//go:build windows
// +build windows
// Windows backend based on ReadDirectoryChangesW()
//
// https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-readdirectorychangesw
//
// Note: the documentation on the Watcher type and methods is generated from
// mkdoc.zsh
package fsnotify
import (
"errors"
"fmt"
"os"
"path/filepath"
"reflect"
"runtime"
"strings"
"sync"
"unsafe"
"golang.org/x/sys/windows"
)
// 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
port windows.Handle // Handle to completion port
input chan *input // Inputs to the reader are sent on this channel
quit chan chan<- error
mu sync.Mutex // Protects access to watches, closed
watches watchMap // Map of watches (key: i-number)
closed bool // Set to true when Close() is first called
}
// NewWatcher creates a new Watcher.
func NewWatcher() (*Watcher, error) {
return NewBufferedWatcher(50)
}
// 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) {
port, err := windows.CreateIoCompletionPort(windows.InvalidHandle, 0, 0, 0)
if err != nil {
return nil, os.NewSyscallError("CreateIoCompletionPort", err)
}
w := &Watcher{
port: port,
watches: make(watchMap),
input: make(chan *input, 1),
Events: make(chan Event, sz),
Errors: make(chan error),
quit: make(chan chan<- error, 1),
}
go w.readEvents()
return w, nil
}
func (w *Watcher) isClosed() bool {
w.mu.Lock()
defer w.mu.Unlock()
return w.closed
}
func (w *Watcher) sendEvent(name string, mask uint64) bool {
if mask == 0 {
return false
}
event := w.newEvent(name, uint32(mask))
select {
case ch := <-w.quit:
w.quit <- ch
case w.Events <- event:
}
return true
}
// 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.quit:
}
return false
}
// Close removes all watches and closes the Events channel.
func (w *Watcher) Close() error {
if w.isClosed() {
return nil
}
w.mu.Lock()
w.closed = true
w.mu.Unlock()
// Send "quit" message to the reader goroutine
ch := make(chan error)
w.quit <- ch
if err := w.wakeupReader(); err != nil {
return err
}
return <-ch
}
// 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 {
if w.isClosed() {
return ErrClosed
}
with := getOptions(opts...)
if with.bufsize < 4096 {
return fmt.Errorf("fsnotify.WithBufferSize: buffer size cannot be smaller than 4096 bytes")
}
in := &input{
op: opAddWatch,
path: filepath.Clean(name),
flags: sysFSALLEVENTS,
reply: make(chan error),
bufsize: with.bufsize,
}
w.input <- in
if err := w.wakeupReader(); err != nil {
return err
}
return <-in.reply
}
// 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 {
if w.isClosed() {
return nil
}
in := &input{
op: opRemoveWatch,
path: filepath.Clean(name),
reply: make(chan error),
}
w.input <- in
if err := w.wakeupReader(); err != nil {
return err
}
return <-in.reply
}
// 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 {
if w.isClosed() {
return nil
}
w.mu.Lock()
defer w.mu.Unlock()
entries := make([]string, 0, len(w.watches))
for _, entry := range w.watches {
for _, watchEntry := range entry {
entries = append(entries, watchEntry.path)
}
}
return entries
}
// These options are from the old golang.org/x/exp/winfsnotify, where you could
// add various options to the watch. This has long since been removed.
//
// The "sys" in the name is misleading as they're not part of any "system".
//
// This should all be removed at some point, and just use windows.FILE_NOTIFY_*
const (
sysFSALLEVENTS = 0xfff
sysFSCREATE = 0x100
sysFSDELETE = 0x200
sysFSDELETESELF = 0x400
sysFSMODIFY = 0x2
sysFSMOVE = 0xc0
sysFSMOVEDFROM = 0x40
sysFSMOVEDTO = 0x80
sysFSMOVESELF = 0x800
sysFSIGNORED = 0x8000
)
func (w *Watcher) newEvent(name string, mask uint32) Event {
e := Event{Name: name}
if mask&sysFSCREATE == sysFSCREATE || mask&sysFSMOVEDTO == sysFSMOVEDTO {
e.Op |= Create
}
if mask&sysFSDELETE == sysFSDELETE || mask&sysFSDELETESELF == sysFSDELETESELF {
e.Op |= Remove
}
if mask&sysFSMODIFY == sysFSMODIFY {
e.Op |= Write
}
if mask&sysFSMOVE == sysFSMOVE || mask&sysFSMOVESELF == sysFSMOVESELF || mask&sysFSMOVEDFROM == sysFSMOVEDFROM {
e.Op |= Rename
}
return e
}
const (
opAddWatch = iota
opRemoveWatch
)
const (
provisional uint64 = 1 << (32 + iota)
)
type input struct {
op int
path string
flags uint32
bufsize int
reply chan error
}
type inode struct {
handle windows.Handle
volume uint32
index uint64
}
type watch struct {
ov windows.Overlapped
ino *inode // i-number
recurse bool // Recursive watch?
