# Message Publisher

Message Publisher provide abstraction to send Message to other Services.\
This way you can send message with simple interface without exposing Message Broker implementation and keeping possibility to easily switch implementation when needed.

### Modules Providing Support

* [RabbitMQ Module](https://docs.ecotone.tech/modules/amqp-support-rabbitmq#message-publisher)

## Message Publisher Interface

```php
interface MessagePublisher
{

    // 1
    public function send(string $data, string $sourceMediaType = MediaType::TEXT_PLAIN) : void;

    // 2
    public function sendWithMetadata(string $data, array $metadata, string $sourceMediaType = MediaType::TEXT_PLAIN) : void;

    // 3
    public function convertAndSend(object|array $data) : void;

    // 4
    public function convertAndSendWithMetadata(object|array $data, array $metadata) : void;
}
```

1. `send` - Send a `string type` via Publisher. It does not need any conversion, you may add additional `Media Type` of `$data`.
2. `sendWithMetadata` - Does the same as `send,` allows for sending additional [Meta data](https://docs.ecotone.tech/tutorial-php-ddd-cqrs-event-sourcing/php-metadata-method-invocation#metadata).
3. `convertAndSend` - Allow for sending types, which needs conversion. Allow for sending objects and array, `Ecotone` make use of [Conversion system](https://docs.ecotone.tech/messaging/conversion/conversion) to convert `$data`.
4. `convertAndSendWithMetadata` - Does the same as `convertAndSend,` allow for sending additional [Meta data](https://docs.ecotone.tech/tutorial-php-ddd-cqrs-event-sourcing/php-metadata-method-invocation#metadata).

## How to use Message Publisher

Publisher is a special type of [Gateway](https://docs.ecotone.tech/messaging/messaging-concepts/messaging-gateway), which implements [Publisher interface](https://docs.ecotone.tech/modules/amqp-support-rabbitmq#available-actions).\
It will be available in your Dependency Container under passed `Reference name.`\
In case interface name `MessagePublisher:class` is used, it will be available using auto-wire.

```php
#[EventHandler] 
public function whenOrderWasPlaced(OrderWasPlaced $event, MessagePublisher $publisher) : void
{
    $publisher->convertAndSendWithMetadata(
        $event,
        [
            "system.executor" => "Johny"
        ]
    );
}
```