text: /* Copyright (c) 2017-2020, The Tor Project, Inc. */
  /* See LICENSE for licensing information */
  
  /**
   * \file hs_circuit.c
   **/
  
  #define HS_CIRCUIT_PRIVATE
  
  #include "core/or/or.h"
  #include "app/config/config.h"
  #include "core/crypto/hs_ntor.h"
  #include "core/or/circuitbuild.h"
  #include "core/or/circuitlist.h"
  #include "core/or/circuituse.h"
  #include "core/or/policies.h"
  #include "core/or/relay.h"
  #include "core/or/crypt_path.h"
  #include "feature/client/circpathbias.h"
  #include "feature/hs/hs_cell.h"
  #include "feature/hs/hs_circuit.h"
  #include "feature/hs/hs_ob.h"
  #include "feature/hs/hs_circuitmap.h"
  #include "feature/hs/hs_client.h"
  #include "feature/hs/hs_ident.h"
  #include "feature/hs/hs_service.h"
  #include "feature/nodelist/describe.h"
  #include "feature/nodelist/nodelist.h"
  #include "feature/rend/rendservice.h"
  #include "feature/rend/rendclient.h"
  #include "feature/stats/rephist.h"
  #include "lib/crypt_ops/crypto_dh.h"
  #include "lib/crypt_ops/crypto_rand.h"
  #include "lib/crypt_ops/crypto_util.h"
  
  /* Trunnel. */
  #include "trunnel/ed25519_cert.h"
  #include "trunnel/hs/cell_common.h"
  #include "trunnel/hs/cell_establish_intro.h"
  
  #include "core/or/cpath_build_state_st.h"
  #include "core/or/crypt_path_st.h"
  #include "feature/nodelist/node_st.h"
  #include "core/or/origin_circuit_st.h"
  
  /** A circuit is about to become an e2e rendezvous circuit. Check
   * <b>circ_purpose</b> and ensure that it's properly set. Return true iff
   * circuit purpose is properly set, otherwise return false. */
  static int
  circuit_purpose_is_correct_for_rend(unsigned int circ_purpose,
                                      int is_service_side)
  {
    if (is_service_side) {
      if (circ_purpose != CIRCUIT_PURPOSE_S_CONNECT_REND) {
        log_warn(LD_BUG,
              "HS e2e circuit setup with wrong purpose (%d)", circ_purpose);
        return 0;
      }
    }
  
    if (!is_service_side) {
      if (circ_purpose != CIRCUIT_PURPOSE_C_REND_READY &&
          circ_purpose != CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED) {
        log_warn(LD_BUG,
              "Client e2e circuit setup with wrong purpose (%d)", circ_purpose);
        return 0;
      }
    }
  
    return 1;
  }
  
  /** Create and return a crypt path for the final hop of a v3 prop224 rendezvous
   * circuit. Initialize the crypt path crypto using the output material from the
   * ntor key exchange at <b>ntor_key_seed</b>.
   *
   * If <b>is_service_side</b> is set, we are the hidden service and the final
   * hop of the rendezvous circuit is the client on the other side. */
  static crypt_path_t *
  create_rend_cpath(const uint8_t *ntor_key_seed, size_t seed_len,
                    int is_service_side)
  {
    uint8_t keys[HS_NTOR_KEY_EXPANSION_KDF_OUT_LEN];
    crypt_path_t *cpath = NULL;
  
    /* Do the key expansion */
    if (hs_ntor_circuit_key_expansion(ntor_key_seed, seed_len,
                                      keys, sizeof(keys)) < 0) {
      goto err;
    }
  
    /* Setup the cpath */
    cpath = tor_malloc_zero(sizeof(crypt_path_t));
    cpath->magic = CRYPT_PATH_MAGIC;
  
    if (cpath_init_circuit_crypto(cpath, (char*)keys, sizeof(keys),
                                  is_service_side, 1) < 0) {
      tor_free(cpath);
      goto err;
    }
  
   err:
    memwipe(keys, 0, sizeof(keys));
    return cpath;
  }
  
  /** We are a v2 legacy HS client: Create and return a crypt path for the hidden
   * service on the other side of the rendezvous circuit <b>circ</b>. Initialize
   * the crypt path crypto using the body of the RENDEZVOUS1 cell at
   * <b>rend_cell_body</b> (which must be at least DH1024_KEY_LEN+DIGEST_LEN
   * bytes).
   */
  static crypt_path_t *
  create_rend_cpath_legacy(origin_circuit_t *circ, const uint8_t *rend_cell_body)
  {
    crypt_path_t *hop = NULL;
    char keys[DIGEST_LEN+CPATH_KEY_MATERIAL_LEN];
  
    /* first DH1024_KEY_LEN bytes are g^y from the service. Finish the dh
     * handshake...*/
    tor_assert(circ->build_state);
    tor_assert(circ->build_state->pending_final_cpath);
    hop = circ->build_state->pending_final_cpath;
  
    tor_assert(hop->rend_dh_handshake_state);
    if (crypto_dh_compute_secret(LOG_PROTOCOL_WARN, hop->rend_dh_handshake_state,
                                 (char*)rend_cell_body, DH1024_KEY_LEN,
                                 keys, DIGEST_LEN+CPATH_KEY_MATERIAL_LEN)<0) {
      log_warn(LD_GENERAL, "Couldn't complete DH handshake.");
      goto err;
    }
    /* ... and set up cpath. */
    if (cpath_init_circuit_crypto(hop,
                                  keys+DIGEST_LEN, sizeof(keys)-DIGEST_LEN,
                                  0, 0) < 0)
      goto err;
  
    /* Check whether the digest is right... */
    if (tor_memneq(keys, rend_cell_body+DH1024_KEY_LEN, DIGEST_LEN)) {
      log_warn(LD_PROTOCOL, "Incorrect digest of key material.");
      goto err;
    }
  
    /* clean up the crypto stuff we just made */
    crypto_dh_free(hop->rend_dh_handshake_state);
    hop->rend_dh_handshake_state = NULL;
  
    goto done;
  
   err:
    hop = NULL;
  
   done:
    memwipe(keys, 0, sizeof(keys));
    return hop;
  }
  
  /** Append the final <b>hop</b> to the cpath of the rend <b>circ</b>, and mark
   * <b>circ</b> ready for use to transfer HS relay cells. */
  static void
  finalize_rend_circuit(origin_circuit_t *circ, crypt_path_t *hop,
                        int is_service_side)
  {
    tor_assert(circ);
    tor_assert(hop);
  
    /* Notify the circuit state machine that we are splicing this circuit */
    int new_circ_purpose = is_service_side ?
      CIRCUIT_PURPOSE_S_REND_JOINED : CIRCUIT_PURPOSE_C_REND_JOINED;
    circuit_change_purpose(TO_CIRCUIT(circ), new_circ_purpose);
  
    /* All is well. Extend the circuit. */
    hop->state = CPATH_STATE_OPEN;
    /* Set the windows to default. */
    hop->package_window = circuit_initial_package_window();
    hop->deliver_window = CIRCWINDOW_START;
  
