From 858d9fc7e8e722604676c90cf2707f0209f935ec Mon Sep 17 00:00:00 2001
From: "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
Date: Mon, 13 Jul 2020 15:47:13 +0200
Subject: [PATCH 1/2] MRF Policies: Return a {:reject, reason} instead of
 {:reject, nil}

---
 .../activity_pub/mrf/anti_followbot_policy.ex  |  2 +-
 .../activity_pub/mrf/anti_link_spam_policy.ex  |  7 +++----
 .../web/activity_pub/mrf/hellthread_policy.ex  |  4 ++--
 .../web/activity_pub/mrf/keyword_policy.ex     |  7 ++++---
 .../web/activity_pub/mrf/mention_policy.ex     |  5 +++--
 .../web/activity_pub/mrf/object_age_policy.ex  |  8 +++-----
 .../web/activity_pub/mrf/reject_non_public.ex  |  2 +-
 .../web/activity_pub/mrf/simple_policy.ex      | 16 ++++++++++------
 lib/pleroma/web/activity_pub/mrf/tag_policy.ex |  7 ++++---
 .../activity_pub/mrf/user_allow_list_policy.ex |  2 +-
 .../web/activity_pub/mrf/vocabulary_policy.ex  | 18 +++++++++++-------
 .../mrf/anti_followbot_policy_test.exs         |  4 ++--
 .../mrf/hellthread_policy_test.exs             |  3 ++-
 .../activity_pub/mrf/keyword_policy_test.exs   | 12 ++++++++----
 .../activity_pub/mrf/mention_policy_test.exs   |  6 ++++--
 .../mrf/reject_non_public_test.exs             |  4 ++--
 .../activity_pub/mrf/simple_policy_test.exs    | 16 ++++++++--------
 test/web/activity_pub/mrf/tag_policy_test.exs  |  6 +++---
 .../mrf/user_allowlist_policy_test.exs         |  2 +-
 .../mrf/vocabulary_policy_test.exs             |  8 ++++----
 20 files changed, 77 insertions(+), 62 deletions(-)

diff --git a/lib/pleroma/web/activity_pub/mrf/anti_followbot_policy.ex b/lib/pleroma/web/activity_pub/mrf/anti_followbot_policy.ex
index 0270b96ae..b96388489 100644
--- a/lib/pleroma/web/activity_pub/mrf/anti_followbot_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/anti_followbot_policy.ex
@@ -60,7 +60,7 @@ def filter(%{"type" => "Follow", "actor" => actor_id} = message) do
     if score < 0.8 do
       {:ok, message}
     else
-      {:reject, nil}
+      {:reject, "[AntiFollowbotPolicy] Scored #{actor_id} as #{score}"}
     end
   end
 
diff --git a/lib/pleroma/web/activity_pub/mrf/anti_link_spam_policy.ex b/lib/pleroma/web/activity_pub/mrf/anti_link_spam_policy.ex
index a7e187b5e..b22464111 100644
--- a/lib/pleroma/web/activity_pub/mrf/anti_link_spam_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/anti_link_spam_policy.ex
@@ -39,14 +39,13 @@ def filter(%{"type" => "Create", "actor" => actor, "object" => object} = message
         {:ok, message}
 
       {:old_user, false} ->
-        {:reject, nil}
+        {:reject, "[AntiLinkSpamPolicy] User has no posts nor followers"}
 
       {:error, _} ->
-        {:reject, nil}
+        {:reject, "[AntiLinkSpamPolicy] Failed to get or fetch user by ap_id"}
 
       e ->
-        Logger.warn("[MRF anti-link-spam] WTF: unhandled error #{inspect(e)}")
-        {:reject, nil}
+        {:reject, "[AntiLinkSpamPolicy] Unhandled error #{inspect(e)}"}
     end
   end
 
diff --git a/lib/pleroma/web/activity_pub/mrf/hellthread_policy.ex b/lib/pleroma/web/activity_pub/mrf/hellthread_policy.ex
index f6b2c4415..9ba07b4e3 100644
--- a/lib/pleroma/web/activity_pub/mrf/hellthread_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/hellthread_policy.ex
@@ -43,7 +43,7 @@ defp delist_message(message, _threshold), do: {:ok, message}
   defp reject_message(message, threshold) when threshold > 0 do
     with {_, recipients} <- get_recipient_count(message) do
       if recipients > threshold do
-        {:reject, nil}
+        {:reject, "[HellthreadPolicy] #{recipients} recipients is over the limit of #{threshold}"}
       else
         {:ok, message}
       end
@@ -87,7 +87,7 @@ def filter(%{"type" => "Create", "object" => %{"type" => object_type}} = message
          {:ok, message} <- delist_message(message, delist_threshold) do
       {:ok, message}
     else
-      _e -> {:reject, nil}
+      e -> e
     end
   end
 
