Google Git
Sign in
fuchsia / third_party / rust / 08351004125c4d49aa757f2c3ec2340f7469ea91 / . / src / libstd / io / mod.rs
blob: be364a10593da6bb9e3178af363f594a6f6fd192 [file] [log] [blame]
//! Traits, helpers, and type definitions for core I/O functionality.
//!
//! The `std::io` module contains a number of common things you'll need
//! when doing input and output. The most core part of this module is
//! the [`Read`] and [`Write`] traits, which provide the
//! most general interface for reading and writing input and output.
//!
//! # Read and Write
//!
//! Because they are traits, [`Read`] and [`Write`] are implemented by a number
//! of other types, and you can implement them for your types too. As such,
//! you'll see a few different types of I/O throughout the documentation in
//! this module: [`File`]s, [`TcpStream`]s, and sometimes even [`Vec<T>`]s. For
//! example, [`Read`] adds a [`read`][`Read::read`] method, which we can use on
//! [`File`]s:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//! let mut f = File::open("foo.txt")?;
//! let mut buffer = [0; 10];
//!
//! // read up to 10 bytes
//! let n = f.read(&mut buffer)?;
//!
//! println!("The bytes: {:?}", &buffer[..n]);
//! Ok(())
//! }
//! ```
//!
//! [`Read`] and [`Write`] are so important, implementors of the two traits have a
//! nickname: readers and writers. So you'll sometimes see 'a reader' instead
//! of 'a type that implements the [`Read`] trait'. Much easier!
//!
//! ## Seek and BufRead
//!
//! Beyond that, there are two important traits that are provided: [`Seek`]
//! and [`BufRead`]. Both of these build on top of a reader to control
//! how the reading happens. [`Seek`] lets you control where the next byte is
//! coming from:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::io::SeekFrom;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//! let mut f = File::open("foo.txt")?;
//! let mut buffer = [0; 10];
//!
//! // skip to the last 10 bytes of the file
//! f.seek(SeekFrom::End(-10))?;
//!
//! // read up to 10 bytes
//! let n = f.read(&mut buffer)?;
//!
//! println!("The bytes: {:?}", &buffer[..n]);
//! Ok(())
//! }
//! ```
//!
//! [`BufRead`] uses an internal buffer to provide a number of other ways to read, but
//! to show it off, we'll need to talk about buffers in general. Keep reading!
//!
//! ## BufReader and BufWriter
//!
//! Byte-based interfaces are unwieldy and can be inefficient, as we'd need to be
//! making near-constant calls to the operating system. To help with this,
//! `std::io` comes with two structs, [`BufReader`] and [`BufWriter`], which wrap
//! readers and writers. The wrapper uses a buffer, reducing the number of
//! calls and providing nicer methods for accessing exactly what you want.
//!
//! For example, [`BufReader`] works with the [`BufRead`] trait to add extra
//! methods to any reader:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::io::BufReader;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//! let f = File::open("foo.txt")?;
//! let mut reader = BufReader::new(f);
//! let mut buffer = String::new();
//!
//! // read a line into buffer
//! reader.read_line(&mut buffer)?;
//!
//! println!("{}", buffer);
//! Ok(())
//! }
//! ```
//!
//! [`BufWriter`] doesn't add any new ways of writing; it just buffers every call
//! to [`write`][`Write::write`]:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::io::BufWriter;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//! let f = File::create("foo.txt")?;
//! {
//! let mut writer = BufWriter::new(f);
//!
//! // write a byte to the buffer
//! writer.write(&[42])?;
//!
//! } // the buffer is flushed once writer goes out of scope
//!
//! Ok(())
//! }
//! ```
//!
//! ## Standard input and output
//!
//! A very common source of input is standard input:
//!
//! ```no_run
//! use std::io;
//!
//! fn main() -> io::Result<()> {
//! let mut input = String::new();
//!
//! io::stdin().read_line(&mut input)?;
//!
//! println!("You typed: {}", input.trim());
//! Ok(())
//! }
//! ```
//!
//! Note that you cannot use the [`?` operator] in functions that do not return
//! a [`Result<T, E>`][`Result`]. Instead, you can call [`.unwrap()`]
//! or `match` on the return value to catch any possible errors:
//!
//! ```no_run
//! use std::io;
//!
//! let mut input = String::new();
//!
//! io::stdin().read_line(&mut input).unwrap();
//! ```
//!
//! And a very common source of output is standard output:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//!
//! fn main() -> io::Result<()> {
//! io::stdout().write(&[42])?;
//! Ok(())
//! }
//! ```
//!
//! Of course, using [`io::stdout`] directly is less common than something like
//! [`println!`].
//!
//! ## Iterator types
//!
//! A large number of the structures provided by `std::io` are for various
//! ways of iterating over I/O. For example, [`Lines`] is used to split over
//! lines:
//!
//! ```no_run
//! use std::io;
//! use std::io::prelude::*;
//! use std::io::BufReader;
//! use std::fs::File;
//!
//! fn main() -> io::Result<()> {
//! let f = File::open("foo.txt")?;
//! let reader = BufReader::new(f);
//!
//! for line in reader.lines() {
//! println!("{}", line?);
//! }
//! Ok(())
//! }
//! ```
//!
//! ## Functions
//!
//! There are a number of [functions][functions-list] that offer access to various
//! features. For example, we can use three of these functions to copy everything
//! from standard input to standard output:
//!
//! ```no_run
//! use std::io;
//!
//! fn main() -> io::Result<()> {
//! io::copy(&mut io::stdin(), &mut io::stdout())?;
//! Ok(())
//! }
//! ```
//!
//! [functions-list]: #functions-1
//!
//! ## io::Result
//!
//! Last, but certainly not least, is [`io::Result`]. This type is used
//! as the return type of many `std::io` functions that can cause an error, and
//! can be returned from your own functions as well. Many of the examples in this
//! module use the [`?` operator]:
//!
//! ```
//! use std::io;
//!
//! fn read_input() -> io::Result<()> {
//! let mut input = String::new();
//!
//! io::stdin().read_line(&mut input)?;
//!
//! println!("You typed: {}", input.trim());
//!
//! Ok(())
//! }
//! ```
//!
//! The return type of `read_input()`, [`io::Result<()>`][`io::Result`], is a very
//! common type for functions which don't have a 'real' return value, but do want to
//! return errors if they happen. In this case, the only purpose of this function is
//! to read the line and print it, so we use `()`.
//!
//! ## Platform-specific behavior
//!
//! Many I/O functions throughout the standard library are documented to indicate
//! what various library or syscalls they are delegated to. This is done to help
//! applications both understand what's happening under the hood as well as investigate
//! any possibly unclear semantics. Note, however, that this is informative, not a binding
//! contract. The implementation of many of these functions are subject to change over
//! time and may call fewer or more syscalls/library functions.
//!
