先起一个目标服务

package main

import (
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"
)

func main() {
	rs1 := &RealServer{Addr: "127.0.0.1:2003"}
	rs1.Run()
	rs2 := &RealServer{Addr: "127.0.0.1:2004"}
	rs2.Run()

	//监听关闭信号
	quit := make(chan os.Signal)
	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
	<-quit
}

type RealServer struct {
	Addr string
}

func (r *RealServer) Run() {
	log.Println("Starting httpserver at " + r.Addr)
	mux := http.NewServeMux()
	mux.HandleFunc("/", r.HelloHandler)
	mux.HandleFunc("/base/error", r.ErrorHandler)
	mux.HandleFunc("/test_http_string/test_http_string/aaa", r.TimeoutHandler)
	server := &http.Server{
		Addr:         r.Addr,
		WriteTimeout: time.Second * 3,
		Handler:      mux,
	}
	go func() {
		log.Fatal(server.ListenAndServe())
	}()
}

func (r *RealServer) HelloHandler(w http.ResponseWriter, req *http.Request) {
	//127.0.0.1:8008/abc?sdsdsa=11
	//r.Addr=127.0.0.1:8008
	//req.URL.Path=/abc
	//fmt.Println(req.Host)
	upath := fmt.Sprintf("http://%s%s\n\n", r.Addr, req.URL.Path)
	realIP := fmt.Sprintf("RemoteAddr=%s,X-Forwarded-For=%v,X-Real-Ip=%v\n\n", req.RemoteAddr, req.Header.Get("X-Forwarded-For"), req.Header.Get("X-Real-Ip"))
	header:=fmt.Sprintf("headers =%v\n\n",req.Header)
	io.WriteString(w, upath)
	io.WriteString(w, realIP)
	io.WriteString(w, header)

}

func (r *RealServer) ErrorHandler(w http.ResponseWriter, req *http.Request) {
	upath := "error handler"
	w.WriteHeader(500)
	io.WriteString(w, upath)
}

func (r *RealServer) TimeoutHandler(w http.ResponseWriter, req *http.Request) {
	time.Sleep(2*time.Second)
	upath := "timeout handler"
	w.WriteHeader(200)
	io.WriteString(w, upath)
}

下边是我们编辑的代理

这里边只是简单代理转发 错误处理,负载等等 均没有实现

package main

import (
	"bufio"
	"fmt"
	"log"
	"net/http"
	"net/url"
)

var (
	proxy_addr = "http://127.0.0.1:2003/111"
	port       = "2002"
)

func handler(w http.ResponseWriter, r *http.Request) {
	//step 1 解析代理地址，并更改请求体的协议和主机
	proxy, err := url.Parse(proxy_addr)
	fmt.Println("proxy",proxy)
	r.URL.Scheme = proxy.Scheme
	r.URL.Host = proxy.Host

	fmt.Println("URL",r.URL.Scheme)

	//step 2 请求下游
	transport := http.DefaultTransport
	resp, err := transport.RoundTrip(r)
	if err != nil {
		log.Print(err)
		return
	}

	//step 3 把下游请求内容返回给上游
	for k, vv := range resp.Header {
		for _, v := range vv {
			w.Header().Add(k, v)
		}
	}
	defer resp.Body.Close()
	bufio.NewReader(resp.Body).WriteTo(w)
}

func main() {
	http.HandleFunc("/", handler)
	log.Println("Start serving on port " + port)
	err := http.ListenAndServe(":"+port, nil)
	if err != nil {
		log.Fatal(err)
	}
}