Implement Websockets for `com.atproto.sync.subscriberepos`

[DrewMcArthur]

background

see the spec on event streams and subscribe endpoints here. see the rocket_ws crate here see the subscription type in the atproto lexicon here

generally, when a client connects to a subscribe endpoint (see here), they connect via websockets to listen to events. they're one way (server -> client), with a few optional parameters including a backfill window or a cursor, allowing the subscriber to catch up on missed messages.

requirements

• [ ] allow a client to make a web socket connection on any path prefixed with subscribe (currently /xrpc/com.atproto.sync.subscribe_repos and /xrpc/com.atproto.label.subscribe_labels)
• [ ] as records are created within a repo or new labels, send them as messages to any subscribed clients
• [ ] add backfill capabilities (given a parameter in the initial request, start sending messages at some point in the past)

[DrewMcArthur]

fyi i've begun work on this in https://github.com/DrewMcArthur/rsky/issues/3

seems like everything runs, i just have to figure out how to test it.

[rudyfraser]

Sick! I had also started on this but I'll work on other stuff for now. As an FYI, I generally have been trying to keep the code as close to the TS implementation as possible https://github.com/bluesky-social/atproto/blob/e956ac06be32cbfef06605cda6298b5fd621513a/packages/pds/src/api/com/atproto/sync/subscribeRepos.ts

For testing, you should be able to use a client like Postman to subscribe to your websocket endpoint and in another client do things like create a new account, update the handle, create a new post, etc. and have the messages come through. All of those endpoints exist today under the com.atproto namespaces.