1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Traits, helpers, and type definitions for core I/O functionality.
13 //! The `std::io` module contains a number of common things you'll need
14 //! when doing input and output. The most core part of this module is
15 //! the [`Read`][read] and [`Write`][write] traits, which provide the
16 //! most general interface for reading and writing input and output.
18 //! [read]: trait.Read.html
19 //! [write]: trait.Write.html
23 //! Because they are traits, `Read` and `Write` are implemented by a number
24 //! of other types, and you can implement them for your types too. As such,
25 //! you'll see a few different types of I/O throughout the documentation in
26 //! this module: `File`s, `TcpStream`s, and sometimes even `Vec<T>`s. For
27 //! example, `Read` adds a `read()` method, which we can use on `File`s:
31 //! use std::io::prelude::*;
32 //! use std::fs::File;
34 //! # fn foo() -> io::Result<()> {
35 //! let mut f = try!(File::open("foo.txt"));
36 //! let mut buffer = [0; 10];
38 //! // read up to 10 bytes
39 //! try!(f.read(&mut buffer));
41 //! println!("The bytes: {:?}", buffer);
46 //! `Read` and `Write` are so important, implementors of the two traits have a
47 //! nickname: readers and writers. So you'll sometimes see 'a reader' instead
48 //! of 'a type that implements the `Read` trait'. Much easier!
50 //! ## Seek and BufRead
52 //! Beyond that, there are two important traits that are provided: [`Seek`][seek]
53 //! and [`BufRead`][bufread]. Both of these build on top of a reader to control
54 //! how the reading happens. `Seek` lets you control where the next byte is
59 //! use std::io::prelude::*;
60 //! use std::io::SeekFrom;
61 //! use std::fs::File;
63 //! # fn foo() -> io::Result<()> {
64 //! let mut f = try!(File::open("foo.txt"));
65 //! let mut buffer = [0; 10];
67 //! // skip to the last 10 bytes of the file
68 //! try!(f.seek(SeekFrom::End(-10)));
70 //! // read up to 10 bytes
71 //! try!(f.read(&mut buffer));
73 //! println!("The bytes: {:?}", buffer);
78 //! [seek]: trait.Seek.html
79 //! [bufread]: trait.BufRead.html
81 //! `BufRead` uses an internal buffer to provide a number of other ways to read, but
82 //! to show it off, we'll need to talk about buffers in general. Keep reading!
84 //! ## BufReader and BufWriter
86 //! Byte-based interfaces are unwieldy and can be inefficient, as we'd need to be
87 //! making near-constant calls to the operating system. To help with this,
88 //! `std::io` comes with two structs, `BufReader` and `BufWriter`, which wrap
89 //! readers and writers. The wrapper uses a buffer, reducing the number of
90 //! calls and providing nicer methods for accessing exactly what you want.
92 //! For example, `BufReader` works with the `BufRead` trait to add extra
93 //! methods to any reader:
97 //! use std::io::prelude::*;
98 //! use std::io::BufReader;
99 //! use std::fs::File;
101 //! # fn foo() -> io::Result<()> {
102 //! let f = try!(File::open("foo.txt"));
103 //! let mut reader = BufReader::new(f);
104 //! let mut buffer = String::new();
106 //! // read a line into buffer
107 //! try!(reader.read_line(&mut buffer));
109 //! println!("{}", buffer);
114 //! `BufWriter` doesn't add any new ways of writing; it just buffers every call
115 //! to [`write()`][write]:
119 //! use std::io::prelude::*;
120 //! use std::io::BufWriter;
121 //! use std::fs::File;
123 //! # fn foo() -> io::Result<()> {
124 //! let f = try!(File::create("foo.txt"));
126 //! let mut writer = BufWriter::new(f);
128 //! // write a byte to the buffer
129 //! try!(writer.write(&[42]));
131 //! } // the buffer is flushed once writer goes out of scope
137 //! [write]: trait.Write.html#tymethod.write
139 //! ## Standard input and output
141 //! A very common source of input is standard input:
146 //! # fn foo() -> io::Result<()> {
147 //! let mut input = String::new();
149 //! try!(io::stdin().read_line(&mut input));
151 //! println!("You typed: {}", input.trim());
156 //! And a very common source of output is standard output:
160 //! use std::io::prelude::*;
162 //! # fn foo() -> io::Result<()> {
163 //! try!(io::stdout().write(&[42]));
168 //! Of course, using `io::stdout()` directly is less common than something like
171 //! ## Iterator types
173 //! A large number of the structures provided by `std::io` are for various
174 //! ways of iterating over I/O. For example, `Lines` is used to split over
179 //! use std::io::prelude::*;
180 //! use std::io::BufReader;
181 //! use std::fs::File;
183 //! # fn foo() -> io::Result<()> {
184 //! let f = try!(File::open("foo.txt"));
185 //! let mut reader = BufReader::new(f);
187 //! for line in reader.lines() {
188 //! let line = try!(line);
189 //! println!("{}", line);
198 //! There are a number of [functions][functions] that offer access to various
199 //! features. For example, we can use three of these functions to copy everything
200 //! from standard input to standard output:
205 //! # fn foo() -> io::Result<()> {
206 //! try!(io::copy(&mut io::stdin(), &mut io::stdout()));
211 //! [functions]: #functions
215 //! Last, but certainly not least, is [`io::Result`][result]. This type is used
216 //! as the return type of many `std::io` functions that can cause an error, and
217 //! can be returned from your own functions as well. Many of the examples in this
218 //! module use the [`try!`][try] macro:
223 //! fn read_input() -> io::Result<()> {
224 //! let mut input = String::new();
226 //! try!(io::stdin().read_line(&mut input));
228 //! println!("You typed: {}", input.trim());
234 //! The return type of `read_input()`, `io::Result<()>`, is a very common type
235 //! for functions which don't have a 'real' return value, but do want to return
236 //! errors if they happen. In this case, the only purpose of this function is
237 //! to read the line and print it, so we use `()`.
