tailscale/net/netcheck/netcheck_test.go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

package netcheck

import (
	"bytes"
	"context"
	"fmt"
	"net"
	"net/http"
	"net/netip"
	"reflect"
	"sort"
	"strconv"
	"strings"
	"sync/atomic"
	"testing"
	"time"

	"tailscale.com/net/interfaces"
	"tailscale.com/net/stun"
	"tailscale.com/net/stun/stuntest"
	"tailscale.com/tailcfg"
	"tailscale.com/tstest"
)

func TestHairpinSTUN(t *testing.T) {
	tx := stun.NewTxID()
	c := &Client{
		curState: &reportState{
			hairTX:      tx,
			gotHairSTUN: make(chan netip.AddrPort, 1),
		},
	}
	req := stun.Request(tx)
	if !stun.Is(req) {
		t.Fatal("expected STUN message")
	}
	if !c.handleHairSTUNLocked(req, netip.AddrPort{}) {
		t.Fatal("expected true")
	}
	select {
	case <-c.curState.gotHairSTUN:
	default:
		t.Fatal("expected value")
	}
}

func TestHairpinWait(t *testing.T) {
	makeClient := func(t *testing.T) (*Client, *reportState) {
		tx := stun.NewTxID()
		c := &Client{}
		req := stun.Request(tx)
		if !stun.Is(req) {
			t.Fatal("expected STUN message")
		}

		var err error
		rs := &reportState{
			c:           c,
			hairTX:      tx,
			gotHairSTUN: make(chan netip.AddrPort, 1),
			hairTimeout: make(chan struct{}),
			report:      newReport(),
		}
		rs.pc4Hair, err = net.ListenUDP("udp4", &net.UDPAddr{
			IP:   net.ParseIP("127.0.0.1"),
			Port: 0,
		})
		if err != nil {
			t.Fatal(err)
		}

		c.curState = rs
		return c, rs
	}

	ll, err := net.ListenPacket("udp", "localhost:0")
	if err != nil {
		t.Fatal(err)
	}
	defer ll.Close()
	dstAddr := netip.MustParseAddrPort(ll.LocalAddr().String())

	t.Run("Success", func(t *testing.T) {
		c, rs := makeClient(t)
		req := stun.Request(rs.hairTX)

		// Start a hairpin check to ourselves.
		rs.startHairCheckLocked(dstAddr)

		// Fake receiving the stun check from ourselves after some period of time.
		src := netip.MustParseAddrPort(rs.pc4Hair.LocalAddr().String())
		c.handleHairSTUNLocked(req, src)

		rs.waitHairCheck(context.Background())

		// Verify that we set HairPinning
		if got := rs.report.HairPinning; !got.EqualBool(true) {
			t.Errorf("wanted HairPinning=true, got %v", got)
		}
	})

	t.Run("LateReply", func(t *testing.T) {
		c, rs := makeClient(t)
		req := stun.Request(rs.hairTX)

		// Start a hairpin check to ourselves.
		rs.startHairCheckLocked(dstAddr)

		// Wait until we've timed out, to mimic the race in #1795.
		<-rs.hairTimeout

		// Fake receiving the stun check from ourselves after some period of time.
		src := netip.MustParseAddrPort(rs.pc4Hair.LocalAddr().String())
		c.handleHairSTUNLocked(req, src)

		// Wait for a hairpin response
		rs.waitHairCheck(context.Background())

		// Verify that we set HairPinning
		if got := rs.report.HairPinning; !got.EqualBool(true) {
			t.Errorf("wanted HairPinning=true, got %v", got)
		}
	})

	t.Run("Timeout", func(t *testing.T) {
		_, rs := makeClient(t)

		// Start a hairpin check to ourselves.
		rs.startHairCheckLocked(dstAddr)

		ctx, cancel := context.WithTimeout(context.Background(), hairpinCheckTimeout*50)
		defer cancel()

		// Wait in the background
		waitDone := make(chan struct{})
		go func() {
			rs.waitHairCheck(ctx)
			close(waitDone)
		}()

