/*
     This file is part of GNUnet.
     Copyright (C) 2013-2017, 2021 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 scalarproduct/gnunet-service-scalarproduct-ecc_bob.c
 * @brief scalarproduct service implementation
 * @author Christian M. Fuchs
 * @author Christian Grothoff
 */
#include "platform.h"
#include <limits.h>
#include <gcrypt.h>
#include "gnunet_util_lib.h"
#include "gnunet_cadet_service.h"
#include "gnunet_protocols.h"
#include "gnunet_scalarproduct_service.h"
#include "gnunet_seti_service.h"
#include "scalarproduct.h"
#include "gnunet-service-scalarproduct-ecc.h"

#define LOG(kind, ...) GNUNET_log_from (kind, "scalarproduct-bob", __VA_ARGS__)


/**
 * An encrypted element key-value pair.
 */
struct MpiElement
{
  /**
   * Key used to identify matching pairs of values to multiply.
   * Points into an existing data structure, to avoid copying
   * and doubling memory use.
   */
  const struct GNUNET_HashCode *key;

  /**
   * Value represented (a).
   */
  int64_t value;
};


/**
 * A scalarproduct session which tracks an offer for a
 * multiplication service by a local client.
 */
struct BobServiceSession
{
  /**
   * The client this request is related to.
   */
  struct GNUNET_SERVICE_Client *client;

  /**
   * Client message queue.
   */
  struct GNUNET_MQ_Handle *client_mq;

  /**
   * All non-0-value'd elements transmitted to us.
   */
  struct GNUNET_CONTAINER_MultiHashMap *intersected_elements;

  /**
   * Set of elements for which we will be conducting an intersection.
   * The resulting elements are then used for computing the scalar product.
   */
  struct GNUNET_SETI_Handle *intersection_set;

  /**
   * Set of elements for which will conduction an intersection.
   * the resulting elements are then used for computing the scalar product.
   */
  struct GNUNET_SETI_OperationHandle *intersection_op;

  /**
   * Our open port.
   */
  struct GNUNET_CADET_Port *port;

  /**
   * b(Bob)
   */
  struct MpiElement *sorted_elements;

  /**
   * Product of the g_i^{b_i}
   */
  struct GNUNET_CRYPTO_EccPoint prod_g_i_b_i;

  /**
   * Product of the h_i^{b_i}
   */
  struct GNUNET_CRYPTO_EccPoint prod_h_i_b_i;

  /**
   * How many elements will be supplied in total from the client.
   */
  uint32_t total;

  /**
   * Already transferred elements (received) for multipart
   * messages from client. Always less than @e total.
   */
  uint32_t client_received_element_count;

  /**
   * How many elements actually are used for the scalar product.
   * Size of the arrays in @e r and @e r_prime.  Also sometimes
   * used as an index into the arrays during construction.
   */
  uint32_t used_element_count;

  /**
   * Counts the number of values received from Alice by us.
   * Always less than @e used_element_count.
   */
  uint32_t cadet_received_element_count;

  /**
   * State of this session.   In
   * #GNUNET_SCALARPRODUCT_STATUS_ACTIVE while operation is
   * ongoing, afterwards in #GNUNET_SCALARPRODUCT_STATUS_SUCCESS or
   * #GNUNET_SCALARPRODUCT_STATUS_FAILURE.
   */
  enum GNUNET_SCALARPRODUCT_ResponseStatus status;

  /**
   * Are we already in #destroy_service_session()?
   */
  int in_destroy;

  /**
   * The CADET channel.
   */
  struct GNUNET_CADET_Channel *channel;

  /**
   * Originator's peer identity. (Only for diagnostics.)
   */
  struct GNUNET_PeerIdentity peer;

  /**
   * (hopefully) unique transaction ID
   */
  struct GNUNET_HashCode session_id;

  /**
   * The message queue for this channel.
   */
  struct GNUNET_MQ_Handle *cadet_mq;
};


/**
 * GNUnet configuration handle
 */
static const struct GNUNET_CONFIGURATION_Handle *cfg;

/**
 * Handle to the CADET service.
 */
static struct GNUNET_CADET_Handle *my_cadet;

/**
 * Context for DLOG operations on a curve.
 */
static struct GNUNET_CRYPTO_EccDlogContext *edc;


