Fixed: Support for SignalR's Server Sent Events transport as an alternative to websockets and long polling

frontend/src/Components/SignalRConnector.js

@@ -84,7 +84,7 @@ class SignalRConnector extends Component {
   constructor(props, context) {
     super(props, context);
 
-    this.signalRconnectionOptions = { transport: ['webSockets', 'longPolling'] };
+    this.signalRconnectionOptions = { transport: ['webSockets', 'serverSentEvents', 'longPolling'] };
     this.signalRconnection = null;
     this.retryInterval = 1;
     this.retryTimeoutId = null;

src/NzbDrone.Host/Owin/MiddleWare/SignalRMiddleWare.cs

@@ -16,9 +16,14 @@ namespace NzbDrone.Host.Owin.MiddleWare
             SignalRDependencyResolver.Register(container);
             SignalRJsonSerializer.Register();
 
-            // Half the default time (110s) to get under nginx's default 60 proxy_read_timeout
-            GlobalHost.Configuration.ConnectionTimeout = TimeSpan.FromSeconds(55);
-            GlobalHost.Configuration.DisconnectTimeout = TimeSpan.FromMinutes(3);
+            // Note there are some important timeouts involved here:
+            // nginx has a default 60 sec proxy_read_timeout, this means the connection will be terminated if the server doesn't send anything within that time.
+            // Previously we lowered the ConnectionTimeout from 110s to 55s to remedy that, however all we should've done is set an appropriate KeepAlive.
+            // By default KeepAlive is 1/3rd of the DisconnectTimeout, which we set incredibly high 5 years ago, resulting in KeepAlive being 1 minute.
+            // So when adjusting these values in the future, please keep that all in mind.
+            GlobalHost.Configuration.ConnectionTimeout = TimeSpan.FromSeconds(110);
+            GlobalHost.Configuration.DisconnectTimeout = TimeSpan.FromSeconds(180);
+            GlobalHost.Configuration.KeepAlive = TimeSpan.FromSeconds(30);
         }
 
         public void Attach(IAppBuilder appBuilder)

src/NzbDrone.SignalR/SignalRJsonSerializer.cs

@@ -13,6 +13,7 @@ namespace NzbDrone.SignalR
         {
             _serializerSettings = Json.GetSerializerSettings();
             _serializerSettings.ContractResolver = new SignalRContractResolver();
+            _serializerSettings.Formatting = Formatting.None; // ServerSentEvents doesn't like newlines
 
             _serializer = JsonSerializer.Create(_serializerSettings);