path: root/pjmedia/src/pjmedia/sdp_neg.c

/* $Id$ */
/* 
 * Copyright (C) 2003-2007 Benny Prijono <benny@prijono.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 
 */
#include <pjmedia/sdp_neg.h>
#include <pjmedia/sdp.h>
#include <pjmedia/errno.h>
#include <pj/assert.h>
#include <pj/pool.h>
#include <pj/string.h>
#include <pj/ctype.h>
#include <pj/array.h>

/**
 * This structure describes SDP media negotiator.
 */
struct pjmedia_sdp_neg
{
    pjmedia_sdp_neg_state state;	    /**< Negotiator state.	     */
    pj_bool_t		  has_remote_answer;
    pj_bool_t		  answer_was_remote;

    pjmedia_sdp_session	*initial_sdp,	    /**< Initial local SDP	     */
			*active_local_sdp,  /**< Currently active local SDP. */
			*active_remote_sdp, /**< Currently active remote's.  */
			*neg_local_sdp,	    /**< Temporary local SDP.	     */
			*neg_remote_sdp;    /**< Temporary remote SDP.	     */
};

static const char *state_str[] = 
{
    "STATE_NULL",
    "STATE_LOCAL_OFFER",
    "STATE_REMOTE_OFFER",
    "STATE_WAIT_NEGO",
    "STATE_DONE",
};

/*
 * Get string representation of negotiator state.
 */
PJ_DEF(const char*) pjmedia_sdp_neg_state_str(pjmedia_sdp_neg_state state)
{
    if (state >=0 && state < PJ_ARRAY_SIZE(state_str))
	return state_str[state];

    return "<?UNKNOWN?>";
}


/*
 * Create with local offer.
 */
PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_create_w_local_offer( pj_pool_t *pool,
				      const pjmedia_sdp_session *local,
				      pjmedia_sdp_neg **p_neg)
{
    pjmedia_sdp_neg *neg;
    pj_status_t status;

    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(pool && local && p_neg, PJ_EINVAL);

    *p_neg = NULL;

    /* Validate local offer. */
    PJ_ASSERT_RETURN((status=pjmedia_sdp_validate(local))==PJ_SUCCESS, status);

    /* Create and initialize negotiator. */
    neg = pj_pool_zalloc(pool, sizeof(pjmedia_sdp_neg));
    PJ_ASSERT_RETURN(neg != NULL, PJ_ENOMEM);

    neg->state = PJMEDIA_SDP_NEG_STATE_LOCAL_OFFER;
    neg->initial_sdp = pjmedia_sdp_session_clone(pool, local);
    neg->neg_local_sdp = pjmedia_sdp_session_clone(pool, local);

    *p_neg = neg;
    return PJ_SUCCESS;
}

/*
 * Create with remote offer and initial local offer/answer.
 */
PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_create_w_remote_offer(pj_pool_t *pool,
				      const pjmedia_sdp_session *initial,
				      const pjmedia_sdp_session *remote,
				      pjmedia_sdp_neg **p_neg)
{
    pjmedia_sdp_neg *neg;
    pj_status_t status;

    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(pool && remote && p_neg, PJ_EINVAL);

    *p_neg = NULL;

    /* Validate remote offer and initial answer */
    status = pjmedia_sdp_validate(remote);
    if (status != PJ_SUCCESS)
	return status;

    /* Create and initialize negotiator. */
    neg = pj_pool_zalloc(pool, sizeof(pjmedia_sdp_neg));
    PJ_ASSERT_RETURN(neg != NULL, PJ_ENOMEM);

    neg->neg_remote_sdp = pjmedia_sdp_session_clone(pool, remote);

    if (initial) {
	PJ_ASSERT_RETURN((status=pjmedia_sdp_validate(initial))==PJ_SUCCESS, 
			 status);

	neg->initial_sdp = pjmedia_sdp_session_clone(pool, initial);
	neg->neg_local_sdp = pjmedia_sdp_session_clone(pool, initial);

	neg->state = PJMEDIA_SDP_NEG_STATE_WAIT_NEGO;

    } else {
	
	neg->state = PJMEDIA_SDP_NEG_STATE_REMOTE_OFFER;

