dhcp4_srv.cc 84.5 KB
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// Copyright (C) 2011-2015 Internet Systems Consortium, Inc. ("ISC")
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//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.

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#include <asiolink/io_address.h>
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#include <dhcp/dhcp4.h>
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#include <dhcp/duid.h>
#include <dhcp/hwaddr.h>
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#include <dhcp/iface_mgr.h>
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#include <dhcp/option4_addrlst.h>
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#include <dhcp/option_int.h>
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#include <dhcp/option_int_array.h>
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#include <dhcp/option_vendor.h>
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#include <dhcp/option_string.h>
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#include <dhcp/pkt4.h>
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#include <dhcp/docsis3_option_defs.h>
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#include <dhcp4/dhcp4_log.h>
#include <dhcp4/dhcp4_srv.h>
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#include <dhcpsrv/addr_utilities.h>
#include <dhcpsrv/callout_handle_store.h>
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#include <dhcpsrv/cfgmgr.h>
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#include <dhcpsrv/cfg_subnets4.h>
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#include <dhcpsrv/lease_mgr.h>
#include <dhcpsrv/lease_mgr_factory.h>
#include <dhcpsrv/subnet.h>
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#include <dhcpsrv/subnet_selector.h>
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#include <dhcpsrv/utils.h>
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#include <dhcpsrv/utils.h>
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#include <hooks/callout_handle.h>
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#include <hooks/hooks_manager.h>
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#include <util/strutil.h>
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#include <asio.hpp>
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#include <boost/bind.hpp>
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#include <boost/foreach.hpp>
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#include <boost/shared_ptr.hpp>
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#include <iomanip>

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using namespace isc;
using namespace isc::asiolink;
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using namespace isc::dhcp;
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using namespace isc::dhcp_ddns;
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using namespace isc::hooks;
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using namespace isc::log;
using namespace std;
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/// Structure that holds registered hook indexes
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struct Dhcp4Hooks {
    int hook_index_buffer4_receive_;///< index for "buffer4_receive" hook point
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    int hook_index_pkt4_receive_;   ///< index for "pkt4_receive" hook point
    int hook_index_subnet4_select_; ///< index for "subnet4_select" hook point
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    int hook_index_lease4_release_; ///< index for "lease4_release" hook point
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    int hook_index_pkt4_send_;      ///< index for "pkt4_send" hook point
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    int hook_index_buffer4_send_;   ///< index for "buffer4_send" hook point
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    /// Constructor that registers hook points for DHCPv4 engine
    Dhcp4Hooks() {
        hook_index_buffer4_receive_= HooksManager::registerHook("buffer4_receive");
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        hook_index_pkt4_receive_   = HooksManager::registerHook("pkt4_receive");
        hook_index_subnet4_select_ = HooksManager::registerHook("subnet4_select");
        hook_index_pkt4_send_      = HooksManager::registerHook("pkt4_send");
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        hook_index_lease4_release_ = HooksManager::registerHook("lease4_release");
        hook_index_buffer4_send_   = HooksManager::registerHook("buffer4_send");
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    }
};

// 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.
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Dhcp4Hooks Hooks;
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namespace isc {
namespace dhcp {
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DHCPv4Exchange::DHCPv4Exchange(const AllocEnginePtr& alloc_engine,
                               const Pkt4Ptr& query)
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    : alloc_engine_(alloc_engine), query_(query), resp_(),
      context_(new AllocEngine::ClientContext4()) {
    // Create response message.
    initResponse();
    // Select subnet for the query message.
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    selectSubnet();
    // Hardware address.
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    context_->hwaddr_ = query->getHWAddr();
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    // Client Identifier
    OptionPtr opt_clientid = query->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (opt_clientid) {
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        context_->clientid_.reset(new ClientId(opt_clientid->getData()));
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    }
    // Check for static reservations.
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    alloc_engine->findReservation(*context_);
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};

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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:
        ;
    }
    if (resp_type > 0) {
        resp_.reset(new Pkt4(resp_type, getQuery()->getTransid()));
    }
}

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void
DHCPv4Exchange::selectSubnet() {
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    context_->subnet_ = selectSubnet(query_);
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}

Subnet4Ptr
DHCPv4Exchange::selectSubnet(const Pkt4Ptr& query) {

    Subnet4Ptr subnet;

    SubnetSelector selector;
    selector.ciaddr_ = query->getCiaddr();
    selector.giaddr_ = query->getGiaddr();
    selector.local_address_ = query->getLocalAddr();
    selector.remote_address_ = query->getRemoteAddr();
    selector.client_classes_ = query->classes_;
    selector.iface_name_ = query->getIface();

