adding xu transport

4 files changed, 2517 insertions, 0 deletions

diff --git a/src/include/gnunet_protocols.h b/src/include/gnunet_protocols.h
index c5e45d5c1e..7040f2cbf5 100644
--- a/src/include/gnunet_protocols.h
+++ b/src/include/gnunet_protocols.h
@@ -252,6 +252,12 @@ extern "C"
 #define GNUNET_MESSAGE_TYPE_DV_BOX 53
 
 
+/**
+ * Experimental message type.
+ */
+#define GNUNET_MESSAGE_TYPE_TRANSPORT_XU_MESSAGE 55
+
+
 /*******************************************************************************
  * Transport-UDP message types
  ******************************************************************************/
diff --git a/src/transport/Makefile.am b/src/transport/Makefile.am
index 2b3f81567d..b04b54e7f3 100644
--- a/src/transport/Makefile.am
+++ b/src/transport/Makefile.am
@@ -282,6 +282,7 @@ plugin_LTLIBRARIES = \
   libgnunet_plugin_transport_tcp.la \
   libgnunet_plugin_transport_xt.la \
   libgnunet_plugin_transport_udp.la \
+  libgnunet_plugin_transport_xu.la \
   $(UNIX_PLUGIN_LA) \
   $(HTTP_CLIENT_PLUGIN_LA) \
   $(HTTPS_CLIENT_PLUGIN_LA) \
@@ -367,6 +368,19 @@ libgnunet_plugin_transport_udp_la_LIBADD = \
 libgnunet_plugin_transport_udp_la_LDFLAGS = \
  $(GN_PLUGIN_LDFLAGS)
 
+libgnunet_plugin_transport_xu_la_SOURCES = \
+  plugin_transport_xu.c plugin_transport_xu.h
+libgnunet_plugin_transport_udp_la_LIBADD = \
+  $(top_builddir)/src/hello/libgnunethello.la \
+  $(top_builddir)/src/fragmentation/libgnunetfragmentation.la \
+  $(top_builddir)/src/statistics/libgnunetstatistics.la \
+  $(top_builddir)/src/peerinfo/libgnunetpeerinfo.la \
+  $(top_builddir)/src/nat/libgnunetnatnew.la \
+  $(top_builddir)/src/util/libgnunetutil.la \
+  $(LTLIBINTL)
+libgnunet_plugin_transport_udp_la_LDFLAGS = \
+ $(GN_PLUGIN_LDFLAGS)
+
 libgnunet_plugin_transport_unix_la_SOURCES = \
   plugin_transport_unix.c
 libgnunet_plugin_transport_unix_la_LIBADD = \
diff --git a/src/transport/plugin_transport_xu.c b/src/transport/plugin_transport_xu.c
new file mode 100644
index 0000000000..ea0d3f065d
--- /dev/null
+++ b/src/transport/plugin_transport_xu.c
@@ -0,0 +1,2492 @@
+/*
+ This file is part of GNUnet
+ Copyright (C) 2010-2017 GNUnet e.V.
+
+ 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., 51 Franklin Street, Fifth Floor,
+ Boston, MA 02110-1301, USA.
+ */
+
+/**
+ * @file transport/plugin_transport_xu.c
+ * @brief Implementation of the XU transport protocol
+ * @author Christian Grothoff
+ * @author Nathan Evans
+ * @author Matthias Wachs
+ */
+#include "platform.h"
+#include "plugin_transport_xu.h"
+#include "gnunet_hello_lib.h"
+#include "gnunet_util_lib.h"
+#include "gnunet_fragmentation_lib.h"
+#include "gnunet_nat_service.h"
+#include "gnunet_protocols.h"
+#include "gnunet_resolver_service.h"
+#include "gnunet_signatures.h"
+#include "gnunet_constants.h"
+#include "gnunet_statistics_service.h"
+#include "gnunet_transport_service.h"
+#include "gnunet_transport_plugin.h"
+#include "transport.h"
+
+#define LOG(kind,...) GNUNET_log_from (kind, "transport-xu", __VA_ARGS__)
+
+/**
+ * After how much inactivity should a XU session time out?
+ */
+#define XU_SESSION_TIME_OUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 60)
+
+
+/**
+ * XU Message-Packet header (after defragmentation).
+ */
+struct XUMessage
+{
+  /**
+   * Message header.
+   */
+  struct GNUNET_MessageHeader header;
+
+  /**
+   * Always zero for now.
+   */
+  uint32_t reserved;
+
+  /**
+   * What is the identity of the sender
+   */
+  struct GNUNET_PeerIdentity sender;
+
+};
+
+
+/**
+ * Closure for #append_port().
+ */
+struct PrettyPrinterContext
+{
+  /**
+   * DLL
+   */
+  struct PrettyPrinterContext *next;
+
+  /**
+   * DLL
+   */
+  struct PrettyPrinterContext *prev;
+
+  /**
+   * Our plugin.
+   */
+  struct Plugin *plugin;
+
+  /**
+   * Resolver handle
+   */
+  struct GNUNET_RESOLVER_RequestHandle *resolver_handle;
+
+  /**
+   * Function to call with the result.
+   */
+  GNUNET_TRANSPORT_AddressStringCallback asc;
+
+  /**
+   * Clsoure for @e asc.
+   */
+  void *asc_cls;
+
+  /**
+   * Timeout task
+   */
+  struct GNUNET_SCHEDULER_Task *timeout_task;
+
+  /**
+   * Is this an IPv6 address?
+   */
+  int ipv6;
+
+  /**
+   * Options
+   */
+  uint32_t options;
+
+  /**
+   * Port to add after the IP address.
+   */
+  uint16_t port;
+
+};
+
+
+/**
+ * Session with another peer.
+ */
+struct GNUNET_ATS_Session
+{
+  /**
+   * Which peer is this session for?
+   */
+  struct GNUNET_PeerIdentity target;
+
+  /**
+   * Tokenizer for inbound messages.
+   */
+  struct GNUNET_MessageStreamTokenizer *mst;
+
+  /**
+   * Plugin this session belongs to.
+   */
+  struct Plugin *plugin;
+
+  /**
+   * Session timeout task
+   */
+  struct GNUNET_SCHEDULER_Task *timeout_task;
+
+  /**
+   * When does this session time out?
+   */
+  struct GNUNET_TIME_Absolute timeout;
+
+  /**
+   * What time did we last transmit?
+   */
+  struct GNUNET_TIME_Absolute last_transmit_time;
+
+  /**
+   * expected delay for ACKs
+   */
+  struct GNUNET_TIME_Relative last_expected_ack_delay;
+
+  /**
+   * desired delay between XU messages
+   */
+  struct GNUNET_TIME_Relative last_expected_msg_delay;
+  
+  /**
+   */
+  struct GNUNET_TIME_Relative flow_delay_for_other_peer;
+  struct GNUNET_TIME_Relative flow_delay_from_other_peer;
+
+  /**
+   * Our own address.
+   */
+  struct GNUNET_HELLO_Address *address;
+
+  /**
+   * Number of bytes waiting for transmission to this peer.
+   */
+  unsigned long long bytes_in_queue;
+
+  /**
+   * Number of messages waiting for transmission to this peer.
+   */
+  unsigned int msgs_in_queue;
+
+  /**
+   * Reference counter to indicate that this session is
+   * currently being used and must not be destroyed;
+   * setting @e in_destroy will destroy it as soon as
+   * possible.
+   */
+  unsigned int rc;
+
+  /**
+   * Network type of the address.
+   */
+  enum GNUNET_ATS_Network_Type scope;
+
+  /**
+   * Is this session about to be destroyed (sometimes we cannot
+   * destroy a session immediately as below us on the stack
+   * there might be code that still uses it; in this case,
+   * @e rc is non-zero).
+   */
+  int in_destroy;
+};
+
+
+
+/**
+ * If a session monitor is attached, notify it about the new
+ * session state.
+ *
+ * @param plugin our plugin
+ * @param session session that changed state
+ * @param state new state of the session
+ */
+static void
+notify_session_monitor (struct Plugin *plugin,
+                        struct GNUNET_ATS_Session *session,
+                        enum GNUNET_TRANSPORT_SessionState state)
+{
+  struct GNUNET_TRANSPORT_SessionInfo info;
+
+  if (NULL == plugin->sic)
+    return;
+  if (GNUNET_YES == session->in_destroy)
+    return; /* already destroyed, just RC>0 left-over actions */
+  memset (&info,
+          0,
+          sizeof (info));
+  info.state = state;
+  info.is_inbound = GNUNET_SYSERR; /* hard to say */
+  info.num_msg_pending = session->msgs_in_queue;
+  info.num_bytes_pending = session->bytes_in_queue;
+  /* info.receive_delay remains zero as this is not supported by XU
+     (cannot selectively not receive from 'some' peer while continuing
+     to receive from others) */
+  info.session_timeout = session->timeout;
+  info.address = session->address;
+  plugin->sic (plugin->sic_cls,
+               session,
+               &info);
+}
+
+
+/**
+ * Return information about the given session to the monitor callback.
+ *
+ * @param cls the `struct Plugin` with the monitor callback (`sic`)
+ * @param peer peer we send information about
+ * @param value our `struct GNUNET_ATS_Session` to send information about
+ * @return #GNUNET_OK (continue to iterate)
+ */
+static int
+send_session_info_iter (void *cls,
+                        const struct GNUNET_PeerIdentity *peer,
+                        void *value)
+{
+  struct Plugin *plugin = cls;
+  struct GNUNET_ATS_Session *session = value;
+
+  (void) peer;
+  notify_session_monitor (plugin,
+                          session,
+                          GNUNET_TRANSPORT_SS_INIT);
+  notify_session_monitor (plugin,
+                          session,
+                          GNUNET_TRANSPORT_SS_UP);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Begin monitoring sessions of a plugin.  There can only
+ * be one active monitor per plugin (i.e. if there are
+ * multiple monitors, the transport service needs to
+ * multiplex the generated events over all of them).
