Support for keepalives. Resolves #12

Author: tpeczek

Lib.AspNetCore.ServerSentEvents/ServerSentEventsKeepaliveMode.cs

@@ -1,17 +1,21 @@
 namespace Lib.AspNetCore.ServerSentEvents
 {
     /// <summary>
-    /// The keepalive event sending mode.
+    /// The keepalive sending mode.
     /// </summary>
     public enum ServerSentEventsKeepaliveMode
     {
         /// <summary>
-        /// Always send keepalive event.
+        /// Always send keepalive.
         /// </summary>
         Always,
         /// <summary>
-        /// Never send keepalive event.
+        /// Never send keepalive.
         /// </summary>
-        Never
+        Never,
+        /// <summary>
+        /// Send keepalive if ANCM is detected.
+        /// </summary>
+        BehindAncm
     }
 }

Lib.AspNetCore.ServerSentEvents/ServerSentEventsKeepaliveService.cs

@@ -11,6 +11,7 @@ internal class ServerSentEventsKeepaliveService<TServerSentEventsService> : IHos
         where TServerSentEventsService : ServerSentEventsService
     {
         #region Fields
+        private readonly bool _isBehindAncm = IsBehindAncm();
         private readonly static ServerSentEventBytes _keepaliveServerSentEventBytes = ServerSentEventsHelper.GetCommentBytes("KEEPALIVE");
 
         private readonly CancellationTokenSource _stoppingCts = new CancellationTokenSource();
@@ -32,7 +33,7 @@ public ServerSentEventsKeepaliveService(TServerSentEventsService serverSentEvent
         #region Methods
         public virtual Task StartAsync(CancellationToken cancellationToken)
         {
-            if (_options.KeepaliveMode == ServerSentEventsKeepaliveMode.Always)
+            if ((_options.KeepaliveMode == ServerSentEventsKeepaliveMode.Always) || ((_options.KeepaliveMode == ServerSentEventsKeepaliveMode.BehindAncm) && _isBehindAncm))
             {
                 _executingTask = ExecuteAsync(_stoppingCts.Token);
 
@@ -73,6 +74,13 @@ private async Task ExecuteAsync(CancellationToken stoppingToken)
             }
         }
 
+        private static bool IsBehindAncm()
+        {
+            return !String.IsNullOrEmpty(Environment.GetEnvironmentVariable($"ASPNETCORE_PORT"))
+                && !String.IsNullOrEmpty(Environment.GetEnvironmentVariable($"ASPNETCORE_APPL_PATH"))
+                && !String.IsNullOrEmpty(Environment.GetEnvironmentVariable($"ASPNETCORE_TOKEN"));
+        }
+
         public virtual void Dispose()
         {
             _stoppingCts.Cancel();

Lib.AspNetCore.ServerSentEvents/ServerSentEventsServiceOptions.cs

@@ -13,12 +13,12 @@ public class ServerSentEventsServiceOptions<TServerSentEventsService> where TSer
         private int _keepaliveInterval = DEFAULT_KEEPALIVE_INTERVAL;
 
         /// <summary>
-        /// Gets or sets the keepalive event sending mode.
+        /// Gets or sets the keepalive sending mode.
         /// </summary>
-        public ServerSentEventsKeepaliveMode KeepaliveMode { get; set; } = ServerSentEventsKeepaliveMode.Never;
+        public ServerSentEventsKeepaliveMode KeepaliveMode { get; set; } = ServerSentEventsKeepaliveMode.BehindAncm;
 
         /// <summary>
-        /// Gets or sets the keepalive event interval (in seconds).
+        /// Gets or sets the keepalive interval (in seconds).
         /// </summary>
         public int KeepaliveInterval
         {