gnunet/src/set/gnunet-service-set_intersection.c

/*
      This file is part of GNUnet
      Copyright (C) 2013-2017 GNUnet e.V.

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

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

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

     SPDX-License-Identifier: AGPL3.0-or-later
 */
/**
 * @file set/gnunet-service-set_intersection.c
 * @brief two-peer set intersection
 * @author Christian Fuchs
 * @author Christian Grothoff
 */
#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_statistics_service.h"
#include "gnunet-service-set.h"
#include "gnunet_block_lib.h"
#include "gnunet-service-set_protocol.h"
#include "gnunet-service-set_intersection.h"
#include <gcrypt.h>


/**
 * Current phase we are in for a intersection operation.
 */
enum IntersectionOperationPhase
{
  /**
   * We are just starting.
   */
  PHASE_INITIAL,

  /**
   * We have send the number of our elements to the other
   * peer, but did not setup our element set yet.
   */
  PHASE_COUNT_SENT,

  /**
   * We have initialized our set and are now reducing it by exchanging
   * Bloom filters until one party notices the their element hashes
   * are equal.
   */
  PHASE_BF_EXCHANGE,

  /**
   * We must next send the P2P DONE message (after finishing mostly
   * with the local client).  Then we will wait for the channel to close.
   */
  PHASE_MUST_SEND_DONE,

  /**
   * We have received the P2P DONE message, and must finish with the
   * local client before terminating the channel.
   */
  PHASE_DONE_RECEIVED,

  /**
   * The protocol is over.  Results may still have to be sent to the
   * client.
   */
  PHASE_FINISHED
};


/**
 * State of an evaluate operation with another peer.
 */
struct OperationState
{
  /**
   * The bf we currently receive
   */
  struct GNUNET_CONTAINER_BloomFilter *remote_bf;

  /**
   * BF of the set's element.
   */
  struct GNUNET_CONTAINER_BloomFilter *local_bf;

  /**
   * Remaining elements in the intersection operation.
   * Maps element-id-hashes to 'elements in our set'.
   */
  struct GNUNET_CONTAINER_MultiHashMap *my_elements;

  /**
   * Iterator for sending the final set of @e my_elements to the client.
   */
  struct GNUNET_CONTAINER_MultiHashMapIterator *full_result_iter;

  /**
   * Evaluate operations are held in a linked list.
   */
  struct OperationState *next;

  /**
   * Evaluate operations are held in a linked list.
   */
  struct OperationState *prev;

  /**
   * For multipart BF transmissions, we have to store the
   * bloomfilter-data until we fully received it.
   */
  char *bf_data;

  /**
   * XOR of the keys of all of the elements (remaining) in my set.
   * Always updated when elements are added or removed to
   * @e my_elements.
   */
  struct GNUNET_HashCode my_xor;

  /**
   * XOR of the keys of all of the elements (remaining) in
   * the other peer's set.  Updated when we receive the
   * other peer's Bloom filter.
   */
  struct GNUNET_HashCode other_xor;

  /**
   * How many bytes of @e bf_data are valid?
   */
  uint32_t bf_data_offset;

  /**
   * Current element count contained within @e my_elements.
   * (May differ briefly during initialization.)
   */
  uint32_t my_element_count;

  /**
   * size of the bloomfilter in @e bf_data.
   */
  uint32_t bf_data_size;

  /**
   * size of the bloomfilter
   */
  uint32_t bf_bits_per_element;

  /**
   * Salt currently used for BF construction (by us or the other peer,
   * depending on where we are in the code).
   */
  uint32_t salt;

  /**
   * Current state of the operation.
   */
  enum IntersectionOperationPhase phase;

  /**
   * Generation in which the operation handle
   * was created.
   */
  unsigned int generation_created;

  /**
   * Did we send the client that we are done?
   */
  int client_done_sent;

  /**
   * Set whenever we reach the state where the death of the
   * channel is perfectly find and should NOT result in the
   * operation being cancelled.
   */
  int channel_death_expected;
};


/**
 * Extra state required for efficient set intersection.
 * Merely tracks the total number of elements.
 */
struct SetState
{
  /**
   * Number of currently valid elements in the set which have not been
   * removed.
   */
  uint32_t current_set_element_count;
};


