tor/src/feature/stats/geoip_stats.c

/* Copyright (c) 2007-2019, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file geoip.c
 * \brief Functions related to maintaining an IP-to-country database;
 * to summarizing client connections by country to entry guards, bridges,
 * and directory servers; and for statistics on answering network status
 * requests.
 *
 * There are two main kinds of functions in this module: geoip functions,
 * which map groups of IPv4 and IPv6 addresses to country codes, and
 * statistical functions, which collect statistics about different kinds of
 * per-country usage.
 *
 * The geoip lookup tables are implemented as sorted lists of disjoint address
 * ranges, each mapping to a singleton geoip_country_t.  These country objects
 * are also indexed by their names in a hashtable.
 *
 * The tables are populated from disk at startup by the geoip_load_file()
 * function.  For more information on the file format they read, see that
 * function.  See the scripts and the README file in src/config for more
 * information about how those files are generated.
 *
 * Tor uses GeoIP information in order to implement user requests (such as
 * ExcludeNodes {cc}), and to keep track of how much usage relays are getting
 * for each country.
 */

#include "core/or/or.h"

#include "ht.h"
#include "lib/buf/buffers.h"
#include "app/config/config.h"
#include "feature/control/control_events.h"
#include "feature/client/dnsserv.h"
#include "core/or/dos.h"
#include "lib/geoip/geoip.h"
#include "feature/stats/geoip_stats.h"
#include "feature/nodelist/routerlist.h"

#include "lib/container/order.h"
#include "lib/time/tvdiff.h"

/** Number of entries in n_v3_ns_requests */
static size_t n_v3_ns_requests_len = 0;
/** Array, indexed by country index, of number of v3 networkstatus requests
 * received from that country */
static uint32_t *n_v3_ns_requests;

/* Total size in bytes of the geoip client history cache. Used by the OOM
 * handler. */
static size_t geoip_client_history_cache_size;

/* Increment the geoip client history cache size counter with the given bytes.
 * This prevents an overflow and set it to its maximum in that case. */
static inline void
geoip_increment_client_history_cache_size(size_t bytes)
{
  /* This is shockingly high, lets log it so it can be reported. */
  IF_BUG_ONCE(geoip_client_history_cache_size > (SIZE_MAX - bytes)) {
    geoip_client_history_cache_size = SIZE_MAX;
    return;
  }
  geoip_client_history_cache_size += bytes;
}

/* Decrement the geoip client history cache size counter with the given bytes.
 * This prevents an underflow and set it to 0 in that case. */
static inline void
geoip_decrement_client_history_cache_size(size_t bytes)
{
  /* Going below 0 means that we either allocated an entry without
   * incrementing the counter or we have different sizes when allocating and
   * freeing. It shouldn't happened so log it. */
  IF_BUG_ONCE(geoip_client_history_cache_size < bytes) {
    geoip_client_history_cache_size = 0;
    return;
  }
  geoip_client_history_cache_size -= bytes;
}

/** Add 1 to the count of v3 ns requests received from <b>country</b>. */
static void
increment_v3_ns_request(country_t country)
{
  if (country < 0)
    return;

  if ((size_t)country >= n_v3_ns_requests_len) {
    /* We need to reallocate the array. */
    size_t new_len;
    if (n_v3_ns_requests_len == 0)
      new_len = 256;
    else
      new_len = n_v3_ns_requests_len * 2;
    if (new_len <= (size_t)country)
      new_len = ((size_t)country)+1;
    n_v3_ns_requests = tor_reallocarray(n_v3_ns_requests, new_len,
                                        sizeof(uint32_t));
    memset(n_v3_ns_requests + n_v3_ns_requests_len, 0,
           sizeof(uint32_t)*(new_len - n_v3_ns_requests_len));
    n_v3_ns_requests_len = new_len;
  }

  n_v3_ns_requests[country] += 1;
}

/** Return 1 if we should collect geoip stats on bridge users, and
 * include them in our extrainfo descriptor. Else return 0. */
int
should_record_bridge_info(const or_options_t *options)
{
  return options->BridgeRelay && options->BridgeRecordUsageByCountry;
}

/** Largest allowable value for last_seen_in_minutes.  (It's a 30-bit field,
 * so it can hold up to (1u<<30)-1, or 0x3fffffffu.
 */
#define MAX_LAST_SEEN_IN_MINUTES 0X3FFFFFFFu

/** Map from client IP address to last time seen. */
static HT_HEAD(clientmap, clientmap_entry_t) client_history =
     HT_INITIALIZER();

/** Hashtable helper: compute a hash of a clientmap_entry_t. */
static inline unsigned
clientmap_entry_hash(const clientmap_entry_t *a)
{
  unsigned h = (unsigned) tor_addr_hash(&a->addr);

  if (a->transport_name)
    h += (unsigned) siphash24g(a->transport_name, strlen(a->transport_name));

  return h;
}
/** Hashtable helper: compare two clientmap_entry_t values for equality. */
static inline int
clientmap_entries_eq(const clientmap_entry_t *a, const clientmap_entry_t *b)
{
  if (strcmp_opt(a->transport_name, b->transport_name))
    return 0;

  return !tor_addr_compare(&a->addr, &b->addr, CMP_EXACT) &&
         a->action == b->action;
}

HT_PROTOTYPE(clientmap, clientmap_entry_t, node, clientmap_entry_hash,
             clientmap_entries_eq)
HT_GENERATE2(clientmap, clientmap_entry_t, node, clientmap_entry_hash,
             clientmap_entries_eq, 0.6, tor_reallocarray_, tor_free_)

#define clientmap_entry_free(ent) \
  FREE_AND_NULL(clientmap_entry_t, clientmap_entry_free_, ent)

/** Return the size of a client map entry. */
static inline size_t
clientmap_entry_size(const clientmap_entry_t *ent)
{
  tor_assert(ent);
  return (sizeof(clientmap_entry_t) +
          (ent->transport_name ? strlen(ent->transport_name) : 0));
}

/** Free all storage held by <b>ent</b>. */
static void
clientmap_entry_free_(clientmap_entry_t *ent)
{
  if (!ent)
    return;

