ssh: allow dialing named services in addition to port numbers

ssh/tcpip.go

@@ -350,7 +350,7 @@ func (c *Client) DialContext(ctx context.Context, n, addr string) (net.Conn, err
 	}
 	ch := make(chan connErr)
 	go func() {
-		conn, err := c.Dial(n, addr)
+		conn, err := c.dialContext(ctx, n, addr)
 		select {
 		case ch <- connErr{conn, err}:
 		case <-ctx.Done():
@@ -369,7 +369,13 @@ func (c *Client) DialContext(ctx context.Context, n, addr string) (net.Conn, err
 
 // Dial initiates a connection to the addr from the remote host.
 // The resulting connection has a zero LocalAddr() and RemoteAddr().
+// For TCP addresses the port section of the address can be a port number or a service name.
+// Service names are resolved at the client side, domain names are resolved on the server.
 func (c *Client) Dial(n, addr string) (net.Conn, error) {
+	return c.dialContext(context.Background(), n, addr)
+}
+
+func (c *Client) dialContext(ctx context.Context, n, addr string) (net.Conn, error) {
 	var ch Channel
 	switch n {
 	case "tcp", "tcp4", "tcp6":
@@ -378,11 +384,11 @@ func (c *Client) Dial(n, addr string) (net.Conn, error) {
 		if err != nil {
 			return nil, err
 		}
-		port, err := strconv.ParseUint(portString, 10, 16)
+		port, err := net.DefaultResolver.LookupPort(ctx, n, portString)
 		if err != nil {
 			return nil, err
 		}
-		ch, err = c.dial(net.IPv4zero.String(), 0, host, int(port))
+		ch, err = c.dial(net.IPv4zero.String(), 0, host, port)
 		if err != nil {
 			return nil, err
 		}
@@ -441,18 +447,18 @@ func (c *Client) DialTCP(n string, laddr, raddr *net.TCPAddr) (net.Conn, error)
 
 // RFC 4254 7.2
 type channelOpenDirectMsg struct {
-	raddr string
-	rport uint32
-	laddr string
-	lport uint32
+	Addr       string
+	Port       uint32
+	OriginAddr string
+	OriginPort uint32
 }
 
 func (c *Client) dial(laddr string, lport int, raddr string, rport int) (Channel, error) {
 	msg := channelOpenDirectMsg{
-		raddr: raddr,
-		rport: uint32(rport),
-		laddr: laddr,
-		lport: uint32(lport),
+		Addr:       raddr,
+		Port:       uint32(rport),
+		OriginAddr: laddr,
+		OriginPort: uint32(lport),
 	}
 	ch, in, err := c.OpenChannel("direct-tcpip", Marshal(&msg))
 	if err != nil {

ssh/tcpip_test.go

@@ -6,6 +6,7 @@ package ssh
 
 import (
 	"context"
+	"fmt"
 	"net"
 	"testing"
 	"time"
@@ -51,3 +52,81 @@ func TestClientDialContextWithDeadline(t *testing.T) {
 		t.Errorf("DialContext: got nil error, expected %v", context.DeadlineExceeded)
 	}
 }
+
+func TestDialNamedPort(t *testing.T) {
+	srvConn, clientConn, err := netPipe()
+	if err != nil {
+		t.Fatalf("netPipe: %v", err)
+	}
+	defer srvConn.Close()
+	defer clientConn.Close()
+
+	serverConf := &ServerConfig{
+		NoClientAuth: true,
+	}
+	serverConf.AddHostKey(testSigners["rsa"])
+	srvErr := make(chan error, 10)
+	go func() {
+		defer close(srvErr)
+		_, chans, req, err := NewServerConn(srvConn, serverConf)
+		if err != nil {
+			srvErr <- fmt.Errorf("NewServerConn: %w", err)
+			return
+		}
+		go DiscardRequests(req)
+		for newChan := range chans {
+			if newChan.ChannelType() != "direct-tcpip" {
+				srvErr <- fmt.Errorf("expected direct-tcpip channel, got=%s", newChan.ChannelType())
+				if err := newChan.Reject(UnknownChannelType, "This test server only supports direct-tcpip"); err != nil {
+					srvErr <- err
+				}
+				continue
+			}
+			data := channelOpenDirectMsg{}
+			if err := Unmarshal(newChan.ExtraData(), &data); err != nil {
+				if err := newChan.Reject(ConnectionFailed, err.Error()); err != nil {
+					srvErr <- err
+				}
+				continue
+			}
+			// Below we dial for service `ssh` which should be translated to 22.
+			if data.Port != 22 {
+				if err := newChan.Reject(ConnectionFailed, fmt.Sprintf("expected port 22 got=%d", data.Port)); err != nil {
+					srvErr <- err
+				}
+				continue
+			}
+			ch, reqs, err := newChan.Accept()
+			if err != nil {
+				srvErr <- fmt.Errorf("Accept: %w", err)
+				continue
+			}
+			go DiscardRequests(reqs)
+			if err := ch.Close(); err != nil {
+				srvErr <- err
+			}
+		}
+	}()
+
+	clientConf := &ClientConfig{
+		User:            "testuser",
+		HostKeyCallback: InsecureIgnoreHostKey(),
+	}
+	sshClientConn, newChans, reqs, err := NewClientConn(clientConn, "", clientConf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	sshClient := NewClient(sshClientConn, newChans, reqs)
+
+	// The port section in the host:port string being a named service `ssh` is the main point of the test.
+	_, err = sshClient.Dial("tcp", "localhost:ssh")
+	if err != nil {
+		t.Error(err)
+	}
+
+	// Stop the ssh server.
+	clientConn.Close()
+	for err := range srvErr {
+		t.Errorf("ssh server: %s", err)
+	}
+}