add kafka extend project.

src/Cap.Consistency.Kafka/Cap.Consistency.Kafka.csproj

+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard1.6</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Confluent.Kafka" Version="0.9.5" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Cap.Consistency\Cap.Consistency.csproj" />
+  </ItemGroup>
+
+</Project>
\ No newline at end of file

src/Cap.Consistency.Kafka/KafkaConsumerClient.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Cap.Consistency.Consumer;
+using Cap.Consistency.Infrastructure;
+using Confluent.Kafka;
+using Confluent.Kafka.Serialization;
+
+namespace Cap.Consistency.Kafka
+{
+    public class KafkaTopicPartition
+    {
+        public string Topic { get; set; }
+
+        public int Partition { get; set; }
+    }
+
+    public class KafkaConsumerClient : IConsumerClient, IDisposable
+    {
+
+        private readonly string _groupId;
+        private readonly string _bootstrapServers;
+
+        private Consumer<Null, string> _consumerClient;
+
+        public event EventHandler<DeliverMessage> MessageReceieved;
+
+        public IDeserializer<string> StringDeserializer { get; set; }
+
+        public KafkaConsumerClient(string groupId, string bootstrapServers) {
+            _groupId = groupId;
+            _bootstrapServers = bootstrapServers;
+
+            StringDeserializer = new StringDeserializer(Encoding.UTF8);
+        }
+
+        public void Subscribe(string topic) {
+            Subscribe(topic, 0);
+        }
+
+        public void Subscribe(string topicName, int partition) {
+
+            if (_consumerClient == null) {
+                InitKafkaClient();
+            }
+            _consumerClient.Assignment.Add(new TopicPartition(topicName, partition));
+        }
+
+        public void Subscribe(IEnumerable<KafkaTopicPartition> topicList) {
+
+            if (_consumerClient == null) {
+                InitKafkaClient();
+            }
+
+            if (topicList == null || topicList.Count() == 0) {
+                throw new ArgumentNullException(nameof(topicList));
+            }
+
+            foreach (var item in topicList) {
+                Subscribe(item.Topic, item.Partition);
+            }
+        }
+
+
+        public void Listening(TimeSpan timeout) {
+            while (true) {
+                _consumerClient.Poll(timeout);
+            }
+        }
+
+        public void Dispose() {
+            _consumerClient.Dispose();
+        }
+
+        #region private methods
+
+        private void InitKafkaClient() {
+            var config = new Dictionary<string, object>{
+                { "group.id", _groupId },
+                { "bootstrap.servers", _bootstrapServers }
+            };
+
+            _consumerClient = new Consumer<Null, string>(config, null, StringDeserializer);
+            _consumerClient.OnMessage += ConsumerClient_OnMessage;
+        }
+
+        private void ConsumerClient_OnMessage(object sender, Message<Null, string> e) {
+            var message = new DeliverMessage {
+                MessageKey = e.Topic,
+                Value = e.Value
+            };
+            MessageReceieved?.Invoke(sender, message);
+        }
+    
+        #endregion
+
+        //public void 
+
+    }
+}

src/Cap.Consistency.Kafka/KafkaConsumerClientFactory.cs

+using System;
+using System.Collections.Generic;
+using System.Text;
+using Cap.Consistency.Consumer;
+
+namespace Cap.Consistency.Kafka
+{
+    public class KafkaConsumerClientFactory : IConsumerClientFactory
+    {
+        public IConsumerClient Create(string groupId, string clientHostAddress) {
+            return new KafkaConsumerClient(groupId, clientHostAddress);
+        }
+    }
+}

src/Cap.Consistency.Kafka/KafkaTopicAttribute.cs

+using System;
+using System.Collections.Generic;
+using System.Text;
+using Cap.Consistency.Abstractions;
+
+namespace Cap.Consistency.Kafka
+{
+    public class KafkaTopicAttribute : TopicAttribute
+    {
+        public KafkaTopicAttribute(string topicName) 
+            : this(topicName, 0) { }
+
+        public KafkaTopicAttribute(string topicName, int partition)
+            : this(topicName, partition, 0) { }
+
+        public KafkaTopicAttribute(string topicName, int partition, long offset)
+            : base(topicName) {
+            Offset = offset;
+            Partition = partition;
+        }
+
+        public int Partition { get; }
+
+        public long Offset { get; }
+
+        public bool IsPartition { get { return Partition == 0; } }
+
+        public bool IsOffset { get { return Offset == 0; } }
+
+        public override string ToString() {
+            return Name;
+        }
+    }
+}