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Simplify some filesystem extensions on Windows #43

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merged 1 commit into from
Feb 13, 2024
Merged

Simplify some filesystem extensions on Windows #43

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145 changes: 19 additions & 126 deletions src/fs/file_io_ext.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ use rustix::io::{preadv, pwritev};
use std::io::{self, IoSlice, IoSliceMut, Seek, SeekFrom};
use std::slice;
#[cfg(windows)]
use {cap_fs_ext::Reopen, fd_lock::RwLock, std::fs, std::os::windows::fs::FileExt};
use {cap_fs_ext::Reopen, std::fs, std::os::windows::fs::FileExt};
#[cfg(not(windows))]
use {rustix::fs::tell, rustix::fs::FileExt};

Expand Down Expand Up @@ -703,144 +703,37 @@ impl FileIoExt for std::fs::File {
fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
// Windows' `seek_write` modifies the current position in the file, so
// re-open the file to leave the original open file unmodified.
//
// We take a lock so that we can test for writing past the end of the
// file and implement writing zeros if the offset is past the end.
//
// Windows documentation [says]:
//
// > A write operation increases the size of the file to the file
// > pointer position plus the size of the buffer written, which results
// > in the intervening bytes uninitialized.
//
// [says]: https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-setfilepointer#remarks
//
// However, our desired behavior is to fill the intervening bytes with
// zeros, so we do it ourselves.
let reopened = reopen_write(self)?;
let mut reopened = RwLock::new(reopened);
let reopened = reopened.write()?;
let mut seek_offset = offset;
let mut write_buf = buf;
let mut prepend_zeros;
let reopened_size = reopened.metadata()?.len();
let num_zeros = offset.saturating_sub(reopened_size);
let num_zeros: usize = num_zeros
.try_into()
.map_err(|_| io::Error::new(io::ErrorKind::OutOfMemory, "write_all_vectored_at"))?;
if num_zeros > 0 {
prepend_zeros = vec![0_u8; num_zeros];
prepend_zeros.extend_from_slice(buf);
seek_offset = reopened_size;
write_buf = &prepend_zeros;
}
let num_written = reopened
.seek_write(write_buf, seek_offset)?
.saturating_sub(num_zeros);
Ok(num_written)
reopen_write(self)?.seek_write(buf, offset)
}

#[inline]
fn write_all_at(&self, buf: &[u8], offset: u64) -> io::Result<()> {
// Similar to `read_exact_at`, re-open the file so that we can do a seek and
// leave the original file unmodified.
//
// Similar to `write_at`, we take a lock to do this.
let reopened = loop {
match reopen_write(self) {
Ok(file) => break file,
Err(err) if err.kind() == io::ErrorKind::Interrupted => continue,
Err(err) => return Err(err),
}
};
let mut reopened = RwLock::new(reopened);
let reopened = reopened.write()?;
let mut seek_offset = offset;
let mut write_buf = buf;
let mut prepend_zeros;
let reopened_size = reopened.metadata()?.len();
let num_zeros = offset.saturating_sub(reopened_size);
let num_zeros: usize = num_zeros
.try_into()
.map_err(|_| io::Error::new(io::ErrorKind::OutOfMemory, "write_all_vectored_at"))?;
if num_zeros > 0 {
prepend_zeros = vec![0_u8; num_zeros];
prepend_zeros.extend_from_slice(buf);
seek_offset = reopened_size;
write_buf = &prepend_zeros;
}
loop {
match reopened.seek(SeekFrom::Start(seek_offset)) {
Ok(_) => break,
Err(err) if err.kind() == io::ErrorKind::Interrupted => continue,
Err(err) => return Err(err),
}
fn write_all_at(&self, mut buf: &[u8], mut offset: u64) -> io::Result<()> {
// Similar to `read_exact_at`, re-open the file so that we can do a seek
// and leave the original file unmodified.
let reopened = reopen_write(self)?;
while buf.len() > 0 {
let n = reopened.seek_write(buf, offset)?;
offset += u64::try_from(n).unwrap();
buf = &buf[n..];
}
reopened.write_all(write_buf)?;
Ok(())
}

