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};
259 #[stable(feature = "rust1", since = "1.0.0")]
260 pub use self::buffered::{BufReader, BufWriter, LineWriter};
261 #[stable(feature = "rust1", since = "1.0.0")]
262 pub use self::buffered::IntoInnerError;
263 #[stable(feature = "rust1", since = "1.0.0")]
264 pub use self::cursor::Cursor;
265 #[stable(feature = "rust1", since = "1.0.0")]
266 pub use self::error::{Result, Error, ErrorKind};
267 #[stable(feature = "rust1", since = "1.0.0")]
268 pub use self::util::{copy, sink, Sink, empty, Empty, repeat, Repeat};
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub use self::stdio::{stdin, stdout, stderr, _print, Stdin, Stdout, Stderr};
271 #[stable(feature = "rust1", since = "1.0.0")]
272 pub use self::stdio::{StdoutLock, StderrLock, StdinLock};
273 #[unstable(feature = "libstd_io_internals", issue = "0")]
274 #[doc(no_inline, hidden)]
275 pub use self::stdio::{set_panic, set_print};
286 const DEFAULT_BUF_SIZE: usize = 64 * 1024;
288 // A few methods below (read_to_string, read_line) will append data into a
289 // `String` buffer, but we need to be pretty careful when doing this. The
290 // implementation will just call `.as_mut_vec()` and then delegate to a
291 // byte-oriented reading method, but we must ensure that when returning we never
292 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
294 // To this end, we use an RAII guard (to protect against panics) which updates
295 // the length of the string when it is dropped. This guard initially truncates
296 // the string to the prior length and only after we've validated that the
297 // new contents are valid UTF-8 do we allow it to set a longer length.
299 // The unsafety in this function is twofold:
301 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
303 // 2. We're passing a raw buffer to the function `f`, and it is expected that
304 // the function only *appends* bytes to the buffer. We'll get undefined
305 // behavior if existing bytes are overwritten to have non-UTF-8 data.
306 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
307 where F: FnOnce(&mut Vec<u8>) -> Result<usize>
309 struct Guard<'a> { s: &'a mut Vec<u8>, len: usize }
310 impl<'a> Drop for Guard<'a> {
312 unsafe { self.s.set_len(self.len); }
317 let mut g = Guard { len: buf.len(), s: buf.as_mut_vec() };
319 if str::from_utf8(&g.s[g.len..]).is_err() {
321 Err(Error::new(ErrorKind::InvalidData,
322 "stream did not contain valid UTF-8"))
331 // This uses an adaptive system to extend the vector when it fills. We want to
332 // avoid paying to allocate and zero a huge chunk of memory if the reader only
333 // has 4 bytes while still making large reads if the reader does have a ton
334 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
335 // time is 4,500 times (!) slower than this if the reader has a very small
336 // amount of data to return.
337 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
338 let start_len = buf.len();
339 let mut len = start_len;
340 let mut new_write_size = 16;
343 if len == buf.len() {
344 if new_write_size < DEFAULT_BUF_SIZE {
347 buf.resize(len + new_write_size, 0);
350 match r.read(&mut buf[len..]) {
352 ret = Ok(len - start_len);
356 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
368 /// The `Read` trait allows for reading bytes from a source.
370 /// Implementors of the `Read` trait are sometimes called 'readers'.
372 /// Readers are defined by one required method, `read()`. Each call to `read`
373 /// will attempt to pull bytes from this source into a provided buffer. A
374 /// number of other methods are implemented in terms of `read()`, giving
375 /// implementors a number of ways to read bytes while only needing to implement
378 /// Readers are intended to be composable with one another. Many implementors
379 /// throughout `std::io` take and provide types which implement the `Read`
382 /// Please note that each call to `read` may involve a system call, and
383 /// therefore, using something that implements [`BufRead`][bufread], such as
384 /// [`BufReader`][bufreader], will be more efficient.
386 /// [bufread]: trait.BufRead.html
387 /// [bufreader]: struct.BufReader.html
391 /// [`File`][file]s implement `Read`:
393 /// [file]: ../std/fs/struct.File.html
397 /// use std::io::prelude::*;
398 /// use std::fs::File;
400 /// # fn foo() -> io::Result<()> {
401 /// let mut f = try!(File::open("foo.txt"));
402 /// let mut buffer = [0; 10];
404 /// // read up to 10 bytes
405 /// try!(f.read(&mut buffer));
407 /// let mut buffer = vec![0; 10];
408 /// // read the whole file
409 /// try!(f.read_to_end(&mut buffer));
411 /// // read into a String, so that you don't need to do the conversion.
412 /// let mut buffer = String::new();
413 /// try!(f.read_to_string(&mut buffer));
415 /// // and more! See the other methods for more details.
419 #[stable(feature = "rust1", since = "1.0.0")]
421 /// Pull some bytes from this source into the specified buffer, returning
422 /// how many bytes were read.
424 /// This function does not provide any guarantees about whether it blocks
425 /// waiting for data, but if an object needs to block for a read but cannot
426 /// it will typically signal this via an `Err` return value.
428 /// If the return value of this method is `Ok(n)`, then it must be
429 /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
430 /// that the buffer `buf` has been filled in with `n` bytes of data from this
431 /// source. If `n` is `0`, then it can indicate one of two scenarios:
433 /// 1. This reader has reached its "end of file" and will likely no longer
434 /// be able to produce bytes. Note that this does not mean that the
435 /// reader will *always* no longer be able to produce bytes.
436 /// 2. The buffer specified was 0 bytes in length.
438 /// No guarantees are provided about the contents of `buf` when this
439 /// function is called, implementations cannot rely on any property of the
440 /// contents of `buf` being true. It is recommended that implementations
441 /// only write data to `buf` instead of reading its contents.
445 /// If this function encounters any form of I/O or other error, an error
446 /// variant will be returned. If an error is returned then it must be
447 /// guaranteed that no bytes were read.
