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// Copyright 2020 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 cfgclient
import (
// Options describe how to configure a LUCI Config client.
type Options struct {
// Vars define how to substitute ${var} placeholders in config sets and paths.
// If nil, vars are not allowed. Pass &vars.Vars explicitly to use the global
// var set.
Vars *vars.VarSet
// ServiceHost is a hostname of a LUCI Config service to use.
// If given, indicates configs should be fetched from the LUCI Config service.
// Requires ClientFactory to be provided as well. Not compatible with
// ConfigsDir.
ServiceHost string
// ConfigsDir is a file system directory to fetch configs from instead of
// a LUCI Config service.
// See for the
// expected layout of this directory.
// Useful when running locally in development mode. Not compatible with
// ServiceHost.
ConfigsDir string
// ClientFactory initializes an authenticating HTTP client on demand.
// It will be used to call LUCI Config service. Must be set if ServiceHost is
// set, ignored otherwise.
ClientFactory func(context.Context) (*http.Client, error)
// New instantiates a LUCI Config client based on the given options.
// The client fetches configs either from a LUCI Config service or from a local
// directory on disk (e.g. when running locally in development mode), depending
// on values of ServiceHost and ConfigsDir. If neither are set, returns a client
// that fails all calls with an error.
func New(opts Options) (config.Interface, error) {
switch {
case opts.ServiceHost == "" && opts.ConfigsDir == "":
return erroring.New(errors.New("LUCI Config client is not configured")), nil
case opts.ServiceHost != "" && opts.ConfigsDir != "":
return nil, errors.New("either a LUCI Config service or a local config directory should be used, not both")
case opts.ServiceHost != "" && opts.ClientFactory == nil:
return nil, errors.New("need a client factory when using a LUCI Config service")
var base config.Interface
switch {
case opts.ServiceHost != "":
base = remote.New(opts.ServiceHost, false, opts.ClientFactory)
case opts.ConfigsDir != "":
var err error
if base, err = filesystem.New(opts.ConfigsDir); err != nil {
return nil, err
varz := opts.Vars
if varz == nil {
varz = &vars.VarSet{} // empty: all var references will result in an error
return resolving.New(varz, base), nil