iOS- Apple push notification resend from APNS

问题:

From Apple's document I understand that if the device is offline, the APNS holds the last notification and sends it to the device when the device is back online. Is there is any mechanism to avoid that resending?

回答1:

The answer is NO

Here is what apple says about it,

If APNs attempts to deliver a notification but the device is offline, the notification is stored for a limited period of time, and delivered to the device when it becomes available.

Only one recent notification for a particular application is stored. If multiple notifications are sent while the device is offline, each new notification causes the prior notification to be discarded. This behavior of keeping only the newest notification is referred to as coalescing notifications.

If the device remains offline for a long time, any notifications that were being stored for it are discarded.

回答2:

The correct answer is YES

If you send notifications using the enhanced binary format (the one that includes message identifier and expiry), you can use the expiry parameter to prevent the notification from being stored in the APN server. This way the notification is delivered only if the device is online when the APN server first tries to deliver it.

Expiry

A fixed UNIX epoch date expressed in seconds (UTC) that identifies when the notification is no longer valid and can be discarded. The expiry value uses network byte order (big endian). If the expiry value is positive, APNs tries to deliver the notification at least once. Specify zero (or a value less than zero) to request that APNs not store the notification at all.

回答3:

I agree with Eran.

This part of your question "the APNS holds the last notification and sends it to the device when the device is back online" is only true if Expiration date is different of zero.

If you do want the message to be delivered when the phone gets online, the message will wait until "Expiration date" before be discarded.

APNS documentation:

Expiration date 4 bytes A UNIX epoch date expressed in seconds (UTC) that identifies when the notification is no longer valid and can be discarded. If this value is non-zero, APNs stores the notification tries to deliver the notification at least once. Specify zero to indicate that the notification expires immediately and that APNs should not store the notification at all.

For more details, refer to https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Chapters/CommunicatingWIthAPS.html