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use bytes::{Buf, BytesMut};
use futures::ready;
use std::cmp;
use std::io::Result;
use std::pin::Pin;
use std::task::{Context, Poll};
use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
macro_rules! delegate_write {
() => {
fn poll_write(
mut self: std::pin::Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<std::io::Result<usize>> {
Pin::new(&mut self.inner).poll_write(cx, buf)
}
};
}
macro_rules! delegate_flush {
() => {
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
Pin::new(&mut self.inner).poll_flush(cx)
}
};
}
macro_rules! delegate_shutdown {
() => {
fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
Pin::new(&mut self.inner).poll_shutdown(cx)
}
};
}
macro_rules! delegate_read {
($type:ident) => {
impl<R: AsyncRead + Unpin> AsyncRead for $type<R> {
fn poll_read(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut ReadBuf<'_>,
) -> Poll<Result<()>> {
Pin::new(&mut self.inner).poll_read(cx, buf)
}
}
};
}
macro_rules! delegate_write_all {
($type:ident) => {
impl<W: AsyncWrite + Unpin> AsyncWrite for $type<W> {
delegate_write!();
delegate_flush!();
delegate_shutdown!();
}
};
}
pub struct PrependReader<R> {
inner: R,
prepend: Option<BytesMut>,
}
impl<R: AsyncRead> PrependReader<R> {
pub fn new<P: Into<BytesMut>>(inner: R, prepend: P) -> Self {
let prepend = prepend.into();
let prepend = if prepend.is_empty() {
None
} else {
Some(prepend)
};
PrependReader { inner, prepend }
}
}
impl<R: AsyncRead + Unpin> AsyncRead for PrependReader<R> {
fn poll_read(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut ReadBuf<'_>,
) -> Poll<Result<()>> {
if let Some(ref mut prepend_buf) = self.prepend {
let n = cmp::min(buf.remaining(), prepend_buf.len());
buf.put_slice(&prepend_buf[..n]);
prepend_buf.advance(n);
if prepend_buf.is_empty() {
self.prepend = None;
}
Poll::Ready(Ok(()))
} else {
Pin::new(&mut self.inner).poll_read(cx, buf)
}
}
}
delegate_write_all!(PrependReader);
pub struct PrependWriter<W> {
inner: W,
prepend: Option<BytesMut>,
len_before_concat: Option<usize>,
written: usize,
}
impl<W: AsyncWrite> PrependWriter<W> {
pub fn new<P: Into<BytesMut>>(inner: W, prepend: P) -> Self {
let prepend = prepend.into();
let prepend = if prepend.is_empty() {
None
} else {
Some(prepend)
};
PrependWriter {
inner,
prepend,
len_before_concat: None,
written: 0,
}
}
}
impl<W: AsyncWrite + Unpin> AsyncWrite for PrependWriter<W> {
fn poll_write(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<Result<usize>> {
let me = &mut *self;
if let Some(ref mut prepend_buf) = me.prepend {
loop {
if me.len_before_concat.is_none() {
me.len_before_concat = Some(prepend_buf.len());
prepend_buf.extend_from_slice(buf);
}
let n = ready!(Pin::new(&mut me.inner).poll_write(cx, &prepend_buf))?;
me.written += n;
if me.written > me.len_before_concat.unwrap() {
me.prepend = None;
return Poll::Ready(Ok(me.written - me.len_before_concat.unwrap()));
}
}
} else {
Pin::new(&mut self.inner).poll_write(cx, buf)
}
}
delegate_flush!();
delegate_shutdown!();
}
delegate_read!(PrependWriter);
#[cfg(test)]
mod test {
use super::*;
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tokio_test::io::Builder;
#[tokio::test]
async fn reader() {
let mock = Builder::new().read(b"AAA").build();
let prepend = b"BBB";
let mut reader = PrependReader::new(mock, &prepend[..]);
let mut buf = vec![];
reader.read_to_end(&mut buf).await.unwrap();
assert_eq!(buf, b"BBBAAA");
}
#[tokio::test]
async fn writer() {
let prepend = b"AAA";
let mock = Builder::new().write(prepend).write(b"BBB").build();
let mut writer = PrependWriter::new(mock, &prepend[..]);
writer.write_all(b"BBB").await.unwrap();
}
}