Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2827 insertions, 0 deletions

diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
new file mode 100644
index 000000000..96addbd1a
--- /dev/null
+++ b/library/std/src/io/mod.rs
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+//! 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.
+//!
+//! [`File`]: crate::fs::File
+//! [`TcpStream`]: crate::net::TcpStream
+//! [`io::stdout`]: stdout
+//! [`io::Result`]: self::Result
+//! [`?` operator]: ../../book/appendix-02-operators.html
+//! [`Result`]: crate::result::Result
+//! [`.unwrap()`]: crate::result::Result::unwrap
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+#[cfg(test)]
+mod tests;
+
+use crate::cmp;
+use crate::fmt;
+use crate::mem::replace;
+use crate::ops::{Deref, DerefMut};
+use crate::slice;
+use crate::str;
+use crate::sys;
+use crate::sys_common::memchr;
+
+#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
+pub use self::buffered::WriterPanicked;
+#[unstable(feature = "internal_output_capture", issue = "none")]
+#[doc(no_inline, hidden)]
+pub use self::stdio::set_output_capture;
+#[unstable(feature = "print_internals", issue = "none")]
+pub use self::stdio::{_eprint, _print};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use self::{
+    buffered::{BufReader, BufWriter, IntoInnerError, LineWriter},
+    copy::copy,
+    cursor::Cursor,
+    error::{Error, ErrorKind, Result},
+    stdio::{stderr, stdin, stdout, Stderr, StderrLock, Stdin, StdinLock, Stdout, StdoutLock},
+    util::{empty, repeat, sink, Empty, Repeat, Sink},
+};
+
+#[unstable(feature = "read_buf", issue = "78485")]
+pub use self::readbuf::ReadBuf;
+pub(crate) use error::const_io_error;
+
+mod buffered;
+pub(crate) mod copy;
+mod cursor;
+mod error;
+mod impls;
+pub mod prelude;
+mod readbuf;
+mod stdio;
+mod util;
+
+const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
+
+pub(crate) use stdio::cleanup;
+
+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);
+        }
+    }
+}
+
+// Several `read_to_string` and `read_line` methods in the standard library 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.
+pub(crate) unsafe fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
+where
+    F: FnOnce(&mut Vec<u8>) -> Result<usize>,
+{
+    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::const_io_error!(
+                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.
+pub(crate) fn default_read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
+    let start_len = buf.len();
+    let start_cap = buf.capacity();
+
+    let mut initialized = 0; // Extra initialized bytes from previous loop iteration
+    loop {
+        if buf.len() == buf.capacity() {
+            buf.reserve(32); // buf is full, need more space
+        }
+
+        let mut read_buf = ReadBuf::uninit(buf.spare_capacity_mut());
+
+        // SAFETY: These bytes were initialized but not filled in the previous loop
+        unsafe {
+            read_buf.assume_init(initialized);
+        }
+
+        match r.read_buf(&mut read_buf) {
+            Ok(()) => {}
+            Err(e) if e.kind() == ErrorKind::Interrupted => continue,
+            Err(e) => return Err(e),
+        }
+
+        if read_buf.filled_len() == 0 {
+            return Ok(buf.len() - start_len);
+        }
+
+        // store how much was initialized but not filled
+        initialized = read_buf.initialized_len() - read_buf.filled_len();
+        let new_len = read_buf.filled_len() + buf.len();
+
+        // SAFETY: ReadBuf's invariants mean this much memory is init
+        unsafe {
+            buf.set_len(new_len);
+        }
+
+        if buf.len() == buf.capacity() && buf.capacity() == start_cap {
+            // The buffer might be an exact fit. Let's read into a probe buffer
+            // and see if it returns `Ok(0)`. If so, we've avoided an
+            // unnecessary doubling of the capacity. But if not, append the
+            // probe buffer to the primary buffer and let its capacity grow.
+            let mut probe = [0u8; 32];
+
+            loop {
+                match r.read(&mut probe) {
+                    Ok(0) => return Ok(buf.len() - start_len),
+                    Ok(n) => {
+                        buf.extend_from_slice(&probe[..n]);
+                        break;
+                    }
+                    Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
+                    Err(e) => return Err(e),
+                }
+            }
+        }
+    }
+}
+
+pub(crate) fn default_read_to_string<R: Read + ?Sized>(
+    r: &mut R,
+    buf: &mut String,
+) -> Result<usize> {
+    // Note that we do *not* call `r.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 `default_read_to_end` implementation which
+    // we know is guaranteed to only read data into the end of the buffer.
