public HeaderFields headers() {
        return headers;
    }
<p>Returns the set of header fields of this Request. These are the meta-data of the Request, and are not applied
to any internal {@link Container} logic. Modifying headers is a thread-unsafe operation -- any changes made after
calling {@link ResponseHandler#handleResponse(Response)} might never become visible to other threads, and might
throw ConcurrentModificationExceptions in other threads.</p>

@return The header fields.
jdisc_core/src/main/java/com/yahoo/jdisc/Response.java