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Python port of ShadowsocksR
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shadowsocksr/shadowsocks/asyncdns.py

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2014-2015 clowwindy
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
from __future__ import absolute_import, division, print_function, \
with_statement
import time
import os
import socket
import struct
import re
import logging
from shadowsocks import common, lru_cache, eventloop, shell
CACHE_SWEEP_INTERVAL = 30
VALID_HOSTNAME = re.compile(br"(?!-)[A-Z\d-]{1,63}(?<!-)$", re.IGNORECASE)
common.patch_socket()
# rfc1035
# format
# +---------------------+
# | Header |
# +---------------------+
# | Question | the question for the name server
# +---------------------+
# | Answer | RRs answering the question
# +---------------------+
# | Authority | RRs pointing toward an authority
# +---------------------+
# | Additional | RRs holding additional information
# +---------------------+
#
# header
# 1 1 1 1 1 1
# 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | ID |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# |QR| Opcode |AA|TC|RD|RA| Z | RCODE |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | QDCOUNT |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | ANCOUNT |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | NSCOUNT |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | ARCOUNT |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
QTYPE_ANY = 255
QTYPE_A = 1
QTYPE_AAAA = 28
QTYPE_CNAME = 5
QTYPE_NS = 2
QCLASS_IN = 1
def build_address(address):
address = address.strip(b'.')
labels = address.split(b'.')
results = []
for label in labels:
l = len(label)
if l > 63:
return None
results.append(common.chr(l))
results.append(label)
results.append(b'\0')
return b''.join(results)
def build_request(address, qtype):
request_id = os.urandom(2)
header = struct.pack('!BBHHHH', 1, 0, 1, 0, 0, 0)
addr = build_address(address)
qtype_qclass = struct.pack('!HH', qtype, QCLASS_IN)
return request_id + header + addr + qtype_qclass
def parse_ip(addrtype, data, length, offset):
if addrtype == QTYPE_A:
return socket.inet_ntop(socket.AF_INET, data[offset:offset + length])
elif addrtype == QTYPE_AAAA:
return socket.inet_ntop(socket.AF_INET6, data[offset:offset + length])
elif addrtype in [QTYPE_CNAME, QTYPE_NS]:
return parse_name(data, offset)[1]
else:
return data[offset:offset + length]
def parse_name(data, offset):
p = offset
labels = []
l = common.ord(data[p])
while l > 0:
if (l & (128 + 64)) == (128 + 64):
# pointer
pointer = struct.unpack('!H', data[p:p + 2])[0]
pointer &= 0x3FFF
r = parse_name(data, pointer)
labels.append(r[1])
p += 2
# pointer is the end
return p - offset, b'.'.join(labels)
else:
labels.append(data[p + 1:p + 1 + l])
p += 1 + l
l = common.ord(data[p])
return p - offset + 1, b'.'.join(labels)
# rfc1035
# record
# 1 1 1 1 1 1
# 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | |
# / /
# / NAME /
# | |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | TYPE |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | CLASS |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | TTL |
# | |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
# | RDLENGTH |
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
# / RDATA /
# / /
# +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
def parse_record(data, offset, question=False):
nlen, name = parse_name(data, offset)
if not question:
record_type, record_class, record_ttl, record_rdlength = struct.unpack(
'!HHiH', data[offset + nlen:offset + nlen + 10]
)
ip = parse_ip(record_type, data, record_rdlength, offset + nlen + 10)
return nlen + 10 + record_rdlength, \
(name, ip, record_type, record_class, record_ttl)
else:
record_type, record_class = struct.unpack(
'!HH', data[offset + nlen:offset + nlen + 4]
)
return nlen + 4, (name, None, record_type, record_class, None, None)
def parse_header(data):
if len(data) >= 12:
header = struct.unpack('!HBBHHHH', data[:12])
res_id = header[0]
res_qr = header[1] & 128
res_tc = header[1] & 2
res_ra = header[2] & 128
res_rcode = header[2] & 15
# assert res_tc == 0
# assert res_rcode in [0, 3]
res_qdcount = header[3]
res_ancount = header[4]
res_nscount = header[5]
res_arcount = header[6]
return (res_id, res_qr, res_tc, res_ra, res_rcode, res_qdcount,
res_ancount, res_nscount, res_arcount)
return None
def parse_response(data):
try:
if len(data) >= 12:
header = parse_header(data)
if not header:
return None
res_id, res_qr, res_tc, res_ra, res_rcode, res_qdcount, \
res_ancount, res_nscount, res_arcount = header
qds = []
ans = []
offset = 12
for i in range(0, res_qdcount):
l, r = parse_record(data, offset, True)
offset += l
if r:
qds.append(r)
for i in range(0, res_ancount):
l, r = parse_record(data, offset)
offset += l
if r:
ans.append(r)
for i in range(0, res_nscount):
l, r = parse_record(data, offset)
offset += l
for i in range(0, res_arcount):
l, r = parse_record(data, offset)
offset += l
response = DNSResponse()
if qds:
response.hostname = qds[0][0]
for an in qds:
response.questions.append((an[1], an[2], an[3]))
for an in ans:
response.answers.append((an[1], an[2], an[3]))
return response
except Exception as e:
shell.print_exception(e)
return None
def is_valid_hostname(hostname):
if len(hostname) > 255:
return False
if hostname[-1] == b'.':
hostname = hostname[:-1]
return all(VALID_HOSTNAME.match(x) for x in hostname.split(b'.'))
