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 //! [`Vec<T>`]: crate::vec::Vec
244 //! [`io::stdout`]: stdout
245 //! [`io::Result`]: crate::io::Result
246 //! [`?` operator]: ../../book/appendix-02-operators.html
247 //! [`Result`]: crate::result::Result
248 //! [`.unwrap()`]: crate::result::Result::unwrap
250 #![stable(feature = "rust1", since = "1.0.0")]
255 use crate::ops::{Deref, DerefMut};
261 #[stable(feature = "rust1", since = "1.0.0")]
262 pub use self::buffered::IntoInnerError;
263 #[stable(feature = "rust1", since = "1.0.0")]
264 pub use self::buffered::{BufReader, BufWriter, LineWriter};
265 #[stable(feature = "rust1", since = "1.0.0")]
266 pub use self::cursor::Cursor;
267 #[stable(feature = "rust1", since = "1.0.0")]
268 pub use self::error::{Error, ErrorKind, Result};
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub use self::stdio::{stderr, stdin, stdout, Stderr, Stdin, Stdout};
271 #[stable(feature = "rust1", since = "1.0.0")]
272 pub use self::stdio::{StderrLock, StdinLock, StdoutLock};
273 #[unstable(feature = "print_internals", issue = "none")]
274 pub use self::stdio::{_eprint, _print};
275 #[unstable(feature = "libstd_io_internals", issue = "42788")]
276 #[doc(no_inline, hidden)]
277 pub use self::stdio::{set_panic, set_print};
278 #[stable(feature = "rust1", since = "1.0.0")]
279 pub use self::util::{copy, empty, repeat, sink, Empty, Repeat, Sink};
290 const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
293 buf: &'a mut Vec<u8>,
297 impl Drop for Guard<'_> {
300 self.buf.set_len(self.len);
305 // A few methods below (read_to_string, read_line) will append data into a
306 // `String` buffer, but we need to be pretty careful when doing this. The
307 // implementation will just call `.as_mut_vec()` and then delegate to a
308 // byte-oriented reading method, but we must ensure that when returning we never
309 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
311 // To this end, we use an RAII guard (to protect against panics) which updates
312 // the length of the string when it is dropped. This guard initially truncates
313 // the string to the prior length and only after we've validated that the
314 // new contents are valid UTF-8 do we allow it to set a longer length.
316 // The unsafety in this function is twofold:
318 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
320 // 2. We're passing a raw buffer to the function `f`, and it is expected that
321 // the function only *appends* bytes to the buffer. We'll get undefined
322 // behavior if existing bytes are overwritten to have non-UTF-8 data.
323 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
325 F: FnOnce(&mut Vec<u8>) -> Result<usize>,
328 let mut g = Guard { len: buf.len(), buf: buf.as_mut_vec() };
330 if str::from_utf8(&g.buf[g.len..]).is_err() {
332 Err(Error::new(ErrorKind::InvalidData, "stream did not contain valid UTF-8"))
341 // This uses an adaptive system to extend the vector when it fills. We want to
342 // avoid paying to allocate and zero a huge chunk of memory if the reader only
343 // has 4 bytes while still making large reads if the reader does have a ton
344 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
345 // time is 4,500 times (!) slower than a default reservation size of 32 if the
346 // reader has a very small amount of data to return.
348 // Because we're extending the buffer with uninitialized data for trusted
349 // readers, we need to make sure to truncate that if any of this panics.
350 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
351 read_to_end_with_reservation(r, buf, |_| 32)
354 fn read_to_end_with_reservation<R, F>(
357 mut reservation_size: F,
361 F: FnMut(&R) -> usize,
363 let start_len = buf.len();
364 let mut g = Guard { len: buf.len(), buf };
367 if g.len == g.buf.len() {
369 // FIXME(danielhenrymantilla): #42788
371 // - This creates a (mut) reference to a slice of
372 // _uninitialized_ integers, which is **undefined behavior**
374 // - Only the standard library gets to soundly "ignore" this,
375 // based on its privileged knowledge of unstable rustc
377 g.buf.reserve(reservation_size(r));
378 let capacity = g.buf.capacity();
379 g.buf.set_len(capacity);
380 r.initializer().initialize(&mut g.buf[g.len..]);
384 match r.read(&mut g.buf[g.len..]) {
386 ret = Ok(g.len - start_len);
390 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
401 pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
403 F: FnOnce(&mut [u8]) -> Result<usize>,
405 let buf = bufs.iter_mut().find(|b| !b.is_empty()).map_or(&mut [][..], |b| &mut **b);
409 pub(crate) fn default_write_vectored<F>(write: F, bufs: &[IoSlice<'_>]) -> Result<usize>
411 F: FnOnce(&[u8]) -> Result<usize>,
413 let buf = bufs.iter().find(|b| !b.is_empty()).map_or(&[][..], |b| &**b);
417 /// The `Read` trait allows for reading bytes from a source.
419 /// Implementors of the `Read` trait are called 'readers'.
421 /// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
422 /// will attempt to pull bytes from this source into a provided buffer. A
423 /// number of other methods are implemented in terms of [`read()`], giving
424 /// implementors a number of ways to read bytes while only needing to implement
427 /// Readers are intended to be composable with one another. Many implementors
428 /// throughout [`std::io`] take and provide types which implement the `Read`
431 /// Please note that each call to [`read()`] may involve a system call, and
432 /// therefore, using something that implements [`BufRead`], such as
433 /// [`BufReader`], will be more efficient.
437 /// [`File`]s implement `Read`:
441 /// use std::io::prelude::*;
442 /// use std::fs::File;
444 /// fn main() -> io::Result<()> {
445 /// let mut f = File::open("foo.txt")?;
446 /// let mut buffer = [0; 10];
448 /// // read up to 10 bytes
449 /// f.read(&mut buffer)?;
451 /// let mut buffer = Vec::new();
452 /// // read the whole file
453 /// f.read_to_end(&mut buffer)?;
455 /// // read into a String, so that you don't need to do the conversion.
456 /// let mut buffer = String::new();
457 /// f.read_to_string(&mut buffer)?;
459 /// // and more! See the other methods for more details.
464 /// Read from [`&str`] because [`&[u8]`][slice] implements `Read`:
468 /// use std::io::prelude::*;
470 /// fn main() -> io::Result<()> {
471 /// let mut b = "This string will be read".as_bytes();
472 /// let mut buffer = [0; 10];
474 /// // read up to 10 bytes
475 /// b.read(&mut buffer)?;
477 /// // etc... it works exactly as a File does!
482 /// [`read()`]: Read::read
484 /// [`std::io`]: self
485 /// [`File`]: crate::fs::File
486 /// [slice]: ../../std/primitive.slice.html
487 #[stable(feature = "rust1", since = "1.0.0")]
490 /// Pull some bytes from this source into the specified buffer, returning
491 /// how many bytes were read.
493 /// This function does not provide any guarantees about whether it blocks
494 /// waiting for data, but if an object needs to block for a read and cannot,
495 /// it will typically signal this via an [`Err`] return value.
497 /// If the return value of this method is [`Ok(n)`], then it must be
498 /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
499 /// that the buffer `buf` has been filled in with `n` bytes of data from this
500 /// source. If `n` is `0`, then it can indicate one of two scenarios:
502 /// 1. This reader has reached its "end of file" and will likely no longer
503 /// be able to produce bytes. Note that this does not mean that the
504 /// reader will *always* no longer be able to produce bytes.
505 /// 2. The buffer specified was 0 bytes in length.
507 /// It is not an error if the returned value `n` is smaller than the buffer size,
508 /// even when the reader is not at the end of the stream yet.
509 /// This may happen for example because fewer bytes are actually available right now
510 /// (e. g. being close to end-of-file) or because read() was interrupted by a signal.
512 /// No guarantees are provided about the contents of `buf` when this
513 /// function is called, implementations cannot rely on any property of the
514 /// contents of `buf` being true. It is recommended that *implementations*
515 /// only write data to `buf` instead of reading its contents.
517 /// Correspondingly, however, *callers* of this method may not assume any guarantees
518 /// about how the implementation uses `buf`. The trait is safe to implement,
519 /// so it is possible that the code that's supposed to write to the buffer might also read
520 /// from it. It is your responsibility to make sure that `buf` is initialized
521 /// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
522 /// obtains via [`MaybeUninit<T>`]) is not safe, and can lead to undefined behavior.
524 /// [`MaybeUninit<T>`]: crate::mem::MaybeUninit
528 /// If this function encounters any form of I/O or other error, an error
529 /// variant will be returned. If an error is returned then it must be
530 /// guaranteed that no bytes were read.
532 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
533 /// operation should be retried if there is nothing else to do.
537 /// [`File`]s implement `Read`:
540 /// [`File`]: crate::fs::File
544 /// use std::io::prelude::*;
545 /// use std::fs::File;
547 /// fn main() -> io::Result<()> {
548 /// let mut f = File::open("foo.txt")?;
549 /// let mut buffer = [0; 10];
551 /// // read up to 10 bytes
552 /// let n = f.read(&mut buffer[..])?;
554 /// println!("The bytes: {:?}", &buffer[..n]);
558 #[stable(feature = "rust1", since = "1.0.0")]
559 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
561 /// Like `read`, except that it reads into a slice of buffers.
563 /// Data is copied to fill each buffer in order, with the final buffer
564 /// written to possibly being only partially filled. This method must
565 /// behave equivalently to a single call to `read` with concatenated
568 /// The default implementation calls `read` with either the first nonempty
569 /// buffer provided, or an empty one if none exists.
