python3-pika 0.11.0-1 / usr / lib / python3 / dist-packages / pika / channel.py

"""The Channel class provides a wrapper for interacting with RabbitMQ
implementing the methods and behaviors for an AMQP Channel.

"""

import collections
import logging
import uuid

import pika.frame as frame
import pika.exceptions as exceptions
import pika.spec as spec
from pika.utils import is_callable
from pika.compat import unicode_type, dictkeys, is_integer


LOGGER = logging.getLogger(__name__)

MAX_CHANNELS = 65535  # per AMQP 0.9.1 spec.


class Channel(object):
    """A Channel is the primary communication method for interacting with
    RabbitMQ. It is recommended that you do not directly invoke
    the creation of a channel object in your application code but rather
    construct the a channel by calling the active connection's channel()
    method.

    """

    # Disable pyling messages concerning "method could be a function"
    # pylint: disable=R0201

    CLOSED = 0
    OPENING = 1
    OPEN = 2
    CLOSING = 3  # client-initiated close in progress

    _STATE_NAMES = {
        CLOSED: 'CLOSED',
        OPENING: 'OPENING',
        OPEN: 'OPEN',
        CLOSING: 'CLOSING'
    }

    _ON_CHANNEL_CLEANUP_CB_KEY = '_on_channel_cleanup'

    def __init__(self, connection, channel_number, on_open_callback):
        """Create a new instance of the Channel

        :param pika.connection.Connection connection: The connection
        :param int channel_number: The channel number for this instance
        :param callable on_open_callback: The callback to call on channel open

        """
        if not isinstance(channel_number, int):
            raise exceptions.InvalidChannelNumber
        self.channel_number = channel_number
        self.callbacks = connection.callbacks
        self.connection = connection

        # Initially, flow is assumed to be active
        self.flow_active = True

        self._content_assembler = ContentFrameAssembler()

        self._blocked = collections.deque(list())
        self._blocking = None
        self._has_on_flow_callback = False
        self._cancelled = set()
        self._consumers = dict()
        self._consumers_with_noack = set()
        self._on_flowok_callback = None
        self._on_getok_callback = None
        self._on_openok_callback = on_open_callback
        self._state = self.CLOSED

        # We save the closing reason code and text to be passed to
        # on-channel-close callback at closing of the channel. Channel.close
        # stores the given reply_code/reply_text if the channel was in OPEN or
        # OPENING states. An incoming Channel.Close AMQP method from broker will
        # override this value. And a sudden loss of connection has the highest
        # prececence to override it.
        self._closing_code_and_text = (0, '')

        # opaque cookie value set by wrapper layer (e.g., BlockingConnection)
        # via _set_cookie
        self._cookie = None

    def __int__(self):
        """Return the channel object as its channel number

        :rtype: int

        """
        return self.channel_number

    def __repr__(self):
        return '<%s number=%s %s conn=%r>' % (self.__class__.__name__,
                                              self.channel_number,
                                              self._STATE_NAMES[self._state],
                                              self.connection)

    def add_callback(self, callback, replies, one_shot=True):
        """Pass in a callback handler and a list replies from the
        RabbitMQ broker which you'd like the callback notified of. Callbacks
        should allow for the frame parameter to be passed in.

        :param callable callback: The callback to call
        :param list replies: The replies to get a callback for
        :param bool one_shot: Only handle the first type callback

        """
        for reply in replies:
            self.callbacks.add(self.channel_number, reply, callback, one_shot)

    def add_on_cancel_callback(self, callback):
        """Pass a callback function that will be called when the basic_cancel
        is sent by the server. The callback function should receive a frame
        parameter.

        :param callable callback: The callback to call on Basic.Cancel from
            broker

        """
        self.callbacks.add(self.channel_number, spec.Basic.Cancel, callback,
                           False)

    def add_on_close_callback(self, callback):
        """Pass a callback function that will be called when the channel is
        closed. The callback function will receive the channel, the
        reply_code (int) and the reply_text (int) describing why the channel was
        closed.

        If the channel is closed by broker via Channel.Close, the callback will
        receive the reply_code/reply_text provided by the broker.

        If channel closing is initiated by user (either directly of indirectly
        by closing a connection containing the channel) and closing
        concludes gracefully without Channel.Close from the broker and without
        loss of connection, the callback will receive 0 as reply_code and empty
        string as reply_text.

        If channel was closed due to loss of connection, the callback will
        receive reply_code and reply_text representing the loss of connection.

        :param callable callback: The callback, having the signature:
            callback(Channel, int reply_code, str reply_text)

        """
        self.callbacks.add(self.channel_number, '_on_channel_close', callback,
                           False, self)

    def add_on_flow_callback(self, callback):
        """Pass a callback function that will be called when Channel.Flow is
        called by the remote server. Note that newer versions of RabbitMQ
        will not issue this but instead use TCP backpressure

        :param callable callback: The callback function

        """
        self._has_on_flow_callback = True
        self.callbacks.add(self.channel_number, spec.Channel.Flow, callback,
                           False)

    def add_on_return_callback(self, callback):
        """Pass a callback function that will be called when basic_publish as
        sent a message that has been rejected and returned by the server.

        :param callable callback: The function to call, having the signature
                                callback(channel, method, properties, body)
                                where
                                channel: pika.Channel
                                method: pika.spec.Basic.Return
                                properties: pika.spec.BasicProperties
                                body: str, unicode, or bytes (python 3.x)

        """
        self.callbacks.add(self.channel_number, '_on_return', callback, False)

    def basic_ack(self, delivery_tag=0, multiple=False):
        """Acknowledge one or more messages. When sent by the client, this
        method acknowledges one or more messages delivered via the Deliver or
        Get-Ok methods. When sent by server, this method acknowledges one or
        more messages published with the Publish method on a channel in
        confirm mode. The acknowledgement can be for a single message or a
        set of messages up to and including a specific message.

