Struct BufReader

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

Available on crate feature std only.

Adds buffering to a reader.

It can be excessively inefficient to work directly with an AsyncRead instance. A BufReader performs large, infrequent reads on the underlying AsyncRead and maintains an in-memory buffer of the incoming byte stream.

BufReader can improve the speed of programs that make small and repeated reads to the same file or networking socket. It does not help when reading very large amounts at once, or reading just once or a few times. It also provides no advantage when reading from a source that is already in memory, like a Vec<u8>.

When a BufReader is dropped, the contents of its buffer are discarded. Creating multiple instances of BufReader on the same reader can cause data loss.

Examples

use futures_lite::io::{AsyncBufReadExt, BufReader};

let input: &[u8] = b"hello";
let mut reader = BufReader::new(input);

let mut line = String::new();
reader.read_line(&mut line).await?;

Implementations

impl<R: AsyncRead> BufReader<R>

pub fn new(inner: R) -> BufReader<R>

Creates a buffered reader with the default buffer capacity.

The default capacity is currently 8 KB, but that may change in the future.

Examples

use futures_lite::io::BufReader;

let input: &[u8] = b"hello";
let reader = BufReader::new(input);

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

Creates a buffered reader with the specified capacity.

Examples

use futures_lite::io::BufReader;

let input: &[u8] = b"hello";
let reader = BufReader::with_capacity(1024, input);

impl<R> BufReader<R>

pub fn get_ref(&self) -> &R

Gets a reference to the underlying reader.

It is not advisable to directly read from the underlying reader.

Examples

use futures_lite::io::BufReader;

let input: &[u8] = b"hello";
let reader = BufReader::new(input);

let r = reader.get_ref();

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

Gets a mutable reference to the underlying reader.

It is not advisable to directly read from the underlying reader.

Examples

use futures_lite::io::BufReader;

let input: &[u8] = b"hello";
let mut reader = BufReader::new(input);

let r = reader.get_mut();

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

Returns a reference to the internal buffer.

This method will not attempt to fill the buffer if it is empty.

Examples

use futures_lite::io::BufReader;

let input: &[u8] = b"hello";
let reader = BufReader::new(input);

// The internal buffer is empty until the first read request.
assert_eq!(reader.buffer(), &[]);

pub fn into_inner(self) -> R

Unwraps the buffered reader, returning the underlying reader.

Note that any leftover data in the internal buffer will be lost.

Examples

use futures_lite::io::BufReader;

let input: &[u8] = b"hello";
let reader = BufReader::new(input);

assert_eq!(reader.into_inner(), input);

Trait Implementations

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

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

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.

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

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

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).

impl<R: 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_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

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

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

Attempt to close the object.

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

Attempt to write bytes from bufs into the object using vectored IO operations.

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

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

Formats the value using the given formatter.

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

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