exp/ssh: general cleanups for client support

common.go:
* simplify findAgreedAlgorithms.
* add channelExtendedData support.

messages.go:
* add clientExtendedData.

server.go:
*  use simplified findAgreedAlgorithms.

server_shell.go:
* fix shadowed err return value.

transport.go:
* introduce separate cipher, mac and compression for each direction.
* added filteredConn and packetWriter interfaces.
* newTransport requires a source of randomness.

R=golang-dev, agl, rsc
CC=golang-dev
https://golang.org/cl/5285044

src/pkg/exp/ssh/common.go

@@ -83,7 +83,7 @@ func findCommonAlgorithm(clientAlgos []string, serverAlgos []string) (commonAlgo
 	return
 }
 
-func findAgreedAlgorithms(clientToServer, serverToClient *transport, clientKexInit, serverKexInit *kexInitMsg) (kexAlgo, hostKeyAlgo string, ok bool) {
+func findAgreedAlgorithms(transport *transport, clientKexInit, serverKexInit *kexInitMsg) (kexAlgo, hostKeyAlgo string, ok bool) {
 	kexAlgo, ok = findCommonAlgorithm(clientKexInit.KexAlgos, serverKexInit.KexAlgos)
 	if !ok {
 		return
@@ -94,32 +94,32 @@ func findAgreedAlgorithms(clientToServer, serverToClient *transport, clientKexIn
 		return
 	}
 
-	clientToServer.cipherAlgo, ok = findCommonAlgorithm(clientKexInit.CiphersClientServer, serverKexInit.CiphersClientServer)
+	transport.writer.cipherAlgo, ok = findCommonAlgorithm(clientKexInit.CiphersClientServer, serverKexInit.CiphersClientServer)
 	if !ok {
 		return
 	}
 
-	serverToClient.cipherAlgo, ok = findCommonAlgorithm(clientKexInit.CiphersServerClient, serverKexInit.CiphersServerClient)
+	transport.reader.cipherAlgo, ok = findCommonAlgorithm(clientKexInit.CiphersServerClient, serverKexInit.CiphersServerClient)
 	if !ok {
 		return
 	}
 
-	clientToServer.macAlgo, ok = findCommonAlgorithm(clientKexInit.MACsClientServer, serverKexInit.MACsClientServer)
+	transport.writer.macAlgo, ok = findCommonAlgorithm(clientKexInit.MACsClientServer, serverKexInit.MACsClientServer)
 	if !ok {
 		return
 	}
 
-	serverToClient.macAlgo, ok = findCommonAlgorithm(clientKexInit.MACsServerClient, serverKexInit.MACsServerClient)
+	transport.reader.macAlgo, ok = findCommonAlgorithm(clientKexInit.MACsServerClient, serverKexInit.MACsServerClient)
 	if !ok {
 		return
 	}
 
-	clientToServer.compressionAlgo, ok = findCommonAlgorithm(clientKexInit.CompressionClientServer, serverKexInit.CompressionClientServer)
+	transport.writer.compressionAlgo, ok = findCommonAlgorithm(clientKexInit.CompressionClientServer, serverKexInit.CompressionClientServer)
 	if !ok {
 		return
 	}
 
-	serverToClient.compressionAlgo, ok = findCommonAlgorithm(clientKexInit.CompressionServerClient, serverKexInit.CompressionServerClient)
+	transport.reader.compressionAlgo, ok = findCommonAlgorithm(clientKexInit.CompressionServerClient, serverKexInit.CompressionServerClient)
 	if !ok {
 		return
 	}

src/pkg/exp/ssh/messages.go

@@ -150,6 +150,13 @@ type channelData struct {
 	Payload []byte `ssh:"rest"`
 }
 
+// See RFC 4254, section 5.2.
+type channelExtendedData struct {
+	PeersId  uint32
+	Datatype uint32
+	Data     string
+}
+
 type channelRequestMsg struct {
 	PeersId             uint32
 	Request             string
@@ -607,6 +614,8 @@ func decode(packet []byte) interface{} {
 		msg = new(windowAdjustMsg)
 	case msgChannelData:
 		msg = new(channelData)
+	case msgChannelExtendedData:
+		msg = new(channelExtendedData)
 	case msgChannelEOF:
 		msg = new(channelEOFMsg)
 	case msgChannelClose:

