text: /**
   * @file
   * Sequential API External module
   *
   * @defgroup netconn Netconn API
   * @ingroup sequential_api
   * Thread-safe, to be called from non-TCPIP threads only.
   * TX/RX handling based on @ref netbuf (containing @ref pbuf)
   * to avoid copying data around.
   *
   * @defgroup netconn_common Common functions
   * @ingroup netconn
   * For use with TCP and UDP
   *
   * @defgroup netconn_tcp TCP only
   * @ingroup netconn
   * TCP only functions
   *
   * @defgroup netconn_udp UDP only
   * @ingroup netconn
   * UDP only functions
   */
  
  /*
   * 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>
   */
  
  /* This is the part of the API that is linked with
     the application */
  
  #include "lwip/opt.h"
  
  #if LWIP_NETCONN /* don't build if not configured for use in lwipopts.h */
  
  #include "lwip/api.h"
  #include "lwip/memp.h"
  
  #include "lwip/ip.h"
  #include "lwip/raw.h"
  #include "lwip/udp.h"
  #include "lwip/priv/api_msg.h"
  #include "lwip/priv/tcp_priv.h"
  #include "lwip/priv/tcpip_priv.h"
  
  #ifdef LWIP_HOOK_FILENAME
  #include LWIP_HOOK_FILENAME
  #endif
  
  #include <string.h>
  
  #define API_MSG_VAR_REF(name)               API_VAR_REF(name)
  #define API_MSG_VAR_DECLARE(name)           API_VAR_DECLARE(struct api_msg, name)
  #define API_MSG_VAR_ALLOC(name)             API_VAR_ALLOC(struct api_msg, MEMP_API_MSG, name, ERR_MEM)
  #define API_MSG_VAR_ALLOC_RETURN_NULL(name) API_VAR_ALLOC(struct api_msg, MEMP_API_MSG, name, NULL)
  #define API_MSG_VAR_FREE(name)              API_VAR_FREE(MEMP_API_MSG, name)
  
  #if TCP_LISTEN_BACKLOG
  /* need to allocate API message for accept so empty message pool does not result in event loss
   * see bug #47512: MPU_COMPATIBLE may fail on empty pool */
  #define API_MSG_VAR_ALLOC_ACCEPT(msg) API_MSG_VAR_ALLOC(msg)
  #define API_MSG_VAR_FREE_ACCEPT(msg) API_MSG_VAR_FREE(msg)
  #else /* TCP_LISTEN_BACKLOG */
  #define API_MSG_VAR_ALLOC_ACCEPT(msg)
  #define API_MSG_VAR_FREE_ACCEPT(msg)
  #endif /* TCP_LISTEN_BACKLOG */
  
  #if LWIP_NETCONN_FULLDUPLEX
  #define NETCONN_RECVMBOX_WAITABLE(conn) (sys_mbox_valid(&(conn)->recvmbox) && (((conn)->flags & NETCONN_FLAG_MBOXINVALID) == 0))
  #define NETCONN_ACCEPTMBOX_WAITABLE(conn) (sys_mbox_valid(&(conn)->acceptmbox) && (((conn)->flags & (NETCONN_FLAG_MBOXCLOSED|NETCONN_FLAG_MBOXINVALID)) == 0))
  #define NETCONN_MBOX_WAITING_INC(conn) SYS_ARCH_INC(conn->mbox_threads_waiting, 1)
  #define NETCONN_MBOX_WAITING_DEC(conn) SYS_ARCH_DEC(conn->mbox_threads_waiting, 1)
  #else /* LWIP_NETCONN_FULLDUPLEX */
  #define NETCONN_RECVMBOX_WAITABLE(conn)   sys_mbox_valid(&(conn)->recvmbox)
  #define NETCONN_ACCEPTMBOX_WAITABLE(conn) (sys_mbox_valid(&(conn)->acceptmbox) && (((conn)->flags & NETCONN_FLAG_MBOXCLOSED) == 0))
  #define NETCONN_MBOX_WAITING_INC(conn)
  #define NETCONN_MBOX_WAITING_DEC(conn)
  #endif /* LWIP_NETCONN_FULLDUPLEX */
  
  static err_t netconn_close_shutdown(struct netconn *conn, u8_t how);
  
  /**
   * Call the lower part of a netconn_* function
   * This function is then running in the thread context
   * of tcpip_thread and has exclusive access to lwIP core code.
   *
   * @param fn function to call
   * @param apimsg a struct containing the function to call and its parameters
   * @return ERR_OK if the function was called, another err_t if not
   */
  static err_t
  netconn_apimsg(tcpip_callback_fn fn, struct api_msg *apimsg)
  {
    err_t err;
  
  #ifdef LWIP_DEBUG
    /* catch functions that don't set err */
    apimsg->err = ERR_VAL;
  #endif /* LWIP_DEBUG */
  
  #if LWIP_NETCONN_SEM_PER_THREAD
    apimsg->op_completed_sem = LWIP_NETCONN_THREAD_SEM_GET();
  #endif /* LWIP_NETCONN_SEM_PER_THREAD */
  
    if (sys_tcpip_thread_check()) {
        fn(apimsg);
        return apimsg->err;
    } else {
        err = tcpip_send_msg_wait_sem(fn, apimsg, LWIP_API_MSG_SEM(apimsg));
  
        if (err == ERR_OK) {
          return apimsg->err;
        }
  
        return err;
    }
  }
  
  /**
   * Create a new netconn (of a specific type) that has a callback function.
   * The corresponding pcb is also created.
   *
   * @param t the type of 'connection' to create (@see enum netconn_type)
   * @param proto the IP protocol for RAW IP pcbs
   * @param callback a function to call on status changes (RX available, TX'ed)
   * @return a newly allocated struct netconn or
   *         NULL on memory error
   */
  struct netconn *
  netconn_new_with_proto_and_callback(enum netconn_type t, u8_t proto, netconn_callback callback)
  {
    struct netconn *conn;
    API_MSG_VAR_DECLARE(msg);
    API_MSG_VAR_ALLOC_RETURN_NULL(msg);
  
    conn = netconn_alloc(t, callback);
    if (conn != NULL) {
      err_t err;
  
