Add SqlClient event listener (#1544)

* Add SqlClient event listener

* comments

* ensure not disposed early

src/Microsoft.SqlTools.Hosting/Utility/SqlClientEventListener.cs

@@ -0,0 +1,51 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Diagnostics.Tracing;
+using Microsoft.SqlTools.Utility;
+
+namespace Microsoft.SqlTools.ServiceLayer.Utility
+{
+
+    /// <summary>
+    /// This listener class will listen for events from the SqlClientEventSource class 
+    /// and forward them to the logger.
+    /// </summary>
+    internal class SqlClientListener : EventListener
+    {
+        protected override void OnEventSourceCreated(EventSource eventSource)
+        {
+            // Only enable events from SqlClientEventSource.
+            if (eventSource.Name.Equals("Microsoft.Data.SqlClient.EventSource"))
+            {
+                // Use EventKeyWord 2 to capture basic application flow events.
+                // See https://docs.microsoft.com/sql/connect/ado-net/enable-eventsource-tracing for all available keywords.
+                EnableEvents(eventSource, EventLevel.Informational, (EventKeywords)2);
+            }
+        }
+
+        /// <summary>
+        /// This callback runs whenever an event is written by SqlClientEventSource.
+        /// Event data is accessed through the EventWrittenEventArgs parameter.
+        /// </summary>
+        /// <param name="eventData">The data for the event</param>
+        protected override void OnEventWritten(EventWrittenEventArgs eventData)
+        {
+            if (eventData.Payload == null)
+            {
+                return;
+            }
+            foreach (object payload in eventData.Payload)
+            {
+                if (payload != null)
+                {
+                    Logger.Verbose(payload.ToString());
+                }
+
+            }
+
+        }
+    }
+}

src/Microsoft.SqlTools.ServiceLayer/Program.cs

@@ -23,6 +23,7 @@ namespace Microsoft.SqlTools.ServiceLayer
         /// </summary>
         internal static void Main(string[] args)
         {
+            SqlClientListener? sqlClientListener = null;
             try
             {
                 // read command-line arguments
@@ -39,6 +40,12 @@ namespace Microsoft.SqlTools.ServiceLayer
                 }
 
                 Logger.Initialize(tracingLevel: commandOptions.TracingLevel, logFilePath: logFilePath, traceSource: "sqltools", commandOptions.AutoFlushLog);
+                // Only enable SQL Client logging when verbose or higher to avoid extra overhead when the
+                // detailed logging it provides isn't needed
+                if (Logger.TracingLevel.HasFlag(SourceLevels.Verbose))
+                {
+                    sqlClientListener = new SqlClientListener();
+                }
 
                 // set up the host details and profile paths 
                 var hostDetails = new HostDetails(version: new Version(1, 0));
@@ -73,6 +80,7 @@ namespace Microsoft.SqlTools.ServiceLayer
             finally
             {
                 Logger.Close();
+                sqlClientListener?.Dispose();
             }
         }