//! [`Read`]: trait.Read.html
//! [`Write`]: trait.Write.html
//! [`Seek`]: trait.Seek.html
//! [`BufRead`]: trait.BufRead.html
//! [`File`]: ../fs/struct.File.html
//! [`TcpStream`]: ../net/struct.TcpStream.html
//! [`Vec<T>`]: ../vec/struct.Vec.html
//! [`BufReader`]: struct.BufReader.html
//! [`BufWriter`]: struct.BufWriter.html
//! [`Write::write`]: trait.Write.html#tymethod.write
//! [`io::stdout`]: fn.stdout.html
//! [`println!`]: ../macro.println.html
//! [`Lines`]: struct.Lines.html
//! [`io::Result`]: type.Result.html
//! [`?` operator]: ../../book/appendix-02-operators.html
//! [`Read::read`]: trait.Read.html#tymethod.read
//! [`Result`]: ../result/enum.Result.html
//! [`.unwrap()`]: ../result/enum.Result.html#method.unwrap
#![stable(feature = "rust1", since = "1.0.0")]
use crate::cmp;
use crate::fmt;
use crate::slice;
use crate::str;
use crate::memchr;
use crate::ops::{Deref, DerefMut};
use crate::ptr;
use crate::sys;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::buffered::{BufReader, BufWriter, LineWriter};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::buffered::IntoInnerError;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::cursor::Cursor;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::error::{Result, Error, ErrorKind};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::util::{copy, sink, Sink, empty, Empty, repeat, Repeat};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::stdio::{stdin, stdout, stderr, Stdin, Stdout, Stderr};
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::stdio::{StdoutLock, StderrLock, StdinLock};
#[unstable(feature = "print_internals", issue = "0")]
pub use self::stdio::{_print, _eprint};
#[unstable(feature = "libstd_io_internals", issue = "42788")]
#[doc(no_inline, hidden)]
pub use self::stdio::{set_panic, set_print};
pub mod prelude;
mod buffered;
mod cursor;
mod error;
mod impls;
mod lazy;
mod util;
mod stdio;
const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
struct Guard<'a> { buf: &'a mut Vec<u8>, len: usize }
impl Drop for Guard<'_> {
fn drop(&mut self) {
unsafe { self.buf.set_len(self.len); }
}
}
// A few methods below (read_to_string, read_line) will append data into a
// `String` buffer, but we need to be pretty careful when doing this. The
// implementation will just call `.as_mut_vec()` and then delegate to a
// byte-oriented reading method, but we must ensure that when returning we never
// leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
//
// To this end, we use an RAII guard (to protect against panics) which updates
// the length of the string when it is dropped. This guard initially truncates
// the string to the prior length and only after we've validated that the
// new contents are valid UTF-8 do we allow it to set a longer length.
//
// The unsafety in this function is twofold:
//
// 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
// checks.
// 2. We're passing a raw buffer to the function `f`, and it is expected that
// the function only *appends* bytes to the buffer. We'll get undefined
// behavior if existing bytes are overwritten to have non-UTF-8 data.
fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
where F: FnOnce(&mut Vec<u8>) -> Result<usize>
{
unsafe {
let mut g = Guard { len: buf.len(), buf: buf.as_mut_vec() };
let ret = f(g.buf);
if str::from_utf8(&g.buf[g.len..]).is_err() {
ret.and_then(|_| {
Err(Error::new(ErrorKind::InvalidData,
"stream did not contain valid UTF-8"))
})
} else {
g.len = g.buf.len();
ret
}
}
}
// This uses an adaptive system to extend the vector when it fills. We want to
// avoid paying to allocate and zero a huge chunk of memory if the reader only
// has 4 bytes while still making large reads if the reader does have a ton
// of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
// time is 4,500 times (!) slower than a default reservation size of 32 if the
// reader has a very small amount of data to return.
//
// Because we're extending the buffer with uninitialized data for trusted
// readers, we need to make sure to truncate that if any of this panics.
fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
read_to_end_with_reservation(r, buf, |_| 32)
}
fn read_to_end_with_reservation<R, F>(
r: &mut R,
buf: &mut Vec<u8>,
mut reservation_size: F,
) -> Result<usize>
where
R: Read + ?Sized,
F: FnMut(&R) -> usize,
{
let start_len = buf.len();
let mut g = Guard { len: buf.len(), buf: buf };
let ret;
loop {
if g.len == g.buf.len() {
unsafe {
// FIXME(danielhenrymantilla): #42788
//
// - This creates a (mut) reference to a slice of
// _uninitialized_ integers, which is **undefined behavior**
//
// - Only the standard library gets to soundly "ignore" this,
// based on its privileged knowledge of unstable rustc
// internals;
g.buf.reserve(reservation_size(r));
let capacity = g.buf.capacity();
g.buf.set_len(capacity);
r.initializer().initialize(&mut g.buf[g.len..]);
}
}
match r.read(&mut g.buf[g.len..]) {
Ok(0) => {
ret = Ok(g.len - start_len);
break;
}
Ok(n) => g.len += n,
Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
Err(e) => {
ret = Err(e);
break;
}
}
}
ret
}
pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
where
F: FnOnce(&mut [u8]) -> Result<usize>
{
let buf = bufs
.iter_mut()
.find(|b| !b.is_empty())
.map_or(&mut [][..], |b| &mut **b);
read(buf)
}
pub(crate) fn default_write_vectored<F>(write: F, bufs: &[IoSlice<'_>]) -> Result<usize>
where
F: FnOnce(&[u8]) -> Result<usize>
{
let buf = bufs
.iter()
.find(|b| !b.is_empty())
.map_or(&[][..], |b| &**b);
write(buf)
}
/// The `Read` trait allows for reading bytes from a source.
///
/// Implementors of the `Read` trait are called 'readers'.
///
/// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
/// will attempt to pull bytes from this source into a provided buffer. A
/// number of other methods are implemented in terms of [`read()`], giving
/// implementors a number of ways to read bytes while only needing to implement
/// a single method.
///
/// Readers are intended to be composable with one another. Many implementors
/// throughout [`std::io`] take and provide types which implement the `Read`
/// trait.
///
/// Please note that each call to [`read()`] may involve a system call, and
/// therefore, using something that implements [`BufRead`], such as
/// [`BufReader`], will be more efficient.
///
/// # Examples
///
/// [`File`]s implement `Read`:
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
/// let mut buffer = [0; 10];
///
/// // read up to 10 bytes
/// f.read(&mut buffer)?;
///
/// let mut buffer = Vec::new();
/// // read the whole file
/// f.read_to_end(&mut buffer)?;
///
/// // read into a String, so that you don't need to do the conversion.
/// let mut buffer = String::new();
/// f.read_to_string(&mut buffer)?;
///
/// // and more! See the other methods for more details.
/// Ok(())
/// }
/// ```
///
/// Read from [`&str`] because [`&[u8]`][slice] implements `Read`:
///
/// ```no_run
/// # use std::io;
/// use std::io::prelude::*;
///
/// fn main() -> io::Result<()> {
/// let mut b = "This string will be read".as_bytes();
/// let mut buffer = [0; 10];
///
/// // read up to 10 bytes
/// b.read(&mut buffer)?;
///
/// // etc... it works exactly as a File does!
/// Ok(())
/// }
/// ```
///
/// [`read()`]: trait.Read.html#tymethod.read
/// [`std::io`]: ../../std/io/index.html
/// [`File`]: ../fs/struct.File.html
/// [`BufRead`]: trait.BufRead.html
/// [`BufReader`]: struct.BufReader.html
/// [`&str`]: ../../std/primitive.str.html
/// [slice]: ../../std/primitive.slice.html
#[stable(feature = "rust1", since = "1.0.0")]
#[doc(spotlight)]
pub trait Read {
/// Pull some bytes from this source into the specified buffer, returning
/// how many bytes were read.
