src/messaging/ExchangeContext.cpp - 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.
  */

 /**
  *    @file
  *      This file implements the ExchangeContext class.
  *
  */
 #ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
 #endif

 #ifndef __STDC_LIMIT_MACROS
 #define __STDC_LIMIT_MACROS
 #endif

 #include <inttypes.h>
 #include <stdint.h>
 #include <stdlib.h>

 #include <core/CHIPCore.h>
 #include <core/CHIPEncoding.h>
 #include <core/CHIPKeyIds.h>
 #include <lib/support/TypeTraits.h>
 #include <messaging/ExchangeContext.h>
 #include <messaging/ExchangeMgr.h>
 #include <protocols/Protocols.h>
 #include <protocols/secure_channel/Constants.h>
 #include <support/Defer.h>
 #include <support/logging/CHIPLogging.h>

 using namespace chip::Encoding;
 using namespace chip::Inet;
 using namespace chip::System;

 namespace chip {
 namespace Messaging {

 static void DefaultOnMessageReceived(ExchangeContext * ec, const PacketHeader & packetHeader, Protocols::Id protocolId,
                                      uint8_t msgType, PacketBufferHandle && payload)
 {
     ChipLogError(ExchangeManager, "Dropping unexpected message %08" PRIX32 ":%d %04" PRIX16 " MsgId:%08" PRIX32,
                  protocolId.ToFullyQualifiedSpecForm(), msgType, ec->GetExchangeId(), packetHeader.GetMessageId());
 }

 bool ExchangeContext::IsInitiator() const
 {
     return mFlags.Has(Flags::kFlagInitiator);
 }

 bool ExchangeContext::IsResponseExpected() const
 {
     return mFlags.Has(Flags::kFlagResponseExpected);
 }

 void ExchangeContext::SetResponseExpected(bool inResponseExpected)
 {
     mFlags.Set(Flags::kFlagResponseExpected, inResponseExpected);
 }

 void ExchangeContext::SetResponseTimeout(Timeout timeout)
 {
     mResponseTimeout = timeout;
 }

 CHIP_ERROR ExchangeContext::SendMessage(Protocols::Id protocolId, uint8_t msgType, PacketBufferHandle && msgBuf,
                                         const SendFlags & sendFlags)
 {
     bool isStandaloneAck =
         (protocolId == Protocols::SecureChannel::Id) && msgType == to_underlying(Protocols::SecureChannel::MsgType::StandaloneAck);
     if (!isStandaloneAck)
     {
         // If we were waiting for a message send, this is it.  Standalone acks
         // are not application-level sends, which is why we don't allow those to
         // clear the WillSendMessage flag.
         mFlags.Clear(Flags::kFlagWillSendMessage);
     }

     Transport::PeerConnectionState * state = nullptr;

     VerifyOrReturnError(mExchangeMgr != nullptr, CHIP_ERROR_INTERNAL);
     VerifyOrReturnError(mSecureSession.HasValue(), CHIP_ERROR_CONNECTION_ABORTED);

     // Don't let method get called on a freed object.
     VerifyOrDie(mExchangeMgr != nullptr && GetReferenceCount() > 0);

     // we hold the exchange context here in case the entity that
     // originally generated it tries to close it as a result of
     // an error arising below. at the end, we have to close it.
     ExchangeHandle ref(*this);

     bool reliableTransmissionRequested = true;

     state = mExchangeMgr->GetSessionMgr()->GetPeerConnectionState(mSecureSession.Value());
     // If sending via UDP and NoAutoRequestAck send flag is not specificed, request reliable transmission.
     if (state != nullptr && state->GetPeerAddress().GetTransportType() != Transport::Type::kUdp)
     {
         reliableTransmissionRequested = false;
     }
     else
     {
         reliableTransmissionRequested = !sendFlags.Has(SendMessageFlags::kNoAutoRequestAck);
     }

     // If a response message is expected...
     if (sendFlags.Has(SendMessageFlags::kExpectResponse))
     {
         // Only one 'response expected' message can be outstanding at a time.
         if (IsResponseExpected())
         {
             // TODO: add a test for this case.
             return CHIP_ERROR_INCORRECT_STATE;
         }

