src/transport/raw/TCP.cpp - third_party/github/project-chip/connectedhomeip - Git at Google

 /*
  *
  *    Copyright (c) 2020-2021 Project CHIP Authors
  *    Copyright (c) 2013-2017 Nest Labs, Inc.
  *    All rights reserved.
  *
  *    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 CHIP Transport object that maintains TCP connections
  *      to peers. Handles both establishing new connections and accepting peer connection
  *      requests.
  */
 #include <transport/raw/TCP.h>

 #include <lib/core/CHIPEncoding.h>
 #include <lib/support/CodeUtils.h>
 #include <lib/support/logging/CHIPLogging.h>
 #include <transport/raw/MessageHeader.h>

 #include <inttypes.h>
 #include <limits>

 namespace chip {
 namespace Transport {
 namespace {

 using namespace chip::Encoding;

 // Packets start with a 16-bit size
 constexpr size_t kPacketSizeBytes = 2;

 // TODO: Actual limit may be lower (spec issue #2119)
 constexpr uint16_t kMaxMessageSize = static_cast<uint16_t>(System::PacketBuffer::kMaxSizeWithoutReserve - kPacketSizeBytes);

 constexpr int kListenBacklogSize = 2;

 } // namespace

 TCPBase::~TCPBase()
 {
     if (mListenSocket != nullptr)
     {
         // endpoint is only non null if it is initialized and listening
         mListenSocket->Free();
         mListenSocket = nullptr;
     }

     CloseActiveConnections();
 }

 void TCPBase::CloseActiveConnections()
 {
     for (size_t i = 0; i < mActiveConnectionsSize; i++)
     {
         if (mActiveConnections[i].InUse())
         {
             mActiveConnections[i].Free();
             mUsedEndPointCount--;
         }
     }
 }

 CHIP_ERROR TCPBase::Init(TcpListenParameters & params)
 {
     CHIP_ERROR err = CHIP_NO_ERROR;

     VerifyOrExit(mState == State::kNotReady, err = CHIP_ERROR_INCORRECT_STATE);

 #if INET_CONFIG_ENABLE_TCP_ENDPOINT
     err = params.GetEndPointManager()->NewEndPoint(&mListenSocket);
 #else
     err = CHIP_ERROR_UNSUPPORTED_CHIP_FEATURE;
 #endif
     SuccessOrExit(err);

     err = mListenSocket->Bind(params.GetAddressType(), Inet::IPAddress::Any, params.GetListenPort(),
                               params.GetInterfaceId().IsPresent());
     SuccessOrExit(err);

     err = mListenSocket->Listen(kListenBacklogSize);
     SuccessOrExit(err);

     mListenSocket->mAppState            = reinterpret_cast<void *>(this);
     mListenSocket->OnDataReceived       = OnTcpReceive;
     mListenSocket->OnConnectComplete    = OnConnectionComplete;
     mListenSocket->OnConnectionClosed   = OnConnectionClosed;
     mListenSocket->OnConnectionReceived = OnConnectionReceived;
     mListenSocket->OnAcceptError        = OnAcceptError;
     mEndpointType                       = params.GetAddressType();

     mState = State::kInitialized;

 exit:
     if (err != CHIP_NO_ERROR)
     {
         ChipLogError(Inet, "Failed to initialize TCP transport: %s", ErrorStr(err));
         if (mListenSocket)
         {
             mListenSocket->Free();
             mListenSocket = nullptr;
         }
     }

     return err;
 }

 void TCPBase::Close()
 {
     if (mListenSocket)
     {
         mListenSocket->Free();
         mListenSocket = nullptr;
     }
     mState = State::kNotReady;
 }

 TCPBase::ActiveConnectionState * TCPBase::FindActiveConnection(const PeerAddress & address)
 {
     if (address.GetTransportType() != Type::kTcp)
     {
         return nullptr;
     }

     for (size_t i = 0; i < mActiveConnectionsSize; i++)
     {
         if (!mActiveConnections[i].InUse())
         {
             continue;
         }
         Inet::IPAddress addr;
         uint16_t port;
         mActiveConnections[i].mEndPoint->GetPeerInfo(&addr, &port);

         if ((addr == address.GetIPAddress()) && (port == address.GetPort()))
         {
             return &mActiveConnections[i];
         }
     }

     return nullptr;
 }

 TCPBase::ActiveConnectionState * TCPBase::FindActiveConnection(const Inet::TCPEndPoint * endPoint)
 {
     for (size_t i = 0; i < mActiveConnectionsSize; i++)
     {
         if (mActiveConnections[i].mEndPoint == endPoint)
         {
             return &mActiveConnections[i];
         }
     }
     return nullptr;
 }

 CHIP_ERROR TCPBase::SendMessage(const Transport::PeerAddress & address, System::PacketBufferHandle && msgBuf)
 {
     // Sent buffer data format is:
     //    - packet size as a uint16_t
     //    - actual data

