/**
 * @file
 *
 * Transmission Control Protocol for IP
 */

/*
 * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
 * All rights reserved. 
 * 
 * Redistribution and use in source and binary forms, with or without modification, 
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission. 
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED 
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 * 
 * Author: Adam Dunkels <adam@sics.se>
 *
 */


/* tcp.c
 *
 * This file contains common functions for the TCP implementation, such as functinos
 * for manipulating the data structures and the TCP timer functions. TCP functions
 * related to input and output is found in tcp_input.c and tcp_output.c respectively.
 *
 */



#include "lwip/opt.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/memp.h"

#include "lwip/tcp.h"

#include "../../SMSUTILS/smsutils.h"

#if LWIP_TCP

/* Incremented every coarse grained timer shot
   (typically every 500 ms, determined by TCP_COARSE_TIMEOUT). */
u32_t      tcp_ticks;
const u8_t tcp_backoff[ 13 ] = {
 1, 2, 3, 4, 5, 6, 7, 7, 7, 7, 7, 7, 7
};

/* The TCP PCB lists. */
struct tcp_pcb_listen *tcp_listen_pcbs;  /* List of all TCP PCBs in LISTEN state. */
struct tcp_pcb *tcp_active_pcbs;  /* List of all TCP PCBs that are in a
         state in which they accept or send
         data. */
struct tcp_pcb *tcp_tw_pcbs;      /* List of all TCP PCBs in TIME-WAIT. */

struct tcp_pcb *tcp_tmp_pcb;

static u8_t tcp_timer;

static u16_t tcp_new_port(void);

/*
 * tcp_init():
 *
 * Initializes the TCP layer.
 */
void tcp_init ( void ) {

 tcp_listen_pcbs = NULL;
 tcp_active_pcbs = NULL;
 tcp_tw_pcbs     = NULL;
 tcp_tmp_pcb     = NULL;
 tcp_ticks       = 0;
 tcp_timer       = 0;

}  /* end tcp_init */
/*
 * tcp_tmr():
 *
 * Called periodically to dispatch TCP timers.
 *
 */
void tcp_tmr ( void ) {

 tcp_fasttmr();

 if ( ++tcp_timer & 2 ) tcp_slowtmr ();

}  /* end tcp_tmr */
/*
 * tcp_close():
 *
 * Closes the connection held by the PCB.
 *
 */

err_t
tcp_close(struct tcp_pcb *pcb)
{
  err_t err;

#if TCP_DEBUG
  LWIP_DEBUGF(TCP_DEBUG, ("tcp_close: closing in state "));
  tcp_debug_print_state(pcb->state);
  LWIP_DEBUGF(TCP_DEBUG, ("\n"));
#endif /* TCP_DEBUG */
  switch (pcb->state) {
  case LISTEN:
    err = ERR_OK;
    tcp_pcb_remove((struct tcp_pcb **)&tcp_listen_pcbs, pcb);
    memp_free(MEMP_TCP_PCB_LISTEN, pcb);
    pcb = NULL;
    break;
  case SYN_SENT:
    err = ERR_OK;
    tcp_pcb_remove(&tcp_active_pcbs, pcb);
    memp_free(MEMP_TCP_PCB, pcb);
    pcb = NULL;
    break;
  case SYN_RCVD:
  case ESTABLISHED:
    err = tcp_send_ctrl(pcb, TCP_FIN);
    if (err == ERR_OK) {
      pcb->state = FIN_WAIT_1;
    }
    break;
  case CLOSE_WAIT:
    err = tcp_send_ctrl(pcb, TCP_FIN);
    if (err == ERR_OK) {
      pcb->state = LAST_ACK;
    }
    break;
  default:
    /* Has already been closed, do nothing. */
    err = ERR_OK;
    pcb = NULL;
    break;
  }

  if (pcb != NULL && err == ERR_OK) {
    err = tcp_output(pcb);
  }
  return err;
}

/*
 * tcp_abort()
 *
 * Aborts a connection by sending a RST to the remote host and deletes
 * the local protocol control block. This is done when a connection is
 * killed because of shortage of memory.
 *
 */

void
tcp_abort(struct tcp_pcb *pcb)
{
  u32_t seqno, ackno;
  u16_t remote_port, local_port;
  struct ip_addr remote_ip, local_ip;
#if LWIP_CALLBACK_API  
  void (* errf)(void *arg, err_t err);
#endif /* LWIP_CALLBACK_API */
  void *errf_arg;

