Tunnel keepalives from client implemented. If client dies/exits unexpectedly the server

tunnel will disconnect from rport in a timely manner.

Signed-off-by: Russ Magee <rmagee@gmail.com>

hkexnet/consts.go

@@ -60,6 +60,7 @@ const (
 	CSOTunAccept    // client -> server: tunnel client got an Accept()
 	CSOTunRefused   // server -> client: tunnel rport connection refused
 	CSOTunData      // packet contains tunnel data [rport:data]
+	CSOTunKeepAlive // client tunnel heartbeat
 	CSOTunDisconn   // server -> client: tunnel rport disconnected
 	CSOTunHangup    // client -> server: tunnel lport hung up
 )

hkexnet/hkexnet.go

@@ -877,6 +877,15 @@ func (hc Conn) Read(b []byte) (n int, err error) {
 				} else {
 					logger.LogDebug(fmt.Sprintf("[Attempt to write data to closed tun [%d:%d]", lport, rport))
 				}
+			} else if ctrlStatOp == CSOTunKeepAlive {
+					// client side has sent keepalive for tunnels -- if client
+					// dies or exits unexpectedly the absence of this will
+					// let the server know to hang up on Dial()ed server rports.
+				_ = binary.BigEndian.Uint16(payloadBytes[0:2])
+				//logger.LogDebug(fmt.Sprintf("[Server] Got CSOTunKeepAlive"))
+				for _, t := range *hc.tuns {
+					t.KeepAlive = 0
+				}
 			} else if ctrlStatOp == CSONone {
 				hc.dBuf.Write(payloadBytes)
 			} else {

hkexnet/hkextun.go

@@ -46,6 +46,7 @@ type (
 		Lport     uint16    // ... ie., RPort is on server, LPort is on client
 		Peer      string    //net.Addr
 		Died      bool      // set by client upon receipt of a CSOTunDisconn
+		KeepAlive uint      // must be reset by client to keep server dial() alive
 		Ctl       chan rune //See TunCtl_* consts
 		Data      chan []byte
 	}
@@ -328,6 +329,14 @@ func (hc *Conn) StartServerTunnel(lport, rport uint16) {
 								rBuf = append(tunDst.Bytes(), rBuf[:n]...)
 								hc.WritePacket(rBuf[:n+4], CSOTunData)
 							}
+
+							if (*hc.tuns)[rport].KeepAlive > 50 {
+									(*hc.tuns)[rport].Died = true
+									logger.LogDebug("[ServerTun] worker A: Oh dear, client appears to have died. Hanging up rport Dial().")
+							} else {
+								(*hc.tuns)[rport].KeepAlive += 1
+							}
+
 						}
 						logger.LogDebug("[ServerTun] worker A: exiting")
 					}()

hkexsh/hkexsh.go

@@ -26,6 +26,7 @@ import (
 	"strings"
 	"sync"
 	"syscall"
+	"time"
 
 	hkexsh "blitter.com/go/hkexsh"
 	"blitter.com/go/hkexsh/hkexnet"
@@ -638,6 +639,14 @@ func main() {
 			defer conn.ShutdownChaff()
 		}
 
+		// Keepalive for any tunnels that may exist
+		go func() {
+			for {
+				time.Sleep(time.Duration(2) * time.Second)
+				conn.WritePacket([]byte{0,0}, hkexnet.CSOTunKeepAlive)
+			}
+		}()
+
 		if shellMode {
 			// TESTING - tunnel
 			remAddrs, _ := net.LookupHost(remoteHost)