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// Copyright 2019 Google Inc. All rights reserved.
// Use of this source code is governed by the Apache 2.0
// license that can be found in the LICENSE file.
package datastore
import (
var keyConversion struct {
mu sync.RWMutex
appID string // read using getKeyConversionAppID
// EnableKeyConversion enables encoded key compatibility with the Cloud
// Datastore client library ( Encoded keys
// generated by the Cloud Datastore client library will be decoded into App
// Engine datastore keys.
// The context provided must be an App Engine context if running in App Engine
// first generation runtime. This can be called in the /_ah/start handler. It is
// safe to call multiple times, and is cheap to call, so can also be inserted as
// middleware.
// Enabling key compatibility does not affect the encoding format used by
// Key.Encode, it only expands the type of keys that are able to be decoded with
// DecodeKey.
func EnableKeyConversion(ctx context.Context) {
// Only attempt to set appID if it's unset.
// If already set, ignore.
if getKeyConversionAppID() != "" {
// Check again to avoid race where another goroutine set appID between the call
// to getKeyConversionAppID above and taking the write lock.
if keyConversion.appID == "" {
keyConversion.appID = internal.FullyQualifiedAppID(ctx)
func getKeyConversionAppID() string {
appID := keyConversion.appID
return appID
// decodeCloudKey attempts to decode the given encoded key generated by the
// Cloud Datastore client library (, returning nil
// if the key couldn't be decoded.
func decodeCloudKey(encoded string) *Key {
appID := getKeyConversionAppID()
if appID == "" {
return nil
k, err := cloudkey.DecodeKey(encoded)
if err != nil {
return nil
return convertCloudKey(k, appID)
// convertCloudKey converts a Cloud Datastore key and converts it to an App
// Engine Datastore key. Cloud Datastore keys don't include the project/app ID,
// so we must add it back in.
func convertCloudKey(key *cloudkey.Key, appID string) *Key {
if key == nil {
return nil
k := &Key{
intID: key.ID,
kind: key.Kind,
namespace: key.Namespace,
parent: convertCloudKey(key.Parent, appID),
stringID: key.Name,
appID: appID,
return k