A production-grade S7 PLC communication library built on node-snap7, featuring high-availability session management, concurrent IO scheduling, automatic reconnection, and heartbeat detection. Designed for industrial PLC communication scenarios with Promise/async-await friendly APIs.

基于 node-snap7 封装的生产级 S7 PLC 通信库，提供高可用的会话管理、并发 IO 调度、自动重连、心跳检测能力，支持 Promise/async-await 风格 API，适配工业场景的 PLC 通信需求。

✅ Layered Design: Lightweight IO client + high-availability session layer (choose as needed)
✅ Auto Reconnection: Exponential backoff retry on connection failures (configurable strategy)
✅ Heartbeat Detection: Toggle-bit/sequence heartbeat modes to detect connection status in real-time
✅ Concurrent Scheduling: Multi-priority IO queues (NORMAL/URGENT/HEARTBEAT/RECONNECT) to eliminate concurrent access conflicts on shared resources (Job/Buffer) in asynchronous scenarios
✅ State Management: State machine-based connection lifecycle with event-driven state notifications
✅ Strict Validation: Built-in input validation to prevent illegal operations
✅ Friendly Error Handling: Classified S7 error types with error codes and context
✅ Thread Safety: Serialized IO operations for multi-scenario invocation

✅ 分层设计：轻量 IO 客户端 + 高可用会话层，按需选择
✅ 自动重连：连接异常时指数退避重试，可配置重试策略
✅ 心跳检测：支持位翻转/序列两种心跳模式，及时感知连接状态
✅ 并发调度：多优先级 IO 队列，避免异步回调导致的共享资源（Job/Buffer）并发访问冲突，支持 NORMAL/URGENT/HEARTBEAT/RECONNECT 四级优先级
✅ 完善的状态管理：基于状态机的连接生命周期管理，事件化状态通知
✅ 严格的参数校验：内置输入参数校验，提前规避非法操作
✅ 友好的错误处理：分类封装 S7 错误类型，附带错误码和上下文信息
✅ 线程安全：串行化 IO 操作，适配多场景调用

# npm
npm install @teamwang-design/s7-runtime

# yarn
yarn add @teamwang-design/s7-runtime

# pnpm
pnpm add @teamwang-design/s7-runtime

For simple PLC read/write without reconnection/heartbeat requirements

适用于简单的 PLC 读写，无重连/心跳需求的场景

import { createS7ScheduleClient, IOLevel } from '@teamwang-design/s7-runtime';

// Create client instance
const client = createS7ScheduleClient();

async function run() {
	try {
		// Connect to PLC
		await client.ConnectTo('192.168.1.10', 0, 1);
		console.log('PLC connected successfully');

		// Read 100 bytes from DB1 offset 0 (URGENT priority)
		const data = await client.DBRead(1, 0, 100, 2000, IOLevel.URGENT);
		console.log('Read data：', data);

		// Write 4 bytes to DB1 offset 0
		const buf = Buffer.alloc(4);
		buf.writeUInt32BE(123456, 0);
		await client.DBWrite(1, 0, 4, buf);

		// Disconnect
		client.Disconnect();
	} catch (error) {
		console.error('Operation failed：', error);
	}
}

run();

For production environments requiring auto-reconnection, heartbeat detection, and state monitoring

适用于生产环境，需要自动重连、心跳检测、状态监控的场景

import {
	S7ClientSession,
	AddressType,
	HeartbeatPingMode,
} from '@teamwang-design/s7-runtime';

// Create session instance (configure reconnection & heartbeat)
const session = new S7ClientSession({
	connect: {
		ip: '192.168.1.10',
		port: 102,
		addressType: AddressType.RACK_SLOT,
		rack: 0,
		slot: 1,
		timeout: 10000, // Connection timeout
	},
	reconnect: {
		disable: false, // Enable auto-reconnection
		initDelay: 1000, // Initial retry delay
		maxDelay: 30000, // Max retry delay
		maxRetries: 10, // Max retry attempts
	},
	heartbeat: {
		interval: 2000, // Heartbeat interval
		maxFailures: 3, // Max heartbeat failures
		mode: HeartbeatPingMode.TOGGLE_BIT, // Toggle-bit heartbeat mode
		dbNumber: 10, // Heartbeat DB number
		start: 0, // Heartbeat offset
		suppressWithTraffic: false, // suppress heartbeat when traffic is detected
	},
});

