How to use ModuleKit to calculate gas consumption of modules

The ModuleKit has an inbuilt helper to granularly calculate the gas costs of UserOperations. For example, it calculates the gas costs of the various phases of the ERC-4337 flow and L2-L1 calldata gas.

Setup

Before using this utility, create a folder called gas_calculations in the root folder of the directory (same level as the src folder) and ensure that you have the right permissions settings set in your foundry.toml file:

fs_permissions = [{ access = "read-write", path = "gas_calculations" }]

Write the test

In the test function(s) that you want to perform, call instance.log4337Gas("identifier") before a UserOperation is executed. This will log the gas used for the UserOperation and use the identifier as the filename for the gas report. Make sure to use a unique identifier for each UserOp, otherwise the gas reports will be overwritten. For example:

// Write gas
instance.log4337Gas("testWriteGas");
 
// Create userOperation
instance.exec({ target: address(1), value: 1 wei, callData: "" });

Run the tests

To run the tests and log gas, run the following command:

GAS=true forge test

Read the gas report

After the tests have finished, the gas reports will be written to the gas_calculations folder in the root of the project. A gas report will look like this:

{
  "Calldata": {
    "Arbitrum": "6504 gas",
    "OP-Stack": "8859 gas"
  },
  "Phases": {
    "Creation": "187_170 gas",
    "Execution": "37_054 gas",
    "Validation": "35_980 gas"
  },
  "Total": "2_550_948 gas"
}

Note that if you re-run gas calculations, then the newest number will be added and every value will be followed by a (diff: ...) that shows the difference, in gas units between the calculations.

Convert the gas units

All numbers are in gas units. To calculate the cost in gwei, follow the instructions below:

On L1: multiply the total gas used by the gas price in gwei: totalGasUsed * gasPrice
On an L2: multiply the total gas used by the L2 gas price in gwei and then add it to to the result of the relevant L2-L1 gas cost muliplied by the L1 gas cost in gwei: totalGasUsed * l2GasPrice + callDataGasUsed * l1GasPrice

Note: if you are calculating the dollar amount of the gas cost, make sure to use the relevant gwei to usd conversions if the L2 has a different gas token to L1.

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