circuitlist.c

/* Copyright 2001 Matej Pfajfar.
 * Copyright (c) 2001-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2019, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file circuitlist.c
 *
 * \brief Manage global structures that list and index circuits, and
 *   look up circuits within them.
 *
 * One of the most frequent operations in Tor occurs every time that
 * a relay cell arrives on a channel.  When that happens, we need to
 * find which circuit it is associated with, based on the channel and the
 * circuit ID in the relay cell.
 *
 * To handle that, we maintain a global list of circuits, and a hashtable
 * mapping [channel,circID] pairs to circuits.  Circuits are added to and
 * removed from this mapping using circuit_set_p_circid_chan() and
 * circuit_set_n_circid_chan().  To look up a circuit from this map, most
 * callers should use circuit_get_by_circid_channel(), though
 * circuit_get_by_circid_channel_even_if_marked() is appropriate under some
 * circumstances.
 *
 * We also need to allow for the possibility that we have blocked use of a
 * circuit ID (because we are waiting to send a DESTROY cell), but the
 * circuit is not there any more.  For that case, we allow placeholder
 * entries in the table, using channel_mark_circid_unusable().
 *
 * To efficiently handle a channel that has just opened, we also maintain a
 * list of the circuits waiting for channels, so we can attach them as
 * needed without iterating through the whole list of circuits, using
 * circuit_get_all_pending_on_channel().
 *
 * In this module, we also handle the list of circuits that have been
 * marked for close elsewhere, and close them as needed.  (We use this
 * "mark now, close later" pattern here and elsewhere to avoid
 * unpredictable recursion if we closed every circuit immediately upon
 * realizing it needed to close.)  See circuit_mark_for_close() for the
 * mark function, and circuit_close_all_marked() for the close function.
 *
 * For hidden services, we need to be able to look up introduction point
 * circuits and rendezvous circuits by cookie, key, etc.  These are
 * currently handled with linear searches in
 * circuit_get_ready_rend_circuit_by_rend_data(),
 * circuit_get_next_by_pk_and_purpose(), and with hash lookups in
 * circuit_get_rendezvous() and circuit_get_intro_point().
 *
 * This module is also the entry point for our out-of-memory handler
 * logic, which was originally circuit-focused.
 **/
#define CIRCUITLIST_PRIVATE
#define OCIRC_EVENT_PRIVATE
#include "lib/cc/torint.h"  /* TOR_PRIuSZ */

#include "core/or/or.h"
#include "core/or/channel.h"
#include "core/or/channeltls.h"
#include "feature/client/circpathbias.h"
#include "core/or/circuitbuild.h"
#include "core/or/circuitlist.h"
#include "core/or/circuituse.h"
#include "core/or/circuitstats.h"
#include "core/or/circuitpadding.h"
#include "core/or/crypt_path.h"
#include "core/mainloop/connection.h"
#include "app/config/config.h"
#include "core/or/connection_edge.h"
#include "core/or/connection_or.h"
#include "feature/control/control_events.h"
#include "lib/crypt_ops/crypto_rand.h"
#include "lib/crypt_ops/crypto_util.h"
#include "lib/crypt_ops/crypto_dh.h"
#include "feature/dircommon/directory.h"
#include "feature/client/entrynodes.h"
#include "core/mainloop/mainloop.h"
#include "feature/hs/hs_circuit.h"
#include "feature/hs/hs_circuitmap.h"
#include "feature/hs/hs_ident.h"
#include "feature/nodelist/networkstatus.h"
#include "feature/nodelist/nodelist.h"
#include "feature/relay/onion_queue.h"
#include "core/crypto/onion_crypto.h"
#include "core/crypto/onion_fast.h"
#include "core/or/policies.h"
#include "core/or/relay.h"
#include "core/crypto/relay_crypto.h"
#include "feature/rend/rendclient.h"
#include "feature/rend/rendcommon.h"
#include "feature/stats/predict_ports.h"
#include "feature/stats/rephist.h"
#include "feature/nodelist/routerlist.h"
#include "feature/nodelist/routerset.h"
#include "core/or/channelpadding.h"
#include "lib/compress/compress.h"
#include "lib/compress/compress_lzma.h"
#include "lib/compress/compress_zlib.h"
#include "lib/compress/compress_zstd.h"
#include "lib/buf/buffers.h"

#define OCIRC_EVENT_PRIVATE
#include "core/or/ocirc_event.h"

#include "ht.h"

#include "core/or/cpath_build_state_st.h"
#include "core/or/crypt_path_reference_st.h"
#include "feature/dircommon/dir_connection_st.h"
#include "core/or/edge_connection_st.h"
#include "core/or/half_edge_st.h"
#include "core/or/extend_info_st.h"
#include "core/or/or_circuit_st.h"
#include "core/or/origin_circuit_st.h"