     VerifyOrReturnError(address.GetTransportType() == Type::kTcp, CHIP_ERROR_INVALID_ARGUMENT);
     VerifyOrReturnError(mState == State::kInitialized, CHIP_ERROR_INCORRECT_STATE);
     VerifyOrReturnError(kPacketSizeBytes + msgBuf->DataLength() <= std::numeric_limits<uint16_t>::max(),
                         CHIP_ERROR_INVALID_ARGUMENT);

     // The check above about kPacketSizeBytes + msgBuf->DataLength() means it definitely fits in uint16_t.
     VerifyOrReturnError(msgBuf->EnsureReservedSize(static_cast<uint16_t>(kPacketSizeBytes)), CHIP_ERROR_NO_MEMORY);

     msgBuf->SetStart(msgBuf->Start() - kPacketSizeBytes);

     uint8_t * output = msgBuf->Start();
     LittleEndian::Write16(output, static_cast<uint16_t>(msgBuf->DataLength() - kPacketSizeBytes));

     // Reuse existing connection if one exists, otherwise a new one
     // will be established
     ActiveConnectionState * connection = FindActiveConnection(address);

     if (connection != nullptr)
     {
         return connection->mEndPoint->Send(std::move(msgBuf));
     }

     return SendAfterConnect(address, std::move(msgBuf));
 }

 CHIP_ERROR TCPBase::SendAfterConnect(const PeerAddress & addr, System::PacketBufferHandle && msg)
 {
     // This will initiate a connection to the specified peer
     bool alreadyConnecting = false;

     // Iterate through the ENTIRE array. If a pending packet for
     // the address already exists, this means a connection is pending and
     // does NOT need to be re-established.
     mPendingPackets.ForEachActiveObject([&](PendingPacket * pending) {
         if (pending->mPeerAddress == addr)
         {
             // same destination exists.
             alreadyConnecting = true;
             pending->mPacketBuffer->AddToEnd(std::move(msg));
             return Loop::Break;
         }
         return Loop::Continue;
     });

     // If already connecting, buffer was just enqueued for more sending
     if (alreadyConnecting)
     {
         return CHIP_NO_ERROR;
     }

     // Ensures sufficient active connections size exist
     VerifyOrReturnError(mUsedEndPointCount < mActiveConnectionsSize, CHIP_ERROR_NO_MEMORY);

 #if INET_CONFIG_ENABLE_TCP_ENDPOINT
     Inet::TCPEndPoint * endPoint = nullptr;
     ReturnErrorOnFailure(mListenSocket->GetEndPointManager().NewEndPoint(&endPoint));
     auto EndPointDeletor = [](Inet::TCPEndPoint * e) { e->Free(); };
     std::unique_ptr<Inet::TCPEndPoint, decltype(EndPointDeletor)> endPointHolder(endPoint, EndPointDeletor);

     endPoint->mAppState            = reinterpret_cast<void *>(this);
     endPoint->OnDataReceived       = OnTcpReceive;
     endPoint->OnConnectComplete    = OnConnectionComplete;
     endPoint->OnConnectionClosed   = OnConnectionClosed;
     endPoint->OnConnectionReceived = OnConnectionReceived;
     endPoint->OnAcceptError        = OnAcceptError;
     endPoint->OnPeerClose          = OnPeerClosed;

     ReturnErrorOnFailure(endPoint->Connect(addr.GetIPAddress(), addr.GetPort(), addr.GetInterface()));

     // enqueue the packet once the connection succeeds
     VerifyOrReturnError(mPendingPackets.CreateObject(addr, std::move(msg)) != nullptr, CHIP_ERROR_NO_MEMORY);
     mUsedEndPointCount++;

     endPointHolder.release();

     return CHIP_NO_ERROR;
 #else
     return CHIP_ERROR_UNSUPPORTED_CHIP_FEATURE;
 #endif
 }

 CHIP_ERROR TCPBase::ProcessReceivedBuffer(Inet::TCPEndPoint * endPoint, const PeerAddress & peerAddress,
                                           System::PacketBufferHandle && buffer)
 {
     ActiveConnectionState * state = FindActiveConnection(endPoint);
     VerifyOrReturnError(state != nullptr, CHIP_ERROR_INTERNAL);
     state->mReceived.AddToEnd(std::move(buffer));

