Including pages with $_GET - php

Question

I want url's like index.php?showuser=512, index.php?shownews=317 for pages i get content from db... and for regular pages index.php?page=about and so on WITHOUT mod-rewrite.
Invision Power Board has urls like this. I have looked through their code but I can't figure out how they do it.
I could do it like this:
if (ctype_digit($_GET['shownews'])) include('shownews.php');
elseif (ctype_digit($_GET['showuser'])) include('showuser.php');
// regular pages
elseif ($_GET['page'] == 'about') include('about.php');
elseif ($_GET['page'] == 'help') include('help.php');
elseif ($_GET['page'] == 'login') include('login.php');
But this feels too messy.
Just curious how IPB does this. Is there a better way do to this? WITHOUT any mod-rewrite. Any one know? I doubt they do it like the above.
I can't do:
if (preg_match('/^[a-z0-9]+$/', $_GET['page'])) include('$_GET['page']');
Then I would get links like index.php?showuser&id=512 and that I dont like. (i know its not safe just showing the princip)
I like it this way, it's not the best but i like it so please be quiet about template engines, frameworks etc. Just be kind and answer my question... I just want to know how IPB does this.
Thanks
Tomek

Answer 1

I don't know how IPB does this, let's get that out of the way. But, this is how I would approach this problem:
First, I recognize that there are two kinds of GET parameters: page/identifier, and just page. These would get tested separately.
Second, I recognize that all all get parameters match their filenames sans the php-suffix, so we can use this to our advantage.
One of the most important things to remember is to never let GET-parameters affect our code unsanitized. In this case, we know which types of pages we can and want to show, so we can create a white-list out of these.
So, onto the pseudo-y dispatcher code:
$pagesWithId = array("shownews", "showuser", "showwhatever");
$justPages = array("about", "help", "login");
foreach ($pagesWithId as $page) {
if (isset($_GET[$page])) {
$id = (int)$_GET[$page];
include($page.'.php');
die();
}
}
if (in_array($_GET['page'], $justPages)) {
include($_GET['page'].'.php');
die();
}
// page not found
show404OrHandleOtherwise();

Answer 2

For pages you just use a simple array.
if (isset($pages[$_GET['page']])) include $pages[$_GET['page']];
For shownews=317 You could make a simple conversion in your app. Depending on how you want to prioritize page or shownews etc:
if (isset($pages[$_GET['page']])) {
include $pages[$_GET['page']];
} else {
$possiblePages = array_filter(array_intersect_key($_GET, $pagesWithId), 'ctype_digit');
if (!empty($possiblePages)) {
$id = reset($possiblePages);
$pageName = key($possiblePages);
$page = $pagesWithId[$pageName];
include $page;
} else {
//no valid pages
}
}
Note: page "names" are array keys, and the value is the path, file and extension to include. More customizable.