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//! Generic Watcher implementation based on polling
//!
//! Checks the `watch`ed paths periodically to detect changes. This implementation only uses
//! Rust stdlib APIs and should work on all of the platforms it supports.
use crate::{EventHandler, RecursiveMode, Watcher, Config};
use std::{
collections::HashMap,
path::{Path, PathBuf},
sync::{
atomic::{AtomicBool, Ordering},
Arc, Mutex,
},
thread,
time::Duration,
};
use data::{DataBuilder, WatchData};
mod data {
use crate::{
event::{CreateKind, DataChange, Event, EventKind, MetadataKind, ModifyKind, RemoveKind},
EventHandler,
};
use filetime::FileTime;
use std::{
cell::RefCell,
collections::{hash_map::RandomState, HashMap},
fmt::{self, Debug},
fs::{self, File, Metadata},
hash::{BuildHasher, Hasher},
io::{self, Read},
path::{Path, PathBuf},
time::Instant,
};
use walkdir::WalkDir;
/// Builder for [`WatchData`] & [`PathData`].
pub(super) struct DataBuilder {
emitter: EventEmitter,
// TODO: May allow user setup their custom BuildHasher / BuildHasherDefault
// in future.
build_hasher: Option<RandomState>,
// current timestamp for building Data.
now: Instant,
}
impl DataBuilder {
pub(super) fn new<F>(event_handler: F, compare_content: bool) -> Self
where
F: EventHandler,
{
Self {
emitter: EventEmitter::new(event_handler),
build_hasher: compare_content.then(RandomState::default),
now: Instant::now(),
}
}
/// Update internal timestamp.
pub(super) fn update_timestamp(&mut self) {
self.now = Instant::now();
}
/// Create [`WatchData`].
///
/// This function will return `Err(_)` if can not retrieve metadata from
/// the path location. (e.g., not found).
pub(super) fn build_watch_data(
&self,
root: PathBuf,
is_recursive: bool,
) -> Option<WatchData> {
WatchData::new(self, root, is_recursive)
}
/// Create [`PathData`].
fn build_path_data(&self, meta_path: &MetaPath) -> PathData {
PathData::new(self, meta_path)
}
}
impl Debug for DataBuilder {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("DataBuilder")
.field("build_hasher", &self.build_hasher)
.field("now", &self.now)
.finish()
}
}
#[derive(Debug)]
pub(super) struct WatchData {
// config part, won't change.
root: PathBuf,
is_recursive: bool,
// current status part.
all_path_data: HashMap<PathBuf, PathData>,
}
impl WatchData {
/// Scan filesystem and create a new `WatchData`.
///
/// # Side effect
///
/// This function may send event by `data_builder.emitter`.
fn new(data_builder: &DataBuilder, root: PathBuf, is_recursive: bool) -> Option<Self> {
// If metadata read error at `root` path, it will emit
// a error event and stop to create the whole `WatchData`.
//
// QUESTION: inconsistent?
//
// When user try to *CREATE* a watch by `poll_watcher.watch(root, ..)`,
// if `root` path hit an io error, then watcher will reject to
// create this new watch.
//
// This may inconsistent with *POLLING* a watch. When watcher
// continue polling, io error at root path will not delete
// a existing watch. polling still working.
//
// So, consider a config file may not exists at first time but may
// create after a while, developer cannot watch it.
//
// FIXME: Can we always allow to watch a path, even file not
// found at this path?
if let Err(e) = fs::metadata(&root) {
data_builder.emitter.emit_io_err(e, &root);
return None;
}
let all_path_data =
Self::scan_all_path_data(data_builder, root.clone(), is_recursive).collect();
Some(Self {
root,
is_recursive,
all_path_data,
})
}
/// Rescan filesystem and update this `WatchData`.
///
/// # Side effect
///
/// This function may emit event by `data_builder.emitter`.
pub(super) fn rescan(&mut self, data_builder: &mut DataBuilder) {
// scan current filesystem.
for (path, new_path_data) in
Self::scan_all_path_data(data_builder, self.root.clone(), self.is_recursive)
{
let old_path_data = self
.all_path_data
.insert(path.clone(), new_path_data.clone());
// emit event
let event =
PathData::compare_to_event(path, old_path_data.as_ref(), Some(&new_path_data));
if let Some(event) = event {
data_builder.emitter.emit_ok(event);
}
}
// scan for disappeared paths.
let mut disappeared_paths = Vec::new();
for (path, path_data) in self.all_path_data.iter() {
if path_data.last_check < data_builder.now {
disappeared_paths.push(path.clone());
}
}
// remove disappeared paths
for path in disappeared_paths {
let old_path_data = self.all_path_data.remove(&path);
// emit event
let event = PathData::compare_to_event(path, old_path_data.as_ref(), None);
if let Some(event) = event {
data_builder.emitter.emit_ok(event);
}
}
}
/// Get all `PathData` by given configuration.
