mod.rs source code [crates/std/src/io/mod.rs]

1	//! Traits, helpers, and type definitions for core I/O functionality.
2	//!
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.
7	//!
8	//! ## Read and Write
9	//!
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
15	//! [`File`]s:
16	//!
17	//! ```no_run
18	//! use std::io;
19	//! use std::io::prelude::*;
20	//! use std::fs::File;
21	//!
22	//! fn main() -> io::Result<()> {
23	//! let mut f = File::open("foo.txt")?;
24	//! let mut buffer = [`0`; `10`];
25	//!
26	//! // read up to 10 bytes
27	//! let n = f.read(&mut buffer)?;
28	//!
29	//! println!("The bytes: {:?}", &buffer[..n]);
30	//! Ok(())
31	//! }
32	//! ```
33	//!
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!
37	//!
38	//! ## Seek and BufRead
39	//!
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
43	//! coming from:
44	//!
45	//! ```no_run
46	//! use std::io;
47	//! use std::io::prelude::*;
48	//! use std::io::SeekFrom;
49	//! use std::fs::File;
50	//!
51	//! fn main() -> io::Result<()> {
52	//! let mut f = File::open("foo.txt")?;
53	//! let mut buffer = [`0`; `10`];
54	//!
55	//! // skip to the last 10 bytes of the file
56	//! f.seek(SeekFrom::End(`-10`))?;
57	//!
58	//! // read up to 10 bytes
59	//! let n = f.read(&mut buffer)?;
60	//!
61	//! println!("The bytes: {:?}", &buffer[..n]);
62	//! Ok(())
63	//! }
64	//! ```
65	//!
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!
68	//!
69	//! ## BufReader and BufWriter
70	//!
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.
76	//!
77	//! For example, [`BufReader`] works with the [`BufRead`] trait to add extra
78	//! methods to any reader:
79	//!
80	//! ```no_run
81	//! use std::io;
82	//! use std::io::prelude::*;
83	//! use std::io::BufReader;
84	//! use std::fs::File;
85	//!
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();
90	//!
91	//! // read a line into buffer
92	//! reader.read_line(&mut buffer)?;
93	//!
94	//! println!("{buffer}");
95	//! Ok(())
96	//! }
97	//! ```
98	//!
99	//! [`BufWriter`] doesn't add any new ways of writing; it just buffers every call
100	//! to [`write`][`Write::write`]:
101	//!
102	//! ```no_run
103	//! use std::io;
104	//! use std::io::prelude::*;
105	//! use std::io::BufWriter;
106	//! use std::fs::File;
107	//!
108	//! fn main() -> io::Result<()> {
109	//! let f = File::create("foo.txt")?;
110	//! {
111	//! let mut writer = BufWriter::new(f);
112	//!
113	//! // write a byte to the buffer
114	//! writer.write(&[`42`])?;
115	//!
116	//! } // the buffer is flushed once writer goes out of scope
117	//!
118	//! Ok(())
119	//! }
120	//! ```
121	//!
122	//! ## Standard input and output
123	//!
124	//! A very common source of input is standard input:
125	//!
126	//! ```no_run
127	//! use std::io;
128	//!
129	//! fn main() -> io::Result<()> {
130	//! let mut input = String::new();
131	//!
132	//! io::stdin().read_line(&mut input)?;
133	//!
134	//! println!("You typed: {}", input.trim());
135	//! Ok(())
136	//! }
137	//! ```
138	//!
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:
142	//!
143	//! ```no_run
144	//! use std::io;
145	//!
146	//! let mut input = String::new();
147	//!
148	//! io::stdin().read_line(&mut input).unwrap();
149	//! ```
150	//!
151	//! And a very common source of output is standard output:
152	//!
153	//! ```no_run
154	//! use std::io;
155	//! use std::io::prelude::*;
156	//!
157	//! fn main() -> io::Result<()> {
158	//! io::stdout().write(&[`42`])?;
159	//! Ok(())
160	//! }
161	//! ```
162	//!
163	//! Of course, using [`io::stdout`] directly is less common than something like
164	//! [`println!`].
165	//!
166	//! ## Iterator types
167	//!
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
170	//! lines:
171	//!
172	//! ```no_run
173	//! use std::io;
174	//! use std::io::prelude::*;
175	//! use std::io::BufReader;
176	//! use std::fs::File;
177	//!
178	//! fn main() -> io::Result<()> {
179	//! let f = File::open("foo.txt")?;
180	//! let reader = BufReader::new(f);
181	//!
182	//! for line in reader.lines() {
183	//! println!("{}", line?);
184	//! }
185	//! Ok(())
186	//! }
187	//! ```
188	//!
189	//! ## Functions
190	//!
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:
194	//!
195	//! ```no_run
196	//! use std::io;
197	//!
198	//! fn main() -> io::Result<()> {
199	//! io::copy(&mut io::stdin(), &mut io::stdout())?;
200	//! Ok(())
201	//! }
202	//! ```
203	//!
204	//! [functions-list]: #functions-1
205	//!
206	//! ## io::Result
207	//!
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]:
212	//!
213	//! ```
214	//! use std::io;
215	//!
216	//! fn read_input() -> io::Result<()> {
217	//! let mut input = String::new();
218	//!
219	//! io::stdin().read_line(&mut input)?;
220	//!
221	//! println!("You typed: {}", input.trim());
222	//!
223	//! Ok(())
224	//! }
225	//! ```
226	//!
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 `()`.
231	//!
232	//! ## Platform-specific behavior
233	//!
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.
240	//!
241	//! ## I/O Safety
242	//!
243	//! Rust follows an I/O safety discipline that is comparable to its memory safety discipline. This
244	//! means that file descriptors can be exclusively owned. (Here, "file descriptor" is meant to
245	//! subsume similar concepts that exist across a wide range of operating systems even if they might
246	//! use a different name, such as "handle".) An exclusively owned file descriptor is one that no
247	//! other code is allowed to access in any way, but the owner is allowed to access and even close
248	//! it any time. A type that owns its file descriptor should usually close it in its `drop`
249	//! function. Types like [`File`] own their file descriptor. Similarly, file descriptors
250	//! can be borrowed, granting the temporary right to perform operations on this file descriptor.
251	//! This indicates that the file descriptor will not be closed for the lifetime of the borrow, but
252	//! it does not* imply any right to close this file descriptor, since it will likely be owned by*
253	//! someone else.
254	//!
255	//! The platform-specific parts of the Rust standard library expose types that reflect these
256	//! concepts, see [`os::unix`] and [`os::windows`].
257	//!
258	//! To uphold I/O safety, it is crucial that no code acts on file descriptors it does not own or
259	//! borrow, and no code closes file descriptors it does not own. In other words, a safe function
260	//! that takes a regular integer, treats it as a file descriptor, and acts on it, is unsound.
261	//!
262	//! Not upholding I/O safety and acting on a file descriptor without proof of ownership can lead to
263	//! misbehavior and even Undefined Behavior in code that relies on ownership of its file
264	//! descriptors: a closed file descriptor could be re-allocated, so the original owner of that file
265	//! descriptor is now working on the wrong file. Some code might even rely on fully encapsulating
266	//! its file descriptors with no operations being performed by any other part of the program.
267	//!
268	//! Note that exclusive ownership of a file descriptor does not* imply exclusive ownership of the*
269	//! underlying kernel object that the file descriptor references (also called "open file description" on
270	//! some operating systems). File descriptors basically work like [`Arc`]: when you receive an owned
271	//! file descriptor, you cannot know whether there are any other file descriptors that reference the
272	//! same kernel object. However, when you create a new kernel object, you know that you are holding
273	//! the only reference to it. Just be careful not to lend it to anyone, since they can obtain a
274	//! clone and then you can no longer know what the reference count is! In that sense, [`OwnedFd`] is
275	//! like `Arc` and [`BorrowedFd<'a>`] is like `&'a Arc` (and similar for the Windows types). In
276	//! particular, given a `BorrowedFd<'a>`, you are not allowed to close the file descriptor -- just
277	//! like how, given a `&'a Arc`, you are not allowed to decrement the reference count and
278	//! potentially free the underlying object. There is no equivalent to `Box` for file descriptors in
279	//! the standard library (that would be a type that guarantees that the reference count is `1`),
280	//! however, it would be possible for a crate to define a type with those semantics.
281	//!
282	//! [`File`]: crate::fs::File
283	//! [`TcpStream`]: crate::net::TcpStream
284	//! [`io::stdout`]: stdout
285	//! [`io::Result`]: self::Result
286	//! [`?` operator]: ../../book/appendix-02-operators.html
287	//! [`Result`]: crate::result::Result
288	//! [`.unwrap()`]: crate::result::Result::unwrap
289	//! [`os::unix`]: ../os/unix/io/index.html
290	//! [`os::windows`]: ../os/windows/io/index.html
291	//! [`OwnedFd`]: ../os/fd/struct.OwnedFd.html
292	//! [`BorrowedFd<'a>`]: ../os/fd/struct.BorrowedFd.html
293	//! [`Arc`]: crate::sync::Arc
294
295	#![stable(feature = "rust1", since = "1.0.0")]
296
297	#[cfg(test)]
298	mod tests;
299
300	#[unstable(feature = "read_buf", issue = "78485")]
301	pub use core::io::{BorrowedBuf, BorrowedCursor};
302	use core::slice::memchr;
303
304	#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
305	pub use self::buffered::WriterPanicked;
306	#[unstable(feature = "raw_os_error_ty", issue = "107792")]
307	pub use self::error::RawOsError;
308	#[doc(hidden)]
309	#[unstable(feature = "io_const_error_internals", issue = "none")]
310	pub use self::error::SimpleMessage;
311	#[unstable(feature = "io_const_error", issue = "133448")]
312	pub use self::error::const_error;
313	#[stable(feature = "anonymous_pipe", since = "1.87.0")]
314	pub use self::pipe::{PipeReader, PipeWriter, pipe};
315	#[stable(feature = "is_terminal", since = "1.70.0")]
316	pub use self::stdio::IsTerminal;
317	pub(crate) use self::stdio::attempt_print_to_stderr;
318	#[unstable(feature = "print_internals", issue = "none")]
319	#[doc(hidden)]
320	pub use self::stdio::{_eprint, _print};
321	#[unstable(feature = "internal_output_capture", issue = "none")]
322	#[doc(no_inline, hidden)]
323	pub use self::stdio::{set_output_capture, try_set_output_capture};
324	#[stable(feature = "rust1", since = "1.0.0")]
325	pub use self::{
326	buffered::{BufReader, BufWriter, IntoInnerError, LineWriter},
327	copy::copy,
328	cursor::Cursor,
329	error::{Error, ErrorKind, Result},
330	stdio::{Stderr, StderrLock, Stdin, StdinLock, Stdout, StdoutLock, stderr, stdin, stdout},
331	util::{Empty, Repeat, Sink, empty, repeat, sink},
332	};
333	use crate::mem::take;
334	use crate::ops::{Deref, DerefMut};
335	use crate::{cmp, fmt, slice, str, sys};
336
337	mod buffered;
338	pub(crate) mod copy;
339	mod cursor;
340	mod error;
341	mod impls;
342	mod pipe;
343	pub mod prelude;
344	mod stdio;
345	mod util;
346
347	const DEFAULT_BUF_SIZE: usize = crate::sys::io::DEFAULT_BUF_SIZE;
348
349	pub(crate) use stdio::cleanup;
350
351	struct Guard<'a> {
352	buf: &'a mut Vec<u8>,
353	len: usize,
354	}
355
356	impl Drop for Guard<'_> {
357	fn drop(&mut self) {
358	unsafe {
359	self.buf.set_len(self.len);
360	}
361	}
362	}
363
364	// Several `read_to_string` and `read_line` methods in the standard library will
365	// append data into a `String` buffer, but we need to be pretty careful when
366	// doing this. The implementation will just call `.as_mut_vec()` and then
367	// delegate to a byte-oriented reading method, but we must ensure that when
368	// returning we never leave `buf` in a state such that it contains invalid UTF-8
369	// in its bounds.
370	//
371	// To this end, we use an RAII guard (to protect against panics) which updates
372	// the length of the string when it is dropped. This guard initially truncates
373	// the string to the prior length and only after we've validated that the
374	// new contents are valid UTF-8 do we allow it to set a longer length.
375	//
376	// The unsafety in this function is twofold:
377	//
378	// 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
379	// checks.
380	// 2. We're passing a raw buffer to the function `f`, and it is expected that
381	// the function only appends* bytes to the buffer. We'll get undefined*
382	// behavior if existing bytes are overwritten to have non-UTF-8 data.
383	pub(crate) unsafe fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
384	where
385	F: FnOnce(&mut Vec<u8>) -> Result<usize>,
386	{
387	let mut g: Guard<'_> = Guard { len: buf.len(), buf: unsafe { buf.as_mut_vec() } };
388	let ret: Result = f(g.buf);
389
390	// SAFETY: the caller promises to only append data to `buf`
391	let appended: &[u8] = unsafe { g.buf.get_unchecked(index:g.len..) };
392	if str::from_utf8(appended).is_err() {
393	ret.and_then(\|_\| Err(Error::INVALID_UTF8))
394	} else {
395	g.len = g.buf.len();
396	ret
397	}
398	}
399
400	// Here we must serve many masters with conflicting goals:
401	//
402	// - avoid allocating unless necessary
403	// - avoid overallocating if we know the exact size (#89165)
404	// - avoid passing large buffers to readers that always initialize the free capacity if they perform short reads (#23815, #23820)
405	// - pass large buffers to readers that do not initialize the spare capacity. this can amortize per-call overheads
406	// - and finally pass not-too-small and not-too-large buffers to Windows read APIs because they manage to suffer from both problems
407	// at the same time, i.e. small reads suffer from syscall overhead, all reads incur costs proportional to buffer size (#110650)
408	//
409	pub(crate) fn default_read_to_end<R: Read + ?Sized>(
410	r: &mut R,
411	buf: &mut Vec<u8>,
412	size_hint: Option<usize>,
413	) -> Result<usize> {
414	let start_len = buf.len();
415	let start_cap = buf.capacity();
416	// Optionally limit the maximum bytes read on each iteration.
417	// This adds an arbitrary fiddle factor to allow for more data than we expect.
418	let mut max_read_size = size_hint
419	.and_then(\|s\| s.checked_add(`1024`)?.checked_next_multiple_of(DEFAULT_BUF_SIZE))
420	.unwrap_or(DEFAULT_BUF_SIZE);
421
422	let mut initialized = `0`; // Extra initialized bytes from previous loop iteration
423
424	const PROBE_SIZE: usize = `32`;
425
426	fn small_probe_read<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
427	let mut probe = [`0u8`; PROBE_SIZE];
428
429	loop {
430	match r.read(&mut probe) {
431	Ok(n) => {
432	// there is no way to recover from allocation failure here
433	// because the data has already been read.
