About the feed name specified in the add_feed()

[tmatsuur]

There is no restriction on the first parameter of the add_feed function, but if it starts with "_" it will not function properly.

function feed2_callback( $is_comment_feed, $feed ) {
	header( 'Content-Type: application/xml; charset=UTF-8', true );
	echo '<?xml version="1.0" encoding="UTF-8" ?>';
?>
<rss version="2.0"
	xmlns:content="http://purl.org/rss/1.0/modules/content/"
	xmlns:dc="http://purl.org/dc/elements/1.1/"
	xmlns:atom="http://www.w3.org/2005/Atom"
>
	<title>Test</title>
</rss>
<?php
}

add_feed( '_feed2', 'feed2_callback' );

Next, update the rewrite rule and access "​http://localhost/_feed2", which will return the following:

<error>
    <code>wp_die</code>
    <title><![CDATA[WordPress &amp;rsaquo; Error]]></title>
    <message><![CDATA[&lt;strong&gt;Error:&lt;/strong&gt; This is not a valid feed template.]]></message>
    <data>
        <status>404</status>
    </data>
</error>

This is not a problem with the code I tried, but because the "_" at the beginning of the feed name is removed in the do_feed function.

function do_feed() {
	global $wp_query;

	$feed = get_query_var( 'feed' );

	// Remove the pad, if present.
	$feed = preg_replace( '/^_+/', '', $feed );

This process results in an action name of 'do_feed_' . 'feed2' when $feed is '_feed2'.

Since this is not done in the add_feed function and the action name specified in the add_action function is 'do_feed_' . '_feed2', it appears that the two action names do not match, resulting in the error indicated in the response.

Should I remove the leading '_' in the feed name in the add_feed function or not remove the '_' in the do_feed function?

In any case, I would like to see consistency in the handling of feed names.

[hellofromTonya]

Hello @tmatsuur,

Welcome to WordPress Core's Trac :)

I'm doing some ticket triage to help each move forward. The preg_replace() in question and the 2 functions were introduced in WordPress 2.1.0 via [3638] / #2433. Updating the Version to match.

[tmatsuur]

Thanks @hellofromTonya,

It is deeply moving to realize that this issue goes back 18 years.

[jorbin]

With the knowledge that this has been in place for so long, my gut leans towards not wanting to make code changes but instead make this a documented part of the function.

[hellofromTonya]

Drilling further backwards in time, the RegEx that strips the _ was first introduced in [1376], 20 years ago. https://core.trac.wordpress.org/browser/trunk/wp-feed.php?rev=1376#L9

I'm not finding a ticket for it, i.e. to review the discussion of why it was needed.

Replying to jorbin:

With the knowledge that this has been in place for so long, my gut leans towards not wanting to make code changes but instead make this a documented part of the function.

Given this feed naming limitation has existed for 20 years, I agree with @jorbin. Though I'd like to know why it's needed, changing this area of the code is risky, i.e. likely will have unintended side effects.

Pulling into 6.5 and adding needs-patch to add the better documentation.

## Ticket: https://core.trac.wordpress.org/ticket/59945

• This PR addresses an issue in the add_feed function where feed names starting with an underscore are not handled properly, leading to errors.
• The function now includes validation to prevent feed names from starting with an underscore, improving overall robustness and developer experience.

## Background:

• The add_feed function allows developers to register custom feed types in WordPress. However, if the feed name starts with an underscore, it is stripped by the do_feed function, causing unexpected errors.
• This PR introduces a validation step to ensure feed names do not start with an underscore, thereby avoiding these issues.

## Changes Made:
### Validation in add_feed Function:

• Added a check to ensure the feed name does not start with an underscore (_).
• If the feed name is invalid, an error is logged using error_log, and the function returns false.

### Proper Initialization Check:

• Ensured that the $wp_rewrite global variable is initialized before proceeding with feed registration.

[oglekler]

PR needs to be tested. There should be the version of WordPress where the message was added (Now it can be 6.6.0) instead of '6.2.0'.

[oglekler]

The patch itself looks very simple, but it has a string, and we have just few days before RC1 with hard string freeze. So, we need to hurry up with this one.

Do we need Unit tests for this, or/and can they be added via another ticket?

[audrasjb]

Thanks for the patch @snehapatil02 but as per comments 3 and 4, it was suggested to only update the function docblock, to avoid breaking change.

Trac ticket: https://core.trac.wordpress.org/ticket/59945

[narenin]

Hi @audrasjb

I have suggest PR with suggested doc changes and also created PR to update in doc function.

​https://github.com/WordPress/Documentation-Issue-Tracker/issues/1616
​https://github.com/WordPress/wordpress-develop/pull/6880

[atachibana]

Replying to narenin:
​https://github.com/WordPress/Documentation-Issue-Tracker/issues/1616 was closed.

Below sentence was added to More Information section of ​add_feed() reference so that it can be reflected without any code changes. After the merge of ​PR 6880, we can remove this sentence.

$feedname parameter should not start with ‘_‘. Please refer #59945.

[audrasjb]

Moving to 6.7 as we're getting really close to 6.6 final release.

[DrewAPicture]

In 59059:

Docs: The $feedname parameter in add_feed() should not start with an underscore.

Props snehapatil02, hellofromtonya, narenin.
Fixes #59945.