ext/webrtc/gstwebrtcbin.c

/* GStreamer
 * Copyright (C) 2017 Matthew Waters <matthew@centricular.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include "gstwebrtcbin.h"
#include "gstwebrtcstats.h"
#include "transportstream.h"
#include "transportreceivebin.h"
#include "utils.h"
#include "webrtcsdp.h"
#include "webrtctransceiver.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define RANDOM_SESSION_ID \
    ((((((guint64) g_random_int()) << 32) | \
       (guint64) g_random_int ())) & \
    G_GUINT64_CONSTANT (0x7fffffffffffffff))

#define PC_GET_LOCK(w) (&w->priv->pc_lock)
#define PC_LOCK(w) (g_mutex_lock (PC_GET_LOCK(w)))
#define PC_UNLOCK(w) (g_mutex_unlock (PC_GET_LOCK(w)))

#define PC_GET_COND(w) (&w->priv->pc_cond)
#define PC_COND_WAIT(w) (g_cond_wait(PC_GET_COND(w), PC_GET_LOCK(w)))
#define PC_COND_BROADCAST(w) (g_cond_broadcast(PC_GET_COND(w)))
#define PC_COND_SIGNAL(w) (g_cond_signal(PC_GET_COND(w)))

/*
 * This webrtcbin implements the majority of the W3's peerconnection API and
 * implementation guide where possible. Generating offers, answers and setting
 * local and remote SDP's are all supported.  To start with, only the media
 * interface has been implemented (no datachannel yet).
 *
 * Each input/output pad is equivalent to a Track in W3 parlance which are
 * added/removed from the bin.  The number of requested sink pads is the number
 * of streams that will be sent to the receiver and will be associated with a
 * GstWebRTCRTPTransceiver (very similar to W3 RTPTransceiver's).
 *
 * On the receiving side, RTPTransceiver's are created in response to setting
 * a remote description.  Output pads for the receiving streams in the set
 * description are also created.
 */

/*
 * TODO:
 * assert sending payload type matches the stream
 * reconfiguration (of anything)
 * LS groups
 * bundling
 * setting custom DTLS certificates
 * data channel
 *
 * seperate session id's from mlineindex properly
 * how to deal with replacing a input/output track/stream
 */

static void _update_need_negotiation (GstWebRTCBin * webrtc);

#define GST_CAT_DEFAULT gst_webrtc_bin_debug
GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);

GQuark
gst_webrtc_bin_error_quark (void)
{
  return g_quark_from_static_string ("gst-webrtc-bin-error-quark");
}

G_DEFINE_TYPE (GstWebRTCBinPad, gst_webrtc_bin_pad, GST_TYPE_GHOST_PAD);

static void
gst_webrtc_bin_pad_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
  switch (prop_id) {
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
gst_webrtc_bin_pad_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec)
{
  switch (prop_id) {
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
gst_webrtc_bin_pad_finalize (GObject * object)
{
  GstWebRTCBinPad *pad = GST_WEBRTC_BIN_PAD (object);

  if (pad->trans)
    gst_object_unref (pad->trans);
  pad->trans = NULL;

  if (pad->received_caps)
    gst_caps_unref (pad->received_caps);
  pad->received_caps = NULL;

  G_OBJECT_CLASS (gst_webrtc_bin_pad_parent_class)->finalize (object);
}

static void
gst_webrtc_bin_pad_class_init (GstWebRTCBinPadClass * klass)
{
  GObjectClass *gobject_class = (GObjectClass *) klass;

  gobject_class->get_property = gst_webrtc_bin_pad_get_property;
  gobject_class->set_property = gst_webrtc_bin_pad_set_property;
  gobject_class->finalize = gst_webrtc_bin_pad_finalize;
}

static GstCaps *
_transport_stream_get_caps_for_pt (TransportStream * stream, guint pt)
{
  guint i, len;

  len = stream->ptmap->len;
  for (i = 0; i < len; i++) {
    PtMapItem *item = &g_array_index (stream->ptmap, PtMapItem, i);
    if (item->pt == pt)
      return item->caps;
  }
  return NULL;
}

static gint
_transport_stream_get_pt (TransportStream * stream, const gchar * encoding_name)
{
  guint i;
  gint ret = 0;

  for (i = 0; i < stream->ptmap->len; i++) {
    PtMapItem *item = &g_array_index (stream->ptmap, PtMapItem, i);
    if (!gst_caps_is_empty (item->caps)) {
      GstStructure *s = gst_caps_get_structure (item->caps, 0);
      if (!g_strcmp0 (gst_structure_get_string (s, "encoding-name"),
              encoding_name)) {
        ret = item->pt;
        break;
      }
    }
  }

  return ret;
}

static gboolean
gst_webrtcbin_sink_event (GstPad * pad, GstObject * parent, GstEvent * event)
{
  GstWebRTCBinPad *wpad = GST_WEBRTC_BIN_PAD (pad);

  if (GST_EVENT_TYPE (event) == GST_EVENT_CAPS) {
    GstCaps *caps;
    gboolean do_update;

    gst_event_parse_caps (event, &caps);
    do_update = (!wpad->received_caps
        || gst_caps_is_equal (wpad->received_caps, caps));
    gst_caps_replace (&wpad->received_caps, caps);

    if (do_update)
      _update_need_negotiation (GST_WEBRTC_BIN (parent));
  }

  return gst_pad_event_default (pad, parent, event);
}

static void
gst_webrtc_bin_pad_init (GstWebRTCBinPad * pad)
{
}

static GstWebRTCBinPad *
gst_webrtc_bin_pad_new (const gchar * name, GstPadDirection direction)
{
  GstWebRTCBinPad *pad =
      g_object_new (gst_webrtc_bin_pad_get_type (), "name", name, "direction",
      direction, NULL);

  gst_pad_set_event_function (GST_PAD (pad), gst_webrtcbin_sink_event);

  if (!gst_ghost_pad_construct (GST_GHOST_PAD (pad))) {
    gst_object_unref (pad);
    return NULL;
  }

  GST_DEBUG_OBJECT (pad, "new visible pad with direction %s",
      direction == GST_PAD_SRC ? "src" : "sink");
  return pad;
}

#define gst_webrtc_bin_parent_class parent_class
G_DEFINE_TYPE_WITH_CODE (GstWebRTCBin, gst_webrtc_bin, GST_TYPE_BIN,
    GST_DEBUG_CATEGORY_INIT (gst_webrtc_bin_debug, "webrtcbin", 0,
        "webrtcbin element"););

static GstPad *_connect_input_stream (GstWebRTCBin * webrtc,
    GstWebRTCBinPad * pad);

static GstStaticPadTemplate sink_template = GST_STATIC_PAD_TEMPLATE ("sink_%u",
    GST_PAD_SINK,
    GST_PAD_REQUEST,
    GST_STATIC_CAPS ("application/x-rtp"));

static GstStaticPadTemplate src_template = GST_STATIC_PAD_TEMPLATE ("src_%u",
    GST_PAD_SRC,
    GST_PAD_SOMETIMES,
    GST_STATIC_CAPS ("application/x-rtp"));

enum
{
  SIGNAL_0,
  CREATE_OFFER_SIGNAL,
  CREATE_ANSWER_SIGNAL,
  SET_LOCAL_DESCRIPTION_SIGNAL,
  SET_REMOTE_DESCRIPTION_SIGNAL,
  ADD_ICE_CANDIDATE_SIGNAL,
  ON_NEGOTIATION_NEEDED_SIGNAL,
  ON_ICE_CANDIDATE_SIGNAL,
  ON_NEW_TRANSCEIVER_SIGNAL,
  GET_STATS_SIGNAL,
  ADD_TRANSCEIVER_SIGNAL,
  GET_TRANSCEIVERS_SIGNAL,
  LAST_SIGNAL,
};

enum
{
  PROP_0,
  PROP_CONNECTION_STATE,
  PROP_SIGNALING_STATE,
  PROP_ICE_GATHERING_STATE,
  PROP_ICE_CONNECTION_STATE,
  PROP_LOCAL_DESCRIPTION,
  PROP_CURRENT_LOCAL_DESCRIPTION,
  PROP_PENDING_LOCAL_DESCRIPTION,
  PROP_REMOTE_DESCRIPTION,
  PROP_CURRENT_REMOTE_DESCRIPTION,
  PROP_PENDING_REMOTE_DESCRIPTION,
  PROP_STUN_SERVER,
  PROP_TURN_SERVER,
};

static guint gst_webrtc_bin_signals[LAST_SIGNAL] = { 0 };

static GstWebRTCDTLSTransport *
_transceiver_get_transport (GstWebRTCRTPTransceiver * trans)
{
  if (trans->sender) {
    return trans->sender->transport;
  } else if (trans->receiver) {
    return trans->receiver->transport;
  }

  return NULL;
}

static GstWebRTCDTLSTransport *
_transceiver_get_rtcp_transport (GstWebRTCRTPTransceiver * trans)
{
  if (trans->sender) {
    return trans->sender->rtcp_transport;
  } else if (trans->receiver) {
    return trans->receiver->rtcp_transport;
  }

  return NULL;
}

typedef struct
{
  guint session_id;
  GstWebRTCICEStream *stream;
} IceStreamItem;

/* FIXME: locking? */
GstWebRTCICEStream *
_find_ice_stream_for_session (GstWebRTCBin * webrtc, guint session_id)
{
  int i;

  for (i = 0; i < webrtc->priv->ice_stream_map->len; i++) {
    IceStreamItem *item =
        &g_array_index (webrtc->priv->ice_stream_map, IceStreamItem, i);

    if (item->session_id == session_id) {
      GST_TRACE_OBJECT (webrtc, "Found ice stream id %" GST_PTR_FORMAT " for "
          "session %u", item->stream, session_id);
      return item->stream;
    }
  }

  GST_TRACE_OBJECT (webrtc, "No ice stream available for session %u",
      session_id);
  return NULL;
}

void
_add_ice_stream_item (GstWebRTCBin * webrtc, guint session_id,
    GstWebRTCICEStream * stream)
{
  IceStreamItem item = { session_id, stream };

  GST_TRACE_OBJECT (webrtc, "adding ice stream %" GST_PTR_FORMAT " for "
      "session %u", stream, session_id);
  g_array_append_val (webrtc->priv->ice_stream_map, item);
}

typedef struct
{
  guint session_id;
  gchar *mid;
} SessionMidItem;

static void
clear_session_mid_item (SessionMidItem * item)
{
  g_free (item->mid);
}

typedef gboolean (*FindTransceiverFunc) (GstWebRTCRTPTransceiver * p1,
    gconstpointer data);

static GstWebRTCRTPTransceiver *
_find_transceiver (GstWebRTCBin * webrtc, gconstpointer data,
    FindTransceiverFunc func)
{
  int i;

  for (i = 0; i < webrtc->priv->transceivers->len; i++) {
    GstWebRTCRTPTransceiver *transceiver =
        g_array_index (webrtc->priv->transceivers, GstWebRTCRTPTransceiver *,
        i);

    if (func (transceiver, data))
      return transceiver;
  }

  return NULL;
}

static gboolean
match_for_mid (GstWebRTCRTPTransceiver * trans, const gchar * mid)
{
  return g_strcmp0 (trans->mid, mid) == 0;
}

static gboolean
transceiver_match_for_mline (GstWebRTCRTPTransceiver * trans, guint * mline)
{
  return trans->mline == *mline;
}

static GstWebRTCRTPTransceiver *
_find_transceiver_for_mline (GstWebRTCBin * webrtc, guint mlineindex)
{
  GstWebRTCRTPTransceiver *trans;

  trans = _find_transceiver (webrtc, &mlineindex,
      (FindTransceiverFunc) transceiver_match_for_mline);

  GST_TRACE_OBJECT (webrtc,
      "Found transceiver %" GST_PTR_FORMAT " for mlineindex %u", trans,
      mlineindex);

  return trans;
}

typedef gboolean (*FindTransportFunc) (TransportStream * p1,
    gconstpointer data);

static TransportStream *
_find_transport (GstWebRTCBin * webrtc, gconstpointer data,
    FindTransportFunc func)
{
  int i;

  for (i = 0; i < webrtc->priv->transports->len; i++) {
    TransportStream *stream =
        g_array_index (webrtc->priv->transports, TransportStream *,
        i);

    if (func (stream, data))
      return stream;
  }

  return NULL;
}

static gboolean
match_stream_for_session (TransportStream * trans, guint * session)
{
  return trans->session_id == *session;
}

static TransportStream *
_find_transport_for_session (GstWebRTCBin * webrtc, guint session_id)
{
  TransportStream *stream;

  stream = _find_transport (webrtc, &session_id,
      (FindTransportFunc) match_stream_for_session);

  GST_TRACE_OBJECT (webrtc,
      "Found transport %" GST_PTR_FORMAT " for session %u", stream, session_id);

  return stream;
}

typedef gboolean (*FindPadFunc) (GstWebRTCBinPad * p1, gconstpointer data);

static GstWebRTCBinPad *
_find_pad (GstWebRTCBin * webrtc, gconstpointer data, FindPadFunc func)
{
  GstElement *element = GST_ELEMENT (webrtc);
  GList *l;

