// Copyright (C) 2011-2025 Internet Systems Consortium, Inc. ("ISC")
//
// 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 <config.h>
#include <kea_version.h>

#include <asiolink/addr_utilities.h>
#include <asiolink/io_address.h>
#include <asiolink/io_service.h>
#include <asiolink/io_service_mgr.h>
#include <cc/data.h>
#include <config/http_command_mgr.h>
#include <cryptolink/cryptolink.h>
#include <dhcp/classify.h>
#include <dhcp/dhcp4.h>
#include <dhcp/docsis3_option_defs.h>
#include <dhcp/duid.h>
#include <dhcp/hwaddr.h>
#include <dhcp/iface_mgr.h>
#include <dhcp/libdhcp++.h>
#include <dhcp/option.h>
#include <dhcp/option4_addrlst.h>
#include <dhcp/option4_client_fqdn.h>
#include <dhcp/option_custom.h>
#include <dhcp/option_data_types.h>
#include <dhcp/option_definition.h>
#include <dhcp/option_int.h>
#include <dhcp/option_int_array.h>
#include <dhcp/option_string.h>
#include <dhcp/option_vendor.h>
#include <dhcp/option_vendor_class.h>
#include <dhcp/pkt.h>
#include <dhcp/pkt4.h>
#include <dhcp/pkt4o6.h>
#include <dhcp/socket_info.h>
#include <dhcp/std_option_defs.h>
#include <dhcp4/client_handler.h>
#include <dhcp4/dhcp4_log.h>
#include <dhcp4/dhcp4_srv.h>
#include <dhcp4/dhcp4to6_ipc.h>
#include <dhcp_ddns/ncr_io.h>
#include <dhcp_ddns/ncr_msg.h>
#include <dhcpsrv/alloc_engine.h>
#include <dhcpsrv/legal_log_mgr_factory.h>
#include <dhcpsrv/callout_handle_store.h>
#include <dhcpsrv/cb_ctl_dhcp4.h>
#include <dhcpsrv/cfg_expiration.h>
#include <dhcpsrv/cfg_globals.h>
#include <dhcpsrv/cfg_host_operations.h>
#include <dhcpsrv/cfg_iface.h>
#include <dhcpsrv/cfg_option.h>
#include <dhcpsrv/cfg_shared_networks.h>
#include <dhcpsrv/cfg_subnets4.h>
#include <dhcpsrv/cfgmgr.h>
#include <dhcpsrv/client_class_def.h>
#include <dhcpsrv/d2_client_cfg.h>
#include <dhcpsrv/d2_client_mgr.h>
#include <dhcpsrv/dhcpsrv_exceptions.h>
#include <dhcpsrv/host.h>
#include <dhcpsrv/host_data_source_factory.h>
#include <dhcpsrv/host_mgr.h>
#include <dhcpsrv/lease.h>
#include <dhcpsrv/lease_mgr_factory.h>
#include <dhcpsrv/ncr_generator.h>
#include <dhcpsrv/network_state.h>
#include <dhcpsrv/packet_fuzzer.h>
#include <dhcpsrv/pool.h>
#include <dhcpsrv/resource_handler.h>
#include <dhcpsrv/shared_network.h>
#include <dhcpsrv/srv_config.h>
#include <dhcpsrv/subnet.h>
#include <dhcpsrv/subnet_id.h>
#include <dhcpsrv/subnet_selector.h>
#include <dhcpsrv/utils.h>
#include <eval/evaluate.h>
#include <eval/token.h>
#include <exceptions/exceptions.h>
#include <hooks/callout_handle.h>
#include <hooks/hooks_log.h>
#include <hooks/hooks_manager.h>
#include <hooks/parking_lots.h>
#include <hooks/server_hooks.h>
#include <log/interprocess/interprocess_sync_file.h>
#include <log/log_dbglevels.h>
#include <log/log_formatter.h>
#include <log/logger.h>
#include <log/macros.h>
#include <stats/stats_mgr.h>
#include <util/multi_threading_mgr.h>
#include <util/optional.h>
#include <util/readwrite_mutex.h>
#include <util/thread_pool.h>
#include <util/triplet.h>

#include <algorithm>
#include <cmath>
#include <cstdint>
#include <cstdlib>
#include <exception>
#include <functional>
#include <list>
#include <map>
#include <memory>
#include <set>
#include <sstream>
#include <string>
#include <tuple>
#include <utility>
#include <vector>

#include <boost/foreach.hpp>
#include <boost/pointer_cast.hpp>
#include <boost/range/adaptor/reversed.hpp>
#include <boost/shared_ptr.hpp>

using namespace isc;
using namespace isc::asiolink;
using namespace isc::cryptolink;
using namespace isc::data;
using namespace isc::dhcp;
using namespace isc::dhcp_ddns;
using namespace isc::hooks;
using namespace isc::log;
using namespace isc::log::interprocess;
using namespace isc::stats;
using namespace isc::util;
using namespace std;
namespace ph = std::placeholders;

namespace {

/// Structure that holds registered hook indexes
struct Dhcp4Hooks {
    int hook_index_buffer4_receive_;        ///< index for "buffer4_receive" hook point
    int hook_index_pkt4_receive_;           ///< index for "pkt4_receive" hook point
    int hook_index_subnet4_select_;         ///< index for "subnet4_select" hook point
    int hook_index_leases4_committed_;      ///< index for "leases4_committed" hook point
    int hook_index_lease4_release_;         ///< index for "lease4_release" hook point
    int hook_index_pkt4_send_;              ///< index for "pkt4_send" hook point
    int hook_index_buffer4_send_;           ///< index for "buffer4_send" hook point
    int hook_index_lease4_decline_;         ///< index for "lease4_decline" hook point
    int hook_index_host4_identifier_;       ///< index for "host4_identifier" hook point
    int hook_index_ddns4_update_;           ///< index for "ddns4_update" hook point
    int hook_index_lease4_offer_;           ///< index for "lease4_offer" hook point
    int hook_index_lease4_server_decline_;  ///< index for "lease4_server_decline" hook point

    /// Constructor that registers hook points for DHCPv4 engine
    Dhcp4Hooks() {
        hook_index_buffer4_receive_         = HooksManager::registerHook("buffer4_receive");
        hook_index_pkt4_receive_            = HooksManager::registerHook("pkt4_receive");
        hook_index_subnet4_select_          = HooksManager::registerHook("subnet4_select");
        hook_index_leases4_committed_       = HooksManager::registerHook("leases4_committed");
        hook_index_lease4_release_          = HooksManager::registerHook("lease4_release");
        hook_index_pkt4_send_               = HooksManager::registerHook("pkt4_send");
        hook_index_buffer4_send_            = HooksManager::registerHook("buffer4_send");
        hook_index_lease4_decline_          = HooksManager::registerHook("lease4_decline");
        hook_index_host4_identifier_        = HooksManager::registerHook("host4_identifier");
        hook_index_ddns4_update_            = HooksManager::registerHook("ddns4_update");
        hook_index_lease4_offer_            = HooksManager::registerHook("lease4_offer");
        hook_index_lease4_server_decline_   = HooksManager::registerHook("lease4_server_decline");
    }
};

/// List of statistics which is initialized to 0 during the DHCPv4
/// server startup.
std::set<std::string> dhcp4_statistics = {
    "pkt4-received",
    "pkt4-discover-received",
    "pkt4-offer-received",
    "pkt4-request-received",
    "pkt4-ack-received",
    "pkt4-nak-received",
    "pkt4-release-received",
    "pkt4-decline-received",
    "pkt4-inform-received",
    "pkt4-unknown-received",
    "pkt4-sent",
    "pkt4-offer-sent",
    "pkt4-ack-sent",
    "pkt4-nak-sent",
    "pkt4-service-disabled",
    "pkt4-parse-failed",
    "pkt4-receive-drop",
    "v4-allocation-fail",
    "v4-allocation-fail-shared-network",
    "v4-allocation-fail-subnet",
    "v4-allocation-fail-no-pools",
    "v4-allocation-fail-classes",
    "v4-reservation-conflicts",
    "v4-lease-reuses",
};

} // end of anonymous namespace

// Declare a Hooks object. As this is outside any function or method, it
// will be instantiated (and the constructor run) when the module is loaded.
// As a result, the hook indexes will be defined before any method in this
// module is called.
Dhcp4Hooks Hooks;

namespace isc {
namespace dhcp {

Dhcpv4Exchange::Dhcpv4Exchange(const AllocEnginePtr& alloc_engine,
                               const Pkt4Ptr& query,
                               AllocEngine::ClientContext4Ptr& context,
                               const ConstSubnet4Ptr& subnet,
                               bool& drop)
    : alloc_engine_(alloc_engine), query_(query), resp_(),
      context_(context), ipv6_only_preferred_(false) {

    if (!alloc_engine_) {
        isc_throw(BadValue, "alloc_engine value must not be NULL"
                  " when creating an instance of the Dhcpv4Exchange");
    }

    if (!query_) {
        isc_throw(BadValue, "query value must not be NULL when"
                  " creating an instance of the Dhcpv4Exchange");
    }

    // Reset the given context argument.
    context.reset();

    // Create response message.
    initResponse();
    // Select subnet for the query message.
    context_->subnet_ = subnet;

    // If subnet found, retrieve client identifier which will be needed
    // for allocations and search for reservations associated with a
    // subnet/shared network.
    SharedNetwork4Ptr sn;
    if (subnet && !context_->early_global_reservations_lookup_) {
        OptionPtr opt_clientid = query->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
        if (opt_clientid) {
            context_->clientid_.reset(new ClientId(opt_clientid->getData()));
        }
    }

    if (subnet) {
        // Find static reservations if not disabled for our subnet.
        if (subnet->getReservationsInSubnet() ||
            subnet->getReservationsGlobal()) {
            // Before we can check for static reservations, we need to prepare a set
            // of identifiers to be used for this.
            if (!context_->early_global_reservations_lookup_) {
                setHostIdentifiers(context_);
            }

            // Check for static reservations.
            alloc_engine->findReservation(*context_);

            // Get shared network to see if it is set for a subnet.
            subnet->getSharedNetwork(sn);
        }
    }

    // Global host reservations are independent of a selected subnet. If the
    // global reservations contain client classes we should use them in case
    // they are meant to affect pool selection. Also, if the subnet does not
    // belong to a shared network we can use the reserved client classes
    // because there is no way our subnet could change. Such classes may
    // affect selection of a pool within the selected subnet.
    auto global_host = context_->globalHost();
    auto current_host = context_->currentHost();
    if ((!context_->early_global_reservations_lookup_ &&
         global_host && !global_host->getClientClasses4().empty()) ||
        (!sn && current_host && !current_host->getClientClasses4().empty())) {
        // We have already evaluated client classes and some of them may
        // be in conflict with the reserved classes. Suppose there are
        // two classes defined in the server configuration: first_class
        // and second_class and the test for the second_class it looks
        // like this: "not member('first_class')". If the first_class
        // initially evaluates to false, the second_class evaluates to
        // true. If the first_class is now set within the hosts reservations
        // and we don't remove the previously evaluated second_class we'd
        // end up with both first_class and second_class evaluated to
        // true. In order to avoid that, we have to remove the classes
        // evaluated in the first pass and evaluate them again. As
        // a result, the first_class set via the host reservation will
        // replace the second_class because the second_class will this
        // time evaluate to false as desired.
        removeDependentEvaluatedClasses(query);
        setReservedClientClasses(context_);
        evaluateClasses(query, false);
    }

    // Set KNOWN builtin class if something was found, UNKNOWN if not.
    if (!context_->hosts_.empty()) {
        query->addClass("KNOWN");
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_ASSIGNED)
            .arg(query->getLabel())
            .arg("KNOWN");
    } else {
        query->addClass("UNKNOWN");
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_ASSIGNED)
            .arg(query->getLabel())
            .arg("UNKNOWN");
    }

    // Perform second pass of classification.
    evaluateClasses(query, true);

    const ClientClasses& classes = query_->getClasses();
    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASSES_ASSIGNED_AFTER_SUBNET_SELECTION)
        .arg(query_->getLabel())
        .arg(classes.toText());

    // Check the DROP special class.
    if (query_->inClass("DROP")) {
        LOG_DEBUG(packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0013)
            .arg(query_->getHWAddrLabel())
            .arg(query_->toText());
        isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                  static_cast<int64_t>(1));
        drop = true;
    }
}

void
Dhcpv4Exchange::initResponse() {
    uint8_t resp_type = 0;
    switch (getQuery()->getType()) {
    case DHCPDISCOVER:
        resp_type = DHCPOFFER;
        break;
    case DHCPREQUEST:
    case DHCPINFORM:
        resp_type = DHCPACK;
        break;
    default:
        ;
    }
    // Only create a response if one is required.
    if (resp_type > 0) {
        resp_.reset(new Pkt4(resp_type, getQuery()->getTransid()));
        copyDefaultFields();
        copyDefaultOptions();

        if (getQuery()->isDhcp4o6()) {
            initResponse4o6();
        }
    }
}

void
Dhcpv4Exchange::initResponse4o6() {
    Pkt4o6Ptr query = boost::dynamic_pointer_cast<Pkt4o6>(getQuery());
    if (!query) {
        return;
    }
    const Pkt6Ptr& query6 = query->getPkt6();
    Pkt6Ptr resp6(new Pkt6(DHCPV6_DHCPV4_RESPONSE, query6->getTransid()));
    // Don't add client-id or server-id
    // But copy relay info
    if (!query6->relay_info_.empty()) {
        resp6->copyRelayInfo(query6);
    }
    // Copy interface, and remote address and port
    resp6->setIface(query6->getIface());
    resp6->setIndex(query6->getIndex());
    resp6->setRemoteAddr(query6->getRemoteAddr());
    resp6->setRemotePort(query6->getRemotePort());
    resp_.reset(new Pkt4o6(resp_, resp6));
}

void
Dhcpv4Exchange::copyDefaultFields() {
    resp_->setIface(query_->getIface());
    resp_->setIndex(query_->getIndex());

    // explicitly set this to 0
    resp_->setSiaddr(IOAddress::IPV4_ZERO_ADDRESS());
    // ciaddr is always 0, except for the Renew/Rebind state and for
    // Inform when it may be set to the ciaddr sent by the client.
    if (query_->getType() == DHCPINFORM) {
        resp_->setCiaddr(query_->getCiaddr());
    } else {
        resp_->setCiaddr(IOAddress::IPV4_ZERO_ADDRESS());
    }
    resp_->setHops(query_->getHops());

    // copy MAC address
    resp_->setHWAddr(query_->getHWAddr());

    // relay address
    resp_->setGiaddr(query_->getGiaddr());

    // If src/dest HW addresses are used by the packet filtering class
    // we need to copy them as well. There is a need to check that the
    // address being set is not-NULL because an attempt to set the NULL
    // HW would result in exception. If these values are not set, the
    // the default HW addresses (zeroed) should be generated by the
    // packet filtering class when creating Ethernet header for
    // outgoing packet.
    HWAddrPtr src_hw_addr = query_->getLocalHWAddr();
    if (src_hw_addr) {
        resp_->setLocalHWAddr(src_hw_addr);
    }
    HWAddrPtr dst_hw_addr = query_->getRemoteHWAddr();
    if (dst_hw_addr) {
        resp_->setRemoteHWAddr(dst_hw_addr);
    }

    // Copy flags from the request to the response per RFC 2131
    resp_->setFlags(query_->getFlags());
}

void
Dhcpv4Exchange::copyDefaultOptions() {
    // Let's copy client-id to response. See RFC6842.
    // It is possible to disable RFC6842 to keep backward compatibility
    bool echo = CfgMgr::instance().getCurrentCfg()->getEchoClientId();
    OptionPtr client_id = query_->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (client_id && echo) {
        resp_->addOption(client_id);
    }

    // RFC 3011 states about the Subnet Selection Option

    // "Servers configured to support this option MUST return an
    //  identical copy of the option to any client that sends it,
    //  regardless of whether or not the client requests the option in
    //  a parameter request list. Clients using this option MUST
    //  discard DHCPOFFER or DHCPACK packets that do not contain this
    //  option."
    OptionPtr subnet_sel = query_->getOption(DHO_SUBNET_SELECTION);
    if (subnet_sel) {
        resp_->addOption(subnet_sel);
    }

    // If this packet is relayed, we want to copy Relay Agent Info option
    // when it is not empty.
    OptionPtr rai = query_->getOption(DHO_DHCP_AGENT_OPTIONS);
    if (!rai || (rai->len() <= Option::OPTION4_HDR_LEN)) {
        return;
    }
    // Do not copy recovered stashed RAI.
    ConstElementPtr sao = CfgMgr::instance().getCurrentCfg()->
        getConfiguredGlobal(CfgGlobals::STASH_AGENT_OPTIONS);
    if (sao && (sao->getType() == Element::boolean) &&
        sao->boolValue() && query_->inClass("STASH_AGENT_OPTIONS")) {
        return;
    }
    resp_->addOption(rai);
}

void
Dhcpv4Exchange::setHostIdentifiers(AllocEngine::ClientContext4Ptr context) {
    const ConstCfgHostOperationsPtr cfg =
        CfgMgr::instance().getCurrentCfg()->getCfgHostOperations4();

    // Collect host identifiers. The identifiers are stored in order of preference.
    // The server will use them in that order to search for host reservations.
    for (auto const& id_type : cfg->getIdentifierTypes()) {
        switch (id_type) {
        case Host::IDENT_HWADDR:
            if (context->hwaddr_ && !context->hwaddr_->hwaddr_.empty()) {
                context->addHostIdentifier(id_type, context->hwaddr_->hwaddr_);
            }
            break;

        case Host::IDENT_DUID:
            if (context->clientid_) {
                const std::vector<uint8_t>& vec = context->clientid_->getClientId();
                if (!vec.empty()) {
                    // Client identifier type = DUID? Client identifier holding a DUID
                    // comprises Type (1 byte), IAID (4 bytes), followed by the actual
                    // DUID. Thus, the minimal length is 6.
                    if ((vec[0] == CLIENT_ID_OPTION_TYPE_DUID) && (vec.size() > 5)) {
                        // Extract DUID, skip IAID.
                        context->addHostIdentifier(id_type,
                                                   std::vector<uint8_t>(vec.begin() + 5,
                                                                        vec.end()));
                    }
                }
            }
            break;

        case Host::IDENT_CIRCUIT_ID:
            {
                OptionPtr rai = context->query_->getOption(DHO_DHCP_AGENT_OPTIONS);
                if (rai) {
                    OptionPtr circuit_id_opt = rai->getOption(RAI_OPTION_AGENT_CIRCUIT_ID);
                    if (circuit_id_opt) {
                        const OptionBuffer& circuit_id_vec = circuit_id_opt->getData();
                        if (!circuit_id_vec.empty()) {
                            context->addHostIdentifier(id_type, circuit_id_vec);
                        }
                    }
                }
            }
            break;

        case Host::IDENT_CLIENT_ID:
            if (context->clientid_) {
                const std::vector<uint8_t>& vec = context->clientid_->getClientId();
                if (!vec.empty()) {
                    context->addHostIdentifier(id_type, vec);
                }
            }
            break;
        case Host::IDENT_FLEX:
            {
                if (!HooksManager::calloutsPresent(Hooks.hook_index_host4_identifier_)) {
                    break;
                }

                CalloutHandlePtr callout_handle = getCalloutHandle(context->query_);

                Host::IdentifierType type = Host::IDENT_FLEX;
                std::vector<uint8_t> id;

                // Use the RAII wrapper to make sure that the callout handle state is
                // reset when this object goes out of scope. All hook points must do
                // it to prevent possible circular dependency between the callout
                // handle and its arguments.
                ScopedCalloutHandleState callout_handle_state(callout_handle);

                // Pass incoming packet as argument
                callout_handle->setArgument("query4", context->query_);
                callout_handle->setArgument("id_type", type);
                callout_handle->setArgument("id_value", id);

                // Call callouts
                HooksManager::callCallouts(Hooks.hook_index_host4_identifier_,
                                           *callout_handle);

                callout_handle->getArgument("id_type", type);
                callout_handle->getArgument("id_value", id);

                if ((callout_handle->getStatus() == CalloutHandle::NEXT_STEP_CONTINUE) &&
                    !id.empty()) {

                    LOG_DEBUG(packet4_logger, DBGLVL_TRACE_BASIC, DHCP4_FLEX_ID)
                        .arg(context->query_->getLabel())
                        .arg(Host::getIdentifierAsText(type, &id[0], id.size()));

                    context->addHostIdentifier(type, id);
                }
                break;
            }
        default:
            ;
        }
    }
}

void
Dhcpv4Exchange::removeDependentEvaluatedClasses(const Pkt4Ptr& query) {
    const ClientClassDictionaryPtr& dict =
        CfgMgr::instance().getCurrentCfg()->getClientClassDictionary();
    const ClientClassDefListPtr& defs_ptr = dict->getClasses();
    for (auto const& def : *defs_ptr) {
        // Only remove evaluated classes. Other classes can be
        // assigned via hooks libraries and we should not remove
        // them because there is no way they can be added back.
        if (def->getMatchExpr()) {
            query->classes_.erase(def->getName());
        }
    }
}

void
Dhcpv4Exchange::setReservedClientClasses(AllocEngine::ClientContext4Ptr context) {
    if (context->currentHost() && context->query_) {
        const ClientClasses& classes = context->currentHost()->getClientClasses4();
        for (auto const& cclass : classes) {
            context->query_->addClass(cclass);
        }
    }
}

void
Dhcpv4Exchange::conditionallySetReservedClientClasses() {
    if (context_->subnet_) {
        SharedNetwork4Ptr shared_network;
        context_->subnet_->getSharedNetwork(shared_network);
        if (shared_network) {
            ConstHostPtr host = context_->currentHost();
            if (host && (host->getIPv4SubnetID() != SUBNET_ID_GLOBAL)) {
                setReservedClientClasses(context_);
            }
        }
    }
}

void
Dhcpv4Exchange::setReservedMessageFields() {
    ConstHostPtr host = context_->currentHost();
    // Nothing to do if host reservations not specified for this client.
    if (host) {
        if (!host->getNextServer().isV4Zero()) {
            resp_->setSiaddr(host->getNextServer());
        }

        std::string sname = host->getServerHostname();
        if (!sname.empty()) {
            resp_->setSname(reinterpret_cast<const uint8_t*>(sname.c_str()),
                            sname.size());
        }

        std::string bootfile = host->getBootFileName();
        if (!bootfile.empty()) {
            resp_->setFile(reinterpret_cast<const uint8_t*>(bootfile.c_str()),
                           bootfile.size());
        }
    }
}

void Dhcpv4Exchange::classifyByVendor(const Pkt4Ptr& pkt) {
    // Built-in vendor class processing
    boost::shared_ptr<OptionString> vendor_class =
        boost::dynamic_pointer_cast<OptionString>(pkt->getOption(DHO_VENDOR_CLASS_IDENTIFIER));

    if (!vendor_class) {
        return;
    }

    pkt->addClass(Dhcpv4Srv::VENDOR_CLASS_PREFIX + vendor_class->getValue());
}

void Dhcpv4Exchange::classifyPacket(const Pkt4Ptr& pkt) {
    // All packets belong to ALL.
    pkt->addClass("ALL");

    // First: built-in vendor class processing.
    classifyByVendor(pkt);

    // Run match expressions on classes not depending on KNOWN/UNKNOWN.
    evaluateClasses(pkt, false);
}

void Dhcpv4Exchange::evaluateClasses(const Pkt4Ptr& pkt, bool depend_on_known) {
    // Note getClientClassDictionary() cannot be null
    const ClientClassDictionaryPtr& dict =
        CfgMgr::instance().getCurrentCfg()->getClientClassDictionary();
    const ClientClassDefListPtr& defs_ptr = dict->getClasses();
    for (auto const& it : *defs_ptr) {
        // Note second cannot be null
        const ExpressionPtr& expr_ptr = it->getMatchExpr();
        // Nothing to do without an expression to evaluate
        if (!expr_ptr) {
            continue;
        }
        // Not the right time if only when additional
        if (it->getAdditional()) {
            continue;
        }
        // Not the right pass.
        if (it->getDependOnKnown() != depend_on_known) {
            continue;
        }
        it->test(pkt, expr_ptr);
    }
}

const std::string Dhcpv4Srv::VENDOR_CLASS_PREFIX("VENDOR_CLASS_");

