Struct tokio::io::util::buf_writer::BufWriter

pub struct BufWriter<W> {
    pub(super) inner: W,
    pub(super) buf: Vec<u8>,
    pub(super) written: usize,
    pub(super) seek_state: SeekState,
}

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

seek_state: SeekState

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.

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

pub fn get_ref(&self) -> &W

Gets a reference to the underlying writer.

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

Gets a mutable reference to the underlying writer.

It is inadvisable to directly write to the underlying writer.

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

Gets a pinned mutable reference to the underlying writer.

It is inadvisable to directly write to the underlying writer.

pub fn into_inner(self) -> W

Consumes this BufWriter, returning the underlying writer.

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

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

Returns a reference to the internally buffered data.

Trait Implementations

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

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

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

Attempts to read from the AsyncRead into buf.

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

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

Seeking always writes out the internal buffer before seeking.

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<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>>

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<W: Debug> Debug for BufWriter<W>

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

Formats the value using the given formatter.

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

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

Converts to this type from the input type.

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

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