test/parallel/test-child-process-stdio-overlapped.js

// Test for "overlapped" stdio option. This test uses the "overlapped-checker"
// helper program which basically a specialized echo program.
//
// The test has two goals:
//
// - Verify that overlapped I/O works on windows. The test program will deadlock
//   if stdin doesn't have the FILE_FLAG_OVERLAPPED flag set on startup (see
//   test/overlapped-checker/main_win.c for more details).
// - Verify that "overlapped" stdio option works transparently as a pipe (on
//   unix/windows)
//
// This is how the test works:
//
// - This script assumes only numeric strings are written to the test program
//   stdout.
// - The test program will be spawned with "overlapped" set on stdin and "pipe"
//   set on stdout/stderr and at startup writes a number to its stdout
// - When this script receives some data, it will parse the number, add 50 and
//   write to the test program's stdin.
// - The test program will then echo the number back to us which will repeat the
//   cycle until the number reaches 200, at which point we send the "exit"
//   string, which causes the test program to exit.
// - Extra assertion: Every time the test program writes a string to its stdout,
//   it will write the number of bytes written to stderr.
// - If overlapped I/O is not setup correctly, this test is going to hang.
'use strict';
const common = require('../common');
const assert = require('assert');
const path = require('path');
const child_process = require('child_process');

const exeExtension = process.platform === 'win32' ? '.exe' : '';
const exe = 'overlapped-checker' + exeExtension;
const exePath = path.join(path.dirname(process.execPath), exe);

if (!require('fs').existsSync(exePath)) {
  common.skip(exe + ' binary is not available');
}

const child = child_process.spawn(exePath, [], {
  stdio: ['overlapped', 'pipe', 'pipe']
});

child.stdin.setEncoding('utf8');
child.stdout.setEncoding('utf8');
child.stderr.setEncoding('utf8');

function writeNext(n) {
  child.stdin.write((n + 50).toString());
}

child.stdout.on('data', (s) => {
  const n = Number(s);
  if (n >= 200) {
    child.stdin.write('exit');
    return;
  }
  writeNext(n);
});

let stderr = '';
child.stderr.on('data', (s) => {
  stderr += s;
});

child.stderr.on('end', common.mustCall(() => {
  // This is the sequence of numbers sent to us:
  // - 0 (1 byte written)
  // - 50 (2 bytes written)
  // - 100 (3 bytes written)
  // - 150 (3 bytes written)
  // - 200 (3 bytes written)
  assert.strictEqual(stderr, '12333');
}));

child.on('exit', common.mustCall((status) => {
  // The test program will return the number of writes as status code.
  assert.strictEqual(status, 0);
}));