gnunet-service-nse.c

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/*
  This file is part of GNUnet.
  Copyright (C) 2009, 2010, 2011, 2012, 2013, 2016 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 <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"
#if ENABLE_NSE_HISTOGRAM
#include "gnunet_testbed_logger_service.h"
#endif
#include "nse.h"
#include <gcrypt.h>


#define USE_RANDOM_DELAYS GNUNET_YES

#define DEBUG_NSE GNUNET_NO

#define HISTORY_SIZE 64

#define NSE_PRIORITY                                       \
  (GNUNET_MQ_PRIO_BACKGROUND | GNUNET_MQ_PREF_UNRELIABLE | \
   GNUNET_MQ_PREF_CORK_ALLOWED)

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

static unsigned long long nse_work_required;

static struct GNUNET_TIME_Relative gnunet_nse_interval;

static struct GNUNET_TIME_Relative proof_find_delay;

#if ENABLE_NSE_HISTOGRAM

struct GNUNET_CLIENT_TestHandle *logger_test;

static struct GNUNET_TESTBED_LOGGER_Handle *lh;

static struct GNUNET_BIO_WriteHandle *histogram;

#endif


struct NSEPeerEntry
{

  struct GNUNET_MQ_Handle *mq;

  const struct GNUNET_PeerIdentity *id;

  struct GNUNET_SCHEDULER_Task *transmit_task;

  int previous_round;

#if ENABLE_NSE_HISTOGRAM

  unsigned int received_messages;

  unsigned int transmitted_messages;

  unsigned int last_transmitted_size;

#endif
};


GNUNET_NETWORK_STRUCT_BEGIN

struct GNUNET_NSE_FloodMessage
{
  struct GNUNET_MessageHeader header;

  uint32_t hop_count GNUNET_PACKED;

  struct GNUNET_CRYPTO_EccSignaturePurpose purpose;

  struct GNUNET_TIME_AbsoluteNBO timestamp;

  uint32_t matching_bits GNUNET_PACKED;

  struct GNUNET_PeerIdentity origin;

  uint64_t proof_of_work GNUNET_PACKED;

  struct GNUNET_CRYPTO_EddsaSignature signature;
};
GNUNET_NETWORK_STRUCT_END

static const struct GNUNET_CONFIGURATION_Handle *cfg;

static struct GNUNET_STATISTICS_Handle *stats;

static struct GNUNET_CORE_Handle *core_api;

static struct GNUNET_CONTAINER_MultiPeerMap *peers;

static double current_size_estimate;

static double current_std_dev = NAN;

static uint32_t hop_count_max;

static struct GNUNET_NSE_FloodMessage next_message;

static struct GNUNET_NSE_FloodMessage size_estimate_messages[HISTORY_SIZE];

static unsigned int estimate_index;

static unsigned int estimate_count;

static struct GNUNET_SCHEDULER_Task *flood_task;

static struct GNUNET_SCHEDULER_Task *proof_task;

static struct GNUNET_NotificationContext *nc;

static struct GNUNET_TIME_Absolute next_timestamp;

static struct GNUNET_TIME_Absolute current_timestamp;

static struct GNUNET_CRYPTO_EddsaPrivateKey *my_private_key;

static struct GNUNET_PeerIdentity my_identity;

static uint64_t my_proof;


static void
setup_estimate_message (struct GNUNET_NSE_ClientMessage *em)
{
  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 (unsigned int i = 0; i < estimate_count; i++)
  {
    unsigned int 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 (unsigned int i = 0; i < estimate_count; i++)
  {
    unsigned int 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 ());
  {
    double se = mean - 0.332747;
    unsigned int j = GNUNET_CONTAINER_multipeermap_size (peers);
    if (0 == j)
      j = 1; /* Avoid log2(0); can only happen if CORE didn't report
                connection to self yet */
    nsize = log2 (j);
    em->size_estimate = GNUNET_hton_double (GNUNET_MAX (se, nsize));
    em->std_deviation = GNUNET_hton_double (std_dev);
    GNUNET_STATISTICS_set (stats,
                           "# nodes in the network (estimate)",
                           (uint64_t) pow (2, GNUNET_MAX (se, nsize)),
                           GNUNET_NO);
  }
}


static void
handle_start (void *cls, const struct GNUNET_MessageHeader *message)
{
  struct GNUNET_SERVICE_Client *client = cls;
  struct GNUNET_MQ_Handle *mq;
  struct GNUNET_NSE_ClientMessage em;
  struct GNUNET_MQ_Envelope *env;

