Reservation lease time; reservations by MAC address or client ID

- A reservation can have its own lease time (--lease-time, the
  reservation dialog), over the subnet's. Schema migration 6.
- A reservation with a MAC address and a client ID matches either one
  (a dual-boot machine sends two client IDs from one MAC); before, it
  was found by MAC and then refused. A lease of the reserved address by
  the client's other identity counts as its own.
- The Leases page shows a client's client ID; reserving a lease uses
  both, or one with --by / the dialog's choice.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/dhcpd/config.go

@@ -125,13 +125,11 @@ type client struct {
 	id  string // client identifier (option 61) in hex, or ""
 }
 
-// matches reports whether a reservation is for the client: by client
-// identifier when the reservation has one, else by MAC address.
+// matches reports whether the reservation is the client's: by its client
+// identifier or its MAC address, either one when the reservation has both
+// (a dual-boot machine sends different client IDs from one MAC address).
 func (cl client) matches(r *model.Reservation) bool {
-	if r.ClientID != "" {
-		return r.ClientID == cl.id
-	}
-	return r.MAC == cl.mac
+	return r.ClientID != "" && r.ClientID == cl.id || r.MAC != "" && r.MAC == cl.mac
 }
 
 func (cl client) String() string {

internal/dhcpd/handle.go

@@ -190,8 +190,9 @@ func (s *Server) usable(cfg *config, own map[netip.Addr]bool, sub *subnet, ip ne
 	if !sub.Prefix.Contains(ip) || ip == sub.network || ip == sub.broadcast || own[ip] {
 		return false
 	}
-	if r := cfg.resByIP[ip]; r != nil {
-		if !cl.matches(r) {
+	res := cfg.resByIP[ip]
+	if res != nil {
+		if !cl.matches(res) {
 			return false
 		}
 	} else {
@@ -211,7 +212,10 @@ func (s *Server) usable(cfg *config, own map[netip.Addr]bool, sub *subnet, ip ne
 			return false
 		}
 	}
-	if l := s.leases[ip]; l != nil && l.HeldAt(now) && (l.State == model.LeaseDeclined || !l.Owns(cl.mac, cl.id)) {
+	// A lease of the reserved address by the reservation's client under
+	// its other identity (the other OS of a dual-boot machine) is its own.
+	if l := s.leases[ip]; l != nil && l.HeldAt(now) && (l.State == model.LeaseDeclined ||
+		!l.Owns(cl.mac, cl.id) && !(res != nil && (client{mac: l.MAC, id: l.ClientID}).matches(res))) {
 		return false
 	}
 	if o, ok := s.offers[ip]; ok && now.Before(o.expires) && o.cl != cl {
@@ -296,8 +300,12 @@ func (s *Server) ack(ctx context.Context, cfg *config, iface string, p *dhcp4.Pa
 			host = l.Hostname
 		}
 	}
+	res := cfg.reservationFor(sub.ID, cl)
+	if res != nil && res.IP != ip {
+		res = nil
+	}
 	l := &model.Lease{IP: ip, SubnetID: sub.ID, MAC: cl.mac, ClientID: cl.id, Hostname: host, State: model.LeaseActive,
-		Start: start, End: now.Add(sub.leaseTime), Interface: iface, LastSeen: seen}
+		Start: start, End: now.Add(leaseTime(sub, res)), Interface: iface, LastSeen: seen}
 	err := s.putLease(ctx, l)
 	delete(s.offers, ip)
 	s.mu.Unlock()
@@ -312,10 +320,6 @@ func (s *Server) ack(ctx context.Context, cfg *config, iface string, p *dhcp4.Pa
 		s.warnOnce("sid "+iface, 10*time.Minute, "can't answer DHCP: "+err.Error(), "interface", iface)
 		return nil
 	}
-	res := cfg.reservationFor(sub.ID, cl)
-	if res != nil && res.IP != ip {
-		res = nil
-	}
 	r := p.Reply(dhcp4.Ack)
 	r.YIAddr = ip
 	r.CIAddr = p.CIAddr
@@ -413,6 +417,14 @@ func (s *Server) inform(cfg *config, iface string, p *dhcp4.Packet, cl client) *
 	return &Outbound{Packet: r, Dst: p.CIAddr}
 }
 
+// leaseTime is a lease's length: the reservation's, else the subnet's.
+func leaseTime(sub *subnet, res *model.Reservation) time.Duration {
+	if res != nil && res.LeaseTime > 0 {
+		return time.Duration(res.LeaseTime) * time.Second
+	}
+	return sub.leaseTime
+}
+
 // ---- options
 
