add broker-list to help build metadata.broker.list strings; change clj-kafka.zk/brokers to return an empty list if zookeeper is available but no kafka brokers are registered.

project.clj

@@ -1,4 +1,4 @@
-(defproject clj-kafka/clj-kafka "0.2.0-0.8"
+(defproject clj-kafka/clj-kafka "0.2.1-0.8"
   :min-lein-version "2.0.0"
   :dependencies [[org.clojure/clojure "1.5.1"]
                  [zookeeper-clj "0.9.3"]

src/clj_kafka/zk.clj

@@ -1,19 +1,29 @@
 (ns clj-kafka.zk
   (:use [clojure.data.json :only (read-str)]
         [clj-kafka.core :only (with-resource)])
-  (:require [zookeeper :as zk]))
+  (:require [zookeeper :as zk]
+            [clojure.string :as s]))
 
 (defn brokers
   "Get brokers from zookeeper"
   [m]
   (with-resource [z (zk/connect (get m "zookeeper.connect"))]
     zk/close
-    (doall (map (comp #(read-str % :key-fn keyword)
-                      #(String. ^bytes %)
-                      :data
-                      #(zk/data z (str "/brokers/ids/" %)))
-                (zk/children z "/brokers/ids")))))
-                
+    (if-let [broker-ids (zk/children z "/brokers/ids")]
+      (doall (map (comp #(read-str % :key-fn keyword)
+                        #(String. ^bytes %)
+                        :data
+                        #(zk/data z (str "/brokers/ids/" %)))
+                  broker-ids))
+      '())))
+
+(defn broker-list
+  "Returns a comma separated list of Kafka brokers, as returned from clj-kafka.zk/brokers.
+   e.g.: (broker-list (brokers {\"zookeeper.connect\" \"127.0.0.1:2181\"})) "
+  [brokers]
+  (when (seq brokers)
+    (s/join "," (map (fn [{:keys [host port]}] (str host ":" port)) brokers))))
+
 (defn- controller-broker-id
   [^String zk-data]
   (get (read-str zk-data) "brokerid"))

test/clj_kafka/test/zk.clj

@@ -12,6 +12,9 @@
          (brokers zk-connect))
        (expect count 1))
 
+(expect nil (broker-list []))
+(expect "localhost:2181" (broker-list [{:host "localhost" :port "2181"}]))
+
 (given (with-test-broker config
          (first (brokers zk-connect)))
        (expect :host "localhost"