Handle invalid STOMP content-length header value

After this change if a content-length header is provided but is less
than 0 or cannot be parsed as a number, it is ignored and the body
is read sequentially, i.e. until we reach a null byte terminator.

This provides better protection against clients that may set the
content-length header in error.

Issue: SPR-11528

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * 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.
@@ -107,6 +107,36 @@ public class StompCodecTests {
 		assertEquals("The body of the message", bodyText);
 	}
 
+	// SPR-11528
+
+	@Test
+	public void decodeFrameWithInvalidContentLength() {
+		Message<byte[]> frame = decode("SEND\ncontent-length:-1\n\nThe body of the message\0");
+		StompHeaderAccessor headers = StompHeaderAccessor.wrap(frame);
+
+		assertEquals(StompCommand.SEND, headers.getCommand());
+
+		assertEquals(1, headers.toStompHeaderMap().size());
+		assertEquals(Integer.valueOf(-1), headers.getContentLength());
+
+		String bodyText = new String(frame.getPayload());
+		assertEquals("The body of the message", bodyText);
+	}
+
+	@Test
+	public void decodeFrameWithContentLengthZero() {
+		Message<byte[]> frame = decode("SEND\ncontent-length:0\n\n\0");
+		StompHeaderAccessor headers = StompHeaderAccessor.wrap(frame);
+
+		assertEquals(StompCommand.SEND, headers.getCommand());
+
+		assertEquals(1, headers.toStompHeaderMap().size());
+		assertEquals(Integer.valueOf(0), headers.getContentLength());
+
+		String bodyText = new String(frame.getPayload());
+		assertEquals("", bodyText);
+	}
+
 	@Test
 	public void decodeFrameWithNullOctectsInTheBody() {
 		Message<byte[]> frame = decode("SEND\ncontent-length:23\n\nThe b\0dy \0f the message\0");