#GOLANG . replace http server request body

middleware.go

package main

import (
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
)

type Middleware func(http.HandlerFunc) http.HandlerFunc

func MiddlewareStack(mws ...Middleware) (handlerFunc http.HandlerFunc) {
	for i := len(mws); i > 0; i-- {
		handlerFunc = mws[i-1](handlerFunc)
	}
	return
}

type Body struct {
	data []byte
}

func (b *Body) Read(bs []byte) (n int, err error) {
	if len(b.data) != 0 {
		n = copy(bs, b.data)
		b.data = b.data[n:]
		return
	}
	err = io.EOF
	return
}
func (b *Body) Close() error {
	return nil
}

var data = "qwertyuiopasdfghjklzxcvbnm"

func MiddleWare1(next http.HandlerFunc) http.HandlerFunc {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		r.Body = &Body{[]byte(data)} //set data
		fmt.Println("MW1->\n")
		next.ServeHTTP(w, r)
		fmt.Println("MW1<-\n")
	})
}

func MiddleWare2(next http.HandlerFunc) http.HandlerFunc {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Println("MW2->\n")
		next.ServeHTTP(w, r)
		fmt.Println("MW2<-\n")
	})
}
func MiddleWare3(next http.HandlerFunc) http.HandlerFunc {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Println("MW3->\n")
		bs, _ := ioutil.ReadAll(r.Body) //get data
		fmt.Println("result:", string(bs), " , expected:", data, "\n")
		//next.ServeHTTP(w, r) //last middleware, next == nil
		fmt.Println("MW3<-\n")
	})
}
func main() {
	http.ListenAndServe(":8080", MiddlewareStack(MiddleWare1, MiddleWare2, MiddleWare3)) //akses: http://localhost:8080
}