summaryrefslogtreecommitdiff
path: root/src/transport/plugin_transport_udp.c
blob: 8f95b9ee6671218d6a487e40e702cc01f8e330f6 (plain)
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/*
     This file is part of GNUnet
     (C) 2010 Christian Grothoff (and other contributing authors)

     GNUnet is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published
     by the Free Software Foundation; either version 3, or (at your
     option) any later version.

     GNUnet is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with GNUnet; see the file COPYING.  If not, write to the
     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
     Boston, MA 02111-1307, USA.
*/

/**
 * @file transport/plugin_transport_udp.c
 * @brief Implementation of the UDP NAT punching
 *        transport service
 * @author Christian Grothoff
 * @author Nathan Evans
 *
 * The idea with this transport is to connect gnunet peers to each other
 * when ONE is behind a NAT.  This is based on pwnat (http://samy.pl/pwnat)
 * created by Samy Kamkar.  When configured with the PWNAT options, this
 * transport will start a server daemon which sends dummy ICMP and UDP
 * messages out to a predefined address (typically 1.2.3.4).
 *
 * When a non-NAT'd peer (the client) learns of the NAT'd peer (the server)
 * address, it will send ICMP RESPONSES to the NAT'd peers external address.
 * The NAT box should forward these faked responses to the server, which
 * can then connect directly to the non-NAT'd peer.
 */

#include "platform.h"
#include "gnunet_hello_lib.h"
#include "gnunet_connection_lib.h"
#include "gnunet_container_lib.h"
#include "gnunet_os_lib.h"
#include "gnunet_peerinfo_service.h"
#include "gnunet_protocols.h"
#include "gnunet_resolver_service.h"
#include "gnunet_server_lib.h"
#include "gnunet_signatures.h"
#include "gnunet_statistics_service.h"
#include "gnunet_transport_service.h"
#include "gnunet_transport_plugin.h"
#include "transport.h"

#define DEBUG_UDP GNUNET_NO

#define MAX_PROBES 20

/*
 * Transport cost to peer, always 1 for UDP (direct connection)
 */
#define UDP_DIRECT_DISTANCE 1

#define DEFAULT_NAT_PORT 0

/**
 * How long until we give up on transmitting the welcome message?
 */
#define HOSTNAME_RESOLVE_TIMEOUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 5)

/**
 * Starting port for listening and sending, eventually a config value
 */
#define UDP_NAT_DEFAULT_PORT 22086

/**
 * UDP Message-Packet header.
 */
struct UDPMessage
{
  /**
   * Message header.
   */
  struct GNUNET_MessageHeader header;

  /**
   * What is the identity of the sender (GNUNET_hash of public key)
   */
  struct GNUNET_PeerIdentity sender;

};

/**
 * Network format for IPv4 addresses.
 */
struct IPv4UdpAddress
{
  /**
   * IPv4 address, in network byte order.
   */
  uint32_t ipv4_addr GNUNET_PACKED;

  /**
   * Port number, in network byte order.
   */
  uint16_t u_port GNUNET_PACKED;
};


/**
 * Network format for IPv6 addresses.
 */
struct IPv6UdpAddress
{
  /**
   * IPv6 address.
   */
  struct in6_addr ipv6_addr GNUNET_PACKED;

  /**
   * Port number, in network byte order.
   */
  uint16_t u6_port GNUNET_PACKED;
};

/* Forward definition */
struct Plugin;

struct PrettyPrinterContext
{
  GNUNET_TRANSPORT_AddressStringCallback asc;
  void *asc_cls;
  uint16_t port;
};

struct MessageQueue
{
  /**
   * Linked List
   */
  struct MessageQueue *next;

  /**
   * Session this message belongs to
   */
  struct PeerSession *session;

  /**
   * Actual message to be sent
   */
  char *msgbuf;

  /**
   * Size of message buffer to be sent
   */
  size_t msgbuf_size;

  /**
   * When to discard this message
   */
  struct GNUNET_TIME_Absolute timeout;

  /**
   * Continuation to call when this message goes out
   */
  GNUNET_TRANSPORT_TransmitContinuation cont;

  /**
   * closure for continuation
   */
  void *cont_cls;

};

/**
 * UDP NAT Probe message definition
 */
struct UDP_NAT_ProbeMessage
{
  /**
   * Message header
   */
  struct GNUNET_MessageHeader header;

};

/**
 * UDP NAT Probe message reply definition
 */
struct UDP_NAT_ProbeMessageReply
{
  /**
   * Message header
   */
  struct GNUNET_MessageHeader header;

};


/**
 * UDP NAT Probe message confirm definition
 */
struct UDP_NAT_ProbeMessageConfirmation
{
  /**
   * Message header
   */
  struct GNUNET_MessageHeader header;

};


/**
 * Local network addresses (actual IP address follows this struct).
 * PORT is NOT included!
 */
struct LocalAddrList
{

  /**
   * This is a doubly linked list.
   */
  struct LocalAddrList *next;

  /**
   * This is a doubly linked list.
   */
  struct LocalAddrList *prev;

  /**
   * Number of bytes of the address that follow
   */
  size_t size;

};


/**
 * UDP NAT "Session"
 */
struct PeerSession
{

  /**
   * Stored in a linked list.
   */
  struct PeerSession *next;

  /**
   * Pointer to the global plugin struct.
   */
  struct Plugin *plugin;

  /**
   * To whom are we talking to (set to our identity
   * if we are still waiting for the welcome message)
   */
  struct GNUNET_PeerIdentity target;

  /**
   * Address of the other peer (either based on our 'connect'
   * call or on our 'accept' call).
   */
  void *connect_addr;

  /**
   * Length of connect_addr.
   */
  size_t connect_alen;

  /**
   * Are we still expecting the welcome message? (GNUNET_YES/GNUNET_NO)
   */
  int expecting_welcome;

  /**
   * From which socket do we need to send to this peer?
   */
  struct GNUNET_NETWORK_Handle *sock;

  /*
   * Queue of messages for this peer, in the case that
   * we have to await a connection...
   */
  struct MessageQueue *messages;

};

struct UDP_NAT_Probes
{

  /**
   * Linked list
   */
  struct UDP_NAT_Probes *next;

  /**
   * Address string that the server process returned to us
   */
  char *address_string;

  /**
   * Timeout for this set of probes
   */
  struct GNUNET_TIME_Absolute timeout;

  /**
   * Count of how many probes we've attempted
   */
  int count;

  /**
   * The plugin this probe belongs to
   */
  struct Plugin *plugin;

  /**
   * The task used to send these probes
   */
  GNUNET_SCHEDULER_TaskIdentifier task;

  /**
   * Network address (always ipv4!)
   */
  struct IPv4UdpAddress addr;

};


/**
 * Information we keep for each of our listen sockets.
 */
struct UDP_Sock_Info
{
  /**
   * The network handle
   */
  struct GNUNET_NETWORK_Handle *desc;

  /**
   * The port we bound to
   */
  uint16_t port;
};


/**
 * Encapsulation of all of the state of the plugin.
 */
struct Plugin
{
  /**
   * Our environment.
   */
  struct GNUNET_TRANSPORT_PluginEnvironment *env;

  /*
   * Session of peers with whom we are currently connected
   */
  struct PeerSession *sessions;

  /**
   * Handle for request of hostname resolution, non-NULL if pending.
   */
  struct GNUNET_RESOLVER_RequestHandle *hostname_dns;

  /**
   * ID of task used to update our addresses when one expires.
   */
  GNUNET_SCHEDULER_TaskIdentifier address_update_task;

  /**
   * ID of select task
   */
  GNUNET_SCHEDULER_TaskIdentifier select_task;

  /**
   * Port to listen on.
   */
  uint16_t port;

  /**
   * The external address given to us by the user.  Must be actual
   * outside visible address for NAT punching to work.
   */
  char *external_address;

  /**
   * The internal address given to us by the user (or discovered).
   */
  char *internal_address;

  /**
   * Address we were told to bind to exclusively (IPv4).
   */
  char *bind_address;

  /**
   * Address we were told to bind to exclusively (IPv6).
   */
  char *bind6_address;

  /**
   * List of our IP addresses.
   */
  struct LocalAddrList *lal_head;

  /**
   * Tail of our IP address list.
   */
  struct LocalAddrList *lal_tail;

  /**
   * FD Read set
   */
  struct GNUNET_NETWORK_FDSet *rs;

  /**
   * stdout pipe handle for the gnunet-nat-server process
   */
  struct GNUNET_DISK_PipeHandle *server_stdout;

  /**
   * stdout file handle (for reading) for the gnunet-nat-server process
   */
  const struct GNUNET_DISK_FileHandle *server_stdout_handle;

  /**
   * Probes in flight
   */
  struct UDP_NAT_Probes *probes;

  /**
   * socket that we transmit all IPv4 data with
   */
  struct UDP_Sock_Info udp_sockv4;

  /**
   * socket that we transmit all IPv6 data with
   */
  struct UDP_Sock_Info udp_sockv6;

  /**
   * ID of select gnunet-nat-server stdout read task
   */
  GNUNET_SCHEDULER_TaskIdentifier server_read_task;

  /**
   * Is this transport configured to be behind a NAT?
   */
  int behind_nat;

  /**
   * Is this transport configured to allow connections to NAT'd peers?
   */
  int allow_nat;

  /**
   * Should this transport advertise only NAT addresses (port set to 0)?
   * If not, all addresses will be duplicated for NAT punching and regular
   * ports.
   */
  int only_nat_addresses;

  /**
   * use local addresses?
   */
  int use_localaddresses;

