# Source code for aioxmpp.node

    ########################################################################
    # File name: node.py
    # This file is part of: aioxmpp
    #
    # LICENSE
    #
    # This program is free software: you can redistribute it and/or modify
    # it under the terms of the GNU Lesser General Public License as
    # published by the Free Software Foundation, either version 3 of the
    # License, or (at your option) any later version.
    #
    # This program is distributed in the hope that it will be useful, but
    # WITHOUT ANY WARRANTY; without even the implied warranty of
    # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    # Lesser General Public License for more details.
    #
    # You should have received a copy of the GNU Lesser General Public
    # License along with this program.  If not, see
    # <http://www.gnu.org/licenses/>.
    #
    ########################################################################
    """
    :mod:`~aioxmpp.node` --- XMPP network nodes (clients, mostly)
    #############################################################

    This module contains functions to connect to an XMPP server, as well as
    maintaining the stream. In addition, a client class which completely manages a
    stream based on a presence setting is provided.

    Using XMPP
    ==========

    .. currentmodule:: aioxmpp

    .. autoclass:: Client

    .. autoclass:: PresenceManagedClient

    .. currentmodule:: aioxmpp.node

    .. class:: AbstractClient

       Alias of :class:`Client`.

       .. deprecated:: 0.8

          The alias will be removed in 1.0.

    Connecting streams low-level
    ============================

    .. autofunction:: discover_connectors

    .. autofunction:: connect_xmlstream

    Utilities
    =========

    .. autoclass:: UseConnected

    """
    import asyncio
    import contextlib
    import logging
    import warnings

    from datetime import timedelta

    import dns.resolver

    import OpenSSL.SSL

    import aiosasl

    from . import (
        connector,
        network,
        protocol,
        errors,
        stream,
        callbacks,
        nonza,
        rfc3921,
        rfc6120,
        stanza,
        structs,
        security_layer,
        dispatcher,
        presence as mod_presence,
    )

    logger = logging.getLogger(__name__)

    async def lookup_addresses(loop, jid):
        addresses = await network.find_xmpp_host_addr(
            loop,
            jid.domain)

        return network.group_and_order_srv_records(addresses)

    async def discover_connectors(domain: str, loop=None, logger=logger):
        """
        Discover all connection options for a domain, in descending order of
        preference.

        This coroutine returns options discovered from SRV records, or if none are
        found, the generic option using the domain name and the default XMPP client
        port.

        Each option is represented by a triple ``(host, port, connector)``.
        `connector` is a :class:`aioxmpp.connector.BaseConnector` instance which is
        suitable to connect to the given host and port.

        `logger` is the logger used by the function.

        The following sources are supported:

        * :rfc:`6120` SRV records. One option is returned per SRV record.

          If one of the SRV records points to the root name (``.``),
          :class:`ValueError` is raised (the domain specifically said that XMPP is
          not supported here).

        * :xep:`368` SRV records. One option is returned per SRV record.

        * :rfc:`6120` fallback process (only if no SRV records are found). One
          option is returned for the host name with the default XMPP client port.

        The options discovered from SRV records are mixed together, ordered by
        priority and then within priorities are shuffled according to their weight.
        Thus, if there are multiple records of equal priority, the result of the
        function is not deterministic.

        .. versionadded:: 0.6
        """

        domain_encoded = domain.encode("idna") + b"."
        starttls_srv_failed = False
        tls_srv_failed = False

        try:
            starttls_srv_records = await network.lookup_srv(
                domain_encoded,
                "xmpp-client",
            )
            starttls_srv_disabled = False
        except dns.resolver.NoNameservers as exc:
            starttls_srv_records = []
            starttls_srv_disabled = False
            starttls_srv_failed = True
            starttls_srv_exc = exc
            logger.debug("xmpp-client SRV lookup for domain %s failed "
                         "(may not be fatal)",
                         domain_encoded,
                         exc_info=True)
        except ValueError:
            starttls_srv_records = []
            starttls_srv_disabled = True

        try:
            tls_srv_records = await network.lookup_srv(
                domain_encoded,
                "xmpps-client",
            )
            tls_srv_disabled = False
        except dns.resolver.NoNameservers:
            tls_srv_records = []
            tls_srv_disabled = False
            tls_srv_failed = True
            logger.debug("xmpps-client SRV lookup for domain %s failed "
                         "(may not be fatal)",
                         domain_encoded,
                         exc_info=True)
        except ValueError:
            tls_srv_records = []
            tls_srv_disabled = True

        if starttls_srv_failed and (tls_srv_failed or tls_srv_records is None):
            # the failure is probably more useful as a diagnostic
            # if we find a good reason to allow this scenario, we might change it
            # later.
            raise starttls_srv_exc

        if starttls_srv_disabled and (tls_srv_disabled or tls_srv_records is None):
            raise ValueError(
                "XMPP not enabled on domain {!r}".format(domain),
            )

        if starttls_srv_records is None and tls_srv_records is None:
            # no SRV records published, fall back
            logger.debug(
                "no SRV records found for %s, falling back",
                domain,
            )
            return [
                (domain, 5222, connector.STARTTLSConnector()),
            ]

        starttls_srv_records = starttls_srv_records or []
        tls_srv_records = tls_srv_records or []

        srv_records = [
            (prio, weight, (host.decode("ascii"), port,
                            connector.STARTTLSConnector()))
            for prio, weight, (host, port) in starttls_srv_records
        ]

        srv_records.extend(
            (prio, weight, (host.decode("ascii"), port,
                            connector.XMPPOverTLSConnector()))
            for prio, weight, (host, port) in tls_srv_records
        )

        options = list(
            network.group_and_order_srv_records(srv_records)
        )

        logger.debug(
            "options for %s: %r",
            domain,
            options,
        )

        return options

    async def _try_options(options, exceptions,
                           jid, metadata, negotiation_timeout, loop, logger):
        """
        Helper function for :func:`connect_xmlstream`.
        """
        for host, port, conn in options:
            logger.debug(
                "domain %s: trying to connect to %r:%s using %r",
                jid.domain, host, port, conn
            )
            try:
                transport, xmlstream, features = await conn.connect(
                    loop,
                    metadata,
                    jid.domain,
                    host,
                    port,
                    negotiation_timeout,
                    base_logger=logger,
                )
            except OSError as exc:
                logger.warning(
                    "connection failed: %s", exc
                )
                exceptions.append(exc)
                continue

