res_pjsip_t38.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013, Digium, Inc.
 *
 * Joshua Colp <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \author Joshua Colp <[email protected]>
 *
 * \brief SIP T.38 handling
 */

/*** MODULEINFO
   <depend>pjproject</depend>
   <depend>res_pjsip</depend>
   <depend>res_pjsip_session</depend>
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include <pjsip.h>
#include <pjsip_ua.h>
#include <pjmedia.h>
#include <pjlib.h>

#include "asterisk/utils.h"
#include "asterisk/module.h"
#include "asterisk/udptl.h"
#include "asterisk/netsock2.h"
#include "asterisk/channel.h"
#include "asterisk/acl.h"
#include "asterisk/stream.h"
#include "asterisk/format_cache.h"

#include "asterisk/res_pjsip.h"
#include "asterisk/res_pjsip_session.h"

/*! \brief The number of seconds after receiving a T.38 re-invite before automatically rejecting it */
#define T38_AUTOMATIC_REJECTION_SECONDS 5

/*! \brief Address for UDPTL */
static struct ast_sockaddr address;

/*! \brief T.38 state information */
struct t38_state {
   /*! \brief Current state */
   enum ast_sip_session_t38state state;
   /*! \brief Our T.38 parameters */
   struct ast_control_t38_parameters our_parms;
   /*! \brief Their T.38 parameters */
   struct ast_control_t38_parameters their_parms;
   /*! \brief Timer entry for automatically rejecting an inbound re-invite */
   pj_timer_entry timer;
   /*! Preserved media state for when T.38 ends */
   struct ast_sip_session_media_state *media_state;
};

/*! \brief Destructor for T.38 state information */
static void t38_state_destroy(void *obj)
{
   struct t38_state *state = obj;

   ast_sip_session_media_state_free(state->media_state);
   ast_free(obj);
}

/*! \brief Datastore for attaching T.38 state information */
static const struct ast_datastore_info t38_datastore = {
   .type = "t38",
   .destroy = t38_state_destroy,
};

/*! \brief Structure for T.38 parameters task data */
struct t38_parameters_task_data {
   /*! \brief Session itself */
   struct ast_sip_session *session;
   /*! \brief T.38 control frame */
   struct ast_frame *frame;
};

/*! \brief Destructor for T.38 data */
static void t38_parameters_task_data_destroy(void *obj)
{
   struct t38_parameters_task_data *data = obj;

   ao2_cleanup(data->session);

   if (data->frame) {
      ast_frfree(data->frame);
   }
}

/*! \brief Allocator for T.38 data */
static struct t38_parameters_task_data *t38_parameters_task_data_alloc(struct ast_sip_session *session,
   struct ast_frame *frame)
{
   struct t38_parameters_task_data *data = ao2_alloc(sizeof(*data), t38_parameters_task_data_destroy);

   if (!data) {
      return NULL;
   }

   data->session = session;
   ao2_ref(session, +1);
   data->frame = ast_frdup(frame);
   if (!data->frame) {
      ao2_ref(data, -1);
      data = NULL;
   }

   return data;
}

/*! \brief Helper function for changing the T.38 state */
static void t38_change_state(struct ast_sip_session *session, struct ast_sip_session_media *session_media,
   struct t38_state *state, enum ast_sip_session_t38state new_state)
{
   enum ast_sip_session_t38state old_state = session->t38state;
   struct ast_control_t38_parameters parameters = { .request_response = 0, };
   pj_time_val delay = { .sec = T38_AUTOMATIC_REJECTION_SECONDS };

   if (old_state == new_state) {
      return;
   }

   session->t38state = new_state;
   ast_debug(2, "T.38 state changed to '%u' from '%u' on channel '%s'\n",
      new_state, old_state,
      session->channel ? ast_channel_name(session->channel) : "<gone>");

   if (pj_timer_heap_cancel_if_active(pjsip_endpt_get_timer_heap(ast_sip_get_pjsip_endpoint()),
      &state->timer, 0)) {
      ast_debug(2, "Automatic T.38 rejection on channel '%s' terminated\n",
         session->channel ? ast_channel_name(session->channel) : "<gone>");
      ao2_ref(session, -1);
   }

   if (!session->channel) {
      return;
   }

   switch (new_state) {
   case T38_PEER_REINVITE:
      ao2_ref(session, +1);
      if (pjsip_endpt_schedule_timer(ast_sip_get_pjsip_endpoint(), &state->timer, &delay) != PJ_SUCCESS) {
         ast_log(LOG_WARNING, "Scheduling of automatic T.38 rejection for channel '%s' failed\n",
            ast_channel_name(session->channel));
         ao2_ref(session, -1);
      }
      parameters = state->their_parms;
      parameters.max_ifp = ast_udptl_get_far_max_ifp(session_media->udptl);
      parameters.request_response = AST_T38_REQUEST_NEGOTIATE;
      ast_udptl_set_tag(session_media->udptl, "%s", ast_channel_name(session->channel));

