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

/*
  This file is part of GNUnet.
  (C) 2009, 2010, 2011 Christian Grothoff (and other contributing authors)

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

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

  You should have received a copy of the GNU General Public License
  along with GNUnet; see the file COPYING.  If not, write to the
  Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  Boston, MA 02111-1307, USA.
 */

/**
 * @file nse/gnunet-service-nse.c
 * @brief network size estimation service
 * @author Nathan Evans
 * @author Christian Grothoff
 *
 * The purpose of this service is to estimate the size of the network.
 * Given a specified interval, each peer hashes the most recent
 * timestamp which is evenly divisible by that interval.  This hash is
 * compared in distance to the peer identity to choose an offset.  The
 * closer the peer identity to the hashed timestamp, the earlier the
 * peer sends out a "nearest peer" message.  The closest peer's
 * message should thus be received before any others, which stops
 * those peer from sending their messages at a later duration.  So
 * every peer should receive the same nearest peer message, and from
 * this can calculate the expected number of peers in the network.
 */
#include "platform.h"
#include <math.h>
#include "gnunet_util_lib.h"
#include "gnunet_constants.h"
#include "gnunet_protocols.h"
#include "gnunet_signatures.h"
#include "gnunet_statistics_service.h"
#include "gnunet_core_service.h"
#include "gnunet_nse_service.h"
#include "nse.h"

/**
 * Should messages be delayed randomly?  This option should be set to
 * GNUNET_NO only for experiments, not in production.  It should also
 * be removed once the initial experiments have been completed.
 */
#define USE_RANDOM_DELAYS GNUNET_YES

/**
 * Should we generate a histogram with the time stamps of when we received
 * NSE messages to disk? (for performance evaluation only, not useful in
 * production).  The associated code should also probably be removed
 * once we're done with experiments.
 */
#define ENABLE_HISTOGRAM GNUNET_NO

/**
 * Over how many values do we calculate the weighted average?
 */
#define HISTORY_SIZE 64

/**
 * Message priority to use.
 */
#define NSE_PRIORITY 5

#if FREEBSD
#define log2(a) (log(a)/log(2))
#endif

/**
 * Amount of work required (W-bit collisions) for NSE proofs, in collision-bits.
 */
static unsigned long long nse_work_required;

/**
 * Interval for sending network size estimation flood requests.
 */
static struct GNUNET_TIME_Relative gnunet_nse_interval;

/**
 * Interval between proof find runs.
 */
static struct GNUNET_TIME_Relative proof_find_delay;

#if ENABLE_HISTOGRAM
/**
 * Handle for writing when we received messages to disk.
 */
static struct GNUNET_BIO_WriteHandle *wh;
#endif


/**
 * Per-peer information.
 */
struct NSEPeerEntry
{

  /**
   * Core handle for sending messages to this peer.
   */
  struct GNUNET_CORE_TransmitHandle *th;

  /**
   * What is the identity of the peer?
   */
  struct GNUNET_PeerIdentity id;

  /**
   * Task scheduled to send message to this peer.
   */
  GNUNET_SCHEDULER_TaskIdentifier transmit_task;

  /**
   * Did we receive or send a message about the previous round
   * to this peer yet?   GNUNET_YES if the previous round has
   * been taken care of.
   */
  int previous_round;
};


/**
 * Network size estimate reply; sent when "this"
 * peer's timer has run out before receiving a
 * valid reply from another peer.
 */
struct GNUNET_NSE_FloodMessage
{
  /**
   * Type: GNUNET_MESSAGE_TYPE_NSE_P2P_FLOOD
   */
  struct GNUNET_MessageHeader header;

  /**
   * Number of hops this message has taken so far.
   */
  uint32_t hop_count GNUNET_PACKED;

  /**
   * Purpose.
   */
  struct GNUNET_CRYPTO_RsaSignaturePurpose purpose;

  /**
   * The current timestamp value (which all
   * peers should agree on).
   */
  struct GNUNET_TIME_AbsoluteNBO timestamp;

  /**
   * Number of matching bits between the hash
   * of timestamp and the initiator's public
   * key.
   */
  uint32_t matching_bits GNUNET_PACKED;

  /**
   * Public key of the originator.
   */
  struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded pkey;

  /**
   * Proof of work, causing leading zeros when hashed with pkey.
   */
  uint64_t proof_of_work GNUNET_PACKED;

  /**
   * Signature (over range specified in purpose).
   */
  struct GNUNET_CRYPTO_RsaSignature signature;
};


/**
 * Handle to our current configuration.
 */
static const struct GNUNET_CONFIGURATION_Handle *cfg;

/**
 * Handle to the statistics service.
 */
static struct GNUNET_STATISTICS_Handle *stats;

/**
 * Handle to the core service.
 */
static struct GNUNET_CORE_Handle *coreAPI;

/**
 * Map of all connected peers.
 */
static struct GNUNET_CONTAINER_MultiHashMap *peers;

/**
 * The current network size estimate.  Number of bits matching on
 * average thus far.
 */
static double current_size_estimate;

/**
 * The standard deviation of the last HISTORY_SIZE network
 * size estimates.
 */
static double current_std_dev = NAN;

/**
 * Current hop counter estimate (estimate for network diameter).
 */
static uint32_t hop_count_max;

/**
 * Message for the next round, if we got any.
 */
static struct GNUNET_NSE_FloodMessage next_message;

/**
 * Array of recent size estimate messages.
 */
static struct GNUNET_NSE_FloodMessage size_estimate_messages[HISTORY_SIZE];

/**
 * Index of most recent estimate.
 */
static unsigned int estimate_index;

/**
 * Number of valid entries in the history.
 */
static unsigned int estimate_count;

