/
watcher.go
165 lines (142 loc) · 3.9 KB
/
watcher.go
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package watcher
import (
"fmt"
"os"
"path"
"path/filepath"
"strings"
"sync"
"github.com/fsnotify/fsnotify"
)
// Listener is an interface for receivers of filesystem events.
type Listener interface {
// Refresh is invoked by the watcher on relevant filesystem events.
// If the listener returns an error, it is served to the user on the current request.
Refresh() error
}
// Watcher allows listeners to register to be notified of changes under a given
// directory.
type Watcher struct {
// Parallel arrays of watcher/listener pairs.
watchers []*fsnotify.Watcher
listeners []Listener
lastError int
notifyMutex sync.Mutex
}
func New() *Watcher {
return &Watcher{
// forceRefresh: true,
lastError: -1,
}
}
// Listen registers for events within the given root directories (recursively).
func (w *Watcher) Listen(listener Listener, roots ...string) error {
watcher, err := fsnotify.NewWatcher()
if err != nil {
return err
}
// Replace the unbuffered Event channel with a buffered one.
// Otherwise multiple change events only come out one at a time, across
// multiple page views. (There appears no way to "pump" the events out of
// the watcher)
watcher.Events = make(chan fsnotify.Event, 100)
watcher.Errors = make(chan error, 10)
// Walk through all files / directories under the root, adding each to watcher.
for _, p := range roots {
// is the directory / file a symlink?
f, err := os.Lstat(p)
if err == nil && f.Mode()&os.ModeSymlink == os.ModeSymlink {
realPath, err := filepath.EvalSymlinks(p)
if err != nil {
panic(err)
}
p = realPath
}
fi, err := os.Stat(p)
if err != nil {
return fmt.Errorf("Failed to stat watched path %s: %w", p, err)
}
// If it is a file, watch that specific file.
if !fi.IsDir() {
err = watcher.Add(p)
if err != nil {
return fmt.Errorf("Failed to watch %s: %w", p, err)
}
continue
}
var watcherWalker func(path string, info os.FileInfo, err error) error
watcherWalker = func(path string, info os.FileInfo, err error) error {
if err != nil {
return err
}
// is it a symlinked template?
link, err := os.Lstat(path)
if err == nil && link.Mode()&os.ModeSymlink == os.ModeSymlink {
// lookup the actual target & check for goodness
targetPath, err := filepath.EvalSymlinks(path)
if err != nil {
return fmt.Errorf("failed to read symlink %s: %w", path, err)
}
targetInfo, err := os.Stat(targetPath)
if err != nil {
return fmt.Errorf("failed to stat symlink target %s of %s: %w", targetPath, path, err)
}
// set the template path to the target of the symlink
path = targetPath
info = targetInfo
if err := filepath.Walk(path, watcherWalker); err != nil {
return err
}
}
if info.IsDir() {
if err := watcher.Add(path); err != nil {
return err
}
}
return nil
}
// Else, walk the directory tree.
if err := filepath.Walk(p, watcherWalker); err != nil {
return fmt.Errorf("error walking path %s: %w", p, err)
}
}
w.watchers = append(w.watchers, watcher)
w.listeners = append(w.listeners, listener)
return nil
}
// Notify causes the watcher to forward any change events to listeners.
// It returns the first (if any) error returned.
func (w *Watcher) Notify() error {
// Serialize Notify() calls.
w.notifyMutex.Lock()
defer w.notifyMutex.Unlock()
for idx, watcher := range w.watchers {
listener := w.listeners[idx]
// Pull all pending events / errors from the watcher.
refresh := false
for {
select {
case ev := <-watcher.Events:
// Ignore changes to dotfiles.
if !strings.HasPrefix(path.Base(ev.Name), ".") {
refresh = true
}
continue
case <-watcher.Errors:
continue
default:
// No events left to pull
}
break
}
if refresh || w.lastError == idx {
err := listener.Refresh()
if err != nil {
w.lastError = idx
return err
}
}
}
w.lastError = -1
return nil
}