How Chainlink VRF fulfillRandomWords() callback function works?

Question

I am using Chainlink VRF2 where I receive random numbers via a callback to this function:

function fulfillRandomWords(
    uint256, /* requestId */
    uint256[] memory randomWords
  ) internal override {
    s_randomWords = randomWords;
  }

This function supposedly will be called by VRF coordinator but the fulfillRandomWords() function has the access modifier internal. How does the VRFCoordinator send this function a random number if it is an external contract?

Answer 1

In the import VRFConsumerBaseV2.sol you will see the actual function being called by the VRFCoordinator is:

function rawFulfillRandomWords(uint256 requestId, uint256[] memory randomWords) external {
    if (msg.sender != vrfCoordinator) {
      revert OnlyCoordinatorCanFulfill(msg.sender, vrfCoordinator);
    }
    fulfillRandomWords(requestId, randomWords);
  }

This external function calls fulfillRandomWords(), and because it is inherited, fulfillRandomWords() can be internal.

Reference: VRFConsumerBaseV2.sol GitHub