Rename vfs -> memofs across the codebase

memofs/src/in_memory_fs.rs

@@ -0,0 +1,249 @@
+use std::collections::{BTreeSet, HashMap, VecDeque};
+use std::io;
+use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex};
+
+use crossbeam_channel::{Receiver, Sender};
+
+use crate::{DirEntry, Metadata, ReadDir, VfsBackend, VfsEvent, VfsSnapshot};
+
+/// In-memory filesystem that can be used as a VFS backend.
+///
+/// Internally reference counted to enable giving a copy to
+/// [`Vfs`](struct.Vfs.html) and keeping the original to mutate the filesystem's
+/// state with.
+#[derive(Debug, Clone)]
+pub struct InMemoryFs {
+    inner: Arc<Mutex<InMemoryFsInner>>,
+}
+
+impl InMemoryFs {
+    /// Create a new empty `InMemoryFs`.
+    pub fn new() -> Self {
+        Self {
+            inner: Arc::new(Mutex::new(InMemoryFsInner::new())),
+        }
+    }
+
+    /// Load a [`VfsSnapshot`](enum.VfsSnapshot.html) into a subtree of the
+    /// in-memory filesystem.
+    ///
+    /// This function will return an error if the operations required to apply
+    /// the snapshot result in errors, like trying to create a file inside a
+    /// file.
+    pub fn load_snapshot<P: Into<PathBuf>>(
+        &mut self,
+        path: P,
+        snapshot: VfsSnapshot,
+    ) -> io::Result<()> {
+        let mut inner = self.inner.lock().unwrap();
+        inner.load_snapshot(path.into(), snapshot)
+    }
+
+    /// Raises a filesystem change event.
+    ///
+    /// If this `InMemoryFs` is being used as the backend of a
+    /// [`Vfs`](struct.Vfs.html), then any listeners be notified of this event.
+    pub fn raise_event(&mut self, event: VfsEvent) {
+        let inner = self.inner.lock().unwrap();
+        inner.event_sender.send(event).unwrap();
+    }
+}
+
+#[derive(Debug)]
+struct InMemoryFsInner {
+    entries: HashMap<PathBuf, Entry>,
+    orphans: BTreeSet<PathBuf>,
+
+    event_receiver: Receiver<VfsEvent>,
+    event_sender: Sender<VfsEvent>,
+}
+
+impl InMemoryFsInner {
+    fn new() -> Self {
+        let (event_sender, event_receiver) = crossbeam_channel::unbounded();
+
+        Self {
+            entries: HashMap::new(),
+            orphans: BTreeSet::new(),
+            event_receiver,
+            event_sender,
+        }
+    }
+
+    fn load_snapshot(&mut self, path: PathBuf, snapshot: VfsSnapshot) -> io::Result<()> {
+        if let Some(parent_path) = path.parent() {
+            if let Some(parent_entry) = self.entries.get_mut(parent_path) {
+                if let Entry::Dir { children } = parent_entry {
+                    children.insert(path.clone());
+                } else {
+                    return must_be_dir(parent_path);
+                }
+            } else {
+                self.orphans.insert(path.clone());
+            }
+        } else {
+            self.orphans.insert(path.clone());
+        }
+
+        match snapshot {
+            VfsSnapshot::File { contents } => {
+                self.entries.insert(path, Entry::File { contents });
+            }
+            VfsSnapshot::Dir { children } => {
+                self.entries.insert(
+                    path.clone(),
+                    Entry::Dir {
+                        children: BTreeSet::new(),
+                    },
+                );
+
+                for (child_name, child) in children {
+                    let full_path = path.join(child_name);
+                    self.load_snapshot(full_path, child)?;
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    fn remove(&mut self, root_path: PathBuf) {
+        self.orphans.remove(&root_path);
+
+        let mut to_remove = VecDeque::new();
+        to_remove.push_back(root_path);
+
+        while let Some(path) = to_remove.pop_front() {
+            if let Some(Entry::Dir { children }) = self.entries.remove(&path) {
+                to_remove.extend(children);
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+enum Entry {
+    File { contents: Vec<u8> },
+
+    Dir { children: BTreeSet<PathBuf> },
+}
+
+impl VfsBackend for InMemoryFs {
+    fn read(&mut self, path: &Path) -> io::Result<Vec<u8>> {
+        let inner = self.inner.lock().unwrap();
+
+        match inner.entries.get(path) {
+            Some(Entry::File { contents }) => Ok(contents.clone()),