434	buf.extend_from_slice(&probe[..n]);
435	return Ok(n);
436	}
437	Err(ref e) if e.is_interrupted() => continue,
438	Err(e) => return Err(e),
439	}
440	}
441	}
442
443	// avoid inflating empty/small vecs before we have determined that there's anything to read
444	if (size_hint.is_none() \|\| size_hint == Some(`0`)) && buf.capacity() - buf.len() < PROBE_SIZE {
445	let read = small_probe_read(r, buf)?;
446
447	if read == `0` {
448	return Ok(`0`);
449	}
450	}
451
452	let mut consecutive_short_reads = `0`;
453
454	loop {
455	if buf.len() == buf.capacity() && buf.capacity() == start_cap {
456	// The buffer might be an exact fit. Let's read into a probe buffer
457	// and see if it returns `Ok(0)`. If so, we've avoided an
458	// unnecessary doubling of the capacity. But if not, append the
459	// probe buffer to the primary buffer and let its capacity grow.
460	let read = small_probe_read(r, buf)?;
461
462	if read == `0` {
463	return Ok(buf.len() - start_len);
464	}
465	}
466
467	if buf.len() == buf.capacity() {
468	// buf is full, need more space
469	buf.try_reserve(PROBE_SIZE)?;
470	}
471
472	let mut spare = buf.spare_capacity_mut();
473	let buf_len = cmp::min(spare.len(), max_read_size);
474	spare = &mut spare[..buf_len];
475	let mut read_buf: BorrowedBuf<'_> = spare.into();
476
477	// SAFETY: These bytes were initialized but not filled in the previous loop
478	unsafe {
479	read_buf.set_init(initialized);
480	}
481
482	let mut cursor = read_buf.unfilled();
483	let result = loop {
484	match r.read_buf(cursor.reborrow()) {
485	Err(e) if e.is_interrupted() => continue,
486	// Do not stop now in case of error: we might have received both data
487	// and an error
488	res => break res,
489	}
490	};
491
492	let unfilled_but_initialized = cursor.init_ref().len();
493	let bytes_read = cursor.written();
494	let was_fully_initialized = read_buf.init_len() == buf_len;
495
496	// SAFETY: BorrowedBuf's invariants mean this much memory is initialized.
497	unsafe {
498	let new_len = bytes_read + buf.len();
499	buf.set_len(new_len);
500	}
501
502	// Now that all data is pushed to the vector, we can fail without data loss
503	result?;
504
505	if bytes_read == `0` {
506	return Ok(buf.len() - start_len);
507	}
508
509	if bytes_read < buf_len {
510	consecutive_short_reads += `1`;
511	} else {
512	consecutive_short_reads = `0`;
513	}
514
515	// store how much was initialized but not filled
516	initialized = unfilled_but_initialized;
517
518	// Use heuristics to determine the max read size if no initial size hint was provided
519	if size_hint.is_none() {
520	// The reader is returning short reads but it doesn't call ensure_init().
521	// In that case we no longer need to restrict read sizes to avoid
522	// initialization costs.
523	// When reading from disk we usually don't get any short reads except at EOF.
524	// So we wait for at least 2 short reads before uncapping the read buffer;
525	// this helps with the Windows issue.
526	if !was_fully_initialized && consecutive_short_reads > `1` {
527	max_read_size = usize::MAX;
528	}
529
530	// we have passed a larger buffer than previously and the
531	// reader still hasn't returned a short read
532	if buf_len >= max_read_size && bytes_read == buf_len {
533	max_read_size = max_read_size.saturating_mul(`2`);
534	}
535	}
536	}
537	}
538
539	pub(crate) fn default_read_to_string<R: Read + ?Sized>(
540	r: &mut R,
541	buf: &mut String,
542	size_hint: Option<usize>,
543	) -> Result<usize> {
544	// Note that we do not* call `r.read_to_end()` here. We are passing*
545	// `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
546	// method to fill it up. An arbitrary implementation could overwrite the
547	// entire contents of the vector, not just append to it (which is what
548	// we are expecting).
549	//
550	// To prevent extraneously checking the UTF-8-ness of the entire buffer
551	// we pass it to our hardcoded `default_read_to_end` implementation which
552	// we know is guaranteed to only read data into the end of the buffer.
553	unsafe { append_to_string(buf, \|b: &mut Vec\| default_read_to_end(r, buf:b, size_hint)) }
554	}
555
556	pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
557	where
558	F: FnOnce(&mut [u8]) -> Result<usize>,
559	{
560	let buf: &mut [u8] = bufs.iter_mut().find(\|b\| !b.is_empty()).map_or(&mut [][..], \|b: &mut IoSliceMut<'_>\| &mut **b);
561	read(buf)
562	}
563
564	pub(crate) fn default_write_vectored<F>(write: F, bufs: &[IoSlice<'_>]) -> Result<usize>
565	where
566	F: FnOnce(&[u8]) -> Result<usize>,
567	{
568	let buf: &[u8] = bufs.iter().find(\|b\| !b.is_empty()).map_or(&[][..], \|b: &IoSlice<'_>\| &**b);
569	write(buf)
570	}
571
572	pub(crate) fn default_read_exact<R: Read + ?Sized>(this: &mut R, mut buf: &mut [u8]) -> Result<()> {
573	while !buf.is_empty() {
574	match this.read(buf) {
575	Ok(`0`) => break,
576	Ok(n: usize) => {
577	buf = &mut buf[n..];
578	}
579	Err(ref e: &Error) if e.is_interrupted() => {}
580	Err(e: Error) => return Err(e),
581	}
582	}
583	if !buf.is_empty() { Err(Error::READ_EXACT_EOF) } else { Ok(()) }
584	}
585
586	pub(crate) fn default_read_buf<F>(read: F, mut cursor: BorrowedCursor<'_>) -> Result<()>
587	where
588	F: FnOnce(&mut [u8]) -> Result<usize>,
589	{
590	let n: usize = read(cursor.ensure_init().init_mut())?;
591	cursor.advance(n);
592	Ok(())
593	}
594
595	pub(crate) fn default_read_buf_exact<R: Read + ?Sized>(
596	this: &mut R,
597	mut cursor: BorrowedCursor<'_>,
598	) -> Result<()> {
599	while cursor.capacity() > `0` {
600	let prev_written: usize = cursor.written();
601	match this.read_buf(cursor.reborrow()) {
602	Ok(()) => {}
603	Err(e: Error) if e.is_interrupted() => continue,
604	Err(e: Error) => return Err(e),
605	}
606
607	if cursor.written() == prev_written {
608	return Err(Error::READ_EXACT_EOF);
609	}
610	}
611
612	Ok(())
613	}
614
615	pub(crate) fn default_write_fmt<W: Write + ?Sized>(
616	this: &mut W,
617	args: fmt::Arguments<'_>,
618	) -> Result<()> {
619	// Create a shim which translates a `Write` to a `fmt::Write` and saves off
620	// I/O errors, instead of discarding them.
621	struct Adapter<'a, T: ?Sized + 'a> {
622	inner: &'a mut T,
623	error: Result<()>,
624	}
625
626	impl<T: Write + ?Sized> fmt::Write for Adapter<'_, T> {
627	fn write_str(&mut self, s: &str) -> fmt::Result {
628	match self.inner.write_all(s.as_bytes()) {
629	Ok(()) => Ok(()),
630	Err(e) => {
631	self.error = Err(e);
632	Err(fmt::Error)
633	}
634	}
635	}
636	}
637
638	let mut output = Adapter { inner: this, error: Ok(()) };
639	match fmt::write(&mut output, args) {
640	Ok(()) => Ok(()),
641	Err(..) => {
642	// Check whether the error came from the underlying `Write`.
643	if output.error.is_err() {
644	output.error
645	} else {
646	// This shouldn't happen: the underlying stream did not error,
647	// but somehow the formatter still errored?
648	panic!(
649	"a formatting trait implementation returned an error when the underlying stream did not"
650	);
651	}
652	}
653	}
654	}
655
656	/// The `Read` trait allows for reading bytes from a source.
657	///
658	/// Implementors of the `Read` trait are called 'readers'.
659	///
660	/// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
661	/// will attempt to pull bytes from this source into a provided buffer. A
662	/// number of other methods are implemented in terms of [`read()`], giving
663	/// implementors a number of ways to read bytes while only needing to implement
664	/// a single method.
665	///
666	/// Readers are intended to be composable with one another. Many implementors
667	/// throughout [`std::io`] take and provide types which implement the `Read`
668	/// trait.
669	///
670	/// Please note that each call to [`read()`] may involve a system call, and
671	/// therefore, using something that implements [`BufRead`], such as
672	/// [`BufReader`], will be more efficient.
673	///
674	/// Repeated calls to the reader use the same cursor, so for example
675	/// calling `read_to_end` twice on a [`File`] will only return the file's
676	/// contents once. It's recommended to first call `rewind()` in that case.
677	///
678	/// # Examples
679	///
680	/// [`File`]s implement `Read`:
681	///
682	/// ```no_run
683	/// use std::io;
684	/// use std::io::prelude::*;
685	/// use std::fs::File;
686	///
687	/// fn main() -> io::Result<()> {
688	/// let mut f = File::open("foo.txt")?;
689	/// let mut buffer = [`0`; `10`];
690	///
691	/// // read up to 10 bytes
692	/// f.read(&mut buffer)?;
693	///
694	/// let mut buffer = Vec::new();
695	/// // read the whole file
696	/// f.read_to_end(&mut buffer)?;
697	///
698	/// // read into a String, so that you don't need to do the conversion.
699	/// let mut buffer = String::new();
700	/// f.read_to_string(&mut buffer)?;
701	///
702	/// // and more! See the other methods for more details.
703	/// Ok(())
704	/// }
705	/// ```
706	///
707	/// Read from [`&str`] because [`&[u8]`][prim@slice] implements `Read`:
708	///
709	/// ```no_run
710	/// # use std::io;
711	/// use std::io::prelude::*;
712	///
713	/// fn main() -> io::Result<()> {
714	/// let mut b = "This string will be read".as_bytes();
715	/// let mut buffer = [`0`; `10`];
716	///
717	/// // read up to 10 bytes
718	/// b.read(&mut buffer)?;
719	///
720	/// // etc... it works exactly as a File does!
721	/// Ok(())
722	/// }
723	/// ```
724	///
725	/// [`read()`]: Read::read
726	/// [`&str`]: prim@str
727	/// [`std::io`]: self
728	/// [`File`]: crate::fs::File
729	#[stable(feature = "rust1", since = "1.0.0")]
730	#[doc(notable_trait)]
731	#[cfg_attr(not(test), rustc_diagnostic_item = "IoRead")]
732	pub trait Read {
733	/// Pull some bytes from this source into the specified buffer, returning
734	/// how many bytes were read.
735	///
736	/// This function does not provide any guarantees about whether it blocks
737	/// waiting for data, but if an object needs to block for a read and cannot,
738	/// it will typically signal this via an [`Err`] return value.
739	///
740	/// If the return value of this method is [`Ok(n)`], then implementations must
741	/// guarantee that `0 <= n <= buf.len()`. A nonzero `n` value indicates
742	/// that the buffer `buf` has been filled in with `n` bytes of data from this
743	/// source. If `n` is `0`, then it can indicate one of two scenarios:
744	///
745	/// 1. This reader has reached its "end of file" and will likely no longer
746	/// be able to produce bytes. Note that this does not mean that the
747	/// reader will always* no longer be able to produce bytes. As an example,*
748	/// on Linux, this method will call the `recv` syscall for a [`TcpStream`],
749	/// where returning zero indicates the connection was shut down correctly. While
750	/// for [`File`], it is possible to reach the end of file and get zero as result,
751	/// but if more data is appended to the file, future calls to `read` will return
752	/// more data.
753	/// 2. The buffer specified was 0 bytes in length.
754	///
755	/// It is not an error if the returned value `n` is smaller than the buffer size,
756	/// even when the reader is not at the end of the stream yet.
757	/// This may happen for example because fewer bytes are actually available right now
758	/// (e. g. being close to end-of-file) or because read() was interrupted by a signal.
759	///
760	/// As this trait is safe to implement, callers in unsafe code cannot rely on
761	/// `n <= buf.len()` for safety.
762	/// Extra care needs to be taken when `unsafe` functions are used to access the read bytes.
763	/// Callers have to ensure that no unchecked out-of-bounds accesses are possible even if
764	/// `n > buf.len()`.
765	///
766	/// Implementations* of this method can make no assumptions about the contents of `buf` when*
767	/// this function is called. It is recommended that implementations only write data to `buf`
768	/// instead of reading its contents.
769	///
770	/// Correspondingly, however, callers* of this method in unsafe code must not assume*
771	/// any guarantees about how the implementation uses `buf`. The trait is safe to implement,
772	/// so it is possible that the code that's supposed to write to the buffer might also read
773	/// from it. It is your responsibility to make sure that `buf` is initialized
774	/// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
775	/// obtains via [`MaybeUninit<T>`]) is not safe, and can lead to undefined behavior.
776	///
777	/// [`MaybeUninit<T>`]: crate::mem::MaybeUninit
778	///
779	/// # Errors
780	///
781	/// If this function encounters any form of I/O or other error, an error
782	/// variant will be returned. If an error is returned then it must be
783	/// guaranteed that no bytes were read.
784	///
785	/// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
786	/// operation should be retried if there is nothing else to do.
787	///
788	/// # Examples
789	///
790	/// [`File`]s implement `Read`:
791	///
792	/// [`Ok(n)`]: Ok
793	/// [`File`]: crate::fs::File
794	/// [`TcpStream`]: crate::net::TcpStream
795	///
796	/// ```no_run
797	/// use std::io;
798	/// use std::io::prelude::*;
799	/// use std::fs::File;
800	///
801	/// fn main() -> io::Result<()> {
802	/// let mut f = File::open("foo.txt")?;
803	/// let mut buffer = [`0`; `10`];
804	///
805	/// // read up to 10 bytes
806	/// let n = f.read(&mut buffer[..])?;
807	///
808	/// println!("The bytes: {:?}", &buffer[..n]);
809	/// Ok(())
810	/// }
811	/// ```
812	#[stable(feature = "rust1", since = "1.0.0")]
813	fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
814
815	/// Like `read`, except that it reads into a slice of buffers.
816	///
817	/// Data is copied to fill each buffer in order, with the final buffer
818	/// written to possibly being only partially filled. This method must
819	/// behave equivalently to a single call to `read` with concatenated
820	/// buffers.
821	///
822	/// The default implementation calls `read` with either the first nonempty
823	/// buffer provided, or an empty one if none exists.
824	#[stable(feature = "iovec", since = "1.36.0")]
825	fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
826	default_read_vectored(\|b\| self.read(b), bufs)
827	}
828
829	/// Determines if this `Read`er has an efficient `read_vectored`
830	/// implementation.