      /* Inform the bridge the channel is in that it needs to be reconfigured */
      ast_channel_set_unbridged(session->channel, 1);
      break;
   case T38_ENABLED:
      parameters = state->their_parms;
      parameters.max_ifp = ast_udptl_get_far_max_ifp(session_media->udptl);
      parameters.request_response = AST_T38_NEGOTIATED;
      ast_udptl_set_tag(session_media->udptl, "%s", ast_channel_name(session->channel));
      break;
   case T38_REJECTED:
   case T38_DISABLED:
      if (old_state == T38_ENABLED) {
         parameters.request_response = AST_T38_TERMINATED;
      } else if (old_state == T38_LOCAL_REINVITE) {
         parameters.request_response = AST_T38_REFUSED;
      }
      break;
   case T38_LOCAL_REINVITE:
      /* Inform the bridge the channel is in that it needs to be reconfigured */
      ast_channel_set_unbridged(session->channel, 1);
      break;
   case T38_MAX_ENUM:
      /* Well, that shouldn't happen */
      ast_assert(0);
      break;
   }

   if (parameters.request_response) {
      ast_queue_control_data(session->channel, AST_CONTROL_T38_PARAMETERS, &parameters, sizeof(parameters));
   }
}

/*! \brief Task function which rejects a T.38 re-invite and resumes handling it */
static int t38_automatic_reject(void *obj)
{
   RAII_VAR(struct ast_sip_session *, session, obj, ao2_cleanup);
   RAII_VAR(struct ast_datastore *, datastore, ast_sip_session_get_datastore(session, "t38"), ao2_cleanup);

   if (!datastore) {
      return 0;
   }

   ast_debug(2, "Automatically rejecting T.38 request on channel '%s'\n",
      session->channel ? ast_channel_name(session->channel) : "<gone>");

   t38_change_state(session, NULL, datastore->data, T38_REJECTED);
   ast_sip_session_resume_reinvite(session);

   return 0;
}

/*! \brief Timer entry callback which queues a task to reject a T.38 re-invite and resume handling it */
static void t38_automatic_reject_timer_cb(pj_timer_heap_t *timer_heap, struct pj_timer_entry *entry)
{
   struct ast_sip_session *session = entry->user_data;

   if (ast_sip_push_task(session->serializer, t38_automatic_reject, session)) {
      ao2_ref(session, -1);
   }
}

/*! \brief Helper function which retrieves or allocates a T.38 state information datastore */
static struct t38_state *t38_state_get_or_alloc(struct ast_sip_session *session)
{
   RAII_VAR(struct ast_datastore *, datastore, ast_sip_session_get_datastore(session, "t38"), ao2_cleanup);
   struct t38_state *state;

   /* While the datastore refcount is decremented this is operating in the serializer so it will remain valid regardless */
   if (datastore) {
      return datastore->data;
   }

   if (!(datastore = ast_sip_session_alloc_datastore(&t38_datastore, "t38"))
      || !(datastore->data = ast_calloc(1, sizeof(struct t38_state)))
      || ast_sip_session_add_datastore(session, datastore)) {
      return NULL;
   }

   state = datastore->data;

   /* This will get bumped up before scheduling */
   pj_timer_entry_init(&state->timer, 0, session, t38_automatic_reject_timer_cb);

   return state;
}

/*! \brief Initializes UDPTL support on a session, only done when actually needed */
static int t38_initialize_session(struct ast_sip_session *session, struct ast_sip_session_media *session_media)
{
   if (session_media->udptl) {
      return 0;
   }

   if (!(session_media->udptl = ast_udptl_new_with_bindaddr(NULL, NULL, 0, &address))) {
      return -1;
   }

   ast_udptl_set_error_correction_scheme(session_media->udptl, session->endpoint->media.t38.error_correction);
   ast_udptl_setnat(session_media->udptl, session->endpoint->media.t38.nat);
   ast_udptl_set_far_max_datagram(session_media->udptl, session->endpoint->media.t38.maxdatagram);
   ast_debug(3, "UDPTL initialized on session for %s\n", ast_channel_name(session->channel));

   return 0;
}

/*! \brief Callback for when T.38 reinvite SDP is created */
static int t38_reinvite_sdp_cb(struct ast_sip_session *session, pjmedia_sdp_session *sdp)
{
   struct t38_state *state;

   state = t38_state_get_or_alloc(session);
   if (!state) {
      return -1;
   }

   state->media_state = ast_sip_session_media_state_clone(session->active_media_state);

   return 0;
}

/*! \brief Callback for when a response is received for a T.38 re-invite */
static int t38_reinvite_response_cb(struct ast_sip_session *session, pjsip_rx_data *rdata)
{
   struct pjsip_status_line status = rdata->msg_info.msg->line.status;
   struct t38_state *state;
   struct ast_sip_session_media *session_media = NULL;

   if (status.code / 100 <= 1) {
      /* Ignore any non-final responses (1xx) */
      return 0;
   }

   if (session->t38state != T38_LOCAL_REINVITE) {
      /* Do nothing.  We have already processed a final response. */
      ast_debug(3, "Received %d response to T.38 re-invite on '%s' but already had a final response (T.38 state:%d)\n",
         status.code,
         session->channel ? ast_channel_name(session->channel) : "unknown channel",
         session->t38state);
      return 0;
   }

   state = t38_state_get_or_alloc(session);
   if (!session->channel || !state) {
      ast_log(LOG_WARNING, "Received %d response to T.38 re-invite on '%s' but state unavailable\n",
         status.code,
         session->channel ? ast_channel_name(session->channel) : "unknown channel");
      return 0;
   }

   if (status.code / 100 == 2) {
      /* Accept any 2xx response as successfully negotiated */
      int index;

      session_media = session->active_media_state->default_session[AST_MEDIA_TYPE_IMAGE];

      /*
       * If there is a session_media object, but no udptl object available
       * then it's assumed the stream was declined.
       */
      if (session_media && !session_media->udptl) {
         session_media = NULL;
      }

      if (!session_media) {
         ast_log(LOG_WARNING, "Received %d response to T.38 re-invite on '%s' but no active session media\n",
               status.code, session->channel ? ast_channel_name(session->channel) : "unknown channel");
      } else {
         t38_change_state(session, session_media, state, T38_ENABLED);

