How does the bridge work?

Sending a Non-Fungible Token (NFT)

For the purposes of outlining the bridge functionality at a simplistic level, we will make reference to:

• The sending blockchain as the source blockchain

• The receiving blockchain as the target blockchain

Non-fungible tokens are transferred between blockchains via the following steps:

1. NFT locked in source blockchain

NFTs are locked in the source blockchain smart contract / pallet (we will call this the native token)

2. Wrapped NFT minted in source blockchain

A 1:1 representation of the native token is minted as a wrapped token in the target blockchain.

3. Wrapped NFT sent to target blockchain

The wrapped token is then sent to the target blockchain via the below function. (Rust example):

4. Validator signatures checked

The bridge validators listen to bridge-related events via the nodes of the linked blockchains and sign the transactions in the target ledger with their private keys.

5. Validator signatures collected

Once all signatures are confirmed to have come from verified validators, their signatures are collected.

6. BFT threshold calculated

The target blockchain smart contract checks that the BFT threshold of the multisignature is reached.

7. Wrapped NFTs released

Wrapped NFTs are then released to the designated receiver account on the target blockchain.

Be sure to try out the Bridge by clicking on this link.

Other Functions

Transferring Fungible Tokens

function validate_transfer(
		uint128 action_id, 
		uint64 chain_nonce, 
		address to, 
		uint256 value
		) public {
				ValidationRes res = validate_action(action_id, Action.Transfer);
				if (res == ValidationRes.Execute) {
					token.mint(to, chain_nonce, value);
				}
}

Sending Wrapped Fungible Tokens to a target blockchain

function withdraw(
		string memory to, 
		uint64 chain_nonce, 
		uint256 value
		) public {
				token.burn(msg.sender, chain_nonce, value);
				emit Unfreeze(action_cnt, chain_nonce, to, value);
				action_cnt += 1;
	}

Transferring NFTs

function validate_transfer_nft(
	uint128 action_id, 
	address to, 
	string calldata data
	) public {
		ValidationRes res = validate_action(action_id, Action.TransferUnique);
		if (res == ValidationRes.Execute) {
			token.mint(to, nft_cnt, 1);
			nft_cnt += 1;
			token.setURI(nft_cnt, data);
		}
	}

Locking a native token & sending its wrapped quantity to a target blockchain

function freeze(uint64 chain_nonce, string memory to) public payable {
		require(msg.value > 0, "value must be > 0!");
		emit Transfer(action_cnt, chain_nonce, to, msg.value);
		action_cnt += 1;
}