+    unsafe { append_to_string(buf, |b| default_read_to_end(r, b)) }
+}
+
+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(crate) fn default_read_exact<R: Read + ?Sized>(this: &mut R, mut buf: &mut [u8]) -> Result<()> {
+    while !buf.is_empty() {
+        match this.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::const_io_error!(ErrorKind::UnexpectedEof, "failed to fill whole buffer"))
+    } else {
+        Ok(())
+    }
+}
+
+pub(crate) fn default_read_buf<F>(read: F, buf: &mut ReadBuf<'_>) -> Result<()>
+where
+    F: FnOnce(&mut [u8]) -> Result<usize>,
+{
+    let n = read(buf.initialize_unfilled())?;
+    buf.add_filled(n);
+    Ok(())
+}
+
+/// 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]`][prim@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
+/// [`&str`]: prim@str
+/// [`std::io`]: self
+/// [`File`]: crate::fs::File
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(notable_trait)]
+#[cfg_attr(not(test), rustc_diagnostic_item = "IoRead")]
+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 and cannot,
+    /// it will typically signal this via an [`Err`] return value.
+    ///
+    /// If the return value of this method is [`Ok(n)`], then implementations must
+    /// guarantee 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. As an example,
+    ///    on Linux, this method will call the `recv` syscall for a [`TcpStream`],
+    ///    where returning zero indicates the connection was shut down correctly. While
+    ///    for [`File`], it is possible to reach the end of file and get zero as result,
+    ///    but if more data is appended to the file, future calls to `read` will return
+    ///    more data.
+    /// 2. The buffer specified was 0 bytes in length.
+    ///
+    /// It is not an error if the returned value `n` is smaller than the buffer size,
+    /// even when the reader is not at the end of the stream yet.
+    /// This may happen for example because fewer bytes are actually available right now
+    /// (e. g. being close to end-of-file) or because read() was interrupted by a signal.
+    ///
+    /// As this trait is safe to implement, callers cannot rely on `n <= buf.len()` for safety.
+    /// Extra care needs to be taken when `unsafe` functions are used to access the read bytes.
+    /// Callers have to ensure that no unchecked out-of-bounds accesses are possible even if
+    /// `n > buf.len()`.
+    ///
+    /// 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.
+    ///
+    /// Correspondingly, however, *callers* of this method must not assume any guarantees
+    /// about how the implementation uses `buf`. The trait is safe to implement,
+    /// so it is possible that the code that's supposed to write to the buffer might also read
+    /// from it. It is your responsibility to make sure that `buf` is initialized
+    /// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
+    /// obtains via [`MaybeUninit<T>`]) is not safe, and can lead to undefined behavior.
+    ///
+    /// [`MaybeUninit<T>`]: crate::mem::MaybeUninit
+    ///
+    /// # 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`:
+    ///
+    /// [`Ok(n)`]: Ok
+    /// [`File`]: crate::fs::File
+    /// [`TcpStream`]: crate::net::TcpStream
+    ///
+    /// ```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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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 equivalently to a single call to `read` with concatenated
+    /// buffers.
+    ///
+    /// The default implementation calls `read` with either the first nonempty
+    /// buffer provided, or an empty one if none exists.
+    #[stable(feature = "iovec", since = "1.36.0")]
+    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
+        default_read_vectored(|b| self.read(b), bufs)
+    }
+
+    /// Determines if this `Read`er has an efficient `read_vectored`
+    /// implementation.
+    ///
+    /// If a `Read`er does not override the default `read_vectored`
+    /// implementation, code using it may want to avoid the method all together
+    /// and coalesce writes into a single buffer for higher performance.
+    ///
+    /// The default implementation returns `false`.
+    #[unstable(feature = "can_vector", issue = "69941")]
+    fn is_read_vectored(&self) -> bool {
+        false
+    }
+
+    /// 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()`]: Read::read
+    /// [`Ok(0)`]: Ok
+    /// [`File`]: crate::fs::File
+    ///
+    /// ```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`]: crate::fs::read
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
+        default_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`] for other error semantics.
+    ///
+    /// [`read_to_end`]: Read::read_to_end
+    ///
+    /// # Examples
+    ///
+    /// [`File`]s implement `Read`:
+    ///
+    /// [`File`]: crate::fs::File
+    ///
+    /// ```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`]: crate::fs::read_to_string
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
+        default_read_to_string(self, buf)
+    }
+
+    /// 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. The
+    /// documentation on [`read`] has a more detailed explanation on this
+    /// subject.
+    ///
+    /// # 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`:
+    ///
+    /// [`read`]: Read::read
+    /// [`File`]: crate::fs::File
+    ///
+    /// ```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(())
+    /// }
+    /// ```
+    #[stable(feature = "read_exact", since = "1.6.0")]
+    fn read_exact(&mut self, buf: &mut [u8]) -> Result<()> {
+        default_read_exact(self, buf)
+    }
+
+    /// Pull some bytes from this source into the specified buffer.
+    ///
+    /// This is equivalent to the [`read`](Read::read) method, except that it is passed a [`ReadBuf`] rather than `[u8]` to allow use
+    /// with uninitialized buffers. The new data will be appended to any existing contents of `buf`.
+    ///
+    /// The default implementation delegates to `read`.
+    #[unstable(feature = "read_buf", issue = "78485")]
+    fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> {
+        default_read_buf(|b| self.read(b), buf)
+    }
+
+    /// Read the exact number of bytes required to fill `buf`.