+            Some(Entry::Dir { .. }) => must_be_file(path),
+            None => not_found(path),
+        }
+    }
+
+    fn write(&mut self, path: &Path, data: &[u8]) -> io::Result<()> {
+        let mut inner = self.inner.lock().unwrap();
+
+        inner.load_snapshot(
+            path.to_path_buf(),
+            VfsSnapshot::File {
+                contents: data.to_owned(),
+            },
+        )
+    }
+
+    fn read_dir(&mut self, path: &Path) -> io::Result<ReadDir> {
+        let inner = self.inner.lock().unwrap();
+
+        match inner.entries.get(path) {
+            Some(Entry::Dir { children }) => {
+                let iter = children
+                    .clone()
+                    .into_iter()
+                    .map(|path| Ok(DirEntry { path }));
+
+                Ok(ReadDir {
+                    inner: Box::new(iter),
+                })
+            }
+            Some(Entry::File { .. }) => must_be_dir(path),
+            None => not_found(path),
+        }
+    }
+
+    fn remove_file(&mut self, path: &Path) -> io::Result<()> {
+        let mut inner = self.inner.lock().unwrap();
+
+        match inner.entries.get(path) {
+            Some(Entry::File { .. }) => {
+                inner.remove(path.to_owned());
+                Ok(())
+            }
+            Some(Entry::Dir { .. }) => must_be_file(path),
+            None => not_found(path),
+        }
+    }
+
+    fn remove_dir_all(&mut self, path: &Path) -> io::Result<()> {
+        let mut inner = self.inner.lock().unwrap();
+
+        match inner.entries.get(path) {
+            Some(Entry::Dir { .. }) => {
+                inner.remove(path.to_owned());
+                Ok(())
+            }
+            Some(Entry::File { .. }) => must_be_dir(path),
+            None => not_found(path),
+        }
+    }
+
+    fn metadata(&mut self, path: &Path) -> io::Result<Metadata> {
+        let inner = self.inner.lock().unwrap();
+
+        match inner.entries.get(path) {
+            Some(Entry::File { .. }) => Ok(Metadata { is_file: true }),
+            Some(Entry::Dir { .. }) => Ok(Metadata { is_file: false }),
+            None => not_found(path),
+        }
+    }
+
+    fn event_receiver(&self) -> crossbeam_channel::Receiver<VfsEvent> {
+        let inner = self.inner.lock().unwrap();
+
+        inner.event_receiver.clone()
+    }
+
+    fn watch(&mut self, _path: &Path) -> io::Result<()> {
+        Ok(())
+    }
+
+    fn unwatch(&mut self, _path: &Path) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+fn must_be_file<T>(path: &Path) -> io::Result<T> {
+    Err(io::Error::new(
+        io::ErrorKind::Other,
+        format!(
+            "path {} was a directory, but must be a file",
+            path.display()
+        ),
+    ))
+}
+
+fn must_be_dir<T>(path: &Path) -> io::Result<T> {
+    Err(io::Error::new(
+        io::ErrorKind::Other,
+        format!(
+            "path {} was a file, but must be a directory",
+            path.display()
+        ),
+    ))
+}
+
+fn not_found<T>(path: &Path) -> io::Result<T> {
+    Err(io::Error::new(
+        io::ErrorKind::NotFound,
+        format!("path {} not found", path.display()),
+    ))
+}

memofs/src/lib.rs

@@ -0,0 +1,404 @@
+/*!
+Implementation of a virtual filesystem with a configurable backend and file
+watching.
+
+memofs is currently an unstable minimum viable library. Its primary consumer is
+[Rojo](https://github.com/rojo-rbx/rojo), a build system for Roblox.
+
+## Current Features
+* API similar to `std::fs`
+* Configurable backends
+    * `StdBackend`, which uses `std::fs` and the `notify` crate
+    * `NoopBackend`, which always throws errors
+    * `InMemoryFs`, a simple in-memory filesystem useful for testing
+
+## Future Features
+* Hash-based hierarchical memoization keys (hence the name)
+* Configurable caching (write-through, write-around, write-back)
+*/
+
+mod in_memory_fs;
+mod noop_backend;
+mod snapshot;
+mod std_backend;
+
+use std::io;
+use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex, MutexGuard};
+
+pub use in_memory_fs::InMemoryFs;
+pub use noop_backend::NoopBackend;
+pub use snapshot::VfsSnapshot;
+pub use std_backend::StdBackend;
+
+mod sealed {
+    use super::*;
+
+    /// Sealing trait for VfsBackend.
