gchq/CyberChef · error · OperationError

Unable to find compression function

Error message

Unable to find compression function

What it means

Thrown by LZString Compress when the selected compression format does not resolve to a function in the COMPRESSION_FUNCTIONS map. The format is a dropdown bound to COMPRESSION_OUTPUT_FORMATS, so this is a defensive guard: it triggers only if the argument is not a key in the map (hand-edited recipe, a format listed in options but missing from the map, or args[0] undefined).

Source

Thrown at src/core/operations/LZStringCompress.mjs:49

                name: "Compression Format",
                type: "option",
                defaultIndex: 0,
                value: COMPRESSION_OUTPUT_FORMATS
            }
        ];
    }

    /**
     * @param {string} input
     * @param {Object[]} args
     * @returns {string}
     */
    run(input, args) {
        const compress = COMPRESSION_FUNCTIONS[args[0]];
        if (compress) {
            return compress(input);
        } else {
            throw new OperationError("Unable to find compression function");
        }
    }

}

export default LZStringCompress;

View on GitHub (pinned to 4290ea7539)

Solutions

1. Pick a format from the operation's dropdown (it lists only valid options).
2. When calling programmatically, check Object.keys(COMPRESSION_FUNCTIONS) for the format first.
3. Keep COMPRESSION_OUTPUT_FORMATS and COMPRESSION_FUNCTIONS in sync when adding formats.
4. Reset the option to its default index to recover a valid value.

Example fix

// before: unknown format
chef.LZStringCompress(text, ['UnknownFormat']);
// after: a format present in the map
chef.LZStringCompress(text, ['Base64']);

function ensureCompressionFormat(format) {
  if (!Object.prototype.hasOwnProperty.call(COMPRESSION_FUNCTIONS, format))
    throw new Error(`Unknown LZ compression format: ${format}`);
  return format;
}

function isKnownCompressionFormat(f) {
  return Object.prototype.hasOwnProperty.call(COMPRESSION_FUNCTIONS, f);
}

try {
  return chef.LZStringCompress(input, [format]);
} catch (e) {
  if (/Unable to find compression function/.test(e.message))
    throw new Error('Pick a format listed in the dropdown');
  throw e;
}

When it happens

Trigger: A recipe supplies a format string absent from COMPRESSION_FUNCTIONS. A mismatch where a value in COMPRESSION_OUTPUT_FORMATS has no matching entry in COMPRESSION_FUNCTIONS (data/config drift). Programmatic call with an unrecognised format.

Common situations: Hand-editing the recipe's option value. Updating the format list without the function map (or vice versa). Importing recipes from a different CyberChef version.

Related errors

• Unable to find decompression function
• Invalid block type while parsing DEFLATE stream at pos ${str
• Malformed LZNT1 stream: Block too small! Has the stream been
• Malformed LZNT1 stream: Invalid shift!
• Invalid block cipher mode: ${mode}

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/8be8df85ac4725af. Report an issue: GitHub.