      API_MSG_VAR_REF(msg).msg.n.proto = proto;
      API_MSG_VAR_REF(msg).conn = conn;
      err = netconn_apimsg(lwip_netconn_do_newconn, &API_MSG_VAR_REF(msg));
      if (err != ERR_OK) {
        LWIP_ASSERT("freeing conn without freeing pcb", conn->pcb.tcp == NULL);
        LWIP_ASSERT("conn has no recvmbox", sys_mbox_valid(&conn->recvmbox));
  #if LWIP_TCP
        LWIP_ASSERT("conn->acceptmbox shouldn't exist", !sys_mbox_valid(&conn->acceptmbox));
  #endif /* LWIP_TCP */
  #if !LWIP_NETCONN_SEM_PER_THREAD
        LWIP_ASSERT("conn has no op_completed", sys_sem_valid(&conn->op_completed));
        sys_sem_free(&conn->op_completed);
  #endif /* !LWIP_NETCONN_SEM_PER_THREAD */
        sys_mbox_free(&conn->recvmbox);
        memp_free(MEMP_NETCONN, conn);
        API_MSG_VAR_FREE(msg);
        return NULL;
      }
    }
    API_MSG_VAR_FREE(msg);
    return conn;
  }
  
  /**
   * @ingroup netconn_common
   * Close a netconn 'connection' and free all its resources but not the netconn itself.
   * UDP and RAW connection are completely closed, TCP pcbs might still be in a waitstate
   * after this returns.
   *
   * @param conn the netconn to delete
   * @return ERR_OK if the connection was deleted
   */
  err_t
  netconn_prepare_delete(struct netconn *conn)
  {
    err_t err;
    API_MSG_VAR_DECLARE(msg);
  
    /* No ASSERT here because possible to get a (conn == NULL) if we got an accept error */
    if (conn == NULL) {
      return ERR_OK;
    }
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
  #if LWIP_SO_SNDTIMEO || LWIP_SO_LINGER
    /* get the time we started, which is later compared to
       sys_now() + conn->send_timeout */
    API_MSG_VAR_REF(msg).msg.sd.time_started = sys_now();
  #else /* LWIP_SO_SNDTIMEO || LWIP_SO_LINGER */
  #if LWIP_TCP
    API_MSG_VAR_REF(msg).msg.sd.polls_left =
      ((LWIP_TCP_CLOSE_TIMEOUT_MS_DEFAULT + TCP_SLOW_INTERVAL - 1) / TCP_SLOW_INTERVAL) + 1;
  #endif /* LWIP_TCP */
  #endif /* LWIP_SO_SNDTIMEO || LWIP_SO_LINGER */
    err = netconn_apimsg(lwip_netconn_do_delconn, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    if (err != ERR_OK) {
      return err;
    }
    return ERR_OK;
  }
  
  /**
   * @ingroup netconn_common
   * Close a netconn 'connection' and free its resources.
   * UDP and RAW connection are completely closed, TCP pcbs might still be in a waitstate
   * after this returns.
   *
   * @param conn the netconn to delete
   * @return ERR_OK if the connection was deleted
   */
  err_t
  netconn_delete(struct netconn *conn)
  {
    err_t err;
  
    /* No ASSERT here because possible to get a (conn == NULL) if we got an accept error */
    if (conn == NULL) {
      return ERR_OK;
    }
  
  #if LWIP_NETCONN_FULLDUPLEX
    if (conn->flags & NETCONN_FLAG_MBOXINVALID) {
      /* Already called netconn_prepare_delete() before */
      err = ERR_OK;
    } else
  #endif /* LWIP_NETCONN_FULLDUPLEX */
    {
      err = netconn_prepare_delete(conn);
    }
    if (err == ERR_OK) {
      netconn_free(conn);
    }
    return err;
  }
  
  /**
   * Get the local or remote IP address and port of a netconn.
   * For RAW netconns, this returns the protocol instead of a port!
   *
   * @param conn the netconn to query
   * @param addr a pointer to which to save the IP address
   * @param port a pointer to which to save the port (or protocol for RAW)
   * @param local 1 to get the local IP address, 0 to get the remote one
   * @return ERR_CONN for invalid connections
   *         ERR_OK if the information was retrieved
   */
  err_t
  netconn_getaddr(struct netconn *conn, ip_addr_t *addr, u16_t *port, u8_t local)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    LWIP_ERROR("netconn_getaddr: invalid conn", (conn != NULL), return ERR_ARG;);
    LWIP_ERROR("netconn_getaddr: invalid addr", (addr != NULL), return ERR_ARG;);
    LWIP_ERROR("netconn_getaddr: invalid port", (port != NULL), return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.ad.local = local;
  #if LWIP_MPU_COMPATIBLE
    err = netconn_apimsg(lwip_netconn_do_getaddr, &API_MSG_VAR_REF(msg));
    *addr = msg->msg.ad.ipaddr;
    *port = msg->msg.ad.port;
  #else /* LWIP_MPU_COMPATIBLE */
    msg.msg.ad.ipaddr = addr;
    msg.msg.ad.port = port;
    err = netconn_apimsg(lwip_netconn_do_getaddr, &msg);
  #endif /* LWIP_MPU_COMPATIBLE */
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  
  /**
   * @ingroup netconn_common
   * Bind a netconn to a specific local IP address and port.
   * Binding one netconn twice might not always be checked correctly!
   *
   * @param conn the netconn to bind
   * @param addr the local IP address to bind the netconn to
   *             (use IP4_ADDR_ANY/IP6_ADDR_ANY to bind to all addresses)
   * @param port the local port to bind the netconn to (not used for RAW)
   * @return ERR_OK if bound, any other err_t on failure
   */
  err_t
  netconn_bind(struct netconn *conn, const ip_addr_t *addr, u16_t port)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    LWIP_ERROR("netconn_bind: invalid conn", (conn != NULL), return ERR_ARG;);
  
  #if LWIP_IPV4
    /* Don't propagate NULL pointer (IP_ADDR_ANY alias) to subsequent functions */
    if (addr == NULL) {
      addr = IP4_ADDR_ANY;
    }
  #endif /* LWIP_IPV4 */
  