         SetResponseExpected(true);

         // Arm the response timer if a timeout has been specified.
         if (mResponseTimeout > 0)
         {
             CHIP_ERROR err = StartResponseTimer();
             if (err != CHIP_NO_ERROR)
             {
                 SetResponseExpected(false);
                 return err;
             }
         }
     }

     {
         // Create a new scope for `err`, to avoid shadowing warning previous `err`.
         CHIP_ERROR err = mDispatch->SendMessage(mSecureSession.Value(), mExchangeId, IsInitiator(), GetReliableMessageContext(),
                                                 reliableTransmissionRequested, protocolId, msgType, std::move(msgBuf));
         if (err != CHIP_NO_ERROR && IsResponseExpected())
         {
             CancelResponseTimer();
             SetResponseExpected(false);
         }

         // Standalone acks are not application-level message sends.
         if (err == CHIP_NO_ERROR && !isStandaloneAck)
         {
             MessageHandled();
         }

         return err;
     }
 }

 void ExchangeContext::DoClose(bool clearRetransTable)
 {
     mFlags.Set(Flags::kFlagClosed);

     // Clear protocol callbacks
     if (mDelegate != nullptr)
     {
         mDelegate->OnExchangeClosing(this);
     }
     mDelegate = nullptr;

     // Closure of an exchange context is based on ref counting. The Protocol, when it calls DoClose(), indicates that
     // it is done with the exchange context and the message layer sets all callbacks to NULL and does not send anything
     // received on the exchange context up to higher layers.  At this point, the message layer needs to handle the
     // remaining work to be done on that exchange, (e.g. send all pending acks) before truly cleaning it up.
     FlushAcks();

     // In case the protocol wants a harder release of the EC right away, such as calling Abort(), exchange
     // needs to clear the MRP retransmission table immediately.
     if (clearRetransTable)
     {
         mExchangeMgr->GetReliableMessageMgr()->ClearRetransTable(static_cast<ReliableMessageContext *>(this));
     }

     // Cancel the response timer.
     CancelResponseTimer();
 }

 /**
  *  Gracefully close an exchange context. This call decrements the
  *  reference count and releases the exchange when the reference
  *  count goes to zero.
  *
  */
 void ExchangeContext::Close()
 {
     VerifyOrDie(mExchangeMgr != nullptr && GetReferenceCount() > 0);

 #if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
     ChipLogDetail(ExchangeManager, "ec id: %d [%04" PRIX16 "], %s", (this - mExchangeMgr->mContextPool.begin()), mExchangeId,
                   __func__);
 #endif

     DoClose(false);
     Release();
 }
 /**
  *  Abort the Exchange context immediately and release all
  *  references to it.
  *
  */
 void ExchangeContext::Abort()
 {
     VerifyOrDie(mExchangeMgr != nullptr && GetReferenceCount() > 0);

 #if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
     ChipLogDetail(ExchangeManager, "ec id: %d [%04" PRIX16 "], %s", (this - mExchangeMgr->mContextPool.begin()), mExchangeId,
                   __func__);
 #endif

     DoClose(true);
     Release();
 }

 void ExchangeContextDeletor::Release(ExchangeContext * ec)
 {
     ec->mExchangeMgr->ReleaseContext(ec);
 }

 ExchangeContext::ExchangeContext(ExchangeManager * em, uint16_t ExchangeId, SessionHandle session, bool Initiator,
                                  ExchangeDelegate * delegate)
 {
     VerifyOrDie(mExchangeMgr == nullptr);

     mExchangeMgr = em;
     mExchangeId  = ExchangeId;
     mSecureSession.SetValue(session);
     mFlags.Set(Flags::kFlagInitiator, Initiator);
     mDelegate = delegate;