831	///
832	/// If a `Read`er does not override the default `read_vectored`
833	/// implementation, code using it may want to avoid the method all together
834	/// and coalesce writes into a single buffer for higher performance.
835	///
836	/// The default implementation returns `false`.
837	#[unstable(feature = "can_vector", issue = "69941")]
838	fn is_read_vectored(&self) -> bool {
839	`false`
840	}
841
842	/// Reads all bytes until EOF in this source, placing them into `buf`.
843	///
844	/// All bytes read from this source will be appended to the specified buffer
845	/// `buf`. This function will continuously call [`read()`] to append more data to
846	/// `buf` until [`read()`] returns either [`Ok(0)`] or an error of
847	/// non-[`ErrorKind::Interrupted`] kind.
848	///
849	/// If successful, this function will return the total number of bytes read.
850	///
851	/// # Errors
852	///
853	/// If this function encounters an error of the kind
854	/// [`ErrorKind::Interrupted`] then the error is ignored and the operation
855	/// will continue.
856	///
857	/// If any other read error is encountered then this function immediately
858	/// returns. Any bytes which have already been read will be appended to
859	/// `buf`.
860	///
861	/// # Examples
862	///
863	/// [`File`]s implement `Read`:
864	///
865	/// [`read()`]: Read::read
866	/// [`Ok(0)`]: Ok
867	/// [`File`]: crate::fs::File
868	///
869	/// ```no_run
870	/// use std::io;
871	/// use std::io::prelude::*;
872	/// use std::fs::File;
873	///
874	/// fn main() -> io::Result<()> {
875	/// let mut f = File::open("foo.txt")?;
876	/// let mut buffer = Vec::new();
877	///
878	/// // read the whole file
879	/// f.read_to_end(&mut buffer)?;
880	/// Ok(())
881	/// }
882	/// ```
883	///
884	/// (See also the [`std::fs::read`] convenience function for reading from a
885	/// file.)
886	///
887	/// [`std::fs::read`]: crate::fs::read
888	///
889	/// ## Implementing `read_to_end`
890	///
891	/// When implementing the `io::Read` trait, it is recommended to allocate
892	/// memory using [`Vec::try_reserve`]. However, this behavior is not guaranteed
893	/// by all implementations, and `read_to_end` may not handle out-of-memory
894	/// situations gracefully.
895	///
896	/// ```no_run
897	/// # use std::io::{self, BufRead};
898	/// # struct Example { example_datasource: io::Empty } impl Example {
899	/// # fn get_some_data_for_the_example(&self) -> &'static [u8] { &[] }
900	/// fn read_to_end(&mut self, dest_vec: &mut Vec<u8>) -> io::Result<usize> {
901	/// let initial_vec_len = dest_vec.len();
902	/// loop {
903	/// let src_buf = self.example_datasource.fill_buf()?;
904	/// if src_buf.is_empty() {
905	/// break;
906	/// }
907	/// dest_vec.try_reserve(src_buf.len())?;
908	/// dest_vec.extend_from_slice(src_buf);
909	///
910	/// // Any irreversible side effects should happen after `try_reserve` succeeds,
911	/// // to avoid losing data on allocation error.
912	/// let read = src_buf.len();
913	/// self.example_datasource.consume(read);
914	/// }
915	/// Ok(dest_vec.len() - initial_vec_len)
916	/// }
917	/// # }
918	/// ```
919	///
920	/// [`Vec::try_reserve`]: crate::vec::Vec::try_reserve
921	#[stable(feature = "rust1", since = "1.0.0")]
922	fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
923	default_read_to_end(self, buf, None)
924	}
925
926	/// Reads all bytes until EOF in this source, appending them to `buf`.
927	///
928	/// If successful, this function returns the number of bytes which were read
929	/// and appended to `buf`.
930	///
931	/// # Errors
932	///
933	/// If the data in this stream is not* valid UTF-8 then an error is*
934	/// returned and `buf` is unchanged.
935	///
936	/// See [`read_to_end`] for other error semantics.
937	///
938	/// [`read_to_end`]: Read::read_to_end
939	///
940	/// # Examples
941	///
942	/// [`File`]s implement `Read`:
943	///
944	/// [`File`]: crate::fs::File
945	///
946	/// ```no_run
947	/// use std::io;
948	/// use std::io::prelude::*;
949	/// use std::fs::File;
950	///
951	/// fn main() -> io::Result<()> {
952	/// let mut f = File::open("foo.txt")?;
953	/// let mut buffer = String::new();
954	///
955	/// f.read_to_string(&mut buffer)?;
956	/// Ok(())
957	/// }
958	/// ```
959	///
960	/// (See also the [`std::fs::read_to_string`] convenience function for
961	/// reading from a file.)
962	///
963	/// [`std::fs::read_to_string`]: crate::fs::read_to_string
964	#[stable(feature = "rust1", since = "1.0.0")]
965	fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
966	default_read_to_string(self, buf, None)
967	}
968
969	/// Reads the exact number of bytes required to fill `buf`.
970	///
971	/// This function reads as many bytes as necessary to completely fill the
972	/// specified buffer `buf`.
973	///
974	/// Implementations* of this method can make no assumptions about the contents of `buf` when*
975	/// this function is called. It is recommended that implementations only write data to `buf`
976	/// instead of reading its contents. The documentation on [`read`] has a more detailed
977	/// explanation of this subject.
978	///
979	/// # Errors
980	///
981	/// If this function encounters an error of the kind
982	/// [`ErrorKind::Interrupted`] then the error is ignored and the operation
983	/// will continue.
984	///
985	/// If this function encounters an "end of file" before completely filling
986	/// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
987	/// The contents of `buf` are unspecified in this case.
988	///
989	/// If any other read error is encountered then this function immediately
990	/// returns. The contents of `buf` are unspecified in this case.
991	///
992	/// If this function returns an error, it is unspecified how many bytes it
993	/// has read, but it will never read more than would be necessary to
994	/// completely fill the buffer.
995	///
996	/// # Examples
997	///
998	/// [`File`]s implement `Read`:
999	///
1000	/// [`read`]: Read::read
1001	/// [`File`]: crate::fs::File
1002	///
1003	/// ```no_run
1004	/// use std::io;
1005	/// use std::io::prelude::*;
1006	/// use std::fs::File;
1007	///
1008	/// fn main() -> io::Result<()> {
1009	/// let mut f = File::open("foo.txt")?;
1010	/// let mut buffer = [`0`; `10`];
1011	///
1012	/// // read exactly 10 bytes
1013	/// f.read_exact(&mut buffer)?;
1014	/// Ok(())
1015	/// }
1016	/// ```
1017	#[stable(feature = "read_exact", since = "1.6.0")]
1018	fn read_exact(&mut self, buf: &mut [u8]) -> Result<()> {
1019	default_read_exact(self, buf)
1020	}
1021
1022	/// Pull some bytes from this source into the specified buffer.
1023	///
1024	/// This is equivalent to the [`read`](Read::read) method, except that it is passed a [`BorrowedCursor`] rather than `[u8]` to allow use
1025	/// with uninitialized buffers. The new data will be appended to any existing contents of `buf`.
1026	///
1027	/// The default implementation delegates to `read`.
1028	///
1029	/// This method makes it possible to return both data and an error but it is advised against.
1030	#[unstable(feature = "read_buf", issue = "78485")]
1031	fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<()> {
1032	default_read_buf(\|b\| self.read(b), buf)
1033	}
1034
1035	/// Reads the exact number of bytes required to fill `cursor`.
1036	///
1037	/// This is similar to the [`read_exact`](Read::read_exact) method, except
1038	/// that it is passed a [`BorrowedCursor`] rather than `[u8]` to allow use
1039	/// with uninitialized buffers.
1040	///
1041	/// # Errors
1042	///
1043	/// If this function encounters an error of the kind [`ErrorKind::Interrupted`]
1044	/// then the error is ignored and the operation will continue.
1045	///
1046	/// If this function encounters an "end of file" before completely filling
1047	/// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
1048	///
1049	/// If any other read error is encountered then this function immediately
1050	/// returns.
1051	///
1052	/// If this function returns an error, all bytes read will be appended to `cursor`.
1053	#[unstable(feature = "read_buf", issue = "78485")]
1054	fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()> {
1055	default_read_buf_exact(self, cursor)
1056	}
1057
1058	/// Creates a "by reference" adaptor for this instance of `Read`.
1059	///
1060	/// The returned adapter also implements `Read` and will simply borrow this
1061	/// current reader.
1062	///
1063	/// # Examples
1064	///
1065	/// [`File`]s implement `Read`:
1066	///
1067	/// [`File`]: crate::fs::File
1068	///
1069	/// ```no_run
1070	/// use std::io;
1071	/// use std::io::Read;
1072	/// use std::fs::File;
1073	///
1074	/// fn main() -> io::Result<()> {
1075	/// let mut f = File::open("foo.txt")?;
1076	/// let mut buffer = Vec::new();
1077	/// let mut other_buffer = Vec::new();
1078	///
1079	/// {
1080	/// let reference = f.by_ref();
1081	///
1082	/// // read at most 5 bytes
1083	/// reference.take(`5`).read_to_end(&mut buffer)?;
1084	///
1085	/// } // drop our &mut reference so we can use f again
1086	///
1087	/// // original file still usable, read the rest
1088	/// f.read_to_end(&mut other_buffer)?;
1089	/// Ok(())
1090	/// }
1091	/// ```
1092	#[stable(feature = "rust1", since = "1.0.0")]
1093	fn by_ref(&mut self) -> &mut Self
1094	where
1095	Self: Sized,
1096	{
1097	self
1098	}
1099
1100	/// Transforms this `Read` instance to an [`Iterator`] over its bytes.
1101	///
1102	/// The returned type implements [`Iterator`] where the [`Item`] is
1103	/// <code>[Result]<[u8], [io::Error]></code>.
1104	/// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
1105	/// otherwise. EOF is mapped to returning [`None`] from this iterator.
1106	///
1107	/// The default implementation calls `read` for each byte,
1108	/// which can be very inefficient for data that's not in memory,
1109	/// such as [`File`]. Consider using a [`BufReader`] in such cases.
1110	///
1111	/// # Examples
1112	///
1113	/// [`File`]s implement `Read`:
1114	///
1115	/// [`Item`]: Iterator::Item
1116	/// [`File`]: crate::fs::File "fs::File"
1117	/// [Result]: crate::result::Result "Result"
1118	/// [io::Error]: self::Error "io::Error"
1119	///
1120	/// ```no_run
1121	/// use std::io;
1122	/// use std::io::prelude::*;
1123	/// use std::io::BufReader;
1124	/// use std::fs::File;
1125	///
1126	/// fn main() -> io::Result<()> {
1127	/// let f = BufReader::new(File::open("foo.txt")?);
1128	///
1129	/// for byte in f.bytes() {
1130	/// println!("{}", byte?);
1131	/// }
1132	/// Ok(())
1133	/// }
1134	/// ```
1135	#[stable(feature = "rust1", since = "1.0.0")]
1136	fn bytes(self) -> Bytes<Self>
1137	where
1138	Self: Sized,
1139	{
1140	Bytes { inner: self }
1141	}
1142
1143	/// Creates an adapter which will chain this stream with another.
1144	///
1145	/// The returned `Read` instance will first read all bytes from this object
1146	/// until EOF is encountered. Afterwards the output is equivalent to the
1147	/// output of `next`.
1148	///
1149	/// # Examples
1150	///
1151	/// [`File`]s implement `Read`:
1152	///
1153	/// [`File`]: crate::fs::File
1154	///
1155	/// ```no_run
1156	/// use std::io;
1157	/// use std::io::prelude::*;
1158	/// use std::fs::File;
1159	///
1160	/// fn main() -> io::Result<()> {
1161	/// let f1 = File::open("foo.txt")?;
1162	/// let f2 = File::open("bar.txt")?;
1163	///
1164	/// let mut handle = f1.chain(f2);
1165	/// let mut buffer = String::new();
1166	///
1167	/// // read the value into a String. We could use any Read method here,
1168	/// // this is just one example.
1169	/// handle.read_to_string(&mut buffer)?;
1170	/// Ok(())
1171	/// }
1172	/// ```
1173	#[stable(feature = "rust1", since = "1.0.0")]
1174	fn chain<R: Read>(self, next: R) -> Chain<Self, R>
1175	where
1176	Self: Sized,
1177	{
1178	Chain { first: self, second: next, done_first: `false` }
1179	}
1180
1181	/// Creates an adapter which will read at most `limit` bytes from it.
1182	///
1183	/// This function returns a new instance of `Read` which will read at most
1184	/// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
1185	/// read errors will not count towards the number of bytes read and future
1186	/// calls to [`read()`] may succeed.
1187	///
1188	/// # Examples
1189	///
1190	/// [`File`]s implement `Read`:
1191	///
1192	/// [`File`]: crate::fs::File
1193	/// [`Ok(0)`]: Ok
1194	/// [`read()`]: Read::read
1195	///
1196	/// ```no_run
1197	/// use std::io;
1198	/// use std::io::prelude::*;
1199	/// use std::fs::File;
1200	///
1201	/// fn main() -> io::Result<()> {
1202	/// let f = File::open("foo.txt")?;
1203	/// let mut buffer = [`0`; `5`];
1204	///
1205	/// // read at most five bytes
1206	/// let mut handle = f.take(`5`);
1207	///
1208	/// handle.read(&mut buffer)?;
1209	/// Ok(())
1210	/// }
1211	/// ```
1212	#[stable(feature = "rust1", since = "1.0.0")]
1213	fn take(self, limit: u64) -> Take<Self>
1214	where
1215	Self: Sized,
1216	{
1217	Take { inner: self, limit }
1218	}
1219	}
1220
1221	/// Reads all bytes from a [reader][Read] into a new [`String`].
1222	///
1223	/// This is a convenience function for [`Read::read_to_string`]. Using this
1224	/// function avoids having to create a variable first and provides more type
1225	/// safety since you can only get the buffer out if there were no errors. (If you
1226	/// use [`Read::read_to_string`] you have to remember to check whether the read
1227	/// succeeded because otherwise your buffer will be empty or only partially full.)
1228	///
1229	/// # Performance
1230	///
1231	/// The downside of this function's increased ease of use and type safety is
1232	/// that it gives you less control over performance. For example, you can't
1233	/// pre-allocate memory like you can using [`String::with_capacity`] and
1234	/// [`Read::read_to_string`]. Also, you can't re-use the buffer if an error
1235	/// occurs while reading.
1236	///
1237	/// In many cases, this function's performance will be adequate and the ease of use
1238	/// and type safety tradeoffs will be worth it. However, there are cases where you
1239	/// need more control over performance, and in those cases you should definitely use
1240	/// [`Read::read_to_string`] directly.
