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;
256 use iter::{Iterator};
258 use ops::{Drop, FnOnce};
259 use option::Option::{self, Some, None};
260 use result::Result::{Ok, Err};
267 #[stable(feature = "rust1", since = "1.0.0")]
268 pub use self::buffered::{BufReader, BufWriter, LineWriter};
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub use self::buffered::IntoInnerError;
271 #[stable(feature = "rust1", since = "1.0.0")]
272 pub use self::cursor::Cursor;
273 #[stable(feature = "rust1", since = "1.0.0")]
274 pub use self::error::{Result, Error, ErrorKind};
275 #[stable(feature = "rust1", since = "1.0.0")]
276 pub use self::util::{copy, sink, Sink, empty, Empty, repeat, Repeat};
277 #[stable(feature = "rust1", since = "1.0.0")]
278 pub use self::stdio::{stdin, stdout, stderr, _print, Stdin, Stdout, Stderr};
279 #[stable(feature = "rust1", since = "1.0.0")]
280 pub use self::stdio::{StdoutLock, StderrLock, StdinLock};
281 #[unstable(feature = "libstd_io_internals", issue = "0")]
282 #[doc(no_inline, hidden)]
283 pub use self::stdio::{set_panic, set_print};
294 const DEFAULT_BUF_SIZE: usize = 8 * 1024;
296 // A few methods below (read_to_string, read_line) will append data into a
297 // `String` buffer, but we need to be pretty careful when doing this. The
298 // implementation will just call `.as_mut_vec()` and then delegate to a
299 // byte-oriented reading method, but we must ensure that when returning we never
300 // leave `buf` in a state such that it contains invalid UTF-8 in its bounds.
302 // To this end, we use an RAII guard (to protect against panics) which updates
303 // the length of the string when it is dropped. This guard initially truncates
304 // the string to the prior length and only after we've validated that the
305 // new contents are valid UTF-8 do we allow it to set a longer length.
307 // The unsafety in this function is twofold:
309 // 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
311 // 2. We're passing a raw buffer to the function `f`, and it is expected that
312 // the function only *appends* bytes to the buffer. We'll get undefined
313 // behavior if existing bytes are overwritten to have non-UTF-8 data.
314 fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
315 where F: FnOnce(&mut Vec<u8>) -> Result<usize>
317 struct Guard<'a> { s: &'a mut Vec<u8>, len: usize }
318 impl<'a> Drop for Guard<'a> {
320 unsafe { self.s.set_len(self.len); }
325 let mut g = Guard { len: buf.len(), s: buf.as_mut_vec() };
327 if str::from_utf8(&g.s[g.len..]).is_err() {
329 Err(Error::new(ErrorKind::InvalidData,
330 "stream did not contain valid UTF-8"))
339 // This uses an adaptive system to extend the vector when it fills. We want to
340 // avoid paying to allocate and zero a huge chunk of memory if the reader only
341 // has 4 bytes while still making large reads if the reader does have a ton
342 // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
343 // time is 4,500 times (!) slower than this if the reader has a very small
344 // amount of data to return.
345 fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
346 let start_len = buf.len();
347 let mut len = start_len;
348 let mut new_write_size = 16;
351 if len == buf.len() {
352 if new_write_size < DEFAULT_BUF_SIZE {
355 buf.resize(len + new_write_size, 0);
358 match r.read(&mut buf[len..]) {
360 ret = Ok(len - start_len);
364 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
376 /// The `Read` trait allows for reading bytes from a source.
378 /// Implementors of the `Read` trait are sometimes called 'readers'.
380 /// Readers are defined by one required method, `read()`. Each call to `read`
381 /// will attempt to pull bytes from this source into a provided buffer. A
382 /// number of other methods are implemented in terms of `read()`, giving
383 /// implementors a number of ways to read bytes while only needing to implement
386 /// Readers are intended to be composable with one another. Many implementors
387 /// throughout `std::io` take and provide types which implement the `Read`
390 /// Please note that each call to `read` may involve a system call, and
391 /// therefore, using something that implements [`BufRead`][bufread], such as
392 /// [`BufReader`][bufreader], will be more efficient.
394 /// [bufread]: trait.BufRead.html
395 /// [bufreader]: struct.BufReader.html
399 /// [`File`][file]s implement `Read`:
401 /// [file]: ../fs/struct.File.html
405 /// use std::io::prelude::*;
406 /// use std::fs::File;
408 /// # fn foo() -> io::Result<()> {
409 /// let mut f = try!(File::open("foo.txt"));
410 /// let mut buffer = [0; 10];
412 /// // read up to 10 bytes
413 /// try!(f.read(&mut buffer));
415 /// let mut buffer = vec![0; 10];
416 /// // read the whole file
417 /// try!(f.read_to_end(&mut buffer));
419 /// // read into a String, so that you don't need to do the conversion.
420 /// let mut buffer = String::new();
421 /// try!(f.read_to_string(&mut buffer));
423 /// // and more! See the other methods for more details.
427 #[stable(feature = "rust1", since = "1.0.0")]
429 /// Pull some bytes from this source into the specified buffer, returning
430 /// how many bytes were read.
432 /// This function does not provide any guarantees about whether it blocks
433 /// waiting for data, but if an object needs to block for a read but cannot
434 /// it will typically signal this via an `Err` return value.
436 /// If the return value of this method is `Ok(n)`, then it must be
437 /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
438 /// that the buffer `buf` has been filled in with `n` bytes of data from this
439 /// source. If `n` is `0`, then it can indicate one of two scenarios:
441 /// 1. This reader has reached its "end of file" and will likely no longer
442 /// be able to produce bytes. Note that this does not mean that the
443 /// reader will *always* no longer be able to produce bytes.
444 /// 2. The buffer specified was 0 bytes in length.
446 /// No guarantees are provided about the contents of `buf` when this
447 /// function is called, implementations cannot rely on any property of the
448 /// contents of `buf` being true. It is recommended that implementations
449 /// only write data to `buf` instead of reading its contents.
