path: root/includes/Html.php

<?php
# Copyright (C) 2009 Aryeh Gregor
# http://www.mediawiki.org/
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
# http://www.gnu.org/copyleft/gpl.html

/**
 * This class is a collection of static functions that serve two purposes:
 *
 * 1) Implement any algorithms specified by HTML5, or other HTML
 * specifications, in a convenient and self-contained way.
 *
 * 2) Allow HTML elements to be conveniently and safely generated, like the
 * current Xml class but a) less confused (Xml supports HTML-specific things,
 * but only sometimes!) and b) not necessarily confined to XML-compatible
 * output.
 *
 * There are two important configuration options this class uses:
 *
 * $wgHtml5: If this is set to false, then all output should be valid XHTML 1.0
 *     Transitional.
 * $wgWellFormedXml: If this is set to true, then all output should be
 *     well-formed XML (quotes on attributes, self-closing tags, etc.).
 *
 * This class is meant to be confined to utility functions that are called from
 * trusted code paths.  It does not do enforcement of policy like not allowing
 * <a> elements.
 */
class Html {
	# List of void elements from HTML5, section 9.1.2 as of 2009-08-10
	private static $voidElements = array(
		'area',
		'base',
		'br',
		'col',
		'command',
		'embed',
		'hr',
		'img',
		'input',
		'keygen',
		'link',
		'meta',
		'param',
		'source',
	);

	# Boolean attributes, which may have the value omitted entirely.  Manually
	# collected from the HTML5 spec as of 2009-08-10.
	private static $boolAttribs = array(
		'async',
		'autobuffer',
		'autofocus',
		'autoplay',
		'checked',
		'controls',
		'defer',
		'disabled',
		'formnovalidate',
		'hidden',
		'ismap',
		'loop',
		'multiple',
		'novalidate',
		'open',
		'readonly',
		'required',
		'reversed',
		'scoped',
		'seamless',
	);

	/**
	 * Returns an HTML element in a string.  The major advantage here over
	 * manually typing out the HTML is that it will escape all attribute
	 * values.  If you're hardcoding all the attributes, or there are none, you
	 * should probably type out the string yourself.
	 *
	 * This is quite similar to Xml::tags(), but it implements some useful
	 * HTML-specific logic.  For instance, there is no $allowShortTag
	 * parameter: the closing tag is magically omitted if $element has an empty
	 * content model.  If $wgWellFormedXml is false, then a few bytes will be
	 * shaved off the HTML output as well.  In the future, other HTML-specific
	 * features might be added, like allowing arrays for the values of
	 * attributes like class= and media=.
	 *
	 * @param $element  string The element's name, e.g., 'a'
	 * @param $attribs  array  Associative array of attributes, e.g., array(
	 *   'href' => 'http://www.mediawiki.org/' ).  See expandAttributes() for
	 *   further documentation.
	 * @param $contents string The raw HTML contents of the element: *not*
	 *   escaped!
	 * @return string Raw HTML
	 */
	public static function rawElement( $element, $attribs = array(), $contents = '' ) {
		global $wgWellFormedXml;
		$start = self::openElement( $element, $attribs );
		if ( in_array( $element, self::$voidElements ) ) {
			if ( $wgWellFormedXml ) {
				# Silly XML.
				return substr( $start, 0, -1 ) . ' />';
			}
			return $start;
		} else {
			return "$start$contents</$element>";
		}
	}

	/**
	 * Identical to rawElement(), but HTML-escapes $contents (like
	 * Xml::element()).
	 */
	public static function element( $element, $attribs = array(), $contents = '' ) {
		return self::rawElement( $element, $attribs, strtr( $contents, array(
			# There's no point in escaping quotes, >, etc. in the contents of
			# elements.
			'&' => '&amp;',
			'<' => '&lt;'
		) ) );
	}

	/**
	 * Identical to rawElement(), but has no third parameter and omits the end
	 * tag (and the self-closing / in XML mode for empty elements).
	 */
	public static function openElement( $element, $attribs = array() ) {
		global $wgHtml5;
		$attribs = (array)$attribs;
		# This is not required in HTML5, but let's do it anyway, for
		# consistency and better compression.
		$element = strtolower( $element );