  /* This entry is about to be freed so pass it to the DoS subsystem to see if
   * any actions can be taken about it. */
  dos_geoip_entry_about_to_free(ent);
  geoip_decrement_client_history_cache_size(clientmap_entry_size(ent));

  tor_free(ent->transport_name);
  tor_free(ent);
}

/* Return a newly allocated clientmap entry with the given action and address
 * that are mandatory. The transport_name can be optional. This can't fail. */
static clientmap_entry_t *
clientmap_entry_new(geoip_client_action_t action, const tor_addr_t *addr,
                    const char *transport_name)
{
  clientmap_entry_t *entry;

  tor_assert(action == GEOIP_CLIENT_CONNECT ||
             action == GEOIP_CLIENT_NETWORKSTATUS);
  tor_assert(addr);

  entry = tor_malloc_zero(sizeof(clientmap_entry_t));
  entry->action = action;
  tor_addr_copy(&entry->addr, addr);
  if (transport_name) {
    entry->transport_name = tor_strdup(transport_name);
  }

  /* Allocated and initialized, note down its size for the OOM handler. */
  geoip_increment_client_history_cache_size(clientmap_entry_size(entry));

  return entry;
}

/** Clear history of connecting clients used by entry and bridge stats. */
static void
client_history_clear(void)
{
  clientmap_entry_t **ent, **next, *this;
  for (ent = HT_START(clientmap, &client_history); ent != NULL;
       ent = next) {
    if ((*ent)->action == GEOIP_CLIENT_CONNECT) {
      this = *ent;
      next = HT_NEXT_RMV(clientmap, &client_history, ent);
      clientmap_entry_free(this);
    } else {
      next = HT_NEXT(clientmap, &client_history, ent);
    }
  }
}

/** Note that we've seen a client connect from the IP <b>addr</b>
 * at time <b>now</b>. Ignored by all but bridges and directories if
 * configured accordingly. */
void
geoip_note_client_seen(geoip_client_action_t action,
                       const tor_addr_t *addr,
                       const char *transport_name,
                       time_t now)
{
  const or_options_t *options = get_options();
  clientmap_entry_t *ent;

  if (action == GEOIP_CLIENT_CONNECT) {
    /* Only remember statistics if the DoS mitigation subsystem is enabled. If
     * not, only if as entry guard or as bridge. */
    if (!dos_enabled()) {
      if (!options->EntryStatistics && !should_record_bridge_info(options)) {
        return;
      }
    }
  } else {
    /* Only gather directory-request statistics if configured, and
     * forcibly disable them on bridge authorities. */
    if (!options->DirReqStatistics || options->BridgeAuthoritativeDir)
      return;
  }

  log_debug(LD_GENERAL, "Seen client from '%s' with transport '%s'.",
            safe_str_client(fmt_addr((addr))),
            transport_name ? transport_name : "<no transport>");

  ent = geoip_lookup_client(addr, transport_name, action);
  if (! ent) {
    ent = clientmap_entry_new(action, addr, transport_name);
    HT_INSERT(clientmap, &client_history, ent);
  }
  if (now / 60 <= (int)MAX_LAST_SEEN_IN_MINUTES && now >= 0)
    ent->last_seen_in_minutes = (unsigned)(now/60);
  else
    ent->last_seen_in_minutes = 0;

  if (action == GEOIP_CLIENT_NETWORKSTATUS) {
    int country_idx = geoip_get_country_by_addr(addr);
    if (country_idx < 0)
      country_idx = 0; /** unresolved requests are stored at index 0. */
    IF_BUG_ONCE(country_idx > COUNTRY_MAX) {
      return;
    }
    increment_v3_ns_request((country_t) country_idx);
  }
}

/** HT_FOREACH helper: remove a clientmap_entry_t from the hashtable if it's
 * older than a certain time. */
static int
remove_old_client_helper_(struct clientmap_entry_t *ent, void *_cutoff)
{
  time_t cutoff = *(time_t*)_cutoff / 60;
  if (ent->last_seen_in_minutes < cutoff) {
    clientmap_entry_free(ent);
    return 1;
  } else {
    return 0;
  }
}

/** Forget about all clients that haven't connected since <b>cutoff</b>. */
void
geoip_remove_old_clients(time_t cutoff)
{
  clientmap_HT_FOREACH_FN(&client_history,
                          remove_old_client_helper_,
                          &cutoff);
}

/* Return a client entry object matching the given address, transport name and
 * geoip action from the clientmap. NULL if not found. The transport_name can
 * be NULL. */
clientmap_entry_t *
geoip_lookup_client(const tor_addr_t *addr, const char *transport_name,
                    geoip_client_action_t action)
{
  clientmap_entry_t lookup;

  tor_assert(addr);

  /* We always look for a client connection with no transport. */
  tor_addr_copy(&lookup.addr, addr);
  lookup.action = action;
  lookup.transport_name = (char *) transport_name;

  return HT_FIND(clientmap, &client_history, &lookup);
}

/* Cleanup client entries older than the cutoff. Used for the OOM. Return the
 * number of bytes freed. If 0 is returned, nothing was freed. */
static size_t
oom_clean_client_entries(time_t cutoff)
{
  size_t bytes = 0;
  clientmap_entry_t **ent, **ent_next;

  for (ent = HT_START(clientmap, &client_history); ent; ent = ent_next) {
    clientmap_entry_t *entry = *ent;
    if (entry->last_seen_in_minutes < (cutoff / 60)) {
      ent_next = HT_NEXT_RMV(clientmap, &client_history, ent);
      bytes += clientmap_entry_size(entry);
      clientmap_entry_free(entry);
    } else {
      ent_next = HT_NEXT(clientmap, &client_history, ent);
    }
  }
  return bytes;
}

/* Below this minimum lifetime, the OOM won't cleanup any entries. */
#define GEOIP_CLIENT_CACHE_OOM_MIN_CUTOFF (4 * 60 * 60)
/* The OOM moves the cutoff by that much every run. */
#define GEOIP_CLIENT_CACHE_OOM_STEP (15 * 50)

/* Cleanup the geoip client history cache called from the OOM handler. Return
 * the amount of bytes removed. This can return a value below or above
 * min_remove_bytes but will stop as oon as the min_remove_bytes has been
 * reached. */
size_t
geoip_client_cache_handle_oom(time_t now, size_t min_remove_bytes)
{
  time_t k;
  size_t bytes_removed = 0;

  /* Our OOM handler called with 0 bytes to remove is a code flow error. */
  tor_assert(min_remove_bytes != 0);

  /* Set k to the initial cutoff of an entry. We then going to move it by step
   * to try to remove as much as we can. */
  k = WRITE_STATS_INTERVAL;

  do {
    time_t cutoff;

