class Rack::Builder

run Heartbeat.new

end
end
[200, { "content-type" => "text/plain" }, ["OK"]]
def call(env)
class Heartbeat

You can also provide a class instance:

run lambda { |env| [200, { "content-type" => "text/plain" }, ["OK"]] }

You can also provide a lambda:

end
[200, { "content-type" => "text/plain" }, ["Hello World!"]]
run do |env|

You can use a block:

returns a Rack response.
Takes a block or argument that is an object that responds to #call and

def run(app = nil, &block)
  raise ArgumentError, "Both app and block given!" if app && block_given?
  @run = app || block
end