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/aghos/os.go

@@ -175,3 +175,13 @@ func RootDirFS() (fsys fs.FS) {
 	// behavior is undocumented but it currently works.
 	return os.DirFS("")
 }
+
+// NotifyShutdownSignal notifies c on receiving shutdown signals.
+func NotifyShutdownSignal(c chan<- os.Signal) {
+	notifyShutdownSignal(c)
+}
+
+// IsShutdownSignal returns true if sig is a shutdown signal.
+func IsShutdownSignal(sig os.Signal) (ok bool) {
+	return isShutdownSignal(sig)
+}

internal/aghos/os_unix.go

@@ -0,0 +1,27 @@
+//go:build darwin || freebsd || linux || openbsd
+// +build darwin freebsd linux openbsd
+
+package aghos
+
+import (
+	"os"
+	"os/signal"
+
+	"golang.org/x/sys/unix"
+)
+
+func notifyShutdownSignal(c chan<- os.Signal) {
+	signal.Notify(c, unix.SIGINT, unix.SIGQUIT, unix.SIGTERM)
+}
+
+func isShutdownSignal(sig os.Signal) (ok bool) {
+	switch sig {
+	case
+		unix.SIGINT,
+		unix.SIGQUIT,
+		unix.SIGTERM:
+		return true
+	default:
+		return false
+	}
+}

internal/aghos/os_windows.go

@@ -4,6 +4,10 @@
 package aghos
 
 import (
+	"os"
+	"os/signal"
+	"syscall"
+
 	"golang.org/x/sys/windows"
 )
 
@@ -35,3 +39,20 @@ func haveAdminRights() (bool, error) {
 func isOpenWrt() (ok bool) {
 	return false
 }
+
+func notifyShutdownSignal(c chan<- os.Signal) {
+	// syscall.SIGTERM is processed automatically.  See go doc os/signal,
+	// section Windows.
+	signal.Notify(c, os.Interrupt)
+}
+
+func isShutdownSignal(sig os.Signal) (ok bool) {
+	switch sig {
+	case
+		os.Interrupt,
+		syscall.SIGTERM:
+		return true
+	default:
+		return false
+	}
+}