    /* If k has reached the minimum lifetime, we have to stop else we might
     * remove every single entries which would be pretty bad for the DoS
     * mitigation subsystem if by just filling the geoip cache, it was enough
     * to trigger the OOM and clean every single entries. */
    if (k <= GEOIP_CLIENT_CACHE_OOM_MIN_CUTOFF) {
      break;
    }

    cutoff = now - k;
    bytes_removed += oom_clean_client_entries(cutoff);
    k -= GEOIP_CLIENT_CACHE_OOM_STEP;
  } while (bytes_removed < min_remove_bytes);

  return bytes_removed;
}

/* Return the total size in bytes of the client history cache. */
size_t
geoip_client_cache_total_allocation(void)
{
  return geoip_client_history_cache_size;
}

/** How many responses are we giving to clients requesting v3 network
 * statuses? */
static uint32_t ns_v3_responses[GEOIP_NS_RESPONSE_NUM];

/** Note that we've rejected a client's request for a v3 network status
 * for reason <b>reason</b> at time <b>now</b>. */
void
geoip_note_ns_response(geoip_ns_response_t response)
{
  static int arrays_initialized = 0;
  if (!get_options()->DirReqStatistics)
    return;
  if (!arrays_initialized) {
    memset(ns_v3_responses, 0, sizeof(ns_v3_responses));
    arrays_initialized = 1;
  }
  tor_assert(response < GEOIP_NS_RESPONSE_NUM);
  ns_v3_responses[response]++;
}

/** Do not mention any country from which fewer than this number of IPs have
 * connected.  This conceivably avoids reporting information that could
 * deanonymize users, though analysis is lacking. */
#define MIN_IPS_TO_NOTE_COUNTRY 1
/** Do not report any geoip data at all if we have fewer than this number of
 * IPs to report about. */
#define MIN_IPS_TO_NOTE_ANYTHING 1
/** When reporting geoip data about countries, round up to the nearest
 * multiple of this value. */
#define IP_GRANULARITY 8

/** Helper type: used to sort per-country totals by value. */
typedef struct c_hist_t {
  char country[3]; /**< Two-letter country code. */
  unsigned total; /**< Total IP addresses seen in this country. */
} c_hist_t;

/** Sorting helper: return -1, 1, or 0 based on comparison of two
 * geoip_ipv4_entry_t.  Sort in descending order of total, and then by country
 * code. */
static int
c_hist_compare_(const void **_a, const void **_b)
{
  const c_hist_t *a = *_a, *b = *_b;
  if (a->total > b->total)
    return -1;
  else if (a->total < b->total)
    return 1;
  else
    return strcmp(a->country, b->country);
}

/** When there are incomplete directory requests at the end of a 24-hour
 * period, consider those requests running for longer than this timeout as
 * failed, the others as still running. */
#define DIRREQ_TIMEOUT (10*60)

/** Entry in a map from either chan->global_identifier for direct requests
 * or a unique circuit identifier for tunneled requests to request time,
 * response size, and completion time of a network status request. Used to
 * measure download times of requests to derive average client
 * bandwidths. */
typedef struct dirreq_map_entry_t {
  HT_ENTRY(dirreq_map_entry_t) node;
  /** Unique identifier for this network status request; this is either the
   * chan->global_identifier of the dir channel (direct request) or a new
   * locally unique identifier of a circuit (tunneled request). This ID is
   * only unique among other direct or tunneled requests, respectively. */
  uint64_t dirreq_id;
  unsigned int state:3; /**< State of this directory request. */
  unsigned int type:1; /**< Is this a direct or a tunneled request? */
  unsigned int completed:1; /**< Is this request complete? */
  /** When did we receive the request and started sending the response? */
  struct timeval request_time;
  size_t response_size; /**< What is the size of the response in bytes? */
  struct timeval completion_time; /**< When did the request succeed? */
} dirreq_map_entry_t;

/** Map of all directory requests asking for v2 or v3 network statuses in
 * the current geoip-stats interval. Values are
 * of type *<b>dirreq_map_entry_t</b>. */
static HT_HEAD(dirreqmap, dirreq_map_entry_t) dirreq_map =
     HT_INITIALIZER();

static int
dirreq_map_ent_eq(const dirreq_map_entry_t *a,
                  const dirreq_map_entry_t *b)
{
  return a->dirreq_id == b->dirreq_id && a->type == b->type;
}

/* DOCDOC dirreq_map_ent_hash */
static unsigned
dirreq_map_ent_hash(const dirreq_map_entry_t *entry)
{
  unsigned u = (unsigned) entry->dirreq_id;
  u += entry->type << 20;
  return u;
}

HT_PROTOTYPE(dirreqmap, dirreq_map_entry_t, node, dirreq_map_ent_hash,
             dirreq_map_ent_eq)
HT_GENERATE2(dirreqmap, dirreq_map_entry_t, node, dirreq_map_ent_hash,
             dirreq_map_ent_eq, 0.6, tor_reallocarray_, tor_free_)

/** Helper: Put <b>entry</b> into map of directory requests using
 * <b>type</b> and <b>dirreq_id</b> as key parts. If there is
 * already an entry for that key, print out a BUG warning and return. */
static void
dirreq_map_put_(dirreq_map_entry_t *entry, dirreq_type_t type,
               uint64_t dirreq_id)
{
  dirreq_map_entry_t *old_ent;
  tor_assert(entry->type == type);
  tor_assert(entry->dirreq_id == dirreq_id);

  /* XXXX we could switch this to HT_INSERT some time, since it seems that
   * this bug doesn't happen. But since this function doesn't seem to be
   * critical-path, it's sane to leave it alone. */
  old_ent = HT_REPLACE(dirreqmap, &dirreq_map, entry);
  if (old_ent && old_ent != entry) {
    log_warn(LD_BUG, "Error when putting directory request into local "
             "map. There was already an entry for the same identifier.");
    return;
  }
}

/** Helper: Look up and return an entry in the map of directory requests
 * using <b>type</b> and <b>dirreq_id</b> as key parts. If there
 * is no such entry, return NULL. */
static dirreq_map_entry_t *
dirreq_map_get_(dirreq_type_t type, uint64_t dirreq_id)
{
  dirreq_map_entry_t lookup;
  lookup.type = type;
  lookup.dirreq_id = dirreq_id;
  return HT_FIND(dirreqmap, &dirreq_map, &lookup);
}

/** Note that an either direct or tunneled (see <b>type</b>) directory
 * request for a v3 network status with unique ID <b>dirreq_id</b> of size
 * <b>response_size</b> has started. */
void
geoip_start_dirreq(uint64_t dirreq_id, size_t response_size,
                   dirreq_type_t type)
{
  dirreq_map_entry_t *ent;
  if (!get_options()->DirReqStatistics)
    return;
  ent = tor_malloc_zero(sizeof(dirreq_map_entry_t));
  ent->dirreq_id = dirreq_id;
  tor_gettimeofday(&ent->request_time);
  ent->response_size = response_size;
  ent->type = type;
  dirreq_map_put_(ent, type, dirreq_id);
}