451 /// [`File`][file]s implement `Read`:
453 /// [file]: ../std/fs/struct.File.html
457 /// use std::io::prelude::*;
458 /// use std::fs::File;
460 /// # fn foo() -> io::Result<()> {
461 /// let mut f = try!(File::open("foo.txt"));
462 /// let mut buffer = [0; 10];
465 /// try!(f.read(&mut buffer[..]));
469 #[stable(feature = "rust1", since = "1.0.0")]
470 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
472 /// Read all bytes until EOF in this source, placing them into `buf`.
474 /// All bytes read from this source will be appended to the specified buffer
475 /// `buf`. This function will continuously call `read` to append more data to
476 /// `buf` until `read` returns either `Ok(0)` or an error of
477 /// non-`ErrorKind::Interrupted` kind.
479 /// If successful, this function will return the total number of bytes read.
483 /// If this function encounters an error of the kind
484 /// `ErrorKind::Interrupted` then the error is ignored and the operation
487 /// If any other read error is encountered then this function immediately
488 /// returns. Any bytes which have already been read will be appended to
493 /// [`File`][file]s implement `Read`:
495 /// [file]: ../std/fs/struct.File.html
499 /// use std::io::prelude::*;
500 /// use std::fs::File;
502 /// # fn foo() -> io::Result<()> {
503 /// let mut f = try!(File::open("foo.txt"));
504 /// let mut buffer = Vec::new();
506 /// // read the whole file
507 /// try!(f.read_to_end(&mut buffer));
511 #[stable(feature = "rust1", since = "1.0.0")]
512 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
513 read_to_end(self, buf)
516 /// Read all bytes until EOF in this source, placing them into `buf`.
518 /// If successful, this function returns the number of bytes which were read
519 /// and appended to `buf`.
523 /// If the data in this stream is *not* valid UTF-8 then an error is
524 /// returned and `buf` is unchanged.
526 /// See [`read_to_end()`][readtoend] for other error semantics.
528 /// [readtoend]: #method.read_to_end
532 /// [`File`][file]s implement `Read`:
534 /// [file]: ../std/fs/struct.File.html
538 /// use std::io::prelude::*;
539 /// use std::fs::File;
541 /// # fn foo() -> io::Result<()> {
542 /// let mut f = try!(File::open("foo.txt"));
543 /// let mut buffer = String::new();
545 /// try!(f.read_to_string(&mut buffer));
549 #[stable(feature = "rust1", since = "1.0.0")]
550 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
551 // Note that we do *not* call `.read_to_end()` here. We are passing
552 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
553 // method to fill it up. An arbitrary implementation could overwrite the
554 // entire contents of the vector, not just append to it (which is what
555 // we are expecting).
557 // To prevent extraneously checking the UTF-8-ness of the entire buffer
558 // we pass it to our hardcoded `read_to_end` implementation which we
559 // know is guaranteed to only read data into the end of the buffer.
560 append_to_string(buf, |b| read_to_end(self, b))
563 /// Read the exact number of bytes required to fill `buf`.
565 /// This function reads as many bytes as necessary to completely fill the
566 /// specified buffer `buf`.
568 /// No guarantees are provided about the contents of `buf` when this
569 /// function is called, implementations cannot rely on any property of the
570 /// contents of `buf` being true. It is recommended that implementations
571 /// only write data to `buf` instead of reading its contents.
575 /// If this function encounters an error of the kind
576 /// `ErrorKind::Interrupted` then the error is ignored and the operation
579 /// If this function encounters an "end of file" before completely filling
580 /// the buffer, it returns an error of the kind `ErrorKind::UnexpectedEof`.
581 /// The contents of `buf` are unspecified in this case.
583 /// If any other read error is encountered then this function immediately
584 /// returns. The contents of `buf` are unspecified in this case.
586 /// If this function returns an error, it is unspecified how many bytes it
587 /// has read, but it will never read more than would be necessary to
588 /// completely fill the buffer.
592 /// [`File`][file]s implement `Read`:
594 /// [file]: ../std/fs/struct.File.html
598 /// use std::io::prelude::*;
599 /// use std::fs::File;
601 /// # fn foo() -> io::Result<()> {
602 /// let mut f = try!(File::open("foo.txt"));
603 /// let mut buffer = [0; 10];
605 /// // read exactly 10 bytes
606 /// try!(f.read_exact(&mut buffer));
610 #[stable(feature = "read_exact", since = "1.6.0")]
611 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
612 while !buf.is_empty() {
613 match self.read(buf) {
615 Ok(n) => { let tmp = buf; buf = &mut tmp[n..]; }
616 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
617 Err(e) => return Err(e),
621 Err(Error::new(ErrorKind::UnexpectedEof,
622 "failed to fill whole buffer"))
628 /// Creates a "by reference" adaptor for this instance of `Read`.
630 /// The returned adaptor also implements `Read` and will simply borrow this
635 /// [`File`][file]s implement `Read`:
637 /// [file]: ../std/fs/struct.File.html
641 /// use std::io::Read;
642 /// use std::fs::File;
644 /// # fn foo() -> io::Result<()> {
645 /// let mut f = try!(File::open("foo.txt"));
646 /// let mut buffer = Vec::new();
647 /// let mut other_buffer = Vec::new();
650 /// let reference = f.by_ref();
652 /// // read at most 5 bytes
653 /// try!(reference.take(5).read_to_end(&mut buffer));
655 /// } // drop our &mut reference so we can use f again
657 /// // original file still usable, read the rest
658 /// try!(f.read_to_end(&mut other_buffer));
662 #[stable(feature = "rust1", since = "1.0.0")]
663 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
665 /// Transforms this `Read` instance to an `Iterator` over its bytes.
