[oweals/gnunet.git] / src / transport / gnunet-service-transport.c

/*
     This file is part of GNUnet.
     (C) 2009 Christian Grothoff (and other contributing authors)

     GNUnet is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published
     by the Free Software Foundation; either version 2, or (at your
     option) any later version.

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

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

/**
 * @file transport/gnunet-service-transport.c
 * @brief low-level P2P messaging
 * @author Christian Grothoff
 *
 * TODO:
 * - if we do not receive an ACK in response to our
 *   HELLO, retransmit HELLO!
 */
#include "platform.h"
#include "gnunet_client_lib.h"
#include "gnunet_constants.h"
#include "gnunet_getopt_lib.h"
#include "gnunet_hello_lib.h"
#include "gnunet_os_lib.h"
#include "gnunet_peerinfo_service.h"
#include "gnunet_plugin_lib.h"
#include "gnunet_protocols.h"
#include "gnunet_service_lib.h"
#include "gnunet_signatures.h"
#include "plugin_transport.h"
#include "transport.h"

/**
 * How many messages can we have pending for a given client process
 * before we start to drop incoming messages?  We typically should
 * have only one client and so this would be the primary buffer for
 * messages, so the number should be chosen rather generously.
 *
 * The expectation here is that most of the time the queue is large
 * enough so that a drop is virtually never required.
 */
#define MAX_PENDING 128

/**
 * How often should we try to reconnect to a peer using a particular
 * transport plugin before giving up?  Note that the plugin may be
 * added back to the list after PLUGIN_RETRY_FREQUENCY expires.
 */
#define MAX_CONNECT_RETRY 3

/**
 * How often must a peer violate bandwidth quotas before we start
 * to simply drop its messages?
 */
#define QUOTA_VIOLATION_DROP_THRESHOLD 100

/**
 * How long until a HELLO verification attempt should time out?
 * Must be rather small, otherwise a partially successful HELLO
 * validation (some addresses working) might not be available
 * before a client's request for a connection fails for good.
 * Besides, if a single request to an address takes a long time,
 * then the peer is unlikely worthwhile anyway.
 */
#define HELLO_VERIFICATION_TIMEOUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 3)

/**
 * How often do we re-add (cheaper) plugins to our list of plugins
 * to try for a given connected peer?
 */
#define PLUGIN_RETRY_FREQUENCY GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MINUTES, 15)

/**
 * After how long do we expire an address in a HELLO
 * that we just validated?  This value is also used
 * for our own addresses when we create a HELLO.
 */
#define HELLO_ADDRESS_EXPIRATION GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_HOURS, 12)


/**
 * Entry in linked list of network addresses.
 */
struct AddressList
{
  /**
   * This is a linked list.
   */
  struct AddressList *next;

  /**
   * The address, actually a pointer to the end
   * of this struct.  Do not free!
   */
  void *addr;

  /**
   * How long until we auto-expire this address (unless it is
   * re-confirmed by the transport)?
   */
  struct GNUNET_TIME_Absolute expires;

  /**
   * Length of addr.
   */
  size_t addrlen;

};


/**
 * Entry in linked list of all of our plugins.
 */
struct TransportPlugin
{

  /**
   * This is a linked list.
   */
  struct TransportPlugin *next;

  /**
   * API of the transport as returned by the plugin's
   * initialization function.
   */
  struct GNUNET_TRANSPORT_PluginFunctions *api;

  /**
   * Short name for the plugin (i.e. "tcp").
   */
  char *short_name;

  /**
   * Name of the library (i.e. "gnunet_plugin_transport_tcp").
   */
  char *lib_name;

  /**
   * List of our known addresses for this transport.
   */
  struct AddressList *addresses;

  /**
   * Environment this transport service is using
   * for this plugin.
   */
  struct GNUNET_TRANSPORT_PluginEnvironment env;

  /**
   * ID of task that is used to clean up expired addresses.
   */
  GNUNET_SCHEDULER_TaskIdentifier address_update_task;


  /**
   * Set to GNUNET_YES if we need to scrap the existing
   * list of "addresses" and start fresh when we receive
   * the next address update from a transport.  Set to
   * GNUNET_NO if we should just add the new address
   * to the list and wait for the commit call.
   */
  int rebuild;
};

struct NeighborList;

/**
 * For each neighbor we keep a list of messages
 * that we still want to transmit to the neighbor.
 */
struct MessageQueue
{

  /**
   * This is a linked list.
   */
  struct MessageQueue *next;

  /**
   * The message we want to transmit.
   */
  struct GNUNET_MessageHeader *message;

  /**
   * Client responsible for queueing the message;
   * used to check that a client has not two messages
   * pending for the same target.  Can be NULL.
   */
  struct TransportClient *client;

  /**
   * Neighbor this entry belongs to.
   */
  struct NeighborList *neighbor;

  /**
   * Plugin that we used for the transmission.
   * NULL until we scheduled a transmission.
   */
  struct TransportPlugin *plugin;

  /**
   * Internal message of the transport system that should not be
   * included in the usual SEND-SEND_OK transmission confirmation
   * traffic management scheme.  Typically, "internal_msg" will
   * be set whenever "client" is NULL (but it is not strictly
   * required).
   */
  int internal_msg;

  /**
   * How important is the message?
   */
  unsigned int priority;

};


/**
 * For a given Neighbor, which plugins are available
 * to talk to this peer and what are their costs?
 */
struct ReadyList
{

  /**
   * This is a linked list.
   */
  struct ReadyList *next;

  /**
   * Which of our transport plugins does this entry
   * represent?
   */
  struct TransportPlugin *plugin;

  /**
   * Neighbor this entry belongs to.
   */
  struct NeighborList *neighbor;

  /**
   * What was the last latency observed for this plugin
   * and peer?  Invalid if connected is GNUNET_NO.
   */
  struct GNUNET_TIME_Relative latency;

  /**
   * If we did not successfully transmit a message to the given peer
   * via this connection during the specified time, we should consider
   * the connection to be dead.  This is used in the case that a TCP
   * transport simply stalls writing to the stream but does not
   * formerly get a signal that the other peer died.
   */
  struct GNUNET_TIME_Absolute timeout;

  /**
   * Is this plugin currently connected?  The first time
   * we transmit or send data to a peer via a particular
   * plugin, we set this to GNUNET_YES.  If we later get
   * an error (disconnect notification or transmission
   * failure), we set it back to GNUNET_NO.  Each time the
   * value is set to GNUNET_YES, we increment the
   * "connect_attempts" counter.  If that one reaches a
   * particular threshold, we consider the plugin to not
   * be working properly at this time for the given peer
   * and remove it from the eligible list.
   */
  int connected;

  /**
   * How often have we tried to connect using this plugin?
   */
  unsigned int connect_attempts;

  /**
   * Is this plugin ready to transmit to the specific target?
   * GNUNET_NO if not.  Initially, all plugins are marked ready.  If a
   * transmission is in progress, "transmit_ready" is set to
   * GNUNET_NO.
   */
  int transmit_ready;

};


/**
 * Entry in linked list of all of our current neighbors.
 */
struct NeighborList
{

  /**
   * This is a linked list.
   */
  struct NeighborList *next;

  /**
   * Which of our transports is connected to this peer
   * and what is their status?
   */
  struct ReadyList *plugins;

  /**
   * List of messages we would like to send to this peer;
   * must contain at most one message per client.
   */
  struct MessageQueue *messages;

  /**
   * Identity of this neighbor.
   */
  struct GNUNET_PeerIdentity id;

  /*
   * Opaque addr of this peer, only known to the plugin
   */
  char *addr;

  /*
   * Size of addr
   */
  size_t addr_len;

  /**
   * ID of task scheduled to run when this peer is about to
   * time out (will free resources associated with the peer).
   */
  GNUNET_SCHEDULER_TaskIdentifier timeout_task;

  /**
   * How long until we should consider this peer dead
   * (if we don't receive another message in the
   * meantime)?
   */
  struct GNUNET_TIME_Absolute peer_timeout;

  /**
   * At what time did we reset last_received last?
   */
  struct GNUNET_TIME_Absolute last_quota_update;

  /**
   * At what time should we try to again add plugins to
   * our ready list?
   */
  struct GNUNET_TIME_Absolute retry_plugins_time;

  /**
   * How many bytes have we received since the "last_quota_update"
   * timestamp?
   */
  uint64_t last_received;

  /**
   * Global quota for inbound traffic for the neighbor in bytes/ms.
   */
  uint32_t quota_in;

  /**
   * How often has the other peer (recently) violated the
   * inbound traffic limit?  Incremented by 10 per violation,
   * decremented by 1 per non-violation (for each
   * time interval).
   */
  unsigned int quota_violation_count;

  /**
   * Have we seen an ACK from this neighbor in the past?
   * (used to make up a fake ACK for clients connecting after
   * the neighbor connected to us).
   */
  int saw_ack;

  /* The latency we have seen for this particular address for
   * this particular peer.  This latency may have been calculated
   * over multiple transports.  This value reflects how long it took
   * us to receive a response when SENDING via this particular
   * transport/neighbor/address combination!
   */
  struct GNUNET_TIME_RelativeNBO latency;

};

/**
 * Message used to ask a peer to validate receipt (to check an address
 * from a HELLO).  Followed by the address used.  Note that the
 * recipients response does not affirm that he has this address,
 * only that he got the challenge message.
 */
struct TransportPingMessage
{

  /**
   * Type will be GNUNET_MESSAGE_TYPE_TRANSPORT_PING
   */
  struct GNUNET_MessageHeader header;

  /**
   * Random challenge number (in network byte order).
   */
  uint32_t challenge GNUNET_PACKED;

  /**
   * Who is the intended recipient?
   */
  struct GNUNET_PeerIdentity target;

};


