path: root/agent/conncheck.c

/*
 * This file is part of the Nice GLib ICE library.
 *
 * (C) 2006-2009 Collabora Ltd.
 *  Contact: Youness Alaoui
 * (C) 2006-2009 Nokia Corporation. All rights reserved.
 *  Contact: Kai Vehmanen
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is the Nice GLib ICE library.
 *
 * The Initial Developers of the Original Code are Collabora Ltd and Nokia
 * Corporation. All Rights Reserved.
 *
 * Contributors:
 *   Kai Vehmanen, Nokia
 *   Youness Alaoui, Collabora Ltd.
 *   Dafydd Harries, Collabora Ltd.
 *
 * Alternatively, the contents of this file may be used under the terms of the
 * the GNU Lesser General Public License Version 2.1 (the "LGPL"), in which
 * case the provisions of LGPL are applicable instead of those above. If you
 * wish to allow use of your version of this file only under the terms of the
 * LGPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replace
 * them with the notice and other provisions required by the LGPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the LGPL.
 */

/*
 * @file conncheck.c
 * @brief ICE connectivity checks
 */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <errno.h>
#include <string.h>

#include <glib.h>

#include "debug.h"

#include "agent.h"
#include "agent-priv.h"
#include "conncheck.h"
#include "discovery.h"
#include "stun/stun5389.h"
#include "stun/usages/ice.h"
#include "stun/usages/bind.h"
#include "stun/usages/turn.h"

static void priv_update_check_list_failed_components (NiceAgent *agent, NiceStream *stream);
static void priv_update_check_list_state_for_ready (NiceAgent *agent, NiceStream *stream, NiceComponent *component);
static guint priv_prune_pending_checks (NiceAgent *agent, NiceStream *stream, guint component_id);
static gboolean priv_schedule_triggered_check (NiceAgent *agent, NiceStream *stream, NiceComponent *component, NiceSocket *local_socket, NiceCandidate *remote_cand);
static void priv_mark_pair_nominated (NiceAgent *agent, NiceStream *stream, NiceComponent *component, NiceCandidate *localcand, NiceCandidate *remotecand);
static size_t priv_create_username (NiceAgent *agent, NiceStream *stream,
    guint component_id, NiceCandidate *remote, NiceCandidate *local,
    uint8_t *dest, guint dest_len, gboolean inbound);
static size_t priv_get_password (NiceAgent *agent, NiceStream *stream,
    NiceCandidate *remote, uint8_t **password);
static void conn_check_free_item (gpointer data);
static CandidateCheckPair *priv_conn_check_add_for_candidate_pair_matched (
    NiceAgent *agent, guint stream_id, NiceComponent *component,
    NiceCandidate *local, NiceCandidate *remote, NiceCheckState initial_state);
static gboolean priv_update_selected_pair (NiceAgent *agent,
    NiceComponent *component, CandidateCheckPair *pair);

static int priv_timer_expired (GTimeVal *timer, GTimeVal *now)
{
  return (now->tv_sec == timer->tv_sec) ?
    now->tv_usec >= timer->tv_usec :
    now->tv_sec >= timer->tv_sec;
}

static unsigned int priv_timer_remainder (GTimeVal *timer, GTimeVal *now)
{
  unsigned int delay;
  if (now->tv_sec > timer->tv_sec ||
      (now->tv_sec == timer->tv_sec && now->tv_usec > timer->tv_usec))
    return 0;
  delay = (timer->tv_sec - now->tv_sec) * 1000;
  delay += ((signed long)(timer->tv_usec - now->tv_usec)) / 1000;
  return delay;
}

static gchar
priv_state_to_gchar (NiceCheckState state)
{
  switch (state) {
    case NICE_CHECK_WAITING:
      return 'W';
    case NICE_CHECK_IN_PROGRESS:
      return 'I';
    case NICE_CHECK_SUCCEEDED:
      return 'S';
    case NICE_CHECK_FAILED:
      return 'F';
    case NICE_CHECK_FROZEN:
      return 'Z';
    case NICE_CHECK_DISCOVERED:
      return 'D';
    default:
      g_assert_not_reached ();
  }
}

static const gchar *
priv_state_to_string (NiceCheckState state)
{
  switch (state) {
    case NICE_CHECK_WAITING:
      return "waiting";
    case NICE_CHECK_IN_PROGRESS:
      return "in progress";
    case NICE_CHECK_SUCCEEDED:
      return "succeeded";
    case NICE_CHECK_FAILED:
      return "failed";
    case NICE_CHECK_FROZEN:
      return "frozen";
    case NICE_CHECK_DISCOVERED:
      return "discovered";
    default:
      g_assert_not_reached ();
  }
}

static const gchar *
priv_ice_return_to_string (StunUsageIceReturn ice_return)
{
  switch (ice_return) {
    case STUN_USAGE_ICE_RETURN_SUCCESS:
      return "success";
    case STUN_USAGE_ICE_RETURN_ERROR:
      return "error";
    case STUN_USAGE_ICE_RETURN_INVALID:
      return "invalid";
    case STUN_USAGE_ICE_RETURN_ROLE_CONFLICT:
      return "role conflict";
    case STUN_USAGE_ICE_RETURN_INVALID_REQUEST:
      return "invalid request";
    case STUN_USAGE_ICE_RETURN_INVALID_METHOD:
      return "invalid method";
    case STUN_USAGE_ICE_RETURN_MEMORY_ERROR:
      return "memory error";
    case STUN_USAGE_ICE_RETURN_INVALID_ADDRESS:
      return "invalid address";
    case STUN_USAGE_ICE_RETURN_NO_MAPPED_ADDRESS:
      return "no mapped address";
    default:
      g_assert_not_reached ();
  }
}

static const gchar *
priv_candidate_type_to_string (NiceCandidateType type)
{
  switch (type) {
    case NICE_CANDIDATE_TYPE_HOST:
      return "host";
    case NICE_CANDIDATE_TYPE_SERVER_REFLEXIVE:
      return "srflx";
    case NICE_CANDIDATE_TYPE_PEER_REFLEXIVE:
      return "prflx";
    case NICE_CANDIDATE_TYPE_RELAYED:
      return "relay";
    default:
      g_assert_not_reached ();
  }
}

/*
 * Dump the conncheck lists of the agent
 */
static void
priv_print_conn_check_lists (NiceAgent *agent, const gchar *where, const gchar *detail)
{
  GSList *i, *k;
  guint j;
  GTimeVal now;

  if (!nice_debug_is_verbose ())
    return;

  g_get_current_time (&now);

#define PRIORITY_LEN 32

  nice_debug ("Agent %p : *** conncheck list DUMP (called from %s%s)",
      agent, where, detail ? detail : "");
  for (i = agent->streams; i ; i = i->next) {
    NiceStream *stream = i->data;
    for (j = 1; j <= stream->n_components; j++) {
      for (k = stream->conncheck_list; k ; k = k->next) {
        CandidateCheckPair *pair = k->data;
        if (pair->component_id == j) {
          gchar local_addr[INET6_ADDRSTRLEN];
          gchar remote_addr[INET6_ADDRSTRLEN];
          StunTimer *timer = &pair->timer;

          nice_address_to_string (&pair->local->addr, local_addr);
          nice_address_to_string (&pair->remote->addr, remote_addr);

          nice_debug ("Agent %p : *** sc=%d/%d : pair %p : "
              "f=%s t=%s:%s timer=%d/%d %d/%dms "
              "[%s]:%u > [%s]:%u state=%c%s%s%s",
              agent, pair->stream_id, pair->component_id, pair,
              pair->foundation,
              priv_candidate_type_to_string (pair->local->type),
              priv_candidate_type_to_string (pair->remote->type),
              timer->retransmissions, timer->max_retransmissions,
              timer->delay - priv_timer_remainder (&pair->next_tick, &now),
              timer->delay,
              local_addr, nice_address_get_port (&pair->local->addr),
              remote_addr, nice_address_get_port (&pair->remote->addr),
              priv_state_to_gchar (pair->state),
              pair->valid ? "V" : "",
              pair->nominated ? "N" : "",
              g_slist_find (agent->triggered_check_queue, pair) ? "T" : "");
        }
      }
    }
  }
}

/* Verify if the pair is in the triggered checks list
 */

static gboolean
priv_is_pair_in_triggered_check_queue (NiceAgent *agent, CandidateCheckPair *pair)
{
  g_assert (pair);
  return (g_slist_find (agent->triggered_check_queue, pair) != NULL);
}

/* Add the pair to the triggered checks list, if not already present
 */
static void
priv_add_pair_to_triggered_check_queue (NiceAgent *agent, CandidateCheckPair *pair)
{
  g_assert (pair);

  pair->state = NICE_CHECK_WAITING;
  nice_debug ("Agent %p : pair %p state WAITING", agent, pair);
  if (agent->triggered_check_queue == NULL ||
      g_slist_find (agent->triggered_check_queue, pair) == NULL)
    agent->triggered_check_queue = g_slist_append (agent->triggered_check_queue, pair);
}

/* Remove the pair from the triggered checks list
 */
static void
priv_remove_pair_from_triggered_check_queue (NiceAgent *agent, CandidateCheckPair *pair)
{
  g_assert (pair);
  agent->triggered_check_queue = g_slist_remove (agent->triggered_check_queue, pair);
}

/* Get the pair from the triggered checks list
 */
static CandidateCheckPair *
priv_get_pair_from_triggered_check_queue (NiceAgent *agent)
{
  CandidateCheckPair *pair = NULL;

  if (agent->triggered_check_queue) {
    pair = (CandidateCheckPair *)agent->triggered_check_queue->data;
    priv_remove_pair_from_triggered_check_queue (agent, pair);
  }
  return pair;
}

/*
 * Check if the conncheck list if Active according to
 * ICE spec, 5.7.4 (Computing States)
 *
 * note: the ICE spec in unclear about that, but the check list should
 * be considered active when there is at least a pair in Waiting state
 * OR a pair in In-Progress state.
 */
static gboolean
priv_is_checklist_active (NiceStream *stream)
{
  GSList *i;

  for (i = stream->conncheck_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->state == NICE_CHECK_WAITING || p->state == NICE_CHECK_IN_PROGRESS)
      return TRUE;
  }
  return FALSE;
}

/*
 * Check if the conncheck list if Frozen according to
 * ICE spec, 5.7.4 (Computing States)
 */
static gboolean
priv_is_checklist_frozen (NiceStream *stream)
{
  GSList *i;

  if (stream->conncheck_list == NULL)
    return FALSE;

  for (i = stream->conncheck_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->state != NICE_CHECK_FROZEN)
      return FALSE;
  }
  return TRUE;
}

/*
 * Check if all components of the stream have
 * a valid pair (used for ICE spec, 7.1.3.2.3, point 2.)
 */
static gboolean
priv_all_components_have_valid_pair (NiceStream *stream)
{
  guint i;
  GSList *j;

  for (i = 1; i <= stream->n_components; i++) {
    for (j = stream->conncheck_list; j ; j = j->next) {
      CandidateCheckPair *p = j->data;
      if (p->component_id == i && p->valid)
        break;
    }
    if (j == NULL)
      return FALSE;
  }
  return TRUE;
}

/*
 * Check if the foundation in parameter matches the foundation
 * of a valid pair in the conncheck list [of stream] (used for ICE spec,
 * 7.1.3.2.3, point 2.)
 */
static gboolean
priv_foundation_matches_a_valid_pair (const gchar *foundation, NiceStream *stream)
{
  GSList *i;

  for (i = stream->conncheck_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->valid &&
        strncmp (p->foundation, foundation,
            NICE_CANDIDATE_PAIR_MAX_FOUNDATION) == 0)
      return TRUE;
  }
  return FALSE;
}

/*
 * Finds the next connectivity check in WAITING state.
 */
static CandidateCheckPair *priv_conn_check_find_next_waiting (GSList *conn_check_list)
{
  GSList *i;

  /* note: list is sorted in priority order to first waiting check has
   *       the highest priority */
  for (i = conn_check_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->state == NICE_CHECK_WAITING)
      return p;
  }

  return NULL;
}

/*
 * Finds the next connectivity check in FROZEN state.
 */
static CandidateCheckPair *
priv_conn_check_find_next_frozen (GSList *conn_check_list)
{
  GSList *i;

  /* note: list is sorted in priority order to first frozen check has
   *       the highest priority */
  for (i = conn_check_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->state == NICE_CHECK_FROZEN)
      return p;
  }

  return NULL;
}

/*
 * Returns the number of check lists of the agent
 */
static guint
priv_number_of_check_lists (NiceAgent *agent)
{
  guint n = 0;
  GSList *i;

  for (i = agent->streams; i ; i = i->next) {
    NiceStream *stream = i->data;
    if (stream->conncheck_list != NULL)
      n++;
  }
  return n;
}

/*
 * Returns the number of active check lists of the agent
 */
static guint
priv_number_of_active_check_lists (NiceAgent *agent)
{
  guint n = 0;
  GSList *i;

  for (i = agent->streams; i ; i = i->next)
    if (priv_is_checklist_active (i->data))
      n++;
  return n;
}

/*
 * Returns the first stream of the agent having a Frozen
 * connection check list
 */
static NiceStream *
priv_find_first_frozen_check_list (NiceAgent *agent)
{
  GSList *i;

  for (i = agent->streams; i ; i = i->next) {
    NiceStream *stream = i->data;
    if (priv_is_checklist_frozen (stream))
      return stream;
  }
  return NULL;
}

/*
 * Initiates a new connectivity check for a ICE candidate pair.
 *
 * @return TRUE on success, FALSE on error
 */
static gboolean priv_conn_check_initiate (NiceAgent *agent, CandidateCheckPair *pair)
{
  pair->state = NICE_CHECK_IN_PROGRESS;
  nice_debug ("Agent %p : pair %p state IN_PROGRESS", agent, pair);
  conn_check_send (agent, pair);
  return TRUE;
}

/*
 * Unfreezes the next connectivity check in the list. Follows the
 * algorithm (2.) defined in 5.7.4 (Computing States) of the ICE spec
 * (RFC5245)
 *
 * See also sect 7.1.2.2.3 (Updating Pair States), and
 * priv_conn_check_unfreeze_related().
 * 
 * @return TRUE on success, and FALSE if no frozen candidates were found.
 */
static gboolean priv_conn_check_unfreeze_next (NiceAgent *agent, NiceStream *stream)
{
  GSList *i, *j;
  GSList *found_list = NULL;
  gboolean result = FALSE;

  priv_print_conn_check_lists (agent, G_STRFUNC, NULL);

  for (i = stream->conncheck_list; i ; i = i->next) {
    CandidateCheckPair *p1 = i->data;
    CandidateCheckPair *pair = NULL;
    guint lowest_component_id = stream->n_components + 1;
    guint64 highest_priority = 0;

    if (g_slist_find_custom (found_list, p1->foundation, (GCompareFunc)strcmp))
      continue;
    found_list = g_slist_prepend (found_list, p1->foundation);

    for (j = stream->conncheck_list; j ; j = j->next) {
      CandidateCheckPair *p2 = i->data;
      if (strncmp (p2->foundation, p1->foundation,
              NICE_CANDIDATE_PAIR_MAX_FOUNDATION) == 0) {
        if (p2->component_id < lowest_component_id ||
            (p2->component_id == lowest_component_id &&
             p2->priority > highest_priority)) {
          pair = p2;
          lowest_component_id = p2->component_id;
          highest_priority = p2->priority;
        }
      }
    }

    if (pair) {
      nice_debug ("Agent %p : Pair %p with s/c-id %u/%u (%s) unfrozen.",
          agent, pair, pair->stream_id, pair->component_id, pair->foundation);
      pair->state = NICE_CHECK_WAITING;
      nice_debug ("Agent %p : pair %p state WAITING", agent, pair);
      result = TRUE;
    }
  }
  g_slist_free (found_list);
  return result;
}

/*
 * Unfreezes the next next connectivity check in the list after
 * check 'success_check' has successfully completed.
 *
 * See sect 7.1.2.2.3 (Updating Pair States) of ICE spec (ID-19).
 * 
 * @param agent context
 * @param ok_check a connectivity check that has just completed
 *
 * @return TRUE on success, and FALSE if no frozen candidates were found.
 */
static void priv_conn_check_unfreeze_related (NiceAgent *agent, NiceStream *stream, CandidateCheckPair *ok_check)
{
  GSList *i, *j;

  g_assert (ok_check);
  g_assert (ok_check->state == NICE_CHECK_SUCCEEDED);
  g_assert (stream);
  g_assert (stream->id == ok_check->stream_id);

  priv_print_conn_check_lists (agent, G_STRFUNC, NULL);

  /* step: perform the step (1) of 'Updating Pair States' */
  for (i = stream->conncheck_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
   
    if (p->stream_id == ok_check->stream_id) {
      if (p->state == NICE_CHECK_FROZEN &&
          strncmp (p->foundation, ok_check->foundation,
              NICE_CANDIDATE_PAIR_MAX_FOUNDATION) == 0) {
	nice_debug ("Agent %p : Unfreezing check %p (after successful check %p).", agent, p, ok_check);
	p->state = NICE_CHECK_WAITING;
        nice_debug ("Agent %p : pair %p state WAITING", agent, p);
      }
    }
  }

  /* step: perform the step (2) of 'Updating Pair States' */
  stream = agent_find_stream (agent, ok_check->stream_id);
  if (priv_all_components_have_valid_pair (stream)) {
    for (i = agent->streams; i ; i = i->next) {
      /* the agent examines the check list for each other
       * media stream in turn
       */
      NiceStream *s = i->data;
      if (s->id == ok_check->stream_id)
        continue;
      if (priv_is_checklist_active (s)) {
        /* checklist is Active
         */
        for (j = s->conncheck_list; j ; j = j->next) {
	  CandidateCheckPair *p = j->data;
          if (p->state == NICE_CHECK_FROZEN &&
              priv_foundation_matches_a_valid_pair (p->foundation, stream)) {
	    nice_debug ("Agent %p : Unfreezing check %p from stream %u (after successful check %p).", agent, p, s->id, ok_check);
	    p->state = NICE_CHECK_WAITING;
            nice_debug ("Agent %p : pair %p state WAITING", agent, p);
          }
        }
      } else if (priv_is_checklist_frozen (s)) {
        /* checklist is Frozen
         */
        gboolean match_found = FALSE;
        /* check if there is one pair in the check list whose
         * foundation matches a pair in the valid list under
         * consideration
         */
        for (j = s->conncheck_list; j ; j = j->next) {
	  CandidateCheckPair *p = j->data;
          if (priv_foundation_matches_a_valid_pair (p->foundation, stream)) {
            match_found = TRUE;
            nice_debug ("Agent %p : Unfreezing check %p from stream %u (after successful check %p).", agent, p, s->id, ok_check);
            p->state = NICE_CHECK_WAITING;
            nice_debug ("Agent %p : pair %p state WAITING", agent, p);
          }
        }

        if (!match_found) {
          /* set the pair with the lowest component ID
           * and highest priority to Waiting
           */
          priv_conn_check_unfreeze_next (agent, s);
        }
      }
    }
  }    
}

static void
candidate_check_pair_fail (NiceStream *stream, NiceAgent *agent, CandidateCheckPair *p)
{
  StunTransactionId id;
  NiceComponent *component;

  component = nice_stream_find_component_by_id (stream, p->component_id);

  p->state = NICE_CHECK_FAILED;
  nice_debug ("Agent %p : pair %p state FAILED", agent, p);

  if (p->stun_message.buffer != NULL) {
    stun_message_id (&p->stun_message, id);
    stun_agent_forget_transaction (&component->stun_agent, id);
  }

  p->stun_message.buffer = NULL;
  p->stun_message.buffer_len = 0;
}

/*
 * Function that resubmits a new connection check, after a previous
 * check in in-progress state got cancelled due to an incoming stun
 * request matching this same pair
 *
 * @return will return TRUE if the pair is scheduled for recheck
 */
static gboolean
priv_conn_recheck_on_timeout (NiceAgent *agent, CandidateCheckPair *p)
{
  if (p->recheck_on_timeout) {
    g_assert (p->state == NICE_CHECK_IN_PROGRESS);
    /* this cancelled pair may have the flag 'mark nominated
     * on response arrival' set, we want to keep it, because
     * this is needed to nominate this pair in aggressive
     * nomination, when the agent is in controlled mode.
     *
     * this cancelled pair may also have the flag 'use candidate
     * on next check' set, that we want to preserve too.
     */
    nice_debug ("Agent %p : pair %p was cancelled, "
        "triggering a new connection check", agent, p);
    priv_add_pair_to_triggered_check_queue (agent, p);
    return TRUE;
  }
  return FALSE;
}

