为什么使用 Node.js 进行实时通信？

在当今的数字世界中，实时通信是必不可少的。无论是聊天应用程序还是实时体育更新，实时通信都是保持用户参与的必要条件。Node.js 因其速度、可扩展性和可靠性而成为开发实时应用程序的常用工具。在本文中，我们将探讨为什么 Node.js 是实时通信的理想选择以及如何实现它。

为什么使用 Node.js 进行实时通信？

Node.js 基于 Google 的 V8 JavaScript 引擎构建，该引擎以其高性能而著称。这使得 Node.js 成为构建需要速度和可扩展性的实时通信应用程序的完美工具。Node.js 还是事件驱动型的，这意味着它可以同时处理多个连接，使其成为构建实时应用程序的完美工具。

协议和库类型

Node.js 提供了多种实现实时数据通信的方法。Node.js 中一些常用的实时数据通信方式包括：

Socket.IO

Socket.IO 是一种流行的实时通信库。它使用 WebSockets 作为传输层，在客户端和服务器之间提供实时通信。Socket.IO 提供了许多功能，如自动重新连接、支持二进制数据以及为不支持 WebSockets 的环境提供回退选项。

WebSockets

WebSockets 是一种支持客户端和服务器之间实时通信的协议。它通过单个 TCP 连接提供全双工通信通道，允许客户端和服务器之间进行实时数据交换。这个名为“ws”的模块可用于实现 WebSockets。

服务器发送事件

服务器发送事件是一个简单的协议，允许服务器通过 HTTP 连接向客户端发送事件。它非常适合需要单向通信的应用程序，例如现场体育赛事比分或股票市场更新。该模块称为“sse”，可用于实现服务器发送事件。

WebRTC

WebRTC 是一种实时通信协议，允许浏览器建立点对点连接。它在客户端之间提供低延迟的通信通道，而无需服务器。这个“node-webrtc”可用于实现 WebRTC。

MQTT

MQTT 是一种轻量级消息传递协议，非常适合 IoT 应用程序。它为客户端和服务器之间的通信提供了发布/订阅模型。该模块称为“mqtt”，可用于实现 MQTT。

如何确保通信安全？

对于任何实时通信应用程序来说，安全都是至关重要的。这个名为 “crypto “的模块可用于确保客户端和服务器之间的通信安全。该模块提供加密和解密功能，可以在客户端和服务器之间发送加密信息。

此外，每种类型都有相应的模块，例如 WebSocket 就有 “ws “模块，安全的方法是用 “https “而不是 “http “来封装它。

代码示例

Socket.IO — 客户端服务器消息示例

服务器端代码：

// Install with 'npm i <module>' & Import necessary modules
const express = require('express');
const app = express();
const server = require('http').Server(app);
const io = require('socket.io')(server);

io.on('connection', (socket) => {
  console.log('User connected');

  socket.on('chat:message', (data) => {
    io.emit('chat:message', data);
  });

  socket.on('disconnect', () => {
    console.log('User disconnected');
  });
});

const PORT = process.env.PORT || 3000;
server.listen(PORT, () => {
  console.log(`Server listening on port ${PORT}`);
});

客户端代码：

<!DOCTYPE html>
<html>
<head>
  <title>Socket.IO Chat</title>
</head>
<body>
  <div id="messages"></div>
  <form id="chat-form">
    <input type="text" id="message-input">
    <button type="submit">Send</button>
  </form>
  <script src="/socket.io/socket.io.js"></script>
  <script>
    const socket = io();
    const messagesDiv = document.getElementById('messages');
    const chatForm = document.getElementById('chat-form');
    const messageInput = document.getElementById('message-input');

    chatForm.addEventListener('submit', (event) => {
      event.preventDefault();
      const message = messageInput.value.trim();
      if (message) {
        socket.emit('chat:message', message);
        messageInput.value = '';
      }
    });

    socket.on('chat:message', (data) => {
      const messageDiv = document.createElement('div');
      messageDiv.innerText = data;
      messagesDiv.appendChild(messageDiv);
    });
  </script>
</body>
</html>