/**
 * If applicable in the current operation mode, send a result message
 * to the client indicating we removed an element.
 *
 * @param op intersection operation
 * @param element element to send
 */
static void
send_client_removed_element (struct Operation *op,
                             struct GNUNET_SET_Element *element)
{
  struct GNUNET_MQ_Envelope *ev;
  struct GNUNET_SET_ResultMessage *rm;

  if (GNUNET_SET_RESULT_REMOVED != op->result_mode)
    return; /* Wrong mode for transmitting removed elements */
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending removed element (size %u) to client\n",
              element->size);
  GNUNET_STATISTICS_update (_GSS_statistics,
                            "# Element removed messages sent",
                            1,
                            GNUNET_NO);
  GNUNET_assert (0 != op->client_request_id);
  ev = GNUNET_MQ_msg_extra (rm,
                            element->size,
                            GNUNET_MESSAGE_TYPE_SET_RESULT);
  if (NULL == ev)
  {
    GNUNET_break (0);
    return;
  }
  rm->result_status = htons (GNUNET_SET_STATUS_OK);
  rm->request_id = htonl (op->client_request_id);
  rm->element_type = element->element_type;
  GNUNET_memcpy (&rm[1],
                 element->data,
                 element->size);
  GNUNET_MQ_send (op->set->cs->mq,
                  ev);
}


/**
 * Fills the "my_elements" hashmap with all relevant elements.
 *
 * @param cls the `struct Operation *` we are performing
 * @param key current key code
 * @param value the `struct ElementEntry *` from the hash map
 * @return #GNUNET_YES (we should continue to iterate)
 */
static int
filtered_map_initialization (void *cls,
                             const struct GNUNET_HashCode *key,
                             void *value)
{
  struct Operation *op = cls;
  struct ElementEntry *ee = value;
  struct GNUNET_HashCode mutated_hash;


  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "FIMA called for %s:%u\n",
              GNUNET_h2s (&ee->element_hash),
              ee->element.size);

  if (GNUNET_NO == _GSS_is_element_of_operation (ee, op))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Reduced initialization, not starting with %s:%u (wrong generation)\n",
                GNUNET_h2s (&ee->element_hash),
                ee->element.size);
    return GNUNET_YES;   /* element not valid in our operation's generation */
  }

  /* Test if element is in other peer's bloomfilter */
  GNUNET_BLOCK_mingle_hash (&ee->element_hash,
                            op->state->salt,
                            &mutated_hash);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Testing mingled hash %s with salt %u\n",
              GNUNET_h2s (&mutated_hash),
              op->state->salt);
  if (GNUNET_NO ==
      GNUNET_CONTAINER_bloomfilter_test (op->state->remote_bf,
                                         &mutated_hash))
  {
    /* remove this element */
    send_client_removed_element (op,
                                 &ee->element);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Reduced initialization, not starting with %s:%u\n",
                GNUNET_h2s (&ee->element_hash),
                ee->element.size);
    return GNUNET_YES;
  }
  op->state->my_element_count++;
  GNUNET_CRYPTO_hash_xor (&op->state->my_xor,
                          &ee->element_hash,
                          &op->state->my_xor);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Filtered initialization of my_elements, adding %s:%u\n",
              GNUNET_h2s (&ee->element_hash),
              ee->element.size);
  GNUNET_break (GNUNET_YES ==
                GNUNET_CONTAINER_multihashmap_put (op->state->my_elements,
                                                   &ee->element_hash,
                                                   ee,
                                                   GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));

  return GNUNET_YES;
}


/**
 * Removes elements from our hashmap if they are not contained within the
 * provided remote bloomfilter.
 *
 * @param cls closure with the `struct Operation *`
 * @param key current key code
 * @param value value in the hash map
 * @return #GNUNET_YES (we should continue to iterate)
 */
static int
iterator_bf_reduce (void *cls,
                    const struct GNUNET_HashCode *key,
                    void *value)
{
  struct Operation *op = cls;
  struct ElementEntry *ee = value;
  struct GNUNET_HashCode mutated_hash;

  GNUNET_BLOCK_mingle_hash (&ee->element_hash,
                            op->state->salt,
                            &mutated_hash);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Testing mingled hash %s with salt %u\n",
              GNUNET_h2s (&mutated_hash),
              op->state->salt);
  if (GNUNET_NO ==
      GNUNET_CONTAINER_bloomfilter_test (op->state->remote_bf,
                                         &mutated_hash))
  {
    GNUNET_break (0 < op->state->my_element_count);
    op->state->my_element_count--;
    GNUNET_CRYPTO_hash_xor (&op->state->my_xor,
                            &ee->element_hash,
                            &op->state->my_xor);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Bloom filter reduction of my_elements, removing %s:%u\n",
                GNUNET_h2s (&ee->element_hash),
                ee->element.size);
    GNUNET_assert (GNUNET_YES ==
                   GNUNET_CONTAINER_multihashmap_remove (op->state->my_elements,
                                                         &ee->element_hash,
                                                         ee));
    send_client_removed_element (op,
                                 &ee->element);
  }
  else
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Bloom filter reduction of my_elements, keeping %s:%u\n",
                GNUNET_h2s (&ee->element_hash),
                ee->element.size);
  }
  return GNUNET_YES;
}


