Diff: api/api_msg.c

Revision:

0:51ac1d130fd4

diff -r 000000000000 -r 51ac1d130fd4 api/api_msg.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/api/api_msg.c	Fri Jun 22 09:25:39 2012 +0000
@@ -0,0 +1,1535 @@
+/**
+ * @file
+ * Sequential API Internal 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>
+ *
+ */
+
+#include "lwip/opt.h"
+
+#if LWIP_NETCONN /* don't build if not configured for use in lwipopts.h */
+
+#include "lwip/api_msg.h"
+
+#include "lwip/ip.h"
+#include "lwip/udp.h"
+#include "lwip/tcp.h"
+#include "lwip/raw.h"
+
+#include "lwip/memp.h"
+#include "lwip/tcpip.h"
+#include "lwip/igmp.h"
+#include "lwip/dns.h"
+
+#include <string.h>
+
+#define SET_NONBLOCKING_CONNECT(conn, val)  do { if(val) { \
+  (conn)->flags |= NETCONN_FLAG_IN_NONBLOCKING_CONNECT; \
+} else { \
+  (conn)->flags &= ~ NETCONN_FLAG_IN_NONBLOCKING_CONNECT; }} while(0)
+#define IN_NONBLOCKING_CONNECT(conn) (((conn)->flags & NETCONN_FLAG_IN_NONBLOCKING_CONNECT) != 0)
+
+/* forward declarations */
+#if LWIP_TCP
+static err_t do_writemore(struct netconn *conn);
+static void do_close_internal(struct netconn *conn);
+#endif
+
+#if LWIP_RAW
+/**
+ * Receive callback function for RAW netconns.
+ * Doesn't 'eat' the packet, only references it and sends it to
+ * conn->recvmbox
+ *
+ * @see raw.h (struct raw_pcb.recv) for parameters and return value
+ */
+static u8_t
+recv_raw(void *arg, struct raw_pcb *pcb, struct pbuf *p,
+    ip_addr_t *addr)
+{
+  struct pbuf *q;
+  struct netbuf *buf;
+  struct netconn *conn;
+
+  LWIP_UNUSED_ARG(addr);
+  conn = (struct netconn *)arg;
+
+  if ((conn != NULL) && sys_mbox_valid(&conn->recvmbox)) {
+#if LWIP_SO_RCVBUF
+    int recv_avail;
+    SYS_ARCH_GET(conn->recv_avail, recv_avail);
+    if ((recv_avail + (int)(p->tot_len)) > conn->recv_bufsize) {
+      return 0;
+    }
+#endif /* LWIP_SO_RCVBUF */
+    /* copy the whole packet into new pbufs */
+    q = pbuf_alloc(PBUF_RAW, p->tot_len, PBUF_RAM);
+    if(q != NULL) {
+      if (pbuf_copy(q, p) != ERR_OK) {
+        pbuf_free(q);
+        q = NULL;
+      }
+    }
+
+    if (q != NULL) {
+      u16_t len;
+      buf = (struct netbuf *)memp_malloc(MEMP_NETBUF);
+      if (buf == NULL) {
+        pbuf_free(q);
+        return 0;
+      }
+
+      buf->p = q;
+      buf->ptr = q;
+      ip_addr_copy(buf->addr, *ip_current_src_addr());
+      buf->port = pcb->protocol;
+
+      len = q->tot_len;
+      if (sys_mbox_trypost(&conn->recvmbox, buf) != ERR_OK) {
+        netbuf_delete(buf);
+        return 0;
+      } else {
+#if LWIP_SO_RCVBUF
+        SYS_ARCH_INC(conn->recv_avail, len);
+#endif /* LWIP_SO_RCVBUF */
+        /* Register event with callback */
+        API_EVENT(conn, NETCONN_EVT_RCVPLUS, len);
+      }
+    }
+  }
+
+  return 0; /* do not eat the packet */
+}
+#endif /* LWIP_RAW*/
+
+#if LWIP_UDP
+/**
+ * Receive callback function for UDP netconns.
+ * Posts the packet to conn->recvmbox or deletes it on memory error.
+ *
+ * @see udp.h (struct udp_pcb.recv) for parameters
+ */
+static void
+recv_udp(void *arg, struct udp_pcb *pcb, struct pbuf *p,
+   ip_addr_t *addr, u16_t port)
+{
+  struct netbuf *buf;
+  struct netconn *conn;
+  u16_t len;
+#if LWIP_SO_RCVBUF
+  int recv_avail;
+#endif /* LWIP_SO_RCVBUF */
+
+  LWIP_UNUSED_ARG(pcb); /* only used for asserts... */
+  LWIP_ASSERT("recv_udp must have a pcb argument", pcb != NULL);
+  LWIP_ASSERT("recv_udp must have an argument", arg != NULL);
+  conn = (struct netconn *)arg;
+  LWIP_ASSERT("recv_udp: recv for wrong pcb!", conn->pcb.udp == pcb);
+
+#if LWIP_SO_RCVBUF
+  SYS_ARCH_GET(conn->recv_avail, recv_avail);
+  if ((conn == NULL) || !sys_mbox_valid(&conn->recvmbox) ||
+      ((recv_avail + (int)(p->tot_len)) > conn->recv_bufsize)) {
+#else  /* LWIP_SO_RCVBUF */
+  if ((conn == NULL) || !sys_mbox_valid(&conn->recvmbox)) {
+#endif /* LWIP_SO_RCVBUF */
+    pbuf_free(p);
+    return;
+  }
+
+  buf = (struct netbuf *)memp_malloc(MEMP_NETBUF);
+  if (buf == NULL) {
+    pbuf_free(p);
+    return;
+  } else {
+    buf->p = p;
+    buf->ptr = p;
+    ip_addr_set(&buf->addr, addr);
+    buf->port = port;
+#if LWIP_NETBUF_RECVINFO
+    {
+      const struct ip_hdr* iphdr = ip_current_header();
+      /* get the UDP header - always in the first pbuf, ensured by udp_input */
+      const struct udp_hdr* udphdr = (void*)(((char*)iphdr) + IPH_LEN(iphdr));
+#if LWIP_CHECKSUM_ON_COPY
+      buf->flags = NETBUF_FLAG_DESTADDR;
+#endif /* LWIP_CHECKSUM_ON_COPY */
+      ip_addr_set(&buf->toaddr, ip_current_dest_addr());
+      buf->toport_chksum = udphdr->dest;
+    }
+#endif /* LWIP_NETBUF_RECVINFO */
+  }
+
+  len = p->tot_len;
+  if (sys_mbox_trypost(&conn->recvmbox, buf) != ERR_OK) {
+    netbuf_delete(buf);
+    return;
+  } else {
+#if LWIP_SO_RCVBUF
+    SYS_ARCH_INC(conn->recv_avail, len);
+#endif /* LWIP_SO_RCVBUF */
+    /* Register event with callback */
+    API_EVENT(conn, NETCONN_EVT_RCVPLUS, len);
+  }
+}
+#endif /* LWIP_UDP */
+
+#if LWIP_TCP
+/**
+ * Receive callback function for TCP netconns.
+ * Posts the packet to conn->recvmbox, but doesn't delete it on errors.
