Add new extension methods.

Frameworks/MQTTnet.NetStandard/ApplicationMessagePublisherExtensions.cs

@@ -1,16 +1,41 @@
 using System;
 using System.Threading.Tasks;
+using MQTTnet.Protocol;
 
 namespace MQTTnet
 {
     public static class ApplicationMessagePublisherExtensions
     {
-        public static Task PublishAsync(this IApplicationMessagePublisher client, params MqttApplicationMessage[] applicationMessages)
+        public static Task PublishAsync(this IApplicationMessagePublisher publisher, params MqttApplicationMessage[] applicationMessages)
         {
-            if (client == null) throw new ArgumentNullException(nameof(client));
+            if (publisher == null) throw new ArgumentNullException(nameof(publisher));
             if (applicationMessages == null) throw new ArgumentNullException(nameof(applicationMessages));
 
-            return client.PublishAsync(applicationMessages);
+            return publisher.PublishAsync(applicationMessages);
+        }
+
+        public static Task PublishAsync(this IApplicationMessagePublisher publisher, string topic)
+        {
+            if (publisher == null) throw new ArgumentNullException(nameof(publisher));
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+            
+            return publisher.PublishAsync(new MqttApplicationMessageBuilder().WithTopic(topic).Build());
+        }
+
+        public static Task PublishAsync(this IApplicationMessagePublisher publisher, string topic, string payload)
+        {
+            if (publisher == null) throw new ArgumentNullException(nameof(publisher));
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+
+            return publisher.PublishAsync(new MqttApplicationMessageBuilder().WithTopic(topic).WithPayload(payload).Build());
+        }
+
+        public static Task PublishAsync(this IApplicationMessagePublisher publisher, string topic, string payload, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        {
+            if (publisher == null) throw new ArgumentNullException(nameof(publisher));
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+
+            return publisher.PublishAsync(new MqttApplicationMessageBuilder().WithTopic(topic).WithPayload(payload).WithQualityOfServiceLevel(qualityOfServiceLevel).Build());
         }
     }
 }

Frameworks/MQTTnet.NetStandard/Client/MqttClientExtensions.cs

@@ -24,6 +24,14 @@ namespace MQTTnet.Client
             return client.SubscribeAsync(new TopicFilterBuilder().WithTopic(topic).WithQualityOfServiceLevel(qualityOfServiceLevel).Build());
         }
 
+        public static Task<IList<MqttSubscribeResult>> SubscribeAsync(this IMqttClient client, string topic)
+        {
+            if (client == null) throw new ArgumentNullException(nameof(client));
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+
+            return client.SubscribeAsync(new TopicFilterBuilder().WithTopic(topic).Build());
+        }
+
         public static Task UnsubscribeAsync(this IMqttClient client, params string[] topicFilters)
         {
             if (client == null) throw new ArgumentNullException(nameof(client));

Frameworks/MQTTnet.NetStandard/ManagedClient/ManagedMqttClientOptionsBuilder.cs

@@ -6,6 +6,7 @@ namespace MQTTnet.ManagedClient
     public class ManagedMqttClientOptionsBuilder
     {
         private readonly ManagedMqttClientOptions _options = new ManagedMqttClientOptions();
+        private MqttClientOptionsBuilder _clientOptionsBuilder;
 
         public ManagedMqttClientOptionsBuilder WithAutoReconnectDelay(TimeSpan value)
         {
@@ -21,7 +22,24 @@ namespace MQTTnet.ManagedClient
 
         public ManagedMqttClientOptionsBuilder WithClientOptions(IMqttClientOptions value)
         {
+            if (_clientOptionsBuilder != null)
+            {
+                throw new InvalidOperationException("Cannot use client options builder and client options at the same time.");
+            }
+
             _options.ClientOptions = value ?? throw new ArgumentNullException(nameof(value));
+
+            return this;
+        }
+
+        public ManagedMqttClientOptionsBuilder WithClientOptions(MqttClientOptionsBuilder builder)
+        {
+            if (_options.ClientOptions != null)
+            {
+                throw new InvalidOperationException("Cannot use client options builder and client options at the same time.");
+            }
+
+            _clientOptionsBuilder = builder;
             return this;
         }
 
@@ -29,15 +47,22 @@ namespace MQTTnet.ManagedClient
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            var builder = new MqttClientOptionsBuilder();
-            options(builder);
-            _options.ClientOptions = builder.Build();
+            if (_clientOptionsBuilder != null)
+            {
+                _clientOptionsBuilder = new MqttClientOptionsBuilder();
+            }
 
+            options(_clientOptionsBuilder);
             return this;
         }
 
         public ManagedMqttClientOptions Build()
         {
+            if (_clientOptionsBuilder != null)
+            {
+                _options.ClientOptions = _clientOptionsBuilder.Build();
+            }
+
             if (_options.ClientOptions == null)
             {
                 throw new InvalidOperationException("The ClientOptions cannot be null.");

Frameworks/MQTTnet.NetStandard/MqttApplicationMessageExtensions.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Text;
+
+namespace MQTTnet
+{
+    public static class MqttApplicationMessageExtensions
+    {
+        public static string ConvertPayloadToString(this MqttApplicationMessage applicationMessage)
+        {
+            if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
+
+            if (applicationMessage.Payload == null)
+            {
+                return null;
+            }
+
+            if (applicationMessage.Payload.Length == 0)
+            {
+                return string.Empty;
+            }
+
+            return Encoding.UTF8.GetString(applicationMessage.Payload, 0, applicationMessage.Payload.Length);
+        }
+    }
+}