Pull request 2470: 7964-fix-log-severity

Updates #7964.

Squashed commit of the following:

commit bd48a1052a441a19a50f8079dd50d6c3ba224fcf
Merge: c183b9c3b 0e6a55efa
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Mon Sep 8 18:07:07 2025 +0300

    Merge branch 'master' into 7964-fix-log-severity

commit c183b9c3b5
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Sep 4 14:29:00 2025 +0300

    filtering: imp code

commit f728b8d059
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Sep 4 14:13:07 2025 +0300

    all: fix log severity

CHANGELOG.md

@@ -30,10 +30,12 @@ NOTE: Add new changes BELOW THIS COMMENT.
 
 ### Fixed
 
+- Lowered the severity of log messages for failed deletion of old filter files ([#7964]).
 - Authentication errors in the Web UI when AdGuard Home is behind a proxy that sets Basic Auth headers ([#7987]).
 - The HTTP API `GET /control/profile` endpoint failing when no users were configured ([#7985]).
 - Missing warning on the *Encryption Settings* page when using a certificate without an IP address.
 
+[#7964]: https://github.com/AdguardTeam/AdGuardHome/issues/7964
 [#7979]: https://github.com/AdguardTeam/AdGuardHome/issues/7979
 [#7985]: https://github.com/AdguardTeam/AdGuardHome/issues/7985
 [#7987]: https://github.com/AdguardTeam/AdGuardHome/issues/7987

internal/filtering/filter.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"log/slog"
 	"net/http"
 	"net/netip"
 	"os"
@@ -448,22 +449,30 @@ func (d *DNSFilter) refreshFiltersIntl(block, allow, force bool) (int, bool) {
 	d.EnableFilters(false)
 
 	for i := range lists {
-		uf := &lists[i]
-		updated := toUpd[i]
-		if !updated {
-			continue
-		}
-
-		p := uf.Path(d.conf.DataDir)
-		err := os.Remove(p + ".old")
-		if err != nil {
-			d.logger.ErrorContext(ctx, "removing old filter", "path", p, slogutil.KeyError, err)
+		if toUpd[i] {
+			removeOldFilterFile(ctx, d.logger, lists[i].Path(d.conf.DataDir))
 		}
 	}
 
 	return updNum, false
 }
 
+// removeOldFilterFile deletes the old filter file and logs any error at the
+// appropriate level.  l must not be nil.
+func removeOldFilterFile(ctx context.Context, l *slog.Logger, fltPath string) {
+	err := os.Remove(fltPath + ".old")
+	if err == nil {
+		return
+	}
+
+	lvl := slog.LevelWarn
+	if errors.Is(err, os.ErrNotExist) {
+		lvl = slog.LevelDebug
+	}
+
+	l.Log(ctx, lvl, "removing old filter", "path", fltPath, slogutil.KeyError, err)
+}
+
 // update refreshes filter's content and a/mtimes of it's file.
 func (d *DNSFilter) update(filter *FilterYAML) (b bool, err error) {
 	ctx := context.TODO()