res_pjsip_refer.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013, Digium, Inc.
 *
 * Joshua Colp <jcolp@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */
 
/*** MODULEINFO
    <depend>pjproject</depend>
    <depend>res_pjsip</depend>
    <depend>res_pjsip_session</depend>
    <depend>res_pjsip_pubsub</depend>
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include <pjsip.h>
#include <pjsip_ua.h>
 
#include "asterisk/res_pjsip.h"
#include "asterisk/res_pjsip_session.h"
#include "asterisk/module.h"
#include "asterisk/pbx.h"
#include "asterisk/taskprocessor.h"
#include "asterisk/bridge.h"
#include "asterisk/framehook.h"
#include "asterisk/stasis_bridges.h"
#include "asterisk/stasis_channels.h"
#include "asterisk/causes.h"
#include "asterisk/refer.h"
 
static struct ast_taskprocessor *refer_serializer;
 
static pj_status_t refer_on_tx_request(pjsip_tx_data *tdata);
static int defer_termination_cancel_task(void *data);
 
struct transfer_ari_state {
    /*! \brief A deferred session used by the ARI only mode */
    struct ast_sip_session *transferer;
    struct ast_channel *transferer_chan;
 
    struct ast_sip_session *other_session;
 
    char exten[AST_MAX_EXTENSION];
    char *referred_by;
 
    char *protocol_id;
    struct ast_refer_params *params;
    int last_response;
};
 
/*! \brief REFER Progress structure */
struct refer_progress {
    /*! \brief Subscription to provide updates on */
    pjsip_evsub *sub;
    /*! \brief Dialog for subscription */
    pjsip_dialog *dlg;
    /*! \brief Received packet, used to construct final response in case no subscription exists */
    pjsip_rx_data *rdata;
    /*! \brief Frame hook for monitoring REFER progress */
    int framehook;
    /*! \brief Last received subclass in frame hook */
    int subclass;
    /*! \brief Serializer for notifications */
    struct ast_taskprocessor *serializer;
    /*! \brief Stasis subscription for bridge events */
    struct stasis_subscription *bridge_sub;
    /*! \brief Reference to transfer_channel_data related to the refer */
    struct transfer_channel_data *transfer_data;
    /*! \brief Uniqueid of transferee channel */
    char *transferee;
    /*! \brief Non-zero if the 100 notify has been sent */
    int sent_100;
    /*! \brief Whether to notifies all the progress details on blind transfer */
    unsigned int refer_blind_progress;
    /*! \brief State related to the transfer in ARI only mode */
    struct transfer_ari_state *ari_state;
    /*! \brief Refer-Sub: false was specified on the REFER */
    int no_refer_sub;
};
 
/*! \brief REFER Progress notification structure */
struct refer_progress_notification {
    /*! \brief Refer progress structure to send notification on */
    struct refer_progress *progress;
    /*! \brief SIP response code to send */
    int response;
    /*! \brief Subscription state */
    pjsip_evsub_state state;
};
 
/*! \brief REFER Progress module, used to attach REFER progress structure to subscriptions */
static pjsip_module refer_progress_module = {
    .name = { "REFER Progress", 14 },
    .id = -1,
};
 
/*! \brief Destructor of the state used for the ARI transfer */
static void transfer_ari_state_destroy(void *obj)
{
    struct transfer_ari_state *state = obj;
    char *chan_name = ast_strdupa(state->transferer_chan ? ast_channel_name(state->transferer_chan) : "unknown");
    SCOPE_ENTER(3, "%s: state destructor", chan_name);
 
    ao2_cleanup(state->transferer);
    ao2_cleanup(state->other_session);
    ast_channel_cleanup(state->transferer_chan);
    ast_free(state->referred_by);
    ast_free(state->protocol_id);
    ao2_cleanup(state->params);
 
    SCOPE_EXIT_RTN("%s: done", chan_name);
}
 
static void refer_params_destroy(void *obj)
{
    struct ast_refer_params *params = obj;
 
    for (int i = 0; i < AST_VECTOR_SIZE(params); ++i) {
        struct ast_refer_param param = AST_VECTOR_GET(params, i);
        ast_free((char *) param.param_name);
        ast_free((char *) param.param_value);
    }
}
 
/*! \brief Destructor for REFER Progress notification structure */
static void refer_progress_notification_destroy(void *obj)
{
    struct refer_progress_notification *notification = obj;
    SCOPE_ENTER(3, "%p\n", obj);
 
    ao2_cleanup(notification->progress);
    SCOPE_EXIT_RTN("%p\n", obj);
}
 
static int ari_notify(struct transfer_ari_state *state)
{
    int res = 0;
    SCOPE_ENTER(3, "%s: state: %s\n", ast_channel_name(state->transferer_chan),
        ast_channel_transfer_state2str(state->last_response));
 
    res = ast_refer_notify_transfer_request(state->transferer_chan, state->referred_by,
                         state->exten, state->protocol_id,
                         state->other_session ? state->other_session->channel : NULL,
                         state->params, state->last_response);
    SCOPE_EXIT_RTN_VALUE(res, "%s: done: %d\n", ast_channel_name(state->transferer_chan), res);
}
 
/*! \brief Allocator for REFER Progress notification structure */
static struct refer_progress_notification *refer_progress_notification_alloc(struct refer_progress *progress, int response,
    pjsip_evsub_state state)
{
    struct refer_progress_notification *notification = ao2_alloc(sizeof(*notification), refer_progress_notification_destroy);
 
    if (!notification) {
        return NULL;
    }
 
    ao2_ref(progress, +1);
    notification->progress = progress;
    notification->response = response;
    notification->state = state;
 
    return notification;
}
 
/*! \brief Serialized callback for subscription notification
 *
 * Locking and serialization:
 *
 * Although refer_progress_notify() always runs in the progress serializer,
 * the pjproject evsub module itself can cause the subscription to be
 * destroyed which then triggers refer_progress_on_evsub_state() to clean
 * it up.  In this case, it's possible that refer_progress_notify() could
 * get the subscription pulled out from under it while it's trying to use it.
 *
 * At one point we tried to have refer_progress_on_evsub_state() push the
 * cleanup to the serializer and wait for its return before returning to
 * pjproject but since pjproject calls its state callbacks with the dialog
 * locked, this required us to unlock the dialog while waiting for the
 * serialized cleanup, then lock it again before returning to pjproject.
 * There were also still some cases where other callers of
 * refer_progress_notify() weren't using the serializer and crashes were
 * resulting.
 *
 * Although all callers of refer_progress_notify() now use the progress
 * serializer, we decided to simplify the locking so we didn't have to
 * unlock and relock the dialog in refer_progress_on_evsub_state().
 *
 * Now, refer_progress_notify() holds the dialog lock for all its work
 * rather than just when calling pjsip_evsub_set_mod_data() to clear the
 * module data.  Since pjproject also holds the dialog lock while calling
 * refer_progress_on_evsub_state(), there should be no more chances for
 * the subscription to be cleaned up while still being used to send NOTIFYs.
 */
static int refer_progress_notify(void *data)
{
    RAII_VAR(struct refer_progress_notification *, notification, data, ao2_cleanup);
    struct transfer_ari_state *ari_state = notification->progress->ari_state;
    pjsip_evsub *sub;
    pjsip_tx_data *tdata;
    SCOPE_ENTER(3, "%s: no_refer_sub: %s\n",
        ari_state ? ast_channel_name(ari_state->transferer_chan) : "????",
        AST_YESNO(notification->progress->no_refer_sub));
 
    /*
     * If the referer included a "Refer-Sub: false" header, we don't want to
     * create the automatic subscription but, if the transfer is being controlled
     * by ARI, we still want the app to get the progress events.
     */
    if (notification->progress->no_refer_sub) {
        if (ari_state) {
            ari_notify(ari_state);
        }
        SCOPE_EXIT_RTN_VALUE(0, "%s: done\n",
            ari_state ? ast_channel_name(ari_state->transferer_chan) : "????");
    }
 
    pjsip_dlg_inc_lock(notification->progress->dlg);
 
    /* If the subscription has already been terminated we can't send a notification */
    if (!(sub = notification->progress->sub)) {
        ast_debug(3, "Not sending NOTIFY of response '%d' and state '%u' on progress monitor '%p' as subscription has been terminated\n",
            notification->response, notification->state, notification->progress);
        pjsip_dlg_dec_lock(notification->progress->dlg);
        SCOPE_EXIT_RTN_VALUE(0, "???\n");
    }
 
    /* Send a deferred initial 100 Trying SIP frag NOTIFY if we haven't already. */
    if (!notification->progress->sent_100) {
        notification->progress->sent_100 = 1;
        if (notification->response != 100) {
            ast_debug(3, "Sending initial 100 Trying NOTIFY for progress monitor '%p'\n",
                notification->progress);
            if (pjsip_xfer_notify(sub, PJSIP_EVSUB_STATE_ACTIVE, 100, NULL, &tdata) == PJ_SUCCESS) {
                pjsip_xfer_send_request(sub, tdata);
            }
        }
    }
 
    ast_debug(3, "Sending NOTIFY with response '%d' and state '%u' on subscription '%p' and progress monitor '%p'\n",
        notification->response, notification->state, sub, notification->progress);
 
    /* Actually send the notification */
    if (pjsip_xfer_notify(sub, notification->state, notification->response, NULL, &tdata) == PJ_SUCCESS) {
        pjsip_xfer_send_request(sub, tdata);
    }
 
 
    if (notification->progress->ari_state) {
        struct transfer_ari_state *ari_state = notification->progress->ari_state;
        ari_notify(ari_state);
    }
 
    pjsip_dlg_dec_lock(notification->progress->dlg);
 
    SCOPE_EXIT_RTN_VALUE(0, "???\n");
}
 
static void refer_progress_bridge(void *data, struct stasis_subscription *sub,
        struct stasis_message *message)
{
    struct refer_progress *progress = data;
    struct ast_bridge_blob *enter_blob;
    struct refer_progress_notification *notification;
    struct ast_channel *chan;
 
    if (stasis_subscription_final_message(sub, message)) {
        ao2_ref(progress, -1);
        return;
    }
 
    if (ast_channel_entered_bridge_type() != stasis_message_type(message)) {
        /* Don't care */
        return;
    }
 
    enter_blob = stasis_message_data(message);
    if (strcmp(enter_blob->channel->base->uniqueid, progress->transferee)) {
        /* Don't care */
        return;
    }
 
    if (!progress->transfer_data->completed) {
        /* We can't act on this message because the transfer_channel_data doesn't show that
         * the transfer is ready to progress */
        return;
    }
 
