dhcp4_srv.cc 56.2 KB
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// Copyright (C) 2011-2013 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/pkt4.h>
#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>
#include <dhcpsrv/lease_mgr.h>
#include <dhcpsrv/lease_mgr_factory.h>
#include <dhcpsrv/subnet.h>
#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 <boost/algorithm/string/erase.hpp>

#include <iomanip>
#include <fstream>

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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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namespace {

// The following constants describe server's behavior with respect to the
// DHCPv4 Client FQDN Option sent by a client. They will be removed
// when DDNS parameters for DHCPv4 are implemented with the ticket #3033.

// Should server always include the FQDN option in its response, regardless
// if it has been requested in Parameter Request List Option (Disabled).
const bool FQDN_ALWAYS_INCLUDE = false;
// Enable A RR update delegation to the client (Disabled).
const bool FQDN_ALLOW_CLIENT_UPDATE = false;
// Globally enable updates (Enabled).
const bool FQDN_ENABLE_UPDATE = true;
// The partial name generated for the client if empty name has been
// supplied.
const char* FQDN_GENERATED_PARTIAL_NAME = "myhost";
// Do update, even if client requested no updates with N flag (Disabled).
const bool FQDN_OVERRIDE_NO_UPDATE = false;
// Server performs an update when client requested delegation (Enabled).
const bool FQDN_OVERRIDE_CLIENT_UPDATE = true;
// The fully qualified domain-name suffix if partial name provided by
// a client.
const char* FQDN_PARTIAL_SUFFIX = "example.com";
// Should server replace the domain-name supplied by the client (Disabled).
const bool FQDN_REPLACE_CLIENT_NAME = false;

}

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/// @brief file name of a server-id file
///
/// Server must store its server identifier in persistent storage that must not
/// change between restarts. This is name of the file that is created in dataDir
/// (see isc::dhcp::CfgMgr::getDataDir()). It is a text file that uses
/// regular IPv4 address, e.g. 192.0.2.1. Server will create it during
/// first run and then use it afterwards.
static const char* SERVER_ID_FILE = "b10-dhcp4-serverid";

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// These are hardcoded parameters. Currently this is a skeleton server that only
// grants those options and a single, fixed, hardcoded lease.

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Dhcpv4Srv::Dhcpv4Srv(uint16_t port, const char* dbconfig, const bool use_bcast,
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                     const bool direct_response_desired)
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: serverid_(), shutdown_(true), alloc_engine_(), port_(port),
    use_bcast_(use_bcast), hook_index_pkt4_receive_(-1),
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    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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        // First call to instance() will create IfaceMgr (it's a singleton)
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        // it may throw something if things go wrong.
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        // The 'true' value of the call to setMatchingPacketFilter imposes
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        // 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.
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        IfaceMgr::instance().setMatchingPacketFilter(direct_response_desired);
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        if (port) {
            // open sockets only if port is non-zero. Port 0 is used
            // for non-socket related testing.
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            IfaceMgr::instance().openSockets4(port_, use_bcast_);
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        }
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        string srvid_file = CfgMgr::instance().getDataDir() + "/" + string(SERVER_ID_FILE);
        if (loadServerID(srvid_file)) {
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_START, DHCP4_SERVERID_LOADED)
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                .arg(srvidToString(getServerID()))
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                .arg(srvid_file);
        } else {
            generateServerID();
            LOG_INFO(dhcp4_logger, DHCP4_SERVERID_GENERATED)
                .arg(srvidToString(getServerID()))
                .arg(srvid_file);

            if (!writeServerID(srvid_file)) {
                LOG_WARN(dhcp4_logger, DHCP4_SERVERID_WRITE_FAIL)
                    .arg(srvid_file);
            }

        }
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        // Instantiate LeaseMgr
        LeaseMgrFactory::create(dbconfig);
        LOG_INFO(dhcp4_logger, DHCP4_DB_BACKEND_STARTED)
            .arg(LeaseMgrFactory::instance().getType())
            .arg(LeaseMgrFactory::instance().getName());

        // Instantiate allocation engine
        alloc_engine_.reset(new AllocEngine(AllocEngine::ALLOC_ITERATIVE, 100));

