dNFT: a smart contract for derivative NFTS

This contract is a part of DeFi & Cross-chain Interoperability Hackathon submission that consists of two parts:

• a cw721 contract with metadata extension, this repository
• front-end dApp

This cw721-compatible contract that allows minting, storing and acessing derivative NFTs.

Build

Install cargo-generate and cargo-run-script. Unless you did that before, run this line now:

cargo install cargo-generate cargo-run-script --features vendored-openssl

To build a wasm and optimize it for deployment run:

cargo wasm
cargo run-script optimize

Deploy

For step-by-step deployment instructions see the dApp repository.

Implementation details

On-chain storage of derivative NFTs

This contract introduces a new DerivativeNft struct field in the Metadata extension. It stores the method used to derive a new NFT, parameters and an ordered list input NFTs used to generate a derivative NFT.

#[derive(Serialize, Deserialize, Clone, PartialEq, JsonSchema, Debug, Default)]
pub struct DerivativeNft {
    // The name of the algorithm used to generate a derivative NFT. Currently it can only be 'styletransfer'
    pub method: String, 
    // Parameters of the generation (e.g. stylization intensity, neural network model used, etc. )
    pub params: Option<String>, 
    // A list of tokein_id of input NFTs fed into the algorithm
    pub source_ids: Vec<String>, 
}

// see: https://docs.opensea.io/docs/metadata-standards
#[derive(Serialize, Deserialize, Clone, PartialEq, JsonSchema, Debug, Default)]
pub struct Metadata {
    pub image: Option<String>,
    pub image_data: Option<String>,
    pub external_url: Option<String>,
    pub description: Option<String>,
    pub name: Option<String>,
    pub attributes: Option<Vec<Trait>>,
    pub background_color: Option<String>,
    pub animation_url: Option<String>,
    pub youtube_url: Option<String>,
    pub derivative: Option<DerivativeNft>,
}

Sample metadata:

{
    "token_uri": null,
    "extension": {
        "image": null,
        "image_data": null,
        "external_url": "https://infura-ipfs.io/ipfs/QmWjPeJW8oXo6vF7Ry4zcyoaYa2q5qp6cEnGHEmqZRytkw",
        "description": null,
        "name": null,
        "attributes": null,
        "background_color": null,
        "animation_url": null,
        "youtube_url": null,
        "derivative": {
            "method": "styletransfer",
            "params": "inception:original:96:256:284",
            "source_ids": [
                "f1_f9",
                "78022_f9"
            ]
        }
    }
}

To access extension data a MetaAccess trait was added introduced:

pub trait MetaAccess {
    fn is_derivative(&self) -> bool;
    fn get_metadata(&self) -> &Metadata;
}

impl MetaAccess for Extension {
    fn is_derivative(&self) -> bool {
        if self.is_some() {
            self.as_ref().unwrap().derivative.is_some()
        } else {
            false
        }
    }
    fn get_metadata(&self) -> &Metadata {
        self.as_ref().unwrap()
    }
}

Minting NFTs

There are two kinds of NFTs that can be minted by this contract:

• "original" NFTs
• derivative NFTs

"Original" NFTs can be minted only by minter specified during contract's initizalization in InstantiateMsg. Derivative NFTs can be minted by any NFT owner if they own all NFTs listed in DerivativeNft.source_ids. Upon receiving mint message the contract checks this that this condition is fulfilled.