truncate-utf8-bytes 1.0.2: truncate string by maximum byte length safely without splitting multi-byte UTF-8 characters

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: truncate string by maximum byte length safely without splitting multi-byte UTF-8 characters
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/truncate-utf8-bytes@1.0.2
Demonstrate these symbols/APIs:
  - truncate-utf8-bytes

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:sha256:689741f302360525dd693202eabeaec08fc0146e950ab363a5eced682c17dc00","contract":["truncate returns the full string when byte length equals or exceeds string byte length","truncate cuts ASCII string at exact byte boundary","truncate safely cuts multi-byte UTF-8 characters without splitting code units","truncate safely handles 4-byte surrogate pair emojis without splitting surrogate units","truncate returns an empty string when max byte length is 0","truncate throws error when input is not a string"],"goal":"truncate string by maximum byte length safely without splitting multi-byte UTF-8 characters","kind":"HOW","packages":["pkg:npm/truncate-utf8-bytes@1.0.2"],"schemaVersion":1,"symbols":["truncate-utf8-bytes"]},"contractCommand":["node","test/contract.js"],"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/truncate-utf8-bytes@1.0.2"],"schemaVersion":1,"subject":"pkg:npm/truncate-utf8-bytes@1.0.2","symbols":["truncate-utf8-bytes"],"verifierAdapter":"node-typescript@1"}

'use strict';

const truncate = require('truncate-utf8-bytes');

/**
 * Truncate a UTF-8 string to a maximum number of bytes without breaking multi-byte characters.
 * @param {string} str - The input string to truncate.
 * @param {number} maxBytes - Maximum allowed bytes.
 * @returns {string} - Truncated string within maxBytes.
 */
function truncateUtf8(str, maxBytes) {
  return truncate(str, maxBytes);
}

module.exports = {
  truncateUtf8,
  truncate
};

{
  "name": "sample-truncate-utf8-bytes",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-truncate-utf8-bytes",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "truncate-utf8-bytes": "1.0.2"
      }
    },
    "node_modules/truncate-utf8-bytes": {
      "version": "1.0.2",
      "resolved": "https://registry.npmjs.org/truncate-utf8-bytes/-/truncate-utf8-bytes-1.0.2.tgz",
      "integrity": "sha512-95Pu1QXQvruGEhv62XCMO3Mm90GscOCClvrIUwCM0PYOXK3kaF3l3sIHxx71ThJfcbM2O5Au6SO3AWCSEfW4mQ==",
      "license": "WTFPL",
      "dependencies": {
        "utf8-byte-length": "^1.0.1"
      }
    },
    "node_modules/utf8-byte-length": {
      "version": "1.0.5",
      "resolved": "https://registry.npmjs.org/utf8-byte-length/-/utf8-byte-length-1.0.5.tgz",
      "integrity": "sha512-Xn0w3MtiQ6zoz2vFyUVruaCL53O/DwUvkEeOvj+uulMm0BkUGYWmBYVyElqZaSLhY6ZD0ulfU3aBra2aVT4xfA==",
      "license": "(WTFPL OR MIT)"
    }
  }
}

{
  "name": "sample-truncate-utf8-bytes",
  "version": "1.0.0",
  "description": "truncate string by maximum byte length safely without splitting multi-byte UTF-8 characters",
  "main": "index.js",
  "scripts": {
    "test": "node test/contract.js"
  },
  "dependencies": {
    "truncate-utf8-bytes": "1.0.2"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "truncate string by maximum byte length safely without splitting multi-byte UTF-8 characters",
  "kind": "HOW",
  "packages": [
    "pkg:npm/truncate-utf8-bytes@1.0.2"
  ],
  "symbols": [
    "truncate-utf8-bytes"
  ]
}

'use strict';

const assert = require('assert');
const truncate = require('truncate-utf8-bytes');
const { truncateUtf8 } = require('../index.js');

// 1. truncate returns the full string when byte length equals or exceeds string byte length
{
  const input = 'hello world';
  assert.strictEqual(truncate(input, 20), 'hello world');
  assert.strictEqual(truncate(input, 11), 'hello world');
  assert.strictEqual(truncateUtf8(input, 20), 'hello world');
}

// 2. truncate cuts ASCII string at exact byte boundary
{
  const input = 'hello world';
  assert.strictEqual(truncate(input, 5), 'hello');
  assert.strictEqual(truncate(input, 4), 'hell');
  assert.strictEqual(truncateUtf8(input, 5), 'hello');
}

// 3. truncate safely cuts multi-byte UTF-8 characters without splitting code units
{
  const input = '안녕하세요';
  assert.strictEqual(Buffer.byteLength(input, 'utf8'), 15);
  assert.strictEqual(truncate(input, 3), '안');
  assert.strictEqual(truncate(input, 4), '안');
  assert.strictEqual(truncate(input, 5), '안');
  assert.strictEqual(truncate(input, 6), '안녕');
  assert.strictEqual(truncate(input, 7), '안녕');
  assert.strictEqual(truncate(input, 8), '안녕');
  assert.strictEqual(truncate(input, 9), '안녕하');
  assert.strictEqual(truncateUtf8(input, 6), '안녕');
}

// 4. truncate safely handles 4-byte surrogate pair emojis without splitting surrogate units
{
  const input = '🐶🐱🐭';
  assert.strictEqual(Buffer.byteLength(input, 'utf8'), 12);
  assert.strictEqual(truncate(input, 3), '');
  assert.strictEqual(truncate(input, 4), '🐶');
  assert.strictEqual(truncate(input, 7), '🐶');
  assert.strictEqual(truncate(input, 8), '🐶🐱');
  assert.strictEqual(truncateUtf8(input, 8), '🐶🐱');
}

// 5. truncate returns an empty string when max byte length is 0
{
  assert.strictEqual(truncate('test', 0), '');
  assert.strictEqual(truncate('한글', 0), '');
  assert.strictEqual(truncateUtf8('test', 0), '');
}

// 6. truncate throws error when input is not a string
{
  assert.throws(() => {
    truncate(123, 5);
  }, /Input must be string/);

  assert.throws(() => {
    truncate(null, 5);
  }, /Input must be string/);
}

console.log('Contract tests passed successfully.');