write-file-atomic 4.0.2: atomically write file with writeFile and sync

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: atomically write file with writeFile and sync
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/write-file-atomic@4.0.2
Demonstrate these symbols/APIs:
  - writeFile
  - writeFile.sync

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:c5fad76b0aa51dac5fc106e5d77634f0370c96fe1bab69ee80e668c2792b3eea","contract":["writeFile writes string or buffer data to target path asynchronously returning a Promise","writeFile supports options including encoding and file mode when writing asynchronously","writeFile.sync atomically writes data to target path synchronously","writeFile.sync supports options including encoding and file mode when writing synchronously","sync named export provides synchronous atomic file writing identical to writeFile.sync","writeFile atomically overwrites existing file with new content without leaving partial state"],"goal":"atomically write file with writeFile and sync","kind":"HOW","packages":["pkg:npm/write-file-atomic@4.0.2"],"schemaVersion":1,"symbols":["writeFile","writeFile.sync"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/write-file-atomic@4.0.2"],"schemaVersion":1,"subject":"pkg:npm/write-file-atomic@4.0.2","symbols":["writeFile","writeFile.sync"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-write-file-atomic",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-write-file-atomic",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "write-file-atomic": "4.0.2"
      }
    },
    "node_modules/imurmurhash": {
      "version": "0.1.4",
      "resolved": "https://registry.npmjs.org/imurmurhash/-/imurmurhash-0.1.4.tgz",
      "integrity": "sha512-JmXMZ6wuvDmLiHEml9ykzqO6lwFbof0GG4IkcGaENdCRDDmMVnny7s5HsIgHCbaq0w2MyPhDqkhTUgS2LU2PHA==",
      "license": "MIT",
      "engines": {
        "node": ">=0.8.19"
      }
    },
    "node_modules/signal-exit": {
      "version": "3.0.7",
      "resolved": "https://registry.npmjs.org/signal-exit/-/signal-exit-3.0.7.tgz",
      "integrity": "sha512-wnD2ZE+l+SPC/uoS0vXeE9L1+0wuaMqKlfz9AMUo38JsyLSBWSFcHR1Rri62LZc12vLr1gb3jl7iwQhgwpAbGQ==",
      "license": "ISC"
    },
    "node_modules/write-file-atomic": {
      "version": "4.0.2",
      "resolved": "https://registry.npmjs.org/write-file-atomic/-/write-file-atomic-4.0.2.tgz",
      "integrity": "sha512-7KxauUdBmSdWnmpaGFg+ppNjKF8uNLry8LyzjauQDOVONfFLNKrKvQOxZ/VuTIcS/gge/YNahf5RIIQWTSarlg==",
      "license": "ISC",
      "dependencies": {
        "imurmurhash": "^0.1.4",
        "signal-exit": "^3.0.7"
      },
      "engines": {
        "node": "^12.13.0 || ^14.15.0 || >=16.0.0"
      }
    }
  }
}

{
  "name": "sample-write-file-atomic",
  "version": "1.0.0",
  "private": true,
  "description": "Clean-room code sample for write-file-atomic",
  "main": "src/index.js",
  "license": "MIT-0",
  "dependencies": {
    "write-file-atomic": "4.0.2"
  }
}

{
  "schemaVersion": 1,
  "goal": "atomically write file with writeFile and sync",
  "kind": "HOW",
  "packages": [
    "pkg:npm/write-file-atomic@4.0.2"
  ],
  "symbols": [
    "writeFile",
    "writeFile.sync"
  ]
}

const writeFile = require('write-file-atomic');

/**
 * Atomically writes data to a file asynchronously.
 *
 * @param {string} filename - Target file path.
 * @param {string|Buffer|Uint8Array} data - Data to write.
 * @param {object|string} [options] - Write options (e.g. encoding, mode).
 * @returns {Promise<void>} Resolves when write is complete.
 */
async function writeAtomic(filename, data, options) {
  return writeFile(filename, data, options);
}

