Skip to content

ULID (Universally Unique Lexicographically Sortable Identifier) for Kotlin Multiplatform

License

Notifications You must be signed in to change notification settings

aallam/ulid-kotlin

Repository files navigation

ULID for Kotlin

Universally Unique Lexicographically Sortable Identifier

Maven Central License Kotlin codecov Documentation

Kotlin implementation of ULID with multiplatform 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)

Install

Add the Maven Central repository if it is not already there:

repositories {
    mavenCentral()
}

Add a dependency to the dependencies block:

dependencies {
    implementation "com.aallam.ulid:ulid-kotlin:$version"
}

Multiplatform

In multiplatform projects, add a dependency to the commonMain source set dependencies.

Usage

  • Generating ULID String:
ULID.randomULID()
  • Generating ULID instance:
val ulid = ULID.nextULID()
val ulidString = ulid.toString()
  • Generating ULID using ULID.Factory
val factory = ULID.Factory()
val ulid = factory.nextULID()
val ulidString = ulid.toString()

The default constructor is using default kotlin.random.Random but you can also use the ULID.Factory(Random) builder function to use a different Random instance.

// generate a ULID String
val ulidString: String = ULID.randomULID()

// generate a ULID instance
val ulid: ULID = ULID.nextULID()

// generate the ByteArray for a ULID instance
val data: ByteArray = ulid.toBytes()

// generate a ULID from given ByteArray using 'fromBytes' function
val ulidFromBytes: ByteArray = ULID.fromBytes(data)

// generate a ULID from given String using 'parseULID' function
val ulidFromString: ULID = ULID.parseULID(ulidString)

// generate a ULID String from ULID instance
val ulidStringFromULID: ULID = ulid.toString()

Monotonicity

Specification

// generate ULID instance using a monotonic factory
val ulid: ULID = ULID.Monotonic.nextULID(previousULID)

// using a monotonic factory, generate a ULID instance or null in case of overflow
val ulidStrict: ULID? = ULID.Monotonic.nextULIDStrict(previousULID)

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

ULID for Kotlin is an open-sourced software licensed under the MIT license.