daemon/fw/strategy.hpp - NFD - Gitiles

 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
  * Copyright (c) 2014-2021,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
  *                           Washington University in St. Louis,
  *                           Beijing Institute of Technology,
  *                           The University of Memphis.
  *
  * This file is part of NFD (Named Data Networking Forwarding Daemon).
  * See AUTHORS.md for complete list of NFD authors and contributors.
  *
  * NFD is free software: you can redistribute it and/or modify it under the terms
  * of the GNU General Public License as published by the Free Software Foundation,
  * either version 3 of the License, or (at your option) any later version.
  *
  * NFD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
  * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
  * PURPOSE.  See the GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License along with
  * NFD, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
  */

 #ifndef NFD_DAEMON_FW_STRATEGY_HPP
 #define NFD_DAEMON_FW_STRATEGY_HPP

 #include "forwarder.hpp"
 #include "table/measurements-accessor.hpp"

 namespace nfd {
 namespace fw {

 /** \brief Represents a forwarding strategy
  */
 class Strategy : noncopyable
 {
 public: // registry
   /** \brief Register a strategy type
    *  \tparam S subclass of Strategy
    *  \param strategyName strategy program name, must contain version
    *  \note It is permitted to register the same strategy type under multiple names,
    *        which is useful in tests and for creating aliases.
    */
   template<typename S>
   static void
   registerType(const Name& strategyName = S::getStrategyName())
   {
     BOOST_ASSERT(strategyName.size() > 1);
     BOOST_ASSERT(strategyName.at(-1).isVersion());
     Registry& registry = getRegistry();
     BOOST_ASSERT(registry.count(strategyName) == 0);
     registry[strategyName] = [] (auto&&... args) {
       return make_unique<S>(std::forward<decltype(args)>(args)...);
     };
   }

   /** \return Whether a strategy instance can be created from \p instanceName
    *  \param instanceName strategy instance name, may contain version and parameters
    *  \note This function finds a strategy type using same rules as \p create ,
    *        but does not attempt to construct an instance.
    */
   static bool
   canCreate(const Name& instanceName);

   /** \return A strategy instance created from \p instanceName
    *  \retval nullptr if !canCreate(instanceName)
    *  \throw std::invalid_argument strategy type constructor does not accept
    *                               specified version or parameters
    */
   static unique_ptr<Strategy>
   create(const Name& instanceName, Forwarder& forwarder);

   /** \return Whether \p instanceNameA and \p instanceNameA will initiate same strategy type
    */
   static bool
   areSameType(const Name& instanceNameA, const Name& instanceNameB);

   /** \return Registered versioned strategy names
    */
   static std::set<Name>
   listRegistered();

 public: // constructor, destructor, strategy info
   /** \brief Construct a strategy instance.
    *  \param forwarder a reference to the forwarder, used to enable actions and accessors.
    *  \note Strategy subclass constructor must not retain a reference to \p forwarder.
    */
   explicit
   Strategy(Forwarder& forwarder);

   virtual
   ~Strategy();

 #ifdef DOXYGEN
   /** \return Strategy program name
    *
    *  The strategy name is defined by the strategy program.
    *  It must end with a version component.
    */
   static const Name&
   getStrategyName();
 #endif

   /** \return Strategy instance name
    *
    *  The instance name is assigned during instantiation.
    *  It contains a version component, and may have extra parameter components.
    */
   const Name&
   getInstanceName() const
   {
     return m_name;
   }

