lokinet/llarp/nodedb.cpp

#include "nodedb.hpp"

#include "crypto/types.hpp"
#include "dht/kademlia.hpp"
#include "messages/fetch.hpp"
#include "router_contact.hpp"
#include "util/time.hpp"

#include <algorithm>
#include <unordered_map>
#include <utility>

static const char skiplist_subdirs[] = "0123456789abcdef";
static const std::string RC_FILE_EXT = ".signed";

namespace llarp
{
  static void
  EnsureSkiplist(fs::path nodedbDir)
  {
    if (not fs::exists(nodedbDir))
    {
      // if the old 'netdb' directory exists, move it to this one
      fs::path parent = nodedbDir.parent_path();
      fs::path old = parent / "netdb";
      if (fs::exists(old))
        fs::rename(old, nodedbDir);
      else
        fs::create_directory(nodedbDir);
    }

    if (not fs::is_directory(nodedbDir))
      throw std::runtime_error{fmt::format("nodedb {} is not a directory", nodedbDir)};

    for (const char& ch : skiplist_subdirs)
    {
      // this seems to be a problem on all targets
      // perhaps cpp17::fs is just as screwed-up
      // attempting to create a folder with no name
      // what does this mean...?
      if (!ch)
        continue;

      fs::path sub = nodedbDir / std::string(&ch, 1);
      fs::create_directory(sub);
    }
  }

  NodeDB::NodeDB(fs::path root, std::function<void(std::function<void()>)> diskCaller, Router* r)
      : _router{*r}
      , _root{std::move(root)}
      , _disk(std::move(diskCaller))
      , _next_flush_time{time_now_ms() + FLUSH_INTERVAL}
  {
    EnsureSkiplist(_root);
    fetch_counters.clear();
  }

  std::optional<RemoteRC>
  NodeDB::get_random_rc() const
  {
    std::optional<RemoteRC> rand = std::nullopt;

    std::sample(known_rcs.begin(), known_rcs.end(), &*rand, 1, csrng);
    return rand;
  }

  std::optional<std::vector<RemoteRC>>
  NodeDB::get_n_random_rcs(size_t n) const
  {
    std::vector<RemoteRC> rand{};

    std::sample(known_rcs.begin(), known_rcs.end(), std::back_inserter(rand), n, csrng);
    return rand.empty() ? std::nullopt : std::make_optional(rand);
  }

  std::optional<RemoteRC>
  NodeDB::get_random_rc_conditional(std::function<bool(RemoteRC)> hook) const
  {
    std::optional<RemoteRC> rand = get_random_rc();

    if (rand and hook(*rand))
      return rand;

    size_t i = 0;

    for (const auto& rc : known_rcs)
    {
      if (not hook(rc))
        continue;

      if (++i <= 1)
      {
        rand = rc;
        continue;
      }

      size_t x = csrng() % (i + 1);
      if (x <= 1)
        rand = rc;
    }

    return rand;
  }

  std::optional<std::vector<RemoteRC>>
  NodeDB::get_n_random_rcs_conditional(size_t n, std::function<bool(RemoteRC)> hook) const
  {
    std::vector<RemoteRC> selected;
    selected.reserve(n);

    size_t i = 0;

    for (const auto& rc : known_rcs)
    {
      // ignore any RC's that do not pass the condition
      if (not hook(rc))
        continue;

      // load the first n RC's that pass the condition into selected
      if (++i <= n)
      {
        selected.push_back(rc);
        continue;
      }

      // replace selections with decreasing probability per iteration
      size_t x = csrng() % (i + 1);
      if (x < n)
        selected[x] = rc;
    }

    return selected.size() == n ? std::make_optional(selected) : std::nullopt;
  }

  void
  NodeDB::Tick(llarp_time_t now)
  {
    if (_next_flush_time == 0s)
      return;

    if (now > _next_flush_time)
    {
      _router.loop()->call([this]() {
        _next_flush_time += FLUSH_INTERVAL;
        // make copy of all rcs
        std::vector<RemoteRC> copy;

        for (const auto& item : rc_lookup)
          copy.push_back(item.second);