  GST_OBJECT_LOCK (webrtc);
  l = element->pads;
  for (; l; l = g_list_next (l)) {
    if (!GST_IS_WEBRTC_BIN_PAD (l->data))
      continue;
    if (func (l->data, data)) {
      gst_object_ref (l->data);
      GST_OBJECT_UNLOCK (webrtc);
      return l->data;
    }
  }

  l = webrtc->priv->pending_pads;
  for (; l; l = g_list_next (l)) {
    if (!GST_IS_WEBRTC_BIN_PAD (l->data))
      continue;
    if (func (l->data, data)) {
      gst_object_ref (l->data);
      GST_OBJECT_UNLOCK (webrtc);
      return l->data;
    }
  }
  GST_OBJECT_UNLOCK (webrtc);

  return NULL;
}

static void
_add_pad_to_list (GstWebRTCBin * webrtc, GstWebRTCBinPad * pad)
{
  GST_OBJECT_LOCK (webrtc);
  webrtc->priv->pending_pads = g_list_prepend (webrtc->priv->pending_pads, pad);
  GST_OBJECT_UNLOCK (webrtc);
}

static void
_remove_pending_pad (GstWebRTCBin * webrtc, GstWebRTCBinPad * pad)
{
  GST_OBJECT_LOCK (webrtc);
  webrtc->priv->pending_pads = g_list_remove (webrtc->priv->pending_pads, pad);
  GST_OBJECT_UNLOCK (webrtc);
}

static void
_add_pad (GstWebRTCBin * webrtc, GstWebRTCBinPad * pad)
{
  _remove_pending_pad (webrtc, pad);

  if (webrtc->priv->running)
    gst_pad_set_active (GST_PAD (pad), TRUE);
  gst_element_add_pad (GST_ELEMENT (webrtc), GST_PAD (pad));
}

static void
_remove_pad (GstWebRTCBin * webrtc, GstWebRTCBinPad * pad)
{
  _remove_pending_pad (webrtc, pad);

  gst_element_remove_pad (GST_ELEMENT (webrtc), GST_PAD (pad));
}

typedef struct
{
  GstPadDirection direction;
  guint mlineindex;
} MLineMatch;

static gboolean
pad_match_for_mline (GstWebRTCBinPad * pad, const MLineMatch * match)
{
  return GST_PAD_DIRECTION (pad) == match->direction
      && pad->mlineindex == match->mlineindex;
}

static GstWebRTCBinPad *
_find_pad_for_mline (GstWebRTCBin * webrtc, GstPadDirection direction,
    guint mlineindex)
{
  MLineMatch m = { direction, mlineindex };

  return _find_pad (webrtc, &m, (FindPadFunc) pad_match_for_mline);
}

typedef struct
{
  GstPadDirection direction;
  GstWebRTCRTPTransceiver *trans;
} TransMatch;

static gboolean
pad_match_for_transceiver (GstWebRTCBinPad * pad, TransMatch * m)
{
  return GST_PAD_DIRECTION (pad) == m->direction && pad->trans == m->trans;
}

static GstWebRTCBinPad *
_find_pad_for_transceiver (GstWebRTCBin * webrtc, GstPadDirection direction,
    GstWebRTCRTPTransceiver * trans)
{
  TransMatch m = { direction, trans };

  return _find_pad (webrtc, &m, (FindPadFunc) pad_match_for_transceiver);
}

#if 0
static gboolean
match_for_ssrc (GstWebRTCBinPad * pad, guint * ssrc)
{
  return pad->ssrc == *ssrc;
}

static gboolean
match_for_pad (GstWebRTCBinPad * pad, GstWebRTCBinPad * other)
{
  return pad == other;
}
#endif

static gboolean
_unlock_pc_thread (GMutex * lock)
{
  g_mutex_unlock (lock);
  return G_SOURCE_REMOVE;
}

static gpointer
_gst_pc_thread (GstWebRTCBin * webrtc)
{
  PC_LOCK (webrtc);
  webrtc->priv->main_context = g_main_context_new ();
  webrtc->priv->loop = g_main_loop_new (webrtc->priv->main_context, FALSE);

  PC_COND_BROADCAST (webrtc);
  g_main_context_invoke (webrtc->priv->main_context,
      (GSourceFunc) _unlock_pc_thread, PC_GET_LOCK (webrtc));

  /* Having the thread be the thread default GMainContext will break the
   * required queue-like ordering (from W3's peerconnection spec) of re-entrant
   * tasks */
  g_main_loop_run (webrtc->priv->loop);

  PC_LOCK (webrtc);
  g_main_context_unref (webrtc->priv->main_context);
  webrtc->priv->main_context = NULL;
  g_main_loop_unref (webrtc->priv->loop);
  webrtc->priv->loop = NULL;
  PC_COND_BROADCAST (webrtc);
  PC_UNLOCK (webrtc);

  return NULL;
}

static void
_start_thread (GstWebRTCBin * webrtc)
{
  PC_LOCK (webrtc);
  webrtc->priv->thread = g_thread_new ("gst-pc-ops",
      (GThreadFunc) _gst_pc_thread, webrtc);

  while (!webrtc->priv->loop)
    PC_COND_WAIT (webrtc);
  webrtc->priv->is_closed = FALSE;
  PC_UNLOCK (webrtc);
}

static void
_stop_thread (GstWebRTCBin * webrtc)
{
  PC_LOCK (webrtc);
  webrtc->priv->is_closed = TRUE;
  g_main_loop_quit (webrtc->priv->loop);
  while (webrtc->priv->loop)
    PC_COND_WAIT (webrtc);
  PC_UNLOCK (webrtc);

  g_thread_unref (webrtc->priv->thread);
}

static gboolean
_execute_op (GstWebRTCBinTask * op)
{
  PC_LOCK (op->webrtc);
  if (op->webrtc->priv->is_closed) {
    GST_DEBUG_OBJECT (op->webrtc,
        "Peerconnection is closed, aborting execution");
    goto out;
  }

  op->op (op->webrtc, op->data);

out:
  PC_UNLOCK (op->webrtc);
  return G_SOURCE_REMOVE;
}

static void
_free_op (GstWebRTCBinTask * op)
{
  if (op->notify)
    op->notify (op->data);
  g_free (op);
}

void
gst_webrtc_bin_enqueue_task (GstWebRTCBin * webrtc, GstWebRTCBinFunc func,
    gpointer data, GDestroyNotify notify)
{
  GstWebRTCBinTask *op;
  GSource *source;

  g_return_if_fail (GST_IS_WEBRTC_BIN (webrtc));

  if (webrtc->priv->is_closed) {
    GST_DEBUG_OBJECT (webrtc, "Peerconnection is closed, aborting execution");
    if (notify)
      notify (data);
    return;
  }
  op = g_new0 (GstWebRTCBinTask, 1);
  op->webrtc = webrtc;
  op->op = func;
  op->data = data;
  op->notify = notify;

  source = g_idle_source_new ();
  g_source_set_priority (source, G_PRIORITY_DEFAULT);
  g_source_set_callback (source, (GSourceFunc) _execute_op, op,
      (GDestroyNotify) _free_op);
  g_source_attach (source, webrtc->priv->main_context);
  g_source_unref (source);
}

/* https://www.w3.org/TR/webrtc/#dom-rtciceconnectionstate */
static GstWebRTCICEConnectionState
_collate_ice_connection_states (GstWebRTCBin * webrtc)
{
#define STATE(val) GST_WEBRTC_ICE_CONNECTION_STATE_ ## val
  GstWebRTCICEConnectionState any_state = 0;
  gboolean all_closed = TRUE;
  int i;

  for (i = 0; i < webrtc->priv->transceivers->len; i++) {
    GstWebRTCRTPTransceiver *rtp_trans =
        g_array_index (webrtc->priv->transceivers, GstWebRTCRTPTransceiver *,
        i);
    WebRTCTransceiver *trans = WEBRTC_TRANSCEIVER (rtp_trans);
    TransportStream *stream = trans->stream;
    GstWebRTCICETransport *transport, *rtcp_transport;
    GstWebRTCICEConnectionState ice_state;
    gboolean rtcp_mux = FALSE;

    if (rtp_trans->stopped)
      continue;
    if (!rtp_trans->mid)
      continue;

    g_object_get (stream, "rtcp-mux", &rtcp_mux, NULL);

    transport = _transceiver_get_transport (rtp_trans)->transport;

    /* get transport state */
    g_object_get (transport, "state", &ice_state, NULL);
    any_state |= (1 << ice_state);
    if (ice_state != STATE (CLOSED))
      all_closed = FALSE;

    rtcp_transport = _transceiver_get_rtcp_transport (rtp_trans)->transport;

    if (!rtcp_mux && rtcp_transport && transport != rtcp_transport) {
      g_object_get (rtcp_transport, "state", &ice_state, NULL);
      any_state |= (1 << ice_state);
      if (ice_state != STATE (CLOSED))
        all_closed = FALSE;
    }
  }

  GST_TRACE_OBJECT (webrtc, "ICE connection state: 0x%x", any_state);

  if (webrtc->priv->is_closed) {
    GST_TRACE_OBJECT (webrtc, "returning closed");
    return STATE (CLOSED);
  }
  /* Any of the RTCIceTransport s are in the failed state. */
  if (any_state & (1 << STATE (FAILED))) {
    GST_TRACE_OBJECT (webrtc, "returning failed");
    return STATE (FAILED);
  }
  /* Any of the RTCIceTransport s are in the disconnected state and
   * none of them are in the failed state. */
  if (any_state & (1 << STATE (DISCONNECTED))) {
    GST_TRACE_OBJECT (webrtc, "returning disconnected");
    return STATE (DISCONNECTED);
  }
  /* Any of the RTCIceTransport's are in the checking state and none of them
   * are in the failed or disconnected state. */
  if (any_state & (1 << STATE (CHECKING))) {
    GST_TRACE_OBJECT (webrtc, "returning checking");
    return STATE (CHECKING);
  }
  /* Any of the RTCIceTransport s are in the new state and none of them are
   * in the checking, failed or disconnected state, or all RTCIceTransport's
   * are in the closed state. */
  if ((any_state & (1 << STATE (NEW))) || all_closed) {
    GST_TRACE_OBJECT (webrtc, "returning new");
    return STATE (NEW);
  }
  /* All RTCIceTransport s are in the connected, completed or closed state
   * and at least one of them is in the connected state. */
  if (any_state & (1 << STATE (CONNECTED) | 1 << STATE (COMPLETED) | 1 <<
          STATE (CLOSED)) && any_state & (1 << STATE (CONNECTED))) {
    GST_TRACE_OBJECT (webrtc, "returning connected");
    return STATE (CONNECTED);
  }
  /* All RTCIceTransport s are in the completed or closed state and at least
   * one of them is in the completed state. */
  if (any_state & (1 << STATE (COMPLETED) | 1 << STATE (CLOSED))
      && any_state & (1 << STATE (COMPLETED))) {
    GST_TRACE_OBJECT (webrtc, "returning connected");
    return STATE (CONNECTED);
  }

  GST_FIXME ("unspecified situation, returning new");
  return STATE (NEW);
#undef STATE
}

/* https://www.w3.org/TR/webrtc/#dom-rtcicegatheringstate */
static GstWebRTCICEGatheringState
_collate_ice_gathering_states (GstWebRTCBin * webrtc)
{
#define STATE(val) GST_WEBRTC_ICE_GATHERING_STATE_ ## val
  GstWebRTCICEGatheringState any_state = 0;
  gboolean all_completed = webrtc->priv->transceivers->len > 0;
  int i;

  for (i = 0; i < webrtc->priv->transceivers->len; i++) {
    GstWebRTCRTPTransceiver *rtp_trans =
        g_array_index (webrtc->priv->transceivers, GstWebRTCRTPTransceiver *,
        i);
    WebRTCTransceiver *trans = WEBRTC_TRANSCEIVER (rtp_trans);
    TransportStream *stream = trans->stream;
    GstWebRTCICETransport *transport, *rtcp_transport;
    GstWebRTCICEGatheringState ice_state;
    gboolean rtcp_mux = FALSE;

    if (rtp_trans->stopped)
      continue;
    if (!rtp_trans->mid)
      continue;

    g_object_get (stream, "rtcp-mux", &rtcp_mux, NULL);

    transport = _transceiver_get_transport (rtp_trans)->transport;

    /* get gathering state */
    g_object_get (transport, "gathering-state", &ice_state, NULL);
    any_state |= (1 << ice_state);
    if (ice_state != STATE (COMPLETE))
      all_completed = FALSE;

    rtcp_transport = _transceiver_get_rtcp_transport (rtp_trans)->transport;

    if (!rtcp_mux && rtcp_transport && rtcp_transport != transport) {
      g_object_get (rtcp_transport, "gathering-state", &ice_state, NULL);
      any_state |= (1 << ice_state);
      if (ice_state != STATE (COMPLETE))
        all_completed = FALSE;
    }
  }

  GST_TRACE_OBJECT (webrtc, "ICE gathering state: 0x%x", any_state);

  /* Any of the RTCIceTransport s are in the gathering state. */
  if (any_state & (1 << STATE (GATHERING))) {
    GST_TRACE_OBJECT (webrtc, "returning gathering");
    return STATE (GATHERING);
  }
  /* At least one RTCIceTransport exists, and all RTCIceTransport s are in
   * the completed gathering state. */
  if (all_completed) {
    GST_TRACE_OBJECT (webrtc, "returning complete");
    return STATE (COMPLETE);
  }

  /* Any of the RTCIceTransport s are in the new gathering state and none
   * of the transports are in the gathering state, or there are no transports. */
  GST_TRACE_OBJECT (webrtc, "returning new");
  return STATE (NEW);
#undef STATE
}

/* https://www.w3.org/TR/webrtc/#rtcpeerconnectionstate-enum */
static GstWebRTCPeerConnectionState
_collate_peer_connection_states (GstWebRTCBin * webrtc)
{
#define STATE(v) GST_WEBRTC_PEER_CONNECTION_STATE_ ## v
#define ICE_STATE(v) GST_WEBRTC_ICE_CONNECTION_STATE_ ## v
#define DTLS_STATE(v) GST_WEBRTC_DTLS_TRANSPORT_STATE_ ## v
  GstWebRTCICEConnectionState any_ice_state = 0;
  GstWebRTCDTLSTransportState any_dtls_state = 0;
  int i;

  for (i = 0; i < webrtc->priv->transceivers->len; i++) {
    GstWebRTCRTPTransceiver *rtp_trans =
        g_array_index (webrtc->priv->transceivers, GstWebRTCRTPTransceiver *,
        i);
    WebRTCTransceiver *trans = WEBRTC_TRANSCEIVER (rtp_trans);
    TransportStream *stream = trans->stream;
    GstWebRTCDTLSTransport *transport, *rtcp_transport;
    GstWebRTCICEGatheringState ice_state;
    GstWebRTCDTLSTransportState dtls_state;
    gboolean rtcp_mux = FALSE;

    if (rtp_trans->stopped)
      continue;
    if (!rtp_trans->mid)
      continue;

    g_object_get (stream, "rtcp-mux", &rtcp_mux, NULL);
    transport = _transceiver_get_transport (rtp_trans);

