Question regarding VRFCoordinatorV2Mock (Who is calling fulfillRandomWords()?)

[deeptshukla]

Hey devs, I have a doubt regarding the VRFCoordinatorV2Mock.

From the contract using VRF (i.e. VRFConsumerBaseV2) vrfCoordinator.requestRandomWords() will be called to obtain random words.

I checked in the VRFCoordinatorV2Mock, requestRandomWords just emits event RandomWordsRequested(...) .
My question is, who calls fulfillRandomWords() to provoke the fulfillRandomWords ?

contract VRFCoordinatorV2Mock is VRFCoordinatorV2Interface {
    .
    ..
    ...

    function requestRandomWords(
        bytes32 _keyHash,
        uint64 _subId,
        uint16 _minimumRequestConfirmations,
        uint32 _callbackGasLimit,
        uint32 _numWords
      ) external override onlyValidConsumer(_subId, msg.sender) returns (uint256) {
        if (s_subscriptions[_subId].owner == address(0)) {
          revert InvalidSubscription();
        }
    
        uint256 requestId = s_nextRequestId++;
        uint256 preSeed = s_nextPreSeed++;
    
        s_requests[requestId] = Request({subId: _subId, callbackGasLimit: _callbackGasLimit, numWords: _numWords});
    
        emit RandomWordsRequested(
          _keyHash,
          requestId,
          preSeed,
          _subId,
          _minimumRequestConfirmations,
          _callbackGasLimit,
          _numWords,
          msg.sender
        );
        return requestId;
      }

      .
      ..
      ...

      function fulfillRandomWords(uint256 _requestId, address _consumer) external {
          fulfillRandomWordsWithOverride(_requestId, _consumer, new uint256[](0));
        }
      
      .
      ..
      ...
}

You can find the VRFCoordinatorV2Mock.sol at chinlink github here:
https://github.com/smartcontractkit/chainlink/blob/3ef265c4fa4de8183cd68651f373420865cab6d7/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol

[deeptshukla]

@alymurtazamemon , can you help me understand this?

[alymurtazamemon]

@deeptshukla Chainlink nodes will call the perform upkeep function from time to time and check if the upkeep is needed or not. If needed they will request the random words. That request words (numbers) will be sent to our fulfillRandomWords function by chainlink nodes. Inside it, we are doing our work and at the end emitting an event so we can know about it.

[deeptshukla]

Thanks @alymurtazamemon for the explaination.
I think I rushed to question, as it has been explained in the later section.