+    pub trait Sealed {}
+
+    impl Sealed for NoopBackend {}
+    impl Sealed for StdBackend {}
+    impl Sealed for InMemoryFs {}
+}
+
+/// Trait that transforms `io::Result<T>` into `io::Result<Option<T>>`.
+///
+/// `Ok(None)` takes the place of IO errors whose `io::ErrorKind` is `NotFound`.
+pub trait IoResultExt<T> {
+    fn with_not_found(self) -> io::Result<Option<T>>;
+}
+
+impl<T> IoResultExt<T> for io::Result<T> {
+    fn with_not_found(self) -> io::Result<Option<T>> {
+        match self {
+            Ok(v) => Ok(Some(v)),
+            Err(err) => {
+                if err.kind() == io::ErrorKind::NotFound {
+                    Ok(None)
+                } else {
+                    Err(err)
+                }
+            }
+        }
+    }
+}
+
+/// Backend that can be used to create a `Vfs`.
+///
+/// This trait is sealed and cannot not be implemented outside this crate.
+pub trait VfsBackend: sealed::Sealed + Send + 'static {
+    fn read(&mut self, path: &Path) -> io::Result<Vec<u8>>;
+    fn write(&mut self, path: &Path, data: &[u8]) -> io::Result<()>;
+    fn read_dir(&mut self, path: &Path) -> io::Result<ReadDir>;
+    fn metadata(&mut self, path: &Path) -> io::Result<Metadata>;
+    fn remove_file(&mut self, path: &Path) -> io::Result<()>;
+    fn remove_dir_all(&mut self, path: &Path) -> io::Result<()>;
+
+    fn event_receiver(&self) -> crossbeam_channel::Receiver<VfsEvent>;
+    fn watch(&mut self, path: &Path) -> io::Result<()>;
+    fn unwatch(&mut self, path: &Path) -> io::Result<()>;
+}
+
+/// Vfs equivalent to [`std::fs::DirEntry`][std::fs::DirEntry].
+///
+/// [std::fs::DirEntry]: https://doc.rust-lang.org/stable/std/fs/struct.DirEntry.html
+pub struct DirEntry {
+    pub(crate) path: PathBuf,
+}
+
+impl DirEntry {
+    pub fn path(&self) -> &Path {
+        &self.path
+    }
+}
+
+/// Vfs equivalent to [`std::fs::ReadDir`][std::fs::ReadDir].
+///
+/// [std::fs::ReadDir]: https://doc.rust-lang.org/stable/std/fs/struct.ReadDir.html
+pub struct ReadDir {
+    pub(crate) inner: Box<dyn Iterator<Item = io::Result<DirEntry>>>,
+}
+
+impl Iterator for ReadDir {
+    type Item = io::Result<DirEntry>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+}
+
+/// Vfs equivalent to [`std::fs::Metadata`][std::fs::Metadata].
+///
+/// [std::fs::Metadata]: https://doc.rust-lang.org/stable/std/fs/struct.Metadata.html
+#[derive(Debug)]
+pub struct Metadata {
+    pub(crate) is_file: bool,
+}
+
+impl Metadata {
+    pub fn is_file(&self) -> bool {
+        self.is_file
+    }
+
+    pub fn is_dir(&self) -> bool {
+        !self.is_file
+    }
+}
+
+/// Represents an event that a filesystem can raise that might need to be
+/// handled.
+#[derive(Debug)]
+#[non_exhaustive]
+pub enum VfsEvent {
+    Create(PathBuf),
+    Write(PathBuf),
+    Remove(PathBuf),
+}
+
+/// Contains implementation details of the Vfs, wrapped by `Vfs` and `VfsLock`,
+/// the public interfaces to this type.