  
  /* Figure out on which TCP PCB list we are, and remove us. If we
     are in an active state, call the receive function associated with
     the PCB with a NULL argument, and send an RST to the remote end. */
  if (pcb->state == TIME_WAIT) {
    tcp_pcb_remove(&tcp_tw_pcbs, pcb);
    memp_free(MEMP_TCP_PCB, pcb);
  } else {
    seqno = pcb->snd_nxt;
    ackno = pcb->rcv_nxt;
    ip_addr_set(&local_ip, &(pcb->local_ip));
    ip_addr_set(&remote_ip, &(pcb->remote_ip));
    local_port = pcb->local_port;
    remote_port = pcb->remote_port;
#if LWIP_CALLBACK_API
    errf = pcb->errf;
#endif /* LWIP_CALLBACK_API */
    errf_arg = pcb->callback_arg;
    tcp_pcb_remove(&tcp_active_pcbs, pcb);
    if (pcb->unacked != NULL) {
      tcp_segs_free(pcb->unacked);
    }
    if (pcb->unsent != NULL) {
      tcp_segs_free(pcb->unsent);
    }
#if TCP_QUEUE_OOSEQ    
    if (pcb->ooseq != NULL) {
      tcp_segs_free(pcb->ooseq);
    }
#endif /* TCP_QUEUE_OOSEQ */
    memp_free(MEMP_TCP_PCB, pcb);
    TCP_EVENT_ERR(errf, errf_arg, ERR_ABRT);
    LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_abort: sending RST\n"));
    tcp_rst(seqno, ackno, &local_ip, &remote_ip, local_port, remote_port);
  }
}

/*
 * tcp_bind():
 *
 * Binds the connection to a local portnumber and IP address. If the
 * IP address is not given (i.e., ipaddr == NULL), the IP address of
 * the outgoing network interface is used instead.
 *
 */

err_t
tcp_bind(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port)
{
  struct tcp_pcb *cpcb;
#ifdef SO_REUSE
  int reuse_port_all_set = 1;
#endif /* SO_REUSE */

  if (port == 0) {
    port = tcp_new_port();
  }
#ifndef SO_REUSE
  /* Check if the address already is in use. */
  for(cpcb = (struct tcp_pcb *)tcp_listen_pcbs;
      cpcb != NULL; cpcb = cpcb->next) {
    if (cpcb->local_port == port) {
      if (ip_addr_isany(&(cpcb->local_ip)) ||
        ip_addr_isany(ipaddr) ||
        ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
          return ERR_USE;
      }
    }
  }
  for(cpcb = tcp_active_pcbs;
      cpcb != NULL; cpcb = cpcb->next) {
    if (cpcb->local_port == port) {
      if (ip_addr_isany(&(cpcb->local_ip)) ||
   ip_addr_isany(ipaddr) ||
   ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
  return ERR_USE;
      }
    }
  }
#else /* SO_REUSE */
  /* Search through list of PCB's in LISTEN state. 
     
  If there is a PCB bound to specified port and IP_ADDR_ANY another PCB can be bound to the interface IP
  or to the loopback address on the same port if SOF_REUSEADDR is set. Any combination of PCB's bound to 
  the same local port, but to one address out of {IP_ADDR_ANY, 127.0.0.1, interface IP} at a time is valid.
  But no two PCB's bound to same local port and same local address is valid.
  
  If SOF_REUSEPORT is set several PCB's can be bound to same local port and same local address also. But then 
  all PCB's must have the SOF_REUSEPORT option set.
  
