src/pkg/exp/ssh/messages.go - go - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package ssh

 import (
 	"big"
 	"bytes"
 	"io"
 	"os"
 	"reflect"
 )

 // These are SSH message type numbers. They are scattered around several
 // documents but many were taken from
 // http://www.iana.org/assignments/ssh-parameters/ssh-parameters.xml#ssh-parameters-1
 const (
 	msgDisconnect     = 1
 	msgIgnore         = 2
 	msgUnimplemented  = 3
 	msgDebug          = 4
 	msgServiceRequest = 5
 	msgServiceAccept  = 6

 	msgKexInit = 20
 	msgNewKeys = 21

 	msgKexDHInit  = 30
 	msgKexDHReply = 31

 	msgUserAuthRequest  = 50
 	msgUserAuthFailure  = 51
 	msgUserAuthSuccess  = 52
 	msgUserAuthBanner   = 53
 	msgUserAuthPubKeyOk = 60

 	msgGlobalRequest  = 80
 	msgRequestSuccess = 81
 	msgRequestFailure = 82

 	msgChannelOpen         = 90
 	msgChannelOpenConfirm  = 91
 	msgChannelOpenFailure  = 92
 	msgChannelWindowAdjust = 93
 	msgChannelData         = 94
 	msgChannelExtendedData = 95
 	msgChannelEOF          = 96
 	msgChannelClose        = 97
 	msgChannelRequest      = 98
 	msgChannelSuccess      = 99
 	msgChannelFailure      = 100
 )

 // SSH messages:
 //
 // These structures mirror the wire format of the corresponding SSH messages.
 // They are marshaled using reflection with the marshal and unmarshal functions
 // in this file. The only wrinkle is that a final member of type []byte with a
 // ssh tag of "rest" receives the remainder of a packet when unmarshaling.

 // See RFC 4253, section 11.1.
 type disconnectMsg struct {
 	Reason   uint32
 	Message  string
 	Language string
 }

 // See RFC 4253, section 7.1.
 type kexInitMsg struct {
 	Cookie                  [16]byte
 	KexAlgos                []string
 	ServerHostKeyAlgos      []string
 	CiphersClientServer     []string
 	CiphersServerClient     []string
 	MACsClientServer        []string
 	MACsServerClient        []string
 	CompressionClientServer []string
 	CompressionServerClient []string
 	LanguagesClientServer   []string
 	LanguagesServerClient   []string
 	FirstKexFollows         bool
 	Reserved                uint32
 }

 // See RFC 4253, section 8.
 type kexDHInitMsg struct {
 	X *big.Int
 }

 type kexDHReplyMsg struct {
 	HostKey   []byte
 	Y         *big.Int
 	Signature []byte
 }

 // See RFC 4253, section 10.
 type serviceRequestMsg struct {
 	Service string
 }

 // See RFC 4253, section 10.
 type serviceAcceptMsg struct {
 	Service string
 }

 // See RFC 4252, section 5.
 type userAuthRequestMsg struct {
 	User    string
 	Service string
 	Method  string
 	Payload []byte `ssh:"rest"`
 }

 // See RFC 4252, section 5.1
 type userAuthFailureMsg struct {
 	Methods        []string
 	PartialSuccess bool
 }

 // See RFC 4254, section 5.1.
 type channelOpenMsg struct {
 	ChanType         string
 	PeersId          uint32
 	PeersWindow      uint32
 	MaxPacketSize    uint32
 	TypeSpecificData []byte `ssh:"rest"`
 }

 // See RFC 4254, section 5.1.
 type channelOpenConfirmMsg struct {
 	PeersId          uint32
 	MyId             uint32
 	MyWindow         uint32
 	MaxPacketSize    uint32
 	TypeSpecificData []byte `ssh:"rest"`
 }

 // See RFC 4254, section 5.1.
 type channelOpenFailureMsg struct {
 	PeersId  uint32
 	Reason   uint32
 	Message  string
 	Language string
 }

 // See RFC 4254, section 5.2.
 type channelData struct {
 	PeersId uint32
 	Payload []byte `ssh:"rest"`
 }

 // See RFC 4254, section 5.2.
 type channelExtendedData struct {
 	PeersId  uint32
 	Datatype uint32
 	Payload  []byte `ssh:"rest"`
 }

 type channelRequestMsg struct {
 	PeersId             uint32
 	Request             string
 	WantReply           bool
 	RequestSpecificData []byte `ssh:"rest"`
 }

 // See RFC 4254, section 5.4.
 type channelRequestSuccessMsg struct {
 	PeersId uint32
 }