  /**
   * The process id of the server process (if behind NAT)
   */
  struct GNUNET_OS_Process *server_proc;

};


/**
 * Forward declaration.
 */
void
udp_probe_continuation (void *cls, const struct GNUNET_PeerIdentity *target, int result);


/**
 * Disconnect from a remote node.  Clean up session if we have one for this peer
 *
 * @param cls closure for this call (should be handle to Plugin)
 * @param target the peeridentity of the peer to disconnect
 * @return GNUNET_OK on success, GNUNET_SYSERR if the operation failed
 */
void
udp_disconnect (void *cls, const struct GNUNET_PeerIdentity *target)
{
  /** TODO: Implement! */
  return;
}

/**
 * Shutdown the server process (stop receiving inbound traffic). Maybe
 * restarted later!
 *
 * @param cls Handle to the plugin for this transport
 *
 * @return returns the number of sockets successfully closed,
 *         should equal the number of sockets successfully opened
 */
static int
udp_transport_server_stop (void *cls)
{
  struct Plugin *plugin = cls;

  if (plugin->select_task != GNUNET_SCHEDULER_NO_TASK)
    {
      GNUNET_SCHEDULER_cancel (plugin->select_task);
      plugin->select_task = GNUNET_SCHEDULER_NO_TASK;
    }
  if (plugin->udp_sockv4.desc != NULL)
    {
      GNUNET_break (GNUNET_OK == GNUNET_NETWORK_socket_close (plugin->udp_sockv4.desc));
      plugin->udp_sockv4.desc = NULL;
    }
  if (plugin->udp_sockv6.desc != NULL)
    {
      GNUNET_break (GNUNET_OK == GNUNET_NETWORK_socket_close (plugin->udp_sockv6.desc));
      plugin->udp_sockv6.desc = NULL;
    }
  if (plugin->behind_nat == GNUNET_YES)
    {
      if (0 != GNUNET_OS_process_kill (plugin->server_proc, SIGTERM))
	GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "kill");
      GNUNET_OS_process_wait (plugin->server_proc);
      GNUNET_OS_process_close (plugin->server_proc);
      plugin->server_proc = NULL;
    }
  return GNUNET_OK;
}


struct PeerSession *
find_session (struct Plugin *plugin,
	      const struct GNUNET_PeerIdentity *peer)
{
  struct PeerSession *pos;

  pos = plugin->sessions;
  while (pos != NULL)
    {
      if (memcmp(&pos->target, peer, sizeof(struct GNUNET_PeerIdentity)) == 0)
        return pos;
      pos = pos->next;
    }

  return pos;
}


/**
 * Actually send out the message, assume we've got the address and
 * send_handle squared away!
 *
 * @param cls closure
 * @param send_handle which handle to send message on
 * @param target who should receive this message (ignored by UDP)
 * @param msgbuf one or more GNUNET_MessageHeader(s) strung together
 * @param msgbuf_size the size of the msgbuf to send
 * @param priority how important is the message (ignored by UDP)
 * @param timeout when should we time out (give up) if we can not transmit?
 * @param addr the addr to send the message to, needs to be a sockaddr for us
 * @param addrlen the len of addr
 * @param cont continuation to call once the message has
 *        been transmitted (or if the transport is ready
 *        for the next transmission call; or if the
 *        peer disconnected...)
 * @param cont_cls closure for cont
 * @return the number of bytes written
 */
static ssize_t
udp_real_send (void *cls,
	       struct GNUNET_NETWORK_Handle *send_handle,
	       const struct GNUNET_PeerIdentity *target,
	       const char *msgbuf,
	       size_t msgbuf_size,
	       unsigned int priority,
	       struct GNUNET_TIME_Relative timeout,
	       const void *addr,
	       size_t addrlen,
	       GNUNET_TRANSPORT_TransmitContinuation cont,
	       void *cont_cls)
{
  struct Plugin *plugin = cls;
  struct UDPMessage *message;
  int ssize;
  ssize_t sent;
  struct sockaddr_in a4;
  struct sockaddr_in6 a6;
  const struct IPv4UdpAddress *t4;
  const struct IPv6UdpAddress *t6;
  const void *sb;
  size_t sbs;

  if (send_handle == NULL)
    {
      /* failed to open send socket for AF */
      if (cont != NULL)
        cont (cont_cls, target, GNUNET_SYSERR);
      return 0;
    }
  if ((addr == NULL) || (addrlen == 0))
    {
#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
		       "udp_real_send called without address, returning!\n");
#endif
      if (cont != NULL)
        cont (cont_cls, target, GNUNET_SYSERR);
      return 0; /* Can never send if we don't have an address!! */
    }

  /* Build the message to be sent */
  message = GNUNET_malloc (sizeof (struct UDPMessage) + msgbuf_size);
  ssize = sizeof (struct UDPMessage) + msgbuf_size;

  message->header.size = htons (ssize);
  message->header.type = htons (0);
  memcpy (&message->sender, plugin->env->my_identity,
          sizeof (struct GNUNET_PeerIdentity));
  memcpy (&message[1], msgbuf, msgbuf_size);

  if (addrlen == sizeof (struct IPv6UdpAddress))
    {
      t6 = addr;
      memset (&a6, 0, sizeof (a6));
#if HAVE_SOCKADDR_IN_SIN_LEN
      a6.sin6_len = sizeof (a6);
#endif
      a6.sin6_family = AF_INET6;
      a6.sin6_port = t6->u6_port;
      memcpy (&a6.sin6_addr,
              &t6->ipv6_addr,
              sizeof (struct in6_addr));
      sb = &a6;
      sbs = sizeof (a6);
    }
  else if (addrlen == sizeof (struct IPv4UdpAddress))
    {
      t4 = addr;
      memset (&a4, 0, sizeof (a4));
#if HAVE_SOCKADDR_IN_SIN_LEN
      a4.sin_len = sizeof (a4);
#endif
      a4.sin_family = AF_INET;
      a4.sin_port = t4->u_port;
      a4.sin_addr.s_addr = t4->ipv4_addr;
      sb = &a4;
      sbs = sizeof (a4);
    }
  else
    {
      GNUNET_break_op (0);
      GNUNET_free (message);
      return -1;
    }

  /* Actually send the message */
  sent =
    GNUNET_NETWORK_socket_sendto (send_handle, message, ssize,
                                  sb,
                                  sbs);
  if (GNUNET_SYSERR == sent)
    GNUNET_log_strerror(GNUNET_ERROR_TYPE_DEBUG, "sendto");
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
	      "UDP transmit %u-byte message to %s (%d: %s)\n",
	      (unsigned int) ssize,
	      GNUNET_a2s (sb, sbs),
	      (int) sent,
	      (sent < 0) ? STRERROR (errno) : "ok");
  if (cont != NULL)
    {
      if (sent == GNUNET_SYSERR)
        cont (cont_cls, target, GNUNET_SYSERR);
      else
        {
          cont (cont_cls, target, GNUNET_OK);
        }
    }

  GNUNET_free (message);
  return sent;
}

/**
 * We learned about a peer (possibly behind NAT) so run the
 * gnunet-nat-client to send dummy ICMP responses
 *
 * @param plugin the plugin for this transport
 * @param addr the address of the peer
 * @param addrlen the length of the address
 */
void
run_gnunet_nat_client (struct Plugin *plugin, const char *addr, size_t addrlen)
{
  char addr_buf[INET_ADDRSTRLEN];
  char *address_as_string;
  char *port_as_string;
  struct GNUNET_OS_Process *proc;
  const struct IPv4UdpAddress *t4;

  GNUNET_assert(addrlen == sizeof(struct IPv4UdpAddress));
  t4 = (struct IPv4UdpAddress *)addr;

  if (NULL == inet_ntop (AF_INET,
                         &t4->ipv4_addr,
                         addr_buf, INET_ADDRSTRLEN))
    {
      GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "inet_ntop");
      return;
    }
  address_as_string = GNUNET_strdup (addr_buf);
  GNUNET_asprintf(&port_as_string, "%d", plugin->port);
#if DEBUG_UDP
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  _("Running gnunet-nat-client with arguments: %s %s %d\n"), plugin->external_address, address_as_string, plugin->port);
#endif

  /* Start the server process */
  proc = GNUNET_OS_start_process (NULL, NULL, "gnunet-nat-client", "gnunet-nat-client", plugin->external_address, address_as_string, port_as_string, NULL);
  GNUNET_free(address_as_string);
  GNUNET_free(port_as_string);
  if (proc != NULL)
    {
      GNUNET_OS_process_wait (proc);
      GNUNET_OS_process_close (proc);
      proc = NULL;
    }
}

