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doc/AddonStorageBackend.md

@@ -336,20 +336,20 @@ function samplestorage_install()
 	DI::storageManager()->register(SampleStorageBackend::class);
 }
 
-function webdav_storage_uninstall()
+function samplestorage_storage_uninstall()
 {
 	DI::storageManager()->unregister(SampleStorageBackend::class);
 }
 
-function webdav_storage_instance(App $a, array &$data)
+function samplestorage_storage_instance(App $a, array &$data)
 {
 	$config          = new SampleStorageBackendConfig(DI::l10n(), DI::config());
 	$data['storage'] = new SampleStorageBackendConfig($config->getFileName());
 }
 
-function webdav_storage_config(App $a, array &$data)
+function samplestorage_storage_config(App $a, array &$data)
 {
-	$data['storage_config'] = new WebDavConfig(DI::l10n(), DI::config());
+	$data['storage_config'] = new SampleStorageBackendConfig(DI::l10n(), DI::config());
 }
 
 ```

doc/Addons.md

@@ -538,6 +538,22 @@ Hook data:
 - **uid** (input): the user id to revoke the block for.
 - **result** (output): a boolean value indicating wether the operation was successful or not.
 
+### storage_instance
+
+Called when a custom storage is used (e.g. webdav_storage)
+
+Hook data:
+- **name** (input): the name of the used storage backend
+- **data['storage']** (output): the storage instance to use (**must** implement `\Friendica\Model\Storage\IWritableStorage`) 
+
+### storage_config
+
+Called when the admin of the node wants to configure a custom storage (e.g. webdav_storage)
+
+Hook data:
+- **name** (input): the name of the used storage backend
+- **data['storage_config']** (output): the storage configuration instance to use (**must** implement `\Friendica\Model\Storage\IStorageConfiguration`)
+
 ## Complete list of hook callbacks
 
 Here is a complete list of all hook callbacks with file locations (as of 24-Sep-2018). Please see the source for details of any hooks not documented above.

src/Model/Storage/Filesystem.php

@@ -45,11 +45,17 @@ class Filesystem implements IWritableStorage
 	 * Filesystem constructor.
 	 *
 	 * @param string $filesystemPath
+	 *
+	 * @throws StorageException in case the path doesn't exist or isn't writeable
 	 */
 	public function __construct(string $filesystemPath = FilesystemConfig::DEFAULT_BASE_FOLDER)
 	{
 		$path           = $filesystemPath;
 		$this->basePath = rtrim($path, '/');
+
+		if (!is_dir($this->basePath) || !is_writable($this->basePath)) {
+			throw new StorageException(sprintf('Path %s does not exist or is not writeable', $this->basePath));
+		}
 	}
 
 	/**