239 //! [result]: type.Result.html
240 //! [try]: macro.try!.html
242 #![stable(feature = "rust1", since = "1.0.0")]
245 use rustc_unicode::str as core_str;
246 use error as std_error;
248 use iter::{Iterator};
250 use ops::{Drop, FnOnce};
251 use option::Option::{self, Some, None};
252 use result::Result::{Ok, Err};
258 #[stable(feature = "rust1", since = "1.0.0")]
259 pub use self::buffered::{BufReader, BufWriter, LineWriter};
260 #[stable(feature = "rust1", since = "1.0.0")]
261 pub use self::buffered::IntoInnerError;
262 #[stable(feature = "rust1", since = "1.0.0")]
263 pub use self::cursor::Cursor;
264 #[stable(feature = "rust1", since = "1.0.0")]
265 pub use self::error::{Result, Error, ErrorKind};
266 #[stable(feature = "rust1", since = "1.0.0")]
267 pub use self::util::{copy, sink, Sink, empty, Empty, repeat, Repeat};
268 #[stable(feature = "rust1", since = "1.0.0")]
269 pub use self::stdio::{stdin, stdout, stderr, _print, Stdin, Stdout, Stderr};
270 #[stable(feature = "rust1", since = "1.0.0")]
271 pub use self::stdio::{StdoutLock, StderrLock, StdinLock};
272 #[unstable(feature = "libstd_io_internals", issue = "0")]
273 #[doc(no_inline, hidden)]
274 pub use self::stdio::{set_panic, set_print};
285 const DEFAULT_BUF_SIZE: usize = 64 * 1024;
287 // A few methods below (read_to_string, read_line) will append data into a
288 // `String` buffer, but we need to be pretty careful when doing this. The
289 // implementation will just call `.as_mut_vec()` and then delegate to a
290 // byte-oriented reading method, but we must ensure that when returning we never
291 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
293 // To this end, we use an RAII guard (to protect against panics) which updates
294 // the length of the string when it is dropped. This guard initially truncates
295 // the string to the prior length and only after we've validated that the
296 // new contents are valid UTF-8 do we allow it to set a longer length.
298 // The unsafety in this function is twofold:
300 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
302 // 2. We're passing a raw buffer to the function `f`, and it is expected that
303 // the function only *appends* bytes to the buffer. We'll get undefined
304 // behavior if existing bytes are overwritten to have non-UTF-8 data.
305 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
306 where F: FnOnce(&mut Vec<u8>) -> Result<usize>
308 struct Guard<'a> { s: &'a mut Vec<u8>, len: usize }
309 impl<'a> Drop for Guard<'a> {
311 unsafe { self.s.set_len(self.len); }
316 let mut g = Guard { len: buf.len(), s: buf.as_mut_vec() };
318 if str::from_utf8(&g.s[g.len..]).is_err() {
320 Err(Error::new(ErrorKind::InvalidData,
321 "stream did not contain valid UTF-8"))
330 // This uses an adaptive system to extend the vector when it fills. We want to
331 // avoid paying to allocate and zero a huge chunk of memory if the reader only
332 // has 4 bytes while still making large reads if the reader does have a ton
333 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
334 // time is 4,500 times (!) slower than this if the reader has a very small
335 // amount of data to return.
336 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
337 let start_len = buf.len();
338 let mut len = start_len;
339 let mut new_write_size = 16;
342 if len == buf.len() {
343 if new_write_size < DEFAULT_BUF_SIZE {
346 buf.resize(len + new_write_size, 0);
349 match r.read(&mut buf[len..]) {
351 ret = Ok(len - start_len);
355 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
367 /// The `Read` trait allows for reading bytes from a source.
369 /// Implementors of the `Read` trait are sometimes called 'readers'.
371 /// Readers are defined by one required method, `read()`. Each call to `read`
372 /// will attempt to pull bytes from this source into a provided buffer. A
373 /// number of other methods are implemented in terms of `read()`, giving
374 /// implementors a number of ways to read bytes while only needing to implement
377 /// Readers are intended to be composable with one another. Many implementors
378 /// throughout `std::io` take and provide types which implement the `Read`
381 /// Please note that each call to `read` may involve a system call, and
382 /// therefore, using something that implements [`BufRead`][bufread], such as
383 /// [`BufReader`][bufreader], will be more efficient.
385 /// [bufread]: trait.BufRead.html
386 /// [bufreader]: struct.BufReader.html
390 /// [`File`][file]s implement `Read`:
392 /// [file]: ../std/fs/struct.File.html
396 /// use std::io::prelude::*;
397 /// use std::fs::File;
399 /// # fn foo() -> io::Result<()> {
400 /// let mut f = try!(File::open("foo.txt"));
401 /// let mut buffer = [0; 10];
403 /// // read up to 10 bytes
404 /// try!(f.read(&mut buffer));
406 /// let mut buffer = vec![0; 10];
407 /// // read the whole file
408 /// try!(f.read_to_end(&mut buffer));
410 /// // read into a String, so that you don't need to do the conversion.
411 /// let mut buffer = String::new();
412 /// try!(f.read_to_string(&mut buffer));
414 /// // and more! See the other methods for more details.
418 #[stable(feature = "rust1", since = "1.0.0")]
420 /// Pull some bytes from this source into the specified buffer, returning
421 /// how many bytes were read.
423 /// This function does not provide any guarantees about whether it blocks
424 /// waiting for data, but if an object needs to block for a read but cannot
425 /// it will typically signal this via an `Err` return value.
427 /// If the return value of this method is `Ok(n)`, then it must be
428 /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
429 /// that the buffer `buf` has been filled in with `n` bytes of data from this
430 /// source. If `n` is `0`, then it can indicate one of two scenarios:
432 /// 1. This reader has reached its "end of file" and will likely no longer
433 /// be able to produce bytes. Note that this does not mean that the
434 /// reader will *always* no longer be able to produce bytes.
435 /// 2. The buffer specified was 0 bytes in length.
437 /// No guarantees are provided about the contents of `buf` when this
438 /// function is called, implementations cannot rely on any property of the
439 /// contents of `buf` being true. It is recommended that implementations
440 /// only write data to `buf` instead of reading its contents.
444 /// If this function encounters any form of I/O or other error, an error
445 /// variant will be returned. If an error is returned then it must be
446 /// guaranteed that no bytes were read.
450 /// [`File`][file]s implement `Read`:
452 /// [file]: ../std/fs/struct.File.html
456 /// use std::io::prelude::*;
457 /// use std::fs::File;
459 /// # fn foo() -> io::Result<()> {
460 /// let mut f = try!(File::open("foo.txt"));
461 /// let mut buffer = [0; 10];
464 /// try!(f.read(&mut buffer[..]));
468 #[stable(feature = "rust1", since = "1.0.0")]
469 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
471 /// Read all bytes until EOF in this source, placing them into `buf`.
473 /// All bytes read from this source will be appended to the specified buffer
474 /// `buf`. This function will continuously call `read` to append more data to
475 /// `buf` until `read` returns either `Ok(0)` or an error of
476 /// non-`ErrorKind::Interrupted` kind.
478 /// If successful, this function will return the total number of bytes read.
