1 //! Traits, helpers, and type definitions for core I/O functionality.
3 //! The `std::io` module contains a number of common things you'll need
4 //! when doing input and output. The most core part of this module is
5 //! the [`Read`] and [`Write`] traits, which provide the
6 //! most general interface for reading and writing input and output.
10 //! Because they are traits, [`Read`] and [`Write`] are implemented by a number
11 //! of other types, and you can implement them for your types too. As such,
12 //! you'll see a few different types of I/O throughout the documentation in
13 //! this module: [`File`]s, [`TcpStream`]s, and sometimes even [`Vec<T>`]s. For
14 //! example, [`Read`] adds a [`read`][`Read::read`] method, which we can use on
19 //! use std::io::prelude::*;
20 //! use std::fs::File;
22 //! fn main() -> io::Result<()> {
23 //! let mut f = File::open("foo.txt")?;
24 //! let mut buffer = [0; 10];
26 //! // read up to 10 bytes
27 //! let n = f.read(&mut buffer)?;
29 //! println!("The bytes: {:?}", &buffer[..n]);
34 //! [`Read`] and [`Write`] are so important, implementors of the two traits have a
35 //! nickname: readers and writers. So you'll sometimes see 'a reader' instead
36 //! of 'a type that implements the [`Read`] trait'. Much easier!
38 //! ## Seek and BufRead
40 //! Beyond that, there are two important traits that are provided: [`Seek`]
41 //! and [`BufRead`]. Both of these build on top of a reader to control
42 //! how the reading happens. [`Seek`] lets you control where the next byte is
47 //! use std::io::prelude::*;
48 //! use std::io::SeekFrom;
49 //! use std::fs::File;
51 //! fn main() -> io::Result<()> {
52 //! let mut f = File::open("foo.txt")?;
53 //! let mut buffer = [0; 10];
55 //! // skip to the last 10 bytes of the file
56 //! f.seek(SeekFrom::End(-10))?;
58 //! // read up to 10 bytes
59 //! let n = f.read(&mut buffer)?;
61 //! println!("The bytes: {:?}", &buffer[..n]);
66 //! [`BufRead`] uses an internal buffer to provide a number of other ways to read, but
67 //! to show it off, we'll need to talk about buffers in general. Keep reading!
69 //! ## BufReader and BufWriter
71 //! Byte-based interfaces are unwieldy and can be inefficient, as we'd need to be
72 //! making near-constant calls to the operating system. To help with this,
73 //! `std::io` comes with two structs, [`BufReader`] and [`BufWriter`], which wrap
74 //! readers and writers. The wrapper uses a buffer, reducing the number of
75 //! calls and providing nicer methods for accessing exactly what you want.
77 //! For example, [`BufReader`] works with the [`BufRead`] trait to add extra
78 //! methods to any reader:
82 //! use std::io::prelude::*;
83 //! use std::io::BufReader;
84 //! use std::fs::File;
86 //! fn main() -> io::Result<()> {
87 //! let f = File::open("foo.txt")?;
88 //! let mut reader = BufReader::new(f);
89 //! let mut buffer = String::new();
91 //! // read a line into buffer
92 //! reader.read_line(&mut buffer)?;
94 //! println!("{}", buffer);
99 //! [`BufWriter`] doesn't add any new ways of writing; it just buffers every call
100 //! to [`write`][`Write::write`]:
104 //! use std::io::prelude::*;
105 //! use std::io::BufWriter;
106 //! use std::fs::File;
108 //! fn main() -> io::Result<()> {
109 //! let f = File::create("foo.txt")?;
111 //! let mut writer = BufWriter::new(f);
113 //! // write a byte to the buffer
114 //! writer.write(&[42])?;
116 //! } // the buffer is flushed once writer goes out of scope
122 //! ## Standard input and output
124 //! A very common source of input is standard input:
129 //! fn main() -> io::Result<()> {
130 //! let mut input = String::new();
132 //! io::stdin().read_line(&mut input)?;
134 //! println!("You typed: {}", input.trim());
139 //! Note that you cannot use the [`?` operator] in functions that do not return
140 //! a [`Result<T, E>`][`Result`]. Instead, you can call [`.unwrap()`]
141 //! or `match` on the return value to catch any possible errors:
146 //! let mut input = String::new();
148 //! io::stdin().read_line(&mut input).unwrap();
151 //! And a very common source of output is standard output:
155 //! use std::io::prelude::*;
157 //! fn main() -> io::Result<()> {
158 //! io::stdout().write(&[42])?;
163 //! Of course, using [`io::stdout`] directly is less common than something like
166 //! ## Iterator types
168 //! A large number of the structures provided by `std::io` are for various
169 //! ways of iterating over I/O. For example, [`Lines`] is used to split over
174 //! use std::io::prelude::*;
175 //! use std::io::BufReader;
176 //! use std::fs::File;
178 //! fn main() -> io::Result<()> {
179 //! let f = File::open("foo.txt")?;
180 //! let reader = BufReader::new(f);
182 //! for line in reader.lines() {
183 //! println!("{}", line?);
191 //! There are a number of [functions][functions-list] that offer access to various
192 //! features. For example, we can use three of these functions to copy everything
193 //! from standard input to standard output:
198 //! fn main() -> io::Result<()> {
199 //! io::copy(&mut io::stdin(), &mut io::stdout())?;
204 //! [functions-list]: #functions-1
208 //! Last, but certainly not least, is [`io::Result`]. This type is used
209 //! as the return type of many `std::io` functions that can cause an error, and
210 //! can be returned from your own functions as well. Many of the examples in this
211 //! module use the [`?` operator]:
216 //! fn read_input() -> io::Result<()> {
217 //! let mut input = String::new();
219 //! io::stdin().read_line(&mut input)?;
221 //! println!("You typed: {}", input.trim());
227 //! The return type of `read_input()`, [`io::Result<()>`][`io::Result`], is a very
228 //! common type for functions which don't have a 'real' return value, but do want to
229 //! return errors if they happen. In this case, the only purpose of this function is
230 //! to read the line and print it, so we use `()`.
232 //! ## Platform-specific behavior
234 //! Many I/O functions throughout the standard library are documented to indicate
235 //! what various library or syscalls they are delegated to. This is done to help
236 //! applications both understand what's happening under the hood as well as investigate
237 //! any possibly unclear semantics. Note, however, that this is informative, not a binding
238 //! contract. The implementation of many of these functions are subject to change over
239 //! time and may call fewer or more syscalls/library functions.
241 //! [`File`]: crate::fs::File
242 //! [`TcpStream`]: crate::net::TcpStream
243 //! [`io::stdout`]: stdout
244 //! [`io::Result`]: self::Result
245 //! [`?` operator]: ../../book/appendix-02-operators.html
246 //! [`Result`]: crate::result::Result
247 //! [`.unwrap()`]: crate::result::Result::unwrap
249 #![stable(feature = "rust1", since = "1.0.0")]
256 use crate::ops::{Deref, DerefMut};
261 use crate::sys_common::memchr;
263 #[stable(feature = "rust1", since = "1.0.0")]
264 pub use self::buffered::IntoInnerError;
265 #[stable(feature = "rust1", since = "1.0.0")]
266 pub use self::buffered::{BufReader, BufWriter, LineWriter};
267 #[stable(feature = "rust1", since = "1.0.0")]
268 pub use self::copy::copy;
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub use self::cursor::Cursor;
271 #[stable(feature = "rust1", since = "1.0.0")]
272 pub use self::error::{Error, ErrorKind, Result};
273 #[unstable(feature = "internal_output_capture", issue = "none")]
274 #[doc(no_inline, hidden)]
275 pub use self::stdio::set_output_capture;
276 #[stable(feature = "rust1", since = "1.0.0")]
277 pub use self::stdio::{stderr, stdin, stdout, Stderr, Stdin, Stdout};
278 #[stable(feature = "rust1", since = "1.0.0")]
279 pub use self::stdio::{StderrLock, StdinLock, StdoutLock};
280 #[unstable(feature = "print_internals", issue = "none")]
281 pub use self::stdio::{_eprint, _print};
282 #[stable(feature = "rust1", since = "1.0.0")]
283 pub use self::util::{empty, repeat, sink, Empty, Repeat, Sink};
294 const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
296 pub(crate) fn cleanup() {
301 buf: &'a mut Vec<u8>,
305 impl Drop for Guard<'_> {
308 self.buf.set_len(self.len);
313 // A few methods below (read_to_string, read_line) will append data into a
314 // `String` buffer, but we need to be pretty careful when doing this. The
315 // implementation will just call `.as_mut_vec()` and then delegate to a
316 // byte-oriented reading method, but we must ensure that when returning we never
317 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
319 // To this end, we use an RAII guard (to protect against panics) which updates
320 // the length of the string when it is dropped. This guard initially truncates
321 // the string to the prior length and only after we've validated that the
322 // new contents are valid UTF-8 do we allow it to set a longer length.