1241	///
1242	/// Note that in some special cases, such as when reading files, this function will
1243	/// pre-allocate memory based on the size of the input it is reading. In those
1244	/// cases, the performance should be as good as if you had used
1245	/// [`Read::read_to_string`] with a manually pre-allocated buffer.
1246	///
1247	/// # Errors
1248	///
1249	/// This function forces you to handle errors because the output (the `String`)
1250	/// is wrapped in a [`Result`]. See [`Read::read_to_string`] for the errors
1251	/// that can occur. If any error occurs, you will get an [`Err`], so you
1252	/// don't have to worry about your buffer being empty or partially full.
1253	///
1254	/// # Examples
1255	///
1256	/// ```no_run
1257	/// # use std::io;
1258	/// fn main() -> io::Result<()> {
1259	/// let stdin = io::read_to_string(io::stdin())?;
1260	/// println!("Stdin was:");
1261	/// println!("{stdin}");
1262	/// Ok(())
1263	/// }
1264	/// ```
1265	#[stable(feature = "io_read_to_string", since = "1.65.0")]
1266	pub fn read_to_string<R: Read>(mut reader: R) -> Result<String> {
1267	let mut buf: String = String::new();
1268	reader.read_to_string(&mut buf)?;
1269	Ok(buf)
1270	}
1271
1272	/// A buffer type used with `Read::read_vectored`.
1273	///
1274	/// It is semantically a wrapper around a `&mut [u8]`, but is guaranteed to be
1275	/// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1276	/// Windows.
1277	#[stable(feature = "iovec", since = "1.36.0")]
1278	#[repr(transparent)]
1279	pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
1280
1281	#[stable(feature = "iovec_send_sync", since = "1.44.0")]
1282	unsafe impl<'a> Send for IoSliceMut<'a> {}
1283
1284	#[stable(feature = "iovec_send_sync", since = "1.44.0")]
1285	unsafe impl<'a> Sync for IoSliceMut<'a> {}
1286
1287	#[stable(feature = "iovec", since = "1.36.0")]
1288	impl<'a> fmt::Debug for IoSliceMut<'a> {
1289	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1290	fmt::Debug::fmt(self.0.as_slice(), f:fmt)
1291	}
1292	}
1293
1294	impl<'a> IoSliceMut<'a> {
1295	/// Creates a new `IoSliceMut` wrapping a byte slice.
1296	///
1297	/// # Panics
1298	///
1299	/// Panics on Windows if the slice is larger than 4GB.
1300	#[stable(feature = "iovec", since = "1.36.0")]
1301	#[inline]
1302	pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
1303	IoSliceMut(sys::io::IoSliceMut::new(buf))
1304	}
1305
1306	/// Advance the internal cursor of the slice.
1307	///
1308	/// Also see [`IoSliceMut::advance_slices`] to advance the cursors of
1309	/// multiple buffers.
1310	///
1311	/// # Panics
1312	///
1313	/// Panics when trying to advance beyond the end of the slice.
1314	///
1315	/// # Examples
1316	///
1317	/// ```
1318	/// use std::io::IoSliceMut;
1319	/// use std::ops::Deref;
1320	///
1321	/// let mut data = [`1`; `8`];
1322	/// let mut buf = IoSliceMut::new(&mut data);
1323	///
1324	/// // Mark 3 bytes as read.
1325	/// buf.advance(`3`);
1326	/// assert_eq!(buf.deref(), [`1`; `5`].as_ref());
1327	/// ```
1328	#[stable(feature = "io_slice_advance", since = "1.81.0")]
1329	#[inline]
1330	pub fn advance(&mut self, n: usize) {
1331	self.0.advance(n)
1332	}
1333
1334	/// Advance a slice of slices.
1335	///
1336	/// Shrinks the slice to remove any `IoSliceMut`s that are fully advanced over.
1337	/// If the cursor ends up in the middle of an `IoSliceMut`, it is modified
1338	/// to start at that cursor.
1339	///
1340	/// For example, if we have a slice of two 8-byte `IoSliceMut`s, and we advance by 10 bytes,
1341	/// the result will only include the second `IoSliceMut`, advanced by 2 bytes.
1342	///
1343	/// # Panics
1344	///
1345	/// Panics when trying to advance beyond the end of the slices.
1346	///
1347	/// # Examples
1348	///
1349	/// ```
1350	/// use std::io::IoSliceMut;
1351	/// use std::ops::Deref;
1352	///
1353	/// let mut buf1 = [`1`; `8`];
1354	/// let mut buf2 = [`2`; `16`];
1355	/// let mut buf3 = [`3`; `8`];
1356	/// let mut bufs = &mut [
1357	/// IoSliceMut::new(&mut buf1),
1358	/// IoSliceMut::new(&mut buf2),
1359	/// IoSliceMut::new(&mut buf3),
1360	/// ][..];
1361	///
1362	/// // Mark 10 bytes as read.
1363	/// IoSliceMut::advance_slices(&mut bufs, `10`);
1364	/// assert_eq!(bufs[`0`].deref(), [`2`; `14`].as_ref());
1365	/// assert_eq!(bufs[`1`].deref(), [`3`; `8`].as_ref());
1366	/// ```
1367	#[stable(feature = "io_slice_advance", since = "1.81.0")]
1368	#[inline]
1369	pub fn advance_slices(bufs: &mut &mut [IoSliceMut<'a>], n: usize) {
1370	// Number of buffers to remove.
1371	let mut remove = `0`;
1372	// Remaining length before reaching n.
1373	let mut left = n;
1374	for buf in bufs.iter() {
1375	if let Some(remainder) = left.checked_sub(buf.len()) {
1376	left = remainder;
1377	remove += `1`;
1378	} else {
1379	break;
1380	}
1381	}
1382
1383	bufs = &mut* take(bufs)[remove..];
1384	if bufs.is_empty() {
1385	assert!(left == `0`, "advancing io slices beyond their length");
1386	} else {
1387	bufs[`0`].advance(left);
1388	}
1389	}
1390
1391	/// Get the underlying bytes as a mutable slice with the original lifetime.
1392	///
1393	/// # Examples
1394	///
1395	/// ```
1396	/// #![feature(io_slice_as_bytes)]
1397	/// use std::io::IoSliceMut;
1398	///
1399	/// let mut data = *b"abcdef";
1400	/// let io_slice = IoSliceMut::new(&mut data);
1401	/// io_slice.into_slice()[`0`] = b'A';
1402	///
1403	/// assert_eq!(&data, b"Abcdef");
1404	/// ```
1405	#[unstable(feature = "io_slice_as_bytes", issue = "132818")]
1406	pub const fn into_slice(self) -> &'a mut [u8] {
1407	self.0.into_slice()
1408	}
1409	}
1410
1411	#[stable(feature = "iovec", since = "1.36.0")]
1412	impl<'a> Deref for IoSliceMut<'a> {
1413	type Target = [u8];
1414
1415	#[inline]
1416	fn deref(&self) -> &[u8] {
1417	self.0.as_slice()
1418	}
1419	}
1420
1421	#[stable(feature = "iovec", since = "1.36.0")]
1422	impl<'a> DerefMut for IoSliceMut<'a> {
1423	#[inline]
1424	fn deref_mut(&mut self) -> &mut [u8] {
1425	self.0.as_mut_slice()
1426	}
1427	}
1428
1429	/// A buffer type used with `Write::write_vectored`.
1430	///
1431	/// It is semantically a wrapper around a `&[u8]`, but is guaranteed to be
1432	/// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1433	/// Windows.
1434	#[stable(feature = "iovec", since = "1.36.0")]
1435	#[derive(Copy, Clone)]
1436	#[repr(transparent)]
1437	pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
1438
1439	#[stable(feature = "iovec_send_sync", since = "1.44.0")]
1440	unsafe impl<'a> Send for IoSlice<'a> {}
1441
1442	#[stable(feature = "iovec_send_sync", since = "1.44.0")]
1443	unsafe impl<'a> Sync for IoSlice<'a> {}
1444
1445	#[stable(feature = "iovec", since = "1.36.0")]
1446	impl<'a> fmt::Debug for IoSlice<'a> {
1447	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1448	fmt::Debug::fmt(self.0.as_slice(), f:fmt)
1449	}
1450	}
1451
1452	impl<'a> IoSlice<'a> {
1453	/// Creates a new `IoSlice` wrapping a byte slice.
1454	///
1455	/// # Panics
1456	///
1457	/// Panics on Windows if the slice is larger than 4GB.
1458	#[stable(feature = "iovec", since = "1.36.0")]
1459	#[must_use]
1460	#[inline]
1461	pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
1462	IoSlice(sys::io::IoSlice::new(buf))
1463	}
1464
1465	/// Advance the internal cursor of the slice.
1466	///
1467	/// Also see [`IoSlice::advance_slices`] to advance the cursors of multiple
1468	/// buffers.
1469	///
1470	/// # Panics
1471	///
1472	/// Panics when trying to advance beyond the end of the slice.
1473	///
1474	/// # Examples
1475	///
1476	/// ```
1477	/// use std::io::IoSlice;
1478	/// use std::ops::Deref;
1479	///
1480	/// let data = [`1`; `8`];
1481	/// let mut buf = IoSlice::new(&data);
1482	///
1483	/// // Mark 3 bytes as read.
1484	/// buf.advance(`3`);
1485	/// assert_eq!(buf.deref(), [`1`; `5`].as_ref());
1486	/// ```
1487	#[stable(feature = "io_slice_advance", since = "1.81.0")]
1488	#[inline]
1489	pub fn advance(&mut self, n: usize) {
1490	self.0.advance(n)
1491	}
1492
1493	/// Advance a slice of slices.
1494	///
1495	/// Shrinks the slice to remove any `IoSlice`s that are fully advanced over.
1496	/// If the cursor ends up in the middle of an `IoSlice`, it is modified
1497	/// to start at that cursor.
1498	///
1499	/// For example, if we have a slice of two 8-byte `IoSlice`s, and we advance by 10 bytes,
1500	/// the result will only include the second `IoSlice`, advanced by 2 bytes.
1501	///
1502	/// # Panics
1503	///
1504	/// Panics when trying to advance beyond the end of the slices.
1505	///
1506	/// # Examples
1507	///
1508	/// ```
1509	/// use std::io::IoSlice;
1510	/// use std::ops::Deref;
1511	///
1512	/// let buf1 = [`1`; `8`];
1513	/// let buf2 = [`2`; `16`];
1514	/// let buf3 = [`3`; `8`];
1515	/// let mut bufs = &mut [
1516	/// IoSlice::new(&buf1),
1517	/// IoSlice::new(&buf2),
1518	/// IoSlice::new(&buf3),
1519	/// ][..];
1520	///
1521	/// // Mark 10 bytes as written.
1522	/// IoSlice::advance_slices(&mut bufs, `10`);
1523	/// assert_eq!(bufs[`0`].deref(), [`2`; `14`].as_ref());
1524	/// assert_eq!(bufs[`1`].deref(), [`3`; `8`].as_ref());
1525	#[stable(feature = "io_slice_advance", since = "1.81.0")]
1526	#[inline]
1527	pub fn advance_slices(bufs: &mut &mut [IoSlice<'a>], n: usize) {
1528	// Number of buffers to remove.
1529	let mut remove = `0`;
1530	// Remaining length before reaching n. This prevents overflow
1531	// that could happen if the length of slices in `bufs` were instead
1532	// accumulated. Those slice may be aliased and, if they are large
1533	// enough, their added length may overflow a `usize`.
1534	let mut left = n;
1535	for buf in bufs.iter() {
1536	if let Some(remainder) = left.checked_sub(buf.len()) {
1537	left = remainder;
1538	remove += `1`;
1539	} else {
1540	break;
1541	}
1542	}
1543
1544	bufs = &mut* take(bufs)[remove..];
1545	if bufs.is_empty() {
1546	assert!(left == `0`, "advancing io slices beyond their length");
1547	} else {
1548	bufs[`0`].advance(left);
1549	}
1550	}
1551
1552	/// Get the underlying bytes as a slice with the original lifetime.
1553	///
1554	/// This doesn't borrow from `self`, so is less restrictive than calling
1555	/// `.deref()`, which does.
1556	///
1557	/// # Examples
1558	///
1559	/// ```
1560	/// #![feature(io_slice_as_bytes)]
1561	/// use std::io::IoSlice;
1562	///
1563	/// let data = b"abcdef";
1564	///
1565	/// let mut io_slice = IoSlice::new(data);
1566	/// let tail = &io_slice.as_slice()[`3`..];
1567	///
1568	/// // This works because `tail` doesn't borrow `io_slice`
1569	/// io_slice = IoSlice::new(tail);
1570	///
1571	/// assert_eq!(io_slice.as_slice(), b"def");
1572	/// ```
1573	#[unstable(feature = "io_slice_as_bytes", issue = "132818")]
1574	pub const fn as_slice(self) -> &'a [u8] {
1575	self.0.as_slice()
1576	}
1577	}
1578
1579	#[stable(feature = "iovec", since = "1.36.0")]
1580	impl<'a> Deref for IoSlice<'a> {
1581	type Target = [u8];
1582
1583	#[inline]
1584	fn deref(&self) -> &[u8] {
1585	self.0.as_slice()
1586	}
1587	}
1588
1589	/// A trait for objects which are byte-oriented sinks.
1590	///
1591	/// Implementors of the `Write` trait are sometimes called 'writers'.
1592	///
1593	/// Writers are defined by two required methods, [`write`] and [`flush`]:
1594	///
1595	/// The* [`write`] method will attempt to write some data into the object,
1596	/// returning how many bytes were successfully written.
1597	///
1598	/// The* [`flush`] method is useful for adapters and explicit buffers
1599	/// themselves for ensuring that all buffered data has been pushed out to the
1600	/// 'true sink'.
1601	///
1602	/// Writers are intended to be composable with one another. Many implementors
1603	/// throughout [`std::io`] take and provide types which implement the `Write`
1604	/// trait.
1605	///
1606	/// [`write`]: Write::write
1607	/// [`flush`]: Write::flush
1608	/// [`std::io`]: self
1609	///
1610	/// # Examples
1611	///
1612	/// ```no_run
1613	/// use std::io::prelude::*;
1614	/// use std::fs::File;
1615	///
1616	/// fn main() -> std::io::Result<()> {
1617	/// let data = b"some bytes";
1618	///
1619	/// let mut pos = `0`;
1620	/// let mut buffer = File::create("foo.txt")?;
1621	///
1622	/// while pos < data.len() {
1623	/// let bytes_written = buffer.write(&data[pos..])?;
1624	/// pos += bytes_written;
1625	/// }
1626	/// Ok(())
1627	/// }
1628	/// ```
1629	///
1630	/// The trait also provides convenience methods like [`write_all`], which calls
1631	/// `write` in a loop until its entire input has been written.
