Peter M. Groen / FlashMQ

#include "mqttpacket.h"
#include <cstring>
#include <iostream>
#include <list>
#include <cassert>

#include "utils.h"

RemainingLength::RemainingLength()
{
    memset(bytes, 0, 4);
}

// constructor for parsing incoming packets
MqttPacket::MqttPacket(CirBuf &buf, size_t packet_len, size_t fixed_header_length, Client_p &sender) :
    bites(packet_len),
    fixed_header_length(fixed_header_length),
    sender(sender)
{
    assert(packet_len > 0);
    buf.read(bites.data(), packet_len);

    first_byte = bites[0];
    unsigned char _packetType = (first_byte & 0xF0) >> 4;
    packetType = (PacketType)_packetType;
    pos += fixed_header_length;
}

// This is easier than using the copy constructor publically, because then I have to keep maintaining a functioning copy constructor.
// Returning shared pointer because that's typically how we need it; we only need to copy it if we pass it around as shared resource.
std::shared_ptr<MqttPacket> MqttPacket::getCopy() const
{
    std::shared_ptr<MqttPacket> copyPacket(new MqttPacket(*this));
    copyPacket->sender.reset();
    return copyPacket;
}

// This constructor cheats and doesn't use calculateRemainingLength, because it's always the same. It allocates enough space in the vector.
MqttPacket::MqttPacket(const ConnAck &connAck) :
    bites(connAck.getLengthWithoutFixedHeader() + 2)
{
    fixed_header_length = 2;
    packetType = PacketType::CONNACK;
    char first_byte = static_cast<char>(packetType) << 4;
    writeByte(first_byte);
    writeByte(2); // length is always 2.
    writeByte(connAck.session_present & 0b00000001); // all connect-ack flags are 0, except session-present. [MQTT-3.2.2.1]
    writeByte(static_cast<char>(connAck.return_code));
}

MqttPacket::MqttPacket(const SubAck &subAck) :
    bites(subAck.getLengthWithoutFixedHeader())
{
    packetType = PacketType::SUBACK;
    first_byte = static_cast<char>(packetType) << 4;
    writeByte((subAck.packet_id & 0xFF00) >> 8);
    writeByte(subAck.packet_id & 0x00FF);

    std::vector<char> returnList;
    for (SubAckReturnCodes code : subAck.responses)
    {
        returnList.push_back(static_cast<char>(code));
    }

    writeBytes(&returnList[0], returnList.size());
    calculateRemainingLength();
}

MqttPacket::MqttPacket(const UnsubAck &unsubAck) :
    bites(unsubAck.getLengthWithoutFixedHeader())
{
    packetType = PacketType::SUBACK;
    first_byte = static_cast<char>(packetType) << 4;
    writeByte((unsubAck.packet_id & 0xFF00) >> 8);
    writeByte(unsubAck.packet_id & 0x00FF);
    calculateRemainingLength();
}

MqttPacket::MqttPacket(const Publish &publish) :
    bites(publish.getLengthWithoutFixedHeader())
{
    if (publish.topic.length() > 0xFFFF)
    {
        throw ProtocolError("Topic path too long.");
    }

    this->topic = publish.topic;

    packetType = PacketType::PUBLISH;
    this->qos = publish.qos;
    first_byte = static_cast<char>(packetType) << 4;
    first_byte |= (publish.qos << 1);
    first_byte |= (static_cast<char>(publish.retain) & 0b00000001);

    char topicLenMSB = (topic.length() & 0xFF00) >> 8;
    char topicLenLSB = topic.length() & 0x00FF;
    writeByte(topicLenMSB);
    writeByte(topicLenLSB);
    writeBytes(topic.c_str(), topic.length());

    if (publish.qos)
    {
        // Reserve the space for the packet id, which will be assigned later.
        packet_id_pos = pos;
        char zero[2];
        writeBytes(zero, 2);
    }

    writeBytes(publish.payload.c_str(), publish.payload.length());
    calculateRemainingLength();
}

