Allow ext storage Local to go unavailable

Whenever an external storage of type Local points at a non-existing
directory, process this as a StorageNotAvailable instead of returning
404.

This makes desktop clients ignore the folder instead of deleting it when
it becomes unavailable.

The code change was limited to external storages to avoid issues during
setup and with the default home storage.
Signed-off-by: Vincent Petry <pvince81@yahoo.fr>

apps/files_external/lib/Lib/Backend/Local.php

@@ -26,8 +26,10 @@ namespace OCA\Files_External\Lib\Backend;
 use OCA\Files_External\Lib\Auth\AuthMechanism;
 use OCA\Files_External\Lib\Auth\NullMechanism;
 use OCA\Files_External\Lib\DefinitionParameter;
+use OCA\Files_External\Lib\StorageConfig;
 use OCA\Files_External\Service\BackendService;
 use OCP\IL10N;
+use OCP\IUser;
 
 class Local extends Backend {
 	public function __construct(IL10N $l, NullMechanism $legacyAuth) {
@@ -45,4 +47,8 @@ class Local extends Backend {
 			->setLegacyAuthMechanism($legacyAuth)
 		;
 	}
+
+	public function manipulateStorageConfig(StorageConfig &$storage, IUser $user = null): void {
+		$storage->setBackendOption('isExternal', true);
+	}
 }

lib/private/Files/Storage/Local.php

@@ -51,6 +51,7 @@ use OCP\Files\ForbiddenException;
 use OCP\Files\GenericFileException;
 use OCP\Files\IMimeTypeDetector;
 use OCP\Files\Storage\IStorage;
+use OCP\Files\StorageNotAvailableException;
 use OCP\IConfig;
 use OCP\Util;
 use Psr\Log\LoggerInterface;
@@ -95,6 +96,12 @@ class Local extends \OC\Files\Storage\Common {
 
 		// support Write-Once-Read-Many file systems
 		$this->unlinkOnTruncate = $this->config->getSystemValueBool('localstorage.unlink_on_truncate', false);
+
+		if (isset($arguments['isExternal']) && $arguments['isExternal'] && !$this->stat('')) {
+			// data dir not accessible or available, can happen when using an external storage of type Local
+			// on an unmounted system mount point
+			throw new StorageNotAvailableException('Local storage path does not exist "' . $this->getSourcePath('') . '"');
+		}
 	}
 
 	public function __destruct() {

tests/lib/Files/Storage/LocalTest.php

@@ -139,4 +139,15 @@ class LocalTest extends Storage {
 		umask($oldMask);
 		$this->assertTrue($this->instance->isUpdatable('test.txt'));
 	}
+
+	public function testUnavailableExternal() {
+		$this->expectException(\OCP\Files\StorageNotAvailableException::class);
+		$this->instance = new \OC\Files\Storage\Local(['datadir' => $this->tmpDir . '/unexist', 'isExternal' => true]);
+	}
+
+	public function testUnavailableNonExternal() {
+		$this->instance = new \OC\Files\Storage\Local(['datadir' => $this->tmpDir . '/unexist']);
+		// no exception thrown
+		$this->assertNotNull($this->instance);
+	}
 }