Add support for different strategies when generating RPC topics.

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -5,6 +5,8 @@ using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Client;
 using MQTTnet.Exceptions;
+using MQTTnet.Extensions.Rpc.Options;
+using MQTTnet.Extensions.Rpc.Options.TopicGeneration;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.Extensions.Rpc
@@ -13,11 +15,18 @@ namespace MQTTnet.Extensions.Rpc
     {
         private readonly ConcurrentDictionary<string, TaskCompletionSource<byte[]>> _waitingCalls = new ConcurrentDictionary<string, TaskCompletionSource<byte[]>>();
         private readonly IMqttClient _mqttClient;
+        private readonly IMqttRpcClientOptions _options;
         private readonly RpcAwareApplicationMessageReceivedHandler _applicationMessageReceivedHandler;
 
-        public MqttRpcClient(IMqttClient mqttClient)
+        [Obsolete("Use MqttRpcClient(IMqttClient mqttClient, IMqttRpcClientOptions options).")]
+        public MqttRpcClient(IMqttClient mqttClient) : this(mqttClient, new MqttRpcClientOptions())
+        {
+        }
+
+        public MqttRpcClient(IMqttClient mqttClient, IMqttRpcClientOptions options)
         {
             _mqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
+            _options = options ?? throw new ArgumentNullException(nameof(options));
 
             _applicationMessageReceivedHandler = new RpcAwareApplicationMessageReceivedHandler(
                 mqttClient.ApplicationMessageReceivedHandler,
@@ -55,8 +64,26 @@ namespace MQTTnet.Extensions.Rpc
                 throw new InvalidOperationException("The application message received handler was modified.");
             }
 
-            var requestTopic = $"MQTTnet.RPC/{Guid.NewGuid():N}/{methodName}";
-            var responseTopic = requestTopic + "/response";
+            var topicNames = _options.TopicGenerationStrategy.CreateRpcTopics(new TopicGenerationContext
+            {
+                MethodName = methodName,
+                QualityOfServiceLevel = qualityOfServiceLevel,
+                MqttClient = _mqttClient,
+                Options = _options
+            });
+
+            var requestTopic = topicNames.RequestTopic;
+            var responseTopic = topicNames.ResponseTopic;
+
+            if (string.IsNullOrWhiteSpace(requestTopic))
+            {
+                throw new MqttProtocolViolationException("RPC request topic is empty.");
+            }
+
+            if (string.IsNullOrWhiteSpace(responseTopic))
+            {
+                throw new MqttProtocolViolationException("RPC response topic is empty.");
+            }
 
             var requestMessage = new MqttApplicationMessageBuilder()
                 .WithTopic(requestTopic)

Source/MQTTnet.Extensions.Rpc/Options/IMqttRpcClientOptions.cs

@@ -0,0 +1,9 @@
+using MQTTnet.Extensions.Rpc.Options.TopicGeneration;
+
+namespace MQTTnet.Extensions.Rpc.Options
+{
+    public interface IMqttRpcClientOptions
+    {
+        IMqttRpcClientTopicGenerationStrategy TopicGenerationStrategy { get; set; }
+    }
+}

Source/MQTTnet.Extensions.Rpc/Options/MqttRpcClientOptions.cs

@@ -0,0 +1,9 @@
+using MQTTnet.Extensions.Rpc.Options.TopicGeneration;
+
+namespace MQTTnet.Extensions.Rpc.Options
+{
+    public class MqttRpcClientOptions : IMqttRpcClientOptions
+    {
+        public IMqttRpcClientTopicGenerationStrategy TopicGenerationStrategy { get; set; } = new DefaultMqttRpcClientTopicGenerationStrategy();
+    }
+}

Source/MQTTnet.Extensions.Rpc/Options/MqttRpcClientOptionsBuilder.cs

@@ -0,0 +1,25 @@
+using MQTTnet.Extensions.Rpc.Options.TopicGeneration;
+using System;
+
+namespace MQTTnet.Extensions.Rpc.Options
+{
+    public class MqttRpcClientOptionsBuilder
+    {
+        IMqttRpcClientTopicGenerationStrategy _topicGenerationStrategy = new DefaultMqttRpcClientTopicGenerationStrategy();
+
+        public MqttRpcClientOptionsBuilder WithTopicGenerationStrategy(IMqttRpcClientTopicGenerationStrategy value)
+        {
+            _topicGenerationStrategy = value ?? throw new ArgumentNullException(nameof(value));
+
+            return this;
+        }
+
+        public IMqttRpcClientOptions Build()
+        {
+            return new MqttRpcClientOptions
+            {
+                TopicGenerationStrategy = _topicGenerationStrategy
+            };
+        }
+    }
+}