///
/// # Side Effect
///
/// This function may emit some IO Error events by `data_builder.emitter`.
fn scan_all_path_data(
data_builder: &'_ DataBuilder,
root: PathBuf,
is_recursive: bool,
) -> impl Iterator<Item = (PathBuf, PathData)> + '_ {
// WalkDir return only one entry if root is a file (not a folder),
// so we can use single logic to do the both file & dir's jobs.
//
// See: https://docs.rs/walkdir/2.0.1/walkdir/struct.WalkDir.html#method.new
WalkDir::new(root)
.follow_links(true)
.max_depth(Self::dir_scan_depth(is_recursive))
.into_iter()
//
// QUESTION: should we ignore IO Error?
//
// current implementation ignore some IO error, e.g.,
//
// - `.filter_map(|entry| entry.ok())`
// - all read error when hashing
//
// but the code also interest with `fs::metadata()` error and
// propagate to event handler. It may not consistent.
//
// FIXME: Should we emit all IO error events? Or ignore them all?
.filter_map(|entry| entry.ok())
.filter_map(|entry| match entry.metadata() {
Ok(metadata) => {
let path = entry.into_path();
let meta_path = MetaPath::from_parts_unchecked(path, metadata);
let data_path = data_builder.build_path_data(&meta_path);
Some((meta_path.into_path(), data_path))
}
Err(e) => {
// emit event.
let path = entry.into_path();
data_builder.emitter.emit_io_err(e, path);
None
}
})
}
fn dir_scan_depth(is_recursive: bool) -> usize {
if is_recursive {
usize::max_value()
} else {
1
}
}
}
/// Stored data for a one path locations.
///
/// See [`WatchData`] for more detail.
#[derive(Debug, Clone)]
struct PathData {
/// File updated time.
mtime: i64,
/// Content's hash value, only available if user request compare file
/// contents and read successful.
hash: Option<u64>,
/// Checked time.
last_check: Instant,
}
impl PathData {
/// Create a new `PathData`.
fn new(data_builder: &DataBuilder, meta_path: &MetaPath) -> PathData {
let metadata = meta_path.metadata();
PathData {
mtime: FileTime::from_last_modification_time(metadata).seconds(),
hash: data_builder
.build_hasher
.as_ref()
.filter(|_| metadata.is_file())
.and_then(|build_hasher| {
Self::get_content_hash(build_hasher, meta_path.path()).ok()
}),
last_check: data_builder.now,
}
}
/// Get hash value for the data content in given file `path`.
fn get_content_hash(build_hasher: &RandomState, path: &Path) -> io::Result<u64> {
let mut hasher = build_hasher.build_hasher();
let mut file = File::open(path)?;
let mut buf = [0; 512];
loop {
let n = match file.read(&mut buf) {
Ok(0) => break,
Ok(len) => len,
Err(e) if e.kind() == io::ErrorKind::Interrupted => continue,
Err(e) => return Err(e),
};
hasher.write(&buf[..n]);
}
Ok(hasher.finish())
}
/// Get [`Event`] by compare two optional [`PathData`].
fn compare_to_event<P>(
path: P,
old: Option<&PathData>,
new: Option<&PathData>,
) -> Option<Event>
where
P: Into<PathBuf>,
{
match (old, new) {
(Some(old), Some(new)) => {
if new.mtime > old.mtime {
Some(EventKind::Modify(ModifyKind::Metadata(
MetadataKind::WriteTime,
)))
} else if new.hash != old.hash {
Some(EventKind::Modify(ModifyKind::Data(DataChange::Any)))
} else {
None
}
}
(None, Some(_new)) => Some(EventKind::Create(CreateKind::Any)),
(Some(_old), None) => Some(EventKind::Remove(RemoveKind::Any)),
(None, None) => None,
}
.map(|event_kind| Event::new(event_kind).add_path(path.into()))
}
}
/// Compose path and its metadata.
///
/// This data structure designed for make sure path and its metadata can be
/// transferred in consistent way, and may avoid some duplicated
/// `fs::metadata()` function call in some situations.
#[derive(Debug)]
pub(super) struct MetaPath {
path: PathBuf,
metadata: Metadata,
}
impl MetaPath {
/// Create `MetaPath` by given parts.
///
/// # Invariant
///
/// User must make sure the input `metadata` are associated with `path`.
fn from_parts_unchecked(path: PathBuf, metadata: Metadata) -> Self {
Self { path, metadata }
}
fn path(&self) -> &Path {
&self.path
}
fn metadata(&self) -> &Metadata {
&self.metadata
}
fn into_path(self) -> PathBuf {
self.path
}
}
/// Thin wrapper for outer event handler, for easy to use.
struct EventEmitter(
// Use `RefCell` to make sure `emit()` only need shared borrow of self (&self).
// Use `Box` to make sure EventEmitter is Sized.
