text: /**
   * @file
   * Sequential API External module
   *
   */
   
  /*
   * 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/tcpip.h"
  #include "lwip/memp.h"
  
  #include "lwip/ip.h"
  #include "lwip/raw.h"
  #include "lwip/udp.h"
  #include "lwip/tcp.h"
  
  #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)
  #define API_MSG_VAR_ALLOC_DONTFAIL(name)  API_VAR_ALLOC_DONTFAIL(struct api_msg, MEMP_API_MSG, name)
  #define API_MSG_VAR_FREE(name)            API_VAR_FREE(MEMP_API_MSG, name)
  
  /**
   * 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);
  
    conn = netconn_alloc(t, callback);
    if (conn != NULL) {
      err_t err;
      API_MSG_VAR_ALLOC_DONTFAIL(msg);
      API_MSG_VAR_REF(msg).msg.msg.n.proto = proto;
      API_MSG_VAR_REF(msg).msg.conn = conn;
      TCPIP_APIMSG(&API_MSG_VAR_REF(msg), lwip_netconn_do_newconn, err);
      API_MSG_VAR_FREE(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);
        return NULL;
      }
    }
    return conn;
  }
  
  /**
   * 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)
  {
    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).function = lwip_netconn_do_delconn;
    API_MSG_VAR_REF(msg).msg.conn = conn;
    tcpip_apimsg(&API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    netconn_free(conn);
  
    /* don't care for return value of lwip_netconn_do_delconn since it only calls void functions */
  
    return ERR_OK;
  }
  
  /**
   * 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).msg.conn = conn;
    API_MSG_VAR_REF(msg).msg.msg.ad.local = local;
  #if LWIP_MPU_COMPATIBLE
    TCPIP_APIMSG(msg, lwip_netconn_do_getaddr, err);
    *addr = *ipX_2_ip(&(msg->msg.msg.ad.ipaddr));
    *port = msg->msg.msg.ad.port;
  #else /* LWIP_MPU_COMPATIBLE */
    msg.msg.msg.ad.ipaddr = ip_2_ipX(addr);
    msg.msg.msg.ad.port = port;
    TCPIP_APIMSG(&msg, lwip_netconn_do_getaddr, err);
  #endif /* LWIP_MPU_COMPATIBLE */
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  }
  
  /**
   * 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 IP_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, 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;);
  
    API_MSG_VAR_ALLOC(msg);
  #if LWIP_MPU_COMPATIBLE
    if (addr == NULL) {
      addr = IP_ADDR_ANY;
    }
  #endif /* LWIP_MPU_COMPATIBLE */
    API_MSG_VAR_REF(msg).msg.conn = conn;
    API_MSG_VAR_REF(msg).msg.msg.bc.ipaddr = API_MSG_VAR_REF(addr);
    API_MSG_VAR_REF(msg).msg.msg.bc.port = port;
    TCPIP_APIMSG(&API_MSG_VAR_REF(msg), lwip_netconn_do_bind, err);
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  }
  
  /**
   * 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, 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;);
  
    API_MSG_VAR_ALLOC(msg);
  #if LWIP_MPU_COMPATIBLE
    if (addr == NULL) {
      addr = IP_ADDR_ANY;
    }
  #endif /* LWIP_MPU_COMPATIBLE */
    API_MSG_VAR_REF(msg).msg.conn = conn;
    API_MSG_VAR_REF(msg).msg.msg.bc.ipaddr = API_MSG_VAR_REF(addr);
    API_MSG_VAR_REF(msg).msg.msg.bc.port = port;
  #if LWIP_TCP
  #if (LWIP_UDP || LWIP_RAW)
    if (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP)
  #endif /* (LWIP_UDP || LWIP_RAW) */
    {
      /* The TCP version waits for the connect to succeed,
         so always needs to use message passing. */
      API_MSG_VAR_REF(msg).function = lwip_netconn_do_connect;
      err = tcpip_apimsg(&API_MSG_VAR_REF(msg));
    }
  #endif /* LWIP_TCP */
  #if (LWIP_UDP || LWIP_RAW) && LWIP_TCP
    else
  #endif /* (LWIP_UDP || LWIP_RAW) && LWIP_TCP */
  #if (LWIP_UDP || LWIP_RAW)
    {
      /* UDP and RAW only set flags, so we can use core-locking. */
      TCPIP_APIMSG(&API_MSG_VAR_REF(msg), lwip_netconn_do_connect, err);
    }
  #endif /* (LWIP_UDP || LWIP_RAW) */
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  }
  
