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

/*
      This file is part of GNUnet
      Copyright (C) 2013, 2014 Christian Grothoff (and other contributing authors)

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

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

      You should have received a copy of the GNU General Public License
      along with GNUnet; see the file COPYING.  If not, write to the
      Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
      Boston, MA 02110-1301, USA.
*/
/**
 * @file set/gnunet-service-set.c
 * @brief two-peer set operations
 * @author Florian Dold
 * @author Christian Grothoff
 */
#include "gnunet-service-set.h"
#include "gnunet-service-set_protocol.h"

/**
 * How long do we hold on to an incoming channel if there is
 * no local listener before giving up?
 */
#define INCOMING_CHANNEL_TIMEOUT GNUNET_TIME_UNIT_MINUTES

/**
 * A listener is inhabited by a client, and waits for evaluation
 * requests from remote peers.
 */
struct Listener
{
  /**
   * Listeners are held in a doubly linked list.
   */
  struct Listener *next;

  /**
   * Listeners are held in a doubly linked list.
   */
  struct Listener *prev;

  /**
   * Client that owns the listener.
   * Only one client may own a listener.
   */
  struct GNUNET_SERVER_Client *client;

  /**
   * Message queue for the client
   */
  struct GNUNET_MQ_Handle *client_mq;

  /**
   * Application ID for the operation, used to distinguish
   * multiple operations of the same type with the same peer.
   */
  struct GNUNET_HashCode app_id;

  /**
   * The type of the operation.
   */
  enum GNUNET_SET_OperationType operation;
};


struct LazyCopyRequest
{
  struct Set *source_set;
  uint32_t cookie;

  struct LazyCopyRequest *prev;
  struct LazyCopyRequest *next;
};


/**
 * Configuration of our local peer.
 */
static const struct GNUNET_CONFIGURATION_Handle *configuration;

/**
 * Handle to the cadet service, used to listen for and connect to
 * remote peers.
 */
static struct GNUNET_CADET_Handle *cadet;

/**
 * Sets are held in a doubly linked list.
 */
static struct Set *sets_head;

/**
 * Sets are held in a doubly linked list.
 */
static struct Set *sets_tail;

/**
 * Listeners are held in a doubly linked list.
 */
static struct Listener *listeners_head;

/**
 * Listeners are held in a doubly linked list.
 */
static struct Listener *listeners_tail;

/**
 * Incoming sockets from remote peers are held in a doubly linked
 * list.
 */
static struct Operation *incoming_head;

/**
 * Incoming sockets from remote peers are held in a doubly linked
 * list.
 */
static struct Operation *incoming_tail;

static struct LazyCopyRequest *lazy_copy_head;
static struct LazyCopyRequest *lazy_copy_tail;

static uint32_t lazy_copy_cookie = 1;

/**
 * Counter for allocating unique IDs for clients, used to identify
 * incoming operation requests from remote peers, that the client can
 * choose to accept or refuse.
 */
static uint32_t suggest_id = 1;


/**
 * Get set that is owned by the given client, if any.
 *
 * @param client client to look for
 * @return set that the client owns, NULL if the client
 *         does not own a set
 */
static struct Set *
set_get (struct GNUNET_SERVER_Client *client)
{
  struct Set *set;

  for (set = sets_head; NULL != set; set = set->next)
    if (set->client == client)
      return set;
  return NULL;
}


/**
 * Get the listener associated with the given client, if any.
 *
 * @param client the client
 * @return listener associated with the client, NULL
 *         if there isn't any
 */
static struct Listener *
listener_get (struct GNUNET_SERVER_Client *client)
{
  struct Listener *listener;

  for (listener = listeners_head; NULL != listener; listener = listener->next)
    if (listener->client == client)
      return listener;
  return NULL;
}


/**
 * Get the incoming socket associated with the given id.
 *
 * @param id id to look for
 * @return the incoming socket associated with the id,
 *         or NULL if there is none
 */
static struct Operation *
get_incoming (uint32_t id)
{
  struct Operation *op;

  for (op = incoming_head; NULL != op; op = op->next)
    if (op->suggest_id == id)
    {
      GNUNET_assert (GNUNET_YES == op->is_incoming);
      return op;
    }
  return NULL;
}


/**
 * Destroy a listener, free all resources associated with it.
 *
 * @param listener listener to destroy
 */
static void
listener_destroy (struct Listener *listener)
{
  /* If the client is not dead yet, destroy it.
   * The client's destroy callback will destroy the listener again. */
  if (NULL != listener->client)
  {
    struct GNUNET_SERVER_Client *client = listener->client;

    listener->client = NULL;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Disconnecting listener client\n");
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  if (NULL != listener->client_mq)
  {
    GNUNET_MQ_destroy (listener->client_mq);
    listener->client_mq = NULL;
  }
  GNUNET_CONTAINER_DLL_remove (listeners_head,
                               listeners_tail,
                               listener);
  GNUNET_free (listener);
}


/**
 * Context for the #garbage_collect_cb().
 */
struct GarbageContext
{

  /**
   * Map for which we are garbage collecting removed elements.
   */
  struct GNUNET_CONTAINER_MultiHashMap *map;

  /**
   * Lowest generation for which an operation is still pending.
   */
  unsigned int min_op_generation;

  /**
   * Largest generation for which an operation is still pending.
   */
  unsigned int max_op_generation;

};


/**
 * Function invoked to check if an element can be removed from
 * the set's history because it is no longer needed.
 *
 * @param cls the `struct GarbageContext *`
 * @param key key of the element in the map
 * @param value the `struct ElementEntry *`
 * @return #GNUNET_OK (continue to iterate)
 */
static int
garbage_collect_cb (void *cls,
                    const struct GNUNET_HashCode *key,
                    void *value)
{
  //struct GarbageContext *gc = cls;
  //struct ElementEntry *ee = value;

  //if (GNUNET_YES != ee->removed)
  //  return GNUNET_OK;
  //if ( (gc->max_op_generation < ee->generation_added) ||
  //     (ee->generation_removed > gc->min_op_generation) )
  //{
  //  GNUNET_assert (GNUNET_YES ==
  //                 GNUNET_CONTAINER_multihashmap_remove (gc->map,
  //                                                       key,
  //                                                       ee));
  //  GNUNET_free (ee);
  //}
  return GNUNET_OK;
}


