First attempt at decoding a PSARC Binary or .PAK file(from No Mans Sky) using Nodejs. This merely decodes the Header and TOC Table

decode.js

const fs = require("node:fs");
const psarc_file = "./NMSARC.5A3E0C7D.pak";
// const psarc_file = "./NMSARC.2E9559C7.pak";
const hexToDecimal = (hex) => parseInt(hex, 16);

// Attempts to read a *pak file and decode it's header and
// return it as an object. Result in file below.
// 
// Yes! This could be written better, but it's first draft.
// Ever wake up one morning and ask yourself, "Self! What's
// this all about? I wonder if we can do that?". 
//
// This is just that. 
//
const decode = fs.readFile(psarc_file, (err, buffer) => {
  if (err) {
    console.log(err);
  }

  // Grab only the header and toc_table of the psarc archive
  let header = buffer.subarray(0, 62);

  /**
   * Converts the section of buffer to decimal.
   * Removes any NULL bytes, then uses parseInt
   * to convert to a decimal. Followed by comcat
   * to conbine the result into a string
   *
   * @param start int
   * @param end int
   * @returns string
   */
  const toDecString = (start, end) => {
    let result = [];
    header.subarray(start, end).forEach((x) => {
      if (x != 00) {
        result.push(parseInt(x));
      }
    });

    const string = "".concat(...result);
    return hexToDecimal(string);
  };

  /**
   * Converts the section of buffer to decimal without
   * destroying the orignal value.
   *
   * @param start int
   * @param end int
   * @returns int
   */
  const fromBinarytoDecString = (start, end) => {
    let result = [];
    const head_section = header.subarray(start, end);
    head_section.forEach((x) => result.push("0" + x));
    const binary = "".concat(...result);
    return hexToDecimal(binary);
  };

  const header_data = {
    magic: header.subarray(0, 4).toString(), // parse to string (type of file/archive)
    version: header.subarray(4, 8), // versinn of archive used
    compression_type: header.subarray(8, 12).toString(), //parse to string (type of compression used)
    toc_length: toDecString(12, 16),
    toc_entry_size: toDecString(16, 20),
    toc_entries: toDecString(20, 24),
    block_size: fromBinarytoDecString(24, 28),
    archive_flags: fromBinarytoDecString(28, 32),
    name_digest: header.subarray(32, 48).toString(),
    block_offset: fromBinarytoDecString(48, 52),
    uncompressed_size: toDecString(52, 57),
    file_offset: toDecString(57, 62),
  };

  console.log(header_data);
});

return decode;

gistfile1.txt

{
  magic: 'PSAR',
  version: <Buffer 00 01 00 04>,
  compression_type: 'zlib',
  toc_length: 82264,
  toc_entry_size: 48,
  toc_entries: 265,
  block_size: 65536,
  archive_flags: 1,
  name_digest: '\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00',
  block_offset: 0,
  uncompressed_size: 9257,
  file_offset: 82264
}