 // See RFC 4254, section 5.4.
 type channelRequestFailureMsg struct {
 	PeersId uint32
 }

 // See RFC 4254, section 5.3
 type channelCloseMsg struct {
 	PeersId uint32
 }

 // See RFC 4254, section 5.3
 type channelEOFMsg struct {
 	PeersId uint32
 }

 // See RFC 4254, section 4
 type globalRequestMsg struct {
 	Type      string
 	WantReply bool
 }

 // See RFC 4254, section 5.2
 type windowAdjustMsg struct {
 	PeersId         uint32
 	AdditionalBytes uint32
 }

 // See RFC 4252, section 7
 type userAuthPubKeyOkMsg struct {
 	Algo   string
 	PubKey string
 }

 // unmarshal parses the SSH wire data in packet into out using reflection.
 // expectedType is the expected SSH message type. It either returns nil on
 // success, or a ParseError or UnexpectedMessageError on error.
 func unmarshal(out interface{}, packet []byte, expectedType uint8) os.Error {
 	if len(packet) == 0 {
 		return ParseError{expectedType}
 	}
 	if packet[0] != expectedType {
 		return UnexpectedMessageError{expectedType, packet[0]}
 	}
 	packet = packet[1:]

 	v := reflect.ValueOf(out).Elem()
 	structType := v.Type()
 	var ok bool
 	for i := 0; i < v.NumField(); i++ {
 		field := v.Field(i)
 		t := field.Type()
 		switch t.Kind() {
 		case reflect.Bool:
 			if len(packet) < 1 {
 				return ParseError{expectedType}
 			}
 			field.SetBool(packet[0] != 0)
 			packet = packet[1:]
 		case reflect.Array:
 			if t.Elem().Kind() != reflect.Uint8 {
 				panic("array of non-uint8")
 			}
 			if len(packet) < t.Len() {
 				return ParseError{expectedType}
 			}
 			for j := 0; j < t.Len(); j++ {
 				field.Index(j).Set(reflect.ValueOf(packet[j]))
 			}
 			packet = packet[t.Len():]
 		case reflect.Uint32:
 			var u32 uint32
 			if u32, packet, ok = parseUint32(packet); !ok {
 				return ParseError{expectedType}
 			}
 			field.SetUint(uint64(u32))
 		case reflect.String:
 			var s []byte
 			if s, packet, ok = parseString(packet); !ok {
 				return ParseError{expectedType}
 			}
 			field.SetString(string(s))
 		case reflect.Slice:
 			switch t.Elem().Kind() {
 			case reflect.Uint8:
 				if structType.Field(i).Tag.Get("ssh") == "rest" {
 					field.Set(reflect.ValueOf(packet))
 					packet = nil
 				} else {
 					var s []byte
 					if s, packet, ok = parseString(packet); !ok {
 						return ParseError{expectedType}
 					}
 					field.Set(reflect.ValueOf(s))
 				}
 			case reflect.String:
 				var nl []string
 				if nl, packet, ok = parseNameList(packet); !ok {
 					return ParseError{expectedType}
 				}
 				field.Set(reflect.ValueOf(nl))
 			default:
 				panic("slice of unknown type")
 			}
 		case reflect.Ptr:
 			if t == bigIntType {
 				var n *big.Int
 				if n, packet, ok = parseInt(packet); !ok {
 					return ParseError{expectedType}
 				}
 				field.Set(reflect.ValueOf(n))
 			} else {
 				panic("pointer to unknown type")
 			}
 		default:
 			panic("unknown type")
 		}
 	}

 	if len(packet) != 0 {
 		return ParseError{expectedType}
 	}

 	return nil
 }

 // marshal serializes the message in msg, using the given message type.
 func marshal(msgType uint8, msg interface{}) []byte {
 	var out []byte
 	out = append(out, msgType)