/**
 * Collect and destroy elements that are not needed anymore, because
 * their lifetime (as determined by their generation) does not overlap
 * with any active set operation.
 *
 * @param set set to garbage collect
 */
static void
collect_generation_garbage (struct Set *set)
{
  struct Operation *op;
  struct GarbageContext gc;

  gc.min_op_generation = UINT_MAX;
  gc.max_op_generation = 0;
  for (op = set->ops_head; NULL != op; op = op->next)
  {
    gc.min_op_generation = GNUNET_MIN (gc.min_op_generation,
                                       op->generation_created);
    gc.max_op_generation = GNUNET_MAX (gc.max_op_generation,
                                       op->generation_created);
  }
  gc.map = set->content->elements;
  GNUNET_CONTAINER_multihashmap_iterate (set->content->elements,
                                         &garbage_collect_cb,
                                         &gc);
}

int
is_excluded_generation (unsigned int generation,
                        struct GenerationRange *excluded,
                        unsigned int excluded_size)
{
  unsigned int i;

  for (i = 0; i < excluded_size; i++)
  {
    if ( (generation >= excluded[i].start) && (generation < excluded[i].end) )
      return GNUNET_YES;
  }

  return GNUNET_NO;
}


int
is_element_of_generation (struct ElementEntry *ee,
                          unsigned int query_generation,
                          struct GenerationRange *excluded,
                          unsigned int excluded_size)
{
  struct MutationEvent *mut;
  int is_present;

  if (NULL == ee->mutations)
    return GNUNET_YES;

  if (GNUNET_YES == is_excluded_generation (query_generation, excluded, excluded_size))
  {
    GNUNET_break (0);
    return GNUNET_NO;
  }

  is_present = GNUNET_YES;

  // Could be made faster with binary search, but lists
  // are small, so why bother.
  for (mut = ee->mutations; 0 != mut->generation; mut++)
  {
    if ( (mut->generation > query_generation) ||
         (GNUNET_YES == is_excluded_generation (mut->generation, excluded, excluded_size)) )
    {
      continue;
    }

    // This would be an inconsistency in how we manage mutations.
    if ( (GNUNET_YES == is_present) && (GNUNET_YES == mut->added) )
      GNUNET_assert (0);

    is_present = mut->added;
  }

  return GNUNET_YES;
}


int
_GSS_is_element_of_set (struct ElementEntry *ee,
                        struct Set *set)
{
  return is_element_of_generation (ee,
                                   set->current_generation,
                                   set->excluded_generations,
                                   set->excluded_generations_size);
}


int
_GSS_is_element_of_operation (struct ElementEntry *ee,
                              struct Operation *op)
{
  return is_element_of_generation (ee,
                                   op->generation_created,
                                   op->spec->set->excluded_generations,
                                   op->spec->set->excluded_generations_size);
}


/**
 * Destroy the given operation.  Call the implementation-specific
 * cancel function of the operation.  Disconnects from the remote
 * peer.  Does not disconnect the client, as there may be multiple
 * operations per set.
 *
 * @param op operation to destroy
 * @param gc #GNUNET_YES to perform garbage collection on the set
 */
void
_GSS_operation_destroy (struct Operation *op,
                        int gc)
{
  struct Set *set;
  struct GNUNET_CADET_Channel *channel;

  if (NULL == op->vt)
  {
    /* already in #_GSS_operation_destroy() */
    return;
  }
  GNUNET_assert (GNUNET_NO == op->is_incoming);
  GNUNET_assert (NULL != op->spec);
  set = op->spec->set;
  GNUNET_CONTAINER_DLL_remove (set->ops_head,
                               set->ops_tail,
                               op);
  op->vt->cancel (op);
  op->vt = NULL;
  if (NULL != op->spec)
  {
    if (NULL != op->spec->context_msg)
    {
      GNUNET_free (op->spec->context_msg);
      op->spec->context_msg = NULL;
    }
    GNUNET_free (op->spec);
    op->spec = NULL;
  }
  if (NULL != op->mq)
  {
    GNUNET_MQ_destroy (op->mq);
    op->mq = NULL;
  }
  if (NULL != (channel = op->channel))
  {
    op->channel = NULL;
    GNUNET_CADET_channel_destroy (channel);
  }
  if (GNUNET_YES == gc)
    collect_generation_garbage (set);
  /* We rely on the channel end handler to free 'op'. When 'op->channel' was NULL,
   * there was a channel end handler that will free 'op' on the call stack. */
}


/**
 * Iterator over hash map entries to free element entries.
 *
 * @param cls closure
 * @param key current key code
 * @param value a `struct ElementEntry *` to be free'd
 * @return #GNUNET_YES (continue to iterate)
 */
static int
destroy_elements_iterator (void *cls,
                           const struct GNUNET_HashCode *key,
                           void *value)
{
  struct ElementEntry *ee = value;

  GNUNET_free_non_null (ee->mutations);

  GNUNET_free (ee);
  return GNUNET_YES;
}


/**
 * Destroy a set, and free all resources and operations associated with it.
 *
 * @param set the set to destroy
 */
static void
set_destroy (struct Set *set)
{
  if (NULL != set->client)
  {
    /* If the client is not dead yet, destroy it.  The client's destroy
     * callback will call `set_destroy()` again in this case.  We do
     * this so that the channel end handler still has a valid set handle
     * to destroy. */
    struct GNUNET_SERVER_Client *client = set->client;

    set->client = NULL;
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  GNUNET_assert (NULL != set->state);
  while (NULL != set->ops_head)
    _GSS_operation_destroy (set->ops_head, GNUNET_NO);
  set->vt->destroy_set (set->state);
  set->state = NULL;
  if (NULL != set->client_mq)
  {
    GNUNET_MQ_destroy (set->client_mq);
    set->client_mq = NULL;
  }
  if (NULL != set->iter)
  {
    GNUNET_CONTAINER_multihashmap_iterator_destroy (set->iter);
    set->iter = NULL;
    set->iteration_id++;
  }
  {
    struct SetContent *content;
    struct PendingMutation *pm;
    struct PendingMutation *pm_current;

    content = set->content;

    // discard any pending mutations that reference this set
    pm = content->pending_mutations_head;
    while (NULL != pm)
    {
      pm_current = pm;
      pm = pm->next;
      if (pm_current-> set == set)
        GNUNET_CONTAINER_DLL_remove (content->pending_mutations_head,
                                     content->pending_mutations_tail,
                                     pm_current);

    }

    set->content = NULL;
    GNUNET_assert (0 != content->refcount);
    content->refcount -= 1;
    if (0 == content->refcount)
    {
      GNUNET_assert (NULL != content->elements);
      GNUNET_CONTAINER_multihashmap_iterate (content->elements,
                                             &destroy_elements_iterator,
                                             NULL);
      GNUNET_CONTAINER_multihashmap_destroy (content->elements);
      content->elements = NULL;
    }
  }
  GNUNET_free_non_null (set->excluded_generations);
  set->excluded_generations = NULL;
  GNUNET_CONTAINER_DLL_remove (sets_head,
                               sets_tail,
                               set);

