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Wasmline

A Kotlin Multiplatform plugin framework powered by Wasmtime, enabling WebAssembly (WASI) plugin loading, packaging, and execution across Android, iOS, Desktop (macOS / Windows / Linux), and, in the future, Web.

Plugins can be developed in any language that compiles to WASI — Kotlin, Rust, C/C++, Go, AssemblyScript, and more.

Platform Support

Platform	Architecture	Runtime	Status
Android	arm64-v8a	Wasmtime (JNI)	✅ Supported
iOS	arm64	Wasmtime (C Interop)	✅ Supported
macOS	arm64	Wasmtime (JNI/Zig)	✅ Supported
Linux	x86_64	Wasmtime (JNI/Zig)	✅ Supported
Windows	x86_64	Wasmtime (JNI/Zig)	✅ Supported
Web	wasm32-wasi	Kotlin/Wasi	🚧 Planned

Architecture

Wasmline architecture overview

Module Structure

wasmline-multiplatform/
├── wasmline/              # Core runtime — WASM module loading & execution
├── wasmline-loader/       # Crypto & manifest — Ed25519/ECDSA-P256 signing, manifest serialization
├── wasmline-cli/          # CLI toolchain — build, compile, manifest, download, key generation
├── wasmline-android/      # Android native bindings (CMake / JNI C++)
├── wasmline-kotlin-plugin/# Kotlin compiler plugin — IR-oriented typed glue generation
├── wasmline-gradle-plugin/# Gradle integration for the Kotlin plugin and tooling
├── wasmline-sample/       # Sample applications (plugin, Android, Desktop, Multiplatform Compose)
└── wasmline-build-logic/  # Shared Gradle convention plugins

Dependency flow: wasmline-cli → wasmline-loader → wasmline (core)

Key Technologies

• Kotlin Multiplatform with custom source set hierarchy
• Wasmtime 41.0.1 as the underlying WASM runtime
• kotlinx.serialization for JSON and Protobuf payloads
• Ed25519 / ECDSA-P256 for manifest signing and verification
• Clikt for the CLI experience
• AOT compilation — .wasm → .cwasm / .pwasm
• Kotlin compiler plugin (IR phase one) for generated Definition / Proxy / Adapter glue

Getting Started

Prerequisites

• Java 21 or later for general builds; use JBR 21 for Gradle tasks covered by ./.github/skills/wasmline/scripts/skill_preflight.sh (especially Compose Desktop / desktop samples)
• Zig 0.15.1 (for native library builds)
• a locally prepared Wasmtime toolchain when building AOT artifacts

Initialization

Initialize the required platform assets (pick one — all three are equivalent):

sh ./scripts/init.sh            # Bash (requires curl + tar/unzip)
python3 ./scripts/init.py       # Python 3.9+ (no third-party deps)
node ./scripts/init.mjs         # Node.js 18+ (no third-party deps)

Build

All Gradle commands run from the wasmline-multiplatform/ directory:

Before running Gradle, verify the current shell with:

bash ./.github/skills/wasmline/scripts/skill_preflight.sh

cd wasmline-multiplatform

# Build everything
./gradlew build

# Run loader tests (manifest, crypto, verification, etc.)
./gradlew :wasmline-loader:jvmTest

# Run CLI tests
./gradlew :wasmline-cli:test

# Compile the WASM plugin sample
./gradlew :wasmline-sample:plugin:compileProductionLibraryKotlinWasmWasiOptimize

# Run compiler-plugin IR box tests
./gradlew :wasmline-kotlin-plugin:test --tests 'crow.wasmline.kotlin.runners.JvmBoxTestGenerated'

Native (Zig) Build

Outputs JNI native libraries for the host platform:

cd wasmline-multiplatform/wasmline

zig build --release=small -p src/jvmMain/resources
zig build -p src/jvmMain/resources

CLI Toolchain

Wasmline provides a CLI for the full plugin build pipeline. All commands run through Gradle:

cd wasmline-multiplatform
./gradlew :wasmline-cli:run --args="<command> [options]"

Command	Description
download	Download Wasmtime releases for target platforms
generate-key-pair	Generate signing key pairs
compile	Compile .wasm to AOT artifacts (.cwasm / .pwasm)
manifest	Generate a signed manifest (.wlm) from compile output
build	Full pipeline: compile → manifest → zip packaging

Example: Full Build Pipeline

cd wasmline-multiplatform

# 1. Download Wasmtime
./gradlew :wasmline-cli:run --args="download -v v41.0.1"

# 2. Generate signing keys
./gradlew :wasmline-cli:run --args="generate-key-pair --save"

# 3. Build plugin (compile → sign → package)
./gradlew :wasmline-cli:run --args="build -i plugin.wasm -wt build/wasmline/wasmtime/wasmtime-v41.0.1-aarch64-macos --key build/wasmline/keys/ed25519_private.key"

Build Output

build/wasmline/
├── output/{name}-{version}/
│   ├── manifest.wlm                # Signed manifest (Protobuf)
│   ├── {name}-pulley64.pwasm       # Pulley portable bytecode
│   ├── {name}-aarch64-android.cwasm
│   ├── {name}-aarch64-macos.cwasm
│   ├── {name}-aarch64-ios.cwasm
│   ├── {name}-x86_64-linux.cwasm
│   ├── {name}-x86_64-windows.cwasm
│   └── debug/
│       ├── compile-result.json
│       └── manifest.json           # Human-readable manifest
├── dist/
│   └── {name}-{version}.zip        # Distributable package
└── keys/
    ├── ed25519_private.key
    └── ed25519_public.key

See wasmline-multiplatform/wasmline-cli for command-level documentation.

Samples

Android sample

Compose Desktop (macOS)

Sample code lives in wasmline-multiplatform/wasmline-sample, including:

• a WASI plugin sample
• Android host sample
• desktop sample
• multiplatform shared sample

Kotlin/Wasi Compatibility

Kotlin/Wasi runtime support status

Wasmline currently expects Kotlin 2.3.20-Beta1 or later for reliable Kotlin/Wasi support. Earlier versions or different runtimes may fail or miss required Wasm features such as GC, function references, and exception handling.

For Developers

If you are working on Wasmline itself, the most useful entry points are:

• wasmline-core — native Wasmtime bridge
• wasmline-multiplatform/wasmline — runtime SPI and public API
• wasmline-multiplatform/wasmline-kotlin-plugin — Kotlin compiler plugin
• wasmline-multiplatform/wasmline-kotlin-plugin/testData/box/README_en.md — IR box testData guide
• .github/skills/wasmline/SKILL.md — repository workflow, preflight, and module routing guide
• .github/plans/ir-planv2.md — current IR / runtime / platform V2 plan and implementation notes

Resources

• wasm-kotlin-exploration — Wasm + Kotlin research and test cases
• Wasmtime on Android (JNI) — Embedding Wasmtime on Android via JNI
• Wasm vs. Wasi Deep Dive — Differences between Wasm and Wasi, and their lifecycles

License

See LICENSE for details.