GO语言HTTP代理服务器

package main

import (
	"fmt"
	"io"
	"log"
	"net/http"
	"net/http/httputil"
	"net/url"
)

func httpUserInfo(w http.ResponseWriter, r *http.Request) {
	ret := "your addr is:" + r.RemoteAddr + "\r\n"
	ret += "request headers:" + fmt.Sprint(r.Header)
	io.WriteString(w, ret)
}

func main() {
	targetURL, err := url.Parse("http://127.0.0.1:80")
	log.Println("program start......")
	if err != nil {
		log.Println("bad url:", err)
		return
	}
	httpProxy := httputil.NewSingleHostReverseProxy(targetURL)
	http.HandleFunc("/myinfo/", httpUserInfo)
	http.Handle("/", httpProxy)
	log.Println("listen http proxy on :8001.....")
	http.ListenAndServe(":8001", nil)
}

以上代码有个缺陷，就是通过HTTP代理后HTTP协议头的Host域不会改变，如代理到 www.qq.com,抓包时:

GET / HTTP/1.1
Host: 127.0.0.1:8001
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
Accept: text/html, application/xhtml+xml, */*
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN
X-Forwarded-For: 192.168.20.155

在服务器没有检查host域的时候用这种方式代理最简单。如果检查host域的网站就自己修改包里面的实现或自己处理http包头，也简单。