mysql_host_data_source.cc

// Copyright (C) 2015-2016 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#include <config.h>

#include <dhcp/libdhcp++.h>
#include <dhcp/option.h>
#include <dhcp/option_definition.h>
#include <dhcp/option_space.h>
#include <dhcpsrv/cfg_option.h>
#include <dhcpsrv/db_exceptions.h>
#include <dhcpsrv/dhcpsrv_log.h>
#include <dhcpsrv/mysql_host_data_source.h>
#include <dhcpsrv/db_exceptions.h>
#include <util/buffer.h>
#include <util/optional_value.h>

#include <boost/algorithm/string/split.hpp>
#include <boost/algorithm/string/classification.hpp>
#include <boost/array.hpp>
#include <boost/pointer_cast.hpp>
#include <boost/static_assert.hpp>

#include <mysql.h>
#include <mysqld_error.h>

#include <stdint.h>
#include <string>

using namespace isc;
using namespace isc::asiolink;
using namespace isc::dhcp;
using namespace isc::util;
using namespace std;

namespace {

/// @brief Maximum size of an IPv6 address represented as a text string.
///
/// This is 32 hexadecimal characters written in 8 groups of four, plus seven
/// colon separators.
const size_t ADDRESS6_TEXT_MAX_LEN = 39;

/// @brief Maximum length of classes stored in a dhcp4/6_client_classes
/// columns.
const size_t CLIENT_CLASSES_MAX_LEN = 255;

/// @brief Maximum length of the hostname stored in DNS.
///
/// This length is restricted by the length of the domain-name carried
/// in the Client FQDN %Option (see RFC4702 and RFC4704).
const size_t HOSTNAME_MAX_LEN = 255;

/// @brief Maximum length of option value.
const size_t OPTION_VALUE_MAX_LEN = 4096;

/// @brief Maximum length of option value specified in textual format.
const size_t OPTION_FORMATTED_VALUE_MAX_LEN = 8192;

/// @brief Maximum length of option space name.
const size_t OPTION_SPACE_MAX_LEN = 128;

/// @brief Maximum length of the server hostname.
const size_t SERVER_HOSTNAME_MAX_LEN = 64;

/// @brief Maximum length of the boot file name.
const size_t BOOT_FILE_NAME_MAX_LEN = 128;

/// @brief Numeric value representing last supported identifier.
///
/// This value is used to validate whether the identifier type stored in
/// a database is within bounds. of supported identifiers.
const uint8_t MAX_IDENTIFIER_TYPE = static_cast<uint8_t>(Host::IDENT_CIRCUIT_ID);

/// @brief This class provides mechanisms for sending and retrieving
/// information from the 'hosts' table.
///
/// This class is used to insert and retrieve entries from the 'hosts' table.
/// The queries used with this class do not retrieve IPv6 reservations or
/// options associated with a host to minimize impact on performance. Other
/// classes derived from @ref MySqlHostExchange should be used to retrieve
/// information about IPv6 reservations and options.
class MySqlHostExchange {
private:

    /// @brief Number of columns returned for SELECT queries send by this class.
    static const size_t HOST_COLUMNS = 12;

public:

    /// @brief Constructor
    ///
    /// @param additional_columns_num This value is set by the derived classes
    /// to indicate how many additional columns will be returned by SELECT
    /// queries performed by the derived class. This constructor will allocate
    /// resources for these columns, e.g. binding table, error indicators.
    MySqlHostExchange(const size_t additional_columns_num = 0)
        : columns_num_(HOST_COLUMNS + additional_columns_num),
          bind_(columns_num_), columns_(columns_num_),
          error_(columns_num_, MLM_FALSE), host_id_(0),
          dhcp_identifier_length_(0), dhcp_identifier_type_(0),
          dhcp4_subnet_id_(0), dhcp6_subnet_id_(0), ipv4_address_(0),
          hostname_length_(0), dhcp4_client_classes_length_(0),
          dhcp6_client_classes_length_(0),
          dhcp4_next_server_(0),
          dhcp4_server_hostname_length_(0),
          dhcp4_boot_file_name_length_(0),
          dhcp4_subnet_id_null_(MLM_FALSE),
          dhcp6_subnet_id_null_(MLM_FALSE),
          ipv4_address_null_(MLM_FALSE), hostname_null_(MLM_FALSE),
          dhcp4_client_classes_null_(MLM_FALSE),
          dhcp6_client_classes_null_(MLM_FALSE),
          dhcp4_next_server_null_(MLM_FALSE),
          dhcp4_server_hostname_null_(MLM_FALSE),
          dhcp4_boot_file_name_null_(MLM_FALSE) {

        // Fill arrays with 0 so as they don't include any garbage.
        memset(dhcp_identifier_buffer_, 0, sizeof(dhcp_identifier_buffer_));
        memset(hostname_, 0, sizeof(hostname_));
        memset(dhcp4_client_classes_, 0, sizeof(dhcp4_client_classes_));
        memset(dhcp6_client_classes_, 0, sizeof(dhcp6_client_classes_));
        memset(dhcp4_server_hostname_, 0, sizeof(dhcp4_server_hostname_));
        memset(dhcp4_boot_file_name_, 0, sizeof(dhcp4_boot_file_name_));

        // Set the column names for use by this class. This only comprises
        // names used by the MySqlHostExchange class. Derived classes will
        // need to set names for the columns they use.
        columns_[0] = "host_id";
        columns_[1] = "dhcp_identifier";
        columns_[2] = "dhcp_identifier_type";
        columns_[3] = "dhcp4_subnet_id";
        columns_[4] = "dhcp6_subnet_id";
        columns_[5] = "ipv4_address";
        columns_[6] = "hostname";
        columns_[7] = "dhcp4_client_classes";
        columns_[8] = "dhcp6_client_classes";
        columns_[9] = "dhcp4_next_server";
        columns_[10] = "dhcp4_server_hostname";
        columns_[11] = "dhcp4_boot_file_name";

        BOOST_STATIC_ASSERT(11 < HOST_COLUMNS);
    };

    /// @brief Virtual destructor.
    virtual ~MySqlHostExchange() {
    }

    /// @brief Returns index of the first uninitialized column name.
    ///
    /// This method is called by the derived classes to determine which
    /// column indexes are available for the derived classes within a
    /// binding array, error array and column names. This method
    /// determines the first available index by searching the first
    /// empty value within the columns_ vector. Previously we relied on
    /// the fixed values set for each class, but this was hard to maintain
    /// when new columns were added to the SELECT queries. It required
    /// modifying indexes in all derived classes.
    ///
    /// Derived classes must call this method in their constructors and
    /// use returned value as an index for the first column used by the
    /// derived class and increment this value for each subsequent column.
    size_t findAvailColumn() const {
        std::vector<std::string>::const_iterator empty_column =
            std::find(columns_.begin(), columns_.end(), std::string());
        return (std::distance(columns_.begin(), empty_column));
    }

    /// @brief Returns value of host id.
    ///
    /// This method is used by derived classes.
    uint64_t getHostId() const {
        return (host_id_);
    };