+    ///
+    /// This is equivalent to the [`read_exact`](Read::read_exact) method, except that it is passed a [`ReadBuf`] rather than `[u8]` to
+    /// allow use with uninitialized buffers.
+    #[unstable(feature = "read_buf", issue = "78485")]
+    fn read_buf_exact(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> {
+        while buf.remaining() > 0 {
+            let prev_filled = buf.filled().len();
+            match self.read_buf(buf) {
+                Ok(()) => {}
+                Err(e) if e.kind() == ErrorKind::Interrupted => continue,
+                Err(e) => return Err(e),
+            }
+
+            if buf.filled().len() == prev_filled {
+                return Err(Error::new(ErrorKind::UnexpectedEof, "failed to fill buffer"));
+            }
+        }
+
+        Ok(())
+    }
+
+    /// Creates a "by reference" adaptor for this instance of `Read`.
+    ///
+    /// The returned adapter also implements `Read` and will simply borrow this
+    /// current reader.
+    ///
+    /// # Examples
+    ///
+    /// [`File`]s implement `Read`:
+    ///
+    /// [`File`]: crate::fs::File
+    ///
+    /// ```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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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
+    /// <code>[Result]<[u8], [io::Error]></code>.
+    /// 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`]s implement `Read`:
+    ///
+    /// [`Item`]: Iterator::Item
+    /// [`File`]: crate::fs::File "fs::File"
+    /// [Result]: crate::result::Result "Result"
+    /// [io::Error]: self::Error "io::Error"
+    ///
+    /// ```no_run
+    /// use std::io;
+    /// use std::io::prelude::*;
+    /// use std::fs::File;
+    ///
+    /// fn main() -> io::Result<()> {
+    ///     let f = File::open("foo.txt")?;
+    ///
+    ///     for byte in f.bytes() {
+    ///         println!("{}", byte.unwrap());
+    ///     }
+    ///     Ok(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn bytes(self) -> Bytes<Self>
+    where
+        Self: Sized,
+    {
+        Bytes { inner: self }
+    }
+
+    /// Creates an adapter 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`]s implement `Read`:
+    ///
+    /// [`File`]: crate::fs::File
+    ///
+    /// ```no_run
+    /// use std::io;
+    /// use std::io::prelude::*;
+    /// use std::fs::File;
+    ///
+    /// fn main() -> io::Result<()> {
+    ///     let f1 = File::open("foo.txt")?;
+    ///     let 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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn chain<R: Read>(self, next: R) -> Chain<Self, R>
+    where
+        Self: Sized,
+    {
+        Chain { first: self, second: next, done_first: false }
+    }
+
+    /// Creates an adapter 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`]: crate::fs::File
+    /// [`Ok(0)`]: Ok
+    /// [`read()`]: Read::read
+    ///
+    /// ```no_run
+    /// use std::io;
+    /// use std::io::prelude::*;
+    /// use std::fs::File;
+    ///
+    /// fn main() -> io::Result<()> {
+    ///     let 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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn take(self, limit: u64) -> Take<Self>
+    where
+        Self: Sized,
+    {
+        Take { inner: self, limit }
+    }
+}
+
+/// Read all bytes from a [reader][Read] into a new [`String`].
+///
+/// This is a convenience function for [`Read::read_to_string`]. Using this
+/// function avoids having to create a variable first and provides more type
+/// safety since you can only get the buffer out if there were no errors. (If you
+/// use [`Read::read_to_string`] you have to remember to check whether the read
+/// succeeded because otherwise your buffer will be empty or only partially full.)
+///
+/// # Performance
+///
+/// The downside of this function's increased ease of use and type safety is
+/// that it gives you less control over performance. For example, you can't
+/// pre-allocate memory like you can using [`String::with_capacity`] and
+/// [`Read::read_to_string`]. Also, you can't re-use the buffer if an error
+/// occurs while reading.
+///
+/// In many cases, this function's performance will be adequate and the ease of use
+/// and type safety tradeoffs will be worth it. However, there are cases where you
+/// need more control over performance, and in those cases you should definitely use
+/// [`Read::read_to_string`] directly.
+///
+/// Note that in some special cases, such as when reading files, this function will
+/// pre-allocate memory based on the size of the input it is reading. In those
+/// cases, the performance should be as good as if you had used
+/// [`Read::read_to_string`] with a manually pre-allocated buffer.
+///
+/// # Errors
+///
+/// This function forces you to handle errors because the output (the `String`)
+/// is wrapped in a [`Result`]. See [`Read::read_to_string`] for the errors
+/// that can occur. If any error occurs, you will get an [`Err`], so you
+/// don't have to worry about your buffer being empty or partially full.
+///
+/// # Examples
+///
+/// ```no_run
+/// #![feature(io_read_to_string)]
+///
+/// # use std::io;
+/// fn main() -> io::Result<()> {
+///     let stdin = io::read_to_string(io::stdin())?;
+///     println!("Stdin was:");
+///     println!("{stdin}");
+///     Ok(())
+/// }
+/// ```
+#[unstable(feature = "io_read_to_string", issue = "80218")]
+pub fn read_to_string<R: Read>(mut reader: R) -> Result<String> {
+    let mut buf = String::new();
+    reader.read_to_string(&mut buf)?;
+    Ok(buf)
+}
+
+/// 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.
