From e62173dfc8b739508345b7ab97477ae04fcdb457 Mon Sep 17 00:00:00 2001
From: lain <lain@soykaf.club>
Date: Wed, 22 Apr 2020 18:40:53 +0200
Subject: [PATCH 1/2] SideEffects: Run in transaction.

This fixes race conditions.
---
 lib/pleroma/web/activity_pub/side_effects.ex | 11 +++++---
 test/web/common_api/common_api_test.exs      | 27 ++++++++++++++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/lib/pleroma/web/activity_pub/side_effects.ex b/lib/pleroma/web/activity_pub/side_effects.ex
index 6a8f1af96..a0f71fd88 100644
--- a/lib/pleroma/web/activity_pub/side_effects.ex
+++ b/lib/pleroma/web/activity_pub/side_effects.ex
@@ -15,12 +15,15 @@ defmodule Pleroma.Web.ActivityPub.SideEffects do
   # - Add like to object
   # - Set up notification
   def handle(%{data: %{"type" => "Like"}} = object, meta) do
-    liked_object = Object.get_by_ap_id(object.data["object"])
-    Utils.add_like_to_object(object, liked_object)
+    Pleroma.Repo.transaction(fn ->
+      liked_object = Object.get_by_ap_id(object.data["object"])
+      Utils.add_like_to_object(object, liked_object)
 
-    Notification.create_notifications(object)
+      Notification.create_notifications(object)
 
-    {:ok, object, meta}
+      {:ok, object, meta}
+    end)
+    |> (fn {:ok, res} -> res end).()
   end
 
   # Nothing to do
diff --git a/test/web/common_api/common_api_test.exs b/test/web/common_api/common_api_test.exs
index e130736ec..68a29108a 100644
--- a/test/web/common_api/common_api_test.exs
+++ b/test/web/common_api/common_api_test.exs
@@ -21,6 +21,33 @@ defmodule Pleroma.Web.CommonAPITest do
   setup do: clear_config([:instance, :limit])
   setup do: clear_config([:instance, :max_pinned_statuses])
 
+  test "favoriting race condition" do
+    user = insert(:user)
+    users_serial = insert_list(10, :user)
+    users = insert_list(10, :user)
+
+    {:ok, activity} = CommonAPI.post(user, %{"status" => "."})
+
+    users_serial
+    |> Enum.map(fn user ->
+      CommonAPI.favorite(user, activity.id)
+    end)
+
+    object = Object.get_by_ap_id(activity.data["object"])
+    assert object.data["like_count"] == 10
+
+    users
+    |> Enum.map(fn user ->
+      Task.async(fn ->
+        CommonAPI.favorite(user, activity.id)
+      end)
+    end)
+    |> Enum.map(&Task.await/1)
+
+    object = Object.get_by_ap_id(activity.data["object"])
+    assert object.data["like_count"] == 20
+  end
+
   test "when replying to a conversation / participation, it will set the correct context id even if no explicit reply_to is given" do
     user = insert(:user)
     {:ok, activity} = CommonAPI.post(user, %{"status" => ".", "visibility" => "direct"})

From 1bcbdc7a9f5df35f42d1ab331bc4b6785e180284 Mon Sep 17 00:00:00 2001
From: lain <lain@soykaf.club>
Date: Wed, 22 Apr 2020 21:21:21 +0200
Subject: [PATCH 2/2] SideEffects: Use less cryptic syntax.

---
 lib/pleroma/web/activity_pub/side_effects.ex | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/lib/pleroma/web/activity_pub/side_effects.ex b/lib/pleroma/web/activity_pub/side_effects.ex
index a0f71fd88..5981e7545 100644
--- a/lib/pleroma/web/activity_pub/side_effects.ex
+++ b/lib/pleroma/web/activity_pub/side_effects.ex
@@ -15,15 +15,17 @@ defmodule Pleroma.Web.ActivityPub.SideEffects do
   # - Add like to object
   # - Set up notification
   def handle(%{data: %{"type" => "Like"}} = object, meta) do
-    Pleroma.Repo.transaction(fn ->
-      liked_object = Object.get_by_ap_id(object.data["object"])
-      Utils.add_like_to_object(object, liked_object)
+    {:ok, result} =
+      Pleroma.Repo.transaction(fn ->
+        liked_object = Object.get_by_ap_id(object.data["object"])
+        Utils.add_like_to_object(object, liked_object)
 
-      Notification.create_notifications(object)
+        Notification.create_notifications(object)
 
-      {:ok, object, meta}
-    end)
-    |> (fn {:ok, res} -> res end).()
+        {:ok, object, meta}
+      end)
+
+    result
   end
 
   # Nothing to do