Support InvalidSession(true)

src/Discord.Net.WebSocket/ConnectionManager.cs

@@ -193,6 +193,12 @@ namespace Discord
             _reconnectCancelToken?.Cancel();
             Error(ex);
         }
+        public void Reconnect()
+        {
+            _readyPromise.TrySetCanceled();
+            _connectionPromise.TrySetCanceled();
+            _connectionCancelToken?.Cancel();
+        }
         private async Task AcquireConnectionLock()
         {
             while (true)

src/Discord.Net.WebSocket/DiscordSocketClient.cs

@@ -433,7 +433,11 @@ namespace Discord.WebSocket
 
                             _sessionId = null;
                             _lastSeq = 0;
-                            await ApiClient.SendIdentifyAsync(shardID: ShardId, totalShards: TotalShards).ConfigureAwait(false);
+                            bool retry = (bool)payload;
+                            if (retry)
+                                _connection.Reconnect(); //TODO: Untested
+                            else
+                                await ApiClient.SendIdentifyAsync(shardID: ShardId, totalShards: TotalShards).ConfigureAwait(false);
                         }
                         break;
                     case GatewayOpCode.Reconnect:

test/Discord.Net.Tests/Net/CachedRestClient.cs

@@ -5,11 +5,11 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Net;
+using System.Reactive.Concurrency;
 using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Splat;
-using System.Reactive.Concurrency;
 
 namespace Discord.Net
 {