     ExchangeMessageDispatch * dispatch = nullptr;
     if (delegate != nullptr)
     {
         dispatch = delegate->GetMessageDispatch(em->GetReliableMessageMgr(), em->GetSessionMgr());
         if (dispatch == nullptr)
         {
             dispatch = &em->mDefaultExchangeDispatch;
         }
     }
     else
     {
         dispatch = &em->mDefaultExchangeDispatch;
     }
     VerifyOrDie(dispatch != nullptr);
     mDispatch = dispatch->Retain();

     SetDropAckDebug(false);
     SetAckPending(false);
     SetMsgRcvdFromPeer(false);
     SetAutoRequestAck(true);

 #if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
     ChipLogDetail(ExchangeManager, "ec++ id: %d", ExchangeId);
 #endif
     SYSTEM_STATS_INCREMENT(chip::System::Stats::kExchangeMgr_NumContexts);
 }

 ExchangeContext::~ExchangeContext()
 {
     VerifyOrDie(mExchangeMgr != nullptr && GetReferenceCount() == 0);
     VerifyOrDie(!IsAckPending());

     // Ideally, in this scenario, the retransmit table should
     // be clear of any outstanding messages for this context and
     // the boolean parameter passed to DoClose() should not matter.

     DoClose(false);
     mExchangeMgr = nullptr;

     if (mExchangeACL != nullptr)
     {
         chip::Platform::Delete(mExchangeACL);
         mExchangeACL = nullptr;
     }

     if (mDispatch != nullptr)
     {
         mDispatch->Release();
         mDispatch = nullptr;
     }

 #if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
     ChipLogDetail(ExchangeManager, "ec-- id: %d", mExchangeId);
 #endif
     SYSTEM_STATS_DECREMENT(chip::System::Stats::kExchangeMgr_NumContexts);
 }

 bool ExchangeContext::MatchExchange(SessionHandle session, const PacketHeader & packetHeader, const PayloadHeader & payloadHeader)
 {
     // A given message is part of a particular exchange if...
     return

         // The exchange identifier of the message matches the exchange identifier of the context.
         (mExchangeId == payloadHeader.GetExchangeID())

         // AND The Session ID associated with the incoming message matches the Session ID associated with the exchange.
         && (mSecureSession.HasValue() && mSecureSession.Value().MatchIncomingSession(session))

         // AND The message was sent by an initiator and the exchange context is a responder (IsInitiator==false)
         //    OR The message was sent by a responder and the exchange context is an initiator (IsInitiator==true) (for the broadcast
         //    case, the initiator is ill defined)

         && (payloadHeader.IsInitiator() != IsInitiator());
 }

 void ExchangeContext::OnConnectionExpired()
 {
     // Reset our mSecureSession to a default-initialized (hence not matching any
     // connection state) value, because it's still referencing the now-expired
     // connection.  This will mean that no more messages can be sent via this
     // exchange, which seems fine given the semantics of connection expiration.
     mSecureSession.ClearValue();

     if (!IsResponseExpected())
     {
         // Nothing to do in this case
         return;
     }

     // If we're waiting on a response, we now know it's never going to show up
     // and we should notify our delegate accordingly.
     CancelResponseTimer();
     SetResponseExpected(false);
     NotifyResponseTimeout();
 }

 CHIP_ERROR ExchangeContext::StartResponseTimer()
 {
     System::Layer * lSystemLayer = mExchangeMgr->GetSessionMgr()->SystemLayer();
     if (lSystemLayer == nullptr)
     {
         // this is an assertion error, which shall never happen
         return CHIP_ERROR_INTERNAL;
     }

     return lSystemLayer->StartTimer(mResponseTimeout, HandleResponseTimeout, this);
 }

 void ExchangeContext::CancelResponseTimer()
 {
     System::Layer * lSystemLayer = mExchangeMgr->GetSessionMgr()->SystemLayer();
     if (lSystemLayer == nullptr)
     {
         // this is an assertion error, which shall never happen
         return;
     }

     lSystemLayer->CancelTimer(HandleResponseTimeout, this);
 }

 void ExchangeContext::HandleResponseTimeout(System::Layer * aSystemLayer, void * aAppState)
 {
     ExchangeContext * ec = reinterpret_cast<ExchangeContext *>(aAppState);

     if (ec == nullptr)
         return;

     ec->NotifyResponseTimeout();
 }

 void ExchangeContext::NotifyResponseTimeout()
 {
     SetResponseExpected(false);