diff --git a/lib/pleroma/web/activity_pub/mrf/keyword_policy.ex b/lib/pleroma/web/activity_pub/mrf/keyword_policy.ex
index 88b0d2b39..15e09dcf0 100644
--- a/lib/pleroma/web/activity_pub/mrf/keyword_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/keyword_policy.ex
@@ -24,7 +24,7 @@ defp check_reject(%{"object" => %{"content" => content, "summary" => summary}} =
     if Enum.any?(Pleroma.Config.get([:mrf_keyword, :reject]), fn pattern ->
          string_matches?(content, pattern) or string_matches?(summary, pattern)
        end) do
-      {:reject, nil}
+      {:reject, "[KeywordPolicy] Matches with rejected keyword"}
     else
       {:ok, message}
     end
@@ -89,8 +89,9 @@ def filter(%{"type" => "Create", "object" => %{"content" => _content}} = message
          {:ok, message} <- check_replace(message) do
       {:ok, message}
     else
-      _e ->
-        {:reject, nil}
+      {:reject, nil} -> {:reject, "[KeywordPolicy] "}
+      {:reject, _} = e -> e
+      _e -> {:reject, "[KeywordPolicy] "}
     end
   end
 
diff --git a/lib/pleroma/web/activity_pub/mrf/mention_policy.ex b/lib/pleroma/web/activity_pub/mrf/mention_policy.ex
index 06f003921..7910ca131 100644
--- a/lib/pleroma/web/activity_pub/mrf/mention_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/mention_policy.ex
@@ -12,8 +12,9 @@ def filter(%{"type" => "Create"} = message) do
     reject_actors = Pleroma.Config.get([:mrf_mention, :actors], [])
     recipients = (message["to"] || []) ++ (message["cc"] || [])
 
-    if Enum.any?(recipients, fn recipient -> Enum.member?(reject_actors, recipient) end) do
-      {:reject, nil}
+    if rejected_mention =
+         Enum.find(recipients, fn recipient -> Enum.member?(reject_actors, recipient) end) do
+      {:reject, "[MentionPolicy] Rejected for mention of #{rejected_mention}"}
     else
       {:ok, message}
     end
diff --git a/lib/pleroma/web/activity_pub/mrf/object_age_policy.ex b/lib/pleroma/web/activity_pub/mrf/object_age_policy.ex
index a62914135..5f111c72f 100644
--- a/lib/pleroma/web/activity_pub/mrf/object_age_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/object_age_policy.ex
@@ -28,7 +28,7 @@ defp check_date(%{"object" => %{"published" => published}} = message) do
 
   defp check_reject(message, actions) do
     if :reject in actions do
-      {:reject, nil}
+      {:reject, "[ObjectAgePolicy]"}
     else
       {:ok, message}
     end
@@ -47,9 +47,8 @@ defp check_delist(message, actions) do
 
         {:ok, message}
       else
-        # Unhandleable error: somebody is messing around, just drop the message.
         _e ->
-          {:reject, nil}
+          {:reject, "[ObjectAgePolicy] Unhandled error"}
       end
     else
       {:ok, message}
@@ -69,9 +68,8 @@ defp check_strip_followers(message, actions) do
 
         {:ok, message}
       else
-        # Unhandleable error: somebody is messing around, just drop the message.
         _e ->
-          {:reject, nil}
+          {:reject, "[ObjectAgePolicy] Unhandled error"}
       end
     else
       {:ok, message}
diff --git a/lib/pleroma/web/activity_pub/mrf/reject_non_public.ex b/lib/pleroma/web/activity_pub/mrf/reject_non_public.ex
index 4fd63106d..0b9ed2224 100644
--- a/lib/pleroma/web/activity_pub/mrf/reject_non_public.ex
+++ b/lib/pleroma/web/activity_pub/mrf/reject_non_public.ex
@@ -38,7 +38,7 @@ def filter(%{"type" => "Create"} = object) do
         {:ok, object}
 