         /* Stop all the streams in the stored away active state, they'll go back to being active once
          * we reinvite back.
          */
         for (index = 0; index < AST_VECTOR_SIZE(&state->media_state->sessions); ++index) {
            struct ast_sip_session_media *session_media = AST_VECTOR_GET(&state->media_state->sessions, index);

            if (session_media && session_media->handler && session_media->handler->stream_stop) {
               session_media->handler->stream_stop(session_media);
            }
         }

         return 0;
      }
   } else {
      session_media = session->pending_media_state->default_session[AST_MEDIA_TYPE_IMAGE];
   }

   /* If no session_media then response contained a declined stream, so disable */
   t38_change_state(session, NULL, state, session_media ? T38_REJECTED : T38_DISABLED);

   /* Abort this attempt at switching to T.38 by resetting the pending state and freeing our stored away active state */
   ast_sip_session_media_state_free(state->media_state);
   state->media_state = NULL;
   ast_sip_session_media_state_reset(session->pending_media_state);

   return 0;
}

/*! \brief Helper function which creates a media state for strictly T.38 */
static struct ast_sip_session_media_state *t38_create_media_state(struct ast_sip_session *session)
{
   struct ast_sip_session_media_state *media_state;
   struct ast_stream *stream;
   struct ast_format_cap *caps;
   struct ast_sip_session_media *session_media;

   media_state = ast_sip_session_media_state_alloc();
   if (!media_state) {
      return NULL;
   }

   media_state->topology = ast_stream_topology_alloc();
   if (!media_state->topology) {
      ast_sip_session_media_state_free(media_state);
      return NULL;
   }

   stream = ast_stream_alloc("t38", AST_MEDIA_TYPE_IMAGE);
   if (!stream) {
      ast_sip_session_media_state_free(media_state);
      return NULL;
   }

   ast_stream_set_state(stream, AST_STREAM_STATE_SENDRECV);
   if (ast_stream_topology_set_stream(media_state->topology, 0, stream)) {
      ast_stream_free(stream);
      ast_sip_session_media_state_free(media_state);
      return NULL;
   }

   caps = ast_format_cap_alloc(AST_FORMAT_CAP_FLAG_DEFAULT);
   if (!caps) {
      ast_sip_session_media_state_free(media_state);
      return NULL;
   }

   ast_stream_set_formats(stream, caps);
   /* stream holds a reference to cap, release the local reference
    * now so we don't have to deal with it in the error condition. */
   ao2_ref(caps, -1);
   if (ast_format_cap_append(caps, ast_format_t38, 0)) {
      ast_sip_session_media_state_free(media_state);
      return NULL;
   }

   session_media = ast_sip_session_media_state_add(session, media_state, AST_MEDIA_TYPE_IMAGE, 0);
   if (!session_media) {
      ast_sip_session_media_state_free(media_state);
      return NULL;
   }

   if (t38_initialize_session(session, session_media)) {
      ast_sip_session_media_state_free(media_state);
      return NULL;
   }

   return media_state;
}

/*! \brief Task for reacting to T.38 control frame */
static int t38_interpret_parameters(void *obj)
{
   RAII_VAR(struct t38_parameters_task_data *, data, obj, ao2_cleanup);
   const struct ast_control_t38_parameters *parameters = data->frame->data.ptr;
   struct t38_state *state = t38_state_get_or_alloc(data->session);
   struct ast_sip_session_media *session_media = NULL;

   if (!state) {
      return 0;
   }

   switch (parameters->request_response) {
   case AST_T38_NEGOTIATED:
   case AST_T38_REQUEST_NEGOTIATE:         /* Request T38 */
      /* Negotiation can not take place without a valid max_ifp value. */
      if (!parameters->max_ifp) {
         if (data->session->t38state == T38_PEER_REINVITE) {
            t38_change_state(data->session, NULL, state, T38_REJECTED);
            ast_sip_session_resume_reinvite(data->session);
         } else if (data->session->t38state == T38_ENABLED) {
            t38_change_state(data->session, NULL, state, T38_DISABLED);
            ast_sip_session_refresh(data->session, NULL, NULL, NULL,
               AST_SIP_SESSION_REFRESH_METHOD_INVITE, 1, state->media_state);
            state->media_state = NULL;
         }
         break;
      } else if (data->session->t38state == T38_PEER_REINVITE) {
         state->our_parms = *parameters;
         /* modify our parameters to conform to the peer's parameters,
          * based on the rules in the ITU T.38 recommendation
          */
         if (!state->their_parms.fill_bit_removal) {
            state->our_parms.fill_bit_removal = 0;
         }
         if (!state->their_parms.transcoding_mmr) {
            state->our_parms.transcoding_mmr = 0;
         }
         if (!state->their_parms.transcoding_jbig) {
            state->our_parms.transcoding_jbig = 0;
         }
         state->our_parms.version = MIN(state->our_parms.version, state->their_parms.version);
         state->our_parms.rate_management = state->their_parms.rate_management;
         session_media = data->session->pending_media_state->default_session[AST_MEDIA_TYPE_IMAGE];
         if (!session_media) {
            ast_log(LOG_ERROR, "Failed to negotiate parameters for reinvite on channel '%s' (No pending session media).\n",
               data->session->channel ? ast_channel_name(data->session->channel) : "unknown channel");
            break;
         }
         ast_udptl_set_local_max_ifp(session_media->udptl, state->our_parms.max_ifp);
         t38_change_state(data->session, session_media, state, T38_ENABLED);
         ast_sip_session_resume_reinvite(data->session);
      } else if ((data->session->t38state != T38_ENABLED) ||
            ((data->session->t38state == T38_ENABLED) &&
                                (parameters->request_response == AST_T38_REQUEST_NEGOTIATE))) {
         struct ast_sip_session_media_state *media_state;

