#    Copyright 2014, Red Hat, Inc.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""
Controller that manages the interface between the driver and the messaging
service.

This module defines a Controller class that is responsible for performing
messaging-related operations (Tasks) requested by the driver, and for managing
the connection to the messaging service.  The Controller creates a background
thread which performs all messaging operations and socket I/O.  The
Controller's messaging logic is executed in the background thread via lambda
functions scheduled by the Controller.
"""

import abc
import collections
import logging
from monotonic import monotonic as now  # noqa
import os
import platform
import random
import sys
import threading
import uuid

import proton
import pyngus
from six import iteritems
from six import itervalues
from six import moves

from oslo_messaging._drivers.amqp1_driver.addressing import AddresserFactory
from oslo_messaging._drivers.amqp1_driver.addressing import keyify
from oslo_messaging._drivers.amqp1_driver.addressing import SERVICE_NOTIFY
from oslo_messaging._drivers.amqp1_driver.addressing import SERVICE_RPC
from oslo_messaging._drivers.amqp1_driver import eventloop
from oslo_messaging._i18n import _LE, _LI, _LW
from oslo_messaging import exceptions
from oslo_messaging.target import Target
from oslo_messaging import transport

LOG = logging.getLogger(__name__)


class Task(object):
    """Run a command on the eventloop thread, wait until it completes
    """

    @abc.abstractmethod
    def wait(self):
        """Called by the client thread to wait for the operation to
        complete. The implementation may optionally return a value.
        """

    @abc.abstractmethod
    def _execute(self, controller):
        """This method will be run on the eventloop thread to perform the
        messaging operation.
        """


class SubscribeTask(Task):
    """A task that creates a subscription to the given target.  Messages
    arriving from the target are given to the listener.
    """
    def __init__(self, target, listener, notifications=False):
        super(SubscribeTask, self).__init__()
        self._target = target()  # mutable - need a copy
        self._subscriber_id = listener.id
        self._in_queue = listener.incoming
        self._service = SERVICE_NOTIFY if notifications else SERVICE_RPC
        self._wakeup = threading.Event()

    def wait(self):
        self._wakeup.wait()

    def _execute(self, controller):
        controller.subscribe(self)
        self._wakeup.set()


class SendTask(Task):
    """This is the class used by the Controller to send messages to a given
    destination.
    """
    def __init__(self, name, message, target, deadline, retry,
                 wait_for_ack, notification=False):
        super(SendTask, self).__init__()
        self.name = name
        # note: target can be either a Target class or a string
        # target is mutable - make copy
        self.target = target() if isinstance(target, Target) else target
        self.message = message
        self.deadline = deadline
        self.retry = retry
        self.wait_for_ack = wait_for_ack
        self.service = SERVICE_NOTIFY if notification else SERVICE_RPC
        self.timer = None
        self._wakeup = threading.Event()
        self._error = None

    def wait(self):
        self._wakeup.wait()
        return self._error

    def _execute(self, controller):
        controller.send(self)

    def _prepare(self, sender):
        """Called immediately before the message is handed off to the i/o
        system.  This implies that the sender link is up.
        """
        if not self.wait_for_ack:
            # sender is not concerned with waiting for acknowledgment
            # "best effort at-most-once delivery"
            self._cleanup()
            self._wakeup.set()

    def _on_ack(self, state, info):
        """Called by eventloop thread when the ack/nack is received from the
        peer.
        """
        if state != pyngus.SenderLink.ACCEPTED:
            # TODO(kgiusti): could retry if deadline not hit
            msg = ("{name} message send to {target} failed: remote"
                   " disposition: {disp}, info:"
                   "{info}".format(name=self.name,
                                   target=self.target,
                                   disp=state,
                                   info=info))
            self._error = exceptions.MessageDeliveryFailure(msg)
            LOG.warning("%s", msg)
        self._cleanup()
        self._wakeup.set()

    def _on_timeout(self):
        """Invoked by the eventloop when the send fails to complete before the
        timeout is reached.
        """
        self.timer = None
        msg = ("{name} message sent to {target} failed: timed"
               " out".format(name=self.name, target=self.target))
        LOG.warning("%s", msg)
        # Only raise a MessagingTimeout if the caller has explicitly specified
        # a timeout.
        self._error = exceptions.MessagingTimeout(msg) \
            if self.message.ttl else \
            exceptions.MessageDeliveryFailure(msg)
        self._cleanup()
        self._wakeup.set()

    def _on_error(self, description):
        """Invoked by the eventloop if the send operation fails for reasons
        other than timeout and nack.
        """
        msg = ("{name} message sent to {target} failed:"
               " {reason}".format(name=self.name,
                                  target=self.target,
                                  reason=description))
        LOG.warning("%s", msg)
        self._error = exceptions.MessageDeliveryFailure(msg)
        self._cleanup()
        self._wakeup.set()

