When you set the threadId property on apn.Notification object (we do this in our code) it is stored in aps property under thread-id key: https://github.com/parse-community/node-apn/blob/master/lib/notification/apsProperties.js#L124. Then iOS assigns this value to UNNotificationContent.threadIdentifier, but the entire aps dictionary is still present userInfo attribute of UNNotificationContent.

Decrypting UNNotificationContent.threadIdentifier is enough to display the right content to the user. Generally we don't any of this if(mutableAps ... statements (apart from the one with @"alert" which is crucial) to display the right content to the user and to store the right data in SQLite. However it just felt odd to propagate notification that still contains encrypted data to the application memory.

Why are we setting this here? Was badge in aps initially?

It wasn't. parse-apn adds badge to aps by default: https://github.com/parse-community/node-apn/blob/master/lib/notification/apsProperties.js#L67, but it does not allow to add it as a string. However we must add it as a string since it is encrypted. Therefore in D7813 I am setting encrypted badge as a string in payload property (which is transformed to userInfo when delivered). I decided it would be wise to add it back to aps after it is decrypted and cast to numerical value again.

Wouldn't this be handled by the code on line 220? (Which I am also confused about... see comment below)

Theoretically we could handle it there, but we would need if(payloadKey -- "badge") since:

1. We cast it to number.
2. We assign it to UNNotificationContent.badge attribute.

We can either handle it as an if statement inside a loop or handle it earlier and omit it inside a loop.

This is basically for body , title and prefix keys. We assign them directly to apn.Notification object as well as to its payload property:
https://github.com/CommE2E/comm/blob/master/keyserver/src/push/send.js#L648-L670

Assigning directly to apn.Notification puts those keys in aps dictionary. Therefore those properties are present in both userInfo and aps. I consider it unwise to have decrypted data in userInfo and encrypted data in aps if those are the same data.

Note: we cannot iterate over both (userInfo and aps) independently since olm throws if we try to decrypt the same data twice.

Here we assign 'rest' to notification.payload. https://github.com/CommE2E/comm/blob/master/keyserver/src/push/send.js#L652-L663. 'rest' comes from notifTexts object that is of type ResolvedNotifText. This type is defined as:

export type ResolvedNotifTexts = {
  +merged: string,
  +body: string,
  +title: string,
  +prefix?: string,
};