482 /// If this function encounters an error of the kind
483 /// `ErrorKind::Interrupted` then the error is ignored and the operation
486 /// If any other read error is encountered then this function immediately
487 /// returns. Any bytes which have already been read will be appended to
492 /// [`File`][file]s implement `Read`:
494 /// [file]: ../std/fs/struct.File.html
498 /// use std::io::prelude::*;
499 /// use std::fs::File;
501 /// # fn foo() -> io::Result<()> {
502 /// let mut f = try!(File::open("foo.txt"));
503 /// let mut buffer = Vec::new();
505 /// // read the whole file
506 /// try!(f.read_to_end(&mut buffer));
510 #[stable(feature = "rust1", since = "1.0.0")]
511 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
512 read_to_end(self, buf)
515 /// Read all bytes until EOF in this source, placing them into `buf`.
517 /// If successful, this function returns the number of bytes which were read
518 /// and appended to `buf`.
522 /// If the data in this stream is *not* valid UTF-8 then an error is
523 /// returned and `buf` is unchanged.
525 /// See [`read_to_end()`][readtoend] for other error semantics.
527 /// [readtoend]: #method.read_to_end
531 /// [`File`][file]s implement `Read`:
533 /// [file]: ../std/fs/struct.File.html
537 /// use std::io::prelude::*;
538 /// use std::fs::File;
540 /// # fn foo() -> io::Result<()> {
541 /// let mut f = try!(File::open("foo.txt"));
542 /// let mut buffer = String::new();
544 /// try!(f.read_to_string(&mut buffer));
548 #[stable(feature = "rust1", since = "1.0.0")]
549 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
550 // Note that we do *not* call `.read_to_end()` here. We are passing
551 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
552 // method to fill it up. An arbitrary implementation could overwrite the
553 // entire contents of the vector, not just append to it (which is what
554 // we are expecting).
556 // To prevent extraneously checking the UTF-8-ness of the entire buffer
557 // we pass it to our hardcoded `read_to_end` implementation which we
558 // know is guaranteed to only read data into the end of the buffer.
559 append_to_string(buf, |b| read_to_end(self, b))
562 /// Read the exact number of bytes required to fill `buf`.
564 /// This function reads as many bytes as necessary to completely fill the
565 /// specified buffer `buf`.
567 /// No guarantees are provided about the contents of `buf` when this
568 /// function is called, implementations cannot rely on any property of the
569 /// contents of `buf` being true. It is recommended that implementations
570 /// only write data to `buf` instead of reading its contents.
574 /// If this function encounters an error of the kind
575 /// `ErrorKind::Interrupted` then the error is ignored and the operation
578 /// If this function encounters an "end of file" before completely filling
579 /// the buffer, it returns an error of the kind `ErrorKind::UnexpectedEOF`.
580 /// The contents of `buf` are unspecified in this case.
582 /// If any other read error is encountered then this function immediately
583 /// returns. The contents of `buf` are unspecified in this case.
585 /// If this function returns an error, it is unspecified how many bytes it
586 /// has read, but it will never read more than would be necessary to
587 /// completely fill the buffer.
591 /// [`File`][file]s implement `Read`:
593 /// [file]: ../std/fs/struct.File.html
597 /// use std::io::prelude::*;
598 /// use std::fs::File;
600 /// # fn foo() -> io::Result<()> {
601 /// let mut f = try!(File::open("foo.txt"));
602 /// let mut buffer = [0; 10];
604 /// // read exactly 10 bytes
605 /// try!(f.read_exact(&mut buffer));
609 #[stable(feature = "read_exact", since = "1.6.0")]
610 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
611 while !buf.is_empty() {
612 match self.read(buf) {
614 Ok(n) => { let tmp = buf; buf = &mut tmp[n..]; }
615 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
616 Err(e) => return Err(e),
620 Err(Error::new(ErrorKind::UnexpectedEof,
621 "failed to fill whole buffer"))
627 /// Creates a "by reference" adaptor for this instance of `Read`.
629 /// The returned adaptor also implements `Read` and will simply borrow this
634 /// [`File`][file]s implement `Read`:
636 /// [file]: ../std/fs/struct.File.html
640 /// use std::io::Read;
641 /// use std::fs::File;
643 /// # fn foo() -> io::Result<()> {
644 /// let mut f = try!(File::open("foo.txt"));
645 /// let mut buffer = Vec::new();
646 /// let mut other_buffer = Vec::new();
649 /// let reference = f.by_ref();
651 /// // read at most 5 bytes
652 /// try!(reference.take(5).read_to_end(&mut buffer));
654 /// } // drop our &mut reference so we can use f again
656 /// // original file still usable, read the rest
657 /// try!(f.read_to_end(&mut other_buffer));
661 #[stable(feature = "rust1", since = "1.0.0")]
662 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
664 /// Transforms this `Read` instance to an `Iterator` over its bytes.
666 /// The returned type implements `Iterator` where the `Item` is `Result<u8,
667 /// R::Err>`. The yielded item is `Ok` if a byte was successfully read and
668 /// `Err` otherwise for I/O errors. EOF is mapped to returning `None` from
673 /// [`File`][file]s implement `Read`:
675 /// [file]: ../std/fs/struct.File.html
679 /// use std::io::prelude::*;
680 /// use std::fs::File;
682 /// # fn foo() -> io::Result<()> {
683 /// let mut f = try!(File::open("foo.txt"));
685 /// for byte in f.bytes() {
686 /// println!("{}", byte.unwrap());
691 #[stable(feature = "rust1", since = "1.0.0")]
692 fn bytes(self) -> Bytes<Self> where Self: Sized {
693 Bytes { inner: self }
696 /// Transforms this `Read` instance to an `Iterator` over `char`s.
698 /// This adaptor will attempt to interpret this reader as a UTF-8 encoded
699 /// sequence of characters. The returned iterator will return `None` once
700 /// EOF is reached for this reader. Otherwise each element yielded will be a
701 /// `Result<char, E>` where `E` may contain information about what I/O error
702 /// occurred or where decoding failed.
704 /// Currently this adaptor will discard intermediate data read, and should
705 /// be avoided if this is not desired.
709 /// [`File`][file]s implement `Read`:
711 /// [file]: ../std/fs/struct.File.html
716 /// use std::io::prelude::*;
717 /// use std::fs::File;
719 /// # fn foo() -> io::Result<()> {
720 /// let mut f = try!(File::open("foo.txt"));
722 /// for c in f.chars() {
723 /// println!("{}", c.unwrap());
728 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
729 of where errors happen is currently \
730 unclear and may change",
732 fn chars(self) -> Chars<Self> where Self: Sized {
733 Chars { inner: self }
736 /// Creates an adaptor which will chain this stream with another.
738 /// The returned `Read` instance will first read all bytes from this object
739 /// until EOF is encountered. Afterwards the output is equivalent to the
740 /// output of `next`.
