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use std::{
collections::HashSet,
fmt::Debug,
io::{self, SeekFrom},
path::{Path, PathBuf},
pin::Pin,
sync::Arc,
task::{Context, Poll},
};
use futures::future::BoxFuture;
use replace_with::replace_with_or_abort;
use tokio::io::{AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};
use crate::{
ops, FileOpener, FileSystem, FileSystems, FsError, Metadata, OpenOptions, OpenOptionsConfig,
ReadDir, VirtualFile,
};
/// A primary filesystem and chain of secondary filesystems that are overlayed
/// on top of each other.
///
/// # Precedence
///
/// The [`OverlayFileSystem`] will execute operations based on precedence.
///
///
/// Most importantly, this means earlier filesystems can shadow files and
/// directories that have a lower precedence.
///
///# Examples
///
/// Something useful to know is that the [`FileSystems`] trait is implemented
/// for both arrays and tuples.
///
/// For example, if you want to create a [`crate::FileSystem`] which will
/// create files in-memory while still being able to read from the host, you
/// might do something like this:
///
/// ```rust
/// use virtual_fs::{
/// mem_fs::FileSystem as MemFS,
/// host_fs::FileSystem as HostFS,
/// OverlayFileSystem,
/// };
///
/// let runtime = tokio::runtime::Builder::new_current_thread()
/// .enable_all()
/// .build()
/// .unwrap();
/// let _guard = runtime.enter();
///
/// let fs = OverlayFileSystem::new(MemFS::default(), [HostFS::new(tokio::runtime::Handle::current(), "/").unwrap()]);
///
/// // This also has the benefit of storing the two values in-line with no extra
/// // overhead or indirection.
/// assert_eq!(
/// std::mem::size_of_val(&fs),
/// std::mem::size_of::<(MemFS, HostFS)>(),
/// );
/// ```
///
/// A more complex example is
#[derive(Clone, PartialEq, Eq)]
pub struct OverlayFileSystem<P, S> {
primary: Arc<P>,
secondaries: S,
}
impl<P, S> OverlayFileSystem<P, S>
where
P: FileSystem + Send + Sync + 'static,
S: for<'a> FileSystems<'a> + Send + Sync + 'static,
{
/// Create a new [`FileSystem`] using a primary [`crate::FileSystem`] and a
/// chain of secondary [`FileSystems`].
pub fn new(primary: P, secondaries: S) -> Self {
OverlayFileSystem {
primary: Arc::new(primary),
secondaries,
}
}
/// Get a reference to the primary filesystem.
pub fn primary(&self) -> &P {
&self.primary
}
/// Get a reference to the secondary filesystems.
pub fn secondaries(&self) -> &S {
&self.secondaries
}
/// Get a mutable reference to the secondary filesystems.
pub fn secondaries_mut(&mut self) -> &mut S {
&mut self.secondaries
}
fn permission_error_or_not_found(&self, path: &Path) -> Result<(), FsError> {
for fs in self.secondaries.filesystems() {
if ops::exists(fs, path) {
return Err(FsError::PermissionDenied);
}
}
Err(FsError::EntryNotFound)
}
}
impl<P, S> FileSystem for OverlayFileSystem<P, S>
where
P: FileSystem + Send + 'static,
S: for<'a> FileSystems<'a> + Send + Sync + 'static,
for<'a> <<S as FileSystems<'a>>::Iter as IntoIterator>::IntoIter: Send,
{
fn readlink(&self, path: &Path) -> crate::Result<PathBuf> {
// Whiteout files can not be read, they are just markers
if ops::is_white_out(path).is_some() {
return Err(FsError::EntryNotFound);
}
// Check if the file is in the primary
match self.primary.readlink(path) {
Ok(meta) => return Ok(meta),
Err(e) if should_continue(e) => {}
Err(e) => return Err(e),
}
// There might be a whiteout, search for this
if ops::has_white_out(&self.primary, path) {
return Err(FsError::EntryNotFound);
}
// Otherwise scan the secondaries
for fs in self.secondaries.filesystems() {
match fs.readlink(path) {
Err(e) if should_continue(e) => continue,
other => return other,
}
}
Err(FsError::EntryNotFound)
}
fn read_dir(&self, path: &Path) -> Result<ReadDir, FsError> {
let mut entries = Vec::new();
let mut had_at_least_one_success = false;
let mut white_outs = HashSet::new();
let filesystems = std::iter::once(&self.primary as &(dyn FileSystem + Send))
.chain(self.secondaries().filesystems());
for fs in filesystems {
match fs.read_dir(path) {
Ok(r) => {
for entry in r {
let entry = entry?;
// White out entries block any later entries in the secondaries
// unless the entry has comes before the white out, thus the order
// that the file systems are parsed is important to this logic.
if let Some(path) = entry.is_white_out() {
tracing::trace!(
path=%path.display(),
"Found whiteout file",
);
white_outs.insert(path);
continue;
} else if white_outs.contains(&entry.path) {
tracing::trace!(
path=%path.display(),
"Skipping path because a whiteout exists",
);
continue;
}
entries.push(entry);
}
had_at_least_one_success = true;
}
Err(e) if should_continue(e) => continue,
Err(e) => return Err(e),
}
}
if had_at_least_one_success {
// Make sure later entries are removed in favour of earlier ones.
