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")]
256 use crate::ops::{Deref, DerefMut};
262 #[stable(feature = "rust1", since = "1.0.0")]
263 pub use self::buffered::IntoInnerError;
264 #[stable(feature = "rust1", since = "1.0.0")]
265 pub use self::buffered::{BufReader, BufWriter, LineWriter};
266 #[stable(feature = "rust1", since = "1.0.0")]
267 pub use self::cursor::Cursor;
268 #[stable(feature = "rust1", since = "1.0.0")]
269 pub use self::error::{Error, ErrorKind, Result};
270 #[stable(feature = "rust1", since = "1.0.0")]
271 pub use self::stdio::{stderr, stdin, stdout, Stderr, Stdin, Stdout};
272 #[stable(feature = "rust1", since = "1.0.0")]
273 pub use self::stdio::{StderrLock, StdinLock, StdoutLock};
274 #[unstable(feature = "print_internals", issue = "none")]
275 pub use self::stdio::{_eprint, _print};
276 #[unstable(feature = "libstd_io_internals", issue = "42788")]
277 #[doc(no_inline, hidden)]
278 pub use self::stdio::{set_panic, set_print};
279 #[stable(feature = "rust1", since = "1.0.0")]
280 pub use self::util::{copy, empty, repeat, sink, Empty, Repeat, Sink};
291 const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
294 buf: &'a mut Vec<u8>,
298 impl Drop for Guard<'_> {
301 self.buf.set_len(self.len);
306 // A few methods below (read_to_string, read_line) will append data into a
307 // `String` buffer, but we need to be pretty careful when doing this. The
308 // implementation will just call `.as_mut_vec()` and then delegate to a
309 // byte-oriented reading method, but we must ensure that when returning we never
310 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
312 // To this end, we use an RAII guard (to protect against panics) which updates
313 // the length of the string when it is dropped. This guard initially truncates
314 // the string to the prior length and only after we've validated that the
315 // new contents are valid UTF-8 do we allow it to set a longer length.
317 // The unsafety in this function is twofold:
319 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
321 // 2. We're passing a raw buffer to the function `f`, and it is expected that
322 // the function only *appends* bytes to the buffer. We'll get undefined
323 // behavior if existing bytes are overwritten to have non-UTF-8 data.
324 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
326 F: FnOnce(&mut Vec<u8>) -> Result<usize>,
329 let mut g = Guard { len: buf.len(), buf: buf.as_mut_vec() };
331 if str::from_utf8(&g.buf[g.len..]).is_err() {
333 Err(Error::new(ErrorKind::InvalidData, "stream did not contain valid UTF-8"))
342 // This uses an adaptive system to extend the vector when it fills. We want to
343 // avoid paying to allocate and zero a huge chunk of memory if the reader only
344 // has 4 bytes while still making large reads if the reader does have a ton
345 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
346 // time is 4,500 times (!) slower than a default reservation size of 32 if the
347 // reader has a very small amount of data to return.
349 // Because we're extending the buffer with uninitialized data for trusted
350 // readers, we need to make sure to truncate that if any of this panics.
351 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
352 read_to_end_with_reservation(r, buf, |_| 32)
355 fn read_to_end_with_reservation<R, F>(
358 mut reservation_size: F,
362 F: FnMut(&R) -> usize,
364 let start_len = buf.len();
365 let mut g = Guard { len: buf.len(), buf };
368 if g.len == g.buf.len() {
370 // FIXME(danielhenrymantilla): #42788
372 // - This creates a (mut) reference to a slice of
373 // _uninitialized_ integers, which is **undefined behavior**
375 // - Only the standard library gets to soundly "ignore" this,
376 // based on its privileged knowledge of unstable rustc
378 g.buf.reserve(reservation_size(r));
379 let capacity = g.buf.capacity();
380 g.buf.set_len(capacity);
381 r.initializer().initialize(&mut g.buf[g.len..]);
385 match r.read(&mut g.buf[g.len..]) {
387 ret = Ok(g.len - start_len);
391 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
402 pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
404 F: FnOnce(&mut [u8]) -> Result<usize>,
406 let buf = bufs.iter_mut().find(|b| !b.is_empty()).map_or(&mut [][..], |b| &mut **b);
410 pub(crate) fn default_write_vectored<F>(write: F, bufs: &[IoSlice<'_>]) -> Result<usize>
412 F: FnOnce(&[u8]) -> Result<usize>,
414 let buf = bufs.iter().find(|b| !b.is_empty()).map_or(&[][..], |b| &**b);
418 /// The `Read` trait allows for reading bytes from a source.
420 /// Implementors of the `Read` trait are called 'readers'.
422 /// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
423 /// will attempt to pull bytes from this source into a provided buffer. A
424 /// number of other methods are implemented in terms of [`read()`], giving
425 /// implementors a number of ways to read bytes while only needing to implement
428 /// Readers are intended to be composable with one another. Many implementors
429 /// throughout [`std::io`] take and provide types which implement the `Read`
432 /// Please note that each call to [`read()`] may involve a system call, and
433 /// therefore, using something that implements [`BufRead`], such as
434 /// [`BufReader`], will be more efficient.
438 /// [`File`]s implement `Read`:
442 /// use std::io::prelude::*;
443 /// use std::fs::File;
445 /// fn main() -> io::Result<()> {
446 /// let mut f = File::open("foo.txt")?;
447 /// let mut buffer = [0; 10];
449 /// // read up to 10 bytes
450 /// f.read(&mut buffer)?;
452 /// let mut buffer = Vec::new();
453 /// // read the whole file
454 /// f.read_to_end(&mut buffer)?;
456 /// // read into a String, so that you don't need to do the conversion.
457 /// let mut buffer = String::new();
458 /// f.read_to_string(&mut buffer)?;
460 /// // and more! See the other methods for more details.
465 /// Read from [`&str`] because [`&[u8]`][slice] implements `Read`:
469 /// use std::io::prelude::*;
471 /// fn main() -> io::Result<()> {
472 /// let mut b = "This string will be read".as_bytes();
473 /// let mut buffer = [0; 10];
475 /// // read up to 10 bytes
476 /// b.read(&mut buffer)?;
478 /// // etc... it works exactly as a File does!
483 /// [`read()`]: Read::read
485 /// [`std::io`]: self
486 /// [`File`]: crate::fs::File
487 /// [slice]: ../../std/primitive.slice.html
488 #[stable(feature = "rust1", since = "1.0.0")]
491 /// Pull some bytes from this source into the specified buffer, returning
492 /// how many bytes were read.
494 /// This function does not provide any guarantees about whether it blocks
495 /// waiting for data, but if an object needs to block for a read and cannot,
496 /// it will typically signal this via an [`Err`] return value.
498 /// If the return value of this method is [`Ok(n)`], then it must be
499 /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
500 /// that the buffer `buf` has been filled in with `n` bytes of data from this
501 /// source. If `n` is `0`, then it can indicate one of two scenarios:
503 /// 1. This reader has reached its "end of file" and will likely no longer
504 /// be able to produce bytes. Note that this does not mean that the
505 /// reader will *always* no longer be able to produce bytes.
506 /// 2. The buffer specified was 0 bytes in length.
508 /// It is not an error if the returned value `n` is smaller than the buffer size,
509 /// even when the reader is not at the end of the stream yet.
510 /// This may happen for example because fewer bytes are actually available right now
511 /// (e. g. being close to end-of-file) or because read() was interrupted by a signal.
513 /// No guarantees are provided about the contents of `buf` when this
514 /// function is called, implementations cannot rely on any property of the
515 /// contents of `buf` being true. It is recommended that *implementations*
516 /// only write data to `buf` instead of reading its contents.
518 /// Correspondingly, however, *callers* of this method may not assume any guarantees
519 /// about how the implementation uses `buf`. The trait is safe to implement,
520 /// so it is possible that the code that's supposed to write to the buffer might also read
521 /// from it. It is your responsibility to make sure that `buf` is initialized
522 /// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
523 /// obtains via [`MaybeUninit<T>`]) is not safe, and can lead to undefined behavior.
525 /// [`MaybeUninit<T>`]: crate::mem::MaybeUninit
529 /// If this function encounters any form of I/O or other error, an error
530 /// variant will be returned. If an error is returned then it must be
531 /// guaranteed that no bytes were read.
533 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
534 /// operation should be retried if there is nothing else to do.
538 /// [`File`]s implement `Read`:
541 /// [`File`]: crate::fs::File
545 /// use std::io::prelude::*;
546 /// use std::fs::File;
548 /// fn main() -> io::Result<()> {
549 /// let mut f = File::open("foo.txt")?;
550 /// let mut buffer = [0; 10];
552 /// // read up to 10 bytes
553 /// let n = f.read(&mut buffer[..])?;
555 /// println!("The bytes: {:?}", &buffer[..n]);
559 #[stable(feature = "rust1", since = "1.0.0")]
560 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
562 /// Like `read`, except that it reads into a slice of buffers.
564 /// Data is copied to fill each buffer in order, with the final buffer
565 /// written to possibly being only partially filled. This method must
566 /// behave equivalently to a single call to `read` with concatenated
569 /// The default implementation calls `read` with either the first nonempty
570 /// buffer provided, or an empty one if none exists.
571 #[stable(feature = "iovec", since = "1.36.0")]
572 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
573 default_read_vectored(|b| self.read(b), bufs)
576 /// Determines if this `Read`er has an efficient `read_vectored`
579 /// If a `Read`er does not override the default `read_vectored`
580 /// implementation, code using it may want to avoid the method all together
581 /// and coalesce writes into a single buffer for higher performance.
