how to parse string indexed from event

[yashtbc]

hi. the way I usually get event params is by declaring an interface and then doing interface.parseLogs(log) on it.

in this case, where the event contains a string indexed, the output is quite different

• the event

event Lock(address indexed user, uint256 amount, string indexed username);

• parsed log args

[           
  '0x1B444446eC828A5cDC8f4c2ab92A9A0DF2095fAE',
  BigNumber { _hex: '0x09a715a8', _isBigNumber: true },
  {
    _isIndexed: true,
    hash: '0xb40123284ea5c832806ac2203e1a779a0b866247d161403705d68cbba78e8a9b',
    constructor: [Function: Indexed] { isIndexed: [Function (anonymous)] }
  }
]

how do I get the username param?

[zemse]

The event indexing works by having a upto 4 bytes32 topics which can be included in the filter. A string value is dynamic and doesn't fit in bytes32 so solidity hashes it so it fits in the bytes32. Basically getting the username param would be finding the preimage of the hash function, which doesn't seem something you can do with keccak256 practically.

You may switch the string type to bytes32, it will limit the username to 32 length (which can be reasonable). If it's necessary to stick with string you can include it again.

event Lock(address indexed user, uint256 amount, string indexed usernameTopic, string username);

[yashtbc]

alright! thanks for the answer 🙏