ton

How can you debug a TON smart contract in FunC and print logs or dump variables?

I'm developing a smart contract for TON blockchain in FunC and I'm trying to find a bug in my code. I'm trying to debug the issue and will appreciate something like console.log() from JavaScript so I can add prints / logs in strategic places and understand what's going on. Can this be done?

Solution

  • The TVM has a special function for dumping variables in debug - ~dump

    Run ~dump(variable_name); to print a variable's contents.

    Run ~dump(12345); to print the number 12345.

    Example:

    () recv_internal(int msg_value, cell in_msg, slice in_msg_body) impure {

  ;; let's say I want to print the value of the variable msg_value
  
  ~dump(msg_value);
}

    Please note that this command will not run on mainnet, so do not deploy production contracts with it. My favorite way to test smart contracts locally is using ton-contract-executor - this awesome library run a local version of the TVM in web-assembly right inside Node.js, which is very convenient for writing JavaScript/TypeScript tests.

    To enable debug prints in ton-contract-executor, when you create your contract instance pass debug: true in SmartContractConfig and print the logs after interacting with the contract:

    import { SmartContract } from "ton-contract-executor";

const contract = await SmartContract.fromCell(codeCell, dataCell, {
  debug: true // enable debug
});

const send = await contract.sendInternalMessage(...);

console.log(send.logs); // print the logs