    /* Now that this circuit has finished connecting to its destination,
     * make sure circuit_get_open_circ_or_launch is willing to return it
     * so we can actually use it. */
    circ->hs_circ_has_timed_out = 0;
  
    /* Append the hop to the cpath of this circuit */
    cpath_extend_linked_list(&circ->cpath, hop);
  
    /* In legacy code, 'pending_final_cpath' points to the final hop we just
     * appended to the cpath. We set the original pointer to NULL so that we
     * don't double free it. */
    if (circ->build_state) {
      circ->build_state->pending_final_cpath = NULL;
    }
  
    /* Finally, mark circuit as ready to be used for client streams */
    if (!is_service_side) {
      circuit_try_attaching_streams(circ);
    }
  }
  
  /** For a given circuit and a service introduction point object, register the
   * intro circuit to the circuitmap. This supports legacy intro point. */
  static void
  register_intro_circ(const hs_service_intro_point_t *ip,
                      origin_circuit_t *circ)
  {
    tor_assert(ip);
    tor_assert(circ);
  
    if (ip->base.is_only_legacy) {
      hs_circuitmap_register_intro_circ_v2_service_side(circ,
                                                        ip->legacy_key_digest);
    } else {
      hs_circuitmap_register_intro_circ_v3_service_side(circ,
                                           &ip->auth_key_kp.pubkey);
    }
  }
  
  /** Return the number of opened introduction circuit for the given circuit that
   * is matching its identity key. */
  static unsigned int
  count_opened_desc_intro_point_circuits(const hs_service_t *service,
                                         const hs_service_descriptor_t *desc)
  {
    unsigned int count = 0;
  
    tor_assert(service);
    tor_assert(desc);
  
    DIGEST256MAP_FOREACH(desc->intro_points.map, key,
                         const hs_service_intro_point_t *, ip) {
      const circuit_t *circ;
      const origin_circuit_t *ocirc = hs_circ_service_get_intro_circ(ip);
      if (ocirc == NULL) {
        continue;
      }
      circ = TO_CIRCUIT(ocirc);
      tor_assert(circ->purpose == CIRCUIT_PURPOSE_S_ESTABLISH_INTRO ||
                 circ->purpose == CIRCUIT_PURPOSE_S_INTRO);
      /* Having a circuit not for the requested service is really bad. */
      tor_assert(ed25519_pubkey_eq(&service->keys.identity_pk,
                                   &ocirc->hs_ident->identity_pk));
      /* Only count opened circuit and skip circuit that will be closed. */
      if (!circ->marked_for_close && circ->state == CIRCUIT_STATE_OPEN) {
        count++;
      }
    } DIGEST256MAP_FOREACH_END;
    return count;
  }
  
  /** From a given service, rendezvous cookie and handshake info, create a
   * rendezvous point circuit identifier. This can't fail. */
  STATIC hs_ident_circuit_t *
  create_rp_circuit_identifier(const hs_service_t *service,
                               const uint8_t *rendezvous_cookie,
                               const curve25519_public_key_t *server_pk,
                               const hs_ntor_rend_cell_keys_t *keys)
  {
    hs_ident_circuit_t *ident;
    uint8_t handshake_info[CURVE25519_PUBKEY_LEN + DIGEST256_LEN];
  
    tor_assert(service);
    tor_assert(rendezvous_cookie);
    tor_assert(server_pk);
    tor_assert(keys);
  
    ident = hs_ident_circuit_new(&service->keys.identity_pk);
    /* Copy the RENDEZVOUS_COOKIE which is the unique identifier. */
    memcpy(ident->rendezvous_cookie, rendezvous_cookie,
           sizeof(ident->rendezvous_cookie));
    /* Build the HANDSHAKE_INFO which looks like this:
     *    SERVER_PK        [32 bytes]
     *    AUTH_INPUT_MAC   [32 bytes]
     */
    memcpy(handshake_info, server_pk->public_key, CURVE25519_PUBKEY_LEN);
    memcpy(handshake_info + CURVE25519_PUBKEY_LEN, keys->rend_cell_auth_mac,
           DIGEST256_LEN);
    tor_assert(sizeof(ident->rendezvous_handshake_info) ==
               sizeof(handshake_info));
    memcpy(ident->rendezvous_handshake_info, handshake_info,
           sizeof(ident->rendezvous_handshake_info));
    /* Finally copy the NTOR_KEY_SEED for e2e encryption on the circuit. */
    tor_assert(sizeof(ident->rendezvous_ntor_key_seed) ==
               sizeof(keys->ntor_key_seed));
    memcpy(ident->rendezvous_ntor_key_seed, keys->ntor_key_seed,
           sizeof(ident->rendezvous_ntor_key_seed));
    return ident;
  }
  
  /** From a given service and service intro point, create an introduction point
   * circuit identifier. This can't fail. */
  static hs_ident_circuit_t *
  create_intro_circuit_identifier(const hs_service_t *service,
                                  const hs_service_intro_point_t *ip)
  {
    hs_ident_circuit_t *ident;
  
    tor_assert(service);
    tor_assert(ip);
  
    ident = hs_ident_circuit_new(&service->keys.identity_pk);
    ed25519_pubkey_copy(&ident->intro_auth_pk, &ip->auth_key_kp.pubkey);
  
    return ident;
  }
  
  /** For a given introduction point and an introduction circuit, send the
   * ESTABLISH_INTRO cell. The service object is used for logging. This can fail
   * and if so, the circuit is closed and the intro point object is flagged
   * that the circuit is not established anymore which is important for the
   * retry mechanism. */
  static void
  send_establish_intro(const hs_service_t *service,
                       hs_service_intro_point_t *ip, origin_circuit_t *circ)
  {
    ssize_t cell_len;
    uint8_t payload[RELAY_PAYLOAD_SIZE];
  
    tor_assert(service);
    tor_assert(ip);
    tor_assert(circ);
  
    /* Encode establish intro cell. */
    cell_len = hs_cell_build_establish_intro(circ->cpath->prev->rend_circ_nonce,
                                             &service->config, ip, payload);
    if (cell_len < 0) {
      log_warn(LD_REND, "Unable to encode ESTABLISH_INTRO cell for service %s "
                        "on circuit %u. Closing circuit.",
               safe_str_client(service->onion_address),
               TO_CIRCUIT(circ)->n_circ_id);
      goto err;
    }
  
    /* Send the cell on the circuit. */
    if (relay_send_command_from_edge(CONTROL_CELL_ID, TO_CIRCUIT(circ),
                                     RELAY_COMMAND_ESTABLISH_INTRO,
                                     (char *) payload, cell_len,
                                     circ->cpath->prev) < 0) {
      log_info(LD_REND, "Unable to send ESTABLISH_INTRO cell for service %s "
                        "on circuit %u.",
               safe_str_client(service->onion_address),
               TO_CIRCUIT(circ)->n_circ_id);
      /* On error, the circuit has been closed. */
      goto done;
    }
  
