ZSTD-KMP

The Zstandard compression library (zstd), packaged for Kotlin multiplatform (kmp).

This is intended to be a small library that supports common Zstandard use-cases with zero additional dependencies. For more advanced features, consider using zstd directly.

This library is packaged as two modules:

• zstd-kmp: direct access to Zstandard APIs.
• zstd-kmp-okio: Okio integration.

Usage with Okio

Gradle Setup

In gradle/libs.versions.toml:

[libraries]
okio-core = { module = "com.squareup.okio:okio", version = "3.15.0" }
zstd-kmp-okio = { module = "com.squareup.zstd:zstd-kmp-okio", version = "0.3.0" }

In build.gradle.kts:

kotlin {
  // ...
  sourceSets {
    val commonMain by getting {
      dependencies {
        implementation(libs.okio.core)
        implementation(libs.zstd.kmp.okio)
      }
    }
  }
}

Compressing a stream of data

Turn a Sink into a zstd-compressing sink with zstdCompress(). All data written to that sink will be compressed and forwarded on. Use buffer() to enable buffering for better performance and a more capable API.

Use flush() to force all data to be emitted immediately.

Be sure to call close() when you're done, both to emit the last frame and to release the native resources held by the zstd context. This example uses use() to call close() even if something throws an exception.

fun compressOneFile(fileSystem: FileSystem, path: Path) {
  val zstdPath = "$path.zst".toPath()
  fileSystem.source(path).use { fileSource ->
    fileSystem.sink(zstdPath).zstdCompress().buffer().use { zstdSink ->
      zstdSink.writeAll(fileSource)
    }
  }
}

Decompressing a stream of data

Turn a Source of zstd-compressed data into its original form with zstdDecompress().

Don't forget to close this source to release resources held by the zstd context. This example also uses use() to call close().

fun decompressOneFile(fileSystem: FileSystem, path: Path) {
  require(path.name.endsWith(".zst")) { "unexpected path: $path"}
  val filePath = path.toString().removeSuffix(".zst").toPath()
  fileSystem.source(path).zstdDecompress().use { zstdSource ->
    fileSystem.sink(filePath).buffer().use { fileSink ->
      fileSink.writeAll(zstdSource)
    }
  }
}

Supported Platforms

• Android (API 21+)
• JVM (JDK 11+)
• Kotlin/Native
  • linuxX64
  • macosX64
  • macosArm64
  • iosArm64
  • iosX64
  • iosSimulatorArm64
  • tvosArm64
  • tvosSimulatorArm64
  • tvosX64

Building

Git Submodules

git submodule init
git submodule update

Build JNI libraries

pushd zstd-kmp
zig build --verbose -p src/jvmMain/resources/jni
popd

Test it:

./gradlew \
  zstd-kmp:jvmTest \
  zstd-kmp-okio:jvmTest \
  zstd-kmp:macosArm64Test \
  zstd-kmp-okio:macosArm64Test

License

Copyright 2025 Square, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.