        :param integer delivery_tag: int/long The server-assigned delivery tag
        :param bool multiple: If set to True, the delivery tag is treated as
                              "up to and including", so that multiple messages
                              can be acknowledged with a single method. If set
                              to False, the delivery tag refers to a single
                              message. If the multiple field is 1, and the
                              delivery tag is zero, this indicates
                              acknowledgement of all outstanding messages.
        """
        if not self.is_open:
            raise exceptions.ChannelClosed()
        return self._send_method(spec.Basic.Ack(delivery_tag, multiple))

    def basic_cancel(self, callback=None, consumer_tag='', nowait=False):
        """This method cancels a consumer. This does not affect already
        delivered messages, but it does mean the server will not send any more
        messages for that consumer. The client may receive an arbitrary number
        of messages in between sending the cancel method and receiving the
        cancel-ok reply. It may also be sent from the server to the client in
        the event of the consumer being unexpectedly cancelled (i.e. cancelled
        for any reason other than the server receiving the corresponding
        basic.cancel from the client). This allows clients to be notified of
        the loss of consumers due to events such as queue deletion.

        :param callable callback: Callback to call for a Basic.CancelOk
            response; MUST be None when nowait=True. MUST be callable when
            nowait=False.
        :param str consumer_tag: Identifier for the consumer
        :param bool nowait: Do not expect a Basic.CancelOk response

        :raises ValueError:

        """
        self._validate_channel_and_callback(callback)

        if nowait:
            if callback is not None:
                raise ValueError(
                    'Completion callback must be None when nowait=True')
        else:
            if callback is None:
                raise ValueError(
                    'Must have completion callback with nowait=False')

        if consumer_tag in self._cancelled:
            # We check for cancelled first, because basic_cancel removes
            # consumers closed with nowait from self._consumers
            LOGGER.warning('basic_cancel - consumer is already cancelling: %s',
                           consumer_tag)
            return

        if consumer_tag not in self._consumers:
            # Could be cancelled by user or broker earlier
            LOGGER.warning('basic_cancel - consumer not found: %s',
                           consumer_tag)
            return

        LOGGER.debug('Cancelling consumer: %s (nowait=%s)',
                     consumer_tag, nowait)

        if nowait:
            # This is our last opportunity while the channel is open to remove
            # this consumer callback and help gc; unfortunately, this consumer's
            # self._cancelled and self._consumers_with_noack (if any) entries
            # will persist until the channel is closed.
            del self._consumers[consumer_tag]

        if callback is not None:
            if nowait:
                raise ValueError('Cannot pass a callback if nowait is True')
            self.callbacks.add(self.channel_number, spec.Basic.CancelOk,
                               callback)

        self._cancelled.add(consumer_tag)

        self._rpc(spec.Basic.Cancel(consumer_tag=consumer_tag, nowait=nowait),
                  self._on_cancelok if not nowait else None,
                  [(spec.Basic.CancelOk, {'consumer_tag': consumer_tag})] if
                  nowait is False else [])

    def basic_consume(self, consumer_callback,
                      queue='',
                      no_ack=False,
                      exclusive=False,
                      consumer_tag=None,
                      arguments=None):
        """Sends the AMQP 0-9-1 command Basic.Consume to the broker and binds messages
        for the consumer_tag to the consumer callback. If you do not pass in
        a consumer_tag, one will be automatically generated for you. Returns
        the consumer tag.

        For more information on basic_consume, see:
        Tutorial 2 at http://www.rabbitmq.com/getstarted.html
        http://www.rabbitmq.com/confirms.html
        http://www.rabbitmq.com/amqp-0-9-1-reference.html#basic.consume


        :param callable consumer_callback: The function to call when consuming
            with the signature consumer_callback(channel, method, properties,
                                                 body), where
                                channel: pika.Channel
                                method: pika.spec.Basic.Deliver
                                properties: pika.spec.BasicProperties
                                body: str, unicode, or bytes (python 3.x)

        :param queue: The queue to consume from
        :type queue: str or unicode
        :param bool no_ack: if set to True, automatic acknowledgement mode will be used
                            (see http://www.rabbitmq.com/confirms.html)
        :param bool exclusive: Don't allow other consumers on the queue
        :param consumer_tag: Specify your own consumer tag
        :type consumer_tag: str or unicode
        :param dict arguments: Custom key/value pair arguments for the consumer
        :rtype: str

        """
        self._validate_channel_and_callback(consumer_callback)

        # If a consumer tag was not passed, create one
        if not consumer_tag:
            consumer_tag = self._generate_consumer_tag()

        if consumer_tag in self._consumers or consumer_tag in self._cancelled:
            raise exceptions.DuplicateConsumerTag(consumer_tag)

        if no_ack:
            self._consumers_with_noack.add(consumer_tag)

        self._consumers[consumer_tag] = consumer_callback
        self._rpc(spec.Basic.Consume(queue=queue,
                                     consumer_tag=consumer_tag,
                                     no_ack=no_ack,
                                     exclusive=exclusive,
                                     arguments=arguments or dict()),
                  self._on_eventok, [(spec.Basic.ConsumeOk,
                                      {'consumer_tag': consumer_tag})])

        return consumer_tag

    def _generate_consumer_tag(self):
        """Generate a consumer tag

        NOTE: this protected method may be called by derived classes

        :returns: consumer tag
        :rtype: str
        """
        return 'ctag%i.%s' % (self.channel_number,
                              uuid.uuid4().hex)

    def basic_get(self, callback=None, queue='', no_ack=False):
        """Get a single message from the AMQP broker. If you want to
        be notified of Basic.GetEmpty, use the Channel.add_callback method
        adding your Basic.GetEmpty callback which should expect only one
        parameter, frame. Due to implementation details, this cannot be called
        a second time until the callback is executed.  For more information on
        basic_get and its parameters, see:

        http://www.rabbitmq.com/amqp-0-9-1-reference.html#basic.get

        :param callable callback: The callback to call with a message that has
            the signature callback(channel, method, properties, body), where:
            channel: pika.Channel
            method: pika.spec.Basic.GetOk
            properties: pika.spec.BasicProperties
            body: str, unicode, or bytes (python 3.x)
        :param queue: The queue to get a message from
        :type queue: str or unicode
        :param bool no_ack: Tell the broker to not expect a reply

