lokinet/llarp/link/link_manager.cpp

#include "link_manager.hpp"

#include "connection.hpp"
#include "contacts.hpp"

#include <llarp/messages/dht.hpp>
#include <llarp/messages/exit.hpp>
#include <llarp/messages/fetch.hpp>
#include <llarp/messages/path.hpp>
#include <llarp/nodedb.hpp>
#include <llarp/path/path.hpp>
#include <llarp/router/router.hpp>

#include <oxenc/bt_producer.h>

#include <algorithm>
#include <exception>
#include <set>

namespace llarp
{
  namespace link
  {
    Endpoint::Endpoint(std::shared_ptr<oxen::quic::Endpoint> ep, LinkManager& lm)
        : endpoint{std::move(ep)}
        , link_manager{lm}
        , _is_service_node{link_manager.is_service_node()}
    {}

    std::shared_ptr<link::Connection>
    Endpoint::get_service_conn(const RouterID& rid) const
    {
      if (auto itr = service_conns.find(rid); itr != service_conns.end())
        return itr->second;

      return nullptr;
    }

    std::shared_ptr<link::Connection>
    Endpoint::get_conn(const RouterID& rid) const
    {
      if (auto itr = service_conns.find(rid); itr != service_conns.end())
        return itr->second;

      if (_is_service_node)
      {
        if (auto itr = client_conns.find(rid); itr != client_conns.end())
          return itr->second;
      }

      return nullptr;
    }

    bool
    Endpoint::have_conn(const RouterID& remote) const
    {
      return have_service_conn(remote) or have_client_conn(remote);
    }

    bool
    Endpoint::have_client_conn(const RouterID& remote) const
    {
      return client_conns.count(remote);
    }

    bool
    Endpoint::have_service_conn(const RouterID& remote) const
    {
      return service_conns.count(remote);
    }

    std::pair<size_t, size_t>
    Endpoint::num_in_out() const
    {
      size_t in{0}, out{0};

      for (const auto& c : service_conns)
      {
        if (c.second->is_inbound())
          ++in;
        else
          ++out;
      }

      for (const auto& c : client_conns)
      {
        if (c.second->is_inbound())
          ++in;
        else
          ++out;
      }

      return {in, out};
    }

    size_t
    Endpoint::num_client_conns() const
    {
      return client_conns.size();
    }

    size_t
    Endpoint::num_router_conns() const
    {
      return service_conns.size();
    }

    void
    Endpoint::for_each_connection(std::function<void(link::Connection&)> func)
    {
      for (const auto& [rid, conn] : service_conns)
        func(*conn);

      if (_is_service_node)
      {
        for (const auto& [rid, conn] : client_conns)
          func(*conn);
      }
    }

    void
    Endpoint::close_connection(RouterID _rid)
    {
      link_manager._router.loop()->call([this, rid = _rid]() {
        if (auto itr = service_conns.find(rid); itr != service_conns.end())
        {
          log::critical(logcat, "Closing connection to relay RID:{}", rid);
          auto& conn = *itr->second->conn;
          conn.close_connection();
        }
        else if (_is_service_node)
        {
          if (auto itr = client_conns.find(rid); itr != client_conns.end())
          {
            log::critical(logcat, "Closing connection to client RID:{}", rid);
            auto& conn = *itr->second->conn;
            conn.close_connection();
          }
        }
        else
          log::critical(logcat, "Could not find connection to RID:{} to close!", rid);
      });
    }
  }  // namespace link

  using messages::serialize_response;

  void
  LinkManager::for_each_connection(std::function<void(link::Connection&)> func)
  {
    if (is_stopping)
      return;

    return ep.for_each_connection(func);
  }

  void
  LinkManager::register_commands(
      std::shared_ptr<oxen::quic::BTRequestStream>& s, const RouterID& router_id, bool)
  {
    log::debug(logcat, "{} called", __PRETTY_FUNCTION__);

    s->register_handler("bfetch_rcs"s, [this](oxen::quic::message m) {
      _router.loop()->call(
          [this, msg = std::move(m)]() mutable { handle_fetch_bootstrap_rcs(std::move(msg)); });
    });

    s->register_handler("fetch_rcs"s, [this](oxen::quic::message m) {
      _router.loop()->call(
          [this, msg = std::move(m)]() mutable { handle_fetch_rcs(std::move(msg)); });
    });

    s->register_handler("fetch_rids"s, [this](oxen::quic::message m) {
      _router.loop()->call(
          [this, msg = std::move(m)]() mutable { handle_fetch_router_ids(std::move(msg)); });
    });

    s->register_handler("path_build"s, [this, rid = router_id](oxen::quic::message m) {
      _router.loop()->call(
          [this, &rid, msg = std::move(m)]() mutable { handle_path_build(std::move(msg), rid); });
    });

    s->register_handler("path_control"s, [this, rid = router_id](oxen::quic::message m) {
      _router.loop()->call(
          [this, &rid, msg = std::move(m)]() mutable { handle_path_control(std::move(msg), rid); });
    });

    s->register_handler("gossip_rc"s, [this](oxen::quic::message m) {
      _router.loop()->call(
          [this, msg = std::move(m)]() mutable { handle_gossip_rc(std::move(msg)); });
    });

    for (auto& method : direct_requests)
    {
      s->register_handler(
          std::string{method.first},
          [this, func = std::move(method.second)](oxen::quic::message m) {
            _router.loop()->call([this, msg = std::move(m), func = std::move(func)]() mutable {
              auto body = msg.body_str();
              auto respond = [m = std::move(msg)](std::string response) mutable {
                m.respond(std::move(response), m.is_error());
              };
              std::invoke(func, this, body, std::move(respond));
            });
          });
    }

    log::critical(logcat, "Registered all commands! (RID:{})", router_id);
  }

  LinkManager::LinkManager(Router& r)
      : _router{r}
      , _is_service_node{_router.is_service_node()}
      , quic{std::make_unique<oxen::quic::Network>()}
      , tls_creds{oxen::quic::GNUTLSCreds::make_from_ed_keys(
            {reinterpret_cast<const char*>(_router.identity().data()), size_t{32}},
            {reinterpret_cast<const char*>(_router.identity().toPublic().data()), size_t{32}})}
      , ep{startup_endpoint(), *this}
  {}

  std::unique_ptr<LinkManager>
  LinkManager::make(Router& r)
  {
    std::unique_ptr<LinkManager> p{new LinkManager(r)};
    return p;
  }

  std::shared_ptr<oxen::quic::Endpoint>
  LinkManager::startup_endpoint()
  {
    /** Parameters:
          - local bind address
          - conection open callback
          - connection close callback
          - stream constructor callback
            - will return a BTRequestStream on the first call to get_new_stream<BTRequestStream>
            - bt stream construction contains a stream close callback that shuts down the connection
              if the btstream closes unexpectedly
    */
    auto e = quic->endpoint(
        _router.listen_addr(),
        [this](oxen::quic::connection_interface& ci) { return on_conn_open(ci); },
        [this](oxen::quic::connection_interface& ci, uint64_t ec) {
          return on_conn_closed(ci, ec);
        },
        [this](oxen::quic::dgram_interface& di, bstring dgram) { recv_data_message(di, dgram); },
        is_service_node() ? alpns::SERVICE_INBOUND : alpns::CLIENT_INBOUND,
        is_service_node() ? alpns::SERVICE_OUTBOUND : alpns::CLIENT_OUTBOUND);

