APNS to support error-response handling(enhanced message) and re-send mechanism for performance

[jimhorng]

The problem of current APNS error-response are: (reference: the problem, official doc -> The Binary Interface and Notification Format)

• async error response (response time varies) => errors not guaranteed to be caught if wait for a fixed time
• success do not response => cannot wait for response forever
• async close write stream connection after error-response
• all message sent after failed msg error are discarded, error-response and write conn close will delay => should be re-sent
• sometimes APNS close arbitrary

From my experiment of getting error-response with enhanced message format:

• if wait for error-response(using select.select()) with given timeout = 0s, it often get NO APNS's error-response in time,
• when I set to 0.3s it got 90% of error-response.
  however, it's not guarantee 100% to get error-response for every failed notification, the network connection might also be a factor of delayed time.

Possible Solution

The solution suggested in the problem is to save sent notification in a queue with no timeout(or minimum), when error-response caught, pop out messages before the error one in queue (considered successfully sent), and re-sent others.
Which will not have performance concern if waiting for error-response in fixed time for each message sent, and also prevent error-response uncaught.

[hagino3000]

I'm using PyAPNs to send 1,000,000 devices/day. And my workarounds are

• Read error-response when queue become empty or sent 500 frames.
• Read error-response with 0.5 sec timeout
• If error response found, create new connection and retry sending after invalid frame.

Code is here
https://github.com/voyagegroup/apns-proxy-server/blob/065775f87dbf25f6b06f24edc73dc5de4481ad36/apns_proxy_server/worker.py#l164-209

Then my idea is 2 phase

(1) Add error handling methods for manual use

• Add method for read error-response
• Add method for reconnection

We can check error-respose any time.

(2) Provide automatic error handling mode

• Save frames to retry
• Read error-response automatically
• Retry frames automatically

[djacobs]

@jimhorng - do you want to make a pull request?