1632	///
1633	/// [`write_all`]: Write::write_all
1634	#[stable(feature = "rust1", since = "1.0.0")]
1635	#[doc(notable_trait)]
1636	#[cfg_attr(not(test), rustc_diagnostic_item = "IoWrite")]
1637	pub trait Write {
1638	/// Writes a buffer into this writer, returning how many bytes were written.
1639	///
1640	/// This function will attempt to write the entire contents of `buf`, but
1641	/// the entire write might not succeed, or the write may also generate an
1642	/// error. Typically, a call to `write` represents one attempt to write to
1643	/// any wrapped object.
1644	///
1645	/// Calls to `write` are not guaranteed to block waiting for data to be
1646	/// written, and a write which would otherwise block can be indicated through
1647	/// an [`Err`] variant.
1648	///
1649	/// If this method consumed `n > 0` bytes of `buf` it must return [`Ok(n)`].
1650	/// If the return value is `Ok(n)` then `n` must satisfy `n <= buf.len()`.
1651	/// A return value of `Ok(0)` typically means that the underlying object is
1652	/// no longer able to accept bytes and will likely not be able to in the
1653	/// future as well, or that the buffer provided is empty.
1654	///
1655	/// # Errors
1656	///
1657	/// Each call to `write` may generate an I/O error indicating that the
1658	/// operation could not be completed. If an error is returned then no bytes
1659	/// in the buffer were written to this writer.
1660	///
1661	/// It is not* considered an error if the entire buffer could not be*
1662	/// written to this writer.
1663	///
1664	/// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
1665	/// write operation should be retried if there is nothing else to do.
1666	///
1667	/// # Examples
1668	///
1669	/// ```no_run
1670	/// use std::io::prelude::*;
1671	/// use std::fs::File;
1672	///
1673	/// fn main() -> std::io::Result<()> {
1674	/// let mut buffer = File::create("foo.txt")?;
1675	///
1676	/// // Writes some prefix of the byte string, not necessarily all of it.
1677	/// buffer.write(b"some bytes")?;
1678	/// Ok(())
1679	/// }
1680	/// ```
1681	///
1682	/// [`Ok(n)`]: Ok
1683	#[stable(feature = "rust1", since = "1.0.0")]
1684	fn write(&mut self, buf: &[u8]) -> Result<usize>;
1685
1686	/// Like [`write`], except that it writes from a slice of buffers.
1687	///
1688	/// Data is copied from each buffer in order, with the final buffer
1689	/// read from possibly being only partially consumed. This method must
1690	/// behave as a call to [`write`] with the buffers concatenated would.
1691	///
1692	/// The default implementation calls [`write`] with either the first nonempty
1693	/// buffer provided, or an empty one if none exists.
1694	///
1695	/// # Examples
1696	///
1697	/// ```no_run
1698	/// use std::io::IoSlice;
1699	/// use std::io::prelude::*;
1700	/// use std::fs::File;
1701	///
1702	/// fn main() -> std::io::Result<()> {
1703	/// let data1 = [`1`; `8`];
1704	/// let data2 = [`15`; `8`];
1705	/// let io_slice1 = IoSlice::new(&data1);
1706	/// let io_slice2 = IoSlice::new(&data2);
1707	///
1708	/// let mut buffer = File::create("foo.txt")?;
1709	///
1710	/// // Writes some prefix of the byte string, not necessarily all of it.
1711	/// buffer.write_vectored(&[io_slice1, io_slice2])?;
1712	/// Ok(())
1713	/// }
1714	/// ```
1715	///
1716	/// [`write`]: Write::write
1717	#[stable(feature = "iovec", since = "1.36.0")]
1718	fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
1719	default_write_vectored(\|b\| self.write(b), bufs)
1720	}
1721
1722	/// Determines if this `Write`r has an efficient [`write_vectored`]
1723	/// implementation.
1724	///
1725	/// If a `Write`r does not override the default [`write_vectored`]
1726	/// implementation, code using it may want to avoid the method all together
1727	/// and coalesce writes into a single buffer for higher performance.
1728	///
1729	/// The default implementation returns `false`.
1730	///
1731	/// [`write_vectored`]: Write::write_vectored
1732	#[unstable(feature = "can_vector", issue = "69941")]
1733	fn is_write_vectored(&self) -> bool {
1734	`false`
1735	}
1736
1737	/// Flushes this output stream, ensuring that all intermediately buffered
1738	/// contents reach their destination.
1739	///
1740	/// # Errors
1741	///
1742	/// It is considered an error if not all bytes could be written due to
1743	/// I/O errors or EOF being reached.
1744	///
1745	/// # Examples
1746	///
1747	/// ```no_run
1748	/// use std::io::prelude::*;
1749	/// use std::io::BufWriter;
1750	/// use std::fs::File;
1751	///
1752	/// fn main() -> std::io::Result<()> {
1753	/// let mut buffer = BufWriter::new(File::create("foo.txt")?);
1754	///
1755	/// buffer.write_all(b"some bytes")?;
1756	/// buffer.flush()?;
1757	/// Ok(())
1758	/// }
1759	/// ```
1760	#[stable(feature = "rust1", since = "1.0.0")]
1761	fn flush(&mut self) -> Result<()>;
1762
1763	/// Attempts to write an entire buffer into this writer.
1764	///
1765	/// This method will continuously call [`write`] until there is no more data
1766	/// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
1767	/// returned. This method will not return until the entire buffer has been
1768	/// successfully written or such an error occurs. The first error that is
1769	/// not of [`ErrorKind::Interrupted`] kind generated from this method will be
1770	/// returned.
1771	///
1772	/// If the buffer contains no data, this will never call [`write`].
1773	///
1774	/// # Errors
1775	///
1776	/// This function will return the first error of
1777	/// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
1778	///
1779	/// [`write`]: Write::write
1780	///
1781	/// # Examples
1782	///
1783	/// ```no_run
1784	/// use std::io::prelude::*;
1785	/// use std::fs::File;
1786	///
1787	/// fn main() -> std::io::Result<()> {
1788	/// let mut buffer = File::create("foo.txt")?;
1789	///
1790	/// buffer.write_all(b"some bytes")?;
1791	/// Ok(())
1792	/// }
1793	/// ```
1794	#[stable(feature = "rust1", since = "1.0.0")]
1795	fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
1796	while !buf.is_empty() {
1797	match self.write(buf) {
1798	Ok(`0`) => {
1799	return Err(Error::WRITE_ALL_EOF);
1800	}
1801	Ok(n) => buf = &buf[n..],
1802	Err(ref e) if e.is_interrupted() => {}
1803	Err(e) => return Err(e),
1804	}
1805	}
1806	Ok(())
1807	}
1808
1809	/// Attempts to write multiple buffers into this writer.
1810	///
1811	/// This method will continuously call [`write_vectored`] until there is no
1812	/// more data to be written or an error of non-[`ErrorKind::Interrupted`]
1813	/// kind is returned. This method will not return until all buffers have
1814	/// been successfully written or such an error occurs. The first error that
1815	/// is not of [`ErrorKind::Interrupted`] kind generated from this method
1816	/// will be returned.
1817	///
1818	/// If the buffer contains no data, this will never call [`write_vectored`].
1819	///
1820	/// # Notes
1821	///
1822	/// Unlike [`write_vectored`], this takes a mutable* reference to*
1823	/// a slice of [`IoSlice`]s, not an immutable one. That's because we need to
1824	/// modify the slice to keep track of the bytes already written.
1825	///
1826	/// Once this function returns, the contents of `bufs` are unspecified, as
1827	/// this depends on how many calls to [`write_vectored`] were necessary. It is
1828	/// best to understand this function as taking ownership of `bufs` and to
1829	/// not use `bufs` afterwards. The underlying buffers, to which the
1830	/// [`IoSlice`]s point (but not the [`IoSlice`]s themselves), are unchanged and
1831	/// can be reused.
1832	///
1833	/// [`write_vectored`]: Write::write_vectored
1834	///
1835	/// # Examples
1836	///
1837	/// ```
1838	/// #![feature(write_all_vectored)]
1839	/// # fn main() -> std::io::Result<()> {
1840	///
1841	/// use std::io::{Write, IoSlice};
1842	///
1843	/// let mut writer = Vec::new();
1844	/// let bufs = &mut [
1845	/// IoSlice::new(&[`1`]),
1846	/// IoSlice::new(&[`2`, `3`]),
1847	/// IoSlice::new(&[`4`, `5`, `6`]),
1848	/// ];
1849	///
1850	/// writer.write_all_vectored(bufs)?;
1851	/// // Note: the contents of `bufs` is now undefined, see the Notes section.
1852	///
1853	/// assert_eq!(writer, &[`1`, `2`, `3`, `4`, `5`, `6`]);
1854	/// # Ok(()) }
1855	/// ```
1856	#[unstable(feature = "write_all_vectored", issue = "70436")]
1857	fn write_all_vectored(&mut self, mut bufs: &mut [IoSlice<'_>]) -> Result<()> {
1858	// Guarantee that bufs is empty if it contains no data,
1859	// to avoid calling write_vectored if there is no data to be written.
1860	IoSlice::advance_slices(&mut bufs, `0`);
1861	while !bufs.is_empty() {
1862	match self.write_vectored(bufs) {
1863	Ok(`0`) => {
1864	return Err(Error::WRITE_ALL_EOF);
1865	}
1866	Ok(n) => IoSlice::advance_slices(&mut bufs, n),
1867	Err(ref e) if e.is_interrupted() => {}
1868	Err(e) => return Err(e),
1869	}
1870	}
1871	Ok(())
1872	}
1873
1874	/// Writes a formatted string into this writer, returning any error
1875	/// encountered.
1876	///
1877	/// This method is primarily used to interface with the
1878	/// [`format_args!()`] macro, and it is rare that this should
1879	/// explicitly be called. The [`write!()`] macro should be favored to
1880	/// invoke this method instead.
1881	///
1882	/// This function internally uses the [`write_all`] method on
1883	/// this trait and hence will continuously write data so long as no errors
1884	/// are received. This also means that partial writes are not indicated in
1885	/// this signature.
1886	///
1887	/// [`write_all`]: Write::write_all
1888	///
1889	/// # Errors
1890	///
1891	/// This function will return any I/O error reported while formatting.
1892	///
1893	/// # Examples
1894	///
1895	/// ```no_run
1896	/// use std::io::prelude::*;
1897	/// use std::fs::File;
1898	///
1899	/// fn main() -> std::io::Result<()> {
1900	/// let mut buffer = File::create("foo.txt")?;
1901	///
1902	/// // this call
1903	/// write!(buffer, "{:.*}", `2`, `1.234567`)?;
1904	/// // turns into this:
1905	/// buffer.write_fmt(format_args!("{:.*}", `2`, `1.234567`))?;
1906	/// Ok(())
1907	/// }
1908	/// ```
1909	#[stable(feature = "rust1", since = "1.0.0")]
1910	fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> Result<()> {
1911	if let Some(s) = args.as_statically_known_str() {
1912	self.write_all(s.as_bytes())
1913	} else {
1914	default_write_fmt(self, args)
1915	}
1916	}
1917
1918	/// Creates a "by reference" adapter for this instance of `Write`.
1919	///
1920	/// The returned adapter also implements `Write` and will simply borrow this
1921	/// current writer.
1922	///
1923	/// # Examples
1924	///
1925	/// ```no_run
1926	/// use std::io::Write;
1927	/// use std::fs::File;
1928	///
1929	/// fn main() -> std::io::Result<()> {
1930	/// let mut buffer = File::create("foo.txt")?;
1931	///
1932	/// let reference = buffer.by_ref();
1933	///
1934	/// // we can use reference just like our original buffer
1935	/// reference.write_all(b"some bytes")?;
1936	/// Ok(())
1937	/// }
1938	/// ```
1939	#[stable(feature = "rust1", since = "1.0.0")]
1940	fn by_ref(&mut self) -> &mut Self
1941	where
1942	Self: Sized,
1943	{
1944	self
1945	}
1946	}
1947
1948	/// The `Seek` trait provides a cursor which can be moved within a stream of
1949	/// bytes.
1950	///
1951	/// The stream typically has a fixed size, allowing seeking relative to either
1952	/// end or the current offset.
1953	///
1954	/// # Examples
1955	///
1956	/// [`File`]s implement `Seek`:
1957	///
1958	/// [`File`]: crate::fs::File
1959	///
1960	/// ```no_run
1961	/// use std::io;
1962	/// use std::io::prelude::*;
1963	/// use std::fs::File;
1964	/// use std::io::SeekFrom;
1965	///
1966	/// fn main() -> io::Result<()> {
1967	/// let mut f = File::open("foo.txt")?;
1968	///
1969	/// // move the cursor 42 bytes from the start of the file
1970	/// f.seek(SeekFrom::Start(`42`))?;
1971	/// Ok(())
1972	/// }
1973	/// ```
1974	#[stable(feature = "rust1", since = "1.0.0")]
1975	#[cfg_attr(not(test), rustc_diagnostic_item = "IoSeek")]
1976	pub trait Seek {
1977	/// Seek to an offset, in bytes, in a stream.
1978	///
1979	/// A seek beyond the end of a stream is allowed, but behavior is defined
1980	/// by the implementation.
1981	///
1982	/// If the seek operation completed successfully,
1983	/// this method returns the new position from the start of the stream.
1984	/// That position can be used later with [`SeekFrom::Start`].
1985	///
1986	/// # Errors
1987	///
1988	/// Seeking can fail, for example because it might involve flushing a buffer.
1989	///
1990	/// Seeking to a negative offset is considered an error.
1991	#[stable(feature = "rust1", since = "1.0.0")]
1992	fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1993
1994	/// Rewind to the beginning of a stream.
1995	///
1996	/// This is a convenience method, equivalent to `seek(SeekFrom::Start(0))`.
1997	///
1998	/// # Errors
1999	///
2000	/// Rewinding can fail, for example because it might involve flushing a buffer.
2001	///
2002	/// # Example
2003	///
2004	/// ```no_run
2005	/// use std::io::{Read, Seek, Write};
2006	/// use std::fs::OpenOptions;
2007	///
2008	/// let mut f = OpenOptions::new()
2009	/// .write(`true`)
2010	/// .read(`true`)
2011	/// .create(`true`)
2012	/// .open("foo.txt")?;
2013	///
2014	/// let hello = "Hello!`\n`";
2015	/// write!(f, "{hello}")?;
2016	/// f.rewind()?;
2017	///
2018	/// let mut buf = String::new();
2019	/// f.read_to_string(&mut buf)?;
2020	/// assert_eq!(&buf, hello);
2021	/// # std::io::Result::Ok(())
2022	/// ```
2023	#[stable(feature = "seek_rewind", since = "1.55.0")]
2024	fn rewind(&mut self) -> Result<()> {
2025	self.seek(SeekFrom::Start(`0`))?;
2026	Ok(())
2027	}
2028
2029	/// Returns the length of this stream (in bytes).
2030	///
2031	/// This method is implemented using up to three seek operations. If this
2032	/// method returns successfully, the seek position is unchanged (i.e. the
2033	/// position before calling this method is the same as afterwards).
2034	/// However, if this method returns an error, the seek position is
2035	/// unspecified.
2036	///
2037	/// If you need to obtain the length of many* streams and you don't care*
2038	/// about the seek position afterwards, you can reduce the number of seek
2039	/// operations by simply calling `seek(SeekFrom::End(0))` and using its
2040	/// return value (it is also the stream length).
2041	///
2042	/// Note that length of a stream can change over time (for example, when
2043	/// data is appended to a file). So calling this method multiple times does
2044	/// not necessarily return the same length each time.
2045	///
2046	/// # Example
2047	///
2048	/// ```no_run
2049	/// #![feature(seek_stream_len)]
2050	/// use std::{
2051	/// io::{self, Seek},
2052	/// fs::File,
2053	/// };
2054	///
2055	/// fn main() -> io::Result<()> {
2056	/// let mut f = File::open("foo.txt")?;
2057	///
2058	/// let len = f.stream_len()?;
2059	/// println!("The file is currently {len} bytes long");
2060	/// Ok(())
2061	/// }
2062	/// ```
2063	#[unstable(feature = "seek_stream_len", issue = "59359")]
2064	fn stream_len(&mut self) -> Result<u64> {
2065	let old_pos = self.stream_position()?;
2066	let len = self.seek(SeekFrom::End(`0`))?;
2067
2068	// Avoid seeking a third time when we were already at the end of the
2069	// stream. The branch is usually way cheaper than a seek operation.
2070	if old_pos != len {
2071	self.seek(SeekFrom::Start(old_pos))?;
2072	}
2073
2074	Ok(len)
2075	}
2076
2077	/// Returns the current seek position from the start of the stream.
2078	///
2079	/// This is equivalent to `self.seek(SeekFrom::Current(0))`.
2080	///
2081	/// # Example
2082	///
2083	/// ```no_run
2084	/// use std::{
2085	/// io::{self, BufRead, BufReader, Seek},
2086	/// fs::File,
2087	/// };
2088	///
2089	/// fn main() -> io::Result<()> {
2090	/// let mut f = BufReader::new(File::open("foo.txt")?);
2091	///
2092	/// let before = f.stream_position()?;
2093	/// f.read_line(&mut String::new())?;
2094	/// let after = f.stream_position()?;
2095	///
2096	/// println!("The first line was {} bytes long", after - before);
2097	/// Ok(())
2098	/// }
2099	/// ```
2100	#[stable(feature = "seek_convenience", since = "1.51.0")]
2101	fn stream_position(&mut self) -> Result<u64> {
2102	self.seek(SeekFrom::Current(`0`))
2103	}
2104
2105	/// Seeks relative to the current position.
2106	///
2107	/// This is equivalent to `self.seek(SeekFrom::Current(offset))` but
2108	/// doesn't return the new position which can allow some implementations
2109	/// such as [`BufReader`] to perform more efficient seeks.
2110	///
2111	/// # Example
2112	///
2113	/// ```no_run
2114	/// use std::{
2115	/// io::{self, Seek},
2116	/// fs::File,
2117	/// };
2118	///
2119	/// fn main() -> io::Result<()> {
2120	/// let mut f = File::open("foo.txt")?;
2121	/// f.seek_relative(`10`)?;
2122	/// assert_eq!(f.stream_position()?, `10`);
2123	/// Ok(())
2124	/// }
2125	/// ```
2126	///
2127	/// [`BufReader`]: crate::io::BufReader
2128	#[stable(feature = "seek_seek_relative", since = "1.80.0")]
2129	fn seek_relative(&mut self, offset: i64) -> Result<()> {
2130	self.seek(SeekFrom::Current(offset))?;
2131	Ok(())
2132	}
2133	}
2134
2135	/// Enumeration of possible methods to seek within an I/O object.
2136	///
2137	/// It is used by the [`Seek`] trait.
2138	#[derive(Copy, PartialEq, Eq, Clone, Debug)]
2139	#[stable(feature = "rust1", since = "1.0.0")]
2140	#[cfg_attr(not(test), rustc_diagnostic_item = "SeekFrom")]
2141	pub enum SeekFrom {
2142	/// Sets the offset to the provided number of bytes.
2143	#[stable(feature = "rust1", since = "1.0.0")]
2144	Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
2145
2146	/// Sets the offset to the size of this object plus the specified number of
2147	/// bytes.
2148	///
2149	/// It is possible to seek beyond the end of an object, but it's an error to
2150	/// seek before byte 0.
2151	#[stable(feature = "rust1", since = "1.0.0")]
2152	End(#[stable(feature = "rust1", since = "1.0.0")] i64),
2153
2154	/// Sets the offset to the current position plus the specified number of
2155	/// bytes.
2156	///
2157	/// It is possible to seek beyond the end of an object, but it's an error to
2158	/// seek before byte 0.
2159	#[stable(feature = "rust1", since = "1.0.0")]
2160	Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
2161	}
2162
2163	fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> Result<usize> {
2164	let mut read = `0`;
2165	loop {
2166	let (done, used) = {
2167	let available = match r.fill_buf() {
2168	Ok(n) => n,
2169	Err(ref e) if e.is_interrupted() => continue,
2170	Err(e) => return Err(e),
2171	};
2172	match memchr::memchr(delim, available) {
2173	Some(i) => {
2174	buf.extend_from_slice(&available[..=i]);
2175	(`true`, i + `1`)
2176	}
2177	None => {
2178	buf.extend_from_slice(available);
2179	(`false`, available.len())
2180	}
2181	}
2182	};
2183	r.consume(used);
2184	read += used;
2185	if done \|\| used == `0` {
2186	return Ok(read);
2187	}
2188	}
2189	}
2190
2191	fn skip_until<R: BufRead + ?Sized>(r: &mut R, delim: u8) -> Result<usize> {
2192	let mut read: usize = `0`;
2193	loop {
2194	let (done: bool, used: usize) = {
2195	let available: &[u8] = match r.fill_buf() {
2196	Ok(n: &[u8]) => n,
2197	Err(ref e: &Error) if e.kind() == ErrorKind::Interrupted => continue,
2198	Err(e: Error) => return Err(e),
2199	};
2200	match memchr::memchr(x:delim, text:available) {
2201	Some(i: usize) => (`true`, i + `1`),
2202	None => (`false`, available.len()),
2203	}
2204	};
2205	r.consume(amount:used);
2206	read += used;
2207	if done \|\| used == `0` {
2208	return Ok(read);
2209	}
2210	}
2211	}
2212
2213	/// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
2214	/// to perform extra ways of reading.
2215	///
2216	/// For example, reading line-by-line is inefficient without using a buffer, so
2217	/// if you want to read by line, you'll need `BufRead`, which includes a
2218	/// [`read_line`] method as well as a [`lines`] iterator.
2219	///
2220	/// # Examples
2221	///
2222	/// A locked standard input implements `BufRead`:
2223	///
2224	/// ```no_run
2225	/// use std::io;
2226	/// use std::io::prelude::*;
2227	///
2228	/// let stdin = io::stdin();
2229	/// for line in stdin.lock().lines() {
2230	/// println!("{}", line?);
2231	/// }
2232	/// # std::io::Result::Ok(())
2233	/// ```
2234	///
2235	/// If you have something that implements [`Read`], you can use the [`BufReader`
2236	/// type][`BufReader`] to turn it into a `BufRead`.
2237	///
2238	/// For example, [`File`] implements [`Read`], but not `BufRead`.
2239	/// [`BufReader`] to the rescue!
2240	///
2241	/// [`File`]: crate::fs::File
2242	/// [`read_line`]: BufRead::read_line
2243	/// [`lines`]: BufRead::lines
2244	///
2245	/// ```no_run
2246	/// use std::io::{self, BufReader};
2247	/// use std::io::prelude::*;
2248	/// use std::fs::File;
2249	///
2250	/// fn main() -> io::Result<()> {
2251	/// let f = File::open("foo.txt")?;
2252	/// let f = BufReader::new(f);
2253	///
2254	/// for line in f.lines() {
2255	/// let line = line?;
2256	/// println!("{line}");
2257	/// }
2258	///
2259	/// Ok(())
2260	/// }
2261	/// ```
2262	#[stable(feature = "rust1", since = "1.0.0")]
2263	#[cfg_attr(not(test), rustc_diagnostic_item = "IoBufRead")]
2264	pub trait BufRead: Read {
2265	/// Returns the contents of the internal buffer, filling it with more data, via `Read` methods, if empty.
2266	///
2267	/// This is a lower-level method and is meant to be used together with [`consume`],
2268	/// which can be used to mark bytes that should not be returned by subsequent calls to `read`.
2269	///
2270	/// [`consume`]: BufRead::consume
2271	///
2272	/// Returns an empty buffer when the stream has reached EOF.
2273	///
2274	/// # Errors
2275	///
2276	/// This function will return an I/O error if a `Read` method was called, but returned an error.
2277	///
2278	/// # Examples
2279	///
2280	/// A locked standard input implements `BufRead`:
2281	///
2282	/// ```no_run
2283	/// use std::io;
2284	/// use std::io::prelude::*;
2285	///
2286	/// let stdin = io::stdin();
2287	/// let mut stdin = stdin.lock();
2288	///
2289	/// let buffer = stdin.fill_buf()?;
2290	///
2291	/// // work with buffer
2292	/// println!("{buffer:?}");
2293	///
2294	/// // mark the bytes we worked with as read
2295	/// let length = buffer.len();
2296	/// stdin.consume(length);
2297	/// # std::io::Result::Ok(())
2298	/// ```
2299	#[stable(feature = "rust1", since = "1.0.0")]
2300	fn fill_buf(&mut self) -> Result<&[u8]>;
2301
2302	/// Marks the given `amount` of additional bytes from the internal buffer as having been read.
2303	/// Subsequent calls to `read` only return bytes that have not been marked as read.
2304	///
2305	/// This is a lower-level method and is meant to be used together with [`fill_buf`],
2306	/// which can be used to fill the internal buffer via `Read` methods.
2307	///
2308	/// It is a logic error if `amount` exceeds the number of unread bytes in the internal buffer, which is returned by [`fill_buf`].
2309	///
2310	/// # Examples
2311	///
2312	/// Since `consume()` is meant to be used with [`fill_buf`],
2313	/// that method's example includes an example of `consume()`.
2314	///
2315	/// [`fill_buf`]: BufRead::fill_buf
2316	#[stable(feature = "rust1", since = "1.0.0")]
2317	fn consume(&mut self, amount: usize);
2318
2319	/// Checks if there is any data left to be `read`.
2320	///
2321	/// This function may fill the buffer to check for data,
2322	/// so this functions returns `Result<bool>`, not `bool`.
2323	///
2324	/// Default implementation calls `fill_buf` and checks that
2325	/// returned slice is empty (which means that there is no data left,
2326	/// since EOF is reached).
2327	///
2328	/// # Errors
2329	///
2330	/// This function will return an I/O error if a `Read` method was called, but returned an error.
2331	///
2332	/// Examples
2333	///
2334	/// ```
2335	/// #![feature(buf_read_has_data_left)]
2336	/// use std::io;
2337	/// use std::io::prelude::*;
2338	///
2339	/// let stdin = io::stdin();
2340	/// let mut stdin = stdin.lock();
2341	///
2342	/// while stdin.has_data_left()? {
2343	/// let mut line = String::new();
2344	/// stdin.read_line(&mut line)?;
2345	/// // work with line
2346	/// println!("{line:?}");
2347	/// }
2348	/// # std::io::Result::Ok(())
2349	/// ```
2350	#[unstable(feature = "buf_read_has_data_left", reason = "recently added", issue = "86423")]
2351	fn has_data_left(&mut self) -> Result<bool> {
2352	self.fill_buf().map(\|b\| !b.is_empty())
2353	}
2354
2355	/// Reads all bytes into `buf` until the delimiter `byte` or EOF is reached.
2356	///
2357	/// This function will read bytes from the underlying stream until the
2358	/// delimiter or EOF is found. Once found, all bytes up to, and including,
2359	/// the delimiter (if found) will be appended to `buf`.
2360	///
2361	/// If successful, this function will return the total number of bytes read.
2362	///
2363	/// This function is blocking and should be used carefully: it is possible for
2364	/// an attacker to continuously send bytes without ever sending the delimiter
2365	/// or EOF.
2366	///
2367	/// # Errors
2368	///
2369	/// This function will ignore all instances of [`ErrorKind::Interrupted`] and
2370	/// will otherwise return any errors returned by [`fill_buf`].
2371	///
2372	/// If an I/O error is encountered then all bytes read so far will be
2373	/// present in `buf` and its length will have been adjusted appropriately.
2374	///
2375	/// [`fill_buf`]: BufRead::fill_buf
2376	///
2377	/// # Examples
2378	///
2379	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2380	/// this example, we use [`Cursor`] to read all the bytes in a byte slice
2381	/// in hyphen delimited segments:
2382	///
2383	/// ```
2384	/// use std::io::{self, BufRead};
2385	///
2386	/// let mut cursor = io::Cursor::new(b"lorem-ipsum");
2387	/// let mut buf = vec![];
2388	///
2389	/// // cursor is at 'l'
2390	/// let num_bytes = cursor.read_until(b'-', &mut buf)
2391	/// .expect("reading from cursor won't fail");
2392	/// assert_eq!(num_bytes, `6`);
2393	/// assert_eq!(buf, b"lorem-");
2394	/// buf.clear();
2395	///
2396	/// // cursor is at 'i'
2397	/// let num_bytes = cursor.read_until(b'-', &mut buf)
2398	/// .expect("reading from cursor won't fail");
2399	/// assert_eq!(num_bytes, `5`);
2400	/// assert_eq!(buf, b"ipsum");
2401	/// buf.clear();
2402	///
2403	/// // cursor is at EOF
2404	/// let num_bytes = cursor.read_until(b'-', &mut buf)
2405	/// .expect("reading from cursor won't fail");
2406	/// assert_eq!(num_bytes, `0`);
2407	/// assert_eq!(buf, b"");
2408	/// ```
2409	#[stable(feature = "rust1", since = "1.0.0")]
2410	fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
2411	read_until(self, byte, buf)
2412	}
2413
2414	/// Skips all bytes until the delimiter `byte` or EOF is reached.
2415	///
2416	/// This function will read (and discard) bytes from the underlying stream until the
2417	/// delimiter or EOF is found.
2418	///
2419	/// If successful, this function will return the total number of bytes read,
2420	/// including the delimiter byte.