     while (!state->mReceived.IsNull())
     {
         uint8_t messageSizeBuf[kPacketSizeBytes];
         CHIP_ERROR err = state->mReceived->Read(messageSizeBuf);
         if (err == CHIP_ERROR_BUFFER_TOO_SMALL)
         {
             // We don't have enough data to read the message size. Wait until there's more.
             return CHIP_NO_ERROR;
         }
         if (err != CHIP_NO_ERROR)
         {
             return err;
         }
         uint16_t messageSize = LittleEndian::Get16(messageSizeBuf);
         if (messageSize >= kMaxMessageSize)
         {
             // This message is too long for upper layers.
             return CHIP_ERROR_MESSAGE_TOO_LONG;
         }
         // The subtraction will not underflow because we successfully read kPacketSizeBytes.
         if (messageSize > (state->mReceived->TotalLength() - kPacketSizeBytes))
         {
             // We have not yet received the complete message.
             return CHIP_NO_ERROR;
         }
         state->mReceived.Consume(kPacketSizeBytes);
         ReturnErrorOnFailure(ProcessSingleMessage(peerAddress, state, messageSize));
     }

     return CHIP_NO_ERROR;
 }

 CHIP_ERROR TCPBase::ProcessSingleMessage(const PeerAddress & peerAddress, ActiveConnectionState * state, uint16_t messageSize)
 {
     // We enter with `state->mReceived` containing at least one full message, perhaps in a chain.
     // `state->mReceived->Start()` currently points to the message data.
     // On exit, `state->mReceived` will have had `messageSize` bytes consumed, no matter what.
     System::PacketBufferHandle message;
     if (state->mReceived->DataLength() == messageSize)
     {
         // In this case, the head packet buffer contains exactly the message.
         // This is common because typical messages fit in a network packet, and are delivered as such.
         // Peel off the head to pass upstream, which effectively consumes it from `state->mReceived`.
         message = state->mReceived.PopHead();
     }
     else
     {
         // The message is either longer or shorter than the head buffer.
         // In either case, copy the message to a fresh linear buffer to pass upstream. We always copy, rather than provide
         // a shared reference to the current buffer, in case upper layers manipulate the buffer in ways that would affect
         // our use, e.g. chaining it elsewhere or reusing space beyond the current message.
         message = System::PacketBufferHandle::New(messageSize, 0);
         if (message.IsNull())
         {
             return CHIP_ERROR_NO_MEMORY;
         }
         CHIP_ERROR err = state->mReceived->Read(message->Start(), messageSize);
         state->mReceived.Consume(messageSize);
         ReturnErrorOnFailure(err);
         message->SetDataLength(messageSize);
     }

     HandleMessageReceived(peerAddress, std::move(message));
     return CHIP_NO_ERROR;
 }

 void TCPBase::ReleaseActiveConnection(Inet::TCPEndPoint * endPoint)
 {
     for (size_t i = 0; i < mActiveConnectionsSize; i++)
     {
         if (mActiveConnections[i].mEndPoint == endPoint)
         {
             mActiveConnections[i].Free();
             mUsedEndPointCount--;
         }
     }
 }

 CHIP_ERROR TCPBase::OnTcpReceive(Inet::TCPEndPoint * endPoint, System::PacketBufferHandle && buffer)
 {
     Inet::IPAddress ipAddress;
     uint16_t port;
     Inet::InterfaceId interfaceId;

     endPoint->GetPeerInfo(&ipAddress, &port);
     endPoint->GetInterfaceId(&interfaceId);
     PeerAddress peerAddress = PeerAddress::TCP(ipAddress, port, interfaceId);

     TCPBase * tcp  = reinterpret_cast<TCPBase *>(endPoint->mAppState);
     CHIP_ERROR err = tcp->ProcessReceivedBuffer(endPoint, peerAddress, std::move(buffer));

     if (err != CHIP_NO_ERROR)
     {
         // Connection could need to be closed at this point
         ChipLogError(Inet, "Failed to accept received TCP message: %s", ErrorStr(err));
         return CHIP_ERROR_UNEXPECTED_EVENT;
     }
     return CHIP_NO_ERROR;
 }

 void TCPBase::OnConnectionComplete(Inet::TCPEndPoint * endPoint, CHIP_ERROR inetErr)
 {
     CHIP_ERROR err          = CHIP_NO_ERROR;
     bool foundPendingPacket = false;
     TCPBase * tcp           = reinterpret_cast<TCPBase *>(endPoint->mAppState);
     Inet::IPAddress ipAddress;
     uint16_t port;
     Inet::InterfaceId interfaceId;

     endPoint->GetPeerInfo(&ipAddress, &port);
     endPoint->GetInterfaceId(&interfaceId);
     PeerAddress addr = PeerAddress::TCP(ipAddress, port, interfaceId);

