pjsip/src/pjsip-ua/sip_timer.c

/* $Id$ */
/* 
 * Copyright (C) 2009 Teluu Inc. (http://www.teluu.com)
 *
 * 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 <pjsip-ua/sip_timer.h>
#include <pjsip/print_util.h>
#include <pjsip/sip_endpoint.h>
#include <pj/log.h>
#include <pj/math.h>
#include <pj/os.h>
#include <pj/pool.h>

#define THIS_FILE		"sip_timer.c"


/* Constant of Session Timers */
#define ABS_MIN_SE		90	/* Absolute Min-SE, in seconds	    */


/* String definitions */
static const pj_str_t STR_SE		= {"Session-Expires", 15};
static const pj_str_t STR_SHORT_SE	= {"x", 1};
static const pj_str_t STR_MIN_SE	= {"Min-SE", 6};
static const pj_str_t STR_REFRESHER	= {"refresher", 9};
static const pj_str_t STR_UAC		= {"uac", 3};
static const pj_str_t STR_UAS		= {"uas", 3};
static const pj_str_t STR_TIMER		= {"timer", 5};


/* Enumeration of refresher */
enum timer_refresher {
    TR_UNKNOWN,
    TR_UAC,
    TR_UAS
};

/* Structure definition of Session Timers */
struct pjsip_timer 
{
    pj_bool_t			 active;	/**< Active/inactive flag   */
    pjsip_timer_setting		 setting;	/**< Session Timers setting */
    enum timer_refresher	 refresher;	/**< Session refresher	    */
    pj_time_val			 last_refresh;	/**< Timestamp of last
						     refresh		    */
    pj_timer_entry		 timer;		/**< Timer entry	    */
    pj_bool_t			 use_update;	/**< Use UPDATE method to
						     refresh the session    */
    pjsip_role_e		 role;		/**< Role in last INVITE/
						     UPDATE transaction.    */

};

/* External global vars */
extern pj_bool_t pjsip_use_compact_form;

/* Local functions & vars */
static void stop_timer(pjsip_inv_session *inv);
static void start_timer(pjsip_inv_session *inv);
static pj_bool_t is_initialized;
const pjsip_method pjsip_update_method = { PJSIP_OTHER_METHOD, {"UPDATE", 6}};
/*
 * Session-Expires header vptr.
 */
static int se_hdr_print(pjsip_sess_expires_hdr *hdr, 
			char *buf, pj_size_t size);
static pjsip_sess_expires_hdr* se_hdr_clone(pj_pool_t *pool, 
					    const pjsip_sess_expires_hdr *hdr);
static pjsip_sess_expires_hdr* se_hdr_shallow_clone( 
					    pj_pool_t *pool,
					    const pjsip_sess_expires_hdr* hdr);

static pjsip_hdr_vptr se_hdr_vptr = 
{
    (pjsip_hdr_clone_fptr) &se_hdr_clone,
    (pjsip_hdr_clone_fptr) &se_hdr_shallow_clone,
    (pjsip_hdr_print_fptr) &se_hdr_print,
};

/*
 * Min-SE header vptr.
 */
static int min_se_hdr_print(pjsip_min_se_hdr *hdr, 
			    char *buf, pj_size_t size);
static pjsip_min_se_hdr* min_se_hdr_clone(pj_pool_t *pool, 
					  const pjsip_min_se_hdr *hdr);
static pjsip_min_se_hdr* min_se_hdr_shallow_clone( 
					  pj_pool_t *pool,
					  const pjsip_min_se_hdr* hdr);

static pjsip_hdr_vptr min_se_hdr_vptr = 
{
    (pjsip_hdr_clone_fptr) &min_se_hdr_clone,
    (pjsip_hdr_clone_fptr) &min_se_hdr_shallow_clone,
    (pjsip_hdr_print_fptr) &min_se_hdr_print,
};

/*
 * Session-Expires header vptr.
 */
static int se_hdr_print(pjsip_sess_expires_hdr *hdr, 
			char *buf, pj_size_t size)
{
    char *p = buf;
    char *endbuf = buf+size;
    int printed;
    const pjsip_parser_const_t *pc = pjsip_parser_const();
    const pj_str_t *hname = pjsip_use_compact_form? &hdr->sname : &hdr->name;

    /* Print header name and value */
    if ((endbuf - p) < (hname->slen + 16))
	return -1;

    copy_advance(p, (*hname));
    *p++ = ':';
    *p++ = ' ';

    printed = pj_utoa(hdr->sess_expires, p);
    p += printed;

