src/libstd/io/util.rs

   1 // Copyright 2014 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.
   4 //
   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.
  10
  11 #![allow(missing_copy_implementations)]
  12
  13 use io::{self, Read, Write, ErrorKind, BufRead};
  14
  15 /// Copies the entire contents of a reader into a writer.
  16 ///
  17 /// This function will continuously read data from `reader` and then
  18 /// write it into `writer` in a streaming fashion until `reader`
  19 /// returns EOF.
  20 ///
  21 /// On success, the total number of bytes that were copied from
  22 /// `reader` to `writer` is returned.
  23 ///
  24 /// # Errors
  25 ///
  26 /// This function will return an error immediately if any call to `read` or
  27 /// `write` returns an error. All instances of `ErrorKind::Interrupted` are
  28 /// handled by this function and the underlying operation is retried.
  29 ///
  30 /// # Examples
  31 ///
  32 /// ```
  33 /// use std::io;
  34 ///
  35 /// # fn foo() -> io::Result<()> {
  36 /// let mut reader: &[u8] = b"hello";
  37 /// let mut writer: Vec<u8> = vec![];
  38 ///
  39 /// try!(io::copy(&mut reader, &mut writer));
  40 ///
  41 /// assert_eq!(reader, &writer[..]);
  42 /// # Ok(())
  43 /// # }
  44 /// ```
  45 #[stable(feature = "rust1", since = "1.0.0")]
  46 pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<u64>
  47     where R: Read, W: Write
  48 {
  49     let mut buf = [0; super::DEFAULT_BUF_SIZE];
  50     let mut written = 0;
  51     loop {
  52         let len = match reader.read(&mut buf) {
  53             Ok(0) => return Ok(written),
  54             Ok(len) => len,
  55             Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
  56             Err(e) => return Err(e),
  57         };
  58         writer.write_all(&buf[..len])?;
  59         written += len as u64;
  60     }
  61 }
  62
  63 /// A reader which is always at EOF.
  64 ///
  65 /// This struct is generally created by calling [`empty()`][empty]. Please see
  66 /// the documentation of `empty()` for more details.
  67 ///
  68 /// [empty]: fn.empty.html
  69 #[stable(feature = "rust1", since = "1.0.0")]
  70 pub struct Empty { _priv: () }
  71
  72 /// Constructs a new handle to an empty reader.
  73 ///
  74 /// All reads from the returned reader will return `Ok(0)`.
  75 ///
  76 /// # Examples
  77 ///
  78 /// A slightly sad example of not reading anything into a buffer:
  79 ///
  80 /// ```
  81 /// use std::io::{self, Read};
  82 ///
  83 /// let mut buffer = String::new();
  84 /// io::empty().read_to_string(&mut buffer).unwrap();
  85 /// assert!(buffer.is_empty());
  86 /// ```
  87 #[stable(feature = "rust1", since = "1.0.0")]
  88 pub fn empty() -> Empty { Empty { _priv: () } }
  89
  90 #[stable(feature = "rust1", since = "1.0.0")]
  91 impl Read for Empty {
  92     fn read(&mut self, _buf: &mut [u8]) -> io::Result<usize> { Ok(0) }
  93 }
  94 #[stable(feature = "rust1", since = "1.0.0")]
  95 impl BufRead for Empty {
  96     fn fill_buf(&mut self) -> io::Result<&[u8]> { Ok(&[]) }
  97     fn consume(&mut self, _n: usize) {}
  98 }
  99
 100 /// A reader which yields one byte over and over and over and over and over and...
 101 ///
 102 /// This struct is generally created by calling [`repeat()`][repeat]. Please
 103 /// see the documentation of `repeat()` for more details.
 104 ///
 105 /// [repeat]: fn.repeat.html
 106 #[stable(feature = "rust1", since = "1.0.0")]
 107 pub struct Repeat { byte: u8 }
 108
 109 /// Creates an instance of a reader that infinitely repeats one byte.
 110 ///
 111 /// All reads from this reader will succeed by filling the specified buffer with
 112 /// the given byte.
