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use crate::bindings::filesystem::types;
use crate::runtime::{spawn_blocking, AbortOnDropJoinHandle};
use crate::{
HostInputStream, HostOutputStream, StreamError, StreamResult, Subscribe, TrappableError,
};
use anyhow::anyhow;
use bytes::{Bytes, BytesMut};
use std::io;
use std::mem;
use std::sync::Arc;
pub type FsResult<T> = Result<T, FsError>;
pub type FsError = TrappableError<types::ErrorCode>;
impl From<wasmtime::component::ResourceTableError> for FsError {
fn from(error: wasmtime::component::ResourceTableError) -> Self {
Self::trap(error)
}
}
impl From<io::Error> for FsError {
fn from(error: io::Error) -> Self {
types::ErrorCode::from(error).into()
}
}
pub enum Descriptor {
File(File),
Dir(Dir),
}
impl Descriptor {
pub fn file(&self) -> Result<&File, types::ErrorCode> {
match self {
Descriptor::File(f) => Ok(f),
Descriptor::Dir(_) => Err(types::ErrorCode::BadDescriptor),
}
}
pub fn dir(&self) -> Result<&Dir, types::ErrorCode> {
match self {
Descriptor::Dir(d) => Ok(d),
Descriptor::File(_) => Err(types::ErrorCode::NotDirectory),
}
}
pub fn is_file(&self) -> bool {
match self {
Descriptor::File(_) => true,
Descriptor::Dir(_) => false,
}
}
pub fn is_dir(&self) -> bool {
match self {
Descriptor::File(_) => false,
Descriptor::Dir(_) => true,
}
}
}
bitflags::bitflags! {
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct FilePerms: usize {
const READ = 0b1;
const WRITE = 0b10;
}
}
bitflags::bitflags! {
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct OpenMode: usize {
const READ = 0b1;
const WRITE = 0b10;
}
}
#[derive(Clone)]
pub struct File {
/// The operating system File this struct is mediating access to.
///
/// Wrapped in an Arc because the same underlying file is used for
/// implementing the stream types. A copy is also needed for
/// [`spawn_blocking`].
///
/// [`spawn_blocking`]: Self::spawn_blocking
pub file: Arc<cap_std::fs::File>,
/// Permissions to enforce on access to the file. These permissions are
/// specified by a user of the `crate::WasiCtxBuilder`, and are
/// enforced prior to any enforced by the underlying operating system.
pub perms: FilePerms,
/// The mode the file was opened under: bits for reading, and writing.
/// Required to correctly report the DescriptorFlags, because cap-std
/// doesn't presently provide a cross-platform equivalent of reading the
/// oflags back out using fcntl.
pub open_mode: OpenMode,
allow_blocking_current_thread: bool,
}
impl File {
pub fn new(
file: cap_std::fs::File,
perms: FilePerms,
open_mode: OpenMode,
allow_blocking_current_thread: bool,
) -> Self {
Self {
file: Arc::new(file),
perms,
open_mode,
allow_blocking_current_thread,
}
}
/// Execute the blocking `body` function.
///
/// Depending on how the WasiCtx was configured, the body may either be:
/// - Executed directly on the current thread. In this case the `async`
/// signature of this method is effectively a lie and the returned
/// Future will always be immediately Ready. Or:
/// - Spawned on a background thread using [`tokio::task::spawn_blocking`]
/// and immediately awaited.
///
/// Intentionally blocking the executor thread might seem unorthodox, but is
/// not actually a problem for specific workloads. See:
/// - [`crate::WasiCtxBuilder::allow_blocking_current_thread`]
/// - [Poor performance of wasmtime file I/O maybe because tokio](https://github.com/bytecodealliance/wasmtime/issues/7973)
/// - [Implement opt-in for enabling WASI to block the current thread](https://github.com/bytecodealliance/wasmtime/pull/8190)
pub(crate) async fn run_blocking<F, R>(&self, body: F) -> R
where
F: FnOnce(&cap_std::fs::File) -> R + Send + 'static,
R: Send + 'static,
{
match self.as_blocking_file() {
Some(file) => body(file),
None => self.spawn_blocking(body).await,
}
}
pub(crate) fn spawn_blocking<F, R>(&self, body: F) -> AbortOnDropJoinHandle<R>
where
F: FnOnce(&cap_std::fs::File) -> R + Send + 'static,
R: Send + 'static,
{
let f = self.file.clone();
spawn_blocking(move || body(&f))
}
/// Returns `Some` when the current thread is allowed to block in filesystem
/// operations, and otherwise returns `None` to indicate that
/// `spawn_blocking` must be used.
pub(crate) fn as_blocking_file(&self) -> Option<&cap_std::fs::File> {
if self.allow_blocking_current_thread {
Some(&self.file)
} else {
None
}
}
}
bitflags::bitflags! {
/// Permission bits for operating on a directory.
