gnunet-service-vpn.c

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/*
     This file is part of GNUnet.
     Copyright (C) 2010, 2011, 2012, 2016, 2017 Christian Grothoff

     GNUnet is free software: you can redistribute it and/or modify it
     under the terms of the GNU Affero General Public License as published
     by the Free Software Foundation, either version 3 of the License,
     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
     Affero General Public License for more details.

     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.

     SPDX-License-Identifier: AGPL3.0-or-later
 */

#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_common.h"
#include "gnunet_protocols.h"
#include "gnunet_applications.h"
#include "gnunet_cadet_service.h"
#include "gnunet_statistics_service.h"
#include "gnunet_constants.h"
#include "gnunet_tun_lib.h"
#include "gnunet_regex_service.h"
#include "vpn.h"
#include "exit.h"


#define MAX_MESSAGE_QUEUE_SIZE 4


struct ChannelState;

struct DestinationEntry;

struct DestinationChannel
{
  struct DestinationChannel *next;

  struct DestinationChannel *prev;

  struct DestinationEntry *destination;

  uint16_t destination_port;
};


struct DestinationEntry
{
  struct GNUNET_HashCode key;

  struct DestinationChannel *dt_head;

  struct DestinationChannel *dt_tail;

  struct GNUNET_CONTAINER_HeapNode *heap_node;

  int is_service;

  union
  {
    struct
    {
      struct GNUNET_HashCode service_descriptor;

      struct GNUNET_PeerIdentity target;
    } service_destination;

    struct
    {
      int af;

      union
      {
        struct in_addr v4;

        struct in6_addr v6;
      } ip;
    } exit_destination;
  } details;
};


struct ChannelMessageQueueEntry
{
  struct ChannelMessageQueueEntry *next;

  struct ChannelMessageQueueEntry *prev;

  size_t len;

  const void *msg;
};


struct ChannelState
{
  struct GNUNET_CADET_Channel *channel;

  struct GNUNET_REGEX_Search *search;

  struct GNUNET_CONTAINER_HeapNode *heap_node;

  struct ChannelMessageQueueEntry *tmq_head;

  struct ChannelMessageQueueEntry *tmq_tail;

  struct DestinationEntry destination;

  int af;

  int is_established;

  unsigned int tmq_length;

  uint8_t protocol;

  union
  {
    struct in_addr v4;

    struct in6_addr v6;
  } source_ip;

  union
  {
    struct in_addr v4;

    struct in6_addr v6;
  } destination_ip;

  uint16_t source_port;

  uint16_t destination_port;
};


static int global_ret;

static const struct GNUNET_CONFIGURATION_Handle *cfg;

static struct GNUNET_CADET_Handle *cadet_handle;

static struct GNUNET_CONTAINER_MultiHashMap *destination_map;

static struct GNUNET_CONTAINER_Heap *destination_heap;

static struct GNUNET_CONTAINER_MultiHashMap *channel_map;

static struct GNUNET_CONTAINER_Heap *channel_heap;

static struct GNUNET_STATISTICS_Handle *stats;

static struct GNUNET_HELPER_Handle *helper_handle;

static char *vpn_argv[7];

static unsigned long long ipv6prefix;

static unsigned long long max_destination_mappings;

static unsigned long long max_channel_mappings;


static void
get_destination_key_from_ip (int af,
                             const void *address,
                             struct GNUNET_HashCode *key)
{
  switch (af)
  {
  case AF_INET:
    GNUNET_CRYPTO_hash (address, sizeof(struct in_addr), key);
    break;

  case AF_INET6:
    GNUNET_CRYPTO_hash (address, sizeof(struct in6_addr), key);
    break;

  default:
    GNUNET_assert (0);
    break;
  }
}


static void
get_channel_key_from_ips (int af,
                          uint8_t protocol,
                          const void *source_ip,
                          uint16_t source_port,
                          const void *destination_ip,
                          uint16_t destination_port,
                          struct GNUNET_HashCode *key)
{
  char *off;

  memset (key, 0, sizeof(struct GNUNET_HashCode));
  /* the GNUnet hashmap only uses the first sizeof(unsigned int) of the hash,
     so we put the ports in there (and hope for few collisions) */
  off = (char *) key;
  GNUNET_memcpy (off, &source_port, sizeof(uint16_t));
  off += sizeof(uint16_t);
  GNUNET_memcpy (off, &destination_port, sizeof(uint16_t));
  off += sizeof(uint16_t);
  switch (af)
  {
  case AF_INET:
    GNUNET_memcpy (off, source_ip, sizeof(struct in_addr));
    off += sizeof(struct in_addr);
    GNUNET_memcpy (off, destination_ip, sizeof(struct in_addr));
    off += sizeof(struct in_addr);
    break;

  case AF_INET6:
    GNUNET_memcpy (off, source_ip, sizeof(struct in6_addr));
    off += sizeof(struct in6_addr);
    GNUNET_memcpy (off, destination_ip, sizeof(struct in6_addr));
    off += sizeof(struct in6_addr);
    break;

  default:
    GNUNET_assert (0);
    break;
  }
  GNUNET_memcpy (off, &protocol, sizeof(uint8_t));
  /* off += sizeof (uint8_t);  */
}


static void
send_client_reply (struct GNUNET_SERVICE_Client *client,
                   uint64_t request_id,
                   int result_af,
                   const void *addr)
{
  struct GNUNET_MQ_Envelope *env;
  struct RedirectToIpResponseMessage *res;
  size_t rlen;

  switch (result_af)
  {
  case AF_INET:
    rlen = sizeof(struct in_addr);
    break;

  case AF_INET6:
    rlen = sizeof(struct in6_addr);
    break;

  case AF_UNSPEC:
    rlen = 0;
    break;

  default:
    GNUNET_assert (0);
    return;
  }
  env = GNUNET_MQ_msg_extra (res, rlen, GNUNET_MESSAGE_TYPE_VPN_CLIENT_USE_IP);
  res->result_af = htonl (result_af);
  res->request_id = request_id;
  GNUNET_memcpy (&res[1], addr, rlen);
  GNUNET_MQ_send (GNUNET_SERVICE_client_get_mq (client), env);
}


static void
free_channel_state (struct ChannelState *ts)
{
  struct GNUNET_HashCode key;
  struct ChannelMessageQueueEntry *tnq;
  struct GNUNET_CADET_Channel *channel;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Cleaning up channel state\n");
  if (NULL != (channel = ts->channel))
  {
    ts->channel = NULL;
    GNUNET_CADET_channel_destroy (channel);
    return;
  }
  GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# Active channels"),
                            -1,
                            GNUNET_NO);
  while (NULL != (tnq = ts->tmq_head))
  {
    GNUNET_CONTAINER_DLL_remove (ts->tmq_head, ts->tmq_tail, tnq);
    ts->tmq_length--;
    GNUNET_free (tnq);
  }
  GNUNET_assert (0 == ts->tmq_length);
  GNUNET_assert (NULL == ts->destination.heap_node);
  if (NULL != ts->search)
  {
    GNUNET_REGEX_search_cancel (ts->search);
    ts->search = NULL;
  }
  if (NULL != ts->heap_node)
  {
    GNUNET_CONTAINER_heap_remove_node (ts->heap_node);
    ts->heap_node = NULL;
    get_channel_key_from_ips (ts->af,
                              ts->protocol,
                              &ts->source_ip,
                              ts->source_port,
                              &ts->destination_ip,
                              ts->destination_port,
                              &key);
    GNUNET_assert (
      GNUNET_YES ==
      GNUNET_CONTAINER_multihashmap_remove (channel_map, &key, ts));
  }
  GNUNET_free (ts);
}


static void
send_to_channel (struct ChannelState *ts, struct GNUNET_MQ_Envelope *env)
{
  struct GNUNET_MQ_Handle *mq;

  GNUNET_assert (NULL != ts->channel);
  mq = GNUNET_CADET_get_mq (ts->channel);
  GNUNET_MQ_env_set_options (env,
                             GNUNET_MQ_PRIO_BEST_EFFORT
                             | GNUNET_MQ_PREF_OUT_OF_ORDER);
  GNUNET_MQ_send (mq, env);
  if (GNUNET_MQ_get_length (mq) > MAX_MESSAGE_QUEUE_SIZE)
  {
    env = GNUNET_MQ_unsent_head (mq);
    GNUNET_assert (NULL != env);
    GNUNET_STATISTICS_update (stats,
                              gettext_noop (
                                "# Messages dropped in cadet queue (overflow)"),
                              1,
                              GNUNET_NO);
    GNUNET_MQ_discard (env);
  }
}


static const char *
print_channel_destination (const struct DestinationEntry *de)
{
  static char dest[256];

  if (de->is_service)
  {
    GNUNET_snprintf (dest,
                     sizeof(dest),
                     "HS: %s-%s",
                     GNUNET_i2s (&de->details.service_destination.target),
                     GNUNET_h2s (
                       &de->details.service_destination.service_descriptor));
  }
  else
  {
    inet_ntop (de->details.exit_destination.af,
               &de->details.exit_destination.ip,
               dest,
               sizeof(dest));
  }
  return dest;
}


static void
channel_cleaner (void *cls, const struct GNUNET_CADET_Channel *channel)
{
  struct ChannelState *ts = cls;

  ts->channel =
    NULL; /* we must not call GNUNET_CADET_channel_destroy() anymore */
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "CADET notified us about death of channel to `%s'\n",
              print_channel_destination (&ts->destination));
  free_channel_state (ts);
}


static void
make_up_icmpv4_payload (struct ChannelState *ts,
                        struct GNUNET_TUN_IPv4Header *ipp,
                        struct GNUNET_TUN_UdpHeader *udp)
{
  GNUNET_TUN_initialize_ipv4_header (ipp,
                                     ts->protocol,
                                     sizeof(struct GNUNET_TUN_TcpHeader),
                                     &ts->source_ip.v4,
                                     &ts->destination_ip.v4);
  udp->source_port = htons (ts->source_port);
  udp->destination_port = htons (ts->destination_port);
  udp->len = htons (0);
  udp->crc = htons (0);
}


static void
make_up_icmpv6_payload (struct ChannelState *ts,
                        struct GNUNET_TUN_IPv6Header *ipp,
                        struct GNUNET_TUN_UdpHeader *udp)
{
  GNUNET_TUN_initialize_ipv6_header (ipp,
                                     ts->protocol,
                                     sizeof(struct GNUNET_TUN_TcpHeader),
                                     &ts->source_ip.v6,
                                     &ts->destination_ip.v6);
  udp->source_port = htons (ts->source_port);
  udp->destination_port = htons (ts->destination_port);
  udp->len = htons (0);
  udp->crc = htons (0);
}


static int
check_icmp_back (void *cls, const struct GNUNET_EXIT_IcmpToVPNMessage *i2v)
{
  struct ChannelState *ts = cls;

  if (NULL == ts->heap_node)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (AF_UNSPEC == ts->af)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
handle_icmp_back (void *cls, const struct GNUNET_EXIT_IcmpToVPNMessage *i2v)
{
  struct ChannelState *ts = cls;
  size_t mlen;

  GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# ICMP packets received from cadet"),
                            1,
                            GNUNET_NO);
  mlen =
    ntohs (i2v->header.size) - sizeof(struct GNUNET_EXIT_IcmpToVPNMessage);
  {
    char sbuf[INET6_ADDRSTRLEN];
    char dbuf[INET6_ADDRSTRLEN];

    GNUNET_log (
      GNUNET_ERROR_TYPE_DEBUG,
      "Received ICMP packet from cadet, sending %u bytes from %s -> %s via TUN\n",
      (unsigned int) mlen,
      inet_ntop (ts->af, &ts->destination_ip, sbuf, sizeof(sbuf)),
      inet_ntop (ts->af, &ts->source_ip, dbuf, sizeof(dbuf)));
  }
  switch (ts->af)
  {
  case AF_INET: {
      size_t size = sizeof(struct GNUNET_TUN_IPv4Header)
                    + sizeof(struct GNUNET_TUN_IcmpHeader)
                    + sizeof(struct GNUNET_MessageHeader)
                    + sizeof(struct GNUNET_TUN_Layer2PacketHeader) + mlen;
      {
        /* reserve some extra space in case we have an ICMP type here where
             we will need to make up the payload ourselves */
        char buf[size + sizeof(struct GNUNET_TUN_IPv4Header) + 8] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun =
          (struct GNUNET_TUN_Layer2PacketHeader *) &msg[1];
        struct GNUNET_TUN_IPv4Header *ipv4 =
          (struct GNUNET_TUN_IPv4Header *) &tun[1];
        struct GNUNET_TUN_IcmpHeader *icmp =
          (struct GNUNET_TUN_IcmpHeader *) &ipv4[1];
        msg->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV4);
        GNUNET_TUN_initialize_ipv4_header (ipv4,
                                           IPPROTO_ICMP,
                                           sizeof(struct GNUNET_TUN_IcmpHeader)
                                           + mlen,
                                           &ts->destination_ip.v4,
                                           &ts->source_ip.v4);
        *icmp = i2v->icmp_header;
        GNUNET_memcpy (&icmp[1], &i2v[1], mlen);
        /* For some ICMP types, we need to adjust (make up) the payload here.
             Also, depending on the AF used on the other side, we have to
             do ICMP PT (translate ICMP types) */
        switch (ntohl (i2v->af))
        {
        case AF_INET:
          switch (icmp->type)
          {
          case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:
          case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:
            break;

          case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
          case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
          case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED: {
              struct GNUNET_TUN_IPv4Header *ipp =
                (struct GNUNET_TUN_IPv4Header *) &icmp[1];
              struct GNUNET_TUN_UdpHeader *udp =
                (struct GNUNET_TUN_UdpHeader *) &ipp[1];

              if (mlen != 0)
              {
                /* sender did not strip ICMP payload? */
                GNUNET_break_op (0);
                return;
              }
              size += sizeof(struct GNUNET_TUN_IPv4Header) + 8;
              GNUNET_assert (8 == sizeof(struct GNUNET_TUN_UdpHeader));
              make_up_icmpv4_payload (ts, ipp, udp);
            }
            break;

          default:
            GNUNET_break_op (0);
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv4 packets dropped (type not allowed)"),
              1,
              GNUNET_NO);
            return;
          }
          /* end AF_INET */
          break;

        case AF_INET6:
          /* ICMP PT 6-to-4 and possibly making up payloads */
          switch (icmp->type)
          {
          case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
            icmp->type = GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE;
            {
              struct GNUNET_TUN_IPv4Header *ipp =
                (struct GNUNET_TUN_IPv4Header *) &icmp[1];
              struct GNUNET_TUN_UdpHeader *udp =
                (struct GNUNET_TUN_UdpHeader *) &ipp[1];

              if (mlen != 0)
              {
                /* sender did not strip ICMP payload? */
                GNUNET_break_op (0);
                return;
              }
              size += sizeof(struct GNUNET_TUN_IPv4Header) + 8;
              GNUNET_assert (8 == sizeof(struct GNUNET_TUN_UdpHeader));
              make_up_icmpv4_payload (ts, ipp, udp);
            }
            break;

          case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
            icmp->type = GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED;
            {
              struct GNUNET_TUN_IPv4Header *ipp =
                (struct GNUNET_TUN_IPv4Header *) &icmp[1];
              struct GNUNET_TUN_UdpHeader *udp =
                (struct GNUNET_TUN_UdpHeader *) &ipp[1];

              if (mlen != 0)
              {
                /* sender did not strip ICMP payload? */
                GNUNET_break_op (0);
                return;
              }
              size += sizeof(struct GNUNET_TUN_IPv4Header) + 8;
              GNUNET_assert (8 == sizeof(struct GNUNET_TUN_UdpHeader));
              make_up_icmpv4_payload (ts, ipp, udp);
            }
            break;

          case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
          case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv6 packets dropped (impossible PT to v4)"),
              1,
              GNUNET_NO);
            return;

          case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
            icmp->type = GNUNET_TUN_ICMPTYPE_ECHO_REQUEST;
            break;

          case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
            icmp->type = GNUNET_TUN_ICMPTYPE_ECHO_REPLY;
            break;

          default:
            GNUNET_break_op (0);
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv6 packets dropped (type not allowed)"),
              1,
              GNUNET_NO);
            return;
          }
          /* end AF_INET6 */
          break;

        default:
          GNUNET_break_op (0);
          return;
        }
        msg->size = htons (size);
        GNUNET_TUN_calculate_icmp_checksum (icmp, &i2v[1], mlen);
        (void) GNUNET_HELPER_send (helper_handle, msg, GNUNET_YES, NULL, NULL);
      }
    }
    break;

  case AF_INET6: {
      size_t size = sizeof(struct GNUNET_TUN_IPv6Header)
                    + sizeof(struct GNUNET_TUN_IcmpHeader)
                    + sizeof(struct GNUNET_MessageHeader)
                    + sizeof(struct GNUNET_TUN_Layer2PacketHeader) + mlen;
      {
        char buf[size + sizeof(struct GNUNET_TUN_IPv6Header) + 8] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun =
          (struct GNUNET_TUN_Layer2PacketHeader *) &msg[1];
        struct GNUNET_TUN_IPv6Header *ipv6 =
          (struct GNUNET_TUN_IPv6Header *) &tun[1];
        struct GNUNET_TUN_IcmpHeader *icmp =
          (struct GNUNET_TUN_IcmpHeader *) &ipv6[1];
        msg->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV6);
        GNUNET_TUN_initialize_ipv6_header (ipv6,
                                           IPPROTO_ICMPV6,
                                           sizeof(struct GNUNET_TUN_IcmpHeader)
                                           + mlen,
                                           &ts->destination_ip.v6,
                                           &ts->source_ip.v6);
        *icmp = i2v->icmp_header;
        GNUNET_memcpy (&icmp[1], &i2v[1], mlen);

        /* For some ICMP types, we need to adjust (make up) the payload here.
             Also, depending on the AF used on the other side, we have to
             do ICMP PT (translate ICMP types) */
        switch (ntohl (i2v->af))
        {
        case AF_INET:
          /* ICMP PT 4-to-6 and possibly making up payloads */
          switch (icmp->type)
          {
          case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:
            icmp->type = GNUNET_TUN_ICMPTYPE6_ECHO_REPLY;
            break;

          case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:
            icmp->type = GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST;
            break;

          case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
            icmp->type = GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE;
            {
              struct GNUNET_TUN_IPv6Header *ipp =
                (struct GNUNET_TUN_IPv6Header *) &icmp[1];
              struct GNUNET_TUN_UdpHeader *udp =
                (struct GNUNET_TUN_UdpHeader *) &ipp[1];

              if (mlen != 0)
              {
                /* sender did not strip ICMP payload? */
                GNUNET_break_op (0);
                return;
              }
              size += sizeof(struct GNUNET_TUN_IPv6Header) + 8;
              GNUNET_assert (8 == sizeof(struct GNUNET_TUN_UdpHeader));
              make_up_icmpv6_payload (ts, ipp, udp);
            }
            break;

          case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED:
            icmp->type = GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED;
            {
              struct GNUNET_TUN_IPv6Header *ipp =
                (struct GNUNET_TUN_IPv6Header *) &icmp[1];
              struct GNUNET_TUN_UdpHeader *udp =
                (struct GNUNET_TUN_UdpHeader *) &ipp[1];

              if (mlen != 0)
              {
                /* sender did not strip ICMP payload? */
                GNUNET_break_op (0);
                return;
              }
              size += sizeof(struct GNUNET_TUN_IPv6Header) + 8;
              GNUNET_assert (8 == sizeof(struct GNUNET_TUN_UdpHeader));
              make_up_icmpv6_payload (ts, ipp, udp);
            }
            break;

          case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv4 packets dropped (impossible PT to v6)"),
              1,
              GNUNET_NO);
            return;

