Gas fees estimation on connected chains

[fadeev]

Implement a system where a contract on a connected chain A can make an on-chain call (let's say to the Gateway on chain A) to get a fee amount required to make a call to chain B.

Right now, for example, when making a call from chain A to chain B (through ZetaChain, of course), a contract on chain A needs the fee amount to be submitted by a user/end-user app.

On ZetaChain gas fees can be queried from ZRC-20s:

protocol-contracts/contracts/zevm/ZRC20.sol

Lines 280 to 290 in e724622

	function withdrawGasFeeWithGasLimit(uint256 gasLimit) public view override returns (address, uint256) {
	address gasZRC20 = ISystem(SYSTEM_CONTRACT_ADDRESS).gasCoinZRC20ByChainId(CHAIN_ID);
	if (gasZRC20 == address(0)) revert ZeroGasCoin();
	uint256 gasPrice = ISystem(SYSTEM_CONTRACT_ADDRESS).gasPriceByChainId(CHAIN_ID);
	if (gasPrice == 0) {
	revert ZeroGasPrice();
	}
	uint256 gasFee = gasPrice * gasLimit + PROTOCOL_FLAT_FEE;
	return (gasZRC20, gasFee);
	}

I think we need the same functionality to be available on connected chains.

Ideally, the gas fee amount required to make a call to chain B, is reported on chain A in the gas token of chain A.

Gas prices are regularly updated by observer-signer validators and are stored in the crosschain module state:

https://zetachain.blockpi.network/lcd/v1/public/zeta-chain/crosschain/gasPrice

I assume that if we set up a system where this information is transferred to connected chains (either by observer-signer validators, or as a CCTX), it should do the trick.

How other projects are handling this:

• https://docs.axelar.dev/dev/gas-service/pricing/
• https://docs.layerzero.network/v2/developers/evm/protocol-gas-settings/gas-fees

[lumtis]

This is a complex task that also has a tokenomic aspect: how to fund the fees for pushing the gas price.

In most isn't enough for the developer to have access to this value with a query and so set this value from the front-end when performing the deposit?

[fadeev]

It is possible to set the value from the frontend, so I'd say this is a nice to have.