+#[stable(feature = "iovec", since = "1.36.0")]
+#[repr(transparent)]
+pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
+
+#[stable(feature = "iovec-send-sync", since = "1.44.0")]
+unsafe impl<'a> Send for IoSliceMut<'a> {}
+
+#[stable(feature = "iovec-send-sync", since = "1.44.0")]
+unsafe impl<'a> Sync for IoSliceMut<'a> {}
+
+#[stable(feature = "iovec", since = "1.36.0")]
+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.
+    #[stable(feature = "iovec", since = "1.36.0")]
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
+        IoSliceMut(sys::io::IoSliceMut::new(buf))
+    }
+
+    /// Advance the internal cursor of the slice.
+    ///
+    /// Also see [`IoSliceMut::advance_slices`] to advance the cursors of
+    /// multiple buffers.
+    ///
+    /// # Panics
+    ///
+    /// Panics when trying to advance beyond the end of the slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(io_slice_advance)]
+    ///
+    /// use std::io::IoSliceMut;
+    /// use std::ops::Deref;
+    ///
+    /// let mut data = [1; 8];
+    /// let mut buf = IoSliceMut::new(&mut data);
+    ///
+    /// // Mark 3 bytes as read.
+    /// buf.advance(3);
+    /// assert_eq!(buf.deref(), [1; 5].as_ref());
+    /// ```
+    #[unstable(feature = "io_slice_advance", issue = "62726")]
+    #[inline]
+    pub fn advance(&mut self, n: usize) {
+        self.0.advance(n)
+    }
+
+    /// Advance a slice of slices.
+    ///
+    /// Shrinks the slice to remove any `IoSliceMut`s that are fully advanced over.
+    /// If the cursor ends up in the middle of an `IoSliceMut`, it is modified
+    /// to start at that cursor.
+    ///
+    /// For example, if we have a slice of two 8-byte `IoSliceMut`s, and we advance by 10 bytes,
+    /// the result will only include the second `IoSliceMut`, advanced by 2 bytes.
+    ///
+    /// # Panics
+    ///
+    /// Panics when trying to advance beyond the end of the slices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(io_slice_advance)]
+    ///
+    /// use std::io::IoSliceMut;
+    /// use std::ops::Deref;
+    ///
+    /// let mut buf1 = [1; 8];
+    /// let mut buf2 = [2; 16];
+    /// let mut buf3 = [3; 8];
+    /// let mut bufs = &mut [
+    ///     IoSliceMut::new(&mut buf1),
+    ///     IoSliceMut::new(&mut buf2),
+    ///     IoSliceMut::new(&mut buf3),
+    /// ][..];
+    ///
+    /// // Mark 10 bytes as read.
+    /// IoSliceMut::advance_slices(&mut bufs, 10);
+    /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
+    /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
+    /// ```
+    #[unstable(feature = "io_slice_advance", issue = "62726")]
+    #[inline]
+    pub fn advance_slices(bufs: &mut &mut [IoSliceMut<'a>], n: usize) {
+        // Number of buffers to remove.
+        let mut remove = 0;
+        // Total length of all the to be removed buffers.
+        let mut accumulated_len = 0;
+        for buf in bufs.iter() {
+            if accumulated_len + buf.len() > n {
+                break;
+            } else {
+                accumulated_len += buf.len();
+                remove += 1;
+            }
+        }
+
+        *bufs = &mut replace(bufs, &mut [])[remove..];
+        if bufs.is_empty() {
+            assert!(n == accumulated_len, "advancing io slices beyond their length");
+        } else {
+            bufs[0].advance(n - accumulated_len)
+        }
+    }
+}
+
+#[stable(feature = "iovec", since = "1.36.0")]
+impl<'a> Deref for IoSliceMut<'a> {
+    type Target = [u8];
+
+    #[inline]
+    fn deref(&self) -> &[u8] {
+        self.0.as_slice()
+    }
+}
+
+#[stable(feature = "iovec", since = "1.36.0")]
+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 a `&[u8]`, but is guaranteed to be
+/// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
+/// Windows.
+#[stable(feature = "iovec", since = "1.36.0")]
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
+
+#[stable(feature = "iovec-send-sync", since = "1.44.0")]
+unsafe impl<'a> Send for IoSlice<'a> {}
+
+#[stable(feature = "iovec-send-sync", since = "1.44.0")]
+unsafe impl<'a> Sync for IoSlice<'a> {}
+
+#[stable(feature = "iovec", since = "1.36.0")]
+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.
+    #[stable(feature = "iovec", since = "1.36.0")]
+    #[must_use]
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
+        IoSlice(sys::io::IoSlice::new(buf))
+    }
+
+    /// Advance the internal cursor of the slice.
