This document is for Kombu's development version, which can be significantly different from previous releases. Get the stable docs here: 5.3.

# Source code for kombu.messaging

    """Sending and receiving messages."""

    from __future__ import annotations

    from itertools import count
    from typing import TYPE_CHECKING

    from .common import maybe_declare
    from .compression import compress
    from .connection import PooledConnection, is_connection, maybe_channel
    from .entity import Exchange, Queue, maybe_delivery_mode
    from .exceptions import ContentDisallowed
    from .serialization import dumps, prepare_accept_content
    from .utils.functional import ChannelPromise, maybe_list

    if TYPE_CHECKING:
        from types import TracebackType

    __all__ = ('Exchange', 'Queue', 'Producer', 'Consumer')

    class Producer:
        """Message Producer.

        Arguments:
        ---------
            channel (kombu.Connection, ChannelT): Connection or channel.
            exchange (kombu.entity.Exchange, str): Optional default exchange.
            routing_key (str): Optional default routing key.
            serializer (str): Default serializer. Default is `"json"`.
            compression (str): Default compression method.
                Default is no compression.
            auto_declare (bool): Automatically declare the default exchange
                at instantiation. Default is :const:`True`.
            on_return (Callable): Callback to call for undeliverable messages,
                when the `mandatory` or `immediate` arguments to
                :meth:`publish` is used. This callback needs the following
                signature: `(exception, exchange, routing_key, message)`.
                Note that the producer needs to drain events to use this feature.
        """

        #: Default exchange
        exchange = None

        #: Default routing key.
        routing_key = ''

        #: Default serializer to use. Default is JSON.
        serializer = None

        #: Default compression method.  Disabled by default.
        compression = None

        #: By default, if a default exchange is set,
        #: that exchange will be declare when publishing a message.
        auto_declare = True

        #: Basic return callback.
        on_return = None

        #: Set if channel argument was a Connection instance (using
        #: default_channel).
        __connection__ = None

        def __init__(self, channel, exchange=None, routing_key=None,
                     serializer=None, auto_declare=None, compression=None,
                     on_return=None):
            self._channel = channel
            self.exchange = exchange
            self.routing_key = routing_key or self.routing_key
            self.serializer = serializer or self.serializer
            self.compression = compression or self.compression
            self.on_return = on_return or self.on_return
            self._channel_promise = None
            if self.exchange is None:
                self.exchange = Exchange('')
            if auto_declare is not None:
                self.auto_declare = auto_declare

            if self._channel:
                self.revive(self._channel)

        def __repr__(self):
            return f'<Producer: {self._channel}>'

        def __reduce__(self):
            return self.__class__, self.__reduce_args__()

        def __reduce_args__(self):
            return (None, self.exchange, self.routing_key, self.serializer,
                    self.auto_declare, self.compression)

        def declare(self):
            """Declare the exchange.

            Note:
            ----
                This happens automatically at instantiation when
                the :attr:`auto_declare` flag is enabled.
            """
            if self.exchange.name:
                self.exchange.declare()

        def maybe_declare(self, entity, retry=False, **retry_policy):
            """Declare exchange if not already declared during this session."""
            if entity:
                return maybe_declare(entity, self.channel, retry, **retry_policy)

        def _delivery_details(self, exchange, delivery_mode=None,
                              maybe_delivery_mode=maybe_delivery_mode,
                              Exchange=Exchange):
            if isinstance(exchange, Exchange):
                return exchange.name, maybe_delivery_mode(
                    delivery_mode or exchange.delivery_mode,
                )
            # exchange is string, so inherit the delivery
            # mode of our default exchange.
            return exchange, maybe_delivery_mode(
                delivery_mode or self.exchange.delivery_mode,
            )

        def publish(self, body, routing_key=None, delivery_mode=None,
                    mandatory=False, immediate=False, priority=0,
                    content_type=None, content_encoding=None, serializer=None,
                    headers=None, compression=None, exchange=None, retry=False,
                    retry_policy=None, declare=None, expiration=None, timeout=None,
                    confirm_timeout=None,
                    **properties):
            """Publish message to the specified exchange.

