Add random partition strategy

Fixes spreedly#4

lib/kaffe/partition_selector.ex

@@ -20,4 +20,8 @@ defmodule Kaffe.PartitionSelector do
       0
     end
   end
+
+  def random(total) do
+    :crypto.rand_uniform(0, total)
+  end
 end

lib/kaffe/producer.ex

@@ -141,4 +141,8 @@ defmodule Kaffe.Producer do
   defp next_partition(_topic, current_partition, partitions_count, _key, _value, :round_robin) do
     Kaffe.PartitionSelector.round_robin(current_partition, partitions_count)
   end
+
+  defp next_partition(_topic, _current_partition, partitions_count, _key, _value, :random) do
+    Kaffe.PartitionSelector.random(partitions_count)
+  end
 end

test/kaffe/producer_test.exs

@@ -47,30 +47,53 @@ defmodule Kaffe.ProducerTest do
     assert_receive [:produce_sync, "topic2", ^partition, "key", "value"]
   end
 
-  test "producer uses the configured partition selection strategy when it chooses the next partition", c do
-    starting_state = c.producer_state
-    assert starting_state.partition_strategy == :round_robin
+  describe "partition selection" do
+    test "round robin strategy", c do
+      state = c.producer_state
+      state = %{state | partition_strategy: :round_robin}
 
-    {:reply, :ok, new_state} = Producer.handle_call(
-      {:produce_sync, "topic", "key", "value"}, self, starting_state)
-    assert_receive [:produce_sync, "topic", 0, "key", "value"]
+      {:reply, :ok, new_state} = Producer.handle_call(
+        {:produce_sync, "topic", "key", "value"}, self, state)
+      assert_receive [:produce_sync, "topic", 0, "key", "value"]
 
-    {:reply, :ok, new_state} = Producer.handle_call(
-      {:produce_sync, "topic", "key", "value"}, self, new_state)
-    assert_receive [:produce_sync, "topic", 1, "key", "value"]
+      {:reply, :ok, new_state} = Producer.handle_call(
+        {:produce_sync, "topic", "key", "value"}, self, new_state)
+      assert_receive [:produce_sync, "topic", 1, "key", "value"]
 
-    Producer.handle_call(
-      {:produce_sync, "topic", "key", "value"}, self, new_state)
-    assert_receive [:produce_sync, "topic", 2, "key", "value"]
-  end
+      {:reply, :ok, _new_state} = Producer.handle_call(
+        {:produce_sync, "topic", "key", "value"}, self, new_state)
+      assert_receive [:produce_sync, "topic", 2, "key", "value"]
+    end
 
-  test "producer does not use the partition selection strategy when given direct partition", c do
-    {:reply, :ok, new_state} = Producer.handle_call(
-     {:produce_sync, "topic", 0, "key", "value"}, self, c.producer_state)
-    assert_receive [:produce_sync, "topic", 0, "key", "value"]
+    test "random partition strategy", c do
+      state = c.producer_state
+      state = %{state | partition_strategy: :random}
 
-    Producer.handle_call(
-      {:produce_sync, "topic", 0, "key", "value"}, self, new_state)
-    assert_receive [:produce_sync, "topic", 0, "key", "value"]
+      {:reply, :ok, new_state} = Producer.handle_call(
+        {:produce_sync, "topic", "key", "value"}, self, state)
+      assert_receive [:produce_sync, "topic", 0, "key", "value"]
+
+      {:reply, :ok, new_state} = Producer.handle_call(
+        {:produce_sync, "topic", "key", "value"}, self, new_state)
+      assert_receive [:produce_sync, "topic", random_partition, "key", "value"]
+
+      assert (0 <= random_partition) && (random_partition <= 19)
+
+      {:reply, :ok, _new_state} = Producer.handle_call(
+        {:produce_sync, "topic", "key", "value"}, self, new_state)
+      assert_receive [:produce_sync, "topic", random_partition, "key", "value"]
+
+      assert (0 <= random_partition) && (random_partition <= 19)
+    end
+
+    test "producer does not use a selection strategy when given a direct partition", c do
+      {:reply, :ok, new_state} = Producer.handle_call(
+       {:produce_sync, "topic", 0, "key", "value"}, self, c.producer_state)
+      assert_receive [:produce_sync, "topic", 0, "key", "value"]
+
+      Producer.handle_call(
+        {:produce_sync, "topic", 0, "key", "value"}, self, new_state)
+      assert_receive [:produce_sync, "topic", 0, "key", "value"]
+    end
   end
 end