files_external: allow to register config handlers for flexible placeholders

* BackendService (directly accessable via \OC_Server) offers registerConfigHandler
* SimpleSubstitutionTrait brings reusable logic for simple string replacments
* internal $user replacement mechanism was migrated

Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>

7 files changed, 282 insertions, 18 deletions

diff --git a/apps/files_external/lib/AppInfo/Application.php b/apps/files_external/lib/AppInfo/Application.php
index 8eebc550d09..5b12377fdb8 100644
--- a/apps/files_external/lib/AppInfo/Application.php
+++ b/apps/files_external/lib/AppInfo/Application.php
@@ -29,6 +29,7 @@
 
 namespace OCA\Files_External\AppInfo;
 
+use OCA\Files_External\Config\UserPlaceholderHandler;
 use OCA\Files_External\Lib\Auth\PublicKey\RSAPrivateKey;
 use OCA\Files_External\Lib\Auth\SMB\KerberosAuth;
 use \OCP\AppFramework\App;
@@ -67,7 +68,12 @@ use OCP\Files\Config\IUserMountCache;
  */
 class Application extends App implements IBackendProvider, IAuthMechanismProvider {
 
-	public function __construct(array $urlParams = array()) {
+	/**
+	 * Application constructor.
+	 *
+	 * @throws \OCP\AppFramework\QueryException
+	 */
+	public function __construct(array $urlParams = []) {
 		parent::__construct('files_external', $urlParams);
 
 		$container = $this->getContainer();
@@ -76,9 +82,13 @@ class Application extends App implements IBackendProvider, IAuthMechanismProvide
 			return $c->getServer()->query('UserMountCache');
 		});
 
+		/** @var BackendService $backendService */
 		$backendService = $container->query(BackendService::class);
 		$backendService->registerBackendProvider($this);
 		$backendService->registerAuthMechanismProvider($this);
+		$backendService->registerConfigHandler('user', function() use ($container) {
+			return $container->query(UserPlaceholderHandler::class);
+		});
 
 		// force-load auth mechanisms since some will register hooks
 		// TODO: obsolete these and use the TokenProvider to get the user's password from the session
diff --git a/apps/files_external/lib/Config/ConfigAdapter.php b/apps/files_external/lib/Config/ConfigAdapter.php
index 34e96df0441..8d9c7ea8d1b 100644
--- a/apps/files_external/lib/Config/ConfigAdapter.php
+++ b/apps/files_external/lib/Config/ConfigAdapter.php
@@ -29,7 +29,6 @@ namespace OCA\Files_External\Config;
 use OC\Files\Storage\Wrapper\Availability;
 use OCA\Files_External\Migration\StorageMigrator;
 use OCP\Files\Storage;
-use OC\Files\Mount\MountPoint;
 use OCP\Files\Storage\IStorageFactory;
 use OCA\Files_External\Lib\PersonalMount;
 use OCP\Files\Config\IMountProvider;
@@ -73,12 +72,11 @@ class ConfigAdapter implements IMountProvider {
 	 *
 	 * @param StorageConfig $storage
 	 * @param IUser $user
+	 * @throws \OCP\AppFramework\QueryException
 	 */
 	private function prepareStorageConfig(StorageConfig &$storage, IUser $user) {
 		foreach ($storage->getBackendOptions() as $option => $value) {
-			$storage->setBackendOption($option, \OC_Mount_Config::setUserVars(
-				$user->getUID(), $value
-			));
+			$storage->setBackendOption($option, \OC_Mount_Config::substitutePlaceholdersInConfig($value));
 		}
 
