- 官方的一段话：
Legacy Notification Format
Figure B-1Legacy notification format
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The first byte in the legacy format is a command value of 0 (zero). The other fields are the same as the enhanced format. Listing B-1 gives an example of a function that sends a remote notification to APNs over the binary interface using the legacy notification format. The example assumes prior SSL connection to gateway.push.apple.com (or gateway.sandbox.push.apple.com) and peer-exchange authentication.
Enhanced Notification Format
The enhanced format has several improvements over the legacy format:
Error response. With the legacy format, if you send a notification packet that is malformed in some way—for example, the payload exceeds the stipulated limit—APNs responds by severing the connection. It gives no indication why it rejected the notification. The enhanced format lets a provider tag a notification with an arbitrary identifier. If there is an error, APNs returns a packet that associates an error code with the identifier. This response enables the provider to locate and correct the malformed notification.
Notification expiration. APNs has a store-and-forward feature that keeps the most recent notification sent to an app on a device. If the device is offline at time of delivery, APNs delivers the notification when the device next comes online. With the legacy format, the notification is delivered regardless of the pertinence of the notification. In other words, the notification can become “stale” over time. The enhanced format includes an expiry value that indicates the period of validity for a notification. APNs discards a notification in store-and-forward when this period expires.
Figure B-2 depicts the format for notification packets.
Identifier—An arbitrary value that identifies this notification. This same identifier is returned in a error-response packet if APNs cannot interpret a notification.
Expiry—A fixed UNIX epoch date expressed in seconds (UTC) that identifies when the notification is no longer valid and can be discarded.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 non-zero, APNs tries to deliver the notification at least once. Specify zero to request that APNs not store the notification at all.
Token length—The length of the device token in network order (that is, big endian)
Device token—The device token in binary form.
Payload length—The length of the payload in network order (that is, big endian). The payload must not exceed 256 bytes and must not be null-terminated.
Payload—The notification payload.
Payload 长度不能超过256个字节，否则会收到errorRespond