    /* OMG the transferee is joining a bridge. His call got answered! */
    notification = refer_progress_notification_alloc(progress, 200, PJSIP_EVSUB_STATE_TERMINATED);
    if (notification) {
        if (ast_sip_push_task(progress->serializer, refer_progress_notify, notification)) {
            ao2_cleanup(notification);
        }
        progress->bridge_sub = stasis_unsubscribe(progress->bridge_sub);
    }
 
    chan = ast_channel_get_by_name(progress->transferee);
    if (!chan) {
        /* The channel is already gone */
        return;
    }
 
    ast_channel_lock(chan);
    ast_debug(3, "Detaching REFER progress monitoring hook from '%s' as it has joined a bridge\n",
        ast_channel_name(chan));
    ast_framehook_detach(chan, progress->framehook);
    ast_channel_unlock(chan);
 
    ast_channel_unref(chan);
}
 
/*! \brief Progress monitoring frame hook - examines frames to determine state of transfer */
static struct ast_frame *refer_progress_framehook(struct ast_channel *chan, struct ast_frame *f,
    enum ast_framehook_event event, void *data)
{
    struct refer_progress *progress = data;
    struct refer_progress_notification *notification = NULL;
 
    /* We only care about frames *to* the channel */
    if (!f || (event != AST_FRAMEHOOK_EVENT_WRITE)) {
        return f;
    }
 
    /* If the completed flag hasn't been raised, skip this pass. */
    if (!progress->transfer_data->completed) {
        return f;
    }
 
    /* Determine the state of the REFER based on the control frames (or voice frames) passing */
    if (f->frametype == AST_FRAME_VOICE && !progress->subclass) {
        /* Media is passing without progress, this means the call has been answered */
        progress->subclass = AST_CONTROL_ANSWER;
        notification = refer_progress_notification_alloc(progress, 200, PJSIP_EVSUB_STATE_TERMINATED);
    } else if (f->frametype == AST_FRAME_CONTROL) {
        /* Based on the control frame being written we can send a NOTIFY advising of the progress */
        if ((f->subclass.integer == AST_CONTROL_RING) || (f->subclass.integer == AST_CONTROL_RINGING)) {
            /* Don't set progress->subclass; an ANSWER can still follow */
            notification = refer_progress_notification_alloc(progress, 180, PJSIP_EVSUB_STATE_ACTIVE);
        } else if (f->subclass.integer == AST_CONTROL_BUSY) {
            progress->subclass = f->subclass.integer;
            notification = refer_progress_notification_alloc(progress, 486, PJSIP_EVSUB_STATE_TERMINATED);
        } else if (f->subclass.integer == AST_CONTROL_CONGESTION) {
            progress->subclass = f->subclass.integer;
            notification = refer_progress_notification_alloc(progress, 503, PJSIP_EVSUB_STATE_TERMINATED);
        } else if (f->subclass.integer == AST_CONTROL_PROGRESS) {
            /* Don't set progress->subclass; an ANSWER can still follow */
            notification = refer_progress_notification_alloc(progress, 183, PJSIP_EVSUB_STATE_ACTIVE);
        } else if (f->subclass.integer == AST_CONTROL_PROCEEDING) {
            /* Don't set progress->subclass; an ANSWER can still follow */
            notification = refer_progress_notification_alloc(progress, 100, PJSIP_EVSUB_STATE_ACTIVE);
        } else if (f->subclass.integer == AST_CONTROL_ANSWER) {
            progress->subclass = f->subclass.integer;
            notification = refer_progress_notification_alloc(progress, 200, PJSIP_EVSUB_STATE_TERMINATED);
        }
    }
 
    /* If a notification is due to be sent push it to the taskpool */
    if (notification) {
        /* If the subscription is being terminated we don't need the frame hook any longer */
        if (notification->state == PJSIP_EVSUB_STATE_TERMINATED) {
            ast_debug(3, "Detaching REFER progress monitoring hook from '%s' as subscription is being terminated\n",
                ast_channel_name(chan));
            ast_framehook_detach(chan, progress->framehook);
        }
 
        if (ast_sip_push_task(progress->serializer, refer_progress_notify, notification)) {
            ao2_cleanup(notification);
        }
    }
 
    return f;
}
 
/*! \brief Progress monitoring frame hook - examines frames to determine state of transfer. Used for the ari-only mode */
static struct ast_frame *refer_ari_progress_framehook(struct ast_channel *chan, struct ast_frame *f, enum ast_framehook_event event, void *data)
{
    struct refer_progress *progress = data;
    struct refer_progress_notification *notification = NULL;
    SCOPE_ENTER(3, "%s\n", ast_channel_name(chan));
 
    /* We only care about frames *to* the channel */
    if (!f || (event != AST_FRAMEHOOK_EVENT_WRITE)) {
        SCOPE_EXIT_RTN_VALUE(f, "%s: Not EVENT_WRITE\n", ast_channel_name(chan));
    }
 
    /* Determine the state of the REFER based on the control frames (or voice frames) passing */
    if (f->frametype == AST_FRAME_CONTROL
        && f->subclass.integer == AST_CONTROL_TRANSFER
        && f->datalen >= sizeof(enum ast_control_transfer)) {
        enum ast_control_transfer *message = f->data.ptr;
        ast_trace(-1, "%s message: %d\n", ast_channel_name(chan), *message);
        switch (*message) {
        case AST_TRANSFER_FAILED:
            notification = refer_progress_notification_alloc(progress, 603, PJSIP_EVSUB_STATE_TERMINATED);
            break;
        case AST_TRANSFER_SUCCESS:
            notification = refer_progress_notification_alloc(progress, 200, PJSIP_EVSUB_STATE_TERMINATED);
            break;
        case AST_TRANSFER_PROGRESS:
            notification = refer_progress_notification_alloc(progress, 100, PJSIP_EVSUB_STATE_ACTIVE);
            break;
        case AST_TRANSFER_UNAVAILABLE:
            notification = refer_progress_notification_alloc(progress, 503, PJSIP_EVSUB_STATE_TERMINATED);
            break;
        case AST_TRANSFER_INVALID:
            break;
        }
        progress->ari_state->last_response = *message;
    }
 
    /* If a notification is due to be sent push it to the taskpool */
    if (notification) {
        /* If the subscription is being terminated we don't need the frame hook any longer */
        if (notification->state == PJSIP_EVSUB_STATE_TERMINATED) {
            ast_trace(-1, "Detaching REFER progress monitoring hook from '%s' as subscription is being terminated\n",
                ast_channel_name(chan));
            ast_framehook_detach(chan, progress->framehook);
        }
 
        /*
         * If the referer specified "Refer-Sub: false", we can call refer_progress_notify()
         * directly without pushing a task because it won't be doing any pjproject wotk.
         * All it will do is send an ARI event.
         */
        if (notification->progress->no_refer_sub) {
            refer_progress_notify(notification);
            SCOPE_EXIT_RTN_VALUE(f, "%s: done ari no refer sub\n",
                progress->ari_state ? ast_channel_name(progress->ari_state->transferer_chan) : "????");
        }
 
        if (ast_sip_push_task(progress->serializer, refer_progress_notify, notification)) {
            ao2_cleanup(notification);
        }
    } else {
        SCOPE_EXIT_RTN_VALUE(f, "%s: Not a transfer event\n", ast_channel_name(chan));
    }
 
    SCOPE_EXIT_RTN_VALUE(f, "%s: done\n", ast_channel_name(chan));
}
 
/*! \brief Destroy callback for monitoring framehook */
static void refer_progress_framehook_destroy(void *data)
{
    struct refer_progress *progress = data;
    struct refer_progress_notification *notification = NULL;
    SCOPE_ENTER(3, "%p\n", progress);
 
    /*
     * If the referer didn't request the subscription be suppressed, we need to do
     * a final notification.
     */
    if (!progress->no_refer_sub) {
        notification = refer_progress_notification_alloc(progress, 503, PJSIP_EVSUB_STATE_TERMINATED);
        if (notification && ast_sip_push_task(progress->serializer, refer_progress_notify, notification)) {
            ao2_cleanup(notification);
        }
    }
 
    if (progress->bridge_sub) {
        progress->bridge_sub = stasis_unsubscribe(progress->bridge_sub);
    }
 
    ao2_cleanup(progress);
    SCOPE_EXIT_RTN("%p\n", progress);
}
 
/*!
 * \brief Callback for REFER subscription state changes
 * \see refer_progress_notify
 *
 * The documentation attached to refer_progress_notify has more
 * information about the locking issues with cleaning up
 * the subscription.
 *
 * \note pjproject holds the dialog lock while calling this function.
 */
static void refer_progress_on_evsub_state(pjsip_evsub *sub, pjsip_event *event)
{
    struct refer_progress *progress = pjsip_evsub_get_mod_data(sub, refer_progress_module.id);
 
    /*
     * If being destroyed, remove the progress object from the subscription
     * and release the reference it had.
     */
    if (progress && (pjsip_evsub_get_state(sub) == PJSIP_EVSUB_STATE_TERMINATED)) {
        pjsip_evsub_set_mod_data(progress->sub, refer_progress_module.id, NULL);
        progress->sub = NULL;
        ao2_cleanup(progress);
    }
}
 
/*! \brief Callback structure for subscription */
static pjsip_evsub_user refer_progress_evsub_cb = {
    .on_evsub_state = refer_progress_on_evsub_state,
};
 
static int dlg_releaser_task(void *data) {
    pjsip_dlg_dec_session((pjsip_dialog *)data, &refer_progress_module);
    return 0;
}
 
/*! \brief Destructor for REFER progress sutrcture */
static void refer_progress_destroy(void *obj)
{
    struct refer_progress *progress = obj;
    SCOPE_ENTER(3, "%p\n", progress);
 
    if (progress->bridge_sub) {
        progress->bridge_sub = stasis_unsubscribe(progress->bridge_sub);
    }
 
    if (progress->dlg) {
        /*
         * Although the dlg session count was incremented in a pjsip servant
         * thread, there's no guarantee that the last thread to unref this progress
         * object was one.  Before we decrement, we need to make sure that this
         * is either a servant thread or that we push the decrement to a
         * serializer that is one.
         *
         * Because pjsip_dlg_dec_session requires the dialog lock, we don't want
         * to wait on the task to complete if we had to push it to a serializer.
         */
        if (ast_sip_thread_is_servant()) {
            pjsip_dlg_dec_session(progress->dlg, &refer_progress_module);
        } else {
            ast_sip_push_task(NULL, dlg_releaser_task, progress->dlg);
        }
    }
 
    ao2_cleanup(progress->transfer_data);
    ao2_cleanup(progress->ari_state);
 
    ast_free(progress->transferee);
    ast_taskprocessor_unreference(progress->serializer);
    SCOPE_EXIT_RTN("%p\n", progress);
}
 
/*! \brief Internal helper function which sets up a refer progress structure if needed */
static int refer_progress_alloc(struct ast_sip_session *session, pjsip_rx_data *rdata, struct refer_progress **progress)
{
    const pj_str_t str_refer_sub = { "Refer-Sub", 9 };
    pjsip_generic_string_hdr *refer_sub = NULL;
    const pj_str_t str_true = { "true", 4 };
    pjsip_hdr hdr_list;
    char tps_name[AST_TASKPROCESSOR_MAX_NAME + 1];
    int no_refer_sub = 0;
    SCOPE_ENTER(3, "%s\n", ast_channel_name(session->channel));
 
