Add target _blank to external link - Parsedown PHP - php

Question

I'm using Parsedown to parse HTML from the database to my site. With Parsedown, you can't really add target="_blank" to the links.
So what I'm trying to do is to add target="_blank" to external links. I've found this function in Parsedown.php:
protected function inlineLink($Excerpt)
{
$Element = array(
'name' => 'a',
'handler' => 'line',
'text' => null,
'attributes' => array(
'href' => null,
'title' => null,
),
);
$extent = 0;
$remainder = $Excerpt['text'];
if (preg_match('/\[((?:[^][]++|(?R))*+)\]/', $remainder, $matches))
{
$Element['text'] = $matches[1];
$extent += strlen($matches[0]);
$remainder = substr($remainder, $extent);
}
else
{
return;
}
if (preg_match('/^[(]\s*+((?:[^ ()]++|[(][^ )]+[)])++)(?:[ ]+("[^"]*"|\'[^\']*\'))?\s*[)]/', $remainder, $matches))
{
$Element['attributes']['href'] = $matches[1];
if (isset($matches[2]))
{
$Element['attributes']['title'] = substr($matches[2], 1, - 1);
}
$extent += strlen($matches[0]);
}
else
{
if (preg_match('/^\s*\[(.*?)\]/', $remainder, $matches))
{
$definition = strlen($matches[1]) ? $matches[1] : $Element['text'];
$definition = strtolower($definition);
$extent += strlen($matches[0]);
}
else
{
$definition = strtolower($Element['text']);
}
if ( ! isset($this->DefinitionData['Reference'][$definition]))
{
return;
}
$Definition = $this->DefinitionData['Reference'][$definition];
$Element['attributes']['href'] = $Definition['url'];
$Element['attributes']['title'] = $Definition['title'];
}
$Element['attributes']['href'] = str_replace(array('&', '<'), array('&', '<'), $Element['attributes']['href']);
return array(
'extent' => $extent,
'element' => $Element,
);
}
Now, what I've tried is this (added a comment of what I changed):
protected function inlineLink($Excerpt)
{
$Element = array(
'name' => 'a',
'handler' => 'line',
'text' => null,
'attributes' => array(
'href' => null,
'target' => null, // added this
'title' => null,
),
);
$extent = 0;
$remainder = $Excerpt['text'];
if (preg_match('/\[((?:[^][]++|(?R))*+)\]/', $remainder, $matches))
{
$Element['text'] = $matches[1];
$extent += strlen($matches[0]);
$remainder = substr($remainder, $extent);
}
else
{
return;
}
if (preg_match('/^[(]\s*+((?:[^ ()]++|[(][^ )]+[)])++)(?:[ ]+("[^"]*"|\'[^\']*\'))?\s*[)]/', $remainder, $matches))
{
$Element['attributes']['href'] = $matches[1];
if (isset($matches[2]))
{
$Element['attributes']['title'] = substr($matches[2], 1, - 1);
}
$extent += strlen($matches[0]);
}
else
{
if (preg_match('/^\s*\[(.*?)\]/', $remainder, $matches))
{
$definition = strlen($matches[1]) ? $matches[1] : $Element['text'];
$definition = strtolower($definition);
$extent += strlen($matches[0]);
}
else
{
$definition = strtolower($Element['text']);
}
if ( ! isset($this->DefinitionData['Reference'][$definition]))
{
return;
}
$Definition = $this->DefinitionData['Reference'][$definition];
$Element['attributes']['href'] = $Definition['url'];
if (strpos($Definition['url'], 'example.com') !== false) { // added this aswell, checking if its our own URL
$Element['attributes']['target'] = '_blank';
}
$Element['attributes']['title'] = $Definition['title'];
}
$Element['attributes']['href'] = str_replace(array('&', '<'), array('&', '<'), $Element['attributes']['href']);
return array(
'extent' => $extent,
'element' => $Element,
);
}
Any suggestions to accomplish this?

