<?php

/**
 * A UTF-8 specific character encoder that handles cleaning and transforming.
 * @note All functions in this class should be static.
 */
class HTMLPurifier_Encoder {
	
	/**
	 * Constructor throws fatal error if you attempt to instantiate class
	 */
	private function __construct() {
		trigger_error ( 'Cannot instantiate encoder, call methods statically', E_USER_ERROR );
	}
	
	/**
	 * Error-handler that mutes errors, alternative to shut-up operator.
	 */
	public static function muteErrorHandler() {
	}
	
	/**
	 * iconv wrapper which mutes errors, but doesn't work around bugs.
	 * 
	 * @param string $in
	 *        	Input encoding
	 * @param string $out
	 *        	Output encoding
	 * @param string $text
	 *        	The text to convert
	 * @return string
	 */
	public static function unsafeIconv($in, $out, $text) {
		set_error_handler ( array (
				'HTMLPurifier_Encoder',
				'muteErrorHandler' 
		) );
		$r = iconv ( $in, $out, $text );
		restore_error_handler ();
		return $r;
	}
	
	/**
	 * iconv wrapper which mutes errors and works around bugs.
	 * 
	 * @param string $in
	 *        	Input encoding
	 * @param string $out
	 *        	Output encoding
	 * @param string $text
	 *        	The text to convert
	 * @param int $max_chunk_size        	
	 * @return string
	 */
	public static function iconv($in, $out, $text, $max_chunk_size = 8000) {
		$code = self::testIconvTruncateBug ();
		if ($code == self::ICONV_OK) {
			return self::unsafeIconv ( $in, $out, $text );
		} elseif ($code == self::ICONV_TRUNCATES) {
			// we can only work around this if the input character set
			// is utf-8
			if ($in == 'utf-8') {
				if ($max_chunk_size < 4) {
					trigger_error ( 'max_chunk_size is too small', E_USER_WARNING );
					return false;
				}
				// split into 8000 byte chunks, but be careful to handle
				// multibyte boundaries properly
				if (($c = strlen ( $text )) <= $max_chunk_size) {
					return self::unsafeIconv ( $in, $out, $text );
				}
				$r = '';
				$i = 0;
				while ( true ) {
					if ($i + $max_chunk_size >= $c) {
						$r .= self::unsafeIconv ( $in, $out, substr ( $text, $i ) );
						break;
					}
					// wibble the boundary
					if (0x80 != (0xC0 & ord ( $text [$i + $max_chunk_size] ))) {
						$chunk_size = $max_chunk_size;
					} elseif (0x80 != (0xC0 & ord ( $text [$i + $max_chunk_size - 1] ))) {
						$chunk_size = $max_chunk_size - 1;
					} elseif (0x80 != (0xC0 & ord ( $text [$i + $max_chunk_size - 2] ))) {
						$chunk_size = $max_chunk_size - 2;
					} elseif (0x80 != (0xC0 & ord ( $text [$i + $max_chunk_size - 3] ))) {
						$chunk_size = $max_chunk_size - 3;
					} else {
						return false; // rather confusing UTF-8...
					}
					$chunk = substr ( $text, $i, $chunk_size ); // substr doesn't mind overlong lengths
					$r .= self::unsafeIconv ( $in, $out, $chunk );
					$i += $chunk_size;
				}
				return $r;
			} else {
				return false;
			}
		} else {
			return false;
		}
	}
	
