WACS.WASI.Preview1 0.13.1

WACS.WASI.Preview1

A C# implementation of WASI Preview 1 for the WACS WebAssembly Interpreter. Supersedes the deprecated WACS.WASIp1 package — see docs/MIGRATION_WASIp1_to_WASI.md for a one-shot sed migration.

Installation

Add the package from NuGet:

dotnet add package WACS.WASI.Preview1

Usage example

Bind WASI Preview 1 to a WasmRuntime:

using System;
using System.IO;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using Wacs.Core;
using Wacs.Core.Runtime;
using Wacs.Core.WASIp1; // IBindable, ErrNo, SystemExitException, SignalException
using Wacs.WASI.Preview1; // Wasi, WasiConfiguration
using Wacs.WASI.Preview1.Types; // FdFlags, etc.

var runtime = new WasmRuntime();
var wasiConfig = new WasiConfiguration
{
 StandardInput = Console.OpenStandardInput(),
 StandardOutput = Console.OpenStandardOutput(),
 StandardError = Console.OpenStandardError(),

 Arguments = Environment.GetCommandLineArgs()
 .Skip(1)
 .ToList(),

 EnvironmentVariables = Environment.GetEnvironmentVariables()
 .Cast<DictionaryEntry>()
 .ToDictionary(de => de.Key.ToString()!, de => de.Value?.ToString() ?? ""),

 HostRootDirectory = Directory.GetCurrentDirectory(),
};
var wasi = new Wasi(wasiConfig);
wasi.BindToRuntime(runtime);

using var fileStream = new FileStream("module.wasm", FileMode.Open);
var module = BinaryModuleParser.ParseWasm(fileStream);
var modInst = runtime.InstantiateModule(module);
runtime.RegisterModule("mymodule", modInst);

if (runtime.TryGetExportedFunction(("mymodule", "main"), out var mainAddr))
{
 try
 {
 var mainInvoker = runtime.CreateInvoker<Func<Value>>(mainAddr);
 int result = mainInvoker();
 Console.Error.WriteLine($"mymodule.main() => {result}");
 }
 catch (TrapException exc)
 {
 Console.Error.WriteLine(exc);
 return 1;
 }
 catch (SignalException exc)
 {
 Console.Error.WriteLine(exc.HumanReadable);
 return exc.Signal;
 }
}

The split between Wacs.Core.WASIp1 (interpreter wiring — IBindable, ErrNo, exceptions) and Wacs.WASI.Preview1 (host implementation — Wasi, WasiConfiguration) is intentional. Migrating from WACS.WASIp1 only changes the second using; the Wacs.Core.WASIp1 namespace stays.

Capability flags

WasiConfiguration exposes a few opt-in capability gates beyond the filesystem preopens:

Network sockets

WASI Preview 1's socket surface is intentionally narrow: there is no sock_open / sock_bind / sock_listen. Listening sockets are handed in by the embedder as preopens (the same model wasmtime serve uses for HTTP), and sock_accept mints connection fds from them.

using System.Net;
using System.Net.Sockets;
using Wacs.WASI.Preview1;
using Wacs.WASI.Preview1.Types;

var listener = new Socket(AddressFamily.InterNetwork,
 SocketType.Stream, ProtocolType.Tcp);
listener.Bind(new IPEndPoint(IPAddress.Loopback, 0));
listener.Listen(8);

var wasiConfig = new WasiConfiguration
{
 HostRootDirectory = Directory.GetCurrentDirectory(),
 AllowNetworkSockets = true,
 PreopenedSockets = { (listener, FdFlags.NonBlock) },
};

The guest's accept(3) on fd 3 (after stdio at 0/1/2) will produce a working TCP connection. Two layers of explicit consent before any network egress: the flag must be on AND the embedder must have already constructed and bound the Socket.

Conformance

Tested continuously against the official WebAssembly/wasi-testsuite fixtures via Wacs.WASI.Preview1.Test. The harness reads each test's *.json manifest, runs the wasm under WACS with the prescribed preopens / args / env, and asserts on exit code + stdout + stderr. The test project's skip.json documents which conformance fixtures are deliberately not yet asserting (each entry carries a reason).

License

WACS is distributed under the Apache 2.0 License, allowing usage in both open-source and commercial projects.