do relogin periodically to refresh account on API side

main.go

@@ -54,6 +54,7 @@ type CLIArgs struct {
 	apiPassword   string
 	apiAddress    string
 	bootstrapDNS  string
+	refresh       time.Duration
 }
 
 func parse_args() CLIArgs {
@@ -76,6 +77,7 @@ func parse_args() CLIArgs {
 		"DNS/DoH/DoT/DoQ resolver for initial discovering of SurfEasy API address. "+
 			"See https://github.com/ameshkov/dnslookup/ for upstream DNS URL format. "+
 			"Examples: https://1.1.1.1/dns-query, quic://dns.adguard.com")
+	flag.DurationVar(&args.refresh, "refresh", 4*time.Hour, "login refresh interval")
 	flag.Parse()
 	if args.country == "" {
 		arg_fail("Country can't be empty string.")
@@ -206,6 +208,18 @@ func run() int {
 	}
 	cl()
 
+	runTicker(context.Background(), args.refresh, func (ctx context.Context) {
+		mainLogger.Info("Refreshing login...")
+		loginCtx, cl := context.WithTimeout(ctx, args.timeout)
+		defer cl()
+		err := seclient.Login(loginCtx)
+		if err != nil {
+			mainLogger.Critical("Login refresh failed: %v", err)
+			return
+		}
+		mainLogger.Info("Login refreshed.")
+	})
+
 	if args.listCountries {
 		return printCountries(mainLogger, args.timeout, seclient)
 	}

utils.go

@@ -12,7 +12,10 @@ import (
 	"time"
 )
 
-const COPY_BUF = 128 * 1024
+const (
+	COPY_BUF = 128 * 1024
+	WALLCLOCK_PRECISION = 1 * time.Second
+)
 
 func basic_auth_header(login, password string) string {
 	return "Basic " + base64.StdEncoding.EncodeToString(
@@ -143,3 +146,40 @@ func copyBody(wr io.Writer, body io.Reader) {
 		}
 	}
 }
+
+func AfterWallClock(d time.Duration) <-chan time.Time {
+    ch := make(chan time.Time, 1)
+    deadline := time.Now().Add(d).Truncate(0)
+    after_ch := time.After(d)
+    ticker := time.NewTicker(WALLCLOCK_PRECISION)
+    go func() {
+        var t time.Time
+        defer ticker.Stop()
+        for {
+            select {
+            case t = <-after_ch:
+                ch <-t
+                return
+            case t = <-ticker.C:
+                if t.After(deadline) {
+                    ch <-t
+                    return
+                }
+            }
+        }
+    }()
+    return ch
+}
+
+func runTicker(ctx context.Context, interval time.Duration, cb func (context.Context)) {
+	go func() {
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-AfterWallClock(interval):
+				cb(ctx)
+			}
+		}
+	}()
+}