	/**
	 * Cleans a UTF-8 string for well-formedness and SGML validity
	 *
	 * It will parse according to UTF-8 and return a valid UTF8 string, with
	 * non-SGML codepoints excluded.
	 *
	 * @param string $str
	 *        	The string to clean
	 * @param bool $force_php        	
	 * @return string @note Just for reference, the non-SGML code points are 0 to 31 and
	 *         127 to 159, inclusive. However, we allow code points 9, 10
	 *         and 13, which are the tab, line feed and carriage return
	 *         respectively. 128 and above the code points map to multibyte
	 *         UTF-8 representations.
	 *        
	 *         @note Fallback code adapted from utf8ToUnicode by Henri Sivonen and
	 *         hsivonen@iki.fi at <http://iki.fi/hsivonen/php-utf8/> under the
	 *         LGPL license. Notes on what changed are inside, but in general,
	 *         the original code transformed UTF-8 text into an array of integer
	 *         Unicode codepoints. Understandably, transforming that back to
	 *         a string would be somewhat expensive, so the function was modded to
	 *         directly operate on the string. However, this discourages code
	 *         reuse, and the logic enumerated here would be useful for any
	 *         function that needs to be able to understand UTF-8 characters.
	 *         As of right now, only smart lossless character encoding converters
	 *         would need that, and I'm probably not going to implement them.
	 *         Once again, PHP 6 should solve all our problems.
	 */
	public static function cleanUTF8($str, $force_php = false) {
		// UTF-8 validity is checked since PHP 4.3.5
		// This is an optimization: if the string is already valid UTF-8, no
		// need to do PHP stuff. 99% of the time, this will be the case.
		// The regexp matches the XML char production, as well as well as excluding
		// non-SGML codepoints U+007F to U+009F
		if (preg_match ( '/^[\x{9}\x{A}\x{D}\x{20}-\x{7E}\x{A0}-\x{D7FF}\x{E000}-\x{FFFD}\x{10000}-\x{10FFFF}]*$/Du', $str )) {
			return $str;
		}
		
		$mState = 0; // cached expected number of octets after the current octet
		             // until the beginning of the next UTF8 character sequence
		$mUcs4 = 0; // cached Unicode character
		$mBytes = 1; // cached expected number of octets in the current sequence
		             
		// original code involved an $out that was an array of Unicode
		             // codepoints. Instead of having to convert back into UTF-8, we've
		             // decided to directly append valid UTF-8 characters onto a string
		             // $out once they're done. $char accumulates raw bytes, while $mUcs4
		             // turns into the Unicode code point, so there's some redundancy.
		
		$out = '';
		$char = '';
		
		$len = strlen ( $str );
		for($i = 0; $i < $len; $i ++) {
			$in = ord ( $str {$i} );
			$char .= $str [$i]; // append byte to char
			if (0 == $mState) {
				// When mState is zero we expect either a US-ASCII character
				// or a multi-octet sequence.
				if (0 == (0x80 & ($in))) {
					// US-ASCII, pass straight through.
					if (($in <= 31 || $in == 127) && ! ($in == 9 || $in == 13 || $in == 10)) // save \r\t\n
{
						// control characters, remove
					} else {
						$out .= $char;
					}
					// reset
					$char = '';
					$mBytes = 1;
				} elseif (0xC0 == (0xE0 & ($in))) {
					// First octet of 2 octet sequence
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 0x1F) << 6;
					$mState = 1;
					$mBytes = 2;
				} elseif (0xE0 == (0xF0 & ($in))) {
					// First octet of 3 octet sequence
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 0x0F) << 12;
					$mState = 2;
					$mBytes = 3;
				} elseif (0xF0 == (0xF8 & ($in))) {
					// First octet of 4 octet sequence
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 0x07) << 18;
					$mState = 3;
					$mBytes = 4;
				} elseif (0xF8 == (0xFC & ($in))) {
					// First octet of 5 octet sequence.
					//
					// This is illegal because the encoded codepoint must be
					// either:
					// (a) not the shortest form or
					// (b) outside the Unicode range of 0-0x10FFFF.
					// Rather than trying to resynchronize, we will carry on
					// until the end of the sequence and let the later error
					// handling code catch it.
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 0x03) << 24;
					$mState = 4;
					$mBytes = 5;
				} elseif (0xFC == (0xFE & ($in))) {
					// First octet of 6 octet sequence, see comments for 5
					// octet sequence.
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 1) << 30;
					$mState = 5;
					$mBytes = 6;
				} else {
					// Current octet is neither in the US-ASCII range nor a
					// legal first octet of a multi-octet sequence.
					$mState = 0;
					$mUcs4 = 0;
					$mBytes = 1;
					$char = '';
				}
			} else {
				// When mState is non-zero, we expect a continuation of the
				// multi-octet sequence
				if (0x80 == (0xC0 & ($in))) {
					// Legal continuation.
					$shift = ($mState - 1) * 6;
					$tmp = $in;
					$tmp = ($tmp & 0x0000003F) << $shift;
					$mUcs4 |= $tmp;
					