  When the two options aren't set and specified port is already bound, ERR_USE is returned saying that 
  address is already in use. */
  for(cpcb = (struct tcp_pcb *)tcp_listen_pcbs; cpcb != NULL; cpcb = cpcb->next) {
    if(cpcb->local_port == port) {
      if(ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
        if(pcb->so_options & SOF_REUSEPORT) {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in listening PCB's: SO_REUSEPORT set and same address.\n"));
          reuse_port_all_set = (reuse_port_all_set && (cpcb->so_options & SOF_REUSEPORT));
        }
        else {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in listening PCB's: SO_REUSEPORT not set and same address.\n"));
          return ERR_USE;
        }
      }
      else if((ip_addr_isany(ipaddr) && !ip_addr_isany(&(cpcb->local_ip))) ||
              (!ip_addr_isany(ipaddr) && ip_addr_isany(&(cpcb->local_ip)))) {
        if(!(pcb->so_options & SOF_REUSEADDR) && !(pcb->so_options & SOF_REUSEPORT)) {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in listening PCB's SO_REUSEPORT or SO_REUSEADDR not set and not the same address.\n"));
          return ERR_USE;
        }      
        else {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in listening PCB's SO_REUSEPORT or SO_REUSEADDR set and not the same address.\n"));
        }     
      }
    }
  }

  /* Search through list of PCB's in a state in which they can accept or send data. Same decription as for 
     PCB's in state LISTEN applies to this PCB's regarding the options SOF_REUSEADDR and SOF_REUSEPORT. */
  for(cpcb = tcp_active_pcbs; cpcb != NULL; cpcb = cpcb->next) {
    if(cpcb->local_port == port) {
      if(ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
        if(pcb->so_options & SOF_REUSEPORT) {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in active PCB's SO_REUSEPORT set and same address.\n"));
          reuse_port_all_set = (reuse_port_all_set && (cpcb->so_options & SOF_REUSEPORT));
        }
        else {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in active PCB's SO_REUSEPORT not set and same address.\n"));
          return ERR_USE;
        }
      }
      else if((ip_addr_isany(ipaddr) && !ip_addr_isany(&(cpcb->local_ip))) ||
              (!ip_addr_isany(ipaddr) && ip_addr_isany(&(cpcb->local_ip)))) {
        if(!(pcb->so_options & SOF_REUSEADDR) && !(pcb->so_options & SOF_REUSEPORT)) {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in active PCB's SO_REUSEPORT or SO_REUSEADDR not set and not the same address.\n"));
          return ERR_USE;
        }   
        else {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in active PCB's SO_REUSEPORT or SO_REUSEADDR set and not the same address.\n"));
        }        
      }
    }
  }

  /* Search through list of PCB's in TIME_WAIT state. If SO_REUSEADDR is set a bound combination [IP, port} 
     can be rebound. The same applies when SOF_REUSEPORT is set. 
     
     If SOF_REUSEPORT is set several PCB's can be bound to same local port and same local address also. But then 
     all PCB's must have the SOF_REUSEPORT option set.
     
     When the two options aren't set and specified port is already bound, ERR_USE is returned saying that 
     address is already in use. */
  for(cpcb = tcp_tw_pcbs; cpcb != NULL; cpcb = cpcb->next) {
    if(cpcb->local_port == port) {
      if(ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
        if(!(pcb->so_options & SOF_REUSEADDR) && !(pcb->so_options & SOF_REUSEPORT)) {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in TIME_WAIT PCB's SO_REUSEPORT or SO_REUSEADDR not set and same address.\n"));
          return ERR_USE;
        }
        else if(pcb->so_options & SOF_REUSEPORT) {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: in TIME_WAIT PCB's SO_REUSEPORT set and same address.\n"));
          reuse_port_all_set = (reuse_port_all_set && (cpcb->so_options & SOF_REUSEPORT));
        }
      }
    }
  }

  /* If SOF_REUSEPORT isn't set in all PCB's bound to specified port and local address specified then 
     {IP, port} can't be reused. */
  if(!reuse_port_all_set) {
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: not all sockets have SO_REUSEPORT set.\n"));
    return ERR_USE;
  }
#endif /* SO_REUSE */

  if (!ip_addr_isany(ipaddr)) {
    pcb->local_ip = *ipaddr;
  }
  pcb->local_port = port;
  LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: bind to port %u\n", port));
  return ERR_OK;
}
#if LWIP_CALLBACK_API
static err_t tcp_accept_null ( void* arg, struct tcp_pcb* pcb, err_t err ) {
 ( void )arg;
 ( void )pcb;
 ( void )err;
 return ERR_ABRT;
}  /* end tcp_accept_null */
#endif  /* LWIP_CALLBACK_API */
/*
 * tcp_listen():
 *
 * Set the state of the connection to be LISTEN, which means that it
 * is able to accept incoming connections. The protocol control block
 * is reallocated in order to consume less memory. Setting the
 * connection to LISTEN is an irreversible process.
 *
 */

struct tcp_pcb *
tcp_listen(struct tcp_pcb *pcb)
{
  struct tcp_pcb_listen *lpcb;

