Fix issue with sub-protocol negotiation and SockJS

Before this change the SockJsWebSocketHandler precluded determination
of the sub-protocols by wrapping the actual target handler.

After this change SockJsWebSocketHandler implements SubProtocolCapable
and returns the list of sub-protocols from the wrapped handler.

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/handler/SockJsWebSocketHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2014 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,14 +16,19 @@
 
 package org.springframework.web.socket.sockjs.transport.handler;
 
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.springframework.util.Assert;
 import org.springframework.web.socket.CloseStatus;
+import org.springframework.web.socket.SubProtocolCapable;
 import org.springframework.web.socket.TextMessage;
 import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.WebSocketSession;
 import org.springframework.web.socket.handler.TextWebSocketHandler;
+import org.springframework.web.socket.handler.WebSocketHandlerDecorator;
 import org.springframework.web.socket.sockjs.transport.SockJsServiceConfig;
 import org.springframework.web.socket.sockjs.transport.session.WebSocketServerSockJsSession;
 
@@ -42,17 +47,19 @@ import org.springframework.web.socket.sockjs.transport.session.WebSocketServerSo
  * @author Rossen Stoyanchev
  * @since 4.0
  */
-public class SockJsWebSocketHandler extends TextWebSocketHandler {
+public class SockJsWebSocketHandler extends TextWebSocketHandler implements SubProtocolCapable {
 
 	private final SockJsServiceConfig sockJsServiceConfig;
 
 	private final WebSocketServerSockJsSession sockJsSession;
 
+	private final List<String> subProtocols;
+
 	private final AtomicInteger sessionCount = new AtomicInteger(0);
 
 
-	public SockJsWebSocketHandler(SockJsServiceConfig serviceConfig,
-			WebSocketHandler webSocketHandler, WebSocketServerSockJsSession sockJsSession) {
+	public SockJsWebSocketHandler(SockJsServiceConfig serviceConfig, WebSocketHandler webSocketHandler,
+			WebSocketServerSockJsSession sockJsSession) {
 
 		Assert.notNull(serviceConfig, "serviceConfig must not be null");
 		Assert.notNull(webSocketHandler, "webSocketHandler must not be null");
@@ -60,6 +67,15 @@ public class SockJsWebSocketHandler extends TextWebSocketHandler {
 
 		this.sockJsServiceConfig = serviceConfig;
 		this.sockJsSession = sockJsSession;
+
+		webSocketHandler = WebSocketHandlerDecorator.unwrap(webSocketHandler);
+		this.subProtocols = ((webSocketHandler instanceof SubProtocolCapable) ?
+				new ArrayList<String>(((SubProtocolCapable) webSocketHandler).getSubProtocols()) : null);
+	}
+
+	@Override
+	public List<String> getSubProtocols() {
+		return this.subProtocols;
 	}
 
 	protected SockJsServiceConfig getSockJsConfig() {

spring-websocket/src/test/java/org/springframework/web/socket/sockjs/transport/handler/SockJsWebSocketHandlerTests.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2002-2014 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.socket.sockjs.transport.handler;
+
+import org.junit.Test;
+import org.springframework.messaging.SubscribableChannel;
+import org.springframework.scheduling.TaskScheduler;
+import org.springframework.web.socket.WebSocketHandler;
+import org.springframework.web.socket.handler.TextWebSocketHandler;
+import org.springframework.web.socket.messaging.StompSubProtocolHandler;
+import org.springframework.web.socket.messaging.SubProtocolWebSocketHandler;
+import org.springframework.web.socket.sockjs.transport.session.WebSocketServerSockJsSession;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Unit tests for {@link SockJsWebSocketHandler}.
+ * @author Rossen Stoyanchev
+ */
+public class SockJsWebSocketHandlerTests {
+
+
+	@Test
+	public void getSubProtocols() throws Exception {
+		SubscribableChannel channel = mock(SubscribableChannel.class);
+		SubProtocolWebSocketHandler handler = new SubProtocolWebSocketHandler(channel, channel);
+		StompSubProtocolHandler stompHandler = new StompSubProtocolHandler();
+		handler.addProtocolHandler(stompHandler);
+
+		TaskScheduler scheduler = mock(TaskScheduler.class);
+		DefaultSockJsService service = new DefaultSockJsService(scheduler);
+		WebSocketServerSockJsSession session = new WebSocketServerSockJsSession("1", service, handler, null);
+		SockJsWebSocketHandler sockJsHandler = new SockJsWebSocketHandler(service, handler, session);
+
+		assertEquals(stompHandler.getSupportedProtocols(), sockJsHandler.getSubProtocols());
+	}
+
+	@Test
+	public void getSubProtocolsNone() throws Exception {
+		WebSocketHandler handler = new TextWebSocketHandler();
+		TaskScheduler scheduler = mock(TaskScheduler.class);
+		DefaultSockJsService service = new DefaultSockJsService(scheduler);
+		WebSocketServerSockJsSession session = new WebSocketServerSockJsSession("1", service, handler, null);
+		SockJsWebSocketHandler sockJsHandler = new SockJsWebSocketHandler(service, handler, session);
+
+		assertNull(sockJsHandler.getSubProtocols());
+	}
+
+}