Transmogrifier: Handle compact objects in undos.

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -753,6 +753,24 @@ def handle_incoming(
     end
   end
 
+  # For Undos that don't have the complete object attached, try to find it in our database.
+  def handle_incoming(
+        %{
+          "type" => "Undo",
+          "object" => object
+        } = activity,
+        options
+      )
+      when is_binary(object) do
+    with %Activity{data: data} <- Activity.get_by_ap_id(object) do
+      activity
+      |> Map.put("object", data)
+      |> handle_incoming(options)
+    else
+      _e -> :error
+    end
+  end
+
   def handle_incoming(_, _), do: :error
 
   def get_obj_helper(id, options \\ []) do

test/fixtures/mastodon-undo-like-compact-object.json

@@ -0,0 +1,29 @@
+{
+  "type": "Undo",
+  "signature": {
+    "type": "RsaSignature2017",
+    "signatureValue": "fdxMfQSMwbC6wP6sh6neS/vM5879K67yQkHTbiT5Npr5wAac0y6+o3Ij+41tN3rL6wfuGTosSBTHOtta6R4GCOOhCaCSLMZKypnp1VltCzLDoyrZELnYQIC8gpUXVmIycZbREk22qWUe/w7DAFaKK4UscBlHDzeDVcA0K3Se5Sluqi9/Zh+ldAnEzj/rSEPDjrtvf5wGNf3fHxbKSRKFt90JvKK6hS+vxKUhlRFDf6/SMETw+EhwJSNW4d10yMUakqUWsFv4Acq5LW7l+HpYMvlYY1FZhNde1+uonnCyuQDyvzkff8zwtEJmAXC4RivO/VVLa17SmqheJZfI8oluVg==",
+    "creator": "http://mastodon.example.org/users/admin#main-key",
+    "created": "2018-05-19T16:36:58Z"
+  },
+  "object": "http://mastodon.example.org/users/admin#likes/2",
+  "nickname": "lain",
+  "id": "http://mastodon.example.org/users/admin#likes/2/undo",
+  "actor": "http://mastodon.example.org/users/admin",
+  "@context": [
+    "https://www.w3.org/ns/activitystreams",
+    "https://w3id.org/security/v1",
+    {
+      "toot": "http://joinmastodon.org/ns#",
+      "sensitive": "as:sensitive",
+      "ostatus": "http://ostatus.org#",
+      "movedTo": "as:movedTo",
+      "manuallyApprovesFollowers": "as:manuallyApprovesFollowers",
+      "inReplyToAtomUri": "ostatus:inReplyToAtomUri",
+      "conversation": "ostatus:conversation",
+      "atomUri": "ostatus:atomUri",
+      "Hashtag": "as:Hashtag",
+      "Emoji": "toot:Emoji"
+    }
+  ]
+}

test/web/activity_pub/transmogrifier_test.exs

@@ -348,6 +348,31 @@ test "it works for incoming unlikes with an existing like activity" do
       assert data["object"]["id"] == "http://mastodon.example.org/users/admin#likes/2"
     end
 
+    test "it works for incoming unlikes with an existing like activity and a compact object" do
+      user = insert(:user)
+      {:ok, activity} = CommonAPI.post(user, %{"status" => "leave a like pls"})
+
+      like_data =
+        File.read!("test/fixtures/mastodon-like.json")
+        |> Poison.decode!()
+        |> Map.put("object", activity.data["object"])
+
+      {:ok, %Activity{data: like_data, local: false}} = Transmogrifier.handle_incoming(like_data)
+
+      data =
+        File.read!("test/fixtures/mastodon-undo-like.json")
+        |> Poison.decode!()
+        |> Map.put("object", like_data["id"])
+        |> Map.put("actor", like_data["actor"])
+
+      {:ok, %Activity{data: data, local: false}} = Transmogrifier.handle_incoming(data)
+
+      assert data["actor"] == "http://mastodon.example.org/users/admin"
+      assert data["type"] == "Undo"
+      assert data["id"] == "http://mastodon.example.org/users/admin#likes/2/undo"
+      assert data["object"]["id"] == "http://mastodon.example.org/users/admin#likes/2"
+    end
+
     test "it works for incoming announces" do
       data = File.read!("test/fixtures/mastodon-announce.json") |> Poison.decode!()