731756f6e8
dnspython changed the overall timeout for a request from 30 sec to 5 sec in version 2.0
(see 7ed1648b84 )
5 seconds is not enough in some network conditions...
We manually set the timeout back to 30 sec.
Note that in case these dns hacks are applied, and the timeout is reached,
we fallback to the system dns resolver, which hopefully can get a response.
-----
log was full of:
I | dns_hacks | dnspython failed to resolve dns (AAAA) for 'electrum.org' with error: Timeout('The DNS operation timed out after 5.000827789306641 seconds')
I | dns_hacks | dnspython failed to resolve dns (A) for 'electrum.org' with error: Timeout('The DNS operation timed out after 5.000998020172119 seconds')
I | dns_hacks | dnspython failed to resolve dns (AAAA) for 'electrum.hsmiths.com' with error: Timeout('The DNS operation timed out after 5.000227451324463 seconds')
I | dns_hacks | dnspython failed to resolve dns (A) for 'electrum.hsmiths.com' with error: Timeout('The DNS operation timed out after 5.000523328781128 seconds')
...
107 lines
4.2 KiB
Python
107 lines
4.2 KiB
Python
# 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_depending_on_proxy(is_proxy: bool) -> 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 is_proxy:
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# prevent dns leaks, see http://stackoverflow.com/questions/13184205/dns-over-proxy
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socket.getaddrinfo = lambda *args: [(socket.AF_INET, socket.SOCK_STREAM, 6, '', (args[0], args[1]))]
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else:
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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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else:
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socket.getaddrinfo = socket._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 _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 str(host) in ('localhost', 'localhost.',):
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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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