Hexadecimal value 0x00 is a invalid character

I am generating an XML document from a StringBuilder, basically something like:

string.Format("<text><row>{0}</row><col>{1}</col><textHeight>{2}</textHeight><textWidth>{3}</textWidth><data>{4}</data><rotation>{5}</rotation></text> 

Later, something like:

XmlDocument document = new XmlDocument(); document.LoadXml(xml); XmlNodeList labelSetNodes = document.GetElementsByTagName("labels"); for (int index = 0; index < labelSetNodes.Count; index++) { //do something } 

All the data comes from a database. Recently I've had a few issues with the error:

Hexadecimal value 0x00 is a invalid character, line 1, position nnnnn

But its not consistent. Sometimes some 'blank' data will work. The 'faulty' data works on some PCs, but not others.

In the database, the data is always a blank string. It is never 'null' and in the XML file, it comes out as < data>< /data>, i.e. no character between opening and closing. (but not sure if this can be relied on as I am pulling it from the 'immediate' window is vis studio and pasting it into textpad).

There is possibly differences in the versions of sql server (2008 is where it would fail, 2005 would work) and collation too. Not sure if any of these are likely causes?

But exactly the same code and data will sometimes fail. Any ideas where the problem lies?

7 Answers

Without your actual data or source, it will be hard for us to diagnose what is going wrong. However, I can make a few suggestions:

• Unicode NUL (0x00) is illegal in all versions of XML and validating parsers must reject input that contains it.
• Despite the above; real-world non-validated XML can contain any kind of garbage ill-formed bytes imaginable.
• XML 1.1 allows zero-width and nonprinting control characters (except NUL), so you cannot look at an XML 1.1 file in a text editor and tell what characters it contains.

Given what you wrote, I suspect whatever converts the database data to XML is broken; it's propagating non-XML characters.

Create some database entries with non-XML characters (NULs, DELs, control characters, et al.) and run your XML converter on it. Output the XML to a file and look at it in a hex editor. If this contains non-XML characters, your converter is broken. Fix it or, if you cannot, create a preprocessor that rejects output with such characters.

If the converter output looks good, the problem is in your XML consumer; it's inserting non-XML characters somewhere. You will have to break your consumption process into separate steps, examine the output at each step, and narrow down what is introducing the bad characters.

Check file encoding (for UTF-16)

Update: I just ran into an example of this myself! What was happening is that the producer was encoding the XML as UTF16 and the consumer was expecting UTF8. Since UTF16 uses 0x00 as the high byte for all ASCII characters and UTF8 doesn't, the consumer was seeing every second byte as a NUL. In my case I could change encoding, but suggested all XML payloads start with a BOM.

In my case, it took some digging, but found it.

My Context

I'm looking at exception/error logs from the website using Elmah. Elmah returns the state of the server at the of time the exception, in the form of a large XML document. For our reporting engine I pretty-print the XML with XmlWriter.

During a website attack, I noticed that some xmls weren't parsing and was receiving this '.', hexadecimal value 0x00, is an invalid character. exception.

NON-RESOLUTION: I converted the document to a byte[] and sanitized it of 0x00, but it found none.

When I scanned the xml document, I found the following:

... <form> ... <item name="SomeField"> <value string="C:\boot.ini&#x0;.htm" /> </item> ... 

There was the nul byte encoded as an html entity � !!!

RESOLUTION: To fix the encoding, I replaced the � value before loading it into my XmlDocument, because loading it will create the nul byte and it will be difficult to sanitize it from the object. Here's my entire process:

XmlDocument xml = new XmlDocument(); details.Xml = details.Xml.Replace("�", "[0x00]"); // in my case I want to see it, otherwise just replace with "" xml.LoadXml(details.Xml); string formattedXml = null; // I have this in a helper function, but for this example I have put it in-line StringBuilder sb = new StringBuilder(); XmlWriterSettings settings = new XmlWriterSettings { OmitXmlDeclaration = true, Indent = true, IndentChars = "\t", NewLineHandling = NewLineHandling.None, }; using (XmlWriter writer = XmlWriter.Create(sb, settings)) { xml.Save(writer); formattedXml = sb.ToString(); } 

LESSON LEARNED: sanitize for illegal bytes using the associated html entity, if your incoming data is html encoded on entry.