/**
 * Function that can be used by the transport service to transmit
 * a message using the plugin.
 *
 * @param cls closure
 * @param target who should receive this message (ignored by UDP)
 * @param msgbuf one or more GNUNET_MessageHeader(s) strung together
 * @param msgbuf_size the size of the msgbuf to send
 * @param priority how important is the message (ignored by UDP)
 * @param timeout when should we time out (give up) if we can not transmit?
 * @param session identifier used for this session (can be NULL)
 * @param addr the addr to send the message to, needs to be a sockaddr for us
 * @param addrlen the len of addr
 * @param force_address not used, we had better have an address to send to
 *        because we are stateless!!
 * @param cont continuation to call once the message has
 *        been transmitted (or if the transport is ready
 *        for the next transmission call; or if the
 *        peer disconnected...)
 * @param cont_cls closure for cont
 *
 * @return the number of bytes written (may return 0 and the message can
 *         still be transmitted later!)
 */
static ssize_t
udp_plugin_send (void *cls,
		     const struct GNUNET_PeerIdentity *target,
		     const char *msgbuf,
		     size_t msgbuf_size,
		     unsigned int priority,
		     struct GNUNET_TIME_Relative timeout,
		     struct Session *session,
		     const void *addr,
		     size_t addrlen,
		     int force_address,
		     GNUNET_TRANSPORT_TransmitContinuation cont, void *cont_cls)
{
  struct Plugin *plugin = cls;
  ssize_t sent;
  struct MessageQueue *temp_message;
  struct PeerSession *peer_session;
  int other_peer_natd;
  const struct IPv4UdpAddress *t4;

  if (force_address == GNUNET_SYSERR)
    return GNUNET_SYSERR;
  GNUNET_assert (NULL == session);

  other_peer_natd = GNUNET_NO;
  if (addrlen == sizeof(struct IPv4UdpAddress))
    {
      t4 = addr;
      if (ntohs(t4->u_port) == 0)
        other_peer_natd = GNUNET_YES;
    }
  else if (addrlen != sizeof(struct IPv6UdpAddress))
    {
      GNUNET_break_op(0);
      return -1; /* Must have an address to send to */
    }

  sent = 0;
  if ((other_peer_natd == GNUNET_YES) && (plugin->allow_nat == GNUNET_YES))
    {
      peer_session = find_session(plugin, target);
      if (peer_session == NULL) /* We have a new peer to add */
        {
          /*
           * The first time, we can assume we have no knowledge of a
           * working port for this peer, call the ICMP/UDP message sender
           * and wait...
           */
          peer_session = GNUNET_malloc(sizeof(struct PeerSession));
          peer_session->connect_addr = GNUNET_malloc(addrlen);
          memcpy(peer_session->connect_addr, addr, addrlen);
          peer_session->connect_alen = addrlen;
          peer_session->plugin = plugin;
          peer_session->sock = NULL;
          memcpy(&peer_session->target, target, sizeof(struct GNUNET_PeerIdentity));
          peer_session->expecting_welcome = GNUNET_YES;

          peer_session->next = plugin->sessions;
          plugin->sessions = peer_session;

          peer_session->messages = GNUNET_malloc(sizeof(struct MessageQueue));
          peer_session->messages->msgbuf = GNUNET_malloc(msgbuf_size);
          memcpy(peer_session->messages->msgbuf, msgbuf, msgbuf_size);
          peer_session->messages->msgbuf_size = msgbuf_size;
          peer_session->messages->timeout = GNUNET_TIME_relative_to_absolute(timeout);
          peer_session->messages->cont = cont;
          peer_session->messages->cont_cls = cont_cls;
#if DEBUG_UDP
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                          _("Other peer is NAT'd, set up peer session for peer %s\n"), GNUNET_i2s(target));
#endif
          run_gnunet_nat_client(plugin, addr, addrlen);
        }
      else
        {
          if (peer_session->expecting_welcome == GNUNET_NO) /* We are "connected" */
            {
              sent = udp_real_send(cls,
				   peer_session->sock,
				   target,
				   msgbuf, msgbuf_size,
				   priority, timeout,
				   peer_session->connect_addr, peer_session->connect_alen,
				   cont, cont_cls);
            }
          else /* Haven't gotten a response from this peer, queue message */
            {
              temp_message = GNUNET_malloc(sizeof(struct MessageQueue));
              temp_message->msgbuf = GNUNET_malloc(msgbuf_size);
              memcpy(temp_message->msgbuf, msgbuf, msgbuf_size);
              temp_message->msgbuf_size = msgbuf_size;
              temp_message->timeout = GNUNET_TIME_relative_to_absolute(timeout);
              temp_message->cont = cont;
              temp_message->cont_cls = cont_cls;
              temp_message->next = peer_session->messages;
              peer_session->messages = temp_message;
            }
        }
    }
  else if (other_peer_natd == GNUNET_NO) /* Other peer not behind a NAT, so we can just send the message as is */
    {
      sent = udp_real_send(cls,
			   (addrlen == sizeof (struct IPv4UdpAddress)) ? plugin->udp_sockv4.desc : plugin->udp_sockv6.desc,
			   target,
			   msgbuf, msgbuf_size,
			   priority, timeout, addr, addrlen,
			   cont, cont_cls);
    }
  else /* Other peer is NAT'd, but we don't want to play with them (or can't!) */
    {
      return GNUNET_SYSERR;
    }

  /* When GNUNET_SYSERR is returned from udp_real_send, we will still call
   * the callback so must not return GNUNET_SYSERR!
   * If we did, then transport context would get freed twice. */
  if (sent == GNUNET_SYSERR)
    return 0;
  return sent;
}


static void
add_to_address_list (struct Plugin *plugin,
		     const void *arg,
		     size_t arg_size)
{
  struct LocalAddrList *lal;

  lal = plugin->lal_head;
  while (NULL != lal)
    {
      if ( (lal->size == arg_size) &&
	   (0 == memcmp (&lal[1], arg, arg_size)) )
	return;
      lal = lal->next;
    }
  lal = GNUNET_malloc (sizeof (struct LocalAddrList) + arg_size);
  lal->size = arg_size;
  memcpy (&lal[1], arg, arg_size);
  GNUNET_CONTAINER_DLL_insert (plugin->lal_head,
			       plugin->lal_tail,
			       lal);
}


static int
check_local_addr (struct Plugin *plugin,
		  const void *arg,
		  size_t arg_size)
{
  struct LocalAddrList *lal;

  lal = plugin->lal_head;
  while (NULL != lal)
    {
      if ( (lal->size == arg_size) &&
	   (0 == memcmp (&lal[1], arg, arg_size)) )
	return GNUNET_OK;
      lal = lal->next;
    }
  return GNUNET_SYSERR;
}

static int check_localaddress (const struct sockaddr *addr, socklen_t addrlen)
{
	uint32_t res = 0;
	int local = GNUNET_NO;
	int af = addr->sa_family;
    switch (af)
    {
      case AF_INET:
      {
    	  uint32_t netmask = 0x7F000000;
    	  uint32_t address = ntohl (((struct sockaddr_in *) addr)->sin_addr.s_addr);
    	  res = (address >> 24) ^ (netmask >> 24);
    	  if (res != 0)
    		  local = GNUNET_NO;
    	  else
    		  local = GNUNET_YES;
#if DEBUG_UDP
    	    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
    			  "Checking IPv4 address `%s': %s\n", GNUNET_a2s (addr, addrlen), (local==GNUNET_YES) ? "local" : "global");
#endif
    	    break;
      }
      case AF_INET6:
      {
    	   if (IN6_IS_ADDR_LOOPBACK  (&((struct sockaddr_in6 *) addr)->sin6_addr) ||
    		   IN6_IS_ADDR_LINKLOCAL (&((struct sockaddr_in6 *) addr)->sin6_addr))
    		   local = GNUNET_YES;
    	   else
    		   local = GNUNET_NO;
#if DEBUG_UDP
    	   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
    			  "Checking IPv6 address `%s' : %s\n", GNUNET_a2s (addr, addrlen), (local==GNUNET_YES) ? "local" : "global");
#endif
    	   break;
      }
    }
	return local;
}


/**
 * Add the IP of our network interface to the list of
 * our external IP addresses.
 */
static int
process_interfaces (void *cls,
                    const char *name,
                    int isDefault,
                    const struct sockaddr *addr, socklen_t addrlen)
{
  struct Plugin *plugin = cls;
  int af;
  struct IPv4UdpAddress t4;
  struct IPv6UdpAddress t6;
  void *arg;
  uint16_t args;
  void *addr_nat;
  char buf[INET6_ADDRSTRLEN];

  addr_nat = NULL;
  af = addr->sa_family;

  if (plugin->use_localaddresses == GNUNET_NO)
  {
	  if (GNUNET_YES == check_localaddress (addr, addrlen))
	  {
#if DEBUG_UDP
          GNUNET_log_from (GNUNET_ERROR_TYPE_DEBUG,
        	   "udp",
			   "Not notifying transport of address `%s' (local address)\n",
			   GNUNET_a2s (addr, addrlen));
#endif
		  return GNUNET_OK;
	  }
  }

