Tcp socket read, without read_with

[MathiasKoch]

Currently this crate implements a slightly modified version of the TcpStack trait from embedded-nal, with the addition of

fn read_with<F>(&self, socket: &mut Self::TcpSocket, f: F) -> nb::Result<usize, Self::Error>
    where
        F: FnOnce(&[u8], Option<&[u8]>) -> usize;

As this allows peeking into the buffer, to selectively do copy, only if a full valid packet is in place (eg an mqtt packet).

We need to figure out a way to either commit the read_with fn upstream, if deemed useful, or use the regular buffered read without introducing additional clones

NOTE
This is the blocking issue for releasing to crates.io, as git dependencies are not allowed on crates.io

[keisrk]

Came from this. As mentioned earlier, we don't want to divide the ecosystem.
Still, can we have a polyfill trait ClosureBasedZeroCopy: TcpClient { fn read_with(..) .. } for the time being? It's just a temporary workaround.

[MathiasKoch]

Yep, i think that would be a great temp solution 👍

I will add it in mqttrust, where the read_with is required

[MathiasKoch]

Hmm.. nope, should probably be added somewhere else? Maybe ublox-cellular? or a completely new repo of temporary extension traits for our device?

[keisrk]

Or maybe we can simply update your factbird-1.0 branch basing on v0.2.0. I just made a PR. I can explore the both approaches:)

[keisrk]

Hi @MathiasKoch , perhaps we can work around the zero-copy part of discussion. I made another PR, so if you have a spare time, can you quickly have a look?