Add partitioner callback to topic configuration

src/topic_configuration.cpp

@@ -1,11 +1,30 @@
 #include "topic_configuration.h"
 #include <librdkafka/rdkafka.h>
 #include "exceptions.h"
+#include "topic.h"
+#include "buffer.h"
 
 using std::string;
 
 namespace cppkafka {
 
+int32_t partitioner_callback_proxy(const rd_kafka_topic_t* handle, const void *key_ptr,
+                                   size_t key_size, int32_t partition_count,
+                                   void* topic_opaque, void* message_opaque) {
+    const TopicConfiguration* config = static_cast<TopicConfiguration*>(topic_opaque);
+    const auto& callback = config->get_partitioner_callback();
+    if (callback) {
+        Topic topic = Topic::make_non_owning(const_cast<rd_kafka_topic_t*>(handle));
+        Buffer key(static_cast<const char*>(key_ptr), key_size);
+        return callback(topic, key, partition_count);
+    }
+    else {
+        return rd_kafka_msg_partitioner_consistent_random(handle, key_ptr, key_size, 
+                                                          partition_count, topic_opaque,
+                                                          message_opaque);
+    }
+}
+
 TopicConfiguration::TopicConfiguration() 
 : handle_(make_handle(rd_kafka_topic_conf_new())) {
 
@@ -26,6 +45,20 @@ void TopicConfiguration::set(const string& name, const string& value) {
     }
 }
 
+void TopicConfiguration::set_partitioner_callback(PartitionerCallback callback) {
+    partitioner_callback_ = move(callback);
+    rd_kafka_topic_conf_set_partitioner_cb(handle_.get(), &partitioner_callback_proxy);
+}
+
+void TopicConfiguration::set_as_opaque() {
+    rd_kafka_topic_conf_set_opaque(handle_.get(), this);
+}
+
+const TopicConfiguration::PartitionerCallback&
+TopicConfiguration::get_partitioner_callback() const {
+    return partitioner_callback_;
+}
+
 rd_kafka_topic_conf_t* TopicConfiguration::get_handle() const {
     return handle_.get();
 }