Struct docktape::io::Cursor

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

A Cursor wraps another type and provides it with a Seek implementation.

Cursors are typically used with in-memory buffers 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]>.

Examples

We may want to write bytes to a File in our production code, but use an in-memory buffer in our tests. We can do this with Cursor:

use std::io::prelude::*;
use std::io::{self, SeekFrom};
use std::fs::File;

// a library function we've written
fn write_ten_bytes_at_end<W: Write + Seek>(writer: &mut W) -> io::Result<()> {
    writer.seek(SeekFrom::End(-10))?;

    for i in 0..10 {
        writer.write(&[i])?;
    }

    // all went well
    Ok(())
}

// Here's some code that uses this library function.
//
// We might want to use a BufReader here for efficiency, but let's
// keep this example focused.
let mut file = File::create("foo.txt")?;

write_ten_bytes_at_end(&mut file)?;

// now let's write a test
#[test]
fn test_writes_bytes() {
    // setting up a real File is much slower than an in-memory buffer,
    // let's use a cursor instead
    use std::io::Cursor;
    let mut buff = Cursor::new(vec![0; 15]);

    write_ten_bytes_at_end(&mut buff).unwrap();

    assert_eq!(&buff.get_ref()[5..15], &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
}

Methods

impl<T> Cursor<T>

Important traits for Cursor<T>

impl<T> Read for Cursor<T> where
    T: AsRef<[u8]>, impl<'a> Write for Cursor<&'a mut Vec<u8>>impl Write for Cursor<Box<[u8]>>impl Write for Cursor<Vec<u8>>impl<'a> Write for Cursor<&'a mut [u8]>

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

Creates a new cursor wrapping the provided underlying I/O object.

Cursor initial position is 0 even if underlying object (e. g. Vec) is not empty. So writing to cursor starts with overwriting Vec content, not with appending to it.

Examples

use std::io::Cursor;

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

pub fn into_inner(self) -> T

Consumes this cursor, returning the underlying value.

Examples

use std::io::Cursor;

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

let vec = buff.into_inner();

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

pub fn get_ref(&self) -> &T

Gets a reference to the underlying value in this cursor.

Examples

use std::io::Cursor;

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

let reference = buff.get_ref();

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

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 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 std::io::Cursor;
use std::io::prelude::*;
use std::io::SeekFrom;

let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);

assert_eq!(buff.position(), 0);

buff.seek(SeekFrom::Current(2)).unwrap();
assert_eq!(buff.position(), 2);

buff.seek(SeekFrom::Current(-1)).unwrap();
assert_eq!(buff.position(), 1);

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

Sets the position of this cursor.

Examples

use 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> Debug for Cursor<T> where     T: Debug,

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

Formats the value using the given formatter.

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

Important traits for Cursor<T>

impl<T> Read for Cursor<T> where
    T: AsRef<[u8]>, impl<'a> Write for Cursor<&'a mut Vec<u8>>impl Write for Cursor<Box<[u8]>>impl Write for Cursor<Vec<u8>>impl<'a> Write for Cursor<&'a mut [u8]>

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> Read for Cursor<T> where     T: AsRef<[u8]>,

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

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

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

Read the exact number of bytes required to fill buf.

unsafe fn initializer(&self) -> Initializer

🔬 This is a nightly-only experimental API. (read_initializer)

Determines if this Reader can work with buffers of uninitialized memory.

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

Read all bytes until EOF in this source, placing them into buf.

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

Read all bytes until EOF in this source, appending them to buf.

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

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

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

Important traits for Bytes<R>

impl<R> Iterator for Bytes<R> where
    R: Read,  type Item = Result<u8, Error>;

fn bytes(self) -> Bytes<Self>

Transforms this Read instance to an [Iterator] over its bytes.

Important traits for Chars<R>

impl<R> Iterator for Chars<R> where
    R: Read,  type Item = Result<char, CharsError>;

fn chars(self) -> Chars<Self>

Deprecated since 1.27.0

: Use str::from_utf8 instead: https://doc.rust-lang.org/nightly/std/str/struct.Utf8Error.html#examples

🔬 This is a nightly-only experimental API. (io)

the semantics of a partial read/write of where errors happen is currently unclear and may change

Transforms this Read instance to an [Iterator] over [char]s.

Important traits for Chain<T, U>

impl<T, U> Read for Chain<T, U> where
    T: Read,
    U: Read, 

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

Creates an adaptor which will chain this stream with another.