         media_state = t38_create_media_state(data->session);
         if (!media_state) {
            break;
         }
         state->our_parms = *parameters;
         session_media = media_state->default_session[AST_MEDIA_TYPE_IMAGE];
         if (!session_media) {
            ast_log(LOG_ERROR, "Failed to negotiate parameters on channel '%s' (No default session media).\n",
               data->session->channel ? ast_channel_name(data->session->channel) : "unknown channel");
            break;
         }
         ast_udptl_set_local_max_ifp(session_media->udptl, state->our_parms.max_ifp);
         t38_change_state(data->session, NULL, state, T38_LOCAL_REINVITE);
         ast_sip_session_refresh(data->session, NULL, t38_reinvite_sdp_cb, t38_reinvite_response_cb,
            AST_SIP_SESSION_REFRESH_METHOD_INVITE, 1, media_state);
      }
      break;
   case AST_T38_TERMINATED:
   case AST_T38_REFUSED:
   case AST_T38_REQUEST_TERMINATE:         /* Shutdown T38 */
      if (data->session->t38state == T38_PEER_REINVITE) {
         t38_change_state(data->session, NULL, state, T38_REJECTED);
         ast_sip_session_resume_reinvite(data->session);
      } else if (data->session->t38state == T38_ENABLED) {
         t38_change_state(data->session, NULL, state, T38_DISABLED);
         ast_sip_session_refresh(data->session, NULL, NULL, NULL, AST_SIP_SESSION_REFRESH_METHOD_INVITE, 1, state->media_state);
         state->media_state = NULL;
      }
      break;
   case AST_T38_REQUEST_PARMS: {    /* Application wants remote's parameters re-sent */
      struct ast_control_t38_parameters parameters = state->their_parms;

      if (data->session->t38state == T38_PEER_REINVITE) {
         session_media = data->session->pending_media_state->default_session[AST_MEDIA_TYPE_IMAGE];
         if (!session_media) {
            ast_log(LOG_ERROR, "Failed to request parameters for reinvite on channel '%s' (No pending session media).\n",
               data->session->channel ? ast_channel_name(data->session->channel) : "unknown channel");
            break;
         }
         parameters.max_ifp = ast_udptl_get_far_max_ifp(session_media->udptl);
         parameters.request_response = AST_T38_REQUEST_NEGOTIATE;
         ast_queue_control_data(data->session->channel, AST_CONTROL_T38_PARAMETERS, &parameters, sizeof(parameters));
      }
      break;
   }
   default:
      break;
   }

   return 0;
}

/*! \brief Frame hook callback for T.38 related stuff */
static struct ast_frame *t38_framehook(struct ast_channel *chan, struct ast_frame *f,
   enum ast_framehook_event event, void *data)
{
   struct ast_sip_channel_pvt *channel = ast_channel_tech_pvt(chan);

   if (event != AST_FRAMEHOOK_EVENT_WRITE) {
      return f;
   }

   if (f->frametype == AST_FRAME_CONTROL
      && f->subclass.integer == AST_CONTROL_T38_PARAMETERS) {
      if (channel->session->endpoint->media.t38.enabled) {
         struct t38_parameters_task_data *task_data;

         task_data = t38_parameters_task_data_alloc(channel->session, f);
         if (task_data
            && ast_sip_push_task(channel->session->serializer,
               t38_interpret_parameters, task_data)) {
            ao2_ref(task_data, -1);
         }
      } else {
         static const struct ast_control_t38_parameters rsp_refused = {
            .request_response = AST_T38_REFUSED,
         };
         static const struct ast_control_t38_parameters rsp_terminated = {
            .request_response = AST_T38_TERMINATED,
         };
         const struct ast_control_t38_parameters *parameters = f->data.ptr;

         switch (parameters->request_response) {
         case AST_T38_REQUEST_NEGOTIATE:
            ast_debug(2, "T.38 support not enabled on %s, refusing T.38 negotiation\n",
               ast_channel_name(chan));
            ast_queue_control_data(chan, AST_CONTROL_T38_PARAMETERS,
               &rsp_refused, sizeof(rsp_refused));
            break;
         case AST_T38_REQUEST_TERMINATE:
            ast_debug(2, "T.38 support not enabled on %s, 'terminating' T.38 session\n",
               ast_channel_name(chan));
            ast_queue_control_data(chan, AST_CONTROL_T38_PARAMETERS,
               &rsp_terminated, sizeof(rsp_terminated));
            break;
         default:
            break;
         }
      }
   }

   return f;
}

static void t38_masq(void *data, int framehook_id,
        struct ast_channel *old_chan, struct ast_channel *new_chan)
{
   if (ast_channel_tech(old_chan) == ast_channel_tech(new_chan)) {
      return;
   }

   /* This framehook is only applicable to PJSIP channels */
   ast_framehook_detach(new_chan, framehook_id);
}

static int t38_consume(void *data, enum ast_frame_type type)
{
   return (type == AST_FRAME_CONTROL) ? 1 : 0;
}

static const struct ast_datastore_info t38_framehook_datastore = {
   .type = "T38 framehook",
};