    *progress = NULL;
 
    /* Grab the optional Refer-Sub header, it can be used to suppress the implicit subscription */
    refer_sub = pjsip_msg_find_hdr_by_name(rdata->msg_info.msg, &str_refer_sub, NULL);
    if ((refer_sub && pj_strnicmp(&refer_sub->hvalue, &str_true, 4))) {
         no_refer_sub = 1;
    }
 
    if (!(*progress = ao2_alloc(sizeof(struct refer_progress), refer_progress_destroy))) {
        SCOPE_EXIT_RTN_VALUE(-1, "%s: done: %d\n", ast_channel_name(session->channel), -1);
    }
 
    (*progress)->no_refer_sub = no_refer_sub;
 
    ast_debug(3, "Created progress monitor '%p' for transfer occurring from channel '%s' and endpoint '%s'\n",
        progress, ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
 
    (*progress)->refer_blind_progress = session->endpoint->refer_blind_progress;
 
    (*progress)->framehook = -1;
 
    /* Create name with seq number appended. */
    ast_taskprocessor_build_name(tps_name, sizeof(tps_name), "pjsip/refer/%s",
        ast_sorcery_object_get_id(session->endpoint));
 
    if (!((*progress)->serializer = ast_sip_create_serializer(tps_name))) {
        goto error;
    }
 
    /*
     * If the referer request the subscription be suppressed, we can stop here.
     */
    if ((*progress)->no_refer_sub) {
        SCOPE_EXIT_RTN_VALUE(0, "%s: done no refer sub: %d\n", ast_channel_name(session->channel), 0);
    }
 
    /* Create the implicit subscription for monitoring of this transfer */
    if (pjsip_xfer_create_uas(session->inv_session->dlg, &refer_progress_evsub_cb, rdata, &(*progress)->sub) != PJ_SUCCESS) {
        goto error;
    }
 
    /* To prevent a potential deadlock we need the dialog so we can lock/unlock */
    (*progress)->dlg = session->inv_session->dlg;
    /* We also need to make sure it stays around until we're done with it */
    pjsip_dlg_inc_session((*progress)->dlg, &refer_progress_module);
 
    /* Associate the REFER progress structure with the subscription */
    ao2_ref(*progress, +1);
    pjsip_evsub_set_mod_data((*progress)->sub, refer_progress_module.id, *progress);
 
    pj_list_init(&hdr_list);
    if (refer_sub) {
        pjsip_hdr *hdr = (pjsip_hdr*)pjsip_generic_string_hdr_create(session->inv_session->dlg->pool, &str_refer_sub, &str_true);
 
        pj_list_push_back(&hdr_list, hdr);
    }
 
    /* Accept the REFER request */
    ast_debug(3, "Accepting REFER request for progress monitor '%p'\n", *progress);
    pjsip_xfer_accept((*progress)->sub, rdata, 202, &hdr_list);
 
    SCOPE_EXIT_RTN_VALUE(0, "%s: done: %d\n", ast_channel_name(session->channel), 0);
 
error:
    ao2_cleanup(*progress);
    *progress = NULL;
    SCOPE_EXIT_RTN_VALUE(-1, "%s: done: %d\n", ast_channel_name(session->channel), -1);
}
 
/*! \brief Structure for attended transfer task */
struct refer_attended {
    /*! \brief Transferer session */
    struct ast_sip_session *transferer;
    /*! \brief Transferer channel */
    struct ast_channel *transferer_chan;
    /*! \brief Second transferer session */
    struct ast_sip_session *transferer_second;
    /*! \brief Optional refer progress structure */
    struct refer_progress *progress;
};
 
/*! \brief Destructor for attended transfer task */
static void refer_attended_destroy(void *obj)
{
    struct refer_attended *attended = obj;
 
    ao2_cleanup(attended->transferer);
    ast_channel_cleanup(attended->transferer_chan);
    ao2_cleanup(attended->transferer_second);
    ao2_cleanup(attended->progress);
}
 
/*! \brief Allocator for attended transfer task */
static struct refer_attended *refer_attended_alloc(struct ast_sip_session *transferer,
    struct ast_sip_session *transferer_second,
    struct refer_progress *progress)
{
    struct refer_attended *attended;
 
    attended = ao2_alloc_options(sizeof(*attended), refer_attended_destroy,
        AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (!attended) {
        return NULL;
    }
 
    ao2_ref(transferer, +1);
    attended->transferer = transferer;
    ast_channel_ref(transferer->channel);
    attended->transferer_chan = transferer->channel;
    ao2_ref(transferer_second, +1);
    attended->transferer_second = transferer_second;
 
    if (progress) {
        ao2_ref(progress, +1);
        attended->progress = progress;
    }
 
    return attended;
}
 
static int session_end_if_deferred_task(void *data)
{
    struct ast_sip_session *session = data;
 
    ast_sip_session_end_if_deferred(session);
    ao2_ref(session, -1);
    return 0;
}
 
static int defer_termination_cancel_task(void *data)
{
    struct ast_sip_session *session = data;
 
    ast_sip_session_end_if_deferred(session);
    ast_sip_session_defer_termination_cancel(session);
    ao2_ref(session, -1);
    return 0;
}
 
/*!
 * \internal
 * \brief Convert transfer enum to SIP response code.
 * \since 13.3.0
 *
 * \param xfer_code Core transfer function enum result.
 *
 * \return SIP response code
 */
static int xfer_response_code2sip(enum ast_transfer_result xfer_code)
{
    int response;
 
    response = 503;
    switch (xfer_code) {
    case AST_BRIDGE_TRANSFER_INVALID:
        response = 400;
        break;
    case AST_BRIDGE_TRANSFER_NOT_PERMITTED:
        response = 403;
        break;
    case AST_BRIDGE_TRANSFER_FAIL:
        response = 500;
        break;
    case AST_BRIDGE_TRANSFER_SUCCESS:
        response = 200;
        break;
    }
    return response;
}
 
/*! \brief Task for attended transfer executed by attended->transferer_second serializer */
static int refer_attended_task(void *data)
{
    struct refer_attended *attended = data;
    int response;
    int (*task_cb)(void *data);
 
    if (attended->transferer_second->channel) {
        ast_debug(3, "Performing a REFER attended transfer - Transferer #1: %s Transferer #2: %s\n",
            ast_channel_name(attended->transferer_chan),
            ast_channel_name(attended->transferer_second->channel));
 
        response = xfer_response_code2sip(ast_bridge_transfer_attended(
            attended->transferer_chan,
            attended->transferer_second->channel));
 
        ast_debug(3, "Final response for REFER attended transfer - Transferer #1: %s Transferer #2: %s is '%d'\n",
            ast_channel_name(attended->transferer_chan),
            ast_channel_name(attended->transferer_second->channel),
            response);
    } else {
        ast_debug(3, "Received REFER request on channel '%s' but other channel has gone.\n",
            ast_channel_name(attended->transferer_chan));
        response = 603;
    }
 
    if (attended->progress) {
        struct refer_progress_notification *notification;
 
        notification = refer_progress_notification_alloc(attended->progress, response,
            PJSIP_EVSUB_STATE_TERMINATED);
        if (notification) {
            if (ast_sip_push_task(attended->progress->serializer, refer_progress_notify, notification)) {
                ao2_cleanup(notification);
            }
        }
    }
 
    if (response == 200) {
        task_cb = session_end_if_deferred_task;
    } else {
        task_cb = defer_termination_cancel_task;
    }
    if (!ast_sip_push_task(attended->transferer->serializer,
        task_cb, attended->transferer)) {
        /* Gave the ref to the pushed task. */
        attended->transferer = NULL;
    } else {
        /* Do this anyway even though it is the wrong serializer. */
        ast_sip_session_end_if_deferred(attended->transferer);
    }
 
    ao2_ref(attended, -1);
    return 0;
}
 
/*! \brief Structure for blind transfer callback details */
struct refer_blind {
    /*! \brief Context being used for transfer */
    const char *context;
    /*! \brief Optional progress structure */
    struct refer_progress *progress;
    /*! \brief REFER message */
    pjsip_rx_data *rdata;
    /*! \brief Optional Replaces header */
    pjsip_replaces_hdr *replaces;
    /*! \brief Optional Refer-To header */
    pjsip_sip_uri *refer_to;
    /*! \brief Attended transfer flag */
    unsigned int attended:1;
};
 
/*! \brief Blind transfer callback function */
static void refer_blind_callback(struct ast_channel *chan, struct transfer_channel_data *user_data_wrapper,
    enum ast_transfer_type transfer_type)
{
    struct refer_blind *refer = user_data_wrapper->data;
    pjsip_generic_string_hdr *referred_by;
 
    static const pj_str_t str_referred_by = { "Referred-By", 11 };
    static const pj_str_t str_referred_by_s = { "b", 1 };
    const char *get_xfrdata;
 
    pbx_builtin_setvar_helper(chan, "SIPTRANSFER", "yes");
 
    if (refer->progress && !refer->attended && !refer->progress->refer_blind_progress) {
        /* If blind transfer and endpoint doesn't want to receive all the progress details */
        struct refer_progress_notification *notification = refer_progress_notification_alloc(refer->progress, 200,
            PJSIP_EVSUB_STATE_TERMINATED);
 
        if (notification) {
            if (ast_sip_push_task(refer->progress->serializer, refer_progress_notify, notification)) {
                ao2_cleanup(notification);
            }
        }
    } else if (refer->progress) {
        /* If attended transfer and progress monitoring is being done attach a frame hook so we can monitor it */
        struct ast_framehook_interface hook = {
            .version = AST_FRAMEHOOK_INTERFACE_VERSION,
            .event_cb = refer_progress_framehook,
            .destroy_cb = refer_progress_framehook_destroy,
            .data = refer->progress,
            .disable_inheritance = 1,
        };
 
        refer->progress->transferee = ast_strdup(ast_channel_uniqueid(chan));
        if (!refer->progress->transferee) {
            struct refer_progress_notification *notification = refer_progress_notification_alloc(refer->progress, 200,
                PJSIP_EVSUB_STATE_TERMINATED);
 
            ast_log(LOG_WARNING, "Could not copy channel name '%s' during transfer - assuming success\n",
                ast_channel_name(chan));
 
            if (notification) {
                if (ast_sip_push_task(refer->progress->serializer, refer_progress_notify, notification)) {
                    ao2_cleanup(notification);
                }
            }
        }
 
        /* Progress needs a reference to the transfer_channel_data so that it can track the completed status of the transfer */
        ao2_ref(user_data_wrapper, +1);
        refer->progress->transfer_data = user_data_wrapper;
 
        /* We need to bump the reference count up on the progress structure since it is in the frame hook now */
        ao2_ref(refer->progress, +1);
 
