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