}
/*-----------------------------------------------------------------------------------*/
/*
 * tcp_connect():
 *
 * Connects to another host. The function given as the "connected"
 * argument will be called when the connection has been established.
 *
 */
/*-----------------------------------------------------------------------------------*/
err_t
tcp_connect(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port,
	    err_t (* connected)(void *arg, struct tcp_pcb *tpcb, err_t err))
{
  u32_t optdata;
  err_t ret;
  u32_t iss;

  DEBUGF(TCP_DEBUG, ("tcp_connect to port %u\n", port));
  if(ipaddr != NULL) {
    pcb->remote_ip = *ipaddr;
  } else {
    return ERR_VAL;
  }
  pcb->remote_port = port;
  if(pcb->local_port == 0) {
    pcb->local_port = tcp_new_port();
  }
  iss = tcp_next_iss();
  pcb->rcv_nxt = 0;
  pcb->snd_nxt = iss;
  pcb->lastack = iss - 1;
  pcb->snd_lbb = iss - 1;
  pcb->rcv_wnd = TCP_WND;
  pcb->snd_wnd = TCP_WND;
  pcb->mss = TCP_MSS;
  pcb->cwnd = 1;
  pcb->ssthresh = pcb->mss * 10;
  pcb->state = SYN_SENT;
#if LWIP_CALLBACK_API  
  pcb->connected = connected;
#endif /* LWIP_CALLBACK_API */  
  TCP_REG(&tcp_active_pcbs, pcb);
  
  /* Build an MSS option */
  optdata = htonl(((u32_t)2 << 24) | 
		  ((u32_t)4 << 16) | 
		  (((u32_t)pcb->mss / 256) << 8) |
		  (pcb->mss & 255));

  ret = tcp_enqueue(pcb, NULL, 0, TCP_SYN, 0, (u8_t *)&optdata, 4);
  if(ret == ERR_OK) { 
    tcp_output(pcb);
  }
  return ret;
} 
/*-----------------------------------------------------------------------------------*/
/*
 * tcp_slowtmr():
 *
 * Called every 500 ms and implements the retransmission timer and the timer that
 * removes PCBs that have been in TIME-WAIT for enough time. It also increments
 * various timers such as the inactivity timer in each PCB.
 */
/*-----------------------------------------------------------------------------------*/
void
tcp_slowtmr(void)
{
  struct tcp_pcb *pcb, *pcb2, *prev;
  u32_t eff_wnd;
  u8_t pcb_remove;      /* flag if a PCB should be removed */
  err_t err;
  
  err = ERR_OK;

  ++tcp_ticks;
  
  /* Steps through all of the active PCBs. */
  prev = NULL;
  pcb = tcp_active_pcbs;
  if (pcb == NULL) DEBUGF(TCP_DEBUG, ("tcp_slowtmr: no active pcbs\n"));
  while(pcb != NULL) {
    DEBUGF(TCP_DEBUG, ("tcp_slowtmr: processing active pcb\n"));
    LWIP_ASSERT("tcp_slowtmr: active pcb->state != CLOSED\n", pcb->state != CLOSED);
    LWIP_ASSERT("tcp_slowtmr: active pcb->state != LISTEN\n", pcb->state != LISTEN);
    LWIP_ASSERT("tcp_slowtmr: active pcb->state != TIME-WAIT\n", pcb->state != TIME_WAIT);

    pcb_remove = 0;

    if(pcb->state == SYN_SENT && pcb->nrtx == TCP_SYNMAXRTX) {
      ++pcb_remove;
      DEBUGF(TCP_DEBUG, ("tcp_slowtmr: max SYN retries reached\n"));
    }
    else if(pcb->nrtx == TCP_MAXRTX) {
      ++pcb_remove;
      DEBUGF(TCP_DEBUG, ("tcp_slowtmr: max DATA retries reached\n"));
    } else {
      ++pcb->rtime;
      if(pcb->unacked != NULL && pcb->rtime >= pcb->rto) {

	/* Time for a retransmission. */
        DEBUGF(TCP_RTO_DEBUG, ("tcp_slowtmr: rtime %u pcb->rto %u\n",
                               pcb->rtime, pcb->rto));

	/* Double retransmission time-out unless we are trying to
           connect to somebody (i.e., we are in SYN_SENT). */
	if(pcb->state != SYN_SENT) {
	  pcb->rto = ((pcb->sa >> 3) + pcb->sv) << tcp_backoff[pcb->nrtx];
	}

	tcp_rexmit(pcb);
	