/********* START VARIABLES **********/

/** A global list of all circuits at this hop. */
static smartlist_t *global_circuitlist = NULL;

/** A global list of all origin circuits. Every element of this is also
 * an element of global_circuitlist. */
static smartlist_t *global_origin_circuit_list = NULL;

/** A list of all the circuits in CIRCUIT_STATE_CHAN_WAIT. */
static smartlist_t *circuits_pending_chans = NULL;

/** List of all the (origin) circuits whose state is
 * CIRCUIT_STATE_GUARD_WAIT. */
static smartlist_t *circuits_pending_other_guards = NULL;

/** A list of all the circuits that have been marked with
 * circuit_mark_for_close and which are waiting for circuit_about_to_free. */
static smartlist_t *circuits_pending_close = NULL;

static void cpath_ref_decref(crypt_path_reference_t *cpath_ref);
static void circuit_about_to_free_atexit(circuit_t *circ);
static void circuit_about_to_free(circuit_t *circ);

/**
 * A cached value of the current state of the origin circuit list.  Has the
 * value 1 if we saw any opened circuits recently (since the last call to
 * circuit_any_opened_circuits(), which gets called around once a second by
 * circuit_expire_building). 0 otherwise.
 */
static int any_opened_circs_cached_val = 0;

/********* END VARIABLES ************/

or_circuit_t *
TO_OR_CIRCUIT(circuit_t *x)
{
  tor_assert(x->magic == OR_CIRCUIT_MAGIC);
  return DOWNCAST(or_circuit_t, x);
}
const or_circuit_t *
CONST_TO_OR_CIRCUIT(const circuit_t *x)
{
  tor_assert(x->magic == OR_CIRCUIT_MAGIC);
  return DOWNCAST(or_circuit_t, x);
}
origin_circuit_t *
TO_ORIGIN_CIRCUIT(circuit_t *x)
{
  tor_assert(x->magic == ORIGIN_CIRCUIT_MAGIC);
  return DOWNCAST(origin_circuit_t, x);
}
const origin_circuit_t *
CONST_TO_ORIGIN_CIRCUIT(const circuit_t *x)
{
  tor_assert(x->magic == ORIGIN_CIRCUIT_MAGIC);
  return DOWNCAST(origin_circuit_t, x);
}

/** A map from channel and circuit ID to circuit.  (Lookup performance is
 * very important here, since we need to do it every time a cell arrives.) */
typedef struct chan_circid_circuit_map_t {
  HT_ENTRY(chan_circid_circuit_map_t) node;
  channel_t *chan;
  circid_t circ_id;
  circuit_t *circuit;
  /* For debugging 12184: when was this placeholder item added? */
  time_t made_placeholder_at;
} chan_circid_circuit_map_t;

/** Helper for hash tables: compare the channel and circuit ID for a and
 * b, and return less than, equal to, or greater than zero appropriately.
 */
static inline int
chan_circid_entries_eq_(chan_circid_circuit_map_t *a,
                        chan_circid_circuit_map_t *b)
{
  return a->chan == b->chan && a->circ_id == b->circ_id;
}

/** Helper: return a hash based on circuit ID and the pointer value of
 * chan in <b>a</b>. */
static inline unsigned int
chan_circid_entry_hash_(chan_circid_circuit_map_t *a)
{
  /* Try to squeze the siphash input into 8 bytes to save any extra siphash
   * rounds.  This hash function is in the critical path. */
  uintptr_t chan = (uintptr_t) (void*) a->chan;
  uint32_t array[2];
  array[0] = a->circ_id;
  /* The low bits of the channel pointer are uninteresting, since the channel
   * is a pretty big structure. */
  array[1] = (uint32_t) (chan >> 6);
  return (unsigned) siphash24g(array, sizeof(array));
}

/** Map from [chan,circid] to circuit. */
static HT_HEAD(chan_circid_map, chan_circid_circuit_map_t)
     chan_circid_map = HT_INITIALIZER();
HT_PROTOTYPE(chan_circid_map, chan_circid_circuit_map_t, node,
             chan_circid_entry_hash_, chan_circid_entries_eq_)
HT_GENERATE2(chan_circid_map, chan_circid_circuit_map_t, node,
             chan_circid_entry_hash_, chan_circid_entries_eq_, 0.6,
             tor_reallocarray_, tor_free_)

/** The most recently returned entry from circuit_get_by_circid_chan;
 * used to improve performance when many cells arrive in a row from the
 * same circuit.
 */
static chan_circid_circuit_map_t *_last_circid_chan_ent = NULL;

