Payload available as a file inside the task, Usually in json format but it's not strictly required. See this helper: https://github.com/iron-io/iron_worker_ruby_ng/blob/master/lib/iron_worker_ng/code/runtime/node.rb#L19
This code in master branch but not yet released, so you could copy contents of the file & use it.
example: https://github.com/thousandsofthem/workers/tree/master/node-0.10