 	v := reflect.ValueOf(msg)
 	structType := v.Type()
 	for i := 0; i < v.NumField(); i++ {
 		field := v.Field(i)
 		t := field.Type()
 		switch t.Kind() {
 		case reflect.Bool:
 			var v uint8
 			if field.Bool() {
 				v = 1
 			}
 			out = append(out, v)
 		case reflect.Array:
 			if t.Elem().Kind() != reflect.Uint8 {
 				panic("array of non-uint8")
 			}
 			for j := 0; j < t.Len(); j++ {
 				out = append(out, byte(field.Index(j).Uint()))
 			}
 		case reflect.Uint32:
 			u32 := uint32(field.Uint())
 			out = append(out, byte(u32>>24))
 			out = append(out, byte(u32>>16))
 			out = append(out, byte(u32>>8))
 			out = append(out, byte(u32))
 		case reflect.String:
 			s := field.String()
 			out = append(out, byte(len(s)>>24))
 			out = append(out, byte(len(s)>>16))
 			out = append(out, byte(len(s)>>8))
 			out = append(out, byte(len(s)))
 			out = append(out, s...)
 		case reflect.Slice:
 			switch t.Elem().Kind() {
 			case reflect.Uint8:
 				length := field.Len()
 				if structType.Field(i).Tag.Get("ssh") != "rest" {
 					out = append(out, byte(length>>24))
 					out = append(out, byte(length>>16))
 					out = append(out, byte(length>>8))
 					out = append(out, byte(length))
 				}
 				for j := 0; j < length; j++ {
 					out = append(out, byte(field.Index(j).Uint()))
 				}
 			case reflect.String:
 				var length int
 				for j := 0; j < field.Len(); j++ {
 					if j != 0 {
 						length++ /* comma */
 					}
 					length += len(field.Index(j).String())
 				}

 				out = append(out, byte(length>>24))
 				out = append(out, byte(length>>16))
 				out = append(out, byte(length>>8))
 				out = append(out, byte(length))
 				for j := 0; j < field.Len(); j++ {
 					if j != 0 {
 						out = append(out, ',')
 					}
 					out = append(out, field.Index(j).String()...)
 				}
 			default:
 				panic("slice of unknown type")
 			}
 		case reflect.Ptr:
 			if t == bigIntType {
 				var n *big.Int
 				nValue := reflect.ValueOf(&n)
 				nValue.Elem().Set(field)
 				needed := intLength(n)
 				oldLength := len(out)

 				if cap(out)-len(out) < needed {
 					newOut := make([]byte, len(out), 2*(len(out)+needed))
 					copy(newOut, out)
 					out = newOut
 				}
 				out = out[:oldLength+needed]
 				marshalInt(out[oldLength:], n)
 			} else {
 				panic("pointer to unknown type")
 			}
 		}
 	}

 	return out
 }

 var bigOne = big.NewInt(1)

 func parseString(in []byte) (out, rest []byte, ok bool) {
 	if len(in) < 4 {
 		return
 	}
 	length := uint32(in[0])<<24 | uint32(in[1])<<16 | uint32(in[2])<<8 | uint32(in[3])
 	if uint32(len(in)) < 4+length {
 		return
 	}
 	out = in[4 : 4+length]
 	rest = in[4+length:]
 	ok = true
 	return
 }

 var comma = []byte{','}

 func parseNameList(in []byte) (out []string, rest []byte, ok bool) {
 	contents, rest, ok := parseString(in)
 	if !ok {
 		return
 	}
 	if len(contents) == 0 {
 		return
 	}
 	parts := bytes.Split(contents, comma)
 	out = make([]string, len(parts))
 	for i, part := range parts {
 		out[i] = string(part)
 	}
 	return
 }

 func parseInt(in []byte) (out *big.Int, rest []byte, ok bool) {
 	contents, rest, ok := parseString(in)
 	if !ok {
 		return
 	}
 	out = new(big.Int)

 	if len(contents) > 0 && contents[0]&0x80 == 0x80 {
 		// This is a negative number
 		notBytes := make([]byte, len(contents))
 		for i := range notBytes {
 			notBytes[i] = ^contents[i]
 		}
 		out.SetBytes(notBytes)
 		out.Add(out, bigOne)
 		out.Neg(out)
 	} else {
 		// Positive number
 		out.SetBytes(contents)
 	}
 	ok = true
 	return
 }

 func parseUint32(in []byte) (out uint32, rest []byte, ok bool) {
 	if len(in) < 4 {
 		return
 	}
 	out = uint32(in[0])<<24 | uint32(in[1])<<16 | uint32(in[2])<<8 | uint32(in[3])
 	rest = in[4:]
 	ok = true
 	return
 }

 const maxPacketSize = 36000

 func nameListLength(namelist []string) int {
 	length := 4 /* uint32 length prefix */
 	for i, name := range namelist {
 		if i != 0 {
 			length++ /* comma */
 		}
 		length += len(name)
 	}
 	return length
 }

 func intLength(n *big.Int) int {
 	length := 4 /* length bytes */
 	if n.Sign() < 0 {
 		nMinus1 := new(big.Int).Neg(n)
 		nMinus1.Sub(nMinus1, bigOne)
 		bitLen := nMinus1.BitLen()
 		if bitLen%8 == 0 {
 			// The number will need 0xff padding
 			length++
 		}
 		length += (bitLen + 7) / 8
 	} else if n.Sign() == 0 {
 		// A zero is the zero length string
 	} else {
 		bitLen := n.BitLen()
 		if bitLen%8 == 0 {
 			// The number will need 0x00 padding
 			length++
 		}
 		length += (bitLen + 7) / 8
 	}