        /* Reduce congestion window and ssthresh. */
        eff_wnd = MIN(pcb->cwnd, pcb->snd_wnd);
        pcb->ssthresh = eff_wnd >> 1;
        if(pcb->ssthresh < pcb->mss) {
          pcb->ssthresh = pcb->mss * 2;
        }
        pcb->cwnd = pcb->mss;

        DEBUGF(TCP_CWND_DEBUG, ("tcp_slowtmr: cwnd %u ssthresh %u\n",
                                pcb->cwnd, pcb->ssthresh));
      }
    }
	  
    /* Check if this PCB has stayed too long in FIN-WAIT-2 */
    if(pcb->state == FIN_WAIT_2) {
      if((u32_t)(tcp_ticks - pcb->tmr) >
	 TCP_FIN_WAIT_TIMEOUT / TCP_SLOW_INTERVAL) {
        ++pcb_remove;
        DEBUGF(TCP_DEBUG, ("tcp_slowtmr: removing pcb stuck in FIN-WAIT-2\n"));
      }
    }

    /* If this PCB has queued out of sequence data, but has been
       inactive for too long, will drop the data (it will eventually
       be retransmitted). */
#if TCP_QUEUE_OOSEQ    
    if(pcb->ooseq != NULL &&
       (u32_t)tcp_ticks - pcb->tmr >=
       pcb->rto * TCP_OOSEQ_TIMEOUT) {
      tcp_segs_free(pcb->ooseq);
      pcb->ooseq = NULL;
      DEBUGF(TCP_CWND_DEBUG, ("tcp_slowtmr: dropping OOSEQ queued data\n"));
    }
#endif /* TCP_QUEUE_OOSEQ */

    /* Check if this PCB has stayed too long in SYN-RCVD */
    if(pcb->state == SYN_RCVD) {
      if((u32_t)(tcp_ticks - pcb->tmr) >
	 TCP_SYN_RCVD_TIMEOUT / TCP_SLOW_INTERVAL) {
        ++pcb_remove;
        DEBUGF(TCP_DEBUG, ("tcp_slowtmr: removing pcb stuck in SYN-RCVD\n"));
      }
    }


    /* If the PCB should be removed, do it. */
    if(pcb_remove) {
      tcp_pcb_purge(pcb);      
      /* Remove PCB from tcp_active_pcbs list. */
      if(prev != NULL) {
	LWIP_ASSERT("tcp_slowtmr: middle tcp != tcp_active_pcbs", pcb != tcp_active_pcbs);
        prev->next = pcb->next;
      } else {
        /* This PCB was the first. */
        LWIP_ASSERT("tcp_slowtmr: first pcb == tcp_active_pcbs", tcp_active_pcbs == pcb);
        tcp_active_pcbs = pcb->next;
      }

      TCP_EVENT_ERR(pcb->errf, pcb->callback_arg, ERR_ABRT);

      pcb2 = pcb->next;
      memp_free(MEMP_TCP_PCB, pcb);
      pcb = pcb2;
    } else {

      /* We check if we should poll the connection. */
      ++pcb->polltmr;
      if(pcb->polltmr >= pcb->pollinterval) {
	pcb->polltmr = 0;
        DEBUGF(TCP_DEBUG, ("tcp_slowtmr: polling application\n"));
	TCP_EVENT_POLL(pcb, err);
	if(err == ERR_OK) {
	  tcp_output(pcb);
	}
      }
      
      prev = pcb;
      pcb = pcb->next;
    }
  }

  
  /* Steps through all of the TIME-WAIT PCBs. */
  prev = NULL;    
  pcb = tcp_tw_pcbs;
  while(pcb != NULL) {
    LWIP_ASSERT("tcp_slowtmr: TIME-WAIT pcb->state == TIME-WAIT", pcb->state == TIME_WAIT);
    pcb_remove = 0;

    /* Check if this PCB has stayed long enough in TIME-WAIT */
    if((u32_t)(tcp_ticks - pcb->tmr) > 2 * TCP_MSL / TCP_SLOW_INTERVAL) {
      ++pcb_remove;
    }
    


    /* If the PCB should be removed, do it. */
    if(pcb_remove) {
      tcp_pcb_purge(pcb);      
      /* Remove PCB from tcp_tw_pcbs list. */
      if(prev != NULL) {
	LWIP_ASSERT("tcp_slowtmr: middle tcp != tcp_tw_pcbs", pcb != tcp_tw_pcbs);
        prev->next = pcb->next;
      } else {
        /* This PCB was the first. */
        LWIP_ASSERT("tcp_slowtmr: first pcb == tcp_tw_pcbs", tcp_tw_pcbs == pcb);
        tcp_tw_pcbs = pcb->next;
      }
      pcb2 = pcb->next;
      memp_free(MEMP_TCP_PCB, pcb);
      pcb = pcb2;
    } else {
      prev = pcb;
      pcb = pcb->next;
    }
  }
}
/*-----------------------------------------------------------------------------------*/
/*
 * tcp_fasttmr():
 *
 * Is called every TCP_FINE_TIMEOUT (100 ms) and sends delayed ACKs.
 */
/*-----------------------------------------------------------------------------------*/
void
tcp_fasttmr(void)
{
  struct tcp_pcb *pcb;