    /// @brief Set error indicators
    ///
    /// Sets the error indicator for each of the MYSQL_BIND elements. It points
    /// the "error" field within an element of the input array to the
    /// corresponding element of the passed error array.
    ///
    /// @param bind Array of BIND elements
    /// @param error Array of error elements.  If there is an error in getting
    ///        data associated with one of the "bind" elements, the
    ///        corresponding element in the error array is set to MLM_TRUE.
    static void setErrorIndicators(std::vector<MYSQL_BIND>& bind,
                                   std::vector<my_bool>& error) {
        for (size_t i = 0; i < error.size(); ++i) {
            error[i] = MLM_FALSE;
            bind[i].error = reinterpret_cast<char*>(&error[i]);
        }
    };

    /// @brief Return columns in error
    ///
    /// If an error is returned from a fetch (in particular, a truncated
    /// status), this method can be called to get the names of the fields in
    /// error.  It returns a string comprising the names of the fields
    /// separated by commas.  In the case of there being no error indicators
    /// set, it returns the string "(None)".
    ///
    /// @param error Array of error elements.  An element is set to MLM_TRUE
    ///        if the corresponding column in the database is the source of
    ///        the error.
    /// @param names Array of column names, the same size as the error array.
    /// @param count Size of each of the arrays.
    static std::string getColumnsInError(std::vector<my_bool>& error,
                                         const std::vector<std::string>& names) {
        std::string result = "";

        // Accumulate list of column names
        for (size_t i = 0; i < names.size(); ++i) {
            if (error[i] == MLM_TRUE) {
                if (!result.empty()) {
                    result += ", ";
                }
                result += names[i];
            }
        }

        if (result.empty()) {
            result = "(None)";
        }

        return (result);
    };

    /// @brief Create MYSQL_BIND objects for Host Pointer
    ///
    /// Fills in the MYSQL_BIND array for sending data stored in the Host object
    /// to the database.
    ///
    /// @param host Host object to be added to the database.
    ///        None of the fields in the host reservation are modified -
    ///        the host data is only read.
    ///
    /// @return Vector of MySQL BIND objects representing the data to be added.
    std::vector<MYSQL_BIND> createBindForSend(const HostPtr& host) {
        // Store host object to ensure it remains valid.
        host_ = host;

        // Initialize prior to constructing the array of MYSQL_BIND structures.
        // It sets all fields, including is_null, to zero, so we need to set
        // is_null only if it should be true. This gives up minor performance
        // benefit while being safe approach.
        memset(&bind_[0], 0, sizeof(MYSQL_BIND) * bind_.size());

        // Set up the structures for the various components of the host structure.

        try {
            // host_id : INT UNSIGNED NOT NULL
            // The host_id is auto_incremented by MySQL database,
            // so we need to pass the NULL value
            host_id_ = 0;
            bind_[0].buffer_type = MYSQL_TYPE_LONG;
            bind_[0].buffer = reinterpret_cast<char*>(&host_id_);
            bind_[0].is_unsigned = MLM_TRUE;

            // dhcp_identifier : VARBINARY(128) NOT NULL
            dhcp_identifier_length_ = host->getIdentifier().size();
            memcpy(static_cast<void*>(dhcp_identifier_buffer_),
                   &(host->getIdentifier())[0],
                   host->getIdentifier().size());

            bind_[1].buffer_type = MYSQL_TYPE_BLOB;
            bind_[1].buffer = dhcp_identifier_buffer_;
            bind_[1].buffer_length = dhcp_identifier_length_;
            bind_[1].length = &dhcp_identifier_length_;

            // dhcp_identifier_type : TINYINT NOT NULL
            dhcp_identifier_type_ = static_cast<uint8_t>(host->getIdentifierType());
            bind_[2].buffer_type = MYSQL_TYPE_TINY;
            bind_[2].buffer = reinterpret_cast<char*>(&dhcp_identifier_type_);
            bind_[2].is_unsigned = MLM_TRUE;

            // dhcp4_subnet_id : INT UNSIGNED NULL
            // Can't take an address of intermediate object, so let's store it
            // in dhcp4_subnet_id_
            dhcp4_subnet_id_ = host->getIPv4SubnetID();
            bind_[3].buffer_type = MYSQL_TYPE_LONG;
            bind_[3].buffer = reinterpret_cast<char*>(&dhcp4_subnet_id_);
            bind_[3].is_unsigned = MLM_TRUE;

            // dhcp6_subnet_id : INT UNSIGNED NULL
            // Can't take an address of intermediate object, so let's store it
            // in dhcp6_subnet_id_
            dhcp6_subnet_id_ = host->getIPv6SubnetID();
            bind_[4].buffer_type = MYSQL_TYPE_LONG;
            bind_[4].buffer = reinterpret_cast<char*>(&dhcp6_subnet_id_);
            bind_[4].is_unsigned = MLM_TRUE;

            // ipv4_address : INT UNSIGNED NULL
            // The address in the Host structure is an IOAddress object.  Convert
            // this to an integer for storage.
            ipv4_address_ = host->getIPv4Reservation().toUint32();
            bind_[5].buffer_type = MYSQL_TYPE_LONG;
            bind_[5].buffer = reinterpret_cast<char*>(&ipv4_address_);
            bind_[5].is_unsigned = MLM_TRUE;
            // bind_[5].is_null = &MLM_FALSE; // commented out for performance
                                                      // reasons, see memset() above

            // hostname : VARCHAR(255) NULL
            strncpy(hostname_, host->getHostname().c_str(), HOSTNAME_MAX_LEN - 1);
            hostname_length_ = host->getHostname().length();
            bind_[6].buffer_type = MYSQL_TYPE_STRING;
            bind_[6].buffer = reinterpret_cast<char*>(hostname_);
            bind_[6].buffer_length = hostname_length_;

            // dhcp4_client_classes : VARCHAR(255) NULL
            bind_[7].buffer_type = MYSQL_TYPE_STRING;
            // Override default separator to not include space after comma.
            string classes4_txt = host->getClientClasses4().toText(",");
            strncpy(dhcp4_client_classes_, classes4_txt.c_str(), CLIENT_CLASSES_MAX_LEN - 1);
            bind_[7].buffer = dhcp4_client_classes_;
            bind_[7].buffer_length = classes4_txt.length();

            // dhcp6_client_classes : VARCHAR(255) NULL
            bind_[8].buffer_type = MYSQL_TYPE_STRING;
            // Override default separator to not include space after comma.
            string classes6_txt = host->getClientClasses6().toText(",");
            strncpy(dhcp6_client_classes_, classes6_txt.c_str(), CLIENT_CLASSES_MAX_LEN - 1);
            bind_[8].buffer = dhcp6_client_classes_;
            bind_[8].buffer_length = classes6_txt.length();