  #if LWIP_IPV4 && LWIP_IPV6
    /* "Socket API like" dual-stack support: If IP to bind to is IP6_ADDR_ANY,
     * and NETCONN_FLAG_IPV6_V6ONLY is 0, use IP_ANY_TYPE to bind
     */
    if ((netconn_get_ipv6only(conn) == 0) &&
        ip_addr_cmp(addr, IP6_ADDR_ANY)) {
      addr = IP_ANY_TYPE;
    }
  #endif /* LWIP_IPV4 && LWIP_IPV6 */
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.bc.ipaddr = API_MSG_VAR_REF(addr);
    API_MSG_VAR_REF(msg).msg.bc.port = port;
    err = netconn_apimsg(lwip_netconn_do_bind, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  
  /**
   * @ingroup netconn_common
   * Bind a netconn to a specific interface and port.
   * Binding one netconn twice might not always be checked correctly!
   *
   * @param conn the netconn to bind
   * @param if_idx the local interface index to bind the netconn to
   * @return ERR_OK if bound, any other err_t on failure
   */
  err_t
  netconn_bind_if(struct netconn *conn, u8_t if_idx)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    LWIP_ERROR("netconn_bind_if: invalid conn", (conn != NULL), return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.bc.if_idx = if_idx;
    err = netconn_apimsg(lwip_netconn_do_bind_if, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  
  /**
   * @ingroup netconn_common
   * Connect a netconn to a specific remote IP address and port.
   *
   * @param conn the netconn to connect
   * @param addr the remote IP address to connect to
   * @param port the remote port to connect to (no used for RAW)
   * @return ERR_OK if connected, return value of tcp_/udp_/raw_connect otherwise
   */
  err_t
  netconn_connect(struct netconn *conn, const ip_addr_t *addr, u16_t port)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    LWIP_ERROR("netconn_connect: invalid conn", (conn != NULL), return ERR_ARG;);
  
  #if LWIP_IPV4
    /* Don't propagate NULL pointer (IP_ADDR_ANY alias) to subsequent functions */
    if (addr == NULL) {
      addr = IP4_ADDR_ANY;
    }
  #endif /* LWIP_IPV4 */
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.bc.ipaddr = API_MSG_VAR_REF(addr);
    API_MSG_VAR_REF(msg).msg.bc.port = port;
    err = netconn_apimsg(lwip_netconn_do_connect, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  
  /**
   * @ingroup netconn_udp
   * Disconnect a netconn from its current peer (only valid for UDP netconns).
   *
   * @param conn the netconn to disconnect
   * @return See @ref err_t
   */
  err_t
  netconn_disconnect(struct netconn *conn)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    LWIP_ERROR("netconn_disconnect: invalid conn", (conn != NULL), return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    err = netconn_apimsg(lwip_netconn_do_disconnect, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  
  /**
   * @ingroup netconn_tcp
   * Set a TCP netconn into listen mode
   *
   * @param conn the tcp netconn to set to listen mode
   * @param backlog the listen backlog, only used if TCP_LISTEN_BACKLOG==1
   * @return ERR_OK if the netconn was set to listen (UDP and RAW netconns
   *         don't return any error (yet?))
   */
  err_t
  netconn_listen_with_backlog(struct netconn *conn, u8_t backlog)
  {
  #if LWIP_TCP
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    /* This does no harm. If TCP_LISTEN_BACKLOG is off, backlog is unused. */
    LWIP_UNUSED_ARG(backlog);
  
    LWIP_ERROR("netconn_listen: invalid conn", (conn != NULL), return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
  #if TCP_LISTEN_BACKLOG
    API_MSG_VAR_REF(msg).msg.lb.backlog = backlog;
  #endif /* TCP_LISTEN_BACKLOG */
    err = netconn_apimsg(lwip_netconn_do_listen, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  #else /* LWIP_TCP */
    LWIP_UNUSED_ARG(conn);
    LWIP_UNUSED_ARG(backlog);
    return ERR_ARG;
  #endif /* LWIP_TCP */
  }
  
  /**
   * @ingroup netconn_tcp
   * Accept a new connection on a TCP listening netconn.
   *
   * @param conn the TCP listen netconn
   * @param new_conn pointer where the new connection is stored
   * @return ERR_OK if a new connection has been received or an error
   *                code otherwise
   */
  err_t
  netconn_accept(struct netconn *conn, struct netconn **new_conn)
  {
  #if LWIP_TCP
    err_t err;
    void *accept_ptr;
    struct netconn *newconn;
  #if TCP_LISTEN_BACKLOG
    API_MSG_VAR_DECLARE(msg);
  #endif /* TCP_LISTEN_BACKLOG */
  
    LWIP_ERROR("netconn_accept: invalid pointer",    (new_conn != NULL),                  return ERR_ARG;);
    *new_conn = NULL;
    LWIP_ERROR("netconn_accept: invalid conn",       (conn != NULL),                      return ERR_ARG;);
  
    /* NOTE: Although the opengroup spec says a pending error shall be returned to
             send/recv/getsockopt(SO_ERROR) only, we return it for listening
             connections also, to handle embedded-system errors */
    err = netconn_err(conn);
    if (err != ERR_OK) {
      /* return pending error */
      return err;
    }
    if (!NETCONN_ACCEPTMBOX_WAITABLE(conn)) {
      /* don't accept if closed: this might block the application task
         waiting on acceptmbox forever! */
      return ERR_CLSD;
    }
  
    API_MSG_VAR_ALLOC_ACCEPT(msg);
  
    NETCONN_MBOX_WAITING_INC(conn);
    if (netconn_is_nonblocking(conn)) {
      if (sys_arch_mbox_tryfetch(&conn->acceptmbox, &accept_ptr) == SYS_ARCH_TIMEOUT) {
        API_MSG_VAR_FREE_ACCEPT(msg);
        NETCONN_MBOX_WAITING_DEC(conn);
        return ERR_WOULDBLOCK;
      }
    } else {
  #if LWIP_SO_RCVTIMEO
      if (sys_arch_mbox_fetch(&conn->acceptmbox, &accept_ptr, conn->recv_timeout) == SYS_ARCH_TIMEOUT) {
        API_MSG_VAR_FREE_ACCEPT(msg);
        NETCONN_MBOX_WAITING_DEC(conn);
        return ERR_TIMEOUT;
      }
  #else
      sys_arch_mbox_fetch(&conn->acceptmbox, &accept_ptr, 0);
  #endif /* LWIP_SO_RCVTIMEO*/
    }
    NETCONN_MBOX_WAITING_DEC(conn);
  #if LWIP_NETCONN_FULLDUPLEX
    if (conn->flags & NETCONN_FLAG_MBOXINVALID) {
      if (lwip_netconn_is_deallocated_msg(accept_ptr)) {
        /* the netconn has been closed from another thread */
        API_MSG_VAR_FREE_ACCEPT(msg);
        return ERR_CONN;
      }
    }
  #endif
  