324 // The unsafety in this function is twofold:
326 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
328 // 2. We're passing a raw buffer to the function `f`, and it is expected that
329 // the function only *appends* bytes to the buffer. We'll get undefined
330 // behavior if existing bytes are overwritten to have non-UTF-8 data.
331 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
333 F: FnOnce(&mut Vec<u8>) -> Result<usize>,
336 let mut g = Guard { len: buf.len(), buf: buf.as_mut_vec() };
338 if str::from_utf8(&g.buf[g.len..]).is_err() {
340 Err(Error::new_const(ErrorKind::InvalidData, &"stream did not contain valid UTF-8"))
349 // This uses an adaptive system to extend the vector when it fills. We want to
350 // avoid paying to allocate and zero a huge chunk of memory if the reader only
351 // has 4 bytes while still making large reads if the reader does have a ton
352 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
353 // time is 4,500 times (!) slower than a default reservation size of 32 if the
354 // reader has a very small amount of data to return.
356 // Because we're extending the buffer with uninitialized data for trusted
357 // readers, we need to make sure to truncate that if any of this panics.
358 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
359 read_to_end_with_reservation(r, buf, |_| 32)
362 fn read_to_end_with_reservation<R, F>(
365 mut reservation_size: F,
369 F: FnMut(&R) -> usize,
371 let start_len = buf.len();
372 let mut g = Guard { len: buf.len(), buf };
374 if g.len == g.buf.len() {
376 // FIXME(danielhenrymantilla): #42788
378 // - This creates a (mut) reference to a slice of
379 // _uninitialized_ integers, which is **undefined behavior**
381 // - Only the standard library gets to soundly "ignore" this,
382 // based on its privileged knowledge of unstable rustc
384 g.buf.reserve(reservation_size(r));
385 let capacity = g.buf.capacity();
386 g.buf.set_len(capacity);
387 r.initializer().initialize(&mut g.buf[g.len..]);
391 let buf = &mut g.buf[g.len..];
393 Ok(0) => return Ok(g.len - start_len),
395 // We can't allow bogus values from read. If it is too large, the returned vec could have its length
396 // set past its capacity, or if it overflows the vec could be shortened which could create an invalid
397 // string if this is called via read_to_string.
398 assert!(n <= buf.len());
401 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
402 Err(e) => return Err(e),
407 pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
409 F: FnOnce(&mut [u8]) -> Result<usize>,
411 let buf = bufs.iter_mut().find(|b| !b.is_empty()).map_or(&mut [][..], |b| &mut **b);
415 pub(crate) fn default_write_vectored<F>(write: F, bufs: &[IoSlice<'_>]) -> Result<usize>
417 F: FnOnce(&[u8]) -> Result<usize>,
419 let buf = bufs.iter().find(|b| !b.is_empty()).map_or(&[][..], |b| &**b);
423 pub(crate) fn default_read_exact<R: Read + ?Sized>(this: &mut R, mut buf: &mut [u8]) -> Result<()> {
424 while !buf.is_empty() {
425 match this.read(buf) {
431 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
432 Err(e) => return Err(e),
436 Err(Error::new_const(ErrorKind::UnexpectedEof, &"failed to fill whole buffer"))
442 /// The `Read` trait allows for reading bytes from a source.
444 /// Implementors of the `Read` trait are called 'readers'.
446 /// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
447 /// will attempt to pull bytes from this source into a provided buffer. A
448 /// number of other methods are implemented in terms of [`read()`], giving
449 /// implementors a number of ways to read bytes while only needing to implement
452 /// Readers are intended to be composable with one another. Many implementors
453 /// throughout [`std::io`] take and provide types which implement the `Read`
456 /// Please note that each call to [`read()`] may involve a system call, and
457 /// therefore, using something that implements [`BufRead`], such as
458 /// [`BufReader`], will be more efficient.
462 /// [`File`]s implement `Read`:
466 /// use std::io::prelude::*;
467 /// use std::fs::File;
469 /// fn main() -> io::Result<()> {
470 /// let mut f = File::open("foo.txt")?;
471 /// let mut buffer = [0; 10];
473 /// // read up to 10 bytes
474 /// f.read(&mut buffer)?;
476 /// let mut buffer = Vec::new();
477 /// // read the whole file
478 /// f.read_to_end(&mut buffer)?;
480 /// // read into a String, so that you don't need to do the conversion.
481 /// let mut buffer = String::new();
482 /// f.read_to_string(&mut buffer)?;
484 /// // and more! See the other methods for more details.
489 /// Read from [`&str`] because [`&[u8]`][prim@slice] implements `Read`:
493 /// use std::io::prelude::*;
495 /// fn main() -> io::Result<()> {
496 /// let mut b = "This string will be read".as_bytes();
497 /// let mut buffer = [0; 10];
499 /// // read up to 10 bytes
500 /// b.read(&mut buffer)?;
502 /// // etc... it works exactly as a File does!
507 /// [`read()`]: Read::read
508 /// [`&str`]: prim@str
509 /// [`std::io`]: self
510 /// [`File`]: crate::fs::File
511 #[stable(feature = "rust1", since = "1.0.0")]
512 #[cfg_attr(bootstrap, doc(spotlight))]
513 #[cfg_attr(not(bootstrap), doc(notable_trait))]
515 /// Pull some bytes from this source into the specified buffer, returning
516 /// how many bytes were read.
518 /// This function does not provide any guarantees about whether it blocks
519 /// waiting for data, but if an object needs to block for a read and cannot,
520 /// it will typically signal this via an [`Err`] return value.
522 /// If the return value of this method is [`Ok(n)`], then implementations must
523 /// guarantee that `0 <= n <= buf.len()`. A nonzero `n` value indicates
524 /// that the buffer `buf` has been filled in with `n` bytes of data from this
525 /// source. If `n` is `0`, then it can indicate one of two scenarios:
527 /// 1. This reader has reached its "end of file" and will likely no longer
528 /// be able to produce bytes. Note that this does not mean that the
529 /// reader will *always* no longer be able to produce bytes.
530 /// 2. The buffer specified was 0 bytes in length.
532 /// It is not an error if the returned value `n` is smaller than the buffer size,
533 /// even when the reader is not at the end of the stream yet.
534 /// This may happen for example because fewer bytes are actually available right now
535 /// (e. g. being close to end-of-file) or because read() was interrupted by a signal.
537 /// As this trait is safe to implement, callers cannot rely on `n <= buf.len()` for safety.
538 /// Extra care needs to be taken when `unsafe` functions are used to access the read bytes.
539 /// Callers have to ensure that no unchecked out-of-bounds accesses are possible even if
542 /// No guarantees are provided about the contents of `buf` when this
543 /// function is called, implementations cannot rely on any property of the
544 /// contents of `buf` being true. It is recommended that *implementations*
545 /// only write data to `buf` instead of reading its contents.
547 /// Correspondingly, however, *callers* of this method may not assume any guarantees
548 /// about how the implementation uses `buf`. The trait is safe to implement,
549 /// so it is possible that the code that's supposed to write to the buffer might also read
550 /// from it. It is your responsibility to make sure that `buf` is initialized
551 /// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
552 /// obtains via [`MaybeUninit<T>`]) is not safe, and can lead to undefined behavior.
554 /// [`MaybeUninit<T>`]: crate::mem::MaybeUninit
558 /// If this function encounters any form of I/O or other error, an error
559 /// variant will be returned. If an error is returned then it must be
560 /// guaranteed that no bytes were read.
562 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
563 /// operation should be retried if there is nothing else to do.
567 /// [`File`]s implement `Read`:
570 /// [`File`]: crate::fs::File
574 /// use std::io::prelude::*;
575 /// use std::fs::File;
577 /// fn main() -> io::Result<()> {
578 /// let mut f = File::open("foo.txt")?;
579 /// let mut buffer = [0; 10];
581 /// // read up to 10 bytes
582 /// let n = f.read(&mut buffer[..])?;
584 /// println!("The bytes: {:?}", &buffer[..n]);
588 #[stable(feature = "rust1", since = "1.0.0")]
589 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
591 /// Like `read`, except that it reads into a slice of buffers.
593 /// Data is copied to fill each buffer in order, with the final buffer
594 /// written to possibly being only partially filled. This method must
595 /// behave equivalently to a single call to `read` with concatenated
598 /// The default implementation calls `read` with either the first nonempty
599 /// buffer provided, or an empty one if none exists.
600 #[stable(feature = "iovec", since = "1.36.0")]
601 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
602 default_read_vectored(|b| self.read(b), bufs)
605 /// Determines if this `Read`er has an efficient `read_vectored`
608 /// If a `Read`er does not override the default `read_vectored`
609 /// implementation, code using it may want to avoid the method all together
610 /// and coalesce writes into a single buffer for higher performance.
612 /// The default implementation returns `false`.
613 #[unstable(feature = "can_vector", issue = "69941")]
614 fn is_read_vectored(&self) -> bool {
618 /// Determines if this `Read`er can work with buffers of uninitialized
621 /// The default implementation returns an initializer which will zero
624 /// If a `Read`er guarantees that it can work properly with uninitialized
625 /// memory, it should call [`Initializer::nop()`]. See the documentation for
626 /// [`Initializer`] for details.
