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.
729 /// If this function encounters an error of the kind
730 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
733 /// If this function encounters an "end of file" before completely filling
734 /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
735 /// The contents of `buf` are unspecified in this case.
737 /// If any other read error is encountered then this function immediately
738 /// returns. The contents of `buf` are unspecified in this case.
740 /// If this function returns an error, it is unspecified how many bytes it
741 /// has read, but it will never read more than would be necessary to
742 /// completely fill the buffer.
746 /// [`File`]s implement `Read`:
748 /// [`File`]: crate::fs::File
752 /// use std::io::prelude::*;
753 /// use std::fs::File;
755 /// fn main() -> io::Result<()> {
756 /// let mut f = File::open("foo.txt")?;
757 /// let mut buffer = [0; 10];
759 /// // read exactly 10 bytes
760 /// f.read_exact(&mut buffer)?;
764 #[stable(feature = "read_exact", since = "1.6.0")]
765 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
766 while !buf.is_empty() {
767 match self.read(buf) {
773 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
774 Err(e) => return Err(e),
778 Err(Error::new(ErrorKind::UnexpectedEof, "failed to fill whole buffer"))
784 /// Creates a "by reference" adaptor for this instance of `Read`.
786 /// The returned adaptor also implements `Read` and will simply borrow this
791 /// [`File`][file]s implement `Read`:
793 /// [file]: crate::fs::File
797 /// use std::io::Read;
798 /// use std::fs::File;
800 /// fn main() -> io::Result<()> {
801 /// let mut f = File::open("foo.txt")?;
802 /// let mut buffer = Vec::new();
803 /// let mut other_buffer = Vec::new();
806 /// let reference = f.by_ref();
808 /// // read at most 5 bytes
809 /// reference.take(5).read_to_end(&mut buffer)?;
811 /// } // drop our &mut reference so we can use f again
813 /// // original file still usable, read the rest
814 /// f.read_to_end(&mut other_buffer)?;
818 #[stable(feature = "rust1", since = "1.0.0")]
819 fn by_ref(&mut self) -> &mut Self
826 /// Transforms this `Read` instance to an [`Iterator`] over its bytes.
828 /// The returned type implements [`Iterator`] where the `Item` is
829 /// [`Result`]`<`[`u8`]`, `[`io::Error`]`>`.
830 /// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
831 /// otherwise. EOF is mapped to returning [`None`] from this iterator.
835 /// [`File`][file]s implement `Read`:
837 /// [file]: crate::fs::File
838 /// [`Iterator`]: crate::iter::Iterator
839 /// [`Result`]: crate::result::Result
840 /// [`io::Error`]: self::Error
844 /// use std::io::prelude::*;
845 /// use std::fs::File;
847 /// fn main() -> io::Result<()> {
848 /// let mut f = File::open("foo.txt")?;
850 /// for byte in f.bytes() {
851 /// println!("{}", byte.unwrap());
856 #[stable(feature = "rust1", since = "1.0.0")]
857 fn bytes(self) -> Bytes<Self>
861 Bytes { inner: self }
864 /// Creates an adaptor which will chain this stream with another.
866 /// The returned `Read` instance will first read all bytes from this object
867 /// until EOF is encountered. Afterwards the output is equivalent to the
868 /// output of `next`.
872 /// [`File`][file]s implement `Read`:
874 /// [file]: crate::fs::File
878 /// use std::io::prelude::*;
879 /// use std::fs::File;
881 /// fn main() -> io::Result<()> {
882 /// let mut f1 = File::open("foo.txt")?;
883 /// let mut f2 = File::open("bar.txt")?;
885 /// let mut handle = f1.chain(f2);
886 /// let mut buffer = String::new();
888 /// // read the value into a String. We could use any Read method here,
889 /// // this is just one example.
890 /// handle.read_to_string(&mut buffer)?;
894 #[stable(feature = "rust1", since = "1.0.0")]
895 fn chain<R: Read>(self, next: R) -> Chain<Self, R>
899 Chain { first: self, second: next, done_first: false }
902 /// Creates an adaptor which will read at most `limit` bytes from it.
904 /// This function returns a new instance of `Read` which will read at most
905 /// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
906 /// read errors will not count towards the number of bytes read and future
907 /// calls to [`read()`] may succeed.
911 /// [`File`]s implement `Read`:
913 /// [`File`]: crate::fs::File
915 /// [`read()`]: Read::read
919 /// use std::io::prelude::*;
920 /// use std::fs::File;
922 /// fn main() -> io::Result<()> {
923 /// let mut f = File::open("foo.txt")?;
924 /// let mut buffer = [0; 5];
926 /// // read at most five bytes
927 /// let mut handle = f.take(5);
929 /// handle.read(&mut buffer)?;
933 #[stable(feature = "rust1", since = "1.0.0")]
934 fn take(self, limit: u64) -> Take<Self>
938 Take { inner: self, limit }
942 /// A buffer type used with `Read::read_vectored`.
944 /// It is semantically a wrapper around an `&mut [u8]`, but is guaranteed to be
945 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
947 #[stable(feature = "iovec", since = "1.36.0")]
949 pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
951 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
952 unsafe impl<'a> Send for IoSliceMut<'a> {}
954 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
955 unsafe impl<'a> Sync for IoSliceMut<'a> {}
957 #[stable(feature = "iovec", since = "1.36.0")]
958 impl<'a> fmt::Debug for IoSliceMut<'a> {
959 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
960 fmt::Debug::fmt(self.0.as_slice(), fmt)
964 impl<'a> IoSliceMut<'a> {
965 /// Creates a new `IoSliceMut` wrapping a byte slice.
969 /// Panics on Windows if the slice is larger than 4GB.
970 #[stable(feature = "iovec", since = "1.36.0")]
972 pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
973 IoSliceMut(sys::io::IoSliceMut::new(buf))
976 /// Advance the internal cursor of the slice.
980 /// Elements in the slice may be modified if the cursor is not advanced to
981 /// the end of the slice. For example if we have a slice of buffers with 2
982 /// `IoSliceMut`s, both of length 8, and we advance the cursor by 10 bytes
983 /// the first `IoSliceMut` will be untouched however the second will be
984 /// modified to remove the first 2 bytes (10 - 8).
989 /// #![feature(io_slice_advance)]
991 /// use std::io::IoSliceMut;
992 /// use std::ops::Deref;
994 /// let mut buf1 = [1; 8];
995 /// let mut buf2 = [2; 16];
996 /// let mut buf3 = [3; 8];
997 /// let mut bufs = &mut [
998 /// IoSliceMut::new(&mut buf1),
999 /// IoSliceMut::new(&mut buf2),
1000 /// IoSliceMut::new(&mut buf3),
1003 /// // Mark 10 bytes as read.
1004 /// bufs = IoSliceMut::advance(bufs, 10);
1005 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1006 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1008 #[unstable(feature = "io_slice_advance", issue = "62726")]
1010 pub fn advance<'b>(bufs: &'b mut [IoSliceMut<'a>], n: usize) -> &'b mut [IoSliceMut<'a>] {
1011 // Number of buffers to remove.
1013 // Total length of all the to be removed buffers.
1014 let mut accumulated_len = 0;
1015 for buf in bufs.iter() {
1016 if accumulated_len + buf.len() > n {
1019 accumulated_len += buf.len();
1024 let bufs = &mut bufs[remove..];
1025 if !bufs.is_empty() {
1026 bufs[0].0.advance(n - accumulated_len)
1032 #[stable(feature = "iovec", since = "1.36.0")]
1033 impl<'a> Deref for IoSliceMut<'a> {
1037 fn deref(&self) -> &[u8] {
1042 #[stable(feature = "iovec", since = "1.36.0")]
1043 impl<'a> DerefMut for IoSliceMut<'a> {
1045 fn deref_mut(&mut self) -> &mut [u8] {
1046 self.0.as_mut_slice()
1050 /// A buffer type used with `Write::write_vectored`.