/**
 * Callback used to free the elements in the map.
 *
 * @param cls NULL
 * @param key key of the element
 * @param value the value to free
 */
static int
free_element_cb (void *cls,
                 const struct GNUNET_HashCode *key,
                 void *value)
{
  struct GNUNET_SCALARPRODUCT_Element *element = value;

  GNUNET_free (element);
  return GNUNET_OK;
}


/**
 * Destroy session state, we are done with it.
 *
 * @param s the session to free elements from
 */
static void
destroy_service_session (struct BobServiceSession *s)
{
  if (GNUNET_YES == s->in_destroy)
    return;
  s->in_destroy = GNUNET_YES;
  if (NULL != s->client)
  {
    struct GNUNET_SERVICE_Client *c = s->client;

    s->client = NULL;
    GNUNET_SERVICE_client_drop (c);
  }
  if (NULL != s->intersected_elements)
  {
    GNUNET_CONTAINER_multihashmap_iterate (s->intersected_elements,
                                           &free_element_cb,
                                           NULL);
    GNUNET_CONTAINER_multihashmap_destroy (s->intersected_elements);
    s->intersected_elements = NULL;
  }
  if (NULL != s->intersection_op)
  {
    GNUNET_SETI_operation_cancel (s->intersection_op);
    s->intersection_op = NULL;
  }
  if (NULL != s->intersection_set)
  {
    GNUNET_SETI_destroy (s->intersection_set);
    s->intersection_set = NULL;
  }
  if (NULL != s->sorted_elements)
  {
    GNUNET_free (s->sorted_elements);
    s->sorted_elements = NULL;
  }
  if (NULL != s->port)
  {
    GNUNET_CADET_close_port (s->port);
    s->port = NULL;
  }
  if (NULL != s->channel)
  {
    GNUNET_CADET_channel_destroy (s->channel);
    s->channel = NULL;
  }
  GNUNET_free (s);
}


/**
 * Notify the client that the session has succeeded or failed.  This
 * message gets sent to Bob's client if the operation completed or
 * Alice disconnected.
 *
 * @param session the associated client session to fail or succeed
 */
static void
prepare_client_end_notification (struct BobServiceSession *session)
{
  struct ClientResponseMessage *msg;
  struct GNUNET_MQ_Envelope *e;

  if (NULL == session->client_mq)
    return; /* no client left to be notified */
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending session-end notification with status %d to client for session %s\n",
              session->status,
              GNUNET_h2s (&session->session_id));
  e = GNUNET_MQ_msg (msg,
                     GNUNET_MESSAGE_TYPE_SCALARPRODUCT_RESULT);
  msg->range = 0;
  msg->product_length = htonl (0);
  msg->status = htonl (session->status);
  GNUNET_MQ_send (session->client_mq,
                  e);
}


/**
 * Function called whenever a channel is destroyed.  Should clean up
 * any associated state.
 *
 * It must NOT call #GNUNET_CADET_channel_destroy() on the channel.
 *
 * @param cls the `struct BobServiceSession`
 * @param channel connection to the other end (henceforth invalid)
 */
static void
cb_channel_destruction (void *cls,
                        const struct GNUNET_CADET_Channel *channel)
{
  struct BobServiceSession *s = cls;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Peer disconnected, terminating session %s with peer %s\n",
              GNUNET_h2s (&s->session_id),
              GNUNET_i2s (&s->peer));
  s->channel = NULL;
  if (GNUNET_SCALARPRODUCT_STATUS_ACTIVE == s->status)
  {
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    prepare_client_end_notification (s);
  }
  destroy_service_session (s);
}


/**
 * MQ finished giving our last message to CADET, now notify
 * the client that we are finished.
 */
static void
bob_cadet_done_cb (void *cls)
{
  struct BobServiceSession *session = cls;

  session->status = GNUNET_SCALARPRODUCT_STATUS_SUCCESS;
  prepare_client_end_notification (session);
}


/**
 * Bob generates the response message to be sent to Alice.
 *
 * @param s the associated requesting session with Alice
 */
static void
transmit_bobs_cryptodata_message (struct BobServiceSession *s)
{
  struct EccBobCryptodataMessage *msg;
  struct GNUNET_MQ_Envelope *e;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending response to Alice\n");
  e = GNUNET_MQ_msg (msg,
                     GNUNET_MESSAGE_TYPE_SCALARPRODUCT_ECC_BOB_CRYPTODATA);
  msg->contained_element_count = htonl (2);
  msg->prod_g_i_b_i = s->prod_g_i_b_i;
  msg->prod_h_i_b_i = s->prod_h_i_b_i;
  GNUNET_MQ_notify_sent (e,
                         &bob_cadet_done_cb,
                         s);
  GNUNET_MQ_send (s->cadet_mq,
                  e);
}