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

    // Let's execute all callouts registered for subnet4_select
    if (HooksManager::calloutsPresent(Hooks.hook_index_subnet4_select_)) {
        CalloutHandlePtr callout_handle = getCalloutHandle(query);

        // We're reusing callout_handle from previous calls
        callout_handle->deleteAllArguments();

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

        // Call user (and server-side) callouts
        HooksManager::callCallouts(Hooks.hook_index_subnet4_select_,
                                   *callout_handle);

        // 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->getSkip()) {
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS,
                      DHCP4_HOOK_SUBNET4_SELECT_SKIP);
            return (Subnet4Ptr());
        }

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

    return (subnet);
}

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

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Dhcpv4Srv::Dhcpv4Srv(uint16_t port, const bool use_bcast,
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                     const bool direct_response_desired)
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    : shutdown_(true), alloc_engine_(), port_(port),
      use_bcast_(use_bcast), hook_index_pkt4_receive_(-1),
      hook_index_subnet4_select_(-1), hook_index_pkt4_send_(-1) {
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    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_START, DHCP4_OPEN_SOCKET).arg(port);
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    try {
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        // 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.
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        if (port) {
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            // 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);
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        }
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        // Instantiate allocation engine
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        alloc_engine_.reset(new AllocEngine(AllocEngine::ALLOC_ITERATIVE, 100,
                                            false /* false = IPv4 */));
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        // Register hook points
        hook_index_pkt4_receive_   = Hooks.hook_index_pkt4_receive_;
        hook_index_subnet4_select_ = Hooks.hook_index_subnet4_select_;
        hook_index_pkt4_send_      = Hooks.hook_index_pkt4_send_;

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

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

Dhcpv4Srv::~Dhcpv4Srv() {
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    IfaceMgr::instance().closeSockets();
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}

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

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isc::dhcp::Subnet4Ptr
Dhcpv4Srv::selectSubnet(const Pkt4Ptr& question) {
    return (DHCPv4Exchange::selectSubnet(question));
}

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

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

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bool
Dhcpv4Srv::run() {
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    while (!shutdown_) {
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        // client's message and server's response
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        Pkt4Ptr query;
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        Pkt4Ptr rsp;
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        try {
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            // The lease database backend may install some timers for which
            // the handlers need to be executed periodically. Retrieve the
            // maximum interval at which the handlers must be executed from
            // the lease manager.
            uint32_t timeout = LeaseMgrFactory::instance().getIOServiceExecInterval();
            // If the returned value is zero it means that there are no
            // timers installed, so use a default value.
            if (timeout == 0) {
                timeout = 1000;
            }
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            query = receivePacket(timeout);
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        } 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 or SIGHUP which are handled by the server. For signals
            // that are not handled by the server we rely on the default
            // behavior of the system, but there is nothing we should log here.
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        } catch (const std::exception& e) {
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            // Log all other errors.
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            LOG_ERROR(dhcp4_logger, DHCP4_PACKET_RECEIVE_FAIL).arg(e.what());
        }

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        // Handle next signal received by the process. It must be called after
        // an attempt to receive a packet to properly handle server shut down.
        // The SIGTERM or SIGINT will be received prior to, or during execution
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        // of select() (select is invoked by receivePacket()). When that
        // happens, select will be interrupted. The signal handler will be
        // invoked immediately after select(). The handler will set the
        // shutdown flag and cause the process to terminate before the next
        // select() function is called. If the function was called before
        // receivePacket the process could wait up to the duration of timeout
        // of select() to terminate.
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        handleSignal();

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        // Execute ready timers for the lease database, e.g. Lease File Cleanup.
        try {
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            LeaseMgrFactory::instance().getIOService()->poll();
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        } catch (const std::exception& ex) {
            LOG_WARN(dhcp4_logger, DHCP4_LEASE_DATABASE_TIMERS_EXEC_FAIL)
                .arg(ex.what());
        }

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        // Timeout may be reached or signal received, which breaks select()
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        // with no reception occurred
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        if (!query) {
            continue;
        }

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        // In order to parse the DHCP options, the server needs to use some
        // configuration information such as: existing option spaces, option
        // definitions etc. This is the kind of information which is not
        // available in the libdhcp, so we need to supply our own implementation
        // of the option parsing function here, which would rely on the
        // configuration data.
        query->setCallback(boost::bind(&Dhcpv4Srv::unpackOptions, this,
                                       _1, _2, _3));

