text: /* Copyright (c) 2015, The Tor Project, Inc. */
  /* See LICENSE for licensing information */
  
  /**
   * \file rendcache.c
   * \brief Hidden service descriptor cache.
   **/
  
  #define RENDCACHE_PRIVATE
  #include "rendcache.h"
  
  #include "config.h"
  #include "rephist.h"
  #include "routerlist.h"
  #include "routerparse.h"
  
  /** Map from service id (as generated by rend_get_service_id) to
   * rend_cache_entry_t. */
  STATIC strmap_t *rend_cache = NULL;
  
  /** Map from descriptor id to rend_cache_entry_t; only for hidden service
   * directories. */
  STATIC digestmap_t *rend_cache_v2_dir = NULL;
  
  /** (Client side only) Map from service id to rend_cache_failure_t. This
   * cache is used to track intro point(IP) failures so we know when to keep
   * or discard a new descriptor we just fetched. Here is a description of the
   * cache behavior.
   *
   * Everytime tor discards an IP (ex: receives a NACK), we add an entry to
   * this cache noting the identity digest of the IP and it's failure type for
   * the service ID. The reason we indexed this cache by service ID is to
   * differentiate errors that can occur only for a specific service like a
   * NACK for instance. It applies for one but maybe not for the others.
   *
   * Once a service descriptor is fetched and considered valid, each IP is
   * looked up in this cache and if present, it is discarded from the fetched
   * descriptor. At the end, all IP(s) in the cache, for a specific service
   * ID, that were NOT present in the descriptor are removed from this cache.
   * Which means that if at least one IP was not in this cache, thus usuable,
   * it's considered a new descriptor so we keep it. Else, if all IPs were in
   * this cache, we discard the descriptor as it's considered unsuable.
   *
   * Once a descriptor is removed from the rend cache or expires, the entry
   * in this cache is also removed for the service ID.
   *
   * This scheme allows us to not realy on the descriptor's timestamp (which
   * is rounded down to the hour) to know if we have a newer descriptor. We
   * only rely on the usability of intro points from an internal state. */
  STATIC strmap_t *rend_cache_failure = NULL;
  
  /** DOCDOC */
  STATIC size_t rend_cache_total_allocation = 0;
  
  /** Initializes the service descriptor cache.
  */
  void
  rend_cache_init(void)
  {
    rend_cache = strmap_new();
    rend_cache_v2_dir = digestmap_new();
    rend_cache_failure = strmap_new();
  }
  
  /** Return the approximate number of bytes needed to hold <b>e</b>. */
  STATIC size_t
  rend_cache_entry_allocation(const rend_cache_entry_t *e)
  {
    if (!e)
      return 0;
  
    /* This doesn't count intro_nodes or key size */
    return sizeof(*e) + e->len + sizeof(*e->parsed);
  }
  
  /** DOCDOC */
  size_t
  rend_cache_get_total_allocation(void)
  {
    return rend_cache_total_allocation;
  }
  
  /** Decrement the total bytes attributed to the rendezvous cache by n. */
  STATIC void
  rend_cache_decrement_allocation(size_t n)
  {
    static int have_underflowed = 0;
  
    if (rend_cache_total_allocation >= n) {
      rend_cache_total_allocation -= n;
    } else {
      rend_cache_total_allocation = 0;
      if (! have_underflowed) {
        have_underflowed = 1;
        log_warn(LD_BUG, "Underflow in rend_cache_decrement_allocation");
      }
    }
  }
  
  /** Increase the total bytes attributed to the rendezvous cache by n. */
  STATIC void
  rend_cache_increment_allocation(size_t n)
  {
    static int have_overflowed = 0;
    if (rend_cache_total_allocation <= SIZE_MAX - n) {
      rend_cache_total_allocation += n;
    } else {
      rend_cache_total_allocation = SIZE_MAX;
      if (! have_overflowed) {
        have_overflowed = 1;
        log_warn(LD_BUG, "Overflow in rend_cache_increment_allocation");
      }
    }
  }
  
  /** Helper: free a rend cache failure intro object. */
  STATIC void
  rend_cache_failure_intro_entry_free(rend_cache_failure_intro_t *entry)
  {
    if (entry == NULL) {
      return;
    }
    tor_free(entry);
  }
  
