C++ TCP_REG函数代码示例

/** Safely bring a tcp_pcb into the requested state */
void
tcp_set_state(struct tcp_pcb* pcb, enum tcp_state state, ip_addr_t* local_ip,
                   ip_addr_t* remote_ip, u16_t local_port, u16_t remote_port)
{
  /* @todo: are these all states? */
  /* @todo: remove from previous list */
  pcb->state = state;
  if (state == ESTABLISHED) {
    TCP_REG(&tcp_active_pcbs, pcb);
    pcb->local_ip.addr = local_ip->addr;
    pcb->local_port = local_port;
    pcb->remote_ip.addr = remote_ip->addr;
    pcb->remote_port = remote_port;
  } else if(state == LISTEN) {
    TCP_REG(&tcp_listen_pcbs.pcbs, pcb);
    pcb->local_ip.addr = local_ip->addr;
    pcb->local_port = local_port;
  } else if(state == TIME_WAIT) {
    TCP_REG(&tcp_tw_pcbs, pcb);
    pcb->local_ip.addr = local_ip->addr;
    pcb->local_port = local_port;
    pcb->remote_ip.addr = remote_ip->addr;
    pcb->remote_port = remote_port;
  } else {
    fail();
  }
}

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.listen_pcbs, lpcb);
  return (struct tcp_pcb *)lpcb;
}

/**
 * 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.
 *
 * @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_OK if bound
 */
err_t
tcp_bind(struct tcp_pcb *pcb, ip_addr_t *ipaddr, u16_t port)
{
  int i;
  int max_pcb_list = NUM_TCP_PCB_LISTS;
  struct tcp_pcb *cpcb;

  LWIP_ERROR("tcp_bind: can only bind in state CLOSED", pcb->state == CLOSED, return ERR_ISCONN);

#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 SO_REUSE
  if ((pcb->so_options & SOF_REUSEADDR) != 0) {
    max_pcb_list = NUM_TCP_PCB_LISTS_NO_TIME_WAIT;
  }
#endif /* SO_REUSE */
#endif /* SO_REUSE */

  if (port == 0) {
    port = tcp_new_port();
  }

  /* 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 (((pcb->so_options & SOF_REUSEADDR) == 0) ||
          ((cpcb->so_options & SOF_REUSEADDR) == 0))
#endif /* SO_REUSE */
        {
          if (ip_addr_isany(&(cpcb->local_ip)) ||
              ip_addr_isany(ipaddr) ||
              ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
            return ERR_USE;
          }
        }
      }
    }
  }

  pcb->bound_to_netif = 0;
  if (!ip_addr_isany(ipaddr)) {
    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;
}

/**
 * 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 (or on error)
 * @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, struct ip_addr *ipaddr, u16_t port,
      err_t (* connected)(void *arg, struct tcp_pcb *tpcb, err_t err))
{
  err_t ret;
  u32_t iss;

  LWIP_ERROR("tcp_connect: can only connected from state CLOSED", pcb->state == CLOSED, return ERR_ISCONN);

  LWIP_DEBUGF(TCP_DEBUG, ("tcp_connect to port %"U16_F"\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->rcv_ann_wnd = TCP_WND;
  pcb->rcv_ann_right_edge = pcb->rcv_nxt;
  pcb->snd_wnd = TCP_WND;
  /* 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, ipaddr);
#endif /* TCP_CALCULATE_EFF_SEND_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_RMV(&tcp_bound_pcbs, pcb);
  TCP_REG(&tcp_active_pcbs, pcb);

  snmp_inc_tcpactiveopens();
  
  ret = tcp_enqueue(pcb, NULL, 0, TCP_SYN, 0, TF_SEG_OPTS_MSS
#if LWIP_TCP_TIMESTAMPS
                    | TF_SEG_OPTS_TS
#endif
                    );
  if (ret == ERR_OK) { 
    tcp_output(pcb);
  }
  return ret;
} 

