[lwip-users] Changing listen port number on the fly

[Enrico Murador - Research & Development - CET]

Hi all,

I'm writing a TCP/UDP server that should allow the user to change the 
TCP/UDP listening port number,
but I'm not sure what is the best way to do this. I think I have to 
close the listening pcb bound to the "old" port number, create a new 
listen PCB
and bind the "new" port number to it... But what I have to do with the 
already active TCP connections?

And if the user "plays around" with port numbers, I think I have to deal 
with ERR_USE failures on bind() call
due to listening connections in TIME_WAIT state (for example, if the 
port number is changed from 1024 to 1025 and then
re-changed to 1024 without leaving the TIME_WAIT period to elapse).
Can I use SO_REUSEADDR on listening PCBs without compromising 
reliability, or it is "safer" to wait?

I was thinking if there is a way to change the port that is already 
bound to a listening TCP pcb, or bound to an UDP pcb,
without closing the pcb and creating a new one, and if this could 
"override" the previous problem.

Thank you very much
Enrico