/**
 * Message used to validate a HELLO.  The challenge is included in the
 * confirmation to make matching of replies to requests possible.  The
 * signature signs the original challenge number, our public key, the
 * sender's address (so that the sender can check that the address we
 * saw is plausible for him and possibly detect a MiM attack) and a
 * timestamp (to limit replay).<p>
 *
 * This message is followed by the address of the
 * client that we are observing (which is part of what
 * is being signed).
 */
struct TransportPongMessage
{

  /**
   * Type will be GNUNET_MESSAGE_TYPE_TRANSPORT_PONG
   */
  struct GNUNET_MessageHeader header;

  /**
   * For padding, always zero.
   */
  uint32_t reserved GNUNET_PACKED;

  /**
   * Signature.
   */
  struct GNUNET_CRYPTO_RsaSignature signature;

  /**
   * What are we signing and why?
   */
  struct GNUNET_CRYPTO_RsaSignaturePurpose purpose;

  /**
   * Random challenge number (in network byte order).
   */
  uint32_t challenge GNUNET_PACKED;

  /**
   * Who signed this message?
   */
  struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded signer;

};

/**
 * Linked list of messages to be transmitted to
 * the client.  Each entry is followed by the
 * actual message.
 */
struct ClientMessageQueueEntry
{
  /**
   * This is a linked list.
   */
  struct ClientMessageQueueEntry *next;
};


/**
 * Client connected to the transport service.
 */
struct TransportClient
{

  /**
   * This is a linked list.
   */
  struct TransportClient *next;

  /**
   * Handle to the client.
   */
  struct GNUNET_SERVER_Client *client;

  /**
   * Linked list of messages yet to be transmitted to
   * the client.
   */
  struct ClientMessageQueueEntry *message_queue_head;

  /**
   * Tail of linked list of messages yet to be transmitted to the
   * client.
   */
  struct ClientMessageQueueEntry *message_queue_tail;

  /**
   * Is a call to "transmit_send_continuation" pending?  If so, we
   * must not free this struct (even if the corresponding client
   * disconnects) and instead only remove it from the linked list and
   * set the "client" field to NULL.
   */
  int tcs_pending;

  /**
   * Length of the list of messages pending for this client.
   */
  unsigned int message_count;

};


/**
 * For each HELLO, we may have to validate multiple addresses;
 * each address gets its own request entry.
 */
struct ValidationAddress
{
  /**
   * This is a linked list.
   */
  struct ValidationAddress *next;

  /**
   * Name of the transport.
   */
  char *transport_name;

  /**
   * When should this validated address expire?
   */
  struct GNUNET_TIME_Absolute expiration;

  /**
   * Length of the address we are validating.
   */
  size_t addr_len;

  /**
   * Challenge number we used.
   */
  uint32_t challenge;

  /**
   * Set to GNUNET_YES if the challenge was met,
   * GNUNET_SYSERR if we know it failed, GNUNET_NO
   * if we are waiting on a response.
   */
  int ok;
};


/**
 * Entry in linked list of all HELLOs awaiting validation.
 */
struct ValidationList
{

  /**
   * This is a linked list.
   */
  struct ValidationList *next;

  /**
   * Linked list with one entry per address from the HELLO
   * that needs to be validated.
   */
  struct ValidationAddress *addresses;

  /**
   * The public key of the peer.
   */
  struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded publicKey;

  /**
   * When does this record time-out? (assuming the
   * challenge goes unanswered)
   */
  struct GNUNET_TIME_Absolute timeout;

};


/**
 * HELLOs awaiting validation.
 */
static struct ValidationList *pending_validations;

/**
 * Our HELLO message.
 */
static struct GNUNET_HELLO_Message *our_hello;

/**
 * "version" of "our_hello".  Used to see if a given
 * neighbor has already been sent the latest version
 * of our HELLO message.
 */
static unsigned int our_hello_version;

/**
 * Our public key.
 */
static struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded my_public_key;

/**
 * Our identity.
 */
static struct GNUNET_PeerIdentity my_identity;

/**
 * Our private key.
 */
static struct GNUNET_CRYPTO_RsaPrivateKey *my_private_key;

/**
 * Our scheduler.
 */
struct GNUNET_SCHEDULER_Handle *sched;

/**
 * Our configuration.
 */
const struct GNUNET_CONFIGURATION_Handle *cfg;

/**
 * Linked list of all clients to this service.
 */
static struct TransportClient *clients;

/**
 * All loaded plugins.
 */
static struct TransportPlugin *plugins;

/**
 * Our server.
 */
static struct GNUNET_SERVER_Handle *server;

/**
 * All known neighbors and their HELLOs.
 */
static struct NeighborList *neighbors;

/**
 * Number of neighbors we'd like to have.
 */
static uint32_t max_connect_per_transport;


/**
 * Find an entry in the neighbor list for a particular peer.
 * if sender_address is not specified (NULL) then return the
 * first matching entry.  If sender_address is specified, then
 * make sure that the address and address_len also matches.
 *
 * @return NULL if not found.
 */
static struct NeighborList *
find_neighbor (const struct GNUNET_PeerIdentity *key, const char *sender_address,
    size_t sender_address_len)
{
  struct NeighborList *head = neighbors;
  if (sender_address == NULL)
    {
      while ((head != NULL) &&
            (0 != memcmp (key, &head->id, sizeof (struct GNUNET_PeerIdentity))))
        head = head->next;
    }
    else
    {
      while ((head != NULL) &&
             (0 != memcmp (key, &head->id, sizeof (struct GNUNET_PeerIdentity))) &&
             (sender_address_len != head->addr_len) &&
             (0 != memcmp (sender_address, &head->addr, head->addr_len)))
        head = head->next;
    }
  return head;
}


/**
 * Find an entry in the transport list for a particular transport.
 *
 * @return NULL if not found.
 */
static struct TransportPlugin *
find_transport (const char *short_name)
{
  struct TransportPlugin *head = plugins;
  while ((head != NULL) && (0 != strcmp (short_name, head->short_name)))
    head = head->next;
  return head;
}


/**
 * Update the quota values for the given neighbor now.
 */
static void
update_quota (struct NeighborList *n)
{
  struct GNUNET_TIME_Relative delta;
  uint64_t allowed;
  uint64_t remaining;

  delta = GNUNET_TIME_absolute_get_duration (n->last_quota_update);
  if (delta.value < MIN_QUOTA_REFRESH_TIME)
    return;                     /* not enough time passed for doing quota update */
  allowed = delta.value * n->quota_in;
  if (n->last_received < allowed)
    {
      remaining = allowed - n->last_received;
      if (n->quota_in > 0)
        remaining /= n->quota_in;
      else
        remaining = 0;
      if (remaining > MAX_BANDWIDTH_CARRY)
        remaining = MAX_BANDWIDTH_CARRY;
      n->last_received = 0;
      n->last_quota_update = GNUNET_TIME_absolute_get ();
      n->last_quota_update.value -= remaining;
      if (n->quota_violation_count > 0)
        n->quota_violation_count--;
    }
  else
    {
      n->last_received -= allowed;
      n->last_quota_update = GNUNET_TIME_absolute_get ();
      if (n->last_received > allowed)
        {
          /* more than twice the allowed rate! */
          n->quota_violation_count += 10;
        }
    }
}


/**
 * Function called to notify a client about the socket
 * being ready to queue more data.  "buf" will be
 * NULL and "size" zero if the socket was closed for
 * writing in the meantime.
 *
 * @param cls closure
 * @param size number of bytes available in buf
 * @param buf where the callee should write the message
 * @return number of bytes written to buf
 */
static size_t
transmit_to_client_callback (void *cls, size_t size, void *buf)
{
  struct TransportClient *client = cls;
  struct ClientMessageQueueEntry *q;
  uint16_t msize;
  size_t tsize;
  const struct GNUNET_MessageHeader *msg;
  struct GNUNET_CONNECTION_TransmitHandle *th;
  char *cbuf;

  if (buf == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Transmission to client failed, closing connection.\n");
      /* fatal error with client, free message queue! */
      while (NULL != (q = client->message_queue_head))
        {
          client->message_queue_head = q->next;
          GNUNET_free (q);
        }
      client->message_queue_tail = NULL;
      client->message_count = 0;
      return 0;
    }
  cbuf = buf;
  tsize = 0;
  while (NULL != (q = client->message_queue_head))
    {
      msg = (const struct GNUNET_MessageHeader *) &q[1];
      msize = ntohs (msg->size);
      if (msize + tsize > size)
        break;
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Transmitting message of type %u to client.\n",
                  ntohs (msg->type));
#endif
      client->message_queue_head = q->next;
      if (q->next == NULL)
        client->message_queue_tail = NULL;
      memcpy (&cbuf[tsize], msg, msize);
      tsize += msize;
      GNUNET_free (q);
      client->message_count--;
    }
  if (NULL != q)
    {
      GNUNET_assert (msize >= sizeof (struct GNUNET_MessageHeader));
      th = GNUNET_SERVER_notify_transmit_ready (client->client,
                                                msize,
                                                GNUNET_TIME_UNIT_FOREVER_REL,
                                                &transmit_to_client_callback,
                                                client);
      GNUNET_assert (th != NULL);
    }
  return tsize;
}


