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 //! ## Platform-specific behavior
244 //! Many I/O functions throughout the standard library are documented to indicate
245 //! what various library or syscalls they are delegated to. This is done to help
246 //! applications both understand what's happening under the hood as well as investigate
247 //! any possibly unclear semantics. Note, however, that this is informative, not a binding
248 //! contract. The implementation of many of these functions are subject to change over
249 //! time and may call fewer or more syscalls/library functions.
251 #![stable(feature = "rust1", since = "1.0.0")]
254 use rustc_unicode::str as core_str;
255 use error as std_error;
257 use iter::{Iterator};
259 use ops::{Drop, FnOnce};
260 use option::Option::{self, Some, None};
261 use result::Result::{Ok, Err};
268 #[stable(feature = "rust1", since = "1.0.0")]
269 pub use self::buffered::{BufReader, BufWriter, LineWriter};
270 #[stable(feature = "rust1", since = "1.0.0")]
271 pub use self::buffered::IntoInnerError;
272 #[stable(feature = "rust1", since = "1.0.0")]
273 pub use self::cursor::Cursor;
274 #[stable(feature = "rust1", since = "1.0.0")]
275 pub use self::error::{Result, Error, ErrorKind};
276 #[stable(feature = "rust1", since = "1.0.0")]
277 pub use self::util::{copy, sink, Sink, empty, Empty, repeat, Repeat};
278 #[stable(feature = "rust1", since = "1.0.0")]
279 pub use self::stdio::{stdin, stdout, stderr, _print, Stdin, Stdout, Stderr};
280 #[stable(feature = "rust1", since = "1.0.0")]
281 pub use self::stdio::{StdoutLock, StderrLock, StdinLock};
282 #[unstable(feature = "libstd_io_internals", issue = "0")]
283 #[doc(no_inline, hidden)]
284 pub use self::stdio::{set_panic, set_print};
295 const DEFAULT_BUF_SIZE: usize = 64 * 1024;
297 // A few methods below (read_to_string, read_line) will append data into a
298 // `String` buffer, but we need to be pretty careful when doing this. The
299 // implementation will just call `.as_mut_vec()` and then delegate to a
300 // byte-oriented reading method, but we must ensure that when returning we never
301 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
303 // To this end, we use an RAII guard (to protect against panics) which updates
304 // the length of the string when it is dropped. This guard initially truncates
305 // the string to the prior length and only after we've validated that the
306 // new contents are valid UTF-8 do we allow it to set a longer length.
308 // The unsafety in this function is twofold:
310 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
312 // 2. We're passing a raw buffer to the function `f`, and it is expected that
313 // the function only *appends* bytes to the buffer. We'll get undefined
314 // behavior if existing bytes are overwritten to have non-UTF-8 data.
315 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
316 where F: FnOnce(&mut Vec<u8>) -> Result<usize>
318 struct Guard<'a> { s: &'a mut Vec<u8>, len: usize }
319 impl<'a> Drop for Guard<'a> {
321 unsafe { self.s.set_len(self.len); }
326 let mut g = Guard { len: buf.len(), s: buf.as_mut_vec() };
328 if str::from_utf8(&g.s[g.len..]).is_err() {
330 Err(Error::new(ErrorKind::InvalidData,
331 "stream did not contain valid UTF-8"))
340 // This uses an adaptive system to extend the vector when it fills. We want to
341 // avoid paying to allocate and zero a huge chunk of memory if the reader only
342 // has 4 bytes while still making large reads if the reader does have a ton
343 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
344 // time is 4,500 times (!) slower than this if the reader has a very small
345 // amount of data to return.
346 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
347 let start_len = buf.len();
348 let mut len = start_len;
349 let mut new_write_size = 16;
352 if len == buf.len() {
353 if new_write_size < DEFAULT_BUF_SIZE {
356 buf.resize(len + new_write_size, 0);
359 match r.read(&mut buf[len..]) {
361 ret = Ok(len - start_len);
365 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
377 /// The `Read` trait allows for reading bytes from a source.
379 /// Implementors of the `Read` trait are sometimes called 'readers'.
381 /// Readers are defined by one required method, `read()`. Each call to `read`
382 /// will attempt to pull bytes from this source into a provided buffer. A
383 /// number of other methods are implemented in terms of `read()`, giving
384 /// implementors a number of ways to read bytes while only needing to implement
387 /// Readers are intended to be composable with one another. Many implementors
388 /// throughout `std::io` take and provide types which implement the `Read`
391 /// Please note that each call to `read` may involve a system call, and
392 /// therefore, using something that implements [`BufRead`][bufread], such as
393 /// [`BufReader`][bufreader], will be more efficient.
395 /// [bufread]: trait.BufRead.html
396 /// [bufreader]: struct.BufReader.html
400 /// [`File`][file]s implement `Read`:
402 /// [file]: ../std/fs/struct.File.html
406 /// use std::io::prelude::*;
407 /// use std::fs::File;
409 /// # fn foo() -> io::Result<()> {
410 /// let mut f = try!(File::open("foo.txt"));
411 /// let mut buffer = [0; 10];
413 /// // read up to 10 bytes
414 /// try!(f.read(&mut buffer));
416 /// let mut buffer = vec![0; 10];
417 /// // read the whole file
418 /// try!(f.read_to_end(&mut buffer));
420 /// // read into a String, so that you don't need to do the conversion.
421 /// let mut buffer = String::new();
422 /// try!(f.read_to_string(&mut buffer));
424 /// // and more! See the other methods for more details.
428 #[stable(feature = "rust1", since = "1.0.0")]
430 /// Pull some bytes from this source into the specified buffer, returning
431 /// how many bytes were read.
433 /// This function does not provide any guarantees about whether it blocks
434 /// waiting for data, but if an object needs to block for a read but cannot
435 /// it will typically signal this via an `Err` return value.
