feat: make DebugToolbar smarter about detecting binary/streamed responses

system/Debug/Toolbar.php

@@ -372,6 +372,10 @@ public function prepare(?RequestInterface $request = null, ?ResponseInterface $r
          * @var IncomingRequest|null $request
          */
         if (CI_DEBUG && ! is_cli()) {
+            if ($this->hasNativeHeaderConflict()) {
+                return;
+            }
+
             $app = service('codeigniter');
 
             $request ??= service('request');
@@ -544,6 +548,32 @@ protected function format(string $data, string $format = 'html'): string
         return $output;
     }
 
+    /**
+     * Checks if the native PHP headers indicate a non-HTML response
+     * or if headers are already sent.
+     */
+    protected function hasNativeHeaderConflict(): bool
+    {
+        // If headers are sent, we can't inject HTML.
+        if (headers_sent()) {
+            return true;
+        }
+
+        // Native Header Inspection
+        foreach (headers_list() as $header) {
+            $lowerHeader = strtolower($header);
+
+            $isNonHtmlContent = str_starts_with($lowerHeader, 'content-type:') && ! str_contains($lowerHeader, 'text/html');
+            $isAttachment     = str_starts_with($lowerHeader, 'content-disposition:') && str_contains($lowerHeader, 'attachment');
+
+            if ($isNonHtmlContent || $isAttachment) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     /**
      * Determine if the toolbar should be disabled based on the request headers.
      *

system/Test/Utilities/NativeHeadersStack.php

@@ -0,0 +1,64 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * 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\Test\Utilities;
+
+/**
+ * A utility class for simulating native PHP header handling in unit tests.
+ *
+ * @internal This class is for testing purposes only.
+ */
+final class NativeHeadersStack
+{
+    /**
+     * Simulates whether headers have been sent.
+     */
+    public static bool $headersSent = false;
+
+    /**
+     * Stores the list of headers.
+     *
+     * @var list<string>
+     */
+    public static array $headers = [];
+
+    /**
+     * Resets the header stack to defaults.
+     * Call this in setUp() to ensure clean state between tests.
+     */
+    public static function reset(): void
+    {
+        self::$headersSent = false;
+        self::$headers     = [];
+    }
+
+    /**
+     * Checks if a specific header exists in the stack.
+     *
+     * @param string $header The exact header string (e.g., 'Content-Type: text/html')
+     */
+    public static function has(string $header): bool
+    {
+        return in_array($header, self::$headers, true);
+    }
+
+    /**
+     * Adds a header to the stack.
+     *
+     * @param string $header The header to add (e.g., 'Content-Type: text/html')
+     */
+    public static function push(string $header): void
+    {
+        self::$headers[] = $header;
+    }
+}

tests/_support/Mock/MockNativeHeaders.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * 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\Debug;
+
+use CodeIgniter\Test\Utilities\NativeHeadersStack;
+
+/**
+ * Mock implementation of the native PHP `headers_sent()` function.
+ *
+ * Instead of checking the actual PHP output buffer, this function
+ * checks the static property in NativeHeadersStack.
+ *
+ * @return bool True if headers are considered sent, false otherwise.
+ */
+function headers_sent(): bool
+{
+    return NativeHeadersStack::$headersSent;
+}
+
+/**
+ * Mock implementation of the native PHP `headers_list()` function.
+ *
+ * Retrieves the array of headers stored in the NativeHeadersStack class
+ * rather than the actual headers sent by the server.
+ *
+ * @return array The list of simulated headers.
+ */
+function headers_list(): array
+{
+    return NativeHeadersStack::$headers;
+}

tests/system/Debug/ToolbarTest.php

@@ -19,6 +19,7 @@
 use CodeIgniter\HTTP\IncomingRequest;
 use CodeIgniter\HTTP\ResponseInterface;
 use CodeIgniter\Test\CIUnitTestCase;
+use CodeIgniter\Test\Utilities\NativeHeadersStack;
 use Config\Toolbar as ToolbarConfig;
 use PHPUnit\Framework\Attributes\BackupGlobals;
 use PHPUnit\Framework\Attributes\Group;
@@ -34,9 +35,20 @@ final class ToolbarTest extends CIUnitTestCase
     private ?IncomingRequest $request    = null;
     private ?ResponseInterface $response = null;
 