/**
 * Create initial bloomfilter based on all the elements given.
 *
 * @param cls the `struct Operation *`
 * @param key current key code
 * @param value the `struct ElementEntry` to process
 * @return #GNUNET_YES (we should continue to iterate)
 */
static int
iterator_bf_create (void *cls,
                    const struct GNUNET_HashCode *key,
                    void *value)
{
  struct Operation *op = cls;
  struct ElementEntry *ee = value;
  struct GNUNET_HashCode mutated_hash;

  GNUNET_BLOCK_mingle_hash (&ee->element_hash,
                            op->state->salt,
                            &mutated_hash);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Initializing BF with hash %s with salt %u\n",
              GNUNET_h2s (&mutated_hash),
              op->state->salt);
  GNUNET_CONTAINER_bloomfilter_add (op->state->local_bf,
                                    &mutated_hash);
  return GNUNET_YES;
}


/**
 * Inform the client that the intersection operation has failed,
 * and proceed to destroy the evaluate operation.
 *
 * @param op the intersection operation to fail
 */
static void
fail_intersection_operation (struct Operation *op)
{
  struct GNUNET_MQ_Envelope *ev;
  struct GNUNET_SET_ResultMessage *msg;

  GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
              "Intersection operation failed\n");
  GNUNET_STATISTICS_update (_GSS_statistics,
                            "# Intersection operations failed",
                            1,
                            GNUNET_NO);
  if (NULL != op->state->my_elements)
  {
    GNUNET_CONTAINER_multihashmap_destroy (op->state->my_elements);
    op->state->my_elements = NULL;
  }
  ev = GNUNET_MQ_msg (msg,
                      GNUNET_MESSAGE_TYPE_SET_RESULT);
  msg->result_status = htons (GNUNET_SET_STATUS_FAILURE);
  msg->request_id = htonl (op->client_request_id);
  msg->element_type = htons (0);
  GNUNET_MQ_send (op->set->cs->mq,
                  ev);
  _GSS_operation_destroy (op,
                          GNUNET_YES);
}


/**
 * Send a bloomfilter to our peer.  After the result done message has
 * been sent to the client, destroy the evaluate operation.
 *
 * @param op intersection operation
 */
static void
send_bloomfilter (struct Operation *op)
{
  struct GNUNET_MQ_Envelope *ev;
  struct BFMessage *msg;
  uint32_t bf_size;
  uint32_t bf_elementbits;
  uint32_t chunk_size;
  char *bf_data;
  uint32_t offset;

  /* We consider the ratio of the set sizes to determine
     the number of bits per element, as the smaller set
     should use more bits to maximize its set reduction
     potential and minimize overall bandwidth consumption. */
  bf_elementbits = 2 + ceil (log2 ((double)
                                   (op->remote_element_count
                                    / (double) op->state->my_element_count)));
  if (bf_elementbits < 1)
    bf_elementbits = 1; /* make sure k is not 0 */
  /* optimize BF-size to ~50% of bits set */
  bf_size = ceil ((double) (op->state->my_element_count
                            * bf_elementbits / log (2)));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending Bloom filter (%u) of size %u bytes\n",
              (unsigned int) bf_elementbits,
              (unsigned int) bf_size);
  op->state->local_bf = GNUNET_CONTAINER_bloomfilter_init (NULL,
                                                           bf_size,
                                                           bf_elementbits);
  op->state->salt = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_NONCE,
                                              UINT32_MAX);
  GNUNET_CONTAINER_multihashmap_iterate (op->state->my_elements,
                                         &iterator_bf_create,
                                         op);

