NetworkConnectionManager.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.CompilerServices;
using Unity.Collections;
using Unity.Collections.LowLevel.Unsafe;
using Unity.Profiling;
using UnityEngine;
using Debug = UnityEngine.Debug;
using Object = UnityEngine.Object;

namespace Unity.Netcode
{
    /// <summary>
    /// The connection event type set within <see cref="ConnectionEventData"/> to signify the type of connection event notification received.
    /// </summary>
    /// <remarks>
    /// <see cref="ConnectionEventData"/> is returned as a parameter of the <see cref="NetworkManager.OnConnectionEvent"/> event notification.
    /// <see cref="ClientConnected"/> and <see cref="ClientDisconnected"/> event types occur on the client-side of the newly connected client and on the server-side. <br />
    /// <see cref="PeerConnected"/> and <see cref="PeerDisconnected"/> event types occur on connected clients to notify that a new client (peer) has joined/connected.
    /// </remarks>
    public enum ConnectionEvent
    {
        /// <summary>
        /// This event is set on the client-side of the newly connected client and on the server-side.<br />
        /// </summary>
        /// <remarks>
        /// On the newly connected client side, the <see cref="ConnectionEventData.ClientId"/> will be the <see cref="NetworkManager.LocalClientId"/>.<br />
        /// On the server side, the <see cref="ConnectionEventData.ClientId"/> will be the ID of the client that just connected.
        /// </remarks>
        ClientConnected,
        /// <summary>
        /// This event is set on clients that are already connected to the session.
        /// </summary>
        /// <remarks>
        /// The <see cref="ConnectionEventData.ClientId"/> will be the ID of the client that just connected.
        /// </remarks>
        PeerConnected,
        /// <summary>
        /// This event is set on the client-side of the client that disconnected client and on the server-side.
        /// </summary>
        /// <remarks>
        /// On the disconnected client side, the <see cref="ConnectionEventData.ClientId"/> will be the <see cref="NetworkManager.LocalClientId"/>.<br />
        /// On the server side, this will be the ID of the client that disconnected.
        /// </remarks>
        ClientDisconnected,
        /// <summary>
        /// This event is set on clients that are already connected to the session.
        /// </summary>
        /// <remarks>
        /// The <see cref="ConnectionEventData.ClientId"/> will be the ID of the client that just disconnected.
        /// </remarks>
        PeerDisconnected
    }

    /// <summary>
    /// Returned as a parameter of the <see cref="NetworkManager.OnConnectionEvent"/> event notification.
    /// </summary>
    /// <remarks>
    /// See <see cref="ConnectionEvent"/> for more details on the types of connection events received.
    /// </remarks>
    public struct ConnectionEventData
    {
        /// <summary>
        /// The type of connection event that occurred
        /// </summary>
        public ConnectionEvent EventType;

        /// <summary>
        /// The client ID for the client that just connected
        /// For the <see cref="ConnectionEvent.ClientConnected"/> and <see cref="ConnectionEvent.ClientDisconnected"/>
        /// events on the client side, this will be LocalClientId.
        /// On the server side, this will be the ID of the client that just connected.
        ///
        /// For the <see cref="ConnectionEvent.PeerConnected"/> and <see cref="ConnectionEvent.PeerDisconnected"/>
        /// events on the client side, this will be the client ID assigned by the server to the remote peer.
        /// </summary>
        public ulong ClientId;

        /// <summary>
        /// This is only populated in <see cref="ConnectionEvent.ClientConnected"/> on the client side, and
        /// contains the list of other peers who were present before you connected. In all other situations,
        /// this array will be uninitialized.
        /// </summary>
        public NativeArray<ulong> PeerClientIds;
    }

    /// <summary>
    /// The NGO connection manager handles:
    /// - Client Connections
    /// - Client Approval
    /// - Processing <see cref="NetworkEvent"/>s.
    /// - Client Disconnection
    /// </summary>
    public sealed class NetworkConnectionManager
    {
#if DEVELOPMENT_BUILD || UNITY_EDITOR
        private static ProfilerMarker s_TransportPollMarker = new ProfilerMarker($"{nameof(NetworkManager)}.TransportPoll");
        private static ProfilerMarker s_TransportConnect = new ProfilerMarker($"{nameof(NetworkManager)}.TransportConnect");
        private static ProfilerMarker s_HandleIncomingData = new ProfilerMarker($"{nameof(NetworkManager)}.{nameof(NetworkMessageManager.HandleIncomingData)}");
        private static ProfilerMarker s_TransportDisconnect = new ProfilerMarker($"{nameof(NetworkManager)}.TransportDisconnect");
#endif

        private string m_DisconnectReason;
        /// <summary>
        /// When disconnected from the server, the server may send a reason. If a reason was sent, this property will
        /// provide disconnect information that will be followed by the server's disconnect reason.
        /// </summary>
        /// <remarks>
        /// On a server or host, this value could no longer exist after all subscribed callbacks are invoked for the
        /// client that disconnected. It is recommended to copy the message to some other property or field when
        /// <see cref="OnClientDisconnectCallback"/> is invoked.
        /// </remarks>
        public string DisconnectReason => GetDisconnectReason(); // fine as function because this call is infrequent

        /// <summary>
        /// Gets the reason for why this client was disconnected if exists.
        /// </summary>
        /// <returns><see cref="ServerDisconnectReason"/> disconnect reason if it exists, otherwise <see cref="m_DisconnectReason"/>.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal string GetDisconnectReason()
        {
            // TODO: fix this properly
            if (!string.IsNullOrEmpty(ServerDisconnectReason))
            {
                return ServerDisconnectReason;
            }
            return m_DisconnectReason;
        }

        /// <summary>
        /// Updated by <see cref="DisconnectReasonMessage"/>.
        /// </summary>
        internal string ServerDisconnectReason;

        /// <summary>
        /// The callback to invoke once a client connects. This callback is only ran on the server and on the local client that connects.
        /// </summary>
        public event Action<ulong> OnClientConnectedCallback = null;

        /// <summary>
        /// The callback to invoke when a client disconnects. This callback is only ran on the server and on the local client that disconnects.
        /// </summary>
        public event Action<ulong> OnClientDisconnectCallback = null;

        /// <summary>
        /// The callback to invoke once a peer connects. This callback is only ran on the server and on the local client that connects.
        /// </summary>
        public event Action<NetworkManager, ConnectionEventData> OnConnectionEvent = null;


        internal void InvokeOnClientConnectedCallback(ulong clientId)
        {
            try
            {
                OnClientConnectedCallback?.Invoke(clientId);
            }
            catch (Exception exception)
            {
                Debug.LogException(exception);
            }

            if (NetworkManager.IsServer || NetworkManager.LocalClient.IsSessionOwner)
            {
                try
                {
                    OnConnectionEvent?.Invoke(NetworkManager, new ConnectionEventData { ClientId = clientId, EventType = ConnectionEvent.ClientConnected });
                }
                catch (Exception exception)
                {
                    Debug.LogException(exception);
                }

                return;
            }

            // Invoking connection event on non-authority local client. Need to calculate PeerIds.
            var peerClientIds = new NativeArray<ulong>(Math.Max(ConnectedClientIds.Count - 1, 0), Allocator.Temp);
            // `using var peerClientIds` or `using(peerClientIds)` renders it immutable...
            using var sentinel = peerClientIds;

            var idx = 0;
            foreach (var peerId in ConnectedClientIds)
            {
                if (peerId == NetworkManager.LocalClientId)
                {
                    continue;
                }