    // While only service nodes accept inbound connections, clients must have this key verify
    // callback set. It will reject any attempted inbound connection to a lokinet client prior to
    // handshake completion
    tls_creds->set_key_verify_callback([this](const ustring_view& key, const ustring_view& alpn) {
      RouterID other{key.data()};
      auto us = router().is_bootstrap_seed() ? "Bootstrap seed node"s : "Service node"s;
      auto is_snode = is_service_node();

      if (is_snode)
      {
        if (alpn == alpns::C_ALPNS)
        {
          log::critical(logcat, "{} node accepting client connection (remote ID:{})!", us, other);
          ep.client_conns.emplace(other, nullptr);
          return true;
        }
        if (alpn == alpns::SN_ALPNS)
        {
          // verify as service node!
          bool result = node_db->registered_routers().count(other);

          log::critical(
              logcat,
              "{} node was {} to confirm remote (RID:{}) is registered; {} connection!",
              us,
              result ? "able" : "unable",
              other,
              result ? "allowing" : "rejecting");

          if (result)
            ep.service_conns.emplace(other, nullptr);

          return result;
        }

        log::critical(logcat, "{} node received unknown ALPN; rejecting connection!", us);
        return false;
      }

      // TESTNET: change this to an error message later; just because someone tries to erroneously
      // connect to a local lokinet client doesn't mean we should kill the program?
      throw std::runtime_error{"Clients should not be validating inbound connections!"};
    });
    if (_router.is_service_node())
    {
      e->listen(tls_creds);
    }
    return e;
  }

  std::shared_ptr<oxen::quic::BTRequestStream>
  LinkManager::make_control(oxen::quic::connection_interface& ci, const RouterID& rid)
  {
    auto control_stream = ci.queue_incoming_stream<oxen::quic::BTRequestStream>(
        [this, rid = rid](oxen::quic::Stream&, uint64_t error_code) {
          log::warning(
              logcat,
              "BTRequestStream closed unexpectedly (ec:{}); closing inbound connection...",
              error_code);
          ep.close_connection(rid);
        });

    log::critical(logcat, "Queued BTStream to be opened (ID:{})", control_stream->stream_id());
    assert(control_stream->stream_id() == 0);
    register_commands(control_stream, rid);

    return control_stream;
  }

  void
  LinkManager::on_inbound_conn(oxen::quic::connection_interface& ci)
  {
    assert(_is_service_node);
    RouterID rid{ci.remote_key()};

    if (auto it = ep.service_conns.find(rid); it != ep.service_conns.end())
    {
      log::critical(logcat, "Configuring inbound connection from relay RID:{}", rid);
      it->second = std::make_shared<link::Connection>(ci.shared_from_this(), make_control(ci, rid));
    }
    else if (auto it = ep.client_conns.find(rid); it != ep.client_conns.end())
    {
      log::critical(logcat, "Configuring inbound connection from client RID:{}", rid);
      it->second =
          std::make_shared<link::Connection>(ci.shared_from_this(), make_control(ci, rid), false);
    }
    else
    {
      log::critical(
          logcat,
          "ERROR: connection accepted from RID:{} that was not logged in key verification!",
          rid);
    }

    log::critical(logcat, "Successfully configured inbound connection fom {}...", rid);
  }

  void
  LinkManager::on_outbound_conn(oxen::quic::connection_interface& ci)
  {
    RouterID rid{ci.remote_key()};

    if (auto it = ep.service_conns.find(rid); it != ep.service_conns.end())
    {
      log::critical(logcat, "Fetched configured outbound connection to relay RID:{}", rid);
    }
    else
    {
      log::critical(
          logcat,
          "ERROR: connection established to RID:{} that was not logged in key verifrication!",
          rid);
    }
  }

  // TODO: should we add routes here now that Router::SessionOpen is gone?
  void
  LinkManager::on_conn_open(oxen::quic::connection_interface& ci)
  {
    _router.loop()->call([this, &conn_interface = ci, is_snode = _is_service_node]() {
      const auto rid = RouterID{conn_interface.remote_key()};
      const auto& remote = conn_interface.remote();

      log::critical(
          logcat,
          "{} (RID:{}) ESTABLISHED CONNECTION TO RID:{}",
          is_snode ? "SERVICE NODE" : "CLIENT",
          _router.local_rid(),
          rid);

      if (conn_interface.is_inbound())
      {
        log::critical(logcat, "Inbound connection from {} (remote:{})", rid, remote);
        on_inbound_conn(conn_interface);
      }
      else
      {
        log::critical(logcat, "Outbound connection from {} (remote:{})", rid, remote);
        on_outbound_conn(conn_interface);
      }
    });
  };

  void
  LinkManager::on_conn_closed(oxen::quic::connection_interface& ci, uint64_t ec)
  {
    _router.loop()->call(
        [this, ref_id = ci.reference_id(), rid = RouterID{ci.remote_key()}, error_code = ec]() {
          log::critical(quic_cat, "Purging quic connection {} (ec:{})", ref_id, error_code);

          if (auto s_itr = ep.service_conns.find(rid); s_itr != ep.service_conns.end())
          {
            log::critical(quic_cat, "Quic connection to relay RID:{} purged successfully", rid);
            ep.service_conns.erase(s_itr);
          }
          else if (auto c_itr = ep.client_conns.find(rid); c_itr != ep.client_conns.end())
          {
            log::critical(quic_cat, "Quic connection to client RID:{} purged successfully", rid);
            ep.client_conns.erase(c_itr);
          }
          else
            log::critical(quic_cat, "Nothing to purge for quic connection {}", ref_id);
        });
  }

  bool
  LinkManager::send_control_message(
      const RouterID& remote,
      std::string endpoint,
      std::string body,
      std::function<void(oxen::quic::message m)> func)
  {
    // DISCUSS: revisit if this assert makes sense. If so, there's no need to if (func) the
    // next logic block
    assert(func);  // makes no sense to send control message and ignore response (maybe gossip?)

    if (is_stopping)
      return false;

    if (func)
    {
      func = [this, f = std::move(func)](oxen::quic::message m) mutable {
        _router.loop()->call(
            [func = std::move(f), msg = std::move(m)]() mutable { func(std::move(msg)); });
      };
    }

    if (auto conn = ep.get_conn(remote); conn)
    {
      conn->control_stream->command(std::move(endpoint), std::move(body), std::move(func));
      return true;
    }

