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207 lines
9.0 KiB
207 lines
9.0 KiB
<?php
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/** @license MIT
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* Copyright 2018 J. King et al.
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* See LICENSE and AUTHORS files for details */
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declare(strict_types=1);
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namespace JKingWeb\URI;
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abstract class UTF8 {
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public static $replacementChar = "\u{FFFD}";
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public static $errMode = self::M_REPLACE;
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const M_REPLACE = 0;
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const M_SKIP = 1;
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const M_HALT = 2;
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/** Retrieve a character from $string starting at byte offset $pos
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*
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* $next is a variable in which to store the next byte offset at which a character starts
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*
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* The returned character may be a replacement character, or the empty string if $pos is beyond the end of $string
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*/
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public static function get(string $string, int $pos, &$next = null, int $errMode = null): string {
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start:
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// get the byte at the specified position
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$b = ($pos < strlen($string)) ? $string[$pos] : "";
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if ($b < "\x80" || $b=="") {
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// if the byte is an ASCII character or end of input, simply return it
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$next = $pos + 1;
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return $b;
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} else {
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$errMode = $errMode ?? self::$errMode;
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// otherwise determine the byte-length of the UTF-8 character
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$l = self::l($b);
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if (!$l && $errMode==self::M_SKIP) {
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// if the byte is invalid and we're supposed to skip, advance the position and start over
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$pos++;
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goto start;
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} elseif (!$l && $errMode == self::M_REPLACE) {
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// if the byte is invalid and we're supposed to replace, return a replacement character
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$next = $pos + 1;
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return self::$replacementChar;
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} elseif (!$l) {
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// if the byte is invalid and we're supposed to halt, halt
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throw new \Exception;
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} else {
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// otherwise collect valid mid-sequence bytes into a buffer until the whole character is retrieved or an invalid byte is encountered
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$buffer = $b;
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do {
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$b = (++$pos < strlen($string)) ? $string[$pos] : "";
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if ($b >= "\x80" && $b <= "\xBF") {
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// if the byte is valid, add it to the buffer
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$buffer .= $b;
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} elseif ($errMode==self::M_SKIP) {
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// if the byte is invalid and we're supposed to skip, start over from the current position
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goto start;
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} elseif ($errMode==self::M_REPLACE) {
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// if the byte is invalid and we're supposed to replace, return a replacement character
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$next = $pos;
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return self::$replacementChar;
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} else {
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// if the byte is invalid and we're supposed to halt, halt
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throw new \Exception;
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}
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} while (strlen($buffer) < $l);
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// return the filled buffer and the position of the next byte
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$next = $pos + 1;
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return $buffer;
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}
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}
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}
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/** Starting from byte offset $pos, advance $num characters through $string and return the byte offset of the found character
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*
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* If $num is negative, the operation will be performed in reverse
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*
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* If $pos is omitted, the start of the string will be used for a forward seek, and the end for a reverse seek
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*/
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public static function seek(string $string, int $num, int $pos = null, int $errMode = null): int {
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$errMode = $errMode ?? self::$errMode;
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if ($num > 0) {
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$pos = $pos ?? 0;
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do {
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$c = self::get($string, $pos, $pos, $errMode); // the current position is getting overwritten with the next position, by reference
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} while (--$num && $c != ""); // stop after we have skipped the desired number of characters, or reached EOF
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return $pos;
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} elseif ($num < 0) {
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$pos = $pos ?? strlen($string);
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if (!$pos) {
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// if we're already at the start of the string, we can't go further back
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return $pos;
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}
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$num = abs($num);
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do {
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$pos = self::sync($string, $pos -1, $errMode);
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$num--;
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} while ($num && $pos);
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return $pos;
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} else {
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// seeking zero characters is equivalent to a sync
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return self::sync($string, $pos, $errMode);
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}
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}
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/** Synchronize to the byte offset of the start of the nearest character at or before byte offset $pos */
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public static function sync(string $string, int $pos, int $errMode = null): int {
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$errMode = $errMode ?? self::$errMode;
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start:
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if (!$pos || $pos >= strlen($string)) {
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// if we're at the start of the string or past its end, then this is the character start
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return $pos;
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}
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// save the start position for later, and increment before the coming decrement loop
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$s = $pos++;
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// examine the current byte and skip up to three continuation bytes, going backward and counting the number of examined bytes (between 1 and 4)
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$t = 0;
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do {
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$pos--;
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$t++;
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$b = ($pos < strlen($string)) ? $string[$pos] : "";
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} while (
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$b >= "\x80" && $b <= "\xBF" && // continuation bytes
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($t < 4 || $errMode==self::M_SKIP) && // stop after four bytes, unless we're skipping invalid sequences
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$pos // stop once the start of the string has been reached
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);
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// get the expected length of the character starting at the last examined byte
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$l = self::l($b);
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if ($l==$t) {
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// if the expected length matches the number of examined bytes, the character is valid
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return $pos;
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} elseif ($errMode==self::M_SKIP) {
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// if we're expected to ignore invalid sequences:
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if ($l && $t > $l) {
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// if the last examined byte is the start of a sequence and we have more than the right amount of continuation characters, return the current position
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return $pos;
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} elseif (!$pos) {
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// if we're already at the start of the string, give up
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return $pos;
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} else {
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// otherwise skip over the last examined byte and start over
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$pos--;
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goto start;
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}
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} elseif ($errMode==self::M_REPLACE) {
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// if we're expected to treat invalid sequences as replacement characters, return
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// the offset of the most recently examined byte if it is the start of a multi-byte
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// sequence, or the starting offset otherwise: in the latter case the original byte
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// is itself a replacement character position
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return ($l > 1) ? $pos: $s;
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} else {
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// if the character is invalid and we're expected to halt, halt
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throw new \Exception;
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}
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}
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public static function len(string $string, int $start = 0, int $end = null, int $errMode = null): int {
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$errMode = $errMode ?? self::$errMode;
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$end = $end ?? strlen($string);
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if (substr($string, $start, ($end - $start)) =="") {
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return 0;
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}
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$count = 0;
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$pos = $start;
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do {
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$c = self::get($string, $pos, $pos, $errMode);
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} while ($c != "" && ++$count && $pos < $end);
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return $count;
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}
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public static function substr(string $str, int $start = 0, int $length = null, &$next = null, int $errMode = null): string {
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$errMode = $errMode ?? self::$errMode;
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if ($length > 0) {
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$pos = $start;
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$buffer = "";
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do {
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$c = self::get($string, $pos, $pos, $errMode); // the current position is getting overwritten with the next position, by reference
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$buffer .= $c;
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} while (--$length && $c != ""); // stop after we have skipped the desired number of characters, or reached EOF
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$next = $pos;
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return $buffer;
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} else {
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$next = self::sync($string, $start, $errMode);
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return "";
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}
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}
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/**
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* Returns the expected byte length of a UTF-8 character starting with byte $b
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*
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* If the byte is not the start of a UTF-8 sequence, 0 is returned
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*/
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protected static function l(string $b): int {
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if ($b >= "\xC0" && $b <= "\xDF") { // two-byte character
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return 2;
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} elseif ($b >= "\xE0" && $b <= "\xEF") { // three-byte character
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return 3;
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} elseif ($b >= "\xF0" && $b <= "\xF7") { // four-byte character
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return 4;
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} elseif ($b < "\x80") { // ASCII byte: one-byte character
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return 1;
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} elseif ($b == "") { // end of input: pretend it's a valid single-byte character
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return 1;
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} else { // invalid byte
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return 0;
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}
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}
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}
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