570 #[stable(feature = "iovec", since = "1.36.0")]
571 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
572 default_read_vectored(|b| self.read(b), bufs)
575 /// Determines if this `Read`er has an efficient `read_vectored`
578 /// If a `Read`er does not override the default `read_vectored`
579 /// implementation, code using it may want to avoid the method all together
580 /// and coalesce writes into a single buffer for higher performance.
582 /// The default implementation returns `false`.
583 #[unstable(feature = "can_vector", issue = "69941")]
584 fn is_read_vectored(&self) -> bool {
588 /// Determines if this `Read`er can work with buffers of uninitialized
591 /// The default implementation returns an initializer which will zero
594 /// If a `Read`er guarantees that it can work properly with uninitialized
595 /// memory, it should call [`Initializer::nop()`]. See the documentation for
596 /// [`Initializer`] for details.
598 /// The behavior of this method must be independent of the state of the
599 /// `Read`er - the method only takes `&self` so that it can be used through
604 /// This method is unsafe because a `Read`er could otherwise return a
605 /// non-zeroing `Initializer` from another `Read` type without an `unsafe`
607 #[unstable(feature = "read_initializer", issue = "42788")]
609 unsafe fn initializer(&self) -> Initializer {
610 Initializer::zeroing()
613 /// Read all bytes until EOF in this source, placing them into `buf`.
615 /// All bytes read from this source will be appended to the specified buffer
616 /// `buf`. This function will continuously call [`read()`] to append more data to
617 /// `buf` until [`read()`] returns either [`Ok(0)`] or an error of
618 /// non-[`ErrorKind::Interrupted`] kind.
620 /// If successful, this function will return the total number of bytes read.
624 /// If this function encounters an error of the kind
625 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
628 /// If any other read error is encountered then this function immediately
629 /// returns. Any bytes which have already been read will be appended to
634 /// [`File`]s implement `Read`:
636 /// [`read()`]: Read::read
638 /// [`File`]: crate::fs::File
642 /// use std::io::prelude::*;
643 /// use std::fs::File;
645 /// fn main() -> io::Result<()> {
646 /// let mut f = File::open("foo.txt")?;
647 /// let mut buffer = Vec::new();
649 /// // read the whole file
650 /// f.read_to_end(&mut buffer)?;
655 /// (See also the [`std::fs::read`] convenience function for reading from a
658 /// [`std::fs::read`]: crate::fs::read
659 #[stable(feature = "rust1", since = "1.0.0")]
660 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
661 read_to_end(self, buf)
664 /// Read all bytes until EOF in this source, appending them to `buf`.
666 /// If successful, this function returns the number of bytes which were read
667 /// and appended to `buf`.
671 /// If the data in this stream is *not* valid UTF-8 then an error is
672 /// returned and `buf` is unchanged.
674 /// See [`read_to_end`][readtoend] for other error semantics.
676 /// [readtoend]: Self::read_to_end
680 /// [`File`][file]s implement `Read`:
682 /// [file]: crate::fs::File
686 /// use std::io::prelude::*;
687 /// use std::fs::File;
689 /// fn main() -> io::Result<()> {
690 /// let mut f = File::open("foo.txt")?;
691 /// let mut buffer = String::new();
693 /// f.read_to_string(&mut buffer)?;
698 /// (See also the [`std::fs::read_to_string`] convenience function for
699 /// reading from a file.)
701 /// [`std::fs::read_to_string`]: crate::fs::read_to_string
702 #[stable(feature = "rust1", since = "1.0.0")]
703 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
704 // Note that we do *not* call `.read_to_end()` here. We are passing
705 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
706 // method to fill it up. An arbitrary implementation could overwrite the
707 // entire contents of the vector, not just append to it (which is what
708 // we are expecting).
710 // To prevent extraneously checking the UTF-8-ness of the entire buffer
711 // we pass it to our hardcoded `read_to_end` implementation which we
712 // know is guaranteed to only read data into the end of the buffer.
713 append_to_string(buf, |b| read_to_end(self, b))
716 /// Read the exact number of bytes required to fill `buf`.
718 /// This function reads as many bytes as necessary to completely fill the
719 /// specified buffer `buf`.
721 /// No guarantees are provided about the contents of `buf` when this
722 /// function is called, implementations cannot rely on any property of the
723 /// contents of `buf` being true. It is recommended that implementations
724 /// only write data to `buf` instead of reading its contents. The
725 /// documentation on [`read`] has a more detailed explanation on this
730 /// If this function encounters an error of the kind
731 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
734 /// If this function encounters an "end of file" before completely filling
735 /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
736 /// The contents of `buf` are unspecified in this case.
738 /// If any other read error is encountered then this function immediately
739 /// returns. The contents of `buf` are unspecified in this case.
741 /// If this function returns an error, it is unspecified how many bytes it
742 /// has read, but it will never read more than would be necessary to
743 /// completely fill the buffer.
747 /// [`File`]s implement `Read`:
749 /// [`read`]: Read::read
750 /// [`File`]: crate::fs::File
754 /// use std::io::prelude::*;
755 /// use std::fs::File;
757 /// fn main() -> io::Result<()> {
758 /// let mut f = File::open("foo.txt")?;
759 /// let mut buffer = [0; 10];
761 /// // read exactly 10 bytes
762 /// f.read_exact(&mut buffer)?;
766 #[stable(feature = "read_exact", since = "1.6.0")]
767 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
768 while !buf.is_empty() {
769 match self.read(buf) {
775 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
776 Err(e) => return Err(e),
780 Err(Error::new(ErrorKind::UnexpectedEof, "failed to fill whole buffer"))
786 /// Creates a "by reference" adaptor for this instance of `Read`.
788 /// The returned adaptor also implements `Read` and will simply borrow this
793 /// [`File`][file]s implement `Read`:
795 /// [file]: crate::fs::File
799 /// use std::io::Read;
800 /// use std::fs::File;
802 /// fn main() -> io::Result<()> {
803 /// let mut f = File::open("foo.txt")?;
804 /// let mut buffer = Vec::new();
805 /// let mut other_buffer = Vec::new();
808 /// let reference = f.by_ref();
810 /// // read at most 5 bytes
811 /// reference.take(5).read_to_end(&mut buffer)?;
813 /// } // drop our &mut reference so we can use f again
815 /// // original file still usable, read the rest
816 /// f.read_to_end(&mut other_buffer)?;
820 #[stable(feature = "rust1", since = "1.0.0")]
821 fn by_ref(&mut self) -> &mut Self
828 /// Transforms this `Read` instance to an [`Iterator`] over its bytes.
830 /// The returned type implements [`Iterator`] where the `Item` is
831 /// [`Result`]`<`[`u8`]`, `[`io::Error`]`>`.
832 /// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
833 /// otherwise. EOF is mapped to returning [`None`] from this iterator.
837 /// [`File`][file]s implement `Read`:
839 /// [file]: crate::fs::File
840 /// [`Iterator`]: crate::iter::Iterator
841 /// [`Result`]: crate::result::Result
842 /// [`io::Error`]: self::Error
846 /// use std::io::prelude::*;
847 /// use std::fs::File;
849 /// fn main() -> io::Result<()> {
850 /// let mut f = File::open("foo.txt")?;
852 /// for byte in f.bytes() {
853 /// println!("{}", byte.unwrap());
858 #[stable(feature = "rust1", since = "1.0.0")]
859 fn bytes(self) -> Bytes<Self>
863 Bytes { inner: self }
866 /// Creates an adaptor which will chain this stream with another.
868 /// The returned `Read` instance will first read all bytes from this object
869 /// until EOF is encountered. Afterwards the output is equivalent to the
870 /// output of `next`.
874 /// [`File`][file]s implement `Read`:
876 /// [file]: crate::fs::File
880 /// use std::io::prelude::*;
881 /// use std::fs::File;
883 /// fn main() -> io::Result<()> {
884 /// let mut f1 = File::open("foo.txt")?;
885 /// let mut f2 = File::open("bar.txt")?;
887 /// let mut handle = f1.chain(f2);
888 /// let mut buffer = String::new();
890 /// // read the value into a String. We could use any Read method here,
891 /// // this is just one example.
892 /// handle.read_to_string(&mut buffer)?;
896 #[stable(feature = "rust1", since = "1.0.0")]
897 fn chain<R: Read>(self, next: R) -> Chain<Self, R>
901 Chain { first: self, second: next, done_first: false }
904 /// Creates an adaptor which will read at most `limit` bytes from it.
906 /// This function returns a new instance of `Read` which will read at most
907 /// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
908 /// read errors will not count towards the number of bytes read and future
909 /// calls to [`read()`] may succeed.
913 /// [`File`]s implement `Read`:
915 /// [`File`]: crate::fs::File
917 /// [`read()`]: Read::read
921 /// use std::io::prelude::*;
922 /// use std::fs::File;
924 /// fn main() -> io::Result<()> {
925 /// let mut f = File::open("foo.txt")?;
926 /// let mut buffer = [0; 5];
928 /// // read at most five bytes
929 /// let mut handle = f.take(5);
931 /// handle.read(&mut buffer)?;
935 #[stable(feature = "rust1", since = "1.0.0")]
936 fn take(self, limit: u64) -> Take<Self>
940 Take { inner: self, limit }
944 /// A buffer type used with `Read::read_vectored`.
946 /// It is semantically a wrapper around an `&mut [u8]`, but is guaranteed to be
947 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
949 #[stable(feature = "iovec", since = "1.36.0")]
951 pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
953 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
954 unsafe impl<'a> Send for IoSliceMut<'a> {}
956 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
957 unsafe impl<'a> Sync for IoSliceMut<'a> {}
959 #[stable(feature = "iovec", since = "1.36.0")]
960 impl<'a> fmt::Debug for IoSliceMut<'a> {
961 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
962 fmt::Debug::fmt(self.0.as_slice(), fmt)
966 impl<'a> IoSliceMut<'a> {
967 /// Creates a new `IoSliceMut` wrapping a byte slice.
