这里的代理服务器，是指二级代理服务器。比如：A可以访问B，B可以访问C，A不能直接访问C。这时，如果在B开一个二级代理，就可实现A访问C。现有的工具有CCProxy。

这里就是使用Python简单的实现一个二级代理。

#coding=utf-8   
import socket   
import select   
import sys   
import threading  
import time  
import logging  
import os  
logsDir = "logs"  
if not os.path.isdir(logsDir):  
    os.mkdir(logsDir)  
      
logging.basicConfig(level=logging.DEBUG,  
                format='%(asctime)s %(filename)s[line:%(lineno)d] %(levelname)s %(message)s',  
                datefmt='%a, %d %b %Y %H:%M:%S',  
                filename='logs/logs.log',  
                filemode='a')  
   
#C的IP和端口   
to_addr = ('0.0.0.0', 8087)  
  
class Proxy:   
    def __init__(self, addr):   
        self.proxy = socket.socket(socket.AF_INET, socket.SOCK_STREAM)   
        self.proxy.bind(addr)   
        self.proxy.listen(10)   
        self.inputs = [self.proxy]   
        self.route = {}   
     
    def serve_forever(self):   
        logging.info('proxy listen...')  
        while 1:   
            readable, _, _ = select.select(self.inputs, [], [])   
            for self.sock in readable:   
                if self.sock == self.proxy:   
                    self.on_join()   
                else:  
                    try:  
                        data = self.sock.recv(8192)  
                    except Exception, e:  
                        logging.error(str(e))  
                        self.on_quit()  
                        continue  
                      
                    if not data:   
                        self.on_quit()   
                    else:  
                        try:  
                            self.route[self.sock].send(data)  
                        except Exception, e:  
                            logging.error(str(e))  
                            self.on_quit()  
                            continue  
     
    def on_join(self):   
        client, addr = self.proxy.accept()   
        logging.info("proxy client " + str(addr) + 'connect')  
        forward = socket.socket(socket.AF_INET, socket.SOCK_STREAM)   
        forward.connect(to_addr)   
        self.inputs += [client, forward]   
        self.route[client] = forward   
        self.route[forward] = client   
      
    #删除连接  
    def on_quit(self):  
        ls = [self.sock]  
        if self.sock in self.route:  
            ls.append(self.route[self.sock])  
        for s in ls:  
            if s in self.inputs:  
                self.inputs.remove(s)  
            if s in self.route:  
                del self.route[s]   
            s.close()   
              
if __name__ == "__main__":  
    try:   
        Proxy(('', 8192)).serve_forever()  
    except KeyboardInterrupt:   
        logging.error("KeyboardInterrupt")  
        return  
  

来自：http://blog.csdn.net/junfeng_feng/article/details/42966363