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routing guide: Clean up language
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Ask Solem committed Mar 12, 2010
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84 changes: 46 additions & 38 deletions docs/userguide/routing.rst
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Expand Up @@ -25,73 +25,81 @@ Exchange type
-------------

The exchange type defines how the messages are routed through the exchange.
The exchanges defined in the standard is ``direct``, ``topic``, ``fanout`` and
``headers``. Also non-standard exchange types available as plugins to RabbitMQ, like
the last value cache plug-in.
The exchange types defined in the standard are ``direct``, ``topic``,
``fanout`` and ``headers``. Also non-standard exchange types are available
as plugins to RabbitMQ, like the ``last-value-cache plug-in`` by Michael
Bridgen.

.. _`last-value-cache plug-in``:
http://github.com/squaremo/rabbitmq-lvc-plugin
Consumers and Producers
-----------------------
TODO

Related API commands
-------------------------
--------------------

* exchange.declare(exchange_name, type, passive, durable, auto_delete, internal)
exchange.declare(exchange_name, type, passive, durable, auto_delete, internal)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Declares an exchange by name.

* ``passive`` means the exchange won't be created, but you can use this to
check if the exchange already exists.
* ``passive`` means the exchange won't be created, but you can use this to
check if the exchange already exists.

* Durable exchanges are persistent. I.e. they survive a broker restart.
* Durable exchanges are persistent. That is - they survive a broker restart.

* ``auto_delete`` means the queue will be deleted by the broker when there
are no more queues using it.
* ``auto_delete`` means the queue will be deleted by the broker when there
are no more queues using it.

* queue.declare(queue_name, passive, durable, exclusive, auto_delete)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Declares a queue by name.

* exclusive queues can only be consumed from by the current connection.
implies ``auto_delete``.
* exclusive queues can only be consumed from by the current connection.
implies ``auto_delete``.

* queue.bind(queue_name, exchange_name, routing_key)
queue.bind(queue_name, exchange_name, routing_key)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Binds a queue to an exchange with a routing key.
Unbound queues will not receive messages, so this is necessary.

* queue.delete(name, if_unused, if_empty)
queue.delete(name, if_unused, if_empty)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Deletes a queue and its binding.

* exchange.delete(name, if_unused)
exchange.delete(name, if_unused)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Deletes an exchange.

**NOTE**: Declaring does not necessarily mean "create". When you declare you
*assert* that the entity exists and it is operable. There is no rule as to
*assert* that the entity exists and that it's operable. There is no rule as to
whom should initially create the exchange/queue/binding, whether consumer
or producer. Usually the first one to need it will create it.

or producer. Usually the first one to need it will be the one to create it.

Hands-on with the API
---------------------

Celery comes with a tool called ``camqadm`` (short for celery AMQP admin).
It's used for simple admnistration tasks like deleting queues/exchanges,
purging queues and creating queue entities. In short it's for simple command
line access to the AMQP API.
It's used for simple admnistration tasks like creating/deleting queues and
exchanges, purging queues and sending messages. In short it's for simple
command-line access to the AMQP API.

You can write commands directly in the arguments to ``camqadm``, or just start
with no arguments which makes it start in shell-mode::
with no arguments to start it in shell-mode::

$ camqadm
-> connecting to amqp://guest@localhost:5672/.
-> connected.
-->

Here, ``-->`` is the prompt. Type ``help`` for a list of commands, there's
Here ``-->`` is the prompt. Type ``help`` for a list of commands, there's
also autocomplete so you can start typing a command then hit ``tab`` to show a
list of possible matches.

Expand All @@ -104,18 +112,24 @@ Now let's create a queue we can send messages to::
--> queue.bind testqueue testexchange testkey
ok.

This created the direct exchange ``testexchange``, and a queue
named ``testqueue``. The queue is bound to the exchange using
the routing key ``testkey``.

Messages are sent with a routing key, to an exchange. This is done using
the ``basic.publish`` command::
From now on all messages sent to the exchange ``testexchange`` with routing
key ``testkey`` will be moved to this queue. We can send a message by
using the ``basic.publish`` command::

--> basic.publish "This is a message!" testexchange testkey
ok.


Now that the message is sent we can retrieve it again, we use the
Now that the message is sent we can retrieve it again. We use the
``basic.get`` command here, which pops a single message off the queue,
this command is not recommended for production as it implies polling, any
real application would declare consumers instead::
real application would declare consumers instead.

Pop a message off the queue::

--> basic.get testqueue
{'body': 'This is a message!',
Expand All @@ -127,30 +141,24 @@ real application would declare consumers instead::
'properties': {}}


AMQP uses acknowledgment to signify a message has been received and processed
successfully. The message is sent to the next receiver if the client
connection is closed, and it has not yet been acknowledged.
AMQP uses acknowledgment to signify that a message has been received
and processed successfully. The message is sent to the next receiver
if it has not been acknowledged before the client connection is closed.

Note the delivery tag listed in the structure above; Within a connection channel,
every received message has a unique delivery tag,
This tag is used to acknowledge the message. Note that
delivery tags are not unique across connections, so in another client
the delivery tag ``1`` might point to a different message than in our channel.
the delivery tag ``1`` might point to a different message than in this channel.

You can acknowledge the message we received using ``basic.ack``::

--> basic.ack 1
ok.


To clean up after ourselves we should delete the entities we just created::
To clean up after our test session we should delete the entities we created::

--> queue.delete testqueue
ok. 0 messages deleted.
--> exchange.delete testexchange
ok.





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