RustyNail

package main

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

func App() {
	listener, err := net.Listen("tcp", ":9999")
	if err != nil {
		println("Failed to start, ", err.Error())
	}
	for {
		client, err := listener.Accept()
		println("New client……")
		if err != nil {
			println("Accept failed, ", err.Error())
		}
		// Dealing with clients' requests
		go func() {
			var b [1024]byte
			n, err := client.Read(b[:])
			if err != nil {
				println("Read head failed,", err.Error())
			}
			var method, host, address string
			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 access
				address = hostPortURL.Scheme + ":443"
			} else {                                            // HTTP access
				if strings.Index(hostPortURL.Host, ":") == -1 { // Host without port, default 80
					address = hostPortURL.Host + ":80"
				} else {
					address = hostPortURL.Host
				}
			}
			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])
			}
			// Forwarding
			go io.Copy(server, client)
			io.Copy(client, server)
		}()
	}
}

func main() {
	App()
}