What is push notification payload maximum size?

Apple Push Notification service (APNs) refuses a notification if the total size of its payload exceeds the following limits:

• FCM - 2 Kb
• VOIP Notification - 5 kb
• For all other remote notification - 4 kb

Difference between FCM and APNS

• FCM is sent as JSON payloads and APNS sends either string or dictionary.
• FCM has a payload of 2KB while APNS has a payload of 4KB.
• APNS saves 1 notification per App while FCM saves 100 notifications per device.
• FCM supports multiple platforms while APNS requires their proprietary platform.
• Acknowledgment can be sent in FCM if using XMPP, but it's not possible on APNS.

Advatage of FCM

• Even if the user disallows notification, you can notify your app if the app is running in the foreground (using shouldEstablishDirectChannel).
• Don't need to create dashboard to send notification on the device.
• Notification analytics on FCM Dashboard.
• Easy to create notification payload structure.
• App Server side handling is easy, Only one key is required for multiple apps and platform (iOS, Android, Web)

How we stop notification to be sent to device who is uninstalled?

Ans :

The push message service has a feedback channel which reports error messages when the application has been removed or the device no longer accepts the push messages.

"The Apple Push Notification service includes a feedback service to give you information about failed remote notifications. When a remote notification cannot be delivered because the intended app does not exist on the device, the feedback service adds that device’s token to its list. Remote notifications that expire before being delivered are not considered a failed delivery and don’t impact the feedback service. By using this information to stop sending remote notifications that will fail to be delivered, you reduce unnecessary message overhead and improve overall system performance."

What is p12 and pem file

Ans : 

p12 : .p12 is an alternate extension for what is generally referred to as a "PFX file", it's the combined format that holds the private key and certificate and is the format most modern signing utilities use. Same with alternate extensions are .PFX, .PKCS12 

pem : this is a container format that may include just the public certificate (such as with Apache installs, and CA certificate files /etc/ssl/certs), or may include an entire certificate chain including public key, private key, and root certificates. 

Convert from .p12 file to .pem file 

cdcd Desktop openssl pkcs12 -in pushcert.p12 -out pushcert.pem -nodes -clcerts