    /* Record the attempt to use this circuit. */
    pathbias_count_use_attempt(circ);
    goto done;
  
   err:
    circuit_mark_for_close(TO_CIRCUIT(circ), END_CIRC_REASON_INTERNAL);
   done:
    memwipe(payload, 0, sizeof(payload));
  }
  
  /** Return a string constant describing the anonymity of service. */
  static const char *
  get_service_anonymity_string(const hs_service_t *service)
  {
    if (service->config.is_single_onion) {
      return "single onion";
    } else {
      return "hidden";
    }
  }
  
  /** For a given service, the ntor onion key and a rendezvous cookie, launch a
   * circuit to the rendezvous point specified by the link specifiers. On
   * success, a circuit identifier is attached to the circuit with the needed
   * data. This function will try to open a circuit for a maximum value of
   * MAX_REND_FAILURES then it will give up. */
  MOCK_IMPL(STATIC void,
  launch_rendezvous_point_circuit,(const hs_service_t *service,
                                   const hs_service_intro_point_t *ip,
                                   const hs_cell_introduce2_data_t *data))
  {
    int circ_needs_uptime;
    time_t now = time(NULL);
    extend_info_t *info = NULL;
    origin_circuit_t *circ;
  
    tor_assert(service);
    tor_assert(ip);
    tor_assert(data);
  
    circ_needs_uptime = hs_service_requires_uptime_circ(service->config.ports);
  
    /* Get the extend info data structure for the chosen rendezvous point
     * specified by the given link specifiers. */
    info = hs_get_extend_info_from_lspecs(data->link_specifiers,
                                          &data->onion_pk,
                                          service->config.is_single_onion);
    if (info == NULL) {
      /* We are done here, we can't extend to the rendezvous point. */
      log_fn(LOG_PROTOCOL_WARN, LD_REND,
             "Not enough info to open a circuit to a rendezvous point for "
             "%s service %s.",
             get_service_anonymity_string(service),
             safe_str_client(service->onion_address));
      goto end;
    }
  
    for (int i = 0; i < MAX_REND_FAILURES; i++) {
      int circ_flags = CIRCLAUNCH_NEED_CAPACITY | CIRCLAUNCH_IS_INTERNAL;
      if (circ_needs_uptime) {
        circ_flags |= CIRCLAUNCH_NEED_UPTIME;
      }
      /* Firewall and policies are checked when getting the extend info.
       *
       * We only use a one-hop path on the first attempt. If the first attempt
       * fails, we use a 3-hop path for reachability / reliability.
       * See the comment in retry_service_rendezvous_point() for details. */
      if (service->config.is_single_onion && i == 0) {
        circ_flags |= CIRCLAUNCH_ONEHOP_TUNNEL;
      }
  
      circ = circuit_launch_by_extend_info(CIRCUIT_PURPOSE_S_CONNECT_REND, info,
                                           circ_flags);
      if (circ != NULL) {
        /* Stop retrying, we have a circuit! */
        break;
      }
    }
    if (circ == NULL) {
      log_warn(LD_REND, "Giving up on launching a rendezvous circuit to %s "
                        "for %s service %s",
               safe_str_client(extend_info_describe(info)),
               get_service_anonymity_string(service),
               safe_str_client(service->onion_address));
      goto end;
    }
    log_info(LD_REND, "Rendezvous circuit launched to %s with cookie %s "
                      "for %s service %s",
             safe_str_client(extend_info_describe(info)),
             safe_str_client(hex_str((const char *) data->rendezvous_cookie,
                                     REND_COOKIE_LEN)),
             get_service_anonymity_string(service),
             safe_str_client(service->onion_address));
    tor_assert(circ->build_state);
    /* Rendezvous circuit have a specific timeout for the time spent on trying
     * to connect to the rendezvous point. */
    circ->build_state->expiry_time = now + MAX_REND_TIMEOUT;
  
    /* Create circuit identifier and key material. */
    {
      hs_ntor_rend_cell_keys_t keys;
      curve25519_keypair_t ephemeral_kp;
      /* No need for extra strong, this is only for this circuit life time. This
       * key will be used for the RENDEZVOUS1 cell that will be sent on the
       * circuit once opened. */
      curve25519_keypair_generate(&ephemeral_kp, 0);
      if (hs_ntor_service_get_rendezvous1_keys(&ip->auth_key_kp.pubkey,
                                               &ip->enc_key_kp,
                                               &ephemeral_kp, &data->client_pk,
                                               &keys) < 0) {
        /* This should not really happened but just in case, don't make tor
         * freak out, close the circuit and move on. */
        log_info(LD_REND, "Unable to get RENDEZVOUS1 key material for "
                          "service %s",
                 safe_str_client(service->onion_address));
        circuit_mark_for_close(TO_CIRCUIT(circ), END_CIRC_REASON_INTERNAL);
        goto end;
      }
      circ->hs_ident = create_rp_circuit_identifier(service,
                                                    data->rendezvous_cookie,
                                                    &ephemeral_kp.pubkey, &keys);
      memwipe(&ephemeral_kp, 0, sizeof(ephemeral_kp));
      memwipe(&keys, 0, sizeof(keys));
      tor_assert(circ->hs_ident);
    }
  
   end:
    extend_info_free(info);
  }
  
  /** Return true iff the given service rendezvous circuit circ is allowed for a
   * relaunch to the rendezvous point. */
  static int
  can_relaunch_service_rendezvous_point(const origin_circuit_t *circ)
  {
    tor_assert(circ);
    /* This is initialized when allocating an origin circuit. */
    tor_assert(circ->build_state);
    tor_assert(TO_CIRCUIT(circ)->purpose == CIRCUIT_PURPOSE_S_CONNECT_REND);
  
    /* XXX: Retrying under certain condition. This is related to #22455. */
  
    /* Avoid to relaunch twice a circuit to the same rendezvous point at the
     * same time. */
    if (circ->hs_service_side_rend_circ_has_been_relaunched) {
      log_info(LD_REND, "Rendezvous circuit to %s has already been retried. "
                        "Skipping retry.",
               safe_str_client(
                    extend_info_describe(circ->build_state->chosen_exit)));
      goto disallow;
    }
  
    /* We check failure_count >= hs_get_service_max_rend_failures()-1 below, and
     * the -1 is because we increment the failure count for our current failure
     * *after* this clause. */
    int max_rend_failures = hs_get_service_max_rend_failures() - 1;
  
    /* A failure count that has reached maximum allowed or circuit that expired,
     * we skip relaunching. */
    if (circ->build_state->failure_count > max_rend_failures ||
        circ->build_state->expiry_time <= time(NULL)) {
      log_info(LD_REND, "Attempt to build a rendezvous circuit to %s has "
                        "failed with %d attempts and expiry time %ld. "
                        "Giving up building.",
               safe_str_client(
                    extend_info_describe(circ->build_state->chosen_exit)),
               circ->build_state->failure_count,
               (long int) circ->build_state->expiry_time);
      goto disallow;
    }
  
