Can a CoAP LUA plugin access header information? (i.e., "Request In:")

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We have modified a CoAP LUA plugin so it can parse our custom payloads. But, to know what the payload is in response to, we need to be able to figure out where the GET request was so we can look at the URI options. The standard "coap" filter does show "[Request In: xxxx]" and "[Response In: xxxx]" and I wondered if there was a way to access this via LUA.

Thanks!