Follow notification

[Aspie96]

Not all users would need this feature, but I'd like to have it.

Currently, the follow list of each user is managed trough NIP-02. A single replaceable kind 3 event lists all users that the author is following.

This is a good system. Retrieving the follow list of a user is trivial.
However, there is effectively no way of knowing when one has a new follower, except by polling the list of followers, which will be both inefficient and somewhat challenging to do.
Personally, I would like to know when I have a new follower.

I suggest that there should be a new kind of event that is produced when a user follows a new account.
This event can then be used by clients to show a "You have been followed by [user]" notification, which can be enabled or disabled by changing the client's settings.
The follow event should only be considered valid, by the client, if the author actually does (still) follow the user (which is checked by retrieving the relevant kind 3 event). No notification is displayed otherwise. Relays are also free to delete follow events which are or become invalid.
A user may follow another account multiple times. In this case, only the most recent follow event is considered valid.

This wouldn't require changing anything in NIP-02 and anything which works well with kind 3 events will continue to.

[vitorpamplona]

Agree, I am currently working with https://github.com/vitorpamplona/nips/blob/relationship-status/81.md to better document these types of notifications. In your case, you would use the public event to build a list of follows.

{
  "kind": 30382,
  "tags": [
    ["d", "<friend's pubkey>"],
    ["n", "Follows"]
  ],
  "content": nip44Encrypt(JSON.stringify([
    ["petname", "friend's private petname"]
  ])),
  // ...other fields
}

Here you can just keep track of all d-tags pointing to your user and you will get every change to them.

[vitorpamplona]

Well, looks like then the only option is to track the changes in that event kind from any of the 3000 relays out there.

[Aspie96]

Usually getting a "You got a mention" kind of notification is rather trivial. Of course, you'll only get it from your relays.
I'm suggesting that a "You got a new follower" kind of notification should be as trivial.

[vitorpamplona]

It's easy to add an event. Hard is to change every client out there to do things twice, in the NIP-02 and as a new event. Unfortunately, it's easier to just track NIP-02 themselves. That's how Primal does it.

[Aspie96]

The issue with tracking NIP-02 is that you need to track changes, so you need to have an initial copy of the follower the account used to have. You'll also be fetching a lot of useless data.

I know clients would have to implement it for it to work. This is true for anything in Nostr.

[vitorpamplona]

Yep, but tracking the changes from an event that almost everyone base their interfaces on will definitely be more accurate that a new optional event that is not used for anything other than notifications.

It all depends on how much compliance do you need, besides the inevitable false positive and false negative rates.