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xdv 0.4b3

XDV implements a subset of Deliverance using a pure XSLT engine. With XDV, you "compile" your theme and ruleset in one step, then use a superfast/simple transform on each request thereafter. Alternatively, compile your theme during development, check it into Subversion, and not touch XDV during deployment.

XDV has been renamed to Diazo. Visit the Diazo website or the Diazo PyPI page for further information.

Introduction

XDV is an implementation of the Deliverance concept using pure XSLT. In short, it is a way to apply a style/theme contained in a static HTML web page (usually with related CSS, JavaScript and image resources) to a dynamic website created using any server-side technology.

Consider a scenario where you have a dynamic website, to which you want to apply a theme built by a web designer. The web designer is not familiar with the technology behind the dynamic website, and so has supplied a "static HTML" version of the site. This consists of an HTML file with more-or-less semantic markup, one or more style sheets, and perhaps some other resources like images or JavaScript files.

Using XDV, you could apply this theme to your dynamic website as follows:

  1. Identify the placeholders in the theme file that need to be replaced with dynamic elements. Ideally, these should be clearly identifiable, for example with a unique HTML id attribute.
  2. Identify the corresponding markup in the dynamic website. Then write a "replace" or "copy" rule using XDV's rules syntax that replaces the theme's static placeholder with the dynamic content.
  3. Identify markup in the dynamic website that should be copied wholesale into the theme. CSS and JavaScript links in the <head /> are often treated this way. Write an XDV "append" or "prepend" rule to copy these elements over.
  4. Identify parts of the theme and/or dynamic website that are superfluous. Write an XDV "drop" rule to remove these elements.

The rules file is written using a simple XML syntax. Elements in the theme and "content" (the dynamic website) can be identified using CSS3 or XPath selectors.

Once you have a theme HTML file and a rules XML file, you compile these using the XDV compiler into a single XSLT file. You can then deploy this XSLT file with your application. An XSLT processor (such as mod_transform in Apache) will then transform the dynamic content from your website into the themed content your end users see. The transformation takes place on-the-fly for each request.

Bear in mind that:

  • You never have to write, or even read, a line of XSLT (unless you want to).
  • The XSLT transformation that takes place for each request is very fast.
  • Static theme resources (like images, stylesheets or JavaScript files) can be served from a static webserver, which is normally much faster than serving them from a dynamic application.
  • You can leave the original theme HTML untouched, with makes it easier to re-use for other scenarios. For example, you can stitch two unrelated applications together by using a single theme file with separate rules files. This would result in two compiled XSLT files. You could use location match rules or similar techniques to choose which one to invoke for a given request.

We will illustrate how to set up XDV for deployment below.

Installation

To install XDV, you should install the xdv egg. You can do that using easy_install, pip or zc.buildout. For example, using easy_install (ideally in a virtualenv):

$ easy_install -U xdv

If using zc.buildout, you can use the following buildout.cfg as a starting point. This will ensure that the console scripts are installed, which is important if you need to execute the XDV compiler manually:

[buildout]
parts =
    xdv

[xdv]
recipe = zc.recipe.egg
eggs = xdv

Note that lxml is a dependency of xdv, so you may need to install the libxml2 and libxslt development packages in order for it to build. On Debian/Ubuntu you can run:

$ sudo apt-get install build-essential python2.6-dev libxslt1-dev

On some operating systems, notably Mac OS X, installing a "good" lxml egg can be problematic, due to a mismatch in the operating system versions of the libxml2 and libxslt libraries that lxml uses. To get around that, you can compile a static lxml egg using the following buildout recipe:

[buildout]
# lxml should be first in the parts list
parts =
    lxml
    xdv

[lxml]
recipe = z3c.recipe.staticlxml
egg = lxml
libxml2-url = http://xmlsoft.org/sources/libxml2-2.7.7.tar.gz
libxslt-url = http://xmlsoft.org/sources/libxslt-1.1.26.tar.gz

[xdv]
recipe = zc.recipe.egg
eggs = xdv

Once installed, you should find xdvcompiler and xdvrun in your bin directory.

Rules file syntax

The rules file, conventionally called rules.xml, is rooted in a tag called <rules />:

<rules xmlns="http://namespaces.plone.org/xdv"
       xmlns:css="http://namespaces.plone.org/xdv+css">

       ...

