text: /**
   * @file
   * Transmission Control Protocol for IP
   *
   * 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_in.c and tcp_out.c respectively.
   *
   */
  
  /*
   * Copyright (c) 2001-2004 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>
   *
   */
  
  #include "lwip/opt.h"
  
  #if LWIP_TCP /* don't build if not configured for use in lwipopts.h */
  
  #include "lwip/def.h"
  #include "lwip/mem.h"
  #include "lwip/memp.h"
  #include "lwip/tcp.h"
  #include "lwip/priv/tcp_priv.h"
  #include "lwip/debug.h"
  #include "lwip/stats.h"
  #include "lwip/ip6.h"
  #include "lwip/ip6_addr.h"
  #include "lwip/nd6.h"
  
  #include <string.h>
  
  #ifndef TCP_LOCAL_PORT_RANGE_START
  /* From http://www.iana.org/assignments/port-numbers:
     "The Dynamic and/or Private Ports are those from 49152 through 65535" */
  #define TCP_LOCAL_PORT_RANGE_START        0xc000
  #define TCP_LOCAL_PORT_RANGE_END          0xffff
  #define TCP_ENSURE_LOCAL_PORT_RANGE(port) ((u16_t)(((port) & ~TCP_LOCAL_PORT_RANGE_START) + TCP_LOCAL_PORT_RANGE_START))
  #endif
  
  #if LWIP_TCP_KEEPALIVE
  #define TCP_KEEP_DUR(pcb)   ((pcb)->keep_cnt * (pcb)->keep_intvl)
  #define TCP_KEEP_INTVL(pcb) ((pcb)->keep_intvl)
  #else /* LWIP_TCP_KEEPALIVE */
  #define TCP_KEEP_DUR(pcb)   TCP_MAXIDLE
  #define TCP_KEEP_INTVL(pcb) TCP_KEEPINTVL_DEFAULT
  #endif /* LWIP_TCP_KEEPALIVE */
  
  const char * const tcp_state_str[] = {
    "CLOSED",
    "LISTEN",
    "SYN_SENT",
    "SYN_RCVD",
    "ESTABLISHED",
    "FIN_WAIT_1",
    "FIN_WAIT_2",
    "CLOSE_WAIT",
    "CLOSING",
    "LAST_ACK",
    "TIME_WAIT"
  };
  
  
  /* last local TCP port */
  static s16_t tcp_port = TCP_LOCAL_PORT_RANGE_START;
  
  /* Incremented every coarse grained timer shot (typically every 500 ms). */
  u32_t tcp_ticks;
  
  const u8_t tcp_backoff[13] = { 1, 2, 3, 4, 5, 6, 7, 7, 7, 7, 7, 7, 7};
   /* Times per slowtmr hits */
  const u8_t tcp_persist_backoff[7] = { 3, 6, 12, 24, 48, 96, 120 };
  
  
  /* The TCP PCB lists. */
  
  /** List of all TCP PCBs bound but not yet (connected || listening) */
  struct tcp_pcb *tcp_bound_pcbs;
  /** List of all TCP PCBs in LISTEN state */
  union tcp_listen_pcbs_t tcp_listen_pcbs;
  /** List of all TCP PCBs that are in a state in which
   * they accept or send data. */
  struct tcp_pcb *tcp_active_pcbs;
  /** List of all TCP PCBs in TIME-WAIT state */
  struct tcp_pcb *tcp_tw_pcbs;
  
  /** An array with all (non-temporary) PCB lists, mainly used for smaller code size */
  struct tcp_pcb ** const tcp_pcb_lists[] = {&tcp_listen_pcbs.pcbs, &tcp_bound_pcbs,
          &tcp_active_pcbs, &tcp_tw_pcbs};
  
  u8_t tcp_active_pcbs_changed;
  
  /** Timer counter to handle calling slow-timer from tcp_tmr() */
  static u8_t tcp_timer;
  static u8_t tcp_timer_ctr;
  static u16_t tcp_new_port(void);
  
  /**
   * Initialize this module.
   */
  void
  tcp_init(void)
  {
  #if LWIP_RANDOMIZE_INITIAL_LOCAL_PORTS && defined(LWIP_RAND)
    tcp_port = TCP_ENSURE_LOCAL_PORT_RANGE(LWIP_RAND());
  #endif /* LWIP_RANDOMIZE_INITIAL_LOCAL_PORTS && defined(LWIP_RAND) */
  }
  
  /**
   * Called periodically to dispatch TCP timers.
   */
  void
  tcp_tmr(void)
  {
    /* Call tcp_fasttmr() every 250 ms */
    tcp_fasttmr();
  
    if (++tcp_timer & 1) {
      /* Call tcp_slowtmr() every 500 ms, i.e., every other timer
         tcp_tmr() is called. */
      tcp_slowtmr();
    }
  }
  
  void
  tcp_set_fin_wait_1(struct tcp_pcb *pcb)
  {
    pcb->state = FIN_WAIT_1;
  #if ESP_LWIP
    pcb->tmr = tcp_ticks;
  #endif
  }
  
  /**
   * Closes the TX side of a connection held by the PCB.
   * For tcp_close(), a RST is sent if the application didn't receive all data
   * (tcp_recved() not called for all data passed to recv callback).
   *
   * Listening pcbs are freed and may not be referenced any more.
   * Connection pcbs are freed if not yet connected and may not be referenced
   * any more. If a connection is established (at least SYN received or in
   * a closing state), the connection is closed, and put in a closing state.
   * The pcb is then automatically freed in tcp_slowtmr(). It is therefore
   * unsafe to reference it.
   *
   * @param pcb the tcp_pcb to close
   * @return ERR_OK if connection has been closed
   *         another err_t if closing failed and pcb is not freed
   */
  static err_t
  tcp_close_shutdown(struct tcp_pcb *pcb, u8_t rst_on_unacked_data)
  {
    err_t err;
  
    if (rst_on_unacked_data && ((pcb->state == ESTABLISHED) || (pcb->state == CLOSE_WAIT))) {
      if ((pcb->refused_data != NULL) || (pcb->rcv_wnd != TCP_WND_MAX(pcb))) {
        /* Not all data received by application, send RST to tell the remote
           side about this. */
        LWIP_ASSERT("pcb->flags & TF_RXCLOSED", pcb->flags & TF_RXCLOSED);
  
        /* don't call tcp_abort here: we must not deallocate the pcb since
           that might not be expected when calling tcp_close */
        tcp_rst(pcb->snd_nxt, pcb->rcv_nxt, &pcb->local_ip, &pcb->remote_ip,
                 pcb->local_port, pcb->remote_port);
  
        tcp_pcb_purge(pcb);
        TCP_RMV_ACTIVE(pcb);
        if (pcb->state == ESTABLISHED) {
          /* move to TIME_WAIT since we close actively */
          pcb->state = TIME_WAIT;
          TCP_REG(&tcp_tw_pcbs, pcb);
        } else {
          /* CLOSE_WAIT: deallocate the pcb since we already sent a RST for it */
          if (tcp_input_pcb == pcb) {
            /* prevent using a deallocated pcb: free it from tcp_input later */
            tcp_trigger_input_pcb_close();
          } else {
            memp_free(MEMP_TCP_PCB, pcb);
          }
        }
        return ERR_OK;
      }
    }
  
    switch (pcb->state) {
    case CLOSED:
      /* Closing a pcb in the CLOSED state might seem erroneous,
       * however, it is in this state once allocated and as yet unused
       * and the user needs some way to free it should the need arise.
       * Calling tcp_close() with a pcb that has already been closed, (i.e. twice)
       * or for a pcb that has been used and then entered the CLOSED state
       * is erroneous, but this should never happen as the pcb has in those cases
       * been freed, and so any remaining handles are bogus. */
      err = ERR_OK;
      if (pcb->local_port != 0) {
        TCP_RMV(&tcp_bound_pcbs, pcb);
      }
      memp_free(MEMP_TCP_PCB, pcb);
      pcb = NULL;
      break;
    case LISTEN:
      err = ERR_OK;
      tcp_pcb_remove(&tcp_listen_pcbs.pcbs, pcb);
      memp_free(MEMP_TCP_PCB_LISTEN, pcb);
      pcb = NULL;
      break;
    case SYN_SENT:
      err = ERR_OK;
      TCP_PCB_REMOVE_ACTIVE(pcb);
      memp_free(MEMP_TCP_PCB, pcb);
      pcb = NULL;
      MIB2_STATS_INC(mib2.tcpattemptfails);
      break;
    case SYN_RCVD:
      err = tcp_send_fin(pcb);
      if (err == ERR_OK) {
        MIB2_STATS_INC(mib2.tcpattemptfails);
        tcp_set_fin_wait_1(pcb);
      }
      break;
    case ESTABLISHED:
      err = tcp_send_fin(pcb);
      if (err == ERR_OK) {
        MIB2_STATS_INC(mib2.tcpestabresets);
        tcp_set_fin_wait_1(pcb);
      }
      break;
    case CLOSE_WAIT:
      err = tcp_send_fin(pcb);
      if (err == ERR_OK) {
        MIB2_STATS_INC(mib2.tcpestabresets);
        pcb->state = LAST_ACK;
      }
      break;
    default:
      /* Has already been closed, do nothing. */
      err = ERR_OK;
      pcb = NULL;
      break;
    }
  
    if (pcb != NULL && err == ERR_OK) {
      /* To ensure all data has been sent when tcp_close returns, we have
         to make sure tcp_output doesn't fail.
         Since we don't really have to ensure all data has been sent when tcp_close
         returns (unsent data is sent from tcp timer functions, also), we don't care
         for the return value of tcp_output for now. */
      tcp_output(pcb);
    }
    return err;
  }
  
