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read.go
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read.go
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package jsonfilelog
import (
"bytes"
"encoding/json"
"fmt"
"io"
"os"
"time"
"github.com/Sirupsen/logrus"
"github.com/docker/docker/daemon/logger"
"github.com/docker/docker/pkg/filenotify"
"github.com/docker/docker/pkg/ioutils"
"github.com/docker/docker/pkg/jsonlog"
"github.com/docker/docker/pkg/tailfile"
)
const maxJSONDecodeRetry = 20000
func decodeLogLine(dec *json.Decoder, l *jsonlog.JSONLog) (*logger.Message, error) {
l.Reset()
if err := dec.Decode(l); err != nil {
return nil, err
}
msg := &logger.Message{
Source: l.Stream,
Timestamp: l.Created,
Line: []byte(l.Log),
}
return msg, nil
}
// ReadLogs implements the logger's LogReader interface for the logs
// created by this driver.
func (l *JSONFileLogger) ReadLogs(config logger.ReadConfig) *logger.LogWatcher {
logWatcher := logger.NewLogWatcher()
go l.readLogs(logWatcher, config)
return logWatcher
}
func (l *JSONFileLogger) readLogs(logWatcher *logger.LogWatcher, config logger.ReadConfig) {
defer close(logWatcher.Msg)
pth := l.writer.LogPath()
var files []io.ReadSeeker
for i := l.writer.MaxFiles(); i > 1; i-- {
f, err := os.Open(fmt.Sprintf("%s.%d", pth, i-1))
if err != nil {
if !os.IsNotExist(err) {
logWatcher.Err <- err
break
}
continue
}
files = append(files, f)
}
latestFile, err := os.Open(pth)
if err != nil {
logWatcher.Err <- err
return
}
if config.Tail != 0 {
tailer := ioutils.MultiReadSeeker(append(files, latestFile)...)
tailFile(tailer, logWatcher, config.Tail, config.Since)
}
// close all the rotated files
for _, f := range files {
if err := f.(io.Closer).Close(); err != nil {
logrus.WithField("logger", "json-file").Warnf("error closing tailed log file: %v", err)
}
}
if !config.Follow {
return
}
if config.Tail >= 0 {
latestFile.Seek(0, os.SEEK_END)
}
l.mu.Lock()
l.readers[logWatcher] = struct{}{}
l.mu.Unlock()
notifyRotate := l.writer.NotifyRotate()
followLogs(latestFile, logWatcher, notifyRotate, config.Since)
l.mu.Lock()
delete(l.readers, logWatcher)
l.mu.Unlock()
l.writer.NotifyRotateEvict(notifyRotate)
}
func tailFile(f io.ReadSeeker, logWatcher *logger.LogWatcher, tail int, since time.Time) {
var rdr io.Reader = f
if tail > 0 {
ls, err := tailfile.TailFile(f, tail)
if err != nil {
logWatcher.Err <- err
return
}
rdr = bytes.NewBuffer(bytes.Join(ls, []byte("\n")))
}
dec := json.NewDecoder(rdr)
l := &jsonlog.JSONLog{}
for {
msg, err := decodeLogLine(dec, l)
if err != nil {
if err != io.EOF {
logWatcher.Err <- err
}
return
}
if !since.IsZero() && msg.Timestamp.Before(since) {
continue
}
logWatcher.Msg <- msg
}
}
func followLogs(f *os.File, logWatcher *logger.LogWatcher, notifyRotate chan interface{}, since time.Time) {
dec := json.NewDecoder(f)
l := &jsonlog.JSONLog{}
fileWatcher, err := filenotify.New()
if err != nil {
logWatcher.Err <- err
}
defer func() {
f.Close()
fileWatcher.Close()
}()
name := f.Name()
if err := fileWatcher.Add(name); err != nil {
logrus.WithField("logger", "json-file").Warnf("falling back to file poller due to error: %v", err)
fileWatcher.Close()
fileWatcher = filenotify.NewPollingWatcher()
if err := fileWatcher.Add(name); err != nil {
logrus.Debugf("error watching log file for modifications: %v", err)
logWatcher.Err <- err
return
}
}
var retries int
for {
msg, err := decodeLogLine(dec, l)
if err != nil {
if err != io.EOF {
// try again because this shouldn't happen
if _, ok := err.(*json.SyntaxError); ok && retries <= maxJSONDecodeRetry {
dec = json.NewDecoder(f)
retries++
continue
}
// io.ErrUnexpectedEOF is returned from json.Decoder when there is
// remaining data in the parser's buffer while an io.EOF occurs.
// If the json logger writes a partial json log entry to the disk
// while at the same time the decoder tries to decode it, the race condition happens.
if err == io.ErrUnexpectedEOF && retries <= maxJSONDecodeRetry {
reader := io.MultiReader(dec.Buffered(), f)
dec = json.NewDecoder(reader)
retries++
continue
}
return
}
select {
case <-fileWatcher.Events():
dec = json.NewDecoder(f)
continue
case <-fileWatcher.Errors():
logWatcher.Err <- err
return
case <-logWatcher.WatchClose():
fileWatcher.Remove(name)
return
case <-notifyRotate:
f.Close()
fileWatcher.Remove(name)
// retry when the file doesn't exist
for retries := 0; retries <= 5; retries++ {
f, err = os.Open(name)
if err == nil || !os.IsNotExist(err) {
break
}
}
if err = fileWatcher.Add(name); err != nil {
logWatcher.Err <- err
return
}
if err != nil {
logWatcher.Err <- err
return
}
dec = json.NewDecoder(f)
continue
}
}
retries = 0 // reset retries since we've succeeded
if !since.IsZero() && msg.Timestamp.Before(since) {
continue
}
select {
case logWatcher.Msg <- msg:
case <-logWatcher.WatchClose():
logWatcher.Msg <- msg
for {
msg, err := decodeLogLine(dec, l)
if err != nil {
return
}
if !since.IsZero() && msg.Timestamp.Before(since) {
continue
}
logWatcher.Msg <- msg
}
}
}
}