    /* Allowed to relaunch. */
    return 1;
   disallow:
    return 0;
  }
  
  /** Retry the rendezvous point of circ by launching a new circuit to it. */
  static void
  retry_service_rendezvous_point(const origin_circuit_t *circ)
  {
    int flags = 0;
    origin_circuit_t *new_circ;
    cpath_build_state_t *bstate;
  
    tor_assert(circ);
    /* This is initialized when allocating an origin circuit. */
    tor_assert(circ->build_state);
    tor_assert(TO_CIRCUIT(circ)->purpose == CIRCUIT_PURPOSE_S_CONNECT_REND);
  
    /* Ease our life. */
    bstate = circ->build_state;
  
    log_info(LD_REND, "Retrying rendezvous point circuit to %s",
             safe_str_client(extend_info_describe(bstate->chosen_exit)));
  
    /* Get the current build state flags for the next circuit. */
    flags |= (bstate->need_uptime) ? CIRCLAUNCH_NEED_UPTIME : 0;
    flags |= (bstate->need_capacity) ? CIRCLAUNCH_NEED_CAPACITY : 0;
    flags |= (bstate->is_internal) ? CIRCLAUNCH_IS_INTERNAL : 0;
  
    /* We do NOT add the onehop tunnel flag even though it might be a single
     * onion service. The reason is that if we failed once to connect to the RP
     * with a direct connection, we consider that chances are that we will fail
     * again so try a 3-hop circuit and hope for the best. Because the service
     * has no anonymity (single onion), this change of behavior won't affect
     * security directly. */
  
    new_circ = circuit_launch_by_extend_info(CIRCUIT_PURPOSE_S_CONNECT_REND,
                                             bstate->chosen_exit, flags);
    if (new_circ == NULL) {
      log_warn(LD_REND, "Failed to launch rendezvous circuit to %s",
               safe_str_client(extend_info_describe(bstate->chosen_exit)));
      goto done;
    }
  
    /* Transfer build state information to the new circuit state in part to
     * catch any other failures. */
    new_circ->build_state->failure_count = bstate->failure_count+1;
    new_circ->build_state->expiry_time = bstate->expiry_time;
    new_circ->hs_ident = hs_ident_circuit_dup(circ->hs_ident);
  
   done:
    return;
  }
  
  /** Using the given descriptor intro point ip, the node of the
   * rendezvous point rp_node and the service's subcredential, populate the
   * already allocated intro1_data object with the needed key material and link
   * specifiers.
   *
   * Return 0 on success or a negative value if we couldn't properly filled the
   * introduce1 data from the RP node. In other word, it means the RP node is
   * unusable to use in the introduction. */
  static int
  setup_introduce1_data(const hs_desc_intro_point_t *ip,
                        const node_t *rp_node,
                        const hs_subcredential_t *subcredential,
                        hs_cell_introduce1_data_t *intro1_data)
  {
    int ret = -1;
    smartlist_t *rp_lspecs;
  
    tor_assert(ip);
    tor_assert(rp_node);
    tor_assert(subcredential);
    tor_assert(intro1_data);
  
    /* Build the link specifiers from the node at the end of the rendezvous
     * circuit that we opened for this introduction. */
    rp_lspecs = node_get_link_specifier_smartlist(rp_node, 0);
    if (smartlist_len(rp_lspecs) == 0) {
      /* We can't rendezvous without link specifiers. */
      smartlist_free(rp_lspecs);
      goto end;
    }
  
    /* Populate the introduce1 data object. */
    memset(intro1_data, 0, sizeof(hs_cell_introduce1_data_t));
    if (ip->legacy.key != NULL) {
      intro1_data->is_legacy = 1;
      intro1_data->legacy_key = ip->legacy.key;
    }
    intro1_data->auth_pk = &ip->auth_key_cert->signed_key;
    intro1_data->enc_pk = &ip->enc_key;
    intro1_data->subcredential = subcredential;
    intro1_data->link_specifiers = rp_lspecs;
    intro1_data->onion_pk = node_get_curve25519_onion_key(rp_node);
    if (intro1_data->onion_pk == NULL) {
      /* We can't rendezvous without the curve25519 onion key. */
      goto end;
    }
    /* Success, we have valid introduce data. */
    ret = 0;
  
   end:
    return ret;
  }
  
  /** Helper: cleanup function for client circuit. This is for every HS version.
   * It is called from hs_circ_cleanup_on_close() entry point. */
  static void
  cleanup_on_close_client_circ(circuit_t *circ)
  {
    tor_assert(circ);
  
    if (circuit_is_hs_v3(circ)) {
      hs_client_circuit_cleanup_on_close(circ);
    }
    /* It is possible the circuit has an HS purpose but no identifier (rend_data
     * or hs_ident). Thus possible that this passes through. */
  }
  
  /** Helper: cleanup function for client circuit. This is for every HS version.
   * It is called from hs_circ_cleanup_on_free() entry point. */
  static void
  cleanup_on_free_client_circ(circuit_t *circ)
  {
    tor_assert(circ);
  
    if (circuit_is_hs_v2(circ)) {
      rend_client_circuit_cleanup_on_free(circ);
    } else if (circuit_is_hs_v3(circ)) {
      hs_client_circuit_cleanup_on_free(circ);
    }
    /* It is possible the circuit has an HS purpose but no identifier (rend_data
     * or hs_ident). Thus possible that this passes through. */
  }
  
  /* ========== */
  /* Public API */
  /* ========== */
  
  /** Return an introduction point circuit matching the given intro point object.
   * NULL is returned is no such circuit can be found. */
  origin_circuit_t *
  hs_circ_service_get_intro_circ(const hs_service_intro_point_t *ip)
  {
    tor_assert(ip);
  
    if (ip->base.is_only_legacy) {
      return hs_circuitmap_get_intro_circ_v2_service_side(ip->legacy_key_digest);
    } else {
      return hs_circuitmap_get_intro_circ_v3_service_side(
                                          &ip->auth_key_kp.pubkey);
    }
  }
  
  /** Return an introduction point established circuit matching the given intro
   * point object. The circuit purpose has to be CIRCUIT_PURPOSE_S_INTRO. NULL
   * is returned is no such circuit can be found. */
  origin_circuit_t *
  hs_circ_service_get_established_intro_circ(const hs_service_intro_point_t *ip)
  {
    origin_circuit_t *circ;
  
    tor_assert(ip);
  
    if (ip->base.is_only_legacy) {
      circ = hs_circuitmap_get_intro_circ_v2_service_side(ip->legacy_key_digest);
    } else {
      circ = hs_circuitmap_get_intro_circ_v3_service_side(
                                          &ip->auth_key_kp.pubkey);
    }
  
    /* Only return circuit if it is established. */
    return (circ && TO_CIRCUIT(circ)->purpose == CIRCUIT_PURPOSE_S_INTRO) ?
            circ : NULL;
  }
  
