ulid

This library implements the ULID specification as defined at https://github.com/ulid/spec.

Installation

1. Add the dependency to your shard.yml:

   dependencies:
     ulid:
       github: davidkellis/ulid
   

2. Run shards install

Usage

require "ulid"

puts ULID.string                # 01FWW2EFES00000005WZ2S1FJ4
puts ULID.uint                  # 1989788620795904033538720336259049107
puts ULID.uuid                  # 017f3827-3dd9-0000-0000-e11234e44a25

puts ULID.monotonic_string      # 01FWW2EFES0000003V8EMT3N0N
puts ULID.monotonic_uint        # 1989788620795904033538533323464025266
puts ULID.monotonic_uuid        # 017f3827-3dd9-0000-0000-2eee411f7b89


t = Time.utc
puts t                          # 2022-02-26 22:29:30 UTC

puts ULID.string(t)             # 01FWW2EFES0000005JH7TWRY67
puts ULID.uint(t)               # 1989788620795904033538751739225489211
puts ULID.uuid(t)               # 017f3827-3dd9-0000-0000-70b68bfe74d9

puts ULID.monotonic_string(t)   # 01FWW2EFES0000002REBEWA7QP
puts ULID.monotonic_uint(t)     # 1989788620795904033538608261870460663
puts ULID.monotonic_uuid(t)     # 017f3827-3dd9-0000-0000-5872ddc51ef8

Specification (per https://github.com/ulid/spec as of 2022-02-24)

Below is the current specification of ULID as implemented in ulid/javascript.

Note: the binary format has not been implemented in JavaScript as of yet.

 01AN4Z07BY      79KA1307SR9X4MV3

|----------|    |----------------|
 Timestamp          Randomness
   48bits             80bits

Components

Timestamp

• 48 bit integer
• UNIX-time in milliseconds
• Won't run out of space 'til the year 10889 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

Canonical String Representation

ttttttttttrrrrrrrrrrrrrrrr

where
t is Timestamp (10 characters)
r is Randomness (16 characters)

Encoding

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

0123456789ABCDEFGHJKMNPQRSTVWXYZ

Monotonicity

When generating a ULID within the same millisecond, we can provide some guarantees regarding sort order. Namely, if the same millisecond is detected, the random component is incremented by 1 bit in the least significant bit position (with carrying). For example:

import { monotonicFactory } from 'ulid'

const ulid = monotonicFactory()

// Assume that these calls occur within the same millisecond
ulid() // 01BX5ZZKBKACTAV9WEVGEMMVRZ
ulid() // 01BX5ZZKBKACTAV9WEVGEMMVS0

If, in the extremely unlikely event that, you manage to generate more than 2⁸⁰ ULIDs within the same millisecond, or cause the random component to overflow with less, the generation will fail.

import { monotonicFactory } from 'ulid'

const ulid = monotonicFactory()

// Assume that these calls occur within the same millisecond
ulid() // 01BX5ZZKBKACTAV9WEVGEMMVRY
ulid() // 01BX5ZZKBKACTAV9WEVGEMMVRZ
ulid() // 01BX5ZZKBKACTAV9WEVGEMMVS0
ulid() // 01BX5ZZKBKACTAV9WEVGEMMVS1
...
ulid() // 01BX5ZZKBKZZZZZZZZZZZZZZZX
ulid() // 01BX5ZZKBKZZZZZZZZZZZZZZZY
ulid() // 01BX5ZZKBKZZZZZZZZZZZZZZZZ
ulid() // throw new Error()!

Overflow Errors when Parsing Base32 Strings

Technically, a 26-character Base32 encoded string can contain 130 bits of information, whereas a ULID must only contain 128 bits. Therefore, the largest valid ULID encoded in Base32 is 7ZZZZZZZZZZZZZZZZZZZZZZZZZ, which corresponds to an epoch time of 281474976710655 or 2 ^ 48 - 1.

Any attempt to decode or encode a ULID larger than this should be rejected by all implementations, to prevent overflow bugs.

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                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Test

crystal spec

Contributors

• David Ellis - creator and maintainer