Middleware

微服务架构的一些常用组件

1. 服务治理。通常是采用注册发现的机制。有一个注册中心


2. 集中式配置


3. 反向代理


4. ADN， CDN


5. 分布式存储


6. 分布式日志


7. 分布式锁


8. 消息队列


9. 分布式文件存储


10. 断路器


11. 分布式数据库
    12.路由与web服务器
    13.RPC框架
    14.缓存服务
    15.分布式事务
    16.任务调度
    17.安全
    https://thinkjs.org/zh-cn/doc/3.0/middleware.html
    https://www.zhihu.com/question/19730582

AOP已经实现了业务隔离。但却带来了一串长长的链式调用，如果处理不当很容易掉链子。另外，这种结构实现异步操作较为麻烦。

多个中间件会形成一个栈结构（middle stack），以”先进后出”（first-in-last-out）的顺序执行，被称为洋葱结构。

Koa的中间件使用。
const logger = (ctx, next) => {
console.log(${Date.now()} ${ctx.request.method} ${ctx.request.url});
next();
}
app.use(logger);

中间件一个奇妙的点在于next函数。如果中间件内部没有调用next函数，那么执行权就不会传递下去

Egg 是基于 Koa 实现的，所以 Egg 的中间件形式和 Koa 的中间件形式是一样的，都是基于洋葱圈模型。
https://eggjs.org/zh-cn/basics/middleware.html

http://c.biancheng.net/view/3860.html

Middleware module Description Replaces built-in function (Express 3)
body-parser Parse HTTP request body. See also: body, co-body, and raw-body. express.bodyParser
compression Compress HTTP responses. express.compress
connect-rid Generate unique request ID. NA
cookie-parser Parse cookie header and populate req.cookies. See also cookies and keygrip. express.cookieParser
cookie-session Establish cookie-based sessions. express.cookieSession
cors Enable cross-origin resource sharing (CORS) with various options. NA
csurf Protect from CSRF exploits. express.csrf
errorhandler Development error-handling/debugging. express.errorHandler
method-override Override HTTP methods using header. express.methodOverride
morgan HTTP request logger. express.logger
multer Handle multi-part form data. express.bodyParser
response-time Record HTTP response time. express.responseTime
serve-favicon Serve a favicon. express.favicon
serve-index Serve directory listing for a given path. express.directory
serve-static Serve static files. express.static
session Establish server-based sessions (development only). express.session
timeout Set a timeout period for HTTP request processing. express.timeout
vhost Create virtual domains. express.vhost
http://expressjs.com/en/resources/middleware.html

Middleware module Description
cls-rtracer Middleware for CLS-based request id generation. An out-of-the-box solution for adding request ids into your logs.
connect-image-optimus Optimize image serving. Switches images to .webp or .jxr, if possible.
express-debug Development tool that adds information about template variables (locals), current session, and so on.
express-partial-response Filters out parts of JSON responses based on the fields query-string; by using Google API’s Partial Response.
express-simple-cdn Use a CDN for static assets, with multiple host support.
express-slash Handles routes with and without trailing slashes.
express-stormpath User storage, authentication, authorization, SSO, and data security.
express-uncapitalize Redirects HTTP requests containing uppercase to a canonical lowercase form.
helmet Helps secure your apps by setting various HTTP headers.
join-io Joins files on the fly to reduce the requests count.
passport Authentication using “strategies” such as OAuth, OpenID and many others. See http://passportjs.org/ for more information.
static-expiry Fingerprint URLs or caching headers for static assets.
view-helpers Common helper methods for views.
sriracha-admin Dynamically generate an admin site for Mongoose.

纵观GO语言，中间件应用比较普遍，主要应用：

记录对服务器发送的请求（request）
处理服务器响应（response ）
请求和处理之间做一个权限认证工作
远程调用
安全

1,单个中间件
type Middleware func(http.HandlerFunc) http.HandlerFunc

2，多个中间件，递归方式使用，洋葱结构，koa、express、echo实现方式
func Chain(f http.HandlerFunc, middlewares …Middleware) http.HandlerFunc {
for _, m := range middlewares {
f = m(f)
}
return f
}

3，多个中间件，全局列表结构，gin框架实现
// HandlersChain defines a HandlerFunc array.
type HandlersChain []HandlerFunc
//模拟的调用堆栈
func (c *Context) Next() {
c.index++
for c.index < int8(len(c.handlers)) {
//按顺序执行HandlersChain内的函数
//如果函数内无c.Next()方法调用则函数顺序执行完
//如果函数内有c.Next()方法调用则代码执行到c.Next()方法处压栈，等待后面的函数执行完在回来执行c.Next()后的命令
c.handlersc.index
c.index++
}
}

https://www.cnblogs.com/maji233/p/11237349.html
https://blog.csdn.net/u014270740/article/details/91401698
https://blog.csdn.net/weixin_30339457/article/details/97592881

1,log
2,header
3,compress
4,auth
5,crsf
https://github.com/clevergo/middleware

服务描述
服务调用首先要解决的问题就是服务如何对外描述。比如服务名、调用这个服务需要提供哪些信息、返回的结果是什么格式的、如何解析等问题。

常用的服务描述方式包括 RESTful API、XML 配置以及 IDL 文件三种。

其中，RESTful API 方式通常用于 HTTP 协议的服务描述，并且常用 Wiki 或者Swagger来进行管理。下面是一个 RESTful API 方式的服务描述的例子。

XML 配置方式多用作 RPC 协议的服务描述，通过 *.xml 配置文件来定义接口名、参数以及返回值类型等。

如motan_server.xml中