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use super::bufreader::DEFAULT_BUF_SIZE;
use futures::io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSliceMut, SeekFrom};
use futures::ready;
use futures::task::{Context, Poll};
use pin_project_lite::pin_project;
use std::io::{self, Read};
use std::pin::Pin;
use std::{cmp, fmt};
pin_project! {
/// The `BufReader` struct adds buffering to any reader.
///
/// It can be excessively inefficient to work directly with a [`AsyncRead`]
/// instance. A `BufReader` performs large, infrequent reads on the underlying
/// [`AsyncRead`] and maintains an in-memory buffer of the results.
///
/// `BufReader` can improve the speed of programs that make *small* and
/// *repeated* read calls to the same file or network socket. It does not
/// help when reading very large amounts at once, or reading just one or a few
/// times. It also provides no advantage when reading from a source that is
/// already in memory, like a `Vec<u8>`.
///
/// When the `BufReader` is dropped, the contents of its buffer will be
/// discarded. Creating multiple instances of a `BufReader` on the same
/// stream can cause data loss.
///
/// **Note: this is a fork from `std::io::BufReader` that reads more data in
/// `fill_buf` even if there is already some data in the buffer**
///
/// [`AsyncRead`]: futures_io::AsyncRead
///
// TODO: Examples
pub struct BufReader<R> {
#[pin]
inner: R,
buffer: Vec<u8>,
pos: usize,
cap: usize,
}
}
impl<R: AsyncRead> BufReader<R> {
/// Creates a new `BufReader` with a default buffer capacity. The default is currently 8 KB,
/// but may change in the future.
pub fn new(inner: R) -> Self {
Self::with_capacity(DEFAULT_BUF_SIZE, inner)
}
/// Creates a new `BufReader` with the specified buffer capacity.
pub fn with_capacity(capacity: usize, inner: R) -> Self {
let buffer = vec![0; capacity];
Self {
inner,
buffer,
pos: 0,
cap: 0,
}
}
/// Acquires a reference to the underlying sink or stream that this combinator is
/// pulling from.
pub fn get_ref(&self) -> &R {
&self.inner
}
/// Acquires a mutable reference to the underlying sink or stream that this
/// combinator is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the
/// sink or stream which may otherwise confuse this combinator.
pub fn get_mut(&mut self) -> &mut R {
&mut self.inner
}
/// Acquires a pinned mutable reference to the underlying sink or stream that this
/// combinator is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the
/// sink or stream which may otherwise confuse this combinator.
pub fn get_pin_mut(self: core::pin::Pin<&mut Self>) -> core::pin::Pin<&mut R> {
self.project().inner
}
/// Consumes this combinator, returning the underlying sink or stream.
///
/// Note that this may discard intermediate state of this combinator, so
/// care should be taken to avoid losing resources when this is called.
pub fn into_inner(self) -> R {
self.inner
}
/// Returns a reference to the internally buffered data.
///
/// Unlike `fill_buf`, this will not attempt to fill the buffer if it is empty.
pub fn buffer(&self) -> &[u8] {
&self.buffer[self.pos..self.cap]
}
/// Invalidates all data in the internal buffer.
#[inline]
fn discard_buffer(self: Pin<&mut Self>) {
let this = self.project();
*this.pos = 0;
*this.cap = 0;
}
}
impl<R: AsyncRead> AsyncRead for BufReader<R> {
fn poll_read(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<io::Result<usize>> {
// If we don't have any buffered data and we're doing a massive read
// (larger than our internal buffer), bypass our internal buffer
// entirely.
if self.pos == self.cap && buf.len() >= self.buffer.len() {
let res = ready!(self.as_mut().project().inner.poll_read(cx, buf));
self.discard_buffer();
return Poll::Ready(res);
}
let mut rem = ready!(self.as_mut().poll_fill_buf(cx))?;
let nread = rem.read(buf)?;
self.consume(nread);
Poll::Ready(Ok(nread))
}
fn poll_read_vectored(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &mut [IoSliceMut<'_>],
) -> Poll<io::Result<usize>> {
let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
if self.pos == self.cap && total_len >= self.buffer.len() {
let res = ready!(self.as_mut().project().inner.poll_read_vectored(cx, bufs));
self.discard_buffer();
return Poll::Ready(res);
}
let mut rem = ready!(self.as_mut().poll_fill_buf(cx))?;
let nread = rem.read_vectored(bufs)?;
self.consume(nread);
Poll::Ready(Ok(nread))
}
// we can't skip unconditionally because of the large buffer case in read.