 public: // triggers
   /** \brief Trigger after Interest is received
    *
    *  The Interest:
    *  - has not exceeded HopLimit
    *  - does not violate Scope
    *  - is not looped
    *  - cannot be satisfied by ContentStore
    *  - is under a namespace managed by this strategy
    *
    *  The PIT entry is set to expire after InterestLifetime has elapsed at each downstream.
    *
    *  The strategy should decide whether and where to forward this Interest.
    *  - If the strategy decides to forward this Interest,
    *    invoke \c sendInterest for each upstream, either now or shortly after via a scheduler event,
    *    but before PIT entry expires.
    *    Optionally, the strategy can invoke \c setExpiryTimer to adjust how long it would wait for a response.
    *  - If the strategy has already forwarded this Interest previously and decides to continue waiting,
    *    do nothing.
    *    Optionally, the strategy can invoke \c setExpiryTimer to adjust how long it would wait for a response.
    *  - If the strategy concludes that this Interest cannot be satisfied,
    *    invoke \c rejectPendingInterest to erase the PIT entry.
    *
    *  \warning The strategy must not retain shared_ptr<pit::Entry>, otherwise undefined behavior
    *           may occur. However, the strategy is allowed to store weak_ptr<pit::Entry>.
    */
   virtual void
   afterReceiveInterest(const FaceEndpoint& ingress, const Interest& interest,
                        const shared_ptr<pit::Entry>& pitEntry) = 0;

   /** \brief Trigger before PIT entry is satisfied
    *
    *  This trigger is invoked when an incoming Data satisfies more than one PIT entry.
    *  The strategy can collect measurements information, but cannot manipulate Data forwarding.
    *  When an incoming Data satisfies only one PIT entry, \c afterReceiveData is invoked instead
    *  and given full control over Data forwarding. If a strategy does not override \c afterReceiveData,
    *  the default implementation invokes \c beforeSatisfyInterest.
    *
    *  Normally, PIT entries would be erased after receiving the first matching Data.
    *  If the strategy wishes to collect responses from additional upstream nodes,
    *  it should invoke \c setExpiryTimer within this function to prolong the PIT entry lifetime.
    *  If a Data arrives from another upstream during the extended PIT entry lifetime, this trigger will be invoked again.
    *  At that time, this function must invoke \c setExpiryTimer again to continue collecting more responses.
    *
    *  In this base class this method does nothing.
    *
    *  \warning The strategy must not retain shared_ptr<pit::Entry>, otherwise undefined behavior
    *           may occur. However, the strategy is allowed to store weak_ptr<pit::Entry>.
    */
   virtual void
   beforeSatisfyInterest(const shared_ptr<pit::Entry>& pitEntry,
                         const FaceEndpoint& ingress, const Data& data);

   /** \brief Trigger after a Data is matched in CS
    *
    *  In the base class this method sends \p data to \p ingress
    */
   virtual void
   afterContentStoreHit(const shared_ptr<pit::Entry>& pitEntry,
                        const FaceEndpoint& ingress, const Data& data);

   /** \brief Trigger after Data is received
    *
    *  This trigger is invoked when an incoming Data satisfies exactly one PIT entry,
    *  and gives the strategy full control over Data forwarding.
    *
    *  When this trigger is invoked:
    *  - The Data has been verified to satisfy the PIT entry.
    *  - The PIT entry expiry timer is set to now
    *
    *  Within this function:
    *  - A strategy should return Data to downstream nodes via \c sendData or \c sendDataToAll.
    *  - A strategy can modify the Data as long as it still satisfies the PIT entry, such as
    *    adding or removing congestion marks.
    *  - A strategy can delay Data forwarding by prolonging the PIT entry lifetime via \c setExpiryTimer,
    *    and forward Data before the PIT entry is erased.
    *  - A strategy can collect measurements about the upstream.
    *  - A strategy can collect responses from additional upstream nodes by prolonging the PIT entry
    *    lifetime via \c setExpiryTimer every time a Data is received. Note that only one Data should
    *    be returned to each downstream node.
    *
    *  In the base class this method invokes \c beforeSatisfyInterest trigger and then returns
    *  the Data to downstream faces via \c sendDataToAll.
    */
   virtual void
   afterReceiveData(const shared_ptr<pit::Entry>& pitEntry,
                    const FaceEndpoint& ingress, const Data& data);

