Tracking Issue for RFC 2930 (read-buf)

[nikomatsakis]

This is a tracking issue for the RFC "2930" (rust-lang/rfcs#2930).
The feature gate for the issue is #![feature(read_buf)].

This is now called BorrowedBuf rather than ReadBuf.

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

• Implement the RFC
  • Initial implementation in Implement most of RFC 2930, providing the ReadBuf abstraction #81156
  • Vectorized APIs (read_buf_vectored, ReadBufs).
• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)
  • Note that this is a use of rustc_must_implement_one_of, which is a language-observable thing, and thus needs some amount of oversight/documentation about that as a prerequisite of stabilization.

Unresolved Questions

• Should read_buf return the number of bytes read like read does or should the ReadBuf track it instead? Some operations, like checking for EOF, are a bit simpler if read_buf returns the value, but the confusion around what is and is not trustworthy is worrysome for unsafe code working with Read implementations.
• What should assume_init be named?
• Should the API use a wrapper around &mut ReadBuf to prevent unexpected swapping of the caller-provided ReadBuf?
• Resolve soundness issue: Unsound BufWriter copy_to specialization with the unstable read_buf feature #93305

Implementation history

• Implement most of RFC 2930, providing the ReadBuf abstraction #81156

[nikomatsakis]

( cc @rust-lang/libs )

[beepster4096]

I'm interested in working on this.

@rustbot claim

[beepster4096]

I am slightly confused by the API of ReadBufs. What return type should methods like initialized have: &[u8] or &[IoSlice]? If its the former, how do you know which slices are initialized/filled? If it's the latter, what happens if a slice is partially initialized/filled?

edit: probably I should ask this on zulip instead of github

[sfackler]

It would return &[IoSliceMut], and only include the slices that are fully initialized.

[programmerjake]

It would return &[IoSliceMut], and only include the slices that are fully initialized.

I would have expected it to return (&[IoSliceMut], &[u8]) where it is some number of fully initialized buffers and the initialized portion of the partially initialized buffer.

[sfackler]

Sure, that makes sense.