External Links Extension

This extension can detect links to external sites and adjust the markup accordingly:

• Make the links open in new tabs/windows
• Adds a rel attribute to the resulting <a> tag with values like "nofollow noopener noreferrer"
• Optionally adds any custom HTML classes

Installation

This extension is bundled with league/commonmark. This library can be installed via Composer:

composer require league/commonmark

See the installation section for more details.

Usage

Configure your Environment as usual and simply add the ExternalLinkExtension provided by this package:

use League\CommonMark\Environment\Environment;
use League\CommonMark\Extension\CommonMark\CommonMarkCoreExtension;
use League\CommonMark\Extension\ExternalLink\ExternalLinkExtension;
use League\CommonMark\MarkdownConverter;

// Define your configuration, if needed
$config = [
    'external_link' => [
        'internal_hosts' => 'www.example.com', // TODO: Don't forget to set this!
        'open_in_new_window' => true,
        'html_class' => 'external-link',
        'nofollow' => '',
        'noopener' => 'external',
        'noreferrer' => 'external',
    ],
];

// Configure the Environment with all the CommonMark parsers/renderers
$environment = new Environment($config);
$environment->addExtension(new CommonMarkCoreExtension());

// Add this extension
$environment->addExtension(new ExternalLinkExtension());

// Instantiate the converter engine and start converting some Markdown!
$converter = new MarkdownConverter($environment);
echo $converter->convert('I successfully installed the <https://github.com/thephpleague/commonmark> project!');

Configuration

This extension supports three configuration options under the external_link configuration:

internal_hosts

This option defines a list of hosts which are considered non-external and should not receive the external link treatment.

This can be a single host name, like 'example.com', which must match exactly.

Wildcard matching is also supported using regular expression like '/(^|\.)example\.com$/'. Note that you must use / characters to delimit your regex.

This configuration option also accepts an array of multiple strings and/or regexes:

$config = [
    'external_link' => [
        'internal_hosts' => ['foo.example.com', 'bar.example.com', '/(^|\.)google\.com$/],
    ],
];

By default, if this option is not provided, all links will be considered external.

open_in_new_window

This option (which defaults to false) determines whether any external links should open in a new tab/window.

html_class

This option allows you to provide a string containing one or more HTML classes that should be added to the external link <a> tags: No classes are added by default.

nofollow, noopener, and noreferrer

These options allow you to configure whether a rel attribute should be applied to links. Each of these options can be set to one of the following string values:

• 'external' - Apply to external links only
• 'internal' - Apply to internal links only
• 'all' - Apply to all links (both internal and external)
• '' (empty string) - Don’t apply to any links

Unless you override these options, nofollow defaults to '' and the others default to 'external'.

Advanced Rendering

When an external link is detected, the ExternalLinkProcessor will set the external data option on the Link node to either true or false. You can therefore create a custom link renderer which checks this value and behaves accordingly:

use League\CommonMark\Extension\CommonMark\Node\Inline\Link;
use League\CommonMark\Renderer\ChildNodeRendererInterface;
use League\CommonMark\Renderer\NodeRendererInterface;
use League\CommonMark\Util\HtmlElement;

class MyCustomLinkRenderer implements NodeRendererInterface
{
    /**
     * @param Node                       $node
     * @param ChildNodeRendererInterface $childRenderer
     *
     * @return HtmlElement
     */
    public function render(Node $node, ChildNodeRendererInterface $childRenderer)
    {
        Link::assertInstanceOf($node);

        if ($node->data->get('external')) {
            // This is an external link - render it accordingly
        } else {
            // This is an internal link
        }

        // ...
    }
}

Adding Icons

You can also use CSS to automagically add an external link icon by targeting the html_class given in the configuration:

// Font Awesome example:
a[target="_blank"]::after,
a.external::after {
   content: "\f08e";
   font: normal normal normal 14px/1 FontAwesome;
}

// Glyphicon example:
a[target="_blank"]::after,
a.external::after {
  @extend .glyphicon;
  content: "\e164";
  margin-left: .5em;
  margin-right: .25em;
}

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