Dhcpv4Srv::Dhcpv4Srv(uint16_t server_port, uint16_t client_port,
                     const bool use_bcast, const bool direct_response_desired)
    : io_service_(new IOService()), server_port_(server_port),
      client_port_(client_port), shutdown_(true),
      alloc_engine_(), use_bcast_(use_bcast),
      network_state_(new NetworkState()),
      cb_control_(new CBControlDHCPv4()),
      test_send_responses_to_source_(false) {

    const char* env = std::getenv("KEA_TEST_SEND_RESPONSES_TO_SOURCE");
    if (env) {
        LOG_WARN(dhcp4_logger, DHCP4_TESTING_MODE_SEND_TO_SOURCE_ENABLED);
        test_send_responses_to_source_ = true;
    }

    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_START, DHCP4_OPEN_SOCKET)
        .arg(server_port);

    try {
        // Port 0 is used for testing purposes where we don't open broadcast
        // capable sockets. So, set the packet filter handling direct traffic
        // only if we are in non-test mode.
        if (server_port) {
            // First call to instance() will create IfaceMgr (it's a singleton)
            // it may throw something if things go wrong.
            // The 'true' value of the call to setMatchingPacketFilter imposes
            // that IfaceMgr will try to use the mechanism to respond directly
            // to the client which doesn't have address assigned. This capability
            // may be lacking on some OSes, so there is no guarantee that server
            // will be able to respond directly.
            IfaceMgr::instance().setMatchingPacketFilter(direct_response_desired);
        }

        // Instantiate allocation engine. The number of allocation attempts equal
        // to zero indicates that the allocation engine will use the number of
        // attempts depending on the pool size.
        alloc_engine_.reset(new AllocEngine(0));

        /// @todo call loadLibraries() when handling configuration changes

    } catch (const std::exception &e) {
        LOG_ERROR(dhcp4_logger, DHCP4_SRV_CONSTRUCT_ERROR).arg(e.what());
        return;
    }

    // Initializing all observations with default value
    setPacketStatisticsDefaults();

    // All done, so can proceed
    shutdown_ = false;
}

void Dhcpv4Srv::setPacketStatisticsDefaults() {
    isc::stats::StatsMgr& stats_mgr = isc::stats::StatsMgr::instance();

    // Iterate over set of observed statistics
    for (auto const& it : dhcp4_statistics) {
        // Initialize them with default value 0
        stats_mgr.setValue(it, static_cast<int64_t>(0));
    }
}

Dhcpv4Srv::~Dhcpv4Srv() {
    // Discard any parked packets
    discardPackets();

    try {
        stopD2();
    } catch (const std::exception& ex) {
        // Highly unlikely, but lets Report it but go on
        LOG_ERROR(dhcp4_logger, DHCP4_SRV_D2STOP_ERROR).arg(ex.what());
    }

    try {
        Dhcp4to6Ipc::instance().close();
    } catch (const std::exception& ex) {
        // Highly unlikely, but lets Report it but go on
        LOG_ERROR(dhcp4_logger, DHCP4_SRV_DHCP4O6_ERROR).arg(ex.what());
    }

    IfaceMgr::instance().closeSockets();

    // The lease manager was instantiated during DHCPv4Srv configuration,
    // so we should clean up after ourselves.
    LeaseMgrFactory::destroy();

    // Destroy the host manager before hooks unload.
    HostMgr::create();

    // Explicitly unload hooks
    HooksManager::prepareUnloadLibraries();
    if (!HooksManager::unloadLibraries()) {
        auto names = HooksManager::getLibraryNames();
        std::string msg;
        if (!names.empty()) {
            msg = names[0];
            for (size_t i = 1; i < names.size(); ++i) {
                msg += std::string(", ") + names[i];
            }
        }
        LOG_ERROR(dhcp4_logger, DHCP4_SRV_UNLOAD_LIBRARIES_ERROR).arg(msg);
    }
    IOServiceMgr::instance().clearIOServices();
    io_service_->stopAndPoll();
}

void
Dhcpv4Srv::shutdown() {
    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_SHUTDOWN_REQUEST);
    shutdown_ = true;
}

isc::dhcp::ConstSubnet4Ptr
Dhcpv4Srv::selectSubnet(const Pkt4Ptr& query, bool& drop, bool allow_answer_park) {
    // DHCPv4-over-DHCPv6 is a special (and complex) case
    if (query->isDhcp4o6()) {
        return (selectSubnet4o6(query, drop, allow_answer_park));
    }

    ConstSubnet4Ptr subnet;

    const SubnetSelector& selector = CfgSubnets4::initSelector(query);

    CfgMgr& cfgmgr = CfgMgr::instance();
    subnet = cfgmgr.getCurrentCfg()->getCfgSubnets4()->selectSubnet(selector);

    // Let's execute all callouts registered for subnet4_select
    // (skip callouts if the selectSubnet was called to do sanity checks only)
    if (HooksManager::calloutsPresent(Hooks.hook_index_subnet4_select_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        shared_ptr<ScopedCalloutHandleState> callout_handle_state(
            std::make_shared<ScopedCalloutHandleState>(callout_handle));

        // Enable copying options from the packet within hook library.
        ScopedEnableOptionsCopy<Pkt4> query4_options_copy(query);

        // Set new arguments
        callout_handle->setArgument("query4", query);
        callout_handle->setArgument("subnet4", subnet);
        callout_handle->setArgument("subnet4collection",
                                    cfgmgr.getCurrentCfg()->
                                    getCfgSubnets4()->getAll());

        auto const tpl(parkingLimitExceeded("subnet4_select"));
        bool const exceeded(get<0>(tpl));
        if (exceeded) {
            uint32_t const limit(get<1>(tpl));
            // We can't park it so we're going to throw it on the floor.
            LOG_DEBUG(packet4_logger, DBGLVL_PKT_HANDLING,
                      DHCP4_HOOK_SUBNET4_SELECT_PARKING_LOT_FULL)
                .arg(limit)
                .arg(query->getLabel());
            return (ConstSubnet4Ptr());
        }

        // We proactively park the packet.
        HooksManager::park(
            "subnet4_select", query, [this, query, allow_answer_park, callout_handle_state]() {
                if (MultiThreadingMgr::instance().getMode()) {
                    boost::shared_ptr<function<void()>> callback(
                        boost::make_shared<function<void()>>(
                            [this, query, allow_answer_park]() mutable {
                                processLocalizedQuery4AndSendResponse(query, allow_answer_park);
                            }));
                    callout_handle_state->on_completion_ = [callback]() {
                        MultiThreadingMgr::instance().getThreadPool().add(callback);
                    };
                } else {
                    processLocalizedQuery4AndSendResponse(query, allow_answer_park);
                }
            });

        // Call user (and server-side) callouts
        try {
            HooksManager::callCallouts(Hooks.hook_index_subnet4_select_,
                                       *callout_handle);
        } catch (...) {
            // Make sure we don't orphan a parked packet.
            HooksManager::drop("subnet4_select", query);
            throw;
        }

        // Callouts parked the packet. Same as drop but callouts will resume
        // processing or drop the packet later.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_PARK) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_PARK)
                .arg(query->getLabel());
            drop = true;
            return (ConstSubnet4Ptr());
        } else {
            HooksManager::drop("subnet4_select", query);
        }

        // Callouts decided to skip this step. This means that no subnet
        // will be selected. Packet processing will continue, but it will
        // be severely limited (i.e. only global options will be assigned)
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_SKIP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_SKIP)
                .arg(query->getLabel());
            return (ConstSubnet4Ptr());
        }

        // Callouts decided to drop the packet. It is a superset of the
        // skip case so no subnet will be selected.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_DROP)
                .arg(query->getLabel());
            drop = true;
            return (ConstSubnet4Ptr());
        }

        // Use whatever subnet was specified by the callout
        callout_handle->getArgument("subnet4", subnet);
    }

    if (subnet) {
        // Log at higher debug level that subnet has been found.
        LOG_DEBUG(packet4_logger, DBG_DHCP4_BASIC_DATA, DHCP4_SUBNET_SELECTED)
            .arg(query->getLabel())
            .arg(subnet->getID());
        // Log detailed information about the selected subnet at the
        // lower debug level.
        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_SUBNET_DATA)
            .arg(query->getLabel())
            .arg(subnet->toText());

    } else {
        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL,
                  DHCP4_SUBNET_SELECTION_FAILED)
            .arg(query->getLabel());
    }

    return (subnet);
}

isc::dhcp::ConstSubnet4Ptr
Dhcpv4Srv::selectSubnet4o6(const Pkt4Ptr& query, bool& drop,
                           bool allow_answer_park) {
    ConstSubnet4Ptr subnet;

    SubnetSelector selector;
    selector.ciaddr_ = query->getCiaddr();
    selector.giaddr_ = query->getGiaddr();
    selector.local_address_ = query->getLocalAddr();
    selector.client_classes_ = query->classes_;
    selector.iface_name_ = query->getIface();
    // Mark it as DHCPv4-over-DHCPv6
    selector.dhcp4o6_ = true;
    // Now the DHCPv6 part
    selector.remote_address_ = query->getRemoteAddr();
    selector.first_relay_linkaddr_ = IOAddress("::");

    // Handle a DHCPv6 relayed query
    Pkt4o6Ptr query4o6 = boost::dynamic_pointer_cast<Pkt4o6>(query);
    if (!query4o6) {
        isc_throw(Unexpected, "Can't get DHCP4o6 message");
    }
    const Pkt6Ptr& query6 = query4o6->getPkt6();

    // Initialize fields specific to relayed messages.
    if (query6 && !query6->relay_info_.empty()) {
        for (auto const& relay : boost::adaptors::reverse(query6->relay_info_)) {
            if (!relay.linkaddr_.isV6Zero() &&
                !relay.linkaddr_.isV6LinkLocal()) {
                selector.first_relay_linkaddr_ = relay.linkaddr_;
                break;
            }
        }
        selector.interface_id_ =
            query6->getAnyRelayOption(D6O_INTERFACE_ID,
                                      Pkt6::RELAY_GET_FIRST);
    }

    // If the Subnet Selection option is present, extract its value.
    OptionPtr sbnsel = query->getOption(DHO_SUBNET_SELECTION);
    if (sbnsel) {
        OptionCustomPtr oc = boost::dynamic_pointer_cast<OptionCustom>(sbnsel);
        if (oc) {
            selector.option_select_ = oc->readAddress();
        }
    }

    CfgMgr& cfgmgr = CfgMgr::instance();
    subnet = cfgmgr.getCurrentCfg()->getCfgSubnets4()->selectSubnet4o6(selector);

    // Let's execute all callouts registered for subnet4_select.
    // (skip callouts if the selectSubnet was called to do sanity checks only)
    if (HooksManager::calloutsPresent(Hooks.hook_index_subnet4_select_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        shared_ptr<ScopedCalloutHandleState> callout_handle_state(
            std::make_shared<ScopedCalloutHandleState>(callout_handle));

        // Enable copying options from the packet within hook library.
        ScopedEnableOptionsCopy<Pkt4> query4_options_copy(query);

        // Set new arguments
        callout_handle->setArgument("query4", query);
        callout_handle->setArgument("subnet4", subnet);
        callout_handle->setArgument("subnet4collection",
                                    cfgmgr.getCurrentCfg()->
                                    getCfgSubnets4()->getAll());

        auto const tpl(parkingLimitExceeded("subnet4_select"));
        bool const exceeded(get<0>(tpl));
        if (exceeded) {
            uint32_t const limit(get<1>(tpl));
            // We can't park it so we're going to throw it on the floor.
            LOG_DEBUG(packet4_logger, DBGLVL_PKT_HANDLING,
                      DHCP4_HOOK_SUBNET4_SELECT_4O6_PARKING_LOT_FULL)
                .arg(limit)
                .arg(query->getLabel());
            return (ConstSubnet4Ptr());
        }

        // We proactively park the packet.
        HooksManager::park(
            "subnet4_select", query, [this, query, allow_answer_park, callout_handle_state]() {
                if (MultiThreadingMgr::instance().getMode()) {
                    boost::shared_ptr<function<void()>> callback(
                        boost::make_shared<function<void()>>(
                            [this, query, allow_answer_park]() mutable {
                                processLocalizedQuery4AndSendResponse(query, allow_answer_park);
                            }));
                    callout_handle_state->on_completion_ = [callback]() {
                        MultiThreadingMgr::instance().getThreadPool().add(callback);
                    };
                } else {
                    processLocalizedQuery4AndSendResponse(query, allow_answer_park);
                }
            });

        // Call user (and server-side) callouts
        try {
            HooksManager::callCallouts(Hooks.hook_index_subnet4_select_,
                                       *callout_handle);
        } catch (...) {
            // Make sure we don't orphan a parked packet.
            HooksManager::drop("subnet4_select", query);
            throw;
        }

        // Callouts parked the packet. Same as drop but callouts will resume
        // processing or drop the packet later.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_PARK) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_PARK)
                .arg(query->getLabel());
            drop = true;
            return (ConstSubnet4Ptr());
        } else {
            HooksManager::drop("subnet4_select", query);
        }

        // Callouts decided to skip this step. This means that no subnet
        // will be selected. Packet processing will continue, but it will
        // be severely limited (i.e. only global options will be assigned)
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_SKIP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_DHCP4O6_HOOK_SUBNET4_SELECT_SKIP)
                .arg(query->getLabel());
            return (ConstSubnet4Ptr());
        }

        // Callouts decided to drop the packet. It is a superset of the
        // skip case so no subnet will be selected.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_DHCP4O6_HOOK_SUBNET4_SELECT_DROP)
                .arg(query->getLabel());
            drop = true;
            return (ConstSubnet4Ptr());
        }

        // Use whatever subnet was specified by the callout
        callout_handle->getArgument("subnet4", subnet);
    }

    if (subnet) {
        // Log at higher debug level that subnet has been found.
        LOG_DEBUG(packet4_logger, DBG_DHCP4_BASIC_DATA,
                  DHCP4_DHCP4O6_SUBNET_SELECTED)
            .arg(query->getLabel())
            .arg(subnet->getID());
        // Log detailed information about the selected subnet at the
        // lower debug level.
        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL_DATA,
                  DHCP4_DHCP4O6_SUBNET_DATA)
            .arg(query->getLabel())
            .arg(subnet->toText());

    } else {
        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL,
                  DHCP4_DHCP4O6_SUBNET_SELECTION_FAILED)
            .arg(query->getLabel());
    }

    return (subnet);
}

Pkt4Ptr
Dhcpv4Srv::receivePacket(int timeout) {
    return (IfaceMgr::instance().receive4(timeout));
}

void
Dhcpv4Srv::sendPacket(const Pkt4Ptr& packet) {
    IfaceMgr::instance().send(packet);
}

void
Dhcpv4Srv::initContext0(const Pkt4Ptr& query,
                        AllocEngine::ClientContext4Ptr ctx) {
    // Pointer to client's query.
    ctx->query_ = query;

    // Hardware address.
    ctx->hwaddr_ = query->getHWAddr();
}

bool
Dhcpv4Srv::earlyGHRLookup(const Pkt4Ptr& query,
                          AllocEngine::ClientContext4Ptr ctx) {

    // First part of context initialization.
    initContext0(query, ctx);

    // Get the early-global-reservations-lookup flag value.
    data::ConstElementPtr egrl = CfgMgr::instance().getCurrentCfg()->
        getConfiguredGlobal(CfgGlobals::EARLY_GLOBAL_RESERVATIONS_LOOKUP);
    if (egrl) {
        ctx->early_global_reservations_lookup_ = egrl->boolValue();
    }

    // Perform early global reservations lookup when wanted.
    if (ctx->early_global_reservations_lookup_) {
        // Retrieve retrieve client identifier.
        OptionPtr opt_clientid = query->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
        if (opt_clientid) {
            ctx->clientid_.reset(new ClientId(opt_clientid->getData()));
        }

        // Get the host identifiers.
        Dhcpv4Exchange::setHostIdentifiers(ctx);

        // Check for global host reservations.
        ConstHostPtr global_host = alloc_engine_->findGlobalReservation(*ctx);

        if (global_host && !global_host->getClientClasses4().empty()) {
            // Remove dependent evaluated classes.
            Dhcpv4Exchange::removeDependentEvaluatedClasses(query);

            // Add classes from the global reservations.
            const ClientClasses& classes = global_host->getClientClasses4();
            for (auto const& cclass : classes) {
                query->addClass(cclass);
            }

            // Evaluate classes before KNOWN.
            Dhcpv4Exchange::evaluateClasses(query, false);
        }

        if (global_host) {
            // Add the KNOWN class;
            query->addClass("KNOWN");
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_ASSIGNED)
                .arg(query->getLabel())
                .arg("KNOWN");

            // Evaluate classes after KNOWN.
            Dhcpv4Exchange::evaluateClasses(query, true);

            // Check the DROP special class.
            if (query->inClass("DROP")) {
                LOG_DEBUG(packet4_logger, DBGLVL_PKT_HANDLING,
                          DHCP4_PACKET_DROP_0014)
                    .arg(query->getHWAddrLabel())
                    .arg(query->toText());
                isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                          static_cast<int64_t>(1));
                return (false);
            }

            // Store the reservation.
            ctx->hosts_[SUBNET_ID_GLOBAL] = global_host;
        }
    }

    return (true);
}

int
Dhcpv4Srv::run() {
#ifdef HAVE_AFL
    // Get the values of the environment variables used to control the
    // fuzzing.

    // Specfies the interface to be used to pass packets from AFL to Kea.
    const char* interface = getenv("KEA_AFL_INTERFACE");
    if (!interface) {
        isc_throw(FuzzInitFail, "no fuzzing interface has been set");
    }

    // The address on the interface to be used.
    const char* address = getenv("KEA_AFL_ADDRESS");
    if (!address) {
        isc_throw(FuzzInitFail, "no fuzzing address has been set");
    }

    // Set up structures needed for fuzzing.
    PacketFuzzer fuzzer(server_port_, interface, address);

    // The next line is needed as a signature for AFL to recognize that we are
    // running persistent fuzzing.  This has to be in the main image file.
    while (__AFL_LOOP(fuzzer.maxLoopCount())) {
        // Read from stdin and put the data read into an address/port on which
        // Kea is listening, read for Kea to read it via asynchronous I/O.
        fuzzer.transfer();
#else
    while (!shutdown_) {
#endif // HAVE_AFL
        try {
            runOne();
            // Handle events registered by hooks using external IOService objects.
            IOServiceMgr::instance().pollIOServices();
            getIOService()->poll();
        } catch (const std::exception& e) {
            // General catch-all standard exceptions that are not caught by more
            // specific catches.
            LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_STD_EXCEPTION_MAIN)
                .arg(e.what());
        } catch (...) {
            // General catch-all exception that are not caught by more specific
            // catches. This one is for other exceptions, not derived from
            // std::exception.
            LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_EXCEPTION_MAIN);
        }
    }

    // Stop everything before we change into single-threaded mode.
    MultiThreadingCriticalSection cs;

    // destroying the thread pool
    MultiThreadingMgr::instance().apply(false, 0, 0);

    return (getExitValue());
}

void
Dhcpv4Srv::runOne() {
    // client's message and server's response
    Pkt4Ptr query;

    try {
        // Set select() timeout to 1s. This value should not be modified
        // because it is important that the select() returns control
        // frequently so as the IOService can be polled for ready handlers.
        uint32_t timeout = 1;
        query = receivePacket(timeout);

        // Log if packet has arrived. We can't log the detailed information
        // about the DHCP message because it hasn't been unpacked/parsed
        // yet, and it can't be parsed at this point because hooks will
        // have to process it first. The only information available at this
        // point are: the interface, source address and destination addresses
        // and ports.
        if (query) {
            LOG_DEBUG(packet4_logger, DBG_DHCP4_BASIC, DHCP4_BUFFER_RECEIVED)
                .arg(query->getRemoteAddr().toText())
                .arg(query->getRemotePort())
                .arg(query->getLocalAddr().toText())
                .arg(query->getLocalPort())
                .arg(query->getIface());

            // Log reception of the packet. We need to increase it early, as
            // any failures in unpacking will cause the packet to be dropped.
            // We will increase type specific statistic further down the road.
            // See processStatsReceived().
            isc::stats::StatsMgr::instance().addValue("pkt4-received",
                                                      static_cast<int64_t>(1));
        }

        // We used to log that the wait was interrupted, but this is no longer
        // the case. Our wait time is 1s now, so the lack of query packet more
        // likely means that nothing new appeared within a second, rather than
        // we were interrupted. And we don't want to print a message every
        // second.

