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prober: add a DERP bandwidth probe

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Updates tailscale/corp#17912

Signed-off-by: Anton Tolchanov <anton@tailscale.com>
This commit is contained in:
Anton Tolchanov 2024-02-28 20:27:44 +00:00 committed by Anton Tolchanov
parent 5018683d58
commit f12d2557f9
3 changed files with 392 additions and 104 deletions
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26
cmd/derpprobe/derpprobe.go
View File

@ -19,18 +19,31 @@
)
var (
derpMapURL = flag.String("derp-map", "https://login.tailscale.com/derpmap/default", "URL to DERP map (https:// or file://)")
listen = flag.String("listen", ":8030", "HTTP listen address")
probeOnce = flag.Bool("once", false, "probe once and print results, then exit; ignores the listen flag")
spread = flag.Bool("spread", true, "whether to spread probing over time")
interval = flag.Duration("interval", 15*time.Second, "probe interval")
derpMapURL = flag.String("derp-map", "https://login.tailscale.com/derpmap/default", "URL to DERP map (https:// or file://)")
listen = flag.String("listen", ":8030", "HTTP listen address")
probeOnce = flag.Bool("once", false, "probe once and print results, then exit; ignores the listen flag")
spread = flag.Bool("spread", true, "whether to spread probing over time")
interval = flag.Duration("interval", 15*time.Second, "probe interval")
meshInterval = flag.Duration("mesh-interval", 15*time.Second, "mesh probe interval")
stunInterval = flag.Duration("stun-interval", 15*time.Second, "STUN probe interval")
tlsInterval = flag.Duration("tls-interval", 15*time.Second, "TLS probe interval")
bwInterval = flag.Duration("bw-interval", 0, "bandwidth probe interval (0 = no bandwidth probing)")
bwSize = flag.Int64("bw-probe-size-bytes", 1_000_000, "bandwidth probe size")
)
func main() {
flag.Parse()
p := prober.New().WithSpread(*spread).WithOnce(*probeOnce).WithMetricNamespace("derpprobe")
dp, err := prober.DERP(p, *derpMapURL, *interval, *interval, *interval)
opts := []prober.DERPOpt{
prober.WithMeshProbing(*meshInterval),
prober.WithSTUNProbing(*stunInterval),
prober.WithTLSProbing(*tlsInterval),
}
if *bwInterval > 0 {
opts = append(opts, prober.WithBandwidthProbing(*bwInterval, *bwSize))
}
dp, err := prober.DERP(p, *derpMapURL, opts...)
if err != nil {
log.Fatal(err)
}
@ -53,6 +66,7 @@ func main() {
mux := http.NewServeMux()
tsweb.Debugger(mux)
mux.HandleFunc("/", http.HandlerFunc(serveFunc(p)))
log.Printf("Listening on %s", *listen)
log.Fatal(http.ListenAndServe(*listen, mux))
}

348
prober/derp.go
View File

@ -5,12 +5,14 @@
import (
"bytes"
"cmp"
"context"
crand "crypto/rand"
"encoding/json"
"errors"
"fmt"
"log"
"maps"
"net"
"net/http"
"strconv"
@ -21,6 +23,7 @@
"tailscale.com/derp"
"tailscale.com/derp/derphttp"
"tailscale.com/net/stun"
"tailscale.com/syncs"
"tailscale.com/tailcfg"
"tailscale.com/types/key"
"tailscale.com/types/logger"
@ -35,10 +38,15 @@ type derpProber struct {
meshInterval time.Duration
tlsInterval time.Duration
// Optional bandwidth probing.
bwInterval time.Duration
bwProbeSize int64
// Probe functions that can be overridden for testing.
tlsProbeFn func(string) ProbeFunc
udpProbeFn func(string, int) ProbeFunc
meshProbeFn func(string, string) ProbeFunc
bwProbeFn func(string, string, int64) ProbeFunc
sync.Mutex
lastDERPMap *tailcfg.DERPMap
@ -47,20 +55,57 @@ type derpProber struct {
probes map[string]*Probe
}
type DERPOpt func(*derpProber)
// WithBandwidthProbing enables bandwidth probing. When enabled, a payload of
// `size` bytes will be regularly transferred through each DERP server, and each
// pair of DERP servers in every region.