///
/// This function does not provide any guarantees about whether it blocks
/// waiting for data, but if an object needs to block for a read but cannot
/// it will typically signal this via an [`Err`] return value.
///
/// If the return value of this method is [`Ok(n)`], then it must be
/// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
/// that the buffer `buf` has been filled in with `n` bytes of data from this
/// source. If `n` is `0`, then it can indicate one of two scenarios:
///
/// 1. This reader has reached its "end of file" and will likely no longer
/// be able to produce bytes. Note that this does not mean that the
/// reader will *always* no longer be able to produce bytes.
/// 2. The buffer specified was 0 bytes in length.
///
/// No guarantees are provided about the contents of `buf` when this
/// function is called, implementations cannot rely on any property of the
/// contents of `buf` being true. It is recommended that *implementations*
/// only write data to `buf` instead of reading its contents.
///
/// Correspondingly, however, *callers* of this method may 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>`]: ../mem/union.MaybeUninit.html
///
/// # Errors
///
/// If this function encounters any form of I/O or other error, an error
/// variant will be returned. If an error is returned then it must be
/// guaranteed that no bytes were read.
///
/// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
/// operation should be retried if there is nothing else to do.
///
/// # Examples
///
/// [`File`]s implement `Read`:
///
/// [`Err`]: ../../std/result/enum.Result.html#variant.Err
/// [`Ok(n)`]: ../../std/result/enum.Result.html#variant.Ok
/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
/// [`File`]: ../fs/struct.File.html
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
/// let mut buffer = [0; 10];
///
/// // read up to 10 bytes
/// let n = f.read(&mut buffer[..])?;
///
/// println!("The bytes: {:?}", &buffer[..n]);
/// Ok(())
/// }
/// ```
#[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
/// as a single call to `read` with the buffers concatenated would.
///
/// The default implementation calls `read` with either the first nonempty
/// buffer provided, or an empty one if none exists.
#[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 can work with buffers of uninitialized
/// memory.
///
/// The default implementation returns an initializer which will zero
/// buffers.
///
/// If a `Read`er guarantees that it can work properly with uninitialized
/// memory, it should call [`Initializer::nop()`]. See the documentation for
/// [`Initializer`] for details.
///
/// The behavior of this method must be independent of the state of the
/// `Read`er - the method only takes `&self` so that it can be used through
/// trait objects.
///
/// # Safety
///
/// This method is unsafe because a `Read`er could otherwise return a
/// non-zeroing `Initializer` from another `Read` type without an `unsafe`
/// block.
///
/// [`Initializer::nop()`]: ../../std/io/struct.Initializer.html#method.nop
/// [`Initializer`]: ../../std/io/struct.Initializer.html
#[unstable(feature = "read_initializer", issue = "42788")]
#[inline]
unsafe fn initializer(&self) -> Initializer {
Initializer::zeroing()
}
/// Read all bytes until EOF in this source, placing them into `buf`.
///
/// All bytes read from this source will be appended to the specified buffer
/// `buf`. This function will continuously call [`read()`] to append more data to
/// `buf` until [`read()`] returns either [`Ok(0)`] or an error of
/// non-[`ErrorKind::Interrupted`] kind.
///
/// If successful, this function will return the total number of bytes read.
///
/// # Errors
///
/// If this function encounters an error of the kind
/// [`ErrorKind::Interrupted`] then the error is ignored and the operation
/// will continue.
///
/// If any other read error is encountered then this function immediately
/// returns. Any bytes which have already been read will be appended to
/// `buf`.
///
/// # Examples
///
/// [`File`]s implement `Read`:
///
/// [`read()`]: trait.Read.html#tymethod.read
/// [`Ok(0)`]: ../../std/result/enum.Result.html#variant.Ok
/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
/// [`File`]: ../fs/struct.File.html
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
/// let mut buffer = Vec::new();
///
/// // read the whole file
/// f.read_to_end(&mut buffer)?;
/// Ok(())
/// }
/// ```
///
/// (See also the [`std::fs::read`] convenience function for reading from a
/// file.)
///
/// [`std::fs::read`]: ../fs/fn.read.html
#[stable(feature = "rust1", since = "1.0.0")]
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
read_to_end(self, buf)
}
/// Read all bytes until EOF in this source, appending them to `buf`.
///
/// If successful, this function returns the number of bytes which were read
/// and appended to `buf`.
///
/// # Errors
///
/// If the data in this stream is *not* valid UTF-8 then an error is
/// returned and `buf` is unchanged.
///
/// See [`read_to_end`][readtoend] for other error semantics.
///
/// [readtoend]: #method.read_to_end
///
/// # Examples
///
/// [`File`][file]s implement `Read`:
///
/// [file]: ../fs/struct.File.html
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
/// let mut buffer = String::new();
///
/// f.read_to_string(&mut buffer)?;
/// Ok(())
/// }
/// ```
///
/// (See also the [`std::fs::read_to_string`] convenience function for
/// reading from a file.)
///
/// [`std::fs::read_to_string`]: ../fs/fn.read_to_string.html
#[stable(feature = "rust1", since = "1.0.0")]
fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
// Note that we do *not* call `.read_to_end()` here. We are passing
// `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
// method to fill it up. An arbitrary implementation could overwrite the
// entire contents of the vector, not just append to it (which is what
// we are expecting).
//
// To prevent extraneously checking the UTF-8-ness of the entire buffer
// we pass it to our hardcoded `read_to_end` implementation which we
// know is guaranteed to only read data into the end of the buffer.
append_to_string(buf, |b| read_to_end(self, b))
}
/// Read the exact number of bytes required to fill `buf`.
///
/// This function reads as many bytes as necessary to completely fill the
/// specified buffer `buf`.
///
/// No guarantees are provided about the contents of `buf` when this
/// function is called, implementations cannot rely on any property of the
/// contents of `buf` being true. It is recommended that implementations
/// only write data to `buf` instead of reading its contents.
///
/// # Errors
///
/// If this function encounters an error of the kind
/// [`ErrorKind::Interrupted`] then the error is ignored and the operation
/// will continue.
///
/// If this function encounters an "end of file" before completely filling
/// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
/// The contents of `buf` are unspecified in this case.
///
/// If any other read error is encountered then this function immediately
/// returns. The contents of `buf` are unspecified in this case.
///
/// If this function returns an error, it is unspecified how many bytes it
/// has read, but it will never read more than would be necessary to
/// completely fill the buffer.
///
/// # Examples
///
/// [`File`]s implement `Read`:
///
/// [`File`]: ../fs/struct.File.html
/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
/// [`ErrorKind::UnexpectedEof`]: ../../std/io/enum.ErrorKind.html#variant.UnexpectedEof
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
/// let mut buffer = [0; 10];
///
/// // read exactly 10 bytes
/// f.read_exact(&mut buffer)?;
/// Ok(())
/// }
/// ```
#[stable(feature = "read_exact", since = "1.6.0")]
fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
while !buf.is_empty() {
match self.read(buf) {
Ok(0) => break,
Ok(n) => { let tmp = buf; buf = &mut tmp[n..]; }
Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
Err(e) => return Err(e),
}
}
if !buf.is_empty() {
Err(Error::new(ErrorKind::UnexpectedEof,
"failed to fill whole buffer"))
} else {
Ok(())
}
}
/// Creates a "by reference" adaptor for this instance of `Read`.
///
/// The returned adaptor also implements `Read` and will simply borrow this
/// current reader.
