bare-buffer 3.7.0: Buffer.prototype.copy

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 Buffer.prototype.copy in pkg:npm/bare-buffer@3.7.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/bare-buffer@3.7.0
Demonstrate these symbols/APIs:
  - Buffer.prototype.copy

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:sha256:89adca9e92cf06b5d57ab4708ace73889f8a6669b4715e97ac61667e1845d332","contract":["Buffer.prototype.copy copies full byte content from source buffer to target buffer and returns bytes copied","Buffer.prototype.copy respects targetStart offset when writing into target buffer","Buffer.prototype.copy copies a slice of source buffer using sourceStart and sourceEnd offsets","Buffer.prototype.copy truncates copied bytes when target remaining capacity is smaller than source range","Buffer.prototype.copy performs in-place overlapping memory copy when source and target are the same buffer","Buffer.prototype.copy returns 0 without modification when sourceEnd is less than or equal to sourceStart","Buffer.prototype.copy returns 0 when targetStart exceeds target buffer length"],"goal":"verify Buffer.prototype.copy in pkg:npm/bare-buffer@3.7.0","kind":"HOW","packages":["pkg:npm/bare-buffer@3.7.0"],"schemaVersion":1,"symbols":["Buffer.prototype.copy"]},"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","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/bare-buffer@3.7.0"],"schemaVersion":1,"subject":"pkg:npm/bare-buffer@3.7.0","symbols":["Buffer.prototype.copy"],"verifierAdapter":"node-typescript@1"}

import { createRequire } from 'node:module';
import path from 'node:path';

const require = createRequire(import.meta.url);

// Ensure binding is available in Node.js environments where require.addon is absent
if (typeof Bare === 'undefined') {
  const nodeBuffer = globalThis.Buffer;
  const mockBinding = {
    constants: {
      MAX_LENGTH: 2147483647,
      MAX_STRING_LENGTH: 1073741799
    },
    alloc(size) { return new ArrayBuffer(size); },
    allocUnsafe(size) { return new ArrayBuffer(size); },
    compare(bufA, offA, lenA, bufB, offB, lenB) {
      const a = nodeBuffer.from(bufA, offA, lenA);
      const b = nodeBuffer.from(bufB, offB, lenB);
      return a.compare(b);
    },
    toStringHex(buf, offset, len) {
      return nodeBuffer.from(buf, offset, len).toString('hex');
    },
    writeHex(buf, offset, len, string) {
      return nodeBuffer.from(buf, offset, len).write(string, 0, len, 'hex');
    },
    toStringBase64(buf, offset, len) {
      return nodeBuffer.from(buf, offset, len).toString('base64');
    },
    writeBase64(buf, offset, len, string) {
      return nodeBuffer.from(buf, offset, len).write(string, 0, len, 'base64');
    },
    toStringBase64URL(buf, offset, len) {
      return nodeBuffer.from(buf, offset, len).toString('base64url');
    },
    writeBase64URL(buf, offset, len, string) {
      return nodeBuffer.from(buf, offset, len).write(string, 0, len, 'base64url');
    },
    toStringUTF8(buf, offset, len) {
      return nodeBuffer.from(buf, offset, len).toString('utf8');
    },
    writeUTF8(buf, offset, len, string) {
      return nodeBuffer.from(buf, offset, len).write(string, 0, len, 'utf8');
    },
    validateUTF8(buf, offset, len) {
      return nodeBuffer.isUtf8 ? nodeBuffer.isUtf8(nodeBuffer.from(buf, offset, len)) : true;
    },
    byteLengthUTF8(string) {
      return nodeBuffer.byteLength(string, 'utf8');
    },
    toStringUTF16LE(buf, offset, len) {
      return nodeBuffer.from(buf, offset, len).toString('utf16le');
    },
    writeUTF16LE(buf, offset, len, string) {
      return nodeBuffer.from(buf, offset, len).write(string, 0, len, 'utf16le');
    },
    toStringLatin1(buf, offset, len) {
      return nodeBuffer.from(buf, offset, len).toString('latin1');
    },
    writeLatin1(buf, offset, len, string) {
      return nodeBuffer.from(buf, offset, len).write(string, 0, len, 'latin1');
    },
    indexOf(bufA, offA, lenA, bufB, offB, lenB, byteOffset) {
      const a = nodeBuffer.from(bufA, offA, lenA);
      const b = nodeBuffer.from(bufB, offB, lenB);
      return a.indexOf(b, byteOffset);
    },
    lastIndexOf(bufA, offA, lenA, bufB, offB, lenB, byteOffset) {
      const a = nodeBuffer.from(bufA, offA, lenA);
      const b = nodeBuffer.from(bufB, offB, lenB);
      return a.lastIndexOf(b, byteOffset);
    },
    swap16(buf, offset, len) {
      nodeBuffer.from(buf, offset, len).swap16();
    },
    swap32(buf, offset, len) {
      nodeBuffer.from(buf, offset, len).swap32();
    },
    swap64(buf, offset, len) {
      nodeBuffer.from(buf, offset, len).swap64();
    }
  };

  const mainPath = require.resolve('bare-buffer');
  const bindingPath = path.join(path.dirname(mainPath), 'binding.js');
  require.cache[bindingPath] = {
    id: bindingPath,
    filename: bindingPath,
    loaded: true,
    exports: mockBinding
  };
}

const Buffer = require('bare-buffer');

export function copyBuffer(source, target, targetStart = 0, sourceStart = 0, sourceEnd = source.byteLength) {
  return source.copy(target, targetStart, sourceStart, sourceEnd);
}

export default Buffer;

