Add iOS10 thread-id to notification

[sideshow]

When displaying notifications, the system visually groups notifications
with the same thread identifier together.

Fixes #40

[coveralls]

Coverage decreased (-13.6%) to 86.395% when pulling 94a3a3c on feature-thread-id into 0ef66aa on master.

[jchambers]

Hello! I'm the main author of Pushy, an APNs library for Java. We're just getting around to adding support for thread-id (oops), but are having a hard time verifying that our changes are actually having an effect. If you have a moment and wouldn't mind providing some advice, I had a couple questions for you:

1. I notice that you've implemented thread-id as a header instead of a field inside the aps section of the payload. The "Payload Key Reference" section of the APNs docs certainly makes it sound like it ought to be in the payload; did you find the docs to be incorrect?
2. What behavior change do you observe when sending notifications with a thread-id header? I haven't been able to spot any changes to message ordering or appearance in my phone's Notification Center in testing. In particular, I've been alternating sending messages with and without a thread ID, but they all seem to just appear serially in the order in which they were received. Have you seen something different?

Thanks very much for your time!

[sideshow]

Hey @jchambers - You're absolutely right and I interpreted the docs incorrectly. I based this implementation of an early version of the docs and obviously got it wrong.

I have patched locally to send via payload and can confirm it is working when sent as aps.thread-id as per the latest docs.

I was also able to confirm it was working in iOS by putting a breakpoint on the UNNotificationContentExtension didReceive method.

Payload:

{
  "aps" : {
    "thread-id" : "my-thread-id",
    "alert" : "Hello!",
    "category": "my-category"
   }
} 

Breakpoint:

With regards to the apple docs which read:

"When displaying notifications, the system visually groups notifications with the same thread identifier together.", as you picked up, this doesn't seem to be the case for iOS.

A better reference and explanation:

"The system calls this method to deliver notifications to your Notification Content app extension. Use this method to configure the contents of your view controller or to incorporate content from a new notification. This method may be called multiple times while your view controller is visible. Specifically, it is called again when a new notification arrives whose threadIdentifier value matches the thread identifier of the notification already being displayed. The method is called on the main thread of your extension".

https://developer.apple.com/reference/usernotificationsui/unnotificationcontentextension/1648525-didreceive

Thanks! Adam

[jchambers]

🤘

Thanks for the detailed explanation, and thanks for the indeed-much-better-explanation of what we're looking for. Hope I can return the favor some time!