    _router.loop()->call([this,
                          remote,
                          endpoint = std::move(endpoint),
                          body = std::move(body),
                          f = std::move(func)]() {
      connect_and_send(remote, std::move(endpoint), std::move(body), std::move(f));
    });

    return false;
  }

  bool
  LinkManager::send_data_message(const RouterID& remote, std::string body)
  {
    if (is_stopping)
      return false;

    if (auto conn = ep.get_service_conn(remote); conn)
    {
      conn->conn->send_datagram(std::move(body));
      return true;
    }

    _router.loop()->call([this, body = std::move(body), remote]() {
      connect_and_send(remote, std::nullopt, std::move(body));
    });

    return false;
  }

  void
  LinkManager::close_connection(RouterID rid)
  {
    return ep.close_connection(rid);
  }

  void
  LinkManager::test_reachability(
      const RouterID& rid, conn_open_hook on_open, conn_closed_hook on_close)
  {
    if (auto rc = node_db->get_rc(rid))
    {
      connect_to(*rc, std::move(on_open), std::move(on_close));
    }
    else
      log::warning(quic_cat, "Could not find RouterContact for connection to rid:{}", rid);
  }

  void
  LinkManager::connect_and_send(
      const RouterID& router,
      std::optional<std::string> endpoint,
      std::string body,
      std::function<void(oxen::quic::message m)> func)
  {
    // by the time we have called this, we have already checked if we have a connection to this RID
    // in ::send_control_message_impl, at which point we will dispatch on that stream
    if (auto rc = node_db->get_rc(router))
    {
      const auto& remote_addr = rc->addr();

      if (auto rv = ep.establish_and_send(
              oxen::quic::RemoteAddress{router.ToView(), remote_addr},
              *rc,
              std::move(endpoint),
              std::move(body),
              std::move(func));
          rv)
      {
        log::info(quic_cat, "Begun establishing connection to {}", remote_addr);
        return;
      }

      log::warning(quic_cat, "Failed to begin establishing connection to {}", remote_addr);
    }
    else
      log::error(
          quic_cat, "Error: Could not find RC for connection to rid:{}, message not sent!", router);
  }

  void
  LinkManager::connect_to(const RemoteRC& rc, conn_open_hook on_open, conn_closed_hook on_close)
  {
    const auto& rid = rc.router_id();

    if (ep.have_service_conn(rid))
    {
      log::warning(logcat, "We already have a connection to {}!", rid);
      // TODO: should implement some connection failed logic, but not the same logic that
      // would be executed for another failure case
      return;
    }

    const auto& remote_addr = rc.addr();

    if (auto rv = ep.establish_connection(
            oxen::quic::RemoteAddress{rid.ToView(), remote_addr},
            rc,
            std::move(on_open),
            std::move(on_close));
        rv)
    {
      log::info(quic_cat, "Begun establishing connection to {}", remote_addr);
      return;
    }
    log::warning(quic_cat, "Failed to begin establishing connection to {}", remote_addr);
  }

  bool
  LinkManager::have_connection_to(const RouterID& remote) const
  {
    return ep.have_conn(remote);
  }

  bool
  LinkManager::have_service_connection_to(const RouterID& remote) const
  {
    return ep.have_service_conn(remote);
  }

  bool
  LinkManager::have_client_connection_to(const RouterID& remote) const
  {
    return ep.have_client_conn(remote);
  }

  void
  LinkManager::stop()
  {
    if (is_stopping)
    {
      return;
    }

    LogInfo("stopping links");
    is_stopping = true;

    quic.reset();
  }

  void
  LinkManager::set_conn_persist(const RouterID& remote, llarp_time_t until)
  {
    if (is_stopping)
      return;

    persisting_conns[remote] = std::max(until, persisting_conns[remote]);
    if (have_client_connection_to(remote))
    {
      // mark this as a client so we don't try to back connect
      clients.Upsert(remote);
    }
  }

  std::pair<size_t, size_t>
  LinkManager::num_in_out() const
  {
    return ep.num_in_out();
  }

  size_t
  LinkManager::get_num_connected_routers() const
  {
    return ep.num_router_conns();
  }

  size_t
  LinkManager::get_num_connected_clients() const
  {
    return ep.num_client_conns();
  }

  bool
  LinkManager::is_service_node() const
  {
    return _is_service_node;
  }

  // TODO: this?  perhaps no longer necessary in the same way?
  void
  LinkManager::check_persisting_conns(llarp_time_t)
  {
    if (is_stopping)
      return;
  }

  // TODO: this
  util::StatusObject
  LinkManager::extract_status() const
  {
    return {};
  }

  void
  LinkManager::init()
  {
    is_stopping = false;
    node_db = _router.node_db();
  }

  void
  LinkManager::connect_to_random(int num_conns, bool client_only)
  {
    auto filter = [this, client_only](const RemoteRC& rc) -> bool {
      const auto& rid = rc.router_id();
      auto res = client_only ? not ep.have_client_conn(rid) : not ep.have_conn(rid);

      log::debug(logcat, "RID:{} {}", rid, res ? "ACCEPTED" : "REJECTED");

      return res;
    };

    if (auto maybe = node_db->get_n_random_rcs_conditional(num_conns, filter))
    {
      std::vector<RemoteRC>& rcs = *maybe;

      for (const auto& rc : rcs)
        connect_to(rc);
    }
    else
      log::warning(
          logcat, "NodeDB query for {} random RCs for connection returned none", num_conns);
  }

  void
  LinkManager::recv_data_message(oxen::quic::dgram_interface&, bstring)
  {
    // TODO: this
  }

  void
  LinkManager::gossip_rc(const RouterID& last_sender, const RemoteRC& rc)
  {
    int count = 0;
    const auto& gossip_src = rc.router_id();

    for (auto& [rid, conn] : ep.service_conns)
    {
      // don't send back to the gossip source or the last sender
      if (rid == gossip_src or rid == last_sender)
        continue;

      send_control_message(
          rid,
          "gossip_rc"s,
          GossipRCMessage::serialize(last_sender, rc),
          [](oxen::quic::message) mutable {
            log::critical(logcat, "PLACEHOLDER FOR GOSSIP RC RESPONSE HANDLER");
          });
      ++count;
    }

    log::critical(logcat, "Dispatched {} GossipRC requests!", count);
  }

  void
  LinkManager::handle_gossip_rc(oxen::quic::message m)
  {
    log::critical(logcat, "Handling GossipRC request...");

    // RemoteRC constructor wraps deserialization in a try/catch
    RemoteRC rc;
    RouterID src, sender;

