clawhdf5: File::storage gives the file's view as a Storage

The bytes File::as_bytes returns (from the superblock on, bounded by the
recorded end of file, a metadata cache image laid over), as a
&(dyn Storage + Send + Sync) for every backend. Code that parses the file
itself with the clawhdf5_format *_in functions — h5rs does — can then
read a file opened with File::open_storage (a remote file) as well as a
local one; in memory its as_contiguous() is as_bytes(), so local reads
stay slices.

Test: for every fixture, File::open's storage() is as_bytes() as its
contiguous view, and File::open_storage over a read_at-only storage gives
the same bytes through storage().read_at.

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

crates/clawhdf5/src/reader.rs

@@ -523,6 +523,17 @@ impl File {
         self.data.contiguous()
     }
 
+    /// The bytes [`as_bytes`](Self::as_bytes) returns, as a [`Storage`],
+    /// for every backend: from the superblock on, bounded by the recorded
+    /// end of file, with a metadata cache image laid over them. Code that
+    /// parses the file itself with the `clawhdf5_format` `*_in` functions
+    /// reads through this, so it works on remote files too; for a file in
+    /// memory its [`Storage::as_contiguous`] is [`as_bytes`](Self::as_bytes)
+    /// (and every read a slice of it).
+    pub fn storage(&self) -> &(dyn Storage + Send + Sync) {
+        &self.data
+    }
+
     /// The error of a metadata cache image libhdf5 cannot load, when the
     /// file has one. Such a file opens, as in libhdf5, and every object
     /// lookup fails with this error; code that parses [`Self::as_bytes`]

crates/clawhdf5/tests/storage_equivalence.rs

@@ -432,3 +432,33 @@ fn storage_backed_files_keep_their_zero_copy_views_only_in_memory() {
         "as_bytes over a range storage must not answer"
     );
 }
+
+/// `File::storage` is the view `as_bytes` gives, for every backend: the
+/// user block skipped, bounded by the end of file, a cache image laid over.
+#[test]
+fn file_storage_is_the_as_bytes_view_for_every_backend() {
+    let root = Path::new(env!("CARGO_MANIFEST_DIR"));
+    let mut files = Vec::new();
+    hdf5_files(&root.join("tests/fixtures"), &mut files);
+    hdf5_files(&root.join("../clawhdf5-format/tests/fixtures"), &mut files);
+    let mut compared = 0;
+    for p in files {
+        let Ok(local) = File::open(&p) else { continue };
+        let bytes = std::fs::read(&p).unwrap();
+        let remote = File::open_storage(Arc::new(CountingStorage::new(bytes))).unwrap();
+        let want = local.as_bytes();
+        let view = local.storage();
+        assert_eq!(view.as_contiguous(), Some(want), "{}", p.display());
+        let got = remote.storage();
+        assert!(got.as_contiguous().is_none());
+        assert_eq!(got.len(), want.len() as u64, "{}", p.display());
+        assert_eq!(
+            &*got.read_at(0, want.len()).unwrap(),
+            want,
+            "{}",
+            p.display()
+        );
+        compared += 1;
+    }
+    assert!(compared >= 40, "{compared}");
+}