Tracking Issue for `read_buf_at`

Feature gate: #![feature(read_buf_at)]

This is a tracking issue for FileExt::read_buf_at() and related methods, providing positioned reads into unintialized buffers.

#![feature(read_buf)] adds support for reads into unintialized buffers via BorrowedBuf and BorrowedCursor. This feature expands that to reads from specific offsets.

Public API

// std::os::unix::fs
trait FileExt {
    // [...] (existing methods)

    /// Equivalent to read_at()
    fn read_buf_at(&self, buf: BorrowedCursor<'_>, offset: u64) -> io::Result<()>;

    /// Equivalent to read_exact_at()
    fn read_buf_exact_at(&self, buf: BorrowedCursor<'_>, offset: u64) -> io::Result<()>;
}

// std::os::windows::fs
trait FileExt {
    // [...] (existing methods)

    /// Equivalent to seek_read()
    fn seek_read_buf(&self, buf: BorrowedCursor<'_>, offset: u64) -> io::Result<()>;
}

Steps / History

• https://github.com/rust-lang/libs-team/issues/581
• Implementation: #140459
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• #![feature(core_io_borrowed_buf)] changes before stabilization?
• #![feature(read_buf)] changes before stabilization?

Start by reviewing implementation PR #140459 and the public APIs in std::os::unix::fs::FileExt and std::os::windows::fs::FileExt, then read the linked read_buf and core_io_borrowed_buf tracking issues. Resolve the listed pre-stabilization questions and complete the FCP and stabilization steps; done means the feature is ready for a stabilization PR.