     ExchangeDelegate * delegate = GetDelegate();

     // Call the user's timeout handler.
     if (delegate != nullptr)
     {
         delegate->OnResponseTimeout(this);
     }

     MessageHandled();
 }

 CHIP_ERROR ExchangeContext::HandleMessage(const PacketHeader & packetHeader, const PayloadHeader & payloadHeader,
                                           const Transport::PeerAddress & peerAddress, MessageFlags msgFlags,
                                           PacketBufferHandle && msgBuf)
 {
     // We hold a reference to the ExchangeContext here to
     // guard against Close() calls(decrementing the reference
     // count) by the protocol before the CHIP Exchange
     // layer has completed its work on the ExchangeContext.
     ExchangeHandle ref(*this);

     // Keep track of whether we're nested under an outer HandleMessage
     // invocation.
     bool alreadyHandlingMessage = mFlags.Has(Flags::kFlagHandlingMessage);
     mFlags.Set(Flags::kFlagHandlingMessage);

     bool isStandaloneAck = payloadHeader.HasMessageType(Protocols::SecureChannel::MsgType::StandaloneAck);
     bool isDuplicate     = msgFlags.Has(MessageFlagValues::kDuplicateMessage);

     auto deferred = MakeDefer([&]() {
         // The alreadyHandlingMessage check is effectively a workaround for the fact that SendMessage() is not calling
         // MessageHandled() yet and will go away when we fix that.
         if (alreadyHandlingMessage)
         {
             // Don't close if there's an outer HandleMessage invocation.  It'll deal with the closing.
             return;
         }
         // We are the outermost HandleMessage invocation.  We're not handling a message anymore.
         mFlags.Clear(Flags::kFlagHandlingMessage);

         // Duplicates and standalone acks are not application-level messages, so they should generally not lead to any state
         // changes.  The one exception to that is that if we have a null mDelegate then our lifetime is not application-defined,
         // since we don't interact with the application at that point.  That can happen when we are already closed (in which case
         // MessageHandled is a no-op) or if we were just created to send a standalone ack for this incoming message, in which case
         // we should treat it as an app-level message for purposes of our state.
         if ((isStandaloneAck || isDuplicate) && mDelegate != nullptr)
         {
             return;
         }

         MessageHandled();
     });

     ReturnErrorOnFailure(mDispatch->OnMessageReceived(packetHeader.GetFlags(), payloadHeader, packetHeader.GetMessageId(),
                                                       peerAddress, msgFlags, GetReliableMessageContext()));

     if (IsAckPending() && !mDelegate)
     {
         // The incoming message wants an ack, but we have no delegate, so
         // there's not going to be a response to piggyback on.  Just flush the
         // ack out right now.
         ReturnErrorOnFailure(FlushAcks());
     }

     // The SecureChannel::StandaloneAck message type is only used for MRP; do not pass such messages to the application layer.
     if (isStandaloneAck)
     {
         return CHIP_NO_ERROR;
     }

     // Since the message is duplicate, let's not forward it up the stack
     if (isDuplicate)
     {
         return CHIP_NO_ERROR;
     }

     // Since we got the response, cancel the response timer.
     CancelResponseTimer();

     // If the context was expecting a response to a previously sent message, this message
     // is implicitly that response.
     SetResponseExpected(false);

     if (mDelegate != nullptr)
     {
         return mDelegate->OnMessageReceived(this, packetHeader, payloadHeader, std::move(msgBuf));
     }
     else
     {
         DefaultOnMessageReceived(this, packetHeader, payloadHeader.GetProtocolID(), payloadHeader.GetMessageType(),
                                  std::move(msgBuf));
         return CHIP_NO_ERROR;
     }
 }

 void ExchangeContext::MessageHandled()
 {
     if (mFlags.Has(Flags::kFlagClosed) || IsResponseExpected() || IsSendExpected())
     {
         return;
     }

     Close();
 }

 } // namespace Messaging
 } // 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.
	*/

