ULID (Universally Unique Lexicographically Sortable Identifier) for Dart

by Flutter Awesome

ulid4d

Universally Unique Lexicographically Sortable Identifier (ULID) implementation for Dart, with binary implementation and monotonicity support.

Background

UUID can be suboptimal for many use-cases because:

  • It isn’t the most character efficient way of encoding 128 bits of randomness
  • UUID v1/v2 is impractical in many environments, as it requires access to a unique, stable MAC address
  • UUID v3/v5 requires a unique seed and produces randomly distributed IDs, which can cause fragmentation in many data structures
  • UUID v4 provides no other information than randomness which can cause fragmentation in many data structures

Instead, herein is proposed ULID:

  • 128-bit compatibility with UUID
  • 1.21e+24 unique ULIDs per millisecond
  • Lexicographically sortable!
  • Canonically encoded as a 26 character string, as opposed to the 36 character UUID
  • Uses Crockford’s base32 for better efficiency and readability (5 bits per character)
  • Case-insensitive
  • No special characters (URL safe)
  • Monotonic sort order (correctly detects and handles the same millisecond)

Usage

  • Generate ULID String:
var ulid = ULID.randomULID();
  • Generate ULID instance:

var ulid = ULID.nextULID();
var ulidString = ulid.toString();
  • Generate ULID using ULIDFactory

var factory = ULIDFactory();
var ulid = factory.nextULID();
var ulidString = ulid.toString();

You can use ULIDFactory(Random) to use a different Random instance.

  • Generating ULID from/to bytes

// generate a ULID instance
var ulid = ULID.nextULID();

// generate byte array (Uint8List) of ULID instance
var data = ulid.toBytes();

// generate a ULID from given byte array using 'fromBytes'
var ulidFromBytes = ULID.fromBytes(data);
  • Generate ULID from/to ULID string

// generate a ULID string
var ulidString = ULID.randomULID();

// generate a ULID from given String using 'fromString'
var ulidFromString = ULID.fromString(ulidString);

// generate a ULID String from ULID instance
var ulidStringFromULID = ulid.toString();

Monotonicity

  • Generate monotonic ULID

// generate ULID instance using a monotonic factory
var ulid = ULID.nextMonotonicULID(ulid);

// using a monotonic factory, generate a ULID instance or null in case
// of overflow
var ulidStrict = ULID.nextMonotonicULIDStrict(ulidMono);
  • Generate ULID using ULIDMonocity factory

// generate ULID using ULID monotonic factory
var factory = ULIDMonotonic();
var ulid = factory.nextULID(ulid);
var ulidStrict = factory.nextULIDStrict(ulid);

Specification

Below is the current specification of ULID as implemented in this repository.

Components

Timestamp

  • 48 bits
  • UNIX-time in milliseconds
  • Won’t run out of space till the year 10889 AD

Entropy

  • 80 bits
  • User defined entropy source.

Encoding

Crockford’s Base32 is used as shown. This alphabet excludes the letters I, L, O, and U to avoid confusion and abuse.

0123456789ABCDEFGHJKMNPQRSTVWXYZ

Binary Layout and Byte Order

The components are encoded as 16 octets. Each component is encoded with the Most Significant Byte first (network byte order).

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      32_bit_uint_time_high                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     16_bit_uint_time_low      |       16_bit_uint_random      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       32_bit_uint_random                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       32_bit_uint_random                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

String Representation

 01AN4Z07BY      79KA1307SR9X4MV3
|----------|    |----------------|
 Timestamp           Entropy
  10 chars           16 chars
   48bits             80bits
   base32             base32

Prior Art

License

ulid4d is an open-sourced software licensed under the BSD 3-clause license.

GitHub

View Github