		// If we do nothing, then we time out; confirm that we set
		// HairPinning to false in this case.
		select {
		case <-waitDone:
			if got := rs.report.HairPinning; !got.EqualBool(false) {
				t.Errorf("wanted HairPinning=false, got %v", got)
			}
		case <-ctx.Done():
			t.Fatalf("timed out waiting for hairpin channel")
		}
	})
}

func TestBasic(t *testing.T) {
	stunAddr, cleanup := stuntest.Serve(t)
	defer cleanup()

	c := &Client{
		Logf:        t.Logf,
		UDPBindAddr: "127.0.0.1:0",
	}

	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
	defer cancel()

	r, err := c.GetReport(ctx, stuntest.DERPMapOf(stunAddr.String()))
	if err != nil {
		t.Fatal(err)
	}
	if !r.UDP {
		t.Error("want UDP")
	}
	if len(r.RegionLatency) != 1 {
		t.Errorf("expected 1 key in DERPLatency; got %+v", r.RegionLatency)
	}
	if _, ok := r.RegionLatency[1]; !ok {
		t.Errorf("expected key 1 in DERPLatency; got %+v", r.RegionLatency)
	}
	if r.GlobalV4 == "" {
		t.Error("expected GlobalV4 set")
	}
	if r.PreferredDERP != 1 {
		t.Errorf("PreferredDERP = %v; want 1", r.PreferredDERP)
	}
}

func TestWorksWhenUDPBlocked(t *testing.T) {
	blackhole, err := net.ListenPacket("udp4", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("failed to open blackhole STUN listener: %v", err)
	}
	defer blackhole.Close()

	stunAddr := blackhole.LocalAddr().String()

	dm := stuntest.DERPMapOf(stunAddr)
	dm.Regions[1].Nodes[0].STUNOnly = true

	c := &Client{
		Logf: t.Logf,
	}
	ctx, cancel := context.WithTimeout(context.Background(), 250*time.Millisecond)
	defer cancel()

	r, err := c.GetReport(ctx, dm)
	if err != nil {
		t.Fatal(err)
	}
	r.UPnP = ""
	r.PMP = ""
	r.PCP = ""

	want := newReport()

	// The IPv4CanSend flag gets set differently across platforms.
	// On Windows this test detects false, while on Linux detects true.
	// That's not relevant to this test, so just accept what we're
	// given.
	want.IPv4CanSend = r.IPv4CanSend
	// OS IPv6 test is irrelevant here, accept whatever the current
	// machine has.
	want.OSHasIPv6 = r.OSHasIPv6
	// Captive portal test is irrelevant; accept what the current report
	// has.
	want.CaptivePortal = r.CaptivePortal

	if !reflect.DeepEqual(r, want) {
		t.Errorf("mismatch\n got: %+v\nwant: %+v\n", r, want)
	}
}

func TestAddReportHistoryAndSetPreferredDERP(t *testing.T) {
	// report returns a *Report from (DERP host, time.Duration)+ pairs.
	report := func(a ...any) *Report {
		r := &Report{RegionLatency: map[int]time.Duration{}}
		for i := 0; i < len(a); i += 2 {
			s := a[i].(string)
			if !strings.HasPrefix(s, "d") {
				t.Fatalf("invalid derp server key %q", s)
			}
			regionID, err := strconv.Atoi(s[1:])
			if err != nil {
				t.Fatalf("invalid derp server key %q", s)
			}