  /** Called when we fail building a rendezvous circuit at some point other than
   * the last hop: launches a new circuit to the same rendezvous point. This
   * supports legacy service.
   *
   * We currently relaunch connections to rendezvous points if:
   * - A rendezvous circuit timed out before connecting to RP.
   * - The rendezvous circuit failed to connect to the RP.
   *
   * We avoid relaunching a connection to this rendezvous point if:
   * - We have already tried MAX_REND_FAILURES times to connect to this RP,
   * - We've been trying to connect to this RP for more than MAX_REND_TIMEOUT
   *   seconds, or
   * - We've already retried this specific rendezvous circuit.
   */
  void
  hs_circ_retry_service_rendezvous_point(origin_circuit_t *circ)
  {
    tor_assert(circ);
    tor_assert(TO_CIRCUIT(circ)->purpose == CIRCUIT_PURPOSE_S_CONNECT_REND);
  
    /* Check if we are allowed to relaunch to the rendezvous point of circ. */
    if (!can_relaunch_service_rendezvous_point(circ)) {
      goto done;
    }
  
    /* Flag the circuit that we are relaunching, to avoid to relaunch twice a
     * circuit to the same rendezvous point at the same time. */
    circ->hs_service_side_rend_circ_has_been_relaunched = 1;
  
    /* Legacy services don't have a hidden service ident. */
    if (circ->hs_ident) {
      retry_service_rendezvous_point(circ);
    } else {
      rend_service_relaunch_rendezvous(circ);
    }
  
   done:
    return;
  }
  
  /** For a given service and a service intro point, launch a circuit to the
   * extend info ei. If the service is a single onion, and direct_conn is true,
   * a one-hop circuit will be requested.
   *
   * Return 0 if the circuit was successfully launched and tagged
   * with the correct identifier. On error, a negative value is returned. */
  int
  hs_circ_launch_intro_point(hs_service_t *service,
                             const hs_service_intro_point_t *ip,
                             extend_info_t *ei,
                             bool direct_conn)
  {
    /* Standard flags for introduction circuit. */
    int ret = -1, circ_flags = CIRCLAUNCH_NEED_UPTIME | CIRCLAUNCH_IS_INTERNAL;
    origin_circuit_t *circ;
  
    tor_assert(service);
    tor_assert(ip);
    tor_assert(ei);
  
    /* Update circuit flags in case of a single onion service that requires a
     * direct connection. */
    tor_assert_nonfatal(ip->circuit_retries > 0);
    /* Only single onion services can make direct conns */
    if (BUG(!service->config.is_single_onion && direct_conn)) {
      goto end;
    }
    /* We only use a one-hop path on the first attempt. If the first attempt
     * fails, we use a 3-hop path for reachability / reliability.
     * (Unlike v2, retries is incremented by the caller before it calls this
     * function.) */
    if (direct_conn && ip->circuit_retries == 1) {
      circ_flags |= CIRCLAUNCH_ONEHOP_TUNNEL;
    }
  
    log_info(LD_REND, "Launching a circuit to intro point %s for service %s.",
             safe_str_client(extend_info_describe(ei)),
             safe_str_client(service->onion_address));
  
    /* Note down the launch for the retry period. Even if the circuit fails to
     * be launched, we still want to respect the retry period to avoid stress on
     * the circuit subsystem. */
    service->state.num_intro_circ_launched++;
    circ = circuit_launch_by_extend_info(CIRCUIT_PURPOSE_S_ESTABLISH_INTRO,
                                         ei, circ_flags);
    if (circ == NULL) {
      goto end;
    }
  
    /* Setup the circuit identifier and attach it to it. */
    circ->hs_ident = create_intro_circuit_identifier(service, ip);
    tor_assert(circ->hs_ident);
    /* Register circuit in the global circuitmap. */
    register_intro_circ(ip, circ);
  
    /* Success. */
    ret = 0;
   end:
    return ret;
  }
  
  /** Called when a service introduction point circuit is done building. Given
   * the service and intro point object, this function will send the
   * ESTABLISH_INTRO cell on the circuit. Return 0 on success. Return 1 if the
   * circuit has been repurposed to General because we already have too many
   * opened. */
  int
  hs_circ_service_intro_has_opened(hs_service_t *service,
                                   hs_service_intro_point_t *ip,
                                   const hs_service_descriptor_t *desc,
                                   origin_circuit_t *circ)
  {
    int ret = 0;
    unsigned int num_intro_circ, num_needed_circ;
  
    tor_assert(service);
    tor_assert(ip);
    tor_assert(desc);
    tor_assert(circ);
  
    /* Cound opened circuits that have sent ESTABLISH_INTRO cells or are already
     * established introduction circuits */
    num_intro_circ = count_opened_desc_intro_point_circuits(service, desc);
    num_needed_circ = service->config.num_intro_points;
    if (num_intro_circ > num_needed_circ) {
      /* There are too many opened valid intro circuit for what the service
       * needs so repurpose this one. */
  
      /* XXX: Legacy code checks options->ExcludeNodes and if not NULL it just
       * closes the circuit. I have NO idea why it does that so it hasn't been
       * added here. I can only assume in case our ExcludeNodes list changes but
       * in that case, all circuit are flagged unusable (config.c). --dgoulet */
  
      log_info(LD_CIRC | LD_REND, "Introduction circuit just opened but we "
                                  "have enough for service %s. Repurposing "
                                  "it to general and leaving internal.",
               safe_str_client(service->onion_address));
      tor_assert(circ->build_state->is_internal);
      /* Remove it from the circuitmap. */
      hs_circuitmap_remove_circuit(TO_CIRCUIT(circ));
      /* Cleaning up the hidden service identifier and repurpose. */
      hs_ident_circuit_free(circ->hs_ident);
      circ->hs_ident = NULL;
      if (circuit_should_use_vanguards(TO_CIRCUIT(circ)->purpose))
        circuit_change_purpose(TO_CIRCUIT(circ), CIRCUIT_PURPOSE_HS_VANGUARDS);
      else
        circuit_change_purpose(TO_CIRCUIT(circ), CIRCUIT_PURPOSE_C_GENERAL);
  
      /* Inform that this circuit just opened for this new purpose. */
      circuit_has_opened(circ);
      /* This return value indicate to the caller that the IP object should be
       * removed from the service because it's corresponding circuit has just
       * been repurposed. */
      ret = 1;
      goto done;
    }
  
    log_info(LD_REND, "Introduction circuit %u established for service %s.",
             TO_CIRCUIT(circ)->n_circ_id,
             safe_str_client(service->onion_address));
    circuit_log_path(LOG_INFO, LD_REND, circ);
  
    /* Time to send an ESTABLISH_INTRO cell on this circuit. On error, this call
     * makes sure the circuit gets closed. */
    send_establish_intro(service, ip, circ);
  
   done:
    return ret;
  }
  
  /** Called when a service rendezvous point circuit is done building. Given the
   * service and the circuit, this function will send a RENDEZVOUS1 cell on the
   * circuit using the information in the circuit identifier. If the cell can't
   * be sent, the circuit is closed. */
  void
  hs_circ_service_rp_has_opened(const hs_service_t *service,
                                origin_circuit_t *circ)
  {
    size_t payload_len;
    uint8_t payload[RELAY_PAYLOAD_SIZE] = {0};
  
    tor_assert(service);
    tor_assert(circ);
    tor_assert(circ->hs_ident);
  