  /**
   * Closes the connection held by the PCB.
   *
   * Listening pcbs are freed and may not be referenced any more.
   * Connection pcbs are freed if not yet connected and may not be referenced
   * any more. If a connection is established (at least SYN received or in
   * a closing state), the connection is closed, and put in a closing state.
   * The pcb is then automatically freed in tcp_slowtmr(). It is therefore
   * unsafe to reference it (unless an error is returned).
   *
   * @param pcb the tcp_pcb to close
   * @return ERR_OK if connection has been closed
   *         another err_t if closing failed and pcb is not freed
   */
  err_t
  tcp_close(struct tcp_pcb *pcb)
  {
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_close: closing in "));
    tcp_debug_print_state(pcb->state);
  
    if (pcb->state != LISTEN) {
      /* Set a flag not to receive any more data... */
      pcb->flags |= TF_RXCLOSED;
    }
    /* ... and close */
    return tcp_close_shutdown(pcb, 1);
  }
  
  /**
   * Causes all or part of a full-duplex connection of this PCB to be shut down.
   * This doesn't deallocate the PCB unless shutting down both sides!
   * Shutting down both sides is the same as calling tcp_close, so if it succeds,
   * the PCB should not be referenced any more.
   *
   * @param pcb PCB to shutdown
   * @param shut_rx shut down receive side if this is != 0
   * @param shut_tx shut down send side if this is != 0
   * @return ERR_OK if shutdown succeeded (or the PCB has already been shut down)
   *         another err_t on error.
   */
  err_t
  tcp_shutdown(struct tcp_pcb *pcb, int shut_rx, int shut_tx)
  {
    if (pcb->state == LISTEN) {
      return ERR_CONN;
    }
    if (shut_rx) {
      /* shut down the receive side: set a flag not to receive any more data... */
      pcb->flags |= TF_RXCLOSED;
      if (shut_tx) {
        /* shutting down the tx AND rx side is the same as closing for the raw API */
        return tcp_close_shutdown(pcb, 1);
      }
      /* ... and free buffered data */
      if (pcb->refused_data != NULL) {
        pbuf_free(pcb->refused_data);
        pcb->refused_data = NULL;
      }
    }
    if (shut_tx) {
      /* This can't happen twice since if it succeeds, the pcb's state is changed.
         Only close in these states as the others directly deallocate the PCB */
      switch (pcb->state) {
      case SYN_RCVD:
      case ESTABLISHED:
      case CLOSE_WAIT:
        return tcp_close_shutdown(pcb, (u8_t)shut_rx);
      default:
        /* Not (yet?) connected, cannot shutdown the TX side as that would bring us
          into CLOSED state, where the PCB is deallocated. */
        return ERR_CONN;
      }
    }
    return ERR_OK;
  }
  
  /**
   * Abandons a connection and optionally sends a RST to the remote
   * host.  Deletes the local protocol control block. This is done when
   * a connection is killed because of shortage of memory.
   *
   * @param pcb the tcp_pcb to abort
   * @param reset boolean to indicate whether a reset should be sent
   */
  void
  tcp_abandon(struct tcp_pcb *pcb, int reset)
  {
    u32_t seqno, ackno;
  #if LWIP_CALLBACK_API
    tcp_err_fn errf;
  #endif /* LWIP_CALLBACK_API */
    void *errf_arg;
  
    /* pcb->state LISTEN not allowed here */
    LWIP_ASSERT("don't call tcp_abort/tcp_abandon for listen-pcbs",
      pcb->state != LISTEN);
    /* 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 {
      int send_rst = 0;
      u16_t local_port = 0;
      seqno = pcb->snd_nxt;
      ackno = pcb->rcv_nxt;
  #if LWIP_CALLBACK_API
      errf = pcb->errf;
  #endif /* LWIP_CALLBACK_API */
      errf_arg = pcb->callback_arg;
      if ((pcb->state == CLOSED) && (pcb->local_port != 0)) {
        /* bound, not yet opened */
        TCP_RMV(&tcp_bound_pcbs, pcb);
      } else {
        send_rst = reset;
        local_port = pcb->local_port;
        TCP_PCB_REMOVE_ACTIVE(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);
        pcb->ooseq = NULL;
      }
  #endif /* TCP_QUEUE_OOSEQ */
      if (send_rst) {
        LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_abandon: sending RST\n"));
        tcp_rst(seqno, ackno, &pcb->local_ip, &pcb->remote_ip, local_port, pcb->remote_port);
      }
      memp_free(MEMP_TCP_PCB, pcb);
      TCP_EVENT_ERR(errf, errf_arg, ERR_ABRT);
    }
  }
  
  /**
   * Aborts the connection by sending a RST (reset) segment to the remote
   * host. The pcb is deallocated. This function never fails.
   *
   * ATTENTION: When calling this from one of the TCP callbacks, make
   * sure you always return ERR_ABRT (and never return ERR_ABRT otherwise
   * or you will risk accessing deallocated memory or memory leaks!
   *
   * @param pcb the tcp pcb to abort
   */
  void
  tcp_abort(struct tcp_pcb *pcb)
  {
    tcp_abandon(pcb, 1);
  }
  
  /**
   * Binds the connection to a local port number 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.
   *
   * @param pcb the tcp_pcb to bind (no check is done whether this pcb is
   *        already bound!)
   * @param ipaddr the local ip address to bind to (use IP_ADDR_ANY to bind
   *        to any local address
   * @param port the local port to bind to
   * @return ERR_USE if the port is already in use
   *         ERR_VAL if bind failed because the PCB is not in a valid state
   *         ERR_OK if bound
   */
  err_t
  tcp_bind(struct tcp_pcb *pcb, const ip_addr_t *ipaddr, u16_t port)
  {
    int i;
    int max_pcb_list = NUM_TCP_PCB_LISTS;
    struct tcp_pcb *cpcb;
  
  #if LWIP_IPV4
    /* Don't propagate NULL pointer (IPv4 ANY) to subsequent functions */
    if (ipaddr == NULL) {
      ipaddr = IP_ADDR_ANY;
    }
  #endif /* LWIP_IPV4 */
  
    /* still need to check for ipaddr == NULL in IPv6 only case */
    if ((pcb == NULL) || (ipaddr == NULL) || !IP_ADDR_PCB_VERSION_MATCH_EXACT(pcb, ipaddr)) {
      return ERR_VAL;
    }
  
    LWIP_ERROR("tcp_bind: can only bind in state CLOSED", pcb->state == CLOSED, return ERR_VAL);
  
  #if SO_REUSE
    /* Unless the REUSEADDR flag is set,
       we have to check the pcbs in TIME-WAIT state, also.
       We do not dump TIME_WAIT pcb's; they can still be matched by incoming
       packets using both local and remote IP addresses and ports to distinguish.
     */
    if (ip_get_option(pcb, SOF_REUSEADDR)) {
      max_pcb_list = NUM_TCP_PCB_LISTS_NO_TIME_WAIT;
    }
  #endif /* SO_REUSE */
  
    if (port == 0) {
      port = tcp_new_port();
      if (port == 0) {
        return ERR_BUF;
      }
    } else {
      /* Check if the address already is in use (on all lists) */
      for (i = 0; i < max_pcb_list; i++) {
        for (cpcb = *tcp_pcb_lists[i]; cpcb != NULL; cpcb = cpcb->next) {
          if (cpcb->local_port == port) {
  #if SO_REUSE
            /* Omit checking for the same port if both pcbs have REUSEADDR set.
               For SO_REUSEADDR, the duplicate-check for a 5-tuple is done in
               tcp_connect. */
            if (!ip_get_option(pcb, SOF_REUSEADDR) ||
                !ip_get_option(cpcb, SOF_REUSEADDR))
  #endif /* SO_REUSE */
            {
              /* @todo: check accept_any_ip_version */
              if ((IP_IS_V6(ipaddr) == IP_IS_V6_VAL(cpcb->local_ip)) &&
                  (ip_addr_isany(&cpcb->local_ip) ||
                  ip_addr_isany(ipaddr) ||
                  ip_addr_cmp(&cpcb->local_ip, ipaddr))) {
                return ERR_USE;
              }
            }
          }
        }
      }
    }
  
    if (!ip_addr_isany(ipaddr)) {
      ip_addr_set(&pcb->local_ip, ipaddr);
    }
    pcb->local_port = port;
    TCP_REG(&tcp_bound_pcbs, pcb);
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: bind to port %"U16_F"\n", port));
    return ERR_OK;
  }
  #if LWIP_CALLBACK_API
  /**
   * Default accept callback if no accept callback is specified by the user.
   */
  static err_t
  tcp_accept_null(void *arg, struct tcp_pcb *pcb, err_t err)
  {
    LWIP_UNUSED_ARG(arg);
    LWIP_UNUSED_ARG(err);
  
    tcp_abort(pcb);
  
    return ERR_ABRT;
  }
  #endif /* LWIP_CALLBACK_API */
  
  /**
   * 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.
   *
   * @param pcb the original tcp_pcb
   * @param backlog the incoming connections queue limit
   * @return tcp_pcb used for listening, consumes less memory.
   *
   * @note The original tcp_pcb is freed. This function therefore has to be
   *       called like this:
   *             tpcb = tcp_listen(tpcb);
   */
  struct tcp_pcb *
  tcp_listen_with_backlog(struct tcp_pcb *pcb, u8_t backlog)
  {
    struct tcp_pcb_listen *lpcb;
  