744 /// [`File`][file]s implement `Read`:
746 /// [file]: ../std/fs/struct.File.html
750 /// use std::io::prelude::*;
751 /// use std::fs::File;
753 /// # fn foo() -> io::Result<()> {
754 /// let mut f1 = try!(File::open("foo.txt"));
755 /// let mut f2 = try!(File::open("bar.txt"));
757 /// let mut handle = f1.chain(f2);
758 /// let mut buffer = String::new();
760 /// // read the value into a String. We could use any Read method here,
761 /// // this is just one example.
762 /// try!(handle.read_to_string(&mut buffer));
766 #[stable(feature = "rust1", since = "1.0.0")]
767 fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized {
768 Chain { first: self, second: next, done_first: false }
771 /// Creates an adaptor which will read at most `limit` bytes from it.
773 /// This function returns a new instance of `Read` which will read at most
774 /// `limit` bytes, after which it will always return EOF (`Ok(0)`). Any
775 /// read errors will not count towards the number of bytes read and future
776 /// calls to `read` may succeed.
780 /// [`File`][file]s implement `Read`:
782 /// [file]: ../std/fs/struct.File.html
786 /// use std::io::prelude::*;
787 /// use std::fs::File;
789 /// # fn foo() -> io::Result<()> {
790 /// let mut f = try!(File::open("foo.txt"));
791 /// let mut buffer = [0; 5];
793 /// // read at most five bytes
794 /// let mut handle = f.take(5);
796 /// try!(handle.read(&mut buffer));
800 #[stable(feature = "rust1", since = "1.0.0")]
801 fn take(self, limit: u64) -> Take<Self> where Self: Sized {
802 Take { inner: self, limit: limit }
805 /// Creates a reader adaptor which will write all read data into the given
808 /// Whenever the returned `Read` instance is read it will write the read
809 /// data to `out`. The current semantics of this implementation imply that
810 /// a `write` error will not report how much data was initially read.
814 /// [`File`][file]s implement `Read`:
816 /// [file]: ../std/fs/struct.File.html
821 /// use std::io::prelude::*;
822 /// use std::fs::File;
824 /// # fn foo() -> io::Result<()> {
825 /// let mut f = try!(File::open("foo.txt"));
826 /// let mut buffer1 = Vec::with_capacity(10);
827 /// let mut buffer2 = Vec::with_capacity(10);
829 /// // write the output to buffer1 as we read
830 /// let mut handle = f.tee(&mut buffer1);
832 /// try!(handle.read(&mut buffer2));
836 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
837 of where errors happen is currently \
838 unclear and may change",
840 #[rustc_deprecated(reason = "error handling semantics unclear and \
841 don't seem to have an ergonomic resolution",
844 fn tee<W: Write>(self, out: W) -> Tee<Self, W> where Self: Sized {
845 Tee { reader: self, writer: out }
849 /// A trait for objects which are byte-oriented sinks.
851 /// Implementors of the `Write` trait are sometimes called 'writers'.
853 /// Writers are defined by two required methods, `write()` and `flush()`:
855 /// * The `write()` method will attempt to write some data into the object,
856 /// returning how many bytes were successfully written.
858 /// * The `flush()` method is useful for adaptors and explicit buffers
859 /// themselves for ensuring that all buffered data has been pushed out to the
862 /// Writers are intended to be composable with one another. Many implementors
863 /// throughout `std::io` take and provide types which implement the `Write`
869 /// use std::io::prelude::*;
870 /// use std::fs::File;
872 /// # fn foo() -> std::io::Result<()> {
873 /// let mut buffer = try!(File::create("foo.txt"));
875 /// try!(buffer.write(b"some bytes"));
879 #[stable(feature = "rust1", since = "1.0.0")]
881 /// Write a buffer into this object, returning how many bytes were written.
883 /// This function will attempt to write the entire contents of `buf`, but
884 /// the entire write may not succeed, or the write may also generate an
885 /// error. A call to `write` represents *at most one* attempt to write to
886 /// any wrapped object.
888 /// Calls to `write` are not guaranteed to block waiting for data to be
889 /// written, and a write which would otherwise block can be indicated through
890 /// an `Err` variant.
892 /// If the return value is `Ok(n)` then it must be guaranteed that
893 /// `0 <= n <= buf.len()`. A return value of `0` typically means that the
894 /// underlying object is no longer able to accept bytes and will likely not
895 /// be able to in the future as well, or that the buffer provided is empty.
899 /// Each call to `write` may generate an I/O error indicating that the
900 /// operation could not be completed. If an error is returned then no bytes
901 /// in the buffer were written to this writer.
903 /// It is **not** considered an error if the entire buffer could not be
904 /// written to this writer.
909 /// use std::io::prelude::*;
910 /// use std::fs::File;
912 /// # fn foo() -> std::io::Result<()> {
913 /// let mut buffer = try!(File::create("foo.txt"));
915 /// try!(buffer.write(b"some bytes"));
919 #[stable(feature = "rust1", since = "1.0.0")]
920 fn write(&mut self, buf: &[u8]) -> Result<usize>;
922 /// Flush this output stream, ensuring that all intermediately buffered
923 /// contents reach their destination.
927 /// It is considered an error if not all bytes could be written due to
928 /// I/O errors or EOF being reached.
933 /// use std::io::prelude::*;
934 /// use std::io::BufWriter;
935 /// use std::fs::File;
937 /// # fn foo() -> std::io::Result<()> {
938 /// let mut buffer = BufWriter::new(try!(File::create("foo.txt")));
940 /// try!(buffer.write(b"some bytes"));
941 /// try!(buffer.flush());
945 #[stable(feature = "rust1", since = "1.0.0")]
946 fn flush(&mut self) -> Result<()>;
948 /// Attempts to write an entire buffer into this write.
950 /// This method will continuously call `write` while there is more data to
951 /// write. This method will not return until the entire buffer has been
952 /// successfully written or an error occurs. The first error generated from
953 /// this method will be returned.
957 /// This function will return the first error that `write` returns.
962 /// use std::io::prelude::*;
963 /// use std::fs::File;
965 /// # fn foo() -> std::io::Result<()> {
966 /// let mut buffer = try!(File::create("foo.txt"));
968 /// try!(buffer.write_all(b"some bytes"));
972 #[stable(feature = "rust1", since = "1.0.0")]
973 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
974 while !buf.is_empty() {
975 match self.write(buf) {
976 Ok(0) => return Err(Error::new(ErrorKind::WriteZero,
977 "failed to write whole buffer")),
978 Ok(n) => buf = &buf[n..],
979 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
980 Err(e) => return Err(e),
986 /// Writes a formatted string into this writer, returning any error
989 /// This method is primarily used to interface with the
990 /// [`format_args!`][formatargs] macro, but it is rare that this should
991 /// explicitly be called. The [`write!`][write] macro should be favored to
992 /// invoke this method instead.