    }

    *p_neg = neg;
    return PJ_SUCCESS;
}

/*
 * Get SDP negotiator state.
 */
PJ_DEF(pjmedia_sdp_neg_state)
pjmedia_sdp_neg_get_state( pjmedia_sdp_neg *neg )
{
    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(neg != NULL, PJMEDIA_SDP_NEG_STATE_NULL);
    return neg->state;
}


PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_get_active_local( pjmedia_sdp_neg *neg,
				  const pjmedia_sdp_session **local)
{
    PJ_ASSERT_RETURN(neg && local, PJ_EINVAL);
    PJ_ASSERT_RETURN(neg->active_local_sdp, PJMEDIA_SDPNEG_ENOACTIVE);

    *local = neg->active_local_sdp;
    return PJ_SUCCESS;
}


PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_get_active_remote( pjmedia_sdp_neg *neg,
				   const pjmedia_sdp_session **remote)
{
    PJ_ASSERT_RETURN(neg && remote, PJ_EINVAL);
    PJ_ASSERT_RETURN(neg->active_remote_sdp, PJMEDIA_SDPNEG_ENOACTIVE);

    *remote = neg->active_remote_sdp;
    return PJ_SUCCESS;
}


PJ_DEF(pj_bool_t)
pjmedia_sdp_neg_was_answer_remote(pjmedia_sdp_neg *neg)
{
    PJ_ASSERT_RETURN(neg, PJ_FALSE);

    return neg->answer_was_remote;
}


PJ_DEF(pj_status_t)
pjmedia_sdp_neg_get_neg_remote( pjmedia_sdp_neg *neg,
				const pjmedia_sdp_session **remote)
{
    PJ_ASSERT_RETURN(neg && remote, PJ_EINVAL);
    PJ_ASSERT_RETURN(neg->neg_remote_sdp, PJMEDIA_SDPNEG_ENONEG);

    *remote = neg->neg_remote_sdp;
    return PJ_SUCCESS;
}

PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_get_neg_local( pjmedia_sdp_neg *neg,
			       const pjmedia_sdp_session **local)
{
    PJ_ASSERT_RETURN(neg && local, PJ_EINVAL);
    PJ_ASSERT_RETURN(neg->neg_local_sdp, PJMEDIA_SDPNEG_ENONEG);

    *local = neg->neg_local_sdp;
    return PJ_SUCCESS;
}


/*
 * Modify local SDP and wait for remote answer.
 */
PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_modify_local_offer( pj_pool_t *pool,
				    pjmedia_sdp_neg *neg,
				    const pjmedia_sdp_session *local)
{
    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(pool && neg && local, PJ_EINVAL);

    /* Can only do this in STATE_DONE. */
    PJ_ASSERT_RETURN(neg->state == PJMEDIA_SDP_NEG_STATE_DONE, 
		     PJMEDIA_SDPNEG_EINSTATE);

    /* Change state to STATE_LOCAL_OFFER */
    neg->state = PJMEDIA_SDP_NEG_STATE_LOCAL_OFFER;
    neg->initial_sdp = pjmedia_sdp_session_clone(pool, local);
    neg->neg_local_sdp = pjmedia_sdp_session_clone(pool, local);

    return PJ_SUCCESS;
}


PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_send_local_offer( pj_pool_t *pool,
				  pjmedia_sdp_neg *neg,
				  const pjmedia_sdp_session **offer)
{
    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(neg && offer, PJ_EINVAL);

    *offer = NULL;

    /* Can only do this in STATE_DONE or STATE_LOCAL_OFFER. */
    PJ_ASSERT_RETURN(neg->state == PJMEDIA_SDP_NEG_STATE_DONE ||
		     neg->state == PJMEDIA_SDP_NEG_STATE_LOCAL_OFFER, 
		     PJMEDIA_SDPNEG_EINSTATE);

    if (neg->state == PJMEDIA_SDP_NEG_STATE_DONE) {
	/* If in STATE_DONE, set the active SDP as the offer. */
	PJ_ASSERT_RETURN(neg->active_local_sdp, PJMEDIA_SDPNEG_ENOACTIVE);

	neg->state = PJMEDIA_SDP_NEG_STATE_LOCAL_OFFER;
	neg->neg_local_sdp = pjmedia_sdp_session_clone(pool, 
						       neg->active_local_sdp);
	*offer = neg->active_local_sdp;

