Python写的一个简单DNS服务器实例

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：

'''
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"