  (void) message;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Received START message from client\n");
  mq = GNUNET_SERVICE_client_get_mq (client);
  GNUNET_notification_context_add (nc, mq);
  setup_estimate_message (&em);
  env = GNUNET_MQ_msg_copy (&em.header);
  GNUNET_MQ_send (mq, env);
  GNUNET_SERVICE_client_continue (client);
}


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_us / (double) 2.0) -
         ((gnunet_nse_interval.rel_value_us / M_PI) *
          atan (matching_bits - current_size_estimate));
}


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;

  d = get_matching_bits_delay (matching_bits);
  i = (uint32_t) (d / (double) (hop_count_max + 1));
  ret.rel_value_us = i;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Randomizing flood using latencies up to %s\n",
              GNUNET_STRINGS_relative_time_to_string (ret, GNUNET_YES));
  ret.rel_value_us =
    GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, i + 1);
  return ret;
#else
  return GNUNET_TIME_UNIT_ZERO;
#endif
}


static void
pow_hash (const void *buf, size_t buf_len, struct GNUNET_HashCode *result)
{
  GNUNET_break (
    0 == gcry_kdf_derive (buf,
                          buf_len,
                          GCRY_KDF_SCRYPT,
                          1 /* subalgo */,
                          "gnunet-proof-of-work",
                          strlen ("gnunet-proof-of-work"),
                          2 /* iterations; keep cost of individual op small */,
                          sizeof (struct GNUNET_HashCode),
                          result));
}


static uint32_t
get_matching_bits (struct GNUNET_TIME_Absolute timestamp,
                   const struct GNUNET_PeerIdentity *id)
{
  struct GNUNET_HashCode timestamp_hash;
  struct GNUNET_HashCode pid_hash;

  GNUNET_CRYPTO_hash (&timestamp.abs_value_us,
                      sizeof (timestamp.abs_value_us),
                      &timestamp_hash);
  GNUNET_CRYPTO_hash (id, sizeof (struct GNUNET_PeerIdentity), &pid_hash);
  return GNUNET_CRYPTO_hash_matching_bits (&timestamp_hash, &pid_hash);
}


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_us =
      GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_WEAK, 50);
#else
    ret = GNUNET_TIME_UNIT_ZERO;
#endif
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Transmitting previous round behind schedule in %s\n",
                GNUNET_STRINGS_relative_time_to_string (ret, GNUNET_YES));
    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_us;
    ret.rel_value_us = (uint64_t) dist_delay;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "For round %s, delay for %u matching bits is %s\n",
                GNUNET_STRINGS_absolute_time_to_string (current_timestamp),
                (unsigned int) matching_bits,
                GNUNET_STRINGS_relative_time_to_string (ret, GNUNET_YES));
    /* 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;
}


static void
transmit_task_cb (void *cls)
{
  struct NSEPeerEntry *peer_entry = cls;
  unsigned int idx;
  struct GNUNET_MQ_Envelope *env;

  peer_entry->transmit_task = NULL;
  idx = estimate_index;
  if (GNUNET_NO == peer_entry->previous_round)
  {
    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_cb,
                                    peer_entry);
  }
  if ((0 == ntohl (size_estimate_messages[idx].hop_count)) &&
      (NULL != proof_task))
  {
    GNUNET_STATISTICS_update (stats,
                              "# flood messages not generated (no proof yet)",
                              1,
                              GNUNET_NO);
    return;
  }
  if (0 == ntohs (size_estimate_messages[idx].header.size))
  {
    GNUNET_STATISTICS_update (stats,
                              "# flood messages not generated (lack of history)",
                              1,
                              GNUNET_NO);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "In round %s, sending to `%s' estimate with %u bits\n",
              GNUNET_STRINGS_absolute_time_to_string (
                GNUNET_TIME_absolute_ntoh (
                  size_estimate_messages[idx].timestamp)),
              GNUNET_i2s (peer_entry->id),
              (unsigned int) ntohl (size_estimate_messages[idx].matching_bits));
  if (0 == ntohl (size_estimate_messages[idx].hop_count))
    GNUNET_STATISTICS_update (stats, "# flood messages started", 1, GNUNET_NO);
  GNUNET_STATISTICS_update (stats,
                            "# flood messages transmitted",
                            1,
                            GNUNET_NO);
#if ENABLE_NSE_HISTOGRAM
  peer_entry->transmitted_messages++;
  peer_entry->last_transmitted_size =
    ntohl (size_estimate_messages[idx].matching_bits);
#endif
  env = GNUNET_MQ_msg_copy (&size_estimate_messages[idx].header);
  GNUNET_MQ_send (peer_entry->mq, env);
}


static void
update_network_size_estimate ()
{
  struct GNUNET_NSE_ClientMessage em;