+    ///
+    /// Also see [`IoSlice::advance_slices`] to advance the cursors of multiple
+    /// buffers.
+    ///
+    /// # Panics
+    ///
+    /// Panics when trying to advance beyond the end of the slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(io_slice_advance)]
+    ///
+    /// use std::io::IoSlice;
+    /// use std::ops::Deref;
+    ///
+    /// let data = [1; 8];
+    /// let mut buf = IoSlice::new(&data);
+    ///
+    /// // Mark 3 bytes as read.
+    /// buf.advance(3);
+    /// assert_eq!(buf.deref(), [1; 5].as_ref());
+    /// ```
+    #[unstable(feature = "io_slice_advance", issue = "62726")]
+    #[inline]
+    pub fn advance(&mut self, n: usize) {
+        self.0.advance(n)
+    }
+
+    /// Advance a slice of slices.
+    ///
+    /// Shrinks the slice to remove any `IoSlice`s that are fully advanced over.
+    /// If the cursor ends up in the middle of an `IoSlice`, it is modified
+    /// to start at that cursor.
+    ///
+    /// For example, if we have a slice of two 8-byte `IoSlice`s, and we advance by 10 bytes,
+    /// the result will only include the second `IoSlice`, advanced by 2 bytes.
+    ///
+    /// # Panics
+    ///
+    /// Panics when trying to advance beyond the end of the slices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(io_slice_advance)]
+    ///
+    /// use std::io::IoSlice;
+    /// use std::ops::Deref;
+    ///
+    /// let buf1 = [1; 8];
+    /// let buf2 = [2; 16];
+    /// let buf3 = [3; 8];
+    /// let mut bufs = &mut [
+    ///     IoSlice::new(&buf1),
+    ///     IoSlice::new(&buf2),
+    ///     IoSlice::new(&buf3),
+    /// ][..];
+    ///
+    /// // Mark 10 bytes as written.
+    /// IoSlice::advance_slices(&mut bufs, 10);
+    /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
+    /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
+    #[unstable(feature = "io_slice_advance", issue = "62726")]
+    #[inline]
+    pub fn advance_slices(bufs: &mut &mut [IoSlice<'a>], n: usize) {
+        // Number of buffers to remove.
+        let mut remove = 0;
+        // Total length of all the to be removed buffers.
+        let mut accumulated_len = 0;
+        for buf in bufs.iter() {
+            if accumulated_len + buf.len() > n {
+                break;
+            } else {
+                accumulated_len += buf.len();
+                remove += 1;
+            }
+        }
+
+        *bufs = &mut replace(bufs, &mut [])[remove..];
+        if bufs.is_empty() {
+            assert!(n == accumulated_len, "advancing io slices beyond their length");
+        } else {
+            bufs[0].advance(n - accumulated_len)
+        }
+    }
+}
+
+#[stable(feature = "iovec", since = "1.36.0")]
+impl<'a> Deref for IoSlice<'a> {
+    type Target = [u8];
+
+    #[inline]
+    fn deref(&self) -> &[u8] {
+        self.0.as_slice()
+    }
+}
+
+/// 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 adapters 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`]: Write::write
+/// [`flush`]: Write::flush
+/// [`std::io`]: self
+///
+/// # 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`]: Write::write_all
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(notable_trait)]
+#[cfg_attr(not(test), rustc_diagnostic_item = "IoWrite")]
+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 might 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
+    /// `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.
+    ///
+    /// # 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(())
+    /// }
+    /// ```
+    ///
+    /// [`Ok(n)`]: Ok
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn write(&mut self, buf: &[u8]) -> Result<usize>;
+
+    /// Like [`write`], except that it writes from a slice of buffers.
+    ///
+    /// Data is copied 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.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use std::io::IoSlice;
+    /// use std::io::prelude::*;
+    /// use std::fs::File;
+    ///
+    /// fn main() -> std::io::Result<()> {
+    ///     let data1 = [1; 8];
+    ///     let data2 = [15; 8];
+    ///     let io_slice1 = IoSlice::new(&data1);
+    ///     let io_slice2 = IoSlice::new(&data2);
+    ///
+    ///     let mut buffer = File::create("foo.txt")?;
+    ///
+    ///     // Writes some prefix of the byte string, not necessarily all of it.
+    ///     buffer.write_vectored(&[io_slice1, io_slice2])?;
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// [`write`]: Write::write
+    #[stable(feature = "iovec", since = "1.36.0")]
+    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
+        default_write_vectored(|b| self.write(b), bufs)
+    }
+
+    /// Determines if this `Write`r has an efficient [`write_vectored`]
+    /// implementation.
+    ///
+    /// If a `Write`r does not override the default [`write_vectored`]
+    /// implementation, code using it may want to avoid the method all together
+    /// and coalesce writes into a single buffer for higher performance.
+    ///
+    /// The default implementation returns `false`.