+ *
+ * @see tcp.h (struct tcp_pcb.recv) for parameters and return value
+ */
+static err_t
+recv_tcp(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
+{
+  struct netconn *conn;
+  u16_t len;
+
+  LWIP_UNUSED_ARG(pcb);
+  LWIP_ASSERT("recv_tcp must have a pcb argument", pcb != NULL);
+  LWIP_ASSERT("recv_tcp must have an argument", arg != NULL);
+  conn = (struct netconn *)arg;
+  LWIP_ASSERT("recv_tcp: recv for wrong pcb!", conn->pcb.tcp == pcb);
+
+  if (conn == NULL) {
+    return ERR_VAL;
+  }
+  if (!sys_mbox_valid(&conn->recvmbox)) {
+    /* recvmbox already deleted */
+    if (p != NULL) {
+      tcp_recved(pcb, p->tot_len);
+      pbuf_free(p);
+    }
+    return ERR_OK;
+  }
+  /* Unlike for UDP or RAW pcbs, don't check for available space
+     using recv_avail since that could break the connection
+     (data is already ACKed) */
+
+  /* don't overwrite fatal errors! */
+  NETCONN_SET_SAFE_ERR(conn, err);
+
+  if (p != NULL) {
+    len = p->tot_len;
+  } else {
+    len = 0;
+  }
+
+  if (sys_mbox_trypost(&conn->recvmbox, p) != ERR_OK) {
+    /* don't deallocate p: it is presented to us later again from tcp_fasttmr! */
+    return ERR_MEM;
+  } else {
+#if LWIP_SO_RCVBUF
+    SYS_ARCH_INC(conn->recv_avail, len);
+#endif /* LWIP_SO_RCVBUF */
+    /* Register event with callback */
+    API_EVENT(conn, NETCONN_EVT_RCVPLUS, len);
+  }
+
+  return ERR_OK;
+}
+
+/**
+ * Poll callback function for TCP netconns.
+ * Wakes up an application thread that waits for a connection to close
+ * or data to be sent. The application thread then takes the
+ * appropriate action to go on.
+ *
+ * Signals the conn->sem.
+ * netconn_close waits for conn->sem if closing failed.
+ *
+ * @see tcp.h (struct tcp_pcb.poll) for parameters and return value
+ */
+static err_t
+poll_tcp(void *arg, struct tcp_pcb *pcb)
+{
+  struct netconn *conn = (struct netconn *)arg;
+
+  LWIP_UNUSED_ARG(pcb);
+  LWIP_ASSERT("conn != NULL", (conn != NULL));
+
+  if (conn->state == NETCONN_WRITE) {
+    do_writemore(conn);
+  } else if (conn->state == NETCONN_CLOSE) {
+    do_close_internal(conn);
+  }
+  /* @todo: implement connect timeout here? */
+
+  /* Did a nonblocking write fail before? Then check available write-space. */
+  if (conn->flags & NETCONN_FLAG_CHECK_WRITESPACE) {
+    /* If the queued byte- or pbuf-count drops below the configured low-water limit,
+       let select mark this pcb as writable again. */
+    if ((conn->pcb.tcp != NULL) && (tcp_sndbuf(conn->pcb.tcp) > TCP_SNDLOWAT) &&
+      (tcp_sndqueuelen(conn->pcb.tcp) < TCP_SNDQUEUELOWAT)) {
+      conn->flags &= ~NETCONN_FLAG_CHECK_WRITESPACE;
+      API_EVENT(conn, NETCONN_EVT_SENDPLUS, 0);
+    }
+  }
+
+  return ERR_OK;
+}
+
+/**
+ * Sent callback function for TCP netconns.
+ * Signals the conn->sem and calls API_EVENT.
+ * netconn_write waits for conn->sem if send buffer is low.
+ *
+ * @see tcp.h (struct tcp_pcb.sent) for parameters and return value
+ */
+static err_t
+sent_tcp(void *arg, struct tcp_pcb *pcb, u16_t len)
+{
+  struct netconn *conn = (struct netconn *)arg;
+
+  LWIP_UNUSED_ARG(pcb);
+  LWIP_ASSERT("conn != NULL", (conn != NULL));
+
+  if (conn->state == NETCONN_WRITE) {
+    do_writemore(conn);
+  } else if (conn->state == NETCONN_CLOSE) {
+    do_close_internal(conn);
+  }
+
+  if (conn) {
+    /* If the queued byte- or pbuf-count drops below the configured low-water limit,
+       let select mark this pcb as writable again. */
+    if ((conn->pcb.tcp != NULL) && (tcp_sndbuf(conn->pcb.tcp) > TCP_SNDLOWAT) &&
+      (tcp_sndqueuelen(conn->pcb.tcp) < TCP_SNDQUEUELOWAT)) {
+      conn->flags &= ~NETCONN_FLAG_CHECK_WRITESPACE;
+      API_EVENT(conn, NETCONN_EVT_SENDPLUS, len);
+    }
+  }
+  
+  return ERR_OK;
+}
+
+/**
+ * Error callback function for TCP netconns.
+ * Signals conn->sem, posts to all conn mboxes and calls API_EVENT.
+ * The application thread has then to decide what to do.
+ *
+ * @see tcp.h (struct tcp_pcb.err) for parameters
+ */
+static void
+err_tcp(void *arg, err_t err)
+{
+  struct netconn *conn;
+  enum netconn_state old_state;
+  SYS_ARCH_DECL_PROTECT(lev);
+
+  conn = (struct netconn *)arg;
+  LWIP_ASSERT("conn != NULL", (conn != NULL));
+
+  conn->pcb.tcp = NULL;
+
+  /* no check since this is always fatal! */
+  SYS_ARCH_PROTECT(lev);
+  conn->last_err = err;
+  SYS_ARCH_UNPROTECT(lev);
+
+  /* reset conn->state now before waking up other threads */
+  old_state = conn->state;
+  conn->state = NETCONN_NONE;
+
+  /* Notify the user layer about a connection error. Used to signal
+     select. */
+  API_EVENT(conn, NETCONN_EVT_ERROR, 0);
+  /* Try to release selects pending on 'read' or 'write', too.
+     They will get an error if they actually try to read or write. */
+  API_EVENT(conn, NETCONN_EVT_RCVPLUS, 0);
+  API_EVENT(conn, NETCONN_EVT_SENDPLUS, 0);
+
+  /* pass NULL-message to recvmbox to wake up pending recv */
+  if (sys_mbox_valid(&conn->recvmbox)) {
+    /* use trypost to prevent deadlock */
+    sys_mbox_trypost(&conn->recvmbox, NULL);
+  }
+  /* pass NULL-message to acceptmbox to wake up pending accept */
+  if (sys_mbox_valid(&conn->acceptmbox)) {
+    /* use trypost to preven deadlock */
+    sys_mbox_trypost(&conn->acceptmbox, NULL);
+  }
+
+  if ((old_state == NETCONN_WRITE) || (old_state == NETCONN_CLOSE) ||
+      (old_state == NETCONN_CONNECT)) {
+    /* calling do_writemore/do_close_internal is not necessary
+       since the pcb has already been deleted! */
+    int was_nonblocking_connect = IN_NONBLOCKING_CONNECT(conn);
+    SET_NONBLOCKING_CONNECT(conn, 0);
+
+    if (!was_nonblocking_connect) {
+      /* set error return code */
+      LWIP_ASSERT("conn->current_msg != NULL", conn->current_msg != NULL);
+      conn->current_msg->err = err;
+      conn->current_msg = NULL;
+      /* wake up the waiting task */
+      sys_sem_signal(&conn->op_completed);
+    }
+  } else {
+    LWIP_ASSERT("conn->current_msg == NULL", conn->current_msg == NULL);
+  }
+}
+
+/**
+ * Setup a tcp_pcb with the correct callback function pointers
+ * and their arguments.