/**
 * Task scheduled to update our flood message for the next round.
 */
static GNUNET_SCHEDULER_TaskIdentifier flood_task;

/**
 * Task scheduled to compute our proof.
 */
static GNUNET_SCHEDULER_TaskIdentifier proof_task;

/**
 * Notification context, simplifies client broadcasts.
 */
static struct GNUNET_SERVER_NotificationContext *nc;

/**
 * The next major time.
 */
static struct GNUNET_TIME_Absolute next_timestamp;

/**
 * The current major time.
 */
static struct GNUNET_TIME_Absolute current_timestamp;

/**
 * The public key of this peer.
 */
static struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded my_public_key;

/**
 * The private key of this peer.
 */
static struct GNUNET_CRYPTO_RsaPrivateKey *my_private_key;

/**
 * The peer identity of this peer.
 */
static struct GNUNET_PeerIdentity my_identity;

/**
 * Proof of work for this peer.
 */
static uint64_t my_proof;


/**
 * Initialize a message to clients with the current network
 * size estimate.
 *
 * @param em message to fill in
 */
static void
setup_estimate_message (struct GNUNET_NSE_ClientMessage *em)
{
  unsigned int i;
  unsigned int j;
  double mean;
  double sum;
  double std_dev;
  double variance;
  double val;
  double nsize;

#define WEST 1
  /* Weighted incremental algorithm for stddev according to West (1979) */
#if WEST
  double sumweight;
  double weight;
  double q;
  double r;
  double temp;

  mean = 0.0;
  sum = 0.0;
  sumweight = 0.0;
  variance = 0.0;
  for (i = 0; i < estimate_count; i++)
  {
    j = (estimate_index - i + HISTORY_SIZE) % HISTORY_SIZE;
    val = htonl (size_estimate_messages[j].matching_bits);
    weight = estimate_count + 1 - i;

    temp = weight + sumweight;
    q = val - mean;
    r = q * weight / temp;
    mean += r;
    sum += sumweight * q * r;
    sumweight = temp;
  }
  if (estimate_count > 0)
    variance = (sum / sumweight) * estimate_count / (estimate_count - 1.0);
#else
  /* trivial version for debugging */
  double vsq;

  /* non-weighted trivial version */
  sum = 0.0;
  vsq = 0.0;
  variance = 0.0;
  mean = 0.0;

  for (i = 0; i < estimate_count; i++)
  {
    j = (estimate_index - i + HISTORY_SIZE) % HISTORY_SIZE;
    val = htonl (size_estimate_messages[j].matching_bits);
    sum += val;
    vsq += val * val;
  }
  if (0 != estimate_count)
  {
    mean = sum / estimate_count;
    variance = (vsq - mean * sum) / (estimate_count - 1.0);     // terrible for numerical stability...
  }
#endif
  if (variance >= 0)
    std_dev = sqrt (variance);
  else
    std_dev = variance;         /* must be infinity due to estimate_count == 0 */
  current_std_dev = std_dev;
  current_size_estimate = mean;

  em->header.size = htons (sizeof (struct GNUNET_NSE_ClientMessage));
  em->header.type = htons (GNUNET_MESSAGE_TYPE_NSE_ESTIMATE);
  em->reserved = htonl (0);
  em->timestamp = GNUNET_TIME_absolute_hton (GNUNET_TIME_absolute_get ());
  em->size_estimate = mean - 0.332747;
  nsize = log2 (GNUNET_CONTAINER_multihashmap_size (peers) + 1);
  if (em->size_estimate < nsize)
    em->size_estimate = nsize;
  em->std_deviation = std_dev;
  GNUNET_STATISTICS_set (stats, "# nodes in the network (estimate)",
                         (uint64_t) pow (2, mean - 1.0 / 3.0), GNUNET_NO);
}


/**
 * Handler for START message from client, triggers an
 * immediate current network estimate notification.
 * Also, we remember the client for updates upon future
 * estimate measurements.
 *
 * @param cls unused
 * @param client who sent the message
 * @param message the message received
 */
static void
handle_start_message (void *cls, struct GNUNET_SERVER_Client *client,
                      const struct GNUNET_MessageHeader *message)
{
  struct GNUNET_NSE_ClientMessage em;

#if DEBUG_NSE
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Received START message from client\n");
#endif
  GNUNET_SERVER_notification_context_add (nc, client);
  setup_estimate_message (&em);
  GNUNET_SERVER_notification_context_unicast (nc, client, &em.header,
                                              GNUNET_YES);
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}


/**
 * How long should we delay a message to go the given number of
 * matching bits?
 *
 * @param matching_bits number of matching bits to consider
 */
static double
get_matching_bits_delay (uint32_t matching_bits)
{
  /* Calculated as: S + f/2 - (f / pi) * (atan(x - p')) */
  // S is next_timestamp (ignored in return value)
  // f is frequency (gnunet_nse_interval)
  // x is matching_bits
  // p' is current_size_estimate
  return ((double) gnunet_nse_interval.rel_value / (double) 2.0) -
      ((gnunet_nse_interval.rel_value / M_PI) *
       atan (matching_bits - current_size_estimate));
}


/**
 * What delay randomization should we apply for a given number of matching bits?
 *
 * @param matching_bits number of matching bits
 * @return random delay to apply
 */
static struct GNUNET_TIME_Relative
get_delay_randomization (uint32_t matching_bits)
{
#if USE_RANDOM_DELAYS
  struct GNUNET_TIME_Relative ret;
  uint32_t i;
  double d;

  if (matching_bits == 0)
    return GNUNET_TIME_UNIT_ZERO;
  d = get_matching_bits_delay (matching_bits - 1);
  i = (uint32_t) (d / (double) (hop_count_max + 1));
  ret.rel_value = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, i + 1);
  return ret;
#else
  return GNUNET_TIME_UNIT_ZERO;
#endif
}


