can1357/oh-my-pi · error · ArchiveError

Invalid ARJ archive: missing main header

Error message

Invalid ARJ archive: missing main header

What it means

This ArchiveError is thrown when the first block parsed from the archive reports isEnd — meaning the parser hit the end-of-archive marker (bodySize 0) immediately, with no main header present. A valid ARJ must start with a main (archive) header before any local file headers.

Source

Thrown at packages/utils/src/ar/arj.ts:242

/** Index an ARJ archive and lazily decode stored, static-Huffman, and fast-LZSS members. */
export const readArj: FormatReader = async (
	source: ByteSource,
	options: FormatReadOptions,
): Promise<ArchiveIndexEntry[]> => {
	assertInMemorySize(source.size, options.limits);
	let bytes: Uint8Array;
	try {
		bytes = await readAllBytes(source);
	} catch (error) {
		if (error instanceof ArchiveError) throw error;
		throw new ArchiveError(`Unable to read ARJ archive: ${error instanceof Error ? error.message : String(error)}`);
	}
	if (bytes.byteLength !== source.size) throw new ArchiveError("Invalid ARJ archive: truncated data");
	if (!sniffArj(bytes)) throw new ArchiveError("Invalid ARJ archive header");

	const main = parseArjBlock(bytes, 0, options);
	if (main.isEnd) throw new ArchiveError("Invalid ARJ archive: missing main header");
	const mainFirstHeaderSize = bytes[main.bodyStart]!;
	if (mainFirstHeaderSize < 30 || mainFirstHeaderSize > main.bodySize || bytes[main.bodyStart + 6] !== 2) {
		throw new ArchiveError("Invalid ARJ main header");
	}
	const mainFlags = bytes[main.bodyStart + 4]!;
	if ((mainFlags & 0x01) !== 0) throw new ArchiveError("Encrypted ARJ archives are unsupported");
	if ((mainFlags & 0x04) !== 0) throw new ArchiveError("Multi-volume ARJ archives are unsupported");

	const entries: ArchiveIndexEntry[] = [];
	let offset = main.nextOffset;
	let metadataSize = main.metadataSize;
	let parsedCount = 0;
	for (;;) {
		const block = parseArjBlock(bytes, offset, options);
		metadataSize += block.metadataSize;
		assertIndexSize(metadataSize, options.limits, "index");
		if (block.isEnd) break;
		assertEntryCount(++parsedCount, options.limits);

View on GitHub (pinned to 9690622007)

Solutions

  1. The archive has no content headers; obtain a complete archive from the source.
  2. Verify the file against the original byte size/checksum to detect truncation.
  3. Re-create the archive; if the producer intentionally made an empty archive, it is still not readable as a member-bearing ARJ by this reader.

Example fix

// before
const entries = await readArj(source, options);
// after
try {
  const entries = await readArj(source, options);
  if (entries.length === 0) console.warn('archive contains no members');
} catch (e) {
  if (e instanceof ArchiveError && e.message.includes('missing main header')) {
    throw new Error('archive is empty or its main header is missing; re-acquire the file');
  }
  throw e;
}
Defensive patterns

Strategy: validation

Validate before calling

if (stat.size < 34) throw new Error(`${path} is too small to be a member-bearing ARJ archive`);

Try / catch

try {
  const entries = await readArj(source, options);
} catch (e) {
  if (e instanceof ArchiveError && e.message.includes('missing main header')) {
    throw new Error('archive is empty or its main header is missing; re-acquire it');
  }
  throw e;
}

Prevention

When it happens

Trigger: Calling readArj on data whose very first block after the signature is an end marker — e.g. an empty/headerless archive, or corruption that zeroed the main header size field.

Common situations: Zero-length archives created by aborted archiver runs, severely truncated/corrupted files, files that only consist of the two signature bytes plus terminator.

Related errors

AI-assisted analysis of can1357/oh-my-pi@9690622007 (2026-08-31). Data as JSON: /api/errors/38024039c19a5ce4. Report an issue: GitHub.