriteProtect            = 12
+	sshFxNoMedia                 = 13
+	sshFxNoSpaceOnFilesystem     = 14
+	sshFxQuotaExceeded           = 15
+	sshFxUnknownPrincipal        = 16
+	sshFxLockConflict            = 17
+	sshFxDirNotEmpty             = 18
+	sshFxNotADirectory           = 19
+	sshFxInvalidFilename         = 20
+	sshFxLinkLoop                = 21
+	sshFxCannotDelete            = 22
+	sshFxInvalidParameter        = 23
+	sshFxFileIsADirectory        = 24
+	sshFxByteRangeLockConflict   = 25
+	sshFxByteRangeLockRefused    = 26
+	sshFxDeletePending           = 27
+	sshFxFileCorrupt             = 28
+	sshFxOwnerInvalid            = 29
+	sshFxGroupInvalid            = 30
+	sshFxNoMatchingByteRangeLock = 31
+)
+
+const (
+	sshFxfRead   = 0x00000001
+	sshFxfWrite  = 0x00000002
+	sshFxfAppend = 0x00000004
+	sshFxfCreat  = 0x00000008
+	sshFxfTrunc  = 0x00000010
+	sshFxfExcl   = 0x00000020
+)
+
+var (
+	// supportedSFTPExtensions defines the supported extensions
+	supportedSFTPExtensions = []sshExtensionPair{
+		{"hardlink@openssh.com", "1"},
+		{"posix-rename@openssh.com", "1"},
+		{"statvfs@openssh.com", "2"},
+	}
+	sftpExtensions = supportedSFTPExtensions
+)
+
+type fxp uint8
+
+func (f fxp) String() string {
+	switch f {
+	case sshFxpInit:
+		return "SSH_FXP_INIT"
+	case sshFxpVersion:
+		return "SSH_FXP_VERSION"
+	case sshFxpOpen:
+		return "SSH_FXP_OPEN"
+	case sshFxpClose:
+		return "SSH_FXP_CLOSE"
+	case sshFxpRead:
+		return "SSH_FXP_READ"
+	case sshFxpWrite:
+		return "SSH_FXP_WRITE"
+	case sshFxpLstat:
+		return "SSH_FXP_LSTAT"
+	case sshFxpFstat:
+		return "SSH_FXP_FSTAT"
+	case sshFxpSetstat:
+		return "SSH_FXP_SETSTAT"
+	case sshFxpFsetstat:
+		return "SSH_FXP_FSETSTAT"
+	case sshFxpOpendir:
+		return "SSH_FXP_OPENDIR"
+	case sshFxpReaddir:
+		return "SSH_FXP_READDIR"
+	case sshFxpRemove:
+		return "SSH_FXP_REMOVE"
+	case sshFxpMkdir:
+		return "SSH_FXP_MKDIR"
+	case sshFxpRmdir:
+		return "SSH_FXP_RMDIR"
+	case sshFxpRealpath:
+		return "SSH_FXP_REALPATH"
+	case sshFxpStat:
+		return "SSH_FXP_STAT"
+	case sshFxpRename:
+		return "SSH_FXP_RENAME"
+	case sshFxpReadlink:
+		return "SSH_FXP_READLINK"
+	case sshFxpSymlink:
+		return "SSH_FXP_SYMLINK"
+	case sshFxpStatus:
+		return "SSH_FXP_STATUS"
+	case sshFxpHandle:
+		return "SSH_FXP_HANDLE"
+	case sshFxpData:
+		return "SSH_FXP_DATA"
+	case sshFxpName:
+		return "SSH_FXP_NAME"
+	case sshFxpAttrs:
+		return "SSH_FXP_ATTRS"
+	case sshFxpExtended:
+		return "SSH_FXP_EXTENDED"
+	case sshFxpExtendedReply:
+		return "SSH_FXP_EXTENDED_REPLY"
+	default:
+		return "unknown"
+	}
+}
+
+type fx uint8
+
+func (f fx) String() string {
+	switch f {
+	case sshFxOk:
+		return "SSH_FX_OK"
+	case sshFxEOF:
+		return "SSH_FX_EOF"
+	case sshFxNoSuchFile:
+		return "SSH_FX_NO_SUCH_FILE"