    } catch (const SignalInterruptOnSelect&) {
        // Packet reception interrupted because a signal has been received.
        // This is not an error because we might have received a SIGTERM,
        // SIGINT, SIGHUP or SIGCHLD which are handled by the server. For
        // signals that are not handled by the server we rely on the default
        // behavior of the system.
        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL, DHCP4_BUFFER_WAIT_SIGNAL);
    } catch (const std::exception& e) {
        // Log all other errors.
        LOG_ERROR(packet4_logger, DHCP4_BUFFER_RECEIVE_FAIL)
            .arg(e.what());
    }

    // Timeout may be reached or signal received, which breaks select()
    // with no reception occurred. No need to log anything here because
    // we have logged right after the call to receivePacket().
    if (!query) {
        return;
    }

    // If the DHCP service has been globally disabled, drop the packet.
    if (!network_state_->isServiceEnabled()) {
        LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0008)
            .arg(query->getLabel());
        // Increase the statistics of service disabled and dropped packets.
        isc::stats::StatsMgr::instance().addValue("pkt4-service-disabled",
                                                  static_cast<int64_t>(1));
        isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                  static_cast<int64_t>(1));
        return;
    } else {
        if (MultiThreadingMgr::instance().getMode()) {
            query->addPktEvent("mt_queued");
            typedef function<void()> CallBack;
            boost::shared_ptr<CallBack> call_back =
                boost::make_shared<CallBack>(std::bind(&Dhcpv4Srv::processPacketAndSendResponseNoThrow,
                                                       this, query));
            if (!MultiThreadingMgr::instance().getThreadPool().add(call_back)) {
                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_PACKET_QUEUE_FULL);
            }
        } else {
            processPacketAndSendResponse(query);
        }
    }
}

void
Dhcpv4Srv::processPacketAndSendResponseNoThrow(Pkt4Ptr query) {
    try {
        processPacketAndSendResponse(query);
    } catch (const std::exception& e) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_STD_EXCEPTION)
            .arg(query->getLabel())
            .arg(e.what());
    } catch (...) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_EXCEPTION).arg(query->getLabel());
    }
}

void
Dhcpv4Srv::processPacketAndSendResponse(Pkt4Ptr query) {
    Pkt4Ptr rsp = processPacket(query);
    if (!rsp) {
        return;
    }

    CalloutHandlePtr callout_handle = getCalloutHandle(query);

    processPacketBufferSend(callout_handle, rsp);
}

Pkt4Ptr
Dhcpv4Srv::processPacket(Pkt4Ptr query, bool allow_answer_park) {
    query->addPktEvent("process_started");

    // All packets belong to ALL.
    query->addClass("ALL");

    bool skip_unpack = false;

    // The packet has just been received so contains the uninterpreted wire
    // data; execute callouts registered for buffer4_receive.
    if (HooksManager::calloutsPresent(Hooks.hook_index_buffer4_receive_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        ScopedCalloutHandleState callout_handle_state(callout_handle);

        // Enable copying options from the packet within hook library.
        ScopedEnableOptionsCopy<Pkt4> query4_options_copy(query);

        // Pass incoming packet as argument
        callout_handle->setArgument("query4", query);

        // Call callouts
        HooksManager::callCallouts(Hooks.hook_index_buffer4_receive_,
                                   *callout_handle);

        // Callouts decided to drop the received packet.
        // The response (rsp) is null so the caller (runOne) will
        // immediately return too.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP) {
            LOG_DEBUG(hooks_logger, DBGLVL_PKT_HANDLING,
                      DHCP4_HOOK_BUFFER_RCVD_DROP)
                .arg(query->getRemoteAddr().toText())
                .arg(query->getLocalAddr().toText())
                .arg(query->getIface());
            return (Pkt4Ptr());;
        }

        // Callouts decided to skip the next processing step. The next
        // processing step would be to parse the packet, so skip at this
        // stage means that callouts did the parsing already, so server
        // should skip parsing.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_SKIP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_DETAIL,
                      DHCP4_HOOK_BUFFER_RCVD_SKIP)
                .arg(query->getRemoteAddr().toText())
                .arg(query->getLocalAddr().toText())
                .arg(query->getIface());
            skip_unpack = true;
        }

        callout_handle->getArgument("query4", query);
    }

    // Unpack the packet information unless the buffer4_receive callouts
    // indicated they did it
    if (!skip_unpack) {
        try {
            LOG_DEBUG(options4_logger, DBG_DHCP4_DETAIL, DHCP4_BUFFER_UNPACK)
                .arg(query->getRemoteAddr().toText())
                .arg(query->getLocalAddr().toText())
                .arg(query->getIface());
            query->unpack();
        } catch (const SkipRemainingOptionsError& e) {
            // An option failed to unpack but we are to attempt to process it
            // anyway.  Log it and let's hope for the best.
            LOG_DEBUG(options4_logger, DBG_DHCP4_DETAIL,
                      DHCP4_PACKET_OPTIONS_SKIPPED)
                .arg(query->getLabel())
                .arg(e.what());
        } catch (const std::exception& e) {
            // Failed to parse the packet.
            LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0001)
                .arg(query->getLabel())
                .arg(query->getRemoteAddr().toText())
                .arg(query->getLocalAddr().toText())
                .arg(query->getIface())
                .arg(e.what())
                .arg(query->getHWAddrLabel());

            // Increase the statistics of parse failures and dropped packets.
            isc::stats::StatsMgr::instance().addValue("pkt4-parse-failed",
                                                      static_cast<int64_t>(1));
            isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                      static_cast<int64_t>(1));
            return (Pkt4Ptr());
        }
    }

    // Classify can emit INFO logs so help to track the query.
    LOG_INFO(dhcp4_logger, DHCP4_QUERY_LABEL)
        .arg(query->getLabel());

    // Update statistics accordingly for received packet.
    processStatsReceived(query);

    // Recover stashed RAI from client address lease.
    try {
        recoverStashedAgentOption(query);
    } catch (const std::exception&) {
        // Ignore exceptions.
    }

    // Assign this packet to one or more classes if needed. We need to do
    // this before calling accept(), because getSubnet4() may need client
    // class information.
    classifyPacket(query);

    // Now it is classified the deferred unpacking can be done.
    deferredUnpack(query);

    // Check whether the message should be further processed or discarded.
    // There is no need to log anything here. This function logs by itself.
    if (!accept(query)) {
        // Increase the statistic of dropped packets.
        isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                  static_cast<int64_t>(1));
        return (Pkt4Ptr());
    }

    // We have sanity checked (in accept() that the Message Type option
    // exists, so we can safely get it here.
    int type = query->getType();
    LOG_INFO(packet4_logger, DHCP4_PACKET_RECEIVED)
        .arg(query->getLabel())
        .arg(query->getName())
        .arg(type)
        .arg(query->getRemoteAddr())
        .arg(query->getLocalAddr())
        .arg(query->getIface());
    LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_QUERY_DATA)
        .arg(query->getLabel())
        .arg(query->toText(true));

    // Let's execute all callouts registered for pkt4_receive
    if (HooksManager::calloutsPresent(Hooks.hook_index_pkt4_receive_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        ScopedCalloutHandleState callout_handle_state(callout_handle);

        // Enable copying options from the packet within hook library.
        ScopedEnableOptionsCopy<Pkt4> query4_options_copy(query);

        // Pass incoming packet as argument
        callout_handle->setArgument("query4", query);

        // Call callouts
        HooksManager::callCallouts(Hooks.hook_index_pkt4_receive_,
                                   *callout_handle);

        // Callouts decided to skip the next processing step. The next
        // processing step would be to process the packet, so skip at this
        // stage means drop.
        if ((callout_handle->getStatus() == CalloutHandle::NEXT_STEP_SKIP) ||
            (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP)) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_PACKET_RCVD_SKIP)
                .arg(query->getLabel());
            return (Pkt4Ptr());
        }

        callout_handle->getArgument("query4", query);
    }

    // Check the DROP special class.
    if (query->inClass("DROP")) {
        LOG_DEBUG(packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0010)
            .arg(query->getHWAddrLabel())
            .arg(query->toText());
        isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                  static_cast<int64_t>(1));
        return (Pkt4Ptr());
    }

    return (processDhcp4Query(query, allow_answer_park));
}

void
Dhcpv4Srv::processDhcp4QueryAndSendResponse(Pkt4Ptr query,
                                            bool allow_answer_park) {
    try {
        Pkt4Ptr rsp = processDhcp4Query(query, allow_answer_park);
        if (!rsp) {
            return;
        }

        CalloutHandlePtr callout_handle = getCalloutHandle(query);
        processPacketBufferSend(callout_handle, rsp);
    } catch (const std::exception& e) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_STD_EXCEPTION)
            .arg(query->getLabel())
            .arg(e.what());
    } catch (...) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_EXCEPTION).arg(query->getLabel());
    }
}

Pkt4Ptr
Dhcpv4Srv::processDhcp4Query(Pkt4Ptr query, bool allow_answer_park) {
    // Create a client race avoidance RAII handler.
    ClientHandler client_handler;

    // Check for lease modifier queries from the same client being processed.
    if (MultiThreadingMgr::instance().getMode() &&
        ((query->getType() == DHCPDISCOVER) ||
         (query->getType() == DHCPREQUEST) ||
         (query->getType() == DHCPRELEASE) ||
         (query->getType() == DHCPDECLINE))) {
        ContinuationPtr cont =
            makeContinuation(std::bind(&Dhcpv4Srv::processDhcp4QueryAndSendResponse,
                                       this, query, allow_answer_park));
        if (!client_handler.tryLock(query, cont)) {
            return (Pkt4Ptr());
        }
    }

    AllocEngine::ClientContext4Ptr ctx(new AllocEngine::ClientContext4());
    if (!earlyGHRLookup(query, ctx)) {
        return (Pkt4Ptr());
    }

    try {
        sanityCheck(query);
        if ((query->getType() == DHCPDISCOVER) ||
            (query->getType() == DHCPREQUEST) ||
            (query->getType() == DHCPINFORM)) {
            bool drop = false;
            ctx->subnet_ = selectSubnet(query, drop, allow_answer_park);
            // Stop here if selectSubnet decided to drop the packet
            if (drop) {
                return (Pkt4Ptr());
            }
        }
    } catch (const std::exception& e) {

        // Catch-all exception (we used to call only isc::Exception, but
        // std::exception could potentially be raised and if we don't catch
        // it here, it would be caught in main() and the process would
        // terminate).  Just log the problem and ignore the packet.
        // (The problem is logged as a debug message because debug is
        // disabled by default - it prevents a DDOS attack based on the
        // sending of problem packets.)
        LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0007)
            .arg(query->getLabel())
            .arg(e.what());

        // Increase the statistic of dropped packets.
        isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                  static_cast<int64_t>(1));
    }

    return (processLocalizedQuery4(ctx, allow_answer_park));
}

void
Dhcpv4Srv::processLocalizedQuery4AndSendResponse(Pkt4Ptr query,
                                                 AllocEngine::ClientContext4Ptr& ctx,
                                                 bool allow_answer_park) {
    try {
        Pkt4Ptr rsp = processLocalizedQuery4(ctx, allow_answer_park);
        if (!rsp) {
            return;
        }

        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        processPacketBufferSend(callout_handle, rsp);
    } catch (const std::exception& e) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_STD_EXCEPTION)
            .arg(query->getLabel())
            .arg(e.what());
    } catch (...) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_EXCEPTION).arg(query->getLabel());
    }
}

void
Dhcpv4Srv::processLocalizedQuery4AndSendResponse(Pkt4Ptr query,
                                                 bool allow_answer_park) {
    // Initialize context.
    AllocEngine::ClientContext4Ptr ctx(new AllocEngine::ClientContext4());
    initContext0(query, ctx);

    // Subnet is cached in the callout context associated to the query.
    try {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);
        callout_handle->getContext("subnet4", ctx->subnet_);
    } catch (const Exception&) {
        // No subnet, leave it to null...
    }

    processLocalizedQuery4AndSendResponse(query, ctx, allow_answer_park);
}

Pkt4Ptr
Dhcpv4Srv::processLocalizedQuery4(AllocEngine::ClientContext4Ptr& ctx,
                                  bool allow_answer_park) {
    if (!ctx) {
        isc_throw(Unexpected, "null context");
    }
    Pkt4Ptr query = ctx->query_;
    Pkt4Ptr rsp;
    try {
        switch (query->getType()) {
        case DHCPDISCOVER:
            rsp = processDiscover(query, ctx);
            break;

        case DHCPREQUEST:
            // Note that REQUEST is used for many things in DHCPv4: for
            // requesting new leases, renewing existing ones and even
            // for rebinding.
            rsp = processRequest(query, ctx);
            break;

        case DHCPRELEASE:
            processRelease(query, ctx);
            break;

        case DHCPDECLINE:
            processDecline(query, ctx);
            break;

        case DHCPINFORM:
            rsp = processInform(query, ctx);
            break;

        default:
            // Only action is to output a message if debug is enabled,
            // and that is covered by the debug statement before the
            // "switch" statement.
            ;
        }
    } catch (const std::exception& e) {

        // Catch-all exception (we used to call only isc::Exception, but
        // std::exception could potentially be raised and if we don't catch
        // it here, it would be caught in main() and the process would
        // terminate).  Just log the problem and ignore the packet.
        // (The problem is logged as a debug message because debug is
        // disabled by default - it prevents a DDOS attack based on the
        // sending of problem packets.)
        LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0007)
            .arg(query->getLabel())
            .arg(e.what());

        // Increase the statistic of dropped packets.
        isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                  static_cast<int64_t>(1));
    }

    CalloutHandlePtr callout_handle = getCalloutHandle(query);
    if (ctx) {
        // leases4_committed and lease4_offer callouts are treated in the same way,
        // so prepare correct set of variables basing on the packet context.
        int hook_idx = Hooks.hook_index_leases4_committed_;
        std::string hook_label = "leases4_committed";
        MessageID pkt_park_msg = DHCP4_HOOK_LEASES4_COMMITTED_PARK;
        MessageID pkt_drop_msg = DHCP4_HOOK_LEASES4_COMMITTED_DROP;
        MessageID parking_lot_full_msg = DHCP4_HOOK_LEASES4_COMMITTED_PARKING_LOT_FULL;
        if (ctx->fake_allocation_) {
            hook_idx = Hooks.hook_index_lease4_offer_;
            hook_label = "lease4_offer";
            pkt_park_msg = DHCP4_HOOK_LEASE4_OFFER_PARK;
            pkt_drop_msg = DHCP4_HOOK_LEASE4_OFFER_DROP;
            parking_lot_full_msg = DHCP4_HOOK_LEASE4_OFFER_PARKING_LOT_FULL;
        }

        if (HooksManager::calloutsPresent(hook_idx)) {
            // The ScopedCalloutHandleState class which guarantees that the task
            // is added to the thread pool after the response is reset (if needed)
            // and CalloutHandle state is reset. In ST it does nothing.
            // A smart pointer is used to store the ScopedCalloutHandleState so that
            // a copy of the pointer is created by the lambda and only on the
            // destruction of the last reference the task is added.
            // In MT there are 2 cases:
            // 1. packet is unparked before current thread smart pointer to
            //    ScopedCalloutHandleState is destroyed:
            //  - the lambda uses the smart pointer to set the callout which adds the
            //    task, but the task is added after ScopedCalloutHandleState is
            //    destroyed, on the destruction of the last reference which is held
            //    by the current thread.
            // 2. packet is unparked after the current thread smart pointer to
            //    ScopedCalloutHandleState is destroyed:
            //  - the current thread reference to ScopedCalloutHandleState is
            //    destroyed, but the reference in the lambda keeps it alive until
            //    the lambda is called and the last reference is released, at which
            //    time the task is actually added.
            // Use the RAII wrapper to make sure that the callout handle state is
            // reset when this object goes out of scope. All hook points must do
            // it to prevent possible circular dependency between the callout
            // handle and its arguments.
            std::shared_ptr<ScopedCalloutHandleState> callout_handle_state =
                std::make_shared<ScopedCalloutHandleState>(callout_handle);

            ScopedEnableOptionsCopy<Pkt4> query4_options_copy(query);

            // Also pass the corresponding query packet as argument
            callout_handle->setArgument("query4", query);

            // Also pass the corresponding response packet as argument
            ScopedEnableOptionsCopy<Pkt4> response4_options_copy(rsp);
            callout_handle->setArgument("response4", rsp);

            Lease4CollectionPtr new_leases(new Lease4Collection());
            // Filter out the new lease if it was reused so not committed.
            if (ctx->new_lease_ && (ctx->new_lease_->reuseable_valid_lft_ == 0)) {
                new_leases->push_back(ctx->new_lease_);
            }
            callout_handle->setArgument("leases4", new_leases);

            if (ctx->fake_allocation_) {
                // Arguments required only for lease4_offer callout.
                callout_handle->setArgument("offer_lifetime", ctx->offer_lft_);
                callout_handle->setArgument("old_lease", ctx->old_lease_);
                callout_handle->setArgument("host", ctx->currentHost());
            } else {
                // Arguments required only for leases4_committed callout.
                Lease4CollectionPtr deleted_leases(new Lease4Collection());
                if (ctx->old_lease_) {
                    if ((!ctx->new_lease_) || (ctx->new_lease_->addr_ != ctx->old_lease_->addr_)) {
                            deleted_leases->push_back(ctx->old_lease_);
                    }
                }
                callout_handle->setArgument("deleted_leases4", deleted_leases);
            }

            if (allow_answer_park) {
                auto const tpl(parkingLimitExceeded(hook_label));
                bool const exceeded(get<0>(tpl));
                if (exceeded) {
                    uint32_t const limit(get<1>(tpl));
                    // We can't park it so we're going to throw it on the floor.
                    LOG_DEBUG(packet4_logger, DBGLVL_PKT_HANDLING, parking_lot_full_msg)
                        .arg(limit)
                        .arg(query->getLabel());
                    isc::stats::StatsMgr::instance().addValue("pkt4-receive-drop",
                                                                static_cast<int64_t>(1));
                    return (Pkt4Ptr());
                }

                // We proactively park the packet. We'll unpark it without invoking
                // the callback (i.e. drop) unless the callout status is set to
                // NEXT_STEP_PARK.  Otherwise the callback we bind here will be
                // executed when the hook library unparks the packet.
                HooksManager::park(
                    hook_label, query,
                    [this, callout_handle, query, rsp, callout_handle_state, hook_idx, ctx]() mutable {
                        if (hook_idx == Hooks.hook_index_lease4_offer_) {
                            bool offer_address_in_use = false;
                            try {
                                callout_handle->getArgument("offer_address_in_use", offer_address_in_use);
                            } catch (const NoSuchArgument& ex) {
                                LOG_ERROR(hooks_logger, DHCP4_HOOK_LEASE4_OFFER_ARGUMENT_MISSING)
                                          .arg(query->getLabel())
                                          .arg(ex.what());
                            }

                            if (offer_address_in_use) {
                                Lease4Ptr lease = ctx->new_lease_;
                                bool lease_exists = (ctx->offer_lft_ > 0);
                                if (MultiThreadingMgr::instance().getMode()) {
                                    typedef function<void()> CallBack;
                                    // We need to pass in the lease and flag as the callback handle state
                                    // gets reset prior to the invocation of the on_completion_ callback.
                                    boost::shared_ptr<CallBack> call_back = boost::make_shared<CallBack>(
                                        std::bind(&Dhcpv4Srv::serverDeclineNoThrow, this,
                                                  callout_handle, query, lease, lease_exists));
                                    callout_handle_state->on_completion_ = [call_back]() {
                                        MultiThreadingMgr::instance().getThreadPool().add(call_back);
                                    };
                                } else {
                                    serverDecline(callout_handle, query, lease, lease_exists);
                                }

                                return;
                            }
                        }

                        // Send the response to the client.
                        if (MultiThreadingMgr::instance().getMode()) {
                            typedef function<void()> CallBack;
                            boost::shared_ptr<CallBack> call_back = boost::make_shared<CallBack>(
                                std::bind(&Dhcpv4Srv::sendResponseNoThrow, this, callout_handle,
                                          query, rsp, ctx->subnet_));
                            callout_handle_state->on_completion_ = [call_back]() {
                                MultiThreadingMgr::instance().getThreadPool().add(call_back);
                            };
                        } else {
                            processPacketPktSend(callout_handle, query, rsp, ctx->subnet_);
                            processPacketBufferSend(callout_handle, rsp);
                        }
                    });
            }

            try {
                // Call all installed callouts
                HooksManager::callCallouts(hook_idx, *callout_handle);
            } catch (...) {
                // Make sure we don't orphan a parked packet.
                if (allow_answer_park) {
                    HooksManager::drop(hook_label, query);
                }

                throw;
            }

            if ((callout_handle->getStatus() == CalloutHandle::NEXT_STEP_PARK) &&
                allow_answer_park) {
                LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS, pkt_park_msg)
                    .arg(query->getLabel());
                // Since the hook library(ies) are going to do the unparking, then
                // reset the pointer to the response to indicate to the caller that
                // it should return, as the packet processing will continue via
                // the callback.
                rsp.reset();
            } else {
                // Drop the park job on the packet, it isn't needed.
                HooksManager::drop(hook_label, query);
                if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP) {
                    LOG_DEBUG(hooks_logger, DBGLVL_PKT_HANDLING, pkt_drop_msg)
                        .arg(query->getLabel());
                    rsp.reset();
                }
            }
        }
    }

    // If we have a response prep it for shipment.
    if (rsp) {
        ConstSubnet4Ptr subnet = (ctx ? ctx->subnet_ : ConstSubnet4Ptr());
        processPacketPktSend(callout_handle, query, rsp, subnet);
    }
    return (rsp);
}

void
Dhcpv4Srv::sendResponseNoThrow(hooks::CalloutHandlePtr& callout_handle,
                               Pkt4Ptr& query, Pkt4Ptr& rsp,
                               ConstSubnet4Ptr& subnet) {
    try {
            processPacketPktSend(callout_handle, query, rsp, subnet);
            processPacketBufferSend(callout_handle, rsp);
        } catch (const std::exception& e) {
            LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_STD_EXCEPTION)
                .arg(query->getLabel())
                .arg(e.what());
    } catch (...) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_EXCEPTION).arg(query->getLabel());
    }
}

void
Dhcpv4Srv::processPacketPktSend(hooks::CalloutHandlePtr& callout_handle,
                                Pkt4Ptr& query, Pkt4Ptr& rsp,
                                ConstSubnet4Ptr& subnet) {
    query->addPktEvent("process_completed");
    if (!rsp) {
        return;
    }

    // Specifies if server should do the packing
    bool skip_pack = false;

    // Execute all callouts registered for pkt4_send
    if (HooksManager::calloutsPresent(Hooks.hook_index_pkt4_send_)) {

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        ScopedCalloutHandleState callout_handle_state(callout_handle);

        // Enable copying options from the query and response packets within
        // hook library.
        ScopedEnableOptionsCopy<Pkt4> query_resp_options_copy(query, rsp);

        // Pass incoming packet as argument
        callout_handle->setArgument("query4", query);

        // Set our response
        callout_handle->setArgument("response4", rsp);

        // Pass in the selected subnet.
        callout_handle->setArgument("subnet4", subnet);

        // Call all installed callouts
        HooksManager::callCallouts(Hooks.hook_index_pkt4_send_,
                                   *callout_handle);

        // Callouts decided to skip the next processing step. The next
        // processing step would be to pack the packet (create wire data).
        // That step will be skipped if any callout sets skip flag.
        // It essentially means that the callout already did packing,
        // so the server does not have to do it again.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_SKIP) {
            LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_PACKET_SEND_SKIP)
                .arg(query->getLabel());
            skip_pack = true;
        }

        /// Callouts decided to drop the packet.
        if (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP) {
            LOG_DEBUG(hooks_logger, DBGLVL_PKT_HANDLING, DHCP4_HOOK_PACKET_SEND_DROP)
                .arg(rsp->getLabel());
            rsp.reset();
            return;
        }
    }

    if (!skip_pack) {
        try {
            LOG_DEBUG(options4_logger, DBG_DHCP4_DETAIL, DHCP4_PACKET_PACK)
                .arg(rsp->getLabel());
            rsp->pack();
        } catch (const std::exception& e) {
            LOG_ERROR(options4_logger, DHCP4_PACKET_PACK_FAIL)
                .arg(rsp->getLabel())
                .arg(e.what());
        }
    }
}

void
Dhcpv4Srv::processPacketBufferSend(CalloutHandlePtr& callout_handle,
                                   Pkt4Ptr& rsp) {
    if (!rsp) {
        return;
    }

    try {
        // Now all fields and options are constructed into output wire buffer.
        // Option objects modification does not make sense anymore. Hooks
        // can only manipulate wire buffer at this stage.
        // Let's execute all callouts registered for buffer4_send
        if (HooksManager::calloutsPresent(Hooks.hook_index_buffer4_send_)) {

            // Use the RAII wrapper to make sure that the callout handle state is
            // reset when this object goes out of scope. All hook points must do
            // it to prevent possible circular dependency between the callout
            // handle and its arguments.
            ScopedCalloutHandleState callout_handle_state(callout_handle);

            // Enable copying options from the packet within hook library.
            ScopedEnableOptionsCopy<Pkt4> resp4_options_copy(rsp);

            // Pass incoming packet as argument
            callout_handle->setArgument("response4", rsp);

            // Call callouts
            HooksManager::callCallouts(Hooks.hook_index_buffer4_send_,
                                       *callout_handle);

            // Callouts decided to skip the next processing step. The next
            // processing step would be to parse the packet, so skip at this
            // stage means drop.
            if ((callout_handle->getStatus() == CalloutHandle::NEXT_STEP_SKIP) ||
                (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP)) {
                LOG_DEBUG(hooks_logger, DBG_DHCP4_HOOKS,
                          DHCP4_HOOK_BUFFER_SEND_SKIP)
                    .arg(rsp->getLabel());
                return;
            }

            callout_handle->getArgument("response4", rsp);
        }

        LOG_INFO(packet4_logger, DHCP4_PACKET_SEND)
            .arg(rsp->getLabel())
            .arg(rsp->getName())
            .arg(static_cast<int>(rsp->getType()))
            .arg(rsp->getLocalAddr().isV4Zero() ? "*" : rsp->getLocalAddr().toText())
            .arg(rsp->getLocalPort())
            .arg(rsp->getRemoteAddr())
            .arg(rsp->getRemotePort())
            .arg(rsp->getIface().empty() ? "to be determined from routing" :
                 rsp->getIface());

        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL_DATA,
                  DHCP4_RESPONSE_DATA)
            .arg(rsp->getLabel())
            .arg(rsp->getName())
            .arg(static_cast<int>(rsp->getType()))
            .arg(rsp->toText(true));
        sendPacket(rsp);

        // Update statistics accordingly for sent packet.
        processStatsSent(rsp);

    } catch (const std::exception& e) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_SEND_FAIL)
            .arg(rsp->getLabel())
            .arg(e.what());
    }
}

string
Dhcpv4Srv::srvidToString(const OptionPtr& srvid) {
    if (!srvid) {
        isc_throw(BadValue, "NULL pointer passed to srvidToString()");
    }
    boost::shared_ptr<Option4AddrLst> generated =
        boost::dynamic_pointer_cast<Option4AddrLst>(srvid);
    if (!srvid) {
        isc_throw(BadValue, "Pointer to invalid option passed to srvidToString()");
    }