583 /// The default implementation returns `false`.
584 #[unstable(feature = "can_vector", issue = "69941")]
585 fn is_read_vectored(&self) -> bool {
589 /// Determines if this `Read`er can work with buffers of uninitialized
592 /// The default implementation returns an initializer which will zero
595 /// If a `Read`er guarantees that it can work properly with uninitialized
596 /// memory, it should call [`Initializer::nop()`]. See the documentation for
597 /// [`Initializer`] for details.
599 /// The behavior of this method must be independent of the state of the
600 /// `Read`er - the method only takes `&self` so that it can be used through
605 /// This method is unsafe because a `Read`er could otherwise return a
606 /// non-zeroing `Initializer` from another `Read` type without an `unsafe`
608 #[unstable(feature = "read_initializer", issue = "42788")]
610 unsafe fn initializer(&self) -> Initializer {
611 Initializer::zeroing()
614 /// Read all bytes until EOF in this source, placing them into `buf`.
616 /// All bytes read from this source will be appended to the specified buffer
617 /// `buf`. This function will continuously call [`read()`] to append more data to
618 /// `buf` until [`read()`] returns either [`Ok(0)`] or an error of
619 /// non-[`ErrorKind::Interrupted`] kind.
621 /// If successful, this function will return the total number of bytes read.
625 /// If this function encounters an error of the kind
626 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
629 /// If any other read error is encountered then this function immediately
630 /// returns. Any bytes which have already been read will be appended to
635 /// [`File`]s implement `Read`:
637 /// [`read()`]: Read::read
639 /// [`File`]: crate::fs::File
643 /// use std::io::prelude::*;
644 /// use std::fs::File;
646 /// fn main() -> io::Result<()> {
647 /// let mut f = File::open("foo.txt")?;
648 /// let mut buffer = Vec::new();
650 /// // read the whole file
651 /// f.read_to_end(&mut buffer)?;
656 /// (See also the [`std::fs::read`] convenience function for reading from a
659 /// [`std::fs::read`]: crate::fs::read
660 #[stable(feature = "rust1", since = "1.0.0")]
661 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
662 read_to_end(self, buf)
665 /// Read all bytes until EOF in this source, appending them to `buf`.
667 /// If successful, this function returns the number of bytes which were read
668 /// and appended to `buf`.
672 /// If the data in this stream is *not* valid UTF-8 then an error is
673 /// returned and `buf` is unchanged.
675 /// See [`read_to_end`][readtoend] for other error semantics.
677 /// [readtoend]: Self::read_to_end
681 /// [`File`][file]s implement `Read`:
683 /// [file]: crate::fs::File
687 /// use std::io::prelude::*;
688 /// use std::fs::File;
690 /// fn main() -> io::Result<()> {
691 /// let mut f = File::open("foo.txt")?;
692 /// let mut buffer = String::new();
694 /// f.read_to_string(&mut buffer)?;
699 /// (See also the [`std::fs::read_to_string`] convenience function for
700 /// reading from a file.)
702 /// [`std::fs::read_to_string`]: crate::fs::read_to_string
703 #[stable(feature = "rust1", since = "1.0.0")]
704 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
705 // Note that we do *not* call `.read_to_end()` here. We are passing
706 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
707 // method to fill it up. An arbitrary implementation could overwrite the
708 // entire contents of the vector, not just append to it (which is what
709 // we are expecting).
711 // To prevent extraneously checking the UTF-8-ness of the entire buffer
712 // we pass it to our hardcoded `read_to_end` implementation which we
713 // know is guaranteed to only read data into the end of the buffer.
714 append_to_string(buf, |b| read_to_end(self, b))
717 /// Read the exact number of bytes required to fill `buf`.
719 /// This function reads as many bytes as necessary to completely fill the
720 /// specified buffer `buf`.
722 /// No guarantees are provided about the contents of `buf` when this
723 /// function is called, implementations cannot rely on any property of the
724 /// contents of `buf` being true. It is recommended that implementations
725 /// only write data to `buf` instead of reading its contents. The
726 /// documentation on [`read`] has a more detailed explanation on this
731 /// If this function encounters an error of the kind
732 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
735 /// If this function encounters an "end of file" before completely filling
736 /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
737 /// The contents of `buf` are unspecified in this case.
739 /// If any other read error is encountered then this function immediately
740 /// returns. The contents of `buf` are unspecified in this case.
742 /// If this function returns an error, it is unspecified how many bytes it
743 /// has read, but it will never read more than would be necessary to
744 /// completely fill the buffer.
748 /// [`File`]s implement `Read`:
750 /// [`read`]: Read::read
751 /// [`File`]: crate::fs::File
755 /// use std::io::prelude::*;
756 /// use std::fs::File;
758 /// fn main() -> io::Result<()> {
759 /// let mut f = File::open("foo.txt")?;
760 /// let mut buffer = [0; 10];
762 /// // read exactly 10 bytes
763 /// f.read_exact(&mut buffer)?;
767 #[stable(feature = "read_exact", since = "1.6.0")]
768 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
769 while !buf.is_empty() {
770 match self.read(buf) {
776 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
777 Err(e) => return Err(e),
781 Err(Error::new(ErrorKind::UnexpectedEof, "failed to fill whole buffer"))
787 /// Creates a "by reference" adaptor for this instance of `Read`.
789 /// The returned adaptor also implements `Read` and will simply borrow this
794 /// [`File`][file]s implement `Read`:
796 /// [file]: crate::fs::File
800 /// use std::io::Read;
801 /// use std::fs::File;
803 /// fn main() -> io::Result<()> {
804 /// let mut f = File::open("foo.txt")?;
805 /// let mut buffer = Vec::new();
806 /// let mut other_buffer = Vec::new();
809 /// let reference = f.by_ref();
811 /// // read at most 5 bytes
812 /// reference.take(5).read_to_end(&mut buffer)?;
814 /// } // drop our &mut reference so we can use f again
816 /// // original file still usable, read the rest
817 /// f.read_to_end(&mut other_buffer)?;
821 #[stable(feature = "rust1", since = "1.0.0")]
822 fn by_ref(&mut self) -> &mut Self
829 /// Transforms this `Read` instance to an [`Iterator`] over its bytes.
831 /// The returned type implements [`Iterator`] where the `Item` is
832 /// [`Result`]`<`[`u8`]`, `[`io::Error`]`>`.
833 /// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
834 /// otherwise. EOF is mapped to returning [`None`] from this iterator.
838 /// [`File`][file]s implement `Read`:
840 /// [file]: crate::fs::File
841 /// [`Iterator`]: crate::iter::Iterator
842 /// [`Result`]: crate::result::Result
843 /// [`io::Error`]: self::Error
847 /// use std::io::prelude::*;
848 /// use std::fs::File;
850 /// fn main() -> io::Result<()> {
851 /// let mut f = File::open("foo.txt")?;
853 /// for byte in f.bytes() {
854 /// println!("{}", byte.unwrap());
859 #[stable(feature = "rust1", since = "1.0.0")]
860 fn bytes(self) -> Bytes<Self>
864 Bytes { inner: self }
867 /// Creates an adaptor which will chain this stream with another.
869 /// The returned `Read` instance will first read all bytes from this object
870 /// until EOF is encountered. Afterwards the output is equivalent to the
871 /// output of `next`.
875 /// [`File`][file]s implement `Read`:
877 /// [file]: crate::fs::File
881 /// use std::io::prelude::*;
882 /// use std::fs::File;
884 /// fn main() -> io::Result<()> {
885 /// let mut f1 = File::open("foo.txt")?;
886 /// let mut f2 = File::open("bar.txt")?;
888 /// let mut handle = f1.chain(f2);
889 /// let mut buffer = String::new();
891 /// // read the value into a String. We could use any Read method here,
892 /// // this is just one example.
893 /// handle.read_to_string(&mut buffer)?;
897 #[stable(feature = "rust1", since = "1.0.0")]
898 fn chain<R: Read>(self, next: R) -> Chain<Self, R>
902 Chain { first: self, second: next, done_first: false }
905 /// Creates an adaptor which will read at most `limit` bytes from it.
907 /// This function returns a new instance of `Read` which will read at most
908 /// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
909 /// read errors will not count towards the number of bytes read and future
910 /// calls to [`read()`] may succeed.
914 /// [`File`]s implement `Read`:
916 /// [`File`]: crate::fs::File
918 /// [`read()`]: Read::read
922 /// use std::io::prelude::*;
923 /// use std::fs::File;
925 /// fn main() -> io::Result<()> {
926 /// let mut f = File::open("foo.txt")?;
927 /// let mut buffer = [0; 5];
929 /// // read at most five bytes
930 /// let mut handle = f.take(5);
932 /// handle.read(&mut buffer)?;
936 #[stable(feature = "rust1", since = "1.0.0")]
937 fn take(self, limit: u64) -> Take<Self>
941 Take { inner: self, limit }
945 /// A buffer type used with `Read::read_vectored`.