+	case sshFxPermissionDenied:
+		return "SSH_FX_PERMISSION_DENIED"
+	case sshFxFailure:
+		return "SSH_FX_FAILURE"
+	case sshFxBadMessage:
+		return "SSH_FX_BAD_MESSAGE"
+	case sshFxNoConnection:
+		return "SSH_FX_NO_CONNECTION"
+	case sshFxConnectionLost:
+		return "SSH_FX_CONNECTION_LOST"
+	case sshFxOPUnsupported:
+		return "SSH_FX_OP_UNSUPPORTED"
+	default:
+		return "unknown"
+	}
+}
+
+type unexpectedPacketErr struct {
+	want, got uint8
+}
+
+func (u *unexpectedPacketErr) Error() string {
+	return fmt.Sprintf("sftp: unexpected packet: want %v, got %v", fxp(u.want), fxp(u.got))
+}
+
+func unimplementedPacketErr(u uint8) error {
+	return fmt.Errorf("sftp: unimplemented packet type: got %v", fxp(u))
+}
+
+type unexpectedIDErr struct{ want, got uint32 }
+
+func (u *unexpectedIDErr) Error() string {
+	return fmt.Sprintf("sftp: unexpected id: want %d, got %d", u.want, u.got)
+}
+
+func unimplementedSeekWhence(whence int) error {
+	return fmt.Errorf("sftp: unimplemented seek whence %d", whence)
+}
+
+func unexpectedCount(want, got uint32) error {
+	return fmt.Errorf("sftp: unexpected count: want %d, got %d", want, got)
+}
+
+type unexpectedVersionErr struct{ want, got uint32 }
+
+func (u *unexpectedVersionErr) Error() string {
+	return fmt.Sprintf("sftp: unexpected server version: want %v, got %v", u.want, u.got)
+}
+
+// A StatusError is returned when an SFTP operation fails, and provides
+// additional information about the failure.
+type StatusError struct {
+	Code      uint32
+	msg, lang string
+}
+
+func (s *StatusError) Error() string {
+	return fmt.Sprintf("sftp: %q (%v)", s.msg, fx(s.Code))
+}
+
+// FxCode returns the error code typed to match against the exported codes
+func (s *StatusError) FxCode() fxerr {
+	return fxerr(s.Code)
+}
+
+func getSupportedExtensionByName(extensionName string) (sshExtensionPair, error) {
+	for _, supportedExtension := range supportedSFTPExtensions {
+		if supportedExtension.Name == extensionName {
+			return supportedExtension, nil
+		}
+	}
+	return sshExtensionPair{}, fmt.Errorf("unsupported extension: %s", extensionName)
+}
+
+// SetSFTPExtensions allows to customize the supported server extensions.
+// See the variable supportedSFTPExtensions for supported extensions.
+// This method accepts a slice of sshExtensionPair names for example 'hardlink@openssh.com'.
+// If an invalid extension is given an error will be returned and nothing will be changed
+func SetSFTPExtensions(extensions ...string) error {
+	tempExtensions := []sshExtensionPair{}
+	for _, extension := range extensions {
+		sftpExtension, err := getSupportedExtensionByName(extension)
+		if err != nil {
+			return err
+		}
+		tempExtensions = append(tempExtensions, sftpExtension)
+	}
+	sftpExtensions = tempExtensions
+	return nil
+}

