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use std::fmt;
use std::pin::Pin;
use pin_project_lite::pin_project;
use crate::io::write::WriteExt;
use crate::io::{self, Seek, SeekFrom, Write, DEFAULT_BUF_SIZE};
use crate::task::{Context, Poll, ready};
pin_project! {
/// Wraps a writer and buffers its output.
///
/// It can be excessively inefficient to work directly with something that
/// implements [`Write`]. For example, every call to
/// [`write`][`TcpStream::write`] on [`TcpStream`] results in a system call. A
/// `BufWriter` keeps an in-memory buffer of data and writes it to an underlying
/// writer in large, infrequent batches.
///
/// `BufWriter` can improve the speed of programs that make *small* and
/// *repeated* write calls to the same file or network socket. It does not
/// help when writing very large amounts at once, or writing just one or a few
/// times. It also provides no advantage when writing to a destination that is
/// in memory, like a `Vec<u8>`.
///
/// Unlike the `BufWriter` type in `std`, this type does not write out the
/// contents of its buffer when it is dropped. Therefore, it is absolutely
/// critical that users explicitly flush the buffer before dropping a
/// `BufWriter`.
///
/// This type is an async version of [`std::io::BufWriter`].
///
/// [`std::io::BufWriter`]: https://doc.rust-lang.org/std/io/struct.BufWriter.html
///
/// # Examples
///
/// Let's write the numbers one through ten to a [`TcpStream`]:
///
/// ```no_run
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::net::TcpStream;
/// use async_std::prelude::*;
///
/// let mut stream = TcpStream::connect("127.0.0.1:34254").await?;
///
/// for i in 0..10 {
/// let arr = [i+1];
/// stream.write(&arr).await?;
/// }
/// #
/// # Ok(()) }) }
/// ```
///
/// Because we're not buffering, we write each one in turn, incurring the
/// overhead of a system call per byte written. We can fix this with a
/// `BufWriter`:
///
/// ```no_run
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::io::BufWriter;
/// use async_std::net::TcpStream;
/// use async_std::prelude::*;
///
/// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").await?);
///
/// for i in 0..10 {
/// let arr = [i+1];
/// stream.write(&arr).await?;
/// };
///
/// stream.flush().await?;
/// #
/// # Ok(()) }) }
/// ```
///
/// By wrapping the stream with a `BufWriter`, these ten writes are all grouped
/// together by the buffer, and will all be written out in one system call when
/// `stream.flush()` completes. (As mentioned above, dropping a `BufWriter`
/// does not flush its buffers, so a `flush` call is essential.)
///
/// [`Write`]: trait.Write.html
/// [`TcpStream::write`]: ../net/struct.TcpStream.html#method.write
/// [`TcpStream`]: ../net/struct.TcpStream.html
/// [`flush`]: trait.Write.html#tymethod.flush
pub struct BufWriter<W> {
#[pin]
inner: W,
buf: Vec<u8>,
written: usize,
}
}
/// An error returned by `into_inner` which combines an error that
/// happened while writing out the buffer, and the buffered writer object
/// which may be used to recover from the condition.
///
/// # Examples
///
/// ```no_run
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::io::BufWriter;
/// use async_std::net::TcpStream;
///
/// let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34251").await?);
///
/// // unwrap the TcpStream and flush the buffer
/// let stream = match buf_writer.into_inner().await {
/// Ok(s) => s,
/// Err(e) => {
/// // Here, e is an IntoInnerError
/// panic!("An error occurred");
/// }
/// };
/// #
/// # Ok(()) }) }
///```
#[derive(Debug)]
pub struct IntoInnerError<W>(W, crate::io::Error);
impl<W: Write> BufWriter<W> {
/// Creates a new `BufWriter` with a default buffer capacity. The default is currently 8 KB,
/// but may change in the future.
///
/// # Examples
///
/// ```no_run
/// # #![allow(unused_mut)]
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::io::BufWriter;
/// use async_std::net::TcpStream;
///
/// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").await?);
/// #
/// # Ok(()) }) }
/// ```
pub fn new(inner: W) -> BufWriter<W> {
BufWriter::with_capacity(DEFAULT_BUF_SIZE, inner)
}
/// Creates a new `BufWriter` with the specified buffer capacity.
///
/// # Examples
///
/// Creating a buffer with a buffer of a hundred bytes.
///
/// ```no_run
/// # #![allow(unused_mut)]
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::io::BufWriter;
/// use async_std::net::TcpStream;
///
/// let stream = TcpStream::connect("127.0.0.1:34254").await?;
/// let mut buffer = BufWriter::with_capacity(100, stream);
/// #
/// # Ok(()) }) }
/// ```
pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> {
BufWriter {
inner,
buf: Vec::with_capacity(capacity),
written: 0,
}
}
/// Gets a reference to the underlying writer.
