Fixed Duplicate key error while following

[PaulB]

Affected version

1.5.21

In Model/User.php, function follow, around line 1760:

The ordering of beginTransaction and removeDuplicateFollowUserIds is wrong. Because removeDuplicateFollowUserIds is performed outside the transaction, a race condition occurs. If the user is experiencing internet connectivity issues and ends up sending multiple follow requests nearly simultaneously, the following can happen:

Zend_Db_Statement_Mysqli_Exception: Mysqli statement execute error : Duplicate entry '123-456' for key 'PRIMARY' - library/Zend/Db/Statement/Mysqli.php:214

To resolve this, beginTransaction needs to be called prior to removeDuplicateFollowUserIds.

Basic patch with minimal testing attached.

 

[XF Bug Bot]

Thank you for reporting this issue. It has now been resolved and we are aiming to include it in a future XF release (1.5.24).

Change log:

Attempt to avoid a duplicate key race condition when following a user.

Any changes made as a result of this issue being resolved may not be rolled out here until later.