  // remove set from pending copy requests
  {
    struct LazyCopyRequest *lcr;
    lcr = lazy_copy_head;
    while (NULL != lcr)
    {
      struct LazyCopyRequest *lcr_current;
      lcr_current = lcr;
      lcr = lcr->next;
      if (lcr_current->source_set == set)
        GNUNET_CONTAINER_DLL_remove (lazy_copy_head,
                                     lazy_copy_tail,
                                     lcr_current);
    }
  }

  GNUNET_free (set);
}


/**
 * Clean up after a client has disconnected
 *
 * @param cls closure, unused
 * @param client the client to clean up after
 */
static void
handle_client_disconnect (void *cls,
                          struct GNUNET_SERVER_Client *client)
{
  struct Set *set;
  struct Listener *listener;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "client disconnected, cleaning up\n");
  set = set_get (client);
  if (NULL != set)
  {
    set->client = NULL;
    set_destroy (set);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Client's set destroyed\n");
  }
  listener = listener_get (client);
  if (NULL != listener)
  {
    listener->client = NULL;
    listener_destroy (listener);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Client's listener destroyed\n");
  }
}


/**
 * Destroy an incoming request from a remote peer
 *
 * @param incoming remote request to destroy
 */
static void
incoming_destroy (struct Operation *incoming)
{
  struct GNUNET_CADET_Channel *channel;

  GNUNET_assert (GNUNET_YES == incoming->is_incoming);
  GNUNET_CONTAINER_DLL_remove (incoming_head,
                               incoming_tail,
                               incoming);
  if (NULL != incoming->timeout_task)
  {
    GNUNET_SCHEDULER_cancel (incoming->timeout_task);
    incoming->timeout_task = NULL;
  }
  /* make sure that the tunnel end handler will not destroy us again */
  incoming->vt = NULL;
  if (NULL != incoming->spec)
  {
    GNUNET_free (incoming->spec);
    incoming->spec = NULL;
  }
  if (NULL != incoming->mq)
  {
    GNUNET_MQ_destroy (incoming->mq);
    incoming->mq = NULL;
  }
  if (NULL != (channel = incoming->channel))
  {
    incoming->channel = NULL;
    GNUNET_CADET_channel_destroy (channel);
  }
}


/**
 * Find a listener that is interested in the given operation type
 * and application id.
 *
 * @param op operation type to look for
 * @param app_id application id to look for
 * @return a matching listener, or NULL if no listener matches the
 *         given operation and application id
 */
static struct Listener *
listener_get_by_target (enum GNUNET_SET_OperationType op,
                        const struct GNUNET_HashCode *app_id)
{
  struct Listener *listener;

  for (listener = listeners_head; NULL != listener; listener = listener->next)
    if ( (listener->operation == op) &&
         (0 == GNUNET_CRYPTO_hash_cmp (app_id, &listener->app_id)) )
      return listener;
  return NULL;
}


/**
 * Suggest the given request to the listener. The listening client can
 * then accept or reject the remote request.
 *
 * @param incoming the incoming peer with the request to suggest
 * @param listener the listener to suggest the request to
 */
static void
incoming_suggest (struct Operation *incoming,
                  struct Listener *listener)
{
  struct GNUNET_MQ_Envelope *mqm;
  struct GNUNET_SET_RequestMessage *cmsg;

  GNUNET_assert (GNUNET_YES == incoming->is_incoming);
  GNUNET_assert (NULL != incoming->spec);
  GNUNET_assert (0 == incoming->suggest_id);
  incoming->suggest_id = suggest_id++;
  if (0 == suggest_id)
    suggest_id++;
  GNUNET_assert (NULL != incoming->timeout_task);
  GNUNET_SCHEDULER_cancel (incoming->timeout_task);
  incoming->timeout_task = NULL;
  mqm = GNUNET_MQ_msg_nested_mh (cmsg,
                                 GNUNET_MESSAGE_TYPE_SET_REQUEST,
                                 incoming->spec->context_msg);
  GNUNET_assert (NULL != mqm);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Suggesting incoming request with accept id %u to listener\n",
              incoming->suggest_id);
  cmsg->accept_id = htonl (incoming->suggest_id);
  cmsg->peer_id = incoming->spec->peer;
  GNUNET_MQ_send (listener->client_mq, mqm);
}


/**
 * Handle a request for a set operation from another peer.  Checks if we
 * have a listener waiting for such a request (and in that case initiates
 * asking the listener about accepting the connection). If no listener
 * is waiting, we queue the operation request in hope that a listener
 * shows up soon (before timeout).
 *
 * This msg is expected as the first and only msg handled through the
 * non-operation bound virtual table, acceptance of this operation replaces
 * our virtual table and subsequent msgs would be routed differently (as
 * we then know what type of operation this is).
 *
 * @param op the operation state
 * @param mh the received message
 * @return #GNUNET_OK if the channel should be kept alive,
 *         #GNUNET_SYSERR to destroy the channel
 */
static int
handle_incoming_msg (struct Operation *op,
                     const struct GNUNET_MessageHeader *mh)
{
  const struct OperationRequestMessage *msg;
  struct Listener *listener;
  struct OperationSpecification *spec;
  const struct GNUNET_MessageHeader *nested_context;

  msg = (const struct OperationRequestMessage *) mh;
  GNUNET_assert (GNUNET_YES == op->is_incoming);
  if (GNUNET_MESSAGE_TYPE_SET_P2P_OPERATION_REQUEST != ntohs (mh->type))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  /* double operation request */
  if (NULL != op->spec)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  spec = GNUNET_new (struct OperationSpecification);
  nested_context = GNUNET_MQ_extract_nested_mh (msg);
  if ( (NULL != nested_context) &&
       (ntohs (nested_context->size) > GNUNET_SET_CONTEXT_MESSAGE_MAX_SIZE) )
  {
    GNUNET_break_op (0);
    GNUNET_free (spec);
    return GNUNET_SYSERR;
  }
  /* Make a copy of the nested_context (application-specific context
     information that is opaque to set) so we can pass it to the
     listener later on */
  if (NULL != nested_context)
    spec->context_msg = GNUNET_copy_message (nested_context);
  spec->operation = ntohl (msg->operation);
  spec->app_id = msg->app_id;
  spec->salt = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_NONCE,
                                         UINT32_MAX);
  spec->peer = op->peer;
  spec->remote_element_count = ntohl (msg->element_count);
  op->spec = spec;

  listener = listener_get_by_target (ntohl (msg->operation),
                                     &msg->app_id);
  if (NULL == listener)
  {
    GNUNET_break (NULL != op->timeout_task);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "No matching listener for incoming request (op %u, app %s), waiting with timeout\n",
                ntohl (msg->operation),
                GNUNET_h2s (&msg->app_id));
    return GNUNET_OK;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received P2P operation request (op %u, app %s) for active listener\n",
              ntohl (msg->operation),
              GNUNET_h2s (&msg->app_id));
  incoming_suggest (op, listener);
  return GNUNET_OK;
}


static void
execute_add (struct Set *set,
             const struct GNUNET_MessageHeader *m)
{
  const struct GNUNET_SET_ElementMessage *msg;
  struct GNUNET_SET_Element el;
  struct ElementEntry *ee;
  struct GNUNET_HashCode hash;

