Add NullStore as preference fallback

refs #4529

application/forms/Config/GeneralForm.php

@@ -275,8 +275,9 @@ class GeneralForm extends Form
                 'required'      => true,
                 'value'         => $backend,
                 'multiOptions'  => array(
-                    'ini'   => 'File System (ini files)',
+                    'ini'   => 'File System (ini Files)',
-                    'db'    => 'Database'
+                    'db'    => 'Database',
+                    'null'  => 'Don\'t Store Preferences'
                 )
             )
         );

doc/preferences.md

@@ -21,7 +21,7 @@ The ini provider uses the directory **config/preferences** to create one ini
 file per user and persists the data into a single file. If you want to drop your
 preferences just drop the file from disk and you'll start with a new profile.
 
-## Database provider
+## Database Provider
 
 To be more flexible in distributed setups you can store preferences in a
 database (pgsql or mysql), a typical configuration looks like the following
@@ -31,6 +31,17 @@ example:
     type=db
     resource=icingaweb-pgsql
 
+## Null Provider
+
+The Null Provider discards all preferences and is mainly used as a fallback when no provider could be
+created (due to permission errors, database outtakes, etc.).
+
+    [preferences]
+    type=null
+
+If your preferences aren't stored it's best to take a look into the logfiles - errors during the preference setup
+are displayed as warnings here.
+
 ### Settings
 
 * **resource**: A reference to a database declared in *resources.ini*. Please read the chapter about

library/Icinga/Application/Web.php

@@ -215,6 +215,23 @@ class Web extends ApplicationBootstrap
         return $this;
     }
 
+    /**
+     * Registers a @see NullStore as the preference provider
+     *
+     * @param Preferences   $preferences    The preference registry to attach the NullStore to
+     * @param User          $user           The user, required for API compliance
+     */
+    private function registerFallbackPreferenceProvider($preferences, $user)
+    {
+        $this->getConfig()->preferences->type = 'null';
+        $preferenceStore = StoreFactory::create(
+            $this->getConfig()->preferences,
+            $user
+        );
+
+        $preferences->attach($preferenceStore);
+    }
+
     /**
      * Create user object and inject preference interface
      *
@@ -261,7 +278,7 @@ class Web extends ApplicationBootstrap
 
                 $path = Config::resolvePath($this->getConfig()->preferences->configPath);
                 if (is_dir($path) === false) {
-                    Logger::error(
+                    Logger::warn(
                         'Path for preferences not found (IniStore, "%s"). Using default one: "%s"',
                         $this->getConfig()->preferences->configPath,
                         $this->getConfigDir('preferences')
@@ -277,14 +294,14 @@ class Web extends ApplicationBootstrap
                         $this->getConfig()->preferences,
                         $user
                     );
-
                     $preferences->attach($preferenceStore);
                 } catch (Exception $e) {
-                    Logger::fatal(
+                    Logger::warn(
-                        'Could not create create preferences provider. '
+                        'Could not create create preferences provider, preferences will be discarded: '
-                        . 'An exception during bootstrap was thrown: %s',
+                        . '"%s"',
                         $e->getMessage()
                     );
+                    $this->registerFallbackPreferenceProvider($preferences, $user);
                 }
 
                 if ($preferencesLoaded === false && $preferenceStore instanceof LoadInterface) {

library/Icinga/User/Preferences/NullStore.php

@@ -0,0 +1,75 @@
+<?php
+// {{{ICINGA_LICENSE_HEADER}}}
+/**
+ * This file is part of Icinga 2 Web.
+ *
+ * Icinga 2 Web - Head for multiple monitoring backends.
+ * Copyright (C) 2013 Icinga Development Team
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * @copyright 2013 Icinga Development Team <info@icinga.org>
+ * @license   http://www.gnu.org/licenses/gpl-2.0.txt GPL, version 2
+ * @author    Icinga Development Team <info@icinga.org>
+ */
+// {{{ICINGA_LICENSE_HEADER}}}
+
+namespace Icinga\User\Preferences;
+
+use Icinga\User;
+use SplSubject;
+
+/**
+ * Preference store that simply discards any settings made
+ *
+ * Mainly used as a fallback provider if no preferences can be created
+ */
+class NullStore implements LoadInterface, FlushObserverInterface
+{
+
+    /**
+     * Setter for user, does nothing
+     *
+     * @param User $user
+     */
+    public function setUser(User $user)
+    {
+    }
+
+    /**
+     * Load preferences from source, return an empty array
+     *
+     * @return array
+     */
+    public function load()
+    {
+        return array();
+    }
+
+    /**
+     *
+     * Receive update from subject
+     *
+     * @link http://php.net/manual/en/splobserver.update.php
+     * @param SplSubject $subject <p>
+     * The <b>SplSubject</b> notifying the observer of an update.
+     * </p>
+     * @return void
+     */
+    public function update(SplSubject $subject)
+    {
+        return null;
+    }
+}