/** Change the state of the either direct or tunneled (see <b>type</b>)
 * directory request with <b>dirreq_id</b> to <b>new_state</b> and
 * possibly mark it as completed. If no entry can be found for the given
 * key parts (e.g., if this is a directory request that we are not
 * measuring, or one that was started in the previous measurement period),
 * or if the state cannot be advanced to <b>new_state</b>, do nothing. */
void
geoip_change_dirreq_state(uint64_t dirreq_id, dirreq_type_t type,
                          dirreq_state_t new_state)
{
  dirreq_map_entry_t *ent;
  if (!get_options()->DirReqStatistics)
    return;
  ent = dirreq_map_get_(type, dirreq_id);
  if (!ent)
    return;
  if (new_state == DIRREQ_IS_FOR_NETWORK_STATUS)
    return;
  if (new_state - 1 != ent->state)
    return;
  ent->state = new_state;
  if ((type == DIRREQ_DIRECT &&
         new_state == DIRREQ_FLUSHING_DIR_CONN_FINISHED) ||
      (type == DIRREQ_TUNNELED &&
         new_state == DIRREQ_CHANNEL_BUFFER_FLUSHED)) {
    tor_gettimeofday(&ent->completion_time);
    ent->completed = 1;
  }
}

/** Return the bridge-ip-transports string that should be inserted in
 *  our extra-info descriptor. Return NULL if the bridge-ip-transports
 *  line should be empty.  */
char *
geoip_get_transport_history(void)
{
  unsigned granularity = IP_GRANULARITY;
  /** String hash table (name of transport) -> (number of users). */
  strmap_t *transport_counts = strmap_new();

  /** Smartlist that contains copies of the names of the transports
      that have been used. */
  smartlist_t *transports_used = smartlist_new();

  /* Special string to signify that no transport was used for this
     connection. Pluggable transport names can't have symbols in their
     names, so this string will never collide with a real transport. */
  static const char* no_transport_str = "<OR>";

  clientmap_entry_t **ent;
  smartlist_t *string_chunks = smartlist_new();
  char *the_string = NULL;

  /* If we haven't seen any clients yet, return NULL. */
  if (HT_EMPTY(&client_history))
    goto done;

  /** We do the following steps to form the transport history string:
   *  a) Foreach client that uses a pluggable transport, we increase the
   *  times that transport was used by one. If the client did not use
   *  a transport, we increase the number of times someone connected
   *  without obfuscation.
   *  b) Foreach transport we observed, we write its transport history
   *  string and push it to string_chunks. So, for example, if we've
   *  seen 665 obfs2 clients, we write "obfs2=665".
   *  c) We concatenate string_chunks to form the final string.
   */

  log_debug(LD_GENERAL,"Starting iteration for transport history. %d clients.",
            HT_SIZE(&client_history));

  /* Loop through all clients. */
  HT_FOREACH(ent, clientmap, &client_history) {
    uintptr_t val;
    void *ptr;
    const char *transport_name = (*ent)->transport_name;
    if (!transport_name)
      transport_name = no_transport_str;

    /* Increase the count for this transport name. */
    ptr = strmap_get(transport_counts, transport_name);
    val = (uintptr_t)ptr;
    val++;
    ptr = (void*)val;
    strmap_set(transport_counts, transport_name, ptr);

    /* If it's the first time we see this transport, note it. */
    if (val == 1)
      smartlist_add_strdup(transports_used, transport_name);

    log_debug(LD_GENERAL, "Client from '%s' with transport '%s'. "
              "I've now seen %d clients.",
              safe_str_client(fmt_addr(&(*ent)->addr)),
              transport_name ? transport_name : "<no transport>",
              (int)val);
  }

  /* Sort the transport names (helps with unit testing). */
  smartlist_sort_strings(transports_used);

  /* Loop through all seen transports. */
  SMARTLIST_FOREACH_BEGIN(transports_used, const char *, transport_name) {
    void *transport_count_ptr = strmap_get(transport_counts, transport_name);
    uintptr_t transport_count = (uintptr_t) transport_count_ptr;

    log_debug(LD_GENERAL, "We got %"PRIu64" clients with transport '%s'.",
              ((uint64_t)transport_count), transport_name);

    smartlist_add_asprintf(string_chunks, "%s=%"PRIu64,
                           transport_name,
                           (round_uint64_to_next_multiple_of(
                                               (uint64_t)transport_count,
                                               granularity)));
  } SMARTLIST_FOREACH_END(transport_name);

  the_string = smartlist_join_strings(string_chunks, ",", 0, NULL);

  log_debug(LD_GENERAL, "Final bridge-ip-transports string: '%s'", the_string);

 done:
  strmap_free(transport_counts, NULL);
  SMARTLIST_FOREACH(transports_used, char *, s, tor_free(s));
  smartlist_free(transports_used);
  SMARTLIST_FOREACH(string_chunks, char *, s, tor_free(s));
  smartlist_free(string_chunks);

  return the_string;
}

/** Return a newly allocated comma-separated string containing statistics
 * on network status downloads. The string contains the number of completed
 * requests, timeouts, and still running requests as well as the download
 * times by deciles and quartiles. Return NULL if we have not observed
 * requests for long enough. */
static char *
geoip_get_dirreq_history(dirreq_type_t type)
{
  char *result = NULL;
  buf_t *buf = NULL;
  smartlist_t *dirreq_completed = NULL;
  uint32_t complete = 0, timeouts = 0, running = 0;
  dirreq_map_entry_t **ptr, **next;
  struct timeval now;

  tor_gettimeofday(&now);
  dirreq_completed = smartlist_new();
  for (ptr = HT_START(dirreqmap, &dirreq_map); ptr; ptr = next) {
    dirreq_map_entry_t *ent = *ptr;
    if (ent->type != type) {
      next = HT_NEXT(dirreqmap, &dirreq_map, ptr);
      continue;
    } else {
      if (ent->completed) {
        smartlist_add(dirreq_completed, ent);
        complete++;
        next = HT_NEXT_RMV(dirreqmap, &dirreq_map, ptr);
      } else {
        if (tv_mdiff(&ent->request_time, &now) / 1000 > DIRREQ_TIMEOUT)
          timeouts++;
        else
          running++;
        next = HT_NEXT_RMV(dirreqmap, &dirreq_map, ptr);
        tor_free(ent);
      }
    }
  }
#define DIR_REQ_GRANULARITY 4
  complete = round_uint32_to_next_multiple_of(complete,
                                              DIR_REQ_GRANULARITY);
  timeouts = round_uint32_to_next_multiple_of(timeouts,
                                              DIR_REQ_GRANULARITY);
  running = round_uint32_to_next_multiple_of(running,
                                             DIR_REQ_GRANULARITY);
  buf = buf_new_with_capacity(1024);
  buf_add_printf(buf, "complete=%u,timeout=%u,"
                 "running=%u", complete, timeouts, running);