947 /// It is semantically a wrapper around an `&mut [u8]`, but is guaranteed to be
948 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
950 #[stable(feature = "iovec", since = "1.36.0")]
952 pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
954 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
955 unsafe impl<'a> Send for IoSliceMut<'a> {}
957 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
958 unsafe impl<'a> Sync for IoSliceMut<'a> {}
960 #[stable(feature = "iovec", since = "1.36.0")]
961 impl<'a> fmt::Debug for IoSliceMut<'a> {
962 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
963 fmt::Debug::fmt(self.0.as_slice(), fmt)
967 impl<'a> IoSliceMut<'a> {
968 /// Creates a new `IoSliceMut` wrapping a byte slice.
972 /// Panics on Windows if the slice is larger than 4GB.
973 #[stable(feature = "iovec", since = "1.36.0")]
975 pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
976 IoSliceMut(sys::io::IoSliceMut::new(buf))
979 /// Advance the internal cursor of the slice.
983 /// Elements in the slice may be modified if the cursor is not advanced to
984 /// the end of the slice. For example if we have a slice of buffers with 2
985 /// `IoSliceMut`s, both of length 8, and we advance the cursor by 10 bytes
986 /// the first `IoSliceMut` will be untouched however the second will be
987 /// modified to remove the first 2 bytes (10 - 8).
992 /// #![feature(io_slice_advance)]
994 /// use std::io::IoSliceMut;
995 /// use std::ops::Deref;
997 /// let mut buf1 = [1; 8];
998 /// let mut buf2 = [2; 16];
999 /// let mut buf3 = [3; 8];
1000 /// let mut bufs = &mut [
1001 /// IoSliceMut::new(&mut buf1),
1002 /// IoSliceMut::new(&mut buf2),
1003 /// IoSliceMut::new(&mut buf3),
1006 /// // Mark 10 bytes as read.
1007 /// bufs = IoSliceMut::advance(bufs, 10);
1008 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1009 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1011 #[unstable(feature = "io_slice_advance", issue = "62726")]
1013 pub fn advance<'b>(bufs: &'b mut [IoSliceMut<'a>], n: usize) -> &'b mut [IoSliceMut<'a>] {
1014 // Number of buffers to remove.
1016 // Total length of all the to be removed buffers.
1017 let mut accumulated_len = 0;
1018 for buf in bufs.iter() {
1019 if accumulated_len + buf.len() > n {
1022 accumulated_len += buf.len();
1027 let bufs = &mut bufs[remove..];
1028 if !bufs.is_empty() {
1029 bufs[0].0.advance(n - accumulated_len)
1035 #[stable(feature = "iovec", since = "1.36.0")]
1036 impl<'a> Deref for IoSliceMut<'a> {
1040 fn deref(&self) -> &[u8] {
1045 #[stable(feature = "iovec", since = "1.36.0")]
1046 impl<'a> DerefMut for IoSliceMut<'a> {
1048 fn deref_mut(&mut self) -> &mut [u8] {
1049 self.0.as_mut_slice()
1053 /// A buffer type used with `Write::write_vectored`.
1055 /// It is semantically a wrapper around an `&[u8]`, but is guaranteed to be
1056 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1058 #[stable(feature = "iovec", since = "1.36.0")]
1059 #[derive(Copy, Clone)]
1060 #[repr(transparent)]
1061 pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
1063 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1064 unsafe impl<'a> Send for IoSlice<'a> {}
1066 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1067 unsafe impl<'a> Sync for IoSlice<'a> {}
1069 #[stable(feature = "iovec", since = "1.36.0")]
1070 impl<'a> fmt::Debug for IoSlice<'a> {
1071 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1072 fmt::Debug::fmt(self.0.as_slice(), fmt)
1076 impl<'a> IoSlice<'a> {
1077 /// Creates a new `IoSlice` wrapping a byte slice.
1081 /// Panics on Windows if the slice is larger than 4GB.
1082 #[stable(feature = "iovec", since = "1.36.0")]
1084 pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
1085 IoSlice(sys::io::IoSlice::new(buf))
1088 /// Advance the internal cursor of the slice.
1092 /// Elements in the slice may be modified if the cursor is not advanced to
1093 /// the end of the slice. For example if we have a slice of buffers with 2
1094 /// `IoSlice`s, both of length 8, and we advance the cursor by 10 bytes the
1095 /// first `IoSlice` will be untouched however the second will be modified to
1096 /// remove the first 2 bytes (10 - 8).
1101 /// #![feature(io_slice_advance)]
1103 /// use std::io::IoSlice;
1104 /// use std::ops::Deref;
1106 /// let buf1 = [1; 8];
1107 /// let buf2 = [2; 16];
1108 /// let buf3 = [3; 8];
1109 /// let mut bufs = &mut [
1110 /// IoSlice::new(&buf1),
1111 /// IoSlice::new(&buf2),
1112 /// IoSlice::new(&buf3),
1115 /// // Mark 10 bytes as written.
1116 /// bufs = IoSlice::advance(bufs, 10);
1117 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1118 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1119 #[unstable(feature = "io_slice_advance", issue = "62726")]
1121 pub fn advance<'b>(bufs: &'b mut [IoSlice<'a>], n: usize) -> &'b mut [IoSlice<'a>] {
1122 // Number of buffers to remove.
1124 // Total length of all the to be removed buffers.
1125 let mut accumulated_len = 0;
1126 for buf in bufs.iter() {
1127 if accumulated_len + buf.len() > n {
1130 accumulated_len += buf.len();
1135 let bufs = &mut bufs[remove..];
1136 if !bufs.is_empty() {
1137 bufs[0].0.advance(n - accumulated_len)
1143 #[stable(feature = "iovec", since = "1.36.0")]
1144 impl<'a> Deref for IoSlice<'a> {
1148 fn deref(&self) -> &[u8] {
1153 /// A type used to conditionally initialize buffers passed to `Read` methods.
1154 #[unstable(feature = "read_initializer", issue = "42788")]
1156 pub struct Initializer(bool);
1159 /// Returns a new `Initializer` which will zero out buffers.
1160 #[unstable(feature = "read_initializer", issue = "42788")]
1162 pub fn zeroing() -> Initializer {
1166 /// Returns a new `Initializer` which will not zero out buffers.
1170 /// This may only be called by `Read`ers which guarantee that they will not
1171 /// read from buffers passed to `Read` methods, and that the return value of
1172 /// the method accurately reflects the number of bytes that have been
1173 /// written to the head of the buffer.
1174 #[unstable(feature = "read_initializer", issue = "42788")]
1176 pub unsafe fn nop() -> Initializer {
1180 /// Indicates if a buffer should be initialized.
1181 #[unstable(feature = "read_initializer", issue = "42788")]
1183 pub fn should_initialize(&self) -> bool {
1187 /// Initializes a buffer if necessary.
1188 #[unstable(feature = "read_initializer", issue = "42788")]
1190 pub fn initialize(&self, buf: &mut [u8]) {
1191 if self.should_initialize() {
1192 unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
1197 /// A trait for objects which are byte-oriented sinks.
1199 /// Implementors of the `Write` trait are sometimes called 'writers'.
1201 /// Writers are defined by two required methods, [`write`] and [`flush`]:
1203 /// * The [`write`] method will attempt to write some data into the object,
1204 /// returning how many bytes were successfully written.
1206 /// * The [`flush`] method is useful for adaptors and explicit buffers
1207 /// themselves for ensuring that all buffered data has been pushed out to the
1210 /// Writers are intended to be composable with one another. Many implementors
1211 /// throughout [`std::io`] take and provide types which implement the `Write`
1214 /// [`write`]: Self::write
1215 /// [`flush`]: Self::flush
1216 /// [`std::io`]: index.html
1221 /// use std::io::prelude::*;
1222 /// use std::fs::File;
1224 /// fn main() -> std::io::Result<()> {
1225 /// let data = b"some bytes";
1227 /// let mut pos = 0;
1228 /// let mut buffer = File::create("foo.txt")?;
1230 /// while pos < data.len() {
1231 /// let bytes_written = buffer.write(&data[pos..])?;
1232 /// pos += bytes_written;
1238 /// The trait also provides convenience methods like [`write_all`], which calls
1239 /// `write` in a loop until its entire input has been written.
1241 /// [`write_all`]: Self::write_all
1242 #[stable(feature = "rust1", since = "1.0.0")]
1245 /// Write a buffer into this writer, returning how many bytes were written.
1247 /// This function will attempt to write the entire contents of `buf`, but
1248 /// the entire write may not succeed, or the write may also generate an
1249 /// error. A call to `write` represents *at most one* attempt to write to
1250 /// any wrapped object.
1252 /// Calls to `write` are not guaranteed to block waiting for data to be
1253 /// written, and a write which would otherwise block can be indicated through
1254 /// an [`Err`] variant.
1256 /// If the return value is [`Ok(n)`] then it must be guaranteed that
1257 /// `n <= buf.len()`. A return value of `0` typically means that the
1258 /// underlying object is no longer able to accept bytes and will likely not
1259 /// be able to in the future as well, or that the buffer provided is empty.
1263 /// Each call to `write` may generate an I/O error indicating that the
1264 /// operation could not be completed. If an error is returned then no bytes
1265 /// in the buffer were written to this writer.
1267 /// It is **not** considered an error if the entire buffer could not be
1268 /// written to this writer.
1270 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
1271 /// write operation should be retried if there is nothing else to do.
1276 /// use std::io::prelude::*;
1277 /// use std::fs::File;
1279 /// fn main() -> std::io::Result<()> {
1280 /// let mut buffer = File::create("foo.txt")?;
1282 /// // Writes some prefix of the byte string, not necessarily all of it.
