crypto/ssh: Allow customization of the client version.

R=agl, golang-dev, dave
CC=golang-dev
https://golang.org/cl/13176044

ssh/client.go

@@ -16,8 +16,8 @@ import (
 	"sync"
 )
 
-// clientVersion is the fixed identification string that the client will use.
-var clientVersion = []byte("SSH-2.0-Go\r\n")
+// clientVersion is the default identification string that the client will use.
+var clientVersion = []byte("SSH-2.0-Go")
 
 // ClientConn represents the client side of an SSH connection.
 type ClientConn struct {
@@ -63,13 +63,20 @@ func clientWithAddress(c net.Conn, addr string, config *ClientConfig) (*ClientCo
 func (c *ClientConn) handshake() error {
 	var magics handshakeMagics
 
-	if _, err := c.Write(clientVersion); err != nil {
+	var version []byte
+	if len(c.config.ClientVersion) > 0 {
+		version = []byte(c.config.ClientVersion)
+	} else {
+		version = clientVersion
+	}
+	magics.clientVersion = version
+	version = append(version, '\r', '\n')
+	if _, err := c.Write(version); err != nil {
 		return err
 	}
 	if err := c.Flush(); err != nil {
 		return err
 	}
-	magics.clientVersion = clientVersion[:len(clientVersion)-2]
 
 	// read remote server version
 	version, err := readVersion(c)
@@ -489,6 +496,10 @@ type ClientConfig struct {
 
 	// Cryptographic-related configuration.
 	Crypto CryptoConfig
+
+	// The identification string that will be used for the connection.
+	// If empty, a reasonable default is used.
+	ClientVersion string
 }
 
 func (c *ClientConfig) rand() io.Reader {

ssh/client_test.go

@@ -0,0 +1,34 @@
+package ssh
+
+import (
+	"net"
+	"testing"
+)
+
+func testClientVersion(t *testing.T, config *ClientConfig, expected string) {
+	clientConn, serverConn := net.Pipe()
+	receivedVersion := make(chan string, 1)
+	go func() {
+		version, err := readVersion(serverConn)
+		if err != nil {
+			receivedVersion <- ""
+		} else {
+			receivedVersion <- string(version)
+		}
+		serverConn.Close()
+	}()
+	Client(clientConn, config)
+	actual := <-receivedVersion
+	if actual != expected {
+		t.Fatalf("got %s; want %s", actual, expected)
+	}
+}
+
+func TestCustomClientVersion(t *testing.T) {
+	version := "Test-Client-Version-0.0"
+	testClientVersion(t, &ClientConfig{ClientVersion: version}, version)
+}
+
+func TestDefaultClientVersion(t *testing.T) {
+	testClientVersion(t, &ClientConfig{}, string(clientVersion))
+}