ssh: add (*Client).DialContext method

Fixes golang/go#20288.

ssh/tcpip.go

@@ -5,6 +5,7 @@
 package ssh
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -332,6 +333,37 @@ func (l *tcpListener) Addr() net.Addr {
 	return l.laddr
 }
 
+// DialContext initiates a connection to the addr from the remote host.
+// If the supplied context is cancelled before the connection can be opened,
+// ctx.Err() will be returned.
+// The resulting connection has a zero LocalAddr() and RemoteAddr().
+func (c *Client) DialContext(ctx context.Context, n, addr string) (net.Conn, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	type connErr struct {
+		conn net.Conn
+		err  error
+	}
+	ch := make(chan connErr)
+	go func() {
+		conn, err := c.Dial(n, addr)
+		select {
+		case ch <- connErr{conn, err}:
+		case <-ctx.Done():
+			if conn != nil {
+				conn.Close()
+			}
+		}
+	}()
+	select {
+	case res := <-ch:
+		return res.conn, res.err
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+}
+
 // Dial initiates a connection to the addr from the remote host.
 // The resulting connection has a zero LocalAddr() and RemoteAddr().
 func (c *Client) Dial(n, addr string) (net.Conn, error) {
@@ -347,7 +379,7 @@ func (c *Client) Dial(n, addr string) (net.Conn, error) {
 		if err != nil {
 			return nil, err
 		}
-		ch, err = c.dial(net.IPv4zero.String(), 0, host, int(port))
+		ch, err = c.dialTCP(net.IPv4zero.String(), 0, host, int(port))
 		if err != nil {
 			return nil, err
 		}
@@ -393,7 +425,7 @@ func (c *Client) DialTCP(n string, laddr, raddr *net.TCPAddr) (net.Conn, error)
 			Port: 0,
 		}
 	}
-	ch, err := c.dial(laddr.IP.String(), laddr.Port, raddr.IP.String(), raddr.Port)
+	ch, err := c.dialTCP(laddr.IP.String(), laddr.Port, raddr.IP.String(), raddr.Port)
 	if err != nil {
 		return nil, err
 	}
@@ -412,7 +444,7 @@ type channelOpenDirectMsg struct {
 	lport uint32
 }
 
-func (c *Client) dial(laddr string, lport int, raddr string, rport int) (Channel, error) {
+func (c *Client) dialTCP(laddr string, lport int, raddr string, rport int) (Channel, error) {
 	msg := channelOpenDirectMsg{
 		raddr: raddr,
 		rport: uint32(rport),

ssh/tcpip_test.go

@@ -5,7 +5,10 @@
 package ssh
 
 import (
+	"context"
+	"net"
 	"testing"
+	"time"
 )
 
 func TestAutoPortListenBroken(t *testing.T) {
@@ -18,3 +21,40 @@ func TestAutoPortListenBroken(t *testing.T) {
 		t.Errorf("version %q marked as broken", works)
 	}
 }
+
+func TestClientImplementsDialContext(t *testing.T) {
+	type ContextDialer interface {
+		DialContext(context.Context, string, string) (net.Conn, error)
+	}
+	var _ ContextDialer = &Client{}
+}
+
+func TestClientDialContextWithCancel(t *testing.T) {
+	c := &Client{}
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	_, err := c.DialContext(ctx, "tcp", "localhost:1000")
+	if err != context.Canceled {
+		t.Errorf("DialContext: got nil error, expected %v", context.Canceled)
+	}
+}
+
+func TestClientDialContextWithDeadline(t *testing.T) {
+	c := &Client{}
+	ctx, cancel := context.WithDeadline(context.Background(), time.Now())
+	defer cancel()
+	_, err := c.DialContext(ctx, "tcp", "localhost:1000")
+	if err != context.DeadlineExceeded {
+		t.Errorf("DialContext: got nil error, expected %v", context.DeadlineExceeded)
+	}
+}
+
+func TestClientDialContextWithTimeout(t *testing.T) {
+	c := &Client{}
+	ctx, cancel := context.WithTimeout(context.Background(), 0)
+	defer cancel()
+	_, err := c.DialContext(ctx, "tcp", "localhost:1000")
+	if err != context.DeadlineExceeded {
+		t.Errorf("DialContext: got nil error, expected %v", context.DeadlineExceeded)
+	}
+}