path string // Directory path
mask uint64 // Directory itself is being watched with these notify flags
names map[string]uint64 // Map of names being watched and their notify flags
rename string // Remembers the old name while renaming a file
buf []byte // buffer, allocated later
}
type (
indexMap map[uint64]*watch
watchMap map[uint32]indexMap
)
func (w *Watcher) wakeupReader() error {
err := windows.PostQueuedCompletionStatus(w.port, 0, 0, nil)
if err != nil {
return os.NewSyscallError("PostQueuedCompletionStatus", err)
}
return nil
}
func (w *Watcher) getDir(pathname string) (dir string, err error) {
attr, err := windows.GetFileAttributes(windows.StringToUTF16Ptr(pathname))
if err != nil {
return "", os.NewSyscallError("GetFileAttributes", err)
}
if attr&windows.FILE_ATTRIBUTE_DIRECTORY != 0 {
dir = pathname
} else {
dir, _ = filepath.Split(pathname)
dir = filepath.Clean(dir)
}
return
}
func (w *Watcher) getIno(path string) (ino *inode, err error) {
h, err := windows.CreateFile(windows.StringToUTF16Ptr(path),
windows.FILE_LIST_DIRECTORY,
windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE|windows.FILE_SHARE_DELETE,
nil, windows.OPEN_EXISTING,
windows.FILE_FLAG_BACKUP_SEMANTICS|windows.FILE_FLAG_OVERLAPPED, 0)
if err != nil {
return nil, os.NewSyscallError("CreateFile", err)
}
var fi windows.ByHandleFileInformation
err = windows.GetFileInformationByHandle(h, &fi)
if err != nil {
windows.CloseHandle(h)
return nil, os.NewSyscallError("GetFileInformationByHandle", err)
}
ino = &inode{
handle: h,
volume: fi.VolumeSerialNumber,
index: uint64(fi.FileIndexHigh)<<32 | uint64(fi.FileIndexLow),
}
return ino, nil
}
// Must run within the I/O thread.
func (m watchMap) get(ino *inode) *watch {
if i := m[ino.volume]; i != nil {
return i[ino.index]
}
return nil
}
// Must run within the I/O thread.
func (m watchMap) set(ino *inode, watch *watch) {
i := m[ino.volume]
if i == nil {
i = make(indexMap)
m[ino.volume] = i
}
i[ino.index] = watch
}
// Must run within the I/O thread.
func (w *Watcher) addWatch(pathname string, flags uint64, bufsize int) error {
//pathname, recurse := recursivePath(pathname)
recurse := false
dir, err := w.getDir(pathname)
if err != nil {
return err
}
ino, err := w.getIno(dir)
if err != nil {
return err
}
w.mu.Lock()
watchEntry := w.watches.get(ino)
w.mu.Unlock()
if watchEntry == nil {
_, err := windows.CreateIoCompletionPort(ino.handle, w.port, 0, 0)
if err != nil {
windows.CloseHandle(ino.handle)
return os.NewSyscallError("CreateIoCompletionPort", err)
}
watchEntry = &watch{
ino: ino,
path: dir,
names: make(map[string]uint64),
recurse: recurse,
buf: make([]byte, bufsize),
}
w.mu.Lock()
w.watches.set(ino, watchEntry)
w.mu.Unlock()
flags |= provisional
} else {
windows.CloseHandle(ino.handle)
}
if pathname == dir {
watchEntry.mask |= flags
} else {
watchEntry.names[filepath.Base(pathname)] |= flags
}
err = w.startRead(watchEntry)
if err != nil {
return err
}
if pathname == dir {
watchEntry.mask &= ^provisional
} else {
watchEntry.names[filepath.Base(pathname)] &= ^provisional
}
return nil
}
// Must run within the I/O thread.