+ *
+ * @param cls closure of the plugin
+ * @param sic callback to invoke, NULL to disable monitor;
+ *            plugin will being by iterating over all active
+ *            sessions immediately and then enter monitor mode
+ * @param sic_cls closure for @a sic
+ */
+static void
+xu_plugin_setup_monitor (void *cls,
+                          GNUNET_TRANSPORT_SessionInfoCallback sic,
+                          void *sic_cls)
+{
+  struct Plugin *plugin = cls;
+
+  plugin->sic = sic;
+  plugin->sic_cls = sic_cls;
+  if (NULL != sic)
+  {
+    GNUNET_CONTAINER_multipeermap_iterate (plugin->sessions,
+                                           &send_session_info_iter,
+                                           plugin);
+    /* signal end of first iteration */
+    sic (sic_cls,
+         NULL,
+         NULL);
+  }
+}
+
+
+/* ****************** Little Helpers ****************** */
+
+
+/**
+ * Function to free last resources associated with a session.
+ *
+ * @param s session to free
+ */
+static void
+free_session (struct GNUNET_ATS_Session *s)
+{
+  if (NULL != s->address)
+  {
+    GNUNET_HELLO_address_free (s->address);
+    s->address = NULL;
+  }
+  if (NULL != s->mst)
+  {
+    GNUNET_MST_destroy (s->mst);
+    s->mst = NULL;
+  }
+  GNUNET_free (s);
+}
+
+
+/**
+ * Function that is called to get the keepalive factor.
+ * #GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT is divided by this number to
+ * calculate the interval between keepalive packets.
+ *
+ * @param cls closure with the `struct Plugin`
+ * @return keepalive factor
+ */
+static unsigned int
+xu_query_keepalive_factor (void *cls)
+{
+  (void) cls;
+  return 15;
+}
+
+
+/**
+ * Function obtain the network type for a session
+ *
+ * @param cls closure (`struct Plugin *`)
+ * @param session the session
+ * @return the network type
+ */
+static enum GNUNET_ATS_Network_Type
+xu_plugin_get_network (void *cls,
+		       struct GNUNET_ATS_Session *session)
+{
+  (void) cls;
+  return session->scope;
+}
+
+
+/**
+ * Function obtain the network type for an address.
+ *
+ * @param cls closure (`struct Plugin *`)
+ * @param address the address
+ * @return the network type
+ */
+static enum GNUNET_ATS_Network_Type
+xu_plugin_get_network_for_address (void *cls,
+				   const struct GNUNET_HELLO_Address *address)
+{
+  struct Plugin *plugin = cls;
+  size_t addrlen;
+  struct sockaddr_in a4;
+  struct sockaddr_in6 a6;
+  const struct IPv4XuAddress *u4;
+  const struct IPv6XuAddress *u6;
+  const void *sb;
+  size_t sbs;
+
+  addrlen = address->address_length;
+  if (addrlen == sizeof(struct IPv6XuAddress))
+  {
+    GNUNET_assert (NULL != address->address); /* make static analysis happy */
+    u6 = address->address;
+    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 = u6->u6_port;
+    GNUNET_memcpy (&a6.sin6_addr, &u6->ipv6_addr, sizeof(struct in6_addr));
+    sb = &a6;
+    sbs = sizeof(a6);
+  }
+  else if (addrlen == sizeof(struct IPv4XuAddress))
+  {
+    GNUNET_assert (NULL != address->address); /* make static analysis happy */
+    u4 = address->address;
+    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 = u4->u4_port;
+    a4.sin_addr.s_addr = u4->ipv4_addr;
+    sb = &a4;
+    sbs = sizeof(a4);
+  }
+  else
+  {
+    GNUNET_break (0);
+    return GNUNET_ATS_NET_UNSPECIFIED;
+  }
+  return plugin->env->get_address_type (plugin->env->cls,
+                                        sb,
+                                        sbs);
+}
+
+
+/* ******************* Event loop ******************** */
+
+/**
+ * We have been notified that our readset 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.
+ *
+ * @param cls the plugin handle
+ */
+static void
+xu_plugin_select_v4 (void *cls);
+
+
+/**
+ * We have been notified that our readset 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.
+ *
+ * @param cls the plugin handle
+ */
+static void
+xu_plugin_select_v6 (void *cls);
+
+
+/**
+ * (re)schedule IPv4-select tasks for this plugin.
+ *
+ * @param plugin plugin to reschedule
+ */
+static void
+schedule_select_v4 (struct Plugin *plugin)
+{
+  if ( (GNUNET_YES != plugin->enable_ipv4) ||
+       (NULL == plugin->sockv4) )
+    return;
+  if (NULL != plugin->select_task_v4)
+    GNUNET_SCHEDULER_cancel (plugin->select_task_v4);
+  plugin->select_task_v4
+    = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+				     plugin->sockv4,
+				     &xu_plugin_select_v4,
+				     plugin);
+}
+
+
+/**
+ * (re)schedule IPv6-select tasks for this plugin.
+ *
+ * @param plugin plugin to reschedule
+ */
+static void
+schedule_select_v6 (struct Plugin *plugin)
+{
+  if ( (GNUNET_YES != plugin->enable_ipv6) ||
+       (NULL == plugin->sockv6) )
+    return;
+  if (NULL != plugin->select_task_v6)
+    GNUNET_SCHEDULER_cancel (plugin->select_task_v6);
+  plugin->select_task_v6
+    = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+				     plugin->sockv6,
+				     &xu_plugin_select_v6,
+				     plugin);
+}
+
+
+/* ******************* Address to string and back ***************** */
+
+
+/**
+ * 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 (a `union XuAddress`)
+ * @param addrlen length of the @a addr
+ * @return string representing the same address
+ */
+const char *
+xu_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 IPv4XuAddress *t4;
+  const struct IPv6XuAddress *t6;
+  int af;
+  uint16_t port;
+  uint32_t options;
+
+  (void) cls;
+  if (NULL == addr)
+  {
+    GNUNET_break_op (0);
+    return NULL;
+  }
+
+  if (addrlen == sizeof(struct IPv6XuAddress))
+  {
+    t6 = addr;
+    af = AF_INET6;
+    options = ntohl (t6->options);
+    port = ntohs (t6->u6_port);
+    a6 = t6->ipv6_addr;
+    sb = &a6;
+  }
+  else if (addrlen == sizeof(struct IPv4XuAddress))
+  {
+    t4 = addr;
+    af = AF_INET;
+    options = ntohl (t4->options);
+    port = ntohs (t4->u4_port);
+    a4.s_addr = t4->ipv4_addr;
+    sb = &a4;
+  }
+  else
+  {
+    GNUNET_break_op (0);
+    return NULL;
+  }
+  inet_ntop (af,
+             sb,
+             buf,
+             INET6_ADDRSTRLEN);
+  GNUNET_snprintf (rbuf,
+                   sizeof(rbuf),
+                   (af == AF_INET6)
+                   ? "%s.%u.[%s]:%u"
+                   : "%s.%u.%s:%u",
+                   PLUGIN_NAME,
+                   options,
+                   buf,
+                   port);
+  return rbuf;
+}
+
+
+/**
+ * Function called to convert a string address to a binary address.
+ *
+ * @param cls closure (`struct Plugin *`)
+ * @param addr string address
+ * @param addrlen length of the address
+ * @param buf location to store the buffer
+ * @param added location to store the number of bytes in the buffer.
+ *        If the function returns #GNUNET_SYSERR, its contents are undefined.
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure
+ */
+static int
+xu_string_to_address (void *cls,
+		      const char *addr,
+		      uint16_t addrlen,
+		      void **buf,
+		      size_t *added)
+{
+  struct sockaddr_storage socket_address;
+  char *address;
+  char *plugin;
+  char *optionstr;
+  uint32_t options;
+
+  (void) cls;
+  /* Format tcp.options.address:port */
+  address = NULL;
+  plugin = NULL;
+  optionstr = NULL;
+
+  if ((NULL == addr) || (0 == addrlen))
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  if ('\0' != addr[addrlen - 1])
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  if (strlen (addr) + 1 != (size_t) addrlen)
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  plugin = GNUNET_strdup (addr);
+  optionstr = strchr (plugin, '.');
+  if (NULL == optionstr)
+  {
+    GNUNET_break (0);
+    GNUNET_free (plugin);
+    return GNUNET_SYSERR;
+  }
+  optionstr[0] = '\0';
+  optionstr++;
+  options = atol (optionstr);
+  address = strchr (optionstr, '.');
+  if (NULL == address)
+  {
+    GNUNET_break (0);
+    GNUNET_free (plugin);
+    return GNUNET_SYSERR;
+  }
+  address[0] = '\0';
+  address++;
+
+  if (GNUNET_OK !=
+      GNUNET_STRINGS_to_address_ip (address,
+                                    strlen (address),
+                                    &socket_address))
+  {
+    GNUNET_break (0);
+    GNUNET_free (plugin);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_free(plugin);
+
+  switch (socket_address.ss_family)
+  {
+  case AF_INET:
+    {
+      struct IPv4XuAddress *u4;
+      const struct sockaddr_in *in4 = (const struct sockaddr_in *) &socket_address;
+
+      u4 = GNUNET_new (struct IPv4XuAddress);
+      u4->options = htonl (options);
+      u4->ipv4_addr = in4->sin_addr.s_addr;
+      u4->u4_port = in4->sin_port;
+      *buf = u4;
+      *added = sizeof (struct IPv4XuAddress);
+      return GNUNET_OK;
+    }
+  case AF_INET6:
+    {
+      struct IPv6XuAddress *u6;
+      const struct sockaddr_in6 *in6 = (const struct sockaddr_in6 *) &socket_address;
+
+      u6 = GNUNET_new (struct IPv6XuAddress);
+      u6->options = htonl (options);
+      u6->ipv6_addr = in6->sin6_addr;
+      u6->u6_port = in6->sin6_port;
+      *buf = u6;
+      *added = sizeof (struct IPv6XuAddress);
+      return GNUNET_OK;
+    }
+  default:
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+}
+
+
+/**
+ * Append our port and forward the result.