/**
 * Get the number of matching bits that the given timestamp has to the given peer ID.
 *
 * @param timestamp time to generate key
 * @param id peer identity to compare with
 * @return number of matching bits
 */
static uint32_t
get_matching_bits (struct GNUNET_TIME_Absolute timestamp,
                   const struct GNUNET_PeerIdentity *id)
{
  GNUNET_HashCode timestamp_hash;

  GNUNET_CRYPTO_hash (&timestamp.abs_value, sizeof (timestamp.abs_value),
                      &timestamp_hash);
  return GNUNET_CRYPTO_hash_matching_bits (&timestamp_hash, &id->hashPubKey);
}


/**
 * Get the transmission delay that should be applied for a
 * particular round.
 *
 * @param round_offset -1 for the previous round (random delay between 0 and 50ms)
 *                      0 for the current round (based on our proximity to time key)
 * @return delay that should be applied
 */
static struct GNUNET_TIME_Relative
get_transmit_delay (int round_offset)
{
  struct GNUNET_TIME_Relative ret;
  struct GNUNET_TIME_Absolute tgt;
  double dist_delay;
  uint32_t matching_bits;

  switch (round_offset)
  {
  case -1:
    /* previous round is randomized between 0 and 50 ms */
#if USE_RANDOM_DELAYS
    ret.rel_value = GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_WEAK, 50);
#else
    ret = GNUNET_TIME_UNIT_ZERO;
#endif
#if DEBUG_NSE
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Transmitting previous round behind schedule in %llu ms\n",
                (unsigned long long) ret.rel_value);
#endif
    return ret;
  case 0:
    /* current round is based on best-known matching_bits */
    matching_bits =
        ntohl (size_estimate_messages[estimate_index].matching_bits);
    dist_delay = get_matching_bits_delay (matching_bits);
    dist_delay += get_delay_randomization (matching_bits).rel_value;
    ret.rel_value = (uint64_t) dist_delay;
#if DEBUG_NSE
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "For round %llu, delay for %u matching bits is %llu ms\n",
                (unsigned long long) current_timestamp.abs_value,
                (unsigned int) matching_bits,
                (unsigned long long) ret.rel_value);
#endif
    /* now consider round start time and add delay to it */
    tgt = GNUNET_TIME_absolute_add (current_timestamp, ret);
    return GNUNET_TIME_absolute_get_remaining (tgt);
  }
  GNUNET_break (0);
  return GNUNET_TIME_UNIT_FOREVER_REL;
}


/**
 * Task that triggers a NSE P2P transmission.
 *
 * @param cls the 'struct NSEPeerEntry'
 * @param tc scheduler context
 */
static void
transmit_task (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc);


/**
 * Called when core is ready to send a message we asked for
 * out to the destination.
 *
 * @param cls closure (NULL)
 * @param size number of bytes available in buf
 * @param buf where the callee should write the message
 * @return number of bytes written to buf
 */
static size_t
transmit_ready (void *cls, size_t size, void *buf)
{
  struct NSEPeerEntry *peer_entry = cls;
  unsigned int idx;

  peer_entry->th = NULL;
  if (buf == NULL)
  {
    /* client disconnected */
    return 0;
  }
  GNUNET_assert (size >= sizeof (struct GNUNET_NSE_FloodMessage));
  idx = estimate_index;
  if (peer_entry->previous_round == GNUNET_NO)
  {
    idx = (idx + HISTORY_SIZE - 1) % HISTORY_SIZE;
    peer_entry->previous_round = GNUNET_YES;
    peer_entry->transmit_task =
        GNUNET_SCHEDULER_add_delayed (get_transmit_delay (0), &transmit_task,
                                      peer_entry);
  }
  if ((ntohl (size_estimate_messages[idx].hop_count) == 0) &&
      (GNUNET_SCHEDULER_NO_TASK != proof_task))
  {
    GNUNET_STATISTICS_update (stats,
                              "# flood messages not generated (no proof yet)",
                              1, GNUNET_NO);
    return 0;
  }
  if (ntohs (size_estimate_messages[idx].header.size) == 0)
  {
    GNUNET_STATISTICS_update (stats,
                              "# flood messages not generated (lack of history)",
                              1, GNUNET_NO);
    return 0;
  }
#if DEBUG_NSE
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "In round %llu, sending to `%s' estimate with %u bits\n",
              (unsigned long long)
              GNUNET_TIME_absolute_ntoh (size_estimate_messages[idx].
                                         timestamp).abs_value,
              GNUNET_i2s (&peer_entry->id),
              (unsigned int) ntohl (size_estimate_messages[idx].matching_bits));
#endif
  if (ntohl (size_estimate_messages[idx].hop_count) == 0)
    GNUNET_STATISTICS_update (stats, "# flood messages started", 1, GNUNET_NO);
  GNUNET_STATISTICS_update (stats, "# flood messages transmitted", 1,
                            GNUNET_NO);
  memcpy (buf, &size_estimate_messages[idx],
          sizeof (struct GNUNET_NSE_FloodMessage));
  GNUNET_STATISTICS_update (stats, "# flood messages sent", 1, GNUNET_NO);
  return sizeof (struct GNUNET_NSE_FloodMessage);
}