2421	///
2422	/// This is useful for efficiently skipping data such as NUL-terminated strings
2423	/// in binary file formats without buffering.
2424	///
2425	/// This function is blocking and should be used carefully: it is possible for
2426	/// an attacker to continuously send bytes without ever sending the delimiter
2427	/// or EOF.
2428	///
2429	/// # Errors
2430	///
2431	/// This function will ignore all instances of [`ErrorKind::Interrupted`] and
2432	/// will otherwise return any errors returned by [`fill_buf`].
2433	///
2434	/// If an I/O error is encountered then all bytes read so far will be
2435	/// present in `buf` and its length will have been adjusted appropriately.
2436	///
2437	/// [`fill_buf`]: BufRead::fill_buf
2438	///
2439	/// # Examples
2440	///
2441	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2442	/// this example, we use [`Cursor`] to read some NUL-terminated information
2443	/// about Ferris from a binary string, skipping the fun fact:
2444	///
2445	/// ```
2446	/// use std::io::{self, BufRead};
2447	///
2448	/// let mut cursor = io::Cursor::new(b"Ferris`\0`Likes long walks on the beach`\0`Crustacean`\0`");
2449	///
2450	/// // read name
2451	/// let mut name = Vec::new();
2452	/// let num_bytes = cursor.read_until(b'`\0`', &mut name)
2453	/// .expect("reading from cursor won't fail");
2454	/// assert_eq!(num_bytes, `7`);
2455	/// assert_eq!(name, b"Ferris`\0`");
2456	///
2457	/// // skip fun fact
2458	/// let num_bytes = cursor.skip_until(b'`\0`')
2459	/// .expect("reading from cursor won't fail");
2460	/// assert_eq!(num_bytes, `30`);
2461	///
2462	/// // read animal type
2463	/// let mut animal = Vec::new();
2464	/// let num_bytes = cursor.read_until(b'`\0`', &mut animal)
2465	/// .expect("reading from cursor won't fail");
2466	/// assert_eq!(num_bytes, `11`);
2467	/// assert_eq!(animal, b"Crustacean`\0`");
2468	/// ```
2469	#[stable(feature = "bufread_skip_until", since = "1.83.0")]
2470	fn skip_until(&mut self, byte: u8) -> Result<usize> {
2471	skip_until(self, byte)
2472	}
2473
2474	/// Reads all bytes until a newline (the `0xA` byte) is reached, and append
2475	/// them to the provided `String` buffer.
2476	///
2477	/// Previous content of the buffer will be preserved. To avoid appending to
2478	/// the buffer, you need to [`clear`] it first.
2479	///
2480	/// This function will read bytes from the underlying stream until the
2481	/// newline delimiter (the `0xA` byte) or EOF is found. Once found, all bytes
2482	/// up to, and including, the delimiter (if found) will be appended to
2483	/// `buf`.
2484	///
2485	/// If successful, this function will return the total number of bytes read.
2486	///
2487	/// If this function returns [`Ok(0)`], the stream has reached EOF.
2488	///
2489	/// This function is blocking and should be used carefully: it is possible for
2490	/// an attacker to continuously send bytes without ever sending a newline
2491	/// or EOF. You can use [`take`] to limit the maximum number of bytes read.
2492	///
2493	/// [`Ok(0)`]: Ok
2494	/// [`clear`]: String::clear
2495	/// [`take`]: crate::io::Read::take
2496	///
2497	/// # Errors
2498	///
2499	/// This function has the same error semantics as [`read_until`] and will
2500	/// also return an error if the read bytes are not valid UTF-8. If an I/O
2501	/// error is encountered then `buf` may contain some bytes already read in
2502	/// the event that all data read so far was valid UTF-8.
2503	///
2504	/// [`read_until`]: BufRead::read_until
2505	///
2506	/// # Examples
2507	///
2508	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2509	/// this example, we use [`Cursor`] to read all the lines in a byte slice:
2510	///
2511	/// ```
2512	/// use std::io::{self, BufRead};
2513	///
2514	/// let mut cursor = io::Cursor::new(b"foo`\n`bar");
2515	/// let mut buf = String::new();
2516	///
2517	/// // cursor is at 'f'
2518	/// let num_bytes = cursor.read_line(&mut buf)
2519	/// .expect("reading from cursor won't fail");
2520	/// assert_eq!(num_bytes, `4`);
2521	/// assert_eq!(buf, "foo`\n`");
2522	/// buf.clear();
2523	///
2524	/// // cursor is at 'b'
2525	/// let num_bytes = cursor.read_line(&mut buf)
2526	/// .expect("reading from cursor won't fail");
2527	/// assert_eq!(num_bytes, `3`);
2528	/// assert_eq!(buf, "bar");
2529	/// buf.clear();
2530	///
2531	/// // cursor is at EOF
2532	/// let num_bytes = cursor.read_line(&mut buf)
2533	/// .expect("reading from cursor won't fail");
2534	/// assert_eq!(num_bytes, `0`);
2535	/// assert_eq!(buf, "");
2536	/// ```
2537	#[stable(feature = "rust1", since = "1.0.0")]
2538	fn read_line(&mut self, buf: &mut String) -> Result<usize> {
2539	// Note that we are not calling the `.read_until` method here, but
2540	// rather our hardcoded implementation. For more details as to why, see
2541	// the comments in `default_read_to_string`.
2542	unsafe { append_to_string(buf, \|b\| read_until(self, b'`\n`', b)) }
2543	}
2544
2545	/// Returns an iterator over the contents of this reader split on the byte
2546	/// `byte`.
2547	///
2548	/// The iterator returned from this function will return instances of
2549	/// <code>[io::Result]<[Vec]\<u8>></code>. Each vector returned will not* have*
2550	/// the delimiter byte at the end.
2551	///
2552	/// This function will yield errors whenever [`read_until`] would have
2553	/// also yielded an error.
2554	///
2555	/// [io::Result]: self::Result "io::Result"
2556	/// [`read_until`]: BufRead::read_until
2557	///
2558	/// # Examples
2559	///
2560	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2561	/// this example, we use [`Cursor`] to iterate over all hyphen delimited
2562	/// segments in a byte slice
2563	///
2564	/// ```
2565	/// use std::io::{self, BufRead};
2566	///
2567	/// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
2568	///
2569	/// let mut split_iter = cursor.split(b'-').map(\|l\| l.unwrap());
2570	/// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
2571	/// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
2572	/// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
2573	/// assert_eq!(split_iter.next(), None);
2574	/// ```
2575	#[stable(feature = "rust1", since = "1.0.0")]
2576	fn split(self, byte: u8) -> Split<Self>
2577	where
2578	Self: Sized,
2579	{
2580	Split { buf: self, delim: byte }
2581	}
2582
2583	/// Returns an iterator over the lines of this reader.
2584	///
2585	/// The iterator returned from this function will yield instances of
2586	/// <code>[io::Result]<[String]></code>. Each string returned will not* have a newline*
2587	/// byte (the `0xA` byte) or `CRLF` (`0xD`, `0xA` bytes) at the end.
2588	///
2589	/// [io::Result]: self::Result "io::Result"
2590	///
2591	/// # Examples
2592	///
2593	/// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2594	/// this example, we use [`Cursor`] to iterate over all the lines in a byte
2595	/// slice.
2596	///
2597	/// ```
2598	/// use std::io::{self, BufRead};
2599	///
2600	/// let cursor = io::Cursor::new(b"lorem`\n`ipsum`\r\n`dolor");
2601	///
2602	/// let mut lines_iter = cursor.lines().map(\|l\| l.unwrap());
2603	/// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
2604	/// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
2605	/// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
2606	/// assert_eq!(lines_iter.next(), None);
2607	/// ```
2608	///
2609	/// # Errors
2610	///
2611	/// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
2612	#[stable(feature = "rust1", since = "1.0.0")]
2613	fn lines(self) -> Lines<Self>
2614	where
2615	Self: Sized,
2616	{
2617	Lines { buf: self }
2618	}
2619	}
2620
2621	/// Adapter to chain together two readers.
2622	///
2623	/// This struct is generally created by calling [`chain`] on a reader.
2624	/// Please see the documentation of [`chain`] for more details.
2625	///
2626	/// [`chain`]: Read::chain
2627	#[stable(feature = "rust1", since = "1.0.0")]
2628	#[derive(Debug)]
2629	pub struct Chain<T, U> {
2630	first: T,
2631	second: U,
2632	done_first: bool,
2633	}
2634
2635	impl<T, U> Chain<T, U> {
2636	/// Consumes the `Chain`, returning the wrapped readers.
2637	///
2638	/// # Examples
2639	///
2640	/// ```no_run
2641	/// use std::io;
2642	/// use std::io::prelude::*;
2643	/// use std::fs::File;
2644	///
2645	/// fn main() -> io::Result<()> {
2646	/// let mut foo_file = File::open("foo.txt")?;
2647	/// let mut bar_file = File::open("bar.txt")?;
2648	///
2649	/// let chain = foo_file.chain(bar_file);
2650	/// let (foo_file, bar_file) = chain.into_inner();
2651	/// Ok(())
2652	/// }
2653	/// ```
2654	#[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2655	pub fn into_inner(self) -> (T, U) {
2656	(self.first, self.second)
2657	}
2658
2659	/// Gets references to the underlying readers in this `Chain`.
2660	///
2661	/// # Examples
2662	///
2663	/// ```no_run
2664	/// use std::io;
2665	/// use std::io::prelude::*;
2666	/// use std::fs::File;
2667	///
2668	/// fn main() -> io::Result<()> {
2669	/// let mut foo_file = File::open("foo.txt")?;
2670	/// let mut bar_file = File::open("bar.txt")?;
2671	///
2672	/// let chain = foo_file.chain(bar_file);
2673	/// let (foo_file, bar_file) = chain.get_ref();
2674	/// Ok(())
2675	/// }
2676	/// ```
2677	#[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2678	pub fn get_ref(&self) -> (&T, &U) {
2679	(&self.first, &self.second)
2680	}
2681
2682	/// Gets mutable references to the underlying readers in this `Chain`.
2683	///
2684	/// Care should be taken to avoid modifying the internal I/O state of the
2685	/// underlying readers as doing so may corrupt the internal state of this
2686	/// `Chain`.
2687	///
2688	/// # Examples
2689	///
2690	/// ```no_run
2691	/// use std::io;
2692	/// use std::io::prelude::*;
2693	/// use std::fs::File;
2694	///
2695	/// fn main() -> io::Result<()> {
2696	/// let mut foo_file = File::open("foo.txt")?;
2697	/// let mut bar_file = File::open("bar.txt")?;
2698	///
2699	/// let mut chain = foo_file.chain(bar_file);
2700	/// let (foo_file, bar_file) = chain.get_mut();
2701	/// Ok(())
2702	/// }
2703	/// ```
2704	#[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2705	pub fn get_mut(&mut self) -> (&mut T, &mut U) {
2706	(&mut self.first, &mut self.second)
2707	}
2708	}
2709
2710	#[stable(feature = "rust1", since = "1.0.0")]
2711	impl<T: Read, U: Read> Read for Chain<T, U> {
2712	fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2713	if !self.done_first {
2714	match self.first.read(buf)? {
2715	`0` if !buf.is_empty() => self.done_first = `true`,
2716	n => return Ok(n),
2717	}
2718	}
2719	self.second.read(buf)
2720	}
2721
2722	fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
2723	if !self.done_first {
2724	match self.first.read_vectored(bufs)? {
2725	`0` if bufs.iter().any(\|b\| !b.is_empty()) => self.done_first = `true`,
2726	n => return Ok(n),
2727	}
2728	}
2729	self.second.read_vectored(bufs)
2730	}
2731
2732	#[inline]
2733	fn is_read_vectored(&self) -> bool {
2734	self.first.is_read_vectored() \|\| self.second.is_read_vectored()
2735	}
2736
2737	fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
2738	let mut read = `0`;
2739	if !self.done_first {
2740	read += self.first.read_to_end(buf)?;
2741	self.done_first = `true`;
2742	}
2743	read += self.second.read_to_end(buf)?;
2744	Ok(read)
2745	}
2746
2747	// We don't override `read_to_string` here because an UTF-8 sequence could
2748	// be split between the two parts of the chain
2749
2750	fn read_buf(&mut self, mut buf: BorrowedCursor<'_>) -> Result<()> {
2751	if buf.capacity() == `0` {
2752	return Ok(());
2753	}
2754
2755	if !self.done_first {
2756	let old_len = buf.written();
2757	self.first.read_buf(buf.reborrow())?;
2758
2759	if buf.written() != old_len {
2760	return Ok(());
2761	} else {
2762	self.done_first = `true`;
2763	}
2764	}
2765	self.second.read_buf(buf)
2766	}
2767	}
2768
2769	#[stable(feature = "chain_bufread", since = "1.9.0")]
2770	impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
2771	fn fill_buf(&mut self) -> Result<&[u8]> {
2772	if !self.done_first {
2773	match self.first.fill_buf()? {
2774	buf if buf.is_empty() => self.done_first = `true`,
2775	buf => return Ok(buf),
2776	}
2777	}
2778	self.second.fill_buf()
2779	}
2780
2781	fn consume(&mut self, amt: usize) {
2782	if !self.done_first { self.first.consume(amt) } else { self.second.consume(amt) }
2783	}
2784
2785	fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
2786	let mut read = `0`;
2787	if !self.done_first {
2788	let n = self.first.read_until(byte, buf)?;
2789	read += n;
2790
2791	match buf.last() {
2792	Some(b) if b == byte && n != `0` => return* Ok(read),
2793	_ => self.done_first = `true`,
2794	}
2795	}
2796	read += self.second.read_until(byte, buf)?;
2797	Ok(read)
2798	}
2799
2800	// We don't override `read_line` here because an UTF-8 sequence could be
2801	// split between the two parts of the chain
2802	}
2803
2804	impl<T, U> SizeHint for Chain<T, U> {
2805	#[inline]
2806	fn lower_bound(&self) -> usize {
2807	SizeHint::lower_bound(&self.first) + SizeHint::lower_bound(&self.second)
2808	}
2809
2810	#[inline]
2811	fn upper_bound(&self) -> Option<usize> {
2812	match (SizeHint::upper_bound(&self.first), SizeHint::upper_bound(&self.second)) {
2813	(Some(first: usize), Some(second: usize)) => first.checked_add(second),
2814	_ => None,
2815	}
2816	}
2817	}
2818
2819	/// Reader adapter which limits the bytes read from an underlying reader.
2820	///
2821	/// This struct is generally created by calling [`take`] on a reader.
2822	/// Please see the documentation of [`take`] for more details.
