Technical details about the NFT OmniBridge AMB extension deployed on top of AMB between the Ethereum Mainnet and the xDai chain
This is an early beta version of the NFT OmniBridge AMB extension. The extension allows users to transfer any non-fungible tokens implemented through ERC721 and EIP1155 compatible token contracts from one chain to another.
The extension works with tokens originally deployed on either side of the bridge. It uses the mirroring concept:
A non-fungible token is locked on one side of the bridge - the OmniBridge mediator contract becomes the owner of the token. For EIP1155 tokens it is possible to send several tokens at once.
The new token is minted on the other side of the bridge with the same Token ID and TokenURI. The owner of the new token is by default set to the same account that sent the token to the bridge in the originating transaction (an alternative receiver feature can be used to specify another token owner). The only thing that can be changed in the bridged token is the owner. No other data like the Token URI can be updated on chain.
If the token is bridged back, it is burned and the token with the corresponding Token ID is unlocked on that side of the bridge where the token originated.
A bridged NFTs uniqueness is provided by making a correspondence between the originating token contract and the contact which appears during the transfer of the first token from this contract. An example:
Consider an ERC721 contract A that has an NFT with ID 1. The bridging of this token causes the deployment of a new contract A* and minting of an NFT with ID 1. If later the token with the ID 1 of another ERC721 contract B is transferred through the bridge, a contract B* will be deployed so the token 1 of the contract A* and the token 1 of the contract B* maintain their uniqueness.