Dandandan commented on code in PR #628:
URL:
https://github.com/apache/arrow-rs-object-store/pull/628#discussion_r2742320131
##########
src/local.rs:
##########
@@ -988,26 +988,79 @@ pub(crate) fn read_range(
// Don't read past end of file
let to_read = range.end.min(file_len) - range.start;
+ let mut buf = Vec::with_capacity(to_read as usize);
- file.seek(SeekFrom::Start(range.start)).map_err(|source| {
- let path = path.into();
- Error::Seek { source, path }
- })?;
+ #[cfg(any(target_family = "unix", target_family = "windows"))]
+ {
+ #[cfg(target_family = "unix")]
+ use std::os::unix::fs::FileExt;
+ #[cfg(target_family = "windows")]
+ use std::os::windows::fs::FileExt;
+
+ // Safety:
+ // Setting the buffer's length to its capacity is safe as it remains
within its allocated memory.
+ // In cases where `read_exact_at` errors, the contents of the buffer
are undefined,
+ // but we discard it without using it.
+ unsafe {
+ buf.set_len(to_read as usize);
+ }
Review Comment:
Or a suggestion by Gemini:
```
use std::os::unix::io::AsRawFd;
let fd = file.as_raw_fd();
let mut buf = Vec::with_capacity(to_read);
let bytes_read = unsafe {
// libc::pread takes a raw pointer (*mut c_void), avoiding the reference
creation UB
libc::pread(
fd,
buf.as_mut_ptr() as *mut _,
to_read,
offset as i64
)
};
if bytes_read >= 0 {
unsafe { buf.set_len(bytes_read as usize) };
} else {
// Handle error
}
```
##########
src/local.rs:
##########
@@ -988,26 +988,79 @@ pub(crate) fn read_range(
// Don't read past end of file
let to_read = range.end.min(file_len) - range.start;
+ let mut buf = Vec::with_capacity(to_read as usize);
- file.seek(SeekFrom::Start(range.start)).map_err(|source| {
- let path = path.into();
- Error::Seek { source, path }
- })?;
+ #[cfg(any(target_family = "unix", target_family = "windows"))]
+ {
+ #[cfg(target_family = "unix")]
+ use std::os::unix::fs::FileExt;
+ #[cfg(target_family = "windows")]
+ use std::os::windows::fs::FileExt;
+
+ // Safety:
+ // Setting the buffer's length to its capacity is safe as it remains
within its allocated memory.
+ // In cases where `read_exact_at` errors, the contents of the buffer
are undefined,
+ // but we discard it without using it.
+ unsafe {
+ buf.set_len(to_read as usize);
+ }
Review Comment:
Or a suggestion by Gemini (raw file IO):
```
use std::os::unix::io::AsRawFd;
let fd = file.as_raw_fd();
let mut buf = Vec::with_capacity(to_read);
let bytes_read = unsafe {
// libc::pread takes a raw pointer (*mut c_void), avoiding the reference
creation UB
libc::pread(
fd,
buf.as_mut_ptr() as *mut _,
to_read,
offset as i64
)
};
if bytes_read >= 0 {
unsafe { buf.set_len(bytes_read as usize) };
} else {
// Handle error
}
```
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