The snd_wnd is either 0 or -1 on iperf 3.11(cJson 1.7,13)

[Pir-CHILD]

With --json flag I can get more info, like snd_wnd.
I'm using iperf3 on wsl 0.70 with kernel version 5.15, I always get the output

...
"intervals":      [{
...
"snd_cwnd":     2750286,
"snd_wnd":      -1,
...
"sender":       true
}],

and

...
"end":      [{
...
"max_snd_cwnd": 3339633,
"max_snd_wnd":  0,
...
"sender":       true
}],

where the snd_wnd is always -1 in every interval and max_snd_wnd: 0 in the end sum.
So I want to figure out how snd_wnd is calculated, directly from the packet head or just the initial value?

iperf 3.11 (cJSON 1.7.13)
Linux Pir-Child-Win 5.15.68.1-microsoft-standard-WSL2 #1 SMP Mon Sep 19 19:14:52 UTC 2022 x86_64
Optional features available: CPU affinity setting, IPv6 flow label, TCP congestion algorithm setting, sendfile / zerocopy, socket pacing, bind to device, support IPv4 don't fragment

[Pir-CHILD]

snd_wnd is right when update iperf3 to 3.12, this discussion is over.
Thanks for your time.