            logger.debug(
                "domain %s: connection succeeded using %r",
                jid.domain,
                conn,
            )

            if not metadata.sasl_providers:
                return transport, xmlstream, features

            try:
                features = await security_layer.negotiate_sasl(
                    transport,
                    xmlstream,
                    metadata.sasl_providers,
                    negotiation_timeout=None,
                    jid=jid,
                    features=features,
                )
            except errors.SASLUnavailable as exc:
                protocol.send_stream_error_and_close(
                    xmlstream,
                    condition=errors.StreamErrorCondition.POLICY_VIOLATION,
                    text=str(exc),
                )
                exceptions.append(exc)
                continue
            except Exception as exc:
                protocol.send_stream_error_and_close(
                    xmlstream,
                    condition=errors.StreamErrorCondition.UNDEFINED_CONDITION,
                    text=str(exc),
                )
                raise

            return transport, xmlstream, features

        return None

    async def connect_xmlstream(
            jid,
            metadata,
            negotiation_timeout=60.,
            override_peer=[],
            loop=None,
            logger=logger):
        """
        Prepare and connect a :class:`aioxmpp.protocol.XMLStream` to a server
        responsible for the given `jid` and authenticate against that server using
        the SASL mechanisms described in `metadata`.

        :param jid: Address of the user for which the connection is made.
        :type jid: :class:`aioxmpp.JID`
        :param metadata: Connection metadata for configuring the TLS usage.
        :type metadata: :class:`~.security_layer.SecurityLayer`
        :param negotiation_timeout: Timeout for each individual negotiation step.
        :type negotiation_timeout: :class:`float` in seconds
        :param override_peer: Sequence of connection options which take precedence
                              over normal discovery methods.
        :type override_peer: sequence of (:class:`str`, :class:`int`,
                             :class:`~.BaseConnector`) triples
        :param loop: asyncio event loop to use (defaults to current)
        :type loop: :class:`asyncio.BaseEventLoop`
        :param logger: Logger to use (defaults to module-wide logger)
        :type logger: :class:`logging.Logger`
        :raises ValueError: if the domain from the `jid` announces that XMPP is not
                            supported at all.
        :raises aioxmpp.errors.TLSFailure: if all connection attempts fail and one
                                           of them is a :class:`~.TLSFailure`.
        :raises aioxmpp.errors.MultiOSError: if all connection attempts fail.
        :return: Transport, XML stream and the current stream features
        :rtype: tuple of (:class:`asyncio.BaseTransport`, :class:`~.XMLStream`,
                :class:`~.nonza.StreamFeatures`)

        The part of the `metadata` specifying the use of TLS is applied. If the
        security layer does not mandate TLS, the resulting XML stream may not be
        using TLS. TLS is used whenever possible.

        The connection options in `override_peer` are tried before any standardised
        discovery of connection options is made. Only if all of them fail,
        automatic discovery of connection options is performed.

        `loop` may be a :class:`asyncio.BaseEventLoop` to use. Defaults to the
        current event loop.

        If the domain from the `jid` announces that XMPP is not supported at all,
        :class:`ValueError` is raised. If no options are returned from
        :func:`discover_connectors` and `override_peer` is empty,
        :class:`ValueError` is raised, too.

        If all connection attempts fail, :class:`aioxmpp.errors.MultiOSError` is
        raised. The error contains one exception for each of the options discovered
        as well as the elements from `override_peer` in the order they were tried.

        A TLS problem is treated like any other connection problem and the other
        connection options are considered. However, if *all* connection options
        fail and the set of encountered errors includes a TLS error, the TLS error
        is re-raised instead of raising a :class:`aioxmpp.errors.MultiOSError`.

        Return a triple ``(transport, xmlstream, features)``. `transport`
        the underlying :class:`asyncio.Transport` which is used for the `xmlstream`
        :class:`~.protocol.XMLStream` instance. `features` is the
        :class:`aioxmpp.nonza.StreamFeatures` instance describing the features of
        the stream.

        .. versionadded:: 0.6

        .. versionchanged:: 0.8

           The explicit raising of TLS errors has been introduced. Before, TLS
           errors were treated like any other connection error, possibly masking
           configuration problems.
        """
        loop = asyncio.get_event_loop() if loop is None else loop

        options = list(override_peer)

        exceptions = []

        result = await _try_options(
            options,
            exceptions,
            jid, metadata, negotiation_timeout, loop, logger,
        )
        if result is not None:
            return result

        options = list(await discover_connectors(
            jid.domain,
            loop=loop,
            logger=logger,
        ))

        result = await _try_options(
            options,
            exceptions,
            jid, metadata, negotiation_timeout, loop, logger,
        )
        if result is not None:
            return result

        if not options and not override_peer:
            raise ValueError("no options to connect to XMPP domain {!r}".format(
                jid.domain
            ))

        for exc in exceptions:
            if isinstance(exc, errors.TLSFailure):
                raise exc

        raise errors.MultiOSError(
            "failed to connect to XMPP domain {!r}".format(jid.domain),
            exceptions
        )

    class Client:
        """
        Base class to implement an XMPP client.

        Args:
            local_jid (:class:`~aioxmpp.JID`): Jabber ID to connect as.
            security_layer (:class:`~aioxmpp.SecurityLayer`): Configuration
                for authentication and TLS.
            negotiation_timeout (:class:`datetime.timedelta`): Timeout for the
                individual stream negotiation steps (bounds initial connect time)
            override_peer: Connection options which take precedence over the
                standardised connection options
            max_inital_attempts (:class:`int`): Maximum number of initial
                connection attempts before giving up.
            loop (:class:`asyncio.BaseEventLoop` or :data:`None`): Override the
                :mod:`asyncio` event loop to use.
            logger (:class:`logging.Logger` or :data:`None`): Override the logger
                to use.

