Test that file EOF is not permanent: reading again should give new data

Author: joshtriplett

src/fs/file.rs

@@ -918,4 +918,40 @@ mod tests {
  assert_eq!(format!("{}", expect), format!("{}", actual));
  })
  }
+
+ #[test]
+ fn file_eof_is_not_permanent() -> crate::io::Result<()> {
+ let tempdir = tempfile::Builder::new()
+ .prefix("async-std-file-eof-test")
+ .tempdir()?;
+ let path = tempdir.path().join("testfile");
+
+ crate::task::block_on(async {
+ let mut file_w = File::create(&path).await?;
+ let mut file_r = File::open(&path).await?;
+
+ file_w.write_all(b"data").await?;
+ file_w.flush().await?;
+
+ let mut buf = [0u8; 4];
+ let mut len = file_r.read(&mut buf).await?;
+ assert_eq!(len, 4);
+ assert_eq!(&buf, b"data");
+
+ len = file_r.read(&mut buf).await?;
+ assert_eq!(len, 0);
+
+ file_w.write_all(b"more").await?;
+ file_w.flush().await?;
+
+ len = file_r.read(&mut buf).await?;
+ assert_eq!(len, 4);
+ assert_eq!(&buf, b"more");
+
+ len = file_r.read(&mut buf).await?;
+ assert_eq!(len, 0);
+
+ Ok(())
+ })
+ }
 }