Alchemy-Websockets - WebSocketClient throws a NullReferenceException

Question

I have two C# programs that should communicate over WebSockets the server is working perfectly (also using Alchemy) and has been for a while now (with javascript clients). However connecting an Alchemy `WebSocketClient` results in an `NullReferenceException` being thrown on the client side. After some debugging I found that the exception is thrown on line 187 of `WebSocketClient.cs` because of the `_context.Connection.Connected` call. The _context.Connection is the same instance as the local `_client` and neither of those are null at that point in time. On the `TcpClient.Connected` page on msdn.microsoft.com there are no possible exceptions listed (indicating to me that it shouldn't throw any exceptions). Going further back I noticed that the `_client` class variable is changed on line 176 of `WebSocketClient.cs` from a normal looking instance to an instance filled with exceptions: BEFORE LINE 176 AFTER LINE 176 Right after this line the Dispose() method of the `Context` that was just…

Accepted Answer

As I see you use TcpClient. This class uses Socket class for data transfer (TcpClient has such field). As far as I know in some cases this field can be null. Property Connected of TcpClient uses Connected property of inner Socket instance. Something like this:

```
public bool Connected 
{
    get 
    {
         return _socket.Connected; // Possible NullRef here!!!
    }
} 
```

So when this field is null you will get NullReferenceException. As far as I know this might happen when connection was not successfully established.

For example I see this in your code:

```
try
{
     _client.EndConnect(result);
}
catch (Exception ex)
{
     Disconnect();
     connectError = true;
}

using (_context = new Context(null, _client))
{
      _context = new Context(null, _client);
      _context.BufferSize = 512;
      // some code
}
```

If connection goes wrong you will get an exception and will do some actions, but in this case your _client will have not initialized Socket field inside. In Context constructor you will try to use it field (in Connected property) and you will get NullReferenceException.

I guess you need to add return in catch block.

OR

Check underlying property Client of your TcpClient (http://msdn.microsoft.com/ru-ru/library/system.net.sockets.tcpclient.client(v=vs.110).aspx) like this:

```
if (_client.Client != null && _client.Connected)
{
    // do what you need
}
```

Hope this will help you.

Alchemy-Websockets - WebSocketClient throws a NullReferenceException

Solution

Problem