apns-push-type header is required on iOS 13 and later

[flexfrank]

https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/sending_notification_requests_to_apns#2947610

[whirosan]

You need to add a new error type “InvalidPushType” to errors.go.
https://github.com/RobotsAndPencils/buford/blob/master/push/errors.go
https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/sending_notification_requests_to_apns#2947619

[flexfrank]

I added InvalidPushType error.
Thanks.

[cubicdaiya]

@RobotsAndPencils @nathany If there is no problem, could you approve and merge this?

[junpayment]

@RobotsAndPencils @nathany
The release of ios13 is approaching 9/19.
I hope you will merge before that.

[nathany]

Thanks. We should probably add something to the README in the headers section.

[nathany]

There were a number of lint issues:

push/header.go:32:6: exported type PushType should have comment or be unexported
push/header.go:32:6: type name will be used as push.PushType by other packages, and that stutters; consider calling this Type
push/header.go:35:2: exported const PushTypeAlert should have comment (or a comment on this block) or be unexported

I've changed the API slightly.

[nathany]

release tagged: 0.14.0