    /* Some useful logging. */
    log_info(LD_REND, "Rendezvous circuit %u has opened with cookie %s "
                      "for service %s",
             TO_CIRCUIT(circ)->n_circ_id,
             hex_str((const char *) circ->hs_ident->rendezvous_cookie,
                     REND_COOKIE_LEN),
             safe_str_client(service->onion_address));
    circuit_log_path(LOG_INFO, LD_REND, circ);
  
    /* This can't fail. */
    payload_len = hs_cell_build_rendezvous1(
                          circ->hs_ident->rendezvous_cookie,
                          sizeof(circ->hs_ident->rendezvous_cookie),
                          circ->hs_ident->rendezvous_handshake_info,
                          sizeof(circ->hs_ident->rendezvous_handshake_info),
                          payload);
  
    /* Pad the payload with random bytes so it matches the size of a legacy cell
     * which is normally always bigger. Also, the size of a legacy cell is
     * always smaller than the RELAY_PAYLOAD_SIZE so this is safe. */
    if (payload_len < HS_LEGACY_RENDEZVOUS_CELL_SIZE) {
      crypto_rand((char *) payload + payload_len,
                  HS_LEGACY_RENDEZVOUS_CELL_SIZE - payload_len);
      payload_len = HS_LEGACY_RENDEZVOUS_CELL_SIZE;
    }
  
    if (relay_send_command_from_edge(CONTROL_CELL_ID, TO_CIRCUIT(circ),
                                     RELAY_COMMAND_RENDEZVOUS1,
                                     (const char *) payload, payload_len,
                                     circ->cpath->prev) < 0) {
      /* On error, circuit is closed. */
      log_warn(LD_REND, "Unable to send RENDEZVOUS1 cell on circuit %u "
                        "for service %s",
               TO_CIRCUIT(circ)->n_circ_id,
               safe_str_client(service->onion_address));
      goto done;
    }
  
    /* Setup end-to-end rendezvous circuit between the client and us. */
    if (hs_circuit_setup_e2e_rend_circ(circ,
                         circ->hs_ident->rendezvous_ntor_key_seed,
                         sizeof(circ->hs_ident->rendezvous_ntor_key_seed),
                         1) < 0) {
      log_warn(LD_GENERAL, "Failed to setup circ");
      goto done;
    }
  
   done:
    memwipe(payload, 0, sizeof(payload));
  }
  
  /** Circ has been expecting an INTRO_ESTABLISHED cell that just arrived. Handle
   * the INTRO_ESTABLISHED cell payload of length payload_len arriving on the
   * given introduction circuit circ. The service is only used for logging
   * purposes. Return 0 on success else a negative value. */
  int
  hs_circ_handle_intro_established(const hs_service_t *service,
                                   const hs_service_intro_point_t *ip,
                                   origin_circuit_t *circ,
                                   const uint8_t *payload, size_t payload_len)
  {
    int ret = -1;
  
    tor_assert(service);
    tor_assert(ip);
    tor_assert(circ);
    tor_assert(payload);
  
    if (BUG(TO_CIRCUIT(circ)->purpose != CIRCUIT_PURPOSE_S_ESTABLISH_INTRO)) {
      goto done;
    }
  
    /* Try to parse the payload into a cell making sure we do actually have a
     * valid cell. For a legacy node, it's an empty payload so as long as we
     * have the cell, we are good. */
    if (!ip->base.is_only_legacy &&
        hs_cell_parse_intro_established(payload, payload_len) < 0) {
      log_warn(LD_REND, "Unable to parse the INTRO_ESTABLISHED cell on "
                        "circuit %u for service %s",
               TO_CIRCUIT(circ)->n_circ_id,
               safe_str_client(service->onion_address));
      goto done;
    }
  
    /* Switch the purpose to a fully working intro point. */
    circuit_change_purpose(TO_CIRCUIT(circ), CIRCUIT_PURPOSE_S_INTRO);
    /* Getting a valid INTRODUCE_ESTABLISHED means we've successfully used the
     * circuit so update our pathbias subsystem. */
    pathbias_mark_use_success(circ);
    /* Success. */
    ret = 0;
  
   done:
    return ret;
  }
  
  /**
   *  Go into <b>data</b> and add the right subcredential to be able to handle
   *  this incoming cell.
   *
   *  <b>desc_subcred</b> is the subcredential of the descriptor that corresponds
   *  to the intro point that received this intro request. This subcredential
   *  should be used if we are not an onionbalance instance.
   *
   *  Return 0 if everything went well, or -1 in case of internal error.
   */
  static int
  get_subcredential_for_handling_intro2_cell(const hs_service_t *service,
                                          hs_cell_introduce2_data_t *data,
                                          const hs_subcredential_t *desc_subcred)
  {
    /* Handle the simple case first: We are not an onionbalance instance and we
     * should just use the regular descriptor subcredential */
    if (!hs_ob_service_is_instance(service)) {
      data->n_subcredentials = 1;
      data->subcredentials = desc_subcred;
      return 0;
    }
  
    /* This should not happen since we should have made onionbalance
     * subcredentials when we created our descriptors. */
    if (BUG(!service->state.ob_subcreds)) {
      return -1;
    }
  
    /* We are an onionbalance instance: */
    data->n_subcredentials = service->state.n_ob_subcreds;
    data->subcredentials = service->state.ob_subcreds;
  
    return 0;
  }
  
  /** We just received an INTRODUCE2 cell on the established introduction circuit
   * circ.  Handle the INTRODUCE2 payload of size payload_len for the given
   * circuit and service. This cell is associated with the intro point object ip
   * and the subcredential. Return 0 on success else a negative value. */
  int
  hs_circ_handle_introduce2(const hs_service_t *service,
                            const origin_circuit_t *circ,
                            hs_service_intro_point_t *ip,
                            const hs_subcredential_t *subcredential,
                            const uint8_t *payload, size_t payload_len)
  {
    int ret = -1;
    time_t elapsed;
    hs_cell_introduce2_data_t data;
  
    tor_assert(service);
    tor_assert(circ);
    tor_assert(ip);
    tor_assert(subcredential);
    tor_assert(payload);
  
    /* Populate the data structure with everything we need for the cell to be
     * parsed, decrypted and key material computed correctly. */
    data.auth_pk = &ip->auth_key_kp.pubkey;
    data.enc_kp = &ip->enc_key_kp;
    data.payload = payload;
    data.payload_len = payload_len;
    data.link_specifiers = smartlist_new();
    data.replay_cache = ip->replay_cache;
  
    if (get_subcredential_for_handling_intro2_cell(service,
                                                   &data, subcredential)) {
      goto done;
    }
  
    if (hs_cell_parse_introduce2(&data, circ, service) < 0) {
      goto done;
    }
  
    /* Check whether we've seen this REND_COOKIE before to detect repeats. */
    if (replaycache_add_test_and_elapsed(
             service->state.replay_cache_rend_cookie,
             data.rendezvous_cookie, sizeof(data.rendezvous_cookie),
             &elapsed)) {
      /* A Tor client will send a new INTRODUCE1 cell with the same REND_COOKIE
       * as its previous one if its intro circ times out while in state
       * CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT. If we received the first
       * INTRODUCE1 cell (the intro-point relay converts it into an INTRODUCE2
       * cell), we are already trying to connect to that rend point (and may
       * have already succeeded); drop this cell. */
      log_info(LD_REND, "We received an INTRODUCE2 cell with same REND_COOKIE "
                        "field %ld seconds ago. Dropping cell.",
               (long int) elapsed);
      goto done;
    }
  
