Struct Cursor 

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

Available on crate feature std only.

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

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

The standard 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 async_std::io::Cursor;

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

pub fn into_inner(self) -> T

Consumes this cursor, returning the underlying value.

Examples

use async_std::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 async_std::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 async_std::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 async_std::io::Cursor;
use async_std::io::prelude::*;
use async_std::io::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 async_std::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> BufRead for Cursor<T>

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

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

Available on crate feature docs only.

Returns the contents of the internal buffer, filling it with more data from the inner reader if it is empty.

fn consume(self: Pin<&mut Self>, amt: usize)

Available on crate feature docs only.

Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to read.

fn read_until<'a>( &'a mut self, byte: u8, buf: &'a mut Vec<u8>, ) -> ImplFuture<usize>

where Self: Unpin,

Available on crate feature docs only.

Reads all bytes into buf until the delimiter byte or EOF is reached.

fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Reads all bytes and appends them into buf until a newline (the 0xA byte) is reached.

fn lines(self) -> Lines<Self>

where Self: Unpin + Sized,

Available on crate feature docs only.

Returns a stream over the lines of this byte stream.

fn split(self, byte: u8) -> Split<Self>

where Self: Sized,

Available on crate feature docs only.

Returns a stream over the contents of this reader split on the byte byte.

impl<T: Clone> Clone for Cursor<T>

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

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for Cursor<T>

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

Formats the value using the given formatter.

impl<T: Default> Default for Cursor<T>

fn default() -> Cursor<T>

Returns the “default value” for a type.

impl<T> Read for Cursor<T>

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

fn poll_read( self: Pin<&mut Self>, _cx: &mut Context<'_>, buf: &mut [u8], ) -> Poll<Result<usize>>

Available on crate feature docs only.

Attempt to read from the AsyncRead into buf.

fn poll_read_vectored( self: Pin<&mut Self>, _: &mut Context<'_>, bufs: &mut [IoSliceMut<'_>], ) -> Poll<Result<usize>>

Available on crate feature docs only.

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

fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Reads some bytes from the byte stream.

fn read_vectored<'a>( &'a mut self, bufs: &'a mut [IoSliceMut<'a>], ) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Like read, except that it reads into a slice of buffers.

fn read_to_end<'a>( &'a mut self, buf: &'a mut Vec<u8>, ) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Reads all bytes from the byte stream.

fn read_to_string<'a>( &'a mut self, buf: &'a mut String, ) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Reads all bytes from the byte stream and appends them into a string.

fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Reads the exact number of bytes required to fill buf.

fn take(self, limit: u64) -> Take<Self>

where Self: Sized,

Available on crate feature docs only.

Creates an adaptor which will read at most limit bytes from it.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Available on crate feature docs only.

Creates a “by reference” adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self>

where Self: Sized,

Available on crate feature docs only.

Transforms this Read instance to a Stream over its bytes.

fn chain<R: Read>(self, next: R) -> Chain<Self, R>

where Self: Sized,

Available on crate feature docs only.

Creates an adaptor which will chain this stream with another.

impl<T> Seek for Cursor<T>

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

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

Available on crate feature docs only.

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

fn seek(&mut self, pos: SeekFrom) -> ImplFuture<Result<u64>>

where Self: Unpin,

Available on crate feature docs only.

Seeks to a new position in a byte stream.

impl Write for Cursor<&mut [u8]>

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

Available on crate feature docs only.

Attempt to write bytes from buf into the object.

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

Available on crate feature docs only.

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

fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>>

Available on crate feature docs only.

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

fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Available on crate feature docs only.

Attempt to close the object.

fn write<'a>(&'a mut self, buf: &'a [u8]) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Writes some bytes into the byte stream.

fn flush(&mut self) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Flushes the stream to ensure that all buffered contents reach their destination.

fn write_vectored<'a>( &'a mut self, bufs: &'a [IoSlice<'a>], ) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Like write, except that it writes from a slice of buffers.

fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Writes an entire buffer into the byte stream.

fn write_fmt<'a>(&'a mut self, fmt: Arguments<'_>) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Writes a formatted string into this writer, returning any error encountered.

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

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

Available on crate feature docs only.

Attempt to write bytes from buf into the object.

fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Available on crate feature docs only.

Attempt to close the object.

fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>>

Available on crate feature docs only.

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>>

Available on crate feature docs only.

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

fn write<'a>(&'a mut self, buf: &'a [u8]) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Writes some bytes into the byte stream.

fn flush(&mut self) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Flushes the stream to ensure that all buffered contents reach their destination.

fn write_vectored<'a>( &'a mut self, bufs: &'a [IoSlice<'a>], ) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Like write, except that it writes from a slice of buffers.

fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Writes an entire buffer into the byte stream.

fn write_fmt<'a>(&'a mut self, fmt: Arguments<'_>) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Writes a formatted string into this writer, returning any error encountered.

impl Write for Cursor<Vec<u8>>

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

Available on crate feature docs only.

Attempt to write bytes from buf into the object.

fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Available on crate feature docs only.

Attempt to close the object.

fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>>

Available on crate feature docs only.

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>>

Available on crate feature docs only.

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

fn write<'a>(&'a mut self, buf: &'a [u8]) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Writes some bytes into the byte stream.

fn flush(&mut self) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Flushes the stream to ensure that all buffered contents reach their destination.

fn write_vectored<'a>( &'a mut self, bufs: &'a [IoSlice<'a>], ) -> ImplFuture<Result<usize>>

where Self: Unpin,

Available on crate feature docs only.

Like write, except that it writes from a slice of buffers.

fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Writes an entire buffer into the byte stream.

fn write_fmt<'a>(&'a mut self, fmt: Arguments<'_>) -> ImplFuture<Result<()>>

where Self: Unpin,

Available on crate feature docs only.

Writes a formatted string into this writer, returning any error encountered.