fflate 0.8.3: gzipSync

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.gzipSync 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.gzipSync

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:sha256:36afe69da15a92e0d9e4171f7ac91dc0c2b8c27ac5f144609fe7ff8e6a1bfc85","constraints":{"executionContext":"node"},"contract":["assert gzipSync compresses a Uint8Array and returns a Uint8Array","assert gzipSync produces valid GZIP header magic bytes 0x1f 0x8b","assert gzipSync produces valid GZIP output decompressible by gunzipSync","assert gzipSync respects compression level options","assert gzipSync handles empty input and produces valid GZIP stream","assert gzipSync compresses repetitive data into significantly smaller output"],"goal":"verify fflate.gzipSync in pkg:npm/fflate@0.8.3","kind":"HOW","packages":["pkg:npm/fflate@0.8.3"],"schemaVersion":1,"symbols":["fflate.gzipSync"]},"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.gzipSync"],"verifierAdapter":"node-typescript@1"}

import { gzipSync, gunzipSync } from 'fflate';

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

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

export { gzipSync, gunzipSync };
export default gzipSync;

{
  "name": "sample-fflate-gzipsync",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-fflate-gzipsync",
      "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-gzipsync",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "license": "MIT-0",
  "dependencies": {
    "fflate": "0.8.3"
  }
}

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

import assert from 'node:assert/strict';
import { gzipSync, gunzipSync, compressGzipSync, decompressGzipSync } from '../index.mjs';

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

// 2. assert gzipSync produces valid GZIP header magic bytes 0x1f 0x8b
{
  const input = new TextEncoder().encode('Testing GZIP header structure');
  const compressed = compressGzipSync(input);
  assert.strictEqual(compressed[0], 0x1f, 'First byte must be GZIP magic 0x1f');
  assert.strictEqual(compressed[1], 0x8b, 'Second byte must be GZIP magic 0x8b');
  assert.strictEqual(compressed[2], 0x08, 'Third byte must be DEFLATE compression method 0x08');
}

// 3. assert gzipSync produces valid GZIP output decompressible by gunzipSync
{
  const input = new TextEncoder().encode('Hello CodeSampleX GZIP round-trip test!');
  const compressed = compressGzipSync(input);
  const decompressed = decompressGzipSync(compressed);
  assert.ok(decompressed instanceof Uint8Array, 'gunzipSync must return a Uint8Array');
  assert.deepStrictEqual(decompressed, input, 'decompressed data must match original input bytes exactly');
}

// 4. assert gzipSync respects compression level options
{
  const repeatedData = new Uint8Array(2000).fill(0x42);
  const compressedL0 = compressGzipSync(repeatedData, { level: 0 });
  const compressedL9 = compressGzipSync(repeatedData, { level: 9 });
  assert.ok(compressedL0.length > repeatedData.length, 'level 0 adds uncompressed GZIP container overhead');
  assert.ok(compressedL9.length < compressedL0.length, 'level 9 must achieve higher compression than level 0');
  assert.deepStrictEqual(decompressGzipSync(compressedL0), repeatedData, 'level 0 decompressed data must match original');
  assert.deepStrictEqual(decompressGzipSync(compressedL9), repeatedData, 'level 9 decompressed data must match original');
}

// 5. assert gzipSync handles empty input and produces valid GZIP stream
{
  const emptyInput = new Uint8Array(0);
  const emptyCompressed = compressGzipSync(emptyInput);
  assert.ok(emptyCompressed instanceof Uint8Array, 'empty input gzipSync must return a Uint8Array');
  assert.ok(emptyCompressed.length >= 10, 'GZIP output must contain at least 10-byte header');
  const emptyDecompressed = decompressGzipSync(emptyCompressed);
  assert.strictEqual(emptyDecompressed.length, 0, 'decompressed empty input must have length 0');
}

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

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