"""  # NOQA
:mod:`aioopenssl` --- A transport for asyncio using :mod:`OpenSSL`
##################################################################

This package provides a socket-based :class:`asyncio.Transport` which uses
:mod:`OpenSSL` to create a TLS connection. Optionally, the TLS handshake can be
deferred and performed later using :meth:`STARTTLSTransport.starttls`.

.. note::

   Use this module at your own risk. It has lower test coverage than I’d like
   it to have; it has been exported from aioxmpp on request, where it undergoes
   implicit testing. If you find bugs, please report them. If possible, add
   regression tests while you’re at it.

   If you find security-critical bugs, please follow the procedure announced in
   the `aioxmpp readme <https://github.com/horazont/aioxmpp>`_.


The following function can be used to create a connection using the
:class:`STARTTLSTransport`, which itself is documented below:

.. autofunction:: create_starttls_connection

The transport implementation is documented below:

.. autoclass:: STARTTLSTransport(loop, rawsock, protocol, ssl_context_factory, [waiter=None], [use_starttls=False], [post_handshake_callback=None], [peer_hostname=None], [server_hostname=None])
   :members:

"""

import asyncio
import logging
import socket
import typing

from enum import Enum

from .version import __version__, version_info, version  # noqa:F401
from .utils import SendWrap

import OpenSSL.SSL

logger = logging.getLogger(__name__)


class _State(Enum):
    RAW_OPEN               = 0x0000  # noqa:E221
    RAW_EOF_RECEIVED       = 0x0001  # noqa:E221

    TLS_HANDSHAKING        = 0x0300  # noqa:E221
    TLS_OPEN               = 0x0100  # noqa:E221
    TLS_EOF_RECEIVED       = 0x0101  # noqa:E221
    TLS_SHUTTING_DOWN      = 0x0102  # noqa:E221
    TLS_SHUT_DOWN          = 0x0103  # noqa:E221

    CLOSED                 = 0x0003  # noqa:E221

    @property
    def eof_received(self) -> bool:
        return bool(self.value & 0x0001)

    @property
    def tls_started(self) -> bool:
        return bool(self.value & 0x0100)

    @property
    def tls_handshaking(self) -> bool:
        return bool(self.value & 0x0200)

    @property
    def is_writable(self) -> bool:
        return not bool(self.value & 0x0002)

    @property
    def is_open(self) -> bool:
        return (self.value & 0x3) == 0


SSLContextFactory = typing.Callable[[asyncio.Transport], OpenSSL.SSL.Context]
PostHandshakeCallback = typing.Callable[
    ["STARTTLSTransport"],
    typing.Coroutine[typing.Any, typing.Any, None],
]


class STARTTLSTransport(asyncio.Transport):
    """
    Create a new :class:`asyncio.Transport` which supports TLS and the deferred
    starting of TLS using the :meth:`starttls` method.

    `loop` must be a :class:`asyncio.BaseEventLoop` with support for
    :meth:`BaseEventLoop.add_reader` as well as removal and the writer
    complements.

    `rawsock` must be a :class:`socket.socket` which will be used as the socket
    for the transport. `protocol` must be a :class:`asyncio.Protocol` which
    will be fed the data the transport receives.

    `ssl_context_factory` must be a callable accepting a single positional
    argument which returns a :class:`OpenSSL.SSL.Context`. The transport will
    be passed as the argument to the factory. The returned context will be used
    to create the :class:`OpenSSL.SSL.Connection` when TLS is enabled on the
    transport. If the callable is :data:`None`, a `ssl_context` must be
    supplied to :meth:`starttls` and `use_starttls` must be true.

    `use_starttls` must be a boolean value. If it is true, TLS is not enabled
    immediately. Instead, the user must call :meth:`starttls` to enable TLS on
    the transport. Until that point, the transport is unencrypted. If it is
    false, the TLS handshake is started immediately. This is roughly equivalent
    to calling :meth:`starttls` immediately.

    `peer_hostname` must be either a :class:`str` or :data:`None`. It may be
    used by certificate validators and must be the host name this transport
    actually connected to. That might be (e.g. in the case of XMPP) different
    from the actual domain name the transport communicates with (and for which
    the service must have a valid certificate). This host name may be used by
    certificate validators implementing e.g. DANE.

