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。