Pull request: all: add stub binary for new api

Merge in DNS/adguard-home from new-api to master

Squashed commit of the following:

commit 83f4418c253b9abc5131d9e2acc2a4a96e4122c4
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Apr 26 19:09:34 2022 +0300

    all: fix build

commit 1fbb53fdf779bde79fab72f9c8eb929e08bb044c
Merge: 73a55197 1c89394a
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Apr 26 18:37:27 2022 +0300

    Merge branch 'master' into new-api

commit 73a5519723f662979bdeb5192bc15835e7f03512
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Apr 26 18:36:50 2022 +0300

    v1: imp names, docs

commit d3fbc2f2082612b8ba438c8216c6c74421cc2df5
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Apr 22 17:55:42 2022 +0300

    cmd: imp docs

commit c2a73aa364a848e8066d1132d4b53bbc3e22db2d
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Apr 22 16:19:14 2022 +0300

    all: add stub binary for new api

internal/v1/cmd/cmd.go

@@ -0,0 +1,69 @@
+// Package cmd is the AdGuard Home entry point.  It contains the on-disk
+// configuration file utilities, signal processing logic, and so on.
+//
+// TODO(a.garipov): Move to the upper-level internal/.
+package cmd
+
+import (
+	"context"
+	"io/fs"
+	"math/rand"
+	"net"
+	"time"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/v1/websvc"
+	"github.com/AdguardTeam/golibs/log"
+	"github.com/AdguardTeam/golibs/netutil"
+)
+
+// Main is the entry point of application.
+func Main(clientBuildFS fs.FS) {
+	// # Initial Configuration
+
+	rand.Seed(time.Now().UnixNano())
+
+	// TODO(a.garipov): Set up logging.
+
+	// # Web Service
+
+	// TODO(a.garipov): Use in the Web service.
+	_ = clientBuildFS
+
+	// TODO(a.garipov): Make configurable.
+	web := websvc.New(&websvc.Config{
+		Addresses: []*netutil.IPPort{{
+			IP:   net.IP{127, 0, 0, 1},
+			Port: 3001,
+		}},
+		Timeout: 60 * time.Second,
+	})
+
+	err := web.Start()
+	fatalOnError(err)
+
+	sigHdlr := newSignalHandler(
+		web,
+	)
+
+	go sigHdlr.handle()
+
+	select {}
+}
+
+// defaultTimeout is the timeout used for some operations where another timeout
+// hasn't been defined yet.
+const defaultTimeout = 15 * time.Second
+
+// ctxWithDefaultTimeout is a helper function that returns a context with
+// timeout set to defaultTimeout.
+func ctxWithDefaultTimeout() (ctx context.Context, cancel context.CancelFunc) {
+	return context.WithTimeout(context.Background(), defaultTimeout)
+}
+
+// fatalOnError is a helper that exits the program with an error code if err is
+// not nil.  It must only be used within Main.
+func fatalOnError(err error) {
+	if err != nil {
+		log.Fatal(err)
+	}
+}

internal/v1/cmd/signal.go

@@ -0,0 +1,70 @@
+package cmd
+
+import (
+	"os"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/aghos"
+	"github.com/AdguardTeam/AdGuardHome/internal/v1/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("signalProcessor.handle")
+
+	for sig := range h.signal {
+		log.Info("sigproc: 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("sigproc: shutting down services")
+	for i, service := range h.services {
+		err := service.Shutdown(ctx)
+		if err != nil {
+			log.Error("sigproc: shutting down service at index %d: %s", i, err)
+			status = statusError
+		}
+	}
+
+	log.Info("sigproc: 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
+}