/** Implementation helper for circuit_set_{p,n}_circid_channel: A circuit ID
 * and/or channel for circ has just changed from <b>old_chan, old_id</b>
 * to <b>chan, id</b>.  Adjust the chan,circid map as appropriate, removing
 * the old entry (if any) and adding a new one. */
static void
circuit_set_circid_chan_helper(circuit_t *circ, int direction,
                               circid_t id,
                               channel_t *chan)
{
  chan_circid_circuit_map_t search;
  chan_circid_circuit_map_t *found;
  channel_t *old_chan, **chan_ptr;
  circid_t old_id, *circid_ptr;
  int make_active, attached = 0;

  if (direction == CELL_DIRECTION_OUT) {
    chan_ptr = &circ->n_chan;
    circid_ptr = &circ->n_circ_id;
    make_active = circ->n_chan_cells.n > 0;
  } else {
    or_circuit_t *c = TO_OR_CIRCUIT(circ);
    chan_ptr = &c->p_chan;
    circid_ptr = &c->p_circ_id;
    make_active = c->p_chan_cells.n > 0;
  }
  old_chan = *chan_ptr;
  old_id = *circid_ptr;

  if (id == old_id && chan == old_chan)
    return;

  if (_last_circid_chan_ent &&
      ((old_id == _last_circid_chan_ent->circ_id &&
        old_chan == _last_circid_chan_ent->chan) ||
       (id == _last_circid_chan_ent->circ_id &&
        chan == _last_circid_chan_ent->chan))) {
    _last_circid_chan_ent = NULL;
  }

  if (old_chan) {
    /*
     * If we're changing channels or ID and had an old channel and a non
     * zero old ID and weren't marked for close (i.e., we should have been
     * attached), detach the circuit. ID changes require this because
     * circuitmux hashes on (channel_id, circuit_id).
     */
    if (old_id != 0 && (old_chan != chan || old_id != id) &&
        !(circ->marked_for_close)) {
      tor_assert(old_chan->cmux);
      circuitmux_detach_circuit(old_chan->cmux, circ);
    }

    /* we may need to remove it from the conn-circid map */
    search.circ_id = old_id;
    search.chan = old_chan;
    found = HT_REMOVE(chan_circid_map, &chan_circid_map, &search);
    if (found) {
      tor_free(found);
      if (direction == CELL_DIRECTION_OUT) {
        /* One fewer circuits use old_chan as n_chan */
        --(old_chan->num_n_circuits);
      } else {
        /* One fewer circuits use old_chan as p_chan */
        --(old_chan->num_p_circuits);
      }
    }
  }

  /* Change the values only after we have possibly made the circuit inactive
   * on the previous chan. */
  *chan_ptr = chan;
  *circid_ptr = id;

  if (chan == NULL)
    return;

  /* now add the new one to the conn-circid map */
  search.circ_id = id;
  search.chan = chan;
  found = HT_FIND(chan_circid_map, &chan_circid_map, &search);
  if (found) {
    found->circuit = circ;
    found->made_placeholder_at = 0;
  } else {
    found = tor_malloc_zero(sizeof(chan_circid_circuit_map_t));
    found->circ_id = id;
    found->chan = chan;
    found->circuit = circ;
    HT_INSERT(chan_circid_map, &chan_circid_map, found);
  }

  /*
   * Attach to the circuitmux if we're changing channels or IDs and
   * have a new channel and ID to use and the circuit is not marked for
   * close.
   */
  if (chan && id != 0 && (old_chan != chan || old_id != id) &&
      !(circ->marked_for_close)) {
    tor_assert(chan->cmux);
    circuitmux_attach_circuit(chan->cmux, circ, direction);
    attached = 1;
  }

  /*
   * This is a no-op if we have no cells, but if we do it marks us active to
   * the circuitmux
   */
  if (make_active && attached)
    update_circuit_on_cmux(circ, direction);

  /* Adjust circuit counts on new channel */
  if (direction == CELL_DIRECTION_OUT) {
    ++chan->num_n_circuits;
  } else {
    ++chan->num_p_circuits;
  }
}

/** Mark that circuit id <b>id</b> shouldn't be used on channel <b>chan</b>,
 * even if there is no circuit on the channel. We use this to keep the
 * circuit id from getting re-used while we have queued but not yet sent
 * a destroy cell. */
void
channel_mark_circid_unusable(channel_t *chan, circid_t id)
{
  chan_circid_circuit_map_t search;
  chan_circid_circuit_map_t *ent;

  /* See if there's an entry there. That wouldn't be good. */
  memset(&search, 0, sizeof(search));
  search.chan = chan;
  search.circ_id = id;
  ent = HT_FIND(chan_circid_map, &chan_circid_map, &search);

  if (ent && ent->circuit) {
    /* we have a problem. */
    log_warn(LD_BUG, "Tried to mark %u unusable on %p, but there was already "
             "a circuit there.", (unsigned)id, chan);
  } else if (ent) {
    /* It's already marked. */
    if (!ent->made_placeholder_at)
      ent->made_placeholder_at = approx_time();
  } else {
    ent = tor_malloc_zero(sizeof(chan_circid_circuit_map_t));
    ent->chan = chan;
    ent->circ_id = id;
    /* leave circuit at NULL. */
    ent->made_placeholder_at = approx_time();
    HT_INSERT(chan_circid_map, &chan_circid_map, ent);
  }
}