453 /// If this function encounters any form of I/O or other error, an error
454 /// variant will be returned. If an error is returned then it must be
455 /// guaranteed that no bytes were read.
459 /// [`File`][file]s implement `Read`:
461 /// [file]: ../fs/struct.File.html
465 /// use std::io::prelude::*;
466 /// use std::fs::File;
468 /// # fn foo() -> io::Result<()> {
469 /// let mut f = try!(File::open("foo.txt"));
470 /// let mut buffer = [0; 10];
473 /// try!(f.read(&mut buffer[..]));
477 #[stable(feature = "rust1", since = "1.0.0")]
478 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
480 /// Read all bytes until EOF in this source, placing them into `buf`.
482 /// All bytes read from this source will be appended to the specified buffer
483 /// `buf`. This function will continuously call `read` to append more data to
484 /// `buf` until `read` returns either `Ok(0)` or an error of
485 /// non-`ErrorKind::Interrupted` kind.
487 /// If successful, this function will return the total number of bytes read.
491 /// If this function encounters an error of the kind
492 /// `ErrorKind::Interrupted` then the error is ignored and the operation
495 /// If any other read error is encountered then this function immediately
496 /// returns. Any bytes which have already been read will be appended to
501 /// [`File`][file]s implement `Read`:
503 /// [file]: ../fs/struct.File.html
507 /// use std::io::prelude::*;
508 /// use std::fs::File;
510 /// # fn foo() -> io::Result<()> {
511 /// let mut f = try!(File::open("foo.txt"));
512 /// let mut buffer = Vec::new();
514 /// // read the whole file
515 /// try!(f.read_to_end(&mut buffer));
519 #[stable(feature = "rust1", since = "1.0.0")]
520 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
521 read_to_end(self, buf)
524 /// Read all bytes until EOF in this source, placing them into `buf`.
526 /// If successful, this function returns the number of bytes which were read
527 /// and appended to `buf`.
531 /// If the data in this stream is *not* valid UTF-8 then an error is
532 /// returned and `buf` is unchanged.
534 /// See [`read_to_end()`][readtoend] for other error semantics.
536 /// [readtoend]: #method.read_to_end
540 /// [`File`][file]s implement `Read`:
542 /// [file]: ../fs/struct.File.html
546 /// use std::io::prelude::*;
547 /// use std::fs::File;
549 /// # fn foo() -> io::Result<()> {
550 /// let mut f = try!(File::open("foo.txt"));
551 /// let mut buffer = String::new();
553 /// try!(f.read_to_string(&mut buffer));
557 #[stable(feature = "rust1", since = "1.0.0")]
558 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
559 // Note that we do *not* call `.read_to_end()` here. We are passing
560 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
561 // method to fill it up. An arbitrary implementation could overwrite the
562 // entire contents of the vector, not just append to it (which is what
563 // we are expecting).
565 // To prevent extraneously checking the UTF-8-ness of the entire buffer
566 // we pass it to our hardcoded `read_to_end` implementation which we
567 // know is guaranteed to only read data into the end of the buffer.
568 append_to_string(buf, |b| read_to_end(self, b))
571 /// Read the exact number of bytes required to fill `buf`.
573 /// This function reads as many bytes as necessary to completely fill the
574 /// specified buffer `buf`.
576 /// No guarantees are provided about the contents of `buf` when this
577 /// function is called, implementations cannot rely on any property of the
578 /// contents of `buf` being true. It is recommended that implementations
579 /// only write data to `buf` instead of reading its contents.
583 /// If this function encounters an error of the kind
584 /// `ErrorKind::Interrupted` then the error is ignored and the operation
587 /// If this function encounters an "end of file" before completely filling
588 /// the buffer, it returns an error of the kind `ErrorKind::UnexpectedEof`.
589 /// The contents of `buf` are unspecified in this case.
591 /// If any other read error is encountered then this function immediately
592 /// returns. The contents of `buf` are unspecified in this case.
594 /// If this function returns an error, it is unspecified how many bytes it
595 /// has read, but it will never read more than would be necessary to
596 /// completely fill the buffer.
600 /// [`File`][file]s implement `Read`:
602 /// [file]: ../fs/struct.File.html
606 /// use std::io::prelude::*;
607 /// use std::fs::File;
609 /// # fn foo() -> io::Result<()> {
610 /// let mut f = try!(File::open("foo.txt"));
611 /// let mut buffer = [0; 10];
613 /// // read exactly 10 bytes
614 /// try!(f.read_exact(&mut buffer));
618 #[stable(feature = "read_exact", since = "1.6.0")]
619 fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
620 while !buf.is_empty() {
621 match self.read(buf) {
623 Ok(n) => { let tmp = buf; buf = &mut tmp[n..]; }
624 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
625 Err(e) => return Err(e),
629 Err(Error::new(ErrorKind::UnexpectedEof,
630 "failed to fill whole buffer"))
636 /// Creates a "by reference" adaptor for this instance of `Read`.
638 /// The returned adaptor also implements `Read` and will simply borrow this
643 /// [`File`][file]s implement `Read`:
645 /// [file]: ../fs/struct.File.html
649 /// use std::io::Read;
650 /// use std::fs::File;
652 /// # fn foo() -> io::Result<()> {
653 /// let mut f = try!(File::open("foo.txt"));
654 /// let mut buffer = Vec::new();
655 /// let mut other_buffer = Vec::new();
658 /// let reference = f.by_ref();
660 /// // read at most 5 bytes
661 /// try!(reference.take(5).read_to_end(&mut buffer));
663 /// } // drop our &mut reference so we can use f again
665 /// // original file still usable, read the rest
666 /// try!(f.read_to_end(&mut other_buffer));
670 #[stable(feature = "rust1", since = "1.0.0")]
671 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
673 /// Transforms this `Read` instance to an `Iterator` over its bytes.
