//go:build freebsd || openbsd || netbsd || dragonfly || darwin
// +build freebsd openbsd netbsd dragonfly darwin
// Note: the documentation on the Watcher type and methods is generated from
// mkdoc.zsh
package fsnotify
import (
"errors"
"fmt"
"os"
"path/filepath"
"sync"
"golang.org/x/sys/unix"
)
// Watcher watches a set of paths, delivering events on a channel.
//
// A watcher should not be copied (e.g. pass it by pointer, rather than by
// value).
//
// # Linux notes
//
// When a file is removed a Remove event won't be emitted until all file
// descriptors are closed, and deletes will always emit a Chmod. For example:
//
// fp := os.Open("file")
// os.Remove("file") // Triggers Chmod
// fp.Close() // Triggers Remove
//
// This is the event that inotify sends, so not much can be changed about this.
//
// The fs.inotify.max_user_watches sysctl variable specifies the upper limit
// for the number of watches per user, and fs.inotify.max_user_instances
// specifies the maximum number of inotify instances per user. Every Watcher you
// create is an "instance", and every path you add is a "watch".
//
// These are also exposed in /proc as /proc/sys/fs/inotify/max_user_watches and
// /proc/sys/fs/inotify/max_user_instances
//
// To increase them you can use sysctl or write the value to the /proc file:
//
// # Default values on Linux 5.18
// sysctl fs.inotify.max_user_watches=124983
// sysctl fs.inotify.max_user_instances=128
//
// To make the changes persist on reboot edit /etc/sysctl.conf or
// /usr/lib/sysctl.d/50-default.conf (details differ per Linux distro; check
// your distro's documentation):
//
// fs.inotify.max_user_watches=124983
// fs.inotify.max_user_instances=128
//
// Reaching the limit will result in a "no space left on device" or "too many open
// files" error.
//
// # kqueue notes (macOS, BSD)
//
// kqueue requires opening a file descriptor for every file that's being watched;
// so if you're watching a directory with five files then that's six file
// descriptors. You will run in to your system's "max open files" limit faster on
// these platforms.
//
// The sysctl variables kern.maxfiles and kern.maxfilesperproc can be used to
// control the maximum number of open files, as well as /etc/login.conf on BSD
// systems.
//
// # Windows notes
//
// Paths can be added as "C:\path\to\dir", but forward slashes
// ("C:/path/to/dir") will also work.
//
// When a watched directory is removed it will always send an event for the
// directory itself, but may not send events for all files in that directory.
// Sometimes it will send events for all times, sometimes it will send no
// events, and often only for some files.
//
// The default ReadDirectoryChangesW() buffer size is 64K, which is the largest
// value that is guaranteed to work with SMB filesystems. If you have many
// events in quick succession this may not be enough, and you will have to use
// [WithBufferSize] to increase the value.
type Watcher struct {
// Events sends the filesystem change events.
//
// fsnotify can send the following events; a "path" here can refer to a
// file, directory, symbolic link, or special file like a FIFO.
//
// fsnotify.Create A new path was created; this may be followed by one
// or more Write events if data also gets written to a
// file.
//
// fsnotify.Remove A path was removed.
//
// fsnotify.Rename A path was renamed. A rename is always sent with the
// old path as Event.Name, and a Create event will be
// sent with the new name. Renames are only sent for
// paths that are currently watched; e.g. moving an
// unmonitored file into a monitored directory will
// show up as just a Create. Similarly, renaming a file
// to outside a monitored directory will show up as
// only a Rename.
//
// fsnotify.Write A file or named pipe was written to. A Truncate will
// also trigger a Write. A single "write action"
// initiated by the user may show up as one or multiple
// writes, depending on when the system syncs things to
// disk. For example when compiling a large Go program
// you may get hundreds of Write events, and you may
// want to wait until you've stopped receiving them
// (see the dedup example in cmd/fsnotify).