///
/// # Examples
///
/// [`File`][file]s implement `Read`:
///
/// [file]: ../fs/struct.File.html
///
/// ```no_run
/// use std::io;
/// use std::io::Read;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
/// let mut buffer = Vec::new();
/// let mut other_buffer = Vec::new();
///
/// {
/// let reference = f.by_ref();
///
/// // read at most 5 bytes
/// reference.take(5).read_to_end(&mut buffer)?;
///
/// } // drop our &mut reference so we can use f again
///
/// // original file still usable, read the rest
/// f.read_to_end(&mut other_buffer)?;
/// Ok(())
/// }
/// ```
#[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
/// [`Result`]`<`[`u8`]`, `[`io::Error`]`>`.
/// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
/// otherwise. EOF is mapped to returning [`None`] from this iterator.
///
/// # Examples
///
/// [`File`][file]s implement `Read`:
///
/// [file]: ../fs/struct.File.html
/// [`Iterator`]: ../../std/iter/trait.Iterator.html
/// [`Result`]: ../../std/result/enum.Result.html
/// [`io::Error`]: ../../std/io/struct.Error.html
/// [`u8`]: ../../std/primitive.u8.html
/// [`Ok`]: ../../std/result/enum.Result.html#variant.Ok
/// [`Err`]: ../../std/result/enum.Result.html#variant.Err
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
///
/// for byte in f.bytes() {
/// println!("{}", byte.unwrap());
/// }
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn bytes(self) -> Bytes<Self> where Self: Sized {
Bytes { inner: self }
}
/// Creates an adaptor which will chain this stream with another.
///
/// The returned `Read` instance will first read all bytes from this object
/// until EOF is encountered. Afterwards the output is equivalent to the
/// output of `next`.
///
/// # Examples
///
/// [`File`][file]s implement `Read`:
///
/// [file]: ../fs/struct.File.html
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f1 = File::open("foo.txt")?;
/// let mut f2 = File::open("bar.txt")?;
///
/// let mut handle = f1.chain(f2);
/// let mut buffer = String::new();
///
/// // read the value into a String. We could use any Read method here,
/// // this is just one example.
/// handle.read_to_string(&mut buffer)?;
/// Ok(())
/// }
/// ```
#[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 adaptor which will read at most `limit` bytes from it.
///
/// This function returns a new instance of `Read` which will read at most
/// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
/// read errors will not count towards the number of bytes read and future
/// calls to [`read()`] may succeed.
///
/// # Examples
///
/// [`File`]s implement `Read`:
///
/// [`File`]: ../fs/struct.File.html
/// [`Ok(0)`]: ../../std/result/enum.Result.html#variant.Ok
/// [`read()`]: trait.Read.html#tymethod.read
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
/// let mut buffer = [0; 5];
///
/// // read at most five bytes
/// let mut handle = f.take(5);
///
/// handle.read(&mut buffer)?;
/// Ok(())
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn take(self, limit: u64) -> Take<Self> where Self: Sized {
Take { inner: self, limit: limit }
}
}
/// A buffer type used with `Read::read_vectored`.
///
/// It is semantically a wrapper around an `&mut [u8]`, but is guaranteed to be
/// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
/// Windows.
#[stable(feature = "iovec", since = "1.36.0")]
#[repr(transparent)]
pub struct IoSliceMut<'a>(sys::io::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.
///
/// # Notes
///
/// Elements in the slice may be modified if the cursor is not advanced to
/// the end of the slice. For example if we have a slice of buffers with 2
/// `IoSliceMut`s, both of length 8, and we advance the cursor by 10 bytes
/// the first `IoSliceMut` will be untouched however the second will be
/// modified to remove the first 2 bytes (10 - 8).
///
/// # Examples
///
/// ```
/// #![feature(io_slice_advance)]
///
/// use std::io::IoSliceMut;
/// use std::mem;
/// 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.
/// bufs = IoSliceMut::advance(mem::replace(&mut bufs, &mut []), 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<'b>(bufs: &'b mut [IoSliceMut<'a>], n: usize) -> &'b mut [IoSliceMut<'a>] {
// 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;
}
}
let bufs = &mut bufs[remove..];
if !bufs.is_empty() {
bufs[0].0.advance(n - accumulated_len)
}
bufs
}
}
#[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 an `&[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 IoSlice<'a>(sys::io::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")]
#[inline]
pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
IoSlice(sys::io::IoSlice::new(buf))
}
/// Advance the internal cursor of the slice.
///
/// # Notes
///
/// Elements in the slice may be modified if the cursor is not advanced to
/// the end of the slice. For example if we have a slice of buffers with 2
/// `IoSlice`s, both of length 8, and we advance the cursor by 10 bytes the
/// first `IoSlice` will be untouched however the second will be modified to
/// remove the first 2 bytes (10 - 8).
///
/// # Examples
///
/// ```
/// #![feature(io_slice_advance)]
///
/// use std::io::IoSlice;
/// use std::mem;
/// use std::ops::Deref;
///
/// let mut buf1 = [1; 8];
/// let mut buf2 = [2; 16];
/// let mut buf3 = [3; 8];
/// let mut bufs = &mut [
/// IoSlice::new(&mut buf1),
/// IoSlice::new(&mut buf2),
/// IoSlice::new(&mut buf3),
/// ][..];
///
/// // Mark 10 bytes as written.
/// bufs = IoSlice::advance(mem::replace(&mut bufs, &mut []), 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<'b>(bufs: &'b mut [IoSlice<'a>], n: usize) -> &'b mut [IoSlice<'a>] {
// 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;
}
}
let bufs = &mut bufs[remove..];
if !bufs.is_empty() {
bufs[0].0.advance(n - accumulated_len)
}
bufs
}
}
#[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 type used to conditionally initialize buffers passed to `Read` methods.
#[unstable(feature = "read_initializer", issue = "42788")]
#[derive(Debug)]
pub struct Initializer(bool);
impl Initializer {
/// Returns a new `Initializer` which will zero out buffers.
#[unstable(feature = "read_initializer", issue = "42788")]
#[inline]
pub fn zeroing() -> Initializer {
Initializer(true)
}
/// Returns a new `Initializer` which will not zero out buffers.
///
/// # Safety
///
/// This may only be called by `Read`ers which guarantee that they will not
/// read from buffers passed to `Read` methods, and that the return value of
/// the method accurately reflects the number of bytes that have been
/// written to the head of the buffer.
#[unstable(feature = "read_initializer", issue = "42788")]
#[inline]
pub unsafe fn nop() -> Initializer {
Initializer(false)
}
/// Indicates if a buffer should be initialized.
#[unstable(feature = "read_initializer", issue = "42788")]
#[inline]
pub fn should_initialize(&self) -> bool {
self.0
}
/// Initializes a buffer if necessary.
#[unstable(feature = "read_initializer", issue = "42788")]
#[inline]
pub fn initialize(&self, buf: &mut [u8]) {
if self.should_initialize() {
unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
}
}
}
/// A trait for objects which are byte-oriented sinks.
///
/// Implementors of the `Write` trait are sometimes called 'writers'.
///
/// Writers are defined by two required methods, [`write`] and [`flush`]:
///
/// * The [`write`] method will attempt to write some data into the object,
/// returning how many bytes were successfully written.
///
/// * The [`flush`] method is useful for adaptors and explicit buffers
/// themselves for ensuring that all buffered data has been pushed out to the
/// 'true sink'.
