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Description:

gocept.amqprun 3.0

gocept.amqprun helps you writing and running AMQP consumers, and sending
AMQP messages. It currently only supports AMQP 0-9-1 and integrates with the
Zope Tool Kit (ZTK) so you can use adapters, utilities and all the buzz.

Contents

Basic concepts and terms
Things you don’t need to take care of
Getting started: receiving messages
Sending messages
Settings
Limitations
Interfacing with the file system
Development
CHANGES

Basic concepts and terms

A message handler is a function which is bound with a routing key to
exactly one queue. It is called for each message on that queue, and may
return a list of messages as a result.
The result messages of one handled message are sent in one transaction
together with the ACK of the handled message.
When an exception is raised during message processing, the transaction is
aborted. (The received message would be NACKed if RabbitMQ was supporting
it.)
A message handler handles exactly one message at a time. Multiple messages
can be processed at the same time using multiple processes. (Each process is
single-threaded.)

Things you don’t need to take care of

Socket handling and locking for communicating with the AMQP broker
Transaction handling
Message ids

Each outgoing message gets an email-like message id.
The correlation id of each outgoing message is set to the message id of
the incoming message.
Each outgoing message gets a custom references header which is set to the
incoming message’s reference header plus the incoming message’s message
id.

Getting started: receiving messages
To get started, define a function which does the work. In this example, we log
the message body and send a message. The declare decorator takes two
arguments, the queue name and the routing key (you can also pass in a list to
bind the function to multiple routing keys). The declare decorator also
supports an optional arguments argument that is a dictionary to be passed
to the AMQP queue_declare call to, e.g., support mirrored queues on RabbitMQ.
The optional argument principal specifies to wrap the handler call into a
zope.security interaction using the given principal id (you need the
[security] setup.py extra to use this integration functionality).
import logging
import gocept.amqprun.handler
import gocept.amqprun.message

log = logging.getLogger(__name__)

@gocept.amqprun.handler.declare('test.queue', 'test.routing')
def log_message_body(message):
log.info(message.body)
msg = gocept.amqprun.message.Message(
header=dict(content_type='text/plain'),
body=u'Thank you for your message.',
routing_key='test.thank.messages')
return [msg]
The handler function needs to be registered as a named utility. With ZCML this
looks like this [1]:
<configure xmlns="http://namespaces.zope.org/zope">
<utility component="your.package.log_message_body" name="basic" />
</configure>
To set up a server, it’s recommended to create a buildout. The following
buildout creates a config file for gocept.amqprun as well as a ZCML file
for the component configuration and uses ZDaemon to daemonize the process:
[buildout]
parts =
config
zcml
app
server

[deployment]
name = queue
recipe = gocept.recipe.deploymentsandbox
root = ${buildout:directory}

[config]
recipe = lovely.recipe:mkfile
path = ${deployment:etc-directory}/queue.conf

amqp-hostname = localhost
amqp-username = guest
amqp-password = guest
amqp-virtualhost = /

eventlog =
<eventlog>
level DEBUG
<logfile>
formatter zope.exceptions.log.Formatter
path STDOUT
</logfile>
</eventlog>
amqp-server =
<amqp-server>
hostname ${:amqp-hostname}
username ${:amqp-username}
password ${:amqp-password}
virtual_host ${:amqp-virtualhost}
</amqp-server>

content =
${:eventlog}
${:amqp-server}
<worker>
component-configuration ${zcml:path}
</worker>
<settings>
your.custom.settings here
</settings>

[zcml]
recipe = lovely.recipe:mkfile
path = ${deployment:etc-directory}/queue.zcml
content =
<configure xmlns="http://namespaces.zope.org/zope">
<include package="your.package" />
</configure>

[app]
recipe = zc.recipe.egg:script
eggs =
gocept.amqprun
your.package
zope.exceptions
arguments = '${config:path}'
scripts = server=app

[server]
recipe = zc.zdaemonrecipe
deployment = deployment
program = ${buildout:bin-directory}/app

[1]
It’s likely that there will be a special ZCML statement and/or grok
support to make registering of handlers easier.

