Add piece expects piece to be truncated to padded size

[pyropy]

Description

I'm unsure if current rust implementation of add_piece is intended to be compatible with lotus or lotus ways of adding new piece but it seems to be vastly different from lotus implementation.

When calling add_piece, it seems like the data needs to be fr32 padded and truncated to padded size (zeroes appended to the right side of the piece.

When calling add_piece where payload size is 1166 B, unpadded piece size is 2032 B and padded piece size is 2048 B I get following error

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: add_piece: invalid bytes amount written'

.. with only 1174 B of unpadded data written to the output car file during `add_piece.

Acceptance criteria

• Being able to add piece without needing to previously pad and or truncate file to padded size

Risks + pitfalls

• Possibly breaking current implementations using this add_piece implementation

Where to begin

This is where the error happens

[vmx]

IIRC there was a discussion about the API back in the days. It was decided that Lotus hands a piece in the correct shape to the proofs system. I don't see a need that the APIs need to match, as Lotus operates on a higher level than the proofs system.

[pyropy]

@vmx Thanks for reply, that makes sense. So lotus will assemble a sector and hand it off to the rust add_piece implementation?