Source code for fedora_messaging.api
"""The API for publishing messages and consuming from message queues."""
import threading
from . import _session, exceptions, config
from .signals import pre_publish_signal, publish_signal, publish_failed_signal
from .message import Message
__all__ = (
"Message",
"consume",
"publish",
"pre_publish_signal",
"publish_signal",
"publish_failed_signal",
)
# Sessions aren't thread-safe, so each thread gets its own
_session_cache = threading.local()
[docs]def consume(callback, bindings=None):
"""
Start a message consumer that executes the provided callback when messages are
received.
This API is blocking and will not return until the process receives a signal
from the operating system.
The callback receives a single positional argument, the message:
>>> from fedora_messaging import api
>>> def my_callback(message):
... print(message)
>>> bindings = [{'exchange': 'amq.topic', 'queue': 'demo', 'routing_keys': ['#']}]
>>> api.consume(my_callback, bindings=bindings)
For complete documentation on writing consumers, see the :ref:`consumers`
documentation.
Args:
callback (callable): A callable object that accepts one positional argument,
a :class:`Message`.
bindings (dict or list of dict): The bindings to use when consuming. This
should be the same format as the :ref:`conf-bindings` configuration.
Raises:
fedora_messaging.exceptions.HaltConsumer: If the consumer requests that
it be stopped.
ValueError: If the consumer provide callback that is not a class that
implements __call__ and is not a function.
"""
if isinstance(bindings, dict):
bindings = [bindings]
session = _session.ConsumerSession()
session.consume(callback, bindings)
[docs]def publish(message, exchange=None):
"""
Publish a message to an exchange.
This is a synchronous call, meaning that when this function returns, an
acknowledgment has been received from the message broker and you can be
certain the message was published successfully.
There are some cases where an error occurs despite your message being
successfully published. For example, if a network partition occurs after
the message is received by the broker. Therefore, you may publish duplicate
messages. For complete details, see the :ref:`publishing` documentation.
>>> from fedora_messaging import api
>>> message = api.Message(body={'Hello': 'world'}, topic='Hi')
>>> api.publish(message)
If an attempt to publish fails because the broker rejects the message, it
is not retried. Connection attempts to the broker can be configured using
the "connection_attempts" and "retry_delay" options in the broker URL. See
:class:`pika.connection.URLParameters` for details.
Args:
message (message.Message): The message to publish.
exchange (str): The name of the AMQP exchange to publish to; defaults to
:ref:`conf-publish-exchange`
Raises:
fedora_messaging.exceptions.PublishReturned: Raised if the broker rejects the
message.
fedora_messaging.exceptions.ConnectionException: Raised if a connection error
occurred before the publish confirmation arrived.
fedora_messaging.exceptions.ValidationError: Raised if the message
fails validation with its JSON schema. This only depends on the
message you are trying to send, the AMQP server is not involved.
"""
pre_publish_signal.send(publish, message=message)
if exchange is None:
exchange = config.conf["publish_exchange"]
global _session_cache
if not hasattr(_session_cache, "session"):
_session_cache.session = _session.PublisherSession()
try:
_session_cache.session.publish(message, exchange=exchange)
publish_signal.send(publish, message=message)
except exceptions.PublishException as e:
publish_failed_signal.send(publish, message=message, reason=e)
raise