628 /// The behavior of this method must be independent of the state of the
629 /// `Read`er - the method only takes `&self` so that it can be used through
634 /// This method is unsafe because a `Read`er could otherwise return a
635 /// non-zeroing `Initializer` from another `Read` type without an `unsafe`
637 #[unstable(feature = "read_initializer", issue = "42788")]
639 unsafe fn initializer(&self) -> Initializer {
640 Initializer::zeroing()
643 /// Read all bytes until EOF in this source, placing them into `buf`.
645 /// All bytes read from this source will be appended to the specified buffer
646 /// `buf`. This function will continuously call [`read()`] to append more data to
647 /// `buf` until [`read()`] returns either [`Ok(0)`] or an error of
648 /// non-[`ErrorKind::Interrupted`] kind.
650 /// If successful, this function will return the total number of bytes read.
654 /// If this function encounters an error of the kind
655 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
658 /// If any other read error is encountered then this function immediately
659 /// returns. Any bytes which have already been read will be appended to
664 /// [`File`]s implement `Read`:
666 /// [`read()`]: Read::read
668 /// [`File`]: crate::fs::File
672 /// use std::io::prelude::*;
673 /// use std::fs::File;
675 /// fn main() -> io::Result<()> {
676 /// let mut f = File::open("foo.txt")?;
677 /// let mut buffer = Vec::new();
679 /// // read the whole file
680 /// f.read_to_end(&mut buffer)?;
685 /// (See also the [`std::fs::read`] convenience function for reading from a
688 /// [`std::fs::read`]: crate::fs::read
689 #[stable(feature = "rust1", since = "1.0.0")]
690 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
691 read_to_end(self, buf)
694 /// Read all bytes until EOF in this source, appending them to `buf`.
696 /// If successful, this function returns the number of bytes which were read
697 /// and appended to `buf`.
701 /// If the data in this stream is *not* valid UTF-8 then an error is
702 /// returned and `buf` is unchanged.
704 /// See [`read_to_end`] for other error semantics.
706 /// [`read_to_end`]: Read::read_to_end
710 /// [`File`]s implement `Read`:
712 /// [`File`]: crate::fs::File
716 /// use std::io::prelude::*;
717 /// use std::fs::File;
719 /// fn main() -> io::Result<()> {
720 /// let mut f = File::open("foo.txt")?;
721 /// let mut buffer = String::new();
723 /// f.read_to_string(&mut buffer)?;
728 /// (See also the [`std::fs::read_to_string`] convenience function for
729 /// reading from a file.)
731 /// [`std::fs::read_to_string`]: crate::fs::read_to_string
732 #[stable(feature = "rust1", since = "1.0.0")]
733 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
734 // Note that we do *not* call `.read_to_end()` here. We are passing
735 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
736 // method to fill it up. An arbitrary implementation could overwrite the
737 // entire contents of the vector, not just append to it (which is what
738 // we are expecting).
740 // To prevent extraneously checking the UTF-8-ness of the entire buffer
741 // we pass it to our hardcoded `read_to_end` implementation which we
742 // know is guaranteed to only read data into the end of the buffer.
743 append_to_string(buf, |b| read_to_end(self, b))
746 /// Read the exact number of bytes required to fill `buf`.
748 /// This function reads as many bytes as necessary to completely fill the
749 /// specified buffer `buf`.
751 /// No guarantees are provided about the contents of `buf` when this
752 /// function is called, implementations cannot rely on any property of the
753 /// contents of `buf` being true. It is recommended that implementations
754 /// only write data to `buf` instead of reading its contents. The
755 /// documentation on [`read`] has a more detailed explanation on this
760 /// If this function encounters an error of the kind
761 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
764 /// If this function encounters an "end of file" before completely filling
765 /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
766 /// The contents of `buf` are unspecified in this case.
768 /// If any other read error is encountered then this function immediately
769 /// returns. The contents of `buf` are unspecified in this case.
771 /// If this function returns an error, it is unspecified how many bytes it
772 /// has read, but it will never read more than would be necessary to
773 /// completely fill the buffer.
777 /// [`File`]s implement `Read`:
779 /// [`read`]: Read::read
780 /// [`File`]: crate::fs::File
784 /// use std::io::prelude::*;
785 /// use std::fs::File;
787 /// fn main() -> io::Result<()> {
788 /// let mut f = File::open("foo.txt")?;
789 /// let mut buffer = [0; 10];
791 /// // read exactly 10 bytes
792 /// f.read_exact(&mut buffer)?;
796 #[stable(feature = "read_exact", since = "1.6.0")]
797 fn read_exact(&mut self, buf: &mut [u8]) -> Result<()> {
798 default_read_exact(self, buf)
801 /// Creates a "by reference" adaptor for this instance of `Read`.
803 /// The returned adaptor also implements `Read` and will simply borrow this
808 /// [`File`]s implement `Read`:
810 /// [`File`]: crate::fs::File
814 /// use std::io::Read;
815 /// use std::fs::File;
817 /// fn main() -> io::Result<()> {
818 /// let mut f = File::open("foo.txt")?;
819 /// let mut buffer = Vec::new();
820 /// let mut other_buffer = Vec::new();
823 /// let reference = f.by_ref();
825 /// // read at most 5 bytes
826 /// reference.take(5).read_to_end(&mut buffer)?;
828 /// } // drop our &mut reference so we can use f again
830 /// // original file still usable, read the rest
831 /// f.read_to_end(&mut other_buffer)?;
835 #[stable(feature = "rust1", since = "1.0.0")]
836 fn by_ref(&mut self) -> &mut Self
843 /// Transforms this `Read` instance to an [`Iterator`] over its bytes.
845 /// The returned type implements [`Iterator`] where the `Item` is
846 /// [`Result`]`<`[`u8`]`, `[`io::Error`]`>`.
847 /// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
848 /// otherwise. EOF is mapped to returning [`None`] from this iterator.
852 /// [`File`]s implement `Read`:
854 /// [`File`]: crate::fs::File
855 /// [`Result`]: crate::result::Result
856 /// [`io::Error`]: self::Error
860 /// use std::io::prelude::*;
861 /// use std::fs::File;
863 /// fn main() -> io::Result<()> {
864 /// let mut f = File::open("foo.txt")?;
866 /// for byte in f.bytes() {
867 /// println!("{}", byte.unwrap());
872 #[stable(feature = "rust1", since = "1.0.0")]
873 fn bytes(self) -> Bytes<Self>
877 Bytes { inner: self }
880 /// Creates an adaptor which will chain this stream with another.
882 /// The returned `Read` instance will first read all bytes from this object
883 /// until EOF is encountered. Afterwards the output is equivalent to the
884 /// output of `next`.
888 /// [`File`]s implement `Read`:
890 /// [`File`]: crate::fs::File
894 /// use std::io::prelude::*;
895 /// use std::fs::File;
897 /// fn main() -> io::Result<()> {
898 /// let mut f1 = File::open("foo.txt")?;
899 /// let mut f2 = File::open("bar.txt")?;
901 /// let mut handle = f1.chain(f2);
902 /// let mut buffer = String::new();
904 /// // read the value into a String. We could use any Read method here,
905 /// // this is just one example.
906 /// handle.read_to_string(&mut buffer)?;
910 #[stable(feature = "rust1", since = "1.0.0")]
911 fn chain<R: Read>(self, next: R) -> Chain<Self, R>
915 Chain { first: self, second: next, done_first: false }
918 /// Creates an adaptor which will read at most `limit` bytes from it.
920 /// This function returns a new instance of `Read` which will read at most
921 /// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
922 /// read errors will not count towards the number of bytes read and future
923 /// calls to [`read()`] may succeed.
927 /// [`File`]s implement `Read`:
929 /// [`File`]: crate::fs::File
931 /// [`read()`]: Read::read
935 /// use std::io::prelude::*;
936 /// use std::fs::File;
938 /// fn main() -> io::Result<()> {
939 /// let mut f = File::open("foo.txt")?;
940 /// let mut buffer = [0; 5];
942 /// // read at most five bytes
943 /// let mut handle = f.take(5);
945 /// handle.read(&mut buffer)?;
949 #[stable(feature = "rust1", since = "1.0.0")]
950 fn take(self, limit: u64) -> Take<Self>
954 Take { inner: self, limit }
958 /// Read all bytes from a [reader][Read] into a new [`String`].
960 /// This is a convenience function for [`Read::read_to_string`]. Using this
961 /// function avoids having to create a variable first and provides more type
962 /// safety since you can only get the buffer out if there were no errors. (If you
963 /// use [`Read::read_to_string`] you have to remember to check whether the read
964 /// succeeded because otherwise your buffer will be empty or only partially full.)
968 /// The downside of this function's increased ease of use and type safety is
969 /// that it gives you less control over performance. For example, you can't
970 /// pre-allocate memory like you can using [`String::with_capacity`] and
971 /// [`Read::read_to_string`]. Also, you can't re-use the buffer if an error
972 /// occurs while reading.
