datastore/key.go
func (k *Key) Encode() string {
	ref := keyToProto("", k)

	b, err := proto.Marshal(ref)
	if err != nil {
		panic(err)
	}

	// Trailing padding is stripped.
	return strings.TrimRight(base64.URLEncoding.EncodeToString(b), "=")
}
func (k *Key) Encode() string {
	ref := keyToProto("", k)

	b, err := proto.Marshal(ref)
	if err != nil {
		panic(err)
	}

	// Trailing padding is stripped.
	return strings.TrimRight(base64.URLEncoding.EncodeToString(b), "=")
}
// Encode returns an opaque representation of the key
// suitable for use in HTML and URLs.
// This is compatible with the Python and Java runtimes.