Make the collection parsing more extensible

little_boxes/activitypub.py

@@ -569,9 +569,7 @@ class BaseActivity(object, metaclass=_ActivityMeta):
 
             # Is the activity a `Collection`/`OrderedCollection`?
             elif actor.ACTIVITY_TYPE in COLLECTION_TYPES:
-                for item in parse_collection(
-                    actor.to_dict(), fetcher=BACKEND.fetch_iri
-                ):
+                for item in BACKEND.parse_collection(actor.to_dict()):
                     # XXX(tsileo): is nested collection support needed here?
 
                     if item in [actor_id, AS_PUBLIC]:

little_boxes/backend.py

@@ -2,10 +2,14 @@ import abc
 import binascii
 import os
 import typing
+from typing import Any
+from typing import Dict
+from typing import Optional
 
 import requests
 
 from .__version__ import __version__
+from .collection import parse_collection
 from .errors import ActivityNotFoundError
 from .errors import RemoteActivityGoneError
 from .urlutils import check_url as check_url
@@ -44,6 +48,11 @@ class Backend(abc.ABC):
 
         return resp
 
+    def parse_collection(
+        self, payload: Optional[Dict[str, Any]] = None, url: Optional[str] = None
+    ):
+        return parse_collection(payload=payload, url=url, fetcher=self.fetch_iri)
+
     def is_from_outbox(
         self, as_actor: "ap.Person", activity: "ap.BaseActivity"
     ) -> bool: