It sounds like you would be reimplementing an entire network and application server from UDP gateway payload -> decoding of the decrypted payload (in JavaScript?). You would likely be better off setting up ChirpStack pulling the data you need via integration and doing something with it.
Yes, you are right the same scenario I want to do but not on ChirpStack. I have my own gateway and I want to send within my gateway through UDP and received on decoding software.