oauthutil: Reload config file off disk before updating token

This fixes the config file being overwritten when two rclones are running.

Fixes #682

fs/config.go

@@ -377,8 +377,11 @@ func LoadConfig() {
 	// Load configuration file.
 	var err error
 	ConfigFile, err = loadConfigFile()
-	if err != nil {
-		log.Fatalf("Failed to config file \"%s\": %v", ConfigPath, err)
+	if err == errorConfigFileNotFound {
+		Log(nil, "Config file %q not found - using defaults", ConfigPath)
+		ConfigFile, _ = goconfig.LoadFromReader(&bytes.Buffer{})
+	} else if err != nil {
+		log.Fatalf("Failed to load config file %q: %v", ConfigPath, err)
 	}
 
 	// Load filters
@@ -391,13 +394,17 @@ func LoadConfig() {
 	startTokenBucket()
 }
 
+var errorConfigFileNotFound = errors.New("config file not found")
+
 // loadConfigFile will load a config file, and
 // automatically decrypt it.
 func loadConfigFile() (*goconfig.ConfigFile, error) {
 	b, err := ioutil.ReadFile(ConfigPath)
 	if err != nil {
-		Log(nil, "Failed to load config file \"%v\" - using defaults: %v", ConfigPath, err)
-		return goconfig.LoadFromReader(&bytes.Buffer{})
+		if os.IsNotExist(err) {
+			return nil, errorConfigFileNotFound
+		}
+		return nil, err
 	}
 
 	// Find first non-empty line
@@ -622,6 +629,34 @@ func SaveConfig() {
 	}
 }
 
+// ConfigSetValueAndSave sets the key to the value and saves just that
+// value in the config file.  It loads the old config file in from
+// disk first and overwrites the given value only.
+func ConfigSetValueAndSave(name, key, value string) (err error) {
+	// Set the value in config in case we fail to reload it
+	ConfigFile.SetValue(name, key, value)
+	// Reload the config file
+	reloadedConfigFile, err := loadConfigFile()
+	if err == errorConfigFileNotFound {
+		// Config file not written yet so ignore reload
+		return nil
+	} else if err != nil {
+		return err
+	}
+	_, err = reloadedConfigFile.GetSection(name)
+	if err != nil {
+		// Section doesn't exist yet so ignore reload
+		return err
+	}
+	// Update the config file with the reloaded version
+	ConfigFile = reloadedConfigFile
+	// Set the value in the reloaded version
+	reloadedConfigFile.SetValue(name, key, value)
+	// Save it again
+	SaveConfig()
+	return nil
+}
+
 // ShowRemotes shows an overview of the config file
 func ShowRemotes() {
 	remotes := ConfigFile.GetSectionList()

oauthutil/oauthutil.go

@@ -99,9 +99,12 @@ func putToken(name string, token *oauth2.Token) error {
 	tokenString := string(tokenBytes)
 	old := fs.ConfigFile.MustValue(name, fs.ConfigToken)
 	if tokenString != old {
-		fs.ConfigFile.SetValue(name, fs.ConfigToken, tokenString)
-		fs.SaveConfig()
-		fs.Debug(name, "Saving new token in config file")
+		err = fs.ConfigSetValueAndSave(name, fs.ConfigToken, tokenString)
+		if err != nil {
+			fs.ErrorLog(nil, "Failed to save new token in config file: %v", err)
+		} else {
+			fs.Debug(name, "Saved new token in config file")
+		}
 	}
 	return nil
 }