在Go中簡單實現HTTP服務中間件

通常一個簡單http服務框架，就是注冊一堆路由，然后根據路由調用不同的邏輯去處理。

但實際上可能有一些統一的處理對幾乎所有的路由都涉及到，比如日志，比如權限等等。

那么這個時候搞一個中間做預處理，是一個不錯的想法。

定義一個中間件單元：

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
}

然后將路由處理函數用中間件入口包裹起來：

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) {
...
}

最后注冊你需要的中間件即可：

mwa = MakeMiddleWareAdaptor() // init middleware
mwa.Regist("/", testMWAfunc, testMWAfunc2) // regist middleware
...
func testMWAfunc(w http.ResponseWriter, r *http.Request) (bool, error) {
    log.Println("我是第一個中間件...")
    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("我是第二個中間件...")
    return false, nil // return false,break follow-up actions.
}

代碼雖然簡單，記錄一個思路。