    } else {
	/* We assume that we're in STATE_LOCAL_OFFER.
	 * In this case set the neg_local_sdp as the offer.
	 */
	*offer = neg->neg_local_sdp;
    }

    
    return PJ_SUCCESS;
}


PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_set_remote_answer( pj_pool_t *pool,
				   pjmedia_sdp_neg *neg,
				   const pjmedia_sdp_session *remote)
{
    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(pool && neg && remote, PJ_EINVAL);

    /* Can only do this in STATE_LOCAL_OFFER.
     * If we haven't provided local offer, then rx_remote_offer() should
     * be called instead of this function.
     */
    PJ_ASSERT_RETURN(neg->state == PJMEDIA_SDP_NEG_STATE_LOCAL_OFFER, 
		     PJMEDIA_SDPNEG_EINSTATE);

    /* We're ready to negotiate. */
    neg->state = PJMEDIA_SDP_NEG_STATE_WAIT_NEGO;
    neg->has_remote_answer = PJ_TRUE;
    neg->neg_remote_sdp = pjmedia_sdp_session_clone(pool, remote);
 
    return PJ_SUCCESS;
}

PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_set_remote_offer( pj_pool_t *pool,
				  pjmedia_sdp_neg *neg,
				  const pjmedia_sdp_session *remote)
{
    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(pool && neg && remote, PJ_EINVAL);

    /* Can only do this in STATE_DONE.
     * If we already provide local offer, then rx_remote_answer() should
     * be called instead of this function.
     */
    PJ_ASSERT_RETURN(neg->state == PJMEDIA_SDP_NEG_STATE_DONE, 
		     PJMEDIA_SDPNEG_EINSTATE);

    /* State now is STATE_REMOTE_OFFER. */
    neg->state = PJMEDIA_SDP_NEG_STATE_REMOTE_OFFER;
    neg->neg_remote_sdp = pjmedia_sdp_session_clone(pool, remote);

    return PJ_SUCCESS;
}

PJ_DEF(pj_status_t) 
pjmedia_sdp_neg_set_local_answer( pj_pool_t *pool,
				  pjmedia_sdp_neg *neg,
				  const pjmedia_sdp_session *local)
{
    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(pool && neg && local, PJ_EINVAL);

    /* Can only do this in STATE_REMOTE_OFFER.
     * If we already provide local offer, then rx_remote_answer() should
     * be called instead of this function.
     */
    PJ_ASSERT_RETURN(neg->state == PJMEDIA_SDP_NEG_STATE_REMOTE_OFFER, 
		     PJMEDIA_SDPNEG_EINSTATE);

    /* State now is STATE_WAIT_NEGO. */
    neg->state = PJMEDIA_SDP_NEG_STATE_WAIT_NEGO;
    if (local)
	neg->neg_local_sdp = pjmedia_sdp_session_clone(pool, local);
    else {
	PJ_ASSERT_RETURN(neg->initial_sdp, PJMEDIA_SDPNEG_ENOINITIAL);
	neg->neg_local_sdp = pjmedia_sdp_session_clone(pool, neg->initial_sdp);
    }

    return PJ_SUCCESS;
}

PJ_DEF(pj_bool_t) pjmedia_sdp_neg_has_local_answer(pjmedia_sdp_neg *neg)
{
    pj_assert(neg && neg->state==PJMEDIA_SDP_NEG_STATE_WAIT_NEGO);
    return !neg->has_remote_answer;
}


/* Swap string. */
static void str_swap(pj_str_t *str1, pj_str_t *str2)
{
    pj_str_t tmp = *str1;
    *str1 = *str2;
    *str2 = tmp;
}

static void remove_all_media_directions(pjmedia_sdp_media *m)
{
    pjmedia_sdp_media_remove_all_attr(m, "inactive");
    pjmedia_sdp_media_remove_all_attr(m, "sendrecv");
    pjmedia_sdp_media_remove_all_attr(m, "sendonly");
    pjmedia_sdp_media_remove_all_attr(m, "recvonly");
}

