LESSON 9: -VRFCoordinatorV2Mock.fulfillRandomWords question

[AlexK020908]

In the unit test following the video, we used the mock to call fulfillRandomWords

                  const tx = await raffle.performUpkeep("0x")
                      const txReceipt = await tx.wait(1)
                      await VRFCoordinatorV2Mock.fulfillRandomWords(
                          txReceipt.events[1].args.requestId,
                          raffle.address
                      )

after calling this we waited for the winnerpicked event , which would set the winner. But looking at the code in the mock contract, the fullfillrandomwords does not assign winner to a winner var, so how does

const recentwinner = await raffle.getRecentWinner()

return a winner that is not undefined?

VRFMock fullfillrandomwords function:

function fulfillRandomWords(uint256 _requestId, address _consumer) external {
    uint256 startGas = gasleft();
    if (s_requests[_requestId].subId == 0) {
      revert("nonexistent request");
    }
    Request memory req = s_requests[_requestId];

    uint256[] memory words = new uint256[](req.numWords);
    for (uint256 i = 0; i < req.numWords; i++) {
      words[i] = uint256(keccak256(abi.encode(_requestId, i)));
    }

    VRFConsumerBaseV2 v;
    bytes memory callReq = abi.encodeWithSelector(v.rawFulfillRandomWords.selector, _requestId, words);
    (bool success, ) = _consumer.call{gas: req.callbackGasLimit}(callReq);

    uint96 payment = uint96(BASE_FEE + ((startGas - gasleft()) * GAS_PRICE_LINK));
    if (s_subscriptions[req.subId].balance < payment) {
      revert InsufficientBalance();
    }
    s_subscriptions[req.subId].balance -= payment;
    delete (s_requests[_requestId]);
    emit RandomWordsFulfilled(_requestId, _requestId, payment, success);
  }

My guess:
is it because we override fullfillrandomwords in raffle.sol? But we are still calling the method on the mock, so I am confused on which fullfillrandomwords() function it will run. I thought the method will correspond to the object called on..

[krakxn]

I can answer "is it because we override fullfillrandomwords in raffle.sol? But we are still calling the method on the mock, so I am confused on which fullfillrandomwords() function it will run. I thought the method will correspond to the object called on.." if you send your VRFCoordinatorV2Mock contract.

[alymurtazamemon]

@AlexK020908 We are calling a fulfillRandomWords of mock contract that will pass the uint256[] memory randomWords array that contains the numbers to our fulfillRandomWords function. And because we only have requested 1 random word that is the reason we are getting number from this array at index 0. We are further doing a calculation and converting it to the index number of a winner and based on that index number getting a winner from the player's array and assigning it to recentWinner variable.

Hope it clears your query.

[AlexK020908]

Hi, thanks for the answer, but I am still confused on where in the fullfillRandomWords in the mock contract function call our fulfillRandomWords function?

[AlexK020908]

is it this line?

 bytes memory callReq = abi.encodeWithSelector(v.rawFulfillRandomWords.selector, _requestId, words);
    (bool success, ) = _consumer.call{gas: req.callbackGasLimit}(callReq);

[Chris-Gan]

here is my shallow understanding and hopes it will help. Personally there are some confusions I met when clarifying myself with the problem above:

1. There are two fulfillRandomWords() method one is from our own Raffle.sol and another is from VRFCoordinatorV2Mock.sol by which both methods will be called sequentially in one random word request, hence there is nothing like overriding occurs here. As a reminder, we need the VRFCoordinatorV2Mock.sol contract because VRFCoordinatorV2Mock.sol is inheriting VRFCoordinatorV2Interface interface and in our Raffle.sol contract, we are having an immutable to store a contract of type VRFCoordinatorV2Interface and we will call the requestRandomWords() inside the performUpkeep() of the Raffle.sol
   

2. when the fulfillRandomWords() in the VRFCoordinatorV2Mock.sol is called, if the random words are requested and fulfilled successfully, the fulfillRandomWords() in the **VRFCoordinatorV2Mock.sol** will pass the random words requested to the "consumer contract", which is in our case here is the Raffle.sol
   

Hope it helps!!