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"
@@ -16,22 +17,23 @@ import (
 )
 
 type Loop struct {
-	statusManager *loopstate.State
-	state         *state.State
-	server        *server.Server
-	filter        *mapfilter.Filter
-	resolvConf    string
-	client        *http.Client
-	logger        Logger
-	userTrigger   bool
-	start         <-chan struct{}
-	running       chan<- models.LoopStatus
-	stop          <-chan struct{}
-	stopped       chan<- struct{}
-	updateTicker  <-chan struct{}
-	backoffTime   time.Duration
-	timeNow       func() time.Time
-	timeSince     func(time.Time) time.Duration
+	statusManager  *loopstate.State
+	state          *state.State
+	server         *server.Server
+	filter         *mapfilter.Filter
+	localResolvers []netip.AddrPort
+	resolvConf     string
+	client         *http.Client
+	logger         Logger
+	userTrigger    bool
+	start          <-chan struct{}
+	running        chan<- models.LoopStatus
+	stop           <-chan struct{}
+	stopped        chan<- struct{}
+	updateTicker   <-chan struct{}
+	backoffTime    time.Duration
+	timeNow        func() time.Time
+	timeSince      func(time.Time) time.Duration
 }
 
 const defaultBackoffTime = 10 * time.Second

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)
 	}