Struct async_std::io::Cursor

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

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]>.

Methods

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]>>

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)

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, 

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, 

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, 

Returns a stream over the lines of this byte stream.

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

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

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>>

Attempt to read from the AsyncRead into buf.

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

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, 

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, 

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, 

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, 

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, 

Reads the exact number of bytes required to fill buf.

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

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

fn by_ref(&mut self) -> &mut Self where
    Self: Sized, 

Creates a "by reference" adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self> where
    Self: Sized, 

Transforms this Read instance to a Stream over its bytes.

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

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>>

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

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

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>>

Attempt to write bytes from buf into the object.

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

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

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

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<()>>

Attempt to close the object.

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

Writes some bytes into the byte stream.

fn flush(&mut self) -> ImplFuture<Result<()>> where
    Self: Unpin, 

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, 

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, 

Writes an entire buffer into the byte stream.

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

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>>

Attempt to write bytes from buf into the object.

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

Attempt to close the object.

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

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>>

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, 

Writes some bytes into the byte stream.

fn flush(&mut self) -> ImplFuture<Result<()>> where
    Self: Unpin, 

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, 

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, 

Writes an entire buffer into the byte stream.

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

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>>

Attempt to write bytes from buf into the object.

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

Attempt to close the object.

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

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>>

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, 

Writes some bytes into the byte stream.

fn flush(&mut self) -> ImplFuture<Result<()>> where
    Self: Unpin, 

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, 

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, 

Writes an entire buffer into the byte stream.

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

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

impl<T: Clone> Clone for Cursor<T>

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: Default> Default for Cursor<T>

fn default() -> Cursor<T>

Returns the "default value" for a type.

impl<T: Debug> Debug for Cursor<T>

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

Formats the value using the given formatter.