#define MIN_DIR_REQ_RESPONSES 16
  if (complete >= MIN_DIR_REQ_RESPONSES) {
    uint32_t *dltimes;
    /* We may have rounded 'completed' up.  Here we want to use the
     * real value. */
    complete = smartlist_len(dirreq_completed);
    dltimes = tor_calloc(complete, sizeof(uint32_t));
    SMARTLIST_FOREACH_BEGIN(dirreq_completed, dirreq_map_entry_t *, ent) {
      uint32_t bytes_per_second;
      uint32_t time_diff_ = (uint32_t) tv_mdiff(&ent->request_time,
                                               &ent->completion_time);
      if (time_diff_ == 0)
        time_diff_ = 1; /* Avoid DIV/0; "instant" answers are impossible
                        * by law of nature or something, but a millisecond
                        * is a bit greater than "instantly" */
      bytes_per_second = (uint32_t)(1000 * ent->response_size / time_diff_);
      dltimes[ent_sl_idx] = bytes_per_second;
    } SMARTLIST_FOREACH_END(ent);
    median_uint32(dltimes, complete); /* sorts as a side effect. */
    buf_add_printf(buf,
                           ",min=%u,d1=%u,d2=%u,q1=%u,d3=%u,d4=%u,md=%u,"
                           "d6=%u,d7=%u,q3=%u,d8=%u,d9=%u,max=%u",
                           dltimes[0],
                           dltimes[1*complete/10-1],
                           dltimes[2*complete/10-1],
                           dltimes[1*complete/4-1],
                           dltimes[3*complete/10-1],
                           dltimes[4*complete/10-1],
                           dltimes[5*complete/10-1],
                           dltimes[6*complete/10-1],
                           dltimes[7*complete/10-1],
                           dltimes[3*complete/4-1],
                           dltimes[8*complete/10-1],
                           dltimes[9*complete/10-1],
                           dltimes[complete-1]);
    tor_free(dltimes);
  }

  result = buf_extract(buf, NULL);

  SMARTLIST_FOREACH(dirreq_completed, dirreq_map_entry_t *, ent,
                    tor_free(ent));
  smartlist_free(dirreq_completed);
  buf_free(buf);
  return result;
}

/** Store a newly allocated comma-separated string in
 * *<a>country_str</a> containing entries for all the countries from
 * which we've seen enough clients connect as a bridge, directory
 * server, or entry guard. The entry format is cc=num where num is the
 * number of IPs we've seen connecting from that country, and cc is a
 * lowercased country code. *<a>country_str</a> is set to NULL if
 * we're not ready to export per country data yet.
 *
 * Store a newly allocated comma-separated string in <a>ipver_str</a>
 * containing entries for clients connecting over IPv4 and IPv6. The
 * format is family=num where num is the nubmer of IPs we've seen
 * connecting over that protocol family, and family is 'v4' or 'v6'.
 *
 * Return 0 on success and -1 if we're missing geoip data. */
int
geoip_get_client_history(geoip_client_action_t action,
                         char **country_str, char **ipver_str)
{
  unsigned granularity = IP_GRANULARITY;
  smartlist_t *entries = NULL;
  int n_countries = geoip_get_n_countries();
  int i;
  clientmap_entry_t **cm_ent;
  unsigned *counts = NULL;
  unsigned total = 0;
  unsigned ipv4_count = 0, ipv6_count = 0;

  if (!geoip_is_loaded(AF_INET) && !geoip_is_loaded(AF_INET6))
    return -1;

  counts = tor_calloc(n_countries, sizeof(unsigned));
  HT_FOREACH(cm_ent, clientmap, &client_history) {
    int country;
    if ((*cm_ent)->action != (int)action)
      continue;
    country = geoip_get_country_by_addr(&(*cm_ent)->addr);
    if (country < 0)
      country = 0; /** unresolved requests are stored at index 0. */
    tor_assert(0 <= country && country < n_countries);
    ++counts[country];
    ++total;
    switch (tor_addr_family(&(*cm_ent)->addr)) {
    case AF_INET:
      ipv4_count++;
      break;
    case AF_INET6:
      ipv6_count++;
      break;
    }
  }
  if (ipver_str) {
    smartlist_t *chunks = smartlist_new();
    smartlist_add_asprintf(chunks, "v4=%u",
                           round_to_next_multiple_of(ipv4_count, granularity));
    smartlist_add_asprintf(chunks, "v6=%u",
                           round_to_next_multiple_of(ipv6_count, granularity));
    *ipver_str = smartlist_join_strings(chunks, ",", 0, NULL);
    SMARTLIST_FOREACH(chunks, char *, c, tor_free(c));
    smartlist_free(chunks);
  }

  /* Don't record per country data if we haven't seen enough IPs. */
  if (total < MIN_IPS_TO_NOTE_ANYTHING) {
    tor_free(counts);
    if (country_str)
      *country_str = NULL;
    return 0;
  }

  /* Make a list of c_hist_t */
  entries = smartlist_new();
  for (i = 0; i < n_countries; ++i) {
    unsigned c = counts[i];
    const char *countrycode;
    c_hist_t *ent;
    /* Only report a country if it has a minimum number of IPs. */
    if (c >= MIN_IPS_TO_NOTE_COUNTRY) {
      c = round_to_next_multiple_of(c, granularity);
      countrycode = geoip_get_country_name(i);
      ent = tor_malloc(sizeof(c_hist_t));
      strlcpy(ent->country, countrycode, sizeof(ent->country));
      ent->total = c;
      smartlist_add(entries, ent);
    }
  }
  /* Sort entries. Note that we must do this _AFTER_ rounding, or else
   * the sort order could leak info. */
  smartlist_sort(entries, c_hist_compare_);

  if (country_str) {
    smartlist_t *chunks = smartlist_new();
    SMARTLIST_FOREACH(entries, c_hist_t *, ch, {
        smartlist_add_asprintf(chunks, "%s=%u", ch->country, ch->total);
      });
    *country_str = smartlist_join_strings(chunks, ",", 0, NULL);
    SMARTLIST_FOREACH(chunks, char *, c, tor_free(c));
    smartlist_free(chunks);
  }