1052 /// It is semantically a wrapper around an `&[u8]`, but is guaranteed to be
1053 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1055 #[stable(feature = "iovec", since = "1.36.0")]
1056 #[derive(Copy, Clone)]
1057 #[repr(transparent)]
1058 pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
1060 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1061 unsafe impl<'a> Send for IoSlice<'a> {}
1063 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1064 unsafe impl<'a> Sync for IoSlice<'a> {}
1066 #[stable(feature = "iovec", since = "1.36.0")]
1067 impl<'a> fmt::Debug for IoSlice<'a> {
1068 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1069 fmt::Debug::fmt(self.0.as_slice(), fmt)
1073 impl<'a> IoSlice<'a> {
1074 /// Creates a new `IoSlice` wrapping a byte slice.
1078 /// Panics on Windows if the slice is larger than 4GB.
1079 #[stable(feature = "iovec", since = "1.36.0")]
1081 pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
1082 IoSlice(sys::io::IoSlice::new(buf))
1085 /// Advance the internal cursor of the slice.
1089 /// Elements in the slice may be modified if the cursor is not advanced to
1090 /// the end of the slice. For example if we have a slice of buffers with 2
1091 /// `IoSlice`s, both of length 8, and we advance the cursor by 10 bytes the
1092 /// first `IoSlice` will be untouched however the second will be modified to
1093 /// remove the first 2 bytes (10 - 8).
1098 /// #![feature(io_slice_advance)]
1100 /// use std::io::IoSlice;
1101 /// use std::ops::Deref;
1103 /// let buf1 = [1; 8];
1104 /// let buf2 = [2; 16];
1105 /// let buf3 = [3; 8];
1106 /// let mut bufs = &mut [
1107 /// IoSlice::new(&buf1),
1108 /// IoSlice::new(&buf2),
1109 /// IoSlice::new(&buf3),
1112 /// // Mark 10 bytes as written.
1113 /// bufs = IoSlice::advance(bufs, 10);
1114 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1115 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1116 #[unstable(feature = "io_slice_advance", issue = "62726")]
1118 pub fn advance<'b>(bufs: &'b mut [IoSlice<'a>], n: usize) -> &'b mut [IoSlice<'a>] {
1119 // Number of buffers to remove.
1121 // Total length of all the to be removed buffers.
1122 let mut accumulated_len = 0;
1123 for buf in bufs.iter() {
1124 if accumulated_len + buf.len() > n {
1127 accumulated_len += buf.len();
1132 let bufs = &mut bufs[remove..];
1133 if !bufs.is_empty() {
1134 bufs[0].0.advance(n - accumulated_len)
1140 #[stable(feature = "iovec", since = "1.36.0")]
1141 impl<'a> Deref for IoSlice<'a> {
1145 fn deref(&self) -> &[u8] {
1150 /// A type used to conditionally initialize buffers passed to `Read` methods.
1151 #[unstable(feature = "read_initializer", issue = "42788")]
1153 pub struct Initializer(bool);
1156 /// Returns a new `Initializer` which will zero out buffers.
1157 #[unstable(feature = "read_initializer", issue = "42788")]
1159 pub fn zeroing() -> Initializer {
1163 /// Returns a new `Initializer` which will not zero out buffers.
1167 /// This may only be called by `Read`ers which guarantee that they will not
1168 /// read from buffers passed to `Read` methods, and that the return value of
1169 /// the method accurately reflects the number of bytes that have been
1170 /// written to the head of the buffer.
1171 #[unstable(feature = "read_initializer", issue = "42788")]
1173 pub unsafe fn nop() -> Initializer {
1177 /// Indicates if a buffer should be initialized.
1178 #[unstable(feature = "read_initializer", issue = "42788")]
1180 pub fn should_initialize(&self) -> bool {
1184 /// Initializes a buffer if necessary.
1185 #[unstable(feature = "read_initializer", issue = "42788")]
1187 pub fn initialize(&self, buf: &mut [u8]) {
1188 if self.should_initialize() {
1189 unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
1194 /// A trait for objects which are byte-oriented sinks.
1196 /// Implementors of the `Write` trait are sometimes called 'writers'.
1198 /// Writers are defined by two required methods, [`write`] and [`flush`]:
1200 /// * The [`write`] method will attempt to write some data into the object,
1201 /// returning how many bytes were successfully written.
1203 /// * The [`flush`] method is useful for adaptors and explicit buffers
1204 /// themselves for ensuring that all buffered data has been pushed out to the
1207 /// Writers are intended to be composable with one another. Many implementors
1208 /// throughout [`std::io`] take and provide types which implement the `Write`
1211 /// [`write`]: Self::write
1212 /// [`flush`]: Self::flush
1213 /// [`std::io`]: index.html
1218 /// use std::io::prelude::*;
1219 /// use std::fs::File;
1221 /// fn main() -> std::io::Result<()> {
1222 /// let data = b"some bytes";
1224 /// let mut pos = 0;
1225 /// let mut buffer = File::create("foo.txt")?;
1227 /// while pos < data.len() {
1228 /// let bytes_written = buffer.write(&data[pos..])?;
1229 /// pos += bytes_written;
1235 /// The trait also provides convenience methods like [`write_all`], which calls
1236 /// `write` in a loop until its entire input has been written.
1238 /// [`write_all`]: Self::write_all
1239 #[stable(feature = "rust1", since = "1.0.0")]
1242 /// Write a buffer into this writer, returning how many bytes were written.
1244 /// This function will attempt to write the entire contents of `buf`, but
1245 /// the entire write may not succeed, or the write may also generate an
1246 /// error. A call to `write` represents *at most one* attempt to write to
1247 /// any wrapped object.
1249 /// Calls to `write` are not guaranteed to block waiting for data to be
1250 /// written, and a write which would otherwise block can be indicated through
1251 /// an [`Err`] variant.
1253 /// If the return value is [`Ok(n)`] then it must be guaranteed that
1254 /// `n <= buf.len()`. A return value of `0` typically means that the
1255 /// underlying object is no longer able to accept bytes and will likely not
1256 /// be able to in the future as well, or that the buffer provided is empty.
1260 /// Each call to `write` may generate an I/O error indicating that the
1261 /// operation could not be completed. If an error is returned then no bytes
1262 /// in the buffer were written to this writer.
1264 /// It is **not** considered an error if the entire buffer could not be
1265 /// written to this writer.
1267 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
1268 /// write operation should be retried if there is nothing else to do.
1273 /// use std::io::prelude::*;
1274 /// use std::fs::File;
1276 /// fn main() -> std::io::Result<()> {
1277 /// let mut buffer = File::create("foo.txt")?;
1279 /// // Writes some prefix of the byte string, not necessarily all of it.
1280 /// buffer.write(b"some bytes")?;
1284 #[stable(feature = "rust1", since = "1.0.0")]
1285 fn write(&mut self, buf: &[u8]) -> Result<usize>;
1287 /// Like `write`, except that it writes from a slice of buffers.
1289 /// Data is copied from each buffer in order, with the final buffer
1290 /// read from possibly being only partially consumed. This method must
1291 /// behave as a call to `write` with the buffers concatenated would.
1293 /// The default implementation calls `write` with either the first nonempty
1294 /// buffer provided, or an empty one if none exists.
1295 #[stable(feature = "iovec", since = "1.36.0")]
1296 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
1297 default_write_vectored(|b| self.write(b), bufs)
1300 /// Determines if this `Write`er has an efficient `write_vectored`
1303 /// If a `Write`er does not override the default `write_vectored`
1304 /// implementation, code using it may want to avoid the method all together
1305 /// and coalesce writes into a single buffer for higher performance.
1307 /// The default implementation returns `false`.
1308 #[unstable(feature = "can_vector", issue = "69941")]
1309 fn is_write_vectored(&self) -> bool {
1313 /// Flush this output stream, ensuring that all intermediately buffered
1314 /// contents reach their destination.
1318 /// It is considered an error if not all bytes could be written due to
1319 /// I/O errors or EOF being reached.
