fetch from remote if parent unknown locally

lib/diaspora_federation/entities/relayable.rb

@@ -198,17 +198,21 @@ module DiasporaFederation
             end
           end
 
-          add_parent(entity_data)
+          fetch_parent(entity_data)
           new(entity_data, xml_order, additional_xml_elements).tap(&:verify_signatures)
         end
 
-        def add_parent(data)
-          data[:parent] = fetch_parent(data)
-        end
-
         def fetch_parent(data)
           type = data[:parent_type] || self::PARENT_TYPE
-          DiasporaFederation.callbacks.trigger(:fetch_related_entity, type, data[:parent_guid])
+          guid = data[:parent_guid]
+
+          data[:parent] = DiasporaFederation.callbacks.trigger(:fetch_related_entity, type, guid)
+
+          unless data[:parent]
+            # fetch and receive parent from remote, if not available locally
+            Federation::Fetcher.fetch_public(data[:author], type, guid)
+            data[:parent] = DiasporaFederation.callbacks.trigger(:fetch_related_entity, type, guid)
+          end
         end
       end
 

spec/lib/diaspora_federation/entities/relayable_spec.rb

@@ -294,5 +294,34 @@ XML
         end
       end
     end
+
+    context "fetch parent" do
+      before do
+        expect_callback(:fetch_public_key, author).and_return(author_pkey.public_key)
+        expect_callback(:fetch_public_key, remote_parent.author).and_return(parent_pkey.public_key)
+        expect_callback(:fetch_private_key, author).and_return(author_pkey)
+        expect_callback(:fetch_private_key, remote_parent.author).and_return(parent_pkey)
+      end
+
+      let(:xml) { SomeRelayable.new(hash).to_xml }
+
+      it "fetches the parent from the backend" do
+        expect_callback(:fetch_related_entity, "Parent", parent_guid).and_return(remote_parent)
+        expect(Federation::Fetcher).not_to receive(:fetch_public)
+
+        entity = SomeRelayable.from_xml(xml)
+
+        expect(entity.parent).to eq(remote_parent)
+      end
+
+      it "fetches the parent from remote if not found on backend" do
+        expect_callback(:fetch_related_entity, "Parent", parent_guid).and_return(nil, remote_parent)
+        expect(Federation::Fetcher).to receive(:fetch_public).with(author, "Parent", parent_guid)
+
+        entity = SomeRelayable.from_xml(xml)
+
+        expect(entity.parent).to eq(remote_parent)
+      end
+    end
   end
 end