compact-encoding 3.3.2: c.string

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: verify c.string in pkg:npm/compact-encoding@3.3.2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/compact-encoding@3.3.2
Demonstrate these symbols/APIs:
  - c.string

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:sha256:4617fbdc69794887bdf1f3cb15ab94abf44b8e4cf00274598f77c3b5819ca4ff","contract":["c.string is exported as a codec object with preencode, encode, decode, and fixed","c.string encodes and decodes standard UTF-8 strings","c.string handles empty strings correctly","c.string handles multi-byte unicode characters and emojis","c.string supports manual state preencoding, encoding, and decoding","c.string supports sequential encoding of multiple strings with state tracking","c.string.fixed creates a fixed-length string codec without length prefix","c.string throws an out of bounds error when decoding truncated buffers","c.string.fixed throws an out of bounds error when decoding insufficient byte buffers"],"goal":"verify c.string in pkg:npm/compact-encoding@3.3.2","kind":"HOW","packages":["pkg:npm/compact-encoding@3.3.2"],"schemaVersion":1,"symbols":["c.string"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/compact-encoding@3.3.2"],"schemaVersion":1,"subject":"pkg:npm/compact-encoding@3.3.2","symbols":["c.string"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-compact-encoding-string",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-compact-encoding-string",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "compact-encoding": "3.3.2"
      }
    },
    "node_modules/b4a": {
      "version": "1.8.1",
      "resolved": "https://registry.npmjs.org/b4a/-/b4a-1.8.1.tgz",
      "integrity": "sha512-aiqre1Nr0B/6DgE2N5vwTc+2/oQZ4Wh1t4NznYY4E00y8LCt6NqdRv81so00oo27D8MVKTpUa/MwUUtBLXCoDw==",
      "license": "Apache-2.0",
      "peerDependencies": {
        "react-native-b4a": "*"
      },
      "peerDependenciesMeta": {
        "react-native-b4a": {
          "optional": true
        }
      }
    },
    "node_modules/compact-encoding": {
      "version": "3.3.2",
      "resolved": "https://registry.npmjs.org/compact-encoding/-/compact-encoding-3.3.2.tgz",
      "integrity": "sha512-bgZ84oVSzjQmVHXBYWON+wQUkdVflrr8fM5+0X6UwQHZyzolsGIkdsjNK3vLLn22dhdASGFz5mS6Lf7rfrPdlg==",
      "license": "Apache-2.0",
      "dependencies": {
        "b4a": "^1.3.0"
      }
    }
  }
}

{
  "name": "sample-compact-encoding-string",
  "version": "1.0.0",
  "private": true,
  "description": "Clean-room verification of c.string in compact-encoding",
  "main": "src/index.js",
  "license": "MIT-0",
  "dependencies": {
    "compact-encoding": "3.3.2"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify c.string in pkg:npm/compact-encoding@3.3.2",
  "kind": "HOW",
  "packages": [
    "pkg:npm/compact-encoding@3.3.2"
  ],
  "symbols": [
    "c.string"
  ]
}

'use strict';

const c = require('compact-encoding');

/**
 * Encode a string using compact-encoding string codec.
 * @param {string} value - string to encode
 * @returns {Buffer|Uint8Array} encoded buffer
 */
function encodeString(value) {
  return c.encode(c.string, value);
}

/**
 * Decode a string from binary buffer using compact-encoding string codec.
 * @param {Buffer|Uint8Array} buffer - binary buffer to decode
 * @returns {string} decoded string
 */
function decodeString(buffer) {
  return c.decode(c.string, buffer);
}

/**
 * Create a fixed-length string codec.
 * @param {number} length - byte length of the string
 * @returns {object} codec
 */
function createFixedStringCodec(length) {
  return c.string.fixed(length);
}

module.exports = {
  c,
  compactEncoding: c,
  string: c.string,
  encodeString,
  decodeString,
  createFixedStringCodec
};

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

const require = createRequire(import.meta.url);
const {
  c,
  compactEncoding,
  string,
  encodeString,
  decodeString,
  createFixedStringCodec
} = require('../src/index.js');