971 /// Panics on Windows if the slice is larger than 4GB.
972 #[stable(feature = "iovec", since = "1.36.0")]
974 pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
975 IoSliceMut(sys::io::IoSliceMut::new(buf))
978 /// Advance the internal cursor of the slice.
982 /// Elements in the slice may be modified if the cursor is not advanced to
983 /// the end of the slice. For example if we have a slice of buffers with 2
984 /// `IoSliceMut`s, both of length 8, and we advance the cursor by 10 bytes
985 /// the first `IoSliceMut` will be untouched however the second will be
986 /// modified to remove the first 2 bytes (10 - 8).
991 /// #![feature(io_slice_advance)]
993 /// use std::io::IoSliceMut;
994 /// use std::ops::Deref;
996 /// let mut buf1 = [1; 8];
997 /// let mut buf2 = [2; 16];
998 /// let mut buf3 = [3; 8];
999 /// let mut bufs = &mut [
1000 /// IoSliceMut::new(&mut buf1),
1001 /// IoSliceMut::new(&mut buf2),
1002 /// IoSliceMut::new(&mut buf3),
1005 /// // Mark 10 bytes as read.
1006 /// bufs = IoSliceMut::advance(bufs, 10);
1007 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1008 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1010 #[unstable(feature = "io_slice_advance", issue = "62726")]
1012 pub fn advance<'b>(bufs: &'b mut [IoSliceMut<'a>], n: usize) -> &'b mut [IoSliceMut<'a>] {
1013 // Number of buffers to remove.
1015 // Total length of all the to be removed buffers.
1016 let mut accumulated_len = 0;
1017 for buf in bufs.iter() {
1018 if accumulated_len + buf.len() > n {
1021 accumulated_len += buf.len();
1026 let bufs = &mut bufs[remove..];
1027 if !bufs.is_empty() {
1028 bufs[0].0.advance(n - accumulated_len)
1034 #[stable(feature = "iovec", since = "1.36.0")]
1035 impl<'a> Deref for IoSliceMut<'a> {
1039 fn deref(&self) -> &[u8] {
1044 #[stable(feature = "iovec", since = "1.36.0")]
1045 impl<'a> DerefMut for IoSliceMut<'a> {
1047 fn deref_mut(&mut self) -> &mut [u8] {
1048 self.0.as_mut_slice()
1052 /// A buffer type used with `Write::write_vectored`.
1054 /// It is semantically a wrapper around an `&[u8]`, but is guaranteed to be
1055 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1057 #[stable(feature = "iovec", since = "1.36.0")]
1058 #[derive(Copy, Clone)]
1059 #[repr(transparent)]
1060 pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
1062 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1063 unsafe impl<'a> Send for IoSlice<'a> {}
1065 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1066 unsafe impl<'a> Sync for IoSlice<'a> {}
1068 #[stable(feature = "iovec", since = "1.36.0")]
1069 impl<'a> fmt::Debug for IoSlice<'a> {
1070 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1071 fmt::Debug::fmt(self.0.as_slice(), fmt)
1075 impl<'a> IoSlice<'a> {
1076 /// Creates a new `IoSlice` wrapping a byte slice.
1080 /// Panics on Windows if the slice is larger than 4GB.
1081 #[stable(feature = "iovec", since = "1.36.0")]
1083 pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
1084 IoSlice(sys::io::IoSlice::new(buf))
1087 /// Advance the internal cursor of the slice.
1091 /// Elements in the slice may be modified if the cursor is not advanced to
1092 /// the end of the slice. For example if we have a slice of buffers with 2
1093 /// `IoSlice`s, both of length 8, and we advance the cursor by 10 bytes the
1094 /// first `IoSlice` will be untouched however the second will be modified to
1095 /// remove the first 2 bytes (10 - 8).
1100 /// #![feature(io_slice_advance)]
1102 /// use std::io::IoSlice;
1103 /// use std::ops::Deref;
1105 /// let buf1 = [1; 8];
1106 /// let buf2 = [2; 16];
1107 /// let buf3 = [3; 8];
1108 /// let mut bufs = &mut [
1109 /// IoSlice::new(&buf1),
1110 /// IoSlice::new(&buf2),
1111 /// IoSlice::new(&buf3),
1114 /// // Mark 10 bytes as written.
1115 /// bufs = IoSlice::advance(bufs, 10);
1116 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1117 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1118 #[unstable(feature = "io_slice_advance", issue = "62726")]
1120 pub fn advance<'b>(bufs: &'b mut [IoSlice<'a>], n: usize) -> &'b mut [IoSlice<'a>] {
1121 // Number of buffers to remove.
1123 // Total length of all the to be removed buffers.
1124 let mut accumulated_len = 0;
1125 for buf in bufs.iter() {
1126 if accumulated_len + buf.len() > n {
1129 accumulated_len += buf.len();
1134 let bufs = &mut bufs[remove..];
1135 if !bufs.is_empty() {
1136 bufs[0].0.advance(n - accumulated_len)
1142 #[stable(feature = "iovec", since = "1.36.0")]
1143 impl<'a> Deref for IoSlice<'a> {
1147 fn deref(&self) -> &[u8] {
1152 /// A type used to conditionally initialize buffers passed to `Read` methods.
1153 #[unstable(feature = "read_initializer", issue = "42788")]
1155 pub struct Initializer(bool);
1158 /// Returns a new `Initializer` which will zero out buffers.
1159 #[unstable(feature = "read_initializer", issue = "42788")]
1161 pub fn zeroing() -> Initializer {
1165 /// Returns a new `Initializer` which will not zero out buffers.
1169 /// This may only be called by `Read`ers which guarantee that they will not
1170 /// read from buffers passed to `Read` methods, and that the return value of
1171 /// the method accurately reflects the number of bytes that have been
1172 /// written to the head of the buffer.
1173 #[unstable(feature = "read_initializer", issue = "42788")]
1175 pub unsafe fn nop() -> Initializer {
1179 /// Indicates if a buffer should be initialized.
1180 #[unstable(feature = "read_initializer", issue = "42788")]
1182 pub fn should_initialize(&self) -> bool {
1186 /// Initializes a buffer if necessary.
1187 #[unstable(feature = "read_initializer", issue = "42788")]
1189 pub fn initialize(&self, buf: &mut [u8]) {
1190 if self.should_initialize() {
1191 unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
1196 /// A trait for objects which are byte-oriented sinks.
1198 /// Implementors of the `Write` trait are sometimes called 'writers'.
1200 /// Writers are defined by two required methods, [`write`] and [`flush`]:
1202 /// * The [`write`] method will attempt to write some data into the object,
1203 /// returning how many bytes were successfully written.
1205 /// * The [`flush`] method is useful for adaptors and explicit buffers
1206 /// themselves for ensuring that all buffered data has been pushed out to the
1209 /// Writers are intended to be composable with one another. Many implementors
1210 /// throughout [`std::io`] take and provide types which implement the `Write`
1213 /// [`write`]: Self::write
1214 /// [`flush`]: Self::flush
1215 /// [`std::io`]: self
1220 /// use std::io::prelude::*;
1221 /// use std::fs::File;
1223 /// fn main() -> std::io::Result<()> {
1224 /// let data = b"some bytes";
1226 /// let mut pos = 0;
1227 /// let mut buffer = File::create("foo.txt")?;
1229 /// while pos < data.len() {
1230 /// let bytes_written = buffer.write(&data[pos..])?;
1231 /// pos += bytes_written;
1237 /// The trait also provides convenience methods like [`write_all`], which calls
1238 /// `write` in a loop until its entire input has been written.
1240 /// [`write_all`]: Self::write_all
1241 #[stable(feature = "rust1", since = "1.0.0")]
1244 /// Write a buffer into this writer, returning how many bytes were written.
1246 /// This function will attempt to write the entire contents of `buf`, but
1247 /// the entire write may not succeed, or the write may also generate an
1248 /// error. A call to `write` represents *at most one* attempt to write to
1249 /// any wrapped object.
1251 /// Calls to `write` are not guaranteed to block waiting for data to be
1252 /// written, and a write which would otherwise block can be indicated through
1253 /// an [`Err`] variant.
1255 /// If the return value is [`Ok(n)`] then it must be guaranteed that
1256 /// `n <= buf.len()`. A return value of `0` typically means that the
1257 /// underlying object is no longer able to accept bytes and will likely not
1258 /// be able to in the future as well, or that the buffer provided is empty.
1262 /// Each call to `write` may generate an I/O error indicating that the
1263 /// operation could not be completed. If an error is returned then no bytes
1264 /// in the buffer were written to this writer.
1266 /// It is **not** considered an error if the entire buffer could not be
1267 /// written to this writer.
1269 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
1270 /// write operation should be retried if there is nothing else to do.
1275 /// use std::io::prelude::*;
1276 /// use std::fs::File;
1278 /// fn main() -> std::io::Result<()> {
1279 /// let mut buffer = File::create("foo.txt")?;
1281 /// // Writes some prefix of the byte string, not necessarily all of it.
1282 /// buffer.write(b"some bytes")?;
1286 #[stable(feature = "rust1", since = "1.0.0")]
1287 fn write(&mut self, buf: &[u8]) -> Result<usize>;
1289 /// Like `write`, except that it writes from a slice of buffers.
1291 /// Data is copied from each buffer in order, with the final buffer
1292 /// read from possibly being only partially consumed. This method must
1293 /// behave as a call to `write` with the buffers concatenated would.
1295 /// The default implementation calls `write` with either the first nonempty
1296 /// buffer provided, or an empty one if none exists.