///
/// Writers are intended to be composable with one another. Many implementors
/// throughout [`std::io`] take and provide types which implement the `Write`
/// trait.
///
/// [`write`]: #tymethod.write
/// [`flush`]: #tymethod.flush
/// [`std::io`]: index.html
///
/// # Examples
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let data = b"some bytes";
///
/// let mut pos = 0;
/// let mut buffer = File::create("foo.txt")?;
///
/// while pos < data.len() {
/// let bytes_written = buffer.write(&data[pos..])?;
/// pos += bytes_written;
/// }
/// Ok(())
/// }
/// ```
///
/// The trait also provides convenience methods like [`write_all`], which calls
/// `write` in a loop until its entire input has been written.
///
/// [`write_all`]: #method.write_all
#[stable(feature = "rust1", since = "1.0.0")]
#[doc(spotlight)]
pub trait Write {
/// Write a buffer into this writer, returning how many bytes were written.
///
/// This function will attempt to write the entire contents of `buf`, but
/// the entire write may not succeed, or the write may also generate an
/// error. A call to `write` represents *at most one* attempt to write to
/// any wrapped object.
///
/// Calls to `write` are not guaranteed to block waiting for data to be
/// written, and a write which would otherwise block can be indicated through
/// an [`Err`] variant.
///
/// If the return value is [`Ok(n)`] then it must be guaranteed that
/// `n <= buf.len()`. A return value of `0` typically means that the
/// underlying object is no longer able to accept bytes and will likely not
/// be able to in the future as well, or that the buffer provided is empty.
///
/// # Errors
///
/// Each call to `write` may generate an I/O error indicating that the
/// operation could not be completed. If an error is returned then no bytes
/// in the buffer were written to this writer.
///
/// It is **not** considered an error if the entire buffer could not be
/// written to this writer.
///
/// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
/// write operation should be retried if there is nothing else to do.
///
/// [`Err`]: ../../std/result/enum.Result.html#variant.Err
/// [`Ok(n)`]: ../../std/result/enum.Result.html#variant.Ok
/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
///
/// # Examples
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let mut buffer = File::create("foo.txt")?;
///
/// // Writes some prefix of the byte string, not necessarily all of it.
/// buffer.write(b"some bytes")?;
/// Ok(())
/// }
/// ```
#[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.
#[stable(feature = "iovec", since = "1.36.0")]
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
default_write_vectored(|b| self.write(b), bufs)
}
/// Flush this output stream, ensuring that all intermediately buffered
/// contents reach their destination.
///
/// # Errors
///
/// It is considered an error if not all bytes could be written due to
/// I/O errors or EOF being reached.
///
/// # Examples
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::io::BufWriter;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let mut buffer = BufWriter::new(File::create("foo.txt")?);
///
/// buffer.write_all(b"some bytes")?;
/// buffer.flush()?;
/// Ok(())
/// }
/// ```
#[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.
///
/// # Errors
///
/// This function will return the first error of
/// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
///
/// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
/// [`write`]: #tymethod.write
///
/// # Examples
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let mut buffer = File::create("foo.txt")?;
///
/// buffer.write_all(b"some bytes")?;
/// Ok(())
/// }
/// ```
#[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::new(ErrorKind::WriteZero,
"failed to write whole buffer")),
Ok(n) => buf = &buf[n..],
Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
Err(e) => return Err(e),
}
}
Ok(())
}
/// Writes a formatted string into this writer, returning any error
/// encountered.
///
/// This method is primarily used to interface with the
/// [`format_args!`][formatargs] macro, but it is rare that this should
/// explicitly be called. The [`write!`][write] macro should be favored to
/// invoke this method instead.
///
/// [formatargs]: ../macro.format_args.html
/// [write]: ../macro.write.html
///
/// This function internally uses the [`write_all`][writeall] method on
/// this trait and hence will continuously write data so long as no errors
/// are received. This also means that partial writes are not indicated in
/// this signature.
///
/// [writeall]: #method.write_all
///
/// # Errors
///
/// This function will return any I/O error reported while formatting.
///
/// # Examples
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let mut buffer = File::create("foo.txt")?;
///
/// // this call
/// write!(buffer, "{:.*}", 2, 1.234567)?;
/// // turns into this:
/// buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))?;
/// Ok(())
/// }
/// ```
#[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 Adaptor<'a, T: ?Sized + 'a> {
inner: &'a mut T,
error: Result<()>,
}
impl<T: Write + ?Sized> fmt::Write for Adaptor<'_, T> {
fn write_str(&mut self, s: &str) -> fmt::Result {
match self.inner.write_all(s.as_bytes()) {
Ok(()) => Ok(()),
Err(e) => {
self.error = Err(e);
Err(fmt::Error)
}
}
}
}
let mut output = Adaptor { inner: self, error: Ok(()) };
match fmt::write(&mut output, fmt) {
Ok(()) => Ok(()),
Err(..) => {
// check if the error came from the underlying `Write` or not
if output.error.is_err() {
output.error
} else {
Err(Error::new(ErrorKind::Other, "formatter error"))
}
}
}
}
/// Creates a "by reference" adaptor for this instance of `Write`.
///
/// The returned adaptor also implements `Write` and will simply borrow this
/// current writer.
///
/// # Examples
///
/// ```no_run
/// use std::io::Write;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
/// let mut buffer = File::create("foo.txt")?;
///
/// let reference = buffer.by_ref();
///
/// // we can use reference just like our original buffer
/// reference.write_all(b"some bytes")?;
/// Ok(())
/// }
/// ```
#[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`][file]s implement `Seek`:
///
/// [file]: ../fs/struct.File.html
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
/// use std::io::SeekFrom;
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
///
/// // move the cursor 42 bytes from the start of the file
/// f.seek(SeekFrom::Start(42))?;
/// Ok(())
/// }
/// ```
#[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 to a negative offset is considered an error.
///
/// [`SeekFrom::Start`]: enum.SeekFrom.html#variant.Start
#[stable(feature = "rust1", since = "1.0.0")]
fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
/// Returns the length of this stream (in bytes).
///
/// This method is implemented using up to three seek operations. If this
/// method returns successfully, the seek position is unchanged (i.e. the
/// position before calling this method is the same as afterwards).
/// However, if this method returns an error, the seek position is
/// unspecified.
///
/// If you need to obtain the length of *many* streams and you don't care
/// about the seek position afterwards, you can reduce the number of seek
/// operations by simply calling `seek(SeekFrom::End(0))` and using its
/// return value (it is also the stream length).
///
/// Note that length of a stream can change over time (for example, when
/// data is appended to a file). So calling this method multiple times does
/// not necessarily return the same length each time.
///
///
/// # Example
///
/// ```no_run
/// #![feature(seek_convenience)]
/// use std::{
/// io::{self, Seek},
/// fs::File,
/// };
///
/// fn main() -> io::Result<()> {
/// let mut f = File::open("foo.txt")?;
///
/// let len = f.stream_len()?;
/// println!("The file is currently {} bytes long", len);
/// Ok(())
/// }
/// ```
#[unstable(feature = "seek_convenience", 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
/// #![feature(seek_convenience)]
/// use std::{
/// io::{self, BufRead, BufReader, Seek},
/// fs::File,
/// };
///
/// fn main() -> io::Result<()> {
/// let mut f = BufReader::new(File::open("foo.txt")?);
///
/// let before = f.stream_position()?;
/// f.read_line(&mut String::new())?;
/// let after = f.stream_position()?;
///
/// println!("The first line was {} bytes long", after - before);
/// Ok(())
/// }
/// ```
#[unstable(feature = "seek_convenience", issue = "59359")]
fn stream_position(&mut self) -> Result<u64> {
self.seek(SeekFrom::Current(0))
}
}
/// Enumeration of possible methods to seek within an I/O object.
