exp/ssh: simplify client channel open logic

This is part one of a small set of CL's that aim to resolve
the outstanding TODOs relating to channel close and blocking
behavior.

Firstly, the hairy handling of assigning the peersId is now
done in one place. The cost of this change is the slightly
paradoxical construction of the partially created clientChan.

Secondly, by creating clientChan.stdin/out/err when the channel
is opened, the creation of consumers like tcpchan and Session
is simplified; they just have to wire themselves up to the
relevant readers/writers.

R=agl, gustav.paul, rsc
CC=golang-dev
https://golang.org/cl/5448073

src/pkg/exp/ssh/client.go

@@ -200,7 +200,7 @@ func (c *ClientConn) mainLoop() {
 			peersId := uint32(packet[1])<<24 | uint32(packet[2])<<16 | uint32(packet[3])<<8 | uint32(packet[4])
 			if length := int(packet[5])<<24 | int(packet[6])<<16 | int(packet[7])<<8 | int(packet[8]); length > 0 {
 				packet = packet[9:]
-				c.getChan(peersId).data <- packet[:length]
+				c.getChan(peersId).stdout.data <- packet[:length]
 			}
 		case msgChannelExtendedData:
 			if len(packet) < 13 {
@@ -215,7 +215,7 @@ func (c *ClientConn) mainLoop() {
 				// for stderr on interactive sessions. Other data types are
 				// silently discarded.
 				if datatype == 1 {
-					c.getChan(peersId).dataExt <- packet[:length]
+					c.getChan(peersId).stderr.data <- packet[:length]
 				}
 			}
 		default:
@@ -228,9 +228,9 @@ func (c *ClientConn) mainLoop() {
 				c.getChan(msg.PeersId).msg <- msg
 			case *channelCloseMsg:
 				ch := c.getChan(msg.PeersId)
-				close(ch.win)
-				close(ch.data)
-				close(ch.dataExt)
+				close(ch.stdin.win)
+				close(ch.stdout.data)
+				close(ch.stderr.data)
 				c.chanlist.remove(msg.PeersId)
 			case *channelEOFMsg:
 				c.getChan(msg.PeersId).msg <- msg
@@ -241,7 +241,7 @@ func (c *ClientConn) mainLoop() {
 			case *channelRequestMsg:
 				c.getChan(msg.PeersId).msg <- msg
 			case *windowAdjustMsg:
-				c.getChan(msg.PeersId).win <- int(msg.AdditionalBytes)
+				c.getChan(msg.PeersId).stdin.win <- int(msg.AdditionalBytes)
 			default:
 				fmt.Printf("mainLoop: unhandled message %T: %v\n", msg, msg)
 			}
@@ -290,21 +290,49 @@ func (c *ClientConfig) rand() io.Reader {
 type clientChan struct {
 	packetWriter
 	id, peersId uint32
-	data        chan []byte      // receives the payload of channelData messages
-	dataExt     chan []byte      // receives the payload of channelExtendedData messages
-	win         chan int         // receives window adjustments
+	stdin       *chanWriter      // receives window adjustments
+	stdout      *chanReader      // receives the payload of channelData messages
+	stderr      *chanReader      // receives the payload of channelExtendedData messages
 	msg         chan interface{} // incoming messages
 }
 
+// newClientChan returns a partially constructed *clientChan
+// using the local id provided. To be usable clientChan.peersId 
+// needs to be assigned once known.
 func newClientChan(t *transport, id uint32) *clientChan {
-	return &clientChan{
+	c := &clientChan{
 		packetWriter: t,
 		id:           id,
-		data:         make(chan []byte, 16),
-		dataExt:      make(chan []byte, 16),
-		win:          make(chan int, 16),
 		msg:          make(chan interface{}, 16),
 	}
+	c.stdin = &chanWriter{
+		win:        make(chan int, 16),
+		clientChan: c,
+	}
+	c.stdout = &chanReader{
+		data:       make(chan []byte, 16),
+		clientChan: c,
+	}
+	c.stderr = &chanReader{
+		data:       make(chan []byte, 16),
+		clientChan: c,
+	}
+	return c
+}
+
+// waitForChannelOpenResponse, if successful, fills out 
+// the peerId and records any initial window advertisement. 
+func (c *clientChan) waitForChannelOpenResponse() error {
+	switch msg := (<-c.msg).(type) {
+	case *channelOpenConfirmMsg:
+		// fixup peersId field
+		c.peersId = msg.MyId
+		c.stdin.win <- int(msg.MyWindow)
+		return nil
+	case *channelOpenFailureMsg:
+		return errors.New(safeString(msg.Message))
+	}
+	return errors.New("unexpected packet")
 }
 
