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/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());
+	}
+
+}