uuid7 0.2.0

An experimental implementation of the proposed UUID Version 7
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uuid7

Crates.io License

An experimental implementation of the proposed UUID Version 7

use uuid7::uuid7;

let uuid = uuid7();
println!("{}", uuid); // e.g. "01809424-3e59-7c05-9219-566f82fff672"
println!("{:?}", uuid.as_bytes()); // as 16-byte big-endian array

let uuid_string: String = uuid7().to_string();

See draft-peabody-dispatch-new-uuid-format-03.

Field and bit layout

This implementation produces identifiers with the following bit layout:

 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  |        counter        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|var|                        counter                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             rand                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where:

  • The 48-bit unix_ts_ms field is dedicated to the Unix timestamp in milliseconds.
  • The 4-bit ver field is set at 0111.
  • The 42-bit counter field accommodates the sequence counter that ensures the monotonic order of IDs generated within the same millisecond. The counter is incremented by one for each new ID generated within the same timestamp and is randomly initialized whenever the unix_ts_ms changes.
  • The 2-bit var field is set at 10.
  • The remaining 32 rand bits are filled with a cryptographically strong random number.

In the very rare circumstances where the 42-bit counter field reaches its maximum value and can no more be incremented within the same timestamp, this library increments the unix_ts_ms; therefore, the unix_ts_ms may have a larger value than that of the real-time clock. This library goes on with such larger unix_ts_ms values caused by counter overflows and system clock rollbacks as long as the difference from the system clock is small enough. If the system clock moves back more than ten seconds, this library resets the generator state and thus breaks the monotonic order of generated identifiers.

Features

Default features:

  • std enables the primary uuid7() function. Without std, this crate provides limited functionality available under no_std environments.

Optional features:

  • uuid (together with std) enables the new_v7() function that returns the popular uuid crate's Uuid objects.

Other functionality

This library also supports the generation of UUID version 4:

use uuid7::uuid4;

let uuid = uuid4();
println!("{}", uuid); // e.g. "2ca4b2ce-6c13-40d4-bccf-37d222820f6f"

gen7::Generator provides a flexible interface to customize the various aspects of the UUIDv7 generation:

use uuid7::gen7::{Generator, Status};

let mut g = Generator::new(rand::rngs::OsRng);
let unix_ts_ms = 0x0123_4567_8901u64;
let (uuid, status) = g.generate_core(unix_ts_ms);
if status == Status::ClockRollback {
    panic!("clock moved back; monotonic order was broken");
} else {
    println!("{}", uuid);
}

License

Licensed under the Apache License, Version 2.0.

See also