   /** \brief Trigger after Nack is received
    *
    *  This trigger is invoked when an incoming Nack is received in response to
    *  an forwarded Interest.
    *  The Nack has been confirmed to be a response to the last Interest forwarded
    *  to that upstream, i.e. the PIT out-record exists and has a matching Nonce.
    *  The NackHeader has been recorded in the PIT out-record.
    *
    *  If the PIT entry is not yet satisfied, its expiry timer remains unchanged.
    *  Otherwise, the PIT entry normally would expire immediately after this function returns.
    *
    *  If the strategy wishes to collect responses from additional upstream nodes,
    *  it should invoke \c setExpiryTimer within this function to retain the PIT entry.
    *  If a Nack arrives from another upstream during the extended PIT entry lifetime, this trigger will be invoked again.
    *  At that time, this function must invoke \c setExpiryTimer again to continue collecting more responses.
    *
    *  In the base class this method does nothing.
    *
    *  \warning The strategy must not retain shared_ptr<pit::Entry>, otherwise undefined behavior
    *           may occur. However, the strategy is allowed to store weak_ptr<pit::Entry>.
    */
   virtual void
   afterReceiveNack(const FaceEndpoint& ingress, const lp::Nack& nack,
                    const shared_ptr<pit::Entry>& pitEntry);

   /** \brief Trigger after Interest dropped (e.g., for exceeding allowed retransmissions)
    *
    *  In the base class this method does nothing.
    */
   virtual void
   onDroppedInterest(const Face& egress, const Interest& interest);

   /** \brief Trigger after new nexthop is added
    *
    *  The strategy should decide whether to send the buffered Interests to the new nexthop.
    *  In the base class, this method does nothing.
    */
   virtual void
   afterNewNextHop(const fib::NextHop& nextHop, const shared_ptr<pit::Entry>& pitEntry);

 protected: // actions
   /** \brief Send an Interest packet.
    *  \param pitEntry the PIT entry
    *  \param egress face through which to send out the Interest
    *  \param interest the Interest packet
    *  \return A pointer to the out-record created or nullptr if the Interest was dropped
    */
   NFD_VIRTUAL_WITH_TESTS pit::OutRecord*
   sendInterest(const shared_ptr<pit::Entry>& pitEntry, Face& egress,
                const Interest& interest);

   /** \brief Send a Data packet.
    *  \param pitEntry the PIT entry
    *  \param data the Data packet
    *  \param egress face through which to send out the Data
    *  \return Whether the Data was sent (true) or dropped (false)
    */
   NFD_VIRTUAL_WITH_TESTS bool
   sendData(const shared_ptr<pit::Entry>& pitEntry, const Data& data, Face& egress);

   /** \brief Send a Data packet to all matched and qualified faces.
    *
    *  A matched face is qualified if it is ad-hoc or it is NOT \p inFace.
    *
    *  \param pitEntry the PIT entry
    *  \param inFace face on which the Data arrived
    *  \param data the Data packet
    */
   NFD_VIRTUAL_WITH_TESTS void
   sendDataToAll(const shared_ptr<pit::Entry>& pitEntry, const Face& inFace, const Data& data);

   /** \brief Schedule the PIT entry for immediate deletion.
    *
    *  This helper function sets the PIT entry expiry time to zero.
    *  The strategy should invoke this function when it concludes that the Interest cannot
    *  be forwarded and it does not want to wait for responses from existing upstream nodes.
    */
   NFD_VIRTUAL_WITH_TESTS void
   rejectPendingInterest(const shared_ptr<pit::Entry>& pitEntry)
   {
     this->setExpiryTimer(pitEntry, 0_ms);
   }

   /** \brief Send a Nack packet.
    *
    *  The egress face must have a PIT in-record, otherwise this method has no effect.
    *
    *  \param pitEntry the PIT entry
    *  \param egress face through which to send out the Nack
    *  \param header the Nack header
    *  \return Whether the Nack was sent (true) or dropped (false)
    */
   NFD_VIRTUAL_WITH_TESTS bool
   sendNack(const shared_ptr<pit::Entry>& pitEntry, Face& egress,
            const lp::NackHeader& header)
   {
     return m_forwarder.onOutgoingNack(pitEntry, egress, header);
   }

