[wp-trac] [WordPress Trac] #31767: insert_with_markers() is not atomic, leading to corrupted .htaccess updates under race conditions

[WordPress Trac]

#31767: insert_with_markers() is not atomic, leading to corrupted .htaccess updates
under race conditions
---------------------------------+-----------------------
 Reporter:  tigertech            |       Owner:  dd32
     Type:  defect (bug)         |      Status:  assigned
 Priority:  normal               |   Milestone:  4.4
Component:  Filesystem API       |     Version:  4.1.1
 Severity:  critical             |  Resolution:
 Keywords:  has-patch 4.4-early  |     Focuses:
---------------------------------+-----------------------

Comment (by tigertech):

 I've tested this, and the good news is that the patch appears to solve the
 corruption problem in the vast majority of cases.

 On systems that support `flock()`, it should completely solve it; on
 systems that don't, the code cleanup of "writing everything all at once"
 will make it much less likely to happen (the new code is also noticeably
 far faster when calling `insert_with_markers` thousands of times in a
 test, reducing the amount of time a race condition could exist).

 However, as @willmot noticed, it has a new bug: it doesn't create a
 missing file any more, and it needs to. Perhaps the fix for could be as
 simple as adding this at the top of the function:

 {{{
 if (!file_exists( $filename ) ) {
     if(!touch( $filename )) {
         return false;
     }
 }
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/31767#comment:18>
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