    Option4AddrLst::AddressContainer addrs = generated->getAddresses();
    if (addrs.size() != 1) {
        isc_throw(BadValue, "Malformed option passed to srvidToString(). "
                  << "Expected to contain a single IPv4 address.");
    }

    return (addrs[0].toText());
}

void
Dhcpv4Srv::appendServerID(Dhcpv4Exchange& ex) {

    // Do not append generated server identifier if there is one appended already.
    // This is when explicitly configured server identifier option is present.
    if (ex.getResponse()->getOption(DHO_DHCP_SERVER_IDENTIFIER)) {
        return;
    }

    // Use local address on which the packet has been received as a
    // server identifier. In some cases it may be a different address,
    // e.g. broadcast packet or DHCPv4o6 packet.
    IOAddress local_addr = ex.getQuery()->getLocalAddr();
    Pkt4Ptr query = ex.getQuery();

    if (local_addr.isV4Bcast() || query->isDhcp4o6()) {
        local_addr = IfaceMgr::instance().getSocket(query).addr_;
    }

    static const OptionDefinition& server_id_def = LibDHCP::DHO_DHCP_SERVER_IDENTIFIER_DEF();
    OptionCustomPtr opt_srvid(new OptionCustom(server_id_def, Option::V4));
    opt_srvid->writeAddress(local_addr);
    ex.getResponse()->addOption(opt_srvid);
}

void
Dhcpv4Srv::buildCfgOptionList(Dhcpv4Exchange& ex) {
    CfgOptionList& co_list = ex.getCfgOptionList();

    // Retrieve subnet.
    ConstSubnet4Ptr subnet = ex.getContext()->subnet_;
    if (!subnet) {
        // All methods using the CfgOptionList object return soon when
        // there is no subnet so do the same
        return;
    }

    // Firstly, host specific options.
    const ConstHostPtr& host = ex.getContext()->currentHost();
    if (host && !host->getCfgOption4()->empty()) {
        co_list.push_back(host->getCfgOption4());
    }

    // Secondly, pool specific options.
    Pkt4Ptr resp = ex.getResponse();
    IOAddress addr = IOAddress::IPV4_ZERO_ADDRESS();
    if (resp) {
        addr = resp->getYiaddr();
    }
    if (!addr.isV4Zero()) {
        PoolPtr pool = subnet->getPool(Lease::TYPE_V4, addr, false);
        if (pool && !pool->getCfgOption()->empty()) {
            co_list.push_back(pool->getCfgOption());
        }
    }

    // Thirdly, subnet configured options.
    if (!subnet->getCfgOption()->empty()) {
        co_list.push_back(subnet->getCfgOption());
    }

    // Fourthly, shared network specific options.
    SharedNetwork4Ptr network;
    subnet->getSharedNetwork(network);
    if (network && !network->getCfgOption()->empty()) {
        co_list.push_back(network->getCfgOption());
    }

    // Each class in the incoming packet
    const ClientClasses& classes = ex.getQuery()->getClasses();
    for (auto const& cclass : classes) {
        // Find the client class definition for this class
        const ClientClassDefPtr& ccdef = CfgMgr::instance().getCurrentCfg()->
            getClientClassDictionary()->findClass(cclass);
        if (!ccdef) {
            // Not found: the class is built-in or not configured
            if (!isClientClassBuiltIn(cclass)) {
                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_UNCONFIGURED)
                    .arg(ex.getQuery()->getLabel())
                    .arg(cclass);
            }
            // Skip it
            continue;
        }

        if (ccdef->getCfgOption()->empty()) {
            // Skip classes which don't configure options
            continue;
        }

        co_list.push_back(ccdef->getCfgOption());
    }

    // Last global options
    if (!CfgMgr::instance().getCurrentCfg()->getCfgOption()->empty()) {
        co_list.push_back(CfgMgr::instance().getCurrentCfg()->getCfgOption());
    }
}

void
Dhcpv4Srv::appendRequestedOptions(Dhcpv4Exchange& ex) {
    // Get the subnet relevant for the client. We will need it
    // to get the options associated with it.
    ConstSubnet4Ptr subnet = ex.getContext()->subnet_;
    // If we can't find the subnet for the client there is no way
    // to get the options to be sent to a client. We don't log an
    // error because it will be logged by the assignLease method
    // anyway.
    if (!subnet) {
        return;
    }

    // Unlikely short cut
    const CfgOptionList& co_list = ex.getCfgOptionList();
    if (co_list.empty()) {
        return;
    }

    Pkt4Ptr query = ex.getQuery();
    Pkt4Ptr resp = ex.getResponse();
    set<uint8_t> requested_opts;

    // try to get the 'Parameter Request List' option which holds the
    // codes of requested options.
    OptionUint8ArrayPtr option_prl = boost::dynamic_pointer_cast<
        OptionUint8Array>(query->getOption(DHO_DHCP_PARAMETER_REQUEST_LIST));

    // Get the list of options that client requested.
    if (option_prl) {
        for (uint16_t code : option_prl->getValues()) {
            static_cast<void>(requested_opts.insert(code));
        }
    }

    std::set<uint8_t> cancelled_opts;
    const auto& cclasses = query->getClasses();

    // Iterate on the configured option list to add persistent and
    // cancelled options.
    for (auto const& copts : co_list) {
        const OptionContainerPtr& opts = copts->getAll(DHCP4_OPTION_SPACE);
        if (!opts) {
            continue;
        }
        // Get persistent options.
        const OptionContainerPersistIndex& pidx = opts->get<2>();
        const OptionContainerPersistRange& prange = pidx.equal_range(true);
        BOOST_FOREACH(auto const& desc, prange) {
            // Add the persistent option code to requested options.
            if (desc.option_) {
                uint8_t code = static_cast<uint8_t>(desc.option_->getType());
                static_cast<void>(requested_opts.insert(code));
            }
        }
        // Get cancelled options.
        const OptionContainerCancelIndex& cidx = opts->get<5>();
        const OptionContainerCancelRange& crange = cidx.equal_range(true);
        BOOST_FOREACH(auto const& desc, crange) {
            // Add the cancelled option code to cancelled options.
            if (desc.option_) {
                uint8_t code = static_cast<uint8_t>(desc.option_->getType());
                static_cast<void>(cancelled_opts.insert(code));
            }
        }
    }

    // For each requested option code get the first instance of the option
    // to be returned to the client.
    for (uint8_t opt : requested_opts) {
        if (cancelled_opts.count(opt) > 0) {
            continue;
        }
        // Skip special cases: DHO_VIVSO_SUBOPTIONS.
        if (opt == DHO_VIVSO_SUBOPTIONS) {
            continue;
        }
        // Add nothing when it is already there.
        if (!resp->getOption(opt)) {
            // Iterate on the configured option list
            for (auto const& copts : co_list) {
                OptionDescriptor desc = copts->allowedForClientClasses(DHCP4_OPTION_SPACE,
                                                                       opt, cclasses);
                if (desc.option_) {
                    // Got it: add it and jump to the outer loop
                    resp->addOption(desc.option_);
                    break;
                }
            }
        }
    }

    // Special cases for vendor class and options which are identified
    // by the code/type and the vendor/enterprise id vs. the code/type only.
    if ((requested_opts.count(DHO_VIVCO_SUBOPTIONS) > 0) &&
        (cancelled_opts.count(DHO_VIVCO_SUBOPTIONS) == 0)) {
        // Keep vendor ids which are already in the response to insert
        // VIVCO options at most once per vendor.
        set<uint32_t> vendor_ids;
        // Get what already exists in the response.
        for (auto const& opt : resp->getOptions(DHO_VIVCO_SUBOPTIONS)) {
            OptionVendorClassPtr vendor_opts;
            vendor_opts = boost::dynamic_pointer_cast<OptionVendorClass>(opt.second);
            if (vendor_opts) {
                uint32_t vendor_id = vendor_opts->getVendorId();
                static_cast<void>(vendor_ids.insert(vendor_id));
            }
        }
        // Iterate on the configured option list.
        for (auto const& copts : co_list) {
            for (auto const& desc : copts->getList(DHCP4_OPTION_SPACE,
                                                        DHO_VIVCO_SUBOPTIONS)) {
                if (!desc.option_ || !desc.allowedForClientClasses(cclasses)) {
                    continue;
                }
                OptionVendorClassPtr vendor_opts =
                    boost::dynamic_pointer_cast<OptionVendorClass>(desc.option_);
                if (!vendor_opts) {
                    continue;
                }
                // Is the vendor id already in the response?
                uint32_t vendor_id = vendor_opts->getVendorId();
                if (vendor_ids.count(vendor_id) > 0) {
                    continue;
                }
                // Got it: add it.
                resp->Pkt::addOption(desc.option_);
                static_cast<void>(vendor_ids.insert(vendor_id));
            }
        }
    }

    if ((requested_opts.count(DHO_VIVSO_SUBOPTIONS) > 0) &&
        (cancelled_opts.count(DHO_VIVSO_SUBOPTIONS) == 0)) {
        // Keep vendor ids which are already in the response to insert
        // VIVSO options at most once per vendor.
        set<uint32_t> vendor_ids;
        // Get what already exists in the response.
        for (auto const& opt : resp->getOptions(DHO_VIVSO_SUBOPTIONS)) {
            OptionVendorPtr vendor_opts;
            vendor_opts = boost::dynamic_pointer_cast<OptionVendor>(opt.second);
            if (vendor_opts) {
                uint32_t vendor_id = vendor_opts->getVendorId();
                static_cast<void>(vendor_ids.insert(vendor_id));
            }
        }
        // Iterate on the configured option list
        for (auto const& copts : co_list) {
            for (auto const& desc : copts->getList(DHCP4_OPTION_SPACE,
                                                   DHO_VIVSO_SUBOPTIONS)) {
                if (!desc.option_ || !desc.allowedForClientClasses(cclasses)) {
                    continue;
                }
                OptionVendorPtr vendor_opts =
                    boost::dynamic_pointer_cast<OptionVendor>(desc.option_);
                if (!vendor_opts) {
                    continue;
                }
                // Is the vendor id already in the response?
                uint32_t vendor_id = vendor_opts->getVendorId();
                if (vendor_ids.count(vendor_id) > 0) {
                    continue;
                }
                // Append a fresh vendor option as the next method should
                // add suboptions to it.
                vendor_opts.reset(new OptionVendor(Option::V4, vendor_id));
                resp->Pkt::addOption(vendor_opts);
                static_cast<void>(vendor_ids.insert(vendor_id));
            }
        }
    }
}

void
Dhcpv4Srv::appendRequestedVendorOptions(Dhcpv4Exchange& ex) {
    // Get the configured subnet suitable for the incoming packet.
    ConstSubnet4Ptr subnet = ex.getContext()->subnet_;

    const CfgOptionList& co_list = ex.getCfgOptionList();

    // Leave if there is no subnet matching the incoming packet.
    // There is no need to log the error message here because
    // it will be logged in the assignLease() when it fails to
    // pick the suitable subnet. We don't want to duplicate
    // error messages in such case.
    //
    // Also, if there's no options to possibly assign, give up.
    if (!subnet || co_list.empty()) {
        return;
    }

    Pkt4Ptr query = ex.getQuery();
    Pkt4Ptr resp = ex.getResponse();
    set<uint32_t> vendor_ids;

    // The server could have provided the option using client classification or
    // hooks. If there're vendor info options in the response already, use them.
    map<uint32_t, OptionVendorPtr> vendor_rsps;
    for (auto const& opt : resp->getOptions(DHO_VIVSO_SUBOPTIONS)) {
        OptionVendorPtr vendor_rsp;
        vendor_rsp = boost::dynamic_pointer_cast<OptionVendor>(opt.second);
        if (vendor_rsp) {
            uint32_t vendor_id = vendor_rsp->getVendorId();
            vendor_rsps[vendor_id] = vendor_rsp;
            static_cast<void>(vendor_ids.insert(vendor_id));
        }
    }

    // Next, try to get the vendor-id from the client packet's
    // vendor-specific information option (125).
    map<uint32_t, OptionVendorPtr> vendor_reqs;
    for (auto const& opt : query->getOptions(DHO_VIVSO_SUBOPTIONS)) {
        OptionVendorPtr vendor_req;
        vendor_req = boost::dynamic_pointer_cast<OptionVendor>(opt.second);
        if (vendor_req) {
            uint32_t vendor_id = vendor_req->getVendorId();
            vendor_reqs[vendor_id] = vendor_req;
            static_cast<void>(vendor_ids.insert(vendor_id));
        }
    }

    // Finally, try to get the vendor-id from the client packet's
    // vendor-specific class option (124).
    for (auto const& opt : query->getOptions(DHO_VIVCO_SUBOPTIONS)) {
        OptionVendorClassPtr vendor_class;
        vendor_class = boost::dynamic_pointer_cast<OptionVendorClass>(opt.second);
        if (vendor_class) {
            uint32_t vendor_id = vendor_class->getVendorId();
            static_cast<void>(vendor_ids.insert(vendor_id));
        }
    }

    // If there's no vendor option in either request or response, then there's no way
    // to figure out what the vendor-id values are and we give up.
    if (vendor_ids.empty()) {
        return;
    }

    map<uint32_t, set<uint8_t> > requested_opts;

    // Let's try to get ORO within that vendor-option.
    // This is specific to vendor-id=4491 (Cable Labs). Other vendors may have
    // different policies.
    OptionUint8ArrayPtr oro;
    if (vendor_reqs.count(VENDOR_ID_CABLE_LABS) > 0) {
        OptionVendorPtr vendor_req = vendor_reqs[VENDOR_ID_CABLE_LABS];
        OptionPtr oro_generic = vendor_req->getOption(DOCSIS3_V4_ORO);
        if (oro_generic) {
            // Vendor ID 4491 makes Kea look at DOCSIS3_V4_OPTION_DEFINITIONS
            // when parsing options. Based on that, oro_generic will have been
            // created as an OptionUint8Array, but might not be for other
            // vendor IDs.
            oro = boost::dynamic_pointer_cast<OptionUint8Array>(oro_generic);
        }
        if (oro) {
            set<uint8_t> oro_req_opts;
            for (uint8_t code : oro->getValues()) {
                static_cast<void>(oro_req_opts.insert(code));
            }
            requested_opts[VENDOR_ID_CABLE_LABS] = oro_req_opts;
        }
    }

    const auto& cclasses = query->getClasses();
    for (uint32_t vendor_id : vendor_ids) {

        std::set<uint8_t> cancelled_opts;

        // Iterate on the configured option list to add persistent and
        // cancelled options,
        for (auto const& copts : co_list) {
            const OptionContainerPtr& opts = copts->getAll(vendor_id);
            if (!opts) {
                continue;
            }

            // Get persistent options.
            const OptionContainerPersistIndex& pidx = opts->get<2>();
            const OptionContainerPersistRange& prange = pidx.equal_range(true);
            BOOST_FOREACH(auto const& desc, prange) {
                // Add the persistent option code to requested options.
                if (desc.option_) {
                    uint8_t code = static_cast<uint8_t>(desc.option_->getType());
                    static_cast<void>(requested_opts[vendor_id].insert(code));
                }
            }

            // Get cancelled options.
            const OptionContainerCancelIndex& cidx = opts->get<5>();
            const OptionContainerCancelRange& crange = cidx.equal_range(true);
            BOOST_FOREACH(auto const& desc, crange) {
                // Add the cancelled option code to cancelled options.
                if (desc.option_) {
                    uint8_t code = static_cast<uint8_t>(desc.option_->getType());
                    static_cast<void>(cancelled_opts.insert(code));
                }
            }
        }

        // If there is nothing to add don't do anything with this vendor.
        // This will explicitly not echo back vendor options from the request
        // that either correspond to a vendor not known to Kea even if the
        // option encapsulates data or there are no persistent options
        // configured for this vendor so Kea does not send any option back.
        if (requested_opts[vendor_id].empty()) {
            continue;
        }


        // It's possible that vivso was inserted already by client class or
        // a hook. If that is so, let's use it.
        OptionVendorPtr vendor_rsp;
        if (vendor_rsps.count(vendor_id) > 0) {
            vendor_rsp = vendor_rsps[vendor_id];
        } else {
            vendor_rsp.reset(new OptionVendor(Option::V4, vendor_id));
        }

        // Get the list of options that client requested.
        bool added = false;

        for (uint8_t opt : requested_opts[vendor_id]) {
            if (cancelled_opts.count(opt) > 0) {
                continue;
            }
            if (!vendor_rsp->getOption(opt)) {
                for (auto const& copts : co_list) {
                    OptionDescriptor desc = copts->allowedForClientClasses(vendor_id,
                                                                           opt, cclasses);
                    if (desc.option_) {
                        vendor_rsp->addOption(desc.option_);
                        added = true;
                        break;
                    }
                }
            }
        }

        // If we added some sub-options and the vendor opts option is not in
        // the response already, then add it.
        if (added && (vendor_rsps.count(vendor_id) == 0)) {
            resp->Pkt::addOption(vendor_rsp);
        }
    }
}

void
Dhcpv4Srv::appendBasicOptions(Dhcpv4Exchange& ex) {
    // Identify options that we always want to send to the
    // client (if they are configured).
    static const std::vector<uint16_t> required_options = {
        DHO_ROUTERS,
        DHO_DOMAIN_NAME_SERVERS,
        DHO_DOMAIN_NAME,
        DHO_DHCP_SERVER_IDENTIFIER };

    // Get the subnet.
    ConstSubnet4Ptr subnet = ex.getContext()->subnet_;
    if (!subnet) {
        return;
    }

    // Unlikely short cut
    const CfgOptionList& co_list = ex.getCfgOptionList();
    if (co_list.empty()) {
        return;
    }

    Pkt4Ptr resp = ex.getResponse();
    const auto& cclasses = ex.getQuery()->getClasses();

    // Try to find all 'required' options in the outgoing
    // message. Those that are not present will be added.
    for (auto const& required : required_options) {
        OptionPtr opt = resp->getOption(required);
        if (!opt) {
            // Check whether option has been configured.
            for (auto const& copts : co_list) {
                OptionDescriptor desc = copts->allowedForClientClasses(DHCP4_OPTION_SPACE,
                                                                       required, cclasses);
                if (desc.option_) {
                    resp->addOption(desc.option_);
                    break;
                }
            }
        }
    }
}

void
Dhcpv4Srv::processClientName(Dhcpv4Exchange& ex) {
    // It is possible that client has sent both Client FQDN and Hostname
    // option. In that the server should prefer Client FQDN option and
    // ignore the Hostname option.
    try {
        Pkt4Ptr query = ex.getQuery();
        Pkt4Ptr resp = ex.getResponse();
        Option4ClientFqdnPtr fqdn = boost::dynamic_pointer_cast<Option4ClientFqdn>
            (query->getOption(DHO_FQDN));
        if (fqdn) {
            LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL, DHCP4_CLIENT_FQDN_PROCESS)
                .arg(query->getLabel());
            processClientFqdnOption(ex);

        } else {
            LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL,
                      DHCP4_CLIENT_HOSTNAME_PROCESS)
                    .arg(query->getLabel());
            processHostnameOption(ex);
        }

        // Based on the output option added to the response above, we figure out
        // the values for the hostname and dns flags to set in the context.  These
        // will be used to populate the lease.
        std::string hostname;
        bool fqdn_fwd = false;
        bool fqdn_rev = false;

        OptionStringPtr opt_hostname;
        fqdn = boost::dynamic_pointer_cast<Option4ClientFqdn>(resp->getOption(DHO_FQDN));
        if (fqdn) {
            hostname = fqdn->getDomainName();
            CfgMgr::instance().getD2ClientMgr().getUpdateDirections(*fqdn, fqdn_fwd, fqdn_rev);
        } else {
            opt_hostname = boost::dynamic_pointer_cast<OptionString>
                           (resp->getOption(DHO_HOST_NAME));

            if (opt_hostname) {
                hostname = opt_hostname->getValue();
                // DHO_HOST_NAME is string option which cannot be blank,
                // we use "." to know we should replace it with a fully
                // generated name. The local string variable needs to be
                // blank in logic below.
                if (hostname == ".") {
                    hostname = "";
                }

                /// @todo It could be configurable what sort of updates the
                /// server is doing when Hostname option was sent.
                if (ex.getContext()->getDdnsParams()->getEnableUpdates()) {
                    fqdn_fwd = true;
                    fqdn_rev = true;
                }
            }
        }

        // Optionally, call a hook that may possibly override the decisions made
        // earlier.
        if (HooksManager::calloutsPresent(Hooks.hook_index_ddns4_update_)) {
            CalloutHandlePtr callout_handle = getCalloutHandle(query);

            // Use the RAII wrapper to make sure that the callout handle state is
            // reset when this object goes out of scope. All hook points must do
            // it to prevent possible circular dependency between the callout
            // handle and its arguments.
            ScopedCalloutHandleState callout_handle_state(callout_handle);

            // Setup the callout arguments.
            ConstSubnet4Ptr subnet = ex.getContext()->subnet_;
            callout_handle->setArgument("query4", query);
            callout_handle->setArgument("response4", resp);
            callout_handle->setArgument("subnet4", subnet);
            callout_handle->setArgument("hostname", hostname);
            callout_handle->setArgument("fwd-update", fqdn_fwd);
            callout_handle->setArgument("rev-update", fqdn_rev);
            callout_handle->setArgument("ddns-params", ex.getContext()->getDdnsParams());

            // Call callouts
            HooksManager::callCallouts(Hooks.hook_index_ddns4_update_, *callout_handle);

            // Let's get the parameters returned by hook.
            string hook_hostname;
            bool hook_fqdn_fwd = false;
            bool hook_fqdn_rev = false;
            callout_handle->getArgument("hostname", hook_hostname);
            callout_handle->getArgument("fwd-update", hook_fqdn_fwd);
            callout_handle->getArgument("rev-update", hook_fqdn_rev);

            // If there's anything changed by the hook, log it and then update
            // the parameters.
            if ((hostname != hook_hostname) || (fqdn_fwd != hook_fqdn_fwd) ||
                (fqdn_rev != hook_fqdn_rev)) {
                LOG_DEBUG(hooks_logger, DBGLVL_PKT_HANDLING, DHCP4_HOOK_DDNS_UPDATE)
                    .arg(hostname).arg(hook_hostname).arg(fqdn_fwd).arg(hook_fqdn_fwd)
                    .arg(fqdn_rev).arg(hook_fqdn_rev);
                hostname = hook_hostname;
                fqdn_fwd = hook_fqdn_fwd;
                fqdn_rev = hook_fqdn_rev;

                // If there's an outbound host-name option in the response we
                // need to updated it with the new host name.
                OptionStringPtr hostname_opt = boost::dynamic_pointer_cast<OptionString>
                                              (resp->getOption(DHO_HOST_NAME));
                if (hostname_opt) {
                    hostname_opt->setValue(hook_hostname);
                }

                // If there's an outbound FQDN option in the response we need
                // to update it with the new host name.
                fqdn = boost::dynamic_pointer_cast<Option4ClientFqdn>(resp->getOption(DHO_FQDN));
                if (fqdn) {
                    fqdn->setDomainName(hook_hostname, Option4ClientFqdn::FULL);
                    // Hook disabled updates, Set flags back to client accordingly.
                    fqdn->setFlag(Option4ClientFqdn::FLAG_S, 0);
                    fqdn->setFlag(Option4ClientFqdn::FLAG_N, 1);
                }
            }
        }

        // Update the context
        auto ctx = ex.getContext();
        ctx->fwd_dns_update_ = fqdn_fwd;
        ctx->rev_dns_update_ = fqdn_rev;
        ctx->hostname_ = hostname;

    } catch (const Exception& e) {
        // In some rare cases it is possible that the client's name processing
        // fails. For example, the Hostname option may be malformed, or there
        // may be an error in the server's logic which would cause multiple
        // attempts to add the same option to the response message. This
        // error message aggregates all these errors so they can be diagnosed
        // from the log. We don't want to throw an exception here because,
        // it will impact the processing of the whole packet. We rather want
        // the processing to continue, even if the client's name is wrong.
        LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_CLIENT_NAME_PROC_FAIL)
            .arg(ex.getQuery()->getLabel())
            .arg(e.what());
    }
}

void
Dhcpv4Srv::processClientFqdnOption(Dhcpv4Exchange& ex) {
    // Obtain the FQDN option from the client's message.
    Option4ClientFqdnPtr fqdn = boost::dynamic_pointer_cast<
        Option4ClientFqdn>(ex.getQuery()->getOption(DHO_FQDN));

    LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_CLIENT_FQDN_DATA)
        .arg(ex.getQuery()->getLabel())
        .arg(fqdn->toText());

    // Create the DHCPv4 Client FQDN Option to be included in the server's
    // response to a client.
    Option4ClientFqdnPtr fqdn_resp(new Option4ClientFqdn(*fqdn));

    // Set the server S, N, and O flags based on client's flags and
    // current configuration.
    D2ClientMgr& d2_mgr = CfgMgr::instance().getD2ClientMgr();
    d2_mgr.adjustFqdnFlags<Option4ClientFqdn>(*fqdn, *fqdn_resp,
                                              *(ex.getContext()->getDdnsParams()));
    // Carry over the client's E flag.
    fqdn_resp->setFlag(Option4ClientFqdn::FLAG_E,
                       fqdn->getFlag(Option4ClientFqdn::FLAG_E));

    if (ex.getContext()->currentHost() &&
        !ex.getContext()->currentHost()->getHostname().empty()) {
        fqdn_resp->setDomainName(d2_mgr.qualifyName(ex.getContext()->currentHost()->getHostname(),
                                                    *(ex.getContext()->getDdnsParams()), true),
                                 Option4ClientFqdn::FULL);

    } else {
        // Adjust the domain name based on domain name value and type sent by the
        // client and current configuration.
        d2_mgr.adjustDomainName<Option4ClientFqdn>(*fqdn, *fqdn_resp,
                                                   *(ex.getContext()->getDdnsParams()));
    }

    // Add FQDN option to the response message. Note that, there may be some
    // cases when server may choose not to include the FQDN option in a
    // response to a client. In such cases, the FQDN should be removed from the
    // outgoing message. In theory we could cease to include the FQDN option
    // in this function until it is confirmed that it should be included.
    // However, we include it here for simplicity. Functions used to acquire
    // lease for a client will scan the response message for FQDN and if it
    // is found they will take necessary actions to store the FQDN information
    // in the lease database as well as to generate NameChangeRequests to DNS.
    // If we don't store the option in the response message, we will have to
    // propagate it in the different way to the functions which acquire the
    // lease. This would require modifications to the API of this class.
    LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_RESPONSE_FQDN_DATA)
        .arg(ex.getQuery()->getLabel())
        .arg(fqdn_resp->toText());
    ex.getResponse()->addOption(fqdn_resp);
}

void
Dhcpv4Srv::processHostnameOption(Dhcpv4Exchange& ex) {
    // Fetch D2 configuration.
    D2ClientMgr& d2_mgr = CfgMgr::instance().getD2ClientMgr();

    // Obtain the Hostname option from the client's message.
    OptionStringPtr opt_hostname = boost::dynamic_pointer_cast<OptionString>
        (ex.getQuery()->getOption(DHO_HOST_NAME));

    if (opt_hostname) {
        LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_CLIENT_HOSTNAME_DATA)
            .arg(ex.getQuery()->getLabel())
            .arg(opt_hostname->getValue());
    }

    AllocEngine::ClientContext4Ptr ctx = ex.getContext();

    // Hostname reservations take precedence over any other configuration,
    // i.e. DDNS configuration.  If we have a reserved hostname we should
    // use it and send it back.
    if (ctx->currentHost() && !ctx->currentHost()->getHostname().empty()) {
        // Qualify if there is a suffix configured.
        std::string hostname = d2_mgr.qualifyName(ctx->currentHost()->getHostname(),
                                                  *(ex.getContext()->getDdnsParams()), false);
        // Convert it to lower case.
        boost::algorithm::to_lower(hostname);
        LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_RESERVED_HOSTNAME_ASSIGNED)
                .arg(ex.getQuery()->getLabel())
                .arg(hostname);

        // Add it to the response
        OptionStringPtr opt_hostname_resp(new OptionString(Option::V4, DHO_HOST_NAME, hostname));
        ex.getResponse()->addOption(opt_hostname_resp);

        // We're done here.
        return;
    }

    // There is no reservation for this client however there is still a
    // possibility that we'll have to send hostname option to this client
    // if the client has included hostname option or the configuration of
    // the server requires that we send the option regardless.
    D2ClientConfig::ReplaceClientNameMode replace_name_mode =
        ex.getContext()->getDdnsParams()->getReplaceClientNameMode();

    // If we don't have a hostname then either we'll supply it or do nothing.
    if (!opt_hostname) {
        // If we're configured to supply it then add it to the response.
        // Use the root domain to signal later on that we should replace it.
        if (replace_name_mode == D2ClientConfig::RCM_ALWAYS ||
            replace_name_mode == D2ClientConfig::RCM_WHEN_NOT_PRESENT) {
            LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL_DATA,
                      DHCP4_GENERATE_FQDN)
                .arg(ex.getQuery()->getLabel());
            OptionStringPtr opt_hostname_resp(new OptionString(Option::V4,
                                                               DHO_HOST_NAME,
                                                               "."));
            ex.getResponse()->addOption(opt_hostname_resp);
        }

        return;
    }

    // Client sent us a hostname option so figure out what to do with it.
    LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_CLIENT_HOSTNAME_DATA)
        .arg(ex.getQuery()->getLabel())
        .arg(opt_hostname->getValue());

    std::string hostname = isc::util::str::trim(opt_hostname->getValue());
    unsigned int label_count;

    try  {
        // Parsing into labels can throw on malformed content so we're
        // going to explicitly catch that here.
        label_count = OptionDataTypeUtil::getLabelCount(hostname);
    } catch (const std::exception& exc) {
        LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL, DHCP4_CLIENT_HOSTNAME_MALFORMED)
            .arg(ex.getQuery()->getLabel())
            .arg(exc.what());
        return;
    }

    // The hostname option sent by the client should be at least 1 octet long.
    // If it isn't we ignore this option. (Per RFC 2131, section 3.14)
    /// @todo It would be more liberal to accept this and let it fall into
    /// the case  of replace or less than two below.
    if (label_count == 0) {
        LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL, DHCP4_EMPTY_HOSTNAME)
            .arg(ex.getQuery()->getLabel());
        return;
    }

    // Stores the value we eventually use, so we can send it back.
    OptionStringPtr opt_hostname_resp;

    // The hostname option may be unqualified or fully qualified. The lab_count
    // holds the number of labels for the name. The number of 1 means that
    // there is only root label "." (even for unqualified names, as the
    // getLabelCount function treats each name as a fully qualified one).
    // By checking the number of labels present in the hostname we may infer
    // whether client has sent the fully qualified or unqualified hostname.

    if ((replace_name_mode == D2ClientConfig::RCM_ALWAYS ||
         replace_name_mode == D2ClientConfig::RCM_WHEN_PRESENT)
        || label_count < 2) {
        // Set to root domain to signal later on that we should replace it.
        // DHO_HOST_NAME is a string option which cannot be empty.
        /// @todo We may want to reconsider whether it is appropriate for the
        /// client to send a root domain name as a Hostname. There are
        /// also extensions to the auto generation of the client's name,
        /// e.g. conversion to the puny code which may be considered at some
        /// point.
        /// For now, we just remain liberal and expect that the DNS will handle
        /// conversion if needed and possible.
        opt_hostname_resp.reset(new OptionString(Option::V4, DHO_HOST_NAME, "."));
    } else {
        // Sanitize the name the client sent us, if we're configured to do so.
        isc::util::str::StringSanitizerPtr sanitizer =
            ex.getContext()->getDdnsParams()->getHostnameSanitizer();

        if (sanitizer) {
            hostname = sanitizer->scrub(hostname);
        }

        // Convert hostname to lower case.
        boost::algorithm::to_lower(hostname);

        if (label_count == 2) {
            // If there are two labels, it means that the client has specified
            // the unqualified name. We have to concatenate the unqualified name
            // with the domain name. The false value passed as a second argument
            // indicates that the trailing dot should not be appended to the
            // hostname. We don't want to append the trailing dot because
            // we don't know whether the hostname is partial or not and some
            // clients do not handle the hostnames with the trailing dot.
            opt_hostname_resp.reset(
                new OptionString(Option::V4, DHO_HOST_NAME,
                                 d2_mgr.qualifyName(hostname, *(ex.getContext()->getDdnsParams()),
                                                    false)));
        } else {
            opt_hostname_resp.reset(new OptionString(Option::V4, DHO_HOST_NAME, hostname));
        }
    }

    LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_RESPONSE_HOSTNAME_DATA)
        .arg(ex.getQuery()->getLabel())
        .arg(opt_hostname_resp->getValue());
    ex.getResponse()->addOption(opt_hostname_resp);
}

void
Dhcpv4Srv::createNameChangeRequests(const Lease4Ptr& lease,
                                    const Lease4Ptr& old_lease,
                                    const DdnsParams& ddns_params) {
    if (!lease) {
        isc_throw(isc::Unexpected,
                  "NULL lease specified when creating NameChangeRequest");
    }

    // Nothing to do if updates are not enabled.
    if (!ddns_params.getEnableUpdates()) {
        return;
    }

    if ((lease->reuseable_valid_lft_ == 0) &&
        (!old_lease || ddns_params.getUpdateOnRenew() ||
         !lease->hasIdenticalFqdn(*old_lease))) {
        if (old_lease) {
            // Queue's up a remove of the old lease's DNS (if needed)
            queueNCR(CHG_REMOVE, old_lease);
        }

        // We may need to generate the NameChangeRequest for the new lease. It
        // will be generated only if hostname is set and if forward or reverse
        // update has been requested.
        queueNCR(CHG_ADD, lease);
    }
}

bool
Dhcpv4Srv::assignZero(ConstSubnet4Ptr& subnet,
                      const ClientClasses& client_classes) {
    ConstSubnet4Ptr current_subnet = subnet;
    // Try subnets.
    while (current_subnet) {
        const ConstCfgOptionPtr& co = current_subnet->getCfgOption();
        if (!co->empty()) {
            OptionDescriptor desc = co->get(DHCP4_OPTION_SPACE,
                                            DHO_V6_ONLY_PREFERRED);
            if (desc.option_) {
                subnet = current_subnet;
                return (true);
            }
        }
        current_subnet = current_subnet->getNextSubnet(subnet, client_classes);
    }
    // Try the shared network.
    SharedNetwork4Ptr network;
    subnet->getSharedNetwork(network);
    if (network) {
        const ConstCfgOptionPtr& co = network->getCfgOption();
        if (!co->empty()) {
            OptionDescriptor desc = co->get(DHCP4_OPTION_SPACE,
                                            DHO_V6_ONLY_PREFERRED);
            if (desc.option_) {
                return (true);
            }
        }
    }
    return (false);
}

void
Dhcpv4Srv::assignLease(Dhcpv4Exchange& ex) {
    // Get the pointers to the query and the response messages.
    Pkt4Ptr query = ex.getQuery();
    Pkt4Ptr resp = ex.getResponse();

    // Get the context.
    AllocEngine::ClientContext4Ptr ctx = ex.getContext();

    // Subnet should have been already selected when the context was created.
    ConstSubnet4Ptr subnet = ctx->subnet_;

    // "Fake" allocation is processing of DISCOVER message. We pretend to do an
    // allocation, but we do not put the lease in the database. That is ok,
    // because we do not guarantee that the user will get that exact lease. If
    // the user selects this server to do actual allocation (i.e. sends REQUEST)
    // it should include this hint. That will help us during the actual lease
    // allocation.
    bool fake_allocation = (query->getType() == DHCPDISCOVER);

    if (subnet) {
        // Check if IPv6-Only Preferred was requested.
        OptionUint8ArrayPtr option_prl = boost::dynamic_pointer_cast<
            OptionUint8Array>(query->getOption(DHO_DHCP_PARAMETER_REQUEST_LIST));
        if (option_prl) {
            auto const& requested_opts = option_prl->getValues();
            if ((std::find(requested_opts.cbegin(), requested_opts.cend(),
                           DHO_V6_ONLY_PREFERRED) != requested_opts.cend()) &&
                assignZero(subnet, query->getClasses())) {
                ex.setIPv6OnlyPreferred(true);
                ctx->subnet_ = subnet;
                resp->setYiaddr(IOAddress::IPV4_ZERO_ADDRESS());
                if (!fake_allocation) {
                    resp->setCiaddr(query->getCiaddr());
                }
                return;
            }
        }
    }

    // Get the server identifier. It will be used to determine the state
    // of the client.
    OptionCustomPtr opt_serverid = boost::dynamic_pointer_cast<
        OptionCustom>(query->getOption(DHO_DHCP_SERVER_IDENTIFIER));

    // Check if the client has sent a requested IP address option or
    // ciaddr.
    OptionCustomPtr opt_requested_address = boost::dynamic_pointer_cast<
        OptionCustom>(query->getOption(DHO_DHCP_REQUESTED_ADDRESS));
    IOAddress hint(IOAddress::IPV4_ZERO_ADDRESS());
    if (opt_requested_address) {
        hint = opt_requested_address->readAddress();

    } else if (!query->getCiaddr().isV4Zero()) {
        hint = query->getCiaddr();

    }

    // This flag controls whether or not the server should respond to the clients
    // in the INIT-REBOOT state. We will initialize it to a configured value only
    // when the client is in that state.
    auto authoritative = false;

    // If there is no server id and there is a Requested IP Address option
    // the client is in the INIT-REBOOT state in which the server has to
    // determine whether the client's notion of the address is correct
    // and whether the client is known, i.e., has a lease.
    auto init_reboot = (!fake_allocation && !opt_serverid && opt_requested_address);

    if (init_reboot) {
        LOG_INFO(lease4_logger, DHCP4_INIT_REBOOT)
            .arg(query->getLabel())
            .arg(hint.toText());

        // Find the authoritative flag configuration.
        if (subnet) {
            authoritative = subnet->getAuthoritative();
        } else {
            // If there is no subnet, use the global value.
            auto flag = CfgMgr::instance().getCurrentCfg()->getConfiguredGlobals()->
                get(CfgGlobals::AUTHORITATIVE);
            if (flag && (flag->getType() == data::Element::boolean)) {
                authoritative = flag->boolValue();
            }
        }
    } else if (fake_allocation) {
        LOG_DEBUG(lease4_logger, DBG_DHCP4_DETAIL, DHCP4_DISCOVER)
            .arg(query->getLabel())
            .arg(hint != IOAddress::IPV4_ZERO_ADDRESS() ? hint.toText() : "(no hint)");
    } else {
        LOG_DEBUG(lease4_logger, DBG_DHCP4_DETAIL, DHCP4_REQUEST)
            .arg(query->getLabel())
            .arg(hint != IOAddress::IPV4_ZERO_ADDRESS() ? hint.toText() : "(no hint)");
    }

    // If there is no subnet configuration for that client we ignore the
    // request from the INIT-REBOOT client if we're not authoritative, because
    // we don't know whether the network configuration is correct for this
    // client. We return DHCPNAK if we're authoritative, though.
    if (!subnet) {
        // This particular client is out of luck today. We do not have
        // information about the subnet he is connected to. This likely means
        // misconfiguration of the server (or some relays).

        // If it's a rebind, quietly drop it.
        if (!fake_allocation && !opt_serverid && !opt_requested_address
            && !query->getCiaddr().isV4Zero() && query->getLocalAddr().isV4Bcast()) {
            ex.deleteResponse();
            return;
        }

        if (!init_reboot || authoritative) {
            // Perhaps this should be logged on some higher level?
            LOG_ERROR(bad_packet4_logger, DHCP4_PACKET_NAK_0001)
                .arg(query->getLabel())
                .arg(query->getRemoteAddr().toText())
                .arg(query->getName());
            resp->setType(DHCPNAK);
            resp->setYiaddr(IOAddress::IPV4_ZERO_ADDRESS());
            return;
        }
    }

    HWAddrPtr hwaddr = query->getHWAddr();

    ConstSubnet4Ptr original_subnet = subnet;

    // Get client-id. It is not mandatory in DHCPv4.
    ClientIdPtr client_id = ex.getContext()->clientid_;

    // In the INIT-REBOOT state, a client remembering its previously assigned
    // address is trying to confirm whether or not this address is still usable.
    if (init_reboot) {
        Lease4Ptr lease;

        auto const& classes = query->getClasses();

        // We used to issue a separate query (two actually: one for client-id
        // and another one for hw-addr for) each subnet in the shared network.
        // That was horribly inefficient if the client didn't have any lease
        // (or there were many subnets and the client happened to be in one
        // of the last subnets).
        //
        // We now issue at most two queries: get all the leases for specific
        // client-id and then get all leases for specific hw-address.
        if (original_subnet && client_id) {

            // Get all the leases for this client-id
            Lease4Collection leases_client_id = LeaseMgrFactory::instance().getLease4(*client_id);
            if (!leases_client_id.empty()) {
                ConstSubnet4Ptr s = original_subnet;

                // Among those returned try to find a lease that belongs to
                // current shared network.
                while (s) {
                    for (auto const& l : leases_client_id) {
                        if (l->subnet_id_ == s->getID()) {
                            lease = l;
                            break;
                        }
                    }

                    if (lease) {
                        break;

                    } else {
                        s = s->getNextSubnet(original_subnet, classes);
                    }
                }
            }
        }

        // If we haven't found a lease yet, try again by hardware-address.
        // The logic is the same.
        if (original_subnet && !lease && hwaddr) {

            // Get all leases for this particular hw-address.
            Lease4Collection leases_hwaddr = LeaseMgrFactory::instance().getLease4(*hwaddr);
            if (!leases_hwaddr.empty()) {
                ConstSubnet4Ptr s = original_subnet;

                // Pick one that belongs to a subnet in this shared network.
                while (s) {
                    for (auto const& l : leases_hwaddr) {
                        if (l->subnet_id_ == s->getID()) {
                            lease = l;
                            break;
                        }
                    }

                    if (lease) {
                        break;

                    } else {
                        s = s->getNextSubnet(original_subnet, classes);
                    }
                }
            }
        }

        // Check the first error case: unknown client. We check this before
        // validating the address sent because we don't want to respond if
        // we don't know this client, except if we're authoritative.
        bool known_client = lease && lease->belongsToClient(hwaddr, client_id);
        if (!authoritative && !known_client) {
            LOG_DEBUG(bad_packet4_logger, DBG_DHCP4_DETAIL,
                      DHCP4_NO_LEASE_INIT_REBOOT)
                .arg(query->getLabel())
                .arg(hint.toText());

            ex.deleteResponse();
            return;
        }

        // If we know this client, check if his notion of the IP address is
        // correct, if we don't know him, check if we are authoritative.
        if ((known_client && (lease->addr_ != hint)) ||
            (!known_client && authoritative) ||
            (!original_subnet)) {
            LOG_DEBUG(bad_packet4_logger, DBG_DHCP4_DETAIL,
                      DHCP4_PACKET_NAK_0002)
                .arg(query->getLabel())
                .arg(hint.toText());

            resp->setType(DHCPNAK);
            resp->setYiaddr(IOAddress::IPV4_ZERO_ADDRESS());
            return;
        }
    }

    CalloutHandlePtr callout_handle = getCalloutHandle(query);

    // We need to set these values in the context as they haven't been set yet.
    ctx->requested_address_ = hint;
    ctx->fake_allocation_ = fake_allocation;
    ctx->callout_handle_ = callout_handle;

    // If client query contains an FQDN or Hostname option, server
    // should respond to the client with the appropriate FQDN or Hostname
    // option to indicate if it takes responsibility for the DNS updates.
    // This is also the source for the hostname and dns flags that are
    // initially added to the lease.  In most cases, this information is
    // good now.  If we end up changing subnets in allocation we'll have to
    // do it again and then update the lease.
    processClientName(ex);

    // Get a lease.
    Lease4Ptr lease = alloc_engine_->allocateLease4(*ctx);

    bool reprocess_client_name = false;
    if (lease) {
        // Since we have a lease check for pool-level DDNS parameters.
        // If there are any we need to call processClientName() again.
        auto ddns_params = ex.getContext()->getDdnsParams();
        auto pool = ddns_params->setPoolFromAddress(lease->addr_);
        if (pool) {
            reprocess_client_name = pool->hasDdnsParameters();
        }
    }

    // Subnet may be modified by the allocation engine, if the initial subnet
    // belongs to a shared network.
    if (subnet && ctx->subnet_ && subnet->getID() != ctx->subnet_->getID()) {
        // We changed subnets and that means DDNS parameters might be different
        // so we need to rerun client name processing logic.  Arguably we could
        // compare DDNS parameters for both subnets and then decide if we need
        // to rerun the name logic, but that's not likely to be any faster than
        // just re-running the name logic.  @todo When inherited parameter
        // performance is improved this argument could be revisited.
        // Another case is the new subnet has a reserved hostname.
        SharedNetwork4Ptr network;
        subnet->getSharedNetwork(network);
        LOG_DEBUG(packet4_logger, DBG_DHCP4_BASIC_DATA, DHCP4_SUBNET_DYNAMICALLY_CHANGED)
                .arg(query->getLabel())
                .arg(subnet->toText())
                .arg(ctx->subnet_->toText())
                .arg(network ? network->getName() : "<no network?>");

        subnet = ctx->subnet_;
        if (lease) {
            reprocess_client_name = true;
        }
    }

    // Tracks whether or not the client name (FQDN or host) has changed since
    // the lease was allocated.
    bool client_name_changed = false;

    if (reprocess_client_name) {
        // First, we need to remove the prior values from the response and reset
        // those in context, to give processClientName a clean slate.
        resp->delOption(DHO_FQDN);
        resp->delOption(DHO_HOST_NAME);
        ctx->hostname_ = "";
        ctx->fwd_dns_update_  = false;
        ctx->rev_dns_update_ = false;

        // Regenerate the name and dns flags.
        processClientName(ex);

        // If the results are different from the values already on the
        // lease, flag it so the lease gets updated down below.
        if ((lease->hostname_ != ctx->hostname_) ||
            (lease->fqdn_fwd_ != ctx->fwd_dns_update_) ||
            (lease->fqdn_rev_ != ctx->rev_dns_update_)) {
            lease->hostname_ = ctx->hostname_;
            lease->fqdn_fwd_ = ctx->fwd_dns_update_;
            lease->fqdn_rev_ = ctx->rev_dns_update_;
            client_name_changed = true;
        }
    }

    if (lease) {
        // We have a lease! Let's set it in the packet and send it back to
        // the client.
        if (fake_allocation) {
            LOG_INFO(lease4_logger, DHCP4_LEASE_OFFER)
                .arg(query->getLabel())
                .arg(lease->addr_.toText());
        } else {
            LOG_INFO(lease4_logger, DHCP4_LEASE_ALLOC)
                .arg(query->getLabel())
                .arg(lease->addr_.toText())
                .arg(Lease::lifetimeToText(lease->valid_lft_));
        }

        // We're logging this here, because this is the place where we know
        // which subnet has been actually used for allocation. If the
        // client identifier matching is disabled, we want to make sure that
        // the user is notified.
        if (!ctx->subnet_->getMatchClientId()) {
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_CLIENTID_IGNORED_FOR_LEASES)
                .arg(ctx->query_->getLabel())
                .arg(ctx->subnet_->getID());
        }

        resp->setYiaddr(lease->addr_);

        /// @todo The server should check what ciaddr the client has supplied
        /// in ciaddr. Currently the ciaddr is ignored except for the subnet
        /// selection. If the client supplied an invalid address, the server
        /// will also return an invalid address here.
        if (!fake_allocation) {
            // If this is a renewing client it will set a ciaddr which the
            // server may include in the response. If this is a new allocation
            // the client will set ciaddr to 0 and this will also be propagated
            // to the server's resp.
            resp->setCiaddr(query->getCiaddr());
        }

        // We may need to update FQDN or hostname if the server is to generate
        // a new name from the allocated IP address or if the allocation engine
        // switched to a different subnet within a shared network.
        postAllocateNameUpdate(ctx, lease, query, resp, client_name_changed);

