* Finds spans of valid and invalid UTF-8 bytes in a given string.
* This is a low-level tool to power various UTF-8 functionality.
* It scans through a string until it finds invalid byte spans.
* When it does this, it does three things:
* - Assigns `$at` to the position after the last successful code point.
* - Assigns `$invalid_length` to the length of the maximal subpart of
* the invalid bytes starting at `$at`.
* - Returns how many code points were successfully scanned.
* This information is enough to build a number of useful UTF-8 functions.
* // ñ is U+F1, which in `ISO-8859-1`/`latin1`/`Windows-1252`/`cp1252` is 0xF1.
* "Pi\xF1a" === $pineapple = mb_convert_encoding( "Piña", 'Windows-1252', 'UTF-8' );
* $at = $invalid_length = 0;
* // The first step finds the invalid 0xF1 byte.
* 2 === _wp_scan_utf8( $pineapple, $at, $invalid_length );
* $at === 2; $invalid_length === 1;
* // The second step continues to the end of the string.
* 1 === _wp_scan_utf8( $pineapple, $at, $invalid_length );
* $at === 4; $invalid_length === 0;
* Note! While passing an options array here might be convenient from a calling-code standpoint,
* this function is intended to serve as a very low-level foundation upon which to build
* higher level functionality. For the sake of keeping costs explicit all arguments are
* @param string $bytes UTF-8 encoded string which might include invalid spans of bytes.
* @param int $at Where to start scanning.
* @param int $invalid_length Will be set to how many bytes are to be ignored after `$at`.
* @param int|null $max_bytes Stop scanning after this many bytes have been seen.
* @param int|null $max_code_points Stop scanning after this many code points have been seen.
* @param bool|null $has_noncharacters Set to indicate if scanned string contained noncharacters.
* @return int How many code points were successfully scanned.
function _wp_scan_utf8( string $bytes, int &$at, int &$invalid_length, ?int $max_bytes = null, ?int $max_code_points = null, ?bool &$has_noncharacters = null ): int {
$byte_length = strlen( $bytes );
$end = min( $byte_length, $at + ( $max_bytes ?? PHP_INT_MAX ) );
$max_count = $max_code_points ?? PHP_INT_MAX;
$has_noncharacters = false;
for ( $i = $at; $i < $end && $count <= $max_count; $i++ ) {
* Quickly skip past US-ASCII bytes, all of which are valid UTF-8.
* This optimization step improves the speed from 10x to 100x
* depending on whether the JIT has optimized the function.
$ascii_byte_count = strspn(
"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f" .
"\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f" .
" !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f",
if ( $count + $ascii_byte_count >= $max_count ) {
$at = $i + ( $max_count - $count );
$count += $ascii_byte_count;
* The above fast-track handled all single-byte UTF-8 characters. What
* follows MUST be a multibyte sequence otherwise there’s invalid UTF-8.
* Therefore everything past here is checking those multibyte sequences.
* It may look like there’s a need to check against the max bytes here,
* but since each match of a single character returns, this functions will
* bail already if crossing the max-bytes threshold. This function SHALL
* NOT return in the middle of a multi-byte character, so if a character
* falls on each side of the max bytes, the entire character will be scanned.
* Because it’s possible that there are truncated characters, the use of
* the null-coalescing operator with "\xC0" is a convenience for skipping
* length checks on every continuation bytes. This works because 0xC0 is
* always invalid in a UTF-8 string, meaning that if the string has been
* truncated, it will find 0xC0 and reject as invalid UTF-8.
* > [The following table] lists all of the byte sequences that are well-formed
* > in UTF-8. A range of byte values such as A0..BF indicates that any byte
* > from A0 to BF (inclusive) is well-formed in that position. Any byte value
* > outside of the ranges listed is ill-formed.