/**
 * Iterator to copy over messages from the hash map
 * into an array for sorting.
 *
 * @param cls the `struct AliceServiceSession *`
 * @param key the key (unused)
 * @param value the `struct GNUNET_SCALARPRODUCT_Element *`
 */
static int
copy_element_cb (void *cls,
                 const struct GNUNET_HashCode *key,
                 void *value)
{
  struct BobServiceSession *s = cls;
  struct GNUNET_SCALARPRODUCT_Element *e = value;

  s->sorted_elements[s->used_element_count].value = (int64_t) GNUNET_ntohll (
    e->value);
  s->sorted_elements[s->used_element_count].key = &e->key;
  s->used_element_count++;
  return GNUNET_OK;
}


/**
 * Compare two `struct MpiValue`s by key for sorting.
 *
 * @param a pointer to first `struct MpiValue *`
 * @param b pointer to first `struct MpiValue *`
 * @return -1 for a < b, 0 for a=b, 1 for a > b.
 * TODO: code duplication with Alice!
 */
static int
element_cmp (const void *a,
             const void *b)
{
  const struct MpiElement *ma = a;
  const struct MpiElement *mb = b;

  return GNUNET_CRYPTO_hash_cmp (ma->key,
                                 mb->key);
}


/**
 * Check a multipart-chunk of a request from another service to
 * calculate a scalarproduct with us.
 *
 * @param cls closure (set from #GNUNET_CADET_connect)
 * @param msg the actual message
 * @return #GNUNET_OK to keep the connection open,
 *         #GNUNET_SYSERR to close it (signal serious error)
 */
static int
check_alices_cryptodata_message (void *cls,
                                 const struct EccAliceCryptodataMessage *msg)
{
  struct BobServiceSession *s = cls;
  uint32_t contained_elements;
  size_t msg_length;
  uint16_t msize;
  unsigned int max;

  msize = ntohs (msg->header.size);
  if (msize <= sizeof(struct EccAliceCryptodataMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  contained_elements = ntohl (msg->contained_element_count);
  /* Our intersection may still be ongoing, but this is nevertheless
     an upper bound on the required array size */
  max = GNUNET_CONTAINER_multihashmap_size (s->intersected_elements);
  msg_length = sizeof(struct EccAliceCryptodataMessage)
               + contained_elements * sizeof(struct GNUNET_CRYPTO_EccPoint) * 2;
  if ((msize != msg_length) ||
      (0 == contained_elements) ||
      (contained_elements > UINT16_MAX) ||
      (max < contained_elements + s->cadet_received_element_count))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Handle a multipart-chunk of a request from another service to
 * calculate a scalarproduct with us.
 *
 * @param cls closure (set from #GNUNET_CADET_connect)
 * @param msg the actual message
 */
static void
handle_alices_cryptodata_message (void *cls,
                                  const struct EccAliceCryptodataMessage *msg)
{
  struct BobServiceSession *s = cls;
  const struct GNUNET_CRYPTO_EccPoint *payload;
  uint32_t contained_elements;
  unsigned int max;
  const struct GNUNET_CRYPTO_EccPoint *g_i;
  const struct GNUNET_CRYPTO_EccPoint *h_i;
  struct GNUNET_CRYPTO_EccPoint g_i_b_i;
  struct GNUNET_CRYPTO_EccPoint h_i_b_i;

  contained_elements = ntohl (msg->contained_element_count);
  max = GNUNET_CONTAINER_multihashmap_size (s->intersected_elements);
  /* sort our vector for the computation */
  if (NULL == s->sorted_elements)
  {
    s->sorted_elements
      = GNUNET_new_array (GNUNET_CONTAINER_multihashmap_size (
                            s->intersected_elements),
                          struct MpiElement);
    s->used_element_count = 0;
    GNUNET_CONTAINER_multihashmap_iterate (s->intersected_elements,
                                           &copy_element_cb,
                                           s);
    qsort (s->sorted_elements,
           s->used_element_count,
           sizeof(struct MpiElement),
           &element_cmp);
  }

