go.crypto/ssh: make {client,server}Chan use common window management

R=agl, gustav.paul, kardianos
CC=golang-dev
https://golang.org/cl/6208043

ssh/client.go

@@ -276,7 +276,7 @@ func (c *ClientConn) mainLoop() {
 			case *channelRequestMsg:
 				c.getChan(msg.PeersId).msg <- msg
 			case *windowAdjustMsg:
-				if !c.getChan(msg.PeersId).stdin.win.add(msg.AdditionalBytes) {
+				if !c.getChan(msg.PeersId).remoteWin.add(msg.AdditionalBytes) {
 					// invalid window update
 					return
 				}
@@ -317,7 +317,7 @@ func (c *ClientConn) handleChanOpen(msg *channelOpenMsg) {
 		}
 		ch := c.newChan(c.transport)
 		ch.remoteId = msg.PeersId
-		ch.stdin.win.add(msg.PeersWindow)
+		ch.remoteWin.add(msg.PeersWindow)
 
 		m := channelOpenConfirmMsg{
 			PeersId:       ch.remoteId,
@@ -438,13 +438,13 @@ type clientChan struct {
 func newClientChan(cc conn, id uint32) *clientChan {
 	c := &clientChan{
 		channel: channel{
-			conn:    cc,
-			localId: id,
+			conn:      cc,
+			localId:   id,
+			remoteWin: window{Cond: newCond()},
 		},
 		msg: make(chan interface{}, 16),
 	}
 	c.stdin = &chanWriter{
-		win:     &window{Cond: sync.NewCond(new(sync.Mutex))},
 		channel: &c.channel,
 	}
 	c.stdout = &chanReader{
@@ -465,7 +465,7 @@ func (c *clientChan) waitForChannelOpenResponse() error {
 	case *channelOpenConfirmMsg:
 		// fixup remoteId field
 		c.remoteId = msg.MyId
-		c.stdin.win.add(msg.MyWindow)
+		c.remoteWin.add(msg.MyWindow)
 		return nil
 	case *channelOpenFailureMsg:
 		return errors.New(safeString(msg.Message))
@@ -542,7 +542,6 @@ func (c *chanList) closeAll() {
 
 // A chanWriter represents the stdin of a remote process.
 type chanWriter struct {
-	win *window
 	*channel
 }
 
@@ -551,7 +550,7 @@ func (w *chanWriter) Write(data []byte) (written int, err error) {
 	for len(data) > 0 {
 		// n cannot be larger than 2^31 as len(data) cannot
 		// be larger than 2^31
-		n := int(w.win.reserve(uint32(len(data))))
+		n := int(w.remoteWin.reserve(uint32(len(data))))
 		remoteId := w.remoteId
 		packet := []byte{
 			msgChannelData,
@@ -621,46 +620,3 @@ func (r *chanReader) Read(data []byte) (int, error) {
 	}
 	panic("unreachable")
 }
-
-// window represents the buffer available to clients 
-// wishing to write to a channel.
-type window struct {
-	*sync.Cond
-	win uint32 // RFC 4254 5.2 says the window size can grow to 2^32-1
-}
-
-// add adds win to the amount of window available
-// for consumers.
-func (w *window) add(win uint32) bool {
-	if win == 0 {
-		return false
-	}
-	w.L.Lock()
-	if w.win+win < win {
-		w.L.Unlock()
-		return false
-	}
-	w.win += win
-	// It is unusual that multiple goroutines would be attempting to reserve
-	// window space, but not guaranteed. Use broadcast to notify all waiters 
-	// that additional window is available.
-	w.Broadcast()
-	w.L.Unlock()
-	return true
-}
-
-// reserve reserves win from the available window capacity.
-// If no capacity remains, reserve will block. reserve may
-// return less than requested.
-func (w *window) reserve(win uint32) uint32 {
-	w.L.Lock()
-	for w.win == 0 {
-		w.Wait()
-	}
-	if w.win < win {
-		win = w.win
-	}
-	w.win -= win
-	w.L.Unlock()
-	return win
-}