 // Close closes the channel. This does not close the underlying connection.
@@ -356,9 +384,8 @@ func (c *chanlist) remove(id uint32) {
 // A chanWriter represents the stdin of a remote process.
 type chanWriter struct {
 	win        chan int    // receives window adjustments
-	peersId      uint32   // the peer's id
 	rwin       int         // current rwin size
-	packetWriter          // for sending channelDataMsg
+	clientChan *clientChan // the channel backing this writer
 }
 
 // Write writes data to the remote process's standard input.
@@ -372,12 +399,13 @@ func (w *chanWriter) Write(data []byte) (n int, err error) {
 			w.rwin += win
 			continue
 		}
+		peersId := w.clientChan.peersId
 		n = len(data)
 		packet := make([]byte, 0, 9+n)
 		packet = append(packet, msgChannelData,
-			byte(w.peersId>>24), byte(w.peersId>>16), byte(w.peersId>>8), byte(w.peersId),
+			byte(peersId>>24), byte(peersId>>16), byte(peersId>>8), byte(peersId),
 			byte(n>>24), byte(n>>16), byte(n>>8), byte(n))
-		err = w.writePacket(append(packet, data...))
+		err = w.clientChan.writePacket(append(packet, data...))
 		w.rwin -= n
 		return
 	}
@@ -385,7 +413,7 @@ func (w *chanWriter) Write(data []byte) (n int, err error) {
 }
 
 func (w *chanWriter) Close() error {
-	return w.writePacket(marshal(msgChannelEOF, channelEOFMsg{w.peersId}))
+	return w.clientChan.writePacket(marshal(msgChannelEOF, channelEOFMsg{w.clientChan.peersId}))
 }
 
 // A chanReader represents stdout or stderr of a remote process.
@@ -394,8 +422,7 @@ type chanReader struct {
 	// If writes to this channel block, they will block mainLoop, making
 	// it unable to receive new messages from the remote side.
 	data       chan []byte // receives data from remote
-	peersId      uint32      // the peer's id
-	packetWriter             // for sending windowAdjustMsg
+	clientChan *clientChan // the channel backing this reader
 	buf        []byte
 }
 
@@ -407,10 +434,10 @@ func (r *chanReader) Read(data []byte) (int, error) {
 			n := copy(data, r.buf)
 			r.buf = r.buf[n:]
 			msg := windowAdjustMsg{
-				PeersId:         r.peersId,
+				PeersId:         r.clientChan.peersId,
 				AdditionalBytes: uint32(n),
 			}
-			return n, r.writePacket(marshal(msgChannelWindowAdjust, msg))
+			return n, r.clientChan.writePacket(marshal(msgChannelWindowAdjust, msg))
 		}
 		r.buf, ok = <-r.data
 		if !ok {