437 /// If the return value of this method is `Ok(n)`, then it must be
438 /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
439 /// that the buffer `buf` has been filled in with `n` bytes of data from this
440 /// source. If `n` is `0`, then it can indicate one of two scenarios:
442 /// 1. This reader has reached its "end of file" and will likely no longer
443 /// be able to produce bytes. Note that this does not mean that the
444 /// reader will *always* no longer be able to produce bytes.
445 /// 2. The buffer specified was 0 bytes in length.
447 /// No guarantees are provided about the contents of `buf` when this
448 /// function is called, implementations cannot rely on any property of the
449 /// contents of `buf` being true. It is recommended that implementations
450 /// only write data to `buf` instead of reading its contents.
454 /// If this function encounters any form of I/O or other error, an error
455 /// variant will be returned. If an error is returned then it must be
456 /// guaranteed that no bytes were read.
460 /// [`File`][file]s implement `Read`:
462 /// [file]: ../std/fs/struct.File.html
466 /// use std::io::prelude::*;
467 /// use std::fs::File;
469 /// # fn foo() -> io::Result<()> {
470 /// let mut f = try!(File::open("foo.txt"));
471 /// let mut buffer = [0; 10];
474 /// try!(f.read(&mut buffer[..]));
478 #[stable(feature = "rust1", since = "1.0.0")]
479 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
481 /// Read all bytes until EOF in this source, placing them into `buf`.
483 /// All bytes read from this source will be appended to the specified buffer
484 /// `buf`. This function will continuously call `read` to append more data to
485 /// `buf` until `read` returns either `Ok(0)` or an error of
486 /// non-`ErrorKind::Interrupted` kind.
488 /// If successful, this function will return the total number of bytes read.
492 /// If this function encounters an error of the kind
493 /// `ErrorKind::Interrupted` then the error is ignored and the operation
496 /// If any other read error is encountered then this function immediately
497 /// returns. Any bytes which have already been read will be appended to
502 /// [`File`][file]s implement `Read`:
504 /// [file]: ../std/fs/struct.File.html
508 /// use std::io::prelude::*;
509 /// use std::fs::File;
511 /// # fn foo() -> io::Result<()> {
512 /// let mut f = try!(File::open("foo.txt"));
513 /// let mut buffer = Vec::new();
515 /// // read the whole file
516 /// try!(f.read_to_end(&mut buffer));
520 #[stable(feature = "rust1", since = "1.0.0")]
521 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
522 read_to_end(self, buf)
525 /// Read all bytes until EOF in this source, placing them into `buf`.
527 /// If successful, this function returns the number of bytes which were read
528 /// and appended to `buf`.
532 /// If the data in this stream is *not* valid UTF-8 then an error is
533 /// returned and `buf` is unchanged.
535 /// See [`read_to_end()`][readtoend] for other error semantics.
537 /// [readtoend]: #method.read_to_end
541 /// [`File`][file]s implement `Read`:
543 /// [file]: ../std/fs/struct.File.html
547 /// use std::io::prelude::*;
548 /// use std::fs::File;
550 /// # fn foo() -> io::Result<()> {
551 /// let mut f = try!(File::open("foo.txt"));
552 /// let mut buffer = String::new();
554 /// try!(f.read_to_string(&mut buffer));
558 #[stable(feature = "rust1", since = "1.0.0")]
559 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
560 // Note that we do *not* call `.read_to_end()` here. We are passing
561 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
562 // method to fill it up. An arbitrary implementation could overwrite the
563 // entire contents of the vector, not just append to it (which is what
564 // we are expecting).
566 // To prevent extraneously checking the UTF-8-ness of the entire buffer
567 // we pass it to our hardcoded `read_to_end` implementation which we
568 // know is guaranteed to only read data into the end of the buffer.
569 append_to_string(buf, |b| read_to_end(self, b))
572 /// Read the exact number of bytes required to fill `buf`.
574 /// This function reads as many bytes as necessary to completely fill the
575 /// specified buffer `buf`.
577 /// No guarantees are provided about the contents of `buf` when this
578 /// function is called, implementations cannot rely on any property of the
579 /// contents of `buf` being true. It is recommended that implementations
580 /// only write data to `buf` instead of reading its contents.
584 /// If this function encounters an error of the kind
585 /// `ErrorKind::Interrupted` then the error is ignored and the operation
588 /// If this function encounters an "end of file" before completely filling
589 /// the buffer, it returns an error of the kind `ErrorKind::UnexpectedEof`.
590 /// The contents of `buf` are unspecified in this case.
592 /// If any other read error is encountered then this function immediately
593 /// returns. The contents of `buf` are unspecified in this case.
595 /// If this function returns an error, it is unspecified how many bytes it
596 /// has read, but it will never read more than would be necessary to
597 /// completely fill the buffer.
601 /// [`File`][file]s implement `Read`:
603 /// [file]: ../std/fs/struct.File.html
607 /// use std::io::prelude::*;
608 /// use std::fs::File;
610 /// # fn foo() -> io::Result<()> {
611 /// let mut f = try!(File::open("foo.txt"));
612 /// let mut buffer = [0; 10];
614 /// // read exactly 10 bytes
615 /// try!(f.read_exact(&mut buffer));
619 #[stable(feature = "read_exact", since = "1.6.0")]
620 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
621 while !buf.is_empty() {
622 match self.read(buf) {
624 Ok(n) => { let tmp = buf; buf = &mut tmp[n..]; }
625 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
626 Err(e) => return Err(e),
630 Err(Error::new(ErrorKind::UnexpectedEof,
631 "failed to fill whole buffer"))
637 /// Creates a "by reference" adaptor for this instance of `Read`.
