First crack at group grain

src/Orleans.AspNetCore.SignalR.Core/Grains/IGroupGrain.cs

@@ -0,0 +1,34 @@
+using Orleans.AspNetCore.SignalR.Observers;
+using System.Threading.Tasks;
+
+namespace Orleans.AspNetCore.SignalR.Grains
+{
+    public interface IGroupGrain : IGrainWithStringKey
+    {
+        /// <summary>
+        /// Adds server to group
+        /// </summary>
+        /// <param name="server">The server</param>
+        /// <returns></returns>
+        Task AddServer(IServerObserver server);
+
+        /// <summary>
+        /// This method is used to confirm the server is still up. The grain implementation will
+        /// expect this method to be invoked after is calls 'IServerObserver.SendToGroup'. IF this
+        /// isn't called after a certain amount of time, the server will be removed from the list of
+        /// servers that hold a connection to this group
+        /// </summary>
+        /// <param name="server"></param>
+        /// <returns></returns>
+        Task ConfirmConnection(IServerObserver server);
+
+        /// <summary>
+        /// Removes server from group
+        /// </summary>
+        /// <param name="server">the server</param>
+        /// <returns></returns>
+        Task RemoveServer(IServerObserver server);
+
+        Task SendMessage(string method, params object[] args);
+    }
+}

src/Orleans.AspNetCore.SignalR.Core/Observers/IServerObserver.cs

@@ -6,5 +6,9 @@ namespace Orleans.AspNetCore.SignalR.Observers
     public interface IServerObserver : IGrainObserver
     {
         void SendHubConnection(string connectionId, Immutable<InvocationMessage> message);
+
+        void SendToGroup(string groupId, Immutable<InvocationMessage> message);
+
+        void SendToUser(string userId, Immutable<InvocationMessage> message);
     }
-}
+}