            // ipv4_address : INT UNSIGNED NULL
            // The address in the Host structure is an IOAddress object.  Convert
            // this to an integer for storage.
            dhcp4_next_server_ = host->getNextServer().toUint32();
            bind_[9].buffer_type = MYSQL_TYPE_LONG;
            bind_[9].buffer = reinterpret_cast<char*>(&dhcp4_next_server_);
            bind_[9].is_unsigned = MLM_TRUE;
            // bind_[9].is_null = &MLM_FALSE; // commented out for performance
                                              // reasons, see memset() above

            // dhcp4_server_hostname
            bind_[10].buffer_type = MYSQL_TYPE_STRING;
            std::string server_hostname = host->getServerHostname();
            strncpy(dhcp4_server_hostname_, server_hostname.c_str(),
                    SERVER_HOSTNAME_MAX_LEN - 1);
            bind_[10].buffer = dhcp4_server_hostname_;
            bind_[10].buffer_length = server_hostname.length();

            // dhcp4_boot_file_name
            bind_[11].buffer_type = MYSQL_TYPE_STRING;
            std::string boot_file_name = host->getBootFileName();
            strncpy(dhcp4_boot_file_name_, boot_file_name.c_str(),
                    BOOT_FILE_NAME_MAX_LEN - 1);
            bind_[11].buffer = dhcp4_boot_file_name_;
            bind_[11].buffer_length = boot_file_name.length();

        } catch (const std::exception& ex) {
            isc_throw(DbOperationError,
                      "Could not create bind array from Host: "
                      << host->getHostname() << ", reason: " << ex.what());
        }

        // Add the data to the vector.  Note the end element is one after the
        // end of the array.
        return (std::vector<MYSQL_BIND>(&bind_[0], &bind_[columns_num_]));
    };

    /// @brief Create BIND array to receive Host data.
    ///
    /// Creates a MYSQL_BIND array to receive Host data from the database.
    /// After data is successfully received, @ref retrieveHost can be called
    /// to retrieve the Host object.
    ///
    /// @return Vector of MYSQL_BIND objects representing data to be retrieved.
    virtual std::vector<MYSQL_BIND> createBindForReceive() {
        // Initialize MYSQL_BIND array.
        // It sets all fields, including is_null, to zero, so we need to set
        // is_null only if it should be true. This gives up minor performance
        // benefit while being safe approach. For improved readability, the
        // code that explicitly sets is_null is there, but is commented out.
        // This also takes care of seeeting bind_[X].is_null to MLM_FALSE.
        memset(&bind_[0], 0, sizeof(MYSQL_BIND) * bind_.size());

        // host_id : INT UNSIGNED NOT NULL
        bind_[0].buffer_type = MYSQL_TYPE_LONG;
        bind_[0].buffer = reinterpret_cast<char*>(&host_id_);
        bind_[0].is_unsigned = MLM_TRUE;

        // dhcp_identifier : VARBINARY(128) NOT NULL
        dhcp_identifier_length_ = sizeof(dhcp_identifier_buffer_);
        bind_[1].buffer_type = MYSQL_TYPE_BLOB;
        bind_[1].buffer = reinterpret_cast<char*>(dhcp_identifier_buffer_);
        bind_[1].buffer_length = dhcp_identifier_length_;
        bind_[1].length = &dhcp_identifier_length_;

        // dhcp_identifier_type : TINYINT NOT NULL
        bind_[2].buffer_type = MYSQL_TYPE_TINY;
        bind_[2].buffer = reinterpret_cast<char*>(&dhcp_identifier_type_);
        bind_[2].is_unsigned = MLM_TRUE;

        // dhcp4_subnet_id : INT UNSIGNED NULL
        dhcp4_subnet_id_null_ = MLM_FALSE;
        bind_[3].buffer_type = MYSQL_TYPE_LONG;
        bind_[3].buffer = reinterpret_cast<char*>(&dhcp4_subnet_id_);
        bind_[3].is_unsigned = MLM_TRUE;
        bind_[3].is_null = &dhcp4_subnet_id_null_;

        // dhcp6_subnet_id : INT UNSIGNED NULL
        dhcp6_subnet_id_null_ = MLM_FALSE;
        bind_[4].buffer_type = MYSQL_TYPE_LONG;
        bind_[4].buffer = reinterpret_cast<char*>(&dhcp6_subnet_id_);
        bind_[4].is_unsigned = MLM_TRUE;
        bind_[4].is_null = &dhcp6_subnet_id_null_;

        // ipv4_address : INT UNSIGNED NULL
        ipv4_address_null_ = MLM_FALSE;
        bind_[5].buffer_type = MYSQL_TYPE_LONG;
        bind_[5].buffer = reinterpret_cast<char*>(&ipv4_address_);
        bind_[5].is_unsigned = MLM_TRUE;
        bind_[5].is_null = &ipv4_address_null_;

        // hostname : VARCHAR(255) NULL
        hostname_null_ = MLM_FALSE;
        hostname_length_ = sizeof(hostname_);
        bind_[6].buffer_type = MYSQL_TYPE_STRING;
        bind_[6].buffer = reinterpret_cast<char*>(hostname_);
        bind_[6].buffer_length = hostname_length_;
        bind_[6].length = &hostname_length_;
        bind_[6].is_null = &hostname_null_;

        // dhcp4_client_classes : VARCHAR(255) NULL
        dhcp4_client_classes_null_ = MLM_FALSE;
        dhcp4_client_classes_length_ = sizeof(dhcp4_client_classes_);
        bind_[7].buffer_type = MYSQL_TYPE_STRING;
        bind_[7].buffer = reinterpret_cast<char*>(dhcp4_client_classes_);
        bind_[7].buffer_length = dhcp4_client_classes_length_;
        bind_[7].length = &dhcp4_client_classes_length_;
        bind_[7].is_null = &dhcp4_client_classes_null_;

        // dhcp6_client_classes : VARCHAR(255) NULL
        dhcp6_client_classes_null_ = MLM_FALSE;
        dhcp6_client_classes_length_ = sizeof(dhcp6_client_classes_);
        bind_[8].buffer_type = MYSQL_TYPE_STRING;
        bind_[8].buffer = reinterpret_cast<char*>(dhcp6_client_classes_);
        bind_[8].buffer_length = dhcp6_client_classes_length_;
        bind_[8].length = &dhcp6_client_classes_length_;
        bind_[8].is_null = &dhcp6_client_classes_null_;

        // dhcp4_next_server
        dhcp4_next_server_null_ = MLM_FALSE;
        bind_[9].buffer_type = MYSQL_TYPE_LONG;
        bind_[9].buffer = reinterpret_cast<char*>(&dhcp4_next_server_);
        bind_[9].is_unsigned = MLM_TRUE;
        bind_[9].is_null = &dhcp4_next_server_null_;

        // dhcp4_server_hostname
        dhcp4_server_hostname_null_ = MLM_FALSE;
        dhcp4_server_hostname_length_ = sizeof(dhcp4_server_hostname_);
        bind_[10].buffer_type = MYSQL_TYPE_STRING;
        bind_[10].buffer = reinterpret_cast<char*>(dhcp4_server_hostname_);
        bind_[10].buffer_length = dhcp4_server_hostname_length_;
        bind_[10].length = &dhcp4_server_hostname_length_;
        bind_[10].is_null = &dhcp4_server_hostname_null_;