639 /// The returned adaptor also implements `Read` and will simply borrow this
644 /// [`File`][file]s implement `Read`:
646 /// [file]: ../std/fs/struct.File.html
650 /// use std::io::Read;
651 /// use std::fs::File;
653 /// # fn foo() -> io::Result<()> {
654 /// let mut f = try!(File::open("foo.txt"));
655 /// let mut buffer = Vec::new();
656 /// let mut other_buffer = Vec::new();
659 /// let reference = f.by_ref();
661 /// // read at most 5 bytes
662 /// try!(reference.take(5).read_to_end(&mut buffer));
664 /// } // drop our &mut reference so we can use f again
666 /// // original file still usable, read the rest
667 /// try!(f.read_to_end(&mut other_buffer));
671 #[stable(feature = "rust1", since = "1.0.0")]
672 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
674 /// Transforms this `Read` instance to an `Iterator` over its bytes.
676 /// The returned type implements `Iterator` where the `Item` is `Result<u8,
677 /// R::Err>`. The yielded item is `Ok` if a byte was successfully read and
678 /// `Err` otherwise for I/O errors. EOF is mapped to returning `None` from
683 /// [`File`][file]s implement `Read`:
685 /// [file]: ../std/fs/struct.File.html
689 /// use std::io::prelude::*;
690 /// use std::fs::File;
692 /// # fn foo() -> io::Result<()> {
693 /// let mut f = try!(File::open("foo.txt"));
695 /// for byte in f.bytes() {
696 /// println!("{}", byte.unwrap());
701 #[stable(feature = "rust1", since = "1.0.0")]
702 fn bytes(self) -> Bytes<Self> where Self: Sized {
703 Bytes { inner: self }
706 /// Transforms this `Read` instance to an `Iterator` over `char`s.
708 /// This adaptor will attempt to interpret this reader as a UTF-8 encoded
709 /// sequence of characters. The returned iterator will return `None` once
710 /// EOF is reached for this reader. Otherwise each element yielded will be a
711 /// `Result<char, E>` where `E` may contain information about what I/O error
712 /// occurred or where decoding failed.
714 /// Currently this adaptor will discard intermediate data read, and should
715 /// be avoided if this is not desired.
719 /// [`File`][file]s implement `Read`:
721 /// [file]: ../std/fs/struct.File.html
726 /// use std::io::prelude::*;
727 /// use std::fs::File;
729 /// # fn foo() -> io::Result<()> {
730 /// let mut f = try!(File::open("foo.txt"));
732 /// for c in f.chars() {
733 /// println!("{}", c.unwrap());
738 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
739 of where errors happen is currently \
740 unclear and may change",
742 fn chars(self) -> Chars<Self> where Self: Sized {
743 Chars { inner: self }
746 /// Creates an adaptor which will chain this stream with another.
748 /// The returned `Read` instance will first read all bytes from this object
749 /// until EOF is encountered. Afterwards the output is equivalent to the
750 /// output of `next`.
754 /// [`File`][file]s implement `Read`:
756 /// [file]: ../std/fs/struct.File.html
760 /// use std::io::prelude::*;
761 /// use std::fs::File;
763 /// # fn foo() -> io::Result<()> {
764 /// let mut f1 = try!(File::open("foo.txt"));
765 /// let mut f2 = try!(File::open("bar.txt"));
767 /// let mut handle = f1.chain(f2);
768 /// let mut buffer = String::new();
770 /// // read the value into a String. We could use any Read method here,
771 /// // this is just one example.
772 /// try!(handle.read_to_string(&mut buffer));
776 #[stable(feature = "rust1", since = "1.0.0")]
777 fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized {
778 Chain { first: self, second: next, done_first: false }
781 /// Creates an adaptor which will read at most `limit` bytes from it.
783 /// This function returns a new instance of `Read` which will read at most
784 /// `limit` bytes, after which it will always return EOF (`Ok(0)`). Any
785 /// read errors will not count towards the number of bytes read and future
786 /// calls to `read` may succeed.
790 /// [`File`][file]s implement `Read`:
792 /// [file]: ../std/fs/struct.File.html
796 /// use std::io::prelude::*;
797 /// use std::fs::File;
799 /// # fn foo() -> io::Result<()> {
800 /// let mut f = try!(File::open("foo.txt"));
801 /// let mut buffer = [0; 5];
803 /// // read at most five bytes
804 /// let mut handle = f.take(5);
806 /// try!(handle.read(&mut buffer));
810 #[stable(feature = "rust1", since = "1.0.0")]
811 fn take(self, limit: u64) -> Take<Self> where Self: Sized {
812 Take { inner: self, limit: limit }
815 /// Creates a reader adaptor which will write all read data into the given
818 /// Whenever the returned `Read` instance is read it will write the read
819 /// data to `out`. The current semantics of this implementation imply that
820 /// a `write` error will not report how much data was initially read.
824 /// [`File`][file]s implement `Read`:
826 /// [file]: ../std/fs/struct.File.html
831 /// use std::io::prelude::*;
832 /// use std::fs::File;
834 /// # fn foo() -> io::Result<()> {
835 /// let mut f = try!(File::open("foo.txt"));
836 /// let mut buffer1 = Vec::with_capacity(10);
837 /// let mut buffer2 = Vec::with_capacity(10);
839 /// // write the output to buffer1 as we read
840 /// let mut handle = f.tee(&mut buffer1);
842 /// try!(handle.read(&mut buffer2));
846 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
847 of where errors happen is currently \
848 unclear and may change",
850 #[rustc_deprecated(reason = "error handling semantics unclear and \
851 don't seem to have an ergonomic resolution",
854 fn tee<W: Write>(self, out: W) -> Tee<Self, W> where Self: Sized {
855 Tee { reader: self, writer: out }
859 /// A trait for objects which are byte-oriented sinks.
861 /// Implementors of the `Write` trait are sometimes called 'writers'.
863 /// Writers are defined by two required methods, `write()` and `flush()`:
865 /// * The `write()` method will attempt to write some data into the object,
866 /// returning how many bytes were successfully written.
868 /// * The `flush()` method is useful for adaptors and explicit buffers
869 /// themselves for ensuring that all buffered data has been pushed out to the
872 /// Writers are intended to be composable with one another. Many implementors
873 /// throughout `std::io` take and provide types which implement the `Write`
879 /// use std::io::prelude::*;
880 /// use std::fs::File;
882 /// # fn foo() -> std::io::Result<()> {
883 /// let mut buffer = try!(File::create("foo.txt"));
885 /// try!(buffer.write(b"some bytes"));
889 #[stable(feature = "rust1", since = "1.0.0")]
891 /// Write a buffer into this object, returning how many bytes were written.
