ndless 0.8.8

//! Traits, helpers, and type definitions for core I/O functionality.
//!
//! The `std::io` module contains a number of common things you'll need
//! when doing input and output. The most core part of this module is
//! the [`Read`] and [`Write`] traits, which provide the
//! most general interface for reading and writing input and output.
//!
//! # Read and Write
//!
//! Because they are traits, [`Read`] and [`Write`] are implemented by a number
//! of other types, and you can implement them for your types too. As such,
//! you'll see a few different types of I/O throughout the documentation in
//! this module: [`File`]s, [`TcpStream`]s, and sometimes even [`Vec<T>`]s. For
//! example, [`Read`] adds a [`read`][`Read::read`] method, which we can use on
//! [`File`]s:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//!     let mut f = File::open("foo.txt")?;
//!     let mut buffer = [0; 10];
//!
//!     // read up to 10 bytes
//!     let n = f.read(&mut buffer)?;
//!
//!     println!("The bytes: {:?}", &buffer[..n]);
//!     Ok(())
//! }
//! ```
//!
//! [`Read`] and [`Write`] are so important, implementors of the two traits have a
//! nickname: readers and writers. So you'll sometimes see 'a reader' instead
//! of 'a type that implements the [`Read`] trait'. Much easier!
//!
//! ## Seek and BufRead
//!
//! Beyond that, there are two important traits that are provided: [`Seek`]
//! and [`BufRead`]. Both of these build on top of a reader to control
//! how the reading happens. [`Seek`] lets you control where the next byte is
//! coming from:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::io::SeekFrom;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//!     let mut f = File::open("foo.txt")?;
//!     let mut buffer = [0; 10];
//!
//!     // skip to the last 10 bytes of the file
//!     f.seek(SeekFrom::End(-10))?;
//!
//!     // read up to 10 bytes
//!     let n = f.read(&mut buffer)?;
//!
//!     println!("The bytes: {:?}", &buffer[..n]);
//!     Ok(())
//! }
//! ```
//!
//! [`BufRead`] uses an internal buffer to provide a number of other ways to read, but
//! to show it off, we'll need to talk about buffers in general. Keep reading!
//!
//! ## BufReader and BufWriter
//!
//! Byte-based interfaces are unwieldy and can be inefficient, as we'd need to be
//! making near-constant calls to the operating system. To help with this,
//! `std::io` comes with two structs, [`BufReader`] and [`BufWriter`], which wrap
//! readers and writers. The wrapper uses a buffer, reducing the number of
//! calls and providing nicer methods for accessing exactly what you want.
//!
//! For example, [`BufReader`] works with the [`BufRead`] trait to add extra
//! methods to any reader:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::io::BufReader;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//!     let f = File::open("foo.txt")?;
//!     let mut reader = BufReader::new(f);
//!     let mut buffer = String::new();
//!
//!     // read a line into buffer
//!     reader.read_line(&mut buffer)?;
//!
//!     println!("{}", buffer);
//!     Ok(())
//! }
//! ```
//!
//! [`BufWriter`] doesn't add any new ways of writing; it just buffers every call
//! to [`write`][`Write::write`]:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::io::BufWriter;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//!     let f = File::create("foo.txt")?;
//!     {
//!         let mut writer = BufWriter::new(f);
//!
//!         // write a byte to the buffer
//!         writer.write(&[42])?;
//!
//!     } // the buffer is flushed once writer goes out of scope
//!
//!     Ok(())
//! }
//! ```
//!
//! ## Standard input and output
//!
//! A very common source of input is standard input:
//!
//! ```no_run
//! use std::io;
//!
//! fn main() -> io::Result<()> {
//!     let mut input = String::new();
//!
//!     io::stdin().read_line(&mut input)?;
//!
//!     println!("You typed: {}", input.trim());
//!     Ok(())
//! }
//! ```
//!
//! Note that you cannot use the [`?` operator] in functions that do not return
//! a [`Result<T, E>`][`Result`]. Instead, you can call [`.unwrap()`]
//! or `match` on the return value to catch any possible errors:
//!
//! ```no_run
//! use std::io;
//!
//! let mut input = String::new();
//!
//! io::stdin().read_line(&mut input).unwrap();
//! ```
//!
//! And a very common source of output is standard output:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//!
//! fn main() -> io::Result<()> {
//!     io::stdout().write(&[42])?;
//!     Ok(())
//! }
//! ```
//!
//! Of course, using [`io::stdout`] directly is less common than something like
//! [`println!`].
//!
//! ## Iterator types
//!
//! A large number of the structures provided by `std::io` are for various
//! ways of iterating over I/O. For example, [`Lines`] is used to split over
//! lines:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::io::BufReader;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//!     let f = File::open("foo.txt")?;
//!     let reader = BufReader::new(f);
//!
//!     for line in reader.lines() {
//!         println!("{}", line?);
//!     }
//!     Ok(())
//! }
//! ```
//!
//! ## Functions
//!
//! There are a number of [functions][functions-list] that offer access to various
//! features. For example, we can use three of these functions to copy everything
//! from standard input to standard output:
//!
//! ```no_run
//! use std::io;
//!
//! fn main() -> io::Result<()> {
//!     io::copy(&mut io::stdin(), &mut io::stdout())?;
//!     Ok(())
//! }
//! ```
//!
//! [functions-list]: #functions-1
//!
//! ## io::Result
//!
//! Last, but certainly not least, is [`io::Result`]. This type is used
//! as the return type of many `std::io` functions that can cause an error, and
//! can be returned from your own functions as well. Many of the examples in this
//! module use the [`?` operator]:
//!
//! ```
//! use std::io;
//!
//! fn read_input() -> io::Result<()> {
//!     let mut input = String::new();
//!
//!     io::stdin().read_line(&mut input)?;
//!
//!     println!("You typed: {}", input.trim());
//!
//!     Ok(())
//! }
//! ```
//!
//! The return type of `read_input()`, [`io::Result<()>`][`io::Result`], is a very
//! common type for functions which don't have a 'real' return value, but do want to
//! return errors if they happen. In this case, the only purpose of this function is
//! to read the line and print it, so we use `()`.
//!
//! ## Platform-specific behavior
//!
//! Many I/O functions throughout the standard library are documented to indicate
//! what various library or syscalls they are delegated to. This is done to help
//! applications both understand what's happening under the hood as well as investigate
//! any possibly unclear semantics. Note, however, that this is informative, not a binding
//! contract. The implementation of many of these functions are subject to change over
//! time and may call fewer or more syscalls/library functions.
//!
//! [`Read`]: trait.Read.html
//! [`Write`]: trait.Write.html
//! [`Seek`]: trait.Seek.html
//! [`BufRead`]: trait.BufRead.html
//! [`File`]: ../fs/struct.File.html
//! [`TcpStream`]: ../net/struct.TcpStream.html
//! [`Vec<T>`]: ../vec/struct.Vec.html
//! [`BufReader`]: struct.BufReader.html
//! [`BufWriter`]: struct.BufWriter.html
//! [`Write::write`]: trait.Write.html#tymethod.write
//! [`io::stdout`]: fn.stdout.html
//! [`println!`]: ../macro.println.html
//! [`Lines`]: struct.Lines.html
//! [`io::Result`]: type.Result.html
//! [`?` operator]: ../../book/appendix-02-operators.html
//! [`Read::read`]: trait.Read.html#tymethod.read
//! [`Result`]: ../result/enum.Result.html
//! [`.unwrap()`]: ../result/enum.Result.html#method.unwrap

use alloc::string::String;
use alloc::vec::Vec;
use core::cmp;
use core::fmt;
use core::ops::{Deref, DerefMut};
use core::ptr;
use core::slice;
use core::str;

use crate::file_io::memchr;
use crate::file_io::sys;

pub use self::buffered::IntoInnerError;
pub use self::buffered::{BufReader, BufWriter, LineWriter};
pub use self::cursor::Cursor;
pub use self::error::{Error, ErrorKind, Result};
pub use self::util::{copy, empty, repeat, sink, Empty, Repeat, Sink};

mod buffered;
mod cursor;
mod error;
mod impls;
pub mod prelude;
mod util;

const DEFAULT_BUF_SIZE: usize = crate::file_io::sys_common::io::DEFAULT_BUF_SIZE;

struct Guard<'a> {
	buf: &'a mut Vec<u8>,
	len: usize,
}

impl Drop for Guard<'_> {
	fn drop(&mut self) {
		unsafe {
			self.buf.set_len(self.len);
		}
	}
}

