Chat: Only create them for valid users for now.

lib/pleroma/chat.ex

@@ -26,6 +26,13 @@ defmodule Pleroma.Chat do
   def creation_cng(struct, params) do
     struct
     |> cast(params, [:user_id, :recipient, :unread])
+    |> validate_change(:recipient, fn
+      :recipient, recipient ->
+        case User.get_cached_by_ap_id(recipient) do
+          nil -> [recipient: "must a an existing user"]
+          _ -> []
+        end
+    end)
     |> validate_required([:user_id, :recipient])
     |> unique_constraint(:user_id, name: :chats_user_id_recipient_index)
   end

test/chat_test.exs

@@ -10,6 +10,13 @@ defmodule Pleroma.ChatTest do
   import Pleroma.Factory
 
   describe "creation and getting" do
+    test "it only works if the recipient is a valid user (for now)" do
+      user = insert(:user)
+
+      assert {:error, _chat} = Chat.bump_or_create(user.id, "http://some/nonexisting/account")
+      assert {:error, _chat} = Chat.get_or_create(user.id, "http://some/nonexisting/account")
+    end
+
     test "it creates a chat for a user and recipient" do
       user = insert(:user)
       other_user = insert(:user)