Move WASM to CoreCLR to unlock more platfroms?

[universorum]

Cloudflare Workers is a hugely popular serverless platform that supports WebAssembly. Today, you can use it to run Hono for path-based request routing, and even execute Rust code compiled to Wasm via the wasm32-unknown-unknown toolchain.

Currently, the only way to run a .NET application on Cloudflare is through containers, which are expensive. If ASP.NET Core could run in Wasm, we could deploy it to Cloudflare Workers without needing a container at all.

However, in .NET 11 Preview 7, attempting to compile an ASP.NET Core Minimal API project for WASM produces the following error: NETSDK1082: There was no runtime pack for Microsoft.AspNetCore.App available for the specified RuntimeIdentifier 'browser-wasm'.

I guess thet is because WASM is using mono, not CoreCLR. Starting .NET 11, WASM is only Microsft supported platform using mono (Unity is not supported by Microsoft and is will be supported s∞n in Unity 6.6(preview)/6.7).

I guess this is because the Wasm runtime uses Mono, not CoreCLR. Starting with .NET 11, Wasm is the only Microsoft-supported platform still running on Mono. (Unity is not supported by Microsoft directly, and it will add .NET support s∞n in Unity 6.6 (preview) or 6.7).

var builder = WebApplication.CreateSlimBuilder(args);
// AOT builder setup

var app = builder.Build();
// Mapping minimal API

var handler = ((IApplicationBuilder)_webApplication).Build();

[JSExport]
static async Task<HttpResponse> HandleAsync(HttpRequest request)
{
  await using var scope = app.Services.CreateAsyncScope();
  var context = new DefaultHttpContext
  {
      RequestServices = scope.ServiceProvider,
      Request = request,
      // {
      //     Method        = HttpMethods.Phst,
      //     Path          = "/echo",
      //     ContentType   = "application/json",
      //     ContentLength = requestStream.Length,
      //     Body          = requestStream
      // },
      Response = { Body = new MemoryStream() }
  };
  
  await pipeline(context);
  
  return context.Response;
}

import { dotnet } from './_framework/dotnet.js'

const { getAssemblyExports, getConfig, runMain } = await dotnet
    .withApplicationArguments("start") // these are the args passed to the program
    .create();

const config = getConfig();

const exports = await getAssemblyExports(config.mainAssemblyName);

export default {
	async fetch(request, env, ctx) {
		return await exports.AspNetCore.handleAsync(request);
	},
};

[Suchiman]

In .NET 11, you can use <UseMonoRuntime>false</UseMonoRuntime> to use CoreCLR with WASM.
The real issue here is that WASM is a sandboxed environment without access to the outer world by default.
In order to receive web requests you need a custom server that receives requests through the cloudflare worker APIs and then channels it through the ASP.NET Core pipeline.

[huoyaoyuan]

wasm on coreclr is still WIP. As announced before it won't come together with mobile platforms in .NET 11. The current ETA is .NET 12.