// A few methods below (read_to_string, read_line) will append data into a
// `String` buffer, but we need to be pretty careful when doing this. The
// implementation will just call `.as_mut_vec()` and then delegate to a
// byte-oriented reading method, but we must ensure that when returning we never
// leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
//
// To this end, we use an RAII guard (to protect against panics) which updates
// the length of the string when it is dropped. This guard initially truncates
// the string to the prior length and only after we've validated that the
// new contents are valid UTF-8 do we allow it to set a longer length.
//
// The unsafety in this function is twofold:
//
// 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
//    checks.
// 2. We're passing a raw buffer to the function `f`, and it is expected that
//    the function only *appends* bytes to the buffer. We'll get undefined
//    behavior if existing bytes are overwritten to have non-UTF-8 data.
fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
where
	F: FnOnce(&mut Vec<u8>) -> Result<usize>,
{
	unsafe {
		let mut g = Guard {
			len: buf.len(),
			buf: buf.as_mut_vec(),
		};
		let ret = f(g.buf);
		if str::from_utf8(&g.buf[g.len..]).is_err() {
			ret.and_then(|_| {
				Err(Error::new(
					ErrorKind::InvalidData,
					"stream did not contain valid UTF-8",
				))
			})
		} else {
			g.len = g.buf.len();
			ret
		}
	}
}

// This uses an adaptive system to extend the vector when it fills. We want to
// avoid paying to allocate and zero a huge chunk of memory if the reader only
// has 4 bytes while still making large reads if the reader does have a ton
// of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
// time is 4,500 times (!) slower than a default reservation size of 32 if the
// reader has a very small amount of data to return.
//
// Because we're extending the buffer with uninitialized data for trusted
// readers, we need to make sure to truncate that if any of this panics.
fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
	read_to_end_with_reservation(r, buf, 32)
}

fn read_to_end_with_reservation<R: Read + ?Sized>(
	r: &mut R,
	buf: &mut Vec<u8>,
	reservation_size: usize,
) -> Result<usize> {
	let start_len = buf.len();
	let mut g = Guard {
		len: buf.len(),
		buf,
	};
	let ret;
	loop {
		if g.len == g.buf.len() {
			unsafe {
				g.buf.reserve(reservation_size);
				let capacity = g.buf.capacity();
				g.buf.set_len(capacity);
				r.initializer().initialize(&mut g.buf[g.len..]);
			}
		}

		match r.read(&mut g.buf[g.len..]) {
			Ok(0) => {
				ret = Ok(g.len - start_len);
				break;
			}
			Ok(n) => g.len += n,
			Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
			Err(e) => {
				ret = Err(e);
				break;
			}
		}
	}

	ret
}

pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
where
	F: FnOnce(&mut [u8]) -> Result<usize>,
{
	let buf = bufs
		.iter_mut()
		.find(|b| !b.is_empty())
		.map_or(&mut [][..], |b| &mut **b);
	read(buf)
}

pub(crate) fn default_write_vectored<F>(write: F, bufs: &[IoSlice<'_>]) -> Result<usize>
where
	F: FnOnce(&[u8]) -> Result<usize>,
{
	let buf = bufs
		.iter()
		.find(|b| !b.is_empty())
		.map_or(&[][..], |b| &**b);
	write(buf)
}

pub struct Stdout {
	inner: super::sys::stdio::Stdout,
}

pub fn stdout() -> Stdout {
	Stdout {
		inner: super::sys::stdio::Stdout::new(),
	}
}

impl Write for Stdout {
	fn write(&mut self, buf: &[u8]) -> Result<usize> {
		self.inner.write(buf)
	}

	fn flush(&mut self) -> Result<()> {
		self.inner.flush()
	}
}

/// The `Read` trait allows for reading bytes from a source.
///
/// Implementors of the `Read` trait are called 'readers'.
///
/// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
/// will attempt to pull bytes from this source into a provided buffer. A
/// number of other methods are implemented in terms of [`read()`], giving
/// implementors a number of ways to read bytes while only needing to implement
/// a single method.
///
/// Readers are intended to be composable with one another. Many implementors
/// throughout [`std::io`] take and provide types which implement the `Read`
/// trait.
///
/// Please note that each call to [`read()`] may involve a system call, and
/// therefore, using something that implements [`BufRead`], such as
/// [`BufReader`], will be more efficient.
///
/// # Examples
///
/// [`File`]s implement `Read`:
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
///     let mut f = File::open("foo.txt")?;
///     let mut buffer = [0; 10];
///
///     // read up to 10 bytes
///     f.read(&mut buffer)?;
///
///     let mut buffer = Vec::new();
///     // read the whole file
///     f.read_to_end(&mut buffer)?;
///
///     // read into a String, so that you don't need to do the conversion.
///     let mut buffer = String::new();
///     f.read_to_string(&mut buffer)?;
///
///     // and more! See the other methods for more details.
///     Ok(())
/// }
/// ```
///
/// Read from [`&str`] because [`&[u8]`][slice] implements `Read`:
///
/// ```no_run
/// # use std::io;
/// use std::io::prelude::*;
///
/// fn main() -> io::Result<()> {
///     let mut b = "This string will be read".as_bytes();
///     let mut buffer = [0; 10];
///
///     // read up to 10 bytes
///     b.read(&mut buffer)?;
///
///     // etc... it works exactly as a File does!
///     Ok(())
/// }
/// ```
///
/// [`read()`]: Read::read
/// [`File`]: super::fs::File
/// [`std::io`]: ../../std/io/index.html
/// [slice]: core::slice
pub trait Read {
	/// Pull some bytes from this source into the specified buffer, returning
	/// how many bytes were read.
	///
	/// This function does not provide any guarantees about whether it blocks
	/// waiting for data, but if an object needs to block for a read but cannot
	/// it will typically signal this via an [`Err`] return value.
	///
	/// If the return value of this method is [`Ok(n)`], then it must be
	/// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
	/// that the buffer `buf` has been filled in with `n` bytes of data from this
	/// source. If `n` is `0`, then it can indicate one of two scenarios:
	///
	/// 1. This reader has reached its "end of file" and will likely no longer
	///    be able to produce bytes. Note that this does not mean that the
	///    reader will *always* no longer be able to produce bytes.
	/// 2. The buffer specified was 0 bytes in length.
	///
	/// No guarantees are provided about the contents of `buf` when this
	/// function is called, implementations cannot rely on any property of the
	/// contents of `buf` being true. It is recommended that implementations
	/// only write data to `buf` instead of reading its contents.
	///
	/// # Errors
	///
	/// If this function encounters any form of I/O or other error, an error
	/// variant will be returned. If an error is returned then it must be
	/// guaranteed that no bytes were read.
	///
	/// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
	/// operation should be retried if there is nothing else to do.
	///
	/// # Examples
	///
	/// [`File`]s implement `Read`:
	///
	/// [`Err`]: ../../std/result/enum.Result.html#variant.Err
	/// [`Ok(n)`]: ../../std/result/enum.Result.html#variant.Ok
	/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
	/// [`File`]: ../fs/struct.File.html
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = File::open("foo.txt")?;
	///     let mut buffer = [0; 10];
	///
	///     // read up to 10 bytes
	///     let n = f.read(&mut buffer[..])?;
	///
	///     println!("The bytes: {:?}", &buffer[..n]);
	///     Ok(())
	/// }
	/// ```

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

	/// Like `read`, except that it reads into a slice of buffers.
	///
	/// Data is copied to fill each buffer in order, with the final buffer
	/// written to possibly being only partially filled. This method must behave
	/// as a single call to `read` with the buffers concatenated would.
	///
	/// The default implementation calls `read` with either the first nonempty
	/// buffer provided, or an empty one if none exists.

	fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
		default_read_vectored(|b| self.read(b), bufs)
	}

	/// Determines if this `Read`er can work with buffers of uninitialized
	/// memory.
	///
	/// The default implementation returns an initializer which will zero
	/// buffers.
	///
	/// If a `Read`er guarantees that it can work properly with uninitialized
	/// memory, it should call [`Initializer::nop()`]. See the documentation for
	/// [`Initializer`] for details.
	///
	/// The behavior of this method must be independent of the state of the
	/// `Read`er - the method only takes `&self` so that it can be used through
	/// trait objects.
	///
	/// # Safety
	///
	/// This method is unsafe because a `Read`er could otherwise return a
	/// non-zeroing `Initializer` from another `Read` type without an `unsafe`
	/// block.
	///
	/// [`Initializer::nop()`]: ../../std/io/struct.Initializer.html#method.nop
	/// [`Initializer`]: ../../std/io/struct.Initializer.html
	#[inline]
	unsafe fn initializer(&self) -> Initializer {
		Initializer::zeroing()
	}