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received %u crypto values from Alice\n",
              (unsigned int) contained_elements);
  payload = (const struct GNUNET_CRYPTO_EccPoint *) &msg[1];

  for (unsigned int i = 0; i < contained_elements; i++)
  {
    int64_t val = s->sorted_elements[i + s->cadet_received_element_count].value;
    struct GNUNET_CRYPTO_EccScalar vali;

    GNUNET_assert (INT64_MIN != val);
    GNUNET_CRYPTO_ecc_scalar_from_int (val > 0 ? val : -val,
                                       &vali);
    if (val < 0)
      crypto_core_ed25519_scalar_negate (vali.v,
                                         vali.v);
    g_i = &payload[i * 2];
    /* g_i_b_i = g_i^vali */
    GNUNET_assert (GNUNET_OK ==
                   GNUNET_CRYPTO_ecc_pmul_mpi (g_i,
                                               &vali,
                                               &g_i_b_i));
    h_i = &payload[i * 2 + 1];
    /* h_i_b_i = h_i^vali */
    GNUNET_assert (GNUNET_OK ==
                   GNUNET_CRYPTO_ecc_pmul_mpi (h_i,
                                               &vali,
                                               &h_i_b_i));
    if (0 == i + s->cadet_received_element_count)
    {
      /* first iteration, nothing to add */
      s->prod_g_i_b_i = g_i_b_i;
      s->prod_h_i_b_i = h_i_b_i;
    }
    else
    {
      /* further iterations, cummulate resulting value */
      GNUNET_assert (GNUNET_OK ==
                     GNUNET_CRYPTO_ecc_add (&s->prod_g_i_b_i,
                                            &g_i_b_i,
                                            &s->prod_g_i_b_i));
      GNUNET_assert (GNUNET_OK ==
                     GNUNET_CRYPTO_ecc_add (&s->prod_h_i_b_i,
                                            &h_i_b_i,
                                            &s->prod_h_i_b_i));
    }
  }
  s->cadet_received_element_count += contained_elements;
  if ((s->cadet_received_element_count == max) &&
      (NULL == s->intersection_op))
  {
    /* intersection has finished also on our side, and
       we got the full set, so we can proceed with the
       CADET response(s) */
    transmit_bobs_cryptodata_message (s);
  }
  GNUNET_CADET_receive_done (s->channel);
}


/**
 * Callback for set operation results. Called for each element
 * that needs to be removed from the result set.
 *
 * @param cls closure with the `struct BobServiceSession`
 * @param element a result element, only valid if status is #GNUNET_SETI_STATUS_OK
 * @param current_size current set size
 * @param status what has happened with the set intersection?
 */
static void
cb_intersection_element_removed (void *cls,
                                 const struct GNUNET_SETI_Element *element,
                                 uint64_t current_size,
                                 enum GNUNET_SETI_Status status)
{
  struct BobServiceSession *s = cls;
  struct GNUNET_SCALARPRODUCT_Element *se;

  switch (status)
  {
  case GNUNET_SETI_STATUS_DEL_LOCAL:
    /* this element has been removed from the set */
    se = GNUNET_CONTAINER_multihashmap_get (s->intersected_elements,
                                            element->data);
    GNUNET_assert (NULL != se);
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Removed element with key %s and value %lld\n",
         GNUNET_h2s (&se->key),
         (long long) GNUNET_ntohll (se->value));
    GNUNET_assert (GNUNET_YES ==
                   GNUNET_CONTAINER_multihashmap_remove (
                     s->intersected_elements,
                     element->data,
                     se));
    GNUNET_free (se);
    return;
  case GNUNET_SETI_STATUS_DONE:
    s->intersection_op = NULL;
    GNUNET_break (NULL == s->intersection_set);
    GNUNET_CADET_receive_done (s->channel);
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Finished intersection, %d items remain\n",
         GNUNET_CONTAINER_multihashmap_size (s->intersected_elements));
    if (s->client_received_element_count ==
        GNUNET_CONTAINER_multihashmap_size (s->intersected_elements))
    {
      /* CADET transmission from Alice is also already done,
         start with our own reply */
      transmit_bobs_cryptodata_message (s);
    }
    return;
  case GNUNET_SETI_STATUS_FAILURE:
    /* unhandled status code */
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Set intersection failed!\n");
    s->intersection_op = NULL;
    if (NULL != s->intersection_set)
    {
      GNUNET_SETI_destroy (s->intersection_set);
      s->intersection_set = NULL;
    }
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    prepare_client_end_notification (s);
    return;

  default:
    GNUNET_break (0);
    return;
  }
}


/**
 * We've paired up a client session with an incoming CADET request.
 * Initiate set intersection work.
 *
 * @param s client session to start intersection for
 */
static void
start_intersection (struct BobServiceSession *s)
{
  struct GNUNET_HashCode set_sid;

