activitypub: splice users into recipient lists when they receive messages at their personal inbox

closes #343

lib/pleroma/web/activity_pub/activity_pub_controller.ex

@@ -4,6 +4,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPubController do
   alias Pleroma.Web.ActivityPub.{ObjectView, UserView}
   alias Pleroma.Web.ActivityPub.ActivityPub
   alias Pleroma.Web.ActivityPub.Relay
+  alias Pleroma.Web.ActivityPub.Utils
   alias Pleroma.Web.Federator
 
   require Logger
@@ -87,7 +88,15 @@ defmodule Pleroma.Web.ActivityPub.ActivityPubController do
     outbox(conn, %{"nickname" => nickname, "max_id" => nil})
   end
 
-  # TODO: Ensure that this inbox is a recipient of the message
+  def inbox(%{assigns: %{valid_signature: true}} = conn, %{"nickname" => nickname} = params) do
+    with %User{} = user <- User.get_cached_by_nickname(nickname),
+         true <- Utils.recipient_in_message(user.ap_id, params),
+         params <- Utils.maybe_splice_recipient(user.ap_id, params) do
+      Federator.enqueue(:incoming_ap_doc, params)
+      json(conn, "ok")
+    end
+  end
+
   def inbox(%{assigns: %{valid_signature: true}} = conn, params) do
     Federator.enqueue(:incoming_ap_doc, params)
     json(conn, "ok")

lib/pleroma/web/activity_pub/utils.ex

@@ -19,6 +19,48 @@ defmodule Pleroma.Web.ActivityPub.Utils do
     Map.put(params, "actor", get_ap_id(params["actor"]))
   end
 
+  defp recipient_in_collection(ap_id, coll) when is_binary(coll), do: ap_id == coll
+  defp recipient_in_collection(ap_id, coll) when is_list(coll), do: ap_id in coll
+  defp recipient_in_collection(_, _), do: false
+
+  def recipient_in_message(ap_id, params) do
+    cond do
+      recipient_in_collection(ap_id, params["to"]) ->
+        true
+
+      recipient_in_collection(ap_id, params["cc"]) ->
+        true
+
+      recipient_in_collection(ap_id, params["bto"]) ->
+        true
+
+      recipient_in_collection(ap_id, params["bcc"]) ->
+        true
+
+      true ->
+        false
+    end
+  end
+
+  defp extract_list(target) when is_binary(target), do: [target]
+  defp extract_list(lst) when is_list(lst), do: lst
+  defp extract_list(_), do: []
+
+  def maybe_splice_recipient(ap_id, params) do
+    need_splice =
+      !recipient_in_collection(ap_id, params["to"]) &&
+        !recipient_in_collection(ap_id, params["cc"])
+
+    cc_list = extract_list(params["cc"])
+
+    if need_splice do
+      params
+      |> Map.put(params, "cc", [ap_id | cc_list])
+    else
+      params
+    end
+  end
+
   def make_json_ld_header do
     %{
       "@context" => [