How to arguments into the Websocket handler?

Question

I am developing a scorecard application where certain group of members are playing and can update their score in chart which needs to be reflected in team members screen too.

For this purpose I am using cboden/ratchet.

Each team have a common team code which I will pass using URL localhost:8000/{token} which will be passed from controller to twig.

I have following in command:

    $server = IoServer::factory(
        new HttpServer(
            new WsServer(
                new ScoreHandler()
            )
        ),
        8080
    );
    $server->run();

ScoreHandler

public function __construct(EntityManagerInterface $entityManager)
{
    $this->connections = new SplObjectStorage;
    $this->entityManager = $entityManager;
}

This returns me Too few arguments to function App\Websocket\ScoreHandler::__construct(), 0 passed error.

I am not sure how to fix this error here. As I am planning to insert into the db and fetch records based on token and return to certain user group.

Can anybody help me ?

Answer 1

Word of Caution

It is strongly discouraged from using PHP with Symfony and/or Doctrine for any long-running background processes (daemon), that listens for WebSocket (or other) connections, using Ratchet/ReactPHP style features in any production/real-world environments. PHP was not designed to run as a daemon. As such, without proper planning, the process will crash with either a Doctrine Connection exception with the MySQL Server Has Gone Away error or from memory leaks caused by maintaining the Entity Manager, Symfony service definitions and logger overflows.

Using PHP as a daemon would require implementing unintuitive workarounds, such as a Messenger Queue (causes long delays between responses) or Lazy Proxy objects (causes code-level maintainability issues) and additional background processes, like supervisor and/or cron jobs to circumvent the inherent issues and recover from crashes.

---

Provided you are using the default autowire configuration for your config/services.yaml and ScoreHandler is not in one of the excluded paths, the following options are feasible using dependency injection.

# config/services.yaml
services:
    # default configuration for services in *this* file
    _defaults:
        autowire: true      # Automatically injects dependencies in your services.
        autoconfigure: true # Automatically registers your services as commands, event subscribers, etc.

    # makes classes in src/ available to be used as services
    # this creates a service per class whose id is the fully-qualified class name
    App\:
        resource: '../src/*'
        exclude: '../src/{DependencyInjection,Entity,Migrations,Tests,Kernel.php}'

    # ...

Inject ScoreHandler as a Service

The recommended approach is to inject the ScoreHandler service into the command, which will also automatically inject the EntityManagerInterface into the ScoreHandler.

class YourCommand extends Command
{

    private $handler;

    public function __construct(ScoreHandler $handler)
    {
        $this->handler = $handler;
        parent::__construct();
    }

    //...

    public function execute(InputInterface $input, OutputInterface $outpu)
    {

        //...

        $server = IoServer::factory(
            new HttpServer(
                new WsServer($this->handler)
            ),
            8080
        );
        $server->run();
    }
}

Inject EntityManagerInterface and pass to ScoreHandler

Since you are creating a new instance of ScoreHandler manually, it requires the EntityManagerInterface to be supplied as an argument to the constructor.

This is not recommended, as a service already exists that is already autowired as in the previous example.

class YourCommand extends Command
{

    private $em;

    public function __construct(EntityManagerInterface $em)
    {
        $this->em = $em;
        parent::__construct();
    }

    //...

    public function execute(InputInterface $input, OutputInterface $outpu)
    {

        //...

        $server = IoServer::factory(
            new HttpServer(
                new WsServer(
                    new ScoreHandler($this->em)
                )
            ),
            8080
        );
        $server->run();
    }
}

---

NodeJS Alternative

While PHP was not designed as a daemon, nodejs and several other platforms are able to facilitate listening for connections. They can be used to forward the request to your Symfony web application and send a response back to the client, as a request broker.

See https://stackoverflow.com/a/68027150/1144627 for an example of a WebSocket Broker Service.