DARB

DARB stands for “dense-ish albeit readable binary”.

It’s a compact way to encode boolean lists into short strings while still keeping them human-readable. The primary use case is shrinking long permission lists inside JWTs, but DARB can be used anywhere you need a balance of efficiency and human-readability.

Why DARB?

• JWT-friendly: Dramatically reduces the size of tokens with long boolean/permission lists.
• Readable at a glance: Unlike raw binary or base-64, you can still tell the list length and understand its contents without tooling.
• Space savings: Up to 75% smaller than a naive string representation.

Note: Don’t use this library for HTTP response body compression. There are already great HTTP compression libraries for that.

Example

val darb = "23.2CB08E"

val booleanList = listOf(
  false, false, true, false,
  true, true, false, false,
  true, false, true, true,
  false, false, false, false,
  true, false, false, false,
  true, true, true,
)

• The prefix (23 in the example above) is the length of the list.
• The body (2CB08E in the example above), where each character represents up to 4 booleans.
  • 2 becomes[false, false, true, false]
  • C becomes[true, true, false, false]
  • B becomes [true, false, true, true]
  • 0 becomes [false, false, false, false]
  • 8 becomes [true, false, false, false]
  • E becomes [true, true, true] (last boolean ignored, since prefix is 23).

In this example, DARB uses 62.5% less space than a plain binary string. For larger lists, the savings approach 75%.

Installation

Install kairo-darb.

build.gradle.kts

dependencies {
  implementation("software.airborne.kairo:kairo-darb")
}

Usage

To encode a boolean list, use DarbEncoder.encode().

DarbEncoder.encode(
  listOf(
    false, false, true, false,
    true, true, false, false,
    true, false, true, true,
    false, false, false, false,
    true, false, false, false,
    true, true, true,
  ),
)
// => 23.2CB08E

To decode a DARB string, use DarbDecoder.decode().

DarbDecoder.decode("23.2CB08E")
// => listOf(false, false, true, false, ...)

Logging config

We recommend excluding logs below the INFO level for this library.

<Logger name="kairo.darb" level="info"/>