1324 /// use std::io::prelude::*;
1325 /// use std::io::BufWriter;
1326 /// use std::fs::File;
1328 /// fn main() -> std::io::Result<()> {
1329 /// let mut buffer = BufWriter::new(File::create("foo.txt")?);
1331 /// buffer.write_all(b"some bytes")?;
1332 /// buffer.flush()?;
1336 #[stable(feature = "rust1", since = "1.0.0")]
1337 fn flush(&mut self) -> Result<()>;
1339 /// Attempts to write an entire buffer into this writer.
1341 /// This method will continuously call [`write`] until there is no more data
1342 /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
1343 /// returned. This method will not return until the entire buffer has been
1344 /// successfully written or such an error occurs. The first error that is
1345 /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
1348 /// If the buffer contains no data, this will never call [`write`].
1352 /// This function will return the first error of
1353 /// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
1355 /// [`write`]: Self::write
1360 /// use std::io::prelude::*;
1361 /// use std::fs::File;
1363 /// fn main() -> std::io::Result<()> {
1364 /// let mut buffer = File::create("foo.txt")?;
1366 /// buffer.write_all(b"some bytes")?;
1370 #[stable(feature = "rust1", since = "1.0.0")]
1371 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
1372 while !buf.is_empty() {
1373 match self.write(buf) {
1375 return Err(Error::new(ErrorKind::WriteZero, "failed to write whole buffer"));
1377 Ok(n) => buf = &buf[n..],
1378 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
1379 Err(e) => return Err(e),
1385 /// Attempts to write multiple buffers into this writer.
1387 /// This method will continuously call [`write_vectored`] until there is no
1388 /// more data to be written or an error of non-[`ErrorKind::Interrupted`]
1389 /// kind is returned. This method will not return until all buffers have
1390 /// been successfully written or such an error occurs. The first error that
1391 /// is not of [`ErrorKind::Interrupted`] kind generated from this method
1392 /// will be returned.
1394 /// If the buffer contains no data, this will never call [`write_vectored`].
1396 /// [`write_vectored`]: Self::write_vectored
1401 /// Unlike `io::Write::write_vectored`, this takes a *mutable* reference to
1402 /// a slice of `IoSlice`s, not an immutable one. That's because we need to
1403 /// modify the slice to keep track of the bytes already written.
1405 /// Once this function returns, the contents of `bufs` are unspecified, as
1406 /// this depends on how many calls to `write_vectored` were necessary. It is
1407 /// best to understand this function as taking ownership of `bufs` and to
1408 /// not use `bufs` afterwards. The underlying buffers, to which the
1409 /// `IoSlice`s point (but not the `IoSlice`s themselves), are unchanged and
1415 /// #![feature(write_all_vectored)]
1416 /// # fn main() -> std::io::Result<()> {
1418 /// use std::io::{Write, IoSlice};
1420 /// let mut writer = Vec::new();
1421 /// let bufs = &mut [
1422 /// IoSlice::new(&[1]),
1423 /// IoSlice::new(&[2, 3]),
1424 /// IoSlice::new(&[4, 5, 6]),
1427 /// writer.write_all_vectored(bufs)?;
1428 /// // Note: the contents of `bufs` is now undefined, see the Notes section.
1430 /// assert_eq!(writer, &[1, 2, 3, 4, 5, 6]);
1433 #[unstable(feature = "write_all_vectored", issue = "70436")]
1434 fn write_all_vectored(&mut self, mut bufs: &mut [IoSlice<'_>]) -> Result<()> {
1435 while !bufs.is_empty() {
1436 match self.write_vectored(bufs) {
1438 return Err(Error::new(ErrorKind::WriteZero, "failed to write whole buffer"));
1440 Ok(n) => bufs = IoSlice::advance(mem::take(&mut bufs), n),
1441 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
1442 Err(e) => return Err(e),
1448 /// Writes a formatted string into this writer, returning any error
1451 /// This method is primarily used to interface with the
1452 /// [`format_args!()`] macro, but it is rare that this should
1453 /// explicitly be called. The [`write!()`] macro should be favored to
1454 /// invoke this method instead.
1456 /// This function internally uses the [`write_all`][writeall] method on
1457 /// this trait and hence will continuously write data so long as no errors
1458 /// are received. This also means that partial writes are not indicated in
1461 /// [writeall]: Self::write_all
1465 /// This function will return any I/O error reported while formatting.
1470 /// use std::io::prelude::*;
1471 /// use std::fs::File;
1473 /// fn main() -> std::io::Result<()> {
1474 /// let mut buffer = File::create("foo.txt")?;
1477 /// write!(buffer, "{:.*}", 2, 1.234567)?;
1478 /// // turns into this:
1479 /// buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))?;
1483 #[stable(feature = "rust1", since = "1.0.0")]
1484 fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> Result<()> {
1485 // Create a shim which translates a Write to a fmt::Write and saves
1486 // off I/O errors. instead of discarding them
1487 struct Adaptor<'a, T: ?Sized + 'a> {
1492 impl<T: Write + ?Sized> fmt::Write for Adaptor<'_, T> {
1493 fn write_str(&mut self, s: &str) -> fmt::Result {
1494 match self.inner.write_all(s.as_bytes()) {
1497 self.error = Err(e);
1504 let mut output = Adaptor { inner: self, error: Ok(()) };
1505 match fmt::write(&mut output, fmt) {
1508 // check if the error came from the underlying `Write` or not
1509 if output.error.is_err() {
1512 Err(Error::new(ErrorKind::Other, "formatter error"))
1518 /// Creates a "by reference" adaptor for this instance of `Write`.
1520 /// The returned adaptor also implements `Write` and will simply borrow this
1526 /// use std::io::Write;
1527 /// use std::fs::File;
1529 /// fn main() -> std::io::Result<()> {
1530 /// let mut buffer = File::create("foo.txt")?;
1532 /// let reference = buffer.by_ref();
1534 /// // we can use reference just like our original buffer
1535 /// reference.write_all(b"some bytes")?;
1539 #[stable(feature = "rust1", since = "1.0.0")]
1540 fn by_ref(&mut self) -> &mut Self
1548 /// The `Seek` trait provides a cursor which can be moved within a stream of
1551 /// The stream typically has a fixed size, allowing seeking relative to either
1552 /// end or the current offset.
1556 /// [`File`][file]s implement `Seek`:
1558 /// [file]: crate::fs::File
1562 /// use std::io::prelude::*;
1563 /// use std::fs::File;
1564 /// use std::io::SeekFrom;
1566 /// fn main() -> io::Result<()> {
1567 /// let mut f = File::open("foo.txt")?;
1569 /// // move the cursor 42 bytes from the start of the file
1570 /// f.seek(SeekFrom::Start(42))?;
1574 #[stable(feature = "rust1", since = "1.0.0")]
1576 /// Seek to an offset, in bytes, in a stream.
1578 /// A seek beyond the end of a stream is allowed, but behavior is defined
1579 /// by the implementation.
1581 /// If the seek operation completed successfully,
1582 /// this method returns the new position from the start of the stream.
1583 /// That position can be used later with [`SeekFrom::Start`].
1587 /// Seeking to a negative offset is considered an error.
1589 /// [`SeekFrom::Start`]: enum.SeekFrom.html#variant.Start
1590 #[stable(feature = "rust1", since = "1.0.0")]
1591 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1593 /// Returns the length of this stream (in bytes).
1595 /// This method is implemented using up to three seek operations. If this
1596 /// method returns successfully, the seek position is unchanged (i.e. the
1597 /// position before calling this method is the same as afterwards).
1598 /// However, if this method returns an error, the seek position is
1601 /// If you need to obtain the length of *many* streams and you don't care
1602 /// about the seek position afterwards, you can reduce the number of seek
1603 /// operations by simply calling `seek(SeekFrom::End(0))` and using its
1604 /// return value (it is also the stream length).
1606 /// Note that length of a stream can change over time (for example, when
1607 /// data is appended to a file). So calling this method multiple times does
1608 /// not necessarily return the same length each time.
