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Package uuid provides RFC4122 and DCE 1.1 UUIDs. Use NewV1, NewV2, NewV3, NewV4, NewV5, for generating new UUIDs. Use New([]byte), NewHex(string), and Parse(string) for creating UUIDs from existing data. The original version was from Krzysztof Kowalik <> Unfortunately, that version was non compliant with RFC4122. The package has since been redesigned. The example code in the specification was also used as reference for design. Copyright (C) 2016 2016 MIT licence


Version published


Go UUID implementation

license GoDoc Build Status Build Status Coverage Status Go Report Card

This package provides RFC 4122 and DCE 1.1 compliant UUIDs. It will generate the following:

  • Version 1: based on a Timestamp and MAC address as Node id
  • Version 2: based on DCE Security - Experimental
  • Version 3: based on MD5 hash
  • Version 4: based on cryptographically secure random numbers
  • Version 5: based on SHA-1 hash

Functions NewV1, NewV2, NewV3, NewV4, NewV5, New, NewHex and Parse() for generating version 1, 2, 3, 4 and 5 Uuid's


Will generally support last 3 versions of Go.

  • 1.8
  • 1.7
  • 1.6


Use the go tool:

$ go get


Typical Usage

See documentation and examples for more information.


import ""

id, _ := uuid.Parse("6ba7b810-9dad-11d1-80b4-00c04fd430c8")

if uuid.Equal(id, uuid.NameSpaceDNS) {
    fmt.Println("Alas these are equal")

if uuid.Compare(id, uuid.NameSpaceDNS) == 0 {
    fmt.Println("They are also equal")

if uuid.Compare(id, uuid.NameSpaceX500) == -1 {
    fmt.Println("id < uuid.NameSpaceX500")

if uuid.Compare(uuid.NameSpaceX50, id) == 1 {
    fmt.Println("uuid.NameSpaceX500 > id")

// Default Format is FormatCanonical
fmt.Println(uuid.Formatter(id, uuid.FormatCanonicalCurly))


Formatting UUIDs

The default format is uuid.FormatCanonical xxxxxxxx-xxxx-xxxx-xxxx-xxxxxx

Any call to uuid.String() will produce this output.

The format is twice as fast as the others at producing a string from the bytes.

To change to another format permanently use:


Once this has been called in an init function all UUID.String() calls will use the new format.

Available formats:

FormatHex              = xxxxxxxxxxxxxxxxxxxxxxxxxx
FormatHexCurly         = {xxxxxxxxxxxxxxxxxxxxxxxxxx}
FormatHexBracket       = (xxxxxxxxxxxxxxxxxxxxxxxxxx)

// This is the default format.
FormatCanonical Format = xxxxxxxx-xxxx-xxxx-xxxx-xxxxxx

FormatCanonicalCurly   = {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxx}
FormatCanonicalBracket = (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxx)
FormatUrn              = urn:uuid:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxx

The uuid.Formatter function also exists and is only ever meant to be used for one time prints where a different format from the default or switched format is required. You can supply your own format as long as it fits the pattern.
which contains %x for the five groups in an UUID. Eg: FormatCanonical = %x-%x-%x-%x-%x

You can also stwict to a custom format

Note: AT this time cutsom formats are not supported for TextMarshalling. If a custom format is deteced it will use the canonical format. Use a call to String() and save as a string instead. 

Version 1 and 2 UUIDs

import ""

id := uuid.NewV1()
fmt.Printf("version %s variant %x: %s\n", u1.Version(), u1.Variant(), id)

id = uuid.NewV2(uuid.DomainUser)
fmt.Printf("version %s variant %x: %s\n", u1.Version(), u1.Variant(), id)

ids := uuid.BulkV1(500)
for _, v := range ids {

ids = make([]UUID, 100)
for _, v := range ids {

// If you wish to register a saving mechanism to keep track of your UUIDs over restarts
// It is recommeneded to add a Saver so as to reduce risk in UUID collisions
saver := savers.FileSystemSaver.Init()

// Must be called before any V1 or V2 UUIDs. Do not call other uuid.Register* if
// registering a Saver

