package main

import (
	"flag"
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"time"
)

func main() {
	var localAddrStr *string = flag.String("l", ":7071",
		"listen address. ':7971' will listen all ip")
	var remoteAddrStr *string = flag.String("r", "localhost:7070", "remote address")
	isPrintHelp := flag.Bool("h", false, "show usage info")
	flag.Parse()

	if *isPrintHelp {
		fmt.Printf("Usage of %s:\n", os.Args[0])
		flag.PrintDefaults()
		os.Exit(1)
	}

	localTCPAddr, err := net.ResolveTCPAddr("tcp", *localAddrStr)
	if localTCPAddr == nil {
		log.Fatalf("net.ResolveTCPAddr failed: %s", err)
	}

	localListerner, err := net.ListenTCP("tcp", localTCPAddr)
	if localListerner == nil {
		log.Fatalf("portforward: %s", err)
	}
	log.Printf("forword tcp connections from: '%s', to: '%s'",
		*localAddrStr, *remoteAddrStr)

	for {
		conn, err := localListerner.Accept()
		if conn == nil {
			log.Printf("accept failed: %s", err)
			time.Sleep(1)
			continue
		}
		go forward(conn, *remoteAddrStr)
	}

}

func forward(localConn net.Conn, remoteAddrStr string) {
	remoteConn, err := net.Dial("tcp", remoteAddrStr)
	if remoteConn == nil {
		log.Printf("remote dial failed: %s\n", err)
		localConn.Close()
		return
	}
	go func() {
		defer localConn.Close()
		io.Copy(localConn, remoteConn)
	}()
	go func() {
		defer remoteConn.Close()
		io.Copy(remoteConn, localConn)
	}()
	log.Printf("forward %s to %s", localConn.RemoteAddr(), remoteAddrStr)
}