            Arguments:
            ---------
                body (Any): Message body.
                routing_key (str): Message routing key.
                delivery_mode (enum): See :attr:`delivery_mode`.
                mandatory (bool): Currently not supported.
                immediate (bool): Currently not supported.
                priority (int): Message priority. A number between 0 and 9.
                content_type (str): Content type. Default is auto-detect.
                content_encoding (str): Content encoding. Default is auto-detect.
                serializer (str): Serializer to use. Default is auto-detect.
                compression (str): Compression method to use.  Default is none.
                headers (Dict): Mapping of arbitrary headers to pass along
                    with the message body.
                exchange (kombu.entity.Exchange, str): Override the exchange.
                    Note that this exchange must have been declared.
                declare (Sequence[EntityT]): Optional list of required entities
                    that must have been declared before publishing the message.
                    The entities will be declared using
                    :func:`~kombu.common.maybe_declare`.
                retry (bool): Retry publishing, or declaring entities if the
                    connection is lost.
                retry_policy (Dict): Retry configuration, this is the keywords
                    supported by :meth:`~kombu.Connection.ensure`.
                expiration (float): A TTL in seconds can be specified per message.
                    Default is no expiration.
                timeout (float): Set timeout to wait maximum timeout second
                    for message to publish.
                confirm_timeout (float): Set confirm timeout to wait maximum timeout second
                    for message to confirm publishing if the channel is set to confirm publish mode.
                **properties (Any): Additional message properties, see AMQP spec.
            """
            _publish = self._publish

            declare = [] if declare is None else declare
            headers = {} if headers is None else headers
            retry_policy = {} if retry_policy is None else retry_policy
            routing_key = self.routing_key if routing_key is None else routing_key
            compression = self.compression if compression is None else compression

            exchange_name, properties['delivery_mode'] = self._delivery_details(
                exchange or self.exchange, delivery_mode,
            )

            if expiration is not None:
                properties['expiration'] = str(int(expiration * 1000))

            body, content_type, content_encoding = self._prepare(
                body, serializer, content_type, content_encoding,
                compression, headers)

            if self.auto_declare and self.exchange.name:
                if self.exchange not in declare:
                    # XXX declare should be a Set.
                    declare.append(self.exchange)

            if retry:
                self.connection.transport_options.update(retry_policy)
                _publish = self.connection.ensure(self, _publish, **retry_policy)
            return _publish(
                body, priority, content_type, content_encoding,
                headers, properties, routing_key, mandatory, immediate,
                exchange_name, declare, timeout, confirm_timeout, retry, retry_policy
            )

        def _publish(self, body, priority, content_type, content_encoding,
                     headers, properties, routing_key, mandatory,
                     immediate, exchange, declare, timeout=None, confirm_timeout=None, retry=False, retry_policy=None):
            retry_policy = {} if retry_policy is None else retry_policy
            channel = self.channel
            message = channel.prepare_message(
                body, priority, content_type,
                content_encoding, headers, properties,
            )
            if declare:
                maybe_declare = self.maybe_declare
                for entity in declare:
                    maybe_declare(entity, retry=retry, **retry_policy)

            # handle autogenerated queue names for reply_to
            reply_to = properties.get('reply_to')
            if isinstance(reply_to, Queue):
                properties['reply_to'] = reply_to.name
            return channel.basic_publish(
                message,
                exchange=exchange, routing_key=routing_key,
                mandatory=mandatory, immediate=immediate,
                timeout=timeout, confirm_timeout=confirm_timeout
            )

        def _get_channel(self):
            channel = self._channel
            if isinstance(channel, ChannelPromise):
                channel = self._channel = channel()
                self.exchange.revive(channel)
                if self.on_return:
                    channel.events['basic_return'].add(self.on_return)
            return channel

        def _set_channel(self, channel):
            self._channel = channel

        channel = property(_get_channel, _set_channel)

        def revive(self, channel):
            """Revive the producer after connection loss."""
            if is_connection(channel):
                connection = channel
                self.__connection__ = connection
                channel = ChannelPromise(lambda: connection.default_channel)
            if isinstance(channel, ChannelPromise):
                self._channel = channel
                self.exchange = self.exchange(channel)
            else:
                # Channel already concrete
                self._channel = channel
                if self.on_return:
                    self._channel.events['basic_return'].add(self.on_return)
                self.exchange = self.exchange(channel)

        def __enter__(self):
            return self

        def __exit__(
            self,
            exc_type: type[BaseException] | None,
            exc_val: BaseException | None,
            exc_tb: TracebackType | None
        ) -> None:
            # In case the connection is part of a pool it needs to be
            # replaced in case of an exception
            if self.__connection__ is not None and exc_type is not None:
                if isinstance(self.__connection__, PooledConnection):
                    self.__connection__._pool.replace(self.__connection__)

            self.release()

        def release(self):
            pass

        close = release

        def _prepare(self, body, serializer=None, content_type=None,
                     content_encoding=None, compression=None, headers=None):

            # No content_type? Then we're serializing the data internally.
            if not content_type:
                serializer = serializer or self.serializer
                (content_type, content_encoding,
                 body) = dumps(body, serializer=serializer)
            else:
                # If the programmer doesn't want us to serialize,
                # make sure content_encoding is set.
                if isinstance(body, str):
                    if not content_encoding:
                        content_encoding = 'utf-8'
                    body = body.encode(content_encoding)

                # If they passed in a string, we can't know anything
                # about it. So assume it's binary data.
                elif not content_encoding:
                    content_encoding = 'binary'

            if compression:
                body, headers['compression'] = compress(body, compression)

            return body, content_type, content_encoding

        @property
        def connection(self):
            try:
                return self.__connection__ or self.channel.connection.client
            except AttributeError:
                pass

    class Consumer:
        """Message consumer.

        Arguments:
        ---------
            channel (kombu.Connection, ChannelT): see :attr:`channel`.
            queues (Sequence[kombu.Queue]): see :attr:`queues`.
            no_ack (bool): see :attr:`no_ack`.
            auto_declare (bool): see :attr:`auto_declare`
            callbacks (Sequence[Callable]): see :attr:`callbacks`.
            on_message (Callable): See :attr:`on_message`
            on_decode_error (Callable): see :attr:`on_decode_error`.
            prefetch_count (int): see :attr:`prefetch_count`.
        """

        ContentDisallowed = ContentDisallowed

        #: The connection/channel to use for this consumer.
        channel = None

        #: A single :class:`~kombu.Queue`, or a list of queues to
        #: consume from.
        queues = None

        #: Flag for automatic message acknowledgment.
        #: If enabled the messages are automatically acknowledged by the
        #: broker.  This can increase performance but means that you
        #: have no control of when the message is removed.
        #:
        #: Disabled by default.
        no_ack = None

        #: By default all entities will be declared at instantiation, if you
        #: want to handle this manually you can set this to :const:`False`.
        auto_declare = True

        #: List of callbacks called in order when a message is received.
        #:
        #: The signature of the callbacks must take two arguments:
        #: `(body, message)`, which is the decoded message body and
        #: the :class:`~kombu.Message` instance.
        callbacks = None

        #: Optional function called whenever a message is received.
        #:
        #: When defined this function will be called instead of the
        #: :meth:`receive` method, and :attr:`callbacks` will be disabled.
        #:
        #: So this can be used as an alternative to :attr:`callbacks` when
        #: you don't want the body to be automatically decoded.
        #: Note that the message will still be decompressed if the message
        #: has the ``compression`` header set.
        #:
        #: The signature of the callback must take a single argument,
        #: which is the :class:`~kombu.Message` object.
        #:
        #: Also note that the ``message.body`` attribute, which is the raw
        #: contents of the message body, may in some cases be a read-only
        #: :class:`buffer` object.
        on_message = None

        #: Callback called when a message can't be decoded.
        #:
        #: The signature of the callback must take two arguments: `(message,
        #: exc)`, which is the message that can't be decoded and the exception
        #: that occurred while trying to decode it.
        on_decode_error = None

