port forward supports

portforward.go

package main

import (
        "flag"
        "io"
        "log"
        "net"
)

func main() {
        var destStr string
        var localStr string
        flag.StringVar(&localStr, "local", "", "local listen addr")
        flag.StringVar(&destStr, "dest", "", "dest forward addr")
        flag.Parse()

        if localStr == "" {
                log.Fatalf("not find local addr")
        }
        if destStr == "" {
                log.Fatalf("not find dest addr")
        }

        localAddr, err := net.ResolveTCPAddr("tcp", localStr)
        if err != nil {
                log.Fatalf("net.ResolveTCPAddr failed: %s", err)
        }
        local, err := net.ListenTCP("tcp", localAddr)
        if err != nil {
                log.Fatalf("portforward: %s", err)
        }
        log.Printf("portforward listen on %s", localAddr)

        for {
                conn, err := local.Accept()
                if conn == nil {
                        log.Fatalf("accept failed: %s", err)
                }
                go forward(conn, destStr)
        }
}

func forward(local net.Conn, remoteAddr string) {
        remote, err := net.Dial("tcp", remoteAddr)
        if err != nil {
                log.Printf("remote dial failed: %v\n", err)
                local.Close()
                return
        }
        go func() {
                defer local.Close()
                //remote.SetReadTimeout(120*1E9)
                io.Copy(local, remote)
        }()
        go func() {
                defer remote.Close()
                //local.SetReadTimeout(120*1E9)
                io.Copy(remote, local)
        }()
}