  GNUNET_CRYPTO_hash (&s->session_id,
                      sizeof(struct GNUNET_HashCode),
                      &set_sid);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Got session with key %s and %u elements, starting intersection.\n",
              GNUNET_h2s (&s->session_id),
              (unsigned int) s->total);

  s->intersection_op
    = GNUNET_SETI_prepare (&s->peer,
                           &set_sid,
                           NULL,
                           (struct GNUNET_SETI_Option[]) { { 0 } },
                           &cb_intersection_element_removed,
                           s);
  if (GNUNET_OK !=
      GNUNET_SETI_commit (s->intersection_op,
                          s->intersection_set))
  {
    GNUNET_break (0);
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    prepare_client_end_notification (s);
    return;
  }
  GNUNET_SETI_destroy (s->intersection_set);
  s->intersection_set = NULL;
}


/**
 * Handle a request from Alice to calculate a scalarproduct with us (Bob).
 *
 * @param cls closure (set from #GNUNET_CADET_connect)
 * @param msg the actual message
 */
static void
handle_alices_computation_request (void *cls,
                                   const struct EccServiceRequestMessage *msg)
{
  struct BobServiceSession *s = cls;

  s->session_id = msg->session_id; // ??
  if (s->client_received_element_count < s->total)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Alice ready, still waiting for Bob client data!\n");
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Both ready, launching intersection!\n");
  start_intersection (s);
}


/**
 * Function called for inbound channels on Bob's end.  Does some
 * preliminary initialization, more happens after we get Alice's first
 * message.
 *
 * @param cls our `struct BobServiceSession`
 * @param channel new handle to the channel
 * @param initiator peer that started the channel
 * @return session associated with the channel
 */
static void *
cb_channel_incoming (void *cls,
                     struct GNUNET_CADET_Channel *channel,
                     const struct GNUNET_PeerIdentity *initiator)
{
  struct BobServiceSession *s = cls;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "New incoming channel from peer %s.\n",
              GNUNET_i2s (initiator));
  GNUNET_CADET_close_port (s->port);
  s->port = NULL;
  s->peer = *initiator;
  s->channel = channel;
  s->cadet_mq = GNUNET_CADET_get_mq (s->channel);
  return s;
}


/**
 * We're receiving additional set data. Check it is well-formed.
 *
 * @param cls identification of the client
 * @param msg the actual message
 * @return #GNUNET_OK if @a msg is well-formed
 */
static int
check_bob_client_message_multipart (
  void *cls,
  const struct ComputationBobCryptodataMultipartMessage *msg)
{
  struct BobServiceSession *s = cls;
  uint32_t contained_count;
  uint16_t msize;

  msize = ntohs (msg->header.size);
  contained_count = ntohl (msg->element_count_contained);
  if ((msize != (sizeof(struct ComputationBobCryptodataMultipartMessage)
                 + contained_count * sizeof(struct
                                            GNUNET_SCALARPRODUCT_Element))) ||
      (0 == contained_count) ||
      (UINT16_MAX < contained_count) ||
      (s->total == s->client_received_element_count) ||
      (s->total < s->client_received_element_count + contained_count))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * We're receiving additional set data. Add it to our
 * set and if we are done, initiate the transaction.
 *
 * @param cls identification of the client
 * @param msg the actual message
 */
static void
handle_bob_client_message_multipart (
  void *cls,
  const struct ComputationBobCryptodataMultipartMessage *msg)
{
  struct BobServiceSession *s = cls;
  uint32_t contained_count;
  const struct GNUNET_SCALARPRODUCT_Element *elements;
  struct GNUNET_SETI_Element set_elem;
  struct GNUNET_SCALARPRODUCT_Element *elem;