  GNUNET_assert (GNUNET_MESSAGE_TYPE_SET_ADD == ntohs (m->type));

  msg = (const struct GNUNET_SET_ElementMessage *) m;
  el.size = ntohs (m->size) - sizeof *msg;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client inserts element of size %u\n",
              el.size);
  el.data = &msg[1];
  GNUNET_CRYPTO_hash (el.data,
                      el.size,
                      &hash);

  ee = GNUNET_CONTAINER_multihashmap_get (set->content->elements,
                                          &hash);

  if (NULL == ee)
  {
    ee = GNUNET_malloc (el.size + sizeof *ee);
    ee->element.size = el.size;
    memcpy (&ee[1],
            el.data,
            el.size);
    ee->element.data = &ee[1];
    ee->remote = GNUNET_NO;
    ee->mutations = NULL;
    ee->mutations_size = 0;
    ee->element_hash = hash;
  } else if (GNUNET_YES == _GSS_is_element_of_set (ee, set)) {
    /* same element inserted twice */
    GNUNET_break (0);
    return;
  }

  if (0 != set->current_generation)
  {
    struct MutationEvent mut = {
      .generation = set->current_generation,
      .added = GNUNET_YES
    };
    GNUNET_array_append (ee->mutations, ee->mutations_size, mut);
    ee->mutations_size += 1;
  }

  GNUNET_break (GNUNET_YES ==
                GNUNET_CONTAINER_multihashmap_put (set->content->elements,
                                                   &ee->element_hash,
                                                   ee,
                                                   GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));
  set->vt->add (set->state, ee);
}


static void
execute_remove (struct Set *set,
                const struct GNUNET_MessageHeader *m)
{
  const struct GNUNET_SET_ElementMessage *msg;
  struct GNUNET_SET_Element el;
  struct ElementEntry *ee;
  struct GNUNET_HashCode hash;

  GNUNET_assert (GNUNET_MESSAGE_TYPE_SET_REMOVE == ntohs (m->type));

  msg = (const struct GNUNET_SET_ElementMessage *) m;
  el.size = ntohs (m->size) - sizeof *msg;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client removes element of size %u\n",
              el.size);
  el.data = &msg[1];
  GNUNET_CRYPTO_hash (el.data,
                      el.size,
                      &hash);
  ee = GNUNET_CONTAINER_multihashmap_get (set->content->elements,
                                          &hash);
  if (NULL == ee)
  {
    /* Client tried to remove non-existing element */
    GNUNET_break (0);
    return;
  }
  if (GNUNET_NO == _GSS_is_element_of_set (ee, set))
  {
    /* Client tried to remove element twice */
    GNUNET_break (0);
    return;
  }
  else if (0 == set->current_generation)
  {
    // If current_generation is 0, then there are no running set operations
    // or lazy copies, thus we can safely remove the element.
    (void) GNUNET_CONTAINER_multihashmap_remove_all (set->content->elements, &hash);
  }
  else
  {
    struct MutationEvent mut = {
      .generation = set->current_generation,
      .added = GNUNET_NO
    };
    GNUNET_array_append (ee->mutations, ee->mutations_size, mut);
    ee->mutations_size += 1;
  }
  set->vt->remove (set->state, ee);
}



static void
execute_mutation (struct Set *set,
                  const struct GNUNET_MessageHeader *m)
{
  switch (ntohs (m->type))
  {
    case GNUNET_MESSAGE_TYPE_SET_ADD:
      execute_add (set, m);
      break;
    case GNUNET_MESSAGE_TYPE_SET_REMOVE:
      execute_remove (set, m);
      break;
    default:
      GNUNET_break (0);
  }
}



/**
 * Send the next element of a set to the set's client.  The next element is given by
 * the set's current hashmap iterator.  The set's iterator will be set to NULL if there
 * are no more elements in the set.  The caller must ensure that the set's iterator is
 * valid.
 *
 * The client will acknowledge each received element with a
 * #GNUNET_MESSAGE_TYPE_SET_ITER_ACK message.  Our
 * #handle_client_iter_ack() will then trigger the next transmission.
 * Note that the #GNUNET_MESSAGE_TYPE_SET_ITER_DONE is not acknowledged.
 *
 * @param set set that should send its next element to its client
 */
static void
send_client_element (struct Set *set)
{
  int ret;
  struct ElementEntry *ee;
  struct GNUNET_MQ_Envelope *ev;
  struct GNUNET_SET_IterResponseMessage *msg;

  GNUNET_assert (NULL != set->iter);
  ret = GNUNET_CONTAINER_multihashmap_iterator_next (set->iter,
                                                     NULL,
                                                     (const void **) &ee);
  if (GNUNET_NO == ret)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Iteration on %p done.\n",
                (void *) set);
    ev = GNUNET_MQ_msg_header (GNUNET_MESSAGE_TYPE_SET_ITER_DONE);
    GNUNET_CONTAINER_multihashmap_iterator_destroy (set->iter);
    set->iter = NULL;
    set->iteration_id++;
    
    GNUNET_assert (set->content->iterator_count > 0);
    set->content->iterator_count -= 1;

    if (0 == set->content->iterator_count)
    {
      while (NULL != set->content->pending_mutations_head)
      {
        struct PendingMutation *pm;

        pm = set->content->pending_mutations_head;
        GNUNET_CONTAINER_DLL_remove (set->content->pending_mutations_head,
                                     set->content->pending_mutations_tail,
                                     pm);
        GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                    "Executing pending mutation on %p.\n",
                    (void *) pm->set);
        execute_mutation (pm->set, pm->mutation_message);
        GNUNET_free (pm->mutation_message);
        GNUNET_free (pm);
      }
    }

  }
  else
  {
    GNUNET_assert (NULL != ee);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Sending iteration element on %p.\n",
                (void *) set);
    ev = GNUNET_MQ_msg_extra (msg,
                              ee->element.size,
                              GNUNET_MESSAGE_TYPE_SET_ITER_ELEMENT);
    memcpy (&msg[1],
            ee->element.data,
            ee->element.size);
    msg->element_type = ee->element.element_type;
    msg->iteration_id = htons (set->iteration_id);
  }
  GNUNET_MQ_send (set->client_mq, ev);
}


