feat(developer): Add documentation for SetupChecks

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

Makefile

@@ -42,4 +42,4 @@ openapi-spec: get-server-sources
 
 
 clean:
-	rm -r admin_manual/_build developer_manual/_build user_manual/_build user_manual_de_/_build
+	rm -vrf admin_manual/_build developer_manual/_build user_manual/_build user_manual_de_/_build

developer_manual/app_publishing_maintenance/app_upgrade_guide/upgrade_to_31.rst

@@ -68,7 +68,7 @@ Back-end changes
 Added APIs
 ^^^^^^^^^^
 
-- TBD
+- ``OCP\SetupCheck\CheckServerResponseTrait`` was added to ease implementing custom :ref:`setup checks<setup-checks>` which need to check HTTP calls to the the server itself.
 
 Changed APIs
 ^^^^^^^^^^^^

developer_manual/digging_deeper/index.rst

@@ -39,6 +39,7 @@ Digging deeper
    web_host_metadata
    status
    security
+   setup_checks
    profile
    user_migration
    profiler

developer_manual/digging_deeper/setup_checks.rst

@@ -0,0 +1,172 @@
+.. _setup-checks:
+
+============
+Setup checks
+============
+
+Setup checks allow to test specific functionality of the server and report issues with configuration
+early to the administrators to prevent run time issues.
+
+One example for setup checks is the JavaScript Modules test that ensures the server is able to
+serve ``.mjs`` files correctly, which is needed for apps that use modern JavaScript for their UI.
+Any issue with the configuration would be reported to the administrator, either on the web interface (admin setting),
+or when running the ``occ setupchecks`` command, before a user experience the issue.
+
+Register a setup check
+----------------------
+
+Setup checks are registered within the registration context of the app bootstrap:
+
+.. code-block:: php
+
+    <?php
+    declare(strict_types=1);
+
+    namespace OCA\MyApp\AppInfo;
+
+    class Application extends App implements IBootstrap {
+
+        public function register(IRegistrationContext $context): void {
+            // Other registration
+            $context->registerSetupCheck(JavaScriptModules::class);
+        }
+
+        // ...
+
+    }
+
+Define a setup check
+--------------------
+
+Defining a custom setup check is done by simply implementing ``OCP\SetupCheck\SetupResult``,
+for this example we will create a check that ensures the Nextcloud instance is not running in debug mode.
+
+.. code-block:: php
+
+    <?php
+    declare(strict_types=1);
+
+    namespace OCA\MyApp\SetupChecks;
+
+    use OCP\IConfig;
+    use OCP\IL10N;
+    use OCP\SetupCheck\ISetupCheck;
+    use OCP\SetupCheck\SetupResult;
+
+    class DebugModeSetupCheck implements ISetupCheck {
+        public function __construct(
+            private IL10N $l10n,
+            private IConfig $config,
+        ) {
+        }
+
+        public function getName(): string {
+            return $this->l10n->t('Debug mode');
+        }
+
+        public function getCategory(): string {
+            return 'system';
+        }
+
+        public function run(): SetupResult {
+            if ($this->config->getSystemValueBool('debug', false)) {
+                return SetupResult::warning($this->l10n->t('This instance is running in debug mode. Only enable this for local development and not in production environments.'));
+            } else {
+                return SetupResult::success($this->l10n->t('Debug mode is disabled.'));
+            }
+        }
+    }
+
+
+First it is required to provide a name, the name which should summarize the check and should be provided as a user visible, thus translated string.
+
+.. code-block:: php
+
+    public function getName(): string {
+        // This is user visible and thus should be translated
+        return $this->l10n->t('Debug mode');
+    }
+
+
+Setup checks are grouped by category, the category should be one of
+
+- ``security``: Related to the security of the instance
+- ``accounts``: Related to user accounts
+- ``system``: System status Related
+- Custom category: Will be merged into system. Examples for existing custom categories are  ``network`` and ``database``.
+
+.. code-block:: php
+
+    public function getCategory(): string {
+        return 'system';
+    }
+
+
+The most important part is the ``run`` function.
+This function should perform the test and report the result as a ``OCP\SetupCheck\SetupResult``.
+Available severity level are:
+
+- ``SetupResult::success``: Test succeeded no action needed.
+- ``SetupResult::info``: No action required but it can not be guaranteed that the check passed (e.g. missing precondition for running the test).
+- ``SetupResult::warning``: The test failed but the result is not fatal, yet the administrator should be warned about this.
+- ``SetupResult::error``: The test failed and some functionality is not available or might be broken.
+
+It is also possible to add a link to documentation to ease administrators solving the issue.
+The link is simply passed as the second parameter to the ``SetupResult``.
+
+Additionally it is also possible to use rich objects (``OCP\RichObjectStrings``) for formatting the message,
+in this case the third parameter should contain the rich object parameters.
+
+.. note::
+    Please be aware that setup checks could be ran from both,
+    the web frontend and from the CLI. Meaning they might use different ``php.ini`` files.
+
+.. code-block:: php
+
+    public function run(): SetupResult {
+        if ($this->config->getSystemValueBool('debug', false)) {
+            return SetupResult::warning($this->l10n->t('This instance is running in debug mode. Only enable this for local development and not in production environments.'));
+        } else {
+            return SetupResult::success($this->l10n->t('Debug mode is disabled.'));
+        }
+    }
+
+
+Running HTTP requests against the server
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+As mentioned in the initial example it is sometimes needed to run HTTP requests
+for a setup check, to ensure configuration is working correctly.
+To ease writing tests like that we provide the ``CheckServerResponseTrait`` trait.
+
+The ``run`` function of the JavaScript modules setup check could look like:
+
+.. code-block:: php
+
+    public function run(): SetupResult {
+        // This is a real existing file
+        $testFile = $this->urlGenerator->linkTo('settings', 'js/esm-test.mjs');
+
+        $noResponse = true;
+        foreach ($this->runRequest('HEAD', $testFile) as $response) {
+            $noResponse = false;
+            if (preg_match('/(text|application)\/javascript/i', $response->getHeader('Content-Type'))) {
+                return SetupResult::success();
+            }
+        }
+
+        if ($noResponse) {
+            return SetupResult::warning($this->l10n->t('Unable to run check for JavaScript support.') . "\n" . $this->serverConfigHelp());
+        }
+        return SetupResult::error($this->l10n->t('Your webserver does not serve `.mjs` files using the JavaScript MIME type. This will break some apps by preventing browsers from executing the JavaScript files.'));
+    }
+
+The ``runRequest`` is provided by the ``CheckServerResponseTrait``, it accepts a HTTP request method
+as the first parameter (in this example ``HEAD``) and an URL with an absolute path, so meaning
+the full path but no host set, like provided when using the URL generator. One example string would be ``nextcloud/apps/settings/js/esm-test.mjs``.
+Internally the function requests that URL on all possible URLs (using the current host, the trusted domains and the cli overwrite URL),
+and then yields a result for each request.
+
+``CheckServerResponseTrait::serverConfigHelp`` provides information about
+common pitfalls that prevent HTTP requests against the current server.
+If no response is yielded from the ``runRequest`` method then this information should be included.