    /* Print 'refresher' param */
    if (hdr->refresher.slen)
    {
	if  ((endbuf - p) < (STR_REFRESHER.slen + 2 + hdr->refresher.slen))
	    return -1;

	*p++ = ';';
	copy_advance(p, STR_REFRESHER);
	*p++ = '=';
	copy_advance(p, hdr->refresher);
    }

    /* Print generic params */
    printed = pjsip_param_print_on(&hdr->other_param, p, endbuf-p,
				   &pc->pjsip_TOKEN_SPEC, 
				   &pc->pjsip_TOKEN_SPEC, ';');
    if (printed < 0)
	return printed;

    p += printed;
    return p - buf;
}

static pjsip_sess_expires_hdr* se_hdr_clone(pj_pool_t *pool, 
					    const pjsip_sess_expires_hdr *hsrc)
{
    pjsip_sess_expires_hdr *hdr = pjsip_sess_expires_hdr_create(pool);
    hdr->sess_expires = hsrc->sess_expires;
    pj_strdup(pool, &hdr->refresher, &hsrc->refresher);
    pjsip_param_clone(pool, &hdr->other_param, &hsrc->other_param);
    return hdr;
}

static pjsip_sess_expires_hdr* se_hdr_shallow_clone( 
					    pj_pool_t *pool,
					    const pjsip_sess_expires_hdr* hsrc)
{
    pjsip_sess_expires_hdr *hdr = PJ_POOL_ALLOC_T(pool,pjsip_sess_expires_hdr);
    pj_memcpy(hdr, hsrc, sizeof(*hdr));
    pjsip_param_shallow_clone(pool, &hdr->other_param, &hsrc->other_param);
    return hdr;
}

/*
 * Min-SE header vptr.
 */
static int min_se_hdr_print(pjsip_min_se_hdr *hdr, 
			    char *buf, pj_size_t size)
{
    char *p = buf;
    char *endbuf = buf+size;
    int printed;
    const pjsip_parser_const_t *pc = pjsip_parser_const();

    /* Print header name and value */
    if ((endbuf - p) < (hdr->name.slen + 16))
	return -1;

    copy_advance(p, hdr->name);
    *p++ = ':';
    *p++ = ' ';

    printed = pj_utoa(hdr->min_se, p);
    p += printed;

    /* Print generic params */
    printed = pjsip_param_print_on(&hdr->other_param, p, endbuf-p,
				   &pc->pjsip_TOKEN_SPEC, 
				   &pc->pjsip_TOKEN_SPEC, ';');
    if (printed < 0)
	return printed;

    p += printed;
    return p - buf;
}

static pjsip_min_se_hdr* min_se_hdr_clone(pj_pool_t *pool, 
					  const pjsip_min_se_hdr *hsrc)
{
    pjsip_min_se_hdr *hdr = pjsip_min_se_hdr_create(pool);
    hdr->min_se = hsrc->min_se;
    pjsip_param_clone(pool, &hdr->other_param, &hsrc->other_param);
    return hdr;
}

static pjsip_min_se_hdr* min_se_hdr_shallow_clone( 
					  pj_pool_t *pool,
					  const pjsip_min_se_hdr* hsrc)
{
    pjsip_min_se_hdr *hdr = PJ_POOL_ALLOC_T(pool, pjsip_min_se_hdr);
    pj_memcpy(hdr, hsrc, sizeof(*hdr));
    pjsip_param_shallow_clone(pool, &hdr->other_param, &hsrc->other_param);
    return hdr;
}


/*
 * Parse Session-Expires header.
 */
static pjsip_hdr *parse_hdr_se(pjsip_parse_ctx *ctx)
{
    pjsip_sess_expires_hdr *hdr = pjsip_sess_expires_hdr_create(ctx->pool);
    const pjsip_parser_const_t *pc = pjsip_parser_const();
    pj_str_t token;

    pj_scan_get(ctx->scanner, &pc->pjsip_DIGIT_SPEC, &token);
    hdr->sess_expires = pj_strtoul(&token);

    while (*ctx->scanner->curptr == ';') {
	pj_str_t pname, pvalue;

	pj_scan_get_char(ctx->scanner);
	pjsip_parse_param_imp(ctx->scanner, ctx->pool, &pname, &pvalue, 0);

	if (pj_stricmp(&pname, &STR_REFRESHER)==0) {
	    hdr->refresher = pvalue;
	} else {
	    pjsip_param *param = PJ_POOL_ALLOC_T(ctx->pool, pjsip_param);
	    param->name = pname;
	    param->value = pvalue;
	    pj_list_push_back(&hdr->other_param, param);
	}
    }
    pjsip_parse_end_hdr_imp( ctx->scanner );
    return (pjsip_hdr*)hdr;
}