		# Remove HTML5-only attributes if we aren't doing HTML5, and disable
		# form validation regardless (see bug 23769 and the more detailed
		# comment in expandAttributes())
		if ( $element == 'input' ) {
			# Whitelist of types that don't cause validation.  All except
			# 'search' are valid in XHTML1.
			$validTypes = array(
				'hidden',
				'text',
				'password',
				'checkbox',
				'radio',
				'file',
				'submit',
				'image',
				'reset',
				'button',
				'search',
			);
			if ( isset( $attribs['type'] )
			&& !in_array( $attribs['type'], $validTypes ) ) {
				unset( $attribs['type'] );
			}
			if ( isset( $attribs['type'] ) && $attribs['type'] == 'search'
			&& !$wgHtml5 ) {
				unset( $attribs['type'] );
			}
			# Here we're blacklisting some HTML5-only attributes...
			$html5attribs = array(
				'autocomplete',
				'autofocus',
				'max',
				'min',
				'multiple',
				'pattern',
				'placeholder',
				'required',
				'step',
				'spellcheck',
			);
			foreach ( $html5attribs as $badAttr ) {
				unset( $attribs[$badAttr] );
			}
		}
		if ( !$wgHtml5 && $element == 'textarea' && isset( $attribs['maxlength'] ) ) {
			unset( $attribs['maxlength'] );
		}

		return "<$element" . self::expandAttributes(
			self::dropDefaults( $element, $attribs ) ) . '>';
	}

	/**
	 * Given an element name and an associative array of element attributes,
	 * return an array that is functionally identical to the input array, but
	 * possibly smaller.  In particular, attributes might be stripped if they
	 * are given their default values.
	 *
	 * This method is not guaranteed to remove all redundant attributes, only
	 * some common ones and some others selected arbitrarily at random.  It
	 * only guarantees that the output array should be functionally identical
	 * to the input array (currently per the HTML 5 draft as of 2009-09-06).
	 *
	 * @param $element string Name of the element, e.g., 'a'
	 * @param $attribs array  Associative array of attributes, e.g., array(
	 *   'href' => 'http://www.mediawiki.org/' ).  See expandAttributes() for
	 *   further documentation.
	 * @return array An array of attributes functionally identical to $attribs
	 */
	private static function dropDefaults( $element, $attribs ) {
		# Don't bother doing anything if we aren't outputting HTML5; it's too
		# much of a pain to maintain two sets of defaults.
		global $wgHtml5;
		if ( !$wgHtml5 ) {
			return $attribs;
		}

		static $attribDefaults = array(
			'area' => array( 'shape' => 'rect' ),
			'button' => array(
				'formaction' => 'GET',
				'formenctype' => 'application/x-www-form-urlencoded',
				'type' => 'submit',
			),
			'canvas' => array(
				'height' => '150',
				'width' => '300',
			),
			'command' => array( 'type' => 'command' ),
			'form' => array(
				'action' => 'GET',
				'autocomplete' => 'on',
				'enctype' => 'application/x-www-form-urlencoded',
			),
			'input' => array(
				'formaction' => 'GET',
				'type' => 'text',
				'value' => '',
			),
			'keygen' => array( 'keytype' => 'rsa' ),
			'link' => array( 'media' => 'all' ),
			'menu' => array( 'type' => 'list' ),
			# Note: the use of text/javascript here instead of other JavaScript
			# MIME types follows the HTML5 spec.
			'script' => array( 'type' => 'text/javascript' ),
			'style' => array(
				'media' => 'all',
				'type' => 'text/css',
			),
			'textarea' => array( 'wrap' => 'soft' ),
		);

		$element = strtolower( $element );

		foreach ( $attribs as $attrib => $value ) {
			$lcattrib = strtolower( $attrib );
			$value = strval( $value );

			# Simple checks using $attribDefaults
			if ( isset( $attribDefaults[$element][$lcattrib] ) &&
			$attribDefaults[$element][$lcattrib] == $value ) {
				unset( $attribs[$attrib] );
			}

			if ( $lcattrib == 'class' && $value == '' ) {
				unset( $attribs[$attrib] );
			}
		}

		# More subtle checks
		if ( $element === 'link' && isset( $attribs['type'] )
		&& strval( $attribs['type'] ) == 'text/css' ) {
			unset( $attribs['type'] );
		}
		if ( $element === 'select' && isset( $attribs['size'] ) ) {
			if ( in_array( 'multiple', $attribs )
				|| ( isset( $attribs['multiple'] ) && $attribs['multiple'] !== false )
			) {
				# A multi-select
				if ( strval( $attribs['size'] ) == '4' ) {
					unset( $attribs['size'] );
				}
			} else {
				# Single select
				if ( strval( $attribs['size'] ) == '1' ) {
					unset( $attribs['size'] );
				}
			}
		}

