ipn,log: add logger for sockstat deltas

Signed-off-by: Will Norris <will@tailscale.com>
Co-authored-by: Melanie Warrick <warrick@tailscale.com>

log/sockstatlog/logger.go

@@ -0,0 +1,124 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package sockstatlog provides a logger for capturing and storing network socket stats.
+package sockstatlog
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"time"
+
+	"tailscale.com/logtail/filch"
+	"tailscale.com/net/sockstats"
+	"tailscale.com/util/mak"
+)
+
+// pollPeriod specifies how often to poll for socket stats.
+const pollPeriod = time.Second / 10
+
+// Logger logs statistics about network sockets.
+type Logger struct {
+	ticker    time.Ticker
+	logbuffer *filch.Filch
+}
+
+// deltaStat represents the bytes transferred during a time period.
+// The first element is transmitted bytes, the second element is received bytes.
+type deltaStat [2]uint64
+
+// event represents the socket stats on a specific interface during a time period.
+type event struct {
+	// Time is when the event started as a Unix timestamp in milliseconds.
+	Time int64 `json:"t"`
+
+	// Duration is the duration of this event in milliseconds.
+	Duration int64 `json:"d"`
+
+	// IsCellularInterface is set to 1 if the traffic was sent over a cellular interface.
+	IsCellularInterface int `json:"c,omitempty"`
+
+	// Stats records the stats for each Label during the time period.
+	Stats map[sockstats.Label]deltaStat `json:"s"`
+}
+
+// NewLogger returns a new Logger that will store stats in logdir.
+// On platforms that do not support sockstat logging, a nil Logger will be returned.
+// The returned Logger is not yet running.
+func NewLogger(logdir string) (*Logger, error) {
+	if !sockstats.IsAvailable {
+		return nil, nil
+	}
+
+	if err := os.MkdirAll(logdir, 0755); err != nil && !os.IsExist(err) {
+		return nil, err
+	}
+	filchPrefix := filepath.Join(logdir, "sockstats")
+	filch, err := filch.New(filchPrefix, filch.Options{ReplaceStderr: false})
+	if err != nil {
+		return nil, err
+	}
+
+	return &Logger{
+		ticker:    *time.NewTicker(pollPeriod),
+		logbuffer: filch,
+	}, nil
+}
+
+func (l *Logger) Start() {
+	go l.poll()
+}
+
+// poll fetches the current socket stats at the configured time interval,
+// calculates the delta since the last poll, and logs any non-zero values.
+// This method does not return.
+func (l *Logger) poll() {
+	// last is the last set of socket stats we saw.
+	var lastStats *sockstats.SockStats
+	var lastTime time.Time
+
+	enc := json.NewEncoder(l.logbuffer)
+	for t := range l.ticker.C {
+		stats := sockstats.Get()
+		if lastStats != nil {
+			diffstats := delta(lastStats, stats)
+			if len(diffstats) > 0 {
+				e := event{
+					Time:     lastTime.UnixMilli(),
+					Duration: t.Sub(lastTime).Milliseconds(),
+					Stats:    diffstats,
+				}
+				if stats.CurrentInterfaceCellular {
+					e.IsCellularInterface = 1
+				}
+				enc.Encode(e)
+			}
+		}
+		lastTime = t
+		lastStats = stats
+	}
+}
+
+func (l *Logger) Shutdown() {
+	l.ticker.Stop()
+	l.logbuffer.Close()
+}
+
+// delta calculates the delta stats between two SockStats snapshots.
+// b is assumed to have occurred after a.
+// Zero values are omitted from the returned map, and an empty map is returned if no bytes were transferred.
+func delta(a, b *sockstats.SockStats) (stats map[sockstats.Label]deltaStat) {
+	if a == nil || b == nil {
+		return nil
+	}
+	for label, bs := range b.Stats {
+		as := a.Stats[label]
+		if as.TxBytes == bs.TxBytes && as.RxBytes == bs.RxBytes {
+			// fast path for unchanged stats
+			continue
+		}
+		mak.Set(&stats, label, deltaStat{bs.TxBytes - as.TxBytes, bs.RxBytes - as.RxBytes})
+	}
+	return stats
+}

log/sockstatlog/logger_test.go

@@ -0,0 +1,119 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package sockstatlog
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"tailscale.com/net/sockstats"
+)
+
+func TestDelta(t *testing.T) {
+	tests := []struct {
+		name      string
+		a, b      *sockstats.SockStats
+		wantStats map[sockstats.Label]deltaStat
+	}{
+		{
+			name:      "nil a stat",
+			a:         nil,
+			b:         &sockstats.SockStats{},
+			wantStats: nil,
+		},
+		{
+			name:      "nil b stat",
+			a:         &sockstats.SockStats{},
+			b:         nil,
+			wantStats: nil,
+		},
+		{
+			name: "no change",
+			a: &sockstats.SockStats{
+				Stats: map[sockstats.Label]sockstats.SockStat{
+					sockstats.LabelDERPHTTPClient: {
+						TxBytes: 10,
+						TxBytesByInterface: map[string]uint64{
+							"en0": 10,
+						},
+					},
+				},
+			},
+			b: &sockstats.SockStats{
+				Stats: map[sockstats.Label]sockstats.SockStat{
+					sockstats.LabelDERPHTTPClient: {
+						TxBytes: 10,
+						TxBytesByInterface: map[string]uint64{
+							"en0": 10,
+						},
+					},
+				},
+			},
+			wantStats: nil,
+		},
+		{
+			name: "tx after empty stat",
+			a:    &sockstats.SockStats{},
+			b: &sockstats.SockStats{
+				Stats: map[sockstats.Label]sockstats.SockStat{
+					sockstats.LabelDERPHTTPClient: {
+						TxBytes: 10,
+						TxBytesByInterface: map[string]uint64{
+							"en0": 10,
+						},
+					},
+				},
+				Interfaces: []string{"en0"},
+			},
+			wantStats: map[sockstats.Label]deltaStat{
+				sockstats.LabelDERPHTTPClient: {10, 0},
+			},
+		},
+		{
+			name: "rx after non-empty stat",
+			a: &sockstats.SockStats{
+				Stats: map[sockstats.Label]sockstats.SockStat{
+					sockstats.LabelDERPHTTPClient: {
+						TxBytes: 10,
+						RxBytes: 10,
+						TxBytesByInterface: map[string]uint64{
+							"en0": 10,
+						},
+						RxBytesByInterface: map[string]uint64{
+							"en0": 10,
+						},
+					},
+				},
+				Interfaces: []string{"en0"},
+			},
+			b: &sockstats.SockStats{
+				Stats: map[sockstats.Label]sockstats.SockStat{
+					sockstats.LabelDERPHTTPClient: {
+						TxBytes: 10,
+						RxBytes: 30,
+						TxBytesByInterface: map[string]uint64{
+							"en0": 10,
+						},
+						RxBytesByInterface: map[string]uint64{
+							"en0": 30,
+						},
+					},
+				},
+				Interfaces: []string{"en0"},
+			},
+			wantStats: map[sockstats.Label]deltaStat{
+				sockstats.LabelDERPHTTPClient: {0, 20},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotStats := delta(tt.a, tt.b)
+			if !cmp.Equal(gotStats, tt.wantStats) {
+				t.Errorf("gotStats = %v, want %v", gotStats, tt.wantStats)
+			}
+		})
+	}
+}