+ *
+ * @param cls a `struct PrettyPrinterContext *`
+ * @param hostname result from DNS resolver
+ */
+static void
+append_port (void *cls,
+             const char *hostname)
+{
+  struct PrettyPrinterContext *ppc = cls;
+  struct Plugin *plugin = ppc->plugin;
+  char *ret;
+
+  if (NULL == hostname)
+  {
+    /* Final call, done */
+    GNUNET_CONTAINER_DLL_remove (plugin->ppc_dll_head,
+                                 plugin->ppc_dll_tail,
+                                 ppc);
+    ppc->resolver_handle = NULL;
+    ppc->asc (ppc->asc_cls,
+              NULL,
+              GNUNET_OK);
+    GNUNET_free (ppc);
+    return;
+  }
+  if (GNUNET_YES == ppc->ipv6)
+    GNUNET_asprintf (&ret,
+                     "%s.%u.[%s]:%d",
+                     PLUGIN_NAME,
+                     ppc->options,
+                     hostname,
+                     ppc->port);
+  else
+    GNUNET_asprintf (&ret,
+                     "%s.%u.%s:%d",
+                     PLUGIN_NAME,
+                     ppc->options,
+                     hostname,
+                     ppc->port);
+  ppc->asc (ppc->asc_cls,
+            ret,
+            GNUNET_OK);
+  GNUNET_free (ret);
+}
+
+
+/**
+ * Convert the transports address to a nice, human-readable format.
+ *
+ * @param cls closure with the `struct Plugin *`
+ * @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;
+ *        a `union XuAddress`
+ * @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 @a asc
+ */
+static void
+xu_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 struct sockaddr *sb;
+  size_t sbs;
+  struct sockaddr_in a4;
+  struct sockaddr_in6 a6;
+  const struct IPv4XuAddress *u4;
+  const struct IPv6XuAddress *u6;
+  uint16_t port;
+  uint32_t options;
+
+  (void) type;
+  if (addrlen == sizeof(struct IPv6XuAddress))
+  {
+    u6 = addr;
+    memset (&a6,
+            0,
+            sizeof (a6));
+    a6.sin6_family = AF_INET6;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    a6.sin6_len = sizeof (a6);
+#endif
+    a6.sin6_port = u6->u6_port;
+    a6.sin6_addr = u6->ipv6_addr;
+    port = ntohs (u6->u6_port);
+    options = ntohl (u6->options);
+    sb = (const struct sockaddr *) &a6;
+    sbs = sizeof (a6);
+  }
+  else if (addrlen == sizeof (struct IPv4XuAddress))
+  {
+    u4 = addr;
+    memset (&a4,
+            0,
+            sizeof(a4));
+    a4.sin_family = AF_INET;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    a4.sin_len = sizeof (a4);
+#endif
+    a4.sin_port = u4->u4_port;
+    a4.sin_addr.s_addr = u4->ipv4_addr;
+    port = ntohs (u4->u4_port);
+    options = ntohl (u4->options);
+    sb = (const struct sockaddr *) &a4;
+    sbs = sizeof(a4);
+  }
+  else
+  {
+    /* invalid address */
+    GNUNET_break_op (0);
+    asc (asc_cls,
+         NULL,
+         GNUNET_SYSERR);
+    asc (asc_cls,
+         NULL,
+         GNUNET_OK);
+    return;
+  }
+  ppc = GNUNET_new (struct PrettyPrinterContext);
+  ppc->plugin = plugin;
+  ppc->asc = asc;
+  ppc->asc_cls = asc_cls;
+  ppc->port = port;
+  ppc->options = options;
+  if (addrlen == sizeof (struct IPv6XuAddress))
+    ppc->ipv6 = GNUNET_YES;
+  else
+    ppc->ipv6 = GNUNET_NO;
+  GNUNET_CONTAINER_DLL_insert (plugin->ppc_dll_head,
+                               plugin->ppc_dll_tail,
+                               ppc);
+  ppc->resolver_handle
+    = GNUNET_RESOLVER_hostname_get (sb,
+                                    sbs,
+                                    ! numeric,
+                                    timeout,
+                                    &append_port,
+                                    ppc);
+}
+
+
+/**
+ * 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 our open or advertised port
+ */
+static int
+check_port (const struct Plugin *plugin,
+            uint16_t in_port)
+{
+  if ( (plugin->port == in_port) ||
+       (plugin->aport == in_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 a `union XuAddress`
+ * @param addrlen length of @a addr
+ * @return #GNUNET_OK if this is a plausible address for this peer
+ *         and transport, #GNUNET_SYSERR if not
+ */
+static int
+xu_plugin_check_address (void *cls,
+			 const void *addr,
+			 size_t addrlen)
+{
+  struct Plugin *plugin = cls;
+  const struct IPv4XuAddress *v4;
+  const struct IPv6XuAddress *v6;
+
+  if (sizeof(struct IPv4XuAddress) == addrlen)
+  {
+    struct sockaddr_in s4;
+
+    v4 = (const struct IPv4XuAddress *) addr;
+    if (GNUNET_OK != check_port (plugin,
+                                 ntohs (v4->u4_port)))
+      return GNUNET_SYSERR;
+    memset (&s4, 0, sizeof (s4));
+    s4.sin_family = AF_INET;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    s4.sin_len = sizeof (s4);
+#endif
+    s4.sin_port = v4->u4_port;
+    s4.sin_addr.s_addr = v4->ipv4_addr;
+
+    if (GNUNET_OK !=
+	GNUNET_NAT_test_address (plugin->nat,
+				 &s4,
+				 sizeof (struct sockaddr_in)))
+      return GNUNET_SYSERR;
+  }
+  else if (sizeof(struct IPv6XuAddress) == addrlen)
+  {
+    struct sockaddr_in6 s6;
+
+    v6 = (const struct IPv6XuAddress *) addr;
+    if (IN6_IS_ADDR_LINKLOCAL (&v6->ipv6_addr))
+      return GNUNET_OK; /* plausible, if unlikely... */
+    memset (&s6, 0, sizeof (s6));
+    s6.sin6_family = AF_INET6;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    s6.sin6_len = sizeof (s6);
+#endif
+    s6.sin6_port = v6->u6_port;
+    s6.sin6_addr = v6->ipv6_addr;
+
+    if (GNUNET_OK !=
+	GNUNET_NAT_test_address (plugin->nat,
+				 &s6,
+				 sizeof(struct sockaddr_in6)))
+      return GNUNET_SYSERR;
+  }
+  else
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Our external IP address/port mapping has changed.
+ *
+ * @param cls closure, the `struct Plugin`
+ * @param add_remove #GNUNET_YES to mean the new public IP address,
+ *                   #GNUNET_NO to mean the previous (now invalid) one
+ * @param ac address class the address belongs to
+ * @param addr either the previous or the new public IP address
+ * @param addrlen actual length of the @a addr
+ */
+static void
+xu_nat_port_map_callback (void *cls,
+                           int add_remove,
+			   enum GNUNET_NAT_AddressClass ac,
+                           const struct sockaddr *addr,
+                           socklen_t addrlen)
+{
+  struct Plugin *plugin = cls;
+  struct GNUNET_HELLO_Address *address;
+  struct IPv4XuAddress u4;
+  struct IPv6XuAddress u6;
+  void *arg;
+  size_t args;
+
+  if (GNUNET_NAT_AC_LOOPBACK == ac)
+    return;
+  if (GNUNET_NAT_AC_LAN == ac)
+    return;
+  if (GNUNET_NAT_AC_LAN_PRIVATE == ac)
+    return;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       (GNUNET_YES == add_remove)
+       ? "NAT notification to add address `%s'\n"
+       : "NAT notification to remove address `%s'\n",
+       GNUNET_a2s (addr,
+                   addrlen));
+  /* convert 'address' to our internal format */
+  switch (addr->sa_family)
+  {
+  case AF_INET:
+    {
+      const struct sockaddr_in *i4;
+
+      GNUNET_assert (sizeof(struct sockaddr_in) == addrlen);
+      i4 = (const struct sockaddr_in *) addr;
+      if (0 == ntohs (i4->sin_port))
+        return; /* Port = 0 means unmapped, ignore these for XU. */
+      memset (&u4,
+              0,
+              sizeof(u4));
+      u4.options = htonl (plugin->myoptions);
+      u4.ipv4_addr = i4->sin_addr.s_addr;
+      u4.u4_port = i4->sin_port;
+      arg = &u4;
+      args = sizeof (struct IPv4XuAddress);
+      break;
+    }
+  case AF_INET6:
+    {
+      const struct sockaddr_in6 *i6;
+
+      GNUNET_assert (sizeof(struct sockaddr_in6) == addrlen);
+      i6 = (const struct sockaddr_in6 *) addr;
+      if (0 == ntohs (i6->sin6_port))
+        return; /* Port = 0 means unmapped, ignore these for XU. */
+      memset (&u6,
+              0,
+              sizeof(u6));
+      u6.options = htonl (plugin->myoptions);
+      u6.ipv6_addr = i6->sin6_addr;
+      u6.u6_port = i6->sin6_port;
+      arg = &u6;
+      args = sizeof (struct IPv6XuAddress);
+      break;
+    }
+  default:
+    GNUNET_break (0);
+    return;
+  }
+  /* modify our published address list */
+  /* TODO: use 'ac' here in the future... */
+  address = GNUNET_HELLO_address_allocate (plugin->env->my_identity,
+                                           PLUGIN_NAME,
+                                           arg,
+                                           args,
+                                           GNUNET_HELLO_ADDRESS_INFO_NONE);
+  plugin->env->notify_address (plugin->env->cls,
+                               add_remove,
+                               address);
+  GNUNET_HELLO_address_free (address);
+}
+
+
+/* ********************* Finding sessions ******************* */
+
+
+/**
+ * Closure for #session_cmp_it().
