Nft 721 spec

[ethanfrey]

Closes #43

Define a 721 spec for NFTs, focusing on transfering and ownership.

• Base 721 Spec
• Metadata and Enumeration extensions
• Reflect on TokenUri? (all metadata off-chain)
• How to make MetaData extensible? (not possible with rust unless I use macros, did research)
• Implement Receiver interface
• Implement helpers (wrappers)
• Unify Expiration type with cw20 (and cw1) -> cw0 common repo? (In Add Expration to cw0 #51)

[ethanfrey]

@sunnya97 @okwme

If you have time, I would love your review on this. If can just be the README file, or you can look at the enums in msg.rs and query.rs but feedback on the interfaces would be great. I know both of you have solid experience with ERC721 and it's usage.

Note for extensibility, a contract can return more info than NftInfoResponse on an NftInfo query. But it must return those fields as a base. A client can parse the result with a superset of this struct if it know there are other fields (like "points") in the result. I chose to keep name and description on-chain for a much nicer interface and only the heavy image off-chain.

Please help me refine this one. Also tips on implementing a specific implementation (like allowing a minter) are welcome, even if they don't make it in the spec.

[okwme]

this could be annoying if i want to list the token for sale on multiple platforms at once?i like the idea of better accounting for approvals in general tho.

[ethanfrey]

I had multiple. But then I saw the erc721 spec which only allows exactly one. And figured it is simpler to implement, and they probably had a reason.

I am happy to allow N if you feel this is a real use case (list on multiple exchanges)

[okwme]

can ApproveAll be given to more than one operator at once?

[ethanfrey]

Yes, any number. Again taken from her 721 specs. Not sure why this is unlimited and approval is limited

[okwme]

Looks good! Sorry for comments that I deleted, I ended up answering them myself just by reading more.

querying contracts in general kinda sucks, i appreciate the note about future improvements to pagination. One reason it sucks is cause you have to do stuff like "get total supply, then use total supply to increment through each index requesting token at index n". It would be nice to have pagination instead, but in lieu of pagination at this point is there the fallback alternative? are NFTs stored in a way that you can still query them if you don't know exactly what their ID is?

[ethanfrey]

I would store them in a prefixed db by id. The sdk doesn't expose raw range searches, just raw key searches I can refine this pagination part and then just saw we implement that. It is not too hard, just a wrapper around the iterators.

[ethanfrey]

Thank you for your review. Are you fine with the metadata definition?

Anything else (besides good pagination) you think would really benefit this spec?