		return $attribs;
	}

	/**
	 * Given an associative array of element attributes, generate a string
	 * to stick after the element name in HTML output.  Like array( 'href' =>
	 * 'http://www.mediawiki.org/' ) becomes something like
	 * ' href="http://www.mediawiki.org"'.  Again, this is like
	 * Xml::expandAttributes(), but it implements some HTML-specific logic.
	 * For instance, it will omit quotation marks if $wgWellFormedXml is false,
	 * and will treat boolean attributes specially.
	 *
	 * @param $attribs array Associative array of attributes, e.g., array(
	 *   'href' => 'http://www.mediawiki.org/' ).  Values will be HTML-escaped.
	 *   A value of false means to omit the attribute.  For boolean attributes,
	 *   you can omit the key, e.g., array( 'checked' ) instead of
	 *   array( 'checked' => 'checked' ) or such.
	 * @return string HTML fragment that goes between element name and '>'
	 *   (starting with a space if at least one attribute is output)
	 */
	public static function expandAttributes( $attribs ) {
		global $wgHtml5, $wgWellFormedXml;

		$ret = '';
		$attribs = (array)$attribs;
		foreach ( $attribs as $key => $value ) {
			if ( $value === false ) {
				continue;
			}

			# For boolean attributes, support array( 'foo' ) instead of
			# requiring array( 'foo' => 'meaningless' ).
			if ( is_int( $key )
			&& in_array( strtolower( $value ), self::$boolAttribs ) ) {
				$key = $value;
			}

			# Not technically required in HTML5, but required in XHTML 1.0,
			# and we'd like consistency and better compression anyway.
			$key = strtolower( $key );

			# Bug 23769: Blacklist all form validation attributes for now.  Current
			# (June 2010) WebKit has no UI, so the form just refuses to submit
			# without telling the user why, which is much worse than failing
			# server-side validation.  Opera is the only other implementation at
			# this time, and has ugly UI, so just kill the feature entirely until
			# we have at least one good implementation.
			if ( in_array( $key, array( 'max', 'min', 'pattern', 'required', 'step' ) ) ) {
				continue;
			}

			# See the "Attributes" section in the HTML syntax part of HTML5,
			# 9.1.2.3 as of 2009-08-10.  Most attributes can have quotation
			# marks omitted, but not all.  (Although a literal " is not
			# permitted, we don't check for that, since it will be escaped
			# anyway.)
			#
			# See also research done on further characters that need to be
			# escaped: http://code.google.com/p/html5lib/issues/detail?id=93
			$badChars = "\\x00- '=<>`/\x{00a0}\x{1680}\x{180e}\x{180F}\x{2000}\x{2001}"
				. "\x{2002}\x{2003}\x{2004}\x{2005}\x{2006}\x{2007}\x{2008}\x{2009}"
				. "\x{200A}\x{2028}\x{2029}\x{202F}\x{205F}\x{3000}";
			if ( $wgWellFormedXml || $value === ''
			|| preg_match( "![$badChars]!u", $value ) ) {
				$quote = '"';
			} else {
				$quote = '';
			}

			if ( in_array( $key, self::$boolAttribs ) ) {
				# In XHTML 1.0 Transitional, the value needs to be equal to the
				# key.  In HTML5, we can leave the value empty instead.  If we
				# don't need well-formed XML, we can omit the = entirely.
				if ( !$wgWellFormedXml ) {
					$ret .= " $key";
				} elseif ( $wgHtml5 ) {
					$ret .= " $key=\"\"";
				} else {
					$ret .= " $key=\"$key\"";
				}
			} else {
				# Apparently we need to entity-encode \n, \r, \t, although the
				# spec doesn't mention that.  Since we're doing strtr() anyway,
				# and we don't need <> escaped here, we may as well not call
				# htmlspecialchars().  FIXME: verify that we actually need to
				# escape \n\r\t here, and explain why, exactly.
				#
				# We could call Sanitizer::encodeAttribute() for this, but we
				# don't because we're stubborn and like our marginal savings on
				# byte size from not having to encode unnecessary quotes.
				$map = array(
					'&' => '&amp;',
					'"' => '&quot;',
					"\n" => '&#10;',
					"\r" => '&#13;',
					"\t" => '&#9;'
				);
				if ( $wgWellFormedXml ) {
					# This is allowed per spec: <http://www.w3.org/TR/xml/#NT-AttValue>
					# But reportedly it breaks some XML tools?  FIXME: is this
					# really true?
					$map['<'] = '&lt;';
				}
				$ret .= " $key=$quote" . strtr( $value, $map ) . $quote;
			}
		}
		return $ret;
	}

