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logroller.go
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logroller.go
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// Copyright 2015 Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
// +build linux darwin freebsd
package log
import (
"fmt"
"math"
"os"
"path/filepath"
"regexp"
"sort"
"strconv"
"sync"
)
var rollPattern = regexp.MustCompile(`^\.([0-9]+)$`)
const rollFormatFormat = "%s.%%0%dd"
type LogRoller struct {
fileName string
fileMaxBytes uint
maxFiles uint
rollFormat string
m sync.Mutex
file *os.File
fileSize uint
}
func NewLogRoller(fileName string, fileMaxBytes, maxFiles uint) (*LogRoller, error) {
// How many digits to append to rolled file name?
// 0 => 0 ; 1 => 1 ; 9 => 1 ; 99 => 2 ; 100 => 3
var digits int
if maxFiles > 0 {
digits = int(math.Log10(float64(maxFiles))) + 1
}
rollFormat := fmt.Sprintf(rollFormatFormat, fileName, digits)
lr := LogRoller{
fileName: fileName,
fileMaxBytes: fileMaxBytes,
maxFiles: maxFiles,
rollFormat: rollFormat,
}
return &lr, nil
}
func (lr *LogRoller) Write(p []byte) (int, error) {
lr.m.Lock()
defer lr.m.Unlock()
if lr.file == nil {
lr.fileSize = 0
if err := lr.openFile(); err != nil {
return 0, err
}
}
written, err := lr.file.Write(p)
if err != nil {
return 0, err
}
lr.fileSize += uint(written)
if lr.fileSize > lr.fileMaxBytes {
lr.file.Close()
lr.file = nil
}
return written, nil
}
// openFile opens a new file for logging, rolling the oldest one if needed.
func (lr *LogRoller) openFile() error {
if err := lr.roll(); err != nil {
return err
}
if f, err := os.Create(lr.fileName); err != nil {
return err
} else {
lr.file = f
}
return nil
}
type sortableNumberStrings []string
func (s sortableNumberStrings) Len() int {
return len(s)
}
func (s sortableNumberStrings) Less(i, j int) bool {
ip, _ := strconv.ParseUint(s[i], 10, 16)
jp, _ := strconv.ParseUint(s[j], 10, 16)
return ip < jp
}
func (s sortableNumberStrings) Swap(i, j int) {
s[i], s[j] = s[j], s[i]
}
// roll deletes old log files until there are lr.maxFiles or fewer,
// and renames remaining log files so that the file named lr.fileName+".3" becomes lr.fileName+".4".
// The file named lr.fileName becomes lr.fileName+".0".
// If lr.fileName does not exist, then this is a noop.
func (lr *LogRoller) roll() error {
if _, err := os.Stat(lr.fileName); os.IsNotExist(err) {
// Nothing to do; the target log file name already does not exist.
return nil
}
// Get all rolled logs, plus some.
allFiles, err := filepath.Glob(lr.fileName + ".*")
if err != nil {
return err
}
// Get number suffixes from the rolled logs; ignore non-matches.
numbers := make(sortableNumberStrings, 0, len(allFiles))
for _, file := range allFiles {
match := rollPattern.FindStringSubmatch(file[len(lr.fileName):])
if len(match) < 2 {
continue
}
if _, err := strconv.ParseUint(match[1], 10, 16); err == nil {
// Keep the string form of the number.
numbers = append(numbers, match[1])
}
}
// Delete old log files and rename the rest.
sort.Sort(numbers)
for i := len(numbers) - 1; i >= 0; i-- {
oldpath := fmt.Sprintf("%s.%s", lr.fileName, numbers[i])
if uint(i+1) >= lr.maxFiles {
err := os.Remove(oldpath)
if err != nil {
return err
}
} else {
n, _ := strconv.ParseUint(numbers[i], 10, 16)
newpath := fmt.Sprintf(lr.rollFormat, n+1)
err := os.Rename(oldpath, newpath)
if err != nil {
return err
}
}
}
if lr.maxFiles > 0 {
newpath := fmt.Sprintf(lr.rollFormat, 0)
err = os.Rename(lr.fileName, newpath)
if err != nil {
return err
}
} // Else the existing file will be truncated.
return nil
}