+ *
+ * @param conn the TCP netconn to setup
+ */
+static void
+setup_tcp(struct netconn *conn)
+{
+  struct tcp_pcb *pcb;
+
+  pcb = conn->pcb.tcp;
+  tcp_arg(pcb, conn);
+  tcp_recv(pcb, recv_tcp);
+  tcp_sent(pcb, sent_tcp);
+  tcp_poll(pcb, poll_tcp, 4);
+  tcp_err(pcb, err_tcp);
+}
+
+/**
+ * Accept callback function for TCP netconns.
+ * Allocates a new netconn and posts that to conn->acceptmbox.
+ *
+ * @see tcp.h (struct tcp_pcb_listen.accept) for parameters and return value
+ */
+static err_t
+accept_function(void *arg, struct tcp_pcb *newpcb, err_t err)
+{
+  struct netconn *newconn;
+  struct netconn *conn = (struct netconn *)arg;
+
+  LWIP_DEBUGF(API_MSG_DEBUG, ("accept_function: newpcb->tate: %s\n", tcp_debug_state_str(newpcb->state)));
+
+  if (!sys_mbox_valid(&conn->acceptmbox)) {
+    LWIP_DEBUGF(API_MSG_DEBUG, ("accept_function: acceptmbox already deleted\n"));
+    return ERR_VAL;
+  }
+
+  /* We have to set the callback here even though
+   * the new socket is unknown. conn->socket is marked as -1. */
+  newconn = netconn_alloc(conn->type, conn->callback);
+  if (newconn == NULL) {
+    return ERR_MEM;
+  }
+  newconn->pcb.tcp = newpcb;
+  setup_tcp(newconn);
+  /* no protection: when creating the pcb, the netconn is not yet known
+     to the application thread */
+  newconn->last_err = err;
+
+  if (sys_mbox_trypost(&conn->acceptmbox, newconn) != ERR_OK) {
+    /* When returning != ERR_OK, the pcb is aborted in tcp_process(),
+       so do nothing here! */
+    newconn->pcb.tcp = NULL;
+    /* no need to drain since we know the recvmbox is empty. */
+    sys_mbox_free(&newconn->recvmbox);
+    sys_mbox_set_invalid(&newconn->recvmbox);
+    netconn_free(newconn);
+    return ERR_MEM;
+  } else {
+    /* Register event with callback */
+    API_EVENT(conn, NETCONN_EVT_RCVPLUS, 0);
+  }
+
+  return ERR_OK;
+}
+#endif /* LWIP_TCP */
+
+/**
+ * Create a new pcb of a specific type.
+ * Called from do_newconn().
+ *
+ * @param msg the api_msg_msg describing the connection type
+ * @return msg->conn->err, but the return value is currently ignored
+ */
+static void
+pcb_new(struct api_msg_msg *msg)
+{
+  LWIP_ASSERT("pcb_new: pcb already allocated", msg->conn->pcb.tcp == NULL);
+
+  /* Allocate a PCB for this connection */
+  switch(NETCONNTYPE_GROUP(msg->conn->type)) {
+#if LWIP_RAW
+  case NETCONN_RAW:
+    msg->conn->pcb.raw = raw_new(msg->msg.n.proto);
+    if(msg->conn->pcb.raw == NULL) {
+      msg->err = ERR_MEM;
+      break;
+    }
+    raw_recv(msg->conn->pcb.raw, recv_raw, msg->conn);
+    break;
+#endif /* LWIP_RAW */
+#if LWIP_UDP
+  case NETCONN_UDP:
+    msg->conn->pcb.udp = udp_new();
+    if(msg->conn->pcb.udp == NULL) {
+      msg->err = ERR_MEM;
+      break;
+    }
+#if LWIP_UDPLITE
+    if (msg->conn->type==NETCONN_UDPLITE) {
+      udp_setflags(msg->conn->pcb.udp, UDP_FLAGS_UDPLITE);
+    }
+#endif /* LWIP_UDPLITE */
+    if (msg->conn->type==NETCONN_UDPNOCHKSUM) {
+      udp_setflags(msg->conn->pcb.udp, UDP_FLAGS_NOCHKSUM);
+    }
+    udp_recv(msg->conn->pcb.udp, recv_udp, msg->conn);
+    break;
+#endif /* LWIP_UDP */
+#if LWIP_TCP
+  case NETCONN_TCP:
+    msg->conn->pcb.tcp = tcp_new();
+    if(msg->conn->pcb.tcp == NULL) {
+      msg->err = ERR_MEM;
+      break;
+    }
+    setup_tcp(msg->conn);
+    break;
+#endif /* LWIP_TCP */
+  default:
+    /* Unsupported netconn type, e.g. protocol disabled */
+    msg->err = ERR_VAL;
+    break;
+  }
+}
+
+/**
+ * Create a new pcb of a specific type inside a netconn.
+ * Called from netconn_new_with_proto_and_callback.
+ *
+ * @param msg the api_msg_msg describing the connection type
+ */
+void
+do_newconn(struct api_msg_msg *msg)
+{
+  msg->err = ERR_OK;
+  if(msg->conn->pcb.tcp == NULL) {
+    pcb_new(msg);
+  }
+  /* Else? This "new" connection already has a PCB allocated. */
+  /* Is this an error condition? Should it be deleted? */
+  /* We currently just are happy and return. */
+
+  TCPIP_APIMSG_ACK(msg);
+}
+
+/**
+ * Create a new netconn (of a specific type) that has a callback function.
+ * The corresponding pcb is NOT 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_alloc(enum netconn_type t, netconn_callback callback)
+{
+  struct netconn *conn;
+  int size;
+
+  conn = (struct netconn *)memp_malloc(MEMP_NETCONN);
+  if (conn == NULL) {
+    return NULL;
+  }
+
+  conn->last_err = ERR_OK;
+  conn->type = t;
+  conn->pcb.tcp = NULL;
+
+#if (DEFAULT_RAW_RECVMBOX_SIZE == DEFAULT_UDP_RECVMBOX_SIZE) && \
+    (DEFAULT_RAW_RECVMBOX_SIZE == DEFAULT_TCP_RECVMBOX_SIZE)
+  size = DEFAULT_RAW_RECVMBOX_SIZE;
+#else
+  switch(NETCONNTYPE_GROUP(t)) {
+#if LWIP_RAW
+  case NETCONN_RAW:
+    size = DEFAULT_RAW_RECVMBOX_SIZE;
+    break;
+#endif /* LWIP_RAW */
+#if LWIP_UDP
+  case NETCONN_UDP:
+    size = DEFAULT_UDP_RECVMBOX_SIZE;
+    break;
+#endif /* LWIP_UDP */
+#if LWIP_TCP
+  case NETCONN_TCP:
+    size = DEFAULT_TCP_RECVMBOX_SIZE;
+    break;
+#endif /* LWIP_TCP */
+  default:
+    LWIP_ASSERT("netconn_alloc: undefined netconn_type", 0);
+    break;
+  }
+#endif
+
+  if (sys_sem_new(&conn->op_completed, 0) != ERR_OK) {
+    memp_free(MEMP_NETCONN, conn);
+    return NULL;
+  }
+  if (sys_mbox_new(&conn->recvmbox, size) != ERR_OK) {
+    sys_sem_free(&conn->op_completed);
+    memp_free(MEMP_NETCONN, conn);
+    return NULL;
+  }
+
+#if LWIP_TCP
+  sys_mbox_set_invalid(&conn->acceptmbox);
+#endif
+  conn->state        = NETCONN_NONE;
+#if LWIP_SOCKET
+  /* initialize socket to -1 since 0 is a valid socket */
+  conn->socket       = -1;
+#endif /* LWIP_SOCKET */
+  conn->callback     = callback;
+#if LWIP_TCP
+  conn->current_msg  = NULL;
+  conn->write_offset = 0;
+#endif /* LWIP_TCP */
+#if LWIP_SO_RCVTIMEO
+  conn->recv_timeout = 0;
+#endif /* LWIP_SO_RCVTIMEO */
+#if LWIP_SO_RCVBUF
+  conn->recv_bufsize = RECV_BUFSIZE_DEFAULT;
+  conn->recv_avail   = 0;
+#endif /* LWIP_SO_RCVBUF */
+  conn->flags = 0;
+  return conn;
+}
+
+/**
+ * Delete a netconn and all its resources.
