dhcpsvc: imp docs

internal/dhcpsvc/dhcpsvc.go

@@ -11,6 +11,10 @@ import (
 	"github.com/AdguardTeam/AdGuardHome/internal/next/agh"
 )
 
+// Interface is a DHCP service.
+//
+// TODO(e.burkov):  Separate HostByIP, MACByIP, IPByHost into a separate
+// interface.  This is also valid for Enabled method.
 type Interface interface {
 	agh.ServiceWithConfig[*Config]
 

internal/dhcpsvc/v4.go

@@ -326,7 +326,7 @@ type netInterfacesV4 []*netInterfaceV4
 // find returns the first network interface within ifaces containing ip.  It
 // returns false if there is no such interface.
 func (ifaces netInterfacesV4) find(ip netip.Addr) (iface4 *netInterface, ok bool) {
-	i := slices.IndexFunc(ifaces, func(iface *netInterfaceV4) bool {
+	i := slices.IndexFunc(ifaces, func(iface *netInterfaceV4) (contains bool) {
 		return iface.subnet.Contains(ip)
 	})
 	if i < 0 {

internal/dhcpsvc/v6.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/AdguardTeam/golibs/log"
+	"github.com/AdguardTeam/golibs/netutil"
 	"github.com/google/gopacket/layers"
 	"golang.org/x/exp/slices"
 )
@@ -140,8 +141,17 @@ type netInterfacesV6 []*netInterfaceV6
 // find returns the first network interface within ifaces containing ip.  It
 // returns false if there is no such interface.
 func (ifaces netInterfacesV6) find(ip netip.Addr) (iface6 *netInterface, ok bool) {
-	i := slices.IndexFunc(ifaces, func(iface *netInterfaceV6) bool {
-		return !iface.rangeStart.Less(ip) && netip.PrefixFrom(iface.rangeStart, 120).Contains(ip)
+	// prefLen is the length of prefix to match ip against.
+	//
+	// TODO(e.burkov):  DHCPv6 inherits the weird behavior of legacy
+	// implementation where the allocated range constrained by the first address
+	// and the first address with last byte set to 0xff.  Proper prefixes should
+	// be used instead.
+	const prefLen = netutil.IPv6BitLen - 8
+
+	i := slices.IndexFunc(ifaces, func(iface *netInterfaceV6) (contains bool) {
+		return !iface.rangeStart.Less(ip) &&
+			netip.PrefixFrom(iface.rangeStart, prefLen).Contains(ip)
 	})
 	if i < 0 {
 		return nil, false