/*
 * Parse Min-SE header.
 */
static pjsip_hdr *parse_hdr_min_se(pjsip_parse_ctx *ctx)
{
    pjsip_min_se_hdr *hdr = pjsip_min_se_hdr_create(ctx->pool);
    const pjsip_parser_const_t *pc = pjsip_parser_const();
    pj_str_t token;

    pj_scan_get(ctx->scanner, &pc->pjsip_DIGIT_SPEC, &token);
    hdr->min_se = pj_strtoul(&token);

    while (*ctx->scanner->curptr == ';') {
	pj_str_t pname, pvalue;
	pjsip_param *param = PJ_POOL_ALLOC_T(ctx->pool, pjsip_param);

	pj_scan_get_char(ctx->scanner);
	pjsip_parse_param_imp(ctx->scanner, ctx->pool, &pname, &pvalue, 0);

	param->name = pname;
	param->value = pvalue;
	pj_list_push_back(&hdr->other_param, param);
    }
    pjsip_parse_end_hdr_imp( ctx->scanner );
    return (pjsip_hdr*)hdr;
}


/* Add "Session-Expires" and "Min-SE" headers. Note that "Min-SE" header
 * can only be added to INVITE/UPDATE request and 422 response.
 */
static void add_timer_headers(pjsip_inv_session *inv, pjsip_tx_data *tdata,
			      pj_bool_t add_se, pj_bool_t add_min_se)
{
    pjsip_timer *timer = inv->timer;

    /* Add Session-Expires header */
    if (add_se) {
	pjsip_sess_expires_hdr *hdr;

	hdr = pjsip_sess_expires_hdr_create(tdata->pool);
	hdr->sess_expires = timer->setting.sess_expires;
	if (timer->refresher != TR_UNKNOWN)
	    hdr->refresher = (timer->refresher == TR_UAC? STR_UAC : STR_UAS);

	pjsip_msg_add_hdr(tdata->msg, (pjsip_hdr*) hdr);
    }

    /* Add Min-SE header */
    if (add_min_se) {
	pjsip_min_se_hdr *hdr;

	hdr = pjsip_min_se_hdr_create(tdata->pool);
	hdr->min_se = timer->setting.min_se;

	pjsip_msg_add_hdr(tdata->msg, (pjsip_hdr*) hdr);
    }
}

/* Timer callback. When the timer is fired, it can be time to refresh
 * the session if UA is the refresher, otherwise it is time to end 
 * the session.
 */
void timer_cb(pj_timer_heap_t *timer_heap, struct pj_timer_entry *entry)
{
    pjsip_inv_session *inv = (pjsip_inv_session*) entry->user_data;
    pjsip_tx_data *tdata = NULL;
    pj_status_t status;
    pj_bool_t as_refresher;

    pj_assert(inv);

    PJ_UNUSED_ARG(timer_heap);

    /* When there is a pending INVITE transaction, delay/reschedule this timer
     * for five seconds to cover the case that pending INVITE fails and the
     * previous session is still active. If the pending INVITE is successful, 
     * timer state will be updated, i.e: restarted or stopped.
     */
    if (inv->invite_tsx != NULL) {
	pj_time_val delay = {5};

	inv->timer->timer.id = 1;
	pjsip_endpt_schedule_timer(inv->dlg->endpt, &inv->timer->timer, &delay);
	return;
    }

    /* Lock dialog. */
    pjsip_dlg_inc_lock(inv->dlg);

    /* Check our role */
    as_refresher = 
	(inv->timer->refresher == TR_UAC && inv->timer->role == PJSIP_ROLE_UAC) ||
	(inv->timer->refresher == TR_UAS && inv->timer->role == PJSIP_ROLE_UAS);

    /* Do action based on role, refresher or refreshee */
    if (as_refresher) {

	pj_time_val now;