+ * The pcb is NOT freed (since we might not be in the right thread context do this).
+ *
+ * @param conn the netconn to free
+ */
+void
+netconn_free(struct netconn *conn)
+{
+  LWIP_ASSERT("PCB must be deallocated outside this function", conn->pcb.tcp == NULL);
+  LWIP_ASSERT("recvmbox must be deallocated before calling this function",
+    !sys_mbox_valid(&conn->recvmbox));
+#if LWIP_TCP
+  LWIP_ASSERT("acceptmbox must be deallocated before calling this function",
+    !sys_mbox_valid(&conn->acceptmbox));
+#endif /* LWIP_TCP */
+
+  sys_sem_free(&conn->op_completed);
+  sys_sem_set_invalid(&conn->op_completed);
+
+  memp_free(MEMP_NETCONN, conn);
+}
+
+/**
+ * Delete rcvmbox and acceptmbox of a netconn and free the left-over data in
+ * these mboxes
+ *
+ * @param conn the netconn to free
+ * @bytes_drained bytes drained from recvmbox
+ * @accepts_drained pending connections drained from acceptmbox
+ */
+static void
+netconn_drain(struct netconn *conn)
+{
+  void *mem;
+#if LWIP_TCP
+  struct pbuf *p;
+#endif /* LWIP_TCP */
+
+  /* This runs in tcpip_thread, so we don't need to lock against rx packets */
+
+  /* Delete and drain the recvmbox. */
+  if (sys_mbox_valid(&conn->recvmbox)) {
+    while (sys_mbox_tryfetch(&conn->recvmbox, &mem) != SYS_MBOX_EMPTY) {
+#if LWIP_TCP
+      if (conn->type == NETCONN_TCP) {
+        if(mem != NULL) {
+          p = (struct pbuf*)mem;
+          /* pcb might be set to NULL already by err_tcp() */
+          if (conn->pcb.tcp != NULL) {
+            tcp_recved(conn->pcb.tcp, p->tot_len);
+          }
+          pbuf_free(p);
+        }
+      } else
+#endif /* LWIP_TCP */
+      {
+        netbuf_delete((struct netbuf *)mem);
+      }
+    }
+    sys_mbox_free(&conn->recvmbox);
+    sys_mbox_set_invalid(&conn->recvmbox);
+  }
+
+  /* Delete and drain the acceptmbox. */
+#if LWIP_TCP
+  if (sys_mbox_valid(&conn->acceptmbox)) {
+    while (sys_mbox_tryfetch(&conn->acceptmbox, &mem) != SYS_MBOX_EMPTY) {
+      struct netconn *newconn = (struct netconn *)mem;
+      /* Only tcp pcbs have an acceptmbox, so no need to check conn->type */
+      /* pcb might be set to NULL already by err_tcp() */
+      if (conn->pcb.tcp != NULL) {
+        tcp_accepted(conn->pcb.tcp);
+      }
+      /* drain recvmbox */
+      netconn_drain(newconn);
+      if (newconn->pcb.tcp != NULL) {
+        tcp_abort(newconn->pcb.tcp);
+        newconn->pcb.tcp = NULL;
+      }
+      netconn_free(newconn);
+    }
+    sys_mbox_free(&conn->acceptmbox);
+    sys_mbox_set_invalid(&conn->acceptmbox);
+  }
+#endif /* LWIP_TCP */
+}
+
+#if LWIP_TCP
+/**
+ * Internal helper function to close a TCP netconn: since this sometimes
+ * doesn't work at the first attempt, this function is called from multiple
+ * places.
+ *
+ * @param conn the TCP netconn to close
+ */
+static void
+do_close_internal(struct netconn *conn)
+{
+  err_t err;
+  u8_t shut, shut_rx, shut_tx, close;
+
+  LWIP_ASSERT("invalid conn", (conn != NULL));
+  LWIP_ASSERT("this is for tcp netconns only", (conn->type == NETCONN_TCP));
+  LWIP_ASSERT("conn must be in state NETCONN_CLOSE", (conn->state == NETCONN_CLOSE));
+  LWIP_ASSERT("pcb already closed", (conn->pcb.tcp != NULL));
+  LWIP_ASSERT("conn->current_msg != NULL", conn->current_msg != NULL);
+
+  shut = conn->current_msg->msg.sd.shut;
+  shut_rx = shut & NETCONN_SHUT_RD;
+  shut_tx = shut & NETCONN_SHUT_WR;
+  /* shutting down both ends is the same as closing */
+  close = shut == NETCONN_SHUT_RDWR;
+
+  /* Set back some callback pointers */
+  if (close) {
+    tcp_arg(conn->pcb.tcp, NULL);
+  }
+  if (conn->pcb.tcp->state == LISTEN) {
+    tcp_accept(conn->pcb.tcp, NULL);
+  } else {
+    /* some callbacks have to be reset if tcp_close is not successful */
+    if (shut_rx) {
+      tcp_recv(conn->pcb.tcp, NULL);
+      tcp_accept(conn->pcb.tcp, NULL);
+    }
+    if (shut_tx) {
+      tcp_sent(conn->pcb.tcp, NULL);
+    }
+    if (close) {
+      tcp_poll(conn->pcb.tcp, NULL, 4);
+      tcp_err(conn->pcb.tcp, NULL);
+    }
+  }
+  /* Try to close the connection */
+  if (shut == NETCONN_SHUT_RDWR) {
+    err = tcp_close(conn->pcb.tcp);
+  } else {
+    err = tcp_shutdown(conn->pcb.tcp, shut & NETCONN_SHUT_RD, shut & NETCONN_SHUT_WR);
+  }
+  if (err == ERR_OK) {
+    /* Closing succeeded */
+    conn->current_msg->err = ERR_OK;
+    conn->current_msg = NULL;
+    conn->state = NETCONN_NONE;
+    /* Set back some callback pointers as conn is going away */
+    conn->pcb.tcp = NULL;
+    /* Trigger select() in socket layer. Make sure everybody notices activity
+       on the connection, error first! */
+    if (close) {
+      API_EVENT(conn, NETCONN_EVT_ERROR, 0);
+    }
+    if (shut_rx) {
+      API_EVENT(conn, NETCONN_EVT_RCVPLUS, 0);
+    }
+    if (shut_tx) {
+      API_EVENT(conn, NETCONN_EVT_SENDPLUS, 0);
+    }
+    /* wake up the application task */
+    sys_sem_signal(&conn->op_completed);
+  } else {
+    /* Closing failed, restore some of the callbacks */
+    /* Closing of listen pcb will never fail! */
+    LWIP_ASSERT("Closing a listen pcb may not fail!", (conn->pcb.tcp->state != LISTEN));
+    tcp_sent(conn->pcb.tcp, sent_tcp);
+    tcp_poll(conn->pcb.tcp, poll_tcp, 4);
+    tcp_err(conn->pcb.tcp, err_tcp);
+    tcp_arg(conn->pcb.tcp, conn);
+    /* don't restore recv callback: we don't want to receive any more data */
+  }
+  /* If closing didn't succeed, we get called again either
+     from poll_tcp or from sent_tcp */
+}
+#endif /* LWIP_TCP */
+
+/**
+ * Delete the pcb inside a netconn.