                // This assures if the server has not timed out prior to the client synchronizing that it doesn't exceed the allocated peer count.
                if (peerClientIds.Length > idx)
                {
                    peerClientIds[idx] = peerId;
                    ++idx;
                }
            }

            try
            {
                OnConnectionEvent?.Invoke(NetworkManager, new ConnectionEventData { ClientId = NetworkManager.LocalClientId, EventType = ConnectionEvent.ClientConnected, PeerClientIds = peerClientIds });
            }
            catch (Exception exception)
            {
                Debug.LogException(exception);
            }
        }

        internal void InvokeOnClientDisconnectCallback(ulong clientId)
        {
            try
            {
                OnClientDisconnectCallback?.Invoke(clientId);
            }
            catch (Exception exception)
            {
                Debug.LogException(exception);
            }
            try
            {
                OnConnectionEvent?.Invoke(NetworkManager, new ConnectionEventData { ClientId = clientId, EventType = ConnectionEvent.ClientDisconnected });
            }
            catch (Exception exception)
            {
                Debug.LogException(exception);
            }
        }

        internal void InvokeOnPeerConnectedCallback(ulong clientId)
        {
            try
            {
                OnConnectionEvent?.Invoke(NetworkManager, new ConnectionEventData { ClientId = clientId, EventType = ConnectionEvent.PeerConnected });
            }
            catch (Exception exception)
            {
                Debug.LogException(exception);
            }
        }
        internal void InvokeOnPeerDisconnectedCallback(ulong clientId)
        {
            try
            {
                OnConnectionEvent?.Invoke(NetworkManager, new ConnectionEventData { ClientId = clientId, EventType = ConnectionEvent.PeerDisconnected });
            }
            catch (Exception exception)
            {
                Debug.LogException(exception);
            }
        }

        /// <summary>
        /// The callback to invoke if the <see cref="NetworkTransport"/> fails.
        /// </summary>
        /// <remarks>
        /// A failure of the transport is always followed by the <see cref="NetworkManager"/> shutting down. Recovering
        /// from a transport failure would normally entail reconfiguring the transport (e.g. re-authenticating, or
        /// recreating a new service allocation depending on the transport) and restarting the client/server/host.
        /// </remarks>
        public event Action OnTransportFailure;

        /// <summary>
        /// Is true when a server or host is listening for connections.
        /// Is true when a client is connecting or connected to a network session.
        /// Is false when not listening, connecting, or connected.
        /// </summary>
        public bool IsListening { get; internal set; }

        internal NetworkManager NetworkManager;
        internal NetworkMessageManager MessageManager;

        internal NetworkClient LocalClient = new NetworkClient();
        internal Dictionary<ulong, NetworkManager.ConnectionApprovalResponse> ClientsToApprove = new Dictionary<ulong, NetworkManager.ConnectionApprovalResponse>();

        internal Dictionary<ulong, NetworkClient> ConnectedClients = new Dictionary<ulong, NetworkClient>();
        internal Dictionary<ulong, ulong> ClientIdToTransportIdMap = new Dictionary<ulong, ulong>();
        internal Dictionary<ulong, ulong> TransportIdToClientIdMap = new Dictionary<ulong, ulong>();
        internal List<NetworkClient> ConnectedClientsList = new List<NetworkClient>();
        internal List<ulong> ConnectedClientIds = new List<ulong>();
        internal Action<NetworkManager.ConnectionApprovalRequest, NetworkManager.ConnectionApprovalResponse> ConnectionApprovalCallback;

        /// <summary>
        /// Use <see cref="AddPendingClient(ulong)"/> and <see cref="RemovePendingClient(ulong)"/> to add or remove
        /// Use <see cref="PendingClients"/> to internally access the pending client dictionary
        /// </summary>
        private Dictionary<ulong, PendingClient> m_PendingClients = new Dictionary<ulong, PendingClient>();

        internal IReadOnlyDictionary<ulong, PendingClient> PendingClients => m_PendingClients;

        internal Coroutine LocalClientApprovalCoroutine;

        /// <summary>
        /// Client-Side:
        /// Starts the client-side approval timeout coroutine
        /// </summary>
        /// <param name="clientId"></param>
        internal void StartClientApprovalCoroutine(ulong clientId)
        {
            LocalClientApprovalCoroutine = NetworkManager.StartCoroutine(ApprovalTimeout(clientId));
        }

        /// <summary>
        /// Client-Side:
        /// Stops the client-side approval timeout when it is approved.
        /// <see cref="ConnectionApprovedMessage.Handle(ref NetworkContext)"/>
        /// </summary>
        internal void StopClientApprovalCoroutine()
        {
            if (LocalClientApprovalCoroutine != null)
            {
                NetworkManager.StopCoroutine(LocalClientApprovalCoroutine);
                LocalClientApprovalCoroutine = null;
            }
        }

        /// <summary>
        /// Server-Side:
        /// Handles the issue with populating NetworkManager.PendingClients
        /// </summary>
        internal void AddPendingClient(ulong clientId)
        {
            m_PendingClients.Add(clientId, new PendingClient()
            {
                ClientId = clientId,
                ConnectionState = PendingClient.State.PendingConnection,
                ApprovalCoroutine = NetworkManager.StartCoroutine(ApprovalTimeout(clientId))
            });

            NetworkManager.PendingClients.Add(clientId, PendingClients[clientId]);
        }

        /// <summary>
        /// Server-Side:
        /// Handles the issue with depopulating NetworkManager.PendingClients
        /// </summary>
        internal void RemovePendingClient(ulong clientId)
        {
            if (m_PendingClients.ContainsKey(clientId) && m_PendingClients[clientId].ApprovalCoroutine != null)
            {
                NetworkManager.StopCoroutine(m_PendingClients[clientId].ApprovalCoroutine);
            }
            m_PendingClients.Remove(clientId);
            NetworkManager.PendingClients.Remove(clientId);
        }

        /// <summary>
        /// Used to generate client identifiers
        /// </summary>
        private ulong m_NextClientId = 1;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal (ulong, bool) TransportIdToClientId(ulong transportId)
        {
            if (transportId == GetServerTransportId())
            {
                return (NetworkManager.ServerClientId, true);
            }

            if (TransportIdToClientIdMap.TryGetValue(transportId, out var clientId))
            {
                return (clientId, true);
            }

            return (default, false);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal (ulong, bool) ClientIdToTransportId(ulong clientId)
        {
            if (clientId == NetworkManager.ServerClientId)
            {
                return (GetServerTransportId(), true);
            }

            if (ClientIdToTransportIdMap.TryGetValue(clientId, out var transportClientId))
            {
                return (transportClientId, true);
            }

            if (NetworkLog.CurrentLogLevel == LogLevel.Developer)
            {
                NetworkLog.LogWarning($"Trying to get the transport client ID map for the NGO client ID ({clientId}) but did not find the map entry! Returning default transport ID value.");
            }

            return (0, false);
        }

        /// <summary>
        /// Gets the networkId of the server
        /// </summary>
        internal ulong ServerTransportId => GetServerTransportId();

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private ulong GetServerTransportId()
        {
            if (NetworkManager != null)
            {
                if (Transport == null && NetworkManager.NetworkConfig.NetworkTransport != null)
                {
                    Transport = NetworkManager.NetworkConfig.NetworkTransport;
                }

                if (Transport)
                {
                    return Transport.ServerClientId;
                }

                throw new NullReferenceException($"The transport in the active {nameof(NetworkConfig)} is null");
            }

            throw new Exception($"There is no {nameof(NetworkManager)} assigned to this instance!");
        }

        /// <summary>
        /// Handles cleaning up the transport id/client id tables after receiving a disconnect event from transport
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal (ulong, bool) TransportIdCleanUp(ulong transportId)
        {
            // This check is for clients that attempted to connect but failed.
            // When this happens, the client will not have an entry within the m_TransportIdToClientIdMap or m_ClientIdToTransportIdMap lookup tables so we exit early and just return 0 to be used for the disconnect event.
            if (!LocalClient.IsServer && !TransportIdToClientIdMap.ContainsKey(transportId))
            {
                return (NetworkManager.LocalClientId, true);
            }

            var (clientId, isConnectedClient) = TransportIdToClientId(transportId);
            if (!isConnectedClient)
            {
                return (default, false);
            }

            TransportIdToClientIdMap.Remove(transportId);
            ClientIdToTransportIdMap.Remove(clientId);
            return (clientId, true);
        }

        internal void PollAndHandleNetworkEvents()
        {
#if DEVELOPMENT_BUILD || UNITY_EDITOR
            s_TransportPollMarker.Begin();
#endif
            NetworkEvent networkEvent;
            do
            {
                networkEvent = Transport.PollEvent(out ulong transportClientId, out ArraySegment<byte> payload, out float receiveTime);
                HandleNetworkEvent(networkEvent, transportClientId, payload, receiveTime);
                if (networkEvent == NetworkEvent.Disconnect || networkEvent == NetworkEvent.TransportFailure)
                {
                    break;
                }
                // Only do another iteration if: there are no more messages AND (there is no limit to max events or we have processed less than the maximum)
            } while (NetworkManager.IsListening && networkEvent != NetworkEvent.Nothing);

