Created
June 16, 2019 08:00
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A simple authoritative DNS server which returns the same answer for all questions
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import time | |
import socket | |
import select | |
import sqlite3 | |
import dns.message | |
import dns.exception | |
DNS_SERVER_PORT = 53 | |
IP4_ADDR = '0.0.0.0' # IPv4 address to return | |
IP6_ADDR = '::' # IPv6 address to return (if you want to support IPv6) | |
def handle_dns_query(raw_query): | |
""" | |
Return the name and wire-formated DNS response | |
""" | |
query = dns.message.from_wire(raw_query) | |
question = str(query.question[0]) | |
name, rtype = [r.strip() for r in question.split('IN')] | |
if rtype == 'A': | |
ip_resp = IP4_ADDR | |
elif rtype == 'AAAA': | |
ip_resp = IP6_ADDR | |
else: | |
print('Only A and AAAA are supoprted') | |
raise NotImplementedError | |
response = dns.message.make_response(query) | |
rrset = dns.rrset.from_text(name, 10, 1, rtype, ip_resp) | |
response.answer.append(rrset) | |
wire_resp = response.to_wire() | |
return name, wire_resp | |
def store(db, name, conn): | |
identifier = int(name.split('.')[0]) | |
ip_addr, *_ = conn | |
db.execute(''' | |
insert into ip (id, ip_addr) values (?, ?) | |
''', (identifier, ip_addr)) | |
db.commit() | |
def main_loop(): | |
db = sqlite3.connect('store.db') | |
db.execute('PRAGMA journal_mode=WAL;') | |
db.execute(''' | |
create table if not exists ip ( | |
id integer primary key not null, | |
ip_addr text not null | |
); | |
''') | |
port = DNS_SERVER_PORT | |
sock6 = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM) # if you want to be IPv6-ready | |
sock6.bind(('::', port)) | |
sock4 = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) | |
sock4.bind(('0.0.0.0', port)) # listen on public interfaces | |
socks = [ sock6, sock4 ] | |
while True: | |
rlist, _, _ = select.select(socks, [], []) | |
for conn in rlist: | |
dgram, addr = conn.recvfrom(4096) | |
# Resolve | |
try: | |
name, wire_resp = handle_dns_query(dgram) | |
except NotImplementedError: | |
continue # ignore the client | |
# Store | |
try: | |
store(db, name, addr) | |
except (sqlite3.Error, ValueError) as e: | |
print(e) | |
continue | |
# Respond | |
conn.sendto(wire_resp, addr) | |
if __name__ == '__main__': | |
while True: | |
try: | |
main_loop() | |
except Exception as e: | |
print(e) | |
time.sleep(3) |
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I'm getting below error Please help on this..
[Errno 48] Address already in use