A WordPress plugin that allow resolving any kind of WordPress url (even from custom rewrite rules) to related main query arguments.

Requirements

• PHP 5.4+
• WordPress 3.9+
• Composer to install

Installation

The plugin is a Composer package and can be installed in plugin directory via:

composer create-project gmazzap/url-to-query --no-dev

What & Why

WP comes with a set of tools to convert custom urls into specific query variables: is possible to change the permalink structure, and there is also an API to add completely custom rules, however, there is not a way to reverse the process: i.e. to know to which query arguments an arbitrary url is connected to.

The url resolving is done in core by parse_request method of WP class saved in the global $wp variable.

Using that method for the purpose explained above is hard/discouraged because:

• it directly accesses to $_SERVER, $_POST and $_GET variables, making hard to parse arbitrary urls not related with current HTTP request
• it triggers some action hooks strictly related to current HTTP request parsing, that makes no sense to trigger for arbitrary urls
• it accesses and modifies properties of global $wp variable that should not be changed after request is parsed or very likely things will break

This is the reason why I wrote this simple plugin, it adds a template tag url_to_query that accepts an url and returns related main query arguments.

How to use

$args = url_to_query( 'http://example.com/sample-page' );
// $args = array(  'pagename' => 'sample-page' );

$args = url_to_query( 'http://example.com/category/uncategorized/' )
// $args = array(  'category_name' => 'uncategorized' );

It is also possible to pass a relative url:

$args = url_to_query( '/sample-page' );
// $args = array(  'pagename' => 'sample-page' );

Using query string

When pretty permalinks are not used, (sometimes even in that case) WordPress can make use of query string in the urls to set query arguments. The plugin works perfectly with them:

$args = url_to_query( '/?attachment_id=880' );
$args = array(  'attachment_id' => '880' );

To simplify this task, url_to_query accepts a second argument: an array of query vars to be considered in the same way core considers $_REQUEST variables when an url is parsed:

$args = url_to_query( '/', array( 'attachment_id' => '880' ) );
// $args = array(  'attachment_id' => '880' );

Note that the array passed as second argument is not straight merged to the query vars, only valid query vars will be used, just like core does when parse urls:

$args = url_to_query( '/', array( 'attachment_id' => '880', 'foo' => 'bar' ) );
// $args = array(  'attachment_id' => '880' );

Custom rewrite rules

Plugin works with no problems with custom rewrite rules, just few things to consider:

• url_to_query have to be called after query rules are added, or it can't recognize them
• just like for core, rewrite rules have to be flushed before url_to_query can recognize a newly added rule
• just like core, if the rule contains custom query variables, they have to be allowed, maybe using add_rewrite_tag or using 'query_vars' filter (see Codex example)

Example:

add_action( 'init', 'my_rew_rules' );

function my_rew_rules() {
  add_rewrite_tag('%food%', '([^&]+)');
  add_rewrite_tag('%variety%', '([^&]+)');
  add_rewrite_rule(
    '^nutrition/([^/]*)/([^/]*)/?',
    'index.php?page_id=12&food=$matches[1]&variety=$matches[2]',
    'top'
  );
}

add_action( 'footer' function() {
  $args = url_to_query( '/nutrition/cake/cherry/' )
  // $args = array( 'page_id' => '12', 'food' => 'cake', 'variety' => 'cherry' );
} );

Plugin classes

Even if plugin provides the 'url_to_query' template tag, it internally uses two classes to resolve urls and it is possible directly use them, instead of the template tag. Indeed, only one of them should be used, the second is used internally.

$resolver = new GM\UrlToQuery();
$args = $resolver->resolve( 'http://example.com/sample-page', array( 'page' => '2' ) );
// $args = array( 'pagename' => 'sample-page', 'page' => '2' );

So resolve() method of GM\UrlToQuery works exactly in the same way url_to_query function does.

The same instance of GM\UrlToQuery can be used to resolve different urls:

$resolver = new GM\UrlToQuery();

$args1 = $resolver->resolve( 'http://example.com/sample-page', array( 'page' => '2' ) );
// $args1 = array( 'pagename' => 'sample-page', 'page' => '2' );

$args2 = $resolver->resolve( '/?attachment_id=880' );
// $args2 = array( 'attachment_id' => '880' );

$args3 = $resolver->resolve( 'http://example.com/category/uncategorized/' );
// $args3 = array( 'category_name' => 'uncategorized' );

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License

Url_To_Query is released under MIT.