WhileMercure is the recommended option for most cases, implementing a custom Server-sent Event (SSE) backend relying on Symfony components is still a good alternative (considering you're building an app with a few users only)

Example using today’s code:

publicfunction__invoke():StreamedResponse{$response =newStreamedResponse(function () {foreach ($this->watchJobsInProgress()as$job) {echo"type: jobs\n";echo"data:".$job->toJson()."\n\n";            StreamedResponse::closeOutputBuffers(0,true);flush();if (connection_aborted()) {break;            }sleep(1);        }    });$response->headers->set('Content-Type','text/event-stream');$response->headers->set('Cache-Control','no-cache');$response->headers->set('Connection','keep-alive');$response->headers->set('X-Accel-Buffering','no');return$response;}

So, this PR simplifies that implementation by adding two new artifacts:

✨ NewServerEvent DTO class

Spec:https://html.spec.whatwg.org/multipage/server-sent-events.html

TheServerEvent class represents individual events streamed from the server to clients. It includes fields likedata,type,id,retry, andcomment, so it can cover a variety of use cases.

One key feature is thegetIterator() method, which automatically concat all these fields into the proper SSE format. This saves us from having to manually format the events, making the process a lot smoother. Plus, it supports iterabledata, meaning it can handle multi-line messages or more complex data structures all in one event.

✨ NewEventStreamResponse class

• Simplified Headers Setup

  returnnewEventStreamResponse(/* ... */);

  This class automatically sets the required headers (Content-Type,Cache-Control, andConnection), ensuring that every response is properly configured for event streaming without additional code.

• Generator-based Event Streaming with Auto Flush

  returnnewEventStreamResponse(function ():\Generator {yieldnewServerEvent(time(), type:'ping');});

  The callback function can nowyield events directly, automatically handling serialization and output buffering as each new event occurs.

• Event Streaming with Sending Control

  returnnewEventStreamResponse(function (EventStreamResponse$response) {$response->sendEvent(newServerEvent('...'));// do something in between ...$response->sendEvent(newServerEvent('...'));});

  The callback function receives a new argument—the response instance—allowing you to manuallysendEvent().

  This method is especially useful whenyield is not possible due to scope limitations. In the example below, the callback handles the event inside an event stream response, listening for Redis messages and directly triggering thesendEvent() method:

  returnnewEventStreamResponse(function (EventStreamResponse$response) {$redis =new \Redis();$redis->connect('127.0.0.1');$redis->subscribe(['message'],function (/* ... */,string$message)use ($response) {$response->sendEvent(newServerEvent($message));      });  });

• Retry Event Fallback

  returnnewEventStreamResponse(/* ... */, retry:1000);

  ServerEvent allows setting individualretry intervals, which take precedence over the default retry configured inEventStreamResponse. If not specified at the event level, the global retry setting applies.

This is the final, optimized version after the proposed improvements:

publicfunction__invoke():EventStreamResponse{returnnewEventStreamResponse(function () {foreach ($this->watchJobsInProgress()as$job) {yieldnewServerEvent($job->toJson(), type:'jobs');sleep(1);        }    });}

Cheers!