Asynchronous publisher example¶
The following example implements a publisher that will respond to RPC commands sent from RabbitMQ and uses delivery confirmations. It will reconnect if RabbitMQ closes the connection and will shutdown if RabbitMQ closes the channel. While it may look intimidating, each method is very short and represents a individual actions that a publisher can do.
publisher.py:
# -*- coding: utf-8 -*-
import logging
import pika
import json
LOG_FORMAT = ('%(levelname) -10s %(asctime)s %(name) -30s %(funcName) '
'-35s %(lineno) -5d: %(message)s')
LOGGER = logging.getLogger(__name__)
class ExamplePublisher(object):
"""This is an example publisher that will handle unexpected interactions
with RabbitMQ such as channel and connection closures.
If RabbitMQ closes the connection, it will reopen it. You should
look at the output, as there are limited reasons why the connection may
be closed, which usually are tied to permission related issues or
socket timeouts.
It uses delivery confirmations and illustrates one way to keep track of
messages that have been sent and if they've been confirmed by RabbitMQ.
"""
EXCHANGE = 'message'
EXCHANGE_TYPE = 'topic'
PUBLISH_INTERVAL = 1
QUEUE = 'text'
ROUTING_KEY = 'example.text'
def __init__(self, amqp_url):
"""Setup the example publisher object, passing in the URL we will use
to connect to RabbitMQ.
:param str amqp_url: The URL for connecting to RabbitMQ
"""
self._connection = None
self._channel = None
self._deliveries = None
self._acked = None
self._nacked = None
self._message_number = None
self._stopping = False
self._url = amqp_url
def connect(self):
"""This method connects to RabbitMQ, returning the connection handle.
When the connection is established, the on_connection_open method
will be invoked by pika.
:rtype: pika.SelectConnection
"""
LOGGER.info('Connecting to %s', self._url)
return pika.SelectConnection(pika.URLParameters(self._url),
on_open_callback=self.on_connection_open,
on_open_error_callback=self.on_connection_open_error,
on_close_callback=self.on_connection_closed)
def on_connection_open(self, unused_connection):
"""This method is called by pika once the connection to RabbitMQ has
been established. It passes the handle to the connection object in
case we need it, but in this case, we'll just mark it unused.
:type unused_connection: pika.SelectConnection
"""
LOGGER.info('Connection opened')
self.open_channel()
def on_connection_open_error(self, unused_connection, err):
"""This method is called by pika if the connection to RabbitMQ
can't be established.
:type unused_connection: pika.SelectConnection
:type err: Exception
"""
LOGGER.error('Connection open failed, reopening in 5 seconds: %s', err)
self._connection.ioloop.call_later(5, self._connection.ioloop.stop)
def on_connection_closed(self, connection, reason):
"""This method is invoked by pika when the connection to RabbitMQ is
closed unexpectedly. Since it is unexpected, we will reconnect to
RabbitMQ if it disconnects.
:param pika.connection.Connection connection: The closed connection obj
:param Exception reason: exception representing reason for loss of
connection.
"""
self._channel = None
if self._stopping:
self._connection.ioloop.stop()
else:
LOGGER.warning('Connection closed, reopening in 5 seconds: %s',
reason)
self._connection.ioloop.call_later(5,
self._connection.ioloop.stop)
def open_channel(self):
"""This method will open a new channel with RabbitMQ by issuing the
Channel.Open RPC command. When RabbitMQ confirms the channel is open
by sending the Channel.OpenOK RPC reply, the on_channel_open method
will be invoked.
"""
LOGGER.info('Creating a new channel')
self._connection.channel(on_open_callback=self.on_channel_open)
def on_channel_open(self, channel):
"""This method is invoked by pika when the channel has been opened.
The channel object is passed in so we can make use of it.
Since the channel is now open, we'll declare the exchange to use.
