Function TestReverseUnixForwarding

ssh/tailssh/tailssh_integration_test.go:505–572

TestReverseUnixForwarding tests streamlocal-forward@openssh.com, which tools like VSCode Remote and Zed use to create Unix domain sockets on the remote host that forward connections back to the client through SSH.

(t *testing.T)

// like VSCode Remote and Zed use to create Unix domain sockets on the remote
// host that forward connections back to the client through SSH.
func TestReverseUnixForwarding(t *testing.T) {
	debugTest.Store(true)
	t.Cleanup(func() {
		debugTest.Store(false)
	})

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

	// Request reverse forwarding -- the server creates a Unix socket and
	// forwards incoming connections back through the SSH tunnel.
	socketDir, err := os.MkdirTemp("", "tailssh-test-")
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { os.RemoveAll(socketDir) })
	remoteSocketPath := filepath.Join(socketDir, "reverse.sock")

	ln, err := cl.ListenUnix(remoteSocketPath)
	if err != nil {
		t.Fatalf("failed to request reverse unix forwarding: %s", err)
	}
	t.Cleanup(func() { ln.Close() })

	// Verify the socket file was created on the server side.
	if _, err := os.Stat(remoteSocketPath); err != nil {
		t.Fatalf("reverse forwarded socket not created: %s", err)
	}

	// Accept a connection from the tunnel (client side) and write data.
	want := "hello from reverse tunnel"
	go func() {
		conn, err := ln.Accept()
		if err != nil {
			return
		}
		defer conn.Close()
		io.WriteString(conn, want)
	}()

	// Connect directly to the socket on the server side, simulating a
	// local process connecting to the VSCode/Zed IPC socket.
	conn, err := net.Dial("unix", remoteSocketPath)
	if err != nil {
		t.Fatalf("failed to connect to reverse forwarded socket: %s", err)
	}