893 /// This function will attempt to write the entire contents of `buf`, but
894 /// the entire write may not succeed, or the write may also generate an
895 /// error. A call to `write` represents *at most one* attempt to write to
896 /// any wrapped object.
898 /// Calls to `write` are not guaranteed to block waiting for data to be
899 /// written, and a write which would otherwise block can be indicated through
900 /// an `Err` variant.
902 /// If the return value is `Ok(n)` then it must be guaranteed that
903 /// `0 <= n <= buf.len()`. A return value of `0` typically means that the
904 /// underlying object is no longer able to accept bytes and will likely not
905 /// be able to in the future as well, or that the buffer provided is empty.
909 /// Each call to `write` may generate an I/O error indicating that the
910 /// operation could not be completed. If an error is returned then no bytes
911 /// in the buffer were written to this writer.
913 /// It is **not** considered an error if the entire buffer could not be
914 /// written to this writer.
919 /// use std::io::prelude::*;
920 /// use std::fs::File;
922 /// # fn foo() -> std::io::Result<()> {
923 /// let mut buffer = try!(File::create("foo.txt"));
925 /// try!(buffer.write(b"some bytes"));
929 #[stable(feature = "rust1", since = "1.0.0")]
930 fn write(&mut self, buf: &[u8]) -> Result<usize>;
932 /// Flush this output stream, ensuring that all intermediately buffered
933 /// contents reach their destination.
937 /// It is considered an error if not all bytes could be written due to
938 /// I/O errors or EOF being reached.
943 /// use std::io::prelude::*;
944 /// use std::io::BufWriter;
945 /// use std::fs::File;
947 /// # fn foo() -> std::io::Result<()> {
948 /// let mut buffer = BufWriter::new(try!(File::create("foo.txt")));
950 /// try!(buffer.write(b"some bytes"));
951 /// try!(buffer.flush());
955 #[stable(feature = "rust1", since = "1.0.0")]
956 fn flush(&mut self) -> Result<()>;
958 /// Attempts to write an entire buffer into this write.
960 /// This method will continuously call `write` while there is more data to
961 /// write. This method will not return until the entire buffer has been
962 /// successfully written or an error occurs. The first error generated from
963 /// this method will be returned.
967 /// This function will return the first error that `write` returns.
972 /// use std::io::prelude::*;
973 /// use std::fs::File;
975 /// # fn foo() -> std::io::Result<()> {
976 /// let mut buffer = try!(File::create("foo.txt"));
978 /// try!(buffer.write_all(b"some bytes"));
982 #[stable(feature = "rust1", since = "1.0.0")]
983 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
984 while !buf.is_empty() {
985 match self.write(buf) {
986 Ok(0) => return Err(Error::new(ErrorKind::WriteZero,
987 "failed to write whole buffer")),
988 Ok(n) => buf = &buf[n..],
989 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
990 Err(e) => return Err(e),
996 /// Writes a formatted string into this writer, returning any error
999 /// This method is primarily used to interface with the
1000 /// [`format_args!`][formatargs] macro, but it is rare that this should
1001 /// explicitly be called. The [`write!`][write] macro should be favored to
1002 /// invoke this method instead.
1004 /// [formatargs]: ../macro.format_args!.html
1005 /// [write]: ../macro.write!.html
1007 /// This function internally uses the [`write_all`][writeall] method on
1008 /// this trait and hence will continuously write data so long as no errors
1009 /// are received. This also means that partial writes are not indicated in
1012 /// [writeall]: #method.write_all
1016 /// This function will return any I/O error reported while formatting.
1021 /// use std::io::prelude::*;
1022 /// use std::fs::File;
1024 /// # fn foo() -> std::io::Result<()> {
1025 /// let mut buffer = try!(File::create("foo.txt"));
1028 /// try!(write!(buffer, "{:.*}", 2, 1.234567));
1029 /// // turns into this:
1030 /// try!(buffer.write_fmt(format_args!("{:.*}", 2, 1.234567)));
1034 #[stable(feature = "rust1", since = "1.0.0")]
1035 fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<()> {
1036 // Create a shim which translates a Write to a fmt::Write and saves
1037 // off I/O errors. instead of discarding them
1038 struct Adaptor<'a, T: ?Sized + 'a> {
1043 impl<'a, T: Write + ?Sized> fmt::Write for Adaptor<'a, T> {
1044 fn write_str(&mut self, s: &str) -> fmt::Result {
1045 match self.inner.write_all(s.as_bytes()) {
1048 self.error = Err(e);
1055 let mut output = Adaptor { inner: self, error: Ok(()) };
1056 match fmt::write(&mut output, fmt) {
1058 Err(..) => output.error
1062 /// Creates a "by reference" adaptor for this instance of `Write`.
1064 /// The returned adaptor also implements `Write` and will simply borrow this
1070 /// use std::io::Write;
1071 /// use std::fs::File;
1073 /// # fn foo() -> std::io::Result<()> {
1074 /// let mut buffer = try!(File::create("foo.txt"));
1076 /// let reference = buffer.by_ref();
1078 /// // we can use reference just like our original buffer
1079 /// try!(reference.write_all(b"some bytes"));
1083 #[stable(feature = "rust1", since = "1.0.0")]
1084 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
1086 /// Creates a new writer which will write all data to both this writer and
1089 /// All data written to the returned writer will both be written to `self`
1090 /// as well as `other`. Note that the error semantics of the current
1091 /// implementation do not precisely track where errors happen. For example
1092 /// an error on the second call to `write` will not report that the first
1093 /// call to `write` succeeded.
