用python gevent简单实现的server，转发dns请求

dns_forwarder.py

#!/usr/bin/python2.7
# Copyright (c) 2012 Denis Bilenko. See LICENSE for details.
"""A simple UDP server.

For every message received, it sends a reply back.

You can use udp_client.py to send a message.
"""
from __future__ import print_function
import argparse,sys
from gevent.server import DatagramServer
from gevent import spawn, joinall,socket,sleep
from Crypto.Cipher import AES
from Crypto.Hash import MD5


TIMEOUT=10
BS = AES.block_size
pad = lambda s: s + (BS - len(s) % BS) * chr(BS - len(s) % BS)
unpad = lambda s : s[0:-ord(s[-1])]


class ServerConfig:
    def __init__(self, arg):
        self.server = arg.server
        self.port = arg.port
        self.key = arg.key
        self.timeout= arg.timeout
        self.client_mode = arg.client
        
class EchoServer(DatagramServer):
    def __init__(self,address, config):
        DatagramServer.__init__(self, address)
        self.config = config
        self.aes = AES.new(MD5.new(config.key).hexdigest())#, AES.MODE_CBC, IV)

    def handle(self, data, address):
        print('%s: got(%d) %r' % (address[0], len(data),data))
        spawn(self.forward,data, address)

    def forward(self,data, address):
        client = socket.socket(
                family=socket.AF_INET, 
                type=socket.SOCK_DGRAM,
                proto=socket.IPPROTO_UDP)
        client.settimeout(self.config.timeout)
        aes = self.aes
        
        if self.config.client_mode:
            data = aes.encrypt(pad(data))
        else:
            data = unpad(aes.decrypt(data))
        #print('==> got(%d) %r' % (len(data),  data))
        client.sendto(data, ( self.config.server, self.config.port) )
        resp = client.recv(1024)
        if self.config.client_mode:
            data = unpad(aes.decrypt(resp))
        else:
            data = aes.encrypt(pad(resp))
        self.socket.sendto(data,  address)


def parse_arg():
    parser = argparse.ArgumentParser()
    parser.add_argument('-s', '--server', required=True, help='server ip/host')
    parser.add_argument('-p', '--port',  required=True,  help='server port' ,type=int,)
    parser.add_argument('-l', '--local',  required=True,  help='local listen port' ,default=':10700')
    parser.add_argument('-t', '--timeout',   help='timeout to connect to server',default=TIMEOUT)
    parser.add_argument('-k', '--key',   required=True,  help='AES encrypt key')
    parser.add_argument('-c', '--client', action="store_true", default=False, help='run in client mode')

    arg = parser.parse_args()
    return arg


if __name__ == '__main__':
    arg = parse_arg()
    config = ServerConfig(arg)

    print('Receiving datagrams on %s' % arg.local )
    EchoServer(arg.local , config).serve_forever()