iperf3 -J – packets transmitted

I’m designing a test that should be able to run TCP or UDP and verify the number of packets transmitted. With UDP I can use -k to control the number of packets, but with TCP I can’t find a way to set or read the number of packets transmitted. I am using -J to make it easier to parse data after the fact. Ideally I’d find a way to set the exact number of packets sent in advance, but failing that I want to know the actual number (a few extras as part of handshake protocol are fine).