/* 
 * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
 * Copyright (C) 2003-2008 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 <pjsip/sip_ua_layer.h>
#include <pjsip/sip_module.h>
#include <pjsip/sip_dialog.h>
#include <pjsip/sip_endpoint.h>
#include <pjsip/sip_errno.h>
#include <pjsip/sip_transaction.h>
#include <pj/os.h>
#include <pj/hash.h>
#include <pj/assert.h>
#include <pj/string.h>
#include <pj/pool.h>
#include <pj/log.h>


#define THIS_FILE    "sip_ua_layer.c"

/*
 * Static prototypes.
 */
static pj_status_t mod_ua_load(pjsip_endpoint *endpt);
static pj_status_t mod_ua_unload(void);
static pj_bool_t   mod_ua_on_rx_request(pjsip_rx_data *rdata);
static pj_bool_t   mod_ua_on_rx_response(pjsip_rx_data *rdata);
static void        mod_ua_on_tsx_state(pjsip_transaction*, pjsip_event*);


extern long pjsip_dlg_lock_tls_id;      /* defined in sip_dialog.c */

/* This struct is used to represent list of dialog inside a dialog set.
 * We don't want to use pjsip_dialog for this purpose, to save some
 * memory (about 100 bytes per dialog set).
 */
struct dlg_set_head
{
    PJ_DECL_LIST_MEMBER(pjsip_dialog);
};

/* This struct represents a dialog set.
 * This is the value that will be put in the UA's hash table.
 */
struct dlg_set
{
    /* To put this node in free dlg_set nodes in UA. */
    PJ_DECL_LIST_MEMBER(struct dlg_set);

    /* This is the buffer to store this entry in the hash table. */
    pj_hash_entry_buf ht_entry;

    /* Entry key in the hash table */
    pj_str_t ht_key;

    /* List of dialog in this dialog set. */
    struct dlg_set_head  dlg_list;
};


/*
 * Module interface.
 */
static struct user_agent
{
    pjsip_module         mod;
    pj_pool_t           *pool;
    pjsip_endpoint      *endpt;
    pj_mutex_t          *mutex;
    pj_hash_table_t     *dlg_table;
    pjsip_ua_init_param  param;
    struct dlg_set       free_dlgset_nodes;

} mod_ua = 
{
  {
    NULL, NULL,             /* prev, next.                      */
    { "mod-ua", 6 },        /* Name.                            */
    -1,                     /* Id                               */
    PJSIP_MOD_PRIORITY_UA_PROXY_LAYER,  /* Priority             */
    &mod_ua_load,           /* load()                           */
    NULL,                   /* start()                          */
    NULL,                   /* stop()                           */
    &mod_ua_unload,         /* unload()                         */
    &mod_ua_on_rx_request,  /* on_rx_request()                  */
    &mod_ua_on_rx_response, /* on_rx_response()                 */
    NULL,                   /* on_tx_request.                   */
    NULL,                   /* on_tx_response()                 */
    &mod_ua_on_tsx_state,   /* on_tsx_state()                   */
  }
};

/* 
 * mod_ua_load()
 *
 * Called when module is being loaded by endpoint.
 */
static pj_status_t mod_ua_load(pjsip_endpoint *endpt)
{
    pj_status_t status;

    /* Initialize the user agent. */
    mod_ua.endpt = endpt;
    mod_ua.pool = pjsip_endpt_create_pool( endpt, "ua%p", PJSIP_POOL_LEN_UA,
                                           PJSIP_POOL_INC_UA);
    if (mod_ua.pool == NULL)
        return PJ_ENOMEM;

    status = pj_mutex_create_recursive(mod_ua.pool, " ua%p", &mod_ua.mutex);
    if (status != PJ_SUCCESS)
        return status;

    mod_ua.dlg_table = pj_hash_create(mod_ua.pool, PJSIP_MAX_DIALOG_COUNT);
    if (mod_ua.dlg_table == NULL)
        return PJ_ENOMEM;

    pj_list_init(&mod_ua.free_dlgset_nodes);

    /* Initialize dialog lock. */
    status = pj_thread_local_alloc(&pjsip_dlg_lock_tls_id);
    if (status != PJ_SUCCESS)
        return status;

    pj_thread_local_set(pjsip_dlg_lock_tls_id, NULL);

    return PJ_SUCCESS;

