import * as framer from '../protocol/framing.js';
import { IModbusProtocol } from '../types/internal.js';
import { ITransport } from '../types/public.js';
/**
 * ModbusProtocol is a low-level class responsible for reliable Modbus ADU (Application Data Unit) exchange.
 * It handles framing (RTU or TCP), request transmission, response reception, and basic error recovery.
 * This class is used internally by ModbusClient and abstracts the differences between RTU and TCP protocols.
 */
export declare class ModbusProtocol implements IModbusProtocol {
    private _transport;
    private _framerClass;
    private minLen;
    /**
     * Creates a new ModbusProtocol instance.
     * @param _transport - Transport layer used for reading and writing raw bytes
     * @param _framerClass - Framer class (RtuFramer or TcpFramer) responsible for ADU construction and parsing
     */
    constructor(_transport: ITransport, _framerClass: typeof framer.RtuFramer | typeof framer.TcpFramer);
    /**
     * Performs a complete Modbus request-response exchange.
     *
     * Steps performed:
     * 1. Builds the ADU (Application Data Unit) from the given PDU using the selected framer
     * 2. Optionally flushes the transport buffer (for serial/RS485)
     * 3. Writes the request to the transport
     * 4. Reads the response in chunks until a valid ADU can be parsed
     * 5. Handles partial responses, CRC errors, and short frames gracefully
     * 6. Returns only the PDU portion of the received ADU
     *
     * @param unitId - Modbus slave/unit identifier (0-255)
     * @param pduRequest - Protocol Data Unit containing function code and data
     * @param timeout - Maximum time in milliseconds to wait for a complete response
     * @returns The parsed PDU from the device's response
     *
     * @throws ModbusCRCError if CRC check fails and enough data was received
     * @throws ModbusResponseError for malformed or incomplete responses
     * @throws Error with timeout message if the operation exceeds the timeout
     */
    exchange(unitId: number, pduRequest: Uint8Array, timeout: number): Promise<Uint8Array>;
    /**
     * Returns the underlying transport instance used by this protocol.
     * Useful for advanced use cases or debugging.
     */
    get transport(): ITransport;
    /**
     * Returns the framer class (RtuFramer or TcpFramer) currently in use.
     * Can be used to inspect which framing protocol is active.
     */
    get framerClass(): typeof framer.RtuFramer | typeof framer.TcpFramer;
}