Function TestLocalUnixForwarding

ssh/tailssh/tailssh_integration_test.go:427–500

TestLocalUnixForwarding tests direct-streamlocal@openssh.com, which is what podman remote (issue #12409) and VSCode Remote (issue #5295) use to reach Unix domain sockets on the remote host through SSH. The client opens a channel to a Unix socket path on the server, and data is proxied through.

(t *testing.T)

// Unix domain sockets on the remote host through SSH. The client opens a
// channel to a Unix socket path on the server, and data is proxied through.
func TestLocalUnixForwarding(t *testing.T) {
	debugTest.Store(true)
	t.Cleanup(func() {
		debugTest.Store(false)
	})

	// Create a Unix socket server in /tmp that simulates a service like
	// podman's API socket at /run/user/<uid>/podman/podman.sock.
	socketDir, err := os.MkdirTemp("", "tailssh-test-")
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { os.RemoveAll(socketDir) })
	socketPath := filepath.Join(socketDir, "test-service.sock")

	ul, err := net.Listen("unix", socketPath)
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { ul.Close() })

	// The service echoes back whatever it receives, like an API server would.
	go func() {
		for {
			conn, err := ul.Accept()
			if err != nil {
				return
			}
			go func() {
				defer conn.Close()
				io.Copy(conn, conn)
			}()
		}
	}()

	// Start Tailscale SSH server with local port forwarding enabled.
	addr := testServerWithOpts(t, testServerOpts{
		username:                 "testuser",
		allowLocalPortForwarding: true,
	})

	// Connect to the Tailscale SSH server.
	cl, err := ssh.Dial("tcp", addr, &ssh.ClientConfig{
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
	})
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { cl.Close() })

	// Open a direct-streamlocal@openssh.com channel to the Unix socket,
	// exactly as podman remote does.
	conn, err := cl.Dial("unix", socketPath)
	if err != nil {
		t.Fatalf("failed to dial unix socket through SSH: %s", err)
	}
	defer conn.Close()