Sender#sendUserNotification

[hypesystem]

The only difference between a regular notification and a user notification is that the user notification uses the notification key to find its recipients (source):

// Regular notification data
{
  data: {
    some: "data"
  },
  registration_ids: [ "some-registration-id", "other-registration-id" ]
}

// User notification data
{
  data: {
    some: "data"
  },
  to: "some-notification-key"
}

It would be pretty straight forward to implement a Sender#sendUserNotification method. At the same time, this would be cause for generalizing a bunch of the code used in Sender#send.

We should probably add Sender#sendUserNotificationNoRetry as well.

The job of creating notification keys can be left out for now. It seems to me that it is immediately most relevant to handle on the client side (source), but I am open for discussion on this.

[hypesystem]

Okay, I did a bit of digging. According to an answer on StackOverflow and accompanying blog post, the correct field to contain the notification key is simply to. I have updated the original issue to reflect this.

The URL is also, according to the blog post, the same as used for regular messages. This makes implementation trivial.

[ToothlessGear]

Yes, seems like the sending part is easy.
Creating those keys also dont look that hard on the server-side, from catching a short glimpse at the docs.

[hypesystem]

I kind of want v0.10 out before we start considering user notifications (v0.11). But if it doesn't seem like too big a task, we could probably fit #108 (creating notification keys) in v0.11, too.

[ToothlessGear]

Sure, go ahead!