From 675e40c32684a7e89987673b82b5241545763fcb Mon Sep 17 00:00:00 2001
From: Mike Perham <mperham@gmail.com>
Date: Thu, 30 Jan 2020 08:52:31 -0800
Subject: [PATCH] Don't calculate Content-Length, let Rack do that for us;
 fixes #4440

---
 Changes.md                     | 5 +++++
 lib/sidekiq/web/application.rb | 8 +++-----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/Changes.md b/Changes.md
index 15fe384f1..de5a411bb 100644
--- a/Changes.md
+++ b/Changes.md
@@ -2,6 +2,11 @@
 
 [Sidekiq Changes](https://github.com/mperham/sidekiq/blob/master/Changes.md) | [Sidekiq Pro Changes](https://github.com/mperham/sidekiq/blob/master/Pro-Changes.md) | [Sidekiq Enterprise Changes](https://github.com/mperham/sidekiq/blob/master/Ent-Changes.md)
 
+HEAD
+---------
+
+- Fix broken Web UI response when using NewRelic and Rack 2.1.2+. [#4440]
+
 6.0.4
 ---------
 
diff --git a/lib/sidekiq/web/application.rb b/lib/sidekiq/web/application.rb
index 6b6e961ad..795154972 100644
--- a/lib/sidekiq/web/application.rb
+++ b/lib/sidekiq/web/application.rb
@@ -300,22 +300,20 @@ def call(env)
 
       resp = case resp
       when Array
+        # redirects go here
         resp
       else
+        # rendered content goes here
         headers = {
           "Content-Type" => "text/html",
           "Cache-Control" => "no-cache",
           "Content-Language" => action.locale,
           "Content-Security-Policy" => CSP_HEADER,
         }
-
+        # we'll let Rack calculate Content-Length for us.
         [200, headers, [resp]]
       end
 
-      resp[1] = resp[1].dup
-
-      resp[1][CONTENT_LENGTH] = resp[2].sum(&:bytesize).to_s
-
       resp
     end