1099 /// use std::io::prelude::*;
1100 /// use std::fs::File;
1102 /// # fn foo() -> std::io::Result<()> {
1103 /// let mut buffer1 = try!(File::create("foo.txt"));
1104 /// let mut buffer2 = Vec::new();
1106 /// // write the output to buffer1 as we read
1107 /// let mut handle = buffer1.broadcast(&mut buffer2);
1109 /// try!(handle.write(b"some bytes"));
1113 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
1114 of where errors happen is currently \
1115 unclear and may change",
1117 #[rustc_deprecated(reason = "error handling semantics unclear and \
1118 don't seem to have an ergonomic resolution",
1120 #[allow(deprecated)]
1121 fn broadcast<W: Write>(self, other: W) -> Broadcast<Self, W>
1124 Broadcast { first: self, second: other }
1128 /// The `Seek` trait provides a cursor which can be moved within a stream of
1131 /// The stream typically has a fixed size, allowing seeking relative to either
1132 /// end or the current offset.
1136 /// [`File`][file]s implement `Seek`:
1138 /// [file]: ../fs/struct.File.html
1142 /// use std::io::prelude::*;
1143 /// use std::fs::File;
1144 /// use std::io::SeekFrom;
1146 /// # fn foo() -> io::Result<()> {
1147 /// let mut f = try!(File::open("foo.txt"));
1149 /// // move the cursor 42 bytes from the start of the file
1150 /// try!(f.seek(SeekFrom::Start(42)));
1154 #[stable(feature = "rust1", since = "1.0.0")]
1156 /// Seek to an offset, in bytes, in a stream.
1158 /// A seek beyond the end of a stream is allowed, but implementation
1161 /// If the seek operation completed successfully,
1162 /// this method returns the new position from the start of the stream.
1163 /// That position can be used later with `SeekFrom::Start`.
1167 /// Seeking to a negative offset is considered an error.
1168 #[stable(feature = "rust1", since = "1.0.0")]
1169 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1172 /// Enumeration of possible methods to seek within an I/O object.
1173 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1174 #[stable(feature = "rust1", since = "1.0.0")]
1176 /// Set the offset to the provided number of bytes.
1177 #[stable(feature = "rust1", since = "1.0.0")]
1180 /// Set the offset to the size of this object plus the specified number of
1183 /// It is possible to seek beyond the end of an object, but it's an error to
1184 /// seek before byte 0.
1185 #[stable(feature = "rust1", since = "1.0.0")]
1188 /// Set the offset to the current position plus the specified number of
1191 /// It is possible to seek beyond the end of an object, but it's an error to
1192 /// seek before byte 0.
1193 #[stable(feature = "rust1", since = "1.0.0")]
1197 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>)
1201 let (done, used) = {
1202 let available = match r.fill_buf() {
1204 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1205 Err(e) => return Err(e)
1207 match memchr::memchr(delim, available) {
1209 buf.extend_from_slice(&available[..i + 1]);
1213 buf.extend_from_slice(available);
1214 (false, available.len())
1220 if done || used == 0 {
1226 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1227 /// to perform extra ways of reading.
1229 /// For example, reading line-by-line is inefficient without using a buffer, so
1230 /// if you want to read by line, you'll need `BufRead`, which includes a
1231 /// [`read_line()`][readline] method as well as a [`lines()`][lines] iterator.
1233 /// [readline]: #method.read_line
1234 /// [lines]: #method.lines
1238 /// A locked standard input implements `BufRead`:
1242 /// use std::io::prelude::*;
1244 /// let stdin = io::stdin();
1245 /// for line in stdin.lock().lines() {
1246 /// println!("{}", line.unwrap());
1250 /// If you have something that implements `Read`, you can use the [`BufReader`
1251 /// type][bufreader] to turn it into a `BufRead`.
1253 /// For example, [`File`][file] implements `Read`, but not `BufRead`.
1254 /// `BufReader` to the rescue!
1256 /// [bufreader]: struct.BufReader.html
1257 /// [file]: ../fs/struct.File.html
1260 /// use std::io::{self, BufReader};
1261 /// use std::io::prelude::*;
1262 /// use std::fs::File;
1264 /// # fn foo() -> io::Result<()> {
1265 /// let f = try!(File::open("foo.txt"));
1266 /// let f = BufReader::new(f);
1268 /// for line in f.lines() {
1269 /// println!("{}", line.unwrap());
1276 #[stable(feature = "rust1", since = "1.0.0")]
1277 pub trait BufRead: Read {
1278 /// Fills the internal buffer of this object, returning the buffer contents.
1280 /// This function is a lower-level call. It needs to be paired with the
1281 /// [`consume`][consume] method to function properly. When calling this
1282 /// method, none of the contents will be "read" in the sense that later
1283 /// calling `read` may return the same contents. As such, `consume` must be
1284 /// called with the number of bytes that are consumed from this buffer to
1285 /// ensure that the bytes are never returned twice.
1287 /// [consume]: #tymethod.consume
1289 /// An empty buffer returned indicates that the stream has reached EOF.
1293 /// This function will return an I/O error if the underlying reader was
1294 /// read, but returned an error.
1298 /// A locked standard input implements `BufRead`:
1302 /// use std::io::prelude::*;
1304 /// let stdin = io::stdin();
1305 /// let mut stdin = stdin.lock();
1307 /// // we can't have two `&mut` references to `stdin`, so use a block
1308 /// // to end the borrow early.
1310 /// let buffer = stdin.fill_buf().unwrap();
1312 /// // work with buffer
1313 /// println!("{:?}", buffer);
1318 /// // ensure the bytes we worked with aren't returned again later
1319 /// stdin.consume(length);
1321 #[stable(feature = "rust1", since = "1.0.0")]
1322 fn fill_buf(&mut self) -> Result<&[u8]>;
1324 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1325 /// so they should no longer be returned in calls to `read`.