// Note: this sort is guaranteed to be stable, meaning filesystems
// "higher up" the chain will be further towards the start and kept
// when deduplicating.
entries.sort_by(|a, b| a.path.cmp(&b.path));
entries.dedup_by(|a, b| a.path == b.path);
Ok(ReadDir::new(entries))
} else {
Err(FsError::BaseNotDirectory)
}
}
fn create_dir(&self, path: &Path) -> Result<(), FsError> {
// You can not create directories that use the whiteout prefix
if ops::is_white_out(path).is_some() {
return Err(FsError::InvalidInput);
}
// It could be the case that the directory was earlier hidden in the secondaries
// by a whiteout file, hence we need to make sure those are cleared out.
ops::remove_white_out(self.primary.as_ref(), path);
// Make sure the parent tree is in place on the primary, this is to cover the
// scenario where the secondaries has a parent structure that is not yet in the
// primary and the primary needs it to create a sub-directory
if let Some(parent) = path.parent() {
if self.read_dir(parent).is_ok() {
ops::create_dir_all(&self.primary, parent).ok();
}
}
// Create the directory in the primary
match self.primary.create_dir(path) {
Err(e) if should_continue(e) => {}
other => return other,
}
self.permission_error_or_not_found(path)
}
fn remove_dir(&self, path: &Path) -> Result<(), FsError> {
// Whiteout files can not be removed, instead the original directory
// must be removed or recreated.
if ops::is_white_out(path).is_some() {
tracing::trace!(
path=%path.display(),
"Unable to remove a whited out directory",
);
return Err(FsError::EntryNotFound);
}
// If the directory is contained in a secondary file system then we need to create a
// whiteout file so that it is suppressed and is no longer returned in `readdir` calls.
let had_at_least_one_success = self.secondaries.filesystems().into_iter().any(|fs| {
fs.read_dir(path).is_ok() && ops::create_white_out(&self.primary, path).is_ok()
});
// Attempt to remove it from the primary, if this succeeds then we may have also
// added the whiteout file in the earlier step, but are required in this case to
// properly delete the directory.
match self.primary.remove_dir(path) {
Err(e) if should_continue(e) => {}
other => return other,
}
if had_at_least_one_success {
return Ok(());
}
self.permission_error_or_not_found(path)
}
fn rename<'a>(&'a self, from: &'a Path, to: &'a Path) -> BoxFuture<'a, Result<(), FsError>> {
let from = from.to_owned();
let to = to.to_owned();
Box::pin(async move {
// Whiteout files can not be renamed
if ops::is_white_out(&from).is_some() {
tracing::trace!(
from=%from.display(),
to=%to.display(),
"Attempting to rename a file that was whited out"
);
return Err(FsError::EntryNotFound);
}
// You can not rename a file into a whiteout file
if ops::is_white_out(&to).is_some() {
tracing::trace!(
from=%from.display(),
to=%to.display(),
"Attempting to rename a file into a whiteout file"
);
return Err(FsError::InvalidInput);
}
// We attempt to rename the file or directory in the primary
// if this succeeds then we also need to ensure the white out
// files are created where we need them, so we do not immediately
// return until that is done
let mut had_at_least_one_success = false;
match self.primary.rename(&from, &to).await {
Err(e) if should_continue(e) => {}
Ok(()) => {
had_at_least_one_success = true;
}
other => return other,
}
// If we have not yet renamed the file it may still reside in
// the secondaries, in which case we need to copy it to the
// primary rather than rename it
if !had_at_least_one_success {
for fs in self.secondaries.filesystems() {
if fs.metadata(&from).is_ok() {
ops::copy_reference_ext(fs, &self.primary, &from, &to).await?;
had_at_least_one_success = true;
break;
}
}
}
// If the rename operation was a success then we need to update any
// whiteout files on the primary before we return success.
if had_at_least_one_success {
for fs in self.secondaries.filesystems() {
if fs.metadata(&from).is_ok() {
tracing::trace!(
path=%from.display(),
"Creating a whiteout for the file that was renamed",
);
ops::create_white_out(&self.primary, &from).ok();
break;
}
}
ops::remove_white_out(&self.primary, &to);
return Ok(());
}
// Otherwise we are in a failure scenario
self.permission_error_or_not_found(&from)
})
}
fn metadata(&self, path: &Path) -> Result<Metadata, FsError> {
// Whiteout files can not be read, they are just markers
if ops::is_white_out(path).is_some() {
return Err(FsError::EntryNotFound);
}
// Check if the file is in the primary
match self.primary.metadata(path) {
Ok(meta) => return Ok(meta),
Err(e) if should_continue(e) => {}
Err(e) => return Err(e),
}
// There might be a whiteout, search for this
if ops::has_white_out(&self.primary, path) {
return Err(FsError::EntryNotFound);
}
// Otherwise scan the secondaries
for fs in self.secondaries.filesystems() {
match fs.metadata(path) {
Err(e) if should_continue(e) => continue,
other => return other,
}
}
Err(FsError::EntryNotFound)
}
fn symlink_metadata(&self, path: &Path) -> crate::Result<Metadata> {
// Whiteout files can not be read, they are just markers
if ops::is_white_out(path).is_some() {
return Err(FsError::EntryNotFound);
}
// Check if the file is in the primary
match self.primary.symlink_metadata(path) {
Ok(meta) => return Ok(meta),
Err(e) if should_continue(e) => {}
Err(e) => return Err(e),
}
// There might be a whiteout, search for this
if ops::has_white_out(&self.primary, path) {
return Err(FsError::EntryNotFound);
}
// Otherwise scan the secondaries
for fs in self.secondaries.filesystems() {
match fs.symlink_metadata(path) {
Err(e) if should_continue(e) => continue,
other => return other,
}
}
Err(FsError::EntryNotFound)
}
fn remove_file(&self, path: &Path) -> Result<(), FsError> {
// It is not possible to delete whiteout files directly, instead
// one must delete the original file
if ops::is_white_out(path).is_some() {
return Err(FsError::InvalidInput);
}
// If the file is contained in a secondary then then we need to create a
// whiteout file so that it is suppressed.
