github.com/rsms/go-uuid

uuid

• Binary sortable universally unique identifier
• 16 bytes long, 6 bytes millisecond timestamp + 10 random bytes
• Efficient base-62 string encoding that is URL safe

Usage

Variables & Constants

var Max = UUID{
  255, 255, 255, 255, 255, 255, 255, 255,
  255, 255, 255, 255, 255, 255, 255, 255,
}

Max is the largest possible UUID (must not be modified)

var Min UUID

Min is the zero UUID (must not be modified)

type UUID

type UUID [16]byte

UUID is a universally unique identifier

UUIDs are binary sortable. The first 6 bytes constitutes a millisecond-precision timestamp in big-endian byte order.

Data layout:

Byte 0-3  timestamp second, big endian
Byte 4-5  timestamp millisecond, big endian
Byte 6-15 random

Data layout example:

00 31 04 39 02 c9 39 ce 14 6c 0b db a1 40 77 78
~~~~~~~~~~~ ----- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 |            |           Random bytes
 |            |
 |           713 milliseconds
 |
3212345 seconds since 2020-09-13 12:26:40
                    = 2020-10-20 16:45:45.713 UTC

Note that while it seems like we could use nanosecond for the timestamp to reduce the random data needed, environments like JavaScript doesn't neccessarily provide high-precision clocks. Doing things this way means that we can generate and parse the embedded timestamp in a wide variety of programming languages.

func Gen() UUID

GenID generates a universally unique UUID suitable to be used for sorted identity

func New(sec int64, nsec int, random []byte) UUID

New creates a new UUID with specific Unix timestamp and random bytes.

nsec is the nanosecond part of the timestamp and should be in the range [0, 999999999]. It's valid to pass values outside this range for nsec. Only the millisecond part of nsec is actually used.

To create an UUID with a time.Time object, do this:

New(t.Unix(), t.Nanosecond(), random)

Up to 10 bytes is used from random. If len(random) < 10, the remaining "random" bytes of UUID are zero.

func FromBytes(verbatim []byte) UUID

FromBytes copies verbatim bytes into an UUID and returns that UUID. verbatim must be at least 16 bytes long or this will panic.

func FromString(encoded string) UUID

FromString decodes a string representation of an UUID (i.e. from String())

func (UUID) Bytes

func (id UUID) Bytes() []byte

Bytes returns the IDs natural 16 byte long value. The returned slice's bytes must not be modified.

func (*UUID) DecodeString

func (id *UUID) DecodeString(src []byte)

DecodeString sets the receiving UUID to the decoded value of src, which is expected to be a string previously encoded using EncodeString (base62 0-9A-Za-z)

func (UUID) EncodeString

func (id UUID) EncodeString(dst []byte) int

EncodeString writes the receiver to dst which must be at least 22 bytes. Returns the start offset (this function starts writing at the end of dst.)

func (UUID) String

func (id UUID) String() string

String returns a string representation of the UUID. The returned string is sortable with the same order as the "raw" UUID bytes and is URL safe.

func (UUID) Time

func (id UUID) Time() time.Time

Time returns the time portion of the UUID

func (UUID) Timestamp

func (id UUID) Timestamp() (sec uint32, millisec uint16)

Timestamp returns the timestamp portion of the UUID