Peter M. Groen / FlashMQ

/*
This file is part of FlashMQ (https://www.flashmq.org)
Copyright (C) 2021 Wiebe Cazemier

FlashMQ is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as
published by the Free Software Foundation, version 3.

FlashMQ is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public
License along with FlashMQ. If not, see <https://www.gnu.org/licenses/>.
*/

#include "cassert"

#include "session.h"
#include "client.h"
#include "threadglobals.h"
#include "threadglobals.h"

std::chrono::time_point<std::chrono::steady_clock> appStartTime = std::chrono::steady_clock::now();

Session::Session()
{
    const Settings &settings = *ThreadGlobals::getSettings();

    // Sessions also get defaults from the handleConnect() method, but when you create sessions elsewhere, we do need some sensible defaults.
    this->maxQosMsgPending = settings.maxQosMsgPendingPerClient;
    this->sessionExpiryInterval = settings.expireSessionsAfterSeconds;
}

int64_t Session::getProgramStartedAtUnixTimestamp()
{
    auto secondsSinceEpoch = std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now().time_since_epoch()).count();
    const std::chrono::seconds age = std::chrono::duration_cast<std::chrono::seconds>(std::chrono::steady_clock::now() - appStartTime);
    int64_t result = secondsSinceEpoch - age.count();
    return result;
}

void Session::setProgramStartedAtUnixTimestamp(const int64_t unix_timestamp)
{
    auto secondsSinceEpoch = std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now().time_since_epoch());
    const std::chrono::seconds _unix_timestamp = std::chrono::seconds(unix_timestamp);
    const std::chrono::seconds age_in_s = secondsSinceEpoch - _unix_timestamp;
    appStartTime = std::chrono::steady_clock::now() - age_in_s;
}


int64_t Session::getSessionRelativeAgeInMs() const
{
    const std::chrono::milliseconds sessionAge = std::chrono::duration_cast<std::chrono::milliseconds>(lastTouched - appStartTime);
    const int64_t sInMs = sessionAge.count();
    return sInMs;
}

void Session::setSessionTouch(int64_t ageInMs)
{
    std::chrono::milliseconds ms(ageInMs);
    std::chrono::time_point<std::chrono::steady_clock> point = appStartTime + ms;
    lastTouched = point;
}

bool Session::requiresPacketRetransmission() const
{
    const std::shared_ptr<Client> client = makeSharedClient();

    if (!client)
        return true;

    // MQTT 3.1: "Brokers, however, should retry any unacknowledged message."
    // MQTT 3.1.1: "This [reconnecting] is the only circumstance where a Client or Server is REQUIRED to redeliver messages."
    if (client->getProtocolVersion() < ProtocolVersion::Mqtt311)
        return true;

    return !destroyOnDisconnect;
}

void Session::increasePacketId()
{
    nextPacketId++;
    if (nextPacketId == 0)
        nextPacketId++;
}

/**
 * @brief Session::Session copy constructor. Was created for session storing, and is explicitely kept private, to avoid making accidental copies.
 * @param other
 *
 * Because it was created for session storing, the fields we're copying are the fields being stored.
 */
Session::Session(const Session &other)
{
    // Only the QoS data is modified by worker threads (vs (locked) timed events), so it could change during copying, because
    // it gets called from a separate thread.
    std::unique_lock<std::mutex> locker(qosQueueMutex);

    this->username = other.username;
    this->client_id = other.client_id;
    this->incomingQoS2MessageIds = other.incomingQoS2MessageIds;
    this->outgoingQoS2MessageIds = other.outgoingQoS2MessageIds;
    this->nextPacketId = other.nextPacketId;
    this->lastTouched = other.lastTouched;

    // TODO: see git history for a change here. We now copy the whole queued publish. Do we want to address that?
    this->qosPacketQueue = other.qosPacketQueue;
}

Session::~Session()
{
    logger->logf(LOG_DEBUG, "Session %s is being destroyed.", getClientId().c_str());
}

std::unique_ptr<Session> Session::getCopy() const
{
    std::unique_ptr<Session> s(new Session(*this));
    return s;
}

/**
 * @brief Session::makeSharedClient get the client of the session, or a null when it has no active current client.
 * @return Returns shared_ptr<Client>, which can contain null when the client has disconnected.
 *
 * The lock() operation is atomic and therefore is the only way to get the current active client without race condition, because
 * typically, this method is called from other client's threads to perform writes, so you have to check validity after
 * obtaining the shared pointer.
 */
std::shared_ptr<Client> Session::makeSharedClient() const
{
    return client.lock();
}

void Session::assignActiveConnection(std::shared_ptr<Client> &client)
{
    this->client = client;
    this->client_id = client->getClientId();
    this->username = client->getUsername();
    this->willPublish = client->getWill();
}