/*
 * Helper function for connectivity check timer callback that
 * runs through the stream specific part of the state machine. 
 *
 * @param schedule if TRUE, schedule a new check
 *
 * @return will return FALSE when no more pending timers.
 */
static gboolean priv_conn_check_tick_stream (NiceStream *stream, NiceAgent *agent)
{
  gboolean keep_timer_going = FALSE;
  GSList *i;
  CandidateCheckPair *pair;
  unsigned int timeout;
  GTimeVal now;

  g_get_current_time (&now);

  /* step: process ongoing STUN transactions */
  for (i = stream->conncheck_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
    gchar tmpbuf1[INET6_ADDRSTRLEN], tmpbuf2[INET6_ADDRSTRLEN];
    NiceComponent *component;

    if (!agent_find_component (agent, p->stream_id, p->component_id,
        NULL, &component))
      continue;

    if (p->state != NICE_CHECK_IN_PROGRESS)
      continue;

    if (p->stun_message.buffer == NULL) {
      nice_debug ("Agent %p : STUN connectivity check was cancelled, marking as done.", agent);
      p->state = NICE_CHECK_FAILED;
      nice_debug ("Agent %p : pair %p state FAILED", agent, p);
      continue;
    }

    if (!priv_timer_expired (&p->next_tick, &now))
      continue;

    switch (stun_timer_refresh (&p->timer)) {
      case STUN_USAGE_TIMER_RETURN_TIMEOUT:
timer_timeout:
        /* case: conncheck cancelled due to in-progress incoming
         * check, requeing the pair, ICE spec, sect 7.2.1.4
         * "Triggered Checks", "If the state of that pair is
         * In-Progress..."
         */
        if (priv_conn_recheck_on_timeout (agent, p))
          break;

        /* case: error, abort processing */
        nice_address_to_string (&p->local->addr, tmpbuf1);
        nice_address_to_string (&p->remote->addr, tmpbuf2);
        nice_debug ("Agent %p : Retransmissions failed, giving up on connectivity check %p", agent, p);
        nice_debug ("Agent %p : Failed pair is [%s]:%u --> [%s]:%u", agent,
            tmpbuf1, nice_address_get_port (&p->local->addr),
            tmpbuf2, nice_address_get_port (&p->remote->addr));
        candidate_check_pair_fail (stream, agent, p);
        priv_print_conn_check_lists (agent, G_STRFUNC,
            ", retransmission failed");

        /* perform a check if a transition state from connected to
         * ready can be performed. This may happen here, when the last
         * in-progress pair has expired its retransmission count
         * in priv_conn_check_tick_stream(), which is a condition to
         * make the transition connected to ready.
         */
        priv_update_check_list_state_for_ready (agent, stream, component);
        break;
      case STUN_USAGE_TIMER_RETURN_RETRANSMIT:
        /* case: retransmission stopped, due to the nomination of
         * a pair with a higher priority than this in-progress pair,
         * ICE spec, sect 8.1.2 "Updating States", item 2.2
         */
        if (!p->retransmit_on_timeout)
          goto timer_timeout;

        /* case: conncheck cancelled due to in-progress incoming
         * check, requeing the pair, ICE spec, sect 7.2.1.4
         * "Triggered Checks", "If the state of that pair is
         * In-Progress..."
         */
        if (priv_conn_recheck_on_timeout (agent, p))
          break;

        /* case: not ready, so schedule a new timeout */
        timeout = stun_timer_remainder (&p->timer);

        nice_debug ("Agent %p :STUN transaction retransmitted on pair %p "
            "(timer=%d/%d %d/%dms).",
            agent, p,
            p->timer.retransmissions, p->timer.max_retransmissions,
            p->timer.delay - timeout, p->timer.delay);

        agent_socket_send (p->sockptr, &p->remote->addr,
            stun_message_length (&p->stun_message),
            (gchar *)p->stun_buffer);


        /* note: convert from milli to microseconds for g_time_val_add() */
        p->next_tick = now;
        g_time_val_add (&p->next_tick, timeout * 1000);

        return TRUE;
      case STUN_USAGE_TIMER_RETURN_SUCCESS:
        timeout = stun_timer_remainder (&p->timer);

        /* note: convert from milli to microseconds for g_time_val_add() */
        p->next_tick = now;
        g_time_val_add (&p->next_tick, timeout * 1000);

        keep_timer_going = TRUE;
        break;
      default:
        /* Nothing to do. */
        break;
    }
  }

  /* step: perform an ordinary check, ICE spec, 5.8 "Scheduling Checks"
   * note: This code is executed when the triggered checks list is
   * empty, and when no STUN message has been sent (pacing constraint)
   */
  pair = priv_conn_check_find_next_waiting (stream->conncheck_list);
  if (pair) {
    /* remove the pair from the triggered check list if needed. This
     * may happen with the cancelled pair, that's just been added
     * in state waiting to the triggered check list above in the
     * same function.
     */
    priv_remove_pair_from_triggered_check_queue (agent, pair);
    priv_print_conn_check_lists (agent, G_STRFUNC,
        ", got a pair in Waiting state");
    priv_conn_check_initiate (agent, pair);
    return TRUE;
  }

  /* note: this is unclear in the ICE spec, but a check list in Frozen
   * state (where all pairs are in Frozen state) is not supposed to
   * change its state by an ordinary check, but only by the success of
   * checks in other check lists, in priv_conn_check_unfreeze_related().
   * The underlying idea is to concentrate the checks on a single check
   * list initially.
   */
  if (priv_is_checklist_frozen (stream))
    return keep_timer_going;

  /* step: ordinary check continued, if there's no pair in the waiting
   * state, pick a pair in the frozen state
   */
  pair = priv_conn_check_find_next_frozen (stream->conncheck_list);
  if (pair) {
    priv_print_conn_check_lists (agent, G_STRFUNC,
        ", got a pair in Frozen state");
    pair->state = NICE_CHECK_WAITING;
    nice_debug ("Agent %p : pair %p state WAITING", agent, pair);
    priv_conn_check_initiate (agent, pair);
    return TRUE;
  }
  return keep_timer_going;
}

static gboolean
priv_conn_check_tick_stream_nominate (NiceStream *stream, NiceAgent *agent)
{
  gboolean keep_timer_going = FALSE;
  guint s_inprogress = 0;
  guint s_succeeded = 0;
  guint s_discovered = 0;
  guint s_nominated = 0;
  guint s_waiting_for_nomination = 0;
  guint s_valid = 0;
  guint frozen = 0;
  guint waiting = 0;
  GSList *i, *k;

  for (i = stream->conncheck_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->state == NICE_CHECK_FROZEN)
      ++frozen;
    else if (p->state == NICE_CHECK_IN_PROGRESS)
      ++s_inprogress;
    else if (p->state == NICE_CHECK_WAITING)
      ++waiting;
    else if (p->state == NICE_CHECK_SUCCEEDED)
      ++s_succeeded;
    else if (p->state == NICE_CHECK_DISCOVERED)
      ++s_discovered;
    if (p->valid)
      ++s_valid;

    if ((p->state == NICE_CHECK_SUCCEEDED || p->state == NICE_CHECK_DISCOVERED)
        && p->nominated)
      ++s_nominated;
    else if ((p->state == NICE_CHECK_SUCCEEDED ||
            p->state == NICE_CHECK_DISCOVERED) && !p->nominated)
      ++s_waiting_for_nomination;
  }

    /* note: keep the timer going as long as there is work to be done */
  if (s_inprogress)
    keep_timer_going = TRUE;
  
  if (s_nominated < stream->n_components &&
      s_waiting_for_nomination) {
    if (NICE_AGENT_IS_COMPATIBLE_WITH_RFC5245_OR_OC2007R2 (agent)) {
      if (agent->nomination_mode == NICE_NOMINATION_MODE_REGULAR &&
          agent->controlling_mode) {
#define NICE_MIN_NUMBER_OF_VALID_PAIRS 2
        /* ICE 8.1.1.1 Regular nomination
         * we choose to nominate the valid pair of a component if
         * - there is no pair left frozen, waiting or in-progress, or
         * - if there are at least two valid pairs, or
         * - if there is at least one valid pair of type HOST-HOST
         *
         * This is the "stopping criterion" described in 8.1.1.1, and is
         * a "local optimization" between accumulating more valid pairs,
         * and limiting the time spent waiting for in-progress connections
         * checks until they finally fail.
         */
        GSList *component_item;

        for (component_item = stream->components; component_item;
             component_item = component_item->next) {
          NiceComponent *component = component_item->data;
          gboolean already_done = FALSE;
          gboolean stopping_criterion = FALSE;
          guint p_valid = 0;
          guint p_frozen = 0;
          guint p_waiting = 0;
          guint p_inprogress = 0;
          guint p_host_host_valid = 0;

          /* verify that the choice of the pair to be nominated
           * has not already been done
           */
          for (k = stream->conncheck_list; k ; k = k->next) {
            CandidateCheckPair *p = k->data;
            if (p->component_id == component->id) {
              if (p->use_candidate_on_next_check)
                already_done = TRUE;
              if (p->state == NICE_CHECK_FROZEN)
                p_frozen++;
              else if (p->state == NICE_CHECK_WAITING)
                p_waiting++;
              else if (p->state == NICE_CHECK_IN_PROGRESS)
                p_inprogress++;
              if (p->valid)
                p_valid++;
              if (p->valid &&
                  p->local->type == NICE_CANDIDATE_TYPE_HOST &&
                  p->remote->type == NICE_CANDIDATE_TYPE_HOST)
                p_host_host_valid++;
            }
          }

          if (already_done)
            continue;

          stopping_criterion =
              (p_host_host_valid > 0 ||
               p_valid >= NICE_MIN_NUMBER_OF_VALID_PAIRS ||
               (p_waiting == 0 && p_inprogress == 0 && p_frozen == 0));

          if (!stopping_criterion)
            continue;

          /* when the stopping criterion is satisfied, we choose
           * a pair to be nominated in the list of valid pairs,
           * and add it to the triggered checks list
           */
          for (k = stream->conncheck_list; k ; k = k->next) {
            CandidateCheckPair *p = k->data;
            /* note: highest priority item selected (list always sorted) */
            if (p->component_id == component->id &&
                !p->nominated &&
                !p->use_candidate_on_next_check &&
                p->valid) {
              /* According a ICE spec, sect 8.1.1.1.  "Regular
               * Nomination", we enqueue the check that produced this
               * valid pair. When this pair has been discovered, we want
               * to test its parent pair instead.
               */
              if (p->succeeded_pair != NULL) {
                g_assert (p->state == NICE_CHECK_DISCOVERED);
                p = p->succeeded_pair;
              }
              g_assert (p->state == NICE_CHECK_SUCCEEDED);
              nice_debug ("Agent %p : restarting check %p with "
                  "USE-CANDIDATE attrib (regular nomination)", agent, p);
              p->recheck_on_timeout = FALSE;
              p->use_candidate_on_next_check = TRUE;
              priv_add_pair_to_triggered_check_queue (agent, p);
              keep_timer_going = TRUE;
              break; /* move to the next component */
            }
          }
        }
      }
    } else if (agent->controlling_mode) {
      GSList *component_item;

      for (component_item = stream->components; component_item;
           component_item = component_item->next) {
        NiceComponent *component = component_item->data;

	for (k = stream->conncheck_list; k ; k = k->next) {
	  CandidateCheckPair *p = k->data;
	  /* note: highest priority item selected (list always sorted) */
	  if (p->component_id == component->id &&
              (p->state == NICE_CHECK_SUCCEEDED ||
               p->state == NICE_CHECK_DISCOVERED)) {
	    nice_debug ("Agent %p : restarting check %p as the nominated pair.", agent, p);
	    p->nominated = TRUE;
            p->recheck_on_timeout = FALSE;
            priv_update_selected_pair (agent, component, p);
            priv_add_pair_to_triggered_check_queue (agent, p);
            keep_timer_going = TRUE;
	    break; /* move to the next component */
	  }
	}
      }
    }
  }
  if (stream->tick_counter++ % 50 == 0)
    nice_debug ("Agent %p : stream %u: timer tick #%u: %u frozen, %u in-progress, "
        "%u waiting, %u succeeded, %u discovered, %u nominated, "
        "%u waiting-for-nom, %u valid.", agent, stream->id,
        stream->tick_counter, frozen, s_inprogress, waiting, s_succeeded,
        s_discovered, s_nominated, s_waiting_for_nomination, s_valid);

  return keep_timer_going;

}

static void
conn_check_stop (NiceAgent *agent)
{
  if (agent->conncheck_timer_source == NULL)
    return;

  g_source_destroy (agent->conncheck_timer_source);
  g_source_unref (agent->conncheck_timer_source);
  agent->conncheck_timer_source = NULL;
  agent->conncheck_timer_grace_period = 0;
}


/*
 * Timer callback that handles initiating and managing connectivity
 * checks (paced by the Ta timer).
 *
 * This function is designed for the g_timeout_add() interface.
 *
 * @return will return FALSE when no more pending timers.
 */
static gboolean priv_conn_check_tick_unlocked (NiceAgent *agent)
{
  CandidateCheckPair *pair = NULL;
  gboolean keep_timer_going = FALSE;
  GSList *i, *j;

  /* the conncheck really starts when we have built
   * a connection check list for each stream
   */
  if (priv_number_of_check_lists (agent) < g_slist_length (agent->streams))
    return TRUE;

  /* configure the initial state of the check lists of the agent
   * as described in ICE spec, 5.7.4
   *
   * if all pairs in all check lists are in frozen state, then
   * we are in the initial state (5.7.4, point 1.)
   */
  if (priv_number_of_active_check_lists (agent) == 0) {
    /* set some pairs of the first stream in the waiting state
     * ICE spec, 5.7.4, point 2.
     *
     * note: we adapt the ICE spec here, by selecting the first
     * frozen check list, which is not necessarily the check
     * list of the first stream (the first stream may be completed)
     */
    NiceStream *stream = priv_find_first_frozen_check_list (agent);
    if (stream)
      priv_conn_check_unfreeze_next (agent, stream);
  }

  /* step: perform a test from the triggered checks list,
   * ICE spec, 5.8 "Scheduling Checks"
   */
  pair = priv_get_pair_from_triggered_check_queue (agent);

  if (pair) {
    priv_print_conn_check_lists (agent, G_STRFUNC,
        ", got a pair from triggered check list");
    priv_conn_check_initiate (agent, pair);
    return TRUE;
  }

  /* step: process ongoing STUN transactions and
   * perform an ordinary check, ICE spec, 5.8, "Scheduling Checks"
   */
  for (i = agent->streams; i ; i = i->next) {
    NiceStream *stream = i->data;
    if (priv_conn_check_tick_stream (stream, agent))
      keep_timer_going = TRUE;
    if (priv_conn_check_tick_stream_nominate (stream, agent))
      keep_timer_going = TRUE;
  }

  /* step: if no work left and a conncheck list of a stream is still
   * frozen, set the pairs to waiting, according to ICE SPEC, sect
   * 7.1.3.3.  "Check List and Timer State Updates"
   */
  if (!keep_timer_going) {
    for (i = agent->streams; i ; i = i->next) {
      NiceStream *stream = i->data;
      if (priv_is_checklist_frozen (stream)) {
        nice_debug ("Agent %p : stream %d conncheck list is still "
            "frozen, while other lists are completed. Unfreeze it.",
            agent, stream->id);
        keep_timer_going = priv_conn_check_unfreeze_next (agent, stream);
      }
    }
  }

  /* note: we provide a grace period before declaring a component as
   * failed. Components marked connected, and then ready follow another
   * code path, and are not concerned by this grace period.
   */
  if (!keep_timer_going && agent->conncheck_timer_grace_period == 0)
    nice_debug ("Agent %p : waiting %d msecs before checking "
        "for failed components.", agent, NICE_AGENT_MAX_TIMER_GRACE_PERIOD);

  if (keep_timer_going)
    agent->conncheck_timer_grace_period = 0;
  else
    agent->conncheck_timer_grace_period += agent->timer_ta;

  /* step: stop timer if no work left */
  if (!keep_timer_going &&
      agent->conncheck_timer_grace_period >= NICE_AGENT_MAX_TIMER_GRACE_PERIOD) {
    nice_debug ("Agent %p : checking for failed components now.", agent);
    for (i = agent->streams; i; i = i->next) {
      NiceStream *stream = i->data;
      priv_update_check_list_failed_components (agent, stream);
      for (j = stream->components; j; j = j->next) {
        NiceComponent *component = j->data;
        priv_update_check_list_state_for_ready (agent, stream, component);
      }
    }

    nice_debug ("Agent %p : %s: stopping conncheck timer", agent, G_STRFUNC);
    priv_print_conn_check_lists (agent, G_STRFUNC,
        ", conncheck timer stopped");

    /* Stopping the timer so destroy the source.. this will allow
       the timer to be reset if we get a set_remote_candidates after this
       point */
    conn_check_stop (agent);

    /* XXX: what to signal, is all processing now really done? */
    nice_debug ("Agent %p : changing conncheck state to COMPLETED.", agent);
    return FALSE;
  }

  return TRUE;
}

static gboolean priv_conn_check_tick (gpointer pointer)
{
  gboolean ret;
  NiceAgent *agent = pointer;

  agent_lock();
  if (g_source_is_destroyed (g_main_current_source ())) {
    nice_debug ("Source was destroyed. "
        "Avoided race condition in priv_conn_check_tick");
    agent_unlock ();
    return FALSE;
  }

  ret = priv_conn_check_tick_unlocked (agent);
  agent_unlock_and_emit (agent);

  return ret;
}

static gboolean priv_conn_keepalive_retransmissions_tick (gpointer pointer)
{
  CandidatePair *pair = (CandidatePair *) pointer;

  agent_lock();

