Pull request 2070: 4923 gopacket DHCP vol.4

Merge in DNS/adguard-home from 4923-gopacket-dhcp-vol.4 to master

Updates #4923.

Squashed commit of the following:

commit 4b87258c70ac98b2abb1ac95f7e916e244b3cd08
Merge: 61458864f 9b91a8740
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Nov 16 14:05:34 2023 +0300

    Merge branch 'master' into 4923-gopacket-dhcp-vol.4

commit 61458864f3df7a027e65060a5f0fb516cc7911a7
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Nov 15 18:48:40 2023 +0300

    all: imp code

commit 506a0ab81e76beebb900f86580577563b471e4e2
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Nov 14 15:59:56 2023 +0300

    all: cleanup moving lease

commit 8d218b732662ac4308ed09d28c1bf9f65906d47c
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Nov 13 18:13:39 2023 +0300

    all: rm old leases type

internal/dhcpsvc/dhcpsvc.go

@@ -10,13 +10,13 @@ import (
 	"time"
 
 	"github.com/AdguardTeam/AdGuardHome/internal/next/agh"
+	"golang.org/x/exp/slices"
 )
 
 // Lease is a DHCP lease.
 //
-// TODO(e.burkov):  Consider it to [agh], since it also may be needed in
-// [websvc].  Also think of implementing iterating methods with appropriate
-// signatures.
+// TODO(e.burkov):  Consider moving it to [agh], since it also may be needed in
+// [websvc].
 type Lease struct {
 	// IP is the IP address leased to the client.
 	IP netip.Addr
@@ -34,6 +34,21 @@ type Lease struct {
 	IsStatic bool
 }
 
+// Clone returns a deep copy of l.
+func (l *Lease) Clone() (clone *Lease) {
+	if l == nil {
+		return nil
+	}
+
+	return &Lease{
+		Expiry:   l.Expiry,
+		Hostname: l.Hostname,
+		HWAddr:   slices.Clone(l.HWAddr),
+		IP:       l.IP,
+		IsStatic: l.IsStatic,
+	}
+}
+
 type Interface interface {
 	agh.ServiceWithConfig[*Config]
 
@@ -57,6 +72,9 @@ type Interface interface {
 	IPByHost(host string) (ip netip.Addr)
 
 	// Leases returns all the active DHCP leases.
+	//
+	// TODO(e.burkov):  Consider implementing iterating methods with appropriate
+	// signatures instead of cloning the whole list.
 	Leases() (ls []*Lease)
 
 	// AddLease adds a new DHCP lease.  It returns an error if the lease is
@@ -91,6 +109,9 @@ func (Empty) Shutdown(_ context.Context) (err error) { return nil }
 // Config implements the [ServiceWithConfig] interface for Empty.
 func (Empty) Config() (conf *Config) { return nil }
 
+// type check
+var _ Interface = Empty{}
+
 // Enabled implements the [Interface] interface for Empty.
 func (Empty) Enabled() (ok bool) { return false }
 
@@ -103,9 +124,6 @@ func (Empty) MACByIP(_ netip.Addr) (mac net.HardwareAddr) { return nil }
 // IPByHost implements the [Interface] interface for Empty.
 func (Empty) IPByHost(_ string) (ip netip.Addr) { return netip.Addr{} }
 
-// type check
-var _ Interface = Empty{}
-
 // Leases implements the [Interface] interface for Empty.
 func (Empty) Leases() (leases []*Lease) { return nil }