					if (0 == -- $mState) {
						// End of the multi-octet sequence. mUcs4 now contains
						// the final Unicode codepoint to be output
						
						// Check for illegal sequences and codepoints.
						
						// From Unicode 3.1, non-shortest form is illegal
						if (((2 == $mBytes) && ($mUcs4 < 0x0080)) || ((3 == $mBytes) && ($mUcs4 < 0x0800)) || ((4 == $mBytes) && ($mUcs4 < 0x10000)) || (4 < $mBytes) || 
						// From Unicode 3.2, surrogate characters = illegal
						(($mUcs4 & 0xFFFFF800) == 0xD800) || 
						// Codepoints outside the Unicode range are illegal
						($mUcs4 > 0x10FFFF)) {
						} elseif (0xFEFF != $mUcs4 && // omit BOM
						                              // check for valid Char unicode codepoints
						(0x9 == $mUcs4 || 0xA == $mUcs4 || 0xD == $mUcs4 || (0x20 <= $mUcs4 && 0x7E >= $mUcs4) || 
						// 7F-9F is not strictly prohibited by XML,
						// but it is non-SGML, and thus we don't allow it
						(0xA0 <= $mUcs4 && 0xD7FF >= $mUcs4) || (0x10000 <= $mUcs4 && 0x10FFFF >= $mUcs4))) {
							$out .= $char;
						}
						// initialize UTF8 cache (reset)
						$mState = 0;
						$mUcs4 = 0;
						$mBytes = 1;
						$char = '';
					}
				} else {
					// ((0xC0 & (*in) != 0x80) && (mState != 0))
					// Incomplete multi-octet sequence.
					// used to result in complete fail, but we'll reset
					$mState = 0;
					$mUcs4 = 0;
					$mBytes = 1;
					$char = '';
				}
			}
		}
		return $out;
	}
	
	/**
	 * Translates a Unicode codepoint into its corresponding UTF-8 character.
	 * @note Based on Feyd's function at
	 * <http://forums.devnetwork.net/viewtopic.php?p=191404#191404>,
	 * which is in public domain.
	 * @note While we're going to do code point parsing anyway, a good
	 * optimization would be to refuse to translate code points that
	 * are non-SGML characters. However, this could lead to duplication.
	 * @note This is very similar to the unichr function in
	 * maintenance/generate-entity-file.php (although this is superior,
	 * due to its sanity checks).
	 */
	
	// +----------+----------+----------+----------+
	// | 33222222 | 22221111 | 111111 | |
	// | 10987654 | 32109876 | 54321098 | 76543210 | bit
	// +----------+----------+----------+----------+
	// | | | | 0xxxxxxx | 1 byte 0x00000000..0x0000007F
	// | | | 110yyyyy | 10xxxxxx | 2 byte 0x00000080..0x000007FF
	// | | 1110zzzz | 10yyyyyy | 10xxxxxx | 3 byte 0x00000800..0x0000FFFF
	// | 11110www | 10wwzzzz | 10yyyyyy | 10xxxxxx | 4 byte 0x00010000..0x0010FFFF
	// +----------+----------+----------+----------+
	// | 00000000 | 00011111 | 11111111 | 11111111 | Theoretical upper limit of legal scalars: 2097151 (0x001FFFFF)
	// | 00000000 | 00010000 | 11111111 | 11111111 | Defined upper limit of legal scalar codes
	// +----------+----------+----------+----------+
	public static function unichr($code) {
		if ($code > 1114111 or $code < 0 or ($code >= 55296 and $code <= 57343)) {
			// bits are set outside the "valid" range as defined
			// by UNICODE 4.1.0
			return '';
		}
		