        // Reuse the lease if possible.
        if (lease->reuseable_valid_lft_ > 0) {
            lease->valid_lft_ = lease->reuseable_valid_lft_;
            LOG_INFO(lease4_logger, DHCP4_LEASE_REUSE)
                .arg(query->getLabel())
                .arg(lease->addr_.toText())
                .arg(Lease::lifetimeToText(lease->valid_lft_));

            // Increment the reuse statistics.
            StatsMgr::instance().addValue("v4-lease-reuses", int64_t(1));
            StatsMgr::instance().addValue(StatsMgr::generateName("subnet", lease->subnet_id_,
                                                                 "v4-lease-reuses"),
                                          int64_t(1));
        }

        // IP Address Lease time (type 51)
        // If we're not allocating on discover  then we just sent the lifetime on the lease.
        // Otherwise (i.e. offer_lft > 0), the lease's lifetime has been set to offer_lft but
        // we want to send the client the proper valid lifetime so we have to fetch it.
        auto send_lft = (ctx->offer_lft_ ? AllocEngine::getValidLft(*ctx) : lease->valid_lft_);
        OptionPtr opt(new OptionUint32(Option::V4, DHO_DHCP_LEASE_TIME, send_lft));

        resp->addOption(opt);

        // Subnet mask (type 1)
        resp->addOption(getNetmaskOption(subnet));

        // Set T1 and T2 per configuration.
        setTeeTimes(lease, subnet, resp);

        // Create NameChangeRequests if this is a real allocation.
        if (!fake_allocation) {
            try {
                createNameChangeRequests(lease, ctx->old_lease_,
                                         *ex.getContext()->getDdnsParams());
            } catch (const Exception& ex) {
                LOG_ERROR(ddns4_logger, DHCP4_NCR_CREATION_FAILED)
                    .arg(query->getLabel())
                    .arg(ex.what());
            }
        }

    } else {
        // Allocation engine did not allocate a lease. The engine logged
        // cause of that failure.
        if (ctx->unknown_requested_addr_) {
            ConstSubnet4Ptr s = original_subnet;
            // Address might have been rejected via class guard (i.e. not
            // allowed for this client). We need to determine if we truly
            // do not know about the address or whether this client just
            // isn't allowed to have that address. We should only DHCPNAK
            // For the latter.
            while (s) {
                if (s->inPool(Lease::TYPE_V4, hint)) {
                    break;
                }

                s = s->getNextSubnet(original_subnet);
            }

            // If we didn't find a subnet, it's not an address we know about
            // so we drop the DHCPNAK.
            if (!s) {
                LOG_DEBUG(bad_packet4_logger, DBG_DHCP4_DETAIL,
                          DHCP4_UNKNOWN_ADDRESS_REQUESTED)
                          .arg(query->getLabel())
                          .arg(query->getCiaddr().toText())
                          .arg(opt_requested_address ?
                          opt_requested_address->readAddress().toText() : "(no address)");
                ex.deleteResponse();
                return;
            }
        }

        LOG_DEBUG(bad_packet4_logger, DBG_DHCP4_DETAIL, fake_allocation ?
                  DHCP4_PACKET_NAK_0003 : DHCP4_PACKET_NAK_0004)
            .arg(query->getLabel())
            .arg(query->getCiaddr().toText())
            .arg(opt_requested_address ?
                 opt_requested_address->readAddress().toText() : "(no address)");

        resp->setType(DHCPNAK);
        resp->setYiaddr(IOAddress::IPV4_ZERO_ADDRESS());

        resp->delOption(DHO_FQDN);
        resp->delOption(DHO_HOST_NAME);
    }
}

void
Dhcpv4Srv::postAllocateNameUpdate(const AllocEngine::ClientContext4Ptr& ctx, const Lease4Ptr& lease,
                                 const Pkt4Ptr& query, const Pkt4Ptr& resp, bool client_name_changed) {
    // We may need to update FQDN or hostname if the server is to generate
    // new name from the allocated IP address or if the allocation engine
    // has switched to a different subnet within a shared network.  Get
    // FQDN and hostname options from the response.
    OptionStringPtr opt_hostname;
    Option4ClientFqdnPtr fqdn = boost::dynamic_pointer_cast<
                Option4ClientFqdn>(resp->getOption(DHO_FQDN));
    if (!fqdn) {
        opt_hostname = boost::dynamic_pointer_cast<OptionString>(resp->getOption(DHO_HOST_NAME));
        if (!opt_hostname) {
            // We don't have either one, nothing to do.
            return;
        }
    }

    // Empty hostname on the lease means we need to generate it.
    if (lease->hostname_.empty()) {
        // Note that if we have received the hostname option, rather than
        // Client FQDN the trailing dot is not appended to the generated
        // hostname because some clients don't handle the trailing dot in
        // the hostname. Whether the trailing dot is appended or not is
        // controlled by the second argument to the generateFqdn().
        lease->hostname_ = CfgMgr::instance().getD2ClientMgr()
                    .generateFqdn(lease->addr_, *(ctx->getDdnsParams()), static_cast<bool>(fqdn));

        LOG_DEBUG(ddns4_logger, DBG_DHCP4_DETAIL, DHCP4_RESPONSE_HOSTNAME_GENERATE)
            .arg(query->getLabel())
            .arg(lease->hostname_);

        client_name_changed = true;
    }

    if (client_name_changed) {
        // The operations below are rather safe, but we want to catch
        // any potential exceptions (e.g. invalid lease database backend
        // implementation) and log an error.
        try {
            /// TKM - do this on committed-discover
            if (!ctx->fake_allocation_ || (ctx->offer_lft_ > 0)) {
                // The lease can't be reused.
                lease->reuseable_valid_lft_ = 0;

                // The lease update should be safe, because the lease should
                // be already in the database. In most cases the exception
                // would be thrown if the lease was missing.
                LeaseMgrFactory::instance().updateLease4(lease);
            }

            // The name update in the outbound option should be also safe,
            // because the generated name is well formed.
            if (fqdn) {
                fqdn->setDomainName(lease->hostname_, Option4ClientFqdn::FULL);
            } else {
                opt_hostname->setValue(lease->hostname_);
            }
        } catch (const Exception& ex) {
            LOG_ERROR(ddns4_logger, DHCP4_POST_ALLOCATION_NAME_UPDATE_FAIL)
                .arg(query->getLabel())
                .arg(lease->hostname_)
                .arg(ex.what());
        }
    }
}

/// @todo This logic to be modified if we decide to support infinite lease times.
void
Dhcpv4Srv::setTeeTimes(const Lease4Ptr& lease, const ConstSubnet4Ptr& subnet, Pkt4Ptr resp) {

    uint32_t t2_time = 0;
    // If T2 is explicitly configured we'll use try value.
    if (!subnet->getT2().unspecified()) {
        t2_time = subnet->getT2();
    } else if (subnet->getCalculateTeeTimes()) {
        // Calculating tee times is enabled, so calculated it.
        t2_time = static_cast<uint32_t>(round(subnet->getT2Percent() * (lease->valid_lft_)));
    }

    // Send the T2 candidate value only if it's sane: to be sane it must be less than
    // the valid life time.
    uint32_t timer_ceiling = lease->valid_lft_;
    if (t2_time > 0 && t2_time < timer_ceiling) {
        OptionUint32Ptr t2(new OptionUint32(Option::V4, DHO_DHCP_REBINDING_TIME, t2_time));
        resp->addOption(t2);
        // When we send T2, timer ceiling for T1 becomes T2.
        timer_ceiling = t2_time;
    }

    uint32_t t1_time = 0;
    // If T1 is explicitly configured we'll use try value.
    if (!subnet->getT1().unspecified()) {
        t1_time = subnet->getT1();
    } else if (subnet->getCalculateTeeTimes()) {
        // Calculating tee times is enabled, so calculate it.
        t1_time = static_cast<uint32_t>(round(subnet->getT1Percent() * (lease->valid_lft_)));
    }

    // Send T1 if it's sane: If we sent T2, T1 must be less than that.  If not it must be
    // less than the valid life time.
    if (t1_time > 0 && t1_time < timer_ceiling) {
        OptionUint32Ptr t1(new OptionUint32(Option::V4, DHO_DHCP_RENEWAL_TIME, t1_time));
        resp->addOption(t1);
    }
}

uint16_t
Dhcpv4Srv::checkRelayPort(const Dhcpv4Exchange& ex) {

    // Look for a relay-port RAI sub-option in the query.
    const Pkt4Ptr& query = ex.getQuery();
    const OptionPtr& rai = query->getOption(DHO_DHCP_AGENT_OPTIONS);
    if (rai && rai->getOption(RAI_OPTION_RELAY_PORT)) {
        // Got the sub-option so use the remote port set by the relay.
        return (query->getRemotePort());
    }
    return (0);
}

void
Dhcpv4Srv::adjustIfaceData(Dhcpv4Exchange& ex) {
    adjustRemoteAddr(ex);

    // Initialize the pointers to the client's message and the server's
    // response.
    Pkt4Ptr query = ex.getQuery();
    Pkt4Ptr response = ex.getResponse();

    // The DHCPINFORM is generally unicast to the client. The only situation
    // when the server is unable to unicast to the client is when the client
    // doesn't include ciaddr and the message is relayed. In this case the
    // server has to reply via relay agent. For other messages we send back
    // through relay if message is relayed, and unicast to the client if the
    // message is not relayed.
    // If client port was set from the command line enforce all responses
    // to it. Of course it is only for testing purposes.
    // Note that the call to this function may throw if invalid combination
    // of hops and giaddr is found (hops = 0 if giaddr = 0 and hops != 0 if
    // giaddr != 0). The exception will propagate down and eventually cause the
    // packet to be discarded.
    if (client_port_) {
        response->setRemotePort(client_port_);
    } else if (((query->getType() == DHCPINFORM) &&
         ((!query->getCiaddr().isV4Zero()) ||
          (!query->isRelayed() && !query->getRemoteAddr().isV4Zero()))) ||
        ((query->getType() != DHCPINFORM) && !query->isRelayed())) {
        response->setRemotePort(DHCP4_CLIENT_PORT);

    } else {
        // RFC 8357 section 5.1
        uint16_t relay_port = checkRelayPort(ex);
        response->setRemotePort(relay_port ? relay_port : DHCP4_SERVER_PORT);
    }

    CfgIfacePtr cfg_iface = CfgMgr::instance().getCurrentCfg()->getCfgIface();
    if (query->isRelayed() &&
        (cfg_iface->getSocketType() == CfgIface::SOCKET_UDP) &&
        (cfg_iface->getOutboundIface() == CfgIface::USE_ROUTING)) {

        // Mark the response to follow routing
        response->setLocalAddr(IOAddress::IPV4_ZERO_ADDRESS());
        response->resetIndex();
        // But keep the interface name
        response->setIface(query->getIface());

    } else {

        IOAddress local_addr = query->getLocalAddr();

        // In many cases the query is sent to a broadcast address. This address
        // appears as a local address in the query message. We can't simply copy
        // this address to a response message and use it as a source address.
        // Instead we will need to use the address assigned to the interface
        // on which the query has been received. In other cases, we will just
        // use this address as a source address for the response.
        // Do the same for DHCPv4-over-DHCPv6 exchanges.
        if (local_addr.isV4Bcast() || query->isDhcp4o6()) {
            local_addr = IfaceMgr::instance().getSocket(query).addr_;
        }

        // We assume that there is an appropriate socket bound to this address
        // and that the address is correct. This is safe assumption because
        // the local address of the query is set when the query is received.
        // The query sent to an incorrect address wouldn't have been received.
        // However, if socket is closed for this address between the reception
        // of the query and sending a response, the IfaceMgr should detect it
        // and return an error.
        response->setLocalAddr(local_addr);
        // In many cases the query is sent to a broadcast address. This address
        // appears as a local address in the query message. Therefore we can't
        // simply copy local address from the query and use it as a source
        // address for the response. Instead, we have to check what address our
        // socket is bound to and use it as a source address. This operation
        // may throw if for some reason the socket is closed.
        /// @todo Consider an optimization that we use local address from
        /// the query if this address is not broadcast.
        response->setIndex(query->getIndex());
        response->setIface(query->getIface());
    }

    if (server_port_) {
        response->setLocalPort(server_port_);
    } else {
        response->setLocalPort(DHCP4_SERVER_PORT);
    }
}

void
Dhcpv4Srv::adjustRemoteAddr(Dhcpv4Exchange& ex) {
    // Initialize the pointers to the client's message and the server's
    // response.
    Pkt4Ptr query = ex.getQuery();
    Pkt4Ptr response = ex.getResponse();

    // DHCPv4-over-DHCPv6 is simple
    if (query->isDhcp4o6()) {
        response->setRemoteAddr(query->getRemoteAddr());
        return;
    }

    // The DHCPINFORM is slightly different than other messages in a sense
    // that the server should always unicast the response to the ciaddr.
    // It appears however that some clients don't set the ciaddr. We still
    // want to provision these clients and we do what we can't to send the
    // packet to the address where client can receive it.
    if (query->getType() == DHCPINFORM) {
        // If client adheres to RFC2131 it will set the ciaddr and in this
        // case we always unicast our response to this address.
        if (!query->getCiaddr().isV4Zero()) {
            response->setRemoteAddr(query->getCiaddr());

        // If we received DHCPINFORM via relay and the ciaddr is not set we
        // will try to send the response via relay. The caveat is that the
        // relay will not have any idea where to forward the packet because
        // the yiaddr is likely not set. So, the broadcast flag is set so
        // as the response may be broadcast.
        } else if (query->isRelayed()) {
            response->setRemoteAddr(query->getGiaddr());
            response->setFlags(response->getFlags() | BOOTP_BROADCAST);

        // If there is no ciaddr and no giaddr the only thing we can do is
        // to use the source address of the packet.
        } else {
            response->setRemoteAddr(query->getRemoteAddr());
        }
        // Remote address is now set so return.
        return;
    }

    // If received relayed message, server responds to the relay address.
    if (query->isRelayed()) {
        // The client should set the ciaddr when sending the DHCPINFORM
        // but in case he didn't, the relay may not be able to determine the
        // address of the client, because yiaddr is not set when responding
        // to Confirm and the only address available was the source address
        // of the client. The source address is however not used here because
        // the message is relayed. Therefore, we set the BROADCAST flag so
        // as the relay can broadcast the packet.
        if ((query->getType() == DHCPINFORM) &&
            query->getCiaddr().isV4Zero()) {
            response->setFlags(BOOTP_BROADCAST);
        }
        response->setRemoteAddr(query->getGiaddr());

    // If giaddr is 0 but client set ciaddr, server should unicast the
    // response to ciaddr.
    } else if (!query->getCiaddr().isV4Zero()) {
        response->setRemoteAddr(query->getCiaddr());

    // We can't unicast the response to the client when sending DHCPNAK,
    // because we haven't allocated address for him. Therefore,
    // DHCPNAK is broadcast.
    } else if (response->getType() == DHCPNAK) {
        response->setRemoteAddr(IOAddress::IPV4_BCAST_ADDRESS());

    // If yiaddr is set it means that we have created a lease for a client.
    } else if (!response->getYiaddr().isV4Zero()) {
        // If the broadcast bit is set in the flags field, we have to
        // send the response to broadcast address. Client may have requested it
        // because it doesn't support reception of messages on the interface
        // which doesn't have an address assigned. The other case when response
        // must be broadcasted is when our server does not support responding
        // directly to a client without address assigned.
        const bool bcast_flag = ((query->getFlags() & Pkt4::FLAG_BROADCAST_MASK) != 0);
        if (!IfaceMgr::instance().isDirectResponseSupported() || bcast_flag) {
            response->setRemoteAddr(IOAddress::IPV4_BCAST_ADDRESS());

        // Client cleared the broadcast bit and we support direct responses
        // so we should unicast the response to a newly allocated address -
        // yiaddr.
        } else {
            response->setRemoteAddr(response ->getYiaddr());

        }

    // In most cases, we should have the remote address found already. If we
    // found ourselves at this point, the rational thing to do is to respond
    // to the address we got the query from.
    } else {
        response->setRemoteAddr(query->getRemoteAddr());
    }

    // For testing *only*.
    if (getSendResponsesToSource()) {
        response->setRemoteAddr(query->getRemoteAddr());
    }
}

void
Dhcpv4Srv::setFixedFields(Dhcpv4Exchange& ex) {
    Pkt4Ptr query = ex.getQuery();
    Pkt4Ptr response = ex.getResponse();

    // Step 1: Start with fixed fields defined on subnet level.
    ConstSubnet4Ptr subnet = ex.getContext()->subnet_;
    if (subnet) {
        IOAddress subnet_next_server = subnet->getSiaddr();
        if (!subnet_next_server.isV4Zero()) {
            response->setSiaddr(subnet_next_server);
        }

        const string& sname = subnet->getSname();
        if (!sname.empty()) {
            // Converting string to (const uint8_t*, size_t len) format is
            // tricky. reinterpret_cast is not the most elegant solution,
            // but it does avoid us making unnecessary copy. We will convert
            // sname and file fields in Pkt4 to string one day and life
            // will be easier.
            response->setSname(reinterpret_cast<const uint8_t*>(sname.c_str()),
                               sname.size());
        }

        const string& filename = subnet->getFilename();
        if (!filename.empty()) {
            // Converting string to (const uint8_t*, size_t len) format is
            // tricky. reinterpret_cast is not the most elegant solution,
            // but it does avoid us making unnecessary copy. We will convert
            // sname and file fields in Pkt4 to string one day and life
            // will be easier.
            response->setFile(reinterpret_cast<const uint8_t*>(filename.c_str()),
                              filename.size());
        }
    }

    // Step 2: Try to set the values based on classes.
    // Any values defined in classes will override those from subnet level.
    const ClientClasses& classes = query->getClasses();
    if (!classes.empty()) {

        // Let's get class definitions
        const ClientClassDictionaryPtr& dict =
            CfgMgr::instance().getCurrentCfg()->getClientClassDictionary();

        // Now we need to iterate over the classes assigned to the
        // query packet and find corresponding class definitions for it.
        // We want the first value found for each field.  We track how
        // many we've found so we can stop if we have all three.
        IOAddress next_server = IOAddress::IPV4_ZERO_ADDRESS();
        string sname;
        string filename;
        size_t found_cnt = 0;  // How many fields we have found.
        for (auto const& name : classes) {

            if (found_cnt >= 3) {
                break;
            }

            ClientClassDefPtr cl = dict->findClass(name);
            if (!cl) {
                // Let's skip classes that don't have definitions. Currently
                // these are automatic classes VENDOR_CLASS_something, but there
                // may be other classes assigned under other circumstances, e.g.
                // by hooks.
                continue;
            }

            if (next_server == IOAddress::IPV4_ZERO_ADDRESS()) {
                next_server = cl->getNextServer();
                if (!next_server.isV4Zero()) {
                    response->setSiaddr(next_server);
                    found_cnt++;
                }
            }

            if (sname.empty()) {
                sname = cl->getSname();
                if (!sname.empty()) {
                    // Converting string to (const uint8_t*, size_t len) format is
                    // tricky. reinterpret_cast is not the most elegant solution,
                    // but it does avoid us making unnecessary copy. We will convert
                    // sname and file fields in Pkt4 to string one day and life
                    // will be easier.
                    response->setSname(reinterpret_cast<const uint8_t*>(sname.c_str()),
                                       sname.size());
                    found_cnt++;
                }
            }

            if (filename.empty()) {
                filename = cl->getFilename();
                if (!filename.empty()) {
                    // Converting string to (const uint8_t*, size_t len) format is
                    // tricky. reinterpret_cast is not the most elegant solution,
                    // but it does avoid us making unnecessary copy. We will convert
                    // sname and file fields in Pkt4 to string one day and life
                    // will be easier.
                    response->setFile(reinterpret_cast<const uint8_t*>(filename.c_str()),
                                     filename.size());
                    found_cnt++;
                }
            }
        }
    }

    // Step 3: try to set values using HR. Any values coming from there will override
    // the subnet or class values.
    ex.setReservedMessageFields();
}

OptionPtr
Dhcpv4Srv::getNetmaskOption(const ConstSubnet4Ptr& subnet) {
    uint32_t netmask = getNetmask4(subnet->get().second).toUint32();

    OptionPtr opt(new OptionInt<uint32_t>(Option::V4,
                  DHO_SUBNET_MASK, netmask));

    return (opt);
}

tuple<bool, uint32_t>
Dhcpv4Srv::parkingLimitExceeded(string const& hook_label) {
    // Get the parking limit. Parsing should ensure the value is present.
    uint32_t parked_packet_limit(0);
    ConstElementPtr const& ppl(
        CfgMgr::instance().getCurrentCfg()->getConfiguredGlobal(CfgGlobals::PARKED_PACKET_LIMIT));
    if (ppl) {
        parked_packet_limit = ppl->intValue();
    }

    if (parked_packet_limit) {
        ParkingLotPtr const& parking_lot(
            ServerHooks::getServerHooks().getParkingLotPtr(hook_label));

        if (parking_lot && parked_packet_limit <= parking_lot->size()) {
            return make_tuple(true, parked_packet_limit);
        }
    }
    return make_tuple(false, parked_packet_limit);
}

Pkt4Ptr
Dhcpv4Srv::processDiscover(Pkt4Ptr& discover, AllocEngine::ClientContext4Ptr& context) {
    bool drop = false;
    Dhcpv4Exchange ex(alloc_engine_, discover, context, context->subnet_, drop);

    // Stop here if Dhcpv4Exchange constructor decided to drop the packet
    if (drop) {
        return (Pkt4Ptr());
    }

    if (MultiThreadingMgr::instance().getMode()) {
        // The lease reclamation cannot run at the same time.
        ReadLockGuard share(alloc_engine_->getReadWriteMutex());

        assignLease(ex);
    } else {
        assignLease(ex);
    }

    if (!ex.getResponse()) {
        // The offer is empty so return it *now*!
        return (Pkt4Ptr());
    }

    // Adding any other options makes sense only when we got the lease
    // or it is for an IPv6-Only client.
    if (!ex.getResponse()->getYiaddr().isV4Zero() || ex.getIPv6OnlyPreferred()) {
        // If this is global reservation or the subnet doesn't belong to a shared
        // network we have already fetched it and evaluated the classes.
        ex.conditionallySetReservedClientClasses();

        // Evaluate additional classes.
        evaluateAdditionalClasses(ex);

        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASSES_ASSIGNED)
            .arg(discover->getLabel())
            .arg(discover->getName())
            .arg(discover->getClasses().toText());

        buildCfgOptionList(ex);
        appendRequestedOptions(ex);
        // Sanity check for IPv6-Only clients.
        if (ex.getIPv6OnlyPreferred()) {
            if (!ex.getResponse()->getOption(DHO_V6_ONLY_PREFERRED)) {
                // Better to drop the packet than to send an insane response.
                LOG_ERROR(packet4_logger, DHCP4_V6_ONLY_PREFERRED_MISSING_IN_OFFER)
                    .arg(discover->getLabel());
                return (Pkt4Ptr());
            }
        }
        appendRequestedVendorOptions(ex);
        // There are a few basic options that we always want to
        // include in the response. If client did not request
        // them we append them for him.
        appendBasicOptions(ex);

        // Set fixed fields (siaddr, sname, filename) if defined in
        // the reservation, class or subnet specific configuration.
        setFixedFields(ex);

    } else {
        // If the server can't offer an address, it drops the packet.
        return (Pkt4Ptr());

    }

    // Set the src/dest IP address, port and interface for the outgoing
    // packet.
    adjustIfaceData(ex);

    appendServerID(ex);

    // Return the pointer to the context, which will be required by the
    // lease4_offer callouts.
    context = ex.getContext();

    return (ex.getResponse());
}

Pkt4Ptr
Dhcpv4Srv::processRequest(Pkt4Ptr& request, AllocEngine::ClientContext4Ptr& context) {
    bool drop = false;
    Dhcpv4Exchange ex(alloc_engine_, request, context, context->subnet_, drop);

    // Stop here if Dhcpv4Exchange constructor decided to drop the packet
    if (drop) {
        return (Pkt4Ptr());
    }

