Add ability to estimate the size of a PropertyMap

service/datastore/key.go

 // Copyright 2015 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 datastore
 
 import (
         "bytes"
         "encoding/base64"
         "encoding/json"
@@ skipping 392 matching lines @@
 //
 // toks is guaranteed to be empty if and only if k is nil. If k is non-nil then
 // it contains at least one token.
 func (k *Key) Split() (appID, namespace string, toks []KeyTok) {
         appID = k.appID
         namespace = k.namespace
         toks = make([]KeyTok, len(k.toks))
         copy(toks, k.toks)
         return
 }
+
+// EstimateSize estimates the size of a Key. If withNamespace is true, then it
+// includes the length of the AppID and Namespace.
+//
+// It uses https://cloud.google.com/appengine/articles/storage_breakdown?csw=1
+// as a guide for these values.
+func (k *Key) EstimateSize(withNamespace bool) int {
+        ret := 0
+        if withNamespace {
+                ret += len(k.appID)
+                ret += len(k.namespace)
+        }
+        for _, t := range k.toks {
+                ret += len(t.Kind)
+                if t.StringID != "" {
+                        ret += len(t.StringID)
+                } else {
+                        ret += 8
+                }
+        }
+        return ret
+}