something can be a message broker or a third party API for example.

**Receiver**:

Responsible for deserializing and forwarding messages to handler(s). This

can be a message queue puller or an API endpoint for example.

Responsible forretrieving,deserializing and forwarding messages to handler(s).

Thiscan be a message queue puller or an API endpoint for example.

**Handler**:

Responsible for handling messages using the business logic applicable to the messages.

#. ``LoggingMiddleware`` (logs the processing of your messages)

#. ``SendMessageMiddleware`` (enables asynchronous processing)

#. ``HandleMessageMiddleware`` (calls the registeredhandle)

#. ``HandleMessageMiddleware`` (calls the registeredhandler)

Example::

If you need to add metadata or some configuration to a message, wrap it with the

:class:`Symfony\\Component\\Messenger\\Envelope` class. For example, to set the

serialization groups used when the message goes through the transport layer, use

the``SerializerConfiguration``envelope::

:class:`Symfony\\Component\\Messenger\\Envelope` class and add stamps.

For example, to set theserialization groups used when the message goes

throughthetransport layer, use the ``SerializerStamp``stamp::

At the moment, the Symfony Messenger has the following built-inenvelopes:

At the moment, the Symfony Messenger has the following built-inenvelope stamps:

#.:class:`Symfony\\Component\\Messenger\\Transport\\Serialization\\SerializerConfiguration`,

#.:class:`Symfony\\Component\\Messenger\\Stamp\\SerializerStamp`,

to configure the serialization groups used by the transport.

#.:class:`Symfony\\Component\\Messenger\\Middleware\\Configuration\\ValidationConfiguration`,

#.:class:`Symfony\\Component\\Messenger\\Stamp\\ValidationStamp`,

to configure the validation groups used when the validation middleware is enabled.

#.:class:`Symfony\\Component\\Messenger\\Asynchronous\\Transport\\ReceivedMessage`,

#.:class:`Symfony\\Component\\Messenger\\Stamp\\ReceivedStamp`,

an internal item that marks the message as received from a transport.

Instead of dealing directly with the messages in the middleware you can receive the

envelope by implementing the:class:`Symfony\\Component\\Messenger\\EnvelopeAwareInterface`

marker, like this::

Instead of dealing directly with the messages in the middleware you receive the envelope.

Hence you can inspect the envelope content and its stamps, or add any::

The above example will forward the message to the next middleware with an additional

envelope item*if* the message has just been received (i.e. has the `ReceivedMessage` item).

You can create your own items by implementing:class:`Symfony\\Component\\Messenger\\EnvelopeAwareInterface`.

stamp*if* the message has just been received (i.e. has the `ReceivedStamp` stamp).

You can create your own items by implementing:class:`Symfony\\Component\\Messenger\\Stamp\\StampInterface`.

Transports

Your own Receiver

A receiver is responsible forreceiving messages from a source and dispatching

A receiver is responsible forgetting messages from a source and dispatching

them to the application.

Imagine you already processed some "orders" in your application using a

To allow sending and receiving messages on the same bus and prevent an infinite

loop, the message bus will add a:class:`Symfony\\Component\\Messenger\\Asynchronous\\Transport\\ReceivedMessage`

envelope itemto the message envelopes and the:class:`Symfony\\Component\\Messenger\\Asynchronous\\Middleware\\SendMessageMiddleware`

loop, the message bus will add a:class:`Symfony\\Component\\Messenger\\Stamp\\ReceivedStamp`

stampto the message envelopes and the:class:`Symfony\\Component\\Messenger\\Middleware\\SendMessageMiddleware`

middleware will know it should not route these messages again to a transport.

.. _blog posts about command buses:https://matthiasnoback.nl/tags/command%20bus/