+struct VfsInner {
+    backend: Box<dyn VfsBackend>,
+}
+
+impl VfsInner {
+    fn read<P: AsRef<Path>>(&mut self, path: P) -> io::Result<Arc<Vec<u8>>> {
+        let path = path.as_ref();
+        let contents = self.backend.read(path)?;
+        self.backend.watch(path)?;
+        Ok(Arc::new(contents))
+    }
+
+    fn write<P: AsRef<Path>, C: AsRef<[u8]>>(&mut self, path: P, contents: C) -> io::Result<()> {
+        let path = path.as_ref();
+        let contents = contents.as_ref();
+        self.backend.write(path, contents)
+    }
+
+    fn read_dir<P: AsRef<Path>>(&mut self, path: P) -> io::Result<ReadDir> {
+        let path = path.as_ref();
+        let dir = self.backend.read_dir(path)?;
+        self.backend.watch(path)?;
+        Ok(dir)
+    }
+
+    fn remove_file<P: AsRef<Path>>(&mut self, path: P) -> io::Result<()> {
+        let path = path.as_ref();
+        let _ = self.backend.unwatch(path);
+        self.backend.remove_file(path)
+    }
+
+    fn remove_dir_all<P: AsRef<Path>>(&mut self, path: P) -> io::Result<()> {
+        let path = path.as_ref();
+        let _ = self.backend.unwatch(path);
+        self.backend.remove_dir_all(path)
+    }
+
+    fn metadata<P: AsRef<Path>>(&mut self, path: P) -> io::Result<Metadata> {
+        let path = path.as_ref();
+        self.backend.metadata(path)
+    }
+
+    fn event_receiver(&self) -> crossbeam_channel::Receiver<VfsEvent> {
+        self.backend.event_receiver()
+    }
+
+    fn commit_event(&mut self, event: &VfsEvent) -> io::Result<()> {
+        match event {
+            VfsEvent::Remove(path) => {
+                let _ = self.backend.unwatch(&path);
+            }
+            _ => {}
+        }
+
+        Ok(())
+    }
+}
+
+/// A virtual filesystem with a configurable backend.
+///
+/// All operations on the Vfs take a lock on an internal backend. For performing
+/// large batches of operations, it might be more performant to call `lock()`
+/// and use [`VfsLock`](struct.VfsLock.html) instead.
+pub struct Vfs {
+    inner: Mutex<VfsInner>,
+}
+
+impl Vfs {
+    /// Creates a new `Vfs` with the default backend, `StdBackend`.
+    pub fn new_default() -> Self {
+        Self::new(StdBackend::new())
+    }
+
+    /// Creates a new `Vfs` with the given backend.
+    pub fn new<B: VfsBackend>(backend: B) -> Self {
+        let lock = VfsInner {
+            backend: Box::new(backend),
+        };
+
+        Self {
+            inner: Mutex::new(lock),
+        }
+    }
+
+    /// Manually lock the Vfs, useful for large batches of operations.
+    pub fn lock(&self) -> VfsLock<'_> {
+        VfsLock {
+            inner: self.inner.lock().unwrap(),
+        }
+    }
+
+    /// Read a file from the VFS, or the underlying backend if it isn't
+    /// resident.
+    ///
+    /// Roughly equivalent to [`std::fs::read`][std::fs::read].
+    ///
+    /// [std::fs::read]: https://doc.rust-lang.org/stable/std/fs/fn.read.html
+    #[inline]
+    pub fn read<P: AsRef<Path>>(&self, path: P) -> io::Result<Arc<Vec<u8>>> {
+        let path = path.as_ref();
+        self.inner.lock().unwrap().read(path)
+    }
+
+    /// Write a file to the VFS and the underlying backend.
+    ///
+    /// Roughly equivalent to [`std::fs::write`][std::fs::write].
+    ///
+    /// [std::fs::write]: https://doc.rust-lang.org/stable/std/fs/fn.write.html
+    #[inline]
+    pub fn write<P: AsRef<Path>, C: AsRef<[u8]>>(&self, path: P, contents: C) -> io::Result<()> {
+        let path = path.as_ref();
+        let contents = contents.as_ref();
+        self.inner.lock().unwrap().write(path, contents)
+    }
+
+    /// Read all of the children of a directory.
+    ///
+    /// Roughly equivalent to [`std::fs::read_dir`][std::fs::read_dir].
+    ///
+    /// [std::fs::read_dir]: https://doc.rust-lang.org/stable/std/fs/fn.read_dir.html
+    #[inline]
+    pub fn read_dir<P: AsRef<Path>>(&self, path: P) -> io::Result<ReadDir> {
+        let path = path.as_ref();
+        self.inner.lock().unwrap().read_dir(path)
+    }
+
+    /// Remove a file.
