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

 #if CONFIG_DEVICE_LAYER
 #include <platform/CHIPDeviceLayer.h>
 #endif

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

 namespace chip {
 namespace Messaging {

 static void DefaultOnMessageReceived(ExchangeContext * ec, Protocols::Id protocolId, uint8_t msgType, uint32_t messageCounter,
                                      PacketBufferHandle && payload)
 {
     ChipLogError(ExchangeManager,
                  "Dropping unexpected message of type " ChipLogFormatMessageType " with protocolId " ChipLogFormatProtocolId
                  " and MessageCounter:" ChipLogFormatMessageCounter " on exchange " ChipLogFormatExchange,
                  msgType, ChipLogValueProtocolId(protocolId), messageCounter, ChipLogValueExchange(ec));
 }

 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;
 }

 #if CONFIG_DEVICE_LAYER && CHIP_DEVICE_CONFIG_ENABLE_SED
 void ExchangeContext::UpdateSEDPollingMode()
 {
     if (!HasSessionHandle())
     {
         // After the session has been deleted, no further communication can occur on the exchange,
         // so withdraw a SED fast-polling mode request.
         UpdateSEDPollingMode(false);
         return;
     }

     Transport::PeerAddress address;

     switch (GetSessionHandle()->GetSessionType())
     {
     case Transport::Session::SessionType::kSecure:
         address = GetSessionHandle()->AsSecureSession()->GetPeerAddress();
         break;
     case Transport::Session::SessionType::kUnauthenticated:
         address = GetSessionHandle()->AsUnauthenticatedSession()->GetPeerAddress();
         break;
     default:
         return;
     }

     VerifyOrReturn(address.GetTransportType() != Transport::Type::kBle);
     UpdateSEDPollingMode(IsResponseExpected() || IsSendExpected() || IsMessageNotAcked());
 }

 void ExchangeContext::UpdateSEDPollingMode(bool fastPollingMode)
 {
     if (fastPollingMode != IsRequestingFastPollingMode())
     {
         SetRequestingFastPollingMode(fastPollingMode);
         DeviceLayer::ConnectivityMgr().RequestSEDFastPollingMode(fastPollingMode);
     }
 }
 #endif

 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);
     }

     VerifyOrReturnError(mExchangeMgr != nullptr, CHIP_ERROR_INTERNAL);
     VerifyOrReturnError(mSession, 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);

     // If session requires MRP, NoAutoRequestAck send flag is not specified and is not a group exchange context, request reliable
     // transmission.
     bool reliableTransmissionRequested =
         GetSessionHandle()->RequireMRP() && !sendFlags.Has(SendMessageFlags::kNoAutoRequestAck) && !IsGroupExchangeContext();

     // If a response message is expected...
     if (sendFlags.Has(SendMessageFlags::kExpectResponse) && !IsGroupExchangeContext())
     {
         // 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 > System::Clock::kZero)
         {
             CHIP_ERROR err = StartResponseTimer();
             if (err != CHIP_NO_ERROR)
             {
                 SetResponseExpected(false);
                 return err;
             }
         }
     }

     {
         // ExchangeContext for group are supposed to always be Initiator
         if (IsGroupExchangeContext() && !IsInitiator())
         {
             return CHIP_ERROR_INTERNAL;
         }

         // Create a new scope for `err`, to avoid shadowing warning previous `err`.
         CHIP_ERROR err = mDispatch.SendMessage(GetExchangeMgr()->GetSessionManager(), mSession.Get(), 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(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 - close[" ChipLogFormatExchange "], %s", ChipLogValueExchange(this), __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 - abort[" ChipLogFormatExchange "], %s", ChipLogValueExchange(this), __func__);
 #endif

     DoClose(true);
     Release();
 }

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

 ExchangeContext::ExchangeContext(ExchangeManager * em, uint16_t ExchangeId, const SessionHandle & session, bool Initiator,
                                  ExchangeDelegate * delegate) :
     mDispatch((delegate != nullptr) ? delegate->GetMessageDispatch() : ApplicationExchangeDispatch::Instance()),
     mSession(*this)
 {
     VerifyOrDie(mExchangeMgr == nullptr);

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

     SetDropAckDebug(false);
     SetAckPending(false);
     SetMsgRcvdFromPeer(false);

     // Do not request Ack for multicast
     SetAutoRequestAck(!session->IsGroupSession());

 #if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
     ChipLogDetail(ExchangeManager, "ec++ id: " ChipLogFormatExchange, ChipLogValueExchange(this));
 #endif
     SYSTEM_STATS_INCREMENT(chip::System::Stats::kExchangeMgr_NumContexts);
 }