675 /// The returned type implements `Iterator` where the `Item` is `Result<u8,
676 /// R::Err>`. The yielded item is `Ok` if a byte was successfully read and
677 /// `Err` otherwise for I/O errors. EOF is mapped to returning `None` from
682 /// [`File`][file]s implement `Read`:
684 /// [file]: ../fs/struct.File.html
688 /// use std::io::prelude::*;
689 /// use std::fs::File;
691 /// # fn foo() -> io::Result<()> {
692 /// let mut f = try!(File::open("foo.txt"));
694 /// for byte in f.bytes() {
695 /// println!("{}", byte.unwrap());
700 #[stable(feature = "rust1", since = "1.0.0")]
701 fn bytes(self) -> Bytes<Self> where Self: Sized {
702 Bytes { inner: self }
705 /// Transforms this `Read` instance to an `Iterator` over `char`s.
707 /// This adaptor will attempt to interpret this reader as a UTF-8 encoded
708 /// sequence of characters. The returned iterator will return `None` once
709 /// EOF is reached for this reader. Otherwise each element yielded will be a
710 /// `Result<char, E>` where `E` may contain information about what I/O error
711 /// occurred or where decoding failed.
713 /// Currently this adaptor will discard intermediate data read, and should
714 /// be avoided if this is not desired.
718 /// [`File`][file]s implement `Read`:
720 /// [file]: ../fs/struct.File.html
725 /// use std::io::prelude::*;
726 /// use std::fs::File;
728 /// # fn foo() -> io::Result<()> {
729 /// let mut f = try!(File::open("foo.txt"));
731 /// for c in f.chars() {
732 /// println!("{}", c.unwrap());
737 #[unstable(feature = "io", reason = "the semantics of a partial read/write \
738 of where errors happen is currently \
739 unclear and may change",
741 fn chars(self) -> Chars<Self> where Self: Sized {
742 Chars { inner: self }
745 /// Creates an adaptor which will chain this stream with another.
747 /// The returned `Read` instance will first read all bytes from this object
748 /// until EOF is encountered. Afterwards the output is equivalent to the
749 /// output of `next`.
753 /// [`File`][file]s implement `Read`:
755 /// [file]: ../fs/struct.File.html
759 /// use std::io::prelude::*;
760 /// use std::fs::File;
762 /// # fn foo() -> io::Result<()> {
763 /// let mut f1 = try!(File::open("foo.txt"));
764 /// let mut f2 = try!(File::open("bar.txt"));
766 /// let mut handle = f1.chain(f2);
767 /// let mut buffer = String::new();
769 /// // read the value into a String. We could use any Read method here,
770 /// // this is just one example.
771 /// try!(handle.read_to_string(&mut buffer));
775 #[stable(feature = "rust1", since = "1.0.0")]
776 fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized {
777 Chain { first: self, second: next, done_first: false }
780 /// Creates an adaptor which will read at most `limit` bytes from it.
782 /// This function returns a new instance of `Read` which will read at most
783 /// `limit` bytes, after which it will always return EOF (`Ok(0)`). Any
784 /// read errors will not count towards the number of bytes read and future
785 /// calls to `read` may succeed.
789 /// [`File`][file]s implement `Read`:
791 /// [file]: ../fs/struct.File.html
795 /// use std::io::prelude::*;
796 /// use std::fs::File;
798 /// # fn foo() -> io::Result<()> {
799 /// let mut f = try!(File::open("foo.txt"));
800 /// let mut buffer = [0; 5];
802 /// // read at most five bytes
803 /// let mut handle = f.take(5);
805 /// try!(handle.read(&mut buffer));
809 #[stable(feature = "rust1", since = "1.0.0")]
810 fn take(self, limit: u64) -> Take<Self> where Self: Sized {
811 Take { inner: self, limit: limit }
815 /// A trait for objects which are byte-oriented sinks.
817 /// Implementors of the `Write` trait are sometimes called 'writers'.
819 /// Writers are defined by two required methods, `write()` and `flush()`:
821 /// * The `write()` method will attempt to write some data into the object,
822 /// returning how many bytes were successfully written.
824 /// * The `flush()` method is useful for adaptors and explicit buffers
825 /// themselves for ensuring that all buffered data has been pushed out to the
828 /// Writers are intended to be composable with one another. Many implementors
829 /// throughout `std::io` take and provide types which implement the `Write`
835 /// use std::io::prelude::*;
836 /// use std::fs::File;
838 /// # fn foo() -> std::io::Result<()> {
839 /// let mut buffer = try!(File::create("foo.txt"));
841 /// try!(buffer.write(b"some bytes"));
845 #[stable(feature = "rust1", since = "1.0.0")]
847 /// Write a buffer into this object, returning how many bytes were written.
849 /// This function will attempt to write the entire contents of `buf`, but
850 /// the entire write may not succeed, or the write may also generate an
851 /// error. A call to `write` represents *at most one* attempt to write to
852 /// any wrapped object.
854 /// Calls to `write` are not guaranteed to block waiting for data to be
855 /// written, and a write which would otherwise block can be indicated through
856 /// an `Err` variant.
858 /// If the return value is `Ok(n)` then it must be guaranteed that
859 /// `0 <= n <= buf.len()`. A return value of `0` typically means that the
860 /// underlying object is no longer able to accept bytes and will likely not
861 /// be able to in the future as well, or that the buffer provided is empty.
865 /// Each call to `write` may generate an I/O error indicating that the
866 /// operation could not be completed. If an error is returned then no bytes
867 /// in the buffer were written to this writer.
869 /// It is **not** considered an error if the entire buffer could not be
870 /// written to this writer.
875 /// use std::io::prelude::*;
876 /// use std::fs::File;
878 /// # fn foo() -> std::io::Result<()> {
879 /// let mut buffer = try!(File::create("foo.txt"));
881 /// try!(buffer.write(b"some bytes"));
885 #[stable(feature = "rust1", since = "1.0.0")]
886 fn write(&mut self, buf: &[u8]) -> Result<usize>;
888 /// Flush this output stream, ensuring that all intermediately buffered
889 /// contents reach their destination.
