sst_handlers.c

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/*
 * $Id: sst_handlers.c 5777 2009-03-30 19:32:53Z henningw $
 *
 * Copyright (C) 2006 SOMA Networks, Inc.
 * Written by Ron Winacott (karwin)
 *
 * This file is part of Kamailio, a free SIP server.
 *
 * Kamailio 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
 *
 * Kamailio 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
 */

/*!
 * \file sst/sst_handlers.c
 * \brief Functions for the SST module
 * \ingroup sst
 * Module: \ref sst
 */

/*!
 * \page SST_support SST support:
 *
 * The Session-Expires header conveys the session interval for a SIP
 * call. It is placed in an INVITE request and is allowed in any 2xx
 * class response to an INVITE. Its presence indicates that the UAC
 * wishes to use the session timer for this call. Unlike the
 * SIP-Expires header, it can only contain a delta-time, which is the
 * current time, plus the session interval from the response.
 *
 * For example, if a UAS generates a 200 OK response to a re-INVITE
 * that contained a Session-Expires header with a value of 1800
 * seconds (30 minutes), the UAS computes the session expiration as 30
 * minutes after the time when the 200 OK response was sent. For each
 * proxy, the session expiration is 30 minutes after the time when the
 * 2xx was received or sent. For the UAC, the expiration time is 30
 * minutes after the receipt of the final response.
 *
 */

#include <stdio.h>  /* for snprintf() */
#include <string.h> /* for memset() */
#include <stdlib.h> /* For atoi() */

#include "../../pvar.h"
#include "../../parser/parse_sst.h"
#include "../../parser/parse_supported.h"
#include "../../mem/mem.h"
#include "../../mem/shm_mem.h"
#include "../../data_lump.h"
#include "../../data_lump_rpl.h"
#include "../../ut.h"
#include "../../dprint.h"
#include "../../sr_module.h" /* Needed for find_export() */
#include "../sl/sl_api.h"

#include "sst_handlers.h"
#include "sst_mi.h"

/*
 * My own LM_*() macros to add the correct message prefix and
 * file/function/line number information to all LOG messages.
 */

#ifdef USE_CONFIRM_CALLBACK
#define DLOGMSG(msg) {                             \
      if (msg->first_line.type == SIP_REQUEST) {         \
         LM_INFO("REQUEST: %.*s\n",                \
               msg->first_line.u.request.method.len,  \
               msg->first_line.u.request.method.s);   \
      }                                      \
      else {                                    \
         LM_INFO("RESPONSE: %d %.*s\n",               \
               msg->first_line.u.reply.statuscode,    \
               msg->first_line.u.reply.reason.len,    \
               msg->first_line.u.reply.reason.s);     \
      }                                      \
}
#endif


/**
 * The binding to the dialog module functions. Most importantly the
 * register_dlgcb function.
 */
extern struct dlg_binds *dlg_binds;

/**
 * A collection of information about SST in the current SIP message
 * being processed.
 */
typedef struct sst_msg_info_st {
   int supported;             /* supported = timer in message */
   unsigned int min_se;    /* The Min-SE: value or zero    */
   unsigned int se;     /* The Sesion-Expires: header   */
   enum sst_refresher refresher;/* The refresher (parse_sst.h)  */
} sst_msg_info_t;

/**
 * Local function prototypes See function definition for
 * documentation.
 */
#ifdef USE_CONFIRM_CALLBACK
static void sst_dialog_confirmed_CB(struct dlg_cell* did, int type,
      struct dlg_cb_params * params);
#endif /* USE_CONFIRM_CALLBACK */
static void sst_dialog_terminate_CB(struct dlg_cell* did, int type,
      struct dlg_cb_params * params);
static void sst_dialog_request_within_CB(struct dlg_cell* did, int type,
      struct dlg_cb_params * params);
static void sst_dialog_response_fwded_CB(struct dlg_cell* did, int type,
      struct dlg_cb_params * params);
static int send_response(struct sip_msg *request, int code, str *reason,
      char *header, int header_len);
static int append_header(struct sip_msg *msg, const char *header);
static int remove_header(struct sip_msg *msg, const char *header);
static int set_timeout_avp(struct sip_msg *msg, unsigned int value);
static int parse_msg_for_sst_info(struct sip_msg *msg, sst_msg_info_t *minfo);
static int send_reject(struct sip_msg *msg, unsigned int min_se);
static void setup_dialog_callbacks(struct dlg_cell *did, sst_info_t *info);

