hugo/watcher/filenotify/poller.go

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// Package filenotify is adapted from https://github.com/moby/moby/tree/master/pkg/filenotify, Apache-2.0 License.
// Hopefully this can be replaced with an external package sometime in the future, see https://github.com/fsnotify/fsnotify/issues/9
package filenotify
import (
"errors"
"fmt"
"os"
"path/filepath"
"sync"
"time"
"github.com/fsnotify/fsnotify"
"github.com/gohugoio/hugo/common/herrors"
)
var (
// errPollerClosed is returned when the poller is closed
errPollerClosed = errors.New("poller is closed")
// errNoSuchWatch is returned when trying to remove a watch that doesn't exist
errNoSuchWatch = errors.New("watch does not exist")
)
// filePoller is used to poll files for changes, especially in cases where fsnotify
// can't be run (e.g. when inotify handles are exhausted)
// filePoller satisfies the FileWatcher interface
type filePoller struct {
// the duration between polls.
interval time.Duration
// watches is the list of files currently being polled, close the associated channel to stop the watch
watches map[string]struct{}
// Will be closed when done.
done chan struct{}
// events is the channel to listen to for watch events
events chan fsnotify.Event
// errors is the channel to listen to for watch errors
errors chan error
// mu locks the poller for modification
mu sync.Mutex
// closed is used to specify when the poller has already closed
closed bool
}
// Add adds a filename to the list of watches
// once added the file is polled for changes in a separate goroutine
func (w *filePoller) Add(name string) error {
w.mu.Lock()
defer w.mu.Unlock()
if w.closed {
return errPollerClosed
}
item, err := newItemToWatch(name)
if err != nil {
return err
}
if item.left.FileInfo == nil {
return os.ErrNotExist
}
if w.watches == nil {
w.watches = make(map[string]struct{})
}
if _, exists := w.watches[name]; exists {
return fmt.Errorf("watch exists")
}
w.watches[name] = struct{}{}
go w.watch(item)
return nil
}
// Remove stops and removes watch with the specified name
func (w *filePoller) Remove(name string) error {
w.mu.Lock()
defer w.mu.Unlock()
return w.remove(name)
}
func (w *filePoller) remove(name string) error {
if w.closed {
return errPollerClosed
}
_, exists := w.watches[name]
if !exists {
return errNoSuchWatch
}
delete(w.watches, name)
return nil
}
// Events returns the event channel
// This is used for notifications on events about watched files
func (w *filePoller) Events() <-chan fsnotify.Event {
return w.events
}
// Errors returns the errors channel
// This is used for notifications about errors on watched files
func (w *filePoller) Errors() <-chan error {
return w.errors
}
// Close closes the poller
// All watches are stopped, removed, and the poller cannot be added to
func (w *filePoller) Close() error {
w.mu.Lock()
defer w.mu.Unlock()
if w.closed {
return nil
}
w.closed = true
close(w.done)
for name := range w.watches {
w.remove(name)
}
return nil
}
// sendEvent publishes the specified event to the events channel
func (w *filePoller) sendEvent(e fsnotify.Event) error {
select {
case w.events <- e:
case <-w.done:
return fmt.Errorf("closed")
}
return nil
}
// sendErr publishes the specified error to the errors channel
func (w *filePoller) sendErr(e error) error {
select {
case w.errors <- e:
case <-w.done:
return fmt.Errorf("closed")
}
return nil
}
// watch watches item for changes until done is closed.
func (w *filePoller) watch(item *itemToWatch) {
ticker := time.NewTicker(w.interval)
defer ticker.Stop()
for {
select {
case <-ticker.C:
case <-w.done:
return
}
evs, err := item.checkForChanges()
if err != nil {
if err := w.sendErr(err); err != nil {
return
}
}
item.left, item.right = item.right, item.left
for _, ev := range evs {
if err := w.sendEvent(ev); err != nil {
return
}
}
}
}
// recording records the state of a file or a dir.
type recording struct {
os.FileInfo
// Set if FileInfo is a dir.
entries map[string]os.FileInfo
}
func (r *recording) clear() {
r.FileInfo = nil
if r.entries != nil {
for k := range r.entries {
delete(r.entries, k)
}
}
}
func (r *recording) record(filename string) error {
r.clear()
fi, err := os.Stat(filename)
if err != nil && !herrors.IsNotExist(err) {
return err
}
if fi == nil {
return nil
}
r.FileInfo = fi
// If fi is a dir, we watch the files inside that directory (not recursively).
// This matches the behaviour of fsnotity.
if fi.IsDir() {
f, err := os.Open(filename)
if err != nil {
if herrors.IsNotExist(err) {
return nil
}
return err
}
defer f.Close()
fis, err := f.Readdir(-1)
if err != nil {
if herrors.IsNotExist(err) {
return nil
}
return err
}
for _, fi := range fis {
r.entries[fi.Name()] = fi
}
}
return nil
}
// itemToWatch may be a file or a dir.
type itemToWatch struct {
// Full path to the filename.
filename string
// Snapshots of the stat state of this file or dir.
left *recording
right *recording
}
func newItemToWatch(filename string) (*itemToWatch, error) {
r := &recording{
entries: make(map[string]os.FileInfo),
}
err := r.record(filename)
if err != nil {
return nil, err
}
return &itemToWatch{filename: filename, left: r}, nil
}
func (item *itemToWatch) checkForChanges() ([]fsnotify.Event, error) {
if item.right == nil {
item.right = &recording{
entries: make(map[string]os.FileInfo),
}
}
err := item.right.record(item.filename)
if err != nil && !herrors.IsNotExist(err) {
return nil, err
}
dirOp := checkChange(item.left.FileInfo, item.right.FileInfo)
if dirOp != 0 {
evs := []fsnotify.Event{fsnotify.Event{Op: dirOp, Name: item.filename}}
return evs, nil
}
if item.left.FileInfo == nil || !item.left.IsDir() {
// Done.
return nil, nil
}
leftIsIn := false
left, right := item.left.entries, item.right.entries
if len(right) > len(left) {
left, right = right, left
leftIsIn = true
}
var evs []fsnotify.Event
for name, fi1 := range left {
fi2 := right[name]
fil, fir := fi1, fi2
if leftIsIn {
fil, fir = fir, fil
}
op := checkChange(fil, fir)
if op != 0 {
evs = append(evs, fsnotify.Event{Op: op, Name: filepath.Join(item.filename, name)})
}
}
return evs, nil
}
func checkChange(fi1, fi2 os.FileInfo) fsnotify.Op {
if fi1 == nil && fi2 != nil {
return fsnotify.Create
}
if fi1 != nil && fi2 == nil {
return fsnotify.Remove
}
if fi1 == nil && fi2 == nil {
return 0
}
if fi1.IsDir() || fi2.IsDir() {
return 0
}
if fi1.Mode() != fi2.Mode() {
return fsnotify.Chmod
}
if fi1.ModTime() != fi2.ModTime() || fi1.Size() != fi2.Size() {
return fsnotify.Write
}
return 0
}