Struct futures_util::io::buf_writer::BufWriter

pub struct BufWriter<W> {
    inner: W,
    buf: Vec<u8>,
    written: usize,
}

Wraps a writer and buffers its output.

It can be excessively inefficient to work directly with something that implements AsyncWrite. A BufWriter keeps an in-memory buffer of data and writes it to an underlying writer in large, infrequent batches.

BufWriter can improve the speed of programs that make small and repeated write calls to the same file or network socket. It does not help when writing very large amounts at once, or writing just one or a few times. It also provides no advantage when writing to a destination that is in memory, like a Vec<u8>.

When the BufWriter is dropped, the contents of its buffer will be discarded. Creating multiple instances of a BufWriter on the same stream can cause data loss. If you need to write out the contents of its buffer, you must manually call flush before the writer is dropped.

Fields

inner: W

buf: Vec<u8>

written: usize

Implementations

impl<W: AsyncWrite> BufWriter<W>

pub fn new(inner: W) -> Self

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

pub fn with_capacity(cap: usize, inner: W) -> Self

Creates a new BufWriter with the specified buffer capacity.

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

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

Write directly using inner, bypassing buffering

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

Write directly using inner, bypassing buffering

impl<W> BufWriter<W>

pub fn get_ref(&self) -> &W

Acquires a reference to the underlying sink or stream that this combinator is pulling from.

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

Acquires a mutable reference to the underlying sink or stream that this combinator is pulling from.

Note that care must be taken to avoid tampering with the state of the sink or stream which may otherwise confuse this combinator.

pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut W>

Acquires a pinned mutable reference to the underlying sink or stream that this combinator is pulling from.

Note that care must be taken to avoid tampering with the state of the sink or stream which may otherwise confuse this combinator.

pub fn into_inner(self) -> W

Consumes this combinator, returning the underlying sink or stream.

Note that this may discard intermediate state of this combinator, so care should be taken to avoid losing resources when this is called.

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

Returns a reference to the internally buffered data.

pub(super) fn capacity(&self) -> usize

Capacity of buf. how many chars can be held in buffer

pub(super) fn spare_capacity(&self) -> usize

Remaining number of bytes to reach buf ’s capacity

pub(super) fn write_to_buf(self: Pin<&mut Self>, buf: &[u8]) -> usize

Write a byte slice directly into buffer

Will truncate the number of bytes written to spare_capacity() so you want to calculate the size of your slice to avoid losing bytes

Based on std::io::BufWriter

unsafe fn write_to_buffer_unchecked(self: Pin<&mut Self>, buf: &[u8])

Write byte slice directly into self.buf

Based on std::io::BufWriter

Trait Implementations

impl<W: AsyncBufRead> AsyncBufRead for BufWriter<W>

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.

impl<W: AsyncRead> AsyncRead for BufWriter<W>

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<W: AsyncWrite + AsyncSeek> AsyncSeek for BufWriter<W>

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

Seek to the offset, in bytes, in the underlying writer.

Seeking always writes out the internal buffer before seeking.

impl<W: AsyncWrite> AsyncWrite for BufWriter<W>

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>>

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

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.

impl<W: Debug> Debug for BufWriter<W>

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

Formats the value using the given formatter.

impl<'__pin, W> Unpin for BufWriter<W>

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