Configurable handlers with PHP attributes

Contributed by Alireza Mirsepassi
in #43588.

PHP attributes are a great way of adding metadata to PHP code. In Symfony
we're adding the option of using PHP attributes to configure most things. That's
why in Symfony 5.4 we're allowing to configure message handlers with attributes.
Instead of having to implement the MessageHandlerInterface, you can now add
the AsMessageHandler attribute to any PHP class and use it as a message handler:

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

use App\Message\OtherSmsNotification;
use App\Message\SmsNotification;
use Symfony\Component\Messenger\Attribute\AsMessageHandler;

#[AsMessageHandler(fromTransport: 'async', priority: 10)]
class SmsNotificationHandler
{
public function __invoke(SmsNotification $message)
{
// ...
}
}

Worker metadata

Contributed by Oleg Krasavin
in #42335.

Currently there's no simple way to get worker metadata such as its transport
name. In Symfony 5.4 we're improving this with the introduction of a new
WorkerMetadata class which is accessible via $worker->getWorkerMetadata().
For example, inside a method of some listener/subscriber that handles
Symfony Messenger events you could use something like this:

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public function resetServices(WorkerRunningEvent $event): void
{
$actualTransportName = $event->getWorker()->getWorkerMetadata()->getTransportName();
if (!$event->isWorkerIdle() || !in_array($actualTransportName, $this->receiversName, true)) {
return;
}

$this->servicesResetter->reset();
}

Reset container services between messages

Contributed by Grégoire Pineau
in #41163
and #43322.

Container services are not reset automatically when handling messages. This can
be a problem for example with the Monolog fingers crossed handler. Since
services are not reset, if the first message triggers an error, the next messages
will log and ultimately overflow the buffer.
In Symfony 5.4 we're improving this situation with the option to automatically
reset services after handling a message. To use this feature, set the new
reset_on_message option to true in your messenger configuration:

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# config/packages/messenger.yaml
framework:
messenger:
reset_on_message: true
transports:
async:
dsn: '%env(MESSENGER_TRANSPORT_DSN)%'
failed: 'doctrine://default?queue_name=failed'
sync: 'sync://'

Handle messages in batches

Contributed by Nicolas Grekas
in #43354.

Sometimes, when using the Messenger component, you could handle multiple
messages at once instead of processing them one by one. In Symfony 5.4 we've
introduced a new BatchHandlerInterface that allows your handlers to process
messages in batches.
Handlers implementing this interface should expect a new $ack optional
argument to be provided when __invoke() is called. If you don't provide the
$ack argument, the message is handled synchronously as usual. If you provide
$ack, __invoke() is expected to buffer the message and its $ack function,
and to return the number of pending messages in the batch. Here is what a batch
handler might look like:

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class MyBatchHandler implements BatchHandlerInterface
{
use BatchHandlerTrait;

public function __invoke(MyMessage $message, Acknowledger $ack = null)
{
return $this->handle($message, $ack);
}

private function process(array $jobs): void
{
foreach ($jobs as [$message, $ack]) {
try {
// [...] compute $result from $message
$ack->ack($result);
} catch (\Throwable $e) {
$ack->nack($e);
}
}
}
}

The size of the batch is controlled by BatchHandlerTrait::shouldFlush()
(defaults to 10).

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