       true ->
-        {:reject, nil}
+        {:reject, "[RejectNonPublic] visibility: #{visibility}"}
     end
   end
 
diff --git a/lib/pleroma/web/activity_pub/mrf/simple_policy.ex b/lib/pleroma/web/activity_pub/mrf/simple_policy.ex
index 70a2ca053..b77b8c7b4 100644
--- a/lib/pleroma/web/activity_pub/mrf/simple_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/simple_policy.ex
@@ -21,7 +21,7 @@ defp check_accept(%{host: actor_host} = _actor_info, object) do
       accepts == [] -> {:ok, object}
       actor_host == Config.get([Pleroma.Web.Endpoint, :url, :host]) -> {:ok, object}
       MRF.subdomain_match?(accepts, actor_host) -> {:ok, object}
-      true -> {:reject, nil}
+      true -> {:reject, "[SimplePolicy] host not in accept list"}
     end
   end
 
@@ -31,7 +31,7 @@ defp check_reject(%{host: actor_host} = _actor_info, object) do
       |> MRF.subdomains_regex()
 
     if MRF.subdomain_match?(rejects, actor_host) do
-      {:reject, nil}
+      {:reject, "[SimplePolicy] host in reject list"}
     else
       {:ok, object}
     end
@@ -114,7 +114,7 @@ defp check_report_removal(%{host: actor_host} = _actor_info, %{"type" => "Flag"}
       |> MRF.subdomains_regex()
 
     if MRF.subdomain_match?(report_removal, actor_host) do
-      {:reject, nil}
+      {:reject, "[SimplePolicy] host in report_removal list"}
     else
       {:ok, object}
     end
@@ -159,7 +159,7 @@ def filter(%{"type" => "Delete", "actor" => actor} = object) do
       |> MRF.subdomains_regex()
 
     if MRF.subdomain_match?(reject_deletes, actor_host) do
-      {:reject, nil}
+      {:reject, "[SimplePolicy] host in reject_deletes list"}
     else
       {:ok, object}
     end
@@ -177,7 +177,9 @@ def filter(%{"actor" => actor} = object) do
          {:ok, object} <- check_report_removal(actor_info, object) do
       {:ok, object}
     else
-      _e -> {:reject, nil}
+      {:reject, nil} -> {:reject, "[SimplePolicy]"}
+      {:reject, _} = e -> e
+      _ -> {:reject, "[SimplePolicy]"}
     end
   end
 
@@ -191,7 +193,9 @@ def filter(%{"id" => actor, "type" => obj_type} = object)
          {:ok, object} <- check_banner_removal(actor_info, object) do
       {:ok, object}
     else
-      _e -> {:reject, nil}
+      {:reject, nil} -> {:reject, "[SimplePolicy]"}
+      {:reject, _} = e -> e
+      _ -> {:reject, "[SimplePolicy]"}
     end
   end
 
diff --git a/lib/pleroma/web/activity_pub/mrf/tag_policy.ex b/lib/pleroma/web/activity_pub/mrf/tag_policy.ex
index c310462cb..febabda08 100644
--- a/lib/pleroma/web/activity_pub/mrf/tag_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/tag_policy.ex
@@ -134,12 +134,13 @@ defp process_tag(
     if user.local == true do
       {:ok, message}
     else
-      {:reject, nil}
+      {:reject,
+       "[TagPolicy] Follow from #{actor} tagged with mrf_tag:disable-remote-subscription"}
     end
   end
 
-  defp process_tag("mrf_tag:disable-any-subscription", %{"type" => "Follow"}),
-    do: {:reject, nil}
+  defp process_tag("mrf_tag:disable-any-subscription", %{"type" => "Follow", "actor" => actor}),
+    do: {:reject, "[TagPolicy] Follow from #{actor} tagged with mrf_tag:disable-any-subscription"}
 
   defp process_tag(_, message), do: {:ok, message}
 
diff --git a/lib/pleroma/web/activity_pub/mrf/user_allow_list_policy.ex b/lib/pleroma/web/activity_pub/mrf/user_allow_list_policy.ex
index 651aed70f..1a28f2ba2 100644
--- a/lib/pleroma/web/activity_pub/mrf/user_allow_list_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/user_allow_list_policy.ex
@@ -14,7 +14,7 @@ defp filter_by_list(%{"actor" => actor} = object, allow_list) do
     if actor in allow_list do
       {:ok, object}
     else
-      {:reject, nil}
+      {:reject, "[UserAllowListPolicy] #{actor} not in the list"}
     end
   end
 