/**
 * Send the specified message to the specified client.  Since multiple
 * messages may be pending for the same client at a time, this code
 * makes sure that no message is lost.
 *
 * @param client client to transmit the message to
 * @param msg the message to send
 * @param may_drop can this message be dropped if the
 *        message queue for this client is getting far too large?
 */
static void
transmit_to_client (struct TransportClient *client,
                    const struct GNUNET_MessageHeader *msg, int may_drop)
{
  struct ClientMessageQueueEntry *q;
  uint16_t msize;
  struct GNUNET_CONNECTION_TransmitHandle *th;

  if ((client->message_count >= MAX_PENDING) && (GNUNET_YES == may_drop))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  _
                  ("Dropping message, have %u messages pending (%u is the soft limit)\n"),
                  client->message_count, MAX_PENDING);
      /* TODO: call to statistics... */
      return;
    }
  client->message_count++;
  msize = ntohs (msg->size);
  GNUNET_assert (msize >= sizeof (struct GNUNET_MessageHeader));
  q = GNUNET_malloc (sizeof (struct ClientMessageQueueEntry) + msize);
  memcpy (&q[1], msg, msize);
  /* append to message queue */
  if (client->message_queue_tail == NULL)
    {
      client->message_queue_tail = q;
    }
  else
    {
      client->message_queue_tail->next = q;
      client->message_queue_tail = q;
    }
  if (client->message_queue_head == NULL)
    {
      client->message_queue_head = q;
      th = GNUNET_SERVER_notify_transmit_ready (client->client,
                                                msize,
                                                GNUNET_TIME_UNIT_FOREVER_REL,
                                                &transmit_to_client_callback,
                                                client);
      GNUNET_assert (th != NULL);
    }
}


/**
 * Find alternative plugins for communication.
 *
 * @param neighbor for which neighbor should we try to find
 *        more plugins?
 */
static void
try_alternative_plugins (struct NeighborList *neighbor)
{
  struct ReadyList *rl;

  if ((neighbor->plugins != NULL) &&
      (neighbor->retry_plugins_time.value >
       GNUNET_TIME_absolute_get ().value))
    return;                     /* don't try right now */
  neighbor->retry_plugins_time
    = GNUNET_TIME_relative_to_absolute (PLUGIN_RETRY_FREQUENCY);

  rl = neighbor->plugins;
  while (rl != NULL)
    {
      if (rl->connect_attempts > 0)
        rl->connect_attempts--; /* amnesty */
      rl = rl->next;
    }

}


/**
 * The peer specified by the given neighbor has timed-out or a plugin
 * has disconnected.  We may either need to do nothing (other plugins
 * still up), or trigger a full disconnect and clean up.  This
 * function updates our state and do the necessary notifications.
 * Also notifies our clients that the neighbor is now officially
 * gone.
 *
 * @param n the neighbor list entry for the peer
 * @param check should we just check if all plugins
 *        disconnected or must we ask all plugins to
 *        disconnect?
 */
static void disconnect_neighbor (struct NeighborList *n, int check);


/**
 * Check the ready list for the given neighbor and
 * if a plugin is ready for transmission (and if we
 * have a message), do so!
 *
 * @param neighbor target peer for which to check the plugins
 */
static void try_transmission_to_peer (struct NeighborList *neighbor);


/**
 * Function called by the GNUNET_TRANSPORT_TransmitFunction
 * upon "completion" of a send request.  This tells the API
 * that it is now legal to send another message to the given
 * peer.
 *
 * @param cls closure, identifies the entry on the
 *            message queue that was transmitted and the
 *            client responsible for queueing the message
 * @param target the peer receiving the message
 * @param result GNUNET_OK on success, if the transmission
 *           failed, we should not tell the client to transmit
 *           more messages
 */
static void
transmit_send_continuation (void *cls,
                            const struct GNUNET_PeerIdentity *target,
                            int result)
{
  struct MessageQueue *mq = cls;
  struct ReadyList *rl;
  struct SendOkMessage send_ok_msg;
  struct NeighborList *n;

  GNUNET_assert (mq != NULL);
  n = mq->neighbor;
  GNUNET_assert (n != NULL);
  GNUNET_assert (0 ==
                 memcmp (&n->id, target,
                         sizeof (struct GNUNET_PeerIdentity)));
  rl = n->plugins;
  while ((rl != NULL) && (rl->plugin != mq->plugin))
    rl = rl->next;
  GNUNET_assert (rl != NULL);
  if (result == GNUNET_OK)
    {
      rl->timeout =
        GNUNET_TIME_relative_to_absolute
        (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
    }
  else
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Transmission to peer `%s' failed, marking connection as down.\n",
                  GNUNET_i2s (target));
      rl->connected = GNUNET_NO;
    }
  if (!mq->internal_msg)
    rl->transmit_ready = GNUNET_YES;
  if (mq->client != NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Notifying client %p about failed transission to peer `%4s'.\n",
                  mq->client, GNUNET_i2s (target));
      send_ok_msg.header.size = htons (sizeof (send_ok_msg));
      send_ok_msg.header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_SEND_OK);
      send_ok_msg.success = htonl (result);
      send_ok_msg.peer = n->id;
      transmit_to_client (mq->client, &send_ok_msg.header, GNUNET_NO);
    }
  GNUNET_free (mq->message);
  GNUNET_free (mq);
  /* one plugin just became ready again, try transmitting
     another message (if available) */
  if (result == GNUNET_OK)
    try_transmission_to_peer (n);
  else
    disconnect_neighbor (n, GNUNET_YES);
}


/**
 * Check the ready list for the given neighbor and
 * if a plugin is ready for transmission (and if we
 * have a message), do so!
 */
static void
try_transmission_to_peer (struct NeighborList *neighbor)
{
  struct ReadyList *pos;
  struct GNUNET_TIME_Relative min_latency;
  struct ReadyList *rl;
  struct MessageQueue *mq;
  struct GNUNET_TIME_Absolute now;

  if (neighbor->messages == NULL)
    return;                     /* nothing to do */
  try_alternative_plugins (neighbor);
  min_latency = GNUNET_TIME_UNIT_FOREVER_REL;
  rl = NULL;
  mq = neighbor->messages;
  now = GNUNET_TIME_absolute_get ();
  pos = neighbor->plugins;
  while (pos != NULL)
    {
      /* set plugins that are inactive for a long time back to disconnected */
      if ((pos->timeout.value < now.value) && (pos->connected == GNUNET_YES))
        {
#if DEBUG_TRANSPORT
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "Marking long-time inactive connection to `%4s' as down.\n",
                      GNUNET_i2s (&neighbor->id));
#endif
          pos->connected = GNUNET_NO;
        }
      if (((GNUNET_YES == pos->transmit_ready) ||
           (mq->internal_msg)) &&
          (pos->connect_attempts < MAX_CONNECT_RETRY) &&
          ((rl == NULL) || (min_latency.value > pos->latency.value)))
        {
          rl = pos;
          min_latency = pos->latency;
        }
      pos = pos->next;
    }
  if (rl == NULL)
    {
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "No plugin ready to transmit message\n");
#endif
      return;                   /* nobody ready */
    }
  if (GNUNET_NO == rl->connected)
    {
      rl->connect_attempts++;
      rl->connected = GNUNET_YES;
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Establishing fresh connection with `%4s' via plugin `%s'\n",
                  GNUNET_i2s (&neighbor->id), rl->plugin->short_name);
#endif
    }
  neighbor->messages = mq->next;
  mq->plugin = rl->plugin;
  if (!mq->internal_msg)
    rl->transmit_ready = GNUNET_NO;
#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Giving message of type `%u' for `%4s' to plugin `%s'\n",
              ntohs (mq->message->type),
              GNUNET_i2s (&neighbor->id), rl->plugin->short_name);
#endif

  rl->plugin->api->send (rl->plugin->api->cls,
                         &neighbor->id,
                         mq->message,
                         mq->priority,
                         GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT,
                         rl->neighbor->addr,
                         rl->neighbor->addr_len,
                         GNUNET_NO,
                         &transmit_send_continuation, mq);
}


/**
 * Send the specified message to the specified peer.
 *
 * @param client source of the transmission request (can be NULL)
 * @param priority how important is the message
 * @param msg message to send
 * @param is_internal is this an internal message
 * @param neighbor handle to the neighbor for transmission
 */
static void
transmit_to_peer (struct TransportClient *client,
                  unsigned int priority,
                  const struct GNUNET_MessageHeader *msg,
                  int is_internal, struct NeighborList *neighbor)
{
  struct MessageQueue *mq;
  struct MessageQueue *mqe;
  struct GNUNET_MessageHeader *m;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              _("Sending message of type %u to peer `%4s'\n"),
              ntohs (msg->type), GNUNET_i2s (&neighbor->id));
#endif
  if (client != NULL)
    {
      /* check for duplicate submission */
      mq = neighbor->messages;
      while (NULL != mq)
        {
          if (mq->client == client)
            {
              /* client transmitted to same peer twice
                 before getting SendOk! */
              GNUNET_break (0);
              return;
            }
          mq = mq->next;
        }
    }
  mq = GNUNET_malloc (sizeof (struct MessageQueue));
  mq->client = client;
  m = GNUNET_malloc (ntohs (msg->size));
  memcpy (m, msg, ntohs (msg->size));
  mq->message = m;
  mq->neighbor = neighbor;
  mq->internal_msg = is_internal;
  mq->priority = priority;

  /* find tail */
  mqe = neighbor->messages;
  if (mqe != NULL)
    while (mqe->next != NULL)
      mqe = mqe->next;
  if (mqe == NULL)
    {
      /* new head */
      neighbor->messages = mq;
      try_transmission_to_peer (neighbor);
    }
  else
    {
      /* append */
      mqe->next = mq;
    }
}


/**
 * FIXME: document.
 */
struct GeneratorContext
{
  struct TransportPlugin *plug_pos;
  struct AddressList *addr_pos;
  struct GNUNET_TIME_Absolute expiration;
};


/**
 * FIXME: document.
 */
static size_t
address_generator (void *cls, size_t max, void *buf)
{
  struct GeneratorContext *gc = cls;
  size_t ret;

  while ((gc->addr_pos == NULL) && (gc->plug_pos != NULL))
    {
      gc->plug_pos = gc->plug_pos->next;
      gc->addr_pos = (gc->plug_pos != NULL) ? gc->plug_pos->addresses : NULL;
    }
  if (NULL == gc->plug_pos)
    return 0;
  ret = GNUNET_HELLO_add_address (gc->plug_pos->short_name,
                                  gc->expiration,
                                  gc->addr_pos->addr,
                                  gc->addr_pos->addrlen, buf, max);
  gc->addr_pos = gc->addr_pos->next;
  return ret;
}


