BoundedBuf.slice() panics for empty bufs

[problame]

Problem

The

impl<T: IoBuf> BoundedBuf for T

panics here

tokio-epoll-uring/uring-common/src/buf/bounded.rs

Lines 108 to 109 in 91d67e2

	assert!(begin < self.bytes_total());

if the T is a zero-capacity IoBuf (e.g., a Vec::new()).

This is unlike regular Rust slices, which are zero-sized:

let v = Vec::new();
&v[..];
&v[0..0];

Workaround

Initially, Pageserver integration PRs neondatabase/neon#6663 dealt with this by checking for empty bufs beforehand.

As of neondatabase/neon#8717, the Pageserver write path uses a newtype that, in addition to mitigating other deficiencies of the tokio_uring::Slice, mitigates this issue here:

 let s = if len == 0 {
    // `BoundedBuf::slice(0..len)` or `BoundedBuf::slice(..)` has an incorrect assertion,
    // causing a panic if len == 0.
    // The Slice::from_buf_bounds has the correct assertion (<= instead of <).
    // => https://github.com/neondatabase/tokio-epoll-uring/issues/46
    let slice = self.slice_full();
    let mut bounds: Range<_> = slice.bounds();
    bounds.end = bounds.start;
    Slice::from_buf_bounds(slice.into_inner(), bounds)
} else {
    self.slice(0..len)
};

https://github.com/neondatabase/neon/blob/a5c062c33619d19b58dbf89517d021199bfd772c/pageserver/src/virtual_file/owned_buffers_io/io_buf_ext.rs#L58-L69