    /* At this point, we just confirmed that the full INTRODUCE2 cell is valid
     * so increment our counter that we've seen one on this intro point. */
    ip->introduce2_count++;
  
    /* Launch rendezvous circuit with the onion key and rend cookie. */
    launch_rendezvous_point_circuit(service, ip, &data);
    /* Success. */
    ret = 0;
  
   done:
    link_specifier_smartlist_free(data.link_specifiers);
    memwipe(&data, 0, sizeof(data));
    return ret;
  }
  
  /** Circuit <b>circ</b> just finished the rend ntor key exchange. Use the key
   * exchange output material at <b>ntor_key_seed</b> and setup <b>circ</b> to
   * serve as a rendezvous end-to-end circuit between the client and the
   * service. If <b>is_service_side</b> is set, then we are the hidden service
   * and the other side is the client.
   *
   * Return 0 if the operation went well; in case of error return -1. */
  int
  hs_circuit_setup_e2e_rend_circ(origin_circuit_t *circ,
                                 const uint8_t *ntor_key_seed, size_t seed_len,
                                 int is_service_side)
  {
    if (BUG(!circuit_purpose_is_correct_for_rend(TO_CIRCUIT(circ)->purpose,
                                          is_service_side))) {
      return -1;
    }
  
    crypt_path_t *hop = create_rend_cpath(ntor_key_seed, seed_len,
                                          is_service_side);
    if (!hop) {
      log_warn(LD_REND, "Couldn't get v3 %s cpath!",
               is_service_side ? "service-side" : "client-side");
      return -1;
    }
  
    finalize_rend_circuit(circ, hop, is_service_side);
  
    return 0;
  }
  
  /** We are a v2 legacy HS client and we just received a RENDEZVOUS1 cell
   * <b>rend_cell_body</b> on <b>circ</b>. Finish up the DH key exchange and then
   * extend the crypt path of <b>circ</b> so that the hidden service is on the
   * other side. */
  int
  hs_circuit_setup_e2e_rend_circ_legacy_client(origin_circuit_t *circ,
                                               const uint8_t *rend_cell_body)
  {
  
    if (BUG(!circuit_purpose_is_correct_for_rend(
                                        TO_CIRCUIT(circ)->purpose, 0))) {
      return -1;
    }
  
    crypt_path_t *hop = create_rend_cpath_legacy(circ, rend_cell_body);
    if (!hop) {
      log_warn(LD_GENERAL, "Couldn't get v2 cpath.");
      return -1;
    }
  
    finalize_rend_circuit(circ, hop, 0);
  
    return 0;
  }
  
  /** Given the introduction circuit intro_circ, the rendezvous circuit
   * rend_circ, a descriptor intro point object ip and the service's
   * subcredential, send an INTRODUCE1 cell on intro_circ.
   *
   * This will also setup the circuit identifier on rend_circ containing the key
   * material for the handshake and e2e encryption. Return 0 on success else
   * negative value. Because relay_send_command_from_edge() closes the circuit
   * on error, it is possible that intro_circ is closed on error. */
  int
  hs_circ_send_introduce1(origin_circuit_t *intro_circ,
                          origin_circuit_t *rend_circ,
                          const hs_desc_intro_point_t *ip,
                          const hs_subcredential_t *subcredential)
  {
    int ret = -1;
    ssize_t payload_len;
    uint8_t payload[RELAY_PAYLOAD_SIZE] = {0};
    hs_cell_introduce1_data_t intro1_data;
  
    tor_assert(intro_circ);
    tor_assert(rend_circ);
    tor_assert(ip);
    tor_assert(subcredential);
  
    /* It is undefined behavior in hs_cell_introduce1_data_clear() if intro1_data
     * has been declared on the stack but not initialized. Here, we set it to 0.
     */
    memset(&intro1_data, 0, sizeof(hs_cell_introduce1_data_t));
  
    /* This takes various objects in order to populate the introduce1 data
     * object which is used to build the content of the cell. */
    const node_t *exit_node = build_state_get_exit_node(rend_circ->build_state);
    if (exit_node == NULL) {
      log_info(LD_REND, "Unable to get rendezvous point for circuit %u. "
               "Failing.", TO_CIRCUIT(intro_circ)->n_circ_id);
      goto done;
    }
  
    /* We should never select an invalid rendezvous point in theory but if we
     * do, this function will fail to populate the introduce data. */
    if (setup_introduce1_data(ip, exit_node, subcredential, &intro1_data) < 0) {
      log_warn(LD_REND, "Unable to setup INTRODUCE1 data. The chosen rendezvous "
                        "point is unusable. Closing circuit.");
      goto close;
    }
  
    /* Final step before we encode a cell, we setup the circuit identifier which
     * will generate both the rendezvous cookie and client keypair for this
     * connection. Those are put in the ident. */
    intro1_data.rendezvous_cookie = rend_circ->hs_ident->rendezvous_cookie;
    intro1_data.client_kp = &rend_circ->hs_ident->rendezvous_client_kp;
  
    memcpy(intro_circ->hs_ident->rendezvous_cookie,
           rend_circ->hs_ident->rendezvous_cookie,
           sizeof(intro_circ->hs_ident->rendezvous_cookie));
  
    /* From the introduce1 data object, this will encode the INTRODUCE1 cell
     * into payload which is then ready to be sent as is. */
    payload_len = hs_cell_build_introduce1(&intro1_data, payload);
    if (BUG(payload_len < 0)) {
      goto close;
    }
  
    if (relay_send_command_from_edge(CONTROL_CELL_ID, TO_CIRCUIT(intro_circ),
                                     RELAY_COMMAND_INTRODUCE1,
                                     (const char *) payload, payload_len,
                                     intro_circ->cpath->prev) < 0) {
      /* On error, circuit is closed. */
      log_warn(LD_REND, "Unable to send INTRODUCE1 cell on circuit %u.",
               TO_CIRCUIT(intro_circ)->n_circ_id);
      goto done;
    }
  
    /* Success. */
    ret = 0;
    goto done;
  
   close:
    circuit_mark_for_close(TO_CIRCUIT(rend_circ), END_CIRC_REASON_INTERNAL);
   done:
    hs_cell_introduce1_data_clear(&intro1_data);
    memwipe(payload, 0, sizeof(payload));
    return ret;
  }
  
