resolver.py

import asyncio
import socket
from typing import Any, List, Tuple, Type, Union

from .abc import AbstractResolver, ResolveResult

__all__ = ("ThreadedResolver", "AsyncResolver", "DefaultResolver")


try:
    import aiodns

    aiodns_default = hasattr(aiodns.DNSResolver, "getaddrinfo")
except ImportError:
    aiodns = None  # type: ignore[assignment]
    aiodns_default = False


_NUMERIC_SOCKET_FLAGS = socket.AI_NUMERICHOST | socket.AI_NUMERICSERV
_NAME_SOCKET_FLAGS = socket.NI_NUMERICHOST | socket.NI_NUMERICSERV


class ThreadedResolver(AbstractResolver):
    """Threaded resolver.

    Uses an Executor for synchronous getaddrinfo() calls.
    concurrent.futures.ThreadPoolExecutor is used by default.
    """

    def __init__(self) -> None:
        self._loop = asyncio.get_running_loop()

    async def resolve(
        self, host: str, port: int = 0, family: socket.AddressFamily = socket.AF_INET
    ) -> List[ResolveResult]:
        infos = await self._loop.getaddrinfo(
            host,
            port,
            type=socket.SOCK_STREAM,
            family=family,
            flags=socket.AI_ADDRCONFIG,
        )

        hosts: List[ResolveResult] = []
        for family, _, proto, _, address in infos:
            if family == socket.AF_INET6:
                if len(address) < 3:
                    # IPv6 is not supported by Python build,
                    # or IPv6 is not enabled in the host
                    continue
                if address[3]:
                    # This is essential for link-local IPv6 addresses.
                    # LL IPv6 is a VERY rare case. Strictly speaking, we should use
                    # getnameinfo() unconditionally, but performance makes sense.
                    resolved_host, _port = await self._loop.getnameinfo(
                        address, _NAME_SOCKET_FLAGS
                    )
                    port = int(_port)
                else:
                    resolved_host, port = address[:2]
            else:  # IPv4
                assert family == socket.AF_INET
                resolved_host, port = address  # type: ignore[misc]
            hosts.append(
                ResolveResult(
                    hostname=host,
                    host=resolved_host,
                    port=port,
                    family=family,
                    proto=proto,
                    flags=_NUMERIC_SOCKET_FLAGS,
                )
            )

        return hosts

    async def close(self) -> None:
        pass


class AsyncResolver(AbstractResolver):
    """Use the `aiodns` package to make asynchronous DNS lookups"""

    def __init__(self, *args: Any, **kwargs: Any) -> None:
        if aiodns is None:
            raise RuntimeError("Resolver requires aiodns library")

        self._resolver = aiodns.DNSResolver(*args, **kwargs)

    async def resolve(
        self, host: str, port: int = 0, family: socket.AddressFamily = socket.AF_INET
    ) -> List[ResolveResult]:
        try:
            resp = await self._resolver.getaddrinfo(
                host,
                port=port,
                type=socket.SOCK_STREAM,
                family=family,
                flags=socket.AI_ADDRCONFIG,
            )
        except aiodns.error.DNSError as exc:
            msg = exc.args[1] if len(exc.args) >= 1 else "DNS lookup failed"
            raise OSError(None, msg) from exc
        hosts: List[ResolveResult] = []
        for node in resp.nodes:
            address: Union[Tuple[bytes, int], Tuple[bytes, int, int, int]] = node.addr
            family = node.family
            if family == socket.AF_INET6:
                if len(address) > 3 and address[3]:
                    # This is essential for link-local IPv6 addresses.
                    # LL IPv6 is a VERY rare case. Strictly speaking, we should use
                    # getnameinfo() unconditionally, but performance makes sense.
                    result = await self._resolver.getnameinfo(
                        (address[0].decode("ascii"), *address[1:]),
                        _NAME_SOCKET_FLAGS,
                    )
                    resolved_host = result.node
                else:
                    resolved_host = address[0].decode("ascii")
                    port = address[1]
            else:  # IPv4
                assert family == socket.AF_INET
                resolved_host = address[0].decode("ascii")
                port = address[1]
            hosts.append(
                ResolveResult(
                    hostname=host,
                    host=resolved_host,
                    port=port,
                    family=family,
                    proto=0,
                    flags=_NUMERIC_SOCKET_FLAGS,
                )
            )

        if not hosts:
            raise OSError(None, "DNS lookup failed")

        return hosts

    async def close(self) -> None:
        self._resolver.cancel()


_DefaultType = Type[Union[AsyncResolver, ThreadedResolver]]
DefaultResolver: _DefaultType = AsyncResolver if aiodns_default else ThreadedResolver