+ */
+struct GNUNET_ATS_SessionCompareContext
+{
+  /**
+   * Set to session matching the address.
+   */
+  struct GNUNET_ATS_Session *res;
+
+  /**
+   * Address we are looking for.
+   */
+  const struct GNUNET_HELLO_Address *address;
+};
+
+
+/**
+ * Find a session with a matching address.
+ *
+ * @param cls the `struct GNUNET_ATS_SessionCompareContext *`
+ * @param key peer identity (unused)
+ * @param value the `struct GNUNET_ATS_Session *`
+ * @return #GNUNET_NO if we found the session, #GNUNET_OK if not
+ */
+static int
+session_cmp_it (void *cls,
+                const struct GNUNET_PeerIdentity *key,
+                void *value)
+{
+  struct GNUNET_ATS_SessionCompareContext *cctx = cls;
+  struct GNUNET_ATS_Session *s = value;
+
+  (void) key;
+  if (0 == GNUNET_HELLO_address_cmp (s->address,
+                                     cctx->address))
+  {
+    GNUNET_assert (GNUNET_NO == s->in_destroy);
+    cctx->res = s;
+    return GNUNET_NO;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Locate an existing session the transport service is using to
+ * send data to another peer.  Performs some basic sanity checks
+ * on the address and then tries to locate a matching session.
+ *
+ * @param cls the plugin
+ * @param address the address we should locate the session by
+ * @return the session if it exists, or NULL if it is not found
+ */
+static struct GNUNET_ATS_Session *
+xu_plugin_lookup_session (void *cls,
+                           const struct GNUNET_HELLO_Address *address)
+{
+  struct Plugin *plugin = cls;
+  const struct IPv6XuAddress *xu_a6;
+  const struct IPv4XuAddress *xu_a4;
+  struct GNUNET_ATS_SessionCompareContext cctx;
+
+  if (NULL == address->address)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  if (sizeof(struct IPv4XuAddress) == address->address_length)
+  {
+    if (NULL == plugin->sockv4)
+      return NULL;
+    xu_a4 = (const struct IPv4XuAddress *) address->address;
+    if (0 == xu_a4->u4_port)
+    {
+      GNUNET_break (0);
+      return NULL;
+    }
+  }
+  else if (sizeof(struct IPv6XuAddress) == address->address_length)
+  {
+    if (NULL == plugin->sockv6)
+      return NULL;
+    xu_a6 = (const struct IPv6XuAddress *) address->address;
+    if (0 == xu_a6->u6_port)
+    {
+      GNUNET_break (0);
+      return NULL;
+    }
+  }
+  else
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+
+  /* check if session already exists */
+  cctx.address = address;
+  cctx.res = NULL;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Looking for existing session for peer `%s' with address `%s'\n",
+       GNUNET_i2s (&address->peer),
+       xu_address_to_string (plugin,
+                              address->address,
+                              address->address_length));
+  GNUNET_CONTAINER_multipeermap_get_multiple (plugin->sessions,
+                                              &address->peer,
+                                              &session_cmp_it,
+                                              &cctx);
+  if (NULL == cctx.res)
+    return NULL;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Found existing session %p\n",
+       cctx.res);
+  return cctx.res;
+}
+
+
+/* ********************** Timeout ****************** */
+
+
+/**
+ * Increment session timeout due to activity.
+ *
+ * @param s session to reschedule timeout activity for
+ */
+static void
+reschedule_session_timeout (struct GNUNET_ATS_Session *s)
+{
+  if (GNUNET_YES == s->in_destroy)
+    return;
+  GNUNET_assert (NULL != s->timeout_task);
+  s->timeout = GNUNET_TIME_relative_to_absolute (XU_SESSION_TIME_OUT);
+}
+
+
+
+/**
+ * Function that will be called whenever the transport service wants to
+ * notify the plugin that a session is still active and in use and
+ * therefore the session timeout for this session has to be updated
+ *
+ * @param cls closure with the `struct Plugin`
+ * @param peer which peer was the session for
+ * @param session which session is being updated
+ */
+static void
+xu_plugin_update_session_timeout (void *cls,
+                                   const struct GNUNET_PeerIdentity *peer,
+                                   struct GNUNET_ATS_Session *session)
+{
+  struct Plugin *plugin = cls;
+
+  if (GNUNET_YES !=
+      GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessions,
+                                                    peer,
+                                                    session))
+  {
+    GNUNET_break (0);
+    return;
+  }
+  /* Reschedule session timeout */
+  reschedule_session_timeout (session);
+}
+
+
+/* ************************* Sending ************************ */
+
+
+/**
+ * We failed to transmit a message via XU. Generate
+ * a descriptive error message.
+ *
+ * @param plugin our plugin
+ * @param sa target address we were trying to reach
+ * @param slen number of bytes in @a sa
+ * @param error the errno value returned from the sendto() call
+ */
+static void
+analyze_send_error (struct Plugin *plugin,
+                    const struct sockaddr *sa,
+                    socklen_t slen,
+                    int error)
+{
+  enum GNUNET_ATS_Network_Type type;
+
+  type = plugin->env->get_address_type (plugin->env->cls,
+                                        sa,
+                                        slen);
+  if ( ( (GNUNET_ATS_NET_LAN == type) ||
+         (GNUNET_ATS_NET_WAN == type) ) &&
+       ( (ENETUNREACH == errno) ||
+         (ENETDOWN == errno) ) )
+  {
+    if (slen == sizeof (struct sockaddr_in))
+    {
+      /* IPv4: "Network unreachable" or "Network down"
+       *
+       * This indicates we do not have connectivity
+       */
+      LOG (GNUNET_ERROR_TYPE_WARNING | GNUNET_ERROR_TYPE_BULK,
+           _("XU could not transmit message to `%s': "
+             "Network seems down, please check your network configuration\n"),
+           GNUNET_a2s (sa,
+                       slen));
+    }
+    if (slen == sizeof (struct sockaddr_in6))
+    {
+      /* IPv6: "Network unreachable" or "Network down"
+       *
+       * This indicates that this system is IPv6 enabled, but does not
+       * have a valid global IPv6 address assigned or we do not have
+       * connectivity
+       */
+      LOG (GNUNET_ERROR_TYPE_WARNING | GNUNET_ERROR_TYPE_BULK,
+           _("XU could not transmit IPv6 message! "
+             "Please check your network configuration and disable IPv6 if your "
+             "connection does not have a global IPv6 address\n"));
+    }
+  }
+  else
+  {
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "XU could not transmit message to `%s': `%s'\n",
+         GNUNET_a2s (sa,
+                     slen),
+         STRERROR (error));
+  }
+}
+
+
+
+
+/**
+ * Function that can be used by the transport service to transmit a
+ * message using the plugin.  Note that in the case of a peer
+ * disconnecting, the continuation MUST be called prior to the
+ * disconnect notification itself.  This function will be called with
+ * this peer's HELLO message to initiate a fresh connection to another
+ * peer.