let had_at_least_one_success = self.secondaries.filesystems().into_iter().any(|fs| {
fs.metadata(path).is_ok() && ops::create_white_out(&self.primary, path).is_ok()
});
// Attempt to remove it from the primary
match self.primary.remove_file(path) {
Err(e) if should_continue(e) => {}
other => return other,
}
if had_at_least_one_success {
return Ok(());
}
self.permission_error_or_not_found(path)
}
fn new_open_options(&self) -> OpenOptions<'_> {
OpenOptions::new(self)
}
fn mount(
&self,
_name: String,
_path: &Path,
_fs: Box<dyn FileSystem + Send + Sync>,
) -> Result<(), FsError> {
Err(FsError::Unsupported)
}
}
impl<P, S> FileOpener for OverlayFileSystem<P, S>
where
P: FileSystem + Send + 'static,
S: for<'a> FileSystems<'a> + Send + Sync + 'static,
for<'a> <<S as FileSystems<'a>>::Iter as IntoIterator>::IntoIter: Send,
{
fn open(
&self,
path: &Path,
conf: &OpenOptionsConfig,
) -> Result<Box<dyn VirtualFile + Send + Sync + 'static>, FsError> {
// Whiteout files can not be read, they are just markers
if ops::is_white_out(path).is_some() {
tracing::trace!(
path=%path.display(),
options=?conf,
"Whiteout files can't be opened",
);
return Err(FsError::InvalidInput);
}
// Check if the file is in the primary (without actually creating it) as
// when the file is in the primary it takes preference over any of file
{
let mut conf = conf.clone();
conf.create = false;
conf.create_new = false;
match self.primary.new_open_options().options(conf).open(path) {
Err(e) if should_continue(e) => {}
other => return other,
}
}
// In the scenario that we are creating the file then there is
// special handling that will ensure its setup correctly
if conf.create_new {
// When the secondary has the directory structure but the primary
// does not then we need to make sure we create all the structure
// in the primary
if let Some(parent) = path.parent() {
if ops::exists(self, parent) {
// We create the directory structure on the primary so that
// the new file can be created, this will make it override
// whatever is in the primary
ops::create_dir_all(&self.primary, parent)?;
} else {
return Err(FsError::EntryNotFound);
}
}
// Remove any whiteout
ops::remove_white_out(&self.primary, path);
// Create the file in the primary
return self
.primary
.new_open_options()
.options(conf.clone())
.open(path);
}
// There might be a whiteout, search for this and if its found then
// we are done as the secondary file or directory has been earlier
// deleted via a white out (when the create flag is set then
// the white out marker is ignored)
if !conf.create && ops::has_white_out(&self.primary, path) {
tracing::trace!(
path=%path.display(),
"The file has been whited out",
);
return Err(FsError::EntryNotFound);
}
// Determine if a mutation will be possible with the opened file
let require_mutations = conf.append || conf.write || conf.create_new | conf.truncate;
// If the file is on a secondary then we should open it
if !ops::has_white_out(&self.primary, path) {
for fs in self.secondaries.filesystems() {
let mut sub_conf = conf.clone();
sub_conf.create = false;
sub_conf.create_new = false;
sub_conf.append = false;
sub_conf.truncate = false;
match fs.new_open_options().options(sub_conf.clone()).open(path) {
Err(e) if should_continue(e) => continue,
Ok(file) if require_mutations => {
// If the file was opened with the ability to mutate then we need
// to return a copy on write emulation so that the file can be
// copied from the secondary to the primary in the scenario that
// it is edited
return open_copy_on_write(path, conf, &self.primary, file);
}
other => return other,
}
}
}
// If we are creating the file then do so
if conf.create {
// Create the parent structure and remove any whiteouts
if let Some(parent) = path.parent() {
if ops::exists(self, parent) {
ops::create_dir_all(&self.primary, parent)?;
}
}
ops::remove_white_out(&self.primary, path);
// Create the file in the primary
return self
.primary
.new_open_options()
.options(conf.clone())
.open(path);
}
// The file does not exist anywhere
Err(FsError::EntryNotFound)
}
}
fn open_copy_on_write<P>(
path: &Path,
conf: &OpenOptionsConfig,
primary: &Arc<P>,
file: Box<dyn VirtualFile + Send + Sync>,
) -> Result<Box<dyn VirtualFile + Send + Sync>, FsError>
where
P: FileSystem,
{
struct CopyOnWriteFile<P> {
path: PathBuf,
primary: Arc<P>,
state: CowState,
readable: bool,
append: bool,
new_size: Option<u64>,
}
enum CowState {
// The original file is still open and can be accessed for all
// read operations
ReadOnly(Box<dyn VirtualFile + Send + Sync>),
// The copy has started but first we need to get the cursor
// position within the source file so that it can be restored
SeekingGet(Box<dyn VirtualFile + Send + Sync>),
// Now we have the original starting cursor location we need
// to move the position of the read to the start of the source
// file
SeekingSet {
original_offset: u64,
src: Box<dyn VirtualFile + Send + Sync>,
},
// We are now copying the data in parts held in the buffer piece
// by piece until the original file is completely copied
Copying {
original_offset: u64,
buf: Vec<u8>,
buf_pos: usize,
dst: Box<dyn VirtualFile + Send + Sync>,
src: Box<dyn VirtualFile + Send + Sync>,
},
// After copying the file we need to seek the position back
// to its original location on the newly copied file
SeekingRestore {
dst: Box<dyn VirtualFile + Send + Sync>,
},
// We have copied the file and can use all the normal operations
Copied(Box<dyn VirtualFile + Send + Sync>),
// An error occurred during the copy operation and we are now in a
// failed state, after the error is consumed it will reset back
// to the original file
Error {
err: io::Error,
src: Box<dyn VirtualFile + Send + Sync>,
},
}
impl CowState {
fn as_ref(&self) -> &(dyn VirtualFile + Send + Sync) {
match self {
Self::ReadOnly(inner) => inner.as_ref(),
Self::SeekingGet(inner) => inner.as_ref(),
Self::SeekingSet { src, .. } => src.as_ref(),
Self::Copying { src, .. } => src.as_ref(),