1614 /// #![feature(seek_convenience)]
1616 /// io::{self, Seek},
1620 /// fn main() -> io::Result<()> {
1621 /// let mut f = File::open("foo.txt")?;
1623 /// let len = f.stream_len()?;
1624 /// println!("The file is currently {} bytes long", len);
1628 #[unstable(feature = "seek_convenience", issue = "59359")]
1629 fn stream_len(&mut self) -> Result<u64> {
1630 let old_pos = self.stream_position()?;
1631 let len = self.seek(SeekFrom::End(0))?;
1633 // Avoid seeking a third time when we were already at the end of the
1634 // stream. The branch is usually way cheaper than a seek operation.
1636 self.seek(SeekFrom::Start(old_pos))?;
1642 /// Returns the current seek position from the start of the stream.
1644 /// This is equivalent to `self.seek(SeekFrom::Current(0))`.
1650 /// #![feature(seek_convenience)]
1652 /// io::{self, BufRead, BufReader, Seek},
1656 /// fn main() -> io::Result<()> {
1657 /// let mut f = BufReader::new(File::open("foo.txt")?);
1659 /// let before = f.stream_position()?;
1660 /// f.read_line(&mut String::new())?;
1661 /// let after = f.stream_position()?;
1663 /// println!("The first line was {} bytes long", after - before);
1667 #[unstable(feature = "seek_convenience", issue = "59359")]
1668 fn stream_position(&mut self) -> Result<u64> {
1669 self.seek(SeekFrom::Current(0))
1673 /// Enumeration of possible methods to seek within an I/O object.
1675 /// It is used by the [`Seek`] trait.
1677 /// [`Seek`]: trait.Seek.html
1678 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1679 #[stable(feature = "rust1", since = "1.0.0")]
1681 /// Sets the offset to the provided number of bytes.
1682 #[stable(feature = "rust1", since = "1.0.0")]
1683 Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
1685 /// Sets the offset to the size of this object plus the specified number of
1688 /// It is possible to seek beyond the end of an object, but it's an error to
1689 /// seek before byte 0.
1690 #[stable(feature = "rust1", since = "1.0.0")]
1691 End(#[stable(feature = "rust1", since = "1.0.0")] i64),
1693 /// Sets the offset to the current position plus the specified number of
1696 /// It is possible to seek beyond the end of an object, but it's an error to
1697 /// seek before byte 0.
1698 #[stable(feature = "rust1", since = "1.0.0")]
1699 Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
1702 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> Result<usize> {
1705 let (done, used) = {
1706 let available = match r.fill_buf() {
1708 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1709 Err(e) => return Err(e),
1711 match memchr::memchr(delim, available) {
1713 buf.extend_from_slice(&available[..=i]);
1717 buf.extend_from_slice(available);
1718 (false, available.len())
1724 if done || used == 0 {
1730 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1731 /// to perform extra ways of reading.
1733 /// For example, reading line-by-line is inefficient without using a buffer, so
1734 /// if you want to read by line, you'll need `BufRead`, which includes a
1735 /// [`read_line`] method as well as a [`lines`] iterator.
1739 /// A locked standard input implements `BufRead`:
1743 /// use std::io::prelude::*;
1745 /// let stdin = io::stdin();
1746 /// for line in stdin.lock().lines() {
1747 /// println!("{}", line.unwrap());
1751 /// If you have something that implements [`Read`], you can use the [`BufReader`
1752 /// type][`BufReader`] to turn it into a `BufRead`.
1754 /// For example, [`File`] implements [`Read`], but not `BufRead`.
1755 /// [`BufReader`] to the rescue!
1757 /// [`BufReader`]: struct.BufReader.html
1758 /// [`File`]: crate::fs::File
1759 /// [`read_line`]: Self::read_line
1760 /// [`lines`]: Self::lines
1761 /// [`Read`]: trait.Read.html
1764 /// use std::io::{self, BufReader};
1765 /// use std::io::prelude::*;
1766 /// use std::fs::File;
1768 /// fn main() -> io::Result<()> {
1769 /// let f = File::open("foo.txt")?;
1770 /// let f = BufReader::new(f);
1772 /// for line in f.lines() {
1773 /// println!("{}", line.unwrap());
1780 #[stable(feature = "rust1", since = "1.0.0")]
1781 pub trait BufRead: Read {
1782 /// Returns the contents of the internal buffer, filling it with more data
1783 /// from the inner reader if it is empty.
1785 /// This function is a lower-level call. It needs to be paired with the
1786 /// [`consume`] method to function properly. When calling this
1787 /// method, none of the contents will be "read" in the sense that later
1788 /// calling `read` may return the same contents. As such, [`consume`] must
1789 /// be called with the number of bytes that are consumed from this buffer to
1790 /// ensure that the bytes are never returned twice.
1792 /// [`consume`]: Self::consume
1794 /// An empty buffer returned indicates that the stream has reached EOF.
1798 /// This function will return an I/O error if the underlying reader was
1799 /// read, but returned an error.
1803 /// A locked standard input implements `BufRead`:
1807 /// use std::io::prelude::*;
1809 /// let stdin = io::stdin();
1810 /// let mut stdin = stdin.lock();
1812 /// let buffer = stdin.fill_buf().unwrap();
1814 /// // work with buffer
1815 /// println!("{:?}", buffer);
1817 /// // ensure the bytes we worked with aren't returned again later
1818 /// let length = buffer.len();
1819 /// stdin.consume(length);
1821 #[stable(feature = "rust1", since = "1.0.0")]
1822 fn fill_buf(&mut self) -> Result<&[u8]>;
1824 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1825 /// so they should no longer be returned in calls to `read`.
1827 /// This function is a lower-level call. It needs to be paired with the
1828 /// [`fill_buf`] method to function properly. This function does
1829 /// not perform any I/O, it simply informs this object that some amount of
1830 /// its buffer, returned from [`fill_buf`], has been consumed and should
1831 /// no longer be returned. As such, this function may do odd things if
1832 /// [`fill_buf`] isn't called before calling it.
1834 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1839 /// Since `consume()` is meant to be used with [`fill_buf`],
1840 /// that method's example includes an example of `consume()`.
1842 /// [`fill_buf`]: Self::fill_buf
1843 #[stable(feature = "rust1", since = "1.0.0")]
1844 fn consume(&mut self, amt: usize);
1846 /// Read all bytes into `buf` until the delimiter `byte` or EOF is reached.
1848 /// This function will read bytes from the underlying stream until the
1849 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1850 /// the delimiter (if found) will be appended to `buf`.
1852 /// If successful, this function will return the total number of bytes read.
1854 /// This function is blocking and should be used carefully: it is possible for
1855 /// an attacker to continuously send bytes without ever sending the delimiter
1860 /// This function will ignore all instances of [`ErrorKind::Interrupted`] and
1861 /// will otherwise return any errors returned by [`fill_buf`].
1863 /// If an I/O error is encountered then all bytes read so far will be
1864 /// present in `buf` and its length will have been adjusted appropriately.
1866 /// [`fill_buf`]: Self::fill_buf
1867 /// [`ErrorKind::Interrupted`]: enum.ErrorKind.html#variant.Interrupted
1871 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1872 /// this example, we use [`Cursor`] to read all the bytes in a byte slice
1873 /// in hyphen delimited segments:
1875 /// [`Cursor`]: struct.Cursor.html
1878 /// use std::io::{self, BufRead};
1880 /// let mut cursor = io::Cursor::new(b"lorem-ipsum");
1881 /// let mut buf = vec![];
1883 /// // cursor is at 'l'
1884 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1885 /// .expect("reading from cursor won't fail");
1886 /// assert_eq!(num_bytes, 6);
1887 /// assert_eq!(buf, b"lorem-");
1890 /// // cursor is at 'i'
1891 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1892 /// .expect("reading from cursor won't fail");
1893 /// assert_eq!(num_bytes, 5);
1894 /// assert_eq!(buf, b"ipsum");
1897 /// // cursor is at EOF
1898 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1899 /// .expect("reading from cursor won't fail");
1900 /// assert_eq!(num_bytes, 0);
1901 /// assert_eq!(buf, b"");
1903 #[stable(feature = "rust1", since = "1.0.0")]
1904 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
1905 read_until(self, byte, buf)
1908 /// Read all bytes until a newline (the 0xA byte) is reached, and append
1909 /// them to the provided buffer.