+ *
+ * @param cls closure
+ * @param s which session must be used
+ * @param msgbuf the message to transmit
+ * @param msgbuf_size number of bytes in @a msgbuf
+ * @param priority how important is the message (most plugins will
+ *                 ignore message priority and just FIFO)
+ * @param to how long to wait at most for the transmission (does not
+ *                require plugins to discard the message after the timeout,
+ *                just advisory for the desired delay; most plugins will ignore
+ *                this as well)
+ * @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...); can be NULL
+ * @param cont_cls closure for @a cont
+ * @return number of bytes used (on the physical network, with overheads);
+ *         -1 on hard errors (i.e. address invalid); 0 is a legal value
+ *         and does NOT mean that the message was not transmitted (DV)
+ */
+static ssize_t
+xu_plugin_send (void *cls,
+		struct GNUNET_ATS_Session *s,
+		const char *msgbuf,
+		size_t msgbuf_size,
+		unsigned int priority,
+		struct GNUNET_TIME_Relative to,
+		GNUNET_TRANSPORT_TransmitContinuation cont,
+		void *cont_cls)
+{
+  struct Plugin *plugin = cls;
+  size_t xumlen = msgbuf_size + sizeof(struct XUMessage);
+  struct XUMessage *xu;
+  char mbuf[xumlen] GNUNET_ALIGN;
+  ssize_t sent;
+  socklen_t slen;
+  const struct sockaddr *a;
+  const struct IPv4XuAddress *u4;
+  struct sockaddr_in a4;
+  const struct IPv6XuAddress *u6;
+  struct sockaddr_in6 a6;
+  struct GNUNET_NETWORK_Handle *sock;
+
+  (void) priority;
+  (void) to;
+  if ( (sizeof(struct IPv6XuAddress) == s->address->address_length) &&
+       (NULL == plugin->sockv6) )
+    return GNUNET_SYSERR;
+  if ( (sizeof(struct IPv4XuAddress) == s->address->address_length) &&
+       (NULL == plugin->sockv4) )
+    return GNUNET_SYSERR;
+  if (xumlen >= GNUNET_MAX_MESSAGE_SIZE)
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_YES !=
+      GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessions,
+                                                    &s->target,
+                                                    s))
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "XU transmits %u-byte message to `%s' using address `%s'\n",
+       xumlen,
+       GNUNET_i2s (&s->target),
+       xu_address_to_string (plugin,
+                              s->address->address,
+                              s->address->address_length));
+  xu = (struct XUMessage *) mbuf;
+  xu->header.size = htons (xumlen);
+  xu->header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_XU_MESSAGE);
+  xu->reserved = htonl (0);
+  xu->sender = *plugin->env->my_identity;
+  GNUNET_memcpy (&xu[1],
+		 msgbuf,
+		 msgbuf_size);
+  
+  if (sizeof (struct IPv4XuAddress) == s->address->address_length)
+  {
+    u4 = s->address->address;
+    memset (&a4,
+	    0,
+	    sizeof(a4));
+    a4.sin_family = AF_INET;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    a4.sin_len = sizeof (a4);
+#endif
+    a4.sin_port = u4->u4_port;
+    a4.sin_addr.s_addr = u4->ipv4_addr;
+    a = (const struct sockaddr *) &a4;
+    slen = sizeof (a4);
+    sock = plugin->sockv4;
+  }
+  else if (sizeof (struct IPv6XuAddress) == s->address->address_length)
+  {
+    u6 = s->address->address;
+    memset (&a6,
+	    0,
+	    sizeof(a6));
+    a6.sin6_family = AF_INET6;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    a6.sin6_len = sizeof (a6);
+#endif
+    a6.sin6_port = u6->u6_port;
+    a6.sin6_addr = u6->ipv6_addr;
+    a = (const struct sockaddr *) &a6;
+    slen = sizeof (a6);
+    sock = plugin->sockv6;
+  }
+  else
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+    
+  sent = GNUNET_NETWORK_socket_sendto (sock,
+				       mbuf,
+				       xumlen,
+				       a,
+				       slen);
+  s->last_transmit_time
+    = GNUNET_TIME_absolute_max (GNUNET_TIME_absolute_get (),
+				s->last_transmit_time);
+  
+  if (GNUNET_SYSERR == sent)
+  {
+    /* Failure */
+    analyze_send_error (plugin,
+			a,
+			slen,
+			errno);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+			      "# XU, total, bytes, sent, failure",
+			      sent,
+			      GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+			      "# XU, total, messages, sent, failure",
+			      1,
+			      GNUNET_NO);
+    return GNUNET_SYSERR;
+  }
+  /* Success */
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "XU transmitted %u-byte message to  `%s' `%s' (%d: %s)\n",
+       (unsigned int) (msgbuf_size),
+       GNUNET_i2s (&s->target),
+       GNUNET_a2s (a,
+		   slen),
+       (int ) sent,
+       (sent < 0) ? STRERROR (errno) : "ok");
+  GNUNET_STATISTICS_update (plugin->env->stats,
+			    "# XU, total, bytes, sent, success",
+			    sent,
+			    GNUNET_NO);
+  GNUNET_STATISTICS_update (plugin->env->stats,
+			    "# XU, total, messages, sent, success",
+			    1,
+			    GNUNET_NO);
+  cont (cont_cls,
+	&s->target,
+	GNUNET_OK,
+	msgbuf_size,
+	xumlen);
+  notify_session_monitor (s->plugin,
+                          s,
+                          GNUNET_TRANSPORT_SS_UPDATE);
+  return xumlen;
+}
+
+
+/* ********************** Receiving ********************** */
+
+
+/**
+ * Functions with this signature are called whenever we need to close
+ * a session due to a disconnect or failure to establish a connection.
+ *
+ * @param cls closure with the `struct Plugin`
+ * @param s session to close down
+ * @return #GNUNET_OK on success
+ */
+static int
+xu_disconnect_session (void *cls,
+                        struct GNUNET_ATS_Session *s)
+{
+  struct Plugin *plugin = cls;
+
+  GNUNET_assert (GNUNET_YES != s->in_destroy);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Session %p to peer `%s' at address %s ended\n",
+       s,
+       GNUNET_i2s (&s->target),
+       xu_address_to_string (plugin,
+                              s->address->address,
+                              s->address->address_length));
+  if (NULL != s->timeout_task)
+  {
+    GNUNET_SCHEDULER_cancel (s->timeout_task);
+    s->timeout_task = NULL;
+  }
+  GNUNET_assert (GNUNET_YES ==
+                 GNUNET_CONTAINER_multipeermap_remove (plugin->sessions,
+                                                       &s->target,
+                                                       s));
+  s->in_destroy = GNUNET_YES;
+  notify_session_monitor (s->plugin,
+                          s,
+                          GNUNET_TRANSPORT_SS_DONE);
+  plugin->env->session_end (plugin->env->cls,
+                            s->address,
+                            s);
+  GNUNET_STATISTICS_set (plugin->env->stats,
+                         "# XU sessions active",
+                         GNUNET_CONTAINER_multipeermap_size (plugin->sessions),
+                         GNUNET_NO);
+  if (0 == s->rc)
+    free_session (s);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Message tokenizer has broken up an incomming message. Pass it on
+ * to the service.
+ *
+ * @param cls the `struct GNUNET_ATS_Session *`
+ * @param hdr the actual message
+ * @return #GNUNET_OK (always)
+ */
+static int
+process_inbound_tokenized_messages (void *cls,
+                                    const struct GNUNET_MessageHeader *hdr)
+{
+  struct GNUNET_ATS_Session *session = cls;
+  struct Plugin *plugin = session->plugin;
+
+  if (GNUNET_YES == session->in_destroy)
+    return GNUNET_OK;
+  reschedule_session_timeout (session);
+  session->flow_delay_for_other_peer
+    = plugin->env->receive (plugin->env->cls,
+                            session->address,
+                            session,
+                            hdr);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Destroy a session, plugin is being unloaded.
+ *
+ * @param cls the `struct Plugin`
+ * @param key hash of public key of target peer
+ * @param value a `struct PeerSession *` to clean up
+ * @return #GNUNET_OK (continue to iterate)
+ */
+static int
+disconnect_and_free_it (void *cls,
+                        const struct GNUNET_PeerIdentity *key,
+                        void *value)
+{
+  struct Plugin *plugin = cls;
+
+  (void) key;
+  xu_disconnect_session (plugin,
+			 value);
+  return GNUNET_OK;
+}
+
+
+/**
+ * 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
+ */
+static void
+xu_disconnect (void *cls,
+                const struct GNUNET_PeerIdentity *target)
+{
+  struct Plugin *plugin = cls;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Disconnecting from peer `%s'\n",
+       GNUNET_i2s (target));
+  GNUNET_CONTAINER_multipeermap_get_multiple (plugin->sessions,
+                                              target,
+                                              &disconnect_and_free_it,
+                                              plugin);
+}
+
+
+/**
+ * Session was idle, so disconnect it.
+ *
+ * @param cls the `struct GNUNET_ATS_Session` to time out
+ */
+static void
+session_timeout (void *cls)
+{
+  struct GNUNET_ATS_Session *s = cls;
+  struct Plugin *plugin = s->plugin;
+  struct GNUNET_TIME_Relative left;
+
+  s->timeout_task = NULL;
+  left = GNUNET_TIME_absolute_get_remaining (s->timeout);
+  if (left.rel_value_us > 0)
+  {
+    /* not actually our turn yet, but let's at least update
+       the monitor, it may think we're about to die ... */
+    notify_session_monitor (s->plugin,
+                            s,
+                            GNUNET_TRANSPORT_SS_UPDATE);
+    s->timeout_task = GNUNET_SCHEDULER_add_delayed (left,
+                                                    &session_timeout,
+                                                    s);
+    return;
+  }
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Session %p was idle for %s, disconnecting\n",
+       s,
+       GNUNET_STRINGS_relative_time_to_string (XU_SESSION_TIME_OUT,
+                                               GNUNET_YES));
+  /* call session destroy function */
+  xu_disconnect_session (plugin,
+                          s);
+}
+
+
+/**
+ * Allocate a new session for the given endpoint address.
+ * Note that this function does not inform the service
+ * of the new session, this is the responsibility of the
+ * caller (if needed).
