Allow array of sanitize_callback parameters in register_rest_route()

[GunGeekATX]

By allowing an array of sanitize callbacks when registering a route, we can easily add support for multiple sanitize functions. For example, registering with the following callbacks would allow a color to be trimmed and then sanitized.

'sanitize_callback' => array(
	'normalize_whitespace',
	'sanitize_hex_color_no_hash',
	),

Example: ​http://src.wordpress-develop.dev/wp-json/test/multisanitize?color=%20ff0000

Another example may be someone parsing post IDs from a list, then sanitizing it down to valid post IDs with a custom function.

'sanitize_callback' => array(
	'wp_parse_id_list',
	'sanitize_post_ids',
	),

The attached patch adds support for multiple sanitize_callback handlers. The same logic could be applied to validate_callback handlers.

[swissspidy]

An array of callbacks executed in a specific order… sounds like we could use filters here.

[rmccue]

Strong -1 on this. If you want to call multiple sanitising functions, make a function that calls them yourself. I don't see a need for this to be included in the general REST API infrastructure.

[jnylen0]

I agree with Ryan here; I think this is uncommon enough that you should just write the function yourself. Then, if certain cases end up being common, they should have their own functions to handle them, and these functions should be documented and tested. After that, we are back to a single sanitize_callback.

Our sanitize and validate infrastructure is already pretty magical and complicated, let's not make it more so.