/**
 * The pointer to the stateless reply function This is used to send a
 * 422 reply if asked to with a Min-SE: header value to small.
 */
extern struct sl_binds slb;

/**
 * The dialog modules timeout AVP spac.
 */
static pv_spec_t *timeout_avp = 0;

/**
 * Our Min-SE: header field value and test.
 */
static unsigned int sst_min_se = 0;

/**
 * Should the SE < sst_min_se be rehected with a 422 reply?
 */
static unsigned int sst_reject = 1;

/**
 * The value of the message flag to flag an INVITE we want to process
 * through the SST module.
 */
static int sst_flag = 0;


static str sst_422_rpl = str_init("Session Timer Too Small");


/* fixme: copied from functions, but size is too much */
#define SST_SE_BUF_SIZE 80
static char sst_se_buf[SST_SE_BUF_SIZE];
static inline int sst_build_minse_hdr(int seval, str *sehdr)
{
   if(sehdr==NULL)
      return -1;

   sehdr->len = snprintf(sst_se_buf, SST_SE_BUF_SIZE,
         "Min-SE: %d\r\n", seval);
   sehdr->s = sst_se_buf;
   return 0;
}
static inline int sst_build_se_hdr(int seval, str *sehdr)
{
   if(sehdr==NULL)
      return -1;

   sehdr->len = snprintf(sst_se_buf, SST_SE_BUF_SIZE,
         "Session-Expires: %d\r\n", seval);
   sehdr->s = sst_se_buf;
   return 0;
}

/**
 * This is not a public API. This function is called when the module
 * is loaded from the mod_init() function in sst.c to initialize the
 * callback handlers and local variables.
 *
 * @param timeout_avp_p - The pointer to the dialog modules timeout AVP.
 * @param min_se - The minimum session expire value allowed by this PROXY.
 * @param flag - sst flag
 * @param reject - reject state
 */
void sst_handler_init(pv_spec_t *timeout_avp_p, unsigned int min_se,
      int flag, unsigned int reject)
{
   timeout_avp = timeout_avp_p;
   sst_min_se = min_se;
   sst_flag = 1 << flag;
   sst_reject = reject;
}

/**
 * Every time a new dialog is created (from a new INVITE) the dialog
 * module will call this callback function. We need to track the
 * dialogs lifespan from this point forward until it is terminated
 * with a BYE, CANCEL, etc. In the process, we will see if either or
 * both ends of the conversation supports SIP Session Timers and setup
 * the dialog timeout to expire at the session timer expire time. Each
 * time the new re-INVITE is seen to update the SST, we will reset the
 * life span of the dialog to match it.
 *
 * This function will setup the other types of dialog callbacks
 * required to track the lifespan of the dialog. It will also start
 * the state tracking to figure out if and who supports SST.
 *
 * As per RFC4028: Request handling:
 * 
 * - The proxy may insert a SE header if none found.
 * - The SE value can be anything >= Min-SE (if found)
 * - The proxy MUST NOT add a refresher parameter to the SE.
 *
 * - If SE is already there, the Proxy can reduce its value but no
 *   lower then the Min-SE value if present.
 * - If the SE value is >= Min-SE the proxy MUST NOT increase it!
 * - If the SE value is < Min-SE (settable by the proxy) the proxy
 *   MUST increase the SE value to >= the new Min-SE.
 * - The proxy MUST NOT insert or change the refresher parameter.
 *
 * - If the supported=timer is found, the proxy may reject the request
 *   with a 422 if the SE value is smaller then the local policy. The
 *   422 MUST hold the proxies Min-SE value >= 90.
 * - If support=timer is NOT indecated, the proxy can't reject with a
 *   422 but can include/increase the MIN-SE: to be = to local policy.
 *   and increase the SE to match the new Min-SE value.
 * - the proxy MUST NOT insert/change the Min-SE header if
 *   supported=timer is present. (DoS attacks)
 *
 * @param did - The dialog ID
 * @param type - The trigger event type (CREATED)
 * @param params - The pointer to nothing. As we did not attach
 *                anything to this callback in the dialog module.
 */
void sst_dialog_created_CB(struct dlg_cell *did, int type,
      struct dlg_cb_params * params)
{
   sst_info_t *info = NULL;
   sst_msg_info_t minfo;
   struct sip_msg* msg = params->msg;

