Some time back in 2009 I blogged about validating Tridion's content delivery configuration files. It was a good idea then, and it's remained a good idea ever since. These days, we're dealing with SDL Web 8 and with the new micro-services architecture, you've got a lot of configuration files to get right. (On my fairly unambitious test system, running staging and live together, I just counted almost 80 configuration files.) Fortunately these seem to be reliably supported with schema files that are simply in each of the microservice folders that you copy during an installation. 

Back when I first wrote the ValidateXmlFile powershell function, I'd left it rather unfinished. It was good enough to let me do some validations and detect problems, but it had a significant flaw, in that if a schema file was not present at the location indicated by the noNamespaceSchemaLocation attribute, it would simply not bother with validation. Considering that we're using an XmlReader to do the validation, this is a pretty reasonable design decision - after all the main purpose is to read in the XML, and validation is perhaps a bit of a side-effect. Fair enough, but it's a nasty hole in our defences, so now that I'm revisiting the technique, I've beefed up the script a bit so that it checks that the location is present and that there's a file in the location. 

I've also made sure that the script does some pushd/popd to make sure that everything is nicely lined up when the location is relative to the file (which it generally is).

Here's the updated script: 

function ValidateXmlFile {
    param ([string]$xmlFile       = $(read-host "Please specify the path to the Xml file"))
	$xmlFile = resolve-path $xmlFile
    "==============================================================="
    "Validating $xmlFile using the schemas locations specified in it"
    "==============================================================="
    # The validating reader silently fails to catch any problems if the schema locations aren't set up properly
    # So attempt to get to the right place....
    pushd (Split-Path $xmlFile)

    try {
        $ns = @{xsi='http://www.w3.org/2001/XMLSchema-instance'}
	# of course, if it's not well formed, it will barf here. Then we've also found a problem
        # use * in the XPath because not all files begin with Configuration any more. We'll still 
        # assume the location is on the root element 
        $locationAttr = Select-Xml -Path $xmlFile -Namespace $ns -XPath */@xsi:noNamespaceSchemaLocation
        if ($locationAttr -eq $null) {throw "Can't find schema location attribute. This ain't gonna work"}

        $schemaLocation = resolve-path $locationAttr.Path
        if ($schemaLocation -eq $null) 
        {
            throw "Can't find schema at location specified in Xml file. Bailing" 
        }

        $settings = new-object System.Xml.XmlReaderSettings
        $settings.ValidationType = [System.Xml.ValidationType]::Schema
        $settings.ValidationFlags = $settings.ValidationFlags `
                -bor [System.Xml.Schema.XmlSchemaValidationFlags]::ProcessSchemaLocation
        $handler = [System.Xml.Schema.ValidationEventHandler] {
            $args = $_ # entering new block so copy $_
            switch ($args.Severity) {
                Error {
                    # Exception is an XmlSchemaException
                    Write-Host "ERROR: line $($args.Exception.LineNumber)" -nonewline
                    Write-Host " position $($args.Exception.LinePosition)"
                    Write-Host $args.Message
                    break
                }
                Warning {
                    # So far, everything that has caused the handler to fire, has caused an Error...
                    # So this /might/ be unreachable
                    Write-Host "Warning:: " + $args.Message
                    break
                }
            }
        }
        $settings.add_ValidationEventHandler($handler)
        $reader = [System.Xml.XmlReader]::Create($xmlfile, $settings)
        while($reader.Read()){}
        $reader.Close()

    }
    catch {
        throw
    }
    finally {
        popd         
    }
}

Of course, what you really want is to be able to verify all your configurations in one go. Once the script is in your powershell $profile, you can put together some fairly simple command-line-fu to take care of that. I have all my microservices in one directory, which I guess is a pretty common pattern, so all I had to do was CD over there and execute the following: 

gci -r -file -include *conf.xml | % {ValidateXmlFile $_}

By running this, I've also picked a couple of things that might be false positives. That aside, this is a real time saver if you're trying to solve issues. There's nothing like being able to eliminate a lot of the stupid typos from consideration all in one go.