class Grape::ServeStream::SendfileResponse

for using Rack::SendFile middleware
Response should respond to to_path method

def respond_to?(method_name, include_all = false) 

def respond_to?(method_name, include_all = false)
  return @body.respond_to?(:to_path, include_all) if method_name == :to_path
  super
end

def to_path 

def to_path
  @body.to_path
end