  /* send our Bloom filter */
  GNUNET_STATISTICS_update (_GSS_statistics,
                            "# Intersection Bloom filters sent",
                            1,
                            GNUNET_NO);
  chunk_size = 60 * 1024 - sizeof(struct BFMessage);
  if (bf_size <= chunk_size)
  {
    /* singlepart */
    chunk_size = bf_size;
    ev = GNUNET_MQ_msg_extra (msg,
                              chunk_size,
                              GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_BF);
    GNUNET_assert (GNUNET_SYSERR !=
                   GNUNET_CONTAINER_bloomfilter_get_raw_data (
                     op->state->local_bf,
                     (char *) &msg[1],
                     bf_size));
    msg->sender_element_count = htonl (op->state->my_element_count);
    msg->bloomfilter_total_length = htonl (bf_size);
    msg->bits_per_element = htonl (bf_elementbits);
    msg->sender_mutator = htonl (op->state->salt);
    msg->element_xor_hash = op->state->my_xor;
    GNUNET_MQ_send (op->mq, ev);
  }
  else
  {
    /* multipart */
    bf_data = GNUNET_malloc (bf_size);
    GNUNET_assert (GNUNET_SYSERR !=
                   GNUNET_CONTAINER_bloomfilter_get_raw_data (
                     op->state->local_bf,
                     bf_data,
                     bf_size));
    offset = 0;
    while (offset < bf_size)
    {
      if (bf_size - chunk_size < offset)
        chunk_size = bf_size - offset;
      ev = GNUNET_MQ_msg_extra (msg,
                                chunk_size,
                                GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_BF);
      GNUNET_memcpy (&msg[1],
                     &bf_data[offset],
                     chunk_size);
      offset += chunk_size;
      msg->sender_element_count = htonl (op->state->my_element_count);
      msg->bloomfilter_total_length = htonl (bf_size);
      msg->bits_per_element = htonl (bf_elementbits);
      msg->sender_mutator = htonl (op->state->salt);
      msg->element_xor_hash = op->state->my_xor;
      GNUNET_MQ_send (op->mq, ev);
    }
    GNUNET_free (bf_data);
  }
  GNUNET_CONTAINER_bloomfilter_free (op->state->local_bf);
  op->state->local_bf = NULL;
}


/**
 * Signal to the client that the operation has finished and
 * destroy the operation.
 *
 * @param cls operation to destroy
 */
static void
send_client_done_and_destroy (void *cls)
{
  struct Operation *op = cls;
  struct GNUNET_MQ_Envelope *ev;
  struct GNUNET_SET_ResultMessage *rm;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Intersection succeeded, sending DONE to local client\n");
  GNUNET_STATISTICS_update (_GSS_statistics,
                            "# Intersection operations succeeded",
                            1,
                            GNUNET_NO);
  ev = GNUNET_MQ_msg (rm,
                      GNUNET_MESSAGE_TYPE_SET_RESULT);
  rm->request_id = htonl (op->client_request_id);
  rm->result_status = htons (GNUNET_SET_STATUS_DONE);
  rm->element_type = htons (0);
  GNUNET_MQ_send (op->set->cs->mq,
                  ev);
  _GSS_operation_destroy (op,
                          GNUNET_YES);
}


/**
 * Remember that we are done dealing with the local client
 * AND have sent the other peer our message that we are done,
 * so we are not just waiting for the channel to die before
 * telling the local client that we are done as our last act.
 *
 * @param cls the `struct Operation`.
 */
static void
finished_local_operations (void *cls)
{
  struct Operation *op = cls;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "DONE sent to other peer, now waiting for other end to close the channel\n");
  op->state->phase = PHASE_FINISHED;
  op->state->channel_death_expected = GNUNET_YES;
}


/**
 * Notify the other peer that we are done.  Once this message
 * is out, we still need to notify the local client that we
 * are done.
 *
 * @param op operation to notify for.
 */
static void
send_p2p_done (struct Operation *op)
{
  struct GNUNET_MQ_Envelope *ev;
  struct IntersectionDoneMessage *idm;

  GNUNET_assert (PHASE_MUST_SEND_DONE == op->state->phase);
  GNUNET_assert (GNUNET_NO == op->state->channel_death_expected);
  ev = GNUNET_MQ_msg (idm,
                      GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_DONE);
  idm->final_element_count = htonl (op->state->my_element_count);
  idm->element_xor_hash = op->state->my_xor;
  GNUNET_MQ_notify_sent (ev,
                         &finished_local_operations,
                         op);
  GNUNET_MQ_send (op->mq,
                  ev);
}


/**
 * Send all elements in the full result iterator.
 *
 * @param cls the `struct Operation *`
 */
static void
send_remaining_elements (void *cls)
{
  struct Operation *op = cls;
  const void *nxt;
  const struct ElementEntry *ee;
  struct GNUNET_MQ_Envelope *ev;
  struct GNUNET_SET_ResultMessage *rm;
  const struct GNUNET_SET_Element *element;
  int res;

