CDN rewriting doesn't work when WP_HOME/WP_SITE_URL scheme is different than the site's URLs

[vmanthos]

When the WP_HOME is using http but the site's URLs are using https, e.g. there is an htaccess redirect from http to https CDN rewriting doesn't take place.

This is because of the str_replace() in the rewrite_url method of the CDN class:

wp-rocket/inc/classes/CDN/CDN.php

Line 120 in 00cf7a1

return str_replace( $home_url, rocket_add_url_protocol( $cdn_url ), $url );

Example:
http://sandbox.onlinephpfunctions.com/code/1521df9f18dd8b11edf02e77f9994656078f6539

To Reproduce

Steps to reproduce the behavior:

1. Make sure the WP_HOME and WP_SITE_URL are using http.
2. Enable http to https redirection in the .htaccess file.
3. Enable the CDN option.
4. Check the website. Static assets will not be rewritten to point to the CDN.

Expected behavior
Static assets should be pointing to the CDN.

Additional context

Using the rocket_is_ssl_website() function before the string_replace() resolves the issue:

if( rocket_is_ssl_website() ) {
    $home_parts['scheme'] = 'https';
}

Related ticket:
https://secure.helpscout.net/conversation/1116358022/153068/

Backlog Grooming (for WP Media dev team use only)

• Reproduce the problem
• Identify the root cause
• Scope a solution
• Estimate the effort

[remyperona]

I think this is a duplicate of #2148

[GeekPress]

It seems, thanks for the catch @Tabrisrp . I closed #2148 as this contains more details of the problem.

[ScottTravisHartley]

I want to comment I noticed this issue as well working on a client site today their previous dev set it up as the issue describes I updated the home and site URLs to https and the rewrite works again.

[remyperona]

Reproduce the issue ✅
Issue reproduced and reported in multiple occasions

Identify the root cause ✅
As noted here and in the duplicate issue, it's happening when there is a difference between the URL set for home/site URL, and the real URL used, when the scheme is not the same.

The difference in scheme is preventing the str_replace from doing its job correctly.

Scope a solution ✅
str_replace can accept an array for the first argument $needle, so we can use an array under the following format to perform the replacement in all cases:
[ 'http://example.org', 'https://example.org' ]

Effort ✅
Effort [S]