==== Setting headers on messages

Messages sent over the event bus can also contain _headers_.

This can be specified by setting options when sending or
publishing:

[source,groovy]
----
def options = [
  headers: [
   "some-header" : "some-value"
  ]
]
vertx.eventBus().send("news.uk.sport", "Yay! Someone kicked a ball", options);
----

On the other side, a consumer can retrieve the headers as follows:

[source,groovy]
----
vertx.eventBus().consumer("news.uk.sport",  { e ->
 println e.headers()["some-header"];
});
----