    LWIP_UNUSED_ARG(backlog);
    LWIP_ERROR("tcp_listen: pcb already connected", pcb->state == CLOSED, return NULL);
  
    /* already listening? */
    if (pcb->state == LISTEN) {
      return pcb;
    }
  #if SO_REUSE
    if (ip_get_option(pcb, SOF_REUSEADDR)) {
      /* Since SOF_REUSEADDR allows reusing a local address before the pcb's usage
         is declared (listen-/connection-pcb), we have to make sure now that
         this port is only used once for every local IP. */
      for (lpcb = tcp_listen_pcbs.listen_pcbs; lpcb != NULL; lpcb = lpcb->next) {
        if ((lpcb->local_port == pcb->local_port) &&
            ip_addr_cmp(&lpcb->local_ip, &pcb->local_ip)) {
          /* this address/port is already used */
          return NULL;
        }
      }
    }
  #endif /* SO_REUSE */
    lpcb = (struct tcp_pcb_listen *)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->prio = pcb->prio;
    lpcb->so_options = pcb->so_options;
    lpcb->ttl = pcb->ttl;
    lpcb->tos = pcb->tos;
  #if LWIP_IPV4 && LWIP_IPV6
    IP_SET_TYPE_VAL(lpcb->remote_ip, pcb->local_ip.type);
  #endif /* LWIP_IPV4 && LWIP_IPV6 */
    ip_addr_copy(lpcb->local_ip, pcb->local_ip);
    if (pcb->local_port != 0) {
      TCP_RMV(&tcp_bound_pcbs, pcb);
    }
    memp_free(MEMP_TCP_PCB, pcb);
  #if LWIP_CALLBACK_API
    lpcb->accept = tcp_accept_null;
  #endif /* LWIP_CALLBACK_API */
  #if TCP_LISTEN_BACKLOG
    lpcb->accepts_pending = 0;
    tcp_backlog_set(lpcb, backlog);
  #endif /* TCP_LISTEN_BACKLOG */
    TCP_REG(&tcp_listen_pcbs.pcbs, (struct tcp_pcb *)lpcb);
    return (struct tcp_pcb *)lpcb;
  }
  
  /**
   * Update the state that tracks the available window space to advertise.
   *
   * Returns how much extra window would be advertised if we sent an
   * update now.
   */
  u32_t tcp_update_rcv_ann_wnd(struct tcp_pcb *pcb)
  {
    u32_t new_right_edge = pcb->rcv_nxt + pcb->rcv_wnd;
  
    if (TCP_SEQ_GEQ(new_right_edge, pcb->rcv_ann_right_edge + LWIP_MIN((TCP_WND(pcb) / 2), pcb->mss))) {
      /* we can advertise more window */
      pcb->rcv_ann_wnd = pcb->rcv_wnd;
      return new_right_edge - pcb->rcv_ann_right_edge;
    } else {
      if (TCP_SEQ_GT(pcb->rcv_nxt, pcb->rcv_ann_right_edge)) {
        /* Can happen due to other end sending out of advertised window,
         * but within actual available (but not yet advertised) window */
        pcb->rcv_ann_wnd = 0;
      } else {
        /* keep the right edge of window constant */
        u32_t new_rcv_ann_wnd = pcb->rcv_ann_right_edge - pcb->rcv_nxt;
  #if !LWIP_WND_SCALE
        LWIP_ASSERT("new_rcv_ann_wnd <= 0xffff", new_rcv_ann_wnd <= 0xffff);
  #endif
        pcb->rcv_ann_wnd = (tcpwnd_size_t)new_rcv_ann_wnd;
      }
      return 0;
    }
  }
  
  /**
   * 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.
   *
   * @param pcb the tcp_pcb for which data is read
   * @param len the amount of bytes that have been read by the application
   */
  void
  tcp_recved(struct tcp_pcb *pcb, u16_t len)
  {
    int wnd_inflation;
  
    /* pcb->state LISTEN not allowed here */
    LWIP_ASSERT("don't call tcp_recved for listen-pcbs",
      pcb->state != LISTEN);
  
    pcb->rcv_wnd += len;
    if (pcb->rcv_wnd > TCP_WND_MAX(pcb)) {
      pcb->rcv_wnd = TCP_WND_MAX(pcb);
    } else if (pcb->rcv_wnd == 0) {
      /* rcv_wnd overflowed */
      if ((pcb->state == CLOSE_WAIT) || (pcb->state == LAST_ACK)) {
        /* In passive close, we allow this, since the FIN bit is added to rcv_wnd
           by the stack itself, since it is not mandatory for an application
           to call tcp_recved() for the FIN bit, but e.g. the netconn API does so. */
        pcb->rcv_wnd = TCP_WND_MAX(pcb);
      } else {
        LWIP_ASSERT("tcp_recved: len wrapped rcv_wnd\n", 0);
      }
    }
  
    wnd_inflation = tcp_update_rcv_ann_wnd(pcb);
  
    /* If the change in the right edge of window is significant (default
     * watermark is TCP_WND(pcb)/4), then send an explicit update now.
     * Otherwise wait for a packet to be sent in the normal course of
     * events (or more window to be available later) */
    if (wnd_inflation >= TCP_WND_UPDATE_THRESHOLD(pcb)) {
      tcp_ack_now(pcb);
      tcp_output(pcb);
    }
  
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_recved: received %"U16_F" bytes, wnd %"TCPWNDSIZE_F" (%"TCPWNDSIZE_F").\n",
           len, pcb->rcv_wnd, TCP_WND_MAX(pcb) - pcb->rcv_wnd));
  }
  
  /**
   * Allocate a new local TCP port.
   *
   * @return a new (free) local TCP port number
   */
  static u16_t
  tcp_new_port(void)
  {
    u8_t i;
    u16_t n = 0;
    struct tcp_pcb *pcb;
  
  again:
  
  #if ESP_RANDOM_TCP_PORT
    tcp_port = abs(LWIP_RAND()) % (TCP_LOCAL_PORT_RANGE_END - TCP_LOCAL_PORT_RANGE_START);
    tcp_port += TCP_LOCAL_PORT_RANGE_START;
  #else
    if (tcp_port++ == TCP_LOCAL_PORT_RANGE_END) {
      tcp_port = TCP_LOCAL_PORT_RANGE_START;
    }
  #endif
  
    /* Check all PCB lists. */
    for (i = 0; i < NUM_TCP_PCB_LISTS; i++) {
      for (pcb = *tcp_pcb_lists[i]; pcb != NULL; pcb = pcb->next) {
        if (pcb->local_port == tcp_port) {
          if (++n > (TCP_LOCAL_PORT_RANGE_END - TCP_LOCAL_PORT_RANGE_START)) {
            return 0;
          }
          goto again;
        }
      }
    }
    return tcp_port;
  }
  
  /**
   * Connects to another host. The function given as the "connected"
   * argument will be called when the connection has been established.
   *
   * @param pcb the tcp_pcb used to establish the connection
   * @param ipaddr the remote ip address to connect to
   * @param port the remote tcp port to connect to
   * @param connected callback function to call when connected (on error,
                      the err calback will be called)
   * @return ERR_VAL if invalid arguments are given
   *         ERR_OK if connect request has been sent
   *         other err_t values if connect request couldn't be sent
   */
  err_t
  tcp_connect(struct tcp_pcb *pcb, const ip_addr_t *ipaddr, u16_t port,
        tcp_connected_fn connected)
  {
    err_t ret;
    u32_t iss;
    u16_t old_local_port;
  
    if ((pcb == NULL) || (ipaddr == NULL) || !IP_ADDR_PCB_VERSION_MATCH_EXACT(pcb, ipaddr)) {
      return ERR_VAL;
    }
  
    LWIP_ERROR("tcp_connect: can only connect from state CLOSED", pcb->state == CLOSED, return ERR_ISCONN);
  
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_connect to port %"U16_F"\n", port));
    ip_addr_set(&pcb->remote_ip, ipaddr);
    pcb->remote_port = port;
  
