"""Asynchronous DNS resolver using mDNS for `aiohttp`."""
from __future__ import annotations
import asyncio
import socket
import sys
from ipaddress import IPv4Address, IPv6Address
from typing import TYPE_CHECKING, Any, TypeVar
from aiohttp.resolver import AsyncResolver, ResolveResult
from zeroconf import (
AddressResolver,
AddressResolverIPv4,
AddressResolverIPv6,
IPVersion,
)
from zeroconf.asyncio import AsyncZeroconf
if TYPE_CHECKING:
from types import TracebackType
DEFAULT_TIMEOUT = 5.0
# Emulates ``typing.Self`` (Python 3.11+) so the context manager helpers keep
# their precise subclass return type while still supporting Python 3.10.
_ResolverT = TypeVar("_ResolverT", bound="_AsyncMDNSResolverBase")
ResolverType = AddressResolver | AddressResolverIPv4 | AddressResolverIPv6
_FAMILY_TO_RESOLVER_CLASS: dict[
socket.AddressFamily,
type[AddressResolver] | type[AddressResolverIPv4] | type[AddressResolverIPv6],
] = {
socket.AF_INET: AddressResolverIPv4,
socket.AF_INET6: AddressResolverIPv6,
socket.AF_UNSPEC: AddressResolver,
}
_FAMILY_TO_IP_VERSION = {
socket.AF_INET: IPVersion.V4Only,
socket.AF_INET6: IPVersion.V6Only,
socket.AF_UNSPEC: IPVersion.All,
}
_IP_VERSION_TO_FAMILY = {
4: socket.AF_INET,
6: socket.AF_INET6,
}
_NUMERIC_SOCKET_FLAGS = socket.AI_NUMERICHOST | socket.AI_NUMERICSERV
def _is_local_name(host: str) -> bool:
"""Return True if the host is in the .local mDNS domain.
RFC 6762 requires the .local suffix to be matched case-insensitively.
"""
return host.lower().endswith((".local", ".local."))
def _to_resolve_result(
hostname: str, port: int, ipaddress: IPv4Address | IPv6Address
) -> ResolveResult:
"""Convert an IP address to a ResolveResult."""
return ResolveResult(
hostname=hostname,
host=ipaddress.compressed,
port=port,
family=_IP_VERSION_TO_FAMILY[ipaddress.version],
proto=0,
flags=_NUMERIC_SOCKET_FLAGS,
)
class _AsyncMDNSResolverBase(AsyncResolver):
"""Use the `aiodns`/`zeroconf` packages to make asynchronous DNS lookups."""
def __init__(
self,
*args: Any,
async_zeroconf: AsyncZeroconf | None = None,
mdns_timeout: float | None = DEFAULT_TIMEOUT,
**kwargs: Any,
) -> None:
"""Initialize the resolver."""
super().__init__(*args, **kwargs)
self._mdns_timeout = mdns_timeout
self._aiozc_owner = async_zeroconf is None
self._aiozc = async_zeroconf or AsyncZeroconf()
def _make_resolver(self, host: str, family: socket.AddressFamily) -> ResolverType:
"""Create an mDNS resolver."""
resolver_class = _FAMILY_TO_RESOLVER_CLASS[family]
return resolver_class(host if host[-1] == "." else f"{host}.")
def _addresses_from_info_or_raise(
self, info: ResolverType, port: int, family: socket.AddressFamily
) -> list[ResolveResult]:
"""Get addresses from info or raise OSError."""
ip_version = _FAMILY_TO_IP_VERSION[family]
if addresses := info.ip_addresses_by_version(ip_version):
if TYPE_CHECKING:
assert info.server is not None
return [
_to_resolve_result(info.server, port, address) for address in addresses
]
raise OSError(None, "MDNS lookup failed")
async def _resolve_mdns(
self, info: ResolverType, port: int, family: socket.AddressFamily
) -> list[ResolveResult]:
"""Resolve a host name to an IP address using mDNS."""
if self._mdns_timeout:
await info.async_request(self._aiozc.zeroconf, self._mdns_timeout * 1000)
return self._addresses_from_info_or_raise(info, port, family)
async def close(self) -> None:
"""Close the resolver.
Safe to call more than once; subsequent calls are no-ops.
