Struct Cursor

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

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

impl<T> Cursor<T>

pub fn new(inner: T) -> Cursor<T>

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());

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();

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();

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();

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);

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

impl<T> AsyncBufRead for Cursor<T>

where T: AsRef<[u8]> + Unpin,

fn poll_fill_buf( self: Pin<&mut Cursor<T>>, _: &mut Context<'_>, ) -> Poll<Result<&[u8], Error>>

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 Cursor<T>>, 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<T> AsyncRead for Cursor<T>

where T: AsRef<[u8]> + Unpin,

fn poll_read( self: Pin<&mut Cursor<T>>, _cx: &mut Context<'_>, buf: &mut [u8], ) -> Poll<Result<usize, Error>>

Attempt to read from the AsyncRead into buf.

fn poll_read_vectored( self: Pin<&mut Cursor<T>>, _: &mut Context<'_>, bufs: &mut [IoSliceMut<'_>], ) -> Poll<Result<usize, Error>>

Attempt to read from the AsyncRead into bufs using vectored IO operations.

impl<T> AsyncSeek for Cursor<T>

where T: AsRef<[u8]> + Unpin,

fn poll_seek( self: Pin<&mut Cursor<T>>, _: &mut Context<'_>, pos: SeekFrom, ) -> Poll<Result<u64, Error>>

Attempt to seek to an offset, in bytes, in a stream.

impl AsyncWrite for Cursor<&mut [u8]>

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

Attempt to write bytes from buf into the object.

fn poll_write_vectored( self: Pin<&mut Cursor<&mut [u8]>>, _: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<Result<usize, Error>>

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

fn poll_flush( self: Pin<&mut Cursor<&mut [u8]>>, _: &mut Context<'_>, ) -> Poll<Result<(), Error>>

Attempt to flush the object, ensuring that any buffered data reach their destination.

fn poll_close( self: Pin<&mut Cursor<&mut [u8]>>, cx: &mut Context<'_>, ) -> Poll<Result<(), Error>>

Attempt to close the object.

impl AsyncWrite for Cursor<&mut Vec<u8>>

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

Attempt to write bytes from buf into the object.

fn poll_write_vectored( self: Pin<&mut Cursor<&mut Vec<u8>>>, _: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<Result<usize, Error>>

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

fn poll_flush( self: Pin<&mut Cursor<&mut Vec<u8>>>, _: &mut Context<'_>, ) -> Poll<Result<(), Error>>

Attempt to flush the object, ensuring that any buffered data reach their destination.

fn poll_close( self: Pin<&mut Cursor<&mut Vec<u8>>>, cx: &mut Context<'_>, ) -> Poll<Result<(), Error>>

Attempt to close the object.

impl AsyncWrite for Cursor<Box<[u8]>>

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

Attempt to write bytes from buf into the object.

fn poll_write_vectored( self: Pin<&mut Cursor<Box<[u8]>>>, _: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<Result<usize, Error>>

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

fn poll_flush( self: Pin<&mut Cursor<Box<[u8]>>>, _: &mut Context<'_>, ) -> Poll<Result<(), Error>>

Attempt to flush the object, ensuring that any buffered data reach their destination.

fn poll_close( self: Pin<&mut Cursor<Box<[u8]>>>, cx: &mut Context<'_>, ) -> Poll<Result<(), Error>>

Attempt to close the object.

impl AsyncWrite for Cursor<Vec<u8>>

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

Attempt to write bytes from buf into the object.

fn poll_write_vectored( self: Pin<&mut Cursor<Vec<u8>>>, _: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<Result<usize, Error>>

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

fn poll_flush( self: Pin<&mut Cursor<Vec<u8>>>, _: &mut Context<'_>, ) -> Poll<Result<(), Error>>

Attempt to flush the object, ensuring that any buffered data reach their destination.

fn poll_close( self: Pin<&mut Cursor<Vec<u8>>>, cx: &mut Context<'_>, ) -> Poll<Result<(), Error>>

Attempt to close the object.

impl<T> Clone for Cursor<T>

where T: Clone,

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

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Debug for Cursor<T>

where T: Debug,

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

Formats the value using the given formatter.

impl<T> Default for Cursor<T>

where T: Default,

fn default() -> Cursor<T>

Returns the “default value” for a type.