Odd Socks

Just another rant about websockets, but this time with a happy ending

2026-02-23, by DrFriendless technologywebsockets

Well, after about a week of effort I’ve succeeded with the proof of concept with the websockets stuff. It turned out to be quite a lot of work, but I’ve built a system I think will be robust for when I have a use for it. The visible effect for users (so far) will be that if they’re looking at their own Updates page, and the downloader finishes processing any of their files, the page will update with the new times. Although users can see other users’ Updates pages, I don’t send messages about that, just to keep the traffic to a sensible level.

In the last thrilling instalment of this rant, we had got to the situation where the server sends a chatter ID to the browser. If the browser wishes to use the websocket, it connects and passes the chatter ID, the geek name, and a topic (which specifies exactly what sort of chatter it’s interested in). The server confirms that the chatter ID matches the geek name, or else denies the connection. The server records the connection’s connection ID, geek, and topic in a table in DynamoDB.

On the server side, from time to time something happens that we might want to tell someone about. The place I’ve instrumented this is in the downloader - when a file is successfully update for a geek, a message is sent out saying “this is for Friendless, the topic is updates, and we would like to say “your plays for 2026 have been updated.”

But where is that message sent to? At the moment it goes to an SQS queue. I’m not sure that I need a queue in this part of the architecture, but last time I had unrestrained parallelism things go a bit out of hand and I had to close the site down.

That SQS queue is serviced by a Lambda which is acting as a message broker. It looks at the subscriptions in DynamoDB and matches them by geek and topic to the message it has to send. It then uses the connection ID to send the message back to anyone who’s listening.

So this isn’t really just a socket. This is a publish and subscribe system, which is a kinda handy thing to have. Well, that’s nice, but I have some more mundane things to be fixing so I’ll keep this capability in my backpack until I find a cool use for it.