974 /// In many cases, this function's performance will be adequate and the ease of use
975 /// and type safety tradeoffs will be worth it. However, there are cases where you
976 /// need more control over performance, and in those cases you should definitely use
977 /// [`Read::read_to_string`] directly.
981 /// This function forces you to handle errors because the output (the `String`)
982 /// is wrapped in a [`Result`]. See [`Read::read_to_string`] for the errors
983 /// that can occur. If any error occurs, you will get an [`Err`], so you
984 /// don't have to worry about your buffer being empty or partially full.
989 /// #![feature(io_read_to_string)]
992 /// fn main() -> io::Result<()> {
993 /// let stdin = io::read_to_string(&mut io::stdin())?;
994 /// println!("Stdin was:");
995 /// println!("{}", stdin);
999 #[unstable(feature = "io_read_to_string", issue = "80218")]
1000 pub fn read_to_string<R: Read>(reader: &mut R) -> Result<String> {
1001 let mut buf = String::new();
1002 reader.read_to_string(&mut buf)?;
1006 /// A buffer type used with `Read::read_vectored`.
1008 /// It is semantically a wrapper around an `&mut [u8]`, but is guaranteed to be
1009 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1011 #[stable(feature = "iovec", since = "1.36.0")]
1012 #[repr(transparent)]
1013 pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
1015 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1016 unsafe impl<'a> Send for IoSliceMut<'a> {}
1018 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1019 unsafe impl<'a> Sync for IoSliceMut<'a> {}
1021 #[stable(feature = "iovec", since = "1.36.0")]
1022 impl<'a> fmt::Debug for IoSliceMut<'a> {
1023 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1024 fmt::Debug::fmt(self.0.as_slice(), fmt)
1028 impl<'a> IoSliceMut<'a> {
1029 /// Creates a new `IoSliceMut` wrapping a byte slice.
1033 /// Panics on Windows if the slice is larger than 4GB.
1034 #[stable(feature = "iovec", since = "1.36.0")]
1036 pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
1037 IoSliceMut(sys::io::IoSliceMut::new(buf))
1040 /// Advance the internal cursor of the slice.
1044 /// Elements in the slice may be modified if the cursor is not advanced to
1045 /// the end of the slice. For example if we have a slice of buffers with 2
1046 /// `IoSliceMut`s, both of length 8, and we advance the cursor by 10 bytes
1047 /// the first `IoSliceMut` will be untouched however the second will be
1048 /// modified to remove the first 2 bytes (10 - 8).
1053 /// #![feature(io_slice_advance)]
1055 /// use std::io::IoSliceMut;
1056 /// use std::ops::Deref;
1058 /// let mut buf1 = [1; 8];
1059 /// let mut buf2 = [2; 16];
1060 /// let mut buf3 = [3; 8];
1061 /// let mut bufs = &mut [
1062 /// IoSliceMut::new(&mut buf1),
1063 /// IoSliceMut::new(&mut buf2),
1064 /// IoSliceMut::new(&mut buf3),
1067 /// // Mark 10 bytes as read.
1068 /// bufs = IoSliceMut::advance(bufs, 10);
1069 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1070 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1072 #[unstable(feature = "io_slice_advance", issue = "62726")]
1074 pub fn advance<'b>(bufs: &'b mut [IoSliceMut<'a>], n: usize) -> &'b mut [IoSliceMut<'a>] {
1075 // Number of buffers to remove.
1077 // Total length of all the to be removed buffers.
1078 let mut accumulated_len = 0;
1079 for buf in bufs.iter() {
1080 if accumulated_len + buf.len() > n {
1083 accumulated_len += buf.len();
1088 let bufs = &mut bufs[remove..];
1089 if !bufs.is_empty() {
1090 bufs[0].0.advance(n - accumulated_len)
1096 #[stable(feature = "iovec", since = "1.36.0")]
1097 impl<'a> Deref for IoSliceMut<'a> {
1101 fn deref(&self) -> &[u8] {
1106 #[stable(feature = "iovec", since = "1.36.0")]
1107 impl<'a> DerefMut for IoSliceMut<'a> {
1109 fn deref_mut(&mut self) -> &mut [u8] {
1110 self.0.as_mut_slice()
1114 /// A buffer type used with `Write::write_vectored`.
1116 /// It is semantically a wrapper around an `&[u8]`, but is guaranteed to be
1117 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1119 #[stable(feature = "iovec", since = "1.36.0")]
1120 #[derive(Copy, Clone)]
1121 #[repr(transparent)]
1122 pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
1124 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1125 unsafe impl<'a> Send for IoSlice<'a> {}
1127 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1128 unsafe impl<'a> Sync for IoSlice<'a> {}
1130 #[stable(feature = "iovec", since = "1.36.0")]
1131 impl<'a> fmt::Debug for IoSlice<'a> {
1132 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1133 fmt::Debug::fmt(self.0.as_slice(), fmt)
1137 impl<'a> IoSlice<'a> {
1138 /// Creates a new `IoSlice` wrapping a byte slice.
1142 /// Panics on Windows if the slice is larger than 4GB.
1143 #[stable(feature = "iovec", since = "1.36.0")]
1145 pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
1146 IoSlice(sys::io::IoSlice::new(buf))
1149 /// Advance the internal cursor of the slice.
1153 /// Elements in the slice may be modified if the cursor is not advanced to
1154 /// the end of the slice. For example if we have a slice of buffers with 2
1155 /// `IoSlice`s, both of length 8, and we advance the cursor by 10 bytes the
1156 /// first `IoSlice` will be untouched however the second will be modified to
1157 /// remove the first 2 bytes (10 - 8).
1162 /// #![feature(io_slice_advance)]
1164 /// use std::io::IoSlice;
1165 /// use std::ops::Deref;
1167 /// let buf1 = [1; 8];
1168 /// let buf2 = [2; 16];
1169 /// let buf3 = [3; 8];
1170 /// let mut bufs = &mut [
1171 /// IoSlice::new(&buf1),
1172 /// IoSlice::new(&buf2),
1173 /// IoSlice::new(&buf3),
1176 /// // Mark 10 bytes as written.
1177 /// bufs = IoSlice::advance(bufs, 10);
1178 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1179 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1180 #[unstable(feature = "io_slice_advance", issue = "62726")]
1182 pub fn advance<'b>(bufs: &'b mut [IoSlice<'a>], n: usize) -> &'b mut [IoSlice<'a>] {
1183 // Number of buffers to remove.
1185 // Total length of all the to be removed buffers.
1186 let mut accumulated_len = 0;
1187 for buf in bufs.iter() {
1188 if accumulated_len + buf.len() > n {
1191 accumulated_len += buf.len();
1196 let bufs = &mut bufs[remove..];
1197 if !bufs.is_empty() {
1198 bufs[0].0.advance(n - accumulated_len)
1204 #[stable(feature = "iovec", since = "1.36.0")]
1205 impl<'a> Deref for IoSlice<'a> {
1209 fn deref(&self) -> &[u8] {
1214 /// A type used to conditionally initialize buffers passed to `Read` methods.
1215 #[unstable(feature = "read_initializer", issue = "42788")]
1217 pub struct Initializer(bool);
1220 /// Returns a new `Initializer` which will zero out buffers.
1221 #[unstable(feature = "read_initializer", issue = "42788")]
1223 pub fn zeroing() -> Initializer {
1227 /// Returns a new `Initializer` which will not zero out buffers.
1231 /// This may only be called by `Read`ers which guarantee that they will not
1232 /// read from buffers passed to `Read` methods, and that the return value of
1233 /// the method accurately reflects the number of bytes that have been
1234 /// written to the head of the buffer.
1235 #[unstable(feature = "read_initializer", issue = "42788")]
1237 pub unsafe fn nop() -> Initializer {
1241 /// Indicates if a buffer should be initialized.
1242 #[unstable(feature = "read_initializer", issue = "42788")]
1244 pub fn should_initialize(&self) -> bool {
1248 /// Initializes a buffer if necessary.
1249 #[unstable(feature = "read_initializer", issue = "42788")]
1251 pub fn initialize(&self, buf: &mut [u8]) {
1252 if self.should_initialize() {
1253 unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
1258 /// A trait for objects which are byte-oriented sinks.
1260 /// Implementors of the `Write` trait are sometimes called 'writers'.
1262 /// Writers are defined by two required methods, [`write`] and [`flush`]:
1264 /// * The [`write`] method will attempt to write some data into the object,
1265 /// returning how many bytes were successfully written.
1267 /// * The [`flush`] method is useful for adaptors and explicit buffers
1268 /// themselves for ensuring that all buffered data has been pushed out to the
1271 /// Writers are intended to be composable with one another. Many implementors
1272 /// throughout [`std::io`] take and provide types which implement the `Write`
1275 /// [`write`]: Write::write
1276 /// [`flush`]: Write::flush
1277 /// [`std::io`]: self
1282 /// use std::io::prelude::*;
1283 /// use std::fs::File;
1285 /// fn main() -> std::io::Result<()> {
1286 /// let data = b"some bytes";
1288 /// let mut pos = 0;
1289 /// let mut buffer = File::create("foo.txt")?;
1291 /// while pos < data.len() {
1292 /// let bytes_written = buffer.write(&data[pos..])?;
1293 /// pos += bytes_written;
1299 /// The trait also provides convenience methods like [`write_all`], which calls
1300 /// `write` in a loop until its entire input has been written.
