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
244 //! [`io::stdout`]: stdout
245 //! [`io::Result`]: self::Result
246 //! [`?` operator]: ../../book/appendix-02-operators.html
247 //! [`Result`]: crate::result::Result
248 //! [`.unwrap()`]: crate::result::Result::unwrap
250 #![stable(feature = "rust1", since = "1.0.0")]
255 use crate::ops
::{Deref, DerefMut}
;
261 #[stable(feature = "rust1", since = "1.0.0")]
262 pub use self::buffered
::IntoInnerError
;
263 #[stable(feature = "rust1", since = "1.0.0")]
264 pub use self::buffered
::{BufReader, BufWriter, LineWriter}
;
265 #[stable(feature = "rust1", since = "1.0.0")]
266 pub use self::cursor
::Cursor
;
267 #[stable(feature = "rust1", since = "1.0.0")]
268 pub use self::error
::{Error, ErrorKind, Result}
;
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub use self::stdio
::{stderr, stdin, stdout, Stderr, Stdin, Stdout}
;
271 #[stable(feature = "rust1", since = "1.0.0")]
272 pub use self::stdio
::{StderrLock, StdinLock, StdoutLock}
;
273 #[unstable(feature = "print_internals", issue = "none")]
274 pub use self::stdio
::{_eprint, _print}
;
275 #[unstable(feature = "libstd_io_internals", issue = "42788")]
276 #[doc(no_inline, hidden)]
277 pub use self::stdio
::{set_panic, set_print}
;
278 #[stable(feature = "rust1", since = "1.0.0")]
279 pub use self::util
::{copy, empty, repeat, sink, Empty, Repeat, Sink}
;
290 const DEFAULT_BUF_SIZE
: usize = crate::sys_common
::io
::DEFAULT_BUF_SIZE
;
293 buf
: &'a
mut Vec
<u8>,
297 impl Drop
for Guard
<'_
> {
300 self.buf
.set_len(self.len
);
305 // A few methods below (read_to_string, read_line) will append data into a
306 // `String` buffer, but we need to be pretty careful when doing this. The
307 // implementation will just call `.as_mut_vec()` and then delegate to a
308 // byte-oriented reading method, but we must ensure that when returning we never
309 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
311 // To this end, we use an RAII guard (to protect against panics) which updates
312 // the length of the string when it is dropped. This guard initially truncates
313 // the string to the prior length and only after we've validated that the
314 // new contents are valid UTF-8 do we allow it to set a longer length.
316 // The unsafety in this function is twofold:
318 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
320 // 2. We're passing a raw buffer to the function `f`, and it is expected that
321 // the function only *appends* bytes to the buffer. We'll get undefined
322 // behavior if existing bytes are overwritten to have non-UTF-8 data.
323 fn append_to_string
<F
>(buf
: &mut String
, f
: F
) -> Result
<usize>
325 F
: FnOnce(&mut Vec
<u8>) -> Result
<usize>,
328 let mut g
= Guard { len: buf.len(), buf: buf.as_mut_vec() }
;
330 if str::from_utf8(&g
.buf
[g
.len
..]).is_err() {
332 Err(Error
::new(ErrorKind
::InvalidData
, "stream did not contain valid UTF-8"))
341 // This uses an adaptive system to extend the vector when it fills. We want to
342 // avoid paying to allocate and zero a huge chunk of memory if the reader only
343 // has 4 bytes while still making large reads if the reader does have a ton
344 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
345 // time is 4,500 times (!) slower than a default reservation size of 32 if the
346 // reader has a very small amount of data to return.
348 // Because we're extending the buffer with uninitialized data for trusted
349 // readers, we need to make sure to truncate that if any of this panics.
350 fn read_to_end
<R
: Read
+ ?Sized
>(r
: &mut R
, buf
: &mut Vec
<u8>) -> Result
<usize> {
351 read_to_end_with_reservation(r
, buf
, |_
| 32)
354 fn read_to_end_with_reservation
<R
, F
>(
357 mut reservation_size
: F
,
361 F
: FnMut(&R
) -> usize,
363 let start_len
= buf
.len();
364 let mut g
= Guard { len: buf.len(), buf }
;
367 if g
.len
== g
.buf
.len() {
369 // FIXME(danielhenrymantilla): #42788
371 // - This creates a (mut) reference to a slice of
372 // _uninitialized_ integers, which is **undefined behavior**
374 // - Only the standard library gets to soundly "ignore" this,
375 // based on its privileged knowledge of unstable rustc
377 g
.buf
.reserve(reservation_size(r
));
378 let capacity
= g
.buf
.capacity();
379 g
.buf
.set_len(capacity
);
380 r
.initializer().initialize(&mut g
.buf
[g
.len
..]);
384 match r
.read(&mut g
.buf
[g
.len
..]) {
386 ret
= Ok(g
.len
- start_len
);
390 Err(ref e
) if e
.kind() == ErrorKind
::Interrupted
=> {}
401 pub(crate) fn default_read_vectored
<F
>(read
: F
, bufs
: &mut [IoSliceMut
<'_
>]) -> Result
<usize>
403 F
: FnOnce(&mut [u8]) -> Result
<usize>,
405 let buf
= bufs
.iter_mut().find(|b
| !b
.is_empty()).map_or(&mut [][..], |b
| &mut **b
);
409 pub(crate) fn default_write_vectored
<F
>(write
: F
, bufs
: &[IoSlice
<'_
>]) -> Result
<usize>
411 F
: FnOnce(&[u8]) -> Result
<usize>,
413 let buf
= bufs
.iter().find(|b
| !b
.is_empty()).map_or(&[][..], |b
| &**b
);
417 /// The `Read` trait allows for reading bytes from a source.
419 /// Implementors of the `Read` trait are called 'readers'.
421 /// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
422 /// will attempt to pull bytes from this source into a provided buffer. A
423 /// number of other methods are implemented in terms of [`read()`], giving
424 /// implementors a number of ways to read bytes while only needing to implement
427 /// Readers are intended to be composable with one another. Many implementors
428 /// throughout [`std::io`] take and provide types which implement the `Read`
431 /// Please note that each call to [`read()`] may involve a system call, and
432 /// therefore, using something that implements [`BufRead`], such as
433 /// [`BufReader`], will be more efficient.
437 /// [`File`]s implement `Read`:
441 /// use std::io::prelude::*;
442 /// use std::fs::File;
444 /// fn main() -> io::Result<()> {
445 /// let mut f = File::open("foo.txt")?;
446 /// let mut buffer = [0; 10];
448 /// // read up to 10 bytes
449 /// f.read(&mut buffer)?;
451 /// let mut buffer = Vec::new();
452 /// // read the whole file
453 /// f.read_to_end(&mut buffer)?;
455 /// // read into a String, so that you don't need to do the conversion.
456 /// let mut buffer = String::new();
457 /// f.read_to_string(&mut buffer)?;
459 /// // and more! See the other methods for more details.
464 /// Read from [`&str`] because [`&[u8]`][slice] implements `Read`:
468 /// use std::io::prelude::*;
470 /// fn main() -> io::Result<()> {
471 /// let mut b = "This string will be read".as_bytes();
472 /// let mut buffer = [0; 10];
474 /// // read up to 10 bytes
475 /// b.read(&mut buffer)?;
477 /// // etc... it works exactly as a File does!
482 /// [`read()`]: Read::read
483 /// [`&str`]: prim@str
484 /// [`std::io`]: self
485 /// [`File`]: crate::fs::File
486 /// [slice]: ../../std/primitive.slice.html
487 #[stable(feature = "rust1", since = "1.0.0")]
490 /// Pull some bytes from this source into the specified buffer, returning
491 /// how many bytes were read.
493 /// This function does not provide any guarantees about whether it blocks
494 /// waiting for data, but if an object needs to block for a read and cannot,
495 /// it will typically signal this via an [`Err`] return value.
497 /// If the return value of this method is [`Ok(n)`], then it must be
498 /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
499 /// that the buffer `buf` has been filled in with `n` bytes of data from this
500 /// source. If `n` is `0`, then it can indicate one of two scenarios:
502 /// 1. This reader has reached its "end of file" and will likely no longer
503 /// be able to produce bytes. Note that this does not mean that the
504 /// reader will *always* no longer be able to produce bytes.
505 /// 2. The buffer specified was 0 bytes in length.
507 /// It is not an error if the returned value `n` is smaller than the buffer size,
508 /// even when the reader is not at the end of the stream yet.
509 /// This may happen for example because fewer bytes are actually available right now
510 /// (e. g. being close to end-of-file) or because read() was interrupted by a signal.
512 /// No guarantees are provided about the contents of `buf` when this
513 /// function is called, implementations cannot rely on any property of the
514 /// contents of `buf` being true. It is recommended that *implementations*
515 /// only write data to `buf` instead of reading its contents.
517 /// Correspondingly, however, *callers* of this method may not assume any guarantees
518 /// about how the implementation uses `buf`. The trait is safe to implement,
519 /// so it is possible that the code that's supposed to write to the buffer might also read
520 /// from it. It is your responsibility to make sure that `buf` is initialized
521 /// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
522 /// obtains via [`MaybeUninit<T>`]) is not safe, and can lead to undefined behavior.
524 /// [`MaybeUninit<T>`]: crate::mem::MaybeUninit
528 /// If this function encounters any form of I/O or other error, an error
529 /// variant will be returned. If an error is returned then it must be
530 /// guaranteed that no bytes were read.
532 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
533 /// operation should be retried if there is nothing else to do.
537 /// [`File`]s implement `Read`:
540 /// [`File`]: crate::fs::File
544 /// use std::io::prelude::*;
545 /// use std::fs::File;
547 /// fn main() -> io::Result<()> {
548 /// let mut f = File::open("foo.txt")?;
549 /// let mut buffer = [0; 10];
551 /// // read up to 10 bytes
552 /// let n = f.read(&mut buffer[..])?;
554 /// println!("The bytes: {:?}", &buffer[..n]);
558 #[stable(feature = "rust1", since = "1.0.0")]
559 fn read(&mut self, buf
: &mut [u8]) -> Result
<usize>;
561 /// Like `read`, except that it reads into a slice of buffers.
