Re: [lwip-users] Problem with NULL pcb->callback_arg

[address@hidden]

Baptiste Chaboud-crousaz wrote:
> Sometimes, the face trouble with my callback http_connect - called by 
> the macro TCP_EVENT_SENT - because "arg" is null.

I don't understand that one:
a) there is no function 'http_connect' in the code you posted
b) TCP_EVENT_SENT calls the function set by calling tcp_sent(pcb, fn) - 
the code you posted doesn't call tcp_sent().
c) I would have thought a connect function would be used with a client, 
not a server - whereas an accept function (as you posted) is used with a 
server, not a client)

> My understanding is that the http_accept function binds a pcb to an 
> argument by a call to tcp_arg(...). I don't undersatnd why sometimes 
> my callback is called with a NULL arg!!!
>
> This issue seems to be avoided/limited by increasing the size of 
> MEM_SIZE and PBUF_POOL_SIZE.

That could be a hint that you are writing beyond allocated memory 
somwhere and overwrite the memory where the PCB lies with zeros...

> If anybody has an idea, let me knwo about it...

Except for the above, I'm afraid I don't have an idea. Unless you call 
*tcp_arg(pcb, NULL) somewhere else, of course...*

Does the argument get NULL during the connection or right at the start?


Simon