Request a new channel to the server. `Channels <.Channel>` are
        socket-like objects used for the actual transfer of data across the
        session. You may only request a channel after negotiating encryption
        (using `connect` or `start_client`) and authenticating.

        .. note:: Modifying the the window and packet sizes might have adverse
            effects on the channel created. The default values are the same
            as in the OpenSSH code base and have been battle tested.

        :param str kind:
            the kind of channel requested (usually ``"session"``,
            ``"forwarded-tcpip"``, ``"direct-tcpip"``, or ``"x11"``)
        :param tuple dest_addr:
            the destination address (address + port tuple) of this port
            forwarding, if ``kind`` is ``"forwarded-tcpip"`` or
            ``"direct-tcpip"`` (ignored for other channel types)
        :param src_addr: the source address of this port forwarding, if
            ``kind`` is ``"forwarded-tcpip"``, ``"direct-tcpip"``, or ``"x11"``
        :param int window_size:
            optional window size for this session.
        :param int max_packet_size:
            optional max packet size for this session.
        :param float timeout:
            optional timeout opening a channel, default 3600s (1h)

        :return: a new `.Channel` on success

        :raises:
            `.SSHException` -- if the request is rejected, the session ends
            prematurely or there is a timeout openning a channel

        .. versionchanged:: 1.15
            Added the ``window_size`` and ``max_packet_size`` arguments.

def open_channel(
        self,
        kind,
        dest_addr=None,
        src_addr=None,
        window_size=None,
        max_packet_size=None,
        timeout=None,
    ):
        """
        Request a new channel to the server. `Channels <.Channel>` are
        socket-like objects used for the actual transfer of data across the
        session. You may only request a channel after negotiating encryption
        (using `connect` or `start_client`) and authenticating.

        .. note:: Modifying the the window and packet sizes might have adverse
            effects on the channel created. The default values are the same
            as in the OpenSSH code base and have been battle tested.

        :param str kind:
            the kind of channel requested (usually ``"session"``,
            ``"forwarded-tcpip"``, ``"direct-tcpip"``, or ``"x11"``)
        :param tuple dest_addr:
            the destination address (address + port tuple) of this port
            forwarding, if ``kind`` is ``"forwarded-tcpip"`` or
            ``"direct-tcpip"`` (ignored for other channel types)
        :param src_addr: the source address of this port forwarding, if
            ``kind`` is ``"forwarded-tcpip"``, ``"direct-tcpip"``, or ``"x11"``
        :param int window_size:
            optional window size for this session.
        :param int max_packet_size:
            optional max packet size for this session.
        :param float timeout:
            optional timeout opening a channel, default 3600s (1h)

        :return: a new `.Channel` on success

        :raises:
            `.SSHException` -- if the request is rejected, the session ends
            prematurely or there is a timeout openning a channel

        .. versionchanged:: 1.15
            Added the ``window_size`` and ``max_packet_size`` arguments.
        """
        if not self.active:
            raise SSHException("SSH session not active")
        timeout = 3600 if timeout is None else timeout
        self.lock.acquire()
        try:
            window_size = self._sanitize_window_size(window_size)
            max_packet_size = self._sanitize_packet_size(max_packet_size)
            chanid = self._next_channel()
            m = Message()
            m.add_byte(cMSG_CHANNEL_OPEN)
            m.add_string(kind)
            m.add_int(chanid)
            m.add_int(window_size)
            m.add_int(max_packet_size)
            if (kind == "forwarded-tcpip") or (kind == "direct-tcpip"):
                m.add_string(dest_addr[0])
                m.add_int(dest_addr[1])
                m.add_string(src_addr[0])
                m.add_int(src_addr[1])
            elif kind == "x11":
                m.add_string(src_addr[0])
                m.add_int(src_addr[1])
            chan = Channel(chanid)
            self._channels.put(chanid, chan)
            self.channel_events[chanid] = event = threading.Event()
            self.channels_seen[chanid] = True
            chan._set_transport(self)
            chan._set_window(window_size, max_packet_size)
        finally:
            self.lock.release()
        self._send_user_message(m)
        start_ts = time.time()
        while True:
            event.wait(0.1)
            if not self.active:
                e = self.get_exception()
                if e is None:
                    e = SSHException("Unable to open channel.")
                raise e
            if event.is_set():
                break
            elif start_ts + timeout < time.time():
                raise SSHException("Timeout opening channel.")
        chan = self._channels.get(chanid)
        if chan is not None:
            return chan
        e = self.get_exception()
        if e is None:
            e = SSHException("Unable to open channel.")
        raise e