</rules>

Here we have defined two namespaces: the default namespace is used for rules and XPath selectors. The css namespace is used for CSS3 selectors. These are functionally equivalent. In fact, CSS selectors are replaced by the equivalent XPath selector during the pre-processing step of the compiler. Thus, they have no performance impact.

XDV supports complex CSS3 and XPath selectors, including things like the nth-child pseudo-selector. You are advised to consult a good reference if you are new to XPath and/or CSS3.

The following elements are allowed inside the <rules /> element:

<theme />

Used to specify the theme file. For example:

<theme href="theme.html"/>

Relative paths are resolved relative to the rules.xml file. For http/https urls, the --network switch must be supplied to xdvcompiler/xdvrun.

<replace />

Used to replace an element in the theme entirely with an element in the content. For example:

<replace theme="/html/head/title" content="/html/head/title"/>

The (near-)equivalent using CSS selectors would be:

<replace css:theme="title" css:content="title"/>

The result of either is that the <title /> element in the theme is replaced with the <title /> element in the (dynamic) content.

<copy />

Used to replace the contents of a placeholder tag with a tag from the theme. For example:

<copy css:theme="#main" css:content="#portal-content > *" />

This would replace any placeholder content inside the element with id main in the theme with all children of the element with id portal-content in the content. The usual reason for using <copy /> instead of <replace />, is that the theme has CSS styles or other behaviour attached to the target element (with id main in this case).

<append /> and <prepend />

Used to copy elements from the content into an element in the theme, leaving existing content in place. <append /> places the matched content directly before the closing tag in the theme; <prepend /> places it directly after the opening tag. For example:

<append theme="/html/head" content="/html/head/link" />

This will copy all <link /> elements in the head of the content into the theme.

As a special case, you can copy individual attributes from a content element to an element in the theme using <prepend />:

<prepend theme="/html/body" content="/html/body/@class" />

This would copy the class attribute of the <body /> element in the content into the theme (replacing an existing attribute with the same name if there is one).

<before /> and <after />

These are equivalent to <append /> and <prepend />, but place the matched content before or after the matched theme element, rather than immediately inside it. For example:

<before css:theme="#content" css:content="#info-box" />

This would place the element with id info-box from the content immediately before the element with id content in the theme. If we wanted the box below the content instead, we could do:

<after css:theme="#content" css:content="#info-box" />

<drop />

Used to drop elements from the theme or the content. This is the only element that accepts either theme or content attributes (or their css: equivalents), but not both:

<drop css:content="#portal-content .about-box" />
<copy css:theme="#content" css:content="#portal-content > *" />

This would copy all children of the element with id portal-content in the theme into the element with id content in the theme, but only after removing any element with class about-box inside the content element first. Similarly:

<drop theme="/html/head/base" />

Would drop the <base /> tag from the head of the theme.

Order of rule execution

In most cases, you should not care too much about the inner workings of the XDV compiler. However, it can sometimes be useful to understand the order in which rules are applied.

  1. <before /> rules are always executed first.
  2. <drop /> rules are executed next.
  3. <replace /> rules are executed next, provided no <drop /> rule was applied to the same theme node.
  4. <prepend />, <copy /> and <append /> rules execute next, provided no <replace /> rule was applied to the same theme node.
  5. <after /> rules are executed last.

Behaviour if theme or content is not matched

If a rule does not match the theme (whether or not it matches the content), it is silently ignored.

If a <replace /> rule matches the theme, but not the content, the matched element will be dropped in the theme:

<replace css:theme="#header" content="#header-element" />

Here, if the element with id header-element is not found in the content, the placeholder with id header in the theme is removed.

Similarly, the contents of a theme node matched with a <copy /> rule will be dropped if there is no matching content. Another way to think of this is that if no content node is matched, XDV uses an empty nodeset when copying or replacing.

If you want the placeholder to stay put in the case of a missing content node, you can make this a conditional rule:

<replace css:theme="#header" content="#header-element" if-content="" />

See below for more details on conditional rules.

Advanced usage

The simple rules above should suffice for most use cases. However, there are a few more advanced tools at your disposal, should you need them.

