adjust log behavior for goc server and agent

pkg/cover/instrument.go

@@ -145,9 +145,10 @@ func clearFileCover(counter []uint32) {
 func registerHandlers() {
 	ln, host, err := listen()
 	if err != nil {
-		log.Fatalf("profile listen failed, err:%v", err)
+		log.Fatalf("listen failed, err:%v", err)
 	}
-	log.Println("profile listen on", host)
+	
+	fmt.Printf("[goc] goc agent listened on: %s \n", host)
 	profileAddr := "http://" + host
 	if resp, err := registerSelf(profileAddr); err != nil {
 		log.Fatalf("register address %v failed, err: %v, response: %v", profileAddr, err, string(resp))
@@ -220,7 +221,7 @@ func registerSelf(address string) ([]byte, error) {
 
 	resp, err := http.DefaultClient.Do(req)
 	if err != nil && isNetworkError(err) {
-		log.Printf("[WARN]error occured:%v, try again", err)
+		log.Printf("[goc][WARN]error occured:%v, try again", err)
 		resp, err = http.DefaultClient.Do(req)
 	}
 	defer resp.Body.Close()

pkg/cover/server.go

@@ -48,16 +48,18 @@ func Run(port string) {
 	if err != nil {
 		log.Fatalf("failed to create log file %s, err: %v", LogFile, err)
 	}
-	r := GocServer(f)
+
+	// both log to stdout and file by default
+	mw := io.MultiWriter(f, os.Stdout)
+	r := GocServer(mw)
 	log.Fatal(r.Run(port))
 }
 
 // GocServer init goc server engine
 func GocServer(w io.Writer) *gin.Engine {
-	if w != nil && w != os.Stdout {
-		gin.DefaultWriter = io.MultiWriter(w, os.Stdout)
+	if w != nil {
+		gin.DefaultWriter = w
 	}
-
 	r := gin.Default()
 	// api to show the registered services
 	r.StaticFile(PersistenceFile, "./"+PersistenceFile)