Consumer: wait for messages by default

Prior to this change min_bytes was 0 by default which causes the fetch
command to unexpectedly return regardless of the max_wait_ms setting.

Also, fixed options for PartitionConsumer#fetch to expect max_wait_ms
and not max_wait.

lib/poseidon/partition_consumer.rb

@@ -48,11 +48,14 @@ def self.consumer_for_partition(client_id, seed_brokers, topic, partition, offse
     #
     # @option options [:max_bytes] Maximum number of bytes to fetch
     #   Default: 1048576 (1MB)
+    #
     # @option options [:max_wait_ms] 
     #   How long to block until the server sends us data.
+    #   NOTE: This is only enforced if min_bytes is > 0.
     #   Default: 100 (100ms)
+    #
     # @option options [:min_bytes] Smallest amount of data the server should send us.
-    #   Default: 0 (Send us data as soon as it is ready)
+    #   Default: 1 (Send us data as soon as it is ready)
     #
     # @api public
     def initialize(client_id, host, port, topic, partition, offset, options = {})
@@ -75,14 +78,16 @@ def initialize(client_id, host, port, topic, partition, offset, options = {})
     #
     # @option options [:max_bytes]
     #   Maximum number of bytes to fetch
+    #
     # @option options [:max_wait_ms]
     #   How long to block until the server sends us data.
+    #
     # @option options [:min_bytes] 
     #   Smallest amount of data the server should send us.
     #
     # @api public
     def fetch(options = {})
-      fetch_max_wait = options.delete(:max_wait) || max_wait_ms
+      fetch_max_wait = options.delete(:max_wait_ms) || max_wait_ms
       fetch_max_bytes = options.delete(:max_bytes) || max_bytes
       fetch_min_bytes = options.delete(:min_bytes) || min_bytes
 
@@ -96,7 +101,8 @@ def fetch(options = {})
       partition_response = topic_response.partition_fetch_responses.first
 
       unless partition_response.error == Errors::NO_ERROR_CODE
-        if @offset < 0 && Errors::ERROR_CODES[partition_response.error] == Errors::OffsetOutOfRange
+        if @offset < 0 &&
+          Errors::ERROR_CODES[partition_response.error] == Errors::OffsetOutOfRange
           @offset = :earliest_offset
           return fetch(options)
         end
@@ -125,7 +131,7 @@ def next_offset
     private
     def handle_options(options)
       @max_bytes    = options.delete(:max_bytes) || 1024*1024
-      @min_bytes    = options.delete(:min_bytes) || 0
+      @min_bytes    = options.delete(:min_bytes) || 1
       @max_wait_ms  = options.delete(:max_wait_ms) || 10_000
       if options.keys.any?
         raise ArgumentError, "Unknown options: #{options.keys.inspect}"

spec/integration/simple/simple_producer_and_consumer_spec.rb

@@ -54,6 +54,23 @@
       expect(messages.empty?).to eq(true)
     end
 
+    it "waits for messages" do
+      # Create topic
+      @c = Connection.new("localhost", 9092, "metadata_fetcher")
+      @c.topic_metadata(["simple_wait_test"])
+
+      sleep 5
+      @consumer = PartitionConsumer.new("test_consumer", "localhost", 9092,
+                                        "simple_wait_test", 0, :earliest_offset,
+                                        :max_wait_ms => 2500)
+
+      require 'benchmark'
+      n = Benchmark.realtime do
+        @consumer.fetch
+      end
+      expect(n).to be_within(0.25).of(2.5)
+    end
+
     # Not sure what's going on here, will revisit.
 =begin
     it "fetches larger messages with a larger max bytes size" do

spec/unit/partition_consumer_spec.rb

@@ -14,13 +14,13 @@
   describe "creation" do
     context "when passed unknown options" do
       it "raises an ArgumentError" do
-        expect { PartitionConsumer.new("test_client", "localhost", 9092, "test_topic", 0,:earliest_offset, :unknown => true) }.to raise_error(ArgumentError)
+        expect { PartitionConsumer.new("test_client", "localhost", 9092, "test_topic", 0, :earliest_offset, :unknown => true) }.to raise_error(ArgumentError)
       end
     end
 
     context "when passed an unknown offset" do
       it "raises an ArgumentError" do
-        expect { PartitionConsumer.new("test_client", "localhost", 9092, "test_topic", 0,:coolest_offset) }.to raise_error(ArgumentError)
+        expect { PartitionConsumer.new("test_client", "localhost", 9092, "test_topic", 0, :coolest_offset) }.to raise_error(ArgumentError)
       end
     end
   end
@@ -97,13 +97,13 @@
     end
 
     it "uses object defaults" do
-      @connection.should_receive(:fetch).with(10_000, 0, anything)
+      @connection.should_receive(:fetch).with(10_000, 1, anything)
       @pc.fetch
     end
 
     context "when options are passed" do
       it "overrides object defaults" do
-        @connection.should_receive(:fetch).with(20_000, 0, anything)
+        @connection.should_receive(:fetch).with(20_000, 1, anything)
         @pc = PartitionConsumer.new("test_client", "localhost", 9092, "test_topic", 0, :earliest_offset, :max_wait_ms => 20_000)
 
         @pc.fetch