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uuid7

A Rust implementation of UUID version 7

let uuid = uuid7::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::uuid7().to_string();

See RFC 9562.

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 a counter that ensures the increasing order of IDs generated within a millisecond. The counter is incremented by one for each new ID and is reset to a random number when 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.

The 42-bit counter is sufficiently large, so you do not usually need to worry about overflow, but in an extremely rare circumstance where it overflows, this library increments the unix_ts_ms field to continue instant monotonic generation. As a result, the unix_ts_ms may have a greater value than that of the system's real-time clock. (See also Why so large counter? (42bits)).

UUIDv7, by design, relies on the system clock to guarantee the monotonically increasing order of generated IDs. A generator may not be able to produce a monotonic sequence if the system clock goes backwards. This library ignores a clock rollback and reuses the previous unix_ts_ms unless the clock rollback is considered significant (by default, more than ten seconds). If such a significant rollback takes place, this library resets the generator by default and thus breaks the increasing order of generated IDs.

Crate features

Default features:

std integrates the library with, among others, the system clock to draw current timestamps. Without std, this crate provides limited functionality available under no_std environments.
global_gen (implies std) enables the primary uuid7() function and the process-wide global generator under the hood.

Optional features:

serde enables the serialization and deserialization of Uuid objects.
uuid (together with global_gen) 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:

let uuid = uuid7::uuid4();
println!("{}", uuid); // e.g., "2ca4b2ce-6c13-40d4-bccf-37d222820f6f"

V7Generator provides an interface that allows finer control over the various aspects of the UUIDv7 generation:

use uuid7::V7Generator;

let mut g = V7Generator::with_rand08(rand::rngs::OsRng);
let custom_unix_ts_ms = 0x0123_4567_8901u64;
let x = g.generate_or_reset_core(custom_unix_ts_ms, 10_000);
println!("{}", x);

let y = g
    .generate_or_abort_core(custom_unix_ts_ms, 10_000)
    .expect("clock went backwards by more than 10_000 milliseconds");
println!("{}", y);

License

Licensed under the Apache License, Version 2.0.