#if DEVELOPMENT_BUILD || UNITY_EDITOR
            s_TransportPollMarker.End();
#endif
        }

        /// <summary>
        /// Event driven NetworkTransports (like UnityTransport) NetworkEvent handling
        /// </summary>
        /// <remarks>
        /// Polling NetworkTransports invoke this directly
        /// </remarks>
        internal void HandleNetworkEvent(NetworkEvent networkEvent, ulong transportClientId, ArraySegment<byte> payload, float receiveTime)
        {
            switch (networkEvent)
            {
                case NetworkEvent.Connect:
                    ConnectEventHandler(transportClientId);
                    break;
                case NetworkEvent.Data:
                    DataEventHandler(transportClientId, ref payload, receiveTime);
                    break;
                case NetworkEvent.Disconnect:
                    DisconnectEventHandler(transportClientId);
                    break;
                case NetworkEvent.TransportFailure:
                    TransportFailureEventHandler();
                    break;
            }
        }

        /// <summary>
        /// Client's save their assigned transport id.
        /// </summary>
        /// <remarks>
        /// Added to be able to appropriately log the client's transport
        /// id when it is shutdown or disconnected.
        /// </remarks>
        private ulong m_LocalClientTransportId;

        internal ulong LocalClientTransportId => m_LocalClientTransportId;

        private bool m_IsTransportConnected = false;

        /// <summary>
        /// Handles a <see cref="NetworkEvent.Connect"/> event.
        /// </summary>
        internal void ConnectEventHandler(ulong transportId)
        {
#if DEVELOPMENT_BUILD || UNITY_EDITOR
            s_TransportConnect.Begin();
#endif
            // Assumptions:
            // - When server receives a connection, it *must be* a client
            // - When client receives one, it *must be* the server
            // Client's can't connect to or talk to other clients.
            // Server is a sentinel so only one exists, if we are server, we can't be connecting to it.

            ulong clientId;

            // If we're the server, then this connect event is firing for a new incoming client connection
            if (LocalClient.IsServer)
            {
                var (_, alreadyConnected) = TransportIdToClientId(transportId);
                if (alreadyConnected)
                {
                    if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
                    {
                        NetworkLog.LogError($"[TransportApproval][Server] TransportId {transportId} is already connected to this server!");
                    }
                    return;
                }

                clientId = m_NextClientId++;
            }
            // Otherwise this connect event is an approved connection from the server
            else
            {
                if (m_IsTransportConnected)
                {
                    if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
                    {
                        NetworkLog.LogError("[TransportApproval][Client] Client received a transport connection event after already connecting!");
                    }
                    return;
                }

                m_IsTransportConnected = true;

                // Cache the local client's transport id.
                m_LocalClientTransportId = transportId;
                clientId = NetworkManager.ServerClientId;
            }

            ClientIdToTransportIdMap[clientId] = transportId;
            TransportIdToClientIdMap[transportId] = clientId;
            MessageManager.ClientConnected(clientId);

            if (LocalClient.IsServer)
            {
                if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
                {
                    var hostServer = NetworkManager.IsHost ? "Host" : "Server";
                    NetworkLog.LogInfo($"[{hostServer}-Side] Transport connection established with pending Client-{clientId}.");
                }
                AddPendingClient(clientId);
            }
            else
            {
                if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
                {
                    var serverOrService = NetworkManager.DistributedAuthorityMode ? NetworkManager.CMBServiceConnection ? "service" : "DAHost" : "server";
                    NetworkLog.LogInfo($"[Approval Pending][Client] Transport connection with {serverOrService} established! Awaiting connection approval...");
                }

                SendConnectionRequest();
                StartClientApprovalCoroutine(clientId);
            }

#if DEVELOPMENT_BUILD || UNITY_EDITOR
            s_TransportConnect.End();
#endif
        }

        /// <summary>
        /// Handles a <see cref="NetworkEvent.Data"/> event.
        /// </summary>
        internal void DataEventHandler(ulong transportClientId, ref ArraySegment<byte> payload, float receiveTime)
        {
#if DEVELOPMENT_BUILD || UNITY_EDITOR
            s_HandleIncomingData.Begin();
#endif
            var (clientId, isConnectedClient) = TransportIdToClientId(transportClientId);
            if (isConnectedClient)
            {
                MessageManager.HandleIncomingData(clientId, payload, receiveTime);
            }

#if DEVELOPMENT_BUILD || UNITY_EDITOR
            s_HandleIncomingData.End();
#endif
        }

        private void GenerateDisconnectInformation(ulong clientId, ulong transportClientId, string reason = null)
        {
            var header = $"[Disconnect Event][Client-{clientId}][TransportClientId-{transportClientId}]";
            var defaultMessage = Transport.DisconnectEventMessage;
            if (reason != null)
            {
                defaultMessage = $"{reason} {defaultMessage}";
            }

            // Just go ahead and set this whether client or server so any subscriptions to a disconnect event can check the DisconnectReason
            // to determine why the client disconnected
            m_DisconnectReason = $"{header}[{Transport.DisconnectEvent}] {defaultMessage}";

            if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
            {
                var serverDisconnectReason = string.IsNullOrEmpty(ServerDisconnectReason) ? string.Empty : $"\n{ServerDisconnectReason}";
                NetworkLog.LogInfo($"{m_DisconnectReason}{serverDisconnectReason}");
            }
        }

        /// <summary>
        /// Handles a <see cref="NetworkEvent.Disconnect"/> event.
        /// </summary>
        internal void DisconnectEventHandler(ulong transportClientId)
        {
            // Check to see if the client has already been removed from the table but
            // do not remove it just yet.
            var (clientId, isConnectedClient) = TransportIdToClientId(transportClientId);

            // If the client is not registered and we are the server or we are connecting to
            // the live CMB service and the client had a transport Id assigned then exit early
            /// <see cref="DisconnectReasonMessage"/> handles disconnecting the client
            if (!isConnectedClient && (NetworkManager.IsServer || (NetworkManager.CMBServiceConnection && m_LocalClientTransportId != 0)))
            {
                // Then exit early
                return;
            }

#if DEVELOPMENT_BUILD || UNITY_EDITOR
            s_TransportDisconnect.Begin();
#endif

            if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
            {
                NetworkLog.LogInfo($"Disconnect Event From {clientId}");
            }

            // If we are a client and we have gotten the ServerClientId back, then use our assigned local id as the client that was
            // disconnected (either the user disconnected or the server disconnected, but the client that disconnected is the LocalClientId)
            if (!NetworkManager.IsServer && clientId == NetworkManager.ServerClientId)
            {
                clientId = NetworkManager.LocalClientId;
            }

            // If the disconnect is due to the transport being shutdown and we have received a notification
            // from transport that we have disconnected, then we are a client that has shutdown the NetworkManager
            // and there is no need to generate any disconnect information as all of that should already be set at this point.
            if (Transport.DisconnectEvent != NetworkTransport.DisconnectEvents.TransportShutdown)
            {
                GenerateDisconnectInformation(clientId, transportClientId);
            }

            // Process the incoming message queue so that we get everything from the server disconnecting us or, if we are the server, so we got everything from that client.
            MessageManager.ProcessIncomingMessageQueue();

            if (LocalClient.IsServer)
            {
                // We need to process the disconnection before notifying
                OnClientDisconnectFromServer(clientId);
            }
            else
            {
                // Client's clean up their transport id separately from the server.
                TransportIdCleanUp(transportClientId);

                try
                {
                    // Notify local client of disconnection
                    InvokeOnClientDisconnectCallback(clientId);
                }
                catch (Exception ex)
                {
                    Debug.LogException(ex);
                }

                // Reset the transport ID
                m_LocalClientTransportId = 0;

                // As long as we are not in the middle of a shutdown
                if (!NetworkManager.ShutdownInProgress)
                {
                    // We must pass true here and not process any sends messages as we are no longer connected.
                    // Otherwise, attempting to process messages here can cause an exception within UnityTransport
                    // as the client ID is no longer valid.
                    NetworkManager.Shutdown(true);
                }
            }
#if DEVELOPMENT_BUILD || UNITY_EDITOR
            s_TransportDisconnect.End();
#endif
        }