    def _cleanup(self):
        if self.timer:
            self.timer.cancel()
            self.timer = None


class RPCCallTask(SendTask):
    """Performs an RPC Call.  Sends the request and waits for a response from
    the destination.
    """

    def __init__(self, target, message, deadline, retry, wait_for_ack):
        super(RPCCallTask, self).__init__("RPC Call", message, target,
                                          deadline, retry, wait_for_ack)
        self._reply_link = None
        self._reply_msg = None
        self._msg_id = None

    def wait(self):
        error = super(RPCCallTask, self).wait()
        return error or self._reply_msg

    def _prepare(self, sender):
        # reserve a message id for mapping the received response
        self._reply_link = sender._reply_link
        rl = self._reply_link
        self._msg_id = rl.prepare_for_response(self.message, self._on_reply)

    def _on_reply(self, message):
        # called if/when the reply message arrives
        if self._wakeup.is_set():
            LOG.debug("RPC Reply received after call completed")
            return
        self._reply_msg = message
        self._reply_link = None
        self._cleanup()
        self._wakeup.set()

    def _on_ack(self, state, info):
        if self._wakeup.is_set():
            LOG.debug("RPC ACKed after call completed: %s %s", state, info)
            return
        if state != pyngus.SenderLink.ACCEPTED:
            super(RPCCallTask, self)._on_ack(state, info)
        # must wait for reply if ACCEPTED

    def _cleanup(self):
        if self._reply_link and self._msg_id:
            self._reply_link.cancel_response(self._msg_id)
            self._msg_id = None
        super(RPCCallTask, self)._cleanup()


class MessageDispositionTask(Task):
    """A task that updates the message disposition as accepted or released
    for a Server
    """
    def __init__(self, disposition, released=False):
        super(MessageDispositionTask, self).__init__()
        self._disposition = disposition
        self._released = released

    def wait(self):
        # disposition update does not have to block the sender since there is
        # no result to pend for.  This avoids a thread context switch with
        # every RPC call
        pass

    def _execute(self, controller):
        try:
            self._disposition(self._released)
        except Exception as e:
            # there's really nothing we can do about a failed disposition.
            LOG.exception(_LE("Message acknowledgment failed: %s"), e)


class Sender(pyngus.SenderEventHandler):
    """A link for sending to a particular destination on the message bus.
    """
    def __init__(self, destination, scheduler, delay, service):
        super(Sender, self).__init__()
        self._destination = destination
        self._service = service
        self._address = None
        self._link = None
        self._scheduler = scheduler
        self._delay = delay  # for re-connecting
        # holds all pending SendTasks
        self._pending_sends = collections.deque()
        # holds all messages sent but not yet acked
        self._unacked = set()
        self._reply_link = None
        self._connection = None

    @property
    def pending_messages(self):
        return len(self._pending_sends)

    def attach(self, connection, reply_link, addresser):
        """Open the link. Called by the Controller when the AMQP connection
        becomes active.
        """
        self._connection = connection
        self._reply_link = reply_link
        self._address = addresser.resolve(self._destination, self._service)
        LOG.debug("Sender %s attached", self._address)
        self._link = self._open_link()

    def detach(self):
        """Close the link.  Called by the controller when shutting down or in
        response to a close requested by the remote.  May be re-attached later
        (after a reset is done)
        """
        LOG.debug("Sender %s detached", self._address)
        self._connection = None
        self._reply_link = None
        if self._link:
            self._link.close()

    def reset(self):
        """Called by the controller on connection failover. Release all link
        resources, abort any in-flight messages, and check the retry limit on
        all pending send requests.
        """
        self._address = None
        self._connection = None
        self._reply_link = None
        if self._link:
            self._link.destroy()
            self._link = None
        self._abort_unacked("Link reset")
        self._check_retry_limit()

    def destroy(self):
        """Destroy the sender and all pending messages.  Called on driver
        shutdown.
        """
        LOG.debug("Sender %s destroyed", self._address)
        self.reset()
        self._abort_pending("Link destroyed")

    def send_message(self, send_task):
        """Send a message out the link.
        """
        if send_task.deadline:
            def timer_callback():
                # may be in either list, or none
                self._unacked.discard(send_task)
                try:
                    self._pending_sends.remove(send_task)
                except ValueError:
                    pass
                send_task._on_timeout()
            send_task.timer = self._scheduler.alarm(timer_callback,
                                                    send_task.deadline)

        if not self._can_send or self._pending_sends:
            self._pending_sends.append(send_task)
        else:
            self._send(send_task)

