Prevent Headers from being sent

Question

How can I prevent Headers from being sent?

I am trying to list (WordPress) blog posts on a non-WordPress site (both sites share a public web folder).

I want to run the following PHP code to get the blog posts:

        <ul class='list-unstyled'>
        <?php
            define('WP_USE_THEMES', false);
            require($_SERVER['DOCUMENT_ROOT'] . '/blog/wp-load.php');
            query_posts('showposts=5');
            while (have_posts()): the_post();
            ?>
                <li><i class='glyphicon glyphicon-menu-right'></i>
                    <h4><a href="<?php the_permalink(); ?>" class="myred text-main"><?php the_title(); ?></a></h4>
                    <p><?php the_date(); ?> | Category: <?php the_category(','); ?> | <?php the_tags(); ?></p>
                </li>
            <?php endwhile; ?>
        </ul>

However, it seems running this code sends payload headers to client. Is there any way to retrieve the blog posts without sending headers?

Answer 1

"Headers already sent" is not a WordPress error, it is PHP processing error message. Good explanation here; https://stackoverflow.com/questions/8028957/how-to-fix-headers-already-sent-error-in-php .

I suspect it might be caused by some characters (probably space characters) sent before your <?php code segment. Even space (or tab [code formatting] ) characters will cause an error.

And perhaps move your <ul> code to just above the while loop.

Answer 2

Output of the page started as your php is executing. Look into into output buffering.

Putting a ob_start() function call before any HTML in the file and a call to ob_get_clean() after should solve the problem.

It would look something like this:

<?php

define('WP_USE_THEMES', false);
require($_SERVER['DOCUMENT_ROOT'] . '/blog/wp-load.php');
//Buffer output instead of immediately sending to the client
//make sure there is only PHP here
ob_start();
?>
//templating stuff...
        <ul class='list-unstyled'>
    <?php
        query_posts('showposts=5');
        while (have_posts()): the_post();
        ?>
            <li><i class='glyphicon glyphicon-menu-right'></i>
                <h4><a href="<?php the_permalink(); ?>" class="myred text-main"><?php the_title(); ?></a></h4>
                <p><?php the_date(); ?> | Category: <?php the_category(','); ?> | <?php the_tags(); ?></p>
            </li>
        <?php endwhile; ?>
    </ul>
//More templating stuff...
<?php
ob_get_clean();
//output starts
?>

Also as Rick Hellewell pointed out in his answer, make sure the file starts with nothing but an opening <?php tag. No blank space, not HTML, nothing.

Answer 3

I solved my problem by installing the REST API plugin, then calling the end point from my non-wordpress site, caching the results, then displaying the blog list from my cache results.