electrum

Electrum Bitcoin wallet
git clone https://git.parazyd.org/electrum
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dns_hacks.py (4285B)

      1 # Copyright (C) 2020 The Electrum developers
      2 # Distributed under the MIT software license, see the accompanying
      3 # file LICENCE or http://www.opensource.org/licenses/mit-license.php
      4 
      5 import sys
      6 import socket
      7 import concurrent
      8 from concurrent import futures
      9 import ipaddress
     10 from typing import Optional
     11 
     12 import dns
     13 import dns.resolver
     14 
     15 from .logging import get_logger
     16 
     17 
     18 _logger = get_logger(__name__)
     19 
     20 _dns_threads_executor = None  # type: Optional[concurrent.futures.Executor]
     21 
     22 
     23 def configure_dns_depending_on_proxy(is_proxy: bool) -> None:
     24     # Store this somewhere so we can un-monkey-patch:
     25     if not hasattr(socket, "_getaddrinfo"):
     26         socket._getaddrinfo = socket.getaddrinfo
     27     if is_proxy:
     28         # prevent dns leaks, see http://stackoverflow.com/questions/13184205/dns-over-proxy
     29         socket.getaddrinfo = lambda *args: [(socket.AF_INET, socket.SOCK_STREAM, 6, '', (args[0], args[1]))]
     30     else:
     31         if sys.platform == 'win32':
     32             # On Windows, socket.getaddrinfo takes a mutex, and might hold it for up to 10 seconds
     33             # when dns-resolving. To speed it up drastically, we resolve dns ourselves, outside that lock.
     34             # See https://github.com/spesmilo/electrum/issues/4421
     35             try:
     36                 _prepare_windows_dns_hack()
     37             except Exception as e:
     38                 _logger.exception('failed to apply windows dns hack.')
     39             else:
     40                 socket.getaddrinfo = _fast_getaddrinfo
     41         else:
     42             socket.getaddrinfo = socket._getaddrinfo
     43 
     44 
     45 def _prepare_windows_dns_hack():
     46     # enable dns cache
     47     resolver = dns.resolver.get_default_resolver()
     48     if resolver.cache is None:
     49         resolver.cache = dns.resolver.Cache()
     50     # ensure overall timeout for requests is long enough
     51     resolver.lifetime = max(resolver.lifetime or 1, 30.0)
     52     # prepare threads
     53     global _dns_threads_executor
     54     if _dns_threads_executor is None:
     55         _dns_threads_executor = concurrent.futures.ThreadPoolExecutor(max_workers=20,
     56                                                                       thread_name_prefix='dns_resolver')
     57 
     58 
     59 def _fast_getaddrinfo(host, *args, **kwargs):
     60     def needs_dns_resolving(host):
     61         try:
     62             ipaddress.ip_address(host)
     63             return False  # already valid IP
     64         except ValueError:
     65             pass  # not an IP
     66         if str(host) in ('localhost', 'localhost.',):
     67             return False
     68         return True
     69 
     70     def resolve_with_dnspython(host):
     71         addrs = []
     72         expected_errors = (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer,
     73                            concurrent.futures.CancelledError, concurrent.futures.TimeoutError)
     74         ipv6_fut = _dns_threads_executor.submit(dns.resolver.resolve, host, dns.rdatatype.AAAA)
     75         ipv4_fut = _dns_threads_executor.submit(dns.resolver.resolve, host, dns.rdatatype.A)
     76         # try IPv6
     77         try:
     78             answers = ipv6_fut.result()
     79             addrs += [str(answer) for answer in answers]
     80         except expected_errors as e:
     81             pass
     82         except BaseException as e:
     83             _logger.info(f'dnspython failed to resolve dns (AAAA) for {repr(host)} with error: {repr(e)}')
     84         # try IPv4
     85         try:
     86             answers = ipv4_fut.result()
     87             addrs += [str(answer) for answer in answers]
     88         except expected_errors as e:
     89             # dns failed for some reason, e.g. dns.resolver.NXDOMAIN this is normal.
     90             # Simply report back failure; except if we already have some results.
     91             if not addrs:
     92                 raise socket.gaierror(11001, 'getaddrinfo failed') from e
     93         except BaseException as e:
     94             # Possibly internal error in dnspython :( see #4483 and #5638
     95             _logger.info(f'dnspython failed to resolve dns (A) for {repr(host)} with error: {repr(e)}')
     96         if addrs:
     97             return addrs
     98         # Fall back to original socket.getaddrinfo to resolve dns.
     99         return [host]
    100 
    101     addrs = [host]
    102     if needs_dns_resolving(host):
    103         addrs = resolve_with_dnspython(host)
    104     list_of_list_of_socketinfos = [socket._getaddrinfo(addr, *args, **kwargs) for addr in addrs]
    105     list_of_socketinfos = [item for lst in list_of_list_of_socketinfos for item in lst]
    106     return list_of_socketinfos