replace old NAT handling (parsing netstat-nat output) with own NAT parsing

Author: dominikh

netstat-nat.go

@@ -2,15 +2,16 @@ package main
 
 import (
 	"github.com/dominikh/simple-router/conntrack"
+	"github.com/dominikh/simple-router/lookup"
+	"github.com/dominikh/simple-router/nat"
 
 	"flag"
 	"fmt"
-	"net"
 	"os"
 	"text/tabwriter"
 )
 
-//       -n: don't resolve host/portnames
+// TODO implement the following flags
 //       -p <protocol>        : display connections by protocol
 //       -s <source-host>     : display connections by source
 //       -d <destination-host>: display connections by destination
@@ -26,65 +27,25 @@ var onlyRouted = flag.Bool("R", false, "Display only connections routed through
 var noResolve = flag.Bool("n", false, "Do not resolve hostnames") // TODO resolve port names as well
 var noHeader = flag.Bool("o", false, "Strip output header")
 
-var (
-	displaySNAT   bool = true
-	displayDNAT   bool = true
-	displayLocal  bool = false
-	displayRouted bool = false
-)
-
-var localIPs = make([]*net.IPNet, 0)
-
-func isLocalIP(ip net.IP) bool {
-	for _, localIP := range localIPs {
-		if localIP.IP.Equal(ip) {
-			return true
-		}
-	}
-
-	return false
-}
-
-func init() {
-	addresses, err := net.InterfaceAddrs()
-	if err != nil {
-		panic(err)
-	}
-
-	for _, address := range addresses {
-		localIPs = append(localIPs, address.(*net.IPNet))
-	}
-}
-
 func main() {
 	flag.Parse()
 
+	var which nat.Flag
+
 	if *onlySNAT {
-		displaySNAT = true
-		displayDNAT = false
-		displayLocal = false
-		displayRouted = false
+		which = nat.SNAT
 	}
 
 	if *onlyDNAT {
-		displaySNAT = false
-		displayDNAT = true
-		displayLocal = false
-		displayRouted = false
+		which = nat.DNAT
 	}
 
 	if *onlyLocal {
-		displaySNAT = false
-		displayDNAT = false
-		displayLocal = true
-		displayRouted = false
+		which = nat.Local
 	}
 
 	if *onlyRouted {
-		displaySNAT = false
-		displayDNAT = false
-		displayLocal = false
-		displayRouted = true
+		which = nat.Routed
 	}
 
 	flows, err := conntrack.Flows()
@@ -99,88 +60,19 @@ func main() {
 		fmt.Fprintln(tabWriter, "Proto\tSource Address\tDestination Address\tState")
 	}
 
-	for _, flow := range flows {
-		if (displaySNAT && isSNAT(flow)) ||
-			(displayDNAT && isDNAT(flow)) ||
-			(displayLocal && isLocal(flow)) ||
-			(displayRouted && isRouted(flow)) {
-
-			sHostname := resolve(flow.Original.Source)
-			dHostname := resolve(flow.Original.Destination)
+	natFlows := nat.GetNAT(flows, which)
+	for _, flow := range natFlows {
+		sHostname := lookup.Resolve(flow.Original.Source, *noResolve)
+		dHostname := lookup.Resolve(flow.Original.Destination, *noResolve)
 
-			fmt.Fprintf(tabWriter, "%s\t%s:%d\t%s:%d\t%s\n",
-				flow.Protocol,
-				sHostname,
-				flow.Original.SPort,
-				dHostname,
-				flow.Original.DPort,
-				flow.State,
-			)
-		}
+		fmt.Fprintf(tabWriter, "%s\t%s:%d\t%s:%d\t%s\n",
+			flow.Protocol,
+			sHostname,
+			flow.Original.SPort,
+			dHostname,
+			flow.Original.DPort,
+			flow.State,
+		)
 	}
 	tabWriter.Flush()
 }
-
-func resolve(ip net.IP) string {
-	if *noResolve {
-		return ip.String()
-	}
-
-	lookup, err := net.LookupAddr(ip.String())
-	if err == nil && len(lookup) > 0 {
-		return lookup[0]
-	}
-
-	return ip.String()
-}
-
-func isSNAT(flow conntrack.Flow) bool {
-	// SNATed flows should reply to our WAN IP, not a LAN IP.
-	if flow.Original.Source.Equal(flow.Reply.Destination) {
-		return false
-	}
-
-	if !flow.Original.Destination.Equal(flow.Reply.Source) {
-		return false
-	}
-
-	return true
-}
-
-func isDNAT(flow conntrack.Flow) bool {
-	// Reply must go back to the source; Reply mustn't come from the WAN IP
-	if flow.Original.Source.Equal(flow.Reply.Destination) && !flow.Original.Destination.Equal(flow.Reply.Source) {
-		return true
-	}
-
-	// Taken straight from original netstat-nat, labelled "DNAT (1 interface)"
-	if !flow.Original.Source.Equal(flow.Reply.Source) && !flow.Original.Source.Equal(flow.Reply.Destination) && !flow.Original.Destination.Equal(flow.Reply.Source) && flow.Original.Destination.Equal(flow.Reply.Destination) {
-		return true
-	}
-
-	return false
-}
-
-func isLocal(flow conntrack.Flow) bool {
-	// no NAT
-	if flow.Original.Source.Equal(flow.Reply.Destination) && flow.Original.Destination.Equal(flow.Reply.Source) {
-		// At least one local address
-		if isLocalIP(flow.Original.Source) || isLocalIP(flow.Original.Destination) || isLocalIP(flow.Reply.Source) || isLocalIP(flow.Reply.Destination) {
-			return true
-		}
-	}
-
-	return false
-}
-
-func isRouted(flow conntrack.Flow) bool {
-	// no NAT
-	if flow.Original.Source.Equal(flow.Reply.Destination) && flow.Original.Destination.Equal(flow.Reply.Source) {
-		// No local addresses
-		if !isLocalIP(flow.Original.Source) && !isLocalIP(flow.Original.Destination) && !isLocalIP(flow.Reply.Source) && !isLocalIP(flow.Reply.Destination) {
-			return true
-		}
-	}
-
-	return false
-}