        These classes deal with managing the :class:`~aioxmpp.stream.StanzaStream`
        and the underlying :class:`~aioxmpp.protocol.XMLStream` instances. The
        abstract client provides functionality for connecting the xmlstream as well
        as signals which indicate changes in the stream state.

        The `security_layer` is best created using the
        :func:`aioxmpp.security_layer.make` function and must provide
        authentication for the given `local_jid`.

        If `loop` is given, it must be a :class:`asyncio.BaseEventLoop`
        instance. If it is not given, the current event loop is used.

        As a glue between the stanza stream and the XML stream, it also knows about
        stream management and performs stream management negotiation. It is
        specialized on client operations, which implies that it will try to keep
        the stream alive as long as wished by the client.

        The client will attempt to connect to the server(s) associated with the
        `local_jid`, using the prioritised `override_peer` setting or the
        standardised options for connecting (see :meth:`discover_connectors`). The
        initial connection attempt must succeed within `max_initial_attempts`.

        If the connection breaks after the first connection attempt, the client
        will try to resume the connection transparently. If the server supports
        stream management (:xep:`198`) with resumption, this is entirely
        transparent to all operations over the stream. If the stream is not
        resumable or the resumption fails and `allow_implicit_reconnect` is true,
        the application and services using the stream are notified about that. If,
        in that situation, `allow_implicit_reconnect` is false instead, the client
        stops with an error.

        The number of reconnection attempts is generally unbounded. The application
        is notified that the stream got interrupted with the
        :meth:`on_stream_suspended` is emitted. After reconnection,
        :meth:`on_stream_established` is emitted (possibly preceded by a
        :meth:`on_stream_destroyed` emission if the stream failed to resume). If
        the application wishes to bound the time the stream tries to transparently
        reconnect, it should connect to the :meth:`on_stream_suspended` signal and
        stop the stream as needed.

        The reconnection attempts are throttled using expenential backoff
        controlled by the :attr:`backoff_start`, :attr:`backoff_factor` and
        :attr:`backoff_cap` attributes.

        .. note::

           If `max_initial_attempts` is :data:`None`, the stream will try
           indefinitely to connect to the server even if the connection has
           never succeeded yet. This is may mask problems with the configuration of
           the client itself, because the client cannot successfully distinguish
           permanent problems arising from the configuration (of the client or the
           server) from problems arising from transient problems such as network
           failures.

           This may severely degrade usabilty, because the client is then stuck in
           a connect loop without any usable feedback. Setting a bound for the
           initial connection attempt is usually better, for interactive
           applications an upper bound of 1 might make most sense (possibly the
           interactive application may retry on its own if the user did not
           indicate that they wish to do so after a timeout). We’ll leave the UX
           considerations up to you.

        .. versionchanged:: 0.4

           Since 0.4, support for legacy XMPP sessions has been implemented. Mainly
           for compatibility with ejabberd.

        .. versionchanged:: 0.8

           The amount of initial connection attempts is now bounded by
           `max_initial_attempts`. The :meth:`on_stream_suspended` signal and the
           associated logic has been introduced.

        Controlling the client:

        .. automethod:: connected

        .. automethod:: start

        .. automethod:: stop

        .. autoattribute:: running

        .. attribute:: negotiation_timeout
            :annotation: = timedelta(seconds=60)

            The timeout applied to the connection process and the individual steps
            of negotiating the stream. See the `negotiation_timeout` argument to
            :func:`connect_xmlstream`.

        .. attribute:: override_peer

           A sequence of triples ``(host, port, connector)``, where `host` must be
           a host name or IP as string, `port` must be a port number and
           `connector` must be a :class:`aioxmpp.connector.BaseConnctor` instance.

           These connection options are passed to :meth:`connect_xmlstream` and
           thus take precedence over the options discovered using
           :meth:`discover_connectors`.

           .. note::

              If Stream Management is used and the peer server provided a location
              to connect to on resumption, that location is preferred even over the
              options set here.

           .. versionadded:: 0.6

        .. autoattribute:: resumption_timeout
            :annotation: = None

        Connection information:

        .. autoattribute:: established

        .. attribute:: established_event

            An :class:`asyncio.Event` which indicates that the stream is
            established. A stream is valid after resource binding and before it has
            been destroyed.

            While this event is cleared, :meth:`enqueue` fails with
            :class:`ConnectionError` and :meth:`send` blocks.

        .. autoattribute:: suspended

        .. autoattribute:: local_jid

        .. attribute:: stream

           The :class:`~aioxmpp.stream.StanzaStream` instance used by the node.

        .. attribute:: stream_features

           An instance of :class:`~aioxmpp.nonza.StreamFeatures`. This is the
           most-recently received stream features information (the one received
           right before resource binding).

           While no stream has been established yet, this is :data:`None`. During
           transparent re-negotiation, that information may be obsolete. However,
           when :attr:`before_stream_established` fires, the information is
           up-to-date.

        Sending stanzas:

        .. automethod:: send

        .. automethod:: enqueue

        Configuration of exponential backoff for reconnects:

        .. attribute:: backoff_start
           :annotation: = timedelta(1)

           When an underlying XML stream fails due to connectivity issues (generic
           :class:`OSError` raised), exponential backoff takes place before
           attempting to reconnect.

           The initial time to wait before reconnecting is described by
           :attr:`backoff_start`.

        .. attribute:: backoff_factor
           :annotation: = 1.2

           Each subsequent time a connection fails, the previous backoff time is
           multiplied with :attr:`backoff_factor`.

        .. attribute:: backoff_cap
           :annotation: = timedelta(60)

           The backoff time is capped to :attr:`backoff_cap`, to avoid having
           unrealistically high values.

        Signals:

        .. signal:: on_failure(err)

           This signal is fired when the client fails and stops.

        .. syncsignal:: before_stream_established()

           This coroutine signal is executed right before
           :meth:`on_stream_established` fires.

        .. signal:: on_stopped()

           Fires when the client stops gracefully. This is the counterpart to
           :meth:`on_failure`.

        .. signal:: on_stream_established()

           When the stream is established and resource binding took place, this
           event is fired. It means that the stream can now be used for XMPP
           interactions.

        .. signal:: on_stream_suspended(reason)

           The stream has been suspened due to a connection failure.

