feat: add PerformanceMetrics filter

system/Filters/PerformanceMetrics.php

@@ -0,0 +1,61 @@
+<?php
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace CodeIgniter\Filters;
+
+use CodeIgniter\HTTP\RequestInterface;
+use CodeIgniter\HTTP\ResponseInterface;
+use Config\Services;
+
+/**
+ * Performance Metrics filter
+ */
+class PerformanceMetrics implements FilterInterface
+{
+    /**
+     * We don't need to do anything here.
+     *
+     * @param array|null $arguments
+     */
+    public function before(RequestInterface $request, $arguments = null)
+    {
+    }
+
+    /**
+     * Replaces the performance metrics.
+     *
+     * @param array|null $arguments
+     *
+     * @return void
+     */
+    public function after(RequestInterface $request, ResponseInterface $response, $arguments = null)
+    {
+        $body = $response->getBody();
+
+        if ($body !== null) {
+            $benchmark = Services::timer();
+
+            $output = str_replace(
+                [
+                    '{elapsed_time}',
+                    '{memory_usage}',
+                ],
+                [
+                    (string) $benchmark->getElapsedTime('total_execution'),
+                    number_format(memory_get_peak_usage() / 1024 / 1024, 3),
+                ],
+                $body
+            );
+
+            $response->setBody($output);
+        }
+    }
+}