在Go中简单实现HTTP服务中间件

通常一个简单http服务框架，就是注册一堆路由，然后根据路由调用不同的逻辑去处理。

但实际上可能有一些统一的处理对几乎所有的路由都涉及到，比如日志，比如权限等等。

那么这个时候搞一个中间做预处理，是一个不错的想法。

定义一个中间件单元：

 package main

 import (
     "net/http"
 )

 // AdaptorHandle middleware func type
 type AdaptorHandle func(w http.ResponseWriter, r *http.Request) (next bool, err error)

 // MiddleWareAdaptor router middlewares mapped by url
 type MiddleWareAdaptor struct {
     URLs map[string][]AdaptorHandle
 }

 // MakeMiddleWareAdaptor make a middleware adaptor
 func MakeMiddleWareAdaptor() *MiddleWareAdaptor {
     mwa := &MiddleWareAdaptor{
         URLs: make(map[string][]AdaptorHandle),
     }

     return mwa
 }

 // Regist regist a adaptor
 func (mw *MiddleWareAdaptor) Regist(url string, Adaptor ...AdaptorHandle) {
     for _, adp := range Adaptor {
         mw.URLs[url] = append(mw.URLs[url], adp)
         // mw.URLs[url] = adp
     }
 }

 // Exec exec middleware adaptor funcs...
 func (mw *MiddleWareAdaptor) Exec(url string, w http.ResponseWriter, r *http.Request) (bool, error) {
     if adps, ok := mw.URLs[url]; ok {
         for _, adp := range adps {
             if next, err := adp(w, r); !next || (err != nil) {
                 return next, err
             }
         }
     }
     return true, nil
 }

然后将路由处理函数用中间件入口包裹起来：

 func middlewareHandler(next http.Handler) http.Handler {
     return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
         // before call handler
         start := time.Now()
         do, _ := mwa.Exec(r.URL.Path, w, r) // exec middleware
         // call next handler
         if do {
             log.Println("middleware done. next...")
             next.ServeHTTP(w, r)
         } else {
             log.Println("middleware done.break...")
         }
         // after call handle
         log.Printf("Comleted %s in %v", r.URL.Path, time.Since(start))
     })
 }

 mux.Handle("/", middlewareHandler(&uPlusRouterHandler{}))

 type uPlusRouterHandler struct {
 }

 func (rh *uPlusRouterHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 ...
 }

最后注册你需要的中间件即可：

mwa = MakeMiddleWareAdaptor() // init middleware
mwa.Regist("/", testMWAfunc, testMWAfunc2) // regist middleware
...
func testMWAfunc(w http.ResponseWriter, r *http.Request) (bool, error) {
    log.Println("我是第一个中间件...")
    log.Printf("Started %s %s", r.Method, r.URL.Path)
    return true, nil
}

func testMWAfunc2(w http.ResponseWriter, r *http.Request) (bool, error) {
    log.Println("我是第二个中间件...")
    return false, nil // return false,break follow-up actions.
}

代码虽然简单，记录一个思路。