/**
 * Called when a client wants to iterate the elements of a set.
 * Checks if we have a set associated with the client and if we
 * can right now start an iteration. If all checks out, starts
 * sending the elements of the set to the client.
 *
 * @param cls unused
 * @param client client that sent the message
 * @param m message sent by the client
 */
static void
handle_client_iterate (void *cls,
                       struct GNUNET_SERVER_Client *client,
                       const struct GNUNET_MessageHeader *m)
{
  struct Set *set;

  set = set_get (client);
  if (NULL == set)
  {
    /* attempt to iterate over a non existing set */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  if (NULL != set->iter)
  {
    /* Only one concurrent iterate-action allowed per set */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Iterating set %p with %u elements\n",
              (void *) set,
              GNUNET_CONTAINER_multihashmap_size (set->content->elements));
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
  set->content->iterator_count += 1;
  set->iter = GNUNET_CONTAINER_multihashmap_iterator_create (set->content->elements);
  send_client_element (set);
}


/**
 * Called when a client wants to create a new set.  This is typically
 * the first request from a client, and includes the type of set
 * operation to be performed.
 *
 * @param cls unused
 * @param client client that sent the message
 * @param m message sent by the client
 */
static void
handle_client_create_set (void *cls,
                          struct GNUNET_SERVER_Client *client,
                          const struct GNUNET_MessageHeader *m)
{
  const struct GNUNET_SET_CreateMessage *msg;
  struct Set *set;

  msg = (const struct GNUNET_SET_CreateMessage *) m;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client created new set (operation %u)\n",
              ntohl (msg->operation));
  if (NULL != set_get (client))
  {
    /* There can only be one set per client */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  set = GNUNET_new (struct Set);
  switch (ntohl (msg->operation))
  {
  case GNUNET_SET_OPERATION_INTERSECTION:
    set->vt = _GSS_intersection_vt ();
    break;
  case GNUNET_SET_OPERATION_UNION:
    set->vt = _GSS_union_vt ();
    break;
  default:
    GNUNET_free (set);
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  set->operation = ntohl (msg->operation);
  set->state = set->vt->create ();
  set->content = GNUNET_new (struct SetContent);
  set->content->refcount = 1;
  set->content->elements = GNUNET_CONTAINER_multihashmap_create (1, GNUNET_YES);
  set->client = client;
  set->client_mq = GNUNET_MQ_queue_for_server_client (client);
  GNUNET_CONTAINER_DLL_insert (sets_head,
                               sets_tail,
                               set);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Called when a client wants to create a new listener.
 *
 * @param cls unused
 * @param client client that sent the message
 * @param m message sent by the client
 */
static void
handle_client_listen (void *cls,
                      struct GNUNET_SERVER_Client *client,
                      const struct GNUNET_MessageHeader *m)
{
  const struct GNUNET_SET_ListenMessage *msg;
  struct Listener *listener;
  struct Operation *op;

  msg = (const struct GNUNET_SET_ListenMessage *) m;
  if (NULL != listener_get (client))
  {
    /* max. one active listener per client! */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  listener = GNUNET_new (struct Listener);
  listener->client = client;
  listener->client_mq = GNUNET_MQ_queue_for_server_client (client);
  listener->app_id = msg->app_id;
  listener->operation = ntohl (msg->operation);
  GNUNET_CONTAINER_DLL_insert_tail (listeners_head,
                                    listeners_tail,
                                    listener);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "New listener created (op %u, app %s)\n",
              listener->operation,
              GNUNET_h2s (&listener->app_id));

  /* check for existing incoming requests the listener might be interested in */
  for (op = incoming_head; NULL != op; op = op->next)
  {
    if (NULL == op->spec)
      continue; /* no details available yet */
    if (0 != op->suggest_id)
      continue; /* this one has been already suggested to a listener */
    if (listener->operation != op->spec->operation)
      continue; /* incompatible operation */
    if (0 != GNUNET_CRYPTO_hash_cmp (&listener->app_id,
                                     &op->spec->app_id))
      continue; /* incompatible appliation */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Found matching existing request\n");
    incoming_suggest (op,
                      listener);
  }
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}


/**
 * Called when the listening client rejects an operation
 * request by another peer.
 *
 * @param cls unused
 * @param client client that sent the message
 * @param m message sent by the client
 */
static void
handle_client_reject (void *cls,
                      struct GNUNET_SERVER_Client *client,
                      const struct GNUNET_MessageHeader *m)
{
  struct Operation *incoming;
  const struct GNUNET_SET_RejectMessage *msg;

  msg = (const struct GNUNET_SET_RejectMessage *) m;
  incoming = get_incoming (ntohl (msg->accept_reject_id));
  if (NULL == incoming)
  {
    /* no matching incoming operation for this reject */
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Peer request (op %u, app %s) rejected by client\n",
              incoming->spec->operation,
              GNUNET_h2s (&incoming->spec->app_id));
  GNUNET_CADET_channel_destroy (incoming->channel);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}



/**
 * Called when a client wants to add or remove an element to a set it inhabits.
 *
 * @param cls unused
 * @param client client that sent the message
 * @param m message sent by the client
 */
static void
handle_client_mutation (void *cls,
                        struct GNUNET_SERVER_Client *client,
                        const struct GNUNET_MessageHeader *m)
{
  struct Set *set;

  set = set_get (client);
  if (NULL == set)
  {
    /* client without a set requested an operation */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }

  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);

  if (0 != set->content->iterator_count)
  {
    struct PendingMutation *pm;

    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Scheduling mutation on set\n");

    pm = GNUNET_new (struct PendingMutation);
    pm->mutation_message = GNUNET_copy_message (m);
    pm->set = set;
    GNUNET_CONTAINER_DLL_insert (set->content->pending_mutations_head,
                                 set->content->pending_mutations_tail,
                                 pm);
    return;
  }

  execute_mutation (set, m);
}


/**
 * Advance the current generation of a set,
 * adding exclusion ranges if necessary.
 *
 * @param set the set where we want to advance the generation
 */
static void
advance_generation (struct Set *set)
{
  struct GenerationRange r;

  if (set->current_generation == set->content->latest_generation)
  {
    set->content->latest_generation += 1;
    set->current_generation += 1;
    return;
  }

  GNUNET_assert (set->current_generation < set->content->latest_generation);

  r.start = set->current_generation + 1;
  r.end = set->content->latest_generation + 1;

  set->content->latest_generation = r.end;
  set->current_generation = r.end;

