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appender.go
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appender.go
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package soba
import (
"fmt"
"io"
"os"
"path/filepath"
"regexp"
"strconv"
"sync"
"github.com/pkg/errors"
"github.com/novln/soba/encoder/json"
)
const (
// ConsoleAppenderType defines the type for a console appender.
ConsoleAppenderType = "console"
// FileAppenderType defines the type for a file appender.
FileAppenderType = "file"
)
// An Appender defines an entity that receives a log entry and logs it somewhere,
// like for example, to a file, the console, or the syslog.
type Appender interface {
// Name returns appender name.
Name() string
// Write receives a log entry.
Write(entry *Entry)
// Close recycles underlying resources of appender.
Close() error
}
// IsAppenderNameValid verify that a Appender name has a valid format.
var IsAppenderNameValid = regexp.MustCompile(`^[a-z]+[a-z._0-9-]+[a-z0-9]+$`).MatchString
// NewAppender creates a new Appender from given configuration.
// To register a custom appender, please use soba.RegisterAppenders() function.
func NewAppender(name string, conf ConfigAppender) (Appender, error) {
err := validateAppenderConfig(name, conf)
if err != nil {
return nil, errors.Wrapf(err, "cannot create appender for %s", name)
}
switch conf.Type {
case ConsoleAppenderType:
appender := NewConsoleAppender(name, os.Stdout)
return appender, nil
case FileAppenderType:
appender, err := NewFileAppender(name, conf.Path, conf.Backup, conf.MaxBytes)
if err != nil {
return nil, errors.Wrapf(err, "cannot create file appender for %s", name)
}
return appender, nil
default:
// Should be handled by validateAppenderConfig function.
return nil, errors.Errorf("unknown appender type for %s: %s", name, conf.Type)
}
}
// ConsoleAppender is an appender that uses stdout to write log entry.
type ConsoleAppender struct {
mutex sync.Mutex
name string
out io.Writer
}
// NewConsoleAppender creates a new ConsoleAppender instance.
func NewConsoleAppender(name string, out io.Writer) *ConsoleAppender {
return &ConsoleAppender{
name: name,
out: out,
}
}
// Name returns appender name.
func (appender *ConsoleAppender) Name() string {
return appender.name
}
// Close recycles underlying resources of appender.
func (appender *ConsoleAppender) Close() error {
return nil
}
// Write receives a log entry.
func (appender *ConsoleAppender) Write(entry *Entry) {
encoder := json.NewEncoder()
defer encoder.Close()
buffer := WriteEntry(entry, encoder)
appender.mutex.Lock()
defer appender.mutex.Unlock()
_, err := appender.out.Write(buffer)
if err != nil {
onAppenderWriteError(err)
}
}
// FileAppender is an appender that uses a file to write log entry.
type FileAppender struct {
mutex sync.Mutex
name string
path string
file *os.File
size int64
backup bool
maxBytes int64
}
// NewFileAppender creates a new FileAppender instance.
func NewFileAppender(name string, path string, backup bool, maxBytes int64) (*FileAppender, error) {
appender := &FileAppender{
name: name,
path: path,
backup: backup,
maxBytes: maxBytes,
}
err := appender.openNew()
if err != nil {
return nil, errors.Wrapf(err, `cannot create file "%s" for appender`, path)
}
return appender, nil
}
// Name returns appender name.
func (appender *FileAppender) Name() string {
return appender.name
}
// Close recycles underlying resources of appender.
func (appender *FileAppender) Close() error {
appender.mutex.Lock()
defer appender.mutex.Unlock()
return appender.close()
}
// Write receives a log entry and writes it on a file.
func (appender *FileAppender) Write(entry *Entry) {
encoder := json.NewEncoder()
defer encoder.Close()
buffer := WriteEntry(entry, encoder)
appender.mutex.Lock()
defer appender.mutex.Unlock()
err := appender.rotate(len(buffer))
if err != nil {
onAppenderWriteError(err)
return
}
n, err := appender.file.Write(buffer)
if err != nil {
onAppenderWriteError(err)
return
}
appender.size += int64(n)
}
// openNew opens a new appender file to write log entry.
func (appender *FileAppender) openNew() error {
if appender.file != nil {
return nil
}
directory := filepath.Dir(appender.path)
err := os.MkdirAll(directory, 0750)
if err != nil {
return errors.WithStack(err)
}
file, err := os.OpenFile(appender.path, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0600)
if err != nil {
return errors.WithStack(err)
}
fstat, err := file.Stat()
if err != nil {
return errors.WithStack(err)
}
appender.file = file
appender.size = fstat.Size()
return nil
}
// close closes the underlying file.
func (appender *FileAppender) close() error {
if appender.file == nil {
return nil
}
file := appender.file
appender.file = nil
appender.size = 0
err := file.Close()
if err != nil {
return errors.WithStack(err)
}
return nil
}
// rotate analyzes if a file rotation is required, and executes it when needed.
func (appender *FileAppender) rotate(toWrite int) error {
if appender.maxBytes == 0 {
return nil
}
finalSize := int64(toWrite) + appender.size
if finalSize < appender.maxBytes {
return nil
}
err := appender.close()
if err != nil {
return err
}
err = appender.doRotate()
if err != nil {
return err
}
err = appender.openNew()
if err != nil {
return err
}
return nil
}
// doRotate executes the file rotation, using backup or rename strategy.
func (appender *FileAppender) doRotate() error {
if appender.backup {
return appender.rotateWithBackup()
}
return appender.rotateWithRename()
}
// rotateWithRename renames the current file by suffixing it with "-".
// If a file with the suffix already exists, it will be replaced.
func (appender *FileAppender) rotateWithRename() error {
backup := fmt.Sprint(appender.path, "-")
err := os.Rename(appender.path, backup)
if err != nil {
return errors.WithStack(err)
}
return nil
}
// rotateWithBackup renames the current file by suffixing it with a backup number.
//
// Let's say with we the following files in the directory:
// - app.log
// - app.log.1
// - app.log.2
// - app.log.3
//
// The current file (app.log) will be rename to "app.log.4".
func (appender *FileAppender) rotateWithBackup() error {
pattern := fmt.Sprint(appender.path, ".*")
list, err := filepath.Glob(pattern)
if err != nil {
return errors.WithStack(err)
}
id := len(list) + 1
backup := fmt.Sprint(appender.path, ".", strconv.FormatInt(int64(id), 10))
err = os.Rename(appender.path, backup)
if err != nil {
return errors.WithStack(err)
}
return nil
}
func onAppenderWriteError(err error) {
// We choose to ignore the error if we cannot log it on stderr.
_, _ = fmt.Fprintln(os.Stderr, err.Error())
}