:param pika.channel.Channel channel: The channel object
"""
LOGGER.info('Channel opened')
self._channel = channel
self.add_on_channel_close_callback()
self.setup_exchange(self.EXCHANGE)
def add_on_channel_close_callback(self):
"""This method tells pika to call the on_channel_closed method if
RabbitMQ unexpectedly closes the channel.
"""
LOGGER.info('Adding channel close callback')
self._channel.add_on_close_callback(self.on_channel_closed)
def on_channel_closed(self, channel, reason):
"""Invoked by pika when RabbitMQ unexpectedly closes the channel.
Channels are usually closed if you attempt to do something that
violates the protocol, such as re-declare an exchange or queue with
different parameters. In this case, we'll close the connection
to shutdown the object.
:param pika.channel.Channel channel: The closed channel
:param Exception reason: why the channel was closed
"""
LOGGER.warning('Channel %i was closed: %s', channel, reason)
self._channel = None
if not self._stopping:
self._connection.close()
def setup_exchange(self, exchange_name):
"""Setup the exchange on RabbitMQ by invoking the Exchange.Declare RPC
command. When it is complete, the on_exchange_declareok method will
be invoked by pika.
:param str|unicode exchange_name: The name of the exchange to declare
"""
LOGGER.info('Declaring exchange %s', exchange_name)
self._channel.exchange_declare(self.on_exchange_declareok,
exchange_name,
self.EXCHANGE_TYPE)
def on_exchange_declareok(self, unused_frame):
"""Invoked by pika when RabbitMQ has finished the Exchange.Declare RPC
command.
:param pika.Frame.Method unused_frame: Exchange.DeclareOk response frame
"""
LOGGER.info('Exchange declared')
self.setup_queue(self.QUEUE)
def setup_queue(self, queue_name):
"""Setup the queue on RabbitMQ by invoking the Queue.Declare RPC
command. When it is complete, the on_queue_declareok method will
be invoked by pika.
:param str|unicode queue_name: The name of the queue to declare.
"""
LOGGER.info('Declaring queue %s', queue_name)
self._channel.queue_declare(queue_name, self.on_queue_declareok)
def on_queue_declareok(self, method_frame):
"""Method invoked by pika when the Queue.Declare RPC call made in
setup_queue has completed. In this method we will bind the queue
and exchange together with the routing key by issuing the Queue.Bind
RPC command. When this command is complete, the on_bindok method will
be invoked by pika.
:param pika.frame.Method method_frame: The Queue.DeclareOk frame
"""
LOGGER.info('Binding %s to %s with %s',
self.EXCHANGE, self.QUEUE, self.ROUTING_KEY)
self._channel.queue_bind(self.on_bindok, self.QUEUE,
self.EXCHANGE, self.ROUTING_KEY)
def on_bindok(self, unused_frame):
"""This method is invoked by pika when it receives the Queue.BindOk
response from RabbitMQ. Since we know we're now setup and bound, it's
time to start publishing."""
LOGGER.info('Queue bound')
self.start_publishing()
def start_publishing(self):
"""This method will enable delivery confirmations and schedule the
first message to be sent to RabbitMQ
"""
LOGGER.info('Issuing consumer related RPC commands')
self.enable_delivery_confirmations()
self.schedule_next_message()
def enable_delivery_confirmations(self):
"""Send the Confirm.Select RPC method to RabbitMQ to enable delivery
confirmations on the channel. The only way to turn this off is to close
the channel and create a new one.
When the message is confirmed from RabbitMQ, the
on_delivery_confirmation method will be invoked passing in a Basic.Ack
or Basic.Nack method from RabbitMQ that will indicate which messages it
is confirming or rejecting.
"""
LOGGER.info('Issuing Confirm.Select RPC command')
self._channel.confirm_delivery(self.on_delivery_confirmation)
def on_delivery_confirmation(self, method_frame):
"""Invoked by pika when RabbitMQ responds to a Basic.Publish RPC
command, passing in either a Basic.Ack or Basic.Nack frame with
the delivery tag of the message that was published. The delivery tag
is an integer counter indicating the message number that was sent
on the channel via Basic.Publish. Here we're just doing house keeping
to keep track of stats and remove message numbers that we expect
a delivery confirmation of from the list used to keep track of messages
that are pending confirmation.