   memset(&minfo, 0, sizeof(sst_msg_info_t));
   /*
    * Only deal with messages flaged as SST interested.
    */
   if ((msg->flags & sst_flag) != sst_flag) {
      LM_DBG("SST flag was not set for this request\n");
      return;
   }

   /* 
    * look only at INVITE
    */
   if (msg->first_line.type != SIP_REQUEST ||
         msg->first_line.u.request.method_value != METHOD_INVITE) {
      LM_WARN("dialog create callback called with a non-INVITE request.\n");
      return;
   }

   /*
    * Gather all he information about SST for this message
    */
   if (parse_msg_for_sst_info(msg, &minfo)) {
      LM_ERR("failed to parse sst information\n");
      return;
   }

   info = (sst_info_t *)shm_malloc(sizeof(sst_info_t));
   memset(info, 0, sizeof(sst_info_t));
   info->requester = (minfo.se?SST_UAC:SST_UNDF);
   info->supported = (minfo.supported?SST_UAC:SST_UNDF);
   info->interval = MAX(sst_min_se, 90); /* For now, will set for real
                                * later */

   if (minfo.se != 0) {
      /* 
       * There is a SE already there, this is good, we just need to
       * check the values out a little before passing it along.
       */
      if (minfo.se < sst_min_se) {
         /* 
          * Problem, the requested Session-Expires is too small for
          * our local policy. We need to fix it, or reject it or
          * ignore it.
          */
         if (!minfo.supported) {
            /* 
             * Increase the Min-SE: value in the request and
             * forward it.
             */
            str msehdr;
            if (minfo.min_se) {
               /* We need to update, which means, remove +
                * insert */
               remove_header(msg, "Min-SE");
            }
            info->interval = MAX(sst_min_se, minfo.min_se);
            sst_build_minse_hdr(info->interval, &msehdr);
            if (append_header(msg, msehdr.s)) {
               LM_ERR("Could not append modified Min-SE: header\n");
            }
         }
         else if (sst_reject) {
            /* Make sure that that all are at least 90 */
            send_reject(msg, MAX(MAX(sst_min_se, minfo.min_se), 90));
            shm_free(info);
            return;
         }
      }  /* end of se < sst_min_se */
      else {
         /* Use the INVITE SE: value */
         info->interval = minfo.se;
      }
   }
   else {
      /* 
       * No Session-Expire: stated in request.
       */
      str msehdr;

      info->interval = MAX(minfo.min_se, sst_min_se);

      if (minfo.min_se && minfo.min_se < sst_min_se) {
         remove_header(msg, "Min-SE");
         sst_build_minse_hdr(info->interval, &msehdr);
         if (append_header(msg, msehdr.s)) {
            LM_ERR("failed to append modified Min-SE: header\n");
            /* What to do? Let is slide, we can still work */
         }
      }
      
      info->requester = SST_PXY;
      sst_build_se_hdr(info->interval, &msehdr);
      if (append_header(msg, msehdr.s)) {
         LM_ERR("failed to append Session-Expires header to proxy "
               "requested SST.\n");
         shm_free(info);
         return; /* Nothing we can do! */
      }
   }
   setup_dialog_callbacks(did, info);
   set_timeout_avp(msg, info->interval);
   return;
}

#ifdef USE_CONFIRM_CALLBACK
/**
 * Play time. Please ignore this call.
 */
static void sst_dialog_confirmed_CB(struct dlg_cell *did, int type,
      struct dlg_cb_params * params)
{
   struct sip_msg* msg = params->msg;

   LM_DBG("confirmed dialog CB %p\n", did);
   DLOGMSG(msg);
}
#endif /* USE_CONFIRM_CALLBACK */

