因为突然有个邪恶的想法，想在自己的Android平板上面搭建一个DNS服务器，因为平板上之前安装过SL4A和Python的解释器，也想继续学学Python因此，就打算用Python实现了。

在Google上面找了一下,Python实现的DNS，没找到我所希望的答案，因此就决定自己来实现了。

现在所实现的没什么高深的，只是能够对A记录查询进行简单的匹配和回复。

实现的代码如下：

复制代码 代码如下:

'''
Created on 2012-10-15

@author: RobinTang
'''

import socketserver
import struct

DNS Query

class SinDNSQuery:
def init(self, data):
i = 1
self.name = ''
while True:
d = data[i]
if d == 0:
break;
if d < 32:
self.name = self.name + '.'
else:
self.name = self.name + chr(d)
i = i + 1
self.querybytes = data[0:i + 1]
(self.type, self.classify) = struct.unpack('>HH', data[i + 1:i + 5])
self.len = i + 5
def getbytes(self):
return self.querybytes + struct.pack('>HH', self.type, self.classify)

DNS Answer RRS

this class is also can be use as Authority RRS or Additional RRS

class SinDNSAnswer:
def init(self, ip):
self.name = 49164
self.type = 1
self.classify = 1
self.timetolive = 190
self.datalength = 4
self.ip = ip
def getbytes(self):
res = struct.pack('>HHHLH', self.name, self.type, self.classify, self.timetolive, self.datalength)
s = self.ip.split('.')
res = res + struct.pack('BBBB', int(s[0]), int(s[1]), int(s[2]), int(s[3]))
return res

DNS frame

must initialized by a DNS query frame

class SinDNSFrame:
def init(self, data):
(self.id, self.flags, self.quests, self.answers, self.author, self.addition) = struct.unpack('>HHHHHH', data[0:12])
self.query = SinDNSQuery(data[12:])
def getname(self):
return self.query.name
def setip(self, ip):
self.answer = SinDNSAnswer(ip)
self.answers = 1
self.flags = 33152
def getbytes(self):
res = struct.pack('>HHHHHH', self.id, self.flags, self.quests, self.answers, self.author, self.addition)
res = res + self.query.getbytes()
if self.answers != 0:
res = res + self.answer.getbytes()
return res

A UDPHandler to handle DNS query

class SinDNSUDPHandler(socketserver.BaseRequestHandler):
def handle(self):
data = self.request[0].strip()
dns = SinDNSFrame(data)
socket = self.request[1]
namemap = SinDNSServer.namemap
if(dns.query.type==1):

If this is query a A record, then response it

        name = dns.getname();  
        if namemap.__contains__(name):  
            # If have record, response it  
            dns.setip(namemap[name])  
            socket.sendto(dns.getbytes(), self.client_address)  
        elif namemap.__contains__('*'):  
            # Response default address  
            dns.setip(namemap['*'])  
            socket.sendto(dns.getbytes(), self.client_address)  
        else:  
            # ignore it  
            socket.sendto(data, self.client_address)  
    else:  
        # If this is not query a A record, ignore it  
        socket.sendto(data, self.client_address)

DNS Server

It only support A record query

user it, U can create a simple DNS server

class SinDNSServer:
def init(self, port=53):
SinDNSServer.namemap = {}
self.port = port
def addname(self, name, ip):
SinDNSServer.namemap[name] = ip
def start(self):
HOST, PORT = "0.0.0.0", self.port
server = socketserver.UDPServer((HOST, PORT), SinDNSUDPHandler)
server.serve_forever()

Now, test it

if name == "main":
sev = SinDNSServer()
sev.addname('www.aa.com', '192.168.0.1') # add a A record
sev.addname('www.bb.com', '192.168.0.2') # add a A record
sev.addname('*', '0.0.0.0') # default address
sev.start() # start DNS server

Now, U can use "nslookup" command to test it

Such as "nslookup www.aa.com"