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104 lines
3.9 KiB
104 lines
3.9 KiB
# Copyright (C) 2020 The Electrum developers |
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# Distributed under the MIT software license, see the accompanying |
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# file LICENCE or http://www.opensource.org/licenses/mit-license.php |
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import sys |
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import socket |
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import concurrent |
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from concurrent import futures |
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import ipaddress |
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from typing import Optional |
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import dns |
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import dns.resolver |
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from .logging import get_logger |
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_logger = get_logger(__name__) |
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_dns_threads_executor = None # type: Optional[concurrent.futures.Executor] |
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def configure_dns_resolver() -> None: |
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# Store this somewhere so we can un-monkey-patch: |
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if not hasattr(socket, "_getaddrinfo"): |
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socket._getaddrinfo = socket.getaddrinfo |
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if sys.platform == 'win32': |
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# On Windows, socket.getaddrinfo takes a mutex, and might hold it for up to 10 seconds |
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# when dns-resolving. To speed it up drastically, we resolve dns ourselves, outside that lock. |
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# See https://github.com/spesmilo/electrum/issues/4421 |
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try: |
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_prepare_windows_dns_hack() |
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except Exception as e: |
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_logger.exception('failed to apply windows dns hack.') |
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else: |
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socket.getaddrinfo = _fast_getaddrinfo |
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def _prepare_windows_dns_hack(): |
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# enable dns cache |
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resolver = dns.resolver.get_default_resolver() |
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if resolver.cache is None: |
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resolver.cache = dns.resolver.Cache() |
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# ensure overall timeout for requests is long enough |
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resolver.lifetime = max(resolver.lifetime or 1, 30.0) |
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# prepare threads |
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global _dns_threads_executor |
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if _dns_threads_executor is None: |
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_dns_threads_executor = concurrent.futures.ThreadPoolExecutor(max_workers=20, |
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thread_name_prefix='dns_resolver') |
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def _is_force_system_dns_for_host(host: str) -> bool: |
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return str(host) in ('localhost', 'localhost.',) |
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def _fast_getaddrinfo(host, *args, **kwargs): |
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def needs_dns_resolving(host): |
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try: |
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ipaddress.ip_address(host) |
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return False # already valid IP |
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except ValueError: |
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pass # not an IP |
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if _is_force_system_dns_for_host(host): |
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return False |
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return True |
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def resolve_with_dnspython(host): |
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addrs = [] |
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expected_errors = (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer, |
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concurrent.futures.CancelledError, concurrent.futures.TimeoutError) |
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ipv6_fut = _dns_threads_executor.submit(dns.resolver.resolve, host, dns.rdatatype.AAAA) |
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ipv4_fut = _dns_threads_executor.submit(dns.resolver.resolve, host, dns.rdatatype.A) |
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# try IPv6 |
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try: |
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answers = ipv6_fut.result() |
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addrs += [str(answer) for answer in answers] |
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except expected_errors as e: |
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pass |
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except BaseException as e: |
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_logger.info(f'dnspython failed to resolve dns (AAAA) for {repr(host)} with error: {repr(e)}') |
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# try IPv4 |
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try: |
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answers = ipv4_fut.result() |
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addrs += [str(answer) for answer in answers] |
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except expected_errors as e: |
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# dns failed for some reason, e.g. dns.resolver.NXDOMAIN this is normal. |
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# Simply report back failure; except if we already have some results. |
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if not addrs: |
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raise socket.gaierror(11001, 'getaddrinfo failed') from e |
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except BaseException as e: |
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# Possibly internal error in dnspython :( see #4483 and #5638 |
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_logger.info(f'dnspython failed to resolve dns (A) for {repr(host)} with error: {repr(e)}') |
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if addrs: |
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return addrs |
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# Fall back to original socket.getaddrinfo to resolve dns. |
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return [host] |
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addrs = [host] |
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if needs_dns_resolving(host): |
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addrs = resolve_with_dnspython(host) |
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list_of_list_of_socketinfos = [socket._getaddrinfo(addr, *args, **kwargs) for addr in addrs] |
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list_of_socketinfos = [item for lst in list_of_list_of_socketinfos for item in lst] |
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return list_of_socketinfos
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