        // flush them to disk in one big job
        // TODO: split this up? idk maybe some day...
        _disk([this, data = std::move(copy)]() {
          for (const auto& rc : data)
            rc.write(get_path_by_pubkey(rc.router_id()));
        });
      });
    }
  }

  fs::path
  NodeDB::get_path_by_pubkey(RouterID pubkey) const
  {
    std::string hexString = oxenc::to_hex(pubkey.begin(), pubkey.end());
    std::string skiplistDir;

    const llarp::RouterID r{pubkey};
    std::string fname = r.ToString();

    skiplistDir += hexString[0];
    fname += RC_FILE_EXT;
    return _root / skiplistDir / fname;
  }

  bool
  NodeDB::want_rc(const RouterID& rid) const
  {
    if (not _router.is_service_node())
      return true;
    return registered_routers.count(rid);
  }

  void
  NodeDB::set_bootstrap_routers(std::unique_ptr<BootstrapList> from_router)
  {
    // TODO: if this needs to be called more than once (ex: drastic failures), then
    // change this assert to a bootstraps.clear() call
    assert(_bootstraps->empty());

    _bootstraps = std::move(from_router);
    _bootstraps->randomize();
  }

  bool
  NodeDB::process_fetched_rcs(std::vector<RemoteRC>& rcs)
  {
    std::unordered_set<RemoteRC> inter_set;

    std::set_intersection(
        known_rcs.begin(),
        known_rcs.end(),
        rcs.begin(),
        rcs.end(),
        std::inserter(inter_set, inter_set.begin()));

    // the total number of rcs received
    const auto num_received = static_cast<double>(rcs.size());
    // the number of returned "good" rcs (that are also found locally)
    const auto inter_size = inter_set.size();
    // the number of rcs currently held locally
    const auto local_count = static_cast<double>(known_rcs.size());

    const auto fetch_threshold = (double)inter_size / num_received;
    const auto local_alignment = (double)inter_size / local_count;

    /** We are checking 3 things here:
        1) The number of "good" rcs is above MIN_GOOD_RC_FETCH_TOTAL
        2) The ratio of "good" rcs to total received is above MIN_GOOD_RC_FETCH_THRESHOLD
        3) The ratio of received and found locally to total found locally is above
           LOCAL_RC_ALIGNMENT_THRESHOLD
    */
    return inter_size > MIN_GOOD_RC_FETCH_TOTAL and fetch_threshold > MIN_GOOD_RC_FETCH_THRESHOLD
        and local_alignment > LOCAL_RC_ALIGNMENT_THRESHOLD;
  }

  bool
  NodeDB::ingest_fetched_rcs(std::vector<RemoteRC> rcs, rc_time timestamp)
  {
    // if we are not bootstrapping, we should check the rc's against the ones we currently hold
    if (not _using_bootstrap_fallback)
    {}

    for (auto& rc : rcs)
      put_rc_if_newer(std::move(rc), timestamp);

    return true;
  }

  void
  NodeDB::ingest_rid_fetch_responses(const RouterID& source, std::unordered_set<RouterID> rids)
  {
    if (rids.empty())
    {
      fail_sources.insert(source);
      return;
    }

    for (const auto& rid : rids)
      fetch_counters[rid] += 1;
  }

  /** We only call into this function after ensuring two conditions:
        1) We have received all 12 responses from the queried RouterID sources, whether that
          response was a timeout or not
        2) Of those responses, less than 4 were errors of any sorts

      Upon receiving each response from the rid fetch sources, the returned rid's are incremented
      in fetch_counters. This greatly simplifies the analysis required by this function to the
      determine success or failure:
        - If the frequency of each rid is above a threshold, it is accepted
        - If the number of accepted rids is below a certain amount, the set is rejected

      Logically, this function performs the following basic analysis of the returned RIDs:
        1) All responses are coalesced into a union set with no repetitions
        2) If we are bootstrapping:
            - The routerID's returned
  */
  bool
  NodeDB::process_fetched_rids()
  {
    std::unordered_set<RouterID> union_set, intersection_set;

    for (const auto& [rid, count] : fetch_counters)
    {
      if (count > MIN_RID_FETCH_FREQ)
        union_set.insert(rid);
    }