/**
 * 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 ((pcb->so_options & SOF_REUSEADDR) != 0) {
    /* 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) {
        if (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->so_options |= SOF_ACCEPTCONN;
  lpcb->ttl = pcb->ttl;
  lpcb->tos = pcb->tos;
  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;
  lpcb->backlog = (backlog ? backlog : 1);
#endif /* TCP_LISTEN_BACKLOG */
  TCP_REG(&tcp_listen_pcbs.pcbs, (struct tcp_pcb *)lpcb);
  return (struct tcp_pcb *)lpcb;
}

/*-----------------------------------------------------------------------------------*/
struct tcp_pcb *
tcp_listen(struct tcp_pcb *pcb)
{
  pcb->state = LISTEN;
  pcb = (struct tcp_pcb*)memp_realloc(MEMP_TCP_PCB, MEMP_TCP_PCB_LISTEN, pcb);
  if(pcb == NULL) {
    return NULL;
  }
  TCP_REG((struct tcp_pcb **)&tcp_listen_pcbs, pcb);
  return pcb;
}

/**
 * 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 %"U16_F"\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);

  snmp_inc_tcpactiveopens();
  
  /* Build an MSS option */
  optdata = htonl(((u32_t)2 << 24) | 
      ((u32_t)4 << 16) | 
      (((u32_t)pcb->mss / 256) << 8) |
      (pcb->mss & 255));

  ret = tcp_enqueue(pcb, NULL, 0, TCP_SYN, 0, (u8_t *)&optdata, 4);
  if (ret == ERR_OK) { 
    tcp_output(pcb);
  }
  return ret;
} 

/**
 * 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;
  }
	/* 分配一个监听状态控制块struct tcp_pcb_listen */
  lpcb = memp_malloc(MEMP_TCP_PCB_LISTEN);
  if (lpcb == NULL) {
    return NULL;
  }
	/* 复制各个字段 */
  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);
	/* 从tcp_bound_pcbs链表删除控制块 */
  TCP_RMV(&tcp_bound_pcbs, pcb);
	/* 释放控制块 */
  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;
  lpcb->backlog = (backlog ? backlog : 1);
#endif /* TCP_LISTEN_BACKLOG */
	/* 把新控制块加入tcp_listen_pcbs链表首部 */
  TCP_REG(&tcp_listen_pcbs.listen_pcbs, lpcb);
	/* 返回新控制块指针 */
  return (struct tcp_pcb *)lpcb;
}

/**
 * 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.
 *
 * @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_OK if bound
 */
err_t
tcp_bind(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port)
{
  struct tcp_pcb *cpcb;

  LWIP_ERROR("tcp_bind: can only bind in state CLOSED", pcb->state == CLOSED, return ERR_ISCONN);

  if (port == 0) {
    port = tcp_new_port();
  }
  /* Check if the address already is in use. */
  /* Check the listen pcbs. */
  for(cpcb = (struct tcp_pcb *)tcp_listen_pcbs.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;
      }
    }
  }
  /* Check the connected pcbs. */
  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;
      }
    }
  }
  /* Check the bound, not yet connected pcbs. */
  for(cpcb = tcp_bound_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;
      }
    }
  }
  /* @todo: until SO_REUSEADDR is implemented (see task #6995 on savannah),
   * we have to check the pcbs in TIME-WAIT state, also: */
  for(cpcb = tcp_tw_pcbs; cpcb != NULL; cpcb = cpcb->next) {
    if (cpcb->local_port == port) {
      if (ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
        return ERR_USE;
      }
    }
  }

  if (!ip_addr_isany(ipaddr)) {
    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;
}

/**
 * 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 (or on error)
 * @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, ip_addr_t *ipaddr, u16_t port,
      tcp_connected_fn connected)
{
  err_t ret;
  u32_t iss;
  u16_t old_local_port;