        /* If we can't attach a frame hook for whatever reason send a notification of success immediately */
        ast_channel_lock(chan);
        refer->progress->framehook = ast_framehook_attach(chan, &hook);
        ast_channel_unlock(chan);
        if (refer->progress->framehook < 0) {
            struct refer_progress_notification *notification = refer_progress_notification_alloc(refer->progress, 200,
                PJSIP_EVSUB_STATE_TERMINATED);
 
            ast_log(LOG_WARNING, "Could not attach REFER transfer progress monitoring hook to channel '%s' - assuming success\n",
                ast_channel_name(chan));
 
            if (notification) {
                if (ast_sip_push_task(refer->progress->serializer, refer_progress_notify, notification)) {
                    ao2_cleanup(notification);
                }
            }
 
            ao2_cleanup(refer->progress);
        }
 
        /* We need to bump the reference count for the stasis subscription */
        ao2_ref(refer->progress, +1);
        /* We also will need to detect if the transferee enters a bridge. This is currently the only reliable way to
         * detect if the transfer target has answered the call
         */
        refer->progress->bridge_sub = stasis_subscribe_pool(ast_bridge_topic_all(), refer_progress_bridge, refer->progress);
        if (!refer->progress->bridge_sub) {
            struct refer_progress_notification *notification = refer_progress_notification_alloc(refer->progress, 200,
                PJSIP_EVSUB_STATE_TERMINATED);
 
            ast_log(LOG_WARNING, "Could not create bridge stasis subscription for monitoring progress on transfer of channel '%s' - assuming success\n",
                    ast_channel_name(chan));
 
            if (notification) {
                if (ast_sip_push_task(refer->progress->serializer, refer_progress_notify, notification)) {
                    ao2_cleanup(notification);
                }
            }
 
            ast_channel_lock(chan);
            ast_framehook_detach(chan, refer->progress->framehook);
            ast_channel_unlock(chan);
 
            ao2_cleanup(refer->progress);
        } else {
            stasis_subscription_accept_message_type(refer->progress->bridge_sub, ast_channel_entered_bridge_type());
            stasis_subscription_accept_message_type(refer->progress->bridge_sub, stasis_subscription_change_type());
            stasis_subscription_set_filter(refer->progress->bridge_sub, STASIS_SUBSCRIPTION_FILTER_SELECTIVE);
        }
    }
 
    pbx_builtin_setvar_helper(chan, "SIPREFERRINGCONTEXT", S_OR(refer->context, NULL));
 
    ast_channel_lock(chan);
    if ((get_xfrdata = pbx_builtin_getvar_helper(chan, "GET_TRANSFERRER_DATA"))) {
        get_xfrdata = ast_strdupa(get_xfrdata);
    }
    ast_channel_unlock(chan);
    if (!ast_strlen_zero(get_xfrdata)) {
        const pjsip_msg * msg = refer->rdata->msg_info.msg;
        const struct pjsip_hdr *end = &msg->hdr;
        struct pjsip_hdr *hdr = end->next;
        struct ast_str *pbxvar = ast_str_create(64); /* initial buffer for variable name, extended on demand */
        char buf[4096]; /* should be enough for one header value */
        const char *prefix = get_xfrdata;
 
        /* The '*' alone matches all headers. */
        if (!strcmp(prefix, "*")) {
            prefix = "";
        }
        if (pbxvar) {
            for (; hdr != end; hdr = hdr->next) {
                if (!pj_strnicmp2(&hdr->name, prefix, strlen(prefix))) {
                    const int hdr_name_strlen = pj_strlen(&hdr->name);
                    const int hdr_name_bytes = hdr_name_strlen + 1; /* +1 for string NULL terminator */
                    char hdr_name[hdr_name_bytes];
                    int len;
                    char *value_str;
 
                    ast_copy_pj_str(hdr_name, &hdr->name, hdr_name_bytes);
                    len = pjsip_hdr_print_on(hdr, buf, sizeof(buf) - 1);
                    if (len < 0) {
                        /* ignore too long headers */
                        ast_log(LOG_WARNING, "Could not store header '%s' from transfer on channel '%s' - too long text\n", hdr_name, ast_channel_name(chan));
                        continue;
                    }
                    buf[len] = '\0';
 
                    /* Get value - remove header name (before ':') from buf and trim blanks. */
                    value_str = strchr(buf, ':');
                    if (!value_str) {
                        /* Ignore header without value */
                        continue;
                    }
                    value_str = ast_strip(value_str + 1); /* +1 to get string right after the ':' delimiter (i.e. header value) */
                    
                    ast_str_set(&pbxvar, -1, "~HASH~TRANSFER_DATA~%.*s~", hdr_name_strlen, hdr_name);
                    pbx_builtin_setvar_helper(chan, ast_str_buffer(pbxvar), value_str);
                    ast_debug(5, "On channel '%s' set TRANSFER_DATA variable '%s' to value '%s' \n", ast_channel_name(chan), hdr_name, value_str);
                }
            }
            ast_free(pbxvar);
        } else {
            ast_log(LOG_ERROR, "Channel '%s' failed to allocate buffer for TRANSFER_DATA variable\n", ast_channel_name(chan));
        }
    }
 
    referred_by = pjsip_msg_find_hdr_by_names(refer->rdata->msg_info.msg,
        &str_referred_by, &str_referred_by_s, NULL);
    if (referred_by) {
        size_t uri_size = pj_strlen(&referred_by->hvalue) + 1;
        char *uri = ast_alloca(uri_size);
 
        ast_copy_pj_str(uri, &referred_by->hvalue, uri_size);
        pbx_builtin_setvar_helper(chan, "__SIPREFERREDBYHDR", S_OR(uri, NULL));
    } else {
        pbx_builtin_setvar_helper(chan, "SIPREFERREDBYHDR", NULL);
    }
 
    if (refer->replaces) {
        char replaces[512];
        char *replaces_val = NULL;
        int len;
 
        len = pjsip_hdr_print_on(refer->replaces, replaces, sizeof(replaces) - 1);
        if (len != -1) {
            /* pjsip_hdr_print_on does not NULL terminate the buffer */
            replaces[len] = '\0';
            replaces_val = replaces + sizeof("Replaces:");
        }
        pbx_builtin_setvar_helper(chan, "__SIPREPLACESHDR", replaces_val);
    } else {
        pbx_builtin_setvar_helper(chan, "SIPREPLACESHDR", NULL);
    }
 
    if (refer->refer_to) {
        char refer_to[PJSIP_MAX_URL_SIZE];
 
        pjsip_uri_print(PJSIP_URI_IN_REQ_URI, refer->refer_to, refer_to, sizeof(refer_to));
        pbx_builtin_setvar_helper(chan, "SIPREFERTOHDR", S_OR(refer_to, NULL));
    } else {
        pbx_builtin_setvar_helper(chan, "SIPREFERTOHDR", NULL);
    }
}
 
/*!
 * \internal
 * \brief Set the passed in context variable to the determined transfer context.
 * \since 13.3.0
 *
 * \param context Set to the determined transfer context.
 * \param session INVITE dialog SIP session.
 */
#define DETERMINE_TRANSFER_CONTEXT(context, session)                                    \
    do {                                                                                \
        ast_channel_lock((session)->channel);                                           \
        context = pbx_builtin_getvar_helper((session)->channel, "TRANSFER_CONTEXT");    \
        if (ast_strlen_zero(context)) {                                                 \
            context = (session)->endpoint->context;                                     \
        } else {                                                                        \
            context = ast_strdupa(context);                                             \
        }                                                                               \
        ast_channel_unlock((session)->channel);                                         \
    } while (0)                                                                         \
 
struct refer_data {
    struct ast_refer *refer;
    char *destination;
    char *from;
    char *refer_to;
    int to_self;
};
 
static void refer_data_destroy(void *obj)
{
    struct refer_data *rdata = obj;
 
    ast_free(rdata->destination);
    ast_free(rdata->from);
    ast_free(rdata->refer_to);
 
    ast_refer_destroy(rdata->refer);
}
 
static struct refer_data *refer_data_create(const struct ast_refer *refer)
{
    char *uri_params;
    const char *destination;
    struct refer_data *rdata = ao2_alloc_options(sizeof(*rdata), refer_data_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
 
    if (!rdata) {
        return NULL;
    }
 
    /* typecast to suppress const warning */
    rdata->refer = ast_refer_ref((struct ast_refer *) refer);
    destination = ast_refer_get_to(refer);
 
    /* To starts with 'pjsip:' which needs to be removed. */
    if (!(destination = strchr(destination, ':'))) {
        goto failure;
    }
    ++destination;/* Now skip the ':' */
 
    rdata->destination = ast_strdup(destination);
    if (!rdata->destination) {
        goto failure;
    }
 
    rdata->from = ast_strdup(ast_refer_get_from(refer));
    if (!rdata->from) {
        goto failure;
    }
 
    rdata->refer_to = ast_strdup(ast_refer_get_refer_to(refer));
    if (!rdata->refer_to) {
        goto failure;
    }
    rdata->to_self = ast_refer_get_to_self(refer);
 
    /*
     * Sometimes from URI can contain URI parameters, so remove them.
     *
     * sip:user;user-options@domain;uri-parameters
     */
    uri_params = strchr(rdata->from, '@');
    if (uri_params && (uri_params = strchr(uri_params, ';'))) {
        *uri_params = '\0';
    }
    return rdata;
 
failure:
    ao2_cleanup(rdata);
    return NULL;
}
 
/*!
 * \internal
 * \brief Checks if the given refer var name should be blocked.
 *
 * \details Some headers are not allowed to be overridden by the user.
 *  Determine if the given var header name from the user is blocked for
 *  an outgoing REFER.
 *
 * \param name name of header to see if it is blocked.
 *
 * \retval TRUE if the given header is blocked.
 */
static int is_refer_var_blocked(const char *name)
{
    int i;
 
    /* Don't block the Max-Forwards header because the user can override it */
    static const char *hdr[] = {
        "To",
        "From",
        "Via",
        "Route",
        "Contact",
        "Call-ID",
        "CSeq",
        "Allow",
        "Content-Length",
        "Content-Type",
        "Request-URI",
    };
 
    for (i = 0; i < ARRAY_LEN(hdr); ++i) {
        if (!strcasecmp(name, hdr[i])) {
            /* Block addition of this header. */
            return 1;
        }
    }
    return 0;
}
 
/*!
 * \internal
 * \brief Copies any other refer vars over to the request headers.
 *
 * \param refer The refer structure to copy headers from
 * \param tdata The SIP transmission data
 */
static enum pjsip_status_code vars_to_headers(const struct ast_refer *refer, pjsip_tx_data *tdata)
{
    const char *name;
    const char *value;
    struct ast_refer_var_iterator *iter;
 
    for (iter = ast_refer_var_iterator_init(refer);
        ast_refer_var_iterator_next(iter, &name, &value);
        ast_refer_var_unref_current(iter)) {
        if (!is_refer_var_blocked(name)) {
            ast_sip_add_header(tdata, name, value);
        }
    }
    ast_refer_var_iterator_destroy(iter);
 
    return PJSIP_SC_OK;
}
 
struct refer_out_of_dialog {
    pjsip_dialog *dlg;
    int authentication_challenge_count;
};
 