Self::SeekingRestore { dst, .. } => dst.as_ref(),
Self::Copied(inner) => inner.as_ref(),
Self::Error { src, .. } => src.as_ref(),
}
}
fn as_mut(&mut self) -> &mut (dyn VirtualFile + Send + Sync) {
match self {
Self::ReadOnly(inner) => inner.as_mut(),
Self::SeekingGet(inner) => inner.as_mut(),
Self::SeekingSet { src, .. } => src.as_mut(),
Self::Copying { src, .. } => src.as_mut(),
Self::SeekingRestore { dst, .. } => dst.as_mut(),
Self::Copied(inner) => inner.as_mut(),
Self::Error { src, .. } => src.as_mut(),
}
}
}
impl<P> CopyOnWriteFile<P>
where
P: FileSystem + 'static,
{
fn poll_copy_progress(&mut self, cx: &mut Context) -> Poll<io::Result<()>> {
// Enter a loop until we go pending
let mut again = true;
while again {
again = false;
// The state machine is updated during the poll operation
replace_with_or_abort(&mut self.state, |state| match state {
// We record the current position of the file so that it can be
// restored after the copy-on-write is finished
CowState::SeekingGet(mut src) => {
match Pin::new(src.as_mut()).poll_complete(cx) {
Poll::Ready(Ok(offset)) => {
if let Err(err) =
Pin::new(src.as_mut()).start_seek(SeekFrom::Start(0))
{
return CowState::Error { err, src };
}
again = true;
CowState::SeekingSet {
original_offset: offset,
src,
}
}
Poll::Ready(Err(err)) => CowState::Error { err, src },
Poll::Pending => CowState::SeekingGet(src),
}
}
// We complete the seek operation to the start of the source file
CowState::SeekingSet {
original_offset,
mut src,
} => {
match Pin::new(src.as_mut()).poll_complete(cx).map_ok(|_| ()) {
Poll::Ready(Ok(())) => {
// Remove the whiteout, create the parent structure and open
// the new file on the primary
if let Some(parent) = self.path.parent() {
ops::create_dir_all(&self.primary, parent).ok();
}
let mut had_white_out = false;
if ops::has_white_out(&self.primary, &self.path) {
ops::remove_white_out(&self.primary, &self.path);
had_white_out = true;
}
let dst = self
.primary
.new_open_options()
.create(true)
.read(self.readable)
.write(true)
.truncate(true)
.open(&self.path);
match dst {
Ok(dst) if had_white_out => {
again = true;
CowState::Copied(dst)
}
Ok(dst) => {
again = true;
CowState::Copying {
original_offset,
buf: Vec::new(),
buf_pos: 0,
src,
dst,
}
}
Err(err) => CowState::Error {
err: err.into(),
src,
},
}
}
Poll::Ready(Err(err)) => CowState::Error { err, src },
Poll::Pending => CowState::SeekingSet {
original_offset,
src,
},
}
}
// We are now copying all the data on blocks
CowState::Copying {
mut src,
mut dst,
mut buf,
mut buf_pos,
original_offset,
} => {
loop {
// We are either copying more data from the source
// or we are copying the data to the destination
if buf_pos < buf.len() {
let dst_pinned = Pin::new(dst.as_mut());
match dst_pinned.poll_write(cx, &buf[buf_pos..]) {
Poll::Ready(Ok(0)) => {}
Poll::Ready(Ok(amt)) => {
buf_pos += amt;
continue;
}
Poll::Ready(Err(err)) => {
return CowState::Error { err, src };
}
Poll::Pending => {}
}
} else {
buf.resize_with(8192, || 0);
buf_pos = 8192;
let mut read_buf = ReadBuf::new(&mut buf);
match Pin::new(src.as_mut()).poll_read(cx, &mut read_buf) {
Poll::Ready(Ok(())) if read_buf.filled().is_empty() => {
again = true;
if self.append {
// When we append then we leave the cursor at the
// end of the file
return CowState::Copied(dst);
} else {
// No more data exists to be read so we now move on to
// restoring the cursor back to the original position
if let Err(err) = Pin::new(dst.as_mut())
.start_seek(SeekFrom::Start(original_offset))
{
return CowState::Error { err, src };
}
return CowState::SeekingRestore { dst };
}
}
Poll::Ready(Ok(())) => {
// There is more data to be processed
let new_len = read_buf.filled().len();
unsafe { buf.set_len(new_len) };
buf_pos = 0;
continue;
}
Poll::Ready(Err(err)) => return CowState::Error { err, src },
Poll::Pending => {}
}
}
return CowState::Copying {
original_offset,
buf,
buf_pos,
src,
dst,
};
}
}
// Now once the restoration of the seek position completes we set the copied state
CowState::SeekingRestore { mut dst } => {
match Pin::new(dst.as_mut()).poll_complete(cx) {
Poll::Ready(_) => {
// If we have changed the length then set it
if let Some(new_size) = self.new_size.take() {
dst.set_len(new_size).ok();
}
CowState::Copied(dst)
}
Poll::Pending => CowState::SeekingRestore { dst },
}
}
s => s,
});
}
// Determine what response to give based off the state, when an error occurs
// this will be returned and the copy-on-write will be reset
let mut ret = Poll::Pending;
replace_with_or_abort(&mut self.state, |state| match state {
CowState::ReadOnly(src) => {
ret = Poll::Ready(Ok(()));
CowState::ReadOnly(src)
}
CowState::Copied(src) => {
ret = Poll::Ready(Ok(()));
CowState::Copied(src)
}
CowState::Error { err, src } => {
ret = Poll::Ready(Err(err));
CowState::ReadOnly(src)
}
state => {
ret = Poll::Pending;
state
}
});
ret
}
fn poll_copy_start_and_progress(&mut self, cx: &mut Context) -> Poll<io::Result<()>> {
replace_with_or_abort(&mut self.state, |state| match state {
CowState::ReadOnly(inner) => {
tracing::trace!("COW file touched, starting file clone",);
CowState::SeekingGet(inner)
}
state => state,
});
self.poll_copy_progress(cx)
}
}
impl<P> Debug for CopyOnWriteFile<P>
where
P: FileSystem + 'static,
{
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("CopyOnWriteFile").finish()
}
}
impl<P> VirtualFile for CopyOnWriteFile<P>
where
P: FileSystem + 'static,
{
fn last_accessed(&self) -> u64 {
self.state.as_ref().last_accessed()
}
fn last_modified(&self) -> u64 {
self.state.as_ref().last_modified()
}
fn created_time(&self) -> u64 {
self.state.as_ref().created_time()
}
fn size(&self) -> u64 {
self.state.as_ref().size()
}
fn set_len(&mut self, new_size: u64) -> crate::Result<()> {
self.new_size = Some(new_size);
replace_with_or_abort(&mut self.state, |state| match state {
CowState::Copied(mut file) => {
file.set_len(new_size).ok();
CowState::Copied(file)
}
state => {
// in the scenario where the length is set but the file is not
