[5.3] Create NotificationFailed event

[barryvdh]

In the case of a failure, which shouldn't be retried, it currently is possible to handle this, right?

I propose we add an event for when a Notification fails, eg. for push notifications when a token is invalid. We would like to respond by removing the push token from the user model (or log/notify/do something else).

Throwing an exception would break the flow (eg. when the 1st of 2 notification channels throws an exception).

[themsaid]

If we catch exceptions while sending to a specific channel and fire an event that'll help not to break the flow, but from inside the listener we need to be able to retry for x times depends on the nature of the exception thrown. I'm not sure but maybe having a way to send a notification to only a single channel can solve this issue.

[barryvdh]

@themsaid I think that is more relevant to issue #14785
This is more for when it's not supposed to retry, but instead a sort of soft-fail, which needs to handling.

Actual example here: https://github.com/fruitcake/laravel-gcm-notification-channel/blob/dd2acc1c22ecab6c5db81b2d39cfbaf27126fdcd/src/GcmChannel.php#L55-L80

1. When it fails because of connection problem etc, it throws an Exception.
2. When the service responds there is something wrong with the token (in this case), it should do some action.

(And yes, this is currently solved by our own Event, but perhaps a Event would be better)

[themsaid]

I like how you handled failure in your channel, and yes there are conditions where a retry won't solve anything, in that case firing an event is a good solution.