ULID

A Crystal port of alizain/ulid.

Universally Unique Lexicographically Sortable Identifier

UUID can be suboptimal for many uses-cases because:

It isn't the most character efficient way of encoding 128 bits of randomness
The string format itself is apparently based on the original MAC & time version (UUIDv1 from Wikipedia)
It provides no other information than randomness

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)

Installation

Add this to your application's shard.yml:

dependencies:
  ulid:
    github: SuperPaintman/ulid

Usage

require "ulid"

ULID.generate
# => "01B3EAF48P97R8MP9WS6MHDTZ3"

Seed Time

You can also input a seed time which will consistently give you the same string for the time component. This is useful for migrating to ulid.

ULID.generate Time.utc + 5.second
# => "01ARYZ6S41TSV4RRFFQ69G5FAV"

Specification

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

Components

Timestamp

48 bit integer
UNIX-time in milliseconds
Won't run out of space till the year 10895 AD.

Randomness

80 bits
Cryptographically secure source of randomness, if possible

Sorting

The left-most character must be sorted first, and the right-most character sorted last (lexical order). The default ASCII character set must be used. Within the same millisecond, sort order is not guaranteed

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_low                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     16_bit_uint_time_high     |       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