// This constructor cheats and doesn't use calculateRemainingLength, because it's always the same. It allocates enough space in the vector.
MqttPacket::MqttPacket(const PubAck &pubAck) :
    bites(pubAck.getLengthWithoutFixedHeader() + 2)
{
    fixed_header_length = 2; // This is the cheat part mentioned above. We're not calculating it dynamically.
    packetType = PacketType::PUBACK;
    first_byte = static_cast<char>(packetType) << 4;
    writeByte(first_byte);
    writeByte(2); // length is always 2.
    char topicLenMSB = (pubAck.packet_id & 0xFF00) >> 8;
    char topicLenLSB = (pubAck.packet_id & 0x00FF);
    writeByte(topicLenMSB);
    writeByte(topicLenLSB);
}

void MqttPacket::handle()
{
    if (packetType == PacketType::Reserved)
        throw ProtocolError("Packet type 0 specified, which is reserved and invalid.");

    if (packetType != PacketType::CONNECT)
    {
        if (!sender->getAuthenticated())
        {
            throw ProtocolError("Non-connect packet from non-authenticated client.");
        }
    }

    if (packetType == PacketType::CONNECT)
        handleConnect();
    else if (packetType == PacketType::DISCONNECT)
        handleDisconnect();
    else if (packetType == PacketType::PINGREQ)
        sender->writePingResp();
    else if (packetType == PacketType::SUBSCRIBE)
        handleSubscribe();
    else if (packetType == PacketType::UNSUBSCRIBE)
        handleUnsubscribe();
    else if (packetType == PacketType::PUBLISH)
        handlePublish();
    else if (packetType == PacketType::PUBACK)
        handlePubAck();
}

void MqttPacket::handleConnect()
{
    if (sender->hasConnectPacketSeen())
        throw ProtocolError("Client already sent a CONNECT.");

    std::shared_ptr<SubscriptionStore> subscriptionStore = sender->getThreadData()->getSubscriptionStore();

    uint16_t variable_header_length = readTwoBytesToUInt16();

    const Settings &settings = sender->getThreadData()->settingsLocalCopy;

    if (variable_header_length == 4 || variable_header_length == 6)
    {
        char *c = readBytes(variable_header_length);
        std::string magic_marker(c, variable_header_length);

        char protocol_level = readByte();

        if (magic_marker == "MQTT" && protocol_level == 0x04)
        {
            protocolVersion = ProtocolVersion::Mqtt311;
        }
        else if (magic_marker == "MQIsdp" && protocol_level == 0x03)
        {
            protocolVersion = ProtocolVersion::Mqtt31;
        }
        else
        {
            ConnAck connAck(ConnAckReturnCodes::UnacceptableProtocolVersion);
            MqttPacket response(connAck);
            sender->setReadyForDisconnect();
            sender->writeMqttPacket(response);
            logger->logf(LOG_ERR, "Rejecting because of invalid protocol version: %s", sender->repr().c_str());
            return;
        }

        char flagByte = readByte();
        bool reserved = !!(flagByte & 0b00000001);

        if (reserved)
            throw ProtocolError("Protocol demands reserved flag in CONNECT is 0");


        bool user_name_flag = !!(flagByte & 0b10000000);
        bool password_flag = !!(flagByte & 0b01000000);
        bool will_retain = !!(flagByte & 0b00100000);
        char will_qos = (flagByte & 0b00011000) >> 3;
        bool will_flag = !!(flagByte & 0b00000100);
        bool clean_session = !!(flagByte & 0b00000010);

        if (will_qos > 2)
            throw ProtocolError("Invalid QoS for will.");

        uint16_t keep_alive = readTwoBytesToUInt16();

        uint16_t client_id_length = readTwoBytesToUInt16();
        std::string client_id(readBytes(client_id_length), client_id_length);

        std::string username = "anonymous";
        std::string password;
        std::string will_topic;
        std::string will_payload;

        if (will_flag)
        {
            uint16_t will_topic_length = readTwoBytesToUInt16();
            will_topic = std::string(readBytes(will_topic_length), will_topic_length);

            uint16_t will_payload_length = readTwoBytesToUInt16();
            will_payload = std::string(readBytes(will_payload_length), will_payload_length);
        }
        if (user_name_flag)
        {
            uint16_t user_name_length = readTwoBytesToUInt16();
            username = std::string(readBytes(user_name_length), user_name_length);

            if (username.empty())
                username = "anonymous";
        }
        if (password_flag)
        {
            uint16_t password_length = readTwoBytesToUInt16();
            password = std::string(readBytes(password_length), password_length);
        }