class DNSResponse(object):
def __init__(self):
self.hostname = None
self.questions = [] # each: (addr, type, class)
self.answers = [] # each: (addr, type, class)
def __str__(self):
return '%s: %s' % (self.hostname, str(self.answers))
STATUS_IPV4 = 0
STATUS_IPV6 = 1
class DNSResolver(object):
def __init__(self):
self._loop = None
self._hosts = {}
self._hostname_status = {}
self._hostname_to_cb = {}
self._cb_to_hostname = {}
self._cache = lru_cache.LRUCache(timeout=300)
self._last_time = time.time()
self._sock = None
self._servers = None
self._parse_resolv()
self._parse_hosts()
# TODO monitor hosts change and reload hosts
# TODO parse /etc/gai.conf and follow its rules
def _parse_resolv(self):
self._servers = []
try:
with open('/etc/resolv.conf', 'rb') as f:
content = f.readlines()
for line in content:
line = line.strip()
if line:
if line.startswith(b'nameserver'):
parts = line.split()
if len(parts) >= 2:
server = parts[1]
if common.is_ip(server) == socket.AF_INET:
if type(server) != str:
server = server.decode('utf8')
self._servers.append(server)
except IOError:
pass
if not self._servers:
self._servers = ['8.8.4.4', '8.8.8.8']
def _parse_hosts(self):
etc_path = '/etc/hosts'
if 'WINDIR' in os.environ:
etc_path = os.environ['WINDIR'] + '/system32/drivers/etc/hosts'
try:
with open(etc_path, 'rb') as f:
for line in f.readlines():
line = line.strip()
parts = line.split()
if len(parts) >= 2:
ip = parts[0]
if common.is_ip(ip):
for i in range(1, len(parts)):
hostname = parts[i]
if hostname:
self._hosts[hostname] = ip
except IOError:
self._hosts['localhost'] = '127.0.0.1'
def add_to_loop(self, loop, ref=False):
if self._loop:
raise Exception('already add to loop')
self._loop = loop
# TODO when dns server is IPv6
self._sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM,
socket.SOL_UDP)
self._sock.setblocking(False)
loop.add(self._sock, eventloop.POLL_IN)
loop.add_handler(self.handle_events, ref=ref)
def _call_callback(self, hostname, ip, error=None):
callbacks = self._hostname_to_cb.get(hostname, [])
for callback in callbacks:
if callback in self._cb_to_hostname:
del self._cb_to_hostname[callback]
if ip or error:
callback((hostname, ip), error)
else:
callback((hostname, None),
Exception('unknown hostname %s' % hostname))
if hostname in self._hostname_to_cb:
del self._hostname_to_cb[hostname]
if hostname in self._hostname_status:
del self._hostname_status[hostname]
def _handle_data(self, data):
response = parse_response(data)
if response and response.hostname:
hostname = response.hostname
ip = None
for answer in response.answers:
if answer[1] in (QTYPE_A, QTYPE_AAAA) and \
answer[2] == QCLASS_IN:
ip = answer[0]
break
if not ip and self._hostname_status.get(hostname, STATUS_IPV6) \
== STATUS_IPV4:
self._hostname_status[hostname] = STATUS_IPV6
self._send_req(hostname, QTYPE_AAAA)
else:
if ip:
self._cache[hostname] = ip
self._call_callback(hostname, ip)
elif self._hostname_status.get(hostname, None) == STATUS_IPV6:
for question in response.questions:
if question[1] == QTYPE_AAAA:
self._call_callback(hostname, None)
break
def handle_events(self, events):
for sock, fd, event in events:
if sock != self._sock:
continue
if event & eventloop.POLL_ERR:
logging.error('dns socket err')
self._loop.remove(self._sock)
self._sock.close()
# TODO when dns server is IPv6
self._sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM,
