I'm trying to connect a computer behind NAT with the internet through a 3rd party server(aka reverse connection). I'm listening on two ports. On one port (dstNet
) is connecting the machine behind NAT and on the other port are connecting the internet clients.
The issue is that I don't know how to handle the disconnection of the machine behind NAT. Even if the machine is connecting again the the traffic is not handled sent/written anymore... I get [DEBUG] socks: Copied 0 bytes to client
which is my warning of course. Below is the code. It's quite long but I can't find what to trim.
// Make a bridge between dstNet which is
// usually behind NAT and srcNet which is usually a client
// which wants to route the traffic though the NAT machine.
package main
import (
"bufio"
"errors"
log "github.com/golang/glog"
"io"
"net"
"time"
)
const (
// listen on the dstNet so that we can
// create a connection with the NAT client
dstNet = "0.0.0.0:9000"
// listen on srcNet so that we can get traffic
// to forward to dstNet
srcNet = "0.0.0.0:9001"
)
var errCh = make(chan error, 1)
// make a channel to send the reverse connections
var lrCh = make(chan net.Conn, 1)
func listenDst() {
// Listen on the dstNet
lr, err := net.Listen("tcp", dstNet)
if err != nil {
log.Error(err)
errCh <- err
return
}
// accept the connection
for {
lrConn, err := lr.Accept()
if err != nil {
log.Error(err)
errCh <- err
return
}
log.Errorf("sent connection")
// lrConn.SetReadDeadline(time.Now().Add(10 * time.Second))
lrCh <- lrConn
}
}
func main() {
go func() {
for err := range errCh {
if err != nil {
panic(err)
}
}
}()
// listen for the nat server
go listenDst()
// listen for clients to connect
l, err := net.Listen("tcp", srcNet)
if err != nil {
log.Error(err)
panic(err)
}
// accept the connection
for {
conn, err := l.Accept()
if err != nil {
log.Error(err)
panic(err)
}
// serve the connection
go func(conn net.Conn) {
defer conn.Close()
bufConn := bufio.NewReader(conn)
dst := <-lrCh
defer dst.Close()
// Start proxying
errCh2 := make(chan error, 2)
go proxy("target", dst, bufConn, errCh2)
go proxy("client", conn, dst, errCh2)
// Wait
var ei int
for err = range errCh2 {
switch {
case err != nil && err.Error() == "no byte":
log.Error(err)
case err != nil && err.Error() == "use of closed network connection":
// if the connection is closed we restart it.
log.Error(err)
// BUG() attempt to write again the bytes
case err != nil:
log.Error(err)
errCh <- err
}
if ei == 1 {
log.Errorf("done with errors")
close(errCh2)
}
ei++
}
}(conn)
}
}
// proxy is used to suffle data from src to destination, and sends errors
// down a dedicated channel
func proxy(name string, dst io.Writer, src io.Reader, errCh2 chan error) {
n, err := io.Copy(dst, src)
// Log, and sleep. This is jank but allows the otherside
// to finish a pending copy
log.Errorf("[DEBUG] socks: Copied %d bytes to %s", n, name)
time.Sleep(10 * time.Millisecond)
// Send any errors
switch {
case err != nil:
log.Error(err)
errCh2 <- err
case n < 1:
errCh2 <- errors.New("no byte")
default:
errCh2 <- nil
}
return
}