Function checkDerp

cmd/tailscaled/debug.go:214–283

(ctx context.Context, derpRegion string)

}

func checkDerp(ctx context.Context, derpRegion string) (err error) {
	bus := eventbus.New()
	defer bus.Close()
	ht := health.NewTracker(bus)
	req, err := http.NewRequestWithContext(ctx, "GET", ipn.DefaultControlURL+"/derpmap/default", nil)
	if err != nil {
		return fmt.Errorf("create derp map request: %w", err)
	}
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		return fmt.Errorf("fetch derp map failed: %w", err)
	}
	defer res.Body.Close()
	b, err := io.ReadAll(io.LimitReader(res.Body, 1<<20))
	if err != nil {
		return fmt.Errorf("fetch derp map failed: %w", err)
	}
	if res.StatusCode != 200 {
		return fmt.Errorf("fetch derp map: %v: %s", res.Status, b)
	}
	var dmap tailcfg.DERPMap
	if err = json.Unmarshal(b, &dmap); err != nil {
		return fmt.Errorf("fetch DERP map: %w", err)
	}
	getRegion := func() *tailcfg.DERPRegion {
		for _, r := range dmap.Regions {
			if r.RegionCode == derpRegion {
				return r
			}
		}
		for _, r := range dmap.Regions {
			log.Printf("Known region: %q", r.RegionCode)
		}
		log.Fatalf("unknown region %q", derpRegion)
		panic("unreachable")
	}

	priv1 := key.NewNode()
	priv2 := key.NewNode()

	c1 := derphttp.NewRegionClient(priv1, log.Printf, nil, getRegion)
	c2 := derphttp.NewRegionClient(priv2, log.Printf, nil, getRegion)
	c1.HealthTracker = ht
	c2.HealthTracker = ht
	defer func() {
		if err != nil {
			c1.Close()
			c2.Close()
		}
	}()

	c2.NotePreferred(true) // just to open it

	m, err := c2.Recv()
	log.Printf("c2 got %T, %v", m, err)

	t0 := time.Now()
	if err := c1.Send(priv2.Public(), []byte("hello")); err != nil {