Express中间件(Middleware)详解：从零开始掌握(2)

1. 请求耗时中间件的增强版

问题：原版只能记录到控制台，如何记录到文件？

改进点：

1. 使用process.hrtime()是什么？获取更高精度的时间
2. 支持将日志写入文件
3. 记录更多信息(IP地址、状态码)
4. 工厂函数模式使中间件可配置

const fs = require('fs');
const path = require('path');// 增强版耗时记录中间件
function createRequestLogger(logFilePath) {const logStream = fs.createWriteStream(path.join(__dirname, logFilePath), { flags: 'a' });return (req, res, next) => {const start = process.hrtime();const startDate = new Date().toISOString();res.on('finish', () => {const duration = process.hrtime(start);const durationMs = (duration[0] * 1e3 + duration[1] / 1e6).toFixed(3);const logEntry = `[${startDate}] ${req.ip} ${req.method} ${req.url} ${res.statusCode} ${durationMs}ms\n`;logStream.write(logEntry);console.log(logEntry.trim());});next();};
}// 使用方式
app.use(createRequestLogger('requests.log'));

2. API密钥验证中间件的进阶版

问题：如何支持多种验证方式？

改进点：

1. 支持多种认证策略(API Key、JWT、Basic Auth)
2. 异步验证支持
3. 统一的错误处理
4. 可扩展的工厂函数设计

// 支持多种验证策略的中间件工厂
function createAuthMiddleware(options = {}) {return async (req, res, next) => {try {// 策略1: API Key验证if (options.apiKey) {const apiKey = req.headers['x-api-key'] || req.query.apiKey;if (!apiKey) throw new Error('Missing API key');if (!options.apiKey.keys.includes(apiKey)) throw new Error('Invalid API key');req.authType = 'apiKey';}// 策略2: JWT验证if (options.jwt) {const token = req.headers.authorization?.split(' ')[1];if (!token) throw new Error('Missing token');const decoded = await verifyJWT(token, options.jwt.secret);req.user = decoded;req.authType = 'jwt';}// 策略3: 基本认证if (options.basicAuth) {const authHeader = req.headers.authorization;if (!authHeader || !authHeader.startsWith('Basic ')) {throw new Error('Missing basic auth');}const credentials = Buffer.from(authHeader.split(' ')[1], 'base64').toString();const [username, password] = credentials.split(':');if (username !== options.basicAuth.user || password !== options.basicAuth.pass) {throw new Error('Invalid credentials');}req.authType = 'basic';}next();} catch (error) {res.status(401).json({ error: 'Authentication failed',message: error.message});}};
}// 使用示例
app.use(createAuthMiddleware({apiKey: {keys: ['123-abc', '456-def']},jwt: {secret: 'my-secret-key'}
}));

3. 组合中间件的模式进阶

问题：如何更灵活地组合中间件？

改进点：

1. 实现了类似Koa的中间件组合机制
2. 添加条件中间件支持
3. 更灵活的路径匹配
4. 错误处理集成

// 中间件组合工具函数
function composeMiddlewares(...middlewares) {return (req, res, next) => {const dispatch = (i) => {if (i >= middlewares.length) return next();const middleware = middlewares[i];try {return middleware(req, res, () => dispatch(i + 1));} catch (err) {return next(err);}};return dispatch(0);};
}// 条件中间件
function conditionalMiddleware(condition, middleware) {return (req, res, next) => {if (condition(req)) {return middleware(req, res, next);}next();};
}// 使用示例
const isAdminRoute = req => req.path.startsWith('/admin');
const isApiRoute = req => req.path.startsWith('/api');app.use(composeMiddlewares(requestLogger,conditionalMiddleware(isApiRoute,apiKeyValidator),conditionalMiddleware(isAdminRoute,adminCheck)
));// 等价于：
// app.use(requestLogger);
// app.use('/api', apiKeyValidator);
// app.use('/admin', adminCheck);

实用中间件模式

1. 数据转换中间件

function transformRequestBody(fields) {return (req, res, next) => {if (req.body) {for (const [field, transform] of Object.entries(fields)) {if (req.body[field] !== undefined) {req.body[field] = transform(req.body[field]);}}}next();};
}// 使用示例
app.use(express.json());
app.use(transformRequestBody({email: v => v.toLowerCase().trim(),age: v => parseInt(v, 10),isActive: v => v === 'true'
}));

2. 响应包装中间件

function responseWrapper() {return (req, res, next) => {const originalSend = res.send;res.send = function(body) {if (res.statusCode >= 400) {originalSend.call(this, {success: false,error: body});} else {originalSend.call(this, {success: true,data: body});}};next();};
}

3. 请求限流中间件

function rateLimiter({ windowMs, maxRequests }) {const requests = new Map();setInterval(() => {requests.clear();}, windowMs);return (req, res, next) => {const ip = req.ip;const count = requests.get(ip) || 0;if (count >= maxRequests) {return res.status(429).send('Too many requests');}requests.set(ip, count + 1);next();};
}

最佳实践建议

1. ​单一职责：每个中间件只做一件事
2. ​可重用性：设计为可配置的工厂函数
3. ​错误处理：始终捕获同步和异步错误
4. ​性能考虑：避免在中间件中进行阻塞操作
5. ​文档注释：清晰说明中间件的用途和参数。

本节就到这里，下节将继续深入讨论示例。

Express中间件(Middleware)详解：从零开始掌握(3)-CSDN博客