Merge branch 'master' into install-plugin

1 files changed, 244 insertions, 1 deletions

diff --git a/Emby.Server.Implementations/Session/SessionWebSocketListener.cs b/Emby.Server.Implementations/Session/SessionWebSocketListener.cs
index d4e4ba1f2..e7b4b0ec3 100644
--- a/Emby.Server.Implementations/Session/SessionWebSocketListener.cs
+++ b/Emby.Server.Implementations/Session/SessionWebSocketListener.cs
@@ -1,8 +1,13 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.WebSockets;
+using System.Threading;
 using System.Threading.Tasks;
 using MediaBrowser.Controller.Net;
 using MediaBrowser.Controller.Session;
 using MediaBrowser.Model.Events;
+using MediaBrowser.Model.Net;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Logging;
 
@@ -14,6 +19,21 @@ namespace Emby.Server.Implementations.Session
     public sealed class SessionWebSocketListener : IWebSocketListener, IDisposable
     {
         /// <summary>
+        /// The timeout in seconds after which a WebSocket is considered to be lost.
+        /// </summary>
+        public const int WebSocketLostTimeout = 60;
+
+        /// <summary>
+        /// The keep-alive interval factor; controls how often the watcher will check on the status of the WebSockets.
+        /// </summary>
+        public const float IntervalFactor = 0.2f;
+
+        /// <summary>
+        /// The ForceKeepAlive factor; controls when a ForceKeepAlive is sent.
+        /// </summary>
+        public const float ForceKeepAliveFactor = 0.75f;
+
+        /// <summary>
         /// The _session manager
         /// </summary>
         private readonly ISessionManager _sessionManager;
@@ -27,6 +47,26 @@ namespace Emby.Server.Implementations.Session
         private readonly IHttpServer _httpServer;
 
         /// <summary>
+        /// The KeepAlive cancellation token.
+        /// </summary>
+        private CancellationTokenSource _keepAliveCancellationToken;
+
+        /// <summary>
+        /// Lock used for accesing the KeepAlive cancellation token.
+        /// </summary>
+        private readonly object _keepAliveLock = new object();
+
+        /// <summary>
+        /// The WebSocket watchlist.
+        /// </summary>
+        private readonly HashSet<IWebSocketConnection> _webSockets = new HashSet<IWebSocketConnection>();
+
+        /// <summary>
+        /// Lock used for accesing the WebSockets watchlist.
+        /// </summary>
+        private readonly object _webSocketsLock = new object();
+
+        /// <summary>
         /// Initializes a new instance of the <see cref="SessionWebSocketListener" /> class.
         /// </summary>
         /// <param name="logger">The logger.</param>
@@ -47,12 +87,13 @@ namespace Emby.Server.Implementations.Session
             httpServer.WebSocketConnected += OnServerManagerWebSocketConnected;
         }
 
-        private void OnServerManagerWebSocketConnected(object sender, GenericEventArgs<IWebSocketConnection> e)
+        private async void OnServerManagerWebSocketConnected(object sender, GenericEventArgs<IWebSocketConnection> e)
         {
             var session = GetSession(e.Argument.QueryString, e.Argument.RemoteEndPoint.ToString());
             if (session != null)
             {
                 EnsureController(session, e.Argument);
+                await KeepAliveWebSocket(e.Argument);
             }
             else
             {
@@ -81,6 +122,7 @@ namespace Emby.Server.Implementations.Session
         public void Dispose()
         {
             _httpServer.WebSocketConnected -= OnServerManagerWebSocketConnected;
+            StopKeepAlive();
         }
 
