I'm getting "invalid opcode: opcode 0xfe not defined", when trying to estimate the gas fees

Question

I'm trying to estimate gas fees of a contract that I'm about to execute. My code is as follows.

import Web3 from "web3";
const web3 = new Web3();

const estimateGasLimit = async (
  fromAddress: string,
  outputAddress: string,
  amount: number,
  gasPrice: number,
  gasLimit: number,
  chain = 1,
  contractAddress: string
) => {
  const contract = new web3.eth.Contract(minABI, contractAddress, {
    from: fromAddress,
  });

  return await contract.methods.transfer(outputAddress, amount).estimateGas();
};

I'm testing for USDT right now, whose contract address is '0xdac17f958d2ee523a2206206994597c13d831ec7'. It works perfectly for amount 1000000, which is 1 USDT as the decimal for USDT is 6, but fails for 10000000 that is 10 USDT. I get the following error

UnhandledPromiseRejectionWarning: Error: Returned error: invalid opcode: opcode 0xfe not defined
    at Object.ErrorResponse (/home/gaurav/Work/Revamped-Everything/wallet/node_modules/web3-core-helpers/lib/errors.js:28:19)
    at /home/gaurav/Work/Revamped-Everything/wallet/node_modules/web3-core-requestmanager/lib/index.js:288:36
    at XMLHttpRequest.request.onreadystatechange (/home/gaurav/Work/Revamped-Everything/wallet/node_modules/web3-providers-http/lib/index.js:98:13)
    at XMLHttpRequestEventTarget.dispatchEvent (/home/gaurav/Work/Revamped-Everything/wallet/node_modules/xhr2-cookies/dist/xml-http-request-event-target.js:34:22)
    at XMLHttpRequest._setReadyState (/home/gaurav/Work/Revamped-Everything/wallet/node_modules/xhr2-cookies/dist/xml-http-request.js:208:14)
    at XMLHttpRequest._onHttpResponseEnd (/home/gaurav/Work/Revamped-Everything/wallet/node_modules/xhr2-cookies/dist/xml-http-request.js:318:14)
    at IncomingMessage.<anonymous> (/home/gaurav/Work/Revamped-Everything/wallet/node_modules/xhr2-cookies/dist/xml-http-request.js:289:61)
    at IncomingMessage.emit (events.js:327:22)
    at IncomingMessage.EventEmitter.emit (domain.js:506:15)
    at endReadableNT (_stream_readable.js:1220:12)
    at processTicksAndRejections (internal/process/task_queues.js:84:21)

I am very new at ethereum and blockchain, so I would appreciate any help that I could get. Thank you.

Answer 1

An invalid opcode is typically the result of either one of the following runtime operations:

1. assert of an expression which evaluates to false
2. array[i] where i >= array.length
3. Dividing by zero
4. Calling a function which receives an enum parameter as input, and passing it a value larger than that enum's maximum value

It is custom to use require in order to verify user input, and assert in order to avoid executing potential bugs in the code.

Therefore, the SafeMath is typically implemented with require and not with assert.

Unfortunately, some earlier implementations of this library have used assert instead of require, and such is the one implemented in the USDT token contract.

Thus, any of the following operations could trigger an invalid opcode:

    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        ...
        assert(c / a == b);
        ...
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        ...
        uint256 c = a / b;
        ...
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        ...
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        ...
        assert(c >= a);
        ...
    }

As you can see, these functions are called from function transfer, which you are trying to execute:

    function transfer(address _to, uint _value) public onlyPayloadSize(2 * 32) {
        uint fee = (_value.mul(basisPointsRate)).div(10000);
        if (fee > maximumFee) {
            fee = maximumFee;
        }
        uint sendAmount = _value.sub(fee);
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(sendAmount);
        if (fee > 0) {
            balances[owner] = balances[owner].add(fee);
            Transfer(msg.sender, owner, fee);
        }
        Transfer(msg.sender, _to, sendAmount);
    }

The most typical reason for this function to revert is when it is called with an input amount larger the amount owned by the caller, which causes balances[msg.sender].sub(_value) to revert.