Buffered I/O wrappers

The default buffer size is the same as the one in Java's BufferedWriter.

We may want BufferedWriter to have a Drop impl that flushes, but that
isn't possible right now due to rust-lang#4252/rust-lang#4430. This would be a bit
awkward due to the possibility of the inner flush failing. For what it's
worth, Java's BufferedReader doesn't have a flushing finalizer, but that
may just be because Java's finalizer support is awful.

Closes rust-lang#8953

Author: sfackler

src/libstd/rt/io/buffered.rs

@@ -0,0 +1,355 @@
+// 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.
+
+//! Buffering wrappers for I/O traits
+//!
+//! It can be excessively inefficient to work directly with a `Reader` or
+//! `Writer`. Every call to `read` or `write` on `TcpStream` results in a
+//! system call, for example. This module provides structures that wrap
+//! `Readers`, `Writers`, and `Streams` and buffer input and output to them.
+//!
+//! # Examples
+//!
+//! ~~~
+//! let tcp_stream = TcpStream::connect(addr);
+//! let reader = BufferedReader::new(tcp_stream);
+//!
+//! let mut buf: ~[u8] = vec::from_elem(100, 0u8);
+//! match reader.read(buf.as_slice()) {
+//!     Some(nread) => println!("Read {} bytes", nread),
+//!     None => println!("At the end of the stream!")
+//! }
+//! ~~~
+//!
+//! ~~~
+//! let tcp_stream = TcpStream::connect(addr);
+//! let writer = BufferedWriter::new(tcp_stream);
+//!
+//! writer.write("hello, world".as_bytes());
+//! writer.flush();
+//! ~~~
+//!
+//! ~~~
+//! let tcp_stream = TcpStream::connect(addr);
+//! let stream = BufferedStream::new(tcp_stream);
+//!
+//! stream.write("hello, world".as_bytes());
+//! stream.flush();
+//!
+//! let mut buf = vec::from_elem(100, 0u8);
+//! match stream.read(buf.as_slice()) {
+//!     Some(nread) => println!("Read {} bytes", nread),
+//!     None => println!("At the end of the stream!")
+//! }
+//! ~~~
+//!
+
+use prelude::*;
+
+use num;
+use vec;
+use super::{Reader, Writer, Stream, Decorator};
+
+// libuv recommends 64k buffers to maximize throughput
+// https://groups.google.com/forum/#!topic/libuv/oQO1HJAIDdA
+static DEFAULT_CAPACITY: uint = 64 * 1024;
+
+/// Wraps a Reader and buffers input from it
+pub struct BufferedReader<R> {
+    priv inner: R,
+    priv buf: ~[u8],
+    priv pos: uint,
+    priv cap: uint
+}
+
+impl<R: Reader> BufferedReader<R> {
+    /// Creates a new `BufferedReader` with with the specified buffer capacity
+    pub fn with_capacity(cap: uint, inner: R) -> BufferedReader<R> {
+        BufferedReader {
+            inner: inner,
+            buf: vec::from_elem(cap, 0u8),
+            pos: 0,
+            cap: 0
+        }
+    }
+
+    /// Creates a new `BufferedReader` with a default buffer capacity
+    pub fn new(inner: R) -> BufferedReader<R> {
+        BufferedReader::with_capacity(DEFAULT_CAPACITY, inner)
+    }
+}
+
+impl<R: Reader> Reader for BufferedReader<R> {
+    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        if self.pos == self.cap {
+            match self.inner.read(self.buf) {
+                Some(cap) => {
+                    self.pos = 0;
+                    self.cap = cap;
+                }
+                None => return None
+            }
+        }
+
+        let src = self.buf.slice(self.pos, self.cap);
+        let nread = num::min(src.len(), buf.len());
+        vec::bytes::copy_memory(buf, src, nread);
+        self.pos += nread;
+        Some(nread)
+    }
+
+    fn eof(&mut self) -> bool {
+        self.pos == self.cap && self.inner.eof()