667 /// The returned type implements `Iterator` where the `Item` is `Result<u8,
668 /// R::Err>`. The yielded item is `Ok` if a byte was successfully read and
669 /// `Err` otherwise for I/O errors. EOF is mapped to returning `None` from
674 /// [`File`][file]s implement `Read`:
676 /// [file]: ../std/fs/struct.File.html
680 /// use std::io::prelude::*;
681 /// use std::fs::File;
683 /// # fn foo() -> io::Result<()> {
684 /// let mut f = try!(File::open("foo.txt"));
686 /// for byte in f.bytes() {
687 /// println!("{}", byte.unwrap());
692 #[stable(feature = "rust1", since = "1.0.0")]
693 fn bytes(self) -> Bytes<Self> where Self: Sized {
694 Bytes { inner: self }
697 /// Transforms this `Read` instance to an `Iterator` over `char`s.
699 /// This adaptor will attempt to interpret this reader as a UTF-8 encoded
700 /// sequence of characters. The returned iterator will return `None` once
701 /// EOF is reached for this reader. Otherwise each element yielded will be a
702 /// `Result<char, E>` where `E` may contain information about what I/O error
703 /// occurred or where decoding failed.
705 /// Currently this adaptor will discard intermediate data read, and should
706 /// be avoided if this is not desired.
710 /// [`File`][file]s implement `Read`:
712 /// [file]: ../std/fs/struct.File.html
717 /// use std::io::prelude::*;
718 /// use std::fs::File;
720 /// # fn foo() -> io::Result<()> {
721 /// let mut f = try!(File::open("foo.txt"));
723 /// for c in f.chars() {
724 /// println!("{}", c.unwrap());
729 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
730 of where errors happen is currently \
731 unclear and may change",
733 fn chars(self) -> Chars<Self> where Self: Sized {
734 Chars { inner: self }
737 /// Creates an adaptor which will chain this stream with another.
739 /// The returned `Read` instance will first read all bytes from this object
740 /// until EOF is encountered. Afterwards the output is equivalent to the
741 /// output of `next`.
745 /// [`File`][file]s implement `Read`:
747 /// [file]: ../std/fs/struct.File.html
751 /// use std::io::prelude::*;
752 /// use std::fs::File;
754 /// # fn foo() -> io::Result<()> {
755 /// let mut f1 = try!(File::open("foo.txt"));
756 /// let mut f2 = try!(File::open("bar.txt"));
758 /// let mut handle = f1.chain(f2);
759 /// let mut buffer = String::new();
761 /// // read the value into a String. We could use any Read method here,
762 /// // this is just one example.
763 /// try!(handle.read_to_string(&mut buffer));
767 #[stable(feature = "rust1", since = "1.0.0")]
768 fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized {
769 Chain { first: self, second: next, done_first: false }
772 /// Creates an adaptor which will read at most `limit` bytes from it.
774 /// This function returns a new instance of `Read` which will read at most
775 /// `limit` bytes, after which it will always return EOF (`Ok(0)`). Any
776 /// read errors will not count towards the number of bytes read and future
777 /// calls to `read` may succeed.
781 /// [`File`][file]s implement `Read`:
783 /// [file]: ../std/fs/struct.File.html
787 /// use std::io::prelude::*;
788 /// use std::fs::File;
790 /// # fn foo() -> io::Result<()> {
791 /// let mut f = try!(File::open("foo.txt"));
792 /// let mut buffer = [0; 5];
794 /// // read at most five bytes
795 /// let mut handle = f.take(5);
797 /// try!(handle.read(&mut buffer));
801 #[stable(feature = "rust1", since = "1.0.0")]
802 fn take(self, limit: u64) -> Take<Self> where Self: Sized {
803 Take { inner: self, limit: limit }
806 /// Creates a reader adaptor which will write all read data into the given
809 /// Whenever the returned `Read` instance is read it will write the read
810 /// data to `out`. The current semantics of this implementation imply that
811 /// a `write` error will not report how much data was initially read.
815 /// [`File`][file]s implement `Read`:
817 /// [file]: ../std/fs/struct.File.html
822 /// use std::io::prelude::*;
823 /// use std::fs::File;
825 /// # fn foo() -> io::Result<()> {
826 /// let mut f = try!(File::open("foo.txt"));
827 /// let mut buffer1 = Vec::with_capacity(10);
828 /// let mut buffer2 = Vec::with_capacity(10);
830 /// // write the output to buffer1 as we read
831 /// let mut handle = f.tee(&mut buffer1);
833 /// try!(handle.read(&mut buffer2));
837 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
838 of where errors happen is currently \
839 unclear and may change",
841 #[rustc_deprecated(reason = "error handling semantics unclear and \
842 don't seem to have an ergonomic resolution",
845 fn tee<W: Write>(self, out: W) -> Tee<Self, W> where Self: Sized {
846 Tee { reader: self, writer: out }
850 /// A trait for objects which are byte-oriented sinks.
852 /// Implementors of the `Write` trait are sometimes called 'writers'.
854 /// Writers are defined by two required methods, `write()` and `flush()`:
856 /// * The `write()` method will attempt to write some data into the object,
857 /// returning how many bytes were successfully written.
859 /// * The `flush()` method is useful for adaptors and explicit buffers
860 /// themselves for ensuring that all buffered data has been pushed out to the
863 /// Writers are intended to be composable with one another. Many implementors
864 /// throughout `std::io` take and provide types which implement the `Write`
870 /// use std::io::prelude::*;
871 /// use std::fs::File;
873 /// # fn foo() -> std::io::Result<()> {
874 /// let mut buffer = try!(File::create("foo.txt"));
876 /// try!(buffer.write(b"some bytes"));
880 #[stable(feature = "rust1", since = "1.0.0")]
882 /// Write a buffer into this object, returning how many bytes were written.
884 /// This function will attempt to write the entire contents of `buf`, but
885 /// the entire write may not succeed, or the write may also generate an
886 /// error. A call to `write` represents *at most one* attempt to write to
887 /// any wrapped object.
889 /// Calls to `write` are not guaranteed to block waiting for data to be
890 /// written, and a write which would otherwise block can be indicated through
891 /// an `Err` variant.
