JSON and Debug feature added. Fixed IPv6 issue on Mac OS X

Author: Code Express

.gitignore

@@ -3,6 +3,7 @@
 *.dll
 *.so
 *.dylib
+binaries/
 
 # Test binary, build with `go test -c`
 *.test

Makefile

@@ -0,0 +1,7 @@
+all:
+	GOOS=windows GOARCH=386 go build -o binaries/respounder-x86.exe respounder.go
+	GOOS=windows GOARCH=amd64 go build -o binaries/respounder-x64.exe respounder.go
+	GOOS=linux GOARCH=386 go build  -o binaries/respounder-x86 respounder.go
+	GOOS=linux GOARCH=amd64 go build -o binaries/respounder-x64 respounder.go
+	GOOS=darwin GOARCH=386 go build -o binaries/respounder-osx respounder.go
+	GOOS=darwin GOARCH=amd64 go build -o binaries/respounder-osx64 respounder.go

respounder.go

@@ -2,7 +2,11 @@ package main
 
 import (
 	"encoding/hex"
+	"encoding/json"
+	"flag"
 	"fmt"
+	"io/ioutil"
+	"log"
 	"math/rand"
 	"net"
 	"os"
@@ -11,39 +15,86 @@ import (
 )
 
 const (
-	banner = `
+	Banner = `
 
-     .´/                              
-    / (           .----------------.    
-    [ ]░░░░░░░░░░░|// RESPOUNDER //|    
-    ) (           '----------------'` + "\n" +
-		"    '-' \n"
+     .´/
+    / (           .----------------.
+    [ ]░░░░░░░░░░░|// RESPOUNDER //|
+    ) (           '----------------'
+    '-'
+`
 
-	timeoutSec = 3
+	Version    = 1.0
+	TimeoutSec = 3
+)
+
+var (
+	// stdout is default output
+	outFile = os.Stdout
+
+	// default logger is set to abyss
+	logger = log.New(ioutil.Discard, "", 0)
+
+	// argument flags
+	jsonPtr = flag.Bool("json", false,
+		`Prints a JSON to STDOUT if a responder is detected on
+	network. Other text is sent to STDERR`)
+
+	debugPtr = flag.Bool("debug", false,
+		`Creates a debug.log file with a trace of the program`)
 )
 
 func main() {
-	fmt.Fprintln(os.Stderr, banner)
+	initFlags()
+
+	fmt.Fprintln(os.Stderr, Banner)
 
 	interfaces, _ := net.Interfaces()
+	logger.Println("======== Starting RESPOUNDER ========")
+	logger.Printf("List of all interfaces: \n %+v\n", interfaces)
+
+	var resultMap []map[string]string
+
 	for _, inf := range interfaces {
-		checkResponderOnInterface(inf)
+		detailsMap := checkResponderOnInterface(inf)
+		if len(detailsMap) > 0 {
+			resultMap = append(resultMap, detailsMap)
+		}
+	}
+
+	if *debugPtr {
+		fmt.Fprintln(os.Stderr, "Debug file 'debug.log' created.")
+	}
+
+	if *jsonPtr {
+		resultJSON, _ := json.Marshal(resultMap)
+		fmt.Println(string(resultJSON))
 	}
+	logger.Println("======== Ending RESPOUNDER Session ========")
 }
 
-func checkResponderOnInterface(inf net.Interface) string {
-	json := ""
+func checkResponderOnInterface(inf net.Interface) map[string]string {
+	var json map[string]string
 	addrs, _ := inf.Addrs()
-	if len(addrs) > 0 {
-		ip := addrs[0].(*net.IPNet).IP
-		if ip.String() != "127.0.0.1" {
-			fmt.Printf("%-10s Sending probe from %s...\t", "["+inf.Name+"]", ip)
-			responderAddr := sendLLMNRProbe(ip)
-			if responderAddr != "" {
-				fmt.Printf("responder detected at %s\n", responderAddr)
-			} else {
-				fmt.Println("responder not detected")
+	logger.Printf("List of all addresses on interface [%s]: %+v\n",
+		inf.Name, addrs)
+	ip := getValidIPv4Addr(addrs)
+	logger.Printf("Bind IP address for interface %+v is %+v\n",
+		inf.Name, ip)
+
+	if ip != nil {
+		fmt.Fprintf(outFile, "%-10s Sending probe from %s...\t",
+			"["+inf.Name+"]", ip)
+		responderIP := sendLLMNRProbe(ip)
+		if responderIP != "" {
+			fmt.Fprintf(outFile, "responder detected at %s\n", responderIP)
+			json = map[string]string{
+				"interface":   inf.Name,
+				"sourceIP":    ip.String(),
+				"responderIP": responderIP,
 			}
+		} else {
+			fmt.Fprintln(outFile, "responder not detected")
 		}
 	}
 	return json
@@ -68,16 +119,59 @@ func sendLLMNRProbe(ip net.IP) string {
 	conn, err := net.ListenUDP("udp", &net.UDPAddr{IP: ip})
 	if err != nil {
 		fmt.Println("Couldn't bind to a UDP interface. Bailing out!")
+		logger.Printf("Bind error: %+v\nSource IP: %v\n", err, ip)
+		fmt.Println(err)
 	}
 
 	defer conn.Close()
 	_, _ = conn.WriteToUDP(n, &remoteAddr)
 
-	conn.SetReadDeadline(time.Now().Add(timeoutSec * time.Second))
+	conn.SetReadDeadline(time.Now().Add(TimeoutSec * time.Second))
 	buffer := make([]byte, 1024)
-	_, clientIP, err := conn.ReadFromUDP(buffer)
+	bytes, clientIP, err := conn.ReadFromUDP(buffer)
 	if err == nil { // no timeout (or any other) error
 		responderIP = strings.Split(clientIP.String(), ":")[0]
+		logger.Printf("Data received on %s from responder IP %s: %x\n",
+			ip, clientIP, buffer[:bytes])
+	} else {
+		logger.Printf("Error getting response:  %s\n", err)
 	}
 	return responderIP
 }
+
+// From all the IP addresses of this interface,
+// extract the IPv4 address where we'll bind to
+func getValidIPv4Addr(addrs []net.Addr) net.IP {
+	var ip net.IP
+	for _, addr := range addrs { // amongst all addrs,
+		ip = addr.(*net.IPNet).IP.To4() // pick the IPv4 addr
+		if ip != nil && ip.String() != "127.0.0.1" {
+			break
+		}
+	}
+	return ip
+}
+
+// parses cmd line flag and set appropriate variables
+func initFlags() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "Respounder version %1.1f\n", Version)
+		fmt.Fprintf(os.Stderr, "Usage: $ respounder [-json] [-debug]")
+		fmt.Fprintf(os.Stderr, "\n\nFlags:\n")
+		flag.PrintDefaults()
+	}
+
+	flag.Parse()
+	if *jsonPtr {
+		outFile = os.Stderr
+	}
+	if *debugPtr {
+		f, err := os.OpenFile("debug.log",
+			os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
+		if err != nil {
+			panic(err)
+		}
+		logger = log.New(f, "", 0)
+		logger.SetPrefix("[" + time.Now().Format("02-Jan-2006 15:04:05 MST") + "]: ")
+	}
+}