sftp/stat_plan9.go

@@ -0,0 +1,103 @@
+package sftp
+
+import (
+	"os"
+	"syscall"
+)
+
+var EBADF = syscall.NewError("fd out of range or not open")
+
+func wrapPathError(filepath string, err error) error {
+	if errno, ok := err.(syscall.ErrorString); ok {
+		return &os.PathError{Path: filepath, Err: errno}
+	}
+	return err
+}
+
+// translateErrno translates a syscall error number to a SFTP error code.
+func translateErrno(errno syscall.ErrorString) uint32 {
+	switch errno {
+	case "":
+		return sshFxOk
+	case syscall.ENOENT:
+		return sshFxNoSuchFile
+	case syscall.EPERM:
+		return sshFxPermissionDenied
+	}
+
+	return sshFxFailure
+}
+
+func translateSyscallError(err error) (uint32, bool) {
+	switch e := err.(type) {
+	case syscall.ErrorString:
+		return translateErrno(e), true
+	case *os.PathError:
+		debug("statusFromError,pathError: error is %T %#v", e.Err, e.Err)
+		if errno, ok := e.Err.(syscall.ErrorString); ok {
+			return translateErrno(errno), true
+		}
+	}
+	return 0, false
+}
+
+// isRegular returns true if the mode describes a regular file.
+func isRegular(mode uint32) bool {
+	return mode&S_IFMT == syscall.S_IFREG
+}
+
+// toFileMode converts sftp filemode bits to the os.FileMode specification
+func toFileMode(mode uint32) os.FileMode {
+	var fm = os.FileMode(mode & 0777)
+
+	switch mode & S_IFMT {
+	case syscall.S_IFBLK:
+		fm |= os.ModeDevice
+	case syscall.S_IFCHR:
+		fm |= os.ModeDevice | os.ModeCharDevice
+	case syscall.S_IFDIR:
+		fm |= os.ModeDir
+	case syscall.S_IFIFO:
+		fm |= os.ModeNamedPipe
+	case syscall.S_IFLNK:
+		fm |= os.ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fm |= os.ModeSocket
+	}
+
+	return fm
+}
+
+// fromFileMode converts from the os.FileMode specification to sftp filemode bits
+func fromFileMode(mode os.FileMode) uint32 {
+	ret := uint32(mode & os.ModePerm)
+
+	switch mode & os.ModeType {
+	case os.ModeDevice | os.ModeCharDevice:
+		ret |= syscall.S_IFCHR
+	case os.ModeDevice:
+		ret |= syscall.S_IFBLK
+	case os.ModeDir:
+		ret |= syscall.S_IFDIR
+	case os.ModeNamedPipe:
+		ret |= syscall.S_IFIFO
+	case os.ModeSymlink:
+		ret |= syscall.S_IFLNK
+	case 0:
+		ret |= syscall.S_IFREG
+	case os.ModeSocket:
+		ret |= syscall.S_IFSOCK
+	}
+
+	return ret
+}
+
+// Plan 9 doesn't have setuid, setgid or sticky, but a Plan 9 client should
+// be able to send these bits to a POSIX server.
+const (
+	s_ISUID = 04000
+	s_ISGID = 02000
+	s_ISVTX = 01000
+)