 	return length
 }

 func marshalInt(to []byte, n *big.Int) []byte {
 	lengthBytes := to
 	to = to[4:]
 	length := 0

 	if n.Sign() < 0 {
 		// A negative number has to be converted to two's-complement
 		// form. So we'll subtract 1 and invert. If the
 		// most-significant-bit isn't set then we'll need to pad the
 		// beginning with 0xff in order to keep the number negative.
 		nMinus1 := new(big.Int).Neg(n)
 		nMinus1.Sub(nMinus1, bigOne)
 		bytes := nMinus1.Bytes()
 		for i := range bytes {
 			bytes[i] ^= 0xff
 		}
 		if len(bytes) == 0 || bytes[0]&0x80 == 0 {
 			to[0] = 0xff
 			to = to[1:]
 			length++
 		}
 		nBytes := copy(to, bytes)
 		to = to[nBytes:]
 		length += nBytes
 	} else if n.Sign() == 0 {
 		// A zero is the zero length string
 	} else {
 		bytes := n.Bytes()
 		if len(bytes) > 0 && bytes[0]&0x80 != 0 {
 			// We'll have to pad this with a 0x00 in order to
 			// stop it looking like a negative number.
 			to[0] = 0
 			to = to[1:]
 			length++
 		}
 		nBytes := copy(to, bytes)
 		to = to[nBytes:]
 		length += nBytes
 	}

 	lengthBytes[0] = byte(length >> 24)
 	lengthBytes[1] = byte(length >> 16)
 	lengthBytes[2] = byte(length >> 8)
 	lengthBytes[3] = byte(length)
 	return to
 }

 func writeInt(w io.Writer, n *big.Int) {
 	length := intLength(n)
 	buf := make([]byte, length)
 	marshalInt(buf, n)
 	w.Write(buf)
 }

 func writeString(w io.Writer, s []byte) {
 	var lengthBytes [4]byte
 	lengthBytes[0] = byte(len(s) >> 24)
 	lengthBytes[1] = byte(len(s) >> 16)
 	lengthBytes[2] = byte(len(s) >> 8)
 	lengthBytes[3] = byte(len(s))
 	w.Write(lengthBytes[:])
 	w.Write(s)
 }

 func stringLength(s []byte) int {
 	return 4 + len(s)
 }

 func marshalString(to []byte, s []byte) []byte {
 	to[0] = byte(len(s) >> 24)
 	to[1] = byte(len(s) >> 16)
 	to[2] = byte(len(s) >> 8)
 	to[3] = byte(len(s))
 	to = to[4:]
 	copy(to, s)
 	return to[len(s):]
 }

 var bigIntType = reflect.TypeOf((*big.Int)(nil))

 // Decode a packet into it's corresponding message.
 func decode(packet []byte) interface{} {
 	var msg interface{}
 	switch packet[0] {
 	case msgDisconnect:
 		msg = new(disconnectMsg)
 	case msgServiceRequest:
 		msg = new(serviceRequestMsg)
 	case msgServiceAccept:
 		msg = new(serviceAcceptMsg)
 	case msgKexInit:
 		msg = new(kexInitMsg)
 	case msgKexDHInit:
 		msg = new(kexDHInitMsg)
 	case msgKexDHReply:
 		msg = new(kexDHReplyMsg)
 	case msgUserAuthRequest:
 		msg = new(userAuthRequestMsg)
 	case msgUserAuthFailure:
 		msg = new(userAuthFailureMsg)
 	case msgUserAuthPubKeyOk:
 		msg = new(userAuthPubKeyOkMsg)
 	case msgGlobalRequest:
 		msg = new(globalRequestMsg)
 	case msgRequestSuccess:
 		msg = new(channelRequestSuccessMsg)
 	case msgRequestFailure:
 		msg = new(channelRequestFailureMsg)
 	case msgChannelOpen:
 		msg = new(channelOpenMsg)
 	case msgChannelOpenConfirm:
 		msg = new(channelOpenConfirmMsg)
 	case msgChannelOpenFailure:
 		msg = new(channelOpenFailureMsg)
 	case msgChannelWindowAdjust:
 		msg = new(windowAdjustMsg)
 	case msgChannelData:
 		msg = new(channelData)
 	case msgChannelExtendedData:
 		msg = new(channelExtendedData)
 	case msgChannelEOF:
 		msg = new(channelEOFMsg)
 	case msgChannelClose:
 		msg = new(channelCloseMsg)
 	case msgChannelRequest:
 		msg = new(channelRequestMsg)
 	case msgChannelSuccess:
 		msg = new(channelRequestSuccessMsg)
 	case msgChannelFailure:
 		msg = new(channelRequestFailureMsg)
 	default:
 		return UnexpectedMessageError{0, packet[0]}
 	}
 	if err := unmarshal(msg, packet, packet[0]); err != nil {
 		return err
 	}
 	return msg
 }
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package ssh

