simplest http proxy server

main1.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"log"
	"net"
	"net/url"
	"strings"
)

func main() {
	log.SetFlags(log.LstdFlags | log.Lshortfile)
	l, err := net.Listen("tcp", ":8787")
	if err != nil {
		log.Panic(err)
	} else {
		log.Println("listening on :8787")
	}

	for {
		client, err := l.Accept()
		if err != nil {
			log.Panic(err)
		} else {
			log.Println(client)
		}

		go handleClientRequest(client)
	}
}

func handleClientRequest(client net.Conn) {
	log.Println(client)
	if client == nil {
		return
	}
	defer client.Close()

	var b [1024]byte
	n, err := client.Read(b[:])
	if err != nil {
		log.Println(err)
		return
	}
	var method, host, address string

	fmt.Println(b)
	fmt.Println(len(b))
  // 打印HTTP HEADER
	fmt.Println(string(b[:]))

	fmt.Sscanf(string(b[:bytes.IndexByte(b[:], '\n')]), "%s%s", &method, &host)
	hostPortURL, err := url.Parse(host)
	if err != nil {
		log.Println(err)
		return
	}

	if hostPortURL.Opaque == "443" { //https访问
		address = hostPortURL.Scheme + ":443"
	} else { //http访问
		if strings.Index(hostPortURL.Host, ":") == -1 { //host不带端口， 默认80
			address = hostPortURL.Host + ":80"
		} else {
			address = hostPortURL.Host
		}
	}

	//获得了请求的host和port，就开始拨号吧
	server, err := net.Dial("tcp", address)
	if err != nil {
		log.Println(err)
		return
	}
	if method == "CONNECT" {
		fmt.Fprint(client, "HTTP/1.1 200 Connection established\r\n\r\n")
	} else {
		server.Write(b[:n])
	}
	//进行转发
	go io.Copy(server, client)
	io.Copy(client, server)
}
// 最简单的demo
// 只为了理解http proxy如何工作
// https://www.jianshu.com/p/53e219fbf3c5
// https://gist.github.com/fabrizioc1/4327250
// https://medium.com/@mlowicki/http-s-proxy-in-golang-in-less-than-100-lines-of-code-6a51c2f2c38c
// https://gist.github.com/yowu/f7dc34bd4736a65ff28d

// 用curl测试
// curl -v -x localhost:8787 baidu.com
// curl -x socks5h://localhost:8001 http://www.baidu.com/
// curl -x socks5://localhost:8001 http://www.baidu.com/
// curl -x socks4h://localhost:8001 http://www.baidu.com/

// curl --socks4 proxy.example.com http://www.example.com/
// curl --socks5 proxy.example.com http://www.example.com/

client
https://play.golang.org/p/l0iLtkD1DV
http://nextdoorhacker.com/2016/05/08/proxy-aware-http-client-in-go/

http://blog.ralch.com/articles/network-programming-and-proxies-in-golang/