+ *
+ * @param cls the `struct Plugin`
+ * @param address address of the other peer to use
+ * @param network_type network type the address belongs to
+ * @return NULL on error, otherwise session handle
+ */
+static struct GNUNET_ATS_Session *
+xu_plugin_create_session (void *cls,
+                           const struct GNUNET_HELLO_Address *address,
+                           enum GNUNET_ATS_Network_Type network_type)
+{
+  struct Plugin *plugin = cls;
+  struct GNUNET_ATS_Session *s;
+
+  s = GNUNET_new (struct GNUNET_ATS_Session);
+  s->mst = GNUNET_MST_create (&process_inbound_tokenized_messages,
+                              s);
+  s->plugin = plugin;
+  s->address = GNUNET_HELLO_address_copy (address);
+  s->target = address->peer;
+  s->last_transmit_time = GNUNET_TIME_absolute_get ();
+  s->last_expected_ack_delay = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MILLISECONDS,
+                                                              250);
+  s->last_expected_msg_delay = GNUNET_TIME_UNIT_MILLISECONDS;
+  s->flow_delay_from_other_peer = GNUNET_TIME_UNIT_ZERO;
+  s->flow_delay_for_other_peer = GNUNET_TIME_UNIT_ZERO;
+  s->timeout = GNUNET_TIME_relative_to_absolute (XU_SESSION_TIME_OUT);
+  s->timeout_task = GNUNET_SCHEDULER_add_delayed (XU_SESSION_TIME_OUT,
+                                                  &session_timeout,
+                                                  s);
+  s->scope = network_type;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Creating new session %p for peer `%s' address `%s'\n",
+       s,
+       GNUNET_i2s (&address->peer),
+       xu_address_to_string (plugin,
+                              address->address,
+                              address->address_length));
+  GNUNET_assert (GNUNET_OK ==
+                 GNUNET_CONTAINER_multipeermap_put (plugin->sessions,
+                                                    &s->target,
+                                                    s,
+                                                    GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE));
+  GNUNET_STATISTICS_set (plugin->env->stats,
+                         "# XU sessions active",
+                         GNUNET_CONTAINER_multipeermap_size (plugin->sessions),
+                         GNUNET_NO);
+  notify_session_monitor (plugin,
+                          s,
+                          GNUNET_TRANSPORT_SS_INIT);
+  return s;
+}
+
+
+/**
+ * Creates a new outbound session the transport service will use to
+ * send data to the peer.
+ *
+ * @param cls the `struct Plugin *`
+ * @param address the address
+ * @return the session or NULL of max connections exceeded
+ */
+static struct GNUNET_ATS_Session *
+xu_plugin_get_session (void *cls,
+                        const struct GNUNET_HELLO_Address *address)
+{
+  struct Plugin *plugin = cls;
+  struct GNUNET_ATS_Session *s;
+  enum GNUNET_ATS_Network_Type network_type = GNUNET_ATS_NET_UNSPECIFIED;
+  const struct IPv4XuAddress *xu_v4;
+  const struct IPv6XuAddress *xu_v6;
+
+  if (NULL == address)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  if ( (address->address_length != sizeof(struct IPv4XuAddress)) &&
+       (address->address_length != sizeof(struct IPv6XuAddress)) )
+  {
+    GNUNET_break_op (0);
+    return NULL;
+  }
+  if (NULL != (s = xu_plugin_lookup_session (cls,
+                                              address)))
+    return s;
+
+  /* need to create new session */
+  if (sizeof (struct IPv4XuAddress) == address->address_length)
+  {
+    struct sockaddr_in v4;
+
+    xu_v4 = (const struct IPv4XuAddress *) address->address;
+    memset (&v4, '\0', sizeof (v4));
+    v4.sin_family = AF_INET;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    v4.sin_len = sizeof (struct sockaddr_in);
+#endif
+    v4.sin_port = xu_v4->u4_port;
+    v4.sin_addr.s_addr = xu_v4->ipv4_addr;
+    network_type = plugin->env->get_address_type (plugin->env->cls,
+                                                  (const struct sockaddr *) &v4,
+                                                  sizeof (v4));
+  }
+  if (sizeof (struct IPv6XuAddress) == address->address_length)
+  {
+    struct sockaddr_in6 v6;
+
+    xu_v6 = (const struct IPv6XuAddress *) address->address;
+    memset (&v6, '\0', sizeof (v6));
+    v6.sin6_family = AF_INET6;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    v6.sin6_len = sizeof (struct sockaddr_in6);
+#endif
+    v6.sin6_port = xu_v6->u6_port;
+    v6.sin6_addr = xu_v6->ipv6_addr;
+    network_type = plugin->env->get_address_type (plugin->env->cls,
+                                                  (const struct sockaddr *) &v6,
+                                                  sizeof (v6));
+  }
+  GNUNET_break (GNUNET_ATS_NET_UNSPECIFIED != network_type);
+  return xu_plugin_create_session (cls,
+				    address,
+				    network_type);
+}
+
+
+/**
+ * We've received a XU Message.  Process it (pass contents to main service).
+ *
+ * @param plugin plugin context
+ * @param msg the message
+ * @param xu_addr sender address
+ * @param xu_addr_len number of bytes in @a xu_addr
+ * @param network_type network type the address belongs to
+ */
+static void
+process_xu_message (struct Plugin *plugin,
+                     const struct XUMessage *msg,
+                     const union XuAddress *xu_addr,
+                     size_t xu_addr_len,
+                     enum GNUNET_ATS_Network_Type network_type)
+{
+  struct GNUNET_ATS_Session *s;
+  struct GNUNET_HELLO_Address *address;
+
+  GNUNET_break (GNUNET_ATS_NET_UNSPECIFIED != network_type);
+  if (0 != ntohl (msg->reserved))
+  {
+    GNUNET_break_op(0);
+    return;
+  }
+  if (ntohs (msg->header.size)
+      < sizeof(struct GNUNET_MessageHeader) + sizeof(struct XUMessage))
+  {
+    GNUNET_break_op(0);
+    return;
+  }
+
+  address = GNUNET_HELLO_address_allocate (&msg->sender,
+                                           PLUGIN_NAME,
+                                           xu_addr,
+                                           xu_addr_len,
+                                           GNUNET_HELLO_ADDRESS_INFO_NONE);
+  if (NULL ==
+      (s = xu_plugin_lookup_session (plugin,
+                                      address)))
+  {
+    s = xu_plugin_create_session (plugin,
+                                   address,
+                                   network_type);
+    plugin->env->session_start (plugin->env->cls,
+                                address,
+                                s,
+                                s->scope);
+    notify_session_monitor (plugin,
+                            s,
+                            GNUNET_TRANSPORT_SS_UP);
+  }
+  GNUNET_free (address);
+
+  s->rc++;
+  GNUNET_MST_from_buffer (s->mst,
+                          (const char *) &msg[1],
+                          ntohs (msg->header.size) - sizeof(struct XUMessage),
+                          GNUNET_YES,
+                          GNUNET_NO);
+  s->rc--;
+  if ( (0 == s->rc) &&
+       (GNUNET_YES == s->in_destroy) )
+    free_session (s);
+}
+
+
+/**
+ * Read and process a message from the given socket.
+ *
+ * @param plugin the overall plugin
+ * @param rsock socket to read from
+ */
+static void
+xu_select_read (struct Plugin *plugin,
+                 struct GNUNET_NETWORK_Handle *rsock)
+{
+  socklen_t fromlen;
+  struct sockaddr_storage addr;
+  char buf[65536] GNUNET_ALIGN;
+  ssize_t size;
+  const struct GNUNET_MessageHeader *msg;
+  struct IPv4XuAddress v4;
+  struct IPv6XuAddress v6;
+  const struct sockaddr *sa;
+  const struct sockaddr_in *sa4;
+  const struct sockaddr_in6 *sa6;
+  const union XuAddress *int_addr;
+  size_t int_addr_len;
+  enum GNUNET_ATS_Network_Type network_type;
+
+  fromlen = sizeof (addr);
+  memset (&addr,
+          0,
+          sizeof(addr));
+  size = GNUNET_NETWORK_socket_recvfrom (rsock,
+                                         buf,
+                                         sizeof (buf),
+                                         (struct sockaddr *) &addr,
+                                         &fromlen);
+  sa = (const struct sockaddr *) &addr;
+#if MINGW
+  /* On SOCK_DGRAM XU sockets recvfrom might fail with a
+   * WSAECONNRESET error to indicate that previous sendto() (yes, sendto!)
+   * on this socket has failed.
+   * Quote from MSDN:
+   *   WSAECONNRESET - The virtual circuit was reset by the remote side
+   *   executing a hard or abortive close. The application should close
+   *   the socket; it is no longer usable. On a XU-datagram socket this
+   *   error indicates a previous send operation resulted in an ICMP Port
+   *   Unreachable message.
+   */
+  if ( (-1 == size) &&
+       (ECONNRESET == errno) )
+    return;
+#endif
+  if (-1 == size)
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "XU failed to receive data: %s\n",
+         STRERROR (errno));
+    /* Connection failure or something. Not a protocol violation. */
+    return;
+  }
+
+  /* Check if this is a STUN packet */
+  if (GNUNET_NO !=
+      GNUNET_NAT_stun_handle_packet (plugin->nat,
+				     (const struct sockaddr *) &addr,
+				     fromlen,
+				     buf,
+				     size))
+    return; /* was STUN, do not process further */
+
+  if (((size_t) size) < sizeof(struct GNUNET_MessageHeader))
+  {
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "XU got %u bytes from %s, which is not enough for a GNUnet message header\n",
+         (unsigned int ) size,
+         GNUNET_a2s (sa,
+                     fromlen));
+    /* _MAY_ be a connection failure (got partial message) */
+    /* But it _MAY_ also be that the other side uses non-GNUnet protocol. */
+    GNUNET_break_op (0);
+    return;
+  }
+
+  msg = (const struct GNUNET_MessageHeader *) buf;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "XU received %u-byte message from `%s' type %u\n",
+       (unsigned int) size,
+       GNUNET_a2s (sa,
+                   fromlen),
+       ntohs (msg->type));
+  if (size != ntohs (msg->size))
+  {
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "XU malformed message (size %u) header from %s\n",
+         (unsigned int) size,
+         GNUNET_a2s (sa,
+                     fromlen));
+    GNUNET_break_op (0);
+    return;
+  }
+  GNUNET_STATISTICS_update (plugin->env->stats,
+                            "# XU, total bytes received",
+                            size,
+                            GNUNET_NO);
+  network_type = plugin->env->get_address_type (plugin->env->cls,
+                                                sa,
+                                                fromlen);
+  switch (sa->sa_family)
+  {
+  case AF_INET:
+    sa4 = (const struct sockaddr_in *) &addr;
+    v4.options = 0;
+    v4.ipv4_addr = sa4->sin_addr.s_addr;
+    v4.u4_port = sa4->sin_port;
+    int_addr = (union XuAddress *) &v4;
+    int_addr_len = sizeof (v4);
+    break;
+  case AF_INET6:
+    sa6 = (const struct sockaddr_in6 *) &addr;
+    v6.options = 0;
+    v6.ipv6_addr = sa6->sin6_addr;
+    v6.u6_port = sa6->sin6_port;
+    int_addr = (union XuAddress *) &v6;
+    int_addr_len = sizeof (v6);
+    break;
+  default:
+    GNUNET_break (0);
+    return;
+  }
+
+  switch (ntohs (msg->type))
+  {
+  case GNUNET_MESSAGE_TYPE_TRANSPORT_XU_MESSAGE:
+    if (ntohs (msg->size) < sizeof(struct XUMessage))
+    {
+      GNUNET_break_op(0);
+      return;
+    }
+    process_xu_message (plugin,
+                         (const struct XUMessage *) msg,
+                         int_addr,
+                         int_addr_len,
+                         network_type);
+    return;
+  default:
+    GNUNET_break_op(0);
+    return;
+  }
+}
+
+
+/* ***************** Event loop (part 2) *************** */
+
+
+/**
+ * We have been notified that our readset 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.