/**
 * Construct our HELLO message from all of the addresses of
 * all of the transports.
 */
static void
refresh_hello ()
{
  struct GNUNET_HELLO_Message *hello;
  struct TransportClient *cpos;
  struct NeighborList *npos;
  struct GeneratorContext gc;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
              "Refreshing my `%s'\n", "HELLO");
#endif
  gc.plug_pos = plugins;
  gc.addr_pos = plugins != NULL ? plugins->addresses : NULL;
  gc.expiration = GNUNET_TIME_relative_to_absolute (HELLO_ADDRESS_EXPIRATION);
  hello = GNUNET_HELLO_create (&my_public_key, &address_generator, &gc);
  cpos = clients;
  while (cpos != NULL)
    {
      transmit_to_client (cpos,
                          (const struct GNUNET_MessageHeader *) hello,
                          GNUNET_NO);
      cpos = cpos->next;
    }

  GNUNET_free_non_null (our_hello);
  our_hello = hello;
  our_hello_version++;
  GNUNET_PEERINFO_add_peer (cfg, sched, &my_identity, our_hello);
  npos = neighbors;
  while (npos != NULL)
    {
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
                  "Transmitting updated `%s' to neighbor `%4s'\n",
                  "HELLO", GNUNET_i2s (&npos->id));
#endif
      transmit_to_peer (NULL, 0,
                        (const struct GNUNET_MessageHeader *) our_hello,
                        GNUNET_YES, npos);
      npos = npos->next;
    }
}


/**
 * Task used to clean up expired addresses for a plugin.
 *
 * @param cls closure
 * @param tc context
 */
static void
expire_address_task (void *cls,
                     const struct GNUNET_SCHEDULER_TaskContext *tc);


/**
 * Update the list of addresses for this plugin,
 * expiring those that are past their expiration date.
 *
 * @param plugin addresses of which plugin should be recomputed?
 * @param fresh set to GNUNET_YES if a new address was added
 *        and we need to regenerate the HELLO even if nobody
 *        expired
 */
static void
update_addresses (struct TransportPlugin *plugin, int fresh)
{
  struct GNUNET_TIME_Relative min_remaining;
  struct GNUNET_TIME_Relative remaining;
  struct GNUNET_TIME_Absolute now;
  struct AddressList *pos;
  struct AddressList *prev;
  struct AddressList *next;
  int expired;

  if (plugin->address_update_task != GNUNET_SCHEDULER_NO_TASK)
    GNUNET_SCHEDULER_cancel (plugin->env.sched, plugin->address_update_task);
  plugin->address_update_task = GNUNET_SCHEDULER_NO_TASK;
  now = GNUNET_TIME_absolute_get ();
  min_remaining = GNUNET_TIME_UNIT_FOREVER_REL;
  expired = GNUNET_NO;
  prev = NULL;
  pos = plugin->addresses;
  while (pos != NULL)
    {
      next = pos->next;
      if (pos->expires.value < now.value)
        {
          expired = GNUNET_YES;
          if (prev == NULL)
            plugin->addresses = pos->next;
          else
            prev->next = pos->next;
          GNUNET_free (pos);
        }
      else
        {
          remaining = GNUNET_TIME_absolute_get_remaining (pos->expires);
          if (remaining.value < min_remaining.value)
            min_remaining = remaining;
          prev = pos;
        }
      pos = next;
    }

  if (expired || fresh)
    refresh_hello ();
  if (min_remaining.value < GNUNET_TIME_UNIT_FOREVER_REL.value)
    plugin->address_update_task
      = GNUNET_SCHEDULER_add_delayed (plugin->env.sched,
                                      min_remaining,
                                      &expire_address_task, plugin);

}


/**
 * Task used to clean up expired addresses for a plugin.
 *
 * @param cls closure
 * @param tc context
 */
static void
expire_address_task (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct TransportPlugin *plugin = cls;
  plugin->address_update_task = GNUNET_SCHEDULER_NO_TASK;
  update_addresses (plugin, GNUNET_NO);
}


/**
 * Function that must be called by each plugin to notify the
 * transport service about the addresses under which the transport
 * provided by the plugin can be reached.
 *
 * @param cls closure
 * @param name name of the transport that generated the address
 * @param addr one of the addresses of the host, NULL for the last address
 *        the specific address format depends on the transport
 * @param addrlen length of the address
 * @param expires when should this address automatically expire?
 */
static void
plugin_env_notify_address (void *cls,
                           const char *name,
                           const void *addr,
                           size_t addrlen,
                           struct GNUNET_TIME_Relative expires)
{
  struct TransportPlugin *p = cls;
  struct AddressList *al;
  struct GNUNET_TIME_Absolute abex;

  abex = GNUNET_TIME_relative_to_absolute (expires);
  GNUNET_assert (p == find_transport (name));

  al = p->addresses;
  while (al != NULL)
    {
      if ((addrlen == al->addrlen) && (0 == memcmp (addr, &al[1], addrlen)))
        {
          if (al->expires.value < abex.value)
            al->expires = abex;
          return;
        }
      al = al->next;
    }
#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Plugin `%s' informs us about a new address `%s'\n", name,
              GNUNET_a2s (addr, addrlen));
#endif
  al = GNUNET_malloc (sizeof (struct AddressList) + addrlen);
  al->addr = &al[1];
  al->next = p->addresses;
  p->addresses = al;
  al->expires = abex;
  al->addrlen = addrlen;
  memcpy (&al[1], addr, addrlen);
  update_addresses (p, GNUNET_YES);
}


/**
 * Notify all of our clients about a peer connecting.
 */
static void
notify_clients_connect (const struct GNUNET_PeerIdentity *peer,
                        struct GNUNET_TIME_Relative latency)
{
  struct ConnectInfoMessage cim;
  struct TransportClient *cpos;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Informing clients about peer `%4s' connecting to us\n",
              GNUNET_i2s (peer));
#endif
  cim.header.size = htons (sizeof (struct ConnectInfoMessage));
  cim.header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_CONNECT);
  cim.quota_out = htonl (GNUNET_CONSTANTS_DEFAULT_BPM_IN_OUT / (60 * 1000));
  cim.latency = GNUNET_TIME_relative_hton (latency);
  memcpy (&cim.id, peer, sizeof (struct GNUNET_PeerIdentity));
  cpos = clients;
  while (cpos != NULL)
    {
      transmit_to_client (cpos, &cim.header, GNUNET_NO);
      cpos = cpos->next;
    }
}


/**
 * Notify all of our clients about a peer disconnecting.
 */
static void
notify_clients_disconnect (const struct GNUNET_PeerIdentity *peer)
{
  struct DisconnectInfoMessage dim;
  struct TransportClient *cpos;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Informing clients about peer `%4s' disconnecting\n",
              GNUNET_i2s (peer));
#endif
  dim.header.size = htons (sizeof (struct DisconnectInfoMessage));
  dim.header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_DISCONNECT);
  dim.reserved = htonl (0);
  memcpy (&dim.peer, peer, sizeof (struct GNUNET_PeerIdentity));
  cpos = clients;
  while (cpos != NULL)
    {
      transmit_to_client (cpos, &dim.header, GNUNET_NO);
      cpos = cpos->next;
    }
}


/**
 * Copy any validated addresses to buf.
 *
 * @return 0 once all addresses have been
 *         returned
 */
static size_t
list_validated_addresses (void *cls, size_t max, void *buf)
{
  struct ValidationAddress **va = cls;
  size_t ret;

  while ((NULL != *va) && ((*va)->ok != GNUNET_YES))
    *va = (*va)->next;
  if (NULL == *va)
    return 0;
  ret = GNUNET_HELLO_add_address ((*va)->transport_name,
                                  (*va)->expiration,
                                  &(*va)[1], (*va)->addr_len, buf, max);
  *va = (*va)->next;
  return ret;
}


/**
 * HELLO validation cleanup task.
 */
static void
cleanup_validation (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct ValidationAddress *va;
  struct ValidationList *pos;
  struct ValidationList *prev;
  struct GNUNET_TIME_Absolute now;
  struct GNUNET_TIME_Absolute first;
  struct GNUNET_HELLO_Message *hello;
  struct GNUNET_PeerIdentity pid;
  struct NeighborList *n;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
              "HELLO validation cleanup background task running...\n");
#endif
  now = GNUNET_TIME_absolute_get ();
  prev = NULL;
  pos = pending_validations;
  while (pos != NULL)
    {
      if (pos->timeout.value < now.value)
        {
          if (prev == NULL)
            pending_validations = pos->next;
          else
            prev->next = pos->next;
          va = pos->addresses;
          hello = GNUNET_HELLO_create (&pos->publicKey,
                                       &list_validated_addresses, &va);
          GNUNET_CRYPTO_hash (&pos->publicKey,
                              sizeof (struct
                                      GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded),
                              &pid.hashPubKey);
#if DEBUG_TRANSPORT
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "Creating persistent `%s' message for peer `%4s' based on confirmed addresses.\n",
                      "HELLO", GNUNET_i2s (&pid));
#endif
          GNUNET_PEERINFO_add_peer (cfg, sched, &pid, hello);
          n = find_neighbor (&pid, NULL, 0);
          if (NULL != n)
            try_transmission_to_peer (n);
          GNUNET_free (hello);
          while (NULL != (va = pos->addresses))
            {
              pos->addresses = va->next;
              GNUNET_free (va->transport_name);
              GNUNET_free (va);
            }
          GNUNET_free (pos);
          if (prev == NULL)
            pos = pending_validations;
          else
            pos = prev->next;
          continue;
        }
      prev = pos;
      pos = pos->next;
    }

