synapse/synapse/util/gai_resolver.py

# This is a direct lift from
# https://github.com/twisted/twisted/blob/release-21.2.0-10091/src/twisted/internet/_resolver.py.
# We copy it here as we need to instantiate `GAIResolver` manually, but it is a
# private class.

from socket import (
    AF_INET,
    AF_INET6,
    AF_UNSPEC,
    SOCK_DGRAM,
    SOCK_STREAM,
    AddressFamily,
    SocketKind,
    gaierror,
    getaddrinfo,
)
from typing import (
    TYPE_CHECKING,
    Callable,
    List,
    NoReturn,
    Optional,
    Sequence,
    Tuple,
    Type,
    Union,
)

from zope.interface import implementer

from twisted.internet.address import IPv4Address, IPv6Address
from twisted.internet.interfaces import (
    IAddress,
    IHostnameResolver,
    IHostResolution,
    IReactorThreads,
    IResolutionReceiver,
)
from twisted.internet.threads import deferToThreadPool

if TYPE_CHECKING:
    # The types below are copied from
    # https://github.com/twisted/twisted/blob/release-21.2.0-10091/src/twisted/internet/interfaces.py
    # so that the type hints can match the interfaces.
    from twisted.python.runtime import platform

    if platform.supportsThreads():
        from twisted.python.threadpool import ThreadPool
    else:
        ThreadPool = object  # type: ignore[misc, assignment]


@implementer(IHostResolution)
class HostResolution:
    """
    The in-progress resolution of a given hostname.
    """

    def __init__(self, name: str):
        """
        Create a L{HostResolution} with the given name.
        """
        self.name = name

    def cancel(self) -> NoReturn:
        # IHostResolution.cancel
        raise NotImplementedError()


_any = frozenset([IPv4Address, IPv6Address])

_typesToAF = {
    frozenset([IPv4Address]): AF_INET,
    frozenset([IPv6Address]): AF_INET6,
    _any: AF_UNSPEC,
}

_afToType = {
    AF_INET: IPv4Address,
    AF_INET6: IPv6Address,
}

_transportToSocket = {
    "TCP": SOCK_STREAM,
    "UDP": SOCK_DGRAM,
}

_socktypeToType = {
    SOCK_STREAM: "TCP",
    SOCK_DGRAM: "UDP",
}


_GETADDRINFO_RESULT = List[
    Tuple[
        AddressFamily,
        SocketKind,
        int,
        str,
        Union[Tuple[str, int], Tuple[str, int, int, int]],
    ]
]


@implementer(IHostnameResolver)
class GAIResolver:
    """
    L{IHostnameResolver} implementation that resolves hostnames by calling
    L{getaddrinfo} in a thread.
    """

    def __init__(
        self,
        reactor: IReactorThreads,
        getThreadPool: Optional[Callable[[], "ThreadPool"]] = None,
        getaddrinfo: Callable[[str, int, int, int], _GETADDRINFO_RESULT] = getaddrinfo,
    ):
        """
        Create a L{GAIResolver}.
        @param reactor: the reactor to schedule result-delivery on
        @type reactor: L{IReactorThreads}
        @param getThreadPool: a function to retrieve the thread pool to use for
            scheduling name resolutions.  If not supplied, the use the given
            C{reactor}'s thread pool.
        @type getThreadPool: 0-argument callable returning a
            L{twisted.python.threadpool.ThreadPool}
        @param getaddrinfo: a reference to the L{getaddrinfo} to use - mainly
            parameterized for testing.
        @type getaddrinfo: callable with the same signature as L{getaddrinfo}
        """
        self._reactor = reactor
        self._getThreadPool = (
            reactor.getThreadPool if getThreadPool is None else getThreadPool
        )
        self._getaddrinfo = getaddrinfo

    # The types on IHostnameResolver is incorrect in Twisted, see
    # https://twistedmatrix.com/trac/ticket/10276
    def resolveHostName(
        self,
        resolutionReceiver: IResolutionReceiver,
        hostName: str,
        portNumber: int = 0,
        addressTypes: Optional[Sequence[Type[IAddress]]] = None,
        transportSemantics: str = "TCP",
    ) -> IHostResolution:
        """
        See L{IHostnameResolver.resolveHostName}
        @param resolutionReceiver: see interface
        @param hostName: see interface
        @param portNumber: see interface
        @param addressTypes: see interface
        @param transportSemantics: see interface
        @return: see interface
        """
        pool = self._getThreadPool()
        addressFamily = _typesToAF[
            _any if addressTypes is None else frozenset(addressTypes)
        ]
        socketType = _transportToSocket[transportSemantics]

        def get() -> _GETADDRINFO_RESULT:
            try:
                return self._getaddrinfo(
                    hostName, portNumber, addressFamily, socketType
                )
            except gaierror:
                return []

        d = deferToThreadPool(self._reactor, pool, get)
        resolution = HostResolution(hostName)
        resolutionReceiver.resolutionBegan(resolution)

        @d.addCallback
        def deliverResults(result: _GETADDRINFO_RESULT) -> None:
            for family, socktype, _proto, _cannoname, sockaddr in result:
                addrType = _afToType[family]
                resolutionReceiver.addressResolved(
                    addrType(_socktypeToType.get(socktype, "TCP"), *sockaddr)
                )
            resolutionReceiver.resolutionComplete()

        return resolution