	/* Refresher, refresh the session */
	if (inv->timer->use_update) {
	    /* Create UPDATE request without offer */
	    status = pjsip_inv_update(inv, NULL, NULL, &tdata);
	} else {
	    /* Create re-INVITE without modifying session */
	    pjsip_msg_body *body;
	    const pjmedia_sdp_session *offer = NULL;

	    pj_assert(pjmedia_sdp_neg_get_state(inv->neg) == 
		      PJMEDIA_SDP_NEG_STATE_DONE);

	    status = pjsip_inv_invite(inv, &tdata);
	    if (status == PJ_SUCCESS)
		status = pjmedia_sdp_neg_send_local_offer(inv->pool_prov, 
							  inv->neg, &offer);
	    if (status == PJ_SUCCESS)
		status = pjmedia_sdp_neg_get_neg_local(inv->neg, &offer);
	    if (status == PJ_SUCCESS) {
		status = pjsip_create_sdp_body(tdata->pool, 
					(pjmedia_sdp_session*)offer, &body);
		tdata->msg->body = body;
	    }
	}

	pj_gettimeofday(&now);
	PJ_LOG(4, (inv->pool->obj_name, 
		   "Refresh session after %ds (expiration period=%ds)",
		   (now.sec-inv->timer->last_refresh.sec),
		   inv->timer->setting.sess_expires));
    } else {
	
	pj_time_val now;

	/* Refreshee, terminate the session */
	status = pjsip_inv_end_session(inv, PJSIP_SC_REQUEST_TIMEOUT, 
				       NULL, &tdata);

	pj_gettimeofday(&now);
	PJ_LOG(3, (inv->pool->obj_name, 
		   "No session refresh received after %ds "
		   "(expiration period=%ds), stopping session now!",
		   (now.sec-inv->timer->last_refresh.sec),
		   inv->timer->setting.sess_expires));
    }

    /* Unlock dialog. */
    pjsip_dlg_dec_lock(inv->dlg);

    /* Send message, if any */
    if (tdata && status == PJ_SUCCESS) {
	status = pjsip_inv_send_msg(inv, tdata);
    }

    /* Print error message, if any */
    if (status != PJ_SUCCESS) {
	char errmsg[PJ_ERR_MSG_SIZE];

	if (tdata)
	    pjsip_tx_data_dec_ref(tdata);

	pj_strerror(status, errmsg, sizeof(errmsg));
	PJ_LOG(2, (inv->pool->obj_name, "Session timer fails in %s session, "
					"err code=%d (%s)",
					(as_refresher? "refreshing" : 
						       "terminating"),
					status, errmsg));					
    }
}

/* Start Session Timers */
static void start_timer(pjsip_inv_session *inv)
{
    pjsip_timer *timer = inv->timer;
    pj_time_val delay = {0};

    pj_assert(inv->timer->active == PJ_TRUE);

    stop_timer(inv);

    pj_timer_entry_init(&timer->timer,
			1,		    /* id */
			inv,		    /* user data */
			timer_cb);	    /* callback */
    
    /* Set delay based on role, refresher or refreshee */
    if ((timer->refresher == TR_UAC && inv->timer->role == PJSIP_ROLE_UAC) ||
	(timer->refresher == TR_UAS && inv->timer->role == PJSIP_ROLE_UAS))
    {
	/* Next refresh, the delay is half of session expire */
	delay.sec = timer->setting.sess_expires / 2;
    } else {
	/* Send BYE if no refresh received until this timer fired, delay
	 * is the minimum of 32 seconds and one third of the session interval
	 * before session expiration.
	 */
	delay.sec = timer->setting.sess_expires - 
		    timer->setting.sess_expires/3;
	delay.sec = PJ_MAX((long)timer->setting.sess_expires-32, delay.sec);
    }

    /* Schedule the timer */
    pjsip_endpt_schedule_timer(inv->dlg->endpt, &timer->timer, &delay);

    /* Update last refresh time */
    pj_gettimeofday(&timer->last_refresh);
}

/* Stop Session Timers */
static void stop_timer(pjsip_inv_session *inv)
{
    if (inv->timer->timer.id != 0) {
	pjsip_endpt_cancel_timer(inv->dlg->endpt, &inv->timer->timer);
	inv->timer->timer.id = 0;
    }
}

/*
 * Initialize Session Timers support in PJSIP. 
 */
PJ_DEF(pj_status_t) pjsip_timer_init_module(pjsip_endpoint *endpt)
{
    pj_status_t status;

    PJ_ASSERT_RETURN(endpt, PJ_EINVAL);

    if (is_initialized)
	return PJ_SUCCESS;

    /* Register Session-Expires header parser */
    status = pjsip_register_hdr_parser( STR_SE.ptr, STR_SHORT_SE.ptr, 
				        &parse_hdr_se);
    if (status != PJ_SUCCESS)
	return status;

    /* Register Min-SE header parser */
    status = pjsip_register_hdr_parser( STR_MIN_SE.ptr, NULL, 
				        &parse_hdr_min_se);
    if (status != PJ_SUCCESS)
	return status;