  /* already listening? */
  if (pcb->state == LISTEN) {
    return pcb;
  }
  lpcb = memp_malloc(MEMP_TCP_PCB_LISTEN);
  if (lpcb == NULL) {
    return NULL;
  }
  lpcb->callback_arg = pcb->callback_arg;
  lpcb->local_port = pcb->local_port;
  lpcb->state = LISTEN;
  lpcb->so_options = pcb->so_options;
  lpcb->so_options |= SOF_ACCEPTCONN;
  lpcb->ttl = pcb->ttl;
  lpcb->tos = pcb->tos;
  ip_addr_set(&lpcb->local_ip, &pcb->local_ip);
  memp_free(MEMP_TCP_PCB, pcb);
#if LWIP_CALLBACK_API
  lpcb->accept = tcp_accept_null;
#endif /* LWIP_CALLBACK_API */
  TCP_REG(&tcp_listen_pcbs, lpcb);
  return (struct tcp_pcb *)lpcb;
}

/*
 * tcp_recved():
 *
 * This function should be called by the application when it has
 * processed the data. The purpose is to advertise a larger window
 * when the data has been processed.
 *
 */
void
tcp_recved(struct tcp_pcb *pcb, u16_t len)
{
  if ((u32_t)pcb->rcv_wnd + len > TCP_WND) {
    pcb->rcv_wnd = TCP_WND;
  } else {
    pcb->rcv_wnd += len;
  }
  if (pcb->flags & TF_ACKNODELAY) {
    tcp_ack_now(pcb);
    pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
  } else if (!(pcb->flags & TF_ACK_DELAY) &&
             !(pcb->flags & TF_ACK_NOW)) {
    tcp_ack(pcb);
  }

}

/*
 * tcp_new_port():
 *
 * A nastly hack featuring 'goto' statements that allocates a
 * new TCP local port.
 */

static u16_t
tcp_new_port(void)
{
  struct tcp_pcb *pcb;
#ifndef TCP_LOCAL_PORT_RANGE_START
#define TCP_LOCAL_PORT_RANGE_START 4096
#define TCP_LOCAL_PORT_RANGE_END   0x7fff
#endif
  static u16_t port = TCP_LOCAL_PORT_RANGE_START;
  
 again:
  if (++port > TCP_LOCAL_PORT_RANGE_END) {
    port = TCP_LOCAL_PORT_RANGE_START;
  }
  
  for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
    if (pcb->local_port == port) {
      goto again;
    }
  }
  for(pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
    if (pcb->local_port == port) {
      goto again;
    }
  }
  for(pcb = (struct tcp_pcb *)tcp_listen_pcbs; pcb != NULL; pcb = pcb->next) {
    if (pcb->local_port == port) {
      goto again;
    }
  }
  return port;
}

/*
 * 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;

  LWIP_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 = ( pcb -> mss << 24 ) | (   (  ( u32_t )pcb -> mss / 256  ) << 16   ) |
            (  ( u32_t )4 << 8 ) | 2;

  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;
 err_t  err = ERR_OK;

 ++tcp_ticks;

 prev = NULL;
 pcb = tcp_active_pcbs;

 while ( pcb != NULL ) {

  u32_t lTicks = ( u32_t )( tcp_ticks - pcb -> tmr );

  pcb_remove = 0;