	/// Read all bytes until EOF in this source, placing them into `buf`.
	///
	/// All bytes read from this source will be appended to the specified buffer
	/// `buf`. This function will continuously call [`read()`] to append more data to
	/// `buf` until [`read()`] returns either [`Ok(0)`] or an error of
	/// non-[`ErrorKind::Interrupted`] kind.
	///
	/// If successful, this function will return the total number of bytes read.
	///
	/// # Errors
	///
	/// If this function encounters an error of the kind
	/// [`ErrorKind::Interrupted`] then the error is ignored and the operation
	/// will continue.
	///
	/// If any other read error is encountered then this function immediately
	/// returns. Any bytes which have already been read will be appended to
	/// `buf`.
	///
	/// # Examples
	///
	/// [`File`]s implement `Read`:
	///
	/// [`read()`]: trait.Read.html#tymethod.read
	/// [`Ok(0)`]: ../../std/result/enum.Result.html#variant.Ok
	/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
	/// [`File`]: ../fs/struct.File.html
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = File::open("foo.txt")?;
	///     let mut buffer = Vec::new();
	///
	///     // read the whole file
	///     f.read_to_end(&mut buffer)?;
	///     Ok(())
	/// }
	/// ```
	///
	/// (See also the [`std::fs::read`] convenience function for reading from a
	/// file.)
	///
	/// [`std::fs::read`]: ../fs/fn.read.html

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

	/// Read all bytes until EOF in this source, appending them to `buf`.
	///
	/// If successful, this function returns the number of bytes which were read
	/// and appended to `buf`.
	///
	/// # Errors
	///
	/// If the data in this stream is *not* valid UTF-8 then an error is
	/// returned and `buf` is unchanged.
	///
	/// See [`read_to_end`][readtoend] for other error semantics.
	///
	/// [readtoend]: #method.read_to_end
	///
	/// # Examples
	///
	/// [`File`][file]s implement `Read`:
	///
	/// [file]: ../fs/struct.File.html
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = File::open("foo.txt")?;
	///     let mut buffer = String::new();
	///
	///     f.read_to_string(&mut buffer)?;
	///     Ok(())
	/// }
	/// ```
	///
	/// (See also the [`std::fs::read_to_string`] convenience function for
	/// reading from a file.)
	///
	/// [`std::fs::read_to_string`]: ../fs/fn.read_to_string.html

	fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
		// Note that we do *not* call `.read_to_end()` here. We are passing
		// `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
		// method to fill it up. An arbitrary implementation could overwrite the
		// entire contents of the vector, not just append to it (which is what
		// we are expecting).
		//
		// To prevent extraneously checking the UTF-8-ness of the entire buffer
		// we pass it to our hardcoded `read_to_end` implementation which we
		// know is guaranteed to only read data into the end of the buffer.
		append_to_string(buf, |b| read_to_end(self, b))
	}

	/// Read the exact number of bytes required to fill `buf`.
	///
	/// This function reads as many bytes as necessary to completely fill the
	/// specified buffer `buf`.
	///
	/// No guarantees are provided about the contents of `buf` when this
	/// function is called, implementations cannot rely on any property of the
	/// contents of `buf` being true. It is recommended that implementations
	/// only write data to `buf` instead of reading its contents.
	///
	/// # Errors
	///
	/// If this function encounters an error of the kind
	/// [`ErrorKind::Interrupted`] then the error is ignored and the operation
	/// will continue.
	///
	/// If this function encounters an "end of file" before completely filling
	/// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
	/// The contents of `buf` are unspecified in this case.
	///
	/// If any other read error is encountered then this function immediately
	/// returns. The contents of `buf` are unspecified in this case.
	///
	/// If this function returns an error, it is unspecified how many bytes it
	/// has read, but it will never read more than would be necessary to
	/// completely fill the buffer.
	///
	/// # Examples
	///
	/// [`File`]s implement `Read`:
	///
	/// [`File`]: ../fs/struct.File.html
	/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
	/// [`ErrorKind::UnexpectedEof`]: ../../std/io/enum.ErrorKind.html#variant.UnexpectedEof
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = File::open("foo.txt")?;
	///     let mut buffer = [0; 10];
	///
	///     // read exactly 10 bytes
	///     f.read_exact(&mut buffer)?;
	///     Ok(())
	/// }
	/// ```

	fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
		while !buf.is_empty() {
			match self.read(buf) {
				Ok(0) => break,
				Ok(n) => {
					let tmp = buf;
					buf = &mut tmp[n..];
				}
				Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
				Err(e) => return Err(e),
			}
		}
		if !buf.is_empty() {
			Err(Error::new(
				ErrorKind::UnexpectedEof,
				"failed to fill whole buffer",
			))
		} else {
			Ok(())
		}
	}

	/// Creates a "by reference" adaptor for this instance of `Read`.
	///
	/// The returned adaptor also implements `Read` and will simply borrow this
	/// current reader.
	///
	/// # Examples
	///
	/// [`File`][file]s implement `Read`:
	///
	/// [file]: ../fs/struct.File.html
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::Read;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = File::open("foo.txt")?;
	///     let mut buffer = Vec::new();
	///     let mut other_buffer = Vec::new();
	///
	///     {
	///         let reference = f.by_ref();
	///
	///         // read at most 5 bytes
	///         reference.take(5).read_to_end(&mut buffer)?;
	///
	///     } // drop our &mut reference so we can use f again
	///
	///     // original file still usable, read the rest
	///     f.read_to_end(&mut other_buffer)?;
	///     Ok(())
	/// }
	/// ```

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

	/// Transforms this `Read` instance to an [`Iterator`] over its bytes.
	///
	/// The returned type implements [`Iterator`] where the `Item` is
	/// [`Result`]`<`[`u8`]`, `[`io::Error`]`>`.
	/// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
	/// otherwise. EOF is mapped to returning [`None`] from this iterator.
	///
	/// # Examples
	///
	/// [`File`][file]s implement `Read`:
	///
	/// [file]: ../fs/struct.File.html
	/// [`Iterator`]: ../../std/iter/trait.Iterator.html
	/// [`Result`]: ../../std/result/enum.Result.html
	/// [`io::Error`]: ../../std/io/struct.Error.html
	/// [`u8`]: ../../std/primitive.u8.html
	/// [`Ok`]: ../../std/result/enum.Result.html#variant.Ok
	/// [`Err`]: ../../std/result/enum.Result.html#variant.Err
	/// [`None`]: ../../std/option/enum.Option.html#variant.None
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = File::open("foo.txt")?;
	///
	///     for byte in f.bytes() {
	///         println!("{}", byte.unwrap());
	///     }
	///     Ok(())
	/// }
	/// ```

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

	/// Creates an adaptor which will chain this stream with another.
	///
	/// The returned `Read` instance will first read all bytes from this object
	/// until EOF is encountered. Afterwards the output is equivalent to the
	/// output of `next`.
	///
	/// # Examples
	///
	/// [`File`][file]s implement `Read`:
	///
	/// [file]: ../fs/struct.File.html
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut f1 = File::open("foo.txt")?;
	///     let mut f2 = File::open("bar.txt")?;
	///
	///     let mut handle = f1.chain(f2);
	///     let mut buffer = String::new();
	///
	///     // read the value into a String. We could use any Read method here,
	///     // this is just one example.
	///     handle.read_to_string(&mut buffer)?;
	///     Ok(())
	/// }
	/// ```

	fn chain<R: Read>(self, next: R) -> Chain<Self, R>
	where
		Self: Sized,
	{
		Chain {
			first: self,
			second: next,
			done_first: false,
		}
	}

	/// Creates an adaptor which will read at most `limit` bytes from it.
	///
	/// This function returns a new instance of `Read` which will read at most
	/// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
	/// read errors will not count towards the number of bytes read and future
	/// calls to [`read()`] may succeed.
	///
	/// # Examples
	///
	/// [`File`]s implement `Read`:
	///
	/// [`File`]: ../fs/struct.File.html
	/// [`Ok(0)`]: ../../std/result/enum.Result.html#variant.Ok
	/// [`read()`]: trait.Read.html#tymethod.read
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = File::open("foo.txt")?;
	///     let mut buffer = [0; 5];
	///
	///     // read at most five bytes
	///     let mut handle = f.take(5);
	///
	///     handle.read(&mut buffer)?;
	///     Ok(())
	/// }
	/// ```

