fmmap 0.5.0

A flexible and convenient high-level mmap for zero-copy file I/O.
Documentation 
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use bytes::Buf;
use pin_project_lite::pin_project;
use std::{
  fmt::{Debug, Formatter},
  io::{Cursor, Error, SeekFrom},
  pin::Pin,
  task::{Context, Poll},
};
use tokio::io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};

declare_and_impl_basic_writer!();

impl AsyncRead for AsyncMmapFileWriter<'_> {
  fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>,
  ) -> Poll<std::io::Result<()>> {
    self.project().w.poll_read(cx, buf)
  }
}

impl AsyncBufRead for AsyncMmapFileWriter<'_> {
  fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<std::io::Result<&[u8]>> {
    self.project().w.poll_fill_buf(cx)
  }

  fn consume(self: Pin<&mut Self>, amt: usize) {
    self.project().w.consume(amt)
  }
}

impl AsyncSeek for AsyncMmapFileWriter<'_> {
  fn start_seek(self: Pin<&mut Self>, position: SeekFrom) -> std::io::Result<()> {
    self.project().w.start_seek(position)
  }

  fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<std::io::Result<u64>> {
    self.project().w.poll_complete(cx)
  }
}

impl AsyncWrite for AsyncMmapFileWriter<'_> {
  fn poll_write(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &[u8],
  ) -> Poll<std::io::Result<usize>> {
    self.project().w.poll_write(cx, buf)
  }

  fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<std::io::Result<()>> {
    self.project().w.poll_flush(cx)
  }

  fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Error>> {
    self.project().w.poll_shutdown(cx)
  }
}

impl Buf for AsyncMmapFileWriter<'_> {
  fn remaining(&self) -> usize {
    self.w.remaining()
  }

  fn chunk(&self) -> &[u8] {
    self.w.chunk()
  }

  fn advance(&mut self, cnt: usize) {
    self.w.advance(cnt)
  }
}

#[cfg(test)]
mod tests {
  use crate::{raw::tokio::AsyncMemoryMmapFileMut, tokio::AsyncMmapFileMutExt};
  use bytes::Buf;
  use tokio::io::{AsyncBufReadExt, AsyncReadExt, AsyncWriteExt};

  #[tokio::test]
  async fn test_writer() {
    let mut file = AsyncMemoryMmapFileMut::from_vec("test.mem", vec![1; 8096]);
    let mut w = file.writer(0).unwrap();
    let _ = format!("{:?}", w);
    assert_eq!(w.len(), 8096);
    assert_eq!(w.offset(), 0);
    let mut buf = [0; 10];
    let n = w.read(&mut buf).await.unwrap();
    assert!(buf[0..n].eq(vec![1; n].as_slice()));
    w.fill_buf().await.unwrap();
    w.consume(8096);
    w.shutdown().await.unwrap();

    let mut w = file.range_writer(100, 100).unwrap();
    assert_eq!(w.remaining(), 100);
    w.advance(10);
    assert_eq!(w.remaining(), 90);
    let buf = w.chunk();
    assert_eq!(buf.len(), 90);
  }
}