[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:  joedolson
     Type:  defect (bug)             |      Status:  accepted
 Priority:  normal                   |   Milestone:  7.0
Component:  Media                    |     Version:  trunk
 Severity:  normal                   |  Resolution:
 Keywords:  has-patch needs-testing  |     Focuses:
-------------------------------------+------------------------

Comment (by alexodiy):

 Tested PR [https://github.com/WordPress/wordpress-develop/pull/11237
 #11237] on PHP 8.5.1 (NTS, Windows x64) against trunk at r61991.

 == Environment ==

 * PHP: 8.5.1 (cli) NTS Visual C++ 2022 x64
 * WordPress: 7.0-beta5 (trunk r61991)
 * OS: Windows 11

 == Reproduction ==

 Created a synthetic binary file where `<x:xmpmeta` starts at byte position
 0, containing valid IPTC `AltTextAccessibility` metadata with value "Test
 alt text from XMP".

 '''Before patch:'''

 `strpos()` returns `int(0)` for `$xmp_start`. The check `if ( ! $xmp_start
 )` evaluates `! 0` as `true`, causing the function to return an empty
 string. Valid XMP metadata is silently ignored.

 '''After patch:'''

 The check `if ( false === $xmp_start )` correctly distinguishes `0` from
 `false`. The function extracts and returns the alt text "Test alt text
 from XMP".

 == Additional test: file_get_contents failure ==

 When `file_get_contents()` returns `false` (e.g., non-existent file path),
 the added guard `if ( false === $img_contents )` prevents passing `false`
 to `strpos()`.

 == Results ==

 ||= Scenario =||= Before Patch =||= After Patch =||
 || XMP at position 0 || Alt text lost (false negative) || Alt text
 correctly extracted ||
 || XMP at position > 0 || Works || Works ||
 || Non-existent file || Passes `false` to `strpos()` || Returns empty
 string safely ||

 Patch looks correct and minimal. +1 for commit.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/64849#comment:7>
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