Struct futures_util::io::BufReader

pub struct BufReader<R> { /* fields omitted */ }

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.

Methods

impl<R: AsyncRead> BufReader<R>

pub fn new(inner: R) -> Self

Creates a new BufReader with a default buffer capacity. The default is currently 8 KB, but may change in the future.

pub fn with_capacity(capacity: usize, inner: R) -> Self

Creates a new BufReader with the specified buffer capacity.

pub fn get_ref(&self) -> &R

Gets a reference to the underlying reader.

It is inadvisable to directly read from the underlying reader.

pub fn get_mut(&mut self) -> &mut R

Gets a 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>

Gets a pinned mutable reference to the underlying reader.

It is inadvisable to directly read from the underlying reader.

pub fn into_inner(self) -> R

Consumes this BufWriter, returning the underlying reader.

Note that any leftover data in the internal buffer is lost.

Important traits for &'_ mut [u8]

impl<'_> Write for &'_ mut [u8]impl<'_> Read for &'_ [u8]

pub fn buffer(&self) -> &[u8]

Returns a reference to the internally buffered data.

Unlike fill_buf, this will not attempt to fill the buffer if it is empty.

impl<R: AsyncRead + AsyncSeek> BufReader<R>

pub fn poll_seek_relative(
    self: Pin<&mut Self>,
    cx: &mut Context,
    offset: i64
) -> Poll<Result<()>>

Seeks relative to the current position. If the new position lies within the buffer, the buffer will not be flushed, allowing for more efficient seeks. This method does not return the location of the underlying reader, so the caller must track this information themselves if it is required.

Trait Implementations

impl<R: AsyncRead + Debug> Debug for BufReader<R>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<R: AsyncRead> AsyncRead for BufReader<R>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context,
    buf: &mut [u8]
) -> Poll<Result<usize>>

Attempt to read from the AsyncRead into buf.

fn poll_read_vectored(
    self: Pin<&mut Self>,
    cx: &mut Context,
    bufs: &mut [IoSliceMut]
) -> Poll<Result<usize>>

Attempt to read from the AsyncRead into bufs using vectored IO operations.

unsafe fn initializer(&self) -> Initializer

Determines if this AsyncReader can work with buffers of uninitialized memory.

impl<R: AsyncRead + AsyncSeek> AsyncSeek for BufReader<R>

fn poll_seek(
    self: Pin<&mut Self>,
    cx: &mut Context,
    pos: SeekFrom
) -> Poll<Result<u64>>

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.

To seek without discarding the internal buffer, use BufReader::poll_seek_relative.

See 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).

impl<R: AsyncRead> AsyncBufRead for BufReader<R>

fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<&[u8]>>

Attempt to return the contents of the internal buffer, filling it with more data from the inner reader if it is empty.

fn consume(self: Pin<&mut Self>, amt: usize)

Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to [poll_read].