src/transport/UnauthenticatedSessionTable.h - third_party/github/project-chip/connectedhomeip - Git at Google

 /*
  *
  *    Copyright (c) 2020 Project CHIP Authors
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
  *    You may obtain a copy of the License at
  *
  *        http://www.apache.org/licenses/LICENSE-2.0
  *
  *    Unless required by applicable law or agreed to in writing, software
  *    distributed under the License is distributed on an "AS IS" BASIS,
  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *    See the License for the specific language governing permissions and
  *    limitations under the License.
  */
 #pragma once

 #include <ble/Ble.h>
 #include <lib/core/CHIPError.h>
 #include <lib/core/ReferenceCounted.h>
 #include <lib/support/CodeUtils.h>
 #include <lib/support/Pool.h>
 #include <messaging/ReliableMessageProtocolConfig.h>
 #include <system/SystemConfig.h>
 #include <system/TimeSource.h>
 #include <transport/PeerMessageCounter.h>
 #include <transport/Session.h>
 #include <transport/raw/PeerAddress.h>

 namespace chip {
 namespace Transport {

 /**
  * @brief
  *   An UnauthenticatedSession stores the binding of TransportAddress, and message counters.
  */
 class UnauthenticatedSession : public Session, public ReferenceCounted<UnauthenticatedSession, UnauthenticatedSession, 0>
 {
 public:
     enum class SessionRole
     {
         kInitiator,
         kResponder,
     };

 protected:
     UnauthenticatedSession(SessionRole sessionRole, NodeId ephemeralInitiatorNodeID, const Transport::PeerAddress & peerAddress,
                            const ReliableMessageProtocolConfig & config) :
         mEphemeralInitiatorNodeId(ephemeralInitiatorNodeID),
         mSessionRole(sessionRole), mPeerAddress(peerAddress), mLastActivityTime(System::SystemClock().GetMonotonicTimestamp()),
         mLastPeerActivityTime(System::Clock::kZero), // Start at zero to default to IDLE state
         mRemoteSessionParams(config)
     {}
     ~UnauthenticatedSession() override { VerifyOrDie(GetReferenceCount() == 0); }

 public:
     UnauthenticatedSession(const UnauthenticatedSession &)             = delete;
     UnauthenticatedSession & operator=(const UnauthenticatedSession &) = delete;
     UnauthenticatedSession(UnauthenticatedSession &&)                  = delete;
     UnauthenticatedSession & operator=(UnauthenticatedSession &&)      = delete;

     System::Clock::Timestamp GetLastActivityTime() const { return mLastActivityTime; }
     System::Clock::Timestamp GetLastPeerActivityTime() const { return mLastPeerActivityTime; }
     void MarkActive() { mLastActivityTime = System::SystemClock().GetMonotonicTimestamp(); }
     void MarkActiveRx()
     {
         mLastPeerActivityTime = System::SystemClock().GetMonotonicTimestamp();
         MarkActive();
     }

     Session::SessionType GetSessionType() const override { return Session::SessionType::kUnauthenticated; }

     void Retain() override { ReferenceCounted<UnauthenticatedSession, UnauthenticatedSession, 0>::Retain(); }
     void Release() override { ReferenceCounted<UnauthenticatedSession, UnauthenticatedSession, 0>::Release(); }

     bool IsActiveSession() const override { return true; }

     ScopedNodeId GetPeer() const override { return ScopedNodeId(GetPeerNodeId(), kUndefinedFabricIndex); }
     ScopedNodeId GetLocalScopedNodeId() const override { return ScopedNodeId(kUndefinedNodeId, kUndefinedFabricIndex); }

     Access::SubjectDescriptor GetSubjectDescriptor() const override
     {
         return Access::SubjectDescriptor(); // return an empty ISD for unauthenticated session.
     }

     bool AllowsMRP() const override { return GetPeerAddress().GetTransportType() == Transport::Type::kUdp; }

     bool AllowsLargePayload() const override { return GetPeerAddress().GetTransportType() == Transport::Type::kTcp; }