Source/MQTTnet.Extensions.Rpc/Options/MqttRpcTopicPair.cs

@@ -0,0 +1,9 @@
+namespace MQTTnet.Extensions.Rpc.Options
+{
+    public class MqttRpcTopicPair
+    {
+        public string RequestTopic { get; set; }
+
+        public string ResponseTopic { get; set; }
+    }
+}

Source/MQTTnet.Extensions.Rpc/Options/TopicGeneration/DefaultMqttRpcClientTopicGenerationStrategy.cs

@@ -0,0 +1,20 @@
+using MQTTnet.Extensions.Rpc.Options.TopicGeneration;
+using System;
+
+namespace MQTTnet.Extensions.Rpc.Options
+{
+    public class DefaultMqttRpcClientTopicGenerationStrategy : IMqttRpcClientTopicGenerationStrategy
+    {
+        public MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context)
+        {
+            var requestTopic = $"MQTTnet.RPC/{Guid.NewGuid():N}/{context.MethodName}";
+            var responseTopic = requestTopic + "/response";
+
+            return new MqttRpcTopicPair
+            {
+                RequestTopic = requestTopic,
+                ResponseTopic = responseTopic
+            };
+        }
+    }
+}

Source/MQTTnet.Extensions.Rpc/Options/TopicGeneration/IMqttRpcClientTopicGenerationStrategy.cs

@@ -0,0 +1,7 @@
+namespace MQTTnet.Extensions.Rpc.Options.TopicGeneration
+{
+    public interface IMqttRpcClientTopicGenerationStrategy
+    {
+        MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context);
+    }
+}

Source/MQTTnet.Extensions.Rpc/Options/TopicGeneration/TopicGenerationContext.cs

@@ -0,0 +1,16 @@
+using MQTTnet.Client;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Extensions.Rpc.Options.TopicGeneration
+{
+    public class TopicGenerationContext
+    {
+        public string MethodName { get; set; }
+
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; }
+
+        public IMqttClient MqttClient { get; set; }
+
+        public IMqttRpcClientOptions Options { get; set; }
+    }
+}

Tests/MQTTnet.Core.Tests/RPC_Tests.cs

@@ -10,6 +10,8 @@ using MQTTnet.Extensions.Rpc;
 using MQTTnet.Protocol;
 using MQTTnet.Client.Options;
 using MQTTnet.Formatter;
+using MQTTnet.Extensions.Rpc.Options;
+using MQTTnet.Extensions.Rpc.Options.TopicGeneration;
 
 namespace MQTTnet.Tests
 {
@@ -62,7 +64,22 @@ namespace MQTTnet.Tests
                 
                 var requestSender = await testEnvironment.ConnectClientAsync();
 
-                var rpcClient = new MqttRpcClient(requestSender);
+                var rpcClient = new MqttRpcClient(requestSender, new MqttRpcClientOptionsBuilder().Build());
+                await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(2), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
+            }
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
+        public async Task Execute_With_Custom_Topic_Names()
+        {
+            using (var testEnvironment = new TestEnvironment())
+            {
+                await testEnvironment.StartServerAsync();
+
+                var requestSender = await testEnvironment.ConnectClientAsync();
+
+                var rpcClient = new MqttRpcClient(requestSender, new MqttRpcClientOptionsBuilder().WithTopicGenerationStrategy(new TestTopicStrategy()) .Build());
                 await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(2), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
             }
         }
@@ -82,11 +99,23 @@ namespace MQTTnet.Tests
 
                 var requestSender = await testEnvironment.ConnectClientAsync();
 
-                var rpcClient = new MqttRpcClient(requestSender);
+                var rpcClient = new MqttRpcClient(requestSender, new MqttRpcClientOptionsBuilder().Build());
                 var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(5), "ping", "", qosLevel);
 
                 Assert.AreEqual("pong", Encoding.UTF8.GetString(response));
             }
         }
+
+        private class TestTopicStrategy : IMqttRpcClientTopicGenerationStrategy
+        {
+            public MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context)
+            {
+                return new MqttRpcTopicPair
+                {
+                    RequestTopic = "a",
+                    ResponseTopic = "b"
+                };
+            }
+        }
     }
 }