+ * Called from netconn_delete.
+ *
+ * @param msg the api_msg_msg pointing to the connection
+ */
+void
+do_delconn(struct api_msg_msg *msg)
+{
+  /* @todo TCP: abort running write/connect? */
+ if ((msg->conn->state != NETCONN_NONE) &&
+     (msg->conn->state != NETCONN_LISTEN) &&
+     (msg->conn->state != NETCONN_CONNECT)) {
+    /* this only happens for TCP netconns */
+    LWIP_ASSERT("msg->conn->type == NETCONN_TCP", msg->conn->type == NETCONN_TCP);
+    msg->err = ERR_INPROGRESS;
+  } else {
+    LWIP_ASSERT("blocking connect in progress",
+      (msg->conn->state != NETCONN_CONNECT) || IN_NONBLOCKING_CONNECT(msg->conn));
+    /* Drain and delete mboxes */
+    netconn_drain(msg->conn);
+
+    if (msg->conn->pcb.tcp != NULL) {
+
+      switch (NETCONNTYPE_GROUP(msg->conn->type)) {
+#if LWIP_RAW
+      case NETCONN_RAW:
+        raw_remove(msg->conn->pcb.raw);
+        break;
+#endif /* LWIP_RAW */
+#if LWIP_UDP
+      case NETCONN_UDP:
+        msg->conn->pcb.udp->recv_arg = NULL;
+        udp_remove(msg->conn->pcb.udp);
+        break;
+#endif /* LWIP_UDP */
+#if LWIP_TCP
+      case NETCONN_TCP:
+        LWIP_ASSERT("already writing or closing", msg->conn->current_msg == NULL &&
+          msg->conn->write_offset == 0);
+        msg->conn->state = NETCONN_CLOSE;
+        msg->msg.sd.shut = NETCONN_SHUT_RDWR;
+        msg->conn->current_msg = msg;
+        do_close_internal(msg->conn);
+        /* API_EVENT is called inside do_close_internal, before releasing
+           the application thread, so we can return at this point! */
+        return;
+#endif /* LWIP_TCP */
+      default:
+        break;
+      }
+      msg->conn->pcb.tcp = NULL;
+    }
+    /* tcp netconns don't come here! */
+
+    /* @todo: this lets select make the socket readable and writable,
+       which is wrong! errfd instead? */
+    API_EVENT(msg->conn, NETCONN_EVT_RCVPLUS, 0);
+    API_EVENT(msg->conn, NETCONN_EVT_SENDPLUS, 0);
+  }
+  if (sys_sem_valid(&msg->conn->op_completed)) {
+    sys_sem_signal(&msg->conn->op_completed);
+  }
+}
+
+/**
+ * Bind a pcb contained in a netconn
+ * Called from netconn_bind.
+ *
+ * @param msg the api_msg_msg pointing to the connection and containing
+ *            the IP address and port to bind to
+ */
+void
+do_bind(struct api_msg_msg *msg)
+{
+  if (ERR_IS_FATAL(msg->conn->last_err)) {
+    msg->err = msg->conn->last_err;
+  } else {
+    msg->err = ERR_VAL;
+    if (msg->conn->pcb.tcp != NULL) {
+      switch (NETCONNTYPE_GROUP(msg->conn->type)) {
+#if LWIP_RAW
+      case NETCONN_RAW:
+        msg->err = raw_bind(msg->conn->pcb.raw, msg->msg.bc.ipaddr);
+        break;
+#endif /* LWIP_RAW */
+#if LWIP_UDP
+      case NETCONN_UDP:
+        msg->err = udp_bind(msg->conn->pcb.udp, msg->msg.bc.ipaddr, msg->msg.bc.port);
+        break;
+#endif /* LWIP_UDP */
+#if LWIP_TCP
+      case NETCONN_TCP:
+        msg->err = tcp_bind(msg->conn->pcb.tcp, msg->msg.bc.ipaddr, msg->msg.bc.port);
+        break;
+#endif /* LWIP_TCP */
+      default:
+        break;
+      }
+    }
+  }
+  TCPIP_APIMSG_ACK(msg);
+}
+
+#if LWIP_TCP
+/**
+ * TCP callback function if a connection (opened by tcp_connect/do_connect) has
+ * been established (or reset by the remote host).
+ *
+ * @see tcp.h (struct tcp_pcb.connected) for parameters and return values
+ */
+static err_t
+do_connected(void *arg, struct tcp_pcb *pcb, err_t err)
+{
+  struct netconn *conn;
+  int was_blocking;
+
+  LWIP_UNUSED_ARG(pcb);
+
+  conn = (struct netconn *)arg;
+
+  if (conn == NULL) {
+    return ERR_VAL;
+  }
+
+  LWIP_ASSERT("conn->state == NETCONN_CONNECT", conn->state == NETCONN_CONNECT);
+  LWIP_ASSERT("(conn->current_msg != NULL) || conn->in_non_blocking_connect",
+    (conn->current_msg != NULL) || IN_NONBLOCKING_CONNECT(conn));
+
+  if (conn->current_msg != NULL) {
+    conn->current_msg->err = err;
+  }
+  if ((conn->type == NETCONN_TCP) && (err == ERR_OK)) {
+    setup_tcp(conn);
+  }
+  was_blocking = !IN_NONBLOCKING_CONNECT(conn);
+  SET_NONBLOCKING_CONNECT(conn, 0);
+  conn->current_msg = NULL;
+  conn->state = NETCONN_NONE;
+  if (!was_blocking) {
+    NETCONN_SET_SAFE_ERR(conn, ERR_OK);
+  }
+  API_EVENT(conn, NETCONN_EVT_SENDPLUS, 0);
+
+  if (was_blocking) {
+    sys_sem_signal(&conn->op_completed);
+  }
+  return ERR_OK;
+}
+#endif /* LWIP_TCP */
+
+/**
+ * Connect a pcb contained inside a netconn
+ * Called from netconn_connect.
