`validTransition` in NitroAdjudicator

[andrewgordstewart]

In order to validate transitions from the client wallet, the NitroAdjudicator should expose Rules.validTransition.

The naive method

    function validTransition(
        Commitment.CommitmentStruct memory agreedCommitment,
        Commitment.CommitmentStruct memory challengeCommitment
    ) public pure returns (bool) {
        return Rules.validTransition(agreedCommitment, challengeCommitment);
    }

seems to require an infinite amount of gas to deploy. I've managed to exceed 8 000 000 000 -- the gas limit on mainnet is currently around 8 000 000.

Setting the gas limit to a googol causes the migrations script to fail silently, perhaps due to truffle or ganache not properly handling numbers greater than 2^256.

The following method, with an unused Signature[] memory argument, works, requiring ~6500000 gas

    function validTransition(
        Commitment.CommitmentStruct memory agreedCommitment,
        Commitment.CommitmentStruct memory challengeCommitment,
        Signature[] memory unusedArg
    ) public pure returns (bool) {
        return Rules.validTransition(agreedCommitment, challengeCommitment);
    }

The following method, with an unused uint[] memory argument also uses at least 8 billion gas:

    function validTransition(
        Commitment.CommitmentStruct memory agreedCommitment,
        Commitment.CommitmentStruct memory challengeCommitment,
        uint[] memory unusedArg
    ) public pure returns (bool) {
        return Rules.validTransition(agreedCommitment, challengeCommitment);
    }

I thought perhaps any array of an arbitrary user-defined struct would work, but this one also uses at least 8 billion gas.

    struct SimpleStruct {
        bool flag;
    }

    function validTransition(
        Commitment.CommitmentStruct memory agreedCommitment,
        Commitment.CommitmentStruct memory challengeCommitment,
        SimpleStruct[] memory unusedArg
    ) public pure returns (bool) {
        return Rules.validTransition(agreedCommitment, challengeCommitment);
    }

[andrewgordstewart]

Note that in order to allow more gas usage in contract deployments, you need to both

• increase the gasLimit when you start ganache, which sets the block gas limit of the network
• increase the gas config option in truffle, which sets how much gas is sent with a transaction by truffle deploys

I patched my local version of magmo-devtools to increase the gasLimit to 8000000000, and also set it to an obscenely high number.

[andrewgordstewart]

I've recorded a couple of the above examples in the solidity-bug branch. Note that the block-gas-limit is the default truffle/ganache value of 6721975. Deploying the TestNitroAdjudicator does use almost that much gas.