FreshRSS plugin which strips intrusive HTML elements

extension.php

<?php
/*
 * Copyright 2015 James Geboski <jgeboski@gmail.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Installing:
 *   1. Move extension.php and metadata.json to <freshrss>/extentions/stripper
 *   2. Enable via the Extentions interface
 */

class StripperExtension extends Minz_Extension
{
    const strip = array('iframe', 'img');

    public function init()
    {
        $func = array($this, 'entryBeforeDisplay');
        $this->registerHook('entry_before_display', $func);
    }

    public function entryBeforeDisplay($entry)
    {
        $data = $entry->content();
        $data = mb_convert_encoding($data, 'HTML-ENTITIES', 'UTF-8');

        $dom = new DOMDocument();
        @$dom->loadHTML($data);
        $xpath = new DOMXpath($dom);

        foreach (self::strip as $name) {
            self::strip($xpath, $name);
        }

        $entry->_content($dom->saveHTML());
        return $entry;
    }

    private static function strip($xpath, $name)
    {
        $nodes = $xpath->query('//' . $name);

        foreach ($nodes as $node) {
            $ops = array(
                'nextSibling'     => NULL,
                'previousSibling' => NULL,
                'parentNode'      => NULL
            );

            foreach ($ops as $op => $n) {
                $ops[$op] = self::getElement($node, $op);
            }

            $node->parentNode->removeChild($node);

            foreach ($ops as $op => $n) {
                while (($n != NULL) && self::isElementEmpty($n)) {
                    $s = self::getElement($n, $op);
                    $n->parentNode->removeChild($n);
                    $n = $s;
                }
            }
        }
    }

    private static function isElementEmpty($node)
    {
        if ($node->nodeType != XML_ELEMENT_NODE) {
            return false;
        }

        $name = strtolower($node->nodeName);

        if (in_array($name, self::strip)) {
            return false;
        }

        foreach ($node->childNodes as $c) {
            if ($node->nodeType != XML_ELEMENT_NODE) {
                continue;
            }

            if (!self::isElementEmpty($c, self::strip)) {
                return false;
            }
        }

        $val = html_entity_decode($node->nodeValue);
        return preg_match('/^\s*$/', $val) == 1;
    }

    private static function getElement($node, $op)
    {
        for ($n = $node->$op; $n != NULL; $n = $n->$op) {
            if ($n->nodeType == XML_ELEMENT_NODE) {
                return $n;
            }
        }

        return NULL;
    }
}
?>

metadata.json

{
    "name": "Stripper",
    "author": "James Geboski",
    "description": "Strip intrusive HTML elements (iframes, images, etc).",
    "version": 0.1,
    "entrypoint": "Stripper",
    "type": "user"
}