code: @SneakyThrows(StreamSegmentException.class)
      public void append(SegmentHandle handle, InputStream data, int length) {
          ensurePreconditions();
          Preconditions.checkArgument(!handle.isReadOnly(), "Cannot append using a read-only handle.");
          getStreamSegmentData(handle.getSegmentName()).append(data, length);
      }
docs: Appends the given data to the end of the StreamSegment.
  Note: since this is a custom operation exposed only on InMemoryStorage, there is no need to make it return a Future.
  
  @param handle A read-write handle for the segment to append to.
  @param data   An InputStream representing the data to append.
  @param length The length of the data to append.