  /* A race condition might happen where the mutex above waits for the lock
   * and in the meantime another thread destroys the source.
   * In that case, we don't need to run our retransmission tick since it should
   * have been cancelled */
  if (g_source_is_destroyed (g_main_current_source ())) {
    nice_debug ("Source was destroyed. "
        "Avoided race condition in priv_conn_keepalive_retransmissions_tick");
    agent_unlock ();
    return FALSE;
  }

  g_source_destroy (pair->keepalive.tick_source);
  g_source_unref (pair->keepalive.tick_source);
  pair->keepalive.tick_source = NULL;

  switch (stun_timer_refresh (&pair->keepalive.timer)) {
    case STUN_USAGE_TIMER_RETURN_TIMEOUT:
      {
        /* Time out */
        StunTransactionId id;
        NiceComponent *component;

        if (!agent_find_component (pair->keepalive.agent,
                pair->keepalive.stream_id, pair->keepalive.component_id,
                NULL, &component)) {
          nice_debug ("Could not find stream or component in"
              " priv_conn_keepalive_retransmissions_tick");
          agent_unlock ();
          return FALSE;
        }

        stun_message_id (&pair->keepalive.stun_message, id);
        stun_agent_forget_transaction (&component->stun_agent, id);
        pair->keepalive.stun_message.buffer = NULL;

        if (pair->keepalive.agent->media_after_tick) {
          nice_debug ("Agent %p : Keepalive conncheck timed out!! "
              "but media was received. Suspecting keepalive lost because of "
              "network bottleneck", pair->keepalive.agent);
        } else {
          nice_debug ("Agent %p : Keepalive conncheck timed out!! "
              "peer probably lost connection", pair->keepalive.agent);
          agent_signal_component_state_change (pair->keepalive.agent,
              pair->keepalive.stream_id, pair->keepalive.component_id,
              NICE_COMPONENT_STATE_FAILED);
        }
        break;
      }
    case STUN_USAGE_TIMER_RETURN_RETRANSMIT:
      /* Retransmit */
      agent_socket_send (pair->local->sockptr, &pair->remote->addr,
          stun_message_length (&pair->keepalive.stun_message),
          (gchar *)pair->keepalive.stun_buffer);

      nice_debug ("Agent %p : Retransmitting keepalive conncheck",
          pair->keepalive.agent);
      agent_timeout_add_with_context (pair->keepalive.agent,
          &pair->keepalive.tick_source,
          "Pair keepalive", stun_timer_remainder (&pair->keepalive.timer),
          priv_conn_keepalive_retransmissions_tick, pair);
      break;
    case STUN_USAGE_TIMER_RETURN_SUCCESS:
      agent_timeout_add_with_context (pair->keepalive.agent,
          &pair->keepalive.tick_source,
          "Pair keepalive", stun_timer_remainder (&pair->keepalive.timer),
          priv_conn_keepalive_retransmissions_tick, pair);
      break;
    default:
      g_assert_not_reached();
      break;
  }


  agent_unlock_and_emit (pair->keepalive.agent);
  return FALSE;
}

static guint32 peer_reflexive_candidate_priority (NiceAgent *agent,
    NiceCandidate *local_candidate)
{
  NiceCandidate *candidate_priority =
      nice_candidate_new (NICE_CANDIDATE_TYPE_PEER_REFLEXIVE);
  guint32 priority;

  candidate_priority->transport = local_candidate->transport;
  candidate_priority->component_id = local_candidate->component_id;
  candidate_priority->base_addr = local_candidate->addr;
  if (agent->compatibility == NICE_COMPATIBILITY_GOOGLE) {
    priority = nice_candidate_jingle_priority (candidate_priority);
  } else if (agent->compatibility == NICE_COMPATIBILITY_MSN ||
             agent->compatibility == NICE_COMPATIBILITY_OC2007) {
    priority = nice_candidate_msn_priority (candidate_priority);
  } else if (agent->compatibility == NICE_COMPATIBILITY_OC2007R2) {
    priority = nice_candidate_ms_ice_priority (candidate_priority,
        agent->reliable, FALSE);
  } else {
    priority = nice_candidate_ice_priority (candidate_priority,
        agent->reliable, FALSE);
  }
  nice_candidate_free (candidate_priority);

  return priority;
}

static void ms_ice2_legacy_conncheck_send(StunMessage *msg, NiceSocket *sock,
    const NiceAddress *remote_addr)
{
  uint32_t *fingerprint_attr;
  uint32_t fingerprint_orig;
  uint16_t fingerprint_len;
  size_t buffer_len;

  if (msg->agent->ms_ice2_send_legacy_connchecks == FALSE) {
    return;
  }

  fingerprint_attr = (uint32_t *)stun_message_find (msg,
      STUN_ATTRIBUTE_FINGERPRINT, &fingerprint_len);

  if (fingerprint_attr == NULL) {
    nice_debug ("FINGERPRINT not found.");
    return;
  }

  if (fingerprint_len != sizeof (fingerprint_orig)) {
    nice_debug ("Unexpected FINGERPRINT length %u.", fingerprint_len);
    return;
  }

  memcpy (&fingerprint_orig, fingerprint_attr, sizeof (fingerprint_orig));

  buffer_len = stun_message_length (msg);

  *fingerprint_attr = stun_fingerprint (msg->buffer, buffer_len, TRUE);

  agent_socket_send (sock, remote_addr, buffer_len, (gchar *)msg->buffer);

  memcpy (fingerprint_attr, &fingerprint_orig, sizeof (fingerprint_orig));
}

/*
 * Timer callback that handles initiating and managing connectivity
 * checks (paced by the Ta timer).
 *
 * This function is designed for the g_timeout_add() interface.
 *
 * @return will return FALSE when no more pending timers.
 */
static gboolean priv_conn_keepalive_tick_unlocked (NiceAgent *agent)
{
  GSList *i, *j, *k;
  int errors = 0;
  gboolean ret = FALSE;
  size_t buf_len = 0;

  /* case 1: session established and media flowing
   *         (ref ICE sect 10 "Keepalives" ID-19)  */
  for (i = agent->streams; i; i = i->next) {

    NiceStream *stream = i->data;
    for (j = stream->components; j; j = j->next) {
      NiceComponent *component = j->data;
      if (component->selected_pair.local != NULL) {
	CandidatePair *p = &component->selected_pair;

        /* Disable keepalive checks on TCP candidates */
        if (p->local->transport != NICE_CANDIDATE_TRANSPORT_UDP)
          continue;

        if (agent->compatibility == NICE_COMPATIBILITY_GOOGLE ||
            agent->keepalive_conncheck) {
          uint8_t uname[NICE_STREAM_MAX_UNAME];
          size_t uname_len =
              priv_create_username (agent, agent_find_stream (agent, stream->id),
                  component->id, p->remote, p->local, uname, sizeof (uname),
                  FALSE);
          uint8_t *password = NULL;
          size_t password_len = priv_get_password (agent,
              agent_find_stream (agent, stream->id), p->remote, &password);

          if (p->keepalive.stun_message.buffer != NULL) {
            nice_debug ("Agent %p: Keepalive for s%u:c%u still"
                " retransmitting, not restarting", agent, stream->id,
                component->id);
            continue;
          }

          if (nice_debug_is_enabled ()) {
            gchar tmpbuf[INET6_ADDRSTRLEN];
            nice_address_to_string (&p->remote->addr, tmpbuf);
            nice_debug ("Agent %p : Keepalive STUN-CC REQ to '%s:%u', "
                "(c-id:%u), username='%.*s' (%" G_GSIZE_FORMAT "), "
                "password='%.*s' (%" G_GSIZE_FORMAT "), priority=%u.", agent,
                tmpbuf, nice_address_get_port (&p->remote->addr),
                component->id, (int) uname_len, uname, uname_len,
                (int) password_len, password, password_len,
                p->prflx_priority);
          }
          if (uname_len > 0) {
            buf_len = stun_usage_ice_conncheck_create (&component->stun_agent,
                &p->keepalive.stun_message, p->keepalive.stun_buffer,
                sizeof(p->keepalive.stun_buffer),
                uname, uname_len, password, password_len,
                agent->controlling_mode, agent->controlling_mode,
                p->prflx_priority,
                agent->tie_breaker,
                NULL,
                agent_to_ice_compatibility (agent));

            nice_debug ("Agent %p: conncheck created %zd - %p",
                agent, buf_len, p->keepalive.stun_message.buffer);

            if (buf_len > 0) {
              stun_timer_start (&p->keepalive.timer,
                  agent->stun_initial_timeout,
                  agent->stun_max_retransmissions);

              agent->media_after_tick = FALSE;

              /* send the conncheck */
              agent_socket_send (p->local->sockptr, &p->remote->addr,
                  buf_len, (gchar *)p->keepalive.stun_buffer);

              p->keepalive.stream_id = stream->id;
              p->keepalive.component_id = component->id;
              p->keepalive.agent = agent;

              agent_timeout_add_with_context (p->keepalive.agent,
                  &p->keepalive.tick_source, "Pair keepalive",
                  stun_timer_remainder (&p->keepalive.timer),
                  priv_conn_keepalive_retransmissions_tick, p);
            } else {
              ++errors;
            }
          }
        } else {
          buf_len = stun_usage_bind_keepalive (&component->stun_agent,
              &p->keepalive.stun_message, p->keepalive.stun_buffer,
              sizeof(p->keepalive.stun_buffer));

          if (buf_len > 0) {
            agent_socket_send (p->local->sockptr, &p->remote->addr, buf_len,
                (gchar *)p->keepalive.stun_buffer);

            if (agent->compatibility == NICE_COMPATIBILITY_OC2007R2) {
              ms_ice2_legacy_conncheck_send (&p->keepalive.stun_message,
                  p->local->sockptr, &p->remote->addr);
            }

            nice_debug ("Agent %p : stun_bind_keepalive for pair %p res %d.",
                agent, p, (int) buf_len);
          } else {
            ++errors;
          }
        }
      }
    }
  }

  /* case 2: connectivity establishment ongoing
   *         (ref ICE sect 4.1.1.4 "Keeping Candidates Alive" ID-19)  */
  for (i = agent->streams; i; i = i->next) {
    NiceStream *stream = i->data;
    for (j = stream->components; j; j = j->next) {
      NiceComponent *component = j->data;
      if (component->state < NICE_COMPONENT_STATE_READY &&
          agent->stun_server_ip) {
        NiceAddress stun_server;
        if (nice_address_set_from_string (&stun_server, agent->stun_server_ip)) {
          StunAgent stun_agent;
          uint8_t stun_buffer[STUN_MAX_MESSAGE_SIZE_IPV6];
          StunMessage stun_message;
          size_t buffer_len = 0;

          nice_address_set_port (&stun_server, agent->stun_server_port);

          nice_agent_init_stun_agent (agent, &stun_agent);

          buffer_len = stun_usage_bind_create (&stun_agent,
              &stun_message, stun_buffer, sizeof(stun_buffer));

          for (k = component->local_candidates; k; k = k->next) {
            NiceCandidate *candidate = (NiceCandidate *) k->data;
            if (candidate->type == NICE_CANDIDATE_TYPE_HOST &&
                candidate->transport == NICE_CANDIDATE_TRANSPORT_UDP) {
              /* send the conncheck */
              nice_debug ("Agent %p : resending STUN on %s to keep the "
                  "candidate alive.", agent, candidate->foundation);
              agent_socket_send (candidate->sockptr, &stun_server,
                  buffer_len, (gchar *)stun_buffer);
            }
          }
        }
      }
    }
  }

  if (errors) {
    nice_debug ("Agent %p : %s: stopping keepalive timer", agent, G_STRFUNC);
    goto done;
  }

  ret = TRUE;

 done:
  return ret;
}

static gboolean priv_conn_keepalive_tick (gpointer pointer)
{
  NiceAgent *agent = pointer;
  gboolean ret;

  agent_lock();
  if (g_source_is_destroyed (g_main_current_source ())) {
    nice_debug ("Source was destroyed. "
        "Avoided race condition in priv_conn_keepalive_tick");
    agent_unlock ();
    return FALSE;
  }

  ret = priv_conn_keepalive_tick_unlocked (agent);
  if (ret == FALSE) {
    if (agent->keepalive_timer_source) {
      g_source_destroy (agent->keepalive_timer_source);
      g_source_unref (agent->keepalive_timer_source);
      agent->keepalive_timer_source = NULL;
    }
  }
  agent_unlock_and_emit (agent);
  return ret;
}


static gboolean priv_turn_allocate_refresh_retransmissions_tick (gpointer pointer)
{
  CandidateRefresh *cand = (CandidateRefresh *) pointer;
  NiceAgent *agent = NULL;

  agent_lock();

  /* A race condition might happen where the mutex above waits for the lock
   * and in the meantime another thread destroys the source.
   * In that case, we don't need to run our retransmission tick since it should
   * have been cancelled */
  if (g_source_is_destroyed (g_main_current_source ())) {
    nice_debug ("Source was destroyed. "
        "Avoided race condition in priv_turn_allocate_refresh_retransmissions_tick");
    agent_unlock ();
    return FALSE;
  }


  g_source_destroy (cand->tick_source);
  g_source_unref (cand->tick_source);
  cand->tick_source = NULL;

  agent = g_object_ref (cand->agent);

  switch (stun_timer_refresh (&cand->timer)) {
    case STUN_USAGE_TIMER_RETURN_TIMEOUT:
      {
        /* Time out */
        StunTransactionId id;

        stun_message_id (&cand->stun_message, id);
        stun_agent_forget_transaction (&cand->stun_agent, id);

        refresh_cancel (cand);
        break;
      }
    case STUN_USAGE_TIMER_RETURN_RETRANSMIT:
      /* Retransmit */
      agent_socket_send (cand->nicesock, &cand->server,
          stun_message_length (&cand->stun_message), (gchar *)cand->stun_buffer);

      agent_timeout_add_with_context (agent, &cand->tick_source,
          "Candidate TURN refresh", stun_timer_remainder (&cand->timer),
          priv_turn_allocate_refresh_retransmissions_tick, cand);
      break;
    case STUN_USAGE_TIMER_RETURN_SUCCESS:
      agent_timeout_add_with_context (agent, &cand->tick_source,
          "Candidate TURN refresh", stun_timer_remainder (&cand->timer),
          priv_turn_allocate_refresh_retransmissions_tick, cand);
      break;
    default:
      /* Nothing to do. */
      break;
  }


  agent_unlock_and_emit (agent);

  g_object_unref (agent);

  return FALSE;
}

static void priv_turn_allocate_refresh_tick_unlocked (CandidateRefresh *cand)
{
  uint8_t *username;
  gsize username_len;
  uint8_t *password;
  gsize password_len;
  size_t buffer_len = 0;
  StunUsageTurnCompatibility turn_compat =
      agent_to_turn_compatibility (cand->agent);

  username = (uint8_t *)cand->candidate->turn->username;
  username_len = (size_t) strlen (cand->candidate->turn->username);
  password = (uint8_t *)cand->candidate->turn->password;
  password_len = (size_t) strlen (cand->candidate->turn->password);

  if (turn_compat == STUN_USAGE_TURN_COMPATIBILITY_MSN ||
      turn_compat == STUN_USAGE_TURN_COMPATIBILITY_OC2007) {
    username = g_base64_decode ((gchar *)username, &username_len);
    password = g_base64_decode ((gchar *)password, &password_len);
  }

  buffer_len = stun_usage_turn_create_refresh (&cand->stun_agent,
      &cand->stun_message,  cand->stun_buffer, sizeof(cand->stun_buffer),
      cand->stun_resp_msg.buffer == NULL ? NULL : &cand->stun_resp_msg, -1,
      username, username_len,
      password, password_len,
      turn_compat);

  if (turn_compat == STUN_USAGE_TURN_COMPATIBILITY_MSN ||
      turn_compat == STUN_USAGE_TURN_COMPATIBILITY_OC2007) {
    g_free (username);
    g_free (password);
  }

  nice_debug ("Agent %p : Sending allocate Refresh %zd", cand->agent,
      buffer_len);

  if (cand->tick_source != NULL) {
    g_source_destroy (cand->tick_source);
    g_source_unref (cand->tick_source);
    cand->tick_source = NULL;
  }

  if (buffer_len > 0) {
    stun_timer_start (&cand->timer,
        cand->agent->stun_initial_timeout,
        cand->agent->stun_max_retransmissions);

    /* send the refresh */
    agent_socket_send (cand->nicesock, &cand->server,
        buffer_len, (gchar *)cand->stun_buffer);

    agent_timeout_add_with_context (cand->agent, &cand->tick_source,
        "Candidate TURN refresh", stun_timer_remainder (&cand->timer),
        priv_turn_allocate_refresh_retransmissions_tick, cand);
  }

}


/*
 * Timer callback that handles refreshing TURN allocations
 *
 * This function is designed for the g_timeout_add() interface.
 *
 * @return will return FALSE when no more pending timers.
 */
static gboolean priv_turn_allocate_refresh_tick (gpointer pointer)
{
  CandidateRefresh *cand = (CandidateRefresh *) pointer;

  agent_lock();
  if (g_source_is_destroyed (g_main_current_source ())) {
    nice_debug ("Source was destroyed. "
        "Avoided race condition in priv_turn_allocate_refresh_tick");
    agent_unlock ();
    return FALSE;
  }

  priv_turn_allocate_refresh_tick_unlocked (cand);
  agent_unlock_and_emit (cand->agent);

  return FALSE;
}


/*
 * Initiates the next pending connectivity check.
 */
void conn_check_schedule_next (NiceAgent *agent)
{
  if (agent->discovery_unsched_items > 0)
    nice_debug ("Agent %p : WARN: starting conn checks before local candidate gathering is finished.", agent);

  /* step: schedule timer if not running yet */
  if (agent->conncheck_timer_source == NULL) {
    agent_timeout_add_with_context (agent, &agent->conncheck_timer_source,
        "Connectivity check schedule", agent->timer_ta,
        priv_conn_check_tick, agent);
  }

  /* step: also start the keepalive timer */
  if (agent->keepalive_timer_source == NULL) {
    agent_timeout_add_with_context (agent, &agent->keepalive_timer_source,
        "Connectivity keepalive timeout", NICE_AGENT_TIMER_TR_DEFAULT,
        priv_conn_keepalive_tick, agent);
  }
}

/*
 * Compares two connectivity check items. Checkpairs are sorted
 * in descending priority order, with highest priority item at
 * the start of the list.
 */
gint conn_check_compare (const CandidateCheckPair *a, const CandidateCheckPair *b)
{
  if (a->priority > b->priority)
    return -1;
  else if (a->priority < b->priority)
    return 1;
  return 0;
}

/*
 * Preprocesses a new connectivity check by going through list 
 * of a any stored early incoming connectivity checks from 
 * the remote peer. If a matching incoming check has been already
 * received, update the state of the new outgoing check 'pair'.
 * 
 * @param agent context pointer
 * @param stream which stream (of the agent)
 * @param component pointer to component object to which 'pair'has been added
 * @param pair newly added connectivity check
 */
static void priv_preprocess_conn_check_pending_data (NiceAgent *agent, NiceStream *stream, NiceComponent *component, CandidateCheckPair *pair)
{
  GSList *i;
  for (i = component->incoming_checks; i; i = i->next) {
    IncomingCheck *icheck = i->data;
    if (nice_address_equal (&icheck->from, &pair->remote->addr) &&
	icheck->local_socket == pair->sockptr) {
      nice_debug ("Agent %p : Updating check %p with stored early-icheck %p, %p/%u/%u (agent/stream/component).", agent, pair, icheck, agent, stream->id, component->id);
      priv_schedule_triggered_check (agent, stream, component,
          icheck->local_socket, pair->remote);
      if (icheck->use_candidate)
	priv_mark_pair_nominated (agent, stream, component, pair->local, pair->remote);
    }
  }
}


/*
 * Handle any processing steps for connectivity checks after
 * remote credentials have been set. This function handles
 * the special case where answerer has sent us connectivity
 * checks before the answer (containing credentials information),
 * reaches us. The special case is documented in sect 7.2 
 * if ICE spec (ID-19).
 */
void conn_check_remote_credentials_set(NiceAgent *agent, NiceStream *stream)
{
  GSList *j, *k, *l, *m, *n, *o;

  for (j = stream->conncheck_list; j ; j = j->next) {
    CandidateCheckPair *pair = j->data;
    NiceComponent *component =
        nice_stream_find_component_by_id (stream, pair->component_id);
    gboolean match = FALSE;

    /* performn delayed processing of spec steps section 7.2.1.4,
       and section 7.2.1.5 */
    priv_preprocess_conn_check_pending_data (agent, stream, component, pair);

    for (k = component->incoming_checks; k; k = k->next) {
      IncomingCheck *icheck = k->data;
      /* sect 7.2.1.3., "Learning Peer Reflexive Candidates", has to
       * be handled separately */
      for (l = component->remote_candidates; l; l = l->next) {
        NiceCandidate *cand = l->data;
        if (nice_address_equal (&icheck->from, &cand->addr)) {
          match = TRUE;
          break;
        }
      }
      if (match != TRUE) {
        /* note: we have gotten an incoming connectivity check from
         *       an address that is not a known remote candidate */

