federation/incoming: improve link_resolve retry decision

To facilitate this ObjectValidator.fetch_actor_and_object is adapted to
return an informative error. Otherwise we’d be unable to make an
informed decision on retrying or not later. There’s no point in
retrying to fetch MRF-blocked stuff or private posts for example.

lib/pleroma/user.ex

@@ -1999,6 +1999,10 @@ def get_or_fetch_by_ap_id(ap_id, options \\ []) do
       {%User{} = user, _} ->
         {:ok, user}
 
+      {_, {:error, {:reject, :mrf}}} ->
+        Logger.debug("Rejected to fetch user due to MRF: #{ap_id}")
+        {:error, {:reject, :mrf}}
+
       e ->
         Logger.error("Could not fetch user #{ap_id}, #{inspect(e)}")
         {:error, :not_found}

lib/pleroma/web/activity_pub/object_validator.ex

@@ -15,6 +15,7 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidator do
   alias Pleroma.EctoType.ActivityPub.ObjectValidators
   alias Pleroma.Object
   alias Pleroma.Object.Containment
+  alias Pleroma.Object.Fetcher
   alias Pleroma.User
   alias Pleroma.Web.ActivityPub.ObjectValidators.AcceptRejectValidator
   alias Pleroma.Web.ActivityPub.ObjectValidators.AddRemoveValidator
@@ -253,11 +254,27 @@ def fetch_actor(object) do
   end
 
   def fetch_actor_and_object(object) do
+    # Fetcher.fetch_object_from_id already first does a local db lookup
     with {:ok, %User{}} <- fetch_actor(object),
-         %Object{} <- Object.normalize(object["object"], fetch: true) do
+         {:ap_id, id} when is_binary(id) <-
+           {:ap_id, Pleroma.Web.ActivityPub.Utils.get_ap_id(object["object"])},
+         {:ok, %Object{}} <- Fetcher.fetch_object_from_id(id) do
       :ok
     else
-      _ -> :error
+      {:ap_id, id} ->
+        {:error, {:validate, "Invalid AP id: #{inspect(id)}"}}
+
+      # if actor: late post from a previously unknown, deleted profile
+      # if object: private post we're not allowed to access
+      # (other HTTP replies might just indicate a temporary network failure though!)
+      {:error, e} when e in [:not_found, :forbidden] ->
+        {:error, :ignore}
+
+      {:error, _} = e ->
+        e
+
+      e ->
+        {:error, e}
     end
   end
 

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -523,6 +523,15 @@ defp handle_incoming_normalised(%{"type" => type} = data, _options)
          {:ok, activity, _meta} <- Pipeline.common_pipeline(data, local: false) do
       {:ok, activity}
     else
+      {:link, {:error, :ignore}} ->
+        {:error, :ignore}
+
+      {:link, {:error, {:validate, _}} = e} ->
+        e
+
+      {:link, {:error, {:reject, _}} = e} ->
+        e
+
       {:link, _} ->
         {:error, :link_resolve_failed}
 

lib/pleroma/workers/receiver_worker.ex

@@ -23,6 +23,9 @@ def perform(%Job{args: %{"op" => "incoming_ap_doc", "params" => params}}) do
       {:error, :already_present} ->
         {:discard, :already_present}
 
+      {:error, :ignore} ->
+        {:discard, :ignore}
+
       # invalid data or e.g. deleting an object we don't know about anyway
       {:error, {:validate, issue}} ->
         Logger.info("Received invalid AP document: #{inspect(issue)}")
@@ -36,7 +39,6 @@ def perform(%Job{args: %{"op" => "incoming_ap_doc", "params" => params}}) do
       # failed to resolve a necessary referenced remote AP object;
       # might be temporary server/network trouble thus reattempt
       {:error, :link_resolve_failed} = e ->
-        # TODO: lower to debug for PR!
         Logger.info("Failed to resolve AP link; may retry: #{inspect(params)}")
         e