APNS 那些事！

        之前在消息推送中间件APush里实现了对APNS的桥接，并利用业余时间阅读了官方指南Local and Push Notification Programming Guide，蛮有心得的。稍作总结，分享给大家，希望能够喜欢，欢迎留言讨论！

1.  APNS 通道环境

      作为一个黑盒的消息推送服务，APNS为我们提供了开发和产品两套环境，这两套环境除了Host name不同外，授权证书也不近相同（证书里面会包含APP相关信息，如application bundle ID，在你创建不同的profile的时候，这些信息会自动添加进去），当然Device Token也不同。下面的英文也许能更好地描述这两套环境的不同：

Development: Use the development environment for initial development and testing of the provider application. It provides the same set of services as the production environment, although with a smaller number of server units. The development environment also acts as a virtual device, enabling simulated end-to-end testing.You access the development environment atgateway.sandbox.push.apple.com , outbound TCP port 2195.

Production: Use the production environment when building the production version of the provider application. Applications using the production environment must meet Apple’s reliability requirements.You access the production environment atgateway.push.apple.com , outbound TCP port 2195.

2.  APNS 消息格式

     APNS 采用二进制消息协议，如下：

     看官方的解释，蛮清晰的：

     注意：

       如果APNS成功接收到你的消息，它将什么也不返回；

       如果你send a notification that is malformed or otherwise unintelligible, APNs returns an error-response packet and closes the connection. Any notifications that you sent after the malformed notification using the same connection are discarded, and must be resent. 这点要格外重要，所以很多开源工具包，比方说pushy提供了一个FailedConnectionListener，你可以通过实现该接口，方便的实现resent，代码片段如下：

private class MyFailedConnectionListener implements FailedConnectionListener<SimpleApnsPushNotification> {

    public void handleFailedConnection(
            final PushManager<? extends SimpleApnsPushNotification> pushManager,
            final Throwable cause) {

        if (cause instanceof SSLHandshakeException) {
            // This is probably a permanent failure, and we should shut down
            // the PushManager.
        }
    }
}

// ...

pushManager.registerFailedConnectionListener(new MyFailedConnectionListener());

         Status code 解释如下：

      A status code of 10 indicates that the APNs server closed the connection (for example, to perform maintenance).The notification identifier in the error response indicates the last notification that was successfully sent. Any notifications you sent after it have been discarded and must be resent. When you receive this status code, stop using this connection and open a new connection.

3.  APNS 消息接收

     An application must register with Apple Push Notification service for the operating systems on a device and on a computer to receive remote notifications sent by the application’s provider. Registration has three stages:

 3.1 The app registers for remote notifications.

 3.2 The system sets up remote notifications for the app and, if registration is successful, passes a device token to the app delegate.

 3.3 The app sends its device token to the push provider.

 3.4 Device tokens can change. Your app needs to reregister every time it is launched—in iOS by calling the registerForRemoteNotificationTypes: method of UIApplication, and in OS X by calling the registerForRemoteNotificationTypes: method of NSApplication.

 3.5 Because the only notification type supported for non-running applications is icon-badging,pass NSRemoteNotificationTypeBadge as the parameter of registerForRemoteNotificationTypes:.

 3.6 If registration is successful, APNs returns a device token to the device and iOS passes the token to the app delegate in the application:didRegisterForRemoteNotificationsWithDeviceToken: method. If there is a problem in obtaining the token, the operating system informs the delegate by calling the application:didFailToRegisterForRemoteNotificationsWithError: method.

      用一幅图来说明这个流程，如下：

4.  APNS Qos

    Apple Push Notification service includes a default Quality of Service (QoS) component that performs a store-and-forward function.
    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.

    注意我字体标黑的这个APNS的特性!