        NiceCandidate *local_candidate = NULL;
        NiceCandidate *remote_candidate = NULL;

        if (agent->compatibility == NICE_COMPATIBILITY_GOOGLE ||
            agent->compatibility == NICE_COMPATIBILITY_MSN ||
            agent->compatibility == NICE_COMPATIBILITY_OC2007) {
          /* We need to find which local candidate was used */
          uint8_t uname[NICE_STREAM_MAX_UNAME];
          guint uname_len;

          nice_debug ("Agent %p: We have a peer-reflexive candidate in a "
              "stored pending check", agent);

          for (m = component->remote_candidates;
               m != NULL && remote_candidate == NULL; m = m->next) {
            for (n = component->local_candidates; n; n = n->next) {
              NiceCandidate *rcand = m->data;
              NiceCandidate *lcand = n->data;

              uname_len = priv_create_username (agent, stream,
                  component->id,  rcand, lcand,
                  uname, sizeof (uname), TRUE);

              stun_debug ("pending check, comparing usernames of len %d and %d, equal=%d",
                  icheck->username_len, uname_len,
                  icheck->username && uname_len == icheck->username_len &&
                  memcmp (uname, icheck->username, icheck->username_len) == 0);
              stun_debug_bytes ("  first username:  ",
                  icheck->username,
                  icheck->username? icheck->username_len : 0);
              stun_debug_bytes ("  second username: ", uname, uname_len);

              if (icheck->username &&
                  uname_len == icheck->username_len &&
                  memcmp (uname, icheck->username, icheck->username_len) == 0) {
                local_candidate = lcand;
                remote_candidate = rcand;
                break;
              }
            }
          }
        } else {
          for (l = component->local_candidates; l; l = l->next) {
            NiceCandidate *cand = l->data;
            if (nice_address_equal (&cand->addr, &icheck->local_socket->addr)) {
              local_candidate = cand;
              break;
            }
          }
        }

        if (agent->compatibility == NICE_COMPATIBILITY_GOOGLE &&
            local_candidate == NULL) {
          /* if we couldn't match the username, then the matching remote
           * candidate hasn't been received yet.. we must wait */
          nice_debug ("Agent %p : Username check failed. pending check has "
              "to wait to be processed", agent);
        } else {
          NiceCandidate *candidate;

          nice_debug ("Agent %p : Discovered peer reflexive from early i-check",
              agent);
          candidate =
              discovery_learn_remote_peer_reflexive_candidate (agent,
                  stream,
                  component,
                  icheck->priority,
                  &icheck->from,
                  icheck->local_socket,
                  local_candidate, remote_candidate);
          if (candidate) {
            if (local_candidate &&
                local_candidate->transport == NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE)
              priv_conn_check_add_for_candidate_pair_matched (agent,
                  stream->id, component, local_candidate, candidate, NICE_CHECK_DISCOVERED);
            else
              conn_check_add_for_candidate (agent, stream->id, component, candidate);

            priv_schedule_triggered_check (agent, stream, component,
                icheck->local_socket, candidate);
            if (icheck->use_candidate)
              priv_mark_pair_nominated (agent, stream, component, local_candidate, candidate);
          }
        }
      }
    }
  }

  /* Once we process the pending checks, we should free them to avoid
   * reprocessing them again if a dribble-mode set_remote_candidates
   * is called */
  for (o = stream->components; o; o = o->next) {
    NiceComponent *component = o->data;
    g_slist_free_full (component->incoming_checks,
        (GDestroyNotify) incoming_check_free);
    component->incoming_checks = NULL;
  }
}

/*
 * Enforces the upper limit for connectivity checks as described
 * in ICE spec section 5.7.3 (ID-19). See also 
 * conn_check_add_for_candidate().
 */
static GSList *priv_limit_conn_check_list_size (GSList *conncheck_list, guint upper_limit)
{
  guint valid = 0;
  guint cancelled = 0;
  GSList *item = conncheck_list;

  while (item) {
    CandidateCheckPair *pair = item->data;
    GSList *next = item->next;

    valid++;
    if (valid > upper_limit) {
        conn_check_free_item (pair);
        conncheck_list = g_slist_delete_link (conncheck_list, item);
        cancelled++;
    }
    item = next;
  }

  if (cancelled > 0)
    nice_debug ("Agent : Pruned %d candidates. Conncheck list has %d elements"
        " left. Maximum connchecks allowed : %d", cancelled, valid,
        upper_limit);
  return conncheck_list;
}

/*
 * Changes the selected pair for the component if 'pair' is nominated
 * and has higher priority than the currently selected pair. See
 * ICE sect 11.1.1. "Procedures for Full Implementations" (ID-19).
 */
static gboolean priv_update_selected_pair (NiceAgent *agent, NiceComponent *component, CandidateCheckPair *pair)
{
  CandidatePair cpair = { 0, };

  g_assert (component);
  g_assert (pair);
  if (pair->priority > component->selected_pair.priority) {
    nice_debug ("Agent %p : changing SELECTED PAIR for component %u: %s:%s "
        "(prio:%" G_GUINT64_FORMAT ").", agent, component->id,
        pair->local->foundation, pair->remote->foundation, pair->priority);

    cpair.local = pair->local;
    cpair.remote = pair->remote;
    cpair.priority = pair->priority;
    /* cpair.keepalive is not used by nice_component_update_selected_pair() */

    nice_component_update_selected_pair (component, &cpair);

    priv_conn_keepalive_tick_unlocked (agent);

    agent_signal_new_selected_pair (agent, pair->stream_id, component->id,
        pair->local, pair->remote);

  }

  return TRUE;
}

/*
 * Updates the check list state.
 *
 * Implements parts of the algorithm described in 
 * ICE sect 8.1.2. "Updating States" (RFC 5245): if for any
 * component, all checks have been completed and have
 * failed to produce a nominated pair, mark that component's
 * state to NICE_CHECK_FAILED.
 *
 * Sends a component state changesignal via 'agent'.
 */
static void priv_update_check_list_failed_components (NiceAgent *agent, NiceStream *stream)
{
  GSList *i;
  gboolean completed;
  guint nominated;
  /* note: emitting a signal might cause the client 
   *       to remove the stream, thus the component count
   *       must be fetched before entering the loop*/
  guint c, components = stream->n_components;

  for (i = agent->discovery_list; i; i = i->next) {
    CandidateDiscovery *d = i->data;

    /* There is still discovery ogoing for this stream,
     * so don't fail any of it's candidates.
     */
    if (d->stream == stream && !d->done)
      return;
  }
  if (agent->discovery_list != NULL)
    return;

  /* note: iterate the conncheck list for each component separately */
  for (c = 0; c < components; c++) {
    NiceComponent *comp = NULL;
    if (!agent_find_component (agent, stream->id, c+1, NULL, &comp))
      continue;

    nominated = 0;
    completed = TRUE;
    for (i = stream->conncheck_list; i; i = i->next) {
      CandidateCheckPair *p = i->data;

      g_assert (p->agent == agent);
      g_assert (p->stream_id == stream->id);

      if (p->component_id == (c + 1)) {
        if (p->nominated)
          ++nominated;
	if (p->state != NICE_CHECK_FAILED &&
            p->state != NICE_CHECK_SUCCEEDED &&
            p->state != NICE_CHECK_DISCOVERED)
	  completed = FALSE;
      }
    }
 
    /* note: all pairs are either failed or succeeded, and the component
     * has not produced a nominated pair.
     * Set the component to FAILED only if it actually had remote candidates
     * that failed.. */
    if (completed && nominated == 0 &&
        comp != NULL && comp->remote_candidates != NULL)
      agent_signal_component_state_change (agent,
					   stream->id,
					   (c + 1), /* component-id */
					   NICE_COMPONENT_STATE_FAILED);
  }
}

/*
 * Updates the check list state for a stream component.
 *
 * Implements the algorithm described in ICE sect 8.1.2 
 * "Updating States" (ID-19) as it applies to checks of 
 * a certain component. If there are any nominated pairs, 
 * ICE processing may be concluded, and component state is 
 * changed to READY.
 *
 * Sends a component state changesignal via 'agent'.
 */
static void priv_update_check_list_state_for_ready (NiceAgent *agent, NiceStream *stream, NiceComponent *component)
{
  GSList *i;
  guint valid = 0, nominated = 0;

  g_assert (component);

  /* step: search for at least one nominated pair */
  for (i = stream->conncheck_list; i; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->component_id == component->id) {
      if (p->valid) {
	++valid;
	if (p->nominated == TRUE) {
          ++nominated;
	}
      }
    }
  }

  if (nominated > 0) {
    /* Only go to READY if no checks are left in progress. If there are
     * any that are kept, then this function will be called again when the
     * conncheck tick timer finishes them all */
    if (priv_prune_pending_checks (agent, stream, component->id) == 0) {
      /* Continue through the states to give client code a nice
       * logical progression. See http://phabricator.freedesktop.org/D218 for
       * discussion. */
      if (component->state < NICE_COMPONENT_STATE_CONNECTING ||
          component->state == NICE_COMPONENT_STATE_FAILED)
        agent_signal_component_state_change (agent, stream->id, component->id,
            NICE_COMPONENT_STATE_CONNECTING);
      if (component->state < NICE_COMPONENT_STATE_CONNECTED)
        agent_signal_component_state_change (agent, stream->id, component->id,
            NICE_COMPONENT_STATE_CONNECTED);
      agent_signal_component_state_change (agent, stream->id,
          component->id, NICE_COMPONENT_STATE_READY);
    }
  }
  nice_debug ("Agent %p : conn.check list status: %u nominated, %u valid, c-id %u.", agent, nominated, valid, component->id);
}

/*
 * The remote party has signalled that the candidate pair
 * described by 'component' and 'remotecand' is nominated
 * for use.
 */
static void priv_mark_pair_nominated (NiceAgent *agent, NiceStream *stream, NiceComponent *component, NiceCandidate *localcand, NiceCandidate *remotecand)
{
  GSList *i;

  g_assert (component);

  if (NICE_AGENT_IS_COMPATIBLE_WITH_RFC5245_OR_OC2007R2 (agent) &&
      agent->controlling_mode)
    return;

  /* step: search for at least one nominated pair */
  for (i = stream->conncheck_list; i; i = i->next) {
    CandidateCheckPair *pair = i->data;
    if (pair->local == localcand && pair->remote == remotecand &&
        NICE_AGENT_IS_COMPATIBLE_WITH_RFC5245_OR_OC2007R2 (agent)) {
      /* ICE, 7.2.1.5. Updating the Nominated Flag */
      /* note: TCP candidates typically produce peer reflexive
       * candidate, generating a "discovered" pair that can be
       * nominated.
       */
      if (pair->state == NICE_CHECK_SUCCEEDED &&
          pair->discovered_pair != NULL) {
        pair = pair->discovered_pair;
        g_assert (pair->state == NICE_CHECK_DISCOVERED);
      }

      if (pair->valid) {
        nice_debug ("Agent %p : marking pair %p (%s) as nominated",
            agent, pair, pair->foundation);
        pair->nominated = TRUE;
        priv_update_selected_pair (agent, component, pair);
        /* Do not step down to CONNECTED if we're already at state READY*/
        if (component->state == NICE_COMPONENT_STATE_FAILED)
          agent_signal_component_state_change (agent,
              stream->id, component->id, NICE_COMPONENT_STATE_CONNECTING);
        if (component->state == NICE_COMPONENT_STATE_CONNECTING)
          /* step: notify the client of a new component state (must be done
           *       before the possible check list state update step */
          agent_signal_component_state_change (agent,
              stream->id, component->id, NICE_COMPONENT_STATE_CONNECTED);
        priv_update_check_list_state_for_ready (agent, stream, component);
      } else if (pair->state == NICE_CHECK_IN_PROGRESS) {
        pair->mark_nominated_on_response_arrival = TRUE;
        nice_debug ("Agent %p : pair %p (%s) is in-progress, "
            "will be nominated on response receipt.",
            agent, pair, pair->foundation);
      }
      /* note: this case is not covered by the ICE spec, 7.2.1.5,
       * "Updating the Nominated Flag", but a pair in waiting state
       * deserves the same treatment than a pair in-progress. A pair
       * can be in waiting state as the result of being enqueued in
       * the triggered check list for example.
       */
      if (pair->state == NICE_CHECK_WAITING) {
        pair->mark_nominated_on_response_arrival = TRUE;
        nice_debug ("Agent %p : pair %p (%s) is waiting, "
            "will be nominated on response receipt.",
            agent, pair, pair->foundation);
      }
    } else if (pair->local == localcand && pair->remote == remotecand) {
      nice_debug ("Agent %p : marking pair %p (%s) as nominated", agent, pair, pair->foundation);
      pair->nominated = TRUE;
      if (pair->valid) {
	priv_update_selected_pair (agent, component, pair);
        /* Do not step down to CONNECTED if we're already at state READY*/
        if (component->state == NICE_COMPONENT_STATE_FAILED)
          agent_signal_component_state_change (agent,
              stream->id, component->id, NICE_COMPONENT_STATE_CONNECTING);
        if (component->state == NICE_COMPONENT_STATE_CONNECTING)
          /* step: notify the client of a new component state (must be done
           *       before the possible check list state update step */
          agent_signal_component_state_change (agent,
              stream->id, component->id, NICE_COMPONENT_STATE_CONNECTED);
      }
      priv_update_check_list_state_for_ready (agent, stream, component);
    }
  }
}

guint32
ensure_unique_priority (NiceComponent *component, guint32 priority)
{
  GSList *item;

 again:
  if (priority == 0)
    priority--;

  for (item = component->local_candidates; item; item = item->next) {
    NiceCandidate *cand = item->data;

    if (cand->priority == priority) {
      priority--;
      goto again;
    }
  }

  for (item = component->stream->conncheck_list; item; item = item->next) {
    CandidateCheckPair *p = item->data;

    if (p->component_id == component->id &&
        p->prflx_priority == priority) {
      priority--;
      goto again;
    }
  }

  return priority;
}


/*
 * Creates a new connectivity check pair and adds it to
 * the agent's list of checks.
 */
static CandidateCheckPair *priv_add_new_check_pair (NiceAgent *agent,
    guint stream_id, NiceComponent *component, NiceCandidate *local,
    NiceCandidate *remote, NiceCheckState initial_state)
{
  NiceStream *stream;
  CandidateCheckPair *pair;

  g_assert (local != NULL);
  g_assert (remote != NULL);

  stream = agent_find_stream (agent, stream_id);
  pair = g_slice_new0 (CandidateCheckPair);

  pair->agent = agent;
  pair->stream_id = stream_id;
  pair->component_id = component->id;;
  pair->local = local;
  pair->remote = remote;
  /* note: we use the remote sockptr only in the case
   * of TCP transport
   */
  if (local->transport == NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE &&
      remote->type == NICE_CANDIDATE_TYPE_PEER_REFLEXIVE)
    pair->sockptr = (NiceSocket *) remote->sockptr;
  else
    pair->sockptr = (NiceSocket *) local->sockptr;
  g_snprintf (pair->foundation, NICE_CANDIDATE_PAIR_MAX_FOUNDATION, "%s:%s", local->foundation, remote->foundation);

  pair->priority = agent_candidate_pair_priority (agent, local, remote);
  pair->state = initial_state;
  nice_debug ("Agent %p : creating new pair %p state %d", agent, pair, initial_state);
  {
      gchar tmpbuf1[INET6_ADDRSTRLEN];
      gchar tmpbuf2[INET6_ADDRSTRLEN];
      nice_address_to_string (&pair->local->addr, tmpbuf1);
      nice_address_to_string (&pair->remote->addr, tmpbuf2);
      nice_debug ("Agent %p : new pair %p : [%s]:%u --> [%s]:%u", agent, pair,
          tmpbuf1, nice_address_get_port (&pair->local->addr),
          tmpbuf2, nice_address_get_port (&pair->remote->addr));
  }
  pair->prflx_priority = ensure_unique_priority (component,
      peer_reflexive_candidate_priority (agent, local));
  pair->retransmit_on_timeout = TRUE;

  stream->conncheck_list = g_slist_insert_sorted (stream->conncheck_list, pair,
      (GCompareFunc)conn_check_compare);

  nice_debug ("Agent %p : added a new conncheck %p with foundation of '%s' to list %u.", agent, pair, pair->foundation, stream_id);

  /* implement the hard upper limit for number of
     checks (see sect 5.7.3 ICE ID-19): */
  if (agent->compatibility == NICE_COMPATIBILITY_RFC5245) {
    stream->conncheck_list = priv_limit_conn_check_list_size (
        stream->conncheck_list, agent->max_conn_checks);
  }

  return pair;
}

NiceCandidateTransport
conn_check_match_transport (NiceCandidateTransport transport)
{
  switch (transport) {
    case NICE_CANDIDATE_TRANSPORT_TCP_ACTIVE:
      return NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE;
      break;
    case NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE:
      return NICE_CANDIDATE_TRANSPORT_TCP_ACTIVE;
      break;
    case NICE_CANDIDATE_TRANSPORT_TCP_SO:
    case NICE_CANDIDATE_TRANSPORT_UDP:
    default:
      return transport;
      break;
  }
}

static CandidateCheckPair *priv_conn_check_add_for_candidate_pair_matched (
    NiceAgent *agent, guint stream_id, NiceComponent *component,
     NiceCandidate *local, NiceCandidate *remote, NiceCheckState initial_state)
{
  CandidateCheckPair *pair;

  nice_debug ("Agent %p : Adding check pair between %s and %s for s%d/c%d",
      agent, local->foundation, remote->foundation,
      stream_id, component->id);
  pair = priv_add_new_check_pair (agent, stream_id, component, local, remote,
      initial_state);
  if (component->state == NICE_COMPONENT_STATE_CONNECTED ||
      component->state == NICE_COMPONENT_STATE_READY) {
    agent_signal_component_state_change (agent,
        stream_id,
        component->id,
        NICE_COMPONENT_STATE_CONNECTED);
  } else {
    agent_signal_component_state_change (agent,
        stream_id,
        component->id,
        NICE_COMPONENT_STATE_CONNECTING);
  }

  return pair;
}

gboolean conn_check_add_for_candidate_pair (NiceAgent *agent,
    guint stream_id, NiceComponent *component, NiceCandidate *local,
    NiceCandidate *remote)
{
  gboolean ret = FALSE;

  g_assert (local != NULL);
  g_assert (remote != NULL);

  /* note: do not create pairs where the local candidate is
   *       a srv-reflexive (ICE 5.7.3. "Pruning the pairs" ID-9) */
  if ((agent->compatibility == NICE_COMPATIBILITY_RFC5245 ||
      agent->compatibility == NICE_COMPATIBILITY_WLM2009 ||
      agent->compatibility == NICE_COMPATIBILITY_OC2007R2) &&
      local->type == NICE_CANDIDATE_TYPE_SERVER_REFLEXIVE) {
    return FALSE;
  }

  /* note: do not create pairs where local candidate has TCP passive transport
   *       (ice-tcp-13 6.2. "Forming the Check Lists") */
  if (local->transport == NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE) {
    return FALSE;
  }

  /* note: match pairs only if transport and address family are the same */
  if (local->transport == conn_check_match_transport (remote->transport) &&
     local->addr.s.addr.sa_family == remote->addr.s.addr.sa_family) {
    priv_conn_check_add_for_candidate_pair_matched (agent, stream_id, component,
        local, remote, NICE_CHECK_FROZEN);
    ret = TRUE;
  }

  return ret;
}

/*
 * Forms new candidate pairs by matching the new remote candidate
 * 'remote_cand' with all existing local candidates of 'component'.
 * Implements the logic described in ICE sect 5.7.1. "Forming Candidate
 * Pairs" (ID-19).
 *
 * @param agent context
 * @param component pointer to the component
 * @param remote remote candidate to match with
 *
 * @return number of checks added, negative on fatal errors
 */
int conn_check_add_for_candidate (NiceAgent *agent, guint stream_id, NiceComponent *component, NiceCandidate *remote)
{
  GSList *i;
  int added = 0;
  int ret = 0;

  g_assert (remote != NULL);

