Commits on May 10, 2024

1. Allow a Hook to reload an individual client session …

   In a clustered environment, client connections are distributed among
   multiple Server instances on different machines. After a client
   disconnects, leaving behind a persistent session state, its next
   login is likely to be on a different node. Because of this, in such a
   setup an individual Server instance should only keep Client instances
   corresponding to online client connections, and it should be able to
   reload an individual client's state (presumably from persistent
   storage) when that client connects.
   
   This commit adds support for such an environment by adding a new hook
   `StoredClientByID`. An implementation finds and returns any
   persistent client data for a given session ID. In practice the only
   necessary information turned out to be the saved subscriptions and
   in-flight ack messages. The hook also returns the prior 'Remote'
   property since the server logs that.
   
   The Server method `inheritClientSession` is extended to call this hook
   if there is no matching in-memory Client session. If the hook returns
   session data, it installs it into the Client object in the same way
   as the existing code.
   
   At the end of the Server method `attachClient`, after disconnection,
   the existence of a `StoredClientByID` hook is checked; if present,
   the method expires the Client instance so it won't hang around in
   memory and so the next connection will go to the hook to reload
   state.

   

   snej committed May 10, 2024
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