func WithBandwidthProbing(interval time.Duration, size int64) DERPOpt {
return func(d *derpProber) {
d.bwInterval = interval
d.bwProbeSize = size
}
}
// WithMeshProbing enables mesh probing. When enabled, a small message will be
// transferred through each DERP server and each pair of DERP servers.
func WithMeshProbing(interval time.Duration) DERPOpt {
return func(d *derpProber) {
d.meshInterval = interval
}
}
// WithSTUNProbing enables STUN/UDP probing, with a STUN request being sent
// to each DERP server every `interval`.
func WithSTUNProbing(interval time.Duration) DERPOpt {
return func(d *derpProber) {
d.udpInterval = interval
}
}
// WithTLSProbing enables TLS probing that will check TLS certificate on port
// 443 of each DERP server every `interval`.
func WithTLSProbing(interval time.Duration) DERPOpt {
return func(d *derpProber) {
d.tlsInterval = interval
}
}
// DERP creates a new derpProber.
func DERP(p *Prober, derpMapURL string, udpInterval, meshInterval, tlsInterval time.Duration) (*derpProber, error) {
func DERP(p *Prober, derpMapURL string, opts ...DERPOpt) (*derpProber, error) {
d := &derpProber{
p: p,
derpMapURL: derpMapURL,
udpInterval: udpInterval,
meshInterval: meshInterval,
tlsInterval: tlsInterval,
tlsProbeFn: TLS,
nodes: make(map[string]*tailcfg.DERPNode),
probes: make(map[string]*Probe),
p: p,
derpMapURL: derpMapURL,
tlsProbeFn: TLS,
nodes: make(map[string]*tailcfg.DERPNode),
probes: make(map[string]*Probe),
}
for _, o := range opts {
o(d)
}
d.udpProbeFn = d.ProbeUDP
d.meshProbeFn = d.probeMesh
d.bwProbeFn = d.probeBandwidth
return d, nil
}
@ -84,42 +129,59 @@ func (d *derpProber) ProbeMap(ctx context.Context) error {
"hostname": server.HostName,
}
n := fmt.Sprintf("derp/%s/%s/tls", region.RegionCode, server.Name)
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP TLS probe for %s (%s)", server.Name, region.RegionName)
derpPort := 443
if server.DERPPort != 0 {
derpPort = server.DERPPort
}
d.probes[n] = d.p.Run(n, d.tlsInterval, labels, d.tlsProbeFn(fmt.Sprintf("%s:%d", server.HostName, derpPort)))
}
for idx, ipStr := range []string{server.IPv6, server.IPv4} {
n = fmt.Sprintf("derp/%s/%s/udp", region.RegionCode, server.Name)
if idx == 0 {
n = n + "6"
}
if ipStr == "" || server.STUNPort == -1 {
continue
}
if d.tlsInterval > 0 {
n := fmt.Sprintf("derp/%s/%s/tls", region.RegionCode, server.Name)
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP UDP probe for %s (%s)", server.Name, n)
d.probes[n] = d.p.Run(n, d.udpInterval, labels, d.udpProbeFn(ipStr, server.STUNPort))
log.Printf("adding DERP TLS probe for %s (%s) every %v", server.Name, region.RegionName, d.tlsInterval)
derpPort := cmp.Or(server.DERPPort, 443)
d.probes[n] = d.p.Run(n, d.tlsInterval, labels, d.tlsProbeFn(fmt.Sprintf("%s:%d", server.HostName, derpPort)))
}
}
if d.udpInterval > 0 {
for idx, ipStr := range []string{server.IPv6, server.IPv4} {
n := fmt.Sprintf("derp/%s/%s/udp", region.RegionCode, server.Name)
if idx == 0 {
n += "6"
}
if ipStr == "" || server.STUNPort == -1 {
continue
}
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP UDP probe for %s (%s) every %v", server.Name, n, d.udpInterval)
d.probes[n] = d.p.Run(n, d.udpInterval, labels, d.udpProbeFn(ipStr, server.STUNPort))
}
}
}
for _, to := range region.Nodes {
n = fmt.Sprintf("derp/%s/%s/%s/mesh", region.RegionCode, server.Name, to.Name)
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP mesh probe for %s->%s (%s)", server.Name, to.Name, region.RegionName)
d.probes[n] = d.p.Run(n, d.meshInterval, labels, d.meshProbeFn(server.HostName, to.HostName))
if d.meshInterval > 0 {
n := fmt.Sprintf("derp/%s/%s/%s/mesh", region.RegionCode, server.Name, to.Name)