  memset(buf, 0, INET6_ADDRSTRLEN);
  if (af == AF_INET)
    {
      t4.ipv4_addr = ((struct sockaddr_in *) addr)->sin_addr.s_addr;
      GNUNET_assert(NULL != inet_ntop(AF_INET, &t4.ipv4_addr, &buf[0], INET_ADDRSTRLEN));
      if ((plugin->bind6_address != NULL) || ((plugin->bind_address != NULL) && (0 != strcmp(buf, plugin->bind_address))))
        {
          GNUNET_log(GNUNET_ERROR_TYPE_DEBUG, "%s: Not notifying transport of address %s\n", "UDP", GNUNET_a2s (addr, addrlen));
          return GNUNET_OK;
        }
      add_to_address_list (plugin, &t4.ipv4_addr, sizeof (uint32_t));
      if ((plugin->behind_nat == GNUNET_YES) && (plugin->only_nat_addresses == GNUNET_YES))
        {
          t4.u_port = htons (DEFAULT_NAT_PORT);
        }
      else if (plugin->behind_nat == GNUNET_YES) /* We are behind NAT, but will advertise NAT and normal addresses */
        {
          addr_nat = GNUNET_malloc(sizeof(t4));
          t4.u_port = htons (DEFAULT_NAT_PORT);
          memcpy(addr_nat, &t4, sizeof(t4));
          t4.u_port = plugin->port;
        }
      else
        {
          t4.u_port = htons(plugin->port);
        }
      arg = &t4;
      args = sizeof (t4);
    }
  else if (af == AF_INET6)
    {
      if (IN6_IS_ADDR_LINKLOCAL (&((struct sockaddr_in6 *) addr)->sin6_addr))
        {
          /* skip link local addresses */
          return GNUNET_OK;
        }
      memcpy (&t6.ipv6_addr,
              &((struct sockaddr_in6 *) addr)->sin6_addr,
              sizeof (struct in6_addr));
      GNUNET_assert(NULL != inet_ntop(AF_INET6, &t6.ipv6_addr, &buf[0], INET6_ADDRSTRLEN));
      if (((plugin->bind_address != NULL) && (0 != strcmp(buf, plugin->bind_address)))
          || ((plugin->bind6_address != NULL) && (0 != strcmp(buf, plugin->bind6_address))))
        {
          GNUNET_log(GNUNET_ERROR_TYPE_DEBUG, "%s: Not notifying transport of address %s\n", "UDP", GNUNET_a2s (addr, addrlen));
          return GNUNET_OK;
        }
      add_to_address_list (plugin, &t6.ipv6_addr, sizeof (struct in6_addr));
      if ((plugin->behind_nat == GNUNET_YES) && (plugin->only_nat_addresses == GNUNET_YES))
        {
          t6.u6_port = htons (DEFAULT_NAT_PORT);
        }
      else if (plugin->behind_nat == GNUNET_YES)
        {
          addr_nat = GNUNET_malloc(sizeof(t6));
          t6.u6_port = htons (DEFAULT_NAT_PORT);
          memcpy(addr_nat, &t6, sizeof(t6));
          t6.u6_port = plugin->port;
        }
      else
        {
          t6.u6_port = htons (plugin->port);
        }

      arg = &t6;
      args = sizeof (t6);
    }
  else
    {
      GNUNET_break (0);
      return GNUNET_OK;
    }

  GNUNET_log (GNUNET_ERROR_TYPE_INFO |
	      GNUNET_ERROR_TYPE_BULK,
	      _("Found address `%s' (%s)\n"),
	      GNUNET_a2s (addr, addrlen), name);

  if (addr_nat != NULL)
    {
      plugin->env->notify_address (plugin->env->cls,
				   "udp",
				   addr_nat, args, GNUNET_TIME_UNIT_FOREVER_REL);
      GNUNET_log (GNUNET_ERROR_TYPE_INFO |
		  GNUNET_ERROR_TYPE_BULK,
		  _("Found NAT address `%s' (%s)\n"),
		  GNUNET_a2s (addr_nat, args), name);
      GNUNET_free(addr_nat);
    }

  plugin->env->notify_address (plugin->env->cls,
			       "udp",
			       arg, args, GNUNET_TIME_UNIT_FOREVER_REL);
  return GNUNET_OK;
}


/**
 * Function called by the resolver for each address obtained from DNS
 * for our own hostname.  Add the addresses to the list of our
 * external IP addresses.
 *
 * @param cls closure
 * @param addr one of the addresses of the host, NULL for the last address
 * @param addrlen length of the address
 */
static void
process_hostname_ips (void *cls,
                      const struct sockaddr *addr, socklen_t addrlen)
{
  struct Plugin *plugin = cls;

  if (addr == NULL)
    {
      plugin->hostname_dns = NULL;
      return;
    }
  process_interfaces (plugin, "<hostname>", GNUNET_YES, addr, addrlen);
}


/**
 * Send UDP probe messages or UDP keepalive messages, depending on the
 * state of the connection.
 *
 * @param cls closure for this call (should be the main Plugin)
 * @param tc task context for running this
 */
static void
send_udp_probe_message (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct UDP_NAT_Probes *probe = cls;
  struct UDP_NAT_ProbeMessage message;
  struct Plugin *plugin = probe->plugin;

  memset (&message, 0, sizeof (message));
  message.header.size = htons(sizeof(struct UDP_NAT_ProbeMessage));
  message.header.type = htons(GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_NAT_PROBE);
  /* If they gave us a port, use that.  If not, try our port. */
  if (ntohs(probe->addr.u_port) == 0)
    probe->addr.u_port = htons(plugin->port);

#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      _("Sending a probe to port %d\n"), ntohs(probe->addr.u_port));
#endif
  probe->count++;
  udp_real_send(plugin,
		plugin->udp_sockv4.desc,
		NULL,
		(char *)&message, ntohs(message.header.size), 0,
		GNUNET_TIME_relative_get_unit(),
		&probe->addr, sizeof(struct IPv4UdpAddress),
		&udp_probe_continuation, probe);
}


/**
 * Continuation for probe sends.  If the last probe was sent
 * "successfully", schedule sending of another one.  If not,
 *
 */
void
udp_probe_continuation (void *cls, const struct GNUNET_PeerIdentity *target, int result)
{
  struct UDP_NAT_Probes *probe = cls;
  /*struct Plugin *plugin = probe->plugin;*/

  if ((result == GNUNET_OK) && (probe->count < MAX_PROBES))
    {
#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                       _("Scheduling next probe for 10000 milliseconds\n"));
#endif
      probe->task = GNUNET_SCHEDULER_add_delayed(GNUNET_TIME_relative_multiply(GNUNET_TIME_UNIT_MILLISECONDS, 10000), &send_udp_probe_message, probe);
    }
  else /* Destroy the probe context. */
    {
#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      _("Sending probe didn't go well...\n"));
#endif
    }
}

/**
 * Find probe message by address
 *
 * @param plugin the plugin for this transport
 * @param address_string the ip address as a string
 */
struct UDP_NAT_Probes *
find_probe(struct Plugin *plugin, char * address_string)
{
  struct UDP_NAT_Probes *pos;

  pos = plugin->probes;
  while (pos != NULL)
    if (strcmp(pos->address_string, address_string) == 0)
      return pos;

  return pos;
}


/*
 * @param cls the plugin handle
 * @param tc the scheduling context (for rescheduling this function again)
 *
 * We have been notified that gnunet-nat-server has written something to stdout.
 * Handle the output, then reschedule this function to be called again once
 * more is available.
 *
 */
static void
udp_plugin_server_read (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct Plugin *plugin = cls;
  char mybuf[40];
  ssize_t bytes;
  memset(&mybuf, 0, sizeof(mybuf));
  int i;
  struct UDP_NAT_Probes *temp_probe;
  int port;
  char *port_start;
  struct IPv4UdpAddress a4;

  if ( (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN) != 0)
    return;

  bytes = GNUNET_DISK_file_read(plugin->server_stdout_handle, &mybuf, sizeof(mybuf));

  if (bytes < 1)
    {
#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      _("Finished reading from server stdout with code: %d\n"), bytes);
#endif
      return;
    }

  port_start = NULL;
  for (i = 0; i < sizeof(mybuf); i++)
    {
      if (mybuf[i] == '\n')
        mybuf[i] = '\0';

      if ((mybuf[i] == ':') && (i + 1 < sizeof(mybuf)))
        {
          mybuf[i] = '\0';
          port_start = &mybuf[i + 1];
        }
    }

  if (port_start != NULL)
    port = atoi(port_start);
  else
    {
      plugin->server_read_task =
           GNUNET_SCHEDULER_add_read_file (GNUNET_TIME_UNIT_FOREVER_REL,
                                           plugin->server_stdout_handle, &udp_plugin_server_read, plugin);
      return;
    }

#if DEBUG_UDP
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  _("nat-server-read read: %s port %d\n"), &mybuf, port);
#endif

  /**
   * We have received an ICMP response, ostensibly from a non-NAT'd peer
   *  that wants to connect to us! Send a message to establish a connection.
   */
  if (inet_pton(AF_INET, &mybuf[0], &a4.ipv4_addr) != 1)
    {

      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  _("nat-server-read malformed address\n"), &mybuf, port);

      plugin->server_read_task =
          GNUNET_SCHEDULER_add_read_file (GNUNET_TIME_UNIT_FOREVER_REL,
                                          plugin->server_stdout_handle, &udp_plugin_server_read, plugin);
      return;
    }

  temp_probe = find_probe(plugin, &mybuf[0]);

  if (temp_probe == NULL)
    {
      temp_probe = GNUNET_malloc(sizeof(struct UDP_NAT_Probes));
      temp_probe->address_string = strdup(&mybuf[0]);
      GNUNET_assert (1 == inet_pton(AF_INET, &mybuf[0], &temp_probe->addr.ipv4_addr));
      temp_probe->addr.u_port = htons(port);
      temp_probe->next = plugin->probes;
      temp_probe->plugin = plugin;
      temp_probe->task = GNUNET_SCHEDULER_add_delayed(GNUNET_TIME_relative_multiply(GNUNET_TIME_UNIT_MILLISECONDS, 500), &send_udp_probe_message, temp_probe);
      plugin->probes = temp_probe;
    }

  plugin->server_read_task =
       GNUNET_SCHEDULER_add_read_file (GNUNET_TIME_UNIT_FOREVER_REL,
                                       plugin->server_stdout_handle, &udp_plugin_server_read, plugin);

