Allow server to re-use previously generated key material in 'non-persist' mode

cmd/server/main.go

@@ -54,6 +54,8 @@ var (
 	defaultConfigFilePath = filepath.Join(defaultStateDir, defaultConfigFile)
 )
 
+var ErrObfs4DataAlreadyExists = errors.New("obfs4 data already exists")
+
 type config struct {
 	addr                  string
 	cfgFile               string
@@ -165,7 +167,7 @@ func genKey(logger *log.Logger) (string, error) {
 	stateDir := getStateDir()
 	stateFile := filepath.Join(stateDir, "obfs4_state.json")
 	if _, err := os.Stat(stateFile); !errors.Is(err, os.ErrNotExist) {
-		return "", fmt.Errorf("%s already exists", stateFile)
+		return stateDir, fmt.Errorf("%w: %s", ErrObfs4DataAlreadyExists, stateFile)
 	}
 	// Try to create the state dir if it does not exist, otherwise
 	// obfs4 will fail to create the state file.
@@ -244,10 +246,13 @@ func main() {
 
 	viper.AutomaticEnv()
 	justGenKey := viper.GetBool(genkey)
-	if justGenKey || !viper.GetBool(persist) {
+	persist := viper.GetBool(persist)
+	if justGenKey || !persist {
 		stateDir, err := genKey(logger)
 		if err != nil {
-			logger.Fatal("error while generating key:" + err.Error())
+			if justGenKey || !errors.Is(err, ErrObfs4DataAlreadyExists) {
+				logger.Fatal("error while generating key: %v", err)
+			}
 		}
 		logger.Println("Done. Key material written to:", stateDir)
 		if justGenKey {