Redirect to archive is single post has a certain term assigned to it?

Question

I want to redirect any single post to its taxonomy term's archive page if it has a specific term assigned to it.

So, if a post of a term "series" at:
domain/series/post/
I want to redirect that single post back to:
domain/series/

I've tried working with php's header() function, but I know that needs to be used before any other headers are sent. I can't seem to detect the terms AND use header() in the same place.

Any help is greatly appreciated!
Thanks!

Answer 1

There is a template_redirect hooks which is perfectly suitable for task like this.

1. Hook into template_redirect
2. Check your context (is_single(), etc)
3. Redirect with wp_safe_redirect() (if it's inside a site)
4. die() to prevent execution from proceeding

Answer 2

Thanks to Rarst for the tip.
Here is the code I came up with to accomplish redirects for two similar taxonomy/post type set ups.
This basically does what I indicated in the OP. If I hit a single post with a top-level term assigned to it, the url will go from
domain/series/post/
to
domain/series/

It simply strips the post's slug from the end of the url.

Obviously, the CPTs, taxonomies and rewrites have to be set up properly to work with this.

I added the $type parameter to the theme_perform_redirect() function so that I can add functionality to it later for other types of redirects.

function theme_perform_redirect($post, $taxonomy, $type) {
    if ($type == 'top-level') {
        $top_level_terms = get_top_level_term_ids( $taxonomy );
        $post_terms = wp_get_post_terms( $post->ID, $taxonomy );
        if ( in_array($post_terms[0]->term_id, $top_level_terms)) {
            // This is the main/top post, redirect it to the archive
            $to_strip = $post->post_name;
            $permalink = get_permalink( $post->ID );
            $go_here = str_replace($to_strip."/", "", $permalink);
            wp_redirect( $go_here );
            exit();
        }
    }
}

function theme_redirects() {
    global $post;
    if ( is_single() ) {
        if (is_singular( 'cartoon-series' )) {
            heman_perform_redirect($post, 'cartoon-features', 'top-level');
        } else if (is_singular( 'movies' )) {
            heman_perform_redirect($post, 'movie-features', 'top-level');
        }
    }
}
add_action( 'template_redirect', 'theme_redirects' );

Note that get_top_level_term_ids() is my own function. It just grabs all the terms with a parent of 0....just in a neater package. :-)

Thanks!