src/api/api_lib.c

/**
 * @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 */

  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_TCP
#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_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_MBOX_EMPTY) {
      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_MBOX_EMPTY) {
      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
/**
 * @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_DNS*/

#if LWIP_NETCONN_SEM_PER_THREAD
void
netconn_thread_init(void)
{
  sys_sem_t *sem = LWIP_NETCONN_THREAD_SEM_GET();
  if (!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 (sys_sem_valid(sem)) {
    /* call free only once */
    LWIP_NETCONN_THREAD_SEM_FREE();
  }
}
#endif /* LWIP_NETCONN_SEM_PER_THREAD */

#endif /* LWIP_NETCONN */