/* Update media direction based on peer's media direction */
static void update_media_direction(pj_pool_t *pool,
				   const pjmedia_sdp_media *remote,
				   pjmedia_sdp_media *local)
{
   if (pjmedia_sdp_media_find_attr2(remote, "inactive", NULL) != NULL) {
	/* If remote has "a=inactive", then local is inactive too */

	pjmedia_sdp_attr *a;

	remove_all_media_directions(local);

	a = pjmedia_sdp_attr_create(pool, "inactive", NULL);
	pjmedia_sdp_media_add_attr(local, a);

    } else if(pjmedia_sdp_media_find_attr2(remote, "sendonly", NULL) != NULL) {
	/* If remote has "a=sendonly", then set local to "recvonly" if
	 * it is currently "sendrecv".
	 */
    
	pjmedia_sdp_attr *a;

	remove_all_media_directions(local);

	a = pjmedia_sdp_attr_create(pool, "recvonly", NULL);
	pjmedia_sdp_media_add_attr(local, a);

    } else if(pjmedia_sdp_media_find_attr2(remote, "recvonly", NULL) != NULL) {
	/* If remote has "a=recvonly", then set local to "sendonly" if
	 * it is currently "sendrecv".
	 */
    
	pjmedia_sdp_attr *a;

	remove_all_media_directions(local);

	a = pjmedia_sdp_attr_create(pool, "sendonly", NULL);
	pjmedia_sdp_media_add_attr(local, a);

    } else if(pjmedia_sdp_media_find_attr2(remote, "sendrecv", NULL) != NULL) {

	pjmedia_sdp_attr *a;

	remove_all_media_directions(local);

	a = pjmedia_sdp_attr_create(pool, "sendrecv", NULL);
	pjmedia_sdp_media_add_attr(local, a);

    } else {
	/* Otherwise remote is set to "sendrecv".
	 */
	remove_all_media_directions(local);
    }
}

/* Update single local media description to after receiving answer
 * from remote.
 */
static pj_status_t process_m_answer( pj_pool_t *pool,
				     pjmedia_sdp_media *offer,
				     pjmedia_sdp_media *answer,
				     pj_bool_t allow_asym)
{
    unsigned i;

    /* Check that the media type match our offer. */

    if (pj_strcmp(&answer->desc.media, &offer->desc.media)!=0) {
	/* The media type in the answer is different than the offer! */
	return PJMEDIA_SDPNEG_EINVANSMEDIA;
    }


    /* Chec that transport in the answer match our offer. */

    if (pj_strcmp(&answer->desc.transport, 
		  &offer->desc.transport)!=0) 
    {
	/* The transport in the answer is different than the offer! */
	return PJMEDIA_SDPNEG_EINVANSTP;
    }

    /* Check if remote has rejected our offer */
    
    if (answer->desc.port == 0) {
	
	/* Remote has rejected our offer. 
	 * Set our port to zero too in active SDP.
	 */
	offer->desc.port = 0;
    }


    /* Process direction attributes */
    update_media_direction(pool, answer, offer);
 
    /* If asymetric media is allowed, then just check that remote answer has 
     * codecs that are within the offer. 
     *
     * Otherwise if asymetric media is not allowed, then we will choose only
     * one codec in our initial offer to match the answer.
     */
    if (allow_asym) {
	for (i=0; i<answer->desc.fmt_count; ++i) {
	    unsigned j;
	    pj_str_t *rem_fmt = &answer->desc.fmt[i];

	    for (j=0; j<offer->desc.fmt_count; ++j) {
		if (pj_strcmp(rem_fmt, &answer->desc.fmt[j])==0)
		    break;
	    }

	    if (j != offer->desc.fmt_count) {
		/* Found at least one common codec. */
		break;
	    }
	}

	if (i == answer->desc.fmt_count) {
	    /* No common codec in the answer! */
	    return PJMEDIA_SDPNEG_EANSNOMEDIA;
	}

	PJ_TODO(CHECK_SDP_NEGOTIATION_WHEN_ASYMETRIC_MEDIA_IS_ALLOWED);

    } else {
	/* Remove all format in the offer that has no matching answer */
	for (i=0; i<offer->desc.fmt_count;) {
	    unsigned pt;
	    pj_uint32_t j;
	    pj_str_t *fmt = &offer->desc.fmt[i];
	    

