retry in streaming response causes corrupt downloads

[jstanley0]

If a socket error occurs while performing a streaming download via the response block provided to transport_request, a retry may cause the response block may be invoked a second time.

For code patterns like this one:

  open('some_file', 'wb') do |io|
    http.request(...) do |response|
      response.read_body do |chunk|
        io.write chunk
      end
    end
  end

The output file will be corrupted since some portion of its data near the beginning will be duplicated.