Add STOMP header without recreating Message on ChannelInterceptorAdapter - spring-websocket

Question

I need to add header to a STOMP message currently it is working as below but i am recreating the message , is it possible to just add native header without having to recreate the message for performance .
public class MyChannelInterceptor extends ChannelInterceptorAdapter {
#Override
public Message<?> preSend(Message<?> message, MessageChannel channel) {
StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
StompCommand command = accessor.getCommand();
if(command != null) {
log.debug("Receiving msg {} from {}",command,accessor.getUser().getName());
if(command == StompCommand.SEND) {
log.debug("Adding expires header to msg {} from {}",command,accessor.getUser().getName());
String ttlString = accessor.getFirstNativeHeader("ttl");
long ttl = 30000;
try {
ttl = Long.parseLong(ttlString);
}
catch(Exception ex) {
log.error("TTL header received but not in correct format {}",ttlString);
}
accessor.addNativeHeader("expires", Long.toString(System.currentTimeMillis() + ttl));
return MessageBuilder.createMessage(message.getPayload(), accessor.getMessageHeaders());
}
}
return message;
}
}

Answer 1

This is what i was looking for
StompHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, StompHeaderAccessor.class);
The above code will get the actual StompHeaderAccessor of the message so if you manipulate the native headers they are directly reflected on the message while
StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
will get a clone of the headers and you have to create a new message with the new cloned headers
full fixed code below
#Override
public Message<?> preSend(Message<?> message, MessageChannel channel) {
StompHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, StompHeaderAccessor.class);
// StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
if(accessor != null) {
StompCommand command = accessor.getCommand();
if(command != null) {
log.debug("Receiving msg {} from {}",command,accessor.getUser().getName());
if(command == StompCommand.SEND) {
log.debug("Adding expires header to msg {} from {}",command,accessor.getUser().getName());
String ttlString = accessor.getFirstNativeHeader("ttl");
long ttl = 30000;
if(ttlString != null) {
try {
ttl = Long.parseLong(ttlString);
}
catch(Exception ex) {
log.error("TTL header received but not in correct format {}",ttlString);
}
}
accessor.addNativeHeader("expires", Long.toString(System.currentTimeMillis() + ttl));
// I don't need any more to create a new message
//return MessageBuilder.createMessage(message.getPayload(), accessor.getMessageHeaders());
}
}
}
return message;
}

Answer 2

Since addNativeHeader succeeds, that indicates the message is still mutable - see addNativeHeader().
In any case, since the NATIVE_HEADERS message header is a MultiValueMap-valued header, you can update the header contents in-place.
Hence, there is no need to create a new message.
You would have to create a new message if you add a new header to the message itself (rather than updating the mutable contents of an existing header).
EDIT
I just ran a test; as long as the message is still mutable, you can change it...
#Test
public void test() {
Map<String, Object> map = new HashMap<String, Object>();
MutableMessageHeaders headers = new MutableMessageHeaders(map);
Message<String> message = MessageBuilder.createMessage("foo", headers);
StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
accessor.addNativeHeader("foo", "bar");
System.out.println(message.getHeaders().get(NativeMessageHeaderAccessor.NATIVE_HEADERS));
accessor.setImmutable();
try {
accessor.addNativeHeader("baz", "qux");
fail("expected IllegalStateException");
}
catch (IllegalStateException e) {
}
}
That said, are you experiencing a performance problem or is this just a perceived issue. Message creation is not expensive.