core.clj

(ns head.core
  (:require [immutant.web :as web]
            [immutant.web.async :as async])
  (:gen-class))

(defn handler
  [req]
  (async/as-channel req
    :on-open (fn [ch]
               (if (= :head (:request-method req))
                 (async/send! ch "" :on-success (partial async/close ch))
                 (async/send! ch "foo")))))

(defn -main [& args]
  (web/run handler))