Mini Shell

import pycares  # type: ignore
import socket

from tornado.concurrent import Future
from tornado import gen
from tornado.ioloop import IOLoop
from tornado.netutil import Resolver, is_valid_ip

import typing

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


class CaresResolver(Resolver):
    """Name resolver based on the c-ares library.

    This is a non-blocking and non-threaded resolver.  It may not produce
    the same results as the system resolver, but can be used for non-blocking
    resolution when threads cannot be used.

    c-ares fails to resolve some names when ``family`` is ``AF_UNSPEC``,
    so it is only recommended for use in ``AF_INET`` (i.e. IPv4).  This is
    the default for ``tornado.simple_httpclient``, but other libraries
    may default to ``AF_UNSPEC``.

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

    def initialize(self) -> None:
        self.io_loop = IOLoop.current()
        self.channel = pycares.Channel(sock_state_cb=self._sock_state_cb)
        self.fds = {}  # type: Dict[int, int]

    def _sock_state_cb(self, fd: int, readable: bool, writable: bool) -> None:
        state = (IOLoop.READ if readable else 0) | (IOLoop.WRITE if writable else 0)
        if not state:
            self.io_loop.remove_handler(fd)
            del self.fds[fd]
        elif fd in self.fds:
            self.io_loop.update_handler(fd, state)
            self.fds[fd] = state
        else:
            self.io_loop.add_handler(fd, self._handle_events, state)
            self.fds[fd] = state

    def _handle_events(self, fd: int, events: int) -> None:
        read_fd = pycares.ARES_SOCKET_BAD
        write_fd = pycares.ARES_SOCKET_BAD
        if events & IOLoop.READ:
            read_fd = fd
        if events & IOLoop.WRITE:
            write_fd = fd
        self.channel.process_fd(read_fd, write_fd)

    @gen.coroutine
    def resolve(
        self, host: str, port: int, family: int = 0
    ) -> "Generator[Any, Any, List[Tuple[int, Any]]]":
        if is_valid_ip(host):
            addresses = [host]
        else:
            # gethostbyname doesn't take callback as a kwarg
            fut = Future()  # type: Future[Tuple[Any, Any]]
            self.channel.gethostbyname(
                host, family, lambda result, error: fut.set_result((result, error))
            )
            result, error = yield fut
            if error:
                raise IOError(
                    "C-Ares returned error %s: %s while resolving %s"
                    % (error, pycares.errno.strerror(error), host)
                )
            addresses = result.addresses
        addrinfo = []
        for address in addresses:
            if "." in address:
                address_family = socket.AF_INET
            elif ":" in address:
                address_family = socket.AF_INET6
            else:
                address_family = socket.AF_UNSPEC
            if family != socket.AF_UNSPEC and family != address_family:
                raise IOError(
                    "Requested socket family %d but got %d" % (family, address_family)
                )
            addrinfo.append((typing.cast(int, address_family), (address, port)))
        return addrinfo