  /** Allocate a rend cache failure intro object and return it. <b>failure</b>
   * is set into the object. This function can not fail. */
  STATIC rend_cache_failure_intro_t *
  rend_cache_failure_intro_entry_new(rend_intro_point_failure_t failure)
  {
    rend_cache_failure_intro_t *entry = tor_malloc(sizeof(*entry));
    entry->failure_type = failure;
    entry->created_ts = time(NULL);
    return entry;
  }
  
  /** Helper: free a rend cache failure object. */
  STATIC void
  rend_cache_failure_entry_free(rend_cache_failure_t *entry)
  {
    if (entry == NULL) {
      return;
    }
  
    /* Free and remove every intro failure object. */
    DIGESTMAP_FOREACH_MODIFY(entry->intro_failures, key,
                             rend_cache_failure_intro_t *, e) {
      rend_cache_failure_intro_entry_free(e);
      MAP_DEL_CURRENT(key);
    } DIGESTMAP_FOREACH_END;
    tor_free(entry);
  }
  
  /** Helper: deallocate a rend_cache_failure_t. (Used with strmap_free(),
   * which requires a function pointer whose argument is void*). */
  static void
  rend_cache_failure_entry_free_(void *entry)
  {
    rend_cache_failure_entry_free(entry);
  }
  
  /** Allocate a rend cache failure object and return it. This function can
   * not fail. */
  STATIC rend_cache_failure_t *
  rend_cache_failure_entry_new(void)
  {
    rend_cache_failure_t *entry = tor_malloc(sizeof(*entry));
    entry->intro_failures = digestmap_new();
    return entry;
  }
  
  /** Remove failure cache entry for the service ID in the given descriptor
   * <b>desc</b>. */
  STATIC void
  rend_cache_failure_remove(rend_service_descriptor_t *desc)
  {
    char service_id[REND_SERVICE_ID_LEN_BASE32 + 1];
    rend_cache_failure_t *entry;
  
    if (desc == NULL) {
      return;
    }
    if (rend_get_service_id(desc->pk, service_id) < 0) {
      return;
    }
    entry = strmap_get_lc(rend_cache_failure, service_id);
    if (entry != NULL) {
      strmap_remove_lc(rend_cache_failure, service_id);
      rend_cache_failure_entry_free(entry);
    }
  }
  
  /** Helper: free storage held by a single service descriptor cache entry. */
  STATIC void
  rend_cache_entry_free(rend_cache_entry_t *e)
  {
    if (!e)
      return;
    rend_cache_decrement_allocation(rend_cache_entry_allocation(e));
    /* We are about to remove a descriptor from the cache so remove the entry
     * in the failure cache. */
    rend_cache_failure_remove(e->parsed);
    rend_service_descriptor_free(e->parsed);
    tor_free(e->desc);
    tor_free(e);
  }
  
  /** Helper: deallocate a rend_cache_entry_t.  (Used with strmap_free(), which
   * requires a function pointer whose argument is void*). */
  static void
  rend_cache_entry_free_(void *p)
  {
    rend_cache_entry_free(p);
  }
  
  /** Free all storage held by the service descriptor cache. */
  void
  rend_cache_free_all(void)
  {
    strmap_free(rend_cache, rend_cache_entry_free_);
    digestmap_free(rend_cache_v2_dir, rend_cache_entry_free_);
    strmap_free(rend_cache_failure, rend_cache_failure_entry_free_);
    rend_cache = NULL;
    rend_cache_v2_dir = NULL;
    rend_cache_failure = NULL;
    rend_cache_total_allocation = 0;
  }
  