///
/// # Examples
///
/// ```no_run
/// # #![allow(unused_mut)]
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::io::BufWriter;
/// use async_std::net::TcpStream;
///
/// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").await?);
///
/// // We can use reference just like buffer
/// let reference = buffer.get_ref();
/// #
/// # Ok(()) }) }
/// ```
pub fn get_ref(&self) -> &W {
&self.inner
}
/// Gets a mutable reference to the underlying writer.
///
/// It is inadvisable to directly write to the underlying writer.
///
/// # Examples
///
/// ```no_run
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::io::BufWriter;
/// use async_std::net::TcpStream;
///
/// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").await?);
///
/// // We can use reference just like buffer
/// let reference = buffer.get_mut();
/// #
/// # Ok(()) }) }
/// ```
pub fn get_mut(&mut self) -> &mut W {
&mut self.inner
}
/// Gets a pinned mutable reference to the underlying writer.
///
/// It is inadvisable to directly write to the underlying writer.
fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut W> {
self.project().inner
}
/// Consumes BufWriter, returning the underlying writer
///
/// This method will not write leftover data, it will be lost.
/// For method that will attempt to write before returning the writer see [`poll_into_inner`]
///
/// [`poll_into_inner`]: #method.poll_into_inner
/// # Examples
///
/// ```no_run
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::io::BufWriter;
/// use async_std::net::TcpStream;
///
/// let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34251").await?);
///
/// // unwrap the TcpStream and flush the buffer
/// let stream = buf_writer.into_inner().await.unwrap();
/// #
/// # Ok(()) }) }
/// ```
pub async fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>>
where
Self: Unpin,
{
match self.flush().await {
Err(e) => Err(IntoInnerError(self, e)),
Ok(()) => Ok(self.inner),
}
}
/// Returns a reference to the internally buffered data.
///
/// # Examples
///
/// ```no_run
/// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
/// use async_std::io::BufWriter;
/// use async_std::net::TcpStream;
///
/// let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34251").await?);
///
/// // See how many bytes are currently buffered
/// let bytes_buffered = buf_writer.buffer().len();
/// #
/// # Ok(()) }) }
/// ```
pub fn buffer(&self) -> &[u8] {
&self.buf
}
/// Poll buffer flushing until completion
///
/// This is used in types that wrap around BufWrite, one such example: [`LineWriter`]
///
/// [`LineWriter`]: struct.LineWriter.html
fn poll_flush_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
let mut this = self.project();
let len = this.buf.len();
let mut ret = Ok(());
while *this.written < len {
match this
.inner
.as_mut()
.poll_write(cx, &this.buf[*this.written..])
{
Poll::Ready(Ok(0)) => {
ret = Err(io::Error::new(
io::ErrorKind::WriteZero,
"Failed to write buffered data",
));
break;
}
Poll::Ready(Ok(n)) => *this.written += n,
Poll::Ready(Err(ref e)) if e.kind() == io::ErrorKind::Interrupted => {}
Poll::Ready(Err(e)) => {
ret = Err(e);
break;
}
Poll::Pending => return Poll::Pending,
}
}
if *this.written > 0 {
this.buf.drain(..*this.written);
}
*this.written = 0;
Poll::Ready(ret)
}
}
impl<W: Write> Write for BufWriter<W> {
fn poll_write(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
if self.buf.len() + buf.len() > self.buf.capacity() {
ready!(self.as_mut().poll_flush_buf(cx))?;
}
if buf.len() >= self.buf.capacity() {
self.get_pin_mut().poll_write(cx, buf)
} else {
Pin::new(&mut *self.project().buf).poll_write(cx, buf)
}
}
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
ready!(self.as_mut().poll_flush_buf(cx))?;
self.get_pin_mut().poll_flush(cx)
}
fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
ready!(self.as_mut().poll_flush_buf(cx))?;
self.get_pin_mut().poll_close(cx)
}
}
impl<W: Write + fmt::Debug> fmt::Debug for BufWriter<W> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("BufWriter")
.field("writer", &self.inner)
.field("buf", &self.buf)
.finish()
}
}
impl<W: Write + Seek> Seek for BufWriter<W> {
/// Seek to the offset, in bytes, in the underlying writer.
///
/// Seeking always writes out the internal buffer before seeking.
fn poll_seek(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<io::Result<u64>> {
ready!(self.as_mut().poll_flush_buf(cx))?;
self.get_pin_mut().poll_seek(cx, pos)
}
}