    `server_hostname` must be either a :class:`str` or :data:`None`. It may be
    used by certificate validators anrd must be the host name for which the
    peer must have a valid certificate (if host name based certificate
    validation is performed). `server_hostname` is also passed via the TLS
    Server Name Indication (SNI) extension if it is given.

    If host names are to be converted to :class:`bytes` by the transport, they
    are encoded using the ``utf-8`` codec.

    If `waiter` is not :data:`None`, it must be a
    :class:`asyncio.Future`. After the stream has been established, the futures
    result is set to a value of :data:`None`. If any errors occur, the
    exception is set on the future.

    If `use_starttls` is true, the future is fulfilled immediately after
    construction, as there is no blocking process which needs to take place. If
    `use_starttls` is false and thus TLS negotiation starts right away, the
    future is fulfilled when TLS negotiation is complete.

    `post_handshake_callback` may be a coroutine or :data:`None`. If it is not
    :data:`None`, it is called asynchronously after the TLS handshake and
    blocks the completion of the TLS handshake until it returns.

    It can be used to perform blocking post-handshake certificate verification,
    e.g. using DANE. The coroutine must not return a value. If it encounters an
    error, an appropriate exception should be raised, which will propagate out
    of :meth:`starttls` and/or passed to the `waiter` future.
    """

    MAX_SIZE = 256 * 1024

    def __init__(
            self,
            loop: asyncio.BaseEventLoop,
            rawsock: socket.socket,
            protocol: asyncio.Protocol,
            ssl_context_factory: typing.Optional[SSLContextFactory] = None,
            waiter: typing.Optional[asyncio.Future] = None,
            use_starttls: bool = False,
            post_handshake_callback: typing.Optional[
                PostHandshakeCallback
            ] = None,
            peer_hostname: typing.Optional[str] = None,
            server_hostname: typing.Optional[str] = None):
        if not use_starttls and not ssl_context_factory:
            raise ValueError("Cannot have STARTTLS disabled (i.e. immediate "
                             "TLS connection) and without SSL context.")

        super().__init__()
        self._rawsock = rawsock
        self._raw_fd = rawsock.fileno()
        self._trace_logger = logger.getChild(
            "trace.fd={}".format(self._raw_fd)
        )
        self._sock = rawsock  # type: typing.Union[socket.socket, OpenSSL.SSL.Connection]  # noqa
        self._send_wrap = SendWrap(self._sock)
        self._protocol = protocol
        self._loop = loop
        self._extra = {
            "socket": rawsock,
        }  # type: typing.Dict[str, typing.Any]
        self._waiter = waiter
        self._conn_lost = 0
        self._buffer = bytearray()
        self._ssl_context_factory = ssl_context_factory
        self._extra.update(
            sslcontext=None,
            ssl_object=None,
            peername=self._rawsock.getpeername(),
            peer_hostname=peer_hostname,
            server_hostname=server_hostname
        )

        # this is a list set of tasks which will also be cancelled if the
        # _waiter is cancelled
        self._chained_pending = set()  # type: typing.Set[asyncio.Future]

        self._paused = False
        self._closing = False

        self._tls_conn = None  # type: typing.Optional[OpenSSL.SSL.Connection]
        self._tls_read_wants_write = False
        self._tls_write_wants_read = False
        self._tls_post_handshake_callback = post_handshake_callback

        self._state = None  # type: typing.Optional[_State]
        if not use_starttls:
            assert ssl_context_factory is not None
            self._ssl_context = ssl_context_factory(self)
            self._extra.update(
                sslcontext=self._ssl_context,
            )
            self._initiate_tls()
        else:
            self._initiate_raw()

    def _waiter_done(self, fut: asyncio.Future) -> None:
        self._trace_logger.debug("_waiter future done (%r)", fut)

        for chained in self._chained_pending:
            self._trace_logger.debug("cancelling chained %r", chained)
            chained.cancel()
        self._chained_pending.clear()

    def _invalid_transition(
            self,
            via: typing.Optional[str] = None,
            to: typing.Optional[_State] = None) -> None:
        via_text = (" via {}".format(via)) if via is not None else ""
        to_text = (" to {}".format(to)) if to is not None else ""
        msg = "Invalid state transition (from {}{}{})".format(
            self._state,
            via_text,
            to_text
        )
        logger.error(msg)
        raise RuntimeError(msg)

