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)
}

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)
}