          default:
            GNUNET_break_op (0);
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv4 packets dropped (type not allowed)"),
              1,
              GNUNET_NO);
            return;
          }
          /* end AF_INET */
          break;

        case AF_INET6:
          switch (icmp->type)
          {
          case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
          case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
          case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
          case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM: {
              struct GNUNET_TUN_IPv6Header *ipp =
                (struct GNUNET_TUN_IPv6Header *) &icmp[1];
              struct GNUNET_TUN_UdpHeader *udp =
                (struct GNUNET_TUN_UdpHeader *) &ipp[1];

              if (mlen != 0)
              {
                /* sender did not strip ICMP payload? */
                GNUNET_break_op (0);
                return;
              }
              size += sizeof(struct GNUNET_TUN_IPv6Header) + 8;
              GNUNET_assert (8 == sizeof(struct GNUNET_TUN_UdpHeader));
              make_up_icmpv6_payload (ts, ipp, udp);
            }
            break;

          case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
            break;

          default:
            GNUNET_break_op (0);
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv6 packets dropped (type not allowed)"),
              1,
              GNUNET_NO);
            return;
          }
          /* end AF_INET6 */
          break;

        default:
          GNUNET_break_op (0);
          return;
        }
        msg->size = htons (size);
        GNUNET_TUN_calculate_icmp_checksum (icmp, &i2v[1], mlen);
        (void) GNUNET_HELPER_send (helper_handle, msg, GNUNET_YES, NULL, NULL);
      }
    }
    break;

  default:
    GNUNET_assert (0);
  }
  GNUNET_CONTAINER_heap_update_cost (ts->heap_node,
                                     GNUNET_TIME_absolute_get ().abs_value_us);
  GNUNET_CADET_receive_done (ts->channel);
}


static int
check_udp_back (void *cls, const struct GNUNET_EXIT_UdpReplyMessage *reply)
{
  struct ChannelState *ts = cls;

  if (NULL == ts->heap_node)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (AF_UNSPEC == ts->af)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
handle_udp_back (void *cls, const struct GNUNET_EXIT_UdpReplyMessage *reply)
{
  struct ChannelState *ts = cls;
  size_t mlen;

  GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# UDP packets received from cadet"),
                            1,
                            GNUNET_NO);
  mlen =
    ntohs (reply->header.size) - sizeof(struct GNUNET_EXIT_UdpReplyMessage);
  {
    char sbuf[INET6_ADDRSTRLEN];
    char dbuf[INET6_ADDRSTRLEN];

    GNUNET_log (
      GNUNET_ERROR_TYPE_DEBUG,
      "Received UDP reply from cadet, sending %u bytes from [%s]:%u -> [%s]:%u via TUN\n",
      (unsigned int) mlen,
      inet_ntop (ts->af, &ts->destination_ip, sbuf, sizeof(sbuf)),
      ts->destination_port,
      inet_ntop (ts->af, &ts->source_ip, dbuf, sizeof(dbuf)),
      ts->source_port);
  }
  switch (ts->af)
  {
  case AF_INET: {
      size_t size = sizeof(struct GNUNET_TUN_IPv4Header)
                    + sizeof(struct GNUNET_TUN_UdpHeader)
                    + sizeof(struct GNUNET_MessageHeader)
                    + sizeof(struct GNUNET_TUN_Layer2PacketHeader) + mlen;
      {
        char buf[size] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun =
          (struct GNUNET_TUN_Layer2PacketHeader *) &msg[1];
        struct GNUNET_TUN_IPv4Header *ipv4 =
          (struct GNUNET_TUN_IPv4Header *) &tun[1];
        struct GNUNET_TUN_UdpHeader *udp =
          (struct GNUNET_TUN_UdpHeader *) &ipv4[1];
        msg->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
        msg->size = htons (size);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV4);
        GNUNET_TUN_initialize_ipv4_header (ipv4,
                                           IPPROTO_UDP,
                                           sizeof(struct GNUNET_TUN_UdpHeader)
                                           + mlen,
                                           &ts->destination_ip.v4,
                                           &ts->source_ip.v4);
        if (0 == ntohs (reply->source_port))
          udp->source_port = htons (ts->destination_port);
        else
          udp->source_port = reply->source_port;
        if (0 == ntohs (reply->destination_port))
          udp->destination_port = htons (ts->source_port);
        else
          udp->destination_port = reply->destination_port;
        udp->len = htons (mlen + sizeof(struct GNUNET_TUN_UdpHeader));
        GNUNET_TUN_calculate_udp4_checksum (ipv4, udp, &reply[1], mlen);
        GNUNET_memcpy (&udp[1], &reply[1], mlen);
        (void) GNUNET_HELPER_send (helper_handle, msg, GNUNET_YES, NULL, NULL);
      }
    }
    break;

  case AF_INET6: {
      size_t size = sizeof(struct GNUNET_TUN_IPv6Header)
                    + sizeof(struct GNUNET_TUN_UdpHeader)
                    + sizeof(struct GNUNET_MessageHeader)
                    + sizeof(struct GNUNET_TUN_Layer2PacketHeader) + mlen;
      {
        char buf[size] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun =
          (struct GNUNET_TUN_Layer2PacketHeader *) &msg[1];
        struct GNUNET_TUN_IPv6Header *ipv6 =
          (struct GNUNET_TUN_IPv6Header *) &tun[1];
        struct GNUNET_TUN_UdpHeader *udp =
          (struct GNUNET_TUN_UdpHeader *) &ipv6[1];
        msg->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
        msg->size = htons (size);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV6);
        GNUNET_TUN_initialize_ipv6_header (ipv6,
                                           IPPROTO_UDP,
                                           sizeof(struct GNUNET_TUN_UdpHeader)
                                           + mlen,
                                           &ts->destination_ip.v6,
                                           &ts->source_ip.v6);
        if (0 == ntohs (reply->source_port))
          udp->source_port = htons (ts->destination_port);
        else
          udp->source_port = reply->source_port;
        if (0 == ntohs (reply->destination_port))
          udp->destination_port = htons (ts->source_port);
        else
          udp->destination_port = reply->destination_port;
        udp->len = htons (mlen + sizeof(struct GNUNET_TUN_UdpHeader));
        GNUNET_TUN_calculate_udp6_checksum (ipv6, udp, &reply[1], mlen);
        GNUNET_memcpy (&udp[1], &reply[1], mlen);
        (void) GNUNET_HELPER_send (helper_handle, msg, GNUNET_YES, NULL, NULL);
      }
    }
    break;

  default:
    GNUNET_assert (0);
  }
  GNUNET_CONTAINER_heap_update_cost (ts->heap_node,
                                     GNUNET_TIME_absolute_get ().abs_value_us);
  GNUNET_CADET_receive_done (ts->channel);
}


static int
check_tcp_back (void *cls, const struct GNUNET_EXIT_TcpDataMessage *data)
{
  struct ChannelState *ts = cls;

  if (NULL == ts->heap_node)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (data->tcp_header.off * 4 < sizeof(struct GNUNET_TUN_TcpHeader))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
handle_tcp_back (void *cls, const struct GNUNET_EXIT_TcpDataMessage *data)
{
  struct ChannelState *ts = cls;
  size_t mlen;

  GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# TCP packets received from cadet"),
                            1,
                            GNUNET_NO);
  mlen = ntohs (data->header.size) - sizeof(struct GNUNET_EXIT_TcpDataMessage);
  {
    char sbuf[INET6_ADDRSTRLEN];
    char dbuf[INET6_ADDRSTRLEN];

    GNUNET_log (
      GNUNET_ERROR_TYPE_DEBUG,
      "Received TCP reply from cadet, sending %u bytes from [%s]:%u -> [%s]:%u via TUN\n",
      (unsigned int) mlen,
      inet_ntop (ts->af, &ts->destination_ip, sbuf, sizeof(sbuf)),
      ts->destination_port,
      inet_ntop (ts->af, &ts->source_ip, dbuf, sizeof(dbuf)),
      ts->source_port);
  }
  switch (ts->af)
  {
  case AF_INET: {
      size_t size = sizeof(struct GNUNET_TUN_IPv4Header)
                    + sizeof(struct GNUNET_TUN_TcpHeader)
                    + sizeof(struct GNUNET_MessageHeader)
                    + sizeof(struct GNUNET_TUN_Layer2PacketHeader) + mlen;
      {
        char buf[size] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun =
          (struct GNUNET_TUN_Layer2PacketHeader *) &msg[1];
        struct GNUNET_TUN_IPv4Header *ipv4 =
          (struct GNUNET_TUN_IPv4Header *) &tun[1];
        struct GNUNET_TUN_TcpHeader *tcp =
          (struct GNUNET_TUN_TcpHeader *) &ipv4[1];
        msg->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
        msg->size = htons (size);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV4);
        GNUNET_TUN_initialize_ipv4_header (ipv4,
                                           IPPROTO_TCP,
                                           sizeof(struct GNUNET_TUN_TcpHeader)
                                           + mlen,
                                           &ts->destination_ip.v4,
                                           &ts->source_ip.v4);
        *tcp = data->tcp_header;
        tcp->source_port = htons (ts->destination_port);
        tcp->destination_port = htons (ts->source_port);
        GNUNET_TUN_calculate_tcp4_checksum (ipv4, tcp, &data[1], mlen);
        GNUNET_memcpy (&tcp[1], &data[1], mlen);
        (void) GNUNET_HELPER_send (helper_handle, msg, GNUNET_YES, NULL, NULL);
      }
    }
    break;

