Question

I’m exploring MSMQ services, and I wrote a simple console client-server application that sends each of the client’s keystrokes to the server. Whenever hit a control character (DEL, ESC, INS, etc) the server understandably throws an error. However, whenever I type a space character, the server receives the packet but doesn’t throw an error and doesn’t display the space.

Server:

namespace QIM
{
    class Program
    {
        const string QUEUE = @".\Private$\qim";
        static MessageQueue _mq;
        static readonly object _mqLock = new object();
        static XmlSerializer xs;

        static void Main(string[] args)
        {
            lock (_mqLock)
            {
                if (!MessageQueue.Exists(QUEUE))
                    _mq = MessageQueue.Create(QUEUE);
                else
                    _mq = new MessageQueue(QUEUE);
            }
            xs = new XmlSerializer(typeof(string));
            _mq.BeginReceive(new TimeSpan(0, 1, 0), new object(), OnReceive);
            while (Console.ReadKey().Key != ConsoleKey.Escape) { }
        }

        static void OnReceive(IAsyncResult result)
        {
            Message msg;
            lock (_mqLock)
            {
                try
                {
                    msg = _mq.EndReceive(result);
                    Console.Write(".");
                    Console.Write(xs.Deserialize(msg.BodyStream));
                }
                catch (Exception ex)
                {
                    Console.Write(ex);
                }
            }
            _mq.BeginReceive(new TimeSpan(0, 1, 0), new object(), OnReceive);
        }
    }
}

Client:

namespace QIM_Client
{
    class Program
    {
        const string QUEUE = @".\Private$\qim";
        static MessageQueue _mq;

        static void Main(string[] args)
        {
            if (!MessageQueue.Exists(QUEUE))
                _mq = MessageQueue.Create(QUEUE);
            else
                _mq = new MessageQueue(QUEUE);
            ConsoleKeyInfo key = new ConsoleKeyInfo();
            while (key.Key != ConsoleKey.Escape)
            {
                key = Console.ReadKey();
                _mq.Send(key.KeyChar.ToString());
            }
        }
    }
}

Client Input:

Testing, Testing…

Server Output:

.T.e.s.t.i.n.g.,..T.e.s.t.i.n.g……

You’ll notice that the space character sends a message, but the character isn’t displayed.

Answer 1

Your issue is not with MSMQ, it’s with the XmlSerializer class. See:

var key = Console.ReadKey();

XmlSerializer s = new XmlSerializer(typeof(string));

using (System.IO.MemoryStream ms = new System.IO.MemoryStream())
{
    s.Serialize(ms, key.KeyChar.ToString());

    ms.Position = 0;

    var foo = (string)s.Deserialize(ms);
}

If you type a space in the console, you’ll see that key.KeyChar.ToString() yields " ", but foo is equal to "". Because of the default implementation of XmlReader, the XmlSerializer class considers a string of only whitespace to be empty; if the string contains any other characters, both leading and trailing spaces are preserved. The whitespace does get serialized, but deserializing it turns it into an empty string.

Use this instead:

Console.Write(
    s.Deserialize(System.Xml.XmlReader.Create(msg.BodyStream, 
                                          new System.Xml.XmlReaderSettings() 
                                          { 
                                              IgnoreWhitespace = false 
                                          })));