Cache storage variables to local variables to save gas

[code423n4]

Handle

shw

Vulnerability details

Impact

In general, if a state variable is read more than once, caching its value to a local variable and reusing it will save gas since a storage read spends more gas than a memory write plus a memory read.

Proof of Concept

Referenced code:
TransactionManager.sol#L122-L125
TransactionManager.sol#L254-L260

Recommended Mitigation Steps

Rewrite #L122-L125 as follows:

uint256 balance = routerBalances[msg.sender][assetId];
require(balance >= amount, "removeLiquidity: INSUFFICIENT_FUNDS");

// Update router balances
routerBalances[msg.sender][assetId] = balance - amount;

Rewrite #L254-L260 as follows:

uint256 balance = routerBalances[invariantData.router][invariantData.receivingAssetId];
require(
    balance >= amount,
    "prepare: INSUFFICIENT_LIQUIDITY"
);

// Decrement the router liquidity
routerBalances[invariantData.router][invariantData.receivingAssetId] = balance - amount;

[sanchaymittal]

connext/monorepo#34