///
/// Directories can be limited to being readonly. This will restrict what
/// can be done with them, for example preventing creation of new files.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct DirPerms: usize {
/// This directory can be read, for example its entries can be iterated
/// over and files can be opened.
const READ = 0b1;
/// This directory can be mutated, for example by creating new files
/// within it.
const MUTATE = 0b10;
}
}
#[derive(Clone)]
pub struct Dir {
/// The operating system file descriptor this struct is mediating access
/// to.
///
/// Wrapped in an Arc because a copy is needed for [`spawn_blocking`].
///
/// [`spawn_blocking`]: Self::spawn_blocking
pub dir: Arc<cap_std::fs::Dir>,
/// Permissions to enforce on access to this directory. These permissions
/// are specified by a user of the `crate::WasiCtxBuilder`, and
/// are enforced prior to any enforced by the underlying operating system.
///
/// These permissions are also enforced on any directories opened under
/// this directory.
pub perms: DirPerms,
/// Permissions to enforce on any files opened under this directory.
pub file_perms: FilePerms,
/// The mode the directory was opened under: bits for reading, and writing.
/// Required to correctly report the DescriptorFlags, because cap-std
/// doesn't presently provide a cross-platform equivalent of reading the
/// oflags back out using fcntl.
pub open_mode: OpenMode,
allow_blocking_current_thread: bool,
}
impl Dir {
pub fn new(
dir: cap_std::fs::Dir,
perms: DirPerms,
file_perms: FilePerms,
open_mode: OpenMode,
allow_blocking_current_thread: bool,
) -> Self {
Dir {
dir: Arc::new(dir),
perms,
file_perms,
open_mode,
allow_blocking_current_thread,
}
}
/// Execute the blocking `body` function.
///
/// Depending on how the WasiCtx was configured, the body may either be:
/// - Executed directly on the current thread. In this case the `async`
/// signature of this method is effectively a lie and the returned
/// Future will always be immediately Ready. Or:
/// - Spawned on a background thread using [`tokio::task::spawn_blocking`]
/// and immediately awaited.
///
/// Intentionally blocking the executor thread might seem unorthodox, but is
/// not actually a problem for specific workloads. See:
/// - [`crate::WasiCtxBuilder::allow_blocking_current_thread`]
/// - [Poor performance of wasmtime file I/O maybe because tokio](https://github.com/bytecodealliance/wasmtime/issues/7973)
/// - [Implement opt-in for enabling WASI to block the current thread](https://github.com/bytecodealliance/wasmtime/pull/8190)
pub(crate) async fn run_blocking<F, R>(&self, body: F) -> R
where
F: FnOnce(&cap_std::fs::Dir) -> R + Send + 'static,
R: Send + 'static,
{
if self.allow_blocking_current_thread {
body(&self.dir)
} else {
let d = self.dir.clone();
spawn_blocking(move || body(&d)).await
}
}
}
pub struct FileInputStream {
file: File,
position: u64,
state: ReadState,
}
enum ReadState {
Idle,
Waiting(AbortOnDropJoinHandle<ReadState>),
DataAvailable(Bytes),
Error(io::Error),
Closed,
}
impl FileInputStream {
pub fn new(file: &File, position: u64) -> Self {
Self {
file: file.clone(),
position,
state: ReadState::Idle,
}
}
fn blocking_read(file: &cap_std::fs::File, offset: u64, size: usize) -> ReadState {
use system_interface::fs::FileIoExt;
let mut buf = BytesMut::zeroed(size);
loop {
match file.read_at(&mut buf, offset) {
Ok(0) => return ReadState::Closed,
Ok(n) => {
buf.truncate(n);
return ReadState::DataAvailable(buf.freeze());
}
Err(e) if e.kind() == std::io::ErrorKind::Interrupted => {
// Try again, continue looping
}
Err(e) => return ReadState::Error(e),
}
}
}
/// Wait for existing background task to finish, without starting any new background reads.