	import (
	"big"
	"bytes"
	"io"
	"os"
	"reflect"
	)

	// These are SSH message type numbers. They are scattered around several
	// documents but many were taken from
	// http://www.iana.org/assignments/ssh-parameters/ssh-parameters.xml#ssh-parameters-1
	const (
	msgDisconnect = 1
	msgIgnore = 2
	msgUnimplemented = 3
	msgDebug = 4
	msgServiceRequest = 5
	msgServiceAccept = 6

	msgKexInit = 20
	msgNewKeys = 21

	msgKexDHInit = 30
	msgKexDHReply = 31

	msgUserAuthRequest = 50
	msgUserAuthFailure = 51
	msgUserAuthSuccess = 52
	msgUserAuthBanner = 53
	msgUserAuthPubKeyOk = 60

	msgGlobalRequest = 80
	msgRequestSuccess = 81
	msgRequestFailure = 82

	msgChannelOpen = 90
	msgChannelOpenConfirm = 91
	msgChannelOpenFailure = 92
	msgChannelWindowAdjust = 93
	msgChannelData = 94
	msgChannelExtendedData = 95
	msgChannelEOF = 96
	msgChannelClose = 97
	msgChannelRequest = 98
	msgChannelSuccess = 99
	msgChannelFailure = 100
	)

	// SSH messages:
	//
	// These structures mirror the wire format of the corresponding SSH messages.
	// They are marshaled using reflection with the marshal and unmarshal functions
	// in this file. The only wrinkle is that a final member of type []byte with a
	// ssh tag of "rest" receives the remainder of a packet when unmarshaling.

	// See RFC 4253, section 11.1.
	type disconnectMsg struct {
	Reason uint32
	Message string
	Language string
	}

	// See RFC 4253, section 7.1.
	type kexInitMsg struct {
	Cookie [16]byte
	KexAlgos []string
	ServerHostKeyAlgos []string
	CiphersClientServer []string
	CiphersServerClient []string
	MACsClientServer []string
	MACsServerClient []string
	CompressionClientServer []string
	CompressionServerClient []string
	LanguagesClientServer []string
	LanguagesServerClient []string
	FirstKexFollows bool
	Reserved uint32
	}

	// See RFC 4253, section 8.
	type kexDHInitMsg struct {
	X *big.Int
	}

	type kexDHReplyMsg struct {
	HostKey []byte
	Y *big.Int
	Signature []byte
	}

	// See RFC 4253, section 10.
	type serviceRequestMsg struct {
	Service string
	}

	// See RFC 4253, section 10.
	type serviceAcceptMsg struct {
	Service string
	}

	// See RFC 4252, section 5.
	type userAuthRequestMsg struct {
	User string
	Service string
	Method string
	Payload []byte `ssh:"rest"`
	}

	// See RFC 4252, section 5.1
	type userAuthFailureMsg struct {
	Methods []string
	PartialSuccess bool
	}

	// See RFC 4254, section 5.1.
	type channelOpenMsg struct {
	ChanType string
	PeersId uint32
	PeersWindow uint32
	MaxPacketSize uint32
	TypeSpecificData []byte `ssh:"rest"`
	}

	// See RFC 4254, section 5.1.
	type channelOpenConfirmMsg struct {
	PeersId uint32
	MyId uint32
	MyWindow uint32
	MaxPacketSize uint32
	TypeSpecificData []byte `ssh:"rest"`
	}

	// See RFC 4254, section 5.1.
	type channelOpenFailureMsg struct {
	PeersId uint32
	Reason uint32
	Message string
	Language string
	}

	// See RFC 4254, section 5.2.
	type channelData struct {
	PeersId uint32
	Payload []byte `ssh:"rest"`
	}

	// See RFC 4254, section 5.2.
	type channelExtendedData struct {
	PeersId uint32
	Datatype uint32
	Payload []byte `ssh:"rest"`
	}

	type channelRequestMsg struct {
	PeersId uint32
	Request string
	WantReply bool
	RequestSpecificData []byte `ssh:"rest"`
	}

