From 06eaf9e546ed98a0f8dba86ea8f9b163cd2b6dfe Mon Sep 17 00:00:00 2001
From: Rafal Studnicki <rafal@whatnot.com>
Date: Tue, 8 Aug 2023 17:54:53 +0200
Subject: [PATCH] Add description on how to use MFA for socket drainer config

---
 lib/phoenix/endpoint.ex | 8 ++++++--
 lib/phoenix/socket.ex   | 2 +-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/lib/phoenix/endpoint.ex b/lib/phoenix/endpoint.ex
index 5514569702..3885f95b83 100644
--- a/lib/phoenix/endpoint.ex
+++ b/lib/phoenix/endpoint.ex
@@ -807,8 +807,12 @@ defmodule Phoenix.Endpoint do
     * `:code_reloader` - enable or disable the code reloader. Defaults to your
       endpoint configuration
 
-    * `:drainer` - a keyword list configuring how to drain sockets
-      on application shutdown. The goal is to notify all channels (and
+    * `:drainer` - a keyword list or a custom MFA function returning a keyword list, for example:
+
+          {MyAppWeb.Socket, :drainer_configuration, []}
+
+      configuring how to drain sockets on application shutdown.
+      The goal is to notify all channels (and
       LiveViews) clients to reconnect. The supported options are:
 
       * `:batch_size` - How many clients to notify at once in a given batch.
diff --git a/lib/phoenix/socket.ex b/lib/phoenix/socket.ex
index c3324bbe95..f8dec6bfed 100644
--- a/lib/phoenix/socket.ex
+++ b/lib/phoenix/socket.ex
@@ -454,7 +454,7 @@ defmodule Phoenix.Socket do
         end
         {Phoenix.Socket.PoolDrainer, {endpoint, handler, drainer}}
     else
-        :ignore
+      :ignore
     end
   end