        """
        self._validate_channel_and_callback(callback)
        # TODO Is basic_get meaningful when callback is None?
        if self._on_getok_callback is not None:
            raise exceptions.DuplicateGetOkCallback()
        self._on_getok_callback = callback
        # TODO Strangely, not using _rpc for the synchronous Basic.Get. Would
        # need to extend _rpc to handle Basic.GetOk method, header, and body
        # frames (or similar)
        self._send_method(spec.Basic.Get(queue=queue, no_ack=no_ack))

    def basic_nack(self, delivery_tag=None, multiple=False, requeue=True):
        """This method allows a client to reject one or more incoming messages.
        It can be used to interrupt and cancel large incoming messages, or
        return untreatable messages to their original queue.

        :param integer delivery-tag: int/long The server-assigned delivery tag
        :param bool multiple: If set to True, the delivery tag is treated as
                              "up to and including", so that multiple messages
                              can be acknowledged with a single method. If set
                              to False, the delivery tag refers to a single
                              message. If the multiple field is 1, and the
                              delivery tag is zero, this indicates
                              acknowledgement of all outstanding messages.
        :param bool requeue: If requeue is true, the server will attempt to
                             requeue the message. If requeue is false or the
                             requeue attempt fails the messages are discarded or
                             dead-lettered.

        """
        if not self.is_open:
            raise exceptions.ChannelClosed()
        return self._send_method(spec.Basic.Nack(delivery_tag, multiple,
                                                 requeue))

    def basic_publish(self, exchange, routing_key, body,
                      properties=None,
                      mandatory=False,
                      immediate=False):
        """Publish to the channel with the given exchange, routing key and body.
        For more information on basic_publish and what the parameters do, see:

        http://www.rabbitmq.com/amqp-0-9-1-reference.html#basic.publish

        :param exchange: The exchange to publish to
        :type exchange: str or unicode
        :param routing_key: The routing key to bind on
        :type routing_key: str or unicode
        :param body: The message body
        :type body: str or unicode
        :param pika.spec.BasicProperties properties: Basic.properties
        :param bool mandatory: The mandatory flag
        :param bool immediate: The immediate flag

        """
        if not self.is_open:
            raise exceptions.ChannelClosed()
        if immediate:
            LOGGER.warning('The immediate flag is deprecated in RabbitMQ')
        if isinstance(body, unicode_type):
            body = body.encode('utf-8')
        properties = properties or spec.BasicProperties()
        self._send_method(spec.Basic.Publish(exchange=exchange,
                                             routing_key=routing_key,
                                             mandatory=mandatory,
                                             immediate=immediate),
                          (properties, body))

    def basic_qos(self,
                  callback=None,
                  prefetch_size=0,
                  prefetch_count=0,
                  all_channels=False):
        """Specify quality of service. This method requests a specific quality
        of service. The QoS can be specified for the current channel or for all
        channels on the connection. The client can request that messages be sent
        in advance so that when the client finishes processing a message, the
        following message is already held locally, rather than needing to be
        sent down the channel. Prefetching gives a performance improvement.

        :param callable callback: The callback to call for Basic.QosOk response
        :param int prefetch_size:  This field specifies the prefetch window
                                   size. The server will send a message in
                                   advance if it is equal to or smaller in size
                                   than the available prefetch size (and also
                                   falls into other prefetch limits). May be set
                                   to zero, meaning "no specific limit",
                                   although other prefetch limits may still
                                   apply. The prefetch-size is ignored if the
                                   no-ack option is set.
        :param int prefetch_count: Specifies a prefetch window in terms of whole
                                   messages. This field may be used in
                                   combination with the prefetch-size field; a
                                   message will only be sent in advance if both
                                   prefetch windows (and those at the channel
                                   and connection level) allow it. The
                                   prefetch-count is ignored if the no-ack
                                   option is set.
        :param bool all_channels: Should the QoS apply to all channels

        """
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Basic.Qos(prefetch_size, prefetch_count,
                                        all_channels),
                         callback, [spec.Basic.QosOk])

    def basic_reject(self, delivery_tag, requeue=True):
        """Reject an incoming message. This method allows a client to reject a
        message. It can be used to interrupt and cancel large incoming messages,
        or return untreatable messages to their original queue.

        :param integer delivery-tag: int/long The server-assigned delivery tag
        :param bool requeue: If requeue is true, the server will attempt to
                             requeue the message. If requeue is false or the
                             requeue attempt fails the messages are discarded or
                             dead-lettered.
        :raises: TypeError

        """
        if not self.is_open:
            raise exceptions.ChannelClosed()
        if not is_integer(delivery_tag):
            raise TypeError('delivery_tag must be an integer')
        return self._send_method(spec.Basic.Reject(delivery_tag, requeue))

    def basic_recover(self, callback=None, requeue=False):
        """This method asks the server to redeliver all unacknowledged messages
        on a specified channel. Zero or more messages may be redelivered. This
        method replaces the asynchronous Recover.

        :param callable callback: Callback to call when receiving
            Basic.RecoverOk
        :param bool requeue: If False, the message will be redelivered to the
                             original recipient. If True, the server will
                             attempt to requeue the message, potentially then
                             delivering it to an alternative subscriber.

        """
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Basic.Recover(requeue), callback,
                         [spec.Basic.RecoverOk])

    def close(self, reply_code=0, reply_text="Normal shutdown"):
        """Invoke a graceful shutdown of the channel with the AMQP Broker.

        If channel is OPENING, transition to CLOSING and suppress the incoming
        Channel.OpenOk, if any.

