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n10n

Overview​

N10N Processor is a middleware between IN10NBroker and router

Why​

  • to avoid router to do the SSE handling:
    • listen for the N10N channel,
    • render events to SSE messages
    • authnz, rate limiting, manage goroutines etc

Principles​

  • work via Bus
    • Router and N10NProc depends on Bus only
    • Router can reuse the existing Bus streaming approach (like for queries)
  • no engines, no workers, no proc bus, 1 request → 1 N10N processor call in request’s goroutine
  • authnz, subscribe, validate etc is done by the processor, not by the router
  • router must not depend on n10n package

Functional design​

  • router accepts request to /notifications/ url part and sends the request using bus.IBus.SendRequest
  • Bus triggers an event that is handled by VVM request handler
  • VVM request handler routes request to the IN10NProc
  • IN10NProc handles validation, authnz, uses IN10NBroker and sends response to bus.IReponsder
    • If expiresIn is not provided, defaults to 24 hours
    • If subscription fails, all previously subscribed projections are automatically unsubscribed
  • router reads chunks from bus and just sends it to the http client (the same streaming as for queries)

Components​

  • processors/n10n/IN10NProc.Handle()
    • no engines, no borrowing, just single interface wired on VVM create
  • router /notifications/ url path handler
    • IBus.SendRequest(bus.Request.IsN10N=true)
    • VVM Request Handler calls IN10NProc.Handle()
  • IN10NProc.Handle() uses sync pipeline to handle the request
  • error is out → bus.ReplyErr() and return
  • subscribe-and-watch is requested ->
    • streamer := bus.IResponser.StreamEvents()
    • IN10NBroker.WatchChannel() is called in a goroutine
      • on event: streamer.Write(string SSE message)
      • VVM ctx or Request ctx closed → WatchChannel exit
      • wait for all goroutines in cleanup on VVM ctx close
  • subscribe on an extra view is requested ->
    • IN10NBroker.Subscribe()
    • 200 ok is responded to the bus
  • unsubscribe is requested ->
    • IN10N.Unsubscribe()
    • 204 no content is responded to the bus

Communication schema​