Context: https://twitter.com/w1nt3r_eth/status/1556048520783638530
v1 — the goal is to be very simple.
NFTBill is an ERC-1155 contract that holds the assets deposited by the users and hands them out corresponding NFTs.
- To deposit ERC-20s or Ether, the user calls
deposit, the contract transfers the funds and gives the user back an NFT that represents ownership of that asset. - To withdraw, the user calls
withdraw, the NFT will be burned and the asset will be transferred back to the user.
NFTBill supports an arbitrary amount of assets in the same contract (i.e. it's a single NFT collection that has all different asset types in it). However, each NFT can only represent a single asset.
The implementation aims to be very gas-efficient. The ERC-20 contract address (or 0x00..00 for Ether) and the asset balance are encoded in the ERC-1155 NFT token id:
Token ID: 0x95ad61b0a150d79219dcf64e1e6cc01f0b64c4ce 000000000000000000000001
^^^^^^^^^ ERC-20 token address ^^^^^^^^^ ^^^^^^^ Balance ^^^^^^^^
This means we only perform a single SSTORE when depositing or withdrawing the NFT.
Limitations:
- Balances larger than
type(uint96).maxare not supported - Deflating or inflating assets are not supported
To make the protocol permissionless and decentralized, the metadata of the NFTs is stored on-chain (so it doesn't depend on any centralized services).
The metadata contract is upgradeable using OZ transparent upgradeable proxy. It allows us to hotfix rendering bugs, but the long-term plan is to renounce ownership. There's no admin functionality in the main contract.
The metadata should include (see screenshot above):
- Underlying asset address
- Underlying asset name and symbol (via ERC-20
nameandsymbol) - Underlying asset value (formatted honoring ERC-20
decimals) - "Fingerprint" visual symbols that make it easier to differentiate
TODO (maybe?):
- Implement on-chain SVG renderer
- Add a registry of popular coins and render them differently to further deter impostors (e.g. adding logos, using different colors, etc)
- Support approving and depositing data in a single tx (via
permit) - Support
permit-like approvals for gasless withdrawals (might be useful for privacy work later) - Support wrapping other NFTs