狭义中间件

前言

狭义中间件的要素常见要素如下所示。

  • 一切皆中间件
  • 中间件内操作请求 request
    • 请求拦截
  • 中间件内操作响应 response
    • 响应拦截
  • 中间件内操作上下文 context
    • 直接上下文代理，初始化实例时候挂载代理在app.context上
    • 请求过程上下文代理，请求时候挂载代理在ctx上
  • 大部分直接被 app.use() 加载
    • 注意: 初始化实例挂载代理context不被app.use()

请求拦截

  1. const Koa = require('koa');
  2. let app = new Koa();
  4. const middleware = async function(ctx, next) {
  5.   // 中间件 拦截请求
  6.   // 把所有请求不是 /page/ 开头的路径全部抛出500错误
  7.   const reqPath = ctx.request.path;
  8.   if( reqPath.indexOf('/page/') !== 0 ) {
  9.     ctx.throw(500)
  10.   }
  11.   await next();
  12. }
  14. const page = async function(ctx, next) {
  15.   ctx.body = `
  16.       <html>
  17.         <head></head>
  18.         <body>
  19.           <h1>${ctx.request.path}</h1>
  20.         </body>
  21.       </html>
  22.     `; 
  23. }
  25. app.use(middleware);
  26. app.use(page);
  28. app.listen(3001, function(){
  29.   console.log('the demo is start at port 3001');
  30. })

响应拦截

  1. const Koa = require('koa');
  2. let app = new Koa();
  4. const middleware = async function(ctx, next) {
  5.   ctx.response.type = 'text/plain';
  6.   await next();
  7. }
  9. const page = async function(ctx, next) {
  10.   ctx.body = `
  11.       <html>
  12.         <head></head>
  13.         <body>
  14.           <h1>${ctx.path}</h1>
  15.         </body>
  16.       </html>
  17.     `; 
  18. }
  20. app.use(middleware);
  21. app.use(page);
  23. app.listen(3001, function(){
  24.   console.log('the demo is start at port 3001');
  25. })

context挂载代理

  • 请求代理注入

    • 直接被app.use
    • 请求时候才有注入
    • 每次请求的注入都不同

  • 初始化实例（应用）代理注入

    • 直接注入到app.context
    • 初始化应用的时候才注入
    • 只注入一次，每次请求都可以使用

请求时挂载代理context

  1. const Koa = require('koa');
  2. let app = new Koa();
  4. const middleware = async function(ctx, next) {
  5.   // 中间件 代理/挂载上下文
  6.   // 把所有当前服务的进程PID，内存使用情况方法代理/挂载在ctx上
  7.   ctx.getServerInfo = function() {
  8.     function parseMem( mem = 0 ) {
  9.       let memVal = mem / 1024 / 1024;
  10.       memVal = memVal.toFixed(2) + 'MB';
  11.       return memVal;
  12.     }
  14.     function getMemInfo() {
  15.       let memUsage = process.memoryUsage();
  16.       let rss = parseMem(memUsage.rss);
  17.       let heapTotal = parseMem(memUsage.heapTotal);
  18.       let heapUsed =  parseMem(memUsage.heapUsed);
  19.       return {
  20.         pid: process.pid,
  21.         rss,
  22.         heapTotal,
  23.         heapUsed
  24.       }
  25.     }
  26.     return getMemInfo()
  27.   };
  28.   await next();
  29. }
  31. const page = async function(ctx, next) {
  32.   const serverInfo = ctx.getServerInfo();
  33.   ctx.body = `
  34.       <html>
  35.         <head></head>
  36.         <body>
  37.           <p>${JSON.stringify(serverInfo)}</p>
  38.         </body>
  39.       </html>
  40.     `; 
  41. }
  43. app.use(middleware);
  44. app.use(page);
  46. app.listen(3001, function(){
  47.   console.log('the demo is start at port 3001');
  48. })

初始化实例挂载代理context

  1. const Koa = require('koa');
  2. let app = new Koa();
  4. const middleware = function(app) {
  5.   // 中间件在初始化实例 把getServerInfo方法 挂载代理到上下文
  6.   app.context.getServerInfo = function() {
  7.     function parseMem( mem = 0 ) {
  8.       let memVal = mem / 1024 / 1024;
  9.       memVal = memVal.toFixed(2) + 'MB';
  10.       return memVal;
  11.     }
  13.     function getMemInfo() {
  14.       let memUsage = process.memoryUsage();
  15.       let rss = parseMem(memUsage.rss);
  16.       let heapTotal = parseMem(memUsage.heapTotal);
  17.       let heapUsed =  parseMem(memUsage.heapUsed);
  18.       return {
  19.         pid: process.pid,
  20.         rss,
  21.         heapTotal,
  22.         heapUsed
  23.       }
  24.     }
  25.     return getMemInfo()
  26.   };
  27. }
  29. middleware(app);
  31. const page = async function(ctx, next) {
  32.   const serverInfo = ctx.getServerInfo();
  33.   ctx.body = `
  34.       <html>
  35.         <head></head>
  36.         <body>
  37.           <p>${JSON.stringify(serverInfo)}</p>
  38.         </body>
  39.       </html>
  40.     `; 
  41. }
  43. app.use(page);
  45. app.listen(3001, function(){
  46.   console.log('the demo is start at port 3001');
  47. })