Add max_id fetching to activity fetching.

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -54,6 +54,12 @@ def fetch_activities(recipients, opts \\ %{}) do
     query = from activity in query,
       where: activity.id > ^since_id
 
+    query = if opts["max_id"] do
+      from activity in query, where: activity.id < ^opts["max_id"]
+    else
+      query
+    end
+
     Repo.all(query)
     |> Enum.reverse
   end

test/web/activity_pub/activity_pub_test.exs

@@ -94,6 +94,20 @@ test "retrieves ids starting from a since_id" do
       assert length(activities) == 10
       assert last == last_expected
     end
+
+    test "retrieves ids up to max_id" do
+      _first_activities = ActivityBuilder.insert_list(10)
+      activities = ActivityBuilder.insert_list(20)
+      later_activities = ActivityBuilder.insert_list(10)
+      max_id = List.first(later_activities).id
+      last_expected = List.last(activities)
+
+      activities = ActivityPub.fetch_public_activities(%{"max_id" => max_id})
+      last = List.last(activities)
+
+      assert length(activities) == 20
+      assert last == last_expected
+    end
   end
 
   describe "uploading files" do