    /* check if we have a route to the remote host */
    if (ip_addr_isany(&pcb->local_ip)) {
      /* no local IP address set, yet. */
      struct netif *netif;
      const ip_addr_t *local_ip;
      ip_route_get_local_ip(&pcb->local_ip, &pcb->remote_ip, netif, local_ip);
      if ((netif == NULL) || (local_ip == NULL)) {
        /* Don't even try to send a SYN packet if we have no route
           since that will fail. */
        return ERR_RTE;
      }
      /* Use the address as local address of the pcb. */
      ip_addr_copy(pcb->local_ip, *local_ip);
    }
  
    old_local_port = pcb->local_port;
    if (pcb->local_port == 0) {
      pcb->local_port = tcp_new_port();
      if (pcb->local_port == 0) {
        return ERR_BUF;
      }
    } else {
  #if SO_REUSE
      if (ip_get_option(pcb, SOF_REUSEADDR)) {
        /* Since SOF_REUSEADDR allows reusing a local address, we have to make sure
           now that the 5-tuple is unique. */
        struct tcp_pcb *cpcb;
        int i;
        /* Don't check listen- and bound-PCBs, check active- and TIME-WAIT PCBs. */
        for (i = 2; i < NUM_TCP_PCB_LISTS; i++) {
          for (cpcb = *tcp_pcb_lists[i]; cpcb != NULL; cpcb = cpcb->next) {
            if ((cpcb->local_port == pcb->local_port) &&
                (cpcb->remote_port == port) &&
                ip_addr_cmp(&cpcb->local_ip, &pcb->local_ip) &&
                ip_addr_cmp(&cpcb->remote_ip, ipaddr)) {
              /* linux returns EISCONN here, but ERR_USE should be OK for us */
              return ERR_USE;
            }
          }
        }
      }
  #endif /* SO_REUSE */
    }
  
    iss = tcp_next_iss();
    pcb->rcv_nxt = 0;
    pcb->snd_nxt = iss;
    pcb->lastack = iss - 1;
    pcb->snd_lbb = iss - 1;
    /* Start with a window that does not need scaling. When window scaling is
       enabled and used, the window is enlarged when both sides agree on scaling. */
    pcb->rcv_wnd = pcb->rcv_ann_wnd = TCPWND_MIN16(TCP_WND(pcb));
    pcb->rcv_ann_right_edge = pcb->rcv_nxt;
    pcb->snd_wnd = TCP_WND(pcb);
    /* As initial send MSS, we use TCP_MSS but limit it to 536.
       The send MSS is updated when an MSS option is received. */
    pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS;
  #if TCP_CALCULATE_EFF_SEND_MSS
    pcb->mss = tcp_eff_send_mss(pcb->mss, &pcb->local_ip, &pcb->remote_ip);
  #endif /* TCP_CALCULATE_EFF_SEND_MSS */
    pcb->cwnd = 1;
    pcb->ssthresh = TCP_WND(pcb);
  #if LWIP_CALLBACK_API
    pcb->connected = connected;
  #else /* LWIP_CALLBACK_API */
    LWIP_UNUSED_ARG(connected);
  #endif /* LWIP_CALLBACK_API */
  
    /* Send a SYN together with the MSS option. */
    ret = tcp_enqueue_flags(pcb, TCP_SYN);
    if (ret == ERR_OK) {
      /* SYN segment was enqueued, changed the pcbs state now */
      pcb->state = SYN_SENT;
      if (old_local_port != 0) {
        TCP_RMV(&tcp_bound_pcbs, pcb);
      }
      TCP_REG_ACTIVE(pcb);
      MIB2_STATS_INC(mib2.tcpactiveopens);
  
      tcp_output(pcb);
    }
    return ret;
  }
  
  /**
   * 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.
   *
   * Automatically called from tcp_tmr().
   */
  void
  tcp_slowtmr(void)
  {
    struct tcp_pcb *pcb, *prev;
    tcpwnd_size_t eff_wnd;
    u8_t pcb_remove;      /* flag if a PCB should be removed */
    u8_t pcb_reset;       /* flag if a RST should be sent when removing */
    err_t err;
  
    err = ERR_OK;
  
    ++tcp_ticks;
    ++tcp_timer_ctr;
  
  tcp_slowtmr_start:
    /* Steps through all of the active PCBs. */
    prev = NULL;
    pcb = tcp_active_pcbs;
    if (pcb == NULL) {
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: no active pcbs\n"));
    }
    while (pcb != NULL) {
      LWIP_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);
      if (pcb->last_timer == tcp_timer_ctr) {
        /* skip this pcb, we have already processed it */
        pcb = pcb->next;
        continue;
      }
      pcb->last_timer = tcp_timer_ctr;
  
      pcb_remove = 0;
      pcb_reset = 0;
  
      if (pcb->state == SYN_SENT && pcb->nrtx == TCP_SYNMAXRTX) {
        ++pcb_remove;
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: max SYN retries reached\n"));
      }
      else if (pcb->nrtx == TCP_MAXRTX) {
        ++pcb_remove;
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: max DATA retries reached\n"));
      } else {
        if (pcb->persist_backoff > 0) {
          
          /* If snd_wnd is zero, use persist timer to send 1 byte probes
           * instead of using the standard retransmission mechanism. */
          u8_t backoff_cnt = tcp_persist_backoff[pcb->persist_backoff-1];
  
          if (pcb->persist_cnt < backoff_cnt) {
            pcb->persist_cnt++;
          }
          if (pcb->persist_cnt >= backoff_cnt) {
            if (tcp_zero_window_probe(pcb) == ERR_OK) {
              pcb->persist_cnt = 0;
              if (pcb->persist_backoff < sizeof(tcp_persist_backoff)) {
                pcb->persist_backoff++;
              }
            }
          }
        } else {
          /* Increase the retransmission timer if it is running */
          if (pcb->rtime >= 0) {
            ++pcb->rtime;
          }
  
          if (pcb->unacked != NULL && pcb->rtime >= pcb->rto) {
            /* Time for a retransmission. */
            LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_slowtmr: rtime %"S16_F
                                        " pcb->rto %"S16_F"\n",
                                        pcb->rtime, pcb->rto));
  
            ESP_STATS_TCP_PCB(pcb);
  
            /* 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];
            }
  
            /* Reset the retransmission timer. */
            pcb->rtime = 0;
  
            /* Reduce congestion window and ssthresh. */
            eff_wnd = LWIP_MIN(pcb->cwnd, pcb->snd_wnd);
            pcb->ssthresh = eff_wnd >> 1;
            if (pcb->ssthresh < (tcpwnd_size_t)(pcb->mss << 1)) {
              pcb->ssthresh = (pcb->mss << 1);
            }
            pcb->cwnd = pcb->mss;
            LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_slowtmr: cwnd %"TCPWNDSIZE_F
                                         " ssthresh %"TCPWNDSIZE_F"\n",
                                         pcb->cwnd, pcb->ssthresh));
  
            /* The following needs to be called AFTER cwnd is set to one
               mss - STJ */
            tcp_rexmit_rto(pcb);
          }
        }
      }
      /* Check if this PCB has stayed too long in FIN-WAIT-2 */
  #if ESP_LWIP
      if ((pcb->state == FIN_WAIT_2) || (pcb->state == FIN_WAIT_1)) {
  #else
      if (pcb->state == FIN_WAIT_2) {
  #endif
        /* If this PCB is in FIN_WAIT_2 because of SHUT_WR don't let it time out. */
        if (pcb->flags & TF_RXCLOSED) {
          /* PCB was fully closed (either through close() or SHUT_RDWR):
             normal FIN-WAIT timeout handling. */
          if ((u32_t)(tcp_ticks - pcb->tmr) >
              TCP_FIN_WAIT_TIMEOUT / TCP_SLOW_INTERVAL) {
            ++pcb_remove;
            LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: removing pcb stuck in FIN-WAIT-2\n"));
          }
        }
      }
  
      /* Check if KEEPALIVE should be sent */
      if (ip_get_option(pcb, SOF_KEEPALIVE) &&
         ((pcb->state == ESTABLISHED) ||
          (pcb->state == CLOSE_WAIT))) {
        if ((u32_t)(tcp_ticks - pcb->tmr) >
           (pcb->keep_idle + TCP_KEEP_DUR(pcb)) / TCP_SLOW_INTERVAL)
        {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: KEEPALIVE timeout. Aborting connection to "));
          ip_addr_debug_print(TCP_DEBUG, &pcb->remote_ip);
          LWIP_DEBUGF(TCP_DEBUG, ("\n"));
  
          ++pcb_remove;
          ++pcb_reset;
        } else if ((u32_t)(tcp_ticks - pcb->tmr) >
                  (pcb->keep_idle + pcb->keep_cnt_sent * TCP_KEEP_INTVL(pcb))
                  / TCP_SLOW_INTERVAL)
        {
          err = tcp_keepalive(pcb);
          if (err == ERR_OK) {
            pcb->keep_cnt_sent++;
          }
        }
      }
  
      /* 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;
        LWIP_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;
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: removing pcb stuck in SYN-RCVD\n"));
        }
      }
  
      /* Check if this PCB has stayed too long in LAST-ACK */
      if (pcb->state == LAST_ACK) {
        if ((u32_t)(tcp_ticks - pcb->tmr) > 2 * TCP_MSL / TCP_SLOW_INTERVAL) {
          ++pcb_remove;
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: removing pcb stuck in LAST-ACK\n"));
        }
      }
  