    # Pyngus callbacks:

    def sender_active(self, sender_link):
        LOG.debug("Sender %s active", self._address)
        self._send_pending()

    def credit_granted(self, sender_link):
        pass

    def sender_remote_closed(self, sender_link, pn_condition):
        # The remote has initiated a close.  This could happen when the message
        # bus is shutting down, or it detected an error
        LOG.warning(_LW("sender %(addr)s failed due to remote initiated close:"
                        " condition=%(cond)s"),
                    {'addr': self._address, 'cond': pn_condition})
        self._link.close()
        # sender_closed() will be called once the link completes closing

    def sender_closed(self, sender_link):
        self._abort_unacked("Sender closed")
        if self._connection:
            # still attached, so attempt to restart the link
            self._check_retry_limit()
            self._scheduler.defer(self._reopen_link, self._delay)

    def sender_failed(self, sender_link, error):
        """Protocol error occurred."""
        LOG.warning(_LW("sender %(addr)s failed error=%(error)s"),
                    {'addr': self._address, 'error': error})
        self.sender_closed(sender_link)

    # end Pyngus callbacks

    def _check_retry_limit(self):
        # Called on recoverable connection or link failure.  Remove any pending
        # sends that have exhausted their retry count:
        expired = set()
        for send_task in self._pending_sends:
            if send_task.retry is not None:
                send_task.retry -= 1
                if send_task.retry <= 0:
                    expired.add(send_task)
                    send_task._on_error("Send retries exhausted")
        while expired:
            self._pending_sends.remove(expired.pop())

    def _abort_unacked(self, error):
        # fail all messages that have been sent to the message bus and have not
        # been acked yet
        while self._unacked:
            send_task = self._unacked.pop()
            send_task._on_error("Message send failed: %s" % error)

    def _abort_pending(self, error):
        # fail all messages that have yet to be sent to the message bus
        while self._pending_sends:
            send_task = self._pending_sends.popleft()
            send_task._on_error("Message send failed: %s" % error)

    @property
    def _can_send(self):
        return self._link and self._link.active

    def _send(self, send_task):
        send_task._prepare(self)
        send_task.message.address = self._address

        def pyngus_callback(link, handle, state, info):
            # invoked when the message bus (n)acks this message
            if state == pyngus.SenderLink.TIMED_OUT:
                # ignore pyngus timeout - we maintain our own timer
                return
            self._unacked.discard(send_task)
            send_task._on_ack(state, info)

        self._unacked.add(send_task)
        self._link.send(send_task.message,
                        delivery_callback=pyngus_callback,
                        handle=self,
                        deadline=send_task.deadline)

    def _send_pending(self):
        # send all pending messages
        if self._can_send:
            while self._pending_sends:
                self._send(self._pending_sends.popleft())

    def _open_link(self):
        name = "openstack.org/om/sender/[%s]/%s" % (self._address,
                                                    uuid.uuid4().hex)
        link = self._connection.create_sender(name=name,
                                              source_address=self._address,
                                              target_address=self._address,
                                              event_handler=self)
        link.open()
        return link

    def _reopen_link(self):
        if self._connection:
            if self._link:
                self._link.destroy()
            self._link = self._open_link()


class Replies(pyngus.ReceiverEventHandler):
    """This is the receiving link for all RPC reply messages.  Messages are
    routed to the proper incoming queue using the correlation-id header in the
    message.
    """
    def __init__(self, connection, on_ready, on_down, capacity):
        self._correlation = {}  # map of correlation-id to response queue
        self._on_ready = on_ready
        self._on_down = on_down
        rname = ("openstack.org/om/receiver/[rpc-response]/%s"
                 % uuid.uuid4().hex)
        self._receiver = connection.create_receiver("rpc-response",
                                                    event_handler=self,
                                                    name=rname)

        # capacity determines the maximum number of reply messages this link is
        # willing to receive. As messages are received and capacity is
        # consumed, this driver will 'top up' the capacity back to max
        # capacity.  This number should be large enough to avoid needlessly
        # flow-controlling the replies.
        self._capacity = capacity
        self._capacity_low = (capacity + 1) / 2
        self._receiver.open()

    def detach(self):
        # close the link
        if self._receiver:
            self._receiver.close()

    def destroy(self):
        self._correlation = None
        if self._receiver:
            self._receiver.destroy()
            self._receiver = None

    def prepare_for_response(self, request, callback):
        """Apply a unique message identifier to this request message. This will
        be used to identify messages sent in reply.  The identifier is placed
        in the 'id' field of the request message.  It is expected that the
        identifier will appear in the 'correlation-id' field of the
        corresponding response message.
        """
        request.id = uuid.uuid4().hex
        # reply is placed on reply_queue
        self._correlation[request.id] = callback
        request.reply_to = self._receiver.source_address
        return request.id

    def cancel_response(self, msg_id):
        """Abort waiting for the response message corresponding to msg_id.
        This can be used if the request fails and no reply is expected.
        """
        if self._correlation:
            try:
                del self._correlation[msg_id]
            except KeyError:
                pass

    @property
    def active(self):
        return self._receiver and self._receiver.active