// polled then we need to make sure we create a file properly
if let Some(parent) = self.path.parent() {
ops::create_dir_all(&self.primary, parent).ok();
}
let dst = self
.primary
.new_open_options()
.create(true)
.write(true)
.open(&self.path);
if let Ok(mut file) = dst {
file.set_len(new_size).ok();
}
state
}
});
Ok(())
}
fn unlink(&mut self) -> crate::Result<()> {
let primary = self.primary.clone();
let path = self.path.clone();
// Create the whiteout file in the primary
let mut had_at_least_one_success = false;
if ops::create_white_out(&primary, &path).is_ok() {
had_at_least_one_success = true;
}
// Attempt to remove it from the primary first
match primary.remove_file(&path) {
Err(e) if should_continue(e) => {}
other => return other,
}
if had_at_least_one_success {
return Ok(());
}
Err(FsError::PermissionDenied)
}
fn poll_read_ready(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> Poll<std::io::Result<usize>> {
match self.poll_copy_progress(cx) {
Poll::Ready(Ok(())) => {}
Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
Poll::Pending => return Poll::Pending,
}
Pin::new(self.state.as_mut()).poll_read_ready(cx)
}
fn poll_write_ready(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> Poll<std::io::Result<usize>> {
match self.poll_copy_progress(cx) {
Poll::Ready(Ok(())) => {}
Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
Poll::Pending => return Poll::Pending,
}
Pin::new(self.state.as_mut()).poll_write_ready(cx)
}
}
impl<P> AsyncWrite for CopyOnWriteFile<P>
where
P: FileSystem + 'static,
{
fn poll_write(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
buf: &[u8],
) -> Poll<Result<usize, std::io::Error>> {
match self.poll_copy_start_and_progress(cx) {
Poll::Pending => return Poll::Pending,
Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
Poll::Ready(Ok(())) => {}
}
Pin::new(self.state.as_mut()).poll_write(cx, buf)
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &[io::IoSlice<'_>],
) -> Poll<Result<usize, io::Error>> {
match self.poll_copy_start_and_progress(cx) {
Poll::Pending => return Poll::Pending,
Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
Poll::Ready(Ok(())) => {}
}
Pin::new(self.state.as_mut()).poll_write_vectored(cx, bufs)
}
fn poll_flush(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> Poll<Result<(), std::io::Error>> {
match self.poll_copy_start_and_progress(cx) {
Poll::Ready(Ok(())) => {}
p => return p,
}
Pin::new(self.state.as_mut()).poll_flush(cx)
}
fn poll_shutdown(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> Poll<Result<(), std::io::Error>> {
match self.poll_copy_start_and_progress(cx) {
Poll::Ready(Ok(())) => {}
p => return p,
}
Pin::new(self.state.as_mut()).poll_shutdown(cx)
}
}
impl<P> AsyncRead for CopyOnWriteFile<P>
where
P: FileSystem + 'static,
{
fn poll_read(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
buf: &mut tokio::io::ReadBuf<'_>,
) -> Poll<std::io::Result<()>> {
match self.poll_copy_progress(cx) {
Poll::Ready(Ok(())) => {}
p => return p,
}
Pin::new(self.state.as_mut()).poll_read(cx, buf)
}
}
impl<P> AsyncSeek for CopyOnWriteFile<P>
where
P: FileSystem + 'static,
{
fn start_seek(
mut self: Pin<&mut Self>,
position: std::io::SeekFrom,
) -> std::io::Result<()> {
match &mut self.state {
CowState::ReadOnly(file)
| CowState::SeekingGet(file)
| CowState::Error { src: file, .. }
| CowState::Copied(file)
| CowState::SeekingRestore { dst: file, .. } => {
Pin::new(file.as_mut()).start_seek(position)
}
CowState::SeekingSet {
original_offset,
src,
..
}
| CowState::Copying {
original_offset,
src,
..
} => {
*original_offset = match position {
SeekFrom::Current(delta) => original_offset
.checked_add_signed(delta)
.unwrap_or(*original_offset),
SeekFrom::Start(pos) => pos,
SeekFrom::End(pos) => src
.size()
.checked_add_signed(pos)
.unwrap_or(*original_offset),
};
Ok(())
}
}
}
fn poll_complete(
mut self: Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> Poll<std::io::Result<u64>> {
match self.poll_copy_progress(cx) {
Poll::Ready(Ok(())) => {}
Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
Poll::Pending => return Poll::Pending,
}
Pin::new(self.state.as_mut()).poll_complete(cx)
}
}
tracing::trace!(
path=%path.display(),
options=?conf,
"Opening the file in copy-on-write mode",
);
Ok(Box::new(CopyOnWriteFile::<P> {
path: path.to_path_buf(),
primary: primary.clone(),
state: CowState::ReadOnly(file),
readable: conf.read,
append: conf.append,
new_size: None,
}))
}
impl<P, S> Debug for OverlayFileSystem<P, S>
where
P: FileSystem,
S: for<'a> FileSystems<'a>,
{
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
struct IterFilesystems<'a, S>(&'a S);
impl<'a, S> Debug for IterFilesystems<'a, S>
where
S: for<'b> FileSystems<'b>,
{
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let mut f = f.debug_list();
for fs in self.0.filesystems() {
f.entry(&fs);
}
f.finish()
}
}
f.debug_struct("OverlayFileSystem")
.field("primary", &self.primary)
.field("secondaries", &IterFilesystems(&self.secondaries))
.finish()
}
}
fn should_continue(e: FsError) -> bool {
// HACK: We shouldn't really be ignoring FsError::BaseNotDirectory, but
// it's needed because the mem_fs::FileSystem doesn't return
// FsError::EntryNotFound when an intermediate directory doesn't exist
// (i.e. the "/path/to" in "/path/to/file.txt").
matches!(
e,
FsError::EntryNotFound | FsError::InvalidInput | FsError::BaseNotDirectory
)
}
#[cfg(test)]
mod tests {
use std::path::PathBuf;
use super::*;
use crate::mem_fs::FileSystem as MemFS;
use tokio::io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt};
#[tokio::test]
async fn remove_directory() {
let primary = MemFS::default();
let secondary = MemFS::default();
let first = Path::new("/first");
let second = Path::new("/second");
let file_txt = second.join("file.txt");
let third = Path::new("/third");
primary.create_dir(first).unwrap();
primary.create_dir(second).unwrap();
primary
.new_open_options()
.create(true)
.write(true)
.open(&file_txt)
.unwrap()
.write_all(b"Hello, World!")
