Raise exception if collection elements missing during download

lib/galaxy/managers/hdcas.py

@@ -42,6 +42,9 @@ def stream_dataset_collection(dataset_collection_instance, upstream_mod_zip=Fals
 def write_dataset_collection(dataset_collection_instance, archive):
     names, hdas = get_hda_and_element_identifiers(dataset_collection_instance)
     for name, hda in zip(names, hdas):
+        if not hda:
+            # TODO should we raise galaxy.exceptions.InternalServerError or create a new exception type?
+            raise Exception("Attempt to write dataset collection with missing elements")
         if hda.state != hda.states.OK:
             continue
         for file_path, relpath in hda.datatype.to_archive(dataset=hda, name=name):

lib/galaxy/webapps/galaxy/api/history_contents.py

@@ -626,8 +626,7 @@ def download_dataset_collection_history_content(
         """Download the content of a history dataset collection as a `zip` archive
         while maintaining approximate collection structure.
         """
-        archive = self.service.get_dataset_collection_archive_for_download(trans, id)
-        return StreamingResponse(archive.response(), headers=archive.get_headers())
+        return self._download_collection(trans, id)
 
     @router.get(
         "/api/dataset_collections/{id}/download",
@@ -644,8 +643,7 @@ def download_dataset_collection(
         """Download the content of a history dataset collection as a `zip` archive
         while maintaining approximate collection structure.
         """
-        archive = self.service.get_dataset_collection_archive_for_download(trans, id)
-        return StreamingResponse(archive.response(), headers=archive.get_headers())
+        return self._download_collection(trans, id)
 
     @router.post(
         "/api/histories/{history_id}/contents/dataset_collections/{id}/prepare_download",
@@ -1033,3 +1031,7 @@ def materialize_to_history(
         )
         rval = self.service.materialize(trans, materialize_request)
         return rval
+
+    def _download_collection(self, trans, id):
+        archive = self.service.get_dataset_collection_archive_for_download(trans, id)
+        return StreamingResponse(archive.response(), headers=archive.get_headers())