}

/*
 * mod_ua_unload()
 *
 * Called when module is being unloaded.
 */
static pj_status_t mod_ua_unload(void)
{
    pj_thread_local_free(pjsip_dlg_lock_tls_id);
    pj_mutex_destroy(mod_ua.mutex);

    /* Release pool */
    if (mod_ua.pool) {
        pjsip_endpt_release_pool( mod_ua.endpt, mod_ua.pool );
    }
    return PJ_SUCCESS;
}

/*
 * mod_ua_on_tsx_stats()
 *
 * Called on changed on transaction state.
 */
static void mod_ua_on_tsx_state( pjsip_transaction *tsx, pjsip_event *e)
{
    pjsip_dialog *dlg;

    /* If the module id is -1, it could mean that the module has been
     * destroyed.
     */
    if (mod_ua.mod.id == -1)
        return;

    /* Get the dialog where this transaction belongs. */
    dlg = (pjsip_dialog*) tsx->mod_data[mod_ua.mod.id];
    
    /* If dialog instance has gone, it could mean that the dialog
     * may has been destroyed.
     */
    if (dlg == NULL)
        return;

    /* Hand over the event to the dialog. */
    pjsip_dlg_on_tsx_state(dlg, tsx, e);
}


/*
 * Init user agent module and register it to the endpoint.
 */
PJ_DEF(pj_status_t) pjsip_ua_init_module( pjsip_endpoint *endpt,
                                          const pjsip_ua_init_param *prm)
{
    pj_status_t status;

    /* Check if module already registered. */
    PJ_ASSERT_RETURN(mod_ua.mod.id == -1, PJ_EINVALIDOP);

    /* Copy param, if exists. */
    if (prm)
        pj_memcpy(&mod_ua.param, prm, sizeof(pjsip_ua_init_param));

    /* Register the module. */
    status = pjsip_endpt_register_module(endpt, &mod_ua.mod);

    return status;
}

/*
 * Get the instance of the user agent.
 *
 */
PJ_DEF(pjsip_user_agent*) pjsip_ua_instance(void)
{
    return &mod_ua.mod;
}


/*
 * Get the endpoint where this UA is currently registered.
 */
PJ_DEF(pjsip_endpoint*) pjsip_ua_get_endpt(pjsip_user_agent *ua)
{
    PJ_UNUSED_ARG(ua);
    pj_assert(ua == &mod_ua.mod);
    return mod_ua.endpt;
}


/*
 * Destroy the user agent layer.
 */
PJ_DEF(pj_status_t) pjsip_ua_destroy(void)
{
    /* Check if module already destroyed. */
    PJ_ASSERT_RETURN(mod_ua.mod.id != -1, PJ_EINVALIDOP);

    return pjsip_endpt_unregister_module(mod_ua.endpt, &mod_ua.mod);
}



/*
 * Create key to identify dialog set.
 */
/*
PJ_DEF(void) pjsip_ua_create_dlg_set_key( pj_pool_t *pool,
                                          pj_str_t *set_key,
                                          const pj_str_t *call_id,
                                          const pj_str_t *local_tag)
{
    PJ_ASSERT_ON_FAIL(pool && set_key && call_id && local_tag, return;);

    set_key->slen = call_id->slen + local_tag->slen + 1;
    set_key->ptr = (char*) pj_pool_alloc(pool, set_key->slen);
    pj_assert(set_key->ptr != NULL);

    pj_memcpy(set_key->ptr, call_id->ptr, call_id->slen);
    set_key->ptr[call_id->slen] = '$';
    pj_memcpy(set_key->ptr + call_id->slen + 1, 
              local_tag->ptr, local_tag->slen);
}
*/

/*
 * Acquire one dlg_set node to be put in the hash table.
 * This will first look in the free nodes list, then allocate
 * a new one from UA's pool when one is not available.
 */
static struct dlg_set *alloc_dlgset_node(void)
{
    struct dlg_set *set;

    if (!pj_list_empty(&mod_ua.free_dlgset_nodes)) {
        set = mod_ua.free_dlgset_nodes.next;
        pj_list_erase(set);
        return set;
    } else {
        set = PJ_POOL_ALLOC_T(mod_ua.pool, struct dlg_set);
        return set;
    }
}

/*
 * Register new dialog. Called by pjsip_dlg_create_uac() and
 * pjsip_dlg_create_uas_and_inc_lock();
 */
PJ_DEF(pj_status_t) pjsip_ua_register_dlg( pjsip_user_agent *ua,
                                           pjsip_dialog *dlg )
{
    /* Sanity check. */
    PJ_ASSERT_RETURN(ua && dlg, PJ_EINVAL);

