I have code that looks like this:
u := make([]byte, 16) _, err := rand.Read(u) if err != nil { return } u[8] = (u[8] | 0x80) & 0xBF // what does this do? u[6] = (u[6] | 0x40) & 0x4F // what does this do? return hex.EncodeToString(u) It returns a string with a length of 32, but I don't think it is a valid UUID. If it is a real UUID, why is it a UUID, and what is the purpose of the code that modifies the value of u[8] and u[6].
Is there a better way of generating UUIDs?
u[8] = (u[8] | 0x80) & 0xBF // what's the purpose ? u[6] = (u[6] | 0x40) & 0x4F // what's the purpose ? These lines clamp the values of byte 6 and 8 to a specific range. rand.Read returns random bytes in the range 0-255, which are not all valid values for a UUID. As far as I can tell, this should be done for all the values in the slice though.
If you are on linux, you can alternatively call /usr/bin/uuidgen.
package main import ( "fmt" "log" "os/exec" ) func main() { out, err := exec.Command("uuidgen").Output() if err != nil { log.Fatal(err) } fmt.Printf("%s", out) } Which yields:
$ go run uuid.go dc9076e9-2fda-4019-bd2c-900a8284b9c4 You can generate UUIDs using the go-uuid library. This can be installed with:
go get github.com/nu7hatch/gouuid You can generate random (version 4) UUIDs with:
import "github.com/nu7hatch/gouuid" ... u, err := uuid.NewV4() The returned UUID type is a 16 byte array, so you can retrieve the binary value easily. It also provides the standard hex string representation via its String() method.
The code you have also looks like it will also generate a valid version 4 UUID: the bitwise manipulation you perform at the end set the version and variant fields of the UUID to correctly identify it as version 4. This is done to distinguish random UUIDs from ones generated via other algorithms (e.g. version 1 UUIDs based on your MAC address and time).
The go-uuid library is NOT RFC4122 compliant. The variant bits are not set correctly. There have been several attempts by community members to have this fixed but pull requests for the fix are not being accepted.
You can generate UUIDs using the Go uuid library I rewrote based on the go-uuid library. There are several fixes and improvements. This can be installed with:
go get github.com/twinj/uuid You can generate random (version 4) UUIDs with:
import "github.com/twinj/uuid" u := uuid.NewV4() The returned UUID type is an interface and the underlying type is an array.
The library also generates v1 UUIDs and correctly generates v3 and 5 UUIDs. There are several new methods to help with printing and formatting and also new general methods to create UUIDs based off of existing data.
"crypto/rand" is cross platform pkg for random bytes generattion
package main import ( "crypto/rand" "fmt" ) func pseudo_uuid() (uuid string) { b := make([]byte, 16) _, err := rand.Read(b) if err != nil { fmt.Println("Error: ", err) return } uuid = fmt.Sprintf("%X-%X-%X-%X-%X", b[0:4], b[4:6], b[6:8], b[8:10], b[10:]) return } From Russ Cox's post:
There's no official library. Ignoring error checking, this seems like it would work fine:
f, _ := os.Open("/dev/urandom") b := make([]byte, 16) f.Read(b) f.Close() uuid := fmt.Sprintf("%x-%x-%x-%x-%x", b[0:4], b[4:6], b[6:8], b[8:10], b[10:]) Note: In the original, pre Go 1 version the first line was:
f, _ := os.Open("/dev/urandom", os.O_RDONLY, 0) Here it compiles and executes, only /dev/urandom returns all zeros in the playground. Should work fine locally.
In the same thread there are some other methods/references/packages found.
FWIW, satori/go.uuid is the most starred UUID package for Go. It supports UUID versions 1-5 and is RFC 4122 and DCE 1.1 compliant.
import "github.com/satori/go.uuid" u := uuid.NewV4() As part of the uuid spec, if you generate a uuid from random it must contain a "4" as the 13th character and a "8", "9", "a", or "b" in the 17th (source).
// this make sure that the 13th character is "4" u[6] = (u[6] | 0x40) & 0x4F // this make sure that the 17th is "8", "9", "a", or "b" u[8] = (u[8] | 0x80) & 0xBF The gorand package has a UUID method that returns a Version 4 (randomly generated) UUID in its canonical string representation ("xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx") and it's RFC 4122 compliant.
It also uses the crypto/rand package to ensure the most cryptographically secure generation of UUIDs across all platforms supported by Go.
import "github.com/leonelquinteros/gorand" func main() { uuid, err := gorand.UUID() if err != nil { panic(err.Error()) } println(uuid) } On Linux, you can read from /proc/sys/kernel/random/uuid:
package main import "io/ioutil" import "fmt" func main() { u, _ := ioutil.ReadFile("/proc/sys/kernel/random/uuid") fmt.Println(string(u)) } No external dependencies!
$ go run uuid.go 3ee995e3-0c96-4e30-ac1e-f7f04fd03e44 For Windows, I did recently this:
// +build windows package main import ( "syscall" "unsafe" ) var ( modrpcrt4 = syscall.NewLazyDLL("rpcrt4.dll") procUuidCreate = modrpcrt4.NewProc("UuidCreate") ) const ( RPC_S_OK = 0 ) func NewUuid() ([]byte, error) { var uuid [16]byte rc, _, e := syscall.Syscall(procUuidCreate.Addr(), 1, uintptr(unsafe.Pointer(&uuid[0])), 0, 0) if int(rc) != RPC_S_OK { if e != 0 { return nil, error(e) } else { return nil, syscall.EINVAL } } return uuid[:], nil } An official implementation by Google is currently under development but not stable yet: https://github.com/google/uuid
Looks like it's the continuation of https://github.com/pborman/uuid from this answer
Generating a version 4 UUID works like this: uuid, err := uuid.NewRandom()
This library is our standard for uuid generation and parsing: