Method AwaitReachable

tailnet/conn.go:607–658

AwaitReachable pings the provided IP continually until the address is reachable. It's the callers responsibility to provide a timeout, otherwise this function will block forever.

(ctx context.Context, ip netip.Addr)

// address is reachable. It's the callers responsibility to provide
// a timeout, otherwise this function will block forever.
func (c *Conn) AwaitReachable(ctx context.Context, ip netip.Addr) bool {
	ctx, cancel := context.WithCancel(ctx)
	defer cancel() // Cancel all pending pings on exit.

	completedCtx, completed := context.WithCancel(context.Background())
	defer completed()

	run := func() {
		// Safety timeout, initially we'll have around 10-20 goroutines
		// running in parallel. The exponential backoff will converge
		// around ~1 ping / 30s, this means we'll have around 10-20
		// goroutines pending towards the end as well.
		ctx, cancel := context.WithTimeout(ctx, 5*time.Minute)
		defer cancel()

		// For reachability, we use TSMP ping, which pings at the IP layer, and
		// therefore requires that wireguard and the netstack are up.  If we
		// don't wait for wireguard to be up, we could miss a handshake, and it
		// might take 5 seconds for the handshake to be retried. A 5s initial
		// round trip can set us up for poor TCP performance, since the initial
		// round-trip-time sets the initial retransmit timeout.
		_, _, _, err := c.pingWithType(ctx, ip, tailcfg.PingTSMP)
		if err == nil {
			completed()
		}
	}

	eb := backoff.NewExponentialBackOff()
	eb.MaxElapsedTime = 0
	eb.InitialInterval = 50 * time.Millisecond
	eb.MaxInterval = 30 * time.Second
	// Consume the first interval since
	// we'll fire off a ping immediately.
	_ = eb.NextBackOff()

	t := backoff.NewTicker(eb)
	defer t.Stop()

	go run()
	for {
		select {
		case <-completedCtx.Done():
			return true
		case <-t.C:
			// Pings can take a while, so we can run multiple
			// in parallel to return ASAP.
			go run()
		case <-ctx.Done():
			return false
		}
	}
}

// Closed is a channel that ends when the connection has
// been closed.