io: add unidirectional stream structure

Up until this patch we had the `DuplexStream` which was backed by
two underlying pipes. This patch makes public this underlying structure
and renames it from the `Pipe` to the `SimplexStream` to provent
name confusion and keep simililiarity with the already existing duplex.

tokio/src/io/mod.rs

@@ -271,8 +271,8 @@ cfg_io_util! {
     pub(crate) mod seek;
     pub(crate) mod util;
     pub use util::{
-        copy, copy_bidirectional, copy_bidirectional_with_sizes, copy_buf, duplex, empty, repeat, sink, AsyncBufReadExt, AsyncReadExt, AsyncSeekExt, AsyncWriteExt,
-        BufReader, BufStream, BufWriter, DuplexStream, Empty, Lines, Repeat, Sink, Split, Take,
+        copy, copy_bidirectional, copy_bidirectional_with_sizes, copy_buf, duplex, empty, repeat, sink, simplex, AsyncBufReadExt, AsyncReadExt, AsyncSeekExt, AsyncWriteExt,
+        BufReader, BufStream, BufWriter, DuplexStream, Empty, Lines, Repeat, Sink, Split, Take, SimplexStream,
     };
 }
 

tokio/src/io/util/mem.rs

@@ -1,6 +1,6 @@
 //! In-process memory IO types.
 
-use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
+use crate::io::{split, AsyncRead, AsyncWrite, ReadBuf, ReadHalf, WriteHalf};
 use crate::loom::sync::Mutex;
 
 use bytes::{Buf, BytesMut};
@@ -47,15 +47,31 @@ use std::{
 #[derive(Debug)]
 #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
 pub struct DuplexStream {
-    read: Arc<Mutex<Pipe>>,
-    write: Arc<Mutex<Pipe>>,
+    read: Arc<Mutex<SimplexStream>>,
+    write: Arc<Mutex<SimplexStream>>,
 }
 
-/// A unidirectional IO over a piece of memory.
+/// A unidirectional pipe to read and write bytes in memory.
 ///
-/// Data can be written to the pipe, and reading will return that data.
+/// # Example
+///
+/// ```
+/// # async fn ex() -> std::io::Result<()> {
+/// # use tokio::io::{AsyncReadExt, AsyncWriteExt};
+/// let (mut receiver, mut sender) = tokio::io::simplex(64);
+///
+/// sender.write_all(b"ping").await?;
+///
+/// let mut buf = [0u8; 4];
+/// receiver.read_exact(&mut buf).await?;
+/// assert_eq!(&buf, b"ping");
+///
+/// # Ok(())
+/// # }
+/// ```
 #[derive(Debug)]
-struct Pipe {
+#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+pub struct SimplexStream {
     /// The buffer storing the bytes written, also read from.
     ///
     /// Using a `BytesMut` because it has efficient `Buf` and `BufMut`
@@ -83,8 +99,10 @@ struct Pipe {
 /// written to a side before the write returns `Poll::Pending`.
 #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
 pub fn duplex(max_buf_size: usize) -> (DuplexStream, DuplexStream) {
-    let one = Arc::new(Mutex::new(Pipe::new(max_buf_size)));
-    let two = Arc::new(Mutex::new(Pipe::new(max_buf_size)));
+    let (reader, writer) = simplex(max_buf_size);
+    let one = Arc::new(Mutex::new(reader.unsplit(writer)));
+    let (reader, writer) = simplex(max_buf_size);
+    let two = Arc::new(Mutex::new(reader.unsplit(writer)));
 
     (
         DuplexStream {
@@ -161,19 +179,24 @@ impl Drop for DuplexStream {
     }
 }
 
-// ===== impl Pipe =====
+// ===== impl SimplexStream =====
 
-impl Pipe {
-    fn new(max_buf_size: usize) -> Self {
-        Pipe {
-            buffer: BytesMut::new(),
-            is_closed: false,
-            max_buf_size,
-            read_waker: None,
-            write_waker: None,
-        }
-    }
+/// Creates unidirectional buffer that acts like a pipe.
+///
+/// The `max_buf_size` argument is the maximum amount of bytes that can be
+/// written to a buffer before the it returns `Poll::Pending`.
+#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+pub fn simplex(max_buf_size: usize) -> (ReadHalf<SimplexStream>, WriteHalf<SimplexStream>) {
+    split(SimplexStream {
+        buffer: BytesMut::new(),
+        is_closed: false,
+        max_buf_size,
+        read_waker: None,
+        write_waker: None,
+    })
+}
 
+impl SimplexStream {
     fn close_write(&mut self) {
         self.is_closed = true;
         // needs to notify any readers that no more data will come
@@ -269,7 +292,7 @@ impl Pipe {
     }
 }
 
-impl AsyncRead for Pipe {
+impl AsyncRead for SimplexStream {
     cfg_coop! {
         fn poll_read(
             self: Pin<&mut Self>,
@@ -299,7 +322,7 @@ impl AsyncRead for Pipe {
     }
 }
 
-impl AsyncWrite for Pipe {
+impl AsyncWrite for SimplexStream {
     cfg_coop! {
         fn poll_write(
             self: Pin<&mut Self>,

tokio/src/io/util/mod.rs

@@ -42,7 +42,7 @@ cfg_io_util! {
     pub use lines::Lines;
 
     mod mem;
-    pub use mem::{duplex, DuplexStream};
+    pub use mem::{duplex, simplex, DuplexStream, SimplexStream};
 
     mod read;
     mod read_buf;