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


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_EddsaSignature));
  fm->matching_bits = htonl (matching_bits);
  fm->timestamp = GNUNET_TIME_absolute_hton (ts);
  fm->origin = my_identity;
  fm->proof_of_work = my_proof;
  if (nse_work_required > 0)
    GNUNET_assert (GNUNET_OK == GNUNET_CRYPTO_eddsa_sign (my_private_key,
                                                          &fm->purpose,
                                                          &fm->signature));
  else
    memset (&fm->signature, 0, sizeof (fm->signature));
}


static int
schedule_current_round (void *cls,
                        const struct GNUNET_PeerIdentity *key,
                        void *value)
{
  struct NSEPeerEntry *peer_entry = value;
  struct GNUNET_TIME_Relative delay;

  (void) cls;
  (void) key;
  if (NULL != peer_entry->transmit_task)
  {
    GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
    peer_entry->previous_round = GNUNET_NO;
  }
#if ENABLE_NSE_HISTOGRAM
  if (peer_entry->received_messages > 1)
    GNUNET_STATISTICS_update (stats,
                              "# extra messages",
                              peer_entry->received_messages - 1,
                              GNUNET_NO);
  peer_entry->transmitted_messages = 0;
  peer_entry->last_transmitted_size = 0;
  peer_entry->received_messages = 0;
#endif
  delay =
    get_transmit_delay ((GNUNET_NO == peer_entry->previous_round) ? -1 : 0);
  peer_entry->transmit_task =
    GNUNET_SCHEDULER_add_delayed (delay, &transmit_task_cb, peer_entry);
  return GNUNET_OK;
}


static void
update_flood_message (void *cls)
{
  struct GNUNET_TIME_Relative offset;

  (void) cls;
  flood_task = NULL;
  offset = GNUNET_TIME_absolute_get_remaining (next_timestamp);
  if (0 != offset.rel_value_us)
  {
    /* somehow run early, delay more */
    flood_task =
      GNUNET_SCHEDULER_add_delayed (offset, &update_flood_message, NULL);
    return;
  }
  estimate_index = (estimate_index + 1) % HISTORY_SIZE;
  if (estimate_count < HISTORY_SIZE)
    estimate_count++;
  current_timestamp = next_timestamp;
  next_timestamp =
    GNUNET_TIME_absolute_add (current_timestamp, gnunet_nse_interval);
  if ((current_timestamp.abs_value_us ==
       GNUNET_TIME_absolute_ntoh (next_message.timestamp).abs_value_us) &&
      (get_matching_bits (current_timestamp, &my_identity) <
       ntohl (next_message.matching_bits)))
  {
    /* 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 (unsigned int i = 0; i < HISTORY_SIZE; i++)
    hop_count_max =
      GNUNET_MAX (ntohl (size_estimate_messages[i].hop_count), hop_count_max);
  GNUNET_CONTAINER_multipeermap_iterate (peers, &schedule_current_round, NULL);
  flood_task =
    GNUNET_SCHEDULER_add_at (next_timestamp, &update_flood_message, NULL);
}


static unsigned int
count_leading_zeroes (const struct 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;
}


static int
check_proof_of_work (const struct GNUNET_CRYPTO_EddsaPublicKey *pkey,
                     uint64_t val)
{
  char buf[sizeof (struct GNUNET_CRYPTO_EddsaPublicKey) +
           sizeof (val)] GNUNET_ALIGN;
  struct GNUNET_HashCode result;

  GNUNET_memcpy (buf, &val, sizeof (val));
  GNUNET_memcpy (&buf[sizeof (val)],
                 pkey,
                 sizeof (struct GNUNET_CRYPTO_EddsaPublicKey));
  pow_hash (buf, sizeof (buf), &result);
  return (count_leading_zeroes (&result) >= nse_work_required) ? GNUNET_YES
                                                               : GNUNET_NO;
}


