use futures_core::task::{Context, Poll}; #[cfg(feature = "read-initializer")] use futures_io::Initializer; use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSlice, IoSliceMut, SeekFrom}; use pin_utils::{unsafe_pinned, unsafe_unpinned}; use std::io::{self, Read}; use std::pin::Pin; use std::{cmp, fmt}; use super::DEFAULT_BUF_SIZE; /// 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. /// /// [`AsyncRead`]: futures_io::AsyncRead /// // TODO: Examples pub struct BufReader<R> { inner: R, buf: Box<[u8]>, pos: usize, cap: usize, } impl<R> BufReader<R> { unsafe_pinned!(inner: R); unsafe_unpinned!(pos: usize); unsafe_unpinned!(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 { unsafe { let mut buffer = Vec::with_capacity(capacity); buffer.set_len(capacity); super::initialize(&inner, &mut buffer); Self { inner, buf: buffer.into_boxed_slice(), pos: 0, cap: 0, } } } /// Gets a reference to the underlying reader. /// /// It is inadvisable to directly read from the underlying reader. pub fn get_ref(&self) -> &R { &self.inner } /// Gets a mutable reference to the underlying reader. /// /// It is inadvisable to directly read from the underlying reader. pub fn get_mut(&mut self) -> &mut R { &mut self.inner } /// Gets a pinned mutable reference to the underlying reader. /// /// It is inadvisable to directly read from the underlying reader. pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut R> { self.inner() } /// Consumes this `BufWriter`, returning the underlying reader. /// /// Note that any leftover data in the internal buffer is lost. 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.buf[self.pos..self.cap] } /// Invalidates all data in the internal buffer. #[inline] fn discard_buffer(mut self: Pin<&mut Self>) { *self.as_mut().pos() = 0; *self.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.buf.len() { let res = ready!(self.as_mut().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.buf.len() { let res = ready!(self.as_mut().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 Self { inner, buf, cap, pos } = unsafe { self.get_unchecked_mut() }; let mut inner = unsafe { Pin::new_unchecked(inner) }; // If we've reached the end of our internal buffer then we need to fetch // some more data from the underlying reader. // Branch using `>=` instead of the more correct `==` // to tell the compiler that the pos..cap slice is always valid. if *pos >= *cap { debug_assert!(*pos == *cap); *cap = ready!(inner.as_mut().poll_read(cx, buf))?; *pos = 0; } Poll::Ready(Ok(&buf[*pos..*cap])) } fn consume(mut self: Pin<&mut Self>, amt: usize) { *self.as_mut().pos() = cmp::min(self.pos + amt, self.cap); } } impl<R: AsyncWrite> AsyncWrite for BufReader<R> { fn poll_write( self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8], ) -> Poll<io::Result<usize>> { self.inner().poll_write(cx, buf) } fn poll_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<io::Result<usize>> { self.inner().poll_write_vectored(cx, bufs) } fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> { self.inner().poll_flush(cx) } fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> { self.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.buf.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().inner().poll_seek(cx, SeekFrom::Current(offset)))?; } else { // seek backwards by our remainder, and then by the offset ready!(self.as_mut().inner().poll_seek(cx, SeekFrom::Current(-remainder)))?; self.as_mut().discard_buffer(); result = ready!(self.as_mut().inner().poll_seek(cx, SeekFrom::Current(n)))?; } } else { // Seeking with Start/End doesn't care about our buffer length. result = ready!(self.as_mut().inner().poll_seek(cx, pos))?; } self.discard_buffer(); Poll::Ready(Ok(result)) } }