    # Pyngus ReceiverLink event callbacks:

    def receiver_active(self, receiver_link):
        """This is a Pyngus callback, invoked by Pyngus when the receiver_link
        has transitioned to the open state and is able to receive incoming
        messages.
        """
        LOG.debug("Replies link active src=%s", self._receiver.source_address)
        receiver_link.add_capacity(self._capacity)
        self._on_ready()

    def receiver_remote_closed(self, receiver, pn_condition):
        """This is a Pyngus callback, invoked by Pyngus when the peer of this
        receiver link has initiated closing the connection.
        """
        if pn_condition:
            LOG.error(_LE("Reply subscription closed by peer: %s"),
                      pn_condition)
        receiver.close()

    def receiver_failed(self, receiver_link, error):
        """Protocol error occurred."""
        LOG.error(_LE("Link to reply queue failed. error=%(error)s"),
                  {"error": error})
        self._on_down()

    def receiver_closed(self, receiver_link):
        self._on_down()

    def message_received(self, receiver, message, handle):
        """This is a Pyngus callback, invoked by Pyngus when a new message
        arrives on this receiver link from the peer.
        """
        key = message.correlation_id
        try:
            self._correlation[key](message)
            # cleanup (only need one response per request)
            del self._correlation[key]
            receiver.message_accepted(handle)
        except KeyError:
            LOG.warning(_LW("Can't find receiver for response msg id=%s, "
                            "dropping!"), key)
            receiver.message_modified(handle, True, True, None)
        # ensure we have enough credit
        if receiver.capacity <= self._capacity_low:
            receiver.add_capacity(self._capacity - receiver.capacity)


class Server(pyngus.ReceiverEventHandler):
    """A group of links that receive messages from a set of addresses derived
    from a given target.  Messages arriving on the links are placed on the
    'incoming' queue.
    """
    def __init__(self, target, incoming, scheduler, delay, capacity):
        self._target = target
        self._incoming = incoming
        self._addresses = []
        self._capacity = capacity   # credit per each link
        self._capacity_low = (capacity + 1) / 2
        self._receivers = []
        self._scheduler = scheduler
        self._delay = delay  # for link re-attach
        self._connection = None
        self._reopen_scheduled = False

    def attach(self, connection):
        """Create receiver links over the given connection for all the
        configured addresses.
        """
        self._connection = connection
        for a in self._addresses:
            name = "openstack.org/om/receiver/[%s]/%s" % (a, uuid.uuid4().hex)
            r = self._open_link(a, name)
            self._receivers.append(r)

    def detach(self):
        """Attempt a clean shutdown of the links"""
        self._connection = None
        self._addresses = []
        for receiver in self._receivers:
            receiver.close()

    def reset(self):
        # destroy the links, but keep the addresses around since we may be
        # failing over.  Since links are destroyed, this cannot be called from
        # any of the following ReceiverLink callbacks.
        self._connection = None
        self._addresses = []
        self._reopen_scheduled = False
        for r in self._receivers:
            r.destroy()
        self._receivers = []

    # Pyngus ReceiverLink event callbacks.  Note that all of the Server's links
    # share this handler

    def receiver_remote_closed(self, receiver, pn_condition):
        """This is a Pyngus callback, invoked by Pyngus when the peer of this
        receiver link has initiated closing the connection.
        """
        LOG.debug("Server subscription to %s remote detach",
                  receiver.source_address)
        if pn_condition:
            vals = {
                "addr": receiver.source_address or receiver.target_address,
                "err_msg": pn_condition
            }
            LOG.error(_LE("Server subscription %(addr)s closed "
                          "by peer: %(err_msg)s"), vals)
        receiver.close()

    def receiver_failed(self, receiver_link, error):
        """Protocol error occurred."""
        LOG.error(_LE("Listener link queue failed. error=%(error)s"),
                  {"error": error})
        self.receiver_closed(receiver_link)

    def receiver_closed(self, receiver_link):
        LOG.debug("Server subscription to %s closed",
                  receiver_link.source_address)
        # If still attached, attempt to re-start link
        if self._connection and not self._reopen_scheduled:
            LOG.debug("Server subscription reopen scheduled")
            self._reopen_scheduled = True
            self._scheduler.defer(self._reopen_links, self._delay)

    def message_received(self, receiver, message, handle):
        """This is a Pyngus callback, invoked by Pyngus when a new message
        arrives on this receiver link from the peer.
        """
        def message_disposition(released=False):
            if receiver in self._receivers and not receiver.closed:
                if released:
                    receiver.message_released(handle)
                else:
                    receiver.message_accepted(handle)
                if receiver.capacity <= self._capacity_low:
                    receiver.add_capacity(self._capacity - receiver.capacity)
            else:
                LOG.debug("Can't find receiver for settlement")

        qentry = {"message": message, "disposition": message_disposition}
        self._incoming.put(qentry)

    def _open_link(self, address, name):
        props = {"snd-settle-mode": "mixed"}
        r = self._connection.create_receiver(source_address=address,
                                             target_address=address,
                                             event_handler=self,
                                             name=name,
                                             properties=props)
        r.add_capacity(self._capacity)
        r.open()
        return r