         /// <summary>
@@ -99,5 +141,206 @@ namespace Emby.Server.Implementations.Session
             var controller = (WebSocketController)controllerInfo.Item1;
             controller.AddWebSocket(connection);
         }
+
+        /// <summary>
+        /// Called when a WebSocket is closed.
+        /// </summary>
+        /// <param name="sender">The WebSocket.</param>
+        /// <param name="e">The event arguments.</param>
+        private void OnWebSocketClosed(object sender, EventArgs e)
+        {
+            var webSocket = (IWebSocketConnection)sender;
+            _logger.LogDebug("WebSocket {0} is closed.", webSocket);
+            RemoveWebSocket(webSocket);
+        }
+
+        /// <summary>
+        /// Adds a WebSocket to the KeepAlive watchlist.
+        /// </summary>
+        /// <param name="webSocket">The WebSocket to monitor.</param>
+        private async Task KeepAliveWebSocket(IWebSocketConnection webSocket)
+        {
+            lock (_webSocketsLock)
+            {
+                if (!_webSockets.Add(webSocket))
+                {
+                    _logger.LogWarning("Multiple attempts to keep alive single WebSocket {0}", webSocket);
+                    return;
+                }
+                webSocket.Closed += OnWebSocketClosed;
+                webSocket.LastKeepAliveDate = DateTime.UtcNow;
+
+                StartKeepAlive();
+            }
+
+            // Notify WebSocket about timeout
+            try
+            {
+                await SendForceKeepAlive(webSocket);
+            }
+            catch (WebSocketException exception)
+            {
+                _logger.LogWarning(exception, "Cannot send ForceKeepAlive message to WebSocket {0}.", webSocket);
+            }
+        }
+
+        /// <summary>
+        /// Removes a WebSocket from the KeepAlive watchlist.
+        /// </summary>
+        /// <param name="webSocket">The WebSocket to remove.</param>
+        private void RemoveWebSocket(IWebSocketConnection webSocket)
+        {
+            lock (_webSocketsLock)
+            {
+                if (!_webSockets.Remove(webSocket))
+                {
+                    _logger.LogWarning("WebSocket {0} not on watchlist.", webSocket);
+                }
+                else
+                {
+                    webSocket.Closed -= OnWebSocketClosed;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Starts the KeepAlive watcher.
+        /// </summary>
+        private void StartKeepAlive()
+        {
+            lock (_keepAliveLock)
+            {
+                if (_keepAliveCancellationToken == null)
+                {
+                    _keepAliveCancellationToken = new CancellationTokenSource();
+                    // Start KeepAlive watcher
+                    _ = RepeatAsyncCallbackEvery(
+                        KeepAliveSockets,
+                        TimeSpan.FromSeconds(WebSocketLostTimeout * IntervalFactor),
+                        _keepAliveCancellationToken.Token);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Stops the KeepAlive watcher.
+        /// </summary>
+        private void StopKeepAlive()
+        {
+            lock (_keepAliveLock)
+            {
+                if (_keepAliveCancellationToken != null)
+                {
+                    _keepAliveCancellationToken.Cancel();
+                    _keepAliveCancellationToken = null;
+                }
+            }
+
+            lock (_webSocketsLock)
+            {
+                foreach (var webSocket in _webSockets)
+                {
+                    webSocket.Closed -= OnWebSocketClosed;
+                }
+
+                _webSockets.Clear();
+            }
+        }
+
+        /// <summary>
+        /// Checks status of KeepAlive of WebSockets.
+        /// </summary>
+        private async Task KeepAliveSockets()
+        {
+            List<IWebSocketConnection> inactive;
+            List<IWebSocketConnection> lost;
+
+            lock (_webSocketsLock)
+            {
+                _logger.LogDebug("Watching {0} WebSockets.", _webSockets.Count);
+
+                inactive = _webSockets.Where(i =>
+                {
+                    var elapsed = (DateTime.UtcNow - i.LastKeepAliveDate).TotalSeconds;
+                    return (elapsed > WebSocketLostTimeout * ForceKeepAliveFactor) && (elapsed < WebSocketLostTimeout);
+                }).ToList();
+                lost = _webSockets.Where(i => (DateTime.UtcNow - i.LastKeepAliveDate).TotalSeconds >= WebSocketLostTimeout).ToList();
+            }
+
+            if (inactive.Any())
+            {
+                _logger.LogInformation("Sending ForceKeepAlive message to {0} inactive WebSockets.", inactive.Count);
+            }
+
+            foreach (var webSocket in inactive)
+            {
+                try
+                {
+                    await SendForceKeepAlive(webSocket);
+                }
+                catch (WebSocketException exception)
+                {
+                    _logger.LogInformation(exception, "Error sending ForceKeepAlive message to WebSocket.");
+                    lost.Add(webSocket);
+                }
+            }
+
+            lock (_webSocketsLock)
+            {
+                if (lost.Any())
+                {
+                    _logger.LogInformation("Lost {0} WebSockets.", lost.Count);
+                    foreach (var webSocket in lost)
+                    {
+                        // TODO: handle session relative to the lost webSocket
+                        RemoveWebSocket(webSocket);
+                    }
+                }
+
+                if (!_webSockets.Any())
+                {
+                    StopKeepAlive();
+                }
+            }
+        }
+
+        /// <summary>
+        /// Sends a ForceKeepAlive message to a WebSocket.
+        /// </summary>
+        /// <param name="webSocket">The WebSocket.</param>
+        /// <returns>Task.</returns>
+        private Task SendForceKeepAlive(IWebSocketConnection webSocket)
+        {
+            return webSocket.SendAsync(new WebSocketMessage<int>
+            {
+                MessageType = "ForceKeepAlive",
+                Data = WebSocketLostTimeout
+            }, CancellationToken.None);
+        }
+
+        /// <summary>
+        /// Runs a given async callback once every specified interval time, until cancelled.
+        /// </summary>
+        /// <param name="callback">The async callback.</param>
+        /// <param name="interval">The interval time.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        /// <returns>Task.</returns>
+        private async Task RepeatAsyncCallbackEvery(Func<Task> callback, TimeSpan interval, CancellationToken cancellationToken)
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                await callback();
+                Task task = Task.Delay(interval, cancellationToken);
+
+                try
+                {
+                    await task;
+                }
+                catch (TaskCanceledException)
+                {
+                    return;
+                }
+            }
+        }
     }
 }