/*! \brief REFER Out-of-dialog module, used to attach session data structure to subscription */
static pjsip_module refer_out_of_dialog_module = {
    .name = { "REFER Out-of-dialog Module", 26 },
    .id = -1,
    .on_tx_request = refer_on_tx_request,
    /* Ensure that we are called after res_pjsp_nat module and before transport priority */
    .priority = PJSIP_MOD_PRIORITY_TSX_LAYER - 4,
};
 
/*! \brief Helper function which returns the name-addr of the Refer-To header or NULL */
static pjsip_uri *get_refer_to_uri(pjsip_tx_data *tdata)
{
    const pj_str_t REFER_TO = { "Refer-To", 8 };
    pjsip_generic_string_hdr *refer_to;
    pjsip_uri *parsed_uri;
 
    if (!(refer_to = pjsip_msg_find_hdr_by_name(tdata->msg, &REFER_TO, NULL))
        || !(parsed_uri = pjsip_parse_uri(tdata->pool, refer_to->hvalue.ptr, refer_to->hvalue.slen, 0))
        || (!PJSIP_URI_SCHEME_IS_SIP(parsed_uri) && !PJSIP_URI_SCHEME_IS_SIPS(parsed_uri))) {
        return NULL;
    }
 
    return parsed_uri;
}
 
static pj_status_t refer_on_tx_request(pjsip_tx_data *tdata) {
    RAII_VAR(struct ast_str *, refer_to_str, ast_str_create(PJSIP_MAX_URL_SIZE), ast_free_ptr);
    const pj_str_t REFER_TO = { "Refer-To", 8 };
    pjsip_generic_string_hdr *refer_to_hdr;
    pjsip_dialog *dlg;
    struct refer_data *refer_data;
    pjsip_uri *parsed_uri;
    pjsip_sip_uri *refer_to_uri;
 
    /*
     * If this is a request in response to a 401/407 Unauthorized challenge, the
     * Refer-To URI has been rewritten already, so don't attempt to re-write it again.
     * Checking for presence of the Authorization header is not an ideal solution. We do this because
     * there exists some race condition where this dialog is not the same as the one used
     * to send the original request in which case we don't have the correct refer_data.
     */
    if (!refer_to_str
        || pjsip_msg_find_hdr(tdata->msg, PJSIP_H_AUTHORIZATION, NULL)
        || !(dlg = pjsip_tdata_get_dlg(tdata))
        || !(refer_data = pjsip_dlg_get_mod_data(dlg, refer_out_of_dialog_module.id))
        || !refer_data->to_self
        || !(parsed_uri = get_refer_to_uri(tdata))) {
        goto out;
    }
    refer_to_uri = pjsip_uri_get_uri(parsed_uri);
    ast_sip_rewrite_uri_to_local(refer_to_uri, tdata);
 
    pjsip_uri_print(PJSIP_URI_IN_CONTACT_HDR, parsed_uri, ast_str_buffer(refer_to_str), ast_str_size(refer_to_str));
    refer_to_hdr = pjsip_msg_find_hdr_by_name(tdata->msg, &REFER_TO, NULL);
    pj_strdup2(tdata->pool, &refer_to_hdr->hvalue, ast_str_buffer(refer_to_str));
 
out:
    return PJ_SUCCESS;
}
 
static int refer_unreference_dialog(void *obj)
{
    struct refer_out_of_dialog *data = obj;
 
    /* This is why we keep the dialog on the subscription. When the subscription
     * is destroyed, there is no guarantee that the underlying dialog is ready
     * to be destroyed. Furthermore, there's no guarantee in the opposite direction
     * either. The dialog could be destroyed before our subscription is. We fix
     * this problem by keeping a reference to the dialog until it is time to
     * destroy the subscription.
     */
    pjsip_dlg_dec_session(data->dlg, &refer_out_of_dialog_module);
    data->dlg = NULL;
 
    return 0;
}
/*! \brief Destructor for REFER out of dialog structure */
static void refer_out_of_dialog_destroy(void *obj) {
    struct refer_out_of_dialog *data = obj;
 
    if (data->dlg) {
        /* ast_sip_push_task_wait_servant should not be called in a destructor,
         * however in this case it seems to be fine.
         */
        ast_sip_push_task_wait_servant(refer_serializer, refer_unreference_dialog, data);
    }
}
 
/*!
 * \internal
 * \brief Callback function to report status of implicit REFER-NOTIFY subscription.
 *
 * This function will be called on any state change in the REFER-NOTIFY subscription.
 * Its primary purpose is to report SUCCESS/FAILURE of a refer initiated via
 * \ref refer_send as well as to terminate the subscription, if necessary.
 */
static void refer_client_on_evsub_state(pjsip_evsub *sub, pjsip_event *event)
{
    pjsip_tx_data *tdata;
    RAII_VAR(struct ast_sip_endpoint *, endpt, NULL, ao2_cleanup);
    struct refer_out_of_dialog *refer_data;
    int refer_success;
    int res = 0;
 
    if (!event) {
        return;
    }
 
    refer_data = pjsip_evsub_get_mod_data(sub, refer_out_of_dialog_module.id);
    if (!refer_data || !refer_data->dlg) {
        return;
    }
 
    endpt = ast_sip_dialog_get_endpoint(refer_data->dlg);
 
    if (pjsip_evsub_get_state(sub) == PJSIP_EVSUB_STATE_ACCEPTED) {
        /* Check if subscription is suppressed and terminate and send completion code, if so. */
        pjsip_rx_data *rdata;
        pjsip_generic_string_hdr *refer_sub;
        const pj_str_t REFER_SUB = { "Refer-Sub", 9 };
 
        ast_debug(3, "Refer accepted by %s\n", endpt ? ast_sorcery_object_get_id(endpt) : "(unknown endpoint)");
 
        /* Check if response message */
        if (event->type == PJSIP_EVENT_TSX_STATE && event->body.tsx_state.type == PJSIP_EVENT_RX_MSG) {
            rdata = event->body.tsx_state.src.rdata;
 
            /* Find Refer-Sub header */
            refer_sub = pjsip_msg_find_hdr_by_name(rdata->msg_info.msg, &REFER_SUB, NULL);
 
            /* Check if subscription is suppressed. If it is, the far end will not terminate it,
             * and the subscription will remain active until it times out.  Terminating it here
             * eliminates the unnecessary timeout.
             */
            if (refer_sub && !pj_stricmp2(&refer_sub->hvalue, "false")) {
                /* Since no subscription is desired, assume that call has been referred successfully
                 * and terminate subscription.
                 */
                pjsip_evsub_set_mod_data(sub, refer_out_of_dialog_module.id, NULL);
                pjsip_evsub_terminate(sub, PJ_TRUE);
                res = -1;
            }
        }
    } else if (pjsip_evsub_get_state(sub) == PJSIP_EVSUB_STATE_ACTIVE ||
            pjsip_evsub_get_state(sub) == PJSIP_EVSUB_STATE_TERMINATED) {
        /* Check for NOTIFY complete or error. */
        pjsip_msg *msg;
        pjsip_msg_body *body;
        pjsip_status_line status_line = { .code = 0 };
        pj_bool_t is_last;
        pj_status_t status;
 
        if (event->type == PJSIP_EVENT_TSX_STATE && event->body.tsx_state.type == PJSIP_EVENT_RX_MSG) {
            pjsip_rx_data *rdata;
            pj_str_t refer_str;
            pj_cstr(&refer_str, "REFER");
 
            rdata = event->body.tsx_state.src.rdata;
            msg = rdata->msg_info.msg;
 
            if (msg->type == PJSIP_RESPONSE_MSG
                && (event->body.tsx_state.tsx->status_code == 401
                    || event->body.tsx_state.tsx->status_code == 407)
                && pj_stristr(&refer_str, &event->body.tsx_state.tsx->method.name)
                && ++refer_data->authentication_challenge_count < MAX_RX_CHALLENGES
                && endpt) {
 
                if (!ast_sip_create_request_with_auth(&endpt->outbound_auths,
                    event->body.tsx_state.src.rdata, event->body.tsx_state.tsx->last_tx, &tdata)) {
                    /* Send authed REFER */
                    ast_sip_send_request(tdata, refer_data->dlg, NULL, NULL, NULL);
                    goto out;
                }
            }
 
            if (msg->type == PJSIP_REQUEST_MSG) {
                if (!pjsip_method_cmp(&msg->line.req.method, pjsip_get_notify_method())) {
                    body = msg->body;
                    if (body && !pj_stricmp2(&body->content_type.type, "message")
                        && !pj_stricmp2(&body->content_type.subtype, "sipfrag")) {
                        pjsip_parse_status_line((char *)body->data, body->len, &status_line);
                    }
                }
            } else {
                status_line.code = msg->line.status.code;
                status_line.reason = msg->line.status.reason;
            }
        } else {
            status_line.code = 500;
            status_line.reason = *pjsip_get_status_text(500);
        }
 
        is_last = (pjsip_evsub_get_state(sub) == PJSIP_EVSUB_STATE_TERMINATED);
        /* If the status code is >= 200, the subscription is finished. */
        if (status_line.code >= 200 || is_last) {
            res = -1;
 
            refer_success = status_line.code >= 200 && status_line.code < 300;
 