1297 #[stable(feature = "iovec", since = "1.36.0")]
1298 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
1299 default_write_vectored(|b| self.write(b), bufs)
1302 /// Determines if this `Write`er has an efficient `write_vectored`
1305 /// If a `Write`er does not override the default `write_vectored`
1306 /// implementation, code using it may want to avoid the method all together
1307 /// and coalesce writes into a single buffer for higher performance.
1309 /// The default implementation returns `false`.
1310 #[unstable(feature = "can_vector", issue = "69941")]
1311 fn is_write_vectored(&self) -> bool {
1315 /// Flush this output stream, ensuring that all intermediately buffered
1316 /// contents reach their destination.
1320 /// It is considered an error if not all bytes could be written due to
1321 /// I/O errors or EOF being reached.
1326 /// use std::io::prelude::*;
1327 /// use std::io::BufWriter;
1328 /// use std::fs::File;
1330 /// fn main() -> std::io::Result<()> {
1331 /// let mut buffer = BufWriter::new(File::create("foo.txt")?);
1333 /// buffer.write_all(b"some bytes")?;
1334 /// buffer.flush()?;
1338 #[stable(feature = "rust1", since = "1.0.0")]
1339 fn flush(&mut self) -> Result<()>;
1341 /// Attempts to write an entire buffer into this writer.
1343 /// This method will continuously call [`write`] until there is no more data
1344 /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
1345 /// returned. This method will not return until the entire buffer has been
1346 /// successfully written or such an error occurs. The first error that is
1347 /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
1350 /// If the buffer contains no data, this will never call [`write`].
1354 /// This function will return the first error of
1355 /// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
1357 /// [`write`]: Self::write
1362 /// use std::io::prelude::*;
1363 /// use std::fs::File;
1365 /// fn main() -> std::io::Result<()> {
1366 /// let mut buffer = File::create("foo.txt")?;
1368 /// buffer.write_all(b"some bytes")?;
1372 #[stable(feature = "rust1", since = "1.0.0")]
1373 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
1374 while !buf.is_empty() {
1375 match self.write(buf) {
1377 return Err(Error::new(ErrorKind::WriteZero, "failed to write whole buffer"));
1379 Ok(n) => buf = &buf[n..],
1380 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
1381 Err(e) => return Err(e),
1387 /// Attempts to write multiple buffers into this writer.
1389 /// This method will continuously call [`write_vectored`] until there is no
1390 /// more data to be written or an error of non-[`ErrorKind::Interrupted`]
1391 /// kind is returned. This method will not return until all buffers have
1392 /// been successfully written or such an error occurs. The first error that
1393 /// is not of [`ErrorKind::Interrupted`] kind generated from this method
1394 /// will be returned.
1396 /// If the buffer contains no data, this will never call [`write_vectored`].
1398 /// [`write_vectored`]: Self::write_vectored
1403 /// Unlike `io::Write::write_vectored`, this takes a *mutable* reference to
1404 /// a slice of `IoSlice`s, not an immutable one. That's because we need to
1405 /// modify the slice to keep track of the bytes already written.
1407 /// Once this function returns, the contents of `bufs` are unspecified, as
1408 /// this depends on how many calls to `write_vectored` were necessary. It is
1409 /// best to understand this function as taking ownership of `bufs` and to
1410 /// not use `bufs` afterwards. The underlying buffers, to which the
1411 /// `IoSlice`s point (but not the `IoSlice`s themselves), are unchanged and
1417 /// #![feature(write_all_vectored)]
1418 /// # fn main() -> std::io::Result<()> {
1420 /// use std::io::{Write, IoSlice};
1422 /// let mut writer = Vec::new();
1423 /// let bufs = &mut [
1424 /// IoSlice::new(&[1]),
1425 /// IoSlice::new(&[2, 3]),
1426 /// IoSlice::new(&[4, 5, 6]),
1429 /// writer.write_all_vectored(bufs)?;
1430 /// // Note: the contents of `bufs` is now undefined, see the Notes section.
1432 /// assert_eq!(writer, &[1, 2, 3, 4, 5, 6]);
1435 #[unstable(feature = "write_all_vectored", issue = "70436")]
1436 fn write_all_vectored(&mut self, mut bufs: &mut [IoSlice<'_>]) -> Result<()> {
1437 // Guarantee that bufs is empty if it contains no data,
1438 // to avoid calling write_vectored if there is no data to be written.
1439 bufs = IoSlice::advance(bufs, 0);
1440 while !bufs.is_empty() {
1441 match self.write_vectored(bufs) {
1443 return Err(Error::new(ErrorKind::WriteZero, "failed to write whole buffer"));
1445 Ok(n) => bufs = IoSlice::advance(bufs, n),
1446 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
1447 Err(e) => return Err(e),
1453 /// Writes a formatted string into this writer, returning any error
1456 /// This method is primarily used to interface with the
1457 /// [`format_args!()`] macro, but it is rare that this should
1458 /// explicitly be called. The [`write!()`] macro should be favored to
1459 /// invoke this method instead.
1461 /// This function internally uses the [`write_all`][writeall] method on
1462 /// this trait and hence will continuously write data so long as no errors
1463 /// are received. This also means that partial writes are not indicated in
1466 /// [writeall]: Self::write_all
1470 /// This function will return any I/O error reported while formatting.
1475 /// use std::io::prelude::*;
1476 /// use std::fs::File;
1478 /// fn main() -> std::io::Result<()> {
1479 /// let mut buffer = File::create("foo.txt")?;
1482 /// write!(buffer, "{:.*}", 2, 1.234567)?;
1483 /// // turns into this:
1484 /// buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))?;
1488 #[stable(feature = "rust1", since = "1.0.0")]
1489 fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> Result<()> {
1490 // Create a shim which translates a Write to a fmt::Write and saves
1491 // off I/O errors. instead of discarding them
1492 struct Adaptor<'a, T: ?Sized + 'a> {
1497 impl<T: Write + ?Sized> fmt::Write for Adaptor<'_, T> {
1498 fn write_str(&mut self, s: &str) -> fmt::Result {
1499 match self.inner.write_all(s.as_bytes()) {
1502 self.error = Err(e);
1509 let mut output = Adaptor { inner: self, error: Ok(()) };
1510 match fmt::write(&mut output, fmt) {
1513 // check if the error came from the underlying `Write` or not
1514 if output.error.is_err() {
1517 Err(Error::new(ErrorKind::Other, "formatter error"))
1523 /// Creates a "by reference" adaptor for this instance of `Write`.
1525 /// The returned adaptor also implements `Write` and will simply borrow this
1531 /// use std::io::Write;
1532 /// use std::fs::File;
1534 /// fn main() -> std::io::Result<()> {
1535 /// let mut buffer = File::create("foo.txt")?;
1537 /// let reference = buffer.by_ref();
1539 /// // we can use reference just like our original buffer
1540 /// reference.write_all(b"some bytes")?;
1544 #[stable(feature = "rust1", since = "1.0.0")]
1545 fn by_ref(&mut self) -> &mut Self
1553 /// The `Seek` trait provides a cursor which can be moved within a stream of
1556 /// The stream typically has a fixed size, allowing seeking relative to either
1557 /// end or the current offset.
1561 /// [`File`][file]s implement `Seek`:
1563 /// [file]: crate::fs::File
1567 /// use std::io::prelude::*;
1568 /// use std::fs::File;
1569 /// use std::io::SeekFrom;
1571 /// fn main() -> io::Result<()> {
1572 /// let mut f = File::open("foo.txt")?;
1574 /// // move the cursor 42 bytes from the start of the file
1575 /// f.seek(SeekFrom::Start(42))?;
1579 #[stable(feature = "rust1", since = "1.0.0")]
1581 /// Seek to an offset, in bytes, in a stream.
1583 /// A seek beyond the end of a stream is allowed, but behavior is defined
1584 /// by the implementation.
1586 /// If the seek operation completed successfully,
1587 /// this method returns the new position from the start of the stream.
1588 /// That position can be used later with [`SeekFrom::Start`].
1592 /// Seeking to a negative offset is considered an error.
1593 #[stable(feature = "rust1", since = "1.0.0")]
1594 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1596 /// Returns the length of this stream (in bytes).
1598 /// This method is implemented using up to three seek operations. If this
1599 /// method returns successfully, the seek position is unchanged (i.e. the
1600 /// position before calling this method is the same as afterwards).
1601 /// However, if this method returns an error, the seek position is
1604 /// If you need to obtain the length of *many* streams and you don't care
1605 /// about the seek position afterwards, you can reduce the number of seek
1606 /// operations by simply calling `seek(SeekFrom::End(0))` and using its
1607 /// return value (it is also the stream length).
1609 /// Note that length of a stream can change over time (for example, when
1610 /// data is appended to a file). So calling this method multiple times does
1611 /// not necessarily return the same length each time.
1617 /// #![feature(seek_convenience)]
1619 /// io::{self, Seek},
1623 /// fn main() -> io::Result<()> {
1624 /// let mut f = File::open("foo.txt")?;
1626 /// let len = f.stream_len()?;
1627 /// println!("The file is currently {} bytes long", len);
1631 #[unstable(feature = "seek_convenience", issue = "59359")]
1632 fn stream_len(&mut self) -> Result<u64> {
1633 let old_pos = self.stream_position()?;
1634 let len = self.seek(SeekFrom::End(0))?;
1636 // Avoid seeking a third time when we were already at the end of the
1637 // stream. The branch is usually way cheaper than a seek operation.
1639 self.seek(SeekFrom::Start(old_pos))?;
1645 /// Returns the current seek position from the start of the stream.
1647 /// This is equivalent to `self.seek(SeekFrom::Current(0))`.