/**
 * Task that triggers a NSE P2P transmission.
 *
 * @param cls the 'struct NSEPeerEntry'
 * @param tc scheduler context
 */
static void
transmit_task (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct NSEPeerEntry *peer_entry = cls;

  peer_entry->transmit_task = GNUNET_SCHEDULER_NO_TASK;
  GNUNET_assert (NULL == peer_entry->th);
  peer_entry->th =
      GNUNET_CORE_notify_transmit_ready (coreAPI, GNUNET_NO, NSE_PRIORITY,
                                         GNUNET_TIME_UNIT_FOREVER_REL,
                                         &peer_entry->id,
                                         sizeof (struct
                                                 GNUNET_NSE_FloodMessage),
                                         &transmit_ready, peer_entry);
}


/**
 * We've sent on our flood message or one that we received which was
 * validated and closer than ours.  Update the global list of recent
 * messages and the average.  Also re-broadcast the message to any
 * clients.
 */
static void
update_network_size_estimate ()
{
  struct GNUNET_NSE_ClientMessage em;

  setup_estimate_message (&em);
  GNUNET_SERVER_notification_context_broadcast (nc, &em.header, GNUNET_YES);
}


/**
 * Setup a flood message in our history array at the given
 * slot offset for the given timestamp.
 *
 * @param slot index to use
 * @param ts timestamp to use
 */
static void
setup_flood_message (unsigned int slot, struct GNUNET_TIME_Absolute ts)
{
  struct GNUNET_NSE_FloodMessage *fm;
  uint32_t matching_bits;

  matching_bits = get_matching_bits (ts, &my_identity);
  fm = &size_estimate_messages[slot];
  fm->header.size = htons (sizeof (struct GNUNET_NSE_FloodMessage));
  fm->header.type = htons (GNUNET_MESSAGE_TYPE_NSE_P2P_FLOOD);
  fm->hop_count = htonl (0);
  fm->purpose.purpose = htonl (GNUNET_SIGNATURE_PURPOSE_NSE_SEND);
  fm->purpose.size =
      htonl (sizeof (struct GNUNET_NSE_FloodMessage) -
             sizeof (struct GNUNET_MessageHeader) - sizeof (uint32_t) -
             sizeof (struct GNUNET_CRYPTO_RsaSignature));
  fm->matching_bits = htonl (matching_bits);
  fm->timestamp = GNUNET_TIME_absolute_hton (ts);
  fm->pkey = my_public_key;
  fm->proof_of_work = my_proof;
  if (nse_work_required > 0)
    GNUNET_assert (GNUNET_OK ==
                   GNUNET_CRYPTO_rsa_sign (my_private_key, &fm->purpose,
                                           &fm->signature));
  else
    memset (&fm->signature, 0, sizeof (fm->signature));
}


/**
 * Schedule transmission for the given peer for the current round based
 * on what we know about the desired delay.
 *
 * @param cls unused
 * @param key hash of peer identity
 * @param value the 'struct NSEPeerEntry'
 * @return GNUNET_OK (continue to iterate)
 */
static int
schedule_current_round (void *cls, const GNUNET_HashCode * key, void *value)
{
  struct NSEPeerEntry *peer_entry = value;
  struct GNUNET_TIME_Relative delay;

  if (peer_entry->th != NULL)
  {
    peer_entry->previous_round = GNUNET_NO;
    return GNUNET_OK;
  }
  if (peer_entry->transmit_task != GNUNET_SCHEDULER_NO_TASK)
  {
    GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
    peer_entry->previous_round = GNUNET_NO;
  }
  delay =
      get_transmit_delay ((peer_entry->previous_round == GNUNET_NO) ? -1 : 0);
  peer_entry->transmit_task =
      GNUNET_SCHEDULER_add_delayed (delay, &transmit_task, peer_entry);
  return GNUNET_OK;
}


/**
 * Update our flood message to be sent (and our timestamps).
 *
 * @param cls unused
 * @param tc context for this message
 */
static void
update_flood_message (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct GNUNET_TIME_Relative offset;
  unsigned int i;

  flood_task = GNUNET_SCHEDULER_NO_TASK;
  if (0 != (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN))
    return;
  offset = GNUNET_TIME_absolute_get_remaining (next_timestamp);
  if (0 != offset.rel_value)
  {
    /* somehow run early, delay more */
    flood_task =
        GNUNET_SCHEDULER_add_delayed (offset, &update_flood_message, NULL);
    return;
  }
  current_timestamp = next_timestamp;
  next_timestamp =
      GNUNET_TIME_absolute_add (current_timestamp, gnunet_nse_interval);
  estimate_index = (estimate_index + 1) % HISTORY_SIZE;
  if (estimate_count < HISTORY_SIZE)
    estimate_count++;
  if (next_timestamp.abs_value ==
      GNUNET_TIME_absolute_ntoh (next_message.timestamp).abs_value)
  {
    /* we received a message for this round way early, use it! */
    size_estimate_messages[estimate_index] = next_message;
    size_estimate_messages[estimate_index].hop_count =
        htonl (1 + ntohl (next_message.hop_count));
  }
  else
    setup_flood_message (estimate_index, current_timestamp);
  next_message.matching_bits = htonl (0);       /* reset for 'next' round */
  hop_count_max = 0;
  for (i = 0; i < HISTORY_SIZE; i++)
    hop_count_max =
        GNUNET_MAX (ntohl (size_estimate_messages[i].hop_count), hop_count_max);
  GNUNET_CONTAINER_multihashmap_iterate (peers, &schedule_current_round, NULL);
  flood_task =
      GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_absolute_get_remaining
                                    (next_timestamp), &update_flood_message,
                                    NULL);
}