1911 /// This function will read bytes from the underlying stream until the
1912 /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
1913 /// up to, and including, the delimiter (if found) will be appended to
1916 /// If successful, this function will return the total number of bytes read.
1918 /// If this function returns `Ok(0)`, the stream has reached EOF.
1920 /// This function is blocking and should be used carefully: it is possible for
1921 /// an attacker to continuously send bytes without ever sending a newline
1926 /// This function has the same error semantics as [`read_until`] and will
1927 /// also return an error if the read bytes are not valid UTF-8. If an I/O
1928 /// error is encountered then `buf` may contain some bytes already read in
1929 /// the event that all data read so far was valid UTF-8.
1931 /// [`read_until`]: Self::read_until
1935 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1936 /// this example, we use [`Cursor`] to read all the lines in a byte slice:
1938 /// [`Cursor`]: struct.Cursor.html
1941 /// use std::io::{self, BufRead};
1943 /// let mut cursor = io::Cursor::new(b"foo\nbar");
1944 /// let mut buf = String::new();
1946 /// // cursor is at 'f'
1947 /// let num_bytes = cursor.read_line(&mut buf)
1948 /// .expect("reading from cursor won't fail");
1949 /// assert_eq!(num_bytes, 4);
1950 /// assert_eq!(buf, "foo\n");
1953 /// // cursor is at 'b'
1954 /// let num_bytes = cursor.read_line(&mut buf)
1955 /// .expect("reading from cursor won't fail");
1956 /// assert_eq!(num_bytes, 3);
1957 /// assert_eq!(buf, "bar");
1960 /// // cursor is at EOF
1961 /// let num_bytes = cursor.read_line(&mut buf)
1962 /// .expect("reading from cursor won't fail");
1963 /// assert_eq!(num_bytes, 0);
1964 /// assert_eq!(buf, "");
1966 #[stable(feature = "rust1", since = "1.0.0")]
1967 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
1968 // Note that we are not calling the `.read_until` method here, but
1969 // rather our hardcoded implementation. For more details as to why, see
1970 // the comments in `read_to_end`.
1971 append_to_string(buf, |b| read_until(self, b'\n', b))
1974 /// Returns an iterator over the contents of this reader split on the byte
1977 /// The iterator returned from this function will return instances of
1978 /// [`io::Result`]`<`[`Vec<u8>`]`>`. Each vector returned will *not* have
1979 /// the delimiter byte at the end.
1981 /// This function will yield errors whenever [`read_until`] would have
1982 /// also yielded an error.
1984 /// [`io::Result`]: self::Result
1985 /// [`Vec<u8>`]: crate::vec::Vec
1986 /// [`read_until`]: Self::read_until
1990 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1991 /// this example, we use [`Cursor`] to iterate over all hyphen delimited
1992 /// segments in a byte slice
1994 /// [`Cursor`]: struct.Cursor.html
1997 /// use std::io::{self, BufRead};
1999 /// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
2001 /// let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
2002 /// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
2003 /// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
2004 /// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
2005 /// assert_eq!(split_iter.next(), None);
2007 #[stable(feature = "rust1", since = "1.0.0")]
2008 fn split(self, byte: u8) -> Split<Self>
2012 Split { buf: self, delim: byte }
2015 /// Returns an iterator over the lines of this reader.
2017 /// The iterator returned from this function will yield instances of
2018 /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
2019 /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
2021 /// [`io::Result`]: self::Result
2025 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2026 /// this example, we use [`Cursor`] to iterate over all the lines in a byte
2030 /// use std::io::{self, BufRead};
2032 /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
2034 /// let mut lines_iter = cursor.lines().map(|l| l.unwrap());
2035 /// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
2036 /// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
2037 /// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
2038 /// assert_eq!(lines_iter.next(), None);
2043 /// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
2045 /// [`BufRead::read_line`]: trait.BufRead.html#method.read_line
2046 #[stable(feature = "rust1", since = "1.0.0")]
2047 fn lines(self) -> Lines<Self>
2055 /// Adaptor to chain together two readers.
2057 /// This struct is generally created by calling [`chain`] on a reader.
2058 /// Please see the documentation of [`chain`] for more details.
2060 /// [`chain`]: trait.Read.html#method.chain
2061 #[stable(feature = "rust1", since = "1.0.0")]
2062 pub struct Chain<T, U> {
2068 impl<T, U> Chain<T, U> {
2069 /// Consumes the `Chain`, returning the wrapped readers.
2075 /// use std::io::prelude::*;
2076 /// use std::fs::File;
2078 /// fn main() -> io::Result<()> {
2079 /// let mut foo_file = File::open("foo.txt")?;
2080 /// let mut bar_file = File::open("bar.txt")?;
2082 /// let chain = foo_file.chain(bar_file);
2083 /// let (foo_file, bar_file) = chain.into_inner();
2087 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2088 pub fn into_inner(self) -> (T, U) {
2089 (self.first, self.second)
2092 /// Gets references to the underlying readers in this `Chain`.
2098 /// use std::io::prelude::*;
2099 /// use std::fs::File;
2101 /// fn main() -> io::Result<()> {
2102 /// let mut foo_file = File::open("foo.txt")?;
2103 /// let mut bar_file = File::open("bar.txt")?;
2105 /// let chain = foo_file.chain(bar_file);
2106 /// let (foo_file, bar_file) = chain.get_ref();
2110 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2111 pub fn get_ref(&self) -> (&T, &U) {
2112 (&self.first, &self.second)
2115 /// Gets mutable references to the underlying readers in this `Chain`.
2117 /// Care should be taken to avoid modifying the internal I/O state of the
2118 /// underlying readers as doing so may corrupt the internal state of this
2125 /// use std::io::prelude::*;
2126 /// use std::fs::File;
2128 /// fn main() -> io::Result<()> {
2129 /// let mut foo_file = File::open("foo.txt")?;
2130 /// let mut bar_file = File::open("bar.txt")?;
2132 /// let mut chain = foo_file.chain(bar_file);
2133 /// let (foo_file, bar_file) = chain.get_mut();
2137 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2138 pub fn get_mut(&mut self) -> (&mut T, &mut U) {
2139 (&mut self.first, &mut self.second)
2143 #[stable(feature = "std_debug", since = "1.16.0")]
2144 impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
2145 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2146 f.debug_struct("Chain").field("t", &self.first).field("u", &self.second).finish()
2150 #[stable(feature = "rust1", since = "1.0.0")]
2151 impl<T: Read, U: Read> Read for Chain<T, U> {
2152 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2153 if !self.done_first {
2154 match self.first.read(buf)? {
2155 0 if !buf.is_empty() => self.done_first = true,
2159 self.second.read(buf)
2162 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
2163 if !self.done_first {
2164 match self.first.read_vectored(bufs)? {
2165 0 if bufs.iter().any(|b| !b.is_empty()) => self.done_first = true,
2169 self.second.read_vectored(bufs)
2172 unsafe fn initializer(&self) -> Initializer {
2173 let initializer = self.first.initializer();
2174 if initializer.should_initialize() { initializer } else { self.second.initializer() }
2178 #[stable(feature = "chain_bufread", since = "1.9.0")]
2179 impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
2180 fn fill_buf(&mut self) -> Result<&[u8]> {
2181 if !self.done_first {
2182 match self.first.fill_buf()? {
2183 buf if buf.is_empty() => {
2184 self.done_first = true;
2186 buf => return Ok(buf),
2189 self.second.fill_buf()
2192 fn consume(&mut self, amt: usize) {
2193 if !self.done_first { self.first.consume(amt) } else { self.second.consume(amt) }
2197 /// Reader adaptor which limits the bytes read from an underlying reader.
2199 /// This struct is generally created by calling [`take`] on a reader.
2200 /// Please see the documentation of [`take`] for more details.
