Domain Substitution for WordPress

A WordPress plugin that substitutes the current domain with a custom domain for all attachment/image URLs; great for running a staging or local development site with images from your live/production site.

Features

• Replaces site domain with custom domain for all attachment URLs
• Works with image srcset for responsive images
• Processes content to replace image URLs in posts and pages
• Perfect for staging/development environments using production images
• Simple settings page for easy configuration
• Lightweight with minimal performance impact

Installation

1. Upload the domain-substitution-for-wordpress folder to /wp-content/plugins/
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Go to Settings → WP Domain Substitution
4. Enter your custom domain (e.g., cdn.example.com or your production site domain)
5. Save settings

Usage

For Site Administrators

1. Navigate to Settings → WP Domain Substitution in your WordPress admin
2. Enter the custom domain you want to use for images (without http:// or https://)
3. Click "Save Changes"
4. All attachment and image URLs will now use the custom domain

Common Use Cases

Staging Site with Production Images

• Problem: You're running a staging site but want to use images from your production site
• Solution: Set custom domain to your production domain (e.g., www.yoursite.com)
• Result: Staging site loads images from production without duplicating files

Local Development

• Problem: Your local environment doesn't have all the media files
• Solution: Set custom domain to your production or staging domain
• Result: Local site loads images from remote server

CDN Configuration

• Problem: You want to serve images from a CDN
• Solution: Set custom domain to your CDN domain (e.g., cdn.example.com)
• Result: All images load from CDN

For Developers

The plugin hooks into multiple WordPress filters to ensure comprehensive URL replacement:

Filters Used:

• wp_get_attachment_url - Substitutes domain in attachment URLs
• wp_get_attachment_image_src - Handles image source arrays
• wp_calculate_image_srcset - Processes responsive image srcsets
• the_content - Replaces domains in post/page content

How it works:

// The plugin replaces the site domain with custom domain
$site_url = parse_url(site_url(), PHP_URL_HOST);
$url = str_replace($site_url, $custom_domain, $url);

Domain Sanitization:

• Removes http:// or https:// protocol
• Trims whitespace
• Removes trailing slashes
• Sanitizes as text field

Requirements

• WordPress 5.0 or higher
• PHP 7.0 or higher

Changelog

1.0.0

• Initial release
• Domain substitution for attachment URLs
• Support for responsive images (srcset)
• Content filtering for embedded images
• Admin settings page

License

GPL v2 or later