/**
 * @brief Session::writePacket is the main way to give a client a packet -> it goes through the session.
 * @param packet is not const. We set the qos and packet id for each publish. This should be safe, because the packet
 *        with original packet id and qos is not saved. This saves unnecessary copying.
 * @param max_qos
 * @param retain. Keep MQTT-3.3.1-9 in mind: existing subscribers don't get retain=1 on packets.
 * @param count. Reference value is updated. It's for statistics.
 */
void Session::writePacket(PublishCopyFactory &copyFactory, const char max_qos, uint64_t &count)
{
    assert(max_qos <= 2);

    const char effectiveQos = copyFactory.getEffectiveQos(max_qos);

    const Settings *settings = ThreadGlobals::getSettings();

    Authentication *_auth = ThreadGlobals::getAuth();
    assert(_auth);
    Authentication &auth = *_auth;
    if (auth.aclCheck(client_id, username, copyFactory.getTopic(), copyFactory.getSubtopics(), AclAccess::read, effectiveQos, copyFactory.getRetain(), copyFactory.getUserProperties()) == AuthResult::success)
    {
        std::shared_ptr<Client> c = makeSharedClient();
        if (effectiveQos == 0)
        {
            if (c)
            {
                count += c->writeMqttPacketAndBlameThisClient(copyFactory, effectiveQos, 0);
            }
        }
        else if (effectiveQos > 0)
        {
            const bool requiresRetransmission = requiresPacketRetransmission();

            if (requiresRetransmission)
            {
                std::unique_lock<std::mutex> locker(qosQueueMutex);

                const size_t totalQosPacketsInTransit = qosPacketQueue.size() + incomingQoS2MessageIds.size() + outgoingQoS2MessageIds.size();
                if (totalQosPacketsInTransit >= maxQosMsgPending
                    || (qosPacketQueue.getByteSize() >= settings->maxQosBytesPendingPerClient && qosPacketQueue.size() > 0))
                {
                    if (QoSLogPrintedAtId != nextPacketId)
                    {
                        logger->logf(LOG_WARNING, "Dropping QoS message(s) for client '%s', because max in-transit packet count reached.", client_id.c_str());
                        QoSLogPrintedAtId = nextPacketId;
                    }
                    return;
                }

                increasePacketId();

                qosPacketQueue.queuePublish(copyFactory, nextPacketId, effectiveQos);

                if (c)
                {
                    count += c->writeMqttPacketAndBlameThisClient(copyFactory, effectiveQos, nextPacketId);
                }
            }
            else
            {
                // We don't need to make a copy of the packet in this branch, because:
                // - The packet to give the client won't shrink in size because source and client have a packet_id.
                // - We don't have to store the copy in the session for retransmission, see Session::requiresPacketRetransmission()
                // So, we just keep altering the original published packet.

                std::unique_lock<std::mutex> locker(qosQueueMutex);

                if (qosInFlightCounter >= 65530) // Includes a small safety margin.
                {
                    if (QoSLogPrintedAtId != nextPacketId)
                    {
                        logger->logf(LOG_WARNING, "Dropping QoS message(s) for client '%s', because it hasn't seen enough PUBACKs to release places.", client_id.c_str());
                        QoSLogPrintedAtId = nextPacketId;
                    }
                    return;
                }

                increasePacketId();

                qosInFlightCounter++;
                assert(c); // with requiresRetransmission==false, there must be a client.
                count += c->writeMqttPacketAndBlameThisClient(copyFactory, effectiveQos, nextPacketId);
            }
        }
    }
}

void Session::clearQosMessage(uint16_t packet_id)
{
#ifndef NDEBUG
    logger->logf(LOG_DEBUG, "Clearing QoS message for '%s', packet id '%d'. Left in queue: %d", client_id.c_str(), packet_id, qosPacketQueue.size());
#endif

    std::lock_guard<std::mutex> locker(qosQueueMutex);
    if (requiresPacketRetransmission())
        qosPacketQueue.erase(packet_id);
    else
    {
        qosInFlightCounter--;
        qosInFlightCounter = std::max<int>(0, qosInFlightCounter); // Should never happen, but in case we receive too many PUBACKs.
    }
}

