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
}