893 /// It is considered an error if not all bytes could be written due to
894 /// I/O errors or EOF being reached.
899 /// use std::io::prelude::*;
900 /// use std::io::BufWriter;
901 /// use std::fs::File;
903 /// # fn foo() -> std::io::Result<()> {
904 /// let mut buffer = BufWriter::new(try!(File::create("foo.txt")));
906 /// try!(buffer.write(b"some bytes"));
907 /// try!(buffer.flush());
911 #[stable(feature = "rust1", since = "1.0.0")]
912 fn flush(&mut self) -> Result<()>;
914 /// Attempts to write an entire buffer into this write.
916 /// This method will continuously call `write` while there is more data to
917 /// write. This method will not return until the entire buffer has been
918 /// successfully written or an error occurs. The first error generated from
919 /// this method will be returned.
923 /// This function will return the first error that `write` returns.
928 /// use std::io::prelude::*;
929 /// use std::fs::File;
931 /// # fn foo() -> std::io::Result<()> {
932 /// let mut buffer = try!(File::create("foo.txt"));
934 /// try!(buffer.write_all(b"some bytes"));
938 #[stable(feature = "rust1", since = "1.0.0")]
939 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
940 while !buf.is_empty() {
941 match self.write(buf) {
942 Ok(0) => return Err(Error::new(ErrorKind::WriteZero,
943 "failed to write whole buffer")),
944 Ok(n) => buf = &buf[n..],
945 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
946 Err(e) => return Err(e),
952 /// Writes a formatted string into this writer, returning any error
955 /// This method is primarily used to interface with the
956 /// [`format_args!`][formatargs] macro, but it is rare that this should
957 /// explicitly be called. The [`write!`][write] macro should be favored to
958 /// invoke this method instead.
960 /// [formatargs]: ../macro.format_args.html
961 /// [write]: ../macro.write.html
963 /// This function internally uses the [`write_all`][writeall] method on
964 /// this trait and hence will continuously write data so long as no errors
965 /// are received. This also means that partial writes are not indicated in
968 /// [writeall]: #method.write_all
972 /// This function will return any I/O error reported while formatting.
977 /// use std::io::prelude::*;
978 /// use std::fs::File;
980 /// # fn foo() -> std::io::Result<()> {
981 /// let mut buffer = try!(File::create("foo.txt"));
984 /// try!(write!(buffer, "{:.*}", 2, 1.234567));
985 /// // turns into this:
986 /// try!(buffer.write_fmt(format_args!("{:.*}", 2, 1.234567)));
990 #[stable(feature = "rust1", since = "1.0.0")]
991 fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<()> {
992 // Create a shim which translates a Write to a fmt::Write and saves
993 // off I/O errors. instead of discarding them
994 struct Adaptor<'a, T: ?Sized + 'a> {
999 impl<'a, T: Write + ?Sized> fmt::Write for Adaptor<'a, T> {
1000 fn write_str(&mut self, s: &str) -> fmt::Result {
1001 match self.inner.write_all(s.as_bytes()) {
1004 self.error = Err(e);
1011 let mut output = Adaptor { inner: self, error: Ok(()) };
1012 match fmt::write(&mut output, fmt) {
1015 // check if the error came from the underlying `Write` or not
1016 if output.error.is_err() {
1019 Err(Error::new(ErrorKind::Other, "formatter error"))
1025 /// Creates a "by reference" adaptor for this instance of `Write`.
1027 /// The returned adaptor also implements `Write` and will simply borrow this
1033 /// use std::io::Write;
1034 /// use std::fs::File;
1036 /// # fn foo() -> std::io::Result<()> {
1037 /// let mut buffer = try!(File::create("foo.txt"));
1039 /// let reference = buffer.by_ref();
1041 /// // we can use reference just like our original buffer
1042 /// try!(reference.write_all(b"some bytes"));
1046 #[stable(feature = "rust1", since = "1.0.0")]
1047 fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
1050 /// The `Seek` trait provides a cursor which can be moved within a stream of
1053 /// The stream typically has a fixed size, allowing seeking relative to either
1054 /// end or the current offset.
1058 /// [`File`][file]s implement `Seek`:
1060 /// [file]: ../fs/struct.File.html
1064 /// use std::io::prelude::*;
1065 /// use std::fs::File;
1066 /// use std::io::SeekFrom;
1068 /// # fn foo() -> io::Result<()> {
1069 /// let mut f = try!(File::open("foo.txt"));
1071 /// // move the cursor 42 bytes from the start of the file
1072 /// try!(f.seek(SeekFrom::Start(42)));
1076 #[stable(feature = "rust1", since = "1.0.0")]
1078 /// Seek to an offset, in bytes, in a stream.
1080 /// A seek beyond the end of a stream is allowed, but implementation
1083 /// If the seek operation completed successfully,
1084 /// this method returns the new position from the start of the stream.
1085 /// That position can be used later with [`SeekFrom::Start`].
1089 /// Seeking to a negative offset is considered an error.
1091 /// [`SeekFrom::Start`]: enum.SeekFrom.html#variant.Start
1092 #[stable(feature = "rust1", since = "1.0.0")]
1093 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
1096 /// Enumeration of possible methods to seek within an I/O object.
1098 /// It is used by the [`Seek`] trait.
1100 /// [`Seek`]: trait.Seek.html
1101 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
1102 #[stable(feature = "rust1", since = "1.0.0")]
1104 /// Set the offset to the provided number of bytes.
1105 #[stable(feature = "rust1", since = "1.0.0")]
1106 Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
1108 /// Set the offset to the size of this object plus the specified number of
1111 /// It is possible to seek beyond the end of an object, but it's an error to
1112 /// seek before byte 0.
