steward/internal/dhcpd/config.go

package dhcpd

import (
	"net/netip"
	"time"

	"steward/internal/dhcp4"
	"steward/internal/model"
)

// config is a configuration prepared for answering requests: subnets by
// interface, reservations indexed, options encoded.
type config struct {
	state   *model.State
	byIface map[string][]*subnet
	// resByIP holds every reservation by address.
	resByIP map[netip.Addr]*model.Reservation
	// resByClient holds reservations per subnet by "mac aa:..." or
	// "id 01aa...".
	resByClient map[int64]map[string]*model.Reservation
	settings    model.Settings
}

type subnet struct {
	*model.Subnet
	network, broadcast netip.Addr
	leaseTime          time.Duration
	// options are the encoded options of the settings and the subnet,
	// the subnet's winning.
	options map[byte][]byte
}

func compile(st *model.State) *config {
	c := &config{
		state:       st,
		byIface:     map[string][]*subnet{},
		resByIP:     map[netip.Addr]*model.Reservation{},
		resByClient: map[int64]map[string]*model.Reservation{},
		settings:    st.Settings,
	}
	global := encodeOptions(st.Settings.Options, nil)
	for _, s := range st.Subnets {
		if s.Disabled || s.Interface == "" || !s.Prefix.Addr().Is4() {
			continue
		}
		lt := s.LeaseTime
		if lt <= 0 {
			lt = st.Settings.EffectiveLeaseTime()
		}
		sc := &subnet{Subnet: s, network: s.Prefix.Addr(), broadcast: model.Last(s.Prefix), leaseTime: time.Duration(lt) * time.Second,
			options: encodeOptions(s.Options, global)}
		c.byIface[s.Interface] = append(c.byIface[s.Interface], sc)
	}
	for _, r := range st.Reservations {
		if r.Disabled {
			continue
		}
		c.resByIP[r.IP] = r
		s := st.SubnetFor(r.IP)
		if s == nil {
			continue
		}
		if c.resByClient[s.ID] == nil {
			c.resByClient[s.ID] = map[string]*model.Reservation{}
		}
		if r.ClientID != "" {
			c.resByClient[s.ID]["id "+r.ClientID] = r
		}
		if r.MAC != "" {
			c.resByClient[s.ID]["mac "+r.MAC] = r
		}
	}
	return c
}

// encodeOptions encodes options over a base set (copied).
func encodeOptions(opts []model.OptionValue, base map[byte][]byte) map[byte][]byte {
	out := map[byte][]byte{}
	for k, v := range base {
		out[k] = v
	}
	for _, o := range opts {
		if o.Code <= 0 || o.Code >= 255 {
			continue
		}
		def := dhcp4.ByCode(byte(o.Code))
		typ := def.Type
		if !dhcp4.Known(byte(o.Code)) && o.Type != "" {
			typ = o.Type
		}
		if b, err := dhcp4.Encode(typ, o.Value); err == nil {
			out[byte(o.Code)] = b
		}
	}
	return out
}

// reservationFor finds the client's reservation in a subnet.
func (c *config) reservationFor(subnetID int64, cl client) *model.Reservation {
	m := c.resByClient[subnetID]
	if m == nil {
		return nil
	}
	if cl.id != "" {
		if r := m["id "+cl.id]; r != nil {
			return r
		}
	}
	return m["mac "+cl.mac]
}

// subnetFor finds the interface's subnet holding a.
func (c *config) subnetFor(iface string, a netip.Addr) *subnet {
	for _, s := range c.byIface[iface] {
		if s.Prefix.Contains(a) {
			return s
		}
	}
	return nil
}

// client identifies who sent a request.
type client struct {
	mac string // aa:bb:cc:dd:ee:ff
	id  string // client identifier (option 61) in hex, or ""
}

// 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 {
	return r.ClientID != "" && r.ClientID == cl.id || r.MAC != "" && r.MAC == cl.mac
}

func (cl client) String() string {
	if cl.id != "" {
		return cl.mac + " (client id " + cl.id + ")"
	}
	return cl.mac
}