Made HttpRequestMessageExtensions compatible with .NET Framework

Author: TalAloni

StandardSocketsHttpHandler/Net/Http/Extensions/HttpRequestMessageExtensions.cs

@@ -8,7 +8,8 @@ internal static class HttpRequestMessageExtensions
     {
         public static bool HasHeaders(this HttpRequestMessage request)
         {
-            string headersFieldName = "_headers";
+            // Note: The field name is _headers in .NET core 
+            string headersFieldName = RuntimeUtils.IsDotNetFramework() ? "headers" : "_headers";
             FieldInfo headersField = typeof(HttpRequestMessage).GetField(headersFieldName, BindingFlags.Instance | BindingFlags.NonPublic);
             HttpRequestHeaders headers = (HttpRequestHeaders)headersField.GetValue(request);
             return headers != null;

StandardSocketsHttpHandler/Utils/RuntimeUtils.cs

@@ -0,0 +1,14 @@
+using System.Runtime.InteropServices;
+
+namespace System
+{
+    internal class RuntimeUtils
+    {
+        public static bool IsDotNetFramework()
+        {
+            const string DotnetFrameworkDescription = ".NET Framework";
+            string frameworkDescription = RuntimeInformation.FrameworkDescription;
+            return frameworkDescription.StartsWith(DotnetFrameworkDescription);
+        }
+    }
+}