/*! \brief Function called to attach T.38 framehook to channel when appropriate */
static void t38_attach_framehook(struct ast_sip_session *session)
{
   int framehook_id;
   struct ast_datastore *datastore = NULL;
   static struct ast_framehook_interface hook = {
      .version = AST_FRAMEHOOK_INTERFACE_VERSION,
      .event_cb = t38_framehook,
      .consume_cb = t38_consume,
      .chan_fixup_cb = t38_masq,
      .chan_breakdown_cb = t38_masq,
   };

   /* If the channel's already gone, bail */
   if (!session->channel) {
      return;
   }

   /* Always attach the framehook so we can quickly reject */

   ast_channel_lock(session->channel);

   /* Skip attaching the framehook if the T.38 datastore already exists for the channel */
   datastore = ast_channel_datastore_find(session->channel, &t38_framehook_datastore,
      NULL);
   if (datastore) {
      ast_channel_unlock(session->channel);
      return;
   }

   framehook_id = ast_framehook_attach(session->channel, &hook);
   if (framehook_id < 0) {
      ast_log(LOG_WARNING, "Could not attach T.38 Frame hook, T.38 will be unavailable on '%s'\n",
         ast_channel_name(session->channel));
      ast_channel_unlock(session->channel);
      return;
   }

   datastore = ast_datastore_alloc(&t38_framehook_datastore, NULL);
   if (!datastore) {
      ast_log(LOG_ERROR, "Could not alloc T.38 Frame hook datastore, T.38 will be unavailable on '%s'\n",
         ast_channel_name(session->channel));
      ast_framehook_detach(session->channel, framehook_id);
      ast_channel_unlock(session->channel);
      return;
   }

   ast_channel_datastore_add(session->channel, datastore);
   ast_channel_unlock(session->channel);
}

/*! \brief Function called when an INVITE arrives */
static int t38_incoming_invite_request(struct ast_sip_session *session, struct pjsip_rx_data *rdata)
{
   t38_attach_framehook(session);
   return 0;
}

/*! \brief Function called when an INVITE is sent */
static void t38_outgoing_invite_request(struct ast_sip_session *session, struct pjsip_tx_data *tdata)
{
   t38_attach_framehook(session);
}

/*! \brief Get Max T.38 Transmission rate from T38 capabilities */
static unsigned int t38_get_rate(enum ast_control_t38_rate rate)
{
   switch (rate) {
   case AST_T38_RATE_2400:
      return 2400;
   case AST_T38_RATE_4800:
      return 4800;
   case AST_T38_RATE_7200:
      return 7200;
   case AST_T38_RATE_9600:
      return 9600;
   case AST_T38_RATE_12000:
      return 12000;
   case AST_T38_RATE_14400:
      return 14400;
   default:
      return 0;
   }
}

/*! \brief Supplement for adding framehook to session channel */
static struct ast_sip_session_supplement t38_supplement = {
   .method = "INVITE",
   .priority = AST_SIP_SUPPLEMENT_PRIORITY_CHANNEL + 1,
   .incoming_request = t38_incoming_invite_request,
   .outgoing_request = t38_outgoing_invite_request,
};

/*! \brief Parse a T.38 image stream and store the attribute information */
static void t38_interpret_sdp(struct t38_state *state, struct ast_sip_session *session, struct ast_sip_session_media *session_media,
   const struct pjmedia_sdp_media *stream)
{
   unsigned int attr_i;

   for (attr_i = 0; attr_i < stream->attr_count; attr_i++) {
      pjmedia_sdp_attr *attr = stream->attr[attr_i];

      if (!pj_stricmp2(&attr->name, "t38faxmaxbuffer")) {
         /* This is purposely left empty, it is unused */
      } else if (!pj_stricmp2(&attr->name, "t38maxbitrate") || !pj_stricmp2(&attr->name, "t38faxmaxrate")) {
         switch (pj_strtoul(&attr->value)) {
         case 14400:
            state->their_parms.rate = AST_T38_RATE_14400;
            break;
         case 12000:
            state->their_parms.rate = AST_T38_RATE_12000;
            break;
         case 9600:
            state->their_parms.rate = AST_T38_RATE_9600;
            break;
         case 7200:
            state->their_parms.rate = AST_T38_RATE_7200;
            break;
         case 4800:
            state->their_parms.rate = AST_T38_RATE_4800;
            break;
         case 2400:
            state->their_parms.rate = AST_T38_RATE_2400;
            break;
         }
      } else if (!pj_stricmp2(&attr->name, "t38faxversion")) {
         state->their_parms.version = pj_strtoul(&attr->value);
      } else if (!pj_stricmp2(&attr->name, "t38faxmaxdatagram") || !pj_stricmp2(&attr->name, "t38maxdatagram")) {
         if (!session->endpoint->media.t38.maxdatagram) {
            ast_udptl_set_far_max_datagram(session_media->udptl, pj_strtoul(&attr->value));
         }
      } else if (!pj_stricmp2(&attr->name, "t38faxfillbitremoval")) {
         state->their_parms.fill_bit_removal = 1;
      } else if (!pj_stricmp2(&attr->name, "t38faxtranscodingmmr")) {
         state->their_parms.transcoding_mmr = 1;
      } else if (!pj_stricmp2(&attr->name, "t38faxtranscodingjbig")) {
         state->their_parms.transcoding_jbig = 1;
      } else if (!pj_stricmp2(&attr->name, "t38faxratemanagement")) {
         if (!pj_stricmp2(&attr->value, "localTCF")) {
            state->their_parms.rate_management = AST_T38_RATE_MANAGEMENT_LOCAL_TCF;
         } else if (!pj_stricmp2(&attr->value, "transferredTCF")) {
            state->their_parms.rate_management = AST_T38_RATE_MANAGEMENT_TRANSFERRED_TCF;
         }
      } else if (!pj_stricmp2(&attr->name, "t38faxudpec")) {
         if (session->t38state == T38_LOCAL_REINVITE) {
            if (session->endpoint->media.t38.error_correction == UDPTL_ERROR_CORRECTION_FEC) {
               if (!pj_stricmp2(&attr->value, "t38UDPFEC")) {
                  ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_FEC);
               } else if (!pj_stricmp2(&attr->value, "t38UDPRedundancy")) {
                  ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_REDUNDANCY);
               } else {
                  ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_NONE);
               }
            } else if (session->endpoint->media.t38.error_correction == UDPTL_ERROR_CORRECTION_REDUNDANCY) {
               if (!pj_stricmp2(&attr->value, "t38UDPRedundancy")) {
                  ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_REDUNDANCY);
               } else {
                  ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_NONE);
               }
            } else {
               ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_NONE);
            }
         } else {
            if (!pj_stricmp2(&attr->value, "t38UDPRedundancy")) {
               ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_REDUNDANCY);
            } else if (!pj_stricmp2(&attr->value, "t38UDPFEC")) {
               ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_FEC);
            } else {
               ast_udptl_set_error_correction_scheme(session_media->udptl, UDPTL_ERROR_CORRECTION_NONE);
            }
         }
      }

