nginx comet

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Readme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)
}