' ', hexadecimal value 0x1F, is an invalid

Question

I am trying to read a xml file from the web and parse it out using XDocument. It normally works fine but sometimes it gives me this error for day:

 **' ', hexadecimal value 0x1F, is an invalid character. Line 1, position 1**

I have tried some solutions from Google but they aren't working for VS 2010 Express Windows Phone 7.

There is a solution which replace the 0x1F character to string.empty but my code return a stream which doesn't have replace method.

s = s.Replace(Convert.ToString((byte)0x1F), string.Empty);

Here is my code:

        void webClient_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
    {
        using (var reader = new StreamReader(e.Result))
        {
            int[] counter = { 1 };  
            string s = reader.ReadToEnd();
            Stream str = e.Result;
       //     s = s.Replace(Convert.ToString((byte)0x1F), string.Empty);
    //        byte[] str = Convert.FromBase64String(s);
     //       Stream memStream = new MemoryStream(str);
            str.Position = 0;
            XDocument xdoc = XDocument.Load(str);                

            var data = from query in xdoc.Descendants("user")
                       select new mobion
                       {
                           index = counter[0]++,
                           avlink = (string)query.Element("user_info").Element("avlink"),
                           nickname = (string)query.Element("user_info").Element("nickname"),
                           track = (string)query.Element("track"),
                           artist = (string)query.Element("artist"),
                       };
            listBox.ItemsSource = data;
        }
    }

XML file: http://music.mobion.vn/api/v1/music/userstop?devid=

Answer 1

0x1f is a Windows control character. It is not valid XML. Your best bet is to replace it.

Instead of using reader.ReadToEnd() (which by the way - for a large file - can use up a lot of memory.. though you can definitely use it) why not try something like:

string input;
while ((input = sr.ReadLine()) != null)
{
    string = string + input.Replace((char)(0x1F), ' ');
}

you can re-convert into a stream if you'd like, to then use as you please.

byte[] byteArray = Encoding.ASCII.GetBytes( input );
MemoryStream stream = new MemoryStream( byteArray );

Or else you could keep doing readToEnd() and then clean that string of illegal characters, and convert back to a stream.

Here's a good resource for cleaning illegal characters in your xml - chances are, youll have others as well...

https://seattlesoftware.wordpress.com/tag/hexadecimal-value-0x-is-an-invalid-character/

Answer 2

I'd guess it's probably an encoding issue but without seeing the XML I can't say for sure.

In terms of your plan to simply replace the character but not being able to, because you have a stream rather than a text, simply read the stream into a string and then remove the characters you don't want.

Answer 3

Consider using System.Web.HttpUtility.HtmlDecode if you're decoding content read from the web.

Answer 4

What could be happening is that the content is compressed in which case you need to decompress it.

With HttpHandler you can do this the following way:

var client = new HttpClient(new HttpClientHandler
{
    AutomaticDecompression = DecompressionMethods.GZip
                             | DecompressionMethods.Deflate
});

With the "old" WebClient you have to derive your own class to achieve the similar effect:

class MyWebClient : WebClient
{
    protected override WebRequest GetWebRequest(Uri address)
    {
        HttpWebRequest request = base.GetWebRequest(address) as HttpWebRequest;
        request.AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip;
        return request;
    }
}

Above taken from here

To use the two you would do something like this:

HttpClient

using (var client = new HttpClient(new HttpClientHandler { AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate }))
{
    using (var stream = client.GetStreamAsync(url))
    {
        using (var sr = new StreamReader(stream.Result))
        {
            using (var reader = XmlReader.Create(sr))
            {
                var feed = System.ServiceModel.Syndication.SyndicationFeed.Load(reader);
                foreach (var item in feed.Items)
                {
                    Console.WriteLine(item.Title.Text);
                }   
            }
        }
    }
}

WebClient

using (var stream = new MyWebClient().OpenRead("http://myrss.url"))
{
    using (var sr = new StreamReader(stream))
    {
        using (var reader = XmlReader.Create(sr))
        {
            var feed = System.ServiceModel.Syndication.SyndicationFeed.Load(reader);
            foreach (var item in feed.Items)
            {
                Console.WriteLine(item.Title.Text);
            }
        }
    }
}

This way you also recieve the benefit of not having to .ReadToEnd() since you are working with the stream instead.

Answer 5

If you are having issues replacing the character

For me there were some issues if you try to replace using the string instead of the char. I suggest trying some testing values using both to see what they turn up. Also how you reference it has some effect.

var a = x.IndexOf('\u001f');                      // 513
var b = x.IndexOf(Convert.ToString((byte)0x1F));  // -1
x = x.Replace(Convert.ToChar((byte)0x1F), ' ');   // Works
x = x.Replace(Convert.ToString((byte)0x1F), " "); // Fails

I blagged this

Answer 6

Nobody can answer if you don't show relevant info - I mean the Xml content.

As a general advice I would put a breakpoint after ReadToEnd() call. Now you can do a couple of things:

• Reveal Xml content to this forum.
• Test it using VS Xml visualizer.
• Copy-paste the string into a txt file and investigate it offline.