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// Copyright 2018 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 pkg
import (
// InstallMode defines how to install a package.
type InstallMode string
const (
// InstallModeSymlink is default (for backward compatibility).
// In this mode all files are extracted to .cipd/*/... and then symlinked to
// the site root directory. Version switch happens atomically.
InstallModeSymlink InstallMode = "symlink"
// InstallModeCopy is used when files should be directly copied.
// This mode is always used on Windows (and can be optionally) used on
// other OSes. If installation is aborted midway, the package may end up
// in inconsistent state.
InstallModeCopy InstallMode = "copy"
// Set is called by 'flag' package when parsing command line options.
func (m *InstallMode) Set(value string) error {
val := InstallMode(value)
if err := ValidateInstallMode(val); err != nil {
return err
*m = val
return nil
// String is needed to conform to flag.Value interface.
func (m InstallMode) String() string {
return string(m)
// ValidateInstallMode returns non nil if install mode is invalid.
// Valid modes are: "" (client will pick platform default), "copy"
// (aka InstallModeCopy), "symlink" (aka InstallModeSymlink).
func ValidateInstallMode(mode InstallMode) error {
if mode == "" || mode == InstallModeCopy || mode == InstallModeSymlink {
return nil
return errors.Reason("invalid install mode %q", mode).Tag(cipderr.BadArgument).Err()
// PickInstallMode validates the install mode and picks the correct default
// for the platform if no install mode is given.
func PickInstallMode(im InstallMode) (InstallMode, error) {
switch {
case runtime.GOOS == "windows":
return InstallModeCopy, nil // Windows supports only 'copy' mode
case im == "":
return InstallModeSymlink, nil // default on other platforms
if err := ValidateInstallMode(im); err != nil {
return "", err
return im, nil