/**
 * Count the leading zeroes in hash.
 *
 * @param hash
 * @return the number of leading zero bits.
 */
static unsigned int
count_leading_zeroes (const GNUNET_HashCode * hash)
{
  unsigned int hash_count;

  hash_count = 0;
  while ((0 == GNUNET_CRYPTO_hash_get_bit (hash, hash_count)))
    hash_count++;
  return hash_count;
}


/**
 * Check whether the given public key
 * and integer are a valid proof of work.
 *
 * @param pkey the public key
 * @param val the integer
 *
 * @return GNUNET_YES if valid, GNUNET_NO if not
 */
static int
check_proof_of_work (const struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded *pkey,
                     uint64_t val)
{
  char buf[sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded) +
           sizeof (val)];
  GNUNET_HashCode result;

  memcpy (buf, &val, sizeof (val));
  memcpy (&buf[sizeof (val)], pkey,
          sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded));
  GNUNET_CRYPTO_hash (buf, sizeof (buf), &result);
  return (count_leading_zeroes (&result) >=
          nse_work_required) ? GNUNET_YES : GNUNET_NO;
}


/**
 * Write our current proof to disk.
 */
static void
write_proof ()
{
  char *proof;

  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_filename (cfg, "NSE", "PROOFFILE", &proof))
    return;
  if (sizeof (my_proof) !=
      GNUNET_DISK_fn_write (proof, &my_proof, sizeof (my_proof),
                            GNUNET_DISK_PERM_USER_READ |
                            GNUNET_DISK_PERM_USER_WRITE))
    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING, "write", proof);
  GNUNET_free (proof);

}


/**
 * Find our proof of work.
 *
 * @param cls closure (unused)
 * @param tc task context
 */
static void
find_proof (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
#define ROUND_SIZE 10
  uint64_t counter;
  char buf[sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded) +
           sizeof (uint64_t)];
  GNUNET_HashCode result;
  unsigned int i;

  proof_task = GNUNET_SCHEDULER_NO_TASK;
  memcpy (&buf[sizeof (uint64_t)], &my_public_key,
          sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded));
  i = 0;
  counter = my_proof;
  while ((counter != UINT64_MAX) && (i < ROUND_SIZE))
  {
    memcpy (buf, &counter, sizeof (uint64_t));
    GNUNET_CRYPTO_hash (buf, sizeof (buf), &result);
    if (nse_work_required <= count_leading_zeroes (&result))
    {
      my_proof = counter;
#if DEBUG_NSE
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Proof of work found: %llu!\n",
                  (unsigned long long) GNUNET_ntohll (counter));
#endif
      write_proof ();
      setup_flood_message (estimate_index, current_timestamp);
      return;
    }
    counter++;
    i++;
  }
  if (my_proof / (100 * ROUND_SIZE) < counter / (100 * ROUND_SIZE))
  {
#if DEBUG_NSE
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Testing proofs currently at %llu\n",
                (unsigned long long) counter);
#endif
    /* remember progress every 100 rounds */
    my_proof = counter;
    write_proof ();
  }
  else
  {
    my_proof = counter;
  }
  proof_task =
      GNUNET_SCHEDULER_add_delayed (proof_find_delay, &find_proof, NULL);
}


/**
 * An incoming flood message has been received which claims
 * to have more bits matching than any we know in this time
 * period.  Verify the signature and/or proof of work.
 *
 * @param incoming_flood the message to verify
 *
 * @return GNUNET_YES if the message is verified
 *         GNUNET_NO if the key/signature don't verify
 */
static int
verify_message_crypto (const struct GNUNET_NSE_FloodMessage *incoming_flood)
{
  if (GNUNET_YES !=
      check_proof_of_work (&incoming_flood->pkey,
                           incoming_flood->proof_of_work))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_INFO, _("Proof of work invalid: %llu!\n"),
                (unsigned long long)
                GNUNET_ntohll (incoming_flood->proof_of_work));
    GNUNET_break_op (0);
    return GNUNET_NO;
  }
  if ((nse_work_required > 0) &&
      (GNUNET_OK !=
       GNUNET_CRYPTO_rsa_verify (GNUNET_SIGNATURE_PURPOSE_NSE_SEND,
                                 &incoming_flood->purpose,
                                 &incoming_flood->signature,
                                 &incoming_flood->pkey)))
  {
    GNUNET_break_op (0);
    return GNUNET_NO;
  }
  return GNUNET_YES;
}


/**
 * Update transmissions for the given peer for the current round based
 * on updated proximity information.
 *
 * @param cls peer entry to exclude from updates
 * @param key hash of peer identity
 * @param value the 'struct NSEPeerEntry'
 * @return GNUNET_OK (continue to iterate)
 */
static int
update_flood_times (void *cls, const GNUNET_HashCode * key, void *value)
{
  struct NSEPeerEntry *exclude = cls;
  struct NSEPeerEntry *peer_entry = value;
  struct GNUNET_TIME_Relative delay;

  if (peer_entry->th != NULL)
    return GNUNET_OK;           /* already active */
  if (peer_entry == exclude)
    return GNUNET_OK;           /* trigger of the update */
  if (peer_entry->previous_round == GNUNET_NO)
  {
    /* still stuck in previous round, no point to update, check that
     * we are active here though... */
    GNUNET_break ((peer_entry->transmit_task != GNUNET_SCHEDULER_NO_TASK) ||
                  (peer_entry->th != NULL));
    return GNUNET_OK;
  }
  if (peer_entry->transmit_task != GNUNET_SCHEDULER_NO_TASK)
  {
    GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
    peer_entry->transmit_task = GNUNET_SCHEDULER_NO_TASK;
  }
  delay = get_transmit_delay (0);
  peer_entry->transmit_task =
      GNUNET_SCHEDULER_add_delayed (delay, &transmit_task, peer_entry);
  return GNUNET_OK;
}


