[lwip-users] Problem re-opening listening pbc

[Keith Rubow]

I'm using LWIP for the first time (2.0.3, NO_SYS=1, callback API). 
Mostly things are going well. But I have an issue with allowing only a 
single TCP connection to a port. I open a listening pcb with tcp_new(), 
tcp_bind(), tcp_listen() and set an accept callback. In the accept 
callback I set up a receive callback, and I use tcp_close() to close the 
listening pcb. This causes any further connection attempts on the port 
to be refused. This works great.

However, the problem is when the connection I accepted is closed. My 
receive callback is called with p=NULL, so I then remove all the 
callbacks and close the active connection with tcp_close(). Then I 
re-open the listening pcb with tcp_new(), tcp_bind(), and tcp_listen(). 
HOWEVER, the tcp_bind() fails with ERR_USE, presumably because the pcb 
for the active connection is not fully closed yet, making the port still 
in use.

I found I can "fix" the problem by closing the active connection with 
tcp_abort() instead of tcp_close(), but this seems kind of wrong. If I 
knew when the pcb for the active connection was really fully closed, I 
could open the listening pcb then. But I don't see any way to tell when 
the close is finished. There is no callback for it, and I am not 
permitted to access the pcb after calling tcp_close().

So how can I re-open a listening pcb on the port after a connection is 
closed?

Keith Rubow