.. index::
   single: Messenger

How to Use the Messenger

Symfony's Messenger provide a message bus and some routing capabilities to send messages within your application and through transports such as message queues. Before using it, read the :doc:`Messenger component docs </components/messenger>` to get familiar with its concepts.

Installation

In applications using :doc:`Symfony Flex </setup/flex>`, run this command to install messenger before using it:

$ composer require messenger

Using the Messenger Service

Once enabled, the message_bus service can be injected in any service where you need it, like in a controller:

// src/Controller/DefaultController.php
namespace App\Controller;

use App\Message\SendNotification;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\Messenger\MessageBusInterface;

class DefaultController extends Controller
{
    public function index(MessageBusInterface $bus)
    {
        $bus->dispatch(new SendNotification('A string to be sent...'));
    }
}

Registering Handlers

In order to do something when your message is dispatched, you need to create a message handler. It's a class with an __invoke method:

// src/MessageHandler/MyMessageHandler.php
namespace App\MessageHandler;

class MyMessageHandler
{
    public function __invoke(MyMessage $message)
    {
        // do something with it.
    }
}

Once you've created your handler, you need to register it:

<service id="App\MessageHandler\MyMessageHandler">
   <tag name="messenger.message_handler" />
</service>

Note

If the message cannot be guessed from the handler's type-hint, use the handles attribute on the tag.

Transports

The communication with queuing system or third parties is delegated to libraries for now. The built-in AMQP transport allows you to communicate with most of the AMQP brokers such as RabbitMQ.

Note

If you need more message brokers, you should have a look to Enqueue's transport which supports things like Kafka, Amazon SQS or Google Pub/Sub.

A transport is registered using a "DSN", which is a string that represents the connection credentials and configuration. By default, when you've installed the messenger component, the following configuration should have been created:

# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            amqp: "%env(MESSENGER_DSN)%"

# .env
###> symfony/messenger ###
MESSENGER_DSN=amqp://guest:guest@localhost:5672/%2f/messages
###< symfony/messenger ###

This is enough to allow you to route your message to the amqp. This will also configure the following services for you:

A messenger.sender.amqp sender to be used when routing messages.
A messenger.receiver.amqp receiver to be used when consuming messages.

Note

In order to use Symfony's built-in AMQP transport, you will need the Serializer Component. Ensure that it is installed with:

$ composer require symfony/serializer-pack

Routing

Instead of calling a handler, you have the option to route your message(s) to a sender. Part of a transport, it is responsible for sending your message somewhere. You can configure which message is routed to which sender with the following configuration:

framework:
    messenger:
        routing:
            'My\Message\Message':  amqp # The name of the defined transport

Such configuration would only route the My\Message\Message message to be asynchronous, the rest of the messages would still be directly handled.

You can route all classes of message to a sender using an asterisk instead of a class name:

framework:
    messenger:
        routing:
            'My\Message\MessageAboutDoingOperationalWork': another_transport
            '*': amqp

A class of message can also be routed to multiple senders by specifying a list:

framework:
    messenger:
        routing:
            'My\Message\ToBeSentToTwoSenders': [amqp, audit]

By specifying a null sender, you can also route a class of messages to a sender while still having them passed to their respective handler:

framework:
    messenger:
        routing:
            'My\Message\ThatIsGoingToBeSentAndHandledLocally': [amqp, ~]

Consuming messages

Once your messages have been routed, you will like to consume your messages in most of the cases. To do so, you can use the messenger:consume-messages command like this:

$ bin/console messenger:consume-messages amqp

The first argument is the receiver's service name. It might have been created by your transports configuration or it can be your own receiver.

Multiple buses

If you are interested into architectures like CQRS, you might want to have multiple buses within your application.

You can create multiple buses (in this example, a command and an event bus) like this:

framework:
    messenger:
        # The bus that is going to be injected when injecting MessageBusInterface:
        default_bus: commands

        # Create buses
        buses:
            messenger.bus.commands: ~
            messenger.bus.events: ~

This will generate the messenger.bus.commands and messenger.bus.events services that you can inject in your services.

Type-hints and auto-wiring

Auto-wiring is a great feature that allows you to reduce the amount of configuration required for your service container to be created. When using multiple buses, by default, the auto-wiring will not work as it won't know why bus to inject in your own services.

In order to clarify this, you can use the DependencyInjection's binding capabilities to clarify which bus will be injected based on the argument's name:

# config/services.yaml
services:
    _defaults:
        # ...

        bind:
            $commandBus: '@messenger.bus.commands'
            $eventBus: '@messenger.bus.events'

Middleware

What happens when you dispatch a message to a message bus(es) depends on its collection of middleware (and their order). By default, the middleware configured for each bus looks like this:

logging middleware. Responsible of logging the beginning and the end of the message within the bus.
_Your own collection of middleware
route_messages middleware. Will route the messages your configured to their corresponding sender and stop the middleware chain.
call_message_handler middleware. Will call the message handler(s) for the given message.

Adding your own middleware

As described in the component documentation, you can add your own middleware within the buses to add some extra capabilities like this:

framework:
    messenger:
        buses:
            messenger.bus.default:
                middleware:
                    - 'App\Middleware\MyMiddleware'
                    - 'App\Middleware\AnotherMiddleware'

Note that if the service is abstract, then a different instance of service will be created per bus.

Disabling default middleware

If you don't want the default collection of middleware to be present on your bus, you can disable them like this:

framework:
    messenger:
        buses:
            messenger.bus.default:
                default_middleware: false

Your own Transport

Once you have written your transport's sender and receiver, you can register your transport factory to be able to use it via a DSN in the Symfony application.

Register your factory

<service id="Your\Transport\YourTransportFactory">
   <tag name="messenger.transport_factory" />
</service>

Use your transport

Within the framework.messenger.transports.* configuration, create your named transport using your own DSN:

framework:
    messenger:
        transports:
            yours: 'my-transport://...'

In addition of being able to route your messages to the yours sender, this will give you access to the following services:

messenger.sender.yours: the sender.
messenger.receiver.yours: the receiver.