        // dhcp4_boot_file_name
        dhcp4_boot_file_name_null_ = MLM_FALSE;
        dhcp4_boot_file_name_length_ = sizeof(dhcp4_boot_file_name_);
        bind_[11].buffer_type = MYSQL_TYPE_STRING;
        bind_[11].buffer = reinterpret_cast<char*>(dhcp4_boot_file_name_);
        bind_[11].buffer_length = dhcp4_boot_file_name_length_;
        bind_[11].length = &dhcp4_boot_file_name_length_;
        bind_[11].is_null = &dhcp4_boot_file_name_null_;

        // Add the error flags
        setErrorIndicators(bind_, error_);

        // Add the data to the vector.  Note the end element is one after the
        // end of the array.
        return (bind_);
    };

    /// @brief Copy received data into Host object
    ///
    /// This function copies information about the host into a newly created
    /// @ref Host object. This method is called after @ref createBindForReceive.
    /// has been used.
    ///
    /// @return Host Pointer to a @ref HostPtr object holding a pointer to the
    /// @ref Host object returned.
    HostPtr retrieveHost() {
        // Check if the identifier stored in the database is correct.
        if (dhcp_identifier_type_ > MAX_IDENTIFIER_TYPE) {
            isc_throw(BadValue, "invalid dhcp identifier type returned: "
                      << static_cast<int>(dhcp_identifier_type_));
        }
        // Set the dhcp identifier type in a variable of the appropriate
        // data type.
        Host::IdentifierType type =
            static_cast<Host::IdentifierType>(dhcp_identifier_type_);

        // Set DHCPv4 subnet ID to the value returned. If NULL returned,
        // set to 0.
        SubnetID ipv4_subnet_id(0);
        if (dhcp4_subnet_id_null_ == MLM_FALSE) {
            ipv4_subnet_id = static_cast<SubnetID>(dhcp4_subnet_id_);
        }

        // Set DHCPv6 subnet ID to the value returned. If NULL returned,
        // set to 0.
        SubnetID ipv6_subnet_id(0);
        if (dhcp6_subnet_id_null_ == MLM_FALSE) {
            ipv6_subnet_id = static_cast<SubnetID>(dhcp6_subnet_id_);
        }

        // Set IPv4 address reservation if it was given, if not, set IPv4 zero
        // address
        asiolink::IOAddress ipv4_reservation = asiolink::IOAddress::IPV4_ZERO_ADDRESS();
        if (ipv4_address_null_ == MLM_FALSE) {
            ipv4_reservation = asiolink::IOAddress(ipv4_address_);
        }

        // Set hostname if non NULL value returned. Otherwise, leave an
        // empty string.
        std::string hostname;
        if (hostname_null_ == MLM_FALSE) {
            hostname = std::string(hostname_, hostname_length_);
        }

        // Set DHCPv4 client classes if non NULL value returned.
        std::string dhcp4_client_classes;
        if (dhcp4_client_classes_null_ == MLM_FALSE) {
            dhcp4_client_classes = std::string(dhcp4_client_classes_,
                                               dhcp4_client_classes_length_);
        }

        // Set DHCPv6 client classes if non NULL value returned.
        std::string dhcp6_client_classes;
        if (dhcp6_client_classes_null_ == MLM_FALSE) {
            dhcp6_client_classes = std::string(dhcp6_client_classes_,
                                               dhcp6_client_classes_length_);
        }

        // Set next server value (siaddr) if non NULL value returned.
        asiolink::IOAddress next_server = asiolink::IOAddress::IPV4_ZERO_ADDRESS();
        if (dhcp4_next_server_null_ == MLM_FALSE) {
            next_server = asiolink::IOAddress(dhcp4_next_server_);
        }

        // Set server hostname (sname) if non NULL value returned.
        std::string dhcp4_server_hostname;
        if (dhcp4_server_hostname_null_ == MLM_FALSE) {
            dhcp4_server_hostname = std::string(dhcp4_server_hostname_,
                                                dhcp4_server_hostname_length_);
        }

        // Set boot file name (file) if non NULL value returned.
        std::string dhcp4_boot_file_name;
        if (dhcp4_boot_file_name_null_ == MLM_FALSE) {
            dhcp4_boot_file_name = std::string(dhcp4_boot_file_name_,
                                               dhcp4_boot_file_name_length_);
        }

        // Create and return Host object from the data gathered.
        HostPtr h(new Host(dhcp_identifier_buffer_, dhcp_identifier_length_,
                           type, ipv4_subnet_id, ipv6_subnet_id, ipv4_reservation,
                           hostname, dhcp4_client_classes, dhcp6_client_classes,
                           next_server, dhcp4_server_hostname,
                           dhcp4_boot_file_name));
        h->setHostId(host_id_);

        return (h);
    };

    /// @brief Processes one row of data fetched from a database.
    ///
    /// The processed data must contain host id, which uniquely identifies a
    /// host. This method creates a host and inserts it to the hosts collection
    /// only if the last inserted host has a different host id. This prevents
    /// adding duplicated hosts to the collection, assuming that processed
    /// rows are primarily ordered by host id column.
    ///
    /// This method must be overriden in the derived classes to also
    /// retrieve IPv6 reservations and DHCP options associated with a host.
    ///
    /// @param [out] hosts Collection of hosts to which a new host created
    ///        from the processed data should be inserted.
    virtual void processFetchedData(ConstHostCollection& hosts) {
        HostPtr host;
        // Add new host only if there are no hosts yet or the host id of the
        // most recently added host is different than the host id of the
        // currently processed host.
        if (hosts.empty() || (hosts.back()->getHostId() != getHostId())) {
            // Create Host object from the fetched data and append it to the
            // collection.
            host = retrieveHost();
            hosts.push_back(host);
        }
    }

    /// @brief Return columns in error
    ///
    /// If an error is returned from a fetch (in particular, a truncated
    /// status), this method can be called to get the names of the fields in
    /// error.  It returns a string comprising the names of the fields
    /// separated by commas.  In the case of there being no error indicators
    /// set, it returns the string "(None)".
    ///
    /// @return Comma-separated list of columns in error, or the string
    ///         "(None)".
    std::string getErrorColumns() {
        return (getColumnsInError(error_, columns_));
    };

protected:

    /// Number of columns returned in queries.
    size_t columns_num_;

    /// Vector of MySQL bindings.
    std::vector<MYSQL_BIND> bind_;

    /// Column names.
    std::vector<std::string> columns_;

    /// Error array.
    std::vector<my_bool> error_;

    /// Pointer to Host object holding information to be inserted into
    /// Hosts table.
    HostPtr host_;

private:

    /// Host identifier (primary key in Hosts table).
    uint64_t host_id_;

    /// Buffer holding client's identifier (e.g. DUID, HW address)
    /// in the binary format.
    uint8_t dhcp_identifier_buffer_[DUID::MAX_DUID_LEN];

    /// Length of a data in the dhcp_identifier_buffer_.
    unsigned long dhcp_identifier_length_;

