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：

 1 package main
 2 
 3 import (
 4     "net/http"
 5 )
 6 
 7 // adaptorhandle middleware func type
 8 type adaptorhandle func(w http.responsewriter, r *http.request) (next bool, err error)
 9 
10 // middlewareadaptor router middlewares mapped by url
11 type middlewareadaptor struct {
12     urls map[string][]adaptorhandle
13 }
14 
15 // makemiddlewareadaptor make a middleware adaptor
16 func makemiddlewareadaptor() *middlewareadaptor {
17     mwa := &middlewareadaptor{
18         urls: make(map[string][]adaptorhandle),
19     }
20 
21     return mwa
22 }
23 
24 // regist regist a adaptor
25 func (mw *middlewareadaptor) regist(url string, adaptor ...adaptorhandle) {
26     for _, adp := range adaptor {
27         mw.urls[url] = append(mw.urls[url], adp)
28         // mw.urls[url] = adp
29     }
30 }
31 
32 // exec exec middleware adaptor funcs...
33 func (mw *middlewareadaptor) exec(url string, w http.responsewriter, r *http.request) (bool, error) {
34     if adps, ok := mw.urls[url]; ok {
35         for _, adp := range adps {
36             if next, err := adp(w, r); !next || (err != nil) {
37                 return next, err
38             }
39         }
40     }
41     return true, nil
42 }

然后将路由处理函数用中间件入口包裹起来：

 1 func middlewarehandler(next http.handler) http.handler {
 2     return http.handlerfunc(func(w http.responsewriter, r *http.request) {
 3         // before call handler
 4         start := time.now()
 5         do, _ := mwa.exec(r.url.path, w, r) // exec middleware
 6         // call next handler
 7         if do {
 8             log.println("middleware done. next...")
 9             next.servehttp(w, r)
10         } else {
11             log.println("middleware done.break...")
12         }
13         // after call handle
14         log.printf("comleted %s in %v", r.url.path, time.since(start))
15     })
16 }
17 
18 mux.handle("/", middlewarehandler(&uplusrouterhandler{}))
19 
20 type uplusrouterhandler struct {
21 }
22 
23 func (rh *uplusrouterhandler) servehttp(w http.responsewriter, r *http.request) {
24 ...
25 }

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。