{
  "name": "sample-bare-buffer-copy",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-bare-buffer-copy",
      "version": "1.0.0",
      "dependencies": {
        "bare-buffer": "3.7.0"
      }
    },
    "node_modules/bare-buffer": {
      "version": "3.7.0",
      "resolved": "https://registry.npmjs.org/bare-buffer/-/bare-buffer-3.7.0.tgz",
      "integrity": "sha512-/xRTbBuLis7sE3Izii0A0yOm+WqH1/gh12UVqkpIAOLZ4gWluyK0THbGB+UysKI8ZBjcZ+MaEs9Auxcyiz2yLA==",
      "license": "Apache-2.0",
      "engines": {
        "bare": ">=1.20.0"
      }
    }
  }
}

{
  "name": "sample-bare-buffer-copy",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "dependencies": {
    "bare-buffer": "3.7.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify Buffer.prototype.copy in pkg:npm/bare-buffer@3.7.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/bare-buffer@3.7.0"
  ],
  "symbols": [
    "Buffer.prototype.copy"
  ]
}

import assert from 'node:assert/strict';
import Buffer, { copyBuffer } from '../index.js';

// 1. Buffer.prototype.copy copies full byte content from source buffer to target buffer and returns bytes copied
const src1 = Buffer.from([1, 2, 3, 4]);
const dst1 = Buffer.alloc(4);
const copied1 = copyBuffer(src1, dst1);
assert.strictEqual(copied1, 4, 'Full copy must return the count of copied bytes (4)');
assert.deepStrictEqual(Array.from(dst1), [1, 2, 3, 4], 'Target buffer content must match source buffer');

// 2. Buffer.prototype.copy respects targetStart offset when writing into target buffer
const src2 = Buffer.from([10, 20]);
const dst2 = Buffer.alloc(5);
const copied2 = copyBuffer(src2, dst2, 2);
assert.strictEqual(copied2, 2, 'Copy with targetStart must return count of copied bytes (2)');
assert.deepStrictEqual(Array.from(dst2), [0, 0, 10, 20, 0], 'Target buffer must contain copied bytes starting at offset 2');

// 3. Buffer.prototype.copy copies a slice of source buffer using sourceStart and sourceEnd offsets
const src3 = Buffer.from([1, 2, 3, 4, 5, 6]);
const dst3 = Buffer.alloc(3);
const copied3 = copyBuffer(src3, dst3, 0, 2, 5);
assert.strictEqual(copied3, 3, 'Sliced copy must return length of source range (3)');
assert.deepStrictEqual(Array.from(dst3), [3, 4, 5], 'Target buffer must contain source bytes from index 2 up to 5');

// 4. Buffer.prototype.copy truncates copied bytes when target remaining capacity is smaller than source range
const src4 = Buffer.from([1, 2, 3, 4, 5]);
const dst4 = Buffer.alloc(3);
const copied4 = copyBuffer(src4, dst4, 1);
assert.strictEqual(copied4, 2, 'Copy must be truncated to remaining capacity of target (2 bytes)');
assert.deepStrictEqual(Array.from(dst4), [0, 1, 2], 'Target buffer must contain truncated bytes starting at targetStart');

// 5. Buffer.prototype.copy performs in-place overlapping memory copy when source and target are the same buffer
const buf5 = Buffer.from([1, 2, 3, 4, 5]);
const copied5 = copyBuffer(buf5, buf5, 1, 0, 3);
assert.strictEqual(copied5, 3, 'In-place copy must return count of copied bytes (3)');
assert.deepStrictEqual(Array.from(buf5), [1, 1, 2, 3, 5], 'Buffer must handle overlapping copy without corrupting intermediate bytes');

// 6. Buffer.prototype.copy returns 0 without modification when sourceEnd is less than or equal to sourceStart
const src6 = Buffer.from([1, 2, 3]);
const dst6 = Buffer.alloc(3);
const copied6 = copyBuffer(src6, dst6, 0, 2, 1);
assert.strictEqual(copied6, 0, 'Copy with sourceEnd <= sourceStart must return 0');
assert.deepStrictEqual(Array.from(dst6), [0, 0, 0], 'Target buffer must remain untouched when copy length is 0');

// 7. Buffer.prototype.copy returns 0 when targetStart exceeds target buffer length
const src7 = Buffer.from([1, 2, 3]);
const dst7 = Buffer.alloc(2);
const copied7 = copyBuffer(src7, dst7, 5);
assert.strictEqual(copied7, 0, 'Copy with out-of-bounds targetStart must return 0');
assert.deepStrictEqual(Array.from(dst7), [0, 0], 'Target buffer must remain untouched when targetStart is out of bounds');

console.log('Contract verification finished successfully.');