/**
 * Atomically writes data to a file synchronously.
 *
 * @param {string} filename - Target file path.
 * @param {string|Buffer|Uint8Array} data - Data to write.
 * @param {object|string} [options] - Write options (e.g. encoding, mode).
 */
function writeAtomicSync(filename, data, options) {
  return writeFile.sync(filename, data, options);
}

module.exports = {
  writeFile,
  sync: writeFile.sync,
  writeAtomic,
  writeAtomicSync
};

import assert from 'node:assert/strict';
import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';
import { createRequire } from 'node:module';

const require = createRequire(import.meta.url);
const {
  writeFile,
  sync,
  writeAtomic,
  writeAtomicSync
} = require('../src/index.js');

async function runTests() {
  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'csx-write-file-atomic-test-'));

  try {
    // 1. writeFile writes string or buffer data to target path asynchronously returning a Promise
    const asyncFilePath = path.join(tmpDir, 'async-test.txt');
    const asyncPromise = writeFile(asyncFilePath, 'async file content');
    assert.ok(asyncPromise && typeof asyncPromise.then === 'function', 'writeFile must return a Promise');
    await asyncPromise;
    assert.equal(fs.readFileSync(asyncFilePath, 'utf8'), 'async file content');

    const bufferFilePath = path.join(tmpDir, 'async-buffer.bin');
    const bufferData = Buffer.from([0x68, 0x65, 0x6c, 0x6c, 0x6f]);
    await writeAtomic(bufferFilePath, bufferData);
    assert.deepEqual(fs.readFileSync(bufferFilePath), bufferData);

    // 2. writeFile supports options including encoding and file mode when writing asynchronously
    const modeFilePath = path.join(tmpDir, 'async-mode.txt');
    await writeFile(modeFilePath, 'custom mode content', { encoding: 'utf8', mode: 0o600 });
    assert.equal(fs.readFileSync(modeFilePath, 'utf8'), 'custom mode content');
    const statAsync = fs.statSync(modeFilePath);
    assert.equal(statAsync.mode & 0o777, 0o600);

    // 3. writeFile.sync atomically writes data to target path synchronously
    const syncFilePath = path.join(tmpDir, 'sync-test.txt');
    writeFile.sync(syncFilePath, 'sync file content');
    assert.equal(fs.readFileSync(syncFilePath, 'utf8'), 'sync file content');

    // 4. writeFile.sync supports options including encoding and file mode when writing synchronously
    const syncModeFilePath = path.join(tmpDir, 'sync-mode.txt');
    writeAtomicSync(syncModeFilePath, 'sync mode content', { encoding: 'utf8', mode: 0o600 });
    assert.equal(fs.readFileSync(syncModeFilePath, 'utf8'), 'sync mode content');
    const statSync = fs.statSync(syncModeFilePath);
    assert.equal(statSync.mode & 0o777, 0o600);

    // 5. sync named export provides synchronous atomic file writing identical to writeFile.sync
    assert.equal(typeof sync, 'function', 'sync export must be a function');
    assert.equal(sync, writeFile.sync, 'sync export must equal writeFile.sync');
    const syncNamedFilePath = path.join(tmpDir, 'sync-named.txt');
    sync(syncNamedFilePath, 'sync named export content');
    assert.equal(fs.readFileSync(syncNamedFilePath, 'utf8'), 'sync named export content');

    // 6. writeFile atomically overwrites existing file with new content without leaving partial state
    const overwriteFilePath = path.join(tmpDir, 'overwrite-test.txt');
    fs.writeFileSync(overwriteFilePath, 'initial content');
    assert.equal(fs.readFileSync(overwriteFilePath, 'utf8'), 'initial content');
    await writeFile(overwriteFilePath, 'overwritten atomic content');
    assert.equal(fs.readFileSync(overwriteFilePath, 'utf8'), 'overwritten atomic content');

    console.log('All contract assertions for write-file-atomic passed successfully.');
  } finally {
    fs.rmSync(tmpDir, { recursive: true, force: true });
  }
}

runTests().catch((err) => {
  console.error('Contract test failed:', err);
  process.exit(1);
});