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);
}


static void
find_proof (void *cls)
{
#define ROUND_SIZE 10
  uint64_t counter;
  char buf[sizeof (struct GNUNET_CRYPTO_EddsaPublicKey) +
           sizeof (uint64_t)] GNUNET_ALIGN;
  struct GNUNET_HashCode result;
  unsigned int i;

  (void) cls;
  proof_task = NULL;
  GNUNET_memcpy (&buf[sizeof (uint64_t)],
                 &my_identity,
                 sizeof (struct GNUNET_PeerIdentity));
  i = 0;
  counter = my_proof;
  while ((counter != UINT64_MAX) && (i < ROUND_SIZE))
  {
    GNUNET_memcpy (buf, &counter, sizeof (uint64_t));
    pow_hash (buf, sizeof (buf), &result);
    if (nse_work_required <= count_leading_zeroes (&result))
    {
      my_proof = counter;
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Proof of work found: %llu!\n",
                  (unsigned long long) GNUNET_ntohll (counter));
      write_proof ();
      setup_flood_message (estimate_index, current_timestamp);
      return;
    }
    counter++;
    i++;
  }
  if (my_proof / (100 * ROUND_SIZE) < counter / (100 * ROUND_SIZE))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Testing proofs currently at %llu\n",
                (unsigned long long) counter);
    /* remember progress every 100 rounds */
    my_proof = counter;
    write_proof ();
  }
  else
  {
    my_proof = counter;
  }
  proof_task =
    GNUNET_SCHEDULER_add_delayed_with_priority (proof_find_delay,
                                                GNUNET_SCHEDULER_PRIORITY_IDLE,
                                                &find_proof,
                                                NULL);
}


static int
verify_message_crypto (const struct GNUNET_NSE_FloodMessage *incoming_flood)
{
  if (GNUNET_YES != check_proof_of_work (&incoming_flood->origin.public_key,
                                         incoming_flood->proof_of_work))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "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_eddsa_verify (GNUNET_SIGNATURE_PURPOSE_NSE_SEND,
                                   &incoming_flood->purpose,
                                   &incoming_flood->signature,
                                   &incoming_flood->origin.public_key)))
  {
    GNUNET_break_op (0);
    return GNUNET_NO;
  }
  return GNUNET_YES;
}


static int
update_flood_times (void *cls,
                    const struct GNUNET_PeerIdentity *key,
                    void *value)
{
  struct NSEPeerEntry *exclude = cls;
  struct NSEPeerEntry *peer_entry = value;
  struct GNUNET_TIME_Relative delay;

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


static void
handle_p2p_estimate (void *cls,
                     const struct GNUNET_NSE_FloodMessage *incoming_flood)
{
  struct NSEPeerEntry *peer_entry = cls;
  struct GNUNET_TIME_Absolute ts;
  uint32_t matching_bits;
  unsigned int idx;

#if ENABLE_NSE_HISTOGRAM
  {
    uint64_t t;

    t = GNUNET_TIME_absolute_get ().abs_value_us;
    if (NULL != lh)
      GNUNET_TESTBED_LOGGER_write (lh, &t, sizeof (uint64_t));
    if (NULL != histogram)
      GNUNET_BIO_write_int64 (histogram, t);
  }
#endif
  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_snprintf (origin,
                     sizeof (origin),
                     "%s",
                     GNUNET_i2s (&incoming_flood->origin));
    GNUNET_snprintf (pred, sizeof (pred), "%s", GNUNET_i2s (peer_entry->id));
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Flood at %s from `%s' via `%s' at `%s' with bits %u\n",
                GNUNET_STRINGS_absolute_time_to_string (
                  GNUNET_TIME_absolute_ntoh (incoming_flood->timestamp)),
                origin,
                pred,
                GNUNET_i2s (&my_identity),
                (unsigned int) matching_bits);
  }
#endif