           :param reason: The exception which terminated the stream.
           :type reason: :class:`Exception`

           This signal may be immediately followed by a
           :meth:`on_stream_destroyed`, if the stream did not support stream
           resumption. Otherwise, a new connection is attempted transparently.

           In general, this signal exists solely for informational purposes. It
           can be used to drive a user interface which indicates that messages may
           be delivered with delay, because the underlying network is transiently
           interrupted.

           :meth:`on_stream_suspended` is not emitted if the stream was stopped on
           user request.

           After :meth:`on_stream_suspended` is emitted, one of the two following
           signals is emitted:

           - :meth:`on_stream_destroyed` indicates that state was actually lost and
             that others most likely see or saw an unavailable presence broadcast
             for the resource.
           - :meth:`on_stream_resumed` indicates that no state was lost and the
             stream is fully usable again.

           .. versionadded:: 0.8

        .. signal:: on_stream_resumed()

            The stream has been resumed after it has been suspended, without loss
            of data.

            This is the counterpart to :meth:`on_stream_suspended`.

            In general, this signal exists solely for informational purposes. It
            can be used to drive a user interface which indicates that messages may
            be delivered with delay, because the underlying network is transiently
            interrupted.

            .. versionadded:: 0.11

        .. signal:: on_stream_destroyed(reason=None)

           This is called whenever a stream is destroyed. The conditions for this
           are the same as for
           :attr:`aioxmpp.stream.StanzaStream.on_stream_destroyed`.

           :param reason: An optional exception which indicates the reason for the
                          destruction of the stream.
           :type reason: :class:`Exception`

           This event can be used to know when to discard all state about the XMPP
           connection, such as roster information. Services implemented in
           :mod:`aioxmpp` generally subscribe to this signal to discard cached
           state.

           `reason` is optional. It is given if there is has been a specific
           exception which describes the cause for the stream destruction, such as
           a :class:`ConnectionError`.

           .. versionchanged:: 0.8

              The `reason` argument was added.

        Services:

        .. automethod:: summon

        Miscellaneous:

        .. attribute:: logger

           The :class:`logging.Logger` instance which is used by the
           :class:`Client`. This is the `logger` passed to the constructor or a
           logger derived from the fully qualified name of the class.

           .. versionadded:: 0.6

              The :attr:`logger` attribute was added.

        """

        on_failure = callbacks.Signal()
        on_stopped = callbacks.Signal()
        on_stream_destroyed = callbacks.Signal()
        on_stream_suspended = callbacks.Signal()
        on_stream_resumed = callbacks.Signal()
        on_stream_established = callbacks.Signal()

        before_stream_established = callbacks.SyncSignal()

        def __init__(self,
                     local_jid,
                     security_layer,
                     *,
                     negotiation_timeout=timedelta(seconds=60),
                     max_initial_attempts=4,
                     override_peer=[],
                     loop=None,
                     logger=None):
            super().__init__()
            self._local_jid = local_jid
            self._loop = loop or asyncio.get_event_loop()
            self._main_task = None
            self._security_layer = security_layer

            self._failure_future = asyncio.Future()
            self.logger = (logger or
                           logging.getLogger(".".join([
                               type(self).__module__,
                               type(self).__qualname__,
                           ])))

            self._backoff_time = None

            self._is_suspended = False

            # track whether the connection succeeded *at least once*
            # used to enforce max_initial_attempts
            self._had_connection = False
            self._nattempt = 0

            self._services = {}

            self.stream_features = None

            self.negotiation_timeout = negotiation_timeout
            self.backoff_start = timedelta(seconds=1)
            self.backoff_factor = 1.2
            self.backoff_cap = timedelta(seconds=60)
            self.override_peer = list(override_peer)
            self.established_event = asyncio.Event()
            self._max_initial_attempts = max_initial_attempts
            self._resumption_timeout = None

            self.on_stopped.logger = self.logger.getChild("on_stopped")
            self.on_failure.logger = self.logger.getChild("on_failure")
            self.on_stream_established.logger = \
                self.logger.getChild("on_stream_established")
            self.on_stream_destroyed.logger = \
                self.logger.getChild("on_stream_destroyed")
            self.on_stream_suspended.logger = \
                self.logger.getChild("on_stream_suspended")

            if logger is not None:
                stream_base_logger = self.logger
            else:
                stream_base_logger = logging.getLogger("aioxmpp")
            self.stream = stream.StanzaStream(
                local_jid.bare(),
                base_logger=stream_base_logger
            )

            self.stream._xxx_message_dispatcher = self.summon(
                dispatcher.SimpleMessageDispatcher,
            )

            self.stream._xxx_presence_dispatcher = self.summon(
                dispatcher.SimplePresenceDispatcher,
            )

            def send_warner(*args, **kwargs):
                warnings.warn("send() on StanzaStream is deprecated and will "
                              "be removed in 1.0. Use send() on the Client "
                              "instead.",
                              DeprecationWarning,
                              stacklevel=1)
                return self.send(*args, **kwargs)

            self.stream.send = send_warner

            def enqueue_warner(*args, **kwargs):
                warnings.warn("enqueue() on StanzaStream is deprecated and will "
                              "be removed in 1.0. Use enqueue() on the Client "
                              "instead.",
                              DeprecationWarning,
                              stacklevel=1)
                return self.enqueue(*args, **kwargs)

            self.stream.enqueue = enqueue_warner

        def _stream_failure(self, exc):
            if self._failure_future.done():
                self.logger.warning(
                    "something is odd: failure future is already done ..."
                )
                return

            if not self._is_suspended:
                self.on_stream_suspended(exc)
                self._is_suspended = True

            self._failure_future.set_result(exc)
            self._failure_future = asyncio.Future()

        def _stream_destroyed(self, reason):
            if not self._is_suspended:
                if not isinstance(reason, stream.DestructionRequested):
                    self.on_stream_suspended(reason)
                self._is_suspended = True

            if self.established_event.is_set():
                self.established_event.clear()
                self.on_stream_destroyed()

        def _on_main_done(self, task):
            try:
                task.result()
            except asyncio.CancelledError:
                # task terminated normally
                self.on_stopped()
            except Exception as err:
                self.logger.exception("main failed")
                self.on_failure(err)