            /* If subscription not terminated and subscription is finished (status code >= 200)
             * terminate it */
            if (!is_last) {
                pjsip_tx_data *tdata;
 
                status = pjsip_evsub_initiate(sub, pjsip_get_subscribe_method(), 0, &tdata);
                if (status == PJ_SUCCESS) {
                    pjsip_evsub_send_request(sub, tdata);
                }
            }
            ast_debug(3, "Refer completed: %d %.*s (%s)\n",
                    status_line.code,
                    (int)status_line.reason.slen, status_line.reason.ptr,
                    refer_success ? "Success" : "Failure");
        }
    }
 
out:
    if (res) {
        ao2_cleanup(refer_data);
    }
}
 
/*!
 * \internal
 * \brief Send a REFER
 *
 * \param data The outbound refer data structure
 *
 * \return 0: success, -1: failure
 */
static int refer_send(void *data)
{
    struct refer_data *rdata = data; /* The caller holds a reference */
    pjsip_tx_data *tdata;
    pjsip_evsub *sub;
    pj_str_t tmp;
    char refer_to_str[PJSIP_MAX_URL_SIZE];
    char disp_name_escaped[128];
    struct refer_out_of_dialog *refer;
    struct pjsip_evsub_user xfer_cb;
    RAII_VAR(char *, uri, NULL, ast_free);
    RAII_VAR(char *, tmp_str, NULL, ast_free);
    RAII_VAR(char *, display_name, NULL, ast_free);
    RAII_VAR(struct ast_sip_endpoint *, endpoint, NULL, ao2_cleanup);
    RAII_VAR(struct ast_sip_endpoint *, refer_to_endpoint, NULL, ao2_cleanup);
 
    endpoint = ast_sip_get_endpoint(rdata->destination, 1, &uri);
    if (!endpoint) {
        ast_log(LOG_ERROR,
            "PJSIP REFER - Could not find endpoint '%s' and no default outbound endpoint configured\n",
            rdata->destination);
        return -1;
    }
    ast_debug(3, "Request URI: %s\n", uri);
 
    refer_to_endpoint = ast_sip_get_endpoint(rdata->refer_to, 0, &tmp_str);
    if (!tmp_str) {
        ast_log(LOG_WARNING, "PJSIP REFER - Refer to not a valid resource identifier or SIP URI\n");
        return -1;
    }
    if (!(refer = ao2_alloc(sizeof(struct refer_out_of_dialog), refer_out_of_dialog_destroy))) {
        ast_log(LOG_ERROR, "PJSIP REFER - Could not allocate resources.\n");
        return -1;
    }
    /* The dialog will be terminated in the subscription event callback
     * when the subscription has terminated. */
    refer->authentication_challenge_count = 0;
    refer->dlg = ast_sip_create_dialog_uac(endpoint, uri, NULL);
    if (!refer->dlg) {
        ast_log(LOG_WARNING, "PJSIP REFER - Could not create dialog\n");
        ao2_cleanup(refer);
        return -1;
    }
    ast_sip_dialog_set_endpoint(refer->dlg, endpoint);
 
    pj_bzero(&xfer_cb, sizeof(xfer_cb));
    xfer_cb.on_evsub_state = &refer_client_on_evsub_state;
    if (pjsip_xfer_create_uac(refer->dlg, &xfer_cb, &sub) != PJ_SUCCESS) {
        ast_log(LOG_WARNING, "PJSIP REFER - Could not create uac\n");
        ao2_cleanup(refer);
        return -1;
    }
 
    display_name = ast_refer_get_var_and_unlink(rdata->refer, "display_name");
    if (display_name) {
        ast_escape_quoted(display_name, disp_name_escaped, sizeof(disp_name_escaped));
        snprintf(refer_to_str, sizeof(refer_to_str), "\"%s\" <%s>", disp_name_escaped, tmp_str);
    } else {
        snprintf(refer_to_str, sizeof(refer_to_str), "%s", tmp_str);
    }
 
    /* refer_out_of_dialog_module requires a reference to dlg
     * which will be released in refer_client_on_evsub_state()
     * when the implicit REFER subscription terminates */
    pjsip_evsub_set_mod_data(sub, refer_out_of_dialog_module.id, refer);
    if (pjsip_xfer_initiate(sub, pj_cstr(&tmp, refer_to_str), &tdata) != PJ_SUCCESS) {
        ast_log(LOG_WARNING, "PJSIP REFER - Could not create request\n");
        goto failure;
    }
 
    if (refer_to_endpoint && rdata->to_self) {
        pjsip_dlg_add_usage(refer->dlg, &refer_out_of_dialog_module, rdata);
    }
 
    ast_sip_update_to_uri(tdata, uri);
    ast_sip_update_from(tdata, rdata->from);
 
    /*
     * This copies any headers found in the refer's variables to
     * tdata.
     */
    vars_to_headers(rdata->refer, tdata);
    ast_debug(1, "Sending REFER to '%s' (via endpoint %s) from '%s'\n",
        rdata->destination, ast_sorcery_object_get_id(endpoint), rdata->from);
 
    if (pjsip_xfer_send_request(sub, tdata) == PJ_SUCCESS) {
        return 0;
    }
 
failure:
    ao2_cleanup(refer);
    pjsip_evsub_set_mod_data(sub, refer_out_of_dialog_module.id, NULL);
    pjsip_evsub_terminate(sub, PJ_FALSE);
    return -1;
}
 
static int sip_refer_send(const struct ast_refer *refer)
{
    struct refer_data *rdata;
    int res;
 
    if (ast_strlen_zero(ast_refer_get_to(refer))) {
        ast_log(LOG_ERROR, "SIP REFER - a 'To' URI  must be specified\n");
        return -1;
    }
 
    rdata = refer_data_create(refer);
    if (!rdata) {
        return -1;
    }
 
    res = ast_sip_push_task_wait_serializer(refer_serializer, refer_send, rdata);
    ao2_ref(rdata, -1);
 
    return res;
}
 
static const struct ast_refer_tech refer_tech = {
    .name = "pjsip",
    .refer_send = sip_refer_send,
};
 
static char *copy_string(struct pj_str_t *str)
{
    int len = pj_strlen(str) + 1;
    char *dst = ast_malloc(len);
    if (!dst) {
        return NULL;
    }
    ast_copy_pj_str(dst, str, len);
    return dst;
}
 
static int add_refer_param(struct ast_refer_params *params, const char *key, struct pj_str_t *str)
{
    struct ast_refer_param param;
 
    param.param_name = ast_strdup(key);
    if (!param.param_name) {
        return 0;
    }
 
    param.param_value = copy_string(str);
    if (!param.param_value) {
        ast_free((char *) param.param_name);
        return 0;
    }
 
    if (AST_VECTOR_APPEND(params, param) != 0) {
        ast_free((char *) param.param_name);
        ast_free((char *) param.param_value);
        return 0;
    }
    return 1;
}
 
 
static int refer_incoming_ari_request(struct ast_sip_session *session, pjsip_rx_data *rdata, pjsip_sip_uri *target,
    pjsip_param *replaces_param, struct refer_progress *progress)
{
    int parsed_len;
    pjsip_replaces_hdr *replaces;
    pjsip_generic_string_hdr *referred_hdr;
 
 
    RAII_VAR(struct transfer_ari_state *, state, NULL, ao2_cleanup);
 
    struct ast_framehook_interface hook = {
        .version = AST_FRAMEHOOK_INTERFACE_VERSION,
        .event_cb = refer_ari_progress_framehook,
        .destroy_cb = refer_progress_framehook_destroy,
        .data = progress,
        .disable_inheritance = 1,
    };
 
    static const pj_str_t str_referred_by = { "Referred-By", 11 };
    static const pj_str_t str_referred_by_s = { "b", 1 };
    static const pj_str_t str_replaces = { "Replaces", 8 };
    SCOPE_ENTER(3, "%s: progress: %p\n", ast_channel_name(session->channel), progress);
 
    if (!progress) {
        SCOPE_EXIT_RTN_VALUE(204, "%s: done: %d\n", ast_channel_name(session->channel), 204);
    }
 
    state = ao2_alloc(sizeof(struct transfer_ari_state), transfer_ari_state_destroy);
    if (!state) {
        SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
    }
 
    state->last_response = AST_TRANSFER_INVALID;
 
    state->params = ao2_alloc(sizeof(struct ast_refer_params), refer_params_destroy);
    if (!state->params) {
        SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
    }
    AST_VECTOR_INIT(state->params, 0);
 
 
    ast_channel_ref(session->channel);
    state->transferer_chan = session->channel;
 
    /* Using the user portion of the target URI see if it exists as a valid extension in their context */
    ast_copy_pj_str(state->exten, &target->user, sizeof(state->exten));
 
    /*
     * We may want to match in the dialplan without any user
     * options getting in the way.
     */
    AST_SIP_USER_OPTIONS_TRUNCATE_CHECK(state->exten);
 
    referred_hdr = pjsip_msg_find_hdr_by_names(rdata->msg_info.msg,
        &str_referred_by, &str_referred_by_s, NULL);
    if (referred_hdr) {
        state->referred_by = copy_string(&referred_hdr->hvalue);
        if (!state->referred_by) {
            SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
        }
    }
 
    if (replaces_param) {
        pjsip_dialog *dlg;
        pj_str_t replaces_content = { 0, };
        pj_strdup_with_null(rdata->tp_info.pool, &replaces_content, &replaces_param->value);
 
        /* Parsing the parameter as a Replaces header easily grabs the needed information */
        if (!(replaces = pjsip_parse_hdr(rdata->tp_info.pool, &str_replaces, replaces_content.ptr,
                         pj_strlen(&replaces_content), &parsed_len))) {
            ast_log(LOG_ERROR, "Received REFER request on channel '%s' from endpoint '%s' with invalid Replaces header, rejecting\n",
                ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
            SCOPE_EXIT_RTN_VALUE(400, "%s: done: %d\n", ast_channel_name(session->channel), 400);
        }
 
        dlg = pjsip_ua_find_dialog(&replaces->call_id, &replaces->to_tag, &replaces->from_tag, PJ_TRUE);
        if (dlg) {
            state->other_session = ast_sip_dialog_get_session(dlg);
            pjsip_dlg_dec_lock(dlg);
        }
 
        state->protocol_id = copy_string(&replaces->call_id);
        if (!state->protocol_id) {
            SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
        }
 
        if (!add_refer_param(state->params, "from", &replaces->from_tag)) {
            SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
        }
 
        if (!add_refer_param(state->params, "to", &replaces->to_tag)) {
            SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
        }
    }
 
    ao2_ref(session, +1);
    state->transferer = session;
 
 
    /* We need to bump the reference count up on the progress structure since it is in the frame hook now */
    ao2_ref(progress, +1);
    ast_channel_lock(session->channel);
    progress->framehook = ast_framehook_attach(session->channel, &hook);
    ast_channel_unlock(session->channel);
 
    if (progress->framehook < 0) {
        ao2_cleanup(progress);
        SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
    }
 
    if (ari_notify(state)) {
        ast_channel_lock(session->channel);
        ast_framehook_detach(session->channel, progress->framehook);
        progress->framehook = -1;
        ao2_cleanup(progress);
        ast_channel_unlock(session->channel);
        SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
    }
 
    /* Transfer ownership to the progress */
    progress->ari_state = state;
    state = NULL;
    SCOPE_EXIT_RTN_VALUE(200, "%s: done: %d\n", ast_channel_name(session->channel), 200);
}
 
static int refer_incoming_attended_request(struct ast_sip_session *session, pjsip_rx_data *rdata, pjsip_sip_uri *target_uri,
    pjsip_param *replaces_param, struct refer_progress *progress)
{
    const pj_str_t str_replaces = { "Replaces", 8 };
    pj_str_t replaces_content;
    pjsip_replaces_hdr *replaces;
    int parsed_len;
    pjsip_dialog *dlg;
    SCOPE_ENTER(3, "%s", ast_channel_name(session->channel));
 
    pj_strdup_with_null(rdata->tp_info.pool, &replaces_content, &replaces_param->value);
 
