Working with Files?

[pwaller]

I had a go at writing a basic program to copy the content of files. However, I found that I can't use monoio::io::copy or monoio::io::zero_copy, I understand because monoio::fs::File only implements positional I/O.

I found my way to BufReader which sounds like what I want, from the docs:

BufReader implements AsyncBufRead and AsyncReadRent, and if the inner io implements AsyncWriteRent, it will delegate the implementation.

However, I do not see an implementation unless the underlying AsyncReadRent.

I'd like to be able to copy or zero-copy file-based file descriptors in an obvious way using the functions provided by the library.

Is this possible currently, or is there some implementation missing?

[Zk2u]

I don't know if this is exactly the same issue, but I'm trying to use BufWriter with File to write to it using AsyncWriteRentExt.

BufWriter states:

BufWriter is a struct with a buffer. BufWriter implements AsyncWriteRent, and if the inner io implements AsyncReadRent, it will delegate the implementation.

However, from the impl<W: AsyncWriteRent> AsyncWriteRent for BufWriter<W>, it appears that it's also delegating AsyncWriteRent. Since File doesn't have AsyncWriteRent, we don't get it using the BufWriter, which conflicts with the statements on BufWriter.

monoio/monoio/src/io/util/buf_writer.rs

Lines 94 to 152 in cdddeff

	impl<W: AsyncWriteRent> AsyncWriteRent for BufWriter<W> {
	async fn write<T: IoBuf>(&mut self, buf: T) -> BufResult<usize, T> {
	let owned_buf = self.buf.as_ref().unwrap();
	let owned_len = owned_buf.len();
	let amt = buf.bytes_init();
	if self.pos + amt > owned_len {
	// Buf can not be copied directly into OwnedBuf,
	// we must flush OwnedBuf first.
	match self.flush_buf().await {
	Ok(_) => (),
	Err(e) => {
	return (Err(e), buf);
	}
	}
	}
	// Now there are two situations here:
	// 1. OwnedBuf has data, and self.pos + amt <= owned_len,
	// which means the data can be copied into OwnedBuf.
	// 2. OwnedBuf is empty. If we can copy buf into OwnedBuf,
	// we will copy it, otherwise we will send it directly(in
	// this situation, the OwnedBuf must be already empty).
	if amt > owned_len {
	self.inner.write(buf).await
	} else {
	unsafe {
	let owned_buf = self.buf.as_mut().unwrap();
	owned_buf
	.as_mut_ptr()
	.add(self.cap)
	.copy_from_nonoverlapping(buf.read_ptr(), amt);
	}
	self.cap += amt;
	(Ok(amt), buf)
	}
	}
	// TODO: implement it as real io_vec
	async fn writev<T: IoVecBuf>(&mut self, buf: T) -> BufResult<usize, T> {
	let slice = match IoVecWrapper::new(buf) {
	Ok(slice) => slice,
	Err(buf) => return (Ok(0), buf),
	};
	let (result, slice) = self.write(slice).await;
	(result, slice.into_inner())
	}
	async fn flush(&mut self) -> std::io::Result<()> {
	self.flush_buf().await?;
	self.inner.flush().await
	}
	async fn shutdown(&mut self) -> std::io::Result<()> {
	self.flush_buf().await?;
	self.inner.shutdown().await
	}
	}

[Lzzzzzt]

Hello guys, the basic file operations should be usable, would you like to have a try? @pwaller @Zk2u

[Zk2u]

Oh awesome thank you. I was actually doing this to try port sled 1.0.0's on disk backend to something completely async for fun using monoio. I'll check it out when I have time. Good job!!