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;
  82 /// use std::io::Read;
  83 ///
  84 /// # fn foo() -> io::Result<String> {
  85 /// let mut buffer = String::new();
  86 /// try!(io::empty().read_to_string(&mut buffer));
  87 /// # Ok(buffer)
  88 /// # }
  89 /// ```
  90 #[stable(feature = "rust1", since = "1.0.0")]
  91 pub fn empty() -> Empty { Empty { _priv: () } }
  92
  93 #[stable(feature = "rust1", since = "1.0.0")]
  94 impl Read for Empty {
  95     fn read(&mut self, _buf: &mut [u8]) -> io::Result<usize> { Ok(0) }
  96 }
  97 #[stable(feature = "rust1", since = "1.0.0")]
  98 impl BufRead for Empty {
  99     fn fill_buf(&mut self) -> io::Result<&[u8]> { Ok(&[]) }
 100     fn consume(&mut self, _n: usize) {}
 101 }
 102
 103 /// A reader which yields one byte over and over and over and over and over and...
 104 ///
 105 /// This struct is generally created by calling [`repeat()`][repeat]. Please
 106 /// see the documentation of `repeat()` for more details.
 107 ///
 108 /// [repeat]: fn.repeat.html
 109 #[stable(feature = "rust1", since = "1.0.0")]
 110 pub struct Repeat { byte: u8 }
 111
 112 /// Creates an instance of a reader that infinitely repeats one byte.
 113 ///
 114 /// All reads from this reader will succeed by filling the specified buffer with
 115 /// the given byte.
 116 #[stable(feature = "rust1", since = "1.0.0")]
 117 pub fn repeat(byte: u8) -> Repeat { Repeat { byte: byte } }
 118
 119 #[stable(feature = "rust1", since = "1.0.0")]
 120 impl Read for Repeat {
 121     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
 122         for slot in &mut *buf {
 123             *slot = self.byte;
 124         }
 125         Ok(buf.len())
 126     }
 127 }
 128
 129 /// A writer which will move data into the void.
 130 ///
 131 /// This struct is generally created by calling [`sink()`][sink]. Please
 132 /// see the documentation of `sink()` for more details.
 133 ///
 134 /// [sink]: fn.sink.html
 135 #[stable(feature = "rust1", since = "1.0.0")]
 136 pub struct Sink { _priv: () }
 137
 138 /// Creates an instance of a writer which will successfully consume all data.
 139 ///
 140 /// All calls to `write` on the returned instance will return `Ok(buf.len())`
 141 /// and the contents of the buffer will not be inspected.
 142 #[stable(feature = "rust1", since = "1.0.0")]
 143 pub fn sink() -> Sink { Sink { _priv: () } }
 144
 145 #[stable(feature = "rust1", since = "1.0.0")]
 146 impl Write for Sink {
 147     fn write(&mut self, buf: &[u8]) -> io::Result<usize> { Ok(buf.len()) }
 148     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 149 }
 150
 151 #[cfg(test)]
 152 mod tests {
 153     use prelude::v1::*;
 154
 155     use io::prelude::*;
 156     use io::{copy, sink, empty, repeat};
 157
 158     #[test]
 159     fn copy_copies() {
 160         let mut r = repeat(0).take(4);
 161         let mut w = sink();
 162         assert_eq!(copy(&mut r, &mut w).unwrap(), 4);
 163
 164         let mut r = repeat(0).take(1 << 17);
 165         assert_eq!(copy(&mut r as &mut Read, &mut w as &mut Write).unwrap(), 1 << 17);
 166     }
 167
 168     #[test]
 169     fn sink_sinks() {
 170         let mut s = sink();
 171         assert_eq!(s.write(&[]).unwrap(), 0);
 172         assert_eq!(s.write(&[0]).unwrap(), 1);
 173         assert_eq!(s.write(&[0; 1024]).unwrap(), 1024);
 174         assert_eq!(s.by_ref().write(&[0; 1024]).unwrap(), 1024);
 175     }
 176
 177     #[test]
 178     fn empty_reads() {
 179         let mut e = empty();
 180         assert_eq!(e.read(&mut []).unwrap(), 0);
 181         assert_eq!(e.read(&mut [0]).unwrap(), 0);
 182         assert_eq!(e.read(&mut [0; 1024]).unwrap(), 0);
 183         assert_eq!(e.by_ref().read(&mut [0; 1024]).unwrap(), 0);
 184     }
 185
 186     #[test]
 187     fn repeat_repeats() {
 188         let mut r = repeat(4);
 189         let mut b = [0; 1024];
 190         assert_eq!(r.read(&mut b).unwrap(), 1024);
 191         assert!(b.iter().all(|b| *b == 4));
 192     }
 193
 194     #[test]
 195     fn take_some_bytes() {
 196         assert_eq!(repeat(4).take(100).bytes().count(), 100);
 197         assert_eq!(repeat(4).take(100).bytes().next().unwrap().unwrap(), 4);
 198         assert_eq!(repeat(1).take(10).chain(repeat(2).take(10)).bytes().count(), 20);
 199     }
 200 }