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RabbitEvents Listener

The RabbitEvents Listener component provides an API for handling events published across the application structure. More information is available in the Nuwber's RabbitEvents documentation.

If you only need to handle events, you can use the RabbitEvents Listener separately from the main library.

Table of Contents

1. Installation via Composer
2. Configuration
3. Register a Listener
4. Defining Listeners
5. Middleware
6. Stopping The Propagation Of An Event
7. Console Commands
8. Logging

Installation via Composer

RabbitEvents Listener can be installed via the Composer package manager:

After installing Listener, you can execute the rabbitevents:install Artisan command, which will install the RabbitEvents configuration file and RabbitEventsServiceProvider into your application:

Configuration

Details about the configuration are described in the library documentation.

Register a Listener

The listen property of RabbitEventsServiceProvider contains an array of all events (keys) and their listeners (values). You can add as many events to this array as your application requires.

You can even register listeners using the * as a wildcard parameter, allowing you to catch multiple events with the same listener. Wildcard listeners receive the event name as their first argument and the entire event data array as their second argument.

Defining Listeners

Event listeners receive the event data in the method provided in the $listen definition. If no method is provided, the handle method will be called. Within the handle method, you can perform actions necessary to respond to the event:

Example of The Event Listener class

Example of The Wildcard Event Listener class

Middleware

A Listener middleware allows you to wrap custom logic around the execution of a listener, reducing boilerplate in the handlers themselves. For example, you have an event charge.succeeded which can be handled in several APIs but only if this payment is for a specific entity.

Without middleware, you had to check the entity type in a listener's handle method.

It is okay if you have only one listener. What if many listeners must implement the same check at the first line of the handle method? The code will become a bit noisy.

Instead of writing the same check at the start of each listener, you could define listener middleware that handles an entity type.

In this example, you see that if you need to stop the propagation, just return false.

After creating listener middleware, they can be attached to a listener by returning them from the listener's middleware method or as an array item from the $middleware attribute.

You can see that you are also able to specify which method of the attached middleware class should be called.

This is just an illustration of how you could pass middleware to the listener. You could choose the way you prefer.

Stopping The Propagation Of An Event

Sometimes, you may wish to stop the propagation of an event to other listeners. You can do so by returning false from your listener's handle method.

Console Commands

Command rabbitevents:listen

There is a command that registers events in RabbitMQ:

This command registers a separate queue in RabbitMQ bound to an event. As rabbitevents:listen registers a queue, you should run this command before you start publishing your events. Nothing will happen if you publish an event first, but it will not be handled by a Listener without the first run.

To start listening to all events registered in the application, you can run without any event names:

or mention events separated by commas:

If the list of events is too long, the queue name will be created as an MD5 checksum of the lengthy queue name. This was implemented because the AMQP driver does not accept longer names.

You can start listening to an event only by using the rabbitevents:listen command, so you could use some system such as Supervisor

or pm2 to control your listeners.

If your listener crashes, then managers will rerun your listener, and all messages sent to a queue will be handled in the same order as they were sent. There is a known problem: as queues are separated and you have messages that affect the same entity, there's no guarantee that all actions will be done in an expected order. To avoid such problems, you can send message time as a part of the payload and handle it internally in your listeners.

Options

--service= - By default, it's config('app.name'). When a queue starts, the name of the service becomes a part of a queue name: service:event.name. You could override the first part of a queue name by this option.\ --memory=128 - The memory limit in megabytes. The RabbitEvents have restarting a worker if the limit is exceeded.\ --timeout=60 - The length of time (in seconds) each Message should be allowed to be handled.\ --tries=1 - The Number of times to attempt to handle a Message before logging it failed.\ --sleep=5 - How long in seconds a worker would wait before the next try to handle a failed message.\ --quiet - Hide console output.\ -v - Verbosity. Enables a stack trace for Exceptions.

Command rabbitevents:list

To get the list of all registered events, please use the command rabbitevents:list.

Supervisor Configuration

The Supervisor configuration is similar to Laravel Queue. We decided not to copy this doc here.

Logging

The package provides 2 ways to see what happens to your listener. By default, it writes processing, processed, failed messages, and occurred exceptions to console output. The message includes service, event, and listener name. To get the exception's trace, run the listener with verbosity >= 1, for example, -v.
If you want to turn this feature off, just run the listener with the --quiet option.

The package also supports your application logger. To use it, set config value rabbitevents.logging.enabled to true and choose a log level.

When choosing to use the application logger, you may configure the package's logging channel using the config value rabbitevents.logging.channel. By default, it will use the value from logging.default.