			switch v := a[i+1].(type) {
			case time.Duration:
				r.RegionLatency[regionID] = v
			case int:
				r.RegionLatency[regionID] = time.Second * time.Duration(v)
			default:
				panic(fmt.Sprintf("unexpected type %T", v))
			}
		}
		return r
	}
	type step struct {
		after time.Duration
		r     *Report
	}
	tests := []struct {
		name        string
		steps       []step
		wantDERP    int // want PreferredDERP on final step
		wantPrevLen int // wanted len(c.prev)
	}{
		{
			name: "first_reading",
			steps: []step{
				{0, report("d1", 2, "d2", 3)},
			},
			wantPrevLen: 1,
			wantDERP:    1,
		},
		{
			name: "with_two",
			steps: []step{
				{0, report("d1", 2, "d2", 3)},
				{1 * time.Second, report("d1", 4, "d2", 3)},
			},
			wantPrevLen: 2,
			wantDERP:    1, // t0's d1 of 2 is still best
		},
		{
			name: "but_now_d1_gone",
			steps: []step{
				{0, report("d1", 2, "d2", 3)},
				{1 * time.Second, report("d1", 4, "d2", 3)},
				{2 * time.Second, report("d2", 3)},
			},
			wantPrevLen: 3,
			wantDERP:    2, // only option
		},
		{
			name: "d1_is_back",
			steps: []step{
				{0, report("d1", 2, "d2", 3)},
				{1 * time.Second, report("d1", 4, "d2", 3)},
				{2 * time.Second, report("d2", 3)},
				{3 * time.Second, report("d1", 4, "d2", 3)}, // same as 2 seconds ago
			},
			wantPrevLen: 4,
			wantDERP:    1, // t0's d1 of 2 is still best
		},
		{
			name: "things_clean_up",
			steps: []step{
				{0, report("d1", 1, "d2", 2)},
				{1 * time.Second, report("d1", 1, "d2", 2)},
				{2 * time.Second, report("d1", 1, "d2", 2)},
				{3 * time.Second, report("d1", 1, "d2", 2)},
				{10 * time.Minute, report("d3", 3)},
			},
			wantPrevLen: 1, // t=[0123]s all gone. (too old, older than 10 min)
			wantDERP:    3, // only option
		},
		{
			name: "preferred_derp_hysteresis_no_switch",
			steps: []step{
				{0 * time.Second, report("d1", 4, "d2", 5)},
				{1 * time.Second, report("d1", 4, "d2", 3)},
			},
			wantPrevLen: 2,
			wantDERP:    1, // 2 didn't get fast enough
		},
		{
			name: "preferred_derp_hysteresis_do_switch",
			steps: []step{
				{0 * time.Second, report("d1", 4, "d2", 5)},
				{1 * time.Second, report("d1", 4, "d2", 1)},
			},
			wantPrevLen: 2,
			wantDERP:    2, // 2 got fast enough
		},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			fakeTime := time.Unix(123, 0)
			c := &Client{
				TimeNow: func() time.Time { return fakeTime },
			}
			for _, s := range tt.steps {
				fakeTime = fakeTime.Add(s.after)
				c.addReportHistoryAndSetPreferredDERP(s.r)
			}
			lastReport := tt.steps[len(tt.steps)-1].r
			if got, want := len(c.prev), tt.wantPrevLen; got != want {
				t.Errorf("len(prev) = %v; want %v", got, want)
			}
			if got, want := lastReport.PreferredDERP, tt.wantDERP; got != want {
				t.Errorf("PreferredDERP = %v; want %v", got, want)
			}
		})
	}
}

func TestMakeProbePlan(t *testing.T) {
	// basicMap has 5 regions. each region has a number of nodes
	// equal to the region number (1 has 1a, 2 has 2a and 2b, etc.)
	basicMap := &tailcfg.DERPMap{
		Regions: map[int]*tailcfg.DERPRegion{},
	}
	for rid := 1; rid <= 5; rid++ {
		var nodes []*tailcfg.DERPNode
		for nid := 0; nid < rid; nid++ {
			nodes = append(nodes, &tailcfg.DERPNode{
				Name:     fmt.Sprintf("%d%c", rid, 'a'+rune(nid)),
				RegionID: rid,
				HostName: fmt.Sprintf("derp%d-%d", rid, nid),
				IPv4:     fmt.Sprintf("%d.0.0.%d", rid, nid),
				IPv6:     fmt.Sprintf("%d::%d", rid, nid),
			})
		}
		basicMap.Regions[rid] = &tailcfg.DERPRegion{
			RegionID: rid,
			Nodes:    nodes,
		}
	}