diff --git a/lib/pleroma/web/activity_pub/mrf/vocabulary_policy.ex b/lib/pleroma/web/activity_pub/mrf/vocabulary_policy.ex
index 6167a74e2..a6c545570 100644
--- a/lib/pleroma/web/activity_pub/mrf/vocabulary_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/vocabulary_policy.ex
@@ -11,22 +11,26 @@ def filter(%{"type" => "Undo", "object" => child_message} = message) do
     with {:ok, _} <- filter(child_message) do
       {:ok, message}
     else
-      {:reject, nil} ->
-        {:reject, nil}
+      {:reject, _} = e -> e
     end
   end
 
   def filter(%{"type" => message_type} = message) do
     with accepted_vocabulary <- Pleroma.Config.get([:mrf_vocabulary, :accept]),
          rejected_vocabulary <- Pleroma.Config.get([:mrf_vocabulary, :reject]),
-         true <-
-           Enum.empty?(accepted_vocabulary) || Enum.member?(accepted_vocabulary, message_type),
-         false <-
-           length(rejected_vocabulary) > 0 && Enum.member?(rejected_vocabulary, message_type),
+         {_, true} <-
+           {:accepted,
+            Enum.empty?(accepted_vocabulary) || Enum.member?(accepted_vocabulary, message_type)},
+         {_, false} <-
+           {:rejected,
+            length(rejected_vocabulary) > 0 && Enum.member?(rejected_vocabulary, message_type)},
          {:ok, _} <- filter(message["object"]) do
       {:ok, message}
     else
-      _ -> {:reject, nil}
+      {:reject, _} = e -> e
+      {:accepted, _} -> {:reject, "[VocabularyPolicy] #{message_type} not in accept list"}
+      {:rejected, _} -> {:reject, "[VocabularyPolicy] #{message_type} in reject list"}
+      _ -> {:reject, "[VocabularyPolicy]"}
     end
   end
 
diff --git a/test/web/activity_pub/mrf/anti_followbot_policy_test.exs b/test/web/activity_pub/mrf/anti_followbot_policy_test.exs
index fca0de7c6..3c795f5ac 100644
--- a/test/web/activity_pub/mrf/anti_followbot_policy_test.exs
+++ b/test/web/activity_pub/mrf/anti_followbot_policy_test.exs
@@ -21,7 +21,7 @@ test "matches followbots by nickname" do
         "id" => "https://example.com/activities/1234"
       }
 
-      {:reject, nil} = AntiFollowbotPolicy.filter(message)
+      assert {:reject, "[AntiFollowbotPolicy]" <> _} = AntiFollowbotPolicy.filter(message)
     end
 
     test "matches followbots by display name" do
@@ -36,7 +36,7 @@ test "matches followbots by display name" do
         "id" => "https://example.com/activities/1234"
       }
 
-      {:reject, nil} = AntiFollowbotPolicy.filter(message)
+      assert {:reject, "[AntiFollowbotPolicy]" <> _} = AntiFollowbotPolicy.filter(message)
     end
   end
 
diff --git a/test/web/activity_pub/mrf/hellthread_policy_test.exs b/test/web/activity_pub/mrf/hellthread_policy_test.exs
index 6e9daa7f9..26f5bcdaa 100644
--- a/test/web/activity_pub/mrf/hellthread_policy_test.exs
+++ b/test/web/activity_pub/mrf/hellthread_policy_test.exs
@@ -50,7 +50,8 @@ test "rejects the message if the recipient count is above reject_threshold", %{
     } do
       Pleroma.Config.put([:mrf_hellthread], %{delist_threshold: 0, reject_threshold: 2})
 
-      {:reject, nil} = filter(message)
+      assert {:reject, "[HellthreadPolicy] 3 recipients is over the limit of 2"} ==
+               filter(message)
     end
 
     test "does not reject the message if the recipient count is below reject_threshold", %{
diff --git a/test/web/activity_pub/mrf/keyword_policy_test.exs b/test/web/activity_pub/mrf/keyword_policy_test.exs
index fd1f7aec8..b3d0f3d90 100644
--- a/test/web/activity_pub/mrf/keyword_policy_test.exs
+++ b/test/web/activity_pub/mrf/keyword_policy_test.exs
@@ -25,7 +25,8 @@ test "rejects if string matches in content" do
         }
       }
 
