[6.1] Add offline mode support in the API

libraries/src/Application/ApiApplication.php

@@ -144,8 +144,32 @@ public function addFormatMap($contentHeader, $format)
 	 */
 	protected function render()
 	{
+		// Trigger the onBeforeRender event.
+		PluginHelper::importPlugin('system');
+		$this->triggerEvent('onBeforeRender');
+
+		// Check we aren't in offline mode. In which case for users who can't access the site the API is disabled
+		// and we won't show anything!
+		if ($this->get('offline') && !$this->getIdentity()->authorise('core.login.offline'))
+		{
+			$offlineMessage = '';
+
+			if ($this->get('display_offline_message', true) == true)
+			{
+				$offlineMessage = $this->get('offline_message');
+			}
+
+			throw new Exception\OfflineWebsiteException($offlineMessage);
+		}
+
 		// Render the document
 		$this->setBody($this->document->render($this->allowCache()));
+
+		// Trigger the onAfterRender event.
+		$this->triggerEvent('onAfterRender');
+
+		// Mark afterRender in the profiler.
+		JDEBUG ? $this->profiler->mark('afterRender') : null;
 	}
 
 	/**

libraries/src/Application/Exception/OfflineWebsiteException.php

@@ -0,0 +1,22 @@
+<?php
+/**
+ * Joomla! Content Management System
+ *
+ * @copyright  (C) 2021 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license    GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\CMS\Application\Exception;
+
+use Throwable;
+
+\defined('JPATH_PLATFORM') or die;
+
+/**
+ * Exception class for a website that is in offline mode!
+ *
+ * @since  __DEPLOY_VERSION__
+ */
+class OfflineWebsiteException extends \RuntimeException
+{
+}

libraries/src/Error/JsonApi/OfflineWebsiteExceptionHandler.php

@@ -0,0 +1,63 @@
+<?php
+/**
+ * Joomla! Content Management System
+ *
+ * @copyright  (C) 2021 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license    GNU General Public License version 2 or later; see LICENSE
+ */
+
+namespace Joomla\CMS\Error\JsonApi;
+
+\defined('JPATH_PLATFORM') or die;
+
+use Exception;
+use Joomla\CMS\Application\Exception\OfflineWebsiteException;
+use Tobscure\JsonApi\Exception\Handler\ExceptionHandlerInterface;
+use Tobscure\JsonApi\Exception\Handler\ResponseBag;
+
+/**
+ * Handler for the site being in offline mode
+ *
+ * @since  4.0.0
+ */
+class OfflineWebsiteExceptionHandler implements ExceptionHandlerInterface
+{
+	/**
+	 * If the exception handler is able to format a response for the provided exception,
+	 * then the implementation should return true.
+	 *
+	 * @param   \Exception  $e  The exception to be handled
+	 *
+	 * @return boolean
+	 *
+	 * @since  4.0.0
+	 */
+	public function manages(Exception $e)
+	{
+		return $e instanceof OfflineWebsiteException;
+	}
+
+	/**
+	 * Handle the provided exception.
+	 *
+	 * @param   Exception  $e  The exception being handled
+	 *
+	 * @return  \Tobscure\JsonApi\Exception\Handler\ResponseBag
+	 *
+	 * @since  4.0.0
+	 */
+	public function handle(Exception $e)
+	{
+		$status = 503;
+		$error = ['title' => $e->getMessage()];
+
+		$code = $e->getCode();
+
+		if ($code)
+		{
+			$error['code'] = $code;
+		}
+
+		return new ResponseBag($status, [$error]);
+	}
+}

libraries/src/Error/Renderer/JsonapiRenderer.php

@@ -17,6 +17,7 @@
 use Joomla\CMS\Error\JsonApi\InvalidRouteExceptionHandler;
 use Joomla\CMS\Error\JsonApi\NotAcceptableExceptionHandler;
 use Joomla\CMS\Error\JsonApi\NotAllowedExceptionHandler;
+use Joomla\CMS\Error\JsonApi\OfflineWebsiteExceptionHandler;
 use Joomla\CMS\Error\JsonApi\ResourceNotFoundExceptionHandler;
 use Joomla\CMS\Error\JsonApi\SaveExceptionHandler;
 use Joomla\CMS\Error\JsonApi\SendEmailExceptionHandler;
@@ -55,6 +56,7 @@ public function render(\Throwable $error): string
 		{
 			$errors = new ErrorHandler;
 
+			$errors->registerHandler(new OfflineWebsiteExceptionHandler);
 			$errors->registerHandler(new InvalidRouteExceptionHandler);
 			$errors->registerHandler(new AuthenticationFailedExceptionHandler);
 			$errors->registerHandler(new NotAcceptableExceptionHandler);