With my UDP Flow Copier working as demonstrated by the fact that it is proxying DNS traffic successfully, I am finally writing tests to verify UDP packet filtering. I'm sending packets to a public UDP echo server and reading the response successfully. In my initial testing however the TransparentProxyProvider System Extension is not intercepting my UDP traffic. handleNewUDPFlow() is being called for DNS but not for my test case UDP echo sends and receives. I've tried sending UDP with both GCDAsyncSocket and NWConnection as:
connection = NWConnection(host: host, port: port, using: .udp)
Is there some other criteria for UDP datagrams to be intercepted? Google search suggests this might be a known issue for connected or async UDP sockets.