UDP port forwarding does not work with iperf3 and lacks tests

[AkihiroSuda]

[jandubois]

There is some discussion about the challenges of testing UDP with nc in #3152 (comment).

I thought there was some other issue/pr/discussion that showed on attempt to modify test-port-forwarding.pl to work for UDP as well (maybe with comments from @nirs?), but I can't find anything else right now.

[AkihiroSuda]

As discussed in today's call, the UDP port forwarding seems broken:

$ lima iperf3 -s

$ iperf3-darwin -c 127.0.0.1 -u 
iperf3: error - unable to connect to server: Connection refused

Tested with Lima v1.1.1, vz

[AkihiroSuda]

@balajiv113 Could you take a look? 🙏

[balajiv113]

@AkihiroSuda UDP forwarding works via application. The problem with iperf is they get a call for tcp and do a switch to udp from there. And they have very low timeout due to which before we acutally create UDP connection they say refused.

If we expose the UDP 5201 port before itself like harcoding iperf3 udp port, then this works

I don't think this is broken rather its not easily testable in our current ways

[nirs]

Can add a test exposing iperf3 port before we run it? I will also server as example for users that need to deal with this issue.