        #: List of accepted content-types.
        #:
        #: An exception will be raised if the consumer receives
        #: a message with an untrusted content type.
        #: By default all content-types are accepted, but not if
        #: :func:`kombu.disable_untrusted_serializers` was called,
        #: in which case only json is allowed.
        accept = None

        #: Initial prefetch count
        #:
        #: If set, the consumer will set the prefetch_count QoS value at startup.
        #: Can also be changed using :meth:`qos`.
        prefetch_count = None

        #: Mapping of queues we consume from.
        _queues = None

        _tags = count(1)  # global

        def __init__(self, channel, queues=None, no_ack=None, auto_declare=None,
                     callbacks=None, on_decode_error=None, on_message=None,
                     accept=None, prefetch_count=None, tag_prefix=None):
            self.channel = channel
            self.queues = maybe_list(queues or [])
            self.no_ack = self.no_ack if no_ack is None else no_ack
            self.callbacks = (self.callbacks or [] if callbacks is None
                              else callbacks)
            self.on_message = on_message
            self.tag_prefix = tag_prefix
            self._active_tags = {}
            if auto_declare is not None:
                self.auto_declare = auto_declare
            if on_decode_error is not None:
                self.on_decode_error = on_decode_error
            self.accept = prepare_accept_content(accept)
            self.prefetch_count = prefetch_count

            if self.channel:
                self.revive(self.channel)

        @property
        def queues(self):  # noqa
            return list(self._queues.values())

        @queues.setter
        def queues(self, queues):
            self._queues = {q.name: q for q in queues}

        def revive(self, channel):
            """Revive consumer after connection loss."""
            self._active_tags.clear()
            channel = self.channel = maybe_channel(channel)
            # modify dict size while iterating over it is not allowed
            for qname, queue in list(self._queues.items()):
                # name may have changed after declare
                self._queues.pop(qname, None)
                queue = self._queues[queue.name] = queue(self.channel)
                queue.revive(channel)

            if self.auto_declare:
                self.declare()

            if self.prefetch_count is not None:
                self.qos(prefetch_count=self.prefetch_count)

        def declare(self):
            """Declare queues, exchanges and bindings.

            Note:
            ----
                This is done automatically at instantiation
                when :attr:`auto_declare` is set.
            """
            for queue in self._queues.values():
                queue.declare()

        def register_callback(self, callback):
            """Register a new callback to be called when a message is received.

            Note:
            ----
                The signature of the callback needs to accept two arguments:
                `(body, message)`, which is the decoded message body
                and the :class:`~kombu.Message` instance.
            """
            self.callbacks.append(callback)

        def __enter__(self):
            self.consume()
            return self

        def __exit__(
            self,
            exc_type: type[BaseException] | None,
            exc_val: BaseException | None,
            exc_tb: TracebackType | None
        ) -> None:
            if self.channel and self.channel.connection:
                conn_errors = self.channel.connection.client.connection_errors
                if not isinstance(exc_val, conn_errors):
                    try:
                        self.cancel()
                    except Exception:
                        pass

        def add_queue(self, queue):
            """Add a queue to the list of queues to consume from.

            Note:
            ----
                This will not start consuming from the queue,
                for that you will have to call :meth:`consume` after.
            """
            queue = queue(self.channel)
            if self.auto_declare:
                queue.declare()
            self._queues[queue.name] = queue
            return queue

        def consume(self, no_ack=None):
            """Start consuming messages.

            Can be called multiple times, but note that while it
            will consume from new queues added since the last call,
            it will not cancel consuming from removed queues (
            use :meth:`cancel_by_queue`).

            Arguments:
            ---------
                no_ack (bool): See :attr:`no_ack`.
            """
            queues = list(self._queues.values())
            if queues:
                no_ack = self.no_ack if no_ack is None else no_ack

                H, T = queues[:-1], queues[-1]
                for queue in H:
                    self._basic_consume(queue, no_ack=no_ack, nowait=True)
                self._basic_consume(T, no_ack=no_ack, nowait=False)

        def cancel(self):
            """End all active queue consumers.

