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// Copyright 2015 The LUCI Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package meta
import (
ds ""
// NamespacesCallback is the callback type used with Namespaces. The callback
// will be invoked with each identified namespace.
// If the callback returns an error, iteration will stop. If the error is
// datastore.Stop, Namespaces will stop iterating and return nil. Otherwise,
// the error will be forwarded.
type NamespacesCallback func(string) error
// Namespaces returns a list of all of the namespaces in the datastore.
// This is done by issuing a datastore query for kind "__namespace__". The
// resulting keys will have IDs for the namespaces, namely:
// - The empty namespace will have integer ID 1. This will be forwarded to the
// callback as "".
// - Other namespaces will have non-zero string IDs.
func Namespaces(c context.Context, cb NamespacesCallback) error {
q := ds.NewQuery("__namespace__").KeysOnly(true)
// Query our datastore for the full set of namespaces.
return ds.Run(c, q, func(k *ds.Key) error {
switch {
case k.IntID() == 1:
return cb("")
case k.IntID() != 0:
return fmt.Errorf("unexpected namepsace integer key (%d)", k.IntID())
return cb(k.StringID())
// NamespacesWithPrefix runs Namespaces, returning only namespaces beginning
// with the supplied prefix string.
func NamespacesWithPrefix(c context.Context, p string, cb NamespacesCallback) error {
// TODO: : When inequality filters are
// supported, implement this using a "Gte" filter.
any := false
return Namespaces(c, func(ns string) error {
if !strings.HasPrefix(ns, p) {
if any {
return ds.Stop
return nil
any = true
return cb(ns)
// NamespacesCollector exposes a NamespacesCallback function that aggregates
// resulting namespaces into the collector slice.
type NamespacesCollector []string
// Callback is a NamespacesCallback which adds each namespace to the collector.
func (c *NamespacesCollector) Callback(v string) error {
*c = append(*c, v)
return nil