		$x = $y = $z = $w = 0;
		if ($code < 128) {
			// regular ASCII character
			$x = $code;
		} else {
			// set up bits for UTF-8
			$x = ($code & 63) | 128;
			if ($code < 2048) {
				$y = (($code & 2047) >> 6) | 192;
			} else {
				$y = (($code & 4032) >> 6) | 128;
				if ($code < 65536) {
					$z = (($code >> 12) & 15) | 224;
				} else {
					$z = (($code >> 12) & 63) | 128;
					$w = (($code >> 18) & 7) | 240;
				}
			}
		}
		// set up the actual character
		$ret = '';
		if ($w) {
			$ret .= chr ( $w );
		}
		if ($z) {
			$ret .= chr ( $z );
		}
		if ($y) {
			$ret .= chr ( $y );
		}
		$ret .= chr ( $x );
		
		return $ret;
	}
	
	/**
	 *
	 * @return bool
	 */
	public static function iconvAvailable() {
		static $iconv = null;
		if ($iconv === null) {
			$iconv = function_exists ( 'iconv' ) && self::testIconvTruncateBug () != self::ICONV_UNUSABLE;
		}
		return $iconv;
	}
	
	/**
	 * Convert a string to UTF-8 based on configuration.
	 * 
	 * @param string $str
	 *        	The string to convert
	 * @param HTMLPurifier_Config $config        	
	 * @param HTMLPurifier_Context $context        	
	 * @return string
	 */
	public static function convertToUTF8($str, $config, $context) {
		$encoding = $config->get ( 'Core.Encoding' );
		if ($encoding === 'utf-8') {
			return $str;
		}
		static $iconv = null;
		if ($iconv === null) {
			$iconv = self::iconvAvailable ();
		}
		if ($iconv && ! $config->get ( 'Test.ForceNoIconv' )) {
			// unaffected by bugs, since UTF-8 support all characters
			$str = self::unsafeIconv ( $encoding, 'utf-8//IGNORE', $str );
			if ($str === false) {
				// $encoding is not a valid encoding
				trigger_error ( 'Invalid encoding ' . $encoding, E_USER_ERROR );
				return '';
			}
			// If the string is bjorked by Shift_JIS or a similar encoding
			// that doesn't support all of ASCII, convert the naughty
			// characters to their true byte-wise ASCII/UTF-8 equivalents.
			$str = strtr ( $str, self::testEncodingSupportsASCII ( $encoding ) );
			return $str;
		} elseif ($encoding === 'iso-8859-1') {
			$str = utf8_encode ( $str );
			return $str;
		}
		$bug = HTMLPurifier_Encoder::testIconvTruncateBug ();
		if ($bug == self::ICONV_OK) {
			trigger_error ( 'Encoding not supported, please install iconv', E_USER_ERROR );
		} else {
			trigger_error ( 'You have a buggy version of iconv, see https://bugs.php.net/bug.php?id=48147 ' . 'and http://sourceware.org/bugzilla/show_bug.cgi?id=13541', E_USER_ERROR );
		}
	}
	