  /* send delayed ACKs */  
  for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
    if(pcb->flags & TF_ACK_DELAY) {
      DEBUGF(TCP_DEBUG, ("tcp_fasttmr: delayed ACK\n"));
      tcp_ack_now(pcb);
      pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
    }
  }
}
/*-----------------------------------------------------------------------------------*/
/*
 * tcp_segs_free():
 *
 * Deallocates a list of TCP segments (tcp_seg structures).
 *
 */
/*-----------------------------------------------------------------------------------*/
u8_t
tcp_segs_free(struct tcp_seg *seg)
{
  u8_t count = 0;
  struct tcp_seg *next;
 again:  
  if(seg != NULL) {
    next = seg->next;
    count += tcp_seg_free(seg);
    seg = next;
    goto again;
  }
  return count;
}
/*-----------------------------------------------------------------------------------*/
/*
 * tcp_seg_free():
 *
 * Frees a TCP segment.
 *
 */
/*-----------------------------------------------------------------------------------*/
u8_t
tcp_seg_free(struct tcp_seg *seg)
{
  u8_t count = 0;
  
  if(seg != NULL) {
    if(seg->p == NULL) {
      memp_free(MEMP_TCP_SEG, seg);
    } else {
      count = pbuf_free(seg->p);
#if TCP_DEBUG
      seg->p = NULL;
#endif /* TCP_DEBUG */
      memp_free(MEMP_TCP_SEG, seg);
    }
  }
  return count;
}
/*-----------------------------------------------------------------------------------*/
/*
 * tcp_setprio():
 *
 * Sets the priority of a connection.
 *
 */
/*-----------------------------------------------------------------------------------*/
void
tcp_setprio(struct tcp_pcb *pcb, u8_t prio)
{
  pcb->prio = prio;
}
/*-----------------------------------------------------------------------------------*/
/*
 * tcp_seg_copy():
 *
 * Returns a copy of the given TCP segment.
 *
 */ 
/*-----------------------------------------------------------------------------------*/
struct tcp_seg *
tcp_seg_copy(struct tcp_seg *seg)
{
  struct tcp_seg *cseg;

  cseg = memp_malloc(MEMP_TCP_SEG);
  if(cseg == NULL) {
    return NULL;
  }
  memcpy((char *)cseg, (const char *)seg, sizeof(struct tcp_seg)); 
  pbuf_ref(cseg->p);
  return cseg;
}
/*-----------------------------------------------------------------------------------*/
#if LWIP_CALLBACK_API
static err_t
tcp_recv_null(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
{
  arg = arg;
  if(p != NULL) {
    pbuf_free(p);
  } else if(err == ERR_OK) {
    return tcp_close(pcb);
  }
  return ERR_OK;
}
#endif /* LWIP_CALLBACK_API */
/*-----------------------------------------------------------------------------------*/
static void
tcp_kill_prio(u8_t prio)
{
  struct tcp_pcb *pcb, *inactive;
  u32_t inactivity;
  u8_t mprio;


  mprio = TCP_PRIO_MAX;
  
  /* We kill the oldest active connection that has lower priority than
     prio. */
  inactivity = 0;
  inactive = NULL;
  for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
    if(pcb->prio <= prio &&
       pcb->prio <= mprio &&
       (u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
      inactivity = tcp_ticks - pcb->tmr;
      inactive = pcb;
      mprio = pcb->prio;
    }
  }
  if(inactive != NULL) {
    DEBUGF(TCP_DEBUG, ("tcp_kill_prio: killing oldest PCB 0x%p (%ld)\n",
		       (void *)inactive, inactivity));
    tcp_abort(inactive);
  }      
}

/*-----------------------------------------------------------------------------------*/
static void
tcp_kill_timewait(void)
{
  struct tcp_pcb *pcb, *inactive;
  u32_t inactivity;

  inactivity = 0;
  inactive = NULL;
  for(pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
    if((u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
      inactivity = tcp_ticks - pcb->tmr;
      inactive = pcb;
    }
  }
  if(inactive != NULL) {
    DEBUGF(TCP_DEBUG, ("tcp_kill_timewait: killing oldest TIME-WAIT PCB 0x%p (%ld)\n",
		       (void *)inactive, inactivity));
    tcp_abort(inactive);
  }      
}