Conditional rules

Sometimes, it is useful to apply a rule only if a given element appears or does not appear in the markup. The if-content attribute can be used with any rule to make it conditional.

if-content should be set an XPath expression. You can also use css:if-content with a CSS3 expression. If the expression matches a node in the content, the rule will be applied:

<copy css:theme="#portlets" css:content=".portlet"/>
<drop css:theme="#portlet-wrapper" if-content="not(//*[@class='portlet'])"/>

This will copy all elements with class portlet into the portlets element. If there are no matching elements in the content we drop the portlet-wrapper element, which is presumably superfluous.

Here is another example using CSS selectors:

<copy css:theme="#header" css:content="#header-box > *"
      css:if-content="#personal-bar"/>

This will copy the children of the element with id header-box in the content into the element with id header in the theme, so long as an element with id personal-bar also appears somewhere in the content.

Above, we also saw the special case of an empty if-content (which also works with an empty css:if-content). This is a shortcut that means "use the expression in the content or css:content` attribute as the condition". Hence the following two rules are equivalent:

<copy css:theme="#header" css:content="#header-box > *"
      css:if-content="#header-box > *"/>
<copy css:theme="#header" css:content="#header-box > *"
      css:if-content=""/>

If multiple rules of the same type match the same theme node but have different if-content expressions, they will be combined as an if..else if...else block:

<copy theme="/html/body/h1" content="/html/body/h1/text()"
      if-content="/html/body/h1"/>
<copy theme="/html/body/h1" content="//h1[@id='first-heading']/text()"
      if-content="//h1[@id='first-heading']"/>
<copy theme="/html/body/h1" content="/html/head/title/text()" />

These rules all attempt to fill the text in the <h1 /> inside the body. The first rule looks for a similar <h1 /> tag and uses its text. If that doesn't match, the second rule looks for any <h1 /> with id first-heading, and uses its text. If that doesn't match either, the final rule will be used as a fallback (since it has no if-content), taking the contents of the <title /> tag in the head of the content document.

Condition grouping and nesting

A condition may be applied to multiple rules by placing it on a <rules> tag:

<rules xmlns="http://namespaces.plone.org/xdv"
       xmlns:css="http://namespaces.plone.org/xdv+css">

    <rules css:if-content="#personal-bar">
        <append css:theme="#header-box" css:content="#user-prefs"/>
        <append css:theme="#header-box" css:content="#logout"/>
    </rules>

    ...

</rules>

Conditions may also be nested, so:

<rules if-content="condition1">
    <rules if-content="condition2">
        <copy if-content="condition3" css:theme="#a" css:content="#b"/>
    </rules>
</rules>

Is equivalent to:

<copy if-content="(condition1) and (condition2) and (condition3)" css:theme="#a" css:content="#b"/>

Multiple themes

It's possible to specify multiple themes using conditions. For instance:

<theme href="theme.html"/>
<theme href="news.html" css:if-content="body.section-news"/>
<theme href="members.html" css:if-content="body.section-members"/>

The unconditional theme is used as a fallback when no other theme's condition is satisfied. If no unconditional theme is specified, the document is passed through without theming.

All rules are applied to all themes. To have a rule apply to only a single theme, use the condition grouping syntax:

<rules css:if-content="body.section-news">
    <theme href="news.html"/>
    <copy css:content="h2.articleheading" css:theme="h1"/>
</rules>

Including external content

Normally, the content attribute of any rule selects nodes from the response being returned by the underlying dynamic web server. However, it is possible to include content from a different URL using the href attribute on any rule (other than <drop />). For example:

<append css:theme="#left-column" css:content="#portlet" href="/extra.html"/>

This will resolve the URL /extra.html, look for an element with id portlet and then append to to the element with id left-column in the theme.

The inclusion can happen in one of three ways:

  • Using the XSLT document() function. This is the default, but it can be explicitly specified by adding an attribute method="document" to the rule element. Whether this is able to resolve the URL depends on how and where the compiled XSLT is being executed:

    <append css:theme="#left-column" css:content="#portlet"
            href="/extra.html" method="document" />
    
  • Via a Server Side Include directive. This can be specified by setting the method attribute to ssi:

    <append css:theme="#left-column" css:content="#portlet"
            href="/extra.html" method="ssi"/>
    

    The output will render like this:

    <!--#include virtual="/extra.html?;filter_xpath=descendant-or-self::*[@id%20=%20'portlet']"-->
    

    This SSI instruction would need to be processed by a fronting web server such as Apache or Nginx. Also note the ;filter_xpath query string parameter. Since we are deferring resolution of the referenced document until SSI processing takes place (i.e. after the compiled XDV XSLT transform has executed), we need to ask the SSI processor to filter out elements in the included file that we are not interested in. This requires specific configuration. An example for Nginx is included below.