 		$objectStore = $storage->getBackendOption('objectstore');
diff --git a/apps/files_external/lib/Config/IConfigHandler.php b/apps/files_external/lib/Config/IConfigHandler.php
new file mode 100644
index 00000000000..3e2ec32ba23
--- /dev/null
+++ b/apps/files_external/lib/Config/IConfigHandler.php
@@ -0,0 +1,39 @@
+<?php
+/**
+ * @copyright Copyright (c) 2019 Arthur Schiwon <blizzz@arthur-schiwon.de>
+ *
+ * @author Arthur Schiwon <blizzz@arthur-schiwon.de>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\Files_External\Config;
+
+/**
+ * Interface IConfigHandler
+ *
+ * @package OCA\Files_External\Config
+ * @since 16.0.0
+ */
+interface IConfigHandler {
+	/**
+	 * @param mixed $optionValue
+	 * @return mixed the same type as $optionValue
+	 * @since 16.0.0
+	 */
+	public function handle($optionValue);
+}
diff --git a/apps/files_external/lib/Config/SimpleSubstitutionTrait.php b/apps/files_external/lib/Config/SimpleSubstitutionTrait.php
new file mode 100644
index 00000000000..9abbfe0df22
--- /dev/null
+++ b/apps/files_external/lib/Config/SimpleSubstitutionTrait.php
@@ -0,0 +1,86 @@
+<?php
+/**
+ * @copyright Copyright (c) 2018 Arthur Schiwon <blizzz@arthur-schiwon.de>
+ *
+ * @author Arthur Schiwon <blizzz@arthur-schiwon.de>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\Files_External\Config;
+
+/**
+ * Trait SimpleSubstitutionTrait
+ *
+ * @package OCA\Files_External\Config
+ * @since 16.0.0
+ */
+trait SimpleSubstitutionTrait {
+	/**
+	 * @var string the placeholder without @ prefix
+	 * @since 16.0.0
+	 */
+	private $placeholder;
+
+	/** @var string */
+	protected $sanitizedPlaceholder;
+
+	/**
+	 * @param mixed $optionValue
+	 * @param string $replacement
+	 * @return mixed
+	 * @since 16.0.0
+	 */
+	private function processInput($optionValue, string $replacement) {
+		$this->checkPlaceholder();
+		if (is_array($optionValue)) {
+			foreach ($optionValue as &$value) {
+				$value = $this->substituteIfString($value, $replacement);
+			}
+		} else {
+			$optionValue = $this->substituteIfString($optionValue, $replacement);
+		}
+		return $optionValue;
+	}
+
+	/**
+	 * @throws \RuntimeException
+	 */
+	protected function checkPlaceholder(): void {
+		$this->sanitizedPlaceholder = trim(strtolower($this->placeholder));
+		if(!(bool)\preg_match('/^[a-z0-9]*$/', $this->sanitizedPlaceholder)) {
+			throw new \RuntimeException(sprintf(
+				'Invalid placeholder %s, only [a-z0-9] are allowed', $this->sanitizedPlaceholder
+			));
+		}
+		if($this->sanitizedPlaceholder === '') {
+			throw new \RuntimeException('Invalid empty placeholder');
+		}
+	}
+
+	/**
+	 * @param mixed $value
+	 * @param string $replacement
+	 * @return mixed
+	 */
+	protected function substituteIfString($value, string $replacement) {
+		if(is_string($value)) {
+			return str_ireplace('$' . $this->sanitizedPlaceholder, $replacement, $value);
+		}
+		return $value;
+	}
+}
diff --git a/apps/files_external/lib/Config/UserPlaceholderHandler.php b/apps/files_external/lib/Config/UserPlaceholderHandler.php
new file mode 100644
index 00000000000..721d3bbe02a
--- /dev/null
+++ b/apps/files_external/lib/Config/UserPlaceholderHandler.php
@@ -0,0 +1,53 @@
+<?php
+/**
+ * @copyright Copyright (c) 2019 Arthur Schiwon <blizzz@arthur-schiwon.de>
+ *
+ * @author Arthur Schiwon <blizzz@arthur-schiwon.de>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\Files_External\Config;
+
+use OCP\IUserSession;
+
+class UserPlaceholderHandler implements IConfigHandler {
+	use SimpleSubstitutionTrait;
+
+	/** @var IUserSession */
+	private $session;
+
+	public function __construct(IUserSession $session) {
+		$this->session = $session;
+		$this->placeholder = 'user';
+	}
+
+	/**
+	 * @param mixed $optionValue
+	 * @return mixed the same type as $optionValue
+	 * @since 16.0.0
+	 */
+	public function handle($optionValue) {
+		$user = $this->session->getUser();
+		if($user === null) {
+			return $optionValue;
+		}
+		$uid = $user->getUID();
+
+		return $this->processInput($optionValue, $uid);
+	}
+}
diff --git a/apps/files_external/lib/Service/BackendService.php b/apps/files_external/lib/Service/BackendService.php
index bd6c525f319..05bda1998da 100644
--- a/apps/files_external/lib/Service/BackendService.php
+++ b/apps/files_external/lib/Service/BackendService.php
@@ -23,6 +23,7 @@
 
 namespace OCA\Files_External\Service;
 
+use OCA\Files_External\Config\IConfigHandler;
 use \OCP\IConfig;
 
 use \OCA\Files_External\Lib\Backend\Backend;
@@ -67,6 +68,11 @@ class BackendService {
 	/** @var IAuthMechanismProvider[] */
 	private $authMechanismProviders = [];
 
