RE: [lwip-users] fundamentally flawed attempt at a TCP send

[sirnails]

Thanks for your reply Bill,

I have modified the code a little and now I am getting weird packets being
reported from wireshark; my new code:



> struct tcp_pcb *pcb;
> 
> err_t foobar(void *arg, struct tcp_pcb *pcb, err_t err)
> {
>       static char data[] = "DAVE";
>       tcp_write(pcb, data, sizeof(data),0);
>       tcp_output(pcb);
>       tcp_close(pcb);
>       return ERR_OK;
> }
>                                                                               
> void dave_init(void)                                          /* The 
> initialization function. */
> {
>       //0xC0A821AF;
>       struct ip_addr *boardip;
>       err_t result;
>       
>       boardip->addr = 0xC0A82199;
> 
>       pcb = tcp_new();
>       tcp_bind(pcb, NULL, 44444);
>       result = tcp_connect(pcb,boardip,55555,foobar);
> }
> 

I think it may be something to do with the callback "foobar" im not sure
about the "void *arg" part, if anyone can clarify I would be very great full
to you!

Thanks in advance for any help!
Dave xx



Bill Auerbach wrote:
> 
> First, the ip address isn't a constant, but a struct ip_addr *.  Your code
> may well compile, but you should observe and correct the warnings.  The
> last
> parameter to tcp_connect should simply be the name of the function which
> lwIP will callback when the connection is made.  This is should not be a
> function call.  The tcp_write would occur after you are notified of the
> connection (by the callback to tcp_connect).
> 
>  
> 
> Bill
> 
>  
> 
> From: address@hidden
> [mailto:address@hidden On Behalf
> Of sirnails
> Sent: Wednesday, September 16, 2009 11:13 AM
> To: address@hidden
> Subject: [lwip-users] fundamentally flawed attempt at a TCP send
> 
>  
> 
> Hello All, 
> I am trying to send a string over TCP and believe i am having fundamental
> understanding problems... 
> The code i am trying to cobble together (based upon
> http://www.nongnu.org/lwip/) is: 
> 
>   _____  
> 
> struct tcp_pcb *pcb;
> 
> static char indexdata[] = "DAVE";
> 
> pcb = tcp_new();
> tcp_bind(pcb, NULL, 44444);
> tcp_connect(pcb,0xC0A821AF,55555,tcp_write(pcb, indexdata,
> sizeof(indexdata), 1));
> 
> tcp_close(pcb);
> 
>   _____  
> 
> a few questions:
> - what is a PCB (Protocol Control Block) and what is it for? is it just a
> unique reference number for the specific connection?
> 
> - the code compiles correctly but when run gives a SIGSEGV fault :
> 
>   _____  
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x02005d48 in tcp_connect (pcb=0x2013d90, ipaddr=0xc0a821af, port=55555, 
> connected=0xfffffffa) at ../lwip/src/core/tcp.c:425
> 425 pcb->remote_ip = *ipaddr;
> 
>   _____  
> 
> Im sorry to be asking such a stupid question, I hope you can help! 
> Dave xx 
> 
>   _____  
> 
> View this message in context: fundamentally
> <http://www.nabble.com/fundamentally-flawed-attempt-at-a-TCP-send-tp25474522
> p25474522.html>  flawed attempt at a TCP send
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> mailing list archive at Nabble.com.
> 
> 
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