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 reader = BufReader::new(f);
187 //! for line in reader.lines() {
188 //! println!("{}", try!(line));
197 //! There are a number of [functions][functions-list] that offer access to various
198 //! features. For example, we can use three of these functions to copy everything
199 //! from standard input to standard output:
204 //! # fn foo() -> io::Result<()> {
205 //! try!(io::copy(&mut io::stdin(), &mut io::stdout()));
210 //! [functions-list]: #functions-1
214 //! Last, but certainly not least, is [`io::Result`][result]. This type is used
215 //! as the return type of many `std::io` functions that can cause an error, and
216 //! can be returned from your own functions as well. Many of the examples in this
217 //! module use the [`try!`][try] macro:
222 //! fn read_input() -> io::Result<()> {
223 //! let mut input = String::new();
225 //! try!(io::stdin().read_line(&mut input));
227 //! println!("You typed: {}", input.trim());
233 //! The return type of `read_input()`, `io::Result<()>`, is a very common type
234 //! for functions which don't have a 'real' return value, but do want to return
235 //! errors if they happen. In this case, the only purpose of this function is
236 //! to read the line and print it, so we use `()`.
238 //! [result]: type.Result.html
239 //! [try]: ../macro.try.html
241 //! ## Platform-specific behavior
243 //! Many I/O functions throughout the standard library are documented to indicate
244 //! what various library or syscalls they are delegated to. This is done to help
245 //! applications both understand what's happening under the hood as well as investigate
246 //! any possibly unclear semantics. Note, however, that this is informative, not a binding
247 //! contract. The implementation of many of these functions are subject to change over
248 //! time and may call fewer or more syscalls/library functions.
250 #![stable(feature = "rust1", since = "1.0.0")]
253 use rustc_unicode::str as core_str;
254 use error as std_error;
260 #[stable(feature = "rust1", since = "1.0.0")]
261 pub use self::buffered::{BufReader, BufWriter, LineWriter};
262 #[stable(feature = "rust1", since = "1.0.0")]
263 pub use self::buffered::IntoInnerError;
264 #[stable(feature = "rust1", since = "1.0.0")]
265 pub use self::cursor::Cursor;
266 #[stable(feature = "rust1", since = "1.0.0")]
267 pub use self::error::{Result, Error, ErrorKind};
268 #[stable(feature = "rust1", since = "1.0.0")]
269 pub use self::util::{copy, sink, Sink, empty, Empty, repeat, Repeat};
270 #[stable(feature = "rust1", since = "1.0.0")]
271 pub use self::stdio::{stdin, stdout, stderr, _print, Stdin, Stdout, Stderr};
272 #[stable(feature = "rust1", since = "1.0.0")]
273 pub use self::stdio::{StdoutLock, StderrLock, StdinLock};
274 #[unstable(feature = "libstd_io_internals", issue = "0")]
275 #[doc(no_inline, hidden)]
276 pub use self::stdio::{set_panic, set_print};
287 const DEFAULT_BUF_SIZE: usize = 8 * 1024;
289 // A few methods below (read_to_string, read_line) will append data into a
290 // `String` buffer, but we need to be pretty careful when doing this. The
291 // implementation will just call `.as_mut_vec()` and then delegate to a
292 // byte-oriented reading method, but we must ensure that when returning we never
293 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
295 // To this end, we use an RAII guard (to protect against panics) which updates
296 // the length of the string when it is dropped. This guard initially truncates
297 // the string to the prior length and only after we've validated that the
298 // new contents are valid UTF-8 do we allow it to set a longer length.
300 // The unsafety in this function is twofold:
302 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
304 // 2. We're passing a raw buffer to the function `f`, and it is expected that
305 // the function only *appends* bytes to the buffer. We'll get undefined
306 // behavior if existing bytes are overwritten to have non-UTF-8 data.
307 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
308 where F: FnOnce(&mut Vec<u8>) -> Result<usize>
310 struct Guard<'a> { s: &'a mut Vec<u8>, len: usize }
311 impl<'a> Drop for Guard<'a> {
313 unsafe { self.s.set_len(self.len); }
318 let mut g = Guard { len: buf.len(), s: buf.as_mut_vec() };
320 if str::from_utf8(&g.s[g.len..]).is_err() {
322 Err(Error::new(ErrorKind::InvalidData,
323 "stream did not contain valid UTF-8"))
332 // This uses an adaptive system to extend the vector when it fills. We want to
333 // avoid paying to allocate and zero a huge chunk of memory if the reader only
334 // has 4 bytes while still making large reads if the reader does have a ton
335 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
336 // time is 4,500 times (!) slower than this if the reader has a very small
337 // amount of data to return.
338 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
339 let start_len = buf.len();
340 let mut len = start_len;
341 let mut new_write_size = 16;
344 if len == buf.len() {
345 if new_write_size < DEFAULT_BUF_SIZE {
348 buf.resize(len + new_write_size, 0);
351 match r.read(&mut buf[len..]) {
353 ret = Ok(len - start_len);
357 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
369 /// The `Read` trait allows for reading bytes from a source.
371 /// Implementors of the `Read` trait are sometimes called 'readers'.
373 /// Readers are defined by one required method, `read()`. Each call to `read`
374 /// will attempt to pull bytes from this source into a provided buffer. A
375 /// number of other methods are implemented in terms of `read()`, giving
376 /// implementors a number of ways to read bytes while only needing to implement
379 /// Readers are intended to be composable with one another. Many implementors
380 /// throughout `std::io` take and provide types which implement the `Read`
383 /// Please note that each call to `read` may involve a system call, and
384 /// therefore, using something that implements [`BufRead`][bufread], such as
385 /// [`BufReader`][bufreader], will be more efficient.
387 /// [bufread]: trait.BufRead.html
388 /// [bufreader]: struct.BufReader.html
392 /// [`File`][file]s implement `Read`:
394 /// [file]: ../fs/struct.File.html
398 /// use std::io::prelude::*;
399 /// use std::fs::File;
401 /// # fn foo() -> io::Result<()> {
402 /// let mut f = try!(File::open("foo.txt"));
403 /// let mut buffer = [0; 10];
405 /// // read up to 10 bytes
406 /// try!(f.read(&mut buffer));
408 /// let mut buffer = vec![0; 10];
409 /// // read the whole file
410 /// try!(f.read_to_end(&mut buffer));
412 /// // read into a String, so that you don't need to do the conversion.
