[lwip-users] Re: Probem sending large files using LwIP (Kieran Mansley)

[Louis Filasky]

 On Sat, 2007-07-14 at 19:24 +0200, Louis Filasky wrote:
 
>         First, we couldn t send more than around 8000 bytes of data.
>         This was fixed by changing the argument in the tcp_write
>         function by choosing
>         not to copy before sending the data.
 
>         Can I just check that you're doing something to make sure the data you
>         send are preserved until you get the tcp_sent() callback?  By specifying
>         not to copy, you're saying the data you pass to tcp_write() are static
>         until the callback is made to say the stack has finished with those
>         data.  It's not just a magic switch to make things faster!
 

Hi everyone,
 
Thanks to your suggestion, I was able to improve my code but I determined what was wrong. In EDK, you are able to change some
values for lwIP using a file xiledk_opt.h. The thing if that if you look at that file in the EDK install directory where the lwIP sources lies, 
it is empty but the lwipopt.h includes th e xiled_opt.h. Then I went in the compiled sources of the project and you can see that
this file is no longer empty and redefines suche variables as MEMORY_SIZE or SND_BUF.
 
Changing the MEMORY_SIZE, I was able to send larger files. I set it up to the maximum file size I could send so now when I ask the server
to change a large file, the client is at least receiving data and creating the file which it was not doing before that.
 
Following Kieran suggestion, I use now the argument 1 when I call tcp_write. However, now I am limited by the size of the send buffer.
 
Whatever the size I choose, if I try to send a file larger than the send buffer, it will only send the maximum send buffer size.
 
Now in my send_data() function, I handle when the data is bigger than the send buffer:
 
void send_data(struct tcp_pcb *pcb, struct connection_state *cs)
{
  u16_t len;
  err_t err;
  
  /* We cannot send more data than space available in the send buffer.*/
  if(tcp_sndbuf(pcb) < (cs->left)) { 
   len = tcp_sndbuf(pcb);
  }
  /* Otherwise, the length is equal to the size of the data to be sent */
  else {
     len = cs->left;
  }   
  
  err = tcp_write(pcb, cs->data, len, 1);
  
  /* Queue the data to be sent, if tcp_write does not send back ERR_OK, force the data transfer. */
  if(ERR_OK==err) {
      cs->data += len;
  cs->left -= len;
  }
  else if(err==ERR_MEM) {
      tcp_output(pcb);
  }
  /* If the data to be send is smaller than the send buffer size, then force the data transfer to speed it up. */
  if(cs->left == 0) {
      tcp_output(pcb);
  } 
} 
 
If I try to send a file of 50.000 bytes and let's say the sendbuffer max size is 40960, the left variable is set to be 9040.
But in my server_sent callback function, if left is > 0, it should call again send_data:
 
err_t server_sent(void *arg, struct tcp_pcb *pcb, u16_t len)
{
  struct connection_state *cs;
  cs = arg;
  xil_printf("tets %d\r\n", cs->left);
  //Once the server has received ACK from client that data has been successfully transmitted,
  //check if there is still some more data to send and initiate transmission.
  if(cs->left >0) {
   send_data(pcb, cs);
   xil_printf("test2");
  }
  return ERR_OK;
}
 
But when I send any data larger than the sendbuffer size, it never goes in the if condition and the xil_printf before the if condition is always
displaying 0.
 
Now, in my server_received callback function, i have the followings:
 
err_t server_recv(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
{
  struct connection_state *cs;
  
  if(err == ERR_OK && p!=NULL) {
  //Inform TCP that received data is being handled:
  tcp_recved(pcb, p->tot_len);
  processCommand(p, pcb, cs);
  tcp_sent(pcb, server_sent);
  }
  else pbuf_free(p);
  
  return ERR_OK;
 
With processCommand being a function which analyzes the command received from the client and send the corresponding data. So the last
line of the function is actually a call to send_data().
 
I must be doing something wrong, so if anyone has got a hint, thanks!
 
Antoine.

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