  res = GNUNET_CONTAINER_multihashmap_iterator_next (
    op->state->full_result_iter,
    NULL,
    &nxt);
  if (GNUNET_NO == res)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Sending done and destroy because iterator ran out\n");
    GNUNET_CONTAINER_multihashmap_iterator_destroy (
      op->state->full_result_iter);
    op->state->full_result_iter = NULL;
    if (PHASE_DONE_RECEIVED == op->state->phase)
    {
      op->state->phase = PHASE_FINISHED;
      send_client_done_and_destroy (op);
    }
    else if (PHASE_MUST_SEND_DONE == op->state->phase)
    {
      send_p2p_done (op);
    }
    else
    {
      GNUNET_assert (0);
    }
    return;
  }
  ee = nxt;
  element = &ee->element;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending element %s:%u to client (full set)\n",
              GNUNET_h2s (&ee->element_hash),
              element->size);
  GNUNET_assert (0 != op->client_request_id);
  ev = GNUNET_MQ_msg_extra (rm,
                            element->size,
                            GNUNET_MESSAGE_TYPE_SET_RESULT);
  GNUNET_assert (NULL != ev);
  rm->result_status = htons (GNUNET_SET_STATUS_OK);
  rm->request_id = htonl (op->client_request_id);
  rm->element_type = element->element_type;
  GNUNET_memcpy (&rm[1],
                 element->data,
                 element->size);
  GNUNET_MQ_notify_sent (ev,
                         &send_remaining_elements,
                         op);
  GNUNET_MQ_send (op->set->cs->mq,
                  ev);
}


/**
 * Fills the "my_elements" hashmap with the initial set of
 * (non-deleted) elements from the set of the specification.
 *
 * @param cls closure with the `struct Operation *`
 * @param key current key code for the element
 * @param value value in the hash map with the `struct ElementEntry *`
 * @return #GNUNET_YES (we should continue to iterate)
 */
static int
initialize_map_unfiltered (void *cls,
                           const struct GNUNET_HashCode *key,
                           void *value)
{
  struct ElementEntry *ee = value;
  struct Operation *op = cls;

  if (GNUNET_NO == _GSS_is_element_of_operation (ee, op))
    return GNUNET_YES; /* element not live in operation's generation */
  GNUNET_CRYPTO_hash_xor (&op->state->my_xor,
                          &ee->element_hash,
                          &op->state->my_xor);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Initial full initialization of my_elements, adding %s:%u\n",
              GNUNET_h2s (&ee->element_hash),
              ee->element.size);
  GNUNET_break (GNUNET_YES ==
                GNUNET_CONTAINER_multihashmap_put (op->state->my_elements,
                                                   &ee->element_hash,
                                                   ee,
                                                   GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));
  return GNUNET_YES;
}


/**
 * Send our element count to the peer, in case our element count is
 * lower than theirs.
 *
 * @param op intersection operation
 */
static void
send_element_count (struct Operation *op)
{
  struct GNUNET_MQ_Envelope *ev;
  struct IntersectionElementInfoMessage *msg;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending our element count (%u)\n",
              op->state->my_element_count);
  ev = GNUNET_MQ_msg (msg,
                      GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_ELEMENT_INFO);
  msg->sender_element_count = htonl (op->state->my_element_count);
  GNUNET_MQ_send (op->mq, ev);
}


/**
 * We go first, initialize our map with all elements and
 * send the first Bloom filter.
 *
 * @param op operation to start exchange for
 */
static void
begin_bf_exchange (struct Operation *op)
{
  op->state->phase = PHASE_BF_EXCHANGE;
  GNUNET_CONTAINER_multihashmap_iterate (op->set->content->elements,
                                         &initialize_map_unfiltered,
                                         op);
  send_bloomfilter (op);
}


/**
 * Handle the initial `struct IntersectionElementInfoMessage` from a
 * remote peer.
 *
 * @param cls the intersection operation
 * @param mh the header of the message
 */
void
handle_intersection_p2p_element_info (void *cls,
                                      const struct
                                      IntersectionElementInfoMessage *msg)
{
  struct Operation *op = cls;

  if (GNUNET_SET_OPERATION_INTERSECTION != op->set->operation)
  {
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;
  }
  op->remote_element_count = ntohl (msg->sender_element_count);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received remote element count (%u), I have %u\n",
              op->remote_element_count,
              op->state->my_element_count);
  if (((PHASE_INITIAL != op->state->phase) &&
       (PHASE_COUNT_SENT != op->state->phase)) ||
      (op->state->my_element_count > op->remote_element_count) ||
      (0 == op->state->my_element_count) ||
      (0 == op->remote_element_count))
  {
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;
  }
  GNUNET_break (NULL == op->state->remote_bf);
  begin_bf_exchange (op);
  GNUNET_CADET_receive_done (op->channel);
}


