dhcp4_srv.cc 41.9 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/option4_client_fqdn.h>
#include <dhcp/option_custom.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::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 {

/// @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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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) {
        processClientFqdnOption(query, answer);

    } else {
        OptionCustomPtr hostname = boost::dynamic_pointer_cast<OptionCustom>
            (query->getOption(DHO_HOST_NAME));
        if (hostname) {
            processHostnameOption(query, answer);
        }

    }
}

void
Dhcpv4Srv::processClientFqdnOption(const Pkt4Ptr&, Pkt4Ptr&) {
}

void
Dhcpv4Srv::processHostnameOption(const Pkt4Ptr&, Pkt4Ptr&) {
}

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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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    // 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, false, false, "",
                                                      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)

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

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

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

    }
}


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OptionPtr
Dhcpv4Srv::getNetmaskOption(const Subnet4Ptr& subnet) {
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    uint32_t netmask = getNetmask4(subnet->get().second);

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

    return (opt);
}

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Pkt4Ptr
Dhcpv4Srv::processDiscover(Pkt4Ptr& discover) {
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    sanityCheck(discover, FORBIDDEN);

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    Pkt4Ptr offer = Pkt4Ptr
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        (new Pkt4(DHCPOFFER, discover->getTransid()));
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    copyDefaultFields(discover, offer);
    appendDefaultOptions(offer, DHCPOFFER);
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    appendRequestedOptions(discover, offer);
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    assignLease(discover, offer);
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    // There are a few basic options that we always want to
    // include in the response. If client did not request
    // them we append them for him.
    appendBasicOptions(discover, offer);

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    return (offer);
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}

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Pkt4Ptr
Dhcpv4Srv::processRequest(Pkt4Ptr& request) {
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    /// @todo Uncomment this (see ticket #3116)
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    // sanityCheck(request, MANDATORY);

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    Pkt4Ptr ack = Pkt4Ptr
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        (new Pkt4(DHCPACK, request->getTransid()));

    copyDefaultFields(request, ack);
    appendDefaultOptions(ack, DHCPACK);
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    appendRequestedOptions(request, ack);
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    // Note that we treat REQUEST message uniformly, regardless if this is a
    // first request (requesting for new address), renewing existing address
    // or even rebinding.
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    assignLease(request, ack);
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    // There are a few basic options that we always want to
    // include in the response. If client did not request
    // them we append them for him.
    appendBasicOptions(request, ack);

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    return (ack);
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}

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void
Dhcpv4Srv::processRelease(Pkt4Ptr& release) {
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    /// @todo Uncomment this (see ticket #3116)
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    // sanityCheck(release, MANDATORY);

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    // Try to find client-id
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    ClientIdPtr client_id;
    OptionPtr opt = release->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
    if (opt) {
        client_id = ClientIdPtr(new ClientId(opt->getData()));
    }

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

        if (!lease) {
            // No such lease - bogus release
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_RELEASE_FAIL_NO_LEASE)
                .arg(release->getYiaddr().toText())
                .arg(release->getHWAddr()->toText())
                .arg(client_id ? client_id->toText() : "(no client-id)");
            return;
        }
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        // Does the hardware address match? We don't want one client releasing
        // second client's leases.
        if (lease->hwaddr_ != release->getHWAddr()->hwaddr_) {
            // @todo: Print hwaddr from lease as part of ticket #2589
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_RELEASE_FAIL_WRONG_HWADDR)
                .arg(release->getYiaddr().toText())
                .arg(client_id ? client_id->toText() : "(no client-id)")
                .arg(release->getHWAddr()->toText());
            return;
        }
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        // Does the lease have client-id info? If it has, then check it with what
        // the client sent us.
        if (lease->client_id_ && client_id && *lease->client_id_ != *client_id) {
            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_RELEASE_FAIL_WRONG_CLIENT_ID)
                .arg(release->getYiaddr().toText())
                .arg(client_id->toText())
                .arg(lease->client_id_->toText());
            return;
        }
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        bool skip = false;
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        // Execute all callouts registered for lease4_release
        if (HooksManager::getHooksManager()
            .calloutsPresent(Hooks.hook_index_lease4_release_)) {
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            CalloutHandlePtr callout_handle = getCalloutHandle(release);

            // Delete all previous arguments
            callout_handle->deleteAllArguments();
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            // Pass the original packet
            callout_handle->setArgument("query4", release);

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

            // Call all installed callouts
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            HooksManager::callCallouts(Hooks.hook_index_lease4_release_,
                                       *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()) {
                skip = true;
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                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS,
                          DHCP4_HOOK_LEASE4_RELEASE_SKIP);
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            }
        }
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        // Ok, hw and client-id match - let's release the lease.
        if (!skip) {
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            bool success = LeaseMgrFactory::instance().deleteLease(lease->addr_);
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            if (success) {
                // Release successful - we're done here
                LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_RELEASE)
                    .arg(lease->addr_.toText())
                    .arg(client_id ? client_id->toText() : "(no client-id)")
                    .arg(release->getHWAddr()->toText());
            } else {
                // Release failed -
                LOG_ERROR(dhcp4_logger, DHCP4_RELEASE_FAIL)
                    .arg(lease->addr_.toText())
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                .arg(client_id ? client_id->toText() : "(no client-id)")
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                    .arg(release->getHWAddr()->toText());
            }
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        }
    } catch (const isc::Exception& ex) {
        // Rethrow the exception with a bit more data.
        LOG_ERROR(dhcp4_logger, DHCP4_RELEASE_EXCEPTION)
            .arg(ex.what())
            .arg(release->getYiaddr());
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    }

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}
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void
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Dhcpv4Srv::processDecline(Pkt4Ptr& /* decline */) {
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    /// @todo Implement this (also see ticket #3116)
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}

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Pkt4Ptr
Dhcpv4Srv::processInform(Pkt4Ptr& inform) {
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    /// @todo Implement this for real. (also see ticket #3116)
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    return (inform);
}
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const char*
Dhcpv4Srv::serverReceivedPacketName(uint8_t type) {
    static const char* DISCOVER = "DISCOVER";
    static const char* REQUEST = "REQUEST";
    static const char* RELEASE = "RELEASE";
    static const char* DECLINE = "DECLINE";
    static const char* INFORM = "INFORM";
    static const char* UNKNOWN = "UNKNOWN";

    switch (type) {
    case DHCPDISCOVER:
        return (DISCOVER);

    case DHCPREQUEST:
        return (REQUEST);

    case DHCPRELEASE:
        return (RELEASE);

    case DHCPDECLINE:
        return (DECLINE);

    case DHCPINFORM:
        return (INFORM);

    default:
        ;
    }
    return (UNKNOWN);
}
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Subnet4Ptr
Dhcpv4Srv::selectSubnet(const Pkt4Ptr& question) {
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    Subnet4Ptr subnet;
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    // Is this relayed message?
    IOAddress relay = question->getGiaddr();
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    static const IOAddress notset("0.0.0.0");
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    if (relay != notset) {
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