Mini Shell

# Author: Ovidiu Predescu
# Date: July 2011
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""Bridges between the Twisted reactor and Tornado IOLoop.

This module lets you run applications and libraries written for
Twisted in a Tornado application.  It can be used in two modes,
depending on which library's underlying event loop you want to use.

This module has been tested with Twisted versions 11.0.0 and newer.
"""

import socket
import sys

import twisted.internet.abstract  # type: ignore
import twisted.internet.asyncioreactor  # type: ignore
from twisted.internet.defer import Deferred  # type: ignore
from twisted.python import failure  # type: ignore
import twisted.names.cache  # type: ignore
import twisted.names.client  # type: ignore
import twisted.names.hosts  # type: ignore
import twisted.names.resolve  # type: ignore


from tornado.concurrent import Future, future_set_exc_info
from tornado.escape import utf8
from tornado import gen
from tornado.netutil import Resolver

import typing

if typing.TYPE_CHECKING:
    from typing import Generator, Any, List, Tuple  # noqa: F401


class TwistedResolver(Resolver):
    """Twisted-based asynchronous resolver.

    This is a non-blocking and non-threaded resolver.  It is
    recommended only when threads cannot be used, since it has
    limitations compared to the standard ``getaddrinfo``-based
    `~tornado.netutil.Resolver` and
    `~tornado.netutil.DefaultExecutorResolver`.  Specifically, it returns at
    most one result, and arguments other than ``host`` and ``family``
    are ignored.  It may fail to resolve when ``family`` is not
    ``socket.AF_UNSPEC``.

    Requires Twisted 12.1 or newer.

    .. versionchanged:: 5.0
       The ``io_loop`` argument (deprecated since version 4.1) has been removed.
    """

    def initialize(self) -> None:
        # partial copy of twisted.names.client.createResolver, which doesn't
        # allow for a reactor to be passed in.
        self.reactor = twisted.internet.asyncioreactor.AsyncioSelectorReactor()

        host_resolver = twisted.names.hosts.Resolver("/etc/hosts")
        cache_resolver = twisted.names.cache.CacheResolver(reactor=self.reactor)
        real_resolver = twisted.names.client.Resolver(
            "/etc/resolv.conf", reactor=self.reactor
        )
        self.resolver = twisted.names.resolve.ResolverChain(
            [host_resolver, cache_resolver, real_resolver]
        )

    @gen.coroutine
    def resolve(
        self, host: str, port: int, family: int = 0
    ) -> "Generator[Any, Any, List[Tuple[int, Any]]]":
        # getHostByName doesn't accept IP addresses, so if the input
        # looks like an IP address just return it immediately.
        if twisted.internet.abstract.isIPAddress(host):
            resolved = host
            resolved_family = socket.AF_INET
        elif twisted.internet.abstract.isIPv6Address(host):
            resolved = host
            resolved_family = socket.AF_INET6
        else:
            deferred = self.resolver.getHostByName(utf8(host))
            fut = Future()  # type: Future[Any]
            deferred.addBoth(fut.set_result)
            resolved = yield fut
            if isinstance(resolved, failure.Failure):
                try:
                    resolved.raiseException()
                except twisted.names.error.DomainError as e:
                    raise IOError(e)
            elif twisted.internet.abstract.isIPAddress(resolved):
                resolved_family = socket.AF_INET
            elif twisted.internet.abstract.isIPv6Address(resolved):
                resolved_family = socket.AF_INET6
            else:
                resolved_family = socket.AF_UNSPEC
        if family != socket.AF_UNSPEC and family != resolved_family:
            raise Exception(
                "Requested socket family %d but got %d" % (family, resolved_family)
            )
        result = [(typing.cast(int, resolved_family), (resolved, port))]
        return result


if hasattr(gen.convert_yielded, "register"):

    @gen.convert_yielded.register(Deferred)  # type: ignore
    def _(d: Deferred) -> Future:
        f = Future()  # type: Future[Any]

        def errback(failure: failure.Failure) -> None:
            try:
                failure.raiseException()
                # Should never happen, but just in case
                raise Exception("errback called without error")
            except:
                future_set_exc_info(f, sys.exc_info())

        d.addCallbacks(f.set_result, errback)
        return f