[11.x] Enhance eventStream to Support Custom Events and Start Messages (#54695)

* feat: add support for optional event stream start and end tokens

* feat: support customizing the event stream name

* style: follow formatting style in phpdoc

* fix: add missing $as use declaration

* formatting

---------

Co-authored-by: Taylor Otwell <[email protected]>

Author: devhammed

src/Illuminate/Routing/ResponseFactory.php

@@ -124,12 +124,23 @@ public function jsonp($callback, $data = [], $status = 200, array $headers = [],
      *
      * @param  \Closure  $callback
      * @param  array  $headers
-     * @param  string  $endStreamWith
+     * @param  string  $as
+     * @param  string|null  $startStreamWith
+     * @param  string|null  $endStreamWith
      * @return \Symfony\Component\HttpFoundation\StreamedResponse
      */
-    public function eventStream(Closure $callback, array $headers = [], string $endStreamWith = '</stream>')
+    public function eventStream(Closure $callback, array $headers = [], string $as = 'update', ?string $startStreamWith = null, ?string $endStreamWith = '</stream>')
     {
-        return $this->stream(function () use ($callback, $endStreamWith) {
+        return $this->stream(function () use ($callback, $as, $startStreamWith, $endStreamWith) {
+            if (filled($startStreamWith)) {
+                echo "event: $as\n";
+                echo 'data: '.$startStreamWith;
+                echo "\n\n";
+
+                ob_flush();
+                flush();
+            }
+
             foreach ($callback() as $message) {
                 if (connection_aborted()) {
                     break;
@@ -139,20 +150,22 @@ public function eventStream(Closure $callback, array $headers = [], string $endS
                     $message = Js::encode($message);
                 }
 
-                echo "event: update\n";
+                echo "event: $as\n";
                 echo 'data: '.$message;
                 echo "\n\n";
 
                 ob_flush();
                 flush();
             }
 
-            echo "event: update\n";
-            echo 'data: '.$endStreamWith;
-            echo "\n\n";
+            if (filled($endStreamWith)) {
+                echo "event: $as\n";
+                echo 'data: '.$endStreamWith;
+                echo "\n\n";
 
-            ob_flush();
-            flush();
+                ob_flush();
+                flush();
+            }
         }, 200, array_merge($headers, [
             'Content-Type' => 'text/event-stream',
             'Cache-Control' => 'no-cache',