feat(storage): STORAGE_FILEPATH option (#2416)

- `STORAGE_FILEPATH=` disables storing to and reading from a local servers.json file
- `STORAGE_FILEPATH` defaults to `/gluetun/servers.json`
- Fix #2074

internal/configuration/settings/settings.go

@@ -22,6 +22,7 @@ type Settings struct {
 	Log           Log
 	PublicIP      PublicIP
 	Shadowsocks   Shadowsocks
+	Storage       Storage
 	System        System
 	Updater       Updater
 	Version       Version
@@ -29,14 +30,14 @@ type Settings struct {
 	Pprof         pprof.Settings
 }
 
-type Storage interface {
+type FilterChoicesGetter interface {
 	GetFilterChoices(provider string) models.FilterChoices
 }
 
 // Validate validates all the settings and returns an error
 // if one of them is not valid.
 // TODO v4 remove pointer for receiver (because of Surfshark).
-func (s *Settings) Validate(storage Storage, ipv6Supported bool,
+func (s *Settings) Validate(filterChoicesGetter FilterChoicesGetter, ipv6Supported bool,
 	warner Warner) (err error) {
 	nameToValidation := map[string]func() error{
 		"control server":  s.ControlServer.validate,
@@ -47,12 +48,13 @@ func (s *Settings) Validate(storage Storage, ipv6Supported bool,
 		"log":             s.Log.validate,
 		"public ip check": s.PublicIP.validate,
 		"shadowsocks":     s.Shadowsocks.validate,
+		"storage":         s.Storage.validate,
 		"system":          s.System.validate,
 		"updater":         s.Updater.Validate,
 		"version":         s.Version.validate,
 		// Pprof validation done in pprof constructor
 		"VPN": func() error {
-			return s.VPN.Validate(storage, ipv6Supported, warner)
+			return s.VPN.Validate(filterChoicesGetter, ipv6Supported, warner)
 		},
 	}
 
@@ -76,6 +78,7 @@ func (s *Settings) copy() (copied Settings) {
 		Log:           s.Log.copy(),
 		PublicIP:      s.PublicIP.copy(),
 		Shadowsocks:   s.Shadowsocks.copy(),
+		Storage:       s.Storage.copy(),
 		System:        s.System.copy(),
 		Updater:       s.Updater.copy(),
 		Version:       s.Version.copy(),
@@ -85,7 +88,7 @@ func (s *Settings) copy() (copied Settings) {
 }
 
 func (s *Settings) OverrideWith(other Settings,
-	storage Storage, ipv6Supported bool, warner Warner) (err error) {
+	filterChoicesGetter FilterChoicesGetter, ipv6Supported bool, warner Warner) (err error) {
 	patchedSettings := s.copy()
 	patchedSettings.ControlServer.overrideWith(other.ControlServer)
 	patchedSettings.DNS.overrideWith(other.DNS)
@@ -95,12 +98,13 @@ func (s *Settings) OverrideWith(other Settings,
 	patchedSettings.Log.overrideWith(other.Log)
 	patchedSettings.PublicIP.overrideWith(other.PublicIP)
 	patchedSettings.Shadowsocks.overrideWith(other.Shadowsocks)
+	patchedSettings.Storage.overrideWith(other.Storage)
 	patchedSettings.System.overrideWith(other.System)
 	patchedSettings.Updater.overrideWith(other.Updater)
 	patchedSettings.Version.overrideWith(other.Version)
 	patchedSettings.VPN.OverrideWith(other.VPN)
 	patchedSettings.Pprof.OverrideWith(other.Pprof)
-	err = patchedSettings.Validate(storage, ipv6Supported, warner)
+	err = patchedSettings.Validate(filterChoicesGetter, ipv6Supported, warner)
 	if err != nil {
 		return err
 	}
@@ -117,6 +121,7 @@ func (s *Settings) SetDefaults() {
 	s.Log.setDefaults()
 	s.PublicIP.setDefaults()
 	s.Shadowsocks.setDefaults()
+	s.Storage.setDefaults()
 	s.System.setDefaults()
 	s.Version.setDefaults()
 	s.VPN.setDefaults()
@@ -139,6 +144,7 @@ func (s Settings) toLinesNode() (node *gotree.Node) {
 	node.AppendNode(s.Shadowsocks.toLinesNode())
 	node.AppendNode(s.HTTPProxy.toLinesNode())
 	node.AppendNode(s.ControlServer.toLinesNode())
+	node.AppendNode(s.Storage.toLinesNode())
 	node.AppendNode(s.System.toLinesNode())
 	node.AppendNode(s.PublicIP.toLinesNode())
 	node.AppendNode(s.Updater.toLinesNode())
@@ -188,6 +194,7 @@ func (s *Settings) Read(r *reader.Reader) (err error) {
 		"log":            s.Log.read,
 		"public ip":      s.PublicIP.read,
 		"shadowsocks":    s.Shadowsocks.read,
+		"storage":        s.Storage.read,
 		"system":         s.System.read,
 		"updater":        s.Updater.read,
 		"version":        s.Version.read,