   /** \brief Send Nack to every face that has an in-record, except those in \p exceptFaces
    *  \param pitEntry the PIT entry
    *  \param header the Nack header
    *  \param exceptFaces list of faces that should be excluded from sending Nacks
    *  \note This is not an action, but a helper that invokes the sendNack() action.
    */
   void
   sendNacks(const shared_ptr<pit::Entry>& pitEntry, const lp::NackHeader& header,
             std::initializer_list<const Face*> exceptFaces = {});

   /** \brief Schedule the PIT entry to be erased after \p duration.
    */
   void
   setExpiryTimer(const shared_ptr<pit::Entry>& pitEntry, time::milliseconds duration)
   {
     m_forwarder.setExpiryTimer(pitEntry, duration);
   }

 protected: // accessors
   /** \brief Performs a FIB lookup, considering Link object if present.
    */
   const fib::Entry&
   lookupFib(const pit::Entry& pitEntry) const;

   MeasurementsAccessor&
   getMeasurements()
   {
     return m_measurements;
   }

   Face*
   getFace(FaceId id) const
   {
     return getFaceTable().get(id);
   }

   const FaceTable&
   getFaceTable() const
   {
     return m_forwarder.m_faceTable;
   }

 protected: // instance name
   struct ParsedInstanceName
   {
     Name strategyName; ///< strategy name without parameters
     optional<uint64_t> version; ///< whether strategyName contains a version component
     PartialName parameters; ///< parameter components
   };

   /** \brief Parse a strategy instance name
    *  \param input strategy instance name, may contain version and parameters
    *  \throw std::invalid_argument input format is unacceptable
    */
   static ParsedInstanceName
   parseInstanceName(const Name& input);

   /** \brief Construct a strategy instance name
    *  \param input strategy instance name, may contain version and parameters
    *  \param strategyName strategy name with version but without parameters;
    *                      typically this should be \p getStrategyName()
    *
    *  If \p input contains a version component, return \p input unchanged.
    *  Otherwise, return \p input plus the version component taken from \p strategyName.
    *  This allows a strategy instance to be constructed with an unversioned name,
    *  but its final instance name should contain the version.
    */
   static Name
   makeInstanceName(const Name& input, const Name& strategyName);

   /** \brief Set strategy instance name
    *  \note This must be called by strategy subclass constructor.
    */
   void
   setInstanceName(const Name& name)
   {
     m_name = name;
   }

 private: // registry
   typedef std::function<unique_ptr<Strategy>(Forwarder& forwarder, const Name& strategyName)> CreateFunc;
   typedef std::map<Name, CreateFunc> Registry; // indexed by strategy name

   static Registry&
   getRegistry();

   static Registry::const_iterator
   find(const Name& instanceName);

 protected: // accessors
   signal::Signal<FaceTable, Face>& afterAddFace;
   signal::Signal<FaceTable, Face>& beforeRemoveFace;

 private: // instance fields
   Name m_name;

   /** \brief Reference to the forwarder
    *
    *  Triggers can access forwarder indirectly via actions.
    */
   Forwarder& m_forwarder;

   MeasurementsAccessor m_measurements;
 };

 } // namespace fw
 } // namespace nfd

 /** \brief Registers a strategy
  *
  *  This macro should appear once in .cpp of each strategy.
  */
 #define NFD_REGISTER_STRATEGY(S)                       \
 static class NfdAuto ## S ## StrategyRegistrationClass \
 {                                                      \
 public:                                                \
   NfdAuto ## S ## StrategyRegistrationClass()          \
   {                                                    \
     ::nfd::fw::Strategy::registerType<S>();            \
   }                                                    \
 } g_nfdAuto ## S ## StrategyRegistrationVariable