    /* Parsing the parameter as a Replaces header easily grabs the needed information */
    if (!(replaces = pjsip_parse_hdr(rdata->tp_info.pool, &str_replaces, replaces_content.ptr,
        pj_strlen(&replaces_content), &parsed_len))) {
        ast_log(LOG_ERROR, "Received REFER request on channel '%s' from endpoint '%s' with invalid Replaces header, rejecting\n",
            ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
        SCOPE_EXIT_RTN_VALUE(400, "%s: done: %d\n", ast_channel_name(session->channel), 400);
    }
 
    /* See if the dialog is local, or remote */
    if ((dlg = pjsip_ua_find_dialog(&replaces->call_id, &replaces->to_tag, &replaces->from_tag, PJ_TRUE))) {
        RAII_VAR(struct ast_sip_session *, other_session, ast_sip_dialog_get_session(dlg), ao2_cleanup);
        struct refer_attended *attended;
 
        pjsip_dlg_dec_lock(dlg);
 
        if (!other_session) {
            ast_debug(3, "Received REFER request on channel '%s' from endpoint '%s' for local dialog but no session exists on it\n",
                ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
            SCOPE_EXIT_RTN_VALUE(503, "%s: done: %d\n", ast_channel_name(session->channel), 603);
        }
 
        /* We defer actually doing the attended transfer to the other session so no deadlock can occur */
        if (!(attended = refer_attended_alloc(session, other_session, progress))) {
            ast_log(LOG_ERROR, "Received REFER request on channel '%s' from endpoint '%s' for local dialog but could not allocate structure to complete, rejecting\n",
                ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
            SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
        }
 
        if (ast_sip_session_defer_termination(session)) {
            ast_log(LOG_ERROR, "Received REFER request on channel '%s' from endpoint '%s' for local dialog but could not defer termination, rejecting\n",
                ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
            ao2_cleanup(attended);
            SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
        }
 
        /* Push it to the other session, which will have both channels with minimal locking */
        if (ast_sip_push_task(other_session->serializer, refer_attended_task, attended)) {
            ast_sip_session_end_if_deferred(session);
            ast_sip_session_defer_termination_cancel(session);
            ao2_cleanup(attended);
            SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
        }
 
        ast_debug(3, "Attended transfer from '%s' pushed to second channel serializer\n",
            ast_channel_name(session->channel));
 
        SCOPE_EXIT_RTN_VALUE(200, "%s: done: %d\n", ast_channel_name(session->channel), 200);
    } else {
        const char *context;
        struct refer_blind refer = { 0, };
        int response;
 
        DETERMINE_TRANSFER_CONTEXT(context, session);
 
        if (!ast_exists_extension(NULL, context, "external_replaces", 1, NULL)) {
            ast_log(LOG_ERROR, "Received REFER for remote session on channel '%s' from endpoint '%s' but 'external_replaces' extension not found in context %s\n",
                ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint), context);
            SCOPE_EXIT_RTN_VALUE(404, "%s: done: %d\n", ast_channel_name(session->channel), 404);
        }
 
        refer.context = context;
        refer.progress = progress;
        refer.rdata = rdata;
        refer.replaces = replaces;
        refer.refer_to = target_uri;
        refer.attended = 1;
 
        if (ast_sip_session_defer_termination(session)) {
            ast_log(LOG_ERROR, "Received REFER for remote session on channel '%s' from endpoint '%s' but could not defer termination, rejecting\n",
                ast_channel_name(session->channel),
                ast_sorcery_object_get_id(session->endpoint));
            SCOPE_EXIT_RTN_VALUE(500, "%s: done: %d\n", ast_channel_name(session->channel), 500);
        }
 
        response = xfer_response_code2sip(ast_bridge_transfer_blind(1, session->channel,
            "external_replaces", context, refer_blind_callback, &refer));
 
        ast_sip_session_end_if_deferred(session);
        if (response != 200) {
            ast_sip_session_defer_termination_cancel(session);
        }
 
        SCOPE_EXIT_RTN_VALUE(response, "%s: done: %d\n", ast_channel_name(session->channel), response);
    }
}
 
static int refer_incoming_blind_request(struct ast_sip_session *session, pjsip_rx_data *rdata, pjsip_sip_uri *target,
    struct refer_progress *progress)
{
    const char *context;
    char exten[AST_MAX_EXTENSION];
    struct refer_blind refer = { 0, };
    int response;
 
    /* If no explicit transfer context has been provided use their configured context */
    DETERMINE_TRANSFER_CONTEXT(context, session);
 
    /* Using the user portion of the target URI see if it exists as a valid extension in their context */
    ast_copy_pj_str(exten, &target->user, sizeof(exten));
 
    /*
     * We may want to match in the dialplan without any user
     * options getting in the way.
     */
    AST_SIP_USER_OPTIONS_TRUNCATE_CHECK(exten);
 
    /* Uri without exten */
    if (ast_strlen_zero(exten)) {
        ast_copy_string(exten, "s", sizeof(exten));
        ast_debug(3, "Channel '%s' from endpoint '%s' attempted blind transfer to a target without extension. Target was set to 's@%s'\n",
            ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint), context);
    }
 
    if (!ast_exists_extension(NULL, context, exten, 1, NULL)) {
        ast_log(LOG_ERROR, "Channel '%s' from endpoint '%s' attempted blind transfer to '%s@%s' but target does not exist\n",
            ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint), exten, context);
        return 404;
    }
 
    refer.context = context;
    refer.progress = progress;
    refer.rdata = rdata;
    refer.refer_to = target;
    refer.attended = 0;
 
    if (ast_sip_session_defer_termination(session)) {
        ast_log(LOG_ERROR, "Channel '%s' from endpoint '%s' attempted blind transfer but could not defer termination, rejecting\n",
            ast_channel_name(session->channel),
            ast_sorcery_object_get_id(session->endpoint));
        return 500;
    }
 
    response = xfer_response_code2sip(ast_bridge_transfer_blind(1, session->channel,
        exten, context, refer_blind_callback, &refer));
 
    ast_sip_session_end_if_deferred(session);
    if (response != 200) {
        ast_sip_session_defer_termination_cancel(session);
    }
 
    return response;
}
 
/*! \brief Structure used to retrieve channel from another session */
struct invite_replaces {
    /*! \brief Session we want the channel from */
    struct ast_sip_session *session;
    /*! \brief Channel from the session (with reference) */
    struct ast_channel *channel;
    /*! \brief Bridge the channel is in */
    struct ast_bridge *bridge;
};
 
/*! \brief Task for invite replaces */
static int invite_replaces(void *data)
{
    struct invite_replaces *invite = data;
 
    if (!invite->session->channel) {
        return -1;
    }
 
    ast_channel_ref(invite->session->channel);
    invite->channel = invite->session->channel;
 
    invite->bridge = ast_bridge_transfer_acquire_bridge(invite->channel);
    return 0;
}
 
static int refer_incoming_invite_request(struct ast_sip_session *session, struct pjsip_rx_data *rdata)
{
    pjsip_dialog *other_dlg = NULL;
    pjsip_tx_data *packet;
    int response = 0;
    RAII_VAR(struct ast_sip_session *, other_session, NULL, ao2_cleanup);
    struct invite_replaces invite;
 
    /* If a Replaces header is present make sure it is valid */
    if (pjsip_replaces_verify_request(rdata, &other_dlg, PJ_TRUE, &packet) != PJ_SUCCESS) {
        response = packet->msg->line.status.code;
        ast_assert(response != 0);
        pjsip_tx_data_dec_ref(packet);
        goto inv_replace_failed;
    }
 
    /* If no other dialog exists then this INVITE request does not have a Replaces header */
    if (!other_dlg) {
        return 0;
    }
 
    other_session = ast_sip_dialog_get_session(other_dlg);
    pjsip_dlg_dec_lock(other_dlg);
 
    /* Don't accept an in-dialog INVITE with Replaces as it does not make much sense */
    if (session->inv_session->dlg->state == PJSIP_DIALOG_STATE_ESTABLISHED) {
        response = 488;
        goto inv_replace_failed;
    }
 
    if (!other_session) {
        ast_debug(3, "INVITE with Replaces received on channel '%s' from endpoint '%s', but requested session does not exist\n",
            ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
        response = 481;
        goto inv_replace_failed;
    }
 
    invite.session = other_session;
 
    if (ast_sip_push_task_wait_serializer(other_session->serializer, invite_replaces,
        &invite)) {
        response = 481;
        goto inv_replace_failed;
    }
 
    ast_channel_lock(session->channel);
    ast_setstate(session->channel, AST_STATE_RING);
    ast_channel_unlock(session->channel);
    ast_raw_answer(session->channel);
 
    ast_debug(3, "INVITE with Replaces being attempted.  '%s' --> '%s'\n",
        ast_channel_name(session->channel), ast_channel_name(invite.channel));
 
    /* Unhold the channel now, as later we are not having access to it anymore */
    ast_queue_unhold(session->channel);
    ast_queue_frame(session->channel, &ast_null_frame);
 
    if (!invite.bridge) {
        struct ast_channel *chan = session->channel;
 
        /*
         * This will use a synchronous task but we aren't operating in
         * the serializer at this point in time, so it won't deadlock.
         */
        if (!ast_channel_move(invite.channel, chan)) {
            /*
             * We can't directly use session->channel because ast_channel_move()
             * does a masquerade which changes session->channel to a different
             * channel.  To ensure we work on the right channel we store a
             * pointer locally before we begin so it remains valid.
             */
            ast_hangup(chan);
        } else {
            response = AST_CAUSE_FAILURE;
        }
    } else {
        if (ast_bridge_impart(invite.bridge, session->channel, invite.channel, NULL,
            AST_BRIDGE_IMPART_CHAN_INDEPENDENT)) {
            response = AST_CAUSE_FAILURE;
        }
    }
 
    ast_channel_unref(invite.channel);
    ao2_cleanup(invite.bridge);
 
    if (!response) {
        /*
         * On success we cannot use session->channel in the debug message.
         * This thread either no longer has a ref to session->channel or
         * session->channel is no longer the original channel.
         */
        ast_debug(3, "INVITE with Replaces successfully completed.\n");
    } else {
        ast_debug(3, "INVITE with Replaces failed on channel '%s', hanging up with cause '%d'\n",
            ast_channel_name(session->channel), response);
        ast_channel_lock(session->channel);
        ast_channel_hangupcause_set(session->channel, response);
        ast_channel_unlock(session->channel);
        ast_hangup(session->channel);
    }
 
    return 1;
 
inv_replace_failed:
    if (session->inv_session->dlg->state != PJSIP_DIALOG_STATE_ESTABLISHED) {
        ast_debug(3, "INVITE with Replaces failed on channel '%s', sending response of '%d'\n",
            ast_channel_name(session->channel), response);
        session->defer_terminate = 1;
        ast_hangup(session->channel);
 
        if (pjsip_inv_end_session(session->inv_session, response, NULL, &packet) == PJ_SUCCESS
            && packet) {
            ast_sip_session_send_response(session, packet);
        }
    } else {
        ast_debug(3, "INVITE with Replaces in-dialog on channel '%s', hanging up\n",
            ast_channel_name(session->channel));
        ast_queue_hangup(session->channel);
    }
 
    return 1;
}
 
static int refer_incoming_refer_request(struct ast_sip_session *session, struct pjsip_rx_data *rdata)
{
    pjsip_generic_string_hdr *refer_to;
    char *uri;
    size_t uri_size;
    pjsip_uri *target;
    pjsip_sip_uri *target_uri;
    RAII_VAR(struct refer_progress *, progress, NULL, ao2_cleanup);
    pjsip_param *replaces;
    int response;
 
    static const pj_str_t str_refer_to = { "Refer-To", 8 };
    static const pj_str_t str_refer_to_s = { "r", 1 };
    static const pj_str_t str_replaces = { "Replaces", 8 };
 