Box<RefCell<dyn EventHandler>>,
);
impl EventEmitter {
fn new<F: EventHandler>(event_handler: F) -> Self {
Self(Box::new(RefCell::new(event_handler)))
}
/// Emit single event.
fn emit(&self, event: crate::Result<Event>) {
self.0.borrow_mut().handle_event(event);
}
/// Emit event.
fn emit_ok(&self, event: Event) {
self.emit(Ok(event))
}
/// Emit io error event.
fn emit_io_err<E, P>(&self, err: E, path: P)
where
E: Into<io::Error>,
P: Into<PathBuf>,
{
self.emit(Err(crate::Error::io(err.into()).add_path(path.into())))
}
}
}
/// Polling based `Watcher` implementation.
///
/// By default scans through all files and checks for changed entries based on their change date.
/// Can also be changed to perform file content change checks.
///
/// See [Config] for more details.
#[derive(Debug)]
pub struct PollWatcher {
watches: Arc<Mutex<HashMap<PathBuf, WatchData>>>,
data_builder: Arc<Mutex<DataBuilder>>,
want_to_stop: Arc<AtomicBool>,
delay: Duration,
}
impl PollWatcher {
/// Create a new [PollWatcher], configured as needed.
pub fn new<F: EventHandler>(
event_handler: F,
config: Config,
) -> crate::Result<PollWatcher> {
let data_builder = DataBuilder::new(event_handler, config.compare_contents());
let poll_watcher = PollWatcher {
watches: Default::default(),
data_builder: Arc::new(Mutex::new(data_builder)),
want_to_stop: Arc::new(AtomicBool::new(false)),
delay: config.poll_interval(),
};
poll_watcher.run();
Ok(poll_watcher)
}
fn run(&self) {
let watches = Arc::clone(&self.watches);
let data_builder = Arc::clone(&self.data_builder);
let want_to_stop = Arc::clone(&self.want_to_stop);
let delay = self.delay;
let _ = thread::Builder::new()
.name("notify-rs poll loop".to_string())
.spawn(move || {
loop {
if want_to_stop.load(Ordering::SeqCst) {
break;
}
// HINT: Make sure always lock in the same order to avoid deadlock.
//
// FIXME: inconsistent: some place mutex poison cause panic,
// some place just ignore.
if let (Ok(mut watches), Ok(mut data_builder)) =
(watches.lock(), data_builder.lock())
{
data_builder.update_timestamp();
let vals = watches.values_mut();
for watch_data in vals {
watch_data.rescan(&mut data_builder);
}
}
// QUESTION: `actual_delay == process_time + delay`. Is it intended to?
//
// If not, consider fix it to:
//
// ```rust
// let still_need_to_delay = delay.checked_sub(data_builder.now.elapsed());
// if let Some(delay) = still_need_to_delay {
// thread::sleep(delay);
// }
// ```
thread::sleep(delay);
}
});
}
/// Watch a path location.
///
/// QUESTION: this function never return an Error, is it as intend?
/// Please also consider the IO Error event problem.
fn watch_inner(&mut self, path: &Path, recursive_mode: RecursiveMode) {
// HINT: Make sure always lock in the same order to avoid deadlock.
//
// FIXME: inconsistent: some place mutex poison cause panic, some place just ignore.
if let (Ok(mut watches), Ok(mut data_builder)) =
(self.watches.lock(), self.data_builder.lock())
{
data_builder.update_timestamp();
let watch_data =
data_builder.build_watch_data(path.to_path_buf(), recursive_mode.is_recursive());
// if create watch_data successful, add it to watching list.
if let Some(watch_data) = watch_data {
watches.insert(path.to_path_buf(), watch_data);
}
}
}
/// Unwatch a path.
///
/// Return `Err(_)` if given path has't be monitored.
fn unwatch_inner(&mut self, path: &Path) -> crate::Result<()> {
// FIXME: inconsistent: some place mutex poison cause panic, some place just ignore.
self.watches
.lock()
.unwrap()
.remove(path)
.map(|_| ())
.ok_or_else(crate::Error::watch_not_found)
}
}
impl Watcher for PollWatcher {
/// Create a new [PollWatcher].
fn new<F: EventHandler>(event_handler: F, config: Config) -> crate::Result<Self> {
Self::new(event_handler, config)
}
fn watch(&mut self, path: &Path, recursive_mode: RecursiveMode) -> crate::Result<()> {
self.watch_inner(path, recursive_mode);
Ok(())
}
fn unwatch(&mut self, path: &Path) -> crate::Result<()> {
self.unwatch_inner(path)
}
fn kind() -> crate::WatcherKind {
crate::WatcherKind::PollWatcher
}
}
impl Drop for PollWatcher {
fn drop(&mut self) {
self.want_to_stop.store(true, Ordering::Relaxed);
}
}
#[test]
fn poll_watcher_is_send_and_sync() {
fn check<T: Send + Sync>() {}
check::<PollWatcher>();
}