1302 /// [`write_all`]: Write::write_all
1303 #[stable(feature = "rust1", since = "1.0.0")]
1304 #[cfg_attr(bootstrap, doc(spotlight))]
1305 #[cfg_attr(not(bootstrap), doc(notable_trait))]
1307 /// Write a buffer into this writer, returning how many bytes were written.
1309 /// This function will attempt to write the entire contents of `buf`, but
1310 /// the entire write may not succeed, or the write may also generate an
1311 /// error. A call to `write` represents *at most one* attempt to write to
1312 /// any wrapped object.
1314 /// Calls to `write` are not guaranteed to block waiting for data to be
1315 /// written, and a write which would otherwise block can be indicated through
1316 /// an [`Err`] variant.
1318 /// If the return value is [`Ok(n)`] then it must be guaranteed that
1319 /// `n <= buf.len()`. A return value of `0` typically means that the
1320 /// underlying object is no longer able to accept bytes and will likely not
1321 /// be able to in the future as well, or that the buffer provided is empty.
1325 /// Each call to `write` may generate an I/O error indicating that the
1326 /// operation could not be completed. If an error is returned then no bytes
1327 /// in the buffer were written to this writer.
1329 /// It is **not** considered an error if the entire buffer could not be
1330 /// written to this writer.
1332 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
1333 /// write operation should be retried if there is nothing else to do.
1338 /// use std::io::prelude::*;
1339 /// use std::fs::File;
1341 /// fn main() -> std::io::Result<()> {
1342 /// let mut buffer = File::create("foo.txt")?;
1344 /// // Writes some prefix of the byte string, not necessarily all of it.
1345 /// buffer.write(b"some bytes")?;
1351 #[stable(feature = "rust1", since = "1.0.0")]
1352 fn write(&mut self, buf: &[u8]) -> Result<usize>;
1354 /// Like [`write`], except that it writes from a slice of buffers.
1356 /// Data is copied from each buffer in order, with the final buffer
1357 /// read from possibly being only partially consumed. This method must
1358 /// behave as a call to [`write`] with the buffers concatenated would.
1360 /// The default implementation calls [`write`] with either the first nonempty
1361 /// buffer provided, or an empty one if none exists.
1363 /// [`write`]: Write::write
1364 #[stable(feature = "iovec", since = "1.36.0")]
1365 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
1366 default_write_vectored(|b| self.write(b), bufs)
1369 /// Determines if this `Write`r has an efficient [`write_vectored`]
1372 /// If a `Write`r does not override the default [`write_vectored`]
1373 /// implementation, code using it may want to avoid the method all together
1374 /// and coalesce writes into a single buffer for higher performance.
1376 /// The default implementation returns `false`.
1378 /// [`write_vectored`]: Write::write_vectored
1379 #[unstable(feature = "can_vector", issue = "69941")]
1380 fn is_write_vectored(&self) -> bool {
1384 /// Flush this output stream, ensuring that all intermediately buffered
1385 /// contents reach their destination.
1389 /// It is considered an error if not all bytes could be written due to
1390 /// I/O errors or EOF being reached.
1395 /// use std::io::prelude::*;
1396 /// use std::io::BufWriter;
1397 /// use std::fs::File;
1399 /// fn main() -> std::io::Result<()> {
1400 /// let mut buffer = BufWriter::new(File::create("foo.txt")?);
1402 /// buffer.write_all(b"some bytes")?;
1403 /// buffer.flush()?;
1407 #[stable(feature = "rust1", since = "1.0.0")]
1408 fn flush(&mut self) -> Result<()>;
1410 /// Attempts to write an entire buffer into this writer.
1412 /// This method will continuously call [`write`] until there is no more data
1413 /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
1414 /// returned. This method will not return until the entire buffer has been
1415 /// successfully written or such an error occurs. The first error that is
1416 /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
1419 /// If the buffer contains no data, this will never call [`write`].
1423 /// This function will return the first error of
1424 /// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
1426 /// [`write`]: Write::write
1431 /// use std::io::prelude::*;
1432 /// use std::fs::File;
1434 /// fn main() -> std::io::Result<()> {
1435 /// let mut buffer = File::create("foo.txt")?;
1437 /// buffer.write_all(b"some bytes")?;
1441 #[stable(feature = "rust1", since = "1.0.0")]
1442 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
1443 while !buf.is_empty() {
1444 match self.write(buf) {
1446 return Err(Error::new_const(
1447 ErrorKind::WriteZero,
1448 &"failed to write whole buffer",
1451 Ok(n) => buf = &buf[n..],
1452 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
1453 Err(e) => return Err(e),
1459 /// Attempts to write multiple buffers into this writer.
1461 /// This method will continuously call [`write_vectored`] until there is no
1462 /// more data to be written or an error of non-[`ErrorKind::Interrupted`]
1463 /// kind is returned. This method will not return until all buffers have
1464 /// been successfully written or such an error occurs. The first error that
1465 /// is not of [`ErrorKind::Interrupted`] kind generated from this method
1466 /// will be returned.
1468 /// If the buffer contains no data, this will never call [`write_vectored`].
1472 /// Unlike [`write_vectored`], this takes a *mutable* reference to
1473 /// a slice of [`IoSlice`]s, not an immutable one. That's because we need to
1474 /// modify the slice to keep track of the bytes already written.
1476 /// Once this function returns, the contents of `bufs` are unspecified, as
1477 /// this depends on how many calls to [`write_vectored`] were necessary. It is
1478 /// best to understand this function as taking ownership of `bufs` and to
1479 /// not use `bufs` afterwards. The underlying buffers, to which the
1480 /// [`IoSlice`]s point (but not the [`IoSlice`]s themselves), are unchanged and
1483 /// [`write_vectored`]: Write::write_vectored
1488 /// #![feature(write_all_vectored)]
1489 /// # fn main() -> std::io::Result<()> {
1491 /// use std::io::{Write, IoSlice};
1493 /// let mut writer = Vec::new();
1494 /// let bufs = &mut [
1495 /// IoSlice::new(&[1]),
1496 /// IoSlice::new(&[2, 3]),
1497 /// IoSlice::new(&[4, 5, 6]),
1500 /// writer.write_all_vectored(bufs)?;
1501 /// // Note: the contents of `bufs` is now undefined, see the Notes section.
1503 /// assert_eq!(writer, &[1, 2, 3, 4, 5, 6]);
1506 #[unstable(feature = "write_all_vectored", issue = "70436")]
1507 fn write_all_vectored(&mut self, mut bufs: &mut [IoSlice<'_>]) -> Result<()> {
1508 // Guarantee that bufs is empty if it contains no data,
1509 // to avoid calling write_vectored if there is no data to be written.
1510 bufs = IoSlice::advance(bufs, 0);
1511 while !bufs.is_empty() {
1512 match self.write_vectored(bufs) {
1514 return Err(Error::new_const(
1515 ErrorKind::WriteZero,
1516 &"failed to write whole buffer",
1519 Ok(n) => bufs = IoSlice::advance(bufs, n),
1520 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
1521 Err(e) => return Err(e),
1527 /// Writes a formatted string into this writer, returning any error
1530 /// This method is primarily used to interface with the
1531 /// [`format_args!()`] macro, but it is rare that this should
1532 /// explicitly be called. The [`write!()`] macro should be favored to
1533 /// invoke this method instead.
1535 /// This function internally uses the [`write_all`] method on
1536 /// this trait and hence will continuously write data so long as no errors
1537 /// are received. This also means that partial writes are not indicated in
1540 /// [`write_all`]: Write::write_all
1544 /// This function will return any I/O error reported while formatting.
1549 /// use std::io::prelude::*;
1550 /// use std::fs::File;
1552 /// fn main() -> std::io::Result<()> {
1553 /// let mut buffer = File::create("foo.txt")?;
1556 /// write!(buffer, "{:.*}", 2, 1.234567)?;
1557 /// // turns into this:
1558 /// buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))?;
1562 #[stable(feature = "rust1", since = "1.0.0")]
1563 fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> Result<()> {
1564 // Create a shim which translates a Write to a fmt::Write and saves
1565 // off I/O errors. instead of discarding them
1566 struct Adaptor<'a, T: ?Sized + 'a> {
1571 impl<T: Write + ?Sized> fmt::Write for Adaptor<'_, T> {
1572 fn write_str(&mut self, s: &str) -> fmt::Result {
1573 match self.inner.write_all(s.as_bytes()) {
1576 self.error = Err(e);
1583 let mut output = Adaptor { inner: self, error: Ok(()) };
1584 match fmt::write(&mut output, fmt) {
1587 // check if the error came from the underlying `Write` or not
1588 if output.error.is_err() {
1591 Err(Error::new_const(ErrorKind::Other, &"formatter error"))
1597 /// Creates a "by reference" adaptor for this instance of `Write`.