413 /// let mut buffer = String::new();
414 /// try!(f.read_to_string(&mut buffer));
416 /// // and more! See the other methods for more details.
420 #[stable(feature = "rust1", since = "1.0.0")]
422 /// Pull some bytes from this source into the specified buffer, returning
423 /// how many bytes were read.
425 /// This function does not provide any guarantees about whether it blocks
426 /// waiting for data, but if an object needs to block for a read but cannot
427 /// it will typically signal this via an `Err` return value.
429 /// If the return value of this method is `Ok(n)`, then it must be
430 /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
431 /// that the buffer `buf` has been filled in with `n` bytes of data from this
432 /// source. If `n` is `0`, then it can indicate one of two scenarios:
434 /// 1. This reader has reached its "end of file" and will likely no longer
435 /// be able to produce bytes. Note that this does not mean that the
436 /// reader will *always* no longer be able to produce bytes.
437 /// 2. The buffer specified was 0 bytes in length.
439 /// No guarantees are provided about the contents of `buf` when this
440 /// function is called, implementations cannot rely on any property of the
441 /// contents of `buf` being true. It is recommended that implementations
442 /// only write data to `buf` instead of reading its contents.
446 /// If this function encounters any form of I/O or other error, an error
447 /// variant will be returned. If an error is returned then it must be
448 /// guaranteed that no bytes were read.
452 /// [`File`][file]s implement `Read`:
454 /// [file]: ../fs/struct.File.html
458 /// use std::io::prelude::*;
459 /// use std::fs::File;
461 /// # fn foo() -> io::Result<()> {
462 /// let mut f = try!(File::open("foo.txt"));
463 /// let mut buffer = [0; 10];
466 /// try!(f.read(&mut buffer[..]));
470 #[stable(feature = "rust1", since = "1.0.0")]
471 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
473 /// Read all bytes until EOF in this source, placing them into `buf`.
475 /// All bytes read from this source will be appended to the specified buffer
476 /// `buf`. This function will continuously call `read` to append more data to
477 /// `buf` until `read` returns either `Ok(0)` or an error of
478 /// non-`ErrorKind::Interrupted` kind.
480 /// If successful, this function will return the total number of bytes read.
484 /// If this function encounters an error of the kind
485 /// `ErrorKind::Interrupted` then the error is ignored and the operation
488 /// If any other read error is encountered then this function immediately
489 /// returns. Any bytes which have already been read will be appended to
494 /// [`File`][file]s implement `Read`:
496 /// [file]: ../fs/struct.File.html
500 /// use std::io::prelude::*;
501 /// use std::fs::File;
503 /// # fn foo() -> io::Result<()> {
504 /// let mut f = try!(File::open("foo.txt"));
505 /// let mut buffer = Vec::new();
507 /// // read the whole file
508 /// try!(f.read_to_end(&mut buffer));
512 #[stable(feature = "rust1", since = "1.0.0")]
513 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
514 read_to_end(self, buf)
517 /// Read all bytes until EOF in this source, placing them into `buf`.
519 /// If successful, this function returns the number of bytes which were read
520 /// and appended to `buf`.
524 /// If the data in this stream is *not* valid UTF-8 then an error is
525 /// returned and `buf` is unchanged.
527 /// See [`read_to_end()`][readtoend] for other error semantics.
529 /// [readtoend]: #method.read_to_end
533 /// [`File`][file]s implement `Read`:
535 /// [file]: ../fs/struct.File.html
539 /// use std::io::prelude::*;
540 /// use std::fs::File;
542 /// # fn foo() -> io::Result<()> {
543 /// let mut f = try!(File::open("foo.txt"));
544 /// let mut buffer = String::new();
546 /// try!(f.read_to_string(&mut buffer));
550 #[stable(feature = "rust1", since = "1.0.0")]
551 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
552 // Note that we do *not* call `.read_to_end()` here. We are passing
553 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
554 // method to fill it up. An arbitrary implementation could overwrite the
555 // entire contents of the vector, not just append to it (which is what
556 // we are expecting).
558 // To prevent extraneously checking the UTF-8-ness of the entire buffer
559 // we pass it to our hardcoded `read_to_end` implementation which we
560 // know is guaranteed to only read data into the end of the buffer.
561 append_to_string(buf, |b| read_to_end(self, b))
564 /// Read the exact number of bytes required to fill `buf`.
566 /// This function reads as many bytes as necessary to completely fill the
567 /// specified buffer `buf`.
569 /// No guarantees are provided about the contents of `buf` when this
570 /// function is called, implementations cannot rely on any property of the
571 /// contents of `buf` being true. It is recommended that implementations
572 /// only write data to `buf` instead of reading its contents.
576 /// If this function encounters an error of the kind
577 /// `ErrorKind::Interrupted` then the error is ignored and the operation
580 /// If this function encounters an "end of file" before completely filling
581 /// the buffer, it returns an error of the kind `ErrorKind::UnexpectedEof`.
582 /// The contents of `buf` are unspecified in this case.
584 /// If any other read error is encountered then this function immediately
585 /// returns. The contents of `buf` are unspecified in this case.
587 /// If this function returns an error, it is unspecified how many bytes it
588 /// has read, but it will never read more than would be necessary to
589 /// completely fill the buffer.
593 /// [`File`][file]s implement `Read`:
595 /// [file]: ../fs/struct.File.html
599 /// use std::io::prelude::*;
600 /// use std::fs::File;
602 /// # fn foo() -> io::Result<()> {
603 /// let mut f = try!(File::open("foo.txt"));
604 /// let mut buffer = [0; 10];
606 /// // read exactly 10 bytes
607 /// try!(f.read_exact(&mut buffer));
611 #[stable(feature = "read_exact", since = "1.6.0")]
612 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
613 while !buf.is_empty() {
614 match self.read(buf) {
616 Ok(n) => { let tmp = buf; buf = &mut tmp[n..]; }
617 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
618 Err(e) => return Err(e),
622 Err(Error::new(ErrorKind::UnexpectedEof,
623 "failed to fill whole buffer"))
629 /// Creates a "by reference" adaptor for this instance of `Read`.