-      assert {:reject, nil} == KeywordPolicy.filter(message)
+      assert {:reject, "[KeywordPolicy] Matches with rejected keyword"} =
+               KeywordPolicy.filter(message)
     end
 
     test "rejects if string matches in summary" do
@@ -39,7 +40,8 @@ test "rejects if string matches in summary" do
         }
       }
 
-      assert {:reject, nil} == KeywordPolicy.filter(message)
+      assert {:reject, "[KeywordPolicy] Matches with rejected keyword"} =
+               KeywordPolicy.filter(message)
     end
 
     test "rejects if regex matches in content" do
@@ -55,7 +57,8 @@ test "rejects if regex matches in content" do
                    }
                  }
 
-                 {:reject, nil} == KeywordPolicy.filter(message)
+                 {:reject, "[KeywordPolicy] Matches with rejected keyword"} ==
+                   KeywordPolicy.filter(message)
                end)
     end
 
@@ -72,7 +75,8 @@ test "rejects if regex matches in summary" do
                    }
                  }
 
-                 {:reject, nil} == KeywordPolicy.filter(message)
+                 {:reject, "[KeywordPolicy] Matches with rejected keyword"} ==
+                   KeywordPolicy.filter(message)
                end)
     end
   end
diff --git a/test/web/activity_pub/mrf/mention_policy_test.exs b/test/web/activity_pub/mrf/mention_policy_test.exs
index aa003bef5..220309cc9 100644
--- a/test/web/activity_pub/mrf/mention_policy_test.exs
+++ b/test/web/activity_pub/mrf/mention_policy_test.exs
@@ -76,7 +76,8 @@ test "to" do
         "to" => ["https://example.com/blocked"]
       }
 
-      assert MentionPolicy.filter(message) == {:reject, nil}
+      assert MentionPolicy.filter(message) ==
+               {:reject, "[MentionPolicy] Rejected for mention of https://example.com/blocked"}
     end
 
     test "cc" do
@@ -88,7 +89,8 @@ test "cc" do
         "cc" => ["https://example.com/blocked"]
       }
 
-      assert MentionPolicy.filter(message) == {:reject, nil}
+      assert MentionPolicy.filter(message) ==
+               {:reject, "[MentionPolicy] Rejected for mention of https://example.com/blocked"}
     end
   end
 end
diff --git a/test/web/activity_pub/mrf/reject_non_public_test.exs b/test/web/activity_pub/mrf/reject_non_public_test.exs
index f36299b86..58b46b9a2 100644
--- a/test/web/activity_pub/mrf/reject_non_public_test.exs
+++ b/test/web/activity_pub/mrf/reject_non_public_test.exs
@@ -64,7 +64,7 @@ test "it's rejected when addrer of message in the follower addresses of user and
       }
 
       Pleroma.Config.put([:mrf_rejectnonpublic, :allow_followersonly], false)
-      assert {:reject, nil} = RejectNonPublic.filter(message)
+      assert {:reject, _} = RejectNonPublic.filter(message)
     end
   end
 
@@ -94,7 +94,7 @@ test "it's reject when direct messages aren't allow" do
       }
 
       Pleroma.Config.put([:mrf_rejectnonpublic, :allow_direct], false)
-      assert {:reject, nil} = RejectNonPublic.filter(message)
+      assert {:reject, _} = RejectNonPublic.filter(message)
     end
   end
 end
diff --git a/test/web/activity_pub/mrf/simple_policy_test.exs b/test/web/activity_pub/mrf/simple_policy_test.exs
index b7b9bc6a2..e842d8d8d 100644
--- a/test/web/activity_pub/mrf/simple_policy_test.exs
+++ b/test/web/activity_pub/mrf/simple_policy_test.exs
@@ -124,7 +124,7 @@ test "has a matching host" do
       report_message = build_report_message()
       local_message = build_local_message()
 
-      assert SimplePolicy.filter(report_message) == {:reject, nil}
+      assert {:reject, _} = SimplePolicy.filter(report_message)
       assert SimplePolicy.filter(local_message) == {:ok, local_message}
     end
 
@@ -133,7 +133,7 @@ test "match with wildcard domain" do
       report_message = build_report_message()
       local_message = build_local_message()
 
-      assert SimplePolicy.filter(report_message) == {:reject, nil}
+      assert {:reject, _} = SimplePolicy.filter(report_message)
       assert SimplePolicy.filter(local_message) == {:ok, local_message}
     end
   end
@@ -241,7 +241,7 @@ test "activity has a matching host" do
 
       remote_message = build_remote_message()
 