+ *
+ * @param cls the plugin handle
+ */
+static void
+xu_plugin_select_v4 (void *cls)
+{
+  struct Plugin *plugin = cls;
+  const struct GNUNET_SCHEDULER_TaskContext *tc;
+
+  plugin->select_task_v4 = NULL;
+  if (NULL == plugin->sockv4)
+    return;
+  tc = GNUNET_SCHEDULER_get_task_context ();
+  if ( (0 != (tc->reason & GNUNET_SCHEDULER_REASON_READ_READY)) &&
+       (GNUNET_NETWORK_fdset_isset (tc->read_ready,
+				    plugin->sockv4)) )
+    xu_select_read (plugin,
+                     plugin->sockv4);
+  schedule_select_v4 (plugin);
+}
+
+
+/**
+ * We have been notified that our readset 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.
+ *
+ * @param cls the plugin handle
+ */
+static void
+xu_plugin_select_v6 (void *cls)
+{
+  struct Plugin *plugin = cls;
+  const struct GNUNET_SCHEDULER_TaskContext *tc;
+
+  plugin->select_task_v6 = NULL;
+  if (NULL == plugin->sockv6)
+    return;
+  tc = GNUNET_SCHEDULER_get_task_context ();
+  if ( (0 != (tc->reason & GNUNET_SCHEDULER_REASON_READ_READY)) &&
+       (GNUNET_NETWORK_fdset_isset (tc->read_ready,
+                                    plugin->sockv6)) )
+    xu_select_read (plugin,
+                     plugin->sockv6);
+  schedule_select_v6 (plugin);
+}
+
+
+/* ******************* Initialization *************** */
+
+
+/**
+ * Setup the XU sockets (for IPv4 and IPv6) for the plugin.
+ *
+ * @param plugin the plugin to initialize
+ * @param bind_v6 IPv6 address to bind to (can be NULL, for 'any')
+ * @param bind_v4 IPv4 address to bind to (can be NULL, for 'any')
+ * @return number of sockets that were successfully bound
+ */
+static unsigned int
+setup_sockets (struct Plugin *plugin,
+               const struct sockaddr_in6 *bind_v6,
+               const struct sockaddr_in *bind_v4)
+{
+  int tries;
+  unsigned int sockets_created = 0;
+  struct sockaddr_in6 server_addrv6;
+  struct sockaddr_in server_addrv4;
+  const struct sockaddr *server_addr;
+  const struct sockaddr *addrs[2];
+  socklen_t addrlens[2];
+  socklen_t addrlen;
+  int eno;
+
+  /* Create IPv6 socket */
+  eno = EINVAL;
+  if (GNUNET_YES == plugin->enable_ipv6)
+  {
+    plugin->sockv6 = GNUNET_NETWORK_socket_create (PF_INET6,
+                                                   SOCK_DGRAM,
+                                                   0);
+    if (NULL == plugin->sockv6)
+    {
+      LOG (GNUNET_ERROR_TYPE_INFO,
+           _("Disabling IPv6 since it is not supported on this system!\n"));
+      plugin->enable_ipv6 = GNUNET_NO;
+    }
+    else
+    {
+      memset (&server_addrv6,
+              0,
+              sizeof(struct sockaddr_in6));
+#if HAVE_SOCKADDR_IN_SIN_LEN
+      server_addrv6.sin6_len = sizeof (struct sockaddr_in6);
+#endif
+      server_addrv6.sin6_family = AF_INET6;
+      if (NULL != bind_v6)
+        server_addrv6.sin6_addr = bind_v6->sin6_addr;
+      else
+        server_addrv6.sin6_addr = in6addr_any;
+
+      if (0 == plugin->port) /* autodetect */
+        server_addrv6.sin6_port
+          = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                             33537)
+                   + 32000);
+      else
+        server_addrv6.sin6_port = htons (plugin->port);
+      addrlen = sizeof (struct sockaddr_in6);
+      server_addr = (const struct sockaddr *) &server_addrv6;
+
+      tries = 0;
+      while (tries < 10)
+      {
+        LOG(GNUNET_ERROR_TYPE_DEBUG,
+            "Binding to IPv6 `%s'\n",
+            GNUNET_a2s (server_addr,
+                        addrlen));
+        /* binding */
+        if (GNUNET_OK ==
+            GNUNET_NETWORK_socket_bind (plugin->sockv6,
+                                        server_addr,
+                                        addrlen))
+          break;
+        eno = errno;
+        if (0 != plugin->port)
+        {
+          tries = 10; /* fail immediately */
+          break; /* bind failed on specific port */
+        }
+        /* autodetect */
+        server_addrv6.sin6_port
+          = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                             33537)
+                   + 32000);
+        tries++;
+      }
+      if (tries >= 10)
+      {
+        GNUNET_NETWORK_socket_close (plugin->sockv6);
+        plugin->enable_ipv6 = GNUNET_NO;
+        plugin->sockv6 = NULL;
+      }
+      else
+      {
+        plugin->port = ntohs (server_addrv6.sin6_port);
+      }
+      if (NULL != plugin->sockv6)
+      {
+        LOG (GNUNET_ERROR_TYPE_DEBUG,
+             "IPv6 XU socket created listinging at %s\n",
+             GNUNET_a2s (server_addr,
+                         addrlen));
+        addrs[sockets_created] = server_addr;
+        addrlens[sockets_created] = addrlen;
+        sockets_created++;
+      }
+      else
+      {
+        LOG (GNUNET_ERROR_TYPE_WARNING,
+             _("Failed to bind XU socket to %s: %s\n"),
+             GNUNET_a2s (server_addr,
+                         addrlen),
+             STRERROR (eno));
+      }
+    }
+  }
+
+  /* Create IPv4 socket */
+  eno = EINVAL;
+  plugin->sockv4 = GNUNET_NETWORK_socket_create (PF_INET,
+                                                 SOCK_DGRAM,
+                                                 0);
+  if (NULL == plugin->sockv4)
+  {
+    GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
+                         "socket");
+    LOG (GNUNET_ERROR_TYPE_INFO,
+         _("Disabling IPv4 since it is not supported on this system!\n"));
+    plugin->enable_ipv4 = GNUNET_NO;
+  }
+  else
+  {
+    memset (&server_addrv4,
+            0,
+            sizeof(struct sockaddr_in));
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    server_addrv4.sin_len = sizeof (struct sockaddr_in);
+#endif
+    server_addrv4.sin_family = AF_INET;
+    if (NULL != bind_v4)
+      server_addrv4.sin_addr = bind_v4->sin_addr;
+    else
+      server_addrv4.sin_addr.s_addr = INADDR_ANY;
+
+    if (0 == plugin->port)
+      /* autodetect */
+      server_addrv4.sin_port
+        = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                           33537)
+                 + 32000);
+    else
+      server_addrv4.sin_port = htons (plugin->port);
+
+    addrlen = sizeof (struct sockaddr_in);
+    server_addr = (const struct sockaddr *) &server_addrv4;
+
+    tries = 0;
+    while (tries < 10)
+    {
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "Binding to IPv4 `%s'\n",
+           GNUNET_a2s (server_addr,
+                       addrlen));
+
+      /* binding */
+      if (GNUNET_OK ==
+          GNUNET_NETWORK_socket_bind (plugin->sockv4,
+                                      server_addr,
+                                      addrlen))
+        break;
+      eno = errno;
+      if (0 != plugin->port)
+      {
+        tries = 10; /* fail */
+        break; /* bind failed on specific port */
+      }
+
+      /* autodetect */
+      server_addrv4.sin_port
+        = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                           33537)
+                 + 32000);
+      tries++;
+    }
+    if (tries >= 10)
+    {
+      GNUNET_NETWORK_socket_close (plugin->sockv4);
+      plugin->enable_ipv4 = GNUNET_NO;
+      plugin->sockv4 = NULL;
+    }
+    else
+    {
+      plugin->port = ntohs (server_addrv4.sin_port);
+    }
+
+    if (NULL != plugin->sockv4)
+    {
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "IPv4 socket created on port %s\n",
+           GNUNET_a2s (server_addr,
+                       addrlen));
+      addrs[sockets_created] = server_addr;
+      addrlens[sockets_created] = addrlen;
+      sockets_created++;
+    }
+    else
+    {
+      LOG (GNUNET_ERROR_TYPE_ERROR,
+           _("Failed to bind XU socket to %s: %s\n"),
+           GNUNET_a2s (server_addr,
+                       addrlen),
+           STRERROR (eno));
+    }
+  }
+
+  if (0 == sockets_created)
+  {
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         _("Failed to open XU sockets\n"));
+    return 0; /* No sockets created, return */
+  }
+  schedule_select_v4 (plugin);
+  schedule_select_v6 (plugin);
+  plugin->nat = GNUNET_NAT_register (plugin->env->cfg,
+				     "transport-xu",
+				     IPPROTO_UDP,
+                                     sockets_created,
+                                     addrs,
+                                     addrlens,
+                                     &xu_nat_port_map_callback,
+                                     NULL,
+                                     plugin);
+  return sockets_created;
+}
+
+
+/**
+ * The exported method. Makes the core api available via a global and
+ * returns the xu transport API.
