plugins/base: support attachments in drafts

References: https://todo.sr.ht/~sircmpwn/koushin/16

plugins/base/imap.go

@@ -144,6 +144,28 @@ func (msg *IMAPMessage) TextPartName() string {
 	return strings.Join(l, ".")
 }
 
+func (msg *IMAPMessage) Attachments() []IMAPPartNode {
+	if msg.BodyStructure == nil {
+		return nil
+	}
+
+	var attachments []IMAPPartNode
+	msg.BodyStructure.Walk(func(path []int, part *imap.BodyStructure) bool {
+		if !strings.EqualFold(part.Disposition, "attachment") {
+			return true
+		}
+
+		filename, _ := part.Filename()
+		attachments = append(attachments, IMAPPartNode{
+			Path:     path,
+			MIMEType: strings.ToLower(part.MIMEType + "/" + part.MIMESubType),
+			Filename: filename,
+		})
+		return true
+	})
+	return attachments
+}
+
 type IMAPPartNode struct {
 	Path     []int
 	MIMEType string

plugins/base/public/compose.html

@@ -25,6 +25,13 @@
   <br><br>
   <label for="attachments">Attachments:</label>
   <input type="file" name="attachments" id="attachments" multiple>
+  {{range .Message.Attachments}}
+    <br>
+    <label>
+      <input type="checkbox" name="prev_attachments" value="{{.Node.PathString}}" checked>
+      {{.Node}}
+    </label>
+  {{end}}
   <br><br>
   <input type="submit" name="save_as_draft" value="Save as draft">
   <input type="submit" value="Send">

plugins/base/routes.go

@@ -1,7 +1,9 @@
 package koushinbase
 
 import (
+	"bytes"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"mime"
 	"net/http"
@@ -14,6 +16,7 @@ import (
 	imapmove "github.com/emersion/go-imap-move"
 	imapclient "github.com/emersion/go-imap/client"
 	"github.com/emersion/go-message"
+	"github.com/emersion/go-message/mail"
 	"github.com/emersion/go-smtp"
 	"github.com/labstack/echo/v4"
 )
@@ -348,7 +351,51 @@ func handleCompose(ctx *koushin.Context, msg *OutgoingMessage, draft *messagePat
 		if err != nil {
 			return fmt.Errorf("failed to get multipart form: %v", err)
 		}
-		msg.Attachments = form.File["attachments"]
+
+		// Fetch previous attachments from draft
+		if draft != nil {
+			for _, s := range form.Value["prev_attachments"] {
+				path, err := parsePartPath(s)
+				if err != nil {
+					return fmt.Errorf("failed to parse draft attachment path: %v", err)
+				}
+
+				var part *message.Entity
+				err = ctx.Session.DoIMAP(func(c *imapclient.Client) error {
+					var err error
+					_, part, err = getMessagePart(c, draft.Mailbox, draft.Uid, path)
+					return err
+				})
+				if err != nil {
+					return fmt.Errorf("failed to fetch attachment from draft: %v", err)
+				}
+
+				var buf bytes.Buffer
+				if _, err := io.Copy(&buf, part.Body); err != nil {
+					return fmt.Errorf("failed to copy attachment from draft: %v", err)
+				}
+
+				h := mail.AttachmentHeader{part.Header}
+				mimeType, _, _ := h.ContentType()
+				filename, _ := h.Filename()
+				msg.Attachments = append(msg.Attachments, &imapAttachment{
+					Mailbox: draft.Mailbox,
+					Uid:     draft.Uid,
+					Node: &IMAPPartNode{
+						Path:     path,
+						MIMEType: mimeType,
+						Filename: filename,
+					},
+					Body: buf.Bytes(),
+				})
+			}
+		} else if len(form.Value["prev_attachments"]) > 0 {
+			return fmt.Errorf("previous attachments specified but no draft available")
+		}
+
+		for _, fh := range form.File["attachments"] {
+			msg.Attachments = append(msg.Attachments, &formAttachment{fh})
+		}
 
 		if saveAsDraft {
 			err = ctx.Session.DoIMAP(func(c *imapclient.Client) error {
@@ -510,7 +557,18 @@ func handleEdit(ctx *koushin.Context) error {
 		msg.Subject = source.Envelope.Subject
 		msg.InReplyTo = source.Envelope.InReplyTo
 		// TODO: preserve Message-Id
-		// TODO: preserve attachments
+
+		attachments := source.Attachments()
+		for i := range attachments {
+			att := &attachments[i]
+			// No need to populate attachment body here, we just need the
+			// metadata
+			msg.Attachments = append(msg.Attachments, &imapAttachment{
+				Mailbox: sourcePath.Mailbox,
+				Uid:     sourcePath.Uid,
+				Node:    att,
+			})
+		}
 	}
 
 	return handleCompose(ctx, &msg, &sourcePath, nil)

plugins/base/smtp.go

@@ -2,8 +2,11 @@ package koushinbase
 
 import (
 	"bufio"
+	"bytes"
 	"fmt"
 	"io"
+	"io/ioutil"
+	"mime"
 	"mime/multipart"
 	"strings"
 	"time"
@@ -26,23 +29,70 @@ func quote(r io.Reader) (string, error) {
 	return builder.String(), nil
 }
 
+type Attachment interface {
+	MIMEType() string
+	Filename() string
+	Open() (io.ReadCloser, error)
+}
+
+type formAttachment struct {
+	*multipart.FileHeader
+}
+
+func (att *formAttachment) Open() (io.ReadCloser, error) {
+	return att.FileHeader.Open()
+}
+
+func (att *formAttachment) MIMEType() string {
+	// TODO: retain params, e.g. "charset"?
+	t, _, _ := mime.ParseMediaType(att.FileHeader.Header.Get("Content-Type"))
+	return t
+}
+
+func (att *formAttachment) Filename() string {
+	return att.FileHeader.Filename
+}
+
+type imapAttachment struct {
+	Mailbox string
+	Uid     uint32
+	Node    *IMAPPartNode
+
+	Body []byte
+}
+
+func (att *imapAttachment) Open() (io.ReadCloser, error) {
+	if att.Body == nil {
+		return nil, fmt.Errorf("IMAP attachment has not been pre-fetched")
+	}
+	return ioutil.NopCloser(bytes.NewReader(att.Body)), nil
+}
+
+func (att *imapAttachment) MIMEType() string {
+	return att.Node.MIMEType
+}
+
+func (att *imapAttachment) Filename() string {
+	return att.Node.Filename
+}
+
 type OutgoingMessage struct {
 	From        string
 	To          []string
 	Subject     string
 	InReplyTo   string
 	Text        string
-	Attachments []*multipart.FileHeader
+	Attachments []Attachment
 }
 
 func (msg *OutgoingMessage) ToString() string {
 	return strings.Join(msg.To, ", ")
 }
 
-func writeAttachment(mw *mail.Writer, att *multipart.FileHeader) error {
+func writeAttachment(mw *mail.Writer, att Attachment) error {
 	var h mail.AttachmentHeader
-	h.Set("Content-Type", att.Header.Get("Content-Type"))
-	h.SetFilename(att.Filename)
+	h.SetContentType(att.MIMEType(), nil)
+	h.SetFilename(att.Filename())
 
 	aw, err := mw.CreateAttachment(h)
 	if err != nil {