      /* If the PCB should be removed, do it. */
      if (pcb_remove) {
        struct tcp_pcb *pcb2;
        tcp_err_fn err_fn;
        void *err_arg;
        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;
        }
  
        if (pcb_reset) {
          tcp_rst(pcb->snd_nxt, pcb->rcv_nxt, &pcb->local_ip, &pcb->remote_ip,
                   pcb->local_port, pcb->remote_port);
        }
  
        err_fn = pcb->errf;
        err_arg = pcb->callback_arg;
        pcb2 = pcb;
        pcb = pcb->next;
        memp_free(MEMP_TCP_PCB, pcb2);
  
        tcp_active_pcbs_changed = 0;
        TCP_EVENT_ERR(err_fn, err_arg, ERR_ABRT);
        if (tcp_active_pcbs_changed) {
          goto tcp_slowtmr_start;
        }
      } else {
        /* get the 'next' element now and work with 'prev' below (in case of abort) */
        prev = pcb;
        pcb = pcb->next;
  
        /* We check if we should poll the connection. */
        ++prev->polltmr;
        if (prev->polltmr >= prev->pollinterval) {
          prev->polltmr = 0;
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: polling application\n"));
          tcp_active_pcbs_changed = 0;
          TCP_EVENT_POLL(prev, err);
          if (tcp_active_pcbs_changed) {
            goto tcp_slowtmr_start;
          }
          /* if err == ERR_ABRT, 'prev' is already deallocated */
          if (err == ERR_OK) {
            tcp_output(prev);
          }
        }
      }
    }
  
  
    /* 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) {
        struct tcp_pcb *pcb2;
        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;
        pcb = pcb->next;
        memp_free(MEMP_TCP_PCB, pcb2);
      } else {
        prev = pcb;
        pcb = pcb->next;
      }
    }
  }
  
  /**
   * Is called every TCP_FAST_INTERVAL (250 ms) and process data previously
   * "refused" by upper layer (application) and sends delayed ACKs.
   *
   * Automatically called from tcp_tmr().
   */
  void
  tcp_fasttmr(void)
  {
    struct tcp_pcb *pcb;
  
    ++tcp_timer_ctr;
  
  tcp_fasttmr_start:
    pcb = tcp_active_pcbs;
  
    while (pcb != NULL) {
      if (pcb->last_timer != tcp_timer_ctr) {
        struct tcp_pcb *next;
        pcb->last_timer = tcp_timer_ctr;
        /* send delayed ACKs */
        if (pcb->flags & TF_ACK_DELAY) {
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_fasttmr: delayed ACK\n"));
          tcp_ack_now(pcb);
          tcp_output(pcb);
          pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
        }
  
        next = pcb->next;
  
        /* If there is data which was previously "refused" by upper layer */
        if (pcb->refused_data != NULL) {
          tcp_active_pcbs_changed = 0;
          tcp_process_refused_data(pcb);
          if (tcp_active_pcbs_changed) {
            /* application callback has changed the pcb list: restart the loop */
            goto tcp_fasttmr_start;
          }
        }
        pcb = next;
      } else {
        pcb = pcb->next;
      }
    }
  }
  
  /** Call tcp_output for all active pcbs that have TF_NAGLEMEMERR set */
  void
  tcp_txnow(void)
  {
    struct tcp_pcb *pcb;
  
    for (pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
      if (pcb->flags & TF_NAGLEMEMERR) {
        tcp_output(pcb);
      }
    }
  }
  
  /** Pass pcb->refused_data to the recv callback */
  err_t
  tcp_process_refused_data(struct tcp_pcb *pcb)
  {
  #if TCP_QUEUE_OOSEQ && LWIP_WND_SCALE
    struct pbuf *rest;
    while (pcb->refused_data != NULL)
  #endif /* TCP_QUEUE_OOSEQ && LWIP_WND_SCALE */
    {
      err_t err;
      u8_t refused_flags = pcb->refused_data->flags;
      /* set pcb->refused_data to NULL in case the callback frees it and then
         closes the pcb */
      struct pbuf *refused_data = pcb->refused_data;
  #if TCP_QUEUE_OOSEQ && LWIP_WND_SCALE
      pbuf_split_64k(refused_data, &rest);
      pcb->refused_data = rest;
  #else /* TCP_QUEUE_OOSEQ && LWIP_WND_SCALE */
      pcb->refused_data = NULL;
  #endif /* TCP_QUEUE_OOSEQ && LWIP_WND_SCALE */
      /* Notify again application with data previously received. */
      LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_input: notify kept packet\n"));
      TCP_EVENT_RECV(pcb, refused_data, ERR_OK, err);
      if (err == ERR_OK) {
        /* did refused_data include a FIN? */
        if (refused_flags & PBUF_FLAG_TCP_FIN
  #if TCP_QUEUE_OOSEQ && LWIP_WND_SCALE
            && (rest == NULL)
  #endif /* TCP_QUEUE_OOSEQ && LWIP_WND_SCALE */
           ) {
          /* correct rcv_wnd as the application won't call tcp_recved()
             for the FIN's seqno */
          if (pcb->rcv_wnd != TCP_WND_MAX(pcb)) {
            pcb->rcv_wnd++;
          }
          TCP_EVENT_CLOSED(pcb, err);
          if (err == ERR_ABRT) {
            return ERR_ABRT;
          }
        }
      } else if (err == ERR_ABRT) {
        /* if err == ERR_ABRT, 'pcb' is already deallocated */
        /* Drop incoming packets because pcb is "full" (only if the incoming
           segment contains data). */
        LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_input: drop incoming packets, because pcb is \"full\"\n"));
        return ERR_ABRT;
      } else {
        /* data is still refused, pbuf is still valid (go on for ACK-only packets) */
  #if TCP_QUEUE_OOSEQ && LWIP_WND_SCALE
        if (rest != NULL) {
          pbuf_cat(refused_data, rest);
        }
  #endif /* TCP_QUEUE_OOSEQ && LWIP_WND_SCALE */
        pcb->refused_data = refused_data;
        return ERR_INPROGRESS;
      }
    }
    return ERR_OK;
  }
  
  /**
   * Deallocates a list of TCP segments (tcp_seg structures).
   *
   * @param seg tcp_seg list of TCP segments to free
   */
  void
  tcp_segs_free(struct tcp_seg *seg)
  {
    while (seg != NULL) {
      struct tcp_seg *next = seg->next;
      tcp_seg_free(seg);
      seg = next;
    }
  }
  
  /**
   * Frees a TCP segment (tcp_seg structure).
   *
   * @param seg single tcp_seg to free
   */
  void
  tcp_seg_free(struct tcp_seg *seg)
  {
    if (seg != NULL) {
      if (seg->p != NULL) {
        pbuf_free(seg->p);
        seg->p = NULL;
      }
      memp_free(MEMP_TCP_SEG, seg);
    }
  }
  
  /**
   * Sets the priority of a connection.
   *
   * @param pcb the tcp_pcb to manipulate
   * @param prio new priority
   */
  void
  tcp_setprio(struct tcp_pcb *pcb, u8_t prio)
  {
    pcb->prio = prio;
  }
  
  #if TCP_QUEUE_OOSEQ
  /**
   * Returns a copy of the given TCP segment.
   * The pbuf and data are not copied, only the pointers
   *
   * @param seg the old tcp_seg
   * @return a copy of seg
   */
  struct tcp_seg *
  tcp_seg_copy(struct tcp_seg *seg)
  {
    struct tcp_seg *cseg;
  
    cseg = (struct tcp_seg *)memp_malloc(MEMP_TCP_SEG);
    if (cseg == NULL) {
      return NULL;
    }
    SMEMCPY((u8_t *)cseg, (const u8_t *)seg, sizeof(struct tcp_seg));
    pbuf_ref(cseg->p);
    return cseg;
  }
  #endif /* TCP_QUEUE_OOSEQ */
  
  #if LWIP_CALLBACK_API
  /**
   * Default receive callback that is called if the user didn't register
   * a recv callback for the pcb.
   */
  err_t
  tcp_recv_null(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
  {
    LWIP_UNUSED_ARG(arg);
    if (p != NULL) {
      tcp_recved(pcb, p->tot_len);
      pbuf_free(p);
    } else if (err == ERR_OK) {
      return tcp_close(pcb);
    }
    return ERR_OK;
  }
  #endif /* LWIP_CALLBACK_API */
  
  /**
   * Kills the oldest active connection that has the same or lower priority than
   * 'prio'.
   *
   * @param prio minimum priority
   */
  static void
  tcp_kill_prio(u8_t prio)
  {
    struct tcp_pcb *pcb, *inactive;
    u32_t inactivity;
    u8_t mprio;
  
    mprio = LWIP_MIN(TCP_PRIO_MAX, prio);
  
    /* 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 <= 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 %p (%"S32_F")\n",
             (void *)inactive, inactivity));
      tcp_abort(inactive);
    }
  }
  