/**
 * This callback is called when ever a dialog is terminated. The cause
 * of the termination can be normal, failed call, or expired. It is
 * the expired dialog we are really interested in.
 *
 * @param did - The Dialog ID / structure pointer. Used as an ID only.
 * @param type - The termination cause/reason.
 * @param params - The sst information
 */
static void sst_dialog_terminate_CB(struct dlg_cell* did, int type,
      struct dlg_cb_params * params)
{
   switch (type) {
      case DLGCB_FAILED:
         LM_DBG("DID %p failed (canceled). "
            "Terminating session.\n", did);
         break;
      case DLGCB_EXPIRED:
         /* In the case of expired, the msg is pointing at a
          * FAKED_REPLY (-1)
          */
         LM_DBG("Terminating session.\n");
         break;
      default: /* Normal termination. */
         LM_DBG("Terminating DID %p session\n", did);
         break;
   }
   /*
    * Free the param sst_info_t memory
    */
   if (*(params->param)) {
      LM_DBG("freeing the sst_info_t from dialog %p\n", did);
      shm_free(*(params->param));
      *(params->param) = NULL;
   }
   return;
}

/**
 * Callback from the dialog module when the dialog is being updated in
 * its life span. We are only interested in the INVITE or UPDATE if
 * SST is supported and active for this dialog. In this case, we need
 * to update the expire time for the dialog based on the
 * Session-Expires: header in the reINVITE/UPDATE request.
 *
 * When this callback returns control to the dialog module it WILL
 * reset the timeout of the dialog. We need to make sure we set the
 * AVP here or the dialog timeout will be reset to the DEFAULT value
 * if this is a different transaction. (so the AVP value is gone)
 *
 * @param did - The dialog structure. The pointer is used as an ID.
 * @param type - The reason for the callback. DLGCB_REQ_WITHIN
 * @param params - The sst information
 */
static void sst_dialog_request_within_CB(struct dlg_cell* did, int type,
      struct dlg_cb_params * params)
{
   sst_info_t *info = (sst_info_t *)*(params->param);
   sst_msg_info_t minfo = {0,0,0,0};
   struct sip_msg* msg = params->msg;

   if (msg->first_line.type == SIP_REQUEST) {
      if ((msg->first_line.u.request.method_value == METHOD_INVITE ||
                  msg->first_line.u.request.method_value == METHOD_UPDATE)) {

         LM_DBG("Update by a REQUEST. %.*s\n", 
               msg->first_line.u.request.method.len, 
               msg->first_line.u.request.method.s);
         if (parse_msg_for_sst_info(msg, &minfo)) {
            LM_ERR("failed to parse sst information\n"); 
            return;
         }
         /* Early resetting of the value here */
         set_timeout_avp(msg, minfo.se);
         info->interval = minfo.se;
      }
      else if (msg->first_line.u.request.method_value == METHOD_PRACK) {
         /* Special case here. The PRACK will cause the dialog
          * module to reset the timeout value to the ldg->lifetime
          * value and look for the new AVP value bound to the
          * 1XX/PRACK/200OK/ACK transaction and not to the
          * INVITE/200OK avp value. So we need to set the AVP
          * again! I think this is a bug in the dialog module,
          * either it should ignore PRACK like it ignored ACK, or
          * the setting of the timeout value when returning to the
          * confiremed callback code should look for the new AVP
          * value, which is does not.
          */
         LM_DBG("PRACK workaround applied!\n");
         set_timeout_avp(msg, info->interval);
      }
   }
   else if (msg->first_line.type == SIP_REPLY) {
      if ((msg->first_line.u.reply.statuscode > 199 &&
                  msg->first_line.u.reply.statuscode < 300)) {
         /*
          * To spec (RFC) the internal time out value so not be reset
          * until here.
          */
         LM_DBG("Update by a REPLY %d %.*s\n", 
               msg->first_line.u.reply.statuscode,
               msg->first_line.u.reply.reason.len, 
               msg->first_line.u.reply.reason.s);
         if (parse_msg_for_sst_info(msg, &minfo)) {
            LM_ERR("failed to parse sst information\n");
            return;
         }
         set_timeout_avp(msg, minfo.se);
         info->interval = minfo.se;
      }
   }
}