     // Send any pending packets
     tcp->mPendingPackets.ForEachActiveObject([&](PendingPacket * pending) {
         if (pending->mPeerAddress == addr)
         {
             foundPendingPacket                = true;
             System::PacketBufferHandle buffer = std::move(pending->mPacketBuffer);
             tcp->mPendingPackets.ReleaseObject(pending);

             if ((inetErr == CHIP_NO_ERROR) && (err == CHIP_NO_ERROR))
             {
                 err = endPoint->Send(std::move(buffer));
             }
         }
         return Loop::Continue;
     });

     if (err == CHIP_NO_ERROR)
     {
         err = inetErr;
     }

     if (!foundPendingPacket && (err == CHIP_NO_ERROR))
     {
         // Force a close: new connections are only expected when a
         // new buffer is being sent.
         ChipLogError(Inet, "Connection accepted without pending buffers");
         err = CHIP_ERROR_CONNECTION_CLOSED_UNEXPECTEDLY;
     }

     // cleanup packets or mark as free
     if (err != CHIP_NO_ERROR)
     {
         ChipLogError(Inet, "Connection complete encountered an error: %s", ErrorStr(err));
         endPoint->Free();
         tcp->mUsedEndPointCount--;
     }
     else
     {
         bool connectionStored = false;
         for (size_t i = 0; i < tcp->mActiveConnectionsSize; i++)
         {
             if (!tcp->mActiveConnections[i].InUse())
             {
                 tcp->mActiveConnections[i].Init(endPoint);
                 connectionStored = true;
                 break;
             }
         }

         // since we track end points counts, we always expect to store the
         // connection.
         if (!connectionStored)
         {
             endPoint->Free();
             ChipLogError(Inet, "Internal logic error: insufficient space to store active connection");
         }
     }
 }

 void TCPBase::OnConnectionClosed(Inet::TCPEndPoint * endPoint, CHIP_ERROR err)
 {
     TCPBase * tcp = reinterpret_cast<TCPBase *>(endPoint->mAppState);

     ChipLogProgress(Inet, "Connection closed.");

     ChipLogProgress(Inet, "Freeing closed connection.");
     tcp->ReleaseActiveConnection(endPoint);
 }

 void TCPBase::OnConnectionReceived(Inet::TCPEndPoint * listenEndPoint, Inet::TCPEndPoint * endPoint,
                                    const Inet::IPAddress & peerAddress, uint16_t peerPort)
 {
     TCPBase * tcp = reinterpret_cast<TCPBase *>(listenEndPoint->mAppState);

     if (tcp->mUsedEndPointCount < tcp->mActiveConnectionsSize)
     {
         // have space to use one more (even if considering pending connections)
         for (size_t i = 0; i < tcp->mActiveConnectionsSize; i++)
         {
             if (!tcp->mActiveConnections[i].InUse())
             {
                 tcp->mActiveConnections[i].Init(endPoint);
                 tcp->mUsedEndPointCount++;
                 break;
             }
         }

         endPoint->mAppState            = listenEndPoint->mAppState;
         endPoint->OnDataReceived       = OnTcpReceive;
         endPoint->OnConnectComplete    = OnConnectionComplete;
         endPoint->OnConnectionClosed   = OnConnectionClosed;
         endPoint->OnConnectionReceived = OnConnectionReceived;
         endPoint->OnAcceptError        = OnAcceptError;
         endPoint->OnPeerClose          = OnPeerClosed;
     }
     else
     {
         ChipLogError(Inet, "Insufficient connection space to accept new connections");
         endPoint->Free();
     }
 }

 void TCPBase::OnAcceptError(Inet::TCPEndPoint * endPoint, CHIP_ERROR err)
 {
     ChipLogError(Inet, "Accept error: %s", ErrorStr(err));
 }

 void TCPBase::Disconnect(const PeerAddress & address)
 {
     // Closes an existing connection
     for (size_t i = 0; i < mActiveConnectionsSize; i++)
     {
         if (mActiveConnections[i].InUse())
         {
             Inet::IPAddress ipAddress;
             uint16_t port;
             Inet::InterfaceId interfaceId;

             mActiveConnections[i].mEndPoint->GetPeerInfo(&ipAddress, &port);
             mActiveConnections[i].mEndPoint->GetInterfaceId(&interfaceId);
             if (address == PeerAddress::TCP(ipAddress, port, interfaceId))
             {
                 // NOTE: this leaves the socket in TIME_WAIT.
                 // Calling Abort() would clean it since SO_LINGER would be set to 0,
                 // however this seems not to be useful.
                 mActiveConnections[i].Free();
                 mUsedEndPointCount--;
             }
         }
     }
 }

 void TCPBase::OnPeerClosed(Inet::TCPEndPoint * endPoint)
 {
     TCPBase * tcp = reinterpret_cast<TCPBase *>(endPoint->mAppState);

