code: protected void prepareIO() {
          // we assume that everything in ByteArray is in AMF3
          Input input = new Input(data);
          input.enforceAMF3();
          dataInput = new DataInput(input);
          Output output = new Output(data);
          output.enforceAMF3();
          dataOutput = new DataOutput(output);
      }
docs: Create internal objects used for reading and writing.