Update TestForward (gravitational#15321)

lib/sshutils/x11/forward_test.go

@@ -16,7 +16,6 @@ package x11
 
 import (
 	"context"
-	"io"
 	"net"
 	"testing"
 
@@ -26,85 +25,62 @@ import (
 func TestForward(t *testing.T) {
 	ctx := context.Background()
 
-	// Create a fake client display. In practice, the display
-	// set in $DISPLAY is used to connect to the client display.
-	fakeClientDisplay, err := net.Listen("tcp", ":0")
-	require.NoError(t, err)
-	t.Cleanup(func() {
-		require.NoError(t, fakeClientDisplay.Close())
-	})
+	// Open a dual sided connection on a new tcp listener
+	openConn := func(t *testing.T) (clientConn net.Conn, serverConn net.Conn) {
+		l, err := net.Listen("tcp", ":0")
+		require.NoError(t, err)
+		t.Cleanup(func() { require.NoError(t, l.Close()) })
 
-	// Handle connections to the client XServer
-	echoMsg := "msg"
-	go func() {
-		for {
-			localConn, err := fakeClientDisplay.Accept()
+		serverErrC := make(chan error)
+		serverConnC := make(chan net.Conn)
+		go func() {
+			serverConn, err := l.Accept()
 			if err != nil {
-				// listener is closed, test is done.
-				return
+				serverErrC <- err
+				close(serverConnC)
 			}
+			serverConnC <- serverConn
+			close(serverErrC)
+		}()
 
-			go func() {
-				defer localConn.Close()
-
-				// read request and expect what was written to server
-				bytes, err := io.ReadAll(localConn)
-				require.NoError(t, err)
-				require.Equal(t, echoMsg, string(bytes))
-			}()
-		}
-	}()
-
-	// Create a fake XServer proxy just like the one in sshserver.
-	sl, serverDisplay, err := OpenNewXServerListener(DefaultDisplayOffset, DefaultMaxDisplays, 0)
-	require.NoError(t, err)
-	t.Cleanup(func() {
-		require.NoError(t, sl.Close())
-	})
+		clientConn, err = net.Dial("tcp", l.Addr().String())
+		require.NoError(t, err)
+		t.Cleanup(func() { clientConn.Close() })
 
-	// Handle connection to XServer proxy
-	go func() {
-		for {
-			serverConn, err := sl.Accept()
-			if err != nil {
-				// listener is closed, test is done.
-				return
-			}
+		serverConn = <-serverConnC
+		require.NoError(t, <-serverErrC)
+		t.Cleanup(func() { serverConn.Close() })
 
-			go func() {
-				defer serverConn.Close()
+		return clientConn, serverConn
+	}
 
-				clientConn, err := net.Dial("tcp", fakeClientDisplay.Addr().String())
-				if err != nil {
-					// fakeClientDisplay is closed, test is done.
-					return
-				}
+	cConn1, sConn1 := openConn(t)
+	cConn2, sConn2 := openConn(t)
 
-				clientXConn, ok := clientConn.(*net.TCPConn)
-				require.True(t, ok)
-				defer clientConn.Close()
+	// Start forwarding between connections so that we get
+	// this flow: cConn1 -> sConn1 -> cConn2 -> sConn2.
+	serverConnToForward, ok := sConn1.(*net.TCPConn)
+	require.True(t, ok)
+	clientConnToForward, ok := cConn2.(*net.TCPConn)
+	require.True(t, ok)
 
-				err = Forward(ctx, clientXConn, serverConn)
-				require.NoError(t, err)
-			}()
-		}
+	forwardErrC := make(chan error, 1)
+	go func() {
+		forwardErrC <- Forward(ctx, serverConnToForward, clientConnToForward)
 	}()
 
-	// Create a fake XServer request to the XServer proxy
-	xreq, err := serverDisplay.Dial()
-	require.NoError(t, err)
-	_, err = xreq.Write([]byte(echoMsg))
+	// Write a msg to client connection 1, which should propagate to server connection 2.
+	message := "msg"
+	_, err := cConn1.Write([]byte(message))
 	require.NoError(t, err)
 
-	// Create a second request simultaneously
-	xreq2, err := serverDisplay.Dial()
-	require.NoError(t, err)
-	_, err = xreq2.Write([]byte(echoMsg))
+	buf := make([]byte, len(message))
+	_, err = sConn2.Read(buf)
 	require.NoError(t, err)
-	xreq2.Close()
+	require.Equal(t, message, string(buf))
 
-	// Close XServer requests, forwarding should stop as soon as
-	// the open connection has been read and forwarded fully.
-	xreq.Close()
-	xreq2.Close()
+	// Fowarding should stop once the other sides of the forwarded connections are closed.
+	require.NoError(t, cConn1.Close())
+	require.NoError(t, sConn2.Close())
+	require.NoError(t, <-forwardErrC)
 }