Using Xpath With Default Namespace in C# for Canonicalisation

Question

I'm trying to apply the C14N transform to some generated XML. It appears I can't use LINQ to retrieve the nodes to perform the canonicalisation so I have to go 'old school' with the DOM but I think I'm falling foul of the default namespace.

Here is a sample of my code.

static void Main(string[] args)
{
    XmlDocument xDoc = new XmlDocument();

    // Load some test xml
    string path = @"..\..\TestFiles\Test_1.xml";
    if (File.Exists(path) == true)
    { 
        xDoc.PreserveWhitespace = true;
        using (FileStream fs = new FileStream(path, FileMode.Open))
        {
            xDoc.Load(fs);
        }
    }

    //Instantiate an XmlNamespaceManager object. 
    System.Xml.XmlNamespaceManager xmlnsManager = new System.Xml.XmlNamespaceManager(xDoc.NameTable);

    //Add the namespaces used in books.xml to the XmlNamespaceManager.
    xmlnsManager.AddNamespace("", "http://www.myApps.co.uk/");

    // Create a list of nodes to have the Canonical treatment
        //Execute the XPath query using the SelectNodes method of the XmlDocument.
        //Supply the XmlNamespaceManager as the nsmgr parameter.
        //The matching nodes will be returned as an XmlNodeList.
    XmlNodeList nodeList = xDoc.SelectNodes("/ApplicationsBatch/Applications|/ApplicationsBatch/Applications//*", xmlnsManager);

    // Perform the C14N transform on the data
    XmlDsigC14NTransform transform = new XmlDsigC14NTransform();

    transform.LoadInput(nodeList);
    MemoryStream ms = (MemoryStream)transform.GetOutput(typeof(Stream));

    File.WriteAllBytes(@"..\..\TestFiles\ModifiedTest_1", ms.ToArray());
}

And my XML:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<ApplicationsBatch xmlns="http://www.myApps.co.uk/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <MessageHeader>
    <MessageID>00000003</MessageID>
    <Body>11223344556</Body>
    <Timestamp>2011-08-02T09:00:00</Timestamp>
    <MessageCheck>?</MessageCheck>
  </MessageHeader>
  <Applications>
    <Application>
      <ApplicantDetails>
        <Title>MR</Title>
        <Forename>HOMER</Forename>
        <Middlenames>
          <Middlename></Middlename>
        </Middlenames>
        <PresentSurname>SIMPSON</PresentSurname>
        <CurrentAddress>
          <Address>
            <AddressLine1>ADDRESS LINE1</AddressLine1>
            <AddressLine2>ADDRESS LINE2</AddressLine2>
            <AddressTown>ADDRESS Town</AddressTown>
            <AddressCounty>COUNTY</AddressCounty>
            <Postcode>POST CODE</Postcode>
            <CountryCode>GB</CountryCode>
          </Address>
          <ResidentFromGyearMonth>2007-01</ResidentFromGyearMonth>
        </CurrentAddress>
      </ApplicantDetails>
    </Application>
    <Application>
      <ApplicantDetails>
        <Title>MR</Title>
        <Forename>BART</Forename>
        <Middlenames>
          <Middlename></Middlename>
        </Middlenames>
        <PresentSurname>SIMPSON</PresentSurname>
        <CurrentAddress>
          <Address>
            <AddressLine1>ADDRESS LINE1</AddressLine1>
            <AddressLine2>ADDRESS LINE2</AddressLine2>
            <AddressTown>ADDRESS Town</AddressTown>
            <AddressCounty>COUNTY</AddressCounty>
            <Postcode>POST CODE</Postcode>
            <CountryCode>GB</CountryCode>
          </Address>
          <ResidentFromGyearMonth>2007-01</ResidentFromGyearMonth>
        </CurrentAddress>
      </ApplicantDetails>
    </Application>
  </Applications>
</ApplicationsBatch>

I've read a few other topics around the area and came across this Gem but it's not solved the problem.

Using the XPath Visualiser shows the required nodes should be selected but my code fails to select any.

score 0 · Accepted Answer · answered Aug 03 '11 at 08:25

I've found a partial answer to my problem.

When a new namespace is added to the manager it appears that the default namespace can't be an empty string. This is what I ended up with:

//Instantiate an XmlNamespaceManager object. 
System.Xml.XmlNamespaceManager xmlnsManager = new System.Xml.XmlNamespaceManager(xDoc.NameTable);

//Add the namespaces used to the XmlNamespaceManager.
xmlnsManager.AddNamespace("x", "http://www.myApps.co.uk/");

I then needed to modify the XPath to reflect the namespace identifier like this:

// Create a list of nodes to have the Canonical treatment
    //Execute the XPath query using the SelectNodes method of the XmlDocument.
    //Supply the XmlNamespaceManager as the nsmgr parameter.
    //The matching nodes will be returned as an XmlNodeList.
XmlNodeList nodeList = xDoc.SelectNodes("/x:ApplicationsBatch/x:Applications|/x:ApplicationsBatch/x:Applications//*", xmlnsManager);

The nodes are now selected and ready for transformation... although that returns the correct structure of XML but all the values have been removed but that is a problem for another question.

You meant to say you cannot specify a default namespace for use with xpath. It makes sense, since xpath will range over multiple nodes with multiple prefixes, and more importantly will have to deal with nodes with a null namespace, which would look like a default namespace in xpath. Within the XML you have the context to help determine if it is a default or a null namespace. — Gerard ONeill, Sep 01 '16 at 18:48

Using Xpath With Default Namespace in C# for Canonicalisation

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