/**
 * Core handler for size estimate flooding messages.
 *
 * @param cls closure unused
 * @param message message
 * @param peer peer identity this message is from (ignored)
 * @param atsi performance data (ignored)
 * @param atsi_count number of records in 'atsi'
 */
static int
handle_p2p_size_estimate (void *cls, const struct GNUNET_PeerIdentity *peer,
                          const struct GNUNET_MessageHeader *message,
                          const struct GNUNET_ATS_Information *atsi,
                          unsigned int atsi_count)
{
  const struct GNUNET_NSE_FloodMessage *incoming_flood;
  struct GNUNET_TIME_Absolute ts;
  struct NSEPeerEntry *peer_entry;
  uint32_t matching_bits;
  unsigned int idx;

#if ENABLE_HISTOGRAM
  if (NULL != wh)
    GNUNET_BIO_write_int64 (wh, GNUNET_TIME_absolute_get ().abs_value);
#endif
  incoming_flood = (const struct GNUNET_NSE_FloodMessage *) message;
  GNUNET_STATISTICS_update (stats, "# flood messages received", 1, GNUNET_NO);
  matching_bits = ntohl (incoming_flood->matching_bits);
#if DEBUG_NSE
  {
    char origin[5];
    char pred[5];
    struct GNUNET_PeerIdentity os;

    GNUNET_CRYPTO_hash (&incoming_flood->pkey,
                        sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded),
                        &os.hashPubKey);
    GNUNET_snprintf (origin, sizeof (origin), "%s", GNUNET_i2s (&os));
    GNUNET_snprintf (pred, sizeof (pred), "%s", GNUNET_i2s (peer));
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Flood at %llu from `%s' via `%s' at `%s' with bits %u\n",
                (unsigned long long)
                GNUNET_TIME_absolute_ntoh (incoming_flood->timestamp).abs_value,
                origin, pred, GNUNET_i2s (&my_identity),
                (unsigned int) matching_bits);
  }
#endif

  peer_entry = GNUNET_CONTAINER_multihashmap_get (peers, &peer->hashPubKey);
  if (NULL == peer_entry)
  {
    GNUNET_break (0);
    return GNUNET_OK;
  }

  ts = GNUNET_TIME_absolute_ntoh (incoming_flood->timestamp);

  if (ts.abs_value == current_timestamp.abs_value)
    idx = estimate_index;
  else if (ts.abs_value ==
           current_timestamp.abs_value - gnunet_nse_interval.rel_value)
    idx = (estimate_index + HISTORY_SIZE - 1) % HISTORY_SIZE;
  else if (ts.abs_value ==
           next_timestamp.abs_value - gnunet_nse_interval.rel_value)
  {
    if (matching_bits <= ntohl (next_message.matching_bits))
      return GNUNET_OK;         /* ignore, simply too early/late */
    if (GNUNET_YES != verify_message_crypto (incoming_flood))
    {
      GNUNET_break_op (0);
      return GNUNET_OK;
    }
    next_message = *incoming_flood;
    return GNUNET_OK;
  }
  else
  {
    GNUNET_STATISTICS_update (stats,
                              "# flood messages discarded (clock skew too large)",
                              1, GNUNET_NO);
    return GNUNET_OK;
  }
  if (0 == (memcmp (peer, &my_identity, sizeof (struct GNUNET_PeerIdentity))))
  {
    /* send to self, update our own estimate IF this also comes from us! */
    if (0 ==
        memcmp (&incoming_flood->pkey, &my_public_key, sizeof (my_public_key)))
      update_network_size_estimate ();
    return GNUNET_OK;
  }
  if (matching_bits >= ntohl (size_estimate_messages[idx].matching_bits))
  {
    /* cancel transmission from us to this peer for this round */
    if (idx == estimate_index)
    {
      if (peer_entry->previous_round == GNUNET_YES)
      {
        /* cancel any activity for current round */
        if (peer_entry->transmit_task != GNUNET_SCHEDULER_NO_TASK)
        {
          GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
          peer_entry->transmit_task = GNUNET_SCHEDULER_NO_TASK;
        }
        if (peer_entry->th != NULL)
        {
          GNUNET_CORE_notify_transmit_ready_cancel (peer_entry->th);
          peer_entry->th = NULL;
        }
      }
    }
    else
    {
      /* cancel previous round only */
      peer_entry->previous_round = GNUNET_YES;
    }
  }
  if (matching_bits == ntohl (size_estimate_messages[idx].matching_bits))
  {
    /* cancel transmission in the other direction, as this peer clearly has
       up-to-date information already */
    if (idx != estimate_index)
    {
      /* do not transmit information for the previous round to this peer 
         anymore (but allow current round) */
      peer_entry->previous_round = GNUNET_YES;
      return GNUNET_OK;
    }
    /* got up-to-date information for current round, cancel transmission altogether */
    if (GNUNET_SCHEDULER_NO_TASK != peer_entry->transmit_task)
    {
      GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
      peer_entry->transmit_task = GNUNET_SCHEDULER_NO_TASK;
    }
    if (peer_entry->th != NULL)
    {
      GNUNET_CORE_notify_transmit_ready_cancel (peer_entry->th);
      peer_entry->th = NULL;
    }
    return GNUNET_OK;
  }
  if (matching_bits <= ntohl (size_estimate_messages[idx].matching_bits))
  {
    if ((idx < estimate_index) && (peer_entry->previous_round == GNUNET_YES))
      peer_entry->previous_round = GNUNET_NO;
    /* push back our result now, that peer is spreading bad information... */
    if (NULL == peer_entry->th)
    {
      if (peer_entry->transmit_task != GNUNET_SCHEDULER_NO_TASK)
        GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
      peer_entry->transmit_task =
          GNUNET_SCHEDULER_add_now (&transmit_task, peer_entry);
    }
    /* Not closer than our most recent message, no need to do work here */
    GNUNET_STATISTICS_update (stats,
                              "# flood messages ignored (had closer already)",
                              1, GNUNET_NO);
    return GNUNET_OK;
  }
  if (GNUNET_YES != verify_message_crypto (incoming_flood))
  {
    GNUNET_break_op (0);
    return GNUNET_OK;
  }
  size_estimate_messages[idx] = *incoming_flood;
  size_estimate_messages[idx].hop_count =
      htonl (ntohl (incoming_flood->hop_count) + 1);
  hop_count_max =
      GNUNET_MAX (ntohl (incoming_flood->hop_count) + 1, hop_count_max);