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

/// A buffer type used with `Read::read_vectored`.
///
/// It is semantically a wrapper around an `&mut [u8]`, but is guaranteed to be
/// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
/// Windows.
#[repr(transparent)]
pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);

impl<'a> fmt::Debug for IoSliceMut<'a> {
	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
		fmt::Debug::fmt(self.0.as_slice(), fmt)
	}
}

impl<'a> IoSliceMut<'a> {
	/// Creates a new `IoSliceMut` wrapping a byte slice.
	///
	/// # Panics
	///
	/// Panics on Windows if the slice is larger than 4GB.
	#[inline]
	pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
		IoSliceMut(sys::io::IoSliceMut::new(buf))
	}
}

impl<'a> Deref for IoSliceMut<'a> {
	type Target = [u8];

	#[inline]
	fn deref(&self) -> &[u8] {
		self.0.as_slice()
	}
}

impl<'a> DerefMut for IoSliceMut<'a> {
	#[inline]
	fn deref_mut(&mut self) -> &mut [u8] {
		self.0.as_mut_slice()
	}
}

/// A buffer type used with `Write::write_vectored`.
///
/// It is semantically a wrapper around an `&[u8]`, but is guaranteed to be
/// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
/// Windows.
#[repr(transparent)]
pub struct IoSlice<'a>(sys::io::IoSlice<'a>);

impl<'a> fmt::Debug for IoSlice<'a> {
	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
		fmt::Debug::fmt(self.0.as_slice(), fmt)
	}
}

impl<'a> IoSlice<'a> {
	/// Creates a new `IoSlice` wrapping a byte slice.
	///
	/// # Panics
	///
	/// Panics on Windows if the slice is larger than 4GB.
	#[inline]
	pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
		IoSlice(sys::io::IoSlice::new(buf))
	}
}

impl<'a> Deref for IoSlice<'a> {
	type Target = [u8];

	#[inline]
	fn deref(&self) -> &[u8] {
		self.0.as_slice()
	}
}

/// A type used to conditionally initialize buffers passed to `Read` methods.
#[derive(Debug)]
pub struct Initializer(bool);

impl Initializer {
	/// Returns a new `Initializer` which will zero out buffers.
	#[inline]
	pub fn zeroing() -> Initializer {
		Initializer(true)
	}

	/// Returns a new `Initializer` which will not zero out buffers.
	///
	/// # Safety
	///
	/// This may only be called by `Read`ers which guarantee that they will not
	/// read from buffers passed to `Read` methods, and that the return value of
	/// the method accurately reflects the number of bytes that have been
	/// written to the head of the buffer.
	#[inline]
	pub unsafe fn nop() -> Initializer {
		Initializer(false)
	}

	/// Indicates if a buffer should be initialized.
	#[inline]
	pub fn should_initialize(&self) -> bool {
		self.0
	}

	/// Initializes a buffer if necessary.
	#[inline]
	pub fn initialize(&self, buf: &mut [u8]) {
		if self.should_initialize() {
			unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
		}
	}
}

/// A trait for objects which are byte-oriented sinks.
///
/// Implementors of the `Write` trait are sometimes called 'writers'.
///
/// Writers are defined by two required methods, [`write`] and [`flush`]:
///
/// * The [`write`] method will attempt to write some data into the object,
///   returning how many bytes were successfully written.
///
/// * The [`flush`] method is useful for adaptors and explicit buffers
///   themselves for ensuring that all buffered data has been pushed out to the
///   'true sink'.
///
/// Writers are intended to be composable with one another. Many implementors
/// throughout [`std::io`] take and provide types which implement the `Write`
/// trait.
///
/// [`write`]: #tymethod.write
/// [`flush`]: #tymethod.flush
/// [`std::io`]: index.html
///
/// # Examples
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
///     let data = b"some bytes";
///
///     let mut pos = 0;
///     let mut buffer = File::create("foo.txt")?;
///
///     while pos < data.len() {
///         let bytes_written = buffer.write(&data[pos..])?;
///         pos += bytes_written;
///     }
///     Ok(())
/// }
/// ```
///
/// The trait also provides convenience methods like [`write_all`], which calls
/// `write` in a loop until its entire input has been written.
///
/// [`write_all`]: #method.write_all
pub trait Write {
	/// Write a buffer into this writer, returning how many bytes were written.
	///
	/// This function will attempt to write the entire contents of `buf`, but
	/// the entire write may not succeed, or the write may also generate an
	/// error. A call to `write` represents *at most one* attempt to write to
	/// any wrapped object.
	///
	/// Calls to `write` are not guaranteed to block waiting for data to be
	/// written, and a write which would otherwise block can be indicated through
	/// an [`Err`] variant.
	///
	/// If the return value is [`Ok(n)`] then it must be guaranteed that
	/// `0 <= n <= buf.len()`. A return value of `0` typically means that the
	/// underlying object is no longer able to accept bytes and will likely not
	/// be able to in the future as well, or that the buffer provided is empty.
	///
	/// # Errors
	///
	/// Each call to `write` may generate an I/O error indicating that the
	/// operation could not be completed. If an error is returned then no bytes
	/// in the buffer were written to this writer.
	///
	/// It is **not** considered an error if the entire buffer could not be
	/// written to this writer.
	///
	/// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
	/// write operation should be retried if there is nothing else to do.
	///
	/// [`Err`]: ../../std/result/enum.Result.html#variant.Err
	/// [`Ok(n)`]:  ../../std/result/enum.Result.html#variant.Ok
	/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let mut buffer = File::create("foo.txt")?;
	///
	///     // Writes some prefix of the byte string, not necessarily all of it.
	///     buffer.write(b"some bytes")?;
	///     Ok(())
	/// }
	/// ```

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

	/// Like `write`, except that it writes from a slice of buffers.
	///
	/// Data is copied to from each buffer in order, with the final buffer
	/// read from possibly being only partially consumed. This method must
	/// behave as a call to `write` with the buffers concatenated would.
	///
	/// The default implementation calls `write` with either the first nonempty
	/// buffer provided, or an empty one if none exists.

	fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
		default_write_vectored(|b| self.write(b), bufs)
	}

	/// Flush this output stream, ensuring that all intermediately buffered
	/// contents reach their destination.
	///
	/// # Errors
	///
	/// It is considered an error if not all bytes could be written due to
	/// I/O errors or EOF being reached.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::prelude::*;
	/// use std::io::BufWriter;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let mut buffer = BufWriter::new(File::create("foo.txt")?);
	///
	///     buffer.write_all(b"some bytes")?;
	///     buffer.flush()?;
	///     Ok(())
	/// }
	/// ```

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

	/// Attempts to write an entire buffer into this writer.
	///
	/// This method will continuously call [`write`] until there is no more data
	/// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
	/// returned. This method will not return until the entire buffer has been
	/// successfully written or such an error occurs. The first error that is
	/// not of [`ErrorKind::Interrupted`] kind generated from this method will be
	/// returned.
	///
	/// # Errors
	///
	/// This function will return the first error of
	/// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
	///
	/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
	/// [`write`]: #tymethod.write
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let mut buffer = File::create("foo.txt")?;
	///
	///     buffer.write_all(b"some bytes")?;
	///     Ok(())
	/// }
	/// ```

	fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
		while !buf.is_empty() {
			match self.write(buf) {
				Ok(0) => {
					return Err(Error::new(
						ErrorKind::WriteZero,
						"failed to write whole buffer",
					))
				}
				Ok(n) => buf = &buf[n..],
				Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
				Err(e) => return Err(e),
			}
		}
		Ok(())
	}