  contained_count = ntohl (msg->element_count_contained);
  elements = (const struct GNUNET_SCALARPRODUCT_Element *) &msg[1];
  for (uint32_t i = 0; i < contained_count; i++)
  {
    elem = GNUNET_new (struct GNUNET_SCALARPRODUCT_Element);
    GNUNET_memcpy (elem,
                   &elements[i],
                   sizeof(struct GNUNET_SCALARPRODUCT_Element));
    if (GNUNET_SYSERR ==
        GNUNET_CONTAINER_multihashmap_put (s->intersected_elements,
                                           &elem->key,
                                           elem,
                                           GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY))
    {
      GNUNET_break (0);
      GNUNET_free (elem);
      continue;
    }
    set_elem.data = &elem->key;
    set_elem.size = sizeof(elem->key);
    set_elem.element_type = 0;
    GNUNET_SETI_add_element (s->intersection_set,
                             &set_elem,
                             NULL, NULL);
  }
  s->client_received_element_count += contained_count;
  GNUNET_SERVICE_client_continue (s->client);
  if (s->total != s->client_received_element_count)
  {
    /* more to come */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Request still partial, waiting for more client data!\n");
    return;
  }
  if (NULL == s->channel)
  {
    /* no Alice waiting for this request, wait for Alice */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Client ready, still waiting for Alice!\n");
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Both ready, launching intersection!\n");
  start_intersection (s);
}


/**
 * Handler for Bob's a client request message.  Check @a msg is
 * well-formed.
 *
 * @param cls identification of the client
 * @param msg the actual message
 * @return #GNUNET_OK if @a msg is well-formed
 */
static int
check_bob_client_message (void *cls,
                          const struct BobComputationMessage *msg)
{
  struct BobServiceSession *s = cls;
  uint32_t contained_count;
  uint32_t total_count;
  uint16_t msize;

  if (GNUNET_SCALARPRODUCT_STATUS_INIT != s->status)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  msize = ntohs (msg->header.size);
  total_count = ntohl (msg->element_count_total);
  contained_count = ntohl (msg->element_count_contained);
  if ((0 == total_count) ||
      (0 == contained_count) ||
      (UINT16_MAX < contained_count) ||
      (msize != (sizeof(struct BobComputationMessage)
                 + contained_count * sizeof(struct
                                            GNUNET_SCALARPRODUCT_Element))))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Handler for Bob's a client request message.  Bob is in the response
 * role, keep the values + session and waiting for a matching session
 * or process a waiting request from Alice.
 *
 * @param cls identification of the client
 * @param msg the actual message
 */
static void
handle_bob_client_message (void *cls,
                           const struct BobComputationMessage *msg)
{
  struct BobServiceSession *s = cls;
  struct GNUNET_MQ_MessageHandler cadet_handlers[] = {
    GNUNET_MQ_hd_fixed_size (alices_computation_request,
                             GNUNET_MESSAGE_TYPE_SCALARPRODUCT_ECC_SESSION_INITIALIZATION,
                             struct EccServiceRequestMessage,
                             s),
    GNUNET_MQ_hd_var_size (alices_cryptodata_message,
                           GNUNET_MESSAGE_TYPE_SCALARPRODUCT_ECC_ALICE_CRYPTODATA,
                           struct EccAliceCryptodataMessage,
                           s),
    GNUNET_MQ_handler_end ()
  };
  uint32_t contained_count;
  uint32_t total_count;
  const struct GNUNET_SCALARPRODUCT_Element *elements;
  struct GNUNET_SETI_Element set_elem;
  struct GNUNET_SCALARPRODUCT_Element *elem;

  total_count = ntohl (msg->element_count_total);
  contained_count = ntohl (msg->element_count_contained);