.await
.unwrap();
secondary.create_dir(third).unwrap();
let overlay = OverlayFileSystem::new(primary, [secondary]);
// Delete a folder on the primary filesystem
overlay.remove_dir(first).unwrap();
assert_eq!(
overlay.primary().metadata(first).unwrap_err(),
FsError::EntryNotFound,
"Deleted from primary"
);
assert!(!ops::exists(&overlay.secondaries[0], second));
// Directory on the primary fs isn't empty
assert_eq!(
overlay.remove_dir(second).unwrap_err(),
FsError::DirectoryNotEmpty,
);
// Try to remove something on one of the overlay filesystems
assert_eq!(overlay.remove_dir(third), Ok(()));
// It should no longer exist
assert_eq!(overlay.metadata(third).unwrap_err(), FsError::EntryNotFound);
assert!(ops::exists(&overlay.secondaries[0], third));
}
#[tokio::test]
async fn open_files() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&primary, "/primary").unwrap();
ops::touch(&primary, "/primary/read.txt").unwrap();
ops::touch(&primary, "/primary/write.txt").unwrap();
ops::create_dir_all(&secondary, "/secondary").unwrap();
ops::touch(&secondary, "/secondary/read.txt").unwrap();
ops::touch(&secondary, "/secondary/write.txt").unwrap();
ops::create_dir_all(&secondary, "/primary").unwrap();
ops::write(&secondary, "/primary/read.txt", "This is shadowed")
.await
.unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
// Any new files will be created on the primary fs
let _ = fs
.new_open_options()
.create(true)
.write(true)
.open("/new.txt")
.unwrap();
assert!(ops::exists(&fs.primary, "/new.txt"));
assert!(!ops::exists(&fs.secondaries[0], "/new.txt"));
// You can open a file for reading and writing on the primary fs
let _ = fs
.new_open_options()
.create(false)
.write(true)
.read(true)
.open("/primary/write.txt")
.unwrap();
// Files on the primary should always shadow the secondary
let content = ops::read_to_string(&fs, "/primary/read.txt").await.unwrap();
assert_ne!(content, "This is shadowed");
}
#[tokio::test]
async fn create_file_that_looks_like_it_is_in_a_secondary_filesystem_folder() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/path/to/").unwrap();
assert!(!ops::is_dir(&primary, "/path/to/"));
let fs = OverlayFileSystem::new(primary, [secondary]);
ops::touch(&fs, "/path/to/file.txt").unwrap();
assert!(ops::is_dir(&fs.primary, "/path/to/"));
assert!(ops::is_file(&fs.primary, "/path/to/file.txt"));
assert!(!ops::is_file(&fs.secondaries[0], "/path/to/file.txt"));
}
#[tokio::test]
async fn listed_files_appear_overlayed() {
let primary = MemFS::default();
let secondary = MemFS::default();
let secondary_overlayed = MemFS::default();
ops::create_dir_all(&primary, "/primary").unwrap();
ops::touch(&primary, "/primary/read.txt").unwrap();
ops::touch(&primary, "/primary/write.txt").unwrap();
ops::create_dir_all(&secondary, "/secondary").unwrap();
ops::touch(&secondary, "/secondary/read.txt").unwrap();
ops::touch(&secondary, "/secondary/write.txt").unwrap();
// This second "secondary" filesystem should share the same folders as
// the first one.
ops::create_dir_all(&secondary_overlayed, "/secondary").unwrap();
ops::touch(&secondary_overlayed, "/secondary/overlayed.txt").unwrap();
let fs = OverlayFileSystem::new(primary, [secondary, secondary_overlayed]);
let paths: Vec<_> = ops::walk(&fs, "/").map(|entry| entry.path()).collect();
assert_eq!(
paths,
vec![
PathBuf::from("/secondary"),
PathBuf::from("/secondary/write.txt"),
PathBuf::from("/secondary/read.txt"),
PathBuf::from("/secondary/overlayed.txt"),
PathBuf::from("/primary"),
PathBuf::from("/primary/write.txt"),
PathBuf::from("/primary/read.txt"),
]
);
}
#[tokio::test]
async fn open_secondary_fs_files_in_write_mode() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/secondary").unwrap();
ops::write(&secondary, "/secondary/file.txt", b"Hello, World!")
.await
.unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
let mut f = fs
.new_open_options()
.write(true)
.read(true)
.open("/secondary/file.txt")
.unwrap();
// reading is fine
let mut buf = String::new();
f.read_to_string(&mut buf).await.unwrap();
assert_eq!(buf, "Hello, World!");
f.seek(SeekFrom::Start(0)).await.unwrap();
// next we will write a new set of bytes
f.set_len(0).unwrap();
assert_eq!(f.write(b"Hi").await.unwrap(), 2);
// Same with flushing
assert_eq!(f.flush().await.unwrap(), (),);
// if we now read it then the data should be different
buf = String::new();
f.seek(SeekFrom::Start(0)).await.unwrap();
f.read_to_string(&mut buf).await.unwrap();
assert_eq!(buf, "Hi");
drop(f);
// including if we open it again
let mut f = fs
.new_open_options()
.read(true)
.open("/secondary/file.txt")
.unwrap();
buf = String::new();
f.read_to_string(&mut buf).await.unwrap();
assert_eq!(buf, "Hi");
}
#[tokio::test]
async fn open_secondary_fs_files_unlink() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/secondary").unwrap();
ops::write(&secondary, "/secondary/file.txt", b"Hello, World!")
.await
.unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
fs.metadata(Path::new("/secondary/file.txt")).unwrap();
// Now delete the file and make sure its not found
fs.remove_file(Path::new("/secondary/file.txt")).unwrap();
assert_eq!(
fs.metadata(Path::new("/secondary/file.txt")).unwrap_err(),
FsError::EntryNotFound
)
}
#[tokio::test]
async fn open_secondary_fs_without_cow() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/secondary").unwrap();
ops::write(&secondary, "/secondary/file.txt", b"Hello, World!")