// 1. c.string is exported as a codec object with preencode, encode, decode, and fixed
assert.equal(typeof string, 'object', 'string codec must be exported as an object');
assert.equal(typeof string.preencode, 'function', 'string.preencode must be a function');
assert.equal(typeof string.encode, 'function', 'string.encode must be a function');
assert.equal(typeof string.decode, 'function', 'string.decode must be a function');
assert.equal(typeof string.fixed, 'function', 'string.fixed must be a function');
assert.equal(typeof c.string, 'object', 'c.string must match exported string');
assert.equal(typeof encodeString, 'function', 'encodeString helper must be a function');
assert.equal(typeof decodeString, 'function', 'decodeString helper must be a function');
assert.equal(typeof createFixedStringCodec, 'function', 'createFixedStringCodec helper must be a function');

// 2. c.string encodes and decodes standard UTF-8 strings
{
  const expected = 'Hello, CodeSampleX clean-room verification!';
  const encoded = encodeString(expected);
  const decoded = decodeString(encoded);
  assert.equal(decoded, expected, 'Decoded string must match original standard ASCII/UTF-8 string');
}

// 3. c.string handles empty strings correctly
{
  const empty = '';
  const encoded = encodeString(empty);
  assert.equal(encoded.length, 1, 'Empty string should encode to a single length prefix byte (0)');
  const decoded = decodeString(encoded);
  assert.equal(decoded, empty, 'Decoded empty string must match empty string');
}

// 4. c.string handles multi-byte unicode characters and emojis
{
  const unicodeText = 'Hello 🌍 세계 🚀 Привет 🦔';
  const encoded = encodeString(unicodeText);
  const decoded = decodeString(encoded);
  assert.equal(decoded, unicodeText, 'Decoded string must match unicode string with emojis');
}

// 5. c.string supports manual state preencoding, encoding, and decoding
{
  const text = 'state-based manual buffer encoding';
  const state = c.state();
  string.preencode(state, text);
  assert.ok(state.end > 0, 'State end pointer must advance after preencode');
  state.buffer = Buffer.allocUnsafe(state.end);
  string.encode(state, text);
  assert.equal(state.start, state.end, 'State start pointer must equal end pointer after encoding');
  state.start = 0;
  const decoded = string.decode(state);
  assert.equal(decoded, text, 'Decoded string from manual state must match original');
}

// 6. c.string supports sequential encoding of multiple strings with state tracking
{
  const state = c.state();
  const first = 'first segment';
  const second = 'second segment';
  string.preencode(state, first);
  string.preencode(state, second);
  state.buffer = Buffer.allocUnsafe(state.end);
  string.encode(state, first);
  string.encode(state, second);
  state.start = 0;
  const decodedFirst = string.decode(state);
  const decodedSecond = string.decode(state);
  assert.equal(decodedFirst, first, 'First sequentially decoded string must match');
  assert.equal(decodedSecond, second, 'Second sequentially decoded string must match');
  assert.equal(state.start, state.end, 'State start pointer must reach end after sequential decoding');
}

// 7. c.string.fixed creates a fixed-length string codec without length prefix
{
  const fixedLen = 11;
  const fixedCodec = createFixedStringCodec(fixedLen);
  assert.equal(typeof fixedCodec.preencode, 'function', 'fixedCodec.preencode must be a function');
  assert.equal(typeof fixedCodec.encode, 'function', 'fixedCodec.encode must be a function');
  assert.equal(typeof fixedCodec.decode, 'function', 'fixedCodec.decode must be a function');

  const text = 'fixedlength';
  const encoded = c.encode(fixedCodec, text);
  assert.equal(encoded.length, fixedLen, 'Fixed string encoding must not include a length prefix byte');
  const decoded = c.decode(fixedCodec, encoded);
  assert.equal(decoded, text, 'Decoded fixed-length string must match original');
}

// 8. c.string throws an out of bounds error when decoding truncated buffers
{
  const truncated = Buffer.from([10, 0x41]);
  assert.throws(
    () => decodeString(truncated),
    /Out of bounds/,
    'c.string must throw Out of bounds error on truncated buffer'
  );
}

// 9. c.string.fixed throws an out of bounds error when decoding insufficient byte buffers
{
  const fixedCodec = createFixedStringCodec(10);
  const truncated = Buffer.from([0x41, 0x42, 0x43]);
  assert.throws(
    () => c.decode(fixedCodec, truncated),
    /Out of bounds/,
    'c.string.fixed must throw Out of bounds error on buffer shorter than fixed length'
  );
}

console.log('Contract assertions passed.');