Answer 1

Ran into this issue today. I wanted to have all links from a different host open up in a new target automatically. Unfortunately, the accepted answer recommends editing the Parsedown class file, which is a bad idea imo.
I created a new PHP class which extends Parsedown, and created an override for the element method. Here is the whole class:
class ParsedownExtended extends Parsedown
{
protected function element(array $Element)
{
if ($this->safeMode) {
$Element = $this->sanitiseElement($Element);
}
$markup = '<' . $Element['name'];
if (isset($Element['name']) && $Element['name'] == 'a') {
$server_host = isset($_SERVER['HTTP_HOST']) ? $_SERVER['HTTP_HOST'] : null;
$href_host = isset($Element['attributes']['href']) ? parse_url($Element['attributes']['href'], PHP_URL_HOST) : null;
if ($server_host != $href_host) {
$Element['attributes']['target'] = '_blank';
}
}
if (isset($Element['attributes'])) {
foreach ($Element['attributes'] as $name => $value) {
if ($value === null) {
continue;
}
$markup .= ' ' . $name . '="' . self::escape($value) . '"';
}
}
if (isset($Element['text'])) {
$markup .= '>';
if (!isset($Element['nonNestables'])) {
$Element['nonNestables'] = array();
}
if (isset($Element['handler'])) {
$markup .= $this->{$Element['handler']}($Element['text'], $Element['nonNestables']);
}
else {
$markup .= self::escape($Element['text'], true);
}
$markup .= '</' . $Element['name'] . '>';
}
else {
$markup .= ' />';
}
return $markup;
}
}
Here is where the magic happens:
if (isset($Element['name']) && $Element['name'] == 'a') {
$server_host = isset($_SERVER['HTTP_HOST']) ? $_SERVER['HTTP_HOST'] : null;
$href_host = isset($Element['attributes']['href']) ? parse_url($Element['attributes']['href'], PHP_URL_HOST) : null;
if ($server_host != $href_host) {
$Element['attributes']['target'] = '_blank';
}
}
Now I simply use ParsedownExtended instead of Parsedown when parsing content, e.g.:
$parsedown = new ParsedownExtended();
return $parsedown->text($this->body);
Hope this helps someone.

Answer 2

Such issue already exists on GitHub. Please see this comment.
My extension can automatically set rel="nofollow" and target="_blank"
attributes to a link when it is detected as an external link. You can
also set those attributes manually through the attribute block:
[text](http://example.com) {rel="nofollow" target="_blank"}
Automatic rel="nofollow" Attribute on External Links
// custom external link attributes
$parser->links_external_attr = array(
'rel' => 'nofollow',
'target' => '_blank'
);
If you want to make changes in Parsedown class without using the parsedown-extra-plugin extension, you can do as follows:
1) In \Parsedown::element method after the first line $markup = '<'.$Element['name']; add this line $Element = $this->additionalProcessElement($Element);
2) Add new method to Parsedown class:
protected function additionalProcessElement($Element) { }
3) Extend Parsedown class and save it as MyParsedown.php file:
<?php
namespace myapps;
require_once __DIR__.'/Parsedown.php';
/**
* Class MyParsedown
* #package app
*/
class MyParsedown extends \Parsedown
{
/**
* #param array $Element
* #return array
*/
protected function additionalProcessElement($Element)
{
if ($Element['name'] == 'a' && $this->isExternalUrl($Element['attributes']['href'])) {
$Element['attributes']['target'] = '_blank';
}
return $Element;
}
/**
* Modification of the funciton from answer to the question "How To Check Whether A URL Is External URL or Internal URL With PHP?"
* #param string $url
* #param null $internalHostName
* #see https://stackoverflow.com/a/22964930/7663972
* #return bool
*/
protected function isExternalUrl($url, $internalHostName = null) {
$components = parse_url($url);
$internalHostName = ($internalHostName == null) ? $_SERVER['HTTP_HOST'] : $internalHostName;
// we will treat url like '/relative.php' as relative
if (empty($components['host'])) {
return false;
}
// url host looks exactly like the local host
if (strcasecmp($components['host'], $internalHostName) === 0) {
return false;
}
$isNotSubdomain = strrpos(strtolower($components['host']), '.'.$internalHostName) !== strlen($components['host']) - strlen('.'.$internalHostName);
return $isNotSubdomain;
}
}
4) Create test.php file and run it:
require_once __DIR__.'/MyParsedown.php';
$parsedown = new \myapps\MyParsedown();
$text = 'External link to [example.com](http://example.com/abc)';
echo $parsedown->text($text);
This HTML code will be displayed on the browser page (if your host is not example.com, of course):
<p>External link to example.com</p>

Answer 3

Just like kjdion84 I'd also extend the Parsedown class. I suggest to not copy and change the element method but overwrite inlineLink; it's less work and more future proof if the base code changes.
Heads up: the urlIsExternal method is by no means complete (host check is missing).
class ParsedownExtended extends Parsedown
{
protected function inlineLink($Excerpt)
{
$link = parent::inlineLink($Excerpt);
if ($this->urlIsExternal($link['element']['attributes']['href'])) {
$link['element']['attributes'] += [
'target' => '_blank',
'rel' => 'nofollow',
];
}
return $link;
}
protected function urlIsExternal($url)
{
$scheme = parse_url($url, PHP_URL_SCHEME);
$host = parse_url($url, PHP_URL_HOST);
if (!$scheme || !$host) {
return false;
}
if (strpos(strtolower($scheme), 'http') !== 0) {
return false;
}
// #TODO check the host
return true;
}
}

Answer 4

This will work.
<?php
declare(strict_types=1);
namespace YourNamespace;
class ParsedownExt extends \Parsedown
{
// Add target to links
protected function element(array $Element)
{
if (strcasecmp($Element['name'], 'a')===0)
$Element['attributes']['target'] = '_blank';
return parent::element($Element);
}
}