Requires Ruby 2.0+.
rack_http_preload is only compatible with Rack apps that provide a response object. This response object should be compatible with Rack::Response, namely it should provide response.headers=.
require "rack"
class MyTestRackApp
include RackHttpPreload
attr_accessor :response
def call(env)
self.response = Rack::Response.new("Hello World!", 200, {})
# If MIME::Types is available, this gem guesses the appropriate `as` and `type`
http_preload "application.js"
response.finish
end
# "Link"=>"<application.js>; rel=preload; as=script"
end