canonicalize_xml.rb

#!/usr/bin/env ruby
require 'nokogiri'
document = Nokogiri::XML.parse(STDIN.read) { |c| c.noent.nonet.strict }
xsl =<<XSL
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" encoding="UTF-8" indent="yes" />
  <xsl:strip-space elements="*" />
  <xsl:template match="/">
    <xsl:copy-of select="." />
  </xsl:template>
</xsl:stylesheet>
XSL
xslt = Nokogiri::XSLT(xsl)
xml = xslt.transform(document).to_xml(indent: 2)
puts Nokogiri::XML.parse(xml) { |c| c.noent.nonet.strict }.canonicalize