Struct futures_util::io::Cursor

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pub struct Cursor<T> { /* private fields */ }
Expand description

A Cursor wraps an in-memory buffer and provides it with a AsyncSeek implementation.

Cursors are used with in-memory buffers, anything implementing AsRef<[u8]>, to allow them to implement AsyncRead and/or AsyncWrite, allowing these buffers to be used anywhere you might use a reader or writer that does actual I/O.

This library implements some I/O traits on various types which are commonly used as a buffer, like Cursor<Vec<u8>> and Cursor<&[u8]>.

Implementations§

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impl<T> Cursor<T>

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pub fn new(inner: T) -> Self

Creates a new cursor wrapping the provided underlying in-memory buffer.

Cursor initial position is 0 even if underlying buffer (e.g., Vec) is not empty. So writing to cursor starts with overwriting Vec content, not with appending to it.

Examples
use futures::io::Cursor;

let buff = Cursor::new(Vec::new());
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pub fn into_inner(self) -> T

Consumes this cursor, returning the underlying value.

Examples
use futures::io::Cursor;

let buff = Cursor::new(Vec::new());

let vec = buff.into_inner();
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pub fn get_ref(&self) -> &T

Gets a reference to the underlying value in this cursor.

Examples
use futures::io::Cursor;

let buff = Cursor::new(Vec::new());

let reference = buff.get_ref();
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pub fn get_mut(&mut self) -> &mut T

Gets a mutable reference to the underlying value in this cursor.

Care should be taken to avoid modifying the internal I/O state of the underlying value as it may corrupt this cursor’s position.

Examples
use futures::io::Cursor;

let mut buff = Cursor::new(Vec::new());

let reference = buff.get_mut();
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pub fn position(&self) -> u64

Returns the current position of this cursor.

Examples
use futures::io::{AsyncSeekExt, Cursor, SeekFrom};

let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);

assert_eq!(buff.position(), 0);

buff.seek(SeekFrom::Current(2)).await?;
assert_eq!(buff.position(), 2);

buff.seek(SeekFrom::Current(-1)).await?;
assert_eq!(buff.position(), 1);
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pub fn set_position(&mut self, pos: u64)

Sets the position of this cursor.

Examples
use futures::io::Cursor;

let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);

assert_eq!(buff.position(), 0);

buff.set_position(2);
assert_eq!(buff.position(), 2);

buff.set_position(4);
assert_eq!(buff.position(), 4);

Trait Implementations§

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impl<T> AsyncBufRead for Cursor<T>where T: AsRef<[u8]> + Unpin,

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fn poll_fill_buf( self: Pin<&mut Self>, _: &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<T: AsRef<[u8]> + Unpin> AsyncRead for Cursor<T>

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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>, _: &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<T> AsyncSeek for Cursor<T>where T: AsRef<[u8]> + Unpin,

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

Attempt to seek to an offset, in bytes, in a stream. Read more
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impl AsyncWrite for Cursor<&mut [u8]>

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fn poll_write( self: Pin<&mut Self>, _: &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>, _: &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>, _: &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 AsyncWrite for Cursor<&mut Vec<u8>>

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fn poll_write( self: Pin<&mut Self>, _: &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>, _: &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>, _: &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 AsyncWrite for Cursor<Box<[u8]>>

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fn poll_write( self: Pin<&mut Self>, _: &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>, _: &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>, _: &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 AsyncWrite for Cursor<Vec<u8>>

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fn poll_write( self: Pin<&mut Self>, _: &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>, _: &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>, _: &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<T: Clone> Clone for Cursor<T>

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fn clone(&self) -> Cursor<T>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<T: Debug> Debug for Cursor<T>

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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<T: Default> Default for Cursor<T>

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fn default() -> Cursor<T>

Returns the “default value” for a type. Read more

Auto Trait Implementations§

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impl<T> RefUnwindSafe for Cursor<T>where T: RefUnwindSafe,

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impl<T> Send for Cursor<T>where T: Send,

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impl<T> Sync for Cursor<T>where T: Sync,

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impl<T> Unpin for Cursor<T>where T: Unpin,

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impl<T> UnwindSafe for Cursor<T>where T: UnwindSafe,

Blanket Implementations§

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impl<T> Any for Twhere 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 Rwhere 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 Rwhere 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 Swhere 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 Wwhere 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 Twhere 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 Twhere T: ?Sized,

const: unstable · source§

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 Twhere 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> ToOwned for Twhere T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
const: unstable · source§

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 Twhere U: TryFrom<T>,

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

The type returned in the event of a conversion error.
const: unstable · source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.