	const ms = time.Millisecond
	p := func(name string, c rune, d ...time.Duration) probe {
		var proto probeProto
		switch c {
		case 4:
			proto = probeIPv4
		case 6:
			proto = probeIPv6
		case 'h':
			proto = probeHTTPS
		}
		pr := probe{node: name, proto: proto}
		if len(d) == 1 {
			pr.delay = d[0]
		} else if len(d) > 1 {
			panic("too many args")
		}
		return pr
	}
	tests := []struct {
		name    string
		dm      *tailcfg.DERPMap
		have6if bool
		no4     bool // no IPv4
		last    *Report
		want    probePlan
	}{
		{
			name:    "initial_v6",
			dm:      basicMap,
			have6if: true,
			last:    nil, // initial
			want: probePlan{
				"region-1-v4": []probe{p("1a", 4), p("1a", 4, 100*ms), p("1a", 4, 200*ms)}, // all a
				"region-1-v6": []probe{p("1a", 6), p("1a", 6, 100*ms), p("1a", 6, 200*ms)},
				"region-2-v4": []probe{p("2a", 4), p("2b", 4, 100*ms), p("2a", 4, 200*ms)}, // a -> b -> a
				"region-2-v6": []probe{p("2a", 6), p("2b", 6, 100*ms), p("2a", 6, 200*ms)},
				"region-3-v4": []probe{p("3a", 4), p("3b", 4, 100*ms), p("3c", 4, 200*ms)}, // a -> b -> c
				"region-3-v6": []probe{p("3a", 6), p("3b", 6, 100*ms), p("3c", 6, 200*ms)},
				"region-4-v4": []probe{p("4a", 4), p("4b", 4, 100*ms), p("4c", 4, 200*ms)},
				"region-4-v6": []probe{p("4a", 6), p("4b", 6, 100*ms), p("4c", 6, 200*ms)},
				"region-5-v4": []probe{p("5a", 4), p("5b", 4, 100*ms), p("5c", 4, 200*ms)},
				"region-5-v6": []probe{p("5a", 6), p("5b", 6, 100*ms), p("5c", 6, 200*ms)},
			},
		},
		{
			name:    "initial_no_v6",
			dm:      basicMap,
			have6if: false,
			last:    nil, // initial
			want: probePlan{
				"region-1-v4": []probe{p("1a", 4), p("1a", 4, 100*ms), p("1a", 4, 200*ms)}, // all a
				"region-2-v4": []probe{p("2a", 4), p("2b", 4, 100*ms), p("2a", 4, 200*ms)}, // a -> b -> a
				"region-3-v4": []probe{p("3a", 4), p("3b", 4, 100*ms), p("3c", 4, 200*ms)}, // a -> b -> c
				"region-4-v4": []probe{p("4a", 4), p("4b", 4, 100*ms), p("4c", 4, 200*ms)},
				"region-5-v4": []probe{p("5a", 4), p("5b", 4, 100*ms), p("5c", 4, 200*ms)},
			},
		},
		{
			name:    "second_v4_no_6if",
			dm:      basicMap,
			have6if: false,
			last: &Report{
				RegionLatency: map[int]time.Duration{
					1: 10 * time.Millisecond,
					2: 20 * time.Millisecond,
					3: 30 * time.Millisecond,
					4: 40 * time.Millisecond,
					// Pretend 5 is missing
				},
				RegionV4Latency: map[int]time.Duration{
					1: 10 * time.Millisecond,
					2: 20 * time.Millisecond,
					3: 30 * time.Millisecond,
					4: 40 * time.Millisecond,
				},
			},
			want: probePlan{
				"region-1-v4": []probe{p("1a", 4), p("1a", 4, 12*ms)},
				"region-2-v4": []probe{p("2a", 4), p("2b", 4, 24*ms)},
				"region-3-v4": []probe{p("3a", 4)},
			},
		},
		{
			name:    "second_v4_only_with_6if",
			dm:      basicMap,
			have6if: true,
			last: &Report{
				RegionLatency: map[int]time.Duration{
					1: 10 * time.Millisecond,
					2: 20 * time.Millisecond,
					3: 30 * time.Millisecond,
					4: 40 * time.Millisecond,
					// Pretend 5 is missing
				},