        :param int reply_code: The reason code to send to broker
        :param str reply_text: The reason text to send to broker

        :raises ChannelClosed: if channel is already closed
        :raises ChannelAlreadyClosing: if channel is already closing
        """
        if self.is_closed:
            # Whoever is calling `close` might expect the on-channel-close-cb
            # to be called, which won't happen when it's already closed
            raise exceptions.ChannelClosed('Already closed: %s' % self)

        if self.is_closing:
            # Whoever is calling `close` might expect their reply_code and
            # reply_text to be sent to broker, which won't happen if we're
            # already closing.
            raise exceptions.ChannelAlreadyClosing('Already closing: %s' % self)

        # If channel is OPENING, we will transition it to CLOSING state,
        # causing the _on_openok method to suppress the OPEN state transition
        # and the on-channel-open-callback

        LOGGER.info('Closing channel (%s): %r on %s',
                    reply_code, reply_text, self)

        for consumer_tag in dictkeys(self._consumers):
            if consumer_tag not in self._cancelled:
                self.basic_cancel(consumer_tag=consumer_tag, nowait=True)

        # Change state after cancelling consumers to avoid ChannelClosed
        # exception from basic_cancel
        self._set_state(self.CLOSING)

        self._rpc(spec.Channel.Close(reply_code, reply_text, 0, 0),
                  self._on_closeok, [spec.Channel.CloseOk])

    def confirm_delivery(self, callback=None, nowait=False):
        """Turn on Confirm mode in the channel. Pass in a callback to be
        notified by the Broker when a message has been confirmed as received or
        rejected (Basic.Ack, Basic.Nack) from the broker to the publisher.

        For more information see:
            http://www.rabbitmq.com/extensions.html#confirms

        :param callable callback: The callback for delivery confirmations that
            has the following signature: callback(pika.frame.Method), where
            method_frame contains either method `spec.Basic.Ack` or
            `spec.Basic.Nack`.
        :param bool nowait: Do not send a reply frame (Confirm.SelectOk)

        """
        self._validate_channel_and_callback(callback)

        # TODO confirm_deliver should require a callback; it's meaningless
        # without a user callback to receieve Basic.Ack/Basic.Nack notifications

        if not (self.connection.publisher_confirms and
                self.connection.basic_nack):
            raise exceptions.MethodNotImplemented('Not Supported on Server')

        # Add the ack and nack callbacks
        if callback is not None:
            self.callbacks.add(self.channel_number, spec.Basic.Ack, callback,
                               False)
            self.callbacks.add(self.channel_number, spec.Basic.Nack, callback,
                               False)

        # Send the RPC command
        self._rpc(spec.Confirm.Select(nowait),
                  self._on_selectok if not nowait else None,
                  [spec.Confirm.SelectOk] if nowait is False else [])

    @property
    def consumer_tags(self):
        """Property method that returns a list of currently active consumers

        :rtype: list

        """
        return dictkeys(self._consumers)

    def exchange_bind(self,
                      callback=None,
                      destination=None,
                      source=None,
                      routing_key='',
                      nowait=False,
                      arguments=None):
        """Bind an exchange to another exchange.

        :param callable callback: The callback to call on Exchange.BindOk; MUST
            be None when nowait=True
        :param destination: The destination exchange to bind
        :type destination: str or unicode
        :param source: The source exchange to bind to
        :type source: str or unicode
        :param routing_key: The routing key to bind on
        :type routing_key: str or unicode
        :param bool nowait: Do not wait for an Exchange.BindOk
        :param dict arguments: Custom key/value pair arguments for the binding

        """
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Exchange.Bind(0, destination, source, routing_key,
                                            nowait, arguments or dict()),
                         callback, [spec.Exchange.BindOk] if nowait is False
                         else [])

    def exchange_declare(self,
                         callback=None,
                         exchange=None,
                         exchange_type='direct',
                         passive=False,
                         durable=False,
                         auto_delete=False,
                         internal=False,
                         nowait=False,
                         arguments=None):
        """This method creates an exchange if it does not already exist, and if
        the exchange exists, verifies that it is of the correct and expected
        class.

        If passive set, the server will reply with Declare-Ok if the exchange
        already exists with the same name, and raise an error if not and if the
        exchange does not already exist, the server MUST raise a channel
        exception with reply code 404 (not found).

        :param callable callback: Call this method on Exchange.DeclareOk; MUST
            be None when nowait=True
        :param exchange: The exchange name consists of a non-empty
        :type exchange: str or unicode
                                     sequence of these characters: letters,
                                     digits, hyphen, underscore, period, or
                                     colon.
        :param str exchange_type: The exchange type to use
        :param bool passive: Perform a declare or just check to see if it exists
        :param bool durable: Survive a reboot of RabbitMQ
        :param bool auto_delete: Remove when no more queues are bound to it
        :param bool internal: Can only be published to by other exchanges
        :param bool nowait: Do not expect an Exchange.DeclareOk response
        :param dict arguments: Custom key/value pair arguments for the exchange

        """
        self._validate_channel_and_callback(callback)

        return self._rpc(spec.Exchange.Declare(0, exchange, exchange_type,
                                               passive, durable, auto_delete,
                                               internal, nowait,
                                               arguments or dict()),
                         callback,
                         [spec.Exchange.DeclareOk] if nowait is False else [])

    def exchange_delete(self,
                        callback=None,
                        exchange=None,
                        if_unused=False,
                        nowait=False):
        """Delete the exchange.

        :param callable callback: The function to call on Exchange.DeleteOk;
            MUST be None when nowait=True.
        :param exchange: The exchange name
        :type exchange: str or unicode
        :param bool if_unused: only delete if the exchange is unused
        :param bool nowait: Do not wait for an Exchange.DeleteOk

        """
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Exchange.Delete(0, exchange, if_unused, nowait),
                         callback, [spec.Exchange.DeleteOk] if nowait is False
                         else [])

    def exchange_unbind(self,
                        callback=None,
                        destination=None,
                        source=None,
                        routing_key='',
                        nowait=False,
                        arguments=None):
        """Unbind an exchange from another exchange.