  /* finally, reschedule cleanup if needed; list is
     ordered by timeout, so we need the last element... */
  if (NULL != pending_validations)
    {
      first = pending_validations->timeout;
      pos = pending_validations;
      while (pos != NULL)
        {
          first = GNUNET_TIME_absolute_min (first, pos->timeout);
          pos = pos->next;
        }
      GNUNET_SCHEDULER_add_delayed (sched,
                                    GNUNET_TIME_absolute_get_remaining
                                    (first), &cleanup_validation, NULL);
    }
}




/**
 * Function that will be called if we receive a validation
 * of an address challenge that we transmitted to another
 * peer.  Note that the validation should only be considered
 * acceptable if the challenge matches AND if the sender
 * address is at least a plausible address for this peer
 * (otherwise we may be seeing a MiM attack).
 *
 * @param cls closure
 * @param name name of the transport that generated the address
 * @param peer who responded to our challenge
 * @param challenge the challenge number we presumably used
 * @param sender_addr string describing our sender address (as observed
 *         by the other peer in human-readable format)
 */
static void
handle_pong (void *cls, const struct GNUNET_MessageHeader *message,
             const struct GNUNET_PeerIdentity *peer,
             const char *sender_address,
             size_t sender_address_len)
{
  unsigned int not_done;
  int matched;
  struct ValidationList *pos;
  struct ValidationAddress *va;
  struct GNUNET_PeerIdentity id;

  int challenge = 1; /* FIXME: Pull this number out of the PONG message */
  pos = pending_validations;
  while (pos != NULL)
    {
      GNUNET_CRYPTO_hash (&pos->publicKey,
                          sizeof (struct
                                  GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded),
                          &id.hashPubKey);
      if (0 == memcmp (peer, &id, sizeof (struct GNUNET_PeerIdentity)))
        break;
      pos = pos->next;
    }
  if (pos == NULL)
    {
      /* TODO: call statistics (unmatched PONG) */
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  _
                  ("Received validation response but have no record of any validation request for `%4s'. Ignoring.\n"),
                  GNUNET_i2s (peer));
      return;
    }
  not_done = 0;
  matched = GNUNET_NO;
  va = pos->addresses;
  while (va != NULL)
    {
      if (va->challenge == challenge)
        {
#if DEBUG_TRANSPORT
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "Confirmed validity of address, peer `%4s' has address `%s'.\n",
                      GNUNET_i2s (peer),
                      GNUNET_a2s ((const struct sockaddr *) &va[1],
                                  va->addr_len));
#endif
          GNUNET_log (GNUNET_ERROR_TYPE_INFO | GNUNET_ERROR_TYPE_BULK,
                      _
                      ("Another peer saw us using the address `%s' via `FIXME'. If this is not plausible, this address should be listed in the configuration as implausible to avoid MiM attacks.\n"),
                      sender_address);
          va->ok = GNUNET_YES;
          va->expiration =
            GNUNET_TIME_relative_to_absolute (HELLO_ADDRESS_EXPIRATION);
          matched = GNUNET_YES;
        }
      if (va->ok != GNUNET_YES)
        not_done++;
      va = va->next;
    }
  if (GNUNET_NO == matched)
    {
      /* TODO: call statistics (unmatched PONG) */
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  _
                  ("Received `%s' message but have no record of a matching `%s' message. Ignoring.\n"),
                  "PONG", "PING");
    }
  if (0 == not_done)
    {
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "All addresses validated, will now construct `%s' for `%4s'.\n",
                  "HELLO", GNUNET_i2s (peer));
#endif
      pos->timeout.value = 0;
      GNUNET_SCHEDULER_add_with_priority (sched,
                                          GNUNET_SCHEDULER_PRIORITY_IDLE,
                                          &cleanup_validation, NULL);
    }
  else
    {
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Still waiting for %u additional `%s' messages before constructing `%s' for `%4s'.\n",
                  not_done, "PONG", "HELLO", GNUNET_i2s (peer));
#endif
    }
}


struct CheckHelloValidatedContext
{
  /**
   * Plugin for which we are validating.
   */
  struct TransportPlugin *plugin;

  /**
   * Hello that we are validating.
   */
  struct GNUNET_HELLO_Message *hello;

  /**
   * Validation list being build.
   */
  struct ValidationList *e;

  /**
   * Context for peerinfo iteration.
   * NULL after we are done processing peerinfo's information.
   */
  struct GNUNET_PEERINFO_IteratorContext *piter;

};


/**
 * Append the given address to the list of entries
 * that need to be validated.
 */
static int
run_validation (void *cls,
                const char *tname,
                struct GNUNET_TIME_Absolute expiration,
                const void *addr, size_t addrlen)
{
  struct ValidationList *e = cls;
  struct TransportPlugin *tp;
  struct ValidationAddress *va;
  struct GNUNET_PeerIdentity id;

  tp = find_transport (tname);
  if (tp == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO |
                  GNUNET_ERROR_TYPE_BULK,
                  _
                  ("Transport `%s' not loaded, will not try to validate peer address using this transport.\n"),
                  tname);
      return GNUNET_OK;
    }
  GNUNET_CRYPTO_hash (&e->publicKey,
                      sizeof (struct
                              GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded),
                      &id.hashPubKey);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Scheduling validation of address `%s' via `%s' for `%4s'\n",
              GNUNET_a2s (addr, addrlen), tname, GNUNET_i2s (&id));

  va = GNUNET_malloc (sizeof (struct ValidationAddress) + addrlen);
  va->next = e->addresses;
  e->addresses = va;
  va->transport_name = GNUNET_strdup (tname);
  va->addr_len = addrlen;
  va->challenge = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK,
                                            (unsigned int) -1);
  memcpy (&va[1], addr, addrlen);
  return GNUNET_OK;
}

/*
 * @param cls handle to the plugin (for sending)
 * @param target the peer identity of the peer we are sending to
 * @param challenge the challenge number
 * @param timeout how long to await validation?
 * @param addr the address to validate
 * @param addrlen the length of the address
 *
 * Perform address validation, which means sending a PING PONG to
 * the address via the transport plugin.  If not validated, then
 * do not count this as a good peer/address...
 *
 */
static void
validate_address (void *cls, struct ValidationAddress *va,
                  const struct GNUNET_PeerIdentity *target,
                  struct GNUNET_TIME_Relative timeout,
                  const void *addr, size_t addrlen)
{
  /* struct Plugin *plugin = cls;
  int challenge = va->challenge; */


  return;
}


/**
 * Check if addresses in validated hello "h" overlap with
 * those in "chvc->hello" and update "chvc->hello" accordingly,
 * removing those addresses that have already been validated.
 */
static void
check_hello_validated (void *cls,
                       const struct GNUNET_PeerIdentity *peer,
                       const struct GNUNET_HELLO_Message *h, uint32_t trust)
{
  struct CheckHelloValidatedContext *chvc = cls;
  struct ValidationAddress *va;
  struct TransportPlugin *tp;
  int first_call;
  struct GNUNET_PeerIdentity apeer;

  first_call = GNUNET_NO;
  if (chvc->e == NULL)
    {
      chvc->piter = NULL;
      first_call = GNUNET_YES;
      chvc->e = GNUNET_malloc (sizeof (struct ValidationList));
      GNUNET_assert (GNUNET_OK ==
                     GNUNET_HELLO_get_key (h != NULL ? h : chvc->hello,
                                           &chvc->e->publicKey));
      chvc->e->timeout =
        GNUNET_TIME_relative_to_absolute (HELLO_VERIFICATION_TIMEOUT);
      chvc->e->next = pending_validations;
      pending_validations = chvc->e;
    }
  if (h != NULL)
    {
      GNUNET_HELLO_iterate_new_addresses (chvc->hello,
                                          h,
                                          GNUNET_TIME_absolute_get (),
                                          &run_validation, chvc->e);
    }
  else if (GNUNET_YES == first_call)
    {
      /* no existing HELLO, all addresses are new */
      GNUNET_HELLO_iterate_addresses (chvc->hello,
                                      GNUNET_NO, &run_validation, chvc->e);
    }
  if (h != NULL)
    return;                     /* wait for next call */
  /* finally, transmit validation attempts */
  GNUNET_assert (GNUNET_OK == GNUNET_HELLO_get_id (chvc->hello, &apeer));
#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Ready to validate addresses from `%s' message for peer `%4s'\n",
              "HELLO", GNUNET_i2s (&apeer));
#endif
  va = chvc->e->addresses;
  while (va != NULL)
    {
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Establishing `%s' connection to validate `%s' address `%s' of `%4s'\n",
                  va->transport_name,
                  "HELLO",
                  GNUNET_a2s ((const struct sockaddr *) &va[1],
                              va->addr_len), GNUNET_i2s (&apeer));
#endif
      tp = find_transport (va->transport_name);
      GNUNET_assert (tp != NULL);
      /* This validation should happen inside the transport, not from the plugin! */
      validate_address (tp->api->cls, va, &apeer,
                        HELLO_VERIFICATION_TIMEOUT,
                        &va[1], va->addr_len);
      /* va->ok = GNUNET_SYSERR; will be set by validate_address! */
      va = va->next;
    }
  GNUNET_SCHEDULER_add_delayed (sched,
                                GNUNET_TIME_absolute_get_remaining (chvc->
                                                                    e->timeout),
                                &cleanup_validation, NULL);
  GNUNET_free (chvc);
}