WebSockets — 客户端服务器消息示例

服务器端代码：

// Install with 'npm i <module>' & Import necessary modules
const WebSocket = require('ws'); // use wss for secured option
const server = new WebSocket.Server({ port: 3000 });

server.on('connection', (socket) => {
  console.log('User connected');

// Handle socket connection
  socket.on('message', (message) => {
    server.clients.forEach((client) => {
      if (client.readyState === WebSocket.OPEN) {
        client.send(message);
      }
    });
  });

  socket.on('close', () => {
    console.log('User disconnected');
  });
});

客户端代码：

<!DOCTYPE html>
<html>
<head>
  <title>WebSockets Chat</title>
</head>
<body>
  <div id="messages"></div>
  <form id="chat-form">
    <input type="text" id="message-input">
    <button type="submit">Send</button>
  </form>
<script>
    const socket = new WebSocket('ws://localhost:3000');
    const messagesDiv = document.getElementById('messages');
    const chatForm = document.getElementById('chat-form');
    const messageInput = document.getElementById('message-input');
    chatForm.addEventListener('submit', (event) => {
      event.preventDefault();
      const message = messageInput.value.trim();
      if (message) {
        socket.send(message);
        messageInput.value = '';
      }
    });
    socket.addEventListener('message', (event) => {
      const messageDiv = document.createElement('div');
      messageDiv.innerText = event.data;
      messagesDiv.appendChild(messageDiv);
    });
  </script>
</body>
</html>

服务器发送事件(SSE) – 时钟事件示例

服务器端代码：

// Install with 'npm i <module>' & Import necessary modules
const express = require('express');
const app = express();

app.get('/events', (req, res) => {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive'
  });

  const interval = setInterval(() => {
    res.write(`data: ${new Date().toLocaleTimeString()}\n\n`);
  }, 1000);

  req.on('close', () => {
    clearInterval(interval);
    res.end();
  });
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server listening on port ${PORT}`);
});

客户端代码：

<!DOCTYPE html>
<html>
<head>
  <title>Server-Sent Events Clock</title>
</head>
<body>
  <div id="clock"></div>
<script>
    const source = new EventSource('/events');
    const clockDiv = document.getElementById('clock');
    
    source.addEventListener('message', (event) => {
      clockDiv.innerText = event.data;
    });
  </script>
</body>
</html>

WebRTC — 视频流示例

服务器端代码：

// Install with 'npm i <module>' & Import necessary modules
const express = require('express');
const app = express();
const http = require('http').createServer(app);
const io = require('socket.io')(http);
const { RTCPeerConnection, RTCSessionDescription, RTCIceCandidate } = require('wrtc');

// Serve static files from public directory
app.use(express.static('public'));

io.on('connection', socket => {
  console.log('Client connected:', socket.id);
  let pc = new RTCPeerConnection();

  // Handle offer from client
  socket.on('offer', offer => {
    console.log('Received offer');

    pc.setRemoteDescription(new RTCSessionDescription(offer))
      .then(() => {
        return navigator.mediaDevices.getUserMedia({ audio: true, video: true });
      })
      .then(stream => {
        console.log('Got local stream');

        // Add local stream to peer connection
        stream.getTracks().forEach(track => {
          pc.addTrack(track, stream);
        });

        // Handle ice candidates
        pc.onicecandidate = event => {
          if (event.candidate) {
            socket.emit('candidate', event.candidate);
          }
        };

        // Handle remote stream
        pc.ontrack = event => {
          console.log('Received remote stream');
          socket.emit('answer', pc.localDescription);
        };

        // Create answer
        pc.createAnswer()
          .then(answer => {
            return pc.setLocalDescription(answer);
          })
          .catch(error => {
            console.log('Error creating answer:', error);
          });
      })
      .catch(error => {
        console.log('Error getting user media:', error);
      });
  });