//
// Some systems may send Write event for directories
// when the directory content changes.
//
// fsnotify.Chmod Attributes were changed. On Linux this is also sent
// when a file is removed (or more accurately, when a
// link to an inode is removed). On kqueue it's sent
// when a file is truncated. On Windows it's never
// sent.
Events chan Event
// Errors sends any errors.
//
// ErrEventOverflow is used to indicate there are too many events:
//
// - inotify: There are too many queued events (fs.inotify.max_queued_events sysctl)
// - windows: The buffer size is too small; WithBufferSize() can be used to increase it.
// - kqueue, fen: Not used.
Errors chan error
done chan struct{}
kq int // File descriptor (as returned by the kqueue() syscall).
closepipe [2]int // Pipe used for closing.
mu sync.Mutex // Protects access to watcher data
watches map[string]int // Watched file descriptors (key: path).
watchesByDir map[string]map[int]struct{} // Watched file descriptors indexed by the parent directory (key: dirname(path)).
userWatches map[string]struct{} // Watches added with Watcher.Add()
dirFlags map[string]uint32 // Watched directories to fflags used in kqueue.
paths map[int]pathInfo // File descriptors to path names for processing kqueue events.
fileExists map[string]struct{} // Keep track of if we know this file exists (to stop duplicate create events).
isClosed bool // Set to true when Close() is first called
}
type pathInfo struct {
name string
isDir bool
}
// NewWatcher creates a new Watcher.
func NewWatcher() (*Watcher, error) {
return NewBufferedWatcher(0)
}
// NewBufferedWatcher creates a new Watcher with a buffered Watcher.Events
// channel.
//
// The main use case for this is situations with a very large number of events
// where the kernel buffer size can't be increased (e.g. due to lack of
// permissions). An unbuffered Watcher will perform better for almost all use
// cases, and whenever possible you will be better off increasing the kernel
// buffers instead of adding a large userspace buffer.
func NewBufferedWatcher(sz uint) (*Watcher, error) {
kq, closepipe, err := newKqueue()
if err != nil {
return nil, err
}
w := &Watcher{
kq: kq,
closepipe: closepipe,
watches: make(map[string]int),
watchesByDir: make(map[string]map[int]struct{}),
dirFlags: make(map[string]uint32),
paths: make(map[int]pathInfo),
fileExists: make(map[string]struct{}),
userWatches: make(map[string]struct{}),
Events: make(chan Event, sz),
Errors: make(chan error),
done: make(chan struct{}),
}
go w.readEvents()
return w, nil
}
// newKqueue creates a new kernel event queue and returns a descriptor.
//
// This registers a new event on closepipe, which will trigger an event when
// it's closed. This way we can use kevent() without timeout/polling; without
// the closepipe, it would block forever and we wouldn't be able to stop it at
// all.
func newKqueue() (kq int, closepipe [2]int, err error) {
kq, err = unix.Kqueue()
if kq == -1 {
return kq, closepipe, err
}
// Register the close pipe.
err = unix.Pipe(closepipe[:])
if err != nil {
unix.Close(kq)
return kq, closepipe, err
}
// Register changes to listen on the closepipe.
changes := make([]unix.Kevent_t, 1)
// SetKevent converts int to the platform-specific types.
unix.SetKevent(&changes[0], closepipe[0], unix.EVFILT_READ,
unix.EV_ADD|unix.EV_ENABLE|unix.EV_ONESHOT)
ok, err := unix.Kevent(kq, changes, nil, nil)
if ok == -1 {
unix.Close(kq)
unix.Close(closepipe[0])
unix.Close(closepipe[1])
return kq, closepipe, err
}
return kq, closepipe, nil
}
// Returns true if the event was sent, or false if watcher is closed.
func (w *Watcher) sendEvent(e Event) bool {
select {
case w.Events <- e:
return true
case <-w.done:
return false
}
}
// Returns true if the error was sent, or false if watcher is closed.