  case AF_INET6: {
      size_t size = sizeof(struct GNUNET_TUN_IPv6Header)
                    + sizeof(struct GNUNET_TUN_TcpHeader)
                    + sizeof(struct GNUNET_MessageHeader)
                    + sizeof(struct GNUNET_TUN_Layer2PacketHeader) + mlen;
      {
        char buf[size] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun =
          (struct GNUNET_TUN_Layer2PacketHeader *) &msg[1];
        struct GNUNET_TUN_IPv6Header *ipv6 =
          (struct GNUNET_TUN_IPv6Header *) &tun[1];
        struct GNUNET_TUN_TcpHeader *tcp =
          (struct GNUNET_TUN_TcpHeader *) &ipv6[1];
        msg->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
        msg->size = htons (size);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV6);
        GNUNET_TUN_initialize_ipv6_header (ipv6,
                                           IPPROTO_TCP,
                                           sizeof(struct GNUNET_TUN_TcpHeader)
                                           + mlen,
                                           &ts->destination_ip.v6,
                                           &ts->source_ip.v6);
        *tcp = data->tcp_header;
        tcp->source_port = htons (ts->destination_port);
        tcp->destination_port = htons (ts->source_port);
        GNUNET_TUN_calculate_tcp6_checksum (ipv6, tcp, &data[1], mlen);
        GNUNET_memcpy (&tcp[1], &data[1], mlen);
        (void) GNUNET_HELPER_send (helper_handle, msg, GNUNET_YES, NULL, NULL);
      }
    }
    break;
  }
  GNUNET_CONTAINER_heap_update_cost (ts->heap_node,
                                     GNUNET_TIME_absolute_get ().abs_value_us);
  GNUNET_CADET_receive_done (ts->channel);
}


static struct GNUNET_CADET_Channel *
create_channel (struct ChannelState *ts,
                const struct GNUNET_PeerIdentity *target,
                const struct GNUNET_HashCode *port)
{
  struct GNUNET_MQ_MessageHandler cadet_handlers[] =
  { GNUNET_MQ_hd_var_size (udp_back,
                           GNUNET_MESSAGE_TYPE_VPN_UDP_REPLY,
                           struct GNUNET_EXIT_UdpReplyMessage,
                           ts),
    GNUNET_MQ_hd_var_size (tcp_back,
                           GNUNET_MESSAGE_TYPE_VPN_TCP_DATA_TO_VPN,
                           struct GNUNET_EXIT_TcpDataMessage,
                           ts),
    GNUNET_MQ_hd_var_size (icmp_back,
                           GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_VPN,
                           struct GNUNET_EXIT_IcmpToVPNMessage,
                           ts),
    GNUNET_MQ_handler_end () };

  return GNUNET_CADET_channel_create (cadet_handle,
                                      ts,
                                      target,
                                      port,
                                      NULL,
                                      &channel_cleaner,
                                      cadet_handlers);
}


static void
handle_regex_result (void *cls,
                     const struct GNUNET_PeerIdentity *id,
                     const struct GNUNET_PeerIdentity *get_path,
                     unsigned int get_path_length,
                     const struct GNUNET_PeerIdentity *put_path,
                     unsigned int put_path_length)
{
  struct ChannelState *ts = cls;
  struct GNUNET_HashCode port;

  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Exit %s found for destination %s!\n",
              GNUNET_i2s (id),
              print_channel_destination (&ts->destination));
  GNUNET_REGEX_search_cancel (ts->search);
  ts->search = NULL;
  switch (ts->af)
  {
  case AF_INET:
    /* these must match the strings used in gnunet-daemon-exit */
    GNUNET_CRYPTO_hash (GNUNET_APPLICATION_PORT_IPV4_GATEWAY,
                        strlen (GNUNET_APPLICATION_PORT_IPV4_GATEWAY),
                        &port);
    break;

  case AF_INET6:
    /* these must match the strings used in gnunet-daemon-exit */
    GNUNET_CRYPTO_hash (GNUNET_APPLICATION_PORT_IPV6_GATEWAY,
                        strlen (GNUNET_APPLICATION_PORT_IPV6_GATEWAY),
                        &port);
    break;

  default:
    GNUNET_break (0);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Creating tunnel to %s for destination %s!\n",
              GNUNET_i2s (id),
              print_channel_destination (&ts->destination));
  ts->channel = create_channel (ts, id, &port);
}


static struct ChannelState *
create_channel_to_destination (struct DestinationChannel *dt, int client_af)
{
  struct ChannelState *ts;

  GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# Cadet channels created"),
                            1,
                            GNUNET_NO);
  ts = GNUNET_new (struct ChannelState);
  ts->af = client_af;
  ts->destination = *dt->destination;
  ts->destination.heap_node = NULL; /* copy is NOT in destination heap */
  ts->destination_port = dt->destination_port;
  if (dt->destination->is_service)
  {
    struct GNUNET_HashCode cadet_port;

    GNUNET_TUN_compute_service_cadet_port (&ts->destination.details
                                           .service_destination
                                           .service_descriptor,
                                           ts->destination_port,
                                           &cadet_port);
    ts->channel =
      create_channel (ts,
                      &dt->destination->details.service_destination.target,
                      &cadet_port);

    if (NULL == ts->channel)
    {
      GNUNET_break (0);
      GNUNET_free (ts);
      return NULL;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Creating channel to peer %s offering service %s on port %u\n",
                GNUNET_i2s (
                  &dt->destination->details.service_destination.target),
                GNUNET_h2s (&ts->destination.details.service_destination
                            .service_descriptor),
                (unsigned int) ts->destination_port);
  }
  else
  {
    char *policy;

    switch (dt->destination->details.exit_destination.af)
    {
    case AF_INET: {
        char address[GNUNET_TUN_IPV4_REGEXLEN];

        GNUNET_TUN_ipv4toregexsearch (&dt->destination->details.exit_destination
                                      .ip.v4,
                                      dt->destination_port,
                                      address);
        GNUNET_asprintf (&policy,
                         "%s%s",
                         GNUNET_APPLICATION_TYPE_EXIT_REGEX_PREFIX,
                         address);
        break;
      }

    case AF_INET6: {
        char address[GNUNET_TUN_IPV6_REGEXLEN];

        GNUNET_TUN_ipv6toregexsearch (&dt->destination->details.exit_destination
                                      .ip.v6,
                                      dt->destination_port,
                                      address);
        GNUNET_asprintf (&policy,
                         "%s%s",
                         GNUNET_APPLICATION_TYPE_EXIT_REGEX_PREFIX,
                         address);
        break;
      }

    default:
      GNUNET_assert (0);
      break;
    }

    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Requesting connect by string: %s\n",
                policy);
    ts->search = GNUNET_REGEX_search (cfg, policy, &handle_regex_result, ts);
    GNUNET_free (policy);
  }
  return ts;
}


static void
expire_channel (struct ChannelState *except)
{
  struct ChannelState *ts;

  ts = GNUNET_CONTAINER_heap_peek (channel_heap);
  GNUNET_assert (NULL != ts);
  if (except == ts)
    return; /* can't do this */
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Tearing down expired channel to %s\n",
              print_channel_destination (&except->destination));
  free_channel_state (ts);
}


static void
route_packet (struct DestinationEntry *destination,
              int af,
              uint8_t protocol,
              const void *source_ip,
              const void *destination_ip,
              const void *payload,
              size_t payload_length)
{
  struct GNUNET_HashCode key;
  struct ChannelState *ts;
  size_t alen;
  size_t mlen;
  struct GNUNET_MQ_Envelope *env;
  const struct GNUNET_TUN_UdpHeader *udp;
  const struct GNUNET_TUN_TcpHeader *tcp;
  const struct GNUNET_TUN_IcmpHeader *icmp;
  struct DestinationChannel *dt;
  uint16_t source_port;
  uint16_t destination_port;

  switch (protocol)
  {
  case IPPROTO_UDP: {
      if (payload_length < sizeof(struct GNUNET_TUN_UdpHeader))
      {
        /* blame kernel? */
        GNUNET_break (0);
        return;
      }
      tcp = NULL; /* make compiler happy */
      icmp = NULL; /* make compiler happy */
      udp = payload;
      if (udp->len < sizeof(struct GNUNET_TUN_UdpHeader))
      {
        GNUNET_break_op (0);
        return;
      }
      source_port = ntohs (udp->source_port);
      destination_port = ntohs (udp->destination_port);
      get_channel_key_from_ips (af,
                                IPPROTO_UDP,
                                source_ip,
                                source_port,
                                destination_ip,
                                destination_port,
                                &key);
    }
    break;

  case IPPROTO_TCP: {
      if (payload_length < sizeof(struct GNUNET_TUN_TcpHeader))
      {
        /* blame kernel? */
        GNUNET_break (0);
        return;
      }
      udp = NULL; /* make compiler happy */
      icmp = NULL; /* make compiler happy */
      tcp = payload;
      if (tcp->off * 4 < sizeof(struct GNUNET_TUN_TcpHeader))
      {
        GNUNET_break_op (0);
        return;
      }
      source_port = ntohs (tcp->source_port);
      destination_port = ntohs (tcp->destination_port);
      get_channel_key_from_ips (af,
                                IPPROTO_TCP,
                                source_ip,
                                source_port,
                                destination_ip,
                                destination_port,
                                &key);
    }
    break;

  case IPPROTO_ICMP:
  case IPPROTO_ICMPV6: {
      if ((AF_INET == af) ^ (protocol == IPPROTO_ICMP))
      {
        GNUNET_break (0);
        return;
      }
      if (payload_length < sizeof(struct GNUNET_TUN_IcmpHeader))
      {
        /* blame kernel? */
        GNUNET_break (0);
        return;
      }
      tcp = NULL; /* make compiler happy */
      udp = NULL; /* make compiler happy */
      icmp = payload;
      source_port = 0;
      destination_port = 0;
      get_channel_key_from_ips (af,
                                protocol,
                                source_ip,
                                0,
                                destination_ip,
                                0,
                                &key);
    }
    break;

  default:
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                _ ("Protocol %u not supported, dropping\n"),
                (unsigned int) protocol);
    return;
  }
  alen = 0;
  if (! destination->is_service)
  {
    switch (destination->details.exit_destination.af)
    {
    case AF_INET:
      alen = sizeof(struct in_addr);
      break;

    case AF_INET6:
      alen = sizeof(struct in6_addr);
      break;

    default:
      GNUNET_assert (0);
    }

    {
      char sbuf[INET6_ADDRSTRLEN];
      char dbuf[INET6_ADDRSTRLEN];
      char xbuf[INET6_ADDRSTRLEN];