  SMARTLIST_FOREACH(entries, c_hist_t *, c, tor_free(c));
  smartlist_free(entries);
  tor_free(counts);

  return 0;
}

/** Return a newly allocated string holding the per-country request history
 * for v3 network statuses in a format suitable for an extra-info document,
 * or NULL on failure. */
char *
geoip_get_request_history(void)
{
  smartlist_t *entries, *strings;
  char *result;
  unsigned granularity = IP_GRANULARITY;

  entries = smartlist_new();
  SMARTLIST_FOREACH_BEGIN(geoip_get_countries(), const geoip_country_t *, c) {
      uint32_t tot = 0;
      c_hist_t *ent;
      if ((size_t)c_sl_idx < n_v3_ns_requests_len)
        tot = n_v3_ns_requests[c_sl_idx];
      else
        tot = 0;
      if (!tot)
        continue;
      ent = tor_malloc_zero(sizeof(c_hist_t));
      strlcpy(ent->country, c->countrycode, sizeof(ent->country));
      ent->total = round_to_next_multiple_of(tot, granularity);
      smartlist_add(entries, ent);
  } SMARTLIST_FOREACH_END(c);
  smartlist_sort(entries, c_hist_compare_);

  strings = smartlist_new();
  SMARTLIST_FOREACH(entries, c_hist_t *, ent, {
      smartlist_add_asprintf(strings, "%s=%u", ent->country, ent->total);
  });
  result = smartlist_join_strings(strings, ",", 0, NULL);
  SMARTLIST_FOREACH(strings, char *, cp, tor_free(cp));
  SMARTLIST_FOREACH(entries, c_hist_t *, ent, tor_free(ent));
  smartlist_free(strings);
  smartlist_free(entries);
  return result;
}

/** Start time of directory request stats or 0 if we're not collecting
 * directory request statistics. */
static time_t start_of_dirreq_stats_interval;

/** Initialize directory request stats. */
void
geoip_dirreq_stats_init(time_t now)
{
  start_of_dirreq_stats_interval = now;
}

/** Reset counters for dirreq stats. */
void
geoip_reset_dirreq_stats(time_t now)
{
  memset(n_v3_ns_requests, 0,
         n_v3_ns_requests_len * sizeof(uint32_t));
  {
    clientmap_entry_t **ent, **next, *this;
    for (ent = HT_START(clientmap, &client_history); ent != NULL;
         ent = next) {
      if ((*ent)->action == GEOIP_CLIENT_NETWORKSTATUS) {
        this = *ent;
        next = HT_NEXT_RMV(clientmap, &client_history, ent);
        clientmap_entry_free(this);
      } else {
        next = HT_NEXT(clientmap, &client_history, ent);
      }
    }
  }
  memset(ns_v3_responses, 0, sizeof(ns_v3_responses));
  {
    dirreq_map_entry_t **ent, **next, *this;
    for (ent = HT_START(dirreqmap, &dirreq_map); ent != NULL; ent = next) {
      this = *ent;
      next = HT_NEXT_RMV(dirreqmap, &dirreq_map, ent);
      tor_free(this);
    }
  }
  start_of_dirreq_stats_interval = now;
}

/** Stop collecting directory request stats in a way that we can re-start
 * doing so in geoip_dirreq_stats_init(). */
void
geoip_dirreq_stats_term(void)
{
  geoip_reset_dirreq_stats(0);
}

/** Return a newly allocated string containing the dirreq statistics
 * until <b>now</b>, or NULL if we're not collecting dirreq stats. Caller
 * must ensure start_of_dirreq_stats_interval is in the past. */
char *
geoip_format_dirreq_stats(time_t now)
{
  char t[ISO_TIME_LEN+1];
  int i;
  char *v3_ips_string = NULL, *v3_reqs_string = NULL,
       *v3_direct_dl_string = NULL, *v3_tunneled_dl_string = NULL;
  char *result = NULL;

  if (!start_of_dirreq_stats_interval)
    return NULL; /* Not initialized. */

  tor_assert(now >= start_of_dirreq_stats_interval);

  format_iso_time(t, now);
  geoip_get_client_history(GEOIP_CLIENT_NETWORKSTATUS, &v3_ips_string, NULL);
  v3_reqs_string = geoip_get_request_history();

#define RESPONSE_GRANULARITY 8
  for (i = 0; i < GEOIP_NS_RESPONSE_NUM; i++) {
    ns_v3_responses[i] = round_uint32_to_next_multiple_of(
                               ns_v3_responses[i], RESPONSE_GRANULARITY);
  }
#undef RESPONSE_GRANULARITY

  v3_direct_dl_string = geoip_get_dirreq_history(DIRREQ_DIRECT);
  v3_tunneled_dl_string = geoip_get_dirreq_history(DIRREQ_TUNNELED);

  /* Put everything together into a single string. */
  tor_asprintf(&result, "dirreq-stats-end %s (%d s)\n"
              "dirreq-v3-ips %s\n"
              "dirreq-v3-reqs %s\n"
              "dirreq-v3-resp ok=%u,not-enough-sigs=%u,unavailable=%u,"
                   "not-found=%u,not-modified=%u,busy=%u\n"
              "dirreq-v3-direct-dl %s\n"
              "dirreq-v3-tunneled-dl %s\n",
              t,
              (unsigned) (now - start_of_dirreq_stats_interval),
              v3_ips_string ? v3_ips_string : "",
              v3_reqs_string ? v3_reqs_string : "",
              ns_v3_responses[GEOIP_SUCCESS],
              ns_v3_responses[GEOIP_REJECT_NOT_ENOUGH_SIGS],
              ns_v3_responses[GEOIP_REJECT_UNAVAILABLE],
              ns_v3_responses[GEOIP_REJECT_NOT_FOUND],
              ns_v3_responses[GEOIP_REJECT_NOT_MODIFIED],
              ns_v3_responses[GEOIP_REJECT_BUSY],
              v3_direct_dl_string ? v3_direct_dl_string : "",
              v3_tunneled_dl_string ? v3_tunneled_dl_string : "");

  /* Free partial strings. */
  tor_free(v3_ips_string);
  tor_free(v3_reqs_string);
  tor_free(v3_direct_dl_string);
  tor_free(v3_tunneled_dl_string);

  return result;
}

/** If 24 hours have passed since the beginning of the current dirreq
 * stats period, write dirreq stats to $DATADIR/stats/dirreq-stats
 * (possibly overwriting an existing file) and reset counters.  Return
 * when we would next want to write dirreq stats or 0 if we never want to
 * write. */
time_t
geoip_dirreq_stats_write(time_t now)
{
  char *str = NULL;

  if (!start_of_dirreq_stats_interval)
    return 0; /* Not initialized. */
  if (start_of_dirreq_stats_interval + WRITE_STATS_INTERVAL > now)
    goto done; /* Not ready to write. */

