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) {

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)
+	}
+}

ssh/test/dial_unix_test.go

@@ -10,6 +10,7 @@ package test
 // direct-tcpip and direct-streamlocal functional tests
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"net"
@@ -47,19 +48,38 @@ func testDial(t *testing.T, n, listenAddr string, x dialTester) {
 		}
 	}()
 
-	conn, err := sshConn.Dial(n, l.Addr().String())
-	if err != nil {
-		t.Fatalf("Dial: %v", err)
-	}
-	x.TestClientConn(t, conn)
-	defer conn.Close()
-	b, err := io.ReadAll(conn)
-	if err != nil {
-		t.Fatalf("ReadAll: %v", err)
+	{
+		conn, err := sshConn.Dial(n, l.Addr().String())
+		if err != nil {
+			t.Fatalf("Dial: %v", err)
+		}
+		x.TestClientConn(t, conn)
+		defer conn.Close()
+		b, err := io.ReadAll(conn)
+		if err != nil {
+			t.Fatalf("ReadAll: %v", err)
+		}
+		t.Logf("got %q", string(b))
+		if string(b) != testData {
+			t.Fatalf("expected %q, got %q", testData, string(b))
+		}
 	}
-	t.Logf("got %q", string(b))
-	if string(b) != testData {
-		t.Fatalf("expected %q, got %q", testData, string(b))
+
+	{
+		conn, err := sshConn.DialContext(context.Background(), n, l.Addr().String())
+		if err != nil {
+			t.Fatalf("Dial: %v", err)
+		}
+		x.TestClientConn(t, conn)
+		defer conn.Close()
+		b, err := io.ReadAll(conn)
+		if err != nil {
+			t.Fatalf("ReadAll: %v", err)
+		}
+		t.Logf("got %q", string(b))
+		if string(b) != testData {
+			t.Fatalf("expected %q, got %q", testData, string(b))
+		}
 	}
 }