563 /// Data is copied to fill each buffer in order, with the final buffer
564 /// written to possibly being only partially filled. This method must
565 /// behave equivalently to a single call to `read` with concatenated
568 /// The default implementation calls `read` with either the first nonempty
569 /// buffer provided, or an empty one if none exists.
570 #[stable(feature = "iovec", since = "1.36.0")]
571 fn read_vectored(&mut self, bufs
: &mut [IoSliceMut
<'_
>]) -> Result
<usize> {
572 default_read_vectored(|b
| self.read(b
), bufs
)
575 /// Determines if this `Read`er has an efficient `read_vectored`
578 /// If a `Read`er does not override the default `read_vectored`
579 /// implementation, code using it may want to avoid the method all together
580 /// and coalesce writes into a single buffer for higher performance.
582 /// The default implementation returns `false`.
583 #[unstable(feature = "can_vector", issue = "69941")]
584 fn is_read_vectored(&self) -> bool
{
588 /// Determines if this `Read`er can work with buffers of uninitialized
591 /// The default implementation returns an initializer which will zero
594 /// If a `Read`er guarantees that it can work properly with uninitialized
595 /// memory, it should call [`Initializer::nop()`]. See the documentation for
596 /// [`Initializer`] for details.
598 /// The behavior of this method must be independent of the state of the
599 /// `Read`er - the method only takes `&self` so that it can be used through
604 /// This method is unsafe because a `Read`er could otherwise return a
605 /// non-zeroing `Initializer` from another `Read` type without an `unsafe`
607 #[unstable(feature = "read_initializer", issue = "42788")]
609 unsafe fn initializer(&self) -> Initializer
{
610 Initializer
::zeroing()
613 /// Read all bytes until EOF in this source, placing them into `buf`.
615 /// All bytes read from this source will be appended to the specified buffer
616 /// `buf`. This function will continuously call [`read()`] to append more data to
617 /// `buf` until [`read()`] returns either [`Ok(0)`] or an error of
618 /// non-[`ErrorKind::Interrupted`] kind.
620 /// If successful, this function will return the total number of bytes read.
624 /// If this function encounters an error of the kind
625 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
628 /// If any other read error is encountered then this function immediately
629 /// returns. Any bytes which have already been read will be appended to
634 /// [`File`]s implement `Read`:
636 /// [`read()`]: Read::read
638 /// [`File`]: crate::fs::File
642 /// use std::io::prelude::*;
643 /// use std::fs::File;
645 /// fn main() -> io::Result<()> {
646 /// let mut f = File::open("foo.txt")?;
647 /// let mut buffer = Vec::new();
649 /// // read the whole file
650 /// f.read_to_end(&mut buffer)?;
655 /// (See also the [`std::fs::read`] convenience function for reading from a
658 /// [`std::fs::read`]: crate::fs::read
659 #[stable(feature = "rust1", since = "1.0.0")]
660 fn read_to_end(&mut self, buf
: &mut Vec
<u8>) -> Result
<usize> {
661 read_to_end(self, buf
)
664 /// Read all bytes until EOF in this source, appending them to `buf`.
666 /// If successful, this function returns the number of bytes which were read
667 /// and appended to `buf`.
671 /// If the data in this stream is *not* valid UTF-8 then an error is
672 /// returned and `buf` is unchanged.
674 /// See [`read_to_end`] for other error semantics.
676 /// [`read_to_end`]: Read::read_to_end
680 /// [`File`]s implement `Read`:
682 /// [`File`]: crate::fs::File
686 /// use std::io::prelude::*;
687 /// use std::fs::File;
689 /// fn main() -> io::Result<()> {
690 /// let mut f = File::open("foo.txt")?;
691 /// let mut buffer = String::new();
693 /// f.read_to_string(&mut buffer)?;
698 /// (See also the [`std::fs::read_to_string`] convenience function for
699 /// reading from a file.)
701 /// [`std::fs::read_to_string`]: crate::fs::read_to_string
702 #[stable(feature = "rust1", since = "1.0.0")]
703 fn read_to_string(&mut self, buf
: &mut String
) -> Result
<usize> {
704 // Note that we do *not* call `.read_to_end()` here. We are passing
705 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
706 // method to fill it up. An arbitrary implementation could overwrite the
707 // entire contents of the vector, not just append to it (which is what
708 // we are expecting).
710 // To prevent extraneously checking the UTF-8-ness of the entire buffer
711 // we pass it to our hardcoded `read_to_end` implementation which we
712 // know is guaranteed to only read data into the end of the buffer.
713 append_to_string(buf
, |b
| read_to_end(self, b
))
716 /// Read the exact number of bytes required to fill `buf`.
718 /// This function reads as many bytes as necessary to completely fill the
719 /// specified buffer `buf`.
721 /// No guarantees are provided about the contents of `buf` when this
722 /// function is called, implementations cannot rely on any property of the
723 /// contents of `buf` being true. It is recommended that implementations
724 /// only write data to `buf` instead of reading its contents. The
725 /// documentation on [`read`] has a more detailed explanation on this
730 /// If this function encounters an error of the kind
731 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
734 /// If this function encounters an "end of file" before completely filling
735 /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
736 /// The contents of `buf` are unspecified in this case.
738 /// If any other read error is encountered then this function immediately
739 /// returns. The contents of `buf` are unspecified in this case.
741 /// If this function returns an error, it is unspecified how many bytes it
742 /// has read, but it will never read more than would be necessary to
743 /// completely fill the buffer.
747 /// [`File`]s implement `Read`:
749 /// [`read`]: Read::read
750 /// [`File`]: crate::fs::File
754 /// use std::io::prelude::*;
755 /// use std::fs::File;
757 /// fn main() -> io::Result<()> {
758 /// let mut f = File::open("foo.txt")?;
759 /// let mut buffer = [0; 10];
761 /// // read exactly 10 bytes
762 /// f.read_exact(&mut buffer)?;
766 #[stable(feature = "read_exact", since = "1.6.0")]
767 fn read_exact(&mut self, mut buf
: &mut [u8]) -> Result
<()> {
768 while !buf
.is_empty() {
769 match self.read(buf
) {
775 Err(ref e
) if e
.kind() == ErrorKind
::Interrupted
=> {}
776 Err(e
) => return Err(e
),
780 Err(Error
::new(ErrorKind
::UnexpectedEof
, "failed to fill whole buffer"))
786 /// Creates a "by reference" adaptor for this instance of `Read`.
788 /// The returned adaptor also implements `Read` and will simply borrow this
793 /// [`File`]s implement `Read`:
795 /// [`File`]: crate::fs::File
799 /// use std::io::Read;
800 /// use std::fs::File;
802 /// fn main() -> io::Result<()> {
803 /// let mut f = File::open("foo.txt")?;
804 /// let mut buffer = Vec::new();
805 /// let mut other_buffer = Vec::new();
808 /// let reference = f.by_ref();
810 /// // read at most 5 bytes
811 /// reference.take(5).read_to_end(&mut buffer)?;
813 /// } // drop our &mut reference so we can use f again
815 /// // original file still usable, read the rest
816 /// f.read_to_end(&mut other_buffer)?;
820 #[stable(feature = "rust1", since = "1.0.0")]
821 fn by_ref(&mut self) -> &mut Self
828 /// Transforms this `Read` instance to an [`Iterator`] over its bytes.
830 /// The returned type implements [`Iterator`] where the `Item` is
831 /// [`Result`]`<`[`u8`]`, `[`io::Error`]`>`.
832 /// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
833 /// otherwise. EOF is mapped to returning [`None`] from this iterator.
837 /// [`File`]s implement `Read`:
839 /// [`File`]: crate::fs::File
840 /// [`Result`]: crate::result::Result
841 /// [`io::Error`]: self::Error
845 /// use std::io::prelude::*;
846 /// use std::fs::File;
848 /// fn main() -> io::Result<()> {
849 /// let mut f = File::open("foo.txt")?;
851 /// for byte in f.bytes() {
852 /// println!("{}", byte.unwrap());
857 #[stable(feature = "rust1", since = "1.0.0")]
858 fn bytes(self) -> Bytes
<Self>
862 Bytes { inner: self }
865 /// Creates an adaptor which will chain this stream with another.
867 /// The returned `Read` instance will first read all bytes from this object
868 /// until EOF is encountered. Afterwards the output is equivalent to the
869 /// output of `next`.
873 /// [`File`]s implement `Read`:
875 /// [`File`]: crate::fs::File
879 /// use std::io::prelude::*;
880 /// use std::fs::File;
882 /// fn main() -> io::Result<()> {
883 /// let mut f1 = File::open("foo.txt")?;
884 /// let mut f2 = File::open("bar.txt")?;
886 /// let mut handle = f1.chain(f2);
887 /// let mut buffer = String::new();
889 /// // read the value into a String. We could use any Read method here,
890 /// // this is just one example.
891 /// handle.read_to_string(&mut buffer)?;
895 #[stable(feature = "rust1", since = "1.0.0")]
896 fn chain
<R
: Read
>(self, next
: R
) -> Chain
<Self, R
>
900 Chain { first: self, second: next, done_first: false }
903 /// Creates an adaptor which will read at most `limit` bytes from it.
905 /// This function returns a new instance of `Read` which will read at most
906 /// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
907 /// read errors will not count towards the number of bytes read and future
908 /// calls to [`read()`] may succeed.
912 /// [`File`]s implement `Read`:
914 /// [`File`]: crate::fs::File
916 /// [`read()`]: Read::read
920 /// use std::io::prelude::*;
921 /// use std::fs::File;
923 /// fn main() -> io::Result<()> {
924 /// let mut f = File::open("foo.txt")?;
925 /// let mut buffer = [0; 5];
927 /// // read at most five bytes
928 /// let mut handle = f.take(5);
930 /// handle.read(&mut buffer)?;
934 #[stable(feature = "rust1", since = "1.0.0")]
935 fn take(self, limit
: u64) -> Take
<Self>
939 Take { inner: self, limit }
943 /// A buffer type used with `Read::read_vectored`.