/**
 * This callback is called on any response message in the lifespan of
 * the dialog. The callback is called just before the message is
 * copied to pkg memory so it is still mutable.
 *
 * @param did - The dialog structure. The pointer is used as an ID.
 * @param type - The reason for the callback. DLGCB_CONFIRMED
 * @param params - The sst information
 */
static void sst_dialog_response_fwded_CB(struct dlg_cell* did, int type,
      struct dlg_cb_params * params) 
{
   struct sip_msg* msg = params->msg;

   /*
    * This test to see if the message is a response sould ALWAYS be
    * true. This callback should not get called for requests. But
    * lets be safe.
    */
   if (msg->first_line.type == SIP_REPLY) {
      sst_msg_info_t minfo = {0,0,0,0};
      sst_info_t *info = (sst_info_t *)*(params->param);

      LM_DBG("Dialog seen REPLY %d %.*s\n", 
            msg->first_line.u.reply.statuscode,
            msg->first_line.u.reply.reason.len, 
            msg->first_line.u.reply.reason.s);
      /*
       * Need to check to see if it is a 422 response. If it is,
       * make sure our Min-SE: for this dialog is set at least as
       * large as in the Min-SE: in the reply 422 message. If not,
       * we will create an INVITE, 422 loop.
       */
      if (msg->first_line.u.reply.statuscode == 422) {
         if (parse_msg_for_sst_info(msg, &minfo)) {
            LM_ERR("failed to parse sst information for the 422 reply\n");
            return;
         }
         /* Make sure we do not try to use anything smaller */
         info->interval = MAX(info->interval, minfo.min_se);
         return; /* There is nothing else to do with this */
      }
      /*
       * We need to get the method this reply is for from the CSEQ
       * body. The RFC states we can only play with 2XX from the
       * INVITE or reINVTE/UPDATE.
       */
      if (!msg->cseq && ((parse_headers(msg, HDR_CSEQ_F, 0) == -1) || !msg->cseq)) {
         LM_ERR("failed to parse CSeq\n");
         return;
      }
      
      /* 2XX replies to INVITES only !*/
      if (msg->first_line.u.reply.statuscode > 199 &&
            msg->first_line.u.reply.statuscode < 300 &&
            (get_cseq(msg)->method_id == METHOD_INVITE ||
                  get_cseq(msg)->method_id == METHOD_UPDATE)) {
         if (parse_msg_for_sst_info(msg, &minfo)) {
            LM_ERR("failed to parse sst information for the 2XX reply\n");
            return;
         }

         if (minfo.se != 0) {
            if (set_timeout_avp(msg, info->interval)) {
               LM_ERR("failed to set the timeout AVP\n");
               return;
            }
         }
         else {
            /* no se header found, we want to resquest it. */
            if (info->requester == SST_PXY || info->supported == SST_UAC) {
               str sehdr;
               
               LM_DBG("appending the Session-Expires: header to the 2XX reply."
                     " UAC will deal with it.\n");
               /*
                * GOOD! we can just insert the Session-Expires:
                * header and forward back to the UAC and it will
                * deal with refreshing the session.
                */
               sst_build_se_hdr(info->interval, &sehdr);
               if (append_header(msg, sehdr.s)) {
                  LM_ERR("failed to append Session-Expires header\n");
                  return;
               }
               /* Set the dialog timeout HERE */
               if (set_timeout_avp(msg, info->interval)) {
                  return;
               }
            }
            else {
               /* We are sunk, uac did not request it, and it
                * does not support it */
               LM_DBG("UAC and UAS do not support timers!"
                     " No session timers for this session.\n");
            }
         }
      } /* End of 2XX for an INVITE */
   } /* If the msg is a repsonse and not a request */
}

/**
 * The sstCheckMin() script command handler. Return 1 (true) if the
 * MIN-SE: of the message is too small compared to the sst_min_se
 * value. This will allow the script to reply to this INVITE with a
 * "422 Session Timer Too Small" response. if sst_min_se was never set
 * the recommended value of 1800 seconds will be used.
 *
 * If the flag (str1) is set to 1, the 422 reply will be sent with the
 * sst MIN_SE value in the header. If the flag is not set or is NULL,
 * no reply is sent.