  /* Discard all items in the client history that are too old. */
  geoip_remove_old_clients(start_of_dirreq_stats_interval);

  /* Generate history string .*/
  str = geoip_format_dirreq_stats(now);
  if (! str)
    goto done;

  /* Write dirreq-stats string to disk. */
  if (!check_or_create_data_subdir("stats")) {
    write_to_data_subdir("stats", "dirreq-stats", str, "dirreq statistics");
    /* Reset measurement interval start. */
    geoip_reset_dirreq_stats(now);
  }

 done:
  tor_free(str);
  return start_of_dirreq_stats_interval + WRITE_STATS_INTERVAL;
}

/** Start time of bridge stats or 0 if we're not collecting bridge
 * statistics. */
static time_t start_of_bridge_stats_interval;

/** Initialize bridge stats. */
void
geoip_bridge_stats_init(time_t now)
{
  start_of_bridge_stats_interval = now;
}

/** Stop collecting bridge stats in a way that we can re-start doing so in
 * geoip_bridge_stats_init(). */
void
geoip_bridge_stats_term(void)
{
  client_history_clear();
  start_of_bridge_stats_interval = 0;
}

/** Validate a bridge statistics string as it would be written to a
 * current extra-info descriptor. Return 1 if the string is valid and
 * recent enough, or 0 otherwise. */
static int
validate_bridge_stats(const char *stats_str, time_t now)
{
  char stats_end_str[ISO_TIME_LEN+1], stats_start_str[ISO_TIME_LEN+1],
       *eos;

  const char *BRIDGE_STATS_END = "bridge-stats-end ";
  const char *BRIDGE_IPS = "bridge-ips ";
  const char *BRIDGE_IPS_EMPTY_LINE = "bridge-ips\n";
  const char *BRIDGE_TRANSPORTS = "bridge-ip-transports ";
  const char *BRIDGE_TRANSPORTS_EMPTY_LINE = "bridge-ip-transports\n";
  const char *tmp;
  time_t stats_end_time;
  int seconds;
  tor_assert(stats_str);

  /* Parse timestamp and number of seconds from
    "bridge-stats-end YYYY-MM-DD HH:MM:SS (N s)" */
  tmp = find_str_at_start_of_line(stats_str, BRIDGE_STATS_END);
  if (!tmp)
    return 0;
  tmp += strlen(BRIDGE_STATS_END);

  if (strlen(tmp) < ISO_TIME_LEN + 6)
    return 0;
  strlcpy(stats_end_str, tmp, sizeof(stats_end_str));
  if (parse_iso_time(stats_end_str, &stats_end_time) < 0)
    return 0;
  if (stats_end_time < now - (25*60*60) ||
      stats_end_time > now + (1*60*60))
    return 0;
  seconds = (int)strtol(tmp + ISO_TIME_LEN + 2, &eos, 10);
  if (!eos || seconds < 23*60*60)
    return 0;
  format_iso_time(stats_start_str, stats_end_time - seconds);

  /* Parse: "bridge-ips CC=N,CC=N,..." */
  tmp = find_str_at_start_of_line(stats_str, BRIDGE_IPS);
  if (!tmp) {
    /* Look if there is an empty "bridge-ips" line */
    tmp = find_str_at_start_of_line(stats_str, BRIDGE_IPS_EMPTY_LINE);
    if (!tmp)
      return 0;
  }

  /* Parse: "bridge-ip-transports PT=N,PT=N,..." */
  tmp = find_str_at_start_of_line(stats_str, BRIDGE_TRANSPORTS);
  if (!tmp) {
    /* Look if there is an empty "bridge-ip-transports" line */
    tmp = find_str_at_start_of_line(stats_str, BRIDGE_TRANSPORTS_EMPTY_LINE);
    if (!tmp)
      return 0;
  }

  return 1;
}

/** Most recent bridge statistics formatted to be written to extra-info
 * descriptors. */
static char *bridge_stats_extrainfo = NULL;

/** Return a newly allocated string holding our bridge usage stats by country
 * in a format suitable for inclusion in an extrainfo document. Return NULL on
 * failure.  */
char *
geoip_format_bridge_stats(time_t now)
{
  char *out = NULL;
  char *country_data = NULL, *ipver_data = NULL, *transport_data = NULL;
  long duration = now - start_of_bridge_stats_interval;
  char written[ISO_TIME_LEN+1];

  if (duration < 0)
    return NULL;
  if (!start_of_bridge_stats_interval)
    return NULL; /* Not initialized. */

  format_iso_time(written, now);
  geoip_get_client_history(GEOIP_CLIENT_CONNECT, &country_data, &ipver_data);
  transport_data = geoip_get_transport_history();

  tor_asprintf(&out,
               "bridge-stats-end %s (%ld s)\n"
               "bridge-ips %s\n"
               "bridge-ip-versions %s\n"
               "bridge-ip-transports %s\n",
               written, duration,
               country_data ? country_data : "",
               ipver_data ? ipver_data : "",
               transport_data ? transport_data : "");
  tor_free(country_data);
  tor_free(ipver_data);
  tor_free(transport_data);

  return out;
}

/** Return a newly allocated string holding our bridge usage stats by country
 * in a format suitable for the answer to a controller request. Return NULL on
 * failure.  */
static char *
format_bridge_stats_controller(time_t now)
{
  char *out = NULL, *country_data = NULL, *ipver_data = NULL;
  char started[ISO_TIME_LEN+1];
  (void) now;

  format_iso_time(started, start_of_bridge_stats_interval);
  geoip_get_client_history(GEOIP_CLIENT_CONNECT, &country_data, &ipver_data);

  tor_asprintf(&out,
               "TimeStarted=\"%s\" CountrySummary=%s IPVersions=%s",
               started,
               country_data ? country_data : "",
               ipver_data ? ipver_data : "");
  tor_free(country_data);
  tor_free(ipver_data);
  return out;
}