/**
 * Process HELLO-message.
 *
 * @param plugin transport involved, may be NULL
 * @param message the actual message
 * @return GNUNET_OK if the HELLO was well-formed, GNUNET_SYSERR otherwise
 */
static int
process_hello (struct TransportPlugin *plugin,
               const struct GNUNET_MessageHeader *message)
{
  struct ValidationList *e;
  uint16_t hsize;
  struct GNUNET_PeerIdentity target;
  const struct GNUNET_HELLO_Message *hello;
  struct CheckHelloValidatedContext *chvc;
  struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded publicKey;

  hsize = ntohs (message->size);
  if ((ntohs (message->type) != GNUNET_MESSAGE_TYPE_HELLO) ||
      (hsize < sizeof (struct GNUNET_MessageHeader)))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
  /* first, check if load is too high */
  if (GNUNET_OS_load_cpu_get (cfg) > 100)
    {
      /* TODO: call to stats? */
      return GNUNET_OK;
    }
  hello = (const struct GNUNET_HELLO_Message *) message;
  if (GNUNET_OK != GNUNET_HELLO_get_key (hello, &publicKey))
    {
      GNUNET_break_op (0);
      return GNUNET_SYSERR;
    }
  GNUNET_CRYPTO_hash (&publicKey,
                      sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded),
                      &target.hashPubKey);
#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Processing `%s' message for `%4s'\n",
              "HELLO", GNUNET_i2s (&target));
#endif
  /* check if a HELLO for this peer is already on the validation list */
  e = pending_validations;
  while (e != NULL)
    {
      if (0 == memcmp (&e->publicKey,
                       &publicKey,
                       sizeof (struct
                               GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded)))
        {
          /* TODO: call to stats? */
#if DEBUG_TRANSPORT
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "`%s' message for peer `%4s' is already pending; ignoring new message\n",
                      "HELLO", GNUNET_i2s (&target));
#endif
          return GNUNET_OK;
        }
      e = e->next;
    }
  chvc = GNUNET_malloc (sizeof (struct CheckHelloValidatedContext) + hsize);
  chvc->plugin = plugin;
  chvc->hello = (struct GNUNET_HELLO_Message *) &chvc[1];
  memcpy (chvc->hello, hello, hsize);
  /* finally, check if HELLO was previously validated
     (continuation will then schedule actual validation) */
  chvc->piter = GNUNET_PEERINFO_iterate (cfg,
                                         sched,
                                         &target,
                                         0,
                                         HELLO_VERIFICATION_TIMEOUT,
                                         &check_hello_validated, chvc);
  return GNUNET_OK;
}


/**
 * The peer specified by the given neighbor has timed-out or a plugin
 * has disconnected.  We may either need to do nothing (other plugins
 * still up), or trigger a full disconnect and clean up.  This
 * function updates our state and do the necessary notifications.
 * Also notifies our clients that the neighbor is now officially
 * gone.
 *
 * @param n the neighbor list entry for the peer
 * @param check should we just check if all plugins
 *        disconnected or must we ask all plugins to
 *        disconnect?
 */
static void
disconnect_neighbor (struct NeighborList *n, int check)
{
  struct ReadyList *rpos;
  struct NeighborList *npos;
  struct NeighborList *nprev;
  struct MessageQueue *mq;

  if (GNUNET_YES == check)
    {
      rpos = n->plugins;
      while (NULL != rpos)
        {
          if (GNUNET_YES == rpos->connected)
            return;             /* still connected */
          rpos = rpos->next;
        }
    }

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
              "Disconnecting from `%4s'\n", GNUNET_i2s (&n->id));
#endif
  /* remove n from neighbors list */
  nprev = NULL;
  npos = neighbors;
  while ((npos != NULL) && (npos != n))
    {
      nprev = npos;
      npos = npos->next;
    }
  GNUNET_assert (npos != NULL);
  if (nprev == NULL)
    neighbors = n->next;
  else
    nprev->next = n->next;

  /* notify all clients about disconnect */
  notify_clients_disconnect (&n->id);

  /* clean up all plugins, cancel connections and pending transmissions */
  while (NULL != (rpos = n->plugins))
    {
      n->plugins = rpos->next;
      GNUNET_assert (rpos->neighbor == n);
      if (GNUNET_YES == rpos->connected)
        rpos->plugin->api->disconnect (rpos->plugin->api->cls, &n->id);
      GNUNET_free (rpos);
    }

  /* free all messages on the queue */
  while (NULL != (mq = n->messages))
    {
      n->messages = mq->next;
      GNUNET_assert (mq->neighbor == n);
      GNUNET_free (mq);
    }
  if (n->timeout_task != GNUNET_SCHEDULER_NO_TASK)
    GNUNET_SCHEDULER_cancel (sched, n->timeout_task);
  /* finally, free n itself */
  GNUNET_free (n);
}


/**
 * Add an entry for each of our transport plugins
 * (that are able to send) to the list of plugins
 * for this neighbor.
 *
 * @param neighbor to initialize
 */
static void
add_plugins (struct NeighborList *neighbor)
{
  struct TransportPlugin *tp;
  struct ReadyList *rl;

  neighbor->retry_plugins_time
    = GNUNET_TIME_relative_to_absolute (PLUGIN_RETRY_FREQUENCY);
  tp = plugins;
  while (tp != NULL)
    {
      if (tp->api->send != NULL)
        {
          rl = GNUNET_malloc (sizeof (struct ReadyList));
          rl->next = neighbor->plugins;
          neighbor->plugins = rl;
          rl->plugin = tp;
          rl->neighbor = neighbor;
          rl->transmit_ready = GNUNET_YES;
        }
      tp = tp->next;
    }
}


static void
neighbor_timeout_task (void *cls,
                        const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct NeighborList *n = cls;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
              "Neighbor `%4s' has timed out!\n", GNUNET_i2s (&n->id));
#endif
  n->timeout_task = GNUNET_SCHEDULER_NO_TASK;
  disconnect_neighbor (n, GNUNET_NO);
}


/**
 * Create a fresh entry in our neighbor list for the given peer.
 * Will try to transmit our current HELLO to the new neighbor.  Also
 * notifies our clients about the new "connection".
 *
 * @param peer the peer for which we create the entry
 * @return the new neighbor list entry
 */
static struct NeighborList *
setup_new_neighbor (const struct GNUNET_PeerIdentity *peer, const char *addr, size_t sender_address_len)
{
  struct NeighborList *n;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
              "Setting up new neighbor `%4s', sending our HELLO to introduce ourselves\n",
              GNUNET_i2s (peer));
#endif
  GNUNET_assert (our_hello != NULL);
  n = GNUNET_malloc (sizeof (struct NeighborList));
  n->next = neighbors;
  neighbors = n;
  n->id = *peer;
  n->last_quota_update = GNUNET_TIME_absolute_get ();
  n->peer_timeout =
    GNUNET_TIME_relative_to_absolute
    (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
  n->quota_in = (GNUNET_CONSTANTS_DEFAULT_BPM_IN_OUT + 59999) / (60 * 1000);
  add_plugins (n);
  n->timeout_task = GNUNET_SCHEDULER_add_delayed (sched,
                                                  GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT,
                                                  &neighbor_timeout_task, n);
  transmit_to_peer (NULL, 0,
                    (const struct GNUNET_MessageHeader *) our_hello,
                    GNUNET_YES, n);
  notify_clients_connect (peer, GNUNET_TIME_UNIT_FOREVER_REL);
  return n;
}

/*
 * We have received a PING message from someone.  Need to send a PONG message
 * in response to the peer by any means necessary.  Of course, with something
 * like TCP where a connection exists, we may want to send it that way.  But
 * we may not be able to make that distinction...
 */
static int handle_ping(void *cls, const struct GNUNET_MessageHeader *message,
                       const struct GNUNET_PeerIdentity *peer,
                       const char *sender_address,
                       size_t sender_address_len)
{

  return GNUNET_OK;
}

/**
 * Function called by the plugin for each received message.
 * Update data volumes, possibly notify plugins about
 * reducing the rate at which they read from the socket
 * and generally forward to our receive callback.
 *
 * @param cls the "struct TransportPlugin *" we gave to the plugin
 * @param message the message, NULL if peer was disconnected
 * @param distance the transport cost to this peer (not latency!)
 * @param sender_address the address that the sender reported
 *        (opaque to transport service)
 * @param sender_address_len the length of the sender address
 * @param peer (claimed) identity of the other peer
 * @return the new service_context that the plugin should use
 *         for future receive calls for messages from this
 *         particular peer
 *
 */
static void
plugin_env_receive (void *cls, const struct GNUNET_PeerIdentity *peer,
                    const struct GNUNET_MessageHeader *message,
                    unsigned int distance, const char *sender_address,
                    size_t sender_address_len)
{
  const struct GNUNET_MessageHeader ack = {
    htons (sizeof (struct GNUNET_MessageHeader)),
    htons (GNUNET_MESSAGE_TYPE_TRANSPORT_ACK)
  };
  struct ReadyList *service_context;
  struct TransportPlugin *plugin = cls;
  struct TransportClient *cpos;
  struct InboundMessage *im;
  uint16_t msize;
  struct NeighborList *n;