1653 /// #![feature(seek_convenience)]
1655 /// io::{self, BufRead, BufReader, Seek},
1659 /// fn main() -> io::Result<()> {
1660 /// let mut f = BufReader::new(File::open("foo.txt")?);
1662 /// let before = f.stream_position()?;
1663 /// f.read_line(&mut String::new())?;
1664 /// let after = f.stream_position()?;
1666 /// println!("The first line was {} bytes long", after - before);
1670 #[unstable(feature = "seek_convenience", issue = "59359")]
1671 fn stream_position(&mut self) -> Result<u64> {
1672 self.seek(SeekFrom::Current(0))
1676 /// Enumeration of possible methods to seek within an I/O object.
1678 /// It is used by the [`Seek`] trait.
1679 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1680 #[stable(feature = "rust1", since = "1.0.0")]
1682 /// Sets the offset to the provided number of bytes.
1683 #[stable(feature = "rust1", since = "1.0.0")]
1684 Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
1686 /// Sets the offset to the size of this object plus the specified number of
1689 /// It is possible to seek beyond the end of an object, but it's an error to
1690 /// seek before byte 0.
1691 #[stable(feature = "rust1", since = "1.0.0")]
1692 End(#[stable(feature = "rust1", since = "1.0.0")] i64),
1694 /// Sets the offset to the current position plus the specified number of
1697 /// It is possible to seek beyond the end of an object, but it's an error to
1698 /// seek before byte 0.
1699 #[stable(feature = "rust1", since = "1.0.0")]
1700 Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
1703 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> Result<usize> {
1706 let (done, used) = {
1707 let available = match r.fill_buf() {
1709 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1710 Err(e) => return Err(e),
1712 match memchr::memchr(delim, available) {
1714 buf.extend_from_slice(&available[..=i]);
1718 buf.extend_from_slice(available);
1719 (false, available.len())
1725 if done || used == 0 {
1731 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1732 /// to perform extra ways of reading.
1734 /// For example, reading line-by-line is inefficient without using a buffer, so
1735 /// if you want to read by line, you'll need `BufRead`, which includes a
1736 /// [`read_line`] method as well as a [`lines`] iterator.
1740 /// A locked standard input implements `BufRead`:
1744 /// use std::io::prelude::*;
1746 /// let stdin = io::stdin();
1747 /// for line in stdin.lock().lines() {
1748 /// println!("{}", line.unwrap());
1752 /// If you have something that implements [`Read`], you can use the [`BufReader`
1753 /// type][`BufReader`] to turn it into a `BufRead`.
1755 /// For example, [`File`] implements [`Read`], but not `BufRead`.
1756 /// [`BufReader`] to the rescue!
1758 /// [`File`]: crate::fs::File
1759 /// [`read_line`]: Self::read_line
1760 /// [`lines`]: Self::lines
1763 /// use std::io::{self, BufReader};
1764 /// use std::io::prelude::*;
1765 /// use std::fs::File;
1767 /// fn main() -> io::Result<()> {
1768 /// let f = File::open("foo.txt")?;
1769 /// let f = BufReader::new(f);
1771 /// for line in f.lines() {
1772 /// println!("{}", line.unwrap());
1779 #[stable(feature = "rust1", since = "1.0.0")]
1780 pub trait BufRead: Read {
1781 /// Returns the contents of the internal buffer, filling it with more data
1782 /// from the inner reader if it is empty.
1784 /// This function is a lower-level call. It needs to be paired with the
1785 /// [`consume`] method to function properly. When calling this
1786 /// method, none of the contents will be "read" in the sense that later
1787 /// calling `read` may return the same contents. As such, [`consume`] must
1788 /// be called with the number of bytes that are consumed from this buffer to
1789 /// ensure that the bytes are never returned twice.
1791 /// [`consume`]: Self::consume
1793 /// An empty buffer returned indicates that the stream has reached EOF.
1797 /// This function will return an I/O error if the underlying reader was
1798 /// read, but returned an error.
1802 /// A locked standard input implements `BufRead`:
1806 /// use std::io::prelude::*;
1808 /// let stdin = io::stdin();
1809 /// let mut stdin = stdin.lock();
1811 /// let buffer = stdin.fill_buf().unwrap();
1813 /// // work with buffer
1814 /// println!("{:?}", buffer);
1816 /// // ensure the bytes we worked with aren't returned again later
1817 /// let length = buffer.len();
1818 /// stdin.consume(length);
1820 #[stable(feature = "rust1", since = "1.0.0")]
1821 fn fill_buf(&mut self) -> Result<&[u8]>;
1823 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1824 /// so they should no longer be returned in calls to `read`.
1826 /// This function is a lower-level call. It needs to be paired with the
1827 /// [`fill_buf`] method to function properly. This function does
1828 /// not perform any I/O, it simply informs this object that some amount of
1829 /// its buffer, returned from [`fill_buf`], has been consumed and should
1830 /// no longer be returned. As such, this function may do odd things if
1831 /// [`fill_buf`] isn't called before calling it.
1833 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1838 /// Since `consume()` is meant to be used with [`fill_buf`],
1839 /// that method's example includes an example of `consume()`.
1841 /// [`fill_buf`]: Self::fill_buf
1842 #[stable(feature = "rust1", since = "1.0.0")]
1843 fn consume(&mut self, amt: usize);
1845 /// Read all bytes into `buf` until the delimiter `byte` or EOF is reached.
1847 /// This function will read bytes from the underlying stream until the
1848 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1849 /// the delimiter (if found) will be appended to `buf`.
1851 /// If successful, this function will return the total number of bytes read.
1853 /// This function is blocking and should be used carefully: it is possible for
1854 /// an attacker to continuously send bytes without ever sending the delimiter
1859 /// This function will ignore all instances of [`ErrorKind::Interrupted`] and
1860 /// will otherwise return any errors returned by [`fill_buf`].
1862 /// If an I/O error is encountered then all bytes read so far will be
1863 /// present in `buf` and its length will have been adjusted appropriately.
1865 /// [`fill_buf`]: Self::fill_buf
1869 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1870 /// this example, we use [`Cursor`] to read all the bytes in a byte slice
1871 /// in hyphen delimited segments:
1874 /// use std::io::{self, BufRead};
1876 /// let mut cursor = io::Cursor::new(b"lorem-ipsum");
1877 /// let mut buf = vec![];
1879 /// // cursor is at 'l'
1880 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1881 /// .expect("reading from cursor won't fail");
1882 /// assert_eq!(num_bytes, 6);
1883 /// assert_eq!(buf, b"lorem-");
1886 /// // cursor is at 'i'
1887 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1888 /// .expect("reading from cursor won't fail");
1889 /// assert_eq!(num_bytes, 5);
1890 /// assert_eq!(buf, b"ipsum");
1893 /// // cursor is at EOF
1894 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1895 /// .expect("reading from cursor won't fail");
1896 /// assert_eq!(num_bytes, 0);
1897 /// assert_eq!(buf, b"");
1899 #[stable(feature = "rust1", since = "1.0.0")]
1900 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
1901 read_until(self, byte, buf)
1904 /// Read all bytes until a newline (the 0xA byte) is reached, and append
1905 /// them to the provided buffer.
1907 /// This function will read bytes from the underlying stream until the
1908 /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
1909 /// up to, and including, the delimiter (if found) will be appended to
1912 /// If successful, this function will return the total number of bytes read.
1914 /// If this function returns `Ok(0)`, the stream has reached EOF.
1916 /// This function is blocking and should be used carefully: it is possible for
1917 /// an attacker to continuously send bytes without ever sending a newline
1922 /// This function has the same error semantics as [`read_until`] and will
1923 /// also return an error if the read bytes are not valid UTF-8. If an I/O
1924 /// error is encountered then `buf` may contain some bytes already read in
1925 /// the event that all data read so far was valid UTF-8.
1927 /// [`read_until`]: Self::read_until
1931 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1932 /// this example, we use [`Cursor`] to read all the lines in a byte slice:
1935 /// use std::io::{self, BufRead};
1937 /// let mut cursor = io::Cursor::new(b"foo\nbar");
1938 /// let mut buf = String::new();
1940 /// // cursor is at 'f'
1941 /// let num_bytes = cursor.read_line(&mut buf)
1942 /// .expect("reading from cursor won't fail");
1943 /// assert_eq!(num_bytes, 4);
1944 /// assert_eq!(buf, "foo\n");
1947 /// // cursor is at 'b'
1948 /// let num_bytes = cursor.read_line(&mut buf)
1949 /// .expect("reading from cursor won't fail");
1950 /// assert_eq!(num_bytes, 3);
1951 /// assert_eq!(buf, "bar");
1954 /// // cursor is at EOF
1955 /// let num_bytes = cursor.read_line(&mut buf)
1956 /// .expect("reading from cursor won't fail");
1957 /// assert_eq!(num_bytes, 0);
1958 /// assert_eq!(buf, "");
1960 #[stable(feature = "rust1", since = "1.0.0")]
1961 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
1962 // Note that we are not calling the `.read_until` method here, but
1963 // rather our hardcoded implementation. For more details as to why, see
1964 // the comments in `read_to_end`.
1965 append_to_string(buf, |b| read_until(self, b'\n', b))
1968 /// Returns an iterator over the contents of this reader split on the byte
1971 /// The iterator returned from this function will return instances of
1972 /// [`io::Result`]`<`[`Vec<u8>`]`>`. Each vector returned will *not* have
1973 /// the delimiter byte at the end.
1975 /// This function will yield errors whenever [`read_until`] would have
1976 /// also yielded an error.
