Pull request 2584: 4923-gopacket-dhcp-vol.20

Updates #4923.

Squashed commit of the following:

commit 6efeea0845921a6ea20c43d5dd937294c271f800
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Feb 13 16:09:10 2026 +0300

    dhcpsvc: imp code

commit 50486ed5dbe3ad28a302ab382e5ad3eef4d9712e
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Feb 12 17:56:34 2026 +0300

    dhcpsvc: close devices

internal/dhcpsvc/networkdevice.go

@@ -2,6 +2,7 @@ package dhcpsvc
 
 import (
 	"context"
+	"io"
 	"net/netip"
 
 	"github.com/AdguardTeam/golibs/errors"
@@ -28,10 +29,10 @@ func (conf *NetworkDeviceConfig) Validate() (err error) {
 }
 
 // NetworkDeviceManager creates and manages network devices.
-//
-// TODO(e.burkov):  Add device closing method.
 type NetworkDeviceManager interface {
 	// Open opens a network device.  conf must be valid.
+	//
+	// An attempt to open the same device multiple times may return an error.
 	Open(ctx context.Context, conf *NetworkDeviceConfig) (dev NetworkDevice, err error)
 }
 
@@ -59,6 +60,9 @@ func (EmptyNetworkDeviceManager) Open(
 type NetworkDevice interface {
 	gopacket.PacketDataSource
 
+	// No methods of a device should be called after Close.
+	io.Closer
+
 	// Addresses returns all IP addresses assigned to the device.
 	Addresses() (ips []netip.Addr)
 
@@ -82,6 +86,12 @@ func (EmptyNetworkDevice) ReadPacketData() (data []byte, ci gopacket.CaptureInfo
 	return nil, gopacket.CaptureInfo{}, nil
 }
 
+// Close implements the [io.Closer] interface for [EmptyNetworkDevice].  It
+// always returns nil.
+func (EmptyNetworkDevice) Close() (err error) {
+	return nil
+}
+
 // Addresses implements the [NetworkDevice] interface for [EmptyNetworkDevice].
 // It always returns nil.
 func (EmptyNetworkDevice) Addresses() (ips []netip.Addr) {

internal/dhcpsvc/networkdevice_test.go

@@ -2,7 +2,9 @@ package dhcpsvc_test
 
 import (
 	"context"
+	"io"
 	"net/netip"
+	"sync/atomic"
 	"testing"
 
 	"github.com/AdguardTeam/AdGuardHome/internal/dhcpsvc"
@@ -41,6 +43,7 @@ func (ndm *testNetworkDeviceManager) Open(
 // TODO(e.burkov):  Move to aghtest.
 type testNetworkDevice struct {
 	onReadPacketData  func() (data []byte, ci gopacket.CaptureInfo, err error)
+	onClose           func() (err error)
 	onAddresses       func() (ips []netip.Addr)
 	onLinkType        func() (lt layers.LinkType)
 	onWritePacketData func(data []byte) (err error)
@@ -55,6 +58,11 @@ func (nd *testNetworkDevice) ReadPacketData() (data []byte, ci gopacket.CaptureI
 	return nd.onReadPacketData()
 }
 
+// Close implements the [io.Closer] interface for *testNetworkDevice.
+func (nd *testNetworkDevice) Close() (err error) {
+	return nd.onClose()
+}
+
 // Addresses implements the [dhcpsvc.NetworkDevice] interface for
 // *testNetworkDevice.
 func (nd *testNetworkDevice) Addresses() (ips []netip.Addr) {
@@ -87,13 +95,19 @@ func newTestNetworkDeviceManager(
 	inCh = make(chan gopacket.Packet)
 	outCh = make(chan []byte)
 
+	isOpened := atomic.Bool{}
+
 	pt := testutil.PanicT{}
 	addrs := []netip.Addr{addr}
 
 	dev := &testNetworkDevice{
 		onReadPacketData: func() (data []byte, ci gopacket.CaptureInfo, err error) {
 			pkt, ok := testutil.RequireReceive(pt, inCh, testTimeout)
-			require.True(pt, ok)
+			require.Equal(pt, isOpened.Load(), ok)
+
+			if !ok {
+				return nil, gopacket.CaptureInfo{}, io.EOF
+			}
 
 			data = pkt.Data()
 			ci = gopacket.CaptureInfo{
@@ -103,6 +117,12 @@ func newTestNetworkDeviceManager(
 
 			return data, ci, nil
 		},
+		onClose: func() (err error) {
+			isOpened.Store(false)
+			close(inCh)
+
+			return nil
+		},
 		onAddresses: func() (ips []netip.Addr) {
 			return addrs
 		},
@@ -121,6 +141,7 @@ func newTestNetworkDeviceManager(
 			_ context.Context,
 			conf *dhcpsvc.NetworkDeviceConfig,
 		) (nd dhcpsvc.NetworkDevice, err error) {
+			isOpened.Store(true)
 			require.Equal(pt, deviceName, conf.Name)
 
 			return dev, nil

internal/dhcpsvc/server.go

@@ -12,6 +12,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/AdguardTeam/golibs/container"
 	"github.com/AdguardTeam/golibs/errors"
 	"github.com/AdguardTeam/golibs/netutil"
 )
@@ -30,6 +31,12 @@ type DHCPServer struct {
 	// deviceManager is the manager of network devices.
 	deviceManager NetworkDeviceManager
 
+	// devices are the network devices opened in [DHCPServer.Start], mapped to
+	// their names.  Those are closed in [DHCPServer.Shutdown].
+	//
+	// TODO(e.burkov):  Consider storing those within interfaces.
+	devices container.KeyValues[string, NetworkDevice]
+
 	// localTLD is the top-level domain name to use for resolving DHCP clients'
 	// hostnames.
 	localTLD string
@@ -137,9 +144,11 @@ func (srv *DHCPServer) Start(ctx context.Context) (err error) {
 
 	var errs []error
 	for _, iface := range srv.interfaces4 {
-		var nd NetworkDevice
-		nd, err = srv.deviceManager.Open(ctx, &NetworkDeviceConfig{
-			Name: iface.common.name,
+		netDevName := iface.common.name
+
+		var netDev NetworkDevice
+		netDev, err = srv.deviceManager.Open(ctx, &NetworkDeviceConfig{
+			Name: netDevName,
 		})
 		if err != nil {
 			errs = append(errs, err)
@@ -147,7 +156,12 @@ func (srv *DHCPServer) Start(ctx context.Context) (err error) {
 			continue
 		}
 
-		go srv.serveEther4(context.WithoutCancel(ctx), iface, nd)
+		srv.devices = append(srv.devices, container.KeyValue[string, NetworkDevice]{
+			Key:   netDevName,
+			Value: netDev,
+		})
+
+		go srv.serveEther4(context.WithoutCancel(ctx), iface, netDev)
 	}
 
 	// TODO(e.burkov):  Serve EthernetTypeIPv6.
@@ -159,9 +173,17 @@ func (srv *DHCPServer) Start(ctx context.Context) (err error) {
 func (srv *DHCPServer) Shutdown(ctx context.Context) (err error) {
 	srv.logger.DebugContext(ctx, "shutting down dhcp server")
 
-	// TODO(e.burkov):  Close the packet source.
+	var errs []error
+	for _, kv := range srv.devices {
+		netDevName, netDev := kv.Key, kv.Value
 
-	return nil
+		err = netDev.Close()
+		if err != nil {
+			errs = append(errs, fmt.Errorf("closing device %q: %w", netDevName, err))
+		}
+	}
+
+	return errors.Join(errs...)
 }
 
 // Enabled implements the [Interface] interface for *DHCPServer.