#if ENABLE_NSE_HISTOGRAM
  peer_entry->received_messages++;
  if (peer_entry->transmitted_messages > 0 &&
      peer_entry->last_transmitted_size >= matching_bits)
    GNUNET_STATISTICS_update (stats, "# cross messages", 1, GNUNET_NO);
#endif

  ts = GNUNET_TIME_absolute_ntoh (incoming_flood->timestamp);
  if (ts.abs_value_us == current_timestamp.abs_value_us)
    idx = estimate_index;
  else if (ts.abs_value_us ==
           current_timestamp.abs_value_us - gnunet_nse_interval.rel_value_us)
    idx = (estimate_index + HISTORY_SIZE - 1) % HISTORY_SIZE;
  else if (ts.abs_value_us == next_timestamp.abs_value_us)
  {
    if (matching_bits <= ntohl (next_message.matching_bits))
      return; /* ignore, simply too early/late */
    if (GNUNET_YES != verify_message_crypto (incoming_flood))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "Peer %s is likely ill-configured!\n",
                  GNUNET_i2s (peer_entry->id));
      GNUNET_break_op (0);
      return;
    }
    next_message = *incoming_flood;
    return;
  }
  else
  {
    GNUNET_STATISTICS_update (stats,
                              "# flood messages discarded (clock skew too large)",
                              1,
                              GNUNET_NO);
    return;
  }
  if (0 == (GNUNET_memcmp (peer_entry->id, &my_identity)))
  {
    /* send to self, update our own estimate IF this also comes from us! */
    if (0 == GNUNET_memcmp (&incoming_flood->origin, &my_identity))
      update_network_size_estimate ();
    return;
  }
  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. Even if we didn't talk to this peer in
       the previous round, we should no longer send it stale information as it
       told us about the current round! */
    peer_entry->previous_round = GNUNET_YES;
    if (idx != estimate_index)
    {
      /* do not transmit information for the previous round to this peer
         anymore (but allow current round) */
      return;
    }
    /* got up-to-date information for current round, cancel transmission to
     * this peer altogether */
    if (NULL != peer_entry->transmit_task)
    {
      GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
      peer_entry->transmit_task = NULL;
    }
    return;
  }
  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->transmit_task)
      GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
    peer_entry->transmit_task =
      GNUNET_SCHEDULER_add_now (&transmit_task_cb, 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;
  }
  if (GNUNET_YES != verify_message_crypto (incoming_flood))
  {
    GNUNET_break_op (0);
    return;
  }
  GNUNET_assert (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.
   */
  peer_entry->previous_round = GNUNET_YES;
  if (idx == estimate_index)
  {
    /* cancel any activity for current round */
    if (NULL != peer_entry->transmit_task)
    {
      GNUNET_SCHEDULER_cancel (peer_entry->transmit_task);
      peer_entry->transmit_task = NULL;
    }
  }
  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);
  GNUNET_STATISTICS_set (stats,
                         "# estimated network diameter",
                         hop_count_max,
                         GNUNET_NO);

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

  /* flood to rest */
  GNUNET_CONTAINER_multipeermap_iterate (peers,
                                         &update_flood_times,
                                         peer_entry);
}


static void *
handle_core_connect (void *cls,
                     const struct GNUNET_PeerIdentity *peer,
                     struct GNUNET_MQ_Handle *mq)
{
  struct NSEPeerEntry *peer_entry;

  (void) cls;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Peer `%s' connected to us\n",
              GNUNET_i2s (peer));
  /* set our default transmission options */
  GNUNET_MQ_set_options (mq, NSE_PRIORITY);
  /* create our peer entry for this peer */
  peer_entry = GNUNET_new (struct NSEPeerEntry);
  peer_entry->id = peer;
  peer_entry->mq = mq;
  GNUNET_assert (GNUNET_OK ==
                 GNUNET_CONTAINER_multipeermap_put (
                   peers,
                   peer_entry->id,
                   peer_entry,
                   GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));
  peer_entry->transmit_task =
    GNUNET_SCHEDULER_add_delayed (get_transmit_delay (-1),
                                  &transmit_task_cb,
                                  peer_entry);
  GNUNET_STATISTICS_update (stats, "# peers connected", 1, GNUNET_NO);
  return peer_entry;
}


static void
handle_core_disconnect (void *cls,
                        const struct GNUNET_PeerIdentity *peer,
                        void *internal_cls)
{
  struct NSEPeerEntry *pos = internal_cls;

  (void) cls;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Peer `%s' disconnected from us\n",
              GNUNET_i2s (peer));
  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CONTAINER_multipeermap_remove (peers, peer, pos));
  if (NULL != pos->transmit_task)
  {
    GNUNET_SCHEDULER_cancel (pos->transmit_task);
    pos->transmit_task = NULL;
  }
  GNUNET_free (pos);
  GNUNET_STATISTICS_update (stats, "# peers connected", -1, GNUNET_NO);
}