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        bool skip_unpack = false;

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

            // Delete previously set arguments
            callout_handle->deleteAllArguments();

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

            // Call callouts
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            HooksManager::callCallouts(Hooks.hook_index_buffer4_receive_,
                                       *callout_handle);
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            // Callouts decided to skip the next processing step. The next
            // processing step would to parse the packet, so skip at this
            // stage means that callouts did the parsing already, so server
            // should skip parsing.
            if (callout_handle->getSkip()) {
                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_BUFFER_RCVD_SKIP);
                skip_unpack = true;
            }

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

        // Unpack the packet information unless the buffer4_receive callouts
        // indicated they did it
        if (!skip_unpack) {
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            try {
                query->unpack();
            } catch (const std::exception& e) {
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                // Failed to parse the packet.
                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL,
                          DHCP4_PACKET_PARSE_FAIL).arg(e.what());
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                continue;
            }
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        }
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        // 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.
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        classifyPacket(query);

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        // 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)) {
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            continue;
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        }
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        // We have sanity checked (in accept() that the Message Type option
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        // exists, so we can safely get it here.
        int type = query->getType();
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        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_PACKET_RECEIVED)
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            .arg(serverReceivedPacketName(type))
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            .arg(type)
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            .arg(query->getIface());
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_QUERY_DATA)
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            .arg(type)
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            .arg(query->toText());

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

            // Delete previously set arguments
            callout_handle->deleteAllArguments();

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

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

            // Callouts decided to skip the next processing step. The next
            // processing step would to process the packet, so skip at this
            // stage means drop.
            if (callout_handle->getSkip()) {
                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_PACKET_RCVD_SKIP);
                continue;
            }
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            callout_handle->getArgument("query4", query);
        }
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        try {
            switch (query->getType()) {
            case DHCPDISCOVER:
                rsp = processDiscover(query);
                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);
                break;

            case DHCPRELEASE:
                processRelease(query);
                break;

            case DHCPDECLINE:
                processDecline(query);
                break;

            case DHCPINFORM:
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                rsp = processInform(query);
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                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.
                ;
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            }
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        } catch (const isc::Exception& e) {

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            // Catch-all exception (at least for ones based on the isc Exception
            // class, which covers more or less all that are explicitly raised
            // in the Kea code).  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.)
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            if (dhcp4_logger.isDebugEnabled(DBG_DHCP4_BASIC)) {
                std::string source = "unknown";
                HWAddrPtr hwptr = query->getHWAddr();
                if (hwptr) {
                    source = hwptr->toText();
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                }
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                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC,
                          DHCP4_PACKET_PROCESS_FAIL)
                    .arg(source).arg(e.what());
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            }
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        }
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        if (!rsp) {
            continue;
        }
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        // Let's do class specific processing. This is done before
        // pkt4_send.
        //
        /// @todo: decide whether we want to add a new hook point for
        /// doing class specific processing.
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        if (!classSpecificProcessing(query, rsp)) {
            /// @todo add more verbosity here
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_BASIC, DHCP4_CLASS_PROCESSING_FAILED);

            continue;
        }

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        // Specifies if server should do the packing
        bool skip_pack = false;
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        // Execute all callouts registered for pkt4_send
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        if (HooksManager::calloutsPresent(hook_index_pkt4_send_)) {
            CalloutHandlePtr callout_handle = getCalloutHandle(query);
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            // Delete all previous arguments
            callout_handle->deleteAllArguments();
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            // Clear skip flag if it was set in previous callouts
            callout_handle->setSkip(false);
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            // Set our response
            callout_handle->setArgument("response4", rsp);
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            // Call all installed callouts
            HooksManager::callCallouts(hook_index_pkt4_send_,
                                       *callout_handle);
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            // Callouts decided to skip the next processing step. The next
            // processing step would to send the packet, so skip at this
            // stage means "drop response".
            if (callout_handle->getSkip()) {
                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_PACKET_SEND_SKIP);
                skip_pack = true;
            }
        }

        if (!skip_pack) {
            try {
                rsp->pack();
            } catch (const std::exception& e) {
                LOG_ERROR(dhcp4_logger, DHCP4_PACKET_SEND_FAIL)
                    .arg(e.what());
            }
        }

