Fix issue with new line handling in StompDecoder

Closes gh-23713

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompDecoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -114,6 +114,10 @@ public List<Message<byte[]>> decode(ByteBuffer byteBuffer,
 			Message<byte[]> message = decodeMessage(byteBuffer, partialMessageHeaders);
 			if (message != null) {
 				messages.add(message);
+				skipEol(byteBuffer);
+				if (!byteBuffer.hasRemaining()) {
+					break;
+				}
 			}
 			else {
 				break;
@@ -128,7 +132,7 @@ public List<Message<byte[]>> decode(ByteBuffer byteBuffer,
 	@Nullable
 	private Message<byte[]> decodeMessage(ByteBuffer byteBuffer, @Nullable MultiValueMap<String, String> headers) {
 		Message<byte[]> decodedMessage = null;
-		skipLeadingEol(byteBuffer);
+		skipEol(byteBuffer);
 
 		// Explicit mark/reset access via Buffer base type for compatibility
 		// with covariant return type on JDK 9's ByteBuffer...
@@ -196,9 +200,10 @@ private void initHeaders(StompHeaderAccessor headerAccessor) {
 
 	/**
 	 * Skip one ore more EOL characters at the start of the given ByteBuffer.
-	 * Those are STOMP heartbeat frames.
+	 * STOMP, section 2.1 says: "The NULL octet can be optionally followed by
+	 * multiple EOLs."
 	 */
-	protected void skipLeadingEol(ByteBuffer byteBuffer) {
+	protected void skipEol(ByteBuffer byteBuffer) {
 		while (true) {
 			if (!tryConsumeEndOfLine(byteBuffer)) {
 				break;

spring-messaging/src/test/java/org/springframework/messaging/simp/stomp/StompDecoderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,7 +16,6 @@
 
 package org.springframework.messaging.simp.stomp;
 
-import java.io.UnsupportedEncodingException;
 import java.nio.ByteBuffer;
 import java.util.List;
 
@@ -78,7 +77,7 @@ public void decodeFrameWithNoBody() {
 	}
 
 	@Test
-	public void decodeFrame() throws UnsupportedEncodingException {
+	public void decodeFrame() {
 		Message<byte[]> frame = decode("SEND\ndestination:test\n\nThe body of the message\0");
 		StompHeaderAccessor headers = StompHeaderAccessor.wrap(frame);
 
@@ -166,6 +165,17 @@ public void decodeFrameBodyNotAllowed() {
 				decode("CONNECT\naccept-version:1.2\n\nThe body of the message\0"));
 	}
 
+	@Test // gh-23713
+	public void decodeFramesWithExtraNewLines() {
+		String frame1 = "SEND\ndestination:test\n\nbody\0\n\n\n";
+		ByteBuffer buffer = ByteBuffer.wrap((frame1).getBytes());
+
+		final List<Message<byte[]>> messages = decoder.decode(buffer);
+
+		assertThat(messages.size()).isEqualTo(1);
+		assertThat(StompHeaderAccessor.wrap(messages.get(0)).getCommand()).isEqualTo(StompCommand.SEND);
+	}
+
 	@Test
 	public void decodeMultipleFramesFromSameBuffer() {
 		String frame1 = "SEND\ndestination:test\n\nThe body of the message\0";
@@ -179,9 +189,7 @@ public void decodeMultipleFramesFromSameBuffer() {
 		assertThat(StompHeaderAccessor.wrap(messages.get(1)).getCommand()).isEqualTo(StompCommand.DISCONNECT);
 	}
 
-	// SPR-13111
-
-	@Test
+	@Test // SPR-13111
 	public void decodeFrameWithHeaderWithEmptyValue() {
 		String accept = "accept-version:1.1\n";
 		String valuelessKey = "key:\n";