Implementing a custom Chatter transport for a service is expected to be an uncommon occurrence. Take a look at Chatter services before implementing a new transport as the service may already have an implementation. The Fake service provides a way for testing messages in a development environment.

If you decide to implement a new Chatter transport for a publicly accessible service, consider making it available as a new contrib project. Contrib projects are able to implement the required code pieces without any modifications to code owned by the Notifier Chat Channel project, as evident below.

Implementation

In a custom module, add the following boilerplate:

Services

services:
  autoconfigure: true
  autowire: true

  Drupal\my_module\MyModuleChatterTransportFactory:
    parent: notifier.transport_factory.abstract
    tags:
      - { name: chatter.transport_factory }

Factory class

namespace Drupal\my_module;

use Symfony\Component\Notifier\Transport\AbstractTransportFactory;
use Symfony\Component\Notifier\Transport\Dsn;
use Symfony\Component\Notifier\Transport\TransportInterface;

final class MyModuleChatterTransportFactory extends AbstractTransportFactory {
  public function __construct(
    private \Psr\Http\Client\ClientInterface $httpClient,
  ) {}

  protected function getSupportedSchemes(): array {
    // Make up a "scheme" which will be used in the `chatter.transports` DSN.
    return ['my-module-chat'];
  }

  public function create(Dsn $dsn): TransportInterface {
    return new MyModuleChatterTransport($this->httpClient);
  }
}

Transport class

namespace Drupal\my_module;

use Symfony\Component\Notifier\Message\ChatMessage;
use Symfony\Component\Notifier\Message\MessageInterface;
use Symfony\Component\Notifier\Message\SentMessage;
use Symfony\Component\Notifier\Transport\AbstractTransport;
use \Symfony\Component\Notifier\Exception\UnsupportedMessageTypeException;

final class MyModuleChatterTransport extends AbstractTransport {
  public function __construct(
    private \Psr\Http\Client\ClientInterface $httpClient,
  ) {}
  
  protected function doSend(MessageInterface $message): SentMessage {
    if (!$message instanceof ChatMessage) {
      throw new UnsupportedMessageTypeException(__CLASS__, ChatMessage::class, $message);
    }
    
    // @todo send the message here.
    $this->httpClient->request('POST', ...);
  }

  public function __toString() {
    // Return the DSN of the transport, the scheme should be the same per factory.
    return 'my-module-chat://default';
  }

  public function supports(MessageInterface $message): bool {
    // Add other criteria if you need the message to have more specific characteristics.
    return $message instanceof ChatMessage;
  }
}

---

Then configure the transport just like other transports.

Configuration

In the site directory, usually sites/default/, create a services.yml file.

Add to settings.php:

$settings['container_yamls'][] = __DIR__ . '/services.yml';

Add to services.yml:

parameters:
  chatter.transports:
    my_chat_transport: 'my-module-chat://default'

Then clear Drupal caches:

drush cr

Sending

To send a message to your Chat channel or user, create a notification then send to the notifier service.

Pass the name of the custom transport as configured in chatter.transports to the Notification::channels() method, prefixed with chat/.

Message body

Chat notifications use subject() for message contents, not contents().

src/MyService.php

namespace Drupal\my_module;

final class MyService {
  public function __construct(
    private readonly \Symfony\Component\Notifier\NotifierInterface $notifier,
  ) {}
  public function myMethod(){
    $notification = (new \Symfony\Component\Notifier\Notification\Notification())
      ->subject('Test message!')
      # Specify the name of the transport as configured in `chatter.transports`.
      ->channels(['chat/my_chat_transport']),
    $this->notifier->send($notification);
  }
}

mymodule.services.yml

services:
  _defaults:
    autowire: true
    
  my_service:
    class: Drupal\my_module\MyService