  // Handle disconnect from client
  socket.on('disconnect', () => {
    console.log('Client disconnected:', socket.id);
    pc.close();
  });
});

const PORT = process.env.PORT || 3000;
http.listen(PORT, () => {
  console.log(`Server listening on port ${PORT}`);
});

客户端代码：

<html>
  <head>
    <meta charset="UTF-8">
    <title>WebRTC Example</title>
  </head>
  <body>
    <h1>WebRTC Example</h1>
    <div>
      <video id="localVideo" autoplay></video>
      <video id="remoteVideo" autoplay></video>
    </div>
    <div>
      <button id="callButton">Call</button>
      <button id="hangupButton" disabled>Hang Up</button>
    </div>
    <script src="/socket.io/socket.io.js"></script>
    <script>
      const socket = io.connect('http://localhost:3000');
      const localVideo = document.getElementById('localVideo');
      const remoteVideo = document.getElementById('remoteVideo');
      const callButton = document.getElementById('callButton');
      const hangupButton = document.getElementById('hangupButton');
      
      let pc = new RTCPeerConnection();
      
      // Disable hang up button initially
      hangupButton.disabled = true;
      
      // Handle call button click
      callButton.onclick = () => {
        console.log('Calling');
      
        navigator.mediaDevices.getUserMedia({ audio: true, video: true })
          .then(stream => {
            console.log('Got local stream');
            localVideo.srcObject = stream;
      
            // Add local stream to peer connection
            stream.getTracks().forEach(track => {
              pc.addTrack(track, stream);
            });
      
            // Handle ice candidates
            pc.onicecandidate = event => {
              if (event.candidate) {
                socket.emit('candidate', event.candidate);
              }
            };
      
            // Handle remote stream
            pc.ontrack = event => {
              console.log('Received remote stream');
              remoteVideo.srcObject = event.streams[0];
            };
      
            // Create offer
            pc.createOffer()
              .then(offer => {
                return pc.setLocalDescription(offer);
              })
              .then(() => {
                socket.emit('offer', pc.localDescription);
              })
              .catch(error => {
                console.log('Error creating offer:', error);
              });
      
            // Enable hang up button
            hangupButton.disabled = false;
      
            // Handle hang up button click
            hangupButton.onclick = () => {
              console.log('Hanging up');
              pc.close();
              remoteVideo.srcObject = null;
              hangupButton.disabled = true;
              callButton.disabled = false;
            };
          })
          .catch(error => {
            console.log('Error getting user media:', error);
          });
      };
      
      // Handle answer from other user
      socket.on('answer', answer => {
        console.log('Received answer');
        pc.setRemoteDescription(new RTCSessionDescription(answer))
          .catch(error => {
            console.log('Error setting remote description:', error);
          });
      });
      
      // Handle ice candidate from other user
      socket.on('candidate', candidate => {
        console.log('Received candidate');
        pc.addIceCandidate(new RTCIceCandidate(candidate))
          .catch(error => {
            console.log('Error adding ice candidate:', error);
          });
      });
    </script>
  </body>
</html>

MQTT 示例

发布方代码：

// Install with 'npm i <module>' & Import necessary modules
const mqtt = require('mqtt');
const client = mqtt.connect('mqtt://test.mosquitto.org');

client.on('connect', () => {
  console.log('connected to MQTT broker');

  setInterval(() => {
    client.publish('test', 'Hello MQTT');
  }, 1000);
});

client.on('error', (error) => {
  console.log(error);
});

订阅者端代码：

// Install with 'npm i <module>' & Import necessary modules
const mqtt = require('mqtt');
const client = mqtt.connect('mqtt://test.mosquitto.org');

client.on('connect', () => {
  console.log('connected to MQTT broker');

  client.subscribe('test', (error) => {
    if (error) {
      console.log(error);
    }
  });
});

client.on('message', (topic, message) => {
  console.log(`${topic}: ${message}`);
});

client.on('error', (error) => {
  console.log(error);
});