2823	///
2824	/// [`take`]: Read::take
2825	#[stable(feature = "rust1", since = "1.0.0")]
2826	#[derive(Debug)]
2827	pub struct Take<T> {
2828	inner: T,
2829	limit: u64,
2830	}
2831
2832	impl<T> Take<T> {
2833	/// Returns the number of bytes that can be read before this instance will
2834	/// return EOF.
2835	///
2836	/// # Note
2837	///
2838	/// This instance may reach `EOF` after reading fewer bytes than indicated by
2839	/// this method if the underlying [`Read`] instance reaches EOF.
2840	///
2841	/// # Examples
2842	///
2843	/// ```no_run
2844	/// use std::io;
2845	/// use std::io::prelude::*;
2846	/// use std::fs::File;
2847	///
2848	/// fn main() -> io::Result<()> {
2849	/// let f = File::open("foo.txt")?;
2850	///
2851	/// // read at most five bytes
2852	/// let handle = f.take(`5`);
2853	///
2854	/// println!("limit: {}", handle.limit());
2855	/// Ok(())
2856	/// }
2857	/// ```
2858	#[stable(feature = "rust1", since = "1.0.0")]
2859	pub fn limit(&self) -> u64 {
2860	self.limit
2861	}
2862
2863	/// Sets the number of bytes that can be read before this instance will
2864	/// return EOF. This is the same as constructing a new `Take` instance, so
2865	/// the amount of bytes read and the previous limit value don't matter when
2866	/// calling this method.
2867	///
2868	/// # Examples
2869	///
2870	/// ```no_run
2871	/// use std::io;
2872	/// use std::io::prelude::*;
2873	/// use std::fs::File;
2874	///
2875	/// fn main() -> io::Result<()> {
2876	/// let f = File::open("foo.txt")?;
2877	///
2878	/// // read at most five bytes
2879	/// let mut handle = f.take(`5`);
2880	/// handle.set_limit(`10`);
2881	///
2882	/// assert_eq!(handle.limit(), `10`);
2883	/// Ok(())
2884	/// }
2885	/// ```
2886	#[stable(feature = "take_set_limit", since = "1.27.0")]
2887	pub fn set_limit(&mut self, limit: u64) {
2888	self.limit = limit;
2889	}
2890
2891	/// Consumes the `Take`, returning the wrapped reader.
2892	///
2893	/// # Examples
2894	///
2895	/// ```no_run
2896	/// use std::io;
2897	/// use std::io::prelude::*;
2898	/// use std::fs::File;
2899	///
2900	/// fn main() -> io::Result<()> {
2901	/// let mut file = File::open("foo.txt")?;
2902	///
2903	/// let mut buffer = [`0`; `5`];
2904	/// let mut handle = file.take(`5`);
2905	/// handle.read(&mut buffer)?;
2906	///
2907	/// let file = handle.into_inner();
2908	/// Ok(())
2909	/// }
2910	/// ```
2911	#[stable(feature = "io_take_into_inner", since = "1.15.0")]
2912	pub fn into_inner(self) -> T {
2913	self.inner
2914	}
2915
2916	/// Gets a reference to the underlying reader.
2917	///
2918	/// # Examples
2919	///
2920	/// ```no_run
2921	/// use std::io;
2922	/// use std::io::prelude::*;
2923	/// use std::fs::File;
2924	///
2925	/// fn main() -> io::Result<()> {
2926	/// let mut file = File::open("foo.txt")?;
2927	///
2928	/// let mut buffer = [`0`; `5`];
2929	/// let mut handle = file.take(`5`);
2930	/// handle.read(&mut buffer)?;
2931	///
2932	/// let file = handle.get_ref();
2933	/// Ok(())
2934	/// }
2935	/// ```
2936	#[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2937	pub fn get_ref(&self) -> &T {
2938	&self.inner
2939	}
2940
2941	/// Gets a mutable reference to the underlying reader.
2942	///
2943	/// Care should be taken to avoid modifying the internal I/O state of the
2944	/// underlying reader as doing so may corrupt the internal limit of this
2945	/// `Take`.
2946	///
2947	/// # Examples
2948	///
2949	/// ```no_run
2950	/// use std::io;
2951	/// use std::io::prelude::*;
2952	/// use std::fs::File;
2953	///
2954	/// fn main() -> io::Result<()> {
2955	/// let mut file = File::open("foo.txt")?;
2956	///
2957	/// let mut buffer = [`0`; `5`];
2958	/// let mut handle = file.take(`5`);
2959	/// handle.read(&mut buffer)?;
2960	///
2961	/// let file = handle.get_mut();
2962	/// Ok(())
2963	/// }
2964	/// ```
2965	#[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2966	pub fn get_mut(&mut self) -> &mut T {
2967	&mut self.inner
2968	}
2969	}
2970
2971	#[stable(feature = "rust1", since = "1.0.0")]
2972	impl<T: Read> Read for Take<T> {
2973	fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2974	// Don't call into inner reader at all at EOF because it may still block
2975	if self.limit == `0` {
2976	return Ok(`0`);
2977	}
2978
2979	let max = cmp::min(buf.len() as u64, self.limit) as usize;
2980	let n = self.inner.read(&mut buf[..max])?;
2981	assert!(n as u64 <= self.limit, "number of read bytes exceeds limit");
2982	self.limit -= n as u64;
2983	Ok(n)
2984	}
2985
2986	fn read_buf(&mut self, mut buf: BorrowedCursor<'_>) -> Result<()> {
2987	// Don't call into inner reader at all at EOF because it may still block
2988	if self.limit == `0` {
2989	return Ok(());
2990	}
2991
2992	if self.limit < buf.capacity() as u64 {
2993	// The condition above guarantees that `self.limit` fits in `usize`.
2994	let limit = self.limit as usize;
2995
2996	let extra_init = cmp::min(limit, buf.init_ref().len());
2997
2998	// SAFETY: no uninit data is written to ibuf
2999	let ibuf = unsafe { &mut buf.as_mut()[..limit] };
3000
3001	let mut sliced_buf: BorrowedBuf<'_> = ibuf.into();
3002
3003	// SAFETY: extra_init bytes of ibuf are known to be initialized
3004	unsafe {
3005	sliced_buf.set_init(extra_init);
3006	}
3007
3008	let mut cursor = sliced_buf.unfilled();
3009	let result = self.inner.read_buf(cursor.reborrow());
3010
3011	let new_init = cursor.init_ref().len();
3012	let filled = sliced_buf.len();
3013
3014	// cursor / sliced_buf / ibuf must drop here
3015
3016	unsafe {
3017	// SAFETY: filled bytes have been filled and therefore initialized
3018	buf.advance_unchecked(filled);
3019	// SAFETY: new_init bytes of buf's unfilled buffer have been initialized
3020	buf.set_init(new_init);
3021	}
3022
3023	self.limit -= filled as u64;
3024
3025	result
3026	} else {
3027	let written = buf.written();
3028	let result = self.inner.read_buf(buf.reborrow());
3029	self.limit -= (buf.written() - written) as u64;
3030	result
3031	}
3032	}
3033	}
3034
3035	#[stable(feature = "rust1", since = "1.0.0")]
3036	impl<T: BufRead> BufRead for Take<T> {
3037	fn fill_buf(&mut self) -> Result<&[u8]> {
3038	// Don't call into inner reader at all at EOF because it may still block
3039	if self.limit == `0` {
3040	return Ok(&[]);
3041	}
3042
3043	let buf: &[u8] = self.inner.fill_buf()?;
3044	let cap: usize = cmp::min(v1:buf.len() as u64, self.limit) as usize;
3045	Ok(&buf[..cap])
3046	}
3047
3048	fn consume(&mut self, amt: usize) {
3049	// Don't let callers reset the limit by passing an overlarge value
3050	let amt: usize = cmp::min(v1:amt as u64, self.limit) as usize;
3051	self.limit -= amt as u64;
3052	self.inner.consume(amount:amt);
3053	}
3054	}
3055
3056	impl<T> SizeHint for Take<T> {
3057	#[inline]
3058	fn lower_bound(&self) -> usize {
3059	cmp::min(v1:SizeHint::lower_bound(&self.inner) as u64, self.limit) as usize
3060	}
3061
3062	#[inline]
3063	fn upper_bound(&self) -> Option<usize> {
3064	match SizeHint::upper_bound(&self.inner) {
3065	Some(upper_bound: usize) => Some(cmp::min(v1:upper_bound as u64, self.limit) as usize),
3066	None => self.limit.try_into().ok(),
3067	}
3068	}
3069	}
3070
3071	/// An iterator over `u8` values of a reader.
3072	///
3073	/// This struct is generally created by calling [`bytes`] on a reader.
3074	/// Please see the documentation of [`bytes`] for more details.
3075	///
3076	/// [`bytes`]: Read::bytes
3077	#[stable(feature = "rust1", since = "1.0.0")]
3078	#[derive(Debug)]
3079	pub struct Bytes<R> {
3080	inner: R,
3081	}
3082
3083	#[stable(feature = "rust1", since = "1.0.0")]
3084	impl<R: Read> Iterator for Bytes<R> {
3085	type Item = Result<u8>;
3086
3087	// Not `#[inline]`. This function gets inlined even without it, but having
3088	// the inline annotation can result in worse code generation. See #116785.
3089	fn next(&mut self) -> Option<Result<u8>> {
3090	SpecReadByte::spec_read_byte(&mut self.inner)
3091	}
3092
3093	#[inline]
3094	fn size_hint(&self) -> (usize, Option<usize>) {
3095	SizeHint::size_hint(&self.inner)
3096	}
3097	}
3098
3099	/// For the specialization of `Bytes::next`.
3100	trait SpecReadByte {
3101	fn spec_read_byte(&mut self) -> Option<Result<u8>>;
3102	}
3103
3104	impl<R> SpecReadByte for R
3105	where
3106	Self: Read,
3107	{
3108	#[inline]
3109	default fn spec_read_byte(&mut self) -> Option<Result<u8>> {
3110	inlined_slow_read_byte(self)
3111	}
3112	}
3113
3114	/// Reads a single byte in a slow, generic way. This is used by the default
3115	/// `spec_read_byte`.
3116	#[inline]
3117	fn inlined_slow_read_byte<R: Read>(reader: &mut R) -> Option<Result<u8>> {
3118	let mut byte: u8 = `0`;
3119	loop {
3120	return match reader.read(buf:slice::from_mut(&mut byte)) {
3121	Ok(`0`) => None,
3122	Ok(..) => Some(Ok(byte)),
3123	Err(ref e: &Error) if e.is_interrupted() => continue,
3124	Err(e: Error) => Some(Err(e)),
3125	};
3126	}
3127	}
3128
3129	// Used by `BufReader::spec_read_byte`, for which the `inline(ever)` is
3130	// important.
3131	#[inline(never)]
3132	fn uninlined_slow_read_byte<R: Read>(reader: &mut R) -> Option<Result<u8>> {
3133	inlined_slow_read_byte(reader)
3134	}
3135
3136	trait SizeHint {
3137	fn lower_bound(&self) -> usize;
3138
3139	fn upper_bound(&self) -> Option<usize>;
3140
3141	fn size_hint(&self) -> (usize, Option<usize>) {
3142	(self.lower_bound(), self.upper_bound())
3143	}
3144	}
3145
3146	impl<T: ?Sized> SizeHint for T {
3147	#[inline]
3148	default fn lower_bound(&self) -> usize {
3149	`0`
3150	}
3151
3152	#[inline]
3153	default fn upper_bound(&self) -> Option<usize> {
3154	None
3155	}
3156	}
3157
3158	impl<T> SizeHint for &mut T {
3159	#[inline]
3160	fn lower_bound(&self) -> usize {
3161	SizeHint::lower_bound(*self)
3162	}
3163
3164	#[inline]
3165	fn upper_bound(&self) -> Option<usize> {
3166	SizeHint::upper_bound(*self)
3167	}
3168	}
3169
3170	impl<T> SizeHint for Box<T> {
3171	#[inline]
3172	fn lower_bound(&self) -> usize {
3173	SizeHint::lower_bound(&**self)
3174	}
3175
3176	#[inline]
3177	fn upper_bound(&self) -> Option<usize> {
3178	SizeHint::upper_bound(&**self)
3179	}
3180	}
3181
3182	impl SizeHint for &[u8] {
3183	#[inline]
3184	fn lower_bound(&self) -> usize {
3185	self.len()
3186	}
3187
3188	#[inline]
3189	fn upper_bound(&self) -> Option<usize> {
3190	Some(self.len())
3191	}
3192	}
3193
3194	/// An iterator over the contents of an instance of `BufRead` split on a
3195	/// particular byte.
3196	///
3197	/// This struct is generally created by calling [`split`] on a `BufRead`.
3198	/// Please see the documentation of [`split`] for more details.
3199	///
3200	/// [`split`]: BufRead::split
3201	#[stable(feature = "rust1", since = "1.0.0")]
3202	#[derive(Debug)]
3203	pub struct Split<B> {
3204	buf: B,
3205	delim: u8,
3206	}
3207
3208	#[stable(feature = "rust1", since = "1.0.0")]
3209	impl<B: BufRead> Iterator for Split<B> {
3210	type Item = Result<Vec<u8>>;
3211
3212	fn next(&mut self) -> Option<Result<Vec<u8>>> {
3213	let mut buf: Vec = Vec::new();
3214	match self.buf.read_until(self.delim, &mut buf) {
3215	Ok(`0`) => None,
3216	Ok(_n: usize) => {
3217	if buf[buf.len() - `1`] == self.delim {
3218	buf.pop();
3219	}
3220	Some(Ok(buf))
3221	}
3222	Err(e: Error) => Some(Err(e)),
3223	}
3224	}
3225	}
3226
3227	/// An iterator over the lines of an instance of `BufRead`.
3228	///
3229	/// This struct is generally created by calling [`lines`] on a `BufRead`.
3230	/// Please see the documentation of [`lines`] for more details.
3231	///
3232	/// [`lines`]: BufRead::lines
3233	#[stable(feature = "rust1", since = "1.0.0")]
3234	#[derive(Debug)]
3235	#[cfg_attr(not(test), rustc_diagnostic_item = "IoLines")]
3236	pub struct Lines<B> {
3237	buf: B,
3238	}
3239
3240	#[stable(feature = "rust1", since = "1.0.0")]
3241	impl<B: BufRead> Iterator for Lines<B> {
3242	type Item = Result<String>;
3243
3244	fn next(&mut self) -> Option<Result<String>> {
3245	let mut buf: String = String::new();
3246	match self.buf.read_line(&mut buf) {
3247	Ok(`0`) => None,
3248	Ok(_n: usize) => {
3249	if buf.ends_with('`\n`') {
3250	buf.pop();
3251	if buf.ends_with('`\r`') {
3252	buf.pop();
3253	}
3254	}
3255	Some(Ok(buf))
3256	}
3257	Err(e: Error) => Some(Err(e)),
3258	}
3259	}
3260	}
3261