        :param callable callback: The callback to call on Exchange.UnbindOk;
            MUST be None when nowait=True.
        :param destination: The destination exchange to unbind
        :type destination: str or unicode
        :param source: The source exchange to unbind from
        :type source: str or unicode
        :param routing_key: The routing key to unbind
        :type routing_key: str or unicode
        :param bool nowait: Do not wait for an Exchange.UnbindOk
        :param dict arguments: Custom key/value pair arguments for the binding

        """
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Exchange.Unbind(0, destination, source,
                                              routing_key, nowait, arguments),
                         callback,
                         [spec.Exchange.UnbindOk] if nowait is False else [])

    def flow(self, callback, active):
        """Turn Channel flow control off and on. Pass a callback to be notified
        of the response from the server. active is a bool. Callback should
        expect a bool in response indicating channel flow state. For more
        information, please reference:

        http://www.rabbitmq.com/amqp-0-9-1-reference.html#channel.flow

        :param callable callback: The callback to call upon completion
        :param bool active: Turn flow on or off

        """
        self._validate_channel_and_callback(callback)
        self._on_flowok_callback = callback
        self._rpc(spec.Channel.Flow(active), self._on_flowok,
                  [spec.Channel.FlowOk])

    @property
    def is_closed(self):
        """Returns True if the channel is closed.

        :rtype: bool

        """
        return self._state == self.CLOSED

    @property
    def is_closing(self):
        """Returns True if client-initiated closing of the channel is in
        progress.

        :rtype: bool

        """
        return self._state == self.CLOSING

    @property
    def is_open(self):
        """Returns True if the channel is open.

        :rtype: bool

        """
        return self._state == self.OPEN

    def open(self):
        """Open the channel"""
        self._set_state(self.OPENING)
        self._add_callbacks()
        self._rpc(spec.Channel.Open(), self._on_openok, [spec.Channel.OpenOk])

    def queue_bind(self, callback, queue, exchange,
                   routing_key=None,
                   nowait=False,
                   arguments=None):
        """Bind the queue to the specified exchange

        :param callable callback: The callback to call on Queue.BindOk;
            MUST be None when nowait=True.
        :param queue: The queue to bind to the exchange
        :type queue: str or unicode
        :param exchange: The source exchange to bind to
        :type exchange: str or unicode
        :param routing_key: The routing key to bind on
        :type routing_key: str or unicode
        :param bool nowait: Do not wait for a Queue.BindOk
        :param dict arguments: Custom key/value pair arguments for the binding

        """
        self._validate_channel_and_callback(callback)
        replies = [spec.Queue.BindOk] if nowait is False else []
        if routing_key is None:
            routing_key = queue
        return self._rpc(spec.Queue.Bind(0, queue, exchange, routing_key,
                                         nowait, arguments or dict()),
                         callback, replies)

    def queue_declare(self, callback,
                      queue='',
                      passive=False,
                      durable=False,
                      exclusive=False,
                      auto_delete=False,
                      nowait=False,
                      arguments=None):
        """Declare queue, create if needed. This method creates or checks a
        queue. When creating a new queue the client can specify various
        properties that control the durability of the queue and its contents,
        and the level of sharing for the queue.

        Leave the queue name empty for a auto-named queue in RabbitMQ

        :param callable callback: callback(pika.frame.Method) for method
          Queue.DeclareOk; MUST be None when nowait=True.
        :param queue: The queue name
        :type queue: str or unicode
        :param bool passive: Only check to see if the queue exists
        :param bool durable: Survive reboots of the broker
        :param bool exclusive: Only allow access by the current connection
        :param bool auto_delete: Delete after consumer cancels or disconnects
        :param bool nowait: Do not wait for a Queue.DeclareOk
        :param dict arguments: Custom key/value arguments for the queue

        """
        if queue:
            condition = (spec.Queue.DeclareOk,
                         {'queue': queue})
        else:
            condition = spec.Queue.DeclareOk  # pylint: disable=R0204
        replies = [condition] if nowait is False else []
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Queue.Declare(0, queue, passive, durable,
                                            exclusive, auto_delete, nowait,
                                            arguments or dict()),
                         callback, replies)

    def queue_delete(self,
                     callback=None,
                     queue='',
                     if_unused=False,
                     if_empty=False,
                     nowait=False):
        """Delete a queue from the broker.

        :param callable callback: The callback to call on Queue.DeleteOk;
            MUST be None when nowait=True.
        :param queue: The queue to delete
        :type queue: str or unicode
        :param bool if_unused: only delete if it's unused
        :param bool if_empty: only delete if the queue is empty
        :param bool nowait: Do not wait for a Queue.DeleteOk

        """
        replies = [spec.Queue.DeleteOk] if nowait is False else []
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Queue.Delete(0, queue, if_unused, if_empty,
                                           nowait),
                         callback, replies)

    def queue_purge(self, callback=None, queue='', nowait=False):
        """Purge all of the messages from the specified queue

        :param callable callback: The callback to call on Queue.PurgeOk;
            MUST be None when nowait=True.
        :param queue: The queue to purge
        :type queue: str or unicode
        :param bool nowait: Do not expect a Queue.PurgeOk response

        """
        replies = [spec.Queue.PurgeOk] if nowait is False else []
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Queue.Purge(0, queue, nowait), callback, replies)

    def queue_unbind(self,
                     callback=None,
                     queue='',
                     exchange=None,
                     routing_key=None,
                     arguments=None):
        """Unbind a queue from an exchange.

