Solidity – How to Test Integer Overflow in Smart Contracts

overflowsoliditytruffle

Good afternoon!

I have a question regarding testing Integer overflows with truffle.

The contract method is:

function sumNumbers(uint256 numberA, uint256 numberB) public view returns(uint256) {
    return numberA.add(numberB);
}

My test code is as follows:

    it('the sum should not overflow', async () => {
        try {
            // Trying to sum 2^256 + 5, which should overflow and throw an exception in the best case
            const sumResult = await _erc20.sumNumbers(2e256, 5);
            assert.ok(false, 'The contract should throw an exception to avoid overflowing and thus making bad calculations')
        } catch(error) {
            assert.ok(true, 'The contract is throwing which is the expected behaviour when you try to overflow')
            console.log(error);
        }
    })

The test result is as follows:

RangeError: Invalid array length
at Object.padLeft (/app/node_modules/truffle/build/webpack:/~/web3/lib/utils/utils.js:81:1)
at SolidityTypeUInt.formatInputInt [as _inputFormatter] (/app/node_modules/truffle/build/webpack:/~/web3/lib/solidity/formatters.js:40:1)
at SolidityTypeUInt.SolidityType.encode (/app/node_modules/truffle/build/webpack:/~/web3/lib/solidity/type.js:188:1)
at /app/node_modules/truffle/build/webpack:/~/web3/lib/solidity/coder.js:91:1
at Array.map (<anonymous>)
at SolidityCoder.encodeParams (/app/node_modules/truffle/build/webpack:/~/web3/lib/solidity/coder.js:90:1)
at SolidityFunction.toPayload (/app/node_modules/truffle/build/webpack:/~/web3/lib/web3/function.js:92:1)
at SolidityFunction.call (/app/node_modules/truffle/build/webpack:/~/web3/lib/web3/function.js:131:1)
at SolidityFunction.execute (/app/node_modules/truffle/build/webpack:/~/web3/lib/web3/function.js:260:1)
at /app/node_modules/truffle/build/webpack:/packages/truffle-contract/contract.js:135:1
at new Promise (<anonymous>)
at /app/node_modules/truffle/build/webpack:/packages/truffle-contract/contract.js:126:1

I just can't figure out what is going wrong, except when I change the value 2e256 to a much lower value, say 5, I don't get this error.

Can anyone help me with this case?

Best Answer

Argument numberA of a function sumNumbers has a data type uint256. Maximum value that numberA can store is 2^256-1.

As numberA cannot store a number greater than 2^256-1 you are getting the error.

As @smax correctly pointed out in javascript 2e10 is 20000000000. You should use bignumber.js for passing a value as an argument to a function.

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