code: public InputStream asInputStream() {
          InputStream is = fromStreamOrBufferOrUrl();
          if (is != null) return is;
          String s = fromStringOrReader();
          if (s != null) return streamFrom(s);
          throw resourceUnaccessible();
      }
docs: Returns the resource as an input stream, converting it if necessary.
  <p>
  See the docs of {@linkplain RResult} for notes on data conversion.
  @return input stream