cipd: Client can resolve tags to instance IDs.

go/src/infra/tools/cipd/common/common.go

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /*
 Package common defines structures and functions used by all other cipd/ packages.
 */
 package common
 
 import (
@@ skipping 60 matching lines @@
                 return fmt.Errorf("The string %q doesn't look like a tag (a key:value pair)", t)
         }
         if len(t) > 400 {
                 return fmt.Errorf("The tag is too long: %q", t)
         }
         if !instanceTagKeyRe.MatchString(chunks[0]) {
                 return fmt.Errorf("Invalid tag key in %q. Should be a lowercase word.", t)
         }
         return nil
 }
+
+// ValidateInstanceVersion return error if a string doesn't look like
+// an instance ID or an instance tag.
+func ValidateInstanceVersion(v string) error {
+        if ValidateInstanceID(v) == nil || ValidateInstanceTag(v) == nil {
+                return nil
+        }
+        return fmt.Errorf("Bad version (not an instance ID or a tag): %q", v)
+}