func (w *Watcher) sendError(err error) bool {
select {
case w.Errors <- err:
return true
case <-w.done:
return false
}
}
// Close removes all watches and closes the Events channel.
func (w *Watcher) Close() error {
w.mu.Lock()
if w.isClosed {
w.mu.Unlock()
return nil
}
w.isClosed = true
// copy paths to remove while locked
pathsToRemove := make([]string, 0, len(w.watches))
for name := range w.watches {
pathsToRemove = append(pathsToRemove, name)
}
w.mu.Unlock() // Unlock before calling Remove, which also locks
for _, name := range pathsToRemove {
w.Remove(name)
}
// Send "quit" message to the reader goroutine.
unix.Close(w.closepipe[1])
close(w.done)
return nil
}
// Add starts monitoring the path for changes.
//
// A path can only be watched once; watching it more than once is a no-op and will
// not return an error. Paths that do not yet exist on the filesystem cannot be
// watched.
//
// A watch will be automatically removed if the watched path is deleted or
// renamed. The exception is the Windows backend, which doesn't remove the
// watcher on renames.
//
// Notifications on network filesystems (NFS, SMB, FUSE, etc.) or special
// filesystems (/proc, /sys, etc.) generally don't work.
//
// Returns [ErrClosed] if [Watcher.Close] was called.
//
// See [Watcher.AddWith] for a version that allows adding options.
//
// # Watching directories
//
// All files in a directory are monitored, including new files that are created
// after the watcher is started. Subdirectories are not watched (i.e. it's
// non-recursive).
//
// # Watching files
//
// Watching individual files (rather than directories) is generally not
// recommended as many programs (especially editors) update files atomically: it
// will write to a temporary file which is then moved to to destination,
// overwriting the original (or some variant thereof). The watcher on the
// original file is now lost, as that no longer exists.
//
// The upshot of this is that a power failure or crash won't leave a
// half-written file.
//
// Watch the parent directory and use Event.Name to filter out files you're not
// interested in. There is an example of this in cmd/fsnotify/file.go.
func (w *Watcher) Add(name string) error { return w.AddWith(name) }
// AddWith is like [Watcher.Add], but allows adding options. When using Add()
// the defaults described below are used.
//
// Possible options are:
//
// - [WithBufferSize] sets the buffer size for the Windows backend; no-op on
// other platforms. The default is 64K (65536 bytes).
func (w *Watcher) AddWith(name string, opts ...addOpt) error {
_ = getOptions(opts...)
w.mu.Lock()
w.userWatches[name] = struct{}{}
w.mu.Unlock()
_, err := w.addWatch(name, noteAllEvents)
return err
}
// Remove stops monitoring the path for changes.
//
// Directories are always removed non-recursively. For example, if you added
// /tmp/dir and /tmp/dir/subdir then you will need to remove both.
//
// Removing a path that has not yet been added returns [ErrNonExistentWatch].
//
// Returns nil if [Watcher.Close] was called.
func (w *Watcher) Remove(name string) error {
return w.remove(name, true)
}
func (w *Watcher) remove(name string, unwatchFiles bool) error {
name = filepath.Clean(name)
w.mu.Lock()
if w.isClosed {
w.mu.Unlock()
return nil
}
watchfd, ok := w.watches[name]
w.mu.Unlock()
if !ok {
return fmt.Errorf("%w: %s", ErrNonExistentWatch, name)
}
err := w.register([]int{watchfd}, unix.EV_DELETE, 0)
if err != nil {
return err
}
unix.Close(watchfd)
w.mu.Lock()
isDir := w.paths[watchfd].isDir
delete(w.watches, name)
delete(w.userWatches, name)
parentName := filepath.Dir(name)
delete(w.watchesByDir[parentName], watchfd)
if len(w.watchesByDir[parentName]) == 0 {
delete(w.watchesByDir, parentName)
}
delete(w.paths, watchfd)
delete(w.dirFlags, name)
delete(w.fileExists, name)
w.mu.Unlock()
// Find all watched paths that are in this directory that are not external.