#[inline]
fn write_vectored_at(&self, bufs: &[IoSlice], offset: u64) -> io::Result<usize> {
// Similar to `read_vectored_at`, re-open the file to avoid adjusting
// the current position of the already-open file.
//
// Similar to `write_at`, we take a lock to do this.
let reopened = reopen_write(self)?;
let mut reopened = RwLock::new(reopened);
let reopened = reopened.write()?;
let mut seek_offset = offset;
let mut write_bufs = bufs;
let zeros;
let mut prepend_zeros;
let reopened_size = reopened.metadata()?.len();
let num_zeros = offset.saturating_sub(reopened_size);
let num_zeros: usize = num_zeros
.try_into()
.map_err(|_| io::Error::new(io::ErrorKind::OutOfMemory, "write_vectored_at"))?;
if num_zeros > 0 {
zeros = vec![0_u8; num_zeros];
prepend_zeros = vec![IoSlice::new(&zeros)];
prepend_zeros.extend_from_slice(bufs);
seek_offset = reopened_size;
write_bufs = &prepend_zeros;
// Windows doesn't have a vectored write for files, so pick the first
// non-empty slice and write that.
match bufs.iter().find(|p| p.len() > 0) {
Some(buf) => self.write_at(buf, offset),
None => Ok(0),
}
reopened.seek(SeekFrom::Start(seek_offset))?;
let num_written = reopened
.write_vectored(write_bufs)?
.saturating_sub(num_zeros);
Ok(num_written)
}

#[inline]
fn write_all_vectored_at(&self, bufs: &mut [IoSlice], offset: u64) -> io::Result<()> {
// Similar to `read_vectored_at`, re-open the file to avoid adjusting
// the current position of the already-open file.
//
// Similar to `write_at`, we take a lock to do this.
let reopened = loop {
match reopen_write(self) {
Ok(file) => break file,
Err(err) if err.kind() == io::ErrorKind::Interrupted => continue,
Err(err) => return Err(err),
}
};
let mut reopened = RwLock::new(reopened);
let reopened = reopened.write()?;
let reopened_size = reopened.metadata()?.len();
let num_zeros = offset.saturating_sub(reopened_size);
let num_zeros: usize = num_zeros
.try_into()
.map_err(|_| io::Error::new(io::ErrorKind::OutOfMemory, "write_vectored_at"))?;
if num_zeros > 0 {
let zeros = vec![0_u8; num_zeros];
let mut prepend_zeros = vec![IoSlice::new(&zeros)];
prepend_zeros.extend_from_slice(bufs);
reopened.seek(SeekFrom::Start(reopened_size))?;
reopened.write_all_vectored(&mut prepend_zeros)?;
} else {
reopened.seek(SeekFrom::Start(offset))?;
reopened.write_all_vectored(bufs)?;
fn write_all_vectored_at(&self, bufs: &mut [IoSlice], mut offset: u64) -> io::Result<()> {
for buf in bufs {
self.write_all_at(buf, offset)?;
offset += u64::try_from(buf.len()).unwrap();
}
Ok(())
}
Expand Down
1 change: 1 addition & 0 deletions tests/vectored_at.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -412,6 +412,7 @@ fn write_vectored_after_end() {
let buf1 = b"MNOPQRST".to_vec();
let bufs = vec![IoSlice::new(&buf0), IoSlice::new(&buf1)];
let nwritten = check!(file.write_vectored_at(&bufs, 32));
assert!(nwritten > 0);
assert_eq!(check!(file.stream_position()), 26);
let mut back = String::new();
check!(file.seek(std::io::SeekFrom::Start(0)));
Expand Down
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