Guest WiFi crendetials aren't guaranteed to be unique

[Trigary]

I received the following error when generating 10 000 users via a seeder:

  Database\Seeders\UsersTableSeeder .......................................................................... RUNNING  

   Illuminate\Database\UniqueConstraintViolationException 

  SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'guest_yhxOYL' for key 'internet_accesses.internet_accesses_wifi_username_unique' (Connection: mysql, SQL: update `internet_accesses` set `wifi_password` = tFnMQeEO, `wifi_username` = guest_yhxOYL, `internet_accesses`.`updated_at` = 2024-06-04 16:19:30 where `user_id` = 8813)                                                    
                                                                                                                                                                                                        
  at vendor/laravel/framework/src/Illuminate/Database/Connection.php:808                                                                                                                                
    804▕         // message to include the bindings with SQL, which will make this exception a                                                                                                          
    805▕         // lot more helpful to the developer instead of just the database's errors.                                                                                                            
    806▕         catch (Exception $e) {                                                                                                                                                                 
    807▕             if ($this->isUniqueConstraintError($e)) {                                                                                                                                          
  ➜ 808▕                 throw new UniqueConstraintViolationException(                                                                                                                                  
    809▕                     $this->getName(), $query, $this->prepareBindings($bindings), $e                                                                                                            
    810▕                 );                                                                                                                                                                             
    811▕             }                                                                                                                                                                                  
    812▕                                                                                                                                                                                                
                                                                                                                                                                                                        
      +11 vendor frames                                                                                                                                                                                 
                                                                                                                                                                                                        
  12  app/Models/Internet/InternetAccess.php:109                                                                                                                                                        
      Illuminate\Database\Eloquent\Model::update()                                                                                                                                                      
                                                                                                                                                                                                        
  13  app/Models/User.php:140                                                                                                                                                                           
      App\Models\Internet\InternetAccess::setWifiCredentials()                                                                                                                                          
                                                                                                                                                                                                        
                                                                                                                                                                                                        
Process finished with exit code 1                                                                                                                                                                       

The culprit is the following line: https://github.com/EotvosCollegium/mars/blob/development/app/Models/Internet/InternetAccess.php#L107C1-L107C100

[machiato32]

Math problem: If you generate N guest wifi usernames with the scheme defined at User.php:140, what is the probability of generating two identical ones in the process?
@kdmnk

[kdmnk]

We need to call Erika that we can't manage her guests anymore... :D

[horcsinbalint]

My math is most probably off, but I think there are 62^6=56800235584 possible ids from Str::random(6).
According to this, it should have a 0.0008798 chance that the issue happens described by @Trigary. So we I will look into this a bit more.

This python script calculates the possibility of the problem described by @Trigary:

import decimal
result = 1
for i in range(0,10000):
     result *= decimal.Decimal(62**6-i)/decimal.Decimal(62**6)

print(decimal.Decimal(1)-result)