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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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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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        /// @todo: calculate actual timeout once we have lease database
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        //cppcheck-suppress variableScope This is temporary anyway
        const int timeout = 1000;
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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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            query = receivePacket(timeout);
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        } catch (const std::exception& e) {
            LOG_ERROR(dhcp4_logger, DHCP4_PACKET_RECEIVE_FAIL).arg(e.what());
        }

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

        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::getHooksManager()
            .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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        // When receiving a packet without message type option, getType() will
        // throw. Let's set type to -1 as default error indicator.
        int type = -1;
        try {
            type = query->getType();
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        } catch (...) {
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_PACKET_DROP_NO_TYPE)
                .arg(query->getIface());
            continue;
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        }
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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:
                processInform(query);
                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) {

            // 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 BIND 10 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.)
            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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        adjustRemoteAddr(query, rsp);
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        if (!rsp->getHops()) {
            rsp->setRemotePort(DHCP4_CLIENT_PORT);
        } else {
            rsp->setRemotePort(DHCP4_SERVER_PORT);
        }
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        rsp->setLocalAddr(query->getLocalAddr());
        rsp->setLocalPort(DHCP4_SERVER_PORT);
        rsp->setIface(query->getIface());
        rsp->setIndex(query->getIndex());
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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
            if (HooksManager::getHooksManager()
                .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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bool
Dhcpv4Srv::loadServerID(const std::string& file_name) {
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    // load content of the file into a string
    fstream f(file_name.c_str(), ios::in);
    if (!f.is_open()) {
        return (false);
    }

    string hex_string;
    f >> hex_string;
    f.close();

    // remove any spaces
    boost::algorithm::erase_all(hex_string, " ");

    try {
        IOAddress addr(hex_string);

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        if (!addr.isV4()) {
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            return (false);
        }

        // Now create server-id option
        serverid_.reset(new Option4AddrLst(DHO_DHCP_SERVER_IDENTIFIER, addr));

    } catch(...) {
        // any kind of malformed input (empty string, IPv6 address, complete
        // garbate etc.)
        return (false);
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    }

    return (true);
}

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void
Dhcpv4Srv::generateServerID() {
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    const IfaceMgr::IfaceCollection& ifaces = IfaceMgr::instance().getIfaces();

    // Let's find suitable interface.
    for (IfaceMgr::IfaceCollection::const_iterator iface = ifaces.begin();
         iface != ifaces.end(); ++iface) {

        // Let's don't use loopback.
        if (iface->flag_loopback_) {
            continue;
        }

        // Let's skip downed interfaces. It is better to use working ones.
        if (!iface->flag_up_) {
            continue;
        }

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        const Iface::AddressCollection addrs = iface->getAddresses();
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        for (Iface::AddressCollection::const_iterator addr = addrs.begin();
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             addr != addrs.end(); ++addr) {
            if (addr->getFamily() != AF_INET) {
                continue;
            }

            serverid_ = OptionPtr(new Option4AddrLst(DHO_DHCP_SERVER_IDENTIFIER,
                                                     *addr));
            return;
        }


    }

    isc_throw(BadValue, "No suitable interfaces for server-identifier found");
}

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bool
Dhcpv4Srv::writeServerID(const std::string& file_name) {
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    fstream f(file_name.c_str(), ios::out | ios::trunc);
    if (!f.good()) {
        return (false);
    }
    f << srvidToString(getServerID());
    f.close();
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    return (true);
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}

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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 {
            HWAddrPtr hwaddr(new HWAddr(lease->hwaddr_, HTYPE_ETHER));
            return (D2Dhcid(hwaddr, fqdn_wire));
        }
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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
Dhcpv4Srv::copyDefaultFields(const Pkt4Ptr& question, Pkt4Ptr& answer) {
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    answer->setIface(question->getIface());
    answer->setIndex(question->getIndex());
    answer->setCiaddr(question->getCiaddr());
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    answer->setSiaddr(IOAddress("0.0.0.0")); // explicitly set this to 0
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    answer->setHops(question->getHops());
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    // copy MAC address
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    answer->setHWAddr(question->getHWAddr());
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    // relay address
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    answer->setGiaddr(question->getGiaddr());

