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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
// Package filelogger provides localdisk log writing & rotation, primarily for Windows
// clients. (We get this for free on other platforms.)
package filelogger
import (
"bytes"
"fmt"
"log"
"os"
"path/filepath"
"runtime"
"strings"
"sync"
"time"
"tailscale.com/types/logger"
)
const (
maxSize = 100 << 20
maxFiles = 50
)
// New returns a logf wrapper that appends to local disk log
// files on Windows, rotating old log files as needed to stay under
// file count & byte limits.
func New(fileBasePrefix, logID string, logf logger.Logf) logger.Logf {
if runtime.GOOS != "windows" {
panic("not yet supported on any platform except Windows")
}
if logf == nil {
panic("nil logf")
}
dir := filepath.Join(os.Getenv("ProgramData"), "Tailscale", "Logs")
if err := os.MkdirAll(dir, 0700); err != nil {
log.Printf("failed to create local log directory; not writing logs to disk: %v", err)
return logf
}
logf("local disk logdir: %v", dir)
lfw := &logFileWriter{
fileBasePrefix: fileBasePrefix,
logID: logID,
dir: dir,
wrappedLogf: logf,
}
return lfw.Logf
}
// logFileWriter is the state for the log writer & rotator.
type logFileWriter struct {
dir string // e.g. `C:\Users\FooBarUser\AppData\Local\Tailscale\Logs`
logID string // hex logID
fileBasePrefix string // e.g. "tailscale-service" or "tailscale-gui"
wrappedLogf logger.Logf // underlying logger to send to
mu sync.Mutex // guards following
buf bytes.Buffer // scratch buffer to avoid allocs
fday civilDay // day that f was opened; zero means no file yet open
f *os.File // file currently opened for append
}
// civilDay is a year, month, and day in the local timezone.
// It's a comparable value type.
type civilDay struct {
year int
month time.Month
day int
}
func dayOf(t time.Time) civilDay {
return civilDay{t.Year(), t.Month(), t.Day()}
}
func (w *logFileWriter) Logf(format string, a ...any) {
w.mu.Lock()
defer w.mu.Unlock()
w.buf.Reset()
fmt.Fprintf(&w.buf, format, a...)
if w.buf.Len() == 0 {
return
}
out := w.buf.Bytes()
w.wrappedLogf("%s", out)
// Make sure there's a final newline before we write to the log file.
if out[len(out)-1] != '\n' {
w.buf.WriteByte('\n')
out = w.buf.Bytes()
}
w.appendToFileLocked(out)
}
// out should end in a newline.
// w.mu must be held.
func (w *logFileWriter) appendToFileLocked(out []byte) {
now := time.Now()
day := dayOf(now)
if w.fday != day {
w.startNewFileLocked()
}
out = removeDatePrefix(out)
if w.f != nil {
// RFC3339Nano but with a fixed number (3) of nanosecond digits:
const formatPre = "2006-01-02T15:04:05"
const formatPost = "Z07:00"
fmt.Fprintf(w.f, "%s.%03d%s: %s",
now.Format(formatPre),
now.Nanosecond()/int(time.Millisecond/time.Nanosecond),
now.Format(formatPost),
out)
}
}
func isNum(b byte) bool { return '0' <= b && b <= '9' }
// removeDatePrefix returns a subslice of v with the log package's
// standard datetime prefix format removed, if present.
func removeDatePrefix(v []byte) []byte {
const format = "2009/01/23 01:23:23 "
if len(v) < len(format) {
return v
}
for i, b := range v[:len(format)] {
fb := format[i]
if isNum(fb) {
if !isNum(b) {
return v
}
continue
}
if b != fb {
return v
}
}
return v[len(format):]
}
// startNewFileLocked opens a new log file for writing
// and also cleans up any old files.
//
// w.mu must be held.
func (w *logFileWriter) startNewFileLocked() {
var oldName string
if w.f != nil {
oldName = filepath.Base(w.f.Name())
w.f.Close()
w.f = nil
w.fday = civilDay{}
}
w.cleanLocked()
now := time.Now()
day := dayOf(now)
name := filepath.Join(w.dir, fmt.Sprintf("%s-%04d%02d%02dT%02d%02d%02d-%d.txt",
w.fileBasePrefix,
day.year,
day.month,
day.day,
now.Hour(),
now.Minute(),
now.Second(),
now.Unix()))
var err error
w.f, err = os.Create(name)
if err != nil {
w.wrappedLogf("failed to create log file: %v", err)
return
}
if oldName != "" {
fmt.Fprintf(w.f, "(logID %q; continued from log file %s)\n", w.logID, oldName)
} else {
fmt.Fprintf(w.f, "(logID %q)\n", w.logID)
}
w.fday = day
}
// cleanLocked cleans up old log files.
//
// w.mu must be held.
func (w *logFileWriter) cleanLocked() {
entries, _ := os.ReadDir(w.dir)
prefix := w.fileBasePrefix + "-"
fileSize := map[string]int64{}
var files []string
var sumSize int64
for _, entry := range entries {
fi, err := entry.Info()
if err != nil {
w.wrappedLogf("error getting log file info: %v", err)
continue
}
baseName := filepath.Base(fi.Name())
if !strings.HasPrefix(baseName, prefix) {
continue
}
size := fi.Size()
fileSize[baseName] = size
sumSize += size
files = append(files, baseName)
}
if sumSize > maxSize {
w.wrappedLogf("cleaning log files; sum byte count %d > %d", sumSize, maxSize)
}
if len(files) > maxFiles {
w.wrappedLogf("cleaning log files; number of files %d > %d", len(files), maxFiles)
}
for (sumSize > maxSize || len(files) > maxFiles) && len(files) > 0 {
target := files[0]
files = files[1:]
targetSize := fileSize[target]
targetFull := filepath.Join(w.dir, target)
err := os.Remove(targetFull)
if err != nil {
w.wrappedLogf("error cleaning log file: %v", err)
} else {
sumSize -= targetSize
w.wrappedLogf("cleaned log file %s (size %d); new bytes=%v, files=%v", targetFull, targetSize, sumSize, len(files))
}
}
}
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