1283 /// buffer.write(b"some bytes")?;
1287 #[stable(feature = "rust1", since = "1.0.0")]
1288 fn write(&mut self, buf: &[u8]) -> Result<usize>;
1290 /// Like `write`, except that it writes from a slice of buffers.
1292 /// Data is copied from each buffer in order, with the final buffer
1293 /// read from possibly being only partially consumed. This method must
1294 /// behave as a call to `write` with the buffers concatenated would.
1296 /// The default implementation calls `write` with either the first nonempty
1297 /// buffer provided, or an empty one if none exists.
1298 #[stable(feature = "iovec", since = "1.36.0")]
1299 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
1300 default_write_vectored(|b| self.write(b), bufs)
1303 /// Determines if this `Write`er has an efficient `write_vectored`
1306 /// If a `Write`er does not override the default `write_vectored`
1307 /// implementation, code using it may want to avoid the method all together
1308 /// and coalesce writes into a single buffer for higher performance.
1310 /// The default implementation returns `false`.
1311 #[unstable(feature = "can_vector", issue = "69941")]
1312 fn is_write_vectored(&self) -> bool {
1316 /// Flush this output stream, ensuring that all intermediately buffered
1317 /// contents reach their destination.
1321 /// It is considered an error if not all bytes could be written due to
1322 /// I/O errors or EOF being reached.
1327 /// use std::io::prelude::*;
1328 /// use std::io::BufWriter;
1329 /// use std::fs::File;
1331 /// fn main() -> std::io::Result<()> {
1332 /// let mut buffer = BufWriter::new(File::create("foo.txt")?);
1334 /// buffer.write_all(b"some bytes")?;
1335 /// buffer.flush()?;
1339 #[stable(feature = "rust1", since = "1.0.0")]
1340 fn flush(&mut self) -> Result<()>;
1342 /// Attempts to write an entire buffer into this writer.
1344 /// This method will continuously call [`write`] until there is no more data
1345 /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
1346 /// returned. This method will not return until the entire buffer has been
1347 /// successfully written or such an error occurs. The first error that is
1348 /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
1351 /// If the buffer contains no data, this will never call [`write`].
1355 /// This function will return the first error of
1356 /// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
1358 /// [`write`]: Self::write
1363 /// use std::io::prelude::*;
1364 /// use std::fs::File;
1366 /// fn main() -> std::io::Result<()> {
1367 /// let mut buffer = File::create("foo.txt")?;
1369 /// buffer.write_all(b"some bytes")?;
1373 #[stable(feature = "rust1", since = "1.0.0")]
1374 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
1375 while !buf.is_empty() {
1376 match self.write(buf) {
1378 return Err(Error::new(ErrorKind::WriteZero, "failed to write whole buffer"));
1380 Ok(n) => buf = &buf[n..],
1381 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
1382 Err(e) => return Err(e),
1388 /// Attempts to write multiple buffers into this writer.
1390 /// This method will continuously call [`write_vectored`] until there is no
1391 /// more data to be written or an error of non-[`ErrorKind::Interrupted`]
1392 /// kind is returned. This method will not return until all buffers have
1393 /// been successfully written or such an error occurs. The first error that
1394 /// is not of [`ErrorKind::Interrupted`] kind generated from this method
1395 /// will be returned.
1397 /// If the buffer contains no data, this will never call [`write_vectored`].
1399 /// [`write_vectored`]: Self::write_vectored
1404 /// Unlike `io::Write::write_vectored`, this takes a *mutable* reference to
1405 /// a slice of `IoSlice`s, not an immutable one. That's because we need to
1406 /// modify the slice to keep track of the bytes already written.
1408 /// Once this function returns, the contents of `bufs` are unspecified, as
1409 /// this depends on how many calls to `write_vectored` were necessary. It is
1410 /// best to understand this function as taking ownership of `bufs` and to
1411 /// not use `bufs` afterwards. The underlying buffers, to which the
1412 /// `IoSlice`s point (but not the `IoSlice`s themselves), are unchanged and
1418 /// #![feature(write_all_vectored)]
1419 /// # fn main() -> std::io::Result<()> {
1421 /// use std::io::{Write, IoSlice};
1423 /// let mut writer = Vec::new();
1424 /// let bufs = &mut [
1425 /// IoSlice::new(&[1]),
1426 /// IoSlice::new(&[2, 3]),
1427 /// IoSlice::new(&[4, 5, 6]),
1430 /// writer.write_all_vectored(bufs)?;
1431 /// // Note: the contents of `bufs` is now undefined, see the Notes section.
1433 /// assert_eq!(writer, &[1, 2, 3, 4, 5, 6]);
1436 #[unstable(feature = "write_all_vectored", issue = "70436")]
1437 fn write_all_vectored(&mut self, mut bufs: &mut [IoSlice<'_>]) -> Result<()> {
1438 while !bufs.is_empty() {
1439 match self.write_vectored(bufs) {
1441 return Err(Error::new(ErrorKind::WriteZero, "failed to write whole buffer"));
1443 Ok(n) => bufs = IoSlice::advance(mem::take(&mut bufs), n),
1444 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
1445 Err(e) => return Err(e),
1451 /// Writes a formatted string into this writer, returning any error
1454 /// This method is primarily used to interface with the
1455 /// [`format_args!()`] macro, but it is rare that this should
1456 /// explicitly be called. The [`write!()`] macro should be favored to
1457 /// invoke this method instead.
1459 /// This function internally uses the [`write_all`][writeall] method on
1460 /// this trait and hence will continuously write data so long as no errors
1461 /// are received. This also means that partial writes are not indicated in
1464 /// [writeall]: Self::write_all
1468 /// This function will return any I/O error reported while formatting.
1473 /// use std::io::prelude::*;
1474 /// use std::fs::File;
1476 /// fn main() -> std::io::Result<()> {
1477 /// let mut buffer = File::create("foo.txt")?;
1480 /// write!(buffer, "{:.*}", 2, 1.234567)?;
1481 /// // turns into this:
1482 /// buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))?;
1486 #[stable(feature = "rust1", since = "1.0.0")]
1487 fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> Result<()> {
1488 // Create a shim which translates a Write to a fmt::Write and saves
1489 // off I/O errors. instead of discarding them
1490 struct Adaptor<'a, T: ?Sized + 'a> {
1495 impl<T: Write + ?Sized> fmt::Write for Adaptor<'_, T> {
1496 fn write_str(&mut self, s: &str) -> fmt::Result {
1497 match self.inner.write_all(s.as_bytes()) {
1500 self.error = Err(e);
1507 let mut output = Adaptor { inner: self, error: Ok(()) };
1508 match fmt::write(&mut output, fmt) {
1511 // check if the error came from the underlying `Write` or not
1512 if output.error.is_err() {
1515 Err(Error::new(ErrorKind::Other, "formatter error"))
1521 /// Creates a "by reference" adaptor for this instance of `Write`.
1523 /// The returned adaptor also implements `Write` and will simply borrow this
1529 /// use std::io::Write;
1530 /// use std::fs::File;
1532 /// fn main() -> std::io::Result<()> {
1533 /// let mut buffer = File::create("foo.txt")?;
1535 /// let reference = buffer.by_ref();
1537 /// // we can use reference just like our original buffer
1538 /// reference.write_all(b"some bytes")?;
1542 #[stable(feature = "rust1", since = "1.0.0")]
1543 fn by_ref(&mut self) -> &mut Self
1551 /// The `Seek` trait provides a cursor which can be moved within a stream of
1554 /// The stream typically has a fixed size, allowing seeking relative to either
1555 /// end or the current offset.
1559 /// [`File`][file]s implement `Seek`:
1561 /// [file]: crate::fs::File
1565 /// use std::io::prelude::*;
1566 /// use std::fs::File;
1567 /// use std::io::SeekFrom;
1569 /// fn main() -> io::Result<()> {
1570 /// let mut f = File::open("foo.txt")?;
1572 /// // move the cursor 42 bytes from the start of the file
1573 /// f.seek(SeekFrom::Start(42))?;
1577 #[stable(feature = "rust1", since = "1.0.0")]
1579 /// Seek to an offset, in bytes, in a stream.
1581 /// A seek beyond the end of a stream is allowed, but behavior is defined
1582 /// by the implementation.
1584 /// If the seek operation completed successfully,
1585 /// this method returns the new position from the start of the stream.
1586 /// That position can be used later with [`SeekFrom::Start`].
1590 /// Seeking to a negative offset is considered an error.
1592 /// [`SeekFrom::Start`]: enum.SeekFrom.html#variant.Start
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.
1680 /// [`Seek`]: trait.Seek.html
1681 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1682 #[stable(feature = "rust1", since = "1.0.0")]
1684 /// Sets the offset to the provided number of bytes.
1685 #[stable(feature = "rust1", since = "1.0.0")]
1686 Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
1688 /// Sets the offset to the size of this object plus the specified number of
1691 /// It is possible to seek beyond the end of an object, but it's an error to
1692 /// seek before byte 0.
1693 #[stable(feature = "rust1", since = "1.0.0")]
1694 End(#[stable(feature = "rust1", since = "1.0.0")] i64),
1696 /// Sets the offset to the current position plus the specified number of
1699 /// It is possible to seek beyond the end of an object, but it's an error to
1700 /// seek before byte 0.