    /* Register event with callback */
    API_EVENT(conn, NETCONN_EVT_RCVMINUS, 0);
  
    if (lwip_netconn_is_err_msg(accept_ptr, &err)) {
      /* a connection has been aborted: e.g. out of pcbs or out of netconns during accept */
      API_MSG_VAR_FREE_ACCEPT(msg);
      return err;
    }
    if (accept_ptr == NULL) {
      /* connection has been aborted */
      API_MSG_VAR_FREE_ACCEPT(msg);
      return ERR_CLSD;
    }
    newconn = (struct netconn *)accept_ptr;
  #if TCP_LISTEN_BACKLOG
    /* Let the stack know that we have accepted the connection. */
    API_MSG_VAR_REF(msg).conn = newconn;
    /* don't care for the return value of lwip_netconn_do_recv */
    netconn_apimsg(lwip_netconn_do_accepted, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  #endif /* TCP_LISTEN_BACKLOG */
  
    *new_conn = newconn;
    /* don't set conn->last_err: it's only ERR_OK, anyway */
    return ERR_OK;
  #else /* LWIP_TCP */
    LWIP_UNUSED_ARG(conn);
    LWIP_UNUSED_ARG(new_conn);
    return ERR_ARG;
  #endif /* LWIP_TCP */
  }
  
  /**
   * @ingroup netconn_common
   * Receive data: actual implementation that doesn't care whether pbuf or netbuf
   * is received (this is internal, it's just here for describing common errors)
   *
   * @param conn the netconn from which to receive data
   * @param new_buf pointer where a new pbuf/netbuf is stored when received data
   * @param apiflags flags that control function behaviour. For now only:
   * - NETCONN_DONTBLOCK: only read data that is available now, don't wait for more data
   * @return ERR_OK if data has been received, an error code otherwise (timeout,
   *                memory error or another error)
   *         ERR_CONN if not connected
   *         ERR_CLSD if TCP connection has been closed
   *         ERR_WOULDBLOCK if the netconn is nonblocking but would block to wait for data
   *         ERR_TIMEOUT if the netconn has a receive timeout and no data was received
   */
  static err_t
  netconn_recv_data(struct netconn *conn, void **new_buf, u8_t apiflags)
  {
    void *buf = NULL;
    u16_t len;
  
    LWIP_ERROR("netconn_recv: invalid pointer", (new_buf != NULL), return ERR_ARG;);
    *new_buf = NULL;
    LWIP_ERROR("netconn_recv: invalid conn",    (conn != NULL),    return ERR_ARG;);
  
    if (!NETCONN_RECVMBOX_WAITABLE(conn)) {
      err_t err = netconn_err(conn);
      if (err != ERR_OK) {
        /* return pending error */
        return err;
      }
      return ERR_CONN;
    }
  
    NETCONN_MBOX_WAITING_INC(conn);
    if (netconn_is_nonblocking(conn) || (apiflags & NETCONN_DONTBLOCK) ||
        (conn->flags & NETCONN_FLAG_MBOXCLOSED) || (conn->pending_err != ERR_OK)) {
      if (sys_arch_mbox_tryfetch(&conn->recvmbox, &buf) == SYS_ARCH_TIMEOUT) {
        err_t err;
        NETCONN_MBOX_WAITING_DEC(conn);
        err = netconn_err(conn);
        if (err != ERR_OK) {
          /* return pending error */
          return err;
        }
        if (conn->flags & NETCONN_FLAG_MBOXCLOSED) {
          return ERR_CONN;
        }
        return ERR_WOULDBLOCK;
      }
    } else {
  #if LWIP_SO_RCVTIMEO
      if (sys_arch_mbox_fetch(&conn->recvmbox, &buf, conn->recv_timeout) == SYS_ARCH_TIMEOUT) {
        NETCONN_MBOX_WAITING_DEC(conn);
        return ERR_TIMEOUT;
      }
  #else
      sys_arch_mbox_fetch(&conn->recvmbox, &buf, 0);
  #endif /* LWIP_SO_RCVTIMEO*/
    }
    NETCONN_MBOX_WAITING_DEC(conn);
  #if LWIP_NETCONN_FULLDUPLEX
    if (conn->flags & NETCONN_FLAG_MBOXINVALID) {
      if (lwip_netconn_is_deallocated_msg(buf)) {
        /* the netconn has been closed from another thread */
        API_MSG_VAR_FREE_ACCEPT(msg);
        return ERR_CONN;
      }
    }
  #endif
  
  #if LWIP_TCP
  #if (LWIP_UDP || LWIP_RAW)
    if (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP)
  #endif /* (LWIP_UDP || LWIP_RAW) */
    {
      err_t err;
      /* Check if this is an error message or a pbuf */
      if (lwip_netconn_is_err_msg(buf, &err)) {
        /* new_buf has been zeroed above already */
        if (err == ERR_CLSD) {
          /* connection closed translates to ERR_OK with *new_buf == NULL */
          return ERR_OK;
        }
        return err;
      }
      len = ((struct pbuf *)buf)->tot_len;
    }
  #endif /* LWIP_TCP */
  #if LWIP_TCP && (LWIP_UDP || LWIP_RAW)
    else
  #endif /* LWIP_TCP && (LWIP_UDP || LWIP_RAW) */
  #if (LWIP_UDP || LWIP_RAW)
    {
      LWIP_ASSERT("buf != NULL", buf != NULL);
      len = netbuf_len((struct netbuf *)buf);
    }
  #endif /* (LWIP_UDP || LWIP_RAW) */
  
  #if LWIP_SO_RCVBUF
    SYS_ARCH_DEC(conn->recv_avail, len);
  #endif /* LWIP_SO_RCVBUF */
    /* Register event with callback */
    API_EVENT(conn, NETCONN_EVT_RCVMINUS, len);
  
    LWIP_DEBUGF(API_LIB_DEBUG, ("netconn_recv_data: received %p, len=%"U16_F"\n", buf, len));
  
    *new_buf = buf;
    /* don't set conn->last_err: it's only ERR_OK, anyway */
    return ERR_OK;
  }
  
