mysql_lease_mgr.h 28.2 KB
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// Copyright (C) 2012 Internet Systems Consortium, Inc. ("ISC")
//
// 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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#ifndef MYSQL_LEASE_MGR_H
#define MYSQL_LEASE_MGR_H
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#include <dhcp/hwaddr.h>
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#include <dhcpsrv/lease_mgr.h>

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#include <boost/scoped_ptr.hpp>
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#include <boost/utility.hpp>
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#include <mysql.h>
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#include <time.h>
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namespace isc {
namespace dhcp {

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/// @brief MySQL Handle Holder
///
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/// Small RAII object for safer initialization, will close the database
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/// connection upon destruction.  This means that if an exception is thrown
/// during database initialization, resources allocated to the database are
/// guaranteed to be freed.
///
/// It makes no sense to copy an object of this class.  After the copy, both
/// objects would contain pointers to the same MySql context object.  The
/// destruction of one would invalid the context in the remaining object.
/// For this reason, the class is declared noncopyable.
class MySqlHolder : public boost::noncopyable {
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public:
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    /// @brief Constructor
    ///
    /// Initialize MySql and store the associated context object.
    ///
    /// @throw DbOpenError Unable to initialize MySql handle.
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    MySqlHolder() : mysql_(mysql_init(NULL)) {
        if (mysql_ == NULL) {
            isc_throw(DbOpenError, "unable to initialize MySQL");
        }
    }

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    /// @brief Destructor
    ///
    /// Frees up resources allocated by the initialization of MySql.
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    ~MySqlHolder() {
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        if (mysql_ != NULL) {
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            mysql_close(mysql_);
        }
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        // The library itself shouldn't be needed anymore
        mysql_library_end();
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    }

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    /// @brief Conversion Operator
    ///
    /// Allows the MySqlHolder object to be passed as the context argument to
    /// mysql_xxx functions.
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    operator MYSQL*() const {
        return (mysql_);
    }

private:
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    MYSQL* mysql_;      ///< Initialization context
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};

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// Define the current database schema values

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const uint32_t CURRENT_VERSION_VERSION = 1;
const uint32_t CURRENT_VERSION_MINOR = 0;
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// Forward declaration of the Lease exchange objects.  These classes are defined
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// in the .cc file.
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class MySqlLease4Exchange;
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class MySqlLease6Exchange;


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/// @brief MySQL Lease Manager
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///
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/// This class provides the \ref isc::dhcp::LeaseMgr interface to the MySQL
/// database.  Use of this backend presupposes that a MySQL database is
/// available and that the Kea schema has been created within it.

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class MySqlLeaseMgr : public LeaseMgr {
public:
    /// @brief Constructor
    ///
    /// Uses the following keywords in the parameters passed to it to
    /// connect to the database:
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    /// - name - Name of the database to which to connect (mandatory)
    /// - host - Host to which to connect (optional, defaults to "localhost")
    /// - user - Username under which to connect (optional)
    /// - password - Password for "user" on the database (optional)
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    ///
    /// If the database is successfully opened, the version number in the
    /// schema_version table will be checked against hard-coded value in
    /// the implementation file.
    ///
    /// Finally, all the SQL commands are pre-compiled.
    ///
    /// @param parameters A data structure relating keywords and values
    ///        concerned with the database.
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    ///
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    /// @throw isc::dhcp::NoDatabaseName Mandatory database name not given
    /// @throw isc::dhcp::DbOpenError Error opening the database
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    MySqlLeaseMgr(const ParameterMap& parameters);

    /// @brief Destructor (closes database)
    virtual ~MySqlLeaseMgr();

