Struct Cursor

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

Gives an in-memory buffer a cursor for reading and writing.

Examples

use futures_lite::io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt, Cursor, SeekFrom};

let mut bytes = b"hello".to_vec();
let mut cursor = Cursor::new(&mut bytes);

// Overwrite 'h' with 'H'.
cursor.write_all(b"H").await?;

// Move the cursor one byte forward.
cursor.seek(SeekFrom::Current(1)).await?;

// Read a byte.
let mut byte = [0];
cursor.read_exact(&mut byte).await?;
assert_eq!(&byte, b"l");

// Check the final buffer.
assert_eq!(bytes, b"Hello");

Implementations

impl<T> Cursor<T>

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

Creates a cursor for an in-memory buffer.

Cursor’s initial position is 0 even if the underlying buffer is not empty. Writing using Cursor will overwrite the existing contents unless the cursor is moved to the end of the buffer using set_position() or seek().

Examples

use futures_lite::io::Cursor;

let cursor = Cursor::new(Vec::<u8>::new());

pub fn get_ref(&self) -> &T

Gets a reference to the underlying buffer.

Examples

use futures_lite::io::Cursor;

let cursor = Cursor::new(Vec::<u8>::new());
let r = cursor.get_ref();

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

Gets a mutable reference to the underlying buffer.

Examples

use futures_lite::io::Cursor;

let mut cursor = Cursor::new(Vec::<u8>::new());
let r = cursor.get_mut();

pub fn into_inner(self) -> T

Unwraps the cursor, returning the underlying buffer.

Examples

use futures_lite::io::Cursor;

let cursor = Cursor::new(vec![1, 2, 3]);
assert_eq!(cursor.into_inner(), [1, 2, 3]);

pub fn position(&self) -> u64

Returns the current position of this cursor.

Examples

use futures_lite::io::{AsyncSeekExt, Cursor, SeekFrom};

let mut cursor = Cursor::new(b"hello");
assert_eq!(cursor.position(), 0);

cursor.seek(SeekFrom::Start(2)).await?;
assert_eq!(cursor.position(), 2);

pub fn set_position(&mut self, pos: u64)

Sets the position of this cursor.

Examples

use futures_lite::io::Cursor;

let mut cursor = Cursor::new(b"hello");
assert_eq!(cursor.position(), 0);

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

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

Attempt to close the object.

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_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<Result<usize, Error>>

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

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

Attempt to close the object.

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_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<Result<usize, Error>>

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

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.