   }
}

/*! \brief Function which defers an incoming media stream */
static enum ast_sip_session_sdp_stream_defer defer_incoming_sdp_stream(
   struct ast_sip_session *session, struct ast_sip_session_media *session_media,
   const struct pjmedia_sdp_session *sdp, const struct pjmedia_sdp_media *stream)
{
   struct t38_state *state;

   if (!session->endpoint->media.t38.enabled) {
      ast_debug(3, "Not deferring incoming SDP stream: T.38 not enabled on %s\n", ast_channel_name(session->channel));
      return AST_SIP_SESSION_SDP_DEFER_NOT_HANDLED;
   }

   if (t38_initialize_session(session, session_media)) {
      ast_debug(3, "Not deferring incoming SDP stream: Failed to initialize UDPTL on %s\n", ast_channel_name(session->channel));
      return AST_SIP_SESSION_SDP_DEFER_ERROR;
   }

   if (!(state = t38_state_get_or_alloc(session))) {
      return AST_SIP_SESSION_SDP_DEFER_ERROR;
   }

   t38_interpret_sdp(state, session, session_media, stream);

   /* If they are initiating the re-invite we need to defer responding until later */
   if (session->t38state == T38_DISABLED) {
      t38_change_state(session, session_media, state, T38_PEER_REINVITE);
      ast_debug(3, "Deferring incoming SDP stream on %s for peer re-invite\n", ast_channel_name(session->channel));
      return AST_SIP_SESSION_SDP_DEFER_NEEDED;
   }

   return AST_SIP_SESSION_SDP_DEFER_NOT_NEEDED;
}

/*! \brief Function which negotiates an incoming media stream */
static int negotiate_incoming_sdp_stream(struct ast_sip_session *session,
   struct ast_sip_session_media *session_media, const struct pjmedia_sdp_session *sdp,
   int index, struct ast_stream *asterisk_stream)
{
   struct t38_state *state;
   char host[NI_MAXHOST];
   pjmedia_sdp_media *stream = sdp->media[index];
   RAII_VAR(struct ast_sockaddr *, addrs, NULL, ast_free);

   if (!session->endpoint->media.t38.enabled) {
      ast_debug(3, "Declining; T.38 not enabled on session\n");
      return 0;
   }

   if (!(state = t38_state_get_or_alloc(session))) {
      return 0;
   }

   if ((session->t38state == T38_REJECTED) || (session->t38state == T38_DISABLED)) {
      ast_debug(3, "Declining; T.38 state is rejected or declined\n");
      t38_change_state(session, NULL, state, T38_DISABLED);
      return 0;
   }

   ast_copy_pj_str(host, stream->conn ? &stream->conn->addr : &sdp->conn->addr, sizeof(host));

   /* Ensure that the address provided is valid */
   if (ast_sockaddr_resolve(&addrs, host, PARSE_PORT_FORBID, AST_AF_INET) <= 0) {
      /* The provided host was actually invalid so we error out this negotiation */
      ast_debug(3, "Declining; provided host is invalid\n");
      return 0;
   }

   /* Check the address family to make sure it matches configured */
   if ((ast_sockaddr_is_ipv6(addrs) && !session->endpoint->media.t38.ipv6) ||
      (ast_sockaddr_is_ipv4(addrs) && session->endpoint->media.t38.ipv6)) {
      /* The address does not match configured */
      ast_debug(3, "Declining, provided host does not match configured address family\n");
      return 0;
   }

