From 059df83d1dcabb27d2e638b4835791bd570ec779 Mon Sep 17 00:00:00 2001
From: Eugen Rochko <eugen@zeonfederated.com>
Date: Wed, 5 May 2021 19:44:35 +0200
Subject: [PATCH] Fix database serialization failure returning HTTP 500
 (#16101)

Database serialization failure occurs when a read-replica is used
and a query takes long enough that rows on the primary database
become unavailable. It should return HTTP 503 as it is temporary.

Re-order rescue definitions according to their status codes
---
 app/controllers/application_controller.rb | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 6361d4b27..b4fb83661 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -18,17 +18,16 @@ class ApplicationController < ActionController::Base
   helper_method :use_seamless_external_login?
   helper_method :whitelist_mode?
 
-  rescue_from ActionController::RoutingError, with: :not_found
-  rescue_from ActionController::InvalidAuthenticityToken, with: :unprocessable_entity
-  rescue_from ActionController::UnknownFormat, with: :not_acceptable
-  rescue_from ActionController::ParameterMissing, with: :bad_request
-  rescue_from Paperclip::AdapterRegistry::NoHandlerError, with: :bad_request
-  rescue_from ActiveRecord::RecordNotFound, with: :not_found
+  rescue_from ActionController::ParameterMissing, Paperclip::AdapterRegistry::NoHandlerError, with: :bad_request
   rescue_from Mastodon::NotPermittedError, with: :forbidden
-  rescue_from HTTP::Error, OpenSSL::SSL::SSLError, with: :internal_server_error
-  rescue_from Mastodon::RaceConditionError, Seahorse::Client::NetworkingError, Stoplight::Error::RedLight, with: :service_unavailable
+  rescue_from ActionController::RoutingError, ActiveRecord::RecordNotFound, with: :not_found
+  rescue_from ActionController::UnknownFormat, with: :not_acceptable
+  rescue_from ActionController::InvalidAuthenticityToken, with: :unprocessable_entity
   rescue_from Mastodon::RateLimitExceededError, with: :too_many_requests
 
+  rescue_from HTTP::Error, OpenSSL::SSL::SSLError, with: :internal_server_error
+  rescue_from Mastodon::RaceConditionError, Seahorse::Client::NetworkingError, Stoplight::Error::RedLight, ActiveRecord::SerializationFailure, with: :service_unavailable
+
   before_action :store_current_location, except: :raise_not_found, unless: :devise_controller?
   before_action :require_functional!, if: :user_signed_in?