Enforce room ID uniqueness

Steps to Reproduce (for bugs)

1. Setup a colyseus cluster with 2 servers and a colyseus proxy (Redis presence and Mongo driver)
2. Create a room with a filter, inspired by step 1 of https://docs.colyseus.io/colyseus/how-to/password-protect-room/

gameServer
  .define("battle", BattleRoom)
  .filterBy(['password'])

1. In the onCreate of BattleRoom, assign a custom roomId

async onCreate(options: any) {
  this.roomId = options.password;
}

1. Use joinOrCreate simultaneously from many clients, with the same password
2. Multiple rooms with the same ID get created, which is at least a problem for the client method joinBy. It seems clients still get split into multiple rooms even if I sort the rooms by ascending creation date.

Context

I was trying to create rooms with a fixed ID matching an ID provided by another service, but this seems to break joinOrCreate. This seems to be due to a race condition in the finding of a suitable room, which checks there is no room available, then creates one. If two requests are processed simultaneously, two rooms will be created. I tried making the roomId index in MongoDB unique, but as the colyseus server did not handle the database errors appropriately, I did not investigate this further. It seems to me we either need:

• to query the DB again for the best available room after creating one
• to make roomIds unique in the DB, and re-query the DB if room creation fails

Your Environment

• Colyseus Version: 0.14.20
• Node.js Version: 14.17.4
• Operating System and version: Ubuntu 20.04