Strathweb.Samples.DotnetWasi

📚 Blog post available here

Prerequisites

1. Install .NET 8 SDK (currently RC1 is the latest)
2. Install the .NET 8 WASI workload
   • dotnet workload install wasi-experimental
3. Download WASI SDK and extract. Then either
   • add WASI_SDK_PATH environment variables pointing to the extracted directory or,
   • you will need to set <WasiSdkRoot></WasiSdkRoot> MSBuild variable in your WASI projects - pointing to the extracted directory
4. Install the preferred WASM runtime/CLI runner. The recommended one is wasmtime
5. (optional) Download binaryen, extract and the extracted bin folder to the PATH. This allows using wasm-opt

Hello world

Basic demo of .NET 8 console application compiled for wasm-wasi. Steps to build:

cd src/WasiDemo
dotnet publish -c Release

Note that we run the publish workflow instead of a normal build, instead of a normal build because this is the only way to get trimming to kick in and reduce the size of the built app.

This can now be run:

wasmtime bin/Release/net8.0/wasi-wasm/AppBundle/WasiDemo.wasm

And it should print:

I'm alive in C#!

Alternatively, it's possible to further optimize the WASM file by first running wasm-opt:

wasm-opt -Oz --enable-bulk-memory bin/Release/net8.0/wasi-wasm/AppBundle/WasiDemo.wasm -o bin/Release/net8.0/wasi-wasm/AppBundle/WasiDemoOpt.wasm
wasmtime bin/Release/net8.0/wasi-wasm/AppBundle/WasiDemoOpt.wasm

The result should be a smaller WASM file.

Exporting a WASM function

Example of surfacing a .NET method as a WASM function. Steps to build:

cd src/WasiExport
dotnet publish -c Release

Instead of going through the WASM entrypoint (the _start() function, which points to Main() in C#).

wasmtime bin/Release/net8.0/wasi-wasm/AppBundle/WasiExport.wasm --invoke hello

Note that a C# Main method is still needed (even if empty) because it will boot the Mono runtime, and it will be internally called prior to our function execution. However, this is needed only once - and is tracked by a static state - so if we load the produced WASM file into another process, and continuously call our function, Main would only be called once on first invocation of our function.

The same optimizations as before can be done on this project too.