+    ///
+    /// [`write_vectored`]: Write::write_vectored
+    #[unstable(feature = "can_vector", issue = "69941")]
+    fn is_write_vectored(&self) -> bool {
+        false
+    }
+
+    /// 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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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.
+    ///
+    /// If the buffer contains no data, this will never call [`write`].
+    ///
+    /// # Errors
+    ///
+    /// This function will return the first error of
+    /// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
+    ///
+    /// [`write`]: Write::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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
+        while !buf.is_empty() {
+            match self.write(buf) {
+                Ok(0) => {
+                    return Err(error::const_io_error!(
+                        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(())
+    }
+
+    /// Attempts to write multiple buffers into this writer.
+    ///
+    /// This method will continuously call [`write_vectored`] 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 all buffers have
+    /// 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.
+    ///
+    /// If the buffer contains no data, this will never call [`write_vectored`].
+    ///
+    /// # Notes
+    ///
+    /// Unlike [`write_vectored`], this takes a *mutable* reference to
+    /// a slice of [`IoSlice`]s, not an immutable one. That's because we need to
+    /// modify the slice to keep track of the bytes already written.
+    ///
+    /// Once this function returns, the contents of `bufs` are unspecified, as
+    /// this depends on how many calls to [`write_vectored`] were necessary. It is
+    /// best to understand this function as taking ownership of `bufs` and to
+    /// not use `bufs` afterwards. The underlying buffers, to which the
+    /// [`IoSlice`]s point (but not the [`IoSlice`]s themselves), are unchanged and
+    /// can be reused.
+    ///
+    /// [`write_vectored`]: Write::write_vectored
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(write_all_vectored)]
+    /// # fn main() -> std::io::Result<()> {
+    ///
+    /// use std::io::{Write, IoSlice};
+    ///
+    /// let mut writer = Vec::new();
+    /// let bufs = &mut [
+    ///     IoSlice::new(&[1]),
+    ///     IoSlice::new(&[2, 3]),
+    ///     IoSlice::new(&[4, 5, 6]),
+    /// ];
+    ///
+    /// writer.write_all_vectored(bufs)?;
+    /// // Note: the contents of `bufs` is now undefined, see the Notes section.
+    ///
+    /// assert_eq!(writer, &[1, 2, 3, 4, 5, 6]);
+    /// # Ok(()) }
+    /// ```
+    #[unstable(feature = "write_all_vectored", issue = "70436")]
+    fn write_all_vectored(&mut self, mut bufs: &mut [IoSlice<'_>]) -> Result<()> {
+        // Guarantee that bufs is empty if it contains no data,
+        // to avoid calling write_vectored if there is no data to be written.
+        IoSlice::advance_slices(&mut bufs, 0);
+        while !bufs.is_empty() {
+            match self.write_vectored(bufs) {
+                Ok(0) => {
+                    return Err(error::const_io_error!(
+                        ErrorKind::WriteZero,
+                        "failed to write whole buffer",
+                    ));
+                }
+                Ok(n) => IoSlice::advance_slices(&mut bufs, 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!()`] macro, and it is rare that this should
+    /// explicitly be called. The [`write!()`] macro should be favored to
+    /// invoke this method instead.
+    ///
+    /// This function internally uses the [`write_all`] 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.
+    ///
+    /// [`write_all`]: Write::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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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 Adapter<'a, T: ?Sized + 'a> {
+            inner: &'a mut T,
+            error: Result<()>,
+        }
+
+        impl<T: Write + ?Sized> fmt::Write for Adapter<'_, 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 = Adapter { 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::const_io_error!(ErrorKind::Uncategorized, "formatter error"))
+                }
+            }
+        }
+    }
+
+    /// Creates a "by reference" adapter for this instance of `Write`.
+    ///
+    /// The returned adapter 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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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`]s implement `Seek`:
+///
+/// [`File`]: crate::fs::File
+///
+/// ```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(())
+/// }
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+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 can fail, for example because it might involve flushing a buffer.
+    ///
+    /// Seeking to a negative offset is considered an error.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
+
+    /// Rewind to the beginning of a stream.
+    ///
+    /// This is a convenience method, equivalent to `seek(SeekFrom::Start(0))`.
+    ///
+    /// # Errors
+    ///
+    /// Rewinding can fail, for example because it might involve flushing a buffer.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use std::io::{Read, Seek, Write};
+    /// use std::fs::OpenOptions;
+    ///
+    /// let mut f = OpenOptions::new()
+    ///     .write(true)
+    ///     .read(true)
+    ///     .create(true)
+    ///     .open("foo.txt").unwrap();
+    ///
+    /// let hello = "Hello!\n";
+    /// write!(f, "{hello}").unwrap();
+    /// f.rewind().unwrap();
+    ///
+    /// let mut buf = String::new();
+    /// f.read_to_string(&mut buf).unwrap();
+    /// assert_eq!(&buf, hello);
+    /// ```
+    #[stable(feature = "seek_rewind", since = "1.55.0")]
+    fn rewind(&mut self) -> Result<()> {
+        self.seek(SeekFrom::Start(0))?;
+        Ok(())
+    }
+
+    /// 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_stream_len)]
+    /// 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 {len} bytes long");
+    ///     Ok(())
+    /// }
+    /// ```
+    #[unstable(feature = "seek_stream_len", issue = "59359")]
+    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
+    /// 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(())
+    /// }
+    /// ```
+    #[stable(feature = "seek_convenience", since = "1.51.0")]
+    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.