  /* note: according to 7.2.1.3, "Learning Peer Reflexive Candidates",
   * the agent does not pair this candidate with any local candidates.
   */
  if (agent->compatibility == NICE_COMPATIBILITY_RFC5245 &&
      remote->type == NICE_CANDIDATE_TYPE_PEER_REFLEXIVE)
  {
    return added;
  }

  for (i = component->local_candidates; i ; i = i->next) {
    NiceCandidate *local = i->data;

    if (agent->force_relay && local->type != NICE_CANDIDATE_TYPE_RELAYED)
        continue;

    ret = conn_check_add_for_candidate_pair (agent, stream_id, component, local, remote);

    if (ret) {
      ++added;
    }
  }

  return added;
}

/*
 * Forms new candidate pairs by matching the new local candidate
 * 'local_cand' with all existing remote candidates of 'component'.
 *
 * @param agent context
 * @param component pointer to the component
 * @param local local candidate to match with
 *
 * @return number of checks added, negative on fatal errors
 */
int conn_check_add_for_local_candidate (NiceAgent *agent, guint stream_id, NiceComponent *component, NiceCandidate *local)
{
  GSList *i;
  int added = 0;
  int ret = 0;

  g_assert (local != NULL);

  /*
   * note: according to 7.1.3.2.1 "Discovering Peer Reflexive
   * Candidates", the peer reflexive candidate is not paired
   * with other remote candidates
   */

  if (agent->compatibility == NICE_COMPATIBILITY_RFC5245 &&
      local->type == NICE_CANDIDATE_TYPE_PEER_REFLEXIVE)
  {
    return added;
  }

  for (i = component->remote_candidates; i ; i = i->next) {

    NiceCandidate *remote = i->data;
    ret = conn_check_add_for_candidate_pair (agent, stream_id, component, local, remote);

    if (ret) {
      ++added;
    }
  }

  return added;
}

/*
 * Frees the CandidateCheckPair structure pointer to 
 * by 'user data'. Compatible with GDestroyNotify.
 */
static void conn_check_free_item (gpointer data)
{
  CandidateCheckPair *pair = data;

  if (pair->agent)
    priv_remove_pair_from_triggered_check_queue (pair->agent, pair);
  pair->stun_message.buffer = NULL;
  pair->stun_message.buffer_len = 0;
  g_slice_free (CandidateCheckPair, pair);
}

/*
 * Frees all resources of all connectivity checks.
 */
void conn_check_free (NiceAgent *agent)
{
  GSList *i;
  for (i = agent->streams; i; i = i->next) {
    NiceStream *stream = i->data;

    if (stream->conncheck_list) {
      nice_debug ("Agent %p, freeing conncheck_list of stream %p", agent,
          stream);
      g_slist_free_full (stream->conncheck_list, conn_check_free_item);
      stream->conncheck_list = NULL;
    }
  }

  conn_check_stop (agent);
}

/*
 * Prunes the list of connectivity checks for items related
 * to stream 'stream_id'. 
 *
 * @return TRUE on success, FALSE on a fatal error
 */
void conn_check_prune_stream (NiceAgent *agent, NiceStream *stream)
{
  GSList *i;
  gboolean keep_going = FALSE;

  if (stream->conncheck_list) {
    nice_debug ("Agent %p, freeing conncheck_list of stream %p", agent, stream);

    g_slist_free_full (stream->conncheck_list, conn_check_free_item);
    stream->conncheck_list = NULL;
  }

  for (i = agent->streams; i; i = i->next) {
    NiceStream *s = i->data;
    if (s->conncheck_list) {
      keep_going = TRUE;
      break;
    }
  }

  if (!keep_going)
    conn_check_stop (agent);
}

/*
 * Fills 'dest' with a username string for use in an outbound connectivity
 * checks. No more than 'dest_len' characters (including terminating
 * NULL) is ever written to the 'dest'.
 */
static
size_t priv_gen_username (NiceAgent *agent, guint component_id,
    gchar *remote, gchar *local, uint8_t *dest, guint dest_len)
{
  guint len = 0;
  gsize remote_len = strlen (remote);
  gsize local_len = strlen (local);

  if (remote_len > 0 && local_len > 0) {
    if (agent->compatibility == NICE_COMPATIBILITY_RFC5245 &&
        dest_len >= remote_len + local_len + 1) {
      memcpy (dest, remote, remote_len);
      len += remote_len;
      memcpy (dest + len, ":", 1);
      len++;
      memcpy (dest + len, local, local_len);
      len += local_len;
    } else if ((agent->compatibility == NICE_COMPATIBILITY_WLM2009 ||
        agent->compatibility == NICE_COMPATIBILITY_OC2007R2) &&
        dest_len >= remote_len + local_len + 4 ) {
      memcpy (dest, remote, remote_len);
      len += remote_len;
      memcpy (dest + len, ":", 1);
      len++;
      memcpy (dest + len, local, local_len);
      len += local_len;
      if (len % 4 != 0) {
        memset (dest + len, 0, 4 - (len % 4));
        len += 4 - (len % 4);
      }
    } else if (agent->compatibility == NICE_COMPATIBILITY_GOOGLE &&
        dest_len >= remote_len + local_len) {
      memcpy (dest, remote, remote_len);
      len += remote_len;
      memcpy (dest + len, local, local_len);
      len += local_len;
    } else if (agent->compatibility == NICE_COMPATIBILITY_MSN ||
	       agent->compatibility == NICE_COMPATIBILITY_OC2007) {
      gchar component_str[10];
      guchar *local_decoded = NULL;
      guchar *remote_decoded = NULL;
      gsize local_decoded_len;
      gsize remote_decoded_len;
      gsize total_len;
      int padding;

      g_snprintf (component_str, sizeof(component_str), "%d", component_id);
      local_decoded = g_base64_decode (local, &local_decoded_len);
      remote_decoded = g_base64_decode (remote, &remote_decoded_len);

      total_len = remote_decoded_len + local_decoded_len + 3 + 2*strlen (component_str);
      padding = 4 - (total_len % 4);

      if (dest_len >= total_len + padding) {
        guchar pad_char[1] = {0};
        int i;

        memcpy (dest, remote_decoded, remote_decoded_len);
        len += remote_decoded_len;
        memcpy (dest + len, ":", 1);
        len++;
        memcpy (dest + len, component_str, strlen (component_str));
        len += strlen (component_str);

        memcpy (dest + len, ":", 1);
        len++;

        memcpy (dest + len, local_decoded, local_decoded_len);
        len += local_decoded_len;
        memcpy (dest + len, ":", 1);
        len++;
        memcpy (dest + len, component_str, strlen (component_str));;
        len += strlen (component_str);

        for (i = 0; i < padding; i++) {
          memcpy (dest + len, pad_char, 1);
          len++;
        }

      }

      g_free (local_decoded);
      g_free (remote_decoded);
    }
  }

  return len;
}

/*
 * Fills 'dest' with a username string for use in an outbound connectivity
 * checks. No more than 'dest_len' characters (including terminating
 * NULL) is ever written to the 'dest'.
 */
static
size_t priv_create_username (NiceAgent *agent, NiceStream *stream,
    guint component_id, NiceCandidate *remote, NiceCandidate *local,
    uint8_t *dest, guint dest_len, gboolean inbound)
{
  gchar *local_username = NULL;
  gchar *remote_username = NULL;


  if (remote && remote->username) {
    remote_username = remote->username;
  }

  if (local && local->username) {
    local_username = local->username;
  }

  if (stream) {
    if (remote_username == NULL) {
      remote_username = stream->remote_ufrag;
    }
    if (local_username == NULL) {
      local_username = stream->local_ufrag;
    }
  }

  if (local_username && remote_username) {
    if (inbound) {
      return priv_gen_username (agent, component_id,
          local_username, remote_username, dest, dest_len);
    } else {
      return priv_gen_username (agent, component_id,
          remote_username, local_username, dest, dest_len);
    }
  }

  return 0;
}

/*
 * Returns a password string for use in an outbound connectivity
 * check.
 */
static
size_t priv_get_password (NiceAgent *agent, NiceStream *stream,
    NiceCandidate *remote, uint8_t **password)
{
  if (agent->compatibility == NICE_COMPATIBILITY_GOOGLE)
    return 0;

  if (remote && remote->password) {
    *password = (uint8_t *)remote->password;
    return strlen (remote->password);
  }

  if (stream) {
    *password = (uint8_t *)stream->remote_password;
    return strlen (stream->remote_password);
  }

  return 0;
}

/* Implement the computation specific in RFC 5245 section 16 */

static unsigned int priv_compute_conncheck_timer (NiceAgent *agent, NiceStream *stream)
{
  GSList *i;
  guint waiting_and_in_progress = 0;
  guint n = 0;
  unsigned int rto = 0;

  for (i = stream->conncheck_list; i ; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->state == NICE_CHECK_IN_PROGRESS ||
        p->state == NICE_CHECK_WAITING)
      waiting_and_in_progress++;
  }

  n = priv_number_of_active_check_lists (agent);
  rto = agent->timer_ta  * n * waiting_and_in_progress;

  /* We assume non-reliable streams are RTP, so we use 100 as the max */
  nice_debug ("Agent %p : timer set to %dms, "
    "waiting+in_progress=%d, nb_active=%d",
    agent, agent->reliable ? MAX (rto, 500) : MAX (rto, 100),
    waiting_and_in_progress, n);
  if (agent->reliable)
    return MAX (rto, 500);
  else
    return MAX (rto, 100);
}

/*
 * Sends a connectivity check over candidate pair 'pair'.
 *
 * @return zero on success, non-zero on error
 */
int conn_check_send (NiceAgent *agent, CandidateCheckPair *pair)
{

  /* note: following information is supplied:
   *  - username (for USERNAME attribute)
   *  - password (for MESSAGE-INTEGRITY)
   *  - priority (for PRIORITY)
   *  - ICE-CONTROLLED/ICE-CONTROLLING (for role conflicts)
   *  - USE-CANDIDATE (if sent by the controlling agent)
   */

  uint8_t uname[NICE_STREAM_MAX_UNAME];
  NiceStream *stream;
  NiceComponent *component;
  gsize uname_len;
  uint8_t *password = NULL;
  gsize password_len;
  bool controlling = agent->controlling_mode;
 /* XXX: add API to support different nomination modes: */
  bool cand_use = controlling;
  size_t buffer_len;
  unsigned int timeout;

  if (!agent_find_component (agent, pair->stream_id, pair->component_id,
          &stream, &component))
    return -1;

  uname_len = priv_create_username (agent, stream, pair->component_id,
      pair->remote, pair->local, uname, sizeof (uname), FALSE);
  password_len = priv_get_password (agent, stream, pair->remote, &password);

  if (password != NULL &&
      (agent->compatibility == NICE_COMPATIBILITY_MSN ||
       agent->compatibility == NICE_COMPATIBILITY_OC2007)) {
    password = g_base64_decode ((gchar *) password, &password_len);
  }

  if (nice_debug_is_enabled ()) {
    gchar tmpbuf1[INET6_ADDRSTRLEN];
    gchar tmpbuf2[INET6_ADDRSTRLEN];
    nice_address_to_string (&pair->local->addr, tmpbuf1);
    nice_address_to_string (&pair->remote->addr, tmpbuf2);
    nice_debug ("Agent %p : STUN-CC REQ [%s]:%u --> [%s]:%u, socket=%u, "
        "pair=%s (c-id:%u), tie=%llu, username='%.*s' (%" G_GSIZE_FORMAT "), "
        "password='%.*s' (%" G_GSIZE_FORMAT "), prio=%u, %s.", agent,
	     tmpbuf1, nice_address_get_port (&pair->local->addr),
	     tmpbuf2, nice_address_get_port (&pair->remote->addr),
             pair->sockptr->fileno ? g_socket_get_fd(pair->sockptr->fileno) : -1,
	     pair->foundation, pair->component_id,
	     (unsigned long long)agent->tie_breaker,
        (int) uname_len, uname, uname_len,
        (int) password_len, password, password_len,
        pair->prflx_priority,
        controlling ? "controlling" : "controlled");
  }

  if (NICE_AGENT_IS_COMPATIBLE_WITH_RFC5245_OR_OC2007R2 (agent)) {
    switch (agent->nomination_mode) {
      case NICE_NOMINATION_MODE_REGULAR:
        /* We are doing regular nomination, so we set the use-candidate
         * attrib, when the controlling agent decided which valid pair to
         * resend with this flag in priv_conn_check_tick_stream()
         */
        cand_use = pair->use_candidate_on_next_check;
        nice_debug ("Agent %p : %s: set cand_use=%d "
            "(regular nomination).", agent, G_STRFUNC, cand_use);
        break;
      case NICE_NOMINATION_MODE_AGGRESSIVE:
        /* We are doing aggressive nomination, we set the use-candidate
         * attrib in every check we send, when we are the controlling
         * agent, RFC 5245, 8.1.1.2
         */
        cand_use = controlling;
        nice_debug ("Agent %p : %s: set cand_use=%d "
            "(aggressive nomination).", agent, G_STRFUNC, cand_use);
        break;
      default:
        /* Nothing to do. */
        break;
    }
  } else if (cand_use)
    pair->nominated = controlling;

  if (uname_len == 0) {
    nice_debug ("Agent %p: no credentials found, cancelling conncheck", agent);
    pair->stun_message.buffer = NULL;
    pair->stun_message.buffer_len = 0;
    return -1;
  }

  buffer_len = stun_usage_ice_conncheck_create (&component->stun_agent,
      &pair->stun_message, pair->stun_buffer, sizeof(pair->stun_buffer),
      uname, uname_len, password, password_len,
      cand_use, controlling, pair->prflx_priority,
      agent->tie_breaker,
      pair->local->foundation,
      agent_to_ice_compatibility (agent));

  nice_debug ("Agent %p: conncheck created %zd - %p", agent, buffer_len,
      pair->stun_message.buffer);

  if (agent->compatibility == NICE_COMPATIBILITY_MSN ||
      agent->compatibility == NICE_COMPATIBILITY_OC2007) {
    g_free (password);
  }

  if (buffer_len == 0) {
    nice_debug ("Agent %p: buffer is empty, cancelling conncheck", agent);
    pair->stun_message.buffer = NULL;
    pair->stun_message.buffer_len = 0;
    return -1;
  }

  if (nice_socket_is_reliable(pair->sockptr)) {
    timeout = agent->stun_reliable_timeout;
    stun_timer_start_reliable(&pair->timer, timeout);
  } else {
    StunTimer *timer = &pair->timer;

    if (pair->recheck_on_timeout) {
      GTimeVal now;
      /* The pair recheck on timeout can easily cause repetitive rechecks in
       * a ping-pong effect, if both peers with the same behaviour try to
       * check the same pair almost simultaneously, and if the network rtt
       * is greater than the initial timer rto. The reply to the initial
       * stun request may arrive after the in-progress conncheck
       * cancellation (described in RFC 5245, sect 7.2.1.4). Cancellation
       * creates a new stun request, and forgets the initial one.
       * The conncheck timer is restarted with the same initial value,
       * so the same situation happens again later.
       *
       * We choose to avoid resetting the timer in such situation.
       * After enough retransmissions, the timeout delay becomes
       * longer than the rtt, and the stun reply can be handled.
       */

      g_get_current_time (&now);
      timeout = priv_timer_remainder (&pair->next_tick, &now);
      nice_debug("Agent %p : reusing timer of pair %p: %d/%d %d/%dms",
          agent, pair,
          timer->retransmissions, timer->max_retransmissions,
          timer->delay - timeout,
          timer->delay);
    } else {
      timeout = priv_compute_conncheck_timer (agent, stream);
      stun_timer_start (timer, timeout, agent->stun_max_retransmissions);
    }
    pair->recheck_on_timeout = FALSE;
  }

  g_get_current_time (&pair->next_tick);
  g_time_val_add (&pair->next_tick, timeout * 1000);

  /* TCP-ACTIVE candidate must create a new socket before sending
   * by connecting to the peer. The new socket is stored in the candidate
   * check pair, until we discover a new local peer reflexive */
  if (pair->sockptr->fileno == NULL &&
      pair->sockptr->type != NICE_SOCKET_TYPE_UDP_TURN &&
      pair->local->transport == NICE_CANDIDATE_TRANSPORT_TCP_ACTIVE) {
    NiceStream *stream2 = NULL;
    NiceComponent *component2 = NULL;
    NiceSocket *new_socket;

    if (agent_find_component (agent, pair->stream_id, pair->component_id,
            &stream2, &component2)) {
      new_socket = nice_tcp_active_socket_connect (pair->sockptr,
          &pair->remote->addr);
      if (new_socket) {
        pair->sockptr = new_socket;
        _priv_set_socket_tos (agent, pair->sockptr, stream2->tos);

        if (agent->reliable)
          nice_socket_set_writable_callback (pair->sockptr,
              _tcp_sock_is_writable, component2);

        nice_component_attach_socket (component2, new_socket);
      }
    }
  }
  /* send the conncheck */
  agent_socket_send (pair->sockptr, &pair->remote->addr,
      buffer_len, (gchar *)pair->stun_buffer);

  if (agent->compatibility == NICE_COMPATIBILITY_OC2007R2)
    ms_ice2_legacy_conncheck_send (&pair->stun_message, pair->sockptr,
        &pair->remote->addr);

  return 0;
}

/*
 * Implemented the pruning steps described in ICE sect 8.1.2
 * "Updating States" (ID-19) after a pair has been nominated.
 *
 * @see priv_update_check_list_state_failed_components()
 */
static guint priv_prune_pending_checks (NiceAgent *agent, NiceStream *stream, guint component_id)
{
  GSList *i;
  guint64 highest_nominated_priority = 0;
  guint in_progress = 0;

  nice_debug ("Agent %p: Finding highest priority for component %d",
      agent, component_id);

  for (i = stream->conncheck_list; i; i = i->next) {
    CandidateCheckPair *p = i->data;
    if (p->component_id == component_id && p->valid == TRUE &&
        p->nominated == TRUE) {
      if (p->priority > highest_nominated_priority) {
        highest_nominated_priority = p->priority;
      }
    }
  }

  nice_debug ("Agent %p: Pruning pending checks. Highest nominated priority "
      "is %" G_GUINT64_FORMAT, agent, highest_nominated_priority);

  /* step: cancel all FROZEN and WAITING pairs for the component */
  /* note: this case is not covered by the ICE spec, 8.1.2
   * "Updating States", but a pair in waiting state which will be
   * nominated on response receipt should be treated the same way
   * that an in-progress pair. A pair in waiting state and in
   * the triggered check list should also be treated like an in-progress
   * pair.
   */
  i = stream->conncheck_list;
  while (i) {
    CandidateCheckPair *p = i->data;
    GSList *next = i->next;

    if (p->component_id == component_id) {
      gboolean like_in_progress =
          p->mark_nominated_on_response_arrival ||
          priv_is_pair_in_triggered_check_queue (agent, p);

      if (p->state == NICE_CHECK_FROZEN ||
          (p->state == NICE_CHECK_WAITING && !like_in_progress)) {
        nice_debug ("Agent %p : pair %p removed.", agent, p);
	conn_check_free_item (p);
        stream->conncheck_list = g_slist_delete_link(stream->conncheck_list, i);
      }