	/**
	 * Output a <script> tag with the given contents.  TODO: do some useful
	 * escaping as well, like if $contents contains literal '</script>' or (for
	 * XML) literal "]]>".
	 *
	 * @param $contents string JavaScript
	 * @return string Raw HTML
	 */
	public static function inlineScript( $contents ) {
		global $wgHtml5, $wgJsMimeType, $wgWellFormedXml;

		$attrs = array();
		if ( !$wgHtml5 ) {
			$attrs['type'] = $wgJsMimeType;
		}
		if ( $wgWellFormedXml && preg_match( '/[<&]/', $contents ) ) {
			$contents = "/*<![CDATA[*/$contents/*]]>*/";
		}
		return self::rawElement( 'script', $attrs, $contents );
	}

	/**
	 * Output a <script> tag linking to the given URL, e.g.,
	 * <script src=foo.js></script>.
	 *
	 * @param $url string
	 * @return string Raw HTML
	 */
	public static function linkedScript( $url ) {
		global $wgHtml5, $wgJsMimeType;

		$attrs = array( 'src' => $url );
		if ( !$wgHtml5 ) {
			$attrs['type'] = $wgJsMimeType;
		}
		return self::element( 'script', $attrs );
	}

	/**
	 * Output a <style> tag with the given contents for the given media type
	 * (if any).  TODO: do some useful escaping as well, like if $contents
	 * contains literal '</style>' (admittedly unlikely).
	 *
	 * @param $contents string CSS
	 * @param $media mixed A media type string, like 'screen'
	 * @return string Raw HTML
	 */
	public static function inlineStyle( $contents, $media = 'all' ) {
		global $wgWellFormedXml;

		if ( $wgWellFormedXml && preg_match( '/[<&]/', $contents ) ) {
			$contents = "/*<![CDATA[*/$contents/*]]>*/";
		}
		return self::rawElement( 'style', array(
			'type' => 'text/css',
			'media' => $media,
		), $contents );
	}

	/**
	 * Output a <link rel=stylesheet> linking to the given URL for the given
	 * media type (if any).
	 *
	 * @param $url string
	 * @param $media mixed A media type string, like 'screen'
	 * @return string Raw HTML
	 */
	public static function linkedStyle( $url, $media = 'all' ) {
		return self::element( 'link', array(
			'rel' => 'stylesheet',
			'href' => $url,
			'type' => 'text/css',
			'media' => $media,
		) );
	}

	/**
	 * Convenience function to produce an <input> element.  This supports the
	 * new HTML5 input types and attributes, and will silently strip them if
	 * $wgHtml5 is false.
	 *
	 * @param $name    string name attribute
	 * @param $value   mixed  value attribute
	 * @param $type    string type attribute
	 * @param $attribs array  Associative array of miscellaneous extra
	 *   attributes, passed to Html::element()
	 * @return string Raw HTML
	 */
	public static function input( $name, $value = '', $type = 'text', $attribs = array() ) {
		$attribs['type'] = $type;
		$attribs['value'] = $value;
		$attribs['name'] = $name;

		return self::element( 'input', $attribs );
	}

	/**
	 * Convenience function to produce an input element with type=hidden, like
	 * Xml::hidden.
	 *
	 * @param $name    string name attribute
	 * @param $value   string value attribute
	 * @param $attribs array  Associative array of miscellaneous extra
	 *   attributes, passed to Html::element()
	 * @return string Raw HTML
	 */
	public static function hidden( $name, $value, $attribs = array() ) {
		return self::input( $name, $value, 'hidden', $attribs );
	}

	/**
	 * Convenience function to produce an <input> element.  This supports leaving
	 * out the cols= and rows= which Xml requires and are required by HTML4/XHTML
	 * but not required by HTML5 and will silently set cols="" and rows="" if
	 * $wgHtml5 is false and cols and rows are omitted (HTML4 validates present
	 * but empty cols="" and rows="" as valid).
	 *
	 * @param $name    string name attribute
	 * @param $value   string value attribute
	 * @param $attribs array  Associative array of miscellaneous extra
	 *   attributes, passed to Html::element()
	 * @return string Raw HTML
	 */
	public static function textarea( $name, $value = '', $attribs = array() ) {
		global $wgHtml5;
		$attribs['name'] = $name;
		if ( !$wgHtml5 ) {
			if ( !isset( $attribs['cols'] ) )
				$attribs['cols'] = "";
			if ( !isset( $attribs['rows'] ) )
				$attribs['rows'] = "";
		}
		return self::element( 'textarea', $attribs, $value );
	}
}