[lwip-users] [lwip] udp server problem (possible problem with pcb->remote_ip)

[David Figueroa]

I have noticed there might be a problem with udp, else maybe I'm overlooking
something trivial.

Once the server has bound to a port and is "receiving"

The first and subsequent requests from the same ip source works just fine.

The second and subsequent requests from a different ip source does not get
accepted.

This is because the "listening" pcb is now set to the first guy's ip
address.  This is set by the udp_connect function:

err_t
udp_connect(struct udp_pcb *pcb, struct ip_addr *ipaddr, u16_t port)
{
  struct udp_pcb *ipcb;
  ip_addr_set(&pcb->remote_ip, ipaddr);
  pcb->remote_port = port;

...

Therefore whenever a new udp packet arrives (and port matches) from a
different ip address it will be rejected because the remote ip address in
pcb (pcb->remote_ip) is no longer NULL i.e. "ip_addr_isany" (in udp_input -
there are 6 different checks to accept/reject udp request).

I have temporarily fixed this by clearing out the pcb->remote_ip after the
"ip_output_if" call in udp_send.


    err = ip_output_if(p, src_ip, &pcb->remote_ip, UDP_TTL, IP_PROTO_UDP,
netif);    
  }

  /**** df temporary fix  ****/

  ip_addr_set(&pcb->remote_ip, NULL);
  pcb->remote_port = 0;

  /**** end df temporary fix ****/

#ifdef UDP_STATS
  ++stats.udp.xmit;
#endif /* UDP_STATS */
  return err;
}

but this cannot be correct.  Should there be a new pcb created to accept the
new udp request?  If so how is this done? And also why can't the existing
pcb be re-used (as I am doing now).  Surely new udp clients should not cause
the pcb list to grow indefinitely...

I apologize if this problem has been reported/fixed; if so please point me
in the right direction.

Thanks for your input,

dave


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