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    // Let's copy client-id to response. See RFC6842.
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    OptionPtr client_id = question->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (client_id) {
        answer->addOption(client_id);
    }
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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 = question->getLocalHWAddr();
    if (src_hw_addr) {
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        answer->setLocalHWAddr(src_hw_addr);
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    }
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    HWAddrPtr dst_hw_addr = question->getRemoteHWAddr();
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    if (dst_hw_addr) {
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        answer->setRemoteHWAddr(dst_hw_addr);
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    }
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}

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void
Dhcpv4Srv::appendDefaultOptions(Pkt4Ptr& msg, uint8_t msg_type) {
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    OptionPtr opt;
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    // add Message Type Option (type 53)
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    msg->setType(msg_type);
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    // DHCP Server Identifier (type 54)
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    msg->addOption(getServerID());
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    // more options will be added here later
}

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void
Dhcpv4Srv::appendRequestedOptions(const Pkt4Ptr& question, Pkt4Ptr& msg) {
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    // Get the subnet relevant for the client. We will need it
    // to get the options associated with it.
    Subnet4Ptr subnet = selectSubnet(question);
    // 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<
        OptionUint8Array>(question->getOption(DHO_DHCP_PARAMETER_REQUEST_LIST));
    // 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) {
        Subnet::OptionDescriptor desc =
            subnet->getOptionDescriptor("dhcp4", *opt);
        if (desc.option) {
            msg->addOption(desc.option);
        }
    }
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}
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void
Dhcpv4Srv::appendBasicOptions(const Pkt4Ptr& question, Pkt4Ptr& msg) {
    // Identify options that we always want to send to the
    // client (if they are configured).
    static const uint16_t required_options[] = {
        DHO_SUBNET_MASK,
        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.
    Subnet4Ptr subnet = selectSubnet(question);
    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) {
        OptionPtr opt = msg->getOption(required_options[i]);
        if (!opt) {
            // Check whether option has been configured.
            Subnet::OptionDescriptor desc =
                subnet->getOptionDescriptor("dhcp4", required_options[i]);
            if (desc.option) {
                msg->addOption(desc.option);
            }
        }
    }
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}
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void
Dhcpv4Srv::processClientName(const Pkt4Ptr& query, Pkt4Ptr& answer) {
    // 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.
    Option4ClientFqdnPtr fqdn = boost::dynamic_pointer_cast<Option4ClientFqdn>
        (query->getOption(DHO_FQDN));
    if (fqdn) {
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        processClientFqdnOption(fqdn, answer);
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    } else {
        OptionCustomPtr hostname = boost::dynamic_pointer_cast<OptionCustom>
            (query->getOption(DHO_HOST_NAME));
        if (hostname) {
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            processHostnameOption(hostname, answer);
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        }

    }
}

void
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Dhcpv4Srv::processClientFqdnOption(const Option4ClientFqdnPtr& fqdn,
                                   Pkt4Ptr& answer) {
    // Create the DHCPv4 Client FQDN Option to be included in the server's
    // response to a client.
    Option4ClientFqdnPtr fqdn_resp(new Option4ClientFqdn(*fqdn));

    // RFC4702, section 4 - set 'NOS' flags to 0.
    fqdn_resp->setFlag(Option4ClientFqdn::FLAG_S, 0);
    fqdn_resp->setFlag(Option4ClientFqdn::FLAG_O, 0);
    fqdn_resp->setFlag(Option4ClientFqdn::FLAG_N, 0);

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    // Conditions when N flag has to be set to indicate that server will not
    // perform DNS updates:
    // 1. Updates are globally disabled,
    // 2. Client requested no update and server respects it,
    // 3. Client requested that the foward DNS update is delegated to the client
    //    but server neither respects requests for forward update delegation nor
    //    it is configured to send update on its own when client requested
    //    delegation.
    if (!FQDN_ENABLE_UPDATE ||
        (fqdn->getFlag(Option4ClientFqdn::FLAG_N) &&
         !FQDN_OVERRIDE_NO_UPDATE) ||
        (!fqdn->getFlag(Option4ClientFqdn::FLAG_S) &&
         !FQDN_ALLOW_CLIENT_UPDATE && !FQDN_OVERRIDE_CLIENT_UPDATE)) {
        fqdn_resp->setFlag(Option4ClientFqdn::FLAG_N, true);