        // The specs don't really say what to do when client id not UTF8, so including here.
        if (!isValidUtf8(client_id) || !isValidUtf8(username) || !isValidUtf8(password) || !isValidUtf8(will_topic))
        {
            ConnAck connAck(ConnAckReturnCodes::MalformedUsernameOrPassword);
            MqttPacket response(connAck);
            sender->setReadyForDisconnect();
            sender->writeMqttPacket(response);
            logger->logf(LOG_ERR, "Client ID, username, password or will topic has invalid UTF8: ", client_id.c_str());
            return;
        }

        bool validClientId = true;

        // Check for wildcard chars in case the client_id ever appears in topics.
        if (!settings.allowUnsafeClientidChars && containsDangerousCharacters(client_id))
        {
            logger->logf(LOG_ERR, "ClientID '%s' has + or # in the id and 'allow_unsafe_clientid_chars' is false.", client_id.c_str());
            validClientId = false;
        }
        else if (!clean_session && client_id.empty())
        {
            logger->logf(LOG_ERR, "ClientID empty and clean session 0, which is incompatible");
            validClientId = false;
        }
        else if (protocolVersion < ProtocolVersion::Mqtt311 && client_id.empty())
        {
            logger->logf(LOG_ERR, "Empty clientID. Connect with protocol 3.1.1 or higher to have one generated securely.");
            validClientId = false;
        }

        if (!validClientId)
        {
            ConnAck connAck(ConnAckReturnCodes::ClientIdRejected);
            MqttPacket response(connAck);
            sender->setDisconnectReason("Invalid clientID");
            sender->setReadyForDisconnect();
            sender->writeMqttPacket(response);
            return;
        }

        if (client_id.empty())
        {
            client_id = getSecureRandomString(23);
        }

        sender->setClientProperties(protocolVersion, client_id, username, true, keep_alive, clean_session);
        sender->setWill(will_topic, will_payload, will_retain, will_qos);

        bool accessGranted = false;
        std::string denyLogMsg;

        if (!settings.allowUnsafeUsernameChars && containsDangerousCharacters(username))
        {
            denyLogMsg = formatString("Username '%s' has + or # in the id and 'allow_unsafe_username_chars' is false.", username.c_str());
            sender->setDisconnectReason("Invalid username character");
            accessGranted = false;
        }
        else if (sender->getThreadData()->authPlugin.unPwdCheck(username, password) == AuthResult::success)
        {
            accessGranted = true;
        }

        if (accessGranted)
        {
            bool sessionPresent = protocolVersion >= ProtocolVersion::Mqtt311 && !clean_session && subscriptionStore->sessionPresent(client_id);
            subscriptionStore->registerClientAndKickExistingOne(sender);

            sender->setAuthenticated(true);
            ConnAck connAck(ConnAckReturnCodes::Accepted, sessionPresent);
            MqttPacket response(connAck);
            sender->writeMqttPacket(response);
            logger->logf(LOG_NOTICE, "User '%s' logged in successfully", username.c_str());
        }
        else
        {
            ConnAck connDeny(ConnAckReturnCodes::NotAuthorized, false);
            MqttPacket response(connDeny);
            sender->setDisconnectReason("Access denied");
            sender->setReadyForDisconnect();
            sender->writeMqttPacket(response);
            if (!denyLogMsg.empty())
                logger->logf(LOG_NOTICE, denyLogMsg.c_str());
            else
                logger->logf(LOG_NOTICE, "User '%s' access denied", username.c_str());
        }
    }
    else
    {
        throw ProtocolError("Invalid variable header length. Garbage?");
    }
}

void MqttPacket::handleDisconnect()
{
    logger->logf(LOG_NOTICE, "Client '%s' cleanly disconnecting", sender->repr().c_str());
    sender->setDisconnectReason("MQTT Disconnect received.");
    sender->markAsDisconnecting();
    sender->clearWill();
    sender->getThreadData()->removeClient(sender);
}