    /* get transport state */
    g_object_get (transport, "state", &dtls_state, NULL);
    any_dtls_state |= (1 << dtls_state);
    g_object_get (transport->transport, "state", &ice_state, NULL);
    any_ice_state |= (1 << ice_state);

    rtcp_transport = _transceiver_get_rtcp_transport (rtp_trans);

    if (!rtcp_mux && rtcp_transport && rtcp_transport != transport) {
      g_object_get (rtcp_transport, "state", &dtls_state, NULL);
      any_dtls_state |= (1 << dtls_state);
      g_object_get (rtcp_transport->transport, "state", &ice_state, NULL);
      any_ice_state |= (1 << ice_state);
    }
  }

  GST_TRACE_OBJECT (webrtc, "ICE connection state: 0x%x. DTLS connection "
      "state: 0x%x", any_ice_state, any_dtls_state);

  /* The RTCPeerConnection object's [[ isClosed]] slot is true.  */
  if (webrtc->priv->is_closed) {
    GST_TRACE_OBJECT (webrtc, "returning closed");
    return STATE (CLOSED);
  }

  /* Any of the RTCIceTransport s or RTCDtlsTransport s are in a failed state. */
  if (any_ice_state & (1 << ICE_STATE (FAILED))) {
    GST_TRACE_OBJECT (webrtc, "returning failed");
    return STATE (FAILED);
  }
  if (any_dtls_state & (1 << DTLS_STATE (FAILED))) {
    GST_TRACE_OBJECT (webrtc, "returning failed");
    return STATE (FAILED);
  }

  /* Any of the RTCIceTransport's or RTCDtlsTransport's are in the connecting
   * or checking state and none of them is in the failed state. */
  if (any_ice_state & (1 << ICE_STATE (CHECKING))) {
    GST_TRACE_OBJECT (webrtc, "returning connecting");
    return STATE (CONNECTING);
  }
  if (any_dtls_state & (1 << DTLS_STATE (CONNECTING))) {
    GST_TRACE_OBJECT (webrtc, "returning connecting");
    return STATE (CONNECTING);
  }

  /* Any of the RTCIceTransport's or RTCDtlsTransport's are in the disconnected
   * state and none of them are in the failed or connecting or checking state. */
  if (any_ice_state & (1 << ICE_STATE (DISCONNECTED))) {
    GST_TRACE_OBJECT (webrtc, "returning disconnected");
    return STATE (DISCONNECTED);
  }

  /* All RTCIceTransport's and RTCDtlsTransport's are in the connected,
   * completed or closed state and at least of them is in the connected or
   * completed state. */
  if (!(any_ice_state & ~(1 << ICE_STATE (CONNECTED) | 1 <<
              ICE_STATE (COMPLETED) | 1 << ICE_STATE (CLOSED)))
      && !(any_dtls_state & ~(1 << DTLS_STATE (CONNECTED) | 1 <<
              DTLS_STATE (CLOSED)))
      && (any_ice_state & (1 << ICE_STATE (CONNECTED) | 1 <<
              ICE_STATE (COMPLETED))
          || any_dtls_state & (1 << DTLS_STATE (CONNECTED)))) {
    GST_TRACE_OBJECT (webrtc, "returning connected");
    return STATE (CONNECTED);
  }

  /* Any of the RTCIceTransport's or RTCDtlsTransport's are in the new state
   * and none of the transports are in the connecting, checking, failed or
   * disconnected state, or all transports are in the closed state. */
  if (!(any_ice_state & ~(1 << ICE_STATE (CLOSED)))) {
    GST_TRACE_OBJECT (webrtc, "returning new");
    return STATE (NEW);
  }
  if ((any_ice_state & (1 << ICE_STATE (NEW))
          || any_dtls_state & (1 << DTLS_STATE (NEW)))
      && !(any_ice_state & (1 << ICE_STATE (CHECKING) | 1 << ICE_STATE (FAILED)
              | (1 << ICE_STATE (DISCONNECTED))))
      && !(any_dtls_state & (1 << DTLS_STATE (CONNECTING) | 1 <<
              DTLS_STATE (FAILED)))) {
    GST_TRACE_OBJECT (webrtc, "returning new");
    return STATE (NEW);
  }

  GST_FIXME_OBJECT (webrtc, "Undefined situation detected, returning new");
  return STATE (NEW);
#undef DTLS_STATE
#undef ICE_STATE
#undef STATE
}

static void
_update_ice_gathering_state_task (GstWebRTCBin * webrtc, gpointer data)
{
  GstWebRTCICEGatheringState old_state = webrtc->ice_gathering_state;
  GstWebRTCICEGatheringState new_state;

  new_state = _collate_ice_gathering_states (webrtc);

  if (new_state != webrtc->ice_gathering_state) {
    gchar *old_s, *new_s;

    old_s = _enum_value_to_string (GST_TYPE_WEBRTC_ICE_GATHERING_STATE,
        old_state);
    new_s = _enum_value_to_string (GST_TYPE_WEBRTC_ICE_GATHERING_STATE,
        new_state);
    GST_INFO_OBJECT (webrtc, "ICE gathering state change from %s(%u) to %s(%u)",
        old_s, old_state, new_s, new_state);
    g_free (old_s);
    g_free (new_s);

    webrtc->ice_gathering_state = new_state;
    PC_UNLOCK (webrtc);
    g_object_notify (G_OBJECT (webrtc), "ice-gathering-state");
    PC_LOCK (webrtc);
  }
}

static void
_update_ice_gathering_state (GstWebRTCBin * webrtc)
{
  gst_webrtc_bin_enqueue_task (webrtc, _update_ice_gathering_state_task, NULL,
      NULL);
}

static void
_update_ice_connection_state_task (GstWebRTCBin * webrtc, gpointer data)
{
  GstWebRTCICEConnectionState old_state = webrtc->ice_connection_state;
  GstWebRTCICEConnectionState new_state;

  new_state = _collate_ice_connection_states (webrtc);

  if (new_state != old_state) {
    gchar *old_s, *new_s;

    old_s = _enum_value_to_string (GST_TYPE_WEBRTC_ICE_CONNECTION_STATE,
        old_state);
    new_s = _enum_value_to_string (GST_TYPE_WEBRTC_ICE_CONNECTION_STATE,
        new_state);
    GST_INFO_OBJECT (webrtc,
        "ICE connection state change from %s(%u) to %s(%u)", old_s, old_state,
        new_s, new_state);
    g_free (old_s);
    g_free (new_s);

    webrtc->ice_connection_state = new_state;
    PC_UNLOCK (webrtc);
    g_object_notify (G_OBJECT (webrtc), "ice-connection-state");
    PC_LOCK (webrtc);
  }
}

static void
_update_ice_connection_state (GstWebRTCBin * webrtc)
{
  gst_webrtc_bin_enqueue_task (webrtc, _update_ice_connection_state_task, NULL,
      NULL);
}

static void
_update_peer_connection_state_task (GstWebRTCBin * webrtc, gpointer data)
{
  GstWebRTCPeerConnectionState old_state = webrtc->peer_connection_state;
  GstWebRTCPeerConnectionState new_state;

  new_state = _collate_peer_connection_states (webrtc);

  if (new_state != old_state) {
    gchar *old_s, *new_s;

    old_s = _enum_value_to_string (GST_TYPE_WEBRTC_PEER_CONNECTION_STATE,
        old_state);
    new_s = _enum_value_to_string (GST_TYPE_WEBRTC_PEER_CONNECTION_STATE,
        new_state);
    GST_INFO_OBJECT (webrtc,
        "Peer connection state change from %s(%u) to %s(%u)", old_s, old_state,
        new_s, new_state);
    g_free (old_s);
    g_free (new_s);

    webrtc->peer_connection_state = new_state;
    PC_UNLOCK (webrtc);
    g_object_notify (G_OBJECT (webrtc), "connection-state");
    PC_LOCK (webrtc);
  }
}

static void
_update_peer_connection_state (GstWebRTCBin * webrtc)
{
  gst_webrtc_bin_enqueue_task (webrtc, _update_peer_connection_state_task,
      NULL, NULL);
}

static gboolean
_all_sinks_have_caps (GstWebRTCBin * webrtc)
{
  GList *l;
  gboolean res = FALSE;

  GST_OBJECT_LOCK (webrtc);
  l = GST_ELEMENT (webrtc)->pads;
  for (; l; l = g_list_next (l)) {
    if (!GST_IS_WEBRTC_BIN_PAD (l->data))
      continue;
    if (!GST_WEBRTC_BIN_PAD (l->data)->received_caps)
      goto done;
  }

  l = webrtc->priv->pending_pads;
  for (; l; l = g_list_next (l)) {
    if (!GST_IS_WEBRTC_BIN_PAD (l->data))
      goto done;
  }

  res = TRUE;

done:
  GST_OBJECT_UNLOCK (webrtc);
  return res;
}

/* http://w3c.github.io/webrtc-pc/#dfn-check-if-negotiation-is-needed */
static gboolean
_check_if_negotiation_is_needed (GstWebRTCBin * webrtc)
{
  int i;

  GST_LOG_OBJECT (webrtc, "checking if negotiation is needed");

  /* We can't negotiate until we have received caps on all our sink pads,
   * as we will need the ssrcs in our offer / answer */
  if (!_all_sinks_have_caps (webrtc)) {
    GST_LOG_OBJECT (webrtc,
        "no negotiation possible until caps have been received on all sink pads");
    return FALSE;
  }

  /* If any implementation-specific negotiation is required, as described at
   * the start of this section, return "true".
   * FIXME */
  /* FIXME: emit when input caps/format changes? */

  /* If connection has created any RTCDataChannel's, and no m= section has
   * been negotiated yet for data, return "true". 
   * FIXME */

  if (!webrtc->current_local_description) {
    GST_LOG_OBJECT (webrtc, "no local description set");
    return TRUE;
  }

  if (!webrtc->current_remote_description) {
    GST_LOG_OBJECT (webrtc, "no remote description set");
    return TRUE;
  }

  for (i = 0; i < webrtc->priv->transceivers->len; i++) {
    GstWebRTCRTPTransceiver *trans;

    trans =
        g_array_index (webrtc->priv->transceivers, GstWebRTCRTPTransceiver *,
        i);

    if (trans->stopped) {
      /* FIXME: If t is stopped and is associated with an m= section according to
       * [JSEP] (section 3.4.1.), but the associated m= section is not yet
       * rejected in connection's currentLocalDescription or
       * currentRemoteDescription , return "true". */
      GST_FIXME_OBJECT (webrtc,
          "check if the transceiver is rejected in descriptions");
    } else {
      const GstSDPMedia *media;
      GstWebRTCRTPTransceiverDirection local_dir, remote_dir;

      if (trans->mline == -1) {
        GST_LOG_OBJECT (webrtc, "unassociated transceiver %i %" GST_PTR_FORMAT,
            i, trans);
        return TRUE;
      }
      /* internal inconsistency */
      g_assert (trans->mline <
          gst_sdp_message_medias_len (webrtc->current_local_description->sdp));
      g_assert (trans->mline <
          gst_sdp_message_medias_len (webrtc->current_remote_description->sdp));

      /* FIXME: msid handling
       * If t's direction is "sendrecv" or "sendonly", and the associated m=
       * section in connection's currentLocalDescription doesn't contain an
       * "a=msid" line, return "true". */

      media =
          gst_sdp_message_get_media (webrtc->current_local_description->sdp,
          trans->mline);
      local_dir = _get_direction_from_media (media);

      media =
          gst_sdp_message_get_media (webrtc->current_remote_description->sdp,
          trans->mline);
      remote_dir = _get_direction_from_media (media);

      if (webrtc->current_local_description->type == GST_WEBRTC_SDP_TYPE_OFFER) {
        /* If connection's currentLocalDescription if of type "offer", and
         * the direction of the associated m= section in neither the offer
         * nor answer matches t's direction, return "true". */

        if (local_dir != trans->direction && remote_dir != trans->direction) {
          GST_LOG_OBJECT (webrtc,
              "transceiver direction doesn't match description");
          return TRUE;
        }
      } else if (webrtc->current_local_description->type ==
          GST_WEBRTC_SDP_TYPE_ANSWER) {
        GstWebRTCRTPTransceiverDirection intersect_dir;

        /* If connection's currentLocalDescription if of type "answer", and
         * the direction of the associated m= section in the answer does not
         * match t's direction intersected with the offered direction (as
         * described in [JSEP] (section 5.3.1.)), return "true". */

        /* remote is the offer, local is the answer */
        intersect_dir = _intersect_answer_directions (remote_dir, local_dir);

        if (intersect_dir != trans->direction) {
          GST_LOG_OBJECT (webrtc,
              "transceiver direction doesn't match description");
          return TRUE;
        }
      }
    }
  }

  GST_LOG_OBJECT (webrtc, "no negotiation needed");
  return FALSE;
}

static void
_check_need_negotiation_task (GstWebRTCBin * webrtc, gpointer unused)
{
  if (webrtc->priv->need_negotiation) {
    GST_TRACE_OBJECT (webrtc, "emitting on-negotiation-needed");
    PC_UNLOCK (webrtc);
    g_signal_emit (webrtc, gst_webrtc_bin_signals[ON_NEGOTIATION_NEEDED_SIGNAL],
        0);
    PC_LOCK (webrtc);
  }
}

