How to validate xml for correct syntax/format(?)

Question

I want to create a function in my custom toolbox-module that uses a custom xml file to provide instructions (passed on using a $xmlpath parameter). How can I validate that the provided xml is using the correct xml type/syntax/format(correct elements, root-node etc.)?

If I use a schema-file: How do I validate xml against it using ex. Test-XML (PSCX cmdlet)? Do I store the xsd file online and specify it's path in the xml-document? Do I store it in my modules-folder and hard-code it into the script? If so, how do I specify schema-path? Codesample:

#Stored in ..\Modules\MyModule\Process-Config.psm1)
function Process-Config
{
    param($xmlpath)
    #Test that file is xml
    try{ $xml = [xml](Get-Content $xmlpath) } catch {}

    #Test that xml-file is valid against schema in Module-folder (Modules\MyModule\xmlschema.xsd)
    #Using Test-XML PSCX cmdlet
    Test-XML -Path $xmlpath -SchemaPath #Schemapath#

}

EDIT: I found out that $PSScriptRoot gives module-location so I can use $PSScriptRoot\Schemas\MySchema.xsd as path. I thought it just worked on scripts, but seems functions work too. Do I specify schema in xml for a local file like this or publish the xsd online with schema-address in the xml file?

Answer 1

If you want a basic test of an XML-File (without validating XML Schemata or a dependency on an external module), you could use the function Test-XMLFile from Jonathan Medd:

function Test-XMLFile {
    <#
        .SYNOPSIS
        Test the validity of an XML file
    #>
    [CmdletBinding()]
    param (
        [parameter(mandatory=$true)][ValidateNotNullorEmpty()][string]$xmlFilePath
    )

    # Check the file exists
    if (!(Test-Path -Path $xmlFilePath)){
        throw "$xmlFilePath is not valid. Please provide a valid path to the .xml fileh"
    }
    # Check for Load or Parse errors when loading the XML file
    $xml = New-Object System.Xml.XmlDocument
    try {
        $xml.Load((Get-ChildItem -Path $xmlFilePath).FullName)
        return $true
    }
    catch [System.Xml.XmlException] {
        Write-Verbose "$xmlFilePath : $($_.toString())"
        return $false
    }
}

and if you want to check a lot of XML-Files, you could use something like

gci -recurse *.xml |% {
 $outcome = Test-XMLFile $_.FullName -Verbose
}

which will show you which XML-File has what problem.

Answer 2

This is not tested, but based on a utility I wrote to check XML against the schemas it declares it uses. At its core it creates an XmlReader configured to perform XSD based validation and allowed to load referenced schemas.

$readerSettings = New-Object 'System.Xml.XmlReaderSettings';
$readerSettings.ValidationFlags = [System.Xml.Schema.XmlSchemaValidationFlags]::ProcessInlineSchema -bor
                                  [System.Xml.Schema.XmlSchemaValidationFlags]::ProcessSchemaLocation -bor
                                  [System.Xml.Schema.XmlSchemaValidationFlags]::ReportValidationWarnings -bor
                                  [System.Xml.Schema.XmlSchemaValidationFlags]::ProcessIdentityConstraints;
$readerSettings.ValidationType = [System.Xml.ValidationType]::Schema;

$results = @()

$valHandler = [System.Xml.Schema.ValidationEventHandler]{
  # $_ is the second argument of type System.Xml.ValidationEventArgs
  $script:results += "{0}: {1}" -f $_.Severity, $_.Message;
}

$readerSettings.add_ValidationEventHandler($valHandler)

$reader = [System.Xml.XmlReader]::Create($xmlFileName, $readerSettings);

while ($reader.Read()) {
  # Do nothing...
}

$results;  # Return the array of validation errors and warnings.

Note:

• There are a number of exceptions that can be thrown, both when creating the reader and while processing the XML (eg. invalid XML, can't find a referenced schema).
• There is a lot more control available than shown here, going through the documentation for XmlReaderSettings and ValidationEventArgs (for a start) will be beneficial.
• The common way to specify the schema (XSD) for a file is the use of a schemaLocation attribute (from the http://www.w3.org/2001/XMLSchema-instance namespace) which contains a list of {namespace, XSD-schmea} pairs. However XmlReaderSettings.Schemas can also be used to specify schema outside the document.

Answer 3

Specify the file path to XSD file, preferably via a relative path unless the XSD is stored in a well known path on each PC you plan to run the script. For relative path, yeah use $PSScriptRoot e.g.

$xsd = $PSScriptRoot\schema.xsd
Test-Xml -XmlPath $xmlPath -SchemaPath $xsd

Answer 4

I'm not quite sure if you mean to check XML validity as a function of a program, or from a service.

First of all, there are a lot of things to learn in XML, I found a resource that I'm working through: learn XML in a weekend. You might find this helpful. You don't have to know everything in it, in one go.

Here is an online service which will check the validity of an XML document.

If you want a program to be able to do that, I think you need some kind of xml lint, maybe something like: xmlint.

Finally, if you want to write a program that uses an xml lint like API, then you should specify which programming language you are using. I hope this helps a little. CHEERS!