Multiple async HTTP requests by using http.async.client callback API

gistfile1.clj

;; (defproject async-test2 "0.1.0-SNAPSHOT"
;;   :description "FIXME: write description"
;;   :url "http://example.com/FIXME"
;;   :license {:name "Eclipse Public License"
;;             :url "http://www.eclipse.org/legal/epl-v10.html"}
;;   :dependencies [[org.clojure/clojure "1.4.0"]
;;                  [http.async.client "0.4.5"]])


(ns async-test2.core
  (:require [http.async.client :as client]
            [http.async.client.request :refer (prepare-request execute-request)]))

(defn gen-url [keyword]
  (format "http://www.google.com/search?q=%s" keyword))

(def urls (concat (map gen-url ["Clojure" "Haskell" "OCaml" "Scala" "F#"])
                  ["http://localhost:3000/"]
                  (map gen-url ["Ruby" "Python" "Perl" "PHP" "JavaScript"])))

(defn async-fetch [cl urls]
  (let [start (System/nanoTime)]
    (doall
      (for [[url i] (map vector urls (drop 1 (range)))]
        (execute-request cl (prepare-request :get url)
          :completed (fn [response]
                       (println (format "%8.3f: %2d: %s => %d"
                                        (/ (- (System/nanoTime) start) 1000000.0)
                                        i url (:code @(:status response)))))
          :error (fn [response exception]
                   (println "Error: " exception)))))))

(defn -main [& args]
  (with-open [cl (client/create-client)]
    (let [responses (async-fetch cl urls)]
      (doseq [response responses] (client/await response))))
  (println "Finish.")
  (System/exit 0))


;; To check async process, prepare a long time request:
;; $ plackup -p 3000 -e 'sub { sleep 5; return [200, ["Content-Type" => "text/plain"], ["Hello World."]] }'
;;
;; $ lein run -m async-test2.core
;; SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
;; SLF4J: Defaulting to no-operation (NOP) logger implementation
;; SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
;;  422.961:  5: http://www.google.com/search?q=F# => 200
;;  444.097: 11: http://www.google.com/search?q=JavaScript => 200
;;  516.303:  7: http://www.google.com/search?q=Ruby => 200
;;  526.895:  2: http://www.google.com/search?q=Haskell => 200
;;  544.540:  9: http://www.google.com/search?q=Perl => 200
;;  546.011:  1: http://www.google.com/search?q=Clojure => 200
;;  547.384:  3: http://www.google.com/search?q=OCaml => 200
;;  577.401: 10: http://www.google.com/search?q=PHP => 200
;;  583.873:  4: http://www.google.com/search?q=Scala => 200
;;  602.113:  8: http://www.google.com/search?q=Python => 200
;; 5229.313:  6: http://localhost:3000/ => 200
;; Finish.