axelpale / filterxml

Simplify your XML by removing XML nodes that match XPath expressions
MIT License
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filterxml

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Keep it simple! Here is a Node.js module to remove unnecessary XML nodes that match given XPath expressions. It uses xpath and xmldom under the hood.

Command-line usageNode APIExamplesWorking with namespaces

Logo

Command-line usage

Install with $ npm install filterxml -g and then:

$ filterxml -e pattern -n prefix=namespaceURI input.xml output.xml

For example, remove Style and StyleMap from a Keyhole Markup Language document with:

$ filterxml --exclude kml:Style --exclude kml:StyleMap \
    --namespace kml=http://www.opengis.net/kml/2.2 \
    source.kml simplified.kml

Specify multiple patterns and namespaces with additional -e, --exclude and -n, --namespace flags. See filterxml --help for details.

Node API usage

Install with $ npm install filterxml and then:

> const filterxml = require('filterxml')
> filterxml(xmlIn, patterns, namespaces, function (err, xmlOut) { ... })

Where

Common XPath expressions to match nodes include:

Limitations

Internally, filterxml depends on xmldom that respects the standard Web API XMLSerializer. The serializer can sometimes produce unexpected results:

Example

Let us filter out all book nodes:

const xmlIn = '<bookstore>' +
    '<book>Animal Farm</book>' +
    '<book>Nineteen Eighty-Four</book>' +
    '<essay>Reflections on Writing</essay>' +
  '</bookstore>'

filterxml(xmlIn, ['book'], {}, function (err, xmlOut) {
  if (err) { throw err }
  console.log(xmlOut)
})

Outputs:

<bookstore><essay>Reflections on Writing</essay></bookstore>

Real-world example

Let us remove Style tags from a Keyhole Markup Language (KML) file:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
  <Document>
    <name>Awesome locations</name>
    <Style id="s_ylw-pushpin060">
      <IconStyle>
        <scale>1.1</scale>
        <Icon>
          <href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>
        </Icon>
        <hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
      </IconStyle>
      <PolyStyle>
        <fill>0</fill>
      </PolyStyle>
    </Style>
    <Placemark>
      <name>Reykjavik</name>
      <Point>
        <coordinates>-21.933333,64.133333,0</coordinates>
      </Point>
    </Placemark>
  </Document>
</kml>

We read the file, filter it, and save the result. Note how we must add a namespace prefix into our pattern to match nodes under the namespace defined in kml node. Note also how we must associate any used prefix with a namespace URI.

const filterxml = require('filterxml')
const fs = require('fs')

const xmlIn = fs.readFileSync('./norway.kml')
const patterns = ['x:Style']
const namespaces = {
  x: 'http://www.opengis.net/kml/2.2'
}

filterxml(xmlIn, patterns, namespaces, function (err, xmlOut) {
  if (err) { throw err }
  fs.writeFileSync('./norway-simplified.kml', xmlOut)
})

The resulting norway-simplified.kml:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
  <Document>
    <name>Awesome locations</name>
    <Placemark>
      <name>Reykjavik</name>
      <Point>
        <coordinates>-21.933333,64.133333,0</coordinates>
      </Point>
    </Placemark>
  </Document>
</kml>

Working with namespaces

Often XML documents specify multiple namespaces. For example:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2">
  <Point>
    <gx:drawOrder>1</gx:drawOrder>
    <coordinates>25.59176188650433,45.6493071755744,0</coordinates>
  </Point>
</kml>

To match and remove the gx:drawOrder node we can not just filterxml(xmlIn, ['gx:drawOrder'], {}, callback). The callback would receive an error No namespace associated with prefix gx in gx:drawOrder. Instead, we must specify what the prefix gx in our XPath pattern means. It misleadingly looks like it has already been specified in the kml tag. We cannot blindly trust it. This is because the same prefix can map to different namespace URI in different part of the document:

<?xml version="1.0" encoding="UTF-8"?>
<mymap>
  <Places xmlns:kml="http://www.opengis.net/kml/2.2">
    <kml:Placemark>
      <kml:name>A place described with OpenGIS markup</kml:name>
    </kml:Placemark>
  </Places>
  <Cities xmlns:kml="http://www.google.com/kml/ext/2.2">
    <kml:Placemark>
      <kml:name>A place described with Google's KML markup</kml:name>
    </kml:Placemark>
  </Cities
</mymap>

Therefore we must always specify the prefixes we use in our XPath patterns. To remove gx:drawOrder the following is a valid approach. Note that we can use whatever prefix we want as long as we associate it with a correct namespace URI.

const patterns = ['foo:drawOrder']
const namespaces = { foo: 'http://www.google.com/kml/ext/2.2' }
filterxml(xmlIn, patterns, namespaces, function (err, xmlOut) {
  ...
})

The snippet above results with xmlOut equal to:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2">
  <Point>
    <coordinates>25.59176188650433,45.6493071755744,0</coordinates>
  </Point>
</kml>

So, always declare your prefixes!

Licence

MIT