/** Mark that a circuit id <b>id</b> can be used again on <b>chan</b>.
 * We use this to re-enable the circuit ID after we've sent a destroy cell.
 */
void
channel_mark_circid_usable(channel_t *chan, circid_t id)
{
  chan_circid_circuit_map_t search;
  chan_circid_circuit_map_t *ent;

  /* See if there's an entry there. That wouldn't be good. */
  memset(&search, 0, sizeof(search));
  search.chan = chan;
  search.circ_id = id;
  ent = HT_REMOVE(chan_circid_map, &chan_circid_map, &search);
  if (ent && ent->circuit) {
    log_warn(LD_BUG, "Tried to mark %u usable on %p, but there was already "
             "a circuit there.", (unsigned)id, chan);
    return;
  }
  if (_last_circid_chan_ent == ent)
    _last_circid_chan_ent = NULL;
  tor_free(ent);
}

/** Called to indicate that a DESTROY is pending on <b>chan</b> with
 * circuit ID <b>id</b>, but hasn't been sent yet. */
void
channel_note_destroy_pending(channel_t *chan, circid_t id)
{
  circuit_t *circ = circuit_get_by_circid_channel_even_if_marked(id,chan);
  if (circ) {
    if (circ->n_chan == chan && circ->n_circ_id == id) {
      circ->n_delete_pending = 1;
    } else {
      or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
      if (orcirc->p_chan == chan && orcirc->p_circ_id == id) {
        circ->p_delete_pending = 1;
      }
    }
    return;
  }
  channel_mark_circid_unusable(chan, id);
}

/** Called to indicate that a DESTROY is no longer pending on <b>chan</b> with
 * circuit ID <b>id</b> -- typically, because it has been sent. */
MOCK_IMPL(void,
channel_note_destroy_not_pending,(channel_t *chan, circid_t id))
{
  circuit_t *circ = circuit_get_by_circid_channel_even_if_marked(id,chan);
  if (circ) {
    if (circ->n_chan == chan && circ->n_circ_id == id) {
      circ->n_delete_pending = 0;
    } else {
      or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
      if (orcirc->p_chan == chan && orcirc->p_circ_id == id) {
        circ->p_delete_pending = 0;
      }
    }
    /* XXXX this shouldn't happen; log a bug here. */
    return;
  }
  channel_mark_circid_usable(chan, id);
}

/** Set the p_conn field of a circuit <b>circ</b>, along
 * with the corresponding circuit ID, and add the circuit as appropriate
 * to the (chan,id)-\>circuit map. */
void
circuit_set_p_circid_chan(or_circuit_t *or_circ, circid_t id,
                          channel_t *chan)
{
  circuit_t *circ = TO_CIRCUIT(or_circ);
  channel_t *old_chan = or_circ->p_chan;
  circid_t old_id = or_circ->p_circ_id;

  circuit_set_circid_chan_helper(circ, CELL_DIRECTION_IN, id, chan);

  if (chan) {
    chan->timestamp_last_had_circuits = approx_time();
  }

  if (circ->p_delete_pending && old_chan) {
    channel_mark_circid_unusable(old_chan, old_id);
    circ->p_delete_pending = 0;
  }
}

/** Set the n_conn field of a circuit <b>circ</b>, along
 * with the corresponding circuit ID, and add the circuit as appropriate
 * to the (chan,id)-\>circuit map. */
void
circuit_set_n_circid_chan(circuit_t *circ, circid_t id,
                          channel_t *chan)
{
  channel_t *old_chan = circ->n_chan;
  circid_t old_id = circ->n_circ_id;

  circuit_set_circid_chan_helper(circ, CELL_DIRECTION_OUT, id, chan);

  if (chan) {
    chan->timestamp_last_had_circuits = approx_time();
  }

  if (circ->n_delete_pending && old_chan) {
    channel_mark_circid_unusable(old_chan, old_id);
    circ->n_delete_pending = 0;
  }
}

/**
 * Helper function to publish a message about events on an origin circuit
 *
 * Publishes a message to subscribers of origin circuit events, and
 * sends the control event.
 **/
int
circuit_event_status(origin_circuit_t *circ, circuit_status_event_t tp,
                     int reason_code)
{
  ocirc_event_msg_t msg;

  tor_assert(circ);

  msg.type = OCIRC_MSGTYPE_CEVENT;
  msg.u.cevent.gid = circ->global_identifier;
  msg.u.cevent.evtype = tp;
  msg.u.cevent.reason = reason_code;
  msg.u.cevent.onehop = circ->build_state->onehop_tunnel;

  ocirc_event_publish(&msg);
  return control_event_circuit_status(circ, tp, reason_code);
}