 #endif // NFD_DAEMON_FW_STRATEGY_HPP
	/* -- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -- */
	/*
	* Copyright (c) 2014-2021, Regents of the University of California,
	* Arizona Board of Regents,
	* Colorado State University,
	* University Pierre & Marie Curie, Sorbonne University,
	* Washington University in St. Louis,
	* Beijing Institute of Technology,
	* The University of Memphis.
	*
	* This file is part of NFD (Named Data Networking Forwarding Daemon).
	* See AUTHORS.md for complete list of NFD authors and contributors.
	*
	* NFD is free software: you can redistribute it and/or modify it under the terms
	* of the GNU General Public License as published by the Free Software Foundation,
	* either version 3 of the License, or (at your option) any later version.
	*
	* NFD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
	* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
	* PURPOSE. See the GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along with
	* NFD, e.g., in COPYING.md file. If not, see <http://www.gnu.org/licenses/>.
	*/

	#ifndef NFD_DAEMON_FW_STRATEGY_HPP
	#define NFD_DAEMON_FW_STRATEGY_HPP

	#include "forwarder.hpp"
	#include "table/measurements-accessor.hpp"

	namespace nfd {
	namespace fw {

	/** \brief Represents a forwarding strategy
	*/
	class Strategy : noncopyable
	{
	public: // registry
	/** \brief Register a strategy type
	* \tparam S subclass of Strategy
	* \param strategyName strategy program name, must contain version
	* \note It is permitted to register the same strategy type under multiple names,
	* which is useful in tests and for creating aliases.
	*/
	template<typename S>
	static void
	registerType(const Name& strategyName = S::getStrategyName())
	{
	BOOST_ASSERT(strategyName.size() > 1);
	BOOST_ASSERT(strategyName.at(-1).isVersion());
	Registry& registry = getRegistry();
	BOOST_ASSERT(registry.count(strategyName) == 0);
	registry[strategyName] = [] (auto&&... args) {
	return make_unique<S>(std::forward<decltype(args)>(args)...);
	};
	}

	/** \return Whether a strategy instance can be created from \p instanceName
	* \param instanceName strategy instance name, may contain version and parameters
	* \note This function finds a strategy type using same rules as \p create ,
	* but does not attempt to construct an instance.
	*/
	static bool
	canCreate(const Name& instanceName);

	/** \return A strategy instance created from \p instanceName
	* \retval nullptr if !canCreate(instanceName)
	* \throw std::invalid_argument strategy type constructor does not accept
	* specified version or parameters
	*/
	static unique_ptr<Strategy>
	create(const Name& instanceName, Forwarder& forwarder);

	/** \return Whether \p instanceNameA and \p instanceNameA will initiate same strategy type
	*/
	static bool
	areSameType(const Name& instanceNameA, const Name& instanceNameB);

	/** \return Registered versioned strategy names
	*/
	static std::set<Name>
	listRegistered();

	public: // constructor, destructor, strategy info
	/** \brief Construct a strategy instance.
	* \param forwarder a reference to the forwarder, used to enable actions and accessors.
	* \note Strategy subclass constructor must not retain a reference to \p forwarder.
	*/
	explicit
	Strategy(Forwarder& forwarder);

	virtual
	~Strategy();

	#ifdef DOXYGEN
	/** \return Strategy program name
	*
	* The strategy name is defined by the strategy program.
	* It must end with a version component.
	*/
	static const Name&
	getStrategyName();
	#endif

