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.
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 -e 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 and -n flags. See filterxml --help for details.
Install with $ npm install filterxml and then:
> var filterxml = require('filterxml');
> filterxml(xmlIn, patterns, namespaces, function (err, xmlOut) { ... })
Where
xmlInis a string representing the input XML document.patternsis an array of XPath expressions, like 'book', '/bookstore/book', or '//html:title'. The matching XML nodes will be removed.namespacesis a map from prefixes to namespace URIs, for example{ html: 'http://www.w3.org/TR/html4/' }xmlOutis a string representing the filtered output XML document.
Common XPath expressions to match nodes include:
x:bookto match all book nodes under a namespace associated with thexprefix innamespaces.x:bookstore/x:bookto match all books directly under a bookstore.x:bookstore//x:bookto match all books somewhere under a bookstore.x:bookstore/x:book[1]to match first book directly under a bookstore.bookto match all book nodes that are not under a namespace. This is a quite rare situation in real-world XML documents.
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>
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.
var filterxml = require('filterxml');
var fs = require('fs');
var xmlIn = fs.readFileSync('./norway.kml');
var patterns = ['x:Style'];
var 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>
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.
var patterns = ['foo:drawOrder'];
var 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!
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