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// Copyright 2021 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 cron
import (
luciflag ""
// ModuleName can be used to refer to this module when declaring dependencies.
var ModuleName = module.RegisterName("")
// ModuleOptions contain configuration of the cron server module.
// It will be used to initialize Default dispatcher.
type ModuleOptions struct {
// Dispatcher is a dispatcher to use.
// Default is the global Default instance.
Dispatcher *Dispatcher
// ServingPrefix is a URL path prefix to serve registered cron handlers from.
// GETs to a URL under this prefix (regardless which one) will be treated
// as Cloud Scheduler calls.
// Must start with "/internal/". Default is "/internal/cron".
ServingPrefix string
// AuthorizedCallers is a list of service accounts Cloud Scheduler may use to
// call cron HTTP endpoints.
// See for details.
// Can be empty on Appengine, since there calls are authenticated using
// "X-Appengine-Cron" header.
// Default is an empty list.
AuthorizedCallers []string
// Register registers the command line flags.
// Mutates `o` by populating defaults.
func (o *ModuleOptions) Register(f *flag.FlagSet) {
if o.ServingPrefix == "" {
o.ServingPrefix = "/internal/cron"
f.StringVar(&o.ServingPrefix, "cron-serving-prefix", o.ServingPrefix,
`URL prefix to serve registered cron handlers from, must start with '/internal/'.`)
f.Var(luciflag.StringSlice(&o.AuthorizedCallers), "cron-authorized-caller",
`Service account email to accept calls from. May be repeated.`)
// NewModule returns a server module that sets up a cron dispatcher.
func NewModule(opts *ModuleOptions) module.Module {
if opts == nil {
opts = &ModuleOptions{}
return &cronModule{opts: opts}
// NewModuleFromFlags is a variant of NewModule that initializes options through
// command line flags.
// Calling this function registers flags in flag.CommandLine. They are usually
// parsed in server.Main(...).
func NewModuleFromFlags() module.Module {
opts := &ModuleOptions{}
return NewModule(opts)
// cronModule implements module.Module.
type cronModule struct {
opts *ModuleOptions
// Name is part of module.Module interface.
func (*cronModule) Name() module.Name {
return ModuleName
// Dependencies is part of module.Module interface.
func (*cronModule) Dependencies() []module.Dependency {
return nil
// Initialize is part of module.Module interface.
func (m *cronModule) Initialize(ctx context.Context, host module.Host, opts module.HostOptions) (context.Context, error) {
logging.Infof(ctx, "Cron is serving handlers from %q", m.opts.ServingPrefix)
if !strings.HasPrefix(m.opts.ServingPrefix, "/internal/") {
return nil, errors.Reason(`-cron-serving-prefix must start with "/internal/", got %q`, m.opts.ServingPrefix).Err()
if m.opts.Dispatcher == nil {
m.opts.Dispatcher = &Default
m.opts.Dispatcher.GAE = opts.GAE
m.opts.Dispatcher.DisableAuth = !opts.Prod
m.opts.Dispatcher.AuthorizedCallers = m.opts.AuthorizedCallers
m.opts.Dispatcher.InstallCronRoutes(host.Routes(), m.opts.ServingPrefix)
return ctx, nil