Add AsyncBufRead implementation for IntoAsyncRead

Author: Nemo157

futures-util/src/try_stream/into_async_read.rs

@@ -1,7 +1,7 @@
 use core::pin::Pin;
 use futures_core::stream::TryStream;
 use futures_core::task::{Context, Poll};
-use futures_io::AsyncRead;
+use futures_io::{AsyncRead, AsyncBufRead};
 use std::cmp;
 use std::io::{Error, Result};
 
@@ -98,6 +98,59 @@ where
     }
 }
 
+impl<St> AsyncBufRead for IntoAsyncRead<St>
+where
+    St: TryStream<Error = Error> + Unpin,
+    St::Ok: AsRef<[u8]>,
+{
+    fn poll_fill_buf<'a>(
+        mut self: Pin<&'a mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<&'a [u8]>> {
+        if let ReadState::PendingChunk = self.state {
+            match ready!(Pin::new(&mut self.stream).try_poll_next(cx)) {
+                Some(Ok(chunk)) => {
+                    self.state = ReadState::Ready {
+                        chunk,
+                        chunk_start: 0,
+                    };
+                }
+                Some(Err(err)) => {
+                    self.state = ReadState::Eof;
+                    return Poll::Ready(Err(err));
+                }
+                None => {
+                    self.state = ReadState::Eof;
+                    return Poll::Ready(Ok(&[]));
+                }
+            }
+        }
+
+        if let ReadState::Ready { ref chunk, chunk_start } = self.into_ref().get_ref().state {
+            let chunk = chunk.as_ref();
+            return Poll::Ready(Ok(&chunk[chunk_start..]));
+        }
+
+        // To get to this point we must be in ReadState::Eof
+        Poll::Ready(Ok(&[]))
+    }
+
+    fn consume(
+        mut self: Pin<&mut Self>,
+        amount: usize,
+    ) {
+        if let ReadState::Ready { chunk, chunk_start } = &mut self.state {
+            *chunk_start += amount;
+            debug_assert!(*chunk_start <= chunk.as_ref().len());
+            if *chunk_start >= chunk.as_ref().len() {
+                self.state = ReadState::PendingChunk;
+            }
+        } else {
+            debug_assert!(false, "Attempted to consume from IntoAsyncRead without chunk");
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -148,4 +201,29 @@ mod tests {
 
         assert_read!(reader, &mut buf, 0);
     }
+
+    #[test]
+    fn test_into_async_bufread() -> std::io::Result<()> {
+        let stream = stream::iter(1..=2).map(|_| Ok(vec![1, 2, 3, 4, 5]));
+        let mut reader = stream.into_async_read();
+
+        let mut cx = noop_context();
+        let mut reader = Pin::new(&mut reader);
+
+        assert_eq!(reader.as_mut().poll_fill_buf(&mut cx)?, Poll::Ready(&[1, 2, 3, 4, 5][..]));
+        reader.as_mut().consume(3);
+
+        assert_eq!(reader.as_mut().poll_fill_buf(&mut cx)?, Poll::Ready(&[4, 5][..]));
+        reader.as_mut().consume(2);
+
+        assert_eq!(reader.as_mut().poll_fill_buf(&mut cx)?, Poll::Ready(&[1, 2, 3, 4, 5][..]));
+        reader.as_mut().consume(2);
+
+        assert_eq!(reader.as_mut().poll_fill_buf(&mut cx)?, Poll::Ready(&[3, 4, 5][..]));
+        reader.as_mut().consume(3);
+
+        assert_eq!(reader.as_mut().poll_fill_buf(&mut cx)?, Poll::Ready(&[][..]));
+
+        Ok(())
+    }
 }