added confluent cloud example (#503)

* added confluent cloud example

* review comments

Author: mhowlett

README.md

@@ -151,6 +151,11 @@ or with specific classes generated using the `avrogen` tool
 dotnet /path/to/avrogen.dll -s your_schema.asvc .
 ```
 
+### Confluent Cloud
+
+The [Confluent Cloud example](examples/ConfluentCloud) demonstrates how to configure the .NET client for use with [Confluent Cloud](https://www.confluent.io/confluent-cloud/).
+
+
 ## Build
 
 To build the library or any test or example project, run the following from within the relevant project directory:

examples/ConfluentCloud/ConfluentCloud.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Confluent.Kafka" Version="0.11.4" />
+  </ItemGroup>
+
+</Project>

examples/ConfluentCloud/Program.cs

@@ -0,0 +1,117 @@
+// Copyright 2018 Confluent Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Refer to LICENSE for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Confluent.Kafka;
+using Confluent.Kafka.Serialization;
+
+
+namespace ConfluentCloudExample
+{
+    /// <summary>
+    ///     This is a simple example demonstrating how to produce a message to 
+    ///     Confluent Cloud then read it back again.
+    ///     
+    ///     https://www.confluent.io/confluent-cloud/
+    /// 
+    ///     Confluent Cloud does not auto-create topics. You will need to use the ccloud 
+    ///     cli to create the dotnet-test-topic topic before running this example. The 
+    ///     <ccloud bootstrap servers>, <ccloud key> and <ccloud secret> parameters are
+    ///     available via the confluent cloud web interface. For more information,
+    ///     refer to the quick-start:
+    ///     
+    ///     https://docs.confluent.io/current/cloud-quickstart.html
+    /// </summary>
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            var pConfig = new Dictionary<string, object>
+            {
+                { "bootstrap.servers", "<ccloud bootstrap servers>" },
+                { "broker.version.fallback", "0.10.0.0" },
+                { "api.version.fallback.ms", 0 },
+                { "sasl.mechanisms", "PLAIN" },
+                { "security.protocol", "SASL_SSL" },
+                // On Windows, default trusted root CA certificates are stored in the Windows Registry. 
+                // They are not automatically discovered by Confluent.Kafka and it's not possible to 
+                // reference them using the `ssl.ca.location` property. You will need to obtain these 
+                // from somewhere else, for example use the cacert.pem file distributed with curl:
+                // https://curl.haxx.se/ca/cacert.pem and reference that file in the `ssl.ca.location`
+                // property:
+                { "ssl.ca.location", "/usr/local/etc/openssl/cert.pem" }, // suitable configuration for linux, osx.
+                // { "ssl.ca.location", "c:\\path\\to\\cacert.pem" },     // windows
+                { "sasl.username", "<ccloud key>" },
+                { "sasl.password", "<ccloud secret>" }
+            };
+
+            using (var producer = new Producer<Null, string>(pConfig, null, new StringSerializer(Encoding.UTF8)))
+            {
+                producer.ProduceAsync("dotnet-test-topic", null, "test value")
+                    .ContinueWith(result => 
+                        {
+                            var msg = result.Result;
+                            if (msg.Error.Code != ErrorCode.NoError)
+                            {
+                                Console.WriteLine($"failed to deliver message: {msg.Error.Reason}");
+                            }
+                            else 
+                            {
+                                Console.WriteLine($"delivered to: {result.Result.TopicPartitionOffset}");
+                            }
+                        });
+
+                producer.Flush(TimeSpan.FromSeconds(10));
+            }
+
+            var cConfig = new Dictionary<string, object>
+            {
+                { "bootstrap.servers", "<confluent cloud bootstrap servers>" },
+                { "broker.version.fallback", "0.10.0.0" },
+                { "api.version.fallback.ms", 0 },
+                { "sasl.mechanisms", "PLAIN" },
+                { "security.protocol", "SASL_SSL" },
+                { "ssl.ca.location", "/usr/local/etc/openssl/cert.pem" }, // suitable configuration for linux, osx.
+                // { "ssl.ca.location", "c:\\path\\to\\cacert.pem" },     // windows
+                { "sasl.username", "<confluent cloud key>" },
+                { "sasl.password", "<confluent cloud secret>" },
+                { "group.id", Guid.NewGuid().ToString() },
+                { "auto.offset.reset", "smallest" }
+            };
+
+            using (var consumer = new Consumer<Null, string>(cConfig, null, new StringDeserializer(Encoding.UTF8)))
+            { 
+                consumer.Subscribe("dotnet-test-topic");
+
+                consumer.OnConsumeError += (_, err)
+                    => Console.WriteLine($"consume error: {err.Error.Reason}");
+
+                consumer.OnMessage += (_, msg)
+                    => Console.WriteLine($"consumed: {msg.Value}");
+
+                consumer.OnPartitionEOF += (_, tpo)
+                    => Console.WriteLine($"end of partition: {tpo}");
+
+                while (true)
+                {
+                    consumer.Poll(TimeSpan.FromMilliseconds(100));
+                }  
+            }
+        }
+    }
+}