Sending messages
If all you want to do is send messages, you don’t have to register any
handlers, but can use gocept.amqprun.server.Server.send() directly. While
the handlers usually run in their own process, started by the server
entrypoint (as described above), if you’re just sending messages, you can also
skip the extra process and run the gocept.amqprun.server.Server in your
original process. Here is some example code to do that:
def start_server(**kw):
server = gocept.amqprun.server.Server(kw, setup_handlers=False)
server.connect()
return server
(When you’re using the ZCA, you’ll probably want to register the Server as
a utility at that point, too, so clients can access it to send messages
easily.)

Settings
For application-specific settings gocept.amqprun makes the <settings>
section from the configuration available via an ISettings utility:
settings = zope.component.getUtility(
gocept.amqprun.interfaces.ISettings)
settings.get('your.settings.key')

Limitations

Currently all messages are sent and received through the amq.topic
exchange. Other exchanges are not supported at the moment.

Interfacing with the file system
Reading
There is a send_files entrypoint in the setup.py. It can be configured with
three arguments: The path of the zconfig file, a watch path and a routing key.
It reads new files in the directory named new in the watch path and sends
a message with its content as the body and the filename as an X-Filename header
to the route. Sent files are moved to the directory called cur in the
watch path.

Development
You can set the AMQP server parameters for running the tests via environment
variables:

AMQP_HOSTNAME:
default: localhost

AMQP_USERNAME:
default: guest

AMQP_PASSWORD:
default: guest

AMQP_VIRTUALHOST:
default: None, so a vhost with a temporary name is created and
deleted automatically (using AMQP_RABBITMQCTL command)

AMQP_RABBITMQCTL:
default: ‘sudo rabbitmqctl’

The source code is available in the mercurial repository at
https://github.com/gocept/gocept.amqprun
Please report any bugs you find at
https://github.com/gocept/gocept.amqprun/issues

bin/test_sender and bin/test_server
test_sender and test_server are scripts that provide basic sender and
handler capabilities to smoke test the behaviour of our current implementation.
When started test_sender emits 10 messages routed to test.routing.
test.server declares a test.queue which all messages from
test.routing are sent to and a handler logging every incoming message from
test.queue.

bin/test_send_files
test_send_files starts a server that watches the ./testdir/new directory
and sends files copied into it as an amqp message to test.routing. Its
entrypoint is gocept.amqprun.readfiles:main.

CHANGES

3.0 (2020-10-06)

Breaking changes

Drop support for Python 2.7.
Drop no longer used exception .interfaces.CounterBelowZero.

Features

Retry errors which happen during a transaction.commit and are configured for
reraise.
Add support for Python 3.9.

2.1 (2020-09-18)

Let the Server exit in case of an socket.error. We lost the re-connection
feature in 2.0 already.

2.1a1 (2020-04-17)

Add support for Python 3.7 and 3.8.

2.0 (2020-04-15)

Add support for zope.interface >= 5.
(#13)
Change CI pipeline from Travis to GitHub Actions.

2.0a1 (2020-03-20)
Breaking changes

Use kombu/py-amqp instead of pika for basic abstraction over amqp methods.
Remove multithreading – servers and workers run in the current process.
Remove gocept.amqprun.main.main_server as main loop.
Remove configure.zcml and meta.zcml.
Remove writing messages in files and the amqp:writefile directive.
Remove writefiles extra in setup.py.
Remove amqp:readfile zcml directive and add send_files entrypoint for
readfiles process. It takes three parameters: a configuration file path, a
watch directory path and a route to send the file to.
(see bin/test_send_files, details are in the README.rst).
Remove .channel.Channel and use amqp.channel.Channel instead.
Remove .interfaces.IChannelManager.
Remove .interfaces.ProcessStarted.
Remove .interfaces.ProcessStopping.
Remove .connection.Connection and use kombu.Connection instead.
Rename conf key heartbeat_interval to heartbeat in zconfig
configuration.
Remove amount from worker zconfig.
Enforce content_encoding header for Message bodies that are unicode.
Rename .message.Message.header.headers to
.message.Message.header.application_headers.
Rename .testing.ZCML_LAYER to .testing.ZCA_LAYER.
Remove .testing.LoopTestCase, use unittest.TestCase instead.
Remove .testing.MainTestCase.wait_for_response, use wait_for_message
instead.
Remove .testing.SettingsLayer as it is not used here.
Move .connection.Parameters to .server, it now returns a dict.

