Struct async_std::io::BufReader

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

Adds buffering to any reader.

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

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.

This type is an async version of std::io::BufReader.

Examples

use async_std::fs::File;
use async_std::io::BufReader;
use async_std::prelude::*;

let mut file = BufReader::new(File::open("a.txt").await?);

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

Methods

impl<R: Read> BufReader<R>

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

Creates a buffered reader with default buffer capacity.

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

Examples

use async_std::fs::File;
use async_std::io::BufReader;

let f = BufReader::new(File::open("a.txt").await?);

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

Creates a new buffered reader with the specified capacity.

Examples

use async_std::fs::File;
use async_std::io::BufReader;

let f = BufReader::with_capacity(1024, File::open("a.txt").await?);

impl<R> BufReader<R>

pub fn get_ref(&self) -> &R

Gets a reference to the underlying reader.

It is inadvisable to directly read from the underlying reader.

Examples

use async_std::fs::File;
use async_std::io::BufReader;

let f = BufReader::new(File::open("a.txt").await?);
let inner = f.get_ref();

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.

Examples

use async_std::fs::File;
use async_std::io::BufReader;

let mut file = BufReader::new(File::open("a.txt").await?);
let inner = file.get_mut();

Important traits for &'_ mut [u8]

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

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

Returns a reference to the internal buffer.

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

Examples

use async_std::fs::File;
use async_std::io::BufReader;

let f = BufReader::new(File::open("a.txt").await?);
let buffer = f.buffer();

pub fn into_inner(self) -> R

Unwraps the buffered reader, returning the underlying reader.

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

Examples

use async_std::fs::File;
use async_std::io::BufReader;

let f = BufReader::new(File::open("a.txt").await?);
let inner = f.into_inner();

Trait Implementations

impl<R: Read> BufRead for BufReader<R>

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

Returns 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 read.

fn read_until<'a>(
    &'a mut self,
    byte: u8,
    buf: &'a mut Vec<u8>
) -> ImplFuture<usize> where
    Self: Unpin, 

Reads all bytes into buf until the delimiter byte or EOF is reached.

fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ImplFuture<Result<usize>> where
    Self: Unpin, 

Reads all bytes and appends them into buf until a newline (the 0xA byte) is reached.

fn lines(self) -> Lines<Self> where
    Self: Unpin + Sized, 

Returns a stream over the lines of this byte stream.

fn split(self, byte: u8) -> Split<Self> where
    Self: Sized, 

Returns a stream over the contents of this reader split on the byte byte.

impl<R: Read> Read 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.

fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> ImplFuture<Result<usize>> where
    Self: Unpin, 

Reads some bytes from the byte stream.

fn read_vectored<'a>(
    &'a mut self,
    bufs: &'a mut [IoSliceMut<'a>]
) -> ImplFuture<Result<usize>> where
    Self: Unpin, 

Like [read], except that it reads into a slice of buffers.

fn read_to_end<'a>(
    &'a mut self,
    buf: &'a mut Vec<u8>
) -> ImplFuture<Result<usize>> where
    Self: Unpin, 

Reads all bytes from the byte stream.

fn read_to_string<'a>(
    &'a mut self,
    buf: &'a mut String
) -> ImplFuture<Result<usize>> where
    Self: Unpin, 

Reads all bytes from the byte stream and appends them into a string.

fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ImplFuture<Result<()>> where
    Self: Unpin, 

Reads the exact number of bytes required to fill buf.

fn take(self, limit: u64) -> Take<Self> where
    Self: Sized, 

Creates an adaptor which will read at most limit bytes from it.

fn by_ref(&mut self) -> &mut Self where
    Self: Sized, 

Creates a "by reference" adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self> where
    Self: Sized, 

Transforms this Read instance to a Stream over its bytes.

fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
    Self: Sized, 

Creates an adaptor which will chain this stream with another.

impl<R: Seek> Seek 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 Seek 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 seek(&mut self, pos: SeekFrom) -> ImplFuture<Result<u64>> where
    Self: Unpin, 

Seeks to a new position in a byte stream.

impl<'__pin, R> Unpin for BufReader<R> where
    __Origin<'__pin, R>: Unpin, 

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

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

Formats the value using the given formatter.