| // Copyright 2023 Google Inc. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package uuid |
| |
| import ( |
| "io" |
| ) |
| |
| // UUID version 7 features a time-ordered value field derived from the widely |
| // implemented and well known Unix Epoch timestamp source, |
| // the number of milliseconds seconds since midnight 1 Jan 1970 UTC, leap seconds excluded. |
| // As well as improved entropy characteristics over versions 1 or 6. |
| // |
| // see https://datatracker.ietf.org/doc/html/draft-peabody-dispatch-new-uuid-format-03#name-uuid-version-7 |
| // |
| // Implementations SHOULD utilize UUID version 7 over UUID version 1 and 6 if possible. |
| // |
| // NewV7 returns a Version 7 UUID based on the current time(Unix Epoch). |
| // Uses the randomness pool if it was enabled with EnableRandPool. |
| // On error, NewV7 returns Nil and an error |
| func NewV7() (UUID, error) { |
| uuid, err := NewRandom() |
| if err != nil { |
| return uuid, err |
| } |
| makeV7(uuid[:]) |
| return uuid, nil |
| } |
| |
| // NewV7FromReader returns a Version 7 UUID based on the current time(Unix Epoch). |
| // it use NewRandomFromReader fill random bits. |
| // On error, NewV7FromReader returns Nil and an error. |
| func NewV7FromReader(r io.Reader) (UUID, error) { |
| uuid, err := NewRandomFromReader(r) |
| if err != nil { |
| return uuid, err |
| } |
| |
| makeV7(uuid[:]) |
| return uuid, nil |
| } |
| |
| // makeV7 fill 48 bits time (uuid[0] - uuid[5]), set version b0111 (uuid[6]) |
| // uuid[8] already has the right version number (Variant is 10) |
| // see function NewV7 and NewV7FromReader |
| func makeV7(uuid []byte) { |
| /* |
| 0 1 2 3 |
| 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | unix_ts_ms | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | unix_ts_ms | ver | rand_a (12 bit seq) | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |var| rand_b | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | rand_b | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| */ |
| _ = uuid[15] // bounds check |
| |
| t, s := getV7Time() |
| |
| uuid[0] = byte(t >> 40) |
| uuid[1] = byte(t >> 32) |
| uuid[2] = byte(t >> 24) |
| uuid[3] = byte(t >> 16) |
| uuid[4] = byte(t >> 8) |
| uuid[5] = byte(t) |
| |
| uuid[6] = 0x70 | (0x0F & byte(s>>8)) |
| uuid[7] = byte(s) |
| } |
| |
| // lastV7time is the last time we returned stored as: |
| // |
| // 52 bits of time in milliseconds since epoch |
| // 12 bits of (fractional nanoseconds) >> 8 |
| var lastV7time int64 |
| |
| const nanoPerMilli = 1000000 |
| |
| // getV7Time returns the time in milliseconds and nanoseconds / 256. |
| // The returned (milli << 12 + seq) is guaranteed to be greater than |
| // (milli << 12 + seq) returned by any previous call to getV7Time. |
| func getV7Time() (milli, seq int64) { |
| timeMu.Lock() |
| defer timeMu.Unlock() |
| |
| nano := timeNow().UnixNano() |
| milli = nano / nanoPerMilli |
| // Sequence number is between 0 and 3906 (nanoPerMilli>>8) |
| seq = (nano - milli*nanoPerMilli) >> 8 |
| now := milli<<12 + seq |
| if now <= lastV7time { |
| now = lastV7time + 1 |
| milli = now >> 12 |
| seq = now & 0xfff |
| } |
| lastV7time = now |
| return milli, seq |
| } |