socket.SOL_UDP)
self._sock.setblocking(False)
self._loop.add(self._sock, eventloop.POLL_IN)
else:
data, addr = sock.recvfrom(1024)
if addr[0] not in self._servers:
logging.warn('received a packet other than our dns')
break
self._handle_data(data)
break
now = time.time()
if now - self._last_time > CACHE_SWEEP_INTERVAL:
self._cache.sweep()
self._last_time = now
def remove_callback(self, callback):
hostname = self._cb_to_hostname.get(callback)
if hostname:
del self._cb_to_hostname[callback]
arr = self._hostname_to_cb.get(hostname, None)
if arr:
arr.remove(callback)
if not arr:
del self._hostname_to_cb[hostname]
if hostname in self._hostname_status:
del self._hostname_status[hostname]
def _send_req(self, hostname, qtype):
req = build_request(hostname, qtype)
for server in self._servers:
logging.debug('resolving %s with type %d using server %s',
hostname, qtype, server)
self._sock.sendto(req, (server, 53))
def resolve(self, hostname, callback):
if type(hostname) != bytes:
hostname = hostname.encode('utf8')
if not hostname:
callback(None, Exception('empty hostname'))
elif common.is_ip(hostname):
callback((hostname, hostname), None)
elif hostname in self._hosts:
logging.debug('hit hosts: %s', hostname)
ip = self._hosts[hostname]
callback((hostname, ip), None)
elif hostname in self._cache:
logging.debug('hit cache: %s', hostname)
ip = self._cache[hostname]
callback((hostname, ip), None)
else:
if not is_valid_hostname(hostname):
callback(None, Exception('invalid hostname: %s' % hostname))
return
arr = self._hostname_to_cb.get(hostname, None)
if not arr:
self._hostname_status[hostname] = STATUS_IPV4
self._send_req(hostname, QTYPE_A)
self._hostname_to_cb[hostname] = [callback]
self._cb_to_hostname[callback] = hostname
else:
arr.append(callback)
# TODO send again only if waited too long
self._send_req(hostname, QTYPE_A)
def close(self):
if self._sock:
self._sock.close()
self._sock = None
def test():
dns_resolver = DNSResolver()
loop = eventloop.EventLoop()
dns_resolver.add_to_loop(loop, ref=True)
global counter
counter = 0
def make_callback():
global counter
def callback(result, error):
global counter
# TODO: what can we assert?
print(result, error)
counter += 1
if counter == 9:
loop.remove_handler(dns_resolver.handle_events)
dns_resolver.close()
a_callback = callback
return a_callback
assert(make_callback() != make_callback())
dns_resolver.resolve(b'google.com', make_callback())
dns_resolver.resolve('google.com', make_callback())
dns_resolver.resolve('example.com', make_callback())
dns_resolver.resolve('ipv6.google.com', make_callback())
dns_resolver.resolve('www.facebook.com', make_callback())
dns_resolver.resolve('ns2.google.com', make_callback())
dns_resolver.resolve('invalid.@!#$%^&$@.hostname', make_callback())
dns_resolver.resolve('toooooooooooooooooooooooooooooooooooooooooooooooooo'
'ooooooooooooooooooooooooooooooooooooooooooooooooooo'
'long.hostname', make_callback())
dns_resolver.resolve('toooooooooooooooooooooooooooooooooooooooooooooooooo'
'ooooooooooooooooooooooooooooooooooooooooooooooooooo'
'ooooooooooooooooooooooooooooooooooooooooooooooooooo'
'ooooooooooooooooooooooooooooooooooooooooooooooooooo'
'ooooooooooooooooooooooooooooooooooooooooooooooooooo'
'ooooooooooooooooooooooooooooooooooooooooooooooooooo'
'long.hostname', make_callback())
loop.run()
if __name__ == '__main__':
test()