    def _reopen_links(self):
        # attempt to re-establish any closed links
        LOG.debug("Server subscription reopening")
        self._reopen_scheduled = False
        if self._connection:
            for i in range(len(self._receivers)):
                link = self._receivers[i]
                if link.closed:
                    addr = link.target_address
                    name = link.name
                    link.destroy()
                    self._receivers[i] = self._open_link(addr, name)


class RPCServer(Server):
    """Subscribes to RPC addresses"""
    def __init__(self, target, incoming, scheduler, delay, capacity):
        super(RPCServer, self).__init__(target, incoming, scheduler, delay,
                                        capacity)

    def attach(self, connection, addresser):
        # Generate the AMQP 1.0 addresses for the base class
        self._addresses = [
            addresser.unicast_address(self._target, SERVICE_RPC),
            addresser.multicast_address(self._target, SERVICE_RPC),
            addresser.anycast_address(self._target, SERVICE_RPC)
        ]
        # now invoke the base class with the generated addresses
        super(RPCServer, self).attach(connection)


class NotificationServer(Server):
    """Subscribes to Notification addresses"""
    def __init__(self, target, incoming, scheduler, delay, capacity):
        super(NotificationServer, self).__init__(target, incoming, scheduler,
                                                 delay, capacity)

    def attach(self, connection, addresser):
        # Generate the AMQP 1.0 addresses for the base class
        self._addresses = [
            addresser.anycast_address(self._target, SERVICE_NOTIFY)
        ]
        # now invoke the base class with the generated addresses
        super(NotificationServer, self).attach(connection)


class Hosts(object):
    """An order list of TransportHost addresses. Connection failover
    progresses from one host to the next.  username and password come from the
    configuration and are used only if no username/password was given in the
    URL.
    """
    def __init__(self, entries=None, default_username=None,
                 default_password=None):
        if entries:
            self._entries = entries[:]
        else:
            self._entries = [transport.TransportHost(hostname="localhost",
                                                     port=5672)]
        for entry in self._entries:
            entry.port = entry.port or 5672
            entry.username = entry.username or default_username
            entry.password = entry.password or default_password
        self._current = random.randint(0, len(self._entries) - 1)

    @property
    def current(self):
        return self._entries[self._current]

    def next(self):
        if len(self._entries) > 1:
            self._current = (self._current + 1) % len(self._entries)
        return self.current

    def __repr__(self):
        return '<Hosts ' + str(self) + '>'

    def __str__(self):
        return ", ".join(["%r" % th for th in self._entries])


class Controller(pyngus.ConnectionEventHandler):
    """Controls the connection to the AMQP messaging service.  This object is
    the 'brains' of the driver.  It maintains the logic for addressing, sending
    and receiving messages, and managing the connection.  All messaging and I/O
    work is done on the Eventloop thread, allowing the driver to run
    asynchronously from the messaging clients.
    """
    def __init__(self, hosts, default_exchange, config):
        self.processor = None
        self._socket_connection = None
        self._node = platform.node() or "<UNKNOWN>"
        self._command = os.path.basename(sys.argv[0])
        self._pid = os.getpid()
        # queue of drivertask objects to execute on the eventloop thread
        self._tasks = moves.queue.Queue(maxsize=500)
        # limit the number of Task()'s to execute per call to _process_tasks().
        # This allows the eventloop main thread to return to servicing socket
        # I/O in a timely manner
        self._max_task_batch = 50
        # cache of all Sender links indexed by address:
        self._all_senders = {}
        # active Sender links indexed by address:
        self._active_senders = set()
        # closing Sender links indexed by address:
        self._purged_senders = []
        # Servers indexed by target. Each entry is a map indexed by the
        # specific ProtonListener's identifier:
        self._servers = {}

        self._container_name = config.oslo_messaging_amqp.container_name
        self.idle_timeout = config.oslo_messaging_amqp.idle_timeout
        self.trace_protocol = config.oslo_messaging_amqp.trace
        self.ssl_ca_file = config.oslo_messaging_amqp.ssl_ca_file
        self.ssl_cert_file = config.oslo_messaging_amqp.ssl_cert_file
        self.ssl_key_file = config.oslo_messaging_amqp.ssl_key_file
        self.ssl_key_password = config.oslo_messaging_amqp.ssl_key_password
        self.ssl_allow_insecure = \
            config.oslo_messaging_amqp.allow_insecure_clients
        self.sasl_mechanisms = config.oslo_messaging_amqp.sasl_mechanisms
        self.sasl_config_dir = config.oslo_messaging_amqp.sasl_config_dir
        self.sasl_config_name = config.oslo_messaging_amqp.sasl_config_name
        self.hosts = Hosts(hosts, config.oslo_messaging_amqp.username,
                           config.oslo_messaging_amqp.password)
        self.conn_retry_interval = \
            config.oslo_messaging_amqp.connection_retry_interval
        self.conn_retry_backoff = \
            config.oslo_messaging_amqp.connection_retry_backoff
        self.conn_retry_interval_max = \
            config.oslo_messaging_amqp.connection_retry_interval_max
        self.link_retry_delay = config.oslo_messaging_amqp.link_retry_delay