/**
 * Process a Bloomfilter once we got all the chunks.
 *
 * @param op the intersection operation
 */
static void
process_bf (struct Operation *op)
{
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received BF in phase %u, foreign count is %u, my element count is %u/%u\n",
              op->state->phase,
              op->remote_element_count,
              op->state->my_element_count,
              GNUNET_CONTAINER_multihashmap_size (op->set->content->elements));
  switch (op->state->phase)
  {
  case PHASE_INITIAL:
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;

  case PHASE_COUNT_SENT:
    /* This is the first BF being sent, build our initial map with
       filtering in place */
    op->state->my_element_count = 0;
    GNUNET_CONTAINER_multihashmap_iterate (op->set->content->elements,
                                           &filtered_map_initialization,
                                           op);
    break;

  case PHASE_BF_EXCHANGE:
    /* Update our set by reduction */
    GNUNET_CONTAINER_multihashmap_iterate (op->state->my_elements,
                                           &iterator_bf_reduce,
                                           op);
    break;

  case PHASE_MUST_SEND_DONE:
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;

  case PHASE_DONE_RECEIVED:
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;

  case PHASE_FINISHED:
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;
  }
  GNUNET_CONTAINER_bloomfilter_free (op->state->remote_bf);
  op->state->remote_bf = NULL;

  if ((0 == op->state->my_element_count) ||  /* fully disjoint */
      ((op->state->my_element_count == op->remote_element_count) &&
       (0 == GNUNET_memcmp (&op->state->my_xor,
                            &op->state->other_xor))))
  {
    /* we are done */
    op->state->phase = PHASE_MUST_SEND_DONE;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Intersection succeeded, sending DONE to other peer\n");
    GNUNET_CONTAINER_bloomfilter_free (op->state->local_bf);
    op->state->local_bf = NULL;
    if (GNUNET_SET_RESULT_FULL == op->result_mode)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sending full result set (%u elements)\n",
                  GNUNET_CONTAINER_multihashmap_size (op->state->my_elements));
      op->state->full_result_iter
        = GNUNET_CONTAINER_multihashmap_iterator_create (
            op->state->my_elements);
      send_remaining_elements (op);
      return;
    }
    send_p2p_done (op);
    return;
  }
  op->state->phase = PHASE_BF_EXCHANGE;
  send_bloomfilter (op);
}


/**
 * Check an BF message from a remote peer.
 *
 * @param cls the intersection operation
 * @param msg the header of the message
 * @return #GNUNET_OK if @a msg is well-formed
 */
int
check_intersection_p2p_bf (void *cls,
                           const struct BFMessage *msg)
{
  struct Operation *op = cls;

  if (GNUNET_SET_OPERATION_INTERSECTION != op->set->operation)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Handle an BF message from a remote peer.
 *
 * @param cls the intersection operation
 * @param msg the header of the message
 */
void
handle_intersection_p2p_bf (void *cls,
                            const struct BFMessage *msg)
{
  struct Operation *op = cls;
  uint32_t bf_size;
  uint32_t chunk_size;
  uint32_t bf_bits_per_element;

  switch (op->state->phase)
  {
  case PHASE_INITIAL:
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;

  case PHASE_COUNT_SENT:
  case PHASE_BF_EXCHANGE:
    bf_size = ntohl (msg->bloomfilter_total_length);
    bf_bits_per_element = ntohl (msg->bits_per_element);
    chunk_size = htons (msg->header.size) - sizeof(struct BFMessage);
    op->state->other_xor = msg->element_xor_hash;
    if (bf_size == chunk_size)
    {
      if (NULL != op->state->bf_data)
      {
        GNUNET_break_op (0);
        fail_intersection_operation (op);
        return;
      }
      /* single part, done here immediately */
      op->state->remote_bf
        = GNUNET_CONTAINER_bloomfilter_init ((const char *) &msg[1],
                                             bf_size,
                                             bf_bits_per_element);
      op->state->salt = ntohl (msg->sender_mutator);
      op->remote_element_count = ntohl (msg->sender_element_count);
      process_bf (op);
      break;
    }
    /* multipart chunk */
    if (NULL == op->state->bf_data)
    {
      /* first chunk, initialize */
      op->state->bf_data = GNUNET_malloc (bf_size);
      op->state->bf_data_size = bf_size;
      op->state->bf_bits_per_element = bf_bits_per_element;
      op->state->bf_data_offset = 0;
      op->state->salt = ntohl (msg->sender_mutator);
      op->remote_element_count = ntohl (msg->sender_element_count);
    }
    else
    {
      /* increment */
      if ((op->state->bf_data_size != bf_size) ||
          (op->state->bf_bits_per_element != bf_bits_per_element) ||
          (op->state->bf_data_offset + chunk_size > bf_size) ||
          (op->state->salt != ntohl (msg->sender_mutator)) ||
          (op->remote_element_count != ntohl (msg->sender_element_count)))
      {
        GNUNET_break_op (0);
        fail_intersection_operation (op);
        return;
      }
    }
    GNUNET_memcpy (&op->state->bf_data[op->state->bf_data_offset],
                   (const char *) &msg[1],
                   chunk_size);
    op->state->bf_data_offset += chunk_size;
    if (op->state->bf_data_offset == bf_size)
    {
      /* last chunk, run! */
      op->state->remote_bf
        = GNUNET_CONTAINER_bloomfilter_init (op->state->bf_data,
                                             bf_size,
                                             bf_bits_per_element);
      GNUNET_free (op->state->bf_data);
      op->state->bf_data = NULL;
      op->state->bf_data_size = 0;
      process_bf (op);
    }
    break;

  default:
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;
  }
  GNUNET_CADET_receive_done (op->channel);
}


