fflate 0.8.3: deflateSync

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 fflate.deflateSync in pkg:npm/fflate@0.8.3
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/fflate@0.8.3
Demonstrate these symbols/APIs:
  - fflate.deflateSync

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:sha256:611129870eff3f0c84c202cb21b74a27498ed0be8fa074358a2e5f77b2e5bd67","constraints":{"executionContext":"node"},"contract":["assert deflateSync compresses a Uint8Array and returns a Uint8Array","assert deflateSync produces valid DEFLATE output decompressible by inflateSync","assert deflateSync respects compression level options","assert deflateSync handles empty input and produces valid DEFLATE stream","assert deflateSync compresses repetitive data into significantly smaller output"],"goal":"verify fflate.deflateSync in pkg:npm/fflate@0.8.3","kind":"HOW","packages":["pkg:npm/fflate@0.8.3"],"schemaVersion":1,"symbols":["fflate.deflateSync"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"esm","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/fflate@0.8.3"],"schemaVersion":1,"subject":"pkg:npm/fflate@0.8.3","symbols":["fflate.deflateSync"],"verifierAdapter":"node-typescript@1"}

import { deflateSync, inflateSync } from 'fflate';

/**
 * Compresses data synchronously using raw DEFLATE format.
 *
 * @param {Uint8Array} data - The uncompressed input bytes.
 * @param {object} [opts] - Compression options (e.g. { level, mem }).
 * @returns {Uint8Array} The compressed DEFLATE bytes.
 */
export function compressDataSync(data, opts) {
  return deflateSync(data, opts);
}

/**
 * Decompresses raw DEFLATE data synchronously.
 *
 * @param {Uint8Array} data - The compressed DEFLATE bytes.
 * @param {object} [opts] - Decompression options.
 * @returns {Uint8Array} The decompressed bytes.
 */
export function decompressDataSync(data, opts) {
  return inflateSync(data, opts);
}

export { deflateSync, inflateSync };
export default deflateSync;

{
  "name": "sample-fflate-deflatesync",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-fflate-deflatesync",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "fflate": "0.8.3"
      }
    },
    "node_modules/fflate": {
      "version": "0.8.3",
      "resolved": "https://registry.npmjs.org/fflate/-/fflate-0.8.3.tgz",
      "integrity": "sha512-tbZNuJrLwGUp3zshBtdy4W+ORxZuIh8a5ilyIEQDC5rY1f3U20JMry0Ll3WBzU58EZKsEuJFXhb5gwv8CsPvgA==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-fflate-deflatesync",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "license": "MIT-0",
  "dependencies": {
    "fflate": "0.8.3"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify fflate.deflateSync in pkg:npm/fflate@0.8.3",
  "kind": "HOW",
  "packages": [
    "pkg:npm/fflate@0.8.3"
  ],
  "symbols": [
    "fflate.deflateSync"
  ]
}

import assert from 'node:assert/strict';
import { deflateSync, inflateSync, compressDataSync, decompressDataSync } from '../index.mjs';

// 1. assert deflateSync compresses a Uint8Array and returns a Uint8Array
{
  const input = new TextEncoder().encode('Hello CodeSampleX fflate deflation test!');
  const compressed = compressDataSync(input);
  assert.ok(compressed instanceof Uint8Array, 'deflateSync must return a Uint8Array');
  assert.ok(compressed.length > 0, 'deflateSync output must not be empty');
}

// 2. assert deflateSync produces valid DEFLATE output decompressible by inflateSync
{
  const input = new TextEncoder().encode('Hello CodeSampleX round-trip test!');
  const compressed = compressDataSync(input);
  const decompressed = decompressDataSync(compressed);
  assert.ok(decompressed instanceof Uint8Array, 'inflateSync must return a Uint8Array');
  assert.deepStrictEqual(decompressed, input, 'decompressed data must match original input bytes exactly');
}

// 3. assert deflateSync respects compression level options
{
  const repeatedData = new Uint8Array(2000).fill(0x42);
  const compressedL0 = compressDataSync(repeatedData, { level: 0 });
  const compressedL9 = compressDataSync(repeatedData, { level: 9 });
  assert.ok(compressedL0.length > repeatedData.length, 'level 0 adds uncompressed DEFLATE block overhead');
  assert.ok(compressedL9.length < compressedL0.length, 'level 9 must achieve higher compression than level 0');
  assert.deepStrictEqual(decompressDataSync(compressedL0), repeatedData, 'level 0 decompressed data must match original');
  assert.deepStrictEqual(decompressDataSync(compressedL9), repeatedData, 'level 9 decompressed data must match original');
}

// 4. assert deflateSync handles empty input and produces valid DEFLATE stream
{
  const emptyInput = new Uint8Array(0);
  const emptyCompressed = compressDataSync(emptyInput);
  assert.ok(emptyCompressed instanceof Uint8Array, 'empty input deflateSync must return a Uint8Array');
  const emptyDecompressed = decompressDataSync(emptyCompressed);
  assert.strictEqual(emptyDecompressed.length, 0, 'decompressed empty input must have length 0');
}

// 5. assert deflateSync compresses repetitive data into significantly smaller output
{
  const repetitive = new TextEncoder().encode('ABCDEF1234567890'.repeat(100));
  const repetitiveCompressed = compressDataSync(repetitive, { level: 6 });
  assert.ok(repetitiveCompressed.length < repetitive.length / 5, 'repetitive data must compress significantly');
  assert.deepStrictEqual(decompressDataSync(repetitiveCompressed), repetitive, 'repetitive decompressed data must match original');
}

console.log('All contract assertions passed.');