        _opts = config.oslo_messaging_amqp
        factory_args = {"legacy_server_prefix": _opts.server_request_prefix,
                        "legacy_broadcast_prefix": _opts.broadcast_prefix,
                        "legacy_group_prefix": _opts.group_request_prefix,
                        "rpc_prefix": _opts.rpc_address_prefix,
                        "notify_prefix": _opts.notify_address_prefix,
                        "multicast": _opts.multicast_address,
                        "unicast": _opts.unicast_address,
                        "anycast": _opts.anycast_address,
                        "notify_exchange": _opts.default_notification_exchange,
                        "rpc_exchange": _opts.default_rpc_exchange}

        self.addresser_factory = AddresserFactory(default_exchange,
                                                  _opts.addressing_mode,
                                                  **factory_args)
        self.addresser = None

        # cannot send an RPC request until the replies link is active, as we
        # need the peer assigned address, so need to delay sending any RPC
        # requests until this link is active:
        self.reply_link = None
        # Set True when the driver is shutting down
        self._closing = False
        # only schedule one outstanding reconnect attempt at a time
        self._reconnecting = False
        self._delay = 1  # seconds between retries
        # prevent queuing up multiple requests to run _process_tasks()
        self._process_tasks_scheduled = False
        self._process_tasks_lock = threading.Lock()
        # credit levels for incoming links
        self._reply_credit = _opts.reply_link_credit
        self._rpc_credit = _opts.rpc_server_credit
        self._notify_credit = _opts.notify_server_credit
        # sender link maintenance timer and interval
        self._link_maint_timer = None
        self._link_maint_timeout = _opts.default_sender_link_timeout

    def connect(self):
        """Connect to the messaging service."""
        self.processor = eventloop.Thread(self._container_name, self._node,
                                          self._command, self._pid)
        self.processor.wakeup(lambda: self._do_connect())

    def add_task(self, task):
        """Add a Task for execution on processor thread."""
        self._tasks.put(task)
        self._schedule_task_processing()

    def shutdown(self, timeout=30):
        """Shutdown the messaging service."""
        LOG.info(_LI("Shutting down the AMQP 1.0 connection"))
        if self.processor:
            self.processor.wakeup(self._start_shutdown)
            LOG.debug("Waiting for eventloop to exit")
            self.processor.join(timeout)
            self._hard_reset()
            for sender in itervalues(self._all_senders):
                sender.destroy()
            self._all_senders.clear()
            self._servers.clear()
            self.processor.destroy()
            self.processor = None
        LOG.debug("Eventloop exited, driver shut down")

    # The remaining methods are reserved to run from the eventloop thread only!
    # They must not be invoked directly!

    # methods executed by Tasks created by the driver:

    def send(self, send_task):
        if send_task.deadline and send_task.deadline <= now():
            send_task._on_timeout()
            return
        if send_task.retry is None or send_task.retry < 0:
            send_task.retry = None
        key = keyify(send_task.target, send_task.service)
        sender = self._all_senders.get(key)
        if not sender:
            sender = Sender(send_task.target, self.processor,
                            self.link_retry_delay, send_task.service)
            self._all_senders[key] = sender
            if self.reply_link and self.reply_link.active:
                sender.attach(self._socket_connection.connection,
                              self.reply_link, self.addresser)
        self._active_senders.add(key)
        sender.send_message(send_task)

    def subscribe(self, subscribe_task):
        """Subscribe to a given target"""
        if subscribe_task._service == SERVICE_NOTIFY:
            t = "notification"
            server = NotificationServer(subscribe_task._target,
                                        subscribe_task._in_queue,
                                        self.processor,
                                        self.link_retry_delay,
                                        self._notify_credit)
        else:
            t = "RPC"
            server = RPCServer(subscribe_task._target,
                               subscribe_task._in_queue,
                               self.processor,
                               self.link_retry_delay,
                               self._rpc_credit)

        LOG.debug("Subscribing to %(type)s target %(target)s",
                  {'type': t, 'target': subscribe_task._target})
        key = keyify(subscribe_task._target, subscribe_task._service)
        servers = self._servers.get(key)
        if servers is None:
            servers = {}
            self._servers[key] = servers
        servers[subscribe_task._subscriber_id] = server
        if self._active:
            server.attach(self._socket_connection.connection,
                          self.addresser)