func (w *Watcher) remWatch(pathname string) error {
pathname, recurse := recursivePath(pathname)
dir, err := w.getDir(pathname)
if err != nil {
return err
}
ino, err := w.getIno(dir)
if err != nil {
return err
}
w.mu.Lock()
watch := w.watches.get(ino)
w.mu.Unlock()
if recurse && !watch.recurse {
return fmt.Errorf("can't use \\... with non-recursive watch %q", pathname)
}
err = windows.CloseHandle(ino.handle)
if err != nil {
w.sendError(os.NewSyscallError("CloseHandle", err))
}
if watch == nil {
return fmt.Errorf("%w: %s", ErrNonExistentWatch, pathname)
}
if pathname == dir {
w.sendEvent(watch.path, watch.mask&sysFSIGNORED)
watch.mask = 0
} else {
name := filepath.Base(pathname)
w.sendEvent(filepath.Join(watch.path, name), watch.names[name]&sysFSIGNORED)
delete(watch.names, name)
}
return w.startRead(watch)
}
// Must run within the I/O thread.
func (w *Watcher) deleteWatch(watch *watch) {
for name, mask := range watch.names {
if mask&provisional == 0 {
w.sendEvent(filepath.Join(watch.path, name), mask&sysFSIGNORED)
}
delete(watch.names, name)
}
if watch.mask != 0 {
if watch.mask&provisional == 0 {
w.sendEvent(watch.path, watch.mask&sysFSIGNORED)
}
watch.mask = 0
}
}
// Must run within the I/O thread.
func (w *Watcher) startRead(watch *watch) error {
err := windows.CancelIo(watch.ino.handle)
if err != nil {
w.sendError(os.NewSyscallError("CancelIo", err))
w.deleteWatch(watch)
}
mask := w.toWindowsFlags(watch.mask)
for _, m := range watch.names {
mask |= w.toWindowsFlags(m)
}
if mask == 0 {
err := windows.CloseHandle(watch.ino.handle)
if err != nil {
w.sendError(os.NewSyscallError("CloseHandle", err))
}
w.mu.Lock()
delete(w.watches[watch.ino.volume], watch.ino.index)
w.mu.Unlock()
return nil
}
// We need to pass the array, rather than the slice.
hdr := (*reflect.SliceHeader)(unsafe.Pointer(&watch.buf))
rdErr := windows.ReadDirectoryChanges(watch.ino.handle,
(*byte)(unsafe.Pointer(hdr.Data)), uint32(hdr.Len),
watch.recurse, mask, nil, &watch.ov, 0)
if rdErr != nil {
err := os.NewSyscallError("ReadDirectoryChanges", rdErr)
if rdErr == windows.ERROR_ACCESS_DENIED && watch.mask&provisional == 0 {
// Watched directory was probably removed
w.sendEvent(watch.path, watch.mask&sysFSDELETESELF)
err = nil
}
w.deleteWatch(watch)
w.startRead(watch)
return err
}
return nil
}
// readEvents reads from the I/O completion port, converts the
// received events into Event objects and sends them via the Events channel.
// Entry point to the I/O thread.
func (w *Watcher) readEvents() {
var (
n uint32
key uintptr
ov *windows.Overlapped
)
runtime.LockOSThread()
for {
// This error is handled after the watch == nil check below.
qErr := windows.GetQueuedCompletionStatus(w.port, &n, &key, &ov, windows.INFINITE)
watch := (*watch)(unsafe.Pointer(ov))
if watch == nil {
select {
case ch := <-w.quit:
w.mu.Lock()
var indexes []indexMap
for _, index := range w.watches {
indexes = append(indexes, index)
}
w.mu.Unlock()
for _, index := range indexes {
for _, watch := range index {
w.deleteWatch(watch)
w.startRead(watch)
}
}
err := windows.CloseHandle(w.port)
if err != nil {
err = os.NewSyscallError("CloseHandle", err)
}
close(w.Events)
close(w.Errors)
ch <- err
return
case in := <-w.input:
switch in.op {
case opAddWatch:
in.reply <- w.addWatch(in.path, uint64(in.flags), in.bufsize)
case opRemoveWatch:
in.reply <- w.remWatch(in.path)
}
default:
}
continue
}
switch qErr {
case nil:
// No error
case windows.ERROR_MORE_DATA:
if watch == nil {
w.sendError(errors.New("ERROR_MORE_DATA has unexpectedly null lpOverlapped buffer"))
} else {
// The i/o succeeded but the buffer is full.