+#[derive(Copy, PartialEq, Eq, Clone, Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub enum SeekFrom {
+    /// Sets the offset to the provided number of bytes.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Start(#[stable(feature = "rust1", since = "1.0.0")] 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.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    End(#[stable(feature = "rust1", since = "1.0.0")] 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.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Current(#[stable(feature = "rust1", since = "1.0.0")] 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!
+///
+/// [`File`]: crate::fs::File
+/// [`read_line`]: BufRead::read_line
+/// [`lines`]: BufRead::lines
+///
+/// ```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(())
+/// }
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+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`]: BufRead::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);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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`]: BufRead::fill_buf
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn consume(&mut self, amt: usize);
+
+    /// Check if the underlying `Read` has any data left to be read.
+    ///
+    /// This function may fill the buffer to check for data,
+    /// so this functions returns `Result<bool>`, not `bool`.
+    ///
+    /// Default implementation calls `fill_buf` and checks that
+    /// returned slice is empty (which means that there is no data left,
+    /// since EOF is reached).
+    ///
+    /// Examples
+    ///
+    /// ```
+    /// #![feature(buf_read_has_data_left)]
+    /// use std::io;
+    /// use std::io::prelude::*;
+    ///
+    /// let stdin = io::stdin();
+    /// let mut stdin = stdin.lock();
+    ///
+    /// while stdin.has_data_left().unwrap() {
+    ///     let mut line = String::new();
+    ///     stdin.read_line(&mut line).unwrap();
+    ///     // work with line
+    ///     println!("{line:?}");
+    /// }
+    /// ```
+    #[unstable(feature = "buf_read_has_data_left", reason = "recently added", issue = "86423")]
+    fn has_data_left(&mut self) -> Result<bool> {
+        self.fill_buf().map(|b| !b.is_empty())
+    }
+
+    /// 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.
+    ///
+    /// This function is blocking and should be used carefully: it is possible for
+    /// an attacker to continuously send bytes without ever sending the delimiter
+    /// or EOF.
+    ///
+    /// # 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`]: BufRead::fill_buf
+    ///
+    /// # 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:
+    ///
+    /// ```
+    /// 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"");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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. You do not need to clear the buffer before
+    /// appending.
+    ///
+    /// 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.
+    ///
+    /// This function is blocking and should be used carefully: it is possible for
+    /// an attacker to continuously send bytes without ever sending a newline
+    /// or EOF.
+    ///
+    /// [`Ok(0)`]: Ok
+    ///
+    /// # 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`]: BufRead::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:
+    ///
+    /// ```
+    /// 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, "");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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`.
+        unsafe { 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
+    /// <code>[io::Result]<[Vec]\<u8>></code>. 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]: self::Result "io::Result"
+    /// [`read_until`]: BufRead::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
+    ///
+    /// ```
+    /// 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);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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
+    /// <code>[io::Result]<[String]></code>. Each string returned will *not* have a newline
+    /// byte (the `0xA` byte) or `CRLF` (`0xD`, `0xA` bytes) at the end.
+    ///
+    /// [io::Result]: self::Result "io::Result"
+    ///
+    /// # 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.
+    ///
+    /// ```
+    /// 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`].
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn lines(self) -> Lines<Self>
+    where
+        Self: Sized,
+    {
+        Lines { buf: self }
+    }
+}
+
+/// Adapter 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`]: Read::chain
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
+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(())
+    /// }
+    /// ```
+    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
+    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(())
+    /// }
+    /// ```
+    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
+    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(())
+    /// }
+    /// ```
+    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
+    pub fn get_mut(&mut self) -> (&mut T, &mut U) {
+        (&mut self.first, &mut self.second)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+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 {
+            match self.first.read_vectored(bufs)? {
+                0 if bufs.iter().any(|b| !b.is_empty()) => self.done_first = true,
+                n => return Ok(n),
+            }
+        }
+        self.second.read_vectored(bufs)
+    }
+}
+
+#[stable(feature = "chain_bufread", since = "1.9.0")]
+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) }
+    }
+}
+
+impl<T, U> SizeHint for Chain<T, U> {
+    #[inline]
+    fn lower_bound(&self) -> usize {
+        SizeHint::lower_bound(&self.first) + SizeHint::lower_bound(&self.second)
+    }
+
+    #[inline]
+    fn upper_bound(&self) -> Option<usize> {
+        match (SizeHint::upper_bound(&self.first), SizeHint::upper_bound(&self.second)) {
+            (Some(first), Some(second)) => first.checked_add(second),
+            _ => None,
+        }
+    }
+}
+
+/// Reader adapter 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`]: Read::take
+#[stable(feature = "rust1", since = "1.0.0")]
+#[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.