  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));
  if (ipaddr != NULL) {
    pcb->remote_ip = *ipaddr;
  } else {
    return ERR_VAL;
  }
  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 = ip_route(&(pcb->remote_ip));
    if (netif == NULL) {
      /* Don't even try to send a SYN packet if we have no route
         since that will fail. */
      return ERR_RTE;
    }
    /* Use the netif's IP address as local address. */
    ip_addr_copy(pcb->local_ip, netif->ip_addr);
  }

  old_local_port = pcb->local_port;
  if (pcb->local_port == 0) {
    pcb->local_port = tcp_new_port();
  }
#if SO_REUSE
  if ((pcb->so_options & SOF_REUSEADDR) != 0) {
    /* 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;
  pcb->rcv_wnd = TCP_WND;
  pcb->rcv_ann_wnd = TCP_WND;
  pcb->rcv_ann_right_edge = pcb->rcv_nxt;
  pcb->snd_wnd = TCP_WND;
  /* 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, ipaddr);
#endif /* TCP_CALCULATE_EFF_SEND_MSS */
  pcb->cwnd = 1;
  pcb->ssthresh = pcb->mss * 10;
#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(&tcp_active_pcbs, pcb);
    snmp_inc_tcpactiveopens();
//.........这里部分代码省略.........

/**
 * 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 != LISTEN)) {
    if ((pcb->refused_data != NULL) || (pcb->rcv_wnd != TCP_WND)) {
      /* 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);

      /* TODO: to which state do we move now? */

      /* move to TIME_WAIT since we close actively */
      TCP_RMV(&tcp_active_pcbs, pcb);
      pcb->state = TIME_WAIT;
      TCP_REG(&tcp_tw_pcbs, 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(&tcp_active_pcbs, pcb);
    memp_free(MEMP_TCP_PCB, pcb);
    pcb = NULL;
    snmp_inc_tcpattemptfails();
    break;
  case SYN_RCVD:
    err = tcp_send_fin(pcb);
    if (err == ERR_OK) {
      snmp_inc_tcpattemptfails();
      pcb->state = FIN_WAIT_1;
    }
    break;
  case ESTABLISHED:
    err = tcp_send_fin(pcb);
    if (err == ERR_OK) {
      snmp_inc_tcpestabresets();
      pcb->state = FIN_WAIT_1;
    }
    break;
  case CLOSE_WAIT:
    err = tcp_send_fin(pcb);
    if (err == ERR_OK) {
      snmp_inc_tcpestabresets();
      pcb->state = LAST_ACK;
    }
    break;
  default:
    /* Has already been closed, do nothing. */
    err = ERR_OK;
    pcb = NULL;
    break;
//.........这里部分代码省略.........

//.........这里部分代码省略.........
       !(flags & TCP_RST)) {
      /* expected ACK number? */
      if (TCP_SEQ_BETWEEN(ackno, pcb->lastack+1, pcb->snd_nxt)) {
        u16_t old_cwnd;
        pcb->state = ESTABLISHED;
        LWIP_DEBUGF(TCP_DEBUG, ("TCP connection established %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
#if LWIP_CALLBACK_API
        LWIP_ASSERT("pcb->accept != NULL", pcb->accept != NULL);
#endif
        /* Call the accept function. */
        TCP_EVENT_ACCEPT(pcb, ERR_OK, err);
        if (err != ERR_OK) {
          /* If the accept function returns with an error, we abort
           * the connection. */
          tcp_abort(pcb);
          return ERR_ABRT;
        }
        old_cwnd = pcb->cwnd;
        /* If there was any data contained within this ACK,
         * we'd better pass it on to the application as well. */
        accepted_inseq = tcp_receive(pcb);

        pcb->cwnd = ((old_cwnd == 1) ? (pcb->mss * 2) : pcb->mss);

