[lwip-users] Lwip 1.3.1 TCP Retransmission problem

[theflasher1986]

Hello, i am new to lwip and at the moment i am trying to send data from a
client to server and back.
First some information: i am using
Lwip version 1.3.1
and RTOS CooCox Coos

I started with a NXP LPC1766 LwIP Example Code from the CooCox page and
improved it a little bit.
As Api i used the netconn-Api:

Ok i have a little server-application.What i am doing with it? I have a
client which sends messages to this server and the server than sends first a
prefix of a message back following by the real message. The Client waits for
this message and than sends the next. Like a circle. 

(if i say send i mean the prefix + message send together)
The problem is, between the eight and ninth send from the server to client i
get a lot of TCP-retransmissions.It takes about 2 secondes before the ninth
send can be done. The same problem occurs after the 17. send or the 26.
send. (8-9, 17-18, 26-27, 35-36 ...) It is periodic.  

I have a wireshark file for you, so you can better understand what i mean. 
http://old.nabble.com/file/p31044517/wireshark.pcap wireshark.pcap 

Below i have posted my source code, so maybe sobody can discover a bug or
anything.

it would be very nice if someone has an advice for me, thats really a tricky
situation for a newbie like me.
I tried to adjust some parameters but nothing helped really.

greetings
theflasher




void http_server(void *pdata) {
  struct netconn *conn, *newconn;
  
  /* Create a new TCP connection handle */
  conn = netconn_new(NETCONN_TCP);
  
  /* Bind to port 80 (HTTP) with default IP address */
  netconn_bind(conn, NULL, 62000);
  
  /* Put the connection into LISTEN state */
  netconn_listen(conn);
  
  while(1) {
    newconn = netconn_accept(conn);
    http_server_serve(newconn);
    netconn_delete(newconn);
  }
}

void http_server_serve(struct netconn *conn)
{
   struct netbuf *inbuf;
   char *buf;
   u16_t buflen;
   char* msg = "SET_PORT_TYPE_OK";    //16 chars long
 
   while(conn->err == ERR_OK)
   {            
 /* Read the data from the port, blocking if nothing yet there. 
    We assume the request (the part we care about) is in one netbuf */

    inbuf = netconn_recv(conn);
  
    if (netconn_err(conn) == ERR_OK)
    {
        netbuf_data(inbuf, (void **)&buf, &buflen);             
        printf("message: %s\n",buf);
        netbuf_delete(inbuf);
        sendPrefix(conn,16);
//sendprefix(..): puts 16 into a char[]-Array, which is 4 Byte long and
sends it by netconn_write(..)    
        netconn_write(conn, msg, 16, NETCONN_COPY);                     
        }
        }
  /* Close the connection (server closes in HTTP) */
  netconn_close(conn);
  
  printf("connection closed\n");        

  /* Delete the buffer (netconn_recv gives us ownership,
   so we have to make sure to deallocate the buffer) */
  netbuf_delete(inbuf);
}



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