force download a file in template_redirect hook

Question

in my functions.php file I've added a custom action for the template_redirect hook which must force download a file stored on the server. The code of the download works fine when it is in a simple PHP file outside of Wordpress. But the feature is broken as soon as I add this code inside my template _redirect hook. Chrome says "The site cannot be reached ... ERR_INVALID_RESPONSE". There is no error 500 or other error...

Here's the download code :

<?php
$filename = $_SERVER['DOCUMENT_ROOT'] . 'path-to-my-wordpress/wp-content/uploads/export/test.html';
header( "Expires: 0" );
header( "Cache-Control: no-cache, no-store, must-revalidate" );
header( 'Cache-Control: pre-check=0, post-check=0, max-age=0', false );
header( "Pragma: no-cache" );
header( "Content-type: text/html" );
header( "Content-Disposition:attachment; filename=\"" . basename( $filename ) . "\"" );
header( "Content-Type: application/force-download" );
readfile( "{$filename}" );
?>

Here's the template_redirect hook :

add_action( 'template_redirect', 'my_template_redirect' );
function my_template_redirect() {
$filename = $_SERVER['DOCUMENT_ROOT'] . 'path-to-my-wordpress/wp-content/uploads/export/test.html';
header( "Expires: 0" );
header( "Cache-Control: no-cache, no-store, must-revalidate" );
header( 'Cache-Control: pre-check=0, post-check=0, max-age=0', false );
header( "Pragma: no-cache" );
header( "Content-type: text/html" );
header( "Content-Disposition:attachment; filename=\"" . basename( $filename ) . "\"" );
header( "Content-Type: application/force-download" );
readfile( "{$filename}" );
exit();
}

Any idea ?

EDIT

After some more tests, the problem seems to come from the specific URL from which I'm trying to run this download. In fact, my code is like this :

add_action( 'template_redirect', 'my_template_redirect' );
function my_template_redirect() {
    if ( preg_match( "/\/wp-admin\/export$/", $_SERVER['REQUEST_URI'] ) ) {
        $filename = $_SERVER['DOCUMENT_ROOT'] . 'path-to-my-wordpress/wp-content/uploads/export/test.html';
        header( "Expires: 0" );
        header( "Cache-Control: no-cache, no-store, must-revalidate" );
        header( 'Cache-Control: pre-check=0, post-check=0, max-age=0', false );
        header( "Pragma: no-cache" );
        header( "Content-type: text/html" );
        header( "Content-Disposition:attachment; filename=\"" . basename( $filename ) . "\"" );
        header( "Content-Type: application/force-download" );
        readfile( "{$filename}" );
        exit();
    }
}

The URL is /wp-admin/export and this should launch the download of the file. Without this URL condition, the code does work when I reach the base site URL (= http://mysite.dev/). But with the condition adn trying to reach http://mysite.dev/wp-admin/export, it breaks. I also tried without the wp-admin prefix, and it also breaks.

Answer 1

The solution is in fact very simple. Just use the action admin_post_(action)...

add_action( 'admin_post_export_page', 'export_page' );
function export_page() {
    // any code you want
}

than you can make custom links admin_url( 'admin-post.php?action=export_page&id=' . $post->ID );

Thanks Milo for giving the solution.

Answer 2

Error 500 This is a server error, so I assume it is related to or read of the file or its delivery to the client.

The problems I currently see as possible that cause the problem are: 1) You have twice submitted the content type but different settings and parallels. 2) The second time you send an application / force-download type, there are servers that are problematic for them if they do not know the mime type that is being sent.

Try the following code:

add_action( 'template_redirect', 'my_template_redirect' );
function my_template_redirect() {
    if ( strpos( $_SERVER['REQUEST_URI'], admin_url( 'export' ) ) !== false ) {
        $upload_dir = wp_upload_dir();
        $filename = $upload_dir['basedir'] . '/export/test.html';

        header( "Expires: 0" );
        header( "cache-Control: no-cache, no-store, must-revalidate" );
        header( "Pragma: no-cache" );
        header( "content-disposition: attachment; filename=" . basename( $filename ) );
        header( "content-type: application/octet-stream" );
        header( "content-length: " . filesize( $file ) );
        readfile( $filename );
        die();
    }
}

Answer 3

Your not adding your redirect page

 add_action( 'template_redirect', 'my_template_redirect' );
    function my_template_redirect() {
    $filename = $_SERVER['DOCUMENT_ROOT'] . 'path-to-my-wordpress/wp-content/uploads/export/test.html';
    header( "Expires: 0" );
    header( "Cache-Control: no-cache, no-store, must-revalidate" );
    header( 'Cache-Control: pre-check=0, post-check=0, max-age=0', false );
    header( "Pragma: no-cache" );
    header( "Content-type: text/html" );
    header( "Content-Disposition:attachment; filename=\"" . basename( $filename ) . "\"" );
    header( "Content-Type: application/force-download" );
    readfile( "{$filename}" );
    // Add your redirect page here
    wp_redirect( home_url( '/pagename/' ) ); /// works on my install sends to new page
    exit();
    }