1327 /// This function is a lower-level call. It needs to be paired with the
1328 /// [`fill_buf`][fillbuf] method to function properly. This function does
1329 /// not perform any I/O, it simply informs this object that some amount of
1330 /// its buffer, returned from `fill_buf`, has been consumed and should no
1331 /// longer be returned. As such, this function may do odd things if
1332 /// `fill_buf` isn't called before calling it.
1334 /// [fillbuf]: #tymethod.fill_buff
1336 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1341 /// Since `consume()` is meant to be used with [`fill_buf()`][fillbuf],
1342 /// that method's example includes an example of `consume()`.
1343 #[stable(feature = "rust1", since = "1.0.0")]
1344 fn consume(&mut self, amt: usize);
1346 /// Read all bytes into `buf` until the delimiter `byte` is reached.
1348 /// This function will read bytes from the underlying stream until the
1349 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1350 /// the delimiter (if found) will be appended to `buf`.
1352 /// If this reader is currently at EOF then this function will not modify
1353 /// `buf` and will return `Ok(n)` where `n` is the number of bytes which
1358 /// This function will ignore all instances of `ErrorKind::Interrupted` and
1359 /// will otherwise return any errors returned by `fill_buf`.
1361 /// If an I/O error is encountered then all bytes read so far will be
1362 /// present in `buf` and its length will have been adjusted appropriately.
1366 /// A locked standard input implements `BufRead`. In this example, we'll
1367 /// read from standard input until we see an `a` byte.
1371 /// use std::io::prelude::*;
1373 /// fn foo() -> io::Result<()> {
1374 /// let stdin = io::stdin();
1375 /// let mut stdin = stdin.lock();
1376 /// let mut buffer = Vec::new();
1378 /// try!(stdin.read_until(b'a', &mut buffer));
1380 /// println!("{:?}", buffer);
1384 #[stable(feature = "rust1", since = "1.0.0")]
1385 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
1386 read_until(self, byte, buf)
1389 /// Read all bytes until a newline (the 0xA byte) is reached, and append
1390 /// them to the provided buffer.
1392 /// This function will read bytes from the underlying stream until the
1393 /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
1394 /// up to, and including, the delimiter (if found) will be appended to
1397 /// If this reader is currently at EOF then this function will not modify
1398 /// `buf` and will return `Ok(n)` where `n` is the number of bytes which
1403 /// This function has the same error semantics as `read_until` and will also
1404 /// return an error if the read bytes are not valid UTF-8. If an I/O error
1405 /// is encountered then `buf` may contain some bytes already read in the
1406 /// event that all data read so far was valid UTF-8.
1410 /// A locked standard input implements `BufRead`. In this example, we'll
1411 /// read all of the lines from standard input. If we were to do this in
1412 /// an actual project, the [`lines()`][lines] method would be easier, of
1415 /// [lines]: #method.lines
1419 /// use std::io::prelude::*;
1421 /// let stdin = io::stdin();
1422 /// let mut stdin = stdin.lock();
1423 /// let mut buffer = String::new();
1425 /// while stdin.read_line(&mut buffer).unwrap() > 0 {
1426 /// // work with buffer
1427 /// println!("{:?}", buffer);
1432 #[stable(feature = "rust1", since = "1.0.0")]
1433 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
1434 // Note that we are not calling the `.read_until` method here, but
1435 // rather our hardcoded implementation. For more details as to why, see
1436 // the comments in `read_to_end`.
1437 append_to_string(buf, |b| read_until(self, b'\n', b))
1440 /// Returns an iterator over the contents of this reader split on the byte
1443 /// The iterator returned from this function will return instances of
1444 /// `io::Result<Vec<u8>>`. Each vector returned will *not* have the
1445 /// delimiter byte at the end.
1447 /// This function will yield errors whenever `read_until` would have also
1448 /// yielded an error.
1452 /// A locked standard input implements `BufRead`. In this example, we'll
1453 /// read some input from standard input, splitting on commas.
1457 /// use std::io::prelude::*;
1459 /// let stdin = io::stdin();
1461 /// for content in stdin.lock().split(b',') {
1462 /// println!("{:?}", content.unwrap());
1465 #[stable(feature = "rust1", since = "1.0.0")]
1466 fn split(self, byte: u8) -> Split<Self> where Self: Sized {
1467 Split { buf: self, delim: byte }
1470 /// Returns an iterator over the lines of this reader.
1472 /// The iterator returned from this function will yield instances of
1473 /// `io::Result<String>`. Each string returned will *not* have a newline
1474 /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
1478 /// A locked standard input implements `BufRead`:
1482 /// use std::io::prelude::*;
1484 /// let stdin = io::stdin();
1486 /// for line in stdin.lock().lines() {
1487 /// println!("{}", line.unwrap());
1490 #[stable(feature = "rust1", since = "1.0.0")]
1491 fn lines(self) -> Lines<Self> where Self: Sized {
1496 /// A `Write` adaptor which will write data to multiple locations.
1498 /// This struct is generally created by calling [`broadcast()`][broadcast] on a
1499 /// writer. Please see the documentation of `broadcast()` for more details.
1501 /// [broadcast]: trait.Write.html#method.broadcast
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 pub struct Broadcast<T, U> {
1512 #[unstable(feature = "io", reason = "awaiting stability of Write::broadcast",
1514 #[rustc_deprecated(reason = "error handling semantics unclear and \
1515 don't seem to have an ergonomic resolution",
1517 #[allow(deprecated)]
1518 impl<T: Write, U: Write> Write for Broadcast<T, U> {
1519 fn write(&mut self, data: &[u8]) -> Result<usize> {
1520 let n = try!(self.first.write(data));
1521 // FIXME: what if the write fails? (we wrote something)
1522 try!(self.second.write_all(&data[..n]));
1526 fn flush(&mut self) -> Result<()> {
1527 self.first.flush().and(self.second.flush())
1531 /// Adaptor to chain together two readers.
1533 /// This struct is generally created by calling [`chain()`][chain] on a reader.
1534 /// Please see the documentation of `chain()` for more details.