1599 /// The returned adaptor also implements `Write` and will simply borrow this
1605 /// use std::io::Write;
1606 /// use std::fs::File;
1608 /// fn main() -> std::io::Result<()> {
1609 /// let mut buffer = File::create("foo.txt")?;
1611 /// let reference = buffer.by_ref();
1613 /// // we can use reference just like our original buffer
1614 /// reference.write_all(b"some bytes")?;
1618 #[stable(feature = "rust1", since = "1.0.0")]
1619 fn by_ref(&mut self) -> &mut Self
1627 /// The `Seek` trait provides a cursor which can be moved within a stream of
1630 /// The stream typically has a fixed size, allowing seeking relative to either
1631 /// end or the current offset.
1635 /// [`File`]s implement `Seek`:
1637 /// [`File`]: crate::fs::File
1641 /// use std::io::prelude::*;
1642 /// use std::fs::File;
1643 /// use std::io::SeekFrom;
1645 /// fn main() -> io::Result<()> {
1646 /// let mut f = File::open("foo.txt")?;
1648 /// // move the cursor 42 bytes from the start of the file
1649 /// f.seek(SeekFrom::Start(42))?;
1653 #[stable(feature = "rust1", since = "1.0.0")]
1655 /// Seek to an offset, in bytes, in a stream.
1657 /// A seek beyond the end of a stream is allowed, but behavior is defined
1658 /// by the implementation.
1660 /// If the seek operation completed successfully,
1661 /// this method returns the new position from the start of the stream.
1662 /// That position can be used later with [`SeekFrom::Start`].
1666 /// Seeking can fail, for example because it might involve flushing a buffer.
1668 /// Seeking to a negative offset is considered an error.
1669 #[stable(feature = "rust1", since = "1.0.0")]
1670 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1672 /// Rewind to the beginning of a stream.
1674 /// This is a convenience method, equivalent to `seek(SeekFrom::Start(0))`.
1678 /// Rewinding can fail, for example because it might involve flushing a buffer.
1683 /// #![feature(seek_rewind)]
1684 /// use std::io::{Read, Seek, Write};
1685 /// use std::fs::OpenOptions;
1687 /// let mut f = OpenOptions::new()
1691 /// .open("foo.txt").unwrap();
1693 /// let hello = "Hello!\n";
1694 /// write!(f, "{}", hello).unwrap();
1695 /// f.rewind().unwrap();
1697 /// let mut buf = String::new();
1698 /// f.read_to_string(&mut buf).unwrap();
1699 /// assert_eq!(&buf, hello);
1701 #[unstable(feature = "seek_rewind", issue = "85149")]
1702 fn rewind(&mut self) -> Result<()> {
1703 self.seek(SeekFrom::Start(0))?;
1707 /// Returns the length of this stream (in bytes).
1709 /// This method is implemented using up to three seek operations. If this
1710 /// method returns successfully, the seek position is unchanged (i.e. the
1711 /// position before calling this method is the same as afterwards).
1712 /// However, if this method returns an error, the seek position is
1715 /// If you need to obtain the length of *many* streams and you don't care
1716 /// about the seek position afterwards, you can reduce the number of seek
1717 /// operations by simply calling `seek(SeekFrom::End(0))` and using its
1718 /// return value (it is also the stream length).
1720 /// Note that length of a stream can change over time (for example, when
1721 /// data is appended to a file). So calling this method multiple times does
1722 /// not necessarily return the same length each time.
1727 /// #![feature(seek_stream_len)]
1729 /// io::{self, Seek},
1733 /// fn main() -> io::Result<()> {
1734 /// let mut f = File::open("foo.txt")?;
1736 /// let len = f.stream_len()?;
1737 /// println!("The file is currently {} bytes long", len);
1741 #[unstable(feature = "seek_stream_len", issue = "59359")]
1742 fn stream_len(&mut self) -> Result<u64> {
1743 let old_pos = self.stream_position()?;
1744 let len = self.seek(SeekFrom::End(0))?;
1746 // Avoid seeking a third time when we were already at the end of the
1747 // stream. The branch is usually way cheaper than a seek operation.
1749 self.seek(SeekFrom::Start(old_pos))?;
1755 /// Returns the current seek position from the start of the stream.
1757 /// This is equivalent to `self.seek(SeekFrom::Current(0))`.
1763 /// io::{self, BufRead, BufReader, Seek},
1767 /// fn main() -> io::Result<()> {
1768 /// let mut f = BufReader::new(File::open("foo.txt")?);
1770 /// let before = f.stream_position()?;
1771 /// f.read_line(&mut String::new())?;
1772 /// let after = f.stream_position()?;
1774 /// println!("The first line was {} bytes long", after - before);
1778 #[stable(feature = "seek_convenience", since = "1.51.0")]
1779 fn stream_position(&mut self) -> Result<u64> {
1780 self.seek(SeekFrom::Current(0))
1784 /// Enumeration of possible methods to seek within an I/O object.
1786 /// It is used by the [`Seek`] trait.
1787 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1788 #[stable(feature = "rust1", since = "1.0.0")]
1790 /// Sets the offset to the provided number of bytes.
1791 #[stable(feature = "rust1", since = "1.0.0")]
1792 Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
1794 /// Sets the offset to the size of this object plus the specified number of
1797 /// It is possible to seek beyond the end of an object, but it's an error to
1798 /// seek before byte 0.
1799 #[stable(feature = "rust1", since = "1.0.0")]
1800 End(#[stable(feature = "rust1", since = "1.0.0")] i64),
1802 /// Sets the offset to the current position plus the specified number of
1805 /// It is possible to seek beyond the end of an object, but it's an error to
1806 /// seek before byte 0.
1807 #[stable(feature = "rust1", since = "1.0.0")]
1808 Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
1811 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> Result<usize> {
1814 let (done, used) = {
1815 let available = match r.fill_buf() {
1817 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1818 Err(e) => return Err(e),
1820 match memchr::memchr(delim, available) {
1822 buf.extend_from_slice(&available[..=i]);
1826 buf.extend_from_slice(available);
1827 (false, available.len())
1833 if done || used == 0 {
1839 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1840 /// to perform extra ways of reading.
1842 /// For example, reading line-by-line is inefficient without using a buffer, so
1843 /// if you want to read by line, you'll need `BufRead`, which includes a
1844 /// [`read_line`] method as well as a [`lines`] iterator.
1848 /// A locked standard input implements `BufRead`:
1852 /// use std::io::prelude::*;
1854 /// let stdin = io::stdin();
1855 /// for line in stdin.lock().lines() {
1856 /// println!("{}", line.unwrap());
1860 /// If you have something that implements [`Read`], you can use the [`BufReader`
1861 /// type][`BufReader`] to turn it into a `BufRead`.
1863 /// For example, [`File`] implements [`Read`], but not `BufRead`.
1864 /// [`BufReader`] to the rescue!
1866 /// [`File`]: crate::fs::File
1867 /// [`read_line`]: BufRead::read_line
1868 /// [`lines`]: BufRead::lines
1871 /// use std::io::{self, BufReader};
1872 /// use std::io::prelude::*;
1873 /// use std::fs::File;
1875 /// fn main() -> io::Result<()> {
1876 /// let f = File::open("foo.txt")?;
1877 /// let f = BufReader::new(f);
1879 /// for line in f.lines() {
1880 /// println!("{}", line.unwrap());
1886 #[stable(feature = "rust1", since = "1.0.0")]
1887 pub trait BufRead: Read {
1888 /// Returns the contents of the internal buffer, filling it with more data
1889 /// from the inner reader if it is empty.
1891 /// This function is a lower-level call. It needs to be paired with the
1892 /// [`consume`] method to function properly. When calling this
1893 /// method, none of the contents will be "read" in the sense that later
1894 /// calling `read` may return the same contents. As such, [`consume`] must
1895 /// be called with the number of bytes that are consumed from this buffer to
1896 /// ensure that the bytes are never returned twice.
1898 /// [`consume`]: BufRead::consume
1900 /// An empty buffer returned indicates that the stream has reached EOF.
1904 /// This function will return an I/O error if the underlying reader was
1905 /// read, but returned an error.
1909 /// A locked standard input implements `BufRead`:
1913 /// use std::io::prelude::*;
1915 /// let stdin = io::stdin();
1916 /// let mut stdin = stdin.lock();
1918 /// let buffer = stdin.fill_buf().unwrap();
1920 /// // work with buffer
1921 /// println!("{:?}", buffer);
1923 /// // ensure the bytes we worked with aren't returned again later
1924 /// let length = buffer.len();
1925 /// stdin.consume(length);
1927 #[stable(feature = "rust1", since = "1.0.0")]
1928 fn fill_buf(&mut self) -> Result<&[u8]>;
1930 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1931 /// so they should no longer be returned in calls to `read`.