        :param callable callback: The callback to call on Queue.UnbindOk
        :param queue: The queue to unbind from the exchange
        :type queue: str or unicode
        :param exchange: The source exchange to bind from
        :type exchange: str or unicode
        :param routing_key: The routing key to unbind
        :type routing_key: str or unicode
        :param dict arguments: Custom key/value pair arguments for the binding

        """
        self._validate_channel_and_callback(callback)
        if routing_key is None:
            routing_key = queue
        return self._rpc(spec.Queue.Unbind(0, queue, exchange, routing_key,
                                           arguments or dict()),
                         callback, [spec.Queue.UnbindOk])

    def tx_commit(self, callback=None):
        """Commit a transaction

        :param callable callback: The callback for delivery confirmations

        """
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Tx.Commit(), callback, [spec.Tx.CommitOk])

    def tx_rollback(self, callback=None):
        """Rollback a transaction.

        :param callable callback: The callback for delivery confirmations

        """
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Tx.Rollback(), callback, [spec.Tx.RollbackOk])

    def tx_select(self, callback=None):
        """Select standard transaction mode. This method sets the channel to use
        standard transactions. The client must use this method at least once on
        a channel before using the Commit or Rollback methods.

        :param callable callback: The callback for delivery confirmations

        """
        self._validate_channel_and_callback(callback)
        return self._rpc(spec.Tx.Select(), callback, [spec.Tx.SelectOk])

    # Internal methods

    def _add_callbacks(self):
        """Callbacks that add the required behavior for a channel when
        connecting and connected to a server.

        """
        # Add a callback for Basic.GetEmpty
        self.callbacks.add(self.channel_number, spec.Basic.GetEmpty,
                           self._on_getempty, False)

        # Add a callback for Basic.Cancel
        self.callbacks.add(self.channel_number, spec.Basic.Cancel,
                           self._on_cancel, False)

        # Deprecated in newer versions of RabbitMQ but still register for it
        self.callbacks.add(self.channel_number, spec.Channel.Flow,
                           self._on_flow, False)

        # Add a callback for when the server closes our channel
        self.callbacks.add(self.channel_number, spec.Channel.Close,
                           self._on_close, True)

    def _add_on_cleanup_callback(self, callback):
        """For internal use only (e.g., Connection needs to remove closed
        channels from its channel container). Pass a callback function that will
        be called when the channel is being cleaned up after all channel-close
        callbacks callbacks.

        :param callable callback: The callback to call, having the
            signature: callback(channel)

        """
        self.callbacks.add(self.channel_number, self._ON_CHANNEL_CLEANUP_CB_KEY,
                           callback, one_shot=True, only_caller=self)

    def _cleanup(self):
        """Remove all consumers and any callbacks for the channel."""
        self.callbacks.process(self.channel_number,
                               self._ON_CHANNEL_CLEANUP_CB_KEY, self,
                               self)
        self._consumers = dict()
        self.callbacks.cleanup(str(self.channel_number))
        self._cookie = None

    def _cleanup_consumer_ref(self, consumer_tag):
        """Remove any references to the consumer tag in internal structures
        for consumer state.

        :param str consumer_tag: The consumer tag to cleanup

        """
        self._consumers_with_noack.discard(consumer_tag)
        self._consumers.pop(consumer_tag, None)
        self._cancelled.discard(consumer_tag)

    def _get_cookie(self):
        """Used by the wrapper implementation (e.g., `BlockingChannel`) to
        retrieve the cookie that it set via `_set_cookie`

        :returns: opaque cookie value that was set via `_set_cookie`
        """
        return self._cookie

    def _handle_content_frame(self, frame_value):
        """This is invoked by the connection when frames that are not registered
        with the CallbackManager have been found. This should only be the case
        when the frames are related to content delivery.

        The _content_assembler will be invoked which will return the fully
        formed message in three parts when all of the body frames have been
        received.

        :param pika.amqp_object.Frame frame_value: The frame to deliver

        """
        try:
            response = self._content_assembler.process(frame_value)
        except exceptions.UnexpectedFrameError:
            self._on_unexpected_frame(frame_value)
            return

        if response:
            if isinstance(response[0].method, spec.Basic.Deliver):
                self._on_deliver(*response)
            elif isinstance(response[0].method, spec.Basic.GetOk):
                self._on_getok(*response)
            elif isinstance(response[0].method, spec.Basic.Return):
                self._on_return(*response)

    def _on_cancel(self, method_frame):
        """When the broker cancels a consumer, delete it from our internal
        dictionary.

        :param pika.frame.Method method_frame: The method frame received

        """
        if method_frame.method.consumer_tag in self._cancelled:
            # User-initiated cancel is waiting for Cancel-ok
            return

        self._cleanup_consumer_ref(method_frame.method.consumer_tag)

    def _on_cancelok(self, method_frame):
        """Called in response to a frame from the Broker when the
         client sends Basic.Cancel

        :param pika.frame.Method method_frame: The method frame received

        """
        self._cleanup_consumer_ref(method_frame.method.consumer_tag)

    def _on_close(self, method_frame):
        """Handle the case where our channel has been closed for us

        :param pika.frame.Method method_frame: Method frame with Channel.Close
            method

        """
        LOGGER.warning('Received remote Channel.Close (%s): %r on %s',
                       method_frame.method.reply_code,
                       method_frame.method.reply_text,
                       self)

        # AMQP 0.9.1 requires CloseOk response to Channel.Close; Note, we should
        # not be called when connection is closed
        self._send_method(spec.Channel.CloseOk())

        if self.is_closing:
            # Since we already sent Channel.Close, we need to wait for CloseOk
            # before cleaning up to avoid a race condition whereby our channel
            # number might get reused before our CloseOk arrives

            # Save the details to provide to user callback when CloseOk arrives
            self._closing_code_and_text = (method_frame.method.reply_code,
                                           method_frame.method.reply_text)
        else:
            self._set_state(self.CLOSED)
            try:
                self.callbacks.process(self.channel_number, '_on_channel_close',
                                       self, self,
                                       method_frame.method.reply_code,
                                       method_frame.method.reply_text)
            finally:
                self._cleanup()

    def _on_close_meta(self, reply_code, reply_text):
        """Handle meta-close request from Connection's cleanup logic after
        sudden connection loss. We use this opportunity to transition to
        CLOSED state, clean up the channel, and dispatch the on-channel-closed
        callbacks.