+    ///
+    /// # 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(())
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    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(())
+    /// }
+    /// ```
+    #[stable(feature = "take_set_limit", since = "1.27.0")]
+    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(())
+    /// }
+    /// ```
+    #[stable(feature = "io_take_into_inner", since = "1.15.0")]
+    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(())
+    /// }
+    /// ```
+    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
+    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(())
+    /// }
+    /// ```
+    #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
+    pub fn get_mut(&mut self) -> &mut T {
+        &mut self.inner
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+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])?;
+        assert!(n as u64 <= self.limit, "number of read bytes exceeds limit");
+        self.limit -= n as u64;
+        Ok(n)
+    }
+
+    fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> {
+        // Don't call into inner reader at all at EOF because it may still block
+        if self.limit == 0 {
+            return Ok(());
+        }
+
+        let prev_filled = buf.filled_len();
+
+        if self.limit <= buf.remaining() as u64 {
+            // if we just use an as cast to convert, limit may wrap around on a 32 bit target
+            let limit = cmp::min(self.limit, usize::MAX as u64) as usize;
+
+            let extra_init = cmp::min(limit as usize, buf.initialized_len() - buf.filled_len());
+
+            // SAFETY: no uninit data is written to ibuf
+            let ibuf = unsafe { &mut buf.unfilled_mut()[..limit] };
+
+            let mut sliced_buf = ReadBuf::uninit(ibuf);
+
+            // SAFETY: extra_init bytes of ibuf are known to be initialized
+            unsafe {
+                sliced_buf.assume_init(extra_init);
+            }
+
+            self.inner.read_buf(&mut sliced_buf)?;
+
+            let new_init = sliced_buf.initialized_len();
+            let filled = sliced_buf.filled_len();
+
+            // sliced_buf / ibuf must drop here
+
+            // SAFETY: new_init bytes of buf's unfilled buffer have been initialized
+            unsafe {
+                buf.assume_init(new_init);
+            }
+
+            buf.add_filled(filled);
+
+            self.limit -= filled as u64;
+        } else {
+            self.inner.read_buf(buf)?;
+
+            //inner may unfill
+            self.limit -= buf.filled_len().saturating_sub(prev_filled) as u64;
+        }
+
+        Ok(())
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+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);
+    }
+}
+
+impl<T> SizeHint for Take<T> {
+    #[inline]
+    fn lower_bound(&self) -> usize {
+        cmp::min(SizeHint::lower_bound(&self.inner) as u64, self.limit) as usize
+    }
+
+    #[inline]
+    fn upper_bound(&self) -> Option<usize> {
+        match SizeHint::upper_bound(&self.inner) {
+            Some(upper_bound) => Some(cmp::min(upper_bound as u64, self.limit) as usize),
+            None => self.limit.try_into().ok(),
+        }
+    }
+}
+
+/// 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`]: Read::bytes
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
+pub struct Bytes<R> {
+    inner: R,
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+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)),
+            };
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        SizeHint::size_hint(&self.inner)
+    }
+}
+
+trait SizeHint {
+    fn lower_bound(&self) -> usize;
+
+    fn upper_bound(&self) -> Option<usize>;
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.lower_bound(), self.upper_bound())
+    }
+}
+
+impl<T> SizeHint for T {
+    #[inline]
+    default fn lower_bound(&self) -> usize {
+        0
+    }
+
+    #[inline]
+    default fn upper_bound(&self) -> Option<usize> {
+        None
+    }
+}
+
+impl<T> SizeHint for &mut T {
+    #[inline]
+    fn lower_bound(&self) -> usize {
+        SizeHint::lower_bound(*self)
+    }
+
+    #[inline]
+    fn upper_bound(&self) -> Option<usize> {
+        SizeHint::upper_bound(*self)
+    }
+}
+
+impl<T> SizeHint for Box<T> {
+    #[inline]
+    fn lower_bound(&self) -> usize {
+        SizeHint::lower_bound(&**self)
+    }
+
+    #[inline]
+    fn upper_bound(&self) -> Option<usize> {
+        SizeHint::upper_bound(&**self)
+    }
+}
+
+impl SizeHint for &[u8] {
+    #[inline]
+    fn lower_bound(&self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn upper_bound(&self) -> Option<usize> {
+        Some(self.len())
+    }
+}
+
+/// An iterator over the contents of an instance of `BufRead` split on a
+/// particular byte.
+///
+/// This struct is generally created by calling [`split`] on a `BufRead`.
+/// Please see the documentation of [`split`] for more details.
+///
+/// [`split`]: BufRead::split
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
+pub struct Split<B> {
+    buf: B,
+    delim: u8,
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+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`] on a `BufRead`.
+/// Please see the documentation of [`lines`] for more details.
+///
+/// [`lines`]: BufRead::lines
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug)]
+pub struct Lines<B> {
+    buf: B,
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+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)),
+        }
+    }
+}