Added support to read diagnostics config from the path defined in environment variable

BASE/Test/Microsoft.ApplicationInsights.Test/Microsoft.ApplicationInsights.Tests/Extensibility/Implementation/Tracing/SelfDiagnostics/SelfDiagnosticsConfigRefresherTest.cs

@@ -1,10 +1,13 @@
 namespace Microsoft.ApplicationInsights.Extensibility.Implementation.Tracing.SelfDiagnostics
 {
+    using System;
     using System.Diagnostics;
     using System.IO;
+    using System.Runtime.InteropServices;
     using System.Text;
     using System.Text.RegularExpressions;
     using Microsoft.VisualStudio.TestTools.UnitTesting;
+    using Newtonsoft.Json.Linq;
 
     [TestClass]
     public class SelfDiagnosticsConfigRefresherTest
@@ -74,6 +77,52 @@ public void SelfDiagnosticsConfigRefresher_CaptureAsConfigured()
             }
         }
 
+        [TestMethod]
+        public void SelfDiagnosticsConfigRefresher_ReadFromEnviornmentVar()
+        {
+
+            var key = "APPLICATIONINSIGHTS_LOG_DIAGNOSTICS";
+            var val = string.Empty;
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                val = @"C:\home\LogFiles\SelfDiagnostics";
+            }
+            else
+            {
+                val = "/home/user/LogFiles/SelfDiagnostics";
+            }
+
+            Environment.SetEnvironmentVariable(key, val);
+
+            try
+            {
+                CreateConfigFile(false);
+                using (var configRefresher = new SelfDiagnosticsConfigRefresher())
+                {
+                    // Emitting event of EventLevel.Error
+                    CoreEventSource.Log.InvalidOperationToStopError();
+                    var filePath = configRefresher.CurrentFilePath;
+
+                    int bufferSize = 512;
+                    byte[] actualBytes = ReadFile(filePath, bufferSize);
+                    string logText = Encoding.UTF8.GetString(actualBytes);
+                    Assert.IsTrue(logText.StartsWith(MessageOnNewFileString));
+
+                    // The event was captured
+                    string logLine = logText.Substring(MessageOnNewFileString.Length);
+                    string logMessage = ParseLogMessage(logLine);
+                    string expectedMessage = "Operation to stop does not match the current operation. Telemetry is not tracked.";
+                    Assert.IsTrue(logMessage.StartsWith(expectedMessage));
+                }
+            }
+            finally
+            {
+                Environment.SetEnvironmentVariable(key, null);
+                Platform.PlatformSingleton.Current = null; // Force reinitialization in future tests so that new environment variables will be loaded.
+                CleanupConfigFile();
+            }
+        }
+
         private static string ParseLogMessage(string logLine)
         {
             int timestampPrefixLength = "2020-08-14T20:33:24.4788109Z:".Length;
@@ -91,13 +140,25 @@ private static byte[] ReadFile(string filePath, int byteCount)
             }
         }
 
-        private static void CreateConfigFile()
+        private static void CreateConfigFile(bool userDefinedLogDirectory = true)
         {
-            string configJson = @"{
+            string configJson = string.Empty;
+            if (!userDefinedLogDirectory)
+            {
+                configJson = @"{
+                    ""FileSize"": 1024,
+                    ""LogLevel"": ""Error""
+                    }";
+            }
+            else
+            {
+                configJson = @"{
                     ""LogDirectory"": ""."",
                     ""FileSize"": 1024,
                     ""LogLevel"": ""Error""
                     }";
+            }
+
             using (FileStream file = File.Open(ConfigFilePath, FileMode.Create, FileAccess.Write))
             {
                 byte[] configBytes = Encoding.UTF8.GetBytes(configJson);

BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/Tracing/SelfDiagnostics/SelfDiagnosticsConfigParser.cs

@@ -5,13 +5,16 @@
     using System.IO;
     using System.Text;
     using System.Text.RegularExpressions;
+    using Microsoft.ApplicationInsights.Extensibility.Implementation.Platform;
 
     internal class SelfDiagnosticsConfigParser
     {
         public const string ConfigFileName = "ApplicationInsightsDiagnostics.json";
         private const int FileSizeLowerLimit = 1024;  // Lower limit for log file size in KB: 1MB
         private const int FileSizeUpperLimit = 128 * 1024;  // Upper limit for log file size in KB: 128MB
 
+        private const string LogDiagnosticsEnvironmentVariable = "APPLICATIONINSIGHTS_LOG_DIAGNOSTICS";
+
         /// <summary>
         /// ConfigBufferSize is the maximum bytes of config file that will be read.
         /// </summary>
@@ -40,16 +43,23 @@ public bool TryGetConfiguration(out string logDirectory, out int fileSizeInKB, o
             {
                 var configFilePath = ConfigFileName;
 
-                // First check using current working directory
-                if (!File.Exists(configFilePath))
+                // First, check whether the enviornment variable was set.
+                if (PlatformSingleton.Current.TryGetEnvironmentVariable(LogDiagnosticsEnvironmentVariable, out string logDiagnosticsPath))
+                {
+                    configFilePath = Path.Combine(logDiagnosticsPath, ConfigFileName);
+                    logDirectory = logDiagnosticsPath;
+                }
+
+                // Second, check using current working directory.
+                else if (!File.Exists(configFilePath))
                 {
 #if NET452
                     configFilePath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, ConfigFileName);
 #else
                     configFilePath = Path.Combine(AppContext.BaseDirectory, ConfigFileName);
 #endif
 
-                    // Second check using application base directory
+                    // Third, check using application base directory.
                     if (!File.Exists(configFilePath))
                     {
                         return false;
@@ -67,7 +77,8 @@ public bool TryGetConfiguration(out string logDirectory, out int fileSizeInKB, o
 
                     file.Read(buffer, 0, buffer.Length);
                     string configJson = Encoding.UTF8.GetString(buffer);
-                    if (!TryParseLogDirectory(configJson, out logDirectory))
+
+                    if (logDirectory == null && !TryParseLogDirectory(configJson, out logDirectory))
                     {
                         return false;
                     }