631 /// The returned adaptor also implements `Read` and will simply borrow this
636 /// [`File`][file]s implement `Read`:
638 /// [file]: ../fs/struct.File.html
642 /// use std::io::Read;
643 /// use std::fs::File;
645 /// # fn foo() -> io::Result<()> {
646 /// let mut f = try!(File::open("foo.txt"));
647 /// let mut buffer = Vec::new();
648 /// let mut other_buffer = Vec::new();
651 /// let reference = f.by_ref();
653 /// // read at most 5 bytes
654 /// try!(reference.take(5).read_to_end(&mut buffer));
656 /// } // drop our &mut reference so we can use f again
658 /// // original file still usable, read the rest
659 /// try!(f.read_to_end(&mut other_buffer));
663 #[stable(feature = "rust1", since = "1.0.0")]
664 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
666 /// Transforms this `Read` instance to an `Iterator` over its bytes.
668 /// The returned type implements `Iterator` where the `Item` is `Result<u8,
669 /// R::Err>`. The yielded item is `Ok` if a byte was successfully read and
670 /// `Err` otherwise for I/O errors. EOF is mapped to returning `None` from
675 /// [`File`][file]s implement `Read`:
677 /// [file]: ../fs/struct.File.html
681 /// use std::io::prelude::*;
682 /// use std::fs::File;
684 /// # fn foo() -> io::Result<()> {
685 /// let mut f = try!(File::open("foo.txt"));
687 /// for byte in f.bytes() {
688 /// println!("{}", byte.unwrap());
693 #[stable(feature = "rust1", since = "1.0.0")]
694 fn bytes(self) -> Bytes<Self> where Self: Sized {
695 Bytes { inner: self }
698 /// Transforms this `Read` instance to an `Iterator` over `char`s.
700 /// This adaptor will attempt to interpret this reader as a UTF-8 encoded
701 /// sequence of characters. The returned iterator will return `None` once
702 /// EOF is reached for this reader. Otherwise each element yielded will be a
703 /// `Result<char, E>` where `E` may contain information about what I/O error
704 /// occurred or where decoding failed.
706 /// Currently this adaptor will discard intermediate data read, and should
707 /// be avoided if this is not desired.
711 /// [`File`][file]s implement `Read`:
713 /// [file]: ../fs/struct.File.html
718 /// use std::io::prelude::*;
719 /// use std::fs::File;
721 /// # fn foo() -> io::Result<()> {
722 /// let mut f = try!(File::open("foo.txt"));
724 /// for c in f.chars() {
725 /// println!("{}", c.unwrap());
730 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
731 of where errors happen is currently \
732 unclear and may change",
734 fn chars(self) -> Chars<Self> where Self: Sized {
735 Chars { inner: self }
738 /// Creates an adaptor which will chain this stream with another.
740 /// The returned `Read` instance will first read all bytes from this object
741 /// until EOF is encountered. Afterwards the output is equivalent to the
742 /// output of `next`.
746 /// [`File`][file]s implement `Read`:
748 /// [file]: ../fs/struct.File.html
752 /// use std::io::prelude::*;
753 /// use std::fs::File;
755 /// # fn foo() -> io::Result<()> {
756 /// let mut f1 = try!(File::open("foo.txt"));
757 /// let mut f2 = try!(File::open("bar.txt"));
759 /// let mut handle = f1.chain(f2);
760 /// let mut buffer = String::new();
762 /// // read the value into a String. We could use any Read method here,
763 /// // this is just one example.
764 /// try!(handle.read_to_string(&mut buffer));
768 #[stable(feature = "rust1", since = "1.0.0")]
769 fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized {
770 Chain { first: self, second: next, done_first: false }
773 /// Creates an adaptor which will read at most `limit` bytes from it.
775 /// This function returns a new instance of `Read` which will read at most
776 /// `limit` bytes, after which it will always return EOF (`Ok(0)`). Any
777 /// read errors will not count towards the number of bytes read and future
778 /// calls to `read` may succeed.
782 /// [`File`][file]s implement `Read`:
784 /// [file]: ../fs/struct.File.html
788 /// use std::io::prelude::*;
789 /// use std::fs::File;
791 /// # fn foo() -> io::Result<()> {
792 /// let mut f = try!(File::open("foo.txt"));
793 /// let mut buffer = [0; 5];
795 /// // read at most five bytes
796 /// let mut handle = f.take(5);
798 /// try!(handle.read(&mut buffer));
802 #[stable(feature = "rust1", since = "1.0.0")]
803 fn take(self, limit: u64) -> Take<Self> where Self: Sized {
804 Take { inner: self, limit: limit }
808 /// A trait for objects which are byte-oriented sinks.
810 /// Implementors of the `Write` trait are sometimes called 'writers'.
812 /// Writers are defined by two required methods, `write()` and `flush()`:
814 /// * The `write()` method will attempt to write some data into the object,
815 /// returning how many bytes were successfully written.
817 /// * The `flush()` method is useful for adaptors and explicit buffers
818 /// themselves for ensuring that all buffered data has been pushed out to the
821 /// Writers are intended to be composable with one another. Many implementors
822 /// throughout `std::io` take and provide types which implement the `Write`
828 /// use std::io::prelude::*;
829 /// use std::fs::File;
831 /// # fn foo() -> std::io::Result<()> {
832 /// let mut buffer = try!(File::create("foo.txt"));
834 /// try!(buffer.write(b"some bytes"));
838 #[stable(feature = "rust1", since = "1.0.0")]
840 /// Write a buffer into this object, returning how many bytes were written.
842 /// This function will attempt to write the entire contents of `buf`, but
843 /// the entire write may not succeed, or the write may also generate an
844 /// error. A call to `write` represents *at most one* attempt to write to
845 /// any wrapped object.
