Error Handling¶

TypedBus handles errors predictably at every level.

Subscriber Exceptions¶

If a subscriber block raises, the delivery is auto-NACKed and routed to the DLQ:

bus.subscribe(:orders) do |delivery|
  raise "something broke"
  # delivery is auto-nacked, exception is logged
end

The exception is rescued within the subscriber's Async task. Other subscribers and the channel continue operating normally.

Type Mismatches¶

Publishing a message that doesn't match the channel's type raises ArgumentError at the publish site:

bus.add_channel(:orders, type: Order)

Async do
  bus.publish(:orders, "not an order")
  # => ArgumentError: Expected Order, got String on channel :orders
end

Unknown Channels¶

All MessageBus methods that take a channel name raise ArgumentError for unknown channels:

bus.publish(:nonexistent, "msg")
# => ArgumentError: Unknown channel: nonexistent

bus.subscribe(:nonexistent) { |d| d.ack! }
# => ArgumentError: Unknown channel: nonexistent

remove_channel is the exception — it's a no-op for unknown channels.

Publishing to a Closed Channel¶

bus.close(:orders)
bus.publish(:orders, "msg")
# => RuntimeError: Channel :orders is closed

Subscribing to a Closed Channel¶

bus.close(:orders)
bus.subscribe(:orders) { |d| d.ack! }
# => RuntimeError: Channel :orders is closed

Double Resolution¶

Calling ack! or nack! on an already-resolved delivery raises RuntimeError:

bus.subscribe(:orders) do |delivery|
  delivery.ack!
  delivery.ack!   # => RuntimeError: Delivery already resolved as acked
end

No Subscribers¶

Messages published with no subscribers go directly to the DLQ:

bus.add_channel(:empty)
Async { bus.publish(:empty, "orphan") }

bus.dead_letters(:empty).size  # => 1

Throttle Validation¶

throttle without max_pending raises ArgumentError
throttle outside (0.0, 1.0) raises ArgumentError

TypedBus::Channel.new(:bad, throttle: 0.5, timeout: 5)
# => ArgumentError: throttle requires max_pending on channel :bad