buf: stream and iter helpers (#1011)

tokio-buf/src/util/stream.rs

@@ -0,0 +1,35 @@
+use bytes::Buf;
+use futures::{Poll, Stream};
+use BufStream;
+
+/// Converts a `Stream` of `Buf` types into a `BufStream`.
+///
+/// While `Stream` and `BufSream` are very similar, they are not identical. The
+/// `stream` function returns a `BufStream` that is backed by the provided
+/// `Stream` type.
+pub fn stream<T>(stream: T) -> FromStream<T>
+where
+    T: Stream,
+    T::Item: Buf,
+{
+    FromStream { stream }
+}
+
+/// `BufStream` returned by the [`stream`] function.
+#[derive(Debug)]
+pub struct FromStream<T> {
+    stream: T,
+}
+
+impl<T> BufStream for FromStream<T>
+where
+    T: Stream,
+    T::Item: Buf,
+{
+    type Item = T::Item;
+    type Error = T::Error;
+
+    fn poll_buf(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
+        self.stream.poll()
+    }
+}