     ChipLogProgress(Inet, "Freeing connection: connection closed by peer");

     tcp->ReleaseActiveConnection(endPoint);
 }

 bool TCPBase::HasActiveConnections() const
 {
     for (size_t i = 0; i < mActiveConnectionsSize; i++)
     {
         if (mActiveConnections[i].InUse())
         {
             return true;
         }
     }

     return false;
 }

 } // namespace Transport
 } // namespace chip
	/*
	*
	* Copyright (c) 2020-2021 Project CHIP Authors
	* Copyright (c) 2013-2017 Nest Labs, Inc.
	* All rights reserved.
	*
	* 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 CHIP Transport object that maintains TCP connections
	* to peers. Handles both establishing new connections and accepting peer connection
	* requests.
	*/
	#include <transport/raw/TCP.h>

	#include <lib/core/CHIPEncoding.h>
	#include <lib/support/CodeUtils.h>
	#include <lib/support/logging/CHIPLogging.h>
	#include <transport/raw/MessageHeader.h>

	#include <inttypes.h>
	#include <limits>

	namespace chip {
	namespace Transport {
	namespace {

	using namespace chip::Encoding;

	// Packets start with a 16-bit size
	constexpr size_t kPacketSizeBytes = 2;

	// TODO: Actual limit may be lower (spec issue #2119)
	constexpr uint16_t kMaxMessageSize = static_cast<uint16_t>(System::PacketBuffer::kMaxSizeWithoutReserve - kPacketSizeBytes);

	constexpr int kListenBacklogSize = 2;

	} // namespace

	TCPBase::~TCPBase()
	{
	if (mListenSocket != nullptr)
	{
	// endpoint is only non null if it is initialized and listening
	mListenSocket->Free();
	mListenSocket = nullptr;
	}

	CloseActiveConnections();
	}

	void TCPBase::CloseActiveConnections()
	{
	for (size_t i = 0; i < mActiveConnectionsSize; i++)
	{
	if (mActiveConnections[i].InUse())
	{
	mActiveConnections[i].Free();
	mUsedEndPointCount--;
	}
	}
	}

	CHIP_ERROR TCPBase::Init(TcpListenParameters & params)
	{
	CHIP_ERROR err = CHIP_NO_ERROR;

	VerifyOrExit(mState == State::kNotReady, err = CHIP_ERROR_INCORRECT_STATE);

	#if INET_CONFIG_ENABLE_TCP_ENDPOINT
	err = params.GetEndPointManager()->NewEndPoint(&mListenSocket);
	#else
	err = CHIP_ERROR_UNSUPPORTED_CHIP_FEATURE;
	#endif
	SuccessOrExit(err);

	err = mListenSocket->Bind(params.GetAddressType(), Inet::IPAddress::Any, params.GetListenPort(),
	params.GetInterfaceId().IsPresent());
	SuccessOrExit(err);

	err = mListenSocket->Listen(kListenBacklogSize);
	SuccessOrExit(err);

	mListenSocket->mAppState = reinterpret_cast<void *>(this);
	mListenSocket->OnDataReceived = OnTcpReceive;
	mListenSocket->OnConnectComplete = OnConnectionComplete;
	mListenSocket->OnConnectionClosed = OnConnectionClosed;
	mListenSocket->OnConnectionReceived = OnConnectionReceived;
	mListenSocket->OnAcceptError = OnAcceptError;
	mEndpointType = params.GetAddressType();

	mState = State::kInitialized;

	exit:
	if (err != CHIP_NO_ERROR)
	{
	ChipLogError(Inet, "Failed to initialize TCP transport: %s", ErrorStr(err));
	if (mListenSocket)
	{
	mListenSocket->Free();
	mListenSocket = nullptr;
	}
	}

	return err;
	}

	void TCPBase::Close()
	{
	if (mListenSocket)
	{
	mListenSocket->Free();
	mListenSocket = nullptr;
	}
	mState = State::kNotReady;
	}

	TCPBase::ActiveConnectionState * TCPBase::FindActiveConnection(const PeerAddress & address)
	{
	if (address.GetTransportType() != Type::kTcp)
	{
	return nullptr;
	}

	for (size_t i = 0; i < mActiveConnectionsSize; i++)
	{
	if (!mActiveConnections[i].InUse())
	{
	continue;
	}
	Inet::IPAddress addr;
	uint16_t port;
	mActiveConnections[i].mEndPoint->GetPeerInfo(&addr, &port);

	if ((addr == address.GetIPAddress()) && (port == address.GetPort()))
	{
	return &mActiveConnections[i];
	}
	}

	return nullptr;
	}

	TCPBase::ActiveConnectionState * TCPBase::FindActiveConnection(const Inet::TCPEndPoint * endPoint)
	{
	for (size_t i = 0; i < mActiveConnectionsSize; i++)
	{
	if (mActiveConnections[i].mEndPoint == endPoint)
	{
	return &mActiveConnections[i];
	}
	}
	return nullptr;
	}

	CHIP_ERROR TCPBase::SendMessage(const Transport::PeerAddress & address, System::PacketBufferHandle && msgBuf)
	{
	// Sent buffer data format is:
	// - packet size as a uint16_t
	// - actual data

