open62541/src/server/ua_subscription.c

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "ua_subscription.h"
#include "ua_server_internal.h"
#include "ua_types_encoding_binary.h"
#include "ua_services.h"
#include "ua_nodestore.h"

#ifdef UA_ENABLE_SUBSCRIPTIONS /* conditional compilation */

#define UA_VALUENCODING_MAXSTACK 512

/*****************/
/* MonitoredItem */
/*****************/

UA_MonitoredItem *
UA_MonitoredItem_new(void) {
    /* Allocate the memory */
    UA_MonitoredItem *newItem =
        (UA_MonitoredItem*)UA_calloc(1, sizeof(UA_MonitoredItem));
    if(!newItem)
        return NULL;

    /* Remaining members are covered by calloc zeroing out the memory */
    newItem->monitoredItemType = UA_MONITOREDITEMTYPE_CHANGENOTIFY; /* currently hardcoded */
    newItem->timestampsToReturn = UA_TIMESTAMPSTORETURN_SOURCE;
    TAILQ_INIT(&newItem->queue);
    return newItem;
}

void
MonitoredItem_delete(UA_Server *server, UA_MonitoredItem *monitoredItem) {
    /* Remove the sampling callback */
    MonitoredItem_unregisterSampleCallback(server, monitoredItem);

    /* Clear the queued samples */
    MonitoredItem_queuedValue *val, *val_tmp;
    TAILQ_FOREACH_SAFE(val, &monitoredItem->queue, listEntry, val_tmp) {
        TAILQ_REMOVE(&monitoredItem->queue, val, listEntry);
        UA_DataValue_deleteMembers(&val->value);
        UA_free(val);
    }
    monitoredItem->currentQueueSize = 0;

    /* Remove the monitored item */
    LIST_REMOVE(monitoredItem, listEntry);
    UA_String_deleteMembers(&monitoredItem->indexRange);
    UA_ByteString_deleteMembers(&monitoredItem->lastSampledValue);
    UA_NodeId_deleteMembers(&monitoredItem->monitoredNodeId);
    UA_free(monitoredItem); // TODO: Use a delayed free
}

static void
ensureSpaceInMonitoredItemQueue(UA_MonitoredItem *mon) {
    /* Enough space, nothing to do here */
    if(mon->currentQueueSize < mon->maxQueueSize)
        return;

    /* Get the item to remove */
    MonitoredItem_queuedValue *queueItem;
    if(mon->discardOldest)
        queueItem = TAILQ_FIRST(&mon->queue);
    else
        queueItem = TAILQ_LAST(&mon->queue, QueuedValueQueue);
    UA_assert(queueItem);

    /* Remove the item */
    TAILQ_REMOVE(&mon->queue, queueItem, listEntry);
    UA_DataValue_deleteMembers(&queueItem->value);
    UA_free(queueItem);
    --mon->currentQueueSize;
}

/* Errors are returned as no change detected */
static UA_Boolean
detectValueChangeWithFilter(UA_MonitoredItem *mon, UA_DataValue *value,
                            UA_ByteString *encoding) {
    /* Encode the data for comparison */
    size_t binsize = UA_calcSizeBinary(value, &UA_TYPES[UA_TYPES_DATAVALUE]);
    if(binsize == 0)
        return false;

    /* Allocate buffer on the heap if necessary */
    if(binsize > UA_VALUENCODING_MAXSTACK &&
       UA_ByteString_allocBuffer(encoding, binsize) != UA_STATUSCODE_GOOD)
        return false;

    /* Encode the value */
    UA_Byte *bufPos = encoding->data;
    const UA_Byte *bufEnd = &encoding->data[encoding->length];
    UA_StatusCode retval = UA_encodeBinary(value, &UA_TYPES[UA_TYPES_DATAVALUE],
                                           &bufPos, &bufEnd, NULL, NULL);
    if(retval != UA_STATUSCODE_GOOD)
        return false;

    /* The value has changed */
    encoding->length = (uintptr_t)bufPos - (uintptr_t)encoding->data;
    return !mon->lastSampledValue.data || !UA_String_equal(encoding, &mon->lastSampledValue);
}

/* Has this sample changed from the last one? The method may allocate additional
 * space for the encoding buffer. Detect the change in encoding->data. */
static UA_Boolean
detectValueChange(UA_MonitoredItem *mon, UA_DataValue *value, UA_ByteString *encoding) {
    /* Apply Filter */
    UA_Boolean hasValue = value->hasValue;
    if(mon->trigger == UA_DATACHANGETRIGGER_STATUS)
        value->hasValue = false;