        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.
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            // Let's execute all callouts registered for buffer4_send
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            if (HooksManager::calloutsPresent(Hooks.hook_index_buffer4_send_)) {
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                CalloutHandlePtr callout_handle = getCalloutHandle(query);
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                // Delete previously set arguments
                callout_handle->deleteAllArguments();
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                // Pass incoming packet as argument
                callout_handle->setArgument("response4", rsp);
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                // Call callouts
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                HooksManager::callCallouts(Hooks.hook_index_buffer4_send_,
                                           *callout_handle);
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                // Callouts decided to skip the next processing step. The next
                // processing step would to parse the packet, so skip at this
                // stage means drop.
                if (callout_handle->getSkip()) {
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                    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS,
                              DHCP4_HOOK_BUFFER_SEND_SKIP);
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                    continue;
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                }
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                callout_handle->getArgument("response4", rsp);
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            }
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            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL_DATA,
                      DHCP4_RESPONSE_DATA)
                .arg(static_cast<int>(rsp->getType())).arg(rsp->toText());

            sendPacket(rsp);
        } catch (const std::exception& e) {
            LOG_ERROR(dhcp4_logger, DHCP4_PACKET_SEND_FAIL)
                .arg(e.what());
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        }
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    }

    return (true);
}

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string
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Dhcpv4Srv::srvidToString(const OptionPtr& srvid) {
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    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());
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}

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isc::dhcp_ddns::D2Dhcid
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Dhcpv4Srv::computeDhcid(const Lease4Ptr& lease) {
    if (!lease) {
        isc_throw(DhcidComputeError, "a pointer to the lease must be not"
                  " NULL to compute DHCID");

    } else if (lease->hostname_.empty()) {
        isc_throw(DhcidComputeError, "unable to compute the DHCID for the"
                  " lease which has empty hostname set");

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    }

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    // In order to compute DHCID the client's hostname must be encoded in
    // canonical wire format. It is unlikely that the FQDN is malformed
    // because it is validated by the classes which encapsulate options
    // carrying client FQDN. However, if the client name was carried in the
    // Hostname option it is more likely as it carries the hostname as a
    // regular string.
    std::vector<uint8_t> fqdn_wire;
    try {
        OptionDataTypeUtil::writeFqdn(lease->hostname_, fqdn_wire, true);
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    } catch (const Exception& ex) {
        isc_throw(DhcidComputeError, "unable to compute DHCID because the"
                  " hostname: " << lease->hostname_ << " is invalid");
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    }
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    // Prefer client id to HW address to compute DHCID. If Client Id is
    // NULL, use HW address.
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    try {
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        if (lease->client_id_) {
            return (D2Dhcid(lease->client_id_->getClientId(), fqdn_wire));

        } else {
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            return (D2Dhcid(lease->hwaddr_, fqdn_wire));
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        }
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    } catch (const Exception& ex) {
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        isc_throw(DhcidComputeError, "unable to compute DHCID: "
                  << ex.what());
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    }
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}

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void
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Dhcpv4Srv::copyDefaultFields(DHCPv4Exchange& ex) {
    ex.getResponse()->setIface(ex.getQuery()->getIface());
    ex.getResponse()->setIndex(ex.getQuery()->getIndex());
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    ex.getResponse()->setSiaddr(IOAddress::IPV4_ZERO_ADDRESS()); // explicitly set this to 0
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    // ciaddr is always 0, except for the Renew/Rebind state when it may
    // be set to the ciaddr sent by the client.
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    ex.getResponse()->setCiaddr(IOAddress::IPV4_ZERO_ADDRESS());
    ex.getResponse()->setHops(ex.getQuery()->getHops());
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    // copy MAC address
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    ex.getResponse()->setHWAddr(ex.getQuery()->getHWAddr());
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    // relay address
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    ex.getResponse()->setGiaddr(ex.getQuery()->getGiaddr());
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    // Let's copy client-id to response. See RFC6842.
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    // It is possible to disable RFC6842 to keep backward compatibility
    bool echo = CfgMgr::instance().echoClientId();
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    OptionPtr client_id = ex.getQuery()->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
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    if (client_id && echo) {
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        ex.getResponse()->addOption(client_id);
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    }
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    // If src/dest HW addresses are used by the packet filtering class
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    // 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.
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    HWAddrPtr src_hw_addr = ex.getQuery()->getLocalHWAddr();
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    if (src_hw_addr) {
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        ex.getResponse()->setLocalHWAddr(src_hw_addr);
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    }
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    HWAddrPtr dst_hw_addr = ex.getQuery()->getRemoteHWAddr();
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    if (dst_hw_addr) {
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        ex.getResponse()->setRemoteHWAddr(dst_hw_addr);
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    }
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    // If this packet is relayed, we want to copy Relay Agent Info option
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    OptionPtr rai = ex.getQuery()->getOption(DHO_DHCP_AGENT_OPTIONS);
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    if (rai) {
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        ex.getResponse()->addOption(rai);
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    }
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}

