Struct futures_lite::io::BufReader

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

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§

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impl<R: AsyncRead> BufReader<R>

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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);
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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);
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impl<R> BufReader<R>

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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();
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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();
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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(), &[]);
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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§

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

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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. Read more
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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. Read more
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impl<R: AsyncRead> AsyncRead for BufReader<R>

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

Attempt to read from the AsyncRead into buf. Read more
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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. Read more
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impl<R: AsyncSeek> AsyncSeek for BufReader<R>

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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).

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

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

Attempt to write bytes from buf into the object. Read more
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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. Read more
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fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempt to close the object. Read more
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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. Read more
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impl<R: Debug> Debug for BufReader<R>

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

Formats the value using the given formatter. Read more
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impl<'__pin, R> Unpin for BufReader<R>
where __Origin<'__pin, R>: Unpin,

Auto Trait Implementations§

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impl<R> Freeze for BufReader<R>
where R: Freeze,

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impl<R> RefUnwindSafe for BufReader<R>
where R: RefUnwindSafe,

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impl<R> Send for BufReader<R>
where R: Send,

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impl<R> Sync for BufReader<R>
where R: Sync,

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impl<R> UnwindSafe for BufReader<R>
where R: UnwindSafe,

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<R> AsyncBufReadExt for R
where R: AsyncBufRead + ?Sized,

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fn fill_buf(&mut self) -> FillBuf<'_, Self>
where Self: Unpin,

Returns the contents of the internal buffer, filling it with more data if empty. Read more
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fn consume(&mut self, amt: usize)
where Self: Unpin,

Consumes amt buffered bytes. Read more
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fn read_until<'a>( &'a mut self, byte: u8, buf: &'a mut Vec<u8> ) -> ReadUntilFuture<'_, Self>
where Self: Unpin,

Reads all bytes and appends them into buf until the delimiter byte or EOF is found. Read more
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fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLineFuture<'_, Self>
where Self: Unpin,

Reads all bytes and appends them into buf until a newline (the 0xA byte) or EOF is found. Read more
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fn lines(self) -> Lines<Self>
where Self: Unpin + Sized,

Returns a stream over the lines of this byte stream. Read more
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fn split(self, byte: u8) -> Split<Self>
where Self: Sized,

Returns a stream over the contents of this reader split on the specified byte. Read more
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impl<R> AsyncReadExt for R
where R: AsyncRead + ?Sized,

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

Reads some bytes from the byte stream. Read more
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fn read_vectored<'a>( &'a mut self, bufs: &'a mut [IoSliceMut<'a>] ) -> ReadVectoredFuture<'a, Self>
where Self: Unpin,

Like read(), except it reads into a slice of buffers. Read more
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fn read_to_end<'a>( &'a mut self, buf: &'a mut Vec<u8> ) -> ReadToEndFuture<'a, Self>
where Self: Unpin,

Reads the entire contents and appends them to a Vec. Read more
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fn read_to_string<'a>( &'a mut self, buf: &'a mut String ) -> ReadToStringFuture<'a, Self>
where Self: Unpin,

Reads the entire contents and appends them to a String. Read more
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fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExactFuture<'a, Self>
where Self: Unpin,

Reads the exact number of bytes required to fill buf. Read more
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fn take(self, limit: u64) -> Take<Self>
where Self: Sized,

Creates an adapter which will read at most limit bytes from it. Read more
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fn bytes(self) -> Bytes<Self>
where Self: Sized,

Converts this AsyncRead into a Stream of bytes. Read more
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fn chain<R: AsyncRead>(self, next: R) -> Chain<Self, R>
where Self: Sized,

Creates an adapter which will chain this stream with another. Read more
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fn boxed_reader<'a>(self) -> Pin<Box<dyn AsyncRead + Send + 'a>>
where Self: Sized + Send + 'a,

Boxes the reader and changes its type to dyn AsyncRead + Send + 'a. Read more
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impl<S> AsyncSeekExt for S
where S: AsyncSeek + ?Sized,

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fn seek(&mut self, pos: SeekFrom) -> SeekFuture<'_, Self>
where Self: Unpin,

Seeks to a new position in a byte stream. Read more
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impl<W> AsyncWriteExt for W
where W: AsyncWrite + ?Sized,

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

Writes some bytes into the byte stream. Read more
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fn write_vectored<'a>( &'a mut self, bufs: &'a [IoSlice<'a>] ) -> WriteVectoredFuture<'a, Self>
where Self: Unpin,

Like write(), except that it writes a slice of buffers. Read more
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fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> WriteAllFuture<'a, Self>
where Self: Unpin,

Writes an entire buffer into the byte stream. Read more
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fn flush(&mut self) -> FlushFuture<'_, Self>
where Self: Unpin,

Flushes the stream to ensure that all buffered contents reach their destination. Read more
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fn close(&mut self) -> CloseFuture<'_, Self>
where Self: Unpin,

Closes the writer. Read more
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fn boxed_writer<'a>(self) -> Pin<Box<dyn AsyncWrite + Send + 'a>>
where Self: Sized + Send + 'a,

Boxes the writer and changes its type to dyn AsyncWrite + Send + 'a. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.