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP mesh probe for %s->%s (%s) every %v", server.Name, to.Name, region.RegionName, d.meshInterval)
d.probes[n] = d.p.Run(n, d.meshInterval, labels, d.meshProbeFn(server.Name, to.Name))
}
}
if d.bwInterval > 0 && d.bwProbeSize > 0 {
bwLabels := maps.Clone(labels)
bwLabels["probe_size_bytes"] = fmt.Sprintf("%d", d.bwProbeSize)
if server.Name == to.Name {
bwLabels["derp_path"] = "single"
} else {
bwLabels["derp_path"] = "mesh"
}
n := fmt.Sprintf("derp/%s/%s/%s/bw", region.RegionCode, server.Name, to.Name)
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP bandwidth probe for %s->%s (%s) %v bytes every %v", server.Name, to.Name, region.RegionName, d.bwProbeSize, d.bwInterval)
d.probes[n] = d.p.Run(n, d.bwInterval, bwLabels, d.bwProbeFn(server.Name, to.Name, d.bwProbeSize))
}
}
}
}
@ -136,26 +198,52 @@ func (d *derpProber) ProbeMap(ctx context.Context) error {
return nil
}
// probeMesh returs a probe func that sends a test packet through a pair of DERP
// servers (or just one server, if 'from' and 'to' are the same). 'from' and 'to'
// are expected to be names (DERPNode.Name) of two DERP servers in the same region.
func (d *derpProber) probeMesh(from, to string) ProbeFunc {
return func(ctx context.Context) error {
d.Lock()
dm := d.lastDERPMap
fromN, ok := d.nodes[from]
if !ok {
d.Unlock()
return fmt.Errorf("could not find derp node %s", from)
fromN, toN, err := d.getNodePair(from, to)
if err != nil {
return err
}
toN, ok := d.nodes[to]
if !ok {
d.Unlock()
return fmt.Errorf("could not find derp node %s", to)
}
d.Unlock()
dm := d.lastDERPMap
return derpProbeNodePair(ctx, dm, fromN, toN)
}
}
// probeBandwidth returs a probe func that sends a payload of a given size
// through a pair of DERP servers (or just one server, if 'from' and 'to' are
// the same). 'from' and 'to' are expected to be names (DERPNode.Name) of two
// DERP servers in the same region.
func (d *derpProber) probeBandwidth(from, to string, size int64) ProbeFunc {
return func(ctx context.Context) error {
fromN, toN, err := d.getNodePair(from, to)
if err != nil {
return err
}
return derpProbeBandwidth(ctx, d.lastDERPMap, fromN, toN, size)
}
}
// getNodePair returns DERPNode objects for two DERP servers based on their
// short names.
func (d *derpProber) getNodePair(n1, n2 string) (ret1, ret2 *tailcfg.DERPNode, _ error) {
d.Lock()
defer d.Unlock()
ret1, ok := d.nodes[n1]
if !ok {
return nil, nil, fmt.Errorf("could not find derp node %s", n1)
}
ret2, ok = d.nodes[n2]
if !ok {
return nil, nil, fmt.Errorf("could not find derp node %s", n2)
}
return ret1, ret2, nil
}
// updateMap refreshes the locally-cached DERP map.
func (d *derpProber) updateMap(ctx context.Context) error {
req, err := http.NewRequestWithContext(ctx, "GET", d.derpMapURL, nil)
if err != nil {
@ -189,13 +277,13 @@ func (d *derpProber) updateMap(ctx context.Context) error {
d.nodes = make(map[string]*tailcfg.DERPNode)
for _, reg := range d.lastDERPMap.Regions {
for _, n := range reg.Nodes {
if existing, ok := d.nodes[n.HostName]; ok {
if existing, ok := d.nodes[n.Name]; ok {
return fmt.Errorf("derpmap has duplicate nodes: %+v and %+v", existing, n)
}
// Allow the prober to monitor nodes marked as
// STUN only in the default map
n.STUNOnly = false
d.nodes[n.HostName] = n
d.nodes[n.Name] = n
}
}
return nil
@ -257,13 +345,17 @@ func derpProbeUDP(ctx context.Context, ipStr string, port int) error {
return nil
}
func derpProbeNodePair(ctx context.Context, dm *tailcfg.DERPMap, from, to *tailcfg.DERPNode) (err error) {
fromc, err := newConn(ctx, dm, from)
// derpProbeBandwidth sends a payload of a given size between two local
// DERP clients connected to two DERP servers.