    /// Type of the identifier in the dhcp_identifier_buffer_. This
    /// value corresponds to the @ref Host::IdentifierType value.
    uint8_t dhcp_identifier_type_;

    /// DHCPv4 subnet identifier.
    uint32_t dhcp4_subnet_id_;

    /// DHCPv6 subnet identifier.
    uint32_t dhcp6_subnet_id_;

    /// Reserved IPv4 address.
    uint32_t ipv4_address_;

    /// Name reserved for the host.
    char hostname_[HOSTNAME_MAX_LEN];

    /// Hostname length.
    unsigned long hostname_length_;

    /// A string holding comma separated list of DHCPv4 client classes.
    char dhcp4_client_classes_[CLIENT_CLASSES_MAX_LEN];

    /// A length of the string holding comma separated list of DHCPv4
    /// client classes.
    unsigned long dhcp4_client_classes_length_;

    /// A string holding comma separated list of DHCPv6 client classes.
    char dhcp6_client_classes_[CLIENT_CLASSES_MAX_LEN];

    /// A length of the string holding comma separated list of DHCPv6
    /// client classes.
    unsigned long dhcp6_client_classes_length_;

    /// Next server address (siaddr).
    uint32_t dhcp4_next_server_;

    /// Server hostname (sname).
    char dhcp4_server_hostname_[SERVER_HOSTNAME_MAX_LEN];

    /// A length of the string holding server hostname.
    unsigned long dhcp4_server_hostname_length_;

    /// Boot file name (file).
    char dhcp4_boot_file_name_[BOOT_FILE_NAME_MAX_LEN];

    /// A length of the string holding boot file name.
    unsigned long dhcp4_boot_file_name_length_;

    /// @name Boolean values indicating if values of specific columns in
    /// the database are NULL.
    //@{
    /// Boolean flag indicating if the value of the DHCPv4 subnet is NULL.
    my_bool dhcp4_subnet_id_null_;

    /// Boolean flag indicating if the value of the DHCPv6 subnet is NULL.
    my_bool dhcp6_subnet_id_null_;

    /// Boolean flag indicating if the value of IPv4 reservation is NULL.
    my_bool ipv4_address_null_;

    /// Boolean flag indicating if the value if hostname is NULL.
    my_bool hostname_null_;

    /// Boolean flag indicating if the value of DHCPv4 client classes is
    /// NULL.
    my_bool dhcp4_client_classes_null_;

    /// Boolean flag indicating if the value of DHCPv6 client classes is
    /// NULL.
    my_bool dhcp6_client_classes_null_;

    /// Boolean flag indicating if the value of next server is NULL.
    my_bool dhcp4_next_server_null_;

    /// Boolean flag indicating if the value of server hostname is NULL.
    my_bool dhcp4_server_hostname_null_;

    /// Boolean flag indicating if the value of boot file name is NULL.
    my_bool dhcp4_boot_file_name_null_;

    //@}

};

/// @brief Extends base exchange class with ability to retrieve DHCP options
/// from the 'dhcp4_options' and 'dhcp6_options' tables.
///
/// This class provides means to retrieve both DHCPv4 and DHCPv6 options
/// along with the host information. It is not used to retrieve IPv6
/// reservations. The following types of queries are supported:
/// - SELECT ? FROM hosts LEFT JOIN dhcp4_options LEFT JOIN dhcp6_options ...
/// - SELECT ? FROM hosts LEFT JOIN dhcp4_options ...
/// - SELECT ? FROM hosts LEFT JOIN dhcp6_options ...
class MySqlHostWithOptionsExchange : public MySqlHostExchange {
private:

    /// @brief Number of columns holding DHCPv4  or DHCPv6 option information.
    static const size_t OPTION_COLUMNS = 6;

    /// @brief Receives DHCPv4 or DHCPv6 options information from the
    /// dhcp4_options or dhcp6_options tables respectively.
    ///
    /// The MySqlHostWithOptionsExchange class holds two respective instances
    /// of this class, one for receiving DHCPv4 options, one for receiving
    /// DHCPv6 options.
    ///
    /// The following are the basic functions of this class:
    /// - bind class members to specific columns in MySQL binding tables,
    /// - set DHCP options specific column names,
    /// - create instances of options retrieved from the database.
    ///
    /// The reason for isolating those functions in a separate C++ class is
    /// to prevent code duplication for handling DHCPv4 and DHCPv6 options.
    class OptionProcessor {
    public:

        /// @brief Constructor.
        ///
        /// @param universe V4 or V6. The type of the options' instances
        /// created by this class depends on this parameter.
        /// @param start_column Index of the first column to be used by this
        /// class.
        OptionProcessor(const Option::Universe& universe,
                        const size_t start_column)
        : universe_(universe), start_column_(start_column), option_id_(0),
          code_(0), value_length_(0), formatted_value_length_(0),
          space_length_(0), persistent_(false), option_id_null_(MLM_FALSE),
          code_null_(MLM_FALSE), value_null_(MLM_FALSE),
          formatted_value_null_(MLM_FALSE), space_null_(MLM_FALSE),
          option_id_index_(start_column), code_index_(start_column_ + 1),
          value_index_(start_column_ + 2),
          formatted_value_index_(start_column_ + 3),
          space_index_(start_column_ + 4),
          persistent_index_(start_column_ + 5),
          most_recent_option_id_(0) {

            memset(value_, 0, sizeof(value_));
            memset(formatted_value_, 0, sizeof(formatted_value_));
            memset(space_, 0, sizeof(space_));
        }

        /// @brief Returns identifier of the currently processed option.
        uint64_t getOptionId() const {
            if (option_id_null_ == MLM_FALSE) {
                return (option_id_);
            }
            return (0);
        }

        /// @brief Creates instance of the currently processed option.
        ///
        /// This method detects if the currently processed option is a new
        /// instance. It makes it determination by comparing the identifier
        /// of the currently processed option, with the most recently processed
        /// option. If the current value is greater than the id of the recently
        /// processed option it is assumed that the processed row holds new
        /// option information. In such case the option instance is created and
        /// inserted into the configuration passed as argument.
        ///
        /// @param cfg Pointer to the configuration object into which new
        /// option instances should be inserted.
        void retrieveOption(const CfgOptionPtr& cfg) {
            // option_id may be NULL if dhcp4_options or dhcp6_options table
            // doesn't contain any options for the particular host. Also, the
            // current option id must be greater than id if the most recent
            // option because options are ordered by option id. Otherwise
            // we assume that this is already processed option.
            if ((option_id_null_ == MLM_TRUE) ||
                (most_recent_option_id_ >= option_id_)) {
                return;
            }

            // Remember current option id as the most recent processed one. We
            // will be comparing it with option ids in subsequent rows.
            most_recent_option_id_ = option_id_;

            // Convert it to string object for easier comparison.
            std::string space;
            if (space_null_ == MLM_FALSE) {
                // Typically, the string values returned by the database are not
                // NULL terminated.
                space_[space_length_] = '\0';
                space.assign(space_);
            }

            // If empty or null space provided, use a default top level space.
            if (space.empty()) {
                space = (universe_ == Option::V4 ? "dhcp4" : "dhcp6");
            }

            // Convert formatted_value to string as well.
            std::string formatted_value;
            if (formatted_value_null_ == MLM_FALSE) {
                formatted_value_[formatted_value_length_] = '\0';
                formatted_value.assign(formatted_value_);
            }

            // Options are held in a binary or textual format in the database.
            // This is similar to having an option specified in a server
            // configuration file. Such option is converted to appropriate C++
            // class, using option definition. Thus, we need to find the
            // option definition for this option code and option space.

