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// Copyright (C) 2022-2023 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/.
#ifndef RANDOM_ALLOCATOR_H
#define RANDOM_ALLOCATOR_H
#include <dhcpsrv/allocator.h>
#include <dhcpsrv/random_allocation_state.h>
#include <dhcpsrv/lease.h>
#include <cstdint>
#include <random>
namespace isc {
namespace dhcp {
/// @brief An allocator offering addresses in a random order.
///
/// This allocator uses @c IPRangePermutation to select random
/// addresses or delegated prefixes from the pools. It guarantees
/// that all offered addresses are unique (do not repeat).
///
/// The allocator also randomly picks pools to ensure that the
/// leases are offered uniformly from the entire subnet rather than
/// from the same pool until it exhausts. When all pools exhaust,
/// the allocator resets their permutations and begins offering
/// leases from these pools again.
class RandomAllocator : public Allocator {
public:
/// @brief Constructor.
///
/// @param type specifies the type of allocated leases.
/// @param subnet weak pointer to the subnet owning the allocator.
RandomAllocator(Lease::Type type, const WeakSubnetPtr& subnet);
/// @brief Returns the allocator type string.
///
/// @return random string.
virtual std::string getType() const {
return ("random");
}
private:
/// @brief Returns a random address from the pools in the subnet.
///
/// Internal thread-unsafe implementation of the @c pickAddress.
///
/// @param client_classes list of classes client belongs to.
/// @param duid client DUID (ignored).
/// @param hint client hint (ignored).
///
/// @return next offered address.
virtual asiolink::IOAddress pickAddressInternal(const ClientClasses& client_classes,
const IdentifierBaseTypePtr& duid,
const asiolink::IOAddress& hint);
/// @brief Picks a delegated prefix.
///
/// Internal thread-unsafe implementation of the @c pickPrefix.
///
/// @param client_classes list of classes client belongs to.
/// @param pool the selected pool satisfying all required conditions.
/// @param duid Client's DUID.
/// @param prefix_length_match type which indicates the selection criteria
/// for the pools relative to the provided hint prefix length
/// @param hint Client's hint.
/// @param hint_prefix_length the hint prefix length that the client
/// provided. The 0 value means that there is no hint and that any
/// pool will suffice.
///
/// @return the next prefix.
virtual asiolink::IOAddress pickPrefixInternal(const ClientClasses& client_classes,
Pool6Ptr& pool,
const IdentifierBaseTypePtr& duid,
PrefixLenMatchType prefix_length_match,
const asiolink::IOAddress& hint,
uint8_t hint_prefix_length);
/// @brief Convenience function returning pool allocation state instance.
///
/// It creates a new pool state instance and assigns it to the pool
/// if it hasn't been initialized.
///
/// @param pool pool instance.
/// @return allocation state instance for the pool.
PoolRandomAllocationStatePtr getPoolState(const PoolPtr& pool) const;
/// @brief Convenience function returning a random number.
///
/// It is used internally by the @c pickAddressInternal function to
/// select a random pool.
///
/// @param limit upper bound of the range.
/// @returns random number between 0 and limit.
uint64_t getRandomNumber(uint64_t limit);
/// @brief Random generator used by this class.
std::mt19937 generator_;
};
} // end of namespace isc::dhcp
} // end of namespace isc
#endif // RANDOM_ALLOCATOR_H
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