Pull request 1897: nextapi-write-conf

Squashed commit of the following:

commit 72f25ffe73d6b8216b01e590fba66fb5f6944113
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Jun 28 21:29:04 2023 +0300

    next: add conf writing, validation

internal/next/cmd/cmd.go

@@ -19,8 +19,6 @@ import (
 func Main(frontend fs.FS) {
 	start := time.Now()
 
-	// Initial Configuration
-
 	cmdName := os.Args[0]
 	opts, err := parseOptions(cmdName, os.Args[1:])
 	exitCode, needExit := processOptions(opts, cmdName, err)
@@ -39,9 +37,7 @@ func Main(frontend fs.FS) {
 		check(err)
 	}
 
-	// Web Service
-
-	confMgr, err := configmgr.New(opts.confFile, frontend, start)
+	confMgr, err := newConfigMgr(opts.confFile, frontend, start)
 	check(err)
 
 	web := confMgr.Web()
@@ -73,6 +69,15 @@ func ctxWithDefaultTimeout() (ctx context.Context, cancel context.CancelFunc) {
 	return context.WithTimeout(context.Background(), defaultTimeout)
 }
 
+// newConfigMgr returns a new configuration manager using defaultTimeout as the
+// context timeout.
+func newConfigMgr(confFile string, frontend fs.FS, start time.Time) (m *configmgr.Manager, err error) {
+	ctx, cancel := ctxWithDefaultTimeout()
+	defer cancel()
+
+	return configmgr.New(ctx, confFile, frontend, start)
+}
+
 // check is a simple error-checking helper.  It must only be used within Main.
 func check(err error) {
 	if err != nil {

internal/next/cmd/opt.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"strings"
 
+	"github.com/AdguardTeam/AdGuardHome/internal/next/configmgr"
 	"github.com/AdguardTeam/AdGuardHome/internal/version"
 	"golang.org/x/exp/slices"
 )
@@ -55,9 +56,8 @@ type options struct {
 	webAddrs []netip.AddrPort
 
 	// checkConfig, if true, instructs AdGuard Home to check the configuration
-	// file and exit with a corresponding exit code.
-	//
-	// TODO(a.garipov): Use.
+	// file, optionally print an error message to stdout, and exit with a
+	// corresponding exit code.
 	checkConfig bool
 
 	// disableUpdate, if true, prevents AdGuard Home from automatically checking
@@ -183,7 +183,7 @@ var commandLineOptions = []*commandLineOption{
 
 	checkConfigIdx: {
 		defaultValue: false,
-		description:  "Check configuration and quit.",
+		description:  "Check configuration, print errors to stdout, and quit.",
 		long:         "check-config",
 		short:        "",
 		valueType:    "",
@@ -399,5 +399,16 @@ func processOptions(
 		return 0, true
 	}
 
+	if opts.checkConfig {
+		err := configmgr.Validate(opts.confFile)
+		if err != nil {
+			_, _ = io.WriteString(os.Stdout, err.Error()+"\n")
+
+			return 1, true
+		}
+
+		return 0, true
+	}
+
 	return 0, false
 }

internal/next/cmd/signal.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/AdguardTeam/AdGuardHome/internal/aghos"
 	"github.com/AdguardTeam/AdGuardHome/internal/next/agh"
-	"github.com/AdguardTeam/AdGuardHome/internal/next/configmgr"
 	"github.com/AdguardTeam/golibs/log"
 )
 
@@ -63,7 +62,7 @@ func (h *signalHandler) reconfigure() {
 	// reconfigured without the full shutdown, and the error handling is
 	// currently not the best.
 
-	confMgr, err := configmgr.New(h.confFile, h.frontend, h.start)
+	confMgr, err := newConfigMgr(h.confFile, h.frontend, h.start)
 	check(err)
 
 	web := confMgr.Web()