Online list

[elmigranto]

Maintains a list of Users who recently had been online.

When the client asks for notifications for user, we add him to the top of this list. Stored as redis' Ordered Set (sorted by -timestamp of request); set is capped at config.options.onlineSize, most recent requests are at the top of the list.

List is publicly available via GET /{prefix}/online.

[elmigranto]

Ready for review and feedback, @j3k0.

[j3k0]

Hey, all good. But can I ask for some refactoring?

• I'd like the online feature to be (eventually) using its own REDIS, with its own ENV (REDIS_ONLINE)
  • "eventually" : because ENV for notifications and online could be set to the same IP and port.
• I'd like the /online API to be in its own folder, as independent from the notification API as possible (online-api/ subfolder, next to notification-api), so it's easier to move it to another server module in the future.

Also, I think you should use LPUSH + LTRIM (both O(1)) instead of ZADD and ZREMOVEBYRANK (O(N) and O(N)+M). No need to sort by timestamp, that'll only sort the list by insertion time.

[elmigranto]

I think you should use LPUSH + LTRIM

The problem with it is duplicate usernames. We'd need to get the whole list every time, remove dupes manually and save the whole list back removing old one resulting in a bunch of O(N) operations.

Also, ZADD is log(N) and ZREMRANGEBYRANK is log(N) + N_removed_elements and we always remove 1 element. Anyway, we only have 20 elements for now, so not much difference here.

Oops, clicked Close&Comment by mistake.

[j3k0]

good point for zadd. i was wrong, it's better the way you did it.

[j3k0]

@elmigranto merged, yet i'd like the cleanup if possible... keeping as little online-related code in the notification-api folder

[elmigranto]

Sure, didn't mentioned it in comment, but will work on decoupling this more later. Will also update it to separate redis config.