   return 1;
}

/*! \brief Function which creates an outgoing stream */
static int create_outgoing_sdp_stream(struct ast_sip_session *session, struct ast_sip_session_media *session_media,
                  struct pjmedia_sdp_session *sdp, const struct pjmedia_sdp_session *remote, struct ast_stream *stream)
{
   pj_pool_t *pool = session->inv_session->pool_prov;
   static const pj_str_t STR_IN = { "IN", 2 };
   static const pj_str_t STR_IP4 = { "IP4", 3};
   static const pj_str_t STR_IP6 = { "IP6", 3};
   static const pj_str_t STR_UDPTL = { "udptl", 5 };
   static const pj_str_t STR_T38 = { "t38", 3 };
   static const pj_str_t STR_TRANSFERREDTCF = { "transferredTCF", 14 };
   static const pj_str_t STR_LOCALTCF = { "localTCF", 8 };
   static const pj_str_t STR_T38UDPFEC = { "t38UDPFEC", 9 };
   static const pj_str_t STR_T38UDPREDUNDANCY = { "t38UDPRedundancy", 16 };
   struct t38_state *state;
   pjmedia_sdp_media *media;
   const char *hostip = NULL;
   struct ast_sockaddr addr;
   char tmp[512];
   pj_str_t stmp;

   if (!session->endpoint->media.t38.enabled) {
      ast_debug(3, "Not creating outgoing SDP stream: T.38 not enabled\n");
      return 1;
   } else if ((session->t38state != T38_LOCAL_REINVITE) && (session->t38state != T38_PEER_REINVITE) &&
      (session->t38state != T38_ENABLED)) {
      ast_debug(3, "Not creating outgoing SDP stream: T.38 not enabled\n");
      return 1;
   } else if (!(state = t38_state_get_or_alloc(session))) {
      return -1;
   } else if (t38_initialize_session(session, session_media)) {
      ast_debug(3, "Not creating outgoing SDP stream: Failed to initialize T.38 session\n");
      return -1;
   }

   if (!(media = pj_pool_zalloc(pool, sizeof(struct pjmedia_sdp_media))) ||
      !(media->conn = pj_pool_zalloc(pool, sizeof(struct pjmedia_sdp_conn)))) {
      return -1;
   }

   pj_strdup2(pool, &media->desc.media, ast_codec_media_type2str(session_media->type));
   media->desc.transport = STR_UDPTL;

   if (ast_strlen_zero(session->endpoint->media.address)) {
      hostip = ast_sip_get_host_ip_string(session->endpoint->media.t38.ipv6 ? pj_AF_INET6() : pj_AF_INET());
   } else {
      hostip = session->endpoint->media.address;
   }

   if (ast_strlen_zero(hostip)) {
      ast_debug(3, "Not creating outgoing SDP stream: no known host IP\n");
      return -1;
   }

   media->conn->net_type = STR_IN;
   media->conn->addr_type = session->endpoint->media.t38.ipv6 ? STR_IP6 : STR_IP4;
   pj_strdup2(pool, &media->conn->addr, hostip);
   ast_udptl_get_us(session_media->udptl, &addr);
   media->desc.port = (pj_uint16_t) ast_sockaddr_port(&addr);
   media->desc.port_count = 1;
   media->desc.fmt[media->desc.fmt_count++] = STR_T38;

   snprintf(tmp, sizeof(tmp), "%u", state->our_parms.version);
   media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxVersion", pj_cstr(&stmp, tmp));

   snprintf(tmp, sizeof(tmp), "%u", t38_get_rate(state->our_parms.rate));
   media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38MaxBitRate", pj_cstr(&stmp, tmp));

   if (state->our_parms.fill_bit_removal) {
      media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxFillBitRemoval", NULL);
   }

   if (state->our_parms.transcoding_mmr) {
      media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxTranscodingMMR", NULL);
   }

   if (state->our_parms.transcoding_jbig) {
      media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxTranscodingJBIG", NULL);
   }

   switch (state->our_parms.rate_management) {
   case AST_T38_RATE_MANAGEMENT_TRANSFERRED_TCF:
      media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxRateManagement", &STR_TRANSFERREDTCF);
      break;
   case AST_T38_RATE_MANAGEMENT_LOCAL_TCF:
      media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxRateManagement", &STR_LOCALTCF);
      break;
   }

   snprintf(tmp, sizeof(tmp), "%u", ast_udptl_get_local_max_datagram(session_media->udptl));
   media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxMaxDatagram", pj_cstr(&stmp, tmp));

   switch (ast_udptl_get_error_correction_scheme(session_media->udptl)) {
   case UDPTL_ERROR_CORRECTION_NONE:
      break;
   case UDPTL_ERROR_CORRECTION_FEC:
      media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxUdpEC", &STR_T38UDPFEC);
      break;
   case UDPTL_ERROR_CORRECTION_REDUNDANCY:
      media->attr[media->attr_count++] = pjmedia_sdp_attr_create(pool, "T38FaxUdpEC", &STR_T38UDPREDUNDANCY);
      break;
   }

   sdp->media[sdp->media_count++] = media;

   return 1;
}

static struct ast_frame *media_session_udptl_read_callback(struct ast_sip_session *session, struct ast_sip_session_media *session_media)
{
   struct ast_frame *frame;

   if (!session_media->udptl) {
      return &ast_null_frame;
   }

   frame = ast_udptl_read(session_media->udptl);
   if (!frame) {
      return NULL;
   }

   frame->stream_num = session_media->stream_num;

   return frame;
}

static int media_session_udptl_write_callback(struct ast_sip_session *session, struct ast_sip_session_media *session_media, struct ast_frame *frame)
{
   if (!session_media->udptl) {
      return 0;
   }

   return ast_udptl_write(session_media->udptl, frame);
}

/*! \brief Function which applies a negotiated stream */
static int apply_negotiated_sdp_stream(struct ast_sip_session *session,
   struct ast_sip_session_media *session_media, const struct pjmedia_sdp_session *local,
   const struct pjmedia_sdp_session *remote, int index, struct ast_stream *asterisk_stream)
{
   RAII_VAR(struct ast_sockaddr *, addrs, NULL, ast_free);
   pjmedia_sdp_media *remote_stream = remote->media[index];
   char host[NI_MAXHOST];
   struct t38_state *state;

   if (!session_media->udptl) {
      ast_debug(3, "Not applying negotiated SDP stream: no UDTPL session\n");
      return 0;
   }

   if (!(state = t38_state_get_or_alloc(session))) {
      return -1;
   }

   ast_copy_pj_str(host, remote_stream->conn ? &remote_stream->conn->addr : &remote->conn->addr, sizeof(host));