	    /* Find matching answer */
	    pt = pj_strtoul(fmt);

	    if (pt < 96) {
		for (j=0; j<answer->desc.fmt_count; ++j) {
		    if (pj_strcmp(fmt, &answer->desc.fmt[j])==0)
			break;
		}
	    } else {
		/* This is dynamic payload type.
		 * For dynamic payload type, we must look the rtpmap and
		 * compare the encoding name.
		 */
		const pjmedia_sdp_attr *a;
		pjmedia_sdp_rtpmap or;

		/* Get the rtpmap for the payload type in the offer. */
		a = pjmedia_sdp_media_find_attr2(offer, "rtpmap", fmt);
		if (!a) {
		    pj_assert(!"Bug! Offer should have been validated");
		    return PJ_EBUG;
		}
		pjmedia_sdp_attr_get_rtpmap(a, &or);

		/* Find paylaod in answer SDP with matching 
		 * encoding name and clock rate.
		 */
		for (j=0; j<answer->desc.fmt_count; ++j) {
		    a = pjmedia_sdp_media_find_attr2(answer, "rtpmap", 
						     &answer->desc.fmt[j]);
		    if (a) {
			pjmedia_sdp_rtpmap ar;
			pjmedia_sdp_attr_get_rtpmap(a, &ar);

			/* See if encoding name, clock rate, and channel
			 * count match 
			 */
			if (!pj_stricmp(&or.enc_name, &ar.enc_name) &&
			    or.clock_rate == ar.clock_rate &&
			    (pj_stricmp(&or.param, &ar.param)==0 ||
			     (ar.param.slen==1 && *ar.param.ptr=='1')))
			{
			    /* Match! */
			    break;
			}
		    }
		}
	    }

	    if (j == answer->desc.fmt_count) {
		/* This format has no matching answer.
		 * Remove it from our offer.
		 */
		pjmedia_sdp_attr *a;

		/* Remove rtpmap associated with this format */
		a = pjmedia_sdp_media_find_attr2(offer, "rtpmap", fmt);
		if (a)
		    pjmedia_sdp_media_remove_attr(offer, a);

		/* Remove fmtp associated with this format */
		a = pjmedia_sdp_media_find_attr2(offer, "fmtp", fmt);
		if (a)
		    pjmedia_sdp_media_remove_attr(offer, a);

		/* Remove this format from offer's array */
		pj_array_erase(offer->desc.fmt, sizeof(offer->desc.fmt[0]),
			       offer->desc.fmt_count, i);
		--offer->desc.fmt_count;

	    } else {
		++i;
	    }
	}

	/* Arrange format in the offer so the order match the priority
	 * in the answer
	 */
	for (i=0; i<answer->desc.fmt_count; ++i) {
	    unsigned j;
	    pj_str_t *fmt = &answer->desc.fmt[i];

	    for (j=i; j<offer->desc.fmt_count; ++j) {
		if (pj_strcmp(fmt, &offer->desc.fmt[j])==0) {
		    str_swap(&offer->desc.fmt[i], &offer->desc.fmt[j]);
		    break;
		}
	    }
	}
    }

    /* Looks okay */
    return PJ_SUCCESS;
}


/* Update local media session (offer) to create active local session
 * after receiving remote answer.
 */
static pj_status_t process_answer(pj_pool_t *pool,
				  pjmedia_sdp_session *offer,
				  pjmedia_sdp_session *answer,
				  pj_bool_t allow_asym,
				  pjmedia_sdp_session **p_active)
{
    unsigned mi;
    pj_bool_t has_active = PJ_FALSE;
    pj_status_t status;

    /* Check arguments. */
    PJ_ASSERT_RETURN(pool && offer && answer && p_active, PJ_EINVAL);

    /* Check that media count match between offer and answer */
    if (offer->media_count != answer->media_count)
	return PJMEDIA_SDPNEG_EMISMEDIA;