        /// <summary>
        /// Handles a <see cref="NetworkEvent.TransportFailure"/> event.
        /// </summary>
        internal void TransportFailureEventHandler(bool duringStart = false)
        {
            var clientSeverOrHost = LocalClient.IsServer ? LocalClient.IsHost ? "Host" : "Server" : "Client";
            var whenFailed = duringStart ? "start failure" : "failure";
            NetworkLog.LogError($"{clientSeverOrHost} is shutting down due to network transport {whenFailed} of {NetworkManager.NetworkConfig.NetworkTransport.GetType().Name}!");
            OnTransportFailure?.Invoke();

            // If we had a transport failure when trying to start, reset the local client roles and directly invoke the internal shutdown.
            if (duringStart)
            {
                LocalClient.SetRole(false, false);
                NetworkManager.ShutdownInternal();
            }
            else
            {
                // Otherwise, stop processing messages and shutdown the normal way
                NetworkManager.Shutdown(true);
            }
        }

        /// <summary>
        /// Client-Side:
        /// Upon transport connecting, the client will send a connection request
        /// </summary>
        private void SendConnectionRequest()
        {
            var message = new ConnectionRequestMessage
            {
                DistributedAuthority = NetworkManager.DistributedAuthorityMode,
                // Since only a remote client will send a connection request, we should always force the rebuilding of the NetworkConfig hash value
                ConfigHash = NetworkManager.NetworkConfig.GetConfig(false),
                ShouldSendConnectionData = NetworkManager.NetworkConfig.ConnectionApproval,
                ConnectionData = NetworkManager.NetworkConfig.ConnectionData,
                MessageVersions = new NativeArray<MessageVersionData>(MessageManager.MessageHandlers.Length, Allocator.Temp)
            };

            if (NetworkManager.DistributedAuthorityMode)
            {
                message.ClientConfig.SessionConfig = NetworkManager.SessionConfig;
                message.ClientConfig.TickRate = NetworkManager.NetworkConfig.TickRate;
                message.ClientConfig.EnableSceneManagement = NetworkManager.NetworkConfig.EnableSceneManagement;
            }

            for (int index = 0; index < MessageManager.MessageHandlers.Length; index++)
            {
                if (MessageManager.MessageTypes[index] != null)
                {
                    var type = MessageManager.MessageTypes[index];
                    message.MessageVersions[index] = new MessageVersionData
                    {
                        Hash = XXHash.Hash32(type.FullName),
                        Version = MessageManager.GetLocalVersion(type)
                    };
                }
            }

            SendMessage(ref message, MessageDeliveryType<ConnectionRequestMessage>.DefaultDelivery, NetworkManager.ServerClientId);
            message.MessageVersions.Dispose();
        }

        /// <summary>
        /// Approval time out coroutine
        /// </summary>
        private IEnumerator ApprovalTimeout(ulong clientId)
        {
            var timeStarted = LocalClient.IsServer ? NetworkManager.LocalTime.TimeAsFloat : NetworkManager.RealTimeProvider.RealTimeSinceStartup;
            var timedOut = false;
            var connectionApproved = false;
            var connectionNotApproved = false;
            var timeoutMarker = timeStarted + NetworkManager.NetworkConfig.ClientConnectionBufferTimeout;

            while (NetworkManager.IsListening && !NetworkManager.ShutdownInProgress && !timedOut && !connectionApproved)
            {
                yield return null;
                // Check if we timed out
                timedOut = timeoutMarker < (LocalClient.IsServer ? NetworkManager.LocalTime.TimeAsFloat : NetworkManager.RealTimeProvider.RealTimeSinceStartup);

                if (LocalClient.IsServer)
                {
                    // When the client is no longer in the pending clients list and is in the connected clients list it has been approved
                    connectionApproved = !PendingClients.ContainsKey(clientId) && ConnectedClients.ContainsKey(clientId);

                    // For the server side, if the client is in neither list then it was declined or the client disconnected
                    connectionNotApproved = !PendingClients.ContainsKey(clientId) && !ConnectedClients.ContainsKey(clientId);
                }
                else
                {
                    connectionApproved = NetworkManager.LocalClient.IsApproved;
                }
            }

            // Exit coroutine if we are no longer listening or a shutdown is in progress (client or server)
            if (!NetworkManager.IsListening || NetworkManager.ShutdownInProgress)
            {
                yield break;
            }

            // If the client timed out or was not approved
            if (timedOut || connectionNotApproved)
            {
                // Timeout
                if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
                {
                    if (timedOut)
                    {
                        if (LocalClient.IsServer)
                        {
                            // Log a warning that the transport detected a connection but then did not receive a follow up connection request message.
                            // (hacking or something happened to the server's network connection)
                            NetworkLog.LogWarning($"Server detected a transport connection from Client-{clientId}, but timed out waiting for the connection request message.");
                        }
                        else
                        {
                            // We only provide informational logging for the client side
                            NetworkLog.LogInfo("Timed out waiting for the server to approve the connection request.");
                        }
                    }
                    else if (connectionNotApproved)
                    {
                        NetworkLog.LogInfo($"Client-{clientId} was either denied approval or disconnected while being approved.");
                    }
                }

                if (LocalClient.IsServer)
                {
                    DisconnectClient(clientId);
                }
                else
                {
                    NetworkManager.Shutdown(true);
                }
            }
        }

        /// <summary>
        /// Server-Side:
        /// Handles approval while processing a client connection request
        /// </summary>
        internal void ApproveConnection(ref ConnectionRequestMessage connectionRequestMessage, ref NetworkContext context)
        {
            if (ConnectionApprovalCallback == null)
            {
                return;
            }
            // Note: Delegate creation allocates.
            // Note: ToArray() also allocates. :(
            var response = new NetworkManager.ConnectionApprovalResponse();
            ClientsToApprove[context.SenderId] = response;
            ConnectionApprovalCallback?.Invoke(
                new NetworkManager.ConnectionApprovalRequest
                {
                    Payload = connectionRequestMessage.ConnectionData,
                    ClientNetworkId = context.SenderId
                }, response);
        }

        /// <summary>
        /// Server-Side:
        /// Processes pending approvals and removes any stale pending clients
        /// </summary>
        internal void ProcessPendingApprovals()
        {
            List<ulong> senders = null;

            foreach (var responsePair in ClientsToApprove)
            {
                var response = responsePair.Value;
                var senderId = responsePair.Key;

                if (!response.Pending)
                {
                    try
                    {
                        if (response.Approved)
                        {
                            HandleConnectionApproval(senderId, response.CreatePlayerObject, response.PlayerPrefabHash, response.Position, response.Rotation);
                        }
                        else
                        {
                            // If the connection wasn't approved, disconnect the pending connection.
                            HandleConnectionDisconnect(senderId, response.Reason);
                        }

                        senders ??= new List<ulong>();
                        senders.Add(senderId);
                    }
                    catch (Exception e)
                    {
                        Debug.LogException(e);
                    }
                }
            }

            if (senders != null)
            {
                foreach (var sender in senders)
                {
                    ClientsToApprove.Remove(sender);
                }
            }
        }

        /// <summary>
        /// Server Side: Handles the denial of a client who sent a connection request
        /// </summary>
        /// <remarks>
        /// This will send a <see cref="DisconnectReasonMessage"/> if a reason is given
        /// </remarks>
        private void HandleConnectionDisconnect(ulong ownerClientId, string reason = "")
        {
            if (!string.IsNullOrEmpty(reason))
            {
                var disconnectReason = new DisconnectReasonMessage
                {
                    Reason = reason
                };
                SendMessage(ref disconnectReason, MessageDeliveryType<DisconnectReasonMessage>.DefaultDelivery, ownerClientId);
                m_ClientsToDisconnect.Add(ownerClientId);
                return;
            }

            DisconnectRemoteClient(ownerClientId);
        }

        private List<ulong> m_ClientsToDisconnect = new List<ulong>();

        internal void ProcessClientsToDisconnect()
        {
            if (m_ClientsToDisconnect.Count == 0)
            {
                return;
            }
            foreach (var clientId in m_ClientsToDisconnect)
            {
                try
                {
                    DisconnectRemoteClient(clientId);
                }
                catch (Exception ex)
                {
                    Debug.LogException(ex);
                }
            }
            m_ClientsToDisconnect.Clear();
        }