    /* For all dialogs, local tag (inc hash) must has been initialized. */
    PJ_ASSERT_RETURN(dlg->local.info && dlg->local.info->tag.slen &&
                     dlg->local.tag_hval != 0, PJ_EBUG);

    /* For UAS dialog, remote tag (inc hash) must have been initialized. */
    //PJ_ASSERT_RETURN(dlg->role==PJSIP_ROLE_UAC ||
    //               (dlg->role==PJSIP_ROLE_UAS && dlg->remote.info->tag.slen
    //                && dlg->remote.tag_hval != 0), PJ_EBUG);

    /* Lock the user agent. */
    pj_mutex_lock(mod_ua.mutex);

    /* For UAC, check if there is existing dialog in the same set. */
    if (dlg->role == PJSIP_ROLE_UAC) {
        struct dlg_set *dlg_set;

        dlg_set = (struct dlg_set*)
                  pj_hash_get_lower( mod_ua.dlg_table,
                                     dlg->local.info->tag.ptr, 
                                     (unsigned)dlg->local.info->tag.slen,
                                     &dlg->local.tag_hval);

        if (dlg_set) {
            /* This is NOT the first dialog in the dialog set. 
             * Just add this dialog in the list.
             */
            pj_assert(dlg_set->dlg_list.next != (void*)&dlg_set->dlg_list);
            pj_list_push_back(&dlg_set->dlg_list, dlg);

            dlg->dlg_set = dlg_set;

        } else {
            /* This is the first dialog in the dialog set. 
             * Create the dialog set and add this dialog to it.
             */
            dlg_set = alloc_dlgset_node();
            dlg_set->ht_key = dlg->local.info->tag;
            pj_list_init(&dlg_set->dlg_list);
            pj_list_push_back(&dlg_set->dlg_list, dlg);

            dlg->dlg_set = dlg_set;

            /* Register the dialog set in the hash table. */
            pj_hash_set_np_lower(mod_ua.dlg_table, 
                                 dlg_set->ht_key.ptr,
                                 (unsigned)dlg_set->ht_key.slen,
                                 dlg->local.tag_hval, dlg_set->ht_entry,
                                 dlg_set);
        }

    } else {
        /* For UAS, create the dialog set with a single dialog as member. */
        struct dlg_set *dlg_set;

        dlg_set = alloc_dlgset_node();
        dlg_set->ht_key = dlg->local.info->tag;
        pj_list_init(&dlg_set->dlg_list);
        pj_list_push_back(&dlg_set->dlg_list, dlg);

        dlg->dlg_set = dlg_set;

        pj_hash_set_np_lower(mod_ua.dlg_table, 
                             dlg_set->ht_key.ptr,
                             (unsigned)dlg_set->ht_key.slen,
                             dlg->local.tag_hval, dlg_set->ht_entry, dlg_set);
    }

    /* Unlock user agent. */
    pj_mutex_unlock(mod_ua.mutex);

    /* Done. */
    return PJ_SUCCESS;
}


PJ_DEF(pj_status_t) pjsip_ua_unregister_dlg( pjsip_user_agent *ua,
                                             pjsip_dialog *dlg )
{
    struct dlg_set *dlg_set;
    pjsip_dialog *d;

    /* Sanity-check arguments. */
    PJ_ASSERT_RETURN(ua && dlg, PJ_EINVAL);

    /* Check that dialog has been registered. */
    PJ_ASSERT_RETURN(dlg->dlg_set, PJ_EINVALIDOP);

    /* Lock user agent. */
    pj_mutex_lock(mod_ua.mutex);

    /* Find this dialog from the dialog set. */
    dlg_set = (struct dlg_set*) dlg->dlg_set;
    d = dlg_set->dlg_list.next;
    while (d != (pjsip_dialog*)&dlg_set->dlg_list && d != dlg) {
        d = d->next;
    }

    if (d != dlg) {
        pj_assert(!"Dialog is not registered!");
        pj_mutex_unlock(mod_ua.mutex);
        return PJ_EINVALIDOP;
    }

    /* Remove this dialog from the list. */
    pj_list_erase(dlg);

    /* If dialog list is empty, remove the dialog set from the hash table. */
    if (pj_list_empty(&dlg_set->dlg_list)) {