  if ( pcb -> state == SYN_SENT && pcb -> nrtx == TCP_SYNMAXRTX ) {
   ++pcb_remove;
  } else if ( pcb -> nrtx == TCP_MAXRTX ) {
   ++pcb_remove;
  } else {
   ++pcb -> rtime;
   if ( pcb -> unacked != NULL && pcb -> rtime >= pcb -> rto ) {
/* Time for a retransmission.                             */
/* 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 = LWIP_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;
   }  /* end if */
  }  /* end else */
/* Check if this PCB has stayed too long in FIN-WAIT-2 */
  if ( pcb -> state == FIN_WAIT_2 && lTicks > TCP_FIN_WAIT_TIMEOUT / TCP_SLOW_INTERVAL ) ++pcb_remove;
/* Check if KEEPALIVE should be sent */
  if (  ( pcb -> so_options & SOF_KEEPALIVE ) && (
         ( pcb -> state == ESTABLISHED ) || ( pcb -> state == CLOSE_WAIT )
        )
  ) {
   if (  lTicks > ( pcb -> keepalive + TCP_MAXIDLE ) / TCP_SLOW_INTERVAL  )  {
    tcp_abort ( pcb );
   } else if (  lTicks > ( pcb -> keepalive + pcb -> keep_cnt * TCP_KEEPINTVL ) / TCP_SLOW_INTERVAL  ) {
    tcp_keepalive ( pcb );
    pcb -> keep_cnt++;
   }  /* end if */
  }  /* end if */
/* 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 && lTicks >= pcb -> rto * TCP_OOSEQ_TIMEOUT ) {
   tcp_segs_free ( pcb -> ooseq );
   pcb -> ooseq = NULL;
  }  /* end if */
#endif  /* TCP_QUEUE_OOSEQ */
/* Check if this PCB has stayed too long in SYN-RCVD */
  if ( pcb -> state == SYN_RCVD ) {
   if (  lTicks > TCP_SYN_RCVD_TIMEOUT / TCP_SLOW_INTERVAL ) ++pcb_remove;
  }  /* end if */
/* 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 ) {
    prev -> next = pcb -> next;
   } else {
/* This PCB was the first. */
    tcp_active_pcbs = pcb -> next;
   }  /* end else */

   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;
    TCP_EVENT_POLL( pcb, err );
    if ( err == ERR_OK ) tcp_output ( pcb );
   }  /* end if */

   prev = pcb;
   pcb  = pcb -> next;
  }  /* end else */

 }  /* end while */
/* Steps through all of the TIME-WAIT PCBs. */
 prev = NULL;    
 pcb  = tcp_tw_pcbs;

 while ( pcb != NULL ) {
/* Check if this PCB has stayed long enough in TIME-WAIT */
  if (  ( u32_t )( tcp_ticks - pcb -> tmr ) > 2 * TCP_MSL / TCP_SLOW_INTERVAL  ) {
/* If the PCB should be removed, do it. */
   tcp_pcb_purge ( pcb );      
/* Remove PCB from tcp_tw_pcbs list. */
   if ( prev != NULL ) {
    prev -> next = pcb -> next;
   } else {
/* This PCB was the first. */
    tcp_tw_pcbs = pcb -> next;
   }  /* end else */
   pcb2 = pcb -> next;
   memp_free ( MEMP_TCP_PCB, pcb );
   pcb = pcb2;
  } else {
   prev = pcb;
   pcb  = pcb -> next;
  }  /* end else */
 }  /* end while */

}  /* end tcp_slowtmr */
/*
 * tcp_fasttmr():
 *
 * Is called every TCP_FAST_INTERVAL (250 ms) and sends delayed ACKs.
 */
void tcp_fasttmr ( void ) {

 struct tcp_pcb* pcb;

 for ( pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb -> next ) {
  if ( pcb -> flags & TF_ACK_DELAY ) {
   tcp_ack_now ( pcb );
   pcb -> flags &= ~( TF_ACK_DELAY | TF_ACK_NOW );
  }  /* end if */
 }  /* end for */

}  /* end tcp_fasttmr */
/*
 * 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;
 while ( seg != NULL ) {
  next = seg -> next;
  count += tcp_seg_free ( seg );
  seg  = next;
 }  /* end while */
 return count;
}  /* end */
/*
 * 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 ) count = pbuf_free ( seg -> p );
  memp_free ( MEMP_TCP_SEG, seg );
 }  /* end if */
 return count;
}  /* end tcp_seg_free */
#if TCP_QUEUE_OOSEQ
/*
 * 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 = memp_malloc ( MEMP_TCP_SEG );
 if ( cseg ) {
  mips_memcpy (  ( char* )cseg, ( const char* )seg, sizeof ( struct tcp_seg )  ); 
  pbuf_ref ( cseg -> p );
 }  /* end if */
 return cseg;
}  /* end tcp_seg_copy */
#endif  /* end TCP_QUEUE_OOSEQ */
#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) {
    LWIP_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) {
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_kill_timewait: killing oldest TIME-WAIT PCB 0x%p (%ld)\n",
           (void *)inactive, inactivity));
    tcp_abort(inactive);
  }      
}