    // Note that we treat REQUEST message uniformly, regardless if this is a
    // first request (requesting for new address), renewing existing address
    // or even rebinding.
    if (MultiThreadingMgr::instance().getMode()) {
        // The lease reclamation cannot run at the same time.
        ReadLockGuard share(alloc_engine_->getReadWriteMutex());

        assignLease(ex);
    } else {
        assignLease(ex);
    }

    Pkt4Ptr response = ex.getResponse();
    if (!response) {
        // The ack is empty so return it *now*!
        return (Pkt4Ptr());
    } else if (request->inClass("BOOTP")) {
        // Put BOOTP responses in the BOOTP class.
        response->addClass("BOOTP");
    }

    // Adding any other options makes sense only when we got the lease
    // or it is for an IPv6-Only client.
    if (!response->getYiaddr().isV4Zero() || ex.getIPv6OnlyPreferred()) {
        // If this is global reservation or the subnet doesn't belong to a shared
        // network we have already fetched it and evaluated the classes.
        ex.conditionallySetReservedClientClasses();

        // Evaluate additional classes.
        evaluateAdditionalClasses(ex);

        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASSES_ASSIGNED)
            .arg(request->getLabel())
            .arg(request->getName())
            .arg(request->getClasses().toText());

        buildCfgOptionList(ex);
        appendRequestedOptions(ex);
        // Sanity check for IPv6-Only clients.
        if (ex.getIPv6OnlyPreferred()) {
            if (!response->getOption(DHO_V6_ONLY_PREFERRED)) {
                // Better to drop the packet than to send an insane response.
                LOG_ERROR(packet4_logger, DHCP4_V6_ONLY_PREFERRED_MISSING_IN_ACK)
                    .arg(request->getLabel());
                return (Pkt4Ptr());
            }
        }
        appendRequestedVendorOptions(ex);
        // There are a few basic options that we always want to
        // include in the response. If client did not request
        // them we append them for him.
        appendBasicOptions(ex);

        // Set fixed fields (siaddr, sname, filename) if defined in
        // the reservation, class or subnet specific configuration.
        setFixedFields(ex);
    }

    // Set the src/dest IP address, port and interface for the outgoing
    // packet.
    adjustIfaceData(ex);

    appendServerID(ex);

    // Return the pointer to the context, which will be required by the
    // leases4_committed callouts.
    context = ex.getContext();

    return (ex.getResponse());
}

void
Dhcpv4Srv::processRelease(Pkt4Ptr& release, AllocEngine::ClientContext4Ptr& context) {
    // Try to find client-id. Note that for the DHCPRELEASE we don't check if the
    // match-client-id configuration parameter is disabled because this parameter
    // is configured for subnets and we don't select subnet for the DHCPRELEASE.
    // Bogus clients usually generate new client identifiers when they first
    // connect to the network, so whatever client identifier has been used to
    // acquire the lease, the client identifier carried in the DHCPRELEASE is
    // likely to be the same and the lease will be correctly identified in the
    // lease database. If supplied client identifier differs from the one used
    // to acquire the lease then the lease will remain in the database and
    // simply expire.
    ClientIdPtr client_id;
    OptionPtr opt = release->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (opt) {
        client_id = ClientIdPtr(new ClientId(opt->getData()));
    }

    try {
        // Do we have a lease for that particular address?
        Lease4Ptr lease = LeaseMgrFactory::instance().getLease4(release->getCiaddr());

        if (!lease) {
            // No such lease - bogus release
            LOG_DEBUG(lease4_logger, DBG_DHCP4_DETAIL, DHCP4_RELEASE_FAIL_NO_LEASE)
                .arg(release->getLabel())
                .arg(release->getCiaddr().toText());
            return;
        }

        if (!lease->belongsToClient(release->getHWAddr(), client_id)) {
            LOG_DEBUG(lease4_logger, DBG_DHCP4_DETAIL, DHCP4_RELEASE_FAIL_WRONG_CLIENT)
                .arg(release->getLabel())
                .arg(release->getCiaddr().toText());
            return;
        }

        bool skip = false;

        // Execute all callouts registered for lease4_release
        if (HooksManager::calloutsPresent(Hooks.hook_index_lease4_release_)) {
            CalloutHandlePtr callout_handle = getCalloutHandle(release);

            // Use the RAII wrapper to make sure that the callout handle state is
            // reset when this object goes out of scope. All hook points must do
            // it to prevent possible circular dependency between the callout
            // handle and its arguments.
            ScopedCalloutHandleState callout_handle_state(callout_handle);

            // Enable copying options from the packet within hook library.
            ScopedEnableOptionsCopy<Pkt4> query4_options_copy(release);

            // Pass the original packet
            callout_handle->setArgument("query4", release);

            // Pass the lease to be updated
            callout_handle->setArgument("lease4", lease);

            // Call all installed callouts
            HooksManager::callCallouts(Hooks.hook_index_lease4_release_,
                                       *callout_handle);

            // Callouts decided to skip the next processing step. The next
            // processing step would be to send the packet, so skip at this
            // stage means "drop response".
            if ((callout_handle->getStatus() == CalloutHandle::NEXT_STEP_SKIP) ||
                (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP)) {
                skip = true;
                LOG_DEBUG(hooks_logger, DBGLVL_PKT_HANDLING,
                          DHCP4_HOOK_LEASE4_RELEASE_SKIP)
                    .arg(release->getLabel());
            }
        }

        // Callout didn't indicate to skip the release process. Let's release
        // the lease.
        if (!skip) {
            // Ok, we've passed all checks. Let's release this address.
            bool success = false; // was the removal operation successful?
            bool expired = false; // explicitly expired instead of removed?
            auto expiration_cfg = CfgMgr::instance().getCurrentCfg()->getCfgExpiration();

            // Delete lease only if affinity is disabled.
            if (expiration_cfg->getFlushReclaimedTimerWaitTime() &&
                expiration_cfg->getHoldReclaimedTime() &&
                lease->valid_lft_ != Lease::INFINITY_LFT) {
                // Expire the lease.
                lease->valid_lft_ = 0;
                // Set the lease state to released to indicate that this lease
                // must be preserved in the database. It is particularly useful
                // in HA to differentiate between the leases that should be
                // updated in the partner's database and deleted from the partner's
                // database.
                lease->state_ = Lease4::STATE_RELEASED;
                LeaseMgrFactory::instance().updateLease4(lease);
                expired = true;
                success = true;
            } else {
                success = LeaseMgrFactory::instance().deleteLease(lease);
            }

            if (success) {
                context.reset(new AllocEngine::ClientContext4());
                context->old_lease_ = lease;

                // Release successful
                LOG_INFO(lease4_logger, DHCP4_RELEASE)
                    .arg(release->getLabel())
                    .arg(lease->addr_.toText());

                if (expired) {
                    LOG_INFO(lease4_logger, DHCP4_RELEASE_EXPIRED)
                                            .arg(release->getLabel())
                                            .arg(lease->addr_.toText());
                } else {
                    LOG_INFO(lease4_logger, DHCP4_RELEASE_DELETED)
                        .arg(release->getLabel())
                        .arg(lease->addr_.toText());

                    // Remove existing DNS entries for the lease, if any.
                    queueNCR(CHG_REMOVE, lease);
                }

                // Need to decrease statistic for assigned addresses.
                StatsMgr::instance().addValue("assigned-addresses", static_cast<int64_t>(-1));

                StatsMgr::instance().addValue(
                    StatsMgr::generateName("subnet", lease->subnet_id_, "assigned-addresses"),
                    static_cast<int64_t>(-1));

                auto const& subnet = CfgMgr::instance().getCurrentCfg()->getCfgSubnets4()->getBySubnetId(lease->subnet_id_);
                if (subnet) {
                    auto const& pool = subnet->getPool(Lease::TYPE_V4, lease->addr_, false);
                    if (pool) {
                        StatsMgr::instance().addValue(
                            StatsMgr::generateName("subnet", subnet->getID(),
                                                   StatsMgr::generateName("pool", pool->getID(), "assigned-addresses")),
                            static_cast<int64_t>(-1));
                    }
                }

            } else {
                // Release failed
                LOG_ERROR(lease4_logger, DHCP4_RELEASE_FAIL)
                    .arg(release->getLabel())
                    .arg(lease->addr_.toText());
            }
        }
    } catch (const isc::Exception& ex) {
        LOG_ERROR(lease4_logger, DHCP4_RELEASE_EXCEPTION)
            .arg(release->getLabel())
            .arg(release->getCiaddr())
            .arg(ex.what());
    }
}

void
Dhcpv4Srv::processDecline(Pkt4Ptr& decline, AllocEngine::ClientContext4Ptr& context) {
    // Client is supposed to specify the address being declined in
    // Requested IP address option, but must not set its ciaddr.
    // (again, see table 5 in RFC2131).

    OptionCustomPtr opt_requested_address = boost::dynamic_pointer_cast<
        OptionCustom>(decline->getOption(DHO_DHCP_REQUESTED_ADDRESS));
    if (!opt_requested_address) {

        isc_throw(RFCViolation, "Mandatory 'Requested IP address' option missing"
                  " in DHCPDECLINE sent from " << decline->getLabel());
    }
    IOAddress addr(opt_requested_address->readAddress());

    // We could also extract client's address from ciaddr, but that's clearly
    // against RFC2131.

    // Now we need to check whether this address really belongs to the client
    // that attempts to decline it.
    const Lease4Ptr lease = LeaseMgrFactory::instance().getLease4(addr);

    if (!lease) {
        // Client tried to decline an address, but we don't have a lease for
        // that address. Let's ignore it.
        //
        // We could assume that we're recovering from a mishandled migration
        // to a new server and mark the address as declined, but the window of
        // opportunity for that to be useful is small and the attack vector
        // would be pretty severe.
        LOG_WARN(dhcp4_logger, DHCP4_DECLINE_LEASE_NOT_FOUND)
            .arg(addr.toText()).arg(decline->getLabel());
        return;
    }

    // Get client-id, if available.
    OptionPtr opt_clientid = decline->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    ClientIdPtr client_id;
    if (opt_clientid) {
        client_id.reset(new ClientId(opt_clientid->getData()));
    }

    // Check if the client attempted to decline an expired lease or a lease
    // it doesn't own. Declining expired leases is typically a client
    // misbehavior and may lead to pool exhaustion in case of a storm of
    // such declines. Only decline the lease if the lease has been recently
    // allocated to the client.
    if (lease->expired() || lease->state_ != Lease::STATE_DEFAULT ||
        !lease->belongsToClient(decline->getHWAddr(), client_id)) {

        // Get printable hardware addresses
        string client_hw = decline->getHWAddr() ?
            decline->getHWAddr()->toText(false) : "(none)";
        string lease_hw = lease->hwaddr_ ?
            lease->hwaddr_->toText(false) : "(none)";

        // Get printable client-ids
        string client_id_txt = client_id ? client_id->toText() : "(none)";
        string lease_id_txt = lease->client_id_ ?
            lease->client_id_->toText() : "(none)";

        // Print the warning and we're done here.
        LOG_WARN(dhcp4_logger, DHCP4_DECLINE_LEASE_MISMATCH)
            .arg(addr.toText()).arg(decline->getLabel())
            .arg(client_hw).arg(lease_hw).arg(client_id_txt).arg(lease_id_txt);

        return;
    }

    // Ok, all is good. The client is reporting its own address. Let's
    // process it.
    declineLease(lease, decline, context);
}

void
Dhcpv4Srv::declineLease(const Lease4Ptr& lease, const Pkt4Ptr& decline,
                        AllocEngine::ClientContext4Ptr& context) {

    // Let's check if there are hooks installed for decline4 hook point.
    // If they are, let's pass the lease and client's packet. If the hook
    // sets status to drop, we reject this Decline.
    if (HooksManager::calloutsPresent(Hooks.hook_index_lease4_decline_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(decline);

        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        ScopedCalloutHandleState callout_handle_state(callout_handle);

        // Enable copying options from the packet within hook library.
        ScopedEnableOptionsCopy<Pkt4> query4_options_copy(decline);

        // Pass the original packet
        callout_handle->setArgument("query4", decline);

        // Pass the lease to be updated
        callout_handle->setArgument("lease4", lease);

        // Call callouts
        HooksManager::callCallouts(Hooks.hook_index_lease4_decline_,
                                   *callout_handle);

        // Check if callouts decided to skip the next processing step.
        // If any of them did, we will drop the packet.
        if ((callout_handle->getStatus() == CalloutHandle::NEXT_STEP_SKIP) ||
            (callout_handle->getStatus() == CalloutHandle::NEXT_STEP_DROP)) {
            LOG_DEBUG(hooks_logger, DBGLVL_PKT_HANDLING, DHCP4_HOOK_DECLINE_SKIP)
                .arg(decline->getLabel()).arg(lease->addr_.toText());
            return;
        }
    }

    Lease4Ptr old_values = boost::make_shared<Lease4>(*lease);

    // @todo: Call hooks.

    // We need to disassociate the lease from the client. Once we move a lease
    // to declined state, it is no longer associated with the client in any
    // way.
    lease->decline(CfgMgr::instance().getCurrentCfg()->getDeclinePeriod());

    try {
        LeaseMgrFactory::instance().updateLease4(lease);
    } catch (const Exception& ex) {
        // Update failed.
        LOG_ERROR(lease4_logger, DHCP4_DECLINE_FAIL)
            .arg(decline->getLabel())
            .arg(lease->addr_.toText())
            .arg(ex.what());
        return;
    }

    // Remove existing DNS entries for the lease, if any.
    // queueNCR will do the necessary checks and will skip the update, if not needed.
    queueNCR(CHG_REMOVE, old_values);

    // Bump up the statistics.

    // Per subnet declined addresses counter.
    StatsMgr::instance().addValue(
        StatsMgr::generateName("subnet", lease->subnet_id_, "declined-addresses"),
        static_cast<int64_t>(1));

    auto const& subnet = CfgMgr::instance().getCurrentCfg()->getCfgSubnets4()->getBySubnetId(lease->subnet_id_);
    if (subnet) {
        auto const& pool = subnet->getPool(Lease::TYPE_V4, lease->addr_, false);
        if (pool) {
            StatsMgr::instance().addValue(
                StatsMgr::generateName("subnet", subnet->getID(),
                                       StatsMgr::generateName("pool", pool->getID(), "declined-addresses")),
                static_cast<int64_t>(1));
        }
    }

    // Global declined addresses counter.
    StatsMgr::instance().addValue("declined-addresses", static_cast<int64_t>(1));

    // We do not want to decrease the assigned-addresses at this time. While
    // technically a declined address is no longer allocated, the primary usage
    // of the assigned-addresses statistic is to monitor pool utilization. Most
    // people would forget to include declined-addresses in the calculation,
    // and simply do assigned-addresses/total-addresses. This would have a bias
    // towards under-representing pool utilization, if we decreased allocated
    // immediately after receiving DHCPDECLINE, rather than later when we recover
    // the address.

    context.reset(new AllocEngine::ClientContext4());
    context->new_lease_ = lease;

    LOG_INFO(lease4_logger, DHCP4_DECLINE_LEASE).arg(lease->addr_.toText())
        .arg(decline->getLabel()).arg(lease->valid_lft_);
}

void
Dhcpv4Srv::serverDecline(hooks::CalloutHandlePtr& callout_handle, Pkt4Ptr& query,
                         Lease4Ptr lease, bool lease_exists) {
    LOG_INFO(lease4_logger, DHCP4_SERVER_INITIATED_DECLINE)
            .arg(query->getLabel())
            .arg(lease->addr_.toText())
            .arg(lease->valid_lft_);

    {
        // Check if the resource is busy i.e. can be modified by another thread
        // for another client. Highly unlikely.
        ResourceHandler4 resource_handler;
        if (MultiThreadingMgr::instance().getMode() && !resource_handler.tryLock4(lease->addr_)) {
            LOG_ERROR(lease4_logger, DHCP4_SERVER_INITIATED_DECLINE_RESOURCE_BUSY)
                .arg(query->getLabel())
                .arg(lease->addr_.toText());
            return;
        }

        // We need to disassociate the lease from the client. Once we move a lease
        // to declined state, it is no longer associated with the client in any
        // way.
        lease->decline(CfgMgr::instance().getCurrentCfg()->getDeclinePeriod());

        // If the lease already exists, update it in the database.
        if (lease_exists) {
            try {
                LeaseMgrFactory::instance().updateLease4(lease);
            } catch (const NoSuchLease& ex) {
                // We expected the lease to exist but it doesn't so let's try
                // to add it.
                lease_exists = false;
            } catch (const Exception& ex) {
                // Update failed.
                LOG_ERROR(lease4_logger, DHCP4_SERVER_INITIATED_DECLINE_UPDATE_FAILED)
                    .arg(query->getLabel())
                    .arg(lease->addr_.toText());
                return;
            }
        }

        if (!lease_exists) {
            try {
                LeaseMgrFactory::instance().addLease(lease);
            } catch (const Exception& ex) {
                LOG_ERROR(lease4_logger, DHCP4_SERVER_INITIATED_DECLINE_ADD_FAILED)
                    .arg(query->getLabel())
                    .arg(lease->addr_.toText());
                return;
            }
        }
    }

    // Bump up the statistics.  If the lease does not exist (i.e. offer-lifetime == 0) we
    // need to increment assigned address stats, otherwise the accounting will be off.
    // This saves us from having to determine later, when declined leases are reclaimed,
    // whether or not we need to decrement assigned stats.  In other words, this keeps
    // a declined lease always counted also as an assigned lease, regardless of how
    // it was declined, until it is reclaimed at which point both groups of stats
    // are decremented.

    // Per subnet declined addresses counter.
    StatsMgr::instance().addValue(
        StatsMgr::generateName("subnet", lease->subnet_id_, "declined-addresses"),
        static_cast<int64_t>(1));

    if (!lease_exists) {
        StatsMgr::instance().addValue(
            StatsMgr::generateName("subnet", lease->subnet_id_, "assigned-addresses"),
            static_cast<int64_t>(1));
    }

    auto const& subnet = CfgMgr::instance().getCurrentCfg()->getCfgSubnets4()->getBySubnetId(lease->subnet_id_);
    if (subnet) {
        auto const& pool = subnet->getPool(Lease::TYPE_V4, lease->addr_, false);
        if (pool) {
            StatsMgr::instance().addValue(
                StatsMgr::generateName("subnet", subnet->getID(),
                                       StatsMgr::generateName("pool", pool->getID(), "declined-addresses")),
                static_cast<int64_t>(1));
            if (!lease_exists) {
                StatsMgr::instance().addValue(
                    StatsMgr::generateName("subnet", subnet->getID(),
                                           StatsMgr::generateName("pool", pool->getID(), "assigned-addresses")),
                    static_cast<int64_t>(1));
            }
        }
    }

    // Global declined addresses counter.
    StatsMgr::instance().addValue("declined-addresses", static_cast<int64_t>(1));
    if (!lease_exists) {
        StatsMgr::instance().addValue("assigned-addresses", static_cast<int64_t>(1));
    }

    // Let's check if there are hooks installed for server decline hook point.
    // If there are, let's pass the DHCPDISCOVER and the declined lease .
    if (HooksManager::calloutsPresent(Hooks.hook_index_lease4_server_decline_)) {
        // Use the RAII wrapper to make sure that the callout handle state is
        // reset when this object goes out of scope. All hook points must do
        // it to prevent possible circular dependency between the callout
        // handle and its arguments.
        ScopedCalloutHandleState callout_handle_state(callout_handle);

        // Pass in the original DHCPDISCOVER
        callout_handle->setArgument("query4", query);

        // Pass in the declined lease.
        callout_handle->setArgument("lease4", lease);

        // Call callouts
        HooksManager::callCallouts(Hooks.hook_index_lease4_server_decline_,
                                   *callout_handle);
    }
}

void
Dhcpv4Srv::serverDeclineNoThrow(hooks::CalloutHandlePtr& callout_handle, Pkt4Ptr& query,
                                Lease4Ptr lease, bool lease_exists) {
    try {
        serverDecline(callout_handle, query, lease, lease_exists);
    } catch (...) {
        LOG_ERROR(packet4_logger, DHCP4_PACKET_PROCESS_EXCEPTION).arg(query->getLabel());
    }
}

Pkt4Ptr
Dhcpv4Srv::processInform(Pkt4Ptr& inform, AllocEngine::ClientContext4Ptr& context) {
    bool drop = false;
    Dhcpv4Exchange ex(alloc_engine_, inform, context, context->subnet_, drop);

    // Stop here if Dhcpv4Exchange constructor decided to drop the packet
    if (drop) {
        return (Pkt4Ptr());
    }

    Pkt4Ptr ack = ex.getResponse();

    // If this is global reservation or the subnet doesn't belong to a shared
    // network we have already fetched it and evaluated the classes.
    ex.conditionallySetReservedClientClasses();

    // Evaluate additional classes.
    evaluateAdditionalClasses(ex);

    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASSES_ASSIGNED)
        .arg(inform->getLabel())
        .arg(inform->getName())
        .arg(inform->getClasses().toText());

    buildCfgOptionList(ex);
    appendRequestedOptions(ex);
    appendRequestedVendorOptions(ex);
    appendBasicOptions(ex);
    adjustIfaceData(ex);

    // Set fixed fields (siaddr, sname, filename) if defined in
    // the reservation, class or subnet specific configuration.
    setFixedFields(ex);

    // There are cases for the DHCPINFORM that the server receives it via
    // relay but will send the response to the client's unicast address
    // carried in the ciaddr. In this case, the giaddr and hops field should
    // be cleared (these fields were copied by the copyDefaultFields function).
    // Also Relay Agent Options should be removed if present.
    if (ack->getRemoteAddr() != inform->getGiaddr()) {
        LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL, DHCP4_INFORM_DIRECT_REPLY)
            .arg(inform->getLabel())
            .arg(ack->getRemoteAddr())
            .arg(ack->getIface());
        ack->setHops(0);
        ack->setGiaddr(IOAddress::IPV4_ZERO_ADDRESS());
        ack->delOption(DHO_DHCP_AGENT_OPTIONS);
    }

    // The DHCPACK must contain server id.
    appendServerID(ex);

    return (ex.getResponse());
}

void
Dhcpv4Srv::recoverStashedAgentOption(const Pkt4Ptr& query) {
    if (query->getCiaddr().isV4Zero() || !query->getGiaddr().isV4Zero()) {
        return;
    }
    ConstElementPtr sao = CfgMgr::instance().getCurrentCfg()->
        getConfiguredGlobal(CfgGlobals::STASH_AGENT_OPTIONS);
    if (!sao || (sao->getType() != Element::boolean) || !sao->boolValue()) {
        return;
    }
    if (query->getType() != DHCPREQUEST) {
        return;
    }
    OptionPtr rai_opt = query->getOption(DHO_DHCP_AGENT_OPTIONS);
    if (rai_opt && (rai_opt->len() > Option::OPTION4_HDR_LEN)) {
        return;
    }
    // Should not happen but makes sense to check and gives a trivial way
    // to disable the feature from previous callout points.
    if (query->inClass("STASH_AGENT_OPTIONS")) {
        return;
    }
    Lease4Ptr lease = LeaseMgrFactory::instance().getLease4(query->getCiaddr());
    if (!lease || lease->expired()) {
        return;
    }
    ConstElementPtr user_context = lease->getContext();
    if (!user_context || (user_context->getType() != Element::map)) {
        return;
    }
    ConstElementPtr isc = user_context->get("ISC");
    if (!isc || (isc->getType() != Element::map)) {
        return;
    }
    ConstElementPtr relay_agent_info = isc->get("relay-agent-info");
    if (!relay_agent_info) {
        return;
    }
    // Compatibility with the old layout.
    if (relay_agent_info->getType() == Element::map) {
        relay_agent_info = relay_agent_info->get("sub-options");
        if (!relay_agent_info) {
            return;
        }
    }
    if (relay_agent_info->getType() != Element::string) {
        return;
    }
    // Check ownership before going further.
    ClientIdPtr client_id;
    OptionPtr opt_clientid = query->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (opt_clientid) {
        client_id.reset(new ClientId(opt_clientid->getData()));
    }
    if (!lease->belongsToClient(query->getHWAddr(), client_id)) {
        return;
    }
    // Extract the RAI.
    string rai_hex = relay_agent_info->stringValue();
    if (rai_hex.empty()) {
        return;
    }
    vector<uint8_t> rai_data;
    str::decodeFormattedHexString(rai_hex, rai_data);
    static const OptionDefinition& rai_def = LibDHCP::DHO_DHCP_AGENT_OPTIONS_DEF();
    OptionCustomPtr rai(new OptionCustom(rai_def, Option::V4, rai_data));
    // unpackOptions is a bit too flexible so check if it got something...
    if (!rai || rai->getOptions().empty()) {
        return;
    }
    // Remove an existing empty RAI.
    if (rai_opt) {
        query->delOption(DHO_DHCP_AGENT_OPTIONS);
    }
    query->addOption(rai);
    query->addClass("STASH_AGENT_OPTIONS");
    LOG_DEBUG(packet4_logger, DBG_DHCP4_DETAIL_DATA,
              DHCP4_RECOVERED_STASHED_RELAY_AGENT_INFO)
      .arg(query->getLabel())
      .arg(query->getCiaddr())
      .arg(rai->toText());
}

bool
Dhcpv4Srv::accept(const Pkt4Ptr& query) {
    // Check that the message type is accepted by the server. We rely on the
    // function called to log a message if needed.
    if (!acceptMessageType(query)) {
        return (false);
    }
    // Check if the message from directly connected client (if directly
    // connected) should be dropped or processed.
    if (!acceptDirectRequest(query)) {
        LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0002)
            .arg(query->getLabel())
            .arg(query->getIface());
        return (false);
    }

