Re: [lwip-users] Problem re-opening listening pbc

[Keith Rubow]

For anyone else interested in the solution, I can now limit the number 
of connections on a port, and refuse connections in excess of the limit.
1) Put #define SO_REUSE    1 in lwiopts.h
2) Whenever the listening socket is being opened call tcp_new(), then 
use ip_set_option(newpcb,SOF_REUSEADDR) to allow re-use of the port 
number before calling tcp_bind();
3) When the last connection is accepted (hitting the max allowed 
connections), in the accept callback call tcp_close() to close the 
LISTENING pcb.
4) Whenever a connection is closed (making another socket available), 
re-open the listening pcb again (as in step 2 above) if it is not 
already open.

This exactly what I wanted. Up to "N" connections accepted 
simultaneously, with excess connection attempts refused. Works great.

Keith Rubow

On 5/14/2018 11:56 AM, address@hidden wrote:
> On 14.05.2018 18:27, Keith Rubow wrote:
> > [..] I would like to have additional connection
> > attempts to be refused. I can achieve this behavior only by closing the
> > listening pcb once I reach the max number of connections, but then I
> > can't re-open the listening pcb until ALL open connections are closed.
> > But some connections might stay open indefinitely, in which case I can
> > never open the listening pcb again.
>
> You don't seem to read the responses to your mails. There were two 
> suggestsions:
> a) do it the standard socket way (even if you are using lwIP callback 
> API) and use REUSEADDR to be able to open the listening socket 
> although connection sockets are active (or in time-wait; this *is* 
> standard behaviour, not an lwIP thing!)
> b) play with backlog.
>
> The default usage of backlog is to decrease it when connections are 
> actually accepted, but you can just use it to only accept new 
> connections after previous connections are closed. To do that, call 
> 'tcp_backlog_delayed()' in your accept callback and call 
> 'tcp_backlog_accepted()' when the pcb is closed (when the 'err' 
> callback is called, the latter is done internally by the stack).
>
> Simon
>
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