[xsl] Cosmetic sorting

[Harry Liljeström <harry.liljestrom@xxxxxxxxxxxxx>]

Hi,

I have following input XML structure, this is simplified:

<policy-rules>
  <fw-rule-order>
     fwrule3
     fwrule1
     fwrule2
  </fw-rule-order>
  <fw-rules>
     <rule name="fwrule1">
        <direction>out</direction>
        <action>pass<action>
        <remote>192.168.129.31</remote>
        <local>192.168.129.67</local>
     </rule>
     <rule name="fwrule2">
        <direction>in</direction>
        <action>drop<action>
        <remote>192.168.129.32</remote>
        <local>192.168.129.67</local>
     </rule>
     <rule name="fwrule3">
        <direction>out</direction>
        <action>pass<action>
        <remote>192.168.129.33</remote>
        <local>192.168.129.67</local>
     </rule>
  </fw-rules>
</policy-rules>

XML transformation in XSLT 1.0
<!-- Global variables -->
<xsl:variable name="rule-order">
  <xsl:value-of select="normalize-space(/policy-rules/fw-rule-order)"/>
</xsl:variable>

<xsl:template match="/">
  <policy>
     <xsl:apply-templates select="//fw-rules/rule"/>
  </policy>
</xsl:template>

<xsl:template match="//fw-rules/rule">
  <xsl:variable name="precedence">
     <xsl:call-template name="determineprecedence">
        <xsl:with-param name="string" select="$rule-order"/>
        <xsl:with-param name="value" select="@name"/>
     </xsl:call-template>
  </xsl:variable>
  <rule type="{action}" precedence="{$precedence}">}">
      <xsl:choose>
         <xsl:when test="direction='in'">
            <src>
               <xsl:apply-templates select="remote"/>
            </src>
            <dst>
               <xsl:apply-templates select="local"/>
            </dst>
         </xsl:when>
         <xsl:otherwise>
            <src>
               <xsl:apply-templates select="local"/>
            </src>
            <dst>
               <xsl:apply-templates select="remote"/>
            </dst>
         </xsl:otherwise>
      </xsl:choose>
  </rule>
</xsl:template>

<xsl:template match="remote">
  <xsl:value-of select="."/>
</xsl:template>

<xsl:template match="local">
  <xsl:value-of select="."/>
</xsl:template>

<!-- Named templates -->
<xsl:template name="determineprecedence">
  <xsl:param name="string"/>
  <xsl:param name="value"/>
  <!-- Returns the precedence of the rule -->
</xsl:template>


Output without sorting, after XSLT processor recursion:
<policy>
 <rule type="pass" precedence="1">
    <src>192.168.129.67</src>
    <dst>192.168.129.31</dst>
 </rule>
 <rule type="drop" precedence="2">
    <src>192.168.129.32</src>
    <dst>192.168.129.67</dst>
 </rule>
 <rule type="pass" precedence="0">
    <src>192.168.129.67</src>
    <dst>192.168.129.33</dst>
 </rule>
</policy>

Desired output:
<policy>
 <rule type="pass" precedence="0">
    <src>192.168.129.67</src>
    <dst>192.168.129.33</dst>
 </rule>
 <rule type="pass" precedence="1">
    <src>192.168.129.67</src>
    <dst>192.168.129.31</dst>
 </rule>
 <rule type="drop" precedence="2">
    <src>192.168.129.32</src>
    <dst>192.168.129.67</dst>
 </rule>
</policy>

I have been looking for some examples of the <xsl:sort> use. But I haven't catched any examples how this could be solved. This problem is only cosmetic, because of the precedence attribute. If there are many rules it is more comfortable to read the output file, if it is sorted by the precedence attribute as shown above.

I'm wondering if it is possible apply some kind of post-sorting in the output tree structure, before it is outputted to XML file? If there exists some sorting examples in the web, please point it out to me.

Atleast one solution could be forcing the apply of '//fw-rules/rule' template in the order <fw-rule-order> specifies.

I'm not looking for a prepared solution. I'm delighted if discussion and ideas appears of how this could be solved.

Thanks and Happy New Year 2007,

Harry