  /** Remove all entries that re REND_CACHE_FAILURE_MAX_AGE old. This is
   * called every second.
   *
   * We have to clean these regurlarly else if for whatever reasons an hidden
   * service goes offline and a client tries to connect to it during that
   * time, a failure entry is created and the client will be unable to connect
   * for a while even though the service has return online.  */
  void
  rend_cache_failure_clean(time_t now)
  {
    time_t cutoff = now - REND_CACHE_FAILURE_MAX_AGE;
    STRMAP_FOREACH_MODIFY(rend_cache_failure, key,
                          rend_cache_failure_t *, ent) {
      /* Free and remove every intro failure object that match the cutoff. */
      DIGESTMAP_FOREACH_MODIFY(ent->intro_failures, ip_key,
                               rend_cache_failure_intro_t *, ip_ent) {
        if (ip_ent->created_ts < cutoff) {
          rend_cache_failure_intro_entry_free(ip_ent);
          MAP_DEL_CURRENT(ip_key);
        }
      } DIGESTMAP_FOREACH_END;
      /* If the entry is now empty of intro point failures, remove it. */
      if (digestmap_isempty(ent->intro_failures)) {
        rend_cache_failure_entry_free(ent);
        MAP_DEL_CURRENT(key);
      }
    } STRMAP_FOREACH_END;
  }
  
  /** Removes all old entries from the service descriptor cache.
  */
  void
  rend_cache_clean(time_t now)
  {
    strmap_iter_t *iter;
    const char *key;
    void *val;
    rend_cache_entry_t *ent;
    time_t cutoff = now - REND_CACHE_MAX_AGE - REND_CACHE_MAX_SKEW;
    for (iter = strmap_iter_init(rend_cache); !strmap_iter_done(iter); ) {
      strmap_iter_get(iter, &key, &val);
      ent = (rend_cache_entry_t*)val;
      if (ent->parsed->timestamp < cutoff) {
        iter = strmap_iter_next_rmv(rend_cache, iter);
        rend_cache_entry_free(ent);
      } else {
        iter = strmap_iter_next(rend_cache, iter);
      }
    }
  }
  
  /** Remove ALL entries from the rendezvous service descriptor cache.
  */
  void
  rend_cache_purge(void)
  {
    if (rend_cache) {
      log_info(LD_REND, "Purging HS descriptor cache");
      strmap_free(rend_cache, rend_cache_entry_free_);
    }
    rend_cache = strmap_new();
  }
  
  /** Remove ALL entries from the failure cache. This is also called when a
   * NEWNYM signal is received. */
  void
  rend_cache_failure_purge(void)
  {
    if (rend_cache_failure) {
      log_info(LD_REND, "Purging HS failure cache");
      strmap_free(rend_cache_failure, rend_cache_failure_entry_free_);
    }
    rend_cache_failure = strmap_new();
  }
  
  /** Lookup the rend failure cache using a relay identity digest in
   * <b>identity</b> and service ID <b>service_id</b>. If found, the intro
   * failure is set in <b>intro_entry</b> else it stays untouched. Return 1
   * iff found else 0. */
  STATIC int
  cache_failure_intro_lookup(const uint8_t *identity, const char *service_id,
                             rend_cache_failure_intro_t **intro_entry)
  {
    rend_cache_failure_t *elem;
    rend_cache_failure_intro_t *intro_elem;
  
    tor_assert(rend_cache_failure);
  
    if (intro_entry) {
      *intro_entry = NULL;
    }
  
    /* Lookup descriptor and return it. */
    elem = strmap_get_lc(rend_cache_failure, service_id);
    if (elem == NULL) {
      goto not_found;
    }
    intro_elem = digestmap_get(elem->intro_failures, (char *) identity);
    if (intro_elem == NULL) {
      goto not_found;
    }
    if (intro_entry) {
      *intro_entry = intro_elem;
    }
    return 1;
   not_found:
    return 0;
  }
  
  /** Add an intro point failure to the failure cache using the relay
   * <b>identity</b> and service ID <b>service_id</b>. Record the
   * <b>failure</b> in that object. */
  STATIC void
  cache_failure_intro_add(const uint8_t *identity, const char *service_id,
                          rend_intro_point_failure_t failure)
  {
    rend_cache_failure_t *fail_entry;
    rend_cache_failure_intro_t *entry;
  
    /* Make sure we have a failure object for this service ID and if not,
     * create it with this new intro failure entry. */
    fail_entry = strmap_get_lc(rend_cache_failure, service_id);
    if (fail_entry == NULL) {
      fail_entry = rend_cache_failure_entry_new();
      /* Add failure entry to global rend failure cache. */
      strmap_set_lc(rend_cache_failure, service_id, fail_entry);
    }
    entry = rend_cache_failure_intro_entry_new(failure);
    digestmap_set(fail_entry->intro_failures, (char *) identity, entry);
  }
  