2202 /// [`take`]: trait.Read.html#method.take
2203 #[stable(feature = "rust1", since = "1.0.0")]
2205 pub struct Take<T> {
2211 /// Returns the number of bytes that can be read before this instance will
2216 /// This instance may reach `EOF` after reading fewer bytes than indicated by
2217 /// this method if the underlying [`Read`] instance reaches EOF.
2223 /// use std::io::prelude::*;
2224 /// use std::fs::File;
2226 /// fn main() -> io::Result<()> {
2227 /// let f = File::open("foo.txt")?;
2229 /// // read at most five bytes
2230 /// let handle = f.take(5);
2232 /// println!("limit: {}", handle.limit());
2236 #[stable(feature = "rust1", since = "1.0.0")]
2237 pub fn limit(&self) -> u64 {
2241 /// Sets the number of bytes that can be read before this instance will
2242 /// return EOF. This is the same as constructing a new `Take` instance, so
2243 /// the amount of bytes read and the previous limit value don't matter when
2244 /// calling this method.
2250 /// use std::io::prelude::*;
2251 /// use std::fs::File;
2253 /// fn main() -> io::Result<()> {
2254 /// let f = File::open("foo.txt")?;
2256 /// // read at most five bytes
2257 /// let mut handle = f.take(5);
2258 /// handle.set_limit(10);
2260 /// assert_eq!(handle.limit(), 10);
2264 #[stable(feature = "take_set_limit", since = "1.27.0")]
2265 pub fn set_limit(&mut self, limit: u64) {
2269 /// Consumes the `Take`, returning the wrapped reader.
2275 /// use std::io::prelude::*;
2276 /// use std::fs::File;
2278 /// fn main() -> io::Result<()> {
2279 /// let mut file = File::open("foo.txt")?;
2281 /// let mut buffer = [0; 5];
2282 /// let mut handle = file.take(5);
2283 /// handle.read(&mut buffer)?;
2285 /// let file = handle.into_inner();
2289 #[stable(feature = "io_take_into_inner", since = "1.15.0")]
2290 pub fn into_inner(self) -> T {
2294 /// Gets a reference to the underlying reader.
2300 /// use std::io::prelude::*;
2301 /// use std::fs::File;
2303 /// fn main() -> io::Result<()> {
2304 /// let mut file = File::open("foo.txt")?;
2306 /// let mut buffer = [0; 5];
2307 /// let mut handle = file.take(5);
2308 /// handle.read(&mut buffer)?;
2310 /// let file = handle.get_ref();
2314 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2315 pub fn get_ref(&self) -> &T {
2319 /// Gets a mutable reference to the underlying reader.
2321 /// Care should be taken to avoid modifying the internal I/O state of the
2322 /// underlying reader as doing so may corrupt the internal limit of this
2329 /// use std::io::prelude::*;
2330 /// use std::fs::File;
2332 /// fn main() -> io::Result<()> {
2333 /// let mut file = File::open("foo.txt")?;
2335 /// let mut buffer = [0; 5];
2336 /// let mut handle = file.take(5);
2337 /// handle.read(&mut buffer)?;
2339 /// let file = handle.get_mut();
2343 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2344 pub fn get_mut(&mut self) -> &mut T {
2349 #[stable(feature = "rust1", since = "1.0.0")]
2350 impl<T: Read> Read for Take<T> {
2351 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2352 // Don't call into inner reader at all at EOF because it may still block
2353 if self.limit == 0 {
2357 let max = cmp::min(buf.len() as u64, self.limit) as usize;
2358 let n = self.inner.read(&mut buf[..max])?;
2359 self.limit -= n as u64;
2363 unsafe fn initializer(&self) -> Initializer {
2364 self.inner.initializer()
2367 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
2368 // Pass in a reservation_size closure that respects the current value
2369 // of limit for each read. If we hit the read limit, this prevents the
2370 // final zero-byte read from allocating again.
2371 read_to_end_with_reservation(self, buf, |self_| cmp::min(self_.limit, 32) as usize)
2375 #[stable(feature = "rust1", since = "1.0.0")]
2376 impl<T: BufRead> BufRead for Take<T> {
2377 fn fill_buf(&mut self) -> Result<&[u8]> {
2378 // Don't call into inner reader at all at EOF because it may still block
2379 if self.limit == 0 {
2383 let buf = self.inner.fill_buf()?;
2384 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
2388 fn consume(&mut self, amt: usize) {
2389 // Don't let callers reset the limit by passing an overlarge value
2390 let amt = cmp::min(amt as u64, self.limit) as usize;
2391 self.limit -= amt as u64;
2392 self.inner.consume(amt);
2396 /// An iterator over `u8` values of a reader.
2398 /// This struct is generally created by calling [`bytes`] on a reader.
2399 /// Please see the documentation of [`bytes`] for more details.
2401 /// [`bytes`]: trait.Read.html#method.bytes
2402 #[stable(feature = "rust1", since = "1.0.0")]
2404 pub struct Bytes<R> {
2408 #[stable(feature = "rust1", since = "1.0.0")]
2409 impl<R: Read> Iterator for Bytes<R> {
2410 type Item = Result<u8>;
2412 fn next(&mut self) -> Option<Result<u8>> {
2415 return match self.inner.read(slice::from_mut(&mut byte)) {
2417 Ok(..) => Some(Ok(byte)),
2418 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
2419 Err(e) => Some(Err(e)),
2425 /// An iterator over the contents of an instance of `BufRead` split on a
2426 /// particular byte.
2428 /// This struct is generally created by calling [`split`] on a `BufRead`.
2429 /// Please see the documentation of [`split`] for more details.
2431 /// [`split`]: trait.BufRead.html#method.split
2432 #[stable(feature = "rust1", since = "1.0.0")]
2434 pub struct Split<B> {
2439 #[stable(feature = "rust1", since = "1.0.0")]
2440 impl<B: BufRead> Iterator for Split<B> {
2441 type Item = Result<Vec<u8>>;
2443 fn next(&mut self) -> Option<Result<Vec<u8>>> {
2444 let mut buf = Vec::new();
2445 match self.buf.read_until(self.delim, &mut buf) {
2448 if buf[buf.len() - 1] == self.delim {
2453 Err(e) => Some(Err(e)),
2458 /// An iterator over the lines of an instance of `BufRead`.
2460 /// This struct is generally created by calling [`lines`] on a `BufRead`.
2461 /// Please see the documentation of [`lines`] for more details.