        if ((flags & TCP_FIN) && accepted_inseq) {
          tcp_ack_now(pcb);
          pcb->state = CLOSE_WAIT;
        }
      }
      /* incorrect ACK number */
      else {
        /* send RST */
        tcp_rst(ackno, seqno + tcplen, &(iphdr->dest), &(iphdr->src),
                tcphdr->dest, tcphdr->src);
      }
    }
    break;
  case CLOSE_WAIT:
    /* FALLTHROUGH */
  case ESTABLISHED:
    accepted_inseq = tcp_receive(pcb);
    if ((flags & TCP_FIN) && accepted_inseq) { /* passive close */
      tcp_ack_now(pcb);
      pcb->state = CLOSE_WAIT;
    }
    break;
  case FIN_WAIT_1:
    tcp_receive(pcb);
    if (flags & TCP_FIN) {
      if (flags & TCP_ACK && ackno == pcb->snd_nxt) {
        LWIP_DEBUGF(TCP_DEBUG,
          ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
        tcp_ack_now(pcb);
        tcp_pcb_purge(pcb);
        TCP_RMV(&tcp_active_pcbs, pcb);
        pcb->state = TIME_WAIT;
        TCP_REG(&tcp_tw_pcbs, pcb);
      } else {
        tcp_ack_now(pcb);
        pcb->state = CLOSING;
      }
    } else if (flags & TCP_ACK && ackno == pcb->snd_nxt) {
      pcb->state = FIN_WAIT_2;
    }
    break;
  case FIN_WAIT_2:
    tcp_receive(pcb);
    if (flags & TCP_FIN) {
      LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
      tcp_ack_now(pcb);
      tcp_pcb_purge(pcb);
      TCP_RMV(&tcp_active_pcbs, pcb);
      pcb->state = TIME_WAIT;
      TCP_REG(&tcp_tw_pcbs, pcb);
    }
    break;
  case CLOSING:
    tcp_receive(pcb);
    if (flags & TCP_ACK && ackno == pcb->snd_nxt) {
      LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
      tcp_ack_now(pcb);
      tcp_pcb_purge(pcb);
      TCP_RMV(&tcp_active_pcbs, pcb);
      pcb->state = TIME_WAIT;
      TCP_REG(&tcp_tw_pcbs, pcb);
    }
    break;
  case LAST_ACK:
    tcp_receive(pcb);
    if (flags & TCP_ACK && ackno == pcb->snd_nxt) {
      LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
      /* bugfix #21699: don't set pcb->state to CLOSED here or we risk leaking segments */
      recv_flags = TF_CLOSED;
    }
    break;
  default:
    break;
  }
  return ERR_OK;
}

/**
 * Called by tcp_input() when a segment arrives for a listening
 * connection (from tcp_input()).
 *
 * @param pcb the tcp_pcb_listen for which a segment arrived
 * @return ERR_OK if the segment was processed
 *         another err_t on error
 *
 * @note the return value is not (yet?) used in tcp_input()
 * @note the segment which arrived is saved in global variables, therefore only the pcb
 *       involved is passed as a parameter to this function
 */
static err_t
tcp_listen_input(struct tcp_pcb_listen *pcb)
{
  struct tcp_pcb *npcb;
  u32_t optdata;

