Method: NATS#request

Defined in:
lib/nats/client.rb

#request(subject, data = nil, opts = {}, &cb) ⇒ Object

Send a request and have the response delivered to the supplied callback.

Parameters:

  • subject (String)
  • msg (Object)
  • callback (Block)

Returns:

  • (Object) —

    sid



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# File 'lib/nats/client.rb', line 623

def request(subject, data=nil, opts={}, &cb)
  return unless subject

  # In case of using async request then fallback to auto unsubscribe
  # based request/response and not break compatibility too much since
  # new request/response style can only be used with fibers.
  if cb
    inbox = "_INBOX.#{@nuid.next}"
    s = subscribe(inbox, opts) { |msg, reply|
      case cb.arity
      when 0 then cb.call
      when 1 then cb.call(msg)
      else cb.call(msg, reply)
      end
    }
    publish(subject, data, inbox)
    return s
  end

  # If this is the first request being made, then need to start
  # the responses mux handler that handles the responses.
  start_resp_mux_sub! unless @resp_sub_prefix

  # Generate unique token for the reply subject.
  token = @nuid.next
  inbox = "#{@resp_sub_prefix}.#{token}"

  # Synchronous request/response requires using a Fiber
  # to be able to await the response.
  f = Fiber.current
  @resp_map[token][:fiber] = f

  # If awaiting more than a single response then use array
  # to include all that could be gathered before the deadline.
  expected = opts[:max] ||= 1
  @resp_map[token][:expected] = expected
  @resp_map[token][:msgs] = [] if expected > 1

  # Announce the request with the inbox using the token.
  publish(subject, data, inbox)

  # If deadline expires, then discard the token and resume fiber
  opts[:timeout] ||= 0.5
  t = EM.add_timer(opts[:timeout]) do
    if expected > 1
      f.resume @resp_map[token][:msgs]
    else
      f.resume
    end

    @resp_map.delete(token)
  end

  # Wait for the response and cancel timeout callback if received.
  if expected > 1
    # Wait to receive all replies that can get before deadline.
    msgs = Fiber.yield
    EM.cancel_timer(t)

    # Slice and throwaway responses that are not needed.
    return msgs.slice(0, expected)
  else
    msg = Fiber.yield
    EM.cancel_timer(t)
    return msg
  end
end