994 /// [formatargs]: ../std/macro.format_args!.html
995 /// [write]: ../std/macro.write!.html
997 /// This function internally uses the [`write_all`][writeall] method on
998 /// this trait and hence will continuously write data so long as no errors
999 /// are received. This also means that partial writes are not indicated in
1002 /// [writeall]: #method.write_all
1006 /// This function will return any I/O error reported while formatting.
1011 /// use std::io::prelude::*;
1012 /// use std::fs::File;
1014 /// # fn foo() -> std::io::Result<()> {
1015 /// let mut buffer = try!(File::create("foo.txt"));
1018 /// try!(write!(buffer, "{:.*}", 2, 1.234567));
1019 /// // turns into this:
1020 /// try!(buffer.write_fmt(format_args!("{:.*}", 2, 1.234567)));
1024 #[stable(feature = "rust1", since = "1.0.0")]
1025 fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<()> {
1026 // Create a shim which translates a Write to a fmt::Write and saves
1027 // off I/O errors. instead of discarding them
1028 struct Adaptor<'a, T: ?Sized + 'a> {
1033 impl<'a, T: Write + ?Sized> fmt::Write for Adaptor<'a, T> {
1034 fn write_str(&mut self, s: &str) -> fmt::Result {
1035 match self.inner.write_all(s.as_bytes()) {
1038 self.error = Err(e);
1045 let mut output = Adaptor { inner: self, error: Ok(()) };
1046 match fmt::write(&mut output, fmt) {
1048 Err(..) => output.error
1052 /// Creates a "by reference" adaptor for this instance of `Write`.
1054 /// The returned adaptor also implements `Write` and will simply borrow this
1060 /// use std::io::Write;
1061 /// use std::fs::File;
1063 /// # fn foo() -> std::io::Result<()> {
1064 /// let mut buffer = try!(File::create("foo.txt"));
1066 /// let reference = buffer.by_ref();
1068 /// // we can use reference just like our original buffer
1069 /// try!(reference.write_all(b"some bytes"));
1073 #[stable(feature = "rust1", since = "1.0.0")]
1074 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
1076 /// Creates a new writer which will write all data to both this writer and
1079 /// All data written to the returned writer will both be written to `self`
1080 /// as well as `other`. Note that the error semantics of the current
1081 /// implementation do not precisely track where errors happen. For example
1082 /// an error on the second call to `write` will not report that the first
1083 /// call to `write` succeeded.
1089 /// use std::io::prelude::*;
1090 /// use std::fs::File;
1092 /// # fn foo() -> std::io::Result<()> {
1093 /// let mut buffer1 = try!(File::create("foo.txt"));
1094 /// let mut buffer2 = Vec::new();
1096 /// // write the output to buffer1 as we read
1097 /// let mut handle = buffer1.broadcast(&mut buffer2);
1099 /// try!(handle.write(b"some bytes"));
1103 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
1104 of where errors happen is currently \
1105 unclear and may change",
1107 #[rustc_deprecated(reason = "error handling semantics unclear and \
1108 don't seem to have an ergonomic resolution",
1110 #[allow(deprecated)]
1111 fn broadcast<W: Write>(self, other: W) -> Broadcast<Self, W>
1114 Broadcast { first: self, second: other }
1118 /// The `Seek` trait provides a cursor which can be moved within a stream of
1121 /// The stream typically has a fixed size, allowing seeking relative to either
1122 /// end or the current offset.
1126 /// [`File`][file]s implement `Seek`:
1128 /// [file]: ../std/fs/struct.File.html
1132 /// use std::io::prelude::*;
1133 /// use std::fs::File;
1134 /// use std::io::SeekFrom;
1136 /// # fn foo() -> io::Result<()> {
1137 /// let mut f = try!(File::open("foo.txt"));
1139 /// // move the cursor 42 bytes from the start of the file
1140 /// try!(f.seek(SeekFrom::Start(42)));
1144 #[stable(feature = "rust1", since = "1.0.0")]
1146 /// Seek to an offset, in bytes, in a stream.
1148 /// A seek beyond the end of a stream is allowed, but implementation
1151 /// If the seek operation completed successfully,
1152 /// this method returns the new position from the start of the stream.
1153 /// That position can be used later with `SeekFrom::Start`.
1157 /// Seeking to a negative offset is considered an error.
1158 #[stable(feature = "rust1", since = "1.0.0")]
1159 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1162 /// Enumeration of possible methods to seek within an I/O object.
1163 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1164 #[stable(feature = "rust1", since = "1.0.0")]
1166 /// Set the offset to the provided number of bytes.
1167 #[stable(feature = "rust1", since = "1.0.0")]
1170 /// Set the offset to the size of this object plus the specified number of
1173 /// It is possible to seek beyond the end of an object, but is an error to
1174 /// seek before byte 0.
1175 #[stable(feature = "rust1", since = "1.0.0")]
1178 /// Set the offset to the current position plus the specified number of
1181 /// It is possible to seek beyond the end of an object, but is an error to
1182 /// seek before byte 0.
1183 #[stable(feature = "rust1", since = "1.0.0")]
1187 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>)
1191 let (done, used) = {
1192 let available = match r.fill_buf() {
1194 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1195 Err(e) => return Err(e)
1197 match available.iter().position(|x| *x == delim) {
1199 buf.extend_from_slice(&available[..i + 1]);
1203 buf.extend_from_slice(available);
1204 (false, available.len())
1210 if done || used == 0 {
1216 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1217 /// to perform extra ways of reading.
1219 /// For example, reading line-by-line is inefficient without using a buffer, so
1220 /// if you want to read by line, you'll need `BufRead`, which includes a
1221 /// [`read_line()`][readline] method as well as a [`lines()`][lines] iterator.
1223 /// [readline]: #method.read_line
1224 /// [lines]: #method.lines
1228 /// A locked standard input implements `BufRead`:
1232 /// use std::io::prelude::*;
1234 /// let stdin = io::stdin();
1235 /// for line in stdin.lock().lines() {
1236 /// println!("{}", line.unwrap());
1240 /// If you have something that implements `Read`, you can use the [`BufReader`
1241 /// type][bufreader] to turn it into a `BufRead`.
1243 /// For example, [`File`][file] implements `Read`, but not `BufRead`.
1244 /// `BufReader` to the rescue!