* > Table 3-7. Well-Formed UTF-8 Byte Sequences
* ╭─────────────────────┬────────────┬──────────────┬─────────────┬──────────────╮
* │ Code Points │ First Byte │ Second Byte │ Third Byte │ Fourth Byte │
* ├─────────────────────┼────────────┼──────────────┼─────────────┼──────────────┤
* │ U+0000..U+007F │ 00..7F │ │ │ │
* │ U+0080..U+07FF │ C2..DF │ 80..BF │ │ │
* │ U+0800..U+0FFF │ E0 │ A0..BF │ 80..BF │ │
* │ U+1000..U+CFFF │ E1..EC │ 80..BF │ 80..BF │ │
* │ U+D000..U+D7FF │ ED │ 80..9F │ 80..BF │ │
* │ U+E000..U+FFFF │ EE..EF │ 80..BF │ 80..BF │ │
* │ U+10000..U+3FFFF │ F0 │ 90..BF │ 80..BF │ 80..BF │
* │ U+40000..U+FFFFF │ F1..F3 │ 80..BF │ 80..BF │ 80..BF │
* │ U+100000..U+10FFFF │ F4 │ 80..8F │ 80..BF │ 80..BF │
* ╰─────────────────────┴────────────┴──────────────┴─────────────┴──────────────╯
* @see https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-3/#G27506
// Valid two-byte code points.
$b1 = ord( $bytes[ $i ] );
$b2 = ord( $bytes[ $i + 1 ] ?? "\xC0" );
if ( $b1 >= 0xC2 && $b1 <= 0xDF && $b2 >= 0x80 && $b2 <= 0xBF ) {
// Valid three-byte code points.
$b3 = ord( $bytes[ $i + 2 ] ?? "\xC0" );
if ( $b3 < 0x80 || $b3 > 0xBF ) {
( 0xE0 === $b1 && $b2 >= 0xA0 && $b2 <= 0xBF ) ||
( $b1 >= 0xE1 && $b1 <= 0xEC && $b2 >= 0x80 && $b2 <= 0xBF ) ||
( 0xED === $b1 && $b2 >= 0x80 && $b2 <= 0x9F ) ||
( $b1 >= 0xEE && $b1 <= 0xEF && $b2 >= 0x80 && $b2 <= 0xBF )
// Covers the range U+FDD0–U+FDEF, U+FFFE, U+FFFF.
( 0xB7 === $b2 && $b3 >= 0x90 && $b3 <= 0xAF ) ||
( 0xBF === $b2 && ( 0xBE === $b3 || 0xBF === $b3 ) )
// Valid four-byte code points.
$b4 = ord( $bytes[ $i + 3 ] ?? "\xC0" );
if ( $b4 < 0x80 || $b4 > 0xBF ) {
( 0xF0 === $b1 && $b2 >= 0x90 && $b2 <= 0xBF ) ||
( $b1 >= 0xF1 && $b1 <= 0xF3 && $b2 >= 0x80 && $b2 <= 0xBF ) ||
( 0xF4 === $b1 && $b2 >= 0x80 && $b2 <= 0x8F )
// Covers U+1FFFE, U+1FFFF, U+2FFFE, U+2FFFF, …, U+10FFFE, U+10FFFF.
( 0x0F === ( $b2 & 0x0F ) ) &&
( 0xBE === $b4 || 0xBF === $b4 )
* When encountering invalid byte sequences, Unicode suggests finding the
* maximal subpart of a text and replacing that subpart with a single
* > This practice is more secure because it does not result in the
* > conversion consuming parts of valid sequences as though they were
* > invalid. It also guarantees at least one replacement character will
* > occur for each instance of an invalid sequence in the original text.
* > Furthermore, this practice can be defined consistently for better
* > interoperability between different implementations of conversion.
