Server accepts a list of ports to try

project.clj

@@ -1,5 +1,6 @@
 (defproject ring-server "0.1.0"
   :description "Library for running Ring web servers"
   :dependencies [[org.clojure/clojure "1.2.1"]
+                 [org.clojure/core.incubator "0.1.0"]
                  [ring "1.0.1"]]
   :dev-dependencies [[clj-http "0.3.1"]])

src/ring/server/options.clj

@@ -0,0 +1,12 @@
+(ns ring.server.options
+  "Functions to retrieve options and settings with sensible defaults"
+  (:use [ring.util.environment :only (*env*)]
+        [clojure.core.incubator :only (-?>)]))
+
+(defn port
+  "Find the port or list of ports specified in the options or environment.
+  Defaults to a range of ports from 3000 to 3010."
+  [options]
+  (or (:port options)
+      (-?> (*env* "PORT") Integer.)
+      (range 3000 3010)))

src/ring/server/standalone.clj

@@ -1,12 +1,20 @@
 (ns ring.server.standalone
   "Functions to start a standalone Ring server."
   (:use ring.adapter.jetty
-        ring.util.environment))
+        ring.server.options))
+
+(defn- try-port [port run-server]
+  (if-not (sequential? port)
+    (run-server port)
+    (try (run-server (first port))
+         (catch Exception _
+           (try-port (next port) run-server)))))
 
 (defn serve
   "Start a web server to run a handler."
   [handler & [{:as options}]]
-  (let [port (Integer. (*env* "PORT" "5000"))]
-    (run-jetty
-      handler
-      (merge {:port port} options))))
+  (try-port (port options)
+    (fn [port]
+      (run-jetty
+        handler
+        (merge {:port port} options)))))

test/ring/server/test/standalone.clj

@@ -11,10 +11,28 @@
        ~@body
        (finally (.stop server#)))))
 
+(defn test-server [& [{:as options}]]
+  (let [handler (constantly (response "Hello World"))]
+    (serve handler (merge {:join? false} options))))
+
+(defn is-server-running-on-port [port] 
+  (let [resp (http/get (str "http://localhost:" port)
+                       {:conn-timeout 1000})]
+    (is (= (:status resp) 200))))
+
 (deftest serve-test
-  (with-env {"PORT" "4563"}
-    (let [handler (constantly (response "Hello World"))]
-      (with-server (serve handler {:join? false})
-        (let [resp (http/get "http://localhost:4563")]
-          (is (= (:status resp) 200))
-          (is (= (:body resp) "Hello World")))))))
+  (testing "default port"
+    (with-server (test-server)
+      (is-server-running-on-port 3000)))
+  (testing "fallback default ports"
+    (with-server (test-server)
+      (with-server (test-server)
+        (is-server-running-on-port 3000)
+        (is-server-running-on-port 3001))))
+  (testing "PORT environment variable"
+    (with-env {"PORT" "4563"}
+      (with-server (test-server) 
+        (is-server-running-on-port 4563))))
+  (testing ":port option"
+    (with-server (test-server {:port 5463})
+      (is-server-running-on-port 5463))))