	/// Writes a formatted string into this writer, returning any error
	/// encountered.
	///
	/// This method is primarily used to interface with the
	/// [`format_args!`][formatargs] macro, but it is rare that this should
	/// explicitly be called. The [`write!`][write] macro should be favored to
	/// invoke this method instead.
	///
	/// [formatargs]: ../macro.format_args.html
	/// [write]: ../macro.write.html
	///
	/// This function internally uses the [`write_all`][writeall] method on
	/// this trait and hence will continuously write data so long as no errors
	/// are received. This also means that partial writes are not indicated in
	/// this signature.
	///
	/// [writeall]: #method.write_all
	///
	/// # Errors
	///
	/// This function will return any I/O error reported while formatting.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let mut buffer = File::create("foo.txt")?;
	///
	///     // this call
	///     write!(buffer, "{:.*}", 2, 1.234567)?;
	///     // turns into this:
	///     buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))?;
	///     Ok(())
	/// }
	/// ```

	fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> Result<()> {
		// Create a shim which translates a Write to a fmt::Write and saves
		// off I/O errors. instead of discarding them
		struct Adaptor<'a, T: ?Sized + 'a> {
			inner: &'a mut T,
			error: Result<()>,
		}

		impl<T: Write + ?Sized> fmt::Write for Adaptor<'_, T> {
			fn write_str(&mut self, s: &str) -> fmt::Result {
				match self.inner.write_all(s.as_bytes()) {
					Ok(()) => Ok(()),
					Err(e) => {
						self.error = Err(e);
						Err(fmt::Error)
					}
				}
			}
		}

		let mut output = Adaptor {
			inner: self,
			error: Ok(()),
		};
		match fmt::write(&mut output, fmt) {
			Ok(()) => Ok(()),
			Err(..) => {
				// check if the error came from the underlying `Write` or not
				if output.error.is_err() {
					output.error
				} else {
					Err(Error::new(ErrorKind::Other, "formatter error"))
				}
			}
		}
	}

	/// Creates a "by reference" adaptor for this instance of `Write`.
	///
	/// The returned adaptor also implements `Write` and will simply borrow this
	/// current writer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::Write;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let mut buffer = File::create("foo.txt")?;
	///
	///     let reference = buffer.by_ref();
	///
	///     // we can use reference just like our original buffer
	///     reference.write_all(b"some bytes")?;
	///     Ok(())
	/// }
	/// ```

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

/// The `Seek` trait provides a cursor which can be moved within a stream of
/// bytes.
///
/// The stream typically has a fixed size, allowing seeking relative to either
/// end or the current offset.
///
/// # Examples
///
/// [`File`][file]s implement `Seek`:
///
/// [file]: ../fs/struct.File.html
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
/// use std::io::SeekFrom;
///
/// fn main() -> io::Result<()> {
///     let mut f = File::open("foo.txt")?;
///
///     // move the cursor 42 bytes from the start of the file
///     f.seek(SeekFrom::Start(42))?;
///     Ok(())
/// }
/// ```

pub trait Seek {
	/// Seek to an offset, in bytes, in a stream.
	///
	/// A seek beyond the end of a stream is allowed, but behavior is defined
	/// by the implementation.
	///
	/// If the seek operation completed successfully,
	/// this method returns the new position from the start of the stream.
	/// That position can be used later with [`SeekFrom::Start`].
	///
	/// # Errors
	///
	/// Seeking to a negative offset is considered an error.
	///
	/// [`SeekFrom::Start`]: enum.SeekFrom.html#variant.Start

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

	/// Returns the length of this stream (in bytes).
	///
	/// This method is implemented using up to three seek operations. If this
	/// method returns successfully, the seek position is unchanged (i.e. the
	/// position before calling this method is the same as afterwards).
	/// However, if this method returns an error, the seek position is
	/// unspecified.
	///
	/// If you need to obtain the length of *many* streams and you don't care
	/// about the seek position afterwards, you can reduce the number of seek
	/// operations by simply calling `seek(SeekFrom::End(0))` and using its
	/// return value (it is also the stream length).
	///
	/// Note that length of a stream can change over time (for example, when
	/// data is appended to a file). So calling this method multiple times does
	/// not necessarily return the same length each time.
	///
	///
	/// # Example
	///
	/// ```no_run
	/// #![feature(seek_convenience)]
	/// use std::{
	///     io::{self, Seek},
	///     fs::File,
	/// };
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = File::open("foo.txt")?;
	///
	///     let len = f.stream_len()?;
	///     println!("The file is currently {} bytes long", len);
	///     Ok(())
	/// }
	/// ```
	fn stream_len(&mut self) -> Result<u64> {
		let old_pos = self.stream_position()?;
		let len = self.seek(SeekFrom::End(0))?;

		// Avoid seeking a third time when we were already at the end of the
		// stream. The branch is usually way cheaper than a seek operation.
		if old_pos != len {
			self.seek(SeekFrom::Start(old_pos))?;
		}

		Ok(len)
	}

	/// Returns the current seek position from the start of the stream.
	///
	/// This is equivalent to `self.seek(SeekFrom::Current(0))`.
	///
	///
	/// # Example
	///
	/// ```no_run
	/// #![feature(seek_convenience)]
	/// use std::{
	///     io::{self, BufRead, BufReader, Seek},
	///     fs::File,
	/// };
	///
	/// fn main() -> io::Result<()> {
	///     let mut f = BufReader::new(File::open("foo.txt")?);
	///
	///     let before = f.stream_position()?;
	///     f.read_line(&mut String::new())?;
	///     let after = f.stream_position()?;
	///
	///     println!("The first line was {} bytes long", after - before);
	///     Ok(())
	/// }
	/// ```
	fn stream_position(&mut self) -> Result<u64> {
		self.seek(SeekFrom::Current(0))
	}
}

/// Enumeration of possible methods to seek within an I/O object.
///
/// It is used by the [`Seek`] trait.
///
/// [`Seek`]: trait.Seek.html
#[derive(Copy, PartialEq, Eq, Clone, Debug)]
pub enum SeekFrom {
	/// Sets the offset to the provided number of bytes.
	Start(u64),

	/// Sets the offset to the size of this object plus the specified number of
	/// bytes.
	///
	/// It is possible to seek beyond the end of an object, but it's an error to
	/// seek before byte 0.
	End(i64),

	/// Sets the offset to the current position plus the specified number of
	/// bytes.
	///
	/// It is possible to seek beyond the end of an object, but it's an error to
	/// seek before byte 0.
	Current(i64),
}

fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> Result<usize> {
	let mut read = 0;
	loop {
		let (done, used) = {
			let available = match r.fill_buf() {
				Ok(n) => n,
				Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
				Err(e) => return Err(e),
			};
			match memchr::memchr(delim, available) {
				Some(i) => {
					buf.extend_from_slice(&available[..=i]);
					(true, i + 1)
				}
				None => {
					buf.extend_from_slice(available);
					(false, available.len())
				}
			}
		};
		r.consume(used);
		read += used;
		if done || used == 0 {
			return Ok(read);
		}
	}
}

/// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
/// to perform extra ways of reading.
///
/// For example, reading line-by-line is inefficient without using a buffer, so
/// if you want to read by line, you'll need `BufRead`, which includes a
/// [`read_line`] method as well as a [`lines`] iterator.
///
/// # Examples
///
/// A locked standard input implements `BufRead`:
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
///
/// let stdin = io::stdin();
/// for line in stdin.lock().lines() {
///     println!("{}", line.unwrap());
/// }
/// ```
///
/// If you have something that implements [`Read`], you can use the [`BufReader`
/// type][`BufReader`] to turn it into a `BufRead`.
///
/// For example, [`File`] implements [`Read`], but not `BufRead`.
/// [`BufReader`] to the rescue!
///
/// [`BufReader`]: struct.BufReader.html
/// [`File`]: ../fs/struct.File.html
/// [`read_line`]: #method.read_line
/// [`lines`]: #method.lines
/// [`Read`]: trait.Read.html
///
/// ```no_run
/// use std::io::{self, BufReader};
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
///     let f = File::open("foo.txt")?;
///     let f = BufReader::new(f);
///
///     for line in f.lines() {
///         println!("{}", line.unwrap());
///     }
///
///     Ok(())
/// }
/// ```
///

pub trait BufRead: Read {
	/// Returns the contents of the internal buffer, filling it with more data
	/// from the inner reader if it is empty.
	///
	/// This function is a lower-level call. It needs to be paired with the
	/// [`consume`] method to function properly. When calling this
	/// method, none of the contents will be "read" in the sense that later
	/// calling `read` may return the same contents. As such, [`consume`] must
	/// be called with the number of bytes that are consumed from this buffer to
	/// ensure that the bytes are never returned twice.
	///
	/// [`consume`]: #tymethod.consume
	///
	/// An empty buffer returned indicates that the stream has reached EOF.
	///
	/// # Errors
	///
	/// This function will return an I/O error if the underlying reader was
	/// read, but returned an error.
	///
	/// # Examples
	///
	/// A locked standard input implements `BufRead`:
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	///
	/// let stdin = io::stdin();
	/// let mut stdin = stdin.lock();
	///
	/// let buffer = stdin.fill_buf().unwrap();
	///
	/// // work with buffer
	/// println!("{:?}", buffer);
	///
	/// // ensure the bytes we worked with aren't returned again later
	/// let length = buffer.len();
	/// stdin.consume(length);
	/// ```