  /**
   * Disconnect a netconn from its current peer (only valid for UDP netconns).
   *
   * @param conn the netconn to disconnect
   * @return TODO: return value is not set here...
   */
  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).msg.conn = conn;
    TCPIP_APIMSG(&API_MSG_VAR_REF(msg), lwip_netconn_do_disconnect, err);
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  }
  
  /**
   * 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).msg.conn = conn;
  #if TCP_LISTEN_BACKLOG
    API_MSG_VAR_REF(msg).msg.msg.lb.backlog = backlog;
  #endif /* TCP_LISTEN_BACKLOG */
    TCPIP_APIMSG(&API_MSG_VAR_REF(msg), lwip_netconn_do_listen, err);
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  #else /* LWIP_TCP */
    LWIP_UNUSED_ARG(conn);
    LWIP_UNUSED_ARG(backlog);
    return ERR_ARG;
  #endif /* LWIP_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
    struct netconn *newconn;
    err_t err;
  #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;);
    LWIP_ERROR("netconn_accept: invalid acceptmbox", sys_mbox_valid(&conn->acceptmbox),   return ERR_ARG;);
  
    err = conn->last_err;
    if (ERR_IS_FATAL(err)) {
      /* don't recv on fatal errors: this might block the application task
         waiting on acceptmbox forever! */
      return err;
    }
  
  #if LWIP_SO_RCVTIMEO
    if (sys_arch_mbox_fetch(&conn->acceptmbox, (void **)&newconn, conn->recv_timeout) == SYS_ARCH_TIMEOUT) {
      NETCONN_SET_SAFE_ERR(conn, ERR_TIMEOUT);
      return ERR_TIMEOUT;
    }
  #else
    sys_arch_mbox_fetch(&conn->acceptmbox, (void **)&newconn, 0);
  #endif /* LWIP_SO_RCVTIMEO*/
    /* Register event with callback */
    API_EVENT(conn, NETCONN_EVT_RCVMINUS, 0);
  
    if (newconn == NULL) {
      /* connection has been aborted */
      NETCONN_SET_SAFE_ERR(conn, ERR_ABRT);
      return ERR_ABRT;
    }
  #if TCP_LISTEN_BACKLOG
    /* Let the stack know that we have accepted the connection. */
    API_MSG_VAR_ALLOC_DONTFAIL(msg);
    API_MSG_VAR_REF(msg).msg.conn = conn;
    /* don't care for the return value of lwip_netconn_do_recv */
    TCPIP_APIMSG_NOERR(&API_MSG_VAR_REF(msg), lwip_netconn_do_recv);
    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 */
  }
  
  /**
   * Receive data: actual implementation that doesn't care whether pbuf or netbuf
   * is received
   *
   * @param conn the netconn from which to receive data
   * @param new_buf pointer where a new pbuf/netbuf is stored when received data
   * @return ERR_OK if data has been received, an error code otherwise (timeout,
   *                memory error or another error)
   */
  static err_t
  netconn_recv_data(struct netconn *conn, void **new_buf)
  {
    void *buf = NULL;
    u16_t len;
    err_t err;
  #if LWIP_TCP
    API_MSG_VAR_DECLARE(msg);
  #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;);
    LWIP_ERROR("netconn_accept: invalid recvmbox", sys_mbox_valid(&conn->recvmbox), return ERR_CONN;);
  
    err = conn->last_err;
    if (ERR_IS_FATAL(err)) {
      /* don't recv on fatal errors: this might block the application task
         waiting on recvmbox forever! */
      /* @todo: this does not allow us to fetch data that has been put into recvmbox
         before the fatal error occurred - is that a problem? */
      return err;
    }
  
  #if LWIP_SO_RCVTIMEO
    if (sys_arch_mbox_fetch(&conn->recvmbox, &buf, conn->recv_timeout) == SYS_ARCH_TIMEOUT) {
      NETCONN_SET_SAFE_ERR(conn, ERR_TIMEOUT);
      return ERR_TIMEOUT;
    }
  #else
    sys_arch_mbox_fetch(&conn->recvmbox, &buf, 0);
  #endif /* LWIP_SO_RCVTIMEO*/
  
