exp/ssh: improve client channel close behavior

R=gustav.paul
CC=golang-dev
https://golang.org/cl/5480062

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).stdout.data <- packet[:length]
+				c.getChan(peersId).stdout.handleData(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).stderr.data <- packet[:length]
+					c.getChan(peersId).stderr.handleData(packet[:length])
 				}
 			}
 		default:
@@ -228,13 +228,22 @@ func (c *ClientConn) mainLoop() {
 				c.getChan(msg.PeersId).msg <- msg
 			case *channelCloseMsg:
 				ch := c.getChan(msg.PeersId)
+				ch.theyClosed = true
 				close(ch.stdin.win)
-				close(ch.stdout.data)
+				ch.stdout.eof()
-				close(ch.stderr.data)
+				ch.stderr.eof()
 				close(ch.msg)
+				if !ch.weClosed {
+					ch.weClosed = true
+					ch.sendClose()
+				}
 				c.chanlist.remove(msg.PeersId)
 			case *channelEOFMsg:
-				c.getChan(msg.PeersId).sendEOF()
+				ch := c.getChan(msg.PeersId)
+				ch.stdout.eof()
+				// RFC 4254 is mute on how EOF affects dataExt messages but
+				// it is logical to signal EOF at the same time.
+				ch.stderr.eof()
 			case *channelRequestSuccessMsg:
 				c.getChan(msg.PeersId).msg <- msg
 			case *channelRequestFailureMsg:
@@ -243,6 +252,8 @@ func (c *ClientConn) mainLoop() {
 				c.getChan(msg.PeersId).msg <- msg
 			case *windowAdjustMsg:
 				c.getChan(msg.PeersId).stdin.win <- int(msg.AdditionalBytes)
+			case *disconnectMsg:
+				break
 			default:
 				fmt.Printf("mainLoop: unhandled message %T: %v\n", msg, msg)
 			}
@@ -295,6 +306,9 @@ type clientChan struct {
 	stdout      *chanReader      // receives the payload of channelData messages
 	stderr      *chanReader      // receives the payload of channelExtendedData messages
 	msg         chan interface{} // incoming messages
+
+	theyClosed bool // indicates the close msg has been received from the remote side
+	weClosed   bool // incidates the close msg has been sent from our side
 }
 
 // newClientChan returns a partially constructed *clientChan
@@ -336,20 +350,29 @@ func (c *clientChan) waitForChannelOpenResponse() error {
 	return errors.New("unexpected packet")
 }
 
-// sendEOF Sends EOF to the server. RFC 4254 Section 5.3
+// sendEOF sends EOF to the server. RFC 4254 Section 5.3
 func (c *clientChan) sendEOF() error {
 	return c.writePacket(marshal(msgChannelEOF, channelEOFMsg{
 		PeersId: c.peersId,
 	}))
 }
 
-// Close closes the channel. This does not close the underlying connection.
+// sendClose signals the intent to close the channel.
-func (c *clientChan) Close() error {
+func (c *clientChan) sendClose() error {
 	return c.writePacket(marshal(msgChannelClose, channelCloseMsg{
 		PeersId: c.peersId,
 	}))
 }
 
+// Close closes the channel. This does not close the underlying connection.
+func (c *clientChan) Close() error {
+	if !c.weClosed {
+		c.weClosed = true
+		return c.sendClose()
+	}
+	return nil
+}
+
 // Thread safe channel list.
 type chanlist struct {
 	// protects concurrent access to chans
@@ -421,7 +444,7 @@ func (w *chanWriter) Write(data []byte) (n int, err error) {
 }
 
 func (w *chanWriter) Close() error {
-	return w.clientChan.writePacket(marshal(msgChannelEOF, channelEOFMsg{w.clientChan.peersId}))
+	return w.clientChan.sendEOF()
 }
 
 // A chanReader represents stdout or stderr of a remote process.
@@ -430,10 +453,27 @@ 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
+	dataClosed bool        // protects data from being closed twice
 	clientChan *clientChan // the channel backing this reader
 	buf        []byte
 }
 
+// eof signals to the consumer that there is no more data to be received.
+func (r *chanReader) eof() {
+	if !r.dataClosed {
+		r.dataClosed = true
+		close(r.data)
+	}
+}
+
+// handleData sends buf to the reader's consumer. If r.data is closed
+// the data will be silently discarded
+func (r *chanReader) handleData(buf []byte) {
+	if !r.dataClosed {
+		r.data <- buf
+	}
+}
+
 // Read reads data from the remote process's stdout or stderr.
 func (r *chanReader) Read(data []byte) (int, error) {
 	var ok bool