tailscale/log/sockstatlog/logger.go

// 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
}