crossbar/internal/wake/wake.go

// Package wake sends wake-on-LAN magic packets and waits for a sleeping host to
// appear healthy in the health table. A sleeping host takes tens of seconds to
// come up, so the Waker remembers when it last sent and wakes a host at most once
// per wait window.
package wake

import (
	"context"
	"fmt"
	"log/slog"
	"net"
	"sync"
	"time"
)

// log reports a broadcast that fails to resolve or send. Wake continues past
// such failures (rule: one dead address must not stop the others), so this is
// the only place the package logs; the address and error are not request data.
var log = slog.New(slog.Default().Handler())

// Target describes how to wake one named host. Broadcast is the single-address
// form (as before); Broadcasts names more than one (a host that roams between
// networks). Wake sends to Broadcast (if set) and then each of Broadcasts.
type Target struct {
	MAC        string
	Broadcast  string
	Broadcasts []string
	Wait       time.Duration
}

// Health reports whether a named host is currently healthy. Implementations must
// be safe for concurrent use.
type Health interface{ Healthy(name string) bool }

// magicPacketLen is six sync bytes plus the MAC repeated sixteen times.
const magicPacketLen = 6 + 6*16

// MagicPacket builds a wake-on-LAN magic packet: six 0xff bytes followed by the
// target MAC sixteen times, a 102-byte frame.
func MagicPacket(mac string) ([]byte, error) {
	m, err := net.ParseMAC(mac)
	if err != nil {
		return nil, fmt.Errorf("wake: parse MAC %q: %w", mac, err)
	}
	if len(m) != 6 {
		return nil, fmt.Errorf("wake: MAC %q is not six bytes", mac)
	}
	pkt := make([]byte, magicPacketLen)
	for i := range pkt[:6] {
		pkt[i] = 0xff
	}
	for i := 0; i < 16; i++ {
		copy(pkt[6+i*6:], m)
	}
	return pkt, nil
}

// Send emits one magic packet for mac to the broadcast address as a single UDP4
// datagram, reporting parse, resolve and write errors.
func Send(mac, broadcast string) error {
	pkt, err := MagicPacket(mac)
	if err != nil {
		return err
	}
	remote, err := net.ResolveUDPAddr("udp4", broadcast)
	if err != nil {
		return fmt.Errorf("wake: resolve broadcast %q: %w", broadcast, err)
	}
	conn, err := net.DialUDP("udp4", nil, remote)
	if err != nil {
		return fmt.Errorf("wake: dial broadcast %q: %w", broadcast, err)
	}
	defer conn.Close()
	if _, err := conn.Write(pkt); err != nil {
		return fmt.Errorf("wake: write packet to %q: %w", broadcast, err)
	}
	return nil
}

// sendAll emits one magic packet for mac to broadcast (if non-empty) and then
// to each address in the rest, in order. An address that fails to resolve or
// send is logged and does not stop the others; it reports whether at least one
// packet went out.
func sendAll(mac, broadcast string, rest []string) bool {
	addrs := append([]string{broadcast}, rest...)
	sent := false
	for _, addr := range addrs {
		if addr == "" {
			continue
		}
		if err := Send(mac, addr); err != nil {
			log.Error("wake broadcast failed", "addr", addr, "err", err)
			continue
		}
		sent = true
	}
	return sent
}

// Waker wakes named hosts at most once per wait window and waits for the health
// table to report them healthy. It is safe for concurrent Wake calls.
type Waker struct {
	mu       sync.Mutex
	targets  map[string]Target
	health   Health
	lastSent map[string]time.Time
	poll     time.Duration
}

// New returns a Waker for the given targets, polling health every second.
func New(targets map[string]Target, h Health) *Waker {
	return &Waker{
		targets:  targets,
		health:   h,
		lastSent: make(map[string]time.Time),
		poll:     time.Second,
	}
}

// PollEvery sets how often Wake re-checks health; it is a test hook. Production
// keeps the 1 s default from New.
func (w *Waker) PollEvery(d time.Duration) {
	w.mu.Lock()
	w.poll = d
	w.mu.Unlock()
}

// Wake sends a magic packet for host to every broadcast address — Broadcast
// (if set) then each of Broadcasts, in order — if none was sent in the last
// Wait, then polls health until the host is healthy, the wait elapses, or ctx is
// done. A broadcast that fails to resolve or send is logged and does not stop
// the others; Wake returns true only when the host becomes healthy, and false
// for an unknown host, on timeout, when ctx ends first, or when no address
// could be sent to.
func (w *Waker) Wake(ctx context.Context, host string) bool {
	w.mu.Lock()
	target, ok := w.targets[host]
	if !ok {
		w.mu.Unlock()
		return false
	}
	now := time.Now()
	if last, sent := w.lastSent[host]; !sent || now.Sub(last) >= target.Wait {
		w.lastSent[host] = now
		w.mu.Unlock()
		if !sendAll(target.MAC, target.Broadcast, target.Broadcasts) {
			return false
		}
		w.mu.Lock()
	}
	poll := w.poll
	deadline := now.Add(target.Wait)
	w.mu.Unlock()

	timer := time.NewTimer(poll)
	defer timer.Stop()
	for {
		if w.health.Healthy(host) {
			return true
		}
		if time.Now().After(deadline) {
			return false
		}
		d := poll
		if rem := time.Until(deadline); rem < d {
			d = rem
		}
		timer.Reset(d)
		select {
		case <-ctx.Done():
			return false
		case <-timer.C:
		}
	}
}