futures_util::io

Struct BufWriter

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pub struct BufWriter<W> { /* private fields */ }
Expand description

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.

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impl<W: AsyncWrite> BufWriter<W>

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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.

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

Creates a new BufWriter with the specified buffer capacity.

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impl<W> BufWriter<W>

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pub fn get_ref(&self) -> &W

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

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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.

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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.

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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.

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

Returns a reference to the internally buffered data.

Trait Implementations§

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

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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. 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<W: AsyncRead> AsyncRead for BufWriter<W>

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

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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.

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

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

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

Auto Trait Implementations§

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impl<W> Freeze for BufWriter<W>
where W: Freeze,

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impl<W> RefUnwindSafe for BufWriter<W>
where W: RefUnwindSafe,

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impl<W> Send for BufWriter<W>
where W: Send,

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impl<W> Sync for BufWriter<W>
where W: Sync,

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impl<W> UnwindSafe for BufWriter<W>
where W: 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,

Creates a future which will wait for a non-empty buffer to be available from this I/O object or EOF to be reached. Read more
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fn consume_unpin(&mut self, amt: usize)
where Self: Unpin,

A convenience for calling AsyncBufRead::consume on Unpin IO types. Read more
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fn read_until<'a>( &'a mut self, byte: u8, buf: &'a mut Vec<u8>, ) -> ReadUntil<'a, Self>
where Self: Unpin,

Creates a future which will read all the bytes associated with this I/O object into buf until the delimiter byte or EOF is reached. This method is the async equivalent to BufRead::read_until. Read more
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fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLine<'a, Self>
where Self: Unpin,

Creates a future which will read all the bytes associated with this I/O object into buf until a newline (the 0xA byte) or EOF is reached, This method is the async equivalent to BufRead::read_line. Read more
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fn lines(self) -> Lines<Self>
where Self: Sized,

Returns a stream over the lines of this reader. This method is the async equivalent to BufRead::lines. Read more
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impl<R> AsyncReadExt for R
where R: AsyncRead + ?Sized,

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

Creates an adaptor which will chain this stream with another. Read more
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fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self>
where Self: Unpin,

Tries to read some bytes directly into the given buf in asynchronous manner, returning a future type. Read more
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fn read_vectored<'a>( &'a mut self, bufs: &'a mut [IoSliceMut<'a>], ) -> ReadVectored<'a, Self>
where Self: Unpin,

Creates a future which will read from the AsyncRead into bufs using vectored IO operations. Read more
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fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExact<'a, Self>
where Self: Unpin,

Creates a future which will read exactly enough bytes to fill buf, returning an error if end of file (EOF) is hit sooner. Read more
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fn read_to_end<'a>(&'a mut self, buf: &'a mut Vec<u8>) -> ReadToEnd<'a, Self>
where Self: Unpin,

Creates a future which will read all the bytes from this AsyncRead. Read more
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fn read_to_string<'a>( &'a mut self, buf: &'a mut String, ) -> ReadToString<'a, Self>
where Self: Unpin,

Creates a future which will read all the bytes from this AsyncRead. Read more
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fn split(self) -> (ReadHalf<Self>, WriteHalf<Self>)
where Self: AsyncWrite + Sized,

Helper method for splitting this read/write object into two halves. Read more
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fn take(self, limit: u64) -> Take<Self>
where Self: Sized,

Creates an AsyncRead adapter which will read at most limit bytes from the underlying reader. 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) -> Seek<'_, Self>
where Self: Unpin,

Creates a future which will seek an IO object, and then yield the new position in the object and the object itself. Read more
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fn stream_position(&mut self) -> Seek<'_, Self>
where Self: Unpin,

Creates a future which will return the current seek position from the start of the stream. Read more
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impl<W> AsyncWriteExt for W
where W: AsyncWrite + ?Sized,

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

Creates a future which will entirely flush this AsyncWrite. Read more
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fn close(&mut self) -> Close<'_, Self>
where Self: Unpin,

Creates a future which will entirely close this AsyncWrite.
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fn write<'a>(&'a mut self, buf: &'a [u8]) -> Write<'a, Self>
where Self: Unpin,

Creates a future which will write bytes from buf into the object. Read more
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fn write_vectored<'a>( &'a mut self, bufs: &'a [IoSlice<'a>], ) -> WriteVectored<'a, Self>
where Self: Unpin,

Creates a future which will write bytes from bufs into the object using vectored IO operations. Read more
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fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> WriteAll<'a, Self>
where Self: Unpin,

Write data into this object. Read more
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fn into_sink<Item: AsRef<[u8]>>(self) -> IntoSink<Self, Item>
where Self: Sized,

Allow using an AsyncWrite as a Sink<Item: AsRef<[u8]>>. 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.