            // Check if this is a standard option.
            OptionDefinitionPtr def = LibDHCP::getOptionDef(space, code_);

            // Otherwise, we may check if this an option encapsulated within the
            // vendor space.
            if (!def && (space != DHCP4_OPTION_SPACE) &&
                (space != DHCP6_OPTION_SPACE)) {
                uint32_t vendor_id = LibDHCP::optionSpaceToVendorId(space);
                if (vendor_id > 0) {
                    def = LibDHCP::getVendorOptionDef(universe_, vendor_id, code_);
                }
            }

            // In all other cases, we use runtime option definitions, which
            // should be also registered within the libdhcp++.
            if (!def) {
                def = LibDHCP::getRuntimeOptionDef(space, code_);
            }

            OptionPtr option;

            if (!def) {
                // If no definition found, we use generic option type.
                OptionBuffer buf(value_, value_ + value_length_);
                option.reset(new Option(universe_, code_, buf.begin(),
                                        buf.end()));
            } else {
                // The option value may be specified in textual or binary format
                // in the database. If formatted_value is empty, the binary
                // format is used. Depending on the format we use a different
                // variant of the optionFactory function.
                if (formatted_value.empty()) {
                    OptionBuffer buf(value_, value_ + value_length_);
                    option = def->optionFactory(universe_, code_, buf.begin(),
                                                buf.end());
                } else {
                    // Spit the value specified in comma separated values
                    // format.
                    std::vector<std::string> split_vec;
                    boost::split(split_vec, formatted_value, boost::is_any_of(","));
                    option = def->optionFactory(universe_, code_, split_vec);
                }
            }

            OptionDescriptor desc(option, persistent_, formatted_value);
            cfg->add(desc, space);
        }

        /// @brief Specify column names.
        ///
        /// @param [out] columns Reference to a vector holding names of option
        /// specific columns.
        void setColumnNames(std::vector<std::string>& columns) {
            columns[option_id_index_] = "option_id";
            columns[code_index_] = "code";
            columns[value_index_] = "value";
            columns[formatted_value_index_] = "formatted_value";
            columns[space_index_] = "space";
            columns[persistent_index_] = "persistent";
        }

        /// @brief Initialize binding table fields for options.
        ///
        /// Resets most_recent_option_id_ value to 0.
        ///
        /// @param [out] bind Binding table.
        void setBindFields(std::vector<MYSQL_BIND>& bind) {
            // This method is called just before making a new query, so we
            // reset the most_recent_option_id_ to start over with options
            // processing.
            most_recent_option_id_ = 0;

            // option_id : INT UNSIGNED NOT NULL AUTO_INCREMENT,
            bind[option_id_index_].buffer_type = MYSQL_TYPE_LONG;
            bind[option_id_index_].buffer = reinterpret_cast<char*>(&option_id_);
            bind[option_id_index_].is_unsigned = MLM_TRUE;

            // code : TINYINT OR SHORT UNSIGNED NOT NULL
            bind[code_index_].buffer_type = MYSQL_TYPE_SHORT;
            bind[code_index_].buffer = reinterpret_cast<char*>(&code_);
            bind[code_index_].is_unsigned = MLM_TRUE;
            bind[code_index_].is_null = &code_null_;

            // value : BLOB NULL
            value_length_ = sizeof(value_);
            bind[value_index_].buffer_type = MYSQL_TYPE_BLOB;
            bind[value_index_].buffer = reinterpret_cast<char*>(value_);
            bind[value_index_].buffer_length = value_length_;
            bind[value_index_].length = &value_length_;
            bind[value_index_].is_null = &value_null_;

            // formatted_value : TEXT NULL
            formatted_value_length_ = sizeof(formatted_value_);
            bind[formatted_value_index_].buffer_type = MYSQL_TYPE_STRING;
            bind[formatted_value_index_].buffer = reinterpret_cast<char*>(formatted_value_);
            bind[formatted_value_index_].buffer_length = formatted_value_length_;
            bind[formatted_value_index_].length = &formatted_value_length_;
            bind[formatted_value_index_].is_null = &formatted_value_null_;

            // space : VARCHAR(128) NULL
            space_length_ = sizeof(space_);
            bind[space_index_].buffer_type = MYSQL_TYPE_STRING;
            bind[space_index_].buffer = reinterpret_cast<char*>(space_);
            bind[space_index_].buffer_length = space_length_;
            bind[space_index_].length = &space_length_;
            bind[space_index_].is_null = &space_null_;

            // persistent : TINYINT(1) NOT NULL DEFAULT 0
            bind[persistent_index_].buffer_type = MYSQL_TYPE_TINY;
            bind[persistent_index_].buffer = reinterpret_cast<char*>(&persistent_);
            bind[persistent_index_].is_unsigned = MLM_TRUE;
        }

    private:

        /// @brief Universe: V4 or V6.
        Option::Universe universe_;

        /// @brief Index of first column used by this class.
        size_t start_column_;

        /// @brief Option id.
        uint32_t option_id_;

        /// @brief Option code.
        uint16_t code_;

        /// @brief Buffer holding binary value of an option.
        uint8_t value_[OPTION_VALUE_MAX_LEN];

        /// @brief Option value length.
        unsigned long value_length_;

        /// @brief Buffer holding textual value of an option.
        char formatted_value_[OPTION_FORMATTED_VALUE_MAX_LEN];

        /// @brief Formatted option value length.
        unsigned long formatted_value_length_;

        /// @brief Buffer holding option space name.
        char space_[OPTION_SPACE_MAX_LEN];

        /// @brief Option space length.
        unsigned long space_length_;

        /// @brief Flag indicating if option is always sent or only if
        /// requested.
        bool persistent_;

        /// @name Boolean values indicating if values of specific columns in
        /// the database are NULL.
        //@{
        /// @brief Boolean flag indicating if the DHCPv4 option id is NULL.
        my_bool option_id_null_;

        /// @brief Boolean flag indicating if the DHCPv4 option code is NULL.
        my_bool code_null_;

        /// @brief Boolean flag indicating if the DHCPv4 option value is NULL.
        my_bool value_null_;

        /// @brief Boolean flag indicating if the DHCPv4 formatted option value
        /// is NULL.
        my_bool formatted_value_null_;

        /// @brief Boolean flag indicating if the DHCPv4 option space is NULL.
        my_bool space_null_;

        //@}

        /// @name Indexes of the specific columns
        //@{
        /// @brief Option id
        size_t option_id_index_;