  n = find_neighbor (peer, sender_address, sender_address_len);
  if (n == NULL)
    {
      if (message == NULL)
        return;                 /* disconnect of peer already marked down */
      n = setup_new_neighbor (peer, sender_address, sender_address_len);
    }
  service_context = n->plugins;
  while ((service_context != NULL) && (plugin != service_context->plugin))
    service_context = service_context->next;
  GNUNET_assert ((plugin->api->send == NULL) || (service_context != NULL));
  if (message == NULL)
    {
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
                  "Receive failed from `%4s', triggering disconnect\n",
                  GNUNET_i2s (&n->id));
#endif
      /* TODO: call stats */
      if (service_context != NULL)
        service_context->connected = GNUNET_NO;
      disconnect_neighbor (n, GNUNET_YES);
      return;
    }
#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
              "Processing message of type `%u' received by plugin...\n",
              ntohs (message->type));
#endif
  if (service_context != NULL)
    {
      if (service_context->connected == GNUNET_NO)
        {
          service_context->connected = GNUNET_YES;
          service_context->transmit_ready = GNUNET_YES;
          service_context->connect_attempts++;
        }
      service_context->timeout
        =
        GNUNET_TIME_relative_to_absolute
        (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
      /* service_context->latency = latency; */ /* This value should be set by us! */
    }
  /* update traffic received amount ... */
  msize = ntohs (message->size);
  n->last_received += msize;
  GNUNET_SCHEDULER_cancel (sched, n->timeout_task);
  n->peer_timeout =
    GNUNET_TIME_relative_to_absolute
    (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
  n->timeout_task =
    GNUNET_SCHEDULER_add_delayed (sched,
                                  GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT,
                                  &neighbor_timeout_task, n);
  update_quota (n);
  if (n->quota_violation_count > QUOTA_VIOLATION_DROP_THRESHOLD)
    {
      /* dropping message due to frequent inbound volume violations! */
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING |
                  GNUNET_ERROR_TYPE_BULK,
                  _
                  ("Dropping incoming message due to repeated bandwidth quota violations.\n"));
      /* TODO: call stats */
      GNUNET_assert ((service_context == NULL) ||
                     (NULL != service_context->neighbor));
      return;
    }
  switch (ntohs (message->type))
    {
    case GNUNET_MESSAGE_TYPE_HELLO:
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Receiving `%s' message from `%4s'.\n", "HELLO",
                  GNUNET_i2s (peer));
#endif
      process_hello (plugin, message);
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sending `%s' message to connecting peer `%4s'.\n", "ACK",
                  GNUNET_i2s (peer));
#endif
      transmit_to_peer (NULL, 0, &ack, GNUNET_YES, n);
      break;
    case GNUNET_MESSAGE_TYPE_TRANSPORT_PING:
      handle_ping(plugin, message, peer, sender_address, sender_address_len);
    case GNUNET_MESSAGE_TYPE_TRANSPORT_PONG:
      handle_pong(plugin, message, peer, sender_address, sender_address_len);
      //plugin_env_notify_validation();
    case GNUNET_MESSAGE_TYPE_TRANSPORT_ACK:
      n->saw_ack = GNUNET_YES;
      /* intentional fall-through! */
    default:
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Received message of type %u from `%4s', sending to all clients.\n",
                  ntohs (message->type), GNUNET_i2s (peer));
#endif
      /* transmit message to all clients */
      im = GNUNET_malloc (sizeof (struct InboundMessage) + msize);
      im->header.size = htons (sizeof (struct InboundMessage) + msize);
      im->header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_RECV);
      im->latency = n->latency;
      im->peer = *peer;
      memcpy (&im[1], message, msize);

      cpos = clients;
      while (cpos != NULL)
        {
          transmit_to_client (cpos, &im->header, GNUNET_YES);
          cpos = cpos->next;
        }
      GNUNET_free (im);
    }
  GNUNET_assert ((service_context == NULL) ||
                 (NULL != service_context->neighbor));
}


/**
 * Handle START-message.  This is the first message sent to us
 * by any client which causes us to add it to our list.
 *
 * @param cls closure (always NULL)
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_start (void *cls,
              struct GNUNET_SERVER_Client *client,
              const struct GNUNET_MessageHeader *message)
{
  struct TransportClient *c;
  struct ConnectInfoMessage cim;
  struct NeighborList *n;
  struct InboundMessage *im;
  struct GNUNET_MessageHeader *ack;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received `%s' request from client\n", "START");
#endif
  c = clients;
  while (c != NULL)
    {
      if (c->client == client)
        {
          /* client already on our list! */
          GNUNET_break (0);
          GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
          return;
        }
      c = c->next;
    }
  c = GNUNET_malloc (sizeof (struct TransportClient));
  c->next = clients;
  clients = c;
  c->client = client;
  if (our_hello != NULL)
    {
#if DEBUG_TRANSPORT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sending our own `%s' to new client\n", "HELLO");
#endif
      transmit_to_client (c,
                          (const struct GNUNET_MessageHeader *) our_hello,
                          GNUNET_NO);
      /* tell new client about all existing connections */
      cim.header.size = htons (sizeof (struct ConnectInfoMessage));
      cim.header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_CONNECT);
      cim.quota_out =
        htonl (GNUNET_CONSTANTS_DEFAULT_BPM_IN_OUT / (60 * 1000));
      cim.latency = GNUNET_TIME_relative_hton (GNUNET_TIME_UNIT_ZERO);  /* FIXME? */
      im = GNUNET_malloc (sizeof (struct InboundMessage) +
                          sizeof (struct GNUNET_MessageHeader));
      im->header.size = htons (sizeof (struct InboundMessage) +
                               sizeof (struct GNUNET_MessageHeader));
      im->header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_RECV);
      im->latency = GNUNET_TIME_relative_hton (GNUNET_TIME_UNIT_ZERO);  /* FIXME? */
      ack = (struct GNUNET_MessageHeader *) &im[1];
      ack->size = htons (sizeof (struct GNUNET_MessageHeader));
      ack->type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_ACK);
      for (n = neighbors; n != NULL; n = n->next)
        {
          cim.id = n->id;
          transmit_to_client (c, &cim.header, GNUNET_NO);
          if (n->saw_ack)
            {
              im->peer = n->id;
              transmit_to_client (c, &im->header, GNUNET_NO);
            }
        }
      GNUNET_free (im);
    }
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}


/**
 * Handle HELLO-message.
 *
 * @param cls closure (always NULL)
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_hello (void *cls,
              struct GNUNET_SERVER_Client *client,
              const struct GNUNET_MessageHeader *message)
{
  int ret;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received `%s' request from client\n", "HELLO");
#endif
  ret = process_hello (NULL, message);
  GNUNET_SERVER_receive_done (client, ret);
}


/**
 * Handle SEND-message.
 *
 * @param cls closure (always NULL)
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_send (void *cls,
             struct GNUNET_SERVER_Client *client,
             const struct GNUNET_MessageHeader *message)
{
  struct TransportClient *tc;
  struct NeighborList *n;
  const struct OutboundMessage *obm;
  const struct GNUNET_MessageHeader *obmm;
  uint16_t size;
  uint16_t msize;

  size = ntohs (message->size);
  if (size <
      sizeof (struct OutboundMessage) + sizeof (struct GNUNET_MessageHeader))
    {
      GNUNET_break (0);
      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  obm = (const struct OutboundMessage *) message;
#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received `%s' request from client with target `%4s'\n",
              "SEND", GNUNET_i2s (&obm->peer));
#endif
  obmm = (const struct GNUNET_MessageHeader *) &obm[1];
  msize = ntohs (obmm->size);
  if (size != msize + sizeof (struct OutboundMessage))
    {
      GNUNET_break (0);
      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  n = find_neighbor (&obm->peer, NULL, 0);
  if (n == NULL)
    n = setup_new_neighbor (&obm->peer, NULL, 0);
  tc = clients;
  while ((tc != NULL) && (tc->client != client))
    tc = tc->next;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client asked to transmit %u-byte message of type %u to `%4s'\n",
              ntohs (obmm->size),
              ntohs (obmm->type), GNUNET_i2s (&obm->peer));
#endif
  transmit_to_peer (tc, ntohl (obm->priority), obmm, GNUNET_NO, n);
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}


/**
 * Handle SET_QUOTA-message.
 *
 * @param cls closure (always NULL)
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_set_quota (void *cls,
                  struct GNUNET_SERVER_Client *client,
                  const struct GNUNET_MessageHeader *message)
{
  const struct QuotaSetMessage *qsm =
    (const struct QuotaSetMessage *) message;
  struct NeighborList *n;
  struct TransportPlugin *p;
  struct ReadyList *rl;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received `%s' request from client for peer `%4s'\n",
              "SET_QUOTA", GNUNET_i2s (&qsm->peer));
#endif
  n = find_neighbor (&qsm->peer, NULL, 0);
  if (n == NULL)
    {
      GNUNET_SERVER_receive_done (client, GNUNET_OK);
      return;
    }
  update_quota (n);
  if (n->quota_in < ntohl (qsm->quota_in))
    n->last_quota_update = GNUNET_TIME_absolute_get ();
  n->quota_in = ntohl (qsm->quota_in);
  rl = n->plugins;
  while (rl != NULL)
    {
      p = rl->plugin;
      p->api->set_receive_quota (p->api->cls,
                                 &qsm->peer, ntohl (qsm->quota_in));
      rl = rl->next;
    }
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}


/**
 * Handle TRY_CONNECT-message.
 *
 * @param cls closure (always NULL)
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_try_connect (void *cls,
                    struct GNUNET_SERVER_Client *client,
                    const struct GNUNET_MessageHeader *message)
{
  const struct TryConnectMessage *tcm;

  tcm = (const struct TryConnectMessage *) message;
#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received `%s' request from client %p asking to connect to `%4s'\n",
              "TRY_CONNECT", client, GNUNET_i2s (&tcm->peer));
#endif
  if (NULL == find_neighbor (&tcm->peer, NULL, 0))
    setup_new_neighbor (&tcm->peer, NULL, 0); /* Can we set up a truly _new_ neighbor without
                                        knowing its address?  Should we ask the plugin
                                        for more information about this peer?  I don't
                                        think we can...  Or set up new peer should only
                                        happen when transport notifies us of an address,
                                        and this setup should check for an address in
                                        the existing list only */
#if DEBUG_TRANSPORT
  else
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Client asked to connect to `%4s', but connection already exists\n",
                "TRY_CONNECT", GNUNET_i2s (&tcm->peer));
#endif
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}

static void
transmit_address_to_client (void *cls, const char *address)
{
  struct GNUNET_SERVER_TransmitContext *tc = cls;
  size_t slen;

  if (NULL == address)
    slen = 0;
  else
    slen = strlen (address) + 1;
  GNUNET_SERVER_transmit_context_append (tc, address, slen,
                                         GNUNET_MESSAGE_TYPE_TRANSPORT_ADDRESS_REPLY);
  if (NULL == address)
    GNUNET_SERVER_transmit_context_run (tc, GNUNET_TIME_UNIT_FOREVER_REL);
}