    For simple SSI includes of a whole document, you may omit the content selector from the rule:

    <append css:theme="#left-column" href="/extra.html" method="ssi"/>
    

    The output then renders like this:

    <!--#include virtual="/extra.html"-->
    

    Some versions of Nginx have required the wait="yes" ssi option to be stable. This can be specified by setting the method attribute to ssiwait.

  • Via an Edge Side Includes directive. This can be specified by setting the method attribute to esi:

    <append css:theme="#left-column" css:content="#portlet"
            href="/extra.html" method="esi"/>
    

    The output is similar to that for the SSI mode:

    <esi:include src="/extra.html?;filter_xpath=descendant-or-self::*[@id%20=%20'portlet']"></esi:include>
    

    Again, the directive would need to be processed by a fronting server, such as Varnish. Chances are an ESI-aware cache server would not support arbitrary XPath filtering. If the referenced file is served by a dynamic web server, it may be able to inspect the ;filter_xpath parameter and return a tailored response. Otherwise, if a server that can be made aware of this is placed in-between the cache server and the underlying web server, that server can perform the necessary filtering.

    For simple ESI includes of a whole document, you may omit the content selector from the rule:

    <append css:theme="#left-column" href="/extra.html" method="esi"/>
    

    The output then renders like this:

    <esi:include src="/extra.html"></esi:include>
    

Modifying the theme on the fly

Sometimes, the theme is almost perfect, but cannot be modified, for example because it is being served from a remote location that you do not have access to, or because it is shared with other applications.

XDV allows you to modify the theme using "inline" markup in the rules file. You can think of this as a rule where the matched content is explicitly stated in the rules file, rather than pulled from the response being styled.

For example:

<rules
    xmlns="http://namespaces.plone.org/xdv"
    xmlns:css="http://namespaces.plone.org/xdv+css"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    >

    <append theme="/html/head">
        <style type="text/css">
            /* From the rules */
            body > h1 { color: red; }
        </style>
    </append>

</xdv:rules>

In the example above, the <append /> rule will copy the <style /> attribute and its contents into the <head /> of the theme. Similar rules can be constructed for <copy />, <replace />, <prepend />, <before /> or <after />.

It is even possible to insert XSLT instructions into the compiled theme in this manner. Having declared the xsl namespace as shown above, we can do something like this:

<replace css:theme="#details">
    <dl id="details">
        <xsl:for-each css:select="table#details > tr">
            <dt><xsl:copy-of select="td[1]/text()"/></dt>
            <dd><xsl:copy-of select="td[2]/node()"/></dd>
        </xsl:for-each>
    </dl>
</replace>

Inline XSL directives

You may supply inline XSL directives in the rules to tweak the final output, for instance to strip space from the output document use:

<rules xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:strip-space elements="*" />

</rules>

Note: this may effect the rendering of the page on the browser.

Doctypes

By default, XDV transforms output pages with the XHTML 1.0 Transitional doctype. To use a strict doctype include this inline XSL:

<xsl:output
    doctype-public="-//W3C//DTD XHTML 1.0 Strict//EN"
    doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"/>

It's important to note that only the XHTML 1.0 Strict and XHTML 1.0 Transitional doctypes trigger the special XHTML compatibility mode of libxml2's XML serializer. This ensures <br/> is rendered as <br /> and <div/> as <div></div>, which is necessary for browsers to correctly parse the document as HTML.

The HTML5 specification lists XHTML 1.0 Strict as as obsolete permitted doctype string, so this doctype is recommended when HTML5 output is desired.

XInclude

You may wish to re-use elements of your rules file across multiple themes. This is particularly useful if you have multiple variations on the same theme used to style different pages on a particular website.

Rules files may be included using the XInclude protocol.

Inclusions use standard XInclude syntax. For example:

<rules
    xmlns="http://namespaces.plone.org/xdv"
    xmlns:css="http://namespaces.plone.org/xdv+css"
    xmlns:xi="http://www.w3.org/2001/XInclude">

    <xi:include href="standard-rules.xml" />

</rules>

Compilation

Once you have written your rules file, you need to compile it to an XSLT for deployment. In some cases, you may have an application server that does this on the fly, e.g. if you are using the collective.xdv package with Plone. For deployment to a web server like Apache or Nginx, however, you will need to perform this step manually.