  /**
   * Kills the oldest connection that is in specific state.
   * Called from tcp_alloc() for LAST_ACK and CLOSING if no more connections are available.
   */
  static void
  tcp_kill_state(enum tcp_state state)
  {
    struct tcp_pcb *pcb, *inactive;
    u32_t inactivity;
  
    inactivity = 0;
    inactive = NULL;
    /* Go through the list of active pcbs and get the oldest pcb that is in state
       CLOSING/LAST_ACK. */
    for (pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
      if (pcb->state == state) {
        if ((u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
          inactivity = tcp_ticks - pcb->tmr;
          inactive = pcb;
        }
      }
    }
    if (inactive != NULL) {
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_kill_closing: killing oldest %s PCB %p (%"S32_F")\n",
             tcp_state_str[state], (void *)inactive, inactivity));
      /* Don't send a RST, since no data is lost. */
      tcp_abandon(inactive, 0);
    }
  }
  
  /**
   * Kills the oldest connection that is in TIME_WAIT state.
   * Called from tcp_alloc() if no more connections are available.
   */
  static void
  tcp_kill_timewait(void)
  {
    struct tcp_pcb *pcb, *inactive;
    u32_t inactivity;
  
    inactivity = 0;
    inactive = NULL;
    /* Go through the list of TIME_WAIT pcbs and get the oldest pcb. */
    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 %p (%"S32_F")\n",
             (void *)inactive, inactivity));
      tcp_abort(inactive);
    }
  }
  
  #if ESP_LWIP
  typedef struct {
      u8_t time_wait;
      u8_t closing;
      u8_t fin_wait2;
      u8_t last_ack;
      u8_t fin_wait1;
      u8_t listen;
      u8_t bound;
      u8_t total;
  }tcp_pcb_num_t;
  
  void tcp_pcb_num_cal(tcp_pcb_num_t *tcp_pcb_num)
  {
      struct tcp_pcb_listen *listen;
      struct tcp_pcb *pcb;
  
      if (!tcp_pcb_num){
          return;
      }
  
      memset(tcp_pcb_num, 0, sizeof(*tcp_pcb_num));
      for(pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
          tcp_pcb_num->total ++;
          tcp_pcb_num->time_wait ++;
      }
  
      for (pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next){
          tcp_pcb_num->total ++;
          if (pcb->state == FIN_WAIT_2){
              tcp_pcb_num->fin_wait2 ++;
          } else if (pcb->state == LAST_ACK) {
              tcp_pcb_num->last_ack ++;
          } else if (pcb->state == CLOSING) {
              tcp_pcb_num->closing ++;
          } else if (pcb->state == FIN_WAIT_1){
              tcp_pcb_num->fin_wait1 ++;
          }
      }
  
      for (listen = tcp_listen_pcbs.listen_pcbs; listen != NULL; listen = listen->next){
          tcp_pcb_num->total ++;
          tcp_pcb_num->listen ++;
      }
  
      for (pcb = tcp_bound_pcbs; pcb != NULL; pcb = pcb->next){
          tcp_pcb_num->total ++;
          tcp_pcb_num->bound ++;
      }
  }
  #endif
  
  
  /**
   * Allocate a new tcp_pcb structure.
   *
   * @param prio priority for the new pcb
   * @return a new tcp_pcb that initially is in state CLOSED
   */
  struct tcp_pcb *
  tcp_alloc(u8_t prio)
  {
    struct tcp_pcb *pcb;
    u32_t iss;
  
  #if ESP_LWIP
      tcp_pcb_num_t tcp_pcb_num;
  
      tcp_pcb_num_cal(&tcp_pcb_num);
  
      if (tcp_pcb_num.total >= MEMP_NUM_TCP_PCB){
          if (tcp_pcb_num.time_wait > 0){
              tcp_kill_timewait();
          } else if (tcp_pcb_num.last_ack > 0){
              tcp_kill_state(LAST_ACK);
          } else if (tcp_pcb_num.closing > 0){
              tcp_kill_state(CLOSING);
          } else if (tcp_pcb_num.fin_wait2 > 0){
              tcp_kill_state(FIN_WAIT_2);
          } else if (tcp_pcb_num.fin_wait1 > 0){
              tcp_kill_state(FIN_WAIT_1);
          } else {
              tcp_kill_prio(prio);
          }
      }
  
      tcp_pcb_num_cal(&tcp_pcb_num);
      if (tcp_pcb_num.total >= MEMP_NUM_TCP_PCB){
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_alloc: no available tcp pcb %d %d %d %d %d %d %d %d\n",
             tcp_pcb_num.total, tcp_pcb_num.time_wait, tcp_pcb_num.last_ack, tcp_pcb_num.closing,
             tcp_pcb_num.fin_wait2, tcp_pcb_num.fin_wait1, tcp_pcb_num.listen, tcp_pcb_num.bound));
          return NULL;
      }
  
  #endif
  
    pcb = (struct tcp_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();
      /* Try to allocate a tcp_pcb again. */
      pcb = (struct tcp_pcb *)memp_malloc(MEMP_TCP_PCB);
      if (pcb == NULL) {
        /* Try killing oldest connection in LAST-ACK (these wouldn't go to TIME-WAIT). */
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_alloc: killing off oldest LAST-ACK connection\n"));
        tcp_kill_state(LAST_ACK);
        /* Try to allocate a tcp_pcb again. */
        pcb = (struct tcp_pcb *)memp_malloc(MEMP_TCP_PCB);
        if (pcb == NULL) {
          /* Try killing oldest connection in CLOSING. */
          LWIP_DEBUGF(TCP_DEBUG, ("tcp_alloc: killing off oldest CLOSING connection\n"));
          tcp_kill_state(CLOSING);
          /* Try to allocate a tcp_pcb again. */
          pcb = (struct tcp_pcb *)memp_malloc(MEMP_TCP_PCB);
          if (pcb == NULL) {
            /* Try killing active connections with lower priority than the new one. */
            LWIP_DEBUGF(TCP_DEBUG, ("tcp_alloc: killing connection with prio lower than %d\n", prio));
            tcp_kill_prio(prio);
            /* Try to allocate a tcp_pcb again. */
            pcb = (struct tcp_pcb *)memp_malloc(MEMP_TCP_PCB);
            if (pcb != NULL) {
              /* adjust err stats: memp_malloc failed multiple times before */
              MEMP_STATS_DEC(err, MEMP_TCP_PCB);
            }
          }
          if (pcb != NULL) {
            /* adjust err stats: memp_malloc failed multiple times before */
            MEMP_STATS_DEC(err, MEMP_TCP_PCB);
          }
        }
        if (pcb != NULL) {
          /* adjust err stats: memp_malloc failed multiple times before */
          MEMP_STATS_DEC(err, MEMP_TCP_PCB);
        }
      }
      if (pcb != NULL) {
        /* adjust err stats: memp_malloc failed above */
        MEMP_STATS_DEC(err, MEMP_TCP_PCB);
      }
    }
    if (pcb != NULL) {
      memset(pcb, 0, sizeof(struct tcp_pcb));
  
  #if ESP_PER_SOC_TCP_WND
      pcb->per_soc_tcp_wnd = TCP_WND_DEFAULT;
      pcb->per_soc_tcp_snd_buf = TCP_SND_BUF_DEFAULT;
  #endif
  
      pcb->prio = prio;
      pcb->snd_buf = TCP_SND_BUF_DEFAULT;
      pcb->snd_queuelen = 0;
      /* Start with a window that does not need scaling. When window scaling is
         enabled and used, the window is enlarged when both sides agree on scaling. */
      pcb->rcv_wnd = pcb->rcv_ann_wnd = TCPWND_MIN16(TCP_WND(pcb));
  #if LWIP_WND_SCALE
      /* snd_scale and rcv_scale are zero unless both sides agree to use scaling */
      pcb->snd_scale = 0;
      pcb->rcv_scale = 0;
  #endif
      pcb->tos = 0;
      pcb->ttl = TCP_TTL;
      /* As initial send MSS, we use TCP_MSS but limit it to 536.
         The send MSS is updated when an MSS option is received. */
      pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS;
      pcb->rto = 3000 / TCP_SLOW_INTERVAL;
      pcb->sa = 0;
      pcb->sv = 3000 / TCP_SLOW_INTERVAL;
      pcb->rtime = -1;
      pcb->cwnd = 1;
      iss = tcp_next_iss();
      pcb->snd_wl2 = iss;
      pcb->snd_nxt = iss;
      pcb->lastack = iss;
      pcb->snd_lbb = iss;
      pcb->tmr = tcp_ticks;
      pcb->last_timer = tcp_timer_ctr;
      pcb->polltmr = 0;
  
  #if LWIP_CALLBACK_API
      pcb->recv = tcp_recv_null;
  #endif /* LWIP_CALLBACK_API */
  
      /* Init KEEPALIVE timer */
      pcb->keep_idle  = TCP_KEEPIDLE_DEFAULT;
  