      GNUNET_log (
        GNUNET_ERROR_TYPE_DEBUG,
        "Routing %s packet from [%s]:%u -> [%s]:%u to destination [%s]:%u\n",
        (protocol == IPPROTO_TCP) ? "TCP" : "UDP",
        inet_ntop (af, source_ip, sbuf, sizeof(sbuf)),
        source_port,
        inet_ntop (af, destination_ip, dbuf, sizeof(dbuf)),
        destination_port,
        inet_ntop (destination->details.exit_destination.af,
                   &destination->details.exit_destination.ip,
                   xbuf,
                   sizeof(xbuf)),
        destination_port);
    }
    for (dt = destination->dt_head; NULL != dt; dt = dt->next)
      if (dt->destination_port == destination_port)
        break;
  }
  else
  {
    {
      char sbuf[INET6_ADDRSTRLEN];
      char dbuf[INET6_ADDRSTRLEN];

      GNUNET_log (
        GNUNET_ERROR_TYPE_DEBUG,
        "Routing %s packet from [%s]:%u -> [%s]:%u to service %s at peer %s\n",
        (protocol == IPPROTO_TCP) ? "TCP" : "UDP",
        inet_ntop (af, source_ip, sbuf, sizeof(sbuf)),
        source_port,
        inet_ntop (af, destination_ip, dbuf, sizeof(dbuf)),
        destination_port,
        GNUNET_h2s (
          &destination->details.service_destination.service_descriptor),
        GNUNET_i2s (&destination->details.service_destination.target));
    }
    for (dt = destination->dt_head; NULL != dt; dt = dt->next)
      if (dt->destination_port == destination_port)
        break;
  }
  if (NULL == dt)
  {
    dt = GNUNET_new (struct DestinationChannel);
    dt->destination = destination;
    GNUNET_CONTAINER_DLL_insert (destination->dt_head,
                                 destination->dt_tail,
                                 dt);
    dt->destination_port = destination_port;
  }

  /* see if we have an existing channel for this destination */
  ts = GNUNET_CONTAINER_multihashmap_get (channel_map, &key);
  if (NULL == ts)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Creating new channel for key %s\n",
                GNUNET_h2s (&key));
    /* need to either use the existing channel from the destination (if still
       available) or create a fresh one */
    ts = create_channel_to_destination (dt, af);
    if (NULL == ts)
      return;
    /* now bind existing "unbound" channel to our IP/port tuple */
    ts->protocol = protocol;
    ts->af = af;
    if (AF_INET == af)
    {
      ts->source_ip.v4 = *(const struct in_addr *) source_ip;
      ts->destination_ip.v4 = *(const struct in_addr *) destination_ip;
    }
    else
    {
      ts->source_ip.v6 = *(const struct in6_addr *) source_ip;
      ts->destination_ip.v6 = *(const struct in6_addr *) destination_ip;
    }
    ts->source_port = source_port;
    ts->destination_port = destination_port;
    ts->heap_node =
      GNUNET_CONTAINER_heap_insert (channel_heap,
                                    ts,
                                    GNUNET_TIME_absolute_get ().abs_value_us);
    GNUNET_assert (GNUNET_YES ==
                   GNUNET_CONTAINER_multihashmap_put (
                     channel_map,
                     &key,
                     ts,
                     GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));
    GNUNET_STATISTICS_update (stats,
                              gettext_noop ("# Active channels"),
                              1,
                              GNUNET_NO);
    while (GNUNET_CONTAINER_multihashmap_size (channel_map) >
           max_channel_mappings)
      expire_channel (ts);
  }
  else
  {
    GNUNET_CONTAINER_heap_update_cost (ts->heap_node,
                                       GNUNET_TIME_absolute_get ()
                                       .abs_value_us);
  }
  if (NULL == ts->channel)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Packet dropped, channel to %s not yet ready (%s)\n",
                print_channel_destination (&ts->destination),
                (NULL == ts->search) ? "EXIT search failed"
                : "EXIT search active");
    GNUNET_STATISTICS_update (stats,
                              gettext_noop (
                                "# Packets dropped (channel not yet online)"),
                              1,
                              GNUNET_NO);
    return;
  }

  /* send via channel */
  switch (protocol)
  {
  case IPPROTO_UDP:
    if (destination->is_service)
    {
      struct GNUNET_EXIT_UdpServiceMessage *usm;

      mlen = sizeof(struct GNUNET_EXIT_UdpServiceMessage) + payload_length
             - sizeof(struct GNUNET_TUN_UdpHeader);
      if (mlen >= GNUNET_MAX_MESSAGE_SIZE)
      {
        GNUNET_break (0);
        return;
      }
      env = GNUNET_MQ_msg_extra (usm,
                                 payload_length
                                 - sizeof(struct GNUNET_TUN_UdpHeader),
                                 GNUNET_MESSAGE_TYPE_VPN_UDP_TO_SERVICE);
      /* if the source port is below 32000, we assume it has a special
         meaning; if not, we pick a random port (this is a heuristic) */
      usm->source_port =
        (ntohs (udp->source_port) < 32000) ? udp->source_port : 0;
      usm->destination_port = udp->destination_port;
      GNUNET_memcpy (&usm[1],
                     &udp[1],
                     payload_length - sizeof(struct GNUNET_TUN_UdpHeader));
    }
    else
    {
      struct GNUNET_EXIT_UdpInternetMessage *uim;
      struct in_addr *ip4dst;
      struct in6_addr *ip6dst;
      void *payload;

      mlen = sizeof(struct GNUNET_EXIT_UdpInternetMessage) + alen
             + payload_length - sizeof(struct GNUNET_TUN_UdpHeader);
      if (mlen >= GNUNET_MAX_MESSAGE_SIZE)
      {
        GNUNET_break (0);
        return;
      }
      env = GNUNET_MQ_msg_extra (uim,
                                 payload_length + alen
                                 - sizeof(struct GNUNET_TUN_UdpHeader),
                                 GNUNET_MESSAGE_TYPE_VPN_UDP_TO_INTERNET);
      uim->af = htonl (destination->details.exit_destination.af);
      uim->source_port =
        (ntohs (udp->source_port) < 32000) ? udp->source_port : 0;
      uim->destination_port = udp->destination_port;
      switch (destination->details.exit_destination.af)
      {
      case AF_INET:
        ip4dst = (struct in_addr *) &uim[1];
        *ip4dst = destination->details.exit_destination.ip.v4;
        payload = &ip4dst[1];
        break;

      case AF_INET6:
        ip6dst = (struct in6_addr *) &uim[1];
        *ip6dst = destination->details.exit_destination.ip.v6;
        payload = &ip6dst[1];
        break;

      default:
        GNUNET_assert (0);
      }
      GNUNET_memcpy (payload,
                     &udp[1],
                     payload_length - sizeof(struct GNUNET_TUN_UdpHeader));
    }
    break;

  case IPPROTO_TCP:
    if (GNUNET_NO == ts->is_established)
    {
      if (destination->is_service)
      {
        struct GNUNET_EXIT_TcpServiceStartMessage *tsm;

        mlen = sizeof(struct GNUNET_EXIT_TcpServiceStartMessage)
               + payload_length - sizeof(struct GNUNET_TUN_TcpHeader);
        if (mlen >= GNUNET_MAX_MESSAGE_SIZE)
        {
          GNUNET_break (0);
          return;
        }
        env =
          GNUNET_MQ_msg_extra (tsm,
                               payload_length
                               - sizeof(struct GNUNET_TUN_TcpHeader),
                               GNUNET_MESSAGE_TYPE_VPN_TCP_TO_SERVICE_START);
        tsm->reserved = htonl (0);
        tsm->tcp_header = *tcp;
        GNUNET_memcpy (&tsm[1],
                       &tcp[1],
                       payload_length - sizeof(struct GNUNET_TUN_TcpHeader));
      }
      else
      {
        struct GNUNET_EXIT_TcpInternetStartMessage *tim;
        struct in_addr *ip4dst;
        struct in6_addr *ip6dst;
        void *payload;

        mlen = sizeof(struct GNUNET_EXIT_TcpInternetStartMessage) + alen
               + payload_length - sizeof(struct GNUNET_TUN_TcpHeader);
        if (mlen >= GNUNET_MAX_MESSAGE_SIZE)
        {
          GNUNET_break (0);
          return;
        }
        env =
          GNUNET_MQ_msg_extra (tim,
                               payload_length + alen
                               - sizeof(struct GNUNET_TUN_TcpHeader),
                               GNUNET_MESSAGE_TYPE_VPN_TCP_TO_INTERNET_START);
        tim->af = htonl (destination->details.exit_destination.af);
        tim->tcp_header = *tcp;
        switch (destination->details.exit_destination.af)
        {
        case AF_INET:
          ip4dst = (struct in_addr *) &tim[1];
          *ip4dst = destination->details.exit_destination.ip.v4;
          payload = &ip4dst[1];
          break;

        case AF_INET6:
          ip6dst = (struct in6_addr *) &tim[1];
          *ip6dst = destination->details.exit_destination.ip.v6;
          payload = &ip6dst[1];
          break;

        default:
          GNUNET_assert (0);
        }
        GNUNET_memcpy (payload,
                       &tcp[1],
                       payload_length - sizeof(struct GNUNET_TUN_TcpHeader));
      }
    }
    else
    {
      struct GNUNET_EXIT_TcpDataMessage *tdm;

      mlen = sizeof(struct GNUNET_EXIT_TcpDataMessage) + payload_length
             - sizeof(struct GNUNET_TUN_TcpHeader);
      if (mlen >= GNUNET_MAX_MESSAGE_SIZE)
      {
        GNUNET_break (0);
        return;
      }
      env = GNUNET_MQ_msg_extra (tdm,
                                 payload_length
                                 - sizeof(struct GNUNET_TUN_TcpHeader),
                                 GNUNET_MESSAGE_TYPE_VPN_TCP_DATA_TO_EXIT);
      tdm->reserved = htonl (0);
      tdm->tcp_header = *tcp;
      GNUNET_memcpy (&tdm[1],
                     &tcp[1],
                     payload_length - sizeof(struct GNUNET_TUN_TcpHeader));
    }
    break;

  case IPPROTO_ICMP:
  case IPPROTO_ICMPV6:
    if (destination->is_service)
    {
      struct GNUNET_EXIT_IcmpServiceMessage *ism;

