if is amp change internal links to amp version (WordPress)

Question

We use WordPress and would like to link amp to amp if the linked page has an amp version. We have amp structured like that: test.de/test/amp

Unfortunately this code in my functions.php isnt applying to links hard-coded inside of the post content. What do I have to change, so its working for every internal link:

add_filter( 'post_link', function( $url, $post ) {
    static $recursing = false;
    if ( $recursing ) {
        return $url;
    }
    $recursing = true;
    if ( ! function_exists( 'post_supports_amp' ) || ! post_supports_amp( $post ) ) {
        return $url;
    }
    if ( function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
        $url = amp_get_permalink( $post->ID );
    }
    $recursing = false;
    return $url;
}, 10, 2 );

At the moment its also applying to the canonical link, which is really bad for seo. How to prevent this?

Outsource WordPress · Accepted Answer · 2018-08-30T17:37:14.230

Add these functions to your theme's 'functions.php'.

/* post link filter */
add_filter( 'post_link', 'change_amp_url', 10, 2 );

function change_amp_url( $url, $postobj ) {
    static $recursing = false;
    if ( $recursing ) {
        return $url;
    }

    $recursing = true;
    if ( function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
        if ( function_exists( 'post_supports_amp' ) && post_supports_amp( $postobj ) ) {
            $url = amp_get_permalink( $postobj->ID );           
        }
    }
    $recursing = false;
    return $url;
}

/* content link filter */
add_filter( 'the_content', 'change_amp_url_content' );

function change_amp_url_content($content)
{
    $dom = new DOMDocument();
    $dom->loadHTML($content);

    $tags = $dom->getElementsByTagName('a');
    foreach ($tags as $tag) {
        $link = $tag->getAttribute('href'); // original url
        $extralink = '';
        if(stristr($link,'#')) {
            $pagelinktemp = explode("#",$link);
            $pagelink = $pagelinktemp[0];
            $extralink = '#'.$pagelinktemp[1];
        } else {
            $pagelink = $link;
        }
        if($pagelink!="") {     
            $postid = url_to_postid($pagelink);
            $postobj = get_post($postid); // getting appropriate post object            
            if($postobj) {          
                $newlink = change_amp_url( $pagelink, $postobj ); //new url
            }
            else {
                $newlink = $link;
            }
        }
        else {
            $newlink = $link;
        }
        if($link != $newlink) // change if only links are different
        {
            $content = str_replace($link, $newlink.$extralink, $content);
        }
    }
    return $content;
}

/* override canonical link */
add_filter( 'wpseo_canonical', 'amp_override_canonical' );

function amp_override_canonical($url) {
    if ( substr($url,-4)=="/amp" ) {    
        $url = substr($url,0,-4);
    }
    return $url;
}

The first function will provide the AMP URL if exists.

The second one will loop through each URL in the content and change to AMP URL if valid.

The last one will rewrite the canonical URL that displayed via Yoast SEO plugin.

Did you removed your old function and added the full content in my answer to the 'functions.php'? — Outsource WordPress, Aug 30 '18 at 06:17
Please add everything and let me know whether everything working fine, we can fix the canonical links after fixing the primary issue. — Outsource WordPress, Aug 30 '18 at 07:07
this is changing some links on amp right, others its changing to link to itself. On non amp its changing all links to link to itself. — Krystian, Aug 30 '18 at 07:12
Seems some issues with `post_supports_amp()` function, will let you know the fix shortly. — Outsource WordPress, Aug 30 '18 at 07:24
and this affects sites which hasnt amp enabled. Thank you very much for helping! — Krystian, Aug 30 '18 at 07:30
non amp are not affected now, but amp every link is changed to link to the post itself — Krystian, Aug 30 '18 at 07:53
It should not, can you confirm whether you have updated the whole code? If possible, can you able to share the URL? — Outsource WordPress, Aug 30 '18 at 07:59
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/179090/discussion-between-krystian-manthey-and-outsource-wordpress). — Krystian, Aug 30 '18 at 08:03

score 1 · Answer 2 · answered Aug 28 '18 at 19:29

If you want to replace hardcoded links inside of your post content I would suggest you use the "the_content" filter for wordpress.

https://codex.wordpress.org/Plugin_API/Filter_Reference/the_content

add_filter( 'the_content', 'filter_function_name' )

From this you should be able to regular expression match the link and append /amp to it.

Pseudo code example:

function my_the_content_filter($content)
{
    if (function_exists('is_amp_endpoint') && is_amp_endpoint()) {
        $patterns = array(
            //patterns
        );
        $replacements = array(
           //replacements

        );
        $content = preg_replace($patterns, $replacements, $content);
    }

    return $content;
}

add_filter('the_content', 'my_the_content_filter');

score 0 · Answer 3 · answered Dec 06 '18 at 21:30

I have tested the code submitted by Outsource WordPress, and in general it works fine but the 'amp_override_canonical function overwrites all the urls of the page removing the /amp.

I have made some changes to this piece of code but they do not work as I expect. It seems that the 'wpseo_canonical' function is being invoked in a different context.

add_filter( 'wpseo_canonical', 'amp_override_canonical' );

function amp_override_canonical($url) {
    if ( substr($url,-4)=="/amp" ) {    
        $url = substr($url,0,-4);
    }
    return $url;
}

if is amp change internal links to amp version (WordPress)

3 Answers3