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void
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Dhcpv4Srv::appendDefaultOptions(DHCPv4Exchange& ex) {
    // no-op at this time
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}

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void
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Dhcpv4Srv::appendServerID(DHCPv4Exchange& ex) {
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    // The source address for the outbound message should have been set already.
    // This is the address that to the best of the server's knowledge will be
    // available from the client.
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    /// @todo: perhaps we should consider some more sophisticated server id
    /// generation, but for the current use cases, it should be ok.
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    ex.getResponse()->addOption(OptionPtr(new Option4AddrLst(DHO_DHCP_SERVER_IDENTIFIER,
                                                             ex.getResponse()->getLocalAddr())));
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}

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void
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Dhcpv4Srv::appendRequestedOptions(DHCPv4Exchange& ex) {
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    // Get the subnet relevant for the client. We will need it
    // to get the options associated with it.
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    Subnet4Ptr subnet = ex.getContext()->subnet_;
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    // 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;
    }
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    // try to get the 'Parameter Request List' option which holds the
    // codes of requested options.
    OptionUint8ArrayPtr option_prl = boost::dynamic_pointer_cast<
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        OptionUint8Array>(ex.getQuery()->getOption(DHO_DHCP_PARAMETER_REQUEST_LIST));
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    // If there is no PRL option in the message from the client then
    // there is nothing to do.
    if (!option_prl) {
        return;
    }
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    // Get the codes of requested options.
    const std::vector<uint8_t>& requested_opts = option_prl->getValues();
    // For each requested option code get the instance of the option
    // to be returned to the client.
    for (std::vector<uint8_t>::const_iterator opt = requested_opts.begin();
         opt != requested_opts.end(); ++opt) {
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        if (!ex.getResponse()->getOption(*opt)) {
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            OptionDescriptor desc = subnet->getCfgOption()->get("dhcp4", *opt);
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            if (desc.option_) {
                ex.getResponse()->addOption(desc.option_);
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            }
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        }
    }
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}
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void
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Dhcpv4Srv::appendRequestedVendorOptions(DHCPv4Exchange& ex) {
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    // Get the configured subnet suitable for the incoming packet.
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    Subnet4Ptr subnet = ex.getContext()->subnet_;
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    // 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.
    if (!subnet) {
        return;
    }

    // Try to get the vendor option
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    boost::shared_ptr<OptionVendor> vendor_req = boost::dynamic_pointer_cast<
        OptionVendor>(ex.getQuery()->getOption(DHO_VIVSO_SUBOPTIONS));
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    if (!vendor_req) {
        return;
    }

    uint32_t vendor_id = vendor_req->getVendorId();

    // Let's try to get ORO within that vendor-option
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    /// @todo This is very specific to vendor-id=4491 (Cable Labs). Other
    /// vendors may have different policies.
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    OptionUint8ArrayPtr oro =
        boost::dynamic_pointer_cast<OptionUint8Array>(vendor_req->getOption(DOCSIS3_V4_ORO));
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    // Option ORO not found. Don't do anything then.
    if (!oro) {
        return;
    }

    boost::shared_ptr<OptionVendor> vendor_rsp(new OptionVendor(Option::V4, vendor_id));

    // Get the list of options that client requested.
    bool added = false;
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    const std::vector<uint8_t>& requested_opts = oro->getValues();
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    for (std::vector<uint8_t>::const_iterator code = requested_opts.begin();
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         code != requested_opts.end(); ++code) {
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        if  (!vendor_rsp->getOption(*code)) {
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            OptionDescriptor desc = subnet->getCfgOption()->get(vendor_id,
                                                                *code);
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            if (desc.option_) {
                vendor_rsp->addOption(desc.option_);
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                added = true;
            }
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        }

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        if (added) {
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            ex.getResponse()->addOption(vendor_rsp);
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        }
    }
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}
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void
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Dhcpv4Srv::appendBasicOptions(DHCPv4Exchange& ex) {
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    // Identify options that we always want to send to the
    // client (if they are configured).
    static const uint16_t required_options[] = {
        DHO_ROUTERS,
        DHO_DOMAIN_NAME_SERVERS,
        DHO_DOMAIN_NAME };
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    static size_t required_options_size =
        sizeof(required_options) / sizeof(required_options[0]);