/** Return a newly allocated string holding our bridge usage stats by
 * country in a format suitable for inclusion in our heartbeat
 * message. Return NULL on failure.  */
char *
format_client_stats_heartbeat(time_t now)
{
  const int n_hours = 6;
  char *out = NULL;
  int n_clients = 0;
  clientmap_entry_t **ent;
  unsigned cutoff = (unsigned)( (now-n_hours*3600)/60 );

  if (!start_of_bridge_stats_interval)
    return NULL; /* Not initialized. */

  /* count unique IPs */
  HT_FOREACH(ent, clientmap, &client_history) {
    /* only count directly connecting clients */
    if ((*ent)->action != GEOIP_CLIENT_CONNECT)
      continue;
    if ((*ent)->last_seen_in_minutes < cutoff)
      continue;
    n_clients++;
  }

  tor_asprintf(&out, "Heartbeat: "
               "In the last %d hours, I have seen %d unique clients.",
               n_hours,
               n_clients);

  return out;
}

/** Write bridge statistics to $DATADIR/stats/bridge-stats and return
 * when we should next try to write statistics. */
time_t
geoip_bridge_stats_write(time_t now)
{
  char *val = NULL;

  /* Check if 24 hours have passed since starting measurements. */
  if (now < start_of_bridge_stats_interval + WRITE_STATS_INTERVAL)
    return start_of_bridge_stats_interval + WRITE_STATS_INTERVAL;

  /* Discard all items in the client history that are too old. */
  geoip_remove_old_clients(start_of_bridge_stats_interval);

  /* Generate formatted string */
  val = geoip_format_bridge_stats(now);
  if (val == NULL)
    goto done;

  /* Update the stored value. */
  tor_free(bridge_stats_extrainfo);
  bridge_stats_extrainfo = val;
  start_of_bridge_stats_interval = now;

  /* Write it to disk. */
  if (!check_or_create_data_subdir("stats")) {
    write_to_data_subdir("stats", "bridge-stats",
                         bridge_stats_extrainfo, "bridge statistics");

    /* Tell the controller, "hey, there are clients!" */
    {
      char *controller_str = format_bridge_stats_controller(now);
      if (controller_str)
        control_event_clients_seen(controller_str);
      tor_free(controller_str);
    }
  }

 done:
  return start_of_bridge_stats_interval + WRITE_STATS_INTERVAL;
}

/** Try to load the most recent bridge statistics from disk, unless we
 * have finished a measurement interval lately, and check whether they
 * are still recent enough. */
static void
load_bridge_stats(time_t now)
{
  char *fname, *contents;
  if (bridge_stats_extrainfo)
    return;

  fname = get_datadir_fname2("stats", "bridge-stats");
  contents = read_file_to_str(fname, RFTS_IGNORE_MISSING, NULL);
  if (contents && validate_bridge_stats(contents, now)) {
    bridge_stats_extrainfo = contents;
  } else {
    tor_free(contents);
  }

  tor_free(fname);
}

/** Return most recent bridge statistics for inclusion in extra-info
 * descriptors, or NULL if we don't have recent bridge statistics. */
const char *
geoip_get_bridge_stats_extrainfo(time_t now)
{
  load_bridge_stats(now);
  return bridge_stats_extrainfo;
}

/** Return a new string containing the recent bridge statistics to be returned
 * to controller clients, or NULL if we don't have any bridge statistics. */
char *
geoip_get_bridge_stats_controller(time_t now)
{
  return format_bridge_stats_controller(now);
}

/** Start time of entry stats or 0 if we're not collecting entry
 * statistics. */
static time_t start_of_entry_stats_interval;

/** Initialize entry stats. */
void
geoip_entry_stats_init(time_t now)
{
  start_of_entry_stats_interval = now;
}

/** Reset counters for entry stats. */
void
geoip_reset_entry_stats(time_t now)
{
  client_history_clear();
  start_of_entry_stats_interval = now;
}

/** Stop collecting entry stats in a way that we can re-start doing so in
 * geoip_entry_stats_init(). */
void
geoip_entry_stats_term(void)
{
  geoip_reset_entry_stats(0);
}

/** Return a newly allocated string containing the entry statistics
 * until <b>now</b>, or NULL if we're not collecting entry stats. Caller
 * must ensure start_of_entry_stats_interval lies in the past. */
char *
geoip_format_entry_stats(time_t now)
{
  char t[ISO_TIME_LEN+1];
  char *data = NULL;
  char *result;

  if (!start_of_entry_stats_interval)
    return NULL; /* Not initialized. */

  tor_assert(now >= start_of_entry_stats_interval);

  geoip_get_client_history(GEOIP_CLIENT_CONNECT, &data, NULL);
  format_iso_time(t, now);
  tor_asprintf(&result,
               "entry-stats-end %s (%u s)\n"
               "entry-ips %s\n",
               t, (unsigned) (now - start_of_entry_stats_interval),
               data ? data : "");
  tor_free(data);
  return result;
}

/** If 24 hours have passed since the beginning of the current entry stats
 * period, write entry stats to $DATADIR/stats/entry-stats (possibly
 * overwriting an existing file) and reset counters.  Return when we would
 * next want to write entry stats or 0 if we never want to write. */
time_t
geoip_entry_stats_write(time_t now)
{
  char *str = NULL;

  if (!start_of_entry_stats_interval)
    return 0; /* Not initialized. */
  if (start_of_entry_stats_interval + WRITE_STATS_INTERVAL > now)
    goto done; /* Not ready to write. */

  /* Discard all items in the client history that are too old. */
  geoip_remove_old_clients(start_of_entry_stats_interval);

  /* Generate history string .*/
  str = geoip_format_entry_stats(now);

  /* Write entry-stats string to disk. */
  if (!check_or_create_data_subdir("stats")) {
    write_to_data_subdir("stats", "entry-stats", str, "entry statistics");

    /* Reset measurement interval start. */
    geoip_reset_entry_stats(now);
  }

 done:
  tor_free(str);
  return start_of_entry_stats_interval + WRITE_STATS_INTERVAL;
}

/** Release all storage held in this file. */
void
geoip_stats_free_all(void)
{
  {
    clientmap_entry_t **ent, **next, *this;
    for (ent = HT_START(clientmap, &client_history); ent != NULL; ent = next) {
      this = *ent;
      next = HT_NEXT_RMV(clientmap, &client_history, ent);
      clientmap_entry_free(this);
    }
    HT_CLEAR(clientmap, &client_history);
  }
  {
    dirreq_map_entry_t **ent, **next, *this;
    for (ent = HT_START(dirreqmap, &dirreq_map); ent != NULL; ent = next) {
      this = *ent;
      next = HT_NEXT_RMV(dirreqmap, &dirreq_map, ent);
      tor_free(this);
    }
    HT_CLEAR(dirreqmap, &dirreq_map);
  }

  tor_free(bridge_stats_extrainfo);
  tor_free(n_v3_ns_requests);
}