added back MqttTrace consuming api

MQTTnet.Core/Diagnostics/MqttNetLogger.cs

@@ -0,0 +1,49 @@
+using System;
+using Microsoft.Extensions.Logging;
+
+namespace MQTTnet.Core.Diagnostics
+{
+    public class MqttNetLogger : ILogger
+    {
+        private readonly string _categoryName;
+        private readonly MqttNetTrace _mqttNetTrace;
+
+        public MqttNetLogger(string categoryName, MqttNetTrace mqttNetTrace)
+        {
+            _categoryName = categoryName;
+            _mqttNetTrace = mqttNetTrace;
+        }
+
+        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
+        {
+            if (formatter == null)
+            {
+                throw new ArgumentNullException(nameof(formatter));
+            }
+
+            var message = formatter(state, exception);
+
+            var traceMessage = new MqttNetTraceMessage(DateTime.Now, Environment.CurrentManagedThreadId, _categoryName, logLevel, message, exception);
+            _mqttNetTrace.Publish(traceMessage);
+        }
+
+        public bool IsEnabled(LogLevel logLevel)
+        {
+            return true;
+        }
+
+        //not supported: async local requires netstandard1.3
+        //for implementation see https://github.com/aspnet/Logging/blob/dev/src/Microsoft.Extensions.Logging.Console/ConsoleLogScope.cs
+        public IDisposable BeginScope<TState>(TState state)
+        {
+            return new DisposableScope();
+        }
+
+        private class DisposableScope : IDisposable
+        {
+            public void Dispose()
+            {
+            }
+        }
+    }
+}

MQTTnet.Core/Diagnostics/MqttNetTrace.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Concurrent;
+using Microsoft.Extensions.Logging;
+
+namespace MQTTnet.Core.Diagnostics
+{
+    public class MqttNetTrace : ILoggerProvider
+    {
+        private readonly ConcurrentDictionary<string, MqttNetLogger> _loggers = new ConcurrentDictionary<string, MqttNetLogger>();
+
+        public static event EventHandler<MqttNetTraceMessagePublishedEventArgs> TraceMessagePublished;
+
+        public void Publish(MqttNetTraceMessage msg)
+        {
+            TraceMessagePublished?.Invoke(this, new MqttNetTraceMessagePublishedEventArgs(msg));
+        }
+
+        public void Dispose()
+        {
+            TraceMessagePublished = null;
+        }
+
+        public ILogger CreateLogger(string categoryName)
+        {
+            return _loggers.GetOrAdd(categoryName, CreateLoggerImplementation);
+        }
+
+        private MqttNetLogger CreateLoggerImplementation(string categoryName)
+        {
+            return new MqttNetLogger(categoryName, this);
+        }
+    }
+}

MQTTnet.Core/Diagnostics/MqttNetTraceMessagePublishedEventArgs.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace MQTTnet.Core.Diagnostics
+{
+    public sealed class MqttNetTraceMessagePublishedEventArgs : EventArgs
+    {
+        public MqttNetTraceMessagePublishedEventArgs(MqttNetTraceMessage traceMessage)
+        {
+            TraceMessage = traceMessage ?? throw new ArgumentNullException(nameof(traceMessage));
+        }
+
+        public MqttNetTraceMessage TraceMessage { get; }
+    }
+}

MQTTnet.Core/Diagnostics/MqttTraceMessage.cs

@@ -0,0 +1,30 @@
+using System;
+using Microsoft.Extensions.Logging;
+
+namespace MQTTnet.Core.Diagnostics
+{
+    public sealed class MqttNetTraceMessage
+    {
+        public MqttNetTraceMessage(DateTime timestamp, int threadId, string source, LogLevel level, string message, Exception exception)
+        {
+            Timestamp = timestamp;
+            ThreadId = threadId;
+            Source = source;
+            Level = level;
+            Message = message;
+            Exception = exception;
+        }
+
+        public DateTime Timestamp { get; }
+
+        public int ThreadId { get; }
+
+        public string Source { get; }
+
+        public LogLevel Level { get; }
+
+        public string Message { get; }
+
+        public Exception Exception { get; }
+    }
+}

MQTTnet.Core/MQTTnet.Core.csproj

@@ -25,6 +25,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="1.1.2" />
     <PackageReference Include="Microsoft.Extensions.Options" Version="1.1.2" />
+    <PackageReference Include="System.Threading" Version="4.3.0" />
   </ItemGroup>
 
 </Project>