    def _invalid_state(
            self,
            what: str,
            exc: typing.Type[Exception] = RuntimeError,
            ) -> Exception:
        msg = "{what} (invalid in state {state}, closing={closing})".format(
            what=what,
            state=self._state,
            closing=self._closing)
        logger.error(msg)
        # raising is optional :)
        return exc(msg)

    def _fatal_error(
            self,
            exc: BaseException,
            msg: str) -> None:
        if not isinstance(exc, (BrokenPipeError, ConnectionResetError)):
            self._loop.call_exception_handler({
                "message": msg,
                "exception": exc,
                "transport": self,
                "protocol": self._protocol
            })

        self._force_close(exc)

    def _force_close(
            self,
            exc: typing.Optional[BaseException],
            ) -> None:
        self._trace_logger.debug("_force_close called")
        self._remove_rw()
        if self._state == _State.CLOSED:
            raise self._invalid_state("_force_close called")

        self._state = _State.CLOSED

        if self._buffer:
            self._buffer.clear()

        if self._waiter is not None and not self._waiter.done():
            self._waiter.set_exception(
                exc or ConnectionError("_force_close() called"),
            )
        self._loop.remove_reader(self._raw_fd)
        self._loop.remove_writer(self._raw_fd)
        self._loop.call_soon(self._call_connection_lost_and_clean_up, exc)

    def _remove_rw(self) -> None:
        self._trace_logger.debug("clearing readers/writers")
        self._loop.remove_reader(self._raw_fd)
        self._loop.remove_writer(self._raw_fd)

    def _call_connection_lost_and_clean_up(
            self,
            exc: Exception,
            ) -> None:
        """
        Clean up all resources and call the protocols connection lost method.
        """

        self._state = _State.CLOSED
        try:
            self._protocol.connection_lost(exc)
        finally:
            self._rawsock.close()
            if self._tls_conn is not None:
                self._tls_conn.set_app_data(None)
                self._tls_conn = None
            self._rawsock = None  # type:ignore
            self._protocol = None  # type:ignore

    def _initiate_raw(self) -> None:
        if self._state is not None:
            self._invalid_transition(via="_initiate_raw", to=_State.RAW_OPEN)

        self._state = _State.RAW_OPEN
        self._loop.add_reader(self._raw_fd, self._read_ready)
        self._loop.call_soon(self._protocol.connection_made, self)
        if self._waiter is not None:
            self._loop.call_soon(self._waiter.set_result, None)
            self._waiter = None

    def _initiate_tls(self) -> None:
        self._trace_logger.debug("_initiate_tls called")
        if self._state is not None and self._state != _State.RAW_OPEN:
            self._invalid_transition(via="_initiate_tls",
                                     to=_State.TLS_HANDSHAKING)

        self._tls_was_starttls = (self._state == _State.RAW_OPEN)
        self._state = _State.TLS_HANDSHAKING
        self._tls_conn = OpenSSL.SSL.Connection(
            self._ssl_context,
            self._sock)
        self._tls_conn.set_connect_state()
        self._tls_conn.set_app_data(self)
        try:
            self._tls_conn.set_tlsext_host_name(
                self._extra["server_hostname"].encode("IDNA"))
        except KeyError:
            pass
        self._sock = self._tls_conn
        self._send_wrap = SendWrap(self._sock)
        self._extra.update(
            ssl_object=self._tls_conn
        )

        self._tls_do_handshake()

    def _tls_do_handshake(self) -> None:
        assert self._tls_conn is not None
        self._trace_logger.debug("_tls_do_handshake called")
        if self._state != _State.TLS_HANDSHAKING:
            raise self._invalid_state("_tls_do_handshake called")

        try:
            self._tls_conn.do_handshake()
        except OpenSSL.SSL.WantReadError:
            self._trace_logger.debug(
                "registering reader for _tls_do_handshake")
            self._loop.add_reader(self._raw_fd, self._tls_do_handshake)
            return
        except OpenSSL.SSL.WantWriteError:
            self._trace_logger.debug(
                "registering writer for _tls_do_handshake")
            self._loop.add_writer(self._raw_fd, self._tls_do_handshake)
            return
        except Exception as exc:
            self._remove_rw()
            self._fatal_error(exc, "Fatal error on tls handshake")
            if self._waiter is not None:
                self._waiter.set_exception(exc)
            return
        except BaseException as exc:
            self._remove_rw()
            if self._waiter is not None:
                self._waiter.set_exception(exc)
            raise

        self._remove_rw()