* @see https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-5/#G40630
// Single-byte and two-byte characters.
if ( ( 0x00 === ( $b1 & 0x80 ) ) || ( 0xC0 === ( $b1 & 0xE0 ) ) ) {
$b2 = ord( $bytes[ $i + 1 ] ?? "\xC0" );
$b3 = ord( $bytes[ $i + 2 ] ?? "\xC0" );
// Find the maximal subpart and skip past it.
if ( 0xE0 === ( $b1 & 0xF0 ) ) {
// Three-byte characters.
( 0xE0 === $b1 && $b2 >= 0xA0 && $b2 <= 0xBF ) ||
( $b1 >= 0xE1 && $b1 <= 0xEC && $b2 >= 0x80 && $b2 <= 0xBF ) ||
( 0xED === $b1 && $b2 >= 0x80 && $b2 <= 0x9F ) ||
( $b1 >= 0xEE && $b1 <= 0xEF && $b2 >= 0x80 && $b2 <= 0xBF )
$invalid_length = min( $end - $i, $b2_valid ? 2 : 1 );
} elseif ( 0xF0 === ( $b1 & 0xF8 ) ) {
( 0xF0 === $b1 && $b2 >= 0x90 && $b2 <= 0xBF ) ||
( $b1 >= 0xF1 && $b1 <= 0xF3 && $b2 >= 0x80 && $b2 <= 0xBF ) ||
( 0xF4 === $b1 && $b2 >= 0x80 && $b2 <= 0x8F )
$b3_valid = $b3 >= 0x80 && $b3 <= 0xBF;
$invalid_length = min( $end - $i, $b2_valid ? ( $b3_valid ? 3 : 2 ) : 1 );
* Fallback mechanism for safely validating UTF-8 bytes.
* @see wp_is_valid_utf8()
* @param string $bytes String which might contain text encoded as UTF-8.
* @return bool Whether the provided bytes can decode as valid UTF-8.
function _wp_is_valid_utf8_fallback( string $bytes ): bool {
$bytes_length = strlen( $bytes );
if ( 0 === $bytes_length ) {
_wp_scan_utf8( $bytes, $next_byte_at, $invalid_length );
return $bytes_length === $next_byte_at && 0 === $invalid_length;
* Fallback mechanism for replacing invalid spans of UTF-8 bytes.
* 'Pi�a' === _wp_scrub_utf8_fallback( "Pi\xF1a" ); // “ñ” is 0xF1 in Windows-1252.
* @param string $bytes UTF-8 encoded string which might contain spans of invalid bytes.
* @return string Input string with spans of invalid bytes swapped with the replacement character.
function _wp_scrub_utf8_fallback( string $bytes ): string {
$bytes_length = strlen( $bytes );
while ( $next_byte_at <= $bytes_length ) {
_wp_scan_utf8( $bytes, $next_byte_at, $invalid_length );
if ( $next_byte_at >= $bytes_length ) {
return $scrubbed . substr( $bytes, $was_at, $next_byte_at - $was_at - $invalid_length );
$scrubbed .= substr( $bytes, $was_at, $next_byte_at - $was_at );
$next_byte_at += $invalid_length;
* Returns how many code points are found in the given UTF-8 string.
* Invalid spans of bytes count as a single code point according
* to the maximal subpart rule. This function is a fallback method
* for calling `mb_strlen( $text, 'UTF-8' )`.
* When negative values are provided for the byte offsets or length,
* this will always report zero code points.
* 4 === _wp_utf8_codepoint_count( 'text' );
* // Groups are 'test', "\x90" as '�', 'wp', "\xE2\x80" as '�', "\xC0" as '�', and 'test'.
* 13 === _wp_utf8_codepoint_count( "test\x90wp\xE2\x80\xC0test" );
* @param string $text Count code points in this string.
* @param ?int $byte_offset Start counting after this many bytes in `$text`. Must be positive.
* @param ?int $max_byte_length Optional. Stop counting after having scanned past this many bytes.
* Default is to scan until the end of the string. Must be positive.