      /* note: a SHOULD level req. in ICE 8.1.2. "Updating States" (ID-19) */
      else if (p->state == NICE_CHECK_IN_PROGRESS ||
          (p->state == NICE_CHECK_WAITING && like_in_progress)) {
        if (highest_nominated_priority != 0 &&
            p->priority < highest_nominated_priority) {
          p->retransmit_on_timeout = FALSE;
          p->recheck_on_timeout = FALSE;
          nice_debug ("Agent %p : pair %p will not be retransmitted.",
              agent, p);
        } else {
          /* We must keep the higher priority pairs running because if a udp
           * packet was lost, we might end up using a bad candidate */
          nice_debug ("Agent %p : pair %p kept IN_PROGRESS because priority %"
              G_GUINT64_FORMAT " is higher than currently nominated pair %"
              G_GUINT64_FORMAT, agent,
              p, p->priority, highest_nominated_priority);
          in_progress++;
        }
      }
    }
    i = next;
  }

  return in_progress;
}

/*
 * Schedules a triggered check after a successfully inbound 
 * connectivity check. Implements ICE sect 7.2.1.4 "Triggered Checks" (ID-19).
 * 
 * @param agent self pointer
 * @param component the check is related to
 * @param local_socket socket from which the inbound check was received
 * @param remote_cand remote candidate from which the inbound check was sent
 */
static gboolean priv_schedule_triggered_check (NiceAgent *agent, NiceStream *stream, NiceComponent *component, NiceSocket *local_socket, NiceCandidate *remote_cand)
{
  GSList *i;
  NiceCandidate *local = NULL;

  g_assert (remote_cand != NULL);

  for (i = stream->conncheck_list; i ; i = i->next) {
      CandidateCheckPair *p = i->data;
      if (p->component_id == component->id &&
	  p->remote == remote_cand &&
          ((p->local->transport == NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE &&
              p->sockptr == local_socket) ||
              (p->local->transport != NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE &&
                  p->local->sockptr == local_socket))) {
        /* We don't check for p->sockptr because in the case of
         * tcp-active we don't want to retrigger a check on a pair that
         * was FAILED when a peer-reflexive pair was created */

        if (p->succeeded_pair != NULL) {
          g_assert (p->state == NICE_CHECK_DISCOVERED);
          p = p->succeeded_pair;
        }

	nice_debug ("Agent %p : Found a matching pair %p (%s) (%s) ...",
            agent, p, p->foundation, priv_state_to_string (p->state));
	
        switch (p->state) {
	  case NICE_CHECK_WAITING:
          case NICE_CHECK_FROZEN:
            nice_debug ("Agent %p : pair %p added for a triggered check.",
                agent, p);
            priv_add_pair_to_triggered_check_queue (agent, p);
            break;
          case NICE_CHECK_IN_PROGRESS:
            /* note: according to ICE SPEC sect 7.2.1.4 "Triggered Checks"
             * we cancel the in-progress transaction, and after the
             * retransmission timeout, we create a new connectivity check
             * for that pair.  The controlling role of this new check may
             * be different from the role of this cancelled check.
             *
             * note: the flag retransmit_on_timeout unset means that
             * another pair, with a higher priority is already nominated,
             * so there's no reason to recheck this pair, since it can in
             * no way replace the nominated one.
             */
            if (!nice_socket_is_reliable (p->sockptr) &&
                p->retransmit_on_timeout) {
                nice_debug ("Agent %p : pair %p will be rechecked "
                    "on stun timer timeout.", agent, p);
                /* this flag will determine the action at the retransmission
                 * timeout of the stun timer
                 */
                p->recheck_on_timeout = TRUE;
            }
            break;
	  case NICE_CHECK_SUCCEEDED:
            nice_debug ("Agent %p : nothing to do for pair %p.", agent, p);
            /* note: this is a bit unsure corner-case -- let's do the
               same state update as for processing responses to our own checks */
            /* note: this update is required by the dribble test, to
             * ensure the transition ready -> connected -> ready, because
             * an incoming stun request generates a discovered peer reflexive,
             * that causes the ready -> connected transition.
             */
            priv_update_check_list_state_for_ready (agent, stream, component);
            break;
          case NICE_CHECK_FAILED:
            /* 7.2.1.4 Triggered Checks
             * If the state of the pair is Failed, it is changed to Waiting
             * and the agent MUST create a new connectivity check for that
             * pair (representing a new STUN Binding request transaction), by
             * enqueueing the pair in the triggered check queue.
             *
             * note: the flag retransmit_on_timeout unset means that
             * another pair, with a higher priority is already nominated,
             * we apply the same strategy than with an in-progress pair
             * above.
             */
            if (p->retransmit_on_timeout) {
              nice_debug ("Agent %p : pair %p added for a triggered check.",
                  agent, p);
              priv_add_pair_to_triggered_check_queue (agent, p);
              /* If the component for this pair is in failed state, move it
               * back to connecting, and reinitiate the timers
               */
              if (component->state == NICE_COMPONENT_STATE_FAILED) {
                agent_signal_component_state_change (agent, stream->id,
                    component->id, NICE_COMPONENT_STATE_CONNECTING);
                conn_check_schedule_next (agent);
              }
            }
            break;
          default:
            break;
        }

	/* note: the spec says the we SHOULD retransmit in-progress
	 *       checks immediately, but we won't do that now */

	return TRUE;
      }
  }

  for (i = component->local_candidates; i ; i = i->next) {
    local = i->data;
    if (local->sockptr == local_socket)
      break;
  }

  if (i) {
    nice_debug ("Agent %p : Adding a triggered check to conn.check list (local=%p).", agent, local);
    priv_add_new_check_pair (agent, stream->id, component,
        local, remote_cand, NICE_CHECK_WAITING);
    return TRUE;
  }
  else {
    nice_debug ("Agent %p : Didn't find a matching pair for triggered check (remote-cand=%p).", agent, remote_cand);
    return FALSE;
  }
}


/*
 * Sends a reply to an successfully received STUN connectivity 
 * check request. Implements parts of the ICE spec section 7.2 (STUN
 * Server Procedures).
 *
 * @param agent context pointer
 * @param stream which stream (of the agent)
 * @param component which component (of the stream)
 * @param rcand remote candidate from which the request came, if NULL,
 *        the response is sent immediately but no other processing is done
 * @param toaddr address to which reply is sent
 * @param socket the socket over which the request came
 * @param rbuf_len length of STUN message to send
 * @param msg the STUN message to send
 * @param use_candidate whether the request had USE_CANDIDATE attribute
 * 
 * @pre (rcand == NULL || nice_address_equal(rcand->addr, toaddr) == TRUE)
 */
static void priv_reply_to_conn_check (NiceAgent *agent, NiceStream *stream,
    NiceComponent *component, NiceCandidate *lcand, NiceCandidate *rcand,
    const NiceAddress *toaddr, NiceSocket *sockptr, size_t rbuf_len,
    StunMessage *msg, gboolean use_candidate)
{
  g_assert (rcand == NULL || nice_address_equal(&rcand->addr, toaddr) == TRUE);

  if (nice_debug_is_enabled ()) {
    gchar tmpbuf[INET6_ADDRSTRLEN];
    nice_address_to_string (toaddr, tmpbuf);
    nice_debug ("Agent %p : STUN-CC RESP to '%s:%u', socket=%u, len=%u, cand=%p (c-id:%u), use-cand=%d.", agent,
	     tmpbuf,
	     nice_address_get_port (toaddr),
             sockptr->fileno ? g_socket_get_fd(sockptr->fileno) : -1,
	     (unsigned)rbuf_len,
	     rcand, component->id,
	     (int)use_candidate);
  }

  agent_socket_send (sockptr, toaddr, rbuf_len, (const gchar*)msg->buffer);
  if (agent->compatibility == NICE_COMPATIBILITY_OC2007R2) {
    ms_ice2_legacy_conncheck_send(msg, sockptr, toaddr);
  }

  if (rcand) {
    priv_schedule_triggered_check (agent, stream, component, sockptr, rcand);
    if (use_candidate)
      priv_mark_pair_nominated (agent, stream, component, lcand, rcand);
  }
}

/*
 * Stores information of an incoming STUN connectivity check
 * for later use. This is only needed when a check is received
 * before we get information about the remote candidates (via
 * SDP or other signaling means).
 *
 * @return non-zero on error, zero on success
 */
static int priv_store_pending_check (NiceAgent *agent, NiceComponent *component,
    const NiceAddress *from, NiceSocket *sockptr, uint8_t *username,
    uint16_t username_len, uint32_t priority, gboolean use_candidate)
{
  IncomingCheck *icheck;
  nice_debug ("Agent %p : Storing pending check.", agent);

  if (component->incoming_checks &&
      g_slist_length (component->incoming_checks) >= 
      NICE_AGENT_MAX_REMOTE_CANDIDATES) {
    nice_debug ("Agent %p : WARN: unable to store information for early incoming check.", agent);
    return -1;
  }

  icheck = g_slice_new0 (IncomingCheck);
  component->incoming_checks = g_slist_append (component->incoming_checks, icheck);
  icheck->from = *from;
  icheck->local_socket = sockptr;
  icheck->priority = priority;
  icheck->use_candidate = use_candidate;
  icheck->username_len = username_len;
  icheck->username = NULL;
  if (username_len > 0)
    icheck->username = g_memdup (username, username_len);

  return 0;
}

/*
 * Adds a new pair, discovered from an incoming STUN response, to 
 * the connectivity check list.
 *
 * @return created pair, or NULL on fatal (memory allocation) errors
 */
static CandidateCheckPair *priv_add_peer_reflexive_pair (NiceAgent *agent, guint stream_id, NiceComponent *component, NiceCandidate *local_cand, CandidateCheckPair *parent_pair)
{
  CandidateCheckPair *pair = g_slice_new0 (CandidateCheckPair);
  NiceStream *stream = agent_find_stream (agent, stream_id);

  pair->agent = agent;
  pair->stream_id = stream_id;
  pair->component_id = component->id;;
  pair->local = local_cand;
  pair->remote = parent_pair->remote;
  pair->sockptr = local_cand->sockptr;
  pair->state = NICE_CHECK_DISCOVERED;
  parent_pair->discovered_pair = pair;
  pair->succeeded_pair = parent_pair;
  nice_debug ("Agent %p : new pair %p state DISCOVERED", agent, pair);
  {
      gchar tmpbuf1[INET6_ADDRSTRLEN];
      gchar tmpbuf2[INET6_ADDRSTRLEN];
      nice_address_to_string (&pair->local->addr, tmpbuf1);
      nice_address_to_string (&pair->remote->addr, tmpbuf2);
      nice_debug ("Agent %p : new pair %p : [%s]:%u --> [%s]:%u", agent, pair,
          tmpbuf1, nice_address_get_port (&pair->local->addr),
          tmpbuf2, nice_address_get_port (&pair->remote->addr));
  }
  g_snprintf (pair->foundation, NICE_CANDIDATE_PAIR_MAX_FOUNDATION, "%s:%s",
      local_cand->foundation, parent_pair->remote->foundation);
  if (agent->controlling_mode == TRUE)
    pair->priority = nice_candidate_pair_priority (pair->local->priority,
        pair->remote->priority);
  else
    pair->priority = nice_candidate_pair_priority (pair->remote->priority,
        pair->local->priority);
  pair->nominated = FALSE;
  pair->prflx_priority = ensure_unique_priority (component,
      peer_reflexive_candidate_priority (agent, local_cand));
  nice_debug ("Agent %p : added a new peer-discovered pair with foundation of '%s'.",  agent, pair->foundation);

  stream->conncheck_list = g_slist_insert_sorted (stream->conncheck_list, pair,
      (GCompareFunc)conn_check_compare);

  return pair;
}

/*
 * Recalculates priorities of all candidate pairs. This
 * is required after a conflict in ICE roles.
 */
static void priv_recalculate_pair_priorities (NiceAgent *agent)
{
  GSList *i, *j;

  for (i = agent->streams; i; i = i->next) {
    NiceStream *stream = i->data;
    for (j = stream->conncheck_list; j; j = j->next) {
      CandidateCheckPair *p = j->data;
      p->priority = agent_candidate_pair_priority (agent, p->local, p->remote);
    }
    stream->conncheck_list = g_slist_sort (stream->conncheck_list,
        (GCompareFunc)conn_check_compare);
  }
}

/*
 * Change the agent role if different from 'control'. Can be
 * initiated both by handling of incoming connectivity checks,
 * and by processing the responses to checks sent by us.
 */
static void priv_check_for_role_conflict (NiceAgent *agent, gboolean control)
{
  /* role conflict, change mode; wait for a new conn. check */
  if (control != agent->controlling_mode) {
    nice_debug ("Agent %p : Role conflict, changing agent role to \"%s\".",
        agent, control ? "controlling" : "controlled");
    agent->controlling_mode = control;
    /* the pair priorities depend on the roles, so recalculation
     * is needed */
    priv_recalculate_pair_priorities (agent);
  }
  else 
    nice_debug ("Agent %p : Role conflict, staying with role \"%s\".",
        agent, control ? "controlling" : "controlled");
}

/*
 * Checks whether the mapped address in connectivity check response 
 * matches any of the known local candidates. If not, apply the
 * mechanism for "Discovering Peer Reflexive Candidates" ICE ID-19)
 *
 * @param agent context pointer
 * @param stream which stream (of the agent)
 * @param component which component (of the stream)
 * @param p the connectivity check pair for which we got a response
 * @param socketptr socket used to send the reply
 * @param mapped_sockaddr mapped address in the response
 *
 * @return pointer to a candidate pair, found in conncheck list or newly created
 */
static CandidateCheckPair *priv_process_response_check_for_reflexive(NiceAgent *agent, NiceStream *stream, NiceComponent *component, CandidateCheckPair *p, NiceSocket *sockptr, struct sockaddr *mapped_sockaddr, NiceCandidate *local_candidate, NiceCandidate *remote_candidate)
{
  CandidateCheckPair *new_pair = NULL;
  NiceAddress mapped;
  GSList *i, *j;
  NiceCandidate *local_cand = NULL;

  nice_address_set_from_sockaddr (&mapped, mapped_sockaddr);

  for (j = component->local_candidates; j; j = j->next) {
    NiceCandidate *cand = j->data;
    if (nice_address_equal (&mapped, &cand->addr)) {
      local_cand = cand;

      /* We always need to select the peer-reflexive Candidate Pair in the case
       * of a TCP-ACTIVE local candidate, so we find it even if an incoming
       * check matched an existing pair because it could be the original
       * ACTIVE-PASSIVE candidate pair which was retriggered */
      for (i = stream->conncheck_list; i; i = i->next) {
        CandidateCheckPair *pair = i->data;
        if (pair->local == cand && remote_candidate == pair->remote) {
          new_pair = pair;
          break;
        }
      }
      break;
    }
  }

  if (new_pair) {
    /* note: when new_pair is distinct from p, it means new_pair is a
     * previously discovered peer-reflexive candidate pair, so we don't
     * set the valid flag on p in this case, because the valid flag is
     * already set on the discovered pair.
     */
    if (new_pair == p)
      p->valid = TRUE;
    p->state = NICE_CHECK_SUCCEEDED;
    /* note: we cancel the potential in-progress transaction
     * cancellation, caused by sect 7.2.1.4 "Triggered Checks", if
     * we receive a valid reply before transmission timeout...
     */
    p->recheck_on_timeout = FALSE;
    /* ... or just after the transmission timeout, while the pair is
     * temporarily put on the triggered check list on the way to be
     * be rechecked: we remove it from the list too.
     */
    priv_remove_pair_from_triggered_check_queue (agent, p);
    nice_debug ("Agent %p : conncheck %p SUCCEEDED.", agent, p);
    nice_component_add_valid_candidate (component, remote_candidate);
  }
  else {
    if (!local_cand) {
      if (!agent->force_relay) {
        /* step: find a new local candidate, see RFC 5245 7.1.3.2.1.
         * "Discovering Peer Reflexive Candidates"
         */
        local_cand = discovery_add_peer_reflexive_candidate (agent,
                                                             stream->id,
                                                             component->id,
                                                            &mapped,
                                                             sockptr,
                                                             local_candidate,
                                                             remote_candidate);
        nice_debug ("Agent %p : added a new peer-reflexive local candidate %p",
            agent, local_cand);
      }
    }

    /* step: add a new discovered pair (see RFC 5245 7.1.3.2.2
	       "Constructing a Valid Pair") */
    if (local_cand)
      new_pair = priv_add_peer_reflexive_pair (agent, stream->id, component,
          local_cand, p);
    /* note: this is same as "adding to VALID LIST" in the spec
       text */
    if (new_pair)
      new_pair->valid = TRUE;
    /* step: The agent sets the state of the pair that *generated* the check to
     * Succeeded, RFC 5245, 7.1.3.2.3, "Updating Pair States"
     */
    p->state = NICE_CHECK_SUCCEEDED;
    p->recheck_on_timeout = FALSE;
    priv_remove_pair_from_triggered_check_queue (agent, p);
    nice_debug ("Agent %p : conncheck %p SUCCEEDED, %p DISCOVERED.",
        agent, p, new_pair);
  }

  if (new_pair && new_pair->valid)
    nice_component_add_valid_candidate (component, remote_candidate);


  return new_pair;
}

/*
 * Tries to match STUN reply in 'buf' to an existing STUN connectivity
 * check transaction. If found, the reply is processed. Implements
 * section 7.1.2 "Processing the Response" of ICE spec (ID-19).
 *
 * @return TRUE if a matching transaction is found
 */
static gboolean priv_map_reply_to_conn_check_request (NiceAgent *agent, NiceStream *stream, NiceComponent *component, NiceSocket *sockptr, const NiceAddress *from, NiceCandidate *local_candidate, NiceCandidate *remote_candidate, StunMessage *resp)
{
  union {
    struct sockaddr_storage storage;
    struct sockaddr addr;
  } sockaddr;
  socklen_t socklen = sizeof (sockaddr);
  GSList *i;
  StunUsageIceReturn res;
  StunTransactionId discovery_id;
  StunTransactionId response_id;
  stun_message_id (resp, response_id);

  for (i = stream->conncheck_list; i; i = i->next) {
    CandidateCheckPair *p = i->data;

    if (p->stun_message.buffer == NULL)
      continue;

    stun_message_id (&p->stun_message, discovery_id);

    if (memcmp (discovery_id, response_id, sizeof(StunTransactionId)))
      continue;

    res = stun_usage_ice_conncheck_process (resp,
        &sockaddr.storage, &socklen,
        agent_to_ice_compatibility (agent));
    nice_debug ("Agent %p : stun_bind_process/conncheck for %p: "
        "%s,res=%s.",
        agent, p,
        agent->controlling_mode ? "controlling" : "controlled",
        priv_ice_return_to_string (res));

    if (res == STUN_USAGE_ICE_RETURN_SUCCESS ||
        res == STUN_USAGE_ICE_RETURN_NO_MAPPED_ADDRESS) {
      /* case: found a matching connectivity check request */

      CandidateCheckPair *ok_pair = NULL;

      nice_debug ("Agent %p : conncheck %p MATCHED.", agent, p);
      p->stun_message.buffer = NULL;
      p->stun_message.buffer_len = 0;

      /* step: verify that response came from the same IP address we
       *       sent the original request to (see 7.1.2.1. "Failure
       *       Cases") */
      if (nice_address_equal (from, &p->remote->addr) == FALSE) {

        p->state = NICE_CHECK_FAILED;
        if (nice_debug_is_enabled ()) {
          gchar tmpbuf[INET6_ADDRSTRLEN];
          gchar tmpbuf2[INET6_ADDRSTRLEN];
          nice_debug ("Agent %p : conncheck %p FAILED"
              " (mismatch of source address).", agent, p);
          nice_address_to_string (&p->remote->addr, tmpbuf);
          nice_address_to_string (from, tmpbuf2);
          nice_debug ("Agent %p : '%s:%u' != '%s:%u'", agent,
              tmpbuf, nice_address_get_port (&p->remote->addr),
              tmpbuf2, nice_address_get_port (from));
        }
        return TRUE;
      }

      /* note: CONNECTED but not yet READY, see docs */

      /* step: handle the possible case of a peer-reflexive
       *       candidate where the mapped-address in response does
       *       not match any local candidate, see 7.1.2.2.1
       *       "Discovering Peer Reflexive Candidates" ICE ID-19) */

      if (res == STUN_USAGE_ICE_RETURN_NO_MAPPED_ADDRESS) {
        p->state = NICE_CHECK_SUCCEEDED;
        p->valid = TRUE;
        nice_debug ("Agent %p : Mapped address not found."
            " conncheck %p SUCCEEDED.", agent, p);
        nice_component_add_valid_candidate (component, p->remote);
      } else
        ok_pair = priv_process_response_check_for_reflexive (agent,
            stream, component, p, sockptr, &sockaddr.addr,
            local_candidate, remote_candidate);

      /* note: The success of this check might also
       * cause the state of other checks to change as well, ICE
       * spec 7.1.3.2.3
       */
      priv_conn_check_unfreeze_related (agent, stream, p);