1701 #[stable(feature = "rust1", since = "1.0.0")]
1702 Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
1705 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> Result<usize> {
1708 let (done, used) = {
1709 let available = match r.fill_buf() {
1711 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1712 Err(e) => return Err(e),
1714 match memchr::memchr(delim, available) {
1716 buf.extend_from_slice(&available[..=i]);
1720 buf.extend_from_slice(available);
1721 (false, available.len())
1727 if done || used == 0 {
1733 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1734 /// to perform extra ways of reading.
1736 /// For example, reading line-by-line is inefficient without using a buffer, so
1737 /// if you want to read by line, you'll need `BufRead`, which includes a
1738 /// [`read_line`] method as well as a [`lines`] iterator.
1742 /// A locked standard input implements `BufRead`:
1746 /// use std::io::prelude::*;
1748 /// let stdin = io::stdin();
1749 /// for line in stdin.lock().lines() {
1750 /// println!("{}", line.unwrap());
1754 /// If you have something that implements [`Read`], you can use the [`BufReader`
1755 /// type][`BufReader`] to turn it into a `BufRead`.
1757 /// For example, [`File`] implements [`Read`], but not `BufRead`.
1758 /// [`BufReader`] to the rescue!
1760 /// [`BufReader`]: struct.BufReader.html
1761 /// [`File`]: crate::fs::File
1762 /// [`read_line`]: Self::read_line
1763 /// [`lines`]: Self::lines
1764 /// [`Read`]: trait.Read.html
1767 /// use std::io::{self, BufReader};
1768 /// use std::io::prelude::*;
1769 /// use std::fs::File;
1771 /// fn main() -> io::Result<()> {
1772 /// let f = File::open("foo.txt")?;
1773 /// let f = BufReader::new(f);
1775 /// for line in f.lines() {
1776 /// println!("{}", line.unwrap());
1783 #[stable(feature = "rust1", since = "1.0.0")]
1784 pub trait BufRead: Read {
1785 /// Returns the contents of the internal buffer, filling it with more data
1786 /// from the inner reader if it is empty.
1788 /// This function is a lower-level call. It needs to be paired with the
1789 /// [`consume`] method to function properly. When calling this
1790 /// method, none of the contents will be "read" in the sense that later
1791 /// calling `read` may return the same contents. As such, [`consume`] must
1792 /// be called with the number of bytes that are consumed from this buffer to
1793 /// ensure that the bytes are never returned twice.
1795 /// [`consume`]: Self::consume
1797 /// An empty buffer returned indicates that the stream has reached EOF.
1801 /// This function will return an I/O error if the underlying reader was
1802 /// read, but returned an error.
1806 /// A locked standard input implements `BufRead`:
1810 /// use std::io::prelude::*;
1812 /// let stdin = io::stdin();
1813 /// let mut stdin = stdin.lock();
1815 /// let buffer = stdin.fill_buf().unwrap();
1817 /// // work with buffer
1818 /// println!("{:?}", buffer);
1820 /// // ensure the bytes we worked with aren't returned again later
1821 /// let length = buffer.len();
1822 /// stdin.consume(length);
1824 #[stable(feature = "rust1", since = "1.0.0")]
1825 fn fill_buf(&mut self) -> Result<&[u8]>;
1827 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1828 /// so they should no longer be returned in calls to `read`.
1830 /// This function is a lower-level call. It needs to be paired with the
1831 /// [`fill_buf`] method to function properly. This function does
1832 /// not perform any I/O, it simply informs this object that some amount of
1833 /// its buffer, returned from [`fill_buf`], has been consumed and should
1834 /// no longer be returned. As such, this function may do odd things if
1835 /// [`fill_buf`] isn't called before calling it.
1837 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1842 /// Since `consume()` is meant to be used with [`fill_buf`],
1843 /// that method's example includes an example of `consume()`.
1845 /// [`fill_buf`]: Self::fill_buf
1846 #[stable(feature = "rust1", since = "1.0.0")]
1847 fn consume(&mut self, amt: usize);
1849 /// Read all bytes into `buf` until the delimiter `byte` or EOF is reached.
1851 /// This function will read bytes from the underlying stream until the
1852 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1853 /// the delimiter (if found) will be appended to `buf`.
1855 /// If successful, this function will return the total number of bytes read.
1857 /// This function is blocking and should be used carefully: it is possible for
1858 /// an attacker to continuously send bytes without ever sending the delimiter
1863 /// This function will ignore all instances of [`ErrorKind::Interrupted`] and
1864 /// will otherwise return any errors returned by [`fill_buf`].
1866 /// If an I/O error is encountered then all bytes read so far will be
1867 /// present in `buf` and its length will have been adjusted appropriately.
1869 /// [`fill_buf`]: Self::fill_buf
1870 /// [`ErrorKind::Interrupted`]: enum.ErrorKind.html#variant.Interrupted
1874 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1875 /// this example, we use [`Cursor`] to read all the bytes in a byte slice
1876 /// in hyphen delimited segments:
1878 /// [`Cursor`]: struct.Cursor.html
1881 /// use std::io::{self, BufRead};
1883 /// let mut cursor = io::Cursor::new(b"lorem-ipsum");
1884 /// let mut buf = vec![];
1886 /// // cursor is at 'l'
1887 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1888 /// .expect("reading from cursor won't fail");
1889 /// assert_eq!(num_bytes, 6);
1890 /// assert_eq!(buf, b"lorem-");
1893 /// // cursor is at 'i'
1894 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1895 /// .expect("reading from cursor won't fail");
1896 /// assert_eq!(num_bytes, 5);
1897 /// assert_eq!(buf, b"ipsum");
1900 /// // cursor is at EOF
1901 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1902 /// .expect("reading from cursor won't fail");
1903 /// assert_eq!(num_bytes, 0);
1904 /// assert_eq!(buf, b"");
1906 #[stable(feature = "rust1", since = "1.0.0")]
1907 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
1908 read_until(self, byte, buf)
1911 /// Read all bytes until a newline (the 0xA byte) is reached, and append
1912 /// them to the provided buffer.
1914 /// This function will read bytes from the underlying stream until the
1915 /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
1916 /// up to, and including, the delimiter (if found) will be appended to
1919 /// If successful, this function will return the total number of bytes read.
1921 /// If this function returns `Ok(0)`, the stream has reached EOF.
1923 /// This function is blocking and should be used carefully: it is possible for
1924 /// an attacker to continuously send bytes without ever sending a newline
1929 /// This function has the same error semantics as [`read_until`] and will
1930 /// also return an error if the read bytes are not valid UTF-8. If an I/O
1931 /// error is encountered then `buf` may contain some bytes already read in
1932 /// the event that all data read so far was valid UTF-8.
1934 /// [`read_until`]: Self::read_until
1938 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1939 /// this example, we use [`Cursor`] to read all the lines in a byte slice:
1941 /// [`Cursor`]: struct.Cursor.html
1944 /// use std::io::{self, BufRead};
1946 /// let mut cursor = io::Cursor::new(b"foo\nbar");
1947 /// let mut buf = String::new();
1949 /// // cursor is at 'f'
1950 /// let num_bytes = cursor.read_line(&mut buf)
1951 /// .expect("reading from cursor won't fail");
1952 /// assert_eq!(num_bytes, 4);
1953 /// assert_eq!(buf, "foo\n");
1956 /// // cursor is at 'b'
1957 /// let num_bytes = cursor.read_line(&mut buf)
1958 /// .expect("reading from cursor won't fail");
1959 /// assert_eq!(num_bytes, 3);
1960 /// assert_eq!(buf, "bar");
1963 /// // cursor is at EOF
1964 /// let num_bytes = cursor.read_line(&mut buf)
1965 /// .expect("reading from cursor won't fail");
1966 /// assert_eq!(num_bytes, 0);
1967 /// assert_eq!(buf, "");
1969 #[stable(feature = "rust1", since = "1.0.0")]
1970 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
1971 // Note that we are not calling the `.read_until` method here, but
1972 // rather our hardcoded implementation. For more details as to why, see
1973 // the comments in `read_to_end`.
1974 append_to_string(buf, |b| read_until(self, b'\n', b))
1977 /// Returns an iterator over the contents of this reader split on the byte
1980 /// The iterator returned from this function will return instances of
1981 /// [`io::Result`]`<`[`Vec<u8>`]`>`. Each vector returned will *not* have
1982 /// the delimiter byte at the end.
1984 /// This function will yield errors whenever [`read_until`] would have
1985 /// also yielded an error.
1987 /// [`io::Result`]: self::Result
1988 /// [`Vec<u8>`]: crate::vec::Vec
1989 /// [`read_until`]: Self::read_until
1993 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1994 /// this example, we use [`Cursor`] to iterate over all hyphen delimited
1995 /// segments in a byte slice
1997 /// [`Cursor`]: struct.Cursor.html
2000 /// use std::io::{self, BufRead};
2002 /// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
2004 /// let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
2005 /// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
2006 /// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
2007 /// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
2008 /// assert_eq!(split_iter.next(), None);
2010 #[stable(feature = "rust1", since = "1.0.0")]
2011 fn split(self, byte: u8) -> Split<Self>
2015 Split { buf: self, delim: byte }
2018 /// Returns an iterator over the lines of this reader.
2020 /// The iterator returned from this function will yield instances of
2021 /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
2022 /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
2024 /// [`io::Result`]: self::Result
2028 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2029 /// this example, we use [`Cursor`] to iterate over all the lines in a byte
2033 /// use std::io::{self, BufRead};
2035 /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
2037 /// let mut lines_iter = cursor.lines().map(|l| l.unwrap());
2038 /// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
2039 /// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
2040 /// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
2041 /// assert_eq!(lines_iter.next(), None);
2046 /// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
2048 /// [`BufRead::read_line`]: trait.BufRead.html#method.read_line
2049 #[stable(feature = "rust1", since = "1.0.0")]
2050 fn lines(self) -> Lines<Self>
2058 /// Adaptor to chain together two readers.