* @return int How many code points were found.
function _wp_utf8_codepoint_count( string $text, ?int $byte_offset = 0, ?int $max_byte_length = PHP_INT_MAX ): int {
if ( $byte_offset < 0 ) {
$max_byte_length = min( $end - $at, $max_byte_length );
while ( $at < $end && ( $at - $byte_offset ) < $max_byte_length ) {
$count += _wp_scan_utf8( $text, $at, $invalid_length, $max_byte_length - ( $at - $byte_offset ) );
$count += $invalid_length > 0 ? 1 : 0;
* Given a starting offset within a string and a maximum number of code points,
* return how many bytes are occupied by the span of characters.
* Invalid spans of bytes count as a single code point according to the maximal
* subpart rule. This function is a fallback method for calling
* `strlen( mb_substr( substr( $text, $at ), 0, $max_code_points ) )`.
* @param string $text Count bytes of span in this text.
* @param int $byte_offset Start counting at this byte offset.
* @param int $max_code_points Stop counting after this many code points have been seen,
* or at the end of the string.
* @param ?int $found_code_points Optional. Will be set to number of found code points in
* span, as this might be smaller than the maximum count if
* the string is not long enough.
* @return int Number of bytes spanned by the code points.
function _wp_utf8_codepoint_span( string $text, int $byte_offset, int $max_code_points, ?int &$found_code_points = 0 ): int {
while ( $byte_offset < $end && $found_code_points < $max_code_points ) {
$needed = $max_code_points - $found_code_points;
$chunk_count = _wp_scan_utf8( $text, $byte_offset, $invalid_length, null, $needed );
$found_code_points += $chunk_count;
// Invalid spans only convey one code point count regardless of how long they are.
if ( 0 !== $invalid_length && $found_code_points < $max_code_points ) {
$byte_offset += $invalid_length;
return $byte_offset - $was_at;
* Fallback support for determining if a string contains Unicode noncharacters.
* @see \wp_has_noncharacters()
* @param string $text Are there noncharacters in this string?
* @return bool Whether noncharacters were found in the string.
function _wp_has_noncharacters_fallback( string $text ): bool {
$has_noncharacters = false;
while ( $at < $end && ! $has_noncharacters ) {
_wp_scan_utf8( $text, $at, $invalid_length, null, null, $has_noncharacters );
return $has_noncharacters;
* Converts a string from ISO-8859-1 to UTF-8, maintaining backwards compatibility
* with the deprecated function from the PHP standard library.
* @param string $iso_8859_1_text Text treated as ISO-8859-1 (latin1) bytes.
* @return string Text converted into UTF-8.
function _wp_utf8_encode_fallback( $iso_8859_1_text ) {
$iso_8859_1_text = (string) $iso_8859_1_text;
$end = strlen( $iso_8859_1_text );
// US-ASCII bytes are identical in ISO-8859-1 and UTF-8. These are 0x00–0x7F.
$ascii_byte_count = strspn(
"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f" .
"\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f" .
" !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f",
if ( $ascii_byte_count > 0 ) {
$at += $ascii_byte_count;
// All other bytes transform into two-byte UTF-8 sequences.
$code_point = ord( $iso_8859_1_text[ $at ] );
$byte1 = chr( 0xC0 | ( $code_point >> 6 ) );
$byte2 = chr( 0x80 | ( $code_point & 0x3F ) );
$utf8 .= substr( $iso_8859_1_text, $was_at, $at - $was_at );
$utf8 .= "{$byte1}{$byte2}";
$utf8 .= substr( $iso_8859_1_text, $was_at );
* Converts a string from UTF-8 to ISO-8859-1, maintaining backwards compatibility
* with the deprecated function from the PHP standard library.
* @param string $utf8_text Text treated as UTF-8 bytes.
* @return string Text converted into ISO-8859-1.
function _wp_utf8_decode_fallback( $utf8_text ) {
$utf8_text = (string) $utf8_text;
$end = strlen( $utf8_text );
It is recommended that you Edit text format, this type of Fix handles quite a lot in one request