945 /// It is semantically a wrapper around an `&mut [u8]`, but is guaranteed to be
946 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
948 #[stable(feature = "iovec", since = "1.36.0")]
950 pub struct IoSliceMut
<'a
>(sys
::io
::IoSliceMut
<'a
>);
952 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
953 unsafe impl<'a
> Send
for IoSliceMut
<'a
> {}
955 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
956 unsafe impl<'a
> Sync
for IoSliceMut
<'a
> {}
958 #[stable(feature = "iovec", since = "1.36.0")]
959 impl<'a
> fmt
::Debug
for IoSliceMut
<'a
> {
960 fn fmt(&self, fmt
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
961 fmt
::Debug
::fmt(self.0.as_slice(), fmt
)
965 impl<'a
> IoSliceMut
<'a
> {
966 /// Creates a new `IoSliceMut` wrapping a byte slice.
970 /// Panics on Windows if the slice is larger than 4GB.
971 #[stable(feature = "iovec", since = "1.36.0")]
973 pub fn new(buf
: &'a
mut [u8]) -> IoSliceMut
<'a
> {
974 IoSliceMut(sys
::io
::IoSliceMut
::new(buf
))
977 /// Advance the internal cursor of the slice.
981 /// Elements in the slice may be modified if the cursor is not advanced to
982 /// the end of the slice. For example if we have a slice of buffers with 2
983 /// `IoSliceMut`s, both of length 8, and we advance the cursor by 10 bytes
984 /// the first `IoSliceMut` will be untouched however the second will be
985 /// modified to remove the first 2 bytes (10 - 8).
990 /// #![feature(io_slice_advance)]
992 /// use std::io::IoSliceMut;
993 /// use std::ops::Deref;
995 /// let mut buf1 = [1; 8];
996 /// let mut buf2 = [2; 16];
997 /// let mut buf3 = [3; 8];
998 /// let mut bufs = &mut [
999 /// IoSliceMut::new(&mut buf1),
1000 /// IoSliceMut::new(&mut buf2),
1001 /// IoSliceMut::new(&mut buf3),
1004 /// // Mark 10 bytes as read.
1005 /// bufs = IoSliceMut::advance(bufs, 10);
1006 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1007 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1009 #[unstable(feature = "io_slice_advance", issue = "62726")]
1011 pub fn advance
<'b
>(bufs
: &'b
mut [IoSliceMut
<'a
>], n
: usize) -> &'b
mut [IoSliceMut
<'a
>] {
1012 // Number of buffers to remove.
1014 // Total length of all the to be removed buffers.
1015 let mut accumulated_len
= 0;
1016 for buf
in bufs
.iter() {
1017 if accumulated_len
+ buf
.len() > n
{
1020 accumulated_len
+= buf
.len();
1025 let bufs
= &mut bufs
[remove
..];
1026 if !bufs
.is_empty() {
1027 bufs
[0].0.advance(n
- accumulated_len
)
1033 #[stable(feature = "iovec", since = "1.36.0")]
1034 impl<'a
> Deref
for IoSliceMut
<'a
> {
1038 fn deref(&self) -> &[u8] {
1043 #[stable(feature = "iovec", since = "1.36.0")]
1044 impl<'a
> DerefMut
for IoSliceMut
<'a
> {
1046 fn deref_mut(&mut self) -> &mut [u8] {
1047 self.0.as_mut_slice()
1051 /// A buffer type used with `Write::write_vectored`.
1053 /// It is semantically a wrapper around an `&[u8]`, but is guaranteed to be
1054 /// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1056 #[stable(feature = "iovec", since = "1.36.0")]
1057 #[derive(Copy, Clone)]
1058 #[repr(transparent)]
1059 pub struct IoSlice
<'a
>(sys
::io
::IoSlice
<'a
>);
1061 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1062 unsafe impl<'a
> Send
for IoSlice
<'a
> {}
1064 #[stable(feature = "iovec-send-sync", since = "1.44.0")]
1065 unsafe impl<'a
> Sync
for IoSlice
<'a
> {}
1067 #[stable(feature = "iovec", since = "1.36.0")]
1068 impl<'a
> fmt
::Debug
for IoSlice
<'a
> {
1069 fn fmt(&self, fmt
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
1070 fmt
::Debug
::fmt(self.0.as_slice(), fmt
)
1074 impl<'a
> IoSlice
<'a
> {
1075 /// Creates a new `IoSlice` wrapping a byte slice.
1079 /// Panics on Windows if the slice is larger than 4GB.
1080 #[stable(feature = "iovec", since = "1.36.0")]
1082 pub fn new(buf
: &'a
[u8]) -> IoSlice
<'a
> {
1083 IoSlice(sys
::io
::IoSlice
::new(buf
))
1086 /// Advance the internal cursor of the slice.
1090 /// Elements in the slice may be modified if the cursor is not advanced to
1091 /// the end of the slice. For example if we have a slice of buffers with 2
1092 /// `IoSlice`s, both of length 8, and we advance the cursor by 10 bytes the
1093 /// first `IoSlice` will be untouched however the second will be modified to
1094 /// remove the first 2 bytes (10 - 8).
1099 /// #![feature(io_slice_advance)]
1101 /// use std::io::IoSlice;
1102 /// use std::ops::Deref;
1104 /// let buf1 = [1; 8];
1105 /// let buf2 = [2; 16];
1106 /// let buf3 = [3; 8];
1107 /// let mut bufs = &mut [
1108 /// IoSlice::new(&buf1),
1109 /// IoSlice::new(&buf2),
1110 /// IoSlice::new(&buf3),
1113 /// // Mark 10 bytes as written.
1114 /// bufs = IoSlice::advance(bufs, 10);
1115 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1116 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1117 #[unstable(feature = "io_slice_advance", issue = "62726")]
1119 pub fn advance
<'b
>(bufs
: &'b
mut [IoSlice
<'a
>], n
: usize) -> &'b
mut [IoSlice
<'a
>] {
1120 // Number of buffers to remove.
1122 // Total length of all the to be removed buffers.
1123 let mut accumulated_len
= 0;
1124 for buf
in bufs
.iter() {
1125 if accumulated_len
+ buf
.len() > n
{
1128 accumulated_len
+= buf
.len();
1133 let bufs
= &mut bufs
[remove
..];
1134 if !bufs
.is_empty() {
1135 bufs
[0].0.advance(n
- accumulated_len
)
1141 #[stable(feature = "iovec", since = "1.36.0")]
1142 impl<'a
> Deref
for IoSlice
<'a
> {
1146 fn deref(&self) -> &[u8] {
1151 /// A type used to conditionally initialize buffers passed to `Read` methods.
1152 #[unstable(feature = "read_initializer", issue = "42788")]
1154 pub struct Initializer(bool
);
1157 /// Returns a new `Initializer` which will zero out buffers.
1158 #[unstable(feature = "read_initializer", issue = "42788")]
1160 pub fn zeroing() -> Initializer
{
1164 /// Returns a new `Initializer` which will not zero out buffers.
1168 /// This may only be called by `Read`ers which guarantee that they will not
1169 /// read from buffers passed to `Read` methods, and that the return value of
1170 /// the method accurately reflects the number of bytes that have been
1171 /// written to the head of the buffer.
1172 #[unstable(feature = "read_initializer", issue = "42788")]
1174 pub unsafe fn nop() -> Initializer
{
1178 /// Indicates if a buffer should be initialized.
1179 #[unstable(feature = "read_initializer", issue = "42788")]
1181 pub fn should_initialize(&self) -> bool
{
1185 /// Initializes a buffer if necessary.
1186 #[unstable(feature = "read_initializer", issue = "42788")]
1188 pub fn initialize(&self, buf
: &mut [u8]) {
1189 if self.should_initialize() {
1190 unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
1195 /// A trait for objects which are byte-oriented sinks.
1197 /// Implementors of the `Write` trait are sometimes called 'writers'.
1199 /// Writers are defined by two required methods, [`write`] and [`flush`]:
1201 /// * The [`write`] method will attempt to write some data into the object,
1202 /// returning how many bytes were successfully written.
1204 /// * The [`flush`] method is useful for adaptors and explicit buffers
1205 /// themselves for ensuring that all buffered data has been pushed out to the
1208 /// Writers are intended to be composable with one another. Many implementors
1209 /// throughout [`std::io`] take and provide types which implement the `Write`
1212 /// [`write`]: Write::write
1213 /// [`flush`]: Write::flush
1214 /// [`std::io`]: self
1219 /// use std::io::prelude::*;
1220 /// use std::fs::File;
1222 /// fn main() -> std::io::Result<()> {
1223 /// let data = b"some bytes";
1225 /// let mut pos = 0;
1226 /// let mut buffer = File::create("foo.txt")?;
1228 /// while pos < data.len() {
1229 /// let bytes_written = buffer.write(&data[pos..])?;
1230 /// pos += bytes_written;
1236 /// The trait also provides convenience methods like [`write_all`], which calls
1237 /// `write` in a loop until its entire input has been written.
1239 /// [`write_all`]: Write::write_all
1240 #[stable(feature = "rust1", since = "1.0.0")]
1243 /// Write a buffer into this writer, returning how many bytes were written.
1245 /// This function will attempt to write the entire contents of `buf`, but
1246 /// the entire write may not succeed, or the write may also generate an
1247 /// error. A call to `write` represents *at most one* attempt to write to
1248 /// any wrapped object.
1250 /// Calls to `write` are not guaranteed to block waiting for data to be
1251 /// written, and a write which would otherwise block can be indicated through
1252 /// an [`Err`] variant.
1254 /// If the return value is [`Ok(n)`] then it must be guaranteed that
1255 /// `n <= buf.len()`. A return value of `0` typically means that the
1256 /// underlying object is no longer able to accept bytes and will likely not
1257 /// be able to in the future as well, or that the buffer provided is empty.
1261 /// Each call to `write` may generate an I/O error indicating that the
1262 /// operation could not be completed. If an error is returned then no bytes
1263 /// in the buffer were written to this writer.
1265 /// It is **not** considered an error if the entire buffer could not be
1266 /// written to this writer.
1268 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
1269 /// write operation should be retried if there is nothing else to do.