 * @param msg  - The sip message from the script (INVITE only)
 * @param flag - Reply mode Flag. 0/NULL do not send reply, 1 send 422
 *               reply if Session-Expires is to small with the MIN-SE
 *               header in the reply
 * @param str2 - Not used.
 *
 * @return 1 if the MIN-SE is too small, -1 if it is OK, or It could
 *         not be checked.
 *
 * NOTE: returning 0 == drop message, 1 == true, -1 == false in the
 *       script.
 */
int sst_check_min(struct sip_msg *msg, char *flag, char *str2)
{
   enum parse_sst_result result;
   struct session_expires se = {0,0};
   unsigned minse = 0;

   /*
    * Only look in INVITES. We can't reply with a 422 to a 2xx reply
    * now can we. This check can ONLY be done on the INVITE/UPDATE.
    */
   if (msg->first_line.type == SIP_REQUEST &&
         msg->first_line.u.request.method_value == METHOD_INVITE) {
      /*
       * First see if there is an Session-Expires: header.  If there
       * is, also look for a MIN-SE: header. If there is, use the
       * minimum value of the two to compare with srt1. All MUST not
       * be less then 90 and 1800 is recomended. See RCF section 4.
       */
      if ((result = parse_session_expires(msg, &se)) != parse_sst_success) {
         if (result != parse_sst_header_not_found) {
            LM_ERR("failed to parse Session-Expires headers.\n");
            return 0; /* Error drop the message */
         }
         /* Session-Expires not supported/stated */
         LM_DBG("No Session-Expires header found. retuning false (-1)\n");
         /*
          * NOTE: 0 == drop message, 1 == true, -1 == false
          */
         return -1;
      }

      /*
       * We have a Session_expire header. Now look for the MIN-SE.
       */
      if ((result = parse_min_se(msg, &minse)) != parse_sst_success) {
         if (result != parse_sst_header_not_found) {
            /*
             * This is an error. The header was found but could
             * not parse it.
             */
            LM_ERR("failed to parse MIN-SE header.\n");
            return -1; 
         }
         /*
          * If not stated, use the value from the session-expires
          * header
          */
         LM_DBG("No MIN-SE header found.\n");
         minse = 90; /* default by RFC4028, $5 */
      }
      
      LM_DBG("Session-Expires: %d; MIN-SE: %d\n",  se.interval, minse);

      /*
       * Now compare our MIN-SE with the messages and see if it is
       * too small. We will take the smaller of the messages
       * Session-expires and min-se if stated.
       */
      if (sst_min_se < MIN(minse, se.interval)) {
         /*
          * Too small. See if we need to send the 422 and are able
          * to send it.
          */
         if (flag) {
            str msehdr;
            sst_build_minse_hdr(sst_min_se, &msehdr);
            LM_DBG("Sending 422: %.*s\n", msehdr.len, msehdr.s);
            if (send_response(msg, 422, &sst_422_rpl, msehdr.s, msehdr.len)){
               LM_ERR("Error sending 422 reply.\n");
            }
         }
         LM_DBG("Done returning true (1)\n");
         return 1; /* return true */
      }
   }
   LM_DBG("Done returning false (-1)\n");
   /*
    * All is good.
    */
   return -1; /* return false */
}

/**
 * Send a reply (response) to the passed in SIP request messsage with
 * the code and reason. If the header is not NULL (and header_len !=
 * 0) the add the header to the reply message.
 *
 * @param request The SIP request message to build the reply from.
 * @param code The response code. i.e 200
 * @param reason The response reason. i.e. "OK"
 * @param header the header block to add to the reply.
 * @param header_len The length of the header block. (header)
 *
 * @return 0 on success, none-zero on an error.
 */
static int send_response(struct sip_msg *request, int code, str *reason,
      char *header, int header_len) 
{

   if (slb.send_reply != 0) {
      /* Add new headers if not null or zero length */
      if ((header) && (header_len)) {
         if (add_lump_rpl(request, header, header_len, LUMP_RPL_HDR) == 0) {
            /* An error with adding the lump */
            LM_ERR("unable to append header.\n");
            return -1;
         }
      }
      /* Now using the sl function, send the reply/response */
      if (slb.send_reply(request, code, reason) < 0) {
         LM_ERR("Unable to sent reply.\n");
         return -1;
      }
   }
   else {
      return -1;
   }
   return(0);
}