847 /// Calls to `write` are not guaranteed to block waiting for data to be
848 /// written, and a write which would otherwise block can be indicated through
849 /// an `Err` variant.
851 /// If the return value is `Ok(n)` then it must be guaranteed that
852 /// `0 <= n <= buf.len()`. A return value of `0` typically means that the
853 /// underlying object is no longer able to accept bytes and will likely not
854 /// be able to in the future as well, or that the buffer provided is empty.
858 /// Each call to `write` may generate an I/O error indicating that the
859 /// operation could not be completed. If an error is returned then no bytes
860 /// in the buffer were written to this writer.
862 /// It is **not** considered an error if the entire buffer could not be
863 /// written to this writer.
868 /// use std::io::prelude::*;
869 /// use std::fs::File;
871 /// # fn foo() -> std::io::Result<()> {
872 /// let mut buffer = try!(File::create("foo.txt"));
874 /// try!(buffer.write(b"some bytes"));
878 #[stable(feature = "rust1", since = "1.0.0")]
879 fn write(&mut self, buf: &[u8]) -> Result<usize>;
881 /// Flush this output stream, ensuring that all intermediately buffered
882 /// contents reach their destination.
886 /// It is considered an error if not all bytes could be written due to
887 /// I/O errors or EOF being reached.
892 /// use std::io::prelude::*;
893 /// use std::io::BufWriter;
894 /// use std::fs::File;
896 /// # fn foo() -> std::io::Result<()> {
897 /// let mut buffer = BufWriter::new(try!(File::create("foo.txt")));
899 /// try!(buffer.write(b"some bytes"));
900 /// try!(buffer.flush());
904 #[stable(feature = "rust1", since = "1.0.0")]
905 fn flush(&mut self) -> Result<()>;
907 /// Attempts to write an entire buffer into this write.
909 /// This method will continuously call `write` while there is more data to
910 /// write. This method will not return until the entire buffer has been
911 /// successfully written or an error occurs. The first error generated from
912 /// this method will be returned.
916 /// This function will return the first error that `write` returns.
921 /// use std::io::prelude::*;
922 /// use std::fs::File;
924 /// # fn foo() -> std::io::Result<()> {
925 /// let mut buffer = try!(File::create("foo.txt"));
927 /// try!(buffer.write_all(b"some bytes"));
931 #[stable(feature = "rust1", since = "1.0.0")]
932 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
933 while !buf.is_empty() {
934 match self.write(buf) {
935 Ok(0) => return Err(Error::new(ErrorKind::WriteZero,
936 "failed to write whole buffer")),
937 Ok(n) => buf = &buf[n..],
938 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
939 Err(e) => return Err(e),
945 /// Writes a formatted string into this writer, returning any error
948 /// This method is primarily used to interface with the
949 /// [`format_args!`][formatargs] macro, but it is rare that this should
950 /// explicitly be called. The [`write!`][write] macro should be favored to
951 /// invoke this method instead.
953 /// [formatargs]: ../macro.format_args.html
954 /// [write]: ../macro.write.html
956 /// This function internally uses the [`write_all`][writeall] method on
957 /// this trait and hence will continuously write data so long as no errors
958 /// are received. This also means that partial writes are not indicated in
961 /// [writeall]: #method.write_all
965 /// This function will return any I/O error reported while formatting.
970 /// use std::io::prelude::*;
971 /// use std::fs::File;
973 /// # fn foo() -> std::io::Result<()> {
974 /// let mut buffer = try!(File::create("foo.txt"));
977 /// try!(write!(buffer, "{:.*}", 2, 1.234567));
978 /// // turns into this:
979 /// try!(buffer.write_fmt(format_args!("{:.*}", 2, 1.234567)));
983 #[stable(feature = "rust1", since = "1.0.0")]
984 fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<()> {
985 // Create a shim which translates a Write to a fmt::Write and saves
986 // off I/O errors. instead of discarding them
987 struct Adaptor<'a, T: ?Sized + 'a> {
992 impl<'a, T: Write + ?Sized> fmt::Write for Adaptor<'a, T> {
993 fn write_str(&mut self, s: &str) -> fmt::Result {
994 match self.inner.write_all(s.as_bytes()) {
1004 let mut output = Adaptor { inner: self, error: Ok(()) };
1005 match fmt::write(&mut output, fmt) {
1008 // check if the error came from the underlying `Write` or not
1009 if output.error.is_err() {
1012 Err(Error::new(ErrorKind::Other, "formatter error"))
1018 /// Creates a "by reference" adaptor for this instance of `Write`.
1020 /// The returned adaptor also implements `Write` and will simply borrow this
1026 /// use std::io::Write;
1027 /// use std::fs::File;
1029 /// # fn foo() -> std::io::Result<()> {
1030 /// let mut buffer = try!(File::create("foo.txt"));
1032 /// let reference = buffer.by_ref();
1034 /// // we can use reference just like our original buffer
1035 /// try!(reference.write_all(b"some bytes"));
1039 #[stable(feature = "rust1", since = "1.0.0")]
1040 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
1043 /// The `Seek` trait provides a cursor which can be moved within a stream of
1046 /// The stream typically has a fixed size, allowing seeking relative to either
1047 /// end or the current offset.
1051 /// [`File`][file]s implement `Seek`:
1053 /// [file]: ../fs/struct.File.html
1057 /// use std::io::prelude::*;
1058 /// use std::fs::File;
1059 /// use std::io::SeekFrom;
1061 /// # fn foo() -> io::Result<()> {
1062 /// let mut f = try!(File::open("foo.txt"));
1064 /// // move the cursor 42 bytes from the start of the file
1065 /// try!(f.seek(SeekFrom::Start(42)));
1069 #[stable(feature = "rust1", since = "1.0.0")]
1071 /// Seek to an offset, in bytes, in a stream.
1073 /// A seek beyond the end of a stream is allowed, but implementation
1076 /// If the seek operation completed successfully,
1077 /// this method returns the new position from the start of the stream.
1078 /// That position can be used later with [`SeekFrom::Start`].