        /// <summary>
        /// Server Side: Handles the approval of a client
        /// </summary>
        /// <remarks>
        /// This will spawn the player prefab as well as start client synchronization if <see cref="NetworkConfig.EnableSceneManagement"/> is enabled
        /// </remarks>
        internal void HandleConnectionApproval(ulong ownerClientId, bool createPlayerObject, uint? playerPrefabHash = null, Vector3? playerPosition = null, Quaternion? playerRotation = null)
        {
            if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
            {
                NetworkLog.LogInfo($"[Server-Side] Pending Client-{ownerClientId} connection approved!");
            }
            // The client was approved, stop the server-side approval time out coroutine
            RemovePendingClient(ownerClientId);

            var client = AddClient(ownerClientId);

            // Set the local settings of the server once the host client has been added.
            if (ownerClientId == NetworkManager.ServerClientId)
            {
                LocalClient = client;
                LocalClient.IsConnected = true;
                LocalClient.IsApproved = true;
            }

            // Server-side spawning (only if there is a prefab hash or player prefab provided)
            var idHashToSpawn = playerPrefabHash ?? NetworkManager.NetworkConfig.PlayerPrefab?.GetComponent<NetworkObject>()?.GlobalObjectIdHash;
            if (!NetworkManager.DistributedAuthorityMode && createPlayerObject && idHashToSpawn.HasValue)
            {
                var playerObject = NetworkManager.SpawnManager.GetNetworkObjectToSpawn(idHashToSpawn.Value, ownerClientId, playerPosition, playerRotation);

                if (playerObject == null)
                {
                    if (NetworkManager.LogLevel <= LogLevel.Error)
                    {
                        NetworkLog.LogError($"[{nameof(NetworkObject)}] Player prefab is null! Cannot spawn player object!");
                    }
                }
                else
                {
                    // Spawn the player NetworkObject locally
                    if (NetworkManager.SpawnManager.AuthorityLocalSpawn(
                        playerObject,
                        NetworkManager.SpawnManager.GetNetworkObjectId(),
                        sceneObject: false,
                        playerObject: true,
                        ownerClientId,
                        destroyWithScene: false))
                    {
                        client.AssignPlayerObject(ref playerObject);
                    }
                    else
                    {
                        if (NetworkManager.LogLevel <= LogLevel.Developer)
                        {
                            NetworkLog.LogError($"[{nameof(NetworkObject)}] Player prefab failed to spawn!");
                        }
                    }

                }
            }

            if (ownerClientId == NetworkManager.ServerClientId || !NetworkManager.NetworkConfig.EnableSceneManagement)
            {
                // Update the observed spawned NetworkObjects always for the server
                // Update for a newly connected player only when scene management is disabled
                NetworkManager.SpawnManager.UpdateObservedNetworkObjects(ownerClientId);
            }

            // Server doesn't send itself the connection approved message
            if (ownerClientId != NetworkManager.ServerClientId)
            {
                SendConnectionApprovedMessage(ownerClientId);

                // If scene management is disabled, then we are done and notify the local host-server the client is connected
                if (!NetworkManager.NetworkConfig.EnableSceneManagement)
                {
                    NetworkManager.ConnectedClients[ownerClientId].IsConnected = true;
                    InvokeOnClientConnectedCallback(ownerClientId);
                    if (LocalClient.IsHost)
                    {
                        InvokeOnPeerConnectedCallback(ownerClientId);
                    }
                    NetworkManager.SpawnManager.DistributeNetworkObjects(ownerClientId);

                }
                else // Otherwise, let NetworkSceneManager handle the initial scene and NetworkObject synchronization
                {
                    if (NetworkManager.DistributedAuthorityMode && NetworkManager.LocalClient.IsSessionOwner)
                    {
                        NetworkManager.SceneManager.SynchronizeNetworkObjects(ownerClientId);
                    }
                    else if (!NetworkManager.DistributedAuthorityMode)
                    {
                        NetworkManager.SceneManager.SynchronizeNetworkObjects(ownerClientId);
                    }
                }
            }
            else // Server just adds itself as an observer to all spawned NetworkObjects
            {
                // If running mock service, then set the instance as the default session owner
                if (NetworkManager.DistributedAuthorityMode && NetworkManager.DAHost)
                {
                    NetworkManager.SetSessionOwner(NetworkManager.LocalClientId);
                    NetworkManager.SceneManager.InitializeScenesLoaded();
                }

                if (NetworkManager.DistributedAuthorityMode && NetworkManager.AutoSpawnPlayerPrefabClientSide)
                {
                    CreateAndSpawnPlayer(ownerClientId);
                }
            }

            // Exit early if no player object was spawned
            if (!createPlayerObject || (playerPrefabHash == null && NetworkManager.NetworkConfig.PlayerPrefab == null))
            {
                return;
            }

            // Players are always spawned by their respective client, exit early. (DAHost mode anyway, CMB Service will never spawn player prefab)
            if (NetworkManager.DistributedAuthorityMode)
            {
                return;
            }

            // Separating this into a contained function call for potential further future separation of when this notification is sent.
            ApprovedPlayerSpawn(ownerClientId, playerPrefabHash ?? NetworkManager.NetworkConfig.PlayerPrefab.GetComponent<NetworkObject>().GlobalObjectIdHash);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void SendConnectionApprovedMessage(ulong approvedClientId)
        {
            var message = new ConnectionApprovedMessage
            {
                OwnerClientId = approvedClientId,
                NetworkTick = NetworkManager.LocalTime.Tick,
                IsDistributedAuthority = NetworkManager.DistributedAuthorityMode,
                ConnectedClientIds = new NativeArray<ulong>(ConnectedClientIds.Count, Allocator.Temp)
            };

            // Do a no-memory allocation copy of the current list of connected clients
            for (int i = 0; i < ConnectedClientIds.Count; i++)
            {
                message.ConnectedClientIds[i] = ConnectedClientIds[i];
            }

            // Send existing spawned objects when scene management is disabled
            if (!NetworkManager.NetworkConfig.EnableSceneManagement && NetworkManager.SpawnManager.SpawnedObjectsList.Count != 0)
            {
                message.SpawnedObjectsList = NetworkManager.SpawnManager.SpawnedObjectsList;
            }

            // Calculate and collate the most recent message versions that can be used based on the newest supported version that the client sent and the server understands.
            message.MessageVersions = new NativeArray<MessageVersionData>(MessageManager.MessageHandlers.Length, Allocator.Temp);
            for (int index = 0; index < MessageManager.MessageHandlers.Length; index++)
            {
                if (MessageManager.MessageTypes[index] != null)
                {
                    var type = MessageManager.MessageTypes[index];
                    message.MessageVersions[index] = new MessageVersionData
                    {
                        Hash = XXHash.Hash32(type.FullName),
                        Version = MessageManager.GetLocalVersion(type)
                    };
                }
            }

            SendMessage(ref message, MessageDeliveryType<ConnectionApprovedMessage>.DefaultDelivery, approvedClientId);

            message.MessageVersions.Dispose();
            message.ConnectedClientIds.Dispose();
        }


        /// <summary>
        /// Client-Side Spawning in distributed authority mode uses this to spawn the player.
        /// </summary>
        internal void CreateAndSpawnPlayer(ulong ownerId)
        {
            var playerPrefab = NetworkManager.FetchLocalPlayerPrefabToSpawn();
            if (playerPrefab == null)
            {
                if (NetworkManager.LogLevel <= LogLevel.Developer)
                {
                    NetworkLog.LogWarning("Could not fetch a local player to spawn. Ensure PlayerPrefab is set in NetcodeConfig.");
                }
                return;
            }
            var prefabObject = playerPrefab.GetComponent<NetworkObject>();
            if (prefabObject == null)
            {
                if (NetworkManager.LogLevel <= LogLevel.Normal)
                {
                    NetworkLog.LogError("Failed to fetch valid player prefab. Ensure PlayerPrefab that is set in NetcodeConfig contains a NetworkObject component.");
                }
                return;
            }
            var networkObject = NetworkManager.SpawnManager.GetNetworkObjectToSpawn(prefabObject.GlobalObjectIdHash, ownerId, playerPrefab.transform.position, playerPrefab.transform.rotation);
            if (networkObject == null)
            {
                if (NetworkManager.LogLevel <= LogLevel.Normal)
                {
                    NetworkLog.LogError("Failed to spawn player prefab!");
                }
                return;
            }

            networkObject.IsSceneObject = false;
            networkObject.NetworkManagerOwner = NetworkManager;
            networkObject.SpawnAsPlayerObject(ownerId, networkObject.DestroyWithScene);
        }