1246 /// [bufreader]: struct.BufReader.html
1247 /// [file]: ../fs/struct.File.html
1250 /// use std::io::{self, BufReader};
1251 /// use std::io::prelude::*;
1252 /// use std::fs::File;
1254 /// # fn foo() -> io::Result<()> {
1255 /// let f = try!(File::open("foo.txt"));
1256 /// let f = BufReader::new(f);
1258 /// for line in f.lines() {
1259 /// println!("{}", line.unwrap());
1266 #[stable(feature = "rust1", since = "1.0.0")]
1267 pub trait BufRead: Read {
1268 /// Fills the internal buffer of this object, returning the buffer contents.
1270 /// This function is a lower-level call. It needs to be paired with the
1271 /// [`consume`][consume] method to function properly. When calling this
1272 /// method, none of the contents will be "read" in the sense that later
1273 /// calling `read` may return the same contents. As such, `consume` must be
1274 /// called with the number of bytes that are consumed from this buffer to
1275 /// ensure that the bytes are never returned twice.
1277 /// [consume]: #tymethod.consume
1279 /// An empty buffer returned indicates that the stream has reached EOF.
1283 /// This function will return an I/O error if the underlying reader was
1284 /// read, but returned an error.
1288 /// A locked standard input implements `BufRead`:
1292 /// use std::io::prelude::*;
1294 /// let stdin = io::stdin();
1295 /// let mut stdin = stdin.lock();
1297 /// // we can't have two `&mut` references to `stdin`, so use a block
1298 /// // to end the borrow early.
1300 /// let buffer = stdin.fill_buf().unwrap();
1302 /// // work with buffer
1303 /// println!("{:?}", buffer);
1308 /// // ensure the bytes we worked with aren't returned again later
1309 /// stdin.consume(length);
1311 #[stable(feature = "rust1", since = "1.0.0")]
1312 fn fill_buf(&mut self) -> Result<&[u8]>;
1314 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1315 /// so they should no longer be returned in calls to `read`.
1317 /// This function is a lower-level call. It needs to be paired with the
1318 /// [`fill_buf`][fillbuf] method to function properly. This function does
1319 /// not perform any I/O, it simply informs this object that some amount of
1320 /// its buffer, returned from `fill_buf`, has been consumed and should no
1321 /// longer be returned. As such, this function may do odd things if
1322 /// `fill_buf` isn't called before calling it.
1324 /// [fillbuf]: #tymethod.fill_buff
1326 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1331 /// Since `consume()` is meant to be used with [`fill_buf()`][fillbuf],
1332 /// that method's example includes an example of `consume()`.
1333 #[stable(feature = "rust1", since = "1.0.0")]
1334 fn consume(&mut self, amt: usize);
1336 /// Read all bytes into `buf` until the delimiter `byte` is reached.
1338 /// This function will read bytes from the underlying stream until the
1339 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1340 /// the delimiter (if found) will be appended to `buf`.
1342 /// If this reader is currently at EOF then this function will not modify
1343 /// `buf` and will return `Ok(n)` where `n` is the number of bytes which
1348 /// This function will ignore all instances of `ErrorKind::Interrupted` and
1349 /// will otherwise return any errors returned by `fill_buf`.
1351 /// If an I/O error is encountered then all bytes read so far will be
1352 /// present in `buf` and its length will have been adjusted appropriately.
1356 /// A locked standard input implements `BufRead`. In this example, we'll
1357 /// read from standard input until we see an `a` byte.
1361 /// use std::io::prelude::*;
1363 /// fn foo() -> io::Result<()> {
1364 /// let stdin = io::stdin();
1365 /// let mut stdin = stdin.lock();
1366 /// let mut buffer = Vec::new();
1368 /// try!(stdin.read_until(b'a', &mut buffer));
1370 /// println!("{:?}", buffer);
1374 #[stable(feature = "rust1", since = "1.0.0")]
1375 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
1376 read_until(self, byte, buf)
1379 /// Read all bytes until a newline (the 0xA byte) is reached, and append
1380 /// them to the provided buffer.
1382 /// This function will read bytes from the underlying stream until the
1383 /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
1384 /// up to, and including, the delimiter (if found) will be appended to
1387 /// If this reader is currently at EOF then this function will not modify
1388 /// `buf` and will return `Ok(n)` where `n` is the number of bytes which
1393 /// This function has the same error semantics as `read_until` and will also
1394 /// return an error if the read bytes are not valid UTF-8. If an I/O error
1395 /// is encountered then `buf` may contain some bytes already read in the
1396 /// event that all data read so far was valid UTF-8.
1400 /// A locked standard input implements `BufRead`. In this example, we'll
1401 /// read all of the lines from standard input. If we were to do this in
1402 /// an actual project, the [`lines()`][lines] method would be easier, of
1405 /// [lines]: #method.lines
1409 /// use std::io::prelude::*;
1411 /// let stdin = io::stdin();
1412 /// let mut stdin = stdin.lock();
1413 /// let mut buffer = String::new();
1415 /// while stdin.read_line(&mut buffer).unwrap() > 0 {
1416 /// // work with buffer
1417 /// println!("{:?}", buffer);
1422 #[stable(feature = "rust1", since = "1.0.0")]
1423 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
1424 // Note that we are not calling the `.read_until` method here, but
1425 // rather our hardcoded implementation. For more details as to why, see
1426 // the comments in `read_to_end`.
1427 append_to_string(buf, |b| read_until(self, b'\n', b))
1430 /// Returns an iterator over the contents of this reader split on the byte
1433 /// The iterator returned from this function will return instances of
1434 /// `io::Result<Vec<u8>>`. Each vector returned will *not* have the
1435 /// delimiter byte at the end.
1437 /// This function will yield errors whenever `read_until` would have also
1438 /// yielded an error.
1442 /// A locked standard input implements `BufRead`. In this example, we'll
1443 /// read some input from standard input, splitting on commas.
1447 /// use std::io::prelude::*;
1449 /// let stdin = io::stdin();
1451 /// for content in stdin.lock().split(b',') {
1452 /// println!("{:?}", content.unwrap());
1455 #[stable(feature = "rust1", since = "1.0.0")]
1456 fn split(self, byte: u8) -> Split<Self> where Self: Sized {
1457 Split { buf: self, delim: byte }
1460 /// Returns an iterator over the lines of this reader.
1462 /// The iterator returned from this function will yield instances of
1463 /// `io::Result<String>`. Each string returned will *not* have a newline
1464 /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
1468 /// A locked standard input implements `BufRead`:
1472 /// use std::io::prelude::*;
1474 /// let stdin = io::stdin();
1476 /// for line in stdin.lock().lines() {
1477 /// println!("{}", line.unwrap());
1480 #[stable(feature = "rust1", since = "1.0.0")]
1481 fn lines(self) -> Lines<Self> where Self: Sized {
1486 /// A `Write` adaptor which will write data to multiple locations.
1488 /// This struct is generally created by calling [`broadcast()`][broadcast] on a
1489 /// writer. Please see the documentation of `broadcast()` for more details.
