Passing around a global context and or client context

[feds01]

I'm not sure if this would be currently possible, but It would be nice to allow for the config to specify an initialisation Context, one that is available across the entire socket handling mechanism. This could be an expansion upon the current way that the logger is passed around, and its in fact just generalised to handle any shape of data, not only just a logger. So for example:

const context = createContext({ ... }) // Returns the shape of something like `{ logger: Logger } & UserDefinedContext`
attachSockets({
        io,
        target: server,
        config: socketConfig,
        actions,
        context,
    });

Furthermore, it could be useful to add client-specific contexts, that can be initialised per-client connection:

type Context {
   ...,
   userService: UserService, // parameterised over the client information sent across (perhaps even auth handling...)
}

/** Of course, this `Context` type can probably be inferred in most cases */
export const config = createSimpleConfig<Context>({
   ...,
   hooks: {
     createContext: async (params: ClientContext): Context => { 
         return { user: new UserService(client.handshake), ... }
     }
 });

When should you initialise the context?

This could be achieved either one of the ideas:

• Either make it so that the onStartup hook actually requires you to return a Context, and hence this is the initialisation mechanism for context.
• Completely abstract context initialisation, and add a new hook, createContext()

Other thoughts

Perhaps its better to add a createContext hook because it can be parameterised over client, making it possible to construct a Context that is client specific.

Perhaps split context into just the current instance context, and a per-client context. The instance context, can be constructed when you call attachSockets (exactly as the current mechanism to pass in the logger).