5.  APNS  FAQ

    a. APNS feedback 服务是用来做什么的？

      The Apple Push Notification Service includes a feedback service to give you information about failed push notifications. When a push 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. Push 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 push notifications that will fail to be delivered, you reduce unnecessary message overhead and improve overall system performance.
      Query the feedback service daily to get the list of device tokens. Use the timestamp to verify that the device tokens haven’t been reregistered since the feedback entry was generated. For each device that has not been reregistered, stop sending notifications. APNs monitors providers for their diligence in checking the feedback service and refraining from sending push notifications to nonexistent applications on devices.    
      The feedback service maintains a separate list for each push topic. If you have multiple apps, you must connect to the feedback service once for each app, using the corresponding certificate, in order to receive all feedback.
      The feedback service has a binary interface similar to the interface used for sending push notifications. You access the production feedback service via feedback.push.apple.com on port 2196 and the development feedback service via feedback.sandbox.push.apple.com on port 2196. As with the binary interface for push notifications, use TLS (or SSL) to establish a secured communications channel. You use the same SSL certificate for connecting to the feedback service as you use for sending notifications. To establish a trusted provider identity, present this certificate to APNs at connection time using peer-to-peer authentication.

      Once you are connected, transmission begins immediately; you do not need to send any command to APNs.Read the stream from the feedback service until there is no more data to read.

      The feedback service’s list is cleared after you read it. Each time you connect to the feedback service, the information it returns lists only the failures that have happened since you last connected.

    b. Best Practices for Managing Connections

       You may establish multiple connections to the same gateway or to multiple gateway instances. If you need to send a large number of push notifications, spread them out over connections to several different gateways.This improves performance compared to using a single connection: it lets you send the push notifications faster, and it lets APNs deliver them faster.
       Keep your connections with APNs open across multiple notifications; don’t repeatedly open and close connections. APNs treats rapid connection and disconnection as a denial-of-service attack. You should leave a connection open unless you know it will be idle for an extended period of time—for example, if you only send notifications to your users once a day it is ok to use a new connection each day.

   c. 接收到APNS消息后，我一般怎么处理呢？

    If your app is frontmost, the application:didReceiveRemoteNotification: or application:didReceiveLocalNotification:method is called on its app delegate;
    If your app is not frontmost or not running, you handle the notifications by checking the options dictionary passed to the application:didFinishLaunchingWithOptions: of your app delegate for either the UIApplicationLaunchOptionsLocalNotificationKey or UIApplicationLaunchOptionsRemoteNotificationKey key.

    实例代码如下：

 (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo {
    // 取得 APNs 标准信息内容
    NSDictionary *aps = [userInfo valueForKey:@"aps"];
    NSString *content = [aps valueForKey:@"alert"]; //推送显示的内容
    NSInteger badge = [[aps valueForKey:@"badge"] integerValue]; //badge数量
    NSString *sound = [aps valueForKey:@"sound"]; //播放的声音
     
    // 取得自定义字段内容
    NSString *customizeField1 = [userInfo valueForKey:@"customizeField1"]; //自定义参数，key是自己定义的
    NSLog(@"content =[%@], badge=[%d], sound=[%@], customize field =[%@]",content,badge,sound,customizeField1);
     
    // Required
    [APService handleRemoteNotification:userInfo];
}



//iOS 7 Remote Notification
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler {
 
    NSLog(@"this is iOS7 Remote Notification");
     
    // Required
    [APService handleRemoteNotification:userInfo];
    completionHandler(UIBackgroundFetchResultNoData);
}

d.  消息发送过程中，突然出现Write failed: Broken pipe

e.  因为APNS发送成功没有任何返回，会不会出现是异常但是异常信息还没返回的现象

   有可能，这个时候可以采取批量发送，等候一段时间，比方说1秒，通过Feedback来检查发送状态。

f.   一些你可能会忽视的细节：

      Each application on a device is limited to 64 scheduled local notifications. The system discards scheduled notifications in excess of this limit, keeping only the 64 notifications that will fire the soonest. Recurring notifications are treated as a single notification.

      Custom sounds must be under 30 seconds when played. If a custom sound is over that limit, the default system sound is played instead.

参考文献：

     1. Local and Push Notification Programming Guide

     2. http://www.easyapns.com/apple-delegate

     3. http://blog.csdn.net/tlq1988/article/details/9612237

     4. http://www.cocoachina.com/bbs/read.php?tid=98797