1933 /// This function is a lower-level call. It needs to be paired with the
1934 /// [`fill_buf`] method to function properly. This function does
1935 /// not perform any I/O, it simply informs this object that some amount of
1936 /// its buffer, returned from [`fill_buf`], has been consumed and should
1937 /// no longer be returned. As such, this function may do odd things if
1938 /// [`fill_buf`] isn't called before calling it.
1940 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1945 /// Since `consume()` is meant to be used with [`fill_buf`],
1946 /// that method's example includes an example of `consume()`.
1948 /// [`fill_buf`]: BufRead::fill_buf
1949 #[stable(feature = "rust1", since = "1.0.0")]
1950 fn consume(&mut self, amt: usize);
1952 /// Read all bytes into `buf` until the delimiter `byte` or EOF is reached.
1954 /// This function will read bytes from the underlying stream until the
1955 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1956 /// the delimiter (if found) will be appended to `buf`.
1958 /// If successful, this function will return the total number of bytes read.
1960 /// This function is blocking and should be used carefully: it is possible for
1961 /// an attacker to continuously send bytes without ever sending the delimiter
1966 /// This function will ignore all instances of [`ErrorKind::Interrupted`] and
1967 /// will otherwise return any errors returned by [`fill_buf`].
1969 /// If an I/O error is encountered then all bytes read so far will be
1970 /// present in `buf` and its length will have been adjusted appropriately.
1972 /// [`fill_buf`]: BufRead::fill_buf
1976 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1977 /// this example, we use [`Cursor`] to read all the bytes in a byte slice
1978 /// in hyphen delimited segments:
1981 /// use std::io::{self, BufRead};
1983 /// let mut cursor = io::Cursor::new(b"lorem-ipsum");
1984 /// let mut buf = vec![];
1986 /// // cursor is at 'l'
1987 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1988 /// .expect("reading from cursor won't fail");
1989 /// assert_eq!(num_bytes, 6);
1990 /// assert_eq!(buf, b"lorem-");
1993 /// // cursor is at 'i'
1994 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1995 /// .expect("reading from cursor won't fail");
1996 /// assert_eq!(num_bytes, 5);
1997 /// assert_eq!(buf, b"ipsum");
2000 /// // cursor is at EOF
2001 /// let num_bytes = cursor.read_until(b'-', &mut buf)
2002 /// .expect("reading from cursor won't fail");
2003 /// assert_eq!(num_bytes, 0);
2004 /// assert_eq!(buf, b"");
2006 #[stable(feature = "rust1", since = "1.0.0")]
2007 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
2008 read_until(self, byte, buf)
2011 /// Read all bytes until a newline (the `0xA` byte) is reached, and append
2012 /// them to the provided buffer.
2014 /// This function will read bytes from the underlying stream until the
2015 /// newline delimiter (the `0xA` byte) or EOF is found. Once found, all bytes
2016 /// up to, and including, the delimiter (if found) will be appended to
2019 /// If successful, this function will return the total number of bytes read.
2021 /// If this function returns [`Ok(0)`], the stream has reached EOF.
2023 /// This function is blocking and should be used carefully: it is possible for
2024 /// an attacker to continuously send bytes without ever sending a newline
2031 /// This function has the same error semantics as [`read_until`] and will
2032 /// also return an error if the read bytes are not valid UTF-8. If an I/O
2033 /// error is encountered then `buf` may contain some bytes already read in
2034 /// the event that all data read so far was valid UTF-8.
2036 /// [`read_until`]: BufRead::read_until
2040 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2041 /// this example, we use [`Cursor`] to read all the lines in a byte slice:
2044 /// use std::io::{self, BufRead};
2046 /// let mut cursor = io::Cursor::new(b"foo\nbar");
2047 /// let mut buf = String::new();
2049 /// // cursor is at 'f'
2050 /// let num_bytes = cursor.read_line(&mut buf)
2051 /// .expect("reading from cursor won't fail");
2052 /// assert_eq!(num_bytes, 4);
2053 /// assert_eq!(buf, "foo\n");
2056 /// // cursor is at 'b'
2057 /// let num_bytes = cursor.read_line(&mut buf)
2058 /// .expect("reading from cursor won't fail");
2059 /// assert_eq!(num_bytes, 3);
2060 /// assert_eq!(buf, "bar");
2063 /// // cursor is at EOF
2064 /// let num_bytes = cursor.read_line(&mut buf)
2065 /// .expect("reading from cursor won't fail");
2066 /// assert_eq!(num_bytes, 0);
2067 /// assert_eq!(buf, "");
2069 #[stable(feature = "rust1", since = "1.0.0")]
2070 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
2071 // Note that we are not calling the `.read_until` method here, but
2072 // rather our hardcoded implementation. For more details as to why, see
2073 // the comments in `read_to_end`.
2074 append_to_string(buf, |b| read_until(self, b'\n', b))
2077 /// Returns an iterator over the contents of this reader split on the byte
2080 /// The iterator returned from this function will return instances of
2081 /// [`io::Result`]`<`[`Vec<u8>`]`>`. Each vector returned will *not* have
2082 /// the delimiter byte at the end.
2084 /// This function will yield errors whenever [`read_until`] would have
2085 /// also yielded an error.
2087 /// [`io::Result`]: self::Result
2088 /// [`read_until`]: BufRead::read_until
2092 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2093 /// this example, we use [`Cursor`] to iterate over all hyphen delimited
2094 /// segments in a byte slice
2097 /// use std::io::{self, BufRead};
2099 /// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
2101 /// let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
2102 /// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
2103 /// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
2104 /// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
2105 /// assert_eq!(split_iter.next(), None);
2107 #[stable(feature = "rust1", since = "1.0.0")]
2108 fn split(self, byte: u8) -> Split<Self>
2112 Split { buf: self, delim: byte }
2115 /// Returns an iterator over the lines of this reader.
2117 /// The iterator returned from this function will yield instances of
2118 /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
2119 /// byte (the `0xA` byte) or `CRLF` (`0xD`, `0xA` bytes) at the end.
2121 /// [`io::Result`]: self::Result
2125 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2126 /// this example, we use [`Cursor`] to iterate over all the lines in a byte
2130 /// use std::io::{self, BufRead};
2132 /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
2134 /// let mut lines_iter = cursor.lines().map(|l| l.unwrap());
2135 /// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
2136 /// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
2137 /// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
2138 /// assert_eq!(lines_iter.next(), None);
2143 /// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
2144 #[stable(feature = "rust1", since = "1.0.0")]
2145 fn lines(self) -> Lines<Self>
2153 /// Adaptor to chain together two readers.
2155 /// This struct is generally created by calling [`chain`] on a reader.
2156 /// Please see the documentation of [`chain`] for more details.
2158 /// [`chain`]: Read::chain
2159 #[stable(feature = "rust1", since = "1.0.0")]
2161 pub struct Chain<T, U> {
2167 impl<T, U> Chain<T, U> {
2168 /// Consumes the `Chain`, returning the wrapped readers.
2174 /// use std::io::prelude::*;
2175 /// use std::fs::File;
2177 /// fn main() -> io::Result<()> {
2178 /// let mut foo_file = File::open("foo.txt")?;
2179 /// let mut bar_file = File::open("bar.txt")?;
2181 /// let chain = foo_file.chain(bar_file);
2182 /// let (foo_file, bar_file) = chain.into_inner();
2186 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2187 pub fn into_inner(self) -> (T, U) {
2188 (self.first, self.second)
2191 /// Gets references to the underlying readers in this `Chain`.
2197 /// use std::io::prelude::*;
2198 /// use std::fs::File;
2200 /// fn main() -> io::Result<()> {
2201 /// let mut foo_file = File::open("foo.txt")?;
2202 /// let mut bar_file = File::open("bar.txt")?;
2204 /// let chain = foo_file.chain(bar_file);
2205 /// let (foo_file, bar_file) = chain.get_ref();
2209 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2210 pub fn get_ref(&self) -> (&T, &U) {
2211 (&self.first, &self.second)
2214 /// Gets mutable references to the underlying readers in this `Chain`.
