receiver_worker: don't reattempt invalid documents

Ideally we’d like to split this up more and count most invalid documents
as an error, but silently drop e.g. Deletes for unknown objects.
However, this is hard to extract from the changeset and jobs canceled
with :discard don’t count as exceptions and I’m not aware of a idiomatic
way to cancel further retries while retaining the exception status.

Thus at least keep a log, but since superfluous "Delete"s
seem kinda frequent, don't log at error, only info level.

lib/pleroma/workers/receiver_worker.ex

@@ -3,6 +3,8 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.Workers.ReceiverWorker do
+  require Logger
+
   alias Pleroma.Web.Federator
 
   use Pleroma.Workers.WorkerHelper, queue: "federator_incoming"
@@ -21,6 +23,16 @@ def perform(%Job{args: %{"op" => "incoming_ap_doc", "params" => params}}) do
       {:error, :already_present} ->
         {:discard, :already_present}
 
+      # invalid data or e.g. deleting an object we don't know about anyway
+      {:error, {:error, {:validate, issue}}} ->
+        Logger.info("Received invalid AP document: #{inspect(issue)}")
+        {:discard, :invalid}
+
+      # rarer, but sometimes there’s an additional :error in front
+      {:error, {:error, {:error, {:validate, issue}}}} ->
+        Logger.info("Received invalid AP document: (3e) #{inspect(issue)}")
+        {:discard, :invalid}
+
       {:error, _} = e ->
         e