  /** Using a parsed descriptor <b>desc</b>, check if the introduction points
   * are present in the failure cache and if so they are removed from the
   * descriptor and kept into the failure cache. Then, each intro points that
   * are NOT in the descriptor but in the failure cache for the given
   * <b>service_id</b> are removed from the failure cache. */
  STATIC void
  validate_intro_point_failure(const rend_service_descriptor_t *desc,
                               const char *service_id)
  {
    rend_cache_failure_t *new_entry, *cur_entry;
    /* New entry for the service ID that will be replacing the one in the
     * failure cache since we have a new descriptor. In the case where all
     * intro points are removed, we are assured that the new entry is the same
     * as the current one. */
    new_entry = tor_malloc(sizeof(*new_entry));
    new_entry->intro_failures = digestmap_new();
  
    tor_assert(desc);
  
    SMARTLIST_FOREACH_BEGIN(desc->intro_nodes, rend_intro_point_t *, intro) {
      int found;
      rend_cache_failure_intro_t *entry;
      const uint8_t *identity =
        (uint8_t *) intro->extend_info->identity_digest;
  
      found = cache_failure_intro_lookup(identity, service_id, &entry);
      if (found) {
        /* This intro point is in our cache, discard it from the descriptor
         * because chances are that it's unusable. */
        SMARTLIST_DEL_CURRENT(desc->intro_nodes, intro);
        rend_intro_point_free(intro);
        /* Keep it for our new entry. */
        digestmap_set(new_entry->intro_failures, (char *) identity, entry);
        continue;
      }
    } SMARTLIST_FOREACH_END(intro);
  
    /* Swap the failure entry in the cache and free the current one. */
    cur_entry = strmap_get_lc(rend_cache_failure, service_id);
    if (cur_entry != NULL) {
      rend_cache_failure_entry_free(cur_entry);
    }
    strmap_set_lc(rend_cache_failure, service_id, new_entry);
  }
  
  /** Note down an intro failure in the rend failure cache using the type of
   * failure in <b>failure</b> for the relay identity digest in
   * <b>identity</b> and service ID <b>service_id</b>. If an entry already
   * exists in the cache, the failure type is changed with <b>failure</b>. */
  void
  rend_cache_intro_failure_note(rend_intro_point_failure_t failure,
                                const uint8_t *identity,
                                const char *service_id)
  {
    int found;
    rend_cache_failure_intro_t *entry;
  
    found = cache_failure_intro_lookup(identity, service_id, &entry);
    if (!found) {
      cache_failure_intro_add(identity, service_id, failure);
    } else {
      /* Replace introduction point failure with this one. */
      entry->failure_type = failure;
    }
  }
  
  /** Remove all old v2 descriptors and those for which this hidden service
   * directory is not responsible for any more.
   *
   * If at all possible, remove at least <b>force_remove</b> bytes of data.
   */
  void
  rend_cache_clean_v2_descs_as_dir(time_t now, size_t force_remove)
  {
    digestmap_iter_t *iter;
    time_t cutoff = now - REND_CACHE_MAX_AGE - REND_CACHE_MAX_SKEW;
    const int LAST_SERVED_CUTOFF_STEP = 1800;
    time_t last_served_cutoff = cutoff;
    size_t bytes_removed = 0;
    do {
      for (iter = digestmap_iter_init(rend_cache_v2_dir);
           !digestmap_iter_done(iter); ) {
        const char *key;
        void *val;
        rend_cache_entry_t *ent;
        digestmap_iter_get(iter, &key, &val);
        ent = val;
        if (ent->parsed->timestamp < cutoff ||
            ent->last_served < last_served_cutoff ||
            !hid_serv_responsible_for_desc_id(key)) {
          char key_base32[REND_DESC_ID_V2_LEN_BASE32 + 1];
          base32_encode(key_base32, sizeof(key_base32), key, DIGEST_LEN);
          log_info(LD_REND, "Removing descriptor with ID '%s' from cache",
                   safe_str_client(key_base32));
          bytes_removed += rend_cache_entry_allocation(ent);
          iter = digestmap_iter_next_rmv(rend_cache_v2_dir, iter);
          rend_cache_entry_free(ent);
        } else {
          iter = digestmap_iter_next(rend_cache_v2_dir, iter);
        }
      }
  