	/**
	* @file
	* This file implements the ExchangeContext class.
	*
	*/
	#ifndef __STDC_FORMAT_MACROS
	#define __STDC_FORMAT_MACROS
	#endif

	#ifndef __STDC_LIMIT_MACROS
	#define __STDC_LIMIT_MACROS
	#endif

	#include <inttypes.h>
	#include <stdint.h>
	#include <stdlib.h>

	#include <core/CHIPCore.h>
	#include <core/CHIPEncoding.h>
	#include <core/CHIPKeyIds.h>
	#include <lib/support/TypeTraits.h>
	#include <messaging/ExchangeContext.h>
	#include <messaging/ExchangeMgr.h>
	#include <protocols/Protocols.h>
	#include <protocols/secure_channel/Constants.h>
	#include <support/Defer.h>
	#include <support/logging/CHIPLogging.h>

	using namespace chip::Encoding;
	using namespace chip::Inet;
	using namespace chip::System;

	namespace chip {
	namespace Messaging {

	static void DefaultOnMessageReceived(ExchangeContext * ec, const PacketHeader & packetHeader, Protocols::Id protocolId,
	uint8_t msgType, PacketBufferHandle && payload)
	{
	ChipLogError(ExchangeManager, "Dropping unexpected message %08" PRIX32 ":%d %04" PRIX16 " MsgId:%08" PRIX32,
	protocolId.ToFullyQualifiedSpecForm(), msgType, ec->GetExchangeId(), packetHeader.GetMessageId());
	}

	bool ExchangeContext::IsInitiator() const
	{
	return mFlags.Has(Flags::kFlagInitiator);
	}

	bool ExchangeContext::IsResponseExpected() const
	{
	return mFlags.Has(Flags::kFlagResponseExpected);
	}

	void ExchangeContext::SetResponseExpected(bool inResponseExpected)
	{
	mFlags.Set(Flags::kFlagResponseExpected, inResponseExpected);
	}

	void ExchangeContext::SetResponseTimeout(Timeout timeout)
	{
	mResponseTimeout = timeout;
	}

	CHIP_ERROR ExchangeContext::SendMessage(Protocols::Id protocolId, uint8_t msgType, PacketBufferHandle && msgBuf,
	const SendFlags & sendFlags)
	{
	bool isStandaloneAck =
	(protocolId == Protocols::SecureChannel::Id) && msgType == to_underlying(Protocols::SecureChannel::MsgType::StandaloneAck);
	if (!isStandaloneAck)
	{
	// If we were waiting for a message send, this is it. Standalone acks
	// are not application-level sends, which is why we don't allow those to
	// clear the WillSendMessage flag.
	mFlags.Clear(Flags::kFlagWillSendMessage);
	}

	Transport::PeerConnectionState * state = nullptr;

	VerifyOrReturnError(mExchangeMgr != nullptr, CHIP_ERROR_INTERNAL);
	VerifyOrReturnError(mSecureSession.HasValue(), CHIP_ERROR_CONNECTION_ABORTED);

	// Don't let method get called on a freed object.
	VerifyOrDie(mExchangeMgr != nullptr && GetReferenceCount() > 0);

	// we hold the exchange context here in case the entity that
	// originally generated it tries to close it as a result of
	// an error arising below. at the end, we have to close it.
	ExchangeHandle ref(*this);

	bool reliableTransmissionRequested = true;

	state = mExchangeMgr->GetSessionMgr()->GetPeerConnectionState(mSecureSession.Value());
	// If sending via UDP and NoAutoRequestAck send flag is not specificed, request reliable transmission.
	if (state != nullptr && state->GetPeerAddress().GetTransportType() != Transport::Type::kUdp)
	{
	reliableTransmissionRequested = false;
	}
	else
	{
	reliableTransmissionRequested = !sendFlags.Has(SendMessageFlags::kNoAutoRequestAck);
	}

	// If a response message is expected...
	if (sendFlags.Has(SendMessageFlags::kExpectResponse))
	{
	// Only one 'response expected' message can be outstanding at a time.
	if (IsResponseExpected())
	{
	// TODO: add a test for this case.
	return CHIP_ERROR_INCORRECT_STATE;
	}