.await
.unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
let mut f = fs
.new_open_options()
.create(true)
.read(true)
.open(Path::new("/secondary/file.txt"))
.unwrap();
assert_eq!(f.size() as usize, 13);
let mut buf = String::new();
f.read_to_string(&mut buf).await.unwrap();
assert_eq!(buf, "Hello, World!");
// it should not be in the primary and nor should the secondary folder
assert!(!ops::is_dir(&fs.primary, "/secondary"));
assert!(!ops::is_file(&fs.primary, "/secondary/file.txt"));
assert!(ops::is_dir(&fs.secondaries[0], "/secondary"));
assert!(ops::is_file(&fs.secondaries[0], "/secondary/file.txt"));
}
#[tokio::test]
async fn create_and_append_secondary_fs_with_cow() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/secondary").unwrap();
ops::write(&secondary, "/secondary/file.txt", b"Hello, World!")
.await
.unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
let mut f = fs
.new_open_options()
.create(true)
.append(true)
.read(true)
.open(Path::new("/secondary/file.txt"))
.unwrap();
assert_eq!(f.size() as usize, 13);
f.write_all(b"asdf").await.unwrap();
assert_eq!(f.size() as usize, 17);
f.seek(SeekFrom::Start(0)).await.unwrap();
let mut buf = String::new();
f.read_to_string(&mut buf).await.unwrap();
assert_eq!(buf, "Hello, World!asdf");
// Now lets check the file systems under
let f = fs
.primary
.new_open_options()
.create(true)
.append(true)
.read(true)
.open(Path::new("/secondary/file.txt"))
.unwrap();
assert_eq!(f.size() as usize, 17);
let f = fs.secondaries[0]
.new_open_options()
.create(true)
.append(true)
.read(true)
.open(Path::new("/secondary/file.txt"))
.unwrap();
assert_eq!(f.size() as usize, 13);
// it should now exist in both the primary and secondary
assert!(ops::is_dir(&fs.primary, "/secondary"));
assert!(ops::is_file(&fs.primary, "/secondary/file.txt"));
assert!(ops::is_dir(&fs.secondaries[0], "/secondary"));
assert!(ops::is_file(&fs.secondaries[0], "/secondary/file.txt"));
}
#[tokio::test]
async fn unlink_file_from_secondary_fs() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/secondary").unwrap();
ops::write(&secondary, "/secondary/file.txt", b"Hello, World!")
.await
.unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
fs.remove_file(Path::new("/secondary/file.txt")).unwrap();
assert_eq!(ops::exists(&fs, Path::new("/secondary/file.txt")), false);
assert!(ops::is_file(&fs.primary, "/secondary/.wh.file.txt"));
assert!(ops::is_file(&fs.secondaries[0], "/secondary/file.txt"));
// Now create the file again after the unlink
let mut f = fs
.new_open_options()
.create(true)
.write(true)
.read(true)
.open(Path::new("/secondary/file.txt"))
.unwrap();
assert_eq!(f.size() as usize, 0);
f.write_all(b"asdf").await.unwrap();
assert_eq!(f.size() as usize, 4);
// The whiteout should be gone and new file exist
assert!(!ops::is_file(&fs.primary, "/secondary/.wh.file.txt"));
assert!(ops::is_file(&fs.primary, "/secondary/file.txt"));
assert!(ops::is_file(&fs.secondaries[0], "/secondary/file.txt"));
}
#[tokio::test]
async fn rmdir_from_secondary_fs() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/secondary").unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
assert!(ops::is_dir(&fs, "/secondary"));
fs.remove_dir(Path::new("/secondary")).unwrap();
assert!(!ops::is_dir(&fs, "/secondary"));
assert!(ops::is_file(&fs.primary, "/.wh.secondary"));
assert!(ops::is_dir(&fs.secondaries[0], "/secondary"));
fs.create_dir(Path::new("/secondary")).unwrap();
assert!(ops::is_dir(&fs, "/secondary"));
assert!(ops::is_dir(&fs.primary, "/secondary"));
assert!(!ops::is_file(&fs.primary, "/.wh.secondary"));
assert!(ops::is_dir(&fs.secondaries[0], "/secondary"));
}
#[tokio::test]
async fn rmdir_sub_from_secondary_fs() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/first/secondary").unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
assert!(ops::is_dir(&fs, "/first/secondary"));
fs.remove_dir(Path::new("/first/secondary")).unwrap();
assert!(!ops::is_dir(&fs, "/first/secondary"));
assert!(ops::is_file(&fs.primary, "/first/.wh.secondary"));
assert!(ops::is_dir(&fs.secondaries[0], "/first/secondary"));
fs.create_dir(Path::new("/first/secondary")).unwrap();
assert!(ops::is_dir(&fs, "/first/secondary"));
assert!(ops::is_dir(&fs.primary, "/first/secondary"));
assert!(!ops::is_file(&fs.primary, "/first/.wh.secondary"));
assert!(ops::is_dir(&fs.secondaries[0], "/first/secondary"));
}
#[tokio::test]
async fn create_new_secondary_fs_without_cow() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/secondary").unwrap();
ops::write(&secondary, "/secondary/file.txt", b"Hello, World!")
.await
.unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
let mut f = fs
.new_open_options()
.create_new(true)
.read(true)
.open(Path::new("/secondary/file.txt"))
.unwrap();
assert_eq!(f.size() as usize, 0);
let mut buf = String::new();
f.read_to_string(&mut buf).await.unwrap();
assert_eq!(buf, "");
// it should now exist in both the primary and secondary
assert!(ops::is_dir(&fs.primary, "/secondary"));
assert!(ops::is_file(&fs.primary, "/secondary/file.txt"));
assert!(ops::is_dir(&fs.secondaries[0], "/secondary"));
assert!(ops::is_file(&fs.secondaries[0], "/secondary/file.txt"));
}
#[tokio::test]
async fn open_secondary_fs_files_remove_dir() {
let primary = MemFS::default();
let secondary = MemFS::default();
ops::create_dir_all(&secondary, "/secondary").unwrap();
let fs = OverlayFileSystem::new(primary, [secondary]);
fs.metadata(Path::new("/secondary")).unwrap();
// Now delete the file and make sure its not found
fs.remove_dir(Path::new("/secondary")).unwrap();
assert_eq!(
fs.metadata(Path::new("/secondary")).unwrap_err(),
FsError::EntryNotFound
)
}
// OLD tests that used WebcFileSystem.
