impl/utils/visualizer/main.go

@@ -24,9 +24,9 @@ import (
 var static embed.FS
 
 func main() {
-	if len(os.Args) != 3 {
+	if len(os.Args) != 2 && len(os.Args) != 3 {
 		log.SetFlags(0)
-		log.Fatalf("usage: %s <fifo> <json-dup-prefix>", os.Args[0])
+		log.Fatalf("usage: %s <fifo> [<json-dup-prefix>]", os.Args[0])
 	}
 
 	var mutex sync.Mutex
@@ -35,16 +35,22 @@ func main() {
 	go func() {
 		for {
 			path := os.Args[1]
-			dupPath := os.Args[2] + "." + time.Now().Format(time.RFC3339)
+			var dupPath string
+			if len(os.Args) == 3 {
+				dupPath = os.Args[2] + "." + time.Now().Format(time.RFC3339)
+			}
 
 			fh, err := os.Open(path)
 			if err != nil {
 				log.Fatal(err)
 			}
-			dupFh, err := os.Create(dupPath)
+			var dupFh *os.File
+			if dupPath != "" {
+				dupFh, err = os.Create(dupPath)
 				if err != nil {
 					log.Fatal(err)
 				}
+			}
 
 			r := bufio.NewReader(fh)
 			for {
@@ -56,10 +62,12 @@ func main() {
 
 				// Duplicate JSON input to a file so it can be replayed later
 				// if necessary
+				if dupFh != nil {
 					_, err = dupFh.WriteString(line)
 					if err != nil {
 						log.Fatalf("write %q: %v", dupPath, err)
 					}
+				}
 
 				// Send to all listeners
 				mutex.Lock()
@@ -73,11 +81,13 @@ func main() {
 			if err != nil {
 				log.Fatalf("close %q: %v", path, err)
 			}
+			if dupFh != nil {
 				err = dupFh.Close()
 				if err != nil {
 					log.Fatalf("close %q: %v", dupPath, err)
 				}
 			}
+		}
 	}()
 
 	// Use existing "./static/" directory for quick changes