        async def _try_resume_stream_management(self, xmlstream, features):
            try:
                await self.stream.resume_sm(xmlstream)
            except errors.StreamNegotiationFailure as exc:
                self.logger.warning("failed to resume stream (%s)", exc)
                return False
            return True

        async def _negotiate_legacy_session(self):
            self.logger.debug(
                "remote server announces support for legacy sessions"
            )
            await self.stream._send_immediately(
                stanza.IQ(type_=structs.IQType.SET,
                          payload=rfc3921.Session())
            )
            self.logger.debug(
                "legacy session negotiated (upgrade your server!)"
            )

        async def _negotiate_stream(self, xmlstream, features):
            server_can_do_sm = True
            try:
                features[nonza.StreamManagementFeature]
            except KeyError:
                if self.stream.sm_enabled:
                    self.logger.warning("server isn’t advertising SM anymore")
                    self.stream.stop_sm()
                server_can_do_sm = False

            self.logger.debug("negotiating stream (server_can_do_sm=%s)",
                              server_can_do_sm)

            if self.stream.sm_enabled:
                resumed = await self._try_resume_stream_management(
                    xmlstream, features)
                if resumed:
                    return features, resumed
            else:
                resumed = False

            self.stream_features = features
            self.stream.start(xmlstream)

            if not resumed:
                self.logger.debug("binding to resource")
                await self._bind()

            if server_can_do_sm:
                self.logger.debug("attempting to start stream management")
                try:
                    await self.stream.start_sm(
                        resumption_timeout=self._resumption_timeout
                    )
                except errors.StreamNegotiationFailure:
                    self.logger.debug("stream management failed to start")
                self.logger.debug("stream management started")

            try:
                session_feature = features[rfc3921.SessionFeature]
            except KeyError:
                pass  # yay
            else:
                if not session_feature.optional:
                    await self._negotiate_legacy_session()
                else:
                    self.logger.debug(
                        "skipping optional legacy session negotiation"
                    )

            self.established_event.set()

            await self.before_stream_established()

            self.on_stream_established()

            return features, resumed

        async def _bind(self):
            iq = stanza.IQ(type_=structs.IQType.SET)
            iq.payload = rfc6120.Bind(resource=self._local_jid.resource)
            try:
                result = await self.stream._send_immediately(iq)
            except errors.XMPPError as exc:
                raise errors.StreamNegotiationFailure(
                    "Resource binding failed: {}".format(exc)
                )

            self._local_jid = result.jid
            self.stream.local_jid = result.jid.bare()
            self.logger.info("bound to jid: %s", self._local_jid)

        async def _main_impl(self):
            failure_future = self._failure_future

            override_peer = []
            if self.stream.sm_enabled:
                sm_location = self.stream.sm_location
                if sm_location:
                    override_peer.append((
                        str(sm_location[0]),
                        sm_location[1],
                        connector.STARTTLSConnector(),
                    ))
            override_peer += self.override_peer

            tls_transport, xmlstream, features = await connect_xmlstream(
                    self._local_jid,
                    self._security_layer,
                    negotiation_timeout=self.negotiation_timeout.total_seconds(),
                    override_peer=override_peer,
                    loop=self._loop,
                    logger=self.logger)

            self._had_connection = True

            try:
                features, sm_resumed = await self._negotiate_stream(
                    xmlstream,
                    features)

                if self._is_suspended:
                    self.on_stream_resumed()
                self._is_suspended = False
                self._backoff_time = None

                exc = await failure_future
                self.logger.error("stream failed: %s", exc)
                raise exc
            except asyncio.CancelledError:
                self.logger.info("client shutting down (on request)")
                # cancelled, this means a clean shutdown is requested
                await self.stream.close()
                raise
            finally:
                self.logger.info("stopping stream")
                self.stream.stop()

        async def _main(self):
            with contextlib.ExitStack() as stack:
                stack.enter_context(
                    self.stream.on_failure.context_connect(self._stream_failure)
                )
                stack.enter_context(
                    self.stream.on_stream_destroyed.context_connect(
                        self._stream_destroyed)
                )
                while True:
                    self._nattempt += 1
                    self._failure_future = asyncio.Future()
                    try:
                        await self._main_impl()
                    except errors.StreamError as err:
                        if err.condition == errors.StreamErrorCondition.CONFLICT:
                            self.logger.debug("conflict!")
                            raise
                    except (errors.StreamNegotiationFailure,
                            aiosasl.SASLError):
                        if self.stream.sm_enabled:
                            self.stream.stop_sm()
                        raise
                    except (OSError, dns.resolver.NoNameservers,
                            OpenSSL.SSL.Error) as exc:
                        self.logger.info("connection error: (%s) %s",
                                         type(exc).__qualname__,
                                         exc)
                        if (not self._had_connection and
                                self._max_initial_attempts is not None and
                                self._nattempt >= self._max_initial_attempts):
                            self.logger.warning("out of connection attempts")
                            raise

                        if self._backoff_time is None:
                            self._backoff_time = self.backoff_start.total_seconds()
                        self.logger.debug("re-trying after %.1f seconds",
                                          self._backoff_time)
                        await asyncio.sleep(self._backoff_time)
                        self._backoff_time *= self.backoff_factor
                        if self._backoff_time > self.backoff_cap.total_seconds():
                            self._backoff_time = self.backoff_cap.total_seconds()
                        continue  # retry

        def start(self):
            """
            Start the client. If it is already :attr:`running`,
            :class:`RuntimeError` is raised.

            While the client is running, it will try to keep an XMPP connection
            open to the server associated with :attr:`local_jid`.
            """
            if self.running:
                raise RuntimeError("client already running")

            self._main_task = asyncio.ensure_future(
                self._main(),
                loop=self._loop
            )
            self._main_task.add_done_callback(self._on_main_done)

        def stop(self):
            """
            Stop the client. This sends a signal to the clients main task which
            makes it terminate.

