Oraclize callback not firing on Ropsten

Question

Testing out oraclize for a smart contract.

function __callback(bytes32 _myid, string result) public {
   if (msg.sender != oraclize_cbAddress()) revert();
    // emit LogOraclizeID(bytes32ToString(_myid));
    // string memory number = result[0].data;
    emit LogQueryEvent("Are we firing here boys?");
    emit LogRandomNumber(result);
}

// This is NOT truly random. Just a proxy for basic testing.
function random() public payable returns (uint) {
    if (oraclize_getPrice("WolframAlpha") > address(this).balance) {
        emit LogQueryEvent("Please send some ETH along to make transaction.");
    } else {
        // string memory numTokensToString = uint2str(tokens.length);
        // string memory queryString = "random number between 0 and ".toSlice().concat(numTokensToString.toSlice());
        // oraclize_query("WolframAlpha", "random number between 0 and 2"); 
        emit LogQueryEvent("Oraclize query was sent, standing by for the answer..");

        oraclize_query("WolframAlpha", "random number between 0 and 2");

    }
    // return uint(keccak256(abi.encodePacked(block.difficulty, now, tokens.length)));

}

Trying to improve randomness on a particular contract. The __callback doesn't appear to fire. Testing this in remix.

Is this an issue with how I'm setting up the call, or a limitation of remix?

Answer 1

To receive a __callback() you need to have the infrastructure of Oraclize running on the same chain. If you using remix you probably using a memory chain, and everytime you refresh the browser its wiped. You need to use Ropsten for that work, or use a ethereum bridge with oraclize.

The simpliest way is using the IDE provided by Oraclize: http://dapps.oraclize.it/browser-solidity/#gist=9817193e5b05206847ed1fcd1d16bd1d&version=soljson-v0.4.25+commit.59dbf8f1.js that would use a memory chain with oraclize supported.

If you need further, you can use https://github.com/oraclize/ethereum-bridge to enable your private ethereum network interfacing with oraclize.

Answer 2

Looks like this is an issue with remix communicating directly with Oraclize.

I built a basic frontend app to watch events on a Ropsten deployed contract, and they showed up as expected in console.