2060 /// This struct is generally created by calling [`chain`] on a reader.
2061 /// Please see the documentation of [`chain`] for more details.
2063 /// [`chain`]: trait.Read.html#method.chain
2064 #[stable(feature = "rust1", since = "1.0.0")]
2065 pub struct Chain<T, U> {
2071 impl<T, U> Chain<T, U> {
2072 /// Consumes the `Chain`, returning the wrapped readers.
2078 /// use std::io::prelude::*;
2079 /// use std::fs::File;
2081 /// fn main() -> io::Result<()> {
2082 /// let mut foo_file = File::open("foo.txt")?;
2083 /// let mut bar_file = File::open("bar.txt")?;
2085 /// let chain = foo_file.chain(bar_file);
2086 /// let (foo_file, bar_file) = chain.into_inner();
2090 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2091 pub fn into_inner(self) -> (T, U) {
2092 (self.first, self.second)
2095 /// Gets references to the underlying readers in this `Chain`.
2101 /// use std::io::prelude::*;
2102 /// use std::fs::File;
2104 /// fn main() -> io::Result<()> {
2105 /// let mut foo_file = File::open("foo.txt")?;
2106 /// let mut bar_file = File::open("bar.txt")?;
2108 /// let chain = foo_file.chain(bar_file);
2109 /// let (foo_file, bar_file) = chain.get_ref();
2113 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2114 pub fn get_ref(&self) -> (&T, &U) {
2115 (&self.first, &self.second)
2118 /// Gets mutable references to the underlying readers in this `Chain`.
2120 /// Care should be taken to avoid modifying the internal I/O state of the
2121 /// underlying readers as doing so may corrupt the internal state of this
2128 /// use std::io::prelude::*;
2129 /// use std::fs::File;
2131 /// fn main() -> io::Result<()> {
2132 /// let mut foo_file = File::open("foo.txt")?;
2133 /// let mut bar_file = File::open("bar.txt")?;
2135 /// let mut chain = foo_file.chain(bar_file);
2136 /// let (foo_file, bar_file) = chain.get_mut();
2140 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2141 pub fn get_mut(&mut self) -> (&mut T, &mut U) {
2142 (&mut self.first, &mut self.second)
2146 #[stable(feature = "std_debug", since = "1.16.0")]
2147 impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
2148 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2149 f.debug_struct("Chain").field("t", &self.first).field("u", &self.second).finish()
2153 #[stable(feature = "rust1", since = "1.0.0")]
2154 impl<T: Read, U: Read> Read for Chain<T, U> {
2155 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2156 if !self.done_first {
2157 match self.first.read(buf)? {
2158 0 if !buf.is_empty() => self.done_first = true,
2162 self.second.read(buf)
2165 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
2166 if !self.done_first {
2167 match self.first.read_vectored(bufs)? {
2168 0 if bufs.iter().any(|b| !b.is_empty()) => self.done_first = true,
2172 self.second.read_vectored(bufs)
2175 unsafe fn initializer(&self) -> Initializer {
2176 let initializer = self.first.initializer();
2177 if initializer.should_initialize() { initializer } else { self.second.initializer() }
2181 #[stable(feature = "chain_bufread", since = "1.9.0")]
2182 impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
2183 fn fill_buf(&mut self) -> Result<&[u8]> {
2184 if !self.done_first {
2185 match self.first.fill_buf()? {
2186 buf if buf.is_empty() => {
2187 self.done_first = true;
2189 buf => return Ok(buf),
2192 self.second.fill_buf()
2195 fn consume(&mut self, amt: usize) {
2196 if !self.done_first { self.first.consume(amt) } else { self.second.consume(amt) }
2200 /// Reader adaptor which limits the bytes read from an underlying reader.
2202 /// This struct is generally created by calling [`take`] on a reader.
2203 /// Please see the documentation of [`take`] for more details.
2205 /// [`take`]: trait.Read.html#method.take
2206 #[stable(feature = "rust1", since = "1.0.0")]
2208 pub struct Take<T> {
2214 /// Returns the number of bytes that can be read before this instance will
2219 /// This instance may reach `EOF` after reading fewer bytes than indicated by
2220 /// this method if the underlying [`Read`] instance reaches EOF.
2226 /// use std::io::prelude::*;
2227 /// use std::fs::File;
2229 /// fn main() -> io::Result<()> {
2230 /// let f = File::open("foo.txt")?;
2232 /// // read at most five bytes
2233 /// let handle = f.take(5);
2235 /// println!("limit: {}", handle.limit());
2239 #[stable(feature = "rust1", since = "1.0.0")]
2240 pub fn limit(&self) -> u64 {
2244 /// Sets the number of bytes that can be read before this instance will
2245 /// return EOF. This is the same as constructing a new `Take` instance, so
2246 /// the amount of bytes read and the previous limit value don't matter when
2247 /// calling this method.
2253 /// use std::io::prelude::*;
2254 /// use std::fs::File;
2256 /// fn main() -> io::Result<()> {
2257 /// let f = File::open("foo.txt")?;
2259 /// // read at most five bytes
2260 /// let mut handle = f.take(5);
2261 /// handle.set_limit(10);
2263 /// assert_eq!(handle.limit(), 10);
2267 #[stable(feature = "take_set_limit", since = "1.27.0")]
2268 pub fn set_limit(&mut self, limit: u64) {
2272 /// Consumes the `Take`, returning the wrapped reader.
2278 /// use std::io::prelude::*;
2279 /// use std::fs::File;
2281 /// fn main() -> io::Result<()> {
2282 /// let mut file = File::open("foo.txt")?;
2284 /// let mut buffer = [0; 5];
2285 /// let mut handle = file.take(5);
2286 /// handle.read(&mut buffer)?;
2288 /// let file = handle.into_inner();
2292 #[stable(feature = "io_take_into_inner", since = "1.15.0")]
2293 pub fn into_inner(self) -> T {
2297 /// Gets a reference to the underlying reader.
2303 /// use std::io::prelude::*;
2304 /// use std::fs::File;
2306 /// fn main() -> io::Result<()> {
2307 /// let mut file = File::open("foo.txt")?;
2309 /// let mut buffer = [0; 5];
2310 /// let mut handle = file.take(5);
2311 /// handle.read(&mut buffer)?;
2313 /// let file = handle.get_ref();
2317 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2318 pub fn get_ref(&self) -> &T {
2322 /// Gets a mutable reference to the underlying reader.
2324 /// Care should be taken to avoid modifying the internal I/O state of the
2325 /// underlying reader as doing so may corrupt the internal limit of this
2332 /// use std::io::prelude::*;
2333 /// use std::fs::File;
2335 /// fn main() -> io::Result<()> {
2336 /// let mut file = File::open("foo.txt")?;
2338 /// let mut buffer = [0; 5];
2339 /// let mut handle = file.take(5);
2340 /// handle.read(&mut buffer)?;
2342 /// let file = handle.get_mut();
2346 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2347 pub fn get_mut(&mut self) -> &mut T {
2352 #[stable(feature = "rust1", since = "1.0.0")]
2353 impl<T: Read> Read for Take<T> {
2354 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2355 // Don't call into inner reader at all at EOF because it may still block
2356 if self.limit == 0 {
2360 let max = cmp::min(buf.len() as u64, self.limit) as usize;
2361 let n = self.inner.read(&mut buf[..max])?;
2362 self.limit -= n as u64;
2366 unsafe fn initializer(&self) -> Initializer {
2367 self.inner.initializer()
2370 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
2371 // Pass in a reservation_size closure that respects the current value
2372 // of limit for each read. If we hit the read limit, this prevents the
2373 // final zero-byte read from allocating again.
2374 read_to_end_with_reservation(self, buf, |self_| cmp::min(self_.limit, 32) as usize)
2378 #[stable(feature = "rust1", since = "1.0.0")]
2379 impl<T: BufRead> BufRead for Take<T> {
2380 fn fill_buf(&mut self) -> Result<&[u8]> {
2381 // Don't call into inner reader at all at EOF because it may still block
2382 if self.limit == 0 {
2386 let buf = self.inner.fill_buf()?;
2387 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
2391 fn consume(&mut self, amt: usize) {
2392 // Don't let callers reset the limit by passing an overlarge value
2393 let amt = cmp::min(amt as u64, self.limit) as usize;
2394 self.limit -= amt as u64;
2395 self.inner.consume(amt);
2399 /// An iterator over `u8` values of a reader.
2401 /// This struct is generally created by calling [`bytes`] on a reader.
2402 /// Please see the documentation of [`bytes`] for more details.
2404 /// [`bytes`]: trait.Read.html#method.bytes
2405 #[stable(feature = "rust1", since = "1.0.0")]
2407 pub struct Bytes<R> {
2411 #[stable(feature = "rust1", since = "1.0.0")]
2412 impl<R: Read> Iterator for Bytes<R> {
2413 type Item = Result<u8>;
2415 fn next(&mut self) -> Option<Result<u8>> {
2418 return match self.inner.read(slice::from_mut(&mut byte)) {
2420 Ok(..) => Some(Ok(byte)),
2421 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
2422 Err(e) => Some(Err(e)),
2428 /// An iterator over the contents of an instance of `BufRead` split on a
2429 /// particular byte.