    UA_Boolean hasServerTimestamp = value->hasServerTimestamp;
    UA_Boolean hasServerPicoseconds = value->hasServerPicoseconds;
    value->hasServerTimestamp = false;
    value->hasServerPicoseconds = false;

    UA_Boolean hasSourceTimestamp = value->hasSourceTimestamp;
    UA_Boolean hasSourcePicoseconds = value->hasSourcePicoseconds;
    if(mon->trigger < UA_DATACHANGETRIGGER_STATUSVALUETIMESTAMP) {
        value->hasSourceTimestamp = false;
        value->hasSourcePicoseconds = false;
    }

    /* Detect the Value Change */
    UA_Boolean res = detectValueChangeWithFilter(mon, value, encoding);

    /* Reset the filter */
    value->hasValue = hasValue;
    value->hasServerTimestamp = hasServerTimestamp;
    value->hasServerPicoseconds = hasServerPicoseconds;
    value->hasSourceTimestamp = hasSourceTimestamp;
    value->hasSourcePicoseconds = hasSourcePicoseconds;
    return res;
}

/* Returns whether a new sample was created */
static UA_Boolean
sampleCallbackWithValue(UA_Server *server, UA_Subscription *sub,
                        UA_MonitoredItem *monitoredItem,
                        UA_DataValue *value,
                        UA_ByteString *valueEncoding) {
    /* Store the pointer to the stack-allocated bytestring to see if a heap-allocation
     * was necessary */
    UA_Byte *stackValueEncoding = valueEncoding->data;

    /* Has the value changed? */
    UA_Boolean changed = detectValueChange(monitoredItem, value, valueEncoding);
    if(!changed)
        return false;

    /* Allocate the entry for the publish queue */
    MonitoredItem_queuedValue *newQueueItem =
        (MonitoredItem_queuedValue *)UA_malloc(sizeof(MonitoredItem_queuedValue));
    if(!newQueueItem) {
        UA_LOG_WARNING_SESSION(server->config.logger, sub->session,
                               "Subscription %u | MonitoredItem %i | "
                               "Item for the publishing queue could not be allocated",
                               sub->subscriptionID, monitoredItem->itemId);
        return false;
    }

    /* Copy valueEncoding on the heap for the next comparison (if not already done) */
    if(valueEncoding->data == stackValueEncoding) {
        UA_ByteString cbs;
        if(UA_ByteString_copy(valueEncoding, &cbs) != UA_STATUSCODE_GOOD) {
            UA_LOG_WARNING_SESSION(server->config.logger, sub->session,
                                   "Subscription %u | MonitoredItem %i | "
                                   "ByteString to compare values could not be created",
                                   sub->subscriptionID, monitoredItem->itemId);
            UA_free(newQueueItem);
            return false;
        }
        *valueEncoding = cbs;
    }

    /* Prepare the newQueueItem */
    if(value->hasValue && value->value.storageType == UA_VARIANT_DATA_NODELETE) {
        /* Make a deep copy of the value */
        if(UA_DataValue_copy(value, &newQueueItem->value) != UA_STATUSCODE_GOOD) {
            UA_LOG_WARNING_SESSION(server->config.logger, sub->session,
                                   "Subscription %u | MonitoredItem %i | "
                                   "Item for the publishing queue could not be prepared",
                                   sub->subscriptionID, monitoredItem->itemId);
            UA_free(newQueueItem);
            return false;
        }
    } else {
        newQueueItem->value = *value; /* Just copy the value and do not release it */
    }
    newQueueItem->clientHandle = monitoredItem->clientHandle;

    /* <-- Point of no return --> */

    UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                         "Subscription %u | MonitoredItem %u | Sampled a new value",
                         sub->subscriptionID, monitoredItem->itemId);

    /* Replace the encoding for comparison */
    UA_ByteString_deleteMembers(&monitoredItem->lastSampledValue);
    monitoredItem->lastSampledValue = *valueEncoding;