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

	/// Tells this buffer that `amt` bytes have been consumed from the buffer,
	/// so they should no longer be returned in calls to `read`.
	///
	/// This function is a lower-level call. It needs to be paired with the
	/// [`fill_buf`] method to function properly. This function does
	/// not perform any I/O, it simply informs this object that some amount of
	/// its buffer, returned from [`fill_buf`], has been consumed and should
	/// no longer be returned. As such, this function may do odd things if
	/// [`fill_buf`] isn't called before calling it.
	///
	/// The `amt` must be `<=` the number of bytes in the buffer returned by
	/// [`fill_buf`].
	///
	/// # Examples
	///
	/// Since `consume()` is meant to be used with [`fill_buf`],
	/// that method's example includes an example of `consume()`.
	///
	/// [`fill_buf`]: #tymethod.fill_buf

	fn consume(&mut self, amt: usize);

	/// Read all bytes into `buf` until the delimiter `byte` or EOF is reached.
	///
	/// This function will read bytes from the underlying stream until the
	/// delimiter or EOF is found. Once found, all bytes up to, and including,
	/// the delimiter (if found) will be appended to `buf`.
	///
	/// If successful, this function will return the total number of bytes read.
	///
	/// # Errors
	///
	/// This function will ignore all instances of [`ErrorKind::Interrupted`] and
	/// will otherwise return any errors returned by [`fill_buf`].
	///
	/// If an I/O error is encountered then all bytes read so far will be
	/// present in `buf` and its length will have been adjusted appropriately.
	///
	/// [`fill_buf`]: #tymethod.fill_buf
	/// [`ErrorKind::Interrupted`]: enum.ErrorKind.html#variant.Interrupted
	///
	/// # Examples
	///
	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
	/// this example, we use [`Cursor`] to read all the bytes in a byte slice
	/// in hyphen delimited segments:
	///
	/// [`Cursor`]: struct.Cursor.html
	///
	/// ```
	/// use std::io::{self, BufRead};
	///
	/// let mut cursor = io::Cursor::new(b"lorem-ipsum");
	/// let mut buf = vec![];
	///
	/// // cursor is at 'l'
	/// let num_bytes = cursor.read_until(b'-', &mut buf)
	///     .expect("reading from cursor won't fail");
	/// assert_eq!(num_bytes, 6);
	/// assert_eq!(buf, b"lorem-");
	/// buf.clear();
	///
	/// // cursor is at 'i'
	/// let num_bytes = cursor.read_until(b'-', &mut buf)
	///     .expect("reading from cursor won't fail");
	/// assert_eq!(num_bytes, 5);
	/// assert_eq!(buf, b"ipsum");
	/// buf.clear();
	///
	/// // cursor is at EOF
	/// let num_bytes = cursor.read_until(b'-', &mut buf)
	///     .expect("reading from cursor won't fail");
	/// assert_eq!(num_bytes, 0);
	/// assert_eq!(buf, b"");
	/// ```

	fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
		read_until(self, byte, buf)
	}

	/// Read all bytes until a newline (the 0xA byte) is reached, and append
	/// them to the provided buffer.
	///
	/// This function will read bytes from the underlying stream until the
	/// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
	/// up to, and including, the delimiter (if found) will be appended to
	/// `buf`.
	///
	/// If successful, this function will return the total number of bytes read.
	///
	/// If this function returns `Ok(0)`, the stream has reached EOF.
	///
	/// # Errors
	///
	/// This function has the same error semantics as [`read_until`] and will
	/// also return an error if the read bytes are not valid UTF-8. If an I/O
	/// error is encountered then `buf` may contain some bytes already read in
	/// the event that all data read so far was valid UTF-8.
	///
	/// [`read_until`]: #method.read_until
	///
	/// # Examples
	///
	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
	/// this example, we use [`Cursor`] to read all the lines in a byte slice:
	///
	/// [`Cursor`]: struct.Cursor.html
	///
	/// ```
	/// use std::io::{self, BufRead};
	///
	/// let mut cursor = io::Cursor::new(b"foo\nbar");
	/// let mut buf = String::new();
	///
	/// // cursor is at 'f'
	/// let num_bytes = cursor.read_line(&mut buf)
	///     .expect("reading from cursor won't fail");
	/// assert_eq!(num_bytes, 4);
	/// assert_eq!(buf, "foo\n");
	/// buf.clear();
	///
	/// // cursor is at 'b'
	/// let num_bytes = cursor.read_line(&mut buf)
	///     .expect("reading from cursor won't fail");
	/// assert_eq!(num_bytes, 3);
	/// assert_eq!(buf, "bar");
	/// buf.clear();
	///
	/// // cursor is at EOF
	/// let num_bytes = cursor.read_line(&mut buf)
	///     .expect("reading from cursor won't fail");
	/// assert_eq!(num_bytes, 0);
	/// assert_eq!(buf, "");
	/// ```

	fn read_line(&mut self, buf: &mut String) -> Result<usize> {
		// Note that we are not calling the `.read_until` method here, but
		// rather our hardcoded implementation. For more details as to why, see
		// the comments in `read_to_end`.
		append_to_string(buf, |b| read_until(self, b'\n', b))
	}

	/// Returns an iterator over the contents of this reader split on the byte
	/// `byte`.
	///
	/// The iterator returned from this function will return instances of
	/// [`io::Result`]`<`[`Vec<u8>`]`>`. Each vector returned will *not* have
	/// the delimiter byte at the end.
	///
	/// This function will yield errors whenever [`read_until`] would have
	/// also yielded an error.
	///
	/// [`io::Result`]: type.Result.html
	/// [`Vec<u8>`]: ../vec/struct.Vec.html
	/// [`read_until`]: #method.read_until
	///
	/// # Examples
	///
	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
	/// this example, we use [`Cursor`] to iterate over all hyphen delimited
	/// segments in a byte slice
	///
	/// [`Cursor`]: struct.Cursor.html
	///
	/// ```
	/// use std::io::{self, BufRead};
	///
	/// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
	///
	/// let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
	/// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
	/// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
	/// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
	/// assert_eq!(split_iter.next(), None);
	/// ```

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

	/// Returns an iterator over the lines of this reader.
	///
	/// The iterator returned from this function will yield instances of
	/// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
	/// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
	///
	/// [`io::Result`]: type.Result.html
	/// [`String`]: ../string/struct.String.html
	///
	/// # Examples
	///
	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
	/// this example, we use [`Cursor`] to iterate over all the lines in a byte
	/// slice.
	///
	/// [`Cursor`]: struct.Cursor.html
	///
	/// ```
	/// use std::io::{self, BufRead};
	///
	/// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
	///
	/// let mut lines_iter = cursor.lines().map(|l| l.unwrap());
	/// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
	/// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
	/// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
	/// assert_eq!(lines_iter.next(), None);
	/// ```
	///
	/// # Errors
	///
	/// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
	///
	/// [`BufRead::read_line`]: trait.BufRead.html#method.read_line

	fn lines(self) -> Lines<Self>
	where
		Self: Sized,
	{
		Lines { buf: self }
	}
}

/// Adaptor to chain together two readers.
///
/// This struct is generally created by calling [`chain`] on a reader.
/// Please see the documentation of [`chain`] for more details.
///
/// [`chain`]: trait.Read.html#method.chain

pub struct Chain<T, U> {
	first: T,
	second: U,
	done_first: bool,
}

impl<T, U> Chain<T, U> {
	/// Consumes the `Chain`, returning the wrapped readers.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut foo_file = File::open("foo.txt")?;
	///     let mut bar_file = File::open("bar.txt")?;
	///
	///     let chain = foo_file.chain(bar_file);
	///     let (foo_file, bar_file) = chain.into_inner();
	///     Ok(())
	/// }
	/// ```

	pub fn into_inner(self) -> (T, U) {
		(self.first, self.second)
	}

	/// Gets references to the underlying readers in this `Chain`.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut foo_file = File::open("foo.txt")?;
	///     let mut bar_file = File::open("bar.txt")?;
	///
	///     let chain = foo_file.chain(bar_file);
	///     let (foo_file, bar_file) = chain.get_ref();
	///     Ok(())
	/// }
	/// ```

