[ZK Stack] - How to obtain MAX_TRANSACTION_GAS_LIMIT inside a contract?

[CodeSandwich]

Team or Project

Drips

Module Affected

• System contracts (era-system-contracts)
• Smart contracts (era-contracts)
• zkEVM (era-zk_evm)
• Server (zksync-era)
• Prover (era-boojum)
• Fee withdrawer (era-fee-withdrawer)
• Block Explorer (clock-explorer)
• Portal - Wallet + Bridge (dapp-portal)
• Other (please specify below)

Rust Version

(The GH discussion template enforces unneeded fields, please consider removing them)

Operating System

• Ubuntu
• MacOS
• Windows
• Other (Please specify below)

Issue Description

My smart contract needs to obtain the maximum gas that can be used by a transaction. This is used for throttling usage of an off-chain resource, the gas cost of requesting it goes up with each call increasing the price until the transaction gas limit is reached and the resource can't be used at all until the cooldown ends. On regular EVM chains I'm using block.gaslimit, which is also the single transaction gas limit. In ZKsync it's different, block.gaslimit is the gas limit of the batch and the single transaction is limited by MAX_TRANSACTION_GAS_LIMIT. How can I obtain MAX_TRANSACTION_GAS_LIMIT inside a smart contact? I couldn't find anything in the system contracts, this value seems to exist only in the bootloader, which itself seems unavailable in L2, it's just an address with an empty account behind it.

(edit) I've found "MAX_GAS_PER_TRANSACTION": 80000000, in SystemConfig.json and uint256 constant MAX_GAS_PER_TRANSACTION = 80_000_000; in L1 Config.sol and in a few more places in the era-contracts repository. Does it mean that 80 million is a hardcoded transaction gas limit I could rely on? Is it at risk of being changed in the future?

Expected Behavior

(The GH discussion template enforces unneeded fields, please consider removing them)

Current Behavior

(The GH discussion template enforces unneeded fields, please consider removing them)

Repository Link (if applicable)

No response

Additional Details

No response

Prior Research

• Yes, I searched for similar issues and did not find any matching ones.

[sarahschwartz]

@CodeSandwich great question! I'm not sure if there is a way to dynamically get this value, but I will confirm. I believe you can rely on this value staying consistent unless there is a governance vote to explicitly approve this change on Era. However for other chains in the Elastic Network, this value may be different depending on their configuration.

Edit: confirmed - there is no way to fetch this from inside a contract.

[CodeSandwich]

That's bad, thanks!