    // Conditions when S flag is set to indicate that server will perform DNS
    // update on its own:
    // 1. Client requested that server performs DNS update and DNS updates are
    //    globally enabled.
    // 2. Client requested that server delegates forward update to the client
    //    but server doesn't respect requests for delegation and it is
    // configured to perform an update on its own when client requested the
    // delegation.
    } else  if (fqdn->getFlag(Option4ClientFqdn::FLAG_S) ||
                (!fqdn->getFlag(Option4ClientFqdn::FLAG_S) &&
                 !FQDN_ALLOW_CLIENT_UPDATE && FQDN_OVERRIDE_CLIENT_UPDATE)) {
        fqdn_resp->setFlag(Option4ClientFqdn::FLAG_S, true);
    }

    // Server MUST set the O flag if it has overriden the client's setting
    // of S flag.
    if (fqdn->getFlag(Option4ClientFqdn::FLAG_S) !=
        fqdn_resp->getFlag(Option4ClientFqdn::FLAG_S)) {
        fqdn_resp->setFlag(Option4ClientFqdn::FLAG_O, true);
    }

    // If client suppled partial or empty domain-name, server should generate
    // one.
    if (fqdn->getDomainNameType() == Option4ClientFqdn::PARTIAL) {
        std::ostringstream name;
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        if (fqdn->getDomainName().empty() || FQDN_REPLACE_CLIENT_NAME) {
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            name << FQDN_GENERATED_PARTIAL_NAME;
        } else {
            name << fqdn->getDomainName();
        }
        name << "." << FQDN_PARTIAL_SUFFIX;
        fqdn_resp->setDomainName(name.str(), Option4ClientFqdn::FULL);

    // Server may be configured to replace a name supplied by a client, even if
    // client supplied fully qualified domain-name.
    } else if(FQDN_REPLACE_CLIENT_NAME) {
        std::ostringstream name;
        name << FQDN_GENERATED_PARTIAL_NAME << "." << FQDN_PARTIAL_SUFFIX;
        fqdn_resp->setDomainName(name.str(), Option4ClientFqdn::FULL);
    }

    // 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 reponse 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.
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    answer->addOption(fqdn_resp);
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}

void
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Dhcpv4Srv::processHostnameOption(const OptionCustomPtr& opt_hostname,
                                 Pkt4Ptr& answer) {
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    // Do nothing if the DNS updates are disabled.
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    if (!FQDN_ENABLE_UPDATE) {
        return;
    }

    std::string hostname = opt_hostname->readString();
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    unsigned int label_count = OptionDataTypeUtil::getLabelCount(hostname);
    // 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.
    OptionCustomPtr opt_hostname_resp(new OptionCustom(*opt_hostname));

    // 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 there is only one label, it is a root. We will have to generate
    // the whole domain name for the client.
    if (FQDN_REPLACE_CLIENT_NAME || (label_count < 2)) {
        std::ostringstream resp_hostname;
        resp_hostname << FQDN_GENERATED_PARTIAL_NAME << "."
                      << FQDN_PARTIAL_SUFFIX << ".";
        opt_hostname_resp->writeString(resp_hostname.str());
    // If there are two labels, it means that the client has specified
    // the unqualified name. We have to concatenate the unqalified name
    // with the domain name.
    } else if (label_count == 2) {
        std::ostringstream resp_hostname;
        resp_hostname << hostname << "." << FQDN_PARTIAL_SUFFIX << ".";
        opt_hostname_resp->writeString(resp_hostname.str());
    }

    answer->addOption(opt_hostname_resp);
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}