void MqttPacket::handleSubscribe()
{
    const char firstByteFirstNibble = (first_byte & 0x0F);

    if (firstByteFirstNibble != 2)
        throw ProtocolError("First LSB of first byte is wrong value for subscribe packet.");

    uint16_t packet_id = readTwoBytesToUInt16();

    std::list<char> subs_reponse_codes;
    while (remainingAfterPos() > 0)
    {
        uint16_t topicLength = readTwoBytesToUInt16();
        std::string topic(readBytes(topicLength), topicLength);

        if (topic.empty() || !isValidUtf8(topic))
            throw ProtocolError("Subscribe topic not valid UTF-8.");

        char qos = readByte();

        if (qos > 2)
            throw ProtocolError("QoS is greater than 2, and/or reserved bytes in QoS field are not 0.");

        logger->logf(LOG_SUBSCRIBE, "Client '%s' subscribed to '%s'", sender->repr().c_str(), topic.c_str());
        sender->getThreadData()->getSubscriptionStore()->addSubscription(sender, topic, qos);
        subs_reponse_codes.push_back(qos);
    }

    SubAck subAck(packet_id, subs_reponse_codes);
    MqttPacket response(subAck);
    sender->writeMqttPacket(response);
}

void MqttPacket::handleUnsubscribe()
{
    const char firstByteFirstNibble = (first_byte & 0x0F);

    if (firstByteFirstNibble != 2)
        throw ProtocolError("First LSB of first byte is wrong value for subscribe packet.");

    uint16_t packet_id = readTwoBytesToUInt16();

    while (remainingAfterPos() > 0)
    {
        uint16_t topicLength = readTwoBytesToUInt16();
        std::string topic(readBytes(topicLength), topicLength);

        if (topic.empty() || !isValidUtf8(topic))
            throw ProtocolError("Subscribe topic not valid UTF-8.");

        sender->getThreadData()->getSubscriptionStore()->removeSubscription(sender, topic);
        logger->logf(LOG_UNSUBSCRIBE, "Client '%s' unsubscribed from '%s'", sender->repr().c_str(), topic.c_str());
    }

    UnsubAck unsubAck(packet_id);
    MqttPacket response(unsubAck);
    sender->writeMqttPacket(response);
}

void MqttPacket::handlePublish()
{
    uint16_t variable_header_length = readTwoBytesToUInt16();

    if (variable_header_length == 0)
        throw ProtocolError("Empty publish topic");

    bool retain = (first_byte & 0b00000001);
    bool dup = !!(first_byte & 0b00001000);
    char qos = (first_byte & 0b00000110) >> 1;

    if (qos == 3)
        throw ProtocolError("QoS 3 is a protocol violation.");
    this->qos = qos;

    if (qos == 0 && dup)
        throw ProtocolError("Duplicate flag is set for QoS 0 packet. This is illegal.");

    topic = std::string(readBytes(variable_header_length), variable_header_length);

    if (!isValidUtf8(topic))
    {
        logger->logf(LOG_WARNING, "Client '%s' published a message with invalid UTF8. Dropping.", sender->repr().c_str());
        return;
    }

    if (!isValidPublishPath(topic))
    {
        logger->logf(LOG_WARNING, "Client '%s' published a message with invalid publish path '%s'. Dropping.", sender->repr().c_str(), topic.c_str());
        return;
    }

    if (qos)
    {
        if (qos > 1)
            throw ProtocolError("Qos > 1 not implemented.");
        packet_id_pos = pos;
        uint16_t packet_id = readTwoBytesToUInt16();

        // Clear the packet ID from this packet, because each new publish must get a new one. It's more of a debug precaution.
        pos -= 2;
        char zero[2]; zero[0] = 0; zero[1] = 0;
        writeBytes(zero, 2);

        PubAck pubAck(packet_id);
        MqttPacket response(pubAck);
        sender->writeMqttPacket(response);
    }

    if (sender->getThreadData()->authPlugin.aclCheck(sender->getClientId(), sender->getUsername(), topic, AclAccess::write) == AuthResult::success)
    {
        if (retain)
        {
            size_t payload_length = remainingAfterPos();
            std::string payload(readBytes(payload_length), payload_length);

            sender->getThreadData()->getSubscriptionStore()->setRetainedMessage(topic, payload, qos);
        }