    /* Add the sample to the queue for publication */
    ensureSpaceInMonitoredItemQueue(monitoredItem);
    TAILQ_INSERT_TAIL(&monitoredItem->queue, newQueueItem, listEntry);
    ++monitoredItem->currentQueueSize;
    return true;;
}

void
UA_MoniteredItem_SampleCallback(UA_Server *server,
                                UA_MonitoredItem *monitoredItem) {
    UA_Subscription *sub = monitoredItem->subscription;
    if(monitoredItem->monitoredItemType != UA_MONITOREDITEMTYPE_CHANGENOTIFY) {
        UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                             "Subscription %u | MonitoredItem %i | "
                             "Not a data change notification",
                             sub->subscriptionID, monitoredItem->itemId);
        return;
    }

    /* Read the value */
    UA_ReadValueId rvid;
    UA_ReadValueId_init(&rvid);
    rvid.nodeId = monitoredItem->monitoredNodeId;
    rvid.attributeId = monitoredItem->attributeID;
    rvid.indexRange = monitoredItem->indexRange;
    UA_DataValue value;
    UA_DataValue_init(&value);
    Service_Read_single(server, sub->session, monitoredItem->timestampsToReturn,
                        &rvid, &value);

    /* Stack-allocate some memory for the value encoding. We might heap-allocate
     * more memory if needed. This is just enough for scalars and small
     * structures. */
    UA_Byte *stackValueEncoding = (UA_Byte *)UA_alloca(UA_VALUENCODING_MAXSTACK);
    UA_ByteString valueEncoding;
    valueEncoding.data = stackValueEncoding;
    valueEncoding.length = UA_VALUENCODING_MAXSTACK;

    /* Create a sample and compare with the last value */
    UA_Boolean newNotification = sampleCallbackWithValue(server, sub, monitoredItem,
                                                         &value, &valueEncoding);

    /* Clean up */
    if(!newNotification) {
        if(valueEncoding.data != stackValueEncoding)
            UA_ByteString_deleteMembers(&valueEncoding);
        UA_DataValue_deleteMembers(&value);
    }
}

UA_StatusCode
MonitoredItem_registerSampleCallback(UA_Server *server, UA_MonitoredItem *mon) {
    UA_StatusCode retval =
        UA_Server_addRepeatedCallback(server, (UA_ServerCallback)UA_MoniteredItem_SampleCallback,
                                      mon, (UA_UInt32)mon->samplingInterval, &mon->sampleCallbackId);
    if(retval == UA_STATUSCODE_GOOD)
        mon->sampleCallbackIsRegistered = true;
    return retval;
}

UA_StatusCode
MonitoredItem_unregisterSampleCallback(UA_Server *server, UA_MonitoredItem *mon) {
    if(!mon->sampleCallbackIsRegistered)
        return UA_STATUSCODE_GOOD;
    mon->sampleCallbackIsRegistered = false;
    return UA_Server_removeRepeatedCallback(server, mon->sampleCallbackId);
}

/****************/
/* Subscription */
/****************/

UA_Subscription *
UA_Subscription_new(UA_Session *session, UA_UInt32 subscriptionID) {
    /* Allocate the memory */
    UA_Subscription *newItem =
        (UA_Subscription*)UA_calloc(1, sizeof(UA_Subscription));
    if(!newItem)
        return NULL;

    /* Remaining members are covered by calloc zeroing out the memory */
    newItem->session = session;
    newItem->subscriptionID = subscriptionID;
    newItem->state = UA_SUBSCRIPTIONSTATE_NORMAL; /* The first publish response is sent immediately */
    TAILQ_INIT(&newItem->retransmissionQueue);
    return newItem;
}

void
UA_Subscription_deleteMembers(UA_Subscription *subscription, UA_Server *server) {
    Subscription_unregisterPublishCallback(server, subscription);

    /* Delete monitored Items */
    UA_MonitoredItem *mon, *tmp_mon;
    LIST_FOREACH_SAFE(mon, &subscription->monitoredItems, listEntry, tmp_mon) {
        LIST_REMOVE(mon, listEntry);
        MonitoredItem_delete(server, mon);
    }

    /* Delete Retransmission Queue */
    UA_NotificationMessageEntry *nme, *nme_tmp;
    TAILQ_FOREACH_SAFE(nme, &subscription->retransmissionQueue, listEntry, nme_tmp) {
        TAILQ_REMOVE(&subscription->retransmissionQueue, nme, listEntry);
        UA_NotificationMessage_deleteMembers(&nme->message);
        UA_free(nme);
    }
    subscription->retransmissionQueueSize = 0;
}