	/**
	 * Converts a string from UTF-8 based on configuration.
	 * 
	 * @param string $str
	 *        	The string to convert
	 * @param HTMLPurifier_Config $config        	
	 * @param HTMLPurifier_Context $context        	
	 * @return string @note Currently, this is a lossy conversion, with unexpressable
	 *         characters being omitted.
	 */
	public static function convertFromUTF8($str, $config, $context) {
		$encoding = $config->get ( 'Core.Encoding' );
		if ($escape = $config->get ( 'Core.EscapeNonASCIICharacters' )) {
			$str = self::convertToASCIIDumbLossless ( $str );
		}
		if ($encoding === 'utf-8') {
			return $str;
		}
		static $iconv = null;
		if ($iconv === null) {
			$iconv = self::iconvAvailable ();
		}
		if ($iconv && ! $config->get ( 'Test.ForceNoIconv' )) {
			// Undo our previous fix in convertToUTF8, otherwise iconv will barf
			$ascii_fix = self::testEncodingSupportsASCII ( $encoding );
			if (! $escape && ! empty ( $ascii_fix )) {
				$clear_fix = array ();
				foreach ( $ascii_fix as $utf8 => $native ) {
					$clear_fix [$utf8] = '';
				}
				$str = strtr ( $str, $clear_fix );
			}
			$str = strtr ( $str, array_flip ( $ascii_fix ) );
			// Normal stuff
			$str = self::iconv ( 'utf-8', $encoding . '//IGNORE', $str );
			return $str;
		} elseif ($encoding === 'iso-8859-1') {
			$str = utf8_decode ( $str );
			return $str;
		}
		trigger_error ( 'Encoding not supported', E_USER_ERROR );
		// You might be tempted to assume that the ASCII representation
		// might be OK, however, this is *not* universally true over all
		// encodings. So we take the conservative route here, rather
		// than forcibly turn on %Core.EscapeNonASCIICharacters
	}
	
	/**
	 * Lossless (character-wise) conversion of HTML to ASCII
	 * 
	 * @param string $str
	 *        	UTF-8 string to be converted to ASCII
	 * @return string ASCII encoded string with non-ASCII character entity-ized
	 *         @warning Adapted from MediaWiki, claiming fair use: this is a common
	 *         algorithm. If you disagree with this license fudgery,
	 *         implement it yourself.
	 *         @note Uses decimal numeric entities since they are best supported.
	 *         @note This is a DUMB function: it has no concept of keeping
	 *         character entities that the projected character encoding
	 *         can allow. We could possibly implement a smart version
	 *         but that would require it to also know which Unicode
	 *         codepoints the charset supported (not an easy task).
	 *         @note Sort of with cleanUTF8() but it assumes that $str is
	 *         well-formed UTF-8
	 */
	public static function convertToASCIIDumbLossless($str) {
		$bytesleft = 0;
		$result = '';
		$working = 0;
		$len = strlen ( $str );
		for($i = 0; $i < $len; $i ++) {
			$bytevalue = ord ( $str [$i] );
			if ($bytevalue <= 0x7F) { // 0xxx xxxx
				$result .= chr ( $bytevalue );
				$bytesleft = 0;
			} elseif ($bytevalue <= 0xBF) { // 10xx xxxx
				$working = $working << 6;
				$working += ($bytevalue & 0x3F);
				$bytesleft --;
				if ($bytesleft <= 0) {
					$result .= "&#" . $working . ";";
				}
			} elseif ($bytevalue <= 0xDF) { // 110x xxxx
				$working = $bytevalue & 0x1F;
				$bytesleft = 1;
			} elseif ($bytevalue <= 0xEF) { // 1110 xxxx
				$working = $bytevalue & 0x0F;
				$bytesleft = 2;
			} else { // 1111 0xxx
				$working = $bytevalue & 0x07;
				$bytesleft = 3;
			}
		}
		return $result;
	}
	
	/**
	 * No bugs detected in iconv.
	 */
	const ICONV_OK = 0;
	
	/**
	 * Iconv truncates output if converting from UTF-8 to another
	 * character set with //IGNORE, and a non-encodable character is found
	 */
	const ICONV_TRUNCATES = 1;
	
	/**
	 * Iconv does not support //IGNORE, making it unusable for
	 * transcoding purposes
	 */
	const ICONV_UNUSABLE = 2;
	
