PHP function for testing for a media type in a Content-Type header, taking in account case insensitivity and the optional parameters like charset.

mediatype.php

<?php

/**
 * @author Robbert Broersma <http://robbertbroersma.nl/>
 * @license Public Domain
 */

/**
 * @see http://tools.ietf.org/html/rfc2046#appendix-A
 * @see http://www.w3.org/Protocols/rfc1341/4_Content-Type.html
 */
function isMediaType($reference, $contentType)
{
	$a = parseContentType($reference);
	$b = parseContentType($contentType);

	return $a && $b && $a['type'] === $b['type'] && $a['subtype'] === $b['subtype'];
}

/**
 * The type, subtype an charset of the Content-Type header are case insensitive,
 * so for convenience they will be converted to lowercase.
 * 
 * @param {String} str
 * @return {Object}
 */
function parseContentType($str)
{
	// Tokens can consist of any character except SPACE, CTLS and except the following:
	// ()<>@,;:\"/[]?.=
	// That results in the following regexp
	// [^\x00-\x20()<>@,;:?.\="\[\]]
	// CTLS are "<any US-ASCII control character (octets 0 - 31) and DEL (127)>"
	// @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec2.html#sec2.2

	$media_type_regex = '/^(application|audio|image|message|multipart|text|video|x-[^\x00-\x20()<>@,;:?.\="\[\]]+)\/([^\x00-\x20()<>@,;:?.\="\[\]]+)(;.+)?$/i';
	$parameters_regex = '/(?:;\s*([^\x00-\x20()<>@,;:?.\="\[\]]+)=(([^\x00-\x20()<>@,;:?.\="\[\]]+|"([^"]*)")))/';

	if (preg_match($media_type_regex, $str, $matches))
	{
		$type = strtolower($matches[1]);
		$subtype = strtolower($matches[2]);
		$params = array();
		$charset = null;

		if (isset($matches[3]))
		{
			if (preg_match_all($parameters_regex, $matches[3], $matches, PREG_SET_ORDER))
			{
				foreach ($matches as $param)
				{
					$name = strtolower($param[1]);

					// There's one item for unquoted and another for quoted values.
					if (isset($param[4]))
						$value = $param[4];
					else if (isset($param[2]))
						$value = $param[2];
					else
						$value = "";

					$params[$name] = $value;
				}
			}
		}

		if (isset($params['charset']))
		{
			$charset = strtolower($params['charset']);
		}
		else
		{
			if ($type === 'text' && $subtype === 'plain')
				$charset = 'us-ascii';
		}

		return array(
			"type" => $type,
			"subtype" => $subtype,
			"charset" => $charset,
			"params" => $params
		);
	}
	return null;
}

var_dump(parseContentType('application/json'));
var_dump(parseContentType('application/json; charset=UTF-8'));
var_dump(parseContentType('text/html; id="abc"; charset="iso-8859-1"'));
var_dump(parseContentType('text/html; id="abc"; charset=iso-8859-1'));
var_dump(parseContentType('application/svg+xml'));
var_dump(parseContentType('text/plain'));

var_dump(isMediaType('application/json', 'application/JSON; charset="UTF-8"'));
var_dump(isMediaType('application/json', 'garbled"'));