= xmlvw by TOYODA Eizi

* Author: TOYODA Eizi <toyoda.eizi@gmail.com>
* Date: 2013-05-07

== What is this

xmlvw is a tiny CGI to apply XSLT stylesheet to any XML online.
The name `xmlvw' comes from XML viewer, but it can be used with
any XSLT that generates meaningful output to web browser.

== How it works

When the CGI is called without any parameter (no PATH_INFO nor
QUERY_STRING), it generates an HTTP form that prompt the user
to specify XSLT and XML.  XSLT can be chosen from a pull-down list
of *.xsl files installed at predefined directory (/usr/local/share/xmlvw).
XML can be specified either by URL or by file upload.

Then the next request to the CGI should be like
http://toyoda-eizi.net/xmlvw?xsl=gmd_txt&url=http://... or its POST
equivalent.

Alternative way to use the CGI is calling it with PATH_INFO.
In that case the first path segment becomes the basename of XSLT,
and the rest (must begin with http://) becomes the URL.

For example http://toyoda-eizi.net/gmd_txt/http://example.com/path
can be used to apply gmd_txt.xsl to the XML located at
http://example.com/path.

Anyway at the final stage the CGI reads specified input (or uses uploaded
file), parses by libxml2, inserts XML processing instruction and echoes it
back as response.  The `xml-stylesheet' processing instruction contains
URL to the XSLT (http://toyoda-eizi.net/gmd_txt/ for above case) and
is interpreted by the web browser.

== Porting tips

This kind of work, applying an XSLT, can also be done by JavaScript,
but it is worth noting that most web browser has limitation on applying XSLT
coming from different host for security reasons.

When called from localhost, the script rewrites URL of itself.  You have to
edit URLFIX constant to preferred hostname of your server.
The script is intended to be run behind some load-balancer or cache proxy.
If that is not the case, you can simply rewrite the definition by
"URLFIX = nil" to disable the function.