    /* Now update each media line in the offer with the answer. */
    for (mi=0; mi<offer->media_count; ++mi) {
	status = process_m_answer(pool, offer->media[mi], answer->media[mi],
				  allow_asym);
	if (status != PJ_SUCCESS)
	    return status;

	if (offer->media[mi]->desc.port != 0)
	    has_active = PJ_TRUE;
    }

    *p_active = offer;

    return has_active ? PJ_SUCCESS : PJMEDIA_SDPNEG_ENOMEDIA;
}

/* Try to match offer with answer. */
static pj_status_t match_offer(pj_pool_t *pool,
			       const pjmedia_sdp_media *offer,
			       const pjmedia_sdp_media *local,
			       pjmedia_sdp_media **p_answer)
{
    unsigned i;
    pj_bool_t offer_has_codec = 0,
	      offer_has_telephone_event = 0,
	      offer_has_other = 0,
	      found_matching_codec = 0,
	      found_matching_telephone_event = 0,
	      found_matching_other = 0;
    unsigned pt_answer_count = 0;
    pj_str_t pt_answer[PJMEDIA_MAX_SDP_FMT];
    pjmedia_sdp_media *answer;

    /* With the addition of telephone-event and dodgy MS RTC SDP, 
     * the answer generation algorithm looks really shitty...
     */
    for (i=0; i<offer->desc.fmt_count; ++i) {
	unsigned j;
	
	if (pj_isdigit(*offer->desc.fmt[i].ptr)) {
	    /* This is normal/standard payload type, where it's identified
	     * by payload number.
	     */
	    unsigned pt;

	    pt = pj_strtoul(&offer->desc.fmt[i]);
	    
	    if (pt < 96) {
		/* For static payload type, it's enough to compare just
		 * the payload number.
		 */

		offer_has_codec = 1;

		/* We just need to select one codec. 
		 * Continue if we have selected matching codec for previous 
		 * payload.
		 */
		if (found_matching_codec)
		    continue;

		/* Find matching codec in local descriptor. */
		for (j=0; j<local->desc.fmt_count; ++j) {
		    unsigned p;
		    p = pj_strtoul(&local->desc.fmt[j]);
		    if (p == pt && pj_isdigit(*local->desc.fmt[j].ptr)) {
			found_matching_codec = 1;
			pt_answer[pt_answer_count++] = local->desc.fmt[j];
			break;
		    }
		}

	    } else {
		/* This is dynamic payload type.
		 * For dynamic payload type, we must look the rtpmap and
		 * compare the encoding name.
		 */
		const pjmedia_sdp_attr *a;
		pjmedia_sdp_rtpmap or;
		pj_bool_t is_codec;

		/* Get the rtpmap for the payload type in the offer. */
		a = pjmedia_sdp_media_find_attr2(offer, "rtpmap", 
						 &offer->desc.fmt[i]);
		if (!a) {
		    pj_assert(!"Bug! Offer should have been validated");
		    return PJMEDIA_SDP_EMISSINGRTPMAP;
		}
		pjmedia_sdp_attr_get_rtpmap(a, &or);

		if (!pj_strcmp2(&or.enc_name, "telephone-event")) {
		    offer_has_telephone_event = 1;
		    if (found_matching_telephone_event)
			continue;
		    is_codec = 0;
		} else {
		    offer_has_codec = 1;
		    if (found_matching_codec)
			continue;
		    is_codec = 1;
		}
		
		/* Find paylaod in our initial SDP with matching 
		 * encoding name and clock rate.
		 */
		for (j=0; j<local->desc.fmt_count; ++j) {
		    a = pjmedia_sdp_media_find_attr2(local, "rtpmap", 
						     &local->desc.fmt[j]);
		    if (a) {
			pjmedia_sdp_rtpmap lr;
			pjmedia_sdp_attr_get_rtpmap(a, &lr);

			/* See if encoding name, clock rate, and
			 * channel count  match 
			 */
			if (!pj_stricmp(&or.enc_name, &lr.enc_name) &&
			    or.clock_rate == lr.clock_rate &&
			    (pj_strcmp(&or.param, &lr.param)==0 ||
			     (or.param.slen==1 && *or.param.ptr=='1'))) 
			{
			    /* Match! */
			    if (is_codec)
				found_matching_codec = 1;
			    else
				found_matching_telephone_event = 1;
			    pt_answer[pt_answer_count++] = local->desc.fmt[j];
			    break;
			}
		    }
		}
	    }