     System::Clock::Milliseconds32 GetAckTimeout() const override
     {
         switch (mPeerAddress.GetTransportType())
         {
         case Transport::Type::kUdp: {
             const ReliableMessageProtocolConfig & remoteMRPConfig = mRemoteSessionParams.GetMRPConfig();
             return GetRetransmissionTimeout(remoteMRPConfig.mActiveRetransTimeout, remoteMRPConfig.mIdleRetransTimeout,
                                             GetLastPeerActivityTime(), remoteMRPConfig.mActiveThresholdTime);
         }
         case Transport::Type::kTcp:
             return System::Clock::Seconds16(30);
         case Transport::Type::kBle:
             return System::Clock::Milliseconds32(BTP_ACK_TIMEOUT_MS);
         default:
             break;
         }
         return System::Clock::Timeout();
     }

     NodeId GetPeerNodeId() const
     {
         if (mSessionRole == SessionRole::kInitiator)
         {
             return kUndefinedNodeId;
         }

         return mEphemeralInitiatorNodeId;
     }

     SessionRole GetSessionRole() const { return mSessionRole; }
     NodeId GetEphemeralInitiatorNodeID() const { return mEphemeralInitiatorNodeId; }
     const PeerAddress & GetPeerAddress() const { return mPeerAddress; }
     void SetPeerAddress(const PeerAddress & peerAddress) { mPeerAddress = peerAddress; }

     bool IsPeerActive() const
     {
         return ((System::SystemClock().GetMonotonicTimestamp() - GetLastPeerActivityTime()) <
                 GetRemoteMRPConfig().mActiveThresholdTime);
     }

     System::Clock::Timestamp GetMRPBaseTimeout() const override
     {
         return IsPeerActive() ? GetRemoteMRPConfig().mActiveRetransTimeout : GetRemoteMRPConfig().mIdleRetransTimeout;
     }

     void SetRemoteSessionParameters(const SessionParameters & sessionParams) { mRemoteSessionParams = sessionParams; }

     const SessionParameters & GetRemoteSessionParameters() const override { return mRemoteSessionParams; }

     PeerMessageCounter & GetPeerMessageCounter() { return mPeerMessageCounter; }

     static void Release(UnauthenticatedSession * obj)
     {
         // When using heap pools, we need to make sure to release ourselves back to
         // the pool.  When not using heap pools, we don't want the extra cost of the
         // table pointer here, and the table itself handles entry reuse and cleanup
         // as needed.
 #if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
         obj->ReleaseSelfToPool();
 #else
         // Just do nothing.
 #endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
     }

 #if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
     virtual void ReleaseSelfToPool() = 0;
 #endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP

 private:
     const NodeId mEphemeralInitiatorNodeId;
     const SessionRole mSessionRole;
     PeerAddress mPeerAddress;
     System::Clock::Timestamp mLastActivityTime;     ///< Timestamp of last tx or rx
     System::Clock::Timestamp mLastPeerActivityTime; ///< Timestamp of last rx
     SessionParameters mRemoteSessionParams;
     PeerMessageCounter mPeerMessageCounter;
 };

 template <size_t kMaxSessionCount>
 class UnauthenticatedSessionTable;

 namespace detail {

 template <size_t kMaxSessionCount>
 class UnauthenticatedSessionPoolEntry : public UnauthenticatedSession
 {
 public:
     UnauthenticatedSessionPoolEntry(SessionRole sessionRole, NodeId ephemeralInitiatorNodeID,
                                     const Transport::PeerAddress & peerAddress, const ReliableMessageProtocolConfig & config,
                                     UnauthenticatedSessionTable<kMaxSessionCount> & sessionTable) :
         UnauthenticatedSession(sessionRole, ephemeralInitiatorNodeID, peerAddress, config)
 #if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
         ,
         mSessionTable(sessionTable)
 #endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
     {}

 private:
 #if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
     virtual void ReleaseSelfToPool();

     UnauthenticatedSessionTable<kMaxSessionCount> & mSessionTable;
 #endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
 };

