Best practice for "finding" sockets when using an adapter

[Thessiah]

Since socket IDs are ephemeral, what would be the best way to find a socket based on my own persistent ID (like user/session ID) when using socket.io with an adapter? I could put the ID on data, call fetchSockets(), then find the ID in that list, but if there are a lot of sockets and this lookup is frequent, it seems like a bad pattern.

The other thing I could think of is just creating a room for every user when they connect, labeling these rooms with their ID, then using .in(userID).fetchSockets() to get them fairly efficiently, however I was concerned that bloating the adapter with a large amount of single person rooms could be bad for whatever service the adapter is integrated with.

Is this concern unfounded or is there a better solution? I am using the Redis Streams adapter, if it's useful for the answer. Thanks!

[Bubuioc]

Have same question :)

[darrachequesne]

Hi!

creating a room for every user when they connect, labeling these rooms with their ID

Yes, that's a good pattern, you can see it for example in our guide with Passport.js: https://socket.io/how-to/use-with-passport#using-the-user-id

I was concerned that bloating the adapter with a large amount of single person rooms

The rooms are stored in the memory of the server the client is currently connected to, basically it's two sets (id to rooms and room to ids).

See also: https://socket.io/docs/v4/rooms/#implementation-details

The adapter based on Redis Streams will only use one single stream, regardless of the number of rooms, so it shouldn't be a concern.

In that case, io.in(userID).fetchSockets() will indeed allow you to check whether a user is currently connected 👍