            It may take some cycles through the event loop to stop the client
            task. To check whether the task has actually stopped, query
            :attr:`running`.
            """
            if not self.running:
                return

            self.logger.debug("stopping main task of %r", self, stack_info=True)
            self._main_task.cancel()

        def _summon(self, class_, visited):
            # this is essentially a topological sort algorithm
            try:
                return self._services[class_]
            except KeyError:
                if class_ in visited:
                    raise ValueError("dependency loop")
                visited.add(class_)

                # summon dependencies before taking len(self._services) as
                # the instantiation index of the service
                dependencies = {
                    depclass: self._summon(depclass, visited)
                    for depclass in class_.PATCHED_ORDER_AFTER
                }

                service_order_index = len(self._services)

                instance = class_(
                    self,
                    logger_base=self.logger,
                    dependencies=dependencies,
                    service_order_index=service_order_index,
                )
                self._services[class_] = instance
                return instance

        def summon(self, class_):
            """
            Summon a :class:`~aioxmpp.service.Service` for the client.

            If the `class_` has already been summoned for the client, it’s instance
            is returned.

            Otherwise, all requirements for the class are first summoned (if they
            are not there already). Afterwards, the class itself is summoned and
            the instance is returned.
            """
            return self._summon(class_, set())

        # properties

        @property
        def local_jid(self):
            """
            The :class:`~aioxmpp.JID` the client currently has. While the
            client is disconnected, which parts of the :attr:`local_jid` can be
            relied upon depends on the authentication mechanism used. For example,
            using anonymous authentication, the server dictates even the local part
            of the JID and it will change after a reconnect. For more common
            authentication schemes (such as normal password-based authentication),
            the localpart is usually chosen by the client.

            For interoperability with different authentication schemes, code must
            invalidate all copies of this attribute when a
            :meth:`on_stream_established` or :meth:`on_stream_destroyed` event is
            emitted.

            Writing this attribute is not allowed, as changing the JID introduces a
            lot of issues with respect to reusability of the stream. Instantiate a
            new :class:`Client` if you need to change the bare part of the JID.

            .. note::

               Changing the resource between reconnects may be allowed later.
            """
            return self._local_jid

        @property
        def running(self):
            """
            true if the client is currently running, false otherwise.
            """
            return self._main_task is not None and not self._main_task.done()

        @property
        def established(self):
            """
            true if the stream is currently established (as defined in
            :attr:`on_stream_established`) and false otherwise.
            """
            return self.established_event.is_set()

        @property
        def suspended(self):
            """
            true if the stream is currently suspended (see
            :meth:`on_stream_suspended`)

            .. versionadded:: 0.11
            """
            return self._is_suspended

        @property
        def resumption_timeout(self):
            """
            The maximum time as integer in seconds for which the server shall hold
            on to the session if the underlying transport breaks.

            This is only relevant if the server supports
            :xep:`Stream Management <198>` and the server may ignore the request
            for a maximum timeout and/or impose its own maximum. After the
            stream has been negotiated, :attr:`.StanzaStream.sm_max` holds the
            actual timeout announced by the server (may be :data:`None` if the
            server did not specify a timeout).

            The default value of :data:`None` does not request any specific
            timeout from the server and leaves it up to the server to decide.

            Setting a :attr:`resumption_timeout` of zero (0) disables resumption.

            .. versionadded:: 0.9
            """
            return self._resumption_timeout

        @resumption_timeout.setter
        def resumption_timeout(self, value):
            if (value is not None and
                    (not isinstance(value, int) or isinstance(value, bool))):
                raise TypeError(
                    "resumption_timeout must be int or None, got {!r}".format(
                        value
                    )
                )
            if value is not None and value < 0:
                raise ValueError(
                    "resumption timeout must be non-negative or None"
                )
            self._resumption_timeout = value

        def connected(self, *, presence=structs.PresenceState(False), **kwargs):
            """
            Return a :class:`.node.UseConnected` context manager which does not
            modify the presence settings.

            The keyword arguments are passed to the :class:`.node.UseConnected`
            context manager constructor.

            .. versionadded:: 0.8
            """
            return UseConnected(self, presence=presence, **kwargs)

        def enqueue(self, stanza, **kwargs):
            """
            Put a `stanza` in the internal transmission queue and return a token to
            track it.

            :param stanza: Stanza to send
            :type stanza: :class:`IQ`, :class:`Message` or :class:`Presence`
            :param kwargs: see :class:`StanzaToken`
            :raises ConnectionError: if the stream is not :attr:`established`
                yet.
            :return: token which tracks the stanza
            :rtype: :class:`StanzaToken`

            The `stanza` is enqueued in the active queue for transmission and will
            be sent on the next opportunity. The relative ordering of stanzas
            enqueued is always preserved.

            Return a fresh :class:`StanzaToken` instance which traks the progress
            of the transmission of the `stanza`. The `kwargs` are forwarded to the
            :class:`StanzaToken` constructor.

            This method calls :meth:`~.stanza.StanzaBase.autoset_id` on the stanza
            automatically.

            .. seealso::

               :meth:`send`
                  for a more high-level way to send stanzas.

            .. versionchanged:: 0.10

                This method has been moved from
                :meth:`aioxmpp.stream.StanzaStream.enqueue`.
            """
            if not self.established_event.is_set():
                raise ConnectionError("stream is not ready")

            return self.stream._enqueue(stanza, **kwargs)

        async def send(self, stanza, *, timeout=None, cb=None):
            """
            Send a stanza.

            :param stanza: Stanza to send
            :type stanza: :class:`~.IQ`, :class:`~.Presence` or :class:`~.Message`
            :param timeout: Maximum time in seconds to wait for an IQ response, or
                            :data:`None` to disable the timeout.
            :type timeout: :class:`~numbers.Real` or :data:`None`
            :param cb: Optional callback which is called synchronously when the
                reply is received (IQ requests only!)
            :raise OSError: if the underlying XML stream fails and stream
                management is not disabled.
            :raise aioxmpp.stream.DestructionRequested:
               if the stream is closed while sending the stanza or waiting for a
               response.
            :raise aioxmpp.errors.XMPPError: if an error IQ response is received
            :raise aioxmpp.errors.ErroneousStanza: if the IQ response could not be
                parsed
            :raise ValueError: if `cb` is given and `stanza` is not an IQ request.
            :return: IQ response :attr:`~.IQ.payload` or :data:`None`

            Send the stanza and wait for it to be sent. If the stanza is an IQ
            request, the response is awaited and the :attr:`~.IQ.payload` of the
            response is returned.