1274 /// use std::io::prelude::*;
1275 /// use std::fs::File;
1277 /// fn main() -> std::io::Result<()> {
1278 /// let mut buffer = File::create("foo.txt")?;
1280 /// // Writes some prefix of the byte string, not necessarily all of it.
1281 /// 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.
1299 /// [`write`]: Write::write
1300 #[stable(feature = "iovec", since = "1.36.0")]
1301 fn write_vectored(&mut self, bufs
: &[IoSlice
<'_
>]) -> Result
<usize> {
1302 default_write_vectored(|b
| self.write(b
), bufs
)
1305 /// Determines if this `Write`er has an efficient [`write_vectored`]
1308 /// If a `Write`er does not override the default [`write_vectored`]
1309 /// implementation, code using it may want to avoid the method all together
1310 /// and coalesce writes into a single buffer for higher performance.
1312 /// The default implementation returns `false`.
1314 /// [`write_vectored`]: Write::write_vectored
1315 #[unstable(feature = "can_vector", issue = "69941")]
1316 fn is_write_vectored(&self) -> bool
{
1320 /// Flush this output stream, ensuring that all intermediately buffered
1321 /// contents reach their destination.
1325 /// It is considered an error if not all bytes could be written due to
1326 /// I/O errors or EOF being reached.
1331 /// use std::io::prelude::*;
1332 /// use std::io::BufWriter;
1333 /// use std::fs::File;
1335 /// fn main() -> std::io::Result<()> {
1336 /// let mut buffer = BufWriter::new(File::create("foo.txt")?);
1338 /// buffer.write_all(b"some bytes")?;
1339 /// buffer.flush()?;
1343 #[stable(feature = "rust1", since = "1.0.0")]
1344 fn flush(&mut self) -> Result
<()>;
1346 /// Attempts to write an entire buffer into this writer.
1348 /// This method will continuously call [`write`] until there is no more data
1349 /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
1350 /// returned. This method will not return until the entire buffer has been
1351 /// successfully written or such an error occurs. The first error that is
1352 /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
1355 /// If the buffer contains no data, this will never call [`write`].
1359 /// This function will return the first error of
1360 /// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
1362 /// [`write`]: Write::write
1367 /// use std::io::prelude::*;
1368 /// use std::fs::File;
1370 /// fn main() -> std::io::Result<()> {
1371 /// let mut buffer = File::create("foo.txt")?;
1373 /// buffer.write_all(b"some bytes")?;
1377 #[stable(feature = "rust1", since = "1.0.0")]
1378 fn write_all(&mut self, mut buf
: &[u8]) -> Result
<()> {
1379 while !buf
.is_empty() {
1380 match self.write(buf
) {
1382 return Err(Error
::new(ErrorKind
::WriteZero
, "failed to write whole buffer"));
1384 Ok(n
) => buf
= &buf
[n
..],
1385 Err(ref e
) if e
.kind() == ErrorKind
::Interrupted
=> {}
1386 Err(e
) => return Err(e
),
1392 /// Attempts to write multiple buffers into this writer.
1394 /// This method will continuously call [`write_vectored`] until there is no
1395 /// more data to be written or an error of non-[`ErrorKind::Interrupted`]
1396 /// kind is returned. This method will not return until all buffers have
1397 /// been successfully written or such an error occurs. The first error that
1398 /// is not of [`ErrorKind::Interrupted`] kind generated from this method
1399 /// will be returned.
1401 /// If the buffer contains no data, this will never call [`write_vectored`].
1405 /// Unlike [`write_vectored`], this takes a *mutable* reference to
1406 /// a slice of [`IoSlice`]s, not an immutable one. That's because we need to
1407 /// modify the slice to keep track of the bytes already written.
1409 /// Once this function returns, the contents of `bufs` are unspecified, as
1410 /// this depends on how many calls to [`write_vectored`] were necessary. It is
1411 /// best to understand this function as taking ownership of `bufs` and to
1412 /// not use `bufs` afterwards. The underlying buffers, to which the
1413 /// [`IoSlice`]s point (but not the [`IoSlice`]s themselves), are unchanged and
1416 /// [`write_vectored`]: Write::write_vectored
1421 /// #![feature(write_all_vectored)]
1422 /// # fn main() -> std::io::Result<()> {
1424 /// use std::io::{Write, IoSlice};
1426 /// let mut writer = Vec::new();
1427 /// let bufs = &mut [
1428 /// IoSlice::new(&[1]),
1429 /// IoSlice::new(&[2, 3]),
1430 /// IoSlice::new(&[4, 5, 6]),
1433 /// writer.write_all_vectored(bufs)?;
1434 /// // Note: the contents of `bufs` is now undefined, see the Notes section.
1436 /// assert_eq!(writer, &[1, 2, 3, 4, 5, 6]);
1439 #[unstable(feature = "write_all_vectored", issue = "70436")]
1440 fn write_all_vectored(&mut self, mut bufs
: &mut [IoSlice
<'_
>]) -> Result
<()> {
1441 // Guarantee that bufs is empty if it contains no data,
1442 // to avoid calling write_vectored if there is no data to be written.
1443 bufs
= IoSlice
::advance(bufs
, 0);
1444 while !bufs
.is_empty() {
1445 match self.write_vectored(bufs
) {
1447 return Err(Error
::new(ErrorKind
::WriteZero
, "failed to write whole buffer"));
1449 Ok(n
) => bufs
= IoSlice
::advance(bufs
, n
),
1450 Err(ref e
) if e
.kind() == ErrorKind
::Interrupted
=> {}
1451 Err(e
) => return Err(e
),
1457 /// Writes a formatted string into this writer, returning any error
1460 /// This method is primarily used to interface with the
1461 /// [`format_args!()`] macro, but it is rare that this should
1462 /// explicitly be called. The [`write!()`] macro should be favored to
1463 /// invoke this method instead.
1465 /// This function internally uses the [`write_all`] method on
1466 /// this trait and hence will continuously write data so long as no errors
1467 /// are received. This also means that partial writes are not indicated in
1470 /// [`write_all`]: Write::write_all
1474 /// This function will return any I/O error reported while formatting.
1479 /// use std::io::prelude::*;
1480 /// use std::fs::File;
1482 /// fn main() -> std::io::Result<()> {
1483 /// let mut buffer = File::create("foo.txt")?;
1486 /// write!(buffer, "{:.*}", 2, 1.234567)?;
1487 /// // turns into this:
1488 /// buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))?;
1492 #[stable(feature = "rust1", since = "1.0.0")]
1493 fn write_fmt(&mut self, fmt
: fmt
::Arguments
<'_
>) -> Result
<()> {
1494 // Create a shim which translates a Write to a fmt::Write and saves
1495 // off I/O errors. instead of discarding them
1496 struct Adaptor
<'a
, T
: ?Sized
+ 'a
> {
1501 impl<T
: Write
+ ?Sized
> fmt
::Write
for Adaptor
<'_
, T
> {
1502 fn write_str(&mut self, s
: &str) -> fmt
::Result
{
1503 match self.inner
.write_all(s
.as_bytes()) {
1506 self.error
= Err(e
);
1513 let mut output
= Adaptor { inner: self, error: Ok(()) }
;
1514 match fmt
::write(&mut output
, fmt
) {
1517 // check if the error came from the underlying `Write` or not
1518 if output
.error
.is_err() {
1521 Err(Error
::new(ErrorKind
::Other
, "formatter error"))
1527 /// Creates a "by reference" adaptor for this instance of `Write`.
1529 /// The returned adaptor also implements `Write` and will simply borrow this
1535 /// use std::io::Write;
1536 /// use std::fs::File;
1538 /// fn main() -> std::io::Result<()> {
1539 /// let mut buffer = File::create("foo.txt")?;
1541 /// let reference = buffer.by_ref();
1543 /// // we can use reference just like our original buffer
1544 /// reference.write_all(b"some bytes")?;
1548 #[stable(feature = "rust1", since = "1.0.0")]
1549 fn by_ref(&mut self) -> &mut Self
1557 /// The `Seek` trait provides a cursor which can be moved within a stream of
1560 /// The stream typically has a fixed size, allowing seeking relative to either
1561 /// end or the current offset.
1565 /// [`File`]s implement `Seek`:
1567 /// [`File`]: crate::fs::File
1571 /// use std::io::prelude::*;
1572 /// use std::fs::File;
1573 /// use std::io::SeekFrom;
1575 /// fn main() -> io::Result<()> {
1576 /// let mut f = File::open("foo.txt")?;
1578 /// // move the cursor 42 bytes from the start of the file
1579 /// f.seek(SeekFrom::Start(42))?;
1583 #[stable(feature = "rust1", since = "1.0.0")]
1585 /// Seek to an offset, in bytes, in a stream.
1587 /// A seek beyond the end of a stream is allowed, but behavior is defined
1588 /// by the implementation.
1590 /// If the seek operation completed successfully,
1591 /// this method returns the new position from the start of the stream.
1592 /// That position can be used later with [`SeekFrom::Start`].
1596 /// Seeking to a negative offset is considered an error.
1597 #[stable(feature = "rust1", since = "1.0.0")]
1598 fn seek(&mut self, pos
: SeekFrom
) -> Result
<u64>;
1600 /// Returns the length of this stream (in bytes).
1602 /// This method is implemented using up to three seek operations. If this
1603 /// method returns successfully, the seek position is unchanged (i.e. the
1604 /// position before calling this method is the same as afterwards).
1605 /// However, if this method returns an error, the seek position is
1608 /// If you need to obtain the length of *many* streams and you don't care
1609 /// about the seek position afterwards, you can reduce the number of seek
1610 /// operations by simply calling `seek(SeekFrom::End(0))` and using its
1611 /// return value (it is also the stream length).
1613 /// Note that length of a stream can change over time (for example, when
1614 /// data is appended to a file). So calling this method multiple times does
1615 /// not necessarily return the same length each time.
1620 /// #![feature(seek_convenience)]
1622 /// io::{self, Seek},
1626 /// fn main() -> io::Result<()> {
1627 /// let mut f = File::open("foo.txt")?;
1629 /// let len = f.stream_len()?;
1630 /// println!("The file is currently {} bytes long", len);
1634 #[unstable(feature = "seek_convenience", issue = "59359")]
1635 fn stream_len(&mut self) -> Result
<u64> {
1636 let old_pos
= self.stream_position()?
