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/test/forward_unix_test.go

@@ -0,0 +1,108 @@
+// 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"
+	"net"
+	"testing"
+)
+
+func TestPortForward(t *testing.T) {
+	server := newServer(t)
+	defer server.Shutdown()
+	conn := server.Dial(clientConfig())
+	defer conn.Close()
+
+	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 (after %d tries)", err, tries)
+	}
+
+	go func() {
+		sshConn, err := sshListener.Accept()
+		if err != nil {
+			t.Fatalf("listen.Accept failed: %v", err)
+		}
+
+		_, err = io.Copy(sshConn, sshConn)
+		if err != nil && err != io.EOF {
+			t.Fatalf("ssh client copy: %v", err)
+		}
+		sshConn.Close()
+	}()
+
+	forwardedAddr := sshListener.Addr().String()
+	tcpConn, err := net.Dial("tcp", forwardedAddr)
+	if err != nil {
+		t.Fatalf("TCP dial failed: %v", err)
+	}
+
+	readChan := make(chan []byte)
+	go func() {
+		data, _ := ioutil.ReadAll(tcpConn)
+		readChan <- data
+	}()
+
+	// Invent some data.
+	data := make([]byte, 100*1000)
+	for i := range data {
+		data[i] = byte(i % 255)
+	}
+
+	var sent []byte
+	for len(sent) < 1000*1000 {
+		// Send random sized chunks
+		m := rand.Intn(len(data))
+		n, err := tcpConn.Write(data[:m])
+		if err != nil {
+			break
+		}
+		sent = append(sent, data[:n]...)
+	}
+	if err := tcpConn.(*net.TCPConn).CloseWrite(); err != nil {
+		t.Errorf("tcpConn.CloseWrite: %v", err)
+	}
+
+	read := <-readChan
+
+	if len(sent) != len(read) {
+		t.Fatalf("got %d bytes, want %d", len(read), len(sent))
+	}
+	if bytes.Compare(sent, read) != 0 {
+		t.Fatalf("read back data does not match")
+	}
+
+	if err := sshListener.Close(); err != nil {
+		t.Fatalf("sshListener.Close: %v", err)
+	}
+
+	// Check that the forward disappeared.
+	tcpConn, err = net.Dial("tcp", forwardedAddr)
+	if err == nil {
+		tcpConn.Close()
+		t.Errorf("still listening to %s after closing", forwardedAddr)
+	}
+}