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@korc
Last active Jan 25, 2023
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Convert DNS UDP to TCP
#!/usr/bin/python
import socket, os, select, struct
import errno
import logging
from logging import info, warn, error
logging.root.setLevel(logging.INFO)
udp_addr=(os.environ.get("LISTEN_IP", "0.0.0.0"), int(os.environ.get("LISTEN_PORT", 53)))
tcp_addr=(os.environ.get("DNS_IP", "0.0.0.0"), int(os.environ.get("DNS_PORT", 53)))
udp_sock=socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
udp_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
try: udp_sock.bind(udp_addr)
except socket.error as e:
error("Cannot bind socket: %s", e)
info("Please configure via {LISTEN,DNS}_{PORT,IP} environment variables")
if e.errno==errno.EACCES:
warn("No permission error. Perhaps set LISTEN_PORT environment variable or run as root?")
elif e.errno==errno.EADDRINUSE:
warn("Address in use error. Perhaps set LISTEN_IP or LISTEN_PORT to different value?")
raise SystemExit(1)
else:
info("Waiting for requests at %s", udp_addr)
tx_map={}
net_short=struct.Struct(">H")
to_recv=0
tcp_data_buf=[]
incoming=[udp_sock]
tcp_sock=None
while True:
s_in, s_out, s_exc=select.select(incoming, [], [], 10)
if udp_sock in s_in:
data, src=udp_sock.recvfrom(8192)
(tx_id,)=net_short.unpack_from(data)
tx_map[tx_id]=src
info("udp recv %d bytes from: %r, tx_id=0x%04x", len(data), src, tx_id)
if tcp_sock is None:
info("Connecting tcp to %r", tcp_addr)
tcp_sock=socket.socket()
try:
tcp_sock.connect(tcp_addr)
except socket.error as e:
error("Failed connecting to %s: %s. Perhaps should set DNS_{IP,PORT} to different values?", tcp_addr, e)
tcp_sock.close()
tcp_sock = None
else:
incoming.append(tcp_sock)
if tcp_sock is None:
udp_sock.sendto(b"".join(map(net_short.pack, (tx_id, 0x8002, 0, 0, 0, 0))), src)
else:
tcp_sock.sendall(net_short.pack(len(data)) + data)
if tcp_sock in s_in:
if not to_recv:
try: data=tcp_sock.recv(2)
except socket.error as e:
warn("Error receiving data from server: %s", e)
data=None
if not data:
info("DNS server closed connection, removing from loop")
incoming.remove(tcp_sock)
tcp_sock.close()
tcp_sock=None
if tx_map: warn("unresolved queries: %r", map(hex, tx_map.keys()))
tx_map.clear()
continue
(to_recv,)=net_short.unpack_from(data)
data=tcp_sock.recv(to_recv)
if not data:
raise EOFError("DNS server closed connection in transit for %d bytes"%(to_recv,))
tcp_data_buf.append(data)
to_recv-=len(data)
if to_recv:
info("tcp need additional %d bytes", to_recv)
continue
data=b"".join(tcp_data_buf)
tcp_data_buf[:]=[]
to_recv=0
(tx_id,)=net_short.unpack_from(data)
send_addr=tx_map.pop(tx_id, None)
info("tcp reply %d bytes to %r, tx_id=0x%04x", len(data), send_addr, tx_id)
if send_addr is None:
warn("No matching tx_id, already processed?")
else: udp_sock.sendto(data, send_addr)
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