fix(containment): return nil for actor shapes without an id

Containment.get_actor raised on remote shapes it did not know, such as
an attributedTo object without an id. This crashed object fetches and
poll refetches. Return nil, so containment rejects the object.

changelog.d/get-actor-crash.fix

@@ -0,0 +1 @@
+Reject fetched objects whose author has no id instead of crashing

lib/pleroma/object/containment.ex

@@ -44,6 +44,9 @@ defmodule Pleroma.Object.Containment do
     id
   end
 
+  # remote data can carry any shape here; callers treat nil as "no actor"
+  def get_actor(_), do: nil
+
   def get_object(%{"object" => id}) when is_binary(id) do
     id
   end

test/pleroma/object/containment_test.exs

@@ -128,6 +128,24 @@ defmodule Pleroma.Object.ContainmentTest do
     end
   end
 
+  describe "get_actor/1" do
+    test "returns nil for actor shapes without an id" do
+      for actor <- [%{"type" => "Person"}, %{"id" => 1}, 1, true] do
+        assert nil == Containment.get_actor(%{"actor" => actor})
+        assert nil == Containment.get_actor(%{"actor" => nil, "attributedTo" => actor})
+      end
+
+      assert nil == Containment.get_actor(%{})
+    end
+
+    test "contain_origin/2 rejects actor shapes without an id" do
+      assert :error ==
+               Containment.contain_origin("https://a.test/o/1", %{
+                 "attributedTo" => %{"type" => "Person"}
+               })
+    end
+  end
+
   describe "contain_id_to_fetch/2" do
     test "matches the exact id" do
       assert :ok =

test/pleroma/object/fetcher_test.exs

@@ -488,6 +488,24 @@ defmodule Pleroma.Object.FetcherTest do
       assert Object.get_by_ap_id("https://mastodon.social/1").data["content"] == "test 1"
     end
 
+    test "it rejects a refetched object whose author has no id", %{object1: object1} do
+      {:ok, o} = Object.create(object1)
+
+      mock(fn %{method: :get, url: "https://mastodon.social/1"} ->
+        %Tesla.Env{
+          status: 200,
+          headers: [{"content-type", "application/activity+json"}],
+          body:
+            object1
+            |> Map.delete("actor")
+            |> Map.put("attributedTo", %{"type" => "Person"})
+            |> Jason.encode!()
+        }
+      end)
+
+      assert {:error, _} = Fetcher.refetch_object(o)
+    end
+
     test "it rejects a refetched object whose id changed", %{object1: object1} do
       {:ok, o} = Object.create(object1)
 
@@ -909,6 +927,25 @@ defmodule Pleroma.Object.FetcherTest do
                )
     end
 
+    test "it rejects objects whose author has no id" do
+      mock(fn %{method: :get, url: "https://host.test/objects/anon" = url} ->
+        %Tesla.Env{
+          status: 200,
+          headers: [{"content-type", "application/activity+json"}],
+          body:
+            Jason.encode!(%{
+              "id" => url,
+              "type" => "Note",
+              "content" => "anon",
+              "attributedTo" => %{"type" => "Person", "name" => "nobody"}
+            })
+        }
+      end)
+
+      assert {:containment, :error} =
+               Fetcher.fetch_object_from_id("https://host.test/objects/anon")
+    end
+
     test "it rejects documents without an id" do
       assert {:error, _} =
                Fetcher.fetch_and_contain_remote_object_from_id("https://host.test/objects/no-id")