Subscribe command not calling the optional callback

[manast]

Hello,

is it expected that when using the subscribe command no callback is called? I would assume that this should work:

client.subscribe("My Channel", function(err, result){ 
  console.log("Subscribed to my channel")
})

But the callback is never called. In contrast the event "subscribe" is fired correctly. Since I do my subscribtion in certain context, I would like to have a callback so that I can do things related to that context.

A bug or something in redis preventing this?

regards.

[mranney]

I'll add this, but there are a couple of subtle and non-obvious things here, which is why I didn't do this at first.

The first is what data should be in the result parameter. In the simple case, it doesn't really matter, so I guess the channel name can go there.

The second issue is that subscribe can take multiple channel names like this:

client.subscribe("chan1", "chan2", "chan3");

The redis server sends back 3 replies to this one command. In order to handle that case properly, we'd have to complicate the logic of return_reply to remember how many channels went out and wait for that many responses to come back before invoking the callback. It's not impossible, but it'd be a pretty big change to some very well-worn paths though the code. Instead, I think we should just invoke the callback when the first subscribe message comes back, and still do an event for every subscribe message. That way if you really need to know what the subscription state and channel count is, you can track it with subscribe listeners.

[manast]

Shouldn't the return parameter of the callback be just err if no other thing is expected?

About your example, I think you really need to only call the callback when all 3 operations have been performed successfully, you can use a lib like async (https://github.com/caolan/async) to fix it easily, I guess you can use async in more places of node_redis, so it will be a good addition anyway. :).

[mranney]

It's not as easy as that, unfortunately. The Redis protocol sends back a variable number of responses, and there is a state machine that parses and routes them. Most commands send back a single response, so it is easy to match this back up with the command that was sent.

[mranney]

I just published v0.7.0 to npm that includes this fix.

[manast]

cool thanks.