 113 ///
 114 /// # Examples
 115 ///
 116 /// ```
 117 /// use std::io::{self, Read};
 118 ///
 119 /// let mut buffer = [0; 3];
 120 /// io::repeat(0b101).read_exact(&mut buffer).unwrap();
 121 /// assert_eq!(buffer, [0b101, 0b101, 0b101]);
 122 /// ```
 123 #[stable(feature = "rust1", since = "1.0.0")]
 124 pub fn repeat(byte: u8) -> Repeat { Repeat { byte: byte } }
 125
 126 #[stable(feature = "rust1", since = "1.0.0")]
 127 impl Read for Repeat {
 128     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
 129         for slot in &mut *buf {
 130             *slot = self.byte;
 131         }
 132         Ok(buf.len())
 133     }
 134 }
 135
 136 /// A writer which will move data into the void.
 137 ///
 138 /// This struct is generally created by calling [`sink()`][sink]. Please
 139 /// see the documentation of `sink()` for more details.
 140 ///
 141 /// [sink]: fn.sink.html
 142 #[stable(feature = "rust1", since = "1.0.0")]
 143 pub struct Sink { _priv: () }
 144
 145 /// Creates an instance of a writer which will successfully consume all data.
 146 ///
 147 /// All calls to `write` on the returned instance will return `Ok(buf.len())`
 148 /// and the contents of the buffer will not be inspected.
 149 ///
 150 /// # Examples
 151 ///
 152 /// ```rust
 153 /// use std::io::{self, Write};
 154 ///
 155 /// let mut buffer = vec![1, 2, 3, 5, 8];
 156 /// let num_bytes = io::sink().write(&mut buffer).unwrap();
 157 /// assert_eq!(num_bytes, 5);
 158 /// ```
 159 #[stable(feature = "rust1", since = "1.0.0")]
 160 pub fn sink() -> Sink { Sink { _priv: () } }
 161
 162 #[stable(feature = "rust1", since = "1.0.0")]
 163 impl Write for Sink {
 164     fn write(&mut self, buf: &[u8]) -> io::Result<usize> { Ok(buf.len()) }
 165     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 166 }
 167
 168 #[cfg(test)]
 169 mod tests {
 170     use prelude::v1::*;
 171
 172     use io::prelude::*;
 173     use io::{copy, sink, empty, repeat};
 174
 175     #[test]
 176     fn copy_copies() {
 177         let mut r = repeat(0).take(4);
 178         let mut w = sink();
 179         assert_eq!(copy(&mut r, &mut w).unwrap(), 4);
 180
 181         let mut r = repeat(0).take(1 << 17);
 182         assert_eq!(copy(&mut r as &mut Read, &mut w as &mut Write).unwrap(), 1 << 17);
 183     }
 184
 185     #[test]
 186     fn sink_sinks() {
 187         let mut s = sink();
 188         assert_eq!(s.write(&[]).unwrap(), 0);
 189         assert_eq!(s.write(&[0]).unwrap(), 1);
 190         assert_eq!(s.write(&[0; 1024]).unwrap(), 1024);
 191         assert_eq!(s.by_ref().write(&[0; 1024]).unwrap(), 1024);
 192     }
 193
 194     #[test]
 195     fn empty_reads() {
 196         let mut e = empty();
 197         assert_eq!(e.read(&mut []).unwrap(), 0);
 198         assert_eq!(e.read(&mut [0]).unwrap(), 0);
 199         assert_eq!(e.read(&mut [0; 1024]).unwrap(), 0);
 200         assert_eq!(e.by_ref().read(&mut [0; 1024]).unwrap(), 0);
 201     }
 202
 203     #[test]
 204     fn repeat_repeats() {
 205         let mut r = repeat(4);
 206         let mut b = [0; 1024];
 207         assert_eq!(r.read(&mut b).unwrap(), 1024);
 208         assert!(b.iter().all(|b| *b == 4));
 209     }
 210
 211     #[test]
 212     fn take_some_bytes() {
 213         assert_eq!(repeat(4).take(100).bytes().count(), 100);
 214         assert_eq!(repeat(4).take(100).bytes().next().unwrap().unwrap(), 4);
 215         assert_eq!(repeat(1).take(10).chain(repeat(2).take(10)).bytes().count(), 20);
 216     }
 217 }