/**
 * Helper function to publish a state change message
 *
 * circuit_set_state() calls this to notify subscribers about a change
 * of the state of an origin circuit.
 **/
static void
circuit_state_publish(const circuit_t *circ)
{
  ocirc_event_msg_t msg;
  const origin_circuit_t *ocirc;

  if (!CIRCUIT_IS_ORIGIN(circ))
    return;
  ocirc = CONST_TO_ORIGIN_CIRCUIT(circ);
  /* Only inbound OR circuits can be in this state, not origin circuits. */
  tor_assert(circ->state != CIRCUIT_STATE_ONIONSKIN_PENDING);

  msg.type = OCIRC_MSGTYPE_STATE;
  msg.u.state.gid = ocirc->global_identifier;
  msg.u.state.state = circ->state;
  msg.u.state.onehop = ocirc->build_state->onehop_tunnel;

  ocirc_event_publish(&msg);
}

/** Change the state of <b>circ</b> to <b>state</b>, adding it to or removing
 * it from lists as appropriate. */
void
circuit_set_state(circuit_t *circ, uint8_t state)
{
  tor_assert(circ);
  if (state == circ->state)
    return;
  if (PREDICT_UNLIKELY(!circuits_pending_chans))
    circuits_pending_chans = smartlist_new();
  if (PREDICT_UNLIKELY(!circuits_pending_other_guards))
    circuits_pending_other_guards = smartlist_new();
  if (circ->state == CIRCUIT_STATE_CHAN_WAIT) {
    /* remove from waiting-circuit list. */
    smartlist_remove(circuits_pending_chans, circ);
  }
  if (state == CIRCUIT_STATE_CHAN_WAIT) {
    /* add to waiting-circuit list. */
    smartlist_add(circuits_pending_chans, circ);
  }
  if (circ->state == CIRCUIT_STATE_GUARD_WAIT) {
    smartlist_remove(circuits_pending_other_guards, circ);
  }
  if (state == CIRCUIT_STATE_GUARD_WAIT) {
    smartlist_add(circuits_pending_other_guards, circ);
  }
  if (state == CIRCUIT_STATE_GUARD_WAIT || state == CIRCUIT_STATE_OPEN)
    tor_assert(!circ->n_chan_create_cell);
  circ->state = state;
  circuit_state_publish(circ);
}

/** Append to <b>out</b> all circuits in state CHAN_WAIT waiting for
 * the given connection. */
void
circuit_get_all_pending_on_channel(smartlist_t *out, channel_t *chan)
{
  tor_assert(out);
  tor_assert(chan);

  if (!circuits_pending_chans)
    return;

  SMARTLIST_FOREACH_BEGIN(circuits_pending_chans, circuit_t *, circ) {
    if (circ->marked_for_close)
      continue;
    if (!circ->n_hop)
      continue;
    tor_assert(circ->state == CIRCUIT_STATE_CHAN_WAIT);
    if (tor_digest_is_zero(circ->n_hop->identity_digest)) {
      /* Look at addr/port. This is an unkeyed connection. */
      if (!channel_matches_extend_info(chan, circ->n_hop))
        continue;
    } else {
      /* We expected a key. See if it's the right one. */
      if (tor_memneq(chan->identity_digest,
                     circ->n_hop->identity_digest, DIGEST_LEN))
        continue;
    }
    smartlist_add(out, circ);
  } SMARTLIST_FOREACH_END(circ);
}

/** Return the number of circuits in state CHAN_WAIT, waiting for the given
 * channel. */
int
circuit_count_pending_on_channel(channel_t *chan)
{
  int cnt;
  smartlist_t *sl = smartlist_new();

  tor_assert(chan);

  circuit_get_all_pending_on_channel(sl, chan);
  cnt = smartlist_len(sl);
  smartlist_free(sl);
  log_debug(LD_CIRC,"or_conn to %s, %d pending circs",
            channel_get_canonical_remote_descr(chan),
            cnt);
  return cnt;
}

/** Remove <b>origin_circ</b> from the global list of origin circuits.
 * Called when we are freeing a circuit.
 */
static void
circuit_remove_from_origin_circuit_list(origin_circuit_t *origin_circ)
{
  int origin_idx = origin_circ->global_origin_circuit_list_idx;
  if (origin_idx < 0)
    return;
  origin_circuit_t *c2;
  tor_assert(origin_idx <= smartlist_len(global_origin_circuit_list));
  c2 = smartlist_get(global_origin_circuit_list, origin_idx);
  tor_assert(origin_circ == c2);
  smartlist_del(global_origin_circuit_list, origin_idx);
  if (origin_idx < smartlist_len(global_origin_circuit_list)) {
    origin_circuit_t *replacement =
      smartlist_get(global_origin_circuit_list, origin_idx);
    replacement->global_origin_circuit_list_idx = origin_idx;
  }
  origin_circ->global_origin_circuit_list_idx = -1;
}

