From 75b69de3b4b8e18c175064cfd21a224cbc0b956a Mon Sep 17 00:00:00 2001
From: Wim Looman <wim.looman@kiwi.ki>
Date: Wed, 7 Mar 2018 16:36:12 +0100
Subject: [PATCH] Add basic io::{Read, Write} traits modeled after futures-io

---
 src/io/mod.rs   |  5 ++++
 src/io/read.rs  | 43 +++++++++++++++++++++++++++++
 src/io/write.rs | 73 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs      |  5 ++++
 4 files changed, 126 insertions(+)
 create mode 100644 src/io/mod.rs
 create mode 100644 src/io/read.rs
 create mode 100644 src/io/write.rs

diff --git a/src/io/mod.rs b/src/io/mod.rs
new file mode 100644
index 0000000..a557f9a
--- /dev/null
+++ b/src/io/mod.rs
@@ -0,0 +1,5 @@
+mod read;
+mod write;
+
+pub use self::read::Read;
+pub use self::write::Write;
diff --git a/src/io/read.rs b/src/io/read.rs
new file mode 100644
index 0000000..1cb275e
--- /dev/null
+++ b/src/io/read.rs
@@ -0,0 +1,43 @@
+use core::cmp;
+
+use Result;
+
+/// Non-blocking reader trait
+pub trait Read {
+    /// An enumeration of possible errors
+    ///
+    /// May be `!` (`never_type`) for infallible implementations
+    type Error;
+
+    /// Pull some bytes from this source into the specified buffer, returning how many bytes were
+    /// read.
+    ///
+    /// If an object needs to block for a read it will return an `Err(nb::Error::WouldBlock)`
+    /// return value.
+    ///
+    /// If the return value of this method is `Ok(n)`, then it must be guaranteed that `0 <= n <=
+    /// buf.len()`. The `n` value indicates that the buffer `buf` has been filled in with `n` bytes
+    /// of data from this source. If `n == 0 && buf.len() > 0` then it can be assumed that this
+    /// reader has run out of data and will not be able service any future read calls.
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error>;
+}
+
+impl<'a, R: ?Sized + Read> Read for &'a mut R {
+    type Error = R::Error;
+
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error> {
+        (**self).read(buf)
+    }
+}
+
+impl<'a> Read for &'a [u8] {
+    type Error = !;
+
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error> {
+        let len = cmp::min(self.len(), buf.len());
+        let (head, tail) = self.split_at(len);
+        buf[..len].copy_from_slice(head);
+        *self = tail;
+        Ok(len)
+    }
+}
diff --git a/src/io/write.rs b/src/io/write.rs
new file mode 100644
index 0000000..e516a85
--- /dev/null
+++ b/src/io/write.rs
@@ -0,0 +1,73 @@
+use core::{cmp, mem};
+
+use Result;
+
+/// Non-blocking writer trait
+pub trait Write {
+    /// An enumeration of possible errors
+    ///
+    /// May be `!` (`never_type`) for infallible implementations
+    type Error;
+
+    /// Push some bytes into this source from the specified buffer, returning how many bytes were
+    /// written.
+    ///
+    /// If an object needs to block for a write it will return an `Err(nb::Error::WouldBlock)`
+    /// return value.
+    ///
+    /// If the return value of this method is `Ok(n)`, then it must be guaranteed that `0 <= n <=
+    /// buf.len()`. The `n` value indicates that `n` bytes from the buffer `buf` have been written
+    /// to this source. If `n == 0 && buf.len() > 0` then it can be assumed that this writer has
+    /// run out of space and will not be able to service future writes.
+    fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error>;
+
+    /// Attempt to flush the object, ensuring that any buffered data reach their destination.
+    ///
+    /// On success, returns `Ok(())`.
+    ///
+    /// If flushing cannot immediately complete, this method returns `Err(nb::Error::WouldBlock)`.
+    fn flush(&mut self) -> Result<(), Self::Error>;
+
+    /// Attempt to close the object.
+    ///
+    /// On success, returns `Ok(())`.
+    ///
+    /// If closing cannot immediately complete, this method returns `Err(nb::Error::WouldBlock)`.
+    fn close(&mut self) -> Result<(), Self::Error>;
+}
+
+impl<'a, W: ?Sized + Write> Write for &'a mut W {
+    type Error = W::Error;
+
+    fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
+        (**self).write(buf)
+    }
+
+    fn flush(&mut self) -> Result<(), Self::Error> {
+        (**self).flush()
+    }
+
+    fn close(&mut self) -> Result<(), Self::Error> {
+        (**self).close()
+    }
+}
+
+impl<'a> Write for &'a mut [u8] {
+    type Error = !;
+
+    fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
+        let len = cmp::min(self.len(), buf.len());
+        let (head, tail) = mem::replace(self, &mut []).split_at_mut(len);
+        head.copy_from_slice(&buf[..len]);
+        *self = tail;
+        Ok(len)
+    }
+
+    fn flush(&mut self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn close(&mut self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 7f0d386..70447ae 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -357,6 +357,11 @@
 #![no_std]
 #![deny(warnings)]
 
+#![cfg_attr(feature = "unstable", feature(never_type))]
+
+#[cfg(feature = "unstable")]
+pub mod io;
+
 use core::fmt;
 
 /// A non-blocking result