code: func GuessJSONStream(r io.Reader, size int) (io.Reader, []byte, bool) {
  	buffer := bufio.NewReaderSize(r, size)
  	b, _ := buffer.Peek(size)
  	return buffer, b, hasJSONPrefix(b)
  }
docs: // GuessJSONStream scans the provided reader up to size, looking
  // for an open brace indicating this is JSON. It will return the
  // bufio.Reader it creates for the consumer.