/** Add <b>origin_circ</b> to the global list of origin circuits. Called
 * when creating the circuit. */
static void
circuit_add_to_origin_circuit_list(origin_circuit_t *origin_circ)
{
  tor_assert(origin_circ->global_origin_circuit_list_idx == -1);
  smartlist_t *lst = circuit_get_global_origin_circuit_list();
  smartlist_add(lst, origin_circ);
  origin_circ->global_origin_circuit_list_idx = smartlist_len(lst) - 1;
}

/** Detach from the global circuit list, and deallocate, all
 * circuits that have been marked for close.
 */
void
circuit_close_all_marked(void)
{
  if (circuits_pending_close == NULL)
    return;

  smartlist_t *lst = circuit_get_global_list();
  SMARTLIST_FOREACH_BEGIN(circuits_pending_close, circuit_t *, circ) {
    tor_assert(circ->marked_for_close);

    /* Remove it from the circuit list. */
    int idx = circ->global_circuitlist_idx;
    smartlist_del(lst, idx);
    if (idx < smartlist_len(lst)) {
      circuit_t *replacement = smartlist_get(lst, idx);
      replacement->global_circuitlist_idx = idx;
    }
    circ->global_circuitlist_idx = -1;

    /* Remove it from the origin circuit list, if appropriate. */
    if (CIRCUIT_IS_ORIGIN(circ)) {
      circuit_remove_from_origin_circuit_list(TO_ORIGIN_CIRCUIT(circ));
    }

    circuit_about_to_free(circ);
    circuit_free(circ);
  } SMARTLIST_FOREACH_END(circ);

  smartlist_clear(circuits_pending_close);
}

/** Return a pointer to the global list of circuits. */
MOCK_IMPL(smartlist_t *,
circuit_get_global_list,(void))
{
  if (NULL == global_circuitlist)
    global_circuitlist = smartlist_new();
  return global_circuitlist;
}

/** Return a pointer to the global list of origin circuits. */
smartlist_t *
circuit_get_global_origin_circuit_list(void)
{
  if (NULL == global_origin_circuit_list)
    global_origin_circuit_list = smartlist_new();
  return global_origin_circuit_list;
}

/**
 * Return true if we have any opened general-purpose 3 hop
 * origin circuits.
 *
 * The result from this function is cached for use by
 * circuit_any_opened_circuits_cached().
 */
int
circuit_any_opened_circuits(void)
{
  SMARTLIST_FOREACH_BEGIN(circuit_get_global_origin_circuit_list(),
          const origin_circuit_t *, next_circ) {
    if (!TO_CIRCUIT(next_circ)->marked_for_close &&
        next_circ->has_opened &&
        TO_CIRCUIT(next_circ)->state == CIRCUIT_STATE_OPEN &&
        TO_CIRCUIT(next_circ)->purpose != CIRCUIT_PURPOSE_C_MEASURE_TIMEOUT &&
        next_circ->build_state &&
        next_circ->build_state->desired_path_len == DEFAULT_ROUTE_LEN) {
      circuit_cache_opened_circuit_state(1);
      return 1;
    }
  } SMARTLIST_FOREACH_END(next_circ);

  circuit_cache_opened_circuit_state(0);
  return 0;
}

/**
 * Cache the "any circuits opened" state, as specified in param
 * circuits_are_opened. This is a helper function to update
 * the circuit opened status whenever we happen to look at the
 * circuit list.
 */
void
circuit_cache_opened_circuit_state(int circuits_are_opened)
{
  any_opened_circs_cached_val = circuits_are_opened;
}

/**
 * Return true if there were any opened circuits since the last call to
 * circuit_any_opened_circuits(), or since circuit_expire_building() last
 * ran (it runs roughly once per second).
 */
int
circuit_any_opened_circuits_cached(void)
{
  return any_opened_circs_cached_val;
}

/** Function to make circ-\>state human-readable */
const char *
circuit_state_to_string(int state)
{
  static char buf[64];
  switch (state) {
    case CIRCUIT_STATE_BUILDING: return "doing handshakes";
    case CIRCUIT_STATE_ONIONSKIN_PENDING: return "processing the onion";
    case CIRCUIT_STATE_CHAN_WAIT: return "connecting to server";
    case CIRCUIT_STATE_GUARD_WAIT: return "waiting to see how other "
      "guards perform";
    case CIRCUIT_STATE_OPEN: return "open";
    default:
      log_warn(LD_BUG, "Unknown circuit state %d", state);
      tor_snprintf(buf, sizeof(buf), "unknown state [%d]", state);
      return buf;
  }
}