1491 /// [broadcast]: trait.Write.html#method.broadcast
1492 #[unstable(feature = "io", reason = "awaiting stability of Write::broadcast",
1494 #[rustc_deprecated(reason = "error handling semantics unclear and \
1495 don't seem to have an ergonomic resolution",
1497 pub struct Broadcast<T, U> {
1502 #[unstable(feature = "io", reason = "awaiting stability of Write::broadcast",
1504 #[rustc_deprecated(reason = "error handling semantics unclear and \
1505 don't seem to have an ergonomic resolution",
1507 #[allow(deprecated)]
1508 impl<T: Write, U: Write> Write for Broadcast<T, U> {
1509 fn write(&mut self, data: &[u8]) -> Result<usize> {
1510 let n = try!(self.first.write(data));
1511 // FIXME: what if the write fails? (we wrote something)
1512 try!(self.second.write_all(&data[..n]));
1516 fn flush(&mut self) -> Result<()> {
1517 self.first.flush().and(self.second.flush())
1521 /// Adaptor to chain together two readers.
1523 /// This struct is generally created by calling [`chain()`][chain] on a reader.
1524 /// Please see the documentation of `chain()` for more details.
1526 /// [chain]: trait.Read.html#method.chain
1527 #[stable(feature = "rust1", since = "1.0.0")]
1528 pub struct Chain<T, U> {
1534 #[stable(feature = "rust1", since = "1.0.0")]
1535 impl<T: Read, U: Read> Read for Chain<T, U> {
1536 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1537 if !self.done_first {
1538 match try!(self.first.read(buf)) {
1539 0 => { self.done_first = true; }
1543 self.second.read(buf)
1547 /// Reader adaptor which limits the bytes read from an underlying reader.
1549 /// This struct is generally created by calling [`take()`][take] on a reader.
1550 /// Please see the documentation of `take()` for more details.
1552 /// [take]: trait.Read.html#method.take
1553 #[stable(feature = "rust1", since = "1.0.0")]
1554 pub struct Take<T> {
1560 /// Returns the number of bytes that can be read before this instance will
1565 /// This instance may reach EOF after reading fewer bytes than indicated by
1566 /// this method if the underlying `Read` instance reaches EOF.
1567 #[stable(feature = "rust1", since = "1.0.0")]
1568 pub fn limit(&self) -> u64 { self.limit }
1571 #[stable(feature = "rust1", since = "1.0.0")]
1572 impl<T: Read> Read for Take<T> {
1573 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1574 // Don't call into inner reader at all at EOF because it may still block
1575 if self.limit == 0 {
1579 let max = cmp::min(buf.len() as u64, self.limit) as usize;
1580 let n = try!(self.inner.read(&mut buf[..max]));
1581 self.limit -= n as u64;
1586 #[stable(feature = "rust1", since = "1.0.0")]
1587 impl<T: BufRead> BufRead for Take<T> {
1588 fn fill_buf(&mut self) -> Result<&[u8]> {
1589 let buf = try!(self.inner.fill_buf());
1590 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
1594 fn consume(&mut self, amt: usize) {
1595 // Don't let callers reset the limit by passing an overlarge value
1596 let amt = cmp::min(amt as u64, self.limit) as usize;
1597 self.limit -= amt as u64;
1598 self.inner.consume(amt);
1602 /// An adaptor which will emit all read data to a specified writer as well.
1604 /// This struct is generally created by calling [`tee()`][tee] on a reader.
1605 /// Please see the documentation of `tee()` for more details.
1607 /// [tee]: trait.Read.html#method.tee
1608 #[unstable(feature = "io", reason = "awaiting stability of Read::tee",
1610 #[rustc_deprecated(reason = "error handling semantics unclear and \
1611 don't seem to have an ergonomic resolution",
1613 pub struct Tee<R, W> {
1618 #[unstable(feature = "io", reason = "awaiting stability of Read::tee",
1620 #[rustc_deprecated(reason = "error handling semantics unclear and \
1621 don't seem to have an ergonomic resolution",
1623 #[allow(deprecated)]
1624 impl<R: Read, W: Write> Read for Tee<R, W> {
1625 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1626 let n = try!(self.reader.read(buf));
1627 // FIXME: what if the write fails? (we read something)
1628 try!(self.writer.write_all(&buf[..n]));
1633 /// An iterator over `u8` values of a reader.
1635 /// This struct is generally created by calling [`bytes()`][bytes] on a reader.
1636 /// Please see the documentation of `bytes()` for more details.
1638 /// [bytes]: trait.Read.html#method.bytes
1639 #[stable(feature = "rust1", since = "1.0.0")]
1640 pub struct Bytes<R> {
1644 #[stable(feature = "rust1", since = "1.0.0")]
1645 impl<R: Read> Iterator for Bytes<R> {
1646 type Item = Result<u8>;
1648 fn next(&mut self) -> Option<Result<u8>> {
1650 match self.inner.read(&mut buf) {
1652 Ok(..) => Some(Ok(buf[0])),
1653 Err(e) => Some(Err(e)),
1658 /// An iterator over the `char`s of a reader.
1660 /// This struct is generally created by calling [`chars()`][chars] on a reader.
1661 /// Please see the documentation of `chars()` for more details.
1663 /// [chars]: trait.Read.html#method.chars
1664 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1666 pub struct Chars<R> {
1670 /// An enumeration of possible errors that can be generated from the `Chars`
1673 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1675 pub enum CharsError {
1676 /// Variant representing that the underlying stream was read successfully
1677 /// but it did not contain valid utf8 data.
1680 /// Variant representing that an I/O error occurred.
1684 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1686 impl<R: Read> Iterator for Chars<R> {
1687 type Item = result::Result<char, CharsError>;
1689 fn next(&mut self) -> Option<result::Result<char, CharsError>> {
1691 let first_byte = match self.inner.read(&mut buf) {
1692 Ok(0) => return None,
1694 Err(e) => return Some(Err(CharsError::Other(e))),
1696 let width = core_str::utf8_char_width(first_byte);
1697 if width == 1 { return Some(Ok(first_byte as char)) }
1698 if width == 0 { return Some(Err(CharsError::NotUtf8)) }
1699 let mut buf = [first_byte, 0, 0, 0];
1702 while start < width {
1703 match self.inner.read(&mut buf[start..width]) {
1704 Ok(0) => return Some(Err(CharsError::NotUtf8)),
1705 Ok(n) => start += n,
1706 Err(e) => return Some(Err(CharsError::Other(e))),
1710 Some(match str::from_utf8(&buf[..width]).ok() {
1711 Some(s) => Ok(s.char_at(0)),
1712 None => Err(CharsError::NotUtf8),
1717 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1719 impl std_error::Error for CharsError {
1720 fn description(&self) -> &str {
1722 CharsError::NotUtf8 => "invalid utf8 encoding",
1723 CharsError::Other(ref e) => std_error::Error::description(e),
1726 fn cause(&self) -> Option<&std_error::Error> {
1728 CharsError::NotUtf8 => None,
1729 CharsError::Other(ref e) => e.cause(),
1734 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1736 impl fmt::Display for CharsError {
1737 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1739 CharsError::NotUtf8 => {
1740 "byte stream did not contain valid utf8".fmt(f)
1742 CharsError::Other(ref e) => e.fmt(f),
1747 /// An iterator over the contents of an instance of `BufRead` split on a
1748 /// particular byte.