UA_MonitoredItem *
UA_Subscription_getMonitoredItem(UA_Subscription *sub,
                                 UA_UInt32 monitoredItemID) {
    UA_MonitoredItem *mon;
    LIST_FOREACH(mon, &sub->monitoredItems, listEntry) {
        if(mon->itemId == monitoredItemID)
            break;
    }
    return mon;
}

UA_StatusCode
UA_Subscription_deleteMonitoredItem(UA_Server *server, UA_Subscription *sub,
                                    UA_UInt32 monitoredItemID) {
    UA_MonitoredItem *mon;
    LIST_FOREACH(mon, &sub->monitoredItems, listEntry) {
        if(mon->itemId == monitoredItemID) {
            LIST_REMOVE(mon, listEntry);
            MonitoredItem_delete(server, mon);
            return UA_STATUSCODE_GOOD;
        }
    }
    return UA_STATUSCODE_BADMONITOREDITEMIDINVALID;
}

static size_t
countQueuedNotifications(UA_Subscription *sub,
                         UA_Boolean *moreNotifications) {
    if(!sub->publishingEnabled)
        return 0;

    size_t notifications = 0;
    UA_MonitoredItem *mon;
    LIST_FOREACH(mon, &sub->monitoredItems, listEntry) {
        MonitoredItem_queuedValue *qv;
        TAILQ_FOREACH(qv, &mon->queue, listEntry) {
            if(notifications >= sub->notificationsPerPublish) {
                *moreNotifications = true;
                break;
            }
            ++notifications;
        }
    }
    return notifications;
}

static void
UA_Subscription_addRetransmissionMessage(UA_Server *server, UA_Subscription *sub,
                                         UA_NotificationMessageEntry *entry) {
    /* Release the oldest entry if there is not enough space */
    if(server->config.maxRetransmissionQueueSize > 0 &&
       sub->retransmissionQueueSize >= server->config.maxRetransmissionQueueSize) {
        UA_NotificationMessageEntry *lastentry =
            TAILQ_LAST(&sub->retransmissionQueue, ListOfNotificationMessages);
        TAILQ_REMOVE(&sub->retransmissionQueue, lastentry, listEntry);
        --sub->retransmissionQueueSize;
        UA_NotificationMessage_deleteMembers(&lastentry->message);
        UA_free(lastentry);
    }

    /* Add entry */
    TAILQ_INSERT_HEAD(&sub->retransmissionQueue, entry, listEntry);
    ++sub->retransmissionQueueSize;
}

UA_StatusCode
UA_Subscription_removeRetransmissionMessage(UA_Subscription *sub,
                                            UA_UInt32 sequenceNumber) {
    UA_NotificationMessageEntry *entry, *entry_tmp;
    TAILQ_FOREACH_SAFE(entry, &sub->retransmissionQueue, listEntry, entry_tmp) {
        if(entry->message.sequenceNumber != sequenceNumber)
            continue;
        TAILQ_REMOVE(&sub->retransmissionQueue, entry, listEntry);
        --sub->retransmissionQueueSize;
        UA_NotificationMessage_deleteMembers(&entry->message);
        UA_free(entry);
        return UA_STATUSCODE_GOOD;
    }
    return UA_STATUSCODE_BADSEQUENCENUMBERUNKNOWN;
}

static UA_StatusCode
prepareNotificationMessage(UA_Subscription *sub,
                           UA_NotificationMessage *message,
                           size_t notifications) {
    /* Array of ExtensionObject to hold different kinds of notifications
       (currently only DataChangeNotifications) */
    message->notificationData = UA_ExtensionObject_new();
    if(!message->notificationData)
        return UA_STATUSCODE_BADOUTOFMEMORY;
    message->notificationDataSize = 1;

    /* Allocate Notification */
    UA_DataChangeNotification *dcn = UA_DataChangeNotification_new();
    if(!dcn) {
        UA_NotificationMessage_deleteMembers(message);
        return UA_STATUSCODE_BADOUTOFMEMORY;
    }
    UA_ExtensionObject *data = message->notificationData;
    data->encoding = UA_EXTENSIONOBJECT_DECODED;
    data->content.decoded.data = dcn;
    data->content.decoded.type = &UA_TYPES[UA_TYPES_DATACHANGENOTIFICATION];

