n2n/src/sn_selection.c

/**
 * (C) 2007-20 - ntop.org and contributors
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not see see <http://www.gnu.org/licenses/>
 *
 */

#include "sn_selection.h"
#include <stdint.h>

static SN_SELECTION_CRITERION_DATA_TYPE sn_selection_criterion_common_read(n2n_edge_t *eee);
static int sn_selection_criterion_sort(peer_info_t *a, peer_info_t *b);

/* ****************************************************************************** */

/* Initialize selection_criterion field in peer_info structure*/
int sn_selection_criterion_init(peer_info_t *peer){
  if(peer != NULL){
    sn_selection_criterion_default(&(peer->selection_criterion));
  }

  return 0; /* OK */
}

/* Set selection_criterion field to default value according to selected strategy. */
int sn_selection_criterion_default(SN_SELECTION_CRITERION_DATA_TYPE *selection_criterion){
  *selection_criterion = (SN_SELECTION_CRITERION_DATA_TYPE) UINT32_MAX >> 1;

  return 0; /* OK */
}

/* Take data from PEER_INFO payload and transform them into a selection_criterion.
 * This function is highly dependant of the chosen selection criterion.
 */
int sn_selection_criterion_calculate(n2n_edge_t *eee, peer_info_t *peer, SN_SELECTION_CRITERION_DATA_TYPE *data){
  SN_SELECTION_CRITERION_DATA_TYPE common_data;
  int sum = 0;

  common_data = sn_selection_criterion_common_read(eee);

  peer->selection_criterion = (SN_SELECTION_CRITERION_DATA_TYPE)(be32toh(*data) + common_data);

  /* Mitigation of the real supernode load in order to see less oscillations.
   * Edges jump from a supernode to another back and forth due to purging.
   * Because this behavior has a cost of switching, the real load is mitigated with a stickyness factor.
   * This factor is dynamically calculated basing on network size and prevent that unnecessary switching */
  if(peer == eee->curr_sn){
    sum = HASH_COUNT(eee->known_peers) + HASH_COUNT(eee->pending_peers);
    peer->selection_criterion = peer->selection_criterion * sum / (sum + 1);
  }

  return 0; /* OK */
}

/* Set sn_selection_criterion_common_data field to default value. */
int sn_selection_criterion_common_data_default(n2n_edge_t *eee){
  SN_SELECTION_CRITERION_DATA_TYPE tmp = 0;

  tmp = HASH_COUNT(eee->pending_peers);

  if(eee->conf.header_encryption == HEADER_ENCRYPTION_ENABLED){
    tmp *= 2;
  }

  eee->sn_selection_criterion_common_data = tmp / HASH_COUNT(eee->conf.supernodes);

  return 0; /* OK */
}

/* Return the value of sn_selection_criterion_common_data field. */
static SN_SELECTION_CRITERION_DATA_TYPE sn_selection_criterion_common_read(n2n_edge_t *eee){
  return eee->sn_selection_criterion_common_data;
}

/* Function that compare two selection_criterion fields and sorts them in ascending order. */
static int sn_selection_criterion_sort(peer_info_t *a, peer_info_t *b){
  // comparison function for sorting supernodes in ascending order of their selection_criterion.
  return (a->selection_criterion - b->selection_criterion);
}

/* Function that sorts peer_list using sn_selection_criterion_sort. */
int sn_selection_sort(peer_info_t **peer_list){
  HASH_SORT(*peer_list, sn_selection_criterion_sort);

  return 0; /* OK */
}

/* Function that gathers requested data on a supernode. */
SN_SELECTION_CRITERION_DATA_TYPE sn_selection_criterion_gather_data(n2n_sn_t *sss){
  SN_SELECTION_CRITERION_DATA_TYPE data = 0, tmp = 0;
  struct sn_community *comm, *tmp_comm;

  HASH_ITER(hh, sss->communities, comm, tmp_comm){
    tmp = HASH_COUNT(comm->edges) + 1; /* number of nodes in the community + the community itself. */
    if(comm->header_encryption == HEADER_ENCRYPTION_ENABLED){ /*double-count encrypted communities (and their nodes): they exert more load on supernode. */
      tmp *= 2;
    }
    data += tmp;
  }

  return htobe32(data);
}

/* Convert selection_criterion field in a string for management port output. */
extern char * sn_selection_criterion_str(selection_criterion_str_t out, peer_info_t *peer){
  if(NULL == out) { return NULL; }
  memset(out, 0, SN_SELECTION_CRITERION_BUF_SIZE);

  snprintf(out, SN_SELECTION_CRITERION_BUF_SIZE -1,  "ld = %d", (short int)(peer->selection_criterion));

  return out;
}