        # handshake complete

        self._trace_logger.debug("handshake complete")
        self._extra.update(
            peercert=self._tls_conn.get_peer_certificate()
        )

        if self._tls_post_handshake_callback:
            self._trace_logger.debug("post handshake scheduled via callback")
            task = asyncio.ensure_future(
                self._tls_post_handshake_callback(self)
            )
            task.add_done_callback(self._tls_post_handshake_done)
            self._chained_pending.add(task)
            self._tls_post_handshake_callback = None
        else:
            self._tls_post_handshake(None)

    def _tls_post_handshake_done(
            self,
            task: asyncio.Future,
            ) -> None:
        self._chained_pending.discard(task)
        try:
            task.result()
        except asyncio.CancelledError:
            # canceled due to closure or something similar
            pass
        except BaseException as err:
            self._tls_post_handshake(err)
        else:
            self._tls_post_handshake(None)

    def _tls_post_handshake(
            self,
            exc: typing.Optional[BaseException],
            ) -> None:
        self._trace_logger.debug("_tls_post_handshake called")
        if exc is not None:
            if self._waiter is not None and not self._waiter.done():
                self._waiter.set_exception(exc)
            self._fatal_error(exc, "Fatal error on post-handshake callback")
            return

        self._tls_read_wants_write = False
        self._tls_write_wants_read = False

        self._state = _State.TLS_OPEN

        self._loop.add_reader(self._raw_fd, self._read_ready)
        if not self._tls_was_starttls:
            self._loop.call_soon(self._protocol.connection_made, self)
        if self._waiter is not None:
            self._loop.call_soon(self._waiter.set_result, None)

    def _tls_do_shutdown(self) -> None:
        self._trace_logger.debug("_tls_do_shutdown called")
        if self._state != _State.TLS_SHUTTING_DOWN:
            raise self._invalid_state("_tls_do_shutdown called")

        assert isinstance(self._sock, OpenSSL.SSL.Connection)
        try:
            self._sock.shutdown()
        except OpenSSL.SSL.WantReadError:
            self._trace_logger.debug("registering reader for _tls_shutdown")
            self._loop.add_reader(self._raw_fd, self._tls_shutdown)
            return
        except OpenSSL.SSL.WantWriteError:
            self._trace_logger.debug("registering writer for _tls_shutdown")
            self._loop.add_writer(self._raw_fd, self._tls_shutdown)
            return
        except Exception as exc:
            # force_close will take care of removing rw handlers
            self._fatal_error(exc, "Fatal error on tls shutdown")
            return
        except BaseException:
            self._remove_rw()
            raise

        self._remove_rw()
        self._state = _State.TLS_SHUT_DOWN
        # continue to raw shut down
        self._raw_shutdown()

    def _tls_shutdown(self) -> None:
        self._state = _State.TLS_SHUTTING_DOWN
        self._tls_do_shutdown()

    def _raw_shutdown(self) -> None:
        self._remove_rw()
        try:
            self._rawsock.shutdown(socket.SHUT_RDWR)
        except OSError:
            # we cannot do anything anyway if this fails
            pass
        self._force_close(None)

    def _read_ready(self) -> None:
        assert self._state is not None
        if self._state.tls_started and self._tls_write_wants_read:
            self._tls_write_wants_read = False
            self._write_ready()

            if self._buffer:
                self._trace_logger.debug("_read_ready: add writer for more"
                                         " data")
                self._loop.add_writer(self._raw_fd, self._write_ready)