        // Set dup flag to 0, because that must not be propagated [MQTT-3.3.1-3].
        // Existing subscribers don't get retain=1. [MQTT-3.3.1-9]
        bites[0] &= 0b11110110;

        // For the existing clients, we can just write the same packet back out, with our small alterations.
        sender->getThreadData()->getSubscriptionStore()->queuePacketAtSubscribers(topic, *this);
    }
}

void MqttPacket::handlePubAck()
{
    uint16_t packet_id = readTwoBytesToUInt16();
    sender->getSession()->clearQosMessage(packet_id);
}

void MqttPacket::calculateRemainingLength()
{
    assert(fixed_header_length == 0); // because you're not supposed to call this on packet that we already know the length of.

    size_t x = bites.size();

    do
    {
        if (remainingLength.len > 4)
            throw std::runtime_error("Calculated remaining length is longer than 4 bytes.");

        char encodedByte = x % 128;
        x = x / 128;
        if (x > 0)
            encodedByte = encodedByte | 128;
        remainingLength.bytes[remainingLength.len++] = encodedByte;
    }
    while(x > 0);
}

RemainingLength MqttPacket::getRemainingLength() const
{
    assert(remainingLength.len > 0);
    return remainingLength;
}

void MqttPacket::setPacketId(uint16_t packet_id)
{
    assert(fixed_header_length == 0 || first_byte == bites[0]);
    assert(packet_id_pos > 0);
    assert(packetType == PacketType::PUBLISH);
    assert(qos > 0);

    pos = packet_id_pos;

    char topicLenMSB = (packet_id & 0xFF00) >> 8;
    char topicLenLSB = (packet_id & 0x00FF);
    writeByte(topicLenMSB);
    writeByte(topicLenLSB);
}

// If I read the specs correctly, the DUP flag is merely for show. It doesn't control anything?
void MqttPacket::setDuplicate()
{
    assert(packetType == PacketType::PUBLISH);
    assert(qos > 0);
    assert(fixed_header_length == 0 || first_byte == bites[0]);

    first_byte |= 0b00001000;

    if (fixed_header_length > 0)
    {
        pos = 0;
        writeByte(first_byte);
    }
}

size_t MqttPacket::getTotalMemoryFootprint()
{
    return bites.size() + sizeof(MqttPacket);
}

size_t MqttPacket::getSizeIncludingNonPresentHeader() const
{
    size_t total = bites.size();

    if (fixed_header_length == 0)
    {
        total++;
        total += remainingLength.len;
    }

    return total;
}

const std::string &MqttPacket::getTopic() const
{
    return this->topic;
}


Client_p MqttPacket::getSender() const
{
    return sender;
}

void MqttPacket::setSender(const Client_p &value)
{
    sender = value;
}

bool MqttPacket::containsFixedHeader() const
{
    return fixed_header_length > 0;
}

char MqttPacket::getFirstByte() const
{
    return first_byte;
}

char *MqttPacket::readBytes(size_t length)
{
    if (pos + length > bites.size())
        throw ProtocolError("Invalid packet: header specifies invalid length.");

    char *b = &bites[pos];
    pos += length;
    return b;
}

char MqttPacket::readByte()
{
    if (pos + 1 > bites.size())
        throw ProtocolError("Invalid packet: header specifies invalid length.");

    char b = bites[pos++];
    return b;
}

void MqttPacket::writeByte(char b)
{
    if (pos + 1 > bites.size())
        throw ProtocolError("Exceeding packet size");

    bites[pos++] = b;
}

void MqttPacket::writeBytes(const char *b, size_t len)
{
    if (pos + len > bites.size())
        throw ProtocolError("Exceeding packet size");

    memcpy(&bites[pos], b, len);
    pos += len;
}

uint16_t MqttPacket::readTwoBytesToUInt16()
{
    if (pos + 2 > bites.size())
        throw ProtocolError("Invalid packet: header specifies invalid length.");

    uint16_t i = bites[pos] << 8 | bites[pos+1];
    pos += 2;
    return i;
}

size_t MqttPacket::remainingAfterPos()
{
    return bites.size() - pos;
}