// Should be re-implemented with WebcVolumeFs
// #[tokio::test]
// async fn wasi_runner_use_case() {
// // Set up some dummy files on the host
// let temp = TempDir::new().unwrap();
// let first = temp.path().join("first");
// let file_txt = first.join("file.txt");
// let second = temp.path().join("second");
// std::fs::create_dir_all(&first).unwrap();
// std::fs::write(&file_txt, b"First!").unwrap();
// std::fs::create_dir_all(&second).unwrap();
// // configure the union FS so things are saved in memory by default
// // (initialized with a set of unix-like folders), but certain folders
// // are first to the host.
// let primary = RootFileSystemBuilder::new().build();
// let host_fs: Arc<dyn FileSystem + Send + Sync> =
// Arc::new(crate::host_fs::FileSystem::default());
// let first_dirs = [(&first, "/first"), (&second, "/second")];
// for (host, guest) in first_dirs {
// primary
// .mount(PathBuf::from(guest), &host_fs, host.clone())
// .unwrap();
// }
// // Set up the secondary file systems
// let webc = WebCOwned::parse(Bytes::from_static(PYTHON), &ParseOptions::default()).unwrap();
// let webc = WebcFileSystem::init_all(Arc::new(webc));
//
// let fs = OverlayFileSystem::new(primary, [webc]);
//
// // We should get all the normal directories from rootfs (primary)
// assert!(ops::is_dir(&fs, "/lib"));
// assert!(ops::is_dir(&fs, "/bin"));
// assert!(ops::is_file(&fs, "/dev/stdin"));
// assert!(ops::is_file(&fs, "/dev/stdout"));
// // We also want to see files from the WEBC volumes (secondary)
// assert!(ops::is_dir(&fs, "/lib/python3.6"));
// assert!(ops::is_file(&fs, "/lib/python3.6/collections/__init__.py"));
// #[cfg(never)]
// {
// // files on a secondary fs aren't writable
// // TODO(Michael-F-Bryan): re-enable this if/when we fix
// // open_readonly_file_hack()
// assert_eq!(
// fs.new_open_options()
// .append(true)
// .open("/lib/python3.6/collections/__init__.py")
// .unwrap_err(),
// FsError::PermissionDenied,
// );
// }
// // you are allowed to create files that look like they are in a secondary
// // folder, though
// ops::touch(&fs, "/lib/python3.6/collections/something-else.py").unwrap();
// // But it'll be on the primary filesystem, not the secondary one
// assert!(ops::is_file(
// &fs.primary,
// "/lib/python3.6/collections/something-else.py"
// ));
// assert!(!ops::is_file(
// &fs.secondaries[0],
// "/lib/python3.6/collections/something-else.py"
// ));
// // You can do the same thing with folders
// fs.create_dir("/lib/python3.6/something-else".as_ref())
// .unwrap();
// assert!(ops::is_dir(&fs.primary, "/lib/python3.6/something-else"));
// assert!(!ops::is_dir(
// &fs.secondaries[0],
// "/lib/python3.6/something-else"
// ));
// // It only works when you are directly inside an existing directory
// // on the secondary filesystem, though
// assert_eq!(
// ops::touch(&fs, "/lib/python3.6/collections/this/doesnt/exist.txt").unwrap_err(),
// FsError::EntryNotFound
// );
// // you should also be able to read files mounted from the host
// assert!(ops::is_dir(&fs, "/first"));
// assert!(ops::is_file(&fs, "/first/file.txt"));
// assert_eq!(
// ops::read_to_string(&fs, "/first/file.txt").await.unwrap(),
// "First!"
// );
// // Overwriting them is fine and we'll see the changes on the host
// ops::write(&fs, "/first/file.txt", "Updated").await.unwrap();
// assert_eq!(std::fs::read_to_string(&file_txt).unwrap(), "Updated");
// // The filesystem will see changes on the host that happened after it was
// // set up
// let another = second.join("another.txt");
// std::fs::write(&another, "asdf").unwrap();
// assert_eq!(
// ops::read_to_string(&fs, "/second/another.txt")
// .await
// .unwrap(),
// "asdf"
// );
// }
//
// #[tokio::test]
// async fn absolute_and_relative_paths_are_passed_through() {
// let python = Arc::new(load_webc(PYTHON));
//
// // The underlying filesystem doesn't care about absolute/relative paths
// assert_eq!(python.read_dir("/lib".as_ref()).unwrap().count(), 4);
// assert_eq!(python.read_dir("lib".as_ref()).unwrap().count(), 4);
//
// // read_dir() should be passed through to the primary
// let webc_primary =
// OverlayFileSystem::new(Arc::clone(&python), [crate::EmptyFileSystem::default()]);
// assert_same_directory_contents(&python, "/lib", &webc_primary);
// assert_same_directory_contents(&python, "lib", &webc_primary);
//
// // read_dir() should also be passed through to the secondary
// let webc_secondary =
// OverlayFileSystem::new(crate::EmptyFileSystem::default(), [Arc::clone(&python)]);
// assert_same_directory_contents(&python, "/lib", &webc_secondary);
// assert_same_directory_contents(&python, "lib", &webc_secondary);
//
// // It should be fine to overlay the root fs on top of our webc file
// let overlay_rootfs = OverlayFileSystem::new(
// RootFileSystemBuilder::default().build(),
// [Arc::clone(&python)],
// );
// assert_same_directory_contents(&python, "/lib", &overlay_rootfs);
// assert_same_directory_contents(&python, "lib", &overlay_rootfs);
// }
// #[track_caller]
// fn assert_same_directory_contents(
// original: &dyn FileSystem,
// path: impl AsRef<Path>,
// candidate: &dyn FileSystem,
// ) {
// let path = path.as_ref();
//
// let original_entries: Vec<_> = original
// .read_dir(path)
// .unwrap()
// .map(|r| r.unwrap())
// .collect();
// let candidate_entries: Vec<_> = candidate
// .read_dir(path)
// .unwrap()
// .map(|r| r.unwrap())
// .collect();
//
// assert_eq!(original_entries, candidate_entries);
// }
}