feat(dns): resolve network-local names (#2970)

internal/dns/loop.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"net/netip"
 	"time"
 
 	"github.com/qdm12/dns/v2/pkg/middlewares/filter/mapfilter"
@@ -20,6 +21,7 @@ type Loop struct {
 	state          *state.State
 	server         *server.Server
 	filter         *mapfilter.Filter
+	localResolvers []netip.AddrPort
 	resolvConf     string
 	client         *http.Client
 	logger         Logger

internal/dns/run.go

@@ -4,12 +4,15 @@ import (
 	"context"
 	"errors"
 
+	"github.com/qdm12/dns/v2/pkg/nameserver"
 	"github.com/qdm12/gluetun/internal/constants"
 )
 
 func (l *Loop) Run(ctx context.Context, done chan<- struct{}) {
 	defer close(done)
 
+	l.localResolvers = nameserver.GetPrivateDNSServers()
+
 	if *l.GetSettings().KeepNameserver {
 		l.logger.Warn("⚠️⚠️⚠️  keeping the default container nameservers, " +
 			"this will likely leak DNS traffic outside the VPN " +

internal/dns/settings.go

@@ -3,6 +3,7 @@ package dns
 import (
 	"context"
 	"fmt"
+	"net/netip"
 
 	"github.com/qdm12/dns/v2/pkg/doh"
 	"github.com/qdm12/dns/v2/pkg/dot"
@@ -10,6 +11,7 @@ import (
 	"github.com/qdm12/dns/v2/pkg/middlewares/cache/lru"
 	filtermiddleware "github.com/qdm12/dns/v2/pkg/middlewares/filter"
 	"github.com/qdm12/dns/v2/pkg/middlewares/filter/mapfilter"
+	"github.com/qdm12/dns/v2/pkg/middlewares/localdns"
 	"github.com/qdm12/dns/v2/pkg/plain"
 	"github.com/qdm12/dns/v2/pkg/provider"
 	"github.com/qdm12/dns/v2/pkg/server"
@@ -25,7 +27,8 @@ func (l *Loop) SetSettings(ctx context.Context, settings settings.DNS) (
 }
 
 func buildServerSettings(settings settings.DNS,
-	filter *mapfilter.Filter, logger Logger) (
+	filter *mapfilter.Filter, localResolvers []netip.AddrPort,
+	logger Logger) (
 	serverSettings server.Settings, err error,
 ) {
 	serverSettings.Logger = logger
@@ -101,5 +104,17 @@ func buildServerSettings(settings settings.DNS,
 	}
 	serverSettings.Middlewares = append(serverSettings.Middlewares, filterMiddleware)
 
+	localDNSMiddleware, err := localdns.New(localdns.Settings{
+		Resolvers: localResolvers, // auto-detected at container start only
+		Logger:    logger,
+	})
+	if err != nil {
+		return server.Settings{}, fmt.Errorf("creating local DNS middleware: %w", err)
+	}
+	// Place after cache middleware, since we want to avoid caching for local
+	// hostnames that may change regularly.
+	// Place after filter middleware to avoid conflicts with the rebinding protection.
+	serverSettings.Middlewares = append(serverSettings.Middlewares, localDNSMiddleware)
+
 	return serverSettings, nil
 }

internal/dns/setup.go

@@ -21,7 +21,7 @@ func (l *Loop) setupServer(ctx context.Context) (runError <-chan error, err erro
 
 	settings := l.GetSettings()
 
-	serverSettings, err := buildServerSettings(settings, l.filter, l.logger)
+	serverSettings, err := buildServerSettings(settings, l.filter, l.localResolvers, l.logger)
 	if err != nil {
 		return nil, fmt.Errorf("building server settings: %w", err)
 	}