893 /// If the return value is `Ok(n)` then it must be guaranteed that
894 /// `0 <= n <= buf.len()`. A return value of `0` typically means that the
895 /// underlying object is no longer able to accept bytes and will likely not
896 /// be able to in the future as well, or that the buffer provided is empty.
900 /// Each call to `write` may generate an I/O error indicating that the
901 /// operation could not be completed. If an error is returned then no bytes
902 /// in the buffer were written to this writer.
904 /// It is **not** considered an error if the entire buffer could not be
905 /// written to this writer.
910 /// use std::io::prelude::*;
911 /// use std::fs::File;
913 /// # fn foo() -> std::io::Result<()> {
914 /// let mut buffer = try!(File::create("foo.txt"));
916 /// try!(buffer.write(b"some bytes"));
920 #[stable(feature = "rust1", since = "1.0.0")]
921 fn write(&mut self, buf: &[u8]) -> Result<usize>;
923 /// Flush this output stream, ensuring that all intermediately buffered
924 /// contents reach their destination.
928 /// It is considered an error if not all bytes could be written due to
929 /// I/O errors or EOF being reached.
934 /// use std::io::prelude::*;
935 /// use std::io::BufWriter;
936 /// use std::fs::File;
938 /// # fn foo() -> std::io::Result<()> {
939 /// let mut buffer = BufWriter::new(try!(File::create("foo.txt")));
941 /// try!(buffer.write(b"some bytes"));
942 /// try!(buffer.flush());
946 #[stable(feature = "rust1", since = "1.0.0")]
947 fn flush(&mut self) -> Result<()>;
949 /// Attempts to write an entire buffer into this write.
951 /// This method will continuously call `write` while there is more data to
952 /// write. This method will not return until the entire buffer has been
953 /// successfully written or an error occurs. The first error generated from
954 /// this method will be returned.
958 /// This function will return the first error that `write` returns.
963 /// use std::io::prelude::*;
964 /// use std::fs::File;
966 /// # fn foo() -> std::io::Result<()> {
967 /// let mut buffer = try!(File::create("foo.txt"));
969 /// try!(buffer.write_all(b"some bytes"));
973 #[stable(feature = "rust1", since = "1.0.0")]
974 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
975 while !buf.is_empty() {
976 match self.write(buf) {
977 Ok(0) => return Err(Error::new(ErrorKind::WriteZero,
978 "failed to write whole buffer")),
979 Ok(n) => buf = &buf[n..],
980 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
981 Err(e) => return Err(e),
987 /// Writes a formatted string into this writer, returning any error
990 /// This method is primarily used to interface with the
991 /// [`format_args!`][formatargs] macro, but it is rare that this should
992 /// explicitly be called. The [`write!`][write] macro should be favored to
993 /// invoke this method instead.
995 /// [formatargs]: ../macro.format_args!.html
996 /// [write]: ../macro.write!.html
998 /// This function internally uses the [`write_all`][writeall] method on
999 /// this trait and hence will continuously write data so long as no errors
1000 /// are received. This also means that partial writes are not indicated in
1003 /// [writeall]: #method.write_all
1007 /// This function will return any I/O error reported while formatting.
1012 /// use std::io::prelude::*;
1013 /// use std::fs::File;
1015 /// # fn foo() -> std::io::Result<()> {
1016 /// let mut buffer = try!(File::create("foo.txt"));
1019 /// try!(write!(buffer, "{:.*}", 2, 1.234567));
1020 /// // turns into this:
1021 /// try!(buffer.write_fmt(format_args!("{:.*}", 2, 1.234567)));
1025 #[stable(feature = "rust1", since = "1.0.0")]
1026 fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<()> {
1027 // Create a shim which translates a Write to a fmt::Write and saves
1028 // off I/O errors. instead of discarding them
1029 struct Adaptor<'a, T: ?Sized + 'a> {
1034 impl<'a, T: Write + ?Sized> fmt::Write for Adaptor<'a, T> {
1035 fn write_str(&mut self, s: &str) -> fmt::Result {
1036 match self.inner.write_all(s.as_bytes()) {
1039 self.error = Err(e);
1046 let mut output = Adaptor { inner: self, error: Ok(()) };
1047 match fmt::write(&mut output, fmt) {
1049 Err(..) => output.error
1053 /// Creates a "by reference" adaptor for this instance of `Write`.
1055 /// The returned adaptor also implements `Write` and will simply borrow this
1061 /// use std::io::Write;
1062 /// use std::fs::File;
1064 /// # fn foo() -> std::io::Result<()> {
1065 /// let mut buffer = try!(File::create("foo.txt"));
1067 /// let reference = buffer.by_ref();
1069 /// // we can use reference just like our original buffer
1070 /// try!(reference.write_all(b"some bytes"));
1074 #[stable(feature = "rust1", since = "1.0.0")]
1075 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
1077 /// Creates a new writer which will write all data to both this writer and
1080 /// All data written to the returned writer will both be written to `self`
1081 /// as well as `other`. Note that the error semantics of the current
1082 /// implementation do not precisely track where errors happen. For example
1083 /// an error on the second call to `write` will not report that the first
1084 /// call to `write` succeeded.
1090 /// use std::io::prelude::*;
1091 /// use std::fs::File;
1093 /// # fn foo() -> std::io::Result<()> {
1094 /// let mut buffer1 = try!(File::create("foo.txt"));
1095 /// let mut buffer2 = Vec::new();
1097 /// // write the output to buffer1 as we read
1098 /// let mut handle = buffer1.broadcast(&mut buffer2);
1100 /// try!(handle.write(b"some bytes"));
1104 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
1105 of where errors happen is currently \
1106 unclear and may change",
1108 #[rustc_deprecated(reason = "error handling semantics unclear and \
1109 don't seem to have an ergonomic resolution",
1111 #[allow(deprecated)]
1112 fn broadcast<W: Write>(self, other: W) -> Broadcast<Self, W>
1115 Broadcast { first: self, second: other }
1119 /// The `Seek` trait provides a cursor which can be moved within a stream of
1122 /// The stream typically has a fixed size, allowing seeking relative to either
1123 /// end or the current offset.