	pub fn get_ref(&self) -> (&T, &U) {
		(&self.first, &self.second)
	}

	/// Gets mutable references to the underlying readers in this `Chain`.
	///
	/// Care should be taken to avoid modifying the internal I/O state of the
	/// underlying readers as doing so may corrupt the internal state of this
	/// `Chain`.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut foo_file = File::open("foo.txt")?;
	///     let mut bar_file = File::open("bar.txt")?;
	///
	///     let mut chain = foo_file.chain(bar_file);
	///     let (foo_file, bar_file) = chain.get_mut();
	///     Ok(())
	/// }
	/// ```

	pub fn get_mut(&mut self) -> (&mut T, &mut U) {
		(&mut self.first, &mut self.second)
	}
}

impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		f.debug_struct("Chain")
			.field("t", &self.first)
			.field("u", &self.second)
			.finish()
	}
}

impl<T: Read, U: Read> Read for Chain<T, U> {
	fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
		if !self.done_first {
			match self.first.read(buf)? {
				0 if !buf.is_empty() => self.done_first = true,
				n => return Ok(n),
			}
		}
		self.second.read(buf)
	}

	fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
		if !self.done_first {
			let read = self.first.read_vectored(bufs)?;
			if read == 0 && bufs.iter().any(|b| !b.is_empty()) {
				self.done_first = true
			} else {
				return Ok(read);
			}
		}
		self.second.read_vectored(bufs)
	}

	unsafe fn initializer(&self) -> Initializer {
		let initializer = self.first.initializer();
		if initializer.should_initialize() {
			initializer
		} else {
			self.second.initializer()
		}
	}
}

impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
	fn fill_buf(&mut self) -> Result<&[u8]> {
		if !self.done_first {
			match self.first.fill_buf()? {
				buf if buf.is_empty() => {
					self.done_first = true;
				}
				buf => return Ok(buf),
			}
		}
		self.second.fill_buf()
	}

	fn consume(&mut self, amt: usize) {
		if !self.done_first {
			self.first.consume(amt)
		} else {
			self.second.consume(amt)
		}
	}
}

/// Reader adaptor which limits the bytes read from an underlying reader.
///
/// This struct is generally created by calling [`take`] on a reader.
/// Please see the documentation of [`take`] for more details.
///
/// [`take`]: trait.Read.html#method.take
#[derive(Debug)]
pub struct Take<T> {
	inner: T,
	limit: u64,
}

impl<T> Take<T> {
	/// Returns the number of bytes that can be read before this instance will
	/// return EOF.
	///
	/// # Note
	///
	/// This instance may reach `EOF` after reading fewer bytes than indicated by
	/// this method if the underlying [`Read`] instance reaches EOF.
	///
	/// [`Read`]: ../../std/io/trait.Read.html
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let f = File::open("foo.txt")?;
	///
	///     // read at most five bytes
	///     let handle = f.take(5);
	///
	///     println!("limit: {}", handle.limit());
	///     Ok(())
	/// }
	/// ```

	pub fn limit(&self) -> u64 {
		self.limit
	}

	/// Sets the number of bytes that can be read before this instance will
	/// return EOF. This is the same as constructing a new `Take` instance, so
	/// the amount of bytes read and the previous limit value don't matter when
	/// calling this method.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let f = File::open("foo.txt")?;
	///
	///     // read at most five bytes
	///     let mut handle = f.take(5);
	///     handle.set_limit(10);
	///
	///     assert_eq!(handle.limit(), 10);
	///     Ok(())
	/// }
	/// ```

	pub fn set_limit(&mut self, limit: u64) {
		self.limit = limit;
	}

	/// Consumes the `Take`, returning the wrapped reader.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut file = File::open("foo.txt")?;
	///
	///     let mut buffer = [0; 5];
	///     let mut handle = file.take(5);
	///     handle.read(&mut buffer)?;
	///
	///     let file = handle.into_inner();
	///     Ok(())
	/// }
	/// ```

	pub fn into_inner(self) -> T {
		self.inner
	}

	/// Gets a reference to the underlying reader.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut file = File::open("foo.txt")?;
	///
	///     let mut buffer = [0; 5];
	///     let mut handle = file.take(5);
	///     handle.read(&mut buffer)?;
	///
	///     let file = handle.get_ref();
	///     Ok(())
	/// }
	/// ```

	pub fn get_ref(&self) -> &T {
		&self.inner
	}

	/// Gets a mutable reference to the underlying reader.
	///
	/// Care should be taken to avoid modifying the internal I/O state of the
	/// underlying reader as doing so may corrupt the internal limit of this
	/// `Take`.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io;
	/// use std::io::prelude::*;
	/// use std::fs::File;
	///
	/// fn main() -> io::Result<()> {
	///     let mut file = File::open("foo.txt")?;
	///
	///     let mut buffer = [0; 5];
	///     let mut handle = file.take(5);
	///     handle.read(&mut buffer)?;
	///
	///     let file = handle.get_mut();
	///     Ok(())
	/// }
	/// ```

	pub fn get_mut(&mut self) -> &mut T {
		&mut self.inner
	}
}

impl<T: Read> Read for Take<T> {
	fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
		// Don't call into inner reader at all at EOF because it may still block
		if self.limit == 0 {
			return Ok(0);
		}

		let max = cmp::min(buf.len() as u64, self.limit) as usize;
		let n = self.inner.read(&mut buf[..max])?;
		self.limit -= n as u64;
		Ok(n)
	}

	unsafe fn initializer(&self) -> Initializer {
		self.inner.initializer()
	}

	fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
		let reservation_size = cmp::min(self.limit, 32) as usize;

		read_to_end_with_reservation(self, buf, reservation_size)
	}
}

impl<T: BufRead> BufRead for Take<T> {
	fn fill_buf(&mut self) -> Result<&[u8]> {
		// Don't call into inner reader at all at EOF because it may still block
		if self.limit == 0 {
			return Ok(&[]);
		}

		let buf = self.inner.fill_buf()?;
		let cap = cmp::min(buf.len() as u64, self.limit) as usize;
		Ok(&buf[..cap])
	}

	fn consume(&mut self, amt: usize) {
		// Don't let callers reset the limit by passing an overlarge value
		let amt = cmp::min(amt as u64, self.limit) as usize;
		self.limit -= amt as u64;
		self.inner.consume(amt);
	}
}

/// An iterator over `u8` values of a reader.
///
/// This struct is generally created by calling [`bytes`] on a reader.
/// Please see the documentation of [`bytes`] for more details.
///
/// [`bytes`]: trait.Read.html#method.bytes
#[derive(Debug)]
pub struct Bytes<R> {
	inner: R,
}

impl<R: Read> Iterator for Bytes<R> {
	type Item = Result<u8>;

	fn next(&mut self) -> Option<Result<u8>> {
		let mut byte = 0;
		loop {
			return match self.inner.read(slice::from_mut(&mut byte)) {
				Ok(0) => None,
				Ok(..) => Some(Ok(byte)),
				Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
				Err(e) => Some(Err(e)),
			};
		}
	}
}

/// An iterator over the contents of an instance of `BufRead` split on a
/// particular byte.
///
/// This struct is generally created by calling [`split`][split] on a
/// `BufRead`. Please see the documentation of `split()` for more details.
///
/// [split]: trait.BufRead.html#method.split
#[derive(Debug)]
pub struct Split<B> {
	buf: B,
	delim: u8,
}

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

	fn next(&mut self) -> Option<Result<Vec<u8>>> {
		let mut buf = Vec::new();
		match self.buf.read_until(self.delim, &mut buf) {
			Ok(0) => None,
			Ok(_n) => {
				if buf[buf.len() - 1] == self.delim {
					buf.pop();
				}
				Some(Ok(buf))
			}
			Err(e) => Some(Err(e)),
		}
	}
}

/// An iterator over the lines of an instance of `BufRead`.
///
/// This struct is generally created by calling [`lines`][lines] on a
/// `BufRead`. Please see the documentation of `lines()` for more details.
///
/// [lines]: trait.BufRead.html#method.lines
#[derive(Debug)]
pub struct Lines<B> {
	buf: B,
}

impl<B: BufRead> Iterator for Lines<B> {
	type Item = Result<String>;

	fn next(&mut self) -> Option<Result<String>> {
		let mut buf = String::new();
		match self.buf.read_line(&mut buf) {
			Ok(0) => None,
			Ok(_n) => {
				if buf.ends_with('\n') {
					buf.pop();
					if buf.ends_with('\r') {
						buf.pop();
					}
				}
				Some(Ok(buf))
			}
			Err(e) => Some(Err(e)),
		}
	}
}