    /* Register 'timer' capability to endpoint */
    status = pjsip_endpt_add_capability(endpt, NULL, PJSIP_H_SUPPORTED,
					NULL, 1, &STR_TIMER);
    if (status != PJ_SUCCESS)
	return status;

    is_initialized = PJ_TRUE;

    return PJ_SUCCESS;
}


/*
 * Initialize Session Timers setting with default values.
 */
PJ_DEF(pj_status_t) pjsip_timer_setting_default(pjsip_timer_setting *setting)
{
    pj_bzero(setting, sizeof(pjsip_timer_setting));

    setting->sess_expires = PJSIP_SESS_TIMER_DEF_SE;
    setting->min_se = ABS_MIN_SE;

    return PJ_SUCCESS;
}

/*
 * Initialize Session Timers in an INVITE session. 
 */
PJ_DEF(pj_status_t) pjsip_timer_init_session(
					pjsip_inv_session *inv,
					const pjsip_timer_setting *setting)
{
    pjsip_timer_setting *s;

    pj_assert(is_initialized);
    PJ_ASSERT_RETURN(inv, PJ_EINVAL);

    /* Allocate and/or reset Session Timers structure */
    if (!inv->timer)
	inv->timer = PJ_POOL_ZALLOC_T(inv->pool, pjsip_timer);
    else
	pj_bzero(inv->timer, sizeof(pjsip_timer));

    s = &inv->timer->setting;

    /* Init Session Timers setting */
    if (setting) {
	PJ_ASSERT_RETURN(setting->min_se >= ABS_MIN_SE,
			 PJ_ETOOSMALL);
	PJ_ASSERT_RETURN(setting->sess_expires >= setting->min_se,
			 PJ_EINVAL);

	pj_memcpy(s, setting, sizeof(*s));
    } else {
	pjsip_timer_setting_default(s);
    }

    return PJ_SUCCESS;
}


/*
 * Create Session-Expires header.
 */
PJ_DEF(pjsip_sess_expires_hdr*) pjsip_sess_expires_hdr_create(
							pj_pool_t *pool)
{
    pjsip_sess_expires_hdr *hdr = PJ_POOL_ZALLOC_T(pool,
						   pjsip_sess_expires_hdr);

    pj_assert(is_initialized);

    hdr->type = PJSIP_H_OTHER;
    hdr->name = STR_SE;
    hdr->sname = STR_SHORT_SE;
    hdr->vptr = &se_hdr_vptr;
    pj_list_init(hdr);
    pj_list_init(&hdr->other_param);
    return hdr;
}


/*
 * Create Min-SE header.
 */
PJ_DEF(pjsip_min_se_hdr*) pjsip_min_se_hdr_create(pj_pool_t *pool)
{
    pjsip_min_se_hdr *hdr = PJ_POOL_ZALLOC_T(pool, pjsip_min_se_hdr);

    pj_assert(is_initialized);

    hdr->type = PJSIP_H_OTHER;
    hdr->name = STR_MIN_SE;
    hdr->vptr = &min_se_hdr_vptr;
    pj_list_init(hdr);
    pj_list_init(&hdr->other_param);
    return hdr;
}


/* 
 * This function generates headers for Session Timers for intial and
 * refresh INVITE or UPDATE.
 */
PJ_DEF(pj_status_t) pjsip_timer_update_req(pjsip_inv_session *inv,
					   pjsip_tx_data *tdata)
{
    PJ_ASSERT_RETURN(inv && tdata, PJ_EINVAL);

    /* Check if Session Timers is supported */
    if ((inv->options & PJSIP_INV_SUPPORT_TIMER) == 0)
	return PJ_SUCCESS;

    pj_assert(is_initialized);

    /* Make sure Session Timers is initialized */
    if (inv->timer == NULL)
	pjsip_timer_init_session(inv, NULL);

    /* If refresher role (i.e: ours or peer) has been set/negotiated, 
     * better to keep it.
     */
    if (inv->timer->refresher != TR_UNKNOWN) {
	pj_bool_t as_refresher;

	/* Check our refresher role */
	as_refresher = 
	    (inv->timer->refresher==TR_UAC && inv->timer->role==PJSIP_ROLE_UAC) ||
	    (inv->timer->refresher==TR_UAS && inv->timer->role==PJSIP_ROLE_UAS);

	/* Update transaction role */
	inv->timer->role = PJSIP_ROLE_UAC;

	/* Update refresher role */
	inv->timer->refresher = as_refresher? TR_UAC : TR_UAS;
    }