1127 /// [`File`][file]s implement `Seek`:
1129 /// [file]: ../fs/struct.File.html
1133 /// use std::io::prelude::*;
1134 /// use std::fs::File;
1135 /// use std::io::SeekFrom;
1137 /// # fn foo() -> io::Result<()> {
1138 /// let mut f = try!(File::open("foo.txt"));
1140 /// // move the cursor 42 bytes from the start of the file
1141 /// try!(f.seek(SeekFrom::Start(42)));
1145 #[stable(feature = "rust1", since = "1.0.0")]
1147 /// Seek to an offset, in bytes, in a stream.
1149 /// A seek beyond the end of a stream is allowed, but implementation
1152 /// If the seek operation completed successfully,
1153 /// this method returns the new position from the start of the stream.
1154 /// That position can be used later with `SeekFrom::Start`.
1158 /// Seeking to a negative offset is considered an error.
1159 #[stable(feature = "rust1", since = "1.0.0")]
1160 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1163 /// Enumeration of possible methods to seek within an I/O object.
1164 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1165 #[stable(feature = "rust1", since = "1.0.0")]
1167 /// Set the offset to the provided number of bytes.
1168 #[stable(feature = "rust1", since = "1.0.0")]
1171 /// Set the offset to the size of this object plus the specified number of
1174 /// It is possible to seek beyond the end of an object, but it's an error to
1175 /// seek before byte 0.
1176 #[stable(feature = "rust1", since = "1.0.0")]
1179 /// Set the offset to the current position plus the specified number of
1182 /// It is possible to seek beyond the end of an object, but it's an error to
1183 /// seek before byte 0.
1184 #[stable(feature = "rust1", since = "1.0.0")]
1188 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>)
1192 let (done, used) = {
1193 let available = match r.fill_buf() {
1195 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1196 Err(e) => return Err(e)
1198 match memchr::memchr(delim, available) {
1200 buf.extend_from_slice(&available[..i + 1]);
1204 buf.extend_from_slice(available);
1205 (false, available.len())
1211 if done || used == 0 {
1217 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1218 /// to perform extra ways of reading.
1220 /// For example, reading line-by-line is inefficient without using a buffer, so
1221 /// if you want to read by line, you'll need `BufRead`, which includes a
1222 /// [`read_line()`][readline] method as well as a [`lines()`][lines] iterator.
1224 /// [readline]: #method.read_line
1225 /// [lines]: #method.lines
1229 /// A locked standard input implements `BufRead`:
1233 /// use std::io::prelude::*;
1235 /// let stdin = io::stdin();
1236 /// for line in stdin.lock().lines() {
1237 /// println!("{}", line.unwrap());
1241 /// If you have something that implements `Read`, you can use the [`BufReader`
1242 /// type][bufreader] to turn it into a `BufRead`.
1244 /// For example, [`File`][file] implements `Read`, but not `BufRead`.
1245 /// `BufReader` to the rescue!
1247 /// [bufreader]: struct.BufReader.html
1248 /// [file]: ../fs/struct.File.html
1251 /// use std::io::{self, BufReader};
1252 /// use std::io::prelude::*;
1253 /// use std::fs::File;
1255 /// # fn foo() -> io::Result<()> {
1256 /// let f = try!(File::open("foo.txt"));
1257 /// let f = BufReader::new(f);
1259 /// for line in f.lines() {
1260 /// println!("{}", line.unwrap());
1267 #[stable(feature = "rust1", since = "1.0.0")]
1268 pub trait BufRead: Read {
1269 /// Fills the internal buffer of this object, returning the buffer contents.
1271 /// This function is a lower-level call. It needs to be paired with the
1272 /// [`consume`][consume] method to function properly. When calling this
1273 /// method, none of the contents will be "read" in the sense that later
1274 /// calling `read` may return the same contents. As such, `consume` must be
1275 /// called with the number of bytes that are consumed from this buffer to
1276 /// ensure that the bytes are never returned twice.
1278 /// [consume]: #tymethod.consume
1280 /// An empty buffer returned indicates that the stream has reached EOF.
1284 /// This function will return an I/O error if the underlying reader was
1285 /// read, but returned an error.
1289 /// A locked standard input implements `BufRead`:
1293 /// use std::io::prelude::*;
1295 /// let stdin = io::stdin();
1296 /// let mut stdin = stdin.lock();
1298 /// // we can't have two `&mut` references to `stdin`, so use a block
1299 /// // to end the borrow early.
1301 /// let buffer = stdin.fill_buf().unwrap();
1303 /// // work with buffer
1304 /// println!("{:?}", buffer);
1309 /// // ensure the bytes we worked with aren't returned again later
1310 /// stdin.consume(length);
1312 #[stable(feature = "rust1", since = "1.0.0")]
1313 fn fill_buf(&mut self) -> Result<&[u8]>;
1315 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1316 /// so they should no longer be returned in calls to `read`.
1318 /// This function is a lower-level call. It needs to be paired with the
1319 /// [`fill_buf`][fillbuf] method to function properly. This function does
1320 /// not perform any I/O, it simply informs this object that some amount of
1321 /// its buffer, returned from `fill_buf`, has been consumed and should no
1322 /// longer be returned. As such, this function may do odd things if
1323 /// `fill_buf` isn't called before calling it.
1325 /// [fillbuf]: #tymethod.fill_buff
1327 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1332 /// Since `consume()` is meant to be used with [`fill_buf()`][fillbuf],
1333 /// that method's example includes an example of `consume()`.
1334 #[stable(feature = "rust1", since = "1.0.0")]
1335 fn consume(&mut self, amt: usize);
1337 /// Read all bytes into `buf` until the delimiter `byte` is reached.