        /* Verify that the dialog set is valid */
        pj_assert(pj_hash_get_lower(mod_ua.dlg_table, dlg_set->ht_key.ptr,
                                    (unsigned)dlg_set->ht_key.slen,
                                    &dlg->local.tag_hval) == dlg_set);

        pj_hash_set_lower(NULL, mod_ua.dlg_table, dlg_set->ht_key.ptr,
                          (unsigned)dlg_set->ht_key.slen,
                          dlg->local.tag_hval, NULL);

        /* Return dlg_set to free nodes. */
        pj_list_push_back(&mod_ua.free_dlgset_nodes, dlg_set);
    } else {
        /* If the just unregistered dialog is being used as hash key,
         * reset the dlg_set entry with a new key (i.e: from the first dialog
         * in dlg_set).
         */
        if (dlg_set->ht_key.ptr  == dlg->local.info->tag.ptr &&
            dlg_set->ht_key.slen == dlg->local.info->tag.slen)
        {
            pjsip_dialog* key_dlg = dlg_set->dlg_list.next;

            /* Verify that the old & new keys share the hash value */
            pj_assert(key_dlg->local.tag_hval == dlg->local.tag_hval);

            pj_hash_set_lower(NULL, mod_ua.dlg_table, dlg_set->ht_key.ptr,
                              (unsigned)dlg_set->ht_key.slen,
                              dlg->local.tag_hval, NULL);

            dlg_set->ht_key = key_dlg->local.info->tag;

            pj_hash_set_np_lower(mod_ua.dlg_table,
                                 dlg_set->ht_key.ptr,
                                 (unsigned)dlg_set->ht_key.slen,
                                 key_dlg->local.tag_hval, dlg_set->ht_entry,
                                 dlg_set);
        }
    }

    /* Unlock user agent. */
    pj_mutex_unlock(mod_ua.mutex);

    /* Done. */
    return PJ_SUCCESS;
}


PJ_DEF(pjsip_dialog*) pjsip_rdata_get_dlg( pjsip_rx_data *rdata )
{
    return (pjsip_dialog*) rdata->endpt_info.mod_data[mod_ua.mod.id];
}

PJ_DEF(pjsip_dialog*) pjsip_tdata_get_dlg( pjsip_tx_data *tdata )
{
    return (pjsip_dialog*) tdata->mod_data[mod_ua.mod.id];
}

PJ_DEF(pjsip_dialog*) pjsip_tsx_get_dlg( pjsip_transaction *tsx )
{
    return (pjsip_dialog*) tsx->mod_data[mod_ua.mod.id];
}


/*
 * Retrieve the current number of dialog-set currently registered
 * in the hash table. 
 */
PJ_DEF(unsigned) pjsip_ua_get_dlg_set_count(void)
{
    unsigned count;

    PJ_ASSERT_RETURN(mod_ua.endpt, 0);

    pj_mutex_lock(mod_ua.mutex);
    count = pj_hash_count(mod_ua.dlg_table);
    pj_mutex_unlock(mod_ua.mutex);

    return count;
}


/* 
 * Find a dialog.
 */
PJ_DEF(pjsip_dialog*) pjsip_ua_find_dialog(const pj_str_t *call_id,
                                           const pj_str_t *local_tag,
                                           const pj_str_t *remote_tag,
                                           pj_bool_t lock_dialog)
{
    struct dlg_set *dlg_set;
    pjsip_dialog *dlg;

    PJ_ASSERT_RETURN(call_id && local_tag && remote_tag, NULL);

    /* Lock user agent. */
    pj_mutex_lock(mod_ua.mutex);

    /* Lookup the dialog set. */
    dlg_set = (struct dlg_set*)
              pj_hash_get_lower(mod_ua.dlg_table, local_tag->ptr,
                                (unsigned)local_tag->slen, NULL);
    if (dlg_set == NULL) {
        /* Not found */
        pj_mutex_unlock(mod_ua.mutex);
        return NULL;
    }

    /* Dialog set is found, now find the matching dialog based on the
     * remote tag.
     */
    dlg = dlg_set->dlg_list.next;
    while (dlg != (pjsip_dialog*)&dlg_set->dlg_list) {  
        if (pj_stricmp(&dlg->remote.info->tag, remote_tag) == 0)
            break;
        dlg = dlg->next;
    }

    if (dlg == (pjsip_dialog*)&dlg_set->dlg_list) {
        /* Not found */
        pj_mutex_unlock(mod_ua.mutex);
        return NULL;
    }