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

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    // If old lease is not NULL, it is an indication that the lease has
    // just been renewed. In such case we may need to generate the
    // additional NameChangeRequest to remove an existing entry before
    // we create a NameChangeRequest to add the entry for an updated lease.
    // We may also decide not to generate any requests at all. This is when
    // we discover that nothing has changed in the client's FQDN data.
    if (old_lease) {
        if (!lease->matches(*old_lease)) {
            isc_throw(isc::Unexpected,
                      "there is no match between the current instance of the"
                      " lease: " << lease->toText() << ", and the previous"
                      " instance: " << lease->toText());
        } else {
            // There will be a NameChangeRequest generated to remove existing
            // DNS entries if the following conditions are met:
            // - The hostname is set for the existing lease, we can't generate
            //   removal request for non-existent hostname.
            // - A server has performed reverse, forward or both updates.
            // - FQDN data between the new and old lease do not match.
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            if  ((lease->hostname_ != old_lease->hostname_) ||
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                 (lease->fqdn_fwd_ != old_lease->fqdn_fwd_) ||
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                 (lease->fqdn_rev_ != old_lease->fqdn_rev_)) {
                queueNameChangeRequest(isc::dhcp_ddns::CHG_REMOVE,
                                       old_lease);
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            // If FQDN data from both leases match, there is no need to update.
            } else if ((lease->hostname_ == old_lease->hostname_) &&
                       (lease->fqdn_fwd_ == old_lease->fqdn_fwd_) &&
                       (lease->fqdn_rev_ == old_lease->fqdn_rev_)) {
                return;
            }

        }
    }

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    // 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.
    queueNameChangeRequest(isc::dhcp_ddns::CHG_ADD, lease);
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}

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void
Dhcpv4Srv::
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queueNameChangeRequest(const isc::dhcp_ddns::NameChangeType chg_type,
                       const Lease4Ptr& lease) {
    // The hostname must not be empty, and at least one type of update
    // should be requested.
    if (!lease || lease->hostname_.empty() ||
        (!lease->fqdn_rev_ && !lease->fqdn_fwd_)) {
        return;
    }
    D2Dhcid dhcid;
    try {
        dhcid  = computeDhcid(lease);

    } catch (const DhcidComputeError& ex) {
        LOG_ERROR(dhcp4_logger, DHCP4_DHCID_COMPUTE_ERROR)
            .arg(lease->toText())
            .arg(ex.what());
        return;

    }
    NameChangeRequest ncr(chg_type, lease->fqdn_fwd_, lease->fqdn_rev_,
                          lease->hostname_, lease->addr_.toText(),
                          dhcid, 0, lease->valid_lft_);
    if (chg_type == isc::dhcp_ddns::CHG_ADD) {
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        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL_DATA,
                  DHCP4_QUEUE_ADDITION_NCR)
            .arg(ncr.toText());

    } else {
        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL_DATA,
                  DHCP4_QUEUE_REMOVAL_NCR)
            .arg(ncr.toText());

    }
    name_change_reqs_.push(ncr);
}

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void
Dhcpv4Srv::assignLease(const Pkt4Ptr& question, Pkt4Ptr& answer) {
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    // We need to select a subnet the client is connected in.
    Subnet4Ptr subnet = selectSubnet(question);
    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). We will continue to
        // process this message, but our response will be almost useless: no
        // addresses or prefixes, no subnet specific configuration etc. The only
        // thing this client can get is some global information (like DNS
        // servers).

        // perhaps this should be logged on some higher level? This is most likely
        // configuration bug.
        LOG_ERROR(dhcp4_logger, DHCP4_SUBNET_SELECTION_FAILED)
            .arg(question->getRemoteAddr().toText())
            .arg(serverReceivedPacketName(question->getType()));
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        answer->setType(DHCPNAK);
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        answer->setYiaddr(IOAddress("0.0.0.0"));
        return;
    }
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    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_SUBNET_SELECTED)
        .arg(subnet->toText());

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    // Get client-id option
    ClientIdPtr client_id;
    OptionPtr opt = question->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (opt) {
        client_id = ClientIdPtr(new ClientId(opt->getData()));
    }
    // client-id is not mandatory in DHCPv4
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    IOAddress hint = question->getYiaddr();
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    HWAddrPtr hwaddr = question->getHWAddr();
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    // "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.
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    bool fake_allocation = (question->getType() == DHCPDISCOVER);
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    CalloutHandlePtr callout_handle = getCalloutHandle(question);