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

      btdc.required("rc");
      rc = RemoteRC{btdc.consume_dict_data()};
      src.from_string(btdc.require<std::string>("sender"));
    }
    catch (const std::exception& e)
    {
      log::info(link_cat, "Exception handling GossipRC request: {}", e.what());
      return;
    }

    if (node_db->verify_store_gossip_rc(rc))
    {
      log::critical(link_cat, "Received updated RC, forwarding to relay peers.");
      gossip_rc(_router.local_rid(), rc);
    }
    else
      log::critical(link_cat, "Received known or old RC, not storing or forwarding.");
  }

  // TODO: can probably use ::send_control_message instead. Need to discuss the potential difference
  // in calling Endpoint::get_service_conn vs Endpoint::get_conn
  void
  LinkManager::fetch_bootstrap_rcs(
      const RemoteRC& source, std::string payload, std::function<void(oxen::quic::message m)> func)
  {
    func = [this, f = std::move(func)](oxen::quic::message m) mutable {
      _router.loop()->call(
          [func = std::move(f), msg = std::move(m)]() mutable { func(std::move(msg)); });
    };

    const auto& rid = source.router_id();

    if (auto conn = ep.get_service_conn(rid); conn)
    {
      conn->control_stream->command("bfetch_rcs"s, std::move(payload), std::move(func));
      log::critical(logcat, "Dispatched bootstrap fetch request!");
      return;
    }

    _router.loop()->call([this, source, payload, f = std::move(func), rid = rid]() mutable {
      connect_and_send(rid, "bfetch_rcs"s, std::move(payload), std::move(f));
    });
  }

  void
  LinkManager::handle_fetch_bootstrap_rcs(oxen::quic::message m)
  {
    // this handler should not be registered for clients
    assert(_router.is_service_node());
    log::critical(logcat, "Handling fetch bootstrap fetch request...");

    std::optional<RemoteRC> remote;
    size_t quantity;

    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
      if (btdc.skip_until("local"))
        remote.emplace(btdc.consume_dict_data());

      quantity = btdc.require<size_t>("quantity");
    }
    catch (const std::exception& e)
    {
      log::info(link_cat, "Exception handling RC Fetch request: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }

    if (remote)
    {
      auto is_snode = _router.is_service_node();
      auto& rid = remote->router_id();

      if (is_snode)
      {
        // we already insert the
        auto& registered = node_db->registered_routers();

        if (auto itr = registered.find(rid); itr != registered.end())
        {
          log::critical(
              logcat,
              "Bootstrap node confirmed RID:{} is registered; approving fetch request and "
              "saving RC!",
              rid);
          node_db->verify_gossip_bfetch_rc(*remote);
        }
      }
    }

    auto& src = node_db->get_known_rcs();
    auto count = src.size();

    // if quantity is 0, then the service node requesting this wants all the RC's; otherwise,
    // send the amount requested in the message
    quantity = quantity == 0 ? count : quantity;

    auto now = llarp::time_now_ms();
    size_t i = 0;

    oxenc::bt_dict_producer btdp;

    {
      auto sublist = btdp.append_list("rcs");

      if (count == 0)
        log::error(logcat, "No known RCs locally to send!");
      else
      {
        for (const auto& rc : src)
        {
          if (not rc.is_expired(now))
            sublist.append_encoded(rc.view());

          if (++i >= quantity)
            break;
        }
      }
    }

    m.respond(std::move(btdp).str(), count == 0);
  }

  void
  LinkManager::fetch_rcs(
      const RouterID& source, std::string payload, std::function<void(oxen::quic::message m)> func)
  {
    // this handler should not be registered for service nodes
    assert(not _router.is_service_node());

    send_control_message(source, "fetch_rcs", std::move(payload), std::move(func));
  }

  void
  LinkManager::handle_fetch_rcs(oxen::quic::message m)
  {
    log::critical(logcat, "Handling FetchRC request...");
    // this handler should not be registered for clients
    assert(_router.is_service_node());

    std::set<RouterID> explicit_ids;
    rc_time since_time;

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

      auto btlc = btdc.require<oxenc::bt_list_consumer>("explicit_ids");

      while (not btlc.is_finished())
        explicit_ids.emplace(btlc.consume<ustring_view>().data());

      since_time = rc_time{std::chrono::seconds{btdc.require<int64_t>("since")}};
    }
    catch (const std::exception& e)
    {
      log::critical(link_cat, "Exception handling RC Fetch request: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }

    const auto& rcs = node_db->get_rcs();

    oxenc::bt_dict_producer btdp;
    // const auto& last_time = node_db->get_last_rc_update_times();

    {
      auto sublist = btdp.append_list("rcs");

      // if since_time isn't epoch start, subtract a bit for buffer
      if (since_time != decltype(since_time)::min())
        since_time -= 5s;

      // Initial fetch: give me all the RC's
      if (explicit_ids.empty())
      {
        log::critical(logcat, "Returning ALL locally held RCs for initial FetchRC request...");
        for (const auto& rc : rcs)
        {
          sublist.append_encoded(rc.view());
        }
      }
      else
      {
        int count = 0;
        for (const auto& rid : explicit_ids)
        {
          if (auto maybe_rc = node_db->get_rc_by_rid(rid))
          {
            sublist.append_encoded(maybe_rc->view());
            ++count;
          }
        }
        log::critical(logcat, "Returning {} RCs for FetchRC request...", count);
      }
    }

    m.respond(std::move(btdp).str());
  }

  void
  LinkManager::fetch_router_ids(
      const RouterID& via, std::string payload, std::function<void(oxen::quic::message m)> func)
  {
    send_control_message(via, "fetch_rids"s, std::move(payload), std::move(func));
  }

  void
  LinkManager::handle_fetch_router_ids(oxen::quic::message m)
  {
    log::critical(logcat, "Handling FetchRIDs request...");

    RouterID source;
    RouterID local = router().local_rid();

    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
      source = RouterID{btdc.require<ustring_view>("source")};
    }
    catch (const std::exception& e)
    {
      log::critical(link_cat, "Error fulfilling FetchRIDs request: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }

    // if bad request, silently fail
    if (source.size() != RouterID::SIZE)
      return;

    if (source != local)
    {
      log::critical(logcat, "Relaying FetchRID request to intended target RID:{}", source);
      send_control_message(
          source,
          "fetch_rids"s,
          m.body_str(),
          [source_rid = std::move(source), original = std::move(m)](oxen::quic::message m) mutable {
            original.respond(m.body_str(), m.is_error());
          });
      return;
    }

    oxenc::bt_dict_producer btdp;