/* http://w3c.github.io/webrtc-pc/#dfn-update-the-negotiation-needed-flag */
static void
_update_need_negotiation (GstWebRTCBin * webrtc)
{
  /* If connection's [[isClosed]] slot is true, abort these steps. */
  if (webrtc->priv->is_closed)
    return;
  /* If connection's signaling state is not "stable", abort these steps. */
  if (webrtc->signaling_state != GST_WEBRTC_SIGNALING_STATE_STABLE)
    return;

  /* If the result of checking if negotiation is needed is "false", clear the
   * negotiation-needed flag by setting connection's [[ needNegotiation]] slot
   * to false, and abort these steps. */
  if (!_check_if_negotiation_is_needed (webrtc)) {
    webrtc->priv->need_negotiation = FALSE;
    return;
  }
  /* If connection's [[needNegotiation]] slot is already true, abort these steps. */
  if (webrtc->priv->need_negotiation)
    return;
  /* Set connection's [[needNegotiation]] slot to true. */
  webrtc->priv->need_negotiation = TRUE;
  /* Queue a task to check connection's [[ needNegotiation]] slot and, if still
   * true, fire a simple event named negotiationneeded at connection. */
  gst_webrtc_bin_enqueue_task (webrtc, _check_need_negotiation_task, NULL,
      NULL);
}

static GstCaps *
_find_codec_preferences (GstWebRTCBin * webrtc, GstWebRTCRTPTransceiver * trans,
    GstPadDirection direction, guint media_idx)
{
  GstCaps *ret = NULL;

  GST_LOG_OBJECT (webrtc, "retreiving codec preferences from %" GST_PTR_FORMAT,
      trans);

  if (trans && trans->codec_preferences) {
    GST_LOG_OBJECT (webrtc, "Using codec preferences: %" GST_PTR_FORMAT,
        trans->codec_preferences);
    ret = gst_caps_ref (trans->codec_preferences);
  } else {
    GstWebRTCBinPad *pad = _find_pad_for_mline (webrtc, direction, media_idx);
    if (pad) {
      GstCaps *caps = gst_pad_get_current_caps (GST_PAD (pad));
      if (caps) {
        GST_LOG_OBJECT (webrtc, "Using current pad caps: %" GST_PTR_FORMAT,
            caps);
      } else {
        if ((caps = gst_pad_peer_query_caps (GST_PAD (pad), NULL)))
          GST_LOG_OBJECT (webrtc, "Using peer query caps: %" GST_PTR_FORMAT,
              caps);
      }
      if (caps)
        ret = caps;
      gst_object_unref (pad);
    }
  }

  return ret;
}

static GstCaps *
_add_supported_attributes_to_caps (GstWebRTCBin * webrtc,
    WebRTCTransceiver * trans, const GstCaps * caps)
{
  GstCaps *ret;
  guint i;

  ret = gst_caps_make_writable (caps);

  for (i = 0; i < gst_caps_get_size (ret); i++) {
    GstStructure *s = gst_caps_get_structure (ret, i);

    if (trans->do_nack)
      if (!gst_structure_has_field (s, "rtcp-fb-nack"))
        gst_structure_set (s, "rtcp-fb-nack", G_TYPE_BOOLEAN, TRUE, NULL);

    if (!gst_structure_has_field (s, "rtcp-fb-nack-pli"))
      gst_structure_set (s, "rtcp-fb-nack-pli", G_TYPE_BOOLEAN, TRUE, NULL);
    /* FIXME: is this needed? */
    /*if (!gst_structure_has_field (s, "rtcp-fb-transport-cc"))
       gst_structure_set (s, "rtcp-fb-nack-pli", G_TYPE_BOOLEAN, TRUE, NULL); */

    /* FIXME: codec-specific paramters? */
  }

  return ret;
}

static void
_on_ice_transport_notify_state (GstWebRTCICETransport * transport,
    GParamSpec * pspec, GstWebRTCBin * webrtc)
{
  _update_ice_connection_state (webrtc);
  _update_peer_connection_state (webrtc);
}

static void
_on_ice_transport_notify_gathering_state (GstWebRTCICETransport * transport,
    GParamSpec * pspec, GstWebRTCBin * webrtc)
{
  _update_ice_gathering_state (webrtc);
}

static void
_on_dtls_transport_notify_state (GstWebRTCDTLSTransport * transport,
    GParamSpec * pspec, GstWebRTCBin * webrtc)
{
  _update_peer_connection_state (webrtc);
}

static WebRTCTransceiver *
_create_webrtc_transceiver (GstWebRTCBin * webrtc,
    GstWebRTCRTPTransceiverDirection direction, guint mline)
{
  WebRTCTransceiver *trans;
  GstWebRTCRTPTransceiver *rtp_trans;
  GstWebRTCRTPSender *sender;
  GstWebRTCRTPReceiver *receiver;

  sender = gst_webrtc_rtp_sender_new ();
  receiver = gst_webrtc_rtp_receiver_new ();
  trans = webrtc_transceiver_new (webrtc, sender, receiver);
  rtp_trans = GST_WEBRTC_RTP_TRANSCEIVER (trans);
  rtp_trans->direction = direction;
  rtp_trans->mline = mline;

  g_array_append_val (webrtc->priv->transceivers, trans);

  gst_object_unref (sender);
  gst_object_unref (receiver);

  g_signal_emit (webrtc, gst_webrtc_bin_signals[ON_NEW_TRANSCEIVER_SIGNAL],
      0, trans);

  return trans;
}

static TransportStream *
_create_transport_channel (GstWebRTCBin * webrtc, guint session_id)
{
  GstWebRTCDTLSTransport *transport;
  TransportStream *ret;
  gchar *pad_name;

  /* FIXME: how to parametrize the sender and the receiver */
  ret = transport_stream_new (webrtc, session_id);
  transport = ret->transport;

  g_signal_connect (G_OBJECT (transport->transport), "notify::state",
      G_CALLBACK (_on_ice_transport_notify_state), webrtc);
  g_signal_connect (G_OBJECT (transport->transport),
      "notify::gathering-state",
      G_CALLBACK (_on_ice_transport_notify_gathering_state), webrtc);
  g_signal_connect (G_OBJECT (transport), "notify::state",
      G_CALLBACK (_on_dtls_transport_notify_state), webrtc);

  if ((transport = ret->rtcp_transport)) {
    g_signal_connect (G_OBJECT (transport->transport),
        "notify::state", G_CALLBACK (_on_ice_transport_notify_state), webrtc);
    g_signal_connect (G_OBJECT (transport->transport),
        "notify::gathering-state",
        G_CALLBACK (_on_ice_transport_notify_gathering_state), webrtc);
    g_signal_connect (G_OBJECT (transport), "notify::state",
        G_CALLBACK (_on_dtls_transport_notify_state), webrtc);
  }

  gst_bin_add (GST_BIN (webrtc), GST_ELEMENT (ret->send_bin));
  gst_bin_add (GST_BIN (webrtc), GST_ELEMENT (ret->receive_bin));

  pad_name = g_strdup_printf ("recv_rtcp_sink_%u", ret->session_id);
  if (!gst_element_link_pads (GST_ELEMENT (ret->receive_bin), "rtcp_src",
          GST_ELEMENT (webrtc->rtpbin), pad_name))
    g_warn_if_reached ();
  g_free (pad_name);

  pad_name = g_strdup_printf ("send_rtcp_src_%u", ret->session_id);
  if (!gst_element_link_pads (GST_ELEMENT (webrtc->rtpbin), pad_name,
          GST_ELEMENT (ret->send_bin), "rtcp_sink"))
    g_warn_if_reached ();
  g_free (pad_name);

  g_array_append_val (webrtc->priv->transports, ret);

  GST_TRACE_OBJECT (webrtc,
      "Create transport %" GST_PTR_FORMAT " for session %u", ret, session_id);

  gst_element_sync_state_with_parent (GST_ELEMENT (ret->send_bin));
  gst_element_sync_state_with_parent (GST_ELEMENT (ret->receive_bin));

  return ret;
}

static guint
g_array_find_uint (GArray * array, guint val)
{
  guint i;

  for (i = 0; i < array->len; i++) {
    if (g_array_index (array, guint, i) == val)
      return i;
  }

  return G_MAXUINT;
}

static gboolean
_pick_available_pt (GArray * reserved_pts, guint * i)
{
  gboolean ret = FALSE;

  for (*i = 96; *i <= 127; (*i)++) {
    if (g_array_find_uint (reserved_pts, *i) == G_MAXUINT) {
      g_array_append_val (reserved_pts, *i);
      ret = TRUE;
      break;
    }
  }

  return ret;
}

static gboolean
_pick_fec_payload_types (GstWebRTCBin * webrtc, WebRTCTransceiver * trans,
    GArray * reserved_pts, gint clockrate, gint * rtx_target_pt,
    GstSDPMedia * media)
{
  gboolean ret = TRUE;

  if (trans->fec_type == GST_WEBRTC_FEC_TYPE_NONE)
    goto done;

  if (trans->fec_type == GST_WEBRTC_FEC_TYPE_ULP_RED && clockrate != -1) {
    guint pt;
    gchar *str;

    if (!(ret = _pick_available_pt (reserved_pts, &pt)))
      goto done;

    /* https://tools.ietf.org/html/rfc5109#section-14.1 */

    str = g_strdup_printf ("%u", pt);
    gst_sdp_media_add_format (media, str);
    g_free (str);
    str = g_strdup_printf ("%u red/%d", pt, clockrate);
    gst_sdp_media_add_attribute (media, "rtpmap", str);
    g_free (str);

    *rtx_target_pt = pt;

    if (!(ret = _pick_available_pt (reserved_pts, &pt)))
      goto done;

    str = g_strdup_printf ("%u", pt);
    gst_sdp_media_add_format (media, str);
    g_free (str);
    str = g_strdup_printf ("%u ulpfec/%d", pt, clockrate);
    gst_sdp_media_add_attribute (media, "rtpmap", str);
    g_free (str);
  }

done:
  return ret;
}

static gboolean
_pick_rtx_payload_types (GstWebRTCBin * webrtc, WebRTCTransceiver * trans,
    GArray * reserved_pts, gint clockrate, gint target_pt, guint target_ssrc,
    GstSDPMedia * media)
{
  gboolean ret = TRUE;

  if (trans->local_rtx_ssrc_map)
    gst_structure_free (trans->local_rtx_ssrc_map);

  trans->local_rtx_ssrc_map =
      gst_structure_new_empty ("application/x-rtp-ssrc-map");

  if (trans->do_nack) {
    guint pt;
    gchar *str;

    if (!(ret = _pick_available_pt (reserved_pts, &pt)))
      goto done;

    /* https://tools.ietf.org/html/rfc4588#section-8.6 */

    str = g_strdup_printf ("%u", target_ssrc);
    gst_structure_set (trans->local_rtx_ssrc_map, str, G_TYPE_UINT,
        g_random_int (), NULL);

    str = g_strdup_printf ("%u", pt);
    gst_sdp_media_add_format (media, str);
    g_free (str);

    str = g_strdup_printf ("%u rtx/%d", pt, clockrate);
    gst_sdp_media_add_attribute (media, "rtpmap", str);
    g_free (str);

    str = g_strdup_printf ("%u apt=%d", pt, target_pt);
    gst_sdp_media_add_attribute (media, "fmtp", str);
    g_free (str);
  }

done:
  return ret;
}

/* https://tools.ietf.org/html/rfc5576#section-4.2 */
static gboolean
_media_add_rtx_ssrc_group (GQuark field_id, const GValue * value,
    GstSDPMedia * media)
{
  gchar *str;

  str =
      g_strdup_printf ("FID %s %u", g_quark_to_string (field_id),
      g_value_get_uint (value));
  gst_sdp_media_add_attribute (media, "ssrc-group", str);

  g_free (str);

  return TRUE;
}

typedef struct
{
  GstSDPMedia *media;
  GstWebRTCBin *webrtc;
  WebRTCTransceiver *trans;
} RtxSsrcData;

static gboolean
_media_add_rtx_ssrc (GQuark field_id, const GValue * value, RtxSsrcData * data)
{
  gchar *str;
  GstStructure *sdes;
  const gchar *cname;

  g_object_get (data->webrtc->rtpbin, "sdes", &sdes, NULL);
  /* http://www.freesoft.org/CIE/RFC/1889/24.htm */
  cname = gst_structure_get_string (sdes, "cname");

  /* https://tools.ietf.org/html/draft-ietf-mmusic-msid-16 */
  str =
      g_strdup_printf ("%u msid:%s %s", g_value_get_uint (value),
      cname, GST_OBJECT_NAME (data->trans));
  gst_sdp_media_add_attribute (data->media, "ssrc", str);
  g_free (str);

  str = g_strdup_printf ("%u cname:%s", g_value_get_uint (value), cname);
  gst_sdp_media_add_attribute (data->media, "ssrc", str);
  g_free (str);

  gst_structure_free (sdes);

  return TRUE;
}

static void
_media_add_ssrcs (GstSDPMedia * media, GstCaps * caps, GstWebRTCBin * webrtc,
    WebRTCTransceiver * trans)
{
  guint i;
  RtxSsrcData data = { media, webrtc, trans };
  const gchar *cname;
  GstStructure *sdes;

  g_object_get (webrtc->rtpbin, "sdes", &sdes, NULL);
  /* http://www.freesoft.org/CIE/RFC/1889/24.htm */
  cname = gst_structure_get_string (sdes, "cname");

  if (trans->local_rtx_ssrc_map)
    gst_structure_foreach (trans->local_rtx_ssrc_map,
        (GstStructureForeachFunc) _media_add_rtx_ssrc_group, media);

  for (i = 0; i < gst_caps_get_size (caps); i++) {
    const GstStructure *s = gst_caps_get_structure (caps, i);
    guint ssrc;

    if (gst_structure_get_uint (s, "ssrc", &ssrc)) {
      gchar *str;