				RegionV4Latency: map[int]time.Duration{
					1: 10 * time.Millisecond,
					2: 20 * time.Millisecond,
					3: 30 * time.Millisecond,
					4: 40 * time.Millisecond,
				},
			},
			want: probePlan{
				"region-1-v4": []probe{p("1a", 4), p("1a", 4, 12*ms)},
				"region-1-v6": []probe{p("1a", 6)},
				"region-2-v4": []probe{p("2a", 4), p("2b", 4, 24*ms)},
				"region-2-v6": []probe{p("2a", 6)},
				"region-3-v4": []probe{p("3a", 4)},
			},
		},
		{
			name:    "second_mixed",
			dm:      basicMap,
			have6if: true,
			last: &Report{
				RegionLatency: map[int]time.Duration{
					1: 10 * time.Millisecond,
					2: 20 * time.Millisecond,
					3: 30 * time.Millisecond,
					4: 40 * time.Millisecond,
					// Pretend 5 is missing
				},
				RegionV4Latency: map[int]time.Duration{
					1: 10 * time.Millisecond,
					2: 20 * time.Millisecond,
				},
				RegionV6Latency: map[int]time.Duration{
					3: 30 * time.Millisecond,
					4: 40 * time.Millisecond,
				},
			},
			want: probePlan{
				"region-1-v4": []probe{p("1a", 4), p("1a", 4, 12*ms)},
				"region-1-v6": []probe{p("1a", 6), p("1a", 6, 12*ms)},
				"region-2-v4": []probe{p("2a", 4), p("2b", 4, 24*ms)},
				"region-2-v6": []probe{p("2a", 6), p("2b", 6, 24*ms)},
				"region-3-v4": []probe{p("3a", 4)},
			},
		},
		{
			name:    "only_v6_initial",
			have6if: true,
			no4:     true,
			dm:      basicMap,
			want: probePlan{
				"region-1-v6": []probe{p("1a", 6), p("1a", 6, 100*ms), p("1a", 6, 200*ms)},
				"region-2-v6": []probe{p("2a", 6), p("2b", 6, 100*ms), p("2a", 6, 200*ms)},
				"region-3-v6": []probe{p("3a", 6), p("3b", 6, 100*ms), p("3c", 6, 200*ms)},
				"region-4-v6": []probe{p("4a", 6), p("4b", 6, 100*ms), p("4c", 6, 200*ms)},
				"region-5-v6": []probe{p("5a", 6), p("5b", 6, 100*ms), p("5c", 6, 200*ms)},
			},
		},
		{
			name:    "try_harder_for_preferred_derp",
			dm:      basicMap,
			have6if: true,
			last: &Report{
				RegionLatency: map[int]time.Duration{
					1: 10 * time.Millisecond,
					2: 20 * time.Millisecond,
					3: 30 * time.Millisecond,
					4: 40 * time.Millisecond,
				},
				RegionV4Latency: map[int]time.Duration{
					1: 10 * time.Millisecond,
					2: 20 * time.Millisecond,
				},
				RegionV6Latency: map[int]time.Duration{
					3: 30 * time.Millisecond,
					4: 40 * time.Millisecond,
				},
				PreferredDERP: 1,
			},
			want: probePlan{
				"region-1-v4": []probe{p("1a", 4), p("1a", 4, 12*ms), p("1a", 4, 124*ms), p("1a", 4, 186*ms)},
				"region-1-v6": []probe{p("1a", 6), p("1a", 6, 12*ms), p("1a", 6, 124*ms), p("1a", 6, 186*ms)},
				"region-2-v4": []probe{p("2a", 4), p("2b", 4, 24*ms)},
				"region-2-v6": []probe{p("2a", 6), p("2b", 6, 24*ms)},
				"region-3-v4": []probe{p("3a", 4)},
			},
		},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			ifState := &interfaces.State{
				HaveV6: tt.have6if,
				HaveV4: !tt.no4,
			}
			got := makeProbePlan(tt.dm, ifState, tt.last)
			if !reflect.DeepEqual(got, tt.want) {
				t.Errorf("unexpected plan; got:\n%v\nwant:\n%v\n", got, tt.want)
			}
		})
	}
}