}


/**
 * Demultiplexer for UDP NAT messages
 *
 * @param plugin the main plugin for this transport
 * @param sender from which peer the message was received
 * @param currhdr pointer to the header of the message
 * @param sender_addr the address from which the message was received
 * @param fromlen the length of the address
 * @param sockinfo which socket did we receive the message on
 */
static void
udp_demultiplexer(struct Plugin *plugin, 
		  struct GNUNET_PeerIdentity *sender,
                  const struct GNUNET_MessageHeader *currhdr,
                  const void *sender_addr,
                  size_t fromlen, struct UDP_Sock_Info *sockinfo)
{
  struct UDP_NAT_ProbeMessageReply *outgoing_probe_reply;
  struct UDP_NAT_ProbeMessageConfirmation *outgoing_probe_confirmation;
  char addr_buf[INET_ADDRSTRLEN];
  struct UDP_NAT_Probes *outgoing_probe;
  struct PeerSession *peer_session;
  struct MessageQueue *pending_message;
  struct MessageQueue *pending_message_temp;
  uint16_t incoming_port;
  struct GNUNET_TRANSPORT_ATS_Information distance[2];
  if (memcmp(sender, plugin->env->my_identity, sizeof(struct GNUNET_PeerIdentity)) == 0)
    {
#if DEBUG_UDP
      GNUNET_log_from (GNUNET_ERROR_TYPE_DEBUG, "udp",
                      _("Received a message from myself, dropping!!!\n"));
#endif
      return;
    }

  incoming_port = 0;
  GNUNET_assert(sender_addr != NULL); /* Can recvfrom have a NULL address? */
  if (fromlen == sizeof(struct IPv4UdpAddress))
    {
      incoming_port = ntohs(((struct IPv4UdpAddress *)sender_addr)->u_port);
    }
  else if (fromlen == sizeof(struct IPv6UdpAddress))
    {
      incoming_port = ntohs(((struct IPv6UdpAddress *)sender_addr)->u6_port);
    }

  switch (ntohs(currhdr->type))
  {
    case GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_NAT_PROBE:
      /* Send probe reply */
      outgoing_probe_reply = GNUNET_malloc(sizeof(struct UDP_NAT_ProbeMessageReply));
      outgoing_probe_reply->header.size = htons(sizeof(struct UDP_NAT_ProbeMessageReply));
      outgoing_probe_reply->header.type = htons(GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_NAT_PROBE_REPLY);

#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  _("Received a probe on listen port %d, sent_from port %d\n"),
                   sockinfo->port, incoming_port);
#endif

      udp_real_send(plugin, sockinfo->desc, NULL,
                    (char *)outgoing_probe_reply,
                    ntohs(outgoing_probe_reply->header.size), 0,
                    GNUNET_TIME_relative_get_unit(),
                    sender_addr, fromlen,
                    NULL, NULL);

#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  _("Sent PROBE REPLY to port %d on outgoing port %d\n"),
                   incoming_port, sockinfo->port);
#endif
      GNUNET_free(outgoing_probe_reply);
      break;
    case GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_NAT_PROBE_REPLY:
      /* Check for existing probe, check ports returned, send confirmation if all is well */
#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  _("Received PROBE REPLY from port %d on incoming port %d\n"), incoming_port, sockinfo->port);
#endif
      if (fromlen == sizeof(struct IPv4UdpAddress))
        {
          memset(&addr_buf, 0, sizeof(addr_buf));
          if (NULL == inet_ntop (AF_INET,
				 &((struct IPv4UdpAddress *) sender_addr)->ipv4_addr, addr_buf,
				 INET_ADDRSTRLEN))
	    {
	      GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "inet_ntop");
	      return;
	    }
          outgoing_probe = find_probe(plugin, &addr_buf[0]);
          if (outgoing_probe != NULL)
            {
#if DEBUG_UDP
              GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                          _("Sending confirmation that we were reached!\n"));
#endif
              outgoing_probe_confirmation = GNUNET_malloc(sizeof(struct UDP_NAT_ProbeMessageConfirmation));
              outgoing_probe_confirmation->header.size = htons(sizeof(struct UDP_NAT_ProbeMessageConfirmation));
              outgoing_probe_confirmation->header.type = htons(GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_NAT_PROBE_CONFIRM);
              udp_real_send(plugin, sockinfo->desc, NULL,
			    (char *)outgoing_probe_confirmation,
			    ntohs(outgoing_probe_confirmation->header.size), 0,
			    GNUNET_TIME_relative_get_unit(),
			    sender_addr, fromlen, NULL, NULL);

              if (outgoing_probe->task != GNUNET_SCHEDULER_NO_TASK)
                {
                  GNUNET_SCHEDULER_cancel(outgoing_probe->task);
                  outgoing_probe->task = GNUNET_SCHEDULER_NO_TASK;
                  /* Schedule task to timeout and remove probe if confirmation not received */
                }
              GNUNET_free(outgoing_probe_confirmation);
            }
          else
            {
#if DEBUG_UDP
              GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                          _("Received a probe reply, but have no record of a sent probe!\n"));
#endif
            }
        }
      else
        {
#if DEBUG_UDP
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      _("Received a probe reply, but sender address size is WRONG (should be %d, is %d)!\n"), sizeof(struct IPv4UdpAddress), fromlen);
#endif
        }
      break;
    case GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_NAT_PROBE_CONFIRM:
      peer_session = find_session(plugin, sender);
#if DEBUG_UDP
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      _("Looking up peer session for peer %s\n"), GNUNET_i2s(sender));
#endif
      if (peer_session == NULL) /* Shouldn't this NOT happen? */
        {
#if DEBUG_UDP
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      _("Peer not in list, adding (THIS MAY BE A MISTAKE) %s\n"), GNUNET_i2s(sender));
#endif
          peer_session = GNUNET_malloc(sizeof(struct PeerSession));
          peer_session->connect_addr = GNUNET_malloc(fromlen);
          memcpy(peer_session->connect_addr, sender_addr, fromlen);
          peer_session->connect_alen = fromlen;
          peer_session->plugin = plugin;
          peer_session->sock = sockinfo->desc;
          memcpy(&peer_session->target, sender, sizeof(struct GNUNET_PeerIdentity));
          peer_session->expecting_welcome = GNUNET_NO;

          peer_session->next = plugin->sessions;
          plugin->sessions = peer_session;

          peer_session->messages = NULL;
        }
      else if (peer_session->expecting_welcome == GNUNET_YES)
        {
          peer_session->expecting_welcome = GNUNET_NO;
          peer_session->sock = sockinfo->desc;
          if (peer_session->connect_alen == sizeof(struct IPv4UdpAddress))
            {
              ((struct IPv4UdpAddress *)peer_session->connect_addr)->u_port = htons(incoming_port);
            }
          else if (peer_session->connect_alen == sizeof(struct IPv4UdpAddress))
            {
              ((struct IPv6UdpAddress *)peer_session->connect_addr)->u6_port = htons(incoming_port);
            }

#if DEBUG_UDP
              GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                          _("Received a probe confirmation, will send to peer on port %d\n"), incoming_port);
#endif
          if (peer_session->messages != NULL)
            {
#if DEBUG_UDP
              GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                          _("Received a probe confirmation, sending queued messages.\n"));
#endif
              pending_message = peer_session->messages;
              int count = 0;
              while (pending_message != NULL)
                {
#if DEBUG_UDP
                  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                              _("sending queued message %d\n"), count);
#endif
                  udp_real_send(plugin,
                                peer_session->sock,
                                &peer_session->target,
                                pending_message->msgbuf,
                                pending_message->msgbuf_size, 0,
                                GNUNET_TIME_relative_get_unit(),
                                peer_session->connect_addr,
                                peer_session->connect_alen,
                                pending_message->cont,
                                pending_message->cont_cls);

                  pending_message_temp = pending_message;
                  pending_message = pending_message->next;
                  GNUNET_free(pending_message_temp->msgbuf);
                  GNUNET_free(pending_message_temp);
#if DEBUG_UDP
                  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                              _("finished sending queued message %d\n"), count);
#endif
                  count++;
                }
            }

        }
      else
        {
#if DEBUG_UDP
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      _("Received probe confirmation for already confirmed peer!\n"));
#endif
        }
      /* Received confirmation, add peer with address/port specified */
      break;
    case GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_NAT_PROBE_KEEPALIVE:
      /* Once we've sent NAT_PROBE_CONFIRM change to sending keepalives */
      /* If we receive these just ignore! */
      break;
    default:

#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sending message type %d to transport!\n",
                  ntohs(currhdr->type));
#endif

      distance[0].type = htonl (GNUNET_TRANSPORT_ATS_QUALITY_NET_DISTANCE);
      distance[0].value = htonl (UDP_DIRECT_DISTANCE);
      distance[1].type = htonl (GNUNET_TRANSPORT_ATS_ARRAY_TERMINATOR);
      distance[1].value = htonl (0);

      plugin->env->receive (plugin->env->cls, sender, currhdr,
    		    (const struct GNUNET_TRANSPORT_ATS_Information *) &distance, 2,
			    NULL, sender_addr, fromlen);
  }

