[lwip-devel] Limiting the number of connections per listening socket by queuing syn requests

[Tobias Wegner]

Hi everyone!

I am using lwip 1.3.0 on an embedded webserver with very limited 
resources (ARM7, 64 kb RAM) and had problems with programs which are 
using more than one single connection. Because my webserver only uses a 
single processing thread, incoming request are only processed one after 
each other. In combination with the few RAM this causes some kind of 
deadlock because unprocessed incoming data blocks the buffer space and 
by that the currently active HTTP connection, so that this connection 
cannot be finished and the buffers are never freed again.

As a measure against this I implemented a queue for the listening port 
where the answers to incoming syn requests are hold back until there is 
no connection to the listening port open anymore. In my specific 
application this allows me to handle 8 concurrent connections 
sequentially without any problems.

First I would like to ask you if you think this is a proper solution and 
second if you are interested in my patch.

Regards,
Tobias Wegner