feat: improve MqttClientWrapper error handling and logging

src/Silverback.Integration.MQTT/Messaging/Broker/Mqtt/MqttClientWrapper.cs

@@ -161,6 +161,7 @@ await Task.Delay(ConnectionMonitorMillisecondsInterval, cancellationToken)
             }
         }
 
+        [SuppressMessage("", "CA1031", Justification = Justifications.ExceptionLogged)]
         private async Task<bool> TryConnectAsync(bool isFirstTry, CancellationToken cancellationToken)
         {
             if (_isConnected)
@@ -193,7 +194,7 @@ private async Task<bool> TryConnectAsync(bool isFirstTry, CancellationToken canc
                 await _brokerCallbacksInvoker.InvokeAsync<IMqttClientConnectedCallback>(handler => handler.OnClientConnectedAsync(ClientConfig))
                     .ConfigureAwait(false);
             }
-            catch (MqttCommunicationException ex)
+            catch (Exception ex)
             {
                 // This might happen if the client briefly connects and then immediately disconnects
                 _logger.LogConnectError(this, ex);
@@ -217,7 +218,10 @@ await MqttClient
                 if (MqttClient is MqttClient)
                     await Task.Delay(ConnectionCheckDelayMilliseconds, cancellationToken).ConfigureAwait(false);
 
-                return MqttClient.IsConnected;
+                if (!MqttClient.IsConnected)
+                    throw new MqttConnectException("The call to ConnectAsync returned but the client is not connected.");
+
+                return true;
             }
             catch (Exception ex)
             {

src/Silverback.Integration.MQTT/Messaging/Broker/Mqtt/MqttConnectException.cs

@@ -0,0 +1,90 @@
+// Copyright (c) 2020 Sergio Aquilini
+// This code is licensed under MIT license (see LICENSE file for details)
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.Serialization;
+using MQTTnet.Client;
+
+namespace Silverback.Messaging.Broker.Mqtt
+{
+    /// <summary>
+    ///     The exception that is thrown when the MQTT client connection fails.
+    /// </summary>
+    [Serializable]
+    [ExcludeFromCodeCoverage]
+    public class MqttConnectException : SilverbackException
+    {
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="MqttConnectException" /> class.
+        /// </summary>
+        public MqttConnectException()
+        {
+        }
+
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="MqttConnectException" /> class with the
+        ///     specified message.
+        /// </summary>
+        /// <param name="message">
+        ///     The exception message.
+        /// </param>
+        public MqttConnectException(string message)
+            : base(message)
+        {
+        }
+
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="MqttConnectException" /> class with the
+        ///     specified message.
+        /// </summary>
+        /// <param name="message">
+        ///     The exception message.
+        /// </param>
+        /// <param name="result">
+        ///     The <see cref="MqttClientPublishResult" />.
+        /// </param>
+        public MqttConnectException(string message, MqttClientPublishResult result)
+            : base(message)
+        {
+            Result = result;
+        }
+
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="MqttConnectException" /> class with the
+        ///     specified message and inner exception.
+        /// </summary>
+        /// <param name="message">
+        ///     The exception message.
+        /// </param>
+        /// <param name="innerException">
+        ///     The inner exception.
+        /// </param>
+        public MqttConnectException(string message, Exception innerException)
+            : base(message, innerException)
+        {
+        }
+
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="MqttConnectException" /> class with the
+        ///     serialized data.
+        /// </summary>
+        /// <param name="info">
+        ///     The <see cref="SerializationInfo" /> that holds the serialized object data about the exception being
+        ///     thrown.
+        /// </param>
+        /// <param name="context">
+        ///     The <see cref="StreamingContext" /> that contains contextual information about the source or
+        ///     destination.
+        /// </param>
+        protected MqttConnectException(SerializationInfo info, StreamingContext context)
+            : base(info, context)
+        {
+        }
+
+        /// <summary>
+        ///     Gets the <see cref="MqttClientPublishResult" /> of the failed publish operation.
+        /// </summary>
+        public MqttClientPublishResult? Result { get; }
+    }
+}