func (plan probePlan) String() string {
	var sb strings.Builder
	keys := []string{}
	for k := range plan {
		keys = append(keys, k)
	}
	sort.Strings(keys)

	for _, key := range keys {
		fmt.Fprintf(&sb, "[%s]", key)
		pv := plan[key]
		for _, p := range pv {
			fmt.Fprintf(&sb, " %v", p)
		}
		sb.WriteByte('\n')
	}
	return sb.String()
}

func (p probe) String() string {
	wait := ""
	if p.wait > 0 {
		wait = "+" + p.wait.String()
	}
	delay := ""
	if p.delay > 0 {
		delay = "@" + p.delay.String()
	}
	return fmt.Sprintf("%s-%s%s%s", p.node, p.proto, delay, wait)
}

func (p probeProto) String() string {
	switch p {
	case probeIPv4:
		return "v4"
	case probeIPv6:
		return "v4"
	case probeHTTPS:
		return "https"
	}
	return "?"
}

func TestLogConciseReport(t *testing.T) {
	dm := &tailcfg.DERPMap{
		Regions: map[int]*tailcfg.DERPRegion{
			1: nil,
			2: nil,
			3: nil,
		},
	}
	const ms = time.Millisecond
	tests := []struct {
		name string
		r    *Report
		want string
	}{
		{
			name: "no_udp",
			r:    &Report{},
			want: "udp=false v4=false icmpv4=false v6=false mapvarydest= hair= portmap=? derp=0",
		},
		{
			name: "no_udp_icmp",
			r:    &Report{ICMPv4: true, IPv4: true},
			want: "udp=false icmpv4=true v6=false mapvarydest= hair= portmap=? derp=0",
		},
		{
			name: "ipv4_one_region",
			r: &Report{
				UDP:           true,
				IPv4:          true,
				PreferredDERP: 1,
				RegionLatency: map[int]time.Duration{
					1: 10 * ms,
				},
				RegionV4Latency: map[int]time.Duration{
					1: 10 * ms,
				},
			},
			want: "udp=true v6=false mapvarydest= hair= portmap=? derp=1 derpdist=1v4:10ms",
		},
		{
			name: "ipv4_all_region",
			r: &Report{
				UDP:           true,
				IPv4:          true,
				PreferredDERP: 1,
				RegionLatency: map[int]time.Duration{
					1: 10 * ms,
					2: 20 * ms,
					3: 30 * ms,
				},
				RegionV4Latency: map[int]time.Duration{
					1: 10 * ms,
					2: 20 * ms,
					3: 30 * ms,
				},
			},
			want: "udp=true v6=false mapvarydest= hair= portmap=? derp=1 derpdist=1v4:10ms,2v4:20ms,3v4:30ms",
		},
		{
			name: "ipboth_all_region",
			r: &Report{
				UDP:           true,
				IPv4:          true,
				IPv6:          true,
				PreferredDERP: 1,
				RegionLatency: map[int]time.Duration{
					1: 10 * ms,
					2: 20 * ms,
					3: 30 * ms,
				},
				RegionV4Latency: map[int]time.Duration{
					1: 10 * ms,
					2: 20 * ms,
					3: 30 * ms,
				},
				RegionV6Latency: map[int]time.Duration{
					1: 10 * ms,
					2: 20 * ms,
					3: 30 * ms,
				},
			},
			want: "udp=true v6=true mapvarydest= hair= portmap=? derp=1 derpdist=1v4:10ms,1v6:10ms,2v4:20ms,2v6:20ms,3v4:30ms,3v6:30ms",
		},
		{
			name: "portmap_all",
			r: &Report{
				UDP:  true,
				UPnP: "true",
				PMP:  "true",
				PCP:  "true",
			},
			want: "udp=true v4=false v6=false mapvarydest= hair= portmap=UMC derp=0",
		},
		{
			name: "portmap_some",
			r: &Report{
				UDP:  true,
				UPnP: "true",
				PMP:  "false",
				PCP:  "true",
			},
			want: "udp=true v4=false v6=false mapvarydest= hair= portmap=UC derp=0",
		},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			var buf bytes.Buffer
			c := &Client{Logf: func(f string, a ...any) { fmt.Fprintf(&buf, f, a...) }}
			c.logConciseReport(tt.r, dm)
			if got, ok := strings.CutPrefix(buf.String(), "[v1] report: "); !ok {
				t.Errorf("unexpected result.\n got: %#q\nwant: %#q\n", got, tt.want)
			}
		})
	}
}

