Struct tokio::io::util::buf_reader::BufReader

pub struct BufReader<R> {
    pub(super) inner: R,
    pub(super) buf: Box<[u8]>,
    pub(super) pos: usize,
    pub(super) cap: usize,
    pub(super) seek_state: SeekState,
}

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.

Fields

inner: R

buf: Box<[u8]>

pos: usize

cap: usize

seek_state: SeekState

Implementations

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 BufReader, returning the underlying reader.

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

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.

fn discard_buffer(self: Pin<&mut Self>)

Invalidates all data in the internal buffer.

Trait Implementations

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

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

Attempts 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.

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

fn poll_read( self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>, ) -> Poll<Result<()>>

Attempts to read from the AsyncRead into buf.

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

Seeks 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 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 start_seek(self: Pin<&mut Self>, pos: SeekFrom) -> Result<()>

Attempts to seek to an offset, in bytes, in a stream.

fn poll_complete( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Result<u64>>

Waits for a seek operation to complete.

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

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

Attempt to write bytes from buf into the object.

fn poll_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<Result<usize>>

Like poll_write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

Determines if this writer has an efficient poll_write_vectored implementation.

fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempts to flush the object, ensuring that any buffered data reach their destination.

fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

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

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

Formats the value using the given formatter.

impl<RW> From<BufReader<BufWriter<RW>>> for BufStream<RW>

fn from(b: BufReader<BufWriter<RW>>) -> Self

Converts to this type from the input type.

impl<'__pin, R> Unpin for BufReader<R>

where PinnedFieldsOf<__Origin<'__pin, R>>: Unpin,