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dns.py
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dns.py
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import struct
import socket
import struct
import bits
import sys
from six import b,s
dns_records = ['',
'A', 'NS', 'MD', 'MF', 'CNAME', 'SOA', 'MB', 'MG', 'MR', 'NULL',
'WKS', 'PTR', 'HINFO', 'MINFO', 'MX', 'TXT', 'RP', 'AFSDB',
'X25', 'ISDN', 'RT', 'NSAP', 'NSAP-PTR', 'SIG', 'KEY', 'PX',
'GPOS', 'AAAA', 'LOC', 'NXT', 'EID', 'NIMLOC', 'SRV', 'ATMA',
'NAPTR', 'KX', 'CERT', 'A6', 'DNAME', 'SINK', 'OPT', 'APL',
'DS', 'SSHFP', 'IPSECKEY', 'RRSIG', 'NSEC', 'DNSKEY', 'DHCID',
'NSEC3', 'NSEC3PARAM', 'TLSA', '', '', 'HIP', 'NINFO', 'RKEY',
'TALINK', 'CDS']
extra_dns_records = { 255: '*' }
def cleanNSLine(line):
line = line.strip()
if line.startswith(';'):
return ''
else:
return line.split(';')[0]
def readEffectiveNSLine(f):
while True:
l = f.readline()
if l == '':
return None
l = cleanNSLine(l)
if l != '':
return l
def readNSEntry(f):
line = readEffectiveNSLine(f)
if line == None:
return None
parens = 0
while line.count('(') != line.count(')'):
n = readEffectiveNSLine(f)
if n == None:
raise Exception("Mismatched Parentheses: " + line)
line += " " + n
while line.count('(') > 0 and line.index('(') < line.index(')'):
line = line.replace('(', '', 1)
line = line[::-1].replace(')', '', 1)[::-1]
if '(' in line or ')' in line:
raise Exception("Mismatched Parentheses: " + line)
return line
def loadNSFile(fname):
entries = {}
f = open(fname)
while True:
entry = readNSEntry(f)
if entry == None:
break
parts = entry.split()
if len(parts) > 2:
if parts[2] == 'SOA':
name, Class, Type, Start, Manager, serial, refresh, retry, expire, \
minimum = parts
if name not in entries:
entries[name] = {}
if Type not in entries[name]:
entries[name][Type] = []
entries[name][Type].append([Start, Manager, int(serial), int(refresh),
int(retry), int(expire), int(minimum)])
elif len(parts) == 4:
name, TTL, Type, Data = parts
if name not in entries:
entries[name] = {}
if Type not in entries[name]:
entries[name][Type] = []
entries[name][Type].append([int(TTL), Data])
# line = f.readline()
return entries
def readDNSName(string):
"""
Reads a name entry in DNS format
"""
chars = struct.unpack_from('!B', b(string))[0]
string = string[1:]
name_parts = []
while chars > 0:
name_parts.append(s(string[:chars]))
string = string[chars:]
chars = struct.unpack_from('!B',b(string))[0]
string = string[1:]
return (name_parts, string)
def writeDNSName(domain):
"""
Take a list of parts and make a DNS name out of them.
"""
if type(domain) == str:
parts = domain.split('.')
else:
parts = domain
retval = b('')
for part in parts:
if len(part) > 0:
retval += struct.pack('!B', len(part))
retval += b(part)
retval += struct.pack('!B', 0)
return retval
class Question:
def __init__(self):
self.name = ""
self.QType = 0
self.QClass = 1
def readFrom(self, m):
"""
Reads data in from a file
"""
self.name, m = readDNSName(m)
self.QType, self.QClass = struct.unpack_from('!H H', b(m))
return m[4:]
def createAnswers(self, data):
"""
Create an Answer from the Question
"""
answers = []
nameStr = '.'.join(self.name) + '.'
if nameStr in data:
records = data[nameStr]
if self.QType == 255:
for typeStr in records:
record = records[typeStr]
for entry in record:
answers.append(Resource(self.name, typeStr, entry))
else:
if dns_records[self.QType] in records:
t = dns_records[self.QType]
record = records[dns_records[self.QType]]
elif dns_records[self.QType] == 'A' and 'CNAME' in records:
t = 'CNAME'
record = records['CNAME']
else:
return answers
if type(record) == str:
record = [record]
for row in record:
r = Resource(self.name, t, row)
answers.append(r)
return answers
def pack(self):
"""
Packs the data from the Question into the response
"""
retval = writeDNSName(self.name)
retval += struct.pack('!H H', self.QType, self.QClass)
return retval
def __str__(self):
retval = ""
retval += '.'.join(self.name)
if self.QType in range(len(dns_records)):
retval += '\t' + dns_records[self.QType]
elif self.QType in extra_dns_records:
retval += '\t' + extra_dns_records[self.QType]
else:
retval += "\t???"
return retval
class Resource:
def __init__(self, entryName = None, entryType = None, entry = None):
if entryName != None and entryType != None and entry != None:
self.name = entryName
self.RType = dns_records.index(entryType)
self.RClass = 1 # Internet
self.TTL = entry[0]
if entryType == 'SOA':
self.TTL = 0
self.RData = writeDNSName(entry[0])
self.RData += writeDNSName(entry[1])
self.RData += struct.pack('!I', entry[2])
self.RData += struct.pack('!I', entry[3])
self.RData += struct.pack('!I', entry[4])
self.RData += struct.pack('!I', entry[5])
self.RData += struct.pack('!I', entry[6])
self.RDLength = len(self.RData)
elif entryType == 'A':
octets = [int(n) for n in entry[1].split('.')]
