Dial(): handle expiring dialCtx correctly

The returned connection must not be affected by an expired dialCtx.
Make this clear through argument names.

Author: problame

dial.go

@@ -110,10 +110,16 @@ var banner_msg = mustMessage("SSHCON_HELO")
 var proxy_error_msg = mustMessage("SSHCON_PROXY_ERROR")
 var begin_msg = mustMessage("SSHCON_BEGIN")
 
-func Dial(ctx context.Context, endpoint Endpoint) (*SSHConn , error) {
+// Dial connects to the remote endpoint where it expects a command executing Proxy().
+// Dial performs a handshake consisting of the exchange of banner messages before returning the connection.
+// If the handshake cannot be completed before dialCtx is Done(), the underlying ssh command is killed
+// and the dialCtx.Err() returned.
+// If the handshake completes, dialCtx's deadline does not affect the returned connection.
+func Dial(dialCtx context.Context, endpoint Endpoint) (*SSHConn , error) {
 
 	sshCmd, sshArgs, sshEnv := endpoint.CmdArgs()
-	cmd, err := rwccmd.CommandContext(ctx, sshCmd, sshArgs, sshEnv)
+	commandCtx, commandCancel := context.WithCancel(context.Background())
+	cmd, err := rwccmd.CommandContext(commandCtx, sshCmd, sshArgs, sshEnv)
 	if err != nil {
 		return nil, err
 	}
@@ -149,10 +155,12 @@ func Dial(ctx context.Context, endpoint Endpoint) (*SSHConn , error) {
 	}()
 
 	select {
-	case <-ctx.Done():
-		return nil, ctx.Err()
+	case <-dialCtx.Done():
+		commandCancel()
+		return nil, dialCtx.Err()
 	case err := <-confErrChan:
 		if err != nil {
+			commandCancel()
 			return nil, err
 		}
 	}

example/cmd/connect.go

@@ -18,6 +18,7 @@ var connectArgs struct {
 	killSSHDuration time.Duration
 	waitBeforeRequestDuration time.Duration
 	responseTimeout time.Duration
+	dialTimeout time.Duration
 	endpoint netssh.Endpoint
 
 }
@@ -29,12 +30,19 @@ var connectCmd = &cobra.Command{
 
 		log := log.New(os.Stdout, "", log.Ltime|log.Lmicroseconds|log.Lshortfile)
 
+		log.Print("dialing %#v", connectArgs.endpoint)
+		log.Printf("timeout %s", connectArgs.dialTimeout)
 		ctx := netssh.ContextWithLog(context.TODO(), log)
 		ctx = rwccmd.ContextWithLog(ctx, log)
-		outstream, err := netssh.Dial(ctx, connectArgs.endpoint)
-		if err != nil {
+		dialCtx, dialCancel := context.WithTimeout(ctx, connectArgs.dialTimeout)
+		outstream, err := netssh.Dial(dialCtx, connectArgs.endpoint)
+		dialCancel()
+		if err == context.DeadlineExceeded {
+			log.Panic("dial timeout exceeded")
+		} else if err != nil {
 			log.Panic(err)
 		}
+
 		defer func() {
 			log.Printf("closing connection in defer")
 			err := outstream.Close()
@@ -86,6 +94,7 @@ func init() {
 	connectCmd.Flags().DurationVar(&connectArgs.killSSHDuration, "killSSH",0, "")
 	connectCmd.Flags().DurationVar(&connectArgs.waitBeforeRequestDuration, "wait",0, "")
 	connectCmd.Flags().DurationVar(&connectArgs.responseTimeout, "responseTimeout",math.MaxInt64, "")
+	connectCmd.Flags().DurationVar(&connectArgs.dialTimeout, "dialTimeout",math.MaxInt64, "")
 	connectCmd.Flags().StringVar(&connectArgs.endpoint.Host, "ssh.host", "", "")
 	connectCmd.Flags().StringVar(&connectArgs.endpoint.User, "ssh.user", "", "")
 	connectCmd.Flags().StringVar(&connectArgs.endpoint.IdentityFile, "ssh.identity", "", "")