    /* Add Session Timers headers */
    add_timer_headers(inv, tdata, PJ_TRUE, PJ_TRUE);

    return PJ_SUCCESS;
}

/* 
 * This function will handle Session Timers part of INVITE/UPDATE 
 * responses with code:
 * - 422 (Session Interval Too Small)
 * - 2xx final response
 */
PJ_DEF(pj_status_t) pjsip_timer_process_resp(pjsip_inv_session *inv,
					     const pjsip_rx_data *rdata,
					     pjsip_status_code *st_code)
{
    const pjsip_msg *msg;

    PJ_ASSERT_ON_FAIL(inv && rdata,
	{if(st_code)*st_code=PJSIP_SC_INTERNAL_SERVER_ERROR;return PJ_EINVAL;});

    /* Check if Session Timers is supported */
    if ((inv->options & PJSIP_INV_SUPPORT_TIMER) == 0)
	return PJ_SUCCESS;

    pj_assert(is_initialized);

    msg = rdata->msg_info.msg;
    pj_assert(msg->type == PJSIP_RESPONSE_MSG);

    /* Only process response of INVITE or UPDATE */
    if (rdata->msg_info.cseq->method.id != PJSIP_INVITE_METHOD &&
	pjsip_method_cmp(&rdata->msg_info.cseq->method, &pjsip_update_method))
    {
	return PJ_SUCCESS;
    }

    if (msg->line.status.code == PJSIP_SC_SESSION_TIMER_TOO_SMALL) {
	/* Our Session-Expires is too small, let's update it based on
	 * Min-SE header in the response.
	 */
	pjsip_tx_data *tdata;
	pjsip_min_se_hdr *min_se_hdr;
	pjsip_hdr *hdr;
	pjsip_via_hdr *via;

	/* Get Min-SE value from response */
	min_se_hdr = (pjsip_min_se_hdr*) 
		     pjsip_msg_find_hdr_by_name(msg, &STR_MIN_SE, NULL);
	if (min_se_hdr == NULL) {
	    /* Response 422 should contain Min-SE header */
	    return PJ_SUCCESS;
	}

	/* Session Timers should have been initialized here */
	pj_assert(inv->timer);

	/* Update Min-SE */
	inv->timer->setting.min_se = PJ_MAX(min_se_hdr->min_se, 
					    inv->timer->setting.min_se);

	/* Update Session Timers setting */
	if (inv->timer->setting.sess_expires < inv->timer->setting.min_se)
	    inv->timer->setting.sess_expires = inv->timer->setting.min_se;

	/* Prepare to restart the request */

	/* Get the original INVITE request. */
	tdata = inv->invite_req;

	/* Remove branch param in Via header. */
	via = (pjsip_via_hdr*) pjsip_msg_find_hdr(tdata->msg, PJSIP_H_VIA, NULL);
	pj_assert(via);
	via->branch_param.slen = 0;

	/* Restore strict route set.
	 * See http://trac.pjsip.org/repos/ticket/492
	 */
	pjsip_restore_strict_route_set(tdata);

	/* Must invalidate the message! */
	pjsip_tx_data_invalidate_msg(tdata);

	pjsip_tx_data_add_ref(tdata);

	/* Update Session Timers headers */
	hdr = (pjsip_hdr*) pjsip_msg_find_hdr_by_name(tdata->msg, 
						      &STR_MIN_SE, NULL);
	if (hdr != NULL) pj_list_erase(hdr);

	hdr = (pjsip_hdr*) pjsip_msg_find_hdr_by_names(tdata->msg, &STR_SE,
						       &STR_SHORT_SE, NULL);
	if (hdr != NULL) pj_list_erase(hdr);

	add_timer_headers(inv, tdata, PJ_TRUE, PJ_TRUE);

	/* Restart UAC */
	pjsip_inv_uac_restart(inv, PJ_FALSE);
	pjsip_inv_send_msg(inv, tdata);

	return PJ_SUCCESS;

    } else if (msg->line.status.code/100 == 2) {

	pjsip_sess_expires_hdr *se_hdr;