        if self._state.eof_received:
            # no further reading
            return

        try:
            data = self._sock.recv(self.MAX_SIZE)
        except (BlockingIOError, InterruptedError, OpenSSL.SSL.WantReadError):
            pass
        except OpenSSL.SSL.WantWriteError:
            assert self._state.tls_started
            self._tls_read_wants_write = True
            self._trace_logger.debug("_read_ready: swap reader for writer")
            self._loop.remove_reader(self._raw_fd)
            self._loop.add_writer(self._raw_fd, self._write_ready)
        except OpenSSL.SSL.SysCallError as exc:
            if self._state in (_State.TLS_SHUT_DOWN,
                               _State.TLS_SHUTTING_DOWN,
                               _State.CLOSED):
                self._trace_logger.debug(
                    "_read_ready: ignoring syscall exception during shutdown: "
                    "%s",
                    exc,
                )
            else:
                self._fatal_error(exc,
                                  "Fatal read error on STARTTLS transport")
        except Exception as err:
            self._fatal_error(err, "Fatal read error on STARTTLS transport")
            return
        else:
            if data:
                self._protocol.data_received(data)
            else:
                keep_open = False
                try:
                    keep_open = bool(self._protocol.eof_received())
                finally:
                    self._eof_received(keep_open)

    def _write_ready(self) -> None:
        assert self._state is not None
        if self._tls_read_wants_write:
            self._tls_read_wants_write = False
            self._read_ready()

            if not self._paused and not self._state.eof_received:
                self._trace_logger.debug("_write_ready: add reader for more"
                                         " data")
                self._loop.add_reader(self._raw_fd, self._read_ready)

        # do not send data during handshake!
        if self._buffer and self._state != _State.TLS_HANDSHAKING:
            try:
                nsent = self._send_wrap.send(self._buffer)
            except (BlockingIOError, InterruptedError,
                    OpenSSL.SSL.WantWriteError):
                nsent = 0
            except OpenSSL.SSL.WantReadError:
                nsent = 0
                assert self._state.tls_started
                self._tls_write_wants_read = True
                self._trace_logger.debug(
                    "_write_ready: swap writer for reader")
                self._loop.remove_writer(self._raw_fd)
                self._loop.add_reader(self._raw_fd, self._read_ready)
            except OpenSSL.SSL.SysCallError as exc:
                if self._state in (_State.TLS_SHUT_DOWN,
                                   _State.TLS_SHUTTING_DOWN,
                                   _State.CLOSED):
                    self._trace_logger.debug(
                        "_write_ready: ignoring syscall exception during "
                        "shutdown: %s",
                        exc,
                    )
                else:
                    self._fatal_error(exc,
                                      "Fatal write error on STARTTLS "
                                      "transport")
            except Exception as err:
                self._fatal_error(err,
                                  "Fatal write error on STARTTLS "
                                  "transport")
                return

            if nsent:
                del self._buffer[:nsent]

        if not self._buffer:
            if not self._tls_read_wants_write:
                self._trace_logger.debug("_write_ready: nothing more to write,"
                                         " removing writer")
                self._loop.remove_writer(self._raw_fd)
            if self._closing:
                if self._state.tls_started:
                    self._tls_shutdown()
                else:
                    self._raw_shutdown()

    def _eof_received(self, keep_open: bool) -> None:
        assert self._state is not None
        self._trace_logger.debug("_eof_received: removing reader")
        self._loop.remove_reader(self._raw_fd)
        if self._state.tls_started:
            assert self._tls_conn is not None
            if self._tls_conn.get_shutdown() & OpenSSL.SSL.RECEIVED_SHUTDOWN:
                # proper TLS shutdown going on
                if keep_open:
                    self._state = _State.TLS_EOF_RECEIVED
                else:
                    self._tls_shutdown()
            else:
                if keep_open:
                    self._trace_logger.warning(
                        "result of eof_received() ignored as shut down is"
                        " improper",
                    )
                self._fatal_error(
                    ConnectionError("Underlying transport closed"),
                    "unexpected eof_received"
                )
        else:
            if keep_open:
                self._state = _State.RAW_EOF_RECEIVED
            else:
                self._raw_shutdown()

    # public API

    def abort(self) -> None:
        """
        Immediately close the stream, without sending remaining buffers or
        performing a proper shutdown.
        """
        if self._state == _State.CLOSED:
            self._invalid_state("abort() called")
            return

        self._force_close(None)

    def can_write_eof(self) -> bool:
        """
        Return :data:`False`.

        .. note::

           Writing of EOF (i.e. closing the sending direction of the stream) is
           theoretically possible. However, it was deemed by the author that
           the case is rare enough to neglect it for the sake of implementation
           simplicity.

        """
        return False

    def close(self) -> None:
        """
        Close the stream. This performs a proper stream shutdown, except if the
        stream is currently performing a TLS handshake. In that case, calling
        :meth:`close` is equivalent to calling :meth:`abort`.

