knbt

An implementation of Minecraft's NBT format for kotlinx.serialization.

Technical information about NBT can be found here.

Features

• Kotlin Multiplatform: JVM, JS, Linux, Windows, macOS, iOS, watchOS
• Serialize any data to/from NBT or SNBT
• Support for all NBT variants: Java, Bedrock Files, Bedrock Network
• Support for all NBT compressions: gzip, zlib
• Type-safe NbtTag classes, with convenient builder DSLs

Serialization

Nbt and StringifiedNbt are used to encode/decode @Serializable data.

Configuration

import net.benwoodworth.knbt.*

val nbt = Nbt {
    variant = NbtVariant. // Java, Bedrock, BedrockNetwork
    compression = NbtCompression. // None, Gzip, Zlib
    //compressionLevel = null // in 0..9
    //encodeDefaults = false
    //ignoreUnknownKeys = false
    //serializersModule = EmptySerializersModule
}

val snbt = StringifiedNbt {
    //prettyPrint = false
    //prettyPrintIndent = "    "
    //encodeDefaults = false
    //ignoreUnknownKeys = false
    //serializersModule = EmptySerializersModule
}

Encoding and Decoding

// ByteArray
byteArray = nbt.encodeToByteArray(data)
data = nbt.decodeFromByteArray(byteArray)

// NbtTag
nbtTag = nbt.encodeToNbtTag(data)
data = nbt.decodeFromNbtTag(nbtTag)

// Okio Sink/Source (Multiplatform)
nbt.encodeToSink(data, sink)
data = nbt.decodeFromSource(source)

// OutputStream/InputStream (JVM)
nbt.encodeToStream(data, outputStream)
data = nbt.decodeFromStream(inputStream)

// SNBT String
string = snbt.encodeToString(data)
data = snbt.decodeFromString(string)

Serializing Classes

Serializable classes will have their @SerialName used for the root tag's name.

@Serializable
@SerialName("root")
class Example(val string: String, val int: Int)

// Serializes to: {root : {string : "Hello, world!", int : 42}}
nbt.encodeToNbtTag(Example(string = "Hello, World!", int = 42))

Reading/Writing NBT Files (JVM)

import kotlin.io.path.*
import net.benwoodworth.knbt.*

val file = Path("file.nbt")

val nbt = Nbt {
    TODO()
}

// Read from file
val tag: NbtTag = file.inputStream().use { input ->
    nbt.decodeFromStream(input)
}

// Write to file
file.outputStream().use { output ->
    nbt.encodeToStream(tag, output)
}

NbtTag Classes

sealed interface NbtTag

class NbtByte : NbtTag
class NbtShort : NbtTag
class NbtInt : NbtTag
class NbtLong : NbtTag
class NbtFloat : NbtTag
class NbtDouble : NbtTag
class NbtString : NbtTag
class NbtByteArray : NbtTag, List<Byte>
class NbtIntArray : NbtTag, List<Int>
class NbtLongArray : NbtTag, List<Long>
class NbtList<T : NbtTag> : NbtTag, List<T> // Only contains entries of a single type
class NbtCompound : NbtTag, Map<String, NbtTag>

Creating NbtTags

NbtTags can be created with constructors and builder functions:

val nbtByte = NbtByte(5)
val boolean = NbtByte(true)

val nbtIntArray = NbtIntArray(intArrayOf(1, 2, 3, 4, 5))

val nbtListOfStrings = buildNbtList {
    add("these")
    add("are")
    add("strings")
}

val nbtCompound = buildNbtCompound {
    put("int", 1)
    put("string", ":)")
    put("byteArray", byteArrayOf(1, 1, 2, 3, 5, 8))

    putNbtList("floatList") {
        add(3f)
        add(1f)
        add(4f)
    }
}

Building bigtest.nbt with the DSL (wiki.vg/NBT#bigtest.nbt)

val bigtest = buildNbtCompound("Level") {
    put("longTest", 9223372036854775807L)
    put("shortTest", 32767.toShort())
    put("stringTest", "HELLO WORLD THIS IS A TEST STRING ÅÄÖ!")
    put("floatTest", 0.49823147f)
    put("intTest", 2147483647)
    putNbtCompound("nested compound test") {
        putNbtCompound("ham") {
            put("name", "Hampus")
            put("value", 0.75f)
        }
        putNbtCompound("egg") {
            put("name", "Eggbert")
            put("value", 0.5f)
        }
    }
    putNbtList("listTest (long)") {
        add(11L)
        add(12L)
        add(13L)
        add(14L)
        add(15L)
    }
    putNbtList("listTest (compound)") {
        addNbtCompound {
            put("name", "Compound tag #0")
            put("created-on", 1264099775885L)
        }
        addNbtCompound {
            put("name", "Compound tag #1")
            put("created-on", 1264099775885L)
        }
    }
    put("byteTest", 127.toByte())
    put(
        "byteArrayTest (the first 1000 values of (n*n*255+n*7)%100, starting with n=0 (0, 62, 34, 16, 8, ...))",
        ByteArray(1000) { n -> ((n * n * 255 + n * 7) % 100).toByte() }
    )
    put("doubleTest", 0.4931287132182315)
}

Setup

Using the same version of kotlinx.serialization is recommended since parts of its API required for custom formats are still experimental, and newer versions may have binary-incompatible changes that could break knbt's implementation.

Upgrading knbt

While in beta, all new minor releases (v0.#.0) will have breaking API/functionality changes. Read the release notes for information.

Replacement refactorings will be provided where possible for broken APIs. Change the minor version one at a time (e.g. 0.1.0 -> 0.2.0 -> 0.3.0) and apply quick fixes. Deprecated APIs will then be removed in 0.#.1 releases.

Gradle

plugins {
    kotlin("jvm") version "1.9.23" // or kotlin("multiplatform"), etc.
    //kotlin("plugin.serialization") version "1.9.23"
}

repositories {
    mavenCentral()
    //maven("https://s01.oss.sonatype.org/content/repositories/snapshots/")
}

dependencies {
    implementation("net.benwoodworth.knbt:knbt:$knbt_version")
    //implementation("com.squareup.okio:okio:3.9.0")
}