 } // namespace detail

 /*
  * @brief
  *   An table which manages UnauthenticatedSessions
  *
  *   The UnauthenticatedSession entries are rotated using LRU, but entry can be hold by using SessionHandle or
  *   SessionHolder, which increase the reference count by 1. If the reference count is not 0, the entry won't be pruned.
  */
 template <size_t kMaxSessionCount>
 class UnauthenticatedSessionTable
 {
 public:
     ~UnauthenticatedSessionTable()
     {
 #if !CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
         // When not using heap pools, our entries never actually get released
         // back to the pool (which lets us make the entries 4 bytes smaller by
         // not storing a reference to the table in them) and we LRU reuse ones
         // that have 0 refcount.  But we should release them all here, to ensure
         // that we don't hit fatal asserts in our pool destructor.
         mEntries.ReleaseAll();
 #endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
     }

     /**
      * Get a responder session with the given ephemeralInitiatorNodeID. If the session doesn't exist in the cache, allocate a new
      * entry for it.
      *
      * @return the session found or allocated, or Optional::Missing if not found and allocation failed.
      */
     CHECK_RETURN_VALUE
     Optional<SessionHandle> FindOrAllocateResponder(NodeId ephemeralInitiatorNodeID, const ReliableMessageProtocolConfig & config,
                                                     const Transport::PeerAddress & peerAddress)
     {
         UnauthenticatedSession * result =
             FindEntry(UnauthenticatedSession::SessionRole::kResponder, ephemeralInitiatorNodeID, peerAddress);
         if (result != nullptr)
             return MakeOptional<SessionHandle>(*result);

         CHIP_ERROR err =
             AllocEntry(UnauthenticatedSession::SessionRole::kResponder, ephemeralInitiatorNodeID, peerAddress, config, result);
         if (err == CHIP_NO_ERROR)
         {
             return MakeOptional<SessionHandle>(*result);
         }

         return Optional<SessionHandle>::Missing();
     }

     CHECK_RETURN_VALUE Optional<SessionHandle> FindInitiator(NodeId ephemeralInitiatorNodeID,
                                                              const Transport::PeerAddress & peerAddress)
     {
         UnauthenticatedSession * result =
             FindEntry(UnauthenticatedSession::SessionRole::kInitiator, ephemeralInitiatorNodeID, peerAddress);
         if (result != nullptr)
         {
             return MakeOptional<SessionHandle>(*result);
         }

         return Optional<SessionHandle>::Missing();
     }

     CHECK_RETURN_VALUE Optional<SessionHandle> AllocInitiator(NodeId ephemeralInitiatorNodeID, const PeerAddress & peerAddress,
                                                               const ReliableMessageProtocolConfig & config)
     {
         UnauthenticatedSession * result = nullptr;
         CHIP_ERROR err =
             AllocEntry(UnauthenticatedSession::SessionRole::kInitiator, ephemeralInitiatorNodeID, peerAddress, config, result);
         if (err == CHIP_NO_ERROR)
         {
             result->SetPeerAddress(peerAddress);
             return MakeOptional<SessionHandle>(*result);
         }

         return Optional<SessionHandle>::Missing();
     }

 private:
     using EntryType = detail::UnauthenticatedSessionPoolEntry<kMaxSessionCount>;
     friend EntryType;

     /**
      * Allocates a new session out of the internal resource pool.
      *
      * @returns CHIP_NO_ERROR if new session created. May fail if maximum session count has been reached (with
      * CHIP_ERROR_NO_MEMORY).
      */
     CHECK_RETURN_VALUE
     CHIP_ERROR AllocEntry(UnauthenticatedSession::SessionRole sessionRole, NodeId ephemeralInitiatorNodeID,
                           const PeerAddress & peerAddress, const ReliableMessageProtocolConfig & config,
                           UnauthenticatedSession *& entry)
     {
         auto entryToUse = mEntries.CreateObject(sessionRole, ephemeralInitiatorNodeID, peerAddress, config, *this);
         if (entryToUse != nullptr)
         {
             entry = entryToUse;
             return CHIP_NO_ERROR;
         }

 #if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
         // permanent failure if heap was insufficient
         return CHIP_ERROR_NO_MEMORY;
 #else
         entryToUse = FindLeastRecentUsedEntry();
         VerifyOrReturnError(entryToUse != nullptr, CHIP_ERROR_NO_MEMORY);

