Handle UTF-8 and text encoding safely in WordPress plugins, especially on WP 6.9+ where wp_is_valid_utf8(), wp_scrub_utf8(), and noncharacter helpers replace older seems_utf8-style checks. Covers when to validate, scrub, reject, or preserve invalid bytes; wp_check_invalid_utf8 behavior; XML/JSON/feed/export boundaries; and avoiding data loss from premature replacement. Use when processing imported text, CSV, XML, feeds, email, REST payloads, AI prompts, logs, filenames, or external API data.
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WordPress 6.9 modernized UTF-8 handling. New code should prefer the explicit UTF-8 helpers instead of older heuristics and hand-written byte regexes.
This skill is for server-side plugin text processing. It is not about block editor text controls.
Trigger when ANY of the following is true:
seems_utf8(), mb_check_encoding(), iconv(), utf8_encode(), utf8_decode(), or byte-level regexes.�, XML generation, REST encoding errors, or noncharacters.| Need | Use |
|---|---|
| Check whether bytes are valid UTF-8 | wp_is_valid_utf8( $bytes ) |
| Replace invalid UTF-8 spans with U+FFFD | wp_scrub_utf8( $text ) |
| Detect Unicode noncharacters | wp_has_noncharacters( $text ) |
| Legacy display/database helper | wp_check_invalid_utf8( $text, $strip ) |
seems_utf8() is deprecated in WP 6.9. Use wp_is_valid_utf8() for validation.
Pick behavior based on the boundary:
| Boundary | Preferred behavior |
|---|---|
| Admin text field save | Usually reject invalid UTF-8 with a validation error. |
| Frontend display of legacy stored text | Scrub for display if rejection is no longer possible. |
| XML, JSON, feed, sitemap, external API | Scrub or reject before serialization; invalid bytes can break the whole document. |
| Security-sensitive identifiers, slugs, tokens | Reject, do not scrub into a different value. |
| Logs/debug dumps | Preserve raw bytes if forensic fidelity matters; scrub only for display. |
| AI/LLM prompt payloads | Scrub before sending unless invalid bytes are semantically important. |
Replacing invalid bytes is lossy. Once U+FFFD is inserted, you cannot know what the original byte sequence was.
Reject invalid imported text:
$name = (string) ( $row['name'] ?? '' );
if ( ! wp_is_valid_utf8( $name ) ) {
return new WP_Error(
'myplugin_invalid_utf8',
__( 'The imported name contains invalid UTF-8 bytes.', 'myplugin' )
);
}
Scrub before XML output:
$title = wp_scrub_utf8( (string) $title );
$xml .= '<title>' . esc_xml( $title ) . '</title>';
Preserve raw bytes in storage, scrub for display:
update_post_meta( $post_id, '_myplugin_raw_payload', $payload );
$safe_for_screen = wp_scrub_utf8( $payload );
echo esc_html( $safe_for_screen );
wp_check_invalid_utf8()wp_check_invalid_utf8( $text, false ) returns an empty string for invalid UTF-8 on UTF-8 sites. Since WP 6.9, wp_check_invalid_utf8( $text, true ) replaces invalid byte sequences with U+FFFD instead of silently removing them.
Use it when you are already in a WordPress escaping/sanitizing path that expects this helper. For new explicit validation logic, prefer wp_is_valid_utf8() and wp_scrub_utf8() because the intent is clearer.
Unicode noncharacters can be valid UTF-8 while still being inappropriate for interchange formats. Use wp_has_noncharacters() when producing XML, strict external API payloads, or data that will be consumed outside WordPress.
if ( wp_has_noncharacters( $text ) ) {
return new WP_Error(
'myplugin_noncharacter_text',
__( 'The text contains Unicode noncharacters that cannot be exported.', 'myplugin' )
);
}
seems_utf8() in new code. It is deprecated as of WP 6.9.// WRONG - deprecated and less explicit.
if ( ! seems_utf8( $value ) ) {
$value = '';
}
// RIGHT - clear validation.
if ( ! wp_is_valid_utf8( $value ) ) {
return new WP_Error( 'invalid_utf8', __( 'Invalid text encoding.', 'myplugin' ) );
}
// WRONG - silently changes an identifier.
$slug = sanitize_key( wp_scrub_utf8( $raw_slug ) );
// RIGHT - reject bad bytes before deriving identifiers.
if ( ! wp_is_valid_utf8( $raw_slug ) ) {
return new WP_Error( 'invalid_slug_encoding', __( 'Invalid slug encoding.', 'myplugin' ) );
}
$slug = sanitize_key( $raw_slug );
wp-security-audit when invalid text comes from uploads, REST, AJAX, or third-party APIs.wp-rest-api when text is accepted or returned through REST schemas.wp-html-api when text is being inserted into HTML fragments.wp_check_invalid_utf8() / seems_utf8(): wp-includes/formatting.php还没有评价。欢迎分享你的使用感受。
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