  #if LWIP_TCP_KEEPALIVE
      pcb->keep_intvl = TCP_KEEPINTVL_DEFAULT;
      pcb->keep_cnt   = TCP_KEEPCNT_DEFAULT;
  #endif /* LWIP_TCP_KEEPALIVE */
  
      pcb->keep_cnt_sent = 0;
    }
  
    return pcb;
  }
  
  /**
   * Creates a new TCP protocol control block but doesn't place it on
   * any of the TCP PCB lists.
   * The pcb is not put on any list until binding using tcp_bind().
   *
   * @internal: Maybe there should be a idle TCP PCB list where these
   * PCBs are put on. Port reservation using tcp_bind() is implemented but
   * allocated pcbs that are not bound can't be killed automatically if wanting
   * to allocate a pcb with higher prio (@see tcp_kill_prio())
   *
   * @return a new tcp_pcb that initially is in state CLOSED
   */
  struct tcp_pcb *
  tcp_new(void)
  {
    return tcp_alloc(TCP_PRIO_NORMAL);
  }
  
  /**
   * Creates a new TCP protocol control block but doesn't
   * place it on any of the TCP PCB lists.
   * The pcb is not put on any list until binding using tcp_bind().
   *
   * @param type IP address type, see IPADDR_TYPE_XX definitions.
   * @return a new tcp_pcb that initially is in state CLOSED
   */
  struct tcp_pcb *
  tcp_new_ip_type(u8_t type)
  {
    struct tcp_pcb * pcb;
    pcb = tcp_alloc(TCP_PRIO_NORMAL);
  #if LWIP_IPV4 && LWIP_IPV6
    if(pcb != NULL) {
      IP_SET_TYPE_VAL(pcb->local_ip, type);
      IP_SET_TYPE_VAL(pcb->remote_ip, type);
    }
  #else
    LWIP_UNUSED_ARG(type);
  #endif /* LWIP_IPV4 && LWIP_IPV6 */
    return pcb;
  }
  
  /**
   * Used to specify the argument that should be passed callback
   * functions.
   *
   * @param pcb tcp_pcb to set the callback argument
   * @param arg void pointer argument to pass to callback functions
   */
  void
  tcp_arg(struct tcp_pcb *pcb, void *arg)
  {
    /* This function is allowed to be called for both listen pcbs and
       connection pcbs. */
    pcb->callback_arg = arg;
  }
  #if LWIP_CALLBACK_API
  
  /**
   * Used to specify the function that should be called when a TCP
   * connection receives data.
   *
   * @param pcb tcp_pcb to set the recv callback
   * @param recv callback function to call for this pcb when data is received
   */
  void
  tcp_recv(struct tcp_pcb *pcb, tcp_recv_fn recv)
  {
    LWIP_ASSERT("invalid socket state for recv callback", pcb->state != LISTEN);
    pcb->recv = recv;
  }
  
  /**
   * Used to specify the function that should be called when TCP data
   * has been successfully delivered to the remote host.
   *
   * @param pcb tcp_pcb to set the sent callback
   * @param sent callback function to call for this pcb when data is successfully sent
   */
  void
  tcp_sent(struct tcp_pcb *pcb, tcp_sent_fn sent)
  {
    LWIP_ASSERT("invalid socket state for sent callback", pcb->state != LISTEN);
    pcb->sent = sent;
  }
  
  /**
   * Used to specify the function that should be called when a fatal error
   * has occurred on the connection.
   *
   * @param pcb tcp_pcb to set the err callback
   * @param err callback function to call for this pcb when a fatal error
   *        has occurred on the connection
   */
  void
  tcp_err(struct tcp_pcb *pcb, tcp_err_fn err)
  {
    LWIP_ASSERT("invalid socket state for err callback", pcb->state != LISTEN);
    pcb->errf = err;
  }
  
  /**
   * Used for specifying the function that should be called when a
   * LISTENing connection has been connected to another host.
   *
   * @param pcb tcp_pcb to set the accept callback
   * @param accept callback function to call for this pcb when LISTENing
   *        connection has been connected to another host
   */
  void
  tcp_accept(struct tcp_pcb *pcb, tcp_accept_fn accept)
  {
    /* This function is allowed to be called for both listen pcbs and
       connection pcbs. */
    pcb->accept = accept;
  }
  #endif /* LWIP_CALLBACK_API */
  
  
  /**
   * Used to specify the function that should be called periodically
   * from TCP. The interval is specified in terms of the TCP coarse
   * timer interval, which is called twice a second.
   *
   */
  void
  tcp_poll(struct tcp_pcb *pcb, tcp_poll_fn poll, u8_t interval)
  {
    LWIP_ASSERT("invalid socket state for poll", pcb->state != LISTEN);
  #if LWIP_CALLBACK_API
    pcb->poll = poll;
  #else /* LWIP_CALLBACK_API */
    LWIP_UNUSED_ARG(poll);
  #endif /* LWIP_CALLBACK_API */
    pcb->pollinterval = interval;
  }
  
  /**
   * Purges a TCP PCB. Removes any buffered data and frees the buffer memory
   * (pcb->ooseq, pcb->unsent and pcb->unacked are freed).
   *
   * @param pcb tcp_pcb to purge. The pcb itself is not deallocated!
   */
  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 TCP_LISTEN_BACKLOG
      if (pcb->state == SYN_RCVD) {
        /* Need to find the corresponding listen_pcb and decrease its accepts_pending */
        struct tcp_pcb_listen *lpcb;
  
        /*
         * The official LWIP will assert the system if tcp_listen_pcbs.listen_pcbs is NULL, it's a bug.
         *
         * Considering following scenario:
         * 1. On TCP server side, one of TCP pcb is in SYNC_RECV state and is waiting for TCP ACK from TCP client.
         * 2. The TCP server is closed by application, which causes the tcp_listen_pcbs.listen_pcbs to become NULL.
         * 3. When SYNC_RECV state timeout (20s by default), tcp_pcb_purge() is called in tcp_slowtmr(), it asserts
         *    the system.
         * This is a normal scenario, should NOT assert the system. So just remove it.
         * 
         */
        if (tcp_listen_pcbs.listen_pcbs) {
          for (lpcb = tcp_listen_pcbs.listen_pcbs; lpcb != NULL; lpcb = lpcb->next) {
            if ((lpcb->local_port == pcb->local_port) &&
                (IP_IS_V6_VAL(pcb->local_ip) == IP_IS_V6_VAL(lpcb->local_ip)) &&
                (ip_addr_isany(&lpcb->local_ip) ||
                 ip_addr_cmp(&pcb->local_ip, &lpcb->local_ip))) {
                /* port and address of the listen pcb match the timed-out pcb */
                LWIP_ASSERT("tcp_pcb_purge: listen pcb does not have accepts pending",
                  lpcb->accepts_pending > 0);
                lpcb->accepts_pending--;
                break;
            }
          }
        }
      }
  #endif /* TCP_LISTEN_BACKLOG */
  
  
      if (pcb->refused_data != NULL) {
        LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->refused_data\n"));
        pbuf_free(pcb->refused_data);
        pcb->refused_data = NULL;
      }
      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
      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 */
  
      /* Stop the retransmission timer as it will expect data on unacked
         queue if it fires */
      pcb->rtime = -1;
  
      tcp_segs_free(pcb->unsent);
      tcp_segs_free(pcb->unacked);
      pcb->unacked = pcb->unsent = NULL;
  #if TCP_OVERSIZE
      pcb->unsent_oversize = 0;
  #endif /* TCP_OVERSIZE */
    }
  }
  
  /**
   * Purges the PCB and removes it from a PCB list. Any delayed ACKs are sent first.
   *
   * @param pcblist PCB list to purge.
   * @param pcb tcp_pcb to purge. The pcb itself is NOT deallocated!
   */
  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);
    }
  
    if (pcb->state != LISTEN) {
      LWIP_ASSERT("unsent segments leaking", pcb->unsent == NULL);
      LWIP_ASSERT("unacked segments leaking", pcb->unacked == NULL);
  #if TCP_QUEUE_OOSEQ
      LWIP_ASSERT("ooseq segments leaking", pcb->ooseq == NULL);
  #endif /* TCP_QUEUE_OOSEQ */
    }
  
    pcb->state = CLOSED;
    /* reset the local port to prevent the pcb from being 'bound' */
    pcb->local_port = 0;
  
