How can I debug the runtime error when call contract.transfer method in Solidity?

Question

I have launched a private network from Ganache and using truffle to deploy my contract to the network. The deployment works fine and I am able to call some methods from contract. But I got an error when try to transfer ether to another account.

My contract code is:

// SPDX-License-Identifier: MIT
pragma solidity >=0.7.4;
pragma experimental ABIEncoderV2;

contract Ledger {

    mapping(address => uint256) balances;

    address payable owner;

    event Transfered(address _from, address _to, uint256 amount);

    constructor() {
        owner = payable(msg.sender);
        balances[tx.origin] = 10000;
    }

    function sendCoin(address payable receiver, uint256 amount)
        payable public
        returns (bool sufficient)
    {
        require(msg.sender == owner);
        if (balances[msg.sender] < amount) return false;
        balances[msg.sender] -= amount;
        balances[receiver] += amount;
        receiver.transfer(amount);
        emit Transfered(msg.sender, receiver, amount);
        return true;
    }

    function getBalance(address addr) public view returns (uint256) {
        return balances[addr];
    }

    function getBalanceInCoin(address addr)
        public
        view
        returns (uint256)
    {
        return convert(getBalance(addr), 100);
    }

    function convert(uint256 amount, uint256 conversionRate)
        public
        pure
        returns (uint256 convertedAmount)
    {
        return amount * conversionRate;
    }
}

When I run it in truffle console:

truffle(development)> let ledger = await Ledger.deployed()
truffle(development)> let accounts = await web3.eth.getAccounts()
truffle(development)> (await ledger.sendCoin(accounts[1], 50))
Uncaught Error: Returned error: VM Exception while processing transaction: revert
    at evalmachine.<anonymous>:1:17
    at evalmachine.<anonymous>:2:49
    at sigintHandlersWrap (vm.js:273:12)
    at Script.runInContext (vm.js:142:14)
    at runScript (/Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/packages/core/lib/console.js:364:1)
    at Console.interpret (/Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/packages/core/lib/console.js:379:1)
    at bound (domain.js:421:15)
    at REPLServer.runBound [as eval] (domain.js:432:12)
    at REPLServer.onLine (repl.js:909:10)
    at REPLServer.emit (events.js:400:28)
    at REPLServer.emit (domain.js:475:12)
    at REPLServer.Interface._onLine (readline.js:434:10)
    at REPLServer.Interface._line (readline.js:791:8)
    at REPLServer.Interface._ttyWrite (readline.js:1136:14) {
  data: {
    '0xebf4283ab2e7ced42b27b67e8a25c73c7c29e26aa3c86a14c5d6bbaba2c5fc55': { error: 'revert', program_counter: 738, return: '0x' },
    stack: 'RuntimeError: VM Exception while processing transaction: revert\n' +
      '    at Function.RuntimeError.fromResults (/Applications/Ganache.app/Contents/Resources/static/node/node_modules/ganache-core/lib/utils/runtimeerror.js:94:13)\n' +
      '    at BlockchainDouble.processBlock (/Applications/Ganache.app/Contents/Resources/static/node/node_modules/ganache-core/lib/blockchain_double.js:627:24)\n' +
      '    at runMicrotasks (<anonymous>)\n' +
      '    at processTicksAndRejections (internal/process/task_queues.js:93:5)',
    name: 'RuntimeError'
  },
  hijackedStack: 'Error: Returned error: VM Exception while processing transaction: revert\n' +
    '    at Object.ErrorResponse (/Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/node_modules/web3-core-helpers/lib/errors.js:28:1)\n' +
    '    at /Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/node_modules/web3/node_modules/web3-core-requestmanager/lib/index.js:302:1\n' +
    '    at /Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/packages/provider/wrapper.js:107:1\n' +
    '    at XMLHttpRequest.request.onreadystatechange (/Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/node_modules/web3/node_modules/web3-providers-http/lib/index.js:98:1)\n' +
    '    at XMLHttpRequestEventTarget.dispatchEvent (/Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request-event-target.js:34:1)\n' +
    '    at XMLHttpRequest.exports.modules.996763.XMLHttpRequest._setReadyState (/Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:208:1)\n' +
    '    at XMLHttpRequest.exports.modules.996763.XMLHttpRequest._onHttpResponseEnd (/Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:318:1)\n' +
    '    at IncomingMessage.<anonymous> (/Users/joey/.nvm/versions/node/v14.18.0/lib/node_modules/truffle/build/webpack:/node_modules/xhr2-cookies/dist/xml-http-request.js:289:47)\n' +
    '    at IncomingMessage.emit (events.js:412:35)\n' +
    '    at IncomingMessage.emit (domain.js:537:15)\n' +
    '    at endReadableNT (internal/streams/readable.js:1334:12)\n' +
    '    at processTicksAndRejections (internal/process/task_queues.js:82:21)'

As you can see above errors which is from transfer method in sendCoin method. How do I know what the error comes from and how should I fix it?

Answer 1

Debugging with truffle is pain in ass. Specially if you have no previous experience of cli-debugging Although here is their complete guide . This includes everything setting breakpoints, displaying variables, execute and print expressions etc

As a rule of thumb if you are working on a project that involves writing single or two smart contract you may wanna use remix IDE. It is very user friendly and has everything. You can code deploy test debug your smart contracts with great ease.