This document describes the current stable version of Celery (3.1). For development docs, go here.
Source code for kombu.messaging
"""
kombu.messaging
===============
Sending and receiving messages.
"""
from __future__ import absolute_import
import numbers
from itertools import count
from .common import maybe_declare
from .compression import compress
from .connection import maybe_channel, is_connection
from .entity import Exchange, Queue, DELIVERY_MODES
from .exceptions import ContentDisallowed
from .five import text_t, values
from .serialization import dumps, prepare_accept_content
from .utils import ChannelPromise, maybe_list
__all__ = ['Exchange', 'Queue', 'Producer', 'Consumer']
class Producer(object):
"""Message Producer.
:param channel: Connection or channel.
:keyword exchange: Optional default exchange.
:keyword routing_key: Optional default routing key.
:keyword serializer: Default serializer. Default is `"json"`.
:keyword compression: Default compression method. Default is no
compression.
:keyword auto_declare: Automatically declare the default exchange
at instantiation. Default is :const:`True`.
:keyword on_return: 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 the exchange is declared at instantiation.
#: If you want to declare manually then you can set this
#: to :const:`False`.
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 '<Producer: {0._channel}>'.format(self)
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.
This happens automatically at instantiation if
:attr:`auto_declare` is enabled.
"""
if self.exchange.name:
self.exchange.declare()
def maybe_declare(self, entity, retry=False, **retry_policy):
"""Declare the exchange if it hasn't already been declared
during this session."""
if entity:
return maybe_declare(entity, self.channel, retry, **retry_policy)
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=[], expiration=None, **properties):
"""Publish message to the specified exchange.
:param body: Message body.
:keyword routing_key: Message routing key.
:keyword delivery_mode: See :attr:`delivery_mode`.
:keyword mandatory: Currently not supported.
:keyword immediate: Currently not supported.
:keyword priority: Message priority. A number between 0 and 9.
:keyword content_type: Content type. Default is auto-detect.
:keyword content_encoding: Content encoding. Default is auto-detect.
:keyword serializer: Serializer to use. Default is auto-detect.
:keyword compression: Compression method to use. Default is none.
:keyword headers: Mapping of arbitrary headers to pass along
with the message body.
:keyword exchange: Override the exchange. Note that this exchange
must have been declared.
:keyword declare: 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`.
:keyword retry: Retry publishing, or declaring entities if the
connection is lost.
:keyword retry_policy: Retry configuration, this is the keywords
supported by :meth:`~kombu.Connection.ensure`.
:keyword expiration: A TTL in seconds can be specified per message.
Default is no expiration.
:keyword \*\*properties: Additional message properties, see AMQP spec.
"""
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 = exchange or self.exchange
if isinstance(exchange, Exchange):
delivery_mode = delivery_mode or exchange.delivery_mode
exchange = exchange.name
else:
delivery_mode = delivery_mode or self.exchange.delivery_mode
if not isinstance(delivery_mode, numbers.Integral):
delivery_mode = DELIVERY_MODES[delivery_mode]
properties['delivery_mode'] = 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)
publish = self._publish
if retry:
publish = self.connection.ensure(self, publish, **retry_policy)
return publish(body, priority, content_type,
content_encoding, headers, properties,
routing_key, mandatory, immediate, exchange, declare)
def _publish(self, body, priority, content_type, content_encoding,
headers, properties, routing_key, mandatory,
immediate, exchange, declare):
channel = self.channel
message = channel.prepare_message(
body, priority, content_type,
content_encoding, headers, properties,
)
if declare:
maybe_declare = self.maybe_declare
[maybe_declare(entity) for entity in declare]
return channel.basic_publish(
message,
exchange=exchange, routing_key=routing_key,
mandatory=mandatory, immediate=immediate,
)
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)
if self.auto_declare:
# auto_decare is not recommended as this will force
# evaluation of the channel.
self.declare()
def __enter__(self):
return self
def __exit__(self, *exc_info):
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, text_t):
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(object):
"""Message consumer.
:param channel: see :attr:`channel`.
:param queues: see :attr:`queues`.
:keyword no_ack: see :attr:`no_ack`.
:keyword auto_declare: see :attr:`auto_declare`
:keyword callbacks: see :attr:`callbacks`.
:keyword on_message: See :attr:`on_message`
:keyword on_decode_error: see :attr:`on_decode_error`.
"""
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 `Message` instance (a subclass of
#: :class:`~kombu.transport.base.Message`).
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 raw message object (a subclass of
#: :class:`~kombu.transport.base.Message`).
#:
#: 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
_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, tag_prefix=None):
self.channel = channel
self.queues = self.queues or [] if queues is None else queues
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)
if self.channel:
self.revive(self.channel)
def revive(self, channel):
"""Revive consumer after connection loss."""
self._active_tags.clear()
channel = self.channel = maybe_channel(channel)
self.queues = [queue(self.channel)
for queue in maybe_list(self.queues)]
for queue in self.queues:
queue.revive(channel)
if self.auto_declare:
self.declare()
def declare(self):
"""Declare queues, exchanges and bindings.
This is done automatically at instantiation if :attr:`auto_declare`
is set.
"""
for queue in self.queues:
queue.declare()
def register_callback(self, callback):
"""Register a new callback to be called when a message
is received.
The signature of the callback needs to accept two arguments:
`(body, message)`, which is the decoded message body
and the `Message` instance (a subclass of
:class:`~kombu.transport.base.Message`.
"""
self.callbacks.append(callback)
def __enter__(self):
self.consume()
return self
def __exit__(self, *exc_info):
try:
self.cancel()
except Exception:
pass
def add_queue(self, queue):
"""Add a queue to the list of queues to consume from.
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.append(queue)
return queue
def add_queue_from_dict(self, queue, **options):
"""This method is deprecated.
Instead please use::
consumer.add_queue(Queue.from_dict(d))
"""
return self.add_queue(Queue.from_dict(queue, **options))
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`).
:param no_ack: See :attr:`no_ack`.
"""
if self.queues:
no_ack = self.no_ack if no_ack is None else no_ack
H, T = self.queues[:-1], self.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.
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 values(self._active_tags):
cancel(tag)
self._active_tags.clear()
close = cancel
def cancel_by_queue(self, queue):
"""Cancel consumer by queue name."""
try:
tag = self._active_tags.pop(queue)
except KeyError:
pass
else:
self.queues[:] = [q for q in self.queues if q.name != queue]
self.channel.basic_cancel(tag)
def consuming_from(self, queue):
"""Return :const:`True` if the consumer is 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)
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.
:param prefetch_size: 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.
:param prefetch_count: Specify the prefetch window in terms of
whole messages.
:param apply_global: 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.
:keyword requeue: 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`.
:param body: The decoded message body.
:param 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 '{0}{1}'.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 '<Consumer: {0.queues}>'.format(self)
@property
def connection(self):
try:
return self.channel.connection.client
except AttributeError:
pass
