gnunet-service-set_intersection.c

Go to the documentation of this file.

/*
      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
 */
#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>
 
 
enum IntersectionOperationPhase
{
  PHASE_INITIAL,
 
  PHASE_COUNT_SENT,
 
  PHASE_BF_EXCHANGE,
 
  PHASE_MUST_SEND_DONE,
 
  PHASE_DONE_RECEIVED,
 
  PHASE_FINISHED
};
 
 
struct OperationState
{
  struct GNUNET_CONTAINER_BloomFilter *remote_bf;
 
  struct GNUNET_CONTAINER_BloomFilter *local_bf;
 
  struct GNUNET_CONTAINER_MultiHashMap *my_elements;
 
  struct GNUNET_CONTAINER_MultiHashMapIterator *full_result_iter;
 
  struct OperationState *next;
 
  struct OperationState *prev;
 
  char *bf_data;
 
  struct GNUNET_HashCode my_xor;
 
  struct GNUNET_HashCode other_xor;
 
  uint32_t bf_data_offset;
 
  uint32_t my_element_count;
 
  uint32_t bf_data_size;
 
  uint32_t bf_bits_per_element;
 
  uint32_t salt;
 
  enum IntersectionOperationPhase phase;
 
  unsigned int generation_created;
 
  int client_done_sent;
 
  int channel_death_expected;
};
 
 
struct SetState
{
  uint32_t current_set_element_count;
};
 
 
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);
}
 
 
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;
}
 
 
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;
}
 
 
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;
}
 
 
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);
}
 
 
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;
}
 
 
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);
}
 
 
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;
}
 
 
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);
}
 
 
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);
}
 
 
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;
}
 
 
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);
}
 
 
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);
}
 
 
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);
}
 
 
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);
}
 
 
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;
}
 
 
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);
}
 
 
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;
}
 
 
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);
}
 
 
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;
}
 
 
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;
}
 
 
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");
}
 
 
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;
}
 
 
static void
intersection_add (struct SetState *set_state,
                  struct ElementEntry *ee)
{
  set_state->current_set_element_count++;
}
 
 
static void
intersection_set_destroy (struct SetState *set_state)
{
  GNUNET_free (set_state);
}
 
 
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--;
}
 
 
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);
  }
}
 
 
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;
}