kotlinx-serialisation-kvon

KVON (or Kotlin Versioned Object Notation) is a made up serialisation format that's very close to JSON, but has implicit redundancy compression for collections of objects.

Huh?

Take the following simple example:

[
    {
        "identity": "test",
        "isTest": true
    },
    {
        "identity": "test",
        "isTest": false
    },
    {
        "identity": "test",
        "isTest": false
    },
    {
        "identity": "test",
        "question": "or is it?"
    }
]

There's a fair amount of duplication here; the 'identity' field is duplicated here across all four objects. However, encoding with KVON -

[
    {
        "identity": "test",
        "isTest": true
    },
    {
        "isTest": false
    },
    {
    },
    {
        "question": "or is it?",
        "isTest": ">\u0018<"
    }
]

KVON strips out the duplicated fields, bumping the file size down to ~70% of what it was.

When a field is removed from future objects, a special string is encoded to indicate that the property has been removed.

But wait, what about compression / msgpack?

Who's to say that compression doesn't stack with KVON? KVON doesn't perform compression on strings or the like, so there's still room to improve with compression.

Now in our simple example above, gz compression actually achieves a smaller file than KVON, even when using KVON + gz, however on larger files the gap starts to widen.

Using some test files from Blaseball -

=====[ Miami Dale vs. Ohio Worms ]=====
Normal JSON (ca251a6a2bc4e227b1a9984ca554695d)
    - 1.59 MB raw [100.0%]
    - 31.59 kB gz  [ 1.99%]

KVON (84d7c76694caf2c763c9e8b83aad17b8)
    - 99.88 kB raw [ 6.29%]
    - 9.46 kB gz  [  0.6%]

Normal JSON w/ MsgPack (d39e09905ffc1d3c4ddb9dc96ba3731d)
    - 1.42 MB raw [89.25%]
    - 31.66 kB gz  [  2.0%]

KVON w/ MsgPack (aed2ab395f899f3f47aa89e53babcad2)
    - 92.13 kB raw [ 5.81%]
    - 9.9 kB gz  [ 0.62%]

While using gz compression drops this file down to ~31 kB normally, coupling KVON with gz gets it down to only 9 kB, which is .6% of the original file size.

MsgPack gives smaller boosts here, but may still be worthwhile - any method of reducing the size of JSON should be fully compatible, since KVON is just a trimmer.

Woah, that's insane! How do I use it?

KVON provides a few different ways of utilising it:

• JsonElement#compressElementWithKvon and JsonElement#decompressElementWithKvon are manual methods that allow you to pass a previous value in, accommodating streaming data from a file or socket.
• Json#encodeToKvonString and Json#decodeFromKvonString, Json#encodeToKvonElement and Json#decodeFromKvonElement allow you to encode an object into KVON, or decode KVON into an object.
• Any place you would pass a serialiser, you can pass KvonSerialiser

Just add the dependency -

Gradle

repositories {
  maven { url "https://maven.brella.dev" }
}

dependencies {
  implementation "dev.brella:kotlinx-serialisation-kvon:1.0.0"
}