/**
 * Remove all elements from our hashmap.
 *
 * @param cls closure with the `struct Operation *`
 * @param key current key code
 * @param value value in the hash map
 * @return #GNUNET_YES (we should continue to iterate)
 */
static int
filter_all (void *cls,
            const struct GNUNET_HashCode *key,
            void *value)
{
  struct Operation *op = cls;
  struct ElementEntry *ee = value;

  GNUNET_break (0 < op->state->my_element_count);
  op->state->my_element_count--;
  GNUNET_CRYPTO_hash_xor (&op->state->my_xor,
                          &ee->element_hash,
                          &op->state->my_xor);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Final reduction of my_elements, removing %s:%u\n",
              GNUNET_h2s (&ee->element_hash),
              ee->element.size);
  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CONTAINER_multihashmap_remove (op->state->my_elements,
                                                       &ee->element_hash,
                                                       ee));
  send_client_removed_element (op,
                               &ee->element);
  return GNUNET_YES;
}


/**
 * Handle a done message from a remote peer
 *
 * @param cls the intersection operation
 * @param mh the message
 */
void
handle_intersection_p2p_done (void *cls,
                              const struct IntersectionDoneMessage *idm)
{
  struct Operation *op = cls;

  if (GNUNET_SET_OPERATION_INTERSECTION != op->set->operation)
  {
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;
  }
  if (PHASE_BF_EXCHANGE != op->state->phase)
  {
    /* wrong phase to conclude? FIXME: Or should we allow this
       if the other peer has _initially_ already an empty set? */
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;
  }
  if (0 == ntohl (idm->final_element_count))
  {
    /* other peer determined empty set is the intersection,
       remove all elements */
    GNUNET_CONTAINER_multihashmap_iterate (op->state->my_elements,
                                           &filter_all,
                                           op);
  }
  if ((op->state->my_element_count != ntohl (idm->final_element_count)) ||
      (0 != GNUNET_memcmp (&op->state->my_xor,
                           &idm->element_xor_hash)))
  {
    /* Other peer thinks we are done, but we disagree on the result! */
    GNUNET_break_op (0);
    fail_intersection_operation (op);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Got IntersectionDoneMessage, have %u elements in intersection\n",
              op->state->my_element_count);
  op->state->phase = PHASE_DONE_RECEIVED;
  GNUNET_CADET_receive_done (op->channel);

  GNUNET_assert (GNUNET_NO == op->state->client_done_sent);
  if (GNUNET_SET_RESULT_FULL == op->result_mode)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Sending full result set to client (%u elements)\n",
                GNUNET_CONTAINER_multihashmap_size (op->state->my_elements));
    op->state->full_result_iter
      = GNUNET_CONTAINER_multihashmap_iterator_create (op->state->my_elements);
    send_remaining_elements (op);
    return;
  }
  op->state->phase = PHASE_FINISHED;
  send_client_done_and_destroy (op);
}


/**
 * Initiate a set intersection operation with a remote peer.
 *
 * @param op operation that is created, should be initialized to
 *        begin the evaluation
 * @param opaque_context message to be transmitted to the listener
 *        to convince it to accept, may be NULL
 * @return operation-specific state to keep in @a op
 */
static struct OperationState *
intersection_evaluate (struct Operation *op,
                       const struct GNUNET_MessageHeader *opaque_context)
{
  struct OperationState *state;
  struct GNUNET_MQ_Envelope *ev;
  struct OperationRequestMessage *msg;

  ev = GNUNET_MQ_msg_nested_mh (msg,
                                GNUNET_MESSAGE_TYPE_SET_P2P_OPERATION_REQUEST,
                                opaque_context);
  if (NULL == ev)
  {
    /* the context message is too large!? */
    GNUNET_break (0);
    return NULL;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Initiating intersection operation evaluation\n");
  state = GNUNET_new (struct OperationState);
  /* we started the operation, thus we have to send the operation request */
  state->phase = PHASE_INITIAL;
  state->my_element_count = op->set->state->current_set_element_count;
  state->my_elements
    = GNUNET_CONTAINER_multihashmap_create (state->my_element_count,
                                            GNUNET_YES);

  msg->operation = htonl (GNUNET_SET_OPERATION_INTERSECTION);
  msg->element_count = htonl (state->my_element_count);
  GNUNET_MQ_send (op->mq,
                  ev);
  state->phase = PHASE_COUNT_SENT;
  if (NULL != opaque_context)
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Sent op request with context message\n");
  else
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Sent op request without context message\n");
  return state;
}