1978 /// [`io::Result`]: self::Result
1979 /// [`Vec<u8>`]: crate::vec::Vec
1980 /// [`read_until`]: Self::read_until
1984 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1985 /// this example, we use [`Cursor`] to iterate over all hyphen delimited
1986 /// segments in a byte slice
1989 /// use std::io::{self, BufRead};
1991 /// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
1993 /// let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
1994 /// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
1995 /// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
1996 /// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
1997 /// assert_eq!(split_iter.next(), None);
1999 #[stable(feature = "rust1", since = "1.0.0")]
2000 fn split(self, byte: u8) -> Split<Self>
2004 Split { buf: self, delim: byte }
2007 /// Returns an iterator over the lines of this reader.
2009 /// The iterator returned from this function will yield instances of
2010 /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
2011 /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
2013 /// [`io::Result`]: self::Result
2017 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2018 /// this example, we use [`Cursor`] to iterate over all the lines in a byte
2022 /// use std::io::{self, BufRead};
2024 /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
2026 /// let mut lines_iter = cursor.lines().map(|l| l.unwrap());
2027 /// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
2028 /// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
2029 /// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
2030 /// assert_eq!(lines_iter.next(), None);
2035 /// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
2036 #[stable(feature = "rust1", since = "1.0.0")]
2037 fn lines(self) -> Lines<Self>
2045 /// Adaptor to chain together two readers.
2047 /// This struct is generally created by calling [`chain`] on a reader.
2048 /// Please see the documentation of [`chain`] for more details.
2050 /// [`chain`]: Read::chain
2051 #[stable(feature = "rust1", since = "1.0.0")]
2052 pub struct Chain<T, U> {
2058 impl<T, U> Chain<T, U> {
2059 /// Consumes the `Chain`, returning the wrapped readers.
2065 /// use std::io::prelude::*;
2066 /// use std::fs::File;
2068 /// fn main() -> io::Result<()> {
2069 /// let mut foo_file = File::open("foo.txt")?;
2070 /// let mut bar_file = File::open("bar.txt")?;
2072 /// let chain = foo_file.chain(bar_file);
2073 /// let (foo_file, bar_file) = chain.into_inner();
2077 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2078 pub fn into_inner(self) -> (T, U) {
2079 (self.first, self.second)
2082 /// Gets references to the underlying readers in this `Chain`.
2088 /// use std::io::prelude::*;
2089 /// use std::fs::File;
2091 /// fn main() -> io::Result<()> {
2092 /// let mut foo_file = File::open("foo.txt")?;
2093 /// let mut bar_file = File::open("bar.txt")?;
2095 /// let chain = foo_file.chain(bar_file);
2096 /// let (foo_file, bar_file) = chain.get_ref();
2100 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2101 pub fn get_ref(&self) -> (&T, &U) {
2102 (&self.first, &self.second)
2105 /// Gets mutable references to the underlying readers in this `Chain`.
2107 /// Care should be taken to avoid modifying the internal I/O state of the
2108 /// underlying readers as doing so may corrupt the internal state of this
2115 /// use std::io::prelude::*;
2116 /// use std::fs::File;
2118 /// fn main() -> io::Result<()> {
2119 /// let mut foo_file = File::open("foo.txt")?;
2120 /// let mut bar_file = File::open("bar.txt")?;
2122 /// let mut chain = foo_file.chain(bar_file);
2123 /// let (foo_file, bar_file) = chain.get_mut();
2127 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2128 pub fn get_mut(&mut self) -> (&mut T, &mut U) {
2129 (&mut self.first, &mut self.second)
2133 #[stable(feature = "std_debug", since = "1.16.0")]
2134 impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
2135 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2136 f.debug_struct("Chain").field("t", &self.first).field("u", &self.second).finish()
2140 #[stable(feature = "rust1", since = "1.0.0")]
2141 impl<T: Read, U: Read> Read for Chain<T, U> {
2142 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2143 if !self.done_first {
2144 match self.first.read(buf)? {
2145 0 if !buf.is_empty() => self.done_first = true,
2149 self.second.read(buf)
2152 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
2153 if !self.done_first {
2154 match self.first.read_vectored(bufs)? {
2155 0 if bufs.iter().any(|b| !b.is_empty()) => self.done_first = true,
2159 self.second.read_vectored(bufs)
2162 unsafe fn initializer(&self) -> Initializer {
2163 let initializer = self.first.initializer();
2164 if initializer.should_initialize() { initializer } else { self.second.initializer() }
2168 #[stable(feature = "chain_bufread", since = "1.9.0")]
2169 impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
2170 fn fill_buf(&mut self) -> Result<&[u8]> {
2171 if !self.done_first {
2172 match self.first.fill_buf()? {
2173 buf if buf.is_empty() => {
2174 self.done_first = true;
2176 buf => return Ok(buf),
2179 self.second.fill_buf()
2182 fn consume(&mut self, amt: usize) {
2183 if !self.done_first { self.first.consume(amt) } else { self.second.consume(amt) }
2187 /// Reader adaptor which limits the bytes read from an underlying reader.
2189 /// This struct is generally created by calling [`take`] on a reader.
2190 /// Please see the documentation of [`take`] for more details.
2192 /// [`take`]: Read::take
2193 #[stable(feature = "rust1", since = "1.0.0")]
2195 pub struct Take<T> {
2201 /// Returns the number of bytes that can be read before this instance will
2206 /// This instance may reach `EOF` after reading fewer bytes than indicated by
2207 /// this method if the underlying [`Read`] instance reaches EOF.
2213 /// use std::io::prelude::*;
2214 /// use std::fs::File;
2216 /// fn main() -> io::Result<()> {
2217 /// let f = File::open("foo.txt")?;
2219 /// // read at most five bytes
2220 /// let handle = f.take(5);
2222 /// println!("limit: {}", handle.limit());
2226 #[stable(feature = "rust1", since = "1.0.0")]
2227 pub fn limit(&self) -> u64 {
2231 /// Sets the number of bytes that can be read before this instance will
2232 /// return EOF. This is the same as constructing a new `Take` instance, so
2233 /// the amount of bytes read and the previous limit value don't matter when
2234 /// calling this method.
2240 /// use std::io::prelude::*;
2241 /// use std::fs::File;
2243 /// fn main() -> io::Result<()> {
2244 /// let f = File::open("foo.txt")?;
2246 /// // read at most five bytes
2247 /// let mut handle = f.take(5);
2248 /// handle.set_limit(10);
2250 /// assert_eq!(handle.limit(), 10);
2254 #[stable(feature = "take_set_limit", since = "1.27.0")]
2255 pub fn set_limit(&mut self, limit: u64) {
2259 /// Consumes the `Take`, returning the wrapped reader.
2265 /// use std::io::prelude::*;
2266 /// use std::fs::File;
2268 /// fn main() -> io::Result<()> {
2269 /// let mut file = File::open("foo.txt")?;
2271 /// let mut buffer = [0; 5];
2272 /// let mut handle = file.take(5);
2273 /// handle.read(&mut buffer)?;
2275 /// let file = handle.into_inner();
2279 #[stable(feature = "io_take_into_inner", since = "1.15.0")]
2280 pub fn into_inner(self) -> T {
2284 /// Gets a reference to the underlying reader.
2290 /// use std::io::prelude::*;
2291 /// use std::fs::File;
2293 /// fn main() -> io::Result<()> {
2294 /// let mut file = File::open("foo.txt")?;
2296 /// let mut buffer = [0; 5];
2297 /// let mut handle = file.take(5);
2298 /// handle.read(&mut buffer)?;
2300 /// let file = handle.get_ref();
2304 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2305 pub fn get_ref(&self) -> &T {
2309 /// Gets a mutable reference to the underlying reader.
2311 /// Care should be taken to avoid modifying the internal I/O state of the
2312 /// underlying reader as doing so may corrupt the internal limit of this
2319 /// use std::io::prelude::*;
2320 /// use std::fs::File;
2322 /// fn main() -> io::Result<()> {
2323 /// let mut file = File::open("foo.txt")?;
2325 /// let mut buffer = [0; 5];
2326 /// let mut handle = file.take(5);
2327 /// handle.read(&mut buffer)?;
2329 /// let file = handle.get_mut();
2333 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2334 pub fn get_mut(&mut self) -> &mut T {
2339 #[stable(feature = "rust1", since = "1.0.0")]
2340 impl<T: Read> Read for Take<T> {
2341 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2342 // Don't call into inner reader at all at EOF because it may still block
2343 if self.limit == 0 {
2347 let max = cmp::min(buf.len() as u64, self.limit) as usize;
2348 let n = self.inner.read(&mut buf[..max])?;
2349 self.limit -= n as u64;
2353 unsafe fn initializer(&self) -> Initializer {
2354 self.inner.initializer()
2357 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
2358 // Pass in a reservation_size closure that respects the current value
2359 // of limit for each read. If we hit the read limit, this prevents the
2360 // final zero-byte read from allocating again.
2361 read_to_end_with_reservation(self, buf, |self_| cmp::min(self_.limit, 32) as usize)
2365 #[stable(feature = "rust1", since = "1.0.0")]
2366 impl<T: BufRead> BufRead for Take<T> {
2367 fn fill_buf(&mut self) -> Result<&[u8]> {
2368 // Don't call into inner reader at all at EOF because it may still block
2369 if self.limit == 0 {
2373 let buf = self.inner.fill_buf()?;
2374 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
2378 fn consume(&mut self, amt: usize) {
2379 // Don't let callers reset the limit by passing an overlarge value
2380 let amt = cmp::min(amt as u64, self.limit) as usize;
2381 self.limit -= amt as u64;
2382 self.inner.consume(amt);
2386 /// An iterator over `u8` values of a reader.
2388 /// This struct is generally created by calling [`bytes`] on a reader.
2389 /// Please see the documentation of [`bytes`] for more details.