async fn wait_ready(&mut self) {
match &mut self.state {
ReadState::Waiting(task) => {
self.state = task.await;
}
_ => {}
}
}
}
#[async_trait::async_trait]
impl HostInputStream for FileInputStream {
fn read(&mut self, size: usize) -> StreamResult<Bytes> {
match &mut self.state {
ReadState::Idle => {
if size == 0 {
return Ok(Bytes::new());
}
let p = self.position;
self.state = ReadState::Waiting(
self.file
.spawn_blocking(move |f| Self::blocking_read(f, p, size)),
);
Ok(Bytes::new())
}
ReadState::DataAvailable(b) => {
let min_len = b.len().min(size);
let chunk = b.split_to(min_len);
if b.len() == 0 {
self.state = ReadState::Idle;
}
self.position += min_len as u64;
Ok(chunk)
}
ReadState::Waiting(_) => Ok(Bytes::new()),
ReadState::Error(_) => match mem::replace(&mut self.state, ReadState::Closed) {
ReadState::Error(e) => Err(StreamError::LastOperationFailed(e.into())),
_ => unreachable!(),
},
ReadState::Closed => Err(StreamError::Closed),
}
}
/// Specialized blocking_* variant to bypass tokio's task spawning & joining
/// overhead on synchronous file I/O.
async fn blocking_read(&mut self, size: usize) -> StreamResult<Bytes> {
self.wait_ready().await;
// Before we defer to the regular `read`, make sure it has data ready to go:
if let ReadState::Idle = self.state {
let p = self.position;
self.state = self
.file
.run_blocking(move |f| Self::blocking_read(f, p, size))
.await;
}
self.read(size)
}
async fn cancel(&mut self) {
match mem::replace(&mut self.state, ReadState::Closed) {
ReadState::Waiting(task) => {
// The task was created using `spawn_blocking`, so unless we're
// lucky enough that the task hasn't started yet, the abort
// signal won't have any effect and we're forced to wait for it
// to run to completion.
// From the guest's point of view, `input-stream::drop` then
// appears to block. Certainly less than ideal, but arguably still
// better than letting the guest rack up an unbounded number of
// background tasks. Also, the guest is only blocked if
// the stream was dropped mid-read, which we don't expect to
// occur frequently.
task.abort_wait().await;
}
_ => {}
}
}
}
#[async_trait::async_trait]
impl Subscribe for FileInputStream {
async fn ready(&mut self) {
if let ReadState::Idle = self.state {
// The guest hasn't initiated any read, but is nonetheless waiting
// for data to be available. We'll start a read for them:
const DEFAULT_READ_SIZE: usize = 4096;
let p = self.position;
self.state = ReadState::Waiting(
self.file
.spawn_blocking(move |f| Self::blocking_read(f, p, DEFAULT_READ_SIZE)),
);
}
self.wait_ready().await
}
}
#[derive(Clone, Copy)]
pub(crate) enum FileOutputMode {
Position(u64),
Append,
}
pub(crate) struct FileOutputStream {
file: File,
mode: FileOutputMode,
state: OutputState,
}
enum OutputState {
Ready,
/// Allows join future to be awaited in a cancellable manner. Gone variant indicates
/// no task is currently outstanding.
Waiting(AbortOnDropJoinHandle<io::Result<usize>>),
/// The last I/O operation failed with this error.
Error(io::Error),
Closed,
}
impl FileOutputStream {
pub fn write_at(file: &File, position: u64) -> Self {
Self {
file: file.clone(),
mode: FileOutputMode::Position(position),
state: OutputState::Ready,
}
}
pub fn append(file: &File) -> Self {
Self {
file: file.clone(),
mode: FileOutputMode::Append,
state: OutputState::Ready,
}
}
fn blocking_write(
file: &cap_std::fs::File,
mut buf: Bytes,
mode: FileOutputMode,
) -> io::Result<usize> {
use system_interface::fs::FileIoExt;
match mode {
FileOutputMode::Position(mut p) => {
let mut total = 0;
loop {
let nwritten = file.write_at(buf.as_ref(), p)?;
// afterwards buf contains [nwritten, len):
let _ = buf.split_to(nwritten);
p += nwritten as u64;
total += nwritten;
if buf.is_empty() {
break;
}
}
Ok(total)
}
FileOutputMode::Append => {
let mut total = 0;
loop {
let nwritten = file.append(buf.as_ref())?;
let _ = buf.split_to(nwritten);
total += nwritten;
if buf.is_empty() {
break;
}
}
Ok(total)
}
}
}
}
// FIXME: configurable? determine from how much space left in file?