;
1637 let len
= self.seek(SeekFrom
::End(0))?
;
1639 // Avoid seeking a third time when we were already at the end of the
1640 // stream. The branch is usually way cheaper than a seek operation.
1642 self.seek(SeekFrom
::Start(old_pos
))?
;
1648 /// Returns the current seek position from the start of the stream.
1650 /// This is equivalent to `self.seek(SeekFrom::Current(0))`.
1655 /// #![feature(seek_convenience)]
1657 /// io::{self, BufRead, BufReader, Seek},
1661 /// fn main() -> io::Result<()> {
1662 /// let mut f = BufReader::new(File::open("foo.txt")?);
1664 /// let before = f.stream_position()?;
1665 /// f.read_line(&mut String::new())?;
1666 /// let after = f.stream_position()?;
1668 /// println!("The first line was {} bytes long", after - before);
1672 #[unstable(feature = "seek_convenience", issue = "59359")]
1673 fn stream_position(&mut self) -> Result
<u64> {
1674 self.seek(SeekFrom
::Current(0))
1678 /// Enumeration of possible methods to seek within an I/O object.
1680 /// It is used by the [`Seek`] trait.
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 /// [`File`]: crate::fs::File
1761 /// [`read_line`]: BufRead::read_line
1762 /// [`lines`]: BufRead::lines
1765 /// use std::io::{self, BufReader};
1766 /// use std::io::prelude::*;
1767 /// use std::fs::File;
1769 /// fn main() -> io::Result<()> {
1770 /// let f = File::open("foo.txt")?;
1771 /// let f = BufReader::new(f);
1773 /// for line in f.lines() {
1774 /// 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`]: BufRead::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`]: BufRead::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`]: BufRead::fill_buf
1870 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1871 /// this example, we use [`Cursor`] to read all the bytes in a byte slice
1872 /// in hyphen delimited segments:
1875 /// use std::io::{self, BufRead};
1877 /// let mut cursor = io::Cursor::new(b"lorem-ipsum");
1878 /// let mut buf = vec![];
1880 /// // cursor is at 'l'
1881 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1882 /// .expect("reading from cursor won't fail");
1883 /// assert_eq!(num_bytes, 6);
1884 /// assert_eq!(buf, b"lorem-");
1887 /// // cursor is at 'i'
1888 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1889 /// .expect("reading from cursor won't fail");
1890 /// assert_eq!(num_bytes, 5);
1891 /// assert_eq!(buf, b"ipsum");
1894 /// // cursor is at EOF
1895 /// let num_bytes = cursor.read_until(b'-', &mut buf)
1896 /// .expect("reading from cursor won't fail");
1897 /// assert_eq!(num_bytes, 0);
1898 /// assert_eq!(buf, b"");
1900 #[stable(feature = "rust1", since = "1.0.0")]
1901 fn read_until(&mut self, byte
: u8, buf
: &mut Vec
<u8>) -> Result
<usize> {
1902 read_until(self, byte
, buf
)
1905 /// Read all bytes until a newline (the `0xA` byte) is reached, and append
1906 /// them to the provided buffer.
1908 /// This function will read bytes from the underlying stream until the
1909 /// newline delimiter (the `0xA` byte) or EOF is found. Once found, all bytes
1910 /// up to, and including, the delimiter (if found) will be appended to
1913 /// If successful, this function will return the total number of bytes read.
1915 /// If this function returns [`Ok(0)`], the stream has reached EOF.
1917 /// This function is blocking and should be used carefully: it is possible for
1918 /// an attacker to continuously send bytes without ever sending a newline
1925 /// This function has the same error semantics as [`read_until`] and will
1926 /// also return an error if the read bytes are not valid UTF-8. If an I/O
1927 /// error is encountered then `buf` may contain some bytes already read in
1928 /// the event that all data read so far was valid UTF-8.
1930 /// [`read_until`]: BufRead::read_until
1934 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1935 /// this example, we use [`Cursor`] to read all the lines in a byte slice:
1938 /// use std::io::{self, BufRead};
1940 /// let mut cursor = io::Cursor::new(b"foo\nbar");
1941 /// let mut buf = String::new();
1943 /// // cursor is at 'f'
1944 /// let num_bytes = cursor.read_line(&mut buf)
1945 /// .expect("reading from cursor won't fail");
1946 /// assert_eq!(num_bytes, 4);
1947 /// assert_eq!(buf, "foo\n");
1950 /// // cursor is at 'b'
1951 /// let num_bytes = cursor.read_line(&mut buf)
1952 /// .expect("reading from cursor won't fail");
1953 /// assert_eq!(num_bytes, 3);
1954 /// assert_eq!(buf, "bar");
1957 /// // cursor is at EOF
1958 /// let num_bytes = cursor.read_line(&mut buf)
1959 /// .expect("reading from cursor won't fail");
1960 /// assert_eq!(num_bytes, 0);
1961 /// assert_eq!(buf, "");
1963 #[stable(feature = "rust1", since = "1.0.0")]
1964 fn read_line(&mut self, buf
: &mut String
) -> Result
<usize> {
1965 // Note that we are not calling the `.read_until` method here, but
1966 // rather our hardcoded implementation. For more details as to why, see
1967 // the comments in `read_to_end`.
1968 append_to_string(buf
, |b
| read_until(self, b'
\n'
, b
))
1971 /// Returns an iterator over the contents of this reader split on the byte
1974 /// The iterator returned from this function will return instances of
1975 /// [`io::Result`]`<`[`Vec<u8>`]`>`. Each vector returned will *not* have
1976 /// the delimiter byte at the end.
1978 /// This function will yield errors whenever [`read_until`] would have
1979 /// also yielded an error.
1981 /// [`io::Result`]: self::Result
1982 /// [`Vec<u8>`]: Vec
1983 /// [`read_until`]: BufRead::read_until
1987 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
1988 /// this example, we use [`Cursor`] to iterate over all hyphen delimited
1989 /// segments in a byte slice
1992 /// use std::io::{self, BufRead};
1994 /// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
1996 /// let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
1997 /// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
1998 /// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
1999 /// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
2000 /// assert_eq!(split_iter.next(), None);
2002 #[stable(feature = "rust1", since = "1.0.0")]
2003 fn split(self, byte
: u8) -> Split
<Self>
2007 Split { buf: self, delim: byte }
2010 /// Returns an iterator over the lines of this reader.
2012 /// The iterator returned from this function will yield instances of
2013 /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
2014 /// byte (the `0xA` byte) or `CRLF` (`0xD`, `0xA` bytes) at the end.
2016 /// [`io::Result`]: self::Result
2020 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2021 /// this example, we use [`Cursor`] to iterate over all the lines in a byte
2025 /// use std::io::{self, BufRead};
2027 /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
2029 /// let mut lines_iter = cursor.lines().map(|l| l.unwrap());
2030 /// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
2031 /// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
2032 /// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
2033 /// assert_eq!(lines_iter.next(), None);
2038 /// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
2039 #[stable(feature = "rust1", since = "1.0.0")]
2040 fn lines(self) -> Lines
<Self>
2048 /// Adaptor to chain together two readers.
2050 /// This struct is generally created by calling [`chain`] on a reader.
2051 /// Please see the documentation of [`chain`] for more details.
2053 /// [`chain`]: Read::chain
2054 #[stable(feature = "rust1", since = "1.0.0")]
2055 pub struct Chain
<T
, U
> {
2061 impl<T
, U
> Chain
<T
, U
> {
2062 /// Consumes the `Chain`, returning the wrapped readers.
2068 /// use std::io::prelude::*;
2069 /// use std::fs::File;
2071 /// fn main() -> io::Result<()> {
2072 /// let mut foo_file = File::open("foo.txt")?;
2073 /// let mut bar_file = File::open("bar.txt")?;
2075 /// let chain = foo_file.chain(bar_file);
2076 /// let (foo_file, bar_file) = chain.into_inner();
2080 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2081 pub fn into_inner(self) -> (T
, U
) {
2082 (self.first
, self.second
)
2085 /// Gets references to the underlying readers in this `Chain`.
2091 /// use std::io::prelude::*;
2092 /// use std::fs::File;
2094 /// fn main() -> io::Result<()> {
2095 /// let mut foo_file = File::open("foo.txt")?;
2096 /// let mut bar_file = File::open("bar.txt")?;
2098 /// let chain = foo_file.chain(bar_file);
2099 /// let (foo_file, bar_file) = chain.get_ref();
2103 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2104 pub fn get_ref(&self) -> (&T
, &U
) {
2105 (&self.first
, &self.second
)
2108 /// Gets mutable references to the underlying readers in this `Chain`.
2110 /// Care should be taken to avoid modifying the internal I/O state of the
2111 /// underlying readers as doing so may corrupt the internal state of this
2118 /// use std::io::prelude::*;
2119 /// use std::fs::File;
2121 /// fn main() -> io::Result<()> {
2122 /// let mut foo_file = File::open("foo.txt")?;
2123 /// let mut bar_file = File::open("bar.txt")?;
2125 /// let mut chain = foo_file.chain(bar_file);
2126 /// let (foo_file, bar_file) = chain.get_mut();
2130 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2131 pub fn get_mut(&mut self) -> (&mut T
, &mut U
) {
2132 (&mut self.first
, &mut self.second
)
2136 #[stable(feature = "std_debug", since = "1.16.0")]
2137 impl<T
: fmt
::Debug
, U
: fmt
::Debug
> fmt
::Debug
for Chain
<T
, U
> {
2138 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
2139 f
.debug_struct("Chain").field("t", &self.first
).field("u", &self.second
).finish()
2143 #[stable(feature = "rust1", since = "1.0.0")]
2144 impl<T
: Read
, U
: Read
> Read
for Chain
<T
, U
> {
2145 fn read(&mut self, buf
: &mut [u8]) -> Result
<usize> {
2146 if !self.done_first
{
2147 match self.first
.read(buf
)?
{
2148 0 if !buf
.is_empty() => self.done_first
= true,
2152 self.second
.read(buf
)
2155 fn read_vectored(&mut self, bufs
: &mut [IoSliceMut
<'_
>]) -> Result
<usize> {
2156 if !self.done_first
{
2157 match self.first
.read_vectored(bufs
)?