/**
 * Given some header text, append it to the passed in message.
 *
 * @param msg The message to append the header text to.
 * @param header The header text to append.
 *
 * @return 0 on success, non-zero on failure.
 */
static int append_header(struct sip_msg *msg, const char *header)
{
   struct lump* anchor = NULL;
   char *s = NULL;
   int len = 0;

   LM_DBG("Appending header: %s", header);

   if (parse_headers(msg, HDR_EOH_F, 0) == -1) {
      LM_ERR("failed to parse headers in message.\n");
      return(1);
   }

   if ((anchor = anchor_lump(msg, msg->unparsed - msg->buf, 0, 0)) == 0) {
      LM_ERR("failed to get anchor to append header\n");
      return(1);
   }
   len = strlen(header);
   if ((s = (char *)pkg_malloc(len)) == 0) {
      LM_ERR("No more pkg memory. (size requested = %d)\n", len);
      return(1);
   }
   memcpy(s, header, len);
   if (insert_new_lump_before(anchor, s, len, 0) == 0) {
      LM_ERR("failed to insert lump\n");
      pkg_free(s);
      return(1);
   }
   LM_DBG("Done appending header successfully.\n");
   return(0);
}

/**
 * Remove a header from a message if found.
 *
 * @param msg The message to look for the header to remove.
 * @param header The header name: text.
 *
 * @return 0 if the header was not found, >0 is successful, -1 on an
 *         error.
 */
static int remove_header(struct sip_msg *msg, const char *header)
{
   struct lump* anchor = NULL;
   struct hdr_field *hf = NULL;
   int cnt = 0;
   int len = strlen(header);

   if (parse_headers(msg, HDR_EOH_F, 0) == -1) {
      LM_ERR("failed to parse headers in message.\n");
      return(-1);
   }
   
   for (hf = msg->headers; hf; hf = hf->next) {
      if (hf->name.len != len) {
         continue;
      }
      if (strncasecmp(hf->name.s, header, hf->name.len) != 0) {
         continue;
      }

      anchor = del_lump(msg, hf->name.s-msg->buf, hf->len, 0);
      if (anchor == 0) {
         LM_ERR("no more pkg memory\n");
         return -1;
      }
      cnt++;
   }
   return cnt;
}

/**
 * Set the dialog's AVP value so the dialog module will use this value
 * and not the default when returning from the dialog callback.
 *
 * @param msg The current message to bind the AVP to.
 * @param value The value you want to set the AVP to.
 *
 * @return 0 on success, -1 on an error.
 */
static int set_timeout_avp(struct sip_msg *msg, unsigned int value)
{
   int rtn = -1; /* assume failure */
   pv_value_t pv_val;
   int result = 0;

   /* Set the dialog timeout HERE */
   if (timeout_avp) {
      if ((result = pv_get_spec_value(msg, timeout_avp, &pv_val)) == 0) {
         /* We now hold a reference to the AVP */
         if (pv_val.flags & PV_VAL_INT && pv_val.ri == value) {
            /* INT AVP with the same value */
            LM_DBG("Current timeout value already set to %d\n",
               value);
            rtn = 0;
         } else {
            /* AVP not found or non-INT value -> add a new one*/
            pv_val.flags = PV_VAL_INT;
            pv_val.ri = value;
            if (timeout_avp->setf(msg,&timeout_avp->pvp,EQ_T,&pv_val)!=0) {
               LM_ERR("failed to set new dialog timeout value\n");
            } else {
               rtn = 0;
            }
         }
      }
      else {
         LM_ERR("SST not reset. get avp result is %d\n", result);
      }
   }
   else {
      LM_ERR("SST needs to know the name of the dialog timeout AVP!\n");
   }
   return(rtn);
}

