URL rewriting template engine

My employer is currently in the process of standing-up a content management system (CMS). In the process of migrating links on our existing site to the new CMS site, there are going to be—at least, at first—a metric tonne of possible URL redirects necessary. Since the majority of these will fall into a handful of categories, I began creating IIRF (Ionic ISAPI Rewrite Filter) URL rewriting rules that would, for instance, move a particular list of “Offices” from /offices/officename to http://newserver/offices/officename. (Note: These directives should be compatible with Apache’s mod_rewrite, and even lighttpd’s url.rewrite, as well.)

There is a specific list of sites that exist on our old server and a specific list of those that exist on the new server (or at least, there is until the migration is complete). Once I started plugging in a regular expression “selection structure” (i.e., (one|two|three) meaning “one or two or three”), it became painfully obvious that this format would quickly spiral into a maintenance nightmare. As such, I have created a small script for building IIRF “templates” that can use placeholders for these mammoth lists of “Offices”.

Here’s the gist: You create a template file identical to your IIRF INI file, except that you replace those cumbersome regex selection structures with placeholders (i.e., {MY_PLACEHOLDER}). Then, for each placeholder you’ve used in your template, you create a map file. This map file contains a list of all the possibilities to be included in the selection structure, each on a new line of the file. The first line of the file, of course, contains the placeholder value to match this selection structure up to the template.

Example template:

RewriteCond %{HTTP_URL} ^/offices/{MY_PLACEHOLDER}.* [I]
RedirectRule ^/offices/(.+) http://newserver/offices/$1

Example map:

MY_PLACEHOLDER
one
two
three

Running the script against the template (understanding that your map file is in the same directory), the outputted INI file will look like this:

Final output:

RewriteCond %{HTTP_URL} ^/offices/(one|two|three).* [I]
RedirectRule ^/offices/(.+) http://newserver/offices/$1

With that in place, http://oldserver/offices/one/anypage will redirect to http://newserver/offices/one/anypage (and so on), while http://oldserver/offices/four/anypage will not be redirected at all.

Without further adieu, here’s the logic:

PHP code:

<?php
/*******************************************************************************
Program:    IIRF Templating Engine
Author:     Todd Boyd
Created:    12/10/2009
Changed:    Never
Description:

This script will load any number of *.map files of the following format:

    PLACEHOLDER_NAME
    map node
    map node
    ...

Any instance of the placeholder's name found in the template file will be
replaced by its node values for use in regular expressions. Map nodes are
concatenated into a regex selection structure, such as "(one|two|three)".
When searching the template file for a placeholder name, the placeholder name
must be surrounded by curly braces, such as "{MY_PLACEHOLDER}". This script can
be used to build and maintain lists of values to be used in IIRF rewrite rules
independently of IIRF's configuration files.
*******************************************************************************/

# check args
if($argc < 3) die("Synax: iirfMap.php <template filename> <ini filename>\n");
# check template
if(! file_exists($argv[1])) die("Template file does not exist.\n");
# load template
$iirf = file_get_contents($argv[1]);
$maps = array();

# load placeholder maps
foreach(glob('*.map') as $f)
{
    $map = fopen($f, 'r');
    # get placeholder name
    $ph = trim(fgets($map));
    $a = 0;
    $maps[$ph] = '(';

    # build selection structure from node values
    while(! feof($map))
    {
        $in = trim(fgets($map));
        if(strlen($in) > 0)
            $maps[$ph] .= ($a++ > 0 ? '|' : '') . $in;
    }

    $maps[$ph] .= ')';
    fclose($map);
}

# replace placeholder values with mapped regex structures
foreach($maps as $p => $m)
    $iirf = str_replace('{' . $p . '}', $m, $iirf);
# create INI file from template
file_put_contents($argv[2], $iirf);