1113 #[stable(feature = "rust1", since = "1.0.0")]
1114 End(#[stable(feature = "rust1", since = "1.0.0")] i64),
1116 /// Set the offset to the current position plus the specified number of
1119 /// It is possible to seek beyond the end of an object, but it's an error to
1120 /// seek before byte 0.
1121 #[stable(feature = "rust1", since = "1.0.0")]
1122 Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
1125 fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>)
1129 let (done, used) = {
1130 let available = match r.fill_buf() {
1132 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1133 Err(e) => return Err(e)
1135 match memchr::memchr(delim, available) {
1137 buf.extend_from_slice(&available[..i + 1]);
1141 buf.extend_from_slice(available);
1142 (false, available.len())
1148 if done || used == 0 {
1154 /// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
1155 /// to perform extra ways of reading.
1157 /// For example, reading line-by-line is inefficient without using a buffer, so
1158 /// if you want to read by line, you'll need `BufRead`, which includes a
1159 /// [`read_line()`][readline] method as well as a [`lines()`][lines] iterator.
1161 /// [readline]: #method.read_line
1162 /// [lines]: #method.lines
1166 /// A locked standard input implements `BufRead`:
1170 /// use std::io::prelude::*;
1172 /// let stdin = io::stdin();
1173 /// for line in stdin.lock().lines() {
1174 /// println!("{}", line.unwrap());
1178 /// If you have something that implements `Read`, you can use the [`BufReader`
1179 /// type][bufreader] to turn it into a `BufRead`.
1181 /// For example, [`File`][file] implements `Read`, but not `BufRead`.
1182 /// `BufReader` to the rescue!
1184 /// [bufreader]: struct.BufReader.html
1185 /// [file]: ../fs/struct.File.html
1188 /// use std::io::{self, BufReader};
1189 /// use std::io::prelude::*;
1190 /// use std::fs::File;
1192 /// # fn foo() -> io::Result<()> {
1193 /// let f = try!(File::open("foo.txt"));
1194 /// let f = BufReader::new(f);
1196 /// for line in f.lines() {
1197 /// println!("{}", line.unwrap());
1204 #[stable(feature = "rust1", since = "1.0.0")]
1205 pub trait BufRead: Read {
1206 /// Fills the internal buffer of this object, returning the buffer contents.
1208 /// This function is a lower-level call. It needs to be paired with the
1209 /// [`consume`][consume] method to function properly. When calling this
1210 /// method, none of the contents will be "read" in the sense that later
1211 /// calling `read` may return the same contents. As such, `consume` must be
1212 /// called with the number of bytes that are consumed from this buffer to
1213 /// ensure that the bytes are never returned twice.
1215 /// [consume]: #tymethod.consume
1217 /// An empty buffer returned indicates that the stream has reached EOF.
1221 /// This function will return an I/O error if the underlying reader was
1222 /// read, but returned an error.
1226 /// A locked standard input implements `BufRead`:
1230 /// use std::io::prelude::*;
1232 /// let stdin = io::stdin();
1233 /// let mut stdin = stdin.lock();
1235 /// // we can't have two `&mut` references to `stdin`, so use a block
1236 /// // to end the borrow early.
1238 /// let buffer = stdin.fill_buf().unwrap();
1240 /// // work with buffer
1241 /// println!("{:?}", buffer);
1246 /// // ensure the bytes we worked with aren't returned again later
1247 /// stdin.consume(length);
1249 #[stable(feature = "rust1", since = "1.0.0")]
1250 fn fill_buf(&mut self) -> Result<&[u8]>;
1252 /// Tells this buffer that `amt` bytes have been consumed from the buffer,
1253 /// so they should no longer be returned in calls to `read`.
1255 /// This function is a lower-level call. It needs to be paired with the
1256 /// [`fill_buf`][fillbuf] method to function properly. This function does
1257 /// not perform any I/O, it simply informs this object that some amount of
1258 /// its buffer, returned from `fill_buf`, has been consumed and should no
1259 /// longer be returned. As such, this function may do odd things if
1260 /// `fill_buf` isn't called before calling it.
1262 /// [fillbuf]: #tymethod.fill_buf
1264 /// The `amt` must be `<=` the number of bytes in the buffer returned by
1269 /// Since `consume()` is meant to be used with [`fill_buf()`][fillbuf],
1270 /// that method's example includes an example of `consume()`.
1271 #[stable(feature = "rust1", since = "1.0.0")]
1272 fn consume(&mut self, amt: usize);
1274 /// Read all bytes into `buf` until the delimiter `byte` is reached.
1276 /// This function will read bytes from the underlying stream until the
1277 /// delimiter or EOF is found. Once found, all bytes up to, and including,
1278 /// the delimiter (if found) will be appended to `buf`.
1280 /// If this reader is currently at EOF then this function will not modify
1281 /// `buf` and will return `Ok(n)` where `n` is the number of bytes which
1286 /// This function will ignore all instances of `ErrorKind::Interrupted` and
1287 /// will otherwise return any errors returned by `fill_buf`.
1289 /// If an I/O error is encountered then all bytes read so far will be
1290 /// present in `buf` and its length will have been adjusted appropriately.
1294 /// A locked standard input implements `BufRead`. In this example, we'll
1295 /// read from standard input until we see an `a` byte.
1299 /// use std::io::prelude::*;
1301 /// fn foo() -> io::Result<()> {
1302 /// let stdin = io::stdin();
1303 /// let mut stdin = stdin.lock();
1304 /// let mut buffer = Vec::new();
1306 /// try!(stdin.read_until(b'a', &mut buffer));
1308 /// println!("{:?}", buffer);
1312 #[stable(feature = "rust1", since = "1.0.0")]
1313 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
1314 read_until(self, byte, buf)
1317 /// Read all bytes until a newline (the 0xA byte) is reached, and append
1318 /// them to the provided buffer.
