Reply To: RSS Feed with Altered Images

[kingkool68]

My gut instinct would be to include width and height attributes on all <img> since you can do this

img {
   height: auto;
    max-width: 100%;
}

to make them scale on your front end. That’s what we’re doing here: http://www.pewresearch.org/fact-tank/2014/04/03/among-afghan-public-mixed-support-for-womens-rights/

But on to your question…

Checkout the add_feed() function (https://codex.wordpress.org/Rewrite_API/add_feed) which you would call by hooking into the init action. It accepts two parameters: 1) the name of the feed that appears in the URL, 2) a callback function to generate the output for the feed.

function css_tricks_custom_feeds() {
    add_feed( 'email', 'get_me_the_email_feed_template');
}
add_action( 'init', 'css_tricks_custom_feeds' );

For the callback function we want to do two things: 1) apply a filter on the_content_feed, 2) include the default RSS feed template so we don’t have to fork it and we’re lazy and all that.

function get_me_the_email_feed_template() {
    add_filter( 'the_content_feed', 'css_tricks_super_awesome_feed_image_magic', 10 );
    include( ABSPATH . '/wp-includes/feed-rss2.php' );
}

Now we just need our function to run over the_feed_content and manipulate the images….

function css_tricks_super_awesome_feed_image_magic( $content ) {
    $doc = new DOMDocument();
    $doc->LoadHTML( $content );
    $images = $doc->getElementsByTagName('img');
    foreach ($images as $image) {
        $image->removeAttribute( 'height' );
        $image->setAttribute( 'width', '320' );
    }
    return $doc->saveHTML();
}

I haven’t tested this. You may need to apply the css_tricks_super_awesome_feed_image_magic() function after other filters that get applied to the_contented_feed. To do that change the number 10 to a higher number in the add_filter() function above.

Here’s the whole thing:

function css_tricks_custom_feeds() {
    add_feed( 'email', 'get_me_the_email_feed_template');
}
add_action( 'init', 'css_tricks_custom_feeds' );

function get_me_the_email_feed_template() {
    add_filter( 'the_content_feed', 'css_tricks_super_awesome_feed_image_magic' );
    include( ABSPATH . '/wp-includes/feed-rss2.php' );
}

function css_tricks_super_awesome_feed_image_magic( $content ) {
    $doc = new DOMDocument();
    $doc->LoadHTML( $content );
    $images = $doc->getElementsByTagName('img');
    foreach ($images as $image) {
        $image->removeAttribute( 'height' );
        $image->setAttribute( 'width', '320' );
    }
    return $doc->saveHTML();
}