/**
 * Gether the message information about SST from the current message
 * being processed.
 *
 * @param msg The current message to parse.
 * @param minfo The SST information found in the message.
 *
 * @return 0 on success, -1 on a parsing error.
 */
static int parse_msg_for_sst_info(struct sip_msg *msg, sst_msg_info_t *minfo)
{
   int rtn = 0;
   struct session_expires se = {0,0};

   if (!msg || !minfo) {
      return (-1);
   }
   
   /* 
    * parse the supported infor
    */
   minfo->supported = 0; /*Clear it */
   minfo->se = 0;
   minfo->refresher = sst_refresher_unspecified;
   minfo->min_se = 0;

   /*
    * The parse_supported() will return 0 if found and parsed OK, -1
    * if not found or an error parsing the one it did find! So assume
    * it is not found if unsuccessfull.
    */
   if ((rtn = parse_supported(msg)) == 0) {
      if ((((struct supported_body*)msg->supported->parsed)->supported_all
                  & F_SUPPORTED_TIMER)) {
         minfo->supported = 1;
      }
   }
   /*
    * Parse the Min-SE: header next.
    */
   minfo->min_se = 0;
   if ((rtn = parse_min_se(msg, &minfo->min_se)) != parse_sst_success) {
      minfo->min_se = 0; /* Make sure it statys clean */
   }
   minfo->se = 0;
   if ((rtn = parse_session_expires(msg, &se)) == parse_sst_success) {
      minfo->se = se.interval;
      minfo->refresher = se.refresher;
   }
   return(0);
}

/**
 * Add the Min-SE: header and send a reply 422.
 *
 * @param msg The message to opperate on.
 * @param min_se The Min-SE: value to use in the heaader.
 *
 * @return 0 on success, -1 on error.
 */
static int send_reject(struct sip_msg *msg, unsigned int min_se) 
{
   str msehdr;

   sst_build_minse_hdr(min_se, &msehdr);

   if (send_response(msg, 422, &sst_422_rpl, msehdr.s, msehdr.len)) {
      LM_ERR("Error sending 422 reply.\n");
      return(-1);
   }
   LM_DBG("Send reject reply 422 with Min-SE: %d\n", min_se);
   return(0);
}

/**
 * A helper function to setup all the callbacks from the dialog module
 * after we find interest in the dialog.
 *
 * @param did The Dialog ID.
 * @param info The sst information.
 *
 */
static void setup_dialog_callbacks(struct dlg_cell *did, sst_info_t *info)
{
   /*
    * Register for the other callbacks from the dialog.
    */

#ifdef USE_CONFIRM_CALLBACK
   LM_DBG("Adding callback DLGCB_CONFIRMED\n");
   dlg_binds->register_dlgcb(did,
         DLGCB_CONFIRMED, sst_dialog_confirmed_CB, info, NULL);
#endif /* USE_CONFIRM_CALLBACK */

   LM_DBG("Adding callback "
         "DLGCB_FAILED|DLGCB_TERMINATED|DLGCB_EXPIRED\n");
   dlg_binds->register_dlgcb(did,
         DLGCB_FAILED|DLGCB_TERMINATED|DLGCB_EXPIRED,
         sst_dialog_terminate_CB, (void *)info, NULL);
   LM_DBG("Adding callback DLGCB_REQ_WITHIN\n");
   /* This is for the reINVITE/UPDATE requests */
   dlg_binds->register_dlgcb(did, DLGCB_REQ_WITHIN,
         sst_dialog_request_within_CB, info, NULL);
   /* 
    * This is for the final configuration of who will do SST for
    * us. In the DLGCB_CONFIRMED callback the message is
    * immutable! we must do all the real work in the DLGCB_FRD
    * callback were we can change the message.
    */
   LM_DBG("Adding callback DLGCB_RESPONSE_FWDED\n");
   dlg_binds->register_dlgcb(did, DLGCB_RESPONSE_FWDED,
         sst_dialog_response_fwded_CB, info, NULL);
   
   LM_DBG("Adding mi handler\n");
   dlg_binds->register_dlgcb(did, DLGCB_MI_CONTEXT,
         sst_dialog_mi_context_CB, info, NULL);
}