+    ///
+    /// Roughly equivalent to [`std::fs::remove_file`][std::fs::remove_file].
+    ///
+    /// [std::fs::remove_file]: https://doc.rust-lang.org/stable/std/fs/fn.remove_file.html
+    #[inline]
+    pub fn remove_file<P: AsRef<Path>>(&self, path: P) -> io::Result<()> {
+        let path = path.as_ref();
+        self.inner.lock().unwrap().remove_file(path)
+    }
+
+    /// Remove a directory and all of its descendants.
+    ///
+    /// Roughly equivalent to [`std::fs::remove_dir_all`][std::fs::remove_dir_all].
+    ///
+    /// [std::fs::remove_dir_all]: https://doc.rust-lang.org/stable/std/fs/fn.remove_dir_all.html
+    #[inline]
+    pub fn remove_dir_all<P: AsRef<Path>>(&self, path: P) -> io::Result<()> {
+        let path = path.as_ref();
+        self.inner.lock().unwrap().remove_dir_all(path)
+    }
+
+    /// Query metadata about the given path.
+    ///
+    /// Roughly equivalent to [`std::fs::metadata`][std::fs::metadata].
+    ///
+    /// [std::fs::metadata]: https://doc.rust-lang.org/stable/std/fs/fn.metadata.html
+    #[inline]
+    pub fn metadata<P: AsRef<Path>>(&self, path: P) -> io::Result<Metadata> {
+        let path = path.as_ref();
+        self.inner.lock().unwrap().metadata(path)
+    }
+
+    /// Retrieve a handle to the event receiver for this `Vfs`.
+    #[inline]
+    pub fn event_receiver(&self) -> crossbeam_channel::Receiver<VfsEvent> {
+        self.inner.lock().unwrap().event_receiver()
+    }
+
+    /// Commit an event to this `Vfs`.
+    #[inline]
+    pub fn commit_event(&self, event: &VfsEvent) -> io::Result<()> {
+        self.inner.lock().unwrap().commit_event(event)
+    }
+}
+
+/// A locked handle to a [`Vfs`](struct.Vfs.html), created by `Vfs::lock`.
+///
+/// Implements roughly the same API as [`Vfs`](struct.Vfs.html).
+pub struct VfsLock<'a> {
+    inner: MutexGuard<'a, VfsInner>,
+}
+
+impl VfsLock<'_> {
+    /// Read a file from the VFS, or the underlying backend if it isn't
+    /// resident.
+    ///
+    /// Roughly equivalent to [`std::fs::read`][std::fs::read].
+    ///
+    /// [std::fs::read]: https://doc.rust-lang.org/stable/std/fs/fn.read.html
+    #[inline]
+    pub fn read<P: AsRef<Path>>(&mut self, path: P) -> io::Result<Arc<Vec<u8>>> {
+        let path = path.as_ref();
+        self.inner.read(path)
+    }
+
+    /// Write a file to the VFS and the underlying backend.
+    ///
+    /// Roughly equivalent to [`std::fs::write`][std::fs::write].
+    ///
+    /// [std::fs::write]: https://doc.rust-lang.org/stable/std/fs/fn.write.html
+    #[inline]
+    pub fn write<P: AsRef<Path>, C: AsRef<[u8]>>(
+        &mut self,
+        path: P,
+        contents: C,
+    ) -> io::Result<()> {
+        let path = path.as_ref();
+        let contents = contents.as_ref();
+        self.inner.write(path, contents)
+    }
+
+    /// Read all of the children of a directory.
+    ///
+    /// Roughly equivalent to [`std::fs::read_dir`][std::fs::read_dir].
+    ///
+    /// [std::fs::read_dir]: https://doc.rust-lang.org/stable/std/fs/fn.read_dir.html
+    #[inline]
+    pub fn read_dir<P: AsRef<Path>>(&mut self, path: P) -> io::Result<ReadDir> {
+        let path = path.as_ref();
+        self.inner.read_dir(path)
+    }
+
+    /// Remove a file.
+    ///
+    /// Roughly equivalent to [`std::fs::remove_file`][std::fs::remove_file].