Features

Add bin/test_sender and bin/test_server scripts to smoke test sending
and receiving behaviour. See README.rst.
Add representation for .handler.Handler class.

1.8 (2019-09-11)

Update to current bootstrap.py
Improve forward compatibility with Python 3.
Fix deprecation warning.
Prevent using pytest >= 5 to keep Python 2 compatibility.
Migrate repository to github.

1.7.1 (2016-08-22)

Fix bug, when a string is passed as a port number to
gocept.amqprun.connection.Parameters.

1.7 (2016-05-31)

Fix possible unresponsiveness of message handlers which occurred after an
exception in the worker. The exception caused a counter under-run which
prevents switching channels. The counter is no longer bound to the
transaction but to the message handling.
Add a save guard which kills the whole process if the reference counter on
the channel falls below zero.
Acquire the channel before putting a task to the worker queue to prevent a
possible race condition.
Release the commit lock if tpc_abort() fails. So the next tpc_begin()
does not wait forever while trying to acquire the lock and thus blocking the
whole process.

1.6 (2016-04-04)

Allow arbitrary keywords in .testing.QueueTestCase.send_message() to be
passed to generated message.

1.5 (2016-02-01)

Add a testing extra which can be used to reuse the test infrastructure of
this package to develop tests on top of it.

1.4 (2015-11-20)

Acknowledge message in ErrorHandlingHandler on non recoverable error.
This got lost in 0.17.0.
Fixes: https://bitbucket.org/gocept/gocept.amqprun/issue/5
The error message of ErrorHandlingHandler on a non recoverable error
references the original message using its correlation_id again.
This got lost in 0.17.0.
Fixes: https://bitbucket.org/gocept/gocept.amqprun/issue/6

1.3 (2015-09-11)

Update the test infrastructure to be able to run with newer RabbitMQ versions
than 3.1.5.

1.2 (2015-09-11)

Add py.test as test runner.
Add settings attribute to IHandler to ease accessing ISettings.

1.1 (2015-09-01)

.connection.Parameters no longer accepts arbitrary keyword parameters.

1.0 (2015-04-10)

Notify IConfigFinished event after gocept.amqprun is fully configured
but before the workers are started. This event can be used to open database
connections for instance.
Bump version to 1.0 as this package is used in production for years.

0.17.0 (2015-04-09)

Abort transaction in ErrorHandlingHandler on non recoverable error.
Fixes: https://bitbucket.org/gocept/gocept.amqprun/issue/4

0.16.0 (2015-03-25)

Raise RuntimeError if connection is not alive after connect. (This can
happen when the credentials are wrong.)

0.15.2 (2015-02-24)

Fix error reporting in .testing.QueueLayer.rabbitmqctl().

0.15.1 (2015-01-21)

Moved code to and bug tracker to Bitbucket.

0.15.0 (2014-10-08)

Pretend to support savepoints so we can work together with other systems that
support (and require) them.

0.14.0 (2014-09-09)

Introduce gocept.amqprun.handler.ErrorHandlingHandler base class.
Run integration tests (MainTestCase) in a separate ZCA, isolated from any
registrations that might have been done by other tests.
Create temporary virtualhost on the rabbitmq server per test run.
Improved test-case method send_message to take headers as a parameter.

0.13.0 (2014-04-16)

Introduce IResponse for transaction-integrated exception handling.
Fix timing bug: when the remote side closes the socket and at the same time a
channel switch is triggered, this used to break down (since the socket is
closed). We now ignore the channel switch attempt and simply wait for the
reconnect, which opens a new channel anyway.

0.12.2 (2014-02-20)

Add xfilename variable to the <amqp:writefiles pattern=""> setting.

0.12.1 (2014-02-20)

Add safeguard that two handlers cannot bind to the same queue.

0.12 (2014-02-13)

Include <amqp:writefiles> into the transaction handling, i.e. write to file
only on commit. Previously, when an error occurred e.g. inside the
MessageStored event, duplicate files would be written (each time the message
was processed again on retry after the error).

0.11 (2014-01-21)

Crash the process on filesystem errors for <amqp:readfiles>. Previously only
the file reading thread crashed, but the process kept running, unaware that
it now was not doing its job anymore, since the thread had died.