struct tcp_pcb *
tcp_alloc(u8_t prio)
{
  struct tcp_pcb *pcb;
  u32_t iss;
  
  pcb = memp_malloc(MEMP_TCP_PCB);
  if (pcb == NULL) {
    /* Try killing oldest connection in TIME-WAIT. */
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_alloc: killing off oldest TIME-WAIT connection\n"));
    tcp_kill_timewait();
    pcb = memp_malloc(MEMP_TCP_PCB);
    if (pcb == NULL) {
      tcp_kill_prio(prio);    
      pcb = memp_malloc(MEMP_TCP_PCB);
    }
  }
  if (pcb != NULL) {
    mips_memset(pcb, 0, sizeof(struct tcp_pcb));
    pcb->prio = TCP_PRIO_NORMAL;
    pcb->snd_buf = TCP_SND_BUF;
    pcb->snd_queuelen = 0;
    pcb->rcv_wnd = TCP_WND;
    pcb->tos = 0;
    pcb->ttl = TCP_TTL;
    pcb->mss = TCP_MSS;
    pcb->rto = 3000 / TCP_SLOW_INTERVAL;
    pcb->sa = 0;
    pcb->sv = 3000 / TCP_SLOW_INTERVAL;
    pcb->rtime = 0;
    pcb->cwnd = 1;
    iss = tcp_next_iss();
    pcb->snd_wl2 = iss;
    pcb->snd_nxt = iss;
    pcb->snd_max = iss;
    pcb->lastack = iss;
    pcb->snd_lbb = iss;   
    pcb->tmr = tcp_ticks;

    pcb->polltmr = 0;

#if LWIP_CALLBACK_API
    pcb->recv = tcp_recv_null;
#endif /* LWIP_CALLBACK_API */  
    
    /* Init KEEPALIVE timer */
    pcb->keepalive = TCP_KEEPDEFAULT;
    pcb->keep_cnt = 0;
  }
  return pcb;
}
/*
 * tcp_pcb_purge():
 *
 * Purges a TCP PCB. Removes any buffered data and frees the buffer memory.
 *
 */

void
tcp_pcb_purge(struct tcp_pcb *pcb)
{
  if (pcb->state != CLOSED &&
     pcb->state != TIME_WAIT &&
     pcb->state != LISTEN) {

    LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge\n"));
    
    if (pcb->unsent != NULL) {    
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: not all data sent\n"));
    }
    if (pcb->unacked != NULL) {    
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->unacked\n"));
    }
#if TCP_QUEUE_OOSEQ /* LW */
    if (pcb->ooseq != NULL) {    
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->ooseq\n"));
    }
    
    tcp_segs_free(pcb->ooseq);
    pcb->ooseq = NULL;
#endif /* TCP_QUEUE_OOSEQ */
    tcp_segs_free(pcb->unsent);
    tcp_segs_free(pcb->unacked);
    pcb->unacked = pcb->unsent = NULL;
  }
}

/*
 * tcp_pcb_remove():
 *
 * Purges the PCB and removes it from a PCB list. Any delayed ACKs are sent first.
 *
 */

void
tcp_pcb_remove(struct tcp_pcb **pcblist, struct tcp_pcb *pcb)
{
  TCP_RMV(pcblist, pcb);

  tcp_pcb_purge(pcb);
  
  /* if there is an outstanding delayed ACKs, send it */
  if (pcb->state != TIME_WAIT &&
     pcb->state != LISTEN &&
     pcb->flags & TF_ACK_DELAY) {
    pcb->flags |= TF_ACK_NOW;
    tcp_output(pcb);
  }  
  pcb->state = CLOSED;

  LWIP_ASSERT("tcp_pcb_remove: tcp_pcbs_sane()", tcp_pcbs_sane());
}
/*
 * tcp_next_iss():
 *
 * Calculates a new initial sequence number for new connections.
 *
 */
u32_t tcp_next_iss ( void ) {
 static u32_t iss = 6510;
 iss += tcp_ticks;
 return iss;
}  /* end tcp_next_iss */
#endif  /* LWIP_TCP */