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    /// @brief Adds an IPv4 lease
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    ///
    /// @param lease lease to be added
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    ///
    /// @result true if the lease was added, false if not (because a lease
    ///         with the same address was already there).
    ///
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual bool addLease(const Lease4Ptr& lease);
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    /// @brief Adds an IPv6 lease
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    ///
    /// @param lease lease to be added
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    ///
    /// @result true if the lease was added, false if not (because a lease
    ///         with the same address was already there).
    ///
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual bool addLease(const Lease6Ptr& lease);
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    /// @brief Returns an IPv4 lease for specified IPv4 address
    ///
    /// This method return a lease that is associated with a given address.
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    /// For other query types (by hardware addr, by Client ID) there can be
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    /// several leases in different subnets (e.g. for mobile clients that
    /// got address in different subnets). However, for a single address
    /// there can be only one lease, so this method returns a pointer to
    /// a single lease, not a container of leases.
    ///
    /// @param addr address of the searched lease
    ///
    /// @return smart pointer to the lease (or NULL if a lease is not found)
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    ///
    /// @throw isc::dhcp::DataTruncation Data was truncated on retrieval to
    ///        fit into the space allocated for the result.  This indicates a
    ///        programming error.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual Lease4Ptr getLease4(const isc::asiolink::IOAddress& addr) const;
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    /// @brief Returns existing IPv4 leases for specified hardware address.
    ///
    /// Although in the usual case there will be only one lease, for mobile
    /// clients or clients with multiple static/fixed/reserved leases there
    /// can be more than one. Thus return type is a container, not a single
    /// pointer.
    ///
    /// @param hwaddr hardware address of the client
    ///
    /// @return lease collection
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    ///
    /// @throw isc::dhcp::DataTruncation Data was truncated on retrieval to
    ///        fit into the space allocated for the result.  This indicates a
    ///        programming error.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual Lease4Collection getLease4(const isc::dhcp::HWAddr& hwaddr) const;
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    /// @brief Returns existing IPv4 leases for specified hardware address
    ///        and a subnet
    ///
    /// There can be at most one lease for a given HW address in a single
    /// pool, so this method with either return a single lease or NULL.
    ///
    /// @param hwaddr hardware address of the client
    /// @param subnet_id identifier of the subnet that lease must belong to
    ///
    /// @return a pointer to the lease (or NULL if a lease is not found)
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    ///
    /// @throw isc::dhcp::DataTruncation Data was truncated on retrieval to
    ///        fit into the space allocated for the result.  This indicates a
    ///        programming error.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual Lease4Ptr getLease4(const isc::dhcp::HWAddr& hwaddr,
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                                SubnetID subnet_id) const;
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    /// @brief Returns existing IPv4 lease for specified client-id
    ///
    /// Although in the usual case there will be only one lease, for mobile
    /// clients or clients with multiple static/fixed/reserved leases there
    /// can be more than one. Thus return type is a container, not a single
    /// pointer.
    ///
    /// @param clientid client identifier
    ///
    /// @return lease collection
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    ///
    /// @throw isc::dhcp::DataTruncation Data was truncated on retrieval to
    ///        fit into the space allocated for the result.  This indicates a
    ///        programming error.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual Lease4Collection getLease4(const ClientId& clientid) const;
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    /// @brief Returns existing IPv4 lease for specified client-id
    ///
    /// There can be at most one lease for a given HW address in a single
    /// pool, so this method with either return a single lease or NULL.
    ///
    /// @param clientid client identifier
    /// @param subnet_id identifier of the subnet that lease must belong to
    ///
    /// @return a pointer to the lease (or NULL if a lease is not found)
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    ///
    /// @throw isc::dhcp::DataTruncation Data was truncated on retrieval to
    ///        fit into the space allocated for the result.  This indicates a
    ///        programming error.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual Lease4Ptr getLease4(const ClientId& clientid,
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                                SubnetID subnet_id) const;
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    /// @brief Returns existing IPv6 lease for a given IPv6 address.
    ///
    /// For a given address, we assume that there will be only one lease.