	// See RFC 4254, section 5.4.
	type channelRequestSuccessMsg struct {
	PeersId uint32
	}

	// See RFC 4254, section 5.4.
	type channelRequestFailureMsg struct {
	PeersId uint32
	}

	// See RFC 4254, section 5.3
	type channelCloseMsg struct {
	PeersId uint32
	}

	// See RFC 4254, section 5.3
	type channelEOFMsg struct {
	PeersId uint32
	}

	// See RFC 4254, section 4
	type globalRequestMsg struct {
	Type string
	WantReply bool
	}

	// See RFC 4254, section 5.2
	type windowAdjustMsg struct {
	PeersId uint32
	AdditionalBytes uint32
	}

	// See RFC 4252, section 7
	type userAuthPubKeyOkMsg struct {
	Algo string
	PubKey string
	}

	// unmarshal parses the SSH wire data in packet into out using reflection.
	// expectedType is the expected SSH message type. It either returns nil on
	// success, or a ParseError or UnexpectedMessageError on error.
	func unmarshal(out interface{}, packet []byte, expectedType uint8) os.Error {
	if len(packet) == 0 {
	return ParseError{expectedType}
	}
	if packet[0] != expectedType {
	return UnexpectedMessageError{expectedType, packet[0]}
	}
	packet = packet[1:]

	v := reflect.ValueOf(out).Elem()
	structType := v.Type()
	var ok bool
	for i := 0; i < v.NumField(); i++ {
	field := v.Field(i)
	t := field.Type()
	switch t.Kind() {
	case reflect.Bool:
	if len(packet) < 1 {
	return ParseError{expectedType}
	}
	field.SetBool(packet[0] != 0)
	packet = packet[1:]
	case reflect.Array:
	if t.Elem().Kind() != reflect.Uint8 {
	panic("array of non-uint8")
	}
	if len(packet) < t.Len() {
	return ParseError{expectedType}
	}
	for j := 0; j < t.Len(); j++ {
	field.Index(j).Set(reflect.ValueOf(packet[j]))
	}
	packet = packet[t.Len():]
	case reflect.Uint32:
	var u32 uint32
	if u32, packet, ok = parseUint32(packet); !ok {
	return ParseError{expectedType}
	}
	field.SetUint(uint64(u32))
	case reflect.String:
	var s []byte
	if s, packet, ok = parseString(packet); !ok {
	return ParseError{expectedType}
	}
	field.SetString(string(s))
	case reflect.Slice:
	switch t.Elem().Kind() {
	case reflect.Uint8:
	if structType.Field(i).Tag.Get("ssh") == "rest" {
	field.Set(reflect.ValueOf(packet))
	packet = nil
	} else {
	var s []byte
	if s, packet, ok = parseString(packet); !ok {
	return ParseError{expectedType}
	}
	field.Set(reflect.ValueOf(s))
	}
	case reflect.String:
	var nl []string
	if nl, packet, ok = parseNameList(packet); !ok {
	return ParseError{expectedType}
	}
	field.Set(reflect.ValueOf(nl))
	default:
	panic("slice of unknown type")
	}
	case reflect.Ptr:
	if t == bigIntType {
	var n *big.Int
	if n, packet, ok = parseInt(packet); !ok {
	return ParseError{expectedType}
	}
	field.Set(reflect.ValueOf(n))
	} else {
	panic("pointer to unknown type")
	}
	default:
	panic("unknown type")
	}
	}

	if len(packet) != 0 {
	return ParseError{expectedType}
	}

	return nil
	}

	// marshal serializes the message in msg, using the given message type.
	func marshal(msgType uint8, msg interface{}) []byte {
	var out []byte
	out = append(out, msgType)