2463 /// [`lines`]: trait.BufRead.html#method.lines
2464 #[stable(feature = "rust1", since = "1.0.0")]
2466 pub struct Lines<B> {
2470 #[stable(feature = "rust1", since = "1.0.0")]
2471 impl<B: BufRead> Iterator for Lines<B> {
2472 type Item = Result<String>;
2474 fn next(&mut self) -> Option<Result<String>> {
2475 let mut buf = String::new();
2476 match self.buf.read_line(&mut buf) {
2479 if buf.ends_with('\n') {
2481 if buf.ends_with('\r') {
2487 Err(e) => Some(Err(e)),
2494 use super::{repeat, Cursor, SeekFrom};
2495 use crate::cmp::{self, min};
2496 use crate::io::prelude::*;
2497 use crate::io::{self, IoSlice, IoSliceMut};
2498 use crate::ops::Deref;
2501 #[cfg_attr(target_os = "emscripten", ignore)]
2503 let mut buf = Cursor::new(&b"12"[..]);
2504 let mut v = Vec::new();
2505 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
2506 assert_eq!(v, b"12");
2508 let mut buf = Cursor::new(&b"1233"[..]);
2509 let mut v = Vec::new();
2510 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
2511 assert_eq!(v, b"123");
2513 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
2514 assert_eq!(v, b"3");
2516 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
2522 let buf = Cursor::new(&b"12"[..]);
2523 let mut s = buf.split(b'3');
2524 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
2525 assert!(s.next().is_none());
2527 let buf = Cursor::new(&b"1233"[..]);
2528 let mut s = buf.split(b'3');
2529 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
2530 assert_eq!(s.next().unwrap().unwrap(), vec![]);
2531 assert!(s.next().is_none());
2536 let mut buf = Cursor::new(&b"12"[..]);
2537 let mut v = String::new();
2538 assert_eq!(buf.read_line(&mut v).unwrap(), 2);
2539 assert_eq!(v, "12");
2541 let mut buf = Cursor::new(&b"12\n\n"[..]);
2542 let mut v = String::new();
2543 assert_eq!(buf.read_line(&mut v).unwrap(), 3);
2544 assert_eq!(v, "12\n");
2546 assert_eq!(buf.read_line(&mut v).unwrap(), 1);
2547 assert_eq!(v, "\n");
2549 assert_eq!(buf.read_line(&mut v).unwrap(), 0);
2555 let buf = Cursor::new(&b"12\r"[..]);
2556 let mut s = buf.lines();
2557 assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
2558 assert!(s.next().is_none());
2560 let buf = Cursor::new(&b"12\r\n\n"[..]);
2561 let mut s = buf.lines();
2562 assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
2563 assert_eq!(s.next().unwrap().unwrap(), "".to_string());
2564 assert!(s.next().is_none());
2569 let mut c = Cursor::new(&b""[..]);
2570 let mut v = Vec::new();
2571 assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
2574 let mut c = Cursor::new(&b"1"[..]);
2575 let mut v = Vec::new();
2576 assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
2577 assert_eq!(v, b"1");
2579 let cap = 1024 * 1024;
2580 let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
2581 let mut v = Vec::new();
2582 let (a, b) = data.split_at(data.len() / 2);
2583 assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
2584 assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
2585 assert_eq!(v, data);
2589 fn read_to_string() {
2590 let mut c = Cursor::new(&b""[..]);
2591 let mut v = String::new();
2592 assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
2595 let mut c = Cursor::new(&b"1"[..]);
2596 let mut v = String::new();
2597 assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
2600 let mut c = Cursor::new(&b"\xff"[..]);
2601 let mut v = String::new();
2602 assert!(c.read_to_string(&mut v).is_err());
2607 let mut buf = [0; 4];
2609 let mut c = Cursor::new(&b""[..]);
2610 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2612 let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
2613 c.read_exact(&mut buf).unwrap();
2614 assert_eq!(&buf, b"1234");
2615 c.read_exact(&mut buf).unwrap();
2616 assert_eq!(&buf, b"5678");
2617 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2621 fn read_exact_slice() {
2622 let mut buf = [0; 4];
2624 let mut c = &b""[..];
2625 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2627 let mut c = &b"123"[..];
2628 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
2629 // make sure the optimized (early returning) method is being used
2630 assert_eq!(&buf, &[0; 4]);
2632 let mut c = &b"1234"[..];
2633 c.read_exact(&mut buf).unwrap();
2634 assert_eq!(&buf, b"1234");
2636 let mut c = &b"56789"[..];
2637 c.read_exact(&mut buf).unwrap();
2638 assert_eq!(&buf, b"5678");
2639 assert_eq!(c, b"9");
2647 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
2648 Err(io::Error::new(io::ErrorKind::Other, ""))
2651 impl BufRead for R {
2652 fn fill_buf(&mut self) -> io::Result<&[u8]> {
2653 Err(io::Error::new(io::ErrorKind::Other, ""))
2655 fn consume(&mut self, _amt: usize) {}
2658 let mut buf = [0; 1];
2659 assert_eq!(0, R.take(0).read(&mut buf).unwrap());
2660 assert_eq!(b"", R.take(0).fill_buf().unwrap());
2663 fn cmp_bufread<Br1: BufRead, Br2: BufRead>(mut br1: Br1, mut br2: Br2, exp: &[u8]) {
2664 let mut cat = Vec::new();
2667 let buf1 = br1.fill_buf().unwrap();
2668 let buf2 = br2.fill_buf().unwrap();
2669 let minlen = if buf1.len() < buf2.len() { buf1.len() } else { buf2.len() };
2670 assert_eq!(buf1[..minlen], buf2[..minlen]);
2671 cat.extend_from_slice(&buf1[..minlen]);
2677 br1.consume(consume);
2678 br2.consume(consume);
2680 assert_eq!(br1.fill_buf().unwrap().len(), 0);
2681 assert_eq!(br2.fill_buf().unwrap().len(), 0);
2682 assert_eq!(&cat[..], &exp[..])
2686 fn chain_bufread() {
2687 let testdata = b"ABCDEFGHIJKL";
2689 (&testdata[..3]).chain(&testdata[3..6]).chain(&testdata[6..9]).chain(&testdata[9..]);
2690 let chain2 = (&testdata[..4]).chain(&testdata[4..8]).chain(&testdata[8..]);
2691 cmp_bufread(chain1, chain2, &testdata[..]);
2695 fn chain_zero_length_read_is_not_eof() {
2698 let mut s = String::new();
2699 let mut chain = (&a[..]).chain(&b[..]);
2700 chain.read(&mut []).unwrap();
2701 chain.read_to_string(&mut s).unwrap();
2702 assert_eq!("AB", s);
2706 #[cfg_attr(target_os = "emscripten", ignore)]
2707 fn bench_read_to_end(b: &mut test::Bencher) {
2709 let mut lr = repeat(1).take(10000000);
2710 let mut vec = Vec::with_capacity(1024);
2711 super::read_to_end(&mut lr, &mut vec)
2716 fn seek_len() -> io::Result<()> {
2717 let mut c = Cursor::new(vec![0; 15]);
2718 assert_eq!(c.stream_len()?, 15);
2720 c.seek(SeekFrom::End(0))?;
2721 let old_pos = c.stream_position()?;
2722 assert_eq!(c.stream_len()?, 15);
2723 assert_eq!(c.stream_position()?, old_pos);
2725 c.seek(SeekFrom::Start(7))?;
2726 c.seek(SeekFrom::Current(2))?;
2727 let old_pos = c.stream_position()?;
2728 assert_eq!(c.stream_len()?, 15);
2729 assert_eq!(c.stream_position()?, old_pos);
2735 fn seek_position() -> io::Result<()> {
2736 // All `asserts` are duplicated here to make sure the method does not
2737 // change anything about the seek state.
2738 let mut c = Cursor::new(vec![0; 15]);
2739 assert_eq!(c.stream_position()?, 0);
2740 assert_eq!(c.stream_position()?, 0);
2742 c.seek(SeekFrom::End(0))?;
2743 assert_eq!(c.stream_position()?, 15);
2744 assert_eq!(c.stream_position()?, 15);
2746 c.seek(SeekFrom::Start(7))?;
2747 c.seek(SeekFrom::Current(2))?;
2748 assert_eq!(c.stream_position()?, 9);
2749 assert_eq!(c.stream_position()?, 9);
2751 c.seek(SeekFrom::End(-3))?;
2752 c.seek(SeekFrom::Current(1))?;
2753 c.seek(SeekFrom::Current(-5))?;
2754 assert_eq!(c.stream_position()?, 8);
2755 assert_eq!(c.stream_position()?, 8);
2760 // A simple example reader which uses the default implementation of
2762 struct ExampleSliceReader<'a> {
2766 impl<'a> Read for ExampleSliceReader<'a> {
2767 fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
2768 let len = cmp::min(self.slice.len(), buf.len());
2769 buf[..len].copy_from_slice(&self.slice[..len]);
2770 self.slice = &self.slice[len..];
2776 fn test_read_to_end_capacity() -> io::Result<()> {
2777 let input = &b"foo"[..];
2779 // read_to_end() generally needs to over-allocate, both for efficiency
2780 // and so that it can distinguish EOF. Assert that this is the case
2781 // with this simple ExampleSliceReader struct, which uses the default
2782 // implementation of read_to_end. Even though vec1 is allocated with
2783 // exactly enough capacity for the read, read_to_end will allocate more
2785 let mut vec1 = Vec::with_capacity(input.len());
2786 ExampleSliceReader { slice: input }.read_to_end(&mut vec1)?;
2787 assert_eq!(vec1.len(), input.len());
2788 assert!(vec1.capacity() > input.len(), "allocated more");
2790 // However, std::io::Take includes an implementation of read_to_end
2791 // that will not allocate when the limit has already been reached. In
2792 // this case, vec2 never grows.
