Support Undo like activities (Fix #139)

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -131,11 +131,19 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
     end
   end
 
-  def unlike(%User{} = actor, %Object{} = object) do
-    with %Activity{} = activity <- get_existing_like(actor.ap_id, object),
-         {:ok, _activity} <- Repo.delete(activity),
-         {:ok, object} <- remove_like_from_object(activity, object) do
-      {:ok, object}
+  def unlike(
+        %User{} = actor,
+        %Object{} = object,
+        activity_id \\ nil,
+        local \\ true
+      ) do
+    with %Activity{} = like_activity <- get_existing_like(actor.ap_id, object),
+         unlike_data <- make_unlike_data(actor, like_activity, activity_id),
+         {:ok, unlike_activity} <- insert(unlike_data, local),
+         {:ok, _activity} <- Repo.delete(like_activity),
+         {:ok, object} <- remove_like_from_object(like_activity, object),
+         :ok <- maybe_federate(unlike_activity) do
+      {:ok, unlike_activity, like_activity, object}
     else
       _e -> {:ok, object}
     end

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -241,6 +241,24 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
+  def handle_incoming(
+        %{
+          "type" => "Undo",
+          "object" => %{"type" => "Like", "object" => object_id},
+          "actor" => actor,
+          "id" => id
+        } = data
+      ) do
+    with %User{} = actor <- User.get_or_fetch_by_ap_id(actor),
+         {:ok, object} <-
+           get_obj_helper(object_id) || ActivityPub.fetch_object_from_id(object_id),
+         {:ok, activity, _, _} <- ActivityPub.unlike(actor, object, id, false) do
+      {:ok, activity}
+    else
+      e -> :error
+    end
+  end
+
   # TODO
   # Accept
   # Undo for non-Announce

lib/pleroma/web/activity_pub/utils.ex

@@ -315,6 +315,23 @@ defmodule Pleroma.Web.ActivityPub.Utils do
     if activity_id, do: Map.put(data, "id", activity_id), else: data
   end
 
+  def make_unlike_data(
+        %User{ap_id: ap_id} = user,
+        %Activity{data: %{"context" => context}} = activity,
+        activity_id
+      ) do
+    data = %{
+      "type" => "Undo",
+      "actor" => ap_id,
+      "object" => activity.data,
+      "to" => [user.follower_address, activity.data["actor"]],
+      "cc" => ["https://www.w3.org/ns/activitystreams#Public"],
+      "context" => context
+    }
+
+    if activity_id, do: Map.put(data, "id", activity_id), else: data
+  end
+
   def add_announce_to_object(%Activity{data: %{"actor" => actor}}, object) do
     with announcements <- [actor | object.data["announcements"] || []] |> Enum.uniq() do
       update_element_in_object("announcement", announcements, object)