[wp-trac] [WordPress Trac] #64849: Media: wp_get_image_alttext() incorrectly treats strpos() position 0 as "not found"

[WordPress Trac]

#64849: Media: wp_get_image_alttext() incorrectly treats strpos() position 0 as
"not found"
--------------------------+-------------------------------------
 Reporter:  suhan2411     |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Media         |    Version:  trunk
 Severity:  normal        |   Keywords:  has-patch needs-testing
  Focuses:                |
--------------------------+-------------------------------------
 The `wp_get_image_alttext()` function in `src/wp-admin/includes/image.php`
 checks for XMP metadata using `strpos()`:

 {{{
 $xmp_start = strpos( $img_contents, '<x:xmpmeta' );
 $xmp_end   = strpos( $img_contents, '</x:xmpmeta>' );

 if ( ! $xmp_start || ! $xmp_end ) {
     return $alt_text;
 }
 }}}

 This logic incorrectly treats a match at position `0` as "not found".

 In PHP, `strpos()` returns:

 {{{
 0     → match found at position 0
 false → no match
 }}}

 Because the code uses `! $xmp_start`, a valid match at position `0` is
 treated as `false`, and the function returns an empty alt text.

 As a result, valid XMP metadata may be ignored when it appears at the
 beginning of the file contents.

 Additionally, `file_get_contents()` may return `false` on failure.

 The current implementation passes that value directly to `strpos()`, which
 can trigger PHP warnings or errors.

 Both issues can be resolved by using strict comparisons for `strpos()` and
 adding a safety check for `file_get_contents()` failure.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/64849>
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