    {
      auto btlp = btdp.append_list("routers");

      const auto& known_rids = node_db->get_known_rids();

      for (const auto& rid : known_rids)
        btlp.append(rid.ToView());
    }

    btdp.append_signature("signature", [this](ustring_view to_sign) {
      std::array<unsigned char, 64> sig;

      if (!crypto::sign(const_cast<unsigned char*>(sig.data()), _router.identity(), to_sign))
        throw std::runtime_error{"Failed to sign fetch RouterIDs response"};

      return sig;
    });

    log::critical(logcat, "Returning ALL locally held RIDs to FetchRIDs request!");
    m.respond(std::move(btdp).str());
  }

  void
  LinkManager::handle_find_name(std::string_view body, std::function<void(std::string)> respond)
  {
    std::string name_hash;

    try
    {
      oxenc::bt_dict_consumer btdp{body};

      name_hash = btdp.require<std::string>("H");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      respond(messages::ERROR_RESPONSE);
      return;
    }

    _router.rpc_client()->lookup_ons_hash(
        name_hash,
        [respond = std::move(respond)](
            [[maybe_unused]] std::optional<service::EncryptedName> maybe) mutable {
          if (maybe)
            respond(serialize_response({{"NAME", maybe->ciphertext}}));
          else
            respond(serialize_response({{messages::STATUS_KEY, FindNameMessage::NOT_FOUND}}));
        });
  }

  void
  LinkManager::handle_find_name_response(oxen::quic::message m)
  {
    if (m.timed_out)
    {
      log::info(link_cat, "FindNameMessage request timed out!");
      return;
    }

    std::string payload;

    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
      payload = btdc.require<std::string>(m ? "NAME" : messages::STATUS_KEY);
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      return;
    }

    if (m)
    {
      // TODO: wtf
    }
    else
    {
      if (payload == "ERROR")
      {
        log::info(link_cat, "FindNameMessage failed with unkown error!");

        // resend?
      }
      else if (payload == FindNameMessage::NOT_FOUND)
      {
        log::info(link_cat, "FindNameMessage failed with unkown error!");
        // what to do here?
      }
      else
        log::info(link_cat, "FindNameMessage failed with unkown error!");
    }
  }

  void
  LinkManager::handle_publish_intro(std::string_view body, std::function<void(std::string)> respond)
  {
    std::string introset, derived_signing_key, payload, sig, nonce;
    uint64_t is_relayed, relay_order;
    std::chrono::milliseconds signed_at;

    try
    {
      oxenc::bt_dict_consumer btdc_a{body};

      introset = btdc_a.require<std::string>("I");
      relay_order = btdc_a.require<uint64_t>("O");
      is_relayed = btdc_a.require<uint64_t>("R");

      oxenc::bt_dict_consumer btdc_b{introset.data()};

      derived_signing_key = btdc_b.require<std::string>("d");
      nonce = btdc_b.require<std::string>("n");
      signed_at = std::chrono::milliseconds{btdc_b.require<uint64_t>("s")};
      payload = btdc_b.require<std::string>("x");
      sig = btdc_b.require<std::string>("z");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      respond(messages::ERROR_RESPONSE);
      return;
    }

    const auto now = _router.now();
    const auto addr = dht::Key_t{reinterpret_cast<uint8_t*>(derived_signing_key.data())};
    const auto local_key = _router.rc().router_id();

    if (not service::EncryptedIntroSet::verify(introset, derived_signing_key, sig))
    {
      log::error(link_cat, "Received PublishIntroMessage with invalid introset: {}", introset);
      respond(serialize_response({{messages::STATUS_KEY, PublishIntroMessage::INVALID_INTROSET}}));
      return;
    }

    if (now + service::MAX_INTROSET_TIME_DELTA > signed_at + path::DEFAULT_LIFETIME)
    {
      log::error(link_cat, "Received PublishIntroMessage with expired introset: {}", introset);
      respond(serialize_response({{messages::STATUS_KEY, PublishIntroMessage::EXPIRED}}));
      return;
    }

    auto closest_rcs = _router.node_db()->find_many_closest_to(addr, INTROSET_STORAGE_REDUNDANCY);

    if (closest_rcs.size() != INTROSET_STORAGE_REDUNDANCY)
    {
      log::error(
          link_cat, "Received PublishIntroMessage but only know {} nodes", closest_rcs.size());
      respond(serialize_response({{messages::STATUS_KEY, PublishIntroMessage::INSUFFICIENT}}));
      return;
    }

    service::EncryptedIntroSet enc{derived_signing_key, signed_at, payload, nonce, sig};

    if (is_relayed)
    {
      if (relay_order >= INTROSET_STORAGE_REDUNDANCY)
      {
        log::error(
            link_cat, "Received PublishIntroMessage with invalide relay order: {}", relay_order);
        respond(serialize_response({{messages::STATUS_KEY, PublishIntroMessage::INVALID_ORDER}}));
        return;
      }

      log::info(link_cat, "Relaying PublishIntroMessage for {}", addr);

      const auto& peer_rc = closest_rcs[relay_order];
      const auto& peer_key = peer_rc.router_id();

      if (peer_key == local_key)
      {
        log::info(
            link_cat,
            "Received PublishIntroMessage in which we are peer index {}.. storing introset",
            relay_order);

        _router.contacts().put_intro(std::move(enc));
        respond(serialize_response({{messages::STATUS_KEY, ""}}));
      }
      else
      {
        log::info(
            link_cat, "Received PublishIntroMessage; propagating to peer index {}", relay_order);

        send_control_message(
            peer_key,
            "publish_intro",
            PublishIntroMessage::serialize(introset, relay_order, is_relayed),
            [respond = std::move(respond)](oxen::quic::message m) {
              if (m.timed_out)
                return;  // drop if timed out; requester will have timed out as well
              respond(m.body_str());
            });
      }

      return;
    }

    int rc_index = -1, index = 0;

    for (const auto& rc : closest_rcs)
    {
      if (rc.router_id() == local_key)
      {
        rc_index = index;
        break;
      }
      ++index;
    }

    if (rc_index >= 0)
    {
      log::info(link_cat, "Received PublishIntroMessage for {} (TXID: {}); we are candidate {}");

      _router.contacts().put_intro(std::move(enc));
      respond(serialize_response({{messages::STATUS_KEY, ""}}));
    }
    else
      log::warning(
          link_cat,
          "Received non-relayed PublishIntroMessage from {}; we are not the candidate",
          addr);
  }

  // DISCUSS: I feel like ::handle_publish_intro_response should be the callback that handles the
  // response to a relayed publish_intro (above line 1131-ish)

  void
  LinkManager::handle_publish_intro_response(oxen::quic::message m)
  {
    if (m.timed_out)
    {
      log::info(link_cat, "PublishIntroMessage timed out!");
      return;
    }

    std::string payload;