Version 3 and 5 UUIDs

import ""

id := uuid.NewV3(uuid.NameSpaceURL, uuid.Name(""))
fmt.Printf("version %s variant %x: %s\n", u1.Version(), u1.Variant(), id)

id := uuid.NewV5(uuid.NameSpaceURL, uuid.Name(""))
fmt.Printf("version %s variant %x: %s\n", u1.Version(), u1.Variant(), id)

id = uuid.NewV5(uuid.NameSpaceURL, id)
fmt.Printf("version %s variant %x: %s\n", u1.Version(), u1.Variant(), id)

Version 4 UUIDs

import ""

// A V4 UUID will panic by default if the systems CPRNG fails - this can
// be changed by registering your own generator
u4 := uuid.NewV4()
fmt.Printf("version %d variant %x: %s\n", u4.Version(), u4.Variant(), u4)

ids := uuid.BulkV4(500)
for _, v := range ids {

ids := make([]UUID, 100)
for _, v := range ids {

Custom Generators

import ""

// Improve resolution for V1 and 2 UUIDs
// The resolution correlates to how many ids can be created before waiting
// for the next unique timestamp. The default is a low 1024, this equates
// to Ids that can be created in 100 nanoseconds. It is low to encourage
// you to set it.
uuid.RegisterGenerator(&GeneratorConfig{Resolution: 18465})

// Provide your own node Id or MAC address
    Id: func() uuid.Node{
        // My Node Id
        // If this returns nil a random one will be generated

// Replace the default Timestamp spinner with your own.
    Next: func()(uuid.Timestamp){
        // My own Timestamp function...
        // Resolution will become reduendant if you set this.
        // The package will increment the clock sequence if you produce equal Timestamps

// Replace the default crypto/rand.Read CPRNG with your own.
    Random: func([]byte)(int, error){
        // My CPRNG function...

// type HandleRandomError func([]byte, int, error) error

// Replace the default random number error handler for V4 UUIDs. This function is called
// when there is an error in the crypto/rand CPRNG. The default error handler function reads 
// from math.Rand as a fallback.
// You can change that behaviour and handle the error by providing your own function.
// Errors could be due to a lack of system entropy or some other serious issue. These issues are rare,
// however, having the tools to handle such issues is important.
// This approach was taken as each user of this package will want to handle this differently.
// For example one user of the package might want to just panic instead. 
//  Returning an error will cause a panic.

    HandleError: func(id []byte, n int, err error)bool{
        return err

// You can also just generate your own completely.
myGenerator := NewGenerator(nil)

id := myGenerator.NewV4()

// You can replace the logger
        Logger: log.New(someWriter, "my-prefix", myFlags),


  • go test -coverprofile cover.out

  • go test -coverprofile cover.out

  • go tool cover -html=cover.out -o cover.html


  1. fork from the master branch to create your own fork
  2. clone from master into $GOPATH/src/
  3. git remote add username
  4. push changes on your fork and track your remote
  5. Remember to create a branch

To ensure you get the correct packages and subpackages install in a gopath which matches go/src/

Design considerations

  • UUID is an interface which correlates to

  • V1 UUIDs are sequential. This can cause the Generator to work more slowly compared to other implementations. It can however be manually tuned to have performance that is on par. This is achieved by setting the Timestamp Resolution. Benchmark tests have been provided to help determine the best setting for your server

    Proper test coverage has determined thant the UUID timestamp spinner works correctly, across multiple clock resolutions. The generator produces timestamps that roll out sequentially and will only modify the clock sequence on very rare circumstances.

    It is highly recommended that you register a uuid.Saver if you use V1 or V2 UUIDs as it will ensure a higher probability of uniqueness.

      Example V1 output:
  • The V1 UUID generator should be file system and server agnostic To achieve this there are: ** No Os locking threads or file system dependant storage ** Provided the uuid.Saver interface so a package can implement its own solution if required

  • The V4 UUID should allow a package to handle any error that can occur in the CPRNG. The default is to read from math.Rand``````.

  • The package should be able to handle multiple instances of Generators so a package can produce UUIDs from multiple sources.

Copyright (C) 2017 See LICENSE file for details.


Last updated on 27 May 2017

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