	/** \return Strategy instance name
	*
	* The instance name is assigned during instantiation.
	* It contains a version component, and may have extra parameter components.
	*/
	const Name&
	getInstanceName() const
	{
	return m_name;
	}

	public: // triggers
	/** \brief Trigger after Interest is received
	*
	* The Interest:
	* - has not exceeded HopLimit
	* - does not violate Scope
	* - is not looped
	* - cannot be satisfied by ContentStore
	* - is under a namespace managed by this strategy
	*
	* The PIT entry is set to expire after InterestLifetime has elapsed at each downstream.
	*
	* The strategy should decide whether and where to forward this Interest.
	* - If the strategy decides to forward this Interest,
	* invoke \c sendInterest for each upstream, either now or shortly after via a scheduler event,
	* but before PIT entry expires.
	* Optionally, the strategy can invoke \c setExpiryTimer to adjust how long it would wait for a response.
	* - If the strategy has already forwarded this Interest previously and decides to continue waiting,
	* do nothing.
	* Optionally, the strategy can invoke \c setExpiryTimer to adjust how long it would wait for a response.
	* - If the strategy concludes that this Interest cannot be satisfied,
	* invoke \c rejectPendingInterest to erase the PIT entry.
	*
	* \warning The strategy must not retain shared_ptr<pit::Entry>, otherwise undefined behavior
	* may occur. However, the strategy is allowed to store weak_ptr<pit::Entry>.
	*/
	virtual void
	afterReceiveInterest(const FaceEndpoint& ingress, const Interest& interest,
	const shared_ptr<pit::Entry>& pitEntry) = 0;

	/** \brief Trigger before PIT entry is satisfied
	*
	* This trigger is invoked when an incoming Data satisfies more than one PIT entry.
	* The strategy can collect measurements information, but cannot manipulate Data forwarding.
	* When an incoming Data satisfies only one PIT entry, \c afterReceiveData is invoked instead
	* and given full control over Data forwarding. If a strategy does not override \c afterReceiveData,
	* the default implementation invokes \c beforeSatisfyInterest.
	*
	* Normally, PIT entries would be erased after receiving the first matching Data.
	* If the strategy wishes to collect responses from additional upstream nodes,
	* it should invoke \c setExpiryTimer within this function to prolong the PIT entry lifetime.
	* If a Data arrives from another upstream during the extended PIT entry lifetime, this trigger will be invoked again.
	* At that time, this function must invoke \c setExpiryTimer again to continue collecting more responses.
	*
	* In this base class this method does nothing.
	*
	* \warning The strategy must not retain shared_ptr<pit::Entry>, otherwise undefined behavior
	* may occur. However, the strategy is allowed to store weak_ptr<pit::Entry>.
	*/
	virtual void
	beforeSatisfyInterest(const shared_ptr<pit::Entry>& pitEntry,
	const FaceEndpoint& ingress, const Data& data);

	/** \brief Trigger after a Data is matched in CS
	*
	* In the base class this method sends \p data to \p ingress
	*/
	virtual void
	afterContentStoreHit(const shared_ptr<pit::Entry>& pitEntry,
	const FaceEndpoint& ingress, const Data& data);

	/** \brief Trigger after Data is received
	*
	* This trigger is invoked when an incoming Data satisfies exactly one PIT entry,
	* and gives the strategy full control over Data forwarding.
	*
	* When this trigger is invoked:
	* - The Data has been verified to satisfy the PIT entry.
	* - The PIT entry expiry timer is set to now
	*
	* Within this function:
	* - A strategy should return Data to downstream nodes via \c sendData or \c sendDataToAll.
	* - A strategy can modify the Data as long as it still satisfies the PIT entry, such as
	* adding or removing congestion marks.
	* - A strategy can delay Data forwarding by prolonging the PIT entry lifetime via \c setExpiryTimer,
	* and forward Data before the PIT entry is erased.
	* - A strategy can collect measurements about the upstream.
	* - A strategy can collect responses from additional upstream nodes by prolonging the PIT entry
	* lifetime via \c setExpiryTimer every time a Data is received. Note that only one Data should
	* be returned to each downstream node.
	*
	* In the base class this method invokes \c beforeSatisfyInterest trigger and then returns
	* the Data to downstream faces via \c sendDataToAll.
	*/
	virtual void
	afterReceiveData(const shared_ptr<pit::Entry>& pitEntry,
	const FaceEndpoint& ingress, const Data& data);

