auto merge of #10895 : sfackler/rust/io-util, r=alexcrichton

This adds a bunch of useful Reader and Writer implementations. I'm not a
huge fan of the name `util` but I can't think of a better name and I
don't want to make `std::io` any longer than it already is.

src/libstd/io/mod.rs

@@ -335,6 +335,9 @@ pub mod native;
 /// Signal handling
 pub mod signal;
 
+/// Utility implementations of Reader and Writer
+pub mod util;
+
 /// The default buffer size for various I/O operations
 static DEFAULT_BUF_SIZE: uint = 1024 * 64;
 

src/libstd/io/util.rs

@@ -0,0 +1,295 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+use prelude::*;
+use cmp;
+use vec::bytes::MutableByteVector;
+
+/// Wraps a `Reader`, limiting the number of bytes that can be read from it.
+pub struct LimitReader<'a, R> {
+    priv limit: uint,
+    priv inner: &'a mut R
+}
+
+impl<'a, R: Reader> LimitReader<'a, R> {
+    /// Creates a new `LimitReader`
+    pub fn new<'a>(r: &'a mut R, limit: uint) -> LimitReader<'a, R> {
+        LimitReader { limit: limit, inner: r }
+    }
+}
+
+impl<'a, R: Reader> Reader for LimitReader<'a, R> {
+    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        if self.limit == 0 {
+            return None;
+        }
+
+        let len = cmp::min(self.limit, buf.len());
+        self.inner.read(buf.mut_slice_to(len)).map(|len| {
+            self.limit -= len;
+            len
+        })
+    }
+
+    fn eof(&mut self) -> bool {
+        self.limit == 0 || self.inner.eof()
+    }
+}
+
+/// A `Writer` which ignores bytes written to it, like /dev/null.
+pub struct NullWriter;
+
+impl Writer for NullWriter {
+    #[inline]
+    fn write(&mut self, _buf: &[u8]) { }
+}
+
+/// A `Reader` which returns an infinite stream of 0 bytes, like /dev/zero.
+pub struct ZeroReader;
+
+impl Reader for ZeroReader {
+    #[inline]
+    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        buf.set_memory(0);
+        Some(buf.len())
+    }
+
+    #[inline]
+    fn eof(&mut self) -> bool {
+        false
+    }
+}
+
+/// A `Reader` which is always at EOF, like /dev/null.
+pub struct NullReader;
+
+impl Reader for NullReader {
+    #[inline]
+    fn read(&mut self, _buf: &mut [u8]) -> Option<uint> {
+        None
+    }
+
+    #[inline]
+    fn eof(&mut self) -> bool {
+        true
+    }
+}
+
+/// A `Writer` which multiplexes writes to a set of `Writers`.
+pub struct MultiWriter {
+    priv writers: ~[~Writer]
+}
+
+impl MultiWriter {
+    /// Creates a new `MultiWriter`
+    pub fn new(writers: ~[~Writer]) -> MultiWriter {
+        MultiWriter { writers: writers }
+    }
+}
+
+impl Writer for MultiWriter {
+    #[inline]
+    fn write(&mut self, buf: &[u8]) {
+        for writer in self.writers.mut_iter() {
+            writer.write(buf);
+        }
+    }
+
+    #[inline]
+    fn flush(&mut self) {
+        for writer in self.writers.mut_iter() {
+            writer.flush();
+        }
+    }
+}
+
+/// A `Reader` which chains input from multiple `Readers`, reading each to
+/// completion before moving onto the next.
+pub struct ChainedReader<I, R> {
+    priv readers: I,
+    priv cur_reader: Option<R>,
+}
+
+impl<R: Reader, I: Iterator<R>> ChainedReader<I, R> {
+    /// Creates a new `ChainedReader`
+    pub fn new(mut readers: I) -> ChainedReader<I, R> {
+        let r = readers.next();
+        ChainedReader { readers: readers, cur_reader: r }
+    }
+}
+
+impl<R: Reader, I: Iterator<R>> Reader for ChainedReader<I, R> {
+    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        loop {
+            match self.cur_reader {
+                Some(ref mut r) => {
+                    match r.read(buf) {
+                        Some(len) => return Some(len),
+                        None => {}
+                    }
+                }
+                None => break
+            }
+            self.cur_reader = self.readers.next()
+        }
+        None
+    }
+
+    fn eof(&mut self) -> bool {
+        self.cur_reader.is_none()
+    }
+}
+
