Cache: add function to get storage id and internal path of a file by id

lib/files/cache/cache.php

@@ -494,4 +494,28 @@ class Cache {
 			return false;
 		}
 	}
+
+	/**
+	 * get the storage id of the storage for a file and the internal path of the file
+	 *
+	 * @return array, first element holding the storage id, second the path
+	 */
+	static public function getById($id) {
+		$query = \OC_DB::prepare('SELECT `storage`, `path` FROM `*PREFIX*filecache` WHERE `fileid` = ?');
+		$result = $query->execute(array($id));
+		if ($row = $result->fetchRow()) {
+			$numericId = $row['storage'];
+			$path = $row['path'];
+		} else {
+			return null;
+		}
+
+		$query = \OC_DB::prepare('SELECT `id` FROM `*PREFIX*storages` WHERE `numeric_id` = ?');
+		$result = $query->execute(array($numericId));
+		if ($row = $result->fetchRow()) {
+			return array($row['id'], $path);
+		} else {
+			return null;
+		}
+	}
 }

tests/lib/files/cache/cache.php

@@ -197,6 +197,13 @@ class Cache extends \PHPUnit_Framework_TestCase {
 		$this->assertEquals(array(), $this->cache->getFolderContents('foo'));
 	}
 
+	function testGetById() {
+		$storageId = $this->storage->getId();
+		$data = array('size' => 1000, 'mtime' => 20, 'mimetype' => 'foo/file');
+		$id = $this->cache->put('foo', $data);
+		$this->assertEquals(array($storageId, 'foo'), \OC\Files\Cache\Cache::getById($id));
+	}
+
 	public function tearDown() {
 		$this->cache->clear();
 	}