title: Saving decoded Protobuf content
body: <p>I'm trying to setup a .py plugin that will save decoded Protobuf responses to file, but whatever I do, the result is always file in byte format (not decoded). I have also tried to do the same by using "w" in Mitmproxy - although on screen I saw decoded data, in the file it was encoded again.
  Any thoughts how to do it correctly?</p>
  
  <p>Sample code for now:</p>
  
  <pre><code>import mitmproxy
  def response(flow):
      # if flow.request.pretty_url.endswith("some-url.com/endpoint"):
      if flow.request.pretty_url.endswith("some-url.com/endpoint"):
          f = open("test.log","ab")
          with decoded(flow.response)
              f.write(flow.request.content)
              f.write(flow.response.content)
  </code></pre>