///
/// It is used by the [`Seek`] trait.
///
/// [`Seek`]: trait.Seek.html
#[derive(Copy, PartialEq, Eq, Clone, Debug)]
#[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!
///
/// [`BufReader`]: struct.BufReader.html
/// [`File`]: ../fs/struct.File.html
/// [`read_line`]: #method.read_line
/// [`lines`]: #method.lines
/// [`Read`]: trait.Read.html
///
/// ```no_run
/// use std::io::{self, BufReader};
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let f = File::open("foo.txt")?;
/// let f = BufReader::new(f);
///
/// for line in f.lines() {
/// println!("{}", line.unwrap());
/// }
///
/// Ok(())
/// }
/// ```
///
#[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`]: #tymethod.consume
///
/// An empty buffer returned indicates that the stream has reached EOF.
///
/// # Errors
///
/// This function will return an I/O error if the underlying reader was
/// read, but returned an error.
///
/// # Examples
///
/// A locked standard input implements `BufRead`:
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
///
/// let stdin = io::stdin();
/// let mut stdin = stdin.lock();
///
/// let buffer = stdin.fill_buf().unwrap();
///
/// // work with buffer
/// println!("{:?}", buffer);
///
/// // ensure the bytes we worked with aren't returned again later
/// let length = buffer.len();
/// stdin.consume(length);
/// ```
#[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`]: #tymethod.fill_buf
#[stable(feature = "rust1", since = "1.0.0")]
fn consume(&mut self, amt: usize);
/// Read all bytes into `buf` until the delimiter `byte` or EOF is reached.
///
/// This function will read bytes from the underlying stream until the
/// delimiter or EOF is found. Once found, all bytes up to, and including,
/// the delimiter (if found) will be appended to `buf`.
///
/// If successful, this function will return the total number of bytes read.
///
/// # Errors
///
/// This function will ignore all instances of [`ErrorKind::Interrupted`] and
/// will otherwise return any errors returned by [`fill_buf`].
///
/// If an I/O error is encountered then all bytes read so far will be
/// present in `buf` and its length will have been adjusted appropriately.
///
/// [`fill_buf`]: #tymethod.fill_buf
/// [`ErrorKind::Interrupted`]: enum.ErrorKind.html#variant.Interrupted
///
/// # Examples
///
/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
/// this example, we use [`Cursor`] to read all the bytes in a byte slice
/// in hyphen delimited segments:
///
/// [`Cursor`]: struct.Cursor.html
///
/// ```
/// use std::io::{self, BufRead};
///
/// let mut cursor = io::Cursor::new(b"lorem-ipsum");
/// let mut buf = vec![];
///
/// // cursor is at 'l'
/// let num_bytes = cursor.read_until(b'-', &mut buf)
/// .expect("reading from cursor won't fail");
/// assert_eq!(num_bytes, 6);
/// assert_eq!(buf, b"lorem-");
/// buf.clear();
///
/// // cursor is at 'i'
/// let num_bytes = cursor.read_until(b'-', &mut buf)
/// .expect("reading from cursor won't fail");
/// assert_eq!(num_bytes, 5);
/// assert_eq!(buf, b"ipsum");
/// buf.clear();
///
/// // cursor is at EOF
/// let num_bytes = cursor.read_until(b'-', &mut buf)
/// .expect("reading from cursor won't fail");
/// assert_eq!(num_bytes, 0);
/// assert_eq!(buf, b"");
/// ```
#[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.
///
/// This function will read bytes from the underlying stream until the
/// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
/// up to, and including, the delimiter (if found) will be appended to
/// `buf`.
///
/// If successful, this function will return the total number of bytes read.
///
/// If this function returns `Ok(0)`, the stream has reached EOF.
///
/// # Errors
///
/// This function has the same error semantics as [`read_until`] and will
/// also return an error if the read bytes are not valid UTF-8. If an I/O
/// error is encountered then `buf` may contain some bytes already read in
/// the event that all data read so far was valid UTF-8.
///
/// [`read_until`]: #method.read_until
///
/// # Examples
///
/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
/// this example, we use [`Cursor`] to read all the lines in a byte slice:
///
/// [`Cursor`]: struct.Cursor.html
///
/// ```
/// use std::io::{self, BufRead};
///
/// let mut cursor = io::Cursor::new(b"foo\nbar");
/// let mut buf = String::new();
///
/// // cursor is at 'f'
/// let num_bytes = cursor.read_line(&mut buf)
/// .expect("reading from cursor won't fail");
/// assert_eq!(num_bytes, 4);
/// assert_eq!(buf, "foo\n");
/// buf.clear();
///
/// // cursor is at 'b'
/// let num_bytes = cursor.read_line(&mut buf)
/// .expect("reading from cursor won't fail");
/// assert_eq!(num_bytes, 3);
/// assert_eq!(buf, "bar");
/// buf.clear();
///
/// // cursor is at EOF
/// let num_bytes = cursor.read_line(&mut buf)
/// .expect("reading from cursor won't fail");
/// assert_eq!(num_bytes, 0);
/// assert_eq!(buf, "");
/// ```
#[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`.
append_to_string(buf, |b| read_until(self, b'\n', b))
}
/// Returns an iterator over the contents of this reader split on the byte
/// `byte`.
///
/// The iterator returned from this function will return instances of
/// [`io::Result`]`<`[`Vec<u8>`]`>`. Each vector returned will *not* have
/// the delimiter byte at the end.
///
/// This function will yield errors whenever [`read_until`] would have
/// also yielded an error.
///
/// [`io::Result`]: type.Result.html
/// [`Vec<u8>`]: ../vec/struct.Vec.html
/// [`read_until`]: #method.read_until
///
/// # Examples
///
/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
/// this example, we use [`Cursor`] to iterate over all hyphen delimited
/// segments in a byte slice
///
/// [`Cursor`]: struct.Cursor.html
///
/// ```
/// use std::io::{self, BufRead};
///
/// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
///
/// let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
/// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
/// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
/// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
/// assert_eq!(split_iter.next(), None);
/// ```
#[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
/// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
/// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
///
/// [`io::Result`]: type.Result.html
/// [`String`]: ../string/struct.String.html
///
/// # Examples
///
/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
/// this example, we use [`Cursor`] to iterate over all the lines in a byte
/// slice.
///
/// [`Cursor`]: struct.Cursor.html
///
/// ```
/// use std::io::{self, BufRead};
///
/// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
///
/// let mut lines_iter = cursor.lines().map(|l| l.unwrap());
/// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
/// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
/// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
/// assert_eq!(lines_iter.next(), None);
/// ```
///
/// # Errors
///
/// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
///
/// [`BufRead::read_line`]: trait.BufRead.html#method.read_line
#[stable(feature = "rust1", since = "1.0.0")]
fn lines(self) -> Lines<Self> where Self: Sized {
Lines { buf: self }
}
}
/// Adaptor to chain together two readers.
///
/// This struct is generally created by calling [`chain`] on a reader.