Important traits for Take<T>

impl<T> Read for Take<T> where
    T: Read, 

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

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

impl<T> BufRead for Cursor<T> where     T: AsRef<[u8]>,

fn fill_buf(&mut self) -> Result<&[u8], Error>

Fills the internal buffer of this object, returning the buffer contents.

fn consume(&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(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize, Error>

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

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

Read all bytes until a newline (the 0xA byte) is reached, and append them to the provided buffer.

Important traits for Split<B>

impl<B> Iterator for Split<B> where
    B: BufRead,  type Item = Result<Vec<u8>, Error>;

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

Returns an iterator over the contents of this reader split on the byte byte.

Important traits for Lines<B>

impl<B> Iterator for Lines<B> where
    B: BufRead,  type Item = Result<String, Error>;

fn lines(self) -> Lines<Self>

Returns an iterator over the lines of this reader.

impl<T> Seek for Cursor<T> where     T: AsRef<[u8]>,

fn seek(&mut self, style: SeekFrom) -> Result<u64, Error>

Seek to an offset, in bytes, in a stream.

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

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

Write a buffer into this object, returning how many bytes were written.

fn flush(&mut self) -> Result<(), Error>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination.

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

Attempts to write an entire buffer into this write.

fn write_fmt(&mut self, fmt: Arguments) -> Result<(), Error>

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

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

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

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

impl Write for Cursor<Box<[u8]>>

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

Write a buffer into this object, returning how many bytes were written.

fn flush(&mut self) -> Result<(), Error>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination.

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

Attempts to write an entire buffer into this write.

fn write_fmt(&mut self, fmt: Arguments) -> Result<(), Error>

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

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

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

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

impl Write for Cursor<Vec<u8>>

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

Write a buffer into this object, returning how many bytes were written.

fn flush(&mut self) -> Result<(), Error>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination.

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

Attempts to write an entire buffer into this write.

fn write_fmt(&mut self, fmt: Arguments) -> Result<(), Error>

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

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

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

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

impl<'a> Write for Cursor<&'a mut [u8]>

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

Write a buffer into this object, returning how many bytes were written.

fn flush(&mut self) -> Result<(), Error>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination.

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

Attempts to write an entire buffer into this write.

fn write_fmt(&mut self, fmt: Arguments) -> Result<(), Error>

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

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

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

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

impl<T> Buf for Cursor<T> where     T: AsRef<[u8]>,

fn remaining(&self) -> usize

Returns the number of bytes between the current position and the end of the buffer.

Important traits for &'a [u8]

impl<'a> Read for &'a [u8]impl<'a> Write for &'a mut [u8]

fn bytes(&self) -> &[u8]

Returns a slice starting at the current position and of length between 0 and Buf::remaining().

fn advance(&mut self, cnt: usize)

Advance the internal cursor of the Buf

fn bytes_vec(&'a self, dst: &mut [&'a IoVec]) -> usize

Fills dst with potentially multiple slices starting at self's current position.

fn has_remaining(&self) -> bool

Returns true if there are any more bytes to consume

fn copy_to_slice(&mut self, dst: &mut [u8])

Copies bytes from self into dst.

fn get_u8(&mut self) -> u8

Gets an unsigned 8 bit integer from self.

fn get_i8(&mut self) -> i8

Gets a signed 8 bit integer from self.

fn get_u16_be(&mut self) -> u16

Gets an unsigned 16 bit integer from self in big-endian byte order.

fn get_u16_le(&mut self) -> u16

Gets an unsigned 16 bit integer from self in little-endian byte order.

fn get_i16_be(&mut self) -> i16

Gets a signed 16 bit integer from self in big-endian byte order.

fn get_i16_le(&mut self) -> i16

Gets a signed 16 bit integer from self in little-endian byte order.

fn get_u32_be(&mut self) -> u32

Gets an unsigned 32 bit integer from self in the big-endian byte order.

fn get_u32_le(&mut self) -> u32

Gets an unsigned 32 bit integer from self in the little-endian byte order.

fn get_i32_be(&mut self) -> i32

Gets a signed 32 bit integer from self in big-endian byte order.

fn get_i32_le(&mut self) -> i32

Gets a signed 32 bit integer from self in little-endian byte order.

fn get_u64_be(&mut self) -> u64

Gets an unsigned 64 bit integer from self in big-endian byte order.

fn get_u64_le(&mut self) -> u64

Gets an unsigned 64 bit integer from self in little-endian byte order.

