A simple DNS server instance written by Python

Because suddenly there is an evil idea, want to build a DNS server on their own Android tablet, because the tablet installed before the sl4a and Python interpreter, but also want to continue to learn python so, it is intended to be implemented in Python.

Looking for a bit on Google, the Python implementation of DNS, did not find the answer I want, so I decided to come true.

Now the implementation of nothing advanced, just can be a record query simple matching and reply.

The implementation code is as follows:
Copy the Code code as follows:

'''
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 = da Ta[i]
If d = = 0:
break;
If D <:
Self.name = Self.name + '. '
Else:
Self.name = Self.name + chr (d)
i = i + 1
self.querybytes = data[0:i + 1]
(Self.type, Self.class ify) = 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 being 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 the 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 was 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 the "nslookup" command to test it
# Such as "nslookup www.aa.com"

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