//! Utilities for encoding and decoding frames.
//!
//! Contains adapters to go from streams of bytes, [`AsyncRead`] and
//! [`AsyncWrite`], to framed streams implementing [`Sink`] and [`Stream`].
//! Framed streams are also known as [transports].
//!
//! [`AsyncRead`]: #
//! [`AsyncWrite`]: #
#![deny(rust_2018_idioms, warnings)]
use std::{io, mem::MaybeUninit, pin::Pin, task::Context, task::Poll};

mod bcodec;
mod decoder;
mod encoder;
mod framed;

pub use self::bcodec::BytesCodec;
pub use self::decoder::Decoder;
pub use self::encoder::Encoder;
pub use self::framed::{Framed, FramedParts};

pub use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};

use bytes::BufMut;

pub fn poll_read_buf<T: AsyncRead>(
    io: Pin<&mut T>,
    cx: &mut Context<'_>,
    buf: &mut bytes::BytesMut,
) -> Poll<io::Result<usize>> {
    if !buf.has_remaining_mut() {
        return Poll::Ready(Ok(0));
    }

    let n = {
        let dst = buf.chunk_mut();
        let dst = unsafe { &mut *(dst as *mut _ as *mut [MaybeUninit<u8>]) };
        let mut buf = ReadBuf::uninit(dst);
        let ptr = buf.filled().as_ptr();
        if io.poll_read(cx, &mut buf)?.is_pending() {
            return Poll::Pending;
        }

        // Ensure the pointer does not change from under us
        assert_eq!(ptr, buf.filled().as_ptr());
        buf.filled().len()
    };

    // Safety: This is guaranteed to be the number of initialized (and read)
    // bytes due to the invariants provided by `ReadBuf::filled`.
    unsafe {
        buf.advance_mut(n);
    }

    Poll::Ready(Ok(n))
}