  /* In the LISTEN state, we check for incoming SYN segments,
     creates a new PCB, and responds with a SYN|ACK. */
  if (flags & TCP_ACK) {
    /* For incoming segments with the ACK flag set, respond with a
       RST. */
    LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_listen_input: ACK in LISTEN, sending reset\n"));
    tcp_rst(ackno + 1, seqno + tcplen,
      &(iphdr->dest), &(iphdr->src),
      tcphdr->dest, tcphdr->src);
  } else if (flags & TCP_SYN) {
    LWIP_DEBUGF(TCP_DEBUG, ("TCP connection request %"U16_F" -> %"U16_F".\n", tcphdr->src, tcphdr->dest));
#if TCP_LISTEN_BACKLOG
    if (pcb->accepts_pending >= pcb->backlog) {
      return ERR_ABRT;
    }
#endif /* TCP_LISTEN_BACKLOG */
    npcb = tcp_alloc(pcb->prio);
    /* If a new PCB could not be created (probably due to lack of memory),
       we don't do anything, but rely on the sender will retransmit the
       SYN at a time when we have more memory available. */
    if (npcb == NULL) {
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_listen_input: could not allocate PCB\n"));
      TCP_STATS_INC(tcp.memerr);
      return ERR_MEM;
    }
#if TCP_LISTEN_BACKLOG
    pcb->accepts_pending++;
#endif /* TCP_LISTEN_BACKLOG */
    /* Set up the new PCB. */
    ip_addr_set(&(npcb->local_ip), &(iphdr->dest));
    npcb->local_port = pcb->local_port;
    ip_addr_set(&(npcb->remote_ip), &(iphdr->src));
    npcb->remote_port = tcphdr->src;
    npcb->state = SYN_RCVD;
    npcb->rcv_nxt = seqno + 1;
    npcb->snd_wnd = tcphdr->wnd;
    npcb->ssthresh = npcb->snd_wnd;
    npcb->snd_wl1 = seqno - 1;/* initialise to seqno-1 to force window update */
    npcb->callback_arg = pcb->callback_arg;
#if LWIP_CALLBACK_API
    npcb->accept = pcb->accept;
#endif /* LWIP_CALLBACK_API */
    /* inherit socket options */
    npcb->so_options = pcb->so_options & (SOF_DEBUG|SOF_DONTROUTE|SOF_KEEPALIVE|SOF_OOBINLINE|SOF_LINGER);
    /* Register the new PCB so that we can begin receiving segments
       for it. */
    TCP_REG(&tcp_active_pcbs, npcb);

    /* Parse any options in the SYN. */
    tcp_parseopt(npcb);
#if TCP_CALCULATE_EFF_SEND_MSS
    npcb->mss = tcp_eff_send_mss(npcb->mss, &(npcb->remote_ip));
#endif /* TCP_CALCULATE_EFF_SEND_MSS */

    snmp_inc_tcppassiveopens();

    /* Build an MSS option. */
    optdata = TCP_BUILD_MSS_OPTION();
    /* Send a SYN|ACK together with the MSS option. */
    tcp_enqueue(npcb, NULL, 0, TCP_SYN | TCP_ACK, 0, (u8_t *)&optdata, 4);
    return tcp_output(npcb);
  }
  return ERR_OK;
}

/**
 * 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 (or on error)
 * @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, struct ip_addr *ipaddr, u16_t port,
      err_t (* connected)(void *arg, struct tcp_pcb *tpcb, err_t err))
{
  err_t ret;
  u32_t iss;

  LWIP_ERROR("tcp_connect: can only connected from state CLOSED", pcb->state == CLOSED, return ERR_ISCONN);