      /* In case we didn't remove enough bytes, advance the cutoff a little. */
      last_served_cutoff += LAST_SERVED_CUTOFF_STEP;
      if (last_served_cutoff > now)
        break;
    } while (bytes_removed < force_remove);
  }
  
  /** Lookup in the client cache the given service ID <b>query</b> for
   * <b>version</b>.
   *
   * Return 0 if found and if <b>e</b> is non NULL, set it with the entry
   * found. Else, a negative value is returned and <b>e</b> is untouched.
   * -EINVAL means that <b>query</b> is not a valid service id.
   * -ENOENT means that no entry in the cache was found. */
  int
  rend_cache_lookup_entry(const char *query, int version, rend_cache_entry_t **e)
  {
    int ret = 0;
    char key[REND_SERVICE_ID_LEN_BASE32 + 2]; /* <version><query>\0 */
    rend_cache_entry_t *entry = NULL;
    static const int default_version = 2;
  
    tor_assert(rend_cache);
    tor_assert(query);
  
    if (!rend_valid_service_id(query)) {
      ret = -EINVAL;
      goto end;
    }
  
    switch (version) {
      case 0:
        log_warn(LD_REND, "Cache lookup of a v0 renddesc is deprecated.");
        break;
      case 2:
        /* Default is version 2. */
      default:
        tor_snprintf(key, sizeof(key), "%d%s", default_version, query);
        entry = strmap_get_lc(rend_cache, key);
        break;
    }
    if (!entry) {
      ret = -ENOENT;
      goto end;
    }
    tor_assert(entry->parsed && entry->parsed->intro_nodes);
  
    if (e) {
      *e = entry;
    }
  
   end:
    return ret;
  }
  
  /** Lookup the v2 service descriptor with base32-encoded <b>desc_id</b> and
   * copy the pointer to it to *<b>desc</b>.  Return 1 on success, 0 on
   * well-formed-but-not-found, and -1 on failure.
   */
  int
  rend_cache_lookup_v2_desc_as_dir(const char *desc_id, const char **desc)
  {
    rend_cache_entry_t *e;
    char desc_id_digest[DIGEST_LEN];
    tor_assert(rend_cache_v2_dir);
    if (base32_decode(desc_id_digest, DIGEST_LEN,
                      desc_id, REND_DESC_ID_V2_LEN_BASE32) < 0) {
      log_fn(LOG_PROTOCOL_WARN, LD_REND,
             "Rejecting v2 rendezvous descriptor request -- descriptor ID "
             "contains illegal characters: %s",
             safe_str(desc_id));
      return -1;
    }
    /* Lookup descriptor and return. */
    e = digestmap_get(rend_cache_v2_dir, desc_id_digest);
    if (e) {
      *desc = e->desc;
      e->last_served = approx_time();
      return 1;
    }
    return 0;
  }
  