	SetResponseExpected(true);

	// Arm the response timer if a timeout has been specified.
	if (mResponseTimeout > 0)
	{
	CHIP_ERROR err = StartResponseTimer();
	if (err != CHIP_NO_ERROR)
	{
	SetResponseExpected(false);
	return err;
	}
	}
	}

	{
	// Create a new scope for `err`, to avoid shadowing warning previous `err`.
	CHIP_ERROR err = mDispatch->SendMessage(mSecureSession.Value(), mExchangeId, IsInitiator(), GetReliableMessageContext(),
	reliableTransmissionRequested, protocolId, msgType, std::move(msgBuf));
	if (err != CHIP_NO_ERROR && IsResponseExpected())
	{
	CancelResponseTimer();
	SetResponseExpected(false);
	}

	// Standalone acks are not application-level message sends.
	if (err == CHIP_NO_ERROR && !isStandaloneAck)
	{
	MessageHandled();
	}

	return err;
	}
	}

	void ExchangeContext::DoClose(bool clearRetransTable)
	{
	mFlags.Set(Flags::kFlagClosed);

	// Clear protocol callbacks
	if (mDelegate != nullptr)
	{
	mDelegate->OnExchangeClosing(this);
	}
	mDelegate = nullptr;

	// Closure of an exchange context is based on ref counting. The Protocol, when it calls DoClose(), indicates that
	// it is done with the exchange context and the message layer sets all callbacks to NULL and does not send anything
	// received on the exchange context up to higher layers. At this point, the message layer needs to handle the
	// remaining work to be done on that exchange, (e.g. send all pending acks) before truly cleaning it up.
	FlushAcks();

	// In case the protocol wants a harder release of the EC right away, such as calling Abort(), exchange
	// needs to clear the MRP retransmission table immediately.
	if (clearRetransTable)
	{
	mExchangeMgr->GetReliableMessageMgr()->ClearRetransTable(static_cast<ReliableMessageContext *>(this));
	}

	// Cancel the response timer.
	CancelResponseTimer();
	}

	/**
	* Gracefully close an exchange context. This call decrements the
	* reference count and releases the exchange when the reference
	* count goes to zero.
	*
	*/
	void ExchangeContext::Close()
	{
	VerifyOrDie(mExchangeMgr != nullptr && GetReferenceCount() > 0);

	#if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
	ChipLogDetail(ExchangeManager, "ec id: %d [%04" PRIX16 "], %s", (this - mExchangeMgr->mContextPool.begin()), mExchangeId,
	__func__);
	#endif

	DoClose(false);
	Release();
	}
	/**
	* Abort the Exchange context immediately and release all
	* references to it.
	*
	*/
	void ExchangeContext::Abort()
	{
	VerifyOrDie(mExchangeMgr != nullptr && GetReferenceCount() > 0);

	#if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
	ChipLogDetail(ExchangeManager, "ec id: %d [%04" PRIX16 "], %s", (this - mExchangeMgr->mContextPool.begin()), mExchangeId,
	__func__);
	#endif

	DoClose(true);
	Release();
	}

	void ExchangeContextDeletor::Release(ExchangeContext * ec)
	{
	ec->mExchangeMgr->ReleaseContext(ec);
	}

	ExchangeContext::ExchangeContext(ExchangeManager * em, uint16_t ExchangeId, SessionHandle session, bool Initiator,
	ExchangeDelegate * delegate)
	{
	VerifyOrDie(mExchangeMgr == nullptr);

	mExchangeMgr = em;
	mExchangeId = ExchangeId;
	mSecureSession.SetValue(session);
	mFlags.Set(Flags::kFlagInitiator, Initiator);
	mDelegate = delegate;