+    }
+}
+
+impl<R: Reader> Decorator<R> for BufferedReader<R> {
+    fn inner(self) -> R {
+        self.inner
+    }
+
+    fn inner_ref<'a>(&'a self) -> &'a R {
+        &self.inner
+    }
+
+    fn inner_mut_ref<'a>(&'a mut self) -> &'a mut R {
+        &mut self.inner
+    }
+}
+
+/// Wraps a Writer and buffers output to it
+///
+/// NOTE: `BufferedWriter` will NOT flush its buffer when dropped.
+pub struct BufferedWriter<W> {
+    priv inner: W,
+    priv buf: ~[u8],
+    priv pos: uint
+}
+
+impl<W: Writer> BufferedWriter<W> {
+    /// Creates a new `BufferedWriter` with with the specified buffer capacity
+    pub fn with_capacity(cap: uint, inner: W) -> BufferedWriter<W> {
+        BufferedWriter {
+            inner: inner,
+            buf: vec::from_elem(cap, 0u8),
+            pos: 0
+        }
+    }
+
+    /// Creates a new `BufferedWriter` with a default buffer capacity
+    pub fn new(inner: W) -> BufferedWriter<W> {
+        BufferedWriter::with_capacity(DEFAULT_CAPACITY, inner)
+    }
+}
+
+impl<W: Writer> Writer for BufferedWriter<W> {
+    fn write(&mut self, buf: &[u8]) {
+        if self.pos + buf.len() > self.buf.len() {
+            self.flush();
+        }
+
+        if buf.len() > self.buf.len() {
+            self.inner.write(buf);
+        } else {
+            let dst = self.buf.mut_slice_from(self.pos);
+            vec::bytes::copy_memory(dst, buf, buf.len());
+            self.pos += buf.len();
+        }
+    }
+
+    fn flush(&mut self) {
+        if self.pos != 0 {
+            self.inner.write(self.buf.slice_to(self.pos));
+            self.pos = 0;
+        }
+        self.inner.flush();
+    }
+}
+
+impl<W: Writer> Decorator<W> for BufferedWriter<W> {
+    fn inner(self) -> W {
+        self.inner
+    }
+
+    fn inner_ref<'a>(&'a self) -> &'a W {
+        &self.inner
+    }
+
+    fn inner_mut_ref<'a>(&'a mut self) -> &'a mut W {
+        &mut self.inner
+    }
+}
+
+struct InternalBufferedWriter<W>(BufferedWriter<W>);
+
+impl<W: Reader> Reader for InternalBufferedWriter<W> {
+    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        self.inner.read(buf)
+    }
+
+    fn eof(&mut self) -> bool {
+        self.inner.eof()
+    }
+}
+
+/// Wraps a Stream and buffers input and output to and from it
+///
+/// NOTE: `BufferedStream` will NOT flush its output buffer when dropped.
+pub struct BufferedStream<S>(BufferedReader<InternalBufferedWriter<S>>);
+
+impl<S: Stream> BufferedStream<S> {
+    pub fn with_capacities(reader_cap: uint, writer_cap: uint, inner: S)
+                           -> BufferedStream<S> {
+        let writer = BufferedWriter::with_capacity(writer_cap, inner);
+        let internal_writer = InternalBufferedWriter(writer);
+        let reader = BufferedReader::with_capacity(reader_cap,
+                                                   internal_writer);
+        BufferedStream(reader)
+    }
+
+    pub fn new(inner: S) -> BufferedStream<S> {
+        BufferedStream::with_capacities(DEFAULT_CAPACITY, DEFAULT_CAPACITY,
+                                        inner)
+    }
+}
+
+impl<S: Stream> Reader for BufferedStream<S> {
+    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        (**self).read(buf)
+    }
+
+    fn eof(&mut self) -> bool {
+        (**self).eof()
+    }
+}
+
+impl<S: Stream> Writer for BufferedStream<S> {
+    fn write(&mut self, buf: &[u8]) {
+        self.inner.write(buf)
+    }
+
+    fn flush(&mut self) {
+        self.inner.flush()
+    }
+}
+
