Client BSD exemple connection close problem in uv5

#include "cmsis_os.h"                   /* CMSIS RTOS definitions             */
#include "rl_net.h"                     /* Network definitions                */

//-------- <<< Use Configuration Wizard in Context Menu >>> -----------------

//   <h>Remote IP Address
//   ====================
//
//     <o>IP1: Address byte 1 <0-255>
//      Default: 192
#define IP1            192

//     <o>IP2: Address byte 2 <0-255>
//      Default: 168
#define IP2            168

//     <o>IP3: Address byte 3 <0-255>
//      Default: 0
#define IP3            1

//     <o>IP4: Address byte 4 <0-255>
//      Default: 100
#define IP4            62

//   </h>

//   <o>Remote Port <1-65535>
//    Do not set number of port too small,
//    maybe it is already used.
//    Default: 1001
#define PORT_NUM       5001

//   <o>Communication Protocol <0=> Stream (TCP) <1=> Datagram (UDP)
//    Selecet a protocol for sending data.
#define PROTOCOL       0

//   <o>LED Blinking speed <1-100>
//    Blinking speed = SPEED * 100ms
//    Default: 2
#define SPEED          1

//------------- <<< end of configuration section >>> -----------------------

#define BLINKLED 0x01                   /* Command for blink the leds        */
#if (PROTOCOL == 0)
 #define SOCKTYPE   SOCK_STREAM
#else
 #define SOCKTYPE   SOCK_DGRAM
#endif

static void Client (void const *arg);
osThreadDef(Client, osPriorityRealtime, 2, 0);

/*----------------------------------------------------------------------------
  Thread 'Client': BSD Client socket process
 *---------------------------------------------------------------------------*/
static void Client (void const *arg) {
  SOCKADDR_IN addr;
  int sock, res;
  char dbuf[4];


  while (1) {
    sock = socket (AF_INET, SOCKTYPE, IPPROTO_TCP );

    addr.sin_port      = htons(PORT_NUM);
    addr.sin_family    = PF_INET;
    addr.sin_addr.s_b1 = IP1;
    addr.sin_addr.s_b2 = IP2;
    addr.sin_addr.s_b3 = IP3;
    addr.sin_addr.s_b4 = IP4;

    connect (sock, (SOCKADDR *)&addr, sizeof (addr));

    while (1) {

      dbuf[0] = 'O';
      dbuf[1] = 'S';
      dbuf[2] = 'C';

      res = send (sock, (char *)&dbuf, 2, 0);
      if (res < 0) {
        break;
      }
      osDelay (100 * SPEED);
    }
    closesocket (sock);
  }
}

/*----------------------------------------------------------------------------
  Main Thread 'main': Run Network
 *---------------------------------------------------------------------------*/
int main (void) {

//  LED_Initialize ();
//  init_display ();
  net_initialize ();

  // Create networking task
  osThreadCreate (osThread(Client), NULL);

  while(1) {
    net_main ();
    osThreadYield ();
  }
}