	VerifyOrReturnError(address.GetTransportType() == Type::kTcp, CHIP_ERROR_INVALID_ARGUMENT);
	VerifyOrReturnError(mState == State::kInitialized, CHIP_ERROR_INCORRECT_STATE);
	VerifyOrReturnError(kPacketSizeBytes + msgBuf->DataLength() <= std::numeric_limits<uint16_t>::max(),
	CHIP_ERROR_INVALID_ARGUMENT);

	// The check above about kPacketSizeBytes + msgBuf->DataLength() means it definitely fits in uint16_t.
	VerifyOrReturnError(msgBuf->EnsureReservedSize(static_cast<uint16_t>(kPacketSizeBytes)), CHIP_ERROR_NO_MEMORY);

	msgBuf->SetStart(msgBuf->Start() - kPacketSizeBytes);

	uint8_t * output = msgBuf->Start();
	LittleEndian::Write16(output, static_cast<uint16_t>(msgBuf->DataLength() - kPacketSizeBytes));

	// Reuse existing connection if one exists, otherwise a new one
	// will be established
	ActiveConnectionState * connection = FindActiveConnection(address);

	if (connection != nullptr)
	{
	return connection->mEndPoint->Send(std::move(msgBuf));
	}

	return SendAfterConnect(address, std::move(msgBuf));
	}

	CHIP_ERROR TCPBase::SendAfterConnect(const PeerAddress & addr, System::PacketBufferHandle && msg)
	{
	// This will initiate a connection to the specified peer
	bool alreadyConnecting = false;

	// Iterate through the ENTIRE array. If a pending packet for
	// the address already exists, this means a connection is pending and
	// does NOT need to be re-established.
	mPendingPackets.ForEachActiveObject([&](PendingPacket * pending) {
	if (pending->mPeerAddress == addr)
	{
	// same destination exists.
	alreadyConnecting = true;
	pending->mPacketBuffer->AddToEnd(std::move(msg));
	return Loop::Break;
	}
	return Loop::Continue;
	});

	// If already connecting, buffer was just enqueued for more sending
	if (alreadyConnecting)
	{
	return CHIP_NO_ERROR;
	}

	// Ensures sufficient active connections size exist
	VerifyOrReturnError(mUsedEndPointCount < mActiveConnectionsSize, CHIP_ERROR_NO_MEMORY);

	#if INET_CONFIG_ENABLE_TCP_ENDPOINT
	Inet::TCPEndPoint * endPoint = nullptr;
	ReturnErrorOnFailure(mListenSocket->GetEndPointManager().NewEndPoint(&endPoint));
	auto EndPointDeletor = [](Inet::TCPEndPoint * e) { e->Free(); };
	std::unique_ptr<Inet::TCPEndPoint, decltype(EndPointDeletor)> endPointHolder(endPoint, EndPointDeletor);

	endPoint->mAppState = reinterpret_cast<void *>(this);
	endPoint->OnDataReceived = OnTcpReceive;
	endPoint->OnConnectComplete = OnConnectionComplete;
	endPoint->OnConnectionClosed = OnConnectionClosed;
	endPoint->OnConnectionReceived = OnConnectionReceived;
	endPoint->OnAcceptError = OnAcceptError;
	endPoint->OnPeerClose = OnPeerClosed;

	ReturnErrorOnFailure(endPoint->Connect(addr.GetIPAddress(), addr.GetPort(), addr.GetInterface()));

	// enqueue the packet once the connection succeeds
	VerifyOrReturnError(mPendingPackets.CreateObject(addr, std::move(msg)) != nullptr, CHIP_ERROR_NO_MEMORY);
	mUsedEndPointCount++;

	endPointHolder.release();

	return CHIP_NO_ERROR;
	#else
	return CHIP_ERROR_UNSUPPORTED_CHIP_FEATURE;
	#endif
	}

	CHIP_ERROR TCPBase::ProcessReceivedBuffer(Inet::TCPEndPoint * endPoint, const PeerAddress & peerAddress,
	System::PacketBufferHandle && buffer)
	{
	ActiveConnectionState * state = FindActiveConnection(endPoint);
	VerifyOrReturnError(state != nullptr, CHIP_ERROR_INTERNAL);
	state->mReceived.AddToEnd(std::move(buffer));