            If the stream is currently not ready, this method blocks until the
            stream is ready to send payload stanzas. Note that this may be before
            initial presence has been sent. To synchronise with that type of
            events, use the appropriate signals.

            The `timeout` as well as any of the exception cases referring to a
            "response" do not apply for IQ response stanzas, message stanzas or
            presence stanzas sent with this method, as this method only waits for
            a reply if an IQ *request* stanza is being sent.

            If `stanza` is an IQ request and the response is not received within
            `timeout` seconds, :class:`TimeoutError` (not
            :class:`asyncio.TimeoutError`!) is raised.

            If `cb` is given, `stanza` must be an IQ request (otherwise,
            :class:`ValueError` is raised before the stanza is sent). It must be a
            callable returning an awaitable. It receives the response stanza as
            first and only argument. The returned awaitable is awaited by
            :meth:`send` and the result is returned instead of the original
            payload. `cb` is called synchronously from the stream handling loop
            when the response is received, so it can benefit from the strong
            ordering guarantees given by XMPP XML Streams.

            The `cb` may also return :data:`None`, in which case :meth:`send` will
            simply return the IQ payload as if `cb` was not given. Since the return
            value of coroutine functions is awaitable, it is valid and supported to
            pass a coroutine function as `cb`.

            .. warning::

                Remember that it is an implementation detail of the event loop when
                a coroutine is scheduled after it awaited an awaitable; this
                implies that if the caller of :meth:`send` is merely awaiting the
                :meth:`send` coroutine, the strong ordering guarantees of XMPP XML
                Streams are lost.

                To regain those, use the `cb` argument.

            .. note::

                For the sake of readability, unless you really need the strong
                ordering guarantees, avoid the use of the `cb` argument. Avoid
                using a coroutine function unless you really need to.

            .. versionchanged:: 0.10

                * This method now waits until the stream is ready to send stanza¸
                  payloads.
                * This method was moved from
                  :meth:`aioxmpp.stream.StanzaStream.send`.

            .. versionchanged:: 0.9

                The `cb` argument was added.

            .. versionadded:: 0.8
            """
            if not self.running:
                raise ConnectionError("client is not running")

            if not self.established:
                self.logger.debug("send(%s): stream not established, waiting",
                                  stanza)
                # wait for the stream to be established
                stopped_fut = self.on_stopped.future()
                failure_fut = self.on_failure.future()
                established_fut = asyncio.ensure_future(
                    self.established_event.wait()
                )
                done, pending = await asyncio.wait(
                    [
                        established_fut,
                        failure_fut,
                        stopped_fut,
                    ],
                    return_when=asyncio.FIRST_COMPLETED,
                )
                if not established_fut.done():
                    established_fut.cancel()
                if failure_fut.done():
                    if not stopped_fut.done():
                        stopped_fut.cancel()
                    failure_fut.exception()
                    raise ConnectionError("client failed to connect")
                if stopped_fut.done():
                    raise ConnectionError("client shut down by user request")

                self.logger.debug("send(%s): stream established, sending")

            return await self.stream._send_immediately(stanza,
                                                       timeout=timeout,
                                                       cb=cb)

    class PresenceManagedClient(Client):
        """
        Client whose connection is controlled by its configured presence.

        .. seealso::

           :class:`Client`
              for a description of the arguments.

        The presence is set using :attr:`presence` or the :class:`PresenceServer`
        service. If the set presence is an *available* presence, the client is
        started (if it is not already running). If the set presence is an
        *unavailable* presence, the unavailable presence is broadcast and the
        client is stopped.

        While the start/stop interfaces of :class:`~.Client` are still available,
        using them may interfere with the behaviour of the presence automagic.

        The initial presence is set to `unavailable`, thus, the client will not
        connect immediately.

        .. autoattribute:: presence

        .. automethod:: set_presence

        .. automethod:: connected

        Signals:

        .. attribute:: on_presence_sent

           The event is fired after :meth:`.Client.on_stream_established` and after
           the current presence has been sent to the server as *initial presence*.

        .. versionchanged:: 0.8

           Since 0.8, the :class:`PresenceManagedClient` is implemented on top of
           :class:`PresenceServer`. Changing the presence via the
           :class:`PresenceServer` has the same effect as writing :attr:`presence`
           or calling :meth:`set_presence`.
        """

        on_presence_sent = callbacks.Signal()

        def __init__(self, jid, security_layer, **kwargs):
            super().__init__(jid, security_layer, **kwargs)
            self._presence_server = self.summon(mod_presence.PresenceServer)
            self._presence_server.on_presence_state_changed.connect(
                self._update_presence
            )
            self.on_stream_established.connect(self._handle_stream_established)

        def _handle_stream_established(self):
            self.on_presence_sent()

        def _update_presence(self):
            if self._presence_server.state.available:
                if not self.running:
                    self.start()
            else:
                if self.running:
                    self.stop()

        @property
        def presence(self):
            """
            Control or query the current presence state (see
            :class:`~.PresenceState`) of the client. Note that when
            reading, the property only returns the "set" value, not the actual
            value known to the server (and others). This may differ if the
            connection is still being established.

            .. seealso::

               Setting the presence state using :attr:`presence` clears the
               `status` of the presence. To set the status and state at once,
               use :meth:`set_presence`.

            Upon setting this attribute, the :class:`PresenceManagedClient` will do
            whatever necessary to achieve the given presence. If the presence is
            an `available` presence, the client will attempt to connect to the
            server. If the presence is `unavailable` and the client is currently
            connected, it will disconnect.

            Instead of setting the presence to unavailable, :meth:`stop` can also
            be called. The :attr:`presence` attribute is *not* affected by calls to
            :meth:`start` or :meth:`stop`.
            """
            return self._presence_server.state

        @presence.setter
        def presence(self, value):
            call_update = value == self.presence
            self._presence_server.set_presence(value)
            if call_update:
                self._update_presence()

        def set_presence(self, state, status):
            """
            Set the presence `state` and `status` on the client. This has the same
            effects as writing `state` to :attr:`presence`, but the status of the
            presence is also set at the same time.