// In theory we should be building up a full packet.
// In practice we can get away with just carrying on.
n = uint32(unsafe.Sizeof(watch.buf))
}
case windows.ERROR_ACCESS_DENIED:
// Watched directory was probably removed
w.sendEvent(watch.path, watch.mask&sysFSDELETESELF)
w.deleteWatch(watch)
w.startRead(watch)
continue
case windows.ERROR_OPERATION_ABORTED:
// CancelIo was called on this handle
continue
default:
w.sendError(os.NewSyscallError("GetQueuedCompletionPort", qErr))
continue
}
var offset uint32
for {
if n == 0 {
w.sendError(ErrEventOverflow)
break
}
// Point "raw" to the event in the buffer
raw := (*windows.FileNotifyInformation)(unsafe.Pointer(&watch.buf[offset]))
// Create a buf that is the size of the path name
size := int(raw.FileNameLength / 2)
var buf []uint16
// TODO: Use unsafe.Slice in Go 1.17; https://stackoverflow.com/questions/51187973
sh := (*reflect.SliceHeader)(unsafe.Pointer(&buf))
sh.Data = uintptr(unsafe.Pointer(&raw.FileName))
sh.Len = size
sh.Cap = size
name := windows.UTF16ToString(buf)
fullname := filepath.Join(watch.path, name)
var mask uint64
switch raw.Action {
case windows.FILE_ACTION_REMOVED:
mask = sysFSDELETESELF
case windows.FILE_ACTION_MODIFIED:
mask = sysFSMODIFY
case windows.FILE_ACTION_RENAMED_OLD_NAME:
watch.rename = name
case windows.FILE_ACTION_RENAMED_NEW_NAME:
// Update saved path of all sub-watches.
old := filepath.Join(watch.path, watch.rename)
w.mu.Lock()
for _, watchMap := range w.watches {
for _, ww := range watchMap {
if strings.HasPrefix(ww.path, old) {
ww.path = filepath.Join(fullname, strings.TrimPrefix(ww.path, old))
}
}
}
w.mu.Unlock()
if watch.names[watch.rename] != 0 {
watch.names[name] |= watch.names[watch.rename]
delete(watch.names, watch.rename)
mask = sysFSMOVESELF
}
}
sendNameEvent := func() {
w.sendEvent(fullname, watch.names[name]&mask)
}
if raw.Action != windows.FILE_ACTION_RENAMED_NEW_NAME {
sendNameEvent()
}
if raw.Action == windows.FILE_ACTION_REMOVED {
w.sendEvent(fullname, watch.names[name]&sysFSIGNORED)
delete(watch.names, name)
}
w.sendEvent(fullname, watch.mask&w.toFSnotifyFlags(raw.Action))
if raw.Action == windows.FILE_ACTION_RENAMED_NEW_NAME {
fullname = filepath.Join(watch.path, watch.rename)
sendNameEvent()
}
// Move to the next event in the buffer
if raw.NextEntryOffset == 0 {
break
}
offset += raw.NextEntryOffset
// Error!
if offset >= n {
//lint:ignore ST1005 Windows should be capitalized
w.sendError(errors.New(
"Windows system assumed buffer larger than it is, events have likely been missed"))
break
}
}
if err := w.startRead(watch); err != nil {
w.sendError(err)
}
}
}
func (w *Watcher) toWindowsFlags(mask uint64) uint32 {
var m uint32
if mask&sysFSMODIFY != 0 {
m |= windows.FILE_NOTIFY_CHANGE_LAST_WRITE
}
if mask&(sysFSMOVE|sysFSCREATE|sysFSDELETE) != 0 {
m |= windows.FILE_NOTIFY_CHANGE_FILE_NAME | windows.FILE_NOTIFY_CHANGE_DIR_NAME
}
return m
}
func (w *Watcher) toFSnotifyFlags(action uint32) uint64 {
switch action {
case windows.FILE_ACTION_ADDED:
return sysFSCREATE
case windows.FILE_ACTION_REMOVED:
return sysFSDELETE
case windows.FILE_ACTION_MODIFIED:
return sysFSMODIFY
case windows.FILE_ACTION_RENAMED_OLD_NAME:
return sysFSMOVEDFROM
case windows.FILE_ACTION_RENAMED_NEW_NAME:
return sysFSMOVEDTO
}
return 0
}
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