      /* Note: this assignment helps to reduce the numbers of cases
       * to be tested. If ok_pair and p refer to distinct pairs, it
       * means that ok_pair is a discovered peer reflexive one,
       * caused by the check made on pair p.  In that case, the
       * flags to be tested are on p, but the nominated flag will be
       * set on ok_pair. When there's no discovered pair, p and
       * ok_pair refer to the same pair.
       * To summarize : p is a SUCCEEDED pair, ok_pair is a
       * DISCOVERED, VALID, and eventually NOMINATED pair. 
       */
      if (!ok_pair)
        ok_pair = p;

      /* step: updating nominated flag (ICE 7.1.2.2.4 "Updating the
         Nominated Flag" (ID-19) */
      if (NICE_AGENT_IS_COMPATIBLE_WITH_RFC5245_OR_OC2007R2 (agent)) {
        nice_debug ("Agent %p : Updating nominated flag (%s): "
            "ok_pair=%p (%d/%d) p=%p (%d/%d) (ucnc/mnora)",
            agent, p->local->transport == NICE_CANDIDATE_TRANSPORT_UDP ?
              "UDP" : "TCP",
            ok_pair, ok_pair->use_candidate_on_next_check,
            ok_pair->mark_nominated_on_response_arrival,
            p, p->use_candidate_on_next_check,
            p->mark_nominated_on_response_arrival);

        if (agent->controlling_mode) {
          switch (agent->nomination_mode) {
            case NICE_NOMINATION_MODE_REGULAR:
              if (p->use_candidate_on_next_check) {
                nice_debug ("Agent %p : marking pair %p (%s) as nominated "
                    "(regular nomination, controlling, "
                    "use_cand_on_next_check=1).",
                    agent, ok_pair, ok_pair->foundation);
                ok_pair->nominated = TRUE;
              }
              break;
            case NICE_NOMINATION_MODE_AGGRESSIVE:
              if (!p->nominated) {
                nice_debug ("Agent %p : marking pair %p (%s) as nominated "
                    "(aggressive nomination, controlling).",
                    agent, ok_pair, ok_pair->foundation);
                ok_pair->nominated = TRUE;
              }
              break;
            default:
              /* Nothing to do */
              break;
          }
        } else {
          if (p->mark_nominated_on_response_arrival) {
            nice_debug ("Agent %p : marking pair %p (%s) as nominated "
                "(%s nomination, controlled, mark_on_response=1).",
                agent, ok_pair, ok_pair->foundation,
                agent->nomination_mode == NICE_NOMINATION_MODE_AGGRESSIVE ?
                  "aggressive" : "regular");
            ok_pair->nominated = TRUE;
          }
        }
      }

      if (ok_pair->nominated == TRUE) {
        priv_update_selected_pair (agent, component, ok_pair);
        priv_print_conn_check_lists (agent, G_STRFUNC,
            ", got a nominated pair");

        /* Do not step down to CONNECTED if we're already at state READY*/
        if (component->state != NICE_COMPONENT_STATE_READY)
          /* step: notify the client of a new component state (must be done
           *       before the possible check list state update step */
          agent_signal_component_state_change (agent,
              stream->id, component->id, NICE_COMPONENT_STATE_CONNECTED);
      }

      /* step: update pair states (ICE 7.1.2.2.3 "Updating pair
         states" and 8.1.2 "Updating States", ID-19) */
      priv_update_check_list_state_for_ready (agent, stream, component);
    } else if (res == STUN_USAGE_ICE_RETURN_ROLE_CONFLICT) {
      /* case: role conflict error, need to restart with new role */
      nice_debug ("Agent %p : conncheck %p ROLE CONFLICT, restarting", agent, p);

      /* note: this res value indicates that the role of the peer
       * agent has not changed after the tie-breaker comparison, so
       * this is our role that must change. see ICE sect. 7.1.3.1
       * "Failure Cases". Our role might already have changed due to
       * an earlier incoming request, but if not, change role now.
       *
       * Sect. 7.1.3.1 is not clear on this point, but we choose to
       * put the candidate pair in the triggered check list even
       * when the agent did not switch its role. The reason for this
       * interpretation is that the reception of the stun reply, even
       * an error reply, is a good sign that this pair will be
       * valid, if we retry the check after the role of both peers
       * has been fixed.
       */

      if (p->stun_message.buffer != NULL) {
        guint64 tie;
        gboolean controlled_mode;

        controlled_mode = (stun_message_find64 (&p->stun_message,
            STUN_ATTRIBUTE_ICE_CONTROLLED, &tie) ==
            STUN_MESSAGE_RETURN_SUCCESS);

        priv_check_for_role_conflict (agent, controlled_mode);

        p->stun_message.buffer = NULL;
        p->stun_message.buffer_len = 0;
        priv_add_pair_to_triggered_check_queue (agent, p);
      }
    } else {
      /* case: STUN error, the check STUN context was freed */
      nice_debug ("Agent %p : conncheck %p FAILED.", agent, p);
      p->stun_message.buffer = NULL;
      p->stun_message.buffer_len = 0;
    }
    return TRUE;
  }

  return FALSE;
}

/*
 * Tries to match STUN reply in 'buf' to an existing STUN discovery
 * transaction. If found, a reply is sent.
 *
 * @return TRUE if a matching transaction is found
 */
static gboolean priv_map_reply_to_discovery_request (NiceAgent *agent, StunMessage *resp)
{
  union {
    struct sockaddr_storage storage;
    struct sockaddr addr;
  } sockaddr;
  socklen_t socklen = sizeof (sockaddr);

  union {
    struct sockaddr_storage storage;
    struct sockaddr addr;
  } alternate;
  socklen_t alternatelen = sizeof (sockaddr);

  GSList *i;
  StunUsageBindReturn res;
  gboolean trans_found = FALSE;
  StunTransactionId discovery_id;
  StunTransactionId response_id;
  stun_message_id (resp, response_id);

  for (i = agent->discovery_list; i && trans_found != TRUE; i = i->next) {
    CandidateDiscovery *d = i->data;

    if (d->type == NICE_CANDIDATE_TYPE_SERVER_REFLEXIVE &&
        d->stun_message.buffer) {
      stun_message_id (&d->stun_message, discovery_id);

      if (memcmp (discovery_id, response_id, sizeof(StunTransactionId)) == 0) {
        res = stun_usage_bind_process (resp, &sockaddr.addr,
            &socklen, &alternate.addr, &alternatelen);
        nice_debug ("Agent %p : stun_bind_process/disc for %p res %d.",
            agent, d, (int)res);

        if (res == STUN_USAGE_BIND_RETURN_ALTERNATE_SERVER) {
          /* handle alternate server */
          NiceAddress niceaddr;
          nice_address_set_from_sockaddr (&niceaddr, &alternate.addr);
          d->server = niceaddr;

          d->pending = FALSE;
        } else if (res == STUN_USAGE_BIND_RETURN_SUCCESS) {
          /* case: successful binding discovery, create a new local candidate */

          if (!agent->force_relay) {
            NiceAddress niceaddr;

            nice_address_set_from_sockaddr (&niceaddr, &sockaddr.addr);
            discovery_add_server_reflexive_candidate (
                d->agent,
                d->stream->id,
                d->component->id,
                &niceaddr,
                NICE_CANDIDATE_TRANSPORT_UDP,
                d->nicesock,
                FALSE);
            if (d->agent->use_ice_tcp)
              discovery_discover_tcp_server_reflexive_candidates (
                  d->agent,
                  d->stream->id,
                  d->component->id,
                  &niceaddr,
                  d->nicesock);
          }
          d->stun_message.buffer = NULL;
          d->stun_message.buffer_len = 0;
          d->done = TRUE;
          trans_found = TRUE;
        } else if (res == STUN_USAGE_BIND_RETURN_ERROR) {
          /* case: STUN error, the check STUN context was freed */
          d->stun_message.buffer = NULL;
          d->stun_message.buffer_len = 0;
          d->done = TRUE;
          trans_found = TRUE;
        }
      }
    }
  }

  return trans_found;
}


static CandidateRefresh *
priv_add_new_turn_refresh (CandidateDiscovery *cdisco, NiceCandidate *relay_cand,
    guint lifetime)
{
  CandidateRefresh *cand;
  NiceAgent *agent = cdisco->agent;

  cand = g_slice_new0 (CandidateRefresh);
  agent->refresh_list = g_slist_append (agent->refresh_list, cand);

  cand->candidate = relay_cand;
  cand->nicesock = cdisco->nicesock;
  cand->server = cdisco->server;
  cand->stream = cdisco->stream;
  cand->component = cdisco->component;
  cand->agent = cdisco->agent;
  memcpy (&cand->stun_agent, &cdisco->stun_agent, sizeof(StunAgent));

  /* Use previous stun response for authentication credentials */
  if (cdisco->stun_resp_msg.buffer != NULL) {
    memcpy(cand->stun_resp_buffer, cdisco->stun_resp_buffer,
        sizeof(cand->stun_resp_buffer));
    memcpy(&cand->stun_resp_msg, &cdisco->stun_resp_msg, sizeof(StunMessage));
    cand->stun_resp_msg.buffer = cand->stun_resp_buffer;
    cand->stun_resp_msg.agent = NULL;
    cand->stun_resp_msg.key = NULL;
  }

  nice_debug ("Agent %p : Adding new refresh candidate %p with timeout %d",
      agent, cand, (lifetime - 60) * 1000);

  /* step: also start the refresh timer */
  /* refresh should be sent 1 minute before it expires */
  agent_timeout_add_with_context (agent, &cand->timer_source,
      "Candidate TURN refresh",
      (lifetime - 60) * 1000, priv_turn_allocate_refresh_tick, cand);

  nice_debug ("timer source is : %p", cand->timer_source);

  return cand;
}

/*
 * Tries to match STUN reply in 'buf' to an existing STUN discovery
 * transaction. If found, a reply is sent.
 * 
 * @return TRUE if a matching transaction is found
 */
static gboolean priv_map_reply_to_relay_request (NiceAgent *agent, StunMessage *resp)
{
  union {
    struct sockaddr_storage storage;
    struct sockaddr addr;
  } sockaddr;
  socklen_t socklen = sizeof (sockaddr);

  union {
    struct sockaddr_storage storage;
    struct sockaddr addr;
  } alternate;
  socklen_t alternatelen = sizeof (alternate);

  union {
    struct sockaddr_storage storage;
    struct sockaddr addr;
  } relayaddr;
  socklen_t relayaddrlen = sizeof (relayaddr);

  uint32_t lifetime;
  uint32_t bandwidth;
  GSList *i;
  StunUsageTurnReturn res;
  gboolean trans_found = FALSE;
  StunTransactionId discovery_id;
  StunTransactionId response_id;
  stun_message_id (resp, response_id);

  for (i = agent->discovery_list; i && trans_found != TRUE; i = i->next) {
    CandidateDiscovery *d = i->data;

    if (d->type == NICE_CANDIDATE_TYPE_RELAYED &&
        d->stun_message.buffer) {
      stun_message_id (&d->stun_message, discovery_id);

      if (memcmp (discovery_id, response_id, sizeof(StunTransactionId)) == 0) {
        res = stun_usage_turn_process (resp,
            &relayaddr.storage, &relayaddrlen,
            &sockaddr.storage, &socklen,
            &alternate.storage, &alternatelen,
            &bandwidth, &lifetime, agent_to_turn_compatibility (agent));
        nice_debug ("Agent %p : stun_turn_process/disc for %p res %d.",
            agent, d, (int)res);

        if (res == STUN_USAGE_TURN_RETURN_ALTERNATE_SERVER) {
          /* handle alternate server */
          nice_address_set_from_sockaddr (&d->server, &alternate.addr);
          nice_address_set_from_sockaddr (&d->turn->server, &alternate.addr);

          d->pending = FALSE;
        } else if (res == STUN_USAGE_TURN_RETURN_RELAY_SUCCESS ||
                   res == STUN_USAGE_TURN_RETURN_MAPPED_SUCCESS) {
          /* case: successful allocate, create a new local candidate */
          NiceAddress niceaddr;
          NiceCandidate *relay_cand;

          if (res == STUN_USAGE_TURN_RETURN_MAPPED_SUCCESS) {
            /* We also received our mapped address */
            nice_address_set_from_sockaddr (&niceaddr, &sockaddr.addr);

            /* TCP or TLS TURNS means the server-reflexive address was
             * on a TCP connection, which cannot be used for server-reflexive
             * discovery of candidates.
             */
            if (d->turn->type == NICE_RELAY_TYPE_TURN_UDP &&
                !agent->force_relay) {
              discovery_add_server_reflexive_candidate (
                  d->agent,
                  d->stream->id,
                  d->component->id,
                  &niceaddr,
                  NICE_CANDIDATE_TRANSPORT_UDP,
                  d->nicesock,
                  FALSE);
            }
            if (d->agent->use_ice_tcp)
              discovery_discover_tcp_server_reflexive_candidates (
                  d->agent,
                  d->stream->id,
                  d->component->id,
                  &niceaddr,
                  d->nicesock);
          }

          nice_address_set_from_sockaddr (&niceaddr, &relayaddr.addr);
          if (nice_socket_is_reliable (d->nicesock)) {
            relay_cand = discovery_add_relay_candidate (
                d->agent,
                d->stream->id,
                d->component->id,
                &niceaddr,
                NICE_CANDIDATE_TRANSPORT_TCP_ACTIVE,
                d->nicesock,
                d->turn);

            if (relay_cand) {
              if (agent->compatibility == NICE_COMPATIBILITY_OC2007 ||
                  agent->compatibility == NICE_COMPATIBILITY_OC2007R2) {
                nice_udp_turn_socket_set_ms_realm(relay_cand->sockptr,
                    &d->stun_message);
                nice_udp_turn_socket_set_ms_connection_id(relay_cand->sockptr,
                    resp);
              } else {
                priv_add_new_turn_refresh (d, relay_cand, lifetime);
              }
            }

            relay_cand = discovery_add_relay_candidate (
                d->agent,
                d->stream->id,
                d->component->id,
                &niceaddr,
                NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE,
                d->nicesock,
                d->turn);
          } else {
            relay_cand = discovery_add_relay_candidate (
                d->agent,
                d->stream->id,
                d->component->id,
                &niceaddr,
                NICE_CANDIDATE_TRANSPORT_UDP,
                d->nicesock,
                d->turn);
          }

          if (relay_cand) {
	    if (d->stun_resp_msg.buffer)
	      nice_udp_turn_socket_cache_realm_nonce (relay_cand->sockptr,
                  &d->stun_resp_msg);
            if (agent->compatibility == NICE_COMPATIBILITY_OC2007 ||
                agent->compatibility == NICE_COMPATIBILITY_OC2007R2) {
              /* These data are needed on TURN socket when sending requests,
               * but never reach nice_turn_socket_parse_recv() where it could
               * be read directly, as the socket does not exist when allocate
               * response arrives to _nice_agent_recv(). We must set them right
               * after socket gets created in discovery_add_relay_candidate(),
               * so we are doing it here. */
              nice_udp_turn_socket_set_ms_realm(relay_cand->sockptr,
                  &d->stun_message);
              nice_udp_turn_socket_set_ms_connection_id(relay_cand->sockptr,
                  resp);
            } else {
              priv_add_new_turn_refresh (d, relay_cand, lifetime);
            }

            /* In case a new candidate has been added */
            conn_check_schedule_next (agent);
          }

          d->stun_message.buffer = NULL;
          d->stun_message.buffer_len = 0;
          d->done = TRUE;
          trans_found = TRUE;
        } else if (res == STUN_USAGE_TURN_RETURN_ERROR) {
          int code = -1;
          uint8_t *sent_realm = NULL;
          uint8_t *recv_realm = NULL;
          uint16_t sent_realm_len = 0;
          uint16_t recv_realm_len = 0;

          sent_realm = (uint8_t *) stun_message_find (&d->stun_message,
              STUN_ATTRIBUTE_REALM, &sent_realm_len);
          recv_realm = (uint8_t *) stun_message_find (resp,
              STUN_ATTRIBUTE_REALM, &recv_realm_len);

          /* check for unauthorized error response */
          if ((agent->compatibility == NICE_COMPATIBILITY_RFC5245 ||
               agent->compatibility == NICE_COMPATIBILITY_OC2007  ||
               agent->compatibility == NICE_COMPATIBILITY_OC2007R2) &&
              stun_message_get_class (resp) == STUN_ERROR &&
              stun_message_find_error (resp, &code) ==
              STUN_MESSAGE_RETURN_SUCCESS &&
              recv_realm != NULL && recv_realm_len > 0) {

            if (code == 438 ||
                (code == 401 &&
                    !(recv_realm_len == sent_realm_len &&
                        sent_realm != NULL &&
                        memcmp (sent_realm, recv_realm, sent_realm_len) == 0))) {
              d->stun_resp_msg = *resp;
              memcpy (d->stun_resp_buffer, resp->buffer,
                  stun_message_length (resp));
              d->stun_resp_msg.buffer = d->stun_resp_buffer;
              d->stun_resp_msg.buffer_len = sizeof(d->stun_resp_buffer);
              d->pending = FALSE;
            } else {
              /* case: a real unauthorized error */
              d->stun_message.buffer = NULL;
              d->stun_message.buffer_len = 0;
              d->done = TRUE;
            }
          } else {
            /* case: STUN error, the check STUN context was freed */
            d->stun_message.buffer = NULL;
            d->stun_message.buffer_len = 0;
            d->done = TRUE;
          }
          trans_found = TRUE;
        }
      }
    }
  }

  return trans_found;
}


/*
 * Tries to match STUN reply in 'buf' to an existing STUN discovery
 * transaction. If found, a reply is sent.
 * 
 * @return TRUE if a matching transaction is found
 */
static gboolean priv_map_reply_to_relay_refresh (NiceAgent *agent, StunMessage *resp)
{
  uint32_t lifetime;
  GSList *i;
  StunUsageTurnReturn res;
  gboolean trans_found = FALSE;
  StunTransactionId refresh_id;
  StunTransactionId response_id;
  stun_message_id (resp, response_id);

  for (i = agent->refresh_list; i && trans_found != TRUE; i = i->next) {
    CandidateRefresh *cand = i->data;

    if (cand->stun_message.buffer) {
      stun_message_id (&cand->stun_message, refresh_id);

      if (memcmp (refresh_id, response_id, sizeof(StunTransactionId)) == 0) {
        res = stun_usage_turn_refresh_process (resp,
            &lifetime, agent_to_turn_compatibility (cand->agent));
        nice_debug ("Agent %p : stun_turn_refresh_process for %p res %d.",
            agent, cand, (int)res);
        if (res == STUN_USAGE_TURN_RETURN_RELAY_SUCCESS) {
          /* refresh should be sent 1 minute before it expires */
          agent_timeout_add_with_context (cand->agent, &cand->timer_source,
              "Candidate TURN refresh", (lifetime - 60) * 1000,
              priv_turn_allocate_refresh_tick, cand);

          g_source_destroy (cand->tick_source);
          g_source_unref (cand->tick_source);
          cand->tick_source = NULL;
        } else if (res == STUN_USAGE_TURN_RETURN_ERROR) {
          int code = -1;
          uint8_t *sent_realm = NULL;
          uint8_t *recv_realm = NULL;
          uint16_t sent_realm_len = 0;
          uint16_t recv_realm_len = 0;

          sent_realm = (uint8_t *) stun_message_find (&cand->stun_message,
              STUN_ATTRIBUTE_REALM, &sent_realm_len);
          recv_realm = (uint8_t *) stun_message_find (resp,
              STUN_ATTRIBUTE_REALM, &recv_realm_len);

