Function parseZipModes

src/utils/dxt/zip.ts:160–203

(data: Uint8Array)

 * which is fine for marketplace zips (~3.5MB) and MCPB bundles.
 */
export function parseZipModes(data: Uint8Array): Record<string, number> {
  // Buffer view for readUInt* methods — shares memory, no copy.
  const buf = Buffer.from(data.buffer, data.byteOffset, data.byteLength)
  const modes: Record<string, number> = {}

  // 1. Find the End of Central Directory record (sig 0x06054b50). It lives in
  //    the trailing 22 + 65535 bytes (fixed EOCD size + max comment length).
  //    Scan backwards — the EOCD is typically the last 22 bytes.
  const minEocd = Math.max(0, buf.length - 22 - 0xffff)
  let eocd = -1
  for (let i = buf.length - 22; i >= minEocd; i--) {
    if (buf.readUInt32LE(i) === 0x06054b50) {
      eocd = i
      break
    }
  }
  if (eocd < 0) return modes // malformed — let fflate's error surface elsewhere

  const entryCount = buf.readUInt16LE(eocd + 10)
  let off = buf.readUInt32LE(eocd + 16) // central directory start offset

  // 2. Walk central directory entries (sig 0x02014b50). Each entry has a
  //    46-byte fixed header followed by variable-length name/extra/comment.
  for (let i = 0; i < entryCount; i++) {
    if (off + 46 > buf.length || buf.readUInt32LE(off) !== 0x02014b50) break
    const versionMadeBy = buf.readUInt16LE(off + 4)
    const nameLen = buf.readUInt16LE(off + 28)
    const extraLen = buf.readUInt16LE(off + 30)
    const commentLen = buf.readUInt16LE(off + 32)
    const externalAttr = buf.readUInt32LE(off + 38)
    const name = buf.toString('utf8', off + 46, off + 46 + nameLen)

    // versionMadeBy high byte = host OS. 3 = Unix. For Unix zips, the high
    // 16 bits of externalAttr hold st_mode (file type + permission bits).
    if (versionMadeBy >> 8 === 3) {
      const mode = (externalAttr >>> 16) & 0xffff
      if (mode) modes[name] = mode
    }

    off += 46 + nameLen + extraLen + commentLen
  }

  return modes
}

/**
 * Reads a zip file from disk asynchronously and unzips it.