Estimate Gas Limit Workaround

[jettblu]

Hi! I recently encountered a 'cannot estimate gas; transaction may fail or may require manual gas limit' error when attempting to estimate the gas limit for a call to the 0x exchange contract.

This error is caused by execution reverting due to an insufficient token allowance. However, as part of the wallet flow, the token allowance is set after estimating the swap gas limit. Is there a parameter that forces the node to estimate the gas limit regardless of whether the call reverts? Of course, a manual gas limit is always possible (but rarely desirable).

[jettblu]

Also, this error (for the same sequence of calls) did not appear before the merge. I wonder if the software update changed how nodes estimate gas.

[zemse]

the token allowance is set after estimating the swap gas limit.

The estimation should be done after the token allowance tx is confirmed. Currently, there is no standard way to estimate gas before the token approve tx.

Currently there are talks to add eth_batchEstimateGas, this will enable a standard way to estimate gas for the interaction without having the allowance tx confirmed.

However, there is a very hacky/advanced way that can be only used in geth. Basically, geth allows include state overrides, so it can possible for someone to override the "allowance" slot to a larger value so that when the gas is estimated then the allowance check will pass. To get the storage slots eth_createAccessList can be helpful.

this error (for the same sequence of calls) did not appear before the merge

That's weird, the behavior should not have changed.

[jettblu]

Thanks for the thorough reply. I did not know about the recent proposal to add eth_bathEstimateGas to Geth. Looks like many folks have already mentioned this specific situation in support of the proposal.