            `status` must be either a string or something which can be passed to
            :class:`dict`. If it is a string, the string is wrapped in a ``{None:
            status}`` dictionary. Otherwise, the dictionary is set as the
            :attr:`~.Presence.status` attribute of the presence stanza. It
            must map :class:`aioxmpp.structs.LanguageTag` instances to strings.

            The `status` is the text shown alongside the `state` (indicating
            availability such as *away*, *do not disturb* and *free to chat*).
            """
            self._presence_server.set_presence(state, status=status)

        def connected(self, **kwargs):
            """
            Return a :class:`.node.UseConnected` context manager which sets the
            presence to available.

            The keyword arguments are passed to the :class:`.node.UseConnected`
            context manager constructor.

            .. note::

               In contrast to the same method on :class:`Client`, this method
               implies setting an available presence.

            .. versionadded:: 0.6
            """
            return UseConnected(self, **kwargs)

    class UseConnected:
        """
        Asynchronous context manager which connects and disconnects a
        :class:`.Client`.

        :param client: The client to manage
        :type client: :class:`.Client`
        :param timeout: Limit on the time it may take to start the client
        :type timeout: :class:`datetime.timedelta` or :data:`None`
        :param presence: Presence state to set on the client (deprecated)
        :type presence: :class:`.PresenceState`

        When the asynchronous context is entered (see :pep:`492`), the client is
        connected. This blocks until the client has finished connecting and the
        stream is established. If the client takes longer than `timeout` to
        connect, :class:`TimeoutError` is raised and the client is stopped. The
        context manager returns the :attr:`~.Client.stream` of the client.

        When the context is exited, the client is disconnected and the context
        manager waits for the client to cleanly shut down the stream.

        If the client is already connected when the context is entered, the
        connection is re-used and not shut down when the context is entered, but
        leaving the context still disconnects the client.

        If the `presence` refers to an available presence, the
        :class:`.PresenceServer` is :meth:`~.Client.summon`\\ -ed on the `client`.
        The presence is set using :meth:`~.PresenceServer.set_presence` (clearing
        the :attr:`~.PresenceServer.status` and resetting
        :attr:`~.PresenceServer.priority` to 0) before the client is connected. If
        the client is already connected, the presence is set when the context is
        entered.

        .. deprecated:: 0.8

           The use of the `presence` argument is deprecated. The deprecation will
           happen in two phases:

           1. Until (but not including the release of) 1.0, passing a presence
              state which refers to an available presence will emit
              :class:`DeprecationWarning`. This *includes* the default of the
              argument, so unless an unavailable presence state is passed
              explicitly, all uses of :class:`UseConnected` emit that warning.

           2. Starting with 1.0, passing an available presence will raise
              :class:`ValueError`.

           3. Starting with a to-be-determined release after 1.0, passing the
              `presence` argument at all will raise :class:`TypeError`.

           Users which previously used the `presence` argument should use the
           :class:`.PresenceServer` service on the client and set the presence
           before using the context manager instead.

        .. autoattribute:: presence

           See the description of the `presence` argument.

           .. deprecated:: 0.8

              Using this attribute (for reading or writing) is deprecated and emits
              a deprecation warning.

        .. autoattribute:: timeout

           See the description of the `timeout` argument.

           .. deprecated:: 0.8

              Using this attribute (for reading or writing) is deprecated and emits
              a deprecation warning.
        """

        def __init__(self, client, *,
                     timeout=None,
                     presence=structs.PresenceState(True)):
            super().__init__()
            self._client = client
            self._timeout = timeout
            self._presence = presence
            if presence.available:
                warnings.warn(
                    "using an available presence state for UseConnected is"
                    " deprecated and will raise ValueError as of 1.0",
                    DeprecationWarning,
                    stacklevel=1,
                )

        @property
        def timeout(self):
            warnings.warn(
                "the timeout attribute is deprecated and will be removed in 1.0",
                DeprecationWarning,
                stacklevel=1,
            )
            return self._timeout

        @timeout.setter
        def timeout(self, value):
            warnings.warn(
                "the timeout attribute is deprecated and will be removed in 1.0",
                DeprecationWarning,
                stacklevel=1,
            )
            self._timeout = value

        @property
        def presence(self):
            warnings.warn(
                "the presence attribute is deprecated and will be removed in 1.0",
                DeprecationWarning,
                stacklevel=1,
            )
            return self._presence

        @presence.setter
        def presence(self, value):
            warnings.warn(
                "the presence attribute is deprecated and will be removed in 1.0",
                DeprecationWarning,
                stacklevel=1,
            )
            self._presence = value

        async def __aenter__(self):
            if self._presence.available:
                svc = self._client.summon(
                    mod_presence.PresenceServer
                )
                svc.set_presence(self._presence)

            if self._client.established:
                return self._client.stream

            conn_future = asyncio.Future()

            self._client.on_stream_established.connect(
                conn_future,
                self._client.on_stream_established.AUTO_FUTURE,
            )

            self._client.on_failure.connect(
                conn_future,
                self._client.on_failure.AUTO_FUTURE,
            )

            if not self._client.running:
                self._client.start()

            if self._timeout is not None:
                try:
                    await asyncio.wait_for(
                        conn_future,
                        self._timeout.total_seconds(),
                    )
                except asyncio.TimeoutError:
                    self._client.stop()
                    raise TimeoutError()
            else:
                await conn_future

            return self._client.stream

        async def __aexit__(self, exc_type, exc_value, exc_traceback):
            if not self._client.running:
                return

            disconn_future = asyncio.Future()

            self._client.on_stopped.connect(
                disconn_future,
                self._client.on_stopped.AUTO_FUTURE,
            )

            self._client.on_failure.connect(
                disconn_future,
                self._client.on_failure.AUTO_FUTURE,
            )

            self._client.stop()

            try:
                await disconn_future
            except Exception:
                # we don’t want to re-raise that; the stream is dead, goal
                # achieved.
                pass