#[cfg(test)]
mod tests {
	use alloc::string::{String, ToString};
	use alloc::vec;
	use alloc::vec::Vec;

	use crate::io;
	use crate::io::prelude::*;

	use super::{Cursor, SeekFrom};

	#[test]
	#[cfg_attr(target_os = "emscripten", ignore)]
	fn read_until() {
		let mut buf = Cursor::new(&b"12"[..]);
		let mut v = Vec::new();
		assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
		assert_eq!(v, b"12");

		let mut buf = Cursor::new(&b"1233"[..]);
		let mut v = Vec::new();
		assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
		assert_eq!(v, b"123");
		v.truncate(0);
		assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
		assert_eq!(v, b"3");
		v.truncate(0);
		assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
		assert_eq!(v, []);
	}

	#[test]
	fn split() {
		let buf = Cursor::new(&b"12"[..]);
		let mut s = buf.split(b'3');
		assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
		assert!(s.next().is_none());

		let buf = Cursor::new(&b"1233"[..]);
		let mut s = buf.split(b'3');
		assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
		assert_eq!(s.next().unwrap().unwrap(), vec![]);
		assert!(s.next().is_none());
	}

	#[test]
	fn read_line() {
		let mut buf = Cursor::new(&b"12"[..]);
		let mut v = String::new();
		assert_eq!(buf.read_line(&mut v).unwrap(), 2);
		assert_eq!(v, "12");

		let mut buf = Cursor::new(&b"12\n\n"[..]);
		let mut v = String::new();
		assert_eq!(buf.read_line(&mut v).unwrap(), 3);
		assert_eq!(v, "12\n");
		v.truncate(0);
		assert_eq!(buf.read_line(&mut v).unwrap(), 1);
		assert_eq!(v, "\n");
		v.truncate(0);
		assert_eq!(buf.read_line(&mut v).unwrap(), 0);
		assert_eq!(v, "");
	}

	#[test]
	fn lines() {
		let buf = Cursor::new(&b"12\r"[..]);
		let mut s = buf.lines();
		assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
		assert!(s.next().is_none());

		let buf = Cursor::new(&b"12\r\n\n"[..]);
		let mut s = buf.lines();
		assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
		assert_eq!(s.next().unwrap().unwrap(), "".to_string());
		assert!(s.next().is_none());
	}

	#[test]
	fn read_to_end() {
		let mut c = Cursor::new(&b""[..]);
		let mut v = Vec::new();
		assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
		assert_eq!(v, []);

		let mut c = Cursor::new(&b"1"[..]);
		let mut v = Vec::new();
		assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
		assert_eq!(v, b"1");

		let cap = 1024 * 1024;
		let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
		let mut v = Vec::new();
		let (a, b) = data.split_at(data.len() / 2);
		assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
		assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
		assert_eq!(v, data);
	}

	#[test]
	fn read_to_string() {
		let mut c = Cursor::new(&b""[..]);
		let mut v = String::new();
		assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
		assert_eq!(v, "");

		let mut c = Cursor::new(&b"1"[..]);
		let mut v = String::new();
		assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
		assert_eq!(v, "1");

		let mut c = Cursor::new(&b"\xff"[..]);
		let mut v = String::new();
		assert!(c.read_to_string(&mut v).is_err());
	}

	#[test]
	fn read_exact() {
		let mut buf = [0; 4];

		let mut c = Cursor::new(&b""[..]);
		assert_eq!(
			c.read_exact(&mut buf).unwrap_err().kind(),
			io::ErrorKind::UnexpectedEof
		);

		let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
		c.read_exact(&mut buf).unwrap();
		assert_eq!(&buf, b"1234");
		c.read_exact(&mut buf).unwrap();
		assert_eq!(&buf, b"5678");
		assert_eq!(
			c.read_exact(&mut buf).unwrap_err().kind(),
			io::ErrorKind::UnexpectedEof
		);
	}

	#[test]
	fn read_exact_slice() {
		let mut buf = [0; 4];

		let mut c = &b""[..];
		assert_eq!(
			c.read_exact(&mut buf).unwrap_err().kind(),
			io::ErrorKind::UnexpectedEof
		);

		let mut c = &b"123"[..];
		assert_eq!(
			c.read_exact(&mut buf).unwrap_err().kind(),
			io::ErrorKind::UnexpectedEof
		);
		// make sure the optimized (early returning) method is being used
		assert_eq!(&buf, &[0; 4]);

		let mut c = &b"1234"[..];
		c.read_exact(&mut buf).unwrap();
		assert_eq!(&buf, b"1234");

		let mut c = &b"56789"[..];
		c.read_exact(&mut buf).unwrap();
		assert_eq!(&buf, b"5678");
		assert_eq!(c, b"9");
	}

	#[test]
	fn take_eof() {
		struct R;

		impl Read for R {
			fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
				Err(io::Error::new(io::ErrorKind::Other, ""))
			}
		}
		impl BufRead for R {
			fn fill_buf(&mut self) -> io::Result<&[u8]> {
				Err(io::Error::new(io::ErrorKind::Other, ""))
			}
			fn consume(&mut self, _amt: usize) {}
		}

		let mut buf = [0; 1];
		assert_eq!(0, R.take(0).read(&mut buf).unwrap());
		assert_eq!(b"", R.take(0).fill_buf().unwrap());
	}

	fn cmp_bufread<Br1: BufRead, Br2: BufRead>(mut br1: Br1, mut br2: Br2, exp: &[u8]) {
		let mut cat = Vec::new();
		loop {
			let consume = {
				let buf1 = br1.fill_buf().unwrap();
				let buf2 = br2.fill_buf().unwrap();
				let minlen = if buf1.len() < buf2.len() {
					buf1.len()
				} else {
					buf2.len()
				};
				assert_eq!(buf1[..minlen], buf2[..minlen]);
				cat.extend_from_slice(&buf1[..minlen]);
				minlen
			};
			if consume == 0 {
				break;
			}
			br1.consume(consume);
			br2.consume(consume);
		}
		assert_eq!(br1.fill_buf().unwrap().len(), 0);
		assert_eq!(br2.fill_buf().unwrap().len(), 0);
		assert_eq!(&cat[..], &exp[..])
	}

	#[test]
	fn chain_bufread() {
		let testdata = b"ABCDEFGHIJKL";
		let chain1 = (&testdata[..3])
			.chain(&testdata[3..6])
			.chain(&testdata[6..9])
			.chain(&testdata[9..]);
		let chain2 = (&testdata[..4])
			.chain(&testdata[4..8])
			.chain(&testdata[8..]);
		cmp_bufread(chain1, chain2, &testdata[..]);
	}

	#[test]
	fn chain_zero_length_read_is_not_eof() {
		let a = b"A";
		let b = b"B";
		let mut s = String::new();
		let mut chain = (&a[..]).chain(&b[..]);
		chain.read(&mut []).unwrap();
		chain.read_to_string(&mut s).unwrap();
		assert_eq!("AB", s);
	}

	#[test]
	fn seek_len() -> io::Result<()> {
		let mut c = Cursor::new(vec![0; 15]);
		assert_eq!(c.stream_len()?, 15);

		c.seek(SeekFrom::End(0))?;
		let old_pos = c.stream_position()?;
		assert_eq!(c.stream_len()?, 15);
		assert_eq!(c.stream_position()?, old_pos);

		c.seek(SeekFrom::Start(7))?;
		c.seek(SeekFrom::Current(2))?;
		let old_pos = c.stream_position()?;
		assert_eq!(c.stream_len()?, 15);
		assert_eq!(c.stream_position()?, old_pos);

		Ok(())
	}

	#[test]
	fn seek_position() -> io::Result<()> {
		// All `asserts` are duplicated here to make sure the method does not
		// change anything about the seek state.
		let mut c = Cursor::new(vec![0; 15]);
		assert_eq!(c.stream_position()?, 0);
		assert_eq!(c.stream_position()?, 0);

		c.seek(SeekFrom::End(0))?;
		assert_eq!(c.stream_position()?, 15);
		assert_eq!(c.stream_position()?, 15);

		c.seek(SeekFrom::Start(7))?;
		c.seek(SeekFrom::Current(2))?;
		assert_eq!(c.stream_position()?, 9);
		assert_eq!(c.stream_position()?, 9);

		c.seek(SeekFrom::End(-3))?;
		c.seek(SeekFrom::Current(1))?;
		c.seek(SeekFrom::Current(-5))?;
		assert_eq!(c.stream_position()?, 8);
		assert_eq!(c.stream_position()?, 8);

		Ok(())
	}
}