gchq/CyberChef · error · OperationError

Invalid file type.

Error message

Invalid file type.

What it means

present() renders the converted output as an <img> for the web UI and re-validates it with isImage() before base64-encoding. If the converted buffer is not recognized as an image, `if (!type)` throws 'Invalid file type.' Reaching here means the transcode produced bytes isImage cannot classify.

Source

Thrown at src/core/operations/ConvertImageFormat.mjs:130

            return buffer.buffer;
        } catch (err) {
            throw new OperationError(`Error converting image format. (${err})`);
        }
    }

    /**
     * Displays the converted image using HTML for web apps
     *
     * @param {ArrayBuffer} data
     * @returns {html}
     */
    present(data) {
        if (!data.byteLength) return "";
        const dataArray = new Uint8Array(data);

        const type = isImage(dataArray);
        if (!type) {
            throw new OperationError("Invalid file type.");
        }

        return `<img src="data:${type};base64,${toBase64(dataArray)}">`;
    }
}

export default ConvertImageFormat;

View on GitHub (pinned to 4290ea7539)

Solutions

1. Convert to a standard format (PNG/JPEG) that isImage reliably recognizes.
2. Inspect the output with Detect File Type to see the actual mime.
3. In the Node API, consume the ArrayBuffer directly if display isn't required.

Example fix

// before: converting to an unrecognized target, present() fails
// after: target PNG so output is reliably detected
recipe: [Convert Image Format (PNG)]

import { isImage } from "src/core/lib/FileType.mjs";
const bytes = new Uint8Array(outputBuffer);
if (!isImage(bytes)) {
  throw new Error("Converted output is not a recognized image; target a standard format.");
}

import { isImage } from "src/core/lib/FileType.mjs";
function isRecognizedOutput(buf) {
  return isImage(buf instanceof ArrayBuffer ? new Uint8Array(buf) : buf) !== false;
}

When it happens

Trigger: Target format produced a container/mime outside isImage's recognized set; encode produced empty/garbage bytes; output mime not in the detector table.

Common situations: Converting to an obscure format; partial/failed encode that still returned a buffer; detector/table mismatch between input and output.

Related errors

• Invalid file type.
• Invalid file format.
• Invalid file type.
• Invalid file type.
• Error loading image. (${err})

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/666441af2f92defe. Report an issue: GitHub.