AdamGS commented on code in PR #628:
URL:
https://github.com/apache/arrow-rs-object-store/pull/628#discussion_r2741285950
##########
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);
+ }
- let mut buf = Vec::with_capacity(to_read as usize);
- let read = file.take(to_read).read_to_end(&mut buf).map_err(|source| {
- let path = path.into();
- Error::UnableToReadBytes { source, path }
- })? as u64;
-
- if read != to_read {
- let error = Error::OutOfRange {
- path: path.into(),
- expected: to_read,
- actual: read,
- };
+ let mut buf_slice = &mut buf[..];
+ let mut offset = range.start;
+
+ while !buf_slice.is_empty() {
Review Comment:
this is roughly the implementation of `read_exact_at`, just allows us to
keep the same errors and track how many bytes we've read for the `OutOfRange`
error branch.
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