    // get the intersection of accepted rids and local rids
    std::set_intersection(
        known_rids.begin(),
        known_rids.end(),
        union_set.begin(),
        union_set.end(),
        std::inserter(intersection_set, intersection_set.begin()));

    // the total number of rids received
    const auto num_received = (double)fetch_counters.size();
    // the total number of received AND accepted rids
    const auto union_size = union_set.size();
    // the number of rids currently held locally
    const auto local_count = (double)known_rids.size();
    // the number of accepted rids that are also found locally
    const auto inter_size = (double)intersection_set.size();

    const auto fetch_threshold = (double)union_size / num_received;
    const auto local_alignment = (double)inter_size / local_count;

    /** We are checking 2, potentially 3 things here:
        1) The ratio of received/accepted to total received is above GOOD_RID_FETCH_THRESHOLD.
           This tells us how well the rid source's sets of rids "agree" with one another
        2) The total number received is above MIN_RID_FETCH_TOTAL. This ensures that we are
           receiving a sufficient amount to make a comparison of any sorts
        3) If we are not bootstrapping, then the ratio of received/accepted found locally to
           the total number locally held is above LOCAL_RID_ALIGNMENT_THRESHOLD. This gives us
           an estimate of how "aligned" the rid source's set of rid's is to ours
    */
    return (fetch_threshold > GOOD_RID_FETCH_THRESHOLD) and (union_size > MIN_GOOD_RID_FETCH_TOTAL)
            and (not _using_bootstrap_fallback)
        ? local_alignment > LOCAL_RID_ALIGNMENT_THRESHOLD
        : true;
  }

  void
  NodeDB::fetch_initial()
  {
    if (known_rids.empty())
    {
      fallback_to_bootstrap();
    }
    else
    {
      // Set fetch source as random selection of known active client routers
      fetch_source = *std::next(known_rids.begin(), csrng() % known_rids.size());
      fetch_rcs(true);
    }
  }

  void
  NodeDB::fetch_rcs(bool initial)
  {
    auto& num_failures = fetch_failures;

    // base case; this function is called recursively
    if (num_failures > MAX_FETCH_ATTEMPTS)
    {
      fetch_rcs_result(initial, true);
      return;
    }

    std::vector<RouterID> needed;
    const auto now = time_point_now();

    for (const auto& [rid, rc] : rc_lookup)
    {
      if (now - rc.timestamp() > RouterContact::OUTDATED_AGE)
        needed.push_back(rid);
    }

    RouterID& src = fetch_source;

    _router.link_manager().fetch_rcs(
        src,
        RCFetchMessage::serialize(_router.last_rc_fetch, needed),
        [this, src, initial](oxen::quic::message m) mutable {
          if (m.timed_out)
          {
            log::info(logcat, "RC fetch to {} timed out", src);
            fetch_rcs_result(initial, true);
            return;
          }
          try
          {
            oxenc::bt_dict_consumer btdc{m.body()};

            if (not m)
            {
              auto reason = btdc.require<std::string_view>(messages::STATUS_KEY);
              log::info(logcat, "RC fetch to {} returned error: {}", src, reason);
              fetch_rcs_result(initial, true);
              return;
            }

            auto btlc = btdc.require<oxenc::bt_list_consumer>("rcs"sv);
            auto timestamp = rc_time{std::chrono::seconds{btdc.require<int64_t>("time"sv)}};

            std::vector<RemoteRC> rcs;

            while (not btlc.is_finished())
              rcs.emplace_back(btlc.consume_dict_consumer());

            // if process_fetched_rcs returns false, then the trust model rejected the fetched RC's
            fetch_rcs_result(initial, not ingest_fetched_rcs(std::move(rcs), timestamp));
          }
          catch (const std::exception& e)
          {
            log::info(logcat, "Failed to parse RC fetch response from {}: {}", src, e.what());
            fetch_rcs_result(initial, true);
            return;
          }
        });
  }

  void
  NodeDB::fetch_rids(bool initial)
  {
    // base case; this function is called recursively
    if (fetch_failures > MAX_FETCH_ATTEMPTS)
    {
      fetch_rids_result(initial);
      return;
    }

    if (rid_sources.empty())
    {
      reselect_router_id_sources(rid_sources);
    }

    if (not initial and rid_sources.empty())
    {
      log::error(logcat, "Attempting to fetch RouterIDs, but have no source from which to do so.");
      fallback_to_bootstrap();
      return;
    }

    fetch_counters.clear();