  #if LWIP_TCP
  #if (LWIP_UDP || LWIP_RAW)
    if (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP)
  #endif /* (LWIP_UDP || LWIP_RAW) */
    {
      if (!netconn_get_noautorecved(conn) || (buf == NULL)) {
        /* Let the stack know that we have taken the data. */
        /* TODO: Speedup: Don't block and wait for the answer here
           (to prevent multiple thread-switches). */
        API_MSG_VAR_ALLOC_DONTFAIL(msg);
        API_MSG_VAR_REF(msg).msg.conn = conn;
        if (buf != NULL) {
          API_MSG_VAR_REF(msg).msg.msg.r.len = ((struct pbuf *)buf)->tot_len;
        } else {
          API_MSG_VAR_REF(msg).msg.msg.r.len = 1;
        }
        /* don't care for the return value of lwip_netconn_do_recv */
        TCPIP_APIMSG_NOERR(&API_MSG_VAR_REF(msg), lwip_netconn_do_recv);
        API_MSG_VAR_FREE(msg);
      }
  
      /* If we are closed, we indicate that we no longer wish to use the socket */
      if (buf == NULL) {
        API_EVENT(conn, NETCONN_EVT_RCVMINUS, 0);
        /* Avoid to lose any previous error code */
        NETCONN_SET_SAFE_ERR(conn, ERR_CLSD);
        return ERR_CLSD;
      }
      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;
  }
  
  /**
   * 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)
   *         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: invalid conn", (conn != NULL) &&
               NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP, return ERR_ARG;);
  
    return netconn_recv_data(conn, (void **)new_buf);
  }
  
  /**
   * 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;);
    LWIP_ERROR("netconn_accept: invalid recvmbox", sys_mbox_valid(&conn->recvmbox), return ERR_CONN;);
  
  #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) {
        NETCONN_SET_SAFE_ERR(conn, ERR_MEM);
        return ERR_MEM;
      }
  
      err = netconn_recv_data(conn, (void **)&p);
      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;
      ipX_addr_set_any(LWIP_IPV6, &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);
  #endif /* (LWIP_UDP || LWIP_RAW) */
    }
  }
  
  /**
   * TCP: update the receive window: by calling this, the application
   * tells the stack that it has processed data and is able to accept
   * new data.
   * ATTENTION: use with care, this is mainly used for sockets!
   * Can only be used when calling netconn_set_noautorecved(conn, 1) before.
   *
   * @param conn the netconn for which to update the receive window
   * @param length amount of data processed (ATTENTION: this must be accurate!)
   */
  void
  netconn_recved(struct netconn *conn, u32_t length)
  {
  #if LWIP_TCP
    if ((conn != NULL) && (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP) &&
        (netconn_get_noautorecved(conn))) {
      API_MSG_VAR_DECLARE(msg);
      /* Let the stack know that we have taken the data. */
      /* TODO: Speedup: Don't block and wait for the answer here
         (to prevent multiple thread-switches). */
      API_MSG_VAR_ALLOC_DONTFAIL(msg);
      API_MSG_VAR_REF(msg).msg.conn = conn;
      API_MSG_VAR_REF(msg).msg.msg.r.len = length;
      /* don't care for the return value of lwip_netconn_do_recv */
      TCPIP_APIMSG_NOERR(&API_MSG_VAR_REF(msg), lwip_netconn_do_recv);
      API_MSG_VAR_FREE(msg);
    }
  #else /* LWIP_TCP */
    LWIP_UNUSED_ARG(conn);
    LWIP_UNUSED_ARG(length);
  #endif /* LWIP_TCP */
  }
  
  /**
   * 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, ip_addr_t *addr, u16_t port)
  {
    if (buf != NULL) {
      ipX_addr_set_ipaddr(PCB_ISIPV6(conn->pcb.ip), &buf->addr, addr);
      buf->port = port;
      return netconn_send(conn, buf);
    }
    return ERR_VAL;
  }
  
  /**
   * 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).msg.conn = conn;
    API_MSG_VAR_REF(msg).msg.msg.b = buf;
    TCPIP_APIMSG(&API_MSG_VAR_REF(msg), lwip_netconn_do_send, err);
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  }
  
  /**
   * 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)
  {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
    u8_t dontblock;
  
    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;);
    if (size == 0) {
      return ERR_OK;
    }
    dontblock = netconn_is_nonblocking(conn) || (apiflags & NETCONN_DONTBLOCK);
    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;
    }
  