  /* have a new, better size estimate, inform clients */
  update_network_size_estimate ();

  /* flood to rest */
  GNUNET_CONTAINER_multihashmap_iterate (peers, &update_flood_times,
                                         peer_entry);
  return GNUNET_OK;
}



/**
 * Method called whenever a peer connects.
 *
 * @param cls closure
 * @param peer peer identity this notification is about
 * @param atsi performance data
 * @param atsi_count number of records in 'atsi'
 */
static void
handle_core_connect (void *cls, const struct GNUNET_PeerIdentity *peer,
                     const struct GNUNET_ATS_Information *atsi,
                     unsigned int atsi_count)
{
  struct NSEPeerEntry *peer_entry;

#if DEBUG_NSE
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Peer `%s' connected to us\n",
              GNUNET_i2s (peer));
#endif
  peer_entry = GNUNET_malloc (sizeof (struct NSEPeerEntry));
  peer_entry->id = *peer;
  GNUNET_assert (GNUNET_OK ==
                 GNUNET_CONTAINER_multihashmap_put (peers, &peer->hashPubKey,
                                                    peer_entry,
                                                    GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));
  peer_entry->transmit_task =
      GNUNET_SCHEDULER_add_delayed (get_transmit_delay (-1), &transmit_task,
                                    peer_entry);
  GNUNET_STATISTICS_update (stats, "# peers", 1, GNUNET_NO);
}


/**
 * Method called whenever a peer disconnects.
 *
 * @param cls closure
 * @param peer peer identity this notification is about
 */
static void
handle_core_disconnect (void *cls, const struct GNUNET_PeerIdentity *peer)
{
  struct NSEPeerEntry *pos;

#if DEBUG_NSE
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Peer `%s' disconnected from us\n",
              GNUNET_i2s (peer));
#endif
  pos = GNUNET_CONTAINER_multihashmap_get (peers, &peer->hashPubKey);
  if (NULL == pos)
  {
    GNUNET_break (0);
    return;
  }
  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CONTAINER_multihashmap_remove (peers, &peer->hashPubKey,
                                                       pos));
  if (pos->transmit_task != GNUNET_SCHEDULER_NO_TASK)
    GNUNET_SCHEDULER_cancel (pos->transmit_task);
  if (pos->th != NULL)
  {
    GNUNET_CORE_notify_transmit_ready_cancel (pos->th);
    pos->th = NULL;
  }
  GNUNET_free (pos);
  GNUNET_STATISTICS_update (stats, "# peers", -1, GNUNET_NO);
}


/**
 * Task run during shutdown.
 *
 * @param cls unused
 * @param tc unused
 */
static void
shutdown_task (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  if (flood_task != GNUNET_SCHEDULER_NO_TASK)
  {
    GNUNET_SCHEDULER_cancel (flood_task);
    flood_task = GNUNET_SCHEDULER_NO_TASK;
  }
  if (proof_task != GNUNET_SCHEDULER_NO_TASK)
  {
    GNUNET_SCHEDULER_cancel (proof_task);
    proof_task = GNUNET_SCHEDULER_NO_TASK;
    write_proof ();             /* remember progress */
  }
  if (nc != NULL)
  {
    GNUNET_SERVER_notification_context_destroy (nc);
    nc = NULL;
  }
  if (coreAPI != NULL)
  {
    GNUNET_CORE_disconnect (coreAPI);
    coreAPI = NULL;
  }
  if (stats != NULL)
  {
    GNUNET_STATISTICS_destroy (stats, GNUNET_NO);
    stats = NULL;
  }
  if (peers != NULL)
  {
    GNUNET_CONTAINER_multihashmap_destroy (peers);
    peers = NULL;
  }
  if (my_private_key != NULL)
  {
    GNUNET_CRYPTO_rsa_key_free (my_private_key);
    my_private_key = NULL;
  }
#if ENABLE_HISTOGRAM
  if (wh != NULL)
  {
    GNUNET_BIO_write_close (wh);
    wh = NULL;
  }
#endif
}


/**
 * Called on core init/fail.
 *
 * @param cls service closure
 * @param server handle to the server for this service
 * @param identity the public identity of this peer
 */
static void
core_init (void *cls, struct GNUNET_CORE_Handle *server,
           const struct GNUNET_PeerIdentity *identity)
{
  struct GNUNET_TIME_Absolute now;
  struct GNUNET_TIME_Absolute prev_time;

  if (server == NULL)
  {
#if DEBUG_NSE
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Connection to core FAILED!\n");
#endif
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  GNUNET_assert (0 ==
                 memcmp (&my_identity, identity,
                         sizeof (struct GNUNET_PeerIdentity)));
  now = GNUNET_TIME_absolute_get ();
  current_timestamp.abs_value =
      (now.abs_value / gnunet_nse_interval.rel_value) *
      gnunet_nse_interval.rel_value;
  next_timestamp.abs_value =
      current_timestamp.abs_value + gnunet_nse_interval.rel_value;
  estimate_index = HISTORY_SIZE - 1;
  estimate_count = 0;
  if (GNUNET_YES == check_proof_of_work (&my_public_key, my_proof))
  {
    prev_time.abs_value =
        current_timestamp.abs_value - (estimate_index -
                                       1) * gnunet_nse_interval.rel_value;
    setup_flood_message (estimate_index, prev_time);
    estimate_count++;
  }
  flood_task =
      GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_absolute_get_remaining
                                    (next_timestamp), &update_flood_message,
                                    NULL);
}