src/pkg/exp/ssh/server.go

@@ -260,7 +260,7 @@ func buildDataSignedForAuth(sessionId []byte, req userAuthRequestMsg, algo, pubK
 // Handshake performs an SSH transport and client authentication on the given ServerConnection.
 func (s *ServerConnection) Handshake(conn net.Conn) os.Error {
 	var magics handshakeMagics
-	s.transport = newTransport(conn)
+	s.transport = newTransport(conn, rand.Reader)
 
 	if _, err := conn.Write(serverVersion); err != nil {
 		return err
@@ -302,7 +302,7 @@ func (s *ServerConnection) Handshake(conn net.Conn) os.Error {
 		return err
 	}
 
-	kexAlgo, hostKeyAlgo, ok := findAgreedAlgorithms(s.transport, s.transport, &clientKexInit, &serverKexInit)
+	kexAlgo, hostKeyAlgo, ok := findAgreedAlgorithms(s.transport, &clientKexInit, &serverKexInit)
 	if !ok {
 		return os.NewError("ssh: no common algorithms")
 	}

src/pkg/exp/ssh/server_shell.go

@@ -340,7 +340,8 @@ func (ss *ServerShell) ReadLine() (line string, err os.Error) {
 		// ss.remainder is a slice at the beginning of ss.inBuf
 		// containing a partial key sequence
 		readBuf := ss.inBuf[len(ss.remainder):]
-		n, err := ss.c.Read(readBuf)
+		var n int
+		n, err = ss.c.Read(readBuf)
 		if err == nil {
 			ss.remainder = ss.inBuf[:n+len(ss.remainder)]
 			rest := ss.remainder

src/pkg/exp/ssh/transport.go

@@ -10,7 +10,6 @@ import (
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/hmac"
-	"crypto/rand"
 	"crypto/subtle"
 	"hash"
 	"io"
@@ -23,17 +22,33 @@ const (
 	paddingMultiple = 16 // TODO(dfc) does this need to be configurable?
 )
 
+// filteredConn reduces the set of methods exposed when embeddeding
+// a net.Conn inside ssh.transport.
+// TODO(dfc) suggestions for a better name will be warmly received.
+type filteredConn interface {
+	// Close closes the connection.
+	Close() os.Error
+
+	// LocalAddr returns the local network address.
+	LocalAddr() net.Addr
+
+	// RemoteAddr returns the remote network address.
+	RemoteAddr() net.Addr
+}
+
+// Types implementing packetWriter provide the ability to send packets to
+// an SSH peer.
+type packetWriter interface {
+	// Encrypt and send a packet of data to the remote peer.
+	writePacket(packet []byte) os.Error
+}
+
 // transport represents the SSH connection to the remote peer.
 type transport struct {
 	reader
 	writer
 
-	cipherAlgo      string
-	macAlgo         string
-	compressionAlgo string
-
-	Close      func() os.Error
-	RemoteAddr func() net.Addr
+	filteredConn
 }
 
 // reader represents the incoming connection state.
@@ -57,6 +72,10 @@ type common struct {
 	seqNum uint32
 	mac    hash.Hash
 	cipher cipher.Stream
+
+	cipherAlgo      string
+	macAlgo         string
+	compressionAlgo string
 }
 
 // Read and decrypt a single packet from the remote peer.
@@ -204,22 +223,17 @@ func (t *transport) sendMessage(typ uint8, msg interface{}) os.Error {
 	return t.writePacket(packet)
 }
 
-func newTransport(conn net.Conn) *transport {
+func newTransport(conn net.Conn, rand io.Reader) *transport {
 	return &transport{
 		reader: reader{
 			Reader: bufio.NewReader(conn),
 		},
 		writer: writer{
 			Writer: bufio.NewWriter(conn),
-			rand:   rand.Reader,
+			rand:   rand,
 			Mutex:  new(sync.Mutex),
 		},
-		Close: func() os.Error {
-			return conn.Close()
-		},
-		RemoteAddr: func() net.Addr {
-			return conn.RemoteAddr()
-		},
+		filteredConn: conn,
 	}
 }