The easiest way to invoke the XDV compiler is via the xdvcompiler command line script which is installed with the xdv egg. To see its help output, do:

$ bin/xdvcompiler --help

To run the compiler with rules.xml:

$ bin/xdvcompiler rules.xml

This will print the compiled XSLT file to the standard output. You can save it to a file instead using:

$ bin/xdvcompiler -o theme.xsl -r rules.xml

The following command line options are available:

  • Use -t theme.html to supply a theme if none is specified in the rules.
  • Use -p to pretty-print the output for improved readability. There is a risk that this could alter rendering in the browser, though, as browsers are sensitive to some kinds of whitespace.
  • Use -a to set an absolute prefix - see below.
  • Use -i to set the default external file inclusion mode to one of document, ssi or esi.
  • Use --trace to output trace logging during the compilation step. This can be helpful in debugging rules.

Check the output of the --help option for more details.

Absolute prefix

The compiler can be passed an "absolute prefix". This is a string that will be prefixed to any relative URL referenced an image, link or stylesheet in the theme HTML file, before the theme is passed to the compiler. This allows a theme to be written so that it can be opened and views standalone on the filesystem, even if at runtime its static resources are going to be served from some other location.

For example, say the theme is written with relative URLs for images and external resources, such as <img src="images/foo.jpg" />. When the compiled theme is applied to a live site, this is unlikely to work for any URL other than a sibling of the images folder.

Let's say the theme's static resources are served from a simple web server and made available under the directory /static. In this case, we can set an absolute prefix of /static. This will modify the <img /> tag in the compiled theme so that it becomes an absolute path that will work for any URL: <img src="/static/images/foo.jpg" />

Testing the compiled theme

To test the compiled theme, you can apply it to a static file representing the content. The easiest way to do this is via the xdvrun script:

$ bin/xdvrun --xsl theme.xsl content.html

This will print the output to the standard output. You can save it to a file instead with:

$ bin/xdvrun -o output.html --xsl theme.xsl content.html

For testing, you can also compile and run the theme in one go, by supplying the -r (rules) argument to xdvrun:

$ bin/xdvrun -o output.html -r rules.xml content.html

To see the built-in help for this command, run:

$ bin/xdvrun --help

Compiling the theme in Python code

You can run the XDV compiler from Python code using the following helper function:

>>> from xdv.compiler import compile_theme

This method takes the following arguments:

  • rules is the rules file, given either as a file name or a string with the file contents.
  • theme is the theme file, given either as a file name or a string with the file contents (deprecated, use inline <theme> instead.)
  • extra is an optional XSLT file with XDV extensions, given as a URI (depracated, use inline xsl in the rules instead)
  • css can be set to False to disable CSS syntax support (providing a moderate speed gain)
  • xinclude can be set to False to enable XInclude support (at a moderate speed cost). If enabled, XInclude syntax can be used to split the rules file into multiple, re-usable fragments.
  • absolute_prefix can be set an string to be used as the "absolute prefix" for relative URLs - see above.
  • update can be set to False to disable the automatic update support for the old Deliverance 0.2 namespace (for a moderate speed gain)
  • trace can be set to True to enable compiler trace information
  • includemode can be set to 'document', 'esi' or 'ssi' to change the way in which includes are processed
  • parser can be set to an lxml parser instance; the default is an HTMLParser
  • compiler_parser` can be set to an lxml parser instance; the default is a XMLParser
  • rules_parser can be set to an lxml parser instance; the default is a XMLParse.

The parser parameters may be used to add custom resolvers for external content if required. See the lxml documentation for details.

compile_theme() returns an XSLT document in lxml's ElementTree format. To set up a transform representing the theme and rules, you can do:

from lxml import etree
from xdv.compiler import compile_theme

absolute_prefix = "/static"

rules = "rules.xml"
theme = "theme.html"

compiled_theme = compile_theme(rules, theme,
                               absolute_prefix=absolute_prefix)

transform = etree.XSLT(compiled_theme)

You can now use this transformation:

content = etree.parse(some_content)
transformed = transform(content)

output = etree.tostring(transformed)

Please see the lxml documentation for more details.

