New PIA servers support (#227)

* Adapt storage: SyncServers write to file option, export FlushToFile
* CLI built-in updater for old and new PIA servers
* Update hardcoded IP addresses for PIA old and new servers
* Add PIA old to allServers struct and update timestamps
* Adapt code to work with new and old PIA servers
* Remove PIA subdomains (unneeded) from resolver tool

internal/updater/updater.go

@@ -0,0 +1,69 @@
+package updater
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gluetun/internal/storage"
+)
+
+type Updater interface {
+	UpdateServers(options Options) error
+}
+
+type updater struct {
+	storage storage.Storage
+	timeNow func() time.Time
+	println func(s string)
+}
+
+func New(storage storage.Storage) Updater {
+	return &updater{
+		storage: storage,
+		timeNow: time.Now,
+		println: func(s string) { fmt.Println(s) },
+	}
+}
+
+func (u *updater) UpdateServers(options Options) error {
+	const writeSync = false
+	allServers, err := u.storage.SyncServers(constants.GetAllServers(), writeSync)
+	if err != nil {
+		return fmt.Errorf("cannot update servers: %w", err)
+	}
+
+	if options.PIA {
+		const newServers = true
+		servers, err := findPIAServers(newServers)
+		if err != nil {
+			return fmt.Errorf("cannot update PIA servers: %w", err)
+		}
+		if options.Stdout {
+			u.println(stringifyPIAServers(servers))
+		}
+		allServers.Pia.Timestamp = u.timeNow().Unix()
+		allServers.Pia.Servers = servers
+	}
+
+	if options.PIAold {
+		const newServers = false
+		servers, err := findPIAServers(newServers)
+		if err != nil {
+			return fmt.Errorf("cannot update PIA old servers: %w", err)
+		}
+		if options.Stdout {
+			u.println(stringifyPIAOldServers(servers))
+		}
+		allServers.PiaOld.Timestamp = u.timeNow().Unix()
+		allServers.PiaOld.Servers = servers
+	}
+
+	if options.File {
+		if err := u.storage.FlushToFile(allServers); err != nil {
+			return fmt.Errorf("cannot update servers: %w", err)
+		}
+	}
+
+	return nil
+}