broken_error_catch.php

<?php

$pageOutput = "";
try
{
    if(!isset($_GET['page_name']) || empty($_GET['page_name'])) throw(new UserErrorException("This page received an invalid request."));

    $database = mysql_db::get();

    $pageName = $_GET['page_name'];
    $safePageName = $database->escape($pageName);

    //page names aren't allowed to have special characters
    if($safePageName !== $pageName) throw(new UserErrorException("This page received an invalid request."));

    $page = $myContentManager->getPageByName($safePageName);
    $myContentManager->assignSmartyFieldsForPage($page, $smarty);

    $pageOutput = $smarty->fetch($page->template . ".tpl");
} catch(RuntimeException $e) {
    $log = new log("page_loader");
    $log->logMessage(new message(MESSAGE_ERROR, "Page Loader", "Loading page", $e->getMessage()));

    $errorMessage = "";
    if($e instanceof UserErrorException)
    {
        $errorMessage = $e->getMessage();
    } else {
        //we do this to hide potentially dangerous info from the user (aka, database layout, etc.)
        $errorMessage = "An unresolved error has occurred.  Please try back later.";
    }

    $smarty->assign("error_message", $errorMessage);
    $pageOutput = $smarty->fetch("error.tpl");
}

print($pageOutput);

?>

error_catch_fix.php

<?php

    ob_clean();
    $smarty->assign("error_message", $errorMessage);
    $pageOutput = $smarty->fetch("error.tpl");

?>

fetch_mockup.php

<?php

public function fetch($templateName) {
    ob_start();
    parseTheTemplate($templateName);
    return ob_get_clean();
}

?>