  GNUNET_array_append (set->excluded_generations,
                       set->excluded_generations_size,
                       r);

  set->excluded_generations_size += 1;
}

/**
 * Called when a client wants to initiate a set operation with another
 * peer.  Initiates the CADET connection to the listener and sends the
 * request.
 *
 * @param cls unused
 * @param client client that sent the message
 * @param m message sent by the client
 */
static void
handle_client_evaluate (void *cls,
                        struct GNUNET_SERVER_Client *client,
                        const struct GNUNET_MessageHeader *m)
{
  struct Set *set;
  const struct GNUNET_SET_EvaluateMessage *msg;
  struct OperationSpecification *spec;
  struct Operation *op;
  const struct GNUNET_MessageHeader *context;

  set = set_get (client);
  if (NULL == set)
  {
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  msg = (const struct GNUNET_SET_EvaluateMessage *) m;
  spec = GNUNET_new (struct OperationSpecification);
  spec->operation = set->operation;
  spec->app_id = msg->app_id;
  spec->salt = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_NONCE,
                                         UINT32_MAX);
  spec->peer = msg->target_peer;
  spec->set = set;
  spec->result_mode = ntohl (msg->result_mode);
  spec->client_request_id = ntohl (msg->request_id);
  context = GNUNET_MQ_extract_nested_mh (msg);
  op = GNUNET_new (struct Operation);
  op->spec = spec;

  // Advance generation values, so that
  // mutations won't interfer with the running operation.
  op->generation_created = set->current_generation;
  advance_generation (set);

  op->vt = set->vt;
  GNUNET_CONTAINER_DLL_insert (set->ops_head,
                               set->ops_tail,
                               op);
  op->channel = GNUNET_CADET_channel_create (cadet,
                                             op,
                                             &msg->target_peer,
                                             GNUNET_APPLICATION_TYPE_SET,
                                             GNUNET_CADET_OPTION_RELIABLE);
  op->mq = GNUNET_CADET_mq_create (op->channel);
  set->vt->evaluate (op,
                     context);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Handle an ack from a client, and send the next element. Note
 * that we only expect acks for set elements, not after the
 * #GNUNET_MESSAGE_TYPE_SET_ITER_DONE message.
 *
 * @param cls unused
 * @param client the client
 * @param m the message
 */
static void
handle_client_iter_ack (void *cls,
                        struct GNUNET_SERVER_Client *client,
                        const struct GNUNET_MessageHeader *m)
{
  const struct GNUNET_SET_IterAckMessage *ack;
  struct Set *set;

  set = set_get (client);
  if (NULL == set)
  {
    /* client without a set acknowledged receiving a value */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  if (NULL == set->iter)
  {
    /* client sent an ack, but we were not expecting one (as
       set iteration has finished) */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  ack = (const struct GNUNET_SET_IterAckMessage *) m;
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
  if (ntohl (ack->send_more))
  {
    send_client_element (set);
  }
  else
  {
    GNUNET_CONTAINER_multihashmap_iterator_destroy (set->iter);
    set->iter = NULL;
    set->iteration_id++;
  }
}


/**
 * Handle a request from the client to
 * copy a set.
 *
 * @param cls unused
 * @param client the client
 * @param mh the message
 */
static void
handle_client_copy_lazy_prepare (void *cls,
                                 struct GNUNET_SERVER_Client *client,
                                 const struct GNUNET_MessageHeader *mh)
{
  struct Set *set;
  struct LazyCopyRequest *cr;
  struct GNUNET_MQ_Envelope *ev;
  struct GNUNET_SET_CopyLazyResponseMessage *resp_msg;

  set = set_get (client);
  if (NULL == set)
  {
    /* client without a set requested an operation */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }

  cr = GNUNET_new (struct LazyCopyRequest);

  cr->cookie = lazy_copy_cookie;
  lazy_copy_cookie += 1;
  cr->source_set = set;

  GNUNET_CONTAINER_DLL_insert (lazy_copy_head,
                               lazy_copy_tail,
                               cr);


  ev = GNUNET_MQ_msg (resp_msg,
                      GNUNET_MESSAGE_TYPE_SET_COPY_LAZY_RESPONSE);
  resp_msg->cookie = cr->cookie;
  GNUNET_MQ_send (set->client_mq, ev);


  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client requested lazy copy\n");
}


/**
 * Handle a request from the client to
 * connect to a copy of a set.
 *
 * @param cls unused
 * @param client the client
 * @param mh the message
 */
static void
handle_client_copy_lazy_connect (void *cls,
                                 struct GNUNET_SERVER_Client *client,
                                 const struct GNUNET_MessageHeader *mh)
{
  struct LazyCopyRequest *cr;
  const struct GNUNET_SET_CopyLazyConnectMessage *msg =
      (const struct GNUNET_SET_CopyLazyConnectMessage *) mh;
  struct Set *set;
  int found;

  if (NULL != set_get (client))
  {
    /* There can only be one set per client */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }

  found = GNUNET_NO;

  for (cr = lazy_copy_head; NULL != cr; cr = cr->next)
  {
    if (cr->cookie == msg->cookie)
    {
      found = GNUNET_YES;
      break;
    } 
  }

  if (GNUNET_NO == found)
  {
    /* client asked for copy with cookie we don't know */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }

  GNUNET_CONTAINER_DLL_remove (lazy_copy_head,
                               lazy_copy_tail,
                               cr);

  set = GNUNET_new (struct Set);

  switch (cr->source_set->operation)
  {
  case GNUNET_SET_OPERATION_INTERSECTION:
    set->vt = _GSS_intersection_vt ();
    break;
  case GNUNET_SET_OPERATION_UNION:
    set->vt = _GSS_union_vt ();
    break;
  default:
    GNUNET_assert (0);
    return;
  }

  if (NULL == set->vt->copy_state) {
    /* Lazy copy not supported for this set operation */
    GNUNET_break (0);
    GNUNET_free (set);
    GNUNET_free (cr);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }

  set->operation = cr->source_set->operation;
  set->state = set->vt->copy_state (cr->source_set);
  set->content = cr->source_set->content;
  set->content->refcount += 1;
  set->client = client;
  set->client_mq = GNUNET_MQ_queue_for_server_client (client);
  GNUNET_CONTAINER_DLL_insert (sets_head,
                               sets_tail,
                               set);

  GNUNET_free (cr);

  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client connected to lazy set\n");
}


