try_read_vectored and try_write_vectored use default implementations that only process the first buffer

[tomashaddad]

Version
1.41.1

Platform
64-bit (Windows)

Description
I was using NamedPipeClient's try_write_vectored exactly as detailed in the documentation but noticed that only the first buffer would ever be written. Looking under the hood, it seems to be using the default implementation from std::io::Write, sans an important caveat in the rustdocs:

The default implementation calls write with either the first nonempty buffer provided, or an empty one if none exists.

i.e.,

pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
where
    F: FnOnce(&mut [u8]) -> Result<usize>,
{
    let buf = bufs.iter_mut().find(|b| !b.is_empty()).map_or(&mut [][..], |b| &mut **b);
    read(buf)
}

Are these meant to be properly implemented?

[Darksonn]

Thanks for reporting this. Yes, we would like these methods to actually perform a vectored read.