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use futures_core::task::{Context, Poll};
use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSlice, IoSliceMut, SeekFrom};
use std::io;
use std::pin::Pin;
/// A `Cursor` wraps an in-memory buffer and provides it with a
/// [`AsyncSeek`] implementation.
///
/// `Cursor`s 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]`][bytes]`>`.
///
/// [`AsyncSeek`]: trait.AsyncSeek.html
/// [`AsyncRead`]: trait.AsyncRead.html
/// [`AsyncWrite`]: trait.AsyncWrite.html
#[derive(Clone, Debug, Default)]
pub struct Cursor<T> {
inner: io::Cursor<T>,
}
impl<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());
/// # fn force_inference(_: &Cursor<Vec<u8>>) {}
/// # force_inference(&buff);
/// ```
pub fn new(inner: T) -> Self {
Self { inner: io::Cursor::new(inner) }
}
/// Consumes this cursor, returning the underlying value.
///
/// # Examples
///
/// ```
/// use futures::io::Cursor;
///
/// let buff = Cursor::new(Vec::new());
/// # fn force_inference(_: &Cursor<Vec<u8>>) {}
/// # force_inference(&buff);
///
/// let vec = buff.into_inner();
/// ```
pub fn into_inner(self) -> T {
self.inner.into_inner()
}
/// Gets a reference to the underlying value in this cursor.
///
/// # Examples
///
/// ```
/// use futures::io::Cursor;
///
/// let buff = Cursor::new(Vec::new());
/// # fn force_inference(_: &Cursor<Vec<u8>>) {}
/// # force_inference(&buff);
///
/// let reference = buff.get_ref();
/// ```
pub fn get_ref(&self) -> &T {
self.inner.get_ref()
}
/// 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());
/// # fn force_inference(_: &Cursor<Vec<u8>>) {}
/// # force_inference(&buff);
///
/// let reference = buff.get_mut();
/// ```
pub fn get_mut(&mut self) -> &mut T {
self.inner.get_mut()
}
/// Returns the current position of this cursor.
///
/// # Examples
///
/// ```
/// # futures::executor::block_on(async {
/// 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);
/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
/// ```
pub fn position(&self) -> u64 {
self.inner.position()
}
/// 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);
/// ```
pub fn set_position(&mut self, pos: u64) {
self.inner.set_position(pos)
}
}
impl<T> AsyncSeek for Cursor<T>
where
T: AsRef<[u8]> + Unpin,
{
fn poll_seek(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<io::Result<u64>> {
Poll::Ready(io::Seek::seek(&mut self.inner, pos))
}
}
impl<T: AsRef<[u8]> + Unpin> AsyncRead for Cursor<T> {
fn poll_read(
mut self: Pin<&mut Self>,
_cx: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Read::read(&mut self.inner, buf))
}
fn poll_read_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &mut [IoSliceMut<'_>],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Read::read_vectored(&mut self.inner, bufs))
}
}
impl<T> AsyncBufRead for Cursor<T>
where
T: AsRef<[u8]> + Unpin,
{
fn poll_fill_buf(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
Poll::Ready(io::BufRead::fill_buf(&mut self.get_mut().inner))
}
fn consume(mut self: Pin<&mut Self>, amt: usize) {
io::BufRead::consume(&mut self.inner, amt)
}
}
macro_rules! delegate_async_write_to_stdio {
() => {
fn poll_write(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write(&mut self.inner, buf))
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write_vectored(&mut self.inner, bufs))
}
fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
Poll::Ready(io::Write::flush(&mut self.inner))
}
fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
self.poll_flush(cx)
}
};
}
impl AsyncWrite for Cursor<&mut [u8]> {
delegate_async_write_to_stdio!();
}
impl AsyncWrite for Cursor<&mut Vec<u8>> {
delegate_async_write_to_stdio!();
}
impl AsyncWrite for Cursor<Vec<u8>> {
delegate_async_write_to_stdio!();
}
impl AsyncWrite for Cursor<Box<[u8]>> {
delegate_async_write_to_stdio!();
}