fn get_i64_be(&mut self) -> i64

Gets a signed 64 bit integer from self in big-endian byte order.

fn get_i64_le(&mut self) -> i64

Gets a signed 64 bit integer from self in little-endian byte order.

fn get_uint_be(&mut self, nbytes: usize) -> u64

Gets an unsigned n-byte integer from self in big-endian byte order.

fn get_uint_le(&mut self, nbytes: usize) -> u64

Gets an unsigned n-byte integer from self in little-endian byte order.

fn get_int_be(&mut self, nbytes: usize) -> i64

Gets a signed n-byte integer from self in big-endian byte order.

fn get_int_le(&mut self, nbytes: usize) -> i64

Gets a signed n-byte integer from self in little-endian byte order.

fn get_f32_be(&mut self) -> f32

Gets an IEEE754 single-precision (4 bytes) floating point number from self in big-endian byte order.

fn get_f32_le(&mut self) -> f32

Gets an IEEE754 single-precision (4 bytes) floating point number from self in little-endian byte order.

fn get_f64_be(&mut self) -> f64

Gets an IEEE754 double-precision (8 bytes) floating point number from self in big-endian byte order.

fn get_f64_le(&mut self) -> f64

Gets an IEEE754 double-precision (8 bytes) floating point number from self in little-endian byte order.

fn collect<B>(self) -> B where     B: FromBuf,

Transforms a Buf into a concrete buffer.

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

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

fn chain<U>(self, next: U) -> Chain<Self, <U as IntoBuf>::Buf> where     U: IntoBuf,

Creates an adaptor which will chain this buffer with another.

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

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

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

Important traits for Reader<B>

impl<B> Read for Reader<B> where
    B: Buf, 

fn reader(self) -> Reader<Self>

Creates an adaptor which implements the Read trait for self.

Important traits for Iter<T>

impl<T> Iterator for Iter<T> where
    T: Buf,  type Item = u8;

fn iter(self) -> Iter<Self>

Returns an iterator over the bytes contained by the buffer.

impl<T> BufMut for Cursor<T> where     T: AsRef<[u8]> + AsMut<[u8]>,

fn remaining_mut(&self) -> usize

Returns the number of bytes that can be written from the current position until the end of the buffer is reached.

unsafe fn advance_mut(&mut self, cnt: usize)

Advance the internal cursor of the BufMut

Important traits for &'a [u8]

impl<'a> Read for &'a [u8]impl<'a> Write for &'a mut [u8]

unsafe fn bytes_mut(&mut self) -> &mut [u8]

Returns a mutable slice starting at the current BufMut position and of length between 0 and BufMut::remaining().

The returned byte slice may represent uninitialized memory.

fn has_remaining_mut(&self) -> bool

Returns true if there is space in self for more bytes.

unsafe fn bytes_vec_mut(&'a mut self, dst: &mut [&'a mut IoVec]) -> usize

Fills dst with potentially multiple mutable slices starting at self's current position.

fn put<T>(&mut self, src: T) where     T: IntoBuf,

Transfer bytes into self from src and advance the cursor by the number of bytes written.

fn put_slice(&mut self, src: &[u8])

Transfer bytes into self from src and advance the cursor by the number of bytes written.

fn put_u8(&mut self, n: u8)

Writes an unsigned 8 bit integer to self.

fn put_i8(&mut self, n: i8)

Writes a signed 8 bit integer to self.

fn put_u16_be(&mut self, n: u16)

Writes an unsigned 16 bit integer to self in big-endian byte order.

fn put_u16_le(&mut self, n: u16)

Writes an unsigned 16 bit integer to self in little-endian byte order.

fn put_i16_be(&mut self, n: i16)

Writes a signed 16 bit integer to self in big-endian byte order.

fn put_i16_le(&mut self, n: i16)

Writes a signed 16 bit integer to self in little-endian byte order.

fn put_u32_be(&mut self, n: u32)

Writes an unsigned 32 bit integer to self in big-endian byte order.

fn put_u32_le(&mut self, n: u32)

Writes an unsigned 32 bit integer to self in little-endian byte order.

fn put_i32_be(&mut self, n: i32)

Writes a signed 32 bit integer to self in big-endian byte order.

fn put_i32_le(&mut self, n: i32)

Writes a signed 32 bit integer to self in little-endian byte order.

fn put_u64_be(&mut self, n: u64)

Writes an unsigned 64 bit integer to self in the big-endian byte order.

fn put_u64_le(&mut self, n: u64)

