How to set dynamic `home` and `siteurl` in WordPress?

I config the multi-language setting dynamically using the `locale` filter. Which fetch the sub-domain name to determine the language.

function load_custom_language($locale) {
// get the locale code according to the sub-domain name.
// en.mysite.com => return `en`
// zh.mysite.com => return `zh_CN`
// tw.mysite.com => return `zh_TW`
// etc..
}
add_filter('locale', 'load_custom_language');

---

That works for the index page, but when I redirect to another page, because of the settings of `home` and `siteurl`, it always redirects my site to the original one (`www.mysite.com`).

So I'm curious to find a dynamic way to filter the `home` and `siteurl` according to the request, because I might use more than one sub-domain for mysite and I have only one settings for the two settings.

I've found another pretty way to achieve the work:

After I checked for the source code of the kernel, I found that there are distinct filters called `option_xxx` on each options.

So, for my task, I tried to use the `option_siteurl` and `option_home` filter to hold that options to load, just to prevent the option to load, maintaining the `SERVER_NAME` it has:

function replace_siteurl($val) {
return 'http://'.$_SERVER['HTTP_HOST'];
}
add_filter('option_siteurl', 'replace_siteurl');
add_filter('option_home', 'replace_siteurl');

Using this way, it has no need to change the `wp_config.php` file, and can be easily add to a theme or a plugin.

To **set dynamically the domain and as well as the protocol** (*http* or *https*), use:

```php
// Identify the relevant protocol for the current request
$protocol = (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off' || $_SERVER['SERVER_PORT'] == 443) ? "https" : "http";

// Set SITEURL and HOME using a dynamic protocol.
define('WP_SITEURL', $protocol . '://' . $_SERVER['HTTP_HOST']);
define('WP_HOME', $protocol . '://' . $_SERVER['HTTP_HOST']);
```

You can override the admin settings in the wp-config.php file.
So if you want something dynamic, the following should work:

//presumes server is set up to deliver over https

define('WP_SITEURL', 'https://' . $_SERVER['HTTP_HOST']);
define('WP_HOME', 'https://' . $_SERVER['HTTP_HOST']);

This needs to added before the line

require_once(ABSPATH . 'wp-settings.php');

or else you may have problems with some content using the wrong URLs, especially theme files.