        :param int reply_code: The reply code to pass to on-close callback
        :param str reply_text: The reply text to pass to on-close callback

        """
        LOGGER.debug('Handling meta-close on %s', self)

        if not self.is_closed:
            self._closing_code_and_text = reply_code, reply_text

            self._set_state(self.CLOSED)

            try:
                self.callbacks.process(self.channel_number, '_on_channel_close',
                                       self, self,
                                       reply_code,
                                       reply_text)
            finally:
                self._cleanup()

    def _on_closeok(self, method_frame):
        """Invoked when RabbitMQ replies to a Channel.Close method

        :param pika.frame.Method method_frame: Method frame with Channel.CloseOk
            method

        """
        LOGGER.info('Received %s on %s', method_frame.method, self)

        self._set_state(self.CLOSED)

        try:
            self.callbacks.process(self.channel_number, '_on_channel_close',
                                   self, self,
                                   self._closing_code_and_text[0],
                                   self._closing_code_and_text[1])
        finally:
            self._cleanup()

    def _on_deliver(self, method_frame, header_frame, body):
        """Cope with reentrancy. If a particular consumer is still active when
        another delivery appears for it, queue the deliveries up until it
        finally exits.

        :param pika.frame.Method method_frame: The method frame received
        :param pika.frame.Header header_frame: The header frame received
        :param body: The body received
        :type body: str or unicode

        """
        consumer_tag = method_frame.method.consumer_tag

        if consumer_tag in self._cancelled:
            if self.is_open and consumer_tag not in self._consumers_with_noack:
                self.basic_reject(method_frame.method.delivery_tag)
            return

        if consumer_tag not in self._consumers:
            LOGGER.error('Unexpected delivery: %r', method_frame)
            return

        self._consumers[consumer_tag](self, method_frame.method,
                                      header_frame.properties, body)

    def _on_eventok(self, method_frame):
        """Generic events that returned ok that may have internal callbacks.
        We keep a list of what we've yet to implement so that we don't silently
        drain events that we don't support.

        :param pika.frame.Method method_frame: The method frame received

        """
        LOGGER.debug('Discarding frame %r', method_frame)

    def _on_flow(self, _method_frame_unused):
        """Called if the server sends a Channel.Flow frame.

        :param pika.frame.Method method_frame_unused: The Channel.Flow frame

        """
        if self._has_on_flow_callback is False:
            LOGGER.warning('Channel.Flow received from server')

    def _on_flowok(self, method_frame):
        """Called in response to us asking the server to toggle on Channel.Flow

        :param pika.frame.Method method_frame: The method frame received

        """
        self.flow_active = method_frame.method.active
        if self._on_flowok_callback:
            self._on_flowok_callback(method_frame.method.active)
            self._on_flowok_callback = None
        else:
            LOGGER.warning('Channel.FlowOk received with no active callbacks')

    def _on_getempty(self, method_frame):
        """When we receive an empty reply do nothing but log it

        :param pika.frame.Method method_frame: The method frame received

        """
        LOGGER.debug('Received Basic.GetEmpty: %r', method_frame)
        if self._on_getok_callback is not None:
            self._on_getok_callback = None

    def _on_getok(self, method_frame, header_frame, body):
        """Called in reply to a Basic.Get when there is a message.

        :param pika.frame.Method method_frame: The method frame received
        :param pika.frame.Header header_frame: The header frame received
        :param body: The body received
        :type body: str or unicode

        """
        if self._on_getok_callback is not None:
            callback = self._on_getok_callback
            self._on_getok_callback = None
            callback(self, method_frame.method, header_frame.properties, body)
        else:
            LOGGER.error('Basic.GetOk received with no active callback')

    def _on_openok(self, method_frame):
        """Called by our callback handler when we receive a Channel.OpenOk and
        subsequently calls our _on_openok_callback which was passed into the
        Channel constructor. The reason we do this is because we want to make
        sure that the on_open_callback parameter passed into the Channel
        constructor is not the first callback we make.

        Suppress the state transition and callback if channel is already in
        CLOSING state.

        :param pika.frame.Method method_frame: Channel.OpenOk frame

        """
        # Suppress OpenOk if the user or Connection.Close started closing it
        # before open completed.
        if self.is_closing:
            LOGGER.debug('Suppressing while in closing state: %s', method_frame)
        else:
            self._set_state(self.OPEN)
            if self._on_openok_callback is not None:
                self._on_openok_callback(self)

    def _on_return(self, method_frame, header_frame, body):
        """Called if the server sends a Basic.Return frame.

        :param pika.frame.Method method_frame: The Basic.Return frame
        :param pika.frame.Header header_frame: The content header frame
        :param body: The message body
        :type body: str or unicode

        """
        if not self.callbacks.process(self.channel_number, '_on_return', self,
                                      self,
                                      method_frame.method,
                                      header_frame.properties,
                                      body):
            LOGGER.warning('Basic.Return received from server (%r, %r)',
                           method_frame.method, header_frame.properties)

    def _on_selectok(self, method_frame):
        """Called when the broker sends a Confirm.SelectOk frame

        :param pika.frame.Method method_frame: The method frame received

        """
        LOGGER.debug("Confirm.SelectOk Received: %r", method_frame)

    def _on_synchronous_complete(self, _method_frame_unused):
        """This is called when a synchronous command is completed. It will undo
        the blocking state and send all the frames that stacked up while we
        were in the blocking state.

        :param pika.frame.Method method_frame_unused: The method frame received

        """
        LOGGER.debug('%i blocked frames', len(self._blocked))
        self._blocking = None
        while self._blocked and self._blocking is None:
            self._rpc(*self._blocked.popleft())

    def _rpc(self, method, callback=None, acceptable_replies=None):
        """Make a syncronous channel RPC call for a synchronous method frame. If
        the channel is already in the blocking state, then enqueue the request,
        but don't send it at this time; it will be eventually sent by
        `_on_synchronous_complete` after the prior blocking request receives a
        resposne. If the channel is not in the blocking state and
        `acceptable_replies` is not empty, transition the channel to the
        blocking state and register for `_on_synchronous_complete` before
        sending the request.