  #if LWIP_TCP
  static err_t
  netconn_tcp_recvd_msg(struct netconn *conn, size_t len, struct api_msg *msg)
  {
    LWIP_ERROR("netconn_recv_tcp_pbuf: invalid conn", (conn != NULL) &&
               NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP, return ERR_ARG;);
  
    msg->conn = conn;
    msg->msg.r.len = len;
  
    return netconn_apimsg(lwip_netconn_do_recv, msg);
  }
  
  err_t
  netconn_tcp_recvd(struct netconn *conn, size_t len)
  {
    err_t err;
    API_MSG_VAR_DECLARE(msg);
    LWIP_ERROR("netconn_recv_tcp_pbuf: invalid conn", (conn != NULL) &&
               NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP, return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
    err = netconn_tcp_recvd_msg(conn, len, &API_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
    return err;
  }
  
  static err_t
  netconn_recv_data_tcp(struct netconn *conn, struct pbuf **new_buf, u8_t apiflags)
  {
    err_t err;
    struct pbuf *buf;
    API_MSG_VAR_DECLARE(msg);
  #if LWIP_MPU_COMPATIBLE
    msg = NULL;
  #endif
  
    if (!NETCONN_RECVMBOX_WAITABLE(conn)) {
      /* This only happens when calling this function more than once *after* receiving FIN */
      return ERR_CONN;
    }
    if (netconn_is_flag_set(conn, NETCONN_FIN_RX_PENDING)) {
      netconn_clear_flags(conn, NETCONN_FIN_RX_PENDING);
      goto handle_fin;
    }
  
    if (!(apiflags & NETCONN_NOAUTORCVD)) {
      /* need to allocate API message here so empty message pool does not result in event loss
        * see bug #47512: MPU_COMPATIBLE may fail on empty pool */
      API_MSG_VAR_ALLOC(msg);
    }
  
    err = netconn_recv_data(conn, (void **)new_buf, apiflags);
    if (err != ERR_OK) {
      if (!(apiflags & NETCONN_NOAUTORCVD)) {
        API_MSG_VAR_FREE(msg);
      }
      return err;
    }
    buf = *new_buf;
    if (!(apiflags & NETCONN_NOAUTORCVD)) {
      /* Let the stack know that we have taken the data. */
      u16_t len = buf ? buf->tot_len : 1;
      /* don't care for the return value of lwip_netconn_do_recv */
      /* @todo: this should really be fixed, e.g. by retrying in poll on error */
      netconn_tcp_recvd_msg(conn, len,  &API_VAR_REF(msg));
      API_MSG_VAR_FREE(msg);
    }
  
    /* If we are closed, we indicate that we no longer wish to use the socket */
    if (buf == NULL) {
      if (apiflags & NETCONN_NOFIN) {
        /* received a FIN but the caller cannot handle it right now:
           re-enqueue it and return "no data" */
        netconn_set_flags(conn, NETCONN_FIN_RX_PENDING);
        return ERR_WOULDBLOCK;
      } else {
  handle_fin:
        API_EVENT(conn, NETCONN_EVT_RCVMINUS, 0);
        if (conn->pcb.ip == NULL) {
          /* race condition: RST during recv */
          err = netconn_err(conn);
          if (err != ERR_OK) {
            return err;
          }
          return ERR_RST;
        }
        /* RX side is closed, so deallocate the recvmbox */
        netconn_close_shutdown(conn, NETCONN_SHUT_RD);
        /* Don' store ERR_CLSD as conn->err since we are only half-closed */
        return ERR_CLSD;
      }
    }
    return err;
  }
  
  /**
   * @ingroup netconn_tcp
   * Receive data (in form of a pbuf) from a TCP netconn
   *
   * @param conn the netconn from which to receive data
   * @param new_buf pointer where a new pbuf is stored when received data
   * @return ERR_OK if data has been received, an error code otherwise (timeout,
   *                memory error or another error, @see netconn_recv_data)
   *         ERR_ARG if conn is not a TCP netconn
   */
  err_t
  netconn_recv_tcp_pbuf(struct netconn *conn, struct pbuf **new_buf)
  {
    LWIP_ERROR("netconn_recv_tcp_pbuf: invalid conn", (conn != NULL) &&
               NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP, return ERR_ARG;);
  
    return netconn_recv_data_tcp(conn, new_buf, 0);
  }
  
  /**
   * @ingroup netconn_tcp
   * Receive data (in form of a pbuf) from a TCP netconn
   *
   * @param conn the netconn from which to receive data
   * @param new_buf pointer where a new pbuf is stored when received data
   * @param apiflags flags that control function behaviour. For now only:
   * - NETCONN_DONTBLOCK: only read data that is available now, don't wait for more data
   * @return ERR_OK if data has been received, an error code otherwise (timeout,
   *                memory error or another error, @see netconn_recv_data)
   *         ERR_ARG if conn is not a TCP netconn
   */
  err_t
  netconn_recv_tcp_pbuf_flags(struct netconn *conn, struct pbuf **new_buf, u8_t apiflags)
  {
    LWIP_ERROR("netconn_recv_tcp_pbuf: invalid conn", (conn != NULL) &&
               NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP, return ERR_ARG;);
  
    return netconn_recv_data_tcp(conn, new_buf, apiflags);
  }
  #endif /* LWIP_TCP */
  
  /**
   * Receive data (in form of a netbuf) from a UDP or RAW netconn
   *
   * @param conn the netconn from which to receive data
   * @param new_buf pointer where a new netbuf is stored when received data
   * @return ERR_OK if data has been received, an error code otherwise (timeout,
   *                memory error or another error)
   *         ERR_ARG if conn is not a UDP/RAW netconn
   */
  err_t
  netconn_recv_udp_raw_netbuf(struct netconn *conn, struct netbuf **new_buf)
  {
    LWIP_ERROR("netconn_recv_udp_raw_netbuf: invalid conn", (conn != NULL) &&
               NETCONNTYPE_GROUP(netconn_type(conn)) != NETCONN_TCP, return ERR_ARG;);
  
    return netconn_recv_data(conn, (void **)new_buf, 0);
  }
  
  /**
   * Receive data (in form of a netbuf) from a UDP or RAW netconn
   *
   * @param conn the netconn from which to receive data
   * @param new_buf pointer where a new netbuf is stored when received data
   * @param apiflags flags that control function behaviour. For now only:
   * - NETCONN_DONTBLOCK: only read data that is available now, don't wait for more data
   * @return ERR_OK if data has been received, an error code otherwise (timeout,
   *                memory error or another error)
   *         ERR_ARG if conn is not a UDP/RAW netconn
   */
  err_t
  netconn_recv_udp_raw_netbuf_flags(struct netconn *conn, struct netbuf **new_buf, u8_t apiflags)
  {
    LWIP_ERROR("netconn_recv_udp_raw_netbuf: invalid conn", (conn != NULL) &&
               NETCONNTYPE_GROUP(netconn_type(conn)) != NETCONN_TCP, return ERR_ARG;);
  
    return netconn_recv_data(conn, (void **)new_buf, apiflags);
  }
  
  /**
   * @ingroup netconn_common
   * Receive data (in form of a netbuf containing a packet buffer) from a netconn
   *
   * @param conn the netconn from which to receive data
   * @param new_buf pointer where a new netbuf is stored when received data
   * @return ERR_OK if data has been received, an error code otherwise (timeout,
   *                memory error or another error)
   */
  err_t
  netconn_recv(struct netconn *conn, struct netbuf **new_buf)
  {
  #if LWIP_TCP
    struct netbuf *buf = NULL;
    err_t err;
  #endif /* LWIP_TCP */
  