  /** Parse the v2 service descriptor(s) in <b>desc</b> and store it/them to the
   * local rend cache. Don't attempt to decrypt the included list of introduction
   * points (as we don't have a descriptor cookie for it).
   *
   * If we have a newer descriptor with the same ID, ignore this one.
   * If we have an older descriptor with the same ID, replace it.
   *
   * Return an appropriate rend_cache_store_status_t.
   */
  rend_cache_store_status_t
  rend_cache_store_v2_desc_as_dir(const char *desc)
  {
    const or_options_t *options = get_options();
    rend_service_descriptor_t *parsed;
    char desc_id[DIGEST_LEN];
    char *intro_content;
    size_t intro_size;
    size_t encoded_size;
    char desc_id_base32[REND_DESC_ID_V2_LEN_BASE32 + 1];
    int number_parsed = 0, number_stored = 0;
    const char *current_desc = desc;
    const char *next_desc;
    rend_cache_entry_t *e;
    time_t now = time(NULL);
    tor_assert(rend_cache_v2_dir);
    tor_assert(desc);
    if (!hid_serv_acting_as_directory()) {
      /* Cannot store descs, because we are (currently) not acting as
       * hidden service directory. */
      log_info(LD_REND, "Cannot store descs: Not acting as hs dir");
      return RCS_NOTDIR;
    }
    while (rend_parse_v2_service_descriptor(&parsed, desc_id, &intro_content,
                                            &intro_size, &encoded_size,
                                            &next_desc, current_desc, 1) >= 0) {
      number_parsed++;
      /* We don't care about the introduction points. */
      tor_free(intro_content);
      /* For pretty log statements. */
      base32_encode(desc_id_base32, sizeof(desc_id_base32),
                    desc_id, DIGEST_LEN);
      /* Is desc ID in the range that we are (directly or indirectly) responsible
       * for? */
      if (!hid_serv_responsible_for_desc_id(desc_id)) {
        log_info(LD_REND, "Service descriptor with desc ID %s is not in "
                 "interval that we are responsible for.",
                 safe_str_client(desc_id_base32));
        goto skip;
      }
      /* Is descriptor too old? */
      if (parsed->timestamp < now - REND_CACHE_MAX_AGE-REND_CACHE_MAX_SKEW) {
        log_info(LD_REND, "Service descriptor with desc ID %s is too old.",
                 safe_str(desc_id_base32));
        goto skip;
      }
      /* Is descriptor too far in the future? */
      if (parsed->timestamp > now + REND_CACHE_MAX_SKEW) {
        log_info(LD_REND, "Service descriptor with desc ID %s is too far in the "
                 "future.",
                 safe_str(desc_id_base32));
        goto skip;
      }
      /* Do we already have a newer descriptor? */
      e = digestmap_get(rend_cache_v2_dir, desc_id);
      if (e && e->parsed->timestamp > parsed->timestamp) {
        log_info(LD_REND, "We already have a newer service descriptor with the "
                 "same desc ID %s and version.",
                 safe_str(desc_id_base32));
        goto skip;
      }
      /* Do we already have this descriptor? */
      if (e && !strcmp(desc, e->desc)) {
        log_info(LD_REND, "We already have this service descriptor with desc "
                 "ID %s.", safe_str(desc_id_base32));
        goto skip;
      }
      /* Store received descriptor. */
      if (!e) {
        e = tor_malloc_zero(sizeof(rend_cache_entry_t));
        digestmap_set(rend_cache_v2_dir, desc_id, e);
        /* Treat something just uploaded as having been served a little
         * while ago, so that flooding with new descriptors doesn't help
         * too much.
         */
        e->last_served = approx_time() - 3600;
      } else {
        rend_cache_decrement_allocation(rend_cache_entry_allocation(e));
        rend_service_descriptor_free(e->parsed);
        tor_free(e->desc);
      }
      e->parsed = parsed;
      e->desc = tor_strndup(current_desc, encoded_size);
      e->len = encoded_size;
      rend_cache_increment_allocation(rend_cache_entry_allocation(e));
      log_info(LD_REND, "Successfully stored service descriptor with desc ID "
               "'%s' and len %d.",
               safe_str(desc_id_base32), (int)encoded_size);
      /* Statistics: Note down this potentially new HS. */
      if (options->HiddenServiceStatistics) {
        rep_hist_stored_maybe_new_hs(e->parsed->pk);
      }
  
      number_stored++;
      goto advance;
   skip:
      rend_service_descriptor_free(parsed);
   advance:
      /* advance to next descriptor, if available. */
      current_desc = next_desc;
      /* check if there is a next descriptor. */
      if (!current_desc ||
          strcmpstart(current_desc, "rendezvous-service-descriptor "))
        break;
    }
    if (!number_parsed) {
      log_info(LD_REND, "Could not parse any descriptor.");
      return RCS_BADDESC;
    }
    log_info(LD_REND, "Parsed %d and added %d descriptor%s.",
             number_parsed, number_stored, number_stored != 1 ? "s" : "");
    return RCS_OKAY;
  }
  
