cant understand what patrick did here

[h0leee]

Hi! I am in the part of raffle contract and in the unit tests i dont understand the parameters that Patrick passed to fullfill random words. Fullfill random words should receive a subscriptionid and an array, but in the second parameter i think patrick sent an address and i dont understand what is happening under the hood.

[pacelliv]

Hello @h0leee, I hope this summary helps up.

After upkeepNeeded is true, we manually call performUpkeep.

Calling performUpkeep will create a transaction, this function makes a contract call to requestRandomWords of the VRFCoordinatorV2Mock, which after executing its logic will emit an event and return the requestId to our contract.

performUpkeep receives the id from the Coordinator and emits a second event from which we grab the requestId with:

txReceipt.events[1].ars.requestId

To complete the mocking of the actual process, we manually call the fulfillRandomWords of the VRFCoordinatorV2Mock and pass the id and the address of the raffle as arguments.

Now, fulfillRandomWords of the Coordinator will create the random words (numbers) and after executing its logic will call our fullfilRandomWords and pass to it the id and the random words.

Our fullfillRandomWords will execute its logic, select the winner and will emit the WinnedPicked event. After the event is picked up, we assert the state of the raffle.

[Ahmedborwin]

Hi PAcelliv,

Thank you for your reply to h0leee. I found it very helpful also. 

I am still unclear on how fullfillRandomWords is triggered in our testnet example. Our chainlink keeper triggers preformUpkeep, which triggers requestRandomWords, but, I can't see what then calls our fullfillRandomWords function. 

Any ideas? Your time is much appreciated!

[pacelliv]

A Chainlink node executes the fulfillRandomWords in VRFCoordinatorV2.sol, computes the words and that function calls the fulfillRandomWords in your contract.

[Ahmedborwin]

Hi pacelliv

If I am not mistaken we set preformUpkeep as our target function for our chainlink keeper.

What then dictates the logic for a chainlink node to trigger fullfillRandomWords?

Thank you
Ahmed

[ugur17]

Hi @pacelliv , thank you for your answer and effort. You said;
"A Chainlink node executes the fulfillRandomWords in VRFCoordinatorV2.sol, computes the words and that function calls the fulfillRandomWords in your contract."
Which part of fulfillRandomWords function code in VRFCoordinatorV2.sol calls our fulfillRandomWords function?

[wxy-sudo]

Hi @ugur17 , I have the same problem with you. Have you got any idea?