	ExchangeMessageDispatch * dispatch = nullptr;
	if (delegate != nullptr)
	{
	dispatch = delegate->GetMessageDispatch(em->GetReliableMessageMgr(), em->GetSessionMgr());
	if (dispatch == nullptr)
	{
	dispatch = &em->mDefaultExchangeDispatch;
	}
	}
	else
	{
	dispatch = &em->mDefaultExchangeDispatch;
	}
	VerifyOrDie(dispatch != nullptr);
	mDispatch = dispatch->Retain();

	SetDropAckDebug(false);
	SetAckPending(false);
	SetMsgRcvdFromPeer(false);
	SetAutoRequestAck(true);

	#if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
	ChipLogDetail(ExchangeManager, "ec++ id: %d", ExchangeId);
	#endif
	SYSTEM_STATS_INCREMENT(chip::System::Stats::kExchangeMgr_NumContexts);
	}

	ExchangeContext::~ExchangeContext()
	{
	VerifyOrDie(mExchangeMgr != nullptr && GetReferenceCount() == 0);
	VerifyOrDie(!IsAckPending());

	// Ideally, in this scenario, the retransmit table should
	// be clear of any outstanding messages for this context and
	// the boolean parameter passed to DoClose() should not matter.

	DoClose(false);
	mExchangeMgr = nullptr;

	if (mExchangeACL != nullptr)
	{
	chip::Platform::Delete(mExchangeACL);
	mExchangeACL = nullptr;
	}

	if (mDispatch != nullptr)
	{
	mDispatch->Release();
	mDispatch = nullptr;
	}

	#if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
	ChipLogDetail(ExchangeManager, "ec-- id: %d", mExchangeId);
	#endif
	SYSTEM_STATS_DECREMENT(chip::System::Stats::kExchangeMgr_NumContexts);
	}

	bool ExchangeContext::MatchExchange(SessionHandle session, const PacketHeader & packetHeader, const PayloadHeader & payloadHeader)
	{
	// A given message is part of a particular exchange if...
	return

	// The exchange identifier of the message matches the exchange identifier of the context.
	(mExchangeId == payloadHeader.GetExchangeID())

	// AND The Session ID associated with the incoming message matches the Session ID associated with the exchange.
	&& (mSecureSession.HasValue() && mSecureSession.Value().MatchIncomingSession(session))

	// AND The message was sent by an initiator and the exchange context is a responder (IsInitiator==false)
	// OR The message was sent by a responder and the exchange context is an initiator (IsInitiator==true) (for the broadcast
	// case, the initiator is ill defined)

	&& (payloadHeader.IsInitiator() != IsInitiator());
	}

	void ExchangeContext::OnConnectionExpired()
	{
	// Reset our mSecureSession to a default-initialized (hence not matching any
	// connection state) value, because it's still referencing the now-expired
	// connection. This will mean that no more messages can be sent via this
	// exchange, which seems fine given the semantics of connection expiration.
	mSecureSession.ClearValue();

	if (!IsResponseExpected())
	{
	// Nothing to do in this case
	return;
	}

	// If we're waiting on a response, we now know it's never going to show up
	// and we should notify our delegate accordingly.
	CancelResponseTimer();
	SetResponseExpected(false);
	NotifyResponseTimeout();
	}

	CHIP_ERROR ExchangeContext::StartResponseTimer()
	{
	System::Layer * lSystemLayer = mExchangeMgr->GetSessionMgr()->SystemLayer();
	if (lSystemLayer == nullptr)
	{
	// this is an assertion error, which shall never happen
	return CHIP_ERROR_INTERNAL;
	}

	return lSystemLayer->StartTimer(mResponseTimeout, HandleResponseTimeout, this);
	}

	void ExchangeContext::CancelResponseTimer()
	{
	System::Layer * lSystemLayer = mExchangeMgr->GetSessionMgr()->SystemLayer();
	if (lSystemLayer == nullptr)
	{
	// this is an assertion error, which shall never happen
	return;
	}

	lSystemLayer->CancelTimer(HandleResponseTimeout, this);
	}

	void ExchangeContext::HandleResponseTimeout(System::Layer * aSystemLayer, void * aAppState)
	{
	ExchangeContext * ec = reinterpret_cast<ExchangeContext *>(aAppState);

	if (ec == nullptr)
	return;

	ec->NotifyResponseTimeout();
	}

	void ExchangeContext::NotifyResponseTimeout()
	{
	SetResponseExpected(false);