  /** Send an ESTABLISH_RENDEZVOUS cell along the rendezvous circuit circ. On
   * success, 0 is returned else -1 and the circuit is marked for close. */
  int
  hs_circ_send_establish_rendezvous(origin_circuit_t *circ)
  {
    ssize_t cell_len = 0;
    uint8_t cell[RELAY_PAYLOAD_SIZE] = {0};
  
    tor_assert(circ);
    tor_assert(TO_CIRCUIT(circ)->purpose == CIRCUIT_PURPOSE_C_ESTABLISH_REND);
  
    log_info(LD_REND, "Send an ESTABLISH_RENDEZVOUS cell on circuit %u",
             TO_CIRCUIT(circ)->n_circ_id);
  
    /* Set timestamp_dirty, because circuit_expire_building expects it,
     * and the rend cookie also means we've used the circ. */
    TO_CIRCUIT(circ)->timestamp_dirty = time(NULL);
  
    /* We've attempted to use this circuit. Probe it if we fail */
    pathbias_count_use_attempt(circ);
  
    /* Generate the RENDEZVOUS_COOKIE and place it in the identifier so we can
     * complete the handshake when receiving the acknowledgement. */
    crypto_rand((char *) circ->hs_ident->rendezvous_cookie, HS_REND_COOKIE_LEN);
    /* Generate the client keypair. No need to be extra strong, not long term */
    curve25519_keypair_generate(&circ->hs_ident->rendezvous_client_kp, 0);
  
    cell_len =
      hs_cell_build_establish_rendezvous(circ->hs_ident->rendezvous_cookie,
                                         cell);
    if (BUG(cell_len < 0)) {
      goto err;
    }
  
    if (relay_send_command_from_edge(CONTROL_CELL_ID, TO_CIRCUIT(circ),
                                     RELAY_COMMAND_ESTABLISH_RENDEZVOUS,
                                     (const char *) cell, cell_len,
                                     circ->cpath->prev) < 0) {
      /* Circuit has been marked for close */
      log_warn(LD_REND, "Unable to send ESTABLISH_RENDEZVOUS cell on "
                        "circuit %u", TO_CIRCUIT(circ)->n_circ_id);
      memwipe(cell, 0, cell_len);
      goto err;
    }
  
    memwipe(cell, 0, cell_len);
    return 0;
   err:
    return -1;
  }
  
  /** Circuit cleanup strategy:
   *
   *  What follows is a series of functions that notifies the HS subsystem of 3
   *  different circuit cleanup phase: close, free and repurpose.
   *
   *  Tor can call any of those in any orders so they have to be safe between
   *  each other. In other words, the free should never depend on close to be
   *  called before.
   *
   *  The "on_close()" is called from circuit_mark_for_close() which is
   *  considered the tor fast path and thus as little work as possible should
   *  done in that function. Currently, we only remove the circuit from the HS
   *  circuit map and move on.
   *
   *  The "on_free()" is called from circuit circuit_free_() and it is very
   *  important that at the end of the function, no state or objects related to
   *  this circuit remains alive.
   *
   *  The "on_repurpose()" is called from circuit_change_purpose() for which we
   *  simply remove it from the HS circuit map. We do not have other cleanup
   *  requirements after that.
   *
   *  NOTE: The onion service code, specifically the service code, cleans up
   *  lingering objects or state if any of its circuit disappear which is why
   *  our cleanup strategy doesn't involve any service specific actions. As long
   *  as the circuit is removed from the HS circuit map, it won't be used.
   */
  
  /** We are about to close this <b>circ</b>. Clean it up from any related HS
   * data structures. This function can be called multiple times safely for the
   * same circuit. */
  void
  hs_circ_cleanup_on_close(circuit_t *circ)
  {
    tor_assert(circ);
  
    if (circuit_purpose_is_hs_client(circ->purpose)) {
      cleanup_on_close_client_circ(circ);
    }
  
    /* On close, we simply remove it from the circuit map. It can not be used
     * anymore. We keep this code path fast and lean. */
  
    if (circ->hs_token) {
      hs_circuitmap_remove_circuit(circ);
    }
  }
  
  /** We are about to free this <b>circ</b>. Clean it up from any related HS
   * data structures. This function can be called multiple times safely for the
   * same circuit. */
  void
  hs_circ_cleanup_on_free(circuit_t *circ)
  {
    tor_assert(circ);
  
    /* NOTE: Bulk of the work of cleaning up a circuit is done here. */
  
    if (circuit_purpose_is_hs_client(circ->purpose)) {
      cleanup_on_free_client_circ(circ);
    }
  
    /* We have no assurance that the given HS circuit has been closed before and
     * thus removed from the HS map. This actually happens in unit tests. */
    if (circ->hs_token) {
      hs_circuitmap_remove_circuit(circ);
    }
  }
  
  /** We are about to repurpose this <b>circ</b>. Clean it up from any related
   * HS data structures. This function can be called multiple times safely for
   * the same circuit. */
  void
  hs_circ_cleanup_on_repurpose(circuit_t *circ)
  {
    tor_assert(circ);
  
    /* On repurpose, we simply remove it from the circuit map but we do not do
     * the on_free actions since we don't treat a repurpose as something we need
     * to report in the client cache failure. */
  
    if (circ->hs_token) {
      hs_circuitmap_remove_circuit(circ);
    }
  }
  
  /** Return true iff the given established client rendezvous circuit was sent
   * into the INTRODUCE1 cell. This is called so we can take a decision on
   * expiring or not the circuit.
   *
   * The caller MUST make sure the circuit is an established client rendezvous
   * circuit (purpose: CIRCUIT_PURPOSE_C_REND_READY).
   *
   * This function supports all onion service versions. */
  bool
  hs_circ_is_rend_sent_in_intro1(const origin_circuit_t *circ)
  {
    tor_assert(circ);
    /* This can only be called for a rendezvous circuit that is an established
     * confirmed rendezsvous circuit but without an introduction ACK. */
    tor_assert(TO_CIRCUIT(circ)->purpose == CIRCUIT_PURPOSE_C_REND_READY);
  
    /* The v2 and v3 circuit are handled differently:
     *
     * v2: A circ's pending_final_cpath field is non-NULL iff it is a rend circ
     * and we have tried to send an INTRODUCE1 cell specifying it. Thus, if the
     * pending_final_cpath field *is* NULL, then we want to not spare it.
     *
     * v3: When the INTRODUCE1 cell is sent, the introduction encryption public
     * key is copied in the rendezvous circuit hs identifier. If it is a valid
     * key, we know that this circuit is waiting the ACK on the introduction
     * circuit. We want to _not_ spare the circuit if the key was never set. */
  
    if (circ->rend_data) {
      /* v2. */
      if (circ->build_state && circ->build_state->pending_final_cpath != NULL) {
        return true;
      }
    } else if (circ->hs_ident) {
      /* v3. */
      if (curve25519_public_key_is_ok(&circ->hs_ident->intro_enc_pk)) {
        return true;
      }
    } else {
      /* A circuit with an HS purpose without an hs_ident or rend_data in theory
       * can not happen. In case, scream loudly and return false to the caller
       * that the rendezvous was not sent in the INTRO1 cell. */
      tor_assert_nonfatal_unreached();
    }
  
    /* The rendezvous has not been specified in the INTRODUCE1 cell. */
    return false;
  }
  