simple port forwarder

pf.go

package main

import (
    "io"
    "log"
    "net"
    "os"
)

func main() {
    if len(os.Args) <= 3 {
        log.Fatalf("usage: %s local remote", os.Args[0])
    }
    localAddrString := os.Args[1]
    remoteAddrString := os.Args[2]
    localAddr, err := net.ResolveTCPAddr("tcp", localAddrString)
    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 err != nil {
            log.Fatalf("accept failed: %s", err)
        }
        go forward(conn, remoteAddrString)
    }
}

func forward(local net.Conn, remoteAddr string) {
    remote, err := net.Dial("tcp", remoteAddr)
    if err != nil {
        log.Printf("remote connection failed: %v", err)
        local.Close()
        return
    }
    go func() {
        defer local.Close()
        io.Copy(local, remote)
    }()
    go func() {
        defer remote.Close()
        io.Copy(remote, local)
    }()
    log.Printf("forwarding %s to %s", local.RemoteAddr(), remoteAddr)
}