   /* Ensure that the address provided is valid */
   if (ast_sockaddr_resolve(&addrs, host, PARSE_PORT_FORBID, AST_AF_UNSPEC) <= 0) {
      /* The provided host was actually invalid so we error out this negotiation */
      ast_debug(3, "Not applying negotiated SDP stream: failed to resolve remote stream host\n");
      return -1;
   }

   ast_sockaddr_set_port(addrs, remote_stream->desc.port);
   ast_udptl_set_peer(session_media->udptl, addrs);

   t38_interpret_sdp(state, session, session_media, remote_stream);

   ast_sip_session_media_set_write_callback(session, session_media, media_session_udptl_write_callback);
   ast_sip_session_media_add_read_callback(session, session_media, ast_udptl_fd(session_media->udptl),
      media_session_udptl_read_callback);

   return 0;
}

/*! \brief Function which updates the media stream with external media address, if applicable */
static void change_outgoing_sdp_stream_media_address(pjsip_tx_data *tdata, struct pjmedia_sdp_media *stream, struct ast_sip_transport *transport)
{
   RAII_VAR(struct ast_sip_transport_state *, transport_state, ast_sip_get_transport_state(ast_sorcery_object_get_id(transport)), ao2_cleanup);
   char host[NI_MAXHOST];
   struct ast_sockaddr our_sdp_addr = { { 0, } };

   /* If the stream has been rejected there will be no connection line */
   if (!stream->conn || !transport_state) {
      return;
   }

   ast_copy_pj_str(host, &stream->conn->addr, sizeof(host));
   ast_sockaddr_parse(&our_sdp_addr, host, PARSE_PORT_FORBID);

   /* Reversed check here. We don't check the remote endpoint being
    * in our local net, but whether our outgoing session IP is
    * local. If it is not, we won't do rewriting. No localnet
    * configured? Always rewrite. */
   if (ast_sip_transport_is_nonlocal(transport_state, &our_sdp_addr) && transport_state->localnet) {
      return;
   }
   ast_debug(5, "Setting media address to %s\n", ast_sockaddr_stringify_host(&transport_state->external_media_address));
   pj_strdup2(tdata->pool, &stream->conn->addr, ast_sockaddr_stringify_host(&transport_state->external_media_address));
}

/*! \brief Function which destroys the UDPTL instance when session ends */
static void stream_destroy(struct ast_sip_session_media *session_media)
{
   if (session_media->udptl) {
      ast_udptl_destroy(session_media->udptl);
   }
   session_media->udptl = NULL;
}

/*! \brief SDP handler for 'image' media stream */
static struct ast_sip_session_sdp_handler image_sdp_handler = {
   .id = "image",
   .defer_incoming_sdp_stream = defer_incoming_sdp_stream,
   .negotiate_incoming_sdp_stream = negotiate_incoming_sdp_stream,
   .create_outgoing_sdp_stream = create_outgoing_sdp_stream,
   .apply_negotiated_sdp_stream = apply_negotiated_sdp_stream,
   .change_outgoing_sdp_stream_media_address = change_outgoing_sdp_stream_media_address,
   .stream_destroy = stream_destroy,
};

/*! \brief Unloads the SIP T.38 module from Asterisk */
static int unload_module(void)
{
   ast_sip_session_unregister_sdp_handler(&image_sdp_handler, "image");
   ast_sip_session_unregister_supplement(&t38_supplement);

   return 0;
}

/*!
 * \brief Load the module
 *
 * Module loading including tests for configuration or dependencies.
 * This function can return AST_MODULE_LOAD_FAILURE, AST_MODULE_LOAD_DECLINE,
 * or AST_MODULE_LOAD_SUCCESS. If a dependency or environment variable fails
 * tests return AST_MODULE_LOAD_FAILURE. If the module can not load the
 * configuration file or other non-critical problem return
 * AST_MODULE_LOAD_DECLINE. On success return AST_MODULE_LOAD_SUCCESS.
 */
static int load_module(void)
{
   if (ast_check_ipv6()) {
      ast_sockaddr_parse(&address, "::", 0);
   } else {
      ast_sockaddr_parse(&address, "0.0.0.0", 0);
   }

   ast_sip_session_register_supplement(&t38_supplement);

   if (ast_sip_session_register_sdp_handler(&image_sdp_handler, "image")) {
      ast_log(LOG_ERROR, "Unable to register SDP handler for image stream type\n");
      goto end;
   }

   return AST_MODULE_LOAD_SUCCESS;
end:
   unload_module();

   return AST_MODULE_LOAD_DECLINE;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "PJSIP T.38 UDPTL Support",
   .support_level = AST_MODULE_SUPPORT_CORE,
   .load = load_module,
   .unload = unload_module,
   .load_pri = AST_MODPRI_CHANNEL_DRIVER,
   .requires = "res_pjsip,res_pjsip_session,udptl",
);