Deployment

Before it can be used, the deployed theme needs to be deployed to a proxying web server which can apply the XSLT to the response coming back from another web application.

In theory, any XSLT processor will do. In practice, however, most websites do not produce 100% well-formed XML (i.e. they do not conform to the XHTML "strict" doctype). For this reason, it is normally necessary to use an XSLT processor that will parse the content using a more lenient parser with some knowledge of HTML. libxml2, the most popular XML processing library on Linux and similar operating systems, contains such a parser.

Plone

If you are working with Plone, the easiest way to use XDV is via the collective.xdv add-on. This provides a control panel for configuring the XDV rules file, theme and other options, and hooks into a transformation chain that executes after Plone has rendered the final page to apply the XDV transform.

Even if you intend to deploy the compiled theme to another web server, collective.xdv is a useful development tool: so long as Zope is in "development mode", it will re-compile the theme on the fly, allowing you to make changes to theme and rules on the fly. It also provides some tools for packaging up your theme and deploying it to different sites.

WSGI

If you are using a WSGI stack, you can use the dv.xdvserver middleware to apply an XDV theme. This supports all the core XDV options, and can be configured to either re-compile the theme on the fly (useful for development), or compile it only once (useful for deployment.)

It is also possible to use this with the Paste proxy middleware to create a standalone XDV proxy for any site. See the dv.xdvserver documentation for details.

Nginx

To deploy an XDV theme to the Nginx web server, you will need to compile Nginx with a special version of the XSLT module that can (optionally) use the HTML parser from libxml2.

In the future, the necessary patches to enable HTML mode parsing will hopefully be part of the standard Nginx distribution. In the meantime, they are maintained in the html-xslt project.

Using a properly patched Nginx, you can configure it with XSLT support like so:

$ ./configure --with-http_xslt_module

If you are using zc.buildout and would like to build Nginx, you can start with the following example:

[buildout]
parts =
    ...
    Nginx

...

[Nginx]
recipe = zc.recipe.cmmi
url = http://html-xslt.googlecode.com/files/Nginx-0.7.67-html-xslt-4.tar.gz
extra_options =
    --conf-path=${buildout:directory}/etc/Nginx.conf
    --sbin-path=${buildout:directory}/bin
    --error-log-path=${buildout:directory}/var/log/Nginx-error.log
    --http-log-path=${buildout:directory}/var/log/Nginx-access.log
    --pid-path=${buildout:directory}/var/Nginx.pid
    --lock-path=${buildout:directory}/var/Nginx.lock
    --with-http_stub_status_module
    --with-http_xslt_module

If libxml2 or libxslt are installed in a non-standard location you may need to supply the --with-libxml2=<path> and --with-libxslt=<path> options. This requires that you set an appropriate LD_LIBRARY_PATH (Linux / BSD) or DYLD_LIBRARY_PATH (Mac OS X) environment variable when running Nginx.

For theming a static site, enable the XSLT transform in the Nginx configuration as follows:

location / {
    xslt_stylesheet /path/to/compiled-theme.xsl;
    xslt_html_parser on;
    xslt_types text/html;
}

Nginx may also be configured as a transforming proxy server:

location / {
    xslt_stylesheet /path/to/compiled-theme.xsl;
    xslt_html_parser on;
    xslt_types text/html;
    rewrite ^(.*)$ /VirtualHostBase/http/localhost/Plone/VirtualHostRoot$1 break;
    proxy_pass http://127.0.0.1:8080;
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-XDV "true";
    proxy_set_header Accept-Encoding "";
}

Removing the Accept-Encoding header is sometimes necessary to prevent the backend server compressing the response (and preventing transformation). The response may be compressed in Nginx by setting gzip on; - see the gzip module documentation for details.

In this example an X-XDV header was set so the backend server may choose to serve different different CSS resources.