func derpProbeBandwidth(ctx context.Context, dm *tailcfg.DERPMap, from, to *tailcfg.DERPNode, size int64) (err error) {
// This probe uses clients with isProber=false to avoid spamming the derper logs with every packet
// sent by the bandwidth probe.
fromc, err := newConn(ctx, dm, from, false)
if err != nil {
return err
}
defer fromc.Close()
toc, err := newConn(ctx, dm, to)
toc, err := newConn(ctx, dm, to, false)
if err != nil {
return err
}
@ -276,71 +368,147 @@ func derpProbeNodePair(ctx context.Context, dm *tailcfg.DERPMap, from, to *tailc
time.Sleep(100 * time.Millisecond) // pretty arbitrary
}
if err := runDerpProbeNodePair(ctx, from, to, fromc, toc); err != nil {
if err := runDerpProbeNodePair(ctx, from, to, fromc, toc, size); err != nil {
// Record pubkeys on failed probes to aid investigation.
return fmt.Errorf("%s -> %s: %w",
fromc.SelfPublicKey().ShortString(),
toc.SelfPublicKey().ShortString(), err)
}
return err
return nil
}
func runDerpProbeNodePair(ctx context.Context, from, to *tailcfg.DERPNode, fromc, toc *derphttp.Client) error {
// Make a random packet
pkt := make([]byte, 8)
crand.Read(pkt)
// derpProbeNodePair sends a small packet between two local DERP clients
// connected to two DERP servers.
func derpProbeNodePair(ctx context.Context, dm *tailcfg.DERPMap, from, to *tailcfg.DERPNode) (err error) {
fromc, err := newConn(ctx, dm, from, true)
if err != nil {
return err
}
defer fromc.Close()
toc, err := newConn(ctx, dm, to, true)
if err != nil {
return err
}
defer toc.Close()
// Send the random packet.
sendc := make(chan error, 1)
go func() {
sendc <- fromc.Send(toc.SelfPublicKey(), pkt)
}()
select {
case <-ctx.Done():
return fmt.Errorf("timeout sending via %q: %w", from.Name, ctx.Err())
case err := <-sendc:
if err != nil {
return fmt.Errorf("error sending via %q: %w", from.Name, err)
}
// Wait a bit for from's node to hear about to existing on the
// other node in the region, in the case where the two nodes
// are different.
if from.Name != to.Name {
time.Sleep(100 * time.Millisecond) // pretty arbitrary
}
// Receive the random packet.
recvc := make(chan any, 1) // either derp.ReceivedPacket or error
const meshProbePacketSize = 8
if err := runDerpProbeNodePair(ctx, from, to, fromc, toc, meshProbePacketSize); err != nil {
// Record pubkeys on failed probes to aid investigation.
return fmt.Errorf("%s -> %s: %w",
fromc.SelfPublicKey().ShortString(),
toc.SelfPublicKey().ShortString(), err)
}
return nil
}
// probePackets stores a pregenerated slice of probe packets keyed by their total size.
var probePackets syncs.Map[int64, [][]byte]
// packetsForSize returns a slice of packet payloads with a given total size.
func packetsForSize(size int64) [][]byte {
// For a small payload, create a unique random packet.
if size <= derp.MaxPacketSize {
pkt := make([]byte, size)
crand.Read(pkt)
return [][]byte{pkt}
}
// For a large payload, create a bunch of packets once and re-use them
// across probes.
pkts, _ := probePackets.LoadOrInit(size, func() [][]byte {
const packetSize = derp.MaxPacketSize
var pkts [][]byte
for remaining := size; remaining > 0; remaining -= packetSize {
pkt := make([]byte, min(remaining, packetSize))
crand.Read(pkt)
pkts = append(pkts, pkt)
}
return pkts
})
return pkts
}
// runDerpProbeNodePair takes two DERP clients (fromc and toc) connected to two
// DERP servers (from and to) and sends a test payload of a given size from one
// to another.
func runDerpProbeNodePair(ctx context.Context, from, to *tailcfg.DERPNode, fromc, toc *derphttp.Client, size int64) error {
// To avoid derper dropping enqueued packets, limit the number of packets in flight.
