http/agent.clj: experimental agent-based HTTP client

src/clojure/contrib/http/agent.clj

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+;;; http/agent.clj: agent-based asynchronous HTTP client
+
+;; by Stuart Sierra, http://stuartsierra.com/
+;; June 8, 2009
+
+;; Copyright (c) Stuart Sierra, 2009. All rights reserved.  The use
+;; and distribution terms for this software are covered by the Eclipse
+;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
+;; which can be found in the file epl-v10.html at the root of this
+;; distribution.  By using this software in any fashion, you are
+;; agreeing to be bound by the terms of this license.  You must not
+;; remove this notice, or any other, from this software.
+
+
+(ns #^{:doc "Agent-based asynchronous HTTP client."}
+  clojure.contrib.http.agent
+  (:require [clojure.contrib.http.connection :as c]
+            [clojure.contrib.duck-streams :as duck]))
+
+(defn- setup-http-connection
+  [conn options]
+  (.setRequestMethod conn (:method options))
+  (.setInstanceFollowRedirects (:follow-redirects options))
+  (doseq [[name value] (:headers options)]
+    (.setRequestProperty conn name value)))
+
+(defn- success? [conn]
+  ;; Is the response in the 2xx range?
+  (= 2 (unchecked-divide (.getResponseCode conn)) 100))
+
+(defn- do-http-agent-request [state options]
+  (let [conn (::connection state)]
+    (setup-http-connection conn options)
+    (c/start-http-connection conn (:body options))
+    (let [bytes (if (success? conn)
+                  (duck/to-byte-array (.getInputStream conn))
+                  (duck/to-byte-array (.getErrorStream conn)))]
+      (.disconnect conn)
+      (assoc state
+        ::response-body-bytes bytes
+        ::state ::completed))))
+
+(def *http-request-defaults*
+  {:method "GET"
+   :headers {}
+   :body nil
+   :connect-timeout 0
+   :read-timeout 0
+   :follow-redirects true})
+
+(defn http-agent
+  "Creates (and immediately returns) an Agent representing an HTTP
+  request running in a new thread.
+
+  options are key/value pairs:
+
+  :method string
+
+  The HTTP method name.  Default is \"GET\".
+
+  :headers h
+
+  HTTP headers, as a Map or a sequence of pairs like 
+  ([key1,value1], [key2,value2])  Default is nil.
+
+  :body b
+  
+  HTTP request entity body, one of nil, String, byte[], InputStream,
+  Reader, or File.  Default is nil.
+
+  :connect-timeout int
+
+  Timeout value, in milliseconds, when opening a connection to the
+  URL.  Default is zero, meaning no timeout.
+
+  :read-timeout int
+
+  Timeout value, in milliseconds, when reading data from the
+  connection.  Default is zero, meaning no timeout.
+
+  :follow-redirects boolean
+
+  If true, HTTP 3xx redirects will be followed automatically.  Default
+  is true.
+  "
+  ([url & options]
+     (let [opts (merge *http-request-defaults* (apply array-map options))]
+       (let [a (agent {::connection (c/http-connection url)
+                       ::state ::created})]
+         (send-off a do-http-agent-request opts)))))
+
+(defn response-body-bytes [a]
+  (when (= (::state @a) ::completed)
+    (::response-body-bytes @a)))
+
+(defn response-body-str [a]
+  (let [da @a]
+    (when (= (::state da) ::completed)
+      (let [conn (::connection da)
+            bytes (::response-body-bytes da)
+            encoding (or (.getContentEncoding conn)
+                         duck/*default-encoding*)]
+        (String. bytes encoding)))))
+
+(defn response-status [a]
+  (.getResponseCode (::connection @a)))
+
+(defn response-message [a]
+  (.getResponseMessage (::connection @a)))
+
+(defn response-headers [a]
+  (.getHeaderFields (::connection @a)))
+
+(defn response-headers-seq
+  "Returns the HTTP response headers in order as a sequence of
+  [String,String] pairs.  The first 'header' name may be null for the
+  HTTP status line."
+  [http-agnt]
+  (let [conn (::connection @http-agnt)
+        f (fn thisfn [i]
+            ;; Get value first because first key may be nil.
+            (when-let [value (.getHeaderField conn i)]
+              (cons [(.getHeaderFieldKey conn i) value]
+                    (thisfn (inc i)))))]
+    (lazy-seq (f 0))))