Merge pull request #886 from PMExtra/feature-userproperties

GetUserProperty extension.

Build/MQTTnet.nuspec

@@ -22,6 +22,7 @@
 * [Server] Added interceptor for unsubscriptions.
 * [MQTTnet.Server] Added interceptor for unsubscriptions.
 * [MQTTnet.AspNetCore] improved compatibility with AspNetCore 3.1
+* [Core] Added MqttApplicationMessage.GetUserProperty() convenience method (thanks to @PMExtra).
 * [Client] Support WithConnectionUri to configure client (thanks to @PMExtra).
 * [Server] Removed exceptions when user properties are set with MQTT protocol version 3.1
     </releaseNotes>

Source/MQTTnet/Extensions/UserPropertyExtension.cs

@@ -0,0 +1,32 @@
+using System;
+using System.ComponentModel;
+using System.Linq;
+
+namespace MQTTnet.Extensions
+{
+    public static class UserPropertyExtension
+    {
+        public static string GetUserProperty(this MqttApplicationMessage message, string propertyName, StringComparison comparisonType = StringComparison.OrdinalIgnoreCase)
+        {
+            if (message == null) throw new ArgumentNullException(nameof(message));
+            if (propertyName == null) throw new ArgumentNullException(nameof(propertyName));
+
+            return message.UserProperties?.SingleOrDefault(up => up.Name.Equals(propertyName, comparisonType))?.Value;
+        }
+
+        public static T GetUserProperty<T>(this MqttApplicationMessage message, string propertyName, StringComparison comparisonType = StringComparison.OrdinalIgnoreCase)
+        {
+            var value = GetUserProperty(message, propertyName, comparisonType);
+
+            var typeDescriptor = TypeDescriptor.GetConverter(typeof(T));
+            try
+            {
+                return (T) typeDescriptor.ConvertFromString(value);
+            }
+            catch (Exception ex)
+            {
+                throw new InvalidOperationException($"Cannot convert value({value ?? "null"}) of UserProperty({propertyName}) to {typeof(T).FullName}.", ex);
+            }
+        }
+    }
+}

Source/MQTTnet/MQTTnet.csproj

@@ -42,6 +42,7 @@
   </PropertyGroup>
 
   <ItemGroup Condition="'$(TargetFramework)'=='netstandard1.3'">
+    <PackageReference Include="System.ComponentModel.TypeConverter" Version="4.3.0" />
     <PackageReference Include="System.Net.Security" Version="4.3.2" />
     <PackageReference Include="System.Net.WebSockets" Version="4.3.0" />
     <PackageReference Include="System.Net.WebSockets.Client" Version="4.3.2" />

Tests/MQTTnet.Core.Tests/MqttApplicationMessage_Tests.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Extensions;
+using MQTTnet.Packets;
+
+namespace MQTTnet.Tests
+{
+    [TestClass]
+    public class MqttApplicationMessage_Tests
+    {
+        [TestMethod]
+        public void GetUserProperty_Test()
+        {
+            var message = new MqttApplicationMessage
+            {
+                UserProperties = new List<MqttUserProperty>
+                {
+                    new MqttUserProperty("foo", "bar"),
+                    new MqttUserProperty("value", "1011"),
+                    new MqttUserProperty("CASE", "insensitive")
+                }
+            };
+
+            Assert.AreEqual("bar", message.GetUserProperty("foo"));
+            Assert.AreEqual(1011, message.GetUserProperty<int>("value"));
+            Assert.AreEqual("insensitive", message.GetUserProperty("case"));
+            Assert.AreEqual(null, message.GetUserProperty("nonExists"));
+            Assert.AreEqual(null, message.GetUserProperty<int?>("nonExists"));
+            Assert.ThrowsException<InvalidOperationException>(() => message.GetUserProperty<int>("nonExists"));
+        }
+    }
+}