Merge pull request karafka#200 from mensfeld/fix-190

fix crash on empty partition key karafka#190

Author: leonmaia

Diff for: lib/rdkafka/bindings.rb

@@ -256,11 +256,11 @@ def self.partitioner(str, partition_count, partitioner_name = "consistent_random
       # Return RD_KAFKA_PARTITION_UA(unassigned partition) when partition count is nil/zero.
       return -1 unless partition_count&.nonzero?
 
-      str_ptr = FFI::MemoryPointer.from_string(str)
+      str_ptr = str.empty? ? FFI::MemoryPointer::NULL : FFI::MemoryPointer.from_string(str)
       method_name = PARTITIONERS.fetch(partitioner_name) do
         raise Rdkafka::Config::ConfigError.new("Unknown partitioner: #{partitioner_name}")
       end
-      public_send(method_name, nil, str_ptr, str.size, partition_count, nil, nil)
+      public_send(method_name, nil, str_ptr, str.size > 0 ? str.size : 1, partition_count, nil, nil)
     end
 
     # Create Topics

Diff for: spec/rdkafka/producer_spec.rb

@@ -251,6 +251,28 @@ def call(_, handle)
     expect(messages[2].key).to eq key
   end
 
+  it "should produce a message with empty string without crashing" do
+    messages = [{key: 'a', partition_key: ''}]
+
+    messages = messages.map do |m|
+      handle = producer.produce(
+        topic:     "partitioner_test_topic",
+        payload:   "payload partition",
+        key:       m[:key],
+        partition_key: m[:partition_key]
+      )
+      report = handle.wait(max_wait_timeout: 5)
+
+      wait_for_message(
+        topic: "partitioner_test_topic",
+        delivery_report: report,
+      )
+    end
+
+    expect(messages[0].partition).to eq 0
+    expect(messages[0].key).to eq 'a'
+  end
+
   it "should produce a message with utf-8 encoding" do
     handle = producer.produce(
       topic:   "produce_test_topic",