      /* https://tools.ietf.org/html/draft-ietf-mmusic-msid-16 */
      str =
          g_strdup_printf ("%u msid:%s %s", ssrc, cname,
          GST_OBJECT_NAME (trans));
      gst_sdp_media_add_attribute (media, "ssrc", str);
      g_free (str);

      str = g_strdup_printf ("%u cname:%s", ssrc, cname);
      gst_sdp_media_add_attribute (media, "ssrc", str);
      g_free (str);
    }
  }

  gst_structure_free (sdes);

  if (trans->local_rtx_ssrc_map)
    gst_structure_foreach (trans->local_rtx_ssrc_map,
        (GstStructureForeachFunc) _media_add_rtx_ssrc, &data);
}

/* based off https://tools.ietf.org/html/draft-ietf-rtcweb-jsep-18#section-5.2.1 */
static gboolean
sdp_media_from_transceiver (GstWebRTCBin * webrtc, GstSDPMedia * media,
    GstWebRTCRTPTransceiver * trans, GstWebRTCSDPType type, guint media_idx)
{
  /* TODO:
   * rtp header extensions
   * ice attributes
   * rtx
   * fec
   * msid-semantics
   * msid
   * dtls fingerprints
   * multiple dtls fingerprints https://tools.ietf.org/html/draft-ietf-mmusic-4572-update-05
   */
  gchar *direction, *sdp_mid;
  GstCaps *caps;
  int i;

  /* "An m= section is generated for each RtpTransceiver that has been added
   * to the Bin, excluding any stopped RtpTransceivers." */
  if (trans->stopped)
    return FALSE;
  if (trans->direction == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_NONE
      || trans->direction == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_INACTIVE)
    return FALSE;

  gst_sdp_media_set_port_info (media, 9, 0);
  gst_sdp_media_set_proto (media, "UDP/TLS/RTP/SAVPF");
  gst_sdp_media_add_connection (media, "IN", "IP4", "0.0.0.0", 0, 0);

  direction =
      _enum_value_to_string (GST_TYPE_WEBRTC_RTP_TRANSCEIVER_DIRECTION,
      trans->direction);
  gst_sdp_media_add_attribute (media, direction, "");
  g_free (direction);
  /* FIXME: negotiate this */
  gst_sdp_media_add_attribute (media, "rtcp-mux", "");
  gst_sdp_media_add_attribute (media, "rtcp-rsize", NULL);

  if (type == GST_WEBRTC_SDP_TYPE_OFFER) {
    caps = _find_codec_preferences (webrtc, trans, GST_PAD_SINK, media_idx);
    caps =
        _add_supported_attributes_to_caps (webrtc, WEBRTC_TRANSCEIVER (trans),
        caps);
  } else if (type == GST_WEBRTC_SDP_TYPE_ANSWER) {
    caps = _find_codec_preferences (webrtc, trans, GST_PAD_SRC, media_idx);
    /* FIXME: add rtcp-fb paramaters */
  } else {
    g_assert_not_reached ();
  }

  if (!caps || gst_caps_is_empty (caps) || gst_caps_is_any (caps)) {
    GST_WARNING_OBJECT (webrtc, "no caps available for transceiver, skipping");
    if (caps)
      gst_caps_unref (caps);
    return FALSE;
  }

  for (i = 0; i < gst_caps_get_size (caps); i++) {
    GstCaps *format = gst_caps_new_empty ();
    const GstStructure *s = gst_caps_get_structure (caps, i);

    gst_caps_append_structure (format, gst_structure_copy (s));

    GST_DEBUG_OBJECT (webrtc, "Adding %u-th caps %" GST_PTR_FORMAT
        " to %u-th media", i, format, media_idx);

    /* this only looks at the first structure so we loop over the given caps
     * and add each structure inside it piecemeal */
    gst_sdp_media_set_media_from_caps (format, media);

    gst_caps_unref (format);
  }

  if (type == GST_WEBRTC_SDP_TYPE_OFFER) {
    GArray *reserved_pts = g_array_new (FALSE, FALSE, sizeof (guint));
    const GstStructure *s = gst_caps_get_structure (caps, 0);
    gint clockrate = -1;
    gint rtx_target_pt;
    gint original_rtx_target_pt;        /* Workaround chrome bug: https://bugs.chromium.org/p/webrtc/issues/detail?id=6196 */
    guint rtx_target_ssrc;

    if (gst_structure_get_int (s, "payload", &rtx_target_pt))
      g_array_append_val (reserved_pts, rtx_target_pt);

    original_rtx_target_pt = rtx_target_pt;

    gst_structure_get_int (s, "clock-rate", &clockrate);
    gst_structure_get_uint (s, "ssrc", &rtx_target_ssrc);

    _pick_fec_payload_types (webrtc, WEBRTC_TRANSCEIVER (trans), reserved_pts,
        clockrate, &rtx_target_pt, media);
    _pick_rtx_payload_types (webrtc, WEBRTC_TRANSCEIVER (trans), reserved_pts,
        clockrate, rtx_target_pt, rtx_target_ssrc, media);
    if (original_rtx_target_pt != rtx_target_pt)
      _pick_rtx_payload_types (webrtc, WEBRTC_TRANSCEIVER (trans), reserved_pts,
          clockrate, original_rtx_target_pt, rtx_target_ssrc, media);
    g_array_free (reserved_pts, TRUE);
  }

  _media_add_ssrcs (media, caps, webrtc, WEBRTC_TRANSCEIVER (trans));

  /* Some identifier; we also add the media name to it so it's identifiable */
  sdp_mid = g_strdup_printf ("%s%u", gst_sdp_media_get_media (media),
      webrtc->priv->media_counter++);
  gst_sdp_media_add_attribute (media, "mid", sdp_mid);
  g_free (sdp_mid);

  if (trans->sender) {
    gchar *cert, *fingerprint, *val;

    if (!trans->sender->transport) {
      TransportStream *item;
      /* FIXME: bundle */
      item = _find_transport_for_session (webrtc, media_idx);
      if (!item)
        item = _create_transport_channel (webrtc, media_idx);
      webrtc_transceiver_set_transport (WEBRTC_TRANSCEIVER (trans), item);
    }

    g_object_get (trans->sender->transport, "certificate", &cert, NULL);

    fingerprint =
        _generate_fingerprint_from_certificate (cert, G_CHECKSUM_SHA256);
    g_free (cert);
    val =
        g_strdup_printf ("%s %s",
        _g_checksum_to_webrtc_string (G_CHECKSUM_SHA256), fingerprint);
    g_free (fingerprint);

    gst_sdp_media_add_attribute (media, "fingerprint", val);
    g_free (val);
  }

  gst_caps_unref (caps);

  return TRUE;
}

static GstSDPMessage *
_create_offer_task (GstWebRTCBin * webrtc, const GstStructure * options)
{
  GstSDPMessage *ret;
  int i;
  gchar *str;

  gst_sdp_message_new (&ret);

  gst_sdp_message_set_version (ret, "0");
  {
    /* FIXME: session id and version need special handling depending on the state we're in */
    gchar *sess_id = g_strdup_printf ("%" G_GUINT64_FORMAT, RANDOM_SESSION_ID);
    gst_sdp_message_set_origin (ret, "-", sess_id, "0", "IN", "IP4", "0.0.0.0");
    g_free (sess_id);
  }
  gst_sdp_message_set_session_name (ret, "-");
  gst_sdp_message_add_time (ret, "0", "0", NULL);
  gst_sdp_message_add_attribute (ret, "ice-options", "trickle");

  /* https://tools.ietf.org/html/draft-ietf-mmusic-msid-05#section-3 */
  str = g_strdup_printf ("WMS %s", GST_OBJECT (webrtc)->name);
  gst_sdp_message_add_attribute (ret, "msid-semantic", str);
  g_free (str);

  /* for each rtp transceiver */
  for (i = 0; i < webrtc->priv->transceivers->len; i++) {
    GstWebRTCRTPTransceiver *trans;
    GstSDPMedia media = { 0, };
    gchar *ufrag, *pwd;

    trans =
        g_array_index (webrtc->priv->transceivers, GstWebRTCRTPTransceiver *,
        i);

    gst_sdp_media_init (&media);
    /* mandated by JSEP */
    gst_sdp_media_add_attribute (&media, "setup", "actpass");

    /* FIXME: only needed when restarting ICE */
    _generate_ice_credentials (&ufrag, &pwd);
    gst_sdp_media_add_attribute (&media, "ice-ufrag", ufrag);
    gst_sdp_media_add_attribute (&media, "ice-pwd", pwd);
    g_free (ufrag);
    g_free (pwd);

    if (sdp_media_from_transceiver (webrtc, &media, trans,
            GST_WEBRTC_SDP_TYPE_OFFER, i))
      gst_sdp_message_add_media (ret, &media);
    else
      gst_sdp_media_uninit (&media);
  }

  /* FIXME: pre-emptively setup receiving elements when needed */

  /* XXX: only true for the initial offerer */
  g_object_set (webrtc->priv->ice, "controller", TRUE, NULL);

  return ret;
}

static void
_media_add_fec (GstSDPMedia * media, WebRTCTransceiver * trans, GstCaps * caps,
    gint * rtx_target_pt)
{
  guint i;

  if (trans->fec_type == GST_WEBRTC_FEC_TYPE_NONE)
    return;

  for (i = 0; i < gst_caps_get_size (caps); i++) {
    const GstStructure *s = gst_caps_get_structure (caps, i);

    if (gst_structure_has_name (s, "application/x-rtp")) {
      const gchar *encoding_name =
          gst_structure_get_string (s, "encoding-name");
      gint clock_rate;
      gint pt;

      if (gst_structure_get_int (s, "clock-rate", &clock_rate) &&
          gst_structure_get_int (s, "payload", &pt)) {
        if (!g_strcmp0 (encoding_name, "RED")) {
          gchar *str;

          str = g_strdup_printf ("%u", pt);
          gst_sdp_media_add_format (media, str);
          g_free (str);
          str = g_strdup_printf ("%u red/%d", pt, clock_rate);
          *rtx_target_pt = pt;
          gst_sdp_media_add_attribute (media, "rtpmap", str);
          g_free (str);
        } else if (!g_strcmp0 (encoding_name, "ULPFEC")) {
          gchar *str;

          str = g_strdup_printf ("%u", pt);
          gst_sdp_media_add_format (media, str);
          g_free (str);
          str = g_strdup_printf ("%u ulpfec/%d", pt, clock_rate);
          gst_sdp_media_add_attribute (media, "rtpmap", str);
          g_free (str);
        }
      }
    }
  }
}

static void
_media_add_rtx (GstSDPMedia * media, WebRTCTransceiver * trans,
    GstCaps * offer_caps, gint target_pt, guint target_ssrc)
{
  guint i;
  const GstStructure *s;

  if (trans->local_rtx_ssrc_map)
    gst_structure_free (trans->local_rtx_ssrc_map);

  trans->local_rtx_ssrc_map =
      gst_structure_new_empty ("application/x-rtp-ssrc-map");

  for (i = 0; i < gst_caps_get_size (offer_caps); i++) {
    s = gst_caps_get_structure (offer_caps, i);

    if (gst_structure_has_name (s, "application/x-rtp")) {
      const gchar *encoding_name =
          gst_structure_get_string (s, "encoding-name");
      const gchar *apt_str = gst_structure_get_string (s, "apt");
      gint apt;
      gint clock_rate;
      gint pt;

      if (!apt_str)
        continue;

      apt = atoi (apt_str);

      if (gst_structure_get_int (s, "clock-rate", &clock_rate) &&
          gst_structure_get_int (s, "payload", &pt) && apt == target_pt) {
        if (!g_strcmp0 (encoding_name, "RTX")) {
          gchar *str;

          str = g_strdup_printf ("%u", pt);
          gst_sdp_media_add_format (media, str);
          g_free (str);
          str = g_strdup_printf ("%u rtx/%d", pt, clock_rate);
          gst_sdp_media_add_attribute (media, "rtpmap", str);
          g_free (str);

          str = g_strdup_printf ("%d apt=%d", pt, apt);
          gst_sdp_media_add_attribute (media, "fmtp", str);
          g_free (str);

          str = g_strdup_printf ("%u", target_ssrc);
          gst_structure_set (trans->local_rtx_ssrc_map, str, G_TYPE_UINT,
              g_random_int (), NULL);
        }
      }
    }
  }
}

static void
_get_rtx_target_pt_and_ssrc_from_caps (GstCaps * answer_caps, gint * target_pt,
    guint * target_ssrc)
{
  const GstStructure *s = gst_caps_get_structure (answer_caps, 0);

  gst_structure_get_int (s, "payload", target_pt);
  gst_structure_get_uint (s, "ssrc", target_ssrc);
}

static GstSDPMessage *
_create_answer_task (GstWebRTCBin * webrtc, const GstStructure * options)
{
  GstSDPMessage *ret = NULL;
  const GstWebRTCSessionDescription *pending_remote =
      webrtc->pending_remote_description;
  guint i;

  if (!webrtc->pending_remote_description) {
    GST_ERROR_OBJECT (webrtc,
        "Asked to create an answer without a remote description");
    return NULL;
  }

  gst_sdp_message_new (&ret);