+impl<S: Stream> Decorator<S> for BufferedStream<S> {
+    fn inner(self) -> S {
+        self.inner.inner()
+    }
+
+    fn inner_ref<'a>(&'a self) -> &'a S {
+        self.inner.inner_ref()
+    }
+
+    fn inner_mut_ref<'a>(&'a mut self) -> &'a mut S {
+        self.inner.inner_mut_ref()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use prelude::*;
+    use super::*;
+    use super::super::mem::{MemReader, MemWriter};
+
+    #[test]
+    fn test_buffered_reader() {
+        let inner = MemReader::new(~[0, 1, 2, 3, 4]);
+        let mut reader = BufferedReader::with_capacity(2, inner);
+
+        let mut buf = [0, 0, 0];
+        let nread = reader.read(buf);
+        assert_eq!(Some(2), nread);
+        assert_eq!([0, 1, 0], buf);
+        assert!(!reader.eof());
+
+        let mut buf = [0];
+        let nread = reader.read(buf);
+        assert_eq!(Some(1), nread);
+        assert_eq!([2], buf);
+        assert!(!reader.eof());
+
+        let mut buf = [0, 0, 0];
+        let nread = reader.read(buf);
+        assert_eq!(Some(1), nread);
+        assert_eq!([3, 0, 0], buf);
+        assert!(!reader.eof());
+
+        let nread = reader.read(buf);
+        assert_eq!(Some(1), nread);
+        assert_eq!([4, 0, 0], buf);
+        assert!(reader.eof());
+
+        assert_eq!(None, reader.read(buf));
+    }
+
+    #[test]
+    fn test_buffered_writer() {
+        let inner = MemWriter::new();
+        let mut writer = BufferedWriter::with_capacity(2, inner);
+
+        writer.write([0, 1]);
+        assert_eq!([], writer.inner_ref().inner_ref().as_slice());
+
+        writer.write([2]);
+        assert_eq!([0, 1], writer.inner_ref().inner_ref().as_slice());
+
+        writer.write([3]);
+        assert_eq!([0, 1], writer.inner_ref().inner_ref().as_slice());
+
+        writer.flush();
+        assert_eq!([0, 1, 2, 3], writer.inner_ref().inner_ref().as_slice());
+
+        writer.write([4]);
+        writer.write([5]);
+        assert_eq!([0, 1, 2, 3], writer.inner_ref().inner_ref().as_slice());
+
+        writer.write([6]);
+        assert_eq!([0, 1, 2, 3, 4, 5],
+                   writer.inner_ref().inner_ref().as_slice());
+
+        writer.write([7, 8]);
+        assert_eq!([0, 1, 2, 3, 4, 5, 6],
+                   writer.inner_ref().inner_ref().as_slice());
+
+        writer.write([9, 10, 11]);
+        assert_eq!([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
+                   writer.inner_ref().inner_ref().as_slice());
+
+        writer.flush();
+        assert_eq!([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
+                   writer.inner_ref().inner_ref().as_slice());
+    }
+
+    // This is just here to make sure that we don't infinite loop in the
+    // newtype struct autoderef weirdness
+    #[test]
+    fn test_buffered_stream() {
+        struct S;
+
+        impl Writer for S {
+            fn write(&mut self, _: &[u8]) {}
+            fn flush(&mut self) {}
+        }
+
+        impl Reader for S {
+            fn read(&mut self, _: &mut [u8]) -> Option<uint> { None }
+            fn eof(&mut self) -> bool { true }
+        }
+
+        let mut stream = BufferedStream::new(S);
+        let mut buf = [];
+        stream.read(buf);
+        stream.eof();
+        stream.write(buf);
+        stream.flush();
+    }
+}

src/libstd/rt/io/mod.rs

@@ -295,6 +295,9 @@ mod support;
 /// Basic Timer
 pub mod timer;
 
+/// Buffered I/O wrappers
+pub mod buffered;
+
 /// Thread-blocking implementations
 pub mod native {
     /// Posix file I/O