func TestSortRegions(t *testing.T) {
	unsortedMap := &tailcfg.DERPMap{
		Regions: map[int]*tailcfg.DERPRegion{},
	}
	for rid := 1; rid <= 5; rid++ {
		var nodes []*tailcfg.DERPNode
		nodes = append(nodes, &tailcfg.DERPNode{
			Name:     fmt.Sprintf("%da", rid),
			RegionID: rid,
			HostName: fmt.Sprintf("derp%d-1", rid),
			IPv4:     fmt.Sprintf("%d.0.0.1", rid),
			IPv6:     fmt.Sprintf("%d::1", rid),
		})
		unsortedMap.Regions[rid] = &tailcfg.DERPRegion{
			RegionID: rid,
			Nodes:    nodes,
		}
	}
	report := newReport()
	report.RegionLatency[1] = time.Second * time.Duration(5)
	report.RegionLatency[2] = time.Second * time.Duration(3)
	report.RegionLatency[3] = time.Second * time.Duration(6)
	report.RegionLatency[4] = time.Second * time.Duration(0)
	report.RegionLatency[5] = time.Second * time.Duration(2)
	sortedMap := sortRegions(unsortedMap, report)

	// Sorting by latency this should result in rid: 5, 2, 1, 3
	// rid 4 with latency 0 should be at the end
	want := []int{5, 2, 1, 3, 4}
	got := make([]int, len(sortedMap))
	for i, r := range sortedMap {
		got[i] = r.RegionID
	}
	if !reflect.DeepEqual(got, want) {
		t.Errorf("got %v; want %v", got, want)
	}
}

func TestNoCaptivePortalWhenUDP(t *testing.T) {
	// Override noRedirectClient to handle the /generate_204 endpoint
	var generate204Called atomic.Bool
	tr := RoundTripFunc(func(req *http.Request) *http.Response {
		if !strings.HasSuffix(req.URL.String(), "/generate_204") {
			panic("bad URL: " + req.URL.String())
		}
		generate204Called.Store(true)
		return &http.Response{
			StatusCode: http.StatusNoContent,
			Header:     make(http.Header),
		}
	})

	tstest.Replace(t, &noRedirectClient.Transport, http.RoundTripper(tr))

	stunAddr, cleanup := stuntest.Serve(t)
	defer cleanup()

	c := &Client{
		Logf:              t.Logf,
		UDPBindAddr:       "127.0.0.1:0",
		testEnoughRegions: 1,

		// Set the delay long enough that we have time to cancel it
		// when our STUN probe succeeds.
		testCaptivePortalDelay: 10 * time.Second,
	}

	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
	defer cancel()

	r, err := c.GetReport(ctx, stuntest.DERPMapOf(stunAddr.String()))
	if err != nil {
		t.Fatal(err)
	}

	// Should not have called our captive portal function.
	if generate204Called.Load() {
		t.Errorf("captive portal check called; expected no call")
	}
	if r.CaptivePortal != "" {
		t.Errorf("got CaptivePortal=%q, want empty", r.CaptivePortal)
	}
}

type RoundTripFunc func(req *http.Request) *http.Response

func (f RoundTripFunc) RoundTrip(req *http.Request) (*http.Response, error) {
	return f(req), nil
}