	} else {
	    /* This is a non-standard, brain damaged SDP where the payload
	     * type is non-numeric. It exists e.g. in Microsoft RTC based
	     * UA, to indicate instant messaging capability.
	     * Example:
	     *	- m=x-ms-message 5060 sip null
	     */
	    offer_has_other = 1;
	    if (found_matching_other)
		continue;

	    for (j=0; j<local->desc.fmt_count; ++j) {
		if (!pj_strcmp(&offer->desc.fmt[i], &local->desc.fmt[j])) {
		    /* Match */
		    found_matching_other = 1;
		    pt_answer[pt_answer_count++] = local->desc.fmt[j];
		    break;
		}
	    }
	}
    }

    /* See if all types of offer can be matched. */
#if 1
    if (offer_has_codec && !found_matching_codec) {
	return PJMEDIA_SDPNEG_NOANSCODEC;
    }

    if (offer_has_telephone_event && !found_matching_telephone_event) {
	return PJMEDIA_SDPNEG_NOANSTELEVENT;
    }

    if (offer_has_other && !found_matching_other) {
	return PJMEDIA_SDPNEG_NOANSUNKNOWN;
    }
#else
    PJ_TODO(FULL_MATCHING_WITH_TELEPHONE_EVENTS);
    if (!found_matching_codec &&
	!found_matching_telephone_event &&
	!found_matching_other)
    {
	/* Some of the payload in the offer has no matching local sdp */
	return PJ_FALSE;
    }
#endif

    /* Seems like everything is in order.
     * Build the answer by cloning from local media, but rearrange the payload
     * to suit the offer.
     */
    answer = pjmedia_sdp_media_clone(pool, local);
    for (i=0; i<pt_answer_count; ++i) {
	unsigned j;
	for (j=i; j<answer->desc.fmt_count; ++j) {
	    if (!pj_strcmp(&answer->desc.fmt[j], &pt_answer[i]))
		break;
	}
	pj_assert(j != answer->desc.fmt_count);
	str_swap(&answer->desc.fmt[i], &answer->desc.fmt[j]);
    }
    
    /* Remove unwanted local formats. */
    for (i=pt_answer_count; i<answer->desc.fmt_count; ++i) {
	pjmedia_sdp_attr *a;

	/* Remove rtpmap for this format */
	a = pjmedia_sdp_media_find_attr2(answer, "rtpmap", 
					 &answer->desc.fmt[i]);
	if (a) {
	    pjmedia_sdp_media_remove_attr(answer, a);
	}

	/* Remove fmtp for this format */
	a = pjmedia_sdp_media_find_attr2(answer, "fmtp", 
					 &answer->desc.fmt[i]);
	if (a) {
	    pjmedia_sdp_media_remove_attr(answer, a);
	}
    }
    answer->desc.fmt_count = pt_answer_count;

    /* If offer has zero port, set our answer with zero port too */
    if (offer->desc.port==0)
	answer->desc.port = 0;

    /* Update media direction. */
    update_media_direction(pool, offer, answer);

    *p_answer = answer;
    return PJ_SUCCESS;
}

/* Create complete answer for remote's offer. */
static pj_status_t create_answer( pj_pool_t *pool,
				  const pjmedia_sdp_session *initial,
				  const pjmedia_sdp_session *offer,
				  pjmedia_sdp_session **p_answer)
{
    pj_status_t status = PJMEDIA_SDPNEG_ENOMEDIA;
    pj_bool_t has_active = PJ_FALSE;
    pjmedia_sdp_session *answer;
    char media_used[PJMEDIA_MAX_SDP_MEDIA];
    unsigned i;

    /* Validate remote offer. 
     * This should have been validated before.
     */
    PJ_ASSERT_RETURN((status=pjmedia_sdp_validate(offer))==PJ_SUCCESS, status);

    /* Create initial answer by duplicating initial SDP,
     * but clear all media lines. The media lines will be filled up later.
     */
    answer = pjmedia_sdp_session_clone(pool, initial);
    PJ_ASSERT_RETURN(answer != NULL, PJ_ENOMEM);

    answer->media_count = 0;

    pj_bzero(media_used, sizeof(media_used));

    /* For each media line, create our answer based on our initial
     * capability.
     */
    for (i=0; i<offer->media_count; ++i) {
	const pjmedia_sdp_media *om;	/* offer */
	const pjmedia_sdp_media *im;	/* initial media */
	pjmedia_sdp_media *am = NULL;	/* answer/result */
	unsigned j;

	om = offer->media[i];

