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本文主要研究一下golang的lumberjack
Logger
lumberjack.v2@v2.0.0/lumberjack.go
type Logger struct {
// Filename is the file to write logs to. Backup log files will be retained
// in the same directory. It uses <processname>-lumberjack.log in
// os.TempDir() if empty.
Filename string `json:"filename" yaml:"filename"`
// MaxSize is the maximum size in megabytes of the log file before it gets
// rotated. It defaults to 100 megabytes.
MaxSize int `json:"maxsize" yaml:"maxsize"`
// MaxAge is the maximum number of days to retain old log files based on the
// timestamp encoded in their filename. Note that a day is defined as 24
// hours and may not exactly correspond to calendar days due to daylight
// savings, leap seconds, etc. The default is not to remove old log files
// based on age.
MaxAge int `json:"maxage" yaml:"maxage"`
// MaxBackups is the maximum number of old log files to retain. The default
// is to retain all old log files (though MaxAge may still cause them to get
// deleted.)
MaxBackups int `json:"maxbackups" yaml:"maxbackups"`
// LocalTime determines if the time used for formatting the timestamps in
// backup files is the computer's local time. The default is to use UTC
// time.
LocalTime bool `json:"localtime" yaml:"localtime"`
// Compress determines if the rotated log files should be compressed
// using gzip. The default is not to perform compression.
Compress bool `json:"compress" yaml:"compress"`
size int64
file *os.File
mu sync.Mutex
millCh chan bool
startMill sync.Once
}Logger定义了Filename、MaxSize(单个文件大小最大值，单位M)、MaxAge(单位天)、MaxBackups、LocalTime、Compress属性，另外还有私有属性size、file、sync.Mutex、millCh、startMill
Write
lumberjack.v2@v2.0.0/lumberjack.go
const (
backupTimeFormat = "2006-01-02T15-04-05.000"
compressSuffix = ".gz"
defaultMaxSize = 100
)
func (l *Logger) Write(p []byte) (n int, err error) {
l.mu.Lock()
defer l.mu.Unlock()
writeLen := int64(len(p))
if writeLen > l.max() {
return 0, fmt.Errorf(
"write length %d exceeds maximum file size %d", writeLen, l.max(),
)
}
if l.file == nil {
if err = l.openExistingOrNew(len(p)); err != nil {
return 0, err
}
}
if l.size+writeLen > l.max() {
if err := l.rotate(); err != nil {
return 0, err
}
}
n, err = l.file.Write(p)
l.size += int64(n)
return n, err
}
func (l *Logger) max() int64 {
if l.MaxSize == 0 {
return int64(defaultMaxSize * megabyte)
}
return int64(l.MaxSize) * int64(megabyte)
}Write方法先判断要写入的长度是否超过l.max()，之后判断file是否为nil，如果为nil则执行l.openExistingOrNew；之后判断l.size+writeLen是否大于l.max()，如果大于则执行l.rotate()，否则执行l.file.Write(p)，然后更新l.size
openExistingOrNew
lumberjack.v2@v2.0.0/lumberjack.go
func (l *Logger) openExistingOrNew(writeLen int) error {
l.mill()
filename := l.filename()
info, err := os_Stat(filename)
if os.IsNotExist(err) {
return l.openNew()
}
if err != nil {
return fmt.Errorf("error getting log file info: %s", err)
}
if info.Size()+int64(writeLen) >= l.max() {
return l.rotate()
}
file, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY, 0644)
if err != nil {
// if we fail to open the old log file for some reason, just ignore
// it and open a new log file.
return l.openNew()
}
l.file = file
l.size = info.Size()
return nil
}openExistingOrNew先执行mill方法，之后判断file是否存在，不存在则执行l.openNew()；若文件大小与要写入的大小之和大于等于l.max()，执行l.rotate()；否则执行os.OpenFile
millRunOnce
lumberjack.v2@v2.0.0/lumberjack.go
func (l *Logger) mill() {
l.startMill.Do(func() {
l.millCh = make(chan bool, 1)
go l.millRun()
})
select {
case l.millCh <- true:
default:
}
}
func (l *Logger) millRun() {
for _ = range l.millCh {
// what am I going to do, log this?
_ = l.millRunOnce()
}
}
func (l *Logger) millRunOnce() error {
if l.MaxBackups == 0 && l.MaxAge == 0 && !l.Compress {
return nil
}
files, err := l.oldLogFiles()
if err != nil {
return err
}
var compress, remove []logInfo
if l.MaxBackups > 0 && l.MaxBackups < len(files) {
preserved := make(map[string]bool)
var remaining []logInfo
for _, f := range files {
// Only count the uncompressed log file or the
// compressed log file, not both.