    RouterID& src = fetch_source;

    for (const auto& target : rid_sources)
    {
      _router.link_manager().fetch_router_ids(
          src,
          FetchRIDMessage::serialize(target),
          [this, src, target, initial](oxen::quic::message m) mutable {
            if (not m)
            {
              log::info(link_cat, "RID fetch from {} via {} timed out", src, target);
              ingest_rid_fetch_responses(target);
              fetch_rids_result(initial);
              return;
            }

            try
            {
              oxenc::bt_dict_consumer btdc{m.body()};

              btdc.required("routers");
              auto router_id_strings = btdc.consume_list<std::vector<ustring>>();

              btdc.require_signature("signature", [&src](ustring_view msg, ustring_view sig) {
                if (sig.size() != 64)
                  throw std::runtime_error{"Invalid signature: not 64 bytes"};
                if (not crypto::verify(src, msg, sig))
                  throw std::runtime_error{
                      "Failed to verify signature for fetch RouterIDs response."};
              });

              std::unordered_set<RouterID> router_ids;

              for (const auto& s : router_id_strings)
              {
                if (s.size() != RouterID::SIZE)
                {
                  log::warning(
                      link_cat, "RID fetch from {} via {} returned bad RouterID", target, src);
                  ingest_rid_fetch_responses(target);
                  fetch_rids_result(initial);
                  return;
                }

                router_ids.emplace(s.data());
              }

              ingest_rid_fetch_responses(target, std::move(router_ids));
              fetch_rids_result(initial);  // success
              return;
            }
            catch (const std::exception& e)
            {
              log::info(link_cat, "Error handling fetch RouterIDs response: {}", e.what());
              ingest_rid_fetch_responses(target);
              fetch_rids_result(initial);
            }
          });
    }
  }

  void
  NodeDB::fetch_rcs_result(bool initial, bool error)
  {
    if (error)
    {
      auto& fail_count = (_using_bootstrap_fallback) ? bootstrap_failures : fetch_failures;
      auto& THRESHOLD =
          (_using_bootstrap_fallback) ? MAX_BOOTSTRAP_FETCH_ATTEMPTS : MAX_FETCH_ATTEMPTS;

      // This catches three different failure cases;
      //  1) bootstrap fetching and over failure threshold
      //  2) bootstrap fetching and more failures to go
      //  3) standard fetching and over threshold
      if (++fail_count >= THRESHOLD || _using_bootstrap_fallback)
      {
        log::info(
            logcat,
            "RC fetching from {} reached failure threshold ({}); falling back to bootstrap...",
            fetch_source,
            THRESHOLD);

        fallback_to_bootstrap();
        return;
      }

      // If we have passed the last last conditional, then it means we are not bootstrapping
      // and the current fetch_source has more attempts before being rotated. As a result, we
      // find new non-bootstrap RC fetch source and try again buddy
      fetch_source = (initial) ? *std::next(known_rids.begin(), csrng() % known_rids.size())
                               : std::next(rc_lookup.begin(), csrng() % rc_lookup.size())->first;

      fetch_rcs(initial);
    }
    else
    {
      log::debug(logcat, "Successfully fetched RC's from {}", fetch_source);
      post_fetch_rcs(initial);
    }
  }

  void
  NodeDB::fetch_rids_result(bool initial)
  {
    if (fetch_failures > MAX_FETCH_ATTEMPTS)
    {
      log::info(
          logcat,
          "Failed {} attempts to fetch RID's from {}; reverting to bootstrap...",
          MAX_FETCH_ATTEMPTS,
          fetch_source);

      fallback_to_bootstrap();
      return;
    }

    auto n_responses = RID_SOURCE_COUNT - fail_sources.size();

    if (n_responses < RID_SOURCE_COUNT)
    {
      log::debug(logcat, "Received {}/{} fetch RID requests", n_responses, RID_SOURCE_COUNT);
      return;
    }

    auto n_fails = fail_sources.size();

    if (n_fails <= MAX_RID_ERRORS)
    {
      log::debug(
          logcat, "RID fetching was successful ({}/{} acceptable errors)", n_fails, MAX_RID_ERRORS);