    LWIP_ERROR("netconn_recv: invalid pointer", (new_buf != NULL), return ERR_ARG;);
    *new_buf = NULL;
    LWIP_ERROR("netconn_recv: invalid conn",    (conn != NULL),    return ERR_ARG;);
  
  #if LWIP_TCP
  #if (LWIP_UDP || LWIP_RAW)
    if (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP)
  #endif /* (LWIP_UDP || LWIP_RAW) */
    {
      struct pbuf *p = NULL;
      /* This is not a listening netconn, since recvmbox is set */
  
      buf = (struct netbuf *)memp_malloc(MEMP_NETBUF);
      if (buf == NULL) {
        return ERR_MEM;
      }
  
      err = netconn_recv_data_tcp(conn, &p, 0);
      if (err != ERR_OK) {
        memp_free(MEMP_NETBUF, buf);
        return err;
      }
      LWIP_ASSERT("p != NULL", p != NULL);
  
      buf->p = p;
      buf->ptr = p;
      buf->port = 0;
      ip_addr_set_zero(&buf->addr);
      *new_buf = buf;
      /* don't set conn->last_err: it's only ERR_OK, anyway */
      return ERR_OK;
    }
  #endif /* LWIP_TCP */
  #if LWIP_TCP && (LWIP_UDP || LWIP_RAW)
    else
  #endif /* LWIP_TCP && (LWIP_UDP || LWIP_RAW) */
    {
  #if (LWIP_UDP || LWIP_RAW)
      return netconn_recv_data(conn, (void **)new_buf, 0);
  #endif /* (LWIP_UDP || LWIP_RAW) */
    }
  }
  
  /**
   * @ingroup netconn_udp
   * Send data (in form of a netbuf) to a specific remote IP address and port.
   * Only to be used for UDP and RAW netconns (not TCP).
   *
   * @param conn the netconn over which to send data
   * @param buf a netbuf containing the data to send
   * @param addr the remote IP address to which to send the data
   * @param port the remote port to which to send the data
   * @return ERR_OK if data was sent, any other err_t on error
   */
  err_t
  netconn_sendto(struct netconn *conn, struct netbuf *buf, const ip_addr_t *addr, u16_t port)
  {
    if (buf != NULL) {
      ip_addr_set(&buf->addr, addr);
      buf->port = port;
      return netconn_send(conn, buf);
    }
    return ERR_VAL;
  }
  
  /**
   * @ingroup netconn_udp
   * Send data over a UDP or RAW netconn (that is already connected).
   *
   * @param conn the UDP or RAW netconn over which to send data
   * @param buf a netbuf containing the data to send
   * @return ERR_OK if data was sent, any other err_t on error
   */
  err_t
  netconn_send(struct netconn *conn, struct netbuf *buf)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    LWIP_ERROR("netconn_send: invalid conn",  (conn != NULL), return ERR_ARG;);
  
    LWIP_DEBUGF(API_LIB_DEBUG, ("netconn_send: sending %"U16_F" bytes\n", buf->p->tot_len));
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.b = buf;
    err = netconn_apimsg(lwip_netconn_do_send, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  
  /**
   * @ingroup netconn_tcp
   * Send data over a TCP netconn.
   *
   * @param conn the TCP netconn over which to send data
   * @param dataptr pointer to the application buffer that contains the data to send
   * @param size size of the application data to send
   * @param apiflags combination of following flags :
   * - NETCONN_COPY: data will be copied into memory belonging to the stack
   * - NETCONN_MORE: for TCP connection, PSH flag will be set on last segment sent
   * - NETCONN_DONTBLOCK: only write the data if all data can be written at once
   * @param bytes_written pointer to a location that receives the number of written bytes
   * @return ERR_OK if data was sent, any other err_t on error
   */
  err_t
  netconn_write_partly(struct netconn *conn, const void *dataptr, size_t size,
                       u8_t apiflags, size_t *bytes_written)
  {
    struct netvector vector;
    vector.ptr = dataptr;
    vector.len = size;
    return netconn_write_vectors_partly(conn, &vector, 1, apiflags, bytes_written);
  }
  
  /**
   * Send vectorized data atomically over a TCP netconn.
   *
   * @param conn the TCP netconn over which to send data
   * @param vectors array of vectors containing data to send
   * @param vectorcnt number of vectors in the array
   * @param apiflags combination of following flags :
   * - NETCONN_COPY: data will be copied into memory belonging to the stack
   * - NETCONN_MORE: for TCP connection, PSH flag will be set on last segment sent
   * - NETCONN_DONTBLOCK: only write the data if all data can be written at once
   * @param bytes_written pointer to a location that receives the number of written bytes
   * @return ERR_OK if data was sent, any other err_t on error
   */
  err_t
  netconn_write_vectors_partly(struct netconn *conn, struct netvector *vectors, u16_t vectorcnt,
                               u8_t apiflags, size_t *bytes_written)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
    u8_t dontblock;
    size_t size;
    int i;
  
    LWIP_ERROR("netconn_write: invalid conn",  (conn != NULL), return ERR_ARG;);
    LWIP_ERROR("netconn_write: invalid conn->type",  (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP), return ERR_VAL;);
    dontblock = netconn_is_nonblocking(conn) || (apiflags & NETCONN_DONTBLOCK);
  #if LWIP_SO_SNDTIMEO
    if (conn->send_timeout != 0) {
      dontblock = 1;
    }
  #endif /* LWIP_SO_SNDTIMEO */
    if (dontblock && !bytes_written) {
      /* This implies netconn_write() cannot be used for non-blocking send, since
         it has no way to return the number of bytes written. */
      return ERR_VAL;
    }
  
    /* sum up the total size */
    size = 0;
    for (i = 0; i < vectorcnt; i++) {
      size += vectors[i].len;
      if (size < vectors[i].len) {
        /* overflow */
        return ERR_VAL;
      }
    }
    if (size == 0) {
      return ERR_OK;
    } else if (size > SSIZE_MAX) {
      ssize_t limited;
      /* this is required by the socket layer (cannot send full size_t range) */
      if (!bytes_written) {
        return ERR_VAL;
      }
      /* limit the amount of data to send */
      limited = SSIZE_MAX;
      size = (size_t)limited;
    }
  
