robreczarek/warsawjs-workshop-5-chat

A command line based chat app in Node.js and LevelDB built during the 5th edition of WarsawJS workshops.

warsawjs-workshop-5-chat's Issues

Existence checks before registering

Currently, LevelAuthentication allows overwriting of other users' accounts. This can be eliminated by checking the database for existing accounts of the same name. Care should be taken to avoid a race condition.

In particular, a race condition might occur with the following sequence of operations taking place:

• Read (existence check) is done for connection A → user does not exist
• Read is done for connection B → user does not exist
• Write for connection A
• Write for connection B → overwrites the user account of A

This can be avoided using an in-process lock, possibly with a single Promise that controls access and makes other such checks/writes wait until the last/current procedure finishes.