	while (!state->mReceived.IsNull())
	{
	uint8_t messageSizeBuf[kPacketSizeBytes];
	CHIP_ERROR err = state->mReceived->Read(messageSizeBuf);
	if (err == CHIP_ERROR_BUFFER_TOO_SMALL)
	{
	// We don't have enough data to read the message size. Wait until there's more.
	return CHIP_NO_ERROR;
	}
	if (err != CHIP_NO_ERROR)
	{
	return err;
	}
	uint16_t messageSize = LittleEndian::Get16(messageSizeBuf);
	if (messageSize >= kMaxMessageSize)
	{
	// This message is too long for upper layers.
	return CHIP_ERROR_MESSAGE_TOO_LONG;
	}
	// The subtraction will not underflow because we successfully read kPacketSizeBytes.
	if (messageSize > (state->mReceived->TotalLength() - kPacketSizeBytes))
	{
	// We have not yet received the complete message.
	return CHIP_NO_ERROR;
	}
	state->mReceived.Consume(kPacketSizeBytes);
	ReturnErrorOnFailure(ProcessSingleMessage(peerAddress, state, messageSize));
	}

	return CHIP_NO_ERROR;
	}

	CHIP_ERROR TCPBase::ProcessSingleMessage(const PeerAddress & peerAddress, ActiveConnectionState * state, uint16_t messageSize)
	{
	// We enter with `state->mReceived` containing at least one full message, perhaps in a chain.
	// `state->mReceived->Start()` currently points to the message data.
	// On exit, `state->mReceived` will have had `messageSize` bytes consumed, no matter what.
	System::PacketBufferHandle message;
	if (state->mReceived->DataLength() == messageSize)
	{
	// In this case, the head packet buffer contains exactly the message.
	// This is common because typical messages fit in a network packet, and are delivered as such.
	// Peel off the head to pass upstream, which effectively consumes it from `state->mReceived`.
	message = state->mReceived.PopHead();
	}
	else
	{
	// The message is either longer or shorter than the head buffer.
	// In either case, copy the message to a fresh linear buffer to pass upstream. We always copy, rather than provide
	// a shared reference to the current buffer, in case upper layers manipulate the buffer in ways that would affect
	// our use, e.g. chaining it elsewhere or reusing space beyond the current message.
	message = System::PacketBufferHandle::New(messageSize, 0);
	if (message.IsNull())
	{
	return CHIP_ERROR_NO_MEMORY;
	}
	CHIP_ERROR err = state->mReceived->Read(message->Start(), messageSize);
	state->mReceived.Consume(messageSize);
	ReturnErrorOnFailure(err);
	message->SetDataLength(messageSize);
	}

	HandleMessageReceived(peerAddress, std::move(message));
	return CHIP_NO_ERROR;
	}

	void TCPBase::ReleaseActiveConnection(Inet::TCPEndPoint * endPoint)
	{
	for (size_t i = 0; i < mActiveConnectionsSize; i++)
	{
	if (mActiveConnections[i].mEndPoint == endPoint)
	{
	mActiveConnections[i].Free();
	mUsedEndPointCount--;
	}
	}
	}

	CHIP_ERROR TCPBase::OnTcpReceive(Inet::TCPEndPoint * endPoint, System::PacketBufferHandle && buffer)
	{
	Inet::IPAddress ipAddress;
	uint16_t port;
	Inet::InterfaceId interfaceId;

	endPoint->GetPeerInfo(&ipAddress, &port);
	endPoint->GetInterfaceId(&interfaceId);
	PeerAddress peerAddress = PeerAddress::TCP(ipAddress, port, interfaceId);

	TCPBase * tcp = reinterpret_cast<TCPBase *>(endPoint->mAppState);
	CHIP_ERROR err = tcp->ProcessReceivedBuffer(endPoint, peerAddress, std::move(buffer));

	if (err != CHIP_NO_ERROR)
	{
	// Connection could need to be closed at this point
	ChipLogError(Inet, "Failed to accept received TCP message: %s", ErrorStr(err));
	return CHIP_ERROR_UNEXPECTED_EVENT;
	}
	return CHIP_NO_ERROR;
	}

	void TCPBase::OnConnectionComplete(Inet::TCPEndPoint * endPoint, CHIP_ERROR inetErr)
	{
	CHIP_ERROR err = CHIP_NO_ERROR;
	bool foundPendingPacket = false;
	TCPBase * tcp = reinterpret_cast<TCPBase *>(endPoint->mAppState);
	Inet::IPAddress ipAddress;
	uint16_t port;
	Inet::InterfaceId interfaceId;

	endPoint->GetPeerInfo(&ipAddress, &port);
	endPoint->GetInterfaceId(&interfaceId);
	PeerAddress addr = PeerAddress::TCP(ipAddress, port, interfaceId);

