Hand to Hand Exchange: Swap

Exchange `x NFT` for `y NFT` without payment (except for gas & platform fees).

Use Case

Alice wants to exchange her NFT for Bob's. 1 NFT can be exchanged for 1 NFT.

Process

Alice signs a tx to exchange her x NFT for Bob's y NFT and gives approval to Swap contract to process the exchange. Bob verifies the NFTs in the dApp interface. If approved, he signs an approval for the echange, grants the rights to Swap to process the swap and publishes the whole tx on-chain. The NFTs are exchanged.

Note:

• Publishing and decoding the signature on-chain can fail if:
  • One party no longer owns the NFT
  • One party lacks funds for the platform or gas fees
  • The signature timestamp is too old
  • One party has not signed

Implementation

Flow Explanation

• Frontend dApp checks before signature:
  • NFT ownership
  • Funds for the platform and gas fees
• First signature is saved in the backend
• Second signature pushes both signatures on-chain
• Swap contract:
  • Decodes both signatures
  • Processes the NFT exchange
  • Take platform fee

Technical Details

To sign an exchange, see scripts/signExchange.js - DATA MUST BE EXACTLY THE SAME FOR BOTH PARTIES

Later

• Use Permit2 instead IERC712.approve(...)
• Add platform fee
• Exchange one to many, many to many...
• Both parties can issue the transaction
• ERC20 payment can be introduced during the exchange
• Platform fee is taken on both sides (encoded in the signature)

Deployed Contracts

• v0.1.0 - bsc testnet: 0x8d67dF98c25e202066230cDBaC17D199eEeF53F6
  • users must approve swap contract with either approve(address(swap), id) or setApprovalForAll(address(swap), true)
• v0.1.1 - pass Data structure in clear, instead of encoding it, in Exchange structure
  • bsc testnet: 0xE2A0488B723B2B108485B624598351eC38c9fE67
  • mumbai testnet: 0x5c47DfBe45Dd95a161F620964926D1D728efb974
  • goerli testnet: 0xC7BFe799195117efde14FABa3b456Ea97585F882