+    public static function setUpBeforeClass(): void
+    {
+        parent::setUpBeforeClass();
+
+        // Load the mock once for the whole test class
+        require_once SUPPORTPATH . 'Mock/MockNativeHeaders.php';
+    }
+
     protected function setUp(): void
     {
         parent::setUp();
+
+        NativeHeadersStack::reset();
+
         Services::reset();
 
         is_cli(false);
@@ -99,4 +111,76 @@ public function testPrepareInjectsNormallyWithoutIgnoredHeader(): void
         // Assertions
         $this->assertStringContainsString('id="debugbar_loader"', (string) $this->response->getBody());
     }
+
+    // -------------------------------------------------------------------------
+    // Native Header Conflicts
+    // -------------------------------------------------------------------------
+
+    public function testPrepareAbortsIfHeadersAlreadySent(): void
+    {
+        // Headers explicitly sent (e.g., echo before execution)
+        NativeHeadersStack::$headersSent = true;
+
+        $this->request  = service('incomingrequest', null, false);
+        $this->response = service('response', null, false);
+        $this->response->setBody('<html><body>Content</body></html>');
+
+        $toolbar = new Toolbar($this->config);
+        $toolbar->prepare($this->request, $this->response);
+
+        // Must NOT inject because we can't modify the body safely
+        $this->assertStringNotContainsString('id="debugbar_loader"', (string) $this->response->getBody());
+    }
+
+    public function testPrepareAbortsIfNativeContentTypeIsNotHtml(): void
+    {
+        // A library (like Dompdf) set a PDF header directly
+        NativeHeadersStack::push('Content-Type: application/pdf');
+
+        $this->request  = service('incomingrequest', null, false);
+        $this->response = service('response', null, false);
+        // Even if the body looks like HTML (before rendering), the header says PDF
+        $this->response->setBody('<html><body>Raw PDF Data</body></html>');
+
+        $toolbar = new Toolbar($this->config);
+        $toolbar->prepare($this->request, $this->response);
+
+        // Must NOT inject into non-HTML content
+        $this->assertStringNotContainsString('id="debugbar_loader"', (string) $this->response->getBody());
+    }
+
+    public function testPrepareAbortsIfNativeContentDispositionIsAttachment(): void
+    {
+        // A file download (even if it is HTML)
+        NativeHeadersStack::$headers = [
+            'Content-Type: text/html',
+            'Content-Disposition: attachment; filename="report.html"',
+        ];
+
+        $this->request  = service('incomingrequest', null, false);
+        $this->response = service('response', null, false);
+        $this->response->setBody('<html><body>Downloadable Report</body></html>');
+
+        $toolbar = new Toolbar($this->config);
+        $toolbar->prepare($this->request, $this->response);
+
+        // Must NOT inject into downloads
+        $this->assertStringNotContainsString('id="debugbar_loader"', (string) $this->response->getBody());
+    }
+
+    public function testPrepareWorksWithNativeHtmlHeader(): void
+    {
+        // Standard scenario where PHP header is text/html
+        NativeHeadersStack::push('Content-Type: text/html; charset=UTF-8');
+
+        $this->request  = service('incomingrequest', null, false);
+        $this->response = service('response', null, false);
+        $this->response->setBody('<html><body>Valid Page</body></html>');
+
+        $toolbar = new Toolbar($this->config);
+        $toolbar->prepare($this->request, $this->response);
+
+        // Should inject normally
+        $this->assertStringContainsString('id="debugbar_loader"', (string) $this->response->getBody());
+    }
 }

user_guide_src/source/changelogs/v4.7.0.rst

@@ -247,6 +247,7 @@ Libraries
 - **Time:** added methods ``Time::addCalendarMonths()`` and ``Time::subCalendarMonths()``
 - **Time:** Added ``Time::isPast()`` and ``Time::isFuture()`` convenience methods. See :ref:`isPast <time-comparing-two-times-isPast>` and :ref:`isFuture <time-comparing-two-times-isFuture>` for details.
 - **View:** Added the ability to override namespaced views (e.g., from modules/packages) by placing a matching file structure within the **app/Views/overrides** directory. See :ref:`Overriding Namespaced Views <views-overriding-namespaced-views>` for details.
+- **Toolbar:** Fixed an issue where the Debug Toolbar was incorrectly injected into responses generated by third-party libraries (e.g., Dompdf) that use native PHP headers instead of the framework's Response object.
 
 
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