    # commands executed on the processor (eventloop) via 'wakeup()':

    def _do_connect(self):
        """Establish connection and reply subscription on processor thread."""
        host = self.hosts.current
        conn_props = {'properties': {u'process': self._command,
                                     u'pid': self._pid,
                                     u'node': self._node},
                      'hostname': host.hostname}
        if self.idle_timeout:
            conn_props["idle-time-out"] = float(self.idle_timeout)
        if self.trace_protocol:
            conn_props["x-trace-protocol"] = self.trace_protocol
        if self.ssl_ca_file:
            conn_props["x-ssl-ca-file"] = self.ssl_ca_file
        if self.ssl_cert_file:
            # assume this connection is for a server.  If client authentication
            # support is developed, we'll need an explicit flag (server or
            # client)
            conn_props["x-ssl-server"] = True
            conn_props["x-ssl-identity"] = (self.ssl_cert_file,
                                            self.ssl_key_file,
                                            self.ssl_key_password)
            conn_props["x-ssl-allow-cleartext"] = self.ssl_allow_insecure
        # SASL configuration:
        if self.sasl_mechanisms:
            conn_props["x-sasl-mechs"] = self.sasl_mechanisms
        if self.sasl_config_dir:
            conn_props["x-sasl-config-dir"] = self.sasl_config_dir
        if self.sasl_config_name:
            conn_props["x-sasl-config-name"] = self.sasl_config_name

        self._socket_connection = self.processor.connect(host,
                                                         handler=self,
                                                         properties=conn_props)
        LOG.debug("Connection initiated")

    def _process_tasks(self):
        """Execute Task objects in the context of the processor thread."""
        with self._process_tasks_lock:
            self._process_tasks_scheduled = False
        count = 0
        while (not self._tasks.empty() and
               count < self._max_task_batch):
            try:
                self._tasks.get(False)._execute(self)
            except Exception as e:
                LOG.exception(_LE("Error processing task: %s"), e)
            count += 1

        # if we hit _max_task_batch, resume task processing later:
        if not self._tasks.empty():
            self._schedule_task_processing()

    def _schedule_task_processing(self):
        """_process_tasks() helper: prevent queuing up multiple requests for
        task processing.  This method is called both by the application thread
        and the processing thread.
        """
        if self.processor:
            with self._process_tasks_lock:
                already_scheduled = self._process_tasks_scheduled
                self._process_tasks_scheduled = True
            if not already_scheduled:
                self.processor.wakeup(lambda: self._process_tasks())

    def _start_shutdown(self):
        """Called when the application is closing the transport.
        Attempt to cleanly flush/close all links.
        """
        self._closing = True
        if self._active:
            # try a clean shutdown
            self._detach_senders()
            self._detach_servers()
            self.reply_link.detach()
            self._socket_connection.connection.close()
        else:
            # don't wait for a close from the remote, may never happen
            self.processor.shutdown()

    # reply link callbacks:

    def _reply_link_ready(self):
        """Invoked when the Replies reply link has become active.  At this
        point, we are ready to receive messages, so start all pending RPC
        requests.
        """
        LOG.info(_LI("Messaging is active (%(hostname)s:%(port)s)"),
                 {'hostname': self.hosts.current.hostname,
                  'port': self.hosts.current.port})
        for sender in itervalues(self._all_senders):
            sender.attach(self._socket_connection.connection,
                          self.reply_link, self.addresser)

    def _reply_link_down(self):
        # Treat it as a recoverable failure because the RPC reply address is
        # now invalid for all in-flight RPC requests.
        if not self._closing:
            self._detach_senders()
            self._detach_servers()
            self._socket_connection.connection.close()
            # once closed, _handle_connection_loss() will initiate reconnect

    # callback from eventloop on socket error

    def socket_error(self, error):
        """Called by eventloop when a socket error occurs."""
        LOG.error(_LE("Socket failure: %s"), error)
        self._handle_connection_loss()

    # Pyngus connection event callbacks (and their helpers), all invoked from
    # the eventloop thread:

    def connection_failed(self, connection, error):
        """This is a Pyngus callback, invoked by Pyngus when a non-recoverable
        error occurs on the connection.
        """
        if connection is not self._socket_connection.connection:
            # pyngus bug: ignore failure callback on destroyed connections
            return
        LOG.debug("AMQP Connection failure: %s", error)
        self._handle_connection_loss()

    def connection_active(self, connection):
        """This is a Pyngus callback, invoked by Pyngus when the connection to
        the peer is up.  At this point, the driver will activate all subscriber
        links (server) and the reply link.
        """
        LOG.debug("Connection active (%(hostname)s:%(port)s), subscribing...",
                  {'hostname': self.hosts.current.hostname,
                   'port': self.hosts.current.port})
        # allocate an addresser based on the advertised properties of the
        # message bus
        props = connection.remote_properties or {}
        self.addresser = self.addresser_factory(props)
        for servers in itervalues(self._servers):
            for server in itervalues(servers):
                server.attach(self._socket_connection.connection,
                              self.addresser)
        self.reply_link = Replies(self._socket_connection.connection,
                                  self._reply_link_ready,
                                  self._reply_link_down,
                                  self._reply_credit)
        self._delay = 1
        # schedule periodic maintenance of sender links
        self._link_maint_timer = self.processor.defer(self._purge_sender_links,
                                                      self._link_maint_timeout)