if unwatchFiles && isDir {
var pathsToRemove []string
w.mu.Lock()
for fd := range w.watchesByDir[name] {
path := w.paths[fd]
if _, ok := w.userWatches[path.name]; !ok {
pathsToRemove = append(pathsToRemove, path.name)
}
}
w.mu.Unlock()
for _, name := range pathsToRemove {
// Since these are internal, not much sense in propagating error to
// the user, as that will just confuse them with an error about a
// path they did not explicitly watch themselves.
w.Remove(name)
}
}
return nil
}
// WatchList returns all paths explicitly added with [Watcher.Add] (and are not
// yet removed).
//
// Returns nil if [Watcher.Close] was called.
func (w *Watcher) WatchList() []string {
w.mu.Lock()
defer w.mu.Unlock()
if w.isClosed {
return nil
}
entries := make([]string, 0, len(w.userWatches))
for pathname := range w.userWatches {
entries = append(entries, pathname)
}
return entries
}
// Watch all events (except NOTE_EXTEND, NOTE_LINK, NOTE_REVOKE)
const noteAllEvents = unix.NOTE_DELETE | unix.NOTE_WRITE | unix.NOTE_ATTRIB | unix.NOTE_RENAME
// addWatch adds name to the watched file set; the flags are interpreted as
// described in kevent(2).
//
// Returns the real path to the file which was added, with symlinks resolved.
func (w *Watcher) addWatch(name string, flags uint32) (string, error) {
var isDir bool
name = filepath.Clean(name)
w.mu.Lock()
if w.isClosed {
w.mu.Unlock()
return "", ErrClosed
}
watchfd, alreadyWatching := w.watches[name]
// We already have a watch, but we can still override flags.
if alreadyWatching {
isDir = w.paths[watchfd].isDir
}
w.mu.Unlock()
if !alreadyWatching {
fi, err := os.Lstat(name)
if err != nil {
return "", err
}
// Don't watch sockets or named pipes
if (fi.Mode()&os.ModeSocket == os.ModeSocket) || (fi.Mode()&os.ModeNamedPipe == os.ModeNamedPipe) {
return "", nil
}
// Follow Symlinks.
if fi.Mode()&os.ModeSymlink == os.ModeSymlink {
link, err := os.Readlink(name)
if err != nil {
// Return nil because Linux can add unresolvable symlinks to the
// watch list without problems, so maintain consistency with
// that. There will be no file events for broken symlinks.
// TODO: more specific check; returns os.PathError; ENOENT?
return "", nil
}
w.mu.Lock()
_, alreadyWatching = w.watches[link]
w.mu.Unlock()
if alreadyWatching {
// Add to watches so we don't get spurious Create events later
// on when we diff the directories.
w.watches[name] = 0
w.fileExists[name] = struct{}{}
return link, nil
}
name = link
fi, err = os.Lstat(name)
if err != nil {
return "", nil
}
}
// Retry on EINTR; open() can return EINTR in practice on macOS.
// See #354, and Go issues 11180 and 39237.