	v := reflect.ValueOf(msg)
	structType := v.Type()
	for i := 0; i < v.NumField(); i++ {
	field := v.Field(i)
	t := field.Type()
	switch t.Kind() {
	case reflect.Bool:
	var v uint8
	if field.Bool() {
	v = 1
	}
	out = append(out, v)
	case reflect.Array:
	if t.Elem().Kind() != reflect.Uint8 {
	panic("array of non-uint8")
	}
	for j := 0; j < t.Len(); j++ {
	out = append(out, byte(field.Index(j).Uint()))
	}
	case reflect.Uint32:
	u32 := uint32(field.Uint())
	out = append(out, byte(u32>>24))
	out = append(out, byte(u32>>16))
	out = append(out, byte(u32>>8))
	out = append(out, byte(u32))
	case reflect.String:
	s := field.String()
	out = append(out, byte(len(s)>>24))
	out = append(out, byte(len(s)>>16))
	out = append(out, byte(len(s)>>8))
	out = append(out, byte(len(s)))
	out = append(out, s...)
	case reflect.Slice:
	switch t.Elem().Kind() {
	case reflect.Uint8:
	length := field.Len()
	if structType.Field(i).Tag.Get("ssh") != "rest" {
	out = append(out, byte(length>>24))
	out = append(out, byte(length>>16))
	out = append(out, byte(length>>8))
	out = append(out, byte(length))
	}
	for j := 0; j < length; j++ {
	out = append(out, byte(field.Index(j).Uint()))
	}
	case reflect.String:
	var length int
	for j := 0; j < field.Len(); j++ {
	if j != 0 {
	length++ /* comma */
	}
	length += len(field.Index(j).String())
	}

	out = append(out, byte(length>>24))
	out = append(out, byte(length>>16))
	out = append(out, byte(length>>8))
	out = append(out, byte(length))
	for j := 0; j < field.Len(); j++ {
	if j != 0 {
	out = append(out, ',')
	}
	out = append(out, field.Index(j).String()...)
	}
	default:
	panic("slice of unknown type")
	}
	case reflect.Ptr:
	if t == bigIntType {
	var n *big.Int
	nValue := reflect.ValueOf(&n)
	nValue.Elem().Set(field)
	needed := intLength(n)
	oldLength := len(out)

	if cap(out)-len(out) < needed {
	newOut := make([]byte, len(out), 2*(len(out)+needed))
	copy(newOut, out)
	out = newOut
	}
	out = out[:oldLength+needed]
	marshalInt(out[oldLength:], n)
	} else {
	panic("pointer to unknown type")
	}
	}
	}

	return out
	}

	var bigOne = big.NewInt(1)

	func parseString(in []byte) (out, rest []byte, ok bool) {
	if len(in) < 4 {
	return
	}
	length := uint32(in[0])<<24 \| uint32(in[1])<<16 \| uint32(in[2])<<8 \| uint32(in[3])
	if uint32(len(in)) < 4+length {
	return
	}
	out = in[4 : 4+length]
	rest = in[4+length:]
	ok = true
	return
	}

	var comma = []byte{','}

	func parseNameList(in []byte) (out []string, rest []byte, ok bool) {
	contents, rest, ok := parseString(in)
	if !ok {
	return
	}
	if len(contents) == 0 {
	return
	}
	parts := bytes.Split(contents, comma)
	out = make([]string, len(parts))
	for i, part := range parts {
	out[i] = string(part)
	}
	return
	}

	func parseInt(in []byte) (out *big.Int, rest []byte, ok bool) {
	contents, rest, ok := parseString(in)
	if !ok {
	return
	}
	out = new(big.Int)

	if len(contents) > 0 && contents[0]&0x80 == 0x80 {
	// This is a negative number
	notBytes := make([]byte, len(contents))
	for i := range notBytes {
	notBytes[i] = ^contents[i]
	}
	out.SetBytes(notBytes)
	out.Add(out, bigOne)
	out.Neg(out)
	} else {
	// Positive number
	out.SetBytes(contents)
	}
	ok = true
	return
	}

	func parseUint32(in []byte) (out uint32, rest []byte, ok bool) {
	if len(in) < 4 {
	return
	}
	out = uint32(in[0])<<24 \| uint32(in[1])<<16 \| uint32(in[2])<<8 \| uint32(in[3])
	rest = in[4:]
	ok = true
	return
	}

	const maxPacketSize = 36000

	func nameListLength(namelist []string) int {
	length := 4 /* uint32 length prefix */
	for i, name := range namelist {
	if i != 0 {
	length++ /* comma */
	}
	length += len(name)
	}
	return length
	}

	func intLength(n *big.Int) int {
	length := 4 /* length bytes */
	if n.Sign() < 0 {
	nMinus1 := new(big.Int).Neg(n)
	nMinus1.Sub(nMinus1, bigOne)
	bitLen := nMinus1.BitLen()
	if bitLen%8 == 0 {
	// The number will need 0xff padding
	length++
	}
	length += (bitLen + 7) / 8
	} else if n.Sign() == 0 {
	// A zero is the zero length string
	} else {
	bitLen := n.BitLen()
	if bitLen%8 == 0 {
	// The number will need 0x00 padding
	length++
	}
	length += (bitLen + 7) / 8
	}