1082 /// Seeking to a negative offset is considered an error.
1084 /// [`SeekFrom::Start`]: enum.SeekFrom.html#variant.Start
1085 #[stable(feature = "rust1", since = "1.0.0")]
1086 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1089 /// Enumeration of possible methods to seek within an I/O object.
1091 /// It is used by the [`Seek`] trait.
1093 /// [`Seek`]: trait.Seek.html
1094 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1095 #[stable(feature = "rust1", since = "1.0.0")]
1097 /// Set the offset to the provided number of bytes.
1098 #[stable(feature = "rust1", since = "1.0.0")]
1099 Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
1101 /// Set the offset to the size of this object plus the specified number of
1104 /// It is possible to seek beyond the end of an object, but it's an error to
1105 /// seek before byte 0.
1106 #[stable(feature = "rust1", since = "1.0.0")]
1107 End(#[stable(feature = "rust1", since = "1.0.0")] i64),
1109 /// Set the offset to the current position plus the specified number of
1112 /// It is possible to seek beyond the end of an object, but it's an error to
1113 /// seek before byte 0.
1114 #[stable(feature = "rust1", since = "1.0.0")]
1115 Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
1118 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>)
1122 let (done, used) = {
1123 let available = match r.fill_buf() {
1125 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1126 Err(e) => return Err(e)
1128 match memchr::memchr(delim, available) {
1130 buf.extend_from_slice(&available[..i + 1]);
1134 buf.extend_from_slice(available);
1135 (false, available.len())
1141 if done || used == 0 {
1147 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1148 /// to perform extra ways of reading.
1150 /// For example, reading line-by-line is inefficient without using a buffer, so
1151 /// if you want to read by line, you'll need `BufRead`, which includes a
1152 /// [`read_line()`][readline] method as well as a [`lines()`][lines] iterator.
1154 /// [readline]: #method.read_line
1155 /// [lines]: #method.lines
1159 /// A locked standard input implements `BufRead`:
1163 /// use std::io::prelude::*;
1165 /// let stdin = io::stdin();
1166 /// for line in stdin.lock().lines() {
1167 /// println!("{}", line.unwrap());
1171 /// If you have something that implements `Read`, you can use the [`BufReader`
1172 /// type][bufreader] to turn it into a `BufRead`.
1174 /// For example, [`File`][file] implements `Read`, but not `BufRead`.
1175 /// `BufReader` to the rescue!
1177 /// [bufreader]: struct.BufReader.html
1178 /// [file]: ../fs/struct.File.html
1181 /// use std::io::{self, BufReader};
1182 /// use std::io::prelude::*;
1183 /// use std::fs::File;
1185 /// # fn foo() -> io::Result<()> {
1186 /// let f = try!(File::open("foo.txt"));
1187 /// let f = BufReader::new(f);
1189 /// for line in f.lines() {
1190 /// println!("{}", line.unwrap());
1197 #[stable(feature = "rust1", since = "1.0.0")]
1198 pub trait BufRead: Read {
1199 /// Fills the internal buffer of this object, returning the buffer contents.
1201 /// This function is a lower-level call. It needs to be paired with the
1202 /// [`consume`][consume] method to function properly. When calling this
1203 /// method, none of the contents will be "read" in the sense that later
1204 /// calling `read` may return the same contents. As such, `consume` must be
1205 /// called with the number of bytes that are consumed from this buffer to
1206 /// ensure that the bytes are never returned twice.
1208 /// [consume]: #tymethod.consume
1210 /// An empty buffer returned indicates that the stream has reached EOF.
1214 /// This function will return an I/O error if the underlying reader was
1215 /// read, but returned an error.
1219 /// A locked standard input implements `BufRead`:
1223 /// use std::io::prelude::*;
1225 /// let stdin = io::stdin();
1226 /// let mut stdin = stdin.lock();
1228 /// // we can't have two `&mut` references to `stdin`, so use a block
1229 /// // to end the borrow early.
1231 /// let buffer = stdin.fill_buf().unwrap();
1233 /// // work with buffer
1234 /// println!("{:?}", buffer);
1239 /// // ensure the bytes we worked with aren't returned again later
1240 /// stdin.consume(length);
1242 #[stable(feature = "rust1", since = "1.0.0")]
1243 fn fill_buf(&mut self) -> Result<&[u8]>;
1245 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1246 /// so they should no longer be returned in calls to `read`.
1248 /// This function is a lower-level call. It needs to be paired with the
1249 /// [`fill_buf`][fillbuf] method to function properly. This function does
1250 /// not perform any I/O, it simply informs this object that some amount of
1251 /// its buffer, returned from `fill_buf`, has been consumed and should no
1252 /// longer be returned. As such, this function may do odd things if
1253 /// `fill_buf` isn't called before calling it.
1255 /// [fillbuf]: #tymethod.fill_buf
1257 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1262 /// Since `consume()` is meant to be used with [`fill_buf()`][fillbuf],
1263 /// that method's example includes an example of `consume()`.
1264 #[stable(feature = "rust1", since = "1.0.0")]
1265 fn consume(&mut self, amt: usize);
1267 /// Read all bytes into `buf` until the delimiter `byte` or EOF is reached.
1269 /// This function will read bytes from the underlying stream until the
1270 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1271 /// the delimiter (if found) will be appended to `buf`.
1273 /// If successful, this function will return the total number of bytes read.
1277 /// This function will ignore all instances of `ErrorKind::Interrupted` and
1278 /// will otherwise return any errors returned by `fill_buf`.
1280 /// If an I/O error is encountered then all bytes read so far will be
1281 /// present in `buf` and its length will have been adjusted appropriately.
1285 /// A locked standard input implements `BufRead`. In this example, we'll
1286 /// read from standard input until we see an `a` byte.
1290 /// use std::io::prelude::*;
1292 /// fn foo() -> io::Result<()> {
1293 /// let stdin = io::stdin();
1294 /// let mut stdin = stdin.lock();
1295 /// let mut buffer = Vec::new();
1297 /// try!(stdin.read_until(b'a', &mut buffer));
1299 /// println!("{:?}", buffer);
1303 #[stable(feature = "rust1", since = "1.0.0")]
1304 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
1305 read_until(self, byte, buf)
1308 /// Read all bytes until a newline (the 0xA byte) is reached, and append
1309 /// them to the provided buffer.