1320 /// This function will read bytes from the underlying stream until the
1321 /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
1322 /// up to, and including, the delimiter (if found) will be appended to
1325 /// If this reader is currently at EOF then this function will not modify
1326 /// `buf` and will return `Ok(n)` where `n` is the number of bytes which
1331 /// This function has the same error semantics as `read_until` and will also
1332 /// return an error if the read bytes are not valid UTF-8. If an I/O error
1333 /// is encountered then `buf` may contain some bytes already read in the
1334 /// event that all data read so far was valid UTF-8.
1338 /// A locked standard input implements `BufRead`. In this example, we'll
1339 /// read all of the lines from standard input. If we were to do this in
1340 /// an actual project, the [`lines()`][lines] method would be easier, of
1343 /// [lines]: #method.lines
1347 /// use std::io::prelude::*;
1349 /// let stdin = io::stdin();
1350 /// let mut stdin = stdin.lock();
1351 /// let mut buffer = String::new();
1353 /// while stdin.read_line(&mut buffer).unwrap() > 0 {
1354 /// // work with buffer
1355 /// println!("{:?}", buffer);
1360 #[stable(feature = "rust1", since = "1.0.0")]
1361 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
1362 // Note that we are not calling the `.read_until` method here, but
1363 // rather our hardcoded implementation. For more details as to why, see
1364 // the comments in `read_to_end`.
1365 append_to_string(buf, |b| read_until(self, b'\n', b))
1368 /// Returns an iterator over the contents of this reader split on the byte
1371 /// The iterator returned from this function will return instances of
1372 /// `io::Result<Vec<u8>>`. Each vector returned will *not* have the
1373 /// delimiter byte at the end.
1375 /// This function will yield errors whenever `read_until` would have also
1376 /// yielded an error.
1380 /// A locked standard input implements `BufRead`. In this example, we'll
1381 /// read some input from standard input, splitting on commas.
1385 /// use std::io::prelude::*;
1387 /// let stdin = io::stdin();
1389 /// for content in stdin.lock().split(b',') {
1390 /// println!("{:?}", content.unwrap());
1393 #[stable(feature = "rust1", since = "1.0.0")]
1394 fn split(self, byte: u8) -> Split<Self> where Self: Sized {
1395 Split { buf: self, delim: byte }
1398 /// Returns an iterator over the lines of this reader.
1400 /// The iterator returned from this function will yield instances of
1401 /// `io::Result<String>`. Each string returned will *not* have a newline
1402 /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
1406 /// A locked standard input implements `BufRead`:
1410 /// use std::io::prelude::*;
1412 /// let stdin = io::stdin();
1414 /// for line in stdin.lock().lines() {
1415 /// println!("{}", line.unwrap());
1418 #[stable(feature = "rust1", since = "1.0.0")]
1419 fn lines(self) -> Lines<Self> where Self: Sized {
1424 /// Adaptor to chain together two readers.
1426 /// This struct is generally created by calling [`chain()`][chain] on a reader.
1427 /// Please see the documentation of `chain()` for more details.
1429 /// [chain]: trait.Read.html#method.chain
1430 #[stable(feature = "rust1", since = "1.0.0")]
1431 pub struct Chain<T, U> {
1437 #[stable(feature = "rust1", since = "1.0.0")]
1438 impl<T: Read, U: Read> Read for Chain<T, U> {
1439 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1440 if !self.done_first {
1441 match self.first.read(buf)? {
1442 0 => { self.done_first = true; }
1446 self.second.read(buf)
1450 #[stable(feature = "chain_bufread", since = "1.9.0")]
1451 impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
1452 fn fill_buf(&mut self) -> Result<&[u8]> {
1453 if !self.done_first {
1454 match self.first.fill_buf()? {
1455 buf if buf.len() == 0 => { self.done_first = true; }
1456 buf => return Ok(buf),
1459 self.second.fill_buf()
1462 fn consume(&mut self, amt: usize) {
1463 if !self.done_first {
1464 self.first.consume(amt)
1466 self.second.consume(amt)
1471 /// Reader adaptor which limits the bytes read from an underlying reader.
1473 /// This struct is generally created by calling [`take()`][take] on a reader.
1474 /// Please see the documentation of `take()` for more details.
1476 /// [take]: trait.Read.html#method.take
1477 #[stable(feature = "rust1", since = "1.0.0")]
1478 pub struct Take<T> {
1484 /// Returns the number of bytes that can be read before this instance will
1489 /// This instance may reach EOF after reading fewer bytes than indicated by
1490 /// this method if the underlying `Read` instance reaches EOF.
1496 /// use std::io::prelude::*;
1497 /// use std::fs::File;
1499 /// # fn foo() -> io::Result<()> {
1500 /// let f = try!(File::open("foo.txt"));
1502 /// // read at most five bytes
1503 /// let handle = f.take(5);
1505 /// println!("limit: {}", handle.limit());
1509 #[stable(feature = "rust1", since = "1.0.0")]
1510 pub fn limit(&self) -> u64 { self.limit }
1513 #[stable(feature = "rust1", since = "1.0.0")]
1514 impl<T: Read> Read for Take<T> {
1515 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
1516 // Don't call into inner reader at all at EOF because it may still block
1517 if self.limit == 0 {
1521 let max = cmp::min(buf.len() as u64, self.limit) as usize;
1522 let n = self.inner.read(&mut buf[..max])?;
1523 self.limit -= n as u64;
1528 #[stable(feature = "rust1", since = "1.0.0")]
1529 impl<T: BufRead> BufRead for Take<T> {
1530 fn fill_buf(&mut self) -> Result<&[u8]> {
1531 // Don't call into inner reader at all at EOF because it may still block
1532 if self.limit == 0 {
1536 let buf = self.inner.fill_buf()?;
1537 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
1541 fn consume(&mut self, amt: usize) {
1542 // Don't let callers reset the limit by passing an overlarge value
1543 let amt = cmp::min(amt as u64, self.limit) as usize;
1544 self.limit -= amt as u64;
1545 self.inner.consume(amt);
1549 fn read_one_byte(reader: &mut Read) -> Option<Result<u8>> {
1552 return match reader.read(&mut buf) {
1554 Ok(..) => Some(Ok(buf[0])),
1555 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1556 Err(e) => Some(Err(e)),
1561 /// An iterator over `u8` values of a reader.