/// Please see the documentation of [`chain`] for more details.
///
/// [`chain`]: trait.Read.html#method.chain
#[stable(feature = "rust1", since = "1.0.0")]
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 = "std_debug", since = "1.16.0")]
impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Chain")
.field("t", &self.first)
.field("u", &self.second)
.finish()
}
}
#[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)
}
unsafe fn initializer(&self) -> Initializer {
let initializer = self.first.initializer();
if initializer.should_initialize() {
initializer
} else {
self.second.initializer()
}
}
}
#[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)
}
}
}
/// Reader adaptor which limits the bytes read from an underlying reader.
///
/// This struct is generally created by calling [`take`] on a reader.
/// Please see the documentation of [`take`] for more details.
///
/// [`take`]: trait.Read.html#method.take
#[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.
///
/// [`Read`]: ../../std/io/trait.Read.html
///
/// # Examples
///
/// ```no_run
/// use std::io;
/// use std::io::prelude::*;
/// use std::fs::File;
///
/// fn main() -> io::Result<()> {
/// let f = File::open("foo.txt")?;
///
/// // read at most five bytes
/// let handle = f.take(5);
///
/// println!("limit: {}", handle.limit());
/// Ok(())
/// }
/// ```
#[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])?;
self.limit -= n as u64;
Ok(n)
}
unsafe fn initializer(&self) -> Initializer {
self.inner.initializer()
}
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
// Pass in a reservation_size closure that respects the current value
// of limit for each read. If we hit the read limit, this prevents the
// final zero-byte read from allocating again.
read_to_end_with_reservation(self, buf, |self_| cmp::min(self_.limit, 32) as usize)
}
}
#[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);
}
}
/// An iterator over `u8` values of a reader.
///
/// This struct is generally created by calling [`bytes`] on a reader.
/// Please see the documentation of [`bytes`] for more details.
///
/// [`bytes`]: trait.Read.html#method.bytes
#[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)),
};
}
}
}
/// 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`]: trait.BufRead.html#method.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`]: trait.BufRead.html#method.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))
}
}
}
#[cfg(test)]
mod tests {
use crate::cmp;
use crate::io::prelude::*;
use super::{Cursor, SeekFrom, repeat};
use crate::io::{self, IoSlice, IoSliceMut};
use crate::mem;
use crate::ops::Deref;
#[test]
#[cfg_attr(target_os = "emscripten", ignore)]
fn read_until() {
let mut buf = Cursor::new(&b"12"[..]);
let mut v = Vec::new();
assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
assert_eq!(v, b"12");
let mut buf = Cursor::new(&b"1233"[..]);
let mut v = Vec::new();
assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
assert_eq!(v, b"123");
v.truncate(0);
assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
assert_eq!(v, b"3");
v.truncate(0);
assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
assert_eq!(v, []);
}
#[test]
fn split() {
let buf = Cursor::new(&b"12"[..]);
let mut s = buf.split(b'3');
assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
assert!(s.next().is_none());
let buf = Cursor::new(&b"1233"[..]);
let mut s = buf.split(b'3');
assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
assert_eq!(s.next().unwrap().unwrap(), vec![]);
assert!(s.next().is_none());
}
#[test]
fn read_line() {
let mut buf = Cursor::new(&b"12"[..]);
let mut v = String::new();
assert_eq!(buf.read_line(&mut v).unwrap(), 2);
assert_eq!(v, "12");
let mut buf = Cursor::new(&b"12\n\n"[..]);
let mut v = String::new();
assert_eq!(buf.read_line(&mut v).unwrap(), 3);
assert_eq!(v, "12\n");
v.truncate(0);
assert_eq!(buf.read_line(&mut v).unwrap(), 1);
assert_eq!(v, "\n");
v.truncate(0);
assert_eq!(buf.read_line(&mut v).unwrap(), 0);
assert_eq!(v, "");
}
#[test]
fn lines() {
let buf = Cursor::new(&b"12\r"[..]);
let mut s = buf.lines();
assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
assert!(s.next().is_none());
let buf = Cursor::new(&b"12\r\n\n"[..]);
let mut s = buf.lines();
assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
assert_eq!(s.next().unwrap().unwrap(), "".to_string());
assert!(s.next().is_none());
}
#[test]
fn read_to_end() {
let mut c = Cursor::new(&b""[..]);
let mut v = Vec::new();
assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
assert_eq!(v, []);
let mut c = Cursor::new(&b"1"[..]);
let mut v = Vec::new();
assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
assert_eq!(v, b"1");
let cap = 1024 * 1024;
let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
let mut v = Vec::new();
let (a, b) = data.split_at(data.len() / 2);
assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
assert_eq!(v, data);
}
#[test]
fn read_to_string() {
let mut c = Cursor::new(&b""[..]);
let mut v = String::new();
assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
assert_eq!(v, "");
let mut c = Cursor::new(&b"1"[..]);
let mut v = String::new();
assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
assert_eq!(v, "1");
let mut c = Cursor::new(&b"\xff"[..]);
let mut v = String::new();
assert!(c.read_to_string(&mut v).is_err());
}
#[test]
fn read_exact() {
let mut buf = [0; 4];
let mut c = Cursor::new(&b""[..]);
assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
io::ErrorKind::UnexpectedEof);
let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
c.read_exact(&mut buf).unwrap();
assert_eq!(&buf, b"1234");
c.read_exact(&mut buf).unwrap();
assert_eq!(&buf, b"5678");
assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
io::ErrorKind::UnexpectedEof);
}
#[test]
fn read_exact_slice() {
let mut buf = [0; 4];
let mut c = &b""[..];
assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
io::ErrorKind::UnexpectedEof);
let mut c = &b"123"[..];
assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
io::ErrorKind::UnexpectedEof);
// make sure the optimized (early returning) method is being used
assert_eq!(&buf, &[0; 4]);
let mut c = &b"1234"[..];
c.read_exact(&mut buf).unwrap();
assert_eq!(&buf, b"1234");
let mut c = &b"56789"[..];
c.read_exact(&mut buf).unwrap();
assert_eq!(&buf, b"5678");
assert_eq!(c, b"9");
}
#[test]
fn take_eof() {
struct R;
impl Read for R {
fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
Err(io::Error::new(io::ErrorKind::Other, ""))
}
}
impl BufRead for R {
fn fill_buf(&mut self) -> io::Result<&[u8]> {
Err(io::Error::new(io::ErrorKind::Other, ""))
}
fn consume(&mut self, _amt: usize) { }
}
let mut buf = [0; 1];
assert_eq!(0, R.take(0).read(&mut buf).unwrap());
assert_eq!(b"", R.take(0).fill_buf().unwrap());
}
fn cmp_bufread<Br1: BufRead, Br2: BufRead>(mut br1: Br1, mut br2: Br2, exp: &[u8]) {
let mut cat = Vec::new();
loop {
let consume = {
let buf1 = br1.fill_buf().unwrap();
let buf2 = br2.fill_buf().unwrap();
let minlen = if buf1.len() < buf2.len() { buf1.len() } else { buf2.len() };
assert_eq!(buf1[..minlen], buf2[..minlen]);
cat.extend_from_slice(&buf1[..minlen]);
minlen
};
if consume == 0 {
break;
}
br1.consume(consume);
br2.consume(consume);
}
assert_eq!(br1.fill_buf().unwrap().len(), 0);
assert_eq!(br2.fill_buf().unwrap().len(), 0);
assert_eq!(&cat[..], &exp[..])