	/* Find Session-Expires header */
	se_hdr = (pjsip_sess_expires_hdr*) pjsip_msg_find_hdr_by_names(
						msg, &STR_SE, 
						&STR_SHORT_SE, NULL);
	if (se_hdr == NULL) {
	    /* Remote doesn't support/want Session Timers, check if local 
	     * require or force to use Session Timers.
	     */
	    if (inv->options & PJSIP_INV_REQUIRE_TIMER) {
		if (st_code)
		    *st_code = PJSIP_SC_EXTENSION_REQUIRED;
		pjsip_timer_end_session(inv);
		return PJSIP_ERRNO_FROM_SIP_STATUS(
					    PJSIP_SC_EXTENSION_REQUIRED);
	    }

	    if ((inv->options & PJSIP_INV_ALWAYS_USE_TIMER) == 0) {
		/* Session Timers not forced */
		pjsip_timer_end_session(inv);
		return PJ_SUCCESS;
	    }
	}
	    
	/* Make sure Session Timers is initialized */
	if (inv->timer == NULL)
	    pjsip_timer_init_session(inv, NULL);

	/* Session expiration period specified by remote is lower than our
	 * Min-SE.
	 */
	if (se_hdr && 
	    se_hdr->sess_expires < inv->timer->setting.min_se)
	{
	    if (st_code)
		*st_code = PJSIP_SC_SESSION_TIMER_TOO_SMALL;
	    pjsip_timer_end_session(inv);
	    return PJSIP_ERRNO_FROM_SIP_STATUS(
					    PJSIP_SC_SESSION_TIMER_TOO_SMALL);
	}

	/* Update SE. Session-Expires in response cannot be lower than Min-SE.
	 * Session-Expires in response can only be equal or lower than in 
	 * request.
	 */
	if (se_hdr && 
	    se_hdr->sess_expires <= inv->timer->setting.sess_expires &&
	    se_hdr->sess_expires >= inv->timer->setting.min_se)
	{
	    /* Good SE from remote, update local SE */
	    inv->timer->setting.sess_expires = se_hdr->sess_expires;
	}

	/* Set the refresher */
	if (se_hdr && pj_stricmp(&se_hdr->refresher, &STR_UAC) == 0)
	    inv->timer->refresher = TR_UAC;
	else if (se_hdr && pj_stricmp(&se_hdr->refresher, &STR_UAS) == 0)
	    inv->timer->refresher = TR_UAS;
	else
	    /* UAS should set the refresher, however, there is a case that
	     * UAS doesn't support/want Session Timers but the UAC insists
	     * to use Session Timers.
	     */
	    inv->timer->refresher = TR_UAC;

	PJ_TODO(CHECK_IF_REMOTE_SUPPORT_UPDATE);

	/* Remember our role in this transaction */
	inv->timer->role = PJSIP_ROLE_UAC;

	/* Finally, set active flag and start the Session Timers */
	inv->timer->active = PJ_TRUE;
	start_timer(inv);
    }

    return PJ_SUCCESS;
}

/*
 * Handle incoming INVITE or UPDATE request.
 */
PJ_DEF(pj_status_t) pjsip_timer_process_req(pjsip_inv_session *inv,
					    const pjsip_rx_data *rdata,
					    pjsip_status_code *st_code)
{
    pjsip_min_se_hdr *min_se_hdr;
    pjsip_sess_expires_hdr *se_hdr;
    const pjsip_msg *msg;
    unsigned min_se;

    PJ_ASSERT_ON_FAIL(inv && rdata,
	{if(st_code)*st_code=PJSIP_SC_INTERNAL_SERVER_ERROR;return PJ_EINVAL;});

    /* Check if Session Timers is supported */
    if ((inv->options & PJSIP_INV_SUPPORT_TIMER) == 0)
	return PJ_SUCCESS;

    pj_assert(is_initialized);

    msg = rdata->msg_info.msg;
    pj_assert(msg->type == PJSIP_REQUEST_MSG);

    /* Only process INVITE or UPDATE request */
    if (msg->line.req.method.id != PJSIP_INVITE_METHOD &&
	pjsip_method_cmp(&rdata->msg_info.cseq->method, &pjsip_update_method))
    {
	return PJ_SUCCESS;
    }

    /* Find Session-Expires header */
    se_hdr = (pjsip_sess_expires_hdr*) pjsip_msg_find_hdr_by_names(
					    msg, &STR_SE, &STR_SHORT_SE, NULL);
    if (se_hdr == NULL) {
	/* Remote doesn't support/want Session Timers, check if local 
	 * require or force to use Session Timers. Note that Supported and 
	 * Require headers negotiation should have been verified by invite 
	 * session.
	 */
	if ((inv->options & 
	    (PJSIP_INV_REQUIRE_TIMER | PJSIP_INV_ALWAYS_USE_TIMER)) == 0)
	{
	    /* Session Timers not forced/required */
	    pjsip_timer_end_session(inv);
	    return PJ_SUCCESS;
	}
    }