+ *
+ * @param msg the api_msg_msg pointing to the connection and containing
+ *            the IP address and port to connect to
+ */
+void
+do_connect(struct api_msg_msg *msg)
+{
+  if (msg->conn->pcb.tcp == NULL) {
+    /* This may happen when calling netconn_connect() a second time */
+    msg->err = ERR_CLSD;
+  } else {
+    switch (NETCONNTYPE_GROUP(msg->conn->type)) {
+#if LWIP_RAW
+  case NETCONN_RAW:
+    msg->err = raw_connect(msg->conn->pcb.raw, msg->msg.bc.ipaddr);
+    break;
+#endif /* LWIP_RAW */
+#if LWIP_UDP
+  case NETCONN_UDP:
+    msg->err = udp_connect(msg->conn->pcb.udp, msg->msg.bc.ipaddr, msg->msg.bc.port);
+    break;
+#endif /* LWIP_UDP */
+#if LWIP_TCP
+  case NETCONN_TCP:
+    /* Prevent connect while doing any other action. */
+    if (msg->conn->state != NETCONN_NONE) {
+      msg->err = ERR_ISCONN;
+    } else {
+      setup_tcp(msg->conn);
+      msg->err = tcp_connect(msg->conn->pcb.tcp, msg->msg.bc.ipaddr,
+        msg->msg.bc.port, do_connected);
+      if (msg->err == ERR_OK) {
+        u8_t non_blocking = netconn_is_nonblocking(msg->conn);
+        msg->conn->state = NETCONN_CONNECT;
+        SET_NONBLOCKING_CONNECT(msg->conn, non_blocking);
+        if (non_blocking) {
+          msg->err = ERR_INPROGRESS;
+        } else {
+          msg->conn->current_msg = msg;
+          /* sys_sem_signal() is called from do_connected (or err_tcp()),
+          * when the connection is established! */
+          return;
+        }
+      }
+    }
+    break;
+#endif /* LWIP_TCP */
+  default:
+    LWIP_ERROR("Invalid netconn type", 0, do{ msg->err = ERR_VAL; }while(0));
+    break;
+    }
+  }
+  sys_sem_signal(&msg->conn->op_completed);
+}
+
+/**
+ * Connect a pcb contained inside a netconn
+ * Only used for UDP netconns.
+ * Called from netconn_disconnect.
+ *
+ * @param msg the api_msg_msg pointing to the connection to disconnect
+ */
+void
+do_disconnect(struct api_msg_msg *msg)
+{
+#if LWIP_UDP
+  if (NETCONNTYPE_GROUP(msg->conn->type) == NETCONN_UDP) {
+    udp_disconnect(msg->conn->pcb.udp);
+    msg->err = ERR_OK;
+  } else
+#endif /* LWIP_UDP */
+  {
+    msg->err = ERR_VAL;
+  }
+  TCPIP_APIMSG_ACK(msg);
+}
+
+#if LWIP_TCP
+/**
+ * Set a TCP pcb contained in a netconn into listen mode
+ * Called from netconn_listen.
+ *
+ * @param msg the api_msg_msg pointing to the connection
+ */
+void
+do_listen(struct api_msg_msg *msg)
+{
+  if (ERR_IS_FATAL(msg->conn->last_err)) {
+    msg->err = msg->conn->last_err;
+  } else {
+    msg->err = ERR_CONN;
+    if (msg->conn->pcb.tcp != NULL) {
+      if (msg->conn->type == NETCONN_TCP) {
+        if (msg->conn->state == NETCONN_NONE) {
+#if TCP_LISTEN_BACKLOG
+          struct tcp_pcb* lpcb = tcp_listen_with_backlog(msg->conn->pcb.tcp, msg->msg.lb.backlog);
+#else  /* TCP_LISTEN_BACKLOG */
+          struct tcp_pcb* lpcb = tcp_listen(msg->conn->pcb.tcp);
+#endif /* TCP_LISTEN_BACKLOG */
+          if (lpcb == NULL) {
+            /* in this case, the old pcb is still allocated */
+            msg->err = ERR_MEM;
+          } else {
+            /* delete the recvmbox and allocate the acceptmbox */
+            if (sys_mbox_valid(&msg->conn->recvmbox)) {
+              /** @todo: should we drain the recvmbox here? */
+              sys_mbox_free(&msg->conn->recvmbox);
+              sys_mbox_set_invalid(&msg->conn->recvmbox);
+            }
+            msg->err = ERR_OK;
+            if (!sys_mbox_valid(&msg->conn->acceptmbox)) {
+              msg->err = sys_mbox_new(&msg->conn->acceptmbox, DEFAULT_ACCEPTMBOX_SIZE);
+            }
+            if (msg->err == ERR_OK) {
+              msg->conn->state = NETCONN_LISTEN;
+              msg->conn->pcb.tcp = lpcb;
+              tcp_arg(msg->conn->pcb.tcp, msg->conn);
+              tcp_accept(msg->conn->pcb.tcp, accept_function);
+            } else {
+              /* since the old pcb is already deallocated, free lpcb now */
+              tcp_close(lpcb);
+              msg->conn->pcb.tcp = NULL;
+            }
+          }
+        }
+      }
+    }
+  }
+  TCPIP_APIMSG_ACK(msg);
+}
+#endif /* LWIP_TCP */
+
+/**
+ * Send some data on a RAW or UDP pcb contained in a netconn
+ * Called from netconn_send
+ *
+ * @param msg the api_msg_msg pointing to the connection
+ */
+void
+do_send(struct api_msg_msg *msg)
+{
+  if (ERR_IS_FATAL(msg->conn->last_err)) {
+    msg->err = msg->conn->last_err;
+  } else {
+    msg->err = ERR_CONN;
+    if (msg->conn->pcb.tcp != NULL) {
+      switch (NETCONNTYPE_GROUP(msg->conn->type)) {
+#if LWIP_RAW
+      case NETCONN_RAW:
+        if (ip_addr_isany(&msg->msg.b->addr)) {
+          msg->err = raw_send(msg->conn->pcb.raw, msg->msg.b->p);
+        } else {
+          msg->err = raw_sendto(msg->conn->pcb.raw, msg->msg.b->p, &msg->msg.b->addr);
+        }
+        break;
+#endif
+#if LWIP_UDP
+      case NETCONN_UDP:
+#if LWIP_CHECKSUM_ON_COPY
+        if (ip_addr_isany(&msg->msg.b->addr)) {
+          msg->err = udp_send_chksum(msg->conn->pcb.udp, msg->msg.b->p,
+            msg->msg.b->flags & NETBUF_FLAG_CHKSUM, msg->msg.b->toport_chksum);
+        } else {
+          msg->err = udp_sendto_chksum(msg->conn->pcb.udp, msg->msg.b->p,
+            &msg->msg.b->addr, msg->msg.b->port,
+            msg->msg.b->flags & NETBUF_FLAG_CHKSUM, msg->msg.b->toport_chksum);
+        }
+#else /* LWIP_CHECKSUM_ON_COPY */
+        if (ip_addr_isany(&msg->msg.b->addr)) {
+          msg->err = udp_send(msg->conn->pcb.udp, msg->msg.b->p);
+        } else {
+          msg->err = udp_sendto(msg->conn->pcb.udp, msg->msg.b->p, &msg->msg.b->addr, msg->msg.b->port);
+        }
+#endif /* LWIP_CHECKSUM_ON_COPY */
+        break;
+#endif /* LWIP_UDP */
+      default:
+        break;
+      }
+    }
+  }
+  TCPIP_APIMSG_ACK(msg);
+}
+
+#if LWIP_TCP
+/**
+ * Indicate data has been received from a TCP pcb contained in a netconn
+ * Called from netconn_recv
+ *
+ * @param msg the api_msg_msg pointing to the connection
+ */
+void
+do_recv(struct api_msg_msg *msg)
+{
+  msg->err = ERR_OK;
+  if (msg->conn->pcb.tcp != NULL) {
+    if (msg->conn->type == NETCONN_TCP) {
+#if TCP_LISTEN_BACKLOG
+      if (msg->conn->pcb.tcp->state == LISTEN) {
+        tcp_accepted(msg->conn->pcb.tcp);
+      } else
+#endif /* TCP_LISTEN_BACKLOG */
+      {
+        u32_t remaining = msg->msg.r.len;
+        do {
+          u16_t recved = (remaining > 0xffff) ? 0xffff : (u16_t)remaining;
+          tcp_recved(msg->conn->pcb.tcp, recved);
+          remaining -= recved;
+        }while(remaining != 0);
+      }
+    }
+  }
+  TCPIP_APIMSG_ACK(msg);
+}
+
+/**
+ * See if more data needs to be written from a previous call to netconn_write.
