wasmtime-dotnet

.NET embedding of Wasmtime

A Bytecode Alliance project

Installation

You can add a package reference with the .NET SDK:

$ dotnet add package wasmtime

Introduction

For this introduction, we'll be using a simple WebAssembly module that imports a hello function and exports a run function:

(module
  (func $hello (import "" "hello"))
  (func (export "run") (call $hello))
)

To use this module from .NET, create a new console project:

$ mkdir wasmintro
$ cd wasmintro
$ dotnet new console

Next, add a reference to the Wasmtime package:

$ dotnet add package wasmtime

Replace the contents of Program.cs with the following code:

using System;
using Wasmtime;

using var engine = new Engine();

using var module = Module.FromText(
    engine,
    "hello",
    "(module (func $hello (import \"\" \"hello\")) (func (export \"run\") (call $hello)))"
);

using var linker = new Linker(engine);
using var store = new Store(engine);

linker.Define(
    "",
    "hello",
    Function.FromCallback(store, () => Console.WriteLine("Hello from C#!"))
);

var instance = linker.Instantiate(store, module);
var run = instance.GetAction("run")!;
run();

An Engine is created and then a WebAssembly module is loaded from a string in WebAssembly text format.

A Linker defines a function called hello that simply prints a hello message.

The module is instantiated and the instance's run export is invoked.

To run the application, simply use dotnet:

$ dotnet run

This should print Hello from C#!.

Contributing

Building

Use dotnet to build the repository:

$ dotnet build Wasmtime.sln

This will download the latest development snapshot of Wasmtime for your platform.

Testing

Use dotnet to run the unit tests:

$ dotnet test Wasmtime.sln

Creating the NuGet package

Use dotnet to create a NuGet package:

$ cd src
$ dotnet pack Wasmtime.sln -c Release /p:Packing=true

This will create a .nupkg file in src/bin/Release.

By default, local builds will use a -dev suffix for the package to differentiate between official packages and development packages.

Updating Wasmtime for a release

To update the Wasmtime library used for a new release, change WasmtimeVersion in Directory.Build.props:

<WasmtimeVersion Condition="'$(WasmtimeVersion)'==''">$VERSION</WasmtimeVersion>

Additionally, edit Wasmtime.csproj to change the PackageReleaseNotes to the new version:

<PackageReleaseNotes>Update Wasmtime to $VERSION.</PackageReleaseNotes>

Publishing the Wasmtime .NET NuGet package

GitHub actions is used to automatically publish a package to NuGet when a tag is pushed to the repository.

To publish a new release, create a release in GitHub and add the relevant release notes.

Use a tag of the format v$VERSION where $VERSION matches the Wasmtime version used by the .NET package; ensure the tagged commit matches the last commit to make for the release.

When the release is published on GitHub, an action should automatically start to build and publish the package to NuGet.