1339 /// This function will read bytes from the underlying stream until the
1340 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1341 /// the delimiter (if found) will be appended to `buf`.
1343 /// If this reader is currently at EOF then this function will not modify
1344 /// `buf` and will return `Ok(n)` where `n` is the number of bytes which
1349 /// This function will ignore all instances of `ErrorKind::Interrupted` and
1350 /// will otherwise return any errors returned by `fill_buf`.
1352 /// If an I/O error is encountered then all bytes read so far will be
1353 /// present in `buf` and its length will have been adjusted appropriately.
1357 /// A locked standard input implements `BufRead`. In this example, we'll
1358 /// read from standard input until we see an `a` byte.
1362 /// use std::io::prelude::*;
1364 /// fn foo() -> io::Result<()> {
1365 /// let stdin = io::stdin();
1366 /// let mut stdin = stdin.lock();
1367 /// let mut buffer = Vec::new();
1369 /// try!(stdin.read_until(b'a', &mut buffer));
1371 /// println!("{:?}", buffer);
1375 #[stable(feature = "rust1", since = "1.0.0")]
1376 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
1377 read_until(self, byte, buf)
1380 /// Read all bytes until a newline (the 0xA byte) is reached, and append
1381 /// them to the provided buffer.
1383 /// This function will read bytes from the underlying stream until the
1384 /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
1385 /// up to, and including, the delimiter (if found) will be appended to
1388 /// If this reader is currently at EOF then this function will not modify
1389 /// `buf` and will return `Ok(n)` where `n` is the number of bytes which
1394 /// This function has the same error semantics as `read_until` and will also
1395 /// return an error if the read bytes are not valid UTF-8. If an I/O error
1396 /// is encountered then `buf` may contain some bytes already read in the
1397 /// event that all data read so far was valid UTF-8.
1401 /// A locked standard input implements `BufRead`. In this example, we'll
1402 /// read all of the lines from standard input. If we were to do this in
1403 /// an actual project, the [`lines()`][lines] method would be easier, of
1406 /// [lines]: #method.lines
1410 /// use std::io::prelude::*;
1412 /// let stdin = io::stdin();
1413 /// let mut stdin = stdin.lock();
1414 /// let mut buffer = String::new();
1416 /// while stdin.read_line(&mut buffer).unwrap() > 0 {
1417 /// // work with buffer
1418 /// println!("{:?}", buffer);
1423 #[stable(feature = "rust1", since = "1.0.0")]
1424 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
1425 // Note that we are not calling the `.read_until` method here, but
1426 // rather our hardcoded implementation. For more details as to why, see
1427 // the comments in `read_to_end`.
1428 append_to_string(buf, |b| read_until(self, b'\n', b))
1431 /// Returns an iterator over the contents of this reader split on the byte
1434 /// The iterator returned from this function will return instances of
1435 /// `io::Result<Vec<u8>>`. Each vector returned will *not* have the
1436 /// delimiter byte at the end.
1438 /// This function will yield errors whenever `read_until` would have also
1439 /// yielded an error.
1443 /// A locked standard input implements `BufRead`. In this example, we'll
1444 /// read some input from standard input, splitting on commas.
1448 /// use std::io::prelude::*;
1450 /// let stdin = io::stdin();
1452 /// for content in stdin.lock().split(b',') {
1453 /// println!("{:?}", content.unwrap());
1456 #[stable(feature = "rust1", since = "1.0.0")]
1457 fn split(self, byte: u8) -> Split<Self> where Self: Sized {
1458 Split { buf: self, delim: byte }
1461 /// Returns an iterator over the lines of this reader.
1463 /// The iterator returned from this function will yield instances of
1464 /// `io::Result<String>`. Each string returned will *not* have a newline
1465 /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
1469 /// A locked standard input implements `BufRead`:
1473 /// use std::io::prelude::*;
1475 /// let stdin = io::stdin();
1477 /// for line in stdin.lock().lines() {
1478 /// println!("{}", line.unwrap());
1481 #[stable(feature = "rust1", since = "1.0.0")]
1482 fn lines(self) -> Lines<Self> where Self: Sized {
1487 /// A `Write` adaptor which will write data to multiple locations.
1489 /// This struct is generally created by calling [`broadcast()`][broadcast] on a
1490 /// writer. Please see the documentation of `broadcast()` for more details.
1492 /// [broadcast]: trait.Write.html#method.broadcast
1493 #[unstable(feature = "io", reason = "awaiting stability of Write::broadcast",
1495 #[rustc_deprecated(reason = "error handling semantics unclear and \
1496 don't seem to have an ergonomic resolution",
1498 pub struct Broadcast<T, U> {
1503 #[unstable(feature = "io", reason = "awaiting stability of Write::broadcast",
1505 #[rustc_deprecated(reason = "error handling semantics unclear and \
1506 don't seem to have an ergonomic resolution",
1508 #[allow(deprecated)]
1509 impl<T: Write, U: Write> Write for Broadcast<T, U> {
1510 fn write(&mut self, data: &[u8]) -> Result<usize> {
1511 let n = try!(self.first.write(data));
1512 // FIXME: what if the write fails? (we wrote something)
1513 try!(self.second.write_all(&data[..n]));
1517 fn flush(&mut self) -> Result<()> {
1518 self.first.flush().and(self.second.flush())
1522 /// Adaptor to chain together two readers.
1524 /// This struct is generally created by calling [`chain()`][chain] on a reader.
1525 /// Please see the documentation of `chain()` for more details.
1527 /// [chain]: trait.Read.html#method.chain
1528 #[stable(feature = "rust1", since = "1.0.0")]
1529 pub struct Chain<T, U> {
1535 #[stable(feature = "rust1", since = "1.0.0")]
1536 impl<T: Read, U: Read> Read for Chain<T, U> {
1537 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1538 if !self.done_first {
1539 match try!(self.first.read(buf)) {
1540 0 => { self.done_first = true; }
1544 self.second.read(buf)
1548 /// Reader adaptor which limits the bytes read from an underlying reader.