+    ///
+    /// [std::fs::remove_file]: https://doc.rust-lang.org/stable/std/fs/fn.remove_file.html
+    #[inline]
+    pub fn remove_file<P: AsRef<Path>>(&mut self, path: P) -> io::Result<()> {
+        let path = path.as_ref();
+        self.inner.remove_file(path)
+    }
+
+    /// Remove a directory and all of its descendants.
+    ///
+    /// Roughly equivalent to [`std::fs::remove_dir_all`][std::fs::remove_dir_all].
+    ///
+    /// [std::fs::remove_dir_all]: https://doc.rust-lang.org/stable/std/fs/fn.remove_dir_all.html
+    #[inline]
+    pub fn remove_dir_all<P: AsRef<Path>>(&mut self, path: P) -> io::Result<()> {
+        let path = path.as_ref();
+        self.inner.remove_dir_all(path)
+    }
+
+    /// Query metadata about the given path.
+    ///
+    /// Roughly equivalent to [`std::fs::metadata`][std::fs::metadata].
+    ///
+    /// [std::fs::metadata]: https://doc.rust-lang.org/stable/std/fs/fn.metadata.html
+    #[inline]
+    pub fn metadata<P: AsRef<Path>>(&mut self, path: P) -> io::Result<Metadata> {
+        let path = path.as_ref();
+        self.inner.metadata(path)
+    }
+
+    /// Retrieve a handle to the event receiver for this `Vfs`.
+    #[inline]
+    pub fn event_receiver(&self) -> crossbeam_channel::Receiver<VfsEvent> {
+        self.inner.event_receiver()
+    }
+
+    /// Commit an event to this `Vfs`.
+    #[inline]
+    pub fn commit_event(&mut self, event: &VfsEvent) -> io::Result<()> {
+        self.inner.commit_event(event)
+    }
+}

memofs/src/noop_backend.rs

@@ -0,0 +1,76 @@
+use std::io;
+use std::path::Path;
+
+use crate::{Metadata, ReadDir, VfsBackend, VfsEvent};
+
+/// `VfsBackend` that returns an error on every operation.
+#[non_exhaustive]
+pub struct NoopBackend;
+
+impl NoopBackend {
+    pub fn new() -> Self {
+        Self
+    }
+}
+
+impl VfsBackend for NoopBackend {
+    fn read(&mut self, _path: &Path) -> io::Result<Vec<u8>> {
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "NoopBackend doesn't do anything",
+        ))
+    }
+
+    fn write(&mut self, _path: &Path, _data: &[u8]) -> io::Result<()> {
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "NoopBackend doesn't do anything",
+        ))
+    }
+
+    fn read_dir(&mut self, _path: &Path) -> io::Result<ReadDir> {
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "NoopBackend doesn't do anything",
+        ))
+    }
+
+    fn remove_file(&mut self, _path: &Path) -> io::Result<()> {
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "NoopBackend doesn't do anything",
+        ))
+    }
+
+    fn remove_dir_all(&mut self, _path: &Path) -> io::Result<()> {
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "NoopBackend doesn't do anything",
+        ))
+    }
+
+    fn metadata(&mut self, _path: &Path) -> io::Result<Metadata> {
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "NoopBackend doesn't do anything",
+        ))
+    }
+
+    fn event_receiver(&self) -> crossbeam_channel::Receiver<VfsEvent> {
+        crossbeam_channel::never()
+    }
+
+    fn watch(&mut self, _path: &Path) -> io::Result<()> {
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "NoopBackend doesn't do anything",
+        ))
+    }
+
+    fn unwatch(&mut self, _path: &Path) -> io::Result<()> {
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "NoopBackend doesn't do anything",
+        ))
+    }
+}

memofs/src/snapshot.rs

@@ -0,0 +1,44 @@
+use std::collections::BTreeMap;
+
+/// A slice of a tree of files. Can be loaded into an
+/// [`InMemoryFs`](struct.InMemoryFs.html).