    /* Allocate array of notifications */
    dcn->monitoredItems = (UA_MonitoredItemNotification *)
        UA_Array_new(notifications, &UA_TYPES[UA_TYPES_MONITOREDITEMNOTIFICATION]);
    if(!dcn->monitoredItems) {
        UA_NotificationMessage_deleteMembers(message);
        return UA_STATUSCODE_BADOUTOFMEMORY;
    }
    dcn->monitoredItemsSize = notifications;

    /* Move notifications into the response .. the point of no return */
    size_t l = 0;
    UA_MonitoredItem *mon;
    LIST_FOREACH(mon, &sub->monitoredItems, listEntry) {
        MonitoredItem_queuedValue *qv, *qv_tmp;
        TAILQ_FOREACH_SAFE(qv, &mon->queue, listEntry, qv_tmp) {
            if(l >= notifications)
                return UA_STATUSCODE_GOOD;
            UA_MonitoredItemNotification *min = &dcn->monitoredItems[l];
            min->clientHandle = qv->clientHandle;
            min->value = qv->value;
            TAILQ_REMOVE(&mon->queue, qv, listEntry);
            UA_free(qv);
            --mon->currentQueueSize;
            ++l;
        }
    }
    return UA_STATUSCODE_GOOD;
}

void
UA_Subscription_publishCallback(UA_Server *server, UA_Subscription *sub) {
    UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                         "Subscription %u | Publish Callback",
                         sub->subscriptionID);

    /* Count the available notifications */
    UA_Boolean moreNotifications = false;
    size_t notifications = countQueuedNotifications(sub, &moreNotifications);

    /* Return if nothing to do */
    if(notifications == 0) {
        ++sub->currentKeepAliveCount;
        if(sub->currentKeepAliveCount < sub->maxKeepAliveCount)
            return;
        UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                             "Subscription %u | Sending a KeepAlive",
                             sub->subscriptionID)
    }

    /* Check if the securechannel is valid */
    UA_SecureChannel *channel = sub->session->channel;
    if(!channel)
        return;

    /* Dequeue a response */
    UA_PublishResponseEntry *pre = SIMPLEQ_FIRST(&sub->session->responseQueue);

    /* Cannot publish without a response */
    if(!pre) {
        UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                             "Subscription %u | Cannot send a publish response "
                             "since the publish queue is empty", sub->subscriptionID)
        if(sub->state != UA_SUBSCRIPTIONSTATE_LATE) {
            sub->state = UA_SUBSCRIPTIONSTATE_LATE;
        } else {
            ++sub->currentLifetimeCount;
            if(sub->currentLifetimeCount > sub->lifeTimeCount) {
                UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                                     "Subscription %u | End of lifetime for subscription",
                                     sub->subscriptionID);
                UA_Session_deleteSubscription(server, sub->session, sub->subscriptionID);
            }
        }
        return;
    }

    UA_PublishResponse *response = &pre->response;
    UA_NotificationMessage *message = &response->notificationMessage;
    UA_NotificationMessageEntry *retransmission = NULL;
    if(notifications > 0) {
        /* Allocate the retransmission entry */
        retransmission =
            (UA_NotificationMessageEntry*)UA_malloc(sizeof(UA_NotificationMessageEntry));
        if(!retransmission) {
            UA_LOG_WARNING_SESSION(server->config.logger, sub->session,
                                   "Subscription %u | Could not allocate memory "
                                   "for retransmission", sub->subscriptionID);
            return;
        }

        /* Prepare the response */
        UA_StatusCode retval =
            prepareNotificationMessage(sub, message, notifications);
        if(retval != UA_STATUSCODE_GOOD) {
            UA_LOG_WARNING_SESSION(server->config.logger, sub->session,
                                   "Subscription %u | Could not prepare the "
                                   "notification message", sub->subscriptionID);
            UA_free(retransmission);
            return;
        }
    }

    /* <-- The point of no return --> */

    /* Remove the response from the response queue */
    SIMPLEQ_REMOVE_HEAD(&sub->session->responseQueue, listEntry);

    /* Set up the response */
    response->responseHeader.timestamp = UA_DateTime_now();
    response->subscriptionId = sub->subscriptionID;
    response->moreNotifications = moreNotifications;
    message->publishTime = response->responseHeader.timestamp;
    if(notifications == 0) {
        /* Send sequence number for the next notification */
        message->sequenceNumber = sub->sequenceNumber + 1;
    } else {
        /* Increase the sequence number */
        message->sequenceNumber = ++sub->sequenceNumber;