          /* check for unauthorized error response */
          if (cand->agent->compatibility == NICE_COMPATIBILITY_RFC5245 &&
              stun_message_get_class (resp) == STUN_ERROR &&
              stun_message_find_error (resp, &code) ==
              STUN_MESSAGE_RETURN_SUCCESS &&
              recv_realm != NULL && recv_realm_len > 0) {

            if (code == 438 ||
                (code == 401 &&
                    !(recv_realm_len == sent_realm_len &&
                        sent_realm != NULL &&
                        memcmp (sent_realm, recv_realm, sent_realm_len) == 0))) {
              cand->stun_resp_msg = *resp;
              memcpy (cand->stun_resp_buffer, resp->buffer,
                  stun_message_length (resp));
              cand->stun_resp_msg.buffer = cand->stun_resp_buffer;
              cand->stun_resp_msg.buffer_len = sizeof(cand->stun_resp_buffer);
              priv_turn_allocate_refresh_tick_unlocked (cand);
            } else {
              /* case: a real unauthorized error */
              refresh_cancel (cand);
            }
          } else {
            /* case: STUN error, the check STUN context was freed */
              refresh_cancel (cand);
          }
          trans_found = TRUE;
        }
      }
    }
  }

  return trans_found;
}


static gboolean priv_map_reply_to_keepalive_conncheck (NiceAgent *agent,
    NiceComponent *component, StunMessage *resp)
{
  StunTransactionId conncheck_id;
  StunTransactionId response_id;
  stun_message_id (resp, response_id);

  if (component->selected_pair.keepalive.stun_message.buffer) {
      stun_message_id (&component->selected_pair.keepalive.stun_message,
          conncheck_id);
      if (memcmp (conncheck_id, response_id, sizeof(StunTransactionId)) == 0) {
        nice_debug ("Agent %p : Keepalive for selected pair received.",
            agent);
        if (component->selected_pair.keepalive.tick_source) {
          g_source_destroy (component->selected_pair.keepalive.tick_source);
          g_source_unref (component->selected_pair.keepalive.tick_source);
          component->selected_pair.keepalive.tick_source = NULL;
        }
        component->selected_pair.keepalive.stun_message.buffer = NULL;
        return TRUE;
      }
  }

  return FALSE;
}


typedef struct {
  NiceAgent *agent;
  NiceStream *stream;
  NiceComponent *component;
  uint8_t *password;
} conncheck_validater_data;

static bool conncheck_stun_validater (StunAgent *agent,
    StunMessage *message, uint8_t *username, uint16_t username_len,
    uint8_t **password, size_t *password_len, void *user_data)
{
  conncheck_validater_data *data = (conncheck_validater_data*) user_data;
  GSList *i;
  gchar *ufrag = NULL;
  gsize ufrag_len;

  gboolean msn_msoc_nice_compatibility =
      data->agent->compatibility == NICE_COMPATIBILITY_MSN ||
      data->agent->compatibility == NICE_COMPATIBILITY_OC2007;

  if (data->agent->compatibility == NICE_COMPATIBILITY_OC2007 &&
      stun_message_get_class (message) == STUN_RESPONSE)
    i = data->component->remote_candidates;
  else
    i = data->component->local_candidates;

  for (; i; i = i->next) {
    NiceCandidate *cand = i->data;

    ufrag = NULL;
    if (cand->username)
      ufrag = cand->username;
    else if (data->stream)
      ufrag = data->stream->local_ufrag;
    ufrag_len = ufrag? strlen (ufrag) : 0;

    if (ufrag && msn_msoc_nice_compatibility)
      ufrag = (gchar *)g_base64_decode (ufrag, &ufrag_len);

    if (ufrag == NULL)
      continue;

    stun_debug ("Comparing username/ufrag of len %d and %" G_GSIZE_FORMAT ", equal=%d",
        username_len, ufrag_len, username_len >= ufrag_len ?
        memcmp (username, ufrag, ufrag_len) : 0);
    stun_debug_bytes ("  username: ", username, username_len);
    stun_debug_bytes ("  ufrag:    ", ufrag, ufrag_len);
    if (ufrag_len > 0 && username_len >= ufrag_len &&
        memcmp (username, ufrag, ufrag_len) == 0) {
      gchar *pass = NULL;

      if (cand->password)
        pass = cand->password;
      else if(data->stream->local_password[0])
        pass = data->stream->local_password;

      if (pass) {
        *password = (uint8_t *) pass;
        *password_len = strlen (pass);

        if (msn_msoc_nice_compatibility) {
          gsize pass_len;

          data->password = g_base64_decode (pass, &pass_len);
          *password = data->password;
          *password_len = pass_len;
        }
      }

      if (msn_msoc_nice_compatibility)
        g_free (ufrag);

      stun_debug ("Found valid username, returning password: '%s'", *password);
      return TRUE;
    }

    if (msn_msoc_nice_compatibility)
      g_free (ufrag);
  }

  return FALSE;
}


/*
 * Processing an incoming STUN message.
 *
 * @param agent self pointer
 * @param stream stream the packet is related to
 * @param component component the packet is related to
 * @param nicesock socket from which the packet was received
 * @param from address of the sender
 * @param buf message contents
 * @param buf message length
 *
 * @pre contents of 'buf' is a STUN message
 *
 * @return XXX (what FALSE means exactly?)
 */
gboolean conn_check_handle_inbound_stun (NiceAgent *agent, NiceStream *stream,
    NiceComponent *component, NiceSocket *nicesock, const NiceAddress *from,
    gchar *buf, guint len)
{
  union {
    struct sockaddr_storage storage;
    struct sockaddr addr;
  } sockaddr;
  uint8_t rbuf[MAX_STUN_DATAGRAM_PAYLOAD];
  ssize_t res;
  size_t rbuf_len = sizeof (rbuf);
  bool control = agent->controlling_mode;
  uint8_t uname[NICE_STREAM_MAX_UNAME];
  guint uname_len;
  uint8_t *username;
  uint16_t username_len;
  StunMessage req;
  StunMessage msg;
  StunValidationStatus valid;
  conncheck_validater_data validater_data = {agent, stream, component, NULL};
  GSList *i, *j;
  NiceCandidate *remote_candidate = NULL;
  NiceCandidate *remote_candidate2 = NULL;
  NiceCandidate *local_candidate = NULL;
  gboolean discovery_msg = FALSE;

  nice_address_copy_to_sockaddr (from, &sockaddr.addr);

  /* note: contents of 'buf' already validated, so it is
   *       a valid and fully received STUN message */

  if (nice_debug_is_enabled ()) {
    gchar tmpbuf[INET6_ADDRSTRLEN];
    nice_address_to_string (from, tmpbuf);
    nice_debug ("Agent %p: inbound STUN packet for %u/%u (stream/component) from [%s]:%u (%u octets) :",
        agent, stream->id, component->id, tmpbuf, nice_address_get_port (from), len);
  }

  /* note: ICE  7.2. "STUN Server Procedures" (ID-19) */

  valid = stun_agent_validate (&component->stun_agent, &req,
      (uint8_t *) buf, len, conncheck_stun_validater, &validater_data);

  /* Check for discovery candidates stun agents */
  if (valid == STUN_VALIDATION_BAD_REQUEST ||
      valid == STUN_VALIDATION_UNMATCHED_RESPONSE) {
    for (i = agent->discovery_list; i; i = i->next) {
      CandidateDiscovery *d = i->data;
      if (d->stream == stream && d->component == component &&
          d->nicesock == nicesock) {
        valid = stun_agent_validate (&d->stun_agent, &req,
            (uint8_t *) buf, len, conncheck_stun_validater, &validater_data);

        if (valid == STUN_VALIDATION_UNMATCHED_RESPONSE)
          continue;

        discovery_msg = TRUE;
        break;
      }
    }
  }
  /* Check for relay refresh stun agents */
  if (valid == STUN_VALIDATION_BAD_REQUEST ||
      valid == STUN_VALIDATION_UNMATCHED_RESPONSE) {
    for (i = agent->refresh_list; i; i = i->next) {
      CandidateRefresh *r = i->data;

      nice_debug_verbose ("Comparing %p to %p, %p to %p and %p and %p to %p",
          r->stream, stream, r->component, component, r->nicesock,
          r->candidate->sockptr, nicesock);

      if (r->stream == stream && r->component == component &&
          (r->nicesock == nicesock || r->candidate->sockptr == nicesock)) {
        valid = stun_agent_validate (&r->stun_agent, &req,
            (uint8_t *) buf, len, conncheck_stun_validater, &validater_data);
        nice_debug ("Validating gave %d", valid);
        if (valid == STUN_VALIDATION_UNMATCHED_RESPONSE)
          continue;
        discovery_msg = TRUE;
        break;
      }
    }
  }

  g_free (validater_data.password);

  if (valid == STUN_VALIDATION_NOT_STUN ||
      valid == STUN_VALIDATION_INCOMPLETE_STUN ||
      valid == STUN_VALIDATION_BAD_REQUEST)
  {
    nice_debug ("Agent %p : Incorrectly multiplexed STUN message ignored.",
        agent);
    return FALSE;
  }

  if (valid == STUN_VALIDATION_UNKNOWN_REQUEST_ATTRIBUTE) {
    nice_debug ("Agent %p : Unknown mandatory attributes in message.", agent);

    if (agent->compatibility != NICE_COMPATIBILITY_MSN &&
        agent->compatibility != NICE_COMPATIBILITY_OC2007) {
      rbuf_len = stun_agent_build_unknown_attributes_error (&component->stun_agent,
          &msg, rbuf, rbuf_len, &req);
      if (rbuf_len != 0)
        agent_socket_send (nicesock, from, rbuf_len, (const gchar*)rbuf);
    }
    return TRUE;
  }

  if (valid == STUN_VALIDATION_UNAUTHORIZED) {
    nice_debug ("Agent %p : Integrity check failed.", agent);

    if (stun_agent_init_error (&component->stun_agent, &msg, rbuf, rbuf_len,
            &req, STUN_ERROR_UNAUTHORIZED)) {
      rbuf_len = stun_agent_finish_message (&component->stun_agent, &msg, NULL, 0);
      if (rbuf_len > 0 && agent->compatibility != NICE_COMPATIBILITY_MSN &&
          agent->compatibility != NICE_COMPATIBILITY_OC2007)
        agent_socket_send (nicesock, from, rbuf_len, (const gchar*)rbuf);
    }
    return TRUE;
  }
  if (valid == STUN_VALIDATION_UNAUTHORIZED_BAD_REQUEST) {
    nice_debug ("Agent %p : Integrity check failed - bad request.", agent);
    if (stun_agent_init_error (&component->stun_agent, &msg, rbuf, rbuf_len,
            &req, STUN_ERROR_BAD_REQUEST)) {
      rbuf_len = stun_agent_finish_message (&component->stun_agent, &msg, NULL, 0);
      if (rbuf_len > 0 && agent->compatibility != NICE_COMPATIBILITY_MSN &&
	  agent->compatibility != NICE_COMPATIBILITY_OC2007)
        agent_socket_send (nicesock, from, rbuf_len, (const gchar*)rbuf);
    }
    return TRUE;
  }

  username = (uint8_t *) stun_message_find (&req, STUN_ATTRIBUTE_USERNAME,
					    &username_len);

  for (i = component->remote_candidates; i; i = i->next) {
    NiceCandidate *cand = i->data;
    if (nice_address_equal (from, &cand->addr)) {
      remote_candidate = cand;
      break;
    }
  }
  for (i = component->local_candidates; i; i = i->next) {
    NiceCandidate *cand = i->data;
    if (nice_address_equal (&nicesock->addr, &cand->addr)) {
      local_candidate = cand;
      break;
    }
  }

  if (agent->compatibility == NICE_COMPATIBILITY_GOOGLE ||
      agent->compatibility == NICE_COMPATIBILITY_MSN ||
      agent->compatibility == NICE_COMPATIBILITY_OC2007) {
    /* We need to find which local candidate was used */
    for (i = component->remote_candidates;
         i != NULL && remote_candidate2 == NULL; i = i->next) {
      for (j = component->local_candidates; j; j = j->next) {
        gboolean inbound = TRUE;
        NiceCandidate *rcand = i->data;
        NiceCandidate *lcand = j->data;

        /* If we receive a response, then the username is local:remote */
        if (agent->compatibility != NICE_COMPATIBILITY_MSN) {
          if (stun_message_get_class (&req) == STUN_REQUEST ||
              stun_message_get_class (&req) == STUN_INDICATION) {
            inbound = TRUE;
          } else {
            inbound = FALSE;
          }
        }

        uname_len = priv_create_username (agent, stream,
            component->id,  rcand, lcand,
            uname, sizeof (uname), inbound);



        stun_debug ("Comparing usernames of size %d and %d: %d",
            username_len, uname_len, username && uname_len == username_len &&
            memcmp (username, uname, uname_len) == 0);
        stun_debug_bytes ("  First username: ", username,
            username ? username_len : 0);
        stun_debug_bytes ("  Second uname:   ", uname, uname_len);

        if (username &&
            uname_len == username_len &&
            memcmp (uname, username, username_len) == 0) {
          local_candidate = lcand;
          remote_candidate2 = rcand;
          break;
        }
      }
    }
  }

  if (component->remote_candidates &&
      agent->compatibility == NICE_COMPATIBILITY_GOOGLE &&
      local_candidate == NULL &&
      discovery_msg == FALSE) {
    /* if we couldn't match the username and the stun agent has
       IGNORE_CREDENTIALS then we have an integrity check failing.
       This could happen with the race condition of receiving connchecks
       before the remote candidates are added. Just drop the message, and let
       the retransmissions make it work. */
    nice_debug ("Agent %p : Username check failed.", agent);
    return TRUE;
  }

  if (valid != STUN_VALIDATION_SUCCESS) {
    nice_debug ("Agent %p : STUN message is unsuccessfull %d, ignoring", agent, valid);
    return FALSE;
  }


  if (stun_message_get_class (&req) == STUN_REQUEST) {
    if (   agent->compatibility == NICE_COMPATIBILITY_MSN
        || agent->compatibility == NICE_COMPATIBILITY_OC2007) {
      if (local_candidate && remote_candidate2) {
        gsize key_len;

	if (agent->compatibility == NICE_COMPATIBILITY_MSN) {
          username = (uint8_t *) stun_message_find (&req,
	  STUN_ATTRIBUTE_USERNAME, &username_len);
	  uname_len = priv_create_username (agent, stream,
              component->id,  remote_candidate2, local_candidate,
	      uname, sizeof (uname), FALSE);
	  memcpy (username, uname, MIN (uname_len, username_len));

	  req.key = g_base64_decode ((gchar *) remote_candidate2->password,
              &key_len);
          req.key_len = key_len;
	} else if (agent->compatibility == NICE_COMPATIBILITY_OC2007) {
          req.key = g_base64_decode ((gchar *) local_candidate->password,
              &key_len);
          req.key_len = key_len;
	}
      } else {
        nice_debug ("Agent %p : received MSN incoming check from unknown remote candidate. "
            "Ignoring request", agent);
        return TRUE;
      }
    }

    rbuf_len = sizeof (rbuf);
    res = stun_usage_ice_conncheck_create_reply (&component->stun_agent, &req,
        &msg, rbuf, &rbuf_len, &sockaddr.storage, sizeof (sockaddr),
        &control, agent->tie_breaker,
        agent_to_ice_compatibility (agent));

    if (   agent->compatibility == NICE_COMPATIBILITY_MSN
        || agent->compatibility == NICE_COMPATIBILITY_OC2007) {
      g_free (req.key);
    }

    if (res == STUN_USAGE_ICE_RETURN_ROLE_CONFLICT)
      priv_check_for_role_conflict (agent, control);

    if (res == STUN_USAGE_ICE_RETURN_SUCCESS ||
        res == STUN_USAGE_ICE_RETURN_ROLE_CONFLICT) {
      /* case 1: valid incoming request, send a reply/error */
      bool use_candidate =
          stun_usage_ice_conncheck_use_candidate (&req);
      uint32_t priority = stun_usage_ice_conncheck_priority (&req);

      if (agent->compatibility == NICE_COMPATIBILITY_GOOGLE ||
          agent->compatibility == NICE_COMPATIBILITY_MSN ||
          agent->compatibility == NICE_COMPATIBILITY_OC2007)
        use_candidate = TRUE;

      if (stream->initial_binding_request_received != TRUE)
        agent_signal_initial_binding_request_received (agent, stream);

      if (remote_candidate == NULL) {
	nice_debug ("Agent %p : No matching remote candidate for incoming check ->"
            "peer-reflexive candidate.", agent);
	remote_candidate = discovery_learn_remote_peer_reflexive_candidate (
            agent, stream, component, priority, from, nicesock,
            local_candidate,
            remote_candidate2 ? remote_candidate2 : remote_candidate);
        if(remote_candidate && stream->remote_ufrag[0]) {
          if (local_candidate &&
              local_candidate->transport == NICE_CANDIDATE_TRANSPORT_TCP_PASSIVE) {
            CandidateCheckPair *pair;

            pair = priv_conn_check_add_for_candidate_pair_matched (agent,
                stream->id, component, local_candidate, remote_candidate,
                NICE_CHECK_SUCCEEDED);
            if (pair) {
              pair->valid = TRUE;
            }
          } else
            conn_check_add_for_candidate (agent, stream->id, component, remote_candidate);
        }
      }

      nice_component_add_valid_candidate (component, remote_candidate);

      priv_reply_to_conn_check (agent, stream, component, local_candidate,
          remote_candidate, from, nicesock, rbuf_len, &msg, use_candidate);

      if (stream->remote_ufrag[0] == 0) {
        /* case: We've got a valid binding request to a local candidate
         *       but we do not yet know remote credentials.
         *       As per sect 7.2 of ICE (ID-19), we send a reply
         *       immediately but postpone all other processing until
         *       we get information about the remote candidates */

        /* step: send a reply immediately but postpone other processing */
        priv_store_pending_check (agent, component, from, nicesock,
            username, username_len, priority, use_candidate);
      }
    } else {
      nice_debug ("Agent %p : Invalid STUN packet, ignoring... %s",
          agent, strerror(errno));
      return FALSE;
    }
  } else {
      /* case 2: not a new request, might be a reply...  */
      gboolean trans_found = FALSE;

      /* note: ICE sect 7.1.2. "Processing the Response" (ID-19) */

      /* step: let's try to match the response to an existing check context */
      if (trans_found != TRUE)
        trans_found = priv_map_reply_to_conn_check_request (agent, stream,
	    component, nicesock, from, local_candidate, remote_candidate, &req);

      /* step: let's try to match the response to an existing discovery */
      if (trans_found != TRUE)
        trans_found = priv_map_reply_to_discovery_request (agent, &req);

      /* step: let's try to match the response to an existing turn allocate */
      if (trans_found != TRUE)
        trans_found = priv_map_reply_to_relay_request (agent, &req);

      /* step: let's try to match the response to an existing turn refresh */
      if (trans_found != TRUE)
        trans_found = priv_map_reply_to_relay_refresh (agent, &req);

      /* step: let's try to match the response to an existing keepalive conncheck */
      if (trans_found != TRUE)
        trans_found = priv_map_reply_to_keepalive_conncheck (agent, component,
            &req);

      if (trans_found != TRUE)
        nice_debug ("Agent %p : Unable to match to an existing transaction, "
            "probably a keepalive.", agent);
  }

  return TRUE;
}

/* Remove all pointers to the given @sock from the connection checking process.
 * These are entirely NiceCandidates pointed to from various places. */
void
conn_check_prune_socket (NiceAgent *agent, NiceStream *stream, NiceComponent *component,
    NiceSocket *sock)
{
  GSList *l;

  if (component->selected_pair.local &&
      component->selected_pair.local->sockptr == sock &&
      component->state == NICE_COMPONENT_STATE_READY) {
    nice_debug ("Agent %p: Selected pair socket %p has been destroyed, "
        "declaring failed", agent, sock);
    agent_signal_component_state_change (agent,
        stream->id, component->id, NICE_COMPONENT_STATE_FAILED);
  }

  /* Prune from the candidate check pairs. */
  for (l = stream->conncheck_list; l != NULL;) {
    CandidateCheckPair *p = l->data;
    GSList *next = l->next;

    if ((p->local != NULL && p->local->sockptr == sock) ||
        (p->remote != NULL && p->remote->sockptr == sock) ||
        (p->sockptr == sock)) {
      nice_debug ("Agent %p : Retransmissions failed, giving up on "
          "connectivity check %p", agent, p);
      candidate_check_pair_fail (stream, agent, p);
      conn_check_free_item (p);
      stream->conncheck_list = g_slist_delete_link (stream->conncheck_list, l);
    }

    l = next;
  }
}