This method is deprecated or moved on the latest stable version. The last existing version (v2.3.8) is shown here.
server_software()
Returns the lowercase name of the HTTP server software.
# File actionpack/lib/action_controller/request.rb, line 256 def server_software (@env['SERVER_SOFTWARE'] && /^([a-zA-Z]+)/ =~ @env['SERVER_SOFTWARE']) ? $1.downcase : nil end