        NOTE: A callback must be accompanied by non-empty acceptable_replies.

        :param pika.amqp_object.Method method: The AMQP method to invoke
        :param callable callback: The callback for the RPC response
        :param acceptable_replies: A (possibly empty) sequence of
            replies this RPC call expects or None
        :type acceptable_replies: list or None

        """
        assert method.synchronous, (
            'Only synchronous-capable methods may be used with _rpc: %r'
            % (method,))

        # Validate we got None or a list of acceptable_replies
        if not isinstance(acceptable_replies, (type(None), list)):
            raise TypeError('acceptable_replies should be list or None')

        if callback is not None:
            # Validate the callback is callable
            if not is_callable(callback):
                raise TypeError(
                    'callback should be None or a callable')

            # Make sure that callback is accompanied by acceptable replies
            if not acceptable_replies:
                raise ValueError(
                    'Unexpected callback for asynchronous (nowait) operation.')

        # Make sure the channel is not closed yet
        if self.is_closed:
            raise exceptions.ChannelClosed

        # If the channel is blocking, add subsequent commands to our stack
        if self._blocking:
            LOGGER.debug('Already in blocking state, so enqueueing method %s; '
                         'acceptable_replies=%r',
                         method, acceptable_replies)
            return self._blocked.append([method, callback, acceptable_replies])

        # If acceptable replies are set, add callbacks
        if acceptable_replies:
            # Block until a response frame is received for synchronous frames
            self._blocking = method.NAME
            LOGGER.debug(
                'Entering blocking state on frame %s; acceptable_replies=%r',
                method, acceptable_replies)

            for reply in acceptable_replies:
                if isinstance(reply, tuple):
                    reply, arguments = reply
                else:
                    arguments = None
                LOGGER.debug('Adding on_synchronous_complete callback')
                self.callbacks.add(self.channel_number, reply,
                                   self._on_synchronous_complete,
                                   arguments=arguments)
                if callback is not None:
                    LOGGER.debug('Adding passed-in callback')
                    self.callbacks.add(self.channel_number, reply, callback,
                                       arguments=arguments)

        self._send_method(method)

    def _send_method(self, method, content=None):
        """Shortcut wrapper to send a method through our connection, passing in
        the channel number

        :param pika.amqp_object.Method method: The method to send
        :param tuple content: If set, is a content frame, is tuple of
                              properties and body.

        """
        # pylint: disable=W0212
        self.connection._send_method(self.channel_number, method, content)

    def _set_cookie(self, cookie):
        """Used by wrapper layer (e.g., `BlockingConnection`) to link the
        channel implementation back to the proxy. See `_get_cookie`.

        :param cookie: an opaque value; typically a proxy channel implementation
            instance (e.g., `BlockingChannel` instance)
        """
        self._cookie = cookie

    def _set_state(self, connection_state):
        """Set the channel connection state to the specified state value.

        :param int connection_state: The connection_state value

        """
        self._state = connection_state

    def _on_unexpected_frame(self, frame_value):
        """Invoked when a frame is received that is not setup to be processed.

        :param pika.frame.Frame frame_value: The frame received

        """
        LOGGER.error('Unexpected frame: %r', frame_value)

    def _validate_channel_and_callback(self, callback):
        """Verify that channel is open and callback is callable if not None

        :raises ChannelClosed: if channel is closed
        :raises ValueError: if callback is not None and is not callable
        """
        if not self.is_open:
            raise exceptions.ChannelClosed()
        if callback is not None and not is_callable(callback):
            raise ValueError('callback must be a function or method')


class ContentFrameAssembler(object):
    """Handle content related frames, building a message and return the message
    back in three parts upon receipt.

    """

    def __init__(self):
        """Create a new instance of the conent frame assembler.

        """
        self._method_frame = None
        self._header_frame = None
        self._seen_so_far = 0
        self._body_fragments = list()

    def process(self, frame_value):
        """Invoked by the Channel object when passed frames that are not
        setup in the rpc process and that don't have explicit reply types
        defined. This includes Basic.Publish, Basic.GetOk and Basic.Return

        :param Method|Header|Body frame_value: The frame to process

        """
        if (isinstance(frame_value, frame.Method) and
                spec.has_content(frame_value.method.INDEX)):
            self._method_frame = frame_value
        elif isinstance(frame_value, frame.Header):
            self._header_frame = frame_value
            if frame_value.body_size == 0:
                return self._finish()
        elif isinstance(frame_value, frame.Body):
            return self._handle_body_frame(frame_value)
        else:
            raise exceptions.UnexpectedFrameError(frame_value)

    def _finish(self):
        """Invoked when all of the message has been received

        :rtype: tuple(pika.frame.Method, pika.frame.Header, str)

        """
        content = (self._method_frame, self._header_frame,
                   b''.join(self._body_fragments))
        self._reset()
        return content

    def _handle_body_frame(self, body_frame):
        """Receive body frames and append them to the stack. When the body size
        matches, call the finish method.

        :param Body body_frame: The body frame
        :raises: pika.exceptions.BodyTooLongError
        :rtype: tuple(pika.frame.Method, pika.frame.Header, str)|None

        """
        self._seen_so_far += len(body_frame.fragment)
        self._body_fragments.append(body_frame.fragment)
        if self._seen_so_far == self._header_frame.body_size:
            return self._finish()
        elif self._seen_so_far > self._header_frame.body_size:
            raise exceptions.BodyTooLongError(self._seen_so_far,
                                              self._header_frame.body_size)
        return None

    def _reset(self):
        """Reset the values for processing frames"""
        self._method_frame = None
        self._header_frame = None
        self._seen_so_far = 0
        self._body_fragments = list()