backuptarget: pseudo target for import and restore

src/backupformat.js

@@ -2,6 +2,7 @@
 
 exports = module.exports = {
     api,
+    validateFormat,
 };
 
 const assert = require('assert'),
@@ -17,3 +18,11 @@ function api(format) {
 
     throw new BoxError(BoxError.INTERNAL_ERROR, `Undefined format ${format}`);
 }
+
+function validateFormat(format) {
+    assert.strictEqual(typeof format, 'string');
+
+    if (format === 'tgz' || format == 'rsync') return null;
+
+    return new BoxError(BoxError.BAD_FIELD, 'Invalid backup format');
+}