  /* FIXME: session id and version need special handling depending on the state we're in */
  gst_sdp_message_set_version (ret, "0");
  {
    const GstSDPOrigin *offer_origin =
        gst_sdp_message_get_origin (pending_remote->sdp);
    gst_sdp_message_set_origin (ret, "-", offer_origin->sess_id, "0", "IN",
        "IP4", "0.0.0.0");
  }
  gst_sdp_message_set_session_name (ret, "-");

  for (i = 0; i < gst_sdp_message_attributes_len (pending_remote->sdp); i++) {
    const GstSDPAttribute *attr =
        gst_sdp_message_get_attribute (pending_remote->sdp, i);

    if (g_strcmp0 (attr->key, "ice-options") == 0) {
      gst_sdp_message_add_attribute (ret, attr->key, attr->value);
    }
  }

  for (i = 0; i < gst_sdp_message_medias_len (pending_remote->sdp); i++) {
    /* FIXME:
     * bundle policy
     */
    GstSDPMedia *media = NULL;
    GstSDPMedia *offer_media;
    GstWebRTCRTPTransceiver *rtp_trans = NULL;
    WebRTCTransceiver *trans = NULL;
    GstWebRTCRTPTransceiverDirection offer_dir, answer_dir;
    GstWebRTCDTLSSetup offer_setup, answer_setup;
    GstCaps *offer_caps, *answer_caps = NULL;
    gchar *cert;
    guint j;
    guint k;
    gint target_pt = -1;
    gint original_target_pt = -1;
    guint target_ssrc = 0;

    gst_sdp_media_new (&media);
    gst_sdp_media_set_port_info (media, 9, 0);
    gst_sdp_media_set_proto (media, "UDP/TLS/RTP/SAVPF");
    gst_sdp_media_add_connection (media, "IN", "IP4", "0.0.0.0", 0, 0);

    {
      /* FIXME: only needed when restarting ICE */
      gchar *ufrag, *pwd;
      _generate_ice_credentials (&ufrag, &pwd);
      gst_sdp_media_add_attribute (media, "ice-ufrag", ufrag);
      gst_sdp_media_add_attribute (media, "ice-pwd", pwd);
      g_free (ufrag);
      g_free (pwd);
    }

    offer_media =
        (GstSDPMedia *) gst_sdp_message_get_media (pending_remote->sdp, i);
    for (j = 0; j < gst_sdp_media_attributes_len (offer_media); j++) {
      const GstSDPAttribute *attr =
          gst_sdp_media_get_attribute (offer_media, j);

      if (g_strcmp0 (attr->key, "mid") == 0
          || g_strcmp0 (attr->key, "rtcp-mux") == 0) {
        gst_sdp_media_add_attribute (media, attr->key, attr->value);
        /* FIXME: handle anything we want to keep */
      }
    }

    offer_caps = gst_caps_new_empty ();
    for (j = 0; j < gst_sdp_media_formats_len (offer_media); j++) {
      guint pt = atoi (gst_sdp_media_get_format (offer_media, j));
      GstCaps *caps;

      caps = gst_sdp_media_get_caps_from_media (offer_media, pt);

      /* gst_sdp_media_get_caps_from_media() produces caps with name
       * "application/x-unknown" which will fail intersection with
       * "application/x-rtp" caps so mangle the returns caps to have the
       * correct name here */
      for (k = 0; k < gst_caps_get_size (caps); k++) {
        GstStructure *s = gst_caps_get_structure (caps, k);
        gst_structure_set_name (s, "application/x-rtp");
      }

      gst_caps_append (offer_caps, caps);
    }

    for (j = 0; j < webrtc->priv->transceivers->len; j++) {
      GstCaps *trans_caps;

      rtp_trans =
          g_array_index (webrtc->priv->transceivers, GstWebRTCRTPTransceiver *,
          j);
      trans_caps = _find_codec_preferences (webrtc, rtp_trans, GST_PAD_SINK, j);

      GST_TRACE_OBJECT (webrtc, "trying to compare %" GST_PTR_FORMAT
          " and %" GST_PTR_FORMAT, offer_caps, trans_caps);

      /* FIXME: technically this is a little overreaching as some fields we
       * we can deal with not having and/or we may have unrecognized fields
       * that we cannot actually support */
      if (trans_caps) {
        answer_caps = gst_caps_intersect (offer_caps, trans_caps);
        if (answer_caps && !gst_caps_is_empty (answer_caps)) {
          GST_LOG_OBJECT (webrtc,
              "found compatible transceiver %" GST_PTR_FORMAT
              " for offer media %u", trans, i);
          if (trans_caps)
            gst_caps_unref (trans_caps);
          break;
        } else {
          if (answer_caps) {
            gst_caps_unref (answer_caps);
            answer_caps = NULL;
          }
          if (trans_caps)
            gst_caps_unref (trans_caps);
          rtp_trans = NULL;
        }
      } else {
        rtp_trans = NULL;
      }
    }

    if (rtp_trans) {
      answer_dir = rtp_trans->direction;
      g_assert (answer_caps != NULL);
    } else {
      /* if no transceiver, then we only receive that stream and respond with
       * the exact same caps */
      /* FIXME: how to validate that subsequent elements can actually receive
       * this payload/format */
      answer_dir = GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_RECVONLY;
      answer_caps = gst_caps_ref (offer_caps);
    }

    if (!rtp_trans) {
      trans = _create_webrtc_transceiver (webrtc, answer_dir, i);
      rtp_trans = GST_WEBRTC_RTP_TRANSCEIVER (trans);
    } else {
      trans = WEBRTC_TRANSCEIVER (rtp_trans);
    }

    if (!trans->do_nack) {
      answer_caps = gst_caps_make_writable (answer_caps);
      for (k = 0; k < gst_caps_get_size (answer_caps); k++) {
        GstStructure *s = gst_caps_get_structure (answer_caps, k);
        gst_structure_remove_fields (s, "rtcp-fb-nack", NULL);
      }
    }

    gst_sdp_media_set_media_from_caps (answer_caps, media);

    _get_rtx_target_pt_and_ssrc_from_caps (answer_caps, &target_pt,
        &target_ssrc);

    original_target_pt = target_pt;

    _media_add_fec (media, trans, offer_caps, &target_pt);
    if (trans->do_nack) {
      _media_add_rtx (media, trans, offer_caps, target_pt, target_ssrc);
      if (target_pt != original_target_pt)
        _media_add_rtx (media, trans, offer_caps, original_target_pt,
            target_ssrc);
    }

    if (answer_dir != GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_RECVONLY)
      _media_add_ssrcs (media, answer_caps, webrtc,
          WEBRTC_TRANSCEIVER (rtp_trans));

    gst_caps_unref (answer_caps);
    answer_caps = NULL;

    /* set the new media direction */
    offer_dir = _get_direction_from_media (offer_media);
    answer_dir = _intersect_answer_directions (offer_dir, answer_dir);
    if (answer_dir == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_NONE) {
      GST_WARNING_OBJECT (webrtc, "Could not intersect offer direction with "
          "transceiver direction");
      goto rejected;
    }
    _media_replace_direction (media, answer_dir);

    /* set the a=setup: attribute */
    offer_setup = _get_dtls_setup_from_media (offer_media);
    answer_setup = _intersect_dtls_setup (offer_setup);
    if (answer_setup == GST_WEBRTC_DTLS_SETUP_NONE) {
      GST_WARNING_OBJECT (webrtc, "Could not intersect offer direction with "
          "transceiver direction");
      goto rejected;
    }
    _media_replace_setup (media, answer_setup);

    /* FIXME: bundle! */
    if (!trans->stream) {
      TransportStream *item = _find_transport_for_session (webrtc, i);
      if (!item)
        item = _create_transport_channel (webrtc, i);
      webrtc_transceiver_set_transport (trans, item);
    }
    /* set the a=fingerprint: for this transport */
    g_object_get (trans->stream->transport, "certificate", &cert, NULL);

    {
      gchar *fingerprint, *val;

      fingerprint =
          _generate_fingerprint_from_certificate (cert, G_CHECKSUM_SHA256);
      g_free (cert);
      val =
          g_strdup_printf ("%s %s",
          _g_checksum_to_webrtc_string (G_CHECKSUM_SHA256), fingerprint);
      g_free (fingerprint);

      gst_sdp_media_add_attribute (media, "fingerprint", val);
      g_free (val);
    }

    if (0) {
    rejected:
      GST_INFO_OBJECT (webrtc, "media %u rejected", i);
      gst_sdp_media_free (media);
      gst_sdp_media_copy (offer_media, &media);
      gst_sdp_media_set_port_info (media, 0, 0);
    }
    gst_sdp_message_add_media (ret, media);
    gst_sdp_media_free (media);

    gst_caps_unref (offer_caps);
  }

  /* FIXME: can we add not matched transceivers? */

  /* XXX: only true for the initial offerer */
  g_object_set (webrtc->priv->ice, "controller", FALSE, NULL);

  return ret;
}

struct create_sdp
{
  GstStructure *options;
  GstPromise *promise;
  GstWebRTCSDPType type;
};

static void
_create_sdp_task (GstWebRTCBin * webrtc, struct create_sdp *data)
{
  GstWebRTCSessionDescription *desc = NULL;
  GstSDPMessage *sdp = NULL;
  GstStructure *s = NULL;

  GST_INFO_OBJECT (webrtc, "creating %s sdp with options %" GST_PTR_FORMAT,
      gst_webrtc_sdp_type_to_string (data->type), data->options);

  if (data->type == GST_WEBRTC_SDP_TYPE_OFFER)
    sdp = _create_offer_task (webrtc, data->options);
  else if (data->type == GST_WEBRTC_SDP_TYPE_ANSWER)
    sdp = _create_answer_task (webrtc, data->options);
  else {
    g_assert_not_reached ();
    goto out;
  }

  if (sdp) {
    desc = gst_webrtc_session_description_new (data->type, sdp);
    s = gst_structure_new ("application/x-gst-promise",
        gst_webrtc_sdp_type_to_string (data->type),
        GST_TYPE_WEBRTC_SESSION_DESCRIPTION, desc, NULL);
  }

out:
  PC_UNLOCK (webrtc);
  gst_promise_reply (data->promise, s);
  PC_LOCK (webrtc);

  if (desc)
    gst_webrtc_session_description_free (desc);
}

static void
_free_create_sdp_data (struct create_sdp *data)
{
  if (data->options)
    gst_structure_free (data->options);
  gst_promise_unref (data->promise);
  g_free (data);
}

static void
gst_webrtc_bin_create_offer (GstWebRTCBin * webrtc,
    const GstStructure * options, GstPromise * promise)
{
  struct create_sdp *data = g_new0 (struct create_sdp, 1);

  if (options)
    data->options = gst_structure_copy (options);
  data->promise = gst_promise_ref (promise);
  data->type = GST_WEBRTC_SDP_TYPE_OFFER;

  gst_webrtc_bin_enqueue_task (webrtc, (GstWebRTCBinFunc) _create_sdp_task,
      data, (GDestroyNotify) _free_create_sdp_data);
}

static void
gst_webrtc_bin_create_answer (GstWebRTCBin * webrtc,
    const GstStructure * options, GstPromise * promise)
{
  struct create_sdp *data = g_new0 (struct create_sdp, 1);

  if (options)
    data->options = gst_structure_copy (options);
  data->promise = gst_promise_ref (promise);
  data->type = GST_WEBRTC_SDP_TYPE_ANSWER;

  gst_webrtc_bin_enqueue_task (webrtc, (GstWebRTCBinFunc) _create_sdp_task,
      data, (GDestroyNotify) _free_create_sdp_data);
}

static GstWebRTCBinPad *
_create_pad_for_sdp_media (GstWebRTCBin * webrtc, GstPadDirection direction,
    guint media_idx)
{
  GstWebRTCBinPad *pad;
  gchar *pad_name;

  pad_name =
      g_strdup_printf ("%s_%u", direction == GST_PAD_SRC ? "src" : "sink",
      media_idx);
  pad = gst_webrtc_bin_pad_new (pad_name, direction);
  g_free (pad_name);
  pad->mlineindex = media_idx;

  return pad;
}

static GstWebRTCRTPTransceiver *
_find_transceiver_for_sdp_media (GstWebRTCBin * webrtc,
    const GstSDPMessage * sdp, guint media_idx)
{
  const GstSDPMedia *media = gst_sdp_message_get_media (sdp, media_idx);
  GstWebRTCRTPTransceiver *ret = NULL;
  int i;

  for (i = 0; i < gst_sdp_media_attributes_len (media); i++) {
    const GstSDPAttribute *attr = gst_sdp_media_get_attribute (media, i);

    if (g_strcmp0 (attr->key, "mid") == 0) {
      if ((ret =
              _find_transceiver (webrtc, attr->value,
                  (FindTransceiverFunc) match_for_mid)))
        goto out;
    }
  }

  ret = _find_transceiver (webrtc, &media_idx,
      (FindTransceiverFunc) transceiver_match_for_mline);

out:
  GST_TRACE_OBJECT (webrtc, "Found transceiver %" GST_PTR_FORMAT, ret);
  return ret;
}

static GstPad *
_connect_input_stream (GstWebRTCBin * webrtc, GstWebRTCBinPad * pad)
{
/*
 * ,-------------------------webrtcbin-------------------------,
 * ;                                                           ;
 * ;          ,-------rtpbin-------,   ,--transport_send_%u--, ;
 * ;          ;    send_rtp_src_%u o---o rtp_sink            ; ;
 * ;          ;                    ;   ;                     ; ;
 * ;          ;   send_rtcp_src_%u o---o rtcp_sink           ; ;
 * ; sink_%u  ;                    ;   '---------------------' ;
 * o----------o send_rtp_sink_%u   ;                           ;
 * ;          '--------------------'                           ;
 * '--------------------- -------------------------------------'
 */
  GstPadTemplate *rtp_templ;
  GstPad *rtp_sink;
  gchar *pad_name;
  WebRTCTransceiver *trans;

  g_return_val_if_fail (pad->trans != NULL, NULL);