{
2158 0 if bufs
.iter().any(|b
| !b
.is_empty()) => self.done_first
= true,
2162 self.second
.read_vectored(bufs
)
2165 unsafe fn initializer(&self) -> Initializer
{
2166 let initializer
= self.first
.initializer();
2167 if initializer
.should_initialize() { initializer }
else { self.second.initializer() }
2171 #[stable(feature = "chain_bufread", since = "1.9.0")]
2172 impl<T
: BufRead
, U
: BufRead
> BufRead
for Chain
<T
, U
> {
2173 fn fill_buf(&mut self) -> Result
<&[u8]> {
2174 if !self.done_first
{
2175 match self.first
.fill_buf()?
{
2176 buf
if buf
.is_empty() => {
2177 self.done_first
= true;
2179 buf
=> return Ok(buf
),
2182 self.second
.fill_buf()
2185 fn consume(&mut self, amt
: usize) {
2186 if !self.done_first { self.first.consume(amt) }
else { self.second.consume(amt) }
2190 /// Reader adaptor which limits the bytes read from an underlying reader.
2192 /// This struct is generally created by calling [`take`] on a reader.
2193 /// Please see the documentation of [`take`] for more details.
2195 /// [`take`]: Read::take
2196 #[stable(feature = "rust1", since = "1.0.0")]
2198 pub struct Take
<T
> {
2204 /// Returns the number of bytes that can be read before this instance will
2209 /// This instance may reach `EOF` after reading fewer bytes than indicated by
2210 /// this method if the underlying [`Read`] instance reaches EOF.
2216 /// use std::io::prelude::*;
2217 /// use std::fs::File;
2219 /// fn main() -> io::Result<()> {
2220 /// let f = File::open("foo.txt")?;
2222 /// // read at most five bytes
2223 /// let handle = f.take(5);
2225 /// println!("limit: {}", handle.limit());
2229 #[stable(feature = "rust1", since = "1.0.0")]
2230 pub fn limit(&self) -> u64 {
2234 /// Sets the number of bytes that can be read before this instance will
2235 /// return EOF. This is the same as constructing a new `Take` instance, so
2236 /// the amount of bytes read and the previous limit value don't matter when
2237 /// calling this method.
2243 /// use std::io::prelude::*;
2244 /// use std::fs::File;
2246 /// fn main() -> io::Result<()> {
2247 /// let f = File::open("foo.txt")?;
2249 /// // read at most five bytes
2250 /// let mut handle = f.take(5);
2251 /// handle.set_limit(10);
2253 /// assert_eq!(handle.limit(), 10);
2257 #[stable(feature = "take_set_limit", since = "1.27.0")]
2258 pub fn set_limit(&mut self, limit
: u64) {
2262 /// Consumes the `Take`, returning the wrapped reader.
2268 /// use std::io::prelude::*;
2269 /// use std::fs::File;
2271 /// fn main() -> io::Result<()> {
2272 /// let mut file = File::open("foo.txt")?;
2274 /// let mut buffer = [0; 5];
2275 /// let mut handle = file.take(5);
2276 /// handle.read(&mut buffer)?;
2278 /// let file = handle.into_inner();
2282 #[stable(feature = "io_take_into_inner", since = "1.15.0")]
2283 pub fn into_inner(self) -> T
{
2287 /// Gets a reference to the underlying reader.
2293 /// use std::io::prelude::*;
2294 /// use std::fs::File;
2296 /// fn main() -> io::Result<()> {
2297 /// let mut file = File::open("foo.txt")?;
2299 /// let mut buffer = [0; 5];
2300 /// let mut handle = file.take(5);
2301 /// handle.read(&mut buffer)?;
2303 /// let file = handle.get_ref();
2307 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2308 pub fn get_ref(&self) -> &T
{
2312 /// Gets a mutable reference to the underlying reader.
2314 /// Care should be taken to avoid modifying the internal I/O state of the
2315 /// underlying reader as doing so may corrupt the internal limit of this
2322 /// use std::io::prelude::*;
2323 /// use std::fs::File;
2325 /// fn main() -> io::Result<()> {
2326 /// let mut file = File::open("foo.txt")?;
2328 /// let mut buffer = [0; 5];
2329 /// let mut handle = file.take(5);
2330 /// handle.read(&mut buffer)?;
2332 /// let file = handle.get_mut();
2336 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2337 pub fn get_mut(&mut self) -> &mut T
{
2342 #[stable(feature = "rust1", since = "1.0.0")]
2343 impl<T
: Read
> Read
for Take
<T
> {
2344 fn read(&mut self, buf
: &mut [u8]) -> Result
<usize> {
2345 // Don't call into inner reader at all at EOF because it may still block
2346 if self.limit
== 0 {
2350 let max
= cmp
::min(buf
.len() as u64, self.limit
) as usize;
2351 let n
= self.inner
.read(&mut buf
[..max
])?
;
2352 self.limit
-= n
as u64;
2356 unsafe fn initializer(&self) -> Initializer
{
2357 self.inner
.initializer()
2360 fn read_to_end(&mut self, buf
: &mut Vec
<u8>) -> Result
<usize> {
2361 // Pass in a reservation_size closure that respects the current value
2362 // of limit for each read. If we hit the read limit, this prevents the
2363 // final zero-byte read from allocating again.
2364 read_to_end_with_reservation(self, buf
, |self_
| cmp
::min(self_
.limit
, 32) as usize)
2368 #[stable(feature = "rust1", since = "1.0.0")]
2369 impl<T
: BufRead
> BufRead
for Take
<T
> {
2370 fn fill_buf(&mut self) -> Result
<&[u8]> {
2371 // Don't call into inner reader at all at EOF because it may still block
2372 if self.limit
== 0 {
2376 let buf
= self.inner
.fill_buf()?
;
2377 let cap
= cmp
::min(buf
.len() as u64, self.limit
) as usize;
2381 fn consume(&mut self, amt
: usize) {
2382 // Don't let callers reset the limit by passing an overlarge value
2383 let amt
= cmp
::min(amt
as u64, self.limit
) as usize;
2384 self.limit
-= amt
as u64;
2385 self.inner
.consume(amt
);
2389 /// An iterator over `u8` values of a reader.
2391 /// This struct is generally created by calling [`bytes`] on a reader.
2392 /// Please see the documentation of [`bytes`] for more details.
2394 /// [`bytes`]: Read::bytes
2395 #[stable(feature = "rust1", since = "1.0.0")]
2397 pub struct Bytes
<R
> {
2401 #[stable(feature = "rust1", since = "1.0.0")]
2402 impl<R
: Read
> Iterator
for Bytes
<R
> {
2403 type Item
= Result
<u8>;
2405 fn next(&mut self) -> Option
<Result
<u8>> {
2408 return match self.inner
.read(slice
::from_mut(&mut byte
)) {
2410 Ok(..) => Some(Ok(byte
)),
2411 Err(ref e
) if e
.kind() == ErrorKind
::Interrupted
=> continue,
2412 Err(e
) => Some(Err(e
)),
2418 /// An iterator over the contents of an instance of `BufRead` split on a
2419 /// particular byte.
2421 /// This struct is generally created by calling [`split`] on a `BufRead`.
2422 /// Please see the documentation of [`split`] for more details.
2424 /// [`split`]: BufRead::split
2425 #[stable(feature = "rust1", since = "1.0.0")]
2427 pub struct Split
<B
> {
2432 #[stable(feature = "rust1", since = "1.0.0")]
2433 impl<B
: BufRead
> Iterator
for Split
<B
> {
2434 type Item
= Result
<Vec
<u8>>;
2436 fn next(&mut self) -> Option
<Result
<Vec
<u8>>> {
2437 let mut buf
= Vec
::new();
2438 match self.buf
.read_until(self.delim
, &mut buf
) {
2441 if buf
[buf
.len() - 1] == self.delim
{
2446 Err(e
) => Some(Err(e
)),
2451 /// An iterator over the lines of an instance of `BufRead`.
2453 /// This struct is generally created by calling [`lines`] on a `BufRead`.
2454 /// Please see the documentation of [`lines`] for more details.