        Otherwise, the transport waits until all buffers are transmitted.
        """

        if self._state == _State.CLOSED:
            self._invalid_state("close() called")
            return

        if self._state == _State.TLS_HANDSHAKING:
            # hard-close
            self._force_close(None)
        elif self._state == _State.TLS_SHUTTING_DOWN:
            # shut down in progress, nothing to do
            pass
        elif self._buffer:
            # there is data to be send left, first wait for it to transmit ...
            self._closing = True
        elif self._state is not None and self._state.tls_started:
            # normal TLS state, nothing left to transmit, shut down
            self._tls_shutdown()
        else:
            # normal non-TLS state, nothing left to transmit, close
            self._raw_shutdown()

    def get_extra_info(
            self,
            name: str,
            default: typing.Optional[typing.Any] = None,
            ) -> typing.Any:
        """
        The following extra information is available:

        * ``socket``: the underlying :mod:`socket` object
        * ``sslcontext``: the :class:`OpenSSL.SSL.Context` object to use (this
          may be :data:`None` until :meth:`starttls` has been called)
        * ``ssl_object``: :class:`OpenSSL.SSL.Connection` object (:data:`None`
          if TLS is not enabled (yet))
        * ``peername``: return value of :meth:`socket.Socket.getpeername`
        * ``peer_hostname``: The `peer_hostname` value passed to the
          constructor.
        * ``server_hostname``: The `server_hostname` value passed to the
          constructor.

        """
        return self._extra.get(name, default)

    async def starttls(
            self,
            ssl_context: typing.Optional[OpenSSL.SSL.Context] = None,
            post_handshake_callback: typing.Optional[
                PostHandshakeCallback
            ] = None,
            ) -> None:
        """
        Start a TLS stream on top of the socket. This is an invalid operation
        if the stream is not in RAW_OPEN state.

        If `ssl_context` is set, it overrides the `ssl_context` passed to the
        constructor. If `post_handshake_callback` is set, it overrides the
        `post_handshake_callback` passed to the constructor.

        .. versionchanged:: 0.4

            This method is now a barrier with respect to reads and writes:
            before the handshake is completed (including the post handshake
            callback, if any), no data is received or sent.
        """
        if self._state != _State.RAW_OPEN or self._closing:
            raise self._invalid_state("starttls() called")

        if ssl_context is not None:
            self._ssl_context = ssl_context
            self._extra.update(
                sslcontext=ssl_context
            )
        else:
            assert self._ssl_context_factory is not None
            self._ssl_context = self._ssl_context_factory(self)

        if post_handshake_callback is not None:
            self._tls_post_handshake_callback = post_handshake_callback

        self._waiter = asyncio.Future()
        self._waiter.add_done_callback(self._waiter_done)
        self._initiate_tls()
        try:
            await self._waiter
        finally:
            self._waiter = None

    def write(self, data: typing.Union[bytes, bytearray, memoryview]) -> None:
        """
        Write data to the transport. This is an invalid operation if the stream
        is not writable, that is, if it is closed. During TLS negotiation, the
        data is buffered.
        """
        if not isinstance(data, (bytes, bytearray, memoryview)):
            raise TypeError('data argument must be byte-ish (%r)',
                            type(data))

        if (self._state is None or
                not self._state.is_writable or
                self._closing):
            raise self._invalid_state("write() called")

        if not data:
            return

        if not self._buffer:
            self._loop.add_writer(self._raw_fd, self._write_ready)

        self._buffer.extend(data)

    def write_eof(self) -> None:
        """
        Writing the EOF has not been implemented, for the sake of simplicity.
        """
        raise NotImplementedError("Cannot write_eof() on STARTTLS transport")

    def can_starttls(self) -> bool:
        """
        Return :data:`True`.
        """
        return True

    def is_closing(self) -> bool:
        return (self._state == _State.TLS_SHUTTING_DOWN or
                self._state == _State.CLOSED)


async def create_starttls_connection(
        loop: asyncio.BaseEventLoop,
        protocol_factory: typing.Callable[[], asyncio.Protocol],
        host: typing.Optional[str] = None,
        port: typing.Optional[int] = None,
        *,
        sock: typing.Optional[socket.socket] = None,
        ssl_context_factory: typing.Optional[SSLContextFactory] = None,
        use_starttls: bool = False,
        local_addr: typing.Any = None,
        **kwargs  # type: typing.Any
        ) -> typing.Tuple[asyncio.Transport, asyncio.Protocol]:
    """
    Create a connection which can later be upgraded to use TLS.

