Lesson 32 of 40 Advanced Topics Expert 45 min

WebAssembly with WASI

Compile .NET applications to WASI WebAssembly for portable, sandboxed execution outside the browser on servers, edge nodes, and IoT.

Part 1: WASI Overview

WASI (WebAssembly System Interface) lets .NET run as WASM outside browsers. Use cases:

Serverless functions on Fastly/Cloudflare Workers
Plugin systems with sandboxed execution
Portable CLI tools
Edge computing

Part 2: Publishing to WASI

<!-- .csproj -->
<RuntimeIdentifier>wasi-wasm</RuntimeIdentifier>
<PublishSingleFile>true</PublishSingleFile>

# Publish
dotnet publish -c Release
# Run with wasmtime:
wasmtime ./bin/Release/wasi-wasm/MyApp.wasm

Part 3: Component Model

The WASM Component Model enables type-safe interop between languages. Define interfaces in WIT (WebAssembly Interface Types):

// orders.wit
interface orders {
  record order { id: u32, total: f64 }
  get-order: func(id: u32) -> order;
}

Part 4: Wasmtime in .NET Host

var engine = new Engine();
var module = Module.FromFile(engine, "plugin.wasm");
var store = new Store(engine);
var instance = Instance.NewStore(store, module);

// Call exported WASM function safely from .NET