Add random computer names

Each request will now send a unique computer name with each request.
There are 4 different buckets of names to choose from and each is chosen
randomly and combined randomly on each function call. Once the computer
name is returned the bytes to broadcast are updated.

The Makefile has also been updated to include the new computers.go file.

Author: jamesbcook

Makefile

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

computernames.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"math/rand"
+	"strings"
+)
+
+var (
+	computerName = []string{"laptop", "workstation", "server"}
+	firstName    = []string{"alice", "bob", "john"}
+	lastName     = []string{"smith", "johnson", "williams"}
+	jobName      = []string{"dev", "qa", "ops", "hr"}
+)
+
+func getRandomNumber(length int) int {
+	return rand.Intn(length)
+}
+
+func getComputerName() string {
+	dstSlice := make([]string, 4)
+	srcSlice := make([]string, 4)
+	srcSlice[0] = computerName[getRandomNumber(len(computerName))]
+	srcSlice[1] = firstName[getRandomNumber(len(firstName))]
+	srcSlice[2] = lastName[getRandomNumber(len(lastName))]
+	srcSlice[3] = jobName[getRandomNumber(len(jobName))]
+	perm := rand.Perm(4)
+	for i, v := range perm {
+		dstSlice[v] = srcSlice[i]
+	}
+	return strings.Join(dstSlice[:], "")
+}

respounder.go

@@ -24,7 +24,7 @@ const (
     '-'
 `
 
-	Version    = 1.0
+	Version    = 1.1
 	TimeoutSec = 3
 	BcastAddr  = "224.0.0.252"
 	LLMNRPort  = 5355
@@ -46,6 +46,10 @@ var (
 		`Creates a debug.log file with a trace of the program`)
 )
 
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
 func main() {
 	initFlags()
 
@@ -107,14 +111,13 @@ func checkResponderOnInterface(inf net.Interface) map[string]string {
 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))
-
+	randomTransactionID := fmt.Sprintf("%04x", rand.Intn(65535))
+	computerName := getComputerName()
+	cNameLen := fmt.Sprintf("%2x", len(computerName))
+	encCName := hex.EncodeToString([]byte(computerName))
 	// LLMNR request in raw bytes
-	// TODO: generate a new computer name evertime instead of the
-	// hardcoded value 'awierdcomputername'
-	llmnrRequest := randomTransactionId +
-		"0000000100000000000012617769657264636f6d70757465726e616d650000010001"
+	llmnrRequest := randomTransactionID +
+		"00000001000000000000" + cNameLen + encCName + "0000010001"
 	n, _ := hex.DecodeString(llmnrRequest)
 
 	remoteAddr := net.UDPAddr{IP: net.ParseIP(BcastAddr), Port: LLMNRPort}