Content-Length: 0 for 304 responses with empty body

Describe the bug We are seeing 304 response with empty body and content-length: 0. Not sure if this is expected, or a bug.

Our clients are not handling it well (probably because of a bug on our side), but looking at the HTTP specs it looks like the server should not send the header (or send the the content-length for the original response)? not sure if i'm reading it correctly or if this is the latest spec, though.

Puma config:

# puma.rb

port 3000
threads 3, 5

To Reproduce

# hello.ru
run lambda { |env| [304, {"Content-Type" => "text/plain"}, []] }

Run it with:

bundle exec puma -C puma.rb hello.ru

Expected behavior

Was expecting that doing curl -s -D - 'http://localhost:3000' would return no content-length header

Desktop (please complete the following information):

• OS: Mac
• Puma Version: 8.0.2
• Ruby Version: 3.4.8