    def connection_closed(self, connection):
        """This is a Pyngus callback, invoked by Pyngus when the connection has
        cleanly closed.  This occurs after the driver closes the connection
        locally, and the peer has acknowledged the close.  At this point, the
        shutdown of the driver's connection is complete.
        """
        LOG.debug("AMQP connection closed.")
        # if the driver isn't being shutdown, failover and reconnect
        self._handle_connection_loss()

    def connection_remote_closed(self, connection, reason):
        """This is a Pyngus callback, invoked by Pyngus when the peer has
        requested that the connection be closed.
        """
        # The messaging service/broker is trying to shut down the
        # connection. Acknowledge the close, and try to reconnect/failover
        # later once the connection has closed (connection_closed is called).
        if reason:
            LOG.info(_LI("Connection closed by peer: %s"), reason)
        self._detach_senders()
        self._detach_servers()
        self.reply_link.detach()
        self._socket_connection.connection.close()

    def sasl_done(self, connection, pn_sasl, outcome):
        """This is a Pyngus callback invoked when the SASL handshake
        has completed.  The outcome of the handshake is passed in the outcome
        argument.
        """
        if outcome == proton.SASL.OK:
            return
        LOG.error(_LE("AUTHENTICATION FAILURE: Cannot connect to "
                      "%(hostname)s:%(port)s as user %(username)s"),
                  {'hostname': self.hosts.current.hostname,
                   'port': self.hosts.current.port,
                   'username': self.hosts.current.username})
        # connection failure will be handled later

    def _handle_connection_loss(self):
        """The connection to the messaging service has been lost.  Try to
        reestablish the connection/failover if not shutting down the driver.
        """
        self.addresser = None
        if self._closing:
            # we're in the middle of shutting down the driver anyways,
            # just consider it done:
            self.processor.shutdown()
        else:
            # for some reason, we've lost the connection to the messaging
            # service.  Try to re-establish the connection:
            if not self._reconnecting:
                self._reconnecting = True
                LOG.info(_LI("delaying reconnect attempt for %d seconds"),
                         self._delay)
                self.processor.defer(self._do_reconnect, self._delay)
                self._delay = min(self._delay * 2, 60)
            if self._link_maint_timer:
                self._link_maint_timer.cancel()
                self._link_maint_timer = None

    def _do_reconnect(self):
        """Invoked on connection/socket failure, failover and re-connect to the
        messaging service.
        """
        self._reconnecting = False
        if not self._closing:
            self._hard_reset()
            host = self.hosts.next()
            LOG.info(_LI("Reconnecting to: %(hostname)s:%(port)s"),
                     {'hostname': host.hostname, 'port': host.port})
            self._socket_connection.connect(host)

    def _hard_reset(self):
        """Reset the controller to its pre-connection state"""
        # note well: since this method destroys the connection, it cannot be
        # invoked directly from a pyngus callback.  Use processor.defer() to
        # run this method on the main loop instead.
        for sender in self._purged_senders:
            sender.destroy()
        del self._purged_senders[:]
        self._active_senders.clear()
        unused = []
        for key, sender in iteritems(self._all_senders):
            # clean up any unused sender links
            if sender.pending_messages == 0:
                unused.append(key)
            else:
                sender.reset()
                self._active_senders.add(key)
        for key in unused:
            self._all_senders[key].destroy()
            del self._all_senders[key]
        for servers in itervalues(self._servers):
            for server in itervalues(servers):
                server.reset()
        if self.reply_link:
            self.reply_link.destroy()
            self.reply_link = None
        if self._socket_connection:
            self._socket_connection.reset()

    def _detach_senders(self):
        """Close all sender links"""
        for sender in itervalues(self._all_senders):
            sender.detach()

    def _detach_servers(self):
        """Close all listener links"""
        for servers in itervalues(self._servers):
            for server in itervalues(servers):
                server.detach()

    def _purge_sender_links(self):
        """Purge inactive sender links"""
        if not self._closing:
            # destroy links that have already been closed
            for sender in self._purged_senders:
                sender.destroy()
            del self._purged_senders[:]

            # determine next set to purge
            purge = set(self._all_senders.keys()) - self._active_senders
            for key in purge:
                sender = self._all_senders[key]
                if sender.pending_messages == 0:
                    sender.detach()
                    self._purged_senders.append(self._all_senders.pop(key))
            self._active_senders.clear()
            self._link_maint_timer = \
                self.processor.defer(self._purge_sender_links,
                                     self._link_maint_timeout)

    @property
    def _active(self):
        # Is the connection up
        return (self._socket_connection
                and self._socket_connection.connection.active)