    // Get the subnet.
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    Subnet4Ptr subnet = ex.getContext()->subnet_;
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    if (!subnet) {
        return;
    }

    // Try to find all 'required' options in the outgoing
    // message. Those that are not present will be added.
    for (int i = 0; i < required_options_size; ++i) {
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        OptionPtr opt = ex.getResponse()->getOption(required_options[i]);
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        if (!opt) {
            // Check whether option has been configured.
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            OptionDescriptor desc = subnet->getCfgOption()->
                get("dhcp4", required_options[i]);
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            if (desc.option_) {
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                ex.getResponse()->addOption(desc.option_);
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            }
        }
    }
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}
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void
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Dhcpv4Srv::processClientName(DHCPv4Exchange& ex) {
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    // It is possible that client has sent both Client FQDN and Hostname
    // option. In such case, server should prefer Client FQDN option and
    // ignore the Hostname option.
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    try {
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        Pkt4Ptr resp = ex.getResponse();
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        Option4ClientFqdnPtr fqdn = boost::dynamic_pointer_cast<Option4ClientFqdn>
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            (ex.getQuery()->getOption(DHO_FQDN));
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        if (fqdn) {
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            processClientFqdnOption(ex);
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        } else {
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            OptionStringPtr hostname = boost::dynamic_pointer_cast<OptionString>
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                (ex.getQuery()->getOption(DHO_HOST_NAME));
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            if (hostname) {
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                processHostnameOption(ex);
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            }
        }
    } catch (const Exception& ex) {
        // 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(dhcp4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_CLIENT_NAME_PROC_FAIL)
            .arg(ex.what());
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    }
}

void
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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));

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

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    // 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);
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    // Carry over the client's E flag.
    fqdn_resp->setFlag(Option4ClientFqdn::FLAG_E,
                       fqdn->getFlag(Option4ClientFqdn::FLAG_E));
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    if (ex.getContext()->host_ && !ex.getContext()->host_->getHostname().empty()) {
        fqdn_resp->setDomainName(ex.getContext()->host_->getHostname(),
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                                 Option4ClientFqdn::FULL);
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    } 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);
    }
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    // 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.
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    // If we don't store the option in the response message, we will have to
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    // propagate it in the different way to the functions which acquire the
    // lease. This would require modifications to the API of this class.
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    ex.getResponse()->addOption(fqdn_resp);
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}

void
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Dhcpv4Srv::processHostnameOption(DHCPv4Exchange& ex) {
    // Obtain the Hostname option from the client's message.
    OptionStringPtr opt_hostname = boost::dynamic_pointer_cast<OptionString>
        (ex.getQuery()->getOption(DHO_HOST_NAME));

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    // Fetch D2 configuration.
    D2ClientMgr& d2_mgr = CfgMgr::instance().getD2ClientMgr();

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    // Do nothing if the DNS updates are disabled.
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    if (!d2_mgr.ddnsEnabled()) {
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        return;
    }

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    std::string hostname = isc::util::str::trim(opt_hostname->getValue());
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    unsigned int label_count = OptionDataTypeUtil::getLabelCount(hostname);
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    // The hostname option sent by the client should be at least 1 octet long.
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    // 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.
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    if (label_count == 0) {
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_EMPTY_HOSTNAME);
        return;
    }
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    // Copy construct the hostname provided by the client. It is entirely
    // possible that we will use the hostname option provided by the client
    // to perform the DNS update and we will send the same option to him to
    // indicate that we accepted this hostname.
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    OptionStringPtr opt_hostname_resp(new OptionString(*opt_hostname));
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    // 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.

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    // If there is a hostname reservation for this client, use it.
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    if (ex.getContext()->host_ && !ex.getContext()->host_->getHostname().empty()) {
        opt_hostname_resp->setValue(ex.getContext()->host_->getHostname());
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    } else if ((d2_mgr.getD2ClientConfig()->getReplaceClientName()) ||
               (label_count < 2)) {
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        // Set to root domain to signal later on that we should replace it.
        // DHO_HOST_NAME is a string option which cannot be empty.
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        /// @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.
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        opt_hostname_resp->setValue(".");
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    } else if (label_count == 2) {
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        // If there are two labels, it means that the client has specified
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        // the unqualified name. We have to concatenate the unqualified name
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