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    /// The assumption here is that there will not be site or link-local
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    /// addresses used, so there is no way of having address duplication.
    ///
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    /// @param type specifies lease type: (NA, TA or PD)
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    /// @param addr address of the searched lease
    ///
    /// @return smart pointer to the lease (or NULL if a lease is not found)
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    ///
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    /// @throw isc::BadValue record retrieved from database had an invalid
    ///        lease type field.
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    /// @throw isc::dhcp::DataTruncation Data was truncated on retrieval to
    ///        fit into the space allocated for the result.  This indicates a
    ///        programming error.
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual Lease6Ptr getLease6(Lease6::LeaseType type,
                                const isc::asiolink::IOAddress& addr) const;
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    /// @brief Returns existing IPv6 leases for a given DUID+IA combination
    ///
    /// Although in the usual case there will be only one lease, for mobile
    /// clients or clients with multiple static/fixed/reserved leases there
    /// can be more than one. Thus return type is a container, not a single
    /// pointer.
    ///
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    /// @param type specifies lease type: (NA, TA or PD)
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    /// @param duid client DUID
    /// @param iaid IA identifier
    ///
    /// @return smart pointer to the lease (or NULL if a lease is not found)
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    ///
    /// @throw isc::BadValue record retrieved from database had an invalid
    ///        lease type field.
    /// @throw isc::dhcp::DataTruncation Data was truncated on retrieval to
    ///        fit into the space allocated for the result.  This indicates a
    ///        programming error.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual Lease6Collection getLease6(Lease6::LeaseType type, const DUID& duid,
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                                       uint32_t iaid) const;
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    /// @brief Returns existing IPv6 lease for a given DUID+IA combination
    ///
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    /// @param type specifies lease type: (NA, TA or PD)
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    /// @param duid client DUID
    /// @param iaid IA identifier
    /// @param subnet_id subnet id of the subnet the lease belongs to
    ///
    /// @return smart pointer to the lease (or NULL if a lease is not found)
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    ///
    /// @throw isc::BadValue record retrieved from database had an invalid
    ///        lease type field.
    /// @throw isc::dhcp::DataTruncation Data was truncated on retrieval to
    ///        fit into the space allocated for the result.  This indicates a
    ///        programming error.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual Lease6Ptr getLease6(Lease6::LeaseType type, const DUID& duid,
                                uint32_t iaid, SubnetID subnet_id) const;
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    /// @brief Updates IPv4 lease.
    ///
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    /// Updates the record of the lease in the database (as identified by the
    /// address) with the data in the passed lease object.
    ///
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    /// @param lease4 The lease to be updated.
    ///
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    /// @throw isc::dhcp::NoSuchLease Attempt to update a lease that did not
    ///        exist.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual void updateLease4(const Lease4Ptr& lease4);
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    /// @brief Updates IPv6 lease.
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    ///
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    /// Updates the record of the lease in the database (as identified by the
    /// address) with the data in the passed lease object.
    ///
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    /// @param lease6 The lease to be updated.
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    ///
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    /// @throw isc::dhcp::NoSuchLease Attempt to update a lease that did not
    ///        exist.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual void updateLease6(const Lease6Ptr& lease6);
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    /// @brief Deletes a lease.
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    ///
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    /// @param addr Address of the lease to be deleted.  This can be an IPv4
    ///             address or an IPv6 address.
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    ///
    /// @return true if deletion was successful, false if no such lease exists
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    ///
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual bool deleteLease(const isc::asiolink::IOAddress& addr);
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    /// @brief Return backend type
    ///
    /// Returns the type of the backend (e.g. "mysql", "memfile" etc.)
    ///
    /// @return Type of the backend.
    virtual std::string getType() const {
        return (std::string("mysql"));
    }

