washm/washm.js

WASM shell: Bash inside WASM

#!/usr/bin/env -S node --no-warnings
// Suppress only the WASI ExperimentalWarning (keeps other warnings intact).
// This is intentionally minimal: wrap `process.emitWarning` and drop ExperimentalWarning messages that mention 'WASI'.
const _originalEmitWarning = process.emitWarning;
process.emitWarning = function(warning, ...args) {
  try {
    const name = (typeof args[0] === 'string' ? args[0] : (warning && warning.name)) || '';
    const message = typeof warning === 'string' ? warning : (warning && warning.message) || '';
    if ((name === 'ExperimentalWarning' || /ExperimentalWarning/.test(name)) && /WASI/.test(message)) return;
  } catch (e) { /* fall through to default behavior */ }
  return _originalEmitWarning.call(process, warning, ...args);
};

const fs = require('fs');
const { WASI } = require('wasi');
const argv = process.argv;

async function main() {
  const wasmPath = __dirname + '/washm.wasm';
  const wasmBuffer = fs.readFileSync(wasmPath);

  const wasi = new WASI({
    args: ['washm.js', ...argv.slice(2)],
    env: process.env,
    preopens: (function() {
      const preopens = { '/': '/' };
      if (process.platform !== 'win32') return preopens;
      const pathModule = require('path');
      const os = require('os');
      const cwdRoot = pathModule.parse(process.cwd()).root;
      const homeRoot = pathModule.parse(os.homedir()).root;
      [cwdRoot, homeRoot].filter(Boolean).forEach(r => {
        const rootPath = r.endsWith('\\') ? r : r + '\\';
        const letter = rootPath[0].toUpperCase();
        preopens[`/${letter}:/`] = rootPath;
      });
      return preopens;
    })(),
    version: 'preview1'
  });

  const wasiSnapshot = {};
  for (const key of Object.keys(wasi.wasiImport)) {
    wasiSnapshot[key] = function () {
      return wasiSnapshot[key].actual.apply(this, arguments);
    };
    wasiSnapshot[key].actual = wasi.wasiImport[key];
  }

  let collectEvalJS = "";
  let instance;
  const importObj = {
    wasi_snapshot_preview1: wasiSnapshot
  };

  // Special handling for bootstrap FD 20251219
  const origFdWrite = wasiSnapshot.fd_write.actual;
  wasiSnapshot.fd_write.actual = (fd, iovs, iovsLen, nwritten) => {
    if (fd === 20251219) {
      const memory = new Uint8Array(instance.exports.memory.buffer);
      const view = new DataView(memory.buffer);
      let total = 0;
      for (let i = 0; i < iovsLen; i++) {
        const ptr = view.getUint32(iovs + i * 8, true);
        const len = view.getUint32(iovs + i * 8 + 4, true);
        const chunk = memory.slice(ptr, ptr + len);
        collectEvalJS += new TextDecoder().decode(chunk);
        total += len;
      }
      view.setUint32(nwritten, total, true);
      return 0;
    }
    return origFdWrite(fd, iovs, iovsLen, nwritten);
  };

  const origFdClose = wasiSnapshot.fd_close.actual;
  wasiSnapshot.fd_close.actual = (fd) => {
    if (fd === 20251219) {
      const js = collectEvalJS;
      collectEvalJS = '';
      eval(js);
      return 0;
    }
    return origFdClose(fd);
  };

  const result = await WebAssembly.instantiate(wasmBuffer, importObj);
  instance = result.instance;

  globalThis.__washm_bootstrap = {
    wasi,
    importObj,
    wasiSnapshot,
    instance,
    require,
  };

  wasi.start(instance);
}

main();