src/pkg/exp/ssh/session.go

@@ -285,13 +285,8 @@ func (s *Session) stdin() error {
 		s.Stdin = new(bytes.Buffer)
 	}
 	s.copyFuncs = append(s.copyFuncs, func() error {
-		w := &chanWriter{
-			packetWriter: s,
-			peersId:      s.peersId,
-			win:          s.win,
-		}
-		_, err := io.Copy(w, s.Stdin)
-		if err1 := w.Close(); err == nil {
+		_, err := io.Copy(s.clientChan.stdin, s.Stdin)
+		if err1 := s.clientChan.stdin.Close(); err == nil {
 			err = err1
 		}
 		return err
@@ -304,12 +299,7 @@ func (s *Session) stdout() error {
 		s.Stdout = ioutil.Discard
 	}
 	s.copyFuncs = append(s.copyFuncs, func() error {
-		r := &chanReader{
-			packetWriter: s,
-			peersId:      s.peersId,
-			data:         s.data,
-		}
-		_, err := io.Copy(s.Stdout, r)
+		_, err := io.Copy(s.Stdout, s.clientChan.stdout)
 		return err
 	})
 	return nil
@@ -320,12 +310,7 @@ func (s *Session) stderr() error {
 		s.Stderr = ioutil.Discard
 	}
 	s.copyFuncs = append(s.copyFuncs, func() error {
-		r := &chanReader{
-			packetWriter: s,
-			peersId:      s.peersId,
-			data:         s.dataExt,
-		}
-		_, err := io.Copy(s.Stderr, r)
+		_, err := io.Copy(s.Stderr, s.clientChan.stderr)
 		return err
 	})
 	return nil
@@ -398,19 +383,11 @@ func (c *ClientConn) NewSession() (*Session, error) {
 		c.chanlist.remove(ch.id)
 		return nil, err
 	}
-	// wait for response
-	msg := <-ch.msg
-	switch msg := msg.(type) {
-	case *channelOpenConfirmMsg:
-		ch.peersId = msg.MyId
-		ch.win <- int(msg.MyWindow)
+	if err := ch.waitForChannelOpenResponse(); err != nil {
+		c.chanlist.remove(ch.id)
+		return nil, fmt.Errorf("ssh: unable to open session: %v", err)
+	}
 	return &Session{
 		clientChan: ch,
 	}, nil
-	case *channelOpenFailureMsg:
-		c.chanlist.remove(ch.id)
-		return nil, fmt.Errorf("ssh: channel open failed: %s", msg.Message)
-	}
-	c.chanlist.remove(ch.id)
-	return nil, fmt.Errorf("ssh: unexpected message %T: %v", msg, msg)
 }

src/pkg/exp/ssh/tcpip.go

@@ -6,6 +6,7 @@ package ssh
 
 import (
 	"errors"
+	"fmt"
 	"io"
 	"net"
 )
@@ -42,9 +43,6 @@ func (c *ClientConn) DialTCP(n string, laddr, raddr *net.TCPAddr) (net.Conn, err
 	}, nil
 }
 
-// dial opens a direct-tcpip connection to the remote server. laddr and raddr are passed as
-// strings and are expected to be resolveable at the remote end.
-func (c *ClientConn) dial(laddr string, lport int, raddr string, rport int) (*tcpchan, error) {
 // RFC 4254 7.2
 type channelOpenDirectMsg struct {
 	ChanType      string
@@ -56,6 +54,10 @@ func (c *ClientConn) dial(laddr string, lport int, raddr string, rport int) (*tc
 	laddr         string
 	lport         uint32
 }
+
+// dial opens a direct-tcpip connection to the remote server. laddr and raddr are passed as
+// strings and are expected to be resolveable at the remote end.
+func (c *ClientConn) dial(laddr string, lport int, raddr string, rport int) (*tcpchan, error) {
 	ch := c.newChan(c.transport)
 	if err := c.writePacket(marshal(msgChannelOpen, channelOpenDirectMsg{
 		ChanType:      "direct-tcpip",
@@ -70,30 +72,14 @@ func (c *ClientConn) dial(laddr string, lport int, raddr string, rport int) (*tc
 		c.chanlist.remove(ch.id)
 		return nil, err
 	}
-	// wait for response
-	switch msg := (<-ch.msg).(type) {
-	case *channelOpenConfirmMsg:
-		ch.peersId = msg.MyId
-		ch.win <- int(msg.MyWindow)
-	case *channelOpenFailureMsg:
+	if err := ch.waitForChannelOpenResponse(); err != nil {
 		c.chanlist.remove(ch.id)
-		return nil, errors.New("ssh: error opening remote TCP connection: " + msg.Message)
-	default:
-		c.chanlist.remove(ch.id)
-		return nil, errors.New("ssh: unexpected packet")
+		return nil, fmt.Errorf("ssh: unable to open direct tcpip connection: %v", err)
 	}
 	return &tcpchan{
 		clientChan: ch,
-		Reader: &chanReader{
-			packetWriter: ch,
-			peersId:      ch.peersId,
-			data:         ch.data,
-		},
-		Writer: &chanWriter{
-			packetWriter: ch,
-			peersId:      ch.peersId,
-			win:          ch.win,
-		},
+		Reader:     ch.stdout,
+		Writer:     ch.stdin,
 	}, nil
 }