    /* Dialog has been found. It SHOULD have the right Call-ID!! */
    if (pj_strcmp(&dlg->call_id->id, call_id)!=0) {

        PJ_LOG(6, (THIS_FILE, "Dialog not found: local and remote tags "
                              "matched but not call id"));

        pj_mutex_unlock(mod_ua.mutex);
        return NULL;
    }

    if (lock_dialog) {
        if (pjsip_dlg_try_inc_lock(dlg) != PJ_SUCCESS) {

            /*
             * Unable to acquire dialog's lock while holding the user
             * agent's mutex. Release the UA mutex before retrying once
             * more.
             *
             * THIS MAY CAUSE RACE CONDITION!
             */

            /* Unlock user agent. */
            pj_mutex_unlock(mod_ua.mutex);
            /* Lock dialog */
            pjsip_dlg_inc_lock(dlg);

        } else {
            /* Unlock user agent. */
            pj_mutex_unlock(mod_ua.mutex);
        }

    } else {
        /* Unlock user agent. */
        pj_mutex_unlock(mod_ua.mutex);
    }

    return dlg;
}


/*
 * Find the first dialog in dialog set in hash table for an incoming message.
 */
static struct dlg_set *find_dlg_set_for_msg( pjsip_rx_data *rdata )
{
    /* CANCEL message doesn't have To tag, so we must lookup the dialog
     * by finding the INVITE UAS transaction being cancelled.
     */
    if (rdata->msg_info.cseq->method.id == PJSIP_CANCEL_METHOD) {

        pjsip_dialog *dlg;

        /* Create key for the rdata, but this time, use INVITE as the
         * method.
         */
        pj_str_t key;
        pjsip_role_e role;
        pjsip_transaction *tsx;

        if (rdata->msg_info.msg->type == PJSIP_REQUEST_MSG)
            role = PJSIP_ROLE_UAS;
        else
            role = PJSIP_ROLE_UAC;

        pjsip_tsx_create_key(rdata->tp_info.pool, &key, role, 
                             pjsip_get_invite_method(), rdata);

        /* Lookup the INVITE transaction */
        tsx = pjsip_tsx_layer_find_tsx2(&key, PJ_TRUE);

        /* We should find the dialog attached to the INVITE transaction */
        if (tsx) {
            dlg = (pjsip_dialog*) tsx->mod_data[mod_ua.mod.id];
            pj_grp_lock_dec_ref(tsx->grp_lock);

            /* Dlg may be NULL on some extreme condition
             * (e.g. during debugging where initially there is a dialog)
             */
            return dlg ? (struct dlg_set*) dlg->dlg_set : NULL;

        } else {
            return NULL;
        }


    } else {
        pj_str_t *tag;
        struct dlg_set *dlg_set;

        if (rdata->msg_info.msg->type == PJSIP_REQUEST_MSG)
            tag = &rdata->msg_info.to->tag;
        else
            tag = &rdata->msg_info.from->tag;

        /* Lookup the dialog set. */
        dlg_set = (struct dlg_set*)
                  pj_hash_get_lower(mod_ua.dlg_table, tag->ptr, 
                                    (unsigned)tag->slen, NULL);
        return dlg_set;
    }
}

/* On received requests. */
static pj_bool_t mod_ua_on_rx_request(pjsip_rx_data *rdata)
{
    struct dlg_set *dlg_set;
    pj_str_t *from_tag;
    pjsip_dialog *dlg;
    pj_status_t status;

    /* Optimized path: bail out early if request is not CANCEL and it doesn't
     * have To tag 
     */
    if (rdata->msg_info.to->tag.slen == 0 && 
        rdata->msg_info.msg->line.req.method.id != PJSIP_CANCEL_METHOD)
    {
        return PJ_FALSE;
    }

    /* Incoming REGISTER may have tags in it */
    if (rdata->msg_info.msg->line.req.method.id == PJSIP_REGISTER_METHOD)
        return PJ_FALSE;

retry_on_deadlock:

    /* Lock user agent before looking up the dialog hash table. */
    pj_mutex_lock(mod_ua.mutex);

    /* Lookup the dialog set, based on the To tag header. */
    dlg_set = find_dlg_set_for_msg(rdata);

