XmlException: Document element did not appear - line 1, position 1

Question

I'm tring to deserialize a xml string, but for some reason I'm getting the error stated in the title.

This is the code I'm deserializing from:

public void recieveObject<T>(ref T t){
        XmlSerializer xs = new XmlSerializer(typeof(T));
        Debug.Log("Waiting for client");
        byte[] recievedData = udpc.Receive(ref recieveFromEndPoint);

        if(recievedData.Length > 0){
            string xmlStr = System.Text.Encoding.UTF8.GetString(recievedData, 0, recievedData.Length);
            //xmlStr = xmlStr.Replace("\r","").Replace("\n", "").Replace("\t","").Replace(" ", "");
            Debug.Log(xmlStr);

            MemoryStream rms = new MemoryStream(1024);
            rms.Write (System.Text.Encoding.UTF8.GetBytes(xmlStr), 0, System.Text.Encoding.UTF8.GetBytes(xmlStr).Length);
            Debug.Log ("ms: " + System.Text.Encoding.UTF8.GetString(rms.ToArray()));
            t = (T) xs.Deserialize(rms);
        }
    }

As you can see from the commented line I even tried stripping out the white space, but that didn't work eather.

This is the call to the recieveObject function in my code:

recieveObject<Player>(ref player);

And here is my Player class:

using UnityEngine;
using System.Collections;
using System.Xml.Serialization;

[XmlRoot("player")]
public class Player{
    [XmlElement("x")]
    public int x;

    [XmlElement("y")]
    public int y;

    [XmlElement("name")]
    public string name;

    private int maxNameLength = 12;

    public Player(){}
    public Player(int x, int y, string name){
        this.x = x;
        this.y = y;
        if(name.Length > maxNameLength) name = name.Substring(0, maxNameLength);
        this.name = name;
    }
}

and finally the Xml I'm tryng to use to deserialize into a player object:

<player>
  <x>50</x>
  <y>100</y>
  <name>Tester</name>
</player>

Can someone please tell me why I'm getting the error in the title?

Thank you for your time.

Answer 1

You're reading from end of memory stream:

MemoryStream rms = new MemoryStream(1024);
rms.Write (...);

// Now cursor is at end of file, nothing to read here
t = (T) xs.Deserialize(rms);

Just move cursor back to beginning before you deserialize:

rms.Seek(0, SeekOrigin.Begin);
t = (T) xs.Deserialize(rms); // Now deserializer has data to read

Finally just two small suggestions. Don't forget to dispose all disposable objects:

MemoryStream rms = new MemoryStream(1024);
{
}

Also you don't need to read a byte of stream into a string (decoding UTF8) then getting bytes back (from UTF8), this double conversion adds nothing (moreover please note you encode twice because you call GetBytes() twice):

if (recievedData.Length > 0) 
{
    using (MemoryStream rms = new MemoryStream(receivedData))
    {
       t = (T) xs.Deserialize(rms);
    }
}

For logging purposes you can write a function like this (UTF8 conversion will be done only if necessary):

static class Logger
{
    [Conditional("DEBUG")]
    public static void Debug(Func<string> text)
    {
        Debug.Log(text());
    }
}

Your logging will be (and it'll be called only if DEBUG symbol is defined):

Logger.Debug(() => "ms: " + Encoding.UTF8.GetString(rms.ToArray()));

It's just a more pretty alternative to:

#if DEBUG
    Debug.Log ("ms: " + System.Text.Encoding.UTF8.GetString(rms.ToArray()));
#endif