  /** Parse the v2 service descriptor in <b>desc</b>, decrypt the included list
   * of introduction points with <b>descriptor_cookie</b> (which may also be
   * <b>NULL</b> if decryption is not necessary), and store the descriptor to
   * the local cache under its version and service id.
   *
   * If we have a newer v2 descriptor with the same ID, ignore this one.
   * If we have an older descriptor with the same ID, replace it.
   * If the descriptor's service ID does not match
   * <b>rend_query</b>-\>onion_address, reject it.
   *
   * If the descriptor's descriptor ID doesn't match <b>desc_id_base32</b>,
   * reject it.
   *
   * Return an appropriate rend_cache_store_status_t. If entry is not NULL,
   * set it with the cache entry pointer of the descriptor.
   */
  rend_cache_store_status_t
  rend_cache_store_v2_desc_as_client(const char *desc,
                                     const char *desc_id_base32,
                                     const rend_data_t *rend_query,
                                     rend_cache_entry_t **entry)
  {
    /*XXXX this seems to have a bit of duplicate code with
     * rend_cache_store_v2_desc_as_dir().  Fix that. */
    /* Though having similar elements, both functions were separated on
     * purpose:
     * - dirs don't care about encoded/encrypted introduction points, clients
     *   do.
     * - dirs store descriptors in a separate cache by descriptor ID, whereas
     *   clients store them by service ID; both caches are different data
     *   structures and have different access methods.
     * - dirs store a descriptor only if they are responsible for its ID,
     *   clients do so in every way (because they have requested it before).
     * - dirs can process multiple concatenated descriptors which is required
     *   for replication, whereas clients only accept a single descriptor.
     * Thus, combining both methods would result in a lot of if statements
     * which probably would not improve, but worsen code readability. -KL */
    rend_service_descriptor_t *parsed = NULL;
    char desc_id[DIGEST_LEN];
    char *intro_content = NULL;
    size_t intro_size;
    size_t encoded_size;
    const char *next_desc;
    time_t now = time(NULL);
    char key[REND_SERVICE_ID_LEN_BASE32+2];
    char service_id[REND_SERVICE_ID_LEN_BASE32+1];
    char want_desc_id[DIGEST_LEN];
    rend_cache_entry_t *e;
    rend_cache_store_status_t retval = RCS_BADDESC;
    tor_assert(rend_cache);
    tor_assert(desc);
    tor_assert(desc_id_base32);
    memset(want_desc_id, 0, sizeof(want_desc_id));
    if (entry) {
      *entry = NULL;
    }
    if (base32_decode(want_desc_id, sizeof(want_desc_id),
                      desc_id_base32, strlen(desc_id_base32)) != 0) {
      log_warn(LD_BUG, "Couldn't decode base32 %s for descriptor id.",
               escaped_safe_str_client(desc_id_base32));
      goto err;
    }
    /* Parse the descriptor. */
    if (rend_parse_v2_service_descriptor(&parsed, desc_id, &intro_content,
                                         &intro_size, &encoded_size,
                                         &next_desc, desc, 0) < 0) {
      log_warn(LD_REND, "Could not parse descriptor.");
      goto err;
    }
    /* Compute service ID from public key. */
    if (rend_get_service_id(parsed->pk, service_id)<0) {
      log_warn(LD_REND, "Couldn't compute service ID.");
      goto err;
    }
    if (rend_query->onion_address[0] != '\0' &&
        strcmp(rend_query->onion_address, service_id)) {
      log_warn(LD_REND, "Received service descriptor for service ID %s; "
               "expected descriptor for service ID %s.",
               service_id, safe_str(rend_query->onion_address));
      goto err;
    }
    if (tor_memneq(desc_id, want_desc_id, DIGEST_LEN)) {
      log_warn(LD_REND, "Received service descriptor for %s with incorrect "
               "descriptor ID.", service_id);
      goto err;
    }
  
    /* Decode/decrypt introduction points. */
    if (intro_content && intro_size > 0) {
      int n_intro_points;
      if (rend_query->auth_type != REND_NO_AUTH &&
          !tor_mem_is_zero(rend_query->descriptor_cookie,
                           sizeof(rend_query->descriptor_cookie))) {
        char *ipos_decrypted = NULL;
        size_t ipos_decrypted_size;
        if (rend_decrypt_introduction_points(&ipos_decrypted,
                                             &ipos_decrypted_size,
                                             rend_query->descriptor_cookie,
                                             intro_content,
                                             intro_size) < 0) {
          log_warn(LD_REND, "Failed to decrypt introduction points. We are "
                   "probably unable to parse the encoded introduction points.");
        } else {
          /* Replace encrypted with decrypted introduction points. */
          log_info(LD_REND, "Successfully decrypted introduction points.");
          tor_free(intro_content);
          intro_content = ipos_decrypted;
          intro_size = ipos_decrypted_size;
        }
      }
      n_intro_points = rend_parse_introduction_points(parsed, intro_content,
                                                      intro_size);
      if (n_intro_points <= 0) {
        log_warn(LD_REND, "Failed to parse introduction points. Either the "
                 "service has published a corrupt descriptor or you have "
                 "provided invalid authorization data.");
        goto err;
      } else if (n_intro_points > MAX_INTRO_POINTS) {
        log_warn(LD_REND, "Found too many introduction points on a hidden "
                 "service descriptor for %s. This is probably a (misguided) "
                 "attempt to improve reliability, but it could also be an "
                 "attempt to do a guard enumeration attack. Rejecting.",
                 safe_str_client(service_id));
  