    /* If dialog is not found, respond with 481 (Call/Transaction
     * Does Not Exist).
     */
    if (dlg_set == NULL) {
        /* Unable to find dialog. */
        pj_mutex_unlock(mod_ua.mutex);

        if (rdata->msg_info.msg->line.req.method.id != PJSIP_ACK_METHOD) {
            PJ_LOG(5,(THIS_FILE, 
                      "Unable to find dialogset for %s, answering with 481",
                      pjsip_rx_data_get_info(rdata)));

            /* Respond with 481 . */
            pjsip_endpt_respond_stateless( mod_ua.endpt, rdata, 481, NULL, 
                                           NULL, NULL );
        }
        return PJ_TRUE;
    }

    /* Dialog set has been found.
     * Find the dialog in the dialog set based on the content of the remote 
     * tag.
     */
    from_tag = &rdata->msg_info.from->tag;
    dlg = dlg_set->dlg_list.next;
    while (dlg != (pjsip_dialog*)&dlg_set->dlg_list) {
        
        if (pj_stricmp(&dlg->remote.info->tag, from_tag) == 0)
            break;

        dlg = dlg->next;
    }

    /* Dialog may not be found, e.g. in this case:
     *  - UAC sends SUBSCRIBE, then UAS sends NOTIFY before answering
     *    SUBSCRIBE request with 2xx.
     *
     * In this case, we can accept the request ONLY when the original 
     * dialog still has empty To tag.
     */
    if (dlg == (pjsip_dialog*)&dlg_set->dlg_list) {

        pjsip_dialog *first_dlg = dlg_set->dlg_list.next;

        if (first_dlg->remote.info->tag.slen != 0) {
            /* Not found. Mulfunction UAC? */
            pj_mutex_unlock(mod_ua.mutex);

            if (rdata->msg_info.msg->line.req.method.id != PJSIP_ACK_METHOD) {
                PJ_LOG(5,(THIS_FILE, 
                          "Unable to find dialog for %s, answering with 481",
                          pjsip_rx_data_get_info(rdata)));

                pjsip_endpt_respond_stateless(mod_ua.endpt, rdata,
                                              PJSIP_SC_CALL_TSX_DOES_NOT_EXIST, 
                                              NULL, NULL, NULL);
            } else {
                PJ_LOG(5,(THIS_FILE, 
                          "Unable to find dialog for %s",
                          pjsip_rx_data_get_info(rdata)));
            }
            return PJ_TRUE;
        }

        dlg = first_dlg;
    }

    /* Mark the dialog id of the request. */
    rdata->endpt_info.mod_data[mod_ua.mod.id] = dlg;

    /* Try to lock the dialog */
    PJ_LOG(6,(dlg->obj_name, "UA layer acquiring dialog lock for request"));
    status = pjsip_dlg_try_inc_lock(dlg);
    if (status != PJ_SUCCESS) {
        /* Failed to acquire dialog mutex immediately, this could be 
         * because of deadlock. Release UA mutex, yield, and retry 
         * the whole thing once again.
         */
        pj_mutex_unlock(mod_ua.mutex);
        pj_thread_sleep(0);
        goto retry_on_deadlock;
    }

    /* Done with processing in UA layer, release lock */
    pj_mutex_unlock(mod_ua.mutex);

    /* Pass to dialog. */
    pjsip_dlg_on_rx_request(dlg, rdata);

    /* Unlock the dialog. This may destroy the dialog */
    pjsip_dlg_dec_lock(dlg);

    /* Report as handled. */
    return PJ_TRUE;
}


/* On rx response notification.
 */
static pj_bool_t mod_ua_on_rx_response(pjsip_rx_data *rdata)
{
    pjsip_transaction *tsx;
    struct dlg_set *dlg_set;
    pjsip_dialog *dlg;
    pj_status_t status;

    /*
     * Find the dialog instance for the response.
     * All outgoing dialog requests are sent statefully, which means
     * there will be an UAC transaction associated with this response,
     * and the dialog instance will be recorded in that transaction.
     *
     * But even when transaction is found, there is possibility that
     * the response is a forked response.
     */

retry_on_deadlock:

    dlg = NULL;

    /* Lock user agent dlg table before we're doing anything. */
    pj_mutex_lock(mod_ua.mutex);

    /* Check if transaction is present. */
    tsx = pjsip_rdata_get_tsx(rdata);
    if (tsx) {
        /* Check if dialog is present in the transaction. */
        dlg = pjsip_tsx_get_dlg(tsx);
        if (!dlg) {
            /* Unlock dialog hash table. */
            pj_mutex_unlock(mod_ua.mutex);
            return PJ_FALSE;
        }