        /// <summary>
        /// Spawns the newly approved player
        /// </summary>
        /// <param name="clientId">new player client identifier</param>
        /// <param name="playerPrefabHash">the prefab GlobalObjectIdHash value for this player</param>
        internal void ApprovedPlayerSpawn(ulong clientId, uint playerPrefabHash)
        {
            foreach (var clientPair in ConnectedClients)
            {
                if (clientPair.Key == clientId ||
                    clientPair.Key == NetworkManager.ServerClientId || // Server already spawned it
                    ConnectedClients[clientId].PlayerObject == null ||
                    !ConnectedClients[clientId].PlayerObject.Observers.Contains(clientPair.Key))
                {
                    continue; //The new client.
                }

                var message = new CreateObjectMessage
                {
                    ObjectInfo = ConnectedClients[clientId].PlayerObject.Serialize(clientPair.Key),
                    IncludesSerializedObject = true,
                };

                message.ObjectInfo.Hash = playerPrefabHash;
                message.ObjectInfo.IsSceneObject = false;
                message.ObjectInfo.HasParent = false;
                message.ObjectInfo.IsPlayerObject = true;
                message.ObjectInfo.OwnerClientId = clientId;
                var size = SendMessage(ref message, MessageDeliveryType<CreateObjectMessage>.DefaultDelivery, clientPair.Key);
                NetworkManager.NetworkMetrics.TrackObjectSpawnSent(clientPair.Key, ConnectedClients[clientId].PlayerObject, size);
            }
        }

        /// <summary>
        /// Server-Side:
        /// Creates a new <see cref="NetworkClient"/> and handles updating the associated
        /// connected clients lists.
        /// </summary>
        internal NetworkClient AddClient(ulong clientId)
        {
            if (ConnectedClients.ContainsKey(clientId) && ConnectedClientIds.Contains(clientId) && ConnectedClientsList.Contains(ConnectedClients[clientId]))
            {
                return ConnectedClients[clientId];
            }

            // If this is not the local client then create a new one
            var networkClient = clientId == NetworkManager.LocalClientId ? LocalClient : new NetworkClient();

            networkClient.SetRole(clientId == NetworkManager.ServerClientId, isClient: true, NetworkManager);
            networkClient.ClientId = clientId;
            if (!ConnectedClients.ContainsKey(clientId))
            {
                ConnectedClients.Add(clientId, networkClient);
            }
            if (!ConnectedClientsList.Contains(networkClient))
            {
                ConnectedClientsList.Add(networkClient);
            }
            var networkDelivery = MessageDeliveryType<ClientConnectedMessage>.DefaultDelivery;
            if (NetworkManager.LocalClientId != clientId)
            {
                if ((!NetworkManager.DistributedAuthorityMode && NetworkManager.IsServer) ||
                    (NetworkManager.DistributedAuthorityMode && NetworkManager.NetworkConfig.EnableSceneManagement && NetworkManager.DAHost && NetworkManager.LocalClient.IsSessionOwner))
                {
                    var message = new ClientConnectedMessage { ClientId = clientId };
                    NetworkManager.MessageManager.SendMessage(ref message, networkDelivery, ConnectedClientIds.Where((c) => c != NetworkManager.LocalClientId).ToArray());
                }
                else if (NetworkManager.DistributedAuthorityMode && NetworkManager.NetworkConfig.EnableSceneManagement && NetworkManager.DAHost && !NetworkManager.LocalClient.IsSessionOwner)
                {
                    var message = new ClientConnectedMessage
                    {
                        ShouldSynchronize = true,
                        ClientId = clientId
                    };
                    NetworkManager.MessageManager.SendMessage(ref message, networkDelivery, NetworkManager.CurrentSessionOwner);
                }
            }

            if (!ConnectedClientIds.Contains(clientId))
            {
                ConnectedClientIds.Add(clientId);
            }

            var distributedAuthority = NetworkManager.DistributedAuthorityMode;

            // If not using DA return early or if using DA and scene management is disabled then exit early Since we use NetworkShow to spawn
            // objects on the newly connected client side.
            if (!distributedAuthority || distributedAuthority && !NetworkManager.NetworkConfig.EnableSceneManagement)
            {
                return networkClient;
            }

            var sessionOwnerId = NetworkManager.CurrentSessionOwner;
            var isSessionOwner = NetworkManager.LocalClient.IsSessionOwner;
            foreach (var networkObject in NetworkManager.SpawnManager.SpawnedObjectsList)
            {
                if (networkObject.SpawnWithObservers)
                {
                    // Don't add the client to the observers if hidden from the session owner
                    if (networkObject.IsOwner && distributedAuthority && !isSessionOwner && !networkObject.Observers.Contains(sessionOwnerId))
                    {
                        continue;
                    }
                    networkObject.Observers.Add(clientId);
                }
            }

            return networkClient;
        }

        /// <summary>
        /// Invoked on clients when another client disconnects
        /// </summary>
        /// <param name="clientId">the client identifier to remove</param>
        internal void RemoveClient(ulong clientId)
        {
            if (ConnectedClientIds.Contains(clientId))
            {
                ConnectedClientIds.Remove(clientId);
            }
            if (ConnectedClients.ContainsKey(clientId))
            {
                ConnectedClientsList.Remove(ConnectedClients[clientId]);
            }

            ConnectedClients.Remove(clientId);

            foreach (var networkObject in NetworkManager.SpawnManager.SpawnedObjectsList)
            {
                networkObject.Observers.Remove(clientId);
            }
        }

        /// <summary>
        /// DANGO-TODO: Until we have the CMB Server end-to-end with all features verified working via integration tests,
        /// I am keeping this debug toggle available. (NSS)
        /// </summary>
        internal bool EnableDistributeLogging;

        /// <summary>
        /// Server-Side:
        /// Invoked when a client is disconnected from a server-host
        /// </summary>
        internal void OnClientDisconnectFromServer(ulong clientId)
        {
            if (!LocalClient.IsServer)
            {
                throw new Exception("[OnClientDisconnectFromServer] Was invoked by non-server instance!");
            }

            // If we are shutting down and this is the server or host disconnecting, then ignore
            // clean up as everything that needs to be destroyed will be during shutdown.
            if (NetworkManager.ShutdownInProgress && clientId == NetworkManager.ServerClientId)
            {
                // Now notify the client has disconnected.
                // (transport id cleanup is handled within)
                InvokeOnClientDisconnectCallback(clientId);

                if (LocalClient.IsHost)
                {
                    InvokeOnPeerDisconnectedCallback(clientId);
                }
                return;
            }

            if (ConnectedClients.TryGetValue(clientId, out NetworkClient networkClient))
            {
                var playerObject = networkClient.PlayerObject;
                if (playerObject != null)
                {
                    if (!playerObject.DontDestroyWithOwner)
                    {
                        if (playerObject.IsSpawned)
                        {
                            // Call despawn to assure NetworkBehaviour.OnNetworkDespawn is invoked on the server-side (when the client side disconnected).
                            // This prevents the issue (when just destroying the GameObject) where any NetworkBehaviour component(s) destroyed before the NetworkObject would not have OnNetworkDespawn invoked.
                            NetworkManager.SpawnManager.DespawnObject(playerObject, true, true);
                        }
                        else
                        {
                            Object.Destroy(playerObject.gameObject);
                        }
                    }
                    else if (!NetworkManager.ShutdownInProgress)
                    {
                        if (NetworkManager.DistributedAuthorityMode)
                        {
                            NetworkManager.SpawnManager.ChangeOwnership(playerObject, NetworkManager.LocalClientId, true);
                        }
                        else
                        {
                            playerObject.RemoveOwnership();
                        }
                    }
                }

                // Get the NetworkObjects owned by the disconnected client
                var clientOwnedObjects = NetworkManager.SpawnManager.SpawnedObjectsList.Where((c) => c.OwnerClientId == clientId).ToList();