2391 /// [`bytes`]: Read::bytes
2392 #[stable(feature = "rust1", since = "1.0.0")]
2394 pub struct Bytes<R> {
2398 #[stable(feature = "rust1", since = "1.0.0")]
2399 impl<R: Read> Iterator for Bytes<R> {
2400 type Item = Result<u8>;
2402 fn next(&mut self) -> Option<Result<u8>> {
2405 return match self.inner.read(slice::from_mut(&mut byte)) {
2407 Ok(..) => Some(Ok(byte)),
2408 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
2409 Err(e) => Some(Err(e)),
2415 /// An iterator over the contents of an instance of `BufRead` split on a
2416 /// particular byte.
2418 /// This struct is generally created by calling [`split`] on a `BufRead`.
2419 /// Please see the documentation of [`split`] for more details.
2421 /// [`split`]: BufRead::split
2422 #[stable(feature = "rust1", since = "1.0.0")]
2424 pub struct Split<B> {
2429 #[stable(feature = "rust1", since = "1.0.0")]
2430 impl<B: BufRead> Iterator for Split<B> {
2431 type Item = Result<Vec<u8>>;
2433 fn next(&mut self) -> Option<Result<Vec<u8>>> {
2434 let mut buf = Vec::new();
2435 match self.buf.read_until(self.delim, &mut buf) {
2438 if buf[buf.len() - 1] == self.delim {
2443 Err(e) => Some(Err(e)),
2448 /// An iterator over the lines of an instance of `BufRead`.
2450 /// This struct is generally created by calling [`lines`] on a `BufRead`.
2451 /// Please see the documentation of [`lines`] for more details.
2453 /// [`lines`]: BufRead::lines
2454 #[stable(feature = "rust1", since = "1.0.0")]
2456 pub struct Lines<B> {
2460 #[stable(feature = "rust1", since = "1.0.0")]
2461 impl<B: BufRead> Iterator for Lines<B> {
2462 type Item = Result<String>;
2464 fn next(&mut self) -> Option<Result<String>> {
2465 let mut buf = String::new();
2466 match self.buf.read_line(&mut buf) {
2469 if buf.ends_with('\n') {
2471 if buf.ends_with('\r') {
2477 Err(e) => Some(Err(e)),
2484 use super::{repeat, Cursor, SeekFrom};
2485 use crate::cmp::{self, min};
2486 use crate::io::prelude::*;
2487 use crate::io::{self, IoSlice, IoSliceMut};
2488 use crate::ops::Deref;
2491 #[cfg_attr(target_os = "emscripten", ignore)]
2493 let mut buf = Cursor::new(&b"12"[..]);
2494 let mut v = Vec::new();
2495 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
2496 assert_eq!(v, b"12");
2498 let mut buf = Cursor::new(&b"1233"[..]);
2499 let mut v = Vec::new();
2500 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
2501 assert_eq!(v, b"123");
2503 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
2504 assert_eq!(v, b"3");
2506 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
2512 let buf = Cursor::new(&b"12"[..]);
2513 let mut s = buf.split(b'3');
2514 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
2515 assert!(s.next().is_none());
2517 let buf = Cursor::new(&b"1233"[..]);
2518 let mut s = buf.split(b'3');
2519 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
2520 assert_eq!(s.next().unwrap().unwrap(), vec![]);
2521 assert!(s.next().is_none());
2526 let mut buf = Cursor::new(&b"12"[..]);
2527 let mut v = String::new();
2528 assert_eq!(buf.read_line(&mut v).unwrap(), 2);
2529 assert_eq!(v, "12");
2531 let mut buf = Cursor::new(&b"12\n\n"[..]);
2532 let mut v = String::new();
2533 assert_eq!(buf.read_line(&mut v).unwrap(), 3);
2534 assert_eq!(v, "12\n");
2536 assert_eq!(buf.read_line(&mut v).unwrap(), 1);
2537 assert_eq!(v, "\n");
2539 assert_eq!(buf.read_line(&mut v).unwrap(), 0);
2545 let buf = Cursor::new(&b"12\r"[..]);
2546 let mut s = buf.lines();
2547 assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
2548 assert!(s.next().is_none());
2550 let buf = Cursor::new(&b"12\r\n\n"[..]);
2551 let mut s = buf.lines();
2552 assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
2553 assert_eq!(s.next().unwrap().unwrap(), "".to_string());
2554 assert!(s.next().is_none());
2559 let mut c = Cursor::new(&b""[..]);
2560 let mut v = Vec::new();
2561 assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
2564 let mut c = Cursor::new(&b"1"[..]);
2565 let mut v = Vec::new();
2566 assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
2567 assert_eq!(v, b"1");
2569 let cap = 1024 * 1024;
2570 let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
2571 let mut v = Vec::new();
2572 let (a, b) = data.split_at(data.len() / 2);
2573 assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
2574 assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
2575 assert_eq!(v, data);
2579 fn read_to_string() {
2580 let mut c = Cursor::new(&b""[..]);
2581 let mut v = String::new();
2582 assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
2585 let mut c = Cursor::new(&b"1"[..]);
2586 let mut v = String::new();
2587 assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
2590 let mut c = Cursor::new(&b"\xff"[..]);
2591 let mut v = String::new();
2592 assert!(c.read_to_string(&mut v).is_err());
2597 let mut buf = [0; 4];
2599 let mut c = Cursor::new(&b""[..]);
2600 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2602 let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
2603 c.read_exact(&mut buf).unwrap();
2604 assert_eq!(&buf, b"1234");
2605 c.read_exact(&mut buf).unwrap();
2606 assert_eq!(&buf, b"5678");
2607 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2611 fn read_exact_slice() {
2612 let mut buf = [0; 4];
2614 let mut c = &b""[..];
2615 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2617 let mut c = &b"123"[..];
2618 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2619 // make sure the optimized (early returning) method is being used
2620 assert_eq!(&buf, &[0; 4]);
2622 let mut c = &b"1234"[..];
2623 c.read_exact(&mut buf).unwrap();
2624 assert_eq!(&buf, b"1234");
2626 let mut c = &b"56789"[..];
2627 c.read_exact(&mut buf).unwrap();
2628 assert_eq!(&buf, b"5678");
2629 assert_eq!(c, b"9");
2637 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
2638 Err(io::Error::new(io::ErrorKind::Other, ""))
2641 impl BufRead for R {
2642 fn fill_buf(&mut self) -> io::Result<&[u8]> {
2643 Err(io::Error::new(io::ErrorKind::Other, ""))
2645 fn consume(&mut self, _amt: usize) {}
2648 let mut buf = [0; 1];
2649 assert_eq!(0, R.take(0).read(&mut buf).unwrap());
2650 assert_eq!(b"", R.take(0).fill_buf().unwrap());
2653 fn cmp_bufread<Br1: BufRead, Br2: BufRead>(mut br1: Br1, mut br2: Br2, exp: &[u8]) {
2654 let mut cat = Vec::new();
2657 let buf1 = br1.fill_buf().unwrap();
2658 let buf2 = br2.fill_buf().unwrap();
2659 let minlen = if buf1.len() < buf2.len() { buf1.len() } else { buf2.len() };
2660 assert_eq!(buf1[..minlen], buf2[..minlen]);
2661 cat.extend_from_slice(&buf1[..minlen]);
2667 br1.consume(consume);
2668 br2.consume(consume);
2670 assert_eq!(br1.fill_buf().unwrap().len(), 0);
2671 assert_eq!(br2.fill_buf().unwrap().len(), 0);
2672 assert_eq!(&cat[..], &exp[..])
2676 fn chain_bufread() {
2677 let testdata = b"ABCDEFGHIJKL";
2679 (&testdata[..3]).chain(&testdata[3..6]).chain(&testdata[6..9]).chain(&testdata[9..]);
2680 let chain2 = (&testdata[..4]).chain(&testdata[4..8]).chain(&testdata[8..]);
2681 cmp_bufread(chain1, chain2, &testdata[..]);
2685 fn chain_zero_length_read_is_not_eof() {
2688 let mut s = String::new();
2689 let mut chain = (&a[..]).chain(&b[..]);
2690 chain.read(&mut []).unwrap();
2691 chain.read_to_string(&mut s).unwrap();
2692 assert_eq!("AB", s);
2696 #[cfg_attr(target_os = "emscripten", ignore)]
2697 fn bench_read_to_end(b: &mut test::Bencher) {
2699 let mut lr = repeat(1).take(10000000);
2700 let mut vec = Vec::with_capacity(1024);
2701 super::read_to_end(&mut lr, &mut vec)
2706 fn seek_len() -> io::Result<()> {
2707 let mut c = Cursor::new(vec![0; 15]);
2708 assert_eq!(c.stream_len()?, 15);
2710 c.seek(SeekFrom::End(0))?;
2711 let old_pos = c.stream_position()?;
2712 assert_eq!(c.stream_len()?, 15);
2713 assert_eq!(c.stream_position()?, old_pos);
2715 c.seek(SeekFrom::Start(7))?;
2716 c.seek(SeekFrom::Current(2))?;
2717 let old_pos = c.stream_position()?;
2718 assert_eq!(c.stream_len()?, 15);
2719 assert_eq!(c.stream_position()?, old_pos);
2725 fn seek_position() -> io::Result<()> {
2726 // All `asserts` are duplicated here to make sure the method does not
2727 // change anything about the seek state.
