Refine condition to send WebSocket binary messages

The following two refinements have been added:
1) SockJS doesn't support binary messages so don't even try
2) don't bother if payload.length == 0

Issue: SPR-12475

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

@@ -28,7 +28,6 @@
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
@@ -52,7 +51,6 @@
 import org.springframework.messaging.support.MessageHeaderAccessor;
 import org.springframework.messaging.support.MessageHeaderInitializer;
 import org.springframework.util.Assert;
-import org.springframework.util.MimeType;
 import org.springframework.util.MimeTypeUtils;
 import org.springframework.web.socket.BinaryMessage;
 import org.springframework.web.socket.CloseStatus;
@@ -356,8 +354,13 @@ else if (StompCommand.CONNECTED.equals(command)) {
 			}
 		}
 		try {
-			byte[] bytes = this.stompEncoder.encode(stompAccessor.getMessageHeaders(), (byte[]) message.getPayload());
-			if (MimeTypeUtils.APPLICATION_OCTET_STREAM.isCompatibleWith(stompAccessor.getContentType())) {
+			byte[] payload = (byte[]) message.getPayload();
+			byte[] bytes = this.stompEncoder.encode(stompAccessor.getMessageHeaders(), payload);
+
+			boolean useBinary = (payload.length > 0 && !(session instanceof SockJsSession) &&
+					MimeTypeUtils.APPLICATION_OCTET_STREAM.isCompatibleWith(stompAccessor.getContentType()));
+
+			if (useBinary) {
 				session.sendMessage(new BinaryMessage(bytes));
 			}
 			else {

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

@@ -16,6 +16,20 @@
 
 package org.springframework.web.socket.messaging;
 
+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.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 java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -28,7 +42,6 @@
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Mockito;
-
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.messaging.Message;
@@ -50,16 +63,14 @@
 import org.springframework.messaging.support.ImmutableMessageChannelInterceptor;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.messaging.support.MessageHeaderAccessor;
+import org.springframework.util.MimeTypeUtils;
+import org.springframework.web.socket.BinaryMessage;
 import org.springframework.web.socket.CloseStatus;
 import org.springframework.web.socket.TextMessage;
 import org.springframework.web.socket.WebSocketMessage;
 import org.springframework.web.socket.handler.TestWebSocketSession;
 import org.springframework.web.socket.sockjs.transport.SockJsSession;
 
-import static org.hamcrest.Matchers.*;
-import static org.junit.Assert.*;
-import static org.mockito.Mockito.*;
-
 /**
  * Test fixture for {@link StompSubProtocolHandler} tests.
  *
@@ -267,6 +278,38 @@ public void handleMessageToClientUserDestination() {
 		assertFalse(((String) textMessage.getPayload()).contains(SimpMessageHeaderAccessor.ORIGINAL_DESTINATION));
 	}
 
+	// SPR-12475
+
+	@Test
+	public void handleMessageToClientBinaryWebSocketMessage() {
+
+		StompHeaderAccessor headers = StompHeaderAccessor.create(StompCommand.MESSAGE);
+		headers.setMessageId("mess0");
+		headers.setSubscriptionId("sub0");
+		headers.setContentType(MimeTypeUtils.APPLICATION_OCTET_STREAM);
+		headers.setDestination("/queue/foo");
+
+		// Non-empty payload
+
+		byte[] payload = new byte[1];
+		Message<byte[]> message = MessageBuilder.createMessage(payload, headers.getMessageHeaders());
+		this.protocolHandler.handleMessageToClient(this.session, message);
+
+		assertEquals(1, this.session.getSentMessages().size());
+		WebSocketMessage<?> webSocketMessage = this.session.getSentMessages().get(0);
+		assertTrue(webSocketMessage instanceof BinaryMessage);
+
+		// Empty payload
+
+		payload = EMPTY_PAYLOAD;
+		message = MessageBuilder.createMessage(payload, headers.getMessageHeaders());
+		this.protocolHandler.handleMessageToClient(this.session, message);
+
+		assertEquals(2, this.session.getSentMessages().size());
+		webSocketMessage = this.session.getSentMessages().get(1);
+		assertTrue(webSocketMessage instanceof TextMessage);
+	}
+
 	@Test
 	public void handleMessageFromClient() {