1311 /// This function will read bytes from the underlying stream until the
1312 /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
1313 /// up to, and including, the delimiter (if found) will be appended to
1316 /// If successful, this function will return the total number of bytes read.
1320 /// This function has the same error semantics as `read_until` and will also
1321 /// return an error if the read bytes are not valid UTF-8. If an I/O error
1322 /// is encountered then `buf` may contain some bytes already read in the
1323 /// event that all data read so far was valid UTF-8.
1327 /// A locked standard input implements `BufRead`. In this example, we'll
1328 /// read all of the lines from standard input. If we were to do this in
1329 /// an actual project, the [`lines()`][lines] method would be easier, of
1332 /// [lines]: #method.lines
1336 /// use std::io::prelude::*;
1338 /// let stdin = io::stdin();
1339 /// let mut stdin = stdin.lock();
1340 /// let mut buffer = String::new();
1342 /// while stdin.read_line(&mut buffer).unwrap() > 0 {
1343 /// // work with buffer
1344 /// println!("{:?}", buffer);
1349 #[stable(feature = "rust1", since = "1.0.0")]
1350 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
1351 // Note that we are not calling the `.read_until` method here, but
1352 // rather our hardcoded implementation. For more details as to why, see
1353 // the comments in `read_to_end`.
1354 append_to_string(buf, |b| read_until(self, b'\n', b))
1357 /// Returns an iterator over the contents of this reader split on the byte
1360 /// The iterator returned from this function will return instances of
1361 /// `io::Result<Vec<u8>>`. Each vector returned will *not* have the
1362 /// delimiter byte at the end.
1364 /// This function will yield errors whenever `read_until` would have also
1365 /// yielded an error.
1369 /// A locked standard input implements `BufRead`. In this example, we'll
1370 /// read some input from standard input, splitting on commas.
1374 /// use std::io::prelude::*;
1376 /// let stdin = io::stdin();
1378 /// for content in stdin.lock().split(b',') {
1379 /// println!("{:?}", content.unwrap());
1382 #[stable(feature = "rust1", since = "1.0.0")]
1383 fn split(self, byte: u8) -> Split<Self> where Self: Sized {
1384 Split { buf: self, delim: byte }
1387 /// Returns an iterator over the lines of this reader.
1389 /// The iterator returned from this function will yield instances of
1390 /// `io::Result<String>`. Each string returned will *not* have a newline
1391 /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
1395 /// A locked standard input implements `BufRead`:
1399 /// use std::io::prelude::*;
1401 /// let stdin = io::stdin();
1403 /// for line in stdin.lock().lines() {
1404 /// println!("{}", line.unwrap());
1407 #[stable(feature = "rust1", since = "1.0.0")]
1408 fn lines(self) -> Lines<Self> where Self: Sized {
1413 /// Adaptor to chain together two readers.
1415 /// This struct is generally created by calling [`chain()`][chain] on a reader.
1416 /// Please see the documentation of `chain()` for more details.
1418 /// [chain]: trait.Read.html#method.chain
1419 #[stable(feature = "rust1", since = "1.0.0")]
1420 pub struct Chain<T, U> {
1426 #[stable(feature = "rust1", since = "1.0.0")]
1427 impl<T: Read, U: Read> Read for Chain<T, U> {
1428 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1429 if !self.done_first {
1430 match self.first.read(buf)? {
1431 0 if buf.len() != 0 => { self.done_first = true; }
1435 self.second.read(buf)
1439 #[stable(feature = "chain_bufread", since = "1.9.0")]
1440 impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
1441 fn fill_buf(&mut self) -> Result<&[u8]> {
1442 if !self.done_first {
1443 match self.first.fill_buf()? {
1444 buf if buf.len() == 0 => { self.done_first = true; }
1445 buf => return Ok(buf),
1448 self.second.fill_buf()
1451 fn consume(&mut self, amt: usize) {
1452 if !self.done_first {
1453 self.first.consume(amt)
1455 self.second.consume(amt)
1460 /// Reader adaptor which limits the bytes read from an underlying reader.
1462 /// This struct is generally created by calling [`take()`][take] on a reader.
1463 /// Please see the documentation of `take()` for more details.
1465 /// [take]: trait.Read.html#method.take
1466 #[stable(feature = "rust1", since = "1.0.0")]
1467 pub struct Take<T> {
1473 /// Returns the number of bytes that can be read before this instance will
1478 /// This instance may reach EOF after reading fewer bytes than indicated by
1479 /// this method if the underlying `Read` instance reaches EOF.
1485 /// use std::io::prelude::*;
1486 /// use std::fs::File;
1488 /// # fn foo() -> io::Result<()> {
1489 /// let f = try!(File::open("foo.txt"));
1491 /// // read at most five bytes
1492 /// let handle = f.take(5);
1494 /// println!("limit: {}", handle.limit());
1498 #[stable(feature = "rust1", since = "1.0.0")]
1499 pub fn limit(&self) -> u64 { self.limit }
1501 /// Consumes the `Take`, returning the wrapped reader.