}


/*
 * @param cls the plugin handle
 * @param tc the scheduling context (for rescheduling this function again)
 *
 * We have been notified that our writeset has something to read.  We don't
 * know which socket needs to be read, so we have to check each one
 * Then reschedule this function to be called again once more is available.
 *
 */
static void
udp_plugin_select (void *cls,
		   const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct Plugin *plugin = cls;
  char buf[65536];
  struct UDPMessage *msg;
  struct GNUNET_PeerIdentity sender;
  socklen_t fromlen;
  char addr[32];
  ssize_t ret;
  int offset;
  int tsize;
  char *msgbuf;
  const struct GNUNET_MessageHeader *currhdr;
  struct IPv4UdpAddress t4;
  struct IPv6UdpAddress t6;
  const struct sockaddr_in *s4;
  const struct sockaddr_in6 *s6;
  const void *ca;
  size_t calen;
  struct UDP_Sock_Info *udp_sock;
  uint16_t csize;

  plugin->select_task = GNUNET_SCHEDULER_NO_TASK;
  if ( (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN) != 0)
    return;
  udp_sock = NULL;
  if (GNUNET_NETWORK_fdset_isset (tc->read_ready,
				  plugin->udp_sockv4.desc))
    udp_sock = &plugin->udp_sockv4;
  else if (GNUNET_NETWORK_fdset_isset (tc->read_ready,
				       plugin->udp_sockv6.desc))
    udp_sock = &plugin->udp_sockv6;
  if (NULL == udp_sock)
    {
      GNUNET_break (0);
      return;
    }
  fromlen = sizeof (addr);
  memset (&addr, 0, sizeof(addr));
  ret =
    GNUNET_NETWORK_socket_recvfrom (udp_sock->desc, buf, sizeof (buf),
                                    (struct sockaddr *)&addr, &fromlen);

  if (AF_INET == ((struct sockaddr *)addr)->sa_family)
    {
      s4 = (const struct sockaddr_in*) &addr;
      t4.u_port = s4->sin_port;
      t4.ipv4_addr = s4->sin_addr.s_addr;
      ca = &t4;
      calen = sizeof (t4);
    }
  else if (AF_INET6 == ((struct sockaddr *)addr)->sa_family)
    {
      s6 = (const struct sockaddr_in6*) &addr;
      t6.u6_port = s6->sin6_port;
      memcpy (&t6.ipv6_addr,
              &s6->sin6_addr,
              sizeof (struct in6_addr));
      ca = &t6;
      calen = sizeof (t6);
    }
  else
    {
      GNUNET_break (0);
      ca = NULL;
      calen = 0;
    }
  if (ret < sizeof (struct UDPMessage))
    {
      GNUNET_break_op (0);
      plugin->select_task =
	GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
				     GNUNET_SCHEDULER_NO_TASK,
				     GNUNET_TIME_UNIT_FOREVER_REL, plugin->rs,
				     NULL, &udp_plugin_select, plugin);
      return;
    }
  msg = (struct UDPMessage *) buf;
  csize = ntohs (msg->header.size);
  if ( (csize < sizeof (struct UDPMessage)) ||
       (csize > ret) )
    {
      GNUNET_break_op (0);
      plugin->select_task =
	GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
				     GNUNET_SCHEDULER_NO_TASK,
				     GNUNET_TIME_UNIT_FOREVER_REL, plugin->rs,
				     NULL, &udp_plugin_select, plugin);
      return;
    }
  msgbuf = (char *)&msg[1];
  memcpy (&sender, &msg->sender, sizeof (struct GNUNET_PeerIdentity));
  offset = 0;
  tsize = csize - sizeof (struct UDPMessage);
  while (offset + sizeof (struct GNUNET_MessageHeader) <= tsize)
    {
      currhdr = (struct GNUNET_MessageHeader *)&msgbuf[offset];
      csize = ntohs (currhdr->size);
      if ( (csize < sizeof (struct GNUNET_MessageHeader)) ||
	   (csize > tsize - offset) )
	{
	  GNUNET_break_op (0);
	  break;
	}
      udp_demultiplexer(plugin, &sender, currhdr, 
			ca, calen, udp_sock);
      offset += csize;
    }
  plugin->select_task =
    GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
                                 GNUNET_SCHEDULER_NO_TASK,
                                 GNUNET_TIME_UNIT_FOREVER_REL, plugin->rs,
                                 NULL, &udp_plugin_select, plugin);

}

/**
 * Create a slew of UDP sockets.  If possible, use IPv6 and IPv4.
 *
 * @param cls closure for server start, should be a struct Plugin *
 * @return number of sockets created or GNUNET_SYSERR on error
*/
static int
udp_transport_server_start (void *cls)
{
  struct Plugin *plugin = cls;
  struct sockaddr_in serverAddrv4;
  struct sockaddr_in6 serverAddrv6;
  struct sockaddr *serverAddr;
  socklen_t addrlen;
  int sockets_created;
  int tries;


  sockets_created = 0;
  if (plugin->behind_nat == GNUNET_YES)
    {
      /* Pipe to read from started processes stdout (on read end) */
      plugin->server_stdout = GNUNET_DISK_pipe(GNUNET_YES, GNUNET_NO, GNUNET_YES);
      if (plugin->server_stdout == NULL)
        return sockets_created;
#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Starting gnunet-nat-server process cmd: %s %s\n",
                  "gnunet-nat-server",
                  plugin->internal_address);
#endif
      /* Start the server process */
      plugin->server_proc = GNUNET_OS_start_process(NULL,
						   plugin->server_stdout,
						   "gnunet-nat-server",
						   "gnunet-nat-server",
						   plugin->internal_address, NULL);
      if (plugin->server_proc == NULL)
        {
#if DEBUG_UDP
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "Failed to start gnunet-nat-server process\n");
#endif
          return GNUNET_SYSERR;
        }
      /* Close the write end of the read pipe */
      GNUNET_DISK_pipe_close_end(plugin->server_stdout, GNUNET_DISK_PIPE_END_WRITE);

      plugin->server_stdout_handle = GNUNET_DISK_pipe_handle(plugin->server_stdout, GNUNET_DISK_PIPE_END_READ);
      plugin->server_read_task =
	GNUNET_SCHEDULER_add_read_file (GNUNET_TIME_UNIT_FOREVER_REL,
					plugin->server_stdout_handle, &udp_plugin_server_read, plugin);
    }

  if ( (GNUNET_YES !=
	GNUNET_CONFIGURATION_get_value_yesno (plugin->env->cfg, "nat",
					      "DISABLEV6")))
    {
      plugin->udp_sockv6.desc = GNUNET_NETWORK_socket_create (PF_INET6, SOCK_DGRAM, 0);
      if (NULL == plugin->udp_sockv6.desc)
	{
	  GNUNET_log_from (GNUNET_ERROR_TYPE_DEBUG, "udp", "socket");
	}
      else
	{
          memset (&serverAddrv6, 0, sizeof (serverAddrv6));
#if HAVE_SOCKADDR_IN_SIN_LEN
          serverAddrv6.sin6_len = sizeof (serverAddrv6);
#endif

          serverAddrv6.sin6_family = AF_INET6;
          serverAddrv6.sin6_addr = in6addr_any;
          if (plugin->bind6_address != NULL)
            {
              if (1 != inet_pton(AF_INET6, plugin->bind6_address, &serverAddrv6.sin6_addr))
                return 0;
            }

          serverAddrv6.sin6_port = htons (plugin->port);
          addrlen = sizeof (serverAddrv6);
          serverAddr = (struct sockaddr *) &serverAddrv6;
#if DEBUG_UDP
	  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
			   "Binding to IPv6 port %d\n",
			   ntohs(serverAddrv6.sin6_port));
#endif
	  tries = 0;
	  while (GNUNET_NETWORK_socket_bind (plugin->udp_sockv6.desc, serverAddr, addrlen) !=
		 GNUNET_OK)
	    {
	      serverAddrv6.sin6_port = htons (GNUNET_CRYPTO_random_u32(GNUNET_CRYPTO_QUALITY_STRONG, 33537) + 32000); /* Find a good, non-root port */
#if DEBUG_UDP
	      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
			       "IPv6 Binding failed, trying new port %d\n",
			       ntohs(serverAddrv6.sin6_port));
#endif
	      tries++;
	      if (tries > 10)
		{
		  GNUNET_NETWORK_socket_close (plugin->udp_sockv6.desc);
		  plugin->udp_sockv6.desc = NULL;
		  break;
		}	
	    }
	  if (plugin->udp_sockv6.desc != NULL)
	    {
	      plugin->udp_sockv6.port = ntohs(serverAddrv6.sin6_port);
	      sockets_created++;
	    }
	}
    }

  plugin->udp_sockv4.desc = GNUNET_NETWORK_socket_create (PF_INET, SOCK_DGRAM, 0);
  if (NULL == plugin->udp_sockv4.desc)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "socket");
    }
  else
    {
      memset (&serverAddrv4, 0, sizeof (serverAddrv4));
#if HAVE_SOCKADDR_IN_SIN_LEN
      serverAddrv4.sin_len = sizeof (serverAddrv4);
#endif
      serverAddrv4.sin_family = AF_INET;
      serverAddrv4.sin_addr.s_addr = INADDR_ANY;
      if (plugin->bind_address != NULL)
        {
          if (1 != inet_pton(AF_INET, plugin->bind_address, &serverAddrv4.sin_addr))
            return 0;
        }
      serverAddrv4.sin_port = htons (plugin->port);
      addrlen = sizeof (serverAddrv4);
      serverAddr = (struct sockaddr *) &serverAddrv4;
#if DEBUG_UDP
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
		       "Binding to IPv4 port %d\n",
		       ntohs(serverAddrv4.sin_port));
#endif
      tries = 0;
      while (GNUNET_NETWORK_socket_bind (plugin->udp_sockv4.desc, serverAddr, addrlen) !=
	     GNUNET_OK)
	{
	  serverAddrv4.sin_port = htons (GNUNET_CRYPTO_random_u32(GNUNET_CRYPTO_QUALITY_STRONG, 33537) + 32000); /* Find a good, non-root port */
#if DEBUG_UDP
	  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
			   "IPv4 Binding failed, trying new port %d\n",
			   ntohs(serverAddrv4.sin_port));
#endif
	  tries++;
	  if (tries > 10)
	    {
	      GNUNET_NETWORK_socket_close (plugin->udp_sockv4.desc);
	      plugin->udp_sockv4.desc = NULL;
	      break;
	    }	
	}
      if (plugin->udp_sockv4.desc != NULL)
	{
	  plugin->udp_sockv4.port = ntohs(serverAddrv4.sin_port);
	  sockets_created++;
	}
    }

  plugin->rs = GNUNET_NETWORK_fdset_create ();
  GNUNET_NETWORK_fdset_zero (plugin->rs);
  if (NULL != plugin->udp_sockv4.desc)
    GNUNET_NETWORK_fdset_set (plugin->rs,
			      plugin->udp_sockv4.desc);
  if (NULL != plugin->udp_sockv6.desc)
    GNUNET_NETWORK_fdset_set (plugin->rs,
			      plugin->udp_sockv6.desc);

  plugin->select_task =
    GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
                                 GNUNET_SCHEDULER_NO_TASK,
                                 GNUNET_TIME_UNIT_FOREVER_REL, plugin->rs,
                                 NULL, &udp_plugin_select, plugin);
  return sockets_created;
}



