Ensure matching user destination returned

Before this change, when a client subscribed to a "user" destination
(e.g. /user/foo), actual messages received in response to that
subscription contained the server-translated, unique user destination
(e.g. /foo-user123).

This is not an issue for clients such as stomp.js since the
subscription is unique and sufficient to match subscription responses.
However, other STOMP clients do additional checks on the destination
of the subscription and the response.

This change ensures that messages sent to clients on user destionations
always contain a destination that matches the one on the original
subscription.

Issue: SPR-11423

spring-websocket/src/test/java/org/springframework/web/socket/messaging/StompSubProtocolHandlerTests.java

@@ -35,6 +35,7 @@ import org.springframework.messaging.simp.stomp.StompDecoder;
 import org.springframework.messaging.simp.stomp.StompHeaderAccessor;
 import org.springframework.messaging.simp.user.DefaultUserSessionRegistry;
 import org.springframework.messaging.simp.user.DestinationUserNameProvider;
+import org.springframework.messaging.simp.user.UserDestinationMessageHandler;
 import org.springframework.messaging.simp.user.UserSessionRegistry;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.web.socket.TextMessage;
@@ -138,6 +139,22 @@ public class StompSubProtocolHandlerTests {
 		assertEquals("joe", replyHeaders.getNativeHeader("user-name").get(0));
 	}
 
+	@Test
+	public void handleMessageToClientUserDestination() {
+
+		StompHeaderAccessor headers = StompHeaderAccessor.create(StompCommand.MESSAGE);
+		headers.setMessageId("mess0");
+		headers.setSubscriptionId("sub0");
+		headers.setDestination("/queue/foo-user123");
+		headers.setHeader(UserDestinationMessageHandler.SUBSCRIBE_DESTINATION, "/user/queue/foo");
+		Message<byte[]> message = MessageBuilder.withPayload(new byte[0]).setHeaders(headers).build();
+		this.protocolHandler.handleMessageToClient(this.session, message);
+
+		assertEquals(1, this.session.getSentMessages().size());
+		WebSocketMessage<?> textMessage = this.session.getSentMessages().get(0);
+		assertTrue(((String) textMessage.getPayload()).contains("destination:/user/queue/foo\n"));
+	}
+
 	@Test
 	public void handleMessageFromClient() {