	ExchangeDelegate * delegate = GetDelegate();

	// Call the user's timeout handler.
	if (delegate != nullptr)
	{
	delegate->OnResponseTimeout(this);
	}

	MessageHandled();
	}

	CHIP_ERROR ExchangeContext::HandleMessage(const PacketHeader & packetHeader, const PayloadHeader & payloadHeader,
	const Transport::PeerAddress & peerAddress, MessageFlags msgFlags,
	PacketBufferHandle && msgBuf)
	{
	// We hold a reference to the ExchangeContext here to
	// guard against Close() calls(decrementing the reference
	// count) by the protocol before the CHIP Exchange
	// layer has completed its work on the ExchangeContext.
	ExchangeHandle ref(*this);

	// Keep track of whether we're nested under an outer HandleMessage
	// invocation.
	bool alreadyHandlingMessage = mFlags.Has(Flags::kFlagHandlingMessage);
	mFlags.Set(Flags::kFlagHandlingMessage);

	bool isStandaloneAck = payloadHeader.HasMessageType(Protocols::SecureChannel::MsgType::StandaloneAck);
	bool isDuplicate = msgFlags.Has(MessageFlagValues::kDuplicateMessage);

	auto deferred = MakeDefer([&]() {
	// The alreadyHandlingMessage check is effectively a workaround for the fact that SendMessage() is not calling
	// MessageHandled() yet and will go away when we fix that.
	if (alreadyHandlingMessage)
	{
	// Don't close if there's an outer HandleMessage invocation. It'll deal with the closing.
	return;
	}
	// We are the outermost HandleMessage invocation. We're not handling a message anymore.
	mFlags.Clear(Flags::kFlagHandlingMessage);

	// Duplicates and standalone acks are not application-level messages, so they should generally not lead to any state
	// changes. The one exception to that is that if we have a null mDelegate then our lifetime is not application-defined,
	// since we don't interact with the application at that point. That can happen when we are already closed (in which case
	// MessageHandled is a no-op) or if we were just created to send a standalone ack for this incoming message, in which case
	// we should treat it as an app-level message for purposes of our state.
	if ((isStandaloneAck \|\| isDuplicate) && mDelegate != nullptr)
	{
	return;
	}

	MessageHandled();
	});

	ReturnErrorOnFailure(mDispatch->OnMessageReceived(packetHeader.GetFlags(), payloadHeader, packetHeader.GetMessageId(),
	peerAddress, msgFlags, GetReliableMessageContext()));

	if (IsAckPending() && !mDelegate)
	{
	// The incoming message wants an ack, but we have no delegate, so
	// there's not going to be a response to piggyback on. Just flush the
	// ack out right now.
	ReturnErrorOnFailure(FlushAcks());
	}

	// The SecureChannel::StandaloneAck message type is only used for MRP; do not pass such messages to the application layer.
	if (isStandaloneAck)
	{
	return CHIP_NO_ERROR;
	}

	// Since the message is duplicate, let's not forward it up the stack
	if (isDuplicate)
	{
	return CHIP_NO_ERROR;
	}

	// Since we got the response, cancel the response timer.
	CancelResponseTimer();

	// If the context was expecting a response to a previously sent message, this message
	// is implicitly that response.
	SetResponseExpected(false);

	if (mDelegate != nullptr)
	{
	return mDelegate->OnMessageReceived(this, packetHeader, payloadHeader, std::move(msgBuf));
	}
	else
	{
	DefaultOnMessageReceived(this, packetHeader, payloadHeader.GetProtocolID(), payloadHeader.GetMessageType(),
	std::move(msgBuf));
	return CHIP_NO_ERROR;
	}
	}

	void ExchangeContext::MessageHandled()
	{
	if (mFlags.Has(Flags::kFlagClosed) \|\| IsResponseExpected() \|\| IsSendExpected())
	{
	return;
	}

	Close();
	}

	} // namespace Messaging
	} // namespace chip