OptionallengthOptionallistingBy default an exported CAR file will include all blocks that make up a directory, and the files that are stored there.
To only include blocks that allow the initial enumeration of the directory,
pass true here
OptionaloffsetInclude blocks that start with this offset.
If the CID being exported is a directory, this option is ignored.
Only include blocks that would include this many file bytes (exclusive, inclusive of offset).
If the CID being exported is a directory, this option is ignored.