2793 let mut vec2 = Vec::with_capacity(input.len());
2794 ExampleSliceReader { slice: input }.take(input.len() as u64).read_to_end(&mut vec2)?;
2795 assert_eq!(vec2.len(), input.len());
2796 assert_eq!(vec2.capacity(), input.len(), "did not allocate more");
2802 fn io_slice_mut_advance() {
2803 let mut buf1 = [1; 8];
2804 let mut buf2 = [2; 16];
2805 let mut buf3 = [3; 8];
2806 let mut bufs = &mut [
2807 IoSliceMut::new(&mut buf1),
2808 IoSliceMut::new(&mut buf2),
2809 IoSliceMut::new(&mut buf3),
2812 // Only in a single buffer..
2813 bufs = IoSliceMut::advance(bufs, 1);
2814 assert_eq!(bufs[0].deref(), [1; 7].as_ref());
2815 assert_eq!(bufs[1].deref(), [2; 16].as_ref());
2816 assert_eq!(bufs[2].deref(), [3; 8].as_ref());
2818 // Removing a buffer, leaving others as is.
2819 bufs = IoSliceMut::advance(bufs, 7);
2820 assert_eq!(bufs[0].deref(), [2; 16].as_ref());
2821 assert_eq!(bufs[1].deref(), [3; 8].as_ref());
2823 // Removing a buffer and removing from the next buffer.
2824 bufs = IoSliceMut::advance(bufs, 18);
2825 assert_eq!(bufs[0].deref(), [3; 6].as_ref());
2829 fn io_slice_mut_advance_empty_slice() {
2830 let empty_bufs = &mut [][..];
2832 IoSliceMut::advance(empty_bufs, 1);
2836 fn io_slice_mut_advance_beyond_total_length() {
2837 let mut buf1 = [1; 8];
2838 let mut bufs = &mut [IoSliceMut::new(&mut buf1)][..];
2840 // Going beyond the total length should be ok.
2841 bufs = IoSliceMut::advance(bufs, 9);
2842 assert!(bufs.is_empty());
2846 fn io_slice_advance() {
2850 let mut bufs = &mut [IoSlice::new(&buf1), IoSlice::new(&buf2), IoSlice::new(&buf3)][..];
2852 // Only in a single buffer..
2853 bufs = IoSlice::advance(bufs, 1);
2854 assert_eq!(bufs[0].deref(), [1; 7].as_ref());
2855 assert_eq!(bufs[1].deref(), [2; 16].as_ref());
2856 assert_eq!(bufs[2].deref(), [3; 8].as_ref());
2858 // Removing a buffer, leaving others as is.
2859 bufs = IoSlice::advance(bufs, 7);
2860 assert_eq!(bufs[0].deref(), [2; 16].as_ref());
2861 assert_eq!(bufs[1].deref(), [3; 8].as_ref());
2863 // Removing a buffer and removing from the next buffer.
2864 bufs = IoSlice::advance(bufs, 18);
2865 assert_eq!(bufs[0].deref(), [3; 6].as_ref());
2869 fn io_slice_advance_empty_slice() {
2870 let empty_bufs = &mut [][..];
2872 IoSlice::advance(empty_bufs, 1);
2876 fn io_slice_advance_beyond_total_length() {
2878 let mut bufs = &mut [IoSlice::new(&buf1)][..];
2880 // Going beyond the total length should be ok.
2881 bufs = IoSlice::advance(bufs, 9);
2882 assert!(bufs.is_empty());
2885 /// Create a new writer that reads from at most `n_bufs` and reads
2886 /// `per_call` bytes (in total) per call to write.
2887 fn test_writer(n_bufs: usize, per_call: usize) -> TestWriter {
2888 TestWriter { n_bufs, per_call, written: Vec::new() }
2897 impl Write for TestWriter {
2898 fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
2899 self.write_vectored(&[IoSlice::new(buf)])
2902 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
2903 let mut left = self.per_call;
2904 let mut written = 0;
2905 for buf in bufs.iter().take(self.n_bufs) {
2906 let n = min(left, buf.len());
2907 self.written.extend_from_slice(&buf[0..n]);
2914 fn flush(&mut self) -> io::Result<()> {
2920 fn test_writer_read_from_one_buf() {
2921 let mut writer = test_writer(1, 2);
2923 assert_eq!(writer.write(&[]).unwrap(), 0);
2924 assert_eq!(writer.write_vectored(&[]).unwrap(), 0);
2926 // Read at most 2 bytes.
2927 assert_eq!(writer.write(&[1, 1, 1]).unwrap(), 2);
2928 let bufs = &[IoSlice::new(&[2, 2, 2])];
2929 assert_eq!(writer.write_vectored(bufs).unwrap(), 2);
2931 // Only read from first buf.
2932 let bufs = &[IoSlice::new(&[3]), IoSlice::new(&[4, 4])];
2933 assert_eq!(writer.write_vectored(bufs).unwrap(), 1);
2935 assert_eq!(writer.written, &[1, 1, 2, 2, 3]);
2939 fn test_writer_read_from_multiple_bufs() {
2940 let mut writer = test_writer(3, 3);
2942 // Read at most 3 bytes from two buffers.
2943 let bufs = &[IoSlice::new(&[1]), IoSlice::new(&[2, 2, 2])];
2944 assert_eq!(writer.write_vectored(bufs).unwrap(), 3);
2946 // Read at most 3 bytes from three buffers.
2947 let bufs = &[IoSlice::new(&[3]), IoSlice::new(&[4]), IoSlice::new(&[5, 5])];
2948 assert_eq!(writer.write_vectored(bufs).unwrap(), 3);
2950 assert_eq!(writer.written, &[1, 2, 2, 3, 4, 5]);
2954 fn test_write_all_vectored() {
2955 #[rustfmt::skip] // Becomes unreadable otherwise.
2956 let tests: Vec<(_, &'static [u8])> = vec![
2958 (vec![IoSlice::new(&[1])], &[1]),
2959 (vec![IoSlice::new(&[1, 2])], &[1, 2]),
2960 (vec![IoSlice::new(&[1, 2, 3])], &[1, 2, 3]),
2961 (vec![IoSlice::new(&[1, 2, 3, 4])], &[1, 2, 3, 4]),
2962 (vec![IoSlice::new(&[1, 2, 3, 4, 5])], &[1, 2, 3, 4, 5]),
2963 (vec![IoSlice::new(&[1]), IoSlice::new(&[2])], &[1, 2]),
2964 (vec![IoSlice::new(&[1]), IoSlice::new(&[2, 2])], &[1, 2, 2]),
2965 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2])], &[1, 1, 2, 2]),
2966 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 2, 2, 2]),
2967 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 2, 2, 2]),
2968 (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 1, 2, 2, 2]),
2969 (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2, 2])], &[1, 1, 1, 2, 2, 2, 2]),
2970 (vec![IoSlice::new(&[1, 1, 1, 1]), IoSlice::new(&[2, 2, 2, 2])], &[1, 1, 1, 1, 2, 2, 2, 2]),
2971 (vec![IoSlice::new(&[1]), IoSlice::new(&[2]), IoSlice::new(&[3])], &[1, 2, 3]),
2972 (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2]), IoSlice::new(&[3, 3])], &[1, 1, 2, 2, 3, 3]),
2973 (vec![IoSlice::new(&[1]), IoSlice::new(&[2, 2]), IoSlice::new(&[3, 3, 3])], &[1, 2, 2, 3, 3, 3]),
2974 (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]),
2977 let writer_configs = &[(1, 1), (1, 2), (1, 3), (2, 2), (2, 3), (3, 3)];
2979 for (n_bufs, per_call) in writer_configs.iter().copied() {
2980 for (mut input, wanted) in tests.clone().into_iter() {
2981 let mut writer = test_writer(n_bufs, per_call);
2982 assert!(writer.write_all_vectored(&mut *input).is_ok());
2983 assert_eq!(&*writer.written, &*wanted);