unsubscribe call behaves unexpectedly

[tsgautier]

I'm trying to implement something like a one-time listener. However, unsubscribing at certain times behaves unexpectedly. Here's some code:

p = require 'postal'

postal = new p()

channel = postal.channel ''

subscription1 = channel.subscribe 'test', ->
  console.log '1 received message'

subscription2 = channel.subscribe 'test', ->
  console.log '2 received message'

channel.publish 'test'
subscription1.unsubscribe()
channel.publish 'test'

The above code behaves as expected, the output is as follows:

1 received message
2 received message
2 received message

However, to implement the "one-time" I did something like this:

p = require 'postal'

postal = new p()

channel = postal.channel ''

subscription1 = channel.subscribe 'test', ->
  console.log '1 received message'
  subscription1.unsubscribe()

subscription2 = channel.subscribe 'test', ->
  console.log '2 received message'

channel.publish 'test'
channel.publish 'test'

This outputs:

1 received message
2 received message

Which is pretty unexpected. Somehow the subscription1.unsubscribe() is unsubscribing both subscriptions.

[ifandelse]

@tsgautier Sorry about the trouble! Looking at this right now....

[tsgautier]

no problem - surprisingly, nextTick works, but leaves the code susceptible to multiple deliveries, so a flag is required to protect that, here's an approximation:

p = require 'postal'

postal = new p()

channel = postal.channel ''

delivered = false
subscription1 = channel.subscribe 'test', ->
  return if delivered
  delivered = true
  console.log '1 received message'
  process.nextTick -> subscription1.unsubscribe()

subscription2 = channel.subscribe 'test', ->
  console.log '2 received message'

channel.publish 'test'
channel.publish 'test'

[ifandelse]

This issue should be resolved - sorry for the woes. I should know better than to iterate over mutating arrays. :-)
Unsubscribe calls are now queued to occur after the publish has completed, but any subscriber that unsubscribes during the publish is immediately marked inactive, so the callback won't be invoked again.

One other thing, you actually don't need the new when you invoke postal = new p(). Instead you can opt for:

postal = require('postal')()
# OR
p = require 'postal'
postal = p()

The node module just returns a factory function that optionally takes underscore as a dependency (it requires underscore for you if it's not passed). This approach is used so that postal and any add-ons are all accessing the same instances of modules...

Let me know if you run into any other issues.

Thanks!