[5.1] SEF: Implementing trailing slash behavior (#42702)

* SEF: Implementing trailing slash behavior
* Use 301 redirects

administrator/language/en-GB/plg_system_sef.ini

@@ -5,5 +5,10 @@
 
 PLG_SEF_DOMAIN_DESCRIPTION="If your site can be accessed through more than one domain enter the preferred (sometimes referred to as canonical) domain here. <br><strong>Note:</strong> https://example.com and https://www.example.com are different domains."
 PLG_SEF_DOMAIN_LABEL="Site Domain"
+PLG_SEF_TRAILINGSLASH_DESCRIPTION="Force Joomla to only use URLs with or without trailing slash. When set, this will force the right URL with redirects and is only applied when 'Add suffix to URL' is disabled."
+PLG_SEF_TRAILINGSLASH_LABEL="Trailing slash for URLs"
+PLG_SEF_TRAILINGSLASH_OPTION_NONE="No change"
+PLG_SEF_TRAILINGSLASH_OPTION_NO_SLASH="Enforce URLs without trailing slash"
+PLG_SEF_TRAILINGSLASH_OPTION_SLASH="Enforce URLs with trailing slash"
 PLG_SEF_XML_DESCRIPTION="Adds SEF support to links in the document. It operates directly on the HTML and does not require a special tag."
 PLG_SYSTEM_SEF="System - SEF"

plugins/system/sef/sef.xml

@@ -30,6 +30,19 @@
 					filter="url"
 					validate="url"
 				/>
+
+				<field
+					name="trailingslash"
+					type="list"
+					label="PLG_SEF_TRAILINGSLASH_LABEL"
+					description="PLG_SEF_TRAILINGSLASH_DESCRIPTION"
+					default="0"
+					filter="option"
+				>
+					<option value="0">PLG_SEF_TRAILINGSLASH_OPTION_NONE</option>
+					<option value="1">PLG_SEF_TRAILINGSLASH_OPTION_NO_SLASH</option>
+					<option value="2">PLG_SEF_TRAILINGSLASH_OPTION_SLASH</option>
+				</field>
 			</fieldset>
 		</fields>
 	</config>

plugins/system/sef/src/Extension/Sef.php

@@ -10,9 +10,13 @@
 
 namespace Joomla\Plugin\System\Sef\Extension;
 
+use Joomla\CMS\Event\Router\AfterInitialiseRouterEvent;
 use Joomla\CMS\Plugin\CMSPlugin;
 use Joomla\CMS\Router\Route;
+use Joomla\CMS\Router\Router;
+use Joomla\CMS\Router\SiteRouter;
 use Joomla\CMS\Uri\Uri;
+use Joomla\Event\SubscriberInterface;
 
 // phpcs:disable PSR1.Files.SideEffects
 \defined('_JEXEC') or die;
@@ -23,8 +27,66 @@
  *
  * @since  1.5
  */
-final class Sef extends CMSPlugin
+final class Sef extends CMSPlugin implements SubscriberInterface
 {
+    /**
+     * Application object.
+     *
+     * @var    \Joomla\CMS\Application\CMSApplication
+     * @since  __DEPLOY_VERSION__
+     */
+    protected $app;
+
+    /**
+     * Returns an array of CMS events this plugin will listen to and the respective handlers.
+     *
+     * @return  array
+     *
+     * @since  __DEPLOY_VERSION__
+     */
+    public static function getSubscribedEvents(): array
+    {
+        /**
+         * Note that onAfterInitialise must be the first handlers to run for this
+         * plugin to operate as expected. These handlers load compatibility code which
+         * might be needed by other plugins
+         */
+        return [
+            'onAfterInitialiseRouter' => 'onAfterInitialiseRouter',
+            'onAfterDispatch'         => 'onAfterDispatch',
+            'onAfterRender'           => 'onAfterRender',
+        ];
+    }
+
+    /**
+     * After initialise router.
+     *
+     * @return  void
+     *
+     * @since   __DEPLOY_VERSION__
+     */
+    public function onAfterInitialiseRouter(AfterInitialiseRouterEvent $event)
+    {
+        if (
+            !is_a($event->getRouter(), SiteRouter::class)
+            || !$this->app->get('sef')
+            || $this->app->get('sef_suffix')
+            || !$this->params->get('trailingslash')
+        ) {
+            return;
+        }
+
+        if ($this->params->get('trailingslash') == 1) {
+            // Remove trailingslash
+            $event->getRouter()->attachBuildRule([$this, 'removeTrailingSlash'], SiteRouter::PROCESS_AFTER);
+        } elseif ($this->params->get('trailingslash') == 2) {
+            // Add trailingslash
+            $event->getRouter()->attachBuildRule([$this, 'addTrailingSlash'], SiteRouter::PROCESS_AFTER);
+        }
+
+        $event->getRouter()->attachParseRule([$this, 'enforceTrailingSlash'], SiteRouter::PROCESS_BEFORE);
+    }
+
     /**
      * Add the canonical uri to the head.
      *
@@ -188,6 +250,74 @@ function ($match) use ($base, $protocols) {
         $this->getApplication()->setBody($buffer);
     }
 
+    /**
+     * Remove any trailing slash from URLs built in Joomla
+     *
+     * @param   Router  &$router  Router object.
+     * @param   Uri     &$uri     Uri object.
+     *
+     * @return  void
+     *
+     * @since   __DEPLOY_VERSION__
+     */
+    public function removeTrailingSlash(&$router, &$uri)
+    {
+        $path = $uri->getPath();
+
+        if (substr($path, -1) == '/') {
+            $uri->setPath(substr($path, 0, -1));
+        }
+    }
+
+    /**
+     * Add trailing slash to URLs built in Joomla
+     *
+     * @param   Router  &$router  Router object.
+     * @param   Uri     &$uri     Uri object.
+     *
+     * @return  void
+     *
+     * @since   __DEPLOY_VERSION__
+     */
+    public function addTrailingSlash(&$router, &$uri)
+    {
+        $path = $uri->getPath();
+
+        if (substr($path, -1) !== '/') {
+            $uri->setPath($path . '/');
+        }
+    }
+
+    /**
+     * Redirect to a URL with or without trailing slash
+     *
+     * @param   Router  &$router  Router object.
+     * @param   Uri     &$uri     Uri object.
+     *
+     * @return  void
+     *
+     * @since   __DEPLOY_VERSION__
+     */
+    public function enforceTrailingSlash(&$router, &$uri)
+    {
+        // We only want to redirect on GET requests
+        if ($this->app->getInput()->getMethod() != 'GET') {
+            return;
+        }
+
+        $originalUri = Uri::getInstance();
+
+        if ($this->params->get('trailingslash') == 1 && substr($originalUri->getPath(), -1) == '/' && $originalUri->toString() != Uri::root()) {
+            // Remove trailingslash
+            $originalUri->setPath(substr($originalUri->getPath(), 0, -1));
+            $this->app->redirect($originalUri->toString(), 301);
+        } elseif ($this->params->get('trailingslash') == 2 && substr($originalUri->getPath(), -1) != '/') {
+            // Add trailingslash
+            $originalUri->setPath($originalUri->getPath() . '/');
+            $this->app->redirect($originalUri->toString(), 301);
+        }
+    }
+
     /**
      * Check the buffer.
      *