feat(protocol): redesign Bridge fee & gasLimit and remove 2-step processing

[dantaik]

Objectives

• Allow users to specify the message's fee to a large value without worrying about that all the fees will be taken by the relayer. The relayer should only make a small profit if the block's base fee is smaller than the message's specified max fee per gas, which is message.fee /message.gasLimit; the relayer will also only charge for the actual gas used.

• Allow the relayer to make simple decision regarding whether it should process a message: if block.basefee <= message.fee /message.gasLimit, process the message, otherwise, no.

• Allow the relayer to use a really large gas limit to transact processMessage without worrying about the actual invocation will eat all gas. The relayer can also simply just use message.gasLimit as the gas limit for his processMessage call, or with a reasonable overhead.

Modifications

• removed two step processing to simplify design/impl, remove suspend message feature.

• message.refundTo is deprecated, the destOwner field is used instead.

• gasLimit no longer means the invocation gas limit, it covers the entire processMessage call. The gas limit for the message invocation is calculated as:

   invocationGasLimit = message.gasLimit - gasDeductedForCallData - _GAS_RESERVE

  • gasDeductedForCallData is the call data gas reseve for the message struct itself, we reserve 32 gas per byte as a message may be processed in two steps.

  • _GAS_RESERVE is a constant value, all processing gas cost will use this part of gas reserve, including the calldata for proof.

    The new implementation ensures even if the relayer specific a large gas limit for his processMessage transaction, the actual invocation will only use up to invocationGasLimit gas.

    @cyberhorsey To calculate the proper message.gasLimit, the relayer can use Bridge.getMessageMinGasLimit(message) + expectedInvocationGasLimit.

• refund 20000 gas per cache operation.

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[openzeppelin-code]

feat(protocol): redesign Bridge fee & gasLimit and remove 2-step processing

Generated at commit: 0ea90a98046754a361bae51c194bbfabfde438a4

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	2 2 0 4 39 47
Dependencies	Critical High Medium Low Note Total	0 0 0 0 0 0

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For more details view the full report in OpenZeppelin Code Inspector

[dantaik]

@Brechtpd please take another look.

I'm considering the removal two-step processing. The goal of introducing this feature is to handle bridge bugs, but its very existence may introduce its own bugs....

See #16744

[Brechtpd]

Will go over the code again later today, but everything looks good so approving so I'm not blocking anything.