What is "selector" in ChainLink API call?

Question

I am using the example from chainlink to call an API; however, I am not sure it does.

function checkProof(string memory JobLocation, int job_id) public {
   Chainlink.Request memory req = buildChainlinkRequest(stringToBytes32(JOBID), address(this), this.fulfill.selector);

   req.add("get",JobLocation);

   req.add("path", "proof");

   sendChainlinkRequestTo(ORACLE_ADDRESS, req, ORACLE_PAYMENT);
}

I know it calls the following function

 function fulfill(bytes32 _requestId, bool _isProofCorrect, unit val) public recordChainlinkFulfillment(_requestId){
        customers[1].proof = _isProofCorrect;
 }

But, what does selector do in the above code (this.fulfill.selecor)?

Answer 1

what does selector do in the above code (this.fulfill.selecor) ?

In your buildChainlinkRequest function, it takes 3 arguments:

• bytes32 _specId
• address _callbackAddress
• bytes4 _callbackFunctionSignature

The bytes4 _callbackFunctionSignature tells the Chainlink node what method to call when it returns the data. It is known as a function selector, and it allows the node to specify exactly what it needs to call back, in your case the fulfill function.

Also, how can I pass an argument to the fulfill function? I am trying to update the proof variable of my customers map by using what chainlink calls.