	/* Find media description in our initial capability that matches
	 * the media type and transport type of offer's media, has
	 * matching codec, and has not been used to answer other offer.
	 */
	for (im=NULL, j=0; j<initial->media_count; ++j) {
	    im = initial->media[j];
	    if (pj_strcmp(&om->desc.media, &im->desc.media)==0 &&
		pj_strcmp(&om->desc.transport, &im->desc.transport)==0 &&
		media_used[j] == 0)
	    {
		/* See if it has matching codec. */
		status = match_offer(pool, om, im, &am);
		if (status == PJ_SUCCESS) {
		    /* Mark media as used. */
		    media_used[j] = 1;
		    break;
		}
	    }
	}

	if (j==initial->media_count) {
	    /* No matching media.
	     * Reject the offer by setting the port to zero in the answer.
	     */
	    pjmedia_sdp_attr *a;

	    /* For simplicity in the construction of the answer, we'll
	     * just clone the media from the offer. Anyway receiver will
	     * ignore anything in the media once it sees that the port
	     * number is zero.
	     */
	    am = pjmedia_sdp_media_clone(pool, om);
	    am->desc.port = 0;

	    /* Remove direction attribute, and replace with inactive */
	    remove_all_media_directions(am);

	    a = pjmedia_sdp_attr_create(pool, "inactive", NULL);
	    pjmedia_sdp_media_add_attr(am, a);

	} else {
	    /* The answer is in am */
	    pj_assert(am != NULL);
	}

	/* Add the media answer */
	answer->media[answer->media_count++] = am;

	/* Check if this media is active.*/
	if (am->desc.port != 0)
	    has_active = PJ_TRUE;
    }

    *p_answer = answer;

    return has_active ? PJ_SUCCESS : status;
}

/* The best bit: SDP negotiation function! */
PJ_DEF(pj_status_t) pjmedia_sdp_neg_negotiate( pj_pool_t *pool,
					       pjmedia_sdp_neg *neg,
					       pj_bool_t allow_asym)
{
    pj_status_t status;

    /* Check arguments are valid. */
    PJ_ASSERT_RETURN(pool && neg, PJ_EINVAL);

    /* Must be in STATE_WAIT_NEGO state. */
    PJ_ASSERT_RETURN(neg->state == PJMEDIA_SDP_NEG_STATE_WAIT_NEGO, 
		     PJMEDIA_SDPNEG_EINSTATE);

    /* Must have remote offer. */
    PJ_ASSERT_RETURN(neg->neg_remote_sdp, PJ_EBUG);

    if (neg->has_remote_answer) {
	pjmedia_sdp_session *active;
	status = process_answer(pool, neg->neg_local_sdp, neg->neg_remote_sdp,
			        allow_asym, &active);
	if (status == PJ_SUCCESS) {
	    /* Only update active SDPs when negotiation is successfull */
	    neg->active_local_sdp = active;
	    neg->active_remote_sdp = neg->neg_remote_sdp;

	}
    } else {
	pjmedia_sdp_session *answer = NULL;

	status = create_answer(pool, neg->neg_local_sdp, neg->neg_remote_sdp,
			       &answer);
	if (status == PJ_SUCCESS) {
	    pj_uint32_t active_ver;

	    if (neg->active_local_sdp)
		active_ver = neg->active_local_sdp->origin.version;
	    else
		active_ver = neg->initial_sdp->origin.version;

	    /* Only update active SDPs when negotiation is successfull */
	    neg->active_local_sdp = answer;
	    neg->active_remote_sdp = neg->neg_remote_sdp;

	    /* Increment SDP version */
	    neg->active_local_sdp->origin.version = ++active_ver;
	}
    }

    /* State is DONE regardless */
    neg->state = PJMEDIA_SDP_NEG_STATE_DONE;

    /* Save state */
    neg->answer_was_remote = neg->has_remote_answer;

    /* Clear temporary SDP */
    neg->neg_local_sdp = neg->neg_remote_sdp = NULL;
    neg->has_remote_answer = PJ_FALSE;

    return status;
}