can1357/oh-my-pi · error · ArchiveError

Invalid ARJ basic header CRC32

Error message

Invalid ARJ basic header CRC32

What it means

ARJ basic headers end with a CRC-32 over the header body, stored immediately after it. parseArjBlock computes crc32 over bytes [bodyStart, bodyEnd) and compares it with the little-endian u32 at bodyEnd. A mismatch means the header bytes were altered or misread, so the parser stops rather than trusting corrupted metadata (names, sizes, timestamps).

Source

Thrown at packages/utils/src/ar/arj.ts:74

	nextOffset: number;
	metadataSize: number;
	isEnd: boolean;
}

function parseArjBlock(bytes: Uint8Array, offset: number, options: FormatReadOptions): ArjBlock {
	assertRange(bytes, offset, offset + 4, "header signature");
	if (bytes[offset] !== ARJ_SIGNATURE_0 || bytes[offset + 1] !== ARJ_SIGNATURE_1) {
		throw new ArchiveError("Invalid ARJ header signature");
	}
	const bodySize = u16(bytes, offset + 2);
	if (bodySize === 0)
		return { bodyStart: offset + 4, bodySize: 0, nextOffset: offset + 4, metadataSize: 4, isEnd: true };
	if (bodySize < 30 || bodySize > ARJ_MAX_BASIC_HEADER) throw new ArchiveError("Invalid ARJ basic header size");
	const bodyStart = offset + 4;
	const bodyEnd = bodyStart + bodySize;
	assertRange(bytes, bodyStart, bodyEnd + 4, "basic header");
	if (crc32(bytes.subarray(bodyStart, bodyEnd)) !== u32(bytes, bodyEnd)) {
		throw new ArchiveError("Invalid ARJ basic header CRC32");
	}
	let cursor = bodyEnd + 4;
	let extensionCount = 0;
	for (;;) {
		assertRange(bytes, cursor, cursor + 2, "extended header size");
		const extensionSize = u16(bytes, cursor);
		cursor += 2;
		if (extensionSize === 0) break;
		if (++extensionCount > 65_535) throw new ArchiveError("Invalid ARJ archive: too many extended headers");
		assertRange(bytes, cursor, cursor + extensionSize + 4, "extended header");
		if (crc32(bytes.subarray(cursor, cursor + extensionSize)) !== u32(bytes, cursor + extensionSize)) {
			throw new ArchiveError("Invalid ARJ extended header CRC32");
		}
		cursor += extensionSize + 4;
		assertIndexSize(cursor - offset, options.limits, "header metadata");
	}
	return { bodyStart, bodySize, nextOffset: cursor, metadataSize: cursor - offset, isEnd: false };
}

View on GitHub (pinned to 9690622007)

Solutions

  1. Verify the archive externally (`arj t archive.arj`, 7-Zip test) to confirm corruption, then restore from a known-good copy.
  2. If the file was transferred, re-transfer in binary mode and compare checksums (sha256sum) between source and destination.
  3. If you generate ARJ files, ensure you CRC-32 the header body and append it little-endian; test with a reference reader.
  4. Never hand-edit ARJ header bytes (filenames, flags) without recomputing the stored CRC-32.

Example fix

// before: editing the header body in place without fixing the CRC
bytes.set(newNameBytes, nameOffset);
// after: rebuild the header, recompute CRC-32, and rewrite both body and CRC
bytes.set(newNameBytes, nameOffset);
const crc = crc32(bytes.subarray(bodyStart, bodyEnd));
new DataView(bytes.buffer).setUint32(bodyEnd, crc, true);
Defensive patterns

Strategy: try-catch

Try / catch

try {
  return readArj(data, options);
} catch (err) {
  if (err instanceof ArchiveError && err.message.includes("basic header CRC32")) {
    // corrupt header — quarantine the file, do not attempt partial extraction
    logger.error("ARJ basic header CRC mismatch", { size: data.byteLength });
    return null;
  }
  throw err;
}

Prevention

When it happens

Trigger: Any single-bit or multi-byte change inside the basic header body, or the size field being wrong so bodyStart/bodyEnd are shifted and a different region is hashed. Thrown from parseArjBlock after assertRange passes.

Common situations: Damaged downloads or media errors, an in-place file edit (e.g. someone patched a stored filename by hand), transmission through a channel that altered bytes (FTP ASCII mode on old tooling), or a generator that writes headers without computing the CRC.

Related errors

AI-assisted analysis of can1357/oh-my-pi@9690622007 (2026-08-31). Data as JSON: /api/errors/8de7e9a9ac4e9c55. Report an issue: GitHub.