1506 /// #![feature(io_take_into_inner)]
1509 /// use std::io::prelude::*;
1510 /// use std::fs::File;
1512 /// # fn foo() -> io::Result<()> {
1513 /// let mut file = try!(File::open("foo.txt"));
1515 /// let mut buffer = [0; 5];
1516 /// let mut handle = file.take(5);
1517 /// try!(handle.read(&mut buffer));
1519 /// let file = handle.into_inner();
1523 #[unstable(feature = "io_take_into_inner", issue = "0")]
1524 pub fn into_inner(self) -> T {
1529 #[stable(feature = "rust1", since = "1.0.0")]
1530 impl<T: Read> Read for Take<T> {
1531 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1532 // Don't call into inner reader at all at EOF because it may still block
1533 if self.limit == 0 {
1537 let max = cmp::min(buf.len() as u64, self.limit) as usize;
1538 let n = self.inner.read(&mut buf[..max])?;
1539 self.limit -= n as u64;
1544 #[stable(feature = "rust1", since = "1.0.0")]
1545 impl<T: BufRead> BufRead for Take<T> {
1546 fn fill_buf(&mut self) -> Result<&[u8]> {
1547 // Don't call into inner reader at all at EOF because it may still block
1548 if self.limit == 0 {
1552 let buf = self.inner.fill_buf()?;
1553 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
1557 fn consume(&mut self, amt: usize) {
1558 // Don't let callers reset the limit by passing an overlarge value
1559 let amt = cmp::min(amt as u64, self.limit) as usize;
1560 self.limit -= amt as u64;
1561 self.inner.consume(amt);
1565 fn read_one_byte(reader: &mut Read) -> Option<Result<u8>> {
1568 return match reader.read(&mut buf) {
1570 Ok(..) => Some(Ok(buf[0])),
1571 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1572 Err(e) => Some(Err(e)),
1577 /// An iterator over `u8` values of a reader.
1579 /// This struct is generally created by calling [`bytes()`][bytes] on a reader.
1580 /// Please see the documentation of `bytes()` for more details.
1582 /// [bytes]: trait.Read.html#method.bytes
1583 #[stable(feature = "rust1", since = "1.0.0")]
1584 pub struct Bytes<R> {
1588 #[stable(feature = "rust1", since = "1.0.0")]
1589 impl<R: Read> Iterator for Bytes<R> {
1590 type Item = Result<u8>;
1592 fn next(&mut self) -> Option<Result<u8>> {
1593 read_one_byte(&mut self.inner)
1597 /// An iterator over the `char`s of a reader.
1599 /// This struct is generally created by calling [`chars()`][chars] on a reader.
1600 /// Please see the documentation of `chars()` for more details.
1602 /// [chars]: trait.Read.html#method.chars
1603 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1605 pub struct Chars<R> {
1609 /// An enumeration of possible errors that can be generated from the `Chars`
1612 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1614 pub enum CharsError {
1615 /// Variant representing that the underlying stream was read successfully
1616 /// but it did not contain valid utf8 data.
1619 /// Variant representing that an I/O error occurred.
1623 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1625 impl<R: Read> Iterator for Chars<R> {
1626 type Item = result::Result<char, CharsError>;
1628 fn next(&mut self) -> Option<result::Result<char, CharsError>> {
1629 let first_byte = match read_one_byte(&mut self.inner) {
1630 None => return None,
1632 Some(Err(e)) => return Some(Err(CharsError::Other(e))),
1634 let width = core_str::utf8_char_width(first_byte);
1635 if width == 1 { return Some(Ok(first_byte as char)) }
1636 if width == 0 { return Some(Err(CharsError::NotUtf8)) }
1637 let mut buf = [first_byte, 0, 0, 0];
1640 while start < width {
1641 match self.inner.read(&mut buf[start..width]) {
1642 Ok(0) => return Some(Err(CharsError::NotUtf8)),
1643 Ok(n) => start += n,
1644 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1645 Err(e) => return Some(Err(CharsError::Other(e))),
1649 Some(match str::from_utf8(&buf[..width]).ok() {
1650 Some(s) => Ok(s.chars().next().unwrap()),
1651 None => Err(CharsError::NotUtf8),
1656 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1658 impl std_error::Error for CharsError {
1659 fn description(&self) -> &str {
1661 CharsError::NotUtf8 => "invalid utf8 encoding",
1662 CharsError::Other(ref e) => std_error::Error::description(e),
1665 fn cause(&self) -> Option<&std_error::Error> {
1667 CharsError::NotUtf8 => None,
1668 CharsError::Other(ref e) => e.cause(),
1673 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1675 impl fmt::Display for CharsError {
1676 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1678 CharsError::NotUtf8 => {
1679 "byte stream did not contain valid utf8".fmt(f)
1681 CharsError::Other(ref e) => e.fmt(f),
1686 /// An iterator over the contents of an instance of `BufRead` split on a
1687 /// particular byte.
1689 /// This struct is generally created by calling [`split()`][split] on a
1690 /// `BufRead`. Please see the documentation of `split()` for more details.
1692 /// [split]: trait.BufRead.html#method.split
1693 #[stable(feature = "rust1", since = "1.0.0")]
1694 pub struct Split<B> {
1699 #[stable(feature = "rust1", since = "1.0.0")]
1700 impl<B: BufRead> Iterator for Split<B> {
1701 type Item = Result<Vec<u8>>;
1703 fn next(&mut self) -> Option<Result<Vec<u8>>> {
1704 let mut buf = Vec::new();
1705 match self.buf.read_until(self.delim, &mut buf) {
1708 if buf[buf.len() - 1] == self.delim {
1713 Err(e) => Some(Err(e))
1718 /// An iterator over the lines of an instance of `BufRead`.
1720 /// This struct is generally created by calling [`lines()`][lines] on a
1721 /// `BufRead`. Please see the documentation of `lines()` for more details.
