url*           (url)       AMQP server endpoint e.g. `amqp://myuser:mypassword@localhost:5672`
exchange       (string)    name of the AMQP exchange
exchange_type  (string)    AMQP exchange type
routing_key    (string)    routing key for publishing
mandatory      (on|off)    quietly ignore undelivered messages when set to 'off', default is 'on'
durable        (on|off)    persist queue across broker restarts when set to 'on', default is 'off'

         * pending, so its `state` field hasn't been nulled out yet.
         *
         * OK, it's technically possible for this to fail in the presence of unsafe publishing, as
         * discussed in the comments in TimeoutFuture. TODO(cpovirk): Maybe check for null before
         * calling recordOutputCancellation?
         */