node/test/wasi/test-wasi-stdio.js

// Flags: --experimental-wasi-unstable-preview1 --experimental-wasm-bigint
'use strict';
require('../common');
const tmpdir = require('../common/tmpdir');
const { strictEqual } = require('assert');
const { closeSync, openSync, readFileSync, writeFileSync } = require('fs');
const { join } = require('path');
const { WASI } = require('wasi');
const modulePath = join(__dirname, 'wasm', 'stdin.wasm');
const buffer = readFileSync(modulePath);
const stdinFile = join(tmpdir.path, 'stdin.txt');
const stdoutFile = join(tmpdir.path, 'stdout.txt');
const stderrFile = join(tmpdir.path, 'stderr.txt');

tmpdir.refresh();
// Write 33 x's. The test's buffer only holds 31 x's + a terminator.
writeFileSync(stdinFile, 'x'.repeat(33));

const stdin = openSync(stdinFile, 'r');
const stdout = openSync(stdoutFile, 'a');
const stderr = openSync(stderrFile, 'a');
const wasi = new WASI({ stdin, stdout, stderr, returnOnExit: true });
const importObject = { wasi_snapshot_preview1: wasi.wasiImport };

(async () => {
  const { instance } = await WebAssembly.instantiate(buffer, importObject);

  strictEqual(wasi.start(instance), 0);
  closeSync(stdin);
  closeSync(stdout);
  closeSync(stderr);
  strictEqual(readFileSync(stdoutFile, 'utf8').trim(), 'x'.repeat(31));
  strictEqual(readFileSync(stderrFile, 'utf8').trim(), '');
})();