This plugin adds a new exchange type to RabbitMQ providing a new routing algorithm based on the evaluation of SQL92 predicates. Also allows to modify the message headers.
The name of the new exchange type is amqp-filter.
Like other exchange types, the binding routing key is used by the routing algorithm.
The binding routing key must be a valid predicate (SQL-like conditional expression).
This predicate may contain properties that must be present in the message header fields.
Due to the binding routing key property is limited to 256 characters, the binding routing key must be specified in the binding arguments. The binding arguments are a list of key-value pairs. The argument used to specify the routing key must have a key with the text routingkey, and a valid predicate as value.
An exchange of type amqp-filter will route a message to a queue if the queue has bound to the exchange with
a binding routing key in form of predicate and the evaluation of this predicate using the message header fields returns true.
The message routing key is ignored.
The predicate must follow the BNF grammar specified here.
Example of valid predicate (binding routing key):
"UserName = 'Nick' And Age > 18"
The evaluation of this predicate will return true (and the message will be routed to the corresponding queue)
if there are two fields in the message headers with names UserName and Age, and values "Nick" (string type) and 18 (number type) respectively.
This plugin provides also a feature that allow to execute some actions that modify the message headers.
The actions use a SQL like expression with a similar syntax to the SQL UPDATE statement.
These actions must be specified in a binding argument with name actions and type string.
Example of valid actions:
Set LastName = 'Miller'; Set CompanyName = 'Twitter';
These actions will add (or update if the property exists) these two fields to the message header. These action are performed on the message inmediately before the message is routed to each queue.
The actual version of this plugin uses Erlang/OTP 20 and RabbitMQ 3.7.0.
RabbitMQ 3rd party plugin directories will differ from platform to platform and installation method to installation method.
Plugin directory can be located by executing the following command:
rabbitmqctl eval 'application:get_env(rabbit, plugins_dir).'
{ok,"/usr/lib/rabbitmq/plugins:/usr/lib/rabbitmq/lib/rabbitmq_server-3.7.7/plugins"}
The first directory in the example above is the 3rd party plugin directory. You must set this value to the RABBITMQ_PLUGINS_DIR variable in the project makefile. By default is /usr/lib/rabbitmq/plugins.
make dist
# generates the ez files in the /plugins folder.
make deploy
# copies the ez files to the RabbitMQ 3rd party plugin directory.
Now you can start the RabbitMQ server and enable the plugin:
rabbitmq-plugins enable amqp_filter_exchange