+ *
+ * @param cls our `struct GNUNET_TRANSPORT_PluginEnvironment`
+ * @return our `struct GNUNET_TRANSPORT_PluginFunctions`
+ */
+void *
+libgnunet_plugin_transport_xu_init (void *cls)
+{
+  struct GNUNET_TRANSPORT_PluginEnvironment *env = cls;
+  struct GNUNET_TRANSPORT_PluginFunctions *api;
+  struct Plugin *p;
+  unsigned long long port;
+  unsigned long long aport;
+  int enable_v6;
+  char *bind4_address;
+  char *bind6_address;
+  struct sockaddr_in server_addrv4;
+  struct sockaddr_in6 server_addrv6;
+  unsigned int res;
+  int have_bind4;
+  int have_bind6;
+
+  if (NULL == env->receive)
+  {
+    /* run in 'stub' mode (i.e. as part of gnunet-peerinfo), don't fully
+     initialze the plugin or the API */
+    api = GNUNET_new (struct GNUNET_TRANSPORT_PluginFunctions);
+    api->cls = NULL;
+    api->address_pretty_printer = &xu_plugin_address_pretty_printer;
+    api->address_to_string = &xu_address_to_string;
+    api->string_to_address = &xu_string_to_address;
+    return api;
+  }
+
+  /* Get port number: port == 0 : autodetect a port,
+   * > 0 : use this port, not given : 2086 default */
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_number (env->cfg,
+                                             "transport-xu",
+                                             "PORT",
+                                             &port))
+    port = 2086;
+  if (port > 65535)
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               "transport-xu",
+                               "PORT",
+                               _("must be in [0,65535]"));
+    return NULL;
+  }
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_number (env->cfg,
+                                             "transport-xu",
+                                             "ADVERTISED_PORT",
+                                             &aport))
+    aport = port;
+  if (aport > 65535)
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               "transport-xu",
+                               "ADVERTISED_PORT",
+                               _("must be in [0,65535]"));
+    return NULL;
+  }
+
+  if (GNUNET_YES ==
+      GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
+                                            "nat",
+                                            "DISABLEV6"))
+    enable_v6 = GNUNET_NO;
+  else
+    enable_v6 = GNUNET_YES;
+
+  have_bind4 = GNUNET_NO;
+  memset (&server_addrv4,
+          0,
+          sizeof (server_addrv4));
+  if (GNUNET_YES ==
+      GNUNET_CONFIGURATION_get_value_string (env->cfg,
+                                             "transport-xu",
+                                             "BINDTO",
+                                             &bind4_address))
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Binding XU plugin to specific address: `%s'\n",
+         bind4_address);
+    if (1 != inet_pton (AF_INET,
+                        bind4_address,
+                        &server_addrv4.sin_addr))
+    {
+      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                                 "transport-xu",
+                                 "BINDTO",
+                                 _("must be valid IPv4 address"));
+      GNUNET_free (bind4_address);
+      return NULL;
+    }
+    have_bind4 = GNUNET_YES;
+  }
+  GNUNET_free_non_null (bind4_address);
+  have_bind6 = GNUNET_NO;
+  memset (&server_addrv6,
+          0,
+          sizeof (server_addrv6));
+  if (GNUNET_YES ==
+      GNUNET_CONFIGURATION_get_value_string (env->cfg,
+                                             "transport-xu",
+                                             "BINDTO6",
+                                             &bind6_address))
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Binding xu plugin to specific address: `%s'\n",
+         bind6_address);
+    if (1 != inet_pton (AF_INET6,
+                        bind6_address,
+                        &server_addrv6.sin6_addr))
+    {
+      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                                 "transport-xu",
+                                 "BINDTO6",
+                                 _("must be valid IPv6 address"));
+      GNUNET_free (bind6_address);
+      return NULL;
+    }
+    have_bind6 = GNUNET_YES;
+  }
+  GNUNET_free_non_null (bind6_address);
+
+  p = GNUNET_new (struct Plugin);
+  p->port = port;
+  p->aport = aport;
+  p->enable_ipv6 = enable_v6;
+  p->enable_ipv4 = GNUNET_YES; /* default */
+  p->env = env;
+  p->sessions = GNUNET_CONTAINER_multipeermap_create (16,
+                                                      GNUNET_NO);
+  res = setup_sockets (p,
+                       (GNUNET_YES == have_bind6) ? &server_addrv6 : NULL,
+                       (GNUNET_YES == have_bind4) ? &server_addrv4 : NULL);
+  if ( (0 == res) ||
+       ( (NULL == p->sockv4) &&
+         (NULL == p->sockv6) ) )
+  {
+    LOG (GNUNET_ERROR_TYPE_ERROR,
+        _("Failed to create XU network sockets\n"));
+    GNUNET_CONTAINER_multipeermap_destroy (p->sessions);
+    if (NULL != p->nat)
+      GNUNET_NAT_unregister (p->nat);
+    GNUNET_free (p);
+    return NULL;
+  }
+
+  api = GNUNET_new (struct GNUNET_TRANSPORT_PluginFunctions);
+  api->cls = p;
+  api->disconnect_session = &xu_disconnect_session;
+  api->query_keepalive_factor = &xu_query_keepalive_factor;
+  api->disconnect_peer = &xu_disconnect;
+  api->address_pretty_printer = &xu_plugin_address_pretty_printer;
+  api->address_to_string = &xu_address_to_string;
+  api->string_to_address = &xu_string_to_address;
+  api->check_address = &xu_plugin_check_address;
+  api->get_session = &xu_plugin_get_session;
+  api->send = &xu_plugin_send;
+  api->get_network = &xu_plugin_get_network;
+  api->get_network_for_address = &xu_plugin_get_network_for_address;
+  api->update_session_timeout = &xu_plugin_update_session_timeout;
+  api->setup_monitor = &xu_plugin_setup_monitor;
+  return api;
+}
+
+
+/**
+ * The exported method. Makes the core api available via a global and
+ * returns the xu transport API.
+ *
+ * @param cls our `struct GNUNET_TRANSPORT_PluginEnvironment`
+ * @return NULL
+ */
+void *
+libgnunet_plugin_transport_xu_done (void *cls)
+{
+  struct GNUNET_TRANSPORT_PluginFunctions *api = cls;
+  struct Plugin *plugin = api->cls;
+  struct PrettyPrinterContext *cur;
+
+  if (NULL == plugin)
+  {
+    GNUNET_free (api);
+    return NULL;
+  }
+  if (NULL != plugin->select_task_v4)
+  {
+    GNUNET_SCHEDULER_cancel (plugin->select_task_v4);
+    plugin->select_task_v4 = NULL;
+  }
+  if (NULL != plugin->select_task_v6)
+  {
+    GNUNET_SCHEDULER_cancel (plugin->select_task_v6);
+    plugin->select_task_v6 = NULL;
+  }
+  if (NULL != plugin->sockv4)
+  {
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_NETWORK_socket_close (plugin->sockv4));
+    plugin->sockv4 = NULL;
+  }
+  if (NULL != plugin->sockv6)
+  {
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_NETWORK_socket_close (plugin->sockv6));
+    plugin->sockv6 = NULL;
+  }
+  if (NULL != plugin->nat)
+  {
+    GNUNET_NAT_unregister (plugin->nat);
+    plugin->nat = NULL;
+  }
+  GNUNET_CONTAINER_multipeermap_destroy (plugin->sessions);
+
+  while (NULL != (cur = plugin->ppc_dll_head))
+  {
+    GNUNET_break (0);
+    GNUNET_CONTAINER_DLL_remove (plugin->ppc_dll_head,
+                                 plugin->ppc_dll_tail,
+                                 cur);
+    GNUNET_RESOLVER_request_cancel (cur->resolver_handle);
+    if (NULL != cur->timeout_task)
+    {
+      GNUNET_SCHEDULER_cancel (cur->timeout_task);
+      cur->timeout_task = NULL;
+    }
+    GNUNET_free (cur);
+  }
+  GNUNET_free (plugin);
+  GNUNET_free (api);
+  return NULL;
+}
+
+/* end of plugin_transport_xu.c */
diff --git a/src/transport/transport.conf.in b/src/transport/transport.conf.in
index a541080ce7..1f56a2fa75 100644
--- a/src/transport/transport.conf.in
+++ b/src/transport/transport.conf.in
@@ -122,6 +122,11 @@ TESTING_IGNORE_KEYS = ACCEPT_FROM;
 # HOLE_EXTERNAL = AUTO:2086
 
 
+[transport-xu]
+# Use PORT = 0 to autodetect a port available
+PORT = 2087
+
+
 [transport-http_client]
 MAX_CONNECTIONS = 128
 TESTING_IGNORE_KEYS = ACCEPT_FROM;