DolphinDB WebSocket接入：实时数据流

目录

• • 摘要
  • 一、WebSocket概述
  • • [1.1 什么是WebSocket](#1.1 什么是WebSocket)
    • [1.2 WebSocket vs HTTP](#1.2 WebSocket vs HTTP)
    • [1.3 适用场景](#1.3 适用场景)
  • [二、DolphinDB WebSocket](#二、DolphinDB WebSocket)
  • • [2.1 创建WebSocket服务](#2.1 创建WebSocket服务)
    • [2.2 连接管理](#2.2 连接管理)
  • 三、实时数据接收
  • • [3.1 连接WebSocket](#3.1 连接WebSocket)
    • [3.2 发送数据](#3.2 发送数据)
    • [3.3 批量发送](#3.3 批量发送)
  • 四、消息处理
  • • [4.1 消息格式](#4.1 消息格式)
    • [4.2 消息处理函数](#4.2 消息处理函数)
  • 五、心跳保活
  • • [5.1 心跳机制](#5.1 心跳机制)
    • [5.2 服务端心跳响应](#5.2 服务端心跳响应)
  • 六、断线重连
  • • [6.1 自动重连](#6.1 自动重连)
    • [6.2 数据缓冲](#6.2 数据缓冲)
  • 七、实战案例
  • • [7.1 实时监控数据推送](#7.1 实时监控数据推送)
  • 八、总结
  • 参考资料

摘要

本文深入讲解DolphinDB WebSocket接入技术。从WebSocket协议原理到连接管理，从实时数据接收到消息处理，从心跳保活到断线重连，全面介绍WebSocket数据接入的核心方法。通过丰富的代码示例，帮助读者掌握实时数据流处理的核心技能。

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一、WebSocket概述

1.1 什么是WebSocket

WebSocket是全双工实时通信协议：
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客户端
WebSocket连接
服务端

DolphinDB
特点
全双工
实时推送
长连接

1.2 WebSocket vs HTTP

特性	HTTP	WebSocket
通信方式	半双工	全双工
连接	短连接	长连接
实时性	轮询	实时推送
开销	高	低

1.3 适用场景

场景	说明
实时监控	实时数据推送
告警通知	实时告警推送
仪表盘	实时数据展示
设备控制	实时指令下发

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二、DolphinDB WebSocket

2.1 创建WebSocket服务

// 创建WebSocket服务
// DolphinDB内置WebSocket支持

// 创建流表接收数据
share streamTable(1:0, 
    `device_id`timestamp`temperature`humidity,
    [SYMBOL, TIMESTAMP, DOUBLE, DOUBLE]) as ws_stream

// WebSocket端点
// ws://localhost:8848/ws

2.2 连接管理

// WebSocket连接配置
config = dict(STRING, ANY, [
    ["maxConnections", 1000],
    ["heartbeatInterval", 30000],
    ["maxMessageSize", 1048576]
])

---

三、实时数据接收

3.1 连接WebSocket

// JavaScript客户端示例
const ws = new WebSocket('ws://localhost:8848/ws');

ws.onopen = function() {
    console.log('WebSocket连接成功');
    // 订阅主题
    ws.send(JSON.stringify({
        action: 'subscribe',
        topic: 'sensor/data'
    }));
};

ws.onmessage = function(event) {
    const data = JSON.parse(event.data);
    console.log('收到数据:', data);
};

ws.onerror = function(error) {
    console.error('WebSocket错误:', error);
};

ws.onclose = function() {
    console.log('WebSocket连接关闭');
};

3.2 发送数据

// 发送数据到DolphinDB
function sendData(data) {
    ws.send(JSON.stringify({
        action: 'write',
        table: 'ws_stream',
        data: data
    }));
}

// 示例
sendData({
    device_id: 'D001',
    timestamp: new Date().toISOString(),
    temperature: 25.5,
    humidity: 50.0
});

3.3 批量发送

// 批量发送数据
function sendBatch(dataList) {
    ws.send(JSON.stringify({
        action: 'write',
        table: 'ws_stream',
        data: dataList
    }));
}

// 示例
const batch = [];
for (let i = 0; i < 100; i++) {
    batch.push({
        device_id: `D${i.toString().padStart(3, '0')}`,
        timestamp: new Date().toISOString(),
        temperature: 20 + Math.random() * 10,
        humidity: 40 + Math.random() * 20
    });
}
sendBatch(batch);

---

四、消息处理

4.1 消息格式

// JSON消息格式
{
    "action": "write",     // 操作类型
    "table": "ws_stream",  // 目标表
    "data": {              // 数据
        "device_id": "D001",
        "timestamp": "2024-01-01T00:00:00",
        "temperature": 25.5,
        "humidity": 50.0
    }
}