1723 /// [lines]: trait.BufRead.html#method.lines
1724 #[stable(feature = "rust1", since = "1.0.0")]
1725 pub struct Lines<B> {
1729 #[stable(feature = "rust1", since = "1.0.0")]
1730 impl<B: BufRead> Iterator for Lines<B> {
1731 type Item = Result<String>;
1733 fn next(&mut self) -> Option<Result<String>> {
1734 let mut buf = String::new();
1735 match self.buf.read_line(&mut buf) {
1738 if buf.ends_with("\n") {
1740 if buf.ends_with("\r") {
1746 Err(e) => Some(Err(e))
1760 #[cfg_attr(target_os = "emscripten", ignore)]
1762 let mut buf = Cursor::new(&b"12"[..]);
1763 let mut v = Vec::new();
1764 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
1765 assert_eq!(v, b"12");
1767 let mut buf = Cursor::new(&b"1233"[..]);
1768 let mut v = Vec::new();
1769 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
1770 assert_eq!(v, b"123");
1772 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
1773 assert_eq!(v, b"3");
1775 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
1781 let buf = Cursor::new(&b"12"[..]);
1782 let mut s = buf.split(b'3');
1783 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1784 assert!(s.next().is_none());
1786 let buf = Cursor::new(&b"1233"[..]);
1787 let mut s = buf.split(b'3');
1788 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1789 assert_eq!(s.next().unwrap().unwrap(), vec![]);
1790 assert!(s.next().is_none());
1795 let mut buf = Cursor::new(&b"12"[..]);
1796 let mut v = String::new();
1797 assert_eq!(buf.read_line(&mut v).unwrap(), 2);
1798 assert_eq!(v, "12");
1800 let mut buf = Cursor::new(&b"12\n\n"[..]);
1801 let mut v = String::new();
1802 assert_eq!(buf.read_line(&mut v).unwrap(), 3);
1803 assert_eq!(v, "12\n");
1805 assert_eq!(buf.read_line(&mut v).unwrap(), 1);
1806 assert_eq!(v, "\n");
1808 assert_eq!(buf.read_line(&mut v).unwrap(), 0);
1814 let buf = Cursor::new(&b"12\r"[..]);
1815 let mut s = buf.lines();
1816 assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
1817 assert!(s.next().is_none());
1819 let buf = Cursor::new(&b"12\r\n\n"[..]);
1820 let mut s = buf.lines();
1821 assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
1822 assert_eq!(s.next().unwrap().unwrap(), "".to_string());
1823 assert!(s.next().is_none());
1828 let mut c = Cursor::new(&b""[..]);
1829 let mut v = Vec::new();
1830 assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
1833 let mut c = Cursor::new(&b"1"[..]);
1834 let mut v = Vec::new();
1835 assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
1836 assert_eq!(v, b"1");
1838 let cap = 1024 * 1024;
1839 let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
1840 let mut v = Vec::new();
1841 let (a, b) = data.split_at(data.len() / 2);
1842 assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
1843 assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
1844 assert_eq!(v, data);
1848 fn read_to_string() {
1849 let mut c = Cursor::new(&b""[..]);
1850 let mut v = String::new();
1851 assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
1854 let mut c = Cursor::new(&b"1"[..]);
1855 let mut v = String::new();
1856 assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
1859 let mut c = Cursor::new(&b"\xff"[..]);
1860 let mut v = String::new();
1861 assert!(c.read_to_string(&mut v).is_err());
1866 let mut buf = [0; 4];
1868 let mut c = Cursor::new(&b""[..]);
1869 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1870 io::ErrorKind::UnexpectedEof);
1872 let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
1873 c.read_exact(&mut buf).unwrap();
1874 assert_eq!(&buf, b"1234");
1875 c.read_exact(&mut buf).unwrap();
1876 assert_eq!(&buf, b"5678");
1877 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1878 io::ErrorKind::UnexpectedEof);
1882 fn read_exact_slice() {
1883 let mut buf = [0; 4];
1885 let mut c = &b""[..];
1886 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1887 io::ErrorKind::UnexpectedEof);
1889 let mut c = &b"123"[..];
1890 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1891 io::ErrorKind::UnexpectedEof);
1892 // make sure the optimized (early returning) method is being used
1893 assert_eq!(&buf, &[0; 4]);
1895 let mut c = &b"1234"[..];
1896 c.read_exact(&mut buf).unwrap();
1897 assert_eq!(&buf, b"1234");
1899 let mut c = &b"56789"[..];
1900 c.read_exact(&mut buf).unwrap();
1901 assert_eq!(&buf, b"5678");
1902 assert_eq!(c, b"9");
1910 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
1911 Err(io::Error::new(io::ErrorKind::Other, ""))
1914 impl BufRead for R {
1915 fn fill_buf(&mut self) -> io::Result<&[u8]> {
1916 Err(io::Error::new(io::ErrorKind::Other, ""))
1918 fn consume(&mut self, _amt: usize) { }
1921 let mut buf = [0; 1];
1922 assert_eq!(0, R.take(0).read(&mut buf).unwrap());
1923 assert_eq!(b"", R.take(0).fill_buf().unwrap());
1926 fn cmp_bufread<Br1: BufRead, Br2: BufRead>(mut br1: Br1, mut br2: Br2, exp: &[u8]) {
1927 let mut cat = Vec::new();
1930 let buf1 = br1.fill_buf().unwrap();
1931 let buf2 = br2.fill_buf().unwrap();
1932 let minlen = if buf1.len() < buf2.len() { buf1.len() } else { buf2.len() };
1933 assert_eq!(buf1[..minlen], buf2[..minlen]);
1934 cat.extend_from_slice(&buf1[..minlen]);
1940 br1.consume(consume);
1941 br2.consume(consume);
1943 assert_eq!(br1.fill_buf().unwrap().len(), 0);
1944 assert_eq!(br2.fill_buf().unwrap().len(), 0);
1945 assert_eq!(&cat[..], &exp[..])
1949 fn chain_bufread() {
1950 let testdata = b"ABCDEFGHIJKL";
1951 let chain1 = (&testdata[..3]).chain(&testdata[3..6])
1952 .chain(&testdata[6..9])
1953 .chain(&testdata[9..]);
1954 let chain2 = (&testdata[..4]).chain(&testdata[4..8])
1955 .chain(&testdata[8..]);
1956 cmp_bufread(chain1, chain2, &testdata[..]);
1960 fn chain_zero_length_read_is_not_eof() {
1963 let mut s = String::new();
1964 let mut chain = (&a[..]).chain(&b[..]);
1965 chain.read(&mut []).unwrap();
1966 chain.read_to_string(&mut s).unwrap();
1967 assert_eq!("AB", s);
1971 #[cfg_attr(target_os = "emscripten", ignore)]
1972 fn bench_read_to_end(b: &mut test::Bencher) {
1974 let mut lr = repeat(1).take(10000000);
1975 let mut vec = Vec::with_capacity(1024);
1976 super::read_to_end(&mut lr, &mut vec)