        /* Put the notification message into the retransmission queue. This needs to
         * be done here, so that the message itself is included in the available
         * sequence numbers for acknowledgement. */
        retransmission->message = response->notificationMessage;
        UA_Subscription_addRetransmissionMessage(server, sub, retransmission);
    }

    /* Get the available sequence numbers from the retransmission queue */
    size_t available = sub->retransmissionQueueSize;
    if(available > 0) {
        response->availableSequenceNumbers =
            (UA_UInt32*)UA_alloca(available * sizeof(UA_UInt32));
        response->availableSequenceNumbersSize = available;
        size_t i = 0;
        UA_NotificationMessageEntry *nme;
        TAILQ_FOREACH(nme, &sub->retransmissionQueue, listEntry) {
            response->availableSequenceNumbers[i] = nme->message.sequenceNumber;
            ++i;
        }
    }

    /* Send the response */
    UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                         "Subscription %u | Sending out a publish response with %u "
                         "notifications", sub->subscriptionID, (UA_UInt32)notifications);
    UA_SecureChannel_sendBinaryMessage(sub->session->channel, pre->requestId, response,
                                       &UA_TYPES[UA_TYPES_PUBLISHRESPONSE]);

    /* Reset subscription state to normal. */
    sub->state = UA_SUBSCRIPTIONSTATE_NORMAL;
    sub->currentKeepAliveCount = 0;
    sub->currentLifetimeCount = 0;

    /* Free the response */
    UA_Array_delete(response->results, response->resultsSize,
                    &UA_TYPES[UA_TYPES_UINT32]);
    UA_free(pre); /* no need for UA_PublishResponse_deleteMembers */

    /* Repeat if there are more notifications to send */
    if(moreNotifications)
        UA_Subscription_publishCallback(server, sub);
}

UA_StatusCode
Subscription_registerPublishCallback(UA_Server *server, UA_Subscription *sub) {
    if(sub->publishCallbackIsRegistered)
        return UA_STATUSCODE_GOOD;

    UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                         "Subscription %u | Register subscription publishing callback",
                         sub->subscriptionID);
    UA_StatusCode retval =
        UA_Server_addRepeatedCallback(server,
                                 (UA_ServerCallback)UA_Subscription_publishCallback,
                                 sub, (UA_UInt32)sub->publishingInterval,
                                 &sub->publishCallbackId);
    if(retval == UA_STATUSCODE_GOOD)
        sub->publishCallbackIsRegistered = true;
    return retval;
}

UA_StatusCode
Subscription_unregisterPublishCallback(UA_Server *server, UA_Subscription *sub) {
    if(!sub->publishCallbackIsRegistered)
        return UA_STATUSCODE_GOOD;
    UA_LOG_DEBUG_SESSION(server->config.logger, sub->session,
                         "Subscription %u | Unregister subscription "
                         "publishing callback", sub->subscriptionID);
    sub->publishCallbackIsRegistered = false;
    return UA_Server_removeRepeatedCallback(server, sub->publishCallbackId);
}

/* When the session has publish requests stored but the last subscription is
   deleted... Send out empty responses */
void
UA_Subscription_answerPublishRequestsNoSubscription(UA_Server *server,
                                                    UA_NodeId *sessionToken) {
    /* Get session */
    UA_Session *session =
        UA_SessionManager_getSession(&server->sessionManager, sessionToken);
    UA_NodeId_delete(sessionToken);

    /* No session or there are remaining subscriptions */
    if(!session || LIST_FIRST(&session->serverSubscriptions))
        return;

    /* Send a response for every queued request */
    UA_PublishResponseEntry *pre;
    while((pre = SIMPLEQ_FIRST(&session->responseQueue))) {
        SIMPLEQ_REMOVE_HEAD(&session->responseQueue, listEntry);
        UA_PublishResponse *response = &pre->response;
        response->responseHeader.serviceResult = UA_STATUSCODE_BADNOSUBSCRIPTION;
        response->responseHeader.timestamp = UA_DateTime_now();
        UA_SecureChannel_sendBinaryMessage(session->channel, pre->requestId, response,
                                           &UA_TYPES[UA_TYPES_PUBLISHRESPONSE]);
        UA_PublishResponse_deleteMembers(response);
        UA_free(pre);
    }
}

#endif /* UA_ENABLE_SUBSCRIPTIONS */