// TailFile begins tailing the file. Output stream is made available
// via the `Tail.Lines` channel. To handle errors during tailing,
// invoke the `Wait` or `Err` method after finishing reading from the
// `Lines` channel.
func TailFile(filename string, config Config) (*Tail, error) {
if config.ReOpen && !config.Follow {
util.Fatal("cannot set ReOpen without Follow.")
}
t := &Tail{
Filename: filename,
Lines: make(chan *Line),
Config: config,
}
// when Logger was not specified in config, use default logger
if t.Logger == nil {
t.Logger = log.New(os.Stderr, "", log.LstdFlags)
}
if t.Poll {
t.watcher = watch.NewPollingFileWatcher(filename)
} else {
t.tracker = watch.NewInotifyTracker()
w, err := t.tracker.NewWatcher()
if err != nil {
return nil, err
}
t.watcher = watch.NewInotifyFileWatcher(filename, w)
}
if t.MustExist {
var err error
t.file, err = OpenFile(t.Filename)
if err != nil {
return nil, err
}
}
go t.tailFileSync()
return t, nil
}
func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, fi os.FileInfo) *FileChanges {
changes := NewFileChanges()
err := fw.w.Watch(fw.Filename)
if err != nil {
util.Fatal("Error watching %v: %v", fw.Filename, err)
}
fw.Size = fi.Size()
go func() {
defer fw.w.RemoveWatch(fw.Filename)
defer changes.Close()
for {
prevSize := fw.Size
var evt *fsnotify.FileEvent
var ok bool
select {
case evt, ok = <-fw.w.Event:
if !ok {
return
}
case <-t.Dying():
return
}
switch {
case evt.IsDelete():
fallthrough
case evt.IsRename():
changes.NotifyDeleted()
return
case evt.IsModify():
fi, err := os.Stat(fw.Filename)
if err != nil {
if os.IsNotExist(err) {
changes.NotifyDeleted()
return
}
// XXX: report this error back to the user
util.Fatal("Failed to stat file %v: %v", fw.Filename, err)
}
fw.Size = fi.Size()
if prevSize > 0 && prevSize > fw.Size {
changes.NotifyTruncated()
} else {
changes.NotifyModified()
}
prevSize = fw.Size
}
}
}()
return changes
}
func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, origFi os.FileInfo) *FileChanges {
changes := NewFileChanges()
var prevModTime time.Time
// XXX: use tomb.Tomb to cleanly manage these goroutines. replace
// the fatal (below) with tomb's Kill.
fw.Size = origFi.Size()
go func() {
defer changes.Close()
var retry int = 0
prevSize := fw.Size
for {
select {
case <-t.Dying():
return
default:
}
time.Sleep(POLL_DURATION)
fi, err := os.Stat(fw.Filename)
if err != nil {
if os.IsNotExist(err) {
// File does not exist (has been deleted).
changes.NotifyDeleted()
return
}
if permissionErrorRetry(err, &retry) {
continue
}
// XXX: report this error back to the user
util.Fatal("Failed to stat file %v: %v", fw.Filename, err)
}
// File got moved/renamed?
if !os.SameFile(origFi, fi) {
changes.NotifyDeleted()
return
}
// File got truncated?
fw.Size = fi.Size()
if prevSize > 0 && prevSize > fw.Size {
changes.NotifyTruncated()
prevSize = fw.Size
continue
}
prevSize = fw.Size
// File was appended to (changed)?
modTime := fi.ModTime()
if modTime != prevModTime {
prevModTime = modTime
changes.NotifyModified()
}
}
}()
return changes
}