How to mimic SimpMessagingTemplate.convertAndSendToUser using RabbitTemplate? - spring

Question

So I've been reading about Spring Message Relay (Spring Messaging stuff) capability with a RabbitMQ broker. What I want to achieve is as follows:
Have a service (1), which acts as a message relay between rabbitmq and a browser. This works fine now. I'm using MessageBrokerRegistry.enableStompBrokerRelay to do that.
Have another service (2) on the back-end, which will send a message to a known queue onto RabbitMQ and have that message routed to a specific user. As a sender, I want to have a control over who the message gets delivered to.
Normally, you'd use SimpMessagingTemplate to do that. Problem is though, that the origin of the message doesn't actually have access to that template, as it's not acting as a relay, it's not using websockets and it doesn't hold mapping of queue names to session ids.
One way I could think of doing it, is writing a simple class on the service 1, which will listen on all queues and forward them using simp template. I fell however this is not an ideal way to do it, and I feel like there might be already a way to do it using Spring.
Can you please advise?

Answer 1

This question got me thinking about the same dilemma I was facing. I have started playing with a custom UserDestinationResolver that arrives at a consistent topic naming scheme that uses just the username and not the session ID used by the default resolver.
That lets me subscribe in JS to "/user/exchange/amq.direct/current-time" but send via a vanilla RabbitMQ application to "/exchange/amqp.direct/users.me.current-time" (to a user named "me").
The latest source code is here and I am "registering" it as a #Bean in an existing #Configuration class that I had.
Here's the custom UserDestinationResolver itself:
public class ConsistentUserDestinationResolver implements UserDestinationResolver {
private static final Pattern USER_DEST_PREFIXING_PATTERN =
Pattern.compile("/user/(?<name>.+?)/(?<routing>.+)/(?<dest>.+?)");
private static final Pattern USER_AUTHENTICATED_PATTERN =
Pattern.compile("/user/(?<routing>.*)/(?<dest>.+?)");
#Override
public UserDestinationResult resolveDestination(Message<?> message) {
SimpMessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, SimpMessageHeaderAccessor.class);
final String destination = accessor.getDestination();
final String authUser = accessor.getUser() != null ? accessor.getUser().getName() : null;
if (destination != null) {
if (SimpMessageType.SUBSCRIBE.equals(accessor.getMessageType()) ||
SimpMessageType.UNSUBSCRIBE.equals(accessor.getMessageType())) {
if (authUser != null) {
final Matcher authMatcher = USER_AUTHENTICATED_PATTERN.matcher(destination);
if (authMatcher.matches()) {
String result = String.format("/%s/users.%s.%s",
authMatcher.group("routing"), authUser, authMatcher.group("dest"));
UserDestinationResult userDestinationResult =
new UserDestinationResult(destination, Collections.singleton(result), result, authUser);
return userDestinationResult;
}
}
}
else if (accessor.getMessageType().equals(SimpMessageType.MESSAGE)) {
final Matcher prefixMatcher = USER_DEST_PREFIXING_PATTERN.matcher(destination);
if (prefixMatcher.matches()) {
String user = prefixMatcher.group("name");
String result = String.format("/%s/users.%s.%s",
prefixMatcher.group("routing"), user, prefixMatcher.group("dest"));
UserDestinationResult userDestinationResult =
new UserDestinationResult(destination, Collections.singleton(result), result, user);
return userDestinationResult;
}
}
}
return null;
}
}