// Listen to session events
session.on('connect', (sessionId) => {
	console.log(`Session connected：${sessionId}`);
});
session.on('disconnect', (sessionId) => {
	console.log(`Session disconnected：${sessionId}`);
});
session.on('waitingForRetry', (sessionId, attempt) => {
	console.log(`Reconnecting [${attempt}]：${sessionId}`);
});
session.on('runtimeError', (sessionId, error) => {
	console.error(`Session error [${sessionId}]：`, error);
});

// Start session
session.start();

// Execute IO operations after connection
session.once('connect', async () => {
	try {
		// Read/write PLC data (session proxies IO methods automatically)
		const data = await session.dbRead(10, 10, 100);
		const buf = Buffer.alloc(4);
		buf.write('test', 'utf-8');
		await session.dbWrite(10, 20, 4, buf);
	} catch (error) {
		console.error('IO operation failed | IO操作失败：', error);
	}
});

// Gracefully close session on process exit
process.on('SIGINT', () => {
	session.end();
	process.exit(0);
});

• IO Priority：NORMAL < HEARTBEAT < URGENT < RECONNECT (scheduler executes serially by priority)

• Connection State：DISCONNECTED → CONNECTING → CONNECTED → WAITING_FOR_RETRY (full event-driven notifications)

• Heartbeat Mode：TOGGLE_BIT (single bit flip) / SEQUENCE (16-bit auto-increment) (adapt to PLC logic)

• IO 优先级：NORMAL < HEARTBEAT < URGENT < RECONNECT，调度器按优先级串行执行

• 连接状态：DISCONNECTED → CONNECTING → CONNECTED → WAITING_FOR_RETRY，全状态事件化通知

• 心跳模式：TOGGLE_BIT（单比特翻转）/ SEQUENCE（16位序列自增），按需选择适配 PLC 逻辑

1. Instance Reuse: One S7ScheduleClient/S7ClientSession per PLC (avoid duplicate creation)
2. Use Session Layer in Production: Recommend S7ClientSession for built-in reconnection/heartbeat (improves availability)
3. Reasonable Timeout Configuration: Increase timeout for unstable networks (connection ≥1000ms, IO ≥10ms)
4. Monitor State Events: Use connect/disconnect/waitingForRetry for business-side monitoring/alerts
5. IO Error Handling: Wrap all IO operations in try/catch (distinguish retryable/fatal errors)
6. Check Connection Before Critical Operations: Validate status with session.isAlive() to avoid invalid IO calls
7. Respect Queue Limits: Do not exceed queue capacity (NORMAL:1000, HEARTBEAT:10, URGENT:20, RECONNECT:2)

1. 实例复用：每个 PLC 对应一个 S7ScheduleClient / S7ClientSession 实例，避免重复创建
2. 生产环境使用会话层：推荐使用 S7ClientSession，自带的重连/心跳能大幅提升可用性
3. 合理配置超时：网络不稳定场景适当增大连接/IO 超时时间，连接超时≥1000ms，IO 超时≥10ms
4. 监听状态事件：通过 connect / disconnect / waitingForRetry 事件实现业务侧的状态监控和告警
5. IO 操作异常处理：所有 IO 操作包裹 try/catch，区分可重试错误（如 ETIMEDOUT）和致命错误（如 ESHUTDOWN）
6. 关键操作前检查连接：通过 session.isAlive() 验证连接状态，避免无效 IO 调用
7. 遵守队列限制：不超过内置队列容量（NORMAL:1000、HEARTBEAT:10、URGENT:20、RECONNECT:2），避免队列溢出

Classified error types for precise business handling:

库中封装了三类核心错误类型，便于业务侧精准处理：

import {
	S7ValidationError,
	S7TimeoutError,
	S7IOError,
} from '@teamwang-design/s7-runtime';

try {
	await session.dbRead(1, -1, 100); // Invalid offset
} catch (error) {
	if (error instanceof S7ValidationError) {
		console.error('Parameter error：', error.message);
	} else if (error instanceof S7TimeoutError) {
		console.error('Operation timeout：', error);
	} else if (error instanceof S7IOError) {
		console.error('Communication error：', error.errno, error.message);
	}
}

This project is open-source under the MIT License - see the LICENSE file for details.

本项目基于 MIT 许可证 开源，详情请查看 LICENSE 文件。

Core underlying dependency: node-snap7 - Node.js binding for S7 protocol

核心底层依赖：node-snap7 - S7 协议的 Node.js 封装实现

💬 Community Tips | 社区提示：
If you encounter issues or have feature requests, please submit an issue on the repository. Contributions are welcome!
如遇问题或有功能需求，欢迎在仓库提交 Issue，也欢迎贡献代码！