      // this is where the trust model will do verification based on the similarity of the sets
      if (process_fetched_rids())
      {
        log::debug(logcat, "Accumulated RID's accepted by trust model");
        post_fetch_rids(initial);
        return;
      }

      log::debug(
          logcat, "Accumulated RID's rejected by trust model, reselecting all RID sources...");
      reselect_router_id_sources(rid_sources);
      ++fetch_failures;
    }
    else
    {
      // we had 4 or more failed requests, so we will need to rotate our rid sources
      log::debug(
          logcat, "RID fetching found {} failures; reselecting failed RID sources...", n_fails);
      ++fetch_failures;
      reselect_router_id_sources(fail_sources);
    }

    fetch_rids(true);
  }

  void
  NodeDB::post_fetch_rcs(bool initial)
  {
    _router.last_rc_fetch = llarp::time_point_now();

    if (initial)
      fetch_rids(initial);
  }

  void
  NodeDB::post_fetch_rids(bool initial)
  {
    fail_sources.clear();
    fetch_failures = 0;
    _router.last_rid_fetch = llarp::time_point_now();
    fetch_counters.clear();
    _needs_rebootstrap = false;

    if (initial)
      _needs_initial_fetch = false;
  }

  void
  NodeDB::fallback_to_bootstrap()
  {
    auto at_max_failures = bootstrap_failures >= MAX_BOOTSTRAP_FETCH_ATTEMPTS;

    // base case: we have failed to query all bootstraps, or we received a sample of
    // the network, but the sample was unusable or unreachable. We will also enter this
    // if we are on our first fallback to bootstrap so we can set the fetch_source (by
    // checking not using_bootstrap_fallback)
    if (at_max_failures || not _using_bootstrap_fallback)
    {
      bootstrap_failures = 0;

      // Fail case: if we have returned to the front of the bootstrap list, we're in a
      // bad spot; we are unable to do anything
      if (_using_bootstrap_fallback)
      {
        auto err = fmt::format(
            "ERROR: ALL BOOTSTRAPS ARE BAD... REATTEMPTING IN {}...", BOOTSTRAP_COOLDOWN);
        log::error(logcat, err);

        bootstrap_cooldown();
        return;
      }

      auto rc = _bootstraps->next();
      fetch_source = rc.router_id();
    }

    // By passing the last conditional, we ensure this is set to true
    _using_bootstrap_fallback = true;
    _needs_rebootstrap = false;

    _router.link_manager().fetch_bootstrap_rcs(
        fetch_source,
        BootstrapFetchMessage::serialize(BOOTSTRAP_SOURCE_COUNT),
        [this](oxen::quic::message m) mutable {
          if (not m)
          {
            ++bootstrap_failures;
            log::warning(
                logcat,
                "BootstrapRC fetch request to {} failed (error {}/{})",
                fetch_source,
                bootstrap_failures,
                MAX_BOOTSTRAP_FETCH_ATTEMPTS);
            fallback_to_bootstrap();
            return;
          }

          std::unordered_set<RouterID> rids;

          try
          {
            oxenc::bt_dict_consumer btdc{m.body()};

            {
              auto btlc = btdc.require<oxenc::bt_list_consumer>("rcs"sv);

              while (not btlc.is_finished())
              {
                auto rc = RemoteRC{btlc.consume_dict_consumer()};
                rids.emplace(rc.router_id());
              }
            }
          }
          catch (const std::exception& e)
          {
            ++bootstrap_failures;
            log::warning(
                logcat,
                "Failed to parse BootstrapRC fetch response from {} (error {}/{}): {}",
                fetch_source,
                bootstrap_failures,
                MAX_BOOTSTRAP_FETCH_ATTEMPTS,
                e.what());
            fallback_to_bootstrap();
            return;
          }

