fix(io): refuse truncated files in the VOL, async and MPI readers

The truncated-file check and the end-of-file clamp reached File,
LazyFile and MmapFile but not clawhdf5-io's readers, which still opened
truncated files and read past the recorded end of file. NativeVol
(open, and read_dataset for from_bytes), AsyncHDF5File::from_bytes and
MpiVol's collective read now view the file through the new
vol::hdf5_view: from the superblock to Superblock::data_end, refusing a
file shorter than that.

MpiVol's read is compiled only with the mpi-io feature, which needs an
MPI installation; it was not built here. The edit there only swaps its
two-line superblock setup for hdf5_view.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5-io/src/async_read.rs

@@ -281,8 +281,13 @@ impl AsyncHDF5File {
         // HDF5 addresses are relative to the superblock: drop any user block
         // so they index `data` directly.
         let user_block = find_signature(&data)?;
+        let whole_len = data.len() as u64;
         data.drain(..user_block);
         let superblock = Superblock::parse(&data, 0)?;
+        // Refuse a truncated file, and keep nothing past the end of file the
+        // superblock records, as libhdf5 does.
+        let end = superblock.data_end(user_block as u64, whole_len)?;
+        data.truncate(end as usize);
         Ok(Self { data, superblock })
     }
 
@@ -605,6 +610,28 @@ mod tests {
         tokio::fs::remove_file(&path).await.ok();
     }
 
+    /// As libhdf5 does: a truncated file is refused, and bytes past the end
+    /// of file the superblock records are dropped.
+    #[tokio::test]
+    async fn async_refuses_truncated_files_and_drops_trailing_bytes() {
+        let bytes = make_test_hdf5_f64("v", &[1.0, 2.0]);
+        let truncated = bytes[..bytes.len() - 8].to_vec();
+        let err = AsyncHDF5File::from_bytes(truncated).err().unwrap();
+        assert!(
+            matches!(
+                err,
+                AsyncHDF5Error::Format(FormatError::TruncatedFile { .. })
+            ),
+            "{err}"
+        );
+
+        let mut appended = bytes.clone();
+        appended.extend_from_slice(&[0xAB; 64]);
+        let file = AsyncHDF5File::from_bytes(appended).unwrap();
+        assert_eq!(file.as_bytes().len(), bytes.len());
+        assert_eq!(file.read_f64("v").await.unwrap(), vec![1.0, 2.0]);
+    }
+
     #[tokio::test]
     async fn async_error_display() {
         let io_err = AsyncHDF5Error::Io(io::Error::new(io::ErrorKind::NotFound, "gone"));