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    std::string hostname;
    bool fqdn_fwd = false;
    bool fqdn_rev = false;
    Option4ClientFqdnPtr fqdn = boost::dynamic_pointer_cast<
        Option4ClientFqdn>(answer->getOption(DHO_FQDN));
    if (fqdn) {
        hostname = fqdn->getDomainName();
        fqdn_fwd = fqdn->getFlag(Option4ClientFqdn::FLAG_S);
        fqdn_rev = !fqdn->getFlag(Option4ClientFqdn::FLAG_N);
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    } else {
        OptionCustomPtr opt_hostname = boost::dynamic_pointer_cast<
            OptionCustom>(answer->getOption(DHO_HOST_NAME));
        if (opt_hostname) {
            hostname = opt_hostname->readString();
            // @todo It could be configurable what sort of updates the server
            // is doing when Hostname option was sent.
            fqdn_fwd = true;
            fqdn_rev = true;
        }
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    }

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    // Use allocation engine to pick a lease for this client. Allocation engine
    // will try to honour the hint, but it is just a hint - some other address
    // may be used instead. If fake_allocation is set to false, the lease will
    // be inserted into the LeaseMgr as well.
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    // @todo pass the actual FQDN data.
    Lease4Ptr old_lease;
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    Lease4Ptr lease = alloc_engine_->allocateAddress4(subnet, client_id, hwaddr,
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                                                      hint, fqdn_fwd, fqdn_rev,
                                                      hostname,
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                                                      fake_allocation,
                                                      callout_handle,
                                                      old_lease);
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    if (lease) {
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        // We have a lease! Let's set it in the packet and send it back to
        // the client.
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        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, fake_allocation?
                  DHCP4_LEASE_ADVERT:DHCP4_LEASE_ALLOC)
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            .arg(lease->addr_.toText())
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            .arg(client_id?client_id->toText():"(no client-id)")
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            .arg(hwaddr?hwaddr->toText():"(no hwaddr info)");
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        answer->setYiaddr(lease->addr_);

        // IP Address Lease time (type 51)
        opt = OptionPtr(new Option(Option::V4, DHO_DHCP_LEASE_TIME));
        opt->setUint32(lease->valid_lft_);
        answer->addOption(opt);

        // Router (type 3)
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        Subnet::OptionDescriptor opt_routers =
            subnet->getOptionDescriptor("dhcp4", DHO_ROUTERS);
        if (opt_routers.option) {
            answer->addOption(opt_routers.option);
        }
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        // Subnet mask (type 1)
        answer->addOption(getNetmaskOption(subnet));

        // @todo: send renew timer option (T1, option 58)
        // @todo: send rebind timer option (T2, option 59)

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        // @todo Currently the NameChangeRequests are always generated if
        // real (not fake) allocation is being performed. Should we have
        // control switch to enable/disable NameChangeRequest creation?
        // Perhaps we need a way to detect whether the b10-dhcp-ddns module
        // is up an running?
        if (!fake_allocation) {
            try {
                createNameChangeRequests(lease, old_lease);
            } catch (const Exception& ex) {
                LOG_ERROR(dhcp4_logger, DHCP4_NCR_CREATION_FAILED)
                    .arg(ex.what());
            }

        }

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    } else {
        // Allocation engine did not allocate a lease. The engine logged
        // cause of that failure. The only thing left is to insert
        // status code to pass the sad news to the client.

        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, fake_allocation?
                  DHCP4_LEASE_ADVERT_FAIL:DHCP4_LEASE_ALLOC_FAIL)
            .arg(client_id?client_id->toText():"(no client-id)")
            .arg(hwaddr?hwaddr->toText():"(no hwaddr info)")
            .arg(hint.toText());

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        answer->setType(DHCPNAK);
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        answer->setYiaddr(IOAddress("0.0.0.0"));
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        answer->delOption(DHO_FQDN);
        answer->delOption(DHO_HOST_NAME);
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    }
}

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void
Dhcpv4Srv::adjustRemoteAddr(const Pkt4Ptr& question, Pkt4Ptr& msg) {
    // Let's create static objects representing zeroed and broadcast
    // addresses. We will use them further in this function to test
    // other addresses against them. Since they are static, they will
    // be created only once.
    static const IOAddress zero_addr("0.0.0.0");
    static const IOAddress bcast_addr("255.255.255.255");

    // If received relayed message, server responds to the relay address.
    if (question->getGiaddr() != zero_addr) {
        msg->setRemoteAddr(question->getGiaddr());

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

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

    // If yiaddr is set it means that we have created a lease for a client.
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    } else if (msg->getYiaddr() != zero_addr) {
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