1750 /// This struct is generally created by calling [`split()`][split] on a
1751 /// `BufRead`. Please see the documentation of `split()` for more details.
1753 /// [split]: trait.BufRead.html#method.split
1754 #[stable(feature = "rust1", since = "1.0.0")]
1755 pub struct Split<B> {
1760 #[stable(feature = "rust1", since = "1.0.0")]
1761 impl<B: BufRead> Iterator for Split<B> {
1762 type Item = Result<Vec<u8>>;
1764 fn next(&mut self) -> Option<Result<Vec<u8>>> {
1765 let mut buf = Vec::new();
1766 match self.buf.read_until(self.delim, &mut buf) {
1769 if buf[buf.len() - 1] == self.delim {
1774 Err(e) => Some(Err(e))
1779 /// An iterator over the lines of an instance of `BufRead`.
1781 /// This struct is generally created by calling [`lines()`][lines] on a
1782 /// `BufRead`. Please see the documentation of `lines()` for more details.
1784 /// [lines]: trait.BufRead.html#method.lines
1785 #[stable(feature = "rust1", since = "1.0.0")]
1786 pub struct Lines<B> {
1790 #[stable(feature = "rust1", since = "1.0.0")]
1791 impl<B: BufRead> Iterator for Lines<B> {
1792 type Item = Result<String>;
1794 fn next(&mut self) -> Option<Result<String>> {
1795 let mut buf = String::new();
1796 match self.buf.read_line(&mut buf) {
1799 if buf.ends_with("\n") {
1801 if buf.ends_with("\r") {
1807 Err(e) => Some(Err(e))
1823 let mut buf = Cursor::new(&b"12"[..]);
1824 let mut v = Vec::new();
1825 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
1826 assert_eq!(v, b"12");
1828 let mut buf = Cursor::new(&b"1233"[..]);
1829 let mut v = Vec::new();
1830 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
1831 assert_eq!(v, b"123");
1833 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
1834 assert_eq!(v, b"3");
1836 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
1842 let buf = Cursor::new(&b"12"[..]);
1843 let mut s = buf.split(b'3');
1844 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1845 assert!(s.next().is_none());
1847 let buf = Cursor::new(&b"1233"[..]);
1848 let mut s = buf.split(b'3');
1849 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1850 assert_eq!(s.next().unwrap().unwrap(), vec![]);
1851 assert!(s.next().is_none());
1856 let mut buf = Cursor::new(&b"12"[..]);
1857 let mut v = String::new();
1858 assert_eq!(buf.read_line(&mut v).unwrap(), 2);
1859 assert_eq!(v, "12");
1861 let mut buf = Cursor::new(&b"12\n\n"[..]);
1862 let mut v = String::new();
1863 assert_eq!(buf.read_line(&mut v).unwrap(), 3);
1864 assert_eq!(v, "12\n");
1866 assert_eq!(buf.read_line(&mut v).unwrap(), 1);
1867 assert_eq!(v, "\n");
1869 assert_eq!(buf.read_line(&mut v).unwrap(), 0);
1875 let buf = Cursor::new(&b"12\r"[..]);
1876 let mut s = buf.lines();
1877 assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
1878 assert!(s.next().is_none());
1880 let buf = Cursor::new(&b"12\r\n\n"[..]);
1881 let mut s = buf.lines();
1882 assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
1883 assert_eq!(s.next().unwrap().unwrap(), "".to_string());
1884 assert!(s.next().is_none());
1889 let mut c = Cursor::new(&b""[..]);
1890 let mut v = Vec::new();
1891 assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
1894 let mut c = Cursor::new(&b"1"[..]);
1895 let mut v = Vec::new();
1896 assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
1897 assert_eq!(v, b"1");
1899 let cap = 1024 * 1024;
1900 let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
1901 let mut v = Vec::new();
1902 let (a, b) = data.split_at(data.len() / 2);
1903 assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
1904 assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
1905 assert_eq!(v, data);
1909 fn read_to_string() {
1910 let mut c = Cursor::new(&b""[..]);
1911 let mut v = String::new();
1912 assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
1915 let mut c = Cursor::new(&b"1"[..]);
1916 let mut v = String::new();
1917 assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
1920 let mut c = Cursor::new(&b"\xff"[..]);
1921 let mut v = String::new();
1922 assert!(c.read_to_string(&mut v).is_err());
1927 let mut buf = [0; 4];
1929 let mut c = Cursor::new(&b""[..]);
1930 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1931 io::ErrorKind::UnexpectedEof);
1933 let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
1934 c.read_exact(&mut buf).unwrap();
1935 assert_eq!(&buf, b"1234");
1936 c.read_exact(&mut buf).unwrap();
1937 assert_eq!(&buf, b"5678");
1938 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1939 io::ErrorKind::UnexpectedEof);
1943 fn read_exact_slice() {
1944 let mut buf = [0; 4];
1946 let mut c = &b""[..];
1947 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1948 io::ErrorKind::UnexpectedEof);
1950 let mut c = &b"123"[..];
1951 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1952 io::ErrorKind::UnexpectedEof);
1953 // make sure the optimized (early returning) method is being used
1954 assert_eq!(&buf, &[0; 4]);
1956 let mut c = &b"1234"[..];
1957 c.read_exact(&mut buf).unwrap();
1958 assert_eq!(&buf, b"1234");
1960 let mut c = &b"56789"[..];
1961 c.read_exact(&mut buf).unwrap();
1962 assert_eq!(&buf, b"5678");
1963 assert_eq!(c, b"9");
1971 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
1972 Err(io::Error::new(io::ErrorKind::Other, ""))
1976 let mut buf = [0; 1];
1977 assert_eq!(0, R.take(0).read(&mut buf).unwrap());
1981 fn bench_read_to_end(b: &mut test::Bencher) {
1983 let mut lr = repeat(1).take(10000000);
1984 let mut vec = Vec::with_capacity(1024);
1985 super::read_to_end(&mut lr, &mut vec);