#if ENABLE_NSE_HISTOGRAM

static void
flush_comp_cb (void *cls, size_t size)
{
  (void) cls;
  (void) size;
  GNUNET_TESTBED_LOGGER_disconnect (lh);
  lh = NULL;
}
#endif


static void
shutdown_task (void *cls)
{
  (void) cls;
  if (NULL != flood_task)
  {
    GNUNET_SCHEDULER_cancel (flood_task);
    flood_task = NULL;
  }
  if (NULL != proof_task)
  {
    GNUNET_SCHEDULER_cancel (proof_task);
    proof_task = NULL;
    write_proof (); /* remember progress */
  }
  if (NULL != nc)
  {
    GNUNET_notification_context_destroy (nc);
    nc = NULL;
  }
  if (NULL != core_api)
  {
    GNUNET_CORE_disconnect (core_api);
    core_api = NULL;
  }
  if (NULL != stats)
  {
    GNUNET_STATISTICS_destroy (stats, GNUNET_NO);
    stats = NULL;
  }
  if (NULL != peers)
  {
    GNUNET_CONTAINER_multipeermap_destroy (peers);
    peers = NULL;
  }
  if (NULL != my_private_key)
  {
    GNUNET_free (my_private_key);
    my_private_key = NULL;
  }
#if ENABLE_NSE_HISTOGRAM
  if (NULL != logger_test)
  {
    GNUNET_CLIENT_service_test_cancel (logger_test);
    logger_test = NULL;
  }
  if (NULL != lh)
  {
    GNUNET_TESTBED_LOGGER_flush (lh, &flush_comp_cb, NULL);
  }
  if (NULL != histogram)
  {
    GNUNET_BIO_write_close (histogram);
    histogram = NULL;
  }
#endif
}


static void
core_init (void *cls, const struct GNUNET_PeerIdentity *identity)
{
  struct GNUNET_TIME_Absolute now;
  struct GNUNET_TIME_Absolute prev_time;

  (void) cls;
  if (NULL == identity)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR, "Connection to core FAILED!\n");
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  GNUNET_assert (0 == GNUNET_memcmp (&my_identity, identity));
  now = GNUNET_TIME_absolute_get ();
  current_timestamp.abs_value_us =
    (now.abs_value_us / gnunet_nse_interval.rel_value_us) *
    gnunet_nse_interval.rel_value_us;
  next_timestamp =
    GNUNET_TIME_absolute_add (current_timestamp, gnunet_nse_interval);
  estimate_index = HISTORY_SIZE - 1;
  estimate_count = 0;
  if (GNUNET_YES == check_proof_of_work (&my_identity.public_key, my_proof))
  {
    int idx = (estimate_index + HISTORY_SIZE - 1) % HISTORY_SIZE;
    prev_time.abs_value_us =
      current_timestamp.abs_value_us - gnunet_nse_interval.rel_value_us;
    setup_flood_message (idx, prev_time);
    setup_flood_message (estimate_index, current_timestamp);
    estimate_count++;
  }
  flood_task =
    GNUNET_SCHEDULER_add_at (next_timestamp, &update_flood_message, NULL);
}


#if ENABLE_NSE_HISTOGRAM

static void
status_cb (void *cls, int status)
{
  (void) cls;
  logger_test = NULL;
  if (GNUNET_YES != status)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING, "Testbed logger not running\n");
    return;
  }
  if (NULL == (lh = GNUNET_TESTBED_LOGGER_connect (cfg)))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Cannot connect to the testbed logger.  Exiting.\n");
    GNUNET_SCHEDULER_shutdown ();
  }
}
#endif


static void
run (void *cls,
     const struct GNUNET_CONFIGURATION_Handle *c,
     struct GNUNET_SERVICE_Handle *service)
{
  struct GNUNET_MQ_MessageHandler core_handlers[] =
    {GNUNET_MQ_hd_fixed_size (p2p_estimate,
                              GNUNET_MESSAGE_TYPE_NSE_P2P_FLOOD,
                              struct GNUNET_NSE_FloodMessage,
                              NULL),
     GNUNET_MQ_handler_end ()};
  char *proof;
  struct GNUNET_CRYPTO_EddsaPrivateKey *pk;