+ * Called initially from do_write. If the first call can't send all data
+ * (because of low memory or empty send-buffer), this function is called again
+ * from sent_tcp() or poll_tcp() to send more data. If all data is sent, the
+ * blocking application thread (waiting in netconn_write) is released.
+ *
+ * @param conn netconn (that is currently in state NETCONN_WRITE) to process
+ * @return ERR_OK
+ *         ERR_MEM if LWIP_TCPIP_CORE_LOCKING=1 and sending hasn't yet finished
+ */
+static err_t
+do_writemore(struct netconn *conn)
+{
+  err_t err = ERR_OK;
+  void *dataptr;
+  u16_t len, available;
+  u8_t write_finished = 0;
+  size_t diff;
+  u8_t dontblock = netconn_is_nonblocking(conn) ||
+       (conn->current_msg->msg.w.apiflags & NETCONN_DONTBLOCK);
+  u8_t apiflags = conn->current_msg->msg.w.apiflags;
+
+  LWIP_ASSERT("conn != NULL", conn != NULL);
+  LWIP_ASSERT("conn->state == NETCONN_WRITE", (conn->state == NETCONN_WRITE));
+  LWIP_ASSERT("conn->current_msg != NULL", conn->current_msg != NULL);
+  LWIP_ASSERT("conn->pcb.tcp != NULL", conn->pcb.tcp != NULL);
+  LWIP_ASSERT("conn->write_offset < conn->current_msg->msg.w.len",
+    conn->write_offset < conn->current_msg->msg.w.len);
+
+  dataptr = (u8_t*)conn->current_msg->msg.w.dataptr + conn->write_offset;
+  diff = conn->current_msg->msg.w.len - conn->write_offset;
+  if (diff > 0xffffUL) { /* max_u16_t */
+    len = 0xffff;
+#if LWIP_TCPIP_CORE_LOCKING
+    conn->flags |= NETCONN_FLAG_WRITE_DELAYED;
+#endif
+    apiflags |= TCP_WRITE_FLAG_MORE;
+  } else {
+    len = (u16_t)diff;
+  }
+  available = tcp_sndbuf(conn->pcb.tcp);
+  if (available < len) {
+    /* don't try to write more than sendbuf */
+    len = available;
+#if LWIP_TCPIP_CORE_LOCKING
+    conn->flags |= NETCONN_FLAG_WRITE_DELAYED;
+#endif
+    apiflags |= TCP_WRITE_FLAG_MORE;
+  }
+  if (dontblock && (len < conn->current_msg->msg.w.len)) {
+    /* failed to send all data at once -> nonblocking write not possible */
+    err = ERR_MEM;
+  }
+  if (err == ERR_OK) {
+    LWIP_ASSERT("do_writemore: invalid length!", ((conn->write_offset + len) <= conn->current_msg->msg.w.len));
+    err = tcp_write(conn->pcb.tcp, dataptr, len, apiflags);
+  }
+  if (dontblock && (err == ERR_MEM)) {
+    /* nonblocking write failed */
+    write_finished = 1;
+    err = ERR_WOULDBLOCK;
+    /* let poll_tcp check writable space to mark the pcb
+       writable again */
+    conn->flags |= NETCONN_FLAG_CHECK_WRITESPACE;
+    /* let select mark this pcb as non-writable. */
+    API_EVENT(conn, NETCONN_EVT_SENDMINUS, len);
+  } else {
+    /* if OK or memory error, check available space */
+    if (((err == ERR_OK) || (err == ERR_MEM)) &&
+        ((tcp_sndbuf(conn->pcb.tcp) <= TCP_SNDLOWAT) ||
+         (tcp_sndqueuelen(conn->pcb.tcp) >= TCP_SNDQUEUELOWAT))) {
+      /* The queued byte- or pbuf-count exceeds the configured low-water limit,
+         let select mark this pcb as non-writable. */
+      API_EVENT(conn, NETCONN_EVT_SENDMINUS, len);
+    }
+
+    if (err == ERR_OK) {
+      conn->write_offset += len;
+      if (conn->write_offset == conn->current_msg->msg.w.len) {
+        /* everything was written */
+        write_finished = 1;
+        conn->write_offset = 0;
+      }
+      tcp_output(conn->pcb.tcp);
+    } else if (err == ERR_MEM) {
+      /* If ERR_MEM, we wait for sent_tcp or poll_tcp to be called
+         we do NOT return to the application thread, since ERR_MEM is
+         only a temporary error! */
+
+      /* tcp_write returned ERR_MEM, try tcp_output anyway */
+      tcp_output(conn->pcb.tcp);
+
+  #if LWIP_TCPIP_CORE_LOCKING
+      conn->flags |= NETCONN_FLAG_WRITE_DELAYED;
+  #endif
+    } else {
+      /* On errors != ERR_MEM, we don't try writing any more but return
+         the error to the application thread. */
+      write_finished = 1;
+    }
+  }
+
+  if (write_finished) {
+    /* everything was written: set back connection state
+       and back to application task */
+    conn->current_msg->err = err;
+    conn->current_msg = NULL;
+    conn->state = NETCONN_NONE;
+#if LWIP_TCPIP_CORE_LOCKING
+    if ((conn->flags & NETCONN_FLAG_WRITE_DELAYED) != 0)
+#endif
+    {
+      sys_sem_signal(&conn->op_completed);
+    }
+  }
+#if LWIP_TCPIP_CORE_LOCKING
+  else
+    return ERR_MEM;
+#endif
+  return ERR_OK;
+}
+#endif /* LWIP_TCP */
+
+/**
+ * Send some data on a TCP pcb contained in a netconn
+ * Called from netconn_write
+ *
+ * @param msg the api_msg_msg pointing to the connection
+ */
+void
+do_write(struct api_msg_msg *msg)
+{
+  if (ERR_IS_FATAL(msg->conn->last_err)) {
+    msg->err = msg->conn->last_err;
+  } else {
+    if (msg->conn->type == NETCONN_TCP) {
+#if LWIP_TCP
+      if (msg->conn->state != NETCONN_NONE) {
+        /* netconn is connecting, closing or in blocking write */
+        msg->err = ERR_INPROGRESS;
+      } else if (msg->conn->pcb.tcp != NULL) {
+        msg->conn->state = NETCONN_WRITE;
+        /* set all the variables used by do_writemore */
+        LWIP_ASSERT("already writing or closing", msg->conn->current_msg == NULL &&
+          msg->conn->write_offset == 0);
+        LWIP_ASSERT("msg->msg.w.len != 0", msg->msg.w.len != 0);
+        msg->conn->current_msg = msg;
+        msg->conn->write_offset = 0;
+#if LWIP_TCPIP_CORE_LOCKING
+        msg->conn->flags &= ~NETCONN_FLAG_WRITE_DELAYED;
+        if (do_writemore(msg->conn) != ERR_OK) {
+          LWIP_ASSERT("state!", msg->conn->state == NETCONN_WRITE);
+          UNLOCK_TCPIP_CORE();
+          sys_arch_sem_wait(&msg->conn->op_completed, 0);
+          LOCK_TCPIP_CORE();