	return length
	}

	func marshalInt(to []byte, n *big.Int) []byte {
	lengthBytes := to
	to = to[4:]
	length := 0

	if n.Sign() < 0 {
	// A negative number has to be converted to two's-complement
	// form. So we'll subtract 1 and invert. If the
	// most-significant-bit isn't set then we'll need to pad the
	// beginning with 0xff in order to keep the number negative.
	nMinus1 := new(big.Int).Neg(n)
	nMinus1.Sub(nMinus1, bigOne)
	bytes := nMinus1.Bytes()
	for i := range bytes {
	bytes[i] ^= 0xff
	}
	if len(bytes) == 0 \|\| bytes[0]&0x80 == 0 {
	to[0] = 0xff
	to = to[1:]
	length++
	}
	nBytes := copy(to, bytes)
	to = to[nBytes:]
	length += nBytes
	} else if n.Sign() == 0 {
	// A zero is the zero length string
	} else {
	bytes := n.Bytes()
	if len(bytes) > 0 && bytes[0]&0x80 != 0 {
	// We'll have to pad this with a 0x00 in order to
	// stop it looking like a negative number.
	to[0] = 0
	to = to[1:]
	length++
	}
	nBytes := copy(to, bytes)
	to = to[nBytes:]
	length += nBytes
	}

	lengthBytes[0] = byte(length >> 24)
	lengthBytes[1] = byte(length >> 16)
	lengthBytes[2] = byte(length >> 8)
	lengthBytes[3] = byte(length)
	return to
	}

	func writeInt(w io.Writer, n *big.Int) {
	length := intLength(n)
	buf := make([]byte, length)
	marshalInt(buf, n)
	w.Write(buf)
	}

	func writeString(w io.Writer, s []byte) {
	var lengthBytes [4]byte
	lengthBytes[0] = byte(len(s) >> 24)
	lengthBytes[1] = byte(len(s) >> 16)
	lengthBytes[2] = byte(len(s) >> 8)
	lengthBytes[3] = byte(len(s))
	w.Write(lengthBytes[:])
	w.Write(s)
	}

	func stringLength(s []byte) int {
	return 4 + len(s)
	}

	func marshalString(to []byte, s []byte) []byte {
	to[0] = byte(len(s) >> 24)
	to[1] = byte(len(s) >> 16)
	to[2] = byte(len(s) >> 8)
	to[3] = byte(len(s))
	to = to[4:]
	copy(to, s)
	return to[len(s):]
	}

	var bigIntType = reflect.TypeOf((*big.Int)(nil))

	// Decode a packet into it's corresponding message.
	func decode(packet []byte) interface{} {
	var msg interface{}
	switch packet[0] {
	case msgDisconnect:
	msg = new(disconnectMsg)
	case msgServiceRequest:
	msg = new(serviceRequestMsg)
	case msgServiceAccept:
	msg = new(serviceAcceptMsg)
	case msgKexInit:
	msg = new(kexInitMsg)
	case msgKexDHInit:
	msg = new(kexDHInitMsg)
	case msgKexDHReply:
	msg = new(kexDHReplyMsg)
	case msgUserAuthRequest:
	msg = new(userAuthRequestMsg)
	case msgUserAuthFailure:
	msg = new(userAuthFailureMsg)
	case msgUserAuthPubKeyOk:
	msg = new(userAuthPubKeyOkMsg)
	case msgGlobalRequest:
	msg = new(globalRequestMsg)
	case msgRequestSuccess:
	msg = new(channelRequestSuccessMsg)
	case msgRequestFailure:
	msg = new(channelRequestFailureMsg)
	case msgChannelOpen:
	msg = new(channelOpenMsg)
	case msgChannelOpenConfirm:
	msg = new(channelOpenConfirmMsg)
	case msgChannelOpenFailure:
	msg = new(channelOpenFailureMsg)
	case msgChannelWindowAdjust:
	msg = new(windowAdjustMsg)
	case msgChannelData:
	msg = new(channelData)
	case msgChannelExtendedData:
	msg = new(channelExtendedData)
	case msgChannelEOF:
	msg = new(channelEOFMsg)
	case msgChannelClose:
	msg = new(channelCloseMsg)
	case msgChannelRequest:
	msg = new(channelRequestMsg)
	case msgChannelSuccess:
	msg = new(channelRequestSuccessMsg)
	case msgChannelFailure:
	msg = new(channelRequestFailureMsg)
	default:
	return UnexpectedMessageError{0, packet[0]}
	}
	if err := unmarshal(msg, packet, packet[0]); err != nil {
	return err
	}
	return msg
	}