ulid

Universally Unique Lexicographically Sortable Identifier implementation for Ruby

Official specification page: https://github.com/ulid/spec

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

gem install ulid

Usage

require 'ulid'

ULID.generate # 01ARZ3NDEKTSV4RRFFQ69G5FAV

I want to generate a ULID using an arbitrary timestamp

You can optionally pass a Time instance to ULID.generate to set an arbitrary timestamp component, i.e. the prefix of the ULID.

time_t1 = Time.now
ulid = ULID.generate(time_t1)

I want to generate a ULID using an arbitrary suffix, i.e. without the randomness component

You can optionally pass a 80-bit hex-encodable String on the argument suffix to ULID.generate. This will replace the randomness component by the suffix provided. This allows for fully deterministic ULIDs.

require 'securerandom'

time = Time.now
an_event_identifier = SecureRandom.uuid
ulid1 = ULID.generate(time, suffix: an_event_identifier)
ulid2 = ULID.generate(time, suffix: an_event_identifier)
ulid1 == ulid2 # true

Specification

Below is the current specification of ULID as implemented in this repository. Note: the binary format has not been implemented.

 01AN4Z07BY      79KA1307SR9X4MV3

|----------|    |----------------|
 Timestamp          Randomness
  10 chars           16 chars
   48bits             80bits
   base32             base32

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. The default ASCII order is used for sorting.

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

ttttttttttrrrrrrrrrrrrrrrr

where
t is Timestamp
r is Randomness

Test Suite

bundle exec rake test

Credits and references:

• https://github.com/ulid/javascript