-      assert SimplePolicy.filter(remote_message) == {:reject, nil}
+      assert {:reject, _} = SimplePolicy.filter(remote_message)
     end
 
     test "activity matches with wildcard domain" do
@@ -249,7 +249,7 @@ test "activity matches with wildcard domain" do
 
       remote_message = build_remote_message()
 
-      assert SimplePolicy.filter(remote_message) == {:reject, nil}
+      assert {:reject, _} = SimplePolicy.filter(remote_message)
     end
 
     test "actor has a matching host" do
@@ -257,7 +257,7 @@ test "actor has a matching host" do
 
       remote_user = build_remote_user()
 
-      assert SimplePolicy.filter(remote_user) == {:reject, nil}
+      assert {:reject, _} = SimplePolicy.filter(remote_user)
     end
   end
 
@@ -279,7 +279,7 @@ test "is not empty but activity doesn't have a matching host" do
       remote_message = build_remote_message()
 
       assert SimplePolicy.filter(local_message) == {:ok, local_message}
-      assert SimplePolicy.filter(remote_message) == {:reject, nil}
+      assert {:reject, _} = SimplePolicy.filter(remote_message)
     end
 
     test "activity has a matching host" do
@@ -429,7 +429,7 @@ test "it accepts deletions even from non-whitelisted servers" do
     test "it rejects the deletion" do
       deletion_message = build_remote_deletion_message()
 
-      assert SimplePolicy.filter(deletion_message) == {:reject, nil}
+      assert {:reject, _} = SimplePolicy.filter(deletion_message)
     end
   end
 
@@ -439,7 +439,7 @@ test "it rejects the deletion" do
     test "it rejects the deletion" do
       deletion_message = build_remote_deletion_message()
 
-      assert SimplePolicy.filter(deletion_message) == {:reject, nil}
+      assert {:reject, _} = SimplePolicy.filter(deletion_message)
     end
   end
 
diff --git a/test/web/activity_pub/mrf/tag_policy_test.exs b/test/web/activity_pub/mrf/tag_policy_test.exs
index e7793641a..6ff71d640 100644
--- a/test/web/activity_pub/mrf/tag_policy_test.exs
+++ b/test/web/activity_pub/mrf/tag_policy_test.exs
@@ -12,8 +12,8 @@ defmodule Pleroma.Web.ActivityPub.MRF.TagPolicyTest do
   describe "mrf_tag:disable-any-subscription" do
     test "rejects message" do
       actor = insert(:user, tags: ["mrf_tag:disable-any-subscription"])
-      message = %{"object" => actor.ap_id, "type" => "Follow"}
-      assert {:reject, nil} = TagPolicy.filter(message)
+      message = %{"object" => actor.ap_id, "type" => "Follow", "actor" => actor.ap_id}
+      assert {:reject, _} = TagPolicy.filter(message)
     end
   end
 
@@ -22,7 +22,7 @@ test "rejects non-local follow requests" do
       actor = insert(:user, tags: ["mrf_tag:disable-remote-subscription"])
       follower = insert(:user, tags: ["mrf_tag:disable-remote-subscription"], local: false)
       message = %{"object" => actor.ap_id, "type" => "Follow", "actor" => follower.ap_id}
-      assert {:reject, nil} = TagPolicy.filter(message)
+      assert {:reject, _} = TagPolicy.filter(message)
     end
 
     test "allows non-local follow requests" do
diff --git a/test/web/activity_pub/mrf/user_allowlist_policy_test.exs b/test/web/activity_pub/mrf/user_allowlist_policy_test.exs
index ba1b69658..8e1ad5bc8 100644
--- a/test/web/activity_pub/mrf/user_allowlist_policy_test.exs
+++ b/test/web/activity_pub/mrf/user_allowlist_policy_test.exs
@@ -26,6 +26,6 @@ test "rejected if allow list isn't empty and user not in allow list" do
     actor = insert(:user)
     Pleroma.Config.put([:mrf_user_allowlist], %{"localhost" => ["test-ap-id"]})
     message = %{"actor" => actor.ap_id}
-    assert UserAllowListPolicy.filter(message) == {:reject, nil}
+    assert {:reject, _} = UserAllowListPolicy.filter(message)
   end
 end
diff --git a/test/web/activity_pub/mrf/vocabulary_policy_test.exs b/test/web/activity_pub/mrf/vocabulary_policy_test.exs
index 69f22bb77..2bceb67ee 100644
--- a/test/web/activity_pub/mrf/vocabulary_policy_test.exs
+++ b/test/web/activity_pub/mrf/vocabulary_policy_test.exs
@@ -46,7 +46,7 @@ test "it does not accept disallowed child objects" do
         }
       }
 
