code: public BlockInStream getInStream(long blockId, InStreamOptions options) throws IOException {
      return getInStream(blockId, options, ImmutableMap.of());
    }
docs: Gets a stream to read the data of a block. This method is primarily responsible for
  determining the data source and type of data source. The latest BlockInfo will be fetched
  from the master to ensure the locations are up to date.
  
  @param blockId the id of the block to read
  @param options the options associated with the read request
  @return a stream which reads from the beginning of the block