    API_MSG_VAR_ALLOC(msg);
    /* non-blocking write sends as much  */
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.w.vector = vectors;
    API_MSG_VAR_REF(msg).msg.w.vector_cnt = vectorcnt;
    API_MSG_VAR_REF(msg).msg.w.vector_off = 0;
    API_MSG_VAR_REF(msg).msg.w.apiflags = apiflags;
    API_MSG_VAR_REF(msg).msg.w.len = size;
    API_MSG_VAR_REF(msg).msg.w.offset = 0;
  #if LWIP_SO_SNDTIMEO
    if (conn->send_timeout != 0) {
      /* get the time we started, which is later compared to
          sys_now() + conn->send_timeout */
      API_MSG_VAR_REF(msg).msg.w.time_started = sys_now();
    } else {
      API_MSG_VAR_REF(msg).msg.w.time_started = 0;
    }
  #endif /* LWIP_SO_SNDTIMEO */
  
    /* For locking the core: this _can_ be delayed on low memory/low send buffer,
       but if it is, this is done inside api_msg.c:do_write(), so we can use the
       non-blocking version here. */
    err = netconn_apimsg(lwip_netconn_do_write, &API_MSG_VAR_REF(msg));
    if (err == ERR_OK) {
      if (bytes_written != NULL) {
        *bytes_written = API_MSG_VAR_REF(msg).msg.w.offset;
      }
      /* for blocking, check all requested bytes were written, NOTE: send_timeout is
         treated as dontblock (see dontblock assignment above) */
      if (!dontblock) {
        LWIP_ASSERT("do_write failed to write all bytes", API_MSG_VAR_REF(msg).msg.w.offset == size);
      }
    }
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  
  /**
   * @ingroup netconn_tcp
   * Close or shutdown a TCP netconn (doesn't delete it).
   *
   * @param conn the TCP netconn to close or shutdown
   * @param how fully close or only shutdown one side?
   * @return ERR_OK if the netconn was closed, any other err_t on error
   */
  static err_t
  netconn_close_shutdown(struct netconn *conn, u8_t how)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
    LWIP_UNUSED_ARG(how);
  
    LWIP_ERROR("netconn_close: invalid conn",  (conn != NULL), return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
  #if LWIP_TCP
    /* shutting down both ends is the same as closing */
    API_MSG_VAR_REF(msg).msg.sd.shut = how;
  #if LWIP_SO_SNDTIMEO || LWIP_SO_LINGER
    /* get the time we started, which is later compared to
       sys_now() + conn->send_timeout */
    API_MSG_VAR_REF(msg).msg.sd.time_started = sys_now();
  #else /* LWIP_SO_SNDTIMEO || LWIP_SO_LINGER */
    API_MSG_VAR_REF(msg).msg.sd.polls_left =
      ((LWIP_TCP_CLOSE_TIMEOUT_MS_DEFAULT + TCP_SLOW_INTERVAL - 1) / TCP_SLOW_INTERVAL) + 1;
  #endif /* LWIP_SO_SNDTIMEO || LWIP_SO_LINGER */
  #endif /* LWIP_TCP */
    err = netconn_apimsg(lwip_netconn_do_close, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  
  /**
   * @ingroup netconn_tcp
   * Close a TCP netconn (doesn't delete it).
   *
   * @param conn the TCP netconn to close
   * @return ERR_OK if the netconn was closed, any other err_t on error
   */
  err_t
  netconn_close(struct netconn *conn)
  {
    /* shutting down both ends is the same as closing */
    return netconn_close_shutdown(conn, NETCONN_SHUT_RDWR);
  }
  
  /**
   * @ingroup netconn_common
   * Get and reset pending error on a netconn
   *
   * @param conn the netconn to get the error from
   * @return and pending error or ERR_OK if no error was pending
   */
  err_t
  netconn_err(struct netconn *conn)
  {
    err_t err;
    SYS_ARCH_DECL_PROTECT(lev);
    if (conn == NULL) {
      return ERR_OK;
    }
    SYS_ARCH_PROTECT(lev);
    err = conn->pending_err;
    conn->pending_err = ERR_OK;
    SYS_ARCH_UNPROTECT(lev);
    return err;
  }
  
  /**
   * @ingroup netconn_tcp
   * Shut down one or both sides of a TCP netconn (doesn't delete it).
   *
   * @param conn the TCP netconn to shut down
   * @param shut_rx shut down the RX side (no more read possible after this)
   * @param shut_tx shut down the TX side (no more write possible after this)
   * @return ERR_OK if the netconn was closed, any other err_t on error
   */
  err_t
  netconn_shutdown(struct netconn *conn, u8_t shut_rx, u8_t shut_tx)
  {
    return netconn_close_shutdown(conn, (u8_t)((shut_rx ? NETCONN_SHUT_RD : 0) | (shut_tx ? NETCONN_SHUT_WR : 0)));
  }
  
  #if LWIP_IGMP || (LWIP_IPV6 && LWIP_IPV6_MLD)
  /**
   * @ingroup netconn_udp
   * Join multicast groups for UDP netconns.
   *
   * @param conn the UDP netconn for which to change multicast addresses
   * @param multiaddr IP address of the multicast group to join or leave
   * @param netif_addr the IP address of the network interface on which to send
   *                  the igmp message
   * @param join_or_leave flag whether to send a join- or leave-message
   * @return ERR_OK if the action was taken, any err_t on error
   */
  err_t
  netconn_join_leave_group(struct netconn *conn,
                           const ip_addr_t *multiaddr,
                           const ip_addr_t *netif_addr,
                           enum netconn_igmp join_or_leave)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    LWIP_ERROR("netconn_join_leave_group: invalid conn",  (conn != NULL), return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
  
  #if LWIP_IPV4
    /* Don't propagate NULL pointer (IP_ADDR_ANY alias) to subsequent functions */
    if (multiaddr == NULL) {
      multiaddr = IP4_ADDR_ANY;
    }
    if (netif_addr == NULL) {
      netif_addr = IP4_ADDR_ANY;
    }
  #endif /* LWIP_IPV4 */
  
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.jl.multiaddr = API_MSG_VAR_REF(multiaddr);
    API_MSG_VAR_REF(msg).msg.jl.netif_addr = API_MSG_VAR_REF(netif_addr);
    API_MSG_VAR_REF(msg).msg.jl.join_or_leave = join_or_leave;
    err = netconn_apimsg(lwip_netconn_do_join_leave_group, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  /**
   * @ingroup netconn_udp
   * Join multicast groups for UDP netconns.
   *
   * @param conn the UDP netconn for which to change multicast addresses
   * @param multiaddr IP address of the multicast group to join or leave
   * @param if_idx the index of the netif
   * @param join_or_leave flag whether to send a join- or leave-message
   * @return ERR_OK if the action was taken, any err_t on error
   */
  err_t
  netconn_join_leave_group_netif(struct netconn *conn,
                                 const ip_addr_t *multiaddr,
                                 u8_t if_idx,
                                 enum netconn_igmp join_or_leave)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
  
