NFT xcm draft design

[shaunxw]

The MultiAsset representation of NFT.

NFT in ORML is represented by MultiAsset::ConcreteNonFungible:

• class: MultiLocation::X2(Junction::Parachain, Junction::GeneralIndex).
  • The parachain id is the id of reserve parachain.
  • The general index is from ClassId in orml-nft.
• instance: AssetInstance::Index.
  • The index is from TokenId in orml-nft.

Sending NFT

Send cross-chain NFT have different scenarios. We use A as parachain 1, B as parachain 2, and R as the reserve chain where NFT issued.

• From chain R to chain A.
  • On reserve chain R:
    • The NFT could only be transferred if not on a chain reserve account (not sent to another chain).
    • The NFT would be transferred from owner to A's reserve account.
  • On A, a NFT could be created under the dest, and a mapping of IDs on R to A would be stored.
• From chain A back to chain R.
  • On A, the created NFT would be removed, along with the mapping.
  • On R, the NFT would be transferred from A's reserve account to dest.
• From chain A to chain B (via R).
  • On A, the created NFT would be removed, along with the mapping.
  • On R, the NFT would be transferred from A's reserve account to B's.
  • On B, a NFT would be created under the dest, and a mapping of IDs on R to B would be stored.

Pseudo XCM

For all cross-chain sending, Alice is the sender and Bob is the receiver.

From chain R to chain A.

Alice.WithdrawAsset {
    assets: nft,
    effects: DepositReserveAsset {
        assets: all,
        dest: A,
        effects: DepositAsset {
            assets: all,
            dest: Bob
        }
    }
}

From chain A to chain R.

Alice.WithdrawAsset {
    assets: nft,
    effects: InitiateReserveWithdraw {
        assets: all,
        reserve: R,
        effects: DepositAsset {
            assets: all,
            dest: Bob
        }
    }
}

From chain A to chain B.

Alice.WithdrawAsset {
    assets: nft,
    effects: InitiateReserveWithdraw {
        assets: all,
        reserve: R,
        effects: DepositReserveAsset {
            assets: all,
            dest: B,
            effects: DepositAsset {
                assets: all,
                dest: Bob
            }
        }
    }
}

[xlc]

Will wait for paritytech/polkadot-sdk#327