/**
 * Handle AddressLookup-message.
 *
 * @param cls closure (always NULL)
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_address_lookup (void *cls,
                       struct GNUNET_SERVER_Client *client,
                       const struct GNUNET_MessageHeader *message)
{
  const struct AddressLookupMessage *alum;
  struct TransportPlugin *lsPlugin;
  const char *nameTransport;
  const char *address;
  uint16_t size;
  struct GNUNET_SERVER_TransmitContext *tc;

  size = ntohs (message->size);
  if (size < sizeof (struct AddressLookupMessage))
    {
      GNUNET_break_op (0);
      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  alum = (const struct AddressLookupMessage *) message;
  uint32_t addressLen = ntohl (alum->addrlen);
  if (size <= sizeof (struct AddressLookupMessage) + addressLen)
    {
      GNUNET_break_op (0);
      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  address = (const char *) &alum[1];
  nameTransport = (const char *) &address[addressLen];
  if (nameTransport
      [size - sizeof (struct AddressLookupMessage) - addressLen - 1] != '\0')
    {
      GNUNET_break_op (0);
      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  struct GNUNET_TIME_Absolute timeout =
    GNUNET_TIME_absolute_ntoh (alum->timeout);
  struct GNUNET_TIME_Relative rtimeout =
    GNUNET_TIME_absolute_get_remaining (timeout);
  lsPlugin = find_transport (nameTransport);
  if (NULL == lsPlugin)
    {
      tc = GNUNET_SERVER_transmit_context_create (client);
      GNUNET_SERVER_transmit_context_append (tc, NULL, 0,
                                             GNUNET_MESSAGE_TYPE_TRANSPORT_ADDRESS_REPLY);
      GNUNET_SERVER_transmit_context_run (tc, rtimeout);
      return;
    }
  tc = GNUNET_SERVER_transmit_context_create (client);
  lsPlugin->api->address_pretty_printer (cls, nameTransport,
                                         address, addressLen, GNUNET_YES,
                                         rtimeout,
                                         &transmit_address_to_client, tc);
}

/**
 * List of handlers for the messages understood by this
 * service.
 */
static struct GNUNET_SERVER_MessageHandler handlers[] = {
  {&handle_start, NULL,
   GNUNET_MESSAGE_TYPE_TRANSPORT_START, 0},
  {&handle_hello, NULL,
   GNUNET_MESSAGE_TYPE_HELLO, 0},
  {&handle_send, NULL,
   GNUNET_MESSAGE_TYPE_TRANSPORT_SEND, 0},
  {&handle_set_quota, NULL,
   GNUNET_MESSAGE_TYPE_TRANSPORT_SET_QUOTA, sizeof (struct QuotaSetMessage)},
  {&handle_try_connect, NULL,
   GNUNET_MESSAGE_TYPE_TRANSPORT_TRY_CONNECT,
   sizeof (struct TryConnectMessage)},
  {&handle_address_lookup, NULL,
   GNUNET_MESSAGE_TYPE_TRANSPORT_ADDRESS_LOOKUP,
   0},
  {NULL, NULL, 0, 0}
};


/**
 * Setup the environment for this plugin.
 */
static void
create_environment (struct TransportPlugin *plug)
{
  plug->env.cfg = cfg;
  plug->env.sched = sched;
  plug->env.my_identity = &my_identity;
  plug->env.cls = plug;
  plug->env.receive = &plugin_env_receive;
  plug->env.notify_address = &plugin_env_notify_address;
  plug->env.default_quota_in =
    (GNUNET_CONSTANTS_DEFAULT_BPM_IN_OUT + 59999) / (60 * 1000);
  plug->env.max_connections = max_connect_per_transport;
}


/**
 * Start the specified transport (load the plugin).
 */
static void
start_transport (struct GNUNET_SERVER_Handle *server, const char *name)
{
  struct TransportPlugin *plug;
  char *libname;

  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              _("Loading `%s' transport plugin\n"), name);
  GNUNET_asprintf (&libname, "libgnunet_plugin_transport_%s", name);
  plug = GNUNET_malloc (sizeof (struct TransportPlugin));
  create_environment (plug);
  plug->short_name = GNUNET_strdup (name);
  plug->lib_name = libname;
  plug->next = plugins;
  plugins = plug;
  plug->api = GNUNET_PLUGIN_load (libname, &plug->env);
  if (plug->api == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _("Failed to load transport plugin for `%s'\n"), name);
      GNUNET_free (plug->short_name);
      plugins = plug->next;
      GNUNET_free (libname);
      GNUNET_free (plug);
    }
}


/**
 * Called whenever a client is disconnected.  Frees our
 * resources associated with that client.
 *
 * @param cls closure
 * @param client identification of the client
 */
static void
client_disconnect_notification (void *cls,
                                struct GNUNET_SERVER_Client *client)
{
  struct TransportClient *pos;
  struct TransportClient *prev;
  struct ClientMessageQueueEntry *mqe;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
              "Client disconnected, cleaning up.\n");
#endif
  prev = NULL;
  pos = clients;
  while ((pos != NULL) && (pos->client != client))
    {
      prev = pos;
      pos = pos->next;
    }
  if (pos == NULL)
    return;
  while (NULL != (mqe = pos->message_queue_head))
    {
      pos->message_queue_head = mqe->next;
      GNUNET_free (mqe);
    }
  pos->message_queue_head = NULL;
  if (prev == NULL)
    clients = pos->next;
  else
    prev->next = pos->next;
  if (GNUNET_YES == pos->tcs_pending)
    {
      pos->client = NULL;
      return;
    }
  GNUNET_free (pos);
}


/**
 * Function called when the service shuts down.  Unloads our plugins.
 *
 * @param cls closure, unused
 * @param tc task context (unused)
 */
static void
unload_plugins (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct TransportPlugin *plug;
  struct AddressList *al;

#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Transport service is unloading plugins...\n");
#endif
  while (NULL != (plug = plugins))
    {
      plugins = plug->next;
      GNUNET_break (NULL == GNUNET_PLUGIN_unload (plug->lib_name, plug->api));
      GNUNET_free (plug->lib_name);
      GNUNET_free (plug->short_name);
      while (NULL != (al = plug->addresses))
        {
          plug->addresses = al->next;
          GNUNET_free (al);
        }
      GNUNET_free (plug);
    }
  if (my_private_key != NULL)
    GNUNET_CRYPTO_rsa_key_free (my_private_key);
  GNUNET_free_non_null (our_hello);
}


/**
 * Initiate transport service.
 *
 * @param cls closure
 * @param s scheduler to use
 * @param serv the initialized server
 * @param c configuration to use
 */
static void
run (void *cls,
     struct GNUNET_SCHEDULER_Handle *s,
     struct GNUNET_SERVER_Handle *serv,
     const struct GNUNET_CONFIGURATION_Handle *c)
{
  char *plugs;
  char *pos;
  int no_transports;
  unsigned long long tneigh;
  char *keyfile;

  sched = s;
  cfg = c;
  /* parse configuration */
  if ((GNUNET_OK !=
       GNUNET_CONFIGURATION_get_value_number (c,
                                              "TRANSPORT",
                                              "NEIGHBOUR_LIMIT",
                                              &tneigh)) ||
      (GNUNET_OK !=
       GNUNET_CONFIGURATION_get_value_filename (c,
                                                "GNUNETD",
                                                "HOSTKEY", &keyfile)))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _
                  ("Transport service is lacking key configuration settings.  Exiting.\n"));
      GNUNET_SCHEDULER_shutdown (s);
      return;
    }
  max_connect_per_transport = (uint32_t) tneigh;
  my_private_key = GNUNET_CRYPTO_rsa_key_create_from_file (keyfile);
  GNUNET_free (keyfile);
  if (my_private_key == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _
                  ("Transport service could not access hostkey.  Exiting.\n"));
      GNUNET_SCHEDULER_shutdown (s);
      return;
    }
  GNUNET_CRYPTO_rsa_key_get_public (my_private_key, &my_public_key);
  GNUNET_CRYPTO_hash (&my_public_key,
                      sizeof (my_public_key), &my_identity.hashPubKey);
  /* setup notification */
  server = serv;
  GNUNET_SERVER_disconnect_notify (server,
                                   &client_disconnect_notification, NULL);
  /* load plugins... */
  no_transports = 1;
  if (GNUNET_OK ==
      GNUNET_CONFIGURATION_get_value_string (c,
                                             "TRANSPORT", "PLUGINS", &plugs))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  _("Starting transport plugins `%s'\n"), plugs);
      pos = strtok (plugs, " ");
      while (pos != NULL)
        {
          start_transport (server, pos);
          no_transports = 0;
          pos = strtok (NULL, " ");
        }
      GNUNET_free (plugs);
    }
  GNUNET_SCHEDULER_add_delayed (sched,
                                GNUNET_TIME_UNIT_FOREVER_REL,
                                &unload_plugins, NULL);
  if (no_transports)
    refresh_hello ();
#if DEBUG_TRANSPORT
  GNUNET_log (GNUNET_ERROR_TYPE_INFO, _("Transport service ready.\n"));
#endif
  /* process client requests */
  GNUNET_SERVER_add_handlers (server, handlers);
}


/**
 * The main function for the transport service.
 *
 * @param argc number of arguments from the command line
 * @param argv command line arguments
 * @return 0 ok, 1 on error
 */
int
main (int argc, char *const *argv)
{
  return (GNUNET_OK ==
          GNUNET_SERVICE_run (argc,
                              argv,
                              "transport",
                              GNUNET_SERVICE_OPTION_NONE,
                              &run, NULL)) ? 0 : 1;
}

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