Writes an unsigned 64 bit integer to self in little-endian byte order.

fn put_i64_be(&mut self, n: i64)

Writes a signed 64 bit integer to self in the big-endian byte order.

fn put_i64_le(&mut self, n: i64)

Writes a signed 64 bit integer to self in little-endian byte order.

fn put_uint_be(&mut self, n: u64, nbytes: usize)

Writes an unsigned n-byte integer to self in big-endian byte order.

fn put_uint_le(&mut self, n: u64, nbytes: usize)

Writes an unsigned n-byte integer to self in the little-endian byte order.

fn put_int_be(&mut self, n: i64, nbytes: usize)

Writes a signed n-byte integer to self in big-endian byte order.

fn put_int_le(&mut self, n: i64, nbytes: usize)

Writes a signed n-byte integer to self in little-endian byte order.

fn put_f32_be(&mut self, n: f32)

Writes an IEEE754 single-precision (4 bytes) floating point number to self in big-endian byte order.

fn put_f32_le(&mut self, n: f32)

Writes an IEEE754 single-precision (4 bytes) floating point number to self in little-endian byte order.

fn put_f64_be(&mut self, n: f64)

Writes an IEEE754 double-precision (8 bytes) floating point number to self in big-endian byte order.

fn put_f64_le(&mut self, n: f64)

Writes an IEEE754 double-precision (8 bytes) floating point number to self in little-endian byte order.

Important traits for &'a mut R

impl<'a, R> Read for &'a mut R where
    R: Read + ?Sized, impl<'a, W> Write for &'a mut W where
    W: Write + ?Sized, impl<'a, I> Iterator for &'a mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;

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

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

Important traits for Writer<B>

impl<B> Write for Writer<B> where
    B: BufMut, 

fn writer(self) -> Writer<Self>

Creates an adaptor which implements the Write trait for self.

impl AsyncWrite for Cursor<Vec<u8>>

fn shutdown(&mut self) -> Result<Async<()>, Error>

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

fn poll_write(&mut self, buf: &[u8]) -> Result<Async<usize>, Error>

Attempt to write bytes from buf into the object.

fn poll_flush(&mut self) -> Result<Async<()>, Error>

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

fn write_buf<B>(&mut self, buf: &mut B) -> Result<Async<usize>, Error> where     B: Buf,

Write a Buf into this value, returning how many bytes were written.

impl AsyncWrite for Cursor<Box<[u8]>>

fn shutdown(&mut self) -> Result<Async<()>, Error>

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

fn poll_write(&mut self, buf: &[u8]) -> Result<Async<usize>, Error>

Attempt to write bytes from buf into the object.

fn poll_flush(&mut self) -> Result<Async<()>, Error>

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

fn write_buf<B>(&mut self, buf: &mut B) -> Result<Async<usize>, Error> where     B: Buf,

Write a Buf into this value, returning how many bytes were written.

impl<'a> AsyncWrite for Cursor<&'a mut [u8]>

fn shutdown(&mut self) -> Result<Async<()>, Error>

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

fn poll_write(&mut self, buf: &[u8]) -> Result<Async<usize>, Error>

Attempt to write bytes from buf into the object.

fn poll_flush(&mut self) -> Result<Async<()>, Error>

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

fn write_buf<B>(&mut self, buf: &mut B) -> Result<Async<usize>, Error> where     B: Buf,

Write a Buf into this value, returning how many bytes were written.

impl<T> AsyncRead for Cursor<T> where     T: AsRef<[u8]>,

unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool

Prepares an uninitialized buffer to be safe to pass to read. Returns true if the supplied buffer was zeroed out.

fn poll_read(&mut self, buf: &mut [u8]) -> Result<Async<usize>, Error>

Attempt to read from the AsyncRead into buf.

fn read_buf<B>(&mut self, buf: &mut B) -> Result<Async<usize>, Error> where     B: BufMut,

Pull some bytes from this source into the specified Buf, returning how many bytes were read.

fn framed<T>(self, codec: T) -> Framed<Self, T> where     Self: AsyncWrite,     T: Decoder + Encoder,

Deprecated since 0.1.7

: Use tokio_codec::Decoder::framed instead

Provides a Stream and Sink interface for reading and writing to this Io object, using Decode and Encode to read and write the raw data.

fn split(self) -> (ReadHalf<Self>, WriteHalf<Self>) where     Self: AsyncWrite,

Helper method for splitting this read/write object into two halves.