feature(dav/file): Add readlink method

Author: taminob

apps/dav/lib/Connector/Sabre/File.php

@@ -557,6 +557,26 @@ public function delete() {
 		}
 	}
 
+	/**
+	 * Return symlink target of the file
+	 *
+	 * @return string|null
+	 * @throws NotFound
+	 * @throws Forbidden
+	 * @throws FileLocked
+	 */
+	public function readlink() {
+		if (!$this->info->isReadable()) {
+			throw new NotFound();
+		}
+
+		try {
+			return $this->fileView->readlink($this->path);
+		} catch (\Exception $e) {
+			$this->convertToSabreException($e);
+		}
+	}
+
 	/**
 	 * Returns the mime-type for a file
 	 *