realm-io: allow underlying buffer without ownership

realm_io/src/lib.rs

@@ -19,12 +19,12 @@
 //!     // zero copy
 //!     bidi_zero_copy(&mut left, &mut right).await;
 //!
-//!     // use custom buffer(vector)
+//!     // use custom buffer(AsMut<[u8]>)
 //!     let buf1 = CopyBuffer::new(vec![0; 0x2000]);
 //!     let buf2 = CopyBuffer::new(vec![0; 0x2000]);
 //!     bidi_copy_buf(&mut left, &mut right, buf1, buf2).await;
 //!
-//!     // use custom buffer(pipe)
+//!     // use custom buffer(Pipe or &mut Pipe)
 //!     let buf1 = CopyBuffer::new(Pipe::new().unwrap());
 //!     let buf2 = CopyBuffer::new(Pipe::new().unwrap());
 //!     bidi_copy_buf(&mut left, &mut right, buf1, buf2).await;

realm_io/src/linux/zero_copy.rs

@@ -79,6 +79,27 @@ where
     }
 }
 
+impl<'a, SR, SW> AsyncIOBuf for CopyBuffer<&'a mut Pipe, SR, SW>
+where
+    SR: AsyncRead + AsyncWrite + AsyncRawIO + Unpin,
+    SW: AsyncRead + AsyncWrite + AsyncRawIO + Unpin,
+{
+    type StreamR = SR;
+    type StreamW = SW;
+
+    fn poll_read_buf(&mut self, cx: &mut Context<'_>, stream: &mut Self::StreamR) -> Poll<Result<usize>> {
+        stream.poll_read_raw(cx, || splice_n(stream.as_raw_fd(), self.buf.1, usize::MAX))
+    }
+
+    fn poll_write_buf(&mut self, cx: &mut Context<'_>, stream: &mut Self::StreamW) -> Poll<Result<usize>> {
+        stream.poll_write_raw(cx, || splice_n(self.buf.0, stream.as_raw_fd(), self.cap - self.pos))
+    }
+
+    fn poll_flush_buf(&mut self, cx: &mut Context<'_>, stream: &mut Self::StreamW) -> Poll<Result<()>> {
+        Pin::new(stream).poll_flush(cx)
+    }
+}
+
 /// Copy data bidirectionally between two streams with pipe.
 pub async fn bidi_zero_copy<A, B>(a: &mut A, b: &mut B) -> Result<(u64, u64)>
 where