Improve close in ConcurrentWebSocketSessionDecorator

Before this commit the concurrent session wrapper mainly protected the
sending of messages. The close itself however may also cause a message
to be sent as is the case of the SockJS protocol.

This change protects the close and checks if the session has exceeded
send time or buffer limits in which case the close status is changed
to SESSION_NOT_RELIABLE (introduced in commit cbd5af3a) which in turn
signals that extra care should be exercised when closing the session.

Issue: SPR-13904

spring-websocket/src/test/java/org/springframework/web/socket/handler/ConcurrentWebSocketSessionDecoratorTests.java

@@ -27,6 +27,7 @@ import org.junit.Test;
 import org.springframework.web.socket.CloseStatus;
 import org.springframework.web.socket.TextMessage;
 import org.springframework.web.socket.WebSocketMessage;
+import org.springframework.web.socket.WebSocketSession;
 
 import static org.junit.Assert.*;
 
@@ -187,6 +188,56 @@ public class ConcurrentWebSocketSessionDecoratorTests {
 		}
 	}
 
+	@Test
+	public void closeStatusNormal() throws Exception {
+
+		BlockingSession delegate = new BlockingSession();
+		delegate.setOpen(true);
+		WebSocketSession decorator = new ConcurrentWebSocketSessionDecorator(delegate, 10 * 1000, 1024);
+
+		decorator.close(CloseStatus.PROTOCOL_ERROR);
+		assertEquals(CloseStatus.PROTOCOL_ERROR, delegate.getCloseStatus());
+
+		decorator.close(CloseStatus.SERVER_ERROR);
+		assertEquals("Should have been ignored", CloseStatus.PROTOCOL_ERROR, delegate.getCloseStatus());
+	}
+
+	@Test
+	public void closeStatusChangesToSessionNotReliable() throws Exception {
+
+		BlockingSession blockingSession = new BlockingSession();
+		blockingSession.setId("123");
+		blockingSession.setOpen(true);
+		CountDownLatch sentMessageLatch = blockingSession.getSentMessageLatch();
+
+		int sendTimeLimit = 100;
+		int bufferSizeLimit = 1024;
+
+		final ConcurrentWebSocketSessionDecorator concurrentSession =
+				new ConcurrentWebSocketSessionDecorator(blockingSession, sendTimeLimit, bufferSizeLimit);
+
+		Executors.newSingleThreadExecutor().submit((Runnable) () -> {
+			TextMessage message = new TextMessage("slow message");
+			try {
+				concurrentSession.sendMessage(message);
+			}
+			catch (IOException e) {
+				e.printStackTrace();
+			}
+		});
+
+		assertTrue(sentMessageLatch.await(5, TimeUnit.SECONDS));
+
+		// ensure some send time elapses
+		Thread.sleep(sendTimeLimit + 100);
+
+		concurrentSession.close(CloseStatus.PROTOCOL_ERROR);
+
+		assertEquals("CloseStatus should have changed to SESSION_NOT_RELIABLE",
+				CloseStatus.SESSION_NOT_RELIABLE, blockingSession.getCloseStatus());
+	}
+
+
 
 	private static class BlockingSession extends TestWebSocketSession {