gchq/CyberChef · error · Error

Input ${error}

Error message

Input ${error}

What it means

Thrown by Protobuf.mergeDecodes when a schema message was resolved (so `message` is truthy) but `message.decode(input)` raised — i.e. the raw bytes do not conform to the selected message type. The underlying protobufjs decode error is appended after 'Input '.

Source

Thrown at src/core/lib/Protobuf.mjs:201

            const packageDecode = message.toObject(message.decode(input), {
                bytes: String,
                longs: Number,
                enums: String,
                defaults: true
            });
            const output = {};

            if (this.showUnknownFields) {
                output[message.name] = packageDecode;
                output["Unknown Fields"] = this.compareFields(rawDecode, message);
                return output;
            } else {
                return packageDecode;
            }

        } catch (error) {
            if (message) {
                throw new Error("Input " + error);
            } else {
                return rawDecode;
            }
        }
    }

    /**
     * Replace fieldnames with fieldname and type
     *
     * @param {Object} schemaRoot
     * @returns {Object}
     */
    static appendTypesToFieldNames(schemaRoot) {
        for (const block of schemaRoot.nestedArray) {
            if (block instanceof protobuf.Type) {
                for (const [fieldName, fieldData] of Object.entries(block.fields)) {
                    schemaRoot.nested[block.name].remove(block.fields[fieldName]);
                    schemaRoot.nested[block.name].add(new protobuf.Field(`${fieldName} (${fieldData.type})`, fieldData.id, fieldData.type, fieldData.rule));

View on GitHub (pinned to 4290ea7539)

Solutions

1. Read the appended decode error to find the offending field.
2. Confirm the .proto matches how the data was encoded (same message, same field numbers/types).
3. Fall back to raw decode by omitting the schema, or pick the correct main message.

Example fix

// before: data encoded as MessageB but schema's first message is MessageA
Protobuf.mergeDecodes(bytes); // throws Input ...
// after: reorder schema so the matching message is first, or use raw decode
const pb = new Protobuf(bytes); return pb._parse();

Protobuf.updateProtoRoot(protoText);
const message = Protobuf.parsedProto.root.nested[Protobuf.mainMessageName];
if (!message) {
  // no schema match — fall back to raw decode instead of risking Input error
  return new Protobuf(input)._parse();
}

function dataMatchesMessage(message, bytes) {
  try { message.decode(bytes); return true; } catch { return false; }
}

try {
  return Protobuf.mergeDecodes(input);
} catch (e) {
  if (/^Input /.test(e.message)) {
    return new Protobuf(input)._parse(); // raw schemaless fallback
  }
  throw e;
}

When it happens

Trigger: Decoding protobuf bytes against a schema where wire data is truncated, a field number/type mismatches the schema, a varint overflows, or the bytes were produced for a different message type than mainMessageName.

Common situations: Wrong .proto selected for the data; bytes were encoded with a different message layout; truncated network capture; decoding a sub-message payload as the top-level message.

Related errors

• Input Error: ${error}
• Schema Error: Schema not defined
• Schema ${error}
• Exhausted Buffer
• Unknown type 0x${type.toString(16)}

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/381ce6bd551b63cf. Report an issue: GitHub.