    LWIP_ASSERT("tcp_pcb_remove: tcp_pcbs_sane()", tcp_pcbs_sane());
  }
  
  /**
   * Calculates a new initial sequence number for new connections.
   *
   * @return u32_t pseudo random sequence number
   */
  u32_t
  tcp_next_iss(void)
  {
    static u32_t iss = 6510;
  
    iss += tcp_ticks;       /* XXX */
    return iss;
  }
  
  #if TCP_CALCULATE_EFF_SEND_MSS
  /**
   * Calculates the effective send mss that can be used for a specific IP address
   * by using ip_route to determine the netif used to send to the address and
   * calculating the minimum of TCP_MSS and that netif's mtu (if set).
   */
  u16_t
  tcp_eff_send_mss_impl(u16_t sendmss, const ip_addr_t *dest
  #if LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING
                       , const ip_addr_t *src
  #endif /* LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING */
                       )
  {
    u16_t mss_s;
    struct netif *outif;
    s16_t mtu;
  
    outif = ip_route(src, dest);
  #if LWIP_IPV6
  #if LWIP_IPV4
    if (IP_IS_V6(dest))
  #endif /* LWIP_IPV4 */
    {
      /* First look in destination cache, to see if there is a Path MTU. */
      mtu = nd6_get_destination_mtu(ip_2_ip6(dest), outif);
    }
  #if LWIP_IPV4
    else
  #endif /* LWIP_IPV4 */
  #endif /* LWIP_IPV6 */
  #if LWIP_IPV4
    {
      if (outif == NULL) {
        return sendmss;
      }
      mtu = outif->mtu;
    }
  #endif /* LWIP_IPV4 */
  
    if (mtu != 0) {
  #if LWIP_IPV6
  #if LWIP_IPV4
      if (IP_IS_V6(dest))
  #endif /* LWIP_IPV4 */
      {
        mss_s = mtu - IP6_HLEN - TCP_HLEN;
      }
  #if LWIP_IPV4
      else
  #endif /* LWIP_IPV4 */
  #endif /* LWIP_IPV6 */
  #if LWIP_IPV4
      {
        mss_s = mtu - IP_HLEN - TCP_HLEN;
      }
  #endif /* LWIP_IPV4 */
      /* RFC 1122, chap 4.2.2.6:
       * Eff.snd.MSS = min(SendMSS+20, MMS_S) - TCPhdrsize - IPoptionsize
       * We correct for TCP options in tcp_write(), and don't support IP options.
       */
      sendmss = LWIP_MIN(sendmss, mss_s);
    }
    return sendmss;
  }
  #endif /* TCP_CALCULATE_EFF_SEND_MSS */
  
  #if LWIP_IPV4
  /** This function is called from netif.c when address is changed or netif is removed
   *
   * @param old_addr IPv4 address of the netif before change
   * @param new_addr IPv4 address of the netif after change or NULL if netif has been removed
   */
  void tcp_netif_ipv4_addr_changed(const ip4_addr_t* old_addr, const ip4_addr_t* new_addr)
  {
    struct tcp_pcb_listen *lpcb, *next;
  
    if (!ip4_addr_isany(new_addr)) {
      /* PCB bound to current local interface address? */
      for (lpcb = tcp_listen_pcbs.listen_pcbs; lpcb != NULL; lpcb = next) {
        next = lpcb->next;
        /* Is this an IPv4 pcb? */
        if (!IP_IS_V6_VAL(lpcb->local_ip)) {
          /* PCB bound to current local interface address? */
          if ((!(ip4_addr_isany(ip_2_ip4(&lpcb->local_ip)))) &&
              (ip4_addr_cmp(ip_2_ip4(&lpcb->local_ip), old_addr))) {
            /* The PCB is listening to the old ipaddr and
             * is set to listen to the new one instead */
                ip_addr_copy_from_ip4(lpcb->local_ip, *new_addr);
          }
        }
      }
    }
  }
  #endif /* LWIP_IPV4 */
  
  const char*
  tcp_debug_state_str(enum tcp_state s)
  {
        return tcp_state_str[s];
  }
  
  #if TCP_DEBUG || TCP_INPUT_DEBUG || TCP_OUTPUT_DEBUG
  /**
   * Print a tcp header for debugging purposes.
   *
   * @param tcphdr pointer to a struct tcp_hdr
   */
  void
  tcp_debug_print(struct tcp_hdr *tcphdr)
  {
    LWIP_DEBUGF(TCP_DEBUG, ("TCP header:\n"));
    LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(TCP_DEBUG, ("|    %5"U16_F"      |    %5"U16_F"      | (src port, dest port)\n",
           ntohs(tcphdr->src), ntohs(tcphdr->dest)));
    LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(TCP_DEBUG, ("|           %010"U32_F"          | (seq no)\n",
            ntohl(tcphdr->seqno)));
    LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(TCP_DEBUG, ("|           %010"U32_F"          | (ack no)\n",
           ntohl(tcphdr->ackno)));
    LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(TCP_DEBUG, ("| %2"U16_F" |   |%"U16_F"%"U16_F"%"U16_F"%"U16_F"%"U16_F"%"U16_F"|     %5"U16_F"     | (hdrlen, flags (",
         TCPH_HDRLEN(tcphdr),
           TCPH_FLAGS(tcphdr) >> 5 & 1,
           TCPH_FLAGS(tcphdr) >> 4 & 1,
           TCPH_FLAGS(tcphdr) >> 3 & 1,
           TCPH_FLAGS(tcphdr) >> 2 & 1,
           TCPH_FLAGS(tcphdr) >> 1 & 1,
           TCPH_FLAGS(tcphdr) & 1,
           ntohs(tcphdr->wnd)));
    tcp_debug_print_flags(TCPH_FLAGS(tcphdr));
    LWIP_DEBUGF(TCP_DEBUG, ("), win)\n"));
    LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(TCP_DEBUG, ("|    0x%04"X16_F"     |     %5"U16_F"     | (chksum, urgp)\n",
           ntohs(tcphdr->chksum), ntohs(tcphdr->urgp)));
    LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
  }
  
  /**
   * Print a tcp state for debugging purposes.
   *
   * @param s enum tcp_state to print
   */
  void
  tcp_debug_print_state(enum tcp_state s)
  {
    LWIP_DEBUGF(TCP_DEBUG, ("State: %s\n", tcp_state_str[s]));
  }
  
  /**
   * Print tcp flags for debugging purposes.
   *
   * @param flags tcp flags, all active flags are printed
   */
  void
  tcp_debug_print_flags(u8_t flags)
  {
    if (flags & TCP_FIN) {
      LWIP_DEBUGF(TCP_DEBUG, ("FIN "));
    }
    if (flags & TCP_SYN) {
      LWIP_DEBUGF(TCP_DEBUG, ("SYN "));
    }
    if (flags & TCP_RST) {
      LWIP_DEBUGF(TCP_DEBUG, ("RST "));
    }
    if (flags & TCP_PSH) {
      LWIP_DEBUGF(TCP_DEBUG, ("PSH "));
    }
    if (flags & TCP_ACK) {
      LWIP_DEBUGF(TCP_DEBUG, ("ACK "));
    }
    if (flags & TCP_URG) {
      LWIP_DEBUGF(TCP_DEBUG, ("URG "));
    }
    if (flags & TCP_ECE) {
      LWIP_DEBUGF(TCP_DEBUG, ("ECE "));
    }
    if (flags & TCP_CWR) {
      LWIP_DEBUGF(TCP_DEBUG, ("CWR "));
    }
    LWIP_DEBUGF(TCP_DEBUG, ("\n"));
  }
  
  /**
   * Print all tcp_pcbs in every list for debugging purposes.
   */
  void
  tcp_debug_print_pcbs(void)
  {
    struct tcp_pcb *pcb;
    LWIP_DEBUGF(TCP_DEBUG, ("Active PCB states:\n"));
    for (pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
      LWIP_DEBUGF(TCP_DEBUG, ("Local port %"U16_F", foreign port %"U16_F" snd_nxt %"U32_F" rcv_nxt %"U32_F" ",
                         pcb->local_port, pcb->remote_port,
                         pcb->snd_nxt, pcb->rcv_nxt));
      tcp_debug_print_state(pcb->state);
    }
    LWIP_DEBUGF(TCP_DEBUG, ("Listen PCB states:\n"));
    for (pcb = (struct tcp_pcb *)tcp_listen_pcbs.pcbs; pcb != NULL; pcb = pcb->next) {
      LWIP_DEBUGF(TCP_DEBUG, ("Local port %"U16_F", foreign port %"U16_F" snd_nxt %"U32_F" rcv_nxt %"U32_F" ",
                         pcb->local_port, pcb->remote_port,
                         pcb->snd_nxt, pcb->rcv_nxt));
      tcp_debug_print_state(pcb->state);
    }
    LWIP_DEBUGF(TCP_DEBUG, ("TIME-WAIT PCB states:\n"));
    for (pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
      LWIP_DEBUGF(TCP_DEBUG, ("Local port %"U16_F", foreign port %"U16_F" snd_nxt %"U32_F" rcv_nxt %"U32_F" ",
                         pcb->local_port, pcb->remote_port,
                         pcb->snd_nxt, pcb->rcv_nxt));
      tcp_debug_print_state(pcb->state);
    }
  }
  
  /**
   * Check state consistency of the tcp_pcb lists.
   */
  s16_t
  tcp_pcbs_sane(void)
  {
    struct tcp_pcb *pcb;
    for (pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
      LWIP_ASSERT("tcp_pcbs_sane: active pcb->state != CLOSED", pcb->state != CLOSED);
      LWIP_ASSERT("tcp_pcbs_sane: active pcb->state != LISTEN", pcb->state != LISTEN);
      LWIP_ASSERT("tcp_pcbs_sane: active pcb->state != TIME-WAIT", pcb->state != TIME_WAIT);
    }
    for (pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
      LWIP_ASSERT("tcp_pcbs_sane: tw pcb->state == TIME-WAIT", pcb->state == TIME_WAIT);
    }
    return 1;
  }
  #endif /* TCP_DEBUG */
  
  #endif /* LWIP_TCP */
  