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))
}