/** Map a circuit purpose to a string suitable to be displayed to a
 * controller. */
const char *
circuit_purpose_to_controller_string(uint8_t purpose)
{
  static char buf[32];
  switch (purpose) {
    case CIRCUIT_PURPOSE_OR:
    case CIRCUIT_PURPOSE_INTRO_POINT:
    case CIRCUIT_PURPOSE_REND_POINT_WAITING:
    case CIRCUIT_PURPOSE_REND_ESTABLISHED:
      return "SERVER"; /* A controller should never see these, actually. */

    case CIRCUIT_PURPOSE_C_GENERAL:
      return "GENERAL";

    case CIRCUIT_PURPOSE_C_HSDIR_GET:
      return "HS_CLIENT_HSDIR";

    case CIRCUIT_PURPOSE_C_INTRODUCING:
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACKED:
      return "HS_CLIENT_INTRO";

    case CIRCUIT_PURPOSE_C_ESTABLISH_REND:
    case CIRCUIT_PURPOSE_C_REND_READY:
    case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
    case CIRCUIT_PURPOSE_C_REND_JOINED:
      return "HS_CLIENT_REND";

    case CIRCUIT_PURPOSE_S_HSDIR_POST:
      return "HS_SERVICE_HSDIR";

    case CIRCUIT_PURPOSE_S_ESTABLISH_INTRO:
    case CIRCUIT_PURPOSE_S_INTRO:
      return "HS_SERVICE_INTRO";

    case CIRCUIT_PURPOSE_S_CONNECT_REND:
    case CIRCUIT_PURPOSE_S_REND_JOINED:
      return "HS_SERVICE_REND";

    case CIRCUIT_PURPOSE_TESTING:
      return "TESTING";
    case CIRCUIT_PURPOSE_C_MEASURE_TIMEOUT:
      return "MEASURE_TIMEOUT";
    case CIRCUIT_PURPOSE_CONTROLLER:
      return "CONTROLLER";
    case CIRCUIT_PURPOSE_PATH_BIAS_TESTING:
      return "PATH_BIAS_TESTING";
    case CIRCUIT_PURPOSE_HS_VANGUARDS:
      return "HS_VANGUARDS";
    case CIRCUIT_PURPOSE_C_CIRCUIT_PADDING:
      return "CIRCUIT_PADDING";

    default:
      tor_snprintf(buf, sizeof(buf), "UNKNOWN_%d", (int)purpose);
      return buf;
  }
}

/** Return a string specifying the state of the hidden-service circuit
 * purpose <b>purpose</b>, or NULL if <b>purpose</b> is not a
 * hidden-service-related circuit purpose. */
const char *
circuit_purpose_to_controller_hs_state_string(uint8_t purpose)
{
  switch (purpose)
    {
    default:
      log_fn(LOG_WARN, LD_BUG,
             "Unrecognized circuit purpose: %d",
             (int)purpose);
      tor_fragile_assert();
      FALLTHROUGH;

    case CIRCUIT_PURPOSE_OR:
    case CIRCUIT_PURPOSE_C_GENERAL:
    case CIRCUIT_PURPOSE_C_MEASURE_TIMEOUT:
    case CIRCUIT_PURPOSE_TESTING:
    case CIRCUIT_PURPOSE_CONTROLLER:
    case CIRCUIT_PURPOSE_PATH_BIAS_TESTING:
    case CIRCUIT_PURPOSE_HS_VANGUARDS:
    case CIRCUIT_PURPOSE_C_CIRCUIT_PADDING:
      return NULL;

    case CIRCUIT_PURPOSE_INTRO_POINT:
      return "OR_HSSI_ESTABLISHED";
    case CIRCUIT_PURPOSE_REND_POINT_WAITING:
      return "OR_HSCR_ESTABLISHED";
    case CIRCUIT_PURPOSE_REND_ESTABLISHED:
      return "OR_HS_R_JOINED";

    case CIRCUIT_PURPOSE_C_HSDIR_GET:
    case CIRCUIT_PURPOSE_C_INTRODUCING:
      return "HSCI_CONNECTING";
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
      return "HSCI_INTRO_SENT";
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACKED:
      return "HSCI_DONE";

    case CIRCUIT_PURPOSE_C_ESTABLISH_REND:
      return "HSCR_CONNECTING";
    case CIRCUIT_PURPOSE_C_REND_READY:
      return "HSCR_ESTABLISHED_IDLE";
    case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
      return "HSCR_ESTABLISHED_WAITING";
    case CIRCUIT_PURPOSE_C_REND_JOINED:
      return "HSCR_JOINED";

    case CIRCUIT_PURPOSE_S_HSDIR_POST:
    case CIRCUIT_PURPOSE_S_ESTABLISH_INTRO:
      return "HSSI_CONNECTING";
    case CIRCUIT_PURPOSE_S_INTRO:
      return "HSSI_ESTABLISHED";

    case CIRCUIT_PURPOSE_S_CONNECT_REND:
      return "HSSR_CONNECTING";
    case CIRCUIT_PURPOSE_S_REND_JOINED:
      return "HSSR_JOINED";
    }
}