                // Handle changing ownership and prefab handlers
                var clientCounter = 0;
                var predictedClientCount = ConnectedClientsList.Count - 1;
                var remainingClients = NetworkManager.DistributedAuthorityMode ? ConnectedClientsList.Where((c) => c.ClientId != clientId).ToList() : null;
                for (int i = clientOwnedObjects.Count - 1; i >= 0; i--)
                {
                    var ownedObject = clientOwnedObjects[i];
                    if (ownedObject)
                    {
                        // If destroying with owner, then always despawn and destroy (or defer destroying to prefab handler)
                        if (!ownedObject.DontDestroyWithOwner)
                        {
                            if (ownedObject.IsSpawned)
                            {
                                NetworkManager.SpawnManager.DespawnObject(ownedObject, true, true);
                            }
                            else
                            {
                                Object.Destroy(ownedObject.gameObject);
                            }
                        }
                        else if (!NetworkManager.ShutdownInProgress)
                        {
                            // NOTE: All of the below code only handles ownership transfer
                            // For client-server, we just remove the ownership.
                            // For distributed authority (DAHost only), we only transfer objects that are not parented or belong to the session owner.
                            // Rust server handles the object redistribution on its end.
                            if (NetworkManager.DistributedAuthorityMode)
                            {
                                if (ownedObject.IsOwnershipSessionOwner || ownedObject.GetCachedParent())
                                {
                                    continue;
                                }

                                if (ownedObject.IsOwnershipLocked)
                                {
                                    ownedObject.SetOwnershipLock(false);
                                }

                                var targetOwner = NetworkManager.ServerClientId;
                                // Cycle through the full count of clients to find
                                // the next viable owner. If none are found, then
                                // the DAHost defaults to the owner.
                                for (int j = 0; j < remainingClients.Count; j++)
                                {
                                    clientCounter++;
                                    clientCounter = clientCounter % predictedClientCount;
                                    if (ownedObject.Observers.Contains(remainingClients[clientCounter].ClientId))
                                    {
                                        targetOwner = remainingClients[clientCounter].ClientId;
                                        break;
                                    }
                                }
                                if (EnableDistributeLogging)
                                {
                                    Debug.Log($"[Disconnected][Client-{clientId}][NetworkObjectId-{ownedObject.NetworkObjectId} Distributed to Client-{targetOwner}");
                                }

                                NetworkManager.SpawnManager.ChangeOwnership(ownedObject, targetOwner, true);

                                // Ownership gets passed down to all children that have the same owner.
                                var childNetworkObjects = ownedObject.GetComponentsInChildren<NetworkObject>();
                                foreach (var childObject in childNetworkObjects)
                                {
                                    // We already changed ownership for this
                                    if (childObject == ownedObject)
                                    {
                                        continue;
                                    }

                                    // Skip destroy with owner objects as they will be processed by the outer loop
                                    if (!childObject.DontDestroyWithOwner)
                                    {
                                        continue;
                                    }
                                    // If the client owner disconnected, it is ok to unlock this at this point in time.
                                    if (childObject.IsOwnershipLocked)
                                    {
                                        childObject.SetOwnershipLock(false);
                                    }

                                    // Ignore session owner marked objects
                                    if (childObject.IsOwnershipSessionOwner)
                                    {
                                        continue;
                                    }

                                    // If the child's owner is not the client disconnected and the objects are marked with either distributable or transferable, then
                                    // do not change ownership.
                                    if (childObject.OwnerClientId != clientId && (childObject.IsOwnershipDistributable || childObject.IsOwnershipTransferable))
                                    {
                                        continue;
                                    }

                                    var childOwner = targetOwner;
                                    if (!childObject.Observers.Contains(childOwner))
                                    {
                                        for (int j = 0; j < remainingClients.Count; j++)
                                        {
                                            clientCounter++;
                                            clientCounter = clientCounter % predictedClientCount;
                                            if (ownedObject.Observers.Contains(remainingClients[clientCounter].ClientId))
                                            {
                                                childOwner = remainingClients[clientCounter].ClientId;
                                                break;
                                            }
                                        }
                                    }

                                    NetworkManager.SpawnManager.ChangeOwnership(childObject, childOwner, true);
                                    if (EnableDistributeLogging)
                                    {
                                        Debug.Log($"[Disconnected][Client-{clientId}][Child of {ownedObject.NetworkObjectId}][NetworkObjectId-{ownedObject.NetworkObjectId} Distributed to Client-{targetOwner}");
                                    }
                                }
                            }
                            else
                            {
                                ownedObject.RemoveOwnership();
                            }
                        }
                    }
                }


                // TODO: Could(should?) be replaced with more memory per client, by storing the visibility
                foreach (var sobj in NetworkManager.SpawnManager.SpawnedObjectsList)
                {
                    sobj.Observers.Remove(clientId);
                }

                if (ConnectedClients.ContainsKey(clientId))
                {
                    ConnectedClientsList.Remove(ConnectedClients[clientId]);
                    ConnectedClients.Remove(clientId);
                }

                ConnectedClientIds.Remove(clientId);

                if (MessageManager != null)
                {
                    var message = new ClientDisconnectedMessage { ClientId = clientId };
                    foreach (var sendToId in ConnectedClientIds)
                    {
                        // Do not send a disconnect message to ourself
                        if (sendToId == NetworkManager.LocalClientId)
                        {
                            continue;
                        }
                        MessageManager.SendMessage(ref message, MessageDeliveryType<ClientDisconnectedMessage>.DefaultDelivery, sendToId);
                    }
                }

                // Used for testing/validation purposes only
                // Promote a new session owner when the ENABLE_DAHOST_AUTOPROMOTE_SESSION_OWNER scripting define is set
                DaHostPromoteSessionOwner();
            }

            // If the client ID transport map exists
            var (transportId, idExists) = ClientIdToTransportId(clientId);
            if (idExists)
            {
                // Clean up the transport to client (and vice versa) mappings
                var (transportIdDisconnected, wasRemoved) = TransportIdCleanUp(transportId);
                if (wasRemoved)
                {
                    NetworkManager.NetworkConfig.NetworkTransport.DisconnectRemoteClient(transportId);
                    InvokeOnClientDisconnectCallback(clientId);

                    if (LocalClient.IsHost)
                    {
                        InvokeOnPeerDisconnectedCallback(clientId);
                    }
                }
            }

            // Assure the client id is no longer in the pending clients list
            // and stop the server-side client approval timeout since the client
            // is no longer connected.
            RemovePendingClient(clientId);

            // Handle cleaning up the server-side client send queue
            MessageManager.ClientDisconnected(clientId);
        }

        /// <summary>
        /// Server-Side:
        /// Invoked when disconnecting a remote client
        /// </summary>
        internal void DisconnectRemoteClient(ulong clientId)
        {
            MessageManager.ProcessSendQueues();
            OnClientDisconnectFromServer(clientId);
        }

        /// <summary>
        /// Server-Side:
        /// Invoked when disconnecting a remote client with the option to provide
        /// a reason.
        /// </summary>
        internal void DisconnectClient(ulong clientId, string reason = null)
        {
            if (!LocalClient.IsServer)
            {
                if (NetworkManager.NetworkConfig.NetworkTopology == NetworkTopologyTypes.ClientServer)
                {
                    throw new NotServerException($"Only server can disconnect remote clients. Please use `{nameof(Shutdown)}()` instead.");
                }
                else
                {
                    Debug.LogWarning($"Currently, clients cannot disconnect other clients from a distributed authority session. Please use `{nameof(Shutdown)}()` instead.");
                    return;
                }
            }

            if (clientId == NetworkManager.ServerClientId)
            {
                Debug.LogWarning($"Disconnecting the local server-host client is not allowed. Use NetworkManager.Shutdown instead.");
                return;
            }

            var transportId = ClientIdToTransportId(clientId);
            if (transportId.Item2)
            {
                GenerateDisconnectInformation(clientId, transportId.Item1, reason);
            }

            HandleConnectionDisconnect(clientId, reason);
        }

        internal NetworkTransport Transport;
        internal NetworkTransport.DisconnectEvents DisconnectEvent => Transport ? Transport.DisconnectEvent : NetworkTransport.DisconnectEvents.Disconnected;

        /// <summary>
        /// Should be invoked when starting a server-host or client
        /// </summary>
        /// <param name="networkManager"></param>
        internal void Initialize(NetworkManager networkManager)
        {
            // Prepare for a new session
            m_LocalClientTransportId = 0;
            LocalClient.IsApproved = false;
            m_PendingClients.Clear();
            ConnectedClients.Clear();
            ConnectedClientsList.Clear();
            ConnectedClientIds.Clear();
            ClientIdToTransportIdMap.Clear();
            TransportIdToClientIdMap.Clear();
            m_IsTransportConnected = false;
            ClientsToApprove.Clear();
            NetworkObject.OrphanChildren.Clear();
            m_DisconnectReason = string.Empty;
            ServerDisconnectReason = string.Empty;

