Substrate off-chain worker (Ethereum Blockchain): how to use built-in http module to fetch real data?

Hi guys, please help me out. I'm trying to write an off-chain worker (OCW), taking substrate/tests.rs at master · paritytech/substrate · GitHub as an reference, my OCW needs to use its built-in http module to fetch data of type JSON out of somewhere, but what I found is that the example in the link requires function price_oracle_response (at line 371) to hardcode JSON, how to tackle this problem?