[lwip-users] netconn/netbuf API

[Hans-Erik Floryd]

Hello,

I am trying to use the netconn API to send UDP messages. Each message 
consists of two sections, an identifer and the payload. Since I will be 
using netconn_sendto I need to construct a netbuf containing the two 
data sections.

At first glance something like this seems like it would work:

   identifier = netbuf_new();
   payload = netbuf_new();

   netbuf_ref (identifier, pId, pIdSize);
   netbuf_ref (payload, pData, pDataSize);
   netbuf_chain (identifier, payload);

   netconn_sendto (conn, identifier, &addr, port);
   netbuf_delete (payload);
   netbuf_delete (identifier);

But netbuf_chain calls memp_free on the tail (i.e. payload), so when 
netbuf_delete(payload) is called, payload is no longer valid. On the 
other hand, if netbuf_delete(payload) is not called, a pbuf is lost 
because the reference count on the payload data is two, so 
netbuf_delete(identifier) will not free the data.

Is it correct for netbuf_chain to free the tail netbuf? If that one line 
is removed the code above works fine.

If it is correct behaviour, any ideas how to best use the netconn API to 
send the message? I have read what documentation I could find on the 
wiki but there doesn't seem to be much information regarding 
netconn/netbuf there.

Thanks for any help!