        /* Get the dialog set. */
        dlg_set = (struct dlg_set*) dlg->dlg_set;

        /* Even if transaction is found and (candidate) dialog has been 
         * identified, it's possible that the request has forked.
         */

    } else {
        /* Transaction is not present.
         * Check if this is a 2xx/OK response to INVITE, which in this
         * case the response will be handled directly by the
         * dialog.
         */
        pjsip_cseq_hdr *cseq_hdr = rdata->msg_info.cseq;

        if (cseq_hdr->method.id != PJSIP_INVITE_METHOD ||
            rdata->msg_info.msg->line.status.code / 100 != 2)
        {
            /* Not a 2xx response to INVITE.
             * This must be some stateless response sent by other modules,
             * or a very late response.
             */
            /* Unlock dialog hash table. */
            pj_mutex_unlock(mod_ua.mutex);
            return PJ_FALSE;
        }


        /* Get the dialog set. */
        dlg_set = (struct dlg_set*)
                  pj_hash_get_lower(mod_ua.dlg_table, 
                                    rdata->msg_info.from->tag.ptr,
                                    (unsigned)rdata->msg_info.from->tag.slen,
                                    NULL);

        if (!dlg_set) {
            /* Unlock dialog hash table. */
            pj_mutex_unlock(mod_ua.mutex);

            /* Strayed 2xx response!! */
            PJ_LOG(4,(THIS_FILE, 
                      "Received strayed 2xx response (no dialog is found)"
                      " from %s:%d: %s",
                      rdata->pkt_info.src_name, rdata->pkt_info.src_port,
                      pjsip_rx_data_get_info(rdata)));

            return PJ_TRUE;
        }
    }

    /* At this point, we must have the dialog set, and the dialog set
     * must have a dialog in the list.
     */
    pj_assert(dlg_set && !pj_list_empty(&dlg_set->dlg_list));

    /* Check for forked response. 
     * Request will fork only for the initial INVITE request.
     */

    //This doesn't work when there is authentication challenge, since 
    //first_cseq evaluation will yield false.
    //if (rdata->msg_info.cseq->method.id == PJSIP_INVITE_METHOD &&
    //  rdata->msg_info.cseq->cseq == dlg_set->dlg_list.next->local.first_cseq)

    if (rdata->msg_info.cseq->method.id == PJSIP_INVITE_METHOD) {
        
        int st_code = rdata->msg_info.msg->line.status.code;
        pj_str_t *to_tag = &rdata->msg_info.to->tag;

        dlg = dlg_set->dlg_list.next;

        while (dlg != (pjsip_dialog*)&dlg_set->dlg_list) {

            /* If there is dialog with no remote tag (i.e. dialog has not
             * been established yet), then send this response to that
             * dialog.
             */
            if (dlg->remote.info->tag.slen == 0)
                break;

            /* Otherwise find the one with matching To tag. */
            if (pj_stricmp(to_tag, &dlg->remote.info->tag) == 0)
                break;

            dlg = dlg->next;
        }

        /* If no dialog with matching remote tag is found, this must be
         * a forked response. Respond to this ONLY when response is non-100
         * provisional response OR a 2xx response.
         */
        if (dlg == (pjsip_dialog*)&dlg_set->dlg_list &&
            ((st_code/100==1 && st_code!=100) || st_code/100==2)) 
        {

            PJ_LOG(5,(THIS_FILE, 
                      "Received forked %s for existing dialog %s",
                      pjsip_rx_data_get_info(rdata), 
                      dlg_set->dlg_list.next->obj_name));

            /* Report to application about forked condition.
             * Application can either create a dialog or ignore the response.
             */
            if (mod_ua.param.on_dlg_forked) {
                dlg = (*mod_ua.param.on_dlg_forked)(dlg_set->dlg_list.next, 
                                                    rdata);
                if (dlg == NULL) {
                    pj_mutex_unlock(mod_ua.mutex);
                    return PJ_TRUE;
                }
            } else {
                dlg = dlg_set->dlg_list.next;

                PJ_LOG(4,(THIS_FILE, 
                          "Unhandled forked %s from %s:%d, response will be "
                          "handed over to the first dialog",
                          pjsip_rx_data_get_info(rdata),
                          rdata->pkt_info.src_name, rdata->pkt_info.src_port));
            }