Including external content

As an event based server, it is not practical to add document() support to the Nginx XSLT module for in-transform inclusion. Instead, external content is included through SSI in a sub-request. The SSI sub-request includes a query string parameter to indicate which parts of the resultant document to include, called ;filter_xpath - see above for a full example. The configuration below uses this parameter to apply a filter:

worker_processes  1;
events {
    worker_connections  1024;
}
http {
    include mime.types;
    gzip on;
    server {
        listen 80;
        server_name localhost;
        root html;

        # Decide if we need to filter
        if ($args ~ "^(.*);filter_xpath=(.*)$") {
            set $newargs $1;
            set $filter_xpath $2;
            # rewrite args to avoid looping
            rewrite    ^(.*)$    /_include$1?$newargs?;
        }

        location @include500 { return 500; }
        location @include404 { return 404; }

        location ^~ /_include {
            # Restrict _include (but not ?;filter_xpath=) to subrequests
            internal;
            error_page 404 = @include404;
            # Cache page fragments in Varnish for 1h when using ESI mode
            expires 1h;
            # Proxy
            rewrite    ^/_include(.*)$    $1    break;
            proxy_pass http://127.0.0.1:80;
            # Protect against infinite loops
            proxy_set_header X-Loop 1$http_X_Loop; # unary count
            proxy_set_header Accept-Encoding "";
            error_page 500 = @include500;
            if ($http_X_Loop ~ "11111") {
                return 500;
            }
            # Filter by xpath
            xslt_stylesheet filter.xsl
                xpath=$filter_xpath
                ;
            xslt_html_parser on;
            xslt_types text/html;
        }

        location / {
            xslt_stylesheet theme.xsl;
            xslt_html_parser on;
            xslt_types text/html;
            ssi on; # Not required in ESI mode
        }
    }
}

In this example the sub-request is set to loop back on itself, so the include is taken from a themed page. filter.xsl (in the lib/xdv directory) and theme.xsl should both be placed in the same directory as Nginx.conf.

An example buildout is available in Nginx.cfg in this package.

Varnish

To enable ESI in Varnish simply add the following to your VCL file:

sub vcl_fetch {
    if (obj.http.Content-Type ~ "text/html") {
        esi;
    }
}

An example buildout is available in varnish.cfg.

Apache

XDV currently requires a version of mod_transform with html parsing support. The latest patched versions may be downloaded from the html-xslt project page.

As well as the libxml2 and libxslt development packages, you will require the appropriate Apache development pacakge:

$ sudo apt-get install libxslt1-dev apache2-threaded-dev

(or apache2-prefork-dev when using PHP.)

Install mod_transform using the standard procedure:

$ ./configure
$ make
$ sudo make install

An example virtual host configuration is shown below:

NameVirtualHost *
LoadModule transform_module /usr/lib/apache2/modules/mod_transform.so
<VirtualHost *>

    FilterDeclare THEME
    FilterProvider THEME XSLT resp=Content-Type $text/html

    TransformOptions ApacheFS HTML HideParseErrors
    TransformSet /theme.xsl
    TransformCache /theme.xsl /etc/apache2/theme.xsl

    <LocationMatch "/">
        FilterChain THEME
    </LocationMatch>

</VirtualHost>

The ApacheFS directive enables XSLT document() inclusion.

Unfortunately it is not possible to theme error responses (such as a 404 Not Found page) with Apache as these do not pass through the filter chain.

Changelog

0.4b3 - unreleased

  • Fix for themes in nested rules tags.

0.4b2 - 2010-08-16

  • When no conditional themes match, pass the document through without theming.
  • Fix loading of compiler stylesheets so as not to be affected by resolvers.

0.4b1 - 2010-08-06

  • Multistage compiler breaks down work into smaller, more easily debugged chunks. (In the spirit of the original DVNG prototype.)
  • Refactoring of generated XSLT to perform its work in a single pass, bringing a 30-50% speedup.
  • Multiple theme support using the new <theme> directive.
  • Nested <rules> and condition merging allows for condition grouping.
  • Allow comments to be selected in the theme.
  • Tweaked ssi includemode for Apache compatibility. The previous wait="yes" behaviour no longer seems necessary with current versions of Nginx, but is available using the ssiwait includemode.
  • CSS expressions are now converted to relative rather than absolute xpaths. While this makes no difference to their use in xdv directives (which are executed in the context of the root node), more flexibility is available when used with inline XSL.
 
File Type Py Version Uploaded on Size
xdv-0.4b3.tar.gz (md5) Source 2010-09-09 179KB
  • Downloads (All Versions):
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  • Author: Paul Everitt, Laurence Rowe and Martin Aspeli.
  • License: New BSD
  • Package Index Owner: laurencerowe, optilude
  • DOAP record: xdv-0.4b3.xml