refactor: simplify and optimize handleRequest method in CodeIgniter

system/CodeIgniter.php

@@ -413,26 +413,27 @@ protected function handleRequest(?RouteCollectionInterface $routes, ?Cache $cach
         // If startController returned a Response (from an attribute or Closure), use it
         if ($returned instanceof ResponseInterface) {
             $this->gatherOutput($returned);
-        }
-        // Closure controller has run in startController() - benchmarks were
-        // stopped there as well.
-        elseif (! is_callable($this->controller)) {
-            $controller = $this->createController();
+        } else {
+            // Closure controller has run in startController() - benchmarks were
+            // stopped there as well.
+            if (! is_callable($this->controller)) {
+                $controller = $this->createController();
 
-            if (! method_exists($controller, '_remap') && ! is_callable([$controller, $this->method], false)) {
-                throw PageNotFoundException::forMethodNotFound($this->method);
-            }
+                if (! method_exists($controller, '_remap') && ! is_callable([$controller, $this->method], false)) {
+                    throw PageNotFoundException::forMethodNotFound($this->method);
+                }
 
-            // Is there a "post_controller_constructor" event?
-            Events::trigger('post_controller_constructor');
+                // Is there a "post_controller_constructor" event?
+                Events::trigger('post_controller_constructor');
 
-            $returned = $this->runController($controller);
-        }
+                $returned = $this->runController($controller);
+            }
 
-        // If $returned is a string, then the controller output something,
-        // probably a view, instead of echoing it directly. Send it along
-        // so it can be used with the output.
-        $this->gatherOutput($returned);
+            // If $returned is a string, then the controller output something,
+            // probably a view, instead of echoing it directly. Send it along
+            // so it can be used with the output.
+            $this->gatherOutput($returned);
+        }
 
         if ($this->enableFilters) {
             /** @var Filters $filters */

tests/system/CodeIgniterTest.php

@@ -1330,4 +1330,37 @@ public function testResetForWorkerModeDoesNotLoadCspWhenDisabled(): void
         $this->assertNull(RichRenderer::$css_nonce);
         $this->assertTrue(RichRenderer::$needs_pre_render);
     }
+
+    public function testGatherOutputCalledOnceWhenControllerReturnsResponse(): void
+    {
+        $this->resetServices();
+
+        $superglobals = service('superglobals');
+        $superglobals->setServer('argv', ['index.php', 'pages/test']);
+        $superglobals->setServer('argc', 2);
+        $superglobals->setServer('REQUEST_URI', '/pages/test');
+        $superglobals->setServer('SCRIPT_NAME', '/index.php');
+
+        $routes = service('routes');
+        $routes->add('pages/test', static fn () => service('response')->setBody('Test Body'));
+
+        $config      = new App();
+        $codeigniter = new class ($config) extends MockCodeIgniter {
+            public int $gatherOutputCalls = 0;
+
+            protected function gatherOutput($returned = null): void
+            {
+                $this->gatherOutputCalls++;
+                parent::gatherOutput($returned);
+            }
+        };
+
+        ob_start();
+        $codeigniter->run($routes);
+        ob_end_clean();
+
+        // When startController() returns a ResponseInterface (e.g. from a closure route),
+        // gatherOutput() must be called exactly once — not twice as in the original bug.
+        $this->assertSame(1, $codeigniter->gatherOutputCalls);
+    }
 }

user_guide_src/source/changelogs/v4.8.0.rst

@@ -401,6 +401,8 @@ Deprecations
 Bugs Fixed
 **********
 
+- **CodeIgniter:** Fixed a bug where ``gatherOutput()`` could be called twice when ``startController()`` returned a ``ResponseInterface`` (e.g., from filter attributes or closure routes).
+
 See the repo's
 `CHANGELOG.md <https://github.com/codeigniter4/CodeIgniter4/blob/develop/CHANGELOG.md>`_
 for a complete list of bugs fixed.