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main.go
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main.go
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package main
import (
"errors"
"io"
"log"
"net"
"os"
"os/signal"
"syscall"
)
var (
optBind = os.Getenv("BIND")
optTarget = os.Getenv("TARGET")
)
func exit(err *error) {
if *err != nil {
log.Printf("exited with error: %s", (*err).Error())
os.Exit(1)
} else {
log.Println("exited")
}
}
func main() {
var err error
defer exit(&err)
if len(optBind) == 0 {
err = errors.New("$BIND not specified")
return
}
if len(optTarget) == 0 {
err = errors.New("$TARGET not specified")
return
}
if _, err = net.ResolveTCPAddr("tcp", optBind); err != nil {
return
}
if _, err = net.ResolveTCPAddr("tcp", optTarget); err != nil {
return
}
log.Printf("forward started, %s -> %s", optBind, optTarget)
var l net.Listener
if l, err = net.Listen("tcp", optBind); err != nil {
return
}
defer l.Close()
done := make(chan interface{})
go func() {
for {
var err error
var c net.Conn
if c, err = l.Accept(); err != nil {
log.Printf("failed to accept connection: %s", err.Error())
break
}
go handle(c)
}
close(done)
}()
sigCh := make(chan os.Signal)
signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
select {
case <-done:
err = errors.New("listener closed unexpectedly")
case sig := <-sigCh:
log.Printf("signal received: %s", sig.String())
}
}
func handle(c net.Conn) {
var err error
defer c.Close()
var t net.Conn
if t, err = net.Dial("tcp", optTarget); err != nil {
log.Printf("failed to dial %s for %s: %s", optTarget, c.RemoteAddr().String(), err.Error())
return
}
defer t.Close()
go io.Copy(c, t)
io.Copy(t, c)
}