-      {:reject, nil} = VocabularyPolicy.filter(message)
+      {:reject, _} = VocabularyPolicy.filter(message)
     end
 
     test "it does not accept disallowed parent types" do
@@ -60,7 +60,7 @@ test "it does not accept disallowed parent types" do
         }
       }
 
-      {:reject, nil} = VocabularyPolicy.filter(message)
+      {:reject, _} = VocabularyPolicy.filter(message)
     end
   end
 
@@ -75,7 +75,7 @@ test "it rejects based on parent activity type" do
         "object" => "whatever"
       }
 
-      {:reject, nil} = VocabularyPolicy.filter(message)
+      {:reject, _} = VocabularyPolicy.filter(message)
     end
 
     test "it rejects based on child object type" do
@@ -89,7 +89,7 @@ test "it rejects based on child object type" do
         }
       }
 
-      {:reject, nil} = VocabularyPolicy.filter(message)
+      {:reject, _} = VocabularyPolicy.filter(message)
     end
 
     test "it passes through objects that aren't disallowed" do

From d29b8997f4a3601eac7f2e1e57de27a67df6699c Mon Sep 17 00:00:00 2001
From: "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
Date: Wed, 15 Jul 2020 15:25:33 +0200
Subject: [PATCH 2/2] MastoAPI: fix & test giving MRF reject reasons

---
 .../mastodon_api/controllers/status_controller.ex   |  5 +++++
 .../controllers/status_controller_test.exs          | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/lib/pleroma/web/mastodon_api/controllers/status_controller.ex b/lib/pleroma/web/mastodon_api/controllers/status_controller.ex
index 12be530c9..9bb2ef117 100644
--- a/lib/pleroma/web/mastodon_api/controllers/status_controller.ex
+++ b/lib/pleroma/web/mastodon_api/controllers/status_controller.ex
@@ -172,6 +172,11 @@ def create(%{assigns: %{user: user}, body_params: %{status: _} = params} = conn,
         with_direct_conversation_id: true
       )
     else
+      {:error, {:reject, message}} ->
+        conn
+        |> put_status(:unprocessable_entity)
+        |> json(%{error: message})
+
       {:error, message} ->
         conn
         |> put_status(:unprocessable_entity)
diff --git a/test/web/mastodon_api/controllers/status_controller_test.exs b/test/web/mastodon_api/controllers/status_controller_test.exs
index fd2de8d80..d34f300da 100644
--- a/test/web/mastodon_api/controllers/status_controller_test.exs
+++ b/test/web/mastodon_api/controllers/status_controller_test.exs
@@ -22,6 +22,8 @@ defmodule Pleroma.Web.MastodonAPI.StatusControllerTest do
   setup do: clear_config([:instance, :federating])
   setup do: clear_config([:instance, :allow_relay])
   setup do: clear_config([:rich_media, :enabled])
+  setup do: clear_config([:mrf, :policies])
+  setup do: clear_config([:mrf_keyword, :reject])
 
   describe "posting statuses" do
     setup do: oauth_access(["write:statuses"])
@@ -157,6 +159,17 @@ test "it fails to create a status if `expires_in` is less or equal than an hour"
                |> json_response_and_validate_schema(422)
     end
 
+    test "Get MRF reason when posting a status is rejected by one", %{conn: conn} do
+      Pleroma.Config.put([:mrf_keyword, :reject], ["GNO"])
+      Pleroma.Config.put([:mrf, :policies], [Pleroma.Web.ActivityPub.MRF.KeywordPolicy])
+
+      assert %{"error" => "[KeywordPolicy] Matches with rejected keyword"} =
+               conn
+               |> put_req_header("content-type", "application/json")
+               |> post("api/v1/statuses", %{"status" => "GNO/Linux"})
+               |> json_response_and_validate_schema(422)
+    end
+
     test "posting an undefined status with an attachment", %{user: user, conn: conn} do
       file = %Plug.Upload{
         content_type: "image/jpg",