First commit ;)

Author: Code Express

.gitignore

@@ -12,3 +12,6 @@
 
 # Project-local glide cache, RE: https://github.com/Masterminds/glide/issues/736
 .glide/
+
+# log files
+*.log

respounder.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+	"encoding/hex"
+	"fmt"
+	"math/rand"
+	"net"
+	"os"
+	"strings"
+	"time"
+)
+
+const (
+	banner = `
+
+     .´/                              
+    / (           .----------------.    
+    [ ]░░░░░░░░░░░|// RESPOUNDER //|    
+    ) (           '----------------'` + "\n" +
+		"    '-' \n"
+
+	timeoutSec = 3
+)
+
+func main() {
+	fmt.Fprintln(os.Stderr, banner)
+
+	interfaces, _ := net.Interfaces()
+	for _, inf := range interfaces {
+		checkResponderOnInterface(inf)
+	}
+}
+
+func checkResponderOnInterface(inf net.Interface) string {
+	json := ""
+	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")
+			}
+		}
+	}
+	return json
+}
+
+// Creates and sends a LLMNR request to the UDP multicast address.
+func sendLLMNRProbe(ip net.IP) string {
+	responderIP := ""
+	// 2 byte random transaction id eg. 0x8e53
+	rand.Seed(time.Now().UnixNano())
+	randomTransactionId := fmt.Sprintf("%04x", rand.Intn(65535))
+
+	// LLMNR request in raw bytes
+	// TODO: generate a new computer name evertime instead of the
+	// hardcoded value 'awierdcomputername'
+	llmnrRequest := randomTransactionId +
+		"0000000100000000000012617769657264636f6d70757465726e616d650000010001"
+	n, _ := hex.DecodeString(llmnrRequest)
+
+	remoteAddr := net.UDPAddr{IP: net.ParseIP("224.0.0.252"), Port: 5355}
+
+	conn, err := net.ListenUDP("udp", &net.UDPAddr{IP: ip})
+	if err != nil {
+		fmt.Println("Couldn't bind to a UDP interface. Bailing out!")
+	}
+
+	defer conn.Close()
+	_, _ = conn.WriteToUDP(n, &remoteAddr)
+
+	conn.SetReadDeadline(time.Now().Add(timeoutSec * time.Second))
+	buffer := make([]byte, 1024)
+	_, clientIP, err := conn.ReadFromUDP(buffer)
+	if err == nil { // no timeout (or any other) error
+		responderIP = strings.Split(clientIP.String(), ":")[0]
+	}
+	return responderIP
+}