	/** \brief Trigger after Nack is received
	*
	* This trigger is invoked when an incoming Nack is received in response to
	* an forwarded Interest.
	* The Nack has been confirmed to be a response to the last Interest forwarded
	* to that upstream, i.e. the PIT out-record exists and has a matching Nonce.
	* The NackHeader has been recorded in the PIT out-record.
	*
	* If the PIT entry is not yet satisfied, its expiry timer remains unchanged.
	* Otherwise, the PIT entry normally would expire immediately after this function returns.
	*
	* If the strategy wishes to collect responses from additional upstream nodes,
	* it should invoke \c setExpiryTimer within this function to retain the PIT entry.
	* If a Nack arrives from another upstream during the extended PIT entry lifetime, this trigger will be invoked again.
	* At that time, this function must invoke \c setExpiryTimer again to continue collecting more responses.
	*
	* In the base class this method does nothing.
	*
	* \warning The strategy must not retain shared_ptr<pit::Entry>, otherwise undefined behavior
	* may occur. However, the strategy is allowed to store weak_ptr<pit::Entry>.
	*/
	virtual void
	afterReceiveNack(const FaceEndpoint& ingress, const lp::Nack& nack,
	const shared_ptr<pit::Entry>& pitEntry);

	/** \brief Trigger after Interest dropped (e.g., for exceeding allowed retransmissions)
	*
	* In the base class this method does nothing.
	*/
	virtual void
	onDroppedInterest(const Face& egress, const Interest& interest);

	/** \brief Trigger after new nexthop is added
	*
	* The strategy should decide whether to send the buffered Interests to the new nexthop.
	* In the base class, this method does nothing.
	*/
	virtual void
	afterNewNextHop(const fib::NextHop& nextHop, const shared_ptr<pit::Entry>& pitEntry);

	protected: // actions
	/** \brief Send an Interest packet.
	* \param pitEntry the PIT entry
	* \param egress face through which to send out the Interest
	* \param interest the Interest packet
	* \return A pointer to the out-record created or nullptr if the Interest was dropped
	*/
	NFD_VIRTUAL_WITH_TESTS pit::OutRecord*
	sendInterest(const shared_ptr<pit::Entry>& pitEntry, Face& egress,
	const Interest& interest);

	/** \brief Send a Data packet.
	* \param pitEntry the PIT entry
	* \param data the Data packet
	* \param egress face through which to send out the Data
	* \return Whether the Data was sent (true) or dropped (false)
	*/
	NFD_VIRTUAL_WITH_TESTS bool
	sendData(const shared_ptr<pit::Entry>& pitEntry, const Data& data, Face& egress);

	/** \brief Send a Data packet to all matched and qualified faces.
	*
	* A matched face is qualified if it is ad-hoc or it is NOT \p inFace.
	*
	* \param pitEntry the PIT entry
	* \param inFace face on which the Data arrived
	* \param data the Data packet
	*/
	NFD_VIRTUAL_WITH_TESTS void
	sendDataToAll(const shared_ptr<pit::Entry>& pitEntry, const Face& inFace, const Data& data);

	/** \brief Schedule the PIT entry for immediate deletion.
	*
	* This helper function sets the PIT entry expiry time to zero.
	* The strategy should invoke this function when it concludes that the Interest cannot
	* be forwarded and it does not want to wait for responses from existing upstream nodes.
	*/
	NFD_VIRTUAL_WITH_TESTS void
	rejectPendingInterest(const shared_ptr<pit::Entry>& pitEntry)
	{
	this->setExpiryTimer(pitEntry, 0_ms);
	}

	/** \brief Send a Nack packet.
	*
	* The egress face must have a PIT in-record, otherwise this method has no effect.
	*
	* \param pitEntry the PIT entry
	* \param egress face through which to send out the Nack
	* \param header the Nack header
	* \return Whether the Nack was sent (true) or dropped (false)
	*/
	NFD_VIRTUAL_WITH_TESTS bool
	sendNack(const shared_ptr<pit::Entry>& pitEntry, Face& egress,
	const lp::NackHeader& header)
	{
	return m_forwarder.onOutgoingNack(pitEntry, egress, header);
	}

