chore(all): memory and thread safe storage

- settings: get filter choices from storage for settings validation
- updater: update servers to the storage
- storage: minimal deep copying and data duplication
- storage: add merged servers mutex for thread safety
- connection: filter servers in storage
- formatter: format servers to Markdown in storage
- PIA: get server by name from storage directly
- Updater: get servers count from storage directly
- Updater: equality check done in storage, fix #882

internal/updater/updater.go

@@ -19,7 +19,7 @@ type Updater struct {
 	options settings.Updater
 
 	// state
-	servers models.AllServers
+	storage Storage
 
 	// Functions for tests
 	logger    Logger
@@ -29,6 +29,12 @@ type Updater struct {
 	unzipper  unzip.Unzipper
 }
 
+type Storage interface {
+	SetServers(provider string, servers []models.Server) (err error)
+	GetServersCount(provider string) (count int)
+	ServersAreEqual(provider string, servers []models.Server) (equal bool)
+}
+
 type Logger interface {
 	Info(s string)
 	Warn(s string)
@@ -36,20 +42,20 @@ type Logger interface {
 }
 
 func New(settings settings.Updater, httpClient *http.Client,
-	currentServers models.AllServers, logger Logger) *Updater {
+	storage Storage, logger Logger) *Updater {
 	unzipper := unzip.New(httpClient)
 	return &Updater{
+		options:   settings,
+		storage:   storage,
 		logger:    logger,
 		timeNow:   time.Now,
 		presolver: resolver.NewParallelResolver(settings.DNSAddress.String()),
 		client:    httpClient,
 		unzipper:  unzipper,
-		options:   settings,
-		servers:   currentServers,
 	}
 }
 
-func (u *Updater) UpdateServers(ctx context.Context) (allServers models.AllServers, err error) {
+func (u *Updater) UpdateServers(ctx context.Context) (err error) {
 	caser := cases.Title(language.English)
 	for _, provider := range u.options.Providers {
 		u.logger.Info("updating " + caser.String(provider) + " servers...")
@@ -62,17 +68,17 @@ func (u *Updater) UpdateServers(ctx context.Context) (allServers models.AllServe
 
 		// return the only error for the single provider.
 		if len(u.options.Providers) == 1 {
-			return allServers, err
+			return err
 		}
 
 		// stop updating the next providers if context is canceled.
 		if ctxErr := ctx.Err(); ctxErr != nil {
-			return allServers, ctxErr
+			return ctxErr
 		}
 
 		// Log the error and continue updating the next provider.
 		u.logger.Error(err.Error())
 	}
 
-	return u.servers, nil
+	return nil
 }