Two Handlers Are Better Than One

Dispatch has so many handy response handlers—but what if you want to use two with the same request? You can’t do that with a stream of the response body, since this can only be consumed once, but for headers it’s essential and straightforward.

Header Chaining

The recommended header-handling verb >:+ provides a header Map and a request object to chain a second handler for the body.

http(:/("dispatch.databinder.net") >:+ { (headers, req) =>
  headers("content-type").filter {
    _.contains("text/html")
  }.headOption.map { _ =>
    req </> { nodes => (nodes \\ "h1").text }
  }.getOrElse {
    req >> { _ => "unknown content type" }
  }
})

To facilitate case-insensitive handling, the keys in the header Map are uniformly lowercase.

The function passed to >:+ should produce a second handler for the body of the response. In this case, it produces different response handlers depending on the headers present.