2431 /// This struct is generally created by calling [`split`] on a `BufRead`.
2432 /// Please see the documentation of [`split`] for more details.
2434 /// [`split`]: trait.BufRead.html#method.split
2435 #[stable(feature = "rust1", since = "1.0.0")]
2437 pub struct Split<B> {
2442 #[stable(feature = "rust1", since = "1.0.0")]
2443 impl<B: BufRead> Iterator for Split<B> {
2444 type Item = Result<Vec<u8>>;
2446 fn next(&mut self) -> Option<Result<Vec<u8>>> {
2447 let mut buf = Vec::new();
2448 match self.buf.read_until(self.delim, &mut buf) {
2451 if buf[buf.len() - 1] == self.delim {
2456 Err(e) => Some(Err(e)),
2461 /// An iterator over the lines of an instance of `BufRead`.
2463 /// This struct is generally created by calling [`lines`] on a `BufRead`.
2464 /// Please see the documentation of [`lines`] for more details.
2466 /// [`lines`]: trait.BufRead.html#method.lines
2467 #[stable(feature = "rust1", since = "1.0.0")]
2469 pub struct Lines<B> {
2473 #[stable(feature = "rust1", since = "1.0.0")]
2474 impl<B: BufRead> Iterator for Lines<B> {
2475 type Item = Result<String>;
2477 fn next(&mut self) -> Option<Result<String>> {
2478 let mut buf = String::new();
2479 match self.buf.read_line(&mut buf) {
2482 if buf.ends_with('\n') {
2484 if buf.ends_with('\r') {
2490 Err(e) => Some(Err(e)),
2497 use super::{repeat, Cursor, SeekFrom};
2498 use crate::cmp::{self, min};
2499 use crate::io::prelude::*;
2500 use crate::io::{self, IoSlice, IoSliceMut};
2501 use crate::ops::Deref;
2504 #[cfg_attr(target_os = "emscripten", ignore)]
2506 let mut buf = Cursor::new(&b"12"[..]);
2507 let mut v = Vec::new();
2508 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
2509 assert_eq!(v, b"12");
2511 let mut buf = Cursor::new(&b"1233"[..]);
2512 let mut v = Vec::new();
2513 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
2514 assert_eq!(v, b"123");
2516 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
2517 assert_eq!(v, b"3");
2519 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
2525 let buf = Cursor::new(&b"12"[..]);
2526 let mut s = buf.split(b'3');
2527 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
2528 assert!(s.next().is_none());
2530 let buf = Cursor::new(&b"1233"[..]);
2531 let mut s = buf.split(b'3');
2532 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
2533 assert_eq!(s.next().unwrap().unwrap(), vec![]);
2534 assert!(s.next().is_none());
2539 let mut buf = Cursor::new(&b"12"[..]);
2540 let mut v = String::new();
2541 assert_eq!(buf.read_line(&mut v).unwrap(), 2);
2542 assert_eq!(v, "12");
2544 let mut buf = Cursor::new(&b"12\n\n"[..]);
2545 let mut v = String::new();
2546 assert_eq!(buf.read_line(&mut v).unwrap(), 3);
2547 assert_eq!(v, "12\n");
2549 assert_eq!(buf.read_line(&mut v).unwrap(), 1);
2550 assert_eq!(v, "\n");
2552 assert_eq!(buf.read_line(&mut v).unwrap(), 0);
2558 let buf = Cursor::new(&b"12\r"[..]);
2559 let mut s = buf.lines();
2560 assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
2561 assert!(s.next().is_none());
2563 let buf = Cursor::new(&b"12\r\n\n"[..]);
2564 let mut s = buf.lines();
2565 assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
2566 assert_eq!(s.next().unwrap().unwrap(), "".to_string());
2567 assert!(s.next().is_none());
2572 let mut c = Cursor::new(&b""[..]);
2573 let mut v = Vec::new();
2574 assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
2577 let mut c = Cursor::new(&b"1"[..]);
2578 let mut v = Vec::new();
2579 assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
2580 assert_eq!(v, b"1");
2582 let cap = 1024 * 1024;
2583 let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
2584 let mut v = Vec::new();
2585 let (a, b) = data.split_at(data.len() / 2);
2586 assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
2587 assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
2588 assert_eq!(v, data);
2592 fn read_to_string() {
2593 let mut c = Cursor::new(&b""[..]);
2594 let mut v = String::new();
2595 assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
2598 let mut c = Cursor::new(&b"1"[..]);
2599 let mut v = String::new();
2600 assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
2603 let mut c = Cursor::new(&b"\xff"[..]);
2604 let mut v = String::new();
2605 assert!(c.read_to_string(&mut v).is_err());
2610 let mut buf = [0; 4];
2612 let mut c = Cursor::new(&b""[..]);
2613 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2615 let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
2616 c.read_exact(&mut buf).unwrap();
2617 assert_eq!(&buf, b"1234");
2618 c.read_exact(&mut buf).unwrap();
2619 assert_eq!(&buf, b"5678");
2620 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2624 fn read_exact_slice() {
2625 let mut buf = [0; 4];
2627 let mut c = &b""[..];
2628 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2630 let mut c = &b"123"[..];
2631 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2632 // make sure the optimized (early returning) method is being used
2633 assert_eq!(&buf, &[0; 4]);
2635 let mut c = &b"1234"[..];
2636 c.read_exact(&mut buf).unwrap();
2637 assert_eq!(&buf, b"1234");
2639 let mut c = &b"56789"[..];
2640 c.read_exact(&mut buf).unwrap();
2641 assert_eq!(&buf, b"5678");
2642 assert_eq!(c, b"9");
2650 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
2651 Err(io::Error::new(io::ErrorKind::Other, ""))
2654 impl BufRead for R {
2655 fn fill_buf(&mut self) -> io::Result<&[u8]> {
2656 Err(io::Error::new(io::ErrorKind::Other, ""))
2658 fn consume(&mut self, _amt: usize) {}
2661 let mut buf = [0; 1];
2662 assert_eq!(0, R.take(0).read(&mut buf).unwrap());
2663 assert_eq!(b"", R.take(0).fill_buf().unwrap());
2666 fn cmp_bufread<Br1: BufRead, Br2: BufRead>(mut br1: Br1, mut br2: Br2, exp: &[u8]) {
2667 let mut cat = Vec::new();
2670 let buf1 = br1.fill_buf().unwrap();
2671 let buf2 = br2.fill_buf().unwrap();
2672 let minlen = if buf1.len() < buf2.len() { buf1.len() } else { buf2.len() };
2673 assert_eq!(buf1[..minlen], buf2[..minlen]);
2674 cat.extend_from_slice(&buf1[..minlen]);
2680 br1.consume(consume);
2681 br2.consume(consume);
2683 assert_eq!(br1.fill_buf().unwrap().len(), 0);
2684 assert_eq!(br2.fill_buf().unwrap().len(), 0);
2685 assert_eq!(&cat[..], &exp[..])
2689 fn chain_bufread() {
2690 let testdata = b"ABCDEFGHIJKL";
2692 (&testdata[..3]).chain(&testdata[3..6]).chain(&testdata[6..9]).chain(&testdata[9..]);
2693 let chain2 = (&testdata[..4]).chain(&testdata[4..8]).chain(&testdata[8..]);
2694 cmp_bufread(chain1, chain2, &testdata[..]);
2698 fn chain_zero_length_read_is_not_eof() {
2701 let mut s = String::new();
2702 let mut chain = (&a[..]).chain(&b[..]);
2703 chain.read(&mut []).unwrap();
2704 chain.read_to_string(&mut s).unwrap();
2705 assert_eq!("AB", s);
2709 #[cfg_attr(target_os = "emscripten", ignore)]
2710 fn bench_read_to_end(b: &mut test::Bencher) {
2712 let mut lr = repeat(1).take(10000000);
2713 let mut vec = Vec::with_capacity(1024);
2714 super::read_to_end(&mut lr, &mut vec)
2719 fn seek_len() -> io::Result<()> {
2720 let mut c = Cursor::new(vec![0; 15]);
2721 assert_eq!(c.stream_len()?, 15);
2723 c.seek(SeekFrom::End(0))?;
2724 let old_pos = c.stream_position()?;
2725 assert_eq!(c.stream_len()?, 15);
2726 assert_eq!(c.stream_position()?, old_pos);
2728 c.seek(SeekFrom::Start(7))?;
2729 c.seek(SeekFrom::Current(2))?;
2730 let old_pos = c.stream_position()?;
2731 assert_eq!(c.stream_len()?, 15);
2732 assert_eq!(c.stream_position()?, old_pos);
2738 fn seek_position() -> io::Result<()> {
2739 // All `asserts` are duplicated here to make sure the method does not
2740 // change anything about the seek state.
