Duplicate move on game

[benjaminpjones]

This game got broken by a duplicate move: https://www.govariants.com/game/65cf8f1ee7d31b1d396fe3c7

[benjaminpjones]

The race could look something like this:

1. User POSTs game/xxx/move twice
   • Not sure how this happens, but server should be prepared for anything
2. Call 1 pulls the game from the database
3. Call 2 pulls the game from the database
4. Call 1 pushes the move onto the end of the array (See updateOne)
5. Call 2 pushes the move onto the end of the array

A couple solutions I can think of:

• place a “pending” field on the game document using findAndModify, return early if the object is already being edited
  • (This one seems really easy to screw up)
• Replace the array ($set) rather than just pushing ($push) the last move, so we always have a valid moves array
• We could add some self-healing, so if the db gets corrupted like this, we just remove the bad moves when the game is requested
  • This could be done in conjunction with fixing the race condition