for {
watchfd, err = unix.Open(name, openMode, 0)
if err == nil {
break
}
if errors.Is(err, unix.EINTR) {
continue
}
return "", err
}
isDir = fi.IsDir()
}
err := w.register([]int{watchfd}, unix.EV_ADD|unix.EV_CLEAR|unix.EV_ENABLE, flags)
if err != nil {
unix.Close(watchfd)
return "", err
}
if !alreadyWatching {
w.mu.Lock()
parentName := filepath.Dir(name)
w.watches[name] = watchfd
watchesByDir, ok := w.watchesByDir[parentName]
if !ok {
watchesByDir = make(map[int]struct{}, 1)
w.watchesByDir[parentName] = watchesByDir
}
watchesByDir[watchfd] = struct{}{}
w.paths[watchfd] = pathInfo{name: name, isDir: isDir}
w.mu.Unlock()
}
if isDir {
// Watch the directory if it has not been watched before, or if it was
// watched before, but perhaps only a NOTE_DELETE (watchDirectoryFiles)
w.mu.Lock()
watchDir := (flags&unix.NOTE_WRITE) == unix.NOTE_WRITE &&
(!alreadyWatching || (w.dirFlags[name]&unix.NOTE_WRITE) != unix.NOTE_WRITE)
// Store flags so this watch can be updated later
w.dirFlags[name] = flags
w.mu.Unlock()
if watchDir {
if err := w.watchDirectoryFiles(name); err != nil {
return "", err
}
}
}
return name, nil
}
// readEvents reads from kqueue and converts the received kevents into
// Event values that it sends down the Events channel.
func (w *Watcher) readEvents() {
defer func() {
close(w.Events)
close(w.Errors)
_ = unix.Close(w.kq)
unix.Close(w.closepipe[0])
}()
eventBuffer := make([]unix.Kevent_t, 10)
for closed := false; !closed; {
kevents, err := w.read(eventBuffer)
// EINTR is okay, the syscall was interrupted before timeout expired.
if err != nil && err != unix.EINTR {
if !w.sendError(fmt.Errorf("fsnotify.readEvents: %w", err)) {
closed = true
}
continue
}
// Flush the events we received to the Events channel
for _, kevent := range kevents {
var (
watchfd = int(kevent.Ident)
mask = uint32(kevent.Fflags)
)
// Shut down the loop when the pipe is closed, but only after all
// other events have been processed.
if watchfd == w.closepipe[0] {
closed = true
continue
}
w.mu.Lock()
path := w.paths[watchfd]
w.mu.Unlock()
event := w.newEvent(path.name, mask)
if event.Has(Rename) || event.Has(Remove) {
w.remove(event.Name, false)
w.mu.Lock()
delete(w.fileExists, event.Name)
w.mu.Unlock()
}
if path.isDir && event.Has(Write) && !event.Has(Remove) {
w.sendDirectoryChangeEvents(event.Name)
} else {
if !w.sendEvent(event) {
closed = true
continue
}
}
if event.Has(Remove) {
// Look for a file that may have overwritten this; for example,
// mv f1 f2 will delete f2, then create f2.
if path.isDir {
fileDir := filepath.Clean(event.Name)
w.mu.Lock()
_, found := w.watches[fileDir]
w.mu.Unlock()
if found {
err := w.sendDirectoryChangeEvents(fileDir)
if err != nil {
if !w.sendError(err) {
closed = true
}
}
}
} else {
filePath := filepath.Clean(event.Name)
if fi, err := os.Lstat(filePath); err == nil {
err := w.sendFileCreatedEventIfNew(filePath, fi)
if err != nil {
if !w.sendError(err) {
closed = true
}
}
}
}
}
}
}
}
// newEvent returns an platform-independent Event based on kqueue Fflags.
func (w *Watcher) newEvent(name string, mask uint32) Event {
e := Event{Name: name}
if mask&unix.NOTE_DELETE == unix.NOTE_DELETE {
e.Op |= Remove
}
if mask&unix.NOTE_WRITE == unix.NOTE_WRITE {
e.Op |= Write
}
if mask&unix.NOTE_RENAME == unix.NOTE_RENAME {
e.Op |= Rename
}
if mask&unix.NOTE_ATTRIB == unix.NOTE_ATTRIB {
e.Op |= Chmod
}
// No point sending a write and delete event at the same time: if it's gone,
// then it's gone.
if e.Op.Has(Write) && e.Op.Has(Remove) {
e.Op &^= Write
}
return e
}
// watchDirectoryFiles to mimic inotify when adding a watch on a directory
func (w *Watcher) watchDirectoryFiles(dirPath string) error {
// Get all files
files, err := os.ReadDir(dirPath)
if err != nil {
return err
}
for _, f := range files {
path := filepath.Join(dirPath, f.Name())
fi, err := f.Info()
if err != nil {
return fmt.Errorf("%q: %w", path, err)
}
cleanPath, err := w.internalWatch(path, fi)
if err != nil {
// No permission to read the file; that's not a problem: just skip.
