package main

import (
	"log"
	"crypto/tls"
	"net"
)

const localAddr string = ":25500"
const remoteAddr string = "127.0.0.1:25501"
const MaxConn int16 = 3

func main() {
	log.SetFlags(log.Lshortfile)

	cer, err := tls.LoadX509KeyPair("server.pem", "server.key")
	if err != nil {
		log.Println(err)
		return
	}

	config := &tls.Config{Certificates: []tls.Certificate{cer}}
	ln, err := tls.Listen("tcp", localAddr, config) 
	if err != nil {
		log.Println(err)
		return
	}
	defer ln.Close()

	log.Printf("Listening: %v -> %v\n\n", localAddr, remoteAddr)

	for {
		conn, err := ln.Accept()
		if err != nil {
			log.Println(err)
			continue
		}
		go proxyConn(conn)
	}
}

func proxyConn(conn net.Conn) {
	defer conn.Close()

	rAddr, err := net.ResolveTCPAddr("tcp", remoteAddr)
	if err != nil {
		log.Print(err)
	}

	rConn, err := net.DialTCP("tcp", nil, rAddr)
	if err != nil {
		log.Print(err)
	}
	defer rConn.Close()

	Pipe(conn, rConn)

	log.Printf("handleConnection end: %s\n", conn.RemoteAddr())
}

func chanFromConn(conn net.Conn) chan []byte {
	c := make(chan []byte)

	go func() {
		b := make([]byte, 1024)

		for {
			n, err := conn.Read(b)
			if n > 0 {
				res := make([]byte, n)
				// Copy the buffer so it doesn't get changed while read by the recipient.
				copy(res, b[:n])
				c <- res
			}
			if err != nil {
				c <- nil
				break
			}
		}
	}()

	return c
}

func Pipe(conn1 net.Conn, conn2 net.Conn) {
	chan1 := chanFromConn(conn1)
	chan2 := chanFromConn(conn2)

	for {
		select {
		case b1 := <-chan1:
			if b1 == nil {
				return
			} else {
				conn2.Write(b1)
			}
		case b2 := <-chan2:
			if b2 == nil {
				return
			} else {
				conn1.Write(b2)
			}
		}
	}
}