core: disconnect clients

[Shubham8287]

Description of Changes

The AutoMigrateStep::DisconnectAllUsers step is implemented as follows:

1. The spacetimedb::db::update::update_database function returns a response of type UpdateDatabaseResult::UpdatePerformedWithClientDisconnect.

2. Upon receiving this response, the host_controller::update_module proceeds to drop the watch::Sender<ModuleHost> field within the core::host_controller::Host and disconnect clients.

companion private PR - https://github.com/clockworklabs/SpacetimeDBPrivate/pull/2095

API and ABI breaking changes

NA

Expected complexity level and risk

Diff code is simple but It depends on the subcription logic to behave correctly.

Testing

Manually.

[gefjon]

Excellent, thanks! This seems like the correct way to disconnect clients.

Actually, I realized I'm not confident that we correctly call the client_disconnected reducers here.

[gefjon]

How does client_disconnected get called for the disconnected clients?

[Shubham8287]

How does client_disconnected get called for the disconnected clients?

Dropping watch::sender leads to exit of ws_client_actor which was awaiting on ws_main_loop.

SpacetimeDB/crates/client-api/src/routes/subscribe.rs

Line 371 in 2b61190

tokio::spawn(client.disconnect());

client.disconnect() imeplementation calls ModuleHost::disconnect_client() which does the job.

[Shubham8287]

How does client_disconnected get called for the disconnected clients?

I fixed disconnect_redudcer not being called by explicitly calling it while updating module.
I also updated smoketest to test the disconnect reducer calls .