"""
if self._aiozc_owner and self._aiozc is not None:
await self._aiozc.async_close()
await super().close()
self._aiozc = None # type: ignore[assignment] # break ref cycles early
async def __aenter__(self: _ResolverT) -> _ResolverT:
"""Return the resolver for use as an async context manager."""
return self
async def __aexit__(
self,
exc_type: type[BaseException] | None,
exc_val: BaseException | None,
exc_tb: TracebackType | None,
) -> None:
"""Close the resolver when leaving an async context manager."""
await self.close()
[docs]
class AsyncMDNSResolver(_AsyncMDNSResolverBase):
"""Use the `aiodns`/`zeroconf` packages to make asynchronous DNS lookups."""
[docs]
async def resolve(
self, host: str, port: int = 0, family: socket.AddressFamily = socket.AF_INET
) -> list[ResolveResult]:
"""Resolve a host name to an IP address."""
if not _is_local_name(host):
return await super().resolve(host, port, family)
info = self._make_resolver(host, family)
if info.load_from_cache(self._aiozc.zeroconf):
return self._addresses_from_info_or_raise(info, port, family)
return await self._resolve_mdns(info, port, family)
[docs]
class AsyncDualMDNSResolver(_AsyncMDNSResolverBase):
"""Use the `aiodns`/`zeroconf` packages to make asynchronous DNS lookups.
This resolver is a variant of `AsyncMDNSResolver` that resolves .local
names with both mDNS and regular DNS.
- The first successful result from either resolver is returned.
- If both resolvers fail, an exception is raised.
- If both resolvers return results at the same time, the results are
combined and duplicates are removed.
"""
[docs]
async def resolve(
self, host: str, port: int = 0, family: socket.AddressFamily = socket.AF_INET
) -> list[ResolveResult]:
"""Resolve a host name to an IP address."""
if not _is_local_name(host):
return await super().resolve(host, port, family)
info = self._make_resolver(host, family)
if info.load_from_cache(self._aiozc.zeroconf):
return self._addresses_from_info_or_raise(info, port, family)
resolve_via_mdns = self._resolve_mdns(info, port, family)
resolve_via_dns = super().resolve(host, port, family)
loop = asyncio.get_running_loop()
if sys.version_info >= (3, 12):
mdns_task = asyncio.Task(resolve_via_mdns, loop=loop, eager_start=True)
dns_task = asyncio.Task(resolve_via_dns, loop=loop, eager_start=True)
else:
mdns_task = loop.create_task(resolve_via_mdns)
dns_task = loop.create_task(resolve_via_dns)
tasks = (mdns_task, dns_task)
try:
await asyncio.wait(tasks, return_when=asyncio.FIRST_COMPLETED)
if mdns_task.done() and mdns_task.exception():
await asyncio.wait((dns_task,), return_when=asyncio.ALL_COMPLETED)
elif dns_task.done() and dns_task.exception():
await asyncio.wait((mdns_task,), return_when=asyncio.ALL_COMPLETED)
resolve_results: list[ResolveResult] = []
exceptions: list[BaseException] = []
seen_results: set[tuple[int, str]] = set()
for task in tasks:
if not task.done():
continue
if exc := task.exception():
exceptions.append(exc)
continue
# If we have multiple results, we need to remove duplicates
# and combine the results. We put the mDNS results first
# to prioritize them. De-duplication keys on (port, host)
# only: the two resolvers report different hostname strings
# for the same name (mDNS uses zeroconf's trailing-dot
# ``info.server`` while DNS echoes the caller's input), so
# including hostname would let the same endpoint through
# twice. Within one resolve() call an (IP, port) pair
# uniquely identifies an endpoint.
for result in task.result():
result_key = (
result["port"],
result["host"],
)
if result_key not in seen_results:
seen_results.add(result_key)
resolve_results.append(result)
if resolve_results:
return resolve_results
exception_strings = ", ".join(
exc.strerror or str(exc) if isinstance(exc, OSError) else str(exc)
for exc in exceptions
)
raise OSError(None, exception_strings)
finally:
# asyncio.wait() does not cancel its child tasks when the awaiting
# coroutine is itself cancelled, so any still-pending task must be
# cancelled here to avoid orphaning work against the shared
# zeroconf instance. Also retrieve exceptions from already-done
# tasks so a fast-failing child cannot trigger a "Task exception
# was never retrieved" warning when the outer coroutine is
# cancelled before the result-collection loop runs.
pending = [task for task in tasks if not task.done()]
for task in tasks:
if task.done() and not task.cancelled():
task.exception()
if pending:
for task in pending:
task.cancel()
# return_exceptions=True ensures a child error cannot escape
# the finally and override the outcome of resolve().
await asyncio.gather(*pending, return_exceptions=True)
if (
sys.version_info >= (3, 11)
and (current_task := asyncio.current_task())
and current_task.cancelling()
):
raise asyncio.CancelledError