1536 /// [chain]: trait.Read.html#method.chain
1537 #[stable(feature = "rust1", since = "1.0.0")]
1538 pub struct Chain<T, U> {
1544 #[stable(feature = "rust1", since = "1.0.0")]
1545 impl<T: Read, U: Read> Read for Chain<T, U> {
1546 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1547 if !self.done_first {
1548 match try!(self.first.read(buf)) {
1549 0 => { self.done_first = true; }
1553 self.second.read(buf)
1557 /// Reader adaptor which limits the bytes read from an underlying reader.
1559 /// This struct is generally created by calling [`take()`][take] on a reader.
1560 /// Please see the documentation of `take()` for more details.
1562 /// [take]: trait.Read.html#method.take
1563 #[stable(feature = "rust1", since = "1.0.0")]
1564 pub struct Take<T> {
1570 /// Returns the number of bytes that can be read before this instance will
1575 /// This instance may reach EOF after reading fewer bytes than indicated by
1576 /// this method if the underlying `Read` instance reaches EOF.
1577 #[stable(feature = "rust1", since = "1.0.0")]
1578 pub fn limit(&self) -> u64 { self.limit }
1581 #[stable(feature = "rust1", since = "1.0.0")]
1582 impl<T: Read> Read for Take<T> {
1583 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1584 // Don't call into inner reader at all at EOF because it may still block
1585 if self.limit == 0 {
1589 let max = cmp::min(buf.len() as u64, self.limit) as usize;
1590 let n = try!(self.inner.read(&mut buf[..max]));
1591 self.limit -= n as u64;
1596 #[stable(feature = "rust1", since = "1.0.0")]
1597 impl<T: BufRead> BufRead for Take<T> {
1598 fn fill_buf(&mut self) -> Result<&[u8]> {
1599 let buf = try!(self.inner.fill_buf());
1600 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
1604 fn consume(&mut self, amt: usize) {
1605 // Don't let callers reset the limit by passing an overlarge value
1606 let amt = cmp::min(amt as u64, self.limit) as usize;
1607 self.limit -= amt as u64;
1608 self.inner.consume(amt);
1612 /// An adaptor which will emit all read data to a specified writer as well.
1614 /// This struct is generally created by calling [`tee()`][tee] on a reader.
1615 /// Please see the documentation of `tee()` for more details.
1617 /// [tee]: trait.Read.html#method.tee
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 pub struct Tee<R, W> {
1628 #[unstable(feature = "io", reason = "awaiting stability of Read::tee",
1630 #[rustc_deprecated(reason = "error handling semantics unclear and \
1631 don't seem to have an ergonomic resolution",
1633 #[allow(deprecated)]
1634 impl<R: Read, W: Write> Read for Tee<R, W> {
1635 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1636 let n = try!(self.reader.read(buf));
1637 // FIXME: what if the write fails? (we read something)
1638 try!(self.writer.write_all(&buf[..n]));
1643 /// An iterator over `u8` values of a reader.
1645 /// This struct is generally created by calling [`bytes()`][bytes] on a reader.
1646 /// Please see the documentation of `bytes()` for more details.
1648 /// [bytes]: trait.Read.html#method.bytes
1649 #[stable(feature = "rust1", since = "1.0.0")]
1650 pub struct Bytes<R> {
1654 #[stable(feature = "rust1", since = "1.0.0")]
1655 impl<R: Read> Iterator for Bytes<R> {
1656 type Item = Result<u8>;
1658 fn next(&mut self) -> Option<Result<u8>> {
1660 match self.inner.read(&mut buf) {
1662 Ok(..) => Some(Ok(buf[0])),
1663 Err(e) => Some(Err(e)),
1668 /// An iterator over the `char`s of a reader.
1670 /// This struct is generally created by calling [`chars()`][chars] on a reader.
1671 /// Please see the documentation of `chars()` for more details.
1673 /// [chars]: trait.Read.html#method.chars
1674 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1676 pub struct Chars<R> {
1680 /// An enumeration of possible errors that can be generated from the `Chars`
1683 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1685 pub enum CharsError {
1686 /// Variant representing that the underlying stream was read successfully
1687 /// but it did not contain valid utf8 data.
1690 /// Variant representing that an I/O error occurred.
1694 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1696 impl<R: Read> Iterator for Chars<R> {
1697 type Item = result::Result<char, CharsError>;
1699 fn next(&mut self) -> Option<result::Result<char, CharsError>> {
1701 let first_byte = match self.inner.read(&mut buf) {
1702 Ok(0) => return None,
1704 Err(e) => return Some(Err(CharsError::Other(e))),
1706 let width = core_str::utf8_char_width(first_byte);
1707 if width == 1 { return Some(Ok(first_byte as char)) }
1708 if width == 0 { return Some(Err(CharsError::NotUtf8)) }
1709 let mut buf = [first_byte, 0, 0, 0];
1712 while start < width {
1713 match self.inner.read(&mut buf[start..width]) {
1714 Ok(0) => return Some(Err(CharsError::NotUtf8)),
1715 Ok(n) => start += n,
1716 Err(e) => return Some(Err(CharsError::Other(e))),
1720 Some(match str::from_utf8(&buf[..width]).ok() {
1721 Some(s) => Ok(s.char_at(0)),
1722 None => Err(CharsError::NotUtf8),
1727 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1729 impl std_error::Error for CharsError {
1730 fn description(&self) -> &str {
1732 CharsError::NotUtf8 => "invalid utf8 encoding",
1733 CharsError::Other(ref e) => std_error::Error::description(e),
1736 fn cause(&self) -> Option<&std_error::Error> {
1738 CharsError::NotUtf8 => None,
1739 CharsError::Other(ref e) => e.cause(),
1744 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1746 impl fmt::Display for CharsError {
1747 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1749 CharsError::NotUtf8 => {
1750 "byte stream did not contain valid utf8".fmt(f)
1752 CharsError::Other(ref e) => e.fmt(f),
1757 /// An iterator over the contents of an instance of `BufRead` split on a
1758 /// particular byte.