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    /// @brief Returns backend name.
    ///
    /// Each backend have specific name, e.g. "mysql" or "sqlite".
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    ///
    /// @return Name of the backend.
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    virtual std::string getName() const;
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    /// @brief Returns description of the backend.
    ///
    /// This description may be multiline text that describes the backend.
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    ///
    /// @return Description of the backend.
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    virtual std::string getDescription() const;
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    /// @brief Returns backend version.
    ///
    /// @return Version number as a pair of unsigned integers.  "first" is the
    ///         major version number, "second" the minor number.
    ///
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    virtual std::pair<uint32_t, uint32_t> getVersion() const;

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    /// @brief Commit Transactions
    ///
    /// Commits all pending database operations.  On databases that don't
    /// support transactions, this is a no-op.
    ///
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    /// @throw DbOperationError Iif the commit failed.
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    virtual void commit();

    /// @brief Rollback Transactions
    ///
    /// Rolls back all pending database operations.  On databases that don't
    /// support transactions, this is a no-op.
    ///
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    /// @throw DbOperationError If the rollback failed.
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    virtual void rollback();

    ///@{
    /// The following methods are used to convert between times and time
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    /// intervals stored in the Lease object, and the times stored in the
    /// database.  The reason for the difference is because in the DHCP server,
    /// the cltt (Client Time Since Last Transmission) is the natural data; in
    /// the lease file - which may be read by the user - it is the expiry time
    /// of the lease.
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    /// @brief Convert Lease Time to Database Times
    ///
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    /// Within the DHCP servers, times are stored as client last transmit time
    /// and valid lifetime.  In the database, the information is stored as
    /// valid lifetime and "expire" (time of expiry of the lease).  They are
    /// related by the equation:
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    ///
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    /// - expire = client last transmit time + valid lifetime
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    ///
    /// This method converts from the times in the lease object into times
    /// able to be added to the database.
    ///
    /// @param cltt Client last transmit time
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    /// @param valid_lifetime Valid lifetime
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    /// @param expire Reference to MYSQL_TIME object where the expiry time of
    ///        the lease will be put.
    static
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    void convertToDatabaseTime(time_t cltt, uint32_t valid_lifetime,
                               MYSQL_TIME& expire);
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    /// @brief Convert Database Time to Lease Times
    ///
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    /// Within the database, time is stored as "expire" (time of expiry of the
    /// lease) and valid lifetime.  In the DHCP server, the information is
    /// stored client last transmit time and valid lifetime.  These are related
    /// by the equation:
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    ///
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    /// - client last transmit time = expire - valid_lifetime
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    ///
    /// This method converts from the times in the database into times
    /// able to be inserted into the lease object.
    ///
    /// @param expire Reference to MYSQL_TIME object from where the expiry
    ///        time of the lease is taken.
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    /// @param valid_lifetime lifetime of the lease.
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    /// @param cltt Reference to location where client last transmit time
    ///        is put.
    static
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    void convertFromDatabaseTime(const MYSQL_TIME& expire,
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                                 uint32_t valid_lifetime, time_t& cltt);
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    ///@}

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    /// @brief Statement Tags
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    ///
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    /// The contents of the enum are indexes into the list of SQL statements
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    enum StatementIndex {
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        DELETE_LEASE4,              // Delete from lease4 by address
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        DELETE_LEASE6,              // Delete from lease6 by address
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        GET_LEASE4_ADDR,            // Get lease4 by address
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        GET_LEASE4_CLIENTID,        // Get lease4 by client ID
        GET_LEASE4_CLIENTID_SUBID,  // Get lease4 by client ID & subnet ID
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        GET_LEASE4_HWADDR,          // Get lease4 by HW address
        GET_LEASE4_HWADDR_SUBID,    // Get lease4 by HW address & subnet ID
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        GET_LEASE6_ADDR,            // Get lease6 by address
        GET_LEASE6_DUID_IAID,       // Get lease6 by DUID and IAID
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        GET_LEASE6_DUID_IAID_SUBID, // Get lease6 by DUID, IAID and subnet ID
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        GET_VERSION,                // Obtain version number
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        INSERT_LEASE4,              // Add entry to lease4 table
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        INSERT_LEASE6,              // Add entry to lease6 table
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        UPDATE_LEASE4,              // Update a Lease4 entry
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        UPDATE_LEASE6,              // Update a Lease6 entry
        NUM_STATEMENTS              // Number of statements
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    };