// The value here is slightly smaller than perClientSendQueueDepth in derp_server.go
inFlight := syncs.NewSemaphore(30)
pkts := packetsForSize(size)
// Send the packets.
sendc := make(chan error, 1)
go func() {
for idx, pkt := range pkts {
inFlight.AcquireContext(ctx)
if err := fromc.Send(toc.SelfPublicKey(), pkt); err != nil {
sendc <- fmt.Errorf("sending packet %d: %w", idx, err)
return
}
}
}()
// Receive the packets.
recvc := make(chan error, 1)
go func() {
defer close(recvc) // to break out of 'select' below.
idx := 0
for {
m, err := toc.Recv()
if err != nil {
recvc <- err
recvc <- fmt.Errorf("after %d data packets: %w", idx, err)
return
}
switch v := m.(type) {
case derp.ReceivedPacket:
recvc <- v
inFlight.Release()
if v.Source != fromc.SelfPublicKey() {
recvc <- fmt.Errorf("got data packet %d from unexpected source, %v", idx, v.Source)
return
}
if got, want := v.Data, pkts[idx]; !bytes.Equal(got, want) {
recvc <- fmt.Errorf("unexpected data packet %d (out of %d)", idx, len(pkts))
return
}
idx += 1
if idx == len(pkts) {
return
}
case derp.KeepAliveMessage:
// Silently ignore.
default:
log.Printf("%v: ignoring Recv frame type %T", to.Name, v)
// Loop.
}
}
}()
select {
case <-ctx.Done():
return fmt.Errorf("timeout receiving from %q: %w", to.Name, ctx.Err())
case v := <-recvc:
if err, ok := v.(error); ok {
return fmt.Errorf("timeout: %w", ctx.Err())
case err := <-sendc:
if err != nil {
return fmt.Errorf("error sending via %q: %w", from.Name, err)
}
case err := <-recvc:
if err != nil {
return fmt.Errorf("error receiving from %q: %w", to.Name, err)
}
p := v.(derp.ReceivedPacket)
if p.Source != fromc.SelfPublicKey() {
return fmt.Errorf("got data packet from unexpected source, %v", p.Source)
}
if !bytes.Equal(p.Data, pkt) {
return fmt.Errorf("unexpected data packet %q", p.Data)
}
}
return nil
}
func newConn(ctx context.Context, dm *tailcfg.DERPMap, n *tailcfg.DERPNode) (*derphttp.Client, error) {
func newConn(ctx context.Context, dm *tailcfg.DERPMap, n *tailcfg.DERPNode, isProber bool) (*derphttp.Client, error) {
// To avoid spamming the log with regular connection messages.