        } else if (dlg == (pjsip_dialog*)&dlg_set->dlg_list) {

            /* For 100 or non-2xx response which has different To tag,
             * pass the response to the first dialog.
             */

            dlg = dlg_set->dlg_list.next;

        }

    } else {
        /* Either this is a non-INVITE response, or subsequent INVITE
         * within dialog. The dialog should have been identified when
         * the transaction was found.
         */
        pj_assert(tsx != NULL);
        pj_assert(dlg != NULL);
    }

    /* The dialog must have been found. */
    pj_assert(dlg != NULL);

    /* Put the dialog instance in the rdata. */
    rdata->endpt_info.mod_data[mod_ua.mod.id] = dlg;

    /* Attempt to acquire lock to the dialog. */
    PJ_LOG(6,(dlg->obj_name, "UA layer acquiring dialog lock for response"));
    status = pjsip_dlg_try_inc_lock(dlg);
    if (status != PJ_SUCCESS) {
        /* Failed to acquire dialog mutex. This could indicate a deadlock
         * situation, and for safety, try to avoid deadlock by releasing
         * UA mutex, yield, and retry the whole processing once again.
         */
        pj_mutex_unlock(mod_ua.mutex);
        pj_thread_sleep(0);
        goto retry_on_deadlock;
    }

    /* We're done with processing in the UA layer, we can release the mutex */
    pj_mutex_unlock(mod_ua.mutex);

    /* Pass the response to the dialog. */
    pjsip_dlg_on_rx_response(dlg, rdata);

    /* Unlock the dialog. This may destroy the dialog. */
    pjsip_dlg_dec_lock(dlg);

    /* Done. */
    return PJ_TRUE;
}


#if PJ_LOG_MAX_LEVEL >= 3
static void print_dialog( const char *title,
                          pjsip_dialog *dlg, char *buf, pj_size_t size)
{
    int len;
    char userinfo[PJSIP_MAX_URL_SIZE];

    len = pjsip_hdr_print_on(dlg->remote.info, userinfo, sizeof(userinfo));
    if (len < 0)
        pj_ansi_strcpy(userinfo, "<--uri too long-->");
    else
        userinfo[len] = '\0';
    
    len = pj_ansi_snprintf(buf, size, "%s[%s]  %s",
                           title,
                           (dlg->state==PJSIP_DIALOG_STATE_NULL ? " - " :
                                                             "est"),
                      userinfo);
    if (len < 1 || len >= (int)size) {
        pj_ansi_strcpy(buf, "<--uri too long-->");
    } else
        buf[len] = '\0';
}
#endif

/*
 * Dump user agent contents (e.g. all dialogs).
 */
PJ_DEF(void) pjsip_ua_dump(pj_bool_t detail)
{
#if PJ_LOG_MAX_LEVEL >= 3
    pj_hash_iterator_t itbuf, *it;
    char dlginfo[128];

    pj_mutex_lock(mod_ua.mutex);

    PJ_LOG(3, (THIS_FILE, "Number of dialog sets: %u", 
                          pj_hash_count(mod_ua.dlg_table)));

    if (detail && pj_hash_count(mod_ua.dlg_table)) {
        PJ_LOG(3, (THIS_FILE, "Dumping dialog sets:"));
        it = pj_hash_first(mod_ua.dlg_table, &itbuf);
        for (; it != NULL; it = pj_hash_next(mod_ua.dlg_table, it))  {
            struct dlg_set *dlg_set;
            pjsip_dialog *dlg;
            const char *title;

            dlg_set = (struct dlg_set*) pj_hash_this(mod_ua.dlg_table, it);
            if (!dlg_set || pj_list_empty(&dlg_set->dlg_list)) continue;

            /* First dialog in dialog set. */
            dlg = dlg_set->dlg_list.next;
            if (dlg->role == PJSIP_ROLE_UAC)
                title = "  [out] ";
            else
                title = "  [in]  ";

            print_dialog(title, dlg, dlginfo, sizeof(dlginfo));
            PJ_LOG(3,(THIS_FILE, "%s", dlginfo));

            /* Next dialog in dialog set (forked) */
            dlg = dlg->next;
            while (dlg != (pjsip_dialog*) &dlg_set->dlg_list) {
                print_dialog("    [forked] ", dlg, dlginfo, sizeof(dlginfo));
                dlg = dlg->next;
            }
        }
    }

    pj_mutex_unlock(mod_ua.mutex);
#endif
}