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private:
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    /// @brief Prepare Single Statement
    ///
    /// Creates a prepared statement from the text given and adds it to the
    /// statements_ vector at the given index.
    ///
    /// @param index Index into the statements_ vector into which the text
    ///        should be placed.  The vector must be big enough for the index
    ///        to be valid, else an exception will be thrown.
    /// @param text Text of the SQL statement to be prepared.
    ///
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
    /// @throw isc::InvalidParameter 'index' is not valid for the vector.
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    void prepareStatement(StatementIndex index, const char* text);

    /// @brief Prepare statements
    ///
    /// Creates the prepared statements for all of the SQL statements used
    /// by the MySQL backend.
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    ///
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
    /// @throw isc::InvalidParameter 'index' is not valid for the vector.  This
    ///        represents an internal error within the code.
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    void prepareStatements();

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    /// @brief Open Database
    ///
    /// Opens the database using the information supplied in the parameters
    /// passed to the constructor.
    ///
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    /// @throw NoDatabaseName Mandatory database name not given
    /// @throw DbOpenError Error opening the database
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    void openDatabase();

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    /// @brief Add Lease Common Code
    ///
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    /// This method performs the common actions for both flavours (V4 and V6)
    /// of the addLease method.  It binds the contents of the lease object to
    /// the prepared statement and adds it to the database.
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    ///
    /// @param stindex Index of statemnent being executed
    /// @param bind MYSQL_BIND array that has been created for the type
    ///        of lease in question.
    ///
    /// @return true if the lease was added, false if it was not added because
    ///         a lease with that address already exists in the database.
    ///
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    bool addLeaseCommon(StatementIndex stindex, std::vector<MYSQL_BIND>& bind);
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    /// @brief Get Lease Collection Common Code
    ///
    /// This method performs the common actions for obtaining multiple leases
    /// from the database.
    ///
    /// @param stindex Index of statement being executed
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    /// @param bind MYSQL_BIND array for input parameters
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    /// @param exchange Exchange object to use
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    /// @param lease LeaseCollection object returned.  Note that any leases in
    ///        the collection when this method is called are not erased: the
    ///        new data is appended to the end.
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    /// @param single If true, only a single data item is to be retrieved.
    ///        If more than one is present, a MultipleRecords exception will
    ///        be thrown.
    ///
    /// @throw isc::dhcp::BadValue Data retrieved from the database was invalid.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
    /// @throw isc::dhcp::MultipleRecords Multiple records were retrieved
    ///        from the database where only one was expected.
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    template <typename Exchange, typename LeaseCollection>
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    void getLeaseCollection(StatementIndex stindex, MYSQL_BIND* bind,
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                            Exchange& exchange, LeaseCollection& result,
                            bool single = false) const;
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    /// @brief Get Lease Collection
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    ///
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    /// Gets a collection of Lease4 objects.  This is just an interface to
    /// the get lease collection common code.
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    ///
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    /// @param stindex Index of statement being executed
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    /// @param bind MYSQL_BIND array for input parameters
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    /// @param lease LeaseCollection object returned.  Note that any leases in
    ///        the collection when this method is called are not erased: the
    ///        new data is appended to the end.
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    ///
    /// @throw isc::dhcp::BadValue Data retrieved from the database was invalid.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
    /// @throw isc::dhcp::MultipleRecords Multiple records were retrieved
    ///        from the database where only one was expected.
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    void getLeaseCollection(StatementIndex stindex, MYSQL_BIND* bind,
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                            Lease4Collection& result) const {
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        getLeaseCollection(stindex, bind, exchange4_, result);
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    }

    /// @brief Get Lease Collection
    ///
    /// Gets a collection of Lease6 objects.  This is just an interface to
    /// the get lease collection common code.
    ///
    /// @param stindex Index of statement being executed
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    /// @param bind MYSQL_BIND array for input parameters
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    /// @param lease LeaseCollection object returned.  Note that any existing
    ///        data in the collection is erased first.
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    ///
    /// @throw isc::dhcp::BadValue Data retrieved from the database was invalid.
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
    /// @throw isc::dhcp::MultipleRecords Multiple records were retrieved
    ///        from the database where only one was expected.
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    void getLeaseCollection(StatementIndex stindex, MYSQL_BIND* bind,
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                            Lease6Collection& result) const {
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        getLeaseCollection(stindex, bind, exchange6_, result);
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    }