	/**
	 * glibc iconv has a known bug where it doesn't handle the magic
	 * //IGNORE stanza correctly.
	 * In particular, rather than ignore
	 * characters, it will return an EILSEQ after consuming some number
	 * of characters, and expect you to restart iconv as if it were
	 * an E2BIG. Old versions of PHP did not respect the errno, and
	 * returned the fragment, so as a result you would see iconv
	 * mysteriously truncating output. We can work around this by
	 * manually chopping our input into segments of about 8000
	 * characters, as long as PHP ignores the error code. If PHP starts
	 * paying attention to the error code, iconv becomes unusable.
	 *
	 * @return int Error code indicating severity of bug.
	 */
	public static function testIconvTruncateBug() {
		static $code = null;
		if ($code === null) {
			// better not use iconv, otherwise infinite loop!
			$r = self::unsafeIconv ( 'utf-8', 'ascii//IGNORE', "\xCE\xB1" . str_repeat ( 'a', 9000 ) );
			if ($r === false) {
				$code = self::ICONV_UNUSABLE;
			} elseif (($c = strlen ( $r )) < 9000) {
				$code = self::ICONV_TRUNCATES;
			} elseif ($c > 9000) {
				trigger_error ( 'Your copy of iconv is extremely buggy. Please notify HTML Purifier maintainers: ' . 'include your iconv version as per phpversion()', E_USER_ERROR );
			} else {
				$code = self::ICONV_OK;
			}
		}
		return $code;
	}
	
	/**
	 * This expensive function tests whether or not a given character
	 * encoding supports ASCII.
	 * 7/8-bit encodings like Shift_JIS will
	 * fail this test, and require special processing. Variable width
	 * encodings shouldn't ever fail.
	 *
	 * @param string $encoding
	 *        	Encoding name to test, as per iconv format
	 * @param bool $bypass
	 *        	Whether or not to bypass the precompiled arrays.
	 * @return Array of UTF-8 characters to their corresponding ASCII,
	 *         which can be used to "undo" any overzealous iconv action.
	 */
	public static function testEncodingSupportsASCII($encoding, $bypass = false) {
		// All calls to iconv here are unsafe, proof by case analysis:
		// If ICONV_OK, no difference.
		// If ICONV_TRUNCATE, all calls involve one character inputs,
		// so bug is not triggered.
		// If ICONV_UNUSABLE, this call is irrelevant
		static $encodings = array ();
		if (! $bypass) {
			if (isset ( $encodings [$encoding] )) {
				return $encodings [$encoding];
			}
			$lenc = strtolower ( $encoding );
			switch ($lenc) {
				case 'shift_jis' :
					return array (
							"\xC2\xA5" => '\\',
							"\xE2\x80\xBE" => '~' 
					);
				case 'johab' :
					return array (
							"\xE2\x82\xA9" => '\\' 
					);
			}
			if (strpos ( $lenc, 'iso-8859-' ) === 0) {
				return array ();
			}
		}
		$ret = array ();
		if (self::unsafeIconv ( 'UTF-8', $encoding, 'a' ) === false) {
			return false;
		}
		for($i = 0x20; $i <= 0x7E; $i ++) { // all printable ASCII chars
			$c = chr ( $i ); // UTF-8 char
			$r = self::unsafeIconv ( 'UTF-8', "$encoding//IGNORE", $c ); // initial conversion
			if ($r === '' || 
			// This line is needed for iconv implementations that do not
			// omit characters that do not exist in the target character set
			($r === $c && self::unsafeIconv ( $encoding, 'UTF-8//IGNORE', $r ) !== $c)) {
				// Reverse engineer: what's the UTF-8 equiv of this byte
				// sequence? This assumes that there's no variable width
				// encoding that doesn't support ASCII.
				$ret [self::unsafeIconv ( $encoding, 'UTF-8//IGNORE', $c )] = $c;
			}
		}
		$encodings [$encoding] = $ret;
		return $ret;
	}
}

// vim: et sw=4 sts=4