/**
 * Check if the given port is plausible (must be either
 * our listen port or our advertised port).  If it is
 * neither, we return GNUNET_SYSERR.
 *
 * @param plugin global variables
 * @param in_port port number to check
 * @return GNUNET_OK if port is either open_port or adv_port
 */
static int
check_port (struct Plugin *plugin, uint16_t in_port)
{
  if ( (plugin->behind_nat == GNUNET_YES) && (in_port == 0) )
    return GNUNET_OK;
  if ( (plugin->only_nat_addresses == GNUNET_YES) &&
       (plugin->behind_nat == GNUNET_YES) )
    return GNUNET_SYSERR; /* odd case... */
  if (in_port == plugin->port)
    return GNUNET_OK;
  return GNUNET_SYSERR;
}


/**
 * Function that will be called to check if a binary address for this
 * plugin is well-formed and corresponds to an address for THIS peer
 * (as per our configuration).  Naturally, if absolutely necessary,
 * plugins can be a bit conservative in their answer, but in general
 * plugins should make sure that the address does not redirect
 * traffic to a 3rd party that might try to man-in-the-middle our
 * traffic.
 *
 * @param cls closure, should be our handle to the Plugin
 * @param addr pointer to the address
 * @param addrlen length of addr
 * @return GNUNET_OK if this is a plausible address for this peer
 *         and transport, GNUNET_SYSERR if not
 *
 */
static int
udp_check_address (void *cls,
		   const void *addr,
		   size_t addrlen)
{
  struct Plugin *plugin = cls;

  const void *sb;
  struct in_addr a4;
  struct in6_addr a6;
  int af;
  struct IPv4UdpAddress *v4;
  struct IPv6UdpAddress *v6;

  if ((addrlen != sizeof (struct IPv4UdpAddress)) &&
      (addrlen != sizeof (struct IPv6UdpAddress)))
    {
      GNUNET_break_op (0);
      return GNUNET_SYSERR;
    }

  if (addrlen == sizeof (struct IPv4UdpAddress))
    {
      v4 = (struct IPv4UdpAddress *) addr;
      if (GNUNET_OK !=
	  check_port (plugin, ntohs (v4->u_port)))
	return GNUNET_SYSERR;
      if (GNUNET_OK !=
	  check_local_addr (plugin, &v4->ipv4_addr, sizeof (uint32_t)))
	return GNUNET_SYSERR;

      af = AF_INET;
      memcpy (&a4, &v4->ipv4_addr, sizeof (a4));
      sb = &a4;
    }
  else
    {
      v6 = (struct IPv6UdpAddress *) addr;
      if (IN6_IS_ADDR_LINKLOCAL (&v6->ipv6_addr))
	{
	  GNUNET_break_op (0);
	  return GNUNET_SYSERR;
	}
      if (GNUNET_OK !=
	  check_port (plugin, ntohs (v6->u6_port)))
	return GNUNET_SYSERR;
      if (GNUNET_OK !=
	  check_local_addr (plugin, &v6->ipv6_addr, sizeof (struct in6_addr)))
	return GNUNET_SYSERR;

      af = AF_INET6;
      memcpy (&a6, &v6->ipv6_addr, sizeof (a6));
      sb = &a6;
    }

  return GNUNET_OK;
}


/**
 * Append our port and forward the result.
 */
static void
append_port (void *cls, const char *hostname)
{
  struct PrettyPrinterContext *ppc = cls;
  char *ret;

  if (hostname == NULL)
    {
      ppc->asc (ppc->asc_cls, NULL);
      GNUNET_free (ppc);
      return;
    }
  GNUNET_asprintf (&ret, "%s:%d", hostname, ppc->port);
  ppc->asc (ppc->asc_cls, ret);
  GNUNET_free (ret);
}


/**
 * Convert the transports address to a nice, human-readable
 * format.
 *
 * @param cls closure
 * @param type name of the transport that generated the address
 * @param addr one of the addresses of the host, NULL for the last address
 *        the specific address format depends on the transport
 * @param addrlen length of the address
 * @param numeric should (IP) addresses be displayed in numeric form?
 * @param timeout after how long should we give up?
 * @param asc function to call on each string
 * @param asc_cls closure for asc
 */
static void
udp_plugin_address_pretty_printer (void *cls,
                                   const char *type,
                                   const void *addr,
                                   size_t addrlen,
                                   int numeric,
                                   struct GNUNET_TIME_Relative timeout,
                                   GNUNET_TRANSPORT_AddressStringCallback asc,
                                   void *asc_cls)
{
  struct Plugin *plugin = cls;
  struct PrettyPrinterContext *ppc;
  const void *sb;
  size_t sbs;
  struct sockaddr_in a4;
  struct sockaddr_in6 a6;
  const struct IPv4UdpAddress *u4;
  const struct IPv6UdpAddress *u6;
  uint16_t port;

  if (addrlen == sizeof (struct IPv6UdpAddress))
    {
      u6 = addr;
      memset (&a6, 0, sizeof (a6));
      a6.sin6_family = AF_INET6;
      a6.sin6_port = u6->u6_port;
      memcpy (&a6.sin6_addr,
              &u6->ipv6_addr,
              sizeof (struct in6_addr));
      port = ntohs (u6->u6_port);
      sb = &a6;
      sbs = sizeof (a6);
    }
  else if (addrlen == sizeof (struct IPv4UdpAddress))
    {
      u4 = addr;
      memset (&a4, 0, sizeof (a4));
      a4.sin_family = AF_INET;
      a4.sin_port = u4->u_port;
      a4.sin_addr.s_addr = u4->ipv4_addr;
      port = ntohs (u4->u_port);
      sb = &a4;
      sbs = sizeof (a4);
    }
  else
    {
      /* invalid address */
      GNUNET_break_op (0);
      asc (asc_cls, NULL);
      return;
    }
  ppc = GNUNET_malloc (sizeof (struct PrettyPrinterContext));
  ppc->asc = asc;
  ppc->asc_cls = asc_cls;
  ppc->port = port;
  GNUNET_RESOLVER_hostname_get (plugin->env->cfg,
                                sb,
                                sbs,
                                !numeric, timeout, &append_port, ppc);
}

/**
 * Return the actual path to a file found in the current
 * PATH environment variable.
 *
 * @param binary the name of the file to find
 */
static char *
get_path_from_PATH (char *binary)
{
  char *path;
  char *pos;
  char *end;
  char *buf;
  const char *p;

  p = getenv ("PATH");
  if (p == NULL)
    return NULL;
  path = GNUNET_strdup (p);     /* because we write on it */
  buf = GNUNET_malloc (strlen (path) + 20);
  pos = path;

  while (NULL != (end = strchr (pos, PATH_SEPARATOR)))
    {
      *end = '\0';
      sprintf (buf, "%s/%s", pos, binary);
      if (GNUNET_DISK_file_test (buf) == GNUNET_YES)
        {
          GNUNET_free (path);
          return buf;
        }
      pos = end + 1;
    }
  sprintf (buf, "%s/%s", pos, binary);
  if (GNUNET_DISK_file_test (buf) == GNUNET_YES)
    {
      GNUNET_free (path);
      return buf;
    }
  GNUNET_free (buf);
  GNUNET_free (path);
  return NULL;
}

/**
 * Check whether the suid bit is set on a file.
 * Attempts to find the file using the current
 * PATH environment variable as a search path.
 *
 * @param binary the name of the file to check
 */
static int
check_gnunet_nat_binary(char *binary)
{
  struct stat statbuf;
  char *p;
#ifdef MINGW
  SOCKET rawsock;
#endif

#ifdef MINGW
  char *binaryexe;
  GNUNET_asprintf (&binaryexe, "%s.exe", binary);
  p = get_path_from_PATH (binaryexe);
  free (binaryexe);
#else
  p = get_path_from_PATH (binary);
#endif
  if (p == NULL)
    return GNUNET_NO;
  if (0 != STAT (p, &statbuf))
    {
      GNUNET_free (p);
      return GNUNET_SYSERR;
    }
  GNUNET_free (p);
#ifndef MINGW
  if ( (0 != (statbuf.st_mode & S_ISUID)) &&
       (statbuf.st_uid == 0) )
    return GNUNET_YES;
  return GNUNET_NO;
#else
  rawsock = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
  if (INVALID_SOCKET == rawsock)
  {
    DWORD err = GetLastError ();
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING, "socket (AF_INET, SOCK_RAW, IPPROTO_ICMP) have failed! GLE = %d\n", err);
    return GNUNET_NO; /* not running as administrator */
  }
  closesocket (rawsock);
  return GNUNET_YES;
#endif
}

