XmlPeek not working correctly for element nodes

[peter-perot]

What You Are Seeing?

I have the following XML document:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <WebPublishMethod>FileSystem</WebPublishMethod>
    <LastUsedBuildConfiguration>DeploymentTemplate</LastUsedBuildConfiguration>
    <LastUsedPlatform>Any CPU</LastUsedPlatform>
    <SiteUrlToLaunchAfterPublish />
    <LaunchSiteAfterPublish>True</LaunchSiteAfterPublish>
    <ExcludeApp_Data>False</ExcludeApp_Data>
    <publishUrl>C:\Deployment\DeploymentTemplate\WebApi</publishUrl>
    <DeleteExistingFiles>False</DeleteExistingFiles>
  </PropertyGroup>
</Project>

The following code does not yield the publishUrl element (instead null ist returned and a warning is logged):

var xmlPeekSettings = new XmlPeekSettings
{
  Namespaces = new Dictionary<string, string>{
    { "msbuild", "http://schemas.microsoft.com/developer/msbuild/2003" }
  }
};

var xmlElementContents = XmlPeek(pubXmlFile,
  "/msbuild:Project/msbuild:PropertyGroup/msbuild:publishUrl", xmlPeekSettings);

Running the same code using the standard .NET XPathDocument works okay.

What is Expected?

XmlPeek should return the contents of the publishUrl element, i.e. C:\Deployment\DeploymentTemplate\WebApi.

When using XPathDocument everything works okay:

using (var stream = new System.IO.FileStream(pubXmlFile.ToString(), FileMode.Open))
{
  var xPathDocument = new System.Xml.XPath.XPathDocument(stream);
  var navigator = xPathDocument.CreateNavigator();

  System.Xml.XmlNamespaceManager ns = null;

  if (navigator.NameTable != null)
  {
    ns = new System.Xml.XmlNamespaceManager(navigator.NameTable);
    ns.AddNamespace("msbuild", "http://schemas.microsoft.com/developer/msbuild/2003");
  }

  var node = navigator.SelectSingleNode(
    "/msbuild:Project/msbuild:PropertyGroup/msbuild:publishUrl", ns);
}

Here node contains the selected node.

What version of Cake are you using?

Version 0.17.0

Are you running on a 32 or 64 bit system?

64bit

What environment are you running on? Windows? Linux? Mac?

Windows

How Did You Get This To Happen? (Steps to Reproduce)

See code above.

[peter-perot]

[Proposal for a Bugfix]

After some investigation I found the bug. Have a look at line

cake/src/Cake.Common/Xml/XmlPeekAliases.cs

Line 141 in 303b1d0

var node = document.SelectSingleNode(xpath, namespaceManager);

:

When calling method SelectSingleNode(...) on an instance of XmlDocument, an XmlNode is returned. Then in turn when reading the Value property of the XmlNode, null is returned for nodes of type XmlNodeType.Element (so say the docs from Microsoft).

This does not happen if you are using an XPathNavigator - yes, this is really weird, but it works.

Here the corrected code:

/// <summary>
/// Gets the value of a target node.
/// </summary>
/// <returns>The value found at the given XPath query (or the first, if multiple eligible nodes are found).</returns>
/// <param name="source">The xml to peek into.</param>
/// <param name="xpath">The xpath of the single node to get.</param>
/// <param name="settings">Additional settings to tweak Xml Peek behavior.</param>
private static string XmlPeek(XmlReader source, string xpath, XmlPeekSettings settings)
{
    if (source == null)
    {
        throw new ArgumentNullException(nameof(source));
    }

    if (string.IsNullOrWhiteSpace(xpath))
    {
        throw new ArgumentNullException(nameof(xpath));
    }

    if (settings == null)
    {
        throw new ArgumentNullException(nameof(settings));
    }

    var document = new XmlDocument();
    document.PreserveWhitespace = settings.PreserveWhitespace;
    document.Load(source);

    var navigator = document.CreateNavigator();
    XmlNamespaceManager namespaceManager = null;

    if (navigator.NameTable != null)
    {
        namespaceManager = new XmlNamespaceManager(navigator.NameTable);
        foreach (var xmlNamespace in settings.Namespaces)
        {
            namespaceManager.AddNamespace(xmlNamespace.Key /* Prefix */, xmlNamespace.Value /* URI */);
        }
    }

    var node = navigator.SelectSingleNode(xpath, namespaceManager);
    return node?.Value;
}

Hint:

Have a look at the XML doc comments in this file - some are misleading. For the method above I already corrected the comments.

[alvaromongon]

I have just updated to Cake version 0.21.1 and it is still happening.

Any estimation about when this will be fixed?

Thanks!

[peter-perot]

Currently I don't have time to drop a pull request, but the code I posted above fixes the issue. Maybe some of the Cake guys can take the code snippet and fix that bug. ;-)

[devlead]

fixed by #1701