    LWIP_ERROR("netconn_join_leave_group: invalid conn",  (conn != NULL), return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
  
  #if LWIP_IPV4
    /* Don't propagate NULL pointer (IP_ADDR_ANY alias) to subsequent functions */
    if (multiaddr == NULL) {
      multiaddr = IP4_ADDR_ANY;
    }
    if (if_idx == NETIF_NO_INDEX) {
      return ERR_IF;
    }
  #endif /* LWIP_IPV4 */
  
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.jl.multiaddr = API_MSG_VAR_REF(multiaddr);
    API_MSG_VAR_REF(msg).msg.jl.if_idx = if_idx;
    API_MSG_VAR_REF(msg).msg.jl.join_or_leave = join_or_leave;
    err = netconn_apimsg(lwip_netconn_do_join_leave_group_netif, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    return err;
  }
  #endif /* LWIP_IGMP || (LWIP_IPV6 && LWIP_IPV6_MLD) */
  
  #if LWIP_DNS
  #if LWIP_FULL_DNS
  
  /**
   * @ingroup netconn_common
   * Execute a DNS query, only one IP address is returned
   *
   * @param name a string representation of the DNS host name to query
   * @param addr a preallocated ip_addr_t where to store the resolved IP address
   * @param dns_addrtype IP address type (IPv4 / IPv6)
   * @return ERR_OK: resolving succeeded
   *         ERR_MEM: memory error, try again later
   *         ERR_ARG: dns client not initialized or invalid hostname
   *         ERR_VAL: dns server response was invalid
   */
  #if LWIP_IPV4 && LWIP_IPV6
  err_t
  netconn_gethostbyname_addrtype(const char *name, ip_addr_t *addr, u8_t dns_addrtype)
  #else
  err_t
  netconn_gethostbyname(const char *name, ip_addr_t *addr)
  #endif
  {
    API_VAR_DECLARE(struct dns_api_msg, msg);
  #if !LWIP_MPU_COMPATIBLE
    sys_sem_t sem;
  #endif /* LWIP_MPU_COMPATIBLE */
    err_t err;
    err_t cberr;
  
    LWIP_ERROR("netconn_gethostbyname: invalid name", (name != NULL), return ERR_ARG;);
    LWIP_ERROR("netconn_gethostbyname: invalid addr", (addr != NULL), return ERR_ARG;);
  #if LWIP_MPU_COMPATIBLE
    if (strlen(name) >= DNS_MAX_NAME_LENGTH) {
      return ERR_ARG;
    }
  #endif
  
  #ifdef LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE
  #if LWIP_IPV4 && LWIP_IPV6
    if (LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE(name, addr, dns_addrtype, &err)) {
  #else
    if (LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE(name, addr, NETCONN_DNS_DEFAULT, &err)) {
  #endif /* LWIP_IPV4 && LWIP_IPV6 */
      return err;
    }
  #endif /* LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE */
  
    API_VAR_ALLOC(struct dns_api_msg, MEMP_DNS_API_MSG, msg, ERR_MEM);
  #if LWIP_MPU_COMPATIBLE
    strncpy(API_VAR_REF(msg).name, name, DNS_MAX_NAME_LENGTH - 1);
    API_VAR_REF(msg).name[DNS_MAX_NAME_LENGTH - 1] = 0;
  #else /* LWIP_MPU_COMPATIBLE */
    msg.err = &err;
    msg.sem = &sem;
    API_VAR_REF(msg).addr = API_VAR_REF(addr);
    API_VAR_REF(msg).name = name;
  #endif /* LWIP_MPU_COMPATIBLE */
  #if LWIP_IPV4 && LWIP_IPV6
    API_VAR_REF(msg).dns_addrtype = dns_addrtype;
  #endif /* LWIP_IPV4 && LWIP_IPV6 */
  #if LWIP_NETCONN_SEM_PER_THREAD
    API_VAR_REF(msg).sem = LWIP_NETCONN_THREAD_SEM_GET();
  #else /* LWIP_NETCONN_SEM_PER_THREAD*/
    err = sys_sem_new(API_EXPR_REF(API_VAR_REF(msg).sem), 0);
    if (err != ERR_OK) {
      API_VAR_FREE(MEMP_DNS_API_MSG, msg);
      return err;
    }
  #endif /* LWIP_NETCONN_SEM_PER_THREAD */
  
    cberr = tcpip_send_msg_wait_sem(lwip_netconn_do_gethostbyname, &API_VAR_REF(msg), API_EXPR_REF(API_VAR_REF(msg).sem));
  #if !LWIP_NETCONN_SEM_PER_THREAD
    sys_sem_free(API_EXPR_REF(API_VAR_REF(msg).sem));
  #endif /* !LWIP_NETCONN_SEM_PER_THREAD */
    if (cberr != ERR_OK) {
      API_VAR_FREE(MEMP_DNS_API_MSG, msg);
      return cberr;
    }
  
  #if LWIP_MPU_COMPATIBLE
    *addr = msg->addr;
    err = msg->err;
  #endif /* LWIP_MPU_COMPATIBLE */
  
    API_VAR_FREE(MEMP_DNS_API_MSG, msg);
    return err;
  }
  
  #endif /* LWIP_FULL_DNS */
  #endif /* LWIP_DNS*/
  
  #if LWIP_NETCONN_SEM_PER_THREAD
  void
  netconn_thread_init(void)
  {
    sys_sem_t *sem = LWIP_NETCONN_THREAD_SEM_GET();
    if ((sem == NULL) || !sys_sem_valid(sem)) {
      /* call alloc only once */
      LWIP_NETCONN_THREAD_SEM_ALLOC();
      LWIP_ASSERT("LWIP_NETCONN_THREAD_SEM_ALLOC() failed", sys_sem_valid(LWIP_NETCONN_THREAD_SEM_GET()));
    }
  }
  
  void
  netconn_thread_cleanup(void)
  {
    sys_sem_t *sem = LWIP_NETCONN_THREAD_SEM_GET();
    if ((sem != NULL) && sys_sem_valid(sem)) {
      /* call free only once */
      LWIP_NETCONN_THREAD_SEM_FREE();
    }
  }
  #endif /* LWIP_NETCONN_SEM_PER_THREAD */
  
  #endif /* LWIP_NETCONN */
  