// But do add it to w.fileExists to prevent it from being picked up
// as a "new" file later (it still shows up in the directory
// listing).
switch {
case errors.Is(err, unix.EACCES) || errors.Is(err, unix.EPERM):
cleanPath = filepath.Clean(path)
default:
return fmt.Errorf("%q: %w", path, err)
}
}
w.mu.Lock()
w.fileExists[cleanPath] = struct{}{}
w.mu.Unlock()
}
return nil
}
// Search the directory for new files and send an event for them.
//
// This functionality is to have the BSD watcher match the inotify, which sends
// a create event for files created in a watched directory.
func (w *Watcher) sendDirectoryChangeEvents(dir string) error {
files, err := os.ReadDir(dir)
if err != nil {
// Directory no longer exists: we can ignore this safely. kqueue will
// still give us the correct events.
if errors.Is(err, os.ErrNotExist) {
return nil
}
return fmt.Errorf("fsnotify.sendDirectoryChangeEvents: %w", err)
}
for _, f := range files {
fi, err := f.Info()
if err != nil {
return fmt.Errorf("fsnotify.sendDirectoryChangeEvents: %w", err)
}
err = w.sendFileCreatedEventIfNew(filepath.Join(dir, fi.Name()), fi)
if err != nil {
// Don't need to send an error if this file isn't readable.
if errors.Is(err, unix.EACCES) || errors.Is(err, unix.EPERM) {
return nil
}
return fmt.Errorf("fsnotify.sendDirectoryChangeEvents: %w", err)
}
}
return nil
}
// sendFileCreatedEvent sends a create event if the file isn't already being tracked.
func (w *Watcher) sendFileCreatedEventIfNew(filePath string, fi os.FileInfo) (err error) {
w.mu.Lock()
_, doesExist := w.fileExists[filePath]
w.mu.Unlock()
if !doesExist {
if !w.sendEvent(Event{Name: filePath, Op: Create}) {
return
}
}
// like watchDirectoryFiles (but without doing another ReadDir)
filePath, err = w.internalWatch(filePath, fi)
if err != nil {
return err
}
w.mu.Lock()
w.fileExists[filePath] = struct{}{}
w.mu.Unlock()
return nil
}
func (w *Watcher) internalWatch(name string, fi os.FileInfo) (string, error) {
if fi.IsDir() {
// mimic Linux providing delete events for subdirectories, but preserve
// the flags used if currently watching subdirectory
w.mu.Lock()
flags := w.dirFlags[name]
w.mu.Unlock()
flags |= unix.NOTE_DELETE | unix.NOTE_RENAME
return w.addWatch(name, flags)
}
// watch file to mimic Linux inotify
return w.addWatch(name, noteAllEvents)
}
// Register events with the queue.
func (w *Watcher) register(fds []int, flags int, fflags uint32) error {
changes := make([]unix.Kevent_t, len(fds))
for i, fd := range fds {
// SetKevent converts int to the platform-specific types.
unix.SetKevent(&changes[i], fd, unix.EVFILT_VNODE, flags)
changes[i].Fflags = fflags
}
// Register the events.
success, err := unix.Kevent(w.kq, changes, nil, nil)
if success == -1 {
return err
}
return nil
}
// read retrieves pending events, or waits until an event occurs.
func (w *Watcher) read(events []unix.Kevent_t) ([]unix.Kevent_t, error) {
n, err := unix.Kevent(w.kq, nil, events, nil)
if err != nil {
return nil, err
}
return events[0:n], nil
}
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