Async function for queue subscribe

Is there a way to use async functions in subscribers? I’m looking for a way to do this:

let sub3 = await nc.subscribe('foo.baz.>', async (err, msg) => {
     // await async task to finish before taking next item in the queue...
}, {queue: 'A'});

[aricart]

Here’s an example of what that would look like:

https://gist.github.com/aricart/0e0641468694ac451592765feea84835

[aricart]

@haywirez thanks for the clarifications, you are effectively describing a work queue. Implicitly it seems that you require in-order processing. The payload I take it is very small. Really what you are looking for is store-and-forward, but have the client be in control of the ‘next’ message.

Just to make sure we are on the same page, a NATS subscription doesn’t hold any sort of queue in the server. So while you want to only ‘take’ the next message, all messages for the subscription are already in the client’s message buffer. If the client were to fail, the messages would be lost.

You could take a look at node-nats-streaming - that will get you somewhat close. You would have to configure the streaming server a bit differently from what a normal configuration is:

• the channel storing messages received from one subject would have to have some age discard (streaming channels typically grow unbounded).
• the client would make a durable subscription (likely in a queue group)
• the client would have to set its ackWait to the maximum amount of time decoding would take + extra.
• the client would have to specify to only get a single message until the previous message is acknowledged

Now your client can process the message, and when done processing ack it (if not acknoledged it will receive the message again, or if in a queue group, a different client could be assigned the message).

This will get you much closer to what you are trying to do, but there may be additional gotchas. @kozlovic can probably inject additional wisdom.