Nginx加Comet:低延迟的服务器端推送

要做实时的网络程序，比如在线聊天等，现在的技术有两种，一种是拉（pull)、一种是推（push)，哪种方式好我相信接触网络的朋友们都知道， 服务器端推送服务这种方式能够满足完全的实时交互，不需要客户端做太多的东西。NGiNX_HTTP_Push_Module这个nginx的插件就是为 了这个目的来做的，它保持客户的长连接状态（当然了，不是每个客户一个线程，而是采用事件方式来处理，即保持了连接状态，又节约了资源，这就是nginx 这个轻量级web服务器的可爱之处）并且维护一个事件队列，提供发布者和订阅者服务。

要使用它，需要编译ngnix，从http://pushmodule.slact.net/下载模块，使用

./configure --add-module=/path/to/plugin && make && make install

进行编译，并参考和http://github.com/slact/nginx_http_push_module/blob/master/protocol.txt这两个文件来学习配置，下面是一个比较简单的发布、订阅模型

 

nginx-push.conf

#user nobody;worker_processes 1; #error_log logs/error.log;#error_log logs/error.log notice;#error_log logs/error.log info;#pid logs/nginx.pid; events {
          worker_connections 1024;} http {
          include mime.types;    default_type application/octet-stream;     #log_format main '$remote_addr - $remote_user [$time_local] $request '    # '"$status" $body_bytes_sent "$http_referer" '    # '"$http_user_agent" "$http_x_forwarded_for"';     #access_log logs/access.log main;    sendfile on;    keepalive_timeout 65; # max allowed memory for buferring    push_max_reserved_memory 10M;     server {
              listen 80;        server_name localhost;         location / {
                  root html;            index index.html index.htm;        }         ###### Push configuration        # internal publish endpoint (keep it private / protected)        location /publish {
                set $push_channel_id $arg_id; #/?id=239aff3 or somesuch          push_publisher;           push_store_messages on; # enable message queueing          push_message_timeout 2h; # expire buffered messages after 2 hours          push_max_message_buffer_length 10; # store 10 messages          push_min_message_recipients 0; # minimum recipients before purge        }         # public long-polling endpoint        location /activity {
                push_subscriber;           # how multiple listener requests to the same channel id are handled          # - last: only the most recent listener request is kept, 409 for others.          # - first: only the oldest listener request is kept, 409 for others.          # - broadcast: any number of listener requests may be long-polling.          push_subscriber_concurrency broadcast;          set $push_channel_id $arg_id;          default_type text/plain;        }         ###### END Push configuration         error_page 404 /404.html;         # redirect server error pages to the static page /50x.html        error_page 500 502 503 504 /50x.html;        location = /50x.html {
                   root html;        }    }}

这是一个ruby实例

require 'rubygems'require 'em-http' def subscribe(opts)  listener = EventMachine::HttpRequest.new('http://127.0.0.1/activity?id='+ opts[:channel]).get :head => opts[:head]  listener.callback {
             # print recieved message, re-subscribe to channel with    # the last-modified header to avoid duplicate messages     puts "Listener recieved: " + listener.response + "\n"     modified = listener.response_header['LAST_MODIFIED']    subscribe({
        :channel => opts[:channel], :head => {
        'If-Modified-Since' => modified}})  }end EventMachine.run {
          channel = "pub"   # Publish new message every 5 seconds  EM.add_periodic_timer(5) do    time = Time.now    publisher = EventMachine::HttpRequest.new('http://127.0.0.1/publish?id='+channel).post :body => "Hello @ #{time}"    publisher.callback {
              puts "Published message @ #{time}"      puts "Response code: " + publisher.response_header.status.to_s      puts "Headers: " + publisher.response_header.inspect      puts "Body: \n" + publisher.response      puts "\n"    }  end   # open two listeners (aka broadcast/pubsub distribution)  subscribe(:channel => channel)  subscribe(:channel => channel)}

上面的这个例子每5秒钟发布一则消息，同时nginx服务器会把消息push到连个订阅客户端