#[cfg(feature = "read-initializer")]
unsafe fn initializer(&self) -> Initializer {
self.inner.initializer()
}
}
impl<R: AsyncRead> AsyncBufRead for BufReader<R> {
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
let this = self.project();
if *this.cap == this.buffer.len() {
if *this.pos == 0 {
return Poll::Ready(Err(io::Error::new(
io::ErrorKind::Interrupted,
"buffer completely filled",
)));
} else {
// reset buffer position
if *this.cap - *this.pos > 0 {
for i in 0..(*this.cap - *this.pos) {
this.buffer[i] = this.buffer[*this.pos + i];
}
}
*this.cap = *this.cap - *this.pos;
*this.pos = 0;
}
}
let read = ready!(this.inner.poll_read(cx, this.buffer))?;
*this.cap += read;
Poll::Ready(Ok(&this.buffer[*this.pos..*this.cap]))
}
fn consume(self: Pin<&mut Self>, amt: usize) {
*self.project().pos = cmp::min(self.pos + amt, self.cap);
}
}
impl<R: AsyncWrite> AsyncWrite for BufReader<R> {
fn poll_write(
self: core::pin::Pin<&mut Self>,
cx: &mut core::task::Context<'_>,
buf: &[u8],
) -> core::task::Poll<std::io::Result<usize>> {
self.project().inner.poll_write(cx, buf)
}
fn poll_write_vectored(
self: core::pin::Pin<&mut Self>,
cx: &mut core::task::Context<'_>,
bufs: &[std::io::IoSlice<'_>],
) -> core::task::Poll<std::io::Result<usize>> {
self.project().inner.poll_write_vectored(cx, bufs)
}
fn poll_flush(
self: core::pin::Pin<&mut Self>,
cx: &mut core::task::Context<'_>,
) -> core::task::Poll<std::io::Result<()>> {
self.project().inner.poll_flush(cx)
}
fn poll_close(
self: core::pin::Pin<&mut Self>,
cx: &mut core::task::Context<'_>,
) -> core::task::Poll<std::io::Result<()>> {
self.project().inner.poll_close(cx)
}
}
impl<R: fmt::Debug> fmt::Debug for BufReader<R> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("BufReader")
.field("reader", &self.inner)
.field(
"buffer",
&format_args!("{}/{}", self.cap - self.pos, self.buffer.len()),
)
.finish()
}
}
impl<R: AsyncRead + AsyncSeek> AsyncSeek for BufReader<R> {
/// Seek to an offset, in bytes, in the underlying reader.
///
/// The position used for seeking with `SeekFrom::Current(_)` is the
/// position the underlying reader would be at if the `BufReader` had no
/// internal buffer.
///
/// Seeking always discards the internal buffer, even if the seek position
/// would otherwise fall within it. This guarantees that calling
/// `.into_inner()` immediately after a seek yields the underlying reader
/// at the same position.
///
/// See [`AsyncSeek`](futures_io::AsyncSeek) for more details.
///
/// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
/// where `n` minus the internal buffer length overflows an `i64`, two
/// seeks will be performed instead of one. If the second seek returns
/// `Err`, the underlying reader will be left at the same position it would
/// have if you called `seek` with `SeekFrom::Current(0)`.
fn poll_seek(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<io::Result<u64>> {
let result: u64;
if let SeekFrom::Current(n) = pos {
let remainder = (self.cap - self.pos) as i64;
// it should be safe to assume that remainder fits within an i64 as the alternative
// means we managed to allocate 8 exbibytes and that's absurd.
// But it's not out of the realm of possibility for some weird underlying reader to
// support seeking by i64::min_value() so we need to handle underflow when subtracting
// remainder.
if let Some(offset) = n.checked_sub(remainder) {
result = ready!(self
.as_mut()
.project()
.inner
.poll_seek(cx, SeekFrom::Current(offset)))?;
} else {
// seek backwards by our remainder, and then by the offset
ready!(self
.as_mut()
.project()
.inner
.poll_seek(cx, SeekFrom::Current(-remainder)))?;
self.as_mut().discard_buffer();
result = ready!(self
.as_mut()
.project()
.inner
.poll_seek(cx, SeekFrom::Current(n)))?;
}
} else {
// Seeking with Start/End doesn't care about our buffer length.
result = ready!(self.as_mut().project().inner.poll_seek(cx, pos))?;
}
self.discard_buffer();
Poll::Ready(Ok(result))
}
}