  (void) cls;
  (void) service;
  cfg = c;
  if (GNUNET_OK != GNUNET_CONFIGURATION_get_value_time (cfg,
                                                        "NSE",
                                                        "INTERVAL",
                                                        &gnunet_nse_interval))
  {
    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR, "NSE", "INTERVAL");
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  if (GNUNET_OK != GNUNET_CONFIGURATION_get_value_time (cfg,
                                                        "NSE",
                                                        "WORKDELAY",
                                                        &proof_find_delay))
  {
    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR, "NSE", "WORKDELAY");
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  if (GNUNET_OK != GNUNET_CONFIGURATION_get_value_number (cfg,
                                                          "NSE",
                                                          "WORKBITS",
                                                          &nse_work_required))
  {
    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR, "NSE", "WORKBITS");
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  if (nse_work_required >= sizeof (struct GNUNET_HashCode) * 8)
  {
    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
                               "NSE",
                               "WORKBITS",
                               _ ("Value is too large.\n"));
    GNUNET_SCHEDULER_shutdown ();
    return;
  }

#if ENABLE_NSE_HISTOGRAM
  {
    char *histogram_dir;
    char *histogram_fn;

    if (GNUNET_OK == GNUNET_CONFIGURATION_get_value_filename (cfg,
                                                              "NSE",
                                                              "HISTOGRAM_DIR",
                                                              &histogram_dir))
    {
      GNUNET_assert (
        0 < GNUNET_asprintf (&histogram_fn, "%s/timestamps", histogram_dir));
      GNUNET_free (histogram_dir);
      histogram = GNUNET_BIO_write_open (histogram_fn);
      if (NULL == histogram)
        GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                    "Unable to open histogram file `%s'\n",
                    histogram_fn);
      GNUNET_free (histogram_fn);
    }
    logger_test = GNUNET_CLIENT_service_test ("testbed-logger",
                                              cfg,
                                              GNUNET_TIME_UNIT_SECONDS,
                                              &status_cb,
                                              NULL);
  }
#endif

  GNUNET_SCHEDULER_add_shutdown (&shutdown_task, NULL);
  pk = GNUNET_CRYPTO_eddsa_key_create_from_configuration (cfg);
  GNUNET_assert (NULL != pk);
  my_private_key = pk;
  GNUNET_CRYPTO_eddsa_key_get_public (my_private_key, &my_identity.public_key);
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_filename (cfg, "NSE", "PROOFFILE", &proof))
  {
    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR, "NSE", "PROOFFILE");
    GNUNET_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_multipeermap_create (128, GNUNET_YES);
  nc = GNUNET_notification_context_create (1);
  /* Connect to core service and register core handlers */
  core_api =
    GNUNET_CORE_connect (cfg, /* Main configuration */
                         NULL, /* Closure passed to functions */
                         &core_init, /* Call core_init once connected */
                         &handle_core_connect, /* Handle connects */
                         &handle_core_disconnect, /* Handle disconnects */
                         core_handlers); /* Register these handlers */
  if (NULL == core_api)
  {
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  stats = GNUNET_STATISTICS_create ("nse", cfg);
}


static void *
client_connect_cb (void *cls,
                   struct GNUNET_SERVICE_Client *c,
                   struct GNUNET_MQ_Handle *mq)
{
  (void) cls;
  (void) mq;
  return c;
}


static void
client_disconnect_cb (void *cls,
                      struct GNUNET_SERVICE_Client *c,
                      void *internal_cls)
{
  (void) cls;
  GNUNET_assert (c == internal_cls);
}


GNUNET_SERVICE_MAIN ("nse",
                     GNUNET_SERVICE_OPTION_NONE,
                     &run,
                     &client_connect_cb,
                     &client_disconnect_cb,
                     NULL,
                     GNUNET_MQ_hd_fixed_size (start,
                                              GNUNET_MESSAGE_TYPE_NSE_START,
                                              struct GNUNET_MessageHeader,
                                              NULL),
                     GNUNET_MQ_handler_end ());


#if defined(LINUX) && defined(__GLIBC__)
#include <malloc.h>

void __attribute__ ((constructor)) GNUNET_ARM_memory_init ()
{
  mallopt (M_TRIM_THRESHOLD, 4 * 1024);
  mallopt (M_TOP_PAD, 1 * 1024);
  malloc_trim (0);
}
#endif


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