l := logger.Filtered(log.Printf, func(s string) bool {
return !strings.Contains(s, "derphttp.Client.Connect: connecting to")
@ -355,7 +523,7 @@ func newConn(ctx context.Context, dm *tailcfg.DERPMap, n *tailcfg.DERPNode) (*de
Nodes: []*tailcfg.DERPNode{n},
}
})
dc.IsProber = true
dc.IsProber = isProber
err := dc.Connect(ctx)
if err != nil {
return nil, err

122
prober/derp_test.go
View File

@ -5,12 +5,19 @@
import (
"context"
"crypto/sha256"
"crypto/tls"
"encoding/json"
"net"
"net/http"
"net/http/httptest"
"testing"
"time"
"tailscale.com/derp"
"tailscale.com/derp/derphttp"
"tailscale.com/tailcfg"
"tailscale.com/types/key"
)
func TestDerpProber(t *testing.T) {
@ -50,18 +57,21 @@ func TestDerpProber(t *testing.T) {
clk := newFakeTime()
p := newForTest(clk.Now, clk.NewTicker)
dp := &derpProber{
p: p,
derpMapURL: srv.URL,
tlsProbeFn: func(_ string) ProbeFunc { return func(context.Context) error { return nil } },
udpProbeFn: func(_ string, _ int) ProbeFunc { return func(context.Context) error { return nil } },
meshProbeFn: func(_, _ string) ProbeFunc { return func(context.Context) error { return nil } },
nodes: make(map[string]*tailcfg.DERPNode),
probes: make(map[string]*Probe),
p: p,
derpMapURL: srv.URL,
tlsInterval: time.Second,
tlsProbeFn: func(_ string) ProbeFunc { return func(context.Context) error { return nil } },
udpInterval: time.Second,
udpProbeFn: func(_ string, _ int) ProbeFunc { return func(context.Context) error { return nil } },
meshInterval: time.Second,
meshProbeFn: func(_, _ string) ProbeFunc { return func(context.Context) error { return nil } },
nodes: make(map[string]*tailcfg.DERPNode),
probes: make(map[string]*Probe),
}
if err := dp.ProbeMap(context.Background()); err != nil {
t.Errorf("unexpected ProbeMap() error: %s", err)
}
if len(dp.nodes) != 2 || dp.nodes["derpn1.tailscale.test"] == nil || dp.nodes["derpn2.tailscale.test"] == nil {
if len(dp.nodes) != 2 || dp.nodes["n1"] == nil || dp.nodes["n2"] == nil {
t.Errorf("unexpected nodes: %+v", dp.nodes)
}
// Probes expected for two nodes:
@ -103,3 +113,99 @@ func TestDerpProber(t *testing.T) {
t.Errorf("unexpected probes: %+v", dp.probes)
}
}
func TestRunDerpProbeNodePair(t *testing.T) {
// os.Setenv("DERP_DEBUG_LOGS", "true")
serverPrivateKey := key.NewNode()
s := derp.NewServer(serverPrivateKey, t.Logf)
defer s.Close()
httpsrv := &http.Server{
TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler)),
Handler: derphttp.Handler(s),
}
ln, err := net.Listen("tcp4", "localhost:0")
if err != nil {
t.Fatal(err)
}
serverURL := "http://" + ln.Addr().String()
t.Logf("server URL: %s", serverURL)
go func() {
if err := httpsrv.Serve(ln); err != nil {
if err == http.ErrServerClosed {
return
}
panic(err)
}
}()
newClient := func() *derphttp.Client {
c, err := derphttp.NewClient(key.NewNode(), serverURL, t.Logf)
if err != nil {
t.Fatalf("NewClient: %v", err)
}
m, err := c.Recv()
if err != nil {
t.Fatalf("Recv: %v", err)
}
switch m.(type) {
case derp.ServerInfoMessage:
default:
t.Fatalf("unexpected first message type %T", m)
}
return c
}
c1 := newClient()
defer c1.Close()
c2 := newClient()
defer c2.Close()
ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
defer cancel()
err = runDerpProbeNodePair(ctx, &tailcfg.DERPNode{Name: "c1"}, &tailcfg.DERPNode{Name: "c2"}, c1, c2, 100_000_000)
if err != nil {
t.Error(err)
}
}
func Test_packetsForSize(t *testing.T) {
tests := []struct {
name string
size int
wantPackets int
wantUnique bool
}{
{"small_unqiue", 8, 1, true},
{"8k_unique", 8192, 1, true},
{"full_size_packet", derp.MaxPacketSize, 1, true},
{"larger_than_one", derp.MaxPacketSize + 1, 2, false},
{"large", 500000, 8, false},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
hashes := make(map[string]int)
for i := 0; i < 5; i++ {
pkts := packetsForSize(int64(tt.size))
if len(pkts) != tt.wantPackets {
t.Errorf("packetsForSize(%d) got %d packets, want %d", tt.size, len(pkts), tt.wantPackets)
}
var total int
hash := sha256.New()
for _, p := range pkts {
hash.Write(p)
total += len(p)
}
hashes[string(hash.Sum(nil))]++
if total != tt.size {
t.Errorf("packetsForSize(%d) returned %d bytes total", tt.size, total)
}
}
unique := len(hashes) > 1
if unique != tt.wantUnique {
t.Errorf("packetsForSize(%d) is unique=%v (returned %d different answers); want unique=%v", tt.size, unique, len(hashes), unique)
}
})
}
}