 // Options always sent when configured, even when the client doesn't ask.
@@ -425,7 +437,7 @@ var essential = []byte{dhcp4.OptSubnetMask, dhcp4.OptRouters, dhcp4.OptDNSServer
 func (s *Server) addOptions(r, req *dhcp4.Packet, sub *subnet, res *model.Reservation, sid netip.Addr, lease bool) {
 	r.Set(dhcp4.OptServerID, dhcp4.IP(sid))
 	if lease {
-		lt := uint32(sub.leaseTime / time.Second)
+		lt := uint32(leaseTime(sub, res) / time.Second)
 		r.Set(dhcp4.OptLeaseTime, dhcp4.U32(lt))
 		r.Set(dhcp4.OptRenewalTime, dhcp4.U32(lt/2))
 		r.Set(dhcp4.OptRebindingTime, dhcp4.U32(lt*7/8))

internal/dhcpd/handle_test.go

@@ -2,6 +2,7 @@ package dhcpd
 
 import (
 	"context"
+	"encoding/binary"
 	"errors"
 	"net"
 	"net/netip"
@@ -115,9 +116,9 @@ func (h *harness) discover(iface string, m net.HardwareAddr, opts ...dhcp4.Optio
 }
 
 // lease runs DISCOVER and REQUEST and returns the ACK.
-func (h *harness) lease(iface string, m net.HardwareAddr) *dhcp4.Packet {
+func (h *harness) lease(iface string, m net.HardwareAddr, opts ...dhcp4.Option) *dhcp4.Packet {
 	h.t.Helper()
-	off := h.discover(iface, m)
+	off := h.discover(iface, m, opts...)
 	if off == nil || off.Packet.Type() != dhcp4.Offer {
 		h.t.Fatalf("no offer for %s on %s", m, iface)
 	}
@@ -126,6 +127,9 @@ func (h *harness) lease(iface string, m net.HardwareAddr) *dhcp4.Packet {
 	req.Set(dhcp4.OptServerID, dhcp4.IP(sid))
 	req.Set(dhcp4.OptRequestedIP, dhcp4.IP(off.Packet.YIAddr))
 	req.Set(dhcp4.OptHostName, []byte("client"+m.String()[15:]))
+	for _, o := range opts {
+		req.Set(o.Code, o.Data)
+	}
 	ack := h.send(iface, req)
 	if ack == nil || ack.Packet.Type() != dhcp4.Ack {
 		h.t.Fatalf("no ACK for %s: %+v", m, ack)
@@ -580,3 +584,31 @@ func TestAddressOrder(t *testing.T) {
 		t.Errorf("a full subnet offered %s", out.Packet.YIAddr)
 	}
 }
+
+func TestReservationLeaseTimeAndClientID(t *testing.T) {
+	h := newHarness(t, func(st *model.State) {
+		st.Reservations[0].LeaseTime = 600
+		st.Reservations[0].ClientID = "ff0102"
+	})
+	u32 := func(p *dhcp4.Packet) uint32 { return binary.BigEndian.Uint32(p.Get(dhcp4.OptLeaseTime)) }
+	id := func(hex ...byte) dhcp4.Option { return dhcp4.Option{Code: dhcp4.OptClientID, Data: hex} }
+	// By its client ID, from any MAC address, with its own lease time.
+	ack := h.lease("eth0", mac(0x50), id(0xff, 1, 2))
+	if ack.YIAddr.String() != "10.0.10.20" || u32(ack) != 600 {
+		t.Errorf("by client id: %s %d", ack.YIAddr, u32(ack))
+	}
+	if l := h.s.Lease(ack.YIAddr); !l.End.Equal(h.clock.Add(10 * time.Minute)) {
+		t.Errorf("lease end %v", l.End)
+	}
+	// By its MAC address with another client ID (the machine's other OS):
+	// the same address, though the first identity's lease is still on.
+	ack = h.lease("eth0", mac(0x99), id(1, 0xaa, 0, 0, 0, 0, 0x99))
+	if ack.YIAddr.String() != "10.0.10.20" {
+		t.Errorf("by MAC: %s", ack.YIAddr)
+	}
+	// Anyone else gets a pool address, with the subnet's lease time.
+	ack = h.lease("eth0", mac(0x51), id(0xff, 9, 9))
+	if ack.YIAddr.String() == "10.0.10.20" || u32(ack) != 43200 {
+		t.Errorf("stranger: %s %d", ack.YIAddr, u32(ack))
+	}
+}