  s->status = GNUNET_SCALARPRODUCT_STATUS_ACTIVE;
  s->total = total_count;
  s->client_received_element_count = contained_count;
  s->session_id = msg->session_key;
  elements = (const struct GNUNET_SCALARPRODUCT_Element *) &msg[1];
  s->intersected_elements
    = GNUNET_CONTAINER_multihashmap_create (s->total,
                                            GNUNET_YES);
  s->intersection_set = GNUNET_SETI_create (cfg);
  for (uint32_t i = 0; i < contained_count; i++)
  {
    if (0 == GNUNET_ntohll (elements[i].value))
      continue;
    elem = GNUNET_new (struct GNUNET_SCALARPRODUCT_Element);
    GNUNET_memcpy (elem,
                   &elements[i],
                   sizeof(struct GNUNET_SCALARPRODUCT_Element));
    if (GNUNET_SYSERR ==
        GNUNET_CONTAINER_multihashmap_put (s->intersected_elements,
                                           &elem->key,
                                           elem,
                                           GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY))
    {
      GNUNET_break (0);
      GNUNET_free (elem);
      continue;
    }
    set_elem.data = &elem->key;
    set_elem.size = sizeof(elem->key);
    set_elem.element_type = 0;
    GNUNET_SETI_add_element (s->intersection_set,
                             &set_elem,
                             NULL, NULL);
    s->used_element_count++;
  }
  GNUNET_SERVICE_client_continue (s->client);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received client request, opening port %s!\n",
              GNUNET_h2s (&msg->session_key));
  s->port = GNUNET_CADET_open_port (my_cadet,
                                    &msg->session_key,
                                    &cb_channel_incoming,
                                    s,
                                    NULL,
                                    &cb_channel_destruction,
                                    cadet_handlers);
  if (NULL == s->port)
  {
    GNUNET_break (0);
    GNUNET_SERVICE_client_drop (s->client);
    return;
  }
}


/**
 * Task run during shutdown.
 *
 * @param cls unused
 */
static void
shutdown_task (void *cls)
{
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Shutting down, initiating cleanup.\n");
  // FIXME: we have to cut our connections to CADET first!
  if (NULL != my_cadet)
  {
    GNUNET_CADET_disconnect (my_cadet);
    my_cadet = NULL;
  }
  if (NULL != edc)
  {
    GNUNET_CRYPTO_ecc_dlog_release (edc);
    edc = NULL;
  }
}


/**
 * A client connected.
 *
 * Setup the associated data structure.
 *
 * @param cls closure, NULL
 * @param client identification of the client
 * @param mq message queue to communicate with @a client
 * @return our `struct BobServiceSession`
 */
static void *
client_connect_cb (void *cls,
                   struct GNUNET_SERVICE_Client *client,
                   struct GNUNET_MQ_Handle *mq)
{
  struct BobServiceSession *s;

  s = GNUNET_new (struct BobServiceSession);
  s->client = client;
  s->client_mq = mq;
  return s;
}


/**
 * A client disconnected.
 *
 * Remove the associated session(s), release data structures
 * and cancel pending outgoing transmissions to the client.
 *
 * @param cls closure, NULL
 * @param client identification of the client
 * @param app_cls our `struct BobServiceSession`
 */
static void
client_disconnect_cb (void *cls,
                      struct GNUNET_SERVICE_Client *client,
                      void *app_cls)
{
  struct BobServiceSession *s = app_cls;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client disconnected from us.\n");
  s->client = NULL;
  destroy_service_session (s);
}


/**
 * Initialization of the program and message handlers
 *
 * @param cls closure
 * @param c configuration to use
 * @param service the initialized service
 */
static void
run (void *cls,
     const struct GNUNET_CONFIGURATION_Handle *c,
     struct GNUNET_SERVICE_Handle *service)
{
  cfg = c;
  /* We don't really do DLOG, so we can setup with very minimal resources */
  edc = GNUNET_CRYPTO_ecc_dlog_prepare (4 /* max value */,
                                        2 /* RAM */);
  my_cadet = GNUNET_CADET_connect (cfg);
  GNUNET_SCHEDULER_add_shutdown (&shutdown_task,
                                 NULL);
  if (NULL == my_cadet)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _ ("Connect to CADET failed\n"));
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
}


/**
 * Define "main" method using service macro.
 */
GNUNET_SERVICE_MAIN
(GNUNET_OS_project_data_gnunet(),
 "scalarproduct-bob",
  GNUNET_SERVICE_OPTION_NONE,
  &run,
  &client_connect_cb,
  &client_disconnect_cb,
  NULL,
  GNUNET_MQ_hd_var_size (bob_client_message,
                         GNUNET_MESSAGE_TYPE_SCALARPRODUCT_CLIENT_TO_BOB,
                         struct BobComputationMessage,
                         NULL),
  GNUNET_MQ_hd_var_size (bob_client_message_multipart,
                         GNUNET_MESSAGE_TYPE_SCALARPRODUCT_CLIENT_MULTIPART_BOB,
                         struct ComputationBobCryptodataMultipartMessage,
                         NULL),
  GNUNET_MQ_handler_end ());


/* end of gnunet-service-scalarproduct-ecc_bob.c */