2216 /// Care should be taken to avoid modifying the internal I/O state of the
2217 /// underlying readers as doing so may corrupt the internal state of this
2224 /// use std::io::prelude::*;
2225 /// use std::fs::File;
2227 /// fn main() -> io::Result<()> {
2228 /// let mut foo_file = File::open("foo.txt")?;
2229 /// let mut bar_file = File::open("bar.txt")?;
2231 /// let mut chain = foo_file.chain(bar_file);
2232 /// let (foo_file, bar_file) = chain.get_mut();
2236 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2237 pub fn get_mut(&mut self) -> (&mut T, &mut U) {
2238 (&mut self.first, &mut self.second)
2242 #[stable(feature = "rust1", since = "1.0.0")]
2243 impl<T: Read, U: Read> Read for Chain<T, U> {
2244 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2245 if !self.done_first {
2246 match self.first.read(buf)? {
2247 0 if !buf.is_empty() => self.done_first = true,
2251 self.second.read(buf)
2254 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
2255 if !self.done_first {
2256 match self.first.read_vectored(bufs)? {
2257 0 if bufs.iter().any(|b| !b.is_empty()) => self.done_first = true,
2261 self.second.read_vectored(bufs)
2264 unsafe fn initializer(&self) -> Initializer {
2265 let initializer = self.first.initializer();
2266 if initializer.should_initialize() { initializer } else { self.second.initializer() }
2270 #[stable(feature = "chain_bufread", since = "1.9.0")]
2271 impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
2272 fn fill_buf(&mut self) -> Result<&[u8]> {
2273 if !self.done_first {
2274 match self.first.fill_buf()? {
2275 buf if buf.is_empty() => {
2276 self.done_first = true;
2278 buf => return Ok(buf),
2281 self.second.fill_buf()
2284 fn consume(&mut self, amt: usize) {
2285 if !self.done_first { self.first.consume(amt) } else { self.second.consume(amt) }
2289 impl<T, U> SizeHint for Chain<T, U> {
2290 fn lower_bound(&self) -> usize {
2291 SizeHint::lower_bound(&self.first) + SizeHint::lower_bound(&self.second)
2294 fn upper_bound(&self) -> Option<usize> {
2295 match (SizeHint::upper_bound(&self.first), SizeHint::upper_bound(&self.second)) {
2296 (Some(first), Some(second)) => Some(first + second),
2302 /// Reader adaptor which limits the bytes read from an underlying reader.
2304 /// This struct is generally created by calling [`take`] on a reader.
2305 /// Please see the documentation of [`take`] for more details.
2307 /// [`take`]: Read::take
2308 #[stable(feature = "rust1", since = "1.0.0")]
2310 pub struct Take<T> {
2316 /// Returns the number of bytes that can be read before this instance will
2321 /// This instance may reach `EOF` after reading fewer bytes than indicated by
2322 /// this method if the underlying [`Read`] instance reaches EOF.
2328 /// use std::io::prelude::*;
2329 /// use std::fs::File;
2331 /// fn main() -> io::Result<()> {
2332 /// let f = File::open("foo.txt")?;
2334 /// // read at most five bytes
2335 /// let handle = f.take(5);
2337 /// println!("limit: {}", handle.limit());
2341 #[stable(feature = "rust1", since = "1.0.0")]
2342 pub fn limit(&self) -> u64 {
2346 /// Sets the number of bytes that can be read before this instance will
2347 /// return EOF. This is the same as constructing a new `Take` instance, so
2348 /// the amount of bytes read and the previous limit value don't matter when
2349 /// calling this method.
2355 /// use std::io::prelude::*;
2356 /// use std::fs::File;
2358 /// fn main() -> io::Result<()> {
2359 /// let f = File::open("foo.txt")?;
2361 /// // read at most five bytes
2362 /// let mut handle = f.take(5);
2363 /// handle.set_limit(10);
2365 /// assert_eq!(handle.limit(), 10);
2369 #[stable(feature = "take_set_limit", since = "1.27.0")]
2370 pub fn set_limit(&mut self, limit: u64) {
2374 /// Consumes the `Take`, returning the wrapped reader.
2380 /// use std::io::prelude::*;
2381 /// use std::fs::File;
2383 /// fn main() -> io::Result<()> {
2384 /// let mut file = File::open("foo.txt")?;
2386 /// let mut buffer = [0; 5];
2387 /// let mut handle = file.take(5);
2388 /// handle.read(&mut buffer)?;
2390 /// let file = handle.into_inner();
2394 #[stable(feature = "io_take_into_inner", since = "1.15.0")]
2395 pub fn into_inner(self) -> T {
2399 /// Gets a reference to the underlying reader.
2405 /// use std::io::prelude::*;
2406 /// use std::fs::File;
2408 /// fn main() -> io::Result<()> {
2409 /// let mut file = File::open("foo.txt")?;
2411 /// let mut buffer = [0; 5];
2412 /// let mut handle = file.take(5);
2413 /// handle.read(&mut buffer)?;
2415 /// let file = handle.get_ref();
2419 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2420 pub fn get_ref(&self) -> &T {
2424 /// Gets a mutable reference to the underlying reader.
2426 /// Care should be taken to avoid modifying the internal I/O state of the
2427 /// underlying reader as doing so may corrupt the internal limit of this
2434 /// use std::io::prelude::*;
2435 /// use std::fs::File;
2437 /// fn main() -> io::Result<()> {
2438 /// let mut file = File::open("foo.txt")?;
2440 /// let mut buffer = [0; 5];
2441 /// let mut handle = file.take(5);
2442 /// handle.read(&mut buffer)?;
2444 /// let file = handle.get_mut();
2448 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2449 pub fn get_mut(&mut self) -> &mut T {
2454 #[stable(feature = "rust1", since = "1.0.0")]
2455 impl<T: Read> Read for Take<T> {
2456 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2457 // Don't call into inner reader at all at EOF because it may still block
2458 if self.limit == 0 {
2462 let max = cmp::min(buf.len() as u64, self.limit) as usize;
2463 let n = self.inner.read(&mut buf[..max])?;
2464 self.limit -= n as u64;
2468 unsafe fn initializer(&self) -> Initializer {
2469 self.inner.initializer()
2472 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
2473 // Pass in a reservation_size closure that respects the current value
2474 // of limit for each read. If we hit the read limit, this prevents the
2475 // final zero-byte read from allocating again.
2476 read_to_end_with_reservation(self, buf, |self_| cmp::min(self_.limit, 32) as usize)
2480 #[stable(feature = "rust1", since = "1.0.0")]
2481 impl<T: BufRead> BufRead for Take<T> {
2482 fn fill_buf(&mut self) -> Result<&[u8]> {
2483 // Don't call into inner reader at all at EOF because it may still block
2484 if self.limit == 0 {
2488 let buf = self.inner.fill_buf()?;
2489 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
2493 fn consume(&mut self, amt: usize) {
2494 // Don't let callers reset the limit by passing an overlarge value
2495 let amt = cmp::min(amt as u64, self.limit) as usize;
2496 self.limit -= amt as u64;
2497 self.inner.consume(amt);
2501 /// An iterator over `u8` values of a reader.
2503 /// This struct is generally created by calling [`bytes`] on a reader.
2504 /// Please see the documentation of [`bytes`] for more details.
2506 /// [`bytes`]: Read::bytes
2507 #[stable(feature = "rust1", since = "1.0.0")]
2509 pub struct Bytes<R> {
2513 #[stable(feature = "rust1", since = "1.0.0")]
2514 impl<R: Read> Iterator for Bytes<R> {
2515 type Item = Result<u8>;
2517 fn next(&mut self) -> Option<Result<u8>> {
2520 return match self.inner.read(slice::from_mut(&mut byte)) {
2522 Ok(..) => Some(Ok(byte)),
2523 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
2524 Err(e) => Some(Err(e)),
2529 fn size_hint(&self) -> (usize, Option<usize>) {
2530 SizeHint::size_hint(&self.inner)
2535 fn lower_bound(&self) -> usize;
2537 fn upper_bound(&self) -> Option<usize>;
2539 fn size_hint(&self) -> (usize, Option<usize>) {
2540 (self.lower_bound(), self.upper_bound())
2544 impl<T> SizeHint for T {
2545 default fn lower_bound(&self) -> usize {
2549 default fn upper_bound(&self) -> Option<usize> {
2554 /// An iterator over the contents of an instance of `BufRead` split on a
2555 /// particular byte.
2557 /// This struct is generally created by calling [`split`] on a `BufRead`.
2558 /// Please see the documentation of [`split`] for more details.
2560 /// [`split`]: BufRead::split
2561 #[stable(feature = "rust1", since = "1.0.0")]
2563 pub struct Split<B> {
2568 #[stable(feature = "rust1", since = "1.0.0")]
2569 impl<B: BufRead> Iterator for Split<B> {
2570 type Item = Result<Vec<u8>>;
2572 fn next(&mut self) -> Option<Result<Vec<u8>>> {
2573 let mut buf = Vec::new();
2574 match self.buf.read_until(self.delim, &mut buf) {
2577 if buf[buf.len() - 1] == self.delim {
2582 Err(e) => Some(Err(e)),
2587 /// An iterator over the lines of an instance of `BufRead`.
2589 /// This struct is generally created by calling [`lines`] on a `BufRead`.
2590 /// Please see the documentation of [`lines`] for more details.
2592 /// [`lines`]: BufRead::lines
2593 #[stable(feature = "rust1", since = "1.0.0")]
2595 pub struct Lines<B> {
2599 #[stable(feature = "rust1", since = "1.0.0")]
2600 impl<B: BufRead> Iterator for Lines<B> {
2601 type Item = Result<String>;
2603 fn next(&mut self) -> Option<Result<String>> {
2604 let mut buf = String::new();
2605 match self.buf.read_line(&mut buf) {
2608 if buf.ends_with('\n') {
2610 if buf.ends_with('\r') {
2616 Err(e) => Some(Err(e)),