2728 let mut c = Cursor::new(vec![0; 15]);
2729 assert_eq!(c.stream_position()?, 0);
2730 assert_eq!(c.stream_position()?, 0);
2732 c.seek(SeekFrom::End(0))?;
2733 assert_eq!(c.stream_position()?, 15);
2734 assert_eq!(c.stream_position()?, 15);
2736 c.seek(SeekFrom::Start(7))?;
2737 c.seek(SeekFrom::Current(2))?;
2738 assert_eq!(c.stream_position()?, 9);
2739 assert_eq!(c.stream_position()?, 9);
2741 c.seek(SeekFrom::End(-3))?;
2742 c.seek(SeekFrom::Current(1))?;
2743 c.seek(SeekFrom::Current(-5))?;
2744 assert_eq!(c.stream_position()?, 8);
2745 assert_eq!(c.stream_position()?, 8);
2750 // A simple example reader which uses the default implementation of
2752 struct ExampleSliceReader<'a> {
2756 impl<'a> Read for ExampleSliceReader<'a> {
2757 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
2758 let len = cmp::min(self.slice.len(), buf.len());
2759 buf[..len].copy_from_slice(&self.slice[..len]);
2760 self.slice = &self.slice[len..];
2766 fn test_read_to_end_capacity() -> io::Result<()> {
2767 let input = &b"foo"[..];
2769 // read_to_end() generally needs to over-allocate, both for efficiency
2770 // and so that it can distinguish EOF. Assert that this is the case
2771 // with this simple ExampleSliceReader struct, which uses the default
2772 // implementation of read_to_end. Even though vec1 is allocated with
2773 // exactly enough capacity for the read, read_to_end will allocate more
2775 let mut vec1 = Vec::with_capacity(input.len());
2776 ExampleSliceReader { slice: input }.read_to_end(&mut vec1)?;
2777 assert_eq!(vec1.len(), input.len());
2778 assert!(vec1.capacity() > input.len(), "allocated more");
2780 // However, std::io::Take includes an implementation of read_to_end
2781 // that will not allocate when the limit has already been reached. In
2782 // this case, vec2 never grows.
2783 let mut vec2 = Vec::with_capacity(input.len());
2784 ExampleSliceReader { slice: input }.take(input.len() as u64).read_to_end(&mut vec2)?;
2785 assert_eq!(vec2.len(), input.len());
2786 assert_eq!(vec2.capacity(), input.len(), "did not allocate more");
2792 fn io_slice_mut_advance() {
2793 let mut buf1 = [1; 8];
2794 let mut buf2 = [2; 16];
2795 let mut buf3 = [3; 8];
2796 let mut bufs = &mut [
2797 IoSliceMut::new(&mut buf1),
2798 IoSliceMut::new(&mut buf2),
2799 IoSliceMut::new(&mut buf3),
2802 // Only in a single buffer..
2803 bufs = IoSliceMut::advance(bufs, 1);
2804 assert_eq!(bufs[0].deref(), [1; 7].as_ref());
2805 assert_eq!(bufs[1].deref(), [2; 16].as_ref());
2806 assert_eq!(bufs[2].deref(), [3; 8].as_ref());
2808 // Removing a buffer, leaving others as is.
2809 bufs = IoSliceMut::advance(bufs, 7);
2810 assert_eq!(bufs[0].deref(), [2; 16].as_ref());
2811 assert_eq!(bufs[1].deref(), [3; 8].as_ref());
2813 // Removing a buffer and removing from the next buffer.
2814 bufs = IoSliceMut::advance(bufs, 18);
2815 assert_eq!(bufs[0].deref(), [3; 6].as_ref());
2819 fn io_slice_mut_advance_empty_slice() {
2820 let empty_bufs = &mut [][..];
2822 IoSliceMut::advance(empty_bufs, 1);
2826 fn io_slice_mut_advance_beyond_total_length() {
2827 let mut buf1 = [1; 8];
2828 let mut bufs = &mut [IoSliceMut::new(&mut buf1)][..];
2830 // Going beyond the total length should be ok.
2831 bufs = IoSliceMut::advance(bufs, 9);
2832 assert!(bufs.is_empty());
2836 fn io_slice_advance() {
2840 let mut bufs = &mut [IoSlice::new(&buf1), IoSlice::new(&buf2), IoSlice::new(&buf3)][..];
2842 // Only in a single buffer..
2843 bufs = IoSlice::advance(bufs, 1);
2844 assert_eq!(bufs[0].deref(), [1; 7].as_ref());
2845 assert_eq!(bufs[1].deref(), [2; 16].as_ref());
2846 assert_eq!(bufs[2].deref(), [3; 8].as_ref());
2848 // Removing a buffer, leaving others as is.
2849 bufs = IoSlice::advance(bufs, 7);
2850 assert_eq!(bufs[0].deref(), [2; 16].as_ref());
2851 assert_eq!(bufs[1].deref(), [3; 8].as_ref());
2853 // Removing a buffer and removing from the next buffer.
2854 bufs = IoSlice::advance(bufs, 18);
2855 assert_eq!(bufs[0].deref(), [3; 6].as_ref());
2859 fn io_slice_advance_empty_slice() {
2860 let empty_bufs = &mut [][..];
2862 IoSlice::advance(empty_bufs, 1);
2866 fn io_slice_advance_beyond_total_length() {
2868 let mut bufs = &mut [IoSlice::new(&buf1)][..];
2870 // Going beyond the total length should be ok.
2871 bufs = IoSlice::advance(bufs, 9);
2872 assert!(bufs.is_empty());
2875 /// Create a new writer that reads from at most `n_bufs` and reads
2876 /// `per_call` bytes (in total) per call to write.
2877 fn test_writer(n_bufs: usize, per_call: usize) -> TestWriter {
2878 TestWriter { n_bufs, per_call, written: Vec::new() }
2887 impl Write for TestWriter {
2888 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
2889 self.write_vectored(&[IoSlice::new(buf)])
2892 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
2893 let mut left = self.per_call;
2894 let mut written = 0;
2895 for buf in bufs.iter().take(self.n_bufs) {
2896 let n = min(left, buf.len());
2897 self.written.extend_from_slice(&buf[0..n]);
2904 fn flush(&mut self) -> io::Result<()> {
2910 fn test_writer_read_from_one_buf() {
2911 let mut writer = test_writer(1, 2);
2913 assert_eq!(writer.write(&[]).unwrap(), 0);
2914 assert_eq!(writer.write_vectored(&[]).unwrap(), 0);
2916 // Read at most 2 bytes.
2917 assert_eq!(writer.write(&[1, 1, 1]).unwrap(), 2);
2918 let bufs = &[IoSlice::new(&[2, 2, 2])];
2919 assert_eq!(writer.write_vectored(bufs).unwrap(), 2);
2921 // Only read from first buf.
2922 let bufs = &[IoSlice::new(&[3]), IoSlice::new(&[4, 4])];
2923 assert_eq!(writer.write_vectored(bufs).unwrap(), 1);
2925 assert_eq!(writer.written, &[1, 1, 2, 2, 3]);
2929 fn test_writer_read_from_multiple_bufs() {
2930 let mut writer = test_writer(3, 3);
2932 // Read at most 3 bytes from two buffers.
2933 let bufs = &[IoSlice::new(&[1]), IoSlice::new(&[2, 2, 2])];
2934 assert_eq!(writer.write_vectored(bufs).unwrap(), 3);
2936 // Read at most 3 bytes from three buffers.
2937 let bufs = &[IoSlice::new(&[3]), IoSlice::new(&[4]), IoSlice::new(&[5, 5])];
2938 assert_eq!(writer.write_vectored(bufs).unwrap(), 3);
2940 assert_eq!(writer.written, &[1, 2, 2, 3, 4, 5]);
2944 fn test_write_all_vectored() {
2945 #[rustfmt::skip] // Becomes unreadable otherwise.
2946 let tests: Vec<(_, &'static [u8])> = vec![
2948 (vec![IoSlice::new(&[]), IoSlice::new(&[])], &[]),
2949 (vec![IoSlice::new(&[1])], &[1]),
2950 (vec![IoSlice::new(&[1, 2])], &[1, 2]),
2951 (vec![IoSlice::new(&[1, 2, 3])], &[1, 2, 3]),
2952 (vec![IoSlice::new(&[1, 2, 3, 4])], &[1, 2, 3, 4]),
2953 (vec![IoSlice::new(&[1, 2, 3, 4, 5])], &[1, 2, 3, 4, 5]),
2954 (vec![IoSlice::new(&[1]), IoSlice::new(&[2])], &[1, 2]),
2955 (vec![IoSlice::new(&[1]), IoSlice::new(&[2, 2])], &[1, 2, 2]),
2956 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2])], &[1, 1, 2, 2]),
2957 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 2, 2, 2]),
2958 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 2, 2, 2]),
2959 (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 1, 2, 2, 2]),
2960 (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2, 2])], &[1, 1, 1, 2, 2, 2, 2]),
2961 (vec![IoSlice::new(&[1, 1, 1, 1]), IoSlice::new(&[2, 2, 2, 2])], &[1, 1, 1, 1, 2, 2, 2, 2]),
2962 (vec![IoSlice::new(&[1]), IoSlice::new(&[2]), IoSlice::new(&[3])], &[1, 2, 3]),
2963 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2]), IoSlice::new(&[3, 3])], &[1, 1, 2, 2, 3, 3]),
2964 (vec![IoSlice::new(&[1]), IoSlice::new(&[2, 2]), IoSlice::new(&[3, 3, 3])], &[1, 2, 2, 3, 3, 3]),
2965 (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2]), IoSlice::new(&[3, 3, 3])], &[1, 1, 1, 2, 2, 2, 3, 3, 3]),
2968 let writer_configs = &[(1, 1), (1, 2), (1, 3), (2, 2), (2, 3), (3, 3)];
2970 for (n_bufs, per_call) in writer_configs.iter().copied() {
2971 for (mut input, wanted) in tests.clone().into_iter() {
2972 let mut writer = test_writer(n_bufs, per_call);
2973 assert!(writer.write_all_vectored(&mut *input).is_ok());
2974 assert_eq!(&*writer.written, &*wanted);