Properly open filehandles for RemoteReadableAssets

dandi/misctypes.py

@@ -345,7 +345,10 @@ def open(self) -> IO[bytes]:
         # Optional dependency:
         import fsspec
 
-        return cast(IO[bytes], fsspec.open(self.url, mode="rb"))
+        # We need to call open() on the return value of fsspec.open() because
+        # otherwise the filehandle will only be opened when used to enter a
+        # context manager.
+        return cast(IO[bytes], fsspec.open(self.url, mode="rb").open())
 
     def get_size(self) -> int:
         return self.size

dandi/tests/test_dandiapi.py

@@ -25,7 +25,13 @@
     dandiset_identifier_regex,
     dandiset_metadata_file,
 )
-from ..dandiapi import DandiAPIClient, RemoteAsset, RemoteZarrAsset, Version
+from ..dandiapi import (
+    DandiAPIClient,
+    RemoteAsset,
+    RemoteBlobAsset,
+    RemoteZarrAsset,
+    Version,
+)
 from ..download import download
 from ..exceptions import NotFoundError, SchemaVersionError
 from ..files import GenericAsset, dandi_file
@@ -745,3 +751,21 @@ def test_rename_type_mismatch(text_dandiset: SampleDandiset, dest: str) -> None:
     assert asset1a.get_raw_metadata()["path"] == "file.txt"
     with pytest.raises(NotFoundError):
         text_dandiset.dandiset.get_asset_by_path(dest)
+
+
+def test_asset_as_readable_open(new_dandiset: SampleDandiset, tmp_path: Path) -> None:
+    p = tmp_path / "foo.txt"
+    # Write bytes so that the LF doesn't get converted on Windows:
+    p.write_bytes(b"This is test text.\n")
+    d = new_dandiset.dandiset
+    d.upload_raw_asset(p, {"path": "foo.txt"})
+    (asset,) = d.get_assets()
+    assert isinstance(asset, RemoteBlobAsset)
+    # The purpose of this test is to check that RemoteReadableAsset.open()
+    # returns a filehandle that can immediately be used, so don't use a `with`
+    # block here, as that opens fsspec file objects.
+    fp = asset.as_readable().open()
+    try:
+        assert fp.read() == b"This is test text.\n"
+    finally:
+        fp.close()