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// Copyright 2017 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 isolated
import (
// ScatterGather represents a mapping of working directories to relative paths.
// The purpose is to represent some notion of "local" vs. "archived" paths.
// All relative paths are relative to both their corresponding working
// directories as well as the root of an archive.
// filepath.Join(working dir, relative path) == location of file or directory
// on the system.
// relative path == location of file or directory in an archive.
// Notably, in such a design, we may not have more than one copy of a relative
// path in the archive, because there is a conflict. In order to efficiently
// check this case at the expense of extra memory, ScatterGather actually
// stores a mapping of relative paths to working directories.
type ScatterGather map[string]string
// Add adds a (working directory, relative path) pair to the ScatterGather.
// Add returns an error if the relative path was already added.
func (sc ScatterGather) Add(wd string, rel string) error {
cleaned := filepath.Clean(rel)
if _, ok := sc[cleaned]; ok {
return errors.Reason("name conflict %q", rel).Err()
sc[cleaned] = wd
return nil
// Set implements the flags.Var interface.
func (sc *ScatterGather) Set(value string) error {
parsed := strings.SplitN(value, ":", 2)
if len(parsed) != 2 {
return errors.Reason("malformed input %q", value).Err()
if *sc == nil {
*sc = ScatterGather{}
return sc.Add(parsed[0], parsed[1])
// String implements the Stringer interface.
func (sc *ScatterGather) String() string {
mapping := make(map[string][]string, len(*sc))
for item, wd := range *sc {
mapping[wd] = append(mapping[wd], item)
return fmt.Sprintf("%v", mapping)