      /* ICMP protocol translation will be done by the receiver (as we don't know
         the target AF); however, we still need to possibly discard the payload
         depending on the ICMP type */
      switch (af)
      {
      case AF_INET:
        switch (icmp->type)
        {
        case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:
        case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:
          break;

        case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
        case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
        case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED:
          /* throw away ICMP payload, won't be useful for the other side anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        default:
          GNUNET_STATISTICS_update (stats,
                                    gettext_noop (
                                      "# ICMPv4 packets dropped (not allowed)"),
                                    1,
                                    GNUNET_NO);
          return;
        }
        /* end of AF_INET */
        break;

      case AF_INET6:
        switch (icmp->type)
        {
        case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
        case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
        case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
        case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
          /* throw away ICMP payload, won't be useful for the other side anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
        case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
          break;

        default:
          GNUNET_STATISTICS_update (stats,
                                    gettext_noop (
                                      "# ICMPv6 packets dropped (not allowed)"),
                                    1,
                                    GNUNET_NO);
          return;
        }
        /* end of AF_INET6 */
        break;

      default:
        GNUNET_assert (0);
        break;
      }

      /* update length calculations, as payload_length may have changed */
      mlen = sizeof(struct GNUNET_EXIT_IcmpServiceMessage) + alen
             + payload_length - sizeof(struct GNUNET_TUN_IcmpHeader);
      if (mlen >= GNUNET_MAX_MESSAGE_SIZE)
      {
        GNUNET_break (0);
        return;
      }

      env = GNUNET_MQ_msg_extra (ism,
                                 payload_length
                                 - sizeof(struct GNUNET_TUN_IcmpHeader),
                                 GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_SERVICE);
      ism->af = htonl (af);    /* need to tell destination ICMP protocol family! */
      ism->icmp_header = *icmp;
      GNUNET_memcpy (&ism[1],
                     &icmp[1],
                     payload_length - sizeof(struct GNUNET_TUN_IcmpHeader));
    }
    else
    {
      struct GNUNET_EXIT_IcmpInternetMessage *iim;
      struct in_addr *ip4dst;
      struct in6_addr *ip6dst;
      void *payload;
      uint8_t new_type;

      new_type = icmp->type;
      /* Perform ICMP protocol-translation (depending on destination AF and source AF)
         and throw away ICMP payload depending on ICMP message type */
      switch (af)
      {
      case AF_INET:
        switch (icmp->type)
        {
        case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:
          if (destination->details.exit_destination.af == AF_INET6)
            new_type = GNUNET_TUN_ICMPTYPE6_ECHO_REPLY;
          break;

        case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:
          if (destination->details.exit_destination.af == AF_INET6)
            new_type = GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST;
          break;

        case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
          if (destination->details.exit_destination.af == AF_INET6)
            new_type = GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE;
          /* throw away IP-payload, exit will have to make it up anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED:
          if (destination->details.exit_destination.af == AF_INET6)
            new_type = GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED;
          /* throw away IP-payload, exit will have to make it up anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
          if (destination->details.exit_destination.af == AF_INET6)
          {
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv4 packets dropped (impossible PT to v6)"),
              1,
              GNUNET_NO);
            return;
          }
          /* throw away IP-payload, exit will have to make it up anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        default:
          GNUNET_STATISTICS_update (
            stats,
            gettext_noop ("# ICMPv4 packets dropped (type not allowed)"),
            1,
            GNUNET_NO);
          return;
        }
        /* end of AF_INET */
        break;

      case AF_INET6:
        switch (icmp->type)
        {
        case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
          if (destination->details.exit_destination.af == AF_INET)
            new_type = GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE;
          /* throw away IP-payload, exit will have to make it up anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
          if (destination->details.exit_destination.af == AF_INET)
            new_type = GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED;
          /* throw away IP-payload, exit will have to make it up anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
          if (destination->details.exit_destination.af == AF_INET)
          {
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv6 packets dropped (impossible PT to v4)"),
              1,
              GNUNET_NO);
            return;
          }
          /* throw away IP-payload, exit will have to make it up anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
          if (destination->details.exit_destination.af == AF_INET)
          {
            GNUNET_STATISTICS_update (
              stats,
              gettext_noop ("# ICMPv6 packets dropped (impossible PT to v4)"),
              1,
              GNUNET_NO);
            return;
          }
          /* throw away IP-payload, exit will have to make it up anyway */
          payload_length = sizeof(struct GNUNET_TUN_IcmpHeader);
          break;

        case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
          if (destination->details.exit_destination.af == AF_INET)
            new_type = GNUNET_TUN_ICMPTYPE_ECHO_REQUEST;
          break;

        case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
          if (destination->details.exit_destination.af == AF_INET)
            new_type = GNUNET_TUN_ICMPTYPE_ECHO_REPLY;
          break;

        default:
          GNUNET_STATISTICS_update (
            stats,
            gettext_noop ("# ICMPv6 packets dropped (type not allowed)"),
            1,
            GNUNET_NO);
          return;
        }
        /* end of AF_INET6 */
        break;

      default:
        GNUNET_assert (0);
      }

      /* update length calculations, as payload_length may have changed */
      mlen = sizeof(struct GNUNET_EXIT_IcmpInternetMessage) + alen
             + payload_length - sizeof(struct GNUNET_TUN_IcmpHeader);
      if (mlen >= GNUNET_MAX_MESSAGE_SIZE)
      {
        GNUNET_break (0);
        return;
      }
      env = GNUNET_MQ_msg_extra (iim,
                                 alen + payload_length
                                 - sizeof(struct GNUNET_TUN_IcmpHeader),
                                 GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_INTERNET);
      iim->icmp_header = *icmp;
      iim->icmp_header.type = new_type;
      iim->af = htonl (destination->details.exit_destination.af);
      switch (destination->details.exit_destination.af)
      {
      case AF_INET:
        ip4dst = (struct in_addr *) &iim[1];
        *ip4dst = destination->details.exit_destination.ip.v4;
        payload = &ip4dst[1];
        break;

      case AF_INET6:
        ip6dst = (struct in6_addr *) &iim[1];
        *ip6dst = destination->details.exit_destination.ip.v6;
        payload = &ip6dst[1];
        break;

      default:
        GNUNET_assert (0);
      }
      GNUNET_memcpy (payload,
                     &icmp[1],
                     payload_length - sizeof(struct GNUNET_TUN_IcmpHeader));
    }
    break;

  default:
    /* not supported above, how can we get here !? */
    GNUNET_assert (0);
    break;
  }
  ts->is_established = GNUNET_YES;
  send_to_channel (ts, env);
}


static int
message_token (void *cls, const struct GNUNET_MessageHeader *message)
{
  const struct GNUNET_TUN_Layer2PacketHeader *tun;
  size_t mlen;
  struct GNUNET_HashCode key;
  struct DestinationEntry *de;

  GNUNET_STATISTICS_update (stats,
                            gettext_noop (
                              "# Packets received from TUN interface"),
                            1,
                            GNUNET_NO);
  mlen = ntohs (message->size);
  if ((ntohs (message->type) != GNUNET_MESSAGE_TYPE_VPN_HELPER) ||
      (mlen < sizeof(struct GNUNET_MessageHeader)
       + sizeof(struct GNUNET_TUN_Layer2PacketHeader)))
  {
    GNUNET_break (0);
    return GNUNET_OK;
  }
  tun = (const struct GNUNET_TUN_Layer2PacketHeader *) &message[1];
  mlen -= (sizeof(struct GNUNET_MessageHeader)
           + sizeof(struct GNUNET_TUN_Layer2PacketHeader));
  switch (ntohs (tun->proto))
  {
  case ETH_P_IPV6: {
      const struct GNUNET_TUN_IPv6Header *pkt6;

      if (mlen < sizeof(struct GNUNET_TUN_IPv6Header))
      {
        /* blame kernel */
        GNUNET_break (0);
        return GNUNET_OK;
      }
      pkt6 = (const struct GNUNET_TUN_IPv6Header *) &tun[1];
      get_destination_key_from_ip (AF_INET6, &pkt6->destination_address, &key);
      de = GNUNET_CONTAINER_multihashmap_get (destination_map, &key);
      if (NULL == de)
      {
        char buf[INET6_ADDRSTRLEN];

        GNUNET_log (
          GNUNET_ERROR_TYPE_INFO,
          _ ("Packet received for unmapped destination `%s' (dropping it)\n"),
          inet_ntop (AF_INET6, &pkt6->destination_address, buf, sizeof(buf)));
        return GNUNET_OK;
      }
      route_packet (de,
                    AF_INET6,
                    pkt6->next_header,
                    &pkt6->source_address,
                    &pkt6->destination_address,
                    &pkt6[1],
                    mlen - sizeof(struct GNUNET_TUN_IPv6Header));
    }
    break;

  case ETH_P_IPV4: {
      struct GNUNET_TUN_IPv4Header *pkt4;

      if (mlen < sizeof(struct GNUNET_TUN_IPv4Header))
      {
        /* blame kernel */
        GNUNET_break (0);
        return GNUNET_OK;
      }
      pkt4 = (struct GNUNET_TUN_IPv4Header *) &tun[1];
      get_destination_key_from_ip (AF_INET, &pkt4->destination_address, &key);
      de = GNUNET_CONTAINER_multihashmap_get (destination_map, &key);
      if (NULL == de)
      {
        char buf[INET_ADDRSTRLEN];

