from moby with some changes
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alessio
parent
6ec3780182
commit
a7e7a3f87d
276
watcher/notify.go
Normal file
276
watcher/notify.go
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@ -0,0 +1,276 @@
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package watcher
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import (
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"errors"
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"fmt"
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"github.com/fsnotify/fsnotify"
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"github.com/sirupsen/logrus"
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"os"
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"sync"
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"time"
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)
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var (
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// errPollerClosed is returned when the poller is closed
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errPollerClosed = errors.New("poller is closed")
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// errNoSuchWatch is returned when trying to remove a watch that doesn't exist
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errNoSuchWatch = errors.New("watch does not exist")
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)
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type (
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// FileWatcher is an interface for implementing file notification watchers
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FileWatcher interface {
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Close() error
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Add(string) error
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Walk(string, bool) string
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Remove(string) error
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Errors() <-chan error
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Events() <-chan fsnotify.Event
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}
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filewatcher struct {
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// force polling instead event watcher
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polling bool
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// polling interval express in milliseconds
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interval time.Duration
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}
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// fsNotifyWatcher wraps the fsnotify package to satisfy the FileNotifier interface
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fsNotifyWatcher struct {
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*fsnotify.Watcher
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}
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// filePoller is used to poll files for changes, especially in cases where fsnotify
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// can't be run (e.g. when inotify handles are exhausted)
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// filePoller satisfies the FileWatcher interface
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filePoller struct {
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// watches is the list of files currently being polled, close the associated channel to stop the watch
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watches map[string]chan struct{}
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// events is the channel to listen to for watch events
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events chan fsnotify.Event
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// errors is the channel to listen to for watch errors
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errors chan error
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// mu locks the poller for modification
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mu sync.Mutex
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// closed is used to specify when the poller has already closed
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closed bool
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}
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)
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// New tries to use an fs-event watcher, and falls back to the poller if there is an error
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func Watcher() (FileWatcher, error) {
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//if w, err := EventWatcher(); err == nil {
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// return w, nil
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//}
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return PollingWatcher(), nil
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}
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// NewPollingWatcher returns a poll-based file watcher
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func PollingWatcher() FileWatcher {
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return &filePoller{
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//interval: f.interval * time.Millisecond,
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events: make(chan fsnotify.Event),
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errors: make(chan error),
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}
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}
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// NewEventWatcher returns an fs-event based file watcher
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func EventWatcher() (FileWatcher, error) {
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w, err := fsnotify.NewWatcher()
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if err != nil {
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return nil, err
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}
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return &fsNotifyWatcher{Watcher: w}, nil
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}
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// Events returns the fsnotify event channel receiver
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func (w *fsNotifyWatcher) Events() <-chan fsnotify.Event {
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return w.Watcher.Events
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}
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// Errors returns the fsnotify error channel receiver
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func (w *fsNotifyWatcher) Errors() <-chan error {
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return w.Watcher.Errors
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}
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func (w *fsNotifyWatcher) Walk(path string, init bool) string {
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if err := w.Add(path); err != nil {
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return ""
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}
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return path
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}
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func (w *filePoller) Walk(path string, init bool) string {
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check := w.watches[path]
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if err := w.Add(path); err != nil {
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return ""
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}
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if check == nil && init {
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_, err := os.Stat(path)
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if err == nil {
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go w.sendEvent(fsnotify.Event{Op: fsnotify.Create, Name: path}, w.watches[path])
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}
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}
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return path
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}
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// Add adds a filename to the list of watches
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// once added the file is polled for changes in a separate goroutine
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func (w *filePoller) Add(name string) error {
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w.mu.Lock()
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defer w.mu.Unlock()
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if w.closed {
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return errPollerClosed
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}
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f, err := os.Open(name)
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if err != nil {
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return err
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}
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fi, err := os.Stat(name)
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if err != nil {
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return err
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}
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if w.watches == nil {
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w.watches = make(map[string]chan struct{})
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}
