[Help] Unable to estimateUserOperationGas

[Troublor]

Hi, very appreciate this great work.
However, I am trying to use alto on a local testnet and could not make estimateUserOperation json-rpc work. The error message is: Cannot decode zero data ("0x") with ABI parameters..

I investigated the code of alto and found that alto seems to call callExecute function in EntryPoint address during simulateHandleOp:

alto/packages/rpc/src/gasEstimation.ts

Lines 197 to 205 in adb3696

	const targetCallData = encodeFunctionData({
	abi: ExecuteSimulatorAbi,
	functionName: "callExecute",
	args: [userOperation.sender, userOperation.callData, 2_000_000n]
	})
	userOperation.callGasLimit = 0n
	const error = await simulateHandleOp(userOperation, entryPoint, publicClient, true, entryPoint, targetCallData)

I don't think there is a function called callExecute in the entrypoint. Then I notice there is a special parameter in the RPC parameters called finalParam, which seems to instruct the RPC backend to replace the bytecode of entrypoint to a given ExecuteSimulator code.

alto/packages/rpc/src/gasEstimation.ts

Lines 24 to 59 in adb3696

	const finalParam = replacedEntryPoint
	? {
	[userOperation.sender]: {
	balance: toHex(100000_000000000000000000n)
	},
	[entryPoint]: {
	code: ExecuteSimulatorDeployedBytecode
	}
	}
	: {
	[userOperation.sender]: {
	balance: toHex(100000_000000000000000000n)
	}
	}
	try {
	await publicClient.request({
	method: "eth_call",
	params: [
	// @ts-ignore
	{
	to: entryPoint,
	data: encodeFunctionData({
	abi: EntryPointAbi,
	functionName: "simulateHandleOp",
	args: [userOperation, targetAddress, targetCallData]
	}),
	gas: toHex(20_000_000)
	},
	// @ts-ignore
	"latest",
	// @ts-ignore
	finalParam
	]
	})
	} catch (e) {

Is this contract bytecode replacement feature in the Ethereum JSON-RPC standard? Or are you using a customized Ethereum node to handle such RPCs? How can I make this work on a local testnet (e.g., anvil)?

[mouseless0x]

bytecode replacement is part of the Ethereum JSON-RPC spec (using StateOverrides). However not all rpc providers allow state overrides.

Anvil does support code overrides but if your rpc doesn't then you can run alto with the --noEthCallOverrideSupport flag