modbus-connect/function-codes/read-device-identification.js

Modbus RTU over Web Serial and Node.js SerialPort

// function-codes/read-device-identification.js

const FUNCTION_CODE = 0x2B;
const MEI_TYPE = 0x0E;
const MIN_RESPONSE_SIZE = 7;
const TEXT_ENCODING = 'windows-1251';

// Создаем декодер один раз для повторного использования
const TEXT_DECODER = new TextDecoder(TEXT_ENCODING);

function buildReadDeviceIdentificationRequest(categoryId = 0x01, objectId = 0x00) {
    // Используем ArrayBuffer + DataView для единообразия
    const buffer = new ArrayBuffer(4);
    const view = new DataView(buffer);
    view.setUint8(0, FUNCTION_CODE);
    view.setUint8(1, MEI_TYPE);
    view.setUint8(2, categoryId);
    view.setUint8(3, objectId);
    return new Uint8Array(buffer);
}

function parseReadDeviceIdentificationResponse(response) {
    if (!(response instanceof Uint8Array)) {
        throw new TypeError('Response must be Uint8Array');
    }

    const responseLength = response.length;
    if (responseLength < MIN_RESPONSE_SIZE) {
        throw new Error(`Response too short: expected at least ${MIN_RESPONSE_SIZE} bytes`);
    }

    // Используем оригинальный буфер без копирования
    const buffer = response.buffer || response;
    const byteOffset = response.byteOffset || 0;
    const view = new DataView(buffer, byteOffset, responseLength);

    const functionCode = view.getUint8(0);
    if (functionCode !== FUNCTION_CODE) {
        throw new Error(`Invalid function code: expected 0x${FUNCTION_CODE.toString(16)}, got 0x${functionCode.toString(16)}`);
    }

    const meiType = view.getUint8(1);
    if (meiType !== MEI_TYPE) {
        throw new Error(`Invalid MEI type: expected 0x${MEI_TYPE.toString(16)}, got 0x${meiType.toString(16)}`);
    }

    const result = {
        functionCode,
        meiType,
        category: view.getUint8(2),
        conformityLevel: view.getUint8(3),
        moreFollows: view.getUint8(4),
        nextObjectId: view.getUint8(5),
        numberOfObjects: view.getUint8(6),
        objects: Object.create(null) // Чистый объект без прототипа
    };

    let offset = 7;
    const objects = result.objects;
    const numberOfObjects = result.numberOfObjects;

    for (let i = 0; i < numberOfObjects; i++) {
        if (offset + 2 > responseLength) {
            throw new Error('Invalid object header length');
        }

        const objectId = view.getUint8(offset);
        const length = view.getUint8(offset + 1);
        offset += 2;

        if (offset + length > responseLength) {
            throw new Error('Invalid object data length');
        }

        // Декодируем строку напрямую из буфера
        objects[objectId] = TEXT_DECODER.decode(
            new Uint8Array(buffer, byteOffset + offset, length)
        );
        offset += length;
    }

    return result;
}

module.exports = {
    buildReadDeviceIdentificationRequest,
    parseReadDeviceIdentificationResponse
};