Echidna won't start if the ERC20 name or symbol begins with 0x

[ChmielewskiKamil]

The contract below is taken from the NaughtCoin level 15 of the Ethernaut wargame.

// ...
contract NaughtCoin is ERC20 {
    // string public constant name = 'NaughtCoin';
    // string public constant symbol = '0x0';
    // uint public constant decimals = 18;
    uint256 public timeLock = block.timestamp + 10 * 365 days;
    uint256 public INITIAL_SUPPLY;
    address public player;

    constructor(address _player) ERC20("NaughtCoin", "0x0") {
        player = _player;
        INITIAL_SUPPLY = 1000000 * (10**uint256(decimals()));
        _mint(player, INITIAL_SUPPLY);
        emit Transfer(address(0), player, INITIAL_SUPPLY);
    }
// ...

If you import this contract into any Echidna test file, Echidna will freeze with the Starting up, please wait... log (similar to the [#889]).

When run with the --format text flag it returns:

echidna-test: invalid b16 decoding of: "0x0"
CallStack (from HasCallStack):
  error, called at lib/Echidna/Processor.hs:123:31 in echidna-2.0.4-IHy1AKktzUiCzJpHK85UVS:Echidna.Processor

Steps to reproduce the issue

I've prepared an example repository.

1. Clone the repo and cd into it: git clone https://github.com/ChmielewskiKamil/naught-coin.git && cd naught-coin
2. Run Echidna: echidna-test src/TestNaughtCoin.sol --contract TestNaughtCoin --config src/config.yaml
3. This results in: echidna-test: invalid b16 decoding of: "0x0"

As soon as you change the symbol to something different, like so:

// change this
constructor(address _player) ERC20("NaughtCoin", "0x0")

// into this
constructor(address _player) ERC20("NaughtCoin", "ABC")

It starts fuzzing correctly.

If the token's name starts with 0x, it does not work either.

// this won't work
constructor(address _player) ERC20("0xNaughtCoin", "ABC")

This results in the same issue: echidna-test: invalid b16 decoding of: "0xNaughtCoin".

Additional info

This was a bit of a headache to debug as I had no idea about the --format text flag or the format = text option in the config.

This option is mentioned at the end of the FAQ section of the building secure contracts repo. I had this "freezing" problem a couple of times in the past and didn't know how to solve it. Adding the information about this format text debug option in a couple more places would be great for newer users to solve problems on their own.

I would be happy to help update the documentation. I had a couple of ideas where such info could be present:

• Main Echidna README in the Getting Help section
• Main README of the Program Analysis - Echidna section of the building secure contracts repo
• Inside Echidna exercises
• In the wiki, it is not possible to make a PR to the wiki as a contributor tho...

Let me know what you think

Thanks!

[ChmielewskiKamil]

This is a pretty niche use case (symbols and names with 0x) but there are a couple of tokens that use this:

name	symbol
ZRX	0x
0xBTC	0xBitcoin
0XMR	0xMonero
ZXC	0xcert

As I am not entirely sure how the Processor.hs work, the scope of the issue might be bigger than the ERC20 construction.

[ggrieco-tob]

This looks like a legitimate issue and I think I know why it fails. Thanks a lot for the report, we will try to fix it for the next release 😄

[ChmielewskiKamil]

@ggrieco-tob Awesome, thank you!

[ggrieco-tob]

Small reproducer:

contract A {
  string public x = "0xa";
  function f() public returns(string) { return x; }
}