  GST_INFO_OBJECT (pad, "linking input stream %u", pad->mlineindex);

  rtp_templ =
      _find_pad_template (webrtc->rtpbin, GST_PAD_SINK, GST_PAD_REQUEST,
      "send_rtp_sink_%u");
  g_assert (rtp_templ);

  pad_name = g_strdup_printf ("send_rtp_sink_%u", pad->mlineindex);
  rtp_sink =
      gst_element_request_pad (webrtc->rtpbin, rtp_templ, pad_name, NULL);
  g_free (pad_name);
  gst_ghost_pad_set_target (GST_GHOST_PAD (pad), rtp_sink);
  gst_object_unref (rtp_sink);

  trans = WEBRTC_TRANSCEIVER (pad->trans);

  if (!trans->stream) {
    TransportStream *item;
    /* FIXME: bundle */
    item = _find_transport_for_session (webrtc, pad->mlineindex);
    if (!item)
      item = _create_transport_channel (webrtc, pad->mlineindex);
    webrtc_transceiver_set_transport (trans, item);
  }

  pad_name = g_strdup_printf ("send_rtp_src_%u", pad->mlineindex);
  if (!gst_element_link_pads (GST_ELEMENT (webrtc->rtpbin), pad_name,
          GST_ELEMENT (trans->stream->send_bin), "rtp_sink"))
    g_warn_if_reached ();
  g_free (pad_name);

  gst_element_sync_state_with_parent (GST_ELEMENT (trans->stream->send_bin));

  return GST_PAD (pad);
}

/* output pads are receiving elements */
static GstWebRTCBinPad *
_connect_output_stream (GstWebRTCBin * webrtc, GstWebRTCBinPad * pad)
{
/*
 * ,------------------------webrtcbin------------------------,
 * ;                             ,---------rtpbin---------,  ;
 * ; ,-transport_receive_%u--,   ;                        ;  ;
 * ; ;               rtp_src o---o recv_rtp_sink_%u       ;  ;
 * ; ;                       ;   ;                        ;  ;
 * ; ;              rtcp_src o---o recv_rtcp_sink_%u      ;  ;
 * ; '-----------------------'   ;                        ;  ; src_%u
 * ;                             ;  recv_rtp_src_%u_%u_%u o--o
 * ;                             '------------------------'  ;
 * '---------------------------------------------------------'
 */
  gchar *pad_name;
  WebRTCTransceiver *trans;

  g_return_val_if_fail (pad->trans != NULL, NULL);

  GST_INFO_OBJECT (pad, "linking output stream %u", pad->mlineindex);

  trans = WEBRTC_TRANSCEIVER (pad->trans);
  if (!trans->stream) {
    TransportStream *item;
    /* FIXME: bundle */
    item = _find_transport_for_session (webrtc, pad->mlineindex);
    if (!item)
      item = _create_transport_channel (webrtc, pad->mlineindex);
    webrtc_transceiver_set_transport (trans, item);
  }

  pad_name = g_strdup_printf ("recv_rtp_sink_%u", pad->mlineindex);
  if (!gst_element_link_pads (GST_ELEMENT (trans->stream->receive_bin),
          "rtp_src", GST_ELEMENT (webrtc->rtpbin), pad_name))
    g_warn_if_reached ();
  g_free (pad_name);

  gst_element_sync_state_with_parent (GST_ELEMENT (trans->stream->receive_bin));

  return pad;
}

typedef struct
{
  guint mlineindex;
  gchar *candidate;
} IceCandidateItem;

static void
_clear_ice_candidate_item (IceCandidateItem ** item)
{
  g_free ((*item)->candidate);
  g_free (*item);
}

static void
_add_ice_candidate (GstWebRTCBin * webrtc, IceCandidateItem * item)
{
  GstWebRTCICEStream *stream;

  stream = _find_ice_stream_for_session (webrtc, item->mlineindex);
  if (stream == NULL) {
    GST_WARNING_OBJECT (webrtc, "Unknown mline %u, ignoring", item->mlineindex);
    return;
  }

  GST_LOG_OBJECT (webrtc, "adding ICE candidate with mline:%u, %s",
      item->mlineindex, item->candidate);

  gst_webrtc_ice_add_candidate (webrtc->priv->ice, stream, item->candidate);
}

static gboolean
_filter_sdp_fields (GQuark field_id, const GValue * value,
    GstStructure * new_structure)
{
  if (!g_str_has_prefix (g_quark_to_string (field_id), "a-")) {
    gst_structure_id_set_value (new_structure, field_id, value);
  }
  return TRUE;
}

static void
_update_transceiver_from_sdp_media (GstWebRTCBin * webrtc,
    const GstSDPMessage * sdp, guint media_idx,
    GstWebRTCRTPTransceiver * rtp_trans)
{
  WebRTCTransceiver *trans = WEBRTC_TRANSCEIVER (rtp_trans);
  TransportStream *stream = trans->stream;
  GstWebRTCRTPTransceiverDirection prev_dir = rtp_trans->current_direction;
  GstWebRTCRTPTransceiverDirection new_dir;
  const GstSDPMedia *media = gst_sdp_message_get_media (sdp, media_idx);
  GstWebRTCDTLSSetup new_setup;
  gboolean new_rtcp_mux, new_rtcp_rsize;
  int i;

  rtp_trans->mline = media_idx;

  for (i = 0; i < gst_sdp_media_attributes_len (media); i++) {
    const GstSDPAttribute *attr = gst_sdp_media_get_attribute (media, i);

    if (g_strcmp0 (attr->key, "mid") == 0) {
      g_free (rtp_trans->mid);
      rtp_trans->mid = g_strdup (attr->value);
    }
  }

  if (!stream) {
    /* FIXME: find an existing transport for e.g. bundle/reconfiguration */
    stream = _find_transport_for_session (webrtc, media_idx);
    if (!stream)
      stream = _create_transport_channel (webrtc, media_idx);
    webrtc_transceiver_set_transport (trans, stream);
  }

  {
    const GstSDPMedia *local_media, *remote_media;
    GstWebRTCRTPTransceiverDirection local_dir, remote_dir;
    GstWebRTCDTLSSetup local_setup, remote_setup;
    guint i, len;
    const gchar *proto;
    GstCaps *global_caps;

    local_media =
        gst_sdp_message_get_media (webrtc->current_local_description->sdp,
        media_idx);
    remote_media =
        gst_sdp_message_get_media (webrtc->current_remote_description->sdp,
        media_idx);

    local_setup = _get_dtls_setup_from_media (local_media);
    remote_setup = _get_dtls_setup_from_media (remote_media);
    new_setup = _get_final_setup (local_setup, remote_setup);
    if (new_setup == GST_WEBRTC_DTLS_SETUP_NONE)
      return;

    local_dir = _get_direction_from_media (local_media);
    remote_dir = _get_direction_from_media (remote_media);
    new_dir = _get_final_direction (local_dir, remote_dir);
    if (new_dir == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_NONE)
      return;

    /* get proto */
    proto = gst_sdp_media_get_proto (media);
    if (proto != NULL) {
      /* Parse global SDP attributes once */
      global_caps = gst_caps_new_empty_simple ("application/x-unknown");
      GST_DEBUG_OBJECT (webrtc, "mapping sdp session level attributes to caps");
      gst_sdp_message_attributes_to_caps (sdp, global_caps);
      GST_DEBUG_OBJECT (webrtc, "mapping sdp media level attributes to caps");
      gst_sdp_media_attributes_to_caps (media, global_caps);

      /* clear the ptmap */
      g_array_set_size (stream->ptmap, 0);

      len = gst_sdp_media_formats_len (media);
      for (i = 0; i < len; i++) {
        GstCaps *caps, *outcaps;
        GstStructure *s;
        PtMapItem item;
        gint pt;
        guint j;

        pt = atoi (gst_sdp_media_get_format (media, i));

        GST_DEBUG_OBJECT (webrtc, " looking at %d pt: %d", i, pt);

        /* convert caps */
        caps = gst_sdp_media_get_caps_from_media (media, pt);
        if (caps == NULL) {
          GST_WARNING_OBJECT (webrtc, " skipping pt %d without caps", pt);
          continue;
        }

        /* Merge in global caps */
        /* Intersect will merge in missing fields to the current caps */
        outcaps = gst_caps_intersect (caps, global_caps);
        gst_caps_unref (caps);

        s = gst_caps_get_structure (outcaps, 0);
        gst_structure_set_name (s, "application/x-rtp");
        if (!g_strcmp0 (gst_structure_get_string (s, "encoding-name"),
                "ULPFEC"))
          gst_structure_set (s, "is-fec", G_TYPE_BOOLEAN, TRUE, NULL);

        item.caps = gst_caps_new_empty ();

        for (j = 0; j < gst_caps_get_size (outcaps); j++) {
          GstStructure *s = gst_caps_get_structure (outcaps, j);
          GstStructure *filtered =
              gst_structure_new_empty (gst_structure_get_name (s));

          gst_structure_foreach (s,
              (GstStructureForeachFunc) _filter_sdp_fields, filtered);
          gst_caps_append_structure (item.caps, filtered);
        }

        item.pt = pt;
        gst_caps_unref (outcaps);

        g_array_append_val (stream->ptmap, item);
      }

      gst_caps_unref (global_caps);
    }

    new_rtcp_mux = _media_has_attribute_key (local_media, "rtcp-mux")
        && _media_has_attribute_key (remote_media, "rtcp-mux");
    new_rtcp_rsize = _media_has_attribute_key (local_media, "rtcp-rsize")
        && _media_has_attribute_key (remote_media, "rtcp-rsize");

    {
      GObject *session;
      g_signal_emit_by_name (webrtc->rtpbin, "get-internal-session",
          media_idx, &session);
      if (session) {
        g_object_set (session, "rtcp-reduced-size", new_rtcp_rsize, NULL);
        g_object_unref (session);
      }
    }
  }

  if (prev_dir != GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_NONE
      && prev_dir != new_dir) {
    GST_FIXME_OBJECT (webrtc, "implement transceiver direction changes");
    return;
  }

  /* FIXME: bundle! */
  g_object_set (stream, "rtcp-mux", new_rtcp_mux, NULL);

  if (new_dir != prev_dir) {
    TransportReceiveBin *receive;

    GST_TRACE_OBJECT (webrtc, "transceiver direction change");

    /* FIXME: this may not always be true. e.g. bundle */
    g_assert (media_idx == stream->session_id);

    if (new_dir == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_SENDONLY ||
        new_dir == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_SENDRECV) {
      GstWebRTCBinPad *pad =
          _find_pad_for_mline (webrtc, GST_PAD_SINK, media_idx);
      if (pad) {
        GST_DEBUG_OBJECT (webrtc, "found existing send pad %" GST_PTR_FORMAT
            " for transceiver %" GST_PTR_FORMAT, pad, trans);
        g_assert (pad->trans == rtp_trans);
        g_assert (pad->mlineindex == media_idx);
        gst_object_unref (pad);
      } else {
        GST_DEBUG_OBJECT (webrtc,
            "creating new pad send pad for transceiver %" GST_PTR_FORMAT,
            trans);
        pad = _create_pad_for_sdp_media (webrtc, GST_PAD_SINK, media_idx);
        pad->trans = gst_object_ref (rtp_trans);
        _connect_input_stream (webrtc, pad);
        _add_pad (webrtc, pad);
      }
      g_object_set (stream, "dtls-client",
          new_setup == GST_WEBRTC_DTLS_SETUP_ACTIVE, NULL);
    }
    if (new_dir == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_RECVONLY ||
        new_dir == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_SENDRECV) {
      GstWebRTCBinPad *pad =
          _find_pad_for_mline (webrtc, GST_PAD_SRC, media_idx);
      if (pad) {
        GST_DEBUG_OBJECT (webrtc, "found existing receive pad %" GST_PTR_FORMAT
            " for transceiver %" GST_PTR_FORMAT, pad, trans);
        g_assert (pad->trans == rtp_trans);
        g_assert (pad->mlineindex == media_idx);
        gst_object_unref (pad);
      } else {
        GST_DEBUG_OBJECT (webrtc,
            "creating new receive pad for transceiver %" GST_PTR_FORMAT, trans);
        pad = _create_pad_for_sdp_media (webrtc, GST_PAD_SRC, media_idx);
        pad->trans = gst_object_ref (rtp_trans);
        _connect_output_stream (webrtc, pad);
        /* delay adding the pad until rtpbin creates the recv output pad
         * to ghost to so queries/events travel through the pipeline correctly
         * as soon as the pad is added */
        _add_pad_to_list (webrtc, pad);
      }
      g_object_set (stream, "dtls-client",
          new_setup == GST_WEBRTC_DTLS_SETUP_ACTIVE, NULL);
    }

    receive = TRANSPORT_RECEIVE_BIN (stream->receive_bin);
    if (new_dir == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_RECVONLY ||
        new_dir == GST_WEBRTC_RTP_TRANSCEIVER_DIRECTION_SENDRECV)
      transport_receive_bin_set_receive_state (receive, RECEIVE_STATE_PASS);
    else
      transport_receive_bin_set_receive_state (receive, RECEIVE_STATE_DROP);

    rtp_trans->mline = media_idx;
    rtp_trans->current_direction = new_dir;
  }
}

static gboolean
_find_compatible_unassociated_transceiver (GstWebRTCRTPTransceiver * p1,
    gconstpointer data)
{
  if (p1->mid)
    return FALSE;
  if (p1->mline != -1)
    return FALSE;

  return TRUE;
}

static gboolean
_update_transceivers_from_sdp (GstWebRTCBin * webrtc, SDPSource source,
    GstWebRTCSessionDescription * sdp)
{
  int i;

  for (i = 0; i < gst_sdp_message_medias_len (sdp->sdp); i++) {
    const GstSDPMedia *media = gst_sdp_message_get_media (sdp->sdp, i);
    GstWebRTCRTPTransceiver *trans;

