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// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
// Copyright (c) 2015 HPE Software Inc. All rights reserved.
// Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
package watch
import (
"os"
"runtime"
"time"
"github.com/nxadm/tail/util"
"gopkg.in/tomb.v1"
)
// PollingFileWatcher polls the file for changes.
type PollingFileWatcher struct {
Filename string
Size int64
}
func NewPollingFileWatcher(filename string) *PollingFileWatcher {
fw := &PollingFileWatcher{filename, 0}
return fw
}
var POLL_DURATION time.Duration
func (fw *PollingFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
for {
if _, err := os.Stat(fw.Filename); err == nil {
return nil
} else if !os.IsNotExist(err) {
return err
}
select {
case <-time.After(POLL_DURATION):
continue
case <-t.Dying():
return tomb.ErrDying
}
}
panic("unreachable")
}
func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChanges, error) {
origFi, err := os.Stat(fw.Filename)
if err != nil {
return nil, err
}
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 = pos
go func() {
prevSize := fw.Size
for {
select {
case <-t.Dying():
return
default:
}
time.Sleep(POLL_DURATION)
fi, err := os.Stat(fw.Filename)
if err != nil {
// Windows cannot delete a file if a handle is still open (tail keeps one open)
// so it gives access denied to anything trying to read it until all handles are released.
if os.IsNotExist(err) || (runtime.GOOS == "windows" && os.IsPermission(err)) {
// File does not exist (has been deleted).
changes.NotifyDeleted()
return
}
// 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
}
// File got bigger?
if prevSize > 0 && prevSize < fw.Size {
changes.NotifyModified()
prevSize = fw.Size
continue
}
prevSize = fw.Size
// File was appended to (changed)?
modTime := fi.ModTime()
if modTime != prevModTime {
prevModTime = modTime
changes.NotifyModified()
}
}
}()
return changes, nil
}
func init() {
POLL_DURATION = 250 * time.Millisecond
}
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