    // Check if the DHCPv4 packet has been sent to us or to someone else.
    // If it hasn't been sent to us, drop it!
    if (!acceptServerId(query)) {
        LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0003)
            .arg(query->getLabel())
            .arg(query->getIface());
        return (false);
    }

    return (true);
}

bool
Dhcpv4Srv::acceptDirectRequest(const Pkt4Ptr& pkt) {
    // Accept all relayed messages.
    if (pkt->isRelayed()) {
        return (true);
    }

    // Accept all DHCPv4-over-DHCPv6 messages.
    if (pkt->isDhcp4o6()) {
        return (true);
    }

    // The source address must not be zero for the DHCPINFORM message from
    // the directly connected client because the server will not know where
    // to respond if the ciaddr was not present.
    try {
        if (pkt->getType() == DHCPINFORM) {
            if (pkt->getRemoteAddr().isV4Zero() &&
                pkt->getCiaddr().isV4Zero()) {
                return (false);
            }
        }
    } catch (...) {
        // If we got here, it is probably because the message type hasn't
        // been set. But, this should not really happen assuming that
        // we validate the message type prior to calling this function.
        return (false);
    }

    return (true);
}

bool
Dhcpv4Srv::acceptMessageType(const Pkt4Ptr& query) const {
    // When receiving a packet without message type option, getType() will
    // throw.
    int type;
    try {
        type = query->getType();

    } catch (...) {
        LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0004)
            .arg(query->getLabel())
            .arg(query->getIface());
        return (false);
    }

    // Once we know that the message type is within a range of defined DHCPv4
    // messages, we do a detailed check to make sure that the received message
    // is targeted at server. Note that we could have received some Offer
    // message broadcasted by the other server to a relay. Even though, the
    // server would rather unicast its response to a relay, let's be on the
    // safe side. Also, we want to drop other messages which we don't support.
    // All these valid messages that we are not going to process are dropped
    // silently.

    switch(type) {
        case DHCPDISCOVER:
        case DHCPREQUEST:
        case DHCPRELEASE:
        case DHCPDECLINE:
        case DHCPINFORM:
            return (true);
            break;

        case DHCP_NOTYPE:
            LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0009)
                     .arg(query->getLabel());
            break;

        default:
            // If we receive a message with a non-existing type, we are logging it.
            if (type >= DHCP_TYPES_EOF) {
                LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0005)
                          .arg(query->getLabel())
                          .arg(type);
            } else {
                // Exists but we don't support it.
                LOG_DEBUG(bad_packet4_logger, DBGLVL_PKT_HANDLING, DHCP4_PACKET_DROP_0006)
                      .arg(query->getLabel())
                      .arg(type);
            }
            break;
    }

    return (false);
}

bool
Dhcpv4Srv::acceptServerId(const Pkt4Ptr& query) const {
    // This function is meant to be called internally by the server class, so
    // we rely on the caller to sanity check the pointer and we don't check
    // it here.

    // Check if server identifier option is present. If it is not present
    // we accept the message because it is targeted to all servers.
    // Note that we don't check cases that server identifier is mandatory
    // but not present. This is meant to be sanity checked in other
    // functions.
    OptionPtr option = query->getOption(DHO_DHCP_SERVER_IDENTIFIER);
    if (!option) {
        return (true);
    }
    // Server identifier is present. Let's convert it to 4-byte address
    // and try to match with server identifiers used by the server.
    OptionCustomPtr option_custom =
        boost::dynamic_pointer_cast<OptionCustom>(option);
    // Unable to convert the option to the option type which encapsulates it.
    // We treat this as non-matching server id.
    if (!option_custom) {
        return (false);
    }
    // The server identifier option should carry exactly one IPv4 address.
    // If the option definition for the server identifier doesn't change,
    // the OptionCustom object should have exactly one IPv4 address and
    // this check is somewhat redundant. On the other hand, if someone
    // breaks option it may be better to check that here.
    if (option_custom->getDataFieldsNum() != 1) {
        return (false);
    }

    // The server identifier MUST be an IPv4 address. If given address is
    // v6, it is wrong.
    IOAddress server_id = option_custom->readAddress();
    if (!server_id.isV4()) {
        return (false);
    }

    // According to RFC5107, the RAI_OPTION_SERVER_ID_OVERRIDE option if
    // present, should match DHO_DHCP_SERVER_IDENTIFIER option.
    OptionPtr rai_option = query->getOption(DHO_DHCP_AGENT_OPTIONS);
    if (rai_option) {
        OptionPtr rai_suboption = rai_option->getOption(RAI_OPTION_SERVER_ID_OVERRIDE);
        if (rai_suboption && (server_id.toBytes() == rai_suboption->toBinary())) {
            return (true);
        }
    }

    // Skip address check if configured to ignore the server id.
    SrvConfigPtr cfg = CfgMgr::instance().getCurrentCfg();
    if (cfg->getIgnoreServerIdentifier()) {
        return (true);
    }

    // This function iterates over all interfaces on which the
    // server is listening to find the one which has a socket bound
    // to the address carried in the server identifier option.
    // This has some performance implications. However, given that
    // typically there will be just a few active interfaces the
    // performance hit should be acceptable. If it turns out to
    // be significant, we will have to cache server identifiers
    // when sockets are opened.
    if (IfaceMgr::instance().hasOpenSocket(server_id)) {
        return (true);
    }

    // There are some cases when an administrator explicitly sets server
    // identifier (option 54) that should be used for a given, subnet,
    // network etc. It doesn't have to be an address assigned to any of
    // the server interfaces. Thus, we have to check if the server
    // identifier received is the one that we explicitly set in the
    // server configuration. At this point, we don't know which subnet
    // the client belongs to so we can't match the server id with any
    // subnet. We simply check if this server identifier is configured
    // anywhere. This should be good enough to eliminate exchanges
    // with other servers in the same network.

    /// @todo Currently we only check server identifiers configured at the
    /// subnet, shared network, client class and global levels.
    /// This should be sufficient for most of cases. At this point, trying to
    /// support server identifiers on the host reservations level seems to be an
    /// overkill and is probably not needed. In fact, at this point we don't
    /// know the reservations for the client communicating with the server.
    /// We may revise some of these choices in the future.

    // Check if there is at least one subnet configured with this server
    // identifier.
    ConstCfgSubnets4Ptr cfg_subnets = cfg->getCfgSubnets4();
    if (cfg_subnets->hasSubnetWithServerId(server_id)) {
        return (true);
    }

    // This server identifier is not configured for any of the subnets, so
    // check on the shared network level.
    CfgSharedNetworks4Ptr cfg_networks = cfg->getCfgSharedNetworks4();
    if (cfg_networks->hasNetworkWithServerId(server_id)) {
        return (true);
    }

    // Check if the server identifier is configured at client class level.
    const ClientClasses& classes = query->getClasses();
    for (auto const& cclass : classes) {
        // Find the client class definition for this class
        const ClientClassDefPtr& ccdef = CfgMgr::instance().getCurrentCfg()->
            getClientClassDictionary()->findClass(cclass);
        if (!ccdef) {
            continue;
        }

        if (ccdef->getCfgOption()->empty()) {
            // Skip classes which don't configure options
            continue;
        }

        OptionCustomPtr context_opt_server_id = boost::dynamic_pointer_cast<OptionCustom>
                (ccdef->getCfgOption()->get(DHCP4_OPTION_SPACE, DHO_DHCP_SERVER_IDENTIFIER).option_);
        if (context_opt_server_id && (context_opt_server_id->readAddress() == server_id)) {
            return (true);
        }
    }

    // Finally, it is possible that the server identifier is specified
    // on the global level.
    ConstCfgOptionPtr cfg_global_options = cfg->getCfgOption();
    OptionCustomPtr opt_server_id = boost::dynamic_pointer_cast<OptionCustom>
        (cfg_global_options->get(DHCP4_OPTION_SPACE, DHO_DHCP_SERVER_IDENTIFIER).option_);

    return (opt_server_id && (opt_server_id->readAddress() == server_id));
}

void
Dhcpv4Srv::sanityCheck(const Pkt4Ptr& query) {
    switch (query->getType()) {
    case DHCPDISCOVER:
        // server-id is forbidden.
        sanityCheck(query, FORBIDDEN);
        break;
    case DHCPREQUEST:
        // Since we cannot distinguish  between client states
        // we'll make server-id is optional for REQUESTs.
        sanityCheck(query, OPTIONAL);
        break;
    case DHCPRELEASE:
        // Server-id is mandatory in DHCPRELEASE (see table 5, RFC2131)
        // but ISC DHCP does not enforce this, so we'll follow suit.
        sanityCheck(query, OPTIONAL);
        break;
    case DHCPDECLINE:
        // Server-id is mandatory in DHCPDECLINE (see table 5, RFC2131)
        // but ISC DHCP does not enforce this, so we'll follow suit.
        sanityCheck(query, OPTIONAL);
        break;
    case DHCPINFORM:
        // server-id is supposed to be forbidden (as is requested address)
        // but ISC DHCP does not enforce either. So neither will we.
        sanityCheck(query, OPTIONAL);
        break;
    }
}

void
Dhcpv4Srv::sanityCheck(const Pkt4Ptr& query, RequirementLevel serverid) {
    OptionPtr server_id = query->getOption(DHO_DHCP_SERVER_IDENTIFIER);
    switch (serverid) {
    case FORBIDDEN:
        if (server_id) {
            isc_throw(RFCViolation, "Server-id option was not expected, but"
                      << " received in message "
                      << query->getName());
        }
        break;

    case MANDATORY:
        if (!server_id) {
            isc_throw(RFCViolation, "Server-id option was expected, but not"
                      " received in message "
                      << query->getName());
        }
        break;

    case OPTIONAL:
        // do nothing here
        ;
    }

    // If there is HWAddress set and it is non-empty, then we're good
    if (query->getHWAddr() && !query->getHWAddr()->hwaddr_.empty()) {
        return;
    }

    // There has to be something to uniquely identify the client:
    // either non-zero MAC address or client-id option present (or both)
    OptionPtr client_id = query->getOption(DHO_DHCP_CLIENT_IDENTIFIER);

    // If there's no client-id (or a useless one is provided, i.e. 0 length)
    if (!client_id || client_id->len() == client_id->getHeaderLen()) {
        isc_throw(RFCViolation, "Missing or useless client-id and no HW address"
                  " provided in message "
                  << query->getName());
    }
}

void Dhcpv4Srv::classifyPacket(const Pkt4Ptr& pkt) {
    Dhcpv4Exchange::classifyPacket(pkt);
}

void Dhcpv4Srv::evaluateAdditionalClasses(Dhcpv4Exchange& ex) {
    // First collect required classes
    Pkt4Ptr query = ex.getQuery();
    ClientClasses classes = query->getAdditionalClasses();
    ConstSubnet4Ptr subnet = ex.getContext()->subnet_;

    if (subnet) {
        // host reservation???

        // Begin by the pool
        Pkt4Ptr resp = ex.getResponse();
        IOAddress addr = IOAddress::IPV4_ZERO_ADDRESS();
        if (resp) {
            addr = resp->getYiaddr();
        }
        if (!addr.isV4Zero()) {
            PoolPtr pool = subnet->getPool(Lease::TYPE_V4, addr, false);
            if (pool) {
                const ClientClasses& pool_to_add = pool->getAdditionalClasses();
                for (auto const& cclass : pool_to_add) {
                    classes.insert(cclass);
                }
            }
        }

        // Followed by the subnet
        const ClientClasses& to_add = subnet->getAdditionalClasses();
        for (auto const& cclass : to_add) {
            classes.insert(cclass);
        }

        // And finish by the shared-network
        SharedNetwork4Ptr network;
        subnet->getSharedNetwork(network);
        if (network) {
            const ClientClasses& net_to_add = network->getAdditionalClasses();
            for (auto const& cclass : net_to_add) {
                classes.insert(cclass);
            }
        }
    }

    // Run match expressions
    // Note getClientClassDictionary() cannot be null
    const ClientClassDictionaryPtr& dict =
        CfgMgr::instance().getCurrentCfg()->getClientClassDictionary();
    for (auto const& cclass : classes) {
        const ClientClassDefPtr class_def = dict->findClass(cclass);
        if (!class_def) {
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC,
                      DHCP4_ADDITIONAL_CLASS_UNDEFINED)
                .arg(cclass);
            // Ignore it as it can't have an attached action
            continue;
        }
        const ExpressionPtr& expr_ptr = class_def->getMatchExpr();
        // Add a class without an expression to evaluate
        if (!expr_ptr) {
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC,
                      DHCP4_ADDITIONAL_CLASS_NO_TEST)
                .arg(cclass);
            query->addClass(cclass);
            continue;
        }
        // Evaluate the expression which can return false (no match),
        // true (match) or raise an exception (error)
        try {
            bool status = evaluateBool(*expr_ptr, *query);
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_ADDITIONAL_CLASS_EVAL_RESULT)
                .arg(query->getLabel())
                .arg(cclass)
                .arg(status ? "true" : "false");
            if (status) {
                // Matching: add the class
                query->addClass(cclass);
            }
        } catch (const Exception& ex) {
            LOG_ERROR(dhcp4_logger, DHCP4_ADDITIONAL_CLASS_EVAL_ERROR)
                .arg(query->getLabel())
                .arg(cclass)
                .arg(ex.what());
        }
    }
}

void
Dhcpv4Srv::deferredUnpack(Pkt4Ptr& query) {
    // Iterate on the list of deferred option codes
    for (auto const& code : query->getDeferredOptions()) {
        OptionDefinitionPtr def;
        // Iterate on client classes
        const ClientClasses& classes = query->getClasses();
        for (auto const& cclass : classes) {
            // Get the client class definition for this class
            const ClientClassDefPtr& ccdef =
                CfgMgr::instance().getCurrentCfg()->
                getClientClassDictionary()->findClass(cclass);
            // If not found skip it
            if (!ccdef) {
                continue;
            }
            // If there is no option definition skip it
            if (!ccdef->getCfgOptionDef()) {
                continue;
            }
            def = ccdef->getCfgOptionDef()->get(DHCP4_OPTION_SPACE, code);
            // Stop at the first client class with a definition
            if (def) {
                break;
            }
        }
        // If not found try the global definition
        if (!def) {
            def = LibDHCP::getOptionDef(DHCP4_OPTION_SPACE, code);
        }
        if (!def) {
            def = LibDHCP::getRuntimeOptionDef(DHCP4_OPTION_SPACE, code);
        }
        // Finish by last resort definition
        if (!def) {
            def = LibDHCP::getLastResortOptionDef(DHCP4_OPTION_SPACE, code);
        }
        // If not defined go to the next option
        if (!def) {
            continue;
        }
        // Get the existing option for its content and remove all
        OptionPtr opt = query->getOption(code);
        if (!opt) {
            // should not happen but do not crash anyway
            LOG_DEBUG(bad_packet4_logger, DBG_DHCP4_DETAIL,
                      DHCP4_DEFERRED_OPTION_MISSING)
                .arg(query->getLabel())
                .arg(code);
            continue;
        }
        // Because options have already been fused, the buffer contains entire
        // data.
        const OptionBuffer buf = opt->getData();
        try {
            // Unpack the option
            opt = def->optionFactory(Option::V4, code, buf);
        } catch (const std::exception& e) {
            // Failed to parse the option.
            LOG_DEBUG(bad_packet4_logger, DBG_DHCP4_DETAIL,
                      DHCP4_DEFERRED_OPTION_UNPACK_FAIL)
                .arg(query->getLabel())
                .arg(code)
                .arg(e.what());
            continue;
        }
        while (query->delOption(code)) {
            // continue
        }
        // Add the unpacked option.
        query->addOption(opt);
    }
}

void
Dhcpv4Srv::startD2() {
    D2ClientMgr& d2_mgr = CfgMgr::instance().getD2ClientMgr();
    if (d2_mgr.ddnsEnabled()) {
        // Updates are enabled, so lets start the sender, passing in
        // our error handler.
        // This may throw so wherever this is called needs to ready.
        d2_mgr.startSender(std::bind(&Dhcpv4Srv::d2ClientErrorHandler,
                                     this, ph::_1, ph::_2));
    }
}

void
Dhcpv4Srv::stopD2() {
    D2ClientMgr& d2_mgr = CfgMgr::instance().getD2ClientMgr();
    if (d2_mgr.ddnsEnabled()) {
        // Updates are enabled, so lets stop the sender
        d2_mgr.stop();
        d2_mgr.stopSender();
    }
}

void
Dhcpv4Srv::d2ClientErrorHandler(const
                                dhcp_ddns::NameChangeSender::Result result,
                                dhcp_ddns::NameChangeRequestPtr& ncr) {
    LOG_ERROR(ddns4_logger, DHCP4_DDNS_REQUEST_SEND_FAILED).
              arg(result).arg((ncr ? ncr->toText() : " NULL "));
    // We cannot communicate with kea-dhcp-ddns, suspend further updates.
    /// @todo We may wish to revisit this, but for now we will simply turn
    /// them off.
    CfgMgr::instance().getD2ClientMgr().suspendUpdates();
}

std::string
Dhcpv4Srv::getVersion(bool extended) {
    std::stringstream tmp;

    tmp << VERSION;
    if (extended) {
        tmp << " (" << EXTENDED_VERSION << ")" << endl;
        tmp << "premium: " << PREMIUM_EXTENDED_VERSION << endl;
        tmp << "linked with:" << endl;
        tmp << "- " << Logger::getVersion() << endl;
        tmp << "- " << CryptoLink::getVersion();
        auto info = LeaseMgrFactory::getDBVersions();
        if (info.size()) {
            tmp << endl << "lease backends:";
            for (auto const& version : info) {
                tmp << endl << "- " << version;
            }
        }
        info = HostDataSourceFactory::getDBVersions();
        if (info.size()) {
            tmp << endl << "host backends:";
            for (auto const& version : info) {
                tmp << endl << "- " << version;
            }
        }
        info = LegalLogMgrFactory::getDBVersions();
        if (info.size()) {
            tmp << endl << "forensic backends:";
            for (auto const& version : info) {
                tmp << endl << "- " << version;
            }
        }
        // @todo: more details about database runtime
    }

    return (tmp.str());
}

void Dhcpv4Srv::processStatsReceived(const Pkt4Ptr& query) {
    // Note that we're not bumping pkt4-received statistic as it was
    // increased early in the packet reception code.

    string stat_name = "pkt4-unknown-received";
    try {
        switch (query->getType()) {
        case DHCPDISCOVER:
            stat_name = "pkt4-discover-received";
            break;
        case DHCPOFFER:
            // Should not happen, but let's keep a counter for it
            stat_name = "pkt4-offer-received";
            break;
        case DHCPREQUEST:
            stat_name = "pkt4-request-received";
            break;
        case DHCPACK:
            // Should not happen, but let's keep a counter for it
            stat_name = "pkt4-ack-received";
            break;
        case DHCPNAK:
            // Should not happen, but let's keep a counter for it
            stat_name = "pkt4-nak-received";
            break;
        case DHCPRELEASE:
            stat_name = "pkt4-release-received";
        break;
        case DHCPDECLINE:
            stat_name = "pkt4-decline-received";
            break;
        case DHCPINFORM:
            stat_name = "pkt4-inform-received";
            break;
        default:
            ; // do nothing
        }
    }
    catch (...) {
        // If the incoming packet doesn't have option 53 (message type)
        // or a hook set pkt4_receive_skip, then Pkt4::getType() may
        // throw an exception. That's ok, we'll then use the default
        // name of pkt4-unknown-received.
    }

    isc::stats::StatsMgr::instance().addValue(stat_name,
                                              static_cast<int64_t>(1));
}

void Dhcpv4Srv::processStatsSent(const Pkt4Ptr& response) {
    // Increase generic counter for sent packets.
    isc::stats::StatsMgr::instance().addValue("pkt4-sent",
                                              static_cast<int64_t>(1));

    // Increase packet type specific counter for packets sent.
    string stat_name;
    switch (response->getType()) {
    case DHCPOFFER:
        stat_name = "pkt4-offer-sent";
        break;
    case DHCPACK:
        stat_name = "pkt4-ack-sent";
        break;
    case DHCPNAK:
        stat_name = "pkt4-nak-sent";
        break;
    default:
        // That should never happen
        return;
    }

    isc::stats::StatsMgr::instance().addValue(stat_name,
                                              static_cast<int64_t>(1));
}

int Dhcpv4Srv::getHookIndexBuffer4Receive() {
    return (Hooks.hook_index_buffer4_receive_);
}

int Dhcpv4Srv::getHookIndexPkt4Receive() {
    return (Hooks.hook_index_pkt4_receive_);
}

int Dhcpv4Srv::getHookIndexSubnet4Select() {
    return (Hooks.hook_index_subnet4_select_);
}

int Dhcpv4Srv::getHookIndexLease4Release() {
    return (Hooks.hook_index_lease4_release_);
}

int Dhcpv4Srv::getHookIndexPkt4Send() {
    return (Hooks.hook_index_pkt4_send_);
}

int Dhcpv4Srv::getHookIndexBuffer4Send() {
    return (Hooks.hook_index_buffer4_send_);
}

int Dhcpv4Srv::getHookIndexLease4Decline() {
    return (Hooks.hook_index_lease4_decline_);
}

void Dhcpv4Srv::discardPackets() {
    // Dump all of our current packets, anything that is mid-stream
    HooksManager::clearParkingLots();
}

uint16_t Dhcpv4Srv::getServerPort() const {
#ifdef FUZZING
    char const* const rotate(getenv("KEA_DHCP4_FUZZING_ROTATE_PORT"));
    if (rotate) {
        InterprocessSyncFile file("kea-dhcp4-fuzzing-rotate-port");
        InterprocessSyncLocker locker(file);
        while (!locker.lock()) {
            this_thread::sleep_for(1s);
        }
        fstream port_file;
        port_file.open("/tmp/port4.txt", ios::in);
        string line;
        int port;
        getline(port_file, line);
        port_file.close();
        if (line.empty()) {
            port = 2000;
        } else {
            port = stoi(line);
            if (port < 3000) {
                ++port;
            } else {
                port = 2000;
            }
        }
        port_file.open("/tmp/port4.txt", ios::out | ios::trunc);
        port_file << to_string(port) << endl;
        port_file.close();
        locker.unlock();
        return port;
    }
#endif  // FUZZING
    return server_port_;
}

std::list<std::list<std::string>> Dhcpv4Srv::jsonPathsToRedact() const {
    static std::list<std::list<std::string>> const list({
        {"config-control", "config-databases", "[]"},
        {"hooks-libraries", "[]", "parameters", "*"},
        {"hosts-database"},
        {"hosts-databases", "[]"},
        {"lease-database"},
    });
    return list;
}

}  // namespace dhcp
}  // namespace isc