	// Send any pending packets
	tcp->mPendingPackets.ForEachActiveObject([&](PendingPacket * pending) {
	if (pending->mPeerAddress == addr)
	{
	foundPendingPacket = true;
	System::PacketBufferHandle buffer = std::move(pending->mPacketBuffer);
	tcp->mPendingPackets.ReleaseObject(pending);

	if ((inetErr == CHIP_NO_ERROR) && (err == CHIP_NO_ERROR))
	{
	err = endPoint->Send(std::move(buffer));
	}
	}
	return Loop::Continue;
	});

	if (err == CHIP_NO_ERROR)
	{
	err = inetErr;
	}

	if (!foundPendingPacket && (err == CHIP_NO_ERROR))
	{
	// Force a close: new connections are only expected when a
	// new buffer is being sent.
	ChipLogError(Inet, "Connection accepted without pending buffers");
	err = CHIP_ERROR_CONNECTION_CLOSED_UNEXPECTEDLY;
	}

	// cleanup packets or mark as free
	if (err != CHIP_NO_ERROR)
	{
	ChipLogError(Inet, "Connection complete encountered an error: %s", ErrorStr(err));
	endPoint->Free();
	tcp->mUsedEndPointCount--;
	}
	else
	{
	bool connectionStored = false;
	for (size_t i = 0; i < tcp->mActiveConnectionsSize; i++)
	{
	if (!tcp->mActiveConnections[i].InUse())
	{
	tcp->mActiveConnections[i].Init(endPoint);
	connectionStored = true;
	break;
	}
	}

	// since we track end points counts, we always expect to store the
	// connection.
	if (!connectionStored)
	{
	endPoint->Free();
	ChipLogError(Inet, "Internal logic error: insufficient space to store active connection");
	}
	}
	}

	void TCPBase::OnConnectionClosed(Inet::TCPEndPoint * endPoint, CHIP_ERROR err)
	{
	TCPBase * tcp = reinterpret_cast<TCPBase *>(endPoint->mAppState);

	ChipLogProgress(Inet, "Connection closed.");

	ChipLogProgress(Inet, "Freeing closed connection.");
	tcp->ReleaseActiveConnection(endPoint);
	}

	void TCPBase::OnConnectionReceived(Inet::TCPEndPoint * listenEndPoint, Inet::TCPEndPoint * endPoint,
	const Inet::IPAddress & peerAddress, uint16_t peerPort)
	{
	TCPBase * tcp = reinterpret_cast<TCPBase *>(listenEndPoint->mAppState);

	if (tcp->mUsedEndPointCount < tcp->mActiveConnectionsSize)
	{
	// have space to use one more (even if considering pending connections)
	for (size_t i = 0; i < tcp->mActiveConnectionsSize; i++)
	{
	if (!tcp->mActiveConnections[i].InUse())
	{
	tcp->mActiveConnections[i].Init(endPoint);
	tcp->mUsedEndPointCount++;
	break;
	}
	}

	endPoint->mAppState = listenEndPoint->mAppState;
	endPoint->OnDataReceived = OnTcpReceive;
	endPoint->OnConnectComplete = OnConnectionComplete;
	endPoint->OnConnectionClosed = OnConnectionClosed;
	endPoint->OnConnectionReceived = OnConnectionReceived;
	endPoint->OnAcceptError = OnAcceptError;
	endPoint->OnPeerClose = OnPeerClosed;
	}
	else
	{
	ChipLogError(Inet, "Insufficient connection space to accept new connections");
	endPoint->Free();
	}
	}

	void TCPBase::OnAcceptError(Inet::TCPEndPoint * endPoint, CHIP_ERROR err)
	{
	ChipLogError(Inet, "Accept error: %s", ErrorStr(err));
	}

	void TCPBase::Disconnect(const PeerAddress & address)
	{
	// Closes an existing connection
	for (size_t i = 0; i < mActiveConnectionsSize; i++)
	{
	if (mActiveConnections[i].InUse())
	{
	Inet::IPAddress ipAddress;
	uint16_t port;
	Inet::InterfaceId interfaceId;

	mActiveConnections[i].mEndPoint->GetPeerInfo(&ipAddress, &port);
	mActiveConnections[i].mEndPoint->GetInterfaceId(&interfaceId);
	if (address == PeerAddress::TCP(ipAddress, port, interfaceId))
	{
	// NOTE: this leaves the socket in TIME_WAIT.
	// Calling Abort() would clean it since SO_LINGER would be set to 0,
	// however this seems not to be useful.
	mActiveConnections[i].Free();
	mUsedEndPointCount--;
	}
	}
	}
	}

	void TCPBase::OnPeerClosed(Inet::TCPEndPoint * endPoint)
	{
	TCPBase * tcp = reinterpret_cast<TCPBase *>(endPoint->mAppState);

	ChipLogProgress(Inet, "Freeing connection: connection closed by peer");

	tcp->ReleaseActiveConnection(endPoint);
	}

	bool TCPBase::HasActiveConnections() const
	{
	for (size_t i = 0; i < mActiveConnectionsSize; i++)
	{
	if (mActiveConnections[i].InUse())
	{
	return true;
	}
	}

	return false;
	}

	} // namespace Transport
	} // namespace chip