Publish events only after successful channel send

The StompSubProtcolHandler now checks the outcome of the send to the
inbound client channel. If the message was prevented from being sent,
e.g. as part of authorization, events are not published

Issue: SPR-13339

Author: rstoyanchev

spring-websocket/src/main/java/org/springframework/web/socket/messaging/StompSubProtocolHandler.java

@@ -277,7 +277,9 @@ else if (StompCommand.DISCONNECT.equals(headerAccessor.getCommand())) {
 
 				try {
 					SimpAttributesContextHolder.setAttributesFromMessage(message);
-					if (this.eventPublisher != null) {
+					boolean sent = outputChannel.send(message);
+
+					if (sent && this.eventPublisher != null) {
 						if (StompCommand.CONNECT.equals(headerAccessor.getCommand())) {
 							publishEvent(new SessionConnectEvent(this, message, user));
 						}
@@ -288,7 +290,6 @@ else if (StompCommand.UNSUBSCRIBE.equals(headerAccessor.getCommand())) {
 							publishEvent(new SessionUnsubscribeEvent(this, message, user));
 						}
 					}
-					outputChannel.send(message);
 				}
 				finally {
 					SimpAttributesContextHolder.resetAttributes();

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

@@ -16,11 +16,6 @@
 
 package org.springframework.web.socket.messaging;
 
-import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.*;
-import static org.mockito.Matchers.any;
-import static org.mockito.Mockito.*;
-
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -61,6 +56,22 @@
 import org.springframework.web.socket.handler.TestWebSocketSession;
 import org.springframework.web.socket.sockjs.transport.SockJsSession;
 
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.reset;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+import static org.mockito.Mockito.verifyZeroInteractions;
+import static org.mockito.Mockito.when;
+
 /**
  * Test fixture for {@link StompSubProtocolHandler} tests.
  *
@@ -86,6 +97,8 @@ public void setup() {
 		this.channel = Mockito.mock(MessageChannel.class);
 		this.messageCaptor = ArgumentCaptor.forClass(Message.class);
 
+		when(this.channel.send(any())).thenReturn(true);
+
 		this.session = new TestWebSocketSession();
 		this.session.setId("s1");
 		this.session.setPrincipal(new TestPrincipal("joe"));