         // Drop the least recent entry to allow for a new alloc.
         mEntries.ReleaseObject(entryToUse);
         entryToUse = mEntries.CreateObject(sessionRole, ephemeralInitiatorNodeID, peerAddress, config, *this);

         if (entryToUse == nullptr)
         {
             // this is NOT expected: we freed an object to have space
             return CHIP_ERROR_INTERNAL;
         }

         entry = entryToUse;
         return CHIP_NO_ERROR;
 #endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
     }

     CHECK_RETURN_VALUE UnauthenticatedSession * FindEntry(UnauthenticatedSession::SessionRole sessionRole,
                                                           NodeId ephemeralInitiatorNodeID,
                                                           const Transport::PeerAddress & peerAddress)
     {
         UnauthenticatedSession * result = nullptr;
         mEntries.ForEachActiveObject([&](UnauthenticatedSession * entry) {
             if (entry->GetSessionRole() == sessionRole && entry->GetEphemeralInitiatorNodeID() == ephemeralInitiatorNodeID &&
                 entry->GetPeerAddress().GetTransportType() == peerAddress.GetTransportType())
             {
                 result = entry;
                 return Loop::Break;
             }
             return Loop::Continue;
         });
         return result;
     }

     EntryType * FindLeastRecentUsedEntry()
     {
         EntryType * result                  = nullptr;
         System::Clock::Timestamp oldestTime = System::Clock::Timestamp(std::numeric_limits<System::Clock::Timestamp::rep>::max());

         mEntries.ForEachActiveObject([&](EntryType * entry) {
             if (entry->GetReferenceCount() == 0 && entry->GetLastActivityTime() < oldestTime)
             {
                 result     = entry;
                 oldestTime = entry->GetLastActivityTime();
             }
             return Loop::Continue;
         });

         return result;
     }

     void ReleaseEntry(EntryType * entry) { mEntries.ReleaseObject(entry); }

     ObjectPool<EntryType, kMaxSessionCount> mEntries;
 };

 #if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
 template <size_t kMaxSessionCount>
 void detail::UnauthenticatedSessionPoolEntry<kMaxSessionCount>::ReleaseSelfToPool()
 {
     mSessionTable.ReleaseEntry(this);
 }
 #endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP

 } // namespace Transport
 } // namespace chip
	/*
	*
	* Copyright (c) 2020 Project CHIP Authors
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	#pragma once

	#include <ble/Ble.h>
	#include <lib/core/CHIPError.h>
	#include <lib/core/ReferenceCounted.h>
	#include <lib/support/CodeUtils.h>
	#include <lib/support/Pool.h>
	#include <messaging/ReliableMessageProtocolConfig.h>
	#include <system/SystemConfig.h>
	#include <system/TimeSource.h>
	#include <transport/PeerMessageCounter.h>
	#include <transport/Session.h>
	#include <transport/raw/PeerAddress.h>

	namespace chip {
	namespace Transport {

	/**
	* @brief
	* An UnauthenticatedSession stores the binding of TransportAddress, and message counters.
	*/
	class UnauthenticatedSession : public Session, public ReferenceCounted<UnauthenticatedSession, UnauthenticatedSession, 0>
	{
	public:
	enum class SessionRole
	{
	kInitiator,
	kResponder,
	};

	protected:
	UnauthenticatedSession(SessionRole sessionRole, NodeId ephemeralInitiatorNodeID, const Transport::PeerAddress & peerAddress,
	const ReliableMessageProtocolConfig & config) :
	mEphemeralInitiatorNodeId(ephemeralInitiatorNodeID),
	mSessionRole(sessionRole), mPeerAddress(peerAddress), mLastActivityTime(System::SystemClock().GetMonotonicTimestamp()),
	mLastPeerActivityTime(System::Clock::kZero), // Start at zero to default to IDLE state
	mRemoteSessionParams(config)
	{}
	~UnauthenticatedSession() override { VerifyOrDie(GetReferenceCount() == 0); }

	public:
	UnauthenticatedSession(const UnauthenticatedSession &) = delete;
	UnauthenticatedSession & operator=(const UnauthenticatedSession &) = delete;
	UnauthenticatedSession(UnauthenticatedSession &&) = delete;
	UnauthenticatedSession & operator=(UnauthenticatedSession &&) = delete;