const FILE_WRITE_CAPACITY: usize = 1024 * 1024;
#[async_trait::async_trait]
impl HostOutputStream for FileOutputStream {
fn write(&mut self, buf: Bytes) -> Result<(), StreamError> {
match self.state {
OutputState::Ready => {}
OutputState::Closed => return Err(StreamError::Closed),
OutputState::Waiting(_) | OutputState::Error(_) => {
// a write is pending - this call was not permitted
return Err(StreamError::Trap(anyhow!(
"write not permitted: check_write not called first"
)));
}
}
let m = self.mode;
self.state = OutputState::Waiting(
self.file
.spawn_blocking(move |f| Self::blocking_write(f, buf, m)),
);
Ok(())
}
/// Specialized blocking_* variant to bypass tokio's task spawning & joining
/// overhead on synchronous file I/O.
async fn blocking_write_and_flush(&mut self, buf: Bytes) -> StreamResult<()> {
self.ready().await;
match self.state {
OutputState::Ready => {}
OutputState::Closed => return Err(StreamError::Closed),
OutputState::Error(_) => match mem::replace(&mut self.state, OutputState::Closed) {
OutputState::Error(e) => return Err(StreamError::LastOperationFailed(e.into())),
_ => unreachable!(),
},
OutputState::Waiting(_) => unreachable!("we've just waited for readiness"),
}
let m = self.mode;
match self
.file
.run_blocking(move |f| Self::blocking_write(f, buf, m))
.await
{
Ok(nwritten) => {
if let FileOutputMode::Position(ref mut p) = &mut self.mode {
*p += nwritten as u64;
}
self.state = OutputState::Ready;
Ok(())
}
Err(e) => {
self.state = OutputState::Closed;
Err(StreamError::LastOperationFailed(e.into()))
}
}
}
fn flush(&mut self) -> Result<(), StreamError> {
match self.state {
// Only userland buffering of file writes is in the blocking task,
// so there's nothing extra that needs to be done to request a
// flush.
OutputState::Ready | OutputState::Waiting(_) => Ok(()),
OutputState::Closed => Err(StreamError::Closed),
OutputState::Error(_) => match mem::replace(&mut self.state, OutputState::Closed) {
OutputState::Error(e) => Err(StreamError::LastOperationFailed(e.into())),
_ => unreachable!(),
},
}
}
fn check_write(&mut self) -> Result<usize, StreamError> {
match self.state {
OutputState::Ready => Ok(FILE_WRITE_CAPACITY),
OutputState::Closed => Err(StreamError::Closed),
OutputState::Error(_) => match mem::replace(&mut self.state, OutputState::Closed) {
OutputState::Error(e) => Err(StreamError::LastOperationFailed(e.into())),
_ => unreachable!(),
},
OutputState::Waiting(_) => Ok(0),
}
}
async fn cancel(&mut self) {
match mem::replace(&mut self.state, OutputState::Closed) {
OutputState::Waiting(task) => {
// The task was created using `spawn_blocking`, so unless we're
// lucky enough that the task hasn't started yet, the abort
// signal won't have any effect and we're forced to wait for it
// to run to completion.
// From the guest's point of view, `output-stream::drop` then
// appears to block. Certainly less than ideal, but arguably still
// better than letting the guest rack up an unbounded number of
// background tasks. Also, the guest is only blocked if
// the stream was dropped mid-write, which we don't expect to
// occur frequently.
task.abort_wait().await;
}
_ => {}
}
}
}
#[async_trait::async_trait]
impl Subscribe for FileOutputStream {
async fn ready(&mut self) {
if let OutputState::Waiting(task) = &mut self.state {
self.state = match task.await {
Ok(nwritten) => {
if let FileOutputMode::Position(ref mut p) = &mut self.mode {
*p += nwritten as u64;
}
OutputState::Ready
}
Err(e) => OutputState::Error(e),
};
}
}
}
pub struct ReaddirIterator(
std::sync::Mutex<Box<dyn Iterator<Item = FsResult<types::DirectoryEntry>> + Send + 'static>>,
);
impl ReaddirIterator {
pub(crate) fn new(
i: impl Iterator<Item = FsResult<types::DirectoryEntry>> + Send + 'static,
) -> Self {
ReaddirIterator(std::sync::Mutex::new(Box::new(i)))
}
pub(crate) fn next(&self) -> FsResult<Option<types::DirectoryEntry>> {
self.0.lock().unwrap().next().transpose()
}
}
impl IntoIterator for ReaddirIterator {
type Item = FsResult<types::DirectoryEntry>;
type IntoIter = Box<dyn Iterator<Item = Self::Item> + Send>;
fn into_iter(self) -> Self::IntoIter {
self.0.into_inner().unwrap()
}
}