+/// A `Reader` which forwards input from another `Reader`, passing it along to
+/// a `Writer` as well. Similar to the `tee(1)` command.
+pub struct TeeReader<R, W> {
+    priv reader: R,
+    priv writer: W
+}
+
+impl<R: Reader, W: Writer> TeeReader<R, W> {
+    /// Creates a new `TeeReader`
+    pub fn new(r: R, w: W) -> TeeReader<R, W> {
+        TeeReader { reader: r, writer: w }
+    }
+
+    /// Consumes the `TeeReader`, returning the underlying `Reader` and
+    /// `Writer`.
+    pub fn unwrap(self) -> (R, W) {
+        let TeeReader { reader, writer } = self;
+        (reader, writer)
+    }
+}
+
+impl<R: Reader, W: Writer> Reader for TeeReader<R, W> {
+    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        self.reader.read(buf).map(|len| {
+            self.writer.write(buf.slice_to(len));
+            len
+        })
+    }
+
+    fn eof(&mut self) -> bool {
+        self.reader.eof()
+    }
+}
+
+/// Copies all data from a `Reader` to a `Writer`.
+pub fn copy<R: Reader, W: Writer>(r: &mut R, w: &mut W) {
+    let mut buf = [0, ..super::DEFAULT_BUF_SIZE];
+    loop {
+        match r.read(buf) {
+            Some(len) => w.write(buf.slice_to(len)),
+            None => break
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use io::mem::{MemReader, MemWriter};
+    use super::*;
+    use prelude::*;
+
+    #[test]
+    fn test_bounded_reader_unlimited() {
+        let mut r = MemReader::new(~[0, 1, 2]);
+        {
+            let mut r = LimitReader::new(&mut r, 4);
+            assert_eq!(~[0, 1, 2], r.read_to_end());
+        }
+        assert!(r.eof());
+    }
+
+    #[test]
+    fn test_bound_reader_limited() {
+        let mut r = MemReader::new(~[0, 1, 2]);
+        {
+            let mut r = LimitReader::new(&mut r, 2);
+            assert_eq!(~[0, 1], r.read_to_end());
+        }
+        assert_eq!(~[2], r.read_to_end());
+    }
+
+    #[test]
+    fn test_null_writer() {
+        let mut s = NullWriter;
+        let mut buf = ~[0, 0, 0];
+        s.write(buf);
+        s.flush();
+    }
+
+    #[test]
+    fn test_zero_reader() {
+        let mut s = ZeroReader;
+        let mut buf = ~[1, 2, 3];
+        assert_eq!(s.read(buf), Some(3));
+        assert_eq!(~[0, 0, 0], buf);
+    }
+
+    #[test]
+    fn test_null_reader() {
+        let mut r = NullReader;
+        let mut buf = ~[0];
+        assert_eq!(r.read(buf), None);
+        assert!(r.eof());
+    }
+
+    #[test]
+    fn test_multi_writer() {
+        static mut writes: uint = 0;
+        static mut flushes: uint = 0;
+
+        struct TestWriter;
+        impl Writer for TestWriter {
+            fn write(&mut self, buf: &[u8]) {
+                unsafe { writes += 1 }
+            }
+
+            fn flush(&mut self) {
+                unsafe { flushes += 1 }
+            }
+        }
+
+        let mut multi = MultiWriter::new(~[~TestWriter as ~Writer,
+                                           ~TestWriter as ~Writer]);
+        multi.write([1, 2, 3]);
+        assert_eq!(2, unsafe { writes });
+        assert_eq!(0, unsafe { flushes });
+        multi.flush();
+        assert_eq!(2, unsafe { writes });
+        assert_eq!(2, unsafe { flushes });
+    }
+
+    #[test]
+    fn test_chained_reader() {
+        let rs = ~[MemReader::new(~[0, 1]), MemReader::new(~[]),
+                   MemReader::new(~[2, 3])];
+        let mut r = ChainedReader::new(rs.move_iter());
+        assert_eq!(~[0, 1, 2, 3], r.read_to_end());
+    }
+
+    #[test]
+    fn test_tee_reader() {
+        let mut r = TeeReader::new(MemReader::new(~[0, 1, 2]),
+                                   MemWriter::new());
+        assert_eq!(~[0, 1, 2], r.read_to_end());
+        let (_, w) = r.unwrap();
+        assert_eq!(~[0, 1, 2], w.inner());
+    }
+
+    #[test]
+    fn test_copy() {
+        let mut r = MemReader::new(~[0, 1, 2, 3, 4]);
+        let mut w = MemWriter::new();
+        copy(&mut r, &mut w);
+        assert!(r.eof());
+        assert_eq!(~[0, 1, 2, 3, 4], w.inner());
+    }
+}