        GNUNET_log (
          GNUNET_ERROR_TYPE_INFO,
          _ ("Packet received for unmapped destination `%s' (dropping it)\n"),
          inet_ntop (AF_INET, &pkt4->destination_address, buf, sizeof(buf)));
        return GNUNET_OK;
      }
      if (pkt4->header_length * 4 != sizeof(struct GNUNET_TUN_IPv4Header))
      {
        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                    _ ("Received IPv4 packet with options (dropping it)\n"));
        return GNUNET_OK;
      }
      route_packet (de,
                    AF_INET,
                    pkt4->protocol,
                    &pkt4->source_address,
                    &pkt4->destination_address,
                    &pkt4[1],
                    mlen - sizeof(struct GNUNET_TUN_IPv4Header));
    }
    break;

  default:
    GNUNET_log (
      GNUNET_ERROR_TYPE_INFO,
      _ ("Received packet of unknown protocol %d from TUN (dropping it)\n"),
      (unsigned int) ntohs (tun->proto));
    break;
  }
  return GNUNET_OK;
}


static int
allocate_v4_address (struct in_addr *v4)
{
  const char *ipv4addr = vpn_argv[4];
  const char *ipv4mask = vpn_argv[5];
  struct in_addr addr;
  struct in_addr mask;
  struct in_addr rnd;
  struct GNUNET_HashCode key;
  unsigned int tries;

  GNUNET_assert (1 == inet_pton (AF_INET, ipv4addr, &addr));
  GNUNET_assert (1 == inet_pton (AF_INET, ipv4mask, &mask));
  /* Given 192.168.0.1/255.255.0.0, we want a mask
     of '192.168.255.255', thus:  */
  mask.s_addr = addr.s_addr | ~mask.s_addr;
  tries = 0;
  do
  {
    tries++;
    if (tries > 16)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  _ (
                    "Failed to find unallocated IPv4 address in VPN's range\n"));
      return GNUNET_SYSERR;
    }
    /* Pick random IPv4 address within the subnet, except 'addr' or 'mask' itself */
    rnd.s_addr =
      GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, UINT32_MAX);
    v4->s_addr = (addr.s_addr | rnd.s_addr) & mask.s_addr;
    get_destination_key_from_ip (AF_INET, v4, &key);
  }
  while ((GNUNET_YES ==
          GNUNET_CONTAINER_multihashmap_contains (destination_map, &key)) ||
         (v4->s_addr == addr.s_addr) || (v4->s_addr == mask.s_addr));
  return GNUNET_OK;
}


static int
allocate_v6_address (struct in6_addr *v6)
{
  const char *ipv6addr = vpn_argv[2];
  struct in6_addr addr;
  struct in6_addr mask;
  struct in6_addr rnd;
  int i;
  struct GNUNET_HashCode key;
  unsigned int tries;

  GNUNET_assert (1 == inet_pton (AF_INET6, ipv6addr, &addr));
  GNUNET_assert (ipv6prefix < 128);
  /* Given ABCD::/96, we want a mask of 'ABCD::FFFF:FFFF,
     thus: */
  mask = addr;
  for (i = 127; i >= ipv6prefix; i--)
    mask.s6_addr[i / 8] |= (1 << (i % 8));

  /* Pick random IPv6 address within the subnet, except 'addr' or 'mask' itself */
  tries = 0;
  do
  {
    tries++;
    if (tries > 16)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  _ (
                    "Failed to find unallocated IPv6 address in VPN's range\n"));
      return GNUNET_SYSERR;
    }
    for (i = 0; i < 16; i++)
    {
      rnd.s6_addr[i] =
        (unsigned char) GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK,
                                                  256);
      v6->s6_addr[i] = (addr.s6_addr[i] | rnd.s6_addr[i]) & mask.s6_addr[i];
    }
    get_destination_key_from_ip (AF_INET6, v6, &key);
  }
  while ((GNUNET_YES ==
          GNUNET_CONTAINER_multihashmap_contains (destination_map, &key)) ||
         (0 == GNUNET_memcmp (v6, &addr)) ||
         (0 == GNUNET_memcmp (v6, &mask)));
  return GNUNET_OK;
}


static void
free_destination_entry (struct DestinationEntry *de)
{
  struct DestinationChannel *dt;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Cleaning up destination entry `%s'\n",
              print_channel_destination (de));
  GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# Active destinations"),
                            -1,
                            GNUNET_NO);
  while (NULL != (dt = de->dt_head))
  {
    GNUNET_CONTAINER_DLL_remove (de->dt_head, de->dt_tail, dt);
    GNUNET_free (dt);
  }
  if (NULL != de->heap_node)
  {
    GNUNET_CONTAINER_heap_remove_node (de->heap_node);
    de->heap_node = NULL;
    GNUNET_assert (
      GNUNET_YES ==
      GNUNET_CONTAINER_multihashmap_remove (destination_map, &de->key, de));
  }
  GNUNET_free (de);
}


static void
expire_destination (struct DestinationEntry *except)
{
  struct DestinationEntry *de;

  de = GNUNET_CONTAINER_heap_peek (destination_heap);
  GNUNET_assert (NULL != de);
  if (except == de)
    return; /* can't do this */
  free_destination_entry (de);
}


static int
allocate_response_ip (int *result_af,
                      void **addr,
                      struct in_addr *v4,
                      struct in6_addr *v6)
{
  *addr = NULL;
  switch (*result_af)
  {
  case AF_INET:
    if (GNUNET_OK != allocate_v4_address (v4))
      *result_af = AF_UNSPEC;
    else
      *addr = v4;
    break;

  case AF_INET6:
    if (GNUNET_OK != allocate_v6_address (v6))
      *result_af = AF_UNSPEC;
    else
      *addr = v6;
    break;

  case AF_UNSPEC:
    if (GNUNET_OK == allocate_v4_address (v4))
    {
      *addr = v4;
      *result_af = AF_INET;
    }
    else if (GNUNET_OK == allocate_v6_address (v6))
    {
      *addr = v6;
      *result_af = AF_INET6;
    }
    break;

  default:
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static int
check_client_redirect_to_ip (void *cls,
                             const struct RedirectToIpRequestMessage *msg)
{
  size_t alen;
  int addr_af;

  alen = ntohs (msg->header.size) - sizeof(struct RedirectToIpRequestMessage);
  addr_af = (int) htonl (msg->addr_af);
  switch (addr_af)
  {
  case AF_INET:
    if (alen != sizeof(struct in_addr))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
    break;

  case AF_INET6:
    if (alen != sizeof(struct in6_addr))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
    break;

  default:
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
handle_client_redirect_to_ip (void *cls,
                              const struct RedirectToIpRequestMessage *msg)
{
  struct GNUNET_SERVICE_Client *client = cls;
  size_t alen;
  int addr_af;
  int result_af;
  struct in_addr v4;
  struct in6_addr v6;
  void *addr;
  struct DestinationEntry *de;
  struct GNUNET_HashCode key;

  alen = ntohs (msg->header.size) - sizeof(struct RedirectToIpRequestMessage);
  addr_af = (int) htonl (msg->addr_af);
  /* allocate response IP */
  result_af = (int) htonl (msg->result_af);
  if (GNUNET_OK != allocate_response_ip (&result_af, &addr, &v4, &v6))
  {
    GNUNET_SERVICE_client_drop (client);
    return;
  }
  /* send reply with our IP address */
  send_client_reply (client, msg->request_id, result_af, addr);
  if (result_af == AF_UNSPEC)
  {
    /* failure, we're done */
    GNUNET_SERVICE_client_continue (client);
    return;
  }

  {
    char sbuf[INET6_ADDRSTRLEN];
    char dbuf[INET6_ADDRSTRLEN];

    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Allocated address %s for redirection via exit to %s\n",
                inet_ntop (result_af, addr, sbuf, sizeof(sbuf)),
                inet_ntop (addr_af, &msg[1], dbuf, sizeof(dbuf)));
  }

  /* setup destination record */
  de = GNUNET_new (struct DestinationEntry);
  de->is_service = GNUNET_NO;
  de->details.exit_destination.af = addr_af;
  GNUNET_memcpy (&de->details.exit_destination.ip, &msg[1], alen);
  get_destination_key_from_ip (result_af, addr, &key);
  de->key = key;
  GNUNET_assert (GNUNET_OK == GNUNET_CONTAINER_multihashmap_put (
                   destination_map,
                   &key,
                   de,
                   GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE));
  de->heap_node = GNUNET_CONTAINER_heap_insert (destination_heap,
                                                de,
                                                GNUNET_TIME_absolute_ntoh (
                                                  msg->expiration_time)
                                                .abs_value_us);
  GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# Active destinations"),
                            1,
                            GNUNET_NO);
  while (GNUNET_CONTAINER_multihashmap_size (destination_map) >
         max_destination_mappings)
    expire_destination (de);
  GNUNET_SERVICE_client_continue (client);
}


static void
handle_client_redirect_to_service (
  void *cls,
  const struct RedirectToServiceRequestMessage *msg)
{
  struct GNUNET_SERVICE_Client *client = cls;
  int result_af;
  struct in_addr v4;
  struct in6_addr v6;
  void *addr;
  struct DestinationEntry *de;
  struct GNUNET_HashCode key;
  struct DestinationChannel *dt;

  /* allocate response IP */
  result_af = (int) htonl (msg->result_af);
  if (GNUNET_OK != allocate_response_ip (&result_af, &addr, &v4, &v6))
  {
    GNUNET_break (0);
    GNUNET_SERVICE_client_drop (client);
    return;
  }
  send_client_reply (client, msg->request_id, result_af, addr);
  if (result_af == AF_UNSPEC)
  {
    /* failure, we're done */
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _ ("Failed to allocate IP address for new destination\n"));
    GNUNET_SERVICE_client_continue (client);
    return;
  }

  {
    char sbuf[INET6_ADDRSTRLEN];

    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Allocated address %s for redirection to service %s on peer %s\n",
                inet_ntop (result_af, addr, sbuf, sizeof(sbuf)),
                GNUNET_h2s (&msg->service_descriptor),
                GNUNET_i2s (&msg->target));
  }