self.RDLength = len(octets)
self.RData = b('')
for octet in octets:
self.RData += struct.pack('!B', octet)
elif entryType in ['NS', 'CNAME']:
self.RData = writeDNSName(entry[1])
self.RDLength = len(self.RData)
else:
self.name = 0
self.RType = 0
self.RClass = 1
self.TTL = 0
self.RDLength = 0
self.RData = ""
def readFrom(self, m):
"""
Reads the data for the Resource from a string
"""
self.name, m = readDNSName(m)
self.RType, self.RClass, self.TTL, self.RDLength \
= struct.unpack_from('!H H I H', b(m))
m = m[10:]
self.RData = m[:self.RDLength]
return m[self.RDLength:]
def pack(self):
"""
Packs the data for the Resource into the response
"""
retval = writeDNSName(self.name)
retval += struct.pack('!H H I H', self.RType, self.RClass, self.TTL,
self.RDLength)
retval += self.RData
return retval
def __str__(self):
retval = ""
retval += '.'.join(self.name) + '.'
retval += '\t' + str(self.TTL) + "\tIN"
retval += '\t' + dns_records[self.RType]
t = dns_records[self.RType]
if t == 'A':
a,b,c,d = struct.unpack_from('!B B B B', self.RData)
retval += '\t%d.%d.%d.%d' % (a,b,c,d)
elif t == 'NS' or t == 'CNAME':
parts = readDNSName(self.RData)[0]
retval += '\t' + '.'.join(parts) + '.'
return retval
class Packet:
def __init__(self, message=None, source=None, ID=None):
if message != None and source != None:
self.message = message
self.source = source
self.parseMessage()
elif ID != None:
self.ID = ID
self.QR = 0
self.opcode = 0
self.AA = 0
self.TC = 0
self.RD = 0
self.RA = 0
self.zero = 0
self.RCode = 0
self.QDCount = 0
self.ANCount = 0
self.NSCount = 0
self.ARCount = 0
self.questions = []
self.answers = []
self.authority = []
self.additional = []
def setMessage(self, m):
self.message = m
def setSource(self, s):
self.source = s
def parseMessage(self):
m = self.message
self.ID, fields, self.QDCount, self.ANCount, self.NSCount, self.ARCount \
= struct.unpack_from('!H H H H H H', m)
m = m[12:]
self.QR, self.opcode, self.AA, self.TC, self.RD, self.RA, self.zero, \
self.RCode = bits.extractBits('1 4 1 1 1 1 3 4', fields)
self.questions = []
self.answers = []
self.authority = []
self.additional = []
for n in range(self.QDCount):
q = Question()
m = q.readFrom(m)
self.questions.append(q)
for n in range(self.ANCount):
r = Resource()
m = r.readFrom(m)
self.answers.append(r)
for n in range(self.NSCount):
r = Resource()
m = r.readFrom(m)
self.authority.append(r)
for n in range(self.ARCount):
r = Resource()
m = r.readFrom(m)
self.additional.append(r)
def pack(self):
retval = b("")
fields = bits.packBits('1 4 1 1 1 1 3 4', self.QR, self.opcode, self.AA,
self.TC, self.RD, self.RA, self.zero, self.RCode)
retval += struct.pack('!H H H H H H', self.ID, fields, self.QDCount,
self.ANCount, self.NSCount, self.ARCount)
for n in range(self.QDCount):
retval += self.questions[n].pack()
for n in range(self.ANCount):
retval += self.answers[n].pack()
for n in range(self.NSCount):
retval += self.authority[n].pack()
for n in range(self.ARCount):
retval += self.additional[n].pack()
return retval
def addQuestion(self, q):
self.QDCount += 1
self.questions.append(q)
def addAnswer(self, a):
self.ANCount += 1
self.answers.append(a)
def copy(self):
retval = Packet()
retval.message = self.message
retval.source = self.source
retval.ID = self.ID
retval.QR = self.QR
retval.opcode = self.opcode
retval.AA = self.AA
retval.TC = self.TC
retval.RD = self.RD
retval.RA = self.RA
retval.zero = self.zero
retval.RCode = self.RCode
retval.QDCount = self.QDCount
retval.ANCount = self.ANCount
retval.NSCount = self.NSCount
retval.ARCount = self.ARCount
retval.questions = list(self.questions)
retval.answers = list(self.answers)
retval.authority = list(self.authority)
retval.additional = list(self.additional)
return retval
def makeResponse(self):
retval = self.copy()
retval.QR = 1
retval.AA = 1
retval.RA = 0
retval.RCode = 0
retval.answers = []
retval.ANCount = 0
retval.authority = []
retval.NSCount = 0
retval.additional = []
retval.ARCount = 0
return retval
def __str__(self):
retval = ""
if self.QR == 0:
retval += "Request from: %s:%s" % self.source
else:
retval += "Response for: %s:%s" % self.source
if self.QDCount > 0:
retval += "\nQuestions:"
for n in range(self.QDCount):
retval += '\n\t' + str(self.questions[n])
if self.ANCount > 0:
retval += "\nAnswers:"
for n in range(self.ANCount):
retval += '\n\t' + str(self.answers[n])
if self.NSCount > 0:
retval += "\nAuthority:"
for n in range(self.NSCount):
retval += '\n\t' + str(self.authority[n])
if self.ARCount > 0:
retval += "\nAdditional:"
for n in range(self.ARCount):
retval += '\n\t' + str(self.additional[n])
return retval
class Server:
def __init__(self, port):
self.s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
self.s.bind(('', port))
self.addr, self.port = self.s.getsockname()
def getRequest(self):
message, source = self.s.recvfrom(4096)
return Packet(message, source)
def sendResponse(self, response):
self.s.sendto(response.pack(), response.source)