What is the default value of the apns-expiration field?

Question

The apns-expiration field governs how long Apple will hold on to an apns message before giving up on delivering it (for example, if the device is turned off).

According to their docs, a value of zero means "no retention": meaning that if the message can't be delivered immediately, its discarded.

But what happens if the header isn't specified? In other words, what is the default behavior?

Medici

Good question. I see nothing about it in the docs. For the old binary "enhanced" format, the expiration value was part of the expected binary message, so it always had a value. – Wrought

@Eran: perhaps you know - the very first version of apns (pre 'enhanced') did not explicitly specify expiration date. Perhaps you know what the retention default for that is? – Medici

I guess I could just test it. – Medici

I have no idea. – Wrought

Good question, but I would advise never rely on something which is not documented. Behavior can change anytime & can make your app suffer. You can always set expiration as '0' for real time notifications which doesn't make sense to be delivered later. :) – Loyceloyd

@ayush - you're right. its not a good practice. However sometimes you're facing a legacy system that does just that... :] – Medici

Answer 1

My information isn't based on documentation but rather on stats gathered from a multi-million users system. The policy at this time is to retain push messages for a long time (exactly how long I dont know - we've seen 1M seconds retention in some cases). Of course, as this isn't documented it could change in the future.

Note that this default value is similar to Google's policy (where the default is 2419200 seconds), with the exception that Google's policy is documented.

Medici

Based on this answer it can be really 28 days, unfortunately the link is dead. apple.stackexchange.com/a/364488 Since FCM can only hold notification for 28 days and that is also the said default value when not specified if that is the case then that will be the possible default value if you are using FCM. – Atlanta

Answer 2

According to the new Apple Docs, for no specified expiration date the notification is stored and retried for upto 30 days.

Maritime

Answer 3

https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/CommunicatingwithAPNs.html#//apple_ref/doc/uid/TP40008194-CH11-SW1

"If this value is nonzero, APNs stores the notification and tries to deliver it at least once, repeating the attempt as needed if it is unable to deliver the notification the first time."

Literally this means that the absence of the value equals to 0.

Promote