1563 /// This struct is generally created by calling [`bytes()`][bytes] on a reader.
1564 /// Please see the documentation of `bytes()` for more details.
1566 /// [bytes]: trait.Read.html#method.bytes
1567 #[stable(feature = "rust1", since = "1.0.0")]
1568 pub struct Bytes<R> {
1572 #[stable(feature = "rust1", since = "1.0.0")]
1573 impl<R: Read> Iterator for Bytes<R> {
1574 type Item = Result<u8>;
1576 fn next(&mut self) -> Option<Result<u8>> {
1577 read_one_byte(&mut self.inner)
1581 /// An iterator over the `char`s of a reader.
1583 /// This struct is generally created by calling [`chars()`][chars] on a reader.
1584 /// Please see the documentation of `chars()` for more details.
1586 /// [chars]: trait.Read.html#method.chars
1587 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1589 pub struct Chars<R> {
1593 /// An enumeration of possible errors that can be generated from the `Chars`
1596 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1598 pub enum CharsError {
1599 /// Variant representing that the underlying stream was read successfully
1600 /// but it did not contain valid utf8 data.
1603 /// Variant representing that an I/O error occurred.
1607 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1609 impl<R: Read> Iterator for Chars<R> {
1610 type Item = result::Result<char, CharsError>;
1612 fn next(&mut self) -> Option<result::Result<char, CharsError>> {
1613 let first_byte = match read_one_byte(&mut self.inner) {
1614 None => return None,
1616 Some(Err(e)) => return Some(Err(CharsError::Other(e))),
1618 let width = core_str::utf8_char_width(first_byte);
1619 if width == 1 { return Some(Ok(first_byte as char)) }
1620 if width == 0 { return Some(Err(CharsError::NotUtf8)) }
1621 let mut buf = [first_byte, 0, 0, 0];
1624 while start < width {
1625 match self.inner.read(&mut buf[start..width]) {
1626 Ok(0) => return Some(Err(CharsError::NotUtf8)),
1627 Ok(n) => start += n,
1628 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
1629 Err(e) => return Some(Err(CharsError::Other(e))),
1633 Some(match str::from_utf8(&buf[..width]).ok() {
1634 Some(s) => Ok(s.chars().next().unwrap()),
1635 None => Err(CharsError::NotUtf8),
1640 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1642 impl std_error::Error for CharsError {
1643 fn description(&self) -> &str {
1645 CharsError::NotUtf8 => "invalid utf8 encoding",
1646 CharsError::Other(ref e) => std_error::Error::description(e),
1649 fn cause(&self) -> Option<&std_error::Error> {
1651 CharsError::NotUtf8 => None,
1652 CharsError::Other(ref e) => e.cause(),
1657 #[unstable(feature = "io", reason = "awaiting stability of Read::chars",
1659 impl fmt::Display for CharsError {
1660 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1662 CharsError::NotUtf8 => {
1663 "byte stream did not contain valid utf8".fmt(f)
1665 CharsError::Other(ref e) => e.fmt(f),
1670 /// An iterator over the contents of an instance of `BufRead` split on a
1671 /// particular byte.
1673 /// This struct is generally created by calling [`split()`][split] on a
1674 /// `BufRead`. Please see the documentation of `split()` for more details.
1676 /// [split]: trait.BufRead.html#method.split
1677 #[stable(feature = "rust1", since = "1.0.0")]
1678 pub struct Split<B> {
1683 #[stable(feature = "rust1", since = "1.0.0")]
1684 impl<B: BufRead> Iterator for Split<B> {
1685 type Item = Result<Vec<u8>>;
1687 fn next(&mut self) -> Option<Result<Vec<u8>>> {
1688 let mut buf = Vec::new();
1689 match self.buf.read_until(self.delim, &mut buf) {
1692 if buf[buf.len() - 1] == self.delim {
1697 Err(e) => Some(Err(e))
1702 /// An iterator over the lines of an instance of `BufRead`.
1704 /// This struct is generally created by calling [`lines()`][lines] on a
1705 /// `BufRead`. Please see the documentation of `lines()` for more details.