+          LWIP_ASSERT("state!", msg->conn->state == NETCONN_NONE);
+        }
+#else /* LWIP_TCPIP_CORE_LOCKING */
+        do_writemore(msg->conn);
+#endif /* LWIP_TCPIP_CORE_LOCKING */
+        /* for both cases: if do_writemore was called, don't ACK the APIMSG
+           since do_writemore ACKs it! */
+        return;
+      } else {
+        msg->err = ERR_CONN;
+      }
+#else /* LWIP_TCP */
+      msg->err = ERR_VAL;
+#endif /* LWIP_TCP */
+#if (LWIP_UDP || LWIP_RAW)
+    } else {
+      msg->err = ERR_VAL;
+#endif /* (LWIP_UDP || LWIP_RAW) */
+    }
+  }
+  TCPIP_APIMSG_ACK(msg);
+}
+
+/**
+ * Return a connection's local or remote address
+ * Called from netconn_getaddr
+ *
+ * @param msg the api_msg_msg pointing to the connection
+ */
+void
+do_getaddr(struct api_msg_msg *msg)
+{
+  if (msg->conn->pcb.ip != NULL) {
+    *(msg->msg.ad.ipaddr) = (msg->msg.ad.local ? msg->conn->pcb.ip->local_ip :
+                             msg->conn->pcb.ip->remote_ip);
+
+    msg->err = ERR_OK;
+    switch (NETCONNTYPE_GROUP(msg->conn->type)) {
+#if LWIP_RAW
+    case NETCONN_RAW:
+      if (msg->msg.ad.local) {
+        *(msg->msg.ad.port) = msg->conn->pcb.raw->protocol;
+      } else {
+        /* return an error as connecting is only a helper for upper layers */
+        msg->err = ERR_CONN;
+      }
+      break;
+#endif /* LWIP_RAW */
+#if LWIP_UDP
+    case NETCONN_UDP:
+      if (msg->msg.ad.local) {
+        *(msg->msg.ad.port) = msg->conn->pcb.udp->local_port;
+      } else {
+        if ((msg->conn->pcb.udp->flags & UDP_FLAGS_CONNECTED) == 0) {
+          msg->err = ERR_CONN;
+        } else {
+          *(msg->msg.ad.port) = msg->conn->pcb.udp->remote_port;
+        }
+      }
+      break;
+#endif /* LWIP_UDP */
+#if LWIP_TCP
+    case NETCONN_TCP:
+      *(msg->msg.ad.port) = (msg->msg.ad.local?msg->conn->pcb.tcp->local_port:msg->conn->pcb.tcp->remote_port);
+      break;
+#endif /* LWIP_TCP */
+    default:
+      LWIP_ASSERT("invalid netconn_type", 0);
+      break;
+    }
+  } else {
+    msg->err = ERR_CONN;
+  }
+  TCPIP_APIMSG_ACK(msg);
+}
+
+/**
+ * Close a TCP pcb contained in a netconn
+ * Called from netconn_close
+ *
+ * @param msg the api_msg_msg pointing to the connection
+ */
+void
+do_close(struct api_msg_msg *msg)
+{
+#if LWIP_TCP
+  /* @todo: abort running write/connect? */
+  if ((msg->conn->state != NETCONN_NONE) && (msg->conn->state != NETCONN_LISTEN)) {
+    /* this only happens for TCP netconns */
+    LWIP_ASSERT("msg->conn->type == NETCONN_TCP", msg->conn->type == NETCONN_TCP);
+    msg->err = ERR_INPROGRESS;
+  } else if ((msg->conn->pcb.tcp != NULL) && (msg->conn->type == NETCONN_TCP)) {
+    if ((msg->msg.sd.shut != NETCONN_SHUT_RDWR) && (msg->conn->state == NETCONN_LISTEN)) {
+      /* LISTEN doesn't support half shutdown */
+      msg->err = ERR_CONN;
+    } else {
+      if (msg->msg.sd.shut & NETCONN_SHUT_RD) {
+        /* Drain and delete mboxes */
+        netconn_drain(msg->conn);
+      }
+      LWIP_ASSERT("already writing or closing", msg->conn->current_msg == NULL &&
+        msg->conn->write_offset == 0);
+      msg->conn->state = NETCONN_CLOSE;
+      msg->conn->current_msg = msg;
+      do_close_internal(msg->conn);
+      /* for tcp netconns, do_close_internal ACKs the message */
+      return;
+    }
+  } else
+#endif /* LWIP_TCP */
+  {
+    msg->err = ERR_VAL;
+  }
+  sys_sem_signal(&msg->conn->op_completed);
+}
+
+#if LWIP_IGMP
+/**
+ * Join multicast groups for UDP netconns.
+ * Called from netconn_join_leave_group
+ *
+ * @param msg the api_msg_msg pointing to the connection
+ */
+void
+do_join_leave_group(struct api_msg_msg *msg)
+{ 
+  if (ERR_IS_FATAL(msg->conn->last_err)) {
+    msg->err = msg->conn->last_err;
+  } else {
+    if (msg->conn->pcb.tcp != NULL) {
+      if (NETCONNTYPE_GROUP(msg->conn->type) == NETCONN_UDP) {
+#if LWIP_UDP
+        if (msg->msg.jl.join_or_leave == NETCONN_JOIN) {
+          msg->err = igmp_joingroup(msg->msg.jl.netif_addr, msg->msg.jl.multiaddr);
+        } else {
+          msg->err = igmp_leavegroup(msg->msg.jl.netif_addr, msg->msg.jl.multiaddr);
+        }
+#endif /* LWIP_UDP */
+#if (LWIP_TCP || LWIP_RAW)
+      } else {
+        msg->err = ERR_VAL;
+#endif /* (LWIP_TCP || LWIP_RAW) */
+      }
+    } else {
+      msg->err = ERR_CONN;
+    }
+  }
+  TCPIP_APIMSG_ACK(msg);
+}
+#endif /* LWIP_IGMP */
+
+#if LWIP_DNS
+/**
+ * Callback function that is called when DNS name is resolved
+ * (or on timeout). A waiting application thread is waked up by
+ * signaling the semaphore.
+ */
+static void
+do_dns_found(const char *name, ip_addr_t *ipaddr, void *arg)
+{
+  struct dns_api_msg *msg = (struct dns_api_msg*)arg;
+
+  LWIP_ASSERT("DNS response for wrong host name", strcmp(msg->name, name) == 0);
+  LWIP_UNUSED_ARG(name);
+
+  if (ipaddr == NULL) {
+    /* timeout or memory error */
+    *msg->err = ERR_VAL;
+  } else {
+    /* address was resolved */
+    *msg->err = ERR_OK;
+    *msg->addr = *ipaddr;
+  }
+  /* wake up the application task waiting in netconn_gethostbyname */
+  sys_sem_signal(msg->sem);
+}
+
+/**
+ * Execute a DNS query
+ * Called from netconn_gethostbyname
+ *
+ * @param arg the dns_api_msg pointing to the query
+ */
+void
+do_gethostbyname(void *arg)
+{
+  struct dns_api_msg *msg = (struct dns_api_msg*)arg;
+
+  *msg->err = dns_gethostbyname(msg->name, msg->addr, do_dns_found, msg);
+  if (*msg->err != ERR_INPROGRESS) {
+    /* on error or immediate success, wake up the application
+     * task waiting in netconn_gethostbyname */
+    sys_sem_signal(msg->sem);
+  }
+}
+#endif /* LWIP_DNS */
+
+#endif /* LWIP_NETCONN */