    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
      payload = btdc.require<std::string>(messages::STATUS_KEY);
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      return;
    }

    if (m)
    {
      // DISCUSS: not sure what to do on success of a publish intro command?
    }
    else
    {
      if (payload == "ERROR")
      {
        log::info(link_cat, "PublishIntroMessage failed with remote exception!");
        // Do something smart here probably
        return;
      }

      log::info(link_cat, "PublishIntroMessage failed with error code: {}", payload);

      if (payload == PublishIntroMessage::INVALID_INTROSET)
      {}
      else if (payload == PublishIntroMessage::EXPIRED)
      {}
      else if (payload == PublishIntroMessage::INSUFFICIENT)
      {}
      else if (payload == PublishIntroMessage::INVALID_ORDER)
      {}
    }
  }

  void
  LinkManager::handle_find_intro(std::string_view body, std::function<void(std::string)> respond)
  {
    ustring location;
    uint64_t relay_order, is_relayed;

    try
    {
      oxenc::bt_dict_consumer btdc{body};

      relay_order = btdc.require<uint64_t>("O");
      is_relayed = btdc.require<uint64_t>("R");
      location = btdc.require<ustring>("S");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      respond(messages::ERROR_RESPONSE);
      return;
    }

    const auto addr = dht::Key_t{location.data()};

    if (is_relayed)
    {
      if (relay_order >= INTROSET_STORAGE_REDUNDANCY)
      {
        log::warning(
            link_cat, "Received FindIntroMessage with invalid relay order: {}", relay_order);
        respond(serialize_response({{messages::STATUS_KEY, FindIntroMessage::INVALID_ORDER}}));
        return;
      }

      auto closest_rcs = _router.node_db()->find_many_closest_to(addr, INTROSET_STORAGE_REDUNDANCY);

      if (closest_rcs.size() != INTROSET_STORAGE_REDUNDANCY)
      {
        log::error(
            link_cat, "Received FindIntroMessage but only know {} nodes", closest_rcs.size());
        respond(serialize_response({{messages::STATUS_KEY, FindIntroMessage::INSUFFICIENT_NODES}}));
        return;
      }

      log::info(link_cat, "Relaying FindIntroMessage for {}", addr);

      const auto& peer_rc = closest_rcs[relay_order];
      const auto& peer_key = peer_rc.router_id();

      send_control_message(
          peer_key,
          "find_intro",
          FindIntroMessage::serialize(dht::Key_t{peer_key}, is_relayed, relay_order),
          [respond = std::move(respond)](oxen::quic::message relay_response) mutable {
            if (relay_response)
              log::info(
                  link_cat,
                  "Relayed FindIntroMessage returned successful response; transmitting to initial "
                  "requester");
            else if (relay_response.timed_out)
              log::critical(
                  link_cat, "Relayed FindIntroMessage timed out! Notifying initial requester");
            else
              log::critical(
                  link_cat, "Relayed FindIntroMessage failed! Notifying initial requester");

            respond(relay_response.body_str());
          });
    }
    else
    {
      if (auto maybe_intro = _router.contacts().get_introset_by_location(addr))
        respond(serialize_response({{"INTROSET", maybe_intro->bt_encode()}}));
      else
      {
        log::warning(
            link_cat,
            "Received FindIntroMessage with relayed == false and no local introset entry");
        respond(serialize_response({{messages::STATUS_KEY, FindIntroMessage::NOT_FOUND}}));
      }
    }
  }

  void
  LinkManager::handle_find_intro_response(oxen::quic::message m)
  {
    if (m.timed_out)
    {
      log::info(link_cat, "FindIntroMessage timed out!");
      return;
    }

    std::string payload;

    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
      payload = btdc.require<std::string>((m) ? "INTROSET" : messages::STATUS_KEY);
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      return;
    }

    // success case, neither timed out nor errored
    if (m)
    {
      service::EncryptedIntroSet enc{payload};
      _router.contacts().put_intro(std::move(enc));
    }
    else
    {
      log::info(link_cat, "FindIntroMessage failed with error: {}", payload);
      // Do something smart here probably
    }
  }

  void
  LinkManager::handle_path_build(oxen::quic::message m, const RouterID& from)
  {
    if (!_router.path_context().is_transit_allowed())
    {
      log::warning(link_cat, "got path build request when not permitting transit");
      m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::NO_TRANSIT}}), true);
      return;
    }

    try
    {
      auto payload_list = oxenc::bt_deserialize<std::deque<ustring>>(m.body());
      if (payload_list.size() != path::MAX_LEN)
      {
        log::info(link_cat, "Path build message with wrong number of frames");
        m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_FRAMES}}), true);
        return;
      }

      oxenc::bt_dict_consumer frame_info{payload_list.front()};
      auto frame = frame_info.require<ustring>("FRAME");
      auto hash = frame_info.require<ustring>("HASH");

      oxenc::bt_dict_consumer hop_dict{frame};
      auto hop_payload = hop_dict.require<ustring>("ENCRYPTED");
      auto outer_nonce = hop_dict.require<ustring>("NONCE");
      auto other_pubkey = hop_dict.require<ustring>("PUBKEY");

      SharedSecret shared;
      // derive shared secret using ephemeral pubkey and our secret key (and nonce)
      if (!crypto::dh_server(
              shared.data(), other_pubkey.data(), _router.pubkey(), outer_nonce.data()))
      {
        log::info(link_cat, "DH server initialization failed during path build");
        m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_CRYPTO}}), true);
        return;
      }

      // hash data and check against given hash
      ShortHash digest;
      if (!crypto::hmac(digest.data(), frame.data(), frame.size(), shared))
      {
        log::error(link_cat, "HMAC failed on path build request");
        m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_CRYPTO}}), true);
        return;
      }
      if (!std::equal(digest.begin(), digest.end(), hash.data()))
      {
        log::info(link_cat, "HMAC mismatch on path build request");
        m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_CRYPTO}}), true);
        return;
      }

      // decrypt frame with our hop info
      if (!crypto::xchacha20(
              hop_payload.data(), hop_payload.size(), shared.data(), outer_nonce.data()))
      {
        log::info(link_cat, "Decrypt failed on path build request");
        m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_CRYPTO}}), true);
        return;
      }

      oxenc::bt_dict_consumer hop_info{hop_payload};
      auto commkey = hop_info.require<std::string>("COMMKEY");
      auto lifetime = hop_info.require<uint64_t>("LIFETIME");
      auto inner_nonce = hop_info.require<ustring>("NONCE");
      auto rx_id = hop_info.require<std::string>("RX");
      auto tx_id = hop_info.require<std::string>("TX");
      auto upstream = hop_info.require<std::string>("UPSTREAM");

      // populate transit hop object with hop info
      // TODO: IP / path build limiting clients
      auto hop = std::make_shared<path::TransitHop>();
      hop->info.downstream = from;

