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watcher.go
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watcher.go
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package main
import (
"bytes"
"fmt"
"github.com/fsnotify/fsnotify"
)
// The Watcher interface the interface the application consumes for file
// watching. The standard implementation is a wrapper for fsnotify.
// EventType represents the kinds of file system events.
type EventType uint32
// The kinds of file system events we're interested in.
const (
Create EventType = 1 << iota
Write
Remove
Rename
)
// A set with the all the defined event types.
var eventTypes = []EventType{
Create,
Write,
Remove,
Rename,
}
func (t EventType) String() string {
var buffer bytes.Buffer
if t&Create == Create {
buffer.WriteString("|CREATE")
}
if t&Remove == Remove {
buffer.WriteString("|REMOVE")
}
if t&Write == Write {
buffer.WriteString("|WRITE")
}
if t&Rename == Rename {
buffer.WriteString("|RENAME")
}
if buffer.Len() == 0 {
return ""
}
return buffer.String()[1:]
}
// An FsEvent represents a file system event.
type FsEvent struct {
// The path to the entry the event occured on.
Path string
// The type of the event that occurred.
Type EventType
}
// A WatcherEvent is raised by a Watcher when an event or error occurs.
type WatcherEvent struct {
// The file system event. If Error is not nil then the meaning of Event is
// undefined.
Event FsEvent
// The error (possibly nil).
Error error
}
// A Watcher raises file system events for watched directories and files.
type Watcher interface {
// Tells the watcher to begin watching the given file or directory (not recursive).
Watch(path string) error
// Stops watching the given file or directory.
Unwatch(path string) error
// The channel that the watcher communicates events and errors on.
Events() <-chan WatcherEvent
// Stops the Watcher.
Stop()
}
// A WatchFilter is a function that indicates whether an FsEvent should be
// filtered out of the event stream emitted by a Watcher.
type WatchFilter func(event FsEvent) (bool, error)
// NewWatcher creates a new Watcher.
// If filter is nil then no events will be filtered out.
func NewWatcher(filter WatchFilter) (Watcher, error) {
fsWatcher, err := fsnotify.NewWatcher()
if err != nil {
return nil, err
}
if filter == nil {
filter = func(event FsEvent) (bool, error) {
return false, nil
}
}
w := &watcherImpl{
fsWatcher: fsWatcher,
events: make(chan WatcherEvent, 1),
filter: filter,
}
go w.start()
return w, nil
}
// An implementation of Watcher using fsnotify.
type watcherImpl struct {
fsWatcher *fsnotify.Watcher
events chan WatcherEvent
filter WatchFilter
}
// Tells the watcher to begin watching the given file or directory (not recursive).
func (w *watcherImpl) Watch(path string) error {
if err := w.fsWatcher.Add(path); err != nil {
return fmt.Errorf("failed to add watcher: %v", err)
}
return nil
}
// Stops watching the given file or directory.
func (w *watcherImpl) Unwatch(path string) error {
if err := w.fsWatcher.Remove(path); err != nil {
return fmt.Errorf("failed to remove watcher: %v", err)
}
return nil
}
// The channel that the watcher communicates events and errors on.
func (w *watcherImpl) Events() <-chan WatcherEvent {
return w.events
}
// Stops the Watcher.
func (w *watcherImpl) Stop() {
if err := w.fsWatcher.Close(); err != nil {
logger.Printf("Error closing fsnotify.Watcher: %v\n", err)
}
}
// Starts consuming the fsnotify events and maps them to WatcherEvents.
func (w *watcherImpl) start() {
defer close(w.events)
for {
select {
case event, ok := <-w.fsWatcher.Events:
if !ok {
return
}
if !isWatchedEvent(event) {
break
}
fsEvent := newEvent(event)
skip, err := w.filter(fsEvent)
if err != nil {
logger.Printf(
"watcher filter error: event=%v, error=%v\n", fsEvent, err)
} else if skip {
logger.Printf("watcher filter: ignoring event %v\n", fsEvent)
break
}
w.events <- WatcherEvent{
Event: fsEvent,
}
case err, ok := <-w.fsWatcher.Errors:
if !ok {
return
}
w.events <- WatcherEvent{
Error: err,
}
}
}
}
// Indicates whether an fsnotify.Event represents and event that we care about.
func isWatchedEvent(event fsnotify.Event) bool {
for _, t := range eventTypes {
if EventType(event.Op) == t {
return true
}
}
return false
}
// Maps an fsnotify.Event to a WatcherEvent.
func newEvent(event fsnotify.Event) FsEvent {
return FsEvent{
Path: event.Name,
Type: EventType(event.Op),
}
}