2456 /// [`lines`]: BufRead::lines
2457 #[stable(feature = "rust1", since = "1.0.0")]
2459 pub struct Lines
<B
> {
2463 #[stable(feature = "rust1", since = "1.0.0")]
2464 impl<B
: BufRead
> Iterator
for Lines
<B
> {
2465 type Item
= Result
<String
>;
2467 fn next(&mut self) -> Option
<Result
<String
>> {
2468 let mut buf
= String
::new();
2469 match self.buf
.read_line(&mut buf
) {
2472 if buf
.ends_with('
\n'
) {
2474 if buf
.ends_with('
\r'
) {
2480 Err(e
) => Some(Err(e
)),
2487 use super::{repeat, Cursor, SeekFrom}
;
2488 use crate::cmp
::{self, min}
;
2489 use crate::io
::prelude
::*;
2490 use crate::io
::{self, IoSlice, IoSliceMut}
;
2491 use crate::ops
::Deref
;
2494 #[cfg_attr(target_os = "emscripten", ignore)]
2496 let mut buf
= Cursor
::new(&b
"12"[..]);
2497 let mut v
= Vec
::new();
2498 assert_eq
!(buf
.read_until(b'
3'
, &mut v
).unwrap(), 2);
2499 assert_eq
!(v
, b
"12");
2501 let mut buf
= Cursor
::new(&b
"1233"[..]);
2502 let mut v
= Vec
::new();
2503 assert_eq
!(buf
.read_until(b'
3'
, &mut v
).unwrap(), 3);
2504 assert_eq
!(v
, b
"123");
2506 assert_eq
!(buf
.read_until(b'
3'
, &mut v
).unwrap(), 1);
2507 assert_eq
!(v
, b
"3");
2509 assert_eq
!(buf
.read_until(b'
3'
, &mut v
).unwrap(), 0);
2515 let buf
= Cursor
::new(&b
"12"[..]);
2516 let mut s
= buf
.split(b'
3'
);
2517 assert_eq
!(s
.next().unwrap().unwrap(), vec
![b'
1'
, b'
2'
]);
2518 assert
!(s
.next().is_none());
2520 let buf
= Cursor
::new(&b
"1233"[..]);
2521 let mut s
= buf
.split(b'
3'
);
2522 assert_eq
!(s
.next().unwrap().unwrap(), vec
![b'
1'
, b'
2'
]);
2523 assert_eq
!(s
.next().unwrap().unwrap(), vec
![]);
2524 assert
!(s
.next().is_none());
2529 let mut buf
= Cursor
::new(&b
"12"[..]);
2530 let mut v
= String
::new();
2531 assert_eq
!(buf
.read_line(&mut v
).unwrap(), 2);
2532 assert_eq
!(v
, "12");
2534 let mut buf
= Cursor
::new(&b
"12\n\n"[..]);
2535 let mut v
= String
::new();
2536 assert_eq
!(buf
.read_line(&mut v
).unwrap(), 3);
2537 assert_eq
!(v
, "12\n");
2539 assert_eq
!(buf
.read_line(&mut v
).unwrap(), 1);
2540 assert_eq
!(v
, "\n");
2542 assert_eq
!(buf
.read_line(&mut v
).unwrap(), 0);
2548 let buf
= Cursor
::new(&b
"12\r"[..]);
2549 let mut s
= buf
.lines();
2550 assert_eq
!(s
.next().unwrap().unwrap(), "12\r".to_string());
2551 assert
!(s
.next().is_none());
2553 let buf
= Cursor
::new(&b
"12\r\n\n"[..]);
2554 let mut s
= buf
.lines();
2555 assert_eq
!(s
.next().unwrap().unwrap(), "12".to_string());
2556 assert_eq
!(s
.next().unwrap().unwrap(), "".to_string());
2557 assert
!(s
.next().is_none());
2562 let mut c
= Cursor
::new(&b
""[..]);
2563 let mut v
= Vec
::new();
2564 assert_eq
!(c
.read_to_end(&mut v
).unwrap(), 0);
2567 let mut c
= Cursor
::new(&b
"1"[..]);
2568 let mut v
= Vec
::new();
2569 assert_eq
!(c
.read_to_end(&mut v
).unwrap(), 1);
2570 assert_eq
!(v
, b
"1");
2572 let cap
= 1024 * 1024;
2573 let data
= (0..cap
).map(|i
| (i
/ 3) as u8).collect
::<Vec
<_
>>();
2574 let mut v
= Vec
::new();
2575 let (a
, b
) = data
.split_at(data
.len() / 2);
2576 assert_eq
!(Cursor
::new(a
).read_to_end(&mut v
).unwrap(), a
.len());
2577 assert_eq
!(Cursor
::new(b
).read_to_end(&mut v
).unwrap(), b
.len());
2578 assert_eq
!(v
, data
);
2582 fn read_to_string() {
2583 let mut c
= Cursor
::new(&b
""[..]);
2584 let mut v
= String
::new();
2585 assert_eq
!(c
.read_to_string(&mut v
).unwrap(), 0);
2588 let mut c
= Cursor
::new(&b
"1"[..]);
2589 let mut v
= String
::new();
2590 assert_eq
!(c
.read_to_string(&mut v
).unwrap(), 1);
2593 let mut c
= Cursor
::new(&b
"\xff"[..]);
2594 let mut v
= String
::new();
2595 assert
!(c
.read_to_string(&mut v
).is_err());
2600 let mut buf
= [0; 4];
2602 let mut c
= Cursor
::new(&b
""[..]);
2603 assert_eq
!(c
.read_exact(&mut buf
).unwrap_err().kind(), io
::ErrorKind
::UnexpectedEof
);
2605 let mut c
= Cursor
::new(&b
"123"[..]).chain(Cursor
::new(&b
"456789"[..]));
2606 c
.read_exact(&mut buf
).unwrap();
2607 assert_eq
!(&buf
, b
"1234");
2608 c
.read_exact(&mut buf
).unwrap();
2609 assert_eq
!(&buf
, b
"5678");
2610 assert_eq
!(c
.read_exact(&mut buf
).unwrap_err().kind(), io
::ErrorKind
::UnexpectedEof
);
2614 fn read_exact_slice() {
2615 let mut buf
= [0; 4];
2617 let mut c
= &b
""[..];
2618 assert_eq
!(c
.read_exact(&mut buf
).unwrap_err().kind(), io
::ErrorKind
::UnexpectedEof
);
2620 let mut c
= &b
"123"[..];
2621 assert_eq
!(c
.read_exact(&mut buf
).unwrap_err().kind(), io
::ErrorKind
::UnexpectedEof
);
2622 // make sure the optimized (early returning) method is being used
2623 assert_eq
!(&buf
, &[0; 4]);
2625 let mut c
= &b
"1234"[..];
2626 c
.read_exact(&mut buf
).unwrap();
2627 assert_eq
!(&buf
, b
"1234");
2629 let mut c
= &b
"56789"[..];
2630 c
.read_exact(&mut buf
).unwrap();
2631 assert_eq
!(&buf
, b
"5678");
2632 assert_eq
!(c
, b
"9");
2640 fn read(&mut self, _
: &mut [u8]) -> io
::Result
<usize> {
2641 Err(io
::Error
::new(io
::ErrorKind
::Other
, ""))
2644 impl BufRead
for R
{
2645 fn fill_buf(&mut self) -> io
::Result
<&[u8]> {
2646 Err(io
::Error
::new(io
::ErrorKind
::Other
, ""))
2648 fn consume(&mut self, _amt
: usize) {}
2651 let mut buf
= [0; 1];
2652 assert_eq
!(0, R
.take(0).read(&mut buf
).unwrap());
2653 assert_eq
!(b
"", R
.take(0).fill_buf().unwrap());
2656 fn cmp_bufread
<Br1
: BufRead
, Br2
: BufRead
>(mut br1
: Br1
, mut br2
: Br2
, exp
: &[u8]) {
2657 let mut cat
= Vec
::new();
2660 let buf1
= br1
.fill_buf().unwrap();
2661 let buf2
= br2
.fill_buf().unwrap();
2662 let minlen
= if buf1
.len() < buf2
.len() { buf1.len() }
else { buf2.len() }
;
2663 assert_eq
!(buf1
[..minlen
], buf2
[..minlen
]);
2664 cat
.extend_from_slice(&buf1
[..minlen
]);
2670 br1
.consume(consume
);
2671 br2
.consume(consume
);
2673 assert_eq
!(br1
.fill_buf().unwrap().len(), 0);
2674 assert_eq
!(br2
.fill_buf().unwrap().len(), 0);
2675 assert_eq
!(&cat
[..], &exp
[..])
2679 fn chain_bufread() {
2680 let testdata
= b
"ABCDEFGHIJKL";
2682 (&testdata
[..3]).chain(&testdata
[3..6]).chain(&testdata
[6..9]).chain(&testdata
[9..]);
2683 let chain2
= (&testdata
[..4]).chain(&testdata
[4..8]).chain(&testdata
[8..]);
2684 cmp_bufread(chain1
, chain2
, &testdata
[..]);
2688 fn chain_zero_length_read_is_not_eof() {
2691 let mut s
= String
::new();
2692 let mut chain
= (&a
[..]).chain(&b
[..]);
2693 chain
.read(&mut []).unwrap();
2694 chain
.read_to_string(&mut s
).unwrap();
2695 assert_eq
!("AB", s
);
2699 #[cfg_attr(target_os = "emscripten", ignore)]
2700 fn bench_read_to_end(b
: &mut test
::Bencher
) {
2702 let mut lr
= repeat(1).take(10000000);
2703 let mut vec
= Vec
::with_capacity(1024);
2704 super::read_to_end(&mut lr
, &mut vec
)
2709 fn seek_len() -> io
::Result
<()> {
2710 let mut c
= Cursor
::new(vec
![0; 15]);
2711 assert_eq
!(c
.stream_len()?
, 15);
2713 c
.seek(SeekFrom
::End(0))?
;
2714 let old_pos
= c
.stream_position()?
;
2715 assert_eq
!(c
.stream_len()?
, 15);
2716 assert_eq
!(c
.stream_position()?
, old_pos
);
2718 c
.seek(SeekFrom
::Start(7))?
;
2719 c
.seek(SeekFrom
::Current(2))?
;
2720 let old_pos
= c
.stream_position()?
;
2721 assert_eq
!(c
.stream_len()?
, 15);
2722 assert_eq
!(c
.stream_position()?
, old_pos
);
2728 fn seek_position() -> io
::Result
<()> {
2729 // All `asserts` are duplicated here to make sure the method does not
2730 // change anything about the seek state.
2731 let mut c
= Cursor
::new(vec
![0; 15]);
2732 assert_eq
!(c
.stream_position()?
, 0);
2733 assert_eq
!(c
.stream_position()?
, 0);
2735 c
.seek(SeekFrom
::End(0))?
;
2736 assert_eq
!(c
.stream_position()?
, 15);
2737 assert_eq
!(c
.stream_position()?
, 15);
2739 c
.seek(SeekFrom
::Start(7))?
;
2740 c
.seek(SeekFrom
::Current(2))?
;
2741 assert_eq
!(c
.stream_position()?
, 9);
2742 assert_eq
!(c
.stream_position()?
, 9);
2744 c
.seek(SeekFrom
::End(-3))?
;
2745 c
.seek(SeekFrom
::Current(1))?
;
2746 c
.seek(SeekFrom
::Current(-5))?
;
2747 assert_eq
!(c
.stream_position()?
, 8);
2748 assert_eq
!(c
.stream_position()?
