浏览器缓存机制

• 一、浏览器缓存机制
  • 1、LastModified
  • 2、ETag
  • 3、expires

一、浏览器缓存机制

1、LastModified

const http = require('http')
const url = require('url')
const path = require('path')
const fs = require('fs')
const mime = require('mime')

http.createServer(function (req, res) {
  const {pathname} = url.parse(req.url, true)
  const filepath = path.join(__dirname, pathname)
  fs.stat(filepath, (err, stats) => {
    if (err) {
      return sendError(req, res)
    } else {
      const ifModifiedSince = req.headers['if-modified-since']
      const LastModified = stats.ctime.toGMTString()
      if (ifModifiedSince === LastModified) {
        res.writeHead(304)
        res.end('')
      } else {
        return send(req, res, filepath, stats)
      }
    }
  })
}).listen(8080)

function sendError(req, res) {
  res.end('Not Found')
}

function send(req, res, filepath, stats) {
  res.setHeader('Content-Type', mime.getType(filepath))
  res.setHeader('Last-Modified', stats.ctime.toGMTString())
  fs.createReadStream(filepath).pipe(res)
}

2、ETag

const http = require('http')
const url = require('url')
const path = require('path')
const fs = require('fs')
const mime = require('mime')
const crypto = require('crypto')

http.createServer(function (req, res) {
  const {pathname} = url.parse(req.url, true)
  const filepath = path.join(__dirname, pathname)
  fs.stat(filepath, (err, stats) => {
    if (err) {
      return sendError(req, res)
    } else {
      const ifNoneMatch = req.headers['if-none-match']
      const out = fs.createReadStream(filepath)
      const md5 = crypto.createHash('md5');
      out.on('data', function (data) {
        md5.update(data)
      })
      out.on('end', function () {
        const etag = md5.digest('hex')
        if (ifNoneMatch === etag) {
          res.writeHead(304)
          res.end('')
        } else {
          return send(req, res, filepath, etag)
        }
      })
    }
  })
}).listen(8080)

function sendError(req, res) {
  res.end('Not Found')
}

function send(req, res, filepath, etag) {
  res.setHeader('Content-Type', mime.getType(filepath))
  res.setHeader('ETag', etag)
  fs.createReadStream(filepath).pipe(res)
}

3、expires

const http = require('http')
const url = require('url')
const path = require('path')
const fs = require('fs')
const mime = require('mime')

http.createServer(function (req, res) {
  const {pathname} = url.parse(req.url, true)
  const filepath = path.join(__dirname, pathname)
  console.log(filepath)
  fs.stat(filepath, (err, stats) => {
    if (err) {
      return sendError(req, res)
    } else {
      return send(req, res, filepath)
    }
  })
}).listen(8080)

function sendError(req, res) {
  res.end('Not Found')
}

function send(req, res, filepath) {
  res.setHeader('Content-Type', mime.getType(filepath))
  // http1.0使用，已弃用
  // res.setHeader('Expires', new Date(Date.now() + 30 * 1000).toUTCString())
  // http1.1使用，优先级高于Expires
  res.setHeader('Cache-Control', 'max-age=30')
  /**
   * 1、private：客户端可以缓存
   * 2、public：客户端和代理服务器都可以缓存
   * 3、max-age=60：缓存内容将在60秒后失效
   * 4、no-cache：需要使用对比缓存验证数据，强制向源服务器再次验证
   * 5、no-store：所有内容都不会缓存，强制缓存和对比缓存都不会触发
   */
  res.setHeader('Cache-Control', 'max-age=30')
  fs.createReadStream(filepath).pipe(res)
}