        goto err;
      }
    } else {
      log_info(LD_REND, "Descriptor does not contain any introduction points.");
      parsed->intro_nodes = smartlist_new();
    }
    /* We don't need the encoded/encrypted introduction points any longer. */
    tor_free(intro_content);
    /* Is descriptor too old? */
    if (parsed->timestamp < now - REND_CACHE_MAX_AGE-REND_CACHE_MAX_SKEW) {
      log_warn(LD_REND, "Service descriptor with service ID %s is too old.",
               safe_str_client(service_id));
      goto err;
    }
    /* Is descriptor too far in the future? */
    if (parsed->timestamp > now + REND_CACHE_MAX_SKEW) {
      log_warn(LD_REND, "Service descriptor with service ID %s is too far in "
               "the future.", safe_str_client(service_id));
      goto err;
    }
    /* Do we have the same exact copy already in our cache? */
    tor_snprintf(key, sizeof(key), "2%s", service_id);
    e = (rend_cache_entry_t*) strmap_get_lc(rend_cache, key);
    if (e && !strcmp(desc, e->desc)) {
      log_info(LD_REND,"We already have this service descriptor %s.",
               safe_str_client(service_id));
      goto okay;
    }
    /* Verify that we are not replacing an older descriptor. It's important to
     * avoid an evil HSDir serving old descriptor. We validate if the
     * timestamp is greater than and not equal because it's a rounded down
     * timestamp to the hour so if the descriptor changed in the same hour,
     * the rend cache failure will tells us if we have a new descriptor. */
    if (e && e->parsed->timestamp > parsed->timestamp) {
      log_info(LD_REND, "We already have a new enough service descriptor for "
               "service ID %s with the same desc ID and version.",
               safe_str_client(service_id));
      goto okay;
    }
    /* Lookup our failure cache for intro point that might be unsuable. */
    validate_intro_point_failure(parsed, service_id);
    /* It's now possible that our intro point list is empty, this means that
     * this descriptor is useless to us because intro points have all failed
     * somehow before. Discard the descriptor. */
    if (smartlist_len(parsed->intro_nodes) == 0) {
      log_info(LD_REND, "Service descriptor with service ID %s, every "
               "intro points are unusable. Discarding it.",
               safe_str_client(service_id));
      goto err;
    }
    /* Now either purge the current one and replace it's content or create a
     * new one and add it to the rend cache. */
    if (!e) {
      e = tor_malloc_zero(sizeof(rend_cache_entry_t));
      strmap_set_lc(rend_cache, key, e);
    } else {
      rend_cache_decrement_allocation(rend_cache_entry_allocation(e));
      rend_cache_failure_remove(e->parsed);
      rend_service_descriptor_free(e->parsed);
      tor_free(e->desc);
    }
    e->parsed = parsed;
    e->desc = tor_malloc_zero(encoded_size + 1);
    strlcpy(e->desc, desc, encoded_size + 1);
    e->len = encoded_size;
    rend_cache_increment_allocation(rend_cache_entry_allocation(e));
    log_debug(LD_REND,"Successfully stored rend desc '%s', len %d.",
              safe_str_client(service_id), (int)encoded_size);
    if (entry) {
      *entry = e;
    }
    return RCS_OKAY;
  
   okay:
    if (entry) {
      *entry = e;
    }
    retval = RCS_OKAY;
  
   err:
    rend_service_descriptor_free(parsed);
    tor_free(intro_content);
    return retval;
  }
  