:param pika.frame.Method method_frame: Basic.Ack or Basic.Nack frame
"""
confirmation_type = method_frame.method.NAME.split('.')[1].lower()
LOGGER.info('Received %s for delivery tag: %i',
confirmation_type,
method_frame.method.delivery_tag)
if confirmation_type == 'ack':
self._acked += 1
elif confirmation_type == 'nack':
self._nacked += 1
self._deliveries.remove(method_frame.method.delivery_tag)
LOGGER.info('Published %i messages, %i have yet to be confirmed, '
'%i were acked and %i were nacked',
self._message_number, len(self._deliveries),
self._acked, self._nacked)
def schedule_next_message(self):
"""If we are not closing our connection to RabbitMQ, schedule another
message to be delivered in PUBLISH_INTERVAL seconds.
"""
LOGGER.info('Scheduling next message for %0.1f seconds',
self.PUBLISH_INTERVAL)
self._connection.ioloop.call_later(self.PUBLISH_INTERVAL,
self.publish_message)
def publish_message(self):
"""If the class is not stopping, publish a message to RabbitMQ,
appending a list of deliveries with the message number that was sent.
This list will be used to check for delivery confirmations in the
on_delivery_confirmations method.
Once the message has been sent, schedule another message to be sent.
The main reason I put scheduling in was just so you can get a good idea
of how the process is flowing by slowing down and speeding up the
delivery intervals by changing the PUBLISH_INTERVAL constant in the
class.
"""
if self._channel is None or not self._channel.is_open:
return
hdrs = {u'مفتاح': u' قيمة',
u'键': u'值',
u'キー': u'値'}
properties = pika.BasicProperties(app_id='example-publisher',
content_type='application/json',
headers=hdrs)
message = u'مفتاح قيمة 键 值 キー 値'
self._channel.basic_publish(self.EXCHANGE, self.ROUTING_KEY,
json.dumps(message, ensure_ascii=False),
properties)
self._message_number += 1
self._deliveries.append(self._message_number)
LOGGER.info('Published message # %i', self._message_number)
self.schedule_next_message()
def run(self):
"""Run the example code by connecting and then starting the IOLoop.
"""
while not self._stopping:
self._connection = None
self._deliveries = []
self._acked = 0
self._nacked = 0
self._message_number = 0
try:
self._connection = self.connect()
self._connection.ioloop.start()
except KeyboardInterrupt:
self.stop()
if (self._connection is not None and
not self._connection.is_closed):
# Finish closing
self._connection.ioloop.start()
LOGGER.info('Stopped')
def stop(self):
"""Stop the example by closing the channel and connection. We
set a flag here so that we stop scheduling new messages to be
published. The IOLoop is started because this method is
invoked by the Try/Catch below when KeyboardInterrupt is caught.
Starting the IOLoop again will allow the publisher to cleanly
disconnect from RabbitMQ.
"""
LOGGER.info('Stopping')
self._stopping = True
self.close_channel()
self.close_connection()
def close_channel(self):
"""Invoke this command to close the channel with RabbitMQ by sending
the Channel.Close RPC command.
"""
if self._channel is not None:
LOGGER.info('Closing the channel')
self._channel.close()
def close_connection(self):
"""This method closes the connection to RabbitMQ."""
if self._connection is not None:
LOGGER.info('Closing connection')
self._connection.close()
def main():
logging.basicConfig(level=logging.DEBUG, format=LOG_FORMAT)
# Connect to localhost:5672 as guest with the password guest and virtual host "/" (%2F)
example = ExamplePublisher('amqp://guest:guest@localhost:5672/%2F?connection_attempts=3&heartbeat_interval=3600')
example.run()
if __name__ == '__main__':
main()