    /* Make sure Session Timers is initialized */
    if (inv->timer == NULL)
	pjsip_timer_init_session(inv, NULL);

    /* Find Min-SE header */
    min_se_hdr = (pjsip_min_se_hdr*) pjsip_msg_find_hdr_by_name(msg, 
							    &STR_MIN_SE, NULL);
    /* Update Min-SE */
    min_se = inv->timer->setting.min_se;
    if (min_se_hdr)
	min_se = PJ_MAX(min_se_hdr->min_se, min_se);

    /* Validate SE. Session-Expires cannot be lower than Min-SE 
     * (or 90 seconds if Min-SE is not set).
     */
    if (se_hdr && se_hdr->sess_expires < min_se) {
	if (st_code)
	    *st_code = PJSIP_SC_SESSION_TIMER_TOO_SMALL;
	return PJSIP_ERRNO_FROM_SIP_STATUS(PJSIP_SC_SESSION_TIMER_TOO_SMALL);
    }

    /* Update SE. Note that there is a case that SE is not available in the
     * request (which means remote doesn't want/support it), but local insists
     * to use Session Timers.
     */
    if (se_hdr) {
	/* Update SE as specified by peer. */
	inv->timer->setting.sess_expires = se_hdr->sess_expires;
    } else if (inv->timer->setting.sess_expires < min_se) {
	/* There is no SE in the request (remote support Session Timers but
	 * doesn't want to use it, it just specify Min-SE) and local SE is 
	 * lower than Min-SE specified by remote.
	 */
	inv->timer->setting.sess_expires = min_se;
    }

    /* Set the refresher */
    if (se_hdr && pj_stricmp(&se_hdr->refresher, &STR_UAC) == 0)
	inv->timer->refresher = TR_UAC;
    else if (se_hdr && pj_stricmp(&se_hdr->refresher, &STR_UAS) == 0)
	inv->timer->refresher = TR_UAS;
    else {
	/* If refresher role (i.e: ours or peer) has been set/negotiated, 
	 * better to keep it.
	 */
	if (inv->timer->refresher != TR_UNKNOWN) {
	    pj_bool_t as_refresher;

	    /* Check our refresher role */
	    as_refresher = 
		(inv->timer->refresher==TR_UAC && inv->timer->role==PJSIP_ROLE_UAC) ||
		(inv->timer->refresher==TR_UAS && inv->timer->role==PJSIP_ROLE_UAS);

	    /* Update refresher role */
	    inv->timer->refresher = as_refresher? TR_UAS : TR_UAC;
	} else {
	    /* If UAC support timer (currently check the existance of 
	     * Session-Expires header in the request), set UAC as refresher.
	     */
	    inv->timer->refresher = se_hdr? TR_UAC : TR_UAS;
	}
    }

    /* Remember our role in this transaction */
    inv->timer->role = PJSIP_ROLE_UAS;

    /* Set active flag */
    inv->timer->active = PJ_TRUE;

    return PJ_SUCCESS;
}

/*
 * Handle outgoing response with status code 2xx & 422.
 */
PJ_DEF(pj_status_t) pjsip_timer_update_resp(pjsip_inv_session *inv,
					    pjsip_tx_data *tdata)
{
    pjsip_msg *msg;

    /* Check if Session Timers is supported */
    if ((inv->options & PJSIP_INV_SUPPORT_TIMER) == 0)
	return PJ_SUCCESS;

    pj_assert(is_initialized);
    PJ_ASSERT_RETURN(inv && tdata, PJ_EINVAL);

    msg = tdata->msg;

    if (msg->line.status.code/100 == 2)
    {
	if (inv->timer && inv->timer->active) {
	    /* Add Session-Expires header and start the timer */
	    add_timer_headers(inv, tdata, PJ_TRUE, PJ_FALSE);
	    start_timer(inv);
	}
    } 
    else if (msg->line.status.code == PJSIP_SC_SESSION_TIMER_TOO_SMALL)
    {
	/* Add Min-SE header */
	add_timer_headers(inv, tdata, PJ_FALSE, PJ_TRUE);
    }

    return PJ_SUCCESS;
}


/*
 * End the Session Timers.
 */
PJ_DEF(pj_status_t) pjsip_timer_end_session(pjsip_inv_session *inv)
{
    PJ_ASSERT_RETURN(inv, PJ_EINVAL);

    if (inv->timer) {
	/* Reset active flag */
	inv->timer->active = PJ_FALSE;

	/* Stop Session Timers */
	stop_timer(inv);
    }

    return PJ_SUCCESS;
}