From 6bcf558bae6d9b789f904f7ea1b8bcd8ddb3ffc5 Mon Sep 17 00:00:00 2001
From: Alan Guo Xiang Tan <gxtan1990@gmail.com>
Date: Thu, 22 Dec 2022 05:30:06 +0800
Subject: [PATCH] PERF: Stop serializing user in
 `ChatChannelSerializer#current_user_membership` (#19527)

The client already has all the information about the current user so
there is no need for us to be serializing the current `User` object each
time per channel that is preloaded.

In production, profiling shows that this unneeded serializing
adds a roughly 5% overhead to a request.
---
 .../base_chat_channel_membership_serializer.rb       | 12 ++++++++++++
 .../chat/app/serializers/chat_channel_serializer.rb  |  3 ++-
 .../user_chat_channel_membership_serializer.rb       | 11 +----------
 plugins/chat/plugin.rb                               |  1 +
 4 files changed, 16 insertions(+), 11 deletions(-)
 create mode 100644 plugins/chat/app/serializers/base_chat_channel_membership_serializer.rb

diff --git a/plugins/chat/app/serializers/base_chat_channel_membership_serializer.rb b/plugins/chat/app/serializers/base_chat_channel_membership_serializer.rb
new file mode 100644
index 00000000000..90cb7827eed
--- /dev/null
+++ b/plugins/chat/app/serializers/base_chat_channel_membership_serializer.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class BaseChatChannelMembershipSerializer < ApplicationSerializer
+  attributes :following,
+             :muted,
+             :desktop_notification_level,
+             :mobile_notification_level,
+             :chat_channel_id,
+             :last_read_message_id,
+             :unread_count,
+             :unread_mentions
+end
diff --git a/plugins/chat/app/serializers/chat_channel_serializer.rb b/plugins/chat/app/serializers/chat_channel_serializer.rb
index 9193334177d..26f8da8fc04 100644
--- a/plugins/chat/app/serializers/chat_channel_serializer.rb
+++ b/plugins/chat/app/serializers/chat_channel_serializer.rb
@@ -94,7 +94,8 @@ class ChatChannelSerializer < ApplicationSerializer
 
   def current_user_membership
     @current_user_membership.chat_channel = object
-    UserChatChannelMembershipSerializer.new(
+
+    BaseChatChannelMembershipSerializer.new(
       @current_user_membership,
       scope: scope,
       root: false,
diff --git a/plugins/chat/app/serializers/user_chat_channel_membership_serializer.rb b/plugins/chat/app/serializers/user_chat_channel_membership_serializer.rb
index 93e7e5bd85c..18c26222e34 100644
--- a/plugins/chat/app/serializers/user_chat_channel_membership_serializer.rb
+++ b/plugins/chat/app/serializers/user_chat_channel_membership_serializer.rb
@@ -1,15 +1,6 @@
 # frozen_string_literal: true
 
-class UserChatChannelMembershipSerializer < ApplicationSerializer
-  attributes :following,
-             :muted,
-             :desktop_notification_level,
-             :mobile_notification_level,
-             :chat_channel_id,
-             :last_read_message_id,
-             :unread_count,
-             :unread_mentions
-
+class UserChatChannelMembershipSerializer < BaseChatChannelMembershipSerializer
   has_one :user, serializer: BasicUserSerializer, embed: :objects
 
   def user
diff --git a/plugins/chat/plugin.rb b/plugins/chat/plugin.rb
index 2e9b6b4fa6d..dd379b2152e 100644
--- a/plugins/chat/plugin.rb
+++ b/plugins/chat/plugin.rb
@@ -145,6 +145,7 @@ after_initialize do
   load File.expand_path("../app/serializers/structured_channel_serializer.rb", __FILE__)
   load File.expand_path("../app/serializers/chat_webhook_event_serializer.rb", __FILE__)
   load File.expand_path("../app/serializers/chat_in_reply_to_serializer.rb", __FILE__)
+  load File.expand_path("../app/serializers/base_chat_channel_membership_serializer.rb", __FILE__)
   load File.expand_path("../app/serializers/user_chat_channel_membership_serializer.rb", __FILE__)
   load File.expand_path("../app/serializers/chat_message_serializer.rb", __FILE__)
   load File.expand_path("../app/serializers/chat_channel_serializer.rb", __FILE__)