/**
 * Handle a request from the client to
 * cancel a running set operation.
 *
 * @param cls unused
 * @param client the client
 * @param mh the message
 */
static void
handle_client_cancel (void *cls,
                      struct GNUNET_SERVER_Client *client,
                      const struct GNUNET_MessageHeader *mh)
{
  const struct GNUNET_SET_CancelMessage *msg =
      (const struct GNUNET_SET_CancelMessage *) mh;
  struct Set *set;
  struct Operation *op;
  int found;

  set = set_get (client);
  if (NULL == set)
  {
    /* client without a set requested an operation */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client requested cancel for op %u\n",
              ntohl (msg->request_id));
  found = GNUNET_NO;
  for (op = set->ops_head; NULL != op; op = op->next)
  {
    if (op->spec->client_request_id == ntohl (msg->request_id))
    {
      found = GNUNET_YES;
      break;
    }
  }
  if (GNUNET_NO == found)
  {
    /* It may happen that the operation was already destroyed due to
     * the other peer disconnecting.  The client may not know about this
     * yet and try to cancel the (just barely non-existent) operation.
     * So this is not a hard error.
     */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Client canceled non-existent op\n");
  }
  else
  {
    _GSS_operation_destroy (op,
                            GNUNET_YES);
  }
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Handle a request from the client to accept a set operation that
 * came from a remote peer.  We forward the accept to the associated
 * operation for handling
 *
 * @param cls unused
 * @param client the client
 * @param mh the message
 */
static void
handle_client_accept (void *cls,
                      struct GNUNET_SERVER_Client *client,
                      const struct GNUNET_MessageHeader *mh)
{
  struct Set *set;
  const struct GNUNET_SET_AcceptMessage *msg;
  struct Operation *op;
  struct GNUNET_SET_ResultMessage *result_message;
  struct GNUNET_MQ_Envelope *ev;

  msg = (const struct GNUNET_SET_AcceptMessage *) mh;
  set = set_get (client);
  if (NULL == set)
  {
    /* client without a set requested to accept */
    GNUNET_break (0);
    GNUNET_SERVER_client_disconnect (client);
    return;
  }
  op = get_incoming (ntohl (msg->accept_reject_id));
  if (NULL == op)
  {
    /* It is not an error if the set op does not exist -- it may
     * have been destroyed when the partner peer disconnected. */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Client accepted request that is no longer active\n");
    ev = GNUNET_MQ_msg (result_message,
                        GNUNET_MESSAGE_TYPE_SET_RESULT);
    result_message->request_id = msg->request_id;
    result_message->element_type = 0;
    result_message->result_status = htons (GNUNET_SET_STATUS_FAILURE);
    GNUNET_MQ_send (set->client_mq, ev);
    GNUNET_SERVER_receive_done (client, GNUNET_OK);
    return;
  }

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client accepting request %u\n",
              ntohl (msg->accept_reject_id));
  GNUNET_assert (GNUNET_YES == op->is_incoming);
  op->is_incoming = GNUNET_NO;
  GNUNET_CONTAINER_DLL_remove (incoming_head,
                               incoming_tail,
                               op);
  op->spec->set = set;
  GNUNET_CONTAINER_DLL_insert (set->ops_head,
                               set->ops_tail,
                               op);
  op->spec->client_request_id = ntohl (msg->request_id);
  op->spec->result_mode = ntohl (msg->result_mode);

  // Advance generation values, so that
  // mutations won't interfer with the running operation.
  op->generation_created = set->current_generation;
  advance_generation (set);

  op->vt = set->vt;
  op->vt->accept (op);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Called to clean up, after a shutdown has been requested.
 *
 * @param cls closure
 * @param tc context information (why was this task triggered now)
 */
static void
shutdown_task (void *cls,
               const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  while (NULL != incoming_head)
    incoming_destroy (incoming_head);
  while (NULL != listeners_head)
    listener_destroy (listeners_head);
  while (NULL != sets_head)
    set_destroy (sets_head);

  /* it's important to destroy cadet at the end, as all channels
   * must be destroyed before the cadet handle! */
  if (NULL != cadet)
  {
    GNUNET_CADET_disconnect (cadet);
    cadet = NULL;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "handled shutdown request\n");
}


/**
 * Timeout happens iff:
 *  - we suggested an operation to our listener,
 *    but did not receive a response in time
 *  - we got the channel from a peer but no #GNUNET_MESSAGE_TYPE_SET_P2P_OPERATION_REQUEST
 *  - shutdown (obviously)
 *
 * @param cls channel context
 * @param tc context information (why was this task triggered now)
 */
static void
incoming_timeout_cb (void *cls,
                     const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct Operation *incoming = cls;

  incoming->timeout_task = NULL;
  GNUNET_assert (GNUNET_YES == incoming->is_incoming);
  if (0 != (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN))
    return;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Remote peer's incoming request timed out\n");
  incoming_destroy (incoming);
}


/**
 * Terminates an incoming operation in case we have not yet received an
 * operation request. Called by the channel destruction handler.
 *
 * @param op the channel context
 */
static void
handle_incoming_disconnect (struct Operation *op)
{
  GNUNET_assert (GNUNET_YES == op->is_incoming);
  /* channel is already dead, incoming_destroy must not
   * destroy it ... */
  op->channel = NULL;
  incoming_destroy (op);
  op->vt = NULL;
}


/**
 * Method called whenever another peer has added us to a channel the
 * other peer initiated.  Only called (once) upon reception of data
 * with a message type which was subscribed to in
 * GNUNET_CADET_connect().
 *
 * The channel context represents the operation itself and gets added to a DLL,
 * from where it gets looked up when our local listener client responds
 * to a proposed/suggested operation or connects and associates with this operation.
 *
 * @param cls closure
 * @param channel new handle to the channel
 * @param initiator peer that started the channel
 * @param port Port this channel is for.
 * @param options Unused.
 * @return initial channel context for the channel
 *         returns NULL on error
 */
static void *
channel_new_cb (void *cls,
                struct GNUNET_CADET_Channel *channel,
                const struct GNUNET_PeerIdentity *initiator,
                uint32_t port,
                enum GNUNET_CADET_ChannelOption options)
{
  static const struct SetVT incoming_vt = {
    .msg_handler = &handle_incoming_msg,
    .peer_disconnect = &handle_incoming_disconnect
  };
  struct Operation *incoming;

  if (GNUNET_APPLICATION_TYPE_SET != port)
  {
    GNUNET_break (0);
    GNUNET_CADET_channel_destroy (channel);
    return NULL;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "New incoming channel\n");
  incoming = GNUNET_new (struct Operation);
  incoming->is_incoming = GNUNET_YES;
  incoming->peer = *initiator;
  incoming->channel = channel;
  incoming->mq = GNUNET_CADET_mq_create (incoming->channel);
  incoming->vt = &incoming_vt;
  incoming->timeout_task
    = GNUNET_SCHEDULER_add_delayed (INCOMING_CHANNEL_TIMEOUT,
                                    &incoming_timeout_cb,
                                    incoming);
  GNUNET_CONTAINER_DLL_insert_tail (incoming_head,
                                    incoming_tail,
                                    incoming);
  return incoming;
}