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if _, exists := w.watches[name]; exists {
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return fmt.Errorf("watch exists")
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}
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chClose := make(chan struct{})
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w.watches[name] = chClose
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go w.watch(f, fi, chClose)
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return nil
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}
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// Remove stops and removes watch with the specified name
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func (w *filePoller) Remove(name string) error {
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w.mu.Lock()
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defer w.mu.Unlock()
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return w.remove(name)
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}
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func (w *filePoller) remove(name string) error {
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if w.closed {
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return errPollerClosed
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}
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chClose, exists := w.watches[name]
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if !exists {
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return errNoSuchWatch
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}
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close(chClose)
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delete(w.watches, name)
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return nil
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}
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// Events returns the event channel
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// This is used for notifications on events about watched files
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func (w *filePoller) Events() <-chan fsnotify.Event {
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return w.events
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}
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// Errors returns the errors channel
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// This is used for notifications about errors on watched files
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func (w *filePoller) Errors() <-chan error {
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return w.errors
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}
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// Close closes the poller
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// All watches are stopped, removed, and the poller cannot be added to
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func (w *filePoller) Close() error {
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w.mu.Lock()
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defer w.mu.Unlock()
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if w.closed {
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return nil
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}
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w.closed = true
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for name := range w.watches {
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w.remove(name)
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delete(w.watches, name)
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}
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return nil
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}
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// sendEvent publishes the specified event to the events channel
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func (w *filePoller) sendEvent(e fsnotify.Event, chClose <-chan struct{}) error {
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select {
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case w.events <- e:
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case <-chClose:
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return fmt.Errorf("closed")
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}
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return nil
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}
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// sendErr publishes the specified error to the errors channel
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func (w *filePoller) sendErr(e error, chClose <-chan struct{}) error {
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select {
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case w.errors <- e:
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case <-chClose:
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return fmt.Errorf("closed")
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}
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return nil
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}
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// watch is responsible for polling the specified file for changes
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// upon finding changes to a file or errors, sendEvent/sendErr is called
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func (w *filePoller) watch(f *os.File, lastFi os.FileInfo, chClose chan struct{}) {
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defer f.Close()
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for {
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time.Sleep(200 * time.Millisecond)
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select {
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case <-chClose:
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logrus.Debugf("watch for %s closed", f.Name())
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return
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default:
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}
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fi, err := os.Stat(f.Name())
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if err != nil {
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// if we got an error here and lastFi is not set, we can presume that nothing has changed
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// This should be safe since before `watch()` is called, a stat is performed, there is any error `watch` is not called
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if lastFi == nil {
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continue
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}
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// If it doesn't exist at this point, it must have been removed
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// no need to send the error here since this is a valid operation
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if os.IsNotExist(err) {
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if err := w.sendEvent(fsnotify.Event{Op: fsnotify.Remove, Name: f.Name()}, chClose); err != nil {
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return
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}
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lastFi = nil
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continue
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}
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// at this point, send the error
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if err := w.sendErr(err, chClose); err != nil {
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return
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}
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continue
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}
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if lastFi == nil {
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if err := w.sendEvent(fsnotify.Event{Op: fsnotify.Create, Name: f.Name()}, chClose); err != nil {
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return
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}
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lastFi = fi
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continue
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}
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if fi.Mode() != lastFi.Mode() {
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if err := w.sendEvent(fsnotify.Event{Op: fsnotify.Chmod, Name: f.Name()}, chClose); err != nil {
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return
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}
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lastFi = fi
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continue
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}
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if fi.ModTime() != lastFi.ModTime() || fi.Size() != lastFi.Size() {
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if err := w.sendEvent(fsnotify.Event{Op: fsnotify.Write, Name: f.Name()}, chClose); err != nil {
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return
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}
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lastFi = fi
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continue
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}
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}
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}
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