        /// @brief Code
        size_t code_index_;

        /// @brief Value
        size_t value_index_;

        /// @brief Formatted value
        size_t formatted_value_index_;

        /// @brief Space
        size_t space_index_;

        /// @brief Persistent
        size_t persistent_index_;
        //@}

        /// @brief Option id for last processed row.
        uint32_t most_recent_option_id_;
    };

    /// @brief Pointer to the @ref OptionProcessor class.
    typedef boost::shared_ptr<OptionProcessor> OptionProcessorPtr;

public:

    /// @brief DHCP option types to be fetched from the database.
    ///
    /// Supported types are:
    /// - Only DHCPv4 options,
    /// - Only DHCPv6 options,
    /// - Both DHCPv4 and DHCPv6 options.
    enum FetchedOptions {
        DHCP4_ONLY,
        DHCP6_ONLY,
        DHCP4_AND_DHCP6
    };

    /// @brief Constructor.
    ///
    /// @param fetched_options Specifies if DHCPv4, DHCPv6 or both should
    /// be fetched from the database for a host.
    /// @param additional_columns_num Number of additional columns for which
    /// resources should be allocated, e.g. binding table, column names etc.
    /// This parameter should be set to a non zero value by derived classes to
    /// allocate resources for the columns supported by derived classes.
    MySqlHostWithOptionsExchange(const FetchedOptions& fetched_options,
                                 const size_t additional_columns_num = 0)
        : MySqlHostExchange(getRequiredColumnsNum(fetched_options)
                            + additional_columns_num),
          opt_proc4_(), opt_proc6_() {

        // Create option processor for DHCPv4 options, if required.
        if ((fetched_options == DHCP4_ONLY) ||
            (fetched_options == DHCP4_AND_DHCP6)) {
            opt_proc4_.reset(new OptionProcessor(Option::V4,
                                                 findAvailColumn()));
            opt_proc4_->setColumnNames(columns_);
        }

        // Create option processor for DHCPv6 options, if required.
        if ((fetched_options == DHCP6_ONLY) ||
            (fetched_options == DHCP4_AND_DHCP6)) {
            opt_proc6_.reset(new OptionProcessor(Option::V6,
                                                 findAvailColumn()));
            opt_proc6_->setColumnNames(columns_);
        }
    }

    /// @brief Processes the current row.
    ///
    /// The processed row includes both host information and DHCP option
    /// information. Because used SELECT query use LEFT JOIN clause, the
    /// some rows contain duplicated host or options entries. This method
    /// detects duplicated information and discards such entries.
    ///
    /// @param [out] hosts Container holding parsed hosts and options.
    virtual void processFetchedData(ConstHostCollection& hosts) {
        // Holds pointer to the previously parsed host.
        HostPtr most_recent_host;
        if (!hosts.empty()) {
            // Const cast is not very elegant way to deal with it, but
            // there is a good reason to use it here. This method is called
            // to build a collection of const hosts to be returned to the
            // caller. If we wanted to use non-const collection we'd need
            // to copy the whole collection before returning it, which has
            // performance implications. Alternatively, we could store the
            // most recently added host in a class member but this would
            // make the code less readable.
            most_recent_host = boost::const_pointer_cast<Host>(hosts.back());
        }

        // If no host has been parsed yet or we're at the row holding next
        // host, we create a new host object and put it at the end of the
        // list.
        if (!most_recent_host || (most_recent_host->getHostId() < getHostId())) {
            HostPtr host = retrieveHost();
            hosts.push_back(host);
            most_recent_host = host;
        }

        // Parse DHCPv4 options if required to do so.
        if (opt_proc4_) {
            CfgOptionPtr cfg = most_recent_host->getCfgOption4();
            opt_proc4_->retrieveOption(cfg);
        }

        // Parse DHCPv6 options if required to do so.
        if (opt_proc6_) {
            CfgOptionPtr cfg = most_recent_host->getCfgOption6();
            opt_proc6_->retrieveOption(cfg);
        }
    }

    /// @brief Bind variables for receiving option data.
    ///
    /// @return Vector of MYSQL_BIND object representing data to be retrieved.
    virtual std::vector<MYSQL_BIND> createBindForReceive() {
        // The following call sets bind_ values between 0 and 8.
        static_cast<void>(MySqlHostExchange::createBindForReceive());

        // Bind variables for DHCPv4 options.
        if (opt_proc4_) {
            opt_proc4_->setBindFields(bind_);
        }

        // Bind variables for DHCPv6 options.
        if (opt_proc6_) {
            opt_proc6_->setBindFields(bind_);
        }

        // Add the error flags
        setErrorIndicators(bind_, error_);

        return (bind_);
    };

private:

    /// @brief Returns a number of columns required to retrieve option data.
    ///
    /// Depending if we need DHCPv4/DHCPv6 options only, or both DHCPv4 and
    /// DHCPv6 a different number of columns is required in the binding array.
    /// This method returns the number of required columns, according to the
    /// value of @c fetched_columns passed in the constructor.
    ///
    /// @param fetched_columns A value which specifies whether DHCPv4, DHCPv6 or
    /// both types of options should be retrieved.
    ///
    /// @return Number of required columns.
    static size_t getRequiredColumnsNum(const FetchedOptions& fetched_options) {
        return (fetched_options == DHCP4_AND_DHCP6 ? 2 * OPTION_COLUMNS :
                OPTION_COLUMNS);
    }

    /// @brief Pointer to DHCPv4 options processor.
    ///
    /// If this object is NULL, the DHCPv4 options are not fetched.
    OptionProcessorPtr opt_proc4_;

    /// @brief Pointer to DHCPv6 options processor.
    ///
    /// If this object is NULL, the DHCPv6 options are not fetched.
    OptionProcessorPtr opt_proc6_;
};

/// @brief This class provides mechanisms for sending and retrieving
/// host information, DHCPv4 options, DHCPv6 options and IPv6 reservations.
///
/// This class extends the @ref MySqlHostWithOptionsExchange class with the
/// mechanisms to retrieve IPv6 reservations. This class is used in situations
/// when it is desired to retrieve DHCPv6 specific information about the host
/// (DHCPv6 options and reservations), or entire information about the host
/// (DHCPv4 options, DHCPv6 options and reservations). The following are the
/// queries used with this class:
/// - SELECT ? FROM hosts LEFT JOIN dhcp4_options LEFT JOIN dhcp6_options
///   LEFT JOIN ipv6_reservations ...
/// - SELECT ? FROM hosts LEFT JOIN dhcp6_options LEFT JOIN ipv6_reservations ..
class MySqlHostIPv6Exchange : public MySqlHostWithOptionsExchange {
private:

    /// @brief Number of columns holding IPv6 reservation information.
    static const size_t RESERVATION_COLUMNS = 5;

public:

    /// @brief Constructor.
    ///
    /// Apart from initializing the base class data structures it also
    /// initializes values representing IPv6 reservation information.
    MySqlHostIPv6Exchange(const FetchedOptions& fetched_options)
        : MySqlHostWithOptionsExchange(fetched_options, RESERVATION_COLUMNS),
          reservation_id_(0),
          reserv_type_(0), reserv_type_null_(MLM_FALSE),
          ipv6_address_buffer_len_(0), prefix_len_(0), iaid_(0),
          reservation_id_index_(findAvailColumn()),
          address_index_(reservation_id_index_ + 1),
          prefix_len_index_(reservation_id_index_ + 2),
          type_index_(reservation_id_index_ + 3),
          iaid_index_(reservation_id_index_ + 4),
          most_recent_reservation_id_(0) {

        memset(ipv6_address_buffer_, 0, sizeof(ipv6_address_buffer_));

        // Provide names of additional columns returned by the queries.
        columns_[reservation_id_index_] = "reservation_id";
        columns_[address_index_] = "address";
        columns_[prefix_len_index_] = "prefix_len";
        columns_[type_index_] = "type";
        columns_[iaid_index_] = "dhcp6_iaid";
    }

    /// @brief Returns last fetched reservation id.
    ///
    /// @return Reservation id or 0 if no reservation data is fetched.
    uint32_t getReservationId() const {
        if (reserv_type_null_ == MLM_FALSE) {
            return (reservation_id_);
        }
        return (0);
    };

    /// @brief Creates IPv6 reservation from the data contained in the
    /// currently processed row.
    ///
    /// Called after the MYSQL_BIND array created by createBindForReceive().
    ///
    /// @return IPv6Resrv object (containing IPv6 address or prefix reservation)
    IPv6Resrv retrieveReservation() {
        // Set the IPv6 Reservation type (0 = IA_NA, 2 = IA_PD)
        IPv6Resrv::Type type = IPv6Resrv::TYPE_NA;

        switch (reserv_type_) {
        case 0:
            type = IPv6Resrv::TYPE_NA;
            break;

        case 2:
            type = IPv6Resrv::TYPE_PD;
            break;

        default:
            isc_throw(BadValue,
                      "invalid IPv6 reservation type returned: "
                      << static_cast<int>(reserv_type_)
                      << ". Only 0 or 2 are allowed.");
        }

        ipv6_address_buffer_[ipv6_address_buffer_len_] = '\0';
        std::string address = ipv6_address_buffer_;
        IPv6Resrv r(type, IOAddress(address), prefix_len_);
        return (r);
    };

    /// @brief Processes one row of data fetched from a database.
    ///
    /// The processed data must contain host id, which uniquely identifies a
    /// host. This method creates a host and inserts it to the hosts collection
    /// only if the last inserted host has a different host id. This prevents
    /// adding duplicated hosts to the collection, assuming that processed
    /// rows are primarily ordered by host id column.
    ///
    /// Depending on the value of the @c fetched_options specified in the
    /// constructor, this method also parses options returned as a result
    /// of SELECT queries.
    ///
    /// For any returned row which contains IPv6 reservation information it
    /// checks if the reservation is not a duplicate of previously parsed
    /// reservation and appends the IPv6Resrv object into the host object
    /// if the parsed row contains new reservation information.
    ///
    /// @param [out] hosts Collection of hosts to which a new host created
    ///        from the processed data should be inserted.
    virtual void processFetchedData(ConstHostCollection& hosts) {

        // Call parent class to fetch host information and options.
        MySqlHostWithOptionsExchange::processFetchedData(hosts);

        if (getReservationId() == 0) {
            return;
        }

        if (hosts.empty()) {
            isc_throw(Unexpected, "no host information while retrieving"
                      " IPv6 reservation");
        }
        HostPtr host = boost::const_pointer_cast<Host>(hosts.back());

        // If we're dealing with a new reservation, let's add it to the
        // host.
        if (getReservationId() > most_recent_reservation_id_) {
            most_recent_reservation_id_ = getReservationId();

            if (most_recent_reservation_id_ > 0) {
                host->addReservation(retrieveReservation());
            }
        }
    }

    /// @brief Create BIND array to receive Host data with IPv6 reservations.
    ///
    /// Creates a MYSQL_BIND array to receive Host data from the database.
    /// After data is successfully received, @ref processedFetchedData is
    /// called for each returned row to build collection of @ref Host
    /// objects with associated IPv6 reservations.
    ///
    /// @return Vector of MYSQL_BIND objects representing data to be retrieved.
    virtual std::vector<MYSQL_BIND> createBindForReceive() {
        // Reset most recent reservation id value because we're now making
        // a new SELECT query.
        most_recent_reservation_id_ = 0;

        // Bind values supported by parent classes.
        static_cast<void>(MySqlHostWithOptionsExchange::createBindForReceive());

        // reservation_id : INT UNSIGNED NOT NULL AUTO_INCREMENT
        bind_[reservation_id_index_].buffer_type = MYSQL_TYPE_LONG;
        bind_[reservation_id_index_].buffer = reinterpret_cast<char*>(&reservation_id_);
        bind_[reservation_id_index_].is_unsigned = MLM_TRUE;

        // IPv6 address/prefix VARCHAR(39)
        ipv6_address_buffer_len_ = sizeof(ipv6_address_buffer_) - 1;
        bind_[address_index_].buffer_type = MYSQL_TYPE_STRING;
        bind_[address_index_].buffer = ipv6_address_buffer_;
        bind_[address_index_].buffer_length = ipv6_address_buffer_len_;
        bind_[address_index_].length = &ipv6_address_buffer_len_;

        // prefix_len : TINYINT
        bind_[prefix_len_index_].buffer_type = MYSQL_TYPE_TINY;
        bind_[prefix_len_index_].buffer = reinterpret_cast<char*>(&prefix_len_);
        bind_[prefix_len_index_].is_unsigned = MLM_TRUE;

        // (reservation) type : TINYINT
        reserv_type_null_ = MLM_FALSE;
        bind_[type_index_].buffer_type = MYSQL_TYPE_TINY;
        bind_[type_index_].buffer = reinterpret_cast<char*>(&reserv_type_);
        bind_[type_index_].is_unsigned = MLM_TRUE;
        bind_[type_index_].is_null = &reserv_type_null_;

        // dhcp6_iaid INT UNSIGNED
        bind_[iaid_index_].buffer_type = MYSQL_TYPE_LONG;
        bind_[iaid_index_].buffer = reinterpret_cast<char*>(&iaid_);
        bind_[iaid_index_].is_unsigned = MLM_TRUE;

        // Add the error flags
        setErrorIndicators(bind_, error_);

        return (bind_);
    };

private:

    /// @brief IPv6 reservation id.
    uint32_t reservation_id_;

    /// @brief IPv6 reservation type.
    uint8_t reserv_type_;

    /// @brief Boolean flag indicating if reservation type field is null.
    ///
    /// This flag is used by the class to determine if the returned row
    /// contains IPv6 reservation information.
    my_bool reserv_type_null_;

    /// @brief Buffer holding IPv6 address/prefix in textual format.
    char ipv6_address_buffer_[ADDRESS6_TEXT_MAX_LEN + 1];