          // We set this to the max allowable value because if this result is bad, we won't
          // try this bootstrap again. If this result is undersized, we roll right into the
          // next call to fallback_to_bootstrap() and hit the base case, rotating sources
          bootstrap_failures = MAX_BOOTSTRAP_FETCH_ATTEMPTS;

          if (rids.size() == BOOTSTRAP_SOURCE_COUNT)
          {
            known_rids.swap(rids);
            fetch_initial();
          }
          else
          {
            ++bootstrap_failures;
            log::warning(
                logcat,
                "BootstrapRC fetch response from {} returned insufficient number of RC's (error "
                "{}/{})",
                fetch_source,
                bootstrap_failures,
                MAX_BOOTSTRAP_FETCH_ATTEMPTS);
            fallback_to_bootstrap();
          }
        });
  }

  void
  NodeDB::bootstrap_cooldown()
  {
    _needs_rebootstrap = true;
    _router.next_bootstrap_attempt = llarp::time_point_now() + BOOTSTRAP_COOLDOWN;
  }

  void
  NodeDB::reselect_router_id_sources(std::unordered_set<RouterID> specific)
  {
    replace_subset(rid_sources, specific, known_rids, RID_SOURCE_COUNT, csrng);
  }

  void
  NodeDB::set_router_whitelist(
      const std::vector<RouterID>& whitelist,
      const std::vector<RouterID>& greylist,
      const std::vector<RouterID>& greenlist)
  {
    if (whitelist.empty())
      return;

    registered_routers.clear();
    registered_routers.insert(whitelist.begin(), whitelist.end());
    registered_routers.insert(greylist.begin(), greylist.end());
    registered_routers.insert(greenlist.begin(), greenlist.end());

    router_whitelist.clear();
    router_whitelist.insert(whitelist.begin(), whitelist.end());
    router_greylist.clear();
    router_greylist.insert(greylist.begin(), greylist.end());
    router_greenlist.clear();
    router_greenlist.insert(greenlist.begin(), greenlist.end());

    log::info(
        logcat, "lokinet service node list now has ", router_whitelist.size(), " active routers");
  }

  std::optional<RouterID>
  NodeDB::get_random_whitelist_router() const
  {
    const auto sz = router_whitelist.size();
    if (sz == 0)
      return std::nullopt;
    auto itr = router_whitelist.begin();
    if (sz > 1)
      std::advance(itr, randint() % sz);
    return *itr;
  }

  bool
  NodeDB::is_connection_allowed(const RouterID& remote) const
  {
    if (_pinned_edges.size() && _pinned_edges.count(remote) == 0
        && not _bootstraps->contains(remote))
      return false;

    if (not _router.is_service_node())
      return true;

    return router_whitelist.count(remote) or router_greylist.count(remote);
  }

  bool
  NodeDB::is_first_hop_allowed(const RouterID& remote) const
  {
    if (_pinned_edges.size() && _pinned_edges.count(remote) == 0)
      return false;

    return true;
  }

  void
  NodeDB::load_from_disk()
  {
    if (_root.empty())
      return;

    std::set<fs::path> purge;

    const auto now = time_now_ms();

    for (const char& ch : skiplist_subdirs)
    {
      if (!ch)
        continue;

      std::string p;
      p += ch;
      fs::path sub = _root / p;

      llarp::util::IterDir(sub, [&](const fs::path& f) -> bool {
        // skip files that are not suffixed with .signed
        if (not(fs::is_regular_file(f) and f.extension() == RC_FILE_EXT))
          return true;

        RemoteRC rc{};

        if (not rc.read(f))
        {
          // try loading it, purge it if it is junk
          purge.emplace(f);
          return true;
        }

        if (rc.is_expired(now))
        {
          // rc expired dont load it and purge it later
          purge.emplace(f);
          return true;
        }

        const auto& rid = rc.router_id();

        auto [itr, b] = known_rcs.emplace(std::move(rc));
        rc_lookup.emplace(rid, *itr);
        known_rids.insert(rid);

        return true;
      });
    }

    if (not purge.empty())
    {
      log::warning(logcat, "removing {} invalid RCs from disk", purge.size());

      for (const auto& fpath : purge)
        fs::remove(fpath);
    }
  }

  void
  NodeDB::save_to_disk() const
  {
    if (_root.empty())
      return;

