在上一篇中，使用scrapy修改源IP发送请求的最后我们提到由于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代理服务器可以解决这个问题，
下面是我用gevent写的小工具，很简单。我们只拦截匹配的A记录，然后发送DNS Response，如果不匹配，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 DatagramServer
Hex = 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 = 0
for s in preg.split(‘*‘):
now = real.find(s)
if now < pre:
return False
pre = now +len(s)
return True
def 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,address
class DnsParser:
@classmethod
def 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.c
6f 6d 00 00 01 00 01 om.....
dns query package like above
03 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)
@classmethod
def 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 = False
for preg,ip in Hosts.iteritems():
if preg_match(preg,query.qname):
find = True
break
if find and query.qtype == "0x0001": #only handle A record
print ‘domain:%s in hosts‘ % query.qname
response = DnsParser.generateReqponse(data,ip)
self.socket.sendto(response,address)
else:
print ‘transfer for %s‘ % query.qname
response,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，各位童鞋可以扩展，代码已经放到github，https://github.com/Skycrab/PyDnsProxy，有兴趣的童鞋一起完善。