post file with multipart

require 'net/http/post/multipart'

url = URI.parse("https://apitransformer.com/api/transform?output=raml%200.8")
req = Net::HTTP::Post::Multipart.new url,
  "file2" => UploadIO.new(File.new("/Users/yetao/SRPAPI.api"), "SRPAPI.api", "SRPAPI.api")
res = Net::HTTP.start(url.host, url.port,:use_ssl => true) do |http|
  puts req
  puts '----------'
  http.request(req)
end
puts res.body