0.10 (2013-05-28)

Support more than one Server in a single process.
Introduce setup_handlers parameter for Server so clients can disable
setting up handlers.
Fix a bug in the <amqp:readfiles> transaction implementation that caused
crash when aborting a transaction (#12437).
Allow test server to take longer time for startup on slow computers.

0.9.5 (2013-04-16)

Refactor Session / DataManager responsibilities (#9988).

0.9.4 (2012-09-07)

Fix IDataManager implementation: abort() may be called multiple times,
regardless of transaction outcome. Only release the channel refcount once.

0.9.3 (2012-09-07)

Improve logging of IDataManager.

0.9.2 (2012-09-07)

Improve logging of IChannelManager.acquire/release.

0.9.1 (2012-09-06)

Fix IDataManager implementation: tpc_abort() may also be called without a
prior tpc_begin() (happens for errors in savepoints, for example).
Fix method signature of Connection.close().

0.9 (2012-08-31)

Introduce optional integration with zope.security: handlers can declare a
principal id with which an interaction will be created.
Use a separate channel for sending messages that are not a response to a
received message.
Introduce SETTINGS_LAYER for tests relying on ISettings.

0.8 (2012-04-04)

Fix race condition that caused messages to be acknowledged on a different
channel than they were received on (#10635).
Fix race condition that caused attempts at sending messages before the
server was started properly (#10620).

0.7 (2012-03-22)

Fix race condition between getting the current channel in the DataManager and
switching the current channel in the Server (#10521).
Make AMQP server configurable for tests (#9232).

0.6.1 (2012-02-23)

Fixed bug in creating references header when parent message has no references
(#10478).

0.6 (2012-02-22)

Features

Changed FileStoreReader from its own process to a thread that uses
gocep.amqprun for sending (previously it used amqplib). Introduced
amqp:readfiles ZCML directive. (#10177)
Changed filestore extra to readfiles extra.
Transmit filename as X-Filename header from amqp:readfiles.
Introduced ISender utility.

Bugs

Fixed bug with acknowledging messages that was introduced in 0.5 (#10030).

Internal

Changed API for MainTestCase from create_reader to start_server.

0.5.1 (2012-01-09)

Bugfix to support unicode arguments for queue declaration as pika
only supports bytestrings here.
Bugfix to make arguments parameter of amqp:writefiles work (#10115).

0.5 (2011-12-08)

General

Added writefiles extra to make ZCML directive amqp:writefiles optional.
Added filestore extra to make gocept.amqprun.filestore optional.
Moved declaration of amqp:writefiles from configure.zcml to
meta.zcml.

Features

Renamed gocept.amqprun.server.MessageReader into
gocept.amqprun.server.Server and added a send method so it can
initiate sending of messages.
Add support for arguments for queue_declare e.g to support x-ha-policy
headers for RabbitMQ mirrored queue deployments (#10036).

Internal

Internal API change in server.AMQPDataManager.__init__: the message
parameter is now optional, so it was moved to the end of the list of
arguments.
Use plone.testing for layer infrastructure.

0.4.2 (2011-08-23)

Add helper methods for dealing with header files to FileWriter (for #9443).

0.4.1 (2011-08-22)

Log Message-ID.

0.4 (2011-07-25)

The message id of outgoing messages is set.
The correlation id of outgoing messages is set to the incoming message’s
message id (if set).
A custom header references is set to the incoming message’s reference
header + the incomming message’s message id (like References in RFC5322).
Fixed broken tests.
Allow upper case in settings keys.
Extend AMQP server configuration for FileStoreReader to include credentials
and virtual host.
Allow specifying multiple routing keys (#9326).
Allow specifying a filename/path pattern (#9327).
The FileWriter stores the headers in addition to the body (#9328).
FileWriter sends IMessageStored event (#9335).

0.3 (2011-02-05)

Renamed decorator from handle to declare.
Added helper method wait_for_response to MainTestCase.
Added an IProcessStarting event which is sent during startup.
Added the <amqp:writefiles/> directive that sets up a handler that writes
incoming messages into files.
Added handling of <logger> directives

0.2 (2010-09-14)

Added a decorator gocept.amqprun.handler.handle(queue_name, routing_key).

0.1 (2010-08-13)

first release.