can1357/oh-my-pi · error · ArchiveError

LZH member '${memberPath}' uses unsupported compression meth

Error message

LZH member '${memberPath}' uses unsupported compression method ${this.#method}

What it means

The member's method string passed the format sniff regex (-lh0..7d, -lz4/5s) but is not one of the methods the decoder implements (lh0/4/5/6/7, lz4, lzs). Rather than attempting unknown decompression, the reader rejects the member with its method name in the message.

Source

Thrown at packages/utils/src/ar/lzh.ts:439

			case "-lh4-":
				output = decompressLhStatic(packed, size, 1 << 12, 4, 13, "LZH -lh4-");
				break;
			case "-lh5-":
				output = decompressLhStatic(packed, size, 1 << 13, 4, 14, "LZH -lh5-");
				break;
			case "-lh6-":
				output = decompressLhStatic(packed, size, 1 << 15, 5, 16, "LZH -lh6-");
				break;
			case "-lh7-":
				output = decompressLhStatic(packed, size, 1 << 16, 5, 17, "LZH -lh7-");
				break;
			case "-lzs-":
				output = decompressLzs(packed, size);
				break;
			case "-lh1-":
				throw new ArchiveError(`LZH member '${memberPath}' uses unsupported dynamic-Huffman method -lh1-`);
			default:
				throw new ArchiveError(`LZH member '${memberPath}' uses unsupported compression method ${this.#method}`);
		}
		if (output.byteLength !== size)
			throw new ArchiveError(`LZH member '${memberPath}' extracted to an unexpected size`);
		if (crc16Arc(output) !== this.#crc)
			throw new ArchiveError(`LZH member '${memberPath}' failed CRC-16 verification`);
		return output;
	}
}

interface ParsedLzhHeader {
	method: string;
	packedSize: number;
	size: number;
	dataStart: number;
	nextOffset: number;
	crc: number;
	path?: string;
	mtimeMs?: number;

View on GitHub (pinned to 9690622007)

Solutions

1. Recompress the archive with a modern compressor to -lh5-/-lh6-/-lh7- (e.g. `lha a -lh5`) before reading
2. Extract the affected members with an external tool (lhasa, 7-Zip) and process the extracted output instead
3. Check for archive corruption: an unexpected method on an otherwise valid archive often means header bytes were damaged
4. If you control archive creation, restrict writers to -lh0-/-lh5-..-lh7- methods this library supports

Example fix

null

// Only these methods are decodable by this library
const SUPPORTED = new Set(["-lh0-","-lh4-","-lh5-","-lh6-","-lh7-","-lz4-","-lzs-"]);
function isSupportedMethod(method: string): boolean {
	return SUPPORTED.has(method);
}

function isSupportedLzhMethod(m: string): m is "-lh0-" | "-lh4-" | "-lh5-" | "-lh6-" | "-lh7-" | "-lz4-" | "-lzs-" {
	return ["-lh0-","-lh4-","-lh5-","-lh6-","-lh7-","-lz4-","-lzs-"].includes(m);
}

try {
	const data = await member.read();
} catch (err) {
	if (err instanceof ArchiveError && /unsupported compression method/.test(err.message)) {
		// extract this member via an external tool or repack the archive
	}
	throw err;
}

When it happens

Trigger: Reading a member compressed with a recognized-but-unimplemented method such as -lh2-, -lh3-, -lz5-, -lhd- data misparse, or any method string matching the pattern that falls through the switch — e.g. -lh2-/-lh3- legacy dynamic Huffman, -lz5-.

Common situations: Archives created by rare/legacy LHA variants using -lh2-/-lh3-/-lz5-; archives whose header bytes were corrupted into a valid-looking but wrong method string; LHARK or other variant files.

Related errors

• LZH member '${memberPath}' uses unsupported dynamic-Huffman
• Unsupported deb tar compression in '${outerEntry.path}'
• Invalid ${label} Huffman table: oversubscribed codes
• Invalid ${label} Huffman table: incomplete codes
• Invalid ${label} Huffman table: prefix collision

AI-assisted analysis of can1357/oh-my-pi@9690622007 (2026-08-31). Data as JSON: /api/errors/cf8c70f3087ed8f8. Report an issue: GitHub.