package main//中间件1：只允许特定host请求过来import (    "fmt"    "net/http")//SingleHost是一个中间件，type SingleHost struct {    hander http.Handler //这不是继承http.Handler接口，后面重写了ServeHTTP方法。    /*        type Handler interface {            ServeHTTP(ResponseWriter, *Request)        }*/    allowedHost string //只准允许某个host发来的请求}//Handler这个接口只有一个方法，SingleHost实现了这个方法就相当于继承了Handler interface接口//请求来的时候会来这里func (this *SingleHost) ServeHTTP(w http.ResponseWriter, r *http.Request) {    fmt.Println(r.Host)    if r.Host == this.allowedHost { //从Request里面可以获取Host        this.hander.ServeHTTP(w, r)    } else {        w.WriteHeader(403)    }}func myHandler(w http.ResponseWriter, r *http.Request) {    w.Write([]byte("helloworld"))}func main() {    sing := &SingleHost{        hander:      http.HandlerFunc(myHandler),        allowedHost: "example.com", //只有example.com过来的才合法    }    http.ListenAndServe(":8080", sing)}

 中间件形式2：函数形式

package main//中间件2：只允许特定host请求过来。//函数的形式。import (    "fmt"    "net/http")/*type HandlerFunc func(ResponseWriter, *Request)// ServeHTTP calls f(w, r).func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {    f(w, r)}*/func SingleHost(handler http.Handler, allowstring string) http.Handler {    fn := func(w http.ResponseWriter, r *http.Request) {        if r.Host == allowstring { //从Request里面可以获取Host            this.hander.ServeHTTP(w, r)        } else {            w.WriteHeader(403)        }    }    return http.HandlerFunc(fn)}func myHandler(w http.ResponseWriter, r *http.Request) {    w.Write([]byte("helloworld"))}func main() {    sing := SingleHost(http.HandlerFunc(myHandler), "example.com")    http.ListenAndServe(":8080", sing)}

 

package main//中间件3：只允许特定host请求过来。//追加内容形式。import (    _ "fmt"    "net/http")type AppendMiddleware struct {    handler http.Handler}func (this *AppendMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) {    this.handler.ServeHTTP(w, r)              //正常是响应    w.Write([]byte("Hey,this is middleware")) //多输出一行内容，告诉用户这是中间价}func myHandler(w http.ResponseWriter, r *http.Request) {    w.Write([]byte("helloworld"))}func main() {    mid := &AppendMiddleware{http.HandlerFunc(myHandler)}    http.ListenAndServe(":8080", mid)}

 

package main//中间件3：只允许特定host请求过来。//自定义响应。import (    _ "fmt"    "net/http"    "net/http/httpest")//先将所有的响应保存起来，完成所有操作之后，然后一起输出type ModifiedMiddleware struct {    handler http.Handler}func (this *ModifiedMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) {    rec := httptest.NewRecorder()    this.handler.ServeHTTP(rec, r) //rec将所有的响应记录下来    for k, v := range rec.Header() {        w.Header()[k] = v    }    w.Header().Set("go-web-foundation", "vip")    w.WriteHeader(418)    w.Write([]byte("this is middleware"))    w.Write(rec.Body.Bytes())}func myHandler(w http.ResponseWriter, r *http.Request) {    w.Write([]byte("helloworld"))}func main() {    mid := &ModifiedMiddleware{http.HandlerFunc(myHandler)}    http.ListenAndServe(":8080", mid)}