moirai-async 0.6.1

use std::future::Future;
use std::io;
use std::pin::Pin;
use std::task::{Context, Poll};

use crate::io::traits::{AsyncRead, AsyncWrite};

/// Extension methods for types implementing [`AsyncRead`].
pub trait AsyncReadExt: AsyncRead {
    /// Read some bytes asynchronously from the reader.
    fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self>
    where
        Self: Unpin,
    {
        Read { reader: self, buf }
    }

    /// Read exactly enough bytes to fill the provided buffer.
    fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExact<'a, Self>
    where
        Self: Unpin,
    {
        ReadExact {
            reader: self,
            buf,
            filled: 0,
        }
    }
}

impl<R: AsyncRead + ?Sized> AsyncReadExt for R {}

/// Future returned by [`AsyncReadExt::read`].
pub struct Read<'a, R: ?Sized> {
    reader: &'a mut R,
    buf: &'a mut [u8],
}

impl<'a, R: AsyncRead + ?Sized + Unpin> Future for Read<'a, R> {
    type Output = io::Result<usize>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = &mut *self;
        Pin::new(&mut *this.reader).poll_read(cx, this.buf)
    }
}

/// Future returned by [`AsyncReadExt::read_exact`].
pub struct ReadExact<'a, R: ?Sized> {
    reader: &'a mut R,
    buf: &'a mut [u8],
    filled: usize,
}

impl<'a, R: AsyncRead + ?Sized + Unpin> Future for ReadExact<'a, R> {
    type Output = io::Result<()>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = &mut *self;
        while this.filled < this.buf.len() {
            let filled = this.filled;
            match Pin::new(&mut *this.reader).poll_read(cx, &mut this.buf[filled..]) {
                Poll::Ready(Ok(0)) => {
                    return Poll::Ready(Err(io::Error::new(
                        io::ErrorKind::UnexpectedEof,
                        "failed to fill whole buffer",
                    )));
                }
                Poll::Ready(Ok(n)) => {
                    this.filled += n;
                }
                Poll::Ready(Err(e)) => return Poll::Ready(Err(e)),
                Poll::Pending => return Poll::Pending,
            }
        }
        Poll::Ready(Ok(()))
    }
}

/// Extension methods for types implementing [`AsyncWrite`].
pub trait AsyncWriteExt: AsyncWrite {
    /// Write some bytes asynchronously.
    fn write<'a>(&'a mut self, buf: &'a [u8]) -> Write<'a, Self>
    where
        Self: Unpin,
    {
        Write { writer: self, buf }
    }

    /// Write all bytes asynchronously.
    fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> WriteAll<'a, Self>
    where
        Self: Unpin,
    {
        WriteAll {
            writer: self,
            buf,
            written: 0,
        }
    }

    /// Flush pending writes asynchronously.
    fn flush(&mut self) -> Flush<'_, Self>
    where
        Self: Unpin,
    {
        Flush { writer: self }
    }

    /// Shutdown the write side of the stream.
    fn shutdown(&mut self) -> Shutdown<'_, Self>
    where
        Self: Unpin,
    {
        Shutdown { writer: self }
    }
}

impl<W: AsyncWrite + ?Sized> AsyncWriteExt for W {}

/// Future returned by [`AsyncWriteExt::write`].
pub struct Write<'a, W: ?Sized> {
    writer: &'a mut W,
    buf: &'a [u8],
}

impl<'a, W: AsyncWrite + ?Sized + Unpin> Future for Write<'a, W> {
    type Output = io::Result<usize>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = &mut *self;
        Pin::new(&mut *this.writer).poll_write(cx, this.buf)
    }
}

/// Future returned by [`AsyncWriteExt::write_all`].
pub struct WriteAll<'a, W: ?Sized> {
    writer: &'a mut W,
    buf: &'a [u8],
    written: usize,
}

impl<'a, W: AsyncWrite + ?Sized + Unpin> Future for WriteAll<'a, W> {
    type Output = io::Result<()>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = &mut *self;
        while this.written < this.buf.len() {
            match Pin::new(&mut *this.writer).poll_write(cx, &this.buf[this.written..]) {
                Poll::Ready(Ok(0)) => {
                    return Poll::Ready(Err(io::Error::new(
                        io::ErrorKind::WriteZero,
                        "failed to write whole buffer",
                    )));
                }
                Poll::Ready(Ok(n)) => {
                    this.written += n;
                }
                Poll::Ready(Err(e)) => return Poll::Ready(Err(e)),
                Poll::Pending => return Poll::Pending,
            }
        }
        Poll::Ready(Ok(()))
    }
}

/// Future returned by [`AsyncWriteExt::flush`].
pub struct Flush<'a, W: ?Sized> {
    writer: &'a mut W,
}

impl<'a, W: AsyncWrite + ?Sized + Unpin> Future for Flush<'a, W> {
    type Output = io::Result<()>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = &mut *self;
        Pin::new(&mut *this.writer).poll_flush(cx)
    }
}

/// Future returned by [`AsyncWriteExt::shutdown`].
pub struct Shutdown<'a, W: ?Sized> {
    writer: &'a mut W,
}

impl<'a, W: AsyncWrite + ?Sized + Unpin> Future for Shutdown<'a, W> {
    type Output = io::Result<()>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = &mut *self;
        Pin::new(&mut *this.writer).poll_shutdown(cx)
    }
}