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    /// @brief Get Lease4 Common Code
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    ///
    /// This method performs the common actions for the various getLease4()
    /// methods.  It acts as an interface to the getLeaseCollection() method,
    /// but retrieveing only a single lease.
    ///
    /// @param stindex Index of statement being executed
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    /// @param bind MYSQL_BIND array for input parameters
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    /// @param lease Lease4 object returned
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    void getLease(StatementIndex stindex, MYSQL_BIND* bind,
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                  Lease4Ptr& result) const;

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    /// @brief Get Lease6 Common Code
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    ///
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    /// This method performs the common actions for the various getLease46)
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    /// methods.  It acts as an interface to the getLeaseCollection() method,
    /// but retrieveing only a single lease.
    ///
    /// @param stindex Index of statement being executed
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    /// @param bind MYSQL_BIND array for input parameters
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    /// @param lease Lease6 object returned
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    void getLease(StatementIndex stindex, MYSQL_BIND* bind,
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                   Lease6Ptr& result) const;

    /// @brief Update lease common code
    ///
    /// Holds the common code for updating a lease.  It binds the parameters
    /// to the prepared statement, executes it, then checks how many rows
    /// were affected.
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    ///
    /// @param stindex Index of prepared statement to be executed
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    /// @param bind Array of MYSQL_BIND objects representing the parameters.
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    ///        (Note that the number is determined by the number of parameters
    ///        in the statement.)
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    /// @param lease Pointer to the lease object whose record is being updated.
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    ///
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    /// @throw NoSuchLease Could not update a lease because no lease matches
    ///        the address given.
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    template <typename LeasePtr>
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    void updateLeaseCommon(StatementIndex stindex, MYSQL_BIND* bind,
                           const LeasePtr& lease);
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    /// @brief Delete lease common code
    ///
    /// Holds the common code for deleting a lease.  It binds the parameters
    /// to the prepared statement, executes the statement and checks to
    /// see how many rows were deleted.
    ///
    /// @param stindex Index of prepared statement to be executed
    /// @param bind Array of MYSQL_BIND objects representing the parameters.
    ///        (Note that the number is determined by the number of parameters
    ///        in the statement.)
    ///
    /// @return true if one or more rows were deleted, false if none were
    ///         deleted.
    ///
    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    bool deleteLeaseCommon(StatementIndex stindex, MYSQL_BIND* bind);
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    /// @brief Check Error and Throw Exception
    ///
    /// Virtually all MySQL functions return a status which, if non-zero,
    /// indicates an error.  This inline function conceals a lot of error
    /// checking/exception-throwing code.
    ///
    /// @param status Status code: non-zero implies an error
    /// @param index Index of statement that caused the error
    /// @param what High-level description of the error
    ///
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    /// @throw isc::dhcp::DbOperationError An operation on the open database has
    ///        failed.
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    inline void checkError(int status, StatementIndex index,
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                           const char* what) const {
        if (status != 0) {
            isc_throw(DbOperationError, what << " for <" <<
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                      text_statements_[index] << ">, reason: " <<
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                      mysql_error(mysql_) << " (error code " <<
                      mysql_errno(mysql_) << ")");
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        }
    }

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    // Members
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    /// The exchange objects are used for transfer of data to/from the database.
    /// They are pointed-to objects as the contents may change in "const" calls,
    /// while the rest of this object does not.  (At alternative would be to
    /// declare them as "mutable".)
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    boost::scoped_ptr<MySqlLease4Exchange> exchange4_; ///< Exchange object
    boost::scoped_ptr<MySqlLease6Exchange> exchange6_; ///< Exchange object
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    MySqlHolder mysql_;
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    std::vector<MYSQL_STMT*> statements_;       ///< Prepared statements
    std::vector<std::string> text_statements_;  ///< Raw text of statements
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};

}; // end of isc::dhcp namespace
}; // end of isc namespace

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#endif // MYSQL_LEASE_MGR_H