1707 /// [lines]: trait.BufRead.html#method.lines
1708 #[stable(feature = "rust1", since = "1.0.0")]
1709 pub struct Lines<B> {
1713 #[stable(feature = "rust1", since = "1.0.0")]
1714 impl<B: BufRead> Iterator for Lines<B> {
1715 type Item = Result<String>;
1717 fn next(&mut self) -> Option<Result<String>> {
1718 let mut buf = String::new();
1719 match self.buf.read_line(&mut buf) {
1722 if buf.ends_with("\n") {
1724 if buf.ends_with("\r") {
1730 Err(e) => Some(Err(e))
1746 let mut buf = Cursor::new(&b"12"[..]);
1747 let mut v = Vec::new();
1748 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 2);
1749 assert_eq!(v, b"12");
1751 let mut buf = Cursor::new(&b"1233"[..]);
1752 let mut v = Vec::new();
1753 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 3);
1754 assert_eq!(v, b"123");
1756 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 1);
1757 assert_eq!(v, b"3");
1759 assert_eq!(buf.read_until(b'3', &mut v).unwrap(), 0);
1765 let buf = Cursor::new(&b"12"[..]);
1766 let mut s = buf.split(b'3');
1767 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1768 assert!(s.next().is_none());
1770 let buf = Cursor::new(&b"1233"[..]);
1771 let mut s = buf.split(b'3');
1772 assert_eq!(s.next().unwrap().unwrap(), vec![b'1', b'2']);
1773 assert_eq!(s.next().unwrap().unwrap(), vec![]);
1774 assert!(s.next().is_none());
1779 let mut buf = Cursor::new(&b"12"[..]);
1780 let mut v = String::new();
1781 assert_eq!(buf.read_line(&mut v).unwrap(), 2);
1782 assert_eq!(v, "12");
1784 let mut buf = Cursor::new(&b"12\n\n"[..]);
1785 let mut v = String::new();
1786 assert_eq!(buf.read_line(&mut v).unwrap(), 3);
1787 assert_eq!(v, "12\n");
1789 assert_eq!(buf.read_line(&mut v).unwrap(), 1);
1790 assert_eq!(v, "\n");
1792 assert_eq!(buf.read_line(&mut v).unwrap(), 0);
1798 let buf = Cursor::new(&b"12\r"[..]);
1799 let mut s = buf.lines();
1800 assert_eq!(s.next().unwrap().unwrap(), "12\r".to_string());
1801 assert!(s.next().is_none());
1803 let buf = Cursor::new(&b"12\r\n\n"[..]);
1804 let mut s = buf.lines();
1805 assert_eq!(s.next().unwrap().unwrap(), "12".to_string());
1806 assert_eq!(s.next().unwrap().unwrap(), "".to_string());
1807 assert!(s.next().is_none());
1812 let mut c = Cursor::new(&b""[..]);
1813 let mut v = Vec::new();
1814 assert_eq!(c.read_to_end(&mut v).unwrap(), 0);
1817 let mut c = Cursor::new(&b"1"[..]);
1818 let mut v = Vec::new();
1819 assert_eq!(c.read_to_end(&mut v).unwrap(), 1);
1820 assert_eq!(v, b"1");
1822 let cap = 1024 * 1024;
1823 let data = (0..cap).map(|i| (i / 3) as u8).collect::<Vec<_>>();
1824 let mut v = Vec::new();
1825 let (a, b) = data.split_at(data.len() / 2);
1826 assert_eq!(Cursor::new(a).read_to_end(&mut v).unwrap(), a.len());
1827 assert_eq!(Cursor::new(b).read_to_end(&mut v).unwrap(), b.len());
1828 assert_eq!(v, data);
1832 fn read_to_string() {
1833 let mut c = Cursor::new(&b""[..]);
1834 let mut v = String::new();
1835 assert_eq!(c.read_to_string(&mut v).unwrap(), 0);
1838 let mut c = Cursor::new(&b"1"[..]);
1839 let mut v = String::new();
1840 assert_eq!(c.read_to_string(&mut v).unwrap(), 1);
1843 let mut c = Cursor::new(&b"\xff"[..]);
1844 let mut v = String::new();
1845 assert!(c.read_to_string(&mut v).is_err());
1850 let mut buf = [0; 4];
1852 let mut c = Cursor::new(&b""[..]);
1853 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1854 io::ErrorKind::UnexpectedEof);
1856 let mut c = Cursor::new(&b"123"[..]).chain(Cursor::new(&b"456789"[..]));
1857 c.read_exact(&mut buf).unwrap();
1858 assert_eq!(&buf, b"1234");
1859 c.read_exact(&mut buf).unwrap();
1860 assert_eq!(&buf, b"5678");
1861 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1862 io::ErrorKind::UnexpectedEof);
1866 fn read_exact_slice() {
1867 let mut buf = [0; 4];
1869 let mut c = &b""[..];
1870 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1871 io::ErrorKind::UnexpectedEof);
1873 let mut c = &b"123"[..];
1874 assert_eq!(c.read_exact(&mut buf).unwrap_err().kind(),
1875 io::ErrorKind::UnexpectedEof);
1876 // make sure the optimized (early returning) method is being used
1877 assert_eq!(&buf, &[0; 4]);
1879 let mut c = &b"1234"[..];
1880 c.read_exact(&mut buf).unwrap();
1881 assert_eq!(&buf, b"1234");
1883 let mut c = &b"56789"[..];
1884 c.read_exact(&mut buf).unwrap();
1885 assert_eq!(&buf, b"5678");
1886 assert_eq!(c, b"9");
1894 fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
1895 Err(io::Error::new(io::ErrorKind::Other, ""))
1898 impl BufRead for R {
1899 fn fill_buf(&mut self) -> io::Result<&[u8]> {
1900 Err(io::Error::new(io::ErrorKind::Other, ""))
1902 fn consume(&mut self, _amt: usize) { }
1905 let mut buf = [0; 1];
1906 assert_eq!(0, R.take(0).read(&mut buf).unwrap());
1907 assert_eq!(b"", R.take(0).fill_buf().unwrap());
1910 fn cmp_bufread<Br1: BufRead, Br2: BufRead>(mut br1: Br1, mut br2: Br2, exp: &[u8]) {
1911 let mut cat = Vec::new();
1914 let buf1 = br1.fill_buf().unwrap();
1915 let buf2 = br2.fill_buf().unwrap();
1916 let minlen = if buf1.len() < buf2.len() { buf1.len() } else { buf2.len() };
1917 assert_eq!(buf1[..minlen], buf2[..minlen]);
1918 cat.extend_from_slice(&buf1[..minlen]);
1924 br1.consume(consume);
1925 br2.consume(consume);
1927 assert_eq!(br1.fill_buf().unwrap().len(), 0);
1928 assert_eq!(br2.fill_buf().unwrap().len(), 0);
1929 assert_eq!(&cat[..], &exp[..])
1933 fn chain_bufread() {
1934 let testdata = b"ABCDEFGHIJKL";
1935 let chain1 = (&testdata[..3]).chain(&testdata[3..6])
1936 .chain(&testdata[6..9])
1937 .chain(&testdata[9..]);
1938 let chain2 = (&testdata[..4]).chain(&testdata[4..8])
1939 .chain(&testdata[8..]);
1940 cmp_bufread(chain1, chain2, &testdata[..]);
1944 fn bench_read_to_end(b: &mut test::Bencher) {
1946 let mut lr = repeat(1).take(10000000);
1947 let mut vec = Vec::with_capacity(1024);
1948 super::read_to_end(&mut lr, &mut vec)