/**
 * Function called for a quick conversion of the binary address to
 * a numeric address.  Note that the caller must not free the
 * address and that the next call to this function is allowed
 * to override the address again.
 *
 * @param cls closure
 * @param addr binary address
 * @param addrlen length of the address
 * @return string representing the same address
 */
static const char*
udp_address_to_string (void *cls,
                       const void *addr,
                       size_t addrlen)
{
  static char rbuf[INET6_ADDRSTRLEN + 10];
  char buf[INET6_ADDRSTRLEN];
  const void *sb;
  struct in_addr a4;
  struct in6_addr a6;
  const struct IPv4UdpAddress *t4;
  const struct IPv6UdpAddress *t6;
  int af;
  uint16_t port;

  if (addrlen == sizeof (struct IPv6UdpAddress))
    {
      t6 = addr;
      af = AF_INET6;
      port = ntohs (t6->u6_port);
      memcpy (&a6, &t6->ipv6_addr, sizeof (a6));
      sb = &a6;
    }
  else if (addrlen == sizeof (struct IPv4UdpAddress))
    {
      t4 = addr;
      af = AF_INET;
      port = ntohs (t4->u_port);
      memcpy (&a4, &t4->ipv4_addr, sizeof (a4));
      sb = &a4;
    }
  else
    return NULL;
  inet_ntop (af, sb, buf, INET6_ADDRSTRLEN);
  GNUNET_snprintf (rbuf,
                   sizeof (rbuf),
                   "%s:%u",
                   buf,
                   port);
  return rbuf;
}

/**
 * The exported method. Makes the core api available via a global and
 * returns the udp transport API.
 */
void *
libgnunet_plugin_transport_udp_init (void *cls)
{
  struct GNUNET_TRANSPORT_PluginEnvironment *env = cls;
  unsigned long long mtu;
  unsigned long long port;
  struct GNUNET_TRANSPORT_PluginFunctions *api;
  struct Plugin *plugin;
  int sockets_created;
  int behind_nat;
  int allow_nat;
  int only_nat_addresses;
  int use_localaddresses;
  char *internal_address;
  char *external_address;
  struct IPv4UdpAddress v4_address;

  if (GNUNET_YES == GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
							  "nat",
							  "BEHIND_NAT"))
    {
      /* We are behind nat (according to the user) */
      if (check_gnunet_nat_binary("gnunet-nat-server") == GNUNET_YES)
        behind_nat = GNUNET_YES;
      else
        {
          behind_nat = GNUNET_NO;
          GNUNET_log (GNUNET_ERROR_TYPE_WARNING, "Configuration specified you are behind a NAT, but gnunet-nat-server is not installed properly (suid bit not set)!\n");
        }
    }
  else
    behind_nat = GNUNET_NO; /* We are not behind nat! */

  if (GNUNET_YES == GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
							  "nat",
							  "ALLOW_NAT"))
    {
      if (check_gnunet_nat_binary("gnunet-nat-client") == GNUNET_YES)
        allow_nat = GNUNET_YES; /* We will try to connect to NAT'd peers */
      else
      {
        allow_nat = GNUNET_NO;
        GNUNET_log (GNUNET_ERROR_TYPE_WARNING, "Configuration specified you want to connect to NAT'd peers, but gnunet-nat-client is not installed properly (suid bit not set)!\n");
      }

    }
  else
    allow_nat = GNUNET_NO; /* We don't want to try to help NAT'd peers */

  if (GNUNET_YES == GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
							  "nat",
							  "ONLY_NAT_ADDRESSES"))
    only_nat_addresses = GNUNET_YES; /* We will only report our addresses as NAT'd */
  else
    only_nat_addresses = GNUNET_NO; /* We will report our addresses as NAT'd and non-NAT'd */

  external_address = NULL;
  if (((GNUNET_YES == behind_nat) || (GNUNET_YES == allow_nat)) && (GNUNET_OK !=
         GNUNET_CONFIGURATION_get_value_string (env->cfg,
                                                "nat",
                                                "EXTERNAL_ADDRESS",
                                                &external_address)))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _("Require EXTERNAL_ADDRESS in section `%s' in configuration (either BEHIND_NAT or ALLOW_NAT set to YES)!\n"),
                  "nat");
      return NULL;
    }

  if ((external_address != NULL) && (inet_pton(AF_INET, external_address, &v4_address.ipv4_addr) != 1))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING, "Malformed EXTERNAL_ADDRESS %s given in configuration!\n", external_address);
    }

  internal_address = NULL;
  if ((GNUNET_YES == behind_nat) && (GNUNET_OK !=
         GNUNET_CONFIGURATION_get_value_string (env->cfg,
                                                "nat",
                                                "INTERNAL_ADDRESS",
                                                &internal_address)))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
		  _("Require INTERNAL_ADDRESS in section `%s' in configuration!\n"),
		  "nat");
      GNUNET_free_non_null(external_address);
      return NULL;
    }

  if ((internal_address != NULL) && (inet_pton(AF_INET, internal_address, &v4_address.ipv4_addr) != 1))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING, "Malformed INTERNAL_ADDRESS %s given in configuration!\n", internal_address);
    }

  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_number (env->cfg,
					     "transport-udp",
					     "PORT",
					     &port))
    port = UDP_NAT_DEFAULT_PORT;
  else if (port > 65535)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  _("Given `%s' option is out of range: %llu > %u\n"),
                  "PORT",
                  port,
                  65535);
      GNUNET_free_non_null(external_address);
      GNUNET_free_non_null(internal_address);
      return NULL;
    }

  mtu = 1240;
  if (mtu < 1200)
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                _("MTU %llu for `%s' is probably too low!\n"), mtu,
                "UDP");

  use_localaddresses = GNUNET_NO;
  if (GNUNET_CONFIGURATION_have_value (env->cfg,
		  "transport-udp", "USE_LOCALADDR"))
    {
      use_localaddresses = GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
								 "transport-udp",
								 "USE_LOCALADDR");
    }

  plugin = GNUNET_malloc (sizeof (struct Plugin));
  plugin->external_address = external_address;
  plugin->internal_address = internal_address;
  plugin->port = port;
  plugin->behind_nat = behind_nat;
  plugin->allow_nat = allow_nat;
  plugin->only_nat_addresses = only_nat_addresses;
  plugin->env = env;
  plugin->use_localaddresses = use_localaddresses;

  api = GNUNET_malloc (sizeof (struct GNUNET_TRANSPORT_PluginFunctions));
  api->cls = plugin;

  api->send = &udp_plugin_send;
  api->disconnect = &udp_disconnect;
  api->address_pretty_printer = &udp_plugin_address_pretty_printer;
  api->address_to_string = &udp_address_to_string;
  api->check_address = &udp_check_address;

  if (GNUNET_YES == GNUNET_CONFIGURATION_get_value_string(env->cfg, "transport-udp", "BINDTO", &plugin->bind_address))
    GNUNET_log(GNUNET_ERROR_TYPE_DEBUG, "Binding udp plugin to specific address: `%s'\n", plugin->bind_address);
  if (GNUNET_YES == GNUNET_CONFIGURATION_get_value_string(env->cfg, "transport-udp", "BINDTO6", &plugin->bind6_address))
    GNUNET_log(GNUNET_ERROR_TYPE_DEBUG, "Binding udp plugin to specific address: `%s'\n", plugin->bind6_address);

  if (plugin->behind_nat == GNUNET_NO)
    {
      GNUNET_OS_network_interfaces_list (&process_interfaces, plugin);
    }

  plugin->hostname_dns = GNUNET_RESOLVER_hostname_resolve (env->cfg,
                                                           AF_UNSPEC,
                                                           HOSTNAME_RESOLVE_TIMEOUT,
                                                           &process_hostname_ips,
                                                           plugin);

  if ((plugin->behind_nat == GNUNET_YES) && (inet_pton(AF_INET, plugin->external_address, &v4_address.ipv4_addr) == 1))
    {
      v4_address.u_port = htons(0);
      plugin->env->notify_address (plugin->env->cls,
                                  "udp",
                                  &v4_address, sizeof(v4_address), GNUNET_TIME_UNIT_FOREVER_REL);
      add_to_address_list (plugin, &v4_address.ipv4_addr, sizeof (uint32_t));
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Notifying plugin of address %s:0\n", plugin->external_address);
    }
  else if ((plugin->external_address != NULL) && (inet_pton(AF_INET, plugin->external_address, &v4_address.ipv4_addr) == 1))
    {
      v4_address.u_port = htons(plugin->port);
      plugin->env->notify_address (plugin->env->cls,
                                  "udp",
                                  &v4_address, sizeof(v4_address), GNUNET_TIME_UNIT_FOREVER_REL);
      add_to_address_list (plugin, &v4_address.ipv4_addr, sizeof (uint32_t));
    }

  sockets_created = udp_transport_server_start (plugin);
  if (sockets_created == 0)
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
		_("Failed to open UDP sockets\n"));
  return api;
}

void *
libgnunet_plugin_transport_udp_done (void *cls)
{
  struct GNUNET_TRANSPORT_PluginFunctions *api = cls;
  struct Plugin *plugin = api->cls;
  struct LocalAddrList *lal;

  udp_transport_server_stop (plugin);
  if (NULL != plugin->hostname_dns)
    {
      GNUNET_RESOLVER_request_cancel (plugin->hostname_dns);
      plugin->hostname_dns = NULL;
    }

  GNUNET_NETWORK_fdset_destroy (plugin->rs);
  while (NULL != (lal = plugin->lal_head))
    {
      GNUNET_CONTAINER_DLL_remove (plugin->lal_head,
				   plugin->lal_tail,
				   lal);
      GNUNET_free (lal);
    }
  GNUNET_free (plugin);
  GNUNET_free (api);
  return NULL;
}

/* end of plugin_transport_udp.c */