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Opened 4 years ago

Last modified 4 months ago

#51725 new defect (bug)

Canonical redirect and user_trailingslashit()

Reported by: mbis's profile mbis Owned by:
Milestone: Awaiting Review Priority: normal
Severity: trivial Version: 5.5.2
Component: Canonical Keywords: has-patch needs-unit-tests
Focuses: Cc:



this bug is quite difficult to spot and it appears only when redirect_canonical() function is used to force the canonical redirect on front page and the trailing slashes are not added to the permalinks. Happily it is nothing serious.

How to reproduce this bug?

Step 1. Remove the trailing slashes from WP permalinks:
First of all, you need to use "Custom structure" mode in Permalinks settings and remove the trailing slash (/%postname%/ => /%postname%) in the adjacent input field. Therefore, the value of $wp_rewrite->use_trailing_slashes is changed to false.

Step 2. Trigger the canonical redirect on front page
Now let's disable the feed URL by redirecting the visitors trying to access it:

function disable_feed() {
        if(is_feed() && is_front_page()) {
add_action('template_redirect', 'disable_feed', 1);

Now, when one tries to access the feed URL linked to front page, (eg., the above hook will be triggered and visitor redirected to the canonical URL ( =>

The problem is that the PHP notice is displayed then:
<b>Notice</b>: Undefined index: path in <b>/var/www/vhosts/</b> on line <b>576</b><br />

I guess that the source of the problem is here (line 501):

$redirect['path'] = user_trailingslashit( $redirect['path'] );

Unfortunately because of user_trailingslashit() function, the slash is removed and value is set to null. The value of $redirect['path'] should not be changed in this particular case (value '/' should be preserved).

My first suggestion is to exclude user_trailingslashit() function there and not use it when value of $redirect['path'] variable is just a single slash '/':

$redirect['path'] = ( $redirect['path'] === '/' ) ? $redirect['path'] : user_trailingslashit( $redirect['path'] );

Another idea is to do the same but directly in user_trailingslashit() function:

Basically this piece of code:

if ( $wp_rewrite->use_trailing_slashes ) {
        $string = trailingslashit( $string );
} else {
        $string = untrailingslashit( $string );

can be replaced with:

if ( $wp_rewrite->use_trailing_slashes ) {
        $string = trailingslashit( $string );
} else if ( $string !== '/' ) {
        $string = untrailingslashit( $string );

Attachments (1)

Settings.png (413.1 KB) - added by mbis 4 years ago.
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Change History (6)

4 years ago

Permalink settings

This ticket was mentioned in PR #705 on WordPress/wordpress-develop by maciejbis.

4 years ago

  • Keywords has-patch added

Both code changes should prevent malformed output of _user_trailingslashit()_ function when the input value is a single slash:
$foo = user_trailingslashit('/');

This is the case, when the trailing slashes are removed from WP permalinks:
$wp_rewrite->use_trailing_slashes = false

and _redirect_canonical()_ function is used to force the canonical redirect on front page.

Trac ticket:

github-actions[bot] commented on PR #705:

4 years ago

Hi @maciejbis! 👋

Thank you for your contribution to WordPress! 💖

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#3 @SergeyBiryukov
4 years ago

  • Component changed from Permalinks to Canonical
  • Focuses performance coding-standards removed
  • Keywords needs-unit-tests added

Hi there, welcome to WordPress Trac! Thanks for the report and the PR.

Just linking to some related tickets here: #34353, #39827, #41577.

#4 @bobz
3 years ago

This was the fix in my case, I'm using relative permalinks without trailing slash.

add_filter( 'redirect_canonical', function( $redirect_url, $requested_url ) {

    $redirect  = parse_url( $redirect_url );
    $requested = parse_url( $requested_url );

    // Prevent redirect to exact same page
    if ( strtolower($redirect['path']) == strtolower($requested['path']) )
        return false;

}, 101, 2 );

#5 @lopo
2 years ago

#55653 was marked as a duplicate.

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