	/** \brief Send Nack to every face that has an in-record, except those in \p exceptFaces
	* \param pitEntry the PIT entry
	* \param header the Nack header
	* \param exceptFaces list of faces that should be excluded from sending Nacks
	* \note This is not an action, but a helper that invokes the sendNack() action.
	*/
	void
	sendNacks(const shared_ptr<pit::Entry>& pitEntry, const lp::NackHeader& header,
	std::initializer_list<const Face*> exceptFaces = {});

	/** \brief Schedule the PIT entry to be erased after \p duration.
	*/
	void
	setExpiryTimer(const shared_ptr<pit::Entry>& pitEntry, time::milliseconds duration)
	{
	m_forwarder.setExpiryTimer(pitEntry, duration);
	}

	protected: // accessors
	/** \brief Performs a FIB lookup, considering Link object if present.
	*/
	const fib::Entry&
	lookupFib(const pit::Entry& pitEntry) const;

	MeasurementsAccessor&
	getMeasurements()
	{
	return m_measurements;
	}

	Face*
	getFace(FaceId id) const
	{
	return getFaceTable().get(id);
	}

	const FaceTable&
	getFaceTable() const
	{
	return m_forwarder.m_faceTable;
	}

	protected: // instance name
	struct ParsedInstanceName
	{
	Name strategyName; ///< strategy name without parameters
	optional<uint64_t> version; ///< whether strategyName contains a version component
	PartialName parameters; ///< parameter components
	};

	/** \brief Parse a strategy instance name
	* \param input strategy instance name, may contain version and parameters
	* \throw std::invalid_argument input format is unacceptable
	*/
	static ParsedInstanceName
	parseInstanceName(const Name& input);

	/** \brief Construct a strategy instance name
	* \param input strategy instance name, may contain version and parameters
	* \param strategyName strategy name with version but without parameters;
	* typically this should be \p getStrategyName()
	*
	* If \p input contains a version component, return \p input unchanged.
	* Otherwise, return \p input plus the version component taken from \p strategyName.
	* This allows a strategy instance to be constructed with an unversioned name,
	* but its final instance name should contain the version.
	*/
	static Name
	makeInstanceName(const Name& input, const Name& strategyName);

	/** \brief Set strategy instance name
	* \note This must be called by strategy subclass constructor.
	*/
	void
	setInstanceName(const Name& name)
	{
	m_name = name;
	}

	private: // registry
	typedef std::function<unique_ptr<Strategy>(Forwarder& forwarder, const Name& strategyName)> CreateFunc;
	typedef std::map<Name, CreateFunc> Registry; // indexed by strategy name

	static Registry&
	getRegistry();

	static Registry::const_iterator
	find(const Name& instanceName);

	protected: // accessors
	signal::Signal<FaceTable, Face>& afterAddFace;
	signal::Signal<FaceTable, Face>& beforeRemoveFace;

	private: // instance fields
	Name m_name;

	/** \brief Reference to the forwarder
	*
	* Triggers can access forwarder indirectly via actions.
	*/
	Forwarder& m_forwarder;

	MeasurementsAccessor m_measurements;
	};

	} // namespace fw
	} // namespace nfd

	/** \brief Registers a strategy
	*
	* This macro should appear once in .cpp of each strategy.
	*/
	#define NFD_REGISTER_STRATEGY(S) \
	static class NfdAuto ## S ## StrategyRegistrationClass \
	{ \
	public: \
	NfdAuto ## S ## StrategyRegistrationClass() \
	{ \
	::nfd::fw::Strategy::registerType<S>(); \
	} \
	} g_nfdAuto ## S ## StrategyRegistrationVariable

	#endif // NFD_DAEMON_FW_STRATEGY_HPP