      // extract pathIDs and check if zero or used
      hop->info.txID.from_string(tx_id);
      hop->info.rxID.from_string(rx_id);

      if (hop->info.txID.IsZero() || hop->info.rxID.IsZero())
      {
        log::warning(link_cat, "Invalid PathID; PathIDs must be non-zero");
        m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_PATHID}}), true);
        return;
      }

      hop->info.upstream.from_string(upstream);

      if (_router.path_context().has_transit_hop(hop->info))
      {
        log::warning(link_cat, "Invalid PathID; PathIDs must be unique");
        m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_PATHID}}), true);
        return;
      }

      if (!crypto::dh_server(
              hop->pathKey.data(), other_pubkey.data(), _router.pubkey(), inner_nonce.data()))
      {
        log::warning(link_cat, "DH failed during path build.");
        m.respond(serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_CRYPTO}}), true);
        return;
      }
      // generate hash of hop key for nonce mutation
      ShortHash xor_hash;
      crypto::shorthash(xor_hash, hop->pathKey.data(), hop->pathKey.size());
      hop->nonceXOR = xor_hash.data();  // nonceXOR is 24 bytes, ShortHash is 32; this will truncate

      // set and check path lifetime
      hop->lifetime = 1ms * lifetime;

      if (hop->lifetime >= path::DEFAULT_LIFETIME)
      {
        log::warning(link_cat, "Path build attempt with too long of a lifetime.");
        m.respond(
            serialize_response({{messages::STATUS_KEY, PathBuildMessage::BAD_LIFETIME}}), true);
        return;
      }

      hop->started = _router.now();
      _router.persist_connection_until(hop->info.downstream, hop->ExpireTime() + 10s);

      if (hop->info.upstream == _router.pubkey())
      {
        hop->terminal_hop = true;
        // we are terminal hop and everything is okay
        _router.path_context().put_transit_hop(hop);
        m.respond(messages::OK_RESPONSE, false);
        return;
      }

      // pop our frame, to be randomized after onion step and appended
      auto end_frame = std::move(payload_list.front());
      payload_list.pop_front();
      auto onion_nonce = SymmNonce{inner_nonce.data()} ^ hop->nonceXOR;
      // (de-)onion each further frame using the established shared secret and
      // onion_nonce = inner_nonce ^ nonceXOR
      // Note: final value passed to crypto::onion is xor factor, but that's for *after* the
      // onion round to compute the return value, so we don't care about it.
      for (auto& element : payload_list)
      {
        crypto::onion(element.data(), element.size(), hop->pathKey, onion_nonce, onion_nonce);
      }
      // randomize final frame.  could probably paste our frame on the end and onion it with the
      // rest, but it gains nothing over random.
      randombytes(end_frame.data(), end_frame.size());
      payload_list.push_back(std::move(end_frame));

      send_control_message(
          hop->info.upstream,
          "path_build",
          oxenc::bt_serialize(payload_list),
          [hop, this, prev_message = std::move(m)](oxen::quic::message m) {
            if (m)
            {
              log::info(
                  link_cat,
                  "Upstream returned successful path build response; giving hop info to Router, "
                  "then relaying response");
              _router.path_context().put_transit_hop(hop);
            }
            if (m.timed_out)
              log::info(link_cat, "Upstream timed out on path build; relaying timeout");
            else
              log::info(link_cat, "Upstream returned path build failure; relaying response");

            m.respond(m.body_str(), m.is_error());
          });
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }
  }

  void
  LinkManager::handle_path_latency(oxen::quic::message m)
  {
    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }
  }

  void
  LinkManager::handle_path_latency_response(oxen::quic::message m)
  {
    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      // m.respond(serialize_response({{messages::STATUS_KEY, "EXCEPTION"}}), true);
      return;
    }
  }

  void
  LinkManager::handle_path_transfer(oxen::quic::message m)
  {
    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }
  }

  void
  LinkManager::handle_path_transfer_response(oxen::quic::message m)
  {
    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }
  }

  void
  LinkManager::handle_obtain_exit(oxen::quic::message m)
  {
    uint64_t flag;
    ustring_view pubkey, sig;
    std::string_view tx_id, dict_data;

    try
    {
      oxenc::bt_list_consumer btlc{m.body()};
      dict_data = btlc.consume_dict_data();
      oxenc::bt_dict_consumer btdc{dict_data};

      sig = to_usv(btlc.consume_string_view());
      flag = btdc.require<uint64_t>("E");
      pubkey = btdc.require<ustring_view>("I");
      tx_id = btdc.require<std::string_view>("T");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      throw;
    }

    RouterID target{pubkey.data()};
    auto transit_hop = _router.path_context().GetTransitHop(target, PathID_t{to_usv(tx_id).data()});

    const auto rx_id = transit_hop->info.rxID;

    auto success =
        (crypto::verify(pubkey, to_usv(dict_data), sig)
         and _router.exitContext().obtain_new_exit(PubKey{pubkey.data()}, rx_id, flag != 0));

    m.respond(
        ObtainExitMessage::sign_and_serialize_response(_router.identity(), tx_id), not success);
  }

  void
  LinkManager::handle_obtain_exit_response(oxen::quic::message m)
  {
    if (m.timed_out)
    {
      log::info(link_cat, "ObtainExitMessage timed out!");
      return;
    }
    if (m.is_error())
    {
      // TODO: what to do here
    }

    std::string_view tx_id, dict_data;
    ustring_view sig;

    try
    {
      oxenc::bt_list_consumer btlc{m.body()};
      dict_data = btlc.consume_dict_data();
      oxenc::bt_dict_consumer btdc{dict_data};

      sig = to_usv(btlc.consume_string_view());
      tx_id = btdc.require<std::string_view>("T");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      throw;
    }

    auto path_ptr = _router.path_context().get_path(PathID_t{to_usv(tx_id).data()});

    if (crypto::verify(_router.pubkey(), to_usv(dict_data), sig))
      path_ptr->enable_exit_traffic();
  }

  void
  LinkManager::handle_update_exit(oxen::quic::message m)
  {
    std::string_view path_id, tx_id, dict_data;
    ustring_view sig;

    try
    {
      oxenc::bt_list_consumer btlc{m.body()};
      dict_data = btlc.consume_dict_data();
      oxenc::bt_dict_consumer btdc{dict_data};

      sig = to_usv(btlc.consume_string_view());
      path_id = btdc.require<std::string_view>("P");
      tx_id = btdc.require<std::string_view>("T");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }

    auto transit_hop =
        _router.path_context().GetTransitHop(_router.pubkey(), PathID_t{to_usv(tx_id).data()});

    if (auto exit_ep =
            _router.exitContext().find_endpoint_for_path(PathID_t{to_usv(path_id).data()}))
    {
      if (crypto::verify(exit_ep->PubKey().data(), to_usv(dict_data), sig))
      {
        (exit_ep->UpdateLocalPath(transit_hop->info.rxID))
            ? m.respond(UpdateExitMessage::sign_and_serialize_response(_router.identity(), tx_id))
            : m.respond(
                serialize_response({{messages::STATUS_KEY, UpdateExitMessage::UPDATE_FAILED}}),
                true);
      }
      // If we fail to verify the message, no-op
    }
  }

