A few years ago when I wanted to use domain mapping for domains in a WordPress network, it was a bit of a chore. At that time I had to use a special domain mapping plugin and another tool called “sunrise.” This week, when setting up domain mapping with a network generated by SpinupWP we discovered things had gotten a lot simpler.
Since WordPress 4.5 domain mapping has become a native feature. All we had to do was use SpinupWP to define additional domains for our network site, create a subsite for that domain on WordPress, and then go to Sites and edit that site to put the domain name into the Site Address (URL).
That worked! But then we decided we also wanted upload URLs that were a bit more friendly than the site numbers that WordPress automatically uses. A typical piece of media on a site mapped subsite would get a URL like https://subsite.com/wp-content/uploads/site/3/2020/2/media.jpg. That works, but I find the site/3 a bit too mysterious and revealing at the same time. It is mysterious in that it really means nothing to a person reading the URL. It is revealing in that it is trivial to guess that there might be a site/4 or a site/5.
We wondered if we could not use something like sub instead, so that the URL would become https://subsite.com/wp-content/uploads/sub/2020/2/media.jpg. This would take two things, (1) a way to define the string to use for a given subsite, and (2) a way to tell WordPress to use that string instead of the blog ID number in the upload URLs.
We decided to keep defining the string as an experts-only affair. Basically, if this string was present then we wanted to assume an expert had decided the substitution should take place. Since only experts were going to do this, we left it to a WPCLI command:
$ wp --url=https://subsite.com option add tg_upload_dir sub
In other words, we created an option to hold the string. If that option exists, we would make the substitution.
To carry out the substitution we create a one-function upload directory modifier plugin to look for that option and use if when found. The heart of this plugin is the following function:
add_filter( 'upload_dir', 'tg_upload_dir_filter' );
function tg_upload_dir_filter( $dirs ) {
global $wpdb;
$directory = get_option('tg_upload_dir');
if (! $directory) {
return $dirs;
}
$dirs['baseurl'] = site_url() . '/wp-content/uploads/' . $directory;
$dirs['basedir'] = ABSPATH . 'wp-content/uploads/' . $directory;
$dirs['path'] = $dirs['basedir'] . $dirs['subdir'];
$dirs['url'] = $dirs['baseurl'] . $dirs['subdir'];
return $dirs;
}
While this gave us the URLs we wanted, we still had to take one more step to get these URLs to work: we had to create a symlink from the directory WordPress had created to the friendlier name we wanted to use. To accomplish this we used SSH to connect to the server behind our SpinupWP site and then did the following:
$ cd files/wp-content/uploads
$ ln -s sites/3 sub
The beauty of this approach is that both the sites/3 URL and the sub URL will work, so we don’t have to search and replace existing media URLs unless we want to.