  /* setup destination record */
  de = GNUNET_new (struct DestinationEntry);
  de->is_service = GNUNET_YES;
  de->details.service_destination.target = msg->target;
  de->details.service_destination.service_descriptor = msg->service_descriptor;
  get_destination_key_from_ip (result_af, addr, &key);
  de->key = key;
  GNUNET_assert (GNUNET_OK == GNUNET_CONTAINER_multihashmap_put (
                   destination_map,
                   &key,
                   de,
                   GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE));
  de->heap_node = GNUNET_CONTAINER_heap_insert (destination_heap,
                                                de,
                                                GNUNET_TIME_absolute_ntoh (
                                                  msg->expiration_time)
                                                .abs_value_us);
  while (GNUNET_CONTAINER_multihashmap_size (destination_map) >
         max_destination_mappings)
    expire_destination (de);

  dt = GNUNET_new (struct DestinationChannel);
  dt->destination = de;
  GNUNET_CONTAINER_DLL_insert (de->dt_head, de->dt_tail, dt);
  /* we're done */
  GNUNET_SERVICE_client_continue (client);
}


static int
cleanup_destination (void *cls, const struct GNUNET_HashCode *key, void *value)
{
  struct DestinationEntry *de = value;

  free_destination_entry (de);
  return GNUNET_OK;
}


static int
cleanup_channel (void *cls, const struct GNUNET_HashCode *key, void *value)
{
  struct ChannelState *ts = value;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Tearing down channel to `%s' during cleanup\n",
              print_channel_destination (&ts->destination));
  free_channel_state (ts);
  return GNUNET_OK;
}


static void
cleanup (void *cls)
{
  unsigned int i;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "VPN is shutting down\n");
  if (NULL != destination_map)
  {
    GNUNET_CONTAINER_multihashmap_iterate (destination_map,
                                           &cleanup_destination,
                                           NULL);
    GNUNET_CONTAINER_multihashmap_destroy (destination_map);
    destination_map = NULL;
  }
  if (NULL != destination_heap)
  {
    GNUNET_CONTAINER_heap_destroy (destination_heap);
    destination_heap = NULL;
  }
  if (NULL != channel_map)
  {
    GNUNET_CONTAINER_multihashmap_iterate (channel_map, &cleanup_channel, NULL);
    GNUNET_CONTAINER_multihashmap_destroy (channel_map);
    channel_map = NULL;
  }
  if (NULL != channel_heap)
  {
    GNUNET_CONTAINER_heap_destroy (channel_heap);
    channel_heap = NULL;
  }
  if (NULL != cadet_handle)
  {
    GNUNET_CADET_disconnect (cadet_handle);
    cadet_handle = NULL;
  }
  if (NULL != helper_handle)
  {
    GNUNET_HELPER_kill (helper_handle, GNUNET_NO);
    GNUNET_HELPER_wait (helper_handle);
    helper_handle = NULL;
  }
  if (NULL != stats)
  {
    GNUNET_STATISTICS_destroy (stats, GNUNET_NO);
    stats = NULL;
  }
  for (i = 0; i < 5; i++)
    GNUNET_free_non_null (vpn_argv[i]);
}


static void *
client_connect_cb (void *cls,
                   struct GNUNET_SERVICE_Client *c,
                   struct GNUNET_MQ_Handle *mq)
{
  return c;
}


static void
client_disconnect_cb (void *cls,
                      struct GNUNET_SERVICE_Client *c,
                      void *internal_cls)
{
  GNUNET_assert (c == internal_cls);
}


static void
run (void *cls,
     const struct GNUNET_CONFIGURATION_Handle *cfg_,
     struct GNUNET_SERVICE_Handle *service)
{
  char *ifname;
  char *ipv6addr;
  char *ipv6prefix_s;
  char *ipv4addr;
  char *ipv4mask;
  struct in_addr v4;
  struct in6_addr v6;
  char *binary;

  binary = GNUNET_OS_get_libexec_binary_path ("gnunet-helper-vpn");

  if (GNUNET_YES !=
      GNUNET_OS_check_helper_binary (
        binary,
        GNUNET_YES,
        "-d gnunet-vpn - - 169.1.3.3.7 255.255.255.0")) // ipv4 only please!
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "`%s' is not SUID, refusing to run.\n",
                "gnunet-helper-vpn");
    GNUNET_free (binary);
    global_ret = 1;
    /* we won't "really" exit here, as the 'service' is still running;
       however, as no handlers are registered, the service won't do
       anything either */
    return;
  }
  GNUNET_free (binary);
  cfg = cfg_;
  stats = GNUNET_STATISTICS_create ("vpn", cfg);
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_number (cfg,
                                             "VPN",
                                             "MAX_MAPPING",
                                             &max_destination_mappings))
    max_destination_mappings = 200;
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_number (cfg,
                                             "VPN",
                                             "MAX_TUNNELS",
                                             &max_channel_mappings))
    max_channel_mappings = 200;

  destination_map =
    GNUNET_CONTAINER_multihashmap_create (max_destination_mappings * 2,
                                          GNUNET_NO);
  destination_heap =
    GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);
  channel_map =
    GNUNET_CONTAINER_multihashmap_create (max_channel_mappings * 2, GNUNET_NO);
  channel_heap = GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);


  vpn_argv[0] = GNUNET_strdup ("vpn-gnunet");
  if (GNUNET_SYSERR ==
      GNUNET_CONFIGURATION_get_value_string (cfg, "VPN", "IFNAME", &ifname))
  {
    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR, "VPN", "IFNAME");
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  vpn_argv[1] = ifname;
  ipv6addr = NULL;
  if (GNUNET_OK == GNUNET_NETWORK_test_pf (PF_INET6))
  {
    if (((GNUNET_SYSERR == GNUNET_CONFIGURATION_get_value_string (cfg,
                                                                  "VPN",
                                                                  "IPV6ADDR",
                                                                  &ipv6addr)) ||
         (1 != inet_pton (AF_INET6, ipv6addr, &v6))))
    {
      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
                                 "VPN",
                                 "IPV6ADDR",
                                 _ ("Must specify valid IPv6 address"));
      GNUNET_SCHEDULER_shutdown ();
      GNUNET_free_non_null (ipv6addr);
      return;
    }
    vpn_argv[2] = ipv6addr;
    ipv6prefix_s = NULL;
    if (GNUNET_SYSERR == GNUNET_CONFIGURATION_get_value_string (cfg,
                                                                "VPN",
                                                                "IPV6PREFIX",
                                                                &ipv6prefix_s))
    {
      GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR, "VPN", "IPV6PREFIX");
      GNUNET_SCHEDULER_shutdown ();
      GNUNET_free_non_null (ipv6prefix_s);
      return;
    }
    vpn_argv[3] = ipv6prefix_s;
    if ((GNUNET_OK != GNUNET_CONFIGURATION_get_value_number (cfg,
                                                             "VPN",
                                                             "IPV6PREFIX",
                                                             &ipv6prefix)) ||
        (ipv6prefix >= 127))
    {
      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
                                 "VPN",
                                 "IPV4MASK",
                                 _ ("Must specify valid IPv6 mask"));
      GNUNET_SCHEDULER_shutdown ();
      return;
    }
  }
  else
  {
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                _ (
                  "IPv6 support disabled as this system does not support IPv6\n"));
    vpn_argv[2] = GNUNET_strdup ("-");
    vpn_argv[3] = GNUNET_strdup ("-");
  }
  if (GNUNET_OK == GNUNET_NETWORK_test_pf (PF_INET))
  {
    ipv4addr = NULL;
    if (((GNUNET_SYSERR == GNUNET_CONFIGURATION_get_value_string (cfg,
                                                                  "vpn",
                                                                  "IPV4ADDR",
                                                                  &ipv4addr)) ||
         (1 != inet_pton (AF_INET, ipv4addr, &v4))))
    {
      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
                                 "VPN",
                                 "IPV4ADDR",
                                 _ ("Must specify valid IPv4 address"));
      GNUNET_SCHEDULER_shutdown ();
      GNUNET_free_non_null (ipv4addr);
      return;
    }
    vpn_argv[4] = ipv4addr;
    ipv4mask = NULL;
    if (((GNUNET_SYSERR == GNUNET_CONFIGURATION_get_value_string (cfg,
                                                                  "vpn",
                                                                  "IPV4MASK",
                                                                  &ipv4mask)) ||
         (1 != inet_pton (AF_INET, ipv4mask, &v4))))
    {
      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
                                 "VPN",
                                 "IPV4MASK",
                                 _ ("Must specify valid IPv4 mask"));
      GNUNET_SCHEDULER_shutdown ();
      GNUNET_free_non_null (ipv4mask);
      return;
    }
    vpn_argv[5] = ipv4mask;
  }
  else
  {
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                _ (
                  "IPv4 support disabled as this system does not support IPv4\n"));
    vpn_argv[4] = GNUNET_strdup ("-");
    vpn_argv[5] = GNUNET_strdup ("-");
  }
  vpn_argv[6] = NULL;

  cadet_handle = GNUNET_CADET_connect (cfg_);
  // FIXME never opens ports???
  helper_handle = GNUNET_HELPER_start (GNUNET_NO,
                                       "gnunet-helper-vpn",
                                       vpn_argv,
                                       &message_token,
                                       NULL,
                                       NULL);
  GNUNET_SCHEDULER_add_shutdown (&cleanup, NULL);
}


GNUNET_SERVICE_MAIN (
  "vpn",
  GNUNET_SERVICE_OPTION_NONE,
  &run,
  &client_connect_cb,
  &client_disconnect_cb,
  NULL,
  GNUNET_MQ_hd_var_size (client_redirect_to_ip,
                         GNUNET_MESSAGE_TYPE_VPN_CLIENT_REDIRECT_TO_IP,
                         struct RedirectToIpRequestMessage,
                         NULL),
  GNUNET_MQ_hd_fixed_size (client_redirect_to_service,
                           GNUNET_MESSAGE_TYPE_VPN_CLIENT_REDIRECT_TO_SERVICE,
                           struct RedirectToServiceRequestMessage,
                           NULL),
  GNUNET_MQ_handler_end ());


/* end of gnunet-service-vpn.c */