sftp/stat_posix.go

@@ -0,0 +1,124 @@
+//go:build !plan9
+// +build !plan9
+
+package sftp
+
+import (
+	"os"
+	"syscall"
+)
+
+const EBADF = syscall.EBADF
+
+func wrapPathError(filepath string, err error) error {
+	if errno, ok := err.(syscall.Errno); ok {
+		return &os.PathError{Path: filepath, Err: errno}
+	}
+	return err
+}
+
+// translateErrno translates a syscall error number to a SFTP error code.
+func translateErrno(errno syscall.Errno) uint32 {
+	switch errno {
+	case 0:
+		return sshFxOk
+	case syscall.ENOENT:
+		return sshFxNoSuchFile
+	case syscall.EACCES, syscall.EPERM:
+		return sshFxPermissionDenied
+	}
+
+	return sshFxFailure
+}
+
+func translateSyscallError(err error) (uint32, bool) {
+	switch e := err.(type) {
+	case syscall.Errno:
+		return translateErrno(e), true
+	case *os.PathError:
+		debug("statusFromError,pathError: error is %T %#v", e.Err, e.Err)
+		if errno, ok := e.Err.(syscall.Errno); ok {
+			return translateErrno(errno), true
+		}
+	}
+	return 0, false
+}
+
+// isRegular returns true if the mode describes a regular file.
+func isRegular(mode uint32) bool {
+	return mode&S_IFMT == syscall.S_IFREG
+}
+
+// toFileMode converts sftp filemode bits to the os.FileMode specification
+func toFileMode(mode uint32) os.FileMode {
+	var fm = os.FileMode(mode & 0777)
+
+	switch mode & S_IFMT {
+	case syscall.S_IFBLK:
+		fm |= os.ModeDevice
+	case syscall.S_IFCHR:
+		fm |= os.ModeDevice | os.ModeCharDevice
+	case syscall.S_IFDIR:
+		fm |= os.ModeDir
+	case syscall.S_IFIFO:
+		fm |= os.ModeNamedPipe
+	case syscall.S_IFLNK:
+		fm |= os.ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fm |= os.ModeSocket
+	}
+
+	if mode&syscall.S_ISUID != 0 {
+		fm |= os.ModeSetuid
+	}
+	if mode&syscall.S_ISGID != 0 {
+		fm |= os.ModeSetgid
+	}
+	if mode&syscall.S_ISVTX != 0 {
+		fm |= os.ModeSticky
+	}
+
+	return fm
+}
+
+// fromFileMode converts from the os.FileMode specification to sftp filemode bits
+func fromFileMode(mode os.FileMode) uint32 {
+	ret := uint32(mode & os.ModePerm)
+
+	switch mode & os.ModeType {
+	case os.ModeDevice | os.ModeCharDevice:
+		ret |= syscall.S_IFCHR
+	case os.ModeDevice:
+		ret |= syscall.S_IFBLK
+	case os.ModeDir:
+		ret |= syscall.S_IFDIR
+	case os.ModeNamedPipe:
+		ret |= syscall.S_IFIFO
+	case os.ModeSymlink:
+		ret |= syscall.S_IFLNK
+	case 0:
+		ret |= syscall.S_IFREG
+	case os.ModeSocket:
+		ret |= syscall.S_IFSOCK
+	}
+
+	if mode&os.ModeSetuid != 0 {
+		ret |= syscall.S_ISUID
+	}
+	if mode&os.ModeSetgid != 0 {
+		ret |= syscall.S_ISGID
+	}
+	if mode&os.ModeSticky != 0 {
+		ret |= syscall.S_ISVTX
+	}
+
+	return ret
+}
+
+const (
+	s_ISUID = syscall.S_ISUID
+	s_ISGID = syscall.S_ISGID
+	s_ISVTX = syscall.S_ISVTX
+)

sftp/syscall_fixed.go

@@ -0,0 +1,9 @@
+// +build plan9 windows js,wasm
+
+// Go defines S_IFMT on windows, plan9 and js/wasm as 0x1f000 instead of
+// 0xf000. None of the the other S_IFxyz values include the "1" (in 0x1f000)
+// which prevents them from matching the bitmask.
+
+package sftp
+
+const S_IFMT = 0xf000

sftp/syscall_good.go

@@ -0,0 +1,8 @@
+// +build !plan9,!windows
+// +build !js !wasm
+
+package sftp
+
+import "syscall"
+
+const S_IFMT = syscall.S_IFMT

webdav.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"github.com/minio/minio-go/v7"
+	"git.deuxfleurs.fr/Deuxfleurs/bagage/s3"
 	"golang.org/x/net/webdav"
 	"log"
 	"net/http"
@@ -15,7 +16,7 @@ func (wd WebDav) WithMC(mc *minio.Client) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		(&webdav.Handler{
 			Prefix:     wd.WithConfig.DavPath,
-			FileSystem: NewS3FS(mc),
+			FileSystem: s3.NewS3FS(mc),
 			LockSystem: webdav.NewMemLS(),
 			Logger: func(r *http.Request, err error) {
 				log.Printf("INFO: %s %s %s\n", r.RemoteAddr, r.Method, r.URL)