2741 let mut c = Cursor::new(vec![0; 15]);
2742 assert_eq!(c.stream_position()?, 0);
2743 assert_eq!(c.stream_position()?, 0);
2745 c.seek(SeekFrom::End(0))?;
2746 assert_eq!(c.stream_position()?, 15);
2747 assert_eq!(c.stream_position()?, 15);
2749 c.seek(SeekFrom::Start(7))?;
2750 c.seek(SeekFrom::Current(2))?;
2751 assert_eq!(c.stream_position()?, 9);
2752 assert_eq!(c.stream_position()?, 9);
2754 c.seek(SeekFrom::End(-3))?;
2755 c.seek(SeekFrom::Current(1))?;
2756 c.seek(SeekFrom::Current(-5))?;
2757 assert_eq!(c.stream_position()?, 8);
2758 assert_eq!(c.stream_position()?, 8);
2763 // A simple example reader which uses the default implementation of
2765 struct ExampleSliceReader<'a> {
2769 impl<'a> Read for ExampleSliceReader<'a> {
2770 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
2771 let len = cmp::min(self.slice.len(), buf.len());
2772 buf[..len].copy_from_slice(&self.slice[..len]);
2773 self.slice = &self.slice[len..];
2779 fn test_read_to_end_capacity() -> io::Result<()> {
2780 let input = &b"foo"[..];
2782 // read_to_end() generally needs to over-allocate, both for efficiency
2783 // and so that it can distinguish EOF. Assert that this is the case
2784 // with this simple ExampleSliceReader struct, which uses the default
2785 // implementation of read_to_end. Even though vec1 is allocated with
2786 // exactly enough capacity for the read, read_to_end will allocate more
2788 let mut vec1 = Vec::with_capacity(input.len());
2789 ExampleSliceReader { slice: input }.read_to_end(&mut vec1)?;
2790 assert_eq!(vec1.len(), input.len());
2791 assert!(vec1.capacity() > input.len(), "allocated more");
2793 // However, std::io::Take includes an implementation of read_to_end
2794 // that will not allocate when the limit has already been reached. In
2795 // this case, vec2 never grows.
2796 let mut vec2 = Vec::with_capacity(input.len());
2797 ExampleSliceReader { slice: input }.take(input.len() as u64).read_to_end(&mut vec2)?;
2798 assert_eq!(vec2.len(), input.len());
2799 assert_eq!(vec2.capacity(), input.len(), "did not allocate more");
2805 fn io_slice_mut_advance() {
2806 let mut buf1 = [1; 8];
2807 let mut buf2 = [2; 16];
2808 let mut buf3 = [3; 8];
2809 let mut bufs = &mut [
2810 IoSliceMut::new(&mut buf1),
2811 IoSliceMut::new(&mut buf2),
2812 IoSliceMut::new(&mut buf3),
2815 // Only in a single buffer..
2816 bufs = IoSliceMut::advance(bufs, 1);
2817 assert_eq!(bufs[0].deref(), [1; 7].as_ref());
2818 assert_eq!(bufs[1].deref(), [2; 16].as_ref());
2819 assert_eq!(bufs[2].deref(), [3; 8].as_ref());
2821 // Removing a buffer, leaving others as is.
2822 bufs = IoSliceMut::advance(bufs, 7);
2823 assert_eq!(bufs[0].deref(), [2; 16].as_ref());
2824 assert_eq!(bufs[1].deref(), [3; 8].as_ref());
2826 // Removing a buffer and removing from the next buffer.
2827 bufs = IoSliceMut::advance(bufs, 18);
2828 assert_eq!(bufs[0].deref(), [3; 6].as_ref());
2832 fn io_slice_mut_advance_empty_slice() {
2833 let empty_bufs = &mut [][..];
2835 IoSliceMut::advance(empty_bufs, 1);
2839 fn io_slice_mut_advance_beyond_total_length() {
2840 let mut buf1 = [1; 8];
2841 let mut bufs = &mut [IoSliceMut::new(&mut buf1)][..];
2843 // Going beyond the total length should be ok.
2844 bufs = IoSliceMut::advance(bufs, 9);
2845 assert!(bufs.is_empty());
2849 fn io_slice_advance() {
2853 let mut bufs = &mut [IoSlice::new(&buf1), IoSlice::new(&buf2), IoSlice::new(&buf3)][..];
2855 // Only in a single buffer..
2856 bufs = IoSlice::advance(bufs, 1);
2857 assert_eq!(bufs[0].deref(), [1; 7].as_ref());
2858 assert_eq!(bufs[1].deref(), [2; 16].as_ref());
2859 assert_eq!(bufs[2].deref(), [3; 8].as_ref());
2861 // Removing a buffer, leaving others as is.
2862 bufs = IoSlice::advance(bufs, 7);
2863 assert_eq!(bufs[0].deref(), [2; 16].as_ref());
2864 assert_eq!(bufs[1].deref(), [3; 8].as_ref());
2866 // Removing a buffer and removing from the next buffer.
2867 bufs = IoSlice::advance(bufs, 18);
2868 assert_eq!(bufs[0].deref(), [3; 6].as_ref());
2872 fn io_slice_advance_empty_slice() {
2873 let empty_bufs = &mut [][..];
2875 IoSlice::advance(empty_bufs, 1);
2879 fn io_slice_advance_beyond_total_length() {
2881 let mut bufs = &mut [IoSlice::new(&buf1)][..];
2883 // Going beyond the total length should be ok.
2884 bufs = IoSlice::advance(bufs, 9);
2885 assert!(bufs.is_empty());
2888 /// Create a new writer that reads from at most `n_bufs` and reads
2889 /// `per_call` bytes (in total) per call to write.
2890 fn test_writer(n_bufs: usize, per_call: usize) -> TestWriter {
2891 TestWriter { n_bufs, per_call, written: Vec::new() }
2900 impl Write for TestWriter {
2901 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
2902 self.write_vectored(&[IoSlice::new(buf)])
2905 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
2906 let mut left = self.per_call;
2907 let mut written = 0;
2908 for buf in bufs.iter().take(self.n_bufs) {
2909 let n = min(left, buf.len());
2910 self.written.extend_from_slice(&buf[0..n]);
2917 fn flush(&mut self) -> io::Result<()> {
2923 fn test_writer_read_from_one_buf() {
2924 let mut writer = test_writer(1, 2);
2926 assert_eq!(writer.write(&[]).unwrap(), 0);
2927 assert_eq!(writer.write_vectored(&[]).unwrap(), 0);
2929 // Read at most 2 bytes.
2930 assert_eq!(writer.write(&[1, 1, 1]).unwrap(), 2);
2931 let bufs = &[IoSlice::new(&[2, 2, 2])];
2932 assert_eq!(writer.write_vectored(bufs).unwrap(), 2);
2934 // Only read from first buf.
2935 let bufs = &[IoSlice::new(&[3]), IoSlice::new(&[4, 4])];
2936 assert_eq!(writer.write_vectored(bufs).unwrap(), 1);
2938 assert_eq!(writer.written, &[1, 1, 2, 2, 3]);
2942 fn test_writer_read_from_multiple_bufs() {
2943 let mut writer = test_writer(3, 3);
2945 // Read at most 3 bytes from two buffers.
2946 let bufs = &[IoSlice::new(&[1]), IoSlice::new(&[2, 2, 2])];
2947 assert_eq!(writer.write_vectored(bufs).unwrap(), 3);
2949 // Read at most 3 bytes from three buffers.
2950 let bufs = &[IoSlice::new(&[3]), IoSlice::new(&[4]), IoSlice::new(&[5, 5])];
2951 assert_eq!(writer.write_vectored(bufs).unwrap(), 3);
2953 assert_eq!(writer.written, &[1, 2, 2, 3, 4, 5]);
2957 fn test_write_all_vectored() {
2958 #[rustfmt::skip] // Becomes unreadable otherwise.
2959 let tests: Vec<(_, &'static [u8])> = vec![
2961 (vec![IoSlice::new(&[1])], &[1]),
2962 (vec![IoSlice::new(&[1, 2])], &[1, 2]),
2963 (vec![IoSlice::new(&[1, 2, 3])], &[1, 2, 3]),
2964 (vec![IoSlice::new(&[1, 2, 3, 4])], &[1, 2, 3, 4]),
2965 (vec![IoSlice::new(&[1, 2, 3, 4, 5])], &[1, 2, 3, 4, 5]),
2966 (vec![IoSlice::new(&[1]), IoSlice::new(&[2])], &[1, 2]),
2967 (vec![IoSlice::new(&[1]), IoSlice::new(&[2, 2])], &[1, 2, 2]),
2968 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2])], &[1, 1, 2, 2]),
2969 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 2, 2, 2]),
2970 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 2, 2, 2]),
2971 (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 1, 2, 2, 2]),
2972 (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2, 2])], &[1, 1, 1, 2, 2, 2, 2]),
2973 (vec![IoSlice::new(&[1, 1, 1, 1]), IoSlice::new(&[2, 2, 2, 2])], &[1, 1, 1, 1, 2, 2, 2, 2]),
2974 (vec![IoSlice::new(&[1]), IoSlice::new(&[2]), IoSlice::new(&[3])], &[1, 2, 3]),
2975 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2]), IoSlice::new(&[3, 3])], &[1, 1, 2, 2, 3, 3]),
2976 (vec![IoSlice::new(&[1]), IoSlice::new(&[2, 2]), IoSlice::new(&[3, 3, 3])], &[1, 2, 2, 3, 3, 3]),
2977 (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]),
2980 let writer_configs = &[(1, 1), (1, 2), (1, 3), (2, 2), (2, 3), (3, 3)];
2982 for (n_bufs, per_call) in writer_configs.iter().copied() {
2983 for (mut input, wanted) in tests.clone().into_iter() {
2984 let mut writer = test_writer(n_bufs, per_call);
2985 assert!(writer.write_all_vectored(&mut *input).is_ok());
2986 assert_eq!(&*writer.written, &*wanted);