Struct smol::io::Cursor

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

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

Examples

use futures_lite::*;

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

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

// Move the cursor one byte forward.
cursor.seek(io::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()][AsyncSeekExt::seek()].

Examples

use futures_lite::*;

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

pub fn get_ref(&self) -> &Tⓘ

Important traits for &'_ mut F

impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;

Gets a reference to the underlying buffer.

Examples

use futures_lite::*;

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

pub fn get_mut(&mut self) -> &mut Tⓘ

Important traits for &'_ mut F

impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;

Gets a mutable reference to the underlying buffer.

Examples

use futures_lite::*;

let mut cursor = io::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::*;

let cursor = io::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::*;

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

cursor.seek(io::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::*;

let mut cursor = io::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<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<'_> 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<&'_ 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<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.