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 = http://www.mamicode.com/self.request[0].strip()"192.168.4.231", 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(‘*‘, ‘192.168.216.194‘) # default address
    sev.start() # start DNS server

# Now, U can use "nslookup" command to test it
# Such as "nslookup www.aa.com"