fn := f.Name()
if strings.HasSuffix(fn, compressSuffix) {
fn = fn[:len(fn)-len(compressSuffix)]
}
preserved[fn] = true
if len(preserved) > l.MaxBackups {
remove = append(remove, f)
} else {
remaining = append(remaining, f)
}
}
files = remaining
}
if l.MaxAge > 0 {
diff := time.Duration(int64(24*time.Hour) * int64(l.MaxAge))
cutoff := currentTime().Add(-1 * diff)
var remaining []logInfo
for _, f := range files {
if f.timestamp.Before(cutoff) {
remove = append(remove, f)
} else {
remaining = append(remaining, f)
}
}
files = remaining
}
if l.Compress {
for _, f := range files {
if !strings.HasSuffix(f.Name(), compressSuffix) {
compress = append(compress, f)
}
}
}
for _, f := range remove {
errRemove := os.Remove(filepath.Join(l.dir(), f.Name()))
if err == nil && errRemove != nil {
err = errRemove
}
}
for _, f := range compress {
fn := filepath.Join(l.dir(), f.Name())
errCompress := compressLogFile(fn, fn+compressSuffix)
if err == nil && errCompress != nil {
err = errCompress
}
}
return err
}millRunOnce通过l.oldLogFiles()获取files，然后对于配置了MaxBackups且该值小于旧文件个数时计算要remove的文件，更新files；若l.MaxAge大于0则再根据日期计算要remove的文件，更新files；若l.Compress为true则计算需要compress的文件；之后遍历remove移除文件，遍历compress执行压缩
oldLogFiles
lumberjack.v2@v2.0.0/lumberjack.go
func (l *Logger) oldLogFiles() ([]logInfo, error) {
files, err := ioutil.ReadDir(l.dir())
if err != nil {
return nil, fmt.Errorf("can't read log file directory: %s", err)
}
logFiles := []logInfo{}
prefix, ext := l.prefixAndExt()
for _, f := range files {
if f.IsDir() {
continue
}
if t, err := l.timeFromName(f.Name(), prefix, ext); err == nil {
logFiles = append(logFiles, logInfo{t, f})
continue
}
if t, err := l.timeFromName(f.Name(), prefix, ext+compressSuffix); err == nil {
logFiles = append(logFiles, logInfo{t, f})
continue
}
// error parsing means that the suffix at the end was not generated
// by lumberjack, and therefore it's not a backup file.
}
sort.Sort(byFormatTime(logFiles))
return logFiles, nil
}
func (l *Logger) prefixAndExt() (prefix, ext string) {
filename := filepath.Base(l.filename())
ext = filepath.Ext(filename)
prefix = filename[:len(filename)-len(ext)] + "-"
return prefix, ext
}
func (l *Logger) timeFromName(filename, prefix, ext string) (time.Time, error) {
if !strings.HasPrefix(filename, prefix) {
return time.Time{}, errors.New("mismatched prefix")
}
if !strings.HasSuffix(filename, ext) {
return time.Time{}, errors.New("mismatched extension")
}
ts := filename[len(prefix) : len(filename)-len(ext)]
return time.Parse(backupTimeFormat, ts)
}
type byFormatTime []logInfo
func (b byFormatTime) Less(i, j int) bool {
return b[i].timestamp.After(b[j].timestamp)
}
func (b byFormatTime) Swap(i, j int) {
b[i], b[j] = b[j], b[i]
}
func (b byFormatTime) Len() int {
return len(b)
}oldLogFiles读取当前目录的文件，然后通过byFormatTime排序，即按时间降序排列
rotate
lumberjack.v2@v2.0.0/lumberjack.go
func (l *Logger) rotate() error {
if err := l.close(); err != nil {
return err
}
if err := l.openNew(); err != nil {
return err
}
l.mill()
return nil
}
func (l *Logger) close() error {
if l.file == nil {
return nil
}
err := l.file.Close()
l.file = nil
return err
}
func (l *Logger) openNew() error {
err := os.MkdirAll(l.dir(), 0744)
if err != nil {
return fmt.Errorf("can't make directories for new logfile: %s", err)
}
name := l.filename()
mode := os.FileMode(0644)
info, err := os_Stat(name)
if err == nil {
// Copy the mode off the old logfile.
mode = info.Mode()
// move the existing file
newname := backupName(name, l.LocalTime)
if err := os.Rename(name, newname); err != nil {
return fmt.Errorf("can't rename log file: %s", err)
}
// this is a no-op anywhere but linux
if err := chown(name, info); err != nil {
return err
}
}
// we use truncate here because this should only get called when we've moved
// the file ourselves. if someone else creates the file in the meantime,
// just wipe out the contents.
f, err := os.OpenFile(name, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, mode)
if err != nil {
return fmt.Errorf("can't open new logfile: %s", err)
}
l.file = f
l.size = 0
return nil
}
func backupName(name string, local bool) string {
dir := filepath.Dir(name)
filename := filepath.Base(name)
ext := filepath.Ext(filename)
prefix := filename[:len(filename)-len(ext)]
t := currentTime()
if !local {
t = t.UTC()
}
timestamp := t.Format(backupTimeFormat)
return filepath.Join(dir, fmt.Sprintf("%s-%s%s", prefix, timestamp, ext))
}rotate方法会close当前文件，然后openNew新文件，最后执行l.mill()；openNew方法先通过backupName计算要备份的文件名，然后执行Rename，将当前文件重命名为备份文件名，然后执行chown，最后执行os.OpenFile打开新文件
小结
Logger定义了Filename、MaxSize(单个文件大小最大值，单位M)、MaxAge(单位天)、MaxBackups、LocalTime、Compress属性；Write方法先判断要写入的长度是否超过l.max()，之后判断file是否为nil，如果为nil则执行l.openExistingOrNew；之后判断l.size+writeLen是否大于l.max()，如果大于则执行l.rotate()，否则执行l.file.Write(p)，然后更新l.size。
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