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Based on an example found here and several others, I am trying to load a non wordpress page from a specific URL while having access to the wordpress core.

I have the following code (which seems to work as expected) to hook into the template_redirect action:

function templateRedirect() {
    global $wp;
    if ( $wp->query_vars['pagename'] == 'nlm-admin-thumbnail' ) {
        global $wp_query;
        // if we have a 404 status
        if ($wp_query->is_404) {
            // set status of 404 to false
            $wp_query->is_404 = false;
            $wp_query->is_archive = true;
        // change the header to 200 OK

        header("HTTP/1.1 200 OK");
        //load our template
        include( dirname( __FILE__ ) . '/thumbnail.php' );

add_action('template_redirect', 'templateRedirect');

My problem comes when executing the code in thumbnail.php. This file is supposed to download a thumbnail of a webpage and output the raw image. The nlm-admin-thumbnail slug is used as the src for an image tag.

When I execute the thumbnail.php I keep getting undefined function some_wp_function(). I have included http.php and class-http.php from the wp-includes folder. Now that I have included those, the next error is undefined function apply_filters().

Does loading a php file in this way not give me access to the wp core, and should apply_filers() not accessable?

share|improve this question
Try loading wp-load.php – user27457 Feb 23 '13 at 2:32
I thought by hooking into template redirect I would avoid that and all the problems that go with it. – Chris Strutton Feb 23 '13 at 2:36
Calling add_action() justs adds some objects? to some array? it doesn't actually load any PHP files that I am aware of. – user27457 Feb 23 '13 at 2:47
I am not sure exactly what you are trying to to but BackPress which is just the WordPress core available as a free download may be something toconsider. – user27457 Feb 23 '13 at 3:06
up vote 2 down vote accepted

I do this pretty regularly and have no issue with using functions in WordPress core. You can hook a bit earlier though and skip the 404 and header bits. In functions.php:

function wpa88013_parse_query( $wp ){
    if ( 'nlm-admin-thumbnail' == $wp->query_vars['pagename'] ) {
        include( dirname( __FILE__ ) . '/thumbnail.php' );
add_action( 'parse_query', 'wpa88013_parse_query' );

And some example code in thumbnail.php:

$content = "foo\n\nbar";
echo apply_filters( 'the_content', $content );

$post_id = 1;
echo get_the_post_thumbnail( $post_id );

I've just tested this in the twentytwelve theme and it works as expected.

share|improve this answer
Thanks @Milo. Will hooking in here let me set my own headers? My script returns an image built in memory (the actual image, not a url to a file). – Chris Strutton Feb 23 '13 at 3:28
hook the parse_request action instead, this happens before WordPress sends any headers. see the action reference for the order of actions. – Milo Feb 23 '13 at 3:34

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