    API_MSG_VAR_ALLOC(msg);
    /* non-blocking write sends as much  */
    API_MSG_VAR_REF(msg).msg.conn = conn;
    API_MSG_VAR_REF(msg).msg.msg.w.dataptr = dataptr;
    API_MSG_VAR_REF(msg).msg.msg.w.apiflags = apiflags;
    API_MSG_VAR_REF(msg).msg.msg.w.len = size;
  #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.msg.w.time_started = sys_now();
    } else {
      API_MSG_VAR_REF(msg).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. */
    TCPIP_APIMSG(&API_MSG_VAR_REF(msg), lwip_netconn_do_write, err);
    if ((err == ERR_OK) && (bytes_written != NULL)) {
      if (dontblock
  #if LWIP_SO_SNDTIMEO
          || (conn->send_timeout != 0)
  #endif /* LWIP_SO_SNDTIMEO */
         ) {
        /* nonblocking write: maybe the data has been sent partly */
        *bytes_written = API_MSG_VAR_REF(msg).msg.msg.w.len;
      } else {
        /* blocking call succeeded: all data has been sent if it */
        *bytes_written = size;
      }
    }
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  }
  
  /**
   * 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_ERROR("netconn_close: invalid conn",  (conn != NULL), return ERR_ARG;);
  
    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).function = lwip_netconn_do_close;
    API_MSG_VAR_REF(msg).msg.conn = conn;
    /* shutting down both ends is the same as closing */
    API_MSG_VAR_REF(msg).msg.msg.sd.shut = how;
    /* because of the LWIP_TCPIP_CORE_LOCKING implementation of lwip_netconn_do_close,
       don't use TCPIP_APIMSG here */
    err = tcpip_apimsg(&API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  }
  
  /**
   * 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);
  }
  
  /**
   * Shut down one or both sides of a TCP netconn (doesn't delete it).
   *
   * @param conn the TCP netconn to shut down
   * @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, (shut_rx ? NETCONN_SHUT_RD : 0) | (shut_tx ? NETCONN_SHUT_WR : 0));
  }
  
  #if LWIP_IGMP || (LWIP_IPV6 && LWIP_IPV6_MLD)
  /**
   * 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,
                           ip_addr_t *multiaddr,
                           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_MPU_COMPATIBLE
    if (multiaddr == NULL) {
      multiaddr = IP_ADDR_ANY;
    }
    if (netif_addr == NULL) {
      netif_addr = IP_ADDR_ANY;
    }
  #endif /* LWIP_MPU_COMPATIBLE */
    API_MSG_VAR_REF(msg).msg.conn = conn;
    API_MSG_VAR_REF(msg).msg.msg.jl.multiaddr = API_MSG_VAR_REF(ip_2_ipX(multiaddr));
    API_MSG_VAR_REF(msg).msg.msg.jl.netif_addr = API_MSG_VAR_REF(ip_2_ipX(netif_addr));
    API_MSG_VAR_REF(msg).msg.msg.jl.join_or_leave = join_or_leave;
    TCPIP_APIMSG(&API_MSG_VAR_REF(msg), lwip_netconn_do_join_leave_group, err);
    API_MSG_VAR_FREE(msg);
  
    NETCONN_SET_SAFE_ERR(conn, err);
    return err;
  }
  #endif /* LWIP_IGMP || (LWIP_IPV6 && LWIP_IPV6_MLD) */
  
  #if LWIP_DNS
  /**
   * 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
   * @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
   */
  err_t
  netconn_gethostbyname(const char *name, ip_addr_t *addr)
  {
    API_VAR_DECLARE(struct dns_api_msg, msg);
  #if !LWIP_MPU_COMPATIBLE
    sys_sem_t sem;
  #endif /* LWIP_MPU_COMPATIBLE */
    err_t err;
  
    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
  
    API_VAR_ALLOC(struct dns_api_msg, MEMP_DNS_API_MSG, msg);
  #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 */
    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;
    }
  
    tcpip_callback(lwip_netconn_do_gethostbyname, &API_VAR_REF(msg));
    sys_sem_wait(API_EXPR_REF(API_VAR_REF(msg).sem));
    sys_sem_free(API_EXPR_REF(API_VAR_REF(msg).sem));
  
  #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 (sem == SYS_SEM_NULL) {
      /* call alloc only once */
      LWIP_NETCONN_THREAD_SEM_ALLOC();
      LWIP_ASSERT("LWIP_NETCONN_THREAD_SEM_ALLOC() failed", LWIP_NETCONN_THREAD_SEM_GET() != SYS_SEM_NULL);
    }
  }
  
  void netconn_thread_cleanup(void)
  {
    sys_sem_t *sem = LWIP_NETCONN_THREAD_SEM_GET();
    if (sem == SYS_SEM_NULL) {
      /* call free only once */
      LWIP_NETCONN_THREAD_SEM_FREE();
    }
  }
  #endif /* LWIP_NETCONN_SEM_PER_THREAD */
  
  #endif /* LWIP_NETCONN */
  