1550 /// This struct is generally created by calling [`take()`][take] on a reader.
1551 /// Please see the documentation of `take()` for more details.
1553 /// [take]: trait.Read.html#method.take
1554 #[stable(feature = "rust1", since = "1.0.0")]
1555 pub struct Take<T> {
1561 /// Returns the number of bytes that can be read before this instance will
1566 /// This instance may reach EOF after reading fewer bytes than indicated by
1567 /// this method if the underlying `Read` instance reaches EOF.
1568 #[stable(feature = "rust1", since = "1.0.0")]
1569 pub fn limit(&self) -> u64 { self.limit }
1572 #[stable(feature = "rust1", since = "1.0.0")]
1573 impl<T: Read> Read for Take<T> {
1574 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1575 // Don't call into inner reader at all at EOF because it may still block
1576 if self.limit == 0 {
1580 let max = cmp::min(buf.len() as u64, self.limit) as usize;
1581 let n = try!(self.inner.read(&mut buf[..max]));
1582 self.limit -= n as u64;
1587 #[stable(feature = "rust1", since = "1.0.0")]
1588 impl<T: BufRead> BufRead for Take<T> {
1589 fn fill_buf(&mut self) -> Result<&[u8]> {
1590 let buf = try!(self.inner.fill_buf());
1591 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
1595 fn consume(&mut self, amt: usize) {
1596 // Don't let callers reset the limit by passing an overlarge value
1597 let amt = cmp::min(amt as u64, self.limit) as usize;
1598 self.limit -= amt as u64;
1599 self.inner.consume(amt);
1603 /// An adaptor which will emit all read data to a specified writer as well.
1605 /// This struct is generally created by calling [`tee()`][tee] on a reader.
1606 /// Please see the documentation of `tee()` for more details.
1608 /// [tee]: trait.Read.html#method.tee
1609 #[unstable(feature = "io", reason = "awaiting stability of Read::tee",
1611 #[rustc_deprecated(reason = "error handling semantics unclear and \
1612 don't seem to have an ergonomic resolution",
1614 pub struct Tee<R, W> {
1619 #[unstable(feature = "io", reason = "awaiting stability of Read::tee",
1621 #[rustc_deprecated(reason = "error handling semantics unclear and \
1622 don't seem to have an ergonomic resolution",
1624 #[allow(deprecated)]
1625 impl<R: Read, W: Write> Read for Tee<R, W> {
1626 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1627 let n = try!(self.reader.read(buf));
1628 // FIXME: what if the write fails? (we read something)
1629 try!(self.writer.write_all(&buf[..n]));
1634 /// An iterator over `u8` values of a reader.
1636 /// This struct is generally created by calling [`bytes()`][bytes] on a reader.
1637 /// Please see the documentation of `bytes()` for more details.
1639 /// [bytes]: trait.Read.html#method.bytes
1640 #[stable(feature = "rust1", since = "1.0.0")]
1641 pub struct Bytes<R> {
1645 #[stable(feature = "rust1", since = "1.0.0")]
1646 impl<R: Read> Iterator for Bytes<R> {
1647 type Item = Result<u8>;
1649 fn next(&mut self) -> Option<Result<u8>> {
1651 match self.inner.read(&mut buf) {
1653 Ok(..) => Some(Ok(buf[0])),
1654 Err(e) => Some(Err(e)),
1659 /// An iterator over the `char`s of a reader.
1661 /// This struct is generally created by calling [`chars()`][chars] on a reader.
1662 /// Please see the documentation of `chars()` for more details.
1664 /// [chars]: trait.Read.html#method.chars
1665 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1667 pub struct Chars<R> {
1671 /// An enumeration of possible errors that can be generated from the `Chars`
1674 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1676 pub enum CharsError {
1677 /// Variant representing that the underlying stream was read successfully
1678 /// but it did not contain valid utf8 data.
1681 /// Variant representing that an I/O error occurred.
1685 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1687 impl<R: Read> Iterator for Chars<R> {
1688 type Item = result::Result<char, CharsError>;
1690 fn next(&mut self) -> Option<result::Result<char, CharsError>> {
1692 let first_byte = match self.inner.read(&mut buf) {
1693 Ok(0) => return None,
1695 Err(e) => return Some(Err(CharsError::Other(e))),
1697 let width = core_str::utf8_char_width(first_byte);
1698 if width == 1 { return Some(Ok(first_byte as char)) }
1699 if width == 0 { return Some(Err(CharsError::NotUtf8)) }
1700 let mut buf = [first_byte, 0, 0, 0];
1703 while start < width {
1704 match self.inner.read(&mut buf[start..width]) {
1705 Ok(0) => return Some(Err(CharsError::NotUtf8)),
1706 Ok(n) => start += n,
1707 Err(e) => return Some(Err(CharsError::Other(e))),
1711 Some(match str::from_utf8(&buf[..width]).ok() {
1712 Some(s) => Ok(s.char_at(0)),
1713 None => Err(CharsError::NotUtf8),
1718 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1720 impl std_error::Error for CharsError {
1721 fn description(&self) -> &str {
1723 CharsError::NotUtf8 => "invalid utf8 encoding",
1724 CharsError::Other(ref e) => std_error::Error::description(e),
1727 fn cause(&self) -> Option<&std_error::Error> {
1729 CharsError::NotUtf8 => None,
1730 CharsError::Other(ref e) => e.cause(),
1735 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1737 impl fmt::Display for CharsError {
1738 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1740 CharsError::NotUtf8 => {
1741 "byte stream did not contain valid utf8".fmt(f)
1743 CharsError::Other(ref e) => e.fmt(f),
1748 /// An iterator over the contents of an instance of `BufRead` split on a
1749 /// particular byte.