}
#[test]
fn chain_bufread() {
let testdata = b"ABCDEFGHIJKL";
let chain1 = (&testdata[..3]).chain(&testdata[3..6])
.chain(&testdata[6..9])
.chain(&testdata[9..]);
let chain2 = (&testdata[..4]).chain(&testdata[4..8])
.chain(&testdata[8..]);
cmp_bufread(chain1, chain2, &testdata[..]);
}
#[test]
fn chain_zero_length_read_is_not_eof() {
let a = b"A";
let b = b"B";
let mut s = String::new();
let mut chain = (&a[..]).chain(&b[..]);
chain.read(&mut []).unwrap();
chain.read_to_string(&mut s).unwrap();
assert_eq!("AB", s);
}
#[bench]
#[cfg_attr(target_os = "emscripten", ignore)]
fn bench_read_to_end(b: &mut test::Bencher) {
b.iter(|| {
let mut lr = repeat(1).take(10000000);
let mut vec = Vec::with_capacity(1024);
super::read_to_end(&mut lr, &mut vec)
});
}
#[test]
fn seek_len() -> io::Result<()> {
let mut c = Cursor::new(vec![0; 15]);
assert_eq!(c.stream_len()?, 15);
c.seek(SeekFrom::End(0))?;
let old_pos = c.stream_position()?;
assert_eq!(c.stream_len()?, 15);
assert_eq!(c.stream_position()?, old_pos);
c.seek(SeekFrom::Start(7))?;
c.seek(SeekFrom::Current(2))?;
let old_pos = c.stream_position()?;
assert_eq!(c.stream_len()?, 15);
assert_eq!(c.stream_position()?, old_pos);
Ok(())
}
#[test]
fn seek_position() -> io::Result<()> {
// All `asserts` are duplicated here to make sure the method does not
// change anything about the seek state.
let mut c = Cursor::new(vec![0; 15]);
assert_eq!(c.stream_position()?, 0);
assert_eq!(c.stream_position()?, 0);
c.seek(SeekFrom::End(0))?;
assert_eq!(c.stream_position()?, 15);
assert_eq!(c.stream_position()?, 15);
c.seek(SeekFrom::Start(7))?;
c.seek(SeekFrom::Current(2))?;
assert_eq!(c.stream_position()?, 9);
assert_eq!(c.stream_position()?, 9);
c.seek(SeekFrom::End(-3))?;
c.seek(SeekFrom::Current(1))?;
c.seek(SeekFrom::Current(-5))?;
assert_eq!(c.stream_position()?, 8);
assert_eq!(c.stream_position()?, 8);
Ok(())
}
// A simple example reader which uses the default implementation of
// read_to_end.
struct ExampleSliceReader<'a> {
slice: &'a [u8],
}
impl<'a> Read for ExampleSliceReader<'a> {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
let len = cmp::min(self.slice.len(), buf.len());
buf[..len].copy_from_slice(&self.slice[..len]);
self.slice = &self.slice[len..];
Ok(len)
}
}
#[test]
fn test_read_to_end_capacity() -> io::Result<()> {
let input = &b"foo"[..];
// read_to_end() generally needs to over-allocate, both for efficiency
// and so that it can distinguish EOF. Assert that this is the case
// with this simple ExampleSliceReader struct, which uses the default
// implementation of read_to_end. Even though vec1 is allocated with
// exactly enough capacity for the read, read_to_end will allocate more
// space here.
let mut vec1 = Vec::with_capacity(input.len());
ExampleSliceReader { slice: input }.read_to_end(&mut vec1)?;
assert_eq!(vec1.len(), input.len());
assert!(vec1.capacity() > input.len(), "allocated more");
// However, std::io::Take includes an implementation of read_to_end
// that will not allocate when the limit has already been reached. In
// this case, vec2 never grows.
let mut vec2 = Vec::with_capacity(input.len());
ExampleSliceReader { slice: input }
.take(input.len() as u64)
.read_to_end(&mut vec2)?;
assert_eq!(vec2.len(), input.len());
assert_eq!(vec2.capacity(), input.len(), "did not allocate more");
Ok(())
}
#[test]
fn io_slice_mut_advance() {
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),
][..];
// Only in a single buffer..
bufs = IoSliceMut::advance(mem::replace(&mut bufs, &mut []), 1);
assert_eq!(bufs[0].deref(), [1; 7].as_ref());
assert_eq!(bufs[1].deref(), [2; 16].as_ref());
assert_eq!(bufs[2].deref(), [3; 8].as_ref());
// Removing a buffer, leaving others as is.
bufs = IoSliceMut::advance(mem::replace(&mut bufs, &mut []), 7);
assert_eq!(bufs[0].deref(), [2; 16].as_ref());
assert_eq!(bufs[1].deref(), [3; 8].as_ref());
// Removing a buffer and removing from the next buffer.
bufs = IoSliceMut::advance(mem::replace(&mut bufs, &mut []), 18);
assert_eq!(bufs[0].deref(), [3; 6].as_ref());
}
#[test]
fn io_slice_mut_advance_empty_slice() {
let mut empty_bufs = &mut [][..];
// Shouldn't panic.
IoSliceMut::advance(&mut empty_bufs, 1);
}
#[test]
fn io_slice_mut_advance_beyond_total_length() {
let mut buf1 = [1; 8];
let mut bufs = &mut [IoSliceMut::new(&mut buf1)][..];
// Going beyond the total length should be ok.
bufs = IoSliceMut::advance(mem::replace(&mut bufs, &mut []), 9);
assert!(bufs.is_empty());
}
#[test]
fn io_slice_advance() {
let mut buf1 = [1; 8];
let mut buf2 = [2; 16];
let mut buf3 = [3; 8];
let mut bufs =
&mut [IoSlice::new(&mut buf1), IoSlice::new(&mut buf2), IoSlice::new(&mut buf3)][..];
// Only in a single buffer..
bufs = IoSlice::advance(mem::replace(&mut bufs, &mut []), 1);
assert_eq!(bufs[0].deref(), [1; 7].as_ref());
assert_eq!(bufs[1].deref(), [2; 16].as_ref());
assert_eq!(bufs[2].deref(), [3; 8].as_ref());
// Removing a buffer, leaving others as is.
bufs = IoSlice::advance(mem::replace(&mut bufs, &mut []), 7);
assert_eq!(bufs[0].deref(), [2; 16].as_ref());
assert_eq!(bufs[1].deref(), [3; 8].as_ref());
// Removing a buffer and removing from the next buffer.
bufs = IoSlice::advance(mem::replace(&mut bufs, &mut []), 18);
assert_eq!(bufs[0].deref(), [3; 6].as_ref());
}
#[test]
fn io_slice_advance_empty_slice() {
let mut empty_bufs = &mut [][..];
// Shouldn't panic.
IoSlice::advance(&mut empty_bufs, 1);
}
#[test]
fn io_slice_advance_beyond_total_length() {
let mut buf1 = [1; 8];
let mut bufs = &mut [IoSlice::new(&mut buf1)][..];
// Going beyond the total length should be ok.
bufs = IoSlice::advance(mem::replace(&mut bufs, &mut []), 9);
assert!(bufs.is_empty());
}
}