Federator: Add option do save failed activities

config/config.exs

@@ -798,6 +798,10 @@ config :floki, :html_parser, Floki.HTMLParser.FastHtml
 
 config :pleroma, Pleroma.Web.Auth.Authenticator, Pleroma.Web.Auth.PleromaAuthenticator
 
+config :pleroma, :debug_failed_activities,
+  enabled: false,
+  folder: "failed_activities"
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{Mix.env()}.exs"

lib/pleroma/web/federator/federator.ex

@@ -86,13 +86,30 @@ defmodule Pleroma.Web.Federator do
         {:error, :already_present}
 
       e ->
-        # Just drop those for now
+        if Pleroma.Config.get([:debug_failed_activities, :enabled]) do
+          save_failed_activity(params)
+        end
+
         Logger.debug("Unhandled activity")
         Logger.debug(Jason.encode!(params, pretty: true))
         {:error, e}
     end
   end
 
+  defp save_failed_activity(params) do
+    folder = Pleroma.Config.get([:debug_failed_activities, :folder], "failed_activities")
+    File.mkdir_p!(folder)
+    filename = URI.encode_www_form(params["id"] || Ecto.UUID.generate())
+
+    case File.write(Path.join([folder, filename]), Jason.encode!(params)) do
+      {:error, e} ->
+        Logger.debug("Can't write failed activity, reason: #{inspect(e)}")
+
+      _ ->
+        nil
+    end
+  end
+
   def ap_enabled_actor(id) do
     user = User.get_cached_by_ap_id(id)
 

test/web/federator_test.exs

@@ -135,6 +135,27 @@ defmodule Pleroma.Web.FederatorTest do
       assert {:error, :already_present} = ObanHelpers.perform(job)
     end
 
+    test "rejects unknown activities" do
+      params = %{
+        "@context" => "https://www.w3.org/ns/activitystreams",
+        "actor" => "http://mastodon.example.org/users/admin",
+        "type" => "Frobnicate",
+        "id" => "http://mastodon.example.org/users/admin/activities/1"
+      }
+
+      assert {:ok, job} = Federator.incoming_ap_doc(params)
+      assert {:error, _activity} = ObanHelpers.perform(job)
+
+      clear_config([:debug_failed_activities, :enabled], true)
+
+      assert {:ok, job} = Federator.incoming_ap_doc(params)
+      assert {:error, _activity} = ObanHelpers.perform(job)
+
+      debug_folder = Pleroma.Config.get([:debug_failed_activities, :folder])
+
+      assert File.exists?(Path.join(debug_folder, URI.encode_www_form(params["id"])))
+    end
+
     test "rejects incoming AP docs with incorrect origin" do
       params = %{
         "@context" => "https://www.w3.org/ns/activitystreams",