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#!/usr/bin/python | |
import socket | |
import struct | |
DNS_QUERY_SECTION_FORMAT = struct.Struct("!2H") | |
DNS_QUERY_MESSAGE_HEADER = struct.Struct("!6H") | |
def decode_question_section(message, offset, qdcount): | |
questions = [] | |
for _ in range(qdcount): | |
qname, offset = decode_labels(message, offset) | |
qtype, qclass = DNS_QUERY_SECTION_FORMAT.unpack_from(message, offset) | |
offset += DNS_QUERY_SECTION_FORMAT.size | |
question = {"domain_name": qname, | |
"query_type": qtype, | |
"query_class": qclass} | |
questions.append(question) | |
return questions, offset | |
def decode_labels(message, offset): | |
labels = [] | |
while True: | |
length, = struct.unpack_from("!B", message, offset) | |
if (length & 0xC0) == 0xC0: | |
pointer, = struct.unpack_from("!H", message, offset) | |
offset += 2 | |
return labels + decode_labels(message, pointer & 0x3FFF), offset | |
if (length & 0xC0) != 0x00: | |
raise StandardError("unknown label encoding") | |
offset += 1 | |
if length == 0: | |
return labels, offset | |
labels.append(*struct.unpack_from("!%ds" % length, message, offset)) | |
offset += length | |
def decode_dns_message(message): | |
id, misc, qdcount, ancount, nscount, arcount = DNS_QUERY_MESSAGE_HEADER.unpack_from(message) | |
qr = (misc & 0x8000) != 0 | |
opcode = (misc & 0x7800) >> 11 | |
aa = (misc & 0x0400) != 0 | |
tc = (misc & 0x200) != 0 | |
rd = (misc & 0x100) != 0 | |
ra = (misc & 0x80) != 0 | |
z = (misc & 0x70) >> 4 | |
rcode = misc & 0xF | |
offset = DNS_QUERY_MESSAGE_HEADER.size | |
questions, offset = decode_question_section(message, offset, qdcount) | |
result = {"id": id, | |
"is_response": qr, | |
"opcode": opcode, | |
"is_authoritative": aa, | |
"is_truncated": tc, | |
"recursion_desired": rd, | |
"recursion_available": ra, | |
"reserved": z, | |
"response_code": rcode, | |
"question_count": qdcount, | |
"answer_count": ancount, | |
"authority_count": nscount, | |
"additional_count": arcount, | |
"questions": questions} | |
return result | |
def save(data): | |
fp = open('output.txt','a') | |
fp.write(data + "\n") | |
fp.close() | |
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) | |
host = '' | |
port = 53 | |
size = 512 | |
s.bind((host, port)) | |
while True: | |
data, addr = s.recvfrom(size) | |
ret = (decode_dns_message(data)) | |
strlog = str({'addr':addr,'message':ret}) | |
save(strlog) | |
print strlog | |
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