1751 /// This struct is generally created by calling [`split()`][split] on a
1752 /// `BufRead`. Please see the documentation of `split()` for more details.
1754 /// [split]: trait.BufRead.html#method.split
1755 #[stable(feature = "rust1", since = "1.0.0")]
1756 pub struct Split<B> {
1761 #[stable(feature = "rust1", since = "1.0.0")]
1762 impl<B: BufRead> Iterator for Split<B> {
1763 type Item = Result<Vec<u8>>;
1765 fn next(&mut self) -> Option<Result<Vec<u8>>> {
1766 let mut buf = Vec::new();
1767 match self.buf.read_until(self.delim, &mut buf) {
1770 if buf[buf.len() - 1] == self.delim {
1775 Err(e) => Some(Err(e))
1780 /// An iterator over the lines of an instance of `BufRead`.
1782 /// This struct is generally created by calling [`lines()`][lines] on a
1783 /// `BufRead`. Please see the documentation of `lines()` for more details.
1785 /// [lines]: trait.BufRead.html#method.lines
1786 #[stable(feature = "rust1", since = "1.0.0")]
1787 pub struct Lines<B> {
1791 #[stable(feature = "rust1", since = "1.0.0")]
1792 impl<B: BufRead> Iterator for Lines<B> {
1793 type Item = Result<String>;
1795 fn next(&mut self) -> Option<Result<String>> {
1796 let mut buf = String::new();
1797 match self.buf.read_line(&mut buf) {
1800 if buf.ends_with("\n") {
1802 if buf.ends_with("\r") {
1808 Err(e) => Some(Err(e))
1824 let mut buf = Cursor::new(&b"12"[..]);
1825 let mut v = Vec::new();
1826 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
1827 assert_eq!(v, b"12");
1829 let mut buf = Cursor::new(&b"1233"[..]);
1830 let mut v = Vec::new();
1831 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
1832 assert_eq!(v, b"123");
1834 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
1835 assert_eq!(v, b"3");
1837 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
1843 let buf = Cursor::new(&b"12"[..]);
1844 let mut s = buf.split(b'3');
1845 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1846 assert!(s.next().is_none());
1848 let buf = Cursor::new(&b"1233"[..]);
1849 let mut s = buf.split(b'3');
1850 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1851 assert_eq!(s.next().unwrap().unwrap(), vec![]);
1852 assert!(s.next().is_none());
1857 let mut buf = Cursor::new(&b"12"[..]);
1858 let mut v = String::new();
1859 assert_eq!(buf.read_line(&mut v).unwrap(), 2);
1860 assert_eq!(v, "12");
1862 let mut buf = Cursor::new(&b"12\n\n"[..]);
1863 let mut v = String::new();
1864 assert_eq!(buf.read_line(&mut v).unwrap(), 3);
1865 assert_eq!(v, "12\n");
1867 assert_eq!(buf.read_line(&mut v).unwrap(), 1);
1868 assert_eq!(v, "\n");
1870 assert_eq!(buf.read_line(&mut v).unwrap(), 0);
1876 let buf = Cursor::new(&b"12\r"[..]);
1877 let mut s = buf.lines();
1878 assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
1879 assert!(s.next().is_none());
1881 let buf = Cursor::new(&b"12\r\n\n"[..]);
1882 let mut s = buf.lines();
1883 assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
1884 assert_eq!(s.next().unwrap().unwrap(), "".to_string());
1885 assert!(s.next().is_none());
1890 let mut c = Cursor::new(&b""[..]);
1891 let mut v = Vec::new();
1892 assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
1895 let mut c = Cursor::new(&b"1"[..]);
1896 let mut v = Vec::new();
1897 assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
1898 assert_eq!(v, b"1");
1900 let cap = 1024 * 1024;
1901 let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
1902 let mut v = Vec::new();
1903 let (a, b) = data.split_at(data.len() / 2);
1904 assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
1905 assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
1906 assert_eq!(v, data);
1910 fn read_to_string() {
1911 let mut c = Cursor::new(&b""[..]);
1912 let mut v = String::new();
1913 assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
1916 let mut c = Cursor::new(&b"1"[..]);
1917 let mut v = String::new();
1918 assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
1921 let mut c = Cursor::new(&b"\xff"[..]);
1922 let mut v = String::new();
1923 assert!(c.read_to_string(&mut v).is_err());
1928 let mut buf = [0; 4];
1930 let mut c = Cursor::new(&b""[..]);
1931 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1932 io::ErrorKind::UnexpectedEof);
1934 let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
1935 c.read_exact(&mut buf).unwrap();
1936 assert_eq!(&buf, b"1234");
1937 c.read_exact(&mut buf).unwrap();
1938 assert_eq!(&buf, b"5678");
1939 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1940 io::ErrorKind::UnexpectedEof);
1944 fn read_exact_slice() {
1945 let mut buf = [0; 4];
1947 let mut c = &b""[..];
1948 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1949 io::ErrorKind::UnexpectedEof);
1951 let mut c = &b"123"[..];
1952 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1953 io::ErrorKind::UnexpectedEof);
1954 // make sure the optimized (early returning) method is being used
1955 assert_eq!(&buf, &[0; 4]);
1957 let mut c = &b"1234"[..];
1958 c.read_exact(&mut buf).unwrap();
1959 assert_eq!(&buf, b"1234");
1961 let mut c = &b"56789"[..];
1962 c.read_exact(&mut buf).unwrap();
1963 assert_eq!(&buf, b"5678");
1964 assert_eq!(c, b"9");
1972 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
1973 Err(io::Error::new(io::ErrorKind::Other, ""))
1977 let mut buf = [0; 1];
1978 assert_eq!(0, R.take(0).read(&mut buf).unwrap());
1982 fn bench_read_to_end(b: &mut test::Bencher) {
1984 let mut lr = repeat(1).take(10000000);
1985 let mut vec = Vec::with_capacity(1024);
1986 super::read_to_end(&mut lr, &mut vec)