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

 #if CONFIG_DEVICE_LAYER && CHIP_DEVICE_CONFIG_ENABLE_SED
     // Make sure that the exchange withdraws the request for Sleepy End Device fast-polling mode.
     UpdateSEDPollingMode(false);
 #endif

     // 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 defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
     ChipLogDetail(ExchangeManager, "ec-- id: " ChipLogFormatExchange, ChipLogValueExchange(this));
 #endif
     SYSTEM_STATS_DECREMENT(chip::System::Stats::kExchangeMgr_NumContexts);
 }

 bool ExchangeContext::MatchExchange(const 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 associated with the incoming message matches the Session associated with the exchange.
         && (mSession.Contains(session))

         // TODO: This check should be already implied by the equality of session check,
         // It should be removed after we have implemented the temporary node id for PASE and CASE sessions
         && (IsEncryptionRequired() == packetHeader.IsEncrypted())

         // 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::OnSessionReleased()
 {
     if (mFlags.Has(Flags::kFlagClosed))
     {
         // Exchange is already being closed. It may occur when closing an exchange after sending
         // RemoveFabric response which triggers removal of all sessions for the given fabric.
         return;
     }

     ExchangeHandle ref(*this);

     if (IsResponseExpected())
     {
         // 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();
     }

     DoClose(true /* clearRetransTable */);
 }

 CHIP_ERROR ExchangeContext::StartResponseTimer()
 {
     System::Layer * lSystemLayer = mExchangeMgr->GetSessionManager()->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->GetSessionManager()->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(uint32_t messageCounter, 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(messageCounter, payloadHeader, 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, payloadHeader, std::move(msgBuf));
     }

     DefaultOnMessageReceived(this, payloadHeader.GetProtocolID(), payloadHeader.GetMessageType(), messageCounter,
                              std::move(msgBuf));
     return CHIP_NO_ERROR;
 }

 void ExchangeContext::MessageHandled()
 {
 #if CONFIG_DEVICE_LAYER && CHIP_DEVICE_CONFIG_ENABLE_SED
     UpdateSEDPollingMode();
 #endif

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

	#if CONFIG_DEVICE_LAYER
	#include <platform/CHIPDeviceLayer.h>
	#endif

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

	namespace chip {
	namespace Messaging {

	static void DefaultOnMessageReceived(ExchangeContext * ec, Protocols::Id protocolId, uint8_t msgType, uint32_t messageCounter,
	PacketBufferHandle && payload)
	{
	ChipLogError(ExchangeManager,
	"Dropping unexpected message of type " ChipLogFormatMessageType " with protocolId " ChipLogFormatProtocolId
	" and MessageCounter:" ChipLogFormatMessageCounter " on exchange " ChipLogFormatExchange,
	msgType, ChipLogValueProtocolId(protocolId), messageCounter, ChipLogValueExchange(ec));
	}

	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;
	}

	#if CONFIG_DEVICE_LAYER && CHIP_DEVICE_CONFIG_ENABLE_SED
	void ExchangeContext::UpdateSEDPollingMode()
	{
	if (!HasSessionHandle())
	{
	// After the session has been deleted, no further communication can occur on the exchange,
	// so withdraw a SED fast-polling mode request.
	UpdateSEDPollingMode(false);
	return;
	}

	Transport::PeerAddress address;

	switch (GetSessionHandle()->GetSessionType())
	{
	case Transport::Session::SessionType::kSecure:
	address = GetSessionHandle()->AsSecureSession()->GetPeerAddress();
	break;
	case Transport::Session::SessionType::kUnauthenticated:
	address = GetSessionHandle()->AsUnauthenticatedSession()->GetPeerAddress();
	break;
	default:
	return;
	}

	VerifyOrReturn(address.GetTransportType() != Transport::Type::kBle);
	UpdateSEDPollingMode(IsResponseExpected() \|\| IsSendExpected() \|\| IsMessageNotAcked());
	}

	void ExchangeContext::UpdateSEDPollingMode(bool fastPollingMode)
	{
	if (fastPollingMode != IsRequestingFastPollingMode())
	{
	SetRequestingFastPollingMode(fastPollingMode);
	DeviceLayer::ConnectivityMgr().RequestSEDFastPollingMode(fastPollingMode);
	}
	}
	#endif

	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);
	}

	VerifyOrReturnError(mExchangeMgr != nullptr, CHIP_ERROR_INTERNAL);
	VerifyOrReturnError(mSession, 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);

