code: private void internalWrite(byte[] b, int off, int len, boolean finish) throws IOException {
          coder.output = embiggen(coder.output, coder.maxOutputSize(len));
          if (!coder.process(b, off, len, finish)) {
              throw new Base64DataException("bad base-64");
          }
          out.write(coder.output, 0, coder.op);
      }
docs: Write the given bytes to the encoder/decoder.
  
  @param finish true if this is the last batch of input, to cause
  encoder/decoder state to be finalized.