/**
 * Accept an intersection operation request from a remote peer.  Only
 * initializes the private operation state.
 *
 * @param op operation that will be accepted as an intersection operation
 */
static struct OperationState *
intersection_accept (struct Operation *op)
{
  struct OperationState *state;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Accepting set intersection operation\n");
  state = GNUNET_new (struct OperationState);
  state->phase = PHASE_INITIAL;
  state->my_element_count
    = op->set->state->current_set_element_count;
  state->my_elements
    = GNUNET_CONTAINER_multihashmap_create (GNUNET_MIN (state->my_element_count,
                                                        op->remote_element_count),
                                            GNUNET_YES);
  op->state = state;
  if (op->remote_element_count < state->my_element_count)
  {
    /* If the other peer (Alice) has fewer elements than us (Bob),
       we just send the count as Alice should send the first BF */
    send_element_count (op);
    state->phase = PHASE_COUNT_SENT;
    return state;
  }
  /* We have fewer elements, so we start with the BF */
  begin_bf_exchange (op);
  return state;
}


/**
 * Destroy the intersection operation.  Only things specific to the
 * intersection operation are destroyed.
 *
 * @param op intersection operation to destroy
 */
static void
intersection_op_cancel (struct Operation *op)
{
  /* check if the op was canceled twice */
  GNUNET_assert (NULL != op->state);
  if (NULL != op->state->remote_bf)
  {
    GNUNET_CONTAINER_bloomfilter_free (op->state->remote_bf);
    op->state->remote_bf = NULL;
  }
  if (NULL != op->state->local_bf)
  {
    GNUNET_CONTAINER_bloomfilter_free (op->state->local_bf);
    op->state->local_bf = NULL;
  }
  if (NULL != op->state->my_elements)
  {
    GNUNET_CONTAINER_multihashmap_destroy (op->state->my_elements);
    op->state->my_elements = NULL;
  }
  if (NULL != op->state->full_result_iter)
  {
    GNUNET_CONTAINER_multihashmap_iterator_destroy (
      op->state->full_result_iter);
    op->state->full_result_iter = NULL;
  }
  GNUNET_free (op->state);
  op->state = NULL;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Destroying intersection op state done\n");
}


/**
 * Create a new set supporting the intersection operation.
 *
 * @return the newly created set
 */
static struct SetState *
intersection_set_create ()
{
  struct SetState *set_state;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Intersection set created\n");
  set_state = GNUNET_new (struct SetState);
  set_state->current_set_element_count = 0;

  return set_state;
}


/**
 * Add the element from the given element message to the set.
 *
 * @param set_state state of the set want to add to
 * @param ee the element to add to the set
 */
static void
intersection_add (struct SetState *set_state,
                  struct ElementEntry *ee)
{
  set_state->current_set_element_count++;
}


/**
 * Destroy a set that supports the intersection operation
 *
 * @param set_state the set to destroy
 */
static void
intersection_set_destroy (struct SetState *set_state)
{
  GNUNET_free (set_state);
}


/**
 * Remove the element given in the element message from the set.
 *
 * @param set_state state of the set to remove from
 * @param element set element to remove
 */
static void
intersection_remove (struct SetState *set_state,
                     struct ElementEntry *element)
{
  GNUNET_assert (0 < set_state->current_set_element_count);
  set_state->current_set_element_count--;
}


/**
 * Callback for channel death for the intersection operation.
 *
 * @param op operation that lost the channel
 */
static void
intersection_channel_death (struct Operation *op)
{
  if (GNUNET_YES == op->state->channel_death_expected)
  {
    /* oh goodie, we are done! */
    send_client_done_and_destroy (op);
  }
  else
  {
    /* sorry, channel went down early, too bad. */
    _GSS_operation_destroy (op,
                            GNUNET_YES);
  }
}


/**
 * Get the table with implementing functions for set intersection.
 *
 * @return the operation specific VTable
 */
const struct SetVT *
_GSS_intersection_vt ()
{
  static const struct SetVT intersection_vt = {
    .create = &intersection_set_create,
    .add = &intersection_add,
    .remove = &intersection_remove,
    .destroy_set = &intersection_set_destroy,
    .evaluate = &intersection_evaluate,
    .accept = &intersection_accept,
    .cancel = &intersection_op_cancel,
    .channel_death = &intersection_channel_death,
  };

  return &intersection_vt;
}