在上一篇中，使用scrapy改动源IP发送请求的最后我们提到因为hosts文件不支持正则，会导致我们的随机域名DNS查询失败。

使用DNS代理服务器能够解决问题，

以下是我用gevent写的小工具。非常easy。我们仅仅拦截匹配的A记录。然后发送DNS Response，假设不匹配，那么我们服务器就是一个DNS代理，转发请求。

# -*- coding=utf-8 -*-
import struct
from cStringIO import StringIO
from collections import namedtuple
from gevent import socket
from gevent.server import DatagramServerHex = lambda x : '0x{0:04x}'.format(x) # Hex(256) => "0x0100"QueryResult = namedtuple("DnsQuery","transactionID,flags,questions,answerRrs \authorityRrs,additionalRrs,qname,qtype,qclass"
)LOCALDNS = ("114.114.114.114",53)Hosts = {"*.ttt.com":"173.194.127.144", # google ip
}def preg_match(preg,real):"""only support '*'>>>preg_match("www.*.test*.com","www.python.test.com")True>>>preg_match("www.*.test*.com","www.python.tes.com")False"""pre = 0for s in preg.split('*'):now = real.find(s)if now < pre:return Falsepre = now +len(s)return Truedef udp_send(address,data):sock = socket.socket(type=socket.SOCK_DGRAM)sock.connect(address)sock.send(data)response, address = sock.recvfrom(8192*4)return response,addressclass DnsParser:@classmethoddef parseQuery(self,query):"""6a 02 01 00 00 01                         j.....00 00 00 00 00 00 03 77 77 77 03 61 61 61 03 63  .......www.aaa.c6f 6d 00 00 01 00 01                             om.....dns query package like above03 77 77 77 : three www"""transactionID,flags,questions,answerRrs,authorityRrs,additionalRrs = map(Hex,struct.unpack("!6H",query[:12]))quries = StringIO(query[12:])c = struct.unpack("!c",quries.read(1))[0]domain = []while  c != '\x00':n = ord(c)domain.append(''.join(struct.unpack("!%sc" % n,quries.read(ord(c)))))c = struct.unpack("!c",quries.read(1))[0]domain = '.'.join(domain)qtype,qclass = map(Hex,struct.unpack("!2H",quries.read()))return QueryResult(transactionID,flags,questions,answerRrs,authorityRrs,additionalRrs,domain,qtype,qclass)@classmethoddef generateReqponse(self,queryData,ip):"""only support ipv4"""return ''.join([queryData[:2],"\x81\x80\x00\x01\x00\x02\x00\x00\x00\x00",queryData[12:],"\xc0\x0c","\x00\x01","\x00\x01","\x00\x00\x00\x1e","\x00\x04",struct.pack('BBBB',*map(int,ip.split('.')))])class DnsServer(DatagramServer):def handle(self,data,address):query = DnsParser.parseQuery(data)print "get dns query from %s,query:%s" %(str(address),str(query))find = Falsefor preg,ip in Hosts.iteritems():if preg_match(preg,query.qname):find = Truebreakif find and query.qtype == "0x0001": #only handle A recordprint 'domain:%s in hosts' % query.qnameresponse = DnsParser.generateReqponse(data,ip)self.socket.sendto(response,address)else:print 'transfer for %s' % query.qnameresponse,serveraddress = udp_send(LOCALDNS,data)self.socket.sendto(response,address)if __name__ == "__main__":DnsServer("192.168.9.178:53").serve_forever()

哈哈，刚好100行，不得不说python的强大。

来个截图：

功能有限。各位童鞋能够扩展，代码已经放到github，https://github.com/Skycrab/PyDnsProxy，有兴趣的童鞋一起完好。