It works

src/file.rs

@@ -147,7 +147,7 @@ mod io_uring {
     };
     use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
     use tokio_uring::{
-        buf::{IoBuf, IoBufMut, Slice},
+        buf::{IoBuf, IoBufMut},
         BufResult,
     };
 
@@ -204,6 +204,8 @@ mod io_uring {
                 cursor += n;
             }
 
+            self.inner.sync_all().await?;
+
             Ok(())
         }
 
@@ -214,13 +216,10 @@ mod io_uring {
         where
             R: AsyncRead + Unpin,
         {
-            let metadata = self.metadata().await?;
-            let size = metadata.len();
-
             let mut cursor: u64 = 0;
 
             loop {
-                let max_size = (size - cursor).min(65_536);
+                let max_size = 65_536;
                 let mut buf = Vec::with_capacity(max_size.try_into().unwrap());
 
                 let n = (&mut reader).take(max_size).read_to_end(&mut buf).await?;
@@ -229,16 +228,24 @@ mod io_uring {
                     break;
                 }
 
-                let mut buf: Slice<Vec<u8>> = buf.slice(..n);
                 let mut position = 0;
 
                 loop {
-                    if position == buf.len() {
+                    if position == n {
                         break;
                     }
 
-                    let (res, slice) = self.write_at(buf.slice(position..), cursor).await;
-                    position += res?;
+                    let position_u64: u64 = position.try_into().unwrap();
+                    let (res, slice) = self
+                        .write_at(buf.slice(position..n), cursor + position_u64)
+                        .await;
+
+                    let n = res?;
+                    if n == 0 {
+                        return Err(std::io::ErrorKind::UnexpectedEof.into());
+                    }
+
+                    position += n;
 
                     buf = slice.into_inner();
                 }
@@ -247,6 +254,8 @@ mod io_uring {
                 cursor += position;
             }
 
+            self.inner.sync_all().await?;
+
             Ok(())
         }
 
@@ -368,4 +377,81 @@ mod io_uring {
             }
         }
     }
+
+    #[cfg(test)]
+    mod tests {
+        use std::io::Read;
+
+        macro_rules! test_on_arbiter {
+            ($fut:expr) => {
+                actix_rt::System::new().block_on(async move {
+                    let arbiter = actix_rt::Arbiter::new();
+
+                    let (tx, rx) = tokio::sync::oneshot::channel();
+
+                    arbiter.spawn(async move {
+                        let handle = actix_rt::spawn($fut);
+
+                        let _ = tx.send(handle.await.unwrap());
+                    });
+
+                    rx.await.unwrap()
+                })
+            };
+        }
+
+        const EARTH_GIF: &'static str = "client-examples/earth.gif";
+
+        #[test]
+        fn read() {
+            let tmp = "/tmp/read-test";
+
+            test_on_arbiter!(async move {
+                let mut file = super::File::open(EARTH_GIF).await.unwrap();
+                let mut tmp_file = tokio::fs::File::create(tmp).await.unwrap();
+                file.read_to_async_write(&mut tmp_file).await.unwrap();
+            });
+
+            let mut source = std::fs::File::open(EARTH_GIF).unwrap();
+            let mut dest = std::fs::File::open(tmp).unwrap();
+
+            let mut source_vec = Vec::new();
+            source.read_to_end(&mut source_vec).unwrap();
+
+            let mut dest_vec = Vec::new();
+            dest.read_to_end(&mut dest_vec).unwrap();
+
+            drop(dest);
+            std::fs::remove_file(tmp).unwrap();
+
+            assert_eq!(source_vec.len(), dest_vec.len());
+            assert_eq!(source_vec, dest_vec);
+        }
+
+        #[test]
+        fn write() {
+            let tmp = "/tmp/write-test";
+
+            test_on_arbiter!(async move {
+                let mut file = tokio::fs::File::open(EARTH_GIF).await.unwrap();
+                let mut tmp_file = super::File::create(tmp).await.unwrap();
+                tmp_file.write_from_async_read(&mut file).await.unwrap();
+            });
+
+            let mut source = std::fs::File::open(EARTH_GIF).unwrap();
+            let mut dest = std::fs::File::open(tmp).unwrap();
+
+            let mut source_vec = Vec::new();
+            source.read_to_end(&mut source_vec).unwrap();
+
+            let mut dest_vec = Vec::new();
+            dest.read_to_end(&mut dest_vec).unwrap();
+
+            drop(dest);
+            std::fs::remove_file(tmp).unwrap();
+
+            assert_eq!(source_vec.len(), dest_vec.len());
+            assert_eq!(source_vec, dest_vec);
+        }
+    }
 }