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watcher.go
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watcher.go
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package util
import (
"github.com/fsnotify/fsnotify"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
"os"
"path/filepath"
"time"
)
func WatchForUpdates(filename string, done <-chan bool, action func()) error {
symlink, err := isSymLink(filename)
if err != nil {
return err
}
if symlink {
return watchLinkForUpdates(filename, done, action)
}
return watchFileForUpdates(filename, done, action)
}
func isSymLink(filename string) (bool, error) {
fileInfo, err := os.Lstat(filename)
if err != nil {
return false, err
}
if fileInfo.Mode()&os.ModeSymlink == os.ModeSymlink {
return true, nil
}
return false, nil
}
func waitForReplacement(filename string, op fsnotify.Op, watcher *fsnotify.Watcher) {
const sleep_interval = 50 * time.Millisecond
// Avoid a race when fsnofity.Remove is preceded by fsnotify.Chmod.
if op&fsnotify.Chmod != 0 {
time.Sleep(sleep_interval)
}
for {
if _, err := os.Stat(filename); err == nil {
if err := watcher.Add(filename); err == nil {
logrus.Debugf("watching resumed for %s", filename)
return
}
}
time.Sleep(sleep_interval)
}
}
func watchFileForUpdates(filename string, done <-chan bool, action func()) error {
filename = filepath.Clean(filename)
watcher, err := fsnotify.NewWatcher()
if err != nil {
return errors.Wrapf(err, "failed to create watcher for %s", filename)
}
go func() {
defer func() {
if r := recover(); r != nil {
var ok bool
err, ok := r.(error)
if ok {
logrus.Errorf("watch file %s for update error %v", filename, err)
}
}
}()
defer watcher.Close()
done:
for {
select {
case _ = <-done:
logrus.Printf("Shutting down watcher for: %s", filename)
break done
case event := <-watcher.Events:
if event.Op&(fsnotify.Remove|fsnotify.Rename|fsnotify.Chmod) != 0 {
logrus.Debugf("watching interrupted on event: %s", event)
watcher.Remove(filename)
waitForReplacement(filename, event.Op, watcher)
}
logrus.Infof("execute action after event %s on %s ", event.Op, event.Name)
action()
case err := <-watcher.Errors:
logrus.Printf("error watching %s: %s", filename, err)
}
}
}()
if err = watcher.Add(filename); err != nil {
return errors.Wrapf(err, "failed to add %s watcher", filename)
}
logrus.Printf("watching %s for updates", filename)
return nil
}
func watchLinkForUpdates(filename string, done <-chan bool, action func()) error {
filename = filepath.Clean(filename)
dirname := filepath.Dir(filename)
watcher, err := fsnotify.NewWatcher()
if err != nil {
return errors.Wrapf(err, "failed to create watcher for file %s in dir %s", filename, dirname)
}
go func() {
defer func() {
if r := recover(); r != nil {
var ok bool
err, ok := r.(error)
if ok {
logrus.Errorf("watch link %s for update error %v", filename, err)
}
}
}()
defer watcher.Close()
done:
for {
select {
case _ = <-done:
logrus.Printf("Shutting down watcher for: %s", dirname)
break done
case event := <-watcher.Events:
if event.Op&(fsnotify.Remove|fsnotify.Rename|fsnotify.Chmod) != 0 {
logrus.Debugf("watching interrupted on event: %s", event)
watcher.Remove(dirname)
waitForReplacement(dirname, event.Op, watcher)
}
if event.Op&(fsnotify.Remove) != 0 {
continue
}
targetname, err := filepath.EvalSymlinks(filename)
if err != nil {
logrus.Printf("error evaluating target symlink %s: %s", targetname, err)
continue
}
name, err := filepath.EvalSymlinks(event.Name)
if err != nil {
logrus.Printf("error evaluating event symlink %s: %s", event.Name, err)
continue
}
if name == targetname {
logrus.Infof("execute action after event %s on %s ", event.Op, event.Name)
action()
} else {
logrus.Debugf("skip action after event: %v", event)
}
case err := <-watcher.Errors:
logrus.Printf("error watching %s: %s", dirname, err)
}
}
}()
if err = watcher.Add(dirname); err != nil {
return errors.Wrapf(err, "failed to add %s watcher", dirname)
}
logrus.Infof("watching %s for updates on link %s", dirname, filename)
return nil
}