WIP

internal/dnsforward/dnsforward.go

@@ -518,6 +518,29 @@ func (s *Server) prepareLocalResolvers(
 	return uc, nil
 }
 
+// LocalResolversError is an error type for errors during local resolvers setup.
+// This is only needed to distinguish these errors from errors returned by
+// creating the proxy.
+type LocalResolversError struct {
+	Err error
+}
+
+// type check
+var _ error = (*LocalResolversError)(nil)
+
+// Error implements the error interface for *localResolversError.
+func (err *LocalResolversError) Error() (s string) {
+	return fmt.Sprintf("creating local resolvers: %s", err.Err)
+}
+
+// type check
+var _ errors.Wrapper = (*LocalResolversError)(nil)
+
+// Unwrap implements the [errors.Wrapper] interface for *localResolversError.
+func (err *LocalResolversError) Unwrap() error {
+	return err.Err
+}
+
 // setupLocalResolvers initializes and sets the resolvers for local addresses.
 // It assumes s.serverLock is locked or s not running.  It returns the upstream
 // configuration used for private PTR resolving, or nil if it's disabled.  Note,
@@ -538,7 +561,7 @@ func (s *Server) setupLocalResolvers(boot upstream.Resolver) (uc *proxy.Upstream
 		UpstreamConfig: uc,
 	})
 	if err != nil {
-		return nil, fmt.Errorf("creating local resolvers: %w", err)
+		return nil, &LocalResolversError{Err: err}
 	}
 
 	// TODO(e.burkov):  Should we also consider the DNS64 usage?

internal/home/dns.go

@@ -18,6 +18,7 @@ import (
 	"github.com/AdguardTeam/AdGuardHome/internal/filtering"
 	"github.com/AdguardTeam/AdGuardHome/internal/querylog"
 	"github.com/AdguardTeam/AdGuardHome/internal/stats"
+	"github.com/AdguardTeam/dnsproxy/upstream"
 	"github.com/AdguardTeam/golibs/errors"
 	"github.com/AdguardTeam/golibs/log"
 	"github.com/AdguardTeam/golibs/netutil"
@@ -157,6 +158,17 @@ func initDNSServer(
 	}
 
 	err = Context.dnsServer.Prepare(dnsConf)
+
+	// TODO(e.burkov):  Recreate the server with private RDNS disabled.  This
+	// should go away once the private RDNS resolution is moved to the proxy.
+	var locResErr *dnsforward.LocalResolversError
+	if errors.As(err, &locResErr) && errors.Is(locResErr.Err, upstream.ErrNoUpstreams) {
+		log.Info("WARNING: no local resolvers configured while private RDNS " +
+			"resolution enabled, trying to disable")
+		dnsConf.UsePrivateRDNS = false
+		err = Context.dnsServer.Prepare(dnsConf)
+	}
+
 	if err != nil {
 		return fmt.Errorf("dnsServer.Prepare: %w", err)
 	}