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// Copyright 2017 Google LLC
// 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 uid supports generating unique IDs. Its chief purpose is to prevent
// multiple test executions from interfering with each other, and to facilitate
// cleanup of old entities that may remain if tests exit early.
package uid
import (
// A Space manages a set of unique IDs distinguished by a prefix.
type Space struct {
Prefix string // Prefix of UIDs. Read-only.
Sep rune // Separates UID parts. Read-only.
Time time.Time // Timestamp for UIDs. Read-only.
re *regexp.Regexp
count int32 // atomic
short bool
// Options are optional values for a Space.
type Options struct {
Sep rune // Separates parts of the UID. Defaults to '-'.
Time time.Time // Timestamp for all UIDs made with this space. Defaults to current time.
// Short, if true, makes the result of space.New shorter by 6 characters.
// This can be useful for character restricted IDs. It will use a shorter
// but less readable time representation, and will only use two characters
// for the count suffix instead of four.
// e.x. normal: gotest-20181030-59751273685000-0001
// e.x. short: gotest-1540917351273685000-01
Short bool
// NewSpace creates a new UID space. A UID Space is used to generate unique IDs.
func NewSpace(prefix string, opts *Options) *Space {
var short bool
sep := '-'
tm := time.Now().UTC()
if opts != nil {
short = opts.Short
if opts.Sep != 0 {
sep = opts.Sep
if !opts.Time.IsZero() {
tm = opts.Time
var re string
if short {
re = fmt.Sprintf(`^%s%[2]c(\d+)%[2]c\d+$`, regexp.QuoteMeta(prefix), sep)
} else {
re = fmt.Sprintf(`^%s%[2]c(\d{4})(\d{2})(\d{2})%[2]c(\d+)%[2]c\d+$`,
regexp.QuoteMeta(prefix), sep)
return &Space{
Prefix: prefix,
Sep: sep,
Time: tm,
re: regexp.MustCompile(re),
short: short,
// New generates a new unique ID. The ID consists of the Space's prefix, a
// timestamp, and a counter value. All unique IDs generated in the same test
// execution will have the same timestamp.
// Aside from the characters in the prefix, IDs contain only letters, numbers
// and sep.
func (s *Space) New() string {
c := atomic.AddInt32(&s.count, 1)
if s.short && c > 99 {
// Short spaces only have space for 99 IDs. (two characters)
panic("Short space called New more than 99 times. Ran out of IDs.")
} else if c > 9999 {
// Spaces only have space for 9999 IDs. (four characters)
panic("New called more than 9999 times. Ran out of IDs.")
if s.short {
return fmt.Sprintf("%s%c%d%c%02d", s.Prefix, s.Sep, s.Time.UnixNano(), s.Sep, c)
// Write the time as a date followed by nanoseconds from midnight of that date.
// That makes it easier to see the approximate time of the ID when it is displayed.
y, m, d := s.Time.Date()
ns := s.Time.Sub(time.Date(y, m, d, 0, 0, 0, 0, time.UTC))
// Zero-pad the counter for lexical sort order for IDs with the same timestamp.
return fmt.Sprintf("%s%c%04d%02d%02d%c%d%c%04d",
s.Prefix, s.Sep, y, m, d, s.Sep, ns, s.Sep, c)
// Timestamp extracts the timestamp of uid, which must have been generated by
// s. The second return value is true on success, false if there was a problem.
func (s *Space) Timestamp(uid string) (time.Time, bool) {
subs :=
if subs == nil {
return time.Time{}, false
if s.short {
ns, err := strconv.ParseInt(subs[1], 10, 64)
if err != nil {
return time.Time{}, false
return time.Unix(ns/1e9, ns%1e9), true
y, err1 := strconv.Atoi(subs[1])
m, err2 := strconv.Atoi(subs[2])
d, err3 := strconv.Atoi(subs[3])
ns, err4 := strconv.Atoi(subs[4])
if err1 != nil || err2 != nil || err3 != nil || err4 != nil {
return time.Time{}, false
return time.Date(y, time.Month(m), d, 0, 0, 0, ns, time.UTC), true
// Older reports whether uid was created by m and has a timestamp older than
// the current time by at least d.
func (s *Space) Older(uid string, d time.Duration) bool {
ts, ok := s.Timestamp(uid)
if !ok {
return false
return time.Since(ts) > d