            NetworkManager = networkManager;
            MessageManager = networkManager.MessageManager;

            Transport = NetworkManager.NetworkConfig.NetworkTransport;
            if (Transport)
            {
                Transport.NetworkMetrics = NetworkManager.MetricsManager.NetworkMetrics;
                Transport.OnTransportEvent += HandleNetworkEvent;
                Transport.Initialize(networkManager);
            }
        }

        /// <summary>
        /// Should be called when shutting down the NetworkManager
        /// </summary>
        internal void Shutdown()
        {
            if (Transport && IsListening)
            {
                Transport.ShuttingDown();
                var clientId = NetworkManager ? NetworkManager.LocalClientId : NetworkManager.ServerClientId;
                // Server and host just log 0 for their transport id while clients will log their cached m_LocalClientTransportId
                var transportId = clientId == NetworkManager.ServerClientId ? 0 : m_LocalClientTransportId;
                GenerateDisconnectInformation(clientId, transportId, $"{nameof(NetworkConnectionManager)} was shutdown.");
            }

            if (LocalClient.IsServer)
            {
                // Build a list of all client ids to be disconnected
                var disconnectedIds = new HashSet<ulong>();

                //Don't know if I have to disconnect the clients. I'm assuming the NetworkTransport does all the cleaning on shutdown. But this way the clients get a disconnect message from server (so long it does't get lost)
                var serverTransportId = GetServerTransportId();
                foreach (KeyValuePair<ulong, NetworkClient> pair in ConnectedClients)
                {
                    if (!disconnectedIds.Contains(pair.Key))
                    {
                        if (pair.Key == serverTransportId)
                        {
                            continue;
                        }

                        disconnectedIds.Add(pair.Key);
                    }
                }

                foreach (KeyValuePair<ulong, PendingClient> pair in PendingClients)
                {
                    if (!disconnectedIds.Contains(pair.Key))
                    {
                        if (pair.Key == serverTransportId)
                        {
                            continue;
                        }

                        disconnectedIds.Add(pair.Key);
                    }
                }

                foreach (var clientId in disconnectedIds)
                {
                    DisconnectRemoteClient(clientId);
                }

                // make sure all messages are flushed before transport disconnects clients
                MessageManager?.ProcessSendQueues();
            }
            else if (NetworkManager != null && NetworkManager.IsListening && LocalClient.IsClient)
            {
                // make sure all messages are flushed before disconnecting
                MessageManager?.ProcessSendQueues();

                // Client only, send disconnect and if transport throws and exception, log the exception and continue the shutdown sequence (or forever be shutting down)
                try
                {
                    Transport?.DisconnectLocalClient();
                }
                catch (Exception ex)
                {
                    Debug.LogException(ex);
                }
            }

            // Reset the approved and connectd flags
            LocalClient.IsApproved = false;
            LocalClient.IsConnected = false;

            // Clear all lists
            ConnectedClients.Clear();
            ConnectedClientIds.Clear();
            ConnectedClientsList.Clear();

            if (NetworkManager != null && NetworkManager.NetworkConfig?.NetworkTransport != null)
            {
                NetworkManager.NetworkConfig.NetworkTransport.OnTransportEvent -= HandleNetworkEvent;
            }

            // This is required for handling the potential scenario where multiple NetworkManager instances are created.
            // See MTT-860 for more information
            if (IsListening)
            {
                //The Transport is set during initialization, thus it is possible for the Transport to be null
                var transport = NetworkManager.NetworkConfig?.NetworkTransport;
                if (transport != null)
                {
                    transport.Shutdown();
                    if (NetworkManager.LogLevel <= LogLevel.Developer)
                    {
                        NetworkLog.LogInfo($"{nameof(NetworkConnectionManager)}.{nameof(Shutdown)}() -> {nameof(IsListening)} && {nameof(NetworkManager.NetworkConfig.NetworkTransport)} != null -> {nameof(NetworkTransport)}.{nameof(NetworkTransport.Shutdown)}()");
                    }
                }
            }
        }

        internal unsafe int SendMessage<TMessageType, TClientIdListType>(ref TMessageType message, NetworkDelivery delivery, in TClientIdListType clientIds)
            where TMessageType : INetworkMessage
            where TClientIdListType : IReadOnlyList<ulong>
        {
            // Prevent server sending to itself
            if (LocalClient.IsServer)
            {
                ulong* nonServerIds = stackalloc ulong[clientIds.Count];
                int newIdx = 0;
                for (int idx = 0; idx < clientIds.Count; ++idx)
                {
                    if (clientIds[idx] == NetworkManager.ServerClientId)
                    {
                        continue;
                    }

                    nonServerIds[newIdx++] = clientIds[idx];
                }

                if (newIdx == 0)
                {
                    return 0;
                }

                return MessageManager.SendMessage(ref message, delivery, nonServerIds, newIdx);
            }

            // else
            if (clientIds.Count != 1 || clientIds[0] != NetworkManager.ServerClientId)
            {
                throw new ArgumentException($"Clients may only send messages to {nameof(NetworkManager.ServerClientId)}");
            }

            return MessageManager.SendMessage(ref message, delivery, clientIds);
        }

        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery, ulong* clientIds, int numClientIds)
            where T : INetworkMessage
        {
            // Prevent server sending to itself
            if (LocalClient.IsServer)
            {
                ulong* nonServerIds = stackalloc ulong[numClientIds];
                int newIdx = 0;
                for (int idx = 0; idx < numClientIds; ++idx)
                {
                    if (clientIds[idx] == NetworkManager.ServerClientId)
                    {
                        continue;
                    }

                    nonServerIds[newIdx++] = clientIds[idx];
                }

                if (newIdx == 0)
                {
                    return 0;
                }

                return MessageManager.SendMessage(ref message, delivery, nonServerIds, newIdx);
            }

            // else
            if (numClientIds != 1 || clientIds[0] != NetworkManager.ServerClientId)
            {
                throw new ArgumentException($"Clients may only send messages to {nameof(NetworkManager.ServerClientId)}");
            }

            return MessageManager.SendMessage(ref message, delivery, clientIds, numClientIds);
        }

        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery, in NativeArray<ulong> clientIds)
            where T : INetworkMessage
        {
            return SendMessage(ref message, delivery, (ulong*)clientIds.GetUnsafePtr(), clientIds.Length);
        }

        internal int SendMessage<T>(ref T message, NetworkDelivery delivery, ulong clientId)
            where T : INetworkMessage
        {
            // Prevent server sending to itself or if there is no MessageManager yet then exit early
            if ((LocalClient.IsServer && clientId == NetworkManager.ServerClientId) || MessageManager == null)
            {
                return 0;
            }

            if (!LocalClient.IsServer && clientId != NetworkManager.ServerClientId)
            {
                throw new ArgumentException($"Clients may only send messages to {nameof(NetworkManager.ServerClientId)}");
            }

            return MessageManager.SendMessage(ref message, delivery, clientId);
        }

        [Conditional("ENABLE_DAHOST_AUTOPROMOTE_SESSION_OWNER")]
        private void DaHostPromoteSessionOwner()
        {
            if (NetworkManager.DistributedAuthorityMode && !NetworkManager.ShutdownInProgress && NetworkManager.IsListening)
            {
                return;
            }

            var newSessionOwner = NetworkManager.LocalClientId;
            if (ConnectedClientIds.Count > 1)
            {
                var lowestRTT = ulong.MaxValue;
                var unityTransport = NetworkManager.NetworkConfig.NetworkTransport as Transports.UTP.UnityTransport;

                foreach (var identifier in ConnectedClientIds)
                {
                    if (identifier == NetworkManager.LocalClientId)
                    {
                        continue;
                    }
                    var rtt = unityTransport.GetCurrentRtt(identifier);
                    if (rtt < lowestRTT)
                    {
                        newSessionOwner = identifier;
                        lowestRTT = rtt;
                    }
                }
            }

            var sessionOwnerMessage = new SessionOwnerMessage()
            {
                SessionOwner = newSessionOwner,
            };
            MessageManager?.SendMessage(ref sessionOwnerMessage, NetworkDelivery.ReliableFragmentedSequenced, ConnectedClientIds);
            NetworkManager.SetSessionOwner(newSessionOwner);
        }
    }
}