Pull request: websvc-config-manager

Merge in DNS/adguard-home from websvc-config-manager to master

Squashed commit of the following:

commit 2143b47c6528030dfe059172888fddf9061e42da
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Oct 4 14:50:47 2022 +0300

    next: add config manager

internal/next/cmd/signal.go

@@ -0,0 +1,70 @@
+package cmd
+
+import (
+	"os"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/aghos"
+	"github.com/AdguardTeam/AdGuardHome/internal/next/agh"
+	"github.com/AdguardTeam/golibs/log"
+)
+
+// signalHandler processes incoming signals and shuts services down.
+type signalHandler struct {
+	signal chan os.Signal
+
+	// services are the services that are shut down before application
+	// exiting.
+	services []agh.Service
+}
+
+// handle processes OS signals.
+func (h *signalHandler) handle() {
+	defer log.OnPanic("signalHandler.handle")
+
+	for sig := range h.signal {
+		log.Info("sighdlr: received signal %q", sig)
+
+		if aghos.IsShutdownSignal(sig) {
+			h.shutdown()
+		}
+	}
+}
+
+// Exit status constants.
+const (
+	statusSuccess = 0
+	statusError   = 1
+)
+
+// shutdown gracefully shuts down all services.
+func (h *signalHandler) shutdown() {
+	ctx, cancel := ctxWithDefaultTimeout()
+	defer cancel()
+
+	status := statusSuccess
+
+	log.Info("sighdlr: shutting down services")
+	for i, service := range h.services {
+		err := service.Shutdown(ctx)
+		if err != nil {
+			log.Error("sighdlr: shutting down service at index %d: %s", i, err)
+			status = statusError
+		}
+	}
+
+	log.Info("sighdlr: shutting down adguard home")
+
+	os.Exit(status)
+}
+
+// newSignalHandler returns a new signalHandler that shuts down svcs.
+func newSignalHandler(svcs ...agh.Service) (h *signalHandler) {
+	h = &signalHandler{
+		signal:   make(chan os.Signal, 1),
+		services: svcs,
+	}
+
+	aghos.NotifyShutdownSignal(h.signal)
+
+	return h
+}