Best way to get notified when fallback arrived

Question

When you request random number, the Chainlink VRF2 returns it by calling following function.

function fulfillRandomWords(
        uint256, /* requestId */
        uint256[] memory randomWords
    ) internal override {
        s_randomWords = randomWords;
        randomNum = s_randomWords[0];
    }

There is not guaranteed time. What is the best way to catch when it is arrived?

What I have:

def request_random():
    account = get_account()
    contract = AdvancedCollectible[-1]

    # Request Random
    tx = contract.requestRandom({"from": account})

    print("Waiting for the callback...")

    tx.wait(5)

    while True:
        random_num = contract.randomNum()

        if random_num != 0:
            print("Finally received random num:", random_num)
            break
        else:
            print("Waiting another 5 sn")
            time.sleep(5)

Another way would be events but since fulfillRandomWords function is called by coordinator, I can't create a transaction to listen event of this function.

I am sure there is better way to do so...

Answer 1

You can create a custom event for the randomNumberConsumer contract that you can listen for in a client (such as a frontend or javascript client).