package main

import (
	"log"
	"net"
)

type Server struct {
	Addr   string
	Target string
}

func (s *Server) ListenAndServe() error {
	listener, err := net.Listen("tcp", s.Addr)
	if err != nil {
		return err
	}
	return s.serve(listener)
}

func (s *Server) serve(ln net.Listener) error {
	for {
		conn, err := ln.Accept()
		if err != nil {
			log.Println(err)
			continue
		}
		go s.handleConn(conn)
	}
}

func (s *Server) handleConn(conn net.Conn) {
	rconn, err := net.Dial("tcp", s.Target)
	if err != nil {
		return
	}

	var pipe = func(src, dst net.Conn) {
		defer func() {
			conn.Close()
			rconn.Close()
		}()

		buff := make([]byte, 65535)
		for {
			n, err := src.Read(buff)
			if err != nil {
				log.Println(err)
				return
			}
			b := buff[:n]

			_, err = dst.Write(b)
			if err != nil {
				log.Println(err)
				return
			}
		}
	}

	go pipe(conn, rconn)
	go pipe(rconn, conn)
}