    .. versionchanged:: 0.4

        The `local_addr` argument was added.

    :param loop: The event loop to use.
    :type loop: :class:`asyncio.BaseEventLoop`
    :param protocol_factory: Factory for the protocol for the connection
    :param host: The host name or address to connect to
    :type host: :class:`str` or :data:`None`
    :param port: The port to connect to
    :type port: :class:`int` or :data:`None`
    :param sock: A socket to wrap (conflicts with `host` and `port`)
    :type sock: :class:`socket.socket`
    :param ssl_context_factory: Function which returns a
        :class:`OpenSSL.SSL.Context` to use for TLS operations
    :param use_starttls: Flag to control whether TLS is negotiated right away
        or deferredly.
    :type use_starttls: :class:`bool`
    :param local_addr: Address to bind to

    This is roughly a copy of the asyncio implementation of
    :meth:`asyncio.BaseEventLoop.create_connection`. It returns a pair
    ``(transport, protocol)``, where `transport` is a newly created
    :class:`STARTTLSTransport` instance. Further keyword arguments are
    forwarded to the constructor of :class:`STARTTLSTransport`.

    `loop` must be a :class:`asyncio.BaseEventLoop`, with support for
    :meth:`asyncio.BaseEventLoop.add_reader` and the corresponding writer and
    removal functions for sockets. This is typically a selector type event
    loop.

    `protocol_factory` must be a callable which (without any arguments) returns
    a :class:`asyncio.Protocol` which will be connected to the STARTTLS
    transport.

    `host` and `port` must be a hostname and a port number, or both
    :data:`None`. Both must be :data:`None`, if and only if `sock` is not
    :data:`None`. In that case, `sock` is used instead of a newly created
    socket. `sock` is put into non-blocking mode and must be a stream socket.

    If `use_starttls` is :data:`True`, no TLS handshake will be performed
    initially. Instead, the connection is established without any
    transport-layer security. It is expected that the
    :meth:`STARTTLSTransport.starttls` method is used when the application
    protocol requires TLS. If `use_starttls` is :data:`False`, the TLS
    handshake is initiated right away.

    `local_addr` may be an address to bind this side of the socket to. If
    omitted or :data:`None`, the local address is assigned by the operating
    system.

    This coroutine returns when the stream is established. If `use_starttls` is
    :data:`False`, this means that the full TLS handshake has to be finished
    for this coroutine to return. Otherwise, no TLS handshake takes place. It
    must be invoked using the :meth:`STARTTLSTransport.starttls` coroutine.
    """

    if host is not None and port is not None:
        host_addrs = await loop.getaddrinfo(
            host, port,
            type=socket.SOCK_STREAM,
        )

        exceptions = []

        for family, type, proto, cname, address in host_addrs:
            sock = None
            try:
                sock = socket.socket(family=family, type=type, proto=proto)
                sock.setblocking(False)
                if local_addr is not None:
                    sock.bind(local_addr)
                await loop.sock_connect(sock, address)
            except OSError as exc:
                if sock is not None:
                    sock.close()
                exceptions.append(exc)
            else:
                break
        else:
            if len(exceptions) == 1:
                raise exceptions[0]

            model = str(exceptions[0])
            if all(str(exc) == model for exc in exceptions):
                raise exceptions[0]

            try:
                from aioxmpp.errors import MultiOSError  # type:ignore
            except ImportError:
                MultiOSError = OSError

            raise MultiOSError(
                "could not connect to [{}]:{}".format(host, port),
                exceptions,
            )
    elif sock is None:
        raise ValueError("sock must not be None if host and/or port are None")
    else:
        sock.setblocking(False)

    protocol = protocol_factory()
    waiter = asyncio.Future(loop=loop)  # type: asyncio.Future[None]
    transport = STARTTLSTransport(loop, sock, protocol,
                                  ssl_context_factory=ssl_context_factory,
                                  waiter=waiter,
                                  use_starttls=use_starttls,
                                  **kwargs)
    await waiter

    return transport, protocol