原理
简单的说，app要单独实现消息动态更新，一种是轮询，这对用户来说会带来额外的流量。另一种方案是push，app client和server直接保持一个长连接，有新的消息时server push给app client。
这两种通过app自身实现的“push”都会面临以下问题：
- 进程被关闭后无法在发送请求
- 大量app开启网络连接对用户的流量和电池都会带来大量消耗
- 通讯安全问题需要app自己提供解决方案
APNS为app开发商提供了一个统一的消息通知平台。apple和每个iOS设备之间保持一个长连接。开发商将消息发送给APNS，APNS将该消息发送到指定的iOS设备，iOS设备展示消息、启动相应的app。
从以上过程可知，为通过APNS实现消息push，一个消息需要标识发送到“哪台iOS设备”的“哪个app”。这两个分别由设备id（deviceToken）和SSL的证书文件（开启消息push的app需要配置一个SSL证书）标识。消息结构体如下：
实现方案
详细过程请参考http://mobiforge.com/developing/story/programming-apple-push-notification-services，一步步来即可。这一过程会生成文件：
- CertificateSigningRequest.certSigningRequest 用于生成SSL证书的中间文件，用后可删除
- aps_developer_identity.cer SSL证书文件，这一证书会关联app id，利用该证书可将消息发送到对应的app。
- [xxx].mobileprovision和上述SSL证书文件绑定的app provision文件，请安装到测试设备。
双击aps_developer_identity.cer将证书文件导入到Keychain Access。
java/php/c++需要的SSL证书和密钥生成如下：
- 将keychain access中的aps_developer_identity.cer导出为[xxx].p12
- 终端下执行： 1
openssl pkcs12 -in[xxx].p12 -out [xxx].pem -nodes
将最终生成的pem文件提供给后台server
后台代码示例
app client请参考上述链接中的示例。
push server:
object c版本 http://stefan.hafeneger.name/download/PushMeBabySource.zip
java版本 http://code.google.com/p/javapns/
php版本 http://code.google.com/p/apns-php/
现在后台技术主要还是c/c++吧，网上一直没找到合适的，自己实现demo，代码如下：
/*** @file main.cpp* @author Maxwin* @description TestPushServer*/#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <openssl/ssl.h>
#include <openssl/rand.h>
#include <openssl/bio.h>
#include <openssl/err.h>
#include <openssl/x509.h>
#include <netinet/in.h>// 证书文件
#define CERTFILE "max.pem"SSL *ssl;
SSL_CTX *ctx;void error(const char *msg)
{printf("[ERROR]:%s\n", msg);exit(1);
}SSL_CTX *setup_client_ctx()
{ctx = SSL_CTX_new(SSLv23_method());if (SSL_CTX_use_certificate_chain_file(ctx, CERTFILE) != 1) {error("Error loading certificate from file\n");}if (SSL_CTX_use_PrivateKey_file(ctx, CERTFILE, SSL_FILETYPE_PEM) != 1) {error("Error loading private key from file\n");}return ctx;
}// 将deviceToken字符串转成对应的binary bytes
void token2bytes(const char *token, char *bytes)
{int val;while (*token) {sscanf(token, "%2x", &val);*(bytes++) = (char)val;token += 2;while (*token == ' ') { // skip space++token;}}
}// 打包消息
unsigned long packMessage(char *message, const unsigned char command, const char *tokenBytes, const char *payload)
{unsigned long payloadLength = strlen(payload);unsigned short networkTokenLength = htons(32);unsigned short networkPayloadLength = htons(payloadLength);memcpy(message, &command, sizeof(unsigned char));message += sizeof(unsigned char);memcpy(message, &networkTokenLength, sizeof(unsigned short));message += sizeof(unsigned short);memcpy(message, tokenBytes, 32);message += 32;memcpy(message, &networkPayloadLength, sizeof(unsigned short));message += sizeof(unsigned short);memcpy(message, payload, payloadLength);return payloadLength + 37;
}int push(const char *token, const char *payload)
{char tokenBytes[32];char message[293];unsigned long msgLength;token2bytes(token, tokenBytes);msgLength = packMessage(message, 0, tokenBytes, payload);return SSL_write(ssl, message, (int)msgLength);
}int main (int argc, const char * argv[])
{char token[] = "2b2474e5 ac7670f3 08fabf3a 9c1d1295 ed50e9aa f11b941a d6e3d213 4f535408";char payload[] = "{\"aps\":{\"alert\":\"Hello world!!!\",\"badge\":1}}";char payload2[] = "{\"aps\":{\"alert\":\"Hello kitty!!!\",\"badge\":12}}";char host[] = "gateway.sandbox.push.apple.com:2195";BIO *conn;// initSSL_library_init();ctx = setup_client_ctx();conn = BIO_new_connect(host);if (!conn) {error("Error creating connection BIO\n");}if (BIO_do_connect(conn) <= 0) {error("Error connection to remote machine");}if (!(ssl = SSL_new(ctx))) {error("Error creating an SSL contexxt");}SSL_set_bio(ssl, conn, conn);if (SSL_connect(ssl) <= 0) {error("Error connecting SSL object");}printf("SSL Connection opened\n");// push messageint ret = push(token, payload);printf("push ret[%d]\n", ret);// push [Hello kitty] after 5ssleep(5);ret = push(token, payload2);printf("push2 ret[%d]\n", ret);printf("Close SSL Connection\n");SSL_shutdown(ssl);SSL_free(ssl);SSL_CTX_free(ctx);return 0;
}
编译运行：
g++ main.cpp -o pushServer -lssl -lcrypto