// 订阅消息
{
    "action": "subscribe",
    "topic": "sensor/data"
}

// 查询消息
{
    "action": "query",
    "sql": "select * from ws_stream limit 10"
}

4.2 消息处理函数

// 消息处理函数
def handleWsMessage(msg) {
    action = msg.action
    
    if (action == "write") {
        // 写入数据
        table = msg.table
        data = msg.data
        // 写入逻辑
    } else if (action == "subscribe") {
        // 订阅主题
        topic = msg.topic
        // 订阅逻辑
    } else if (action == "query") {
        // 查询数据
        sql = msg.sql
        // 查询逻辑
    }
}

---

五、心跳保活

5.1 心跳机制

// 客户端心跳
let heartbeatInterval;

function startHeartbeat() {
    heartbeatInterval = setInterval(() => {
        if (ws.readyState === WebSocket.OPEN) {
            ws.send(JSON.stringify({ action: 'ping' }));
        }
    }, 30000);  // 每30秒发送心跳
}

function stopHeartbeat() {
    clearInterval(heartbeatInterval);
}

ws.onopen = function() {
    startHeartbeat();
};

ws.onclose = function() {
    stopHeartbeat();
};

5.2 服务端心跳响应

// 服务端心跳处理
def handleHeartbeat(conn) {
    // 收到ping，返回pong
    ws::send(conn, {action: "pong", timestamp: now()})
}

---

六、断线重连

6.1 自动重连

// 自动重连机制
let ws;
let reconnectAttempts = 0;
const maxReconnectAttempts = 5;

function connect() {
    ws = new WebSocket('ws://localhost:8848/ws');
    
    ws.onopen = function() {
        console.log('WebSocket连接成功');
        reconnectAttempts = 0;
    };
    
    ws.onclose = function() {
        console.log('WebSocket连接关闭');
        if (reconnectAttempts < maxReconnectAttempts) {
            reconnectAttempts++;
            console.log(`尝试重连 (${reconnectAttempts}/${maxReconnectAttempts})`);
            setTimeout(connect, 3000);
        }
    };
    
    ws.onerror = function(error) {
        console.error('WebSocket错误:', error);
    };
}

connect();

6.2 数据缓冲

// 断线时缓冲数据
const dataBuffer = [];
const maxBufferSize = 10000;

function sendDataWithBuffer(data) {
    if (ws.readyState === WebSocket.OPEN) {
        ws.send(JSON.stringify(data));
        // 发送缓冲数据
        while (dataBuffer.length > 0) {
            ws.send(JSON.stringify(dataBuffer.shift()));
        }
    } else {
        // 缓冲数据
        if (dataBuffer.length < maxBufferSize) {
            dataBuffer.push(data);
        }
    }
}

---

七、实战案例

7.1 实时监控数据推送

// ========== 实时监控数据推送 ==========

// 1. 创建流表
share streamTable(100000:0, 
    `device_id`timestamp`temperature`humidity`pressure,
    [SYMBOL, TIMESTAMP, DOUBLE, DOUBLE, DOUBLE]) as monitor_stream

// 2. 启用持久化
enableTablePersistence(monitor_stream, true, true, 1000000)

// 3. 创建分布式表
db = database("dfs://ws_db", VALUE, 1..1000)
schema = table(1:0, `device_id`timestamp`temperature`humidity`pressure,
               [SYMBOL, TIMESTAMP, DOUBLE, DOUBLE, DOUBLE])
db.createPartitionedTable(schema, `monitor_data, `device_id)

// 4. 订阅写入
subscribeTable(, "monitor_stream", "persist", -1,
    def(msg) {
        loadTable("dfs://ws_db", "monitor_data").append!(msg)
    }, 10000, 5000)

// 5. WebSocket端点
// ws://localhost:8848/ws

// 6. 客户端示例（JavaScript）
/*
const ws = new WebSocket('ws://localhost:8848/ws');

ws.onopen = function() {
    console.log('连接成功');
};

function pushData(deviceId, temp, humid, press) {
    ws.send(JSON.stringify({
        action: 'write',
        table: 'monitor_stream',
        data: {
            device_id: deviceId,
            timestamp: new Date().toISOString(),
            temperature: temp,
            humidity: humid,
            pressure: press
        }
    }));
}
*/

print("实时监控数据推送系统已就绪")

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八、总结

本文详细介绍了DolphinDB WebSocket接入：

1. WebSocket原理：全双工、实时推送、长连接
2. 连接管理：创建连接、配置参数
3. 数据接收：连接、发送、批量发送
4. 消息处理：消息格式、处理函数
5. 心跳保活：心跳机制、响应处理
6. 断线重连：自动重连、数据缓冲

思考题：

1. WebSocket相比HTTP有什么优势？
2. 如何设计可靠的WebSocket连接？
3. 如何处理WebSocket断线问题？

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参考资料

• DolphinDB WebSocket
• WebSocket协议

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