CODEWITHSUNDEEP
rabbitmqrpcstomp
Eduardo Pinheiro
Eduardo Pinheiro

Reputation: 3779

Rabbitmq + web stomp plugin with rpc - reply-to

I'm trying to perform an RPC with RabbitMQ's STOMP adapter. As the client lib I'm using the STOMP over WebSocket (https://github.com/jmesnil/stomp-websocket/) library.

From the documentation (http://www.rabbitmq.com/stomp.html#d.tqd) I see that I have to set the reply-to header. I've done that by specifying something like "reply-to: /temp-queue/foo" and I saw in my server-side client (node-amqp) that the replyTo header is set correctly (example: replyTo: '/reply-queue/amq.gen-w2jykNGp4DNDBADm3C4Cdx'). Still in my server-side client, I can reply to the message just by publishing a message to "/reply-queue/amq.gen-w2jykNGp4DNDBADm3C4Cdx".

However, how do I get this reply it in my client code where the RPC call was initiated? The documentation states "SEND and SUBSCRIBE frames must not contain /temp-queue destinations (...) subscriptions to reply queues are created automatically."

So, how do I subscribe to the reply-to queue? How can I get the results of RPC calls?

Thanks in advance.

Upvotes: 3

Views: 3024

Answers (3)

Rossen Stoyanchev
Rossen Stoyanchev

Reputation: 5008

The answer to the original question:

However, how do I get this reply it in my client code where the RPC call was initiated? The documentation states "SEND and SUBSCRIBE frames must not contain /temp-queue destinations (...) subscriptions to reply queues are created automatically."

So, how do I subscribe to the reply-to queue? How can I get the results of RPC calls?

Rabbit automatically subscribes the current STOMP session to the temp queue. The client doesn't know the temp queue name and cannot subscribe to it. However, when Rabbit sends a STOMP MESSAGE frame it sets the subscription header to the "reply-to" value (e.g. "/temp-queue/foo"). Although the STOMP over WebSocket client wasn't written with this in mind, a subscription could be registered as follows:

stompClient.subscriptions['/temp-queue/foo'] = function(message) {
  // ...
};

I'd be happy to hear if there is another solution.

Upvotes: 1

Le chat du rabbin
Le chat du rabbin

Reputation: 515

NB: There is no more '/reply-queue/' in the replyTo since RabbitMQ 3.0.0
I spent about a 4 hours to find what was the problem. Use .replace('/reply-queue/', '') instead of .substring(13)!

Upvotes: 0

Eduardo Pinheiro
Eduardo Pinheiro

Reputation: 3779

The answer is:

When you receive the rpc call in the server worker you get the header replyTo. That header comes like:

replyTo: '/reply-queue/[queue_name]'

for example: replyTo:'/reply-queue/amqp.fe43gggr5g54g54ggfd_'

The trick is:

  • you have to parse it and only answer to the queue_name [for example: amqp.fe43gggr5g54g54ggfd_]
  • You have to answer to the default exchange and not to any other exchange

Example of an answer in nodejs:

function onRpcReceived(message, headers, deliveryInfo, m) {
    var reply_to = m.replyTo.toString().substr(13, m.replyTo.toString().length);

    connection.publish(reply_to, {response:"OK", reply:"The time is 13h35m"}, {
                contentType:'application/json',
                contentEncoding:'utf-8',
                correlationId:m. correlationId
    });
}

Now i just wonder why the web-stomp-plugin adds the /reply-queue/ string to the attribute "replyTo" on the header instead of only add the queue name....! If someone knows the reason i would like to know.

Upvotes: 6

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