[wp-trac] [WordPress Trac] #51725: Canonical redirect and user_trailingslashit()

[WordPress Trac]

#51725: Canonical redirect and user_trailingslashit()
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 Reporter:  mbis                           |      Owner:  (none)
     Type:  defect (bug)                   |     Status:  new
 Priority:  normal                         |  Milestone:  Awaiting Review
Component:  Permalinks                     |    Version:  5.5.2
 Severity:  trivial                        |   Keywords:
  Focuses:  performance, coding-standards  |
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 Hi,

 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:
 {{{#!php
 <?php
 function disable_feed() {
         if(is_feed() && is_front_page()) {
                 redirect_canonical();
         }
 }
 add_action('template_redirect', 'disable_feed', 1);
 }}}


 Now, when one tries to access the feed URL linked to front page, (eg.
 http://example.com/feed), the above hook will be triggered and visitor
 redirected to the canonical URL (''http://example.com/feed'' =>
 ''http://example.com'').

 The problem is that the PHP notice is displayed then:
 ''<b>Notice</b>:  Undefined index: path in
 <b>/var/www/vhosts/maciejbis.net/example.com/wp-includes/canonical.php</b>
 on line <b>576</b><br />''

 I guess that the source of the problem is here (line 501):
 https://core.trac.wordpress.org/browser/tags/5.5.1/src/wp-
 includes/canonical.php#L501

 {{{#!php
 $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 '/':

 {{{#!php
 $redirect['path'] = ( $redirect['path'] === '/' ) ? $redirect['path'] :
 user_trailingslashit( $redirect['path'] );
 }}}

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

 https://core.trac.wordpress.org/browser/tags/5.5.1/src/wp-includes/link-
 template.php#L51

 Basically this piece of code:
 {{{#!php
 if ( $wp_rewrite->use_trailing_slashes ) {
         $string = trailingslashit( $string );
 } else {
         $string = untrailingslashit( $string );
 }
 }}}

 can be replaced with:

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

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/51725>
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