    /* skip rejected media */
    if (gst_sdp_media_get_port (media) == 0)
      continue;

    trans = _find_transceiver_for_sdp_media (webrtc, sdp->sdp, i);

    if (source == SDP_LOCAL && sdp->type == GST_WEBRTC_SDP_TYPE_OFFER && !trans) {
      GST_ERROR ("State mismatch.  Could not find local transceiver by mline.");
      return FALSE;
    } else {
      if (trans) {
        _update_transceiver_from_sdp_media (webrtc, sdp->sdp, i, trans);
      } else {
        trans = _find_transceiver (webrtc, NULL,
            (FindTransceiverFunc) _find_compatible_unassociated_transceiver);
        /* XXX: default to the advertised direction in the sdp for new
         * transceviers.  The spec doesn't actually say what happens here, only
         * that calls to setDirection will change the value.  Nothing about
         * a default value when the transceiver is created internally */
        if (!trans)
          trans =
              GST_WEBRTC_RTP_TRANSCEIVER (_create_webrtc_transceiver (webrtc,
                  _get_direction_from_media (media), i));
        _update_transceiver_from_sdp_media (webrtc, sdp->sdp, i, trans);
      }
    }
  }

  return TRUE;
}

static void
_get_ice_credentials_from_sdp_media (const GstSDPMessage * sdp, guint media_idx,
    gchar ** ufrag, gchar ** pwd)
{
  int i;

  *ufrag = NULL;
  *pwd = NULL;

  {
    /* search in the corresponding media section */
    const GstSDPMedia *media = gst_sdp_message_get_media (sdp, media_idx);
    const gchar *tmp_ufrag =
        gst_sdp_media_get_attribute_val (media, "ice-ufrag");
    const gchar *tmp_pwd = gst_sdp_media_get_attribute_val (media, "ice-pwd");
    if (tmp_ufrag && tmp_pwd) {
      *ufrag = g_strdup (tmp_ufrag);
      *pwd = g_strdup (tmp_pwd);
      return;
    }
  }

  /* then in the sdp message itself */
  for (i = 0; i < gst_sdp_message_attributes_len (sdp); i++) {
    const GstSDPAttribute *attr = gst_sdp_message_get_attribute (sdp, i);

    if (g_strcmp0 (attr->key, "ice-ufrag") == 0) {
      g_assert (!*ufrag);
      *ufrag = g_strdup (attr->value);
    } else if (g_strcmp0 (attr->key, "ice-pwd") == 0) {
      g_assert (!*pwd);
      *pwd = g_strdup (attr->value);
    }
  }
  if (!*ufrag && !*pwd) {
    /* Check in the medias themselves. According to JSEP, they should be
     * identical FIXME: only for bundle-d streams */
    for (i = 0; i < gst_sdp_message_medias_len (sdp); i++) {
      const GstSDPMedia *media = gst_sdp_message_get_media (sdp, i);
      const gchar *tmp_ufrag =
          gst_sdp_media_get_attribute_val (media, "ice-ufrag");
      const gchar *tmp_pwd = gst_sdp_media_get_attribute_val (media, "ice-pwd");
      if (tmp_ufrag && tmp_pwd) {
        *ufrag = g_strdup (tmp_ufrag);
        *pwd = g_strdup (tmp_pwd);
        break;
      }
    }
  }
}

struct set_description
{
  GstPromise *promise;
  SDPSource source;
  GstWebRTCSessionDescription *sdp;
};

/* http://w3c.github.io/webrtc-pc/#set-description */
static void
_set_description_task (GstWebRTCBin * webrtc, struct set_description *sd)
{
  GstWebRTCSignalingState new_signaling_state = webrtc->signaling_state;
  GError *error = NULL;

  {
    gchar *state = _enum_value_to_string (GST_TYPE_WEBRTC_SIGNALING_STATE,
        webrtc->signaling_state);
    gchar *type_str =
        _enum_value_to_string (GST_TYPE_WEBRTC_SDP_TYPE, sd->sdp->type);
    gchar *sdp_text = gst_sdp_message_as_text (sd->sdp->sdp);
    GST_INFO_OBJECT (webrtc, "Attempting to set %s %s in the %s state",
        _sdp_source_to_string (sd->source), type_str, state);
    GST_TRACE_OBJECT (webrtc, "SDP contents\n%s", sdp_text);
    g_free (sdp_text);
    g_free (state);
    g_free (type_str);
  }

  if (!validate_sdp (webrtc, sd->source, sd->sdp, &error)) {
    GST_ERROR_OBJECT (webrtc, "%s", error->message);
    goto out;
  }

  if (webrtc->priv->is_closed) {
    GST_WARNING_OBJECT (webrtc, "we are closed");
    goto out;
  }

  switch (sd->sdp->type) {
    case GST_WEBRTC_SDP_TYPE_OFFER:{
      if (sd->source == SDP_LOCAL) {
        if (webrtc->pending_local_description)
          gst_webrtc_session_description_free
              (webrtc->pending_local_description);
        webrtc->pending_local_description =
            gst_webrtc_session_description_copy (sd->sdp);
        new_signaling_state = GST_WEBRTC_SIGNALING_STATE_HAVE_LOCAL_OFFER;
      } else {
        if (webrtc->pending_remote_description)
          gst_webrtc_session_description_free
              (webrtc->pending_remote_description);
        webrtc->pending_remote_description =
            gst_webrtc_session_description_copy (sd->sdp);
        new_signaling_state = GST_WEBRTC_SIGNALING_STATE_HAVE_REMOTE_OFFER;
      }
      break;
    }
    case GST_WEBRTC_SDP_TYPE_ANSWER:{
      if (sd->source == SDP_LOCAL) {
        if (webrtc->current_local_description)
          gst_webrtc_session_description_free
              (webrtc->current_local_description);
        webrtc->current_local_description =
            gst_webrtc_session_description_copy (sd->sdp);

        if (webrtc->current_remote_description)
          gst_webrtc_session_description_free
              (webrtc->current_remote_description);
        webrtc->current_remote_description = webrtc->pending_remote_description;
        webrtc->pending_remote_description = NULL;
      } else {
        if (webrtc->current_remote_description)
          gst_webrtc_session_description_free
              (webrtc->current_remote_description);
        webrtc->current_remote_description =
            gst_webrtc_session_description_copy (sd->sdp);

        if (webrtc->current_local_description)
          gst_webrtc_session_description_free
              (webrtc->current_local_description);
        webrtc->current_local_description = webrtc->pending_local_description;
        webrtc->pending_local_description = NULL;
      }

      if (webrtc->pending_local_description)
        gst_webrtc_session_description_free (webrtc->pending_local_description);
      webrtc->pending_local_description = NULL;

      if (webrtc->pending_remote_description)
        gst_webrtc_session_description_free
            (webrtc->pending_remote_description);
      webrtc->pending_remote_description = NULL;

      new_signaling_state = GST_WEBRTC_SIGNALING_STATE_STABLE;
      break;
    }
    case GST_WEBRTC_SDP_TYPE_ROLLBACK:{
      GST_FIXME_OBJECT (webrtc, "rollbacks are completely untested");
      if (sd->source == SDP_LOCAL) {
        if (webrtc->pending_local_description)
          gst_webrtc_session_description_free
              (webrtc->pending_local_description);
        webrtc->pending_local_description = NULL;
      } else {
        if (webrtc->pending_remote_description)
          gst_webrtc_session_description_free
              (webrtc->pending_remote_description);
        webrtc->pending_remote_description = NULL;
      }

      new_signaling_state = GST_WEBRTC_SIGNALING_STATE_STABLE;
      break;
    }
    case GST_WEBRTC_SDP_TYPE_PRANSWER:{
      GST_FIXME_OBJECT (webrtc, "pranswers are completely untested");
      if (sd->source == SDP_LOCAL) {
        if (webrtc->pending_local_description)
          gst_webrtc_session_description_free
              (webrtc->pending_local_description);
        webrtc->pending_local_description =
            gst_webrtc_session_description_copy (sd->sdp);

        new_signaling_state = GST_WEBRTC_SIGNALING_STATE_HAVE_LOCAL_PRANSWER;
      } else {
        if (webrtc->pending_remote_description)
          gst_webrtc_session_description_free
              (webrtc->pending_remote_description);
        webrtc->pending_remote_description =
            gst_webrtc_session_description_copy (sd->sdp);

        new_signaling_state = GST_WEBRTC_SIGNALING_STATE_HAVE_REMOTE_PRANSWER;
      }
      break;
    }
  }

  if (new_signaling_state != webrtc->signaling_state) {
    gchar *from = _enum_value_to_string (GST_TYPE_WEBRTC_SIGNALING_STATE,
        webrtc->signaling_state);
    gchar *to = _enum_value_to_string (GST_TYPE_WEBRTC_SIGNALING_STATE,
        new_signaling_state);
    GST_TRACE_OBJECT (webrtc, "notify signaling-state from %s "
        "to %s", from, to);
    webrtc->signaling_state = new_signaling_state;
    PC_UNLOCK (webrtc);
    g_object_notify (G_OBJECT (webrtc), "signaling-state");
    PC_LOCK (webrtc);

    g_free (from);
    g_free (to);
  }

  /* TODO: necessary data channel modifications */

  if (sd->sdp->type == GST_WEBRTC_SDP_TYPE_ROLLBACK) {
    /* FIXME:
     * If the mid value of an RTCRtpTransceiver was set to a non-null value 
     * by the RTCSessionDescription that is being rolled back, set the mid
     * value of that transceiver to null, as described by [JSEP]
     * (section 4.1.7.2.).
     * If an RTCRtpTransceiver was created by applying the
     * RTCSessionDescription that is being rolled back, and a track has not
     * been attached to it via addTrack, remove that transceiver from
     * connection's set of transceivers, as described by [JSEP]
     * (section 4.1.7.2.).
     * Restore the value of connection's [[ sctpTransport]] internal slot
     * to its value at the last stable signaling state.
     */
  }

  if (webrtc->signaling_state == GST_WEBRTC_SIGNALING_STATE_STABLE) {
    GList *tmp;
    gboolean prev_need_negotiation = webrtc->priv->need_negotiation;

    /* media modifications */
    _update_transceivers_from_sdp (webrtc, sd->source, sd->sdp);

    for (tmp = webrtc->priv->pending_sink_transceivers; tmp; tmp = tmp->next) {
      GstWebRTCBinPad *pad = GST_WEBRTC_BIN_PAD (tmp->data);

      _connect_input_stream (webrtc, pad);
      gst_pad_remove_probe (GST_PAD (pad), pad->block_id);
      pad->block_id = 0;
    }

    g_list_free_full (webrtc->priv->pending_sink_transceivers,
        (GDestroyNotify) gst_object_unref);
    webrtc->priv->pending_sink_transceivers = NULL;

    /* If connection's signaling state is now stable, update the
     * negotiation-needed flag. If connection's [[ needNegotiation]] slot
     * was true both before and after this update, queue a task to check
     * connection's [[needNegotiation]] slot and, if still true, fire a
     * simple event named negotiationneeded at connection.*/
    _update_need_negotiation (webrtc);
    if (prev_need_negotiation && webrtc->priv->need_negotiation) {
      _check_need_negotiation_task (webrtc, NULL);
    }
  }

  if (sd->source == SDP_LOCAL) {
    int i;

    for (i = 0; i < gst_sdp_message_medias_len (sd->sdp->sdp); i++) {
      gchar *ufrag, *pwd;
      TransportStream *item;

      /* FIXME: bundle */
      item = _find_transport_for_session (webrtc, i);
      if (!item)
        item = _create_transport_channel (webrtc, i);

      _get_ice_credentials_from_sdp_media (sd->sdp->sdp, i, &ufrag, &pwd);
      gst_webrtc_ice_set_local_credentials (webrtc->priv->ice,
          item->stream, ufrag, pwd);
      g_free (ufrag);
      g_free (pwd);
    }
  }

  if (sd->source == SDP_REMOTE) {
    int i;

    for (i = 0; i < gst_sdp_message_medias_len (sd->sdp->sdp); i++) {
      gchar *ufrag, *pwd;
      TransportStream *item;

      /* FIXME: bundle */
      item = _find_transport_for_session (webrtc, i);
      if (!item)
        item = _create_transport_channel (webrtc, i);

      _get_ice_credentials_from_sdp_media (sd->sdp->sdp, i, &ufrag, &pwd);
      gst_webrtc_ice_set_remote_credentials (webrtc->priv->ice,
          item->stream, ufrag, pwd);
      g_free (ufrag);
      g_free (pwd);
    }
  }

  {
    int i;
    for (i = 0; i < webrtc->priv->ice_stream_map->len; i++) {
      IceStreamItem *item =
          &g_array_index (webrtc->priv->ice_stream_map, IceStreamItem, i);

      gst_webrtc_ice_gather_candidates (webrtc->priv->ice, item->stream);
    }
  }

  if (webrtc->current_local_description && webrtc->current_remote_description) {
    int i;

    for (i = 0; i < webrtc->priv->pending_ice_candidates->len; i++) {
      IceCandidateItem *item =
          g_array_index (webrtc->priv->pending_ice_candidates,
          IceCandidateItem *, i);

      _add_ice_candidate (webrtc, item);
    }
    g_array_set_size (webrtc->priv->pending_ice_candidates, 0);
  }

out:
  PC_UNLOCK (webrtc);
  gst_promise_reply (sd->promise, NULL);
  PC_LOCK (webrtc);
}

static void
_free_set_description_data (struct set_description *sd)
{
  if (sd->promise)
    gst_promise_unref (sd->promise);
  if (sd->sdp)
    gst_webrtc_session_description_free (sd->sdp);
  g_free (sd);
}

static void
gst_webrtc_bin_set_remote_description (GstWebRTCBin * webrtc,
    GstWebRTCSessionDescription * remote_sdp, GstPromise * promise)