+	/** @var callable[] */
+	private $configHandlerLoaders = [];
+
+	private $configHandlers = [];
+
 	/**
 	 * @param IConfig $config
 	 */
@@ -280,4 +286,66 @@ class BackendService {
 	protected function isAllowedAuthMechanism(AuthMechanism $authMechanism) {
 		return true; // not implemented
 	}
+
+	/**
+	 * registers a configuration handler
+	 *
+	 * The function of the provided $placeholder is mostly to act a sorting
+	 * criteria, so longer placeholders are replaced first. This avoids
+	 * "@user" overwriting parts of "@userMail" and "@userLang", for example.
+	 * The provided value should not contain the @ prefix, only a-z0-9 are
+	 * allowed. Upper case letters are lower cased, the replacement is case-
+	 * insensitive.
+	 *
+	 * The configHandlerLoader should just instantiate the handler on demand.
+	 * For now all handlers are instantiated when a mount is loaded, independent
+	 * of whether the placeholder is present or not. This may change in future.
+	 *
+	 * @since 16.0.0
+	 */
+	public function registerConfigHandler(string $placeholder, callable $configHandlerLoader) {
+		$placeholder = trim(strtolower($placeholder));
+		if(!(bool)\preg_match('/^[a-z0-9]*$/', $placeholder)) {
+			throw new \RuntimeException(sprintf(
+				'Invalid placeholder %s, only [a-z0-9] are allowed', $placeholder
+			));
+		}
+		if($placeholder === '') {
+			throw new \RuntimeException('Invalid empty placeholder');
+		}
+		if(isset($this->configHandlerLoaders[$placeholder]) || isset($this->configHandlers[$placeholder])) {
+			throw new \RuntimeException(sprintf('A handler is already registered for %s', $placeholder));
+		}
+		$this->configHandlerLoaders[$placeholder] = $configHandlerLoader;
+	}
+
+	protected function loadConfigHandlers():void {
+		$newLoaded = false;
+		foreach ($this->configHandlerLoaders as $placeholder => $loader) {
+			$handler = $loader();
+			if(!$handler instanceof IConfigHandler) {
+				throw new \RuntimeException(sprintf(
+					'Handler for %s is not an instance of IConfigHandler', $placeholder
+				));
+			}
+			$this->configHandlers[] = $handler;
+			$newLoaded = true;
+		}
+		$this->configHandlerLoaders = [];
+		if($newLoaded) {
+			// ensure those with longest placeholders come first,
+			// to avoid substring matches
+			uksort($this->configHandlers, function ($phA, $phB) {
+				return strlen($phB) <=> strlen($phA);
+			});
+		}
+	}
+
+	/**
+	 * @since 16.0.0
+	 */
+	public function getConfigHandlers() {
+		$this->loadConfigHandlers();
+		return $this->configHandlers;
+	}
 }
diff --git a/apps/files_external/lib/config.php b/apps/files_external/lib/config.php
index 7fb118c2de5..2078abc029e 100644
--- a/apps/files_external/lib/config.php
+++ b/apps/files_external/lib/config.php
@@ -35,6 +35,8 @@
  *
  */
 
+use OCA\Files_External\Config\IConfigHandler;
+use OCA\Files_External\Config\UserPlaceholderHandler;
 use phpseclib\Crypt\AES;
 use \OCA\Files_External\AppInfo\Application;
 use \OCA\Files_External\Lib\Backend\LegacyBackend;
@@ -104,7 +106,7 @@ class OC_Mount_Config {
 			$mountPoint = '/'.$uid.'/files'.$storage->getMountPoint();
 			$mountEntry = self::prepareMountPointEntry($storage, false);
 			foreach ($mountEntry['options'] as &$option) {
-				$option = self::setUserVars($uid, $option);
+				$option = self::substitutePlaceholdersInConfig($option);
 			}
 			$mountPoints[$mountPoint] = $mountEntry;
 		}
@@ -113,7 +115,7 @@ class OC_Mount_Config {
 			$mountPoint = '/'.$uid.'/files'.$storage->getMountPoint();
 			$mountEntry = self::prepareMountPointEntry($storage, true);
 			foreach ($mountEntry['options'] as &$option) {
-				$option = self::setUserVars($uid, $option);
+				$option = self::substitutePlaceholdersInConfig($uid, $option);
 			}
 			$mountPoints[$mountPoint] = $mountEntry;
 		}
@@ -199,18 +201,26 @@ class OC_Mount_Config {
 	 * @param string $user user value
 	 * @param string|array $input
 	 * @return string
+	 * @deprecated use self::substitutePlaceholdersInConfig($input)
 	 */
 	public static function setUserVars($user, $input) {
-		if (is_array($input)) {
-			foreach ($input as &$value) {
-				if (is_string($value)) {
-					$value = str_replace('$user', $user, $value);
-				}
-			}
-		} else {
-			if (is_string($input)) {
-				$input = str_replace('$user', $user, $input);
-			}
+		$handler = self::$app->getContainer()->query(UserPlaceholderHandler::class);
+		return $handler->handle($input);
+	}
+
+	/**
+	 * @param mixed $input
+	 * @return mixed
+	 * @throws \OCP\AppFramework\QueryException
+	 * @since 16.0.0
+	 */
+	public static function substitutePlaceholdersInConfig($input) {
+		/** @var BackendService $backendService */
+		$backendService = self::$app->getContainer()->query(BackendService::class);
+		/** @var IConfigHandler[] $handlers */
+		$handlers = $backendService->getConfigHandlers();
+		foreach ($handlers as $handler) {
+			$input = $handler->handle($input);
 		}
 		return $input;
 	}
@@ -229,7 +239,7 @@ class OC_Mount_Config {
 			return StorageNotAvailableException::STATUS_SUCCESS;
 		}
 		foreach ($options as &$option) {
-			$option = self::setUserVars(OCP\User::getUser(), $option);
+			$option = self::substitutePlaceholdersInConfig($option);
 		}
 		if (class_exists($class)) {
 			try {