/**
 * Function called whenever a channel is destroyed.  Should clean up
 * any associated state.  It must NOT call
 * GNUNET_CADET_channel_destroy() on the channel.
 *
 * The peer_disconnect function is part of a a virtual table set initially either
 * when a peer creates a new channel with us (#channel_new_cb()), or once we create
 * a new channel ourselves (evaluate).
 *
 * Once we know the exact type of operation (union/intersection), the vt is
 * replaced with an operation specific instance (_GSS_[op]_vt).
 *
 * @param cls closure (set from GNUNET_CADET_connect())
 * @param channel connection to the other end (henceforth invalid)
 * @param channel_ctx place where local state associated
 *                   with the channel is stored
 */
static void
channel_end_cb (void *cls,
                const struct GNUNET_CADET_Channel *channel,
                void *channel_ctx)
{
  struct Operation *op = channel_ctx;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "channel_end_cb called\n");
  op->channel = NULL;
  op->keep++;
  /* the vt can be null if a client already requested canceling op. */
  if (NULL != op->vt)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "calling peer disconnect due to channel end\n");
    op->vt->peer_disconnect (op);
  }
  op->keep--;
  if (0 == op->keep)
  {
    /* cadet will never call us with the context again! */
    GNUNET_free (op);
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "channel_end_cb finished\n");
}


/**
 * Functions with this signature are called whenever a message is
 * received via a cadet channel.
 *
 * The msg_handler is a virtual table set in initially either when a peer
 * creates a new channel with us (channel_new_cb), or once we create a new channel
 * ourselves (evaluate).
 *
 * Once we know the exact type of operation (union/intersection), the vt is
 * replaced with an operation specific instance (_GSS_[op]_vt).
 *
 * @param cls Closure (set from GNUNET_CADET_connect()).
 * @param channel Connection to the other end.
 * @param channel_ctx Place to store local state associated with the channel.
 * @param message The actual message.
 * @return #GNUNET_OK to keep the channel open,
 *         #GNUNET_SYSERR to close it (signal serious error).
 */
static int
dispatch_p2p_message (void *cls,
                      struct GNUNET_CADET_Channel *channel,
                      void **channel_ctx,
                      const struct GNUNET_MessageHeader *message)
{
  struct Operation *op = *channel_ctx;
  int ret;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Dispatching cadet message (type: %u)\n",
              ntohs (message->type));
  /* do this before the handler, as the handler might kill the channel */
  GNUNET_CADET_receive_done (channel);
  if (NULL != op->vt)
    ret = op->vt->msg_handler (op,
                               message);
  else
    ret = GNUNET_SYSERR;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Handled cadet message (type: %u)\n",
              ntohs (message->type));
  return ret;
}


/**
 * Function called by the service's run
 * method to run service-specific setup code.
 *
 * @param cls closure
 * @param server the initialized server
 * @param cfg configuration to use
 */
static void
run (void *cls,
     struct GNUNET_SERVER_Handle *server,
     const struct GNUNET_CONFIGURATION_Handle *cfg)
{
  static const struct GNUNET_SERVER_MessageHandler server_handlers[] = {
    { &handle_client_accept, NULL,
      GNUNET_MESSAGE_TYPE_SET_ACCEPT,
      sizeof (struct GNUNET_SET_AcceptMessage)},
    { &handle_client_iter_ack, NULL,
      GNUNET_MESSAGE_TYPE_SET_ITER_ACK,
      sizeof (struct GNUNET_SET_IterAckMessage) },
    { &handle_client_mutation, NULL,
      GNUNET_MESSAGE_TYPE_SET_ADD,
      0},
    { &handle_client_create_set, NULL,
      GNUNET_MESSAGE_TYPE_SET_CREATE,
      sizeof (struct GNUNET_SET_CreateMessage)},
    { &handle_client_iterate, NULL,
      GNUNET_MESSAGE_TYPE_SET_ITER_REQUEST,
      sizeof (struct GNUNET_MessageHeader)},
    { &handle_client_evaluate, NULL,
      GNUNET_MESSAGE_TYPE_SET_EVALUATE,
      0},
    { &handle_client_listen, NULL,
      GNUNET_MESSAGE_TYPE_SET_LISTEN,
      sizeof (struct GNUNET_SET_ListenMessage)},
    { &handle_client_reject, NULL,
      GNUNET_MESSAGE_TYPE_SET_REJECT,
      sizeof (struct GNUNET_SET_RejectMessage)},
    { &handle_client_mutation, NULL,
      GNUNET_MESSAGE_TYPE_SET_REMOVE,
      0},
    { &handle_client_cancel, NULL,
      GNUNET_MESSAGE_TYPE_SET_CANCEL,
      sizeof (struct GNUNET_SET_CancelMessage)},
    { &handle_client_copy_lazy_prepare, NULL,
      GNUNET_MESSAGE_TYPE_SET_COPY_LAZY_PREPARE,
      sizeof (struct GNUNET_MessageHeader)},
    { &handle_client_copy_lazy_connect, NULL,
      GNUNET_MESSAGE_TYPE_SET_COPY_LAZY_CONNECT,
      sizeof (struct GNUNET_SET_CopyLazyConnectMessage)},
    { NULL, NULL, 0, 0}
  };
  static const struct GNUNET_CADET_MessageHandler cadet_handlers[] = {
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_P2P_OPERATION_REQUEST, 0},
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_UNION_P2P_IBF, 0},
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_P2P_ELEMENTS, 0},
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_UNION_P2P_DONE, 0},
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_P2P_ELEMENT_REQUESTS, 0},
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_UNION_P2P_SE, 0},
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_ELEMENT_INFO, 0},
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_BF, 0},
    { &dispatch_p2p_message, GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_DONE, 0},
    {NULL, 0, 0}
  };
  static const uint32_t cadet_ports[] = {GNUNET_APPLICATION_TYPE_SET, 0};

  configuration = cfg;
  GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_UNIT_FOREVER_REL,
                                &shutdown_task, NULL);
  GNUNET_SERVER_disconnect_notify (server,
                                   &handle_client_disconnect, NULL);
  GNUNET_SERVER_add_handlers (server,
                              server_handlers);
  cadet = GNUNET_CADET_connect (cfg, NULL,
                                &channel_new_cb,
                                &channel_end_cb,
                                cadet_handlers,
                                cadet_ports);
  if (NULL == cadet)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _("Could not connect to cadet service\n"));
    return;
  }
}


/**
 * The main function for the set 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)
{
  int ret;

  ret = GNUNET_SERVICE_run (argc, argv, "set",
                            GNUNET_SERVICE_OPTION_NONE,
                            &run, NULL);
  return (GNUNET_OK == ret) ? 0 : 1;
}

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