go.crypto/ssh: fix test breakages introduced by 125:40246d2ae2eb

* Remove special handling for dynamically allocated
  ports. This was a bug in OpenSSH 5.x sshd.

* Run the test with a preselected port number.

* Run TestPortForward only on unix platforms.

R=dave, agl
CC=golang-dev
https://golang.org/cl/10049045

ssh/tcpip.go

@@ -48,15 +48,8 @@ func (c *ClientConn) ListenTCP(laddr *net.TCPAddr) (net.Listener, error) {
 		return nil, err
 	}
 
-	// Register this forward, using the port number we requested.
-	// If we requested port 0 (auto allocated port), we have to
-	// register under 0, since the channelOpenMsg will list 0
-	// rather than the allocated port number.
-	ch := c.forwardList.add(*laddr)
-
 	// If the original port was 0, then the remote side will
 	// supply a real port number in the response.
-	origPort := uint32(laddr.Port)
 	if laddr.Port == 0 {
 		port, _, ok := parseUint32(resp.Data)
 		if !ok {
@@ -65,7 +58,14 @@ func (c *ClientConn) ListenTCP(laddr *net.TCPAddr) (net.Listener, error) {
 		laddr.Port = int(port)
 	}
 
-	return &tcpListener{laddr, origPort, c, ch}, nil
+	// Register this forward, using the port number we obtained.
+	//
+	// This does not work on OpenSSH < 6.0, which will send a
+	// channelOpenMsg with port number 0, rather than the actual
+	// port number.
+	ch := c.forwardList.add(*laddr)
+
+	return &tcpListener{laddr, c, ch}, nil
 }
 
 // forwardList stores a mapping between remote
@@ -126,10 +126,8 @@ func (l *forwardList) lookup(addr net.TCPAddr) (chan forward, bool) {
 type tcpListener struct {
 	laddr *net.TCPAddr
 
-	// The port with which we made the request, which can be 0.
-	origPort uint32
-	conn     *ClientConn
-	in       <-chan forward
+	conn *ClientConn
+	in   <-chan forward
 }
 
 // Accept waits for and returns the next connection to the listener.
@@ -155,13 +153,9 @@ func (l *tcpListener) Close() error {
 		"cancel-tcpip-forward",
 		true,
 		l.laddr.IP.String(),
-		l.origPort,
+		uint32(l.laddr.Port),
 	}
-	origAddr := net.TCPAddr{
-		IP:   l.laddr.IP,
-		Port: int(l.origPort),
-	}
-	l.conn.forwardList.remove(origAddr)
+	l.conn.forwardList.remove(*l.laddr)
 	if _, err := l.conn.sendGlobalRequest(m); err != nil {
 		return err
 	}

ssh/test/forward_unix_test.go

@@ -1,7 +1,14 @@
+// Copyright 2012 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.
+
+// +build darwin freebsd linux netbsd openbsd
+
 package test
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"math/rand"
@@ -15,9 +22,23 @@ func TestPortForward(t *testing.T) {
 	conn := server.Dial(clientConfig())
 	defer conn.Close()
 
-	sshListener, err := conn.Listen("tcp", "127.0.0.1:0")
+	var sshListener net.Listener
+	var err error
+	tries := 10
+	for i := 0; i < tries; i++ {
+		port := 1024 + rand.Intn(50000)
+
+		// We can't reliably test dynamic port allocation, as it does
+		// not work correctly with OpenSSH before 6.0. See also
+		// https://bugzilla.mindrot.org/show_bug.cgi?id=2017
+		sshListener, err = conn.Listen("tcp", fmt.Sprintf("127.0.0.1:%d", port))
+		if err == nil {
+			break
+		}
+	}
+
 	if err != nil {
-		t.Fatalf("conn.Listen failed: %v", err)
+		t.Fatalf("conn.Listen failed: %v (after %d tries)", err, tries)
 	}
 
 	go func() {