config: --config "" or "/notfound" for in memory config only #4996

If `--config` is set to empty string or the special value `/notfound`
then rclone will keep the config file in memory only.

docs/content/docs.md

@@ -554,6 +554,9 @@ location is for you.
 Use this flag to override the config location, e.g. `rclone
 --config=".myconfig" .config`.
 
+If this is set to empty string or the special value `/notfound` then
+rclone will keep the config file in memory only.
+
 ### --contimeout=TIME ###
 
 Set the connection timeout. This should be in go time format which

fs/config/config.go

@@ -242,8 +242,7 @@ func SaveConfig() {
 		waitingTimeMs := mathrand.Intn(1000)
 		time.Sleep(time.Duration(waitingTimeMs) * time.Millisecond)
 	}
-	log.Fatalf("Failed to save config after %d tries: %v", ci.LowLevelRetries, err)
-
+	fs.Errorf(nil, "Failed to save config after %d tries: %v", ci.LowLevelRetries, err)
 	return
 }
 

fs/config/configfile/configfile.go

@@ -15,6 +15,9 @@ import (
 	"github.com/rclone/rclone/fs/config"
 )
 
+// Special value indicating in memory config file. Empty string works also.
+const noConfigFile = "/notfound"
+
 // LoadConfig installs the config file handler and calls config.LoadConfig
 func LoadConfig(ctx context.Context) {
 	config.Data = &Storage{}
@@ -29,11 +32,20 @@ type Storage struct {
 	fi os.FileInfo          // stat of the file when last loaded
 }
 
+// Return whether we have a real config file or not
+func (s *Storage) noConfig() bool {
+	return config.ConfigPath == "" || config.ConfigPath == noConfigFile
+}
+
 // Check to see if we need to reload the config
 func (s *Storage) check() {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
+	if s.noConfig() {
+		return
+	}
+
 	// Check to see if config file has changed since it was last loaded
 	fi, err := os.Stat(config.ConfigPath)
 	if err == nil {
@@ -59,6 +71,10 @@ func (s *Storage) _load() (err error) {
 		}
 	}()
 
+	if s.noConfig() {
+		return config.ErrorConfigFileNotFound
+	}
+
 	fd, err := os.Open(config.ConfigPath)
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -97,6 +113,10 @@ func (s *Storage) Save() error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
+	if s.noConfig() {
+		return nil
+	}
+
 	dir, name := filepath.Split(config.ConfigPath)
 	err := os.MkdirAll(dir, os.ModePerm)
 	if err != nil {

fs/config/configfile/configfile_test.go

@@ -213,3 +213,33 @@ func TestConfigFileDoesNotExist(t *testing.T) {
 	assert.False(t, ok)
 	assert.Equal(t, "", value)
 }
+
+func testConfigFileNoConfig(t *testing.T, configPath string) {
+	config.ConfigPath = configPath
+	data := &Storage{}
+
+	err := data.Load()
+	require.Equal(t, config.ErrorConfigFileNotFound, err)
+
+	data.SetValue("one", "extra", "42")
+	value, ok := data.GetValue("one", "extra")
+	assert.True(t, ok)
+	assert.Equal(t, "42", value)
+
+	err = data.Save()
+	require.NoError(t, err)
+}
+
+func TestConfigFileNoConfig(t *testing.T) {
+	old := config.ConfigPath
+	defer func() {
+		config.ConfigPath = old
+	}()
+
+	t.Run("Empty", func(t *testing.T) {
+		testConfigFileNoConfig(t, "")
+	})
+	t.Run("NotFound", func(t *testing.T) {
+		testConfigFileNoConfig(t, "/notfound")
+	})
+}