  void
  LinkManager::handle_update_exit_response(oxen::quic::message m)
  {
    if (m.timed_out)
    {
      log::info(link_cat, "UpdateExitMessage timed out!");
      return;
    }
    if (m.is_error())
    {
      // TODO: what to do here
    }

    std::string tx_id;
    std::string_view dict_data;
    ustring_view sig;

    try
    {
      oxenc::bt_list_consumer btlc{m.body()};
      dict_data = btlc.consume_dict_data();
      oxenc::bt_dict_consumer btdc{dict_data};

      sig = to_usv(btlc.consume_string_view());
      tx_id = btdc.require<std::string_view>("T");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      return;
    }

    auto path_ptr = _router.path_context().get_path(PathID_t{to_usv(tx_id).data()});

    if (crypto::verify(_router.pubkey(), to_usv(dict_data), sig))
    {
      if (path_ptr->update_exit(std::stoul(tx_id)))
      {
        // TODO: talk to tom and Jason about how this stupid shit was a no-op originally
        // see Path::HandleUpdateExitVerifyMessage
      }
      else
      {}
    }
  }

  void
  LinkManager::handle_close_exit(oxen::quic::message m)
  {
    std::string_view tx_id, dict_data;
    ustring_view sig;

    try
    {
      oxenc::bt_list_consumer btlc{m.body()};
      dict_data = btlc.consume_dict_data();
      oxenc::bt_dict_consumer btdc{dict_data};

      sig = to_usv(btlc.consume_string_view());
      tx_id = btdc.require<std::string_view>("T");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      m.respond(messages::ERROR_RESPONSE, true);
      return;
    }

    auto transit_hop =
        _router.path_context().GetTransitHop(_router.pubkey(), PathID_t{to_usv(tx_id).data()});

    const auto rx_id = transit_hop->info.rxID;

    if (auto exit_ep = router().exitContext().find_endpoint_for_path(rx_id))
    {
      if (crypto::verify(exit_ep->PubKey().data(), to_usv(dict_data), sig))
      {
        exit_ep->Close();
        m.respond(CloseExitMessage::sign_and_serialize_response(_router.identity(), tx_id));
      }
    }

    m.respond(serialize_response({{messages::STATUS_KEY, CloseExitMessage::UPDATE_FAILED}}), true);
  }

  void
  LinkManager::handle_close_exit_response(oxen::quic::message m)
  {
    if (m.timed_out)
    {
      log::info(link_cat, "CloseExitMessage timed out!");
      return;
    }
    if (m.is_error())
    {
      // TODO: what to do here
    }

    std::string_view nonce, tx_id, dict_data;
    ustring_view sig;

    try
    {
      oxenc::bt_list_consumer btlc{m.body()};
      dict_data = btlc.consume_dict_data();
      oxenc::bt_dict_consumer btdc{dict_data};

      sig = to_usv(btlc.consume_string_view());
      tx_id = btdc.require<std::string_view>("T");
      nonce = btdc.require<std::string_view>("Y");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      return;
    }

    auto path_ptr = _router.path_context().get_path(PathID_t{to_usv(tx_id).data()});

    if (path_ptr->SupportsAnyRoles(path::ePathRoleExit | path::ePathRoleSVC)
        and crypto::verify(_router.pubkey(), to_usv(dict_data), sig))
      path_ptr->mark_exit_closed();
  }

  void
  LinkManager::handle_path_control(oxen::quic::message m, const RouterID& from)
  {
    ustring_view nonce, path_id_str;
    std::string payload;

    try
    {
      oxenc::bt_dict_consumer btdc{m.body()};
      nonce = btdc.require<ustring_view>("NONCE");
      path_id_str = btdc.require<ustring_view>("PATHID");
      payload = btdc.require<std::string>("PAYLOAD");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      return;
    }

    auto symnonce = SymmNonce{nonce.data()};
    auto path_id = PathID_t{path_id_str.data()};
    auto hop = _router.path_context().GetTransitHop(from, path_id);

    // TODO: use "path_control" for both directions?  If not, drop message on
    // floor if we don't have the path_id in question; if we decide to make this
    // bidirectional, will need to check if we have a Path with path_id.
    if (not hop)
      return;

    // if terminal hop, payload should contain a request (e.g. "find_name"); handle and respond.
    if (hop->terminal_hop)
    {
      hop->onion(payload, symnonce, false);
      handle_inner_request(std::move(m), std::move(payload), std::move(hop));
      return;
    }

    auto& next_id = path_id == hop->info.rxID ? hop->info.txID : hop->info.rxID;
    auto& next_router = path_id == hop->info.rxID ? hop->info.upstream : hop->info.downstream;

    std::string new_payload = hop->onion_and_payload(payload, next_id, symnonce);

    send_control_message(
        next_router,
        "path_control"s,
        std::move(new_payload),
        [hop_weak = hop->weak_from_this(), path_id, prev_message = std::move(m)](
            oxen::quic::message response) mutable {
          auto hop = hop_weak.lock();

          if (not hop)
            return;

          ustring_view nonce;
          std::string payload, response_body;

          try
          {
            oxenc::bt_dict_consumer btdc{response.body()};
            nonce = btdc.require<ustring_view>("NONCE");
            payload = btdc.require<std::string>("PAYLOAD");
          }
          catch (const std::exception& e)
          {
            log::warning(link_cat, "Exception: {}", e.what());
            return;
          }

          auto symnonce = SymmNonce{nonce.data()};
          auto resp_payload = hop->onion_and_payload(payload, path_id, symnonce);
          prev_message.respond(std::move(resp_payload), false);
        });
  }

  void
  LinkManager::handle_inner_request(
      oxen::quic::message m, std::string payload, std::shared_ptr<path::TransitHop> hop)
  {
    std::string_view body, method;

    try
    {
      oxenc::bt_dict_consumer btdc{payload};
      body = btdc.require<std::string_view>("BODY");
      method = btdc.require<std::string_view>("METHOD");
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      return;
    }

    // If a handler exists for "method", call it; else drop request on the floor.
    auto itr = path_requests.find(method);

    if (itr == path_requests.end())
    {
      log::info(link_cat, "Received path control request \"{}\", which has no handler.", method);
      return;
    }

    auto respond = [m = std::move(m),
                    hop_weak = hop->weak_from_this()](std::string response) mutable {
      auto hop = hop_weak.lock();
      if (not hop)
        return;  // transit hop gone, drop response

      m.respond(hop->onion_and_payload(response, hop->info.rxID), false);
    };

    std::invoke(itr->second, this, std::move(body), std::move(respond));
  }

  void
  LinkManager::handle_convo_intro(oxen::quic::message m)
  {
    if (not m)
    {
      log::info(link_cat, "Path control message timed out!");
      return;
    }

    try
    {
      //
    }
    catch (const std::exception& e)
    {
      log::warning(link_cat, "Exception: {}", e.what());
      return;
    }
  }

}  // namespace llarp