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libphutil/src/utils/utf8.php
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<?php
/*
* Copyright 2011 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* Convert a string into valid UTF-8. This function is quite slow.
*
* When invalid byte subsequences are encountered, they will be replaced with
* U+FFFD, the Unicode replacement character.
*
* @param string String to convert to valid UTF-8.
* @return string String with invalid UTF-8 byte subsequences replaced with
* U+FFFD.
* @group utf8
*/
function phutil_utf8ize($string) {
if (phutil_is_utf8($string)) {
return $string;
}
// There is no function to do this in iconv, mbstring or ICU to do this, so
// do it (very very slowly) in pure PHP.
// TODO: Provide an optional fast C implementation ala fb_utf8ize() if this
// ever shows up in profiles?
$result = array();
$regex =
"/([\x01-\x7F]".
"|[\xC2-\xDF][\x80-\xBF]".
"|[\xE0-\xEF][\x80-\xBF][\x80-\xBF]".
"|[\xF0-\xF4][\x80-\xBF][\x80-\xBF][\x80-\xBF])".
"|(.)/";
$offset = 0;
$matches = null;
while (preg_match($regex, $string, $matches, 0, $offset)) {
if (!isset($matches[2])) {
$result[] = $matches[1];
} else {
// Unicode replacement character, U+FFFD.
$result[] = "\xEF\xBF\xBD";
}
$offset += strlen($matches[0]);
}
return implode('', $result);
}
/**
* Determine if a string is valid UTF-8.
*
* @param string Some string which may or may not be valid UTF-8.
* @return bool True if the string is valid UTF-8.
* @group utf8
*/
function phutil_is_utf8($string) {
if (function_exists('mb_check_encoding')) {
// If mbstring is available, this is significantly faster than using PHP
// regexps.
return mb_check_encoding($string, 'UTF-8');
}
$regex =
"/^(".
"[\x01-\x7F]+".
"|([\xC2-\xDF][\x80-\xBF])".
"|([\xE0-\xEF][\x80-\xBF][\x80-\xBF])".
"|([\xF0-\xF4][\x80-\xBF][\x80-\xBF][\x80-\xBF]))*\$/";
return preg_match($regex, $string);
}
/**
* Find the character length of a UTF-8 string.
*
* @param string A valid utf-8 string.
* @return int The character length of the string.
* @group utf8
*/
function phutil_utf8_strlen($string) {
if (function_exists('mb_strlen')) {
return mb_strlen($string, 'UTF-8');
}
// TODO: This is terrifically slow.
return count(phutil_utf8v($string));
}
/**
* Split a UTF-8 string into an array of characters.
*
* NOTE: This function does not deal properly with combining characters.
*
* @param string A valid utf-8 string.
* @return list A list of characters in the string.
* @group utf8
*/
function phutil_utf8v($string) {
$res = array();
$len = strlen($string);
$ii = 0;
while ($ii < $len) {
$byte = $string[$ii];
if ($byte <= "\x7F") {
$res[] = $byte;
$ii += 1;
continue;
} else if ($byte < "\xC0") {
throw new Exception("Invalid UTF-8 string passed to phutil_utf8v().");
} else if ($byte <= "\xDF") {
$seq_len = 2;
} else if ($byte <= "\xEF") {
$seq_len = 3;
} else if ($byte <= "\xF7") {
$seq_len = 4;
} else if ($byte <= "\xFB") {
$seq_len = 5;
} else if ($byte <= "\xFD") {
$seq_len = 6;
} else {
throw new Exception("Invalid UTF-8 string passed to phutil_utf8v().");
}
if ($ii + $seq_len > $len) {
throw new Exception("Invalid UTF-8 string passed to phutil_utf8v().");
}
for ($jj = 1; $jj < $seq_len; ++$jj) {
if ($string[$ii + $jj] >= "\xC0") {
throw new Exception("Invalid UTF-8 string passed to phutil_utf8v().");
}
}
$res[] = substr($string, $ii, $seq_len);
$ii += $seq_len;
}
return $res;
}
/**
* Shorten a string to provide a summary, respecting UTF-8 characters. This
* function attempts to truncate strings at word boundaries.
*
* NOTE: This function makes a best effort to apply some reasonable rules but
* will not work well for the full range of unicode languages. For instance,
* no effort is made to deal with combining characters.
*
* @param string UTF-8 string to shorten.
* @param int Maximum length of the result.
* @param string If the string is shortened, add this at the end. Defaults to
* horizontal ellipsis.
* @return string A string with no more than the specified character length.
*/
function phutil_utf8_shorten($string, $length, $terminal = "\xE2\x80\xA6") {
$terminal_len = count(phutil_utf8v($terminal));
if ($terminal_len >= $length) {
// If you provide a terminal we still enforce that the result (including
// the terminal) is no longer than $length, but we can't do that if the
// terminal is too long.
throw new Exception(
"String terminal length must be less than string length!");
}
$string_v = phutil_utf8v($string);
$string_len = count($string_v);
if ($string_len <= $length) {
// If the string is already shorter than the requested length, simply return
// it unmodified.
return $string;
}
// NOTE: This is not complete, and there are many other word boundary
// characters and reasonable places to break words in the UTF-8 character
// space. For now, this gives us reasonable behavior for latin langauges. We
// don't necessarily have access to PCRE+Unicode so there isn't a great way
// for us to look up character attributes.
// If we encounter these, prefer to break on them instead of cutting the
// string off in the middle of a word.
static $break_characters = array(
' ' => true,
"\n" => true,
';' => true,
':' => true,
'[' => true,
'(' => true,
',' => true,
'-' => true,
);
// If we encounter these, shorten to this character exactly without appending
// the terminal.
static $stop_characters = array(
'.' => true,
'!' => true,
'?' => true,
);
// Search backward in the string, looking for reasonable places to break it.
$word_boundary = null;
$stop_boundary = null;
// If we do a word break with a terminal, we have to look beyond at least the
// number of characters in the terminal.
$terminal_area = $length - $terminal_len;
for ($ii = $length; $ii >= 0; $ii--) {
$c = $string_v[$ii];
if (isset($break_characters[$c]) && ($ii <= $terminal_area)) {
$word_boundary = $ii;
} else if (isset($stop_characters[$c]) && ($ii < $length)) {
$stop_boundary = $ii + 1;
break;
} else {
if ($word_boundary !== null) {
break;
}
}
}
if ($stop_boundary !== null) {
// We found a character like ".". Cut the string there, without appending
// the terminal.
$string_part = array_slice($string_v, 0, $stop_boundary);
return implode('', $string_part);
}
// If we didn't find any boundary characters or we found ONLY boundary
// characters, just break at the maximum character length.
if ($word_boundary === null || $word_boundary === 0) {
$word_boundary = $length - $terminal_len;
}
$string_part = array_slice($string_v, 0, $word_boundary);
$string_part = implode('', $string_part);
return $string_part.$terminal;
}
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