/** Return a human-readable string for the circuit purpose <b>purpose</b>. */
const char *
circuit_purpose_to_string(uint8_t purpose)
{
  static char buf[32];

  switch (purpose)
    {
    case CIRCUIT_PURPOSE_OR:
      return "Circuit at relay";
    case CIRCUIT_PURPOSE_INTRO_POINT:
      return "Acting as intro point";
    case CIRCUIT_PURPOSE_REND_POINT_WAITING:
      return "Acting as rendezvous (pending)";
    case CIRCUIT_PURPOSE_REND_ESTABLISHED:
      return "Acting as rendezvous (established)";
    case CIRCUIT_PURPOSE_C_GENERAL:
      return "General-purpose client";
    case CIRCUIT_PURPOSE_C_INTRODUCING:
      return "Hidden service client: Connecting to intro point";
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
      return "Hidden service client: Waiting for ack from intro point";
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACKED:
      return "Hidden service client: Received ack from intro point";
    case CIRCUIT_PURPOSE_C_ESTABLISH_REND:
      return "Hidden service client: Establishing rendezvous point";
    case CIRCUIT_PURPOSE_C_REND_READY:
      return "Hidden service client: Pending rendezvous point";
    case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
      return "Hidden service client: Pending rendezvous point (ack received)";
    case CIRCUIT_PURPOSE_C_REND_JOINED:
      return "Hidden service client: Active rendezvous point";
    case CIRCUIT_PURPOSE_C_HSDIR_GET:
      return "Hidden service client: Fetching HS descriptor";

    case CIRCUIT_PURPOSE_C_MEASURE_TIMEOUT:
      return "Measuring circuit timeout";

    case CIRCUIT_PURPOSE_S_ESTABLISH_INTRO:
      return "Hidden service: Establishing introduction point";
    case CIRCUIT_PURPOSE_S_INTRO:
      return "Hidden service: Introduction point";
    case CIRCUIT_PURPOSE_S_CONNECT_REND:
      return "Hidden service: Connecting to rendezvous point";
    case CIRCUIT_PURPOSE_S_REND_JOINED:
      return "Hidden service: Active rendezvous point";
    case CIRCUIT_PURPOSE_S_HSDIR_POST:
      return "Hidden service: Uploading HS descriptor";

    case CIRCUIT_PURPOSE_TESTING:
      return "Testing circuit";

    case CIRCUIT_PURPOSE_CONTROLLER:
      return "Circuit made by controller";

    case CIRCUIT_PURPOSE_PATH_BIAS_TESTING:
      return "Path-bias testing circuit";

    case CIRCUIT_PURPOSE_HS_VANGUARDS:
      return "Hidden service: Pre-built vanguard circuit";

    case CIRCUIT_PURPOSE_C_CIRCUIT_PADDING:
      return "Circuit kept open for padding";

    default:
      tor_snprintf(buf, sizeof(buf), "UNKNOWN_%d", (int)purpose);
      return buf;
  }
}

/** Pick a reasonable package_window to start out for our circuits.
 * Originally this was hard-coded at 1000, but now the consensus votes
 * on the answer. See proposal 168. */
int32_t
circuit_initial_package_window(void)
{
  int32_t num = networkstatus_get_param(NULL, "circwindow", CIRCWINDOW_START,
                                        CIRCWINDOW_START_MIN,
                                        CIRCWINDOW_START_MAX);
  /* If the consensus tells us a negative number, we'd assert. */
  if (num < 0)
    num = CIRCWINDOW_START;
  return num;
}

/** Initialize the common elements in a circuit_t, and add it to the global
 * list. */
static void
init_circuit_base(circuit_t *circ)
{
  tor_gettimeofday(&circ->timestamp_created);

  // Gets reset when we send CREATE_FAST.
  // circuit_expire_building() expects these to be equal
  // until the orconn is built.
  circ->timestamp_began = circ->timestamp_created;

  circ->package_window = circuit_initial_package_window();
  circ->deliver_window = CIRCWINDOW_START;
  circuit_reset_sendme_randomness(circ);
  cell_queue_init(&circ->n_chan_cells);

  smartlist_add(circuit_get_global_list(), circ);
  circ->global_circuitlist_idx = smartlist_len(circuit_get_global_list()) - 1;