1760 /// This struct is generally created by calling [`split()`][split] on a
1761 /// `BufRead`. Please see the documentation of `split()` for more details.
1763 /// [split]: trait.BufRead.html#method.split
1764 #[stable(feature = "rust1", since = "1.0.0")]
1765 pub struct Split<B> {
1770 #[stable(feature = "rust1", since = "1.0.0")]
1771 impl<B: BufRead> Iterator for Split<B> {
1772 type Item = Result<Vec<u8>>;
1774 fn next(&mut self) -> Option<Result<Vec<u8>>> {
1775 let mut buf = Vec::new();
1776 match self.buf.read_until(self.delim, &mut buf) {
1779 if buf[buf.len() - 1] == self.delim {
1784 Err(e) => Some(Err(e))
1789 /// An iterator over the lines of an instance of `BufRead`.
1791 /// This struct is generally created by calling [`lines()`][lines] on a
1792 /// `BufRead`. Please see the documentation of `lines()` for more details.
1794 /// [lines]: trait.BufRead.html#method.lines
1795 #[stable(feature = "rust1", since = "1.0.0")]
1796 pub struct Lines<B> {
1800 #[stable(feature = "rust1", since = "1.0.0")]
1801 impl<B: BufRead> Iterator for Lines<B> {
1802 type Item = Result<String>;
1804 fn next(&mut self) -> Option<Result<String>> {
1805 let mut buf = String::new();
1806 match self.buf.read_line(&mut buf) {
1809 if buf.ends_with("\n") {
1811 if buf.ends_with("\r") {
1817 Err(e) => Some(Err(e))
1833 let mut buf = Cursor::new(&b"12"[..]);
1834 let mut v = Vec::new();
1835 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
1836 assert_eq!(v, b"12");
1838 let mut buf = Cursor::new(&b"1233"[..]);
1839 let mut v = Vec::new();
1840 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
1841 assert_eq!(v, b"123");
1843 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
1844 assert_eq!(v, b"3");
1846 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
1852 let buf = Cursor::new(&b"12"[..]);
1853 let mut s = buf.split(b'3');
1854 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1855 assert!(s.next().is_none());
1857 let buf = Cursor::new(&b"1233"[..]);
1858 let mut s = buf.split(b'3');
1859 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1860 assert_eq!(s.next().unwrap().unwrap(), vec![]);
1861 assert!(s.next().is_none());
1866 let mut buf = Cursor::new(&b"12"[..]);
1867 let mut v = String::new();
1868 assert_eq!(buf.read_line(&mut v).unwrap(), 2);
1869 assert_eq!(v, "12");
1871 let mut buf = Cursor::new(&b"12\n\n"[..]);
1872 let mut v = String::new();
1873 assert_eq!(buf.read_line(&mut v).unwrap(), 3);
1874 assert_eq!(v, "12\n");
1876 assert_eq!(buf.read_line(&mut v).unwrap(), 1);
1877 assert_eq!(v, "\n");
1879 assert_eq!(buf.read_line(&mut v).unwrap(), 0);
1885 let buf = Cursor::new(&b"12\r"[..]);
1886 let mut s = buf.lines();
1887 assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
1888 assert!(s.next().is_none());
1890 let buf = Cursor::new(&b"12\r\n\n"[..]);
1891 let mut s = buf.lines();
1892 assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
1893 assert_eq!(s.next().unwrap().unwrap(), "".to_string());
1894 assert!(s.next().is_none());
1899 let mut c = Cursor::new(&b""[..]);
1900 let mut v = Vec::new();
1901 assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
1904 let mut c = Cursor::new(&b"1"[..]);
1905 let mut v = Vec::new();
1906 assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
1907 assert_eq!(v, b"1");
1909 let cap = 1024 * 1024;
1910 let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
1911 let mut v = Vec::new();
1912 let (a, b) = data.split_at(data.len() / 2);
1913 assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
1914 assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
1915 assert_eq!(v, data);
1919 fn read_to_string() {
1920 let mut c = Cursor::new(&b""[..]);
1921 let mut v = String::new();
1922 assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
1925 let mut c = Cursor::new(&b"1"[..]);
1926 let mut v = String::new();
1927 assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
1930 let mut c = Cursor::new(&b"\xff"[..]);
1931 let mut v = String::new();
1932 assert!(c.read_to_string(&mut v).is_err());
1937 let mut buf = [0; 4];
1939 let mut c = Cursor::new(&b""[..]);
1940 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1941 io::ErrorKind::UnexpectedEof);
1943 let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
1944 c.read_exact(&mut buf).unwrap();
1945 assert_eq!(&buf, b"1234");
1946 c.read_exact(&mut buf).unwrap();
1947 assert_eq!(&buf, b"5678");
1948 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1949 io::ErrorKind::UnexpectedEof);
1953 fn read_exact_slice() {
1954 let mut buf = [0; 4];
1956 let mut c = &b""[..];
1957 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1958 io::ErrorKind::UnexpectedEof);
1960 let mut c = &b"123"[..];
1961 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1962 io::ErrorKind::UnexpectedEof);
1963 // make sure the optimized (early returning) method is being used
1964 assert_eq!(&buf, &[0; 4]);
1966 let mut c = &b"1234"[..];
1967 c.read_exact(&mut buf).unwrap();
1968 assert_eq!(&buf, b"1234");
1970 let mut c = &b"56789"[..];
1971 c.read_exact(&mut buf).unwrap();
1972 assert_eq!(&buf, b"5678");
1973 assert_eq!(c, b"9");
1981 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
1982 Err(io::Error::new(io::ErrorKind::Other, ""))
1986 let mut buf = [0; 1];
1987 assert_eq!(0, R.take(0).read(&mut buf).unwrap());
1991 fn bench_read_to_end(b: &mut test::Bencher) {
1993 let mut lr = repeat(1).take(10000000);
1994 let mut vec = Vec::with_capacity(1024);
1995 super::read_to_end(&mut lr, &mut vec)