+#[derive(Debug)]
+#[non_exhaustive]
+pub enum VfsSnapshot {
+    File {
+        contents: Vec<u8>,
+    },
+
+    Dir {
+        children: BTreeMap<String, VfsSnapshot>,
+    },
+}
+
+impl VfsSnapshot {
+    pub fn file<C: Into<Vec<u8>>>(contents: C) -> Self {
+        Self::File {
+            contents: contents.into(),
+        }
+    }
+
+    pub fn dir<K: Into<String>, I: IntoIterator<Item = (K, VfsSnapshot)>>(children: I) -> Self {
+        Self::Dir {
+            children: children
+                .into_iter()
+                .map(|(key, value)| (key.into(), value))
+                .collect(),
+        }
+    }
+
+    pub fn empty_file() -> Self {
+        Self::File {
+            contents: Vec::new(),
+        }
+    }
+
+    pub fn empty_dir() -> Self {
+        Self::Dir {
+            children: BTreeMap::new(),
+        }
+    }
+}

memofs/src/std_backend.rs

@@ -0,0 +1,111 @@
+use std::fs;
+use std::io;
+use std::path::Path;
+use std::sync::mpsc;
+use std::thread;
+use std::time::Duration;
+
+use crossbeam_channel::Receiver;
+use notify::{watcher, DebouncedEvent, RecommendedWatcher, RecursiveMode, Watcher};
+
+use crate::{DirEntry, Metadata, ReadDir, VfsBackend, VfsEvent};
+
+/// `VfsBackend` that uses `std::fs` and the `notify` crate.
+pub struct StdBackend {
+    watcher: RecommendedWatcher,
+    watcher_receiver: Receiver<VfsEvent>,
+}
+
+impl StdBackend {
+    pub fn new() -> StdBackend {
+        let (notify_tx, notify_rx) = mpsc::channel();
+        let watcher = watcher(notify_tx, Duration::from_millis(50)).unwrap();
+
+        let (tx, rx) = crossbeam_channel::unbounded();
+
+        thread::spawn(move || {
+            for event in notify_rx {
+                match event {
+                    DebouncedEvent::Create(path) => {
+                        tx.send(VfsEvent::Create(path))?;
+                    }
+                    DebouncedEvent::Write(path) => {
+                        tx.send(VfsEvent::Write(path))?;
+                    }
+                    DebouncedEvent::Remove(path) => {
+                        tx.send(VfsEvent::Remove(path))?;
+                    }
+                    DebouncedEvent::Rename(from, to) => {
+                        tx.send(VfsEvent::Remove(from))?;
+                        tx.send(VfsEvent::Create(to))?;
+                    }
+                    _ => {}
+                }
+            }
+
+            Result::<(), crossbeam_channel::SendError<VfsEvent>>::Ok(())
+        });
+
+        Self {
+            watcher,
+            watcher_receiver: rx,
+        }
+    }
+}
+
+impl VfsBackend for StdBackend {
+    fn read(&mut self, path: &Path) -> io::Result<Vec<u8>> {
+        fs::read(path)
+    }
+
+    fn write(&mut self, path: &Path, data: &[u8]) -> io::Result<()> {
+        fs::write(path, data)
+    }
+
+    fn read_dir(&mut self, path: &Path) -> io::Result<ReadDir> {
+        let entries: Result<Vec<_>, _> = fs::read_dir(path)?.collect();
+        let mut entries = entries?;
+
+        entries.sort_by_cached_key(|entry| entry.file_name());
+
+        let inner = entries
+            .into_iter()
+            .map(|entry| Ok(DirEntry { path: entry.path() }));
+
+        Ok(ReadDir {
+            inner: Box::new(inner),
+        })
+    }
+
+    fn remove_file(&mut self, path: &Path) -> io::Result<()> {
+        fs::remove_file(path)
+    }
+
+    fn remove_dir_all(&mut self, path: &Path) -> io::Result<()> {
+        fs::remove_dir_all(path)
+    }
+
+    fn metadata(&mut self, path: &Path) -> io::Result<Metadata> {
+        let inner = fs::metadata(path)?;
+
+        Ok(Metadata {
+            is_file: inner.is_file(),
+        })
+    }
+
+    fn event_receiver(&self) -> crossbeam_channel::Receiver<VfsEvent> {
+        self.watcher_receiver.clone()
+    }
+
+    fn watch(&mut self, path: &Path) -> io::Result<()> {
+        self.watcher
+            .watch(path, RecursiveMode::NonRecursive)
+            .map_err(|inner| io::Error::new(io::ErrorKind::Other, inner))
+    }
+
+    fn unwatch(&mut self, path: &Path) -> io::Result<()> {
+        self.watcher
+            .unwatch(path)
+            .map_err(|inner| io::Error::new(io::ErrorKind::Other, inner))
+    }
+}