package main

import (
	"io"
	"log"
	"net"
	"net/http"
	"strings"
)

/*
*
@author: sre
@date: 2022/8/21 0021
@desc: todo
*
*/

type goPrivoxy struct {
}

func (p *goPrivoxy) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	log.Printf("接受请求 %s %s %s\n", req.Method, req.Host, req.RemoteAddr)

	transport := http.DefaultTransport

	// 第一步： 代理接受到客户端的请求，复制原来的请求对象，并根据数据配置新请求的各种参数(添加上X-Forward-For头部等)
	outReq := new(http.Request)
	*outReq = *req // 这只是一个浅层拷贝

	clientIP, _, err := net.SplitHostPort(req.RemoteAddr)
	if err == nil {
		prior, ok := outReq.Header["X-Forwarded-For"]
		if ok {
			clientIP = strings.Join(prior, ", ") + ", " + clientIP
		}
		outReq.Header.Set("X-Forwarded-For", clientIP)
	}

	// 第二步： 把新请求复制到服务器端，并接收到服务器端返回的响应
	res, err := transport.RoundTrip(outReq)
	if err != nil {
		w.WriteHeader(http.StatusBadGateway) // 502
		return
	}

	// 第三步：代理服务器对响应做一些处理，然后返回给客户端
	for key, value := range res.Header {
		for _, v := range value {
			w.Header().Add(key, v)
		}
	}

	w.WriteHeader(res.StatusCode)
	io.Copy(w, res.Body)
	res.Body.Close()
}

func main() {
	log.Println("goPrivoxy start at 0.0.0.0:8118")
	http.Handle("/", &goPrivoxy{})
	http.ListenAndServe("0.0.0.0:8118", nil)
}