    _router.loop()->call([this]() {
      for (const auto& rc : rc_lookup)
      {
        rc.second.write(get_path_by_pubkey(rc.first));
      }
    });
  }

  bool
  NodeDB::has_rc(RouterID pk) const
  {
    return rc_lookup.count(pk);
  }

  std::optional<RemoteRC>
  NodeDB::get_rc(RouterID pk) const
  {
    if (auto itr = rc_lookup.find(pk); itr != rc_lookup.end())
      return itr->second;

    return std::nullopt;
  }

  void
  NodeDB::remove_router(RouterID pk)
  {
    _router.loop()->call([this, pk]() {
      rc_lookup.erase(pk);
      remove_many_from_disk_async({pk});
    });
  }

  void
  NodeDB::remove_stale_rcs()
  {
    auto cutoff_time = time_point_now();

    cutoff_time -=
        _router.is_service_node() ? RouterContact::OUTDATED_AGE : RouterContact::LIFETIME;

    for (auto itr = rc_lookup.begin(); itr != rc_lookup.end();)
    {
      if (cutoff_time > itr->second.timestamp())
      {
        log::info(logcat, "Pruning RC for {}, as it is too old to keep.", itr->first);
        known_rcs.erase(itr->second);
        rc_lookup.erase(itr);
        continue;
      }
      itr++;
    }
  }

  bool
  NodeDB::put_rc(RemoteRC rc, rc_time now)
  {
    const auto& rid = rc.router_id();

    if (not want_rc(rid))
      return false;

    known_rcs.erase(rc);
    rc_lookup.erase(rid);

    auto [itr, b] = known_rcs.emplace(std::move(rc));
    rc_lookup.emplace(rid, *itr);
    known_rids.insert(rid);

    last_rc_update_times[rid] = now;
    return true;
  }

  size_t
  NodeDB::num_loaded() const
  {
    return _router.loop()->call_get([this]() { return known_rcs.size(); });
  }

  bool
  NodeDB::put_rc_if_newer(RemoteRC rc, rc_time now)
  {
    if (auto itr = rc_lookup.find(rc.router_id());
        itr == rc_lookup.end() or itr->second.other_is_newer(rc))
      return put_rc(std::move(rc), now);

    return false;
  }

  void
  NodeDB::remove_many_from_disk_async(std::unordered_set<RouterID> remove) const
  {
    if (_root.empty())
      return;

    // build file list
    std::set<fs::path> files;

    for (auto id : remove)
      files.emplace(get_path_by_pubkey(std::move(id)));

    // remove them from the disk via the diskio thread
    _disk([files]() {
      for (auto fpath : files)
        fs::remove(fpath);
    });
  }

  RemoteRC
  NodeDB::find_closest_to(llarp::dht::Key_t location) const
  {
    return _router.loop()->call_get([this, location]() -> RemoteRC {
      RemoteRC rc{};
      const llarp::dht::XorMetric compare(location);

      VisitAll([&rc, compare](const auto& otherRC) {
        const auto& rid = rc.router_id();

        if (rid.IsZero() || compare(dht::Key_t{otherRC.router_id()}, dht::Key_t{rid}))
        {
          rc = otherRC;
          return;
        }
      });
      return rc;
    });
  }

  std::vector<RemoteRC>
  NodeDB::find_many_closest_to(llarp::dht::Key_t location, uint32_t numRouters) const
  {
    return _router.loop()->call_get([this, location, numRouters]() -> std::vector<RemoteRC> {
      std::vector<const RemoteRC*> all;

      all.reserve(known_rcs.size());

      for (auto& entry : rc_lookup)
      {
        all.push_back(&entry.second);
      }

      auto it_mid = numRouters < all.size() ? all.begin() + numRouters : all.end();

      std::partial_sort(
          all.begin(), it_mid, all.end(), [compare = dht::XorMetric{location}](auto* a, auto* b) {
            return compare(*a, *b);
          });

      std::vector<RemoteRC> closest;
      closest.reserve(numRouters);
      for (auto it = all.begin(); it != it_mid; ++it)
        closest.push_back(**it);

      return closest;
    });
  }
}  // namespace llarp