To add to Sonz's answer above, following worked for us.

//Instead of XmlString.Replace("�", "[0x00]"); // use this XmlString.Replace("\x00", "[0x00]"); 

I also get the same error in an ASP.NET application when I saved some unicode data (Hindi) in the Web.config file and saved it with "Unicode" encoding.

It fixed the error for me when I saved the Web.config file with "UTF-8" encoding.

As kind of a late answer:

I've had this problem with SSRS ReportService2005.asmx when uploading a report.

 Public Shared Sub CreateReport(ByVal strFileNameAndPath As String, ByVal strReportName As String, ByVal strReportingPath As String, Optional ByVal bOverwrite As Boolean = True) Dim rs As SSRS_2005_Administration_WithFOA = New SSRS_2005_Administration_WithFOA rs.Credentials = ReportingServiceInterface.GetMyCredentials(strCredentialsURL) rs.Timeout = ReportingServiceInterface.iTimeout rs.Url = ReportingServiceInterface.strReportingServiceURL rs.UnsafeAuthenticatedConnectionSharing = True Dim btBuffer As Byte() = Nothing Dim rsWarnings As Warning() = Nothing Try Dim fstrStream As System.IO.FileStream = System.IO.File.OpenRead(strFileNameAndPath) btBuffer = New Byte(fstrStream.Length - 1) {} fstrStream.Read(btBuffer, 0, CInt(fstrStream.Length)) fstrStream.Close() Catch ex As System.IO.IOException Throw New Exception(ex.Message) End Try Try rsWarnings = rs.CreateReport(strReportName, strReportingPath, bOverwrite, btBuffer, Nothing) If Not (rsWarnings Is Nothing) Then Dim warning As Warning For Each warning In rsWarnings Log(warning.Message) Next warning Else Log("Report: {0} created successfully with no warnings", strReportName) End If Catch ex As System.Web.Services.Protocols.SoapException Log(ex.Detail.InnerXml.ToString()) Catch ex As Exception Log("Error at creating report. Invalid server name/timeout?" + vbCrLf + vbCrLf + "Error Description: " + vbCrLf + ex.Message) Console.ReadKey() System.Environment.Exit(1) End Try End Sub ' End Function CreateThisReport 

The problem occurs when you allocate a byte array that is at least 1 byte larger than the RDL (XML) file.

Specifically, I used a C# to vb.net converter, that converted

 btBuffer = new byte[fstrStream.Length]; 

into

 btBuffer = New Byte(fstrStream.Length) {} 

But because in C# the number denotes the NUMBER OF ELEMENTS in the array, and in VB.NET, that number denotes the UPPER BOUND of the array, I had an excess byte, causing this error.

So the problem's solution is simply:

 btBuffer = New Byte(fstrStream.Length - 1) {} 

I'm using IronPython here (same as .NET API) and reading the file as UTF-8 in order to properly handle the BOM fixed the problem for me:

xmlFile = Path.Combine(directory_str, 'file.xml') doc = XPathDocument(XmlTextReader(StreamReader(xmlFile.ToString(), Encoding.UTF8))) 

It would work as well with the XmlDocument:

doc = XmlDocument() doc.Load(XmlTextReader(StreamReader(xmlFile.ToString(), Encoding.UTF8))) 

I haved the same issue, when I tried to save the file, whole code is perfect but in the last procedure, the follow error message appears: "'.', Hexadecimal value 0x00 is a invalid character."

1.Looking in the develop tool, I found in the name assigned to sheets collection {Hoja1}, {Cartera}, {JennyG, {MariaD, ...

2.Then I saw last character '}' in the name of sheets should be lost to the any time in the algorithm process to assign names of the sheet from a DataTable Object.

3.On the Name property the real Name of the sheet is "MariaD\0\0\0\0\0\0\0\0\0\0\0\0\0\0", the hidden character in property name is not supported "\0".

4.Finally, the solution is replace current character with "" empty string in the all sheets name.