	// If session requires MRP, NoAutoRequestAck send flag is not specified and is not a group exchange context, request reliable
	// transmission.
	bool reliableTransmissionRequested =
	GetSessionHandle()->RequireMRP() && !sendFlags.Has(SendMessageFlags::kNoAutoRequestAck) && !IsGroupExchangeContext();

	// If a response message is expected...
	if (sendFlags.Has(SendMessageFlags::kExpectResponse) && !IsGroupExchangeContext())
	{
	// 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 > System::Clock::kZero)
	{
	CHIP_ERROR err = StartResponseTimer();
	if (err != CHIP_NO_ERROR)
	{
	SetResponseExpected(false);
	return err;
	}
	}
	}

	{
	// ExchangeContext for group are supposed to always be Initiator
	if (IsGroupExchangeContext() && !IsInitiator())
	{
	return CHIP_ERROR_INTERNAL;
	}

	// Create a new scope for `err`, to avoid shadowing warning previous `err`.
	CHIP_ERROR err = mDispatch.SendMessage(GetExchangeMgr()->GetSessionManager(), mSession.Get(), 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(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 - close[" ChipLogFormatExchange "], %s", ChipLogValueExchange(this), __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 - abort[" ChipLogFormatExchange "], %s", ChipLogValueExchange(this), __func__);
	#endif

	DoClose(true);
	Release();
	}

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

	ExchangeContext::ExchangeContext(ExchangeManager * em, uint16_t ExchangeId, const SessionHandle & session, bool Initiator,
	ExchangeDelegate * delegate) :
	mDispatch((delegate != nullptr) ? delegate->GetMessageDispatch() : ApplicationExchangeDispatch::Instance()),
	mSession(*this)
	{
	VerifyOrDie(mExchangeMgr == nullptr);

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

	SetDropAckDebug(false);
	SetAckPending(false);
	SetMsgRcvdFromPeer(false);

	// Do not request Ack for multicast
	SetAutoRequestAck(!session->IsGroupSession());

	#if defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
	ChipLogDetail(ExchangeManager, "ec++ id: " ChipLogFormatExchange, ChipLogValueExchange(this));
	#endif
	SYSTEM_STATS_INCREMENT(chip::System::Stats::kExchangeMgr_NumContexts);
	}

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

	#if CONFIG_DEVICE_LAYER && CHIP_DEVICE_CONFIG_ENABLE_SED
	// Make sure that the exchange withdraws the request for Sleepy End Device fast-polling mode.
	UpdateSEDPollingMode(false);
	#endif

	// 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 defined(CHIP_EXCHANGE_CONTEXT_DETAIL_LOGGING)
	ChipLogDetail(ExchangeManager, "ec-- id: " ChipLogFormatExchange, ChipLogValueExchange(this));
	#endif
	SYSTEM_STATS_DECREMENT(chip::System::Stats::kExchangeMgr_NumContexts);
	}

	bool ExchangeContext::MatchExchange(const 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 associated with the incoming message matches the Session associated with the exchange.
	&& (mSession.Contains(session))

	// TODO: This check should be already implied by the equality of session check,
	// It should be removed after we have implemented the temporary node id for PASE and CASE sessions
	&& (IsEncryptionRequired() == packetHeader.IsEncrypted())

	// 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::OnSessionReleased()
	{
	if (mFlags.Has(Flags::kFlagClosed))
	{
	// Exchange is already being closed. It may occur when closing an exchange after sending
	// RemoveFabric response which triggers removal of all sessions for the given fabric.
	return;
	}

	ExchangeHandle ref(*this);

	if (IsResponseExpected())
	{
	// 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();
	}

	DoClose(true /* clearRetransTable */);
	}

	CHIP_ERROR ExchangeContext::StartResponseTimer()
	{
	System::Layer * lSystemLayer = mExchangeMgr->GetSessionManager()->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->GetSessionManager()->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(uint32_t messageCounter, 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(messageCounter, payloadHeader, 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, payloadHeader, std::move(msgBuf));
	}

	DefaultOnMessageReceived(this, payloadHeader.GetProtocolID(), payloadHeader.GetMessageType(), messageCounter,
	std::move(msgBuf));
	return CHIP_NO_ERROR;
	}

	void ExchangeContext::MessageHandled()
	{
	#if CONFIG_DEVICE_LAYER && CHIP_DEVICE_CONFIG_ENABLE_SED
	UpdateSEDPollingMode();
	#endif

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

	Close();
	}

	} // namespace Messaging
	} // namespace chip