  LWIP_DEBUGF(TCP_DEBUG, ("tcp_connect to port %"U16_F"\n", port));
	/* 远端IP地址有效，则记录到TCP控制块中 */
  if (ipaddr != NULL) {
    pcb->remote_ip = *ipaddr;
  } else {
    return ERR_VAL;
  }
	/* 记录远端PORT */
  pcb->remote_port = port;
	/* 如果本地端口未绑定，则绑定一个短暂端口 */
  if (pcb->local_port == 0) {
    pcb->local_port = tcp_new_port();
  }
	/* 获取初始序号 */
  iss = tcp_next_iss();
	/* 设置接收窗口下一个接收的序号 */
  pcb->rcv_nxt = 0;
	/* 设置发送窗口各个字段 */
  pcb->snd_nxt = iss;
  pcb->lastack = iss - 1;
  pcb->snd_lbb = iss - 1;
	/* 设置接收窗口各个字段 */
  pcb->rcv_wnd = TCP_WND;
  pcb->rcv_ann_wnd = TCP_WND;
  pcb->rcv_ann_right_edge = pcb->rcv_nxt;
  pcb->snd_wnd = TCP_WND;
  /* As initial send MSS, we use TCP_MSS but limit it to 536.
     The send MSS is updated when an MSS option is received. */
	/* 设置MSS */
  pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS;
#if TCP_CALCULATE_EFF_SEND_MSS
  pcb->mss = tcp_eff_send_mss(pcb->mss, ipaddr);
#endif /* TCP_CALCULATE_EFF_SEND_MSS */
	/* 初始化阻塞窗口 */
  pcb->cwnd = 1;
  pcb->ssthresh = pcb->mss * 10;
	/* TCP控制块状态设为SYN_SENT */
  pcb->state = SYN_SENT;
#if LWIP_CALLBACK_API
	/* 设置回调函数 */
  pcb->connected = connected;
#endif /* LWIP_CALLBACK_API */
	/* 把TCP控制块从tcp_bound_pcbs链表移除 */
  TCP_RMV(&tcp_bound_pcbs, pcb);
	/* 把TCP控制块插入tcp_active_pcbs链表 */
  TCP_REG(&tcp_active_pcbs, pcb);

  snmp_inc_tcpactiveopens();
  
	/* 构造TCP报文，长度为0，SYN置1，并包含MSS选项字段 */
  ret = tcp_enqueue(pcb, NULL, 0, TCP_SYN, 0, TF_SEG_OPTS_MSS
#if LWIP_TCP_TIMESTAMPS
                    | TF_SEG_OPTS_TS
#endif
                    );
  if (ret == ERR_OK) { 
		/* 发送构造的TCP报文 */
    tcp_output(pcb);
  }
  return ret;
} 

/* 绑定TCP控制块到本地端口 */
err_t
tcp_bind(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port)
{
  struct tcp_pcb *cpcb;

  LWIP_ERROR("tcp_bind: can only bind in state CLOSED", pcb->state == CLOSED, return ERR_ISCONN);

	/* 未指定端口号，则自动分配 */
  if (port == 0) {
    port = tcp_new_port();
  }
  /* Check if the address already is in use. */
  /* Check the listen pcbs. */
	/* 检查指定的 IP:端口号 有没有被其它TCP控制块占用 */
	/* 先检查处于LISTEN状态的TCP控制块 */
  for(cpcb = (struct tcp_pcb *)tcp_listen_pcbs.pcbs;
      cpcb != NULL; cpcb = cpcb->next) {
		/* 端口号相同 */
    if (cpcb->local_port == port) {
			/* 其它TCP控制块绑定到本地所有IP
			 * 或要绑定的TCP控制块绑定到本地所有IP
			 * 或要绑定的IP和其它TCP控制块的本地IP相同
			 */
      if (ip_addr_isany(&(cpcb->local_ip)) ||
          ip_addr_isany(ipaddr) ||
          ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
				/* 该本地IP:本地PORT已经被占用，返回错误 */
        return ERR_USE;
      }
    }
  }
  /* Check the connected pcbs. */
	/* 检查处于连接状态TCP控制块 */
  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;
      }
    }
  }
  /* Check the bound, not yet connected pcbs. */
	/* 检查已绑定但未连接的TCP控制块 */
  for(cpcb = tcp_bound_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;
      }
    }
  }
  /* @todo: until SO_REUSEADDR is implemented (see task #6995 on savannah),
   * we have to check the pcbs in TIME-WAIT state, also: */
	/* 检查处于TIME-WAIT状态的TCP控制块 */
  for(cpcb = tcp_tw_pcbs; cpcb != NULL; cpcb = cpcb->next) {
    if (cpcb->local_port == port) {
      if (ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
        return ERR_USE;
      }
    }
  }

	/* 设置TCP控制块中的本地IP */
  if (!ip_addr_isany(ipaddr)) {
    pcb->local_ip = *ipaddr;
  }
	/* 设置TCP控制块的本地端口号 */
  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;
}