Make FlashMessage instance available through a ServerRequest.

src/Http/ServerRequest.php

@@ -161,6 +161,13 @@ class ServerRequest implements ServerRequestInterface
     protected $session;
 
     /**
+     * Instance of a FlashMessage object relative to this request
+     *
+     * @var \Cake\Http\FlashMessage
+     */
+    protected $flash;
+
+    /**
      * Store the additional attributes attached to the request.
      *
      * @var array
@@ -172,7 +179,7 @@ class ServerRequest implements ServerRequestInterface
      *
      * @var array
      */
-    protected $emulatedAttributes = ['session', 'webroot', 'base', 'params', 'here'];
+    protected $emulatedAttributes = ['session', 'flash', 'webroot', 'base', 'params', 'here'];
 
     /**
      * Array of Psr\Http\Message\UploadedFileInterface objects.
@@ -288,6 +295,7 @@ class ServerRequest implements ServerRequestInterface
         $this->query = $config['query'];
         $this->params = $config['params'];
         $this->session = $config['session'];
+        $this->flash = new FlashMessage($this->session);
     }
 
     /**
@@ -342,6 +350,16 @@ class ServerRequest implements ServerRequestInterface
     }
 
     /**
+     * Returns the instance of the FlashMessage object for this request
+     *
+     * @return \Cake\Http\FlashMessage
+     */
+    public function getFlash(): FlashMessage
+    {
+        return $this->flash;
+    }
+
+    /**
      * Get the IP the client is using, or says they are using.
      *
      * @return string The client IP.

src/TestSuite/MiddlewareDispatcher.php

@@ -18,6 +18,7 @@ namespace Cake\TestSuite;
 use Cake\Core\Configure;
 use Cake\Core\PluginApplicationInterface;
 use Cake\Event\EventManager;
+use Cake\Http\FlashMessage;
 use Cake\Http\Server;
 use Cake\Http\ServerRequest;
 use Cake\Http\ServerRequestFactory;
@@ -164,7 +165,9 @@ class MiddlewareDispatcher
             $spec['cookies'],
             $spec['files']
         );
-        $request = $request->withAttribute('session', $spec['session']);
+        $request = $request
+            ->withAttribute('session', $spec['session'])
+            ->withAttribute('flash', new FlashMessage($spec['session']));
 
         return $request;
     }

tests/TestCase/Http/ServerRequestTest.php

@@ -20,6 +20,7 @@ use Cake\Core\Configure;
 use Cake\Http\Cookie\Cookie;
 use Cake\Http\Cookie\CookieCollection;
 use Cake\Http\Exception\MethodNotAllowedException;
+use Cake\Http\FlashMessage;
 use Cake\Http\ServerRequest;
 use Cake\Http\Session;
 use Cake\TestSuite\TestCase;
@@ -99,8 +100,14 @@ class ServerRequestTest extends TestCase
         $this->assertFalse($request->is('json'));
     }
 
+    public function testConstructor()
+    {
+        $request = new ServerRequest();
+        $this->assertInstanceOf(FlashMessage::class, $request->getAttribute('flash'));
+    }
+
     /**
-     * Test construction
+     * Test construction with query data
      *
      * @return void
      */
@@ -1856,6 +1863,12 @@ XML;
         $this->assertEquals($session, $request->getSession());
     }
 
+    public function testGetFlash()
+    {
+        $request = new ServerRequest();
+        $this->assertInstanceOf(FlashMessage::class, $request->getFlash());
+    }
+
     /**
      * Test the content type method.
      *