// [MQTT-4.4.0-1]: "When a Client reconnects with CleanSession set to 0, both the Client and Server MUST re-send any
// unacknowledged PUBLISH Packets (where QoS > 0) and PUBREL Packets using their original Packet Identifiers. This
// is the only circumstance where a Client or Server is REQUIRED to redeliver messages."
//
// There is a bit of a hole there, I think. When we write out a packet to a receiver, it may decide to drop it, if its buffers
// are full, for instance. We are not required to (periodically) retry. TODO Perhaps I will implement that retry anyway.
uint64_t Session::sendPendingQosMessages()
{
    uint64_t count = 0;

    std::shared_ptr<Client> c = makeSharedClient();
    if (c)
    {
        std::lock_guard<std::mutex> locker(qosQueueMutex);
        for (const QueuedPublish &queuedPublish : qosPacketQueue)
        {
            MqttPacket p(c->getProtocolVersion(), queuedPublish.getPublish());
            p.setDuplicate();

            count += c->writeMqttPacketAndBlameThisClient(p);
        }

        for (const uint16_t packet_id : outgoingQoS2MessageIds)
        {
            PubRel pubRel(packet_id);
            MqttPacket packet(pubRel);
            count += c->writeMqttPacketAndBlameThisClient(packet);
        }
    }

    return count;
}

/**
 * @brief Session::touch with a time value allowed touching without causing another sys/lib call to get the time.
 * @param newval
 */
void Session::touch(std::chrono::time_point<std::chrono::steady_clock> newval)
{
    lastTouched = newval;
}

void Session::touch()
{
    lastTouched = std::chrono::steady_clock::now();
}

bool Session::hasExpired() const
{
    if (!client.expired())
        return false;

    std::chrono::seconds expireAfter(sessionExpiryInterval);
    std::chrono::time_point<std::chrono::steady_clock> now = std::chrono::steady_clock::now();
    return (lastTouched + expireAfter) < now;
}

void Session::clearWill()
{
    this->willPublish.reset();
}

std::shared_ptr<Publish> &Session::getWill()
{
    return this->willPublish;
}

void Session::addIncomingQoS2MessageId(uint16_t packet_id)
{
    std::unique_lock<std::mutex> locker(qosQueueMutex);
    incomingQoS2MessageIds.insert(packet_id);
}

bool Session::incomingQoS2MessageIdInTransit(uint16_t packet_id)
{
    std::unique_lock<std::mutex> locker(qosQueueMutex);
    const auto it = incomingQoS2MessageIds.find(packet_id);
    return it != incomingQoS2MessageIds.end();
}

void Session::removeIncomingQoS2MessageId(u_int16_t packet_id)
{
    std::unique_lock<std::mutex> locker(qosQueueMutex);

#ifndef NDEBUG
    logger->logf(LOG_DEBUG, "As QoS 2 receiver: publish released (PUBREL) for '%s', packet id '%d'. Left in queue: %d", client_id.c_str(), packet_id, incomingQoS2MessageIds.size());
#endif

    const auto it = incomingQoS2MessageIds.find(packet_id);
    if (it != incomingQoS2MessageIds.end())
        incomingQoS2MessageIds.erase(it);
}

void Session::addOutgoingQoS2MessageId(uint16_t packet_id)
{
    std::unique_lock<std::mutex> locker(qosQueueMutex);
    outgoingQoS2MessageIds.insert(packet_id);
}

void Session::removeOutgoingQoS2MessageId(u_int16_t packet_id)
{
    std::unique_lock<std::mutex> locker(qosQueueMutex);

#ifndef NDEBUG
    logger->logf(LOG_DEBUG, "As QoS 2 sender: publish complete (PUBCOMP) for '%s', packet id '%d'. Left in queue: %d", client_id.c_str(), packet_id, outgoingQoS2MessageIds.size());
#endif

    const auto it = outgoingQoS2MessageIds.find(packet_id);
    if (it != outgoingQoS2MessageIds.end())
        outgoingQoS2MessageIds.erase(it);
}

/**
 * @brief Session::getDestroyOnDisconnect
 * @return
 *
 * MQTT5: Setting Clean Start to 1 and a Session Expiry Interval of 0, is equivalent to setting CleanSession to 1 in the MQTT Specification Version 3.1.1.
 */
bool Session::getDestroyOnDisconnect() const
{
    return destroyOnDisconnect;
}

void Session::setSessionProperties(uint16_t maxQosPackets, uint32_t sessionExpiryInterval, bool clean_start, ProtocolVersion protocol_version)
{
    this->maxQosMsgPending = maxQosPackets;
    this->sessionExpiryInterval = sessionExpiryInterval;

    if (protocol_version <= ProtocolVersion::Mqtt311 && clean_start)
        destroyOnDisconnect = true;
    else
        destroyOnDisconnect = sessionExpiryInterval == 0;
}

uint32_t Session::getSessionExpiryInterval() const
{
    return this->sessionExpiryInterval;
}