            Note:
            ----
                This does not affect already delivered messages, but it does
                mean the server will not send any more messages for this consumer.
            """
            cancel = self.channel.basic_cancel
            for tag in self._active_tags.values():
                cancel(tag)
            self._active_tags.clear()

        close = cancel

        def cancel_by_queue(self, queue):
            """Cancel consumer by queue name."""
            qname = queue.name if isinstance(queue, Queue) else queue
            try:
                tag = self._active_tags.pop(qname)
            except KeyError:
                pass
            else:
                self.channel.basic_cancel(tag)
            finally:
                self._queues.pop(qname, None)

        def consuming_from(self, queue):
            """Return :const:`True` if currently consuming from queue'."""
            name = queue
            if isinstance(queue, Queue):
                name = queue.name
            return name in self._active_tags

        def purge(self):
            """Purge messages from all queues.

            Warning:
            -------
                This will *delete all ready messages*, there is no undo operation.
            """
            return sum(queue.purge() for queue in self._queues.values())

        def flow(self, active):
            """Enable/disable flow from peer.

            This is a simple flow-control mechanism that a peer can use
            to avoid overflowing its queues or otherwise finding itself
            receiving more messages than it can process.

            The peer that receives a request to stop sending content
            will finish sending the current content (if any), and then wait
            until flow is reactivated.
            """
            self.channel.flow(active)

        def qos(self, prefetch_size=0, prefetch_count=0, apply_global=False):
            """Specify quality of service.

            The client can request that messages should 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.

            The prefetch window is Ignored if the :attr:`no_ack` option is set.

            Arguments:
            ---------
                prefetch_size (int): Specify the prefetch window in octets.
                    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 within other prefetch limits). May be set to zero,
                    meaning "no specific limit", although other prefetch limits
                    may still apply.

                prefetch_count (int): Specify the prefetch window in terms of
                    whole messages.

                apply_global (bool): Apply new settings globally on all channels.
            """
            return self.channel.basic_qos(prefetch_size,
                                          prefetch_count,
                                          apply_global)

        def recover(self, requeue=False):
            """Redeliver unacknowledged messages.

            Asks the broker to redeliver all unacknowledged messages
            on the specified channel.

            Arguments:
            ---------
                requeue (bool): By default the messages will be redelivered
                    to the original recipient. With `requeue` set to true, the
                    server will attempt to requeue the message, potentially then
                    delivering it to an alternative subscriber.
            """
            return self.channel.basic_recover(requeue=requeue)

        def receive(self, body, message):
            """Method called when a message is received.

            This dispatches to the registered :attr:`callbacks`.

            Arguments:
            ---------
                body (Any): The decoded message body.
                message (~kombu.Message): The message instance.

            Raises
            ------
                NotImplementedError: If no consumer callbacks have been
                    registered.
            """
            callbacks = self.callbacks
            if not callbacks:
                raise NotImplementedError('Consumer does not have any callbacks')
            [callback(body, message) for callback in callbacks]

        def _basic_consume(self, queue, consumer_tag=None,
                           no_ack=no_ack, nowait=True):
            tag = self._active_tags.get(queue.name)
            if tag is None:
                tag = self._add_tag(queue, consumer_tag)
                queue.consume(tag, self._receive_callback,
                              no_ack=no_ack, nowait=nowait)
            return tag

        def _add_tag(self, queue, consumer_tag=None):
            tag = consumer_tag or '{}{}'.format(
                self.tag_prefix, next(self._tags))
            self._active_tags[queue.name] = tag
            return tag

        def _receive_callback(self, message):
            accept = self.accept
            on_m, channel, decoded = self.on_message, self.channel, None
            try:
                m2p = getattr(channel, 'message_to_python', None)
                if m2p:
                    message = m2p(message)
                if accept is not None:
                    message.accept = accept
                if message.errors:
                    return message._reraise_error(self.on_decode_error)
                decoded = None if on_m else message.decode()
            except Exception as exc:
                if not self.on_decode_error:
                    raise
                self.on_decode_error(message, exc)
            else:
                return on_m(message) if on_m else self.receive(decoded, message)

        def __repr__(self):
            return f'<{type(self).__name__}: {self.queues}>'

        @property
        def connection(self):
            try:
                return self.channel.connection.client
            except AttributeError:
                pass