    SCOPE_ENTER(3, "%s\n", session->channel ? ast_channel_name(session->channel) : "unknown");
 
    if (!session->channel) {
        /* No channel to refer.  Likely because the call was just hung up. */
        pjsip_dlg_respond(session->inv_session->dlg, rdata, 404, NULL, NULL, NULL);
        ast_debug(3, "Received a REFER on a session with no channel from endpoint '%s'.\n",
            ast_sorcery_object_get_id(session->endpoint));
        SCOPE_EXIT_RTN_VALUE(0, "%s: done: %d\n", ast_channel_name(session->channel), 0);
    }
 
    if (!session->endpoint->allowtransfer) {
        pjsip_dlg_respond(session->inv_session->dlg, rdata, 603, NULL, NULL, NULL);
        ast_log(LOG_WARNING, "Endpoint %s transfer attempt blocked due to configuration\n",
                ast_sorcery_object_get_id(session->endpoint));
        SCOPE_EXIT_RTN_VALUE(0, "%s: done: %d\n", ast_channel_name(session->channel), 0);
    }
 
    /* A Refer-To header is required */
    refer_to = pjsip_msg_find_hdr_by_names(rdata->msg_info.msg, &str_refer_to, &str_refer_to_s, NULL);
    if (!refer_to) {
        pjsip_dlg_respond(session->inv_session->dlg, rdata, 400, NULL, NULL, NULL);
        ast_debug(3, "Received a REFER without Refer-To on channel '%s' from endpoint '%s'\n",
            ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
        SCOPE_EXIT_RTN_VALUE(0, "%s: done: %d\n", ast_channel_name(session->channel), 0);
    }
 
    /* The ast_copy_pj_str to uri is needed because it puts the NULL terminator to the uri
     * as pjsip_parse_uri require a NULL terminated uri
     */
 
    uri_size = pj_strlen(&refer_to->hvalue) + 1;
    uri = ast_alloca(uri_size);
    ast_copy_pj_str(uri, &refer_to->hvalue, uri_size);
 
    target = pjsip_parse_uri(rdata->tp_info.pool, uri, uri_size - 1, 0);
 
    if (!target
        || (!PJSIP_URI_SCHEME_IS_SIP(target)
            && !PJSIP_URI_SCHEME_IS_SIPS(target))) {
 
        pjsip_dlg_respond(session->inv_session->dlg, rdata, 400, NULL, NULL, NULL);
        ast_debug(3, "Received a REFER without a parseable Refer-To ('%s') on channel '%s' from endpoint '%s'\n",
            uri, ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
        SCOPE_EXIT_RTN_VALUE(0, "%s: done: %d\n", ast_channel_name(session->channel), 0);
    }
    target_uri = pjsip_uri_get_uri(target);
 
    /* Set up REFER progress subscription if requested/possible */
    if (refer_progress_alloc(session, rdata, &progress)) {
        pjsip_dlg_respond(session->inv_session->dlg, rdata, 500, NULL, NULL, NULL);
        ast_debug(3, "Could not set up subscription for REFER on channel '%s' from endpoint '%s'\n",
            ast_channel_name(session->channel), ast_sorcery_object_get_id(session->endpoint));
        SCOPE_EXIT_RTN_VALUE(0, "%s: done: %d\n", ast_channel_name(session->channel), 0);
    }
 
    replaces = pjsip_param_find(&target_uri->header_param, &str_replaces);
    if (!replaces) {
        replaces = pjsip_param_find(&target_uri->other_param, &str_replaces);
    }
 
    /* Determine if this is handled externally or an attended or blind transfer */
    if (session->transferhandling_ari) {
        ast_trace(-1, "%s: incoming ari\n", session->channel ? ast_channel_name(session->channel) : "unknown");
        response = refer_incoming_ari_request(session, rdata, target_uri, replaces, progress);
    } else if (replaces) {
        ast_trace(-1, "%s: incoming attended\n", session->channel ? ast_channel_name(session->channel) : "unknown");
        response = refer_incoming_attended_request(session, rdata, target_uri, replaces, progress);
    } else {
        ast_trace(-1, "%s: incoming blind\n", session->channel ? ast_channel_name(session->channel) : "unknown");
        response = refer_incoming_blind_request(session, rdata, target_uri, progress);
    }
 
    if (progress->no_refer_sub) {
        /* The transferer has requested no subscription, so send a final response immediately */
        pjsip_tx_data *tdata;
        const pj_str_t str_refer_sub = { "Refer-Sub", 9 };
        const pj_str_t str_false = { "false", 5 };
        pjsip_hdr *hdr;
 
        ast_trace(-1, "%s: No refer sub from endpoint '%s'.  Sending reponse %d\n", ast_channel_name(session->channel),
            ast_sorcery_object_get_id(session->endpoint), response);
 
        if (pjsip_dlg_create_response(session->inv_session->dlg, rdata, response, NULL, &tdata) != PJ_SUCCESS) {
            pjsip_dlg_respond(session->inv_session->dlg, rdata, response, NULL, NULL, NULL);
            SCOPE_EXIT_RTN_VALUE(0, "%s: done: %d\n", ast_channel_name(session->channel), 0);
        }
 
        hdr = (pjsip_hdr*)pjsip_generic_string_hdr_create(tdata->pool, &str_refer_sub, &str_false);
        pjsip_msg_add_hdr(tdata->msg, hdr);
 
        pjsip_dlg_send_response(session->inv_session->dlg, pjsip_rdata_get_tsx(rdata), tdata);
 
    } else if (response != 200) {
        /* Since this failed we can send a final NOTIFY now and terminate the subscription */
        struct refer_progress_notification *notification = refer_progress_notification_alloc(progress, response, PJSIP_EVSUB_STATE_TERMINATED);
 
        if (notification) {
            /* The refer_progress_notify function will call ao2_cleanup on this for us */
            if (ast_sip_push_task(progress->serializer, refer_progress_notify, notification)) {
                ao2_cleanup(notification);
            }
        }
    }
 
    SCOPE_EXIT_RTN_VALUE(0, "%s: done: %d\n", ast_channel_name(session->channel), 0);
}
 
static int refer_incoming_request(struct ast_sip_session *session, pjsip_rx_data *rdata)
{
    if (!pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, pjsip_get_refer_method())) {
        return refer_incoming_refer_request(session, rdata);
    } else if (!pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, &pjsip_invite_method)) {
        return refer_incoming_invite_request(session, rdata);
    } else {
        return 0;
    }
}
 
/*!
 * \brief Use the value of a channel variable as the value of a SIP header
 *
 * This looks up a variable name on a channel, then takes that value and adds
 * it to an outgoing SIP request. If the header already exists on the message,
 * then no action is taken.
 *
 * \pre chan is locked.
 *
 * \param chan The channel on which to find the variable.
 * \param var_name The name of the channel variable to use.
 * \param header_name The name of the SIP header to add to the outgoing message.
 * \param tdata The outgoing SIP message on which to add the header
 */
static void add_header_from_channel_var(struct ast_channel *chan, const char *var_name, const char *header_name, pjsip_tx_data *tdata)
{
    const char *var_value;
    pj_str_t pj_header_name;
    pjsip_hdr *header;
 
    var_value = pbx_builtin_getvar_helper(chan, var_name);
    if (ast_strlen_zero(var_value)) {
        return;
    }
 
    pj_cstr(&pj_header_name, header_name);
    header = pjsip_msg_find_hdr_by_name(tdata->msg, &pj_header_name, NULL);
    if (header) {
        return;
    }
    ast_sip_add_header(tdata, header_name, var_value);
}
 
static void refer_outgoing_request(struct ast_sip_session *session, struct pjsip_tx_data *tdata)
{
    if (pjsip_method_cmp(&tdata->msg->line.req.method, &pjsip_invite_method)
        || !session->channel
        || session->inv_session->state != PJSIP_INV_STATE_NULL) {
        return;
    }
 
    ast_channel_lock(session->channel);
    add_header_from_channel_var(session->channel, "SIPREPLACESHDR", "Replaces", tdata);
    add_header_from_channel_var(session->channel, "SIPREFERREDBYHDR", "Referred-By", tdata);
    ast_channel_unlock(session->channel);
}
 
static struct ast_sip_session_supplement refer_supplement = {
    .priority = AST_SIP_SUPPLEMENT_PRIORITY_CHANNEL + 1,
    .incoming_request = refer_incoming_request,
    .outgoing_request = refer_outgoing_request,
};
 
static int load_module(void)
{
    const pj_str_t str_norefersub = { "norefersub", 10 };
 
    pjsip_replaces_init_module(ast_sip_get_pjsip_endpoint());
    pjsip_xfer_init_module(ast_sip_get_pjsip_endpoint());
 
    if (ast_sip_get_norefersub()) {
        pjsip_endpt_add_capability(ast_sip_get_pjsip_endpoint(), NULL, PJSIP_H_SUPPORTED, NULL, 1, &str_norefersub);
    }
 
    if (ast_refer_tech_register(&refer_tech)) {
        return AST_MODULE_LOAD_DECLINE;
    }
 
    refer_serializer = ast_sip_create_serializer("pjsip/refer");
    if (!refer_serializer) {
        ast_refer_tech_unregister(&refer_tech);
        return AST_MODULE_LOAD_DECLINE;
    }
 
    ast_sip_register_service(&refer_out_of_dialog_module);
    ast_sip_register_service(&refer_progress_module);
    ast_sip_session_register_supplement(&refer_supplement);
 
    ast_module_shutdown_ref(ast_module_info->self);
 
    return AST_MODULE_LOAD_SUCCESS;
}
 
static int unload_module(void)
{
    ast_sip_session_unregister_supplement(&refer_supplement);
    ast_sip_unregister_service(&refer_out_of_dialog_module);
    ast_sip_unregister_service(&refer_progress_module);
    ast_taskprocessor_unreference(refer_serializer);
 
    return 0;
}
 
AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "PJSIP Blind and Attended Transfer Support",
    .support_level = AST_MODULE_SUPPORT_CORE,
    .load = load_module,
    .unload = unload_module,
    .load_pri = AST_MODPRI_APP_DEPEND,
    .requires = "res_pjsip,res_pjsip_session,res_pjsip_pubsub",
);