, 8);
2753 // A simple example reader which uses the default implementation of
2755 struct ExampleSliceReader
<'a
> {
2759 impl<'a
> Read
for ExampleSliceReader
<'a
> {
2760 fn read(&mut self, buf
: &mut [u8]) -> io
::Result
<usize> {
2761 let len
= cmp
::min(self.slice
.len(), buf
.len());
2762 buf
[..len
].copy_from_slice(&self.slice
[..len
]);
2763 self.slice
= &self.slice
[len
..];
2769 fn test_read_to_end_capacity() -> io
::Result
<()> {
2770 let input
= &b
"foo"[..];
2772 // read_to_end() generally needs to over-allocate, both for efficiency
2773 // and so that it can distinguish EOF. Assert that this is the case
2774 // with this simple ExampleSliceReader struct, which uses the default
2775 // implementation of read_to_end. Even though vec1 is allocated with
2776 // exactly enough capacity for the read, read_to_end will allocate more
2778 let mut vec1
= Vec
::with_capacity(input
.len());
2779 ExampleSliceReader { slice: input }
.read_to_end(&mut vec1
)?
;
2780 assert_eq
!(vec1
.len(), input
.len());
2781 assert
!(vec1
.capacity() > input
.len(), "allocated more");
2783 // However, std::io::Take includes an implementation of read_to_end
2784 // that will not allocate when the limit has already been reached. In
2785 // this case, vec2 never grows.
2786 let mut vec2
= Vec
::with_capacity(input
.len());
2787 ExampleSliceReader { slice: input }
.take(input
.len() as u64).read_to_end(&mut vec2
)?
;
2788 assert_eq
!(vec2
.len(), input
.len());
2789 assert_eq
!(vec2
.capacity(), input
.len(), "did not allocate more");
2795 fn io_slice_mut_advance() {
2796 let mut buf1
= [1; 8];
2797 let mut buf2
= [2; 16];
2798 let mut buf3
= [3; 8];
2799 let mut bufs
= &mut [
2800 IoSliceMut
::new(&mut buf1
),
2801 IoSliceMut
::new(&mut buf2
),
2802 IoSliceMut
::new(&mut buf3
),
2805 // Only in a single buffer..
2806 bufs
= IoSliceMut
::advance(bufs
, 1);
2807 assert_eq
!(bufs
[0].deref(), [1; 7].as_ref());
2808 assert_eq
!(bufs
[1].deref(), [2; 16].as_ref());
2809 assert_eq
!(bufs
[2].deref(), [3; 8].as_ref());
2811 // Removing a buffer, leaving others as is.
2812 bufs
= IoSliceMut
::advance(bufs
, 7);
2813 assert_eq
!(bufs
[0].deref(), [2; 16].as_ref());
2814 assert_eq
!(bufs
[1].deref(), [3; 8].as_ref());
2816 // Removing a buffer and removing from the next buffer.
2817 bufs
= IoSliceMut
::advance(bufs
, 18);
2818 assert_eq
!(bufs
[0].deref(), [3; 6].as_ref());
2822 fn io_slice_mut_advance_empty_slice() {
2823 let empty_bufs
= &mut [][..];
2825 IoSliceMut
::advance(empty_bufs
, 1);
2829 fn io_slice_mut_advance_beyond_total_length() {
2830 let mut buf1
= [1; 8];
2831 let mut bufs
= &mut [IoSliceMut
::new(&mut buf1
)][..];
2833 // Going beyond the total length should be ok.
2834 bufs
= IoSliceMut
::advance(bufs
, 9);
2835 assert
!(bufs
.is_empty());
2839 fn io_slice_advance() {
2843 let mut bufs
= &mut [IoSlice
::new(&buf1
), IoSlice
::new(&buf2
), IoSlice
::new(&buf3
)][..];
2845 // Only in a single buffer..
2846 bufs
= IoSlice
::advance(bufs
, 1);
2847 assert_eq
!(bufs
[0].deref(), [1; 7].as_ref());
2848 assert_eq
!(bufs
[1].deref(), [2; 16].as_ref());
2849 assert_eq
!(bufs
[2].deref(), [3; 8].as_ref());
2851 // Removing a buffer, leaving others as is.
2852 bufs
= IoSlice
::advance(bufs
, 7);
2853 assert_eq
!(bufs
[0].deref(), [2; 16].as_ref());
2854 assert_eq
!(bufs
[1].deref(), [3; 8].as_ref());
2856 // Removing a buffer and removing from the next buffer.
2857 bufs
= IoSlice
::advance(bufs
, 18);
2858 assert_eq
!(bufs
[0].deref(), [3; 6].as_ref());
2862 fn io_slice_advance_empty_slice() {
2863 let empty_bufs
= &mut [][..];
2865 IoSlice
::advance(empty_bufs
, 1);
2869 fn io_slice_advance_beyond_total_length() {
2871 let mut bufs
= &mut [IoSlice
::new(&buf1
)][..];
2873 // Going beyond the total length should be ok.
2874 bufs
= IoSlice
::advance(bufs
, 9);
2875 assert
!(bufs
.is_empty());
2878 /// Create a new writer that reads from at most `n_bufs` and reads
2879 /// `per_call` bytes (in total) per call to write.
2880 fn test_writer(n_bufs
: usize, per_call
: usize) -> TestWriter
{
2881 TestWriter { n_bufs, per_call, written: Vec::new() }
2890 impl Write
for TestWriter
{
2891 fn write(&mut self, buf
: &[u8]) -> io
::Result
<usize> {
2892 self.write_vectored(&[IoSlice
::new(buf
)])
2895 fn write_vectored(&mut self, bufs
: &[IoSlice
<'_
>]) -> io
::Result
<usize> {
2896 let mut left
= self.per_call
;
2897 let mut written
= 0;
2898 for buf
in bufs
.iter().take(self.n_bufs
) {
2899 let n
= min(left
, buf
.len());
2900 self.written
.extend_from_slice(&buf
[0..n
]);
2907 fn flush(&mut self) -> io
::Result
<()> {
2913 fn test_writer_read_from_one_buf() {
2914 let mut writer
= test_writer(1, 2);
2916 assert_eq
!(writer
.write(&[]).unwrap(), 0);
2917 assert_eq
!(writer
.write_vectored(&[]).unwrap(), 0);
2919 // Read at most 2 bytes.
2920 assert_eq
!(writer
.write(&[1, 1, 1]).unwrap(), 2);
2921 let bufs
= &[IoSlice
::new(&[2, 2, 2])];
2922 assert_eq
!(writer
.write_vectored(bufs
).unwrap(), 2);
2924 // Only read from first buf.
2925 let bufs
= &[IoSlice
::new(&[3]), IoSlice
::new(&[4, 4])];
2926 assert_eq
!(writer
.write_vectored(bufs
).unwrap(), 1);
2928 assert_eq
!(writer
.written
, &[1, 1, 2, 2, 3]);
2932 fn test_writer_read_from_multiple_bufs() {
2933 let mut writer
= test_writer(3, 3);
2935 // Read at most 3 bytes from two buffers.
2936 let bufs
= &[IoSlice
::new(&[1]), IoSlice
::new(&[2, 2, 2])];
2937 assert_eq
!(writer
.write_vectored(bufs
).unwrap(), 3);
2939 // Read at most 3 bytes from three buffers.
2940 let bufs
= &[IoSlice
::new(&[3]), IoSlice
::new(&[4]), IoSlice
::new(&[5, 5])];
2941 assert_eq
!(writer
.write_vectored(bufs
).unwrap(), 3);
2943 assert_eq
!(writer
.written
, &[1, 2, 2, 3, 4, 5]);
2947 fn test_write_all_vectored() {
2948 #[rustfmt::skip] // Becomes unreadable otherwise.
2949 let tests
: Vec
<(_
, &'
static [u8])> = vec
![
2951 (vec
![IoSlice
::new(&[]), IoSlice
::new(&[])], &[]),
2952 (vec
![IoSlice
::new(&[1])], &[1]),
2953 (vec
![IoSlice
::new(&[1, 2])], &[1, 2]),
2954 (vec
![IoSlice
::new(&[1, 2, 3])], &[1, 2, 3]),
2955 (vec
![IoSlice
::new(&[1, 2, 3, 4])], &[1, 2, 3, 4]),
2956 (vec
![IoSlice
::new(&[1, 2, 3, 4, 5])], &[1, 2, 3, 4, 5]),
2957 (vec
![IoSlice
::new(&[1]), IoSlice
::new(&[2])], &[1, 2]),
2958 (vec
![IoSlice
::new(&[1]), IoSlice
::new(&[2, 2])], &[1, 2, 2]),
2959 (vec
![IoSlice
::new(&[1, 1]), IoSlice
::new(&[2, 2])], &[1, 1, 2, 2]),
2960 (vec
![IoSlice
::new(&[1, 1]), IoSlice
::new(&[2, 2, 2])], &[1, 1, 2, 2, 2]),
2961 (vec
![IoSlice
::new(&[1, 1]), IoSlice
::new(&[2, 2, 2])], &[1, 1, 2, 2, 2]),
2962 (vec
![IoSlice
::new(&[1, 1, 1]), IoSlice
::new(&[2, 2, 2])], &[1, 1, 1, 2, 2, 2]),
2963 (vec
![IoSlice
::new(&[1, 1, 1]), IoSlice
::new(&[2, 2, 2, 2])], &[1, 1, 1, 2, 2, 2, 2]),
2964 (vec
![IoSlice
::new(&[1, 1, 1, 1]), IoSlice
::new(&[2, 2, 2, 2])], &[1, 1, 1, 1, 2, 2, 2, 2]),
2965 (vec
![IoSlice
::new(&[1]), IoSlice
::new(&[2]), IoSlice
::new(&[3])], &[1, 2, 3]),
2966 (vec
![IoSlice
::new(&[1, 1]), IoSlice
::new(&[2, 2]), IoSlice
::new(&[3, 3])], &[1, 1, 2, 2, 3, 3]),
2967 (vec
![IoSlice
::new(&[1]), IoSlice
::new(&[2, 2]), IoSlice
::new(&[3, 3, 3])], &[1, 2, 2, 3, 3, 3]),
2968 (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]),
2971 let writer_configs
= &[(1, 1), (1, 2), (1, 3), (2, 2), (2, 3), (3, 3)];
2973 for (n_bufs
, per_call
) in writer_configs
.iter().copied() {
2974 for (mut input
, wanted
) in tests
.clone().into_iter() {
2975 let mut writer
= test_writer(n_bufs
, per_call
);
2976 assert
!(writer
.write_all_vectored(&mut *input
).is_ok());
2977 assert_eq
!(&*writer
.written
, &*wanted
);