/**
 * Handle network size estimate clients.
 *
 * @param cls closure
 * @param server the initialized server
 * @param c configuration to use
 */
static void
run (void *cls, struct GNUNET_SERVER_Handle *server,
     const struct GNUNET_CONFIGURATION_Handle *c)
{
  char *keyfile;
  char *proof;

  static const struct GNUNET_SERVER_MessageHandler handlers[] = {
    {&handle_start_message, NULL, GNUNET_MESSAGE_TYPE_NSE_START,
     sizeof (struct GNUNET_MessageHeader)},
    {NULL, NULL, 0, 0}
  };
  static const struct GNUNET_CORE_MessageHandler core_handlers[] = {
    {&handle_p2p_size_estimate, GNUNET_MESSAGE_TYPE_NSE_P2P_FLOOD,
     sizeof (struct GNUNET_NSE_FloodMessage)},
    {NULL, 0, 0}
  };
  cfg = c;

  if ((GNUNET_OK !=
       GNUNET_CONFIGURATION_get_value_time (cfg, "NSE", "INTERVAL",
                                            &gnunet_nse_interval)) ||
      (GNUNET_OK !=
       GNUNET_CONFIGURATION_get_value_time (cfg, "NSE", "WORKDELAY",
                                            &proof_find_delay)) ||
      (GNUNET_OK !=
       GNUNET_CONFIGURATION_get_value_number (cfg, "NSE", "WORKBITS",
                                              &nse_work_required)))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _
                ("NSE service is lacking key configuration settings.  Exiting.\n"));
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  if (nse_work_required >= sizeof (GNUNET_HashCode) * 8)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _("Invalid work requirement for NSE service. Exiting.\n"));
    GNUNET_SCHEDULER_shutdown ();
    return;
  }


  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_filename (cfg, "GNUNETD", "HOSTKEY",
                                               &keyfile))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _
                ("NSE service is lacking key configuration settings.  Exiting.\n"));
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  my_private_key = GNUNET_CRYPTO_rsa_key_create_from_file (keyfile);
  GNUNET_free (keyfile);
  if (my_private_key == NULL)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _("NSE service could not access hostkey.  Exiting.\n"));
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  GNUNET_CRYPTO_rsa_key_get_public (my_private_key, &my_public_key);
  GNUNET_CRYPTO_hash (&my_public_key, sizeof (my_public_key),
                      &my_identity.hashPubKey);
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_filename (cfg, "NSE", "PROOFFILE", &proof))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _
                ("NSE service is lacking key configuration settings.  Exiting.\n"));
    if (my_private_key != NULL)
    {
      GNUNET_CRYPTO_rsa_key_free (my_private_key);
      my_private_key = NULL;
    }
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  if ((GNUNET_YES != GNUNET_DISK_file_test (proof)) ||
      (sizeof (my_proof) !=
       GNUNET_DISK_fn_read (proof, &my_proof, sizeof (my_proof))))
    my_proof = 0;
  GNUNET_free (proof);
  proof_task =
      GNUNET_SCHEDULER_add_with_priority (GNUNET_SCHEDULER_PRIORITY_IDLE,
                                          &find_proof, NULL);

  peers = GNUNET_CONTAINER_multihashmap_create (128);
  GNUNET_SERVER_add_handlers (server, handlers);
  nc = GNUNET_SERVER_notification_context_create (server, 1);
  /* Connect to core service and register core handlers */
  coreAPI = GNUNET_CORE_connect (cfg,   /* Main configuration */
                                 1, NULL,       /* Closure passed to functions */
                                 &core_init,    /* Call core_init once connected */
                                 &handle_core_connect,  /* Handle connects */
                                 &handle_core_disconnect,       /* Handle disconnects */
                                 NULL,  /* Don't want notified about all incoming messages */
                                 GNUNET_NO,     /* For header only inbound notification */
                                 NULL,  /* Don't want notified about all outbound messages */
                                 GNUNET_NO,     /* For header only outbound notification */
                                 core_handlers);        /* Register these handlers */
  GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_UNIT_FOREVER_REL, &shutdown_task,
                                NULL);
#if ENABLE_HISTOGRAM
  if (GNUNET_OK ==
      GNUNET_CONFIGURATION_get_value_filename (cfg, "NSE", "HISTOGRAM", &proof))
  {
    wh = GNUNET_BIO_write_open (proof);
    GNUNET_free (proof);
  }
#endif
  if (coreAPI == NULL)
  {
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  stats = GNUNET_STATISTICS_create ("nse", cfg);
}


/**
 * The main function for the statistics service.
 *
 * @param argc number of arguments from the command line
 * @param argv command line arguments
 * @return 0 ok, 1 on error
 */
int
main (int argc, char *const *argv)
{
  return (GNUNET_OK ==
          GNUNET_SERVICE_run (argc, argv, "nse", GNUNET_SERVICE_OPTION_NONE,
                              &run, NULL)) ? 0 : 1;
}

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