	System::Clock::Timestamp GetLastActivityTime() const { return mLastActivityTime; }
	System::Clock::Timestamp GetLastPeerActivityTime() const { return mLastPeerActivityTime; }
	void MarkActive() { mLastActivityTime = System::SystemClock().GetMonotonicTimestamp(); }
	void MarkActiveRx()
	{
	mLastPeerActivityTime = System::SystemClock().GetMonotonicTimestamp();
	MarkActive();
	}

	Session::SessionType GetSessionType() const override { return Session::SessionType::kUnauthenticated; }

	void Retain() override { ReferenceCounted<UnauthenticatedSession, UnauthenticatedSession, 0>::Retain(); }
	void Release() override { ReferenceCounted<UnauthenticatedSession, UnauthenticatedSession, 0>::Release(); }

	bool IsActiveSession() const override { return true; }

	ScopedNodeId GetPeer() const override { return ScopedNodeId(GetPeerNodeId(), kUndefinedFabricIndex); }
	ScopedNodeId GetLocalScopedNodeId() const override { return ScopedNodeId(kUndefinedNodeId, kUndefinedFabricIndex); }

	Access::SubjectDescriptor GetSubjectDescriptor() const override
	{
	return Access::SubjectDescriptor(); // return an empty ISD for unauthenticated session.
	}

	bool AllowsMRP() const override { return GetPeerAddress().GetTransportType() == Transport::Type::kUdp; }

	bool AllowsLargePayload() const override { return GetPeerAddress().GetTransportType() == Transport::Type::kTcp; }

	System::Clock::Milliseconds32 GetAckTimeout() const override
	{
	switch (mPeerAddress.GetTransportType())
	{
	case Transport::Type::kUdp: {
	const ReliableMessageProtocolConfig & remoteMRPConfig = mRemoteSessionParams.GetMRPConfig();
	return GetRetransmissionTimeout(remoteMRPConfig.mActiveRetransTimeout, remoteMRPConfig.mIdleRetransTimeout,
	GetLastPeerActivityTime(), remoteMRPConfig.mActiveThresholdTime);
	}
	case Transport::Type::kTcp:
	return System::Clock::Seconds16(30);
	case Transport::Type::kBle:
	return System::Clock::Milliseconds32(BTP_ACK_TIMEOUT_MS);
	default:
	break;
	}
	return System::Clock::Timeout();
	}

	NodeId GetPeerNodeId() const
	{
	if (mSessionRole == SessionRole::kInitiator)
	{
	return kUndefinedNodeId;
	}

	return mEphemeralInitiatorNodeId;
	}

	SessionRole GetSessionRole() const { return mSessionRole; }
	NodeId GetEphemeralInitiatorNodeID() const { return mEphemeralInitiatorNodeId; }
	const PeerAddress & GetPeerAddress() const { return mPeerAddress; }
	void SetPeerAddress(const PeerAddress & peerAddress) { mPeerAddress = peerAddress; }

	bool IsPeerActive() const
	{
	return ((System::SystemClock().GetMonotonicTimestamp() - GetLastPeerActivityTime()) <
	GetRemoteMRPConfig().mActiveThresholdTime);
	}

	System::Clock::Timestamp GetMRPBaseTimeout() const override
	{
	return IsPeerActive() ? GetRemoteMRPConfig().mActiveRetransTimeout : GetRemoteMRPConfig().mIdleRetransTimeout;
	}

	void SetRemoteSessionParameters(const SessionParameters & sessionParams) { mRemoteSessionParams = sessionParams; }

	const SessionParameters & GetRemoteSessionParameters() const override { return mRemoteSessionParams; }

	PeerMessageCounter & GetPeerMessageCounter() { return mPeerMessageCounter; }

	static void Release(UnauthenticatedSession * obj)
	{
	// When using heap pools, we need to make sure to release ourselves back to
	// the pool. When not using heap pools, we don't want the extra cost of the
	// table pointer here, and the table itself handles entry reuse and cleanup
	// as needed.
	#if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	obj->ReleaseSelfToPool();
	#else
	// Just do nothing.
	#endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	}

	#if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	virtual void ReleaseSelfToPool() = 0;
	#endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP

	private:
	const NodeId mEphemeralInitiatorNodeId;
	const SessionRole mSessionRole;
	PeerAddress mPeerAddress;
	System::Clock::Timestamp mLastActivityTime; ///< Timestamp of last tx or rx
	System::Clock::Timestamp mLastPeerActivityTime; ///< Timestamp of last rx
	SessionParameters mRemoteSessionParams;
	PeerMessageCounter mPeerMessageCounter;
	};

	template <size_t kMaxSessionCount>
	class UnauthenticatedSessionTable;

	namespace detail {

	template <size_t kMaxSessionCount>
	class UnauthenticatedSessionPoolEntry : public UnauthenticatedSession
	{
	public:
	UnauthenticatedSessionPoolEntry(SessionRole sessionRole, NodeId ephemeralInitiatorNodeID,
	const Transport::PeerAddress & peerAddress, const ReliableMessageProtocolConfig & config,
	UnauthenticatedSessionTable<kMaxSessionCount> & sessionTable) :
	UnauthenticatedSession(sessionRole, ephemeralInitiatorNodeID, peerAddress, config)
	#if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	,
	mSessionTable(sessionTable)
	#endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	{}

	private:
	#if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	virtual void ReleaseSelfToPool();

	UnauthenticatedSessionTable<kMaxSessionCount> & mSessionTable;
	#endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	};

	} // namespace detail

	/*
	* @brief
	* An table which manages UnauthenticatedSessions
	*
	* The UnauthenticatedSession entries are rotated using LRU, but entry can be hold by using SessionHandle or
	* SessionHolder, which increase the reference count by 1. If the reference count is not 0, the entry won't be pruned.
	*/
	template <size_t kMaxSessionCount>
	class UnauthenticatedSessionTable
	{
	public:
	~UnauthenticatedSessionTable()
	{
	#if !CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	// When not using heap pools, our entries never actually get released
	// back to the pool (which lets us make the entries 4 bytes smaller by
	// not storing a reference to the table in them) and we LRU reuse ones
	// that have 0 refcount. But we should release them all here, to ensure
	// that we don't hit fatal asserts in our pool destructor.
	mEntries.ReleaseAll();
	#endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	}

	/**
	* Get a responder session with the given ephemeralInitiatorNodeID. If the session doesn't exist in the cache, allocate a new
	* entry for it.
	*
	* @return the session found or allocated, or Optional::Missing if not found and allocation failed.
	*/
	CHECK_RETURN_VALUE
	Optional<SessionHandle> FindOrAllocateResponder(NodeId ephemeralInitiatorNodeID, const ReliableMessageProtocolConfig & config,
	const Transport::PeerAddress & peerAddress)
	{
	UnauthenticatedSession * result =
	FindEntry(UnauthenticatedSession::SessionRole::kResponder, ephemeralInitiatorNodeID, peerAddress);
	if (result != nullptr)
	return MakeOptional<SessionHandle>(*result);

	CHIP_ERROR err =
	AllocEntry(UnauthenticatedSession::SessionRole::kResponder, ephemeralInitiatorNodeID, peerAddress, config, result);
	if (err == CHIP_NO_ERROR)
	{
	return MakeOptional<SessionHandle>(*result);
	}

	return Optional<SessionHandle>::Missing();
	}

	CHECK_RETURN_VALUE Optional<SessionHandle> FindInitiator(NodeId ephemeralInitiatorNodeID,
	const Transport::PeerAddress & peerAddress)
	{
	UnauthenticatedSession * result =
	FindEntry(UnauthenticatedSession::SessionRole::kInitiator, ephemeralInitiatorNodeID, peerAddress);
	if (result != nullptr)
	{
	return MakeOptional<SessionHandle>(*result);
	}

	return Optional<SessionHandle>::Missing();
	}

	CHECK_RETURN_VALUE Optional<SessionHandle> AllocInitiator(NodeId ephemeralInitiatorNodeID, const PeerAddress & peerAddress,
	const ReliableMessageProtocolConfig & config)
	{
	UnauthenticatedSession * result = nullptr;
	CHIP_ERROR err =
	AllocEntry(UnauthenticatedSession::SessionRole::kInitiator, ephemeralInitiatorNodeID, peerAddress, config, result);
	if (err == CHIP_NO_ERROR)
	{
	result->SetPeerAddress(peerAddress);
	return MakeOptional<SessionHandle>(*result);
	}

	return Optional<SessionHandle>::Missing();
	}

	private:
	using EntryType = detail::UnauthenticatedSessionPoolEntry<kMaxSessionCount>;
	friend EntryType;

	/**
	* Allocates a new session out of the internal resource pool.
	*
	* @returns CHIP_NO_ERROR if new session created. May fail if maximum session count has been reached (with
	* CHIP_ERROR_NO_MEMORY).
	*/
	CHECK_RETURN_VALUE
	CHIP_ERROR AllocEntry(UnauthenticatedSession::SessionRole sessionRole, NodeId ephemeralInitiatorNodeID,
	const PeerAddress & peerAddress, const ReliableMessageProtocolConfig & config,
	UnauthenticatedSession *& entry)
	{
	auto entryToUse = mEntries.CreateObject(sessionRole, ephemeralInitiatorNodeID, peerAddress, config, *this);
	if (entryToUse != nullptr)
	{
	entry = entryToUse;
	return CHIP_NO_ERROR;
	}

	#if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	// permanent failure if heap was insufficient
	return CHIP_ERROR_NO_MEMORY;
	#else
	entryToUse = FindLeastRecentUsedEntry();
	VerifyOrReturnError(entryToUse != nullptr, CHIP_ERROR_NO_MEMORY);

	// Drop the least recent entry to allow for a new alloc.
	mEntries.ReleaseObject(entryToUse);
	entryToUse = mEntries.CreateObject(sessionRole, ephemeralInitiatorNodeID, peerAddress, config, *this);

	if (entryToUse == nullptr)
	{
	// this is NOT expected: we freed an object to have space
	return CHIP_ERROR_INTERNAL;
	}

	entry = entryToUse;
	return CHIP_NO_ERROR;
	#endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	}

	CHECK_RETURN_VALUE UnauthenticatedSession * FindEntry(UnauthenticatedSession::SessionRole sessionRole,
	NodeId ephemeralInitiatorNodeID,
	const Transport::PeerAddress & peerAddress)
	{
	UnauthenticatedSession * result = nullptr;
	mEntries.ForEachActiveObject([&](UnauthenticatedSession * entry) {
	if (entry->GetSessionRole() == sessionRole && entry->GetEphemeralInitiatorNodeID() == ephemeralInitiatorNodeID &&
	entry->GetPeerAddress().GetTransportType() == peerAddress.GetTransportType())
	{
	result = entry;
	return Loop::Break;
	}
	return Loop::Continue;
	});
	return result;
	}

	EntryType * FindLeastRecentUsedEntry()
	{
	EntryType * result = nullptr;
	System::Clock::Timestamp oldestTime = System::Clock::Timestamp(std::numeric_limits<System::Clock::Timestamp::rep>::max());

	mEntries.ForEachActiveObject([&](EntryType * entry) {
	if (entry->GetReferenceCount() == 0 && entry->GetLastActivityTime() < oldestTime)
	{
	result = entry;
	oldestTime